1. |
- Grunhut, H, et al.
(författare)
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Discovery of a magnetic field in the O9 sub-giant star HD 57682 by the MiMeS Collaboration
- 2009
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 400:1, s. L94-L98
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of a strong, organized magnetic field in the O9IV star HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the 3.6-m Canada-France-Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Programme. From the fitting of our spectra using non-local thermodynamic equilibrium model atmospheres, we determined that HD 57682 is a 17(-9)(+19)M(circle dot) star with a radius of 7.0(-1.8)(+2.4)R(circle dot) and a relatively low mass-loss rate of 1.4(-0.95)(+3.1) x 10(-9) M-circle dot yr(-1). The photospheric absorption lines are narrow, and we use the Fourier transform technique to infer v sin i = 15 +/- 3 km s(-1). This v sin i implies a maximum rotational period of 31.5 d, a value qualitatively consistent with the observed variability of the optical absorption and emission lines, as well as the Stokes V profiles and longitudinal field. Using a Bayesian analysis of the velocity-resolved Stokes V profiles to infer the magnetic field characteristics, we tentatively derive a dipole field strength of 1680(-356)(+134)G. The derived field strength and wind characteristics imply a wind that is strongly confined by the magnetic field.
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2. |
- Thébault, Philippe, et al.
(författare)
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Planet formation in the habitable zone of α Centauri B
- 2009
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 393:1, s. L21-L25
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that α Centauri B might be, from an observational point of view, an ideal candidate for the detection of an Earth-like planet in or near its habitable zone (0.5-0.9au). We study here if such habitable planets can form, by numerically investigating the planet-formation stage which is probably the most sensitive to binarity effects: the mutual accretion of km-sized planetesimals. Using a state-of-the-art algorithm for computing the impact velocities within a test planetesimal population, we find that planetesimal growth is only possible, although marginally, in the innermost part of the habitable zone (HZ) around 0.5au. Beyond this point, the combination of secular perturbations by the binary companion and gas drag drives the mutual velocities beyond the erosion limit. Impact velocities might later decrease during the gas removal phase, but this probably happens too late for preventing most km-sized objects to be removed by inward drift, thus preventing accretion from starting anew. A more promising hypothesis is that the binary formed in a crowded cluster, where it might have been wider in its initial stages, when planetary formation was ongoing. We explore this scenario and find that a starting separation roughly 15au wider, or an eccentricity 2.5 times lower than the present ones, is required to have an accretion-friendly environment in the whole HZ.
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3. |
- Thoudam, Satyendra
(författare)
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Revisiting the effect of nearby supernova remnants on local cosmic rays
- 2007
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 380:1, s. L1-L5
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Tidskriftsartikel (refereegranskat)abstract
- In an earlier paper, the effect of the nearby known supernova remnants (SNRs) on the local cosmic rays (CRs) was studied, considering different possible forms of the particle injection time. The present work is a continuation of the previous work, but assumes a more realistic model of CR propagation in the Galaxy. The previous work assumed an unbounded three-dimensional diffusion region, whereas the present one considers a flat cylindrical disc bounded in both the radial and vertical directions. The study has found that the effect of the vertical halo boundary H on the local SNR contribution to the observed CR anisotropy is negligible as long as H≳ 2 kpc. Considering the values of the halo height H≳ 2 kpc obtained by different authors, the present work suggests that the study of the effect of local sources on the CR anisotropy can be carried out without having much information on H, and hence using the much simpler three-dimensional unbounded solution. Finally, the present work discusses the possibility of explaining the observed anisotropy below the knee by a single dominant source with properly chosen source parameters, and claims that the source may be an undetected old SNR with a characteristic age of ∼1.5 × 105 yr located at a distance of ∼0.57 kpc from the Sun.
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4. |
- Algeri, Sara, et al.
(författare)
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A method for comparing non-nested models with application to astrophysical searches for new physics
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 458:1, s. L84-L88
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Tidskriftsartikel (refereegranskat)abstract
- Searches for unknown physics and decisions between competing astrophysical models to explain data both rely on statistical hypothesis testing. The usual approach in searches for new physical phenomena is based on the statistical likelihood ratio test and its asymptotic properties. In the common situation, when neither of the two models under comparison is a special case of the other i.e. when the hypotheses are non-nested, this test is not applicable. In astrophysics, this problem occurs when two models that reside in different parameter spaces are to be compared. An important example is the recently reported excess emission in astrophysical gamma-rays and the question whether its origin is known astrophysics or dark matter. We develop and study a new, simple, generally applicable, frequentist method and validate its statistical properties using a suite of simulations studies. We exemplify it on realistic simulated data of the Fermi-Large Area Telescope gamma-ray satellite, where non-nested hypotheses testing appears in the search for particle dark matter.
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5. |
- Amarsi, A. M., et al.
(författare)
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The Galactic chemical evolution of oxygen inferred from 3D non-LTE spectral-line-formation calculations
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 454:1, s. L11-L15
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Tidskriftsartikel (refereegranskat)abstract
- We revisit the Galactic chemical evolution of oxygen, addressing the systematic errors inherent in classical determinations of the oxygen abundance that arise from the use of one-dimensional (1D) hydrostatic model atmospheres and from the assumption of local thermodynamic equilibrium (LTE). We perform detailed 3D non-LTE radiative-transfer calculations for atomic oxygen lines across a grid of 3D hydrodynamic STAGGER model atmospheres for dwarfs and subgiants. We apply our grid of predicted line strengths of the [O I] 630 nm and O I 777 nm lines using accurate stellar parameters from the literature. We infer a steep decay in [O/Fe] for [Fe/H] greater than or similar to -1.0, a plateau [O/Fe] approximate to 0.5 down to [Fe/H] approximate to -2.5, and an increasing trend for [Fe/H] less than or similar to -2.5. Our 3D non-LTE calculations yield overall concordant results from the two oxygen abundance diagnostics.
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6. |
- Arentsen, A., et al.
(författare)
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The Pristine Inner Galaxy Survey (PIGS) I : tracing the kinematics of metal-poor stars in the Galactic bulge
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 491:1, s. L11-L16
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Tidskriftsartikel (refereegranskat)abstract
- Our Galaxy is known to contain a central boxy/peanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large sample of metal-poor ([Fe/H] < -1.0) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H], until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for -3.0 < [Fe/II] < -0.5, with a gradient of -44 +/- 41un s(-1)dex(-1). These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy/peanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy.
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7. |
- Chauvin, Maxime, et al.
(författare)
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Observation of polarized hard X-ray emission from the Crab by the PoGOLite Pathfinder
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 456:1, s. L84-L88
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the linear polarization of hard X-ray emission from the Crab in a previously unexplored energy interval, 20-120 keV. The introduction of two new observational parameters, the polarization fraction and angle stands to disentangle geometrical and physical effects, thereby providing information on the pulsar wind geometry and magnetic field environment. Measurements are conducted using the PoGOLite Pathfinder - a balloon-borne polarimeter. Polarization is determined by measuring the azimuthal Compton scattering angle of incident X-rays in an array of plastic scintillators housed in an anticoincidence well. The polarimetric response has been characterized prior to flight using both polarized and unpolarized calibration sources. We address possible systematic effects through observations of a background field. The measured polarization fraction for the integrated Crab light curve is 18.4(-10.6)(+9.8) per cent, corresponding to an upper limit (99 per cent credibility) of 42.4 per cent, for a polarization angle of (149.2 +/- 16.0)degrees.
