SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "AMNE:(NATURVETENSKAP Fysik Astronomi, astrofysik och kosmologi) "

Sökning: AMNE:(NATURVETENSKAP Fysik Astronomi, astrofysik och kosmologi)

Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • 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.
  •  
2.
  • 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.
  •  
3.
  • 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.
  •  
4.
  • Nordin, Jakob, et al. (författare)
  • Evidence for a correlation between the SiII λ4000 width and Type Ia supernova color
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357.
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the pseudo equivalent width of the SiII λ4000 feature of Type Iasupernovae (SNe Ia) in the redshift range 0.0024 ≤z ≤0.634. We find that this spectral indicator correlateswith the light curve color excess SALT2 c as well as previouslydefined spectroscopic subclasses (Branch types) and theevolution of the  SiII λ6150 velocity, i.e., the so called velocitygradient. Based on our study of 55 objects from different surveys, we find indications that the SiII λ4000 spectral indicatorcould provide important information to improve cosmological distancemeasurements with SNe Ia.
  •  
5.
  • 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.
  •  
6.
  • 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.
  •  
7.
  • Abbasi, R., et al. (författare)
  • Calibration and characterization of the IceCube photomultiplier tube
  • 2010
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 618:1-3, s. 139-152
  • Tidskriftsartikel (refereegranskat)abstract
    • Over 5000 PMTs are being deployed at the South Pole to compose the IceCube neutrino observatory. Many are placed deep in the ice to detect Cherenkov light emitted by the products of high-energy neutrino interactions, and others are frozen into tanks on the surface to detect particles from atmospheric cosmic ray showers. IceCube is using the 10-in. diameter R7081-02 made by Hamamatsu Photonics. This paper describes the laboratory characterization and calibration of these PMTs before deployment. PMTs were illuminated with pulses ranging from single photons to saturation level. Parameterizations are given for the single photoelectron charge spectrum and the saturation behavior. Time resolution, late pulses and afterpulses are characterized. Because the PMTs are relatively large, the cathode sensitivity uniformity was measured. The absolute photon detection efficiency was calibrated using Rayleigh-scattered photons from a nitrogen laser. Measured characteristics are discussed in the context of their relevance to IceCube event reconstruction and simulation efforts. (C) 2010 Elsevier B.V. All rights reserved.
  •  
8.
  • Abbasi, R., et al. (författare)
  • Search for muon neutrinos from gamma-ray bursts with the IceCube neutrino telescope
  • 2010
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 710:1, s. 346-359
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results of searches for high-energy muon neutrinos from 41 gamma-ray bursts (GRBs) in the northern sky with the IceCube detector in its 22 string configuration active in 2007/2008. The searches cover both the prompt and a possible precursor emission as well as a model-independent, wide time window of -1 hr to + 3 hr around each GRB. In contrast to previous searches with a large GRB population, we do not utilize a standard Waxman-Bahcall GRB flux for the prompt emission but calculate individual neutrino spectra for all 41 GRBs from the burst parameters measured by satellites. For all of the three time windows, the best estimate for the number of signal events is zero. Therefore, we place 90% CL upper limits on the fluence from the prompt phase of 3.7 x 10(-3) erg cm(-2) (72 TeV-6.5 PeV) and on the fluence from the precursor phase of 2.3 x 10(-3) erg cm(-2) (2.2-55 TeV), where the quoted energy ranges contain 90% of the expected signal events in the detector. The 90% CL upper limit for the wide time window is 2.7 x 10(-3) erg cm(-2) (3 TeV-2.8 PeV) assuming an E-2 flux.
  •  
9.
  • Scott, Pat, 1982- (författare)
  • Searches for Particle Dark Matter : Dark stars, dark galaxies, dark halos and global supersymmetric fits
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation cross-section of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordially-produced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.
  •  
10.
  • Hartman, Henrik, et al. (författare)
  • The FERRUM project : experimental and theoretical transition rates of forbidden [Sc II] lines and radiative lifetimes of metastable ScII levels
  • 2008
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 480:2, s. 575-580
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. In many plasmas, long-lived metastable atomic levels are depopulated by collisions (quenched) before they decay radiatively. In low-density regions, however, the low collision rate may allow depopulation by electric dipole (E1) forbidden radiative transitions, so-called forbidden lines (mainly M1 and E2 transitions). If the atomic transition data are known, these lines are indicators of physical plasma conditions and used for abundance determination. Aims. Transition rates can be derived by combining relative intensities between the decay channels, so-called branching fractions (BFs), and the radiative lifetime of the common upper level. We use this approach for forbidden [Sc II] lines, along with new calculations. Methods. Neither BFs for forbidden lines, nor lifetimes of metastable levels, are easily measured in a laboratory. Therefore, astrophysical BFs measured in Space Telescope Imaging Spectrograph (STIS) spectra of the strontium filament of Eta Carinae are combined with lifetime measurements using a laser probing technique on a stored ion-beam (CRYRING facility, MSL, Stockholm). These quantities are used to derive the absolute transition rates (A-values). New theoretical transition rates and lifetimes are calulated using the CIV3 code. Results. We report experimental lifetimes of the Sc II levels 3d(2) a(3)P(0,1,2) with lifetimes 1.28, 1.42, and 1.24 s, respectively, and transition rates for lines from these levels down to 3d4s a(3)D in the region 8270-8390 angstrom. These are the most important forbidden [Sc II] transitions. New calculations for lines and metastable lifetimes are also presented, and are in good agreement with the experimental data.
  •  
Skapa referenser, mejla, bekava och länka
Typ av publikation
tidskriftsartikel (9116)
konferensbidrag (1386)
doktorsavhandling (358)
forskningsöversikt (191)
annan publikation (130)
licentiatavhