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1.	Gerlee, Philip, 1980, et al. (författare) Scientific Models : Red Atoms, White Lies and Black Boxes in a Yellow Book 2016 Bok (övrigt vetenskapligt/konstnärligt)abstract A zebrafish, the hull of a miniature ship, a mathematical equation and a food chain - what do these things have in common? They are examples of models used by scientists to isolate and study particular aspects of the world around us. This book begins by introducing the concept of a scientific model from an intuitive perspective, drawing parallels to mental models and artistic representations. It then recounts the history of modelling from the 16th century up until the present day. The iterative process of model building is described and discussed in the context of complex models with high predictive accuracy versus simpler models that provide more of a conceptual understanding. To illustrate the diversity of opinions within the scientific community, we also present the results of an interview study, in which ten scientists from different disciplines describe their views on modelling and how models feature in their work. Lastly, it includes a number of worked examples that span different modelling approaches and techniques. It provides a comprehensive introduction to scientific models and shows how models are constructed and used in modern science. It also addresses the approach to, and the culture surrounding modelling in different scientific disciplines. It serves as an inspiration for model building and also facilitates interdisciplinary collaborations by showing how models are used in different scientific fields. The book is aimed primarily at students in the sciences and engineering, as well as students at teacher training colleges but will also appeal to interested readers wanting to get an overview of scientific modelling in general and different modelling approaches in particular.
2.	Gerlee, Philip, 1980, et al. (författare) Scientific Models 2016 Bok (övrigt vetenskapligt/konstnärligt)abstract A zebrafish, the hull of a miniature ship, a mathematical equation and a food chain - what do these things have in common? They are examples of models used by scientists to isolate and study particular aspects of the world around us. This book begins by introducing the concept of a scientific model from an intuitive perspective, drawing parallels to mental models and artistic representations. It then recounts the history of modelling from the 16th century up until the present day. The iterative process of model building is described and discussed in the context of complex models with high predictive accuracy versus simpler models that provide more of a conceptual understanding. To illustrate the diversity of opinions within the scientific community, we also present the results of an interview study, in which ten scientists from different disciplines describe their views on modelling and how models feature in their work. Lastly, it includes a number of worked examples that span different modelling approaches and techniques. It provides a comprehensive introduction to scientific models and shows how models are constructed and used in modern science. It also addresses the approach to, and the culture surrounding modelling in different scientific disciplines. It serves as an inspiration for model building and also facilitates interdisciplinary collaborations by showing how models are used in different scientific fields. The book is aimed primarily at students in the sciences and engineering, as well as students at teacher training colleges but will also appeal to interested readers wanting to get an overview of scientific modelling in general and different modelling approaches in particular.
3.	Checinska, Aleksandra, et al. (författare) Microbiomes of the dust particles collected from the International Space Station and Spacecraft Assembly Facilities 2015 Ingår i: Microbiome. - : Springer Science and Business Media LLC. - 2049-2618. ; 3 Tidskriftsartikel (refereegranskat)abstract Background - The International Space Station (ISS) is a unique built environment due to the effects of microgravity, space radiation, elevated carbon dioxide levels, and especially continuous human habitation. Understanding the composition of the ISS microbial community will facilitate further development of safety and maintenance practices. The primary goal of this study was to characterize the viable microbiome of the ISS-built environment. A second objective was to determine if the built environments of Earth-based cleanrooms associated with space exploration are an appropriate model of the ISS environment. Results - Samples collected from the ISS and two cleanrooms at the Jet Propulsion Laboratory (JPL, Pasadena, CA) were analyzed by traditional cultivation, adenosine triphosphate (ATP), and propidium monoazide–quantitative polymerase chain reaction (PMA-qPCR) assays to estimate viable microbial populations. The 16S rRNA gene Illumina iTag sequencing was used to elucidate microbial diversity and explore differences between ISS and cleanroom microbiomes. Statistical analyses showed that members of the phyla Actinobacteria, Firmicutes, and Proteobacteria were dominant in the samples examined but varied in abundance. Actinobacteria were predominant in the ISS samples whereas Proteobacteria, least abundant in the ISS, dominated in the cleanroom samples. The viable bacterial populations seen by PMA treatment were greatly decreased. However, the treatment did not appear to have an effect on the bacterial composition (diversity) associated with each sampling site. Conclusions - The results of this study provide strong evidence that specific human skin-associated microorganisms make a substantial contribution to the ISS microbiome, which is not the case in Earth-based cleanrooms. For example, Corynebacterium and Propionibacterium (Actinobacteria) but not Staphylococcus (Firmicutes) species are dominant on the ISS in terms of viable and total bacterial community composition. The results obtained will facilitate future studies to determine how stable the ISS environment is over time. The present results also demonstrate the value of measuring viable cell diversity and population size at any sampling site. This information can be used to identify sites that can be targeted for more stringent cleaning. Finally, the results will allow comparisons with other built sites and facilitate future improvements on the ISS that will ensure astronaut health.
4.	Blomqvist, Michael, et al. (författare) Constraining dark energy fluctuations with supernova correlations 2010 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 10, s. 018- Tidskriftsartikel (refereegranskat)abstract We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state is not equal to -1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.
5.	Blomqvist, Michael, 1980-, et al. (författare) Supernovae as seen by off-center observers in a local void 2010 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 05, s. 006- Tidskriftsartikel (refereegranskat)abstract Inhomogeneous universe models have been proposed as an alternative explanation for the apparent acceleration of the cosmic expansion that does not require dark energy. In the simplest class of inhomogeneous models, we live within a large, spherically symmetric void. Several studies have shown that such a model can be made consistent with many observations, in particular the redshift-luminosity distance relation for type Ia supernovae, provided that the void is of Gpc size and that we live close to the center. Such a scenario challenges the Copernican principle that we do not occupy a special place in the universe. We use the first-year Sloan Digital Sky Survey-II supernova search data set as well as the Constitution supernova data set to put constraints on the observer position in void models, using the fact that off-center observers will observe an anisotropic universe. We first show that a spherically symmetric void can give good fits to the supernova data for an on-center observer, but that the two data sets prefer very different voids. We then continue to show that the observer can be displaced at least fifteen percent of the void scale radius from the center and still give an acceptable fit to the supernova data. When combined with the observed dipole anisotropy of the cosmic microwave background however, we find that the data compells the observer to be located within about one percent of the void scale radius. Based on these results, we conclude that considerable fine-tuning of our position within the void is needed tofit the supernova data, strongly disfavouring the model from a Copernican principle point of view.
6.	Abdo, A. A., et al. (författare) BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THE FERMI LARGE AREA TELESCOPE ALL-SKY SURVEY 2009 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 700:1, s. 597-622 Tidskriftsartikel (refereegranskat)abstract The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at \|b\| > 10 degrees with test statistic greater than 100 ( corresponding to about 10 sigma). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at \|b\| < 10 degrees, were previously detected with Energetic Gamma-Ray Experiment Telescope( EGRET), probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak gamma-ray fluxes is observed. Blazar log N-log S distributions and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BL Lacs. The contribution of LAT blazars to the total extragalactic gamma-ray intensity is estimated.