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8. |
- Chauvin, Maxime, et al.
(författare)
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PoGO + polarimetric constraint on the synchrotron jet emission of Cygnus X-1
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society: Letters. - : Oxford University Press. - 1745-3925 .- 1745-3933 .- 0035-8711 .- 1365-2966. ; 483:1, s. L138-L143
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Tidskriftsartikel (refereegranskat)abstract
- We report a polarimetric constraint on the hard X-ray synchrotron jet emission from the Cygnus X-1 black hole binary system. The observational data were obtained using the PoGO+ hard X-ray polarimeter in 2016 July, when Cygnus X-1 was in the hard state. We have previously reported that emission from an extended corona with a low polarization fraction is dominating, and that the polarization angle is perpendicular to the disc surface. In the soft gamma-ray regime, a highly polarized synchrotron jet is reported with INTEGRAL observations. To constrain the polarization fraction and flux of such a jet component in the hard X-ray regime, we now extend analyses through vector calculations in the Stokes QU plane, where the dominant corona emission and the jet component are considered simultaneously. The presence of another emission component with different polarization angle could partly cancel out the net polarization. The 90 per cent upper limit of the polarization fraction for the additional synchrotron jet component is estimated as <10 per cent, <5 per cent, and <5 per cent for polarization angle perpendicular to the disc surface, parallel to the surface, and aligned with the emission reported by INTEGRAL data, respectively. From the 20-180 keV total flux of 2.6 × 10 -8 erg s -1 cm -2, the upper limit of the polarized flux is estimated as < 3 × 10 -9 erg s -1 cm -2.
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9. |
- Chauvin, Maxime, et al.
(författare)
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The PoGO plus view on Crab off-pulse hard X-ray polarization
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 477:1, s. L45-L49
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Tidskriftsartikel (refereegranskat)abstract
- The linear polarization fraction (PF) and angle of the hard X-ray emission from the Crab provide unique insight into high-energy radiation mechanisms, complementing the usual imaging, timing, and spectroscopic approaches. Results have recently been presented by two missions operating in partially overlapping energy bands, PoGO+ (18-160 keV) and AstroSat CZTI (100-380 keV). We previously reported PoGO+ results on the polarization parameters integrated across the light curve and for the entire nebula-dominated off-pulse region. We now introduce finer phase binning, in light of the AstroSat CZTI claim that the PF varies across the off-pulse region. Since both missions are operating in a regime where errors on the reconstructed polarization parameters are non-Gaussian, we adopt a Bayesian approach to compare results from each mission. We find no statistically significant variation in off-pulse polarization parameters, neither when considering the mission data separately nor when they are combined. This supports expectations from standard high-energy emission models.
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10. |
- Dell'Agli, F., et al.
(författare)
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Are extreme asymptotic giant branch stars post-common envelope binaries?
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 502:1, s. L35-L39
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Tidskriftsartikel (refereegranskat)abstract
- Modelling dust formation in single stars evolving through the carbon-star stage of the asymptotic giant branch (AGB) reproduces well the mid-infrared colours and magnitudes of most of the C-rich sources in the Large Magellanic Cloud (LMC), apart from a small subset of extremely red objects (EROs). An analysis of the spectral energy distributions of EROs suggests the presence of large quantities of dust, which demand gas densities in the outflow significantly higher than expected from theoretical modelling. We propose that binary interaction mechanisms that involve common envelope (CE) evolution could be a possible explanation for these peculiar stars; the CE phase is favoured by the rapid growth of the stellar radius occurring after C/O overcomes unity. Our modelling of the dust provides results consistent with the observations for mass-loss rates (M) over dot similar to 5 x 10(-4) M-circle dot yr(-1), a lower limit to the rapid loss of the envelope experienced in the CE phase. We propose that EROs could possibly hide binaries with orbital periods of about days and are likely to be responsible for a large fraction of the dust production rate in galaxies.
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11. |
- Desmond, Harry, et al.
(författare)
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The fifth force in the local cosmic web
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 483:1, s. l64-L68
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Tidskriftsartikel (refereegranskat)abstract
- Extensions of the standard models of particle physics and cosmology often lead to long-range fifth forces with properties dependent on gravitational environment. Fifth forces on astrophysical scales are best studied in the cosmic web where perturbation theory breaks down. We present constraints on chameleon-and symmetron-screened fifth forces with Yukawa coupling and megaparsec range - as well as unscreened fifth forces with differential coupling to galactic mass components - by searching for the displacements they predict between galaxies' stars and gas. Taking data from the Alfalfa HI survey, identifying galaxies' gravitational environments with the maps of Desmond et al. and forward modelling with a Bayesian likelihood framework, we set upper bounds on fifth-force strength relative to Newtonian gravity from similar to few x 10(-4) (1 sigma) for range lambda(C) = 50 Mpc, to similar to 0.1 for lambda(C) = 500 kpc. In f(R) gravity this requires f(R0) <= few x 10(-8). The analogous bounds without screening are similar to few x 10(-4) and few x 10(-3). These are the tightest and among the only fifth-force constraints on galaxy scales. We show how our results may be strengthened with future survey data and identify the key features of an observational programme for furthering fifth-force tests beyond the Solar system.
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12. |
- Dessauges-Zavadsky, Miroslava, et al.
(författare)
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First constraints on the stellar mass function of star-forming clumps at the peak of cosmic star formation
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 479:1, s. L118-L122
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Tidskriftsartikel (refereegranskat)abstract
- Star-forming clumps dominate the rest-frame ultraviolet morphology of galaxies at the peak of cosmic star formation. If turbulence driven fragmentation is the mechanism responsible for their formation, we expect their stellar mass function to follow a power law of slope close to -2. We test this hypothesis performing the first analysis of the stellar mass function of clumps hosted in galaxies at z similar to 1-3.5. The clump sample is gathered from the literature with similar detection thresholds and stellar masses determined in a homogeneous way. To overcome the small number statistics per galaxy (each galaxy hosts up to a few tens of clumps only), we combine all high-redshift clumps. The resulting clump mass function follows a power law of slope similar to-1.7 and flattens at masses below 2 x 10(7) M-circle dot. By means of randomly sampled clump populations, drawn out of a power-law mass function of slope -2, we test the effect of combining small clump populations, detection limits of the surveys, and blending on the mass function. Our numerical exercise reproduces all the features observed in the real clump mass function confirming that it is consistent with a power law of slope similar or equal to-2. This result supports the high-redshift clump formation through fragmentation in a similar fashion as in local galaxies, but under different gas conditions.
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13. |
- Dhawan, Suhail, et al.
(författare)
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Non-parametric spatial curvature inference using late-Universe cosmological probes
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 506:1, s. L1-L5
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Tidskriftsartikel (refereegranskat)abstract
- Inferring high-fidelity constraints on the spatial curvature parameter, ΩK, under as few assumptions as possible, is of fundamental importance in cosmology. We propose a method to non-parametrically infer ΩK from late-Universe probes alone. Using Gaussian processes (GPs) to reconstruct the expansion history, we combine cosmic chronometers (CCs) and type Ia supernovae (SNe Ia) data to infer constraints on curvature, marginalized over the expansion history, calibration of the CC and SNe Ia data, and the GP hyper-parameters. The obtained constraints on ΩK are free from parametric model assumptions for the expansion history and are insensitive to the overall calibration of both the CC and SNe Ia data (being sensitive only to relative distances and expansion rates). Applying this method to Pantheon SNe Ia and the latest compilation of CCs, we find ΩK = −0.03 ± 0.26, consistent with spatial flatness at the O(10−1) level, and independent of any early-Universe probes. Applying our methodology to future baryon acoustic oscillations and SNe Ia data from upcoming Stage IV surveys, we forecast the ability to constrain ΩK at the O(10−2) level.
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14. |
- Feeney, Stephen M., et al.
(författare)
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Cosmic microwave background science at commercial airline altitudes
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 469:1, s. l6-L10
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Tidskriftsartikel (refereegranskat)abstract
- Obtaining high-sensitivity measurements of degree-scale cosmic microwave background (CMB) polarization is the most direct path to detecting primordial gravitational waves. Robustly recovering any primordial signal from the dominant foreground emission will require high-fidelity observations at multiple frequencies, with excellent control of systematics. We explore the potential for a new platform for CMB observations, the Airlander 10 hybrid air vehicle, to perform this task. We show that the Airlander 10 platform, operating at commercial airline altitudes, is well suited to mapping frequencies above 220 GHz, which are critical for cleaning CMB maps of dust emission. Optimizing the distribution of detectors across frequencies, we forecast the ability of Airlander 10 to clean foregrounds of varying complexity as a function of altitude, demonstrating its complementarity with both existing (Planck) and ongoing (C-BASS) foreground observations. This novel platform could play a key role in defining our ultimate view of the polarized microwave sky.
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15. |
- Font, Joan, et al.
(författare)
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The ratio of pattern speeds in double-barred galaxies
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 444:1, s. l85-L89
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Tidskriftsartikel (refereegranskat)abstract
- We have obtained two-dimensional velocity fields in the ionized gas of a set of eight double-barred galaxies, at high spatial and spectral resolution, using their H alpha emission fields measured with a scanning Fabry-Perot spectrometer. Using the technique by which phase reversals in the non-circular motion indicate a radius of corotation, taking advantage of the high angular and velocity resolution, we have obtained the corotation radii and the pattern speeds of both the major bar and the small central bar in each of the galaxies; there are few such measurements in the literature. Our results show that the inner bar rotates more rapidly than the outer bar by a factor between 3.3 and 3.6.
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16. |
- Galametz, M., et al.
(författare)
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Water, methanol and dense gas tracers in the local ULIRG Arp 220: results from the new SEPIA Band 5 Science Verification campaign
- 2016
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 462:1, s. L36-L40
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Tidskriftsartikel (refereegranskat)abstract
- We present a line survey of the ultraluminous infrared galaxy Arp 220, taken with the newly installed SEPIA (Swedish-European Southern Observatory PI receiver for APEX) Band 5 instrument on APEX (Atacama Pathfinder Experiment). We illustrate the capacity of SEPIA to detect the 183.3 GHz H(2)O3(1,3)-2(2,0) line against the atmospheric H2O absorption feature. We confirm the previous detection of the HCN(2-1) line, and detect new transitions of standard dense gas tracers such as HNC(2-1), HCO+(2-1), CS(4-3), (CS)-S-34(4-3) and HC3N(20-19). We also detect HCN(2-1) v(2) = 1 and the 193.5 GHz methanol (4-3) group for the first time. The absence of time variations in the megamaser water line compared to previous observations seems to rule out an AGN nuclear origin for the line. It could, on the contrary, favour a thermal origin instead, but also possibly be a sign that the megamaser emission is associated with star-forming cores washed out in the beam. We finally discuss how the new transitions of HCN, HNC and HCO+ refine our knowledge of the interstellar medium physical conditions in Arp 220.
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17. |
- Gao, Xudong, et al.
(författare)
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The GALAH survey : a new constraint on cosmological lithium and Galactic lithium evolution from warm dwarf stars
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 497:1, s. L30-L34
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Tidskriftsartikel (refereegranskat)abstract
- Lithium depletion and enrichment in the cosmos is not yet well understood. To help tighten constraints on stellar and Galactic evolution models, we present the largest high-resolution analysis of Li abundances A(Li) to date, with results for over 100000 GALAH (Galactic Archeology with HERMES) field stars spanning effective temperatures 5900K≲Teff≲7000K and metallicities −3 ≲ [Fe/H] ≲ +0.5. We separated these stars into two groups, on the warm and cool sides of the so-called Li dip, a localized region of the Kiel diagram wherein lithium is severely depleted. We discovered that stars in these two groups show similar trends in the A(Li)–[Fe/H] plane, but with a roughly constant offset in A(Li) of 0.4dex, the warm group having higher Li abundances. At [Fe/H]≳−0.5, a significant increase in Li abundance with increasing metallicity is evident in both groups, signalling the onset of significant Galactic production. At lower metallicity, stars in the cool group sit on the Spite plateau, showing a reduced lithium of around 0.4dex relative to the primordial value predicted from big bang nucleosynthesis (BBN). However, stars in the warm group between [Fe/H] = −1.0 and −0.5 form an elevated plateau that is largely consistent with the BBN prediction. This may indicate that these stars in fact preserve the primordial Li produced in the early Universe.
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18. |
- Goobar, Ariel, et al.
(författare)
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The cosmic transparency measured with Type Ia supernovae : implications for intergalactic dust
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 477:1, s. l75-L79
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Tidskriftsartikel (refereegranskat)abstract
- Observations of high-redshift Type Ia supernovae (SNe Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat Lambda cold dark matter (Lambda CDM) cosmological model based on baryon acoustic oscillations and cosmic microwave background measurements, redshift dependent deviations of SN Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a 0.03 +/- 0.01 (stat) mag discrepancy in the distant supernova distance moduli relative to the Lambda CDM model anchored by supernovae at z < 0.05. While there are known systematic uncertainties that combined could explain the observed offset, here we entertain the possibility that the discrepancy may instead be explained by scattering of supernova light in the intergalactic medium (IGM). We focus on two effects: Compton scattering by free electrons and extinction by dust in the IGM. We find that if the discrepancy is entirely due to dimming by dust, the measurements can be modelled with a cosmic dust density Omega(dust)(IGM) = 8 x 10(-5)(1 + z)(-1), corresponding to an average attenuation of 2 x 10(-5) mag Mpc(-1) in V band. Forthcoming SN Ia studies may provide a definitive measurement of the IGM dust properties, while still providing an unbiased estimate of cosmological parameters by introducing additional parameters in the global fits to the observations.
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19. |
- Hayes, Matthew J., 1977-
(författare)
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Accelerating galaxy winds during the big bang of starbursts
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 519:1, s. L26-L31
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Tidskriftsartikel (refereegranskat)abstract
- We develop a new method to infer the temporal, geometric, and energetic properties of galaxy outflows, by combining stellar spectral modelling to infer starburst ages, and absorption lines to measure velocities. If winds are accelerated with time during a starburst event, then these two measurements enable us to solve for the wind radius, similarly to length-scales and the Hubble parameter in big bang cosmology. This wind radius is the vital, but hard-to-constrain parameter in wind physics. We demonstrate the method using spectra of 87 starburst galaxies at z = 0.05 − 0.44, finding that winds accelerate throughout the starburst phase and grow to typical radii of ≈1 kpc in ≈10 Myr. Mass flow rates increase rapidly with time, and the mass-loading factor exceeds unity at about 10 Myr – while still being accelerated, the gas will likely unbind from the local potential and enrich the circumgalactic medium. We model the mechanical energy available from stellar winds and supernovae, and estimate that a negligible amount is accounted for in the cool outflow at early times. However, the energy deposition increases rapidly and ∼10 per cent of the budget is accounted for in the cool flow at 10 Myr, similar to some recent hydrodynamical simulations. We discuss how this model can be developed, especially for high-redshift galaxies.