7.	Abdo, A. A., et al. (författare) EARLY FERMI GAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE QUASAR 3C 454.3 2009 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 699:1, s. 817-823 Tidskriftsartikel (refereegranskat)abstract This is the first report of Fermi Gamma-Ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope, covering 2008 July 7-October 6, indicate strong, highly variable.-ray emission with an average flux of similar to 3 x 10 (6) photons cm(-2) s(-1), for energies > 100 MeV. The gamma-ray flux is variable, with strong, distinct, symmetrically shaped flares for which the flux increases by a factor of several on a timescale of about 3 days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair production implies relativistic beaming with Doppler factor delta > 8, consistent with the values inferred from Very Long Baseline Interferometry observations of superluminal expansion (delta similar to 25). The observed gamma-ray spectrum is not consistent with a simple power law, but instead steepens strongly above similar to 2 GeV, and is well described by a broken power law with photon indices of similar to 2.3 and similar to 3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high-luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to gamma-ray absorption via photon-photon pair production on the soft X-ray photon field of the host active galactic nucleus, but such an interpretation would require the dissipation region to be located very close (less than or similar to 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.
8.	Hooton, M.J., et al. (författare) Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection 2022 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 658 Tidskriftsartikel (refereegranskat)abstract Context. The light curves of tidally locked hot Jupiters transiting fast-rotating, early-type stars are a rich source of information about both the planet and star, with full-phase coverage enabling a detailed atmospheric characterisation of the planet. Although it is possible to determine the true spin-orbit angle ψ-a notoriously difficult parameter to measure-from any transit asymmetry resulting from gravity darkening induced by the stellar rotation, the correlations that exist between the transit parameters have led to large disagreements in published values of ψ for some systems. Aims. We aimed to study these phenomena in the light curves of the ultra-hot Jupiter MASCARA-1 b, which is characteristically similar to well-studied contemporaries such as KELT-9 b and WASP-33 b. Methods. We obtained optical CHaracterising ExOPlanet Satellite (CHEOPS) transit and occultation light curves of MASCARA-1 b, and analysed them jointly with a Spitzer/IRAC 4.5 μm full-phase curve to model the asymmetric transits, occultations, and phase-dependent flux modulation. For the latter, we employed a novel physics-driven approach to jointly fit the phase modulation by generating a single 2D temperature map and integrating it over the two bandpasses as a function of phase to account for the differing planet-star flux contrasts. The reflected light component was modelled using the general ab initio solution for a semi-infinite atmosphere. Results. When fitting the CHEOPS and Spitzer transits together, the degeneracies are greatly diminished and return results consistent with previously published Doppler tomography. Placing priors informed by the tomography achieves even better precision, allowing a determination of ψ = 72.1-2.4+2.5 deg. From the occultations and phase variations, we derived dayside and nightside temperatures of 3062-68+66 K and 1720 ± 330 K, respectively.Our retrieval suggests that the dayside emission spectrum closely follows that of a blackbody. As the CHEOPS occultation is too deep to be attributed to blackbody flux alone, we could separately derive geometric albedo Ag = 0.171-0.068+0.066 and spherical albedo As = 0.266-0.100+0.097 from the CHEOPS data, and Bond albedoAB = 0.057-0.101+0.083 from the Spitzer phase curve.Although small, the Ag and As indicate that MASCARA-1 b is more reflective than most other ultra-hot Jupiters, where H- absorption is expected to dominate. Conclusions. Where possible, priors informed by Doppler tomography should be used when fitting transits of fast-rotating stars, though multi-colour photometry may also unlock an accurate measurement of ψ. Our approach to modelling the phase variations at different wavelengths provides a template for how to separate thermal emission from reflected light in spectrally resolved James Webb Space Telescope phase curve data.
9.	Morris, B. M., et al. (författare) CHEOPS precision phase curve of the Super-Earth 55 Cancri e 2021 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 653 Tidskriftsartikel (refereegranskat)abstract Context. 55 Cnc e is a transiting super-Earth (radius 1.88 R-circle plus and mass 8 M-circle plus) orbiting a G8V host star on a 17-h orbit. Spitzer observations of the planet's phase curve at 4.5 mu m revealed a time-varying occultation depth, and MOST optical observations are consistent with a time-varying phase curve amplitude and phase offset of maximum light. Both broadband and high-resolution spectroscopic analyses are consistent with either a high mean molecular weight atmosphere or no atmosphere for planet e. A long-term photometric monitoring campaign on an independent optical telescope is needed to probe the variability in this system. Aims. We seek to measure the phase variations of 55 Cnc e with a broadband optical filter with the 30 cm effective aperture space telescope CHEOPS and explore how the precision photometry narrows down the range of possible scenarios. Methods. We observed 55 Cnc for 1.6 orbital phases in March of 2020. We designed a phase curve detrending toolkit for CHEOPS photometry which allowed us to study the underlying flux variations in the 55 Cnc system. Results. We detected a phase variation with a full-amplitude of 72 +/- 7 ppm, but did not detect a significant secondary eclipse of the planet. The shape of the phase variation resembles that of a piecewise-Lambertian; however, the non-detection of the planetary secondary eclipse, and the large amplitude of the variations exclude reflection from the planetary surface as a possible origin of the observed phase variations. They are also likely incompatible with magnetospheric interactions between the star and planet, but may imply that circumplanetary or circumstellar material modulate the flux of the system. Conclusions. This year, further precision photometry of 55 Cnc from CHEOPS will measure variations in the phase curve amplitude and shape over time.
10.	Laursen, Peter, 1975-, et al. (författare) Intergalactic Transmission and its Impact on the Ly{\alpha} Line 2011 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 728:1, s. 52- Tidskriftsartikel (populärvet., debatt m.m.)abstract We study the intergalactic transmission of radiation in the vicinity of the Ly{\alpha} wavelength. Simulating sightlines through the intergalactic medium (IGM) in detailed cosmological hydrosimulations, the impact of the IGM on the shape of the line profile from Ly{\alpha} emitting galaxies at redshifts 2.5 to 6.5 is investigated. In particular we show that taking into account the correlation of the density and velocity fields of the IGM with the galaxies, the blue part of the spectrum may be appreciably reduced, even at relatively low redshifts. This may in some cases provide an alternative to the often-invoked outflow scenario, although it is concluded that this model is still a plausible explanation of the many asymmetric Ly{\alpha} profiles observed. Applying the calculated wavelength dependent transmission to simulated spectra from Ly{\alpha} emitting galaxies, we derive the fraction of photons that are lost in the IGM, in addition to what is absorbed internally in the galaxies due to dust. Moreover, by comparing the calculated transmission of radiation blueward of the Ly{\alpha} line, the total optical depth to Thomson scattering of cosmic microwave background, with corresponding observations, we are able to constrain the epoch when the Universe was reionized to z <~ 8.5.
11.	Nordin, Jakob, 1979- (författare) Spectral Properties of Type Ia Supernovae and Implications for Cosmology 2011 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Type Ia supernovae can, for a short period of time, reach the same brightness as an entire galaxy. They are responsible for the creation of a large fraction of all heavy elements and can be used, as standard candles, to prove that the expansion of the universe is accelerating. Yet, we do not fully understand them. A basic picture where Type Ia supernovae are caused by thermonuclear explosions of white dwarfs is generally accepted, but the details are still debated. These unknowns propagate into systematic uncertainties in the estimates of cosmological parameters. A Monte Carlo framework, SMOCK, designed to model this error propagation, is presented. Evolution with time/distance and the nature of reddening are studied as the dominant astrophysical uncertainties. Optical spectra of Type Ia supernovae contain a wealth of information regarding the nature of these events, and can be used both to understand supernovae and to limit the systematic uncertainties in cosmological parameter estimates. We have reduced spectra observed with the Nordic Optical Telescope and the New Technology Telescope in conjunction with the SDSS-II supernova survey, and compared spectral properties (pseudo-Equivalent Widths and line velocities) of this sample with local supernovae.We have further studied possible systematic difficulties in such comparisons between nearby and distant supernovae, caused by noise and host galaxy contamination.Taking such uncertainties into account, we find a tentative evolution in supernova properties with redshift, compatible with expected demographic changes. Correlations with light curve shape found by other studies are confirmed. A tentative correlation with light curve colour is also presented. The latter could indicate an intrinsic component of the observed reddening, i.e. independent of interstellar dust in the host galaxy.
12.	Sollerman, J., et al. (författare) First-Year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results : Constraints on Nonstandard Cosmological Models 2009 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 703:2, s. 1374-1385 Tidskriftsartikel (refereegranskat)abstract We use the new Type Ia supernovae discovered by the Sloan Digital Sky Survey-II supernova survey, together with additional supernova data sets as well as observations of the cosmic microwave background and baryon acoustic oscillations to constrain cosmological models. This complements the standard cosmology analysis presented by Kessler et al. in that we discuss and rank a number of the most popular nonstandard cosmology scenarios. When this combined data set is analyzed using the MLCS2k2 light-curve fitter, we find that more exotic models for cosmic acceleration provide a better fit to the data than the ΛCDM model. For example, the flat Dvali-Gabadadze-Porrati model is ranked higher by our information-criteria (IC) tests than the standard model with a flat universe and a cosmological constant. When the supernova data set is instead analyzed using the SALT-II light-curve fitter, the standard cosmological-constant model fares best. This investigation of how sensitive cosmological model selection is to assumptions about, and within, the light-curve fitters thereby highlights the need for an improved understanding of these unresolved systematic effects. Our investigation also includes inhomogeneous Lemaître-Tolman-Bondi (LTB) models. While our LTB models can be made to fit the supernova data as well as any other model, the extra parameters they require are not supported by our IC analysis. Finally, we explore more model-independent ways to investigate the cosmic expansion based on this new data set.
13.	Wu, X., et al. (författare) PANGU : A high resolution gamma-ray space telescope 2015 Ingår i: Proceedings of the 11th Frascati Workshops on Multifrequency Behaviour of High Energy Cosmic Sources Workshop, MULTIF 2015. - : Sissa Medialab Srl. Konferensbidrag (refereegranskat)abstract PANGU (the PAir-productioN Gamma-ray Unit) is a small astrophysics mission with wide field of view optimized for spectro-imaging, timing and polarisation studies. It will map the gamma-ray sky from 10 MeV to a few GeV with unprecedented spatial resolution. This window on the Universe is unique to detect photons emitted directly by relativistic particles, via the decay of neutral pions, or the annihilation or decay light from anti-matter and the putative light dark matter candidates. A wealth of questions can be probed among the most important themes of modern physics and astrophysics. The PANGU instrument is a pair-conversion gamma-ray telescope based on an innovative design of a silicon strip tracker. It is light, compact and accurate. It consists of 100 layers of silicon micro-strip detector of 40 x 40 cm2 in area, stacked to height of about 90 cm, and covered by a top anticoincidence detector. PANGU relies on multiple scattering effects for energy measurement, reaching an energy resolution between 30-50% for 10 MeV - 1 GeV. The novel tracker will allow the first polarisation measurement and provide the best angular resolution ever obtained in the soft gamma ray and GeV band. PANGU has been proposed to the recent ESA-CAS Call for Joint Small Science Mission. In this contribution, the key science objectives, the payload concept and the expected performance will be presented.
14.	Scandariato, Gaetano, et al. (författare) Phase curve and geometric albedo of WASP-43b measured with CHEOPS, TESS, and HST WFC3/UVIS 2022 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668 Tidskriftsartikel (refereegranskat)abstract Context. Observations of the phase curves and secondary eclipses of extrasolar planets provide a window onto the composition and thermal structure of the planetary atmospheres. For example, the photometric observations of secondary eclipses lead to the measurement of the planetary geometric albedo, Ag, which is an indicator of the presence of clouds in the atmosphere. Aims. In this work, we aim to measure the Ag in the optical domain of WASP-43b, a moderately irradiated giant planet with an equilibrium temperature of ~1400 K. Methods. For this purpose, we analyzed the secondary eclipse light curves collected by CHEOPS together with TESS along with observations of the system and the publicly available photometry obtained with HST WFC3/UVIS. We also analyzed the archival infrared observations of the eclipses and retrieve the thermal emission spectrum of the planet. By extrapolating the thermal spectrum to the optical bands, we corrected for the optical eclipses for thermal emission and derived the optical Ag. Results. The fit of the optical data leads to a marginal detection of the phase-curve signal, characterized by an amplitude of 160 ± 60 ppm and 80a-? 50+60 ppm in the CHEOPS and TESS passbands, respectively, with an eastward phase shift of ~50 (1.5Ï ? detection). The analysis of the infrared data suggests a non-inverted thermal profile and solar-like metallicity. The combination of the optical and infrared analyses allows us to derive an upper limit for the optical albedo of Ag< 0.087, with a confidence of 99.9%. Conclusions. Our analysis of the atmosphere of WASP-43b places this planet in the sample of irradiated hot Jupiters, with monotonic temperature-pressure profile and no indication of condensation of reflective clouds on the planetary dayside.
15.	Patel, Jayshil Ashokkumar, et al. (författare) CHEOPS and TESS view of the ultra-short-period super-Earth TOI-561 b 2023 Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 679 Tidskriftsartikel (refereegranskat)abstract Context. Ultra-short-period planets (USPs) are a unique class of super-Earths with an orbital period of less than a day, and hence they are subject to intense radiation from their host star. These planets cannot retain a primordial H/He atmosphere, and most of them are indeed consistent with being bare rocky cores. A few USPs, however, show evidence for a heavyweight envelope, which could be a water layer resilient to evaporation or a secondary metal-rich atmosphere sustained by outgassing of the molten volcanic surface. Much thus remains to be learned about the nature and formation of USPs. Aims. The prime goal of the present work is to refine the bulk planetary properties of the recently discovered TOI-561 b through the study of its transits and occultations. This is crucial in order to understand the internal structure of this USP and to assess the presence of an atmosphere. Methods. We obtained ultra-precise transit photometry of TOI-561 b with CHEOPS, and performed a joint analysis of these data along with three archival visits from CHEOPS and four TESS sectors. Results. Our analysis of TOI-561 b transit photometry put strong constraints on its properties. In particular, we restrict the uncertainties on the planetary radius at similar to 2% retrieving R-p = 1.42 +/- 0.02 R-circle plus. This result informs our internal structure modelling of the planet, which shows that the observations are consistent with a negligible H/He atmosphere; however, other lighter materials are required, in addition to a pure iron core and a silicate mantle, to explain the observed density. We find that this can be explained by the inclusion of a water layer in our model. Additionally, we ran a grid of forward models with a water-enriched atmosphere to explain the transit radius. We searched for variability in the measured R-p/R-star over time, which could trace changes in the structure of the planetary envelope. However, no temporal variations are recovered within the present data precision. In addition to the transit event, we tentatively detect an occultation signal in the TESS data with an eclipse depth L = 27.40(-11.35)(+10.87) ppm. We use models of outgassed atmospheres from the literature to explain this eclipse signal. We find that the thermal emission from the planet can mostly explain the observation. Based on this, we predict that near- to mid-infrared observations with the James Webb Space Telescope should be able to detect silicate species in the atmosphere of the planet. This could also reveal important clues about the planetary interior and help disentangle planet formation and evolution models.