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20. |
- Huynh, M. T., et al.
(författare)
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Physical conditions of the gas in an ALMA C II -identified submillimetre galaxy at z=4.44
- 2013
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 431:1, s. L88-L92
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Tidskriftsartikel (refereegranskat)abstract
- We present (CO)-C-12(2-1) observations of the submillimetre galaxy ALESS65.1 performed with the Australia Telescope Compact Array (ATCA) at 42.3 GHz. A previous Atacama Large Millimeter Array study of submillimetre galaxies (SMGs) in the Extended Chandra Deep Field South detected [C II] 157.74 mu m emission from this galaxy at a redshift of z= 4.44. No (CO)-C-12(21) emission was detected but we derive a firm upper limit to the cold gas mass in ALESS65.1 of M-gas 4 SMGs being the likely progenitors of massive red-and-dead galaxies at z > 2. The ratio of the [CII], (CO)-C-12 and far-infrared luminosities implies a strong far-ultraviolet field of G(0) greater than or similar to 103, as seen in Galactic star-forming regions or local ultraluminous infrared galaxies (ULIRGs). The observed L-[C II]/L-FIR = 2.3 x 10(-3) is high compared to local ULIRGs and, combined withLL([CII])/L-CO greater than or similar to 2700, it is consistent with ALESS65.1 either having an extended (several kpc) [C II] emitting region or lower than solar metallicity.
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21. |
- Johansson, Joel, et al.
(författare)
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Herschel limits on far-infrared emission from circumstellar dust around three nearby Type Ia supernovae
- 2013
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 431:1, s. L43-L47
-
Tidskriftsartikel (refereegranskat)abstract
- We report upper limits on dust emission at far-infrared (IR) wavelengths from three nearby Type Ia supernovae: SNe 2011by, 2011fe and 2012cg. Observations were carried out at 70 and 160 mu m with the Photodetector Array Camera and Spectrometer onboard the Herschel Space Observatory. None of the supernovae were detected in the far-IR, allowing us to place upper limits on the amount of pre-existing dust in the circumstellar environment. Due to its proximity, SN 2011fe provides the tightest constraints, M-dust less than or similar to 7 x 10(-3)M(circle dot) at a 3 sigma level for dust temperatures T-dust similar to 500K assuming silicate or graphite dust grains of size a = 0.1 mu m. For SNe 2011by and 2012cg the corresponding upper limits are less stringent, with M-dust less than or similar to 10(-1)M(circle dot) for the same assumptions.
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22. |
- Kajava, J. J. E., et al.
(författare)
-
Detection of burning ashes from thermonuclear X-ray bursts
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 464:1, s. L6-L10
-
Tidskriftsartikel (refereegranskat)abstract
- When neutron stars (NS) accrete gas from low-mass binary companions, explosive nuclear burning reactions in the NS envelope fuse hydrogen and helium into heavier elements. The resulting thermonuclear (type-I) X-ray bursts produce energy spectra that are fit well with black bodies, but a significant number of burst observations show deviations from Planck spectra. Here we present our analysis of RXTE/ PCA observations of X-ray bursts from the NS low-mass X-ray binary HETE J1900.1-2455. We have discovered that the non-Planckian spectra are caused by photoionization edges. The anticorrelation between the strength of the edges and the colour temperature suggests that the edges are produced by the nuclear burning ashes that have been transported upwards by convection and become exposed at the photosphere. The atmosphere model fits show that occasionally the photosphere can consist entirely of metals, and that the peculiar changes in blackbody temperature and radius can be attributed to the emergence and disappearance of metals in the photosphere. As the metals are detected already in the Eddington-limited phase, it is possible that a radiatively driven wind ejects some of the burning ashes into the interstellar space.
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23. |
- Kajava, J. J. E., et al.
(författare)
-
X-ray dips and a complex UV/X-ray cross-correlation function in the black hole candidate MAXI J1820+070
- 2019
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 488:1, s. L18-L23
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Tidskriftsartikel (refereegranskat)abstract
- MAXI J1820+070, a black hole candidate first detected in early 2018 March, was observed by XMM-Newton during the outburst rise. In this letter we report on the spectral and timing analysis of the XMM-Newton X-ray and UV data, as well as contemporaneous X-ray data from the Swift satellite. The X-ray spectrum is well described by a hard thermal Comptonization continuum. The XMM-Newton X-ray light curve shows a pronounced dipping interval, and spectral analysis indicates that it is caused by a moderately ionized partial covering absorber. The XMM-Newton/OM U-filter data do not reveal any signs of the 17 h orbital modulation that was seen later on during the outburst decay. The UV/X-ray cross-correlation function shows a complex shape, with a peak at positive lags of about 4 s and a precognition dip at negative lags, which is absent during the X-ray dipping episode. Such shape could arise if the UV emission comes partially from synchrotron self-Compton emission near the black hole, as well as from reprocessing of the X-rays in the colder accretion disc further out.
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24. |
- Karovicova, I., et al.
(författare)
-
Accurate effective temperatures of the metal-poor benchmark stars HD140283, HD122563, and HD103095 from CHARA interferometry
- 2018
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 475:1, s. L81-L85
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Tidskriftsartikel (refereegranskat)abstract
- Large stellar surveys of the MilkyWay require validation with reference to a set of 'benchmark' stars whose fundamental properties are well determined. For metal-poor benchmark stars, disagreement between spectroscopic and interferometric effective temperatures has called the reliability of the temperature scale into question. We present new interferometric measurements of three metal-poor benchmark stars, HD140283, HD122563, and HD103095, from which we determine their effective temperatures. The angular sizes of all the stars were determined from observations with the PAVO beam combiner at visible wavelengths at the CHARA array, with additional observations of HD103095 made with the VEGA instrument, also at the CHARA array. Together with photometrically derived bolometric fluxes, the angular diameters give a direct measurement of the effective temperature. For HD140283, we find theta(LD) = 0.324 +/- 0.005 mas, T-eff = 5787 +/- 48 K; for HD122563,theta(LD) = 0.926 +/- 0.011 mas, T-eff = 4636 +/- 37 K; and for HD103095,theta(LD) = 0.595 +/- 0.007 mas, T-eff = 5140 +/- 49 K. Our temperatures for HD140283 and HD103095 are hotter than the previous interferometric measurements by 253 and 322 K, respectively. We find good agreement between our temperatures and recent spectroscopic and photometric estimates. We conclude some previous interferometric measurements have been affected by systematic uncertainties larger than their quoted errors.
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25. |
- Khouri, Theo, 1985, et al.
(författare)
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ALMA observations of the vibrationally excited rotational CO transition v=1, J=3-2 towards five AGB stars
- 2016
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 463:1, s. L74-L78
-
Tidskriftsartikel (refereegranskat)abstract
- We report the serendipitous detection with the Atacama Large Millimeter/submillimeter Array (ALMA) of the vibrationally excited pure-rotational CO transition, J = 3 - 2 towards five asymptotic giant branch (AGB) stars, Cet, R Aqr, R Scl, W Aql, and pi(1) Gru. The observed lines are formed in the poorly understood region located between the stellar surface and the region where the wind starts, the so-called warm molecular layer. We successfully reproduce the observed lines profiles using a simple model. We constrain the extents, densities, and kinematics of the region where the lines are produced. R Aqr and R Scl show inverse P-Cygni line profiles which indicate infall of material on to the stars. The line profiles of Cet and R Scl show variability. The serendipitous detection towards these five sources shows that vibrationally excited rotational lines can be observed towards a large number of nearby AGB stars using ALMA. This opens a new possibility for the study of the innermost regions of AGB circumstellar envelopes.