16.	Barros, S. C. C., et al. (författare) Detection of the tidal deformation of WASP-103b at 3σ with CHEOPS 2022 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 657 Tidskriftsartikel (refereegranskat)abstract Context. Ultra-short period planets undergo strong tidal interactions with their host star which lead to planet deformation and orbital tidal decay.Aims. WASP-103b is the exoplanet with the highest expected deformation signature in its transit light curve and one of the shortest expected spiral-in times. Measuring the tidal deformation of the planet would allow us to estimate the second degree fluid Love number and gain insight into the planet's internal structure. Moreover, measuring the tidal decay timescale would allow us to estimate the stellar tidal quality factor, which is key to constraining stellar physics.Methods. We obtained 12 transit light curves of WASP-103b with the CHaracterising ExOplanet Satellite (CHEOPS) to estimate the tidal deformation and tidal decay of this extreme system. We modelled the high-precision CHEOPS transit light curves together with systematic instrumental noise using multi-dimensional Gaussian process regression informed by a set of instrumental parameters. To model the tidal deformation, we used a parametrisation model which allowed us to determine the second degree fluid Love number of the planet. We combined our light curves with previously observed transits of WASP-103b with the Hubble Space Telescope (HST) and Spitzer to increase the signal-to-noise of the light curve and better distinguish the minute signal expected from the planetary deformation.Results. We estimate the radial Love number of WASP-103b to be h(f) = 1.59(-0.53)(+0.45). This is the first time that the tidal deformation is directly detected (at 3 sigma) from the transit light curve of an exoplanet. Combining the transit times derived from CHEOPS, HST, and Spitzer light curves with the other transit times available in the literature, we find no significant orbital period variation for WASP-103b. However, the data show a hint of an orbital period increase instead of a decrease, as is expected for tidal decay. This could be either due to a visual companion star if this star is bound, the Applegate effect, or a statistical artefact.Conclusions. The estimated Love number of WASP-103b is similar to Jupiter's. This will allow us to constrain the internal structure and composition of WASP-103b, which could provide clues on the inflation of hot Jupiters. Future observations with James Webb Space Telescope can better constrain the radial Love number of WASP-103b due to their high signal-to-noise and the smaller signature of limb darkening in the infrared. A longer time baseline is needed to constrain the tidal decay in this system.
17.	Abdo, A. A., et al. (författare) DISCOVERY OF PULSATIONS FROM THE PULSAR J0205+6449 IN SNR 3C 58 WITH THE FERMI GAMMA-RAY SPACE TELESCOPE 2009 Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 0004-637X .- 1538-4357. ; 699:2, s. L102-L107 Tidskriftsartikel (refereegranskat)abstract We report the discovery of gamma-ray pulsations (>= 0.1 GeV) from the young radio and X-ray pulsar PSR J0205 + 6449 located in the Galactic supernova remnant 3C 58. Data in the gamma-ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope (formerly GLAST), while the radio rotational ephemeris used to fold gamma-rays was obtained using both the Green Bank Telescope and the Lovell telescope at Jodrell Bank. The light curve consists of two peaks separated by 0.49 +/- 0.01 +/- 0.01 cycles which are aligned with the X-ray peaks. The first gamma-ray peak trails the radio pulse by 0.08 +/- 0.01 +/- 0.01, while its amplitude decreases with increasing energy as for the other gamma-ray pulsars. Spectral analysis of the pulsed gamma-ray emission suggests a simple power law of index -2.1 +/- 0.1 +/- 0.2 with an exponential cutoff at 3.0(-0.7)(+1.1) +/- 0.4 GeV. The first uncertainty is statistical and the second is systematic. The integral gamma-ray photon flux above 0.1 GeV is (13.7 +/- 1.4 +/- 3.0) x 10(-8) cm(-2) s(-1), which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3 x 10(34) erg s(-1) and an efficiency eta of 0.3%. Finally, we report a 95% upper limit on the flux of 1.7 x 10(-8) cm(-2) s(-1) for off-pulse emission from the object.
18.	Abdo, A. A., et al. (författare) Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C 2009 Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 323:5922, s. 1688-1693 Tidskriftsartikel (refereegranskat)abstract Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.
19.	Bergstrom, S., et al. (författare) J-factors for self-interacting dark matter in 20 dwarf spheroidal galaxies 2018 Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 98:4 Tidskriftsartikel (refereegranskat)abstract Dwarf spheroidal galaxies are among the most promising targets for indirect dark matter (DM) searches in gamma rays. The gamma-ray flux from DM annihilation in a dwarf spheroidal galaxy is proportional to the J-factor of the source. The J-factor of a dwarf spheroidal galaxy is the line-of-sight integral of the DM mass density squared times /(0), where sigma(ann)v(rel) is the DM annihilation cross-section times relative velocity v(rel) = vertical bar v(rel)vertical bar angle brackets denote average over v(rel), and (sigma(ann)v(rel)) is the v(rel)-independent part of sigma(ann)v(rel). If sigma(ann)v(rel) is constant in v(rel), J-factors only depend on the DM space distribution in the source. However, if sigma(ann)v(rel) varies with v(rel), as in the presence of DM self-interactions, J-factors also depend on the DM velocity distribution, and on the strength and range of the DM self-interaction. Models for self interacting DM are increasingly important in the study of the small scale clustering of DM, and are compatible with current astronomical and cosmological observations. Here we derive the J-factor of 20 dwarf spheroidal galaxies from stellar kinematic data under the assumption of Yukawa DM self-interactions. J-factors are derived through a profile likelihood approach, assuming either NavarroFrenk-White (NEW) or cored DM profiles. We also compare our results with J-factors derived assuming the same velocity for all DM particles in the target galaxy. We find that this common approximation overestimates the Mactors by up to 1 order of magnitude. J-factors for a sample of DM particle masses and self-interaction coupling constants, as well as for NFW and cored density profiles, are provided electronically, ready to he used in other projects.
20.	Franz, Jan, 1973, et al. (författare) Formation of carbon monoxide by radiative association: A quantum-mechanical study 2010 Ingår i: XVIII European Conference on Dynamics of Molecular Systems. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
21.	Franz, Jan, 1973, et al. (författare) Molecule Formation by Radiative Association 2010 Ingår i: The Chemical Cosmos: Understanding Chemistry in Astronomical Environments. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
22.	Franz, Jan, 1973, et al. (författare) Molecule Formation in Interstellar Space 2010 Ingår i: Department of Chemical- and Biological Engineering at Chalmers University of Technology and Chemistry at University of Gothenburg. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
23.	Franz, Jan, 1973 (författare) On some molecular reactions of astrophysical interest 2010 Ingår i: Dynamics workshop by Lake Vänern. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
24.	Forsberg, Mats, 1978- (författare) Gravitational perturbations in plasmas and cosmology 2010 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Gravitational perturbations can be in the form of scalars, vectors or tensors. This thesis focuses on the evolution of scalar perturbations in cosmology, and interactions between tensor perturbations, in the form of gravitational waves, and plasma waves. The gravitational waves studied in this thesis are assumed to have small amplitudes and wavelengths much shorter than the background length scale, allowing for the assumption of a flat background metric. Interactions between gravitational waves and plasmas are described by the Einstein-Maxwell-Vlasov, or the Einstein-Maxwell-fluid equations, depending on the level of detail required. Using such models, linear wave excitation of various waves by gravitational waves in astrophysical plasmas are studied, with a focus on resonance effects. Furthermore, the influence of strong magnetic field quantum electrodynamics, leading to detuning of the gravitational wave-electromagnetic wave resonances, is considered. Various nonlinear phenomena, including parametric excitation and wave steepening are also studied in different astrophysical settings. In cosmology the evolution of gravitational perturbations are of interest in processes such as structure formation and generation of large scale magnetic fields. Here, the growth of density perturbations in Kantowski-Sachs cosmologies with positive cosmological constant is studied.
25.	Persson, Jonas, et al. (författare) Planetarium software in the classroom 2016 Ingår i: Physics Education. - : Institute of Physics (IOP). - 0031-9120 .- 1361-6552. ; 51:2 Tidskriftsartikel (refereegranskat)abstract Students often find astronomy and astrophysics to be most interesting and exciting, but the Universe is difficult to access using only one's eyes or simple equipment available at different educational settings. To open up the Universe and enhance learning astronomy and astrophysics different planetarium software can be used. In this article we discuss the usefulness of such simulation software and give four examples of how such software can be used for teaching and learning astronomy and astrophysics.
26.	Lestinsky, M., et al. (författare) Physics book: CRYRING@ESR 2016 Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 225:5, s. 797-882 Forskningsöversikt (refereegranskat)abstract The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).
27.	Aartsen, M. G., et al. (författare) Computational techniques for the analysis of small signals in high-statistics neutrino oscillation experiments 2020 Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 977 Tidskriftsartikel (refereegranskat)abstract The current and upcoming generation of Very Large Volume Neutrino Telescopes - collecting unprecedented quantities of neutrino events - can be used to explore subtle effects in oscillation physics, such as (but not restricted to) the neutrino mass ordering. The sensitivity of an experiment to these effects can be estimated from Monte Carlo simulations. With the high number of events that will be collected, there is a trade-off between the computational expense of running such simulations and the inherent statistical uncertainty in the determined values. In such a scenario, it becomes impractical to produce and use adequately-sized sets of simulated events with traditional methods, such as Monte Carlo weighting. In this work we present a staged approach to the generation of expected distributions of observables in order to overcome these challenges. By combining multiple integration and smoothing techniques which address limited statistics from simulation it arrives at reliable analysis results using modest computational resources.
28.	Eriksson, Urban, Lektor i fysik med inriktning mot fysikdidaktik, 1968- (författare) Disciplinary discernment : reading the sky in astronomy education 2019 Ingår i: Physical review physics education research. - : American Physical Society. - 2469-9896. ; 15:1 Tidskriftsartikel (refereegranskat)abstract This theoretical paper introduces a new way to view and characterize learning astronomy. It describes a framework, based on results from empirical data, analyzed through standard qualitative research method- ology, in which a theoretical model for a vital competency of learning astronomy is proposed: reading the sky, a broad description under with various skills and competencies are included. This model takes into account not only disciplinary knowledge but also disciplinary discernment and extrapolating three dimensionality. Together, these constitute the foundation for the competency referred to as reading the sky. In this paper, these competencies are described and discussed and merged to form a new framework vital for learning astronomy to better match the challenges students face when entering the discipline of astronomy.
29.	Malbet, F., et al. (författare) Faint objects in motion: the new frontier of high precision astrometry 2021 Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 51:3, s. 845-886 Tidskriftsartikel (refereegranskat)abstract Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles.
30.	Hartman, Henrik, et al. (författare) First storage of ion beams in the Double Electrostatic Ion-Ring Experiment : DESIREE 2013 Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 84:5 Tidskriftsartikel (refereegranskat)abstract We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (Cn-, n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2- molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10-14 mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.
31.	Abdo, A. A., et al. (författare) Measurement of the Cosmic Ray e(+)+e(-) Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope 2009 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:Article number: 181101 Tidskriftsartikel (refereegranskat)abstract Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m(2) sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.
32.	Akrami, Yashar, 1980-, et al. (författare) How well will ton-scale dark matter direct detection experiments constrain minimal supersymmetry? 2011 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :4, s. 012- Tidskriftsartikel (refereegranskat)abstract Weakly interacting massive particles (WIMPs) are amongst the most interesting dark matter (DM) candidates. Many DM candidates naturally arise in theories beyond the standard model (SM) of particle physics, like weak-scale supersymmetry (SUSY). Experiments aim to detect WIMPs by scattering, annihilation or direct production, and thereby determine the underlying theory to which they belong, along with its parameters. Here we examine the prospects for further constraining the Constrained Minimal Supersymmetric Standard Model (CMSSM) with future ton-scale direct detection experiments. We consider ton-scale extrapolations of three current experiments: CDMS, XENON and COUPP, with 1000 kg-years of raw exposure each. We assume energy resolutions, energy ranges and efficiencies similar to the current versions of the experiments, and include backgrounds at target levels. Our analysis is based on full likelihood constructions for the experiments. We also take into account present uncertainties on hadronic matrix elements for neutralino-quark couplings, and on halo model parameters. We generate synthetic data based on four benchmark points and scan over the CMSSM parameter space using nested sampling. We construct both Bayesian posterior PDFs and frequentist profile likelihoods for the model parameters, as well as the mass and various cross-sections of the lightest neutralino. Future ton-scale experiments will help substantially in constraining supersymmetry, especially when results of experiments primarily targeting spin-dependent nuclear scattering are combined with those directed more toward spin-independent interactions.
33.	Akrami, Yashar, 1980-, et al. (författare) Statistical coverage for supersymmetric parameter estimation : a case study with direct detection of dark matter 2011 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :7, s. 002- Tidskriftsartikel (refereegranskat)abstract Models of weak-scale supersymmetry offer viable dark matter (DM) candidates. Their parameter spaces are however rather large and complex, such that pinning down the actual parameter values from experimental data can depend strongly on the employed statistical framework and scanning algorithm. In frequentist parameter estimation, a central requirement for properly constructed confidence intervals is that they cover true parameter values, preferably at exactly the stated confidence level when experiments are repeated infinitely many times. Since most widely-used scanning techniques are optimised for Bayesian statistics, one needs to assess their abilities in providing correct confidence intervals in terms of the statistical coverage. Here we investigate this for the Constrained Minimal Supersymmetric Standard Model (CMSSM) when only constrained by data from direct searches for dark matter. We construct confidence intervals from one-dimensional profile likelihoods and study the coverage by generating several pseudo-experiments for two benchmark sets of pseudo-true parameters. We use nested sampling to scan the parameter space and evaluate the coverage for the two benchmarks when either flat or logarithmic priors are imposed on gaugino and scalar mass parameters. We observe both under- and over-coverage, which in some cases vary quite dramatically when benchmarks or priors are modified. We show how most of the variation can be explained as the impact of explicit and implicit priors, where the latter are indirectly imposed by physicality conditions. For comparison, we also evaluate the coverage for Bayesian credible intervals, and (predictably) observe significant under-coverage in those cases.
34.	Blomqvist, Michael, et al. (författare) Probing dark energy inhomogeneities with supernovae 2008 Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 06, s. 027- Tidskriftsartikel (refereegranskat)abstract We discuss the possibility of identifying anisotropic and/or inhomogeneous cosmological models using type Ia supernova data. A search for correlations in current type Ia peak magnitudes over a large range of angular scales yields a null result. However, the same analysis limited to supernovae at low redshift shows a feeble anticorrelation at the 2σ level at angular scales θ≈40°. Upcoming data from, e.g., the SNLS (Supernova Legacy Survey) and the SDSS-II (SDSS: Sloan Digital Sky Survey) supernova searches will improve our limits on the size of—or possibly detect—possible correlations also at high redshift at the per cent level in the near future. With data from the proposed SNAP (SuperNova Acceleration Probe) satellite, we will be able to detect the induced correlations from gravitational lensing on type Ia peak magnitudes on scales less than a degree.