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26. |
- Knudsen, Kirsten Kraiberg, 1976, et al.
(författare)
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C II emission in z similar to 6 strongly lensed, star-forming galaxies
- 2016
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 462:1, s. L6-L10
-
Tidskriftsartikel (refereegranskat)abstract
- The far-infrared fine-structure line [C II] at 1900.5 GHz is known to be one of the brightest cooling lines in local galaxies, and therefore it has been suggested to be an efficient tracer for star formation in very high redshift galaxies. However, recent results for galaxies at z > 6 have yielded numerous non-detections in star-forming galaxies, except for quasars and submillimetre galaxies. We report the results of ALMA observations of two lensed, star-forming galaxies at z = 6.029 and z = 6.703. The galaxy A383-5.1 (star formation rate [SFR] of 3.2 M-circle dot yr(-1) and magnification of mu = 11.4 +/- 1.9) shows a line detection with L-[C II] = 8.9 x 10(6) L-circle dot, making it the lowest L-[C II] detection at z > 6. For MS0451-H (SFR = 0.4 M-circle dot yr(-1) and mu = 100 +/- 20) we provide an upper limit of L-[C II] 6; however, other effects could also play a role in terms of decreasing L-[CII]. The detection of A383-5.1 is encouraging and suggests that detections are possible, but much fainter than initially predicted.
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27. |
- Kobyakov, D., et al.
(författare)
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Elastic properties of polycrystalline dense matter
- 2015
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 449:1, s. l110-L112
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Tidskriftsartikel (refereegranskat)abstract
- Elastic properties of the solid regions of neutron star crusts and white dwarfs play an important role in theories of stellar oscillations. Matter in compact stars is presumably polycrystalline and, since the elastic properties of single crystals of such matter are very anisotropic, it is necessary to relate elastic properties of the polycrystal to those of a single crystal. We calculate the effective shear modulus of polycrystalline matter with randomly oriented crystallites using a self-consistent theory that has been very successful in applications to terrestrial materials and show that previous calculations overestimate the shear modulus by approximately 28 per cent.
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28. |
- Kochukhov, Oleg, et al.
(författare)
-
New eclipsing binaries with mercury-manganese stars
- 2021
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 506:1, s. L40-L44
-
Tidskriftsartikel (refereegranskat)abstract
- Eclipsing binary stars are rare and extremely valuable astrophysical laboratories that make possible precise determination of fundamental stellar parameters. Investigation of early-type chemically peculiar stars in eclipsing binaries provides important information for understanding the origin and evolutionary context of their anomalous surface chemistry. In this study, we discuss observations of eclipse variability in six mercury-manganese (HgMn) stars monitored by the Transiting Exoplanet Survey Satellite (TESS) satellite. These discoveries double the number of known eclipsing HgMn stars and yield several interesting objects requiring further study. In particular, we confirm eclipses in HD 72208, thereby establishing this object as the longestperiod eclipsing HgMn star. Among five other eclipsing binaries, reported here for the first time, HD 36892 and HD 53004 stand out as eccentric systems showing heartbeat variability in addition to eclipses. The latter object has the highest eccentricity among eclipsing HgMn stars and also exhibits tidally induced oscillations. Finally, we find evidence that HD 55776 may be orbited by a white dwarf companion.
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29. |
- Kosenkov, Ilia A., et al.
(författare)
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Disc and wind in black hole X-ray binary MAXI J1820+070 observed through polarized light during its 2018 outburst
- 2020
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 496:1, s. L96-L100
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Tidskriftsartikel (refereegranskat)abstract
- We describe the first complete polarimetric data set of the entire outburst of a low-mass black hole X-ray binary system and discuss the constraints for geometry and radiative mechanisms it imposes. During the decaying hard state, when the optical flux is dominated by the non-thermal component, the observed polarization is consistent with the interstellar values in all filters. During the soft state, the intrinsic polarization of the source is small, similar to 0.15 per cent in B and V filters, and is likely produced in the irradiated disc. A much higher polarization, reaching similar to 0.5 per cent in V and R filters, at a position angle of similar to 25 degrees observed in the rising hard state coincides in time with the detection of winds in the system. This angle coincides with the position angle of the jet. The detected optical polarization is best explained by scattering of the non-thermal (hot flow or jet base) radiation in an equatorial wind.
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30. |
- Maund, J. R., et al.
(författare)
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Supernova 2012ec : identification of the progenitor and early monitoring with PESSTO
- 2013
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 431:1, s. l102-L106
-
Tidskriftsartikel (refereegranskat)abstract
- We present the identification of the progenitor of the Type IIP SN 2012ec in archival pre-explosion Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) and Advanced Camera for Surveys Wide Field Channel F814W images. The properties of the progenitor are further constrained by non-detections in pre-explosion WFPC2 F450W and F606W images. We report a series of early photometric and spectroscopic observations of SN 2012ec. The r' -band light curve shows a plateau with M-r' = -17.0. The early spectrum is similar to the Type IIP SN 1999em, with the expansion velocity measured at Ha absorption minimum of -11 700 km s(-1) (at 1 d post-discovery). The photometric and spectroscopic evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days post-explosion (<6 d). We derive a luminosity for the progenitor, in comparison with MARCS model spectral energy distributions, of log L/L-circle dot = 5.15 +/- 0.19, from which we infer an initial mass range of 14-22M(circle dot). This is the first SN with an identified progenitor to be followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO).
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31. |
- Mesa, D., et al.
(författare)
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Upper limits for mass and radius of objects around Proxima Cen from SPHERE/VLT
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 466:1, s. l118-L122
-
Tidskriftsartikel (refereegranskat)abstract
- The recent discovery of an earth-like planet around Proxima Centauri has drawn much attention to this star and its environment. We performed a series of observations of Proxima Centauri using Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), the planet-finder instrument installed at the European Southern Observatory (ESO) Very Large Telescope (VLT) UT3, using its near-infrared modules, InfraRed Dual-band Imager and Spectrograph (IRDIS) and IFS. No planet was detected directly, but we set upper limits on the mass up to 7 au by exploiting the AMES-COND models. Our IFS observations reveal that no planet more massive than similar to 6-7 M-Jup can be present within 1 au. The dual-band imaging camera IRDIS also enables us to probe larger separations than other techniques such as radial velocity or astrometry. We obtained mass limits of the order of 4 M-Jup at separations of 2 au or larger, representing the most stringent mass limits at separations larger than 5 au available at the moment. We also made an attempt to estimate the radius of possible planets around Proxima using the reflected light. Since the residual noise for the observations is dominated by photon noise and thermal background, longer exposures in good observing conditions could improve the achievable contrast limit further.
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32. |
- Monari, Giacomo, et al.