35.	Fabbian, D., et al. (författare) Neutral oxygen spectral line formation revisited with new collisional data : large departures from LTE at low metallicity 2009 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 500, s. 1221-1238 Tidskriftsartikel (refereegranskat)abstract Aims: A detailed study is presented, including estimates of the impact on elemental abundance analysis, of the non-local thermodynamic equilibrium (non-LTE) formation of the high-excitation neutral oxygen 777 nm triplet in model atmospheres representative of stars with spectral types F to K. Methods: We have applied the statistical equilibrium code MULTI to a number of plane-parallel MARCS atmospheric models covering late-type stars (4500 ≤ T_eff ≤ 6500 K, 2 ≤ log g ≤ 5 [cgs], and -3.5 ≤ [Fe/H] ≤ 0). The atomic model employed includes, in particular, recent quantum-mechanical electron collision data. Results: We confirm that the O i triplet lines form under non-LTE conditions in late-type stars, suffering negative abundance corrections with respect to LTE. At solar metallicity, the non-LTE effect, mainly attributed in previous studies to photon losses in the triplet itself, is also driven by an additional significant contribution from line opacity. At low metallicity, the very pronounced departures from LTE are due to overpopulation of the lower level (3s ^5S^o) of the transition. Large line opacity stems from triplet-quintet intersystem electron collisions, a form of coupling previously not considered or seriously underestimated. The non-LTE effects generally become severe for models (both giants and dwarfs) with higher T_eff. Interestingly, in metal-poor turn-off stars, the negative non-LTE abundance corrections tend to rapidly become more severe towards lower metallicity. When neglecting H collisions, they amount to as much as \|Δlog ɛ_O\| ~ 0.9 dex and ~1.2 dex, respectively at [Fe/H] = -3 and [Fe/H] = -3.5. Even when such collisions are included, the LTE abundance remains a serious overestimate, correspondingly by \|Δlog ɛ_O\| ~ 0.5 dex and ~0.9 dex at such low metallicities. Although the poorly known inelastic hydrogen collisions thus remain an important uncertainty, the large metallicity-dependent non-LTE effects seem to point to a resulting “low” (compared to LTE) [O/Fe] in metal-poor halo stars. Conclusions: Our results may be important in solving the long-standing [O/Fe] debate. When applying the derived non-LTE corrections, the LTE oxygen abundance inferred from the 777 nm permitted triplet will be decreased substantially at low metallicity. If the classical Drawin formula is employed for O+H collisions, the derived [O/Fe] trend becomes almost flat below [Fe/H] ~ -1, in better agreement with recent literature estimates generally obtained from other oxygen abundance indicators. A value of [O/Fe] ⪉ +0.5 may therefore be appropriate, as suggested by standard theoretical models of type II supernovae nucleosynthetic yields. If neglecting impacts with H atoms instead, [O/Fe] decreases towards lower [Fe/H], which would open new questions. Our tests using ATLAS model atmospheres show that, though non-LTE corrections for metal-poor dwarfs are smaller (by ~0.2 dex when adopting efficient H collisions) than in the MARCS case, our main conclusions are preserved, and that the LTE approach tends to seriously overestimate the O abundance at low metallicity. However, in order to finally reach consistency between oxygen abundances from the different available spectral features, it is of high priority to reduce the large uncertainty regarding H collisions, to undertake a full investigation of the interplay of non-LTE and 3D effects, and to clarify the issue of the temperature scale at low metallicity.
36.	Nordin, Jakob, et al. (författare) Spectral properties of Type Ia supernovae up to z~0.3 2011 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 526, s. A119- Tidskriftsartikel (refereegranskat)abstract Aims: Spectroscopic observations of type Ia supernovae obtained at the New Technology Telescope (NTT) and the Nordic Optical Telescope (NOT), in conjunction with the SDSS-II Supernova Survey, are analysed. We use spectral indicators measured up to a month after the lightcurve peak luminosity to characterise the supernova properties, and examine these for potential correlations with host galaxy type, lightcurve shape, colour excess, and redshift. Methods: Our analysis is based on 89 type Ia supernovae at a redshift interval z = 0.05-0.3, for which multiband SDSS photometry is available. A lower-z spectroscopy reference sample was used for comparisons over cosmic time. We present measurements of time series of pseudo equivalent widths and line velocities of the main spectral features in type Ia supernovae. Results: Supernovae with shallower features are found predominantly among the intrinsically brighter slow declining supernovae. We detect the strongest correlation between lightcurve stretch and the Si ii λ4000 absorption feature, which also correlates with the estimated mass and star formation rate of the host galaxy. We also report a tentative correlation between colour excess and spectral properties. If confirmed, this would suggest that moderate reddening of type Ia supernovae is dominated by effects in the explosion or its immediate environment, as opposed to extinction by interstellar dust.
37.	Puschnig, Johannes, 1980- (författare) How ISM properties drive Lyman Continuum Escape 2016 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The thesis introduces physical processes that are at work in astrophysical plasmas and reviews the current state of research related to the emission of ionizing photons, i.e. Lyman continuum (LyC). Star forming galaxies and active galactic nuclei are discussed as sources of LyC. Observations of LyC leakage at all redshifts are summarized and escape fractions are brought into a cosmological context, i.e. its implications for the reionization of the Universe, one of the major gas phase changes that was completed already after ∼1Gyr after the Big Bang at redshift z∼6.The main work focuses on observations of the local LyC leaking galaxy Tololo 1247-232. Physical properties of the interstellar medium, its porosity and neutral medium column density, could be derived using newly obtained Hubble Space Telescope (HST) data. The work is based on spectroscopy obtained with the Cosmic Origins Spectrograph (COS), as well as optical and ultraviolet multi-band imaging with the Wide Field Camera 3 (WFC3). An improved COS data reduction procedure was adopted. The recent detection of ionizing radiation emerging from Tololo 1247-232 could be confirmed. A LyC escape fraction of 6.6% was derived, in agreement with previous results. We used FUV absorption lines of Si II and Si IV as a probe of the neutral and ionized interstellar medium and find that most of the ISM gas is ionized, likely facilitating LyC escape from density bounded regions. Neutral gas covering as a function of line-of-sight velocity is derived using the apparent optical depth method. The ISM is found to be sufficiently clumpy, supporting the direct escape of LyC photons. We further report on broadband UV and optical continuum imaging as well as narrowband imaging of Lyα, Hα and Hβ. We also performed VLA 21cm imaging. The hydrogen hyperfine transition was not detected, but a deep upper limit atomic gas mass of 10^9 Mo could be derived. The upper limit gas fraction is only 20 percent. Evidence is found that the H I gas halo is relatively small compared to other Lyman Alpha emitters.
38.	Rubin, D., et al. (författare) Looking Beyond Lambda with the Union Supernova Compilation 2009 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 695, s. 391-403 Tidskriftsartikel (refereegranskat)abstract The recent robust and homogeneous analysis of the world's supernova distance-redshift data, together with cosmic microwave background and baryon acoustic oscillation data—provides a powerful tool for constraining cosmological models. Here we examine particular classes of scalar field, modified gravity, and phenomenological models to assess whether they are consistent with observations even when their behavior deviates from the cosmological constant Λ. Some models have tension with the data, while others survive only by approaching the cosmological constant, and a couple are statistically favored over Λ cold dark matter. Dark energy described by two equation-of-state parameters has considerable phase space to avoid Λ and next-generation data will be required to constrain such physics, with the level of complementarity between probes varying with cosmology.
39.	Sordo, Rosanna, et al. (författare) Synthetic stellar and SSP libraries as templates for Gaia simulations 2010 Ingår i: Astrophysics and Space Science. - : Springer Science and Business Media LLC. - 0004-640X .- 1572-946X. ; 328:1-2, s. 331-335 Tidskriftsartikel (refereegranskat)abstract ESA's Gaia mission will collect low resolution spectroscopy in the optical range for 109 objects. Complete and up-to-date libraries of synthetic stellar spectra are needed to built algorithms aimed to automatically derive the classification and the parametrization of this huge amount of data. In addition, libraries of stellar spectra are one of the main ingredients of stellar population synthesis models, aiming to derive the properties of unresolved stellar populations from their integrated light. We present (a) the newly computed libraries of synthetic spectra built by the Gaia community, covering the whole optical range (300-1100 nm) at medium-high resolution of (0.3 nm) for stars spanning the most different types, from M to O, from A-peculiar to Emission lines to White Dwarfs, and (b) the implementation of those libraries in our SSP code (Tantalo in The Initial Mass Function 50 Years Later, 327:235 2005), exploring different stellar evolution models.
40.	Thomas, Rajat M., et al. (författare) Fast large-scale reionization simulations 2009 Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 393, s. 32-48 Tidskriftsartikel (refereegranskat)abstract We present an efficient method to generate large simulations of the epoch of reionization without the need for a full three-dimensional radiative transfer code. Large dark-matter-only simulations are post-processed to produce maps of the redshifted 21-cm emission from neutral hydrogen. Dark matter haloes are embedded with sources of radiation whose properties are either based on semi-analytical prescriptions or derived from hydrodynamical simulations. These sources could either be stars or power-law sources with varying spectral indices. Assuming spherical symmetry, ionized bubbles are created around these sources, whose radial ionized fraction and temperature profiles are derived from a catalogue of one-dimensional radiative transfer experiments. In case of overlap of these spheres, photons are conserved by redistributing them around the connected ionized regions corresponding to the spheres. The efficiency with which these maps are created allows us to span the large parameter space typically encountered in reionization simulations. We compare our results with other, more accurate, three-dimensional radiative transfer simulations and find excellent agreement for the redshifts and the spatial scales of interest to upcoming 21-cm experiments. We generate a contiguous observational cube spanning redshift 6 to 12 and use these simulations to study the differences in the reionization histories between stars and quasars. Finally, the signal is convolved with the Low Frequency Array (LOFAR) beam response and its effects are analysed and quantified. Statistics performed on this mock data set shed light on possible observational strategies for LOFAR.
41.	Östman, Linda, et al. (författare) NTT and NOT spectroscopy of SDSS-II supernovae 2011 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 526, s. A28- Tidskriftsartikel (refereegranskat)abstract Context. The Sloan Digital Sky Survey II (SDSS-II) Supernova Survey, conducted between 2005 and 2007, was designed to detect a large number of type Ia supernovae around z ~ 0.2, the redshift "gap" between low-z and high-z supernova searches. The survey has provided multi-band (ugriz) photometric lightcurves for variable targets, and supernova candidates were scheduled for spectroscopic observations, primarily to provide supernova classification and accurate redshifts. We present supernova spectra obtained in 2006 and 2007 using the New Technology Telescope (NTT) and the Nordic Optical Telescope (NOT). Aims: We provide an atlas of supernova spectra in the range z = 0.03-0.32 that complements the well-sampled lightcurves from SDSS-II in the forthcoming three-year SDSS supernova cosmology analysis. The sample can, for example, be used for spectral studies of type Ia supernovae, which are critical for understanding potential systematic effects when supernovae are used to determine cosmological distances. Methods: The spectra were reduced in a uniform manner, and special care was taken in estimating the uncertainties for the different processing steps. Host-galaxy light was subtracted when possible and the supernova type fitted using the SuperNova IDentification code (SNID). We also present comparisons between spectral and photometric dating using SALT lightcurve fits to the photometry from SDSS-II, as well as the global distribution of our sample in terms of the lightcurve parameters: stretch and colour. Results: We report new spectroscopic data from 141 type Ia supernovae, mainly between -9 and +15 days from lightcurve maximum, including a few cases of multi-epoch observations. This homogeneous, host-galaxy subtracted, type Ia supernova spectroscopic sample is among the largest such data sets and unique in its redshift interval. The sample includes two potential SN 1991T-like supernovae (SN 2006on and SN 2007ni) and one potential SN 2002cx-like supernova (SN 2007ie). In addition, the new compilation includes spectra from 23 confirmed type II and 8 type Ib/c supernovae.
42.	Bonfanti, A., et al. (författare) CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii 2021 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 646 Tidskriftsartikel (refereegranskat)abstract Context. The detection of a super-Earth and three mini-Neptunes transiting the bright (V = 9.2 mag) star HD 108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based light curves. Aims. We perform a first characterisation of the HD 108236 planetary system through high-precision CHEOPS photometry and improve the transit ephemerides and system parameters. Methods. We characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method. We constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. We analyse the available TESS light curves and one CHEOPS transit light curve for each known planet in the system. Results. We find that HD 108236 is a Sun-like star with R? = 0.877 ± 0.008 R? , M? = 0.869-0.048+0.050 M? , and an age of 6.7-5.1+4.0 Gyr. We report the serendipitous detection of an additional planet, HD 108236 f, in one of the CHEOPS light curves. For this planet, the combined analysis of the TESS and CHEOPS light curves leads to a tentative orbital period of about 29.5 days. From the light curve analysis, we obtain radii of 1.615 ± 0.051, 2.071 ± 0.052, 2.539-0.065+0.062, 3.083 ± 0.052, and 2.017-0.057+0.052 R? for planets HD 108236 b to HD 108236 f, respectively. These values are in agreement with previous TESS-based estimates, but with an improved precision of about a factor of two. We perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. We also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that HD 108236 b and HD 108236 c should have an Earth-like density, while the outer planets should host a low mean molecular weight envelope. Conclusions. The detection of the fifth planet makes HD 108236 the third system brighter than V = 10 mag to host more than four transiting planets. The longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. A comparison of the results obtained from the TESS and CHEOPS light curves indicates that for a V - 9 mag solar-like star and a transit signal of -500 ppm, one CHEOPS transit light curve ensures the same level of photometric precision as eight TESS transits combined, although this conclusion depends on the length and position of the gaps in the light curve.
43.	Hobiger, Thomas, 1978, et al. (författare) Hard- and software tools for the education of Geodetic VLBI 2016 Ingår i: 9th IVS General Meeting, March 2016, Johannesburg, South Africa. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Onsala Space Observatory hosts two 2.3 m radio telescopes called SALSA ("Such a lovely small antenna") which are utilised to bring front-line interactive astronomy to the classroom. Until now SALSA has been used for astronomical educational purposes solely, in particular demonstrating the concept of single dish measurements. However, it is possible to combine both SALSAs to an interferometer by making use of hardware which has been developed for software-defined radio. In doing so, one can utilise the SALSA antenna pair as a student demonstrator for geodetic Very Long Baseline Interferometry. We will discuss the COTS hardware components that are necessary to turn the SALSA installation into an interferometer. Moreover, we will show how a simple correlator has been used to detect fringes and provide single-band delays. Such delays were then processed with our analysis software c5++. We are going to discuss how it is possible to mimic the complete processing chain of geodetic VLBI and how this can be used for training of students and other interested parties.
44.	Szabo, Gy M., et al. (författare) Transit timing variations of AU Microscopii b and c* 2022 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 659 Tidskriftsartikel (refereegranskat)abstract Here we report large-amplitude transit timing variations (TTVs) for AU Microcopii b and c as detected in combined TESS (2018, 2020) and CHEOPS (2020, 2021) transit observations. AU Mic is a young planetary system with a debris disk and two transiting warm Neptunes. A TTV on the order of several minutes was previously reported for AU Mic b, which was suggested to be an outcome of mutual perturbations between the planets in the system. In 2021, we observed AU Mic b (five transits) and c (three transits) with the CHEOPS space telescope to follow-up the TTV of AU Mic b and possibly detect a TTV for AU Mic c. When analyzing TESS and CHEOPS 2020-2021 measurements together, we find that a prominent TTV emerges with a full span of >= 23 min between the two TTV extrema. Assuming that the period change results from a periodic process -such as mutual perturbations- we demonstrate that the times of transits in the summer of 2022 are expected to be 30-85 min later than predicted by the available linear ephemeris.