(författare)
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Tracing the Hercules stream with Gaia and LAMOST : new evidence for a fast bar in the Milky Way
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 466:1, s. l113-L117
-
Tidskriftsartikel (refereegranskat)abstract
- The length and pattern speed of the Milky Way bar are still controversial. Photometric and spectroscopic surveys of the inner Galaxy, as well as gas kinematics, favour a long and slowly rotating bar, with corotation around a Galactocentric radius of 6 kpc. On the other hand, the existence of the Hercules stream in local velocity space favours a short and fast bar with corotation around 4 kpc. This follows from the fact that the Hercules stream looks like a typical signature of the outer Lindblad resonance of the bar. As we showed recently, reconciling this local stream with a slow bar would need to find a yet unknown alternative explanation, based, for instance, on the effect of spiral arms. Here, by combining the TGAS catalogue of the Gaia DR1 with LAMOST radial velocities, we show that the position of Hercules in velocity space as a function of radius in the outer Galaxy indeed varies exactly as predicted by fast bar models with a pattern speed no less than 1.8 times the circular frequency at the Sun's position.
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33. |
- Mondal, Rajesh, et al.
(författare)
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The effect of non-Gaussianity on error predictions for the Epoch of Reionization (EoR) 21-cm power spectrum
- 2015
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 449:1, s. l41-L45
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Tidskriftsartikel (refereegranskat)abstract
- The Epoch of Reionization (EoR) 21-cm signal is expected to become increasingly non-Gaussian as reionization proceeds. We have used seminumerical simulations to study how this affects the error predictions for the EoR 21-cm power spectrum. We expect SNR = root N-k for a Gaussian random field where N-k is the number of Fourier modes in each k bin. We find that non-Gaussianity is important at high SNR where it imposes an upper limit [SNR](l). For a fixed volume V, it is not possible to achieve SNR > [SNR](l) even if N-k is increased. The value of [SNR](l) falls as reionization proceeds, dropping from similar to 500 at (x) over bar}(H1) = 0.15 for a [150.08 Mpc](3) simulation. We show that it is possible to interpret [SNR](l) in terms of the trispectrum, and we expect [SNR](l) proportional to root V if the volume is increased. For SNR << [SNR](l) we find SNR = root N-k/A with A similar to 0.95-1.75, roughly consistent with the Gaussian prediction. We present a fitting formula for the SNR as a function of N-k, with two parameters A and [SNR](l) that have to be determined using simulations. Our results are relevant for predicting the sensitivity of different instruments to measure the EoR 21-cm power spectrum, which till date have been largely based on the Gaussian assumption.
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34. |
- Nagao, T., et al.
(författare)
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The aspherical explosion of the Type IIP SN 2017gmr
- 2019
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 489:1, s. L69-L74
-
Tidskriftsartikel (refereegranskat)abstract
- Type IIP supernovae (SNe IIP), which represent the most common class of core-collapse (CC) SNe, show a rapid increase in continuum polarization just after entering the tail phase. This feature can be explained by a highly asymmetric helium core, which is exposed when the hydrogen envelope becomes transparent. Here we report the case of an SN IIP (SN 2017 gmr) that shows an unusually early rise of the polarization, greater than or similar to 30 d before the start of the tail phase. This implies that SN 2017gmr is an SN IIP that has very extended asphericity. The asymmetries are not confined to the helium core, but reach out to a significant part of the outer hydrogen envelope, hence clearly indicating a marked intrinsic diversity in the aspherical structure of CC explosions. These observations provide new constraints on the explosion mechanism, where viable models must be able to produce such extended deviations from spherical symmetry, and account for the observed geometrical diversity.
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35. |
- Nandi, Sumana, et al.
(författare)
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Tale of J1328+2752 : a misaligned double-double radio galaxy hosted by a binary black hole?
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 467:1, s. L56-L60
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Tidskriftsartikel (refereegranskat)abstract
- We present a radio and optical study of the double-double radio galaxy J1328+2752 based on new low-frequency Giant Metrewave Radio Telescope observations and Sloan Digital Sky Survey (SDSS) data. The radio data were used to investigate the morphology and to perform a spectral index analysis. In this source, we find that the inner double is misaligned by similar to 30 degrees from the axis of the outer diffuse structure. The SDSS spectrum shows that the central component has double-peaked line profiles with different emission strengths. The average velocity offset of the two components is 235 +/- 10.5 kms(-1). The misaligned radio morphology along with the double-peaked emission lines indicate that this source is a potential candidate binary supermassive black hole. This study further supports mergers as a possible explanation for repeated jet activity in radio sources.
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36. |
- Nordlander, T., et al.
(författare)
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The lowest detected stellar Fe abundance : the halo star SMSS J160540.18-144323.1
- 2019
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 488:1, s. L109-L113
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of SMSS J160540.18-144323.1, a new ultra metal-poor halo star discovered with the SkyMapper telescope. We measure [Fe/H] = -6.2 +/- 0.2 (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, [C/Fe] = 3.9 +/- 0.2, while other abundances are compatible with an alpha-enhanced solar-like pattern with [Ca/Fe] = 0.4 +/- 0.2, [Mg/Fe] = 0.6 +/- 0.2, [Ti/Fe] = 0.8 +/- 0.2, and no significant s- or r-process enrichment, [Sr/Fe] < 0.2 and [Ba/Fe] < 1.0 (3 sigma limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about 10 M circle dot imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly 20 M circle dot are incompatible with the observed abundance pattern.
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37. |
- Paice, J. A., et al.
(författare)
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A black hole X-ray binary at similar to 100 Hz : multiwavelength timing of MAXIJ1820+070 with HiPERCAM and NICER
- 2019
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 490:1, s. L62-L66
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Tidskriftsartikel (refereegranskat)abstract
- We report on simultaneous sub-second optical and X-ray timing observations of the low-mass X-ray binary black hole candidate MAXI J1820+070. The bright 2018 outburst rise allowed simultaneous photometry in five optical bands (ugrizs) with HiPERCAM/GTC (Optical) at frame rates over 100 Hz, together with NICER/ISS observations (X-rays). Intense (factor of 2) red flaring activity in the optical is seen over a broad range of time-scales down to similar to 10 ms. Cross-correlating the bands reveals a prominent anticorrelation on time-scales of similar to seconds, and a narrow sub-second correlation at a lag of approximate to+165 ms (optical lagging X-rays). This lag increases with optical wavelength, and is approximately constant over Fourier frequencies of similar to 0.3-10 Hz. These features are consistent with an origin in the inner accretion flow and jet base within similar to 5000 Gravitational radii. An additional similar to+5 s lag feature may be ascribable to disc reprocessing. MAXI J1820+070 is the third black hole transient to display a clear similar to 0.1 s optical lag, which may be common feature in such objects. The sub-second lag variation with wavelength is novel, and may allow constraints on internal shock jet stratification models.
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38. |
- Perez-Sanchez, A.F., et al.
(författare)
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A synchrotron jet from a post-asymptotic giant branch star
- 2013
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 436:1, s. L79-L83
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of low- and intermediate-initial-mass stars beyond the asymptotic giant branch (AGB) remains poorly understood. High-velocity outflows launched shortly after the AGB phase are thought to be the primary shaping mechanism of bipolar and multipolar planetary nebulae. However, little is known about the launching and driving mechanism for these jets, whose momentum and energy often far exceed the energy that can be provided by radiation pressure alone. Here, we report on the direct evidence of a magnetically collimated jet shaping the bipolar morphology of the circumstellar envelope of a post-AGB star. We present radio continuum observations of the post-AGB star IRAS 15445-5449 (OH 326.5-0.4) which has water masers tracing a fast bipolar outflow. Our observations confirm the earlier observed steep negative spectral index of the spectral energy distribution (SED) above similar to 3 GHz, and resolve, for the first time, the emission to originate from a radio jet, proving the existence of such jets around a post-AGB star. The SED is consistent with a synchrotron jet embedded in a sheath of thermal electrons. We find a close correspondence between the extent and direction of the synchrotron jet and the bipolar shape of the object observed at other wavelengths, suggesting that the jet is responsible for the source morphology. The jet is collimated by a magnetic field of the order of mG at almost 7000 au from the central star. We recover observations from the Australia Telescope Compact Array archive that indicate that the emission measure of the thermal component has increased by a factor of 3 between 1998 and 2005 after which it has remained constant. The short time-scale evolution of the radio emission suggests a short lifetime for the jet. The observations of a synchrotron jet from a post-AGB star with characteristics similar to those from protostars and young stellar objects, for instance, suggest that magnetic launching and collimation is a common feature of astrophysical jets.
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39. |
- Pozzi, F., et al.
(författare)
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CO excitation in the Seyfert galaxy NGC 7130
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 470:1, s. L64-L68
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Tidskriftsartikel (refereegranskat)abstract
- We present a coherent multiband modelling of the carbon monoxide (CO) spectral energy distribution of the local Seyfert galaxy NGC 7130 to assess the impact of the active galactic nucleus (AGN) activity on the molecular gas. We take advantage of all the available data from X-ray to the submillimetre, including ALMA data. The high-resolution (~0.2 arcsec) ALMA CO(6-5) data constrain the spatial extension of the CO emission down to an ~70 pc scale. From the analysis of the archival Chandra and NuSTAR data, we infer the presence of a buried, Compton-thick AGN of moderate luminosity, L2-10 keV ~1.6 × 1043 erg s-1. We explore photodissociation and X-ray-dominated-region (PDR and XDR) models to reproduce the CO emission. We find that PDRs can reproduce the CO lines up to J ~ 6; however, the higher rotational ladder requires the presence of a separate source of excitation. We consider X-ray heating by the AGNs as a source of excitation, and find that it can reproduce the observed CO spectral energy distribution. By adopting a composite PDR+XDR model, we derivemolecular cloud properties. Our study clearly indicates the capabilities offered by the current generation of instruments to shed light on the properties of nearby galaxies by adopting state-of-the-art physical modelling.
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40. |
-
Probing the Cyclotron line characteristics of 4U 1538-522 using AstroSat-LAXPC
- 2019
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 484:1, s. L1-L6
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Tidskriftsartikel (refereegranskat)abstract
- We report the first report on cyclotron line studies with the LAXPC instrument onboard AstroSat of the high-mass X-ray binary pulsar 4U 1538-52. During the observation of source that spanned about 1 d with a net exposure of 50 ks, the source X-ray flux remained constant. Pulse profile is double peaked in low-energy range and has a single peak in high-energy range, the transition taking place around the cyclotron line energy of the source. Cyclotron scattering feature (CRSF) is detected at similar to 22 keV with a very high significance in phase averaged spectrum, It is one of the highest signal to noise ratio detections of CRSF for this source. We performed detailed pulse-phase-resolved spectral analysis with 10 independent phase bins. We report the results of pulse-phase-resolved spectroscopy of the continuum and CRSF parameters. The cyclotron line parameters show pulse phase dependence over the entire phase with a CRSF energy variation of similar to 13 per cent, which is in agreement with previous studies, We also confirm the increase ill the centroid energy of the CRSF observed between the 1996-2004 (RXTE) and the 2012 (Suzaku) observations, reinforcing that the increase was a long-term change.
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41. |
- Rosén, Lisa, et al.
(författare)
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Strong variable linear polarization in the cool active star II Peg
- 2013
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 436:1, s. L10-L14
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic fields of cool active stars are currently studied polarimetrically using only circular polarization observations. Including linear polarization in the reconstruction of stellar magnetic fields allows more information about the magnetic field to be extracted and significantly improves the reliability of stellar magnetic field maps. The goal of this study is to initiate systematic observations of active stars in all four Stokes parameters and to identify cool stars for which linear polarization can be detected at a level sufficient for Zeeman-Doppler Imaging (ZDI). Four active RS CVn binaries, II Peg, HR 1099, IM Peg and sigma Gem, were observed with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope during a time period from 2012 February to 2013 January. The least-squares deconvolution procedure was applied to derive mean polarization profiles of all four Stokes parameters. Linear polarization was detected in all four stars in at least one observation. At the same time, II Peg showed an exceptionally strong and highly variable linear polarization signature throughout all observations. This establishes II Peg as the first promising target for ZDI in all four Stokes parameters and suggests the feasibility of such an analysis with existing equipment for at least a few of the most active cool stars.
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42. |
- Sestito, Federico, et al.
(författare)
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The Pristine survey – X. A large population of low-metallicity stars permeates the Galactic disc
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 497:1, s. L7-L12
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Tidskriftsartikel (refereegranskat)abstract
- The orbits of the least chemically enriched stars open a window on the formation of our Galaxy when it was still in its infancy. The common picture is that these low-metallicity stars are distributed as an isotropic, pressure-supported component since these stars were either accreted from the early building blocks of the assembling Milky Way (MW), or were later brought by the accretion of faint dwarf galaxies. Combining the metallicities and radial velocities from the Pristine and LAMOST surveys and Gaia DR2 parallaxes and proper motions for an unprecedented large and unbiased sample of 1027 very metal poor stars at [Fe/H] ≤ −2.5 dex, we show that this picture is incomplete. We find that 31 per cent of the stars that currently reside spatially in the disc (|Z|≤3kpc) do not venture outside of the disc plane throughout their orbit. Moreover, this sample shows strong statistical evidence (at the 5.0σ level) of asymmetry in their kinematics, favouring prograde motion. The discovery of this population implies that a significant fraction of stars with iron abundances [Fe/H] ≤ −2.5 dex merged into, formed within, or formed concurrently with the MW disc and that the history of the disc was quiet enough to allow them to retain their disc-like orbital properties, challenging theoretical and cosmological models.
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43. |
- Silva-Villa, E., et al.
(författare)
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The age distribution of stellar clusters in M83
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3933 .- 1745-3925. ; 440:1, s. L116-L120
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Tidskriftsartikel (refereegranskat)abstract
- In order to empirically determine the time-scale and environmental dependence of stellar cluster disruption, we have undertaken an analysis of the unprecedented multipointing (seven), multiwavelength (U, B, V, H alpha, and I) Hubble Space Telescope imaging survey of the nearby, face-on spiral galaxy M83. The images are used to locate stellar clusters and stellar associations throughout the galaxy. Estimation of cluster properties (age, mass, and extinction) was done through a comparison of their spectral energy distributions with simple stellar population models. We constructed the largest catalogue of stellar clusters and associations in this galaxy to-date, with similar to 1800 sources with masses above similar to 5000 M-circle dot and ages younger than similar to 300 Myr. In this Letter, we focus on the age distribution of the resulting clusters and associations. In particular, we explicitly test whether the age distributions are related with the ambient environment. Our results are in excellent agreement with previous studies of age distributions in the centre of the galaxy, which gives us confidence to expand out to search for similarities or differences in the other fields which sample different environments. We find that the age distribution of the clusters inside M83 varies strongly as a function of position within the galaxy, indicating a strong correlation with the galactic environment. If the age distributions are approximated as a power law of the form dN/dt alpha t(zeta), we find zeta values between 0 and -0.62 (zeta similar to -0.40 for the whole galaxy), in good agreement with previous results and theoretical predictions.