45.	Milstead, David A., et al. (författare) Study of the material of the ATLAS inner detector for Run 2 of the LHC 2017 Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 12:12 Tidskriftsartikel (refereegranskat)abstract The ATLAS inner detector comprises three different sub-detectors: the pixel detector, the silicon strip tracker, and the transition-radiation drift-tube tracker. The Insertable B-Layer, a new innermost pixel layer, was installed during the shutdown period in 2014, together with modifications to the layout of the cables and support structures of the existing pixel detector. The material in the inner detector is studied with several methods, using a low-luminosity s=13 TeV pp collision sample corresponding to around 2.0 nb-1 collected in 2015 with the ATLAS experiment at the LHC. In this paper, the material within the innermost barrel region is studied using reconstructed hadronic interaction and photon conversion vertices. For the forward rapidity region, the material is probed by a measurement of the efficiency with which single tracks reconstructed from pixel detector hits alone can be extended with hits on the track in the strip layers. The results of these studies have been taken into account in an improved description of the material in the ATLAS inner detector simulation, resulting in a reduction in the uncertainties associated with the charged-particle reconstruction efficiency determined from simulation. © 2017 CERN.
46.	Kawamuro, Taiki, et al. (författare) AGN X-Ray Irradiation of CO Gas in NGC 2110 Revealed by Chandra and ALMA 2020 Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 895:2 Tidskriftsartikel (refereegranskat)abstract We report spatial distributions of the Fe-K alpha line at 6.4 keV and the CO(J = 2-1) line at 230.538 GHz in NGC 2110, which are, respectively, revealed by Chandra and Atacama Large Millimeter/submillimeter Array (ALMA) at 05. A Chandra 6.2-6.5 keV to 3.0-6.0 keV image suggests that the Fe-K alpha emission extends preferentially in a northwest to southeast direction out to 3 '', or similar to 500 pc, on each side. Spatially resolved spectral analyses support this by finding significant Fe-K alpha emission lines only in the northwest and southeast regions. Moreover, their equivalent widths are found to be similar to 1.5 keV, indicative for the fluorescence by nuclear X-ray irradiation as the physical origin. By contrast, CO(J = 2-1) emission is weak therein. For quantitative discussion, we derive ionization parameters by following an X-ray dominated region (XDR) model. We then find them high enough to interpret the weakness as the result of X-ray dissociation of CO and/or H-2. Another possibility also remains that CO molecules follow a superthermal distribution, resulting in brighter emission in higher-J lines. Further follow-up observations are encouraged to draw a conclusion on what predominantly changes the interstellar matter properties and whether the X-ray irradiation eventually affects the surrounding star formation as active galactic nucleus (AGN) feedback.
47.	Bourrier, V., et al. (författare) A CHEOPS-enhanced view of the HD 3167 system 2022 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668 Tidskriftsartikel (refereegranskat)abstract Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations.
48.	Benmahi, B., et al. (författare) Monitoring of the evolution of H2O vapor in the stratosphere of Jupiter over an 18-yr period with the Odin space telescope 2020 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 641 Tidskriftsartikel (refereegranskat)abstract Context. The comet Shoemaker-Levy 9 impacted Jupiter in July 1994, leaving its stratosphere with several new species, with water vapor (H2O) among them. Aims. With the aid of a photochemical model, H2O can be used as a dynamical tracer in the Jovian stratosphere. In this paper, we aim to constrain the vertical eddy diffusion (Kzz) at levels where H2O is present. Methods. We monitored the H2O disk-averaged emission at 556.936 GHz with the space telescope between 2002 and 2019, covering nearly two decades. We analyzed the data with a combination of 1D photochemical and radiative transfer models to constrain the vertical eddy diffusion in the stratosphere of Jupiter. Results. Odin observations show us that the emission of H2O has an almost linear decrease of about 40% between 2002 and 2019. We can only reproduce our time series if we increase the magnitude of Kzz in the pressure range where H2O diffuses downward from 2002 to 2019, that is, from ~0.2 mbar to ~5 mbar. However, this modified Kzz is incompatible with hydrocarbon observations. We find that even if an allowance is made for the initially large abundances of H2O and CO at the impact latitudes, the photochemical conversion of H2O to CO2 is not sufficient to explain the progressive decline of the H2O line emission, which is suggestive of additional loss mechanisms. Conclusions. The Kzz we derived from the Odin observations of H2O can only be viewed as an upper limit in the ~0.2 mbar to ~5 mbar pressure range. The incompatibility between the interpretations made from H2O and hydrocarbon observations probably results from 1D modeling limitations. Meridional variability of H2O, most probably at auroral latitudes, would need to be assessed and compared with that of hydrocarbons to quantify the role of auroral chemistry in the temporal evolution of the H2O abundance since the SL9 impacts. Modeling the temporal evolution of SL9 species with a 2D model would naturally be the next step in this area of study.
49.	Abdo, A. A., et al. (författare) FERMI/LARGE AREA TELESCOPE DISCOVERY OF GAMMA-RAY EMISSION FROM A RELATIVISTIC JET IN THE NARROW-LINE QUASAR PMN J0948+0022 2009 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 699:2, s. 976-984 Tidskriftsartikel (refereegranskat)abstract We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy. gamma-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.5846). The optical spectrum of this object exhibits rather narrow H beta (FWHM(H beta) similar to 1500 km s(-1)), weak forbidden lines, and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at a high Eddington ratio. The radio loudness and variability of the compact radio core indicate the presence of a relativistic jet. Quasi-simultaneous radio/optical/X-ray and gamma-ray observations are presented. Both radio and gamma-ray emissions (observed over five months) are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broadband spectral energy distribution (SED) and, in particular, the gamma-ray spectrum measured by Fermi are similar to those of more powerful Flat-Spectrum Radio Quasars (FSRQs). A comparison of the radio and gamma-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and gamma-ray power with respect to other FSRQs. The physical parameters obtained from modeling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti & Ghisellini. We suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.
50.	Abdo, A. A., et al. (författare) PULSED GAMMA RAYS FROM THE MILLISECOND PULSAR J0030+0451 WITH THE FERMI LARGE AREA TELESCOPE 2009 Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 699:2, s. 1171-1177 Tidskriftsartikel (refereegranskat)abstract We report the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar (MSP) PSR J0030+0451 with the Large Area Telescope on the Fermi Gamma-ray Space Telescope (formerly GLAST). This discovery makes PSR J0030+0451 the second MSP to be detected in gamma rays after PSR J0218+4232, observed by the EGRET instrument on the Compton Gamma-Ray Observatory. The spin-down power (E) over dot = 3.5 x 10(33) erg s(-1) is an order of magnitude lower than the empirical lower bound of previously known gamma-ray pulsars. The emission profile is characterized by two narrow peaks, 0.07 +/- 0.01 and 0.08 +/- 0.02 wide, respectively, separated by 0.44 +/- 0.02 in phase. The first gamma-ray peak falls 0.15 +/- 0.01 after the main radio peak. The pulse shape is similar to that of the "normal" gamma-ray pulsars. An exponentially cutoff power-law fit of the emission spectrum leads to an integral photon flux above 100 MeV of (6.76 +/- 1.05 +/- 1.35) x 10(-8) cm(-2) s(-1) with cutoff energy (1.7 +/- 0.4 +/- 0.5) GeV. Based on its parallax distance of (300 +/- 90) pc, we obtain a gamma-ray efficiency L-gamma/E similar or equal to 15% for the conversion of spin-down energy rate into gamma-ray radiation, assuming isotropic emission.

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