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44. |
- Tamburini, Fabrizio, et al.
(författare)
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Measurement of the spin of the M87 black hole from its observed twisted light
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 492:1, s. L22-L27
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Tidskriftsartikel (refereegranskat)abstract
- We present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum (OAM). This physical observable allows a direct measurement of the rotation of the black hole. We extracted the OAM spectra from the radio intensity data collected by the Event Horizon Telescope from around the black hole M87 - by using wavefront reconstruction and phase recovery techniques and from the visibility amplitude and phase maps. This method is robust and complementary to black hole shadow circularity analyses. It shows that the M87 - rotates clockwise with an estimated rotation parameter a = 0.90 +/- 0.05 with an similar to 95 per cent confidence level (c.l.) and an inclination i = 17 degrees +/- 2 degrees, equivalent to a magnetic arrested disc with an inclination i = 163 degrees +/- 2 degrees. From our analysis, we conclude that, within a 6 sigma c.l., the M87* is rotating.
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45. |
- Taubenberger, S., et al.
(författare)
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Spectroscopy of the Type Ia supernova 2011fe past 1000 d
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 448:1, s. L48-L52
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and Local Group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comparing this extremely late spectrum to an earlier one taken 331 d after the explosion, we find that the most prominent feature at 331 d - [Fe III] emission around 4700 angstrom - has entirely faded away, suggesting a significant change in the ionization state. Instead, [Fe II] lines are probably responsible for most of the emission at 1034 d. An emission feature at 6300-6400 angstrom has newly developed at 1034 d, which we tentatively identify with Fe I lambda 6359, [Fe I] lambda lambda 6231, 6394 or [O I] lambda lambda 6300, 6364. Interestingly, the features in the 1034 d spectrum seem to be collectively redshifted, a phenomenon that we currently have no convincing explanation for. We discuss the implications of our findings for explosion models, but conclude that sophisticated spectral modelling is required for any firm statement.
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46. |
- Tsygankov, Sergey S., et al.
(författare)
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On the magnetic field of the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 479:1, s. L134-L138
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Tidskriftsartikel (refereegranskat)abstract
- We report on the monitoring of the final stage of the outburst from the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124, which reached similar to 40 Eddington luminosities. The main aim of the monitoring program with the Swift/XRT telescope was to measure the magnetic field of the neutron star using the luminosity of transition to the 'propeller' state. The visibility constraints, unfortunately, did not permit us to observe the source down to the fluxes low enough to detect such a transition. The tight upper limit on the propeller luminosity L-prop < 6.8x10(35) erg s(-1) implies the dipole component of the magnetic field B< 10(13) G. On the other hand, the observed evolution of the pulse profile and of the pulsed fraction with flux points to a change of the emission region geometry at the critical luminosity L-crit similar to 3 x 10(38) erg s(-1) both in the rising and declining parts of the outburst. We associate the observed change with the onset of the accretion column, which allows us to get an independent estimate of the magnetic field strength close to the neutron stars surface of B > 10(13) G. Given the existing uncertainty in the effective magnetosphere size, we conclude that both estimates are marginally compatible with each other.
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47. |
- Verhamme, A., et al.
(författare)
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Recovering the systemic redshift of galaxies from their Lyman alpha line profile
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 478:1, s. L60-L65
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Tidskriftsartikel (refereegranskat)abstract
- The Lyman alpha (Ly alpha) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km s(-1) compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics, and correlations with quasar absorption lines when only Ly alpha is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the Ly alpha line profile. We use spectroscopic observations of Ly alpha emitters for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z approximate to 3 and z approximate to 6 as part of various multi-unit spectroscopic explorer guaranteed time observations. We also include a compilation of spectroscopic Ly alpha data from the literature spanning a wide redshift range (z approximate to 0-8). First, restricting our analysis to double-peaked Ly alpha spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, V-peak(red), and the separation of the peaks. Secondly, we find a correlation between V-peak(red) and the full width at half-maximum of the Ly alpha line. Fitting formulas to estimate systemic redshifts of galaxies with an accuracy of <= 100 km s(-1), when only the Ly alpha emission line is available, are given for the two methods.
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48. |
- Yang, Jun, 1979, et al.
(författare)
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No apparent superluminal motion in the first-known jetted tidal disruption event Swift J1644+5734
- 2016
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 462:1, s. L66-L70
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Tidskriftsartikel (refereegranskat)abstract
- The first-known tidal disruption event (TDE) with strong evidence for a relativistic jet - based on extensive multiwavelength campaigns - is Swift J1644+5734. In order to directly measure the apparent speed of the radio jet, we performed very long baseline interferometry (VLBI) observations with the European VLBI network (EVN) at 5 GHz. Our observing strategy was to identify a very nearby and compact radio source with the real-time e-EVN, and then utilize this source as a stationary astrometry reference point in the later five deep EVN observations. With respect to the in-beam source FIRST J1644+5736, we have achieved a statistical astrometric precision about 12 mu as (68 per cent confidence level) per epoch. This is one of the best phase-referencing measurements available to date. No proper motion has been detected in the Swift J1644+5734 radio ejecta. We conclude that the apparent average ejection speed between 2012.2 and 2015.2 was less than 0.3c with a confidence level of 99 per cent. This tight limit is direct observational evidence for either a very small viewing angle or a strong jet deceleration due to interactions with a dense circum-nuclear medium, in agreement with some recent theoretical studies.
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49. |
- Yoast-Hull, T. M., et al.
(författare)
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γ-Ray emission from Arp 220: indications of an active galactic nucleus
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 469:1, s. L89-L93
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Tidskriftsartikel (refereegranskat)abstract
- Extragalactic cosmic ray populations are important diagnostic tools for tracking the distribution of energy in nuclei and for distinguishing between activity powered by star formation versus active galactic nuclei (AGNs). Here, we compare different diagnostics of the cosmic ray populations of the nuclei of Arp 220 based on radio synchrotron observations and the recent gamma-ray detection. We find the gamma-ray and radio emission to be incompatible; a joint solution requires at minimum a factor of 4-8 times more energy coming from supernovae and a factor of 40-70 more mass in molecular gas than that is observed. We conclude that this excess of the gamma-ray flux in comparison to all other diagnostics of star-forming activity indicates that there is an AGN present that is providing the extra cosmic rays, likely in the western nucleus.
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50. |
- Zackrisson, Erik, et al.
(författare)
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Observational constraints on supermassive dark stars
- 2010
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1745-3925 .- 1365-2966. ; 407:1, s. L74-L78
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Tidskriftsartikel (refereegranskat)abstract
- Some of the first stars could be cooler and more massive than standard stellar models would suggest, due to the effects of dark matter annihilation in their cores. It has recently been argued that such objects may attain masses in the 104-107Msolar range and that such supermassive dark stars should be within reach of the upcoming James Webb Space Telescope. Notwithstanding theoretical difficulties with this proposal, we argue here that some of these objects should also be readily detectable with both the Hubble Space Telescope and ground-based 8-10 m class telescopes. Existing survey data already place strong constraints on 107Msolar dark stars at z ~ 10. We show that such objects must be exceedingly rare or short lived to have avoided detection.
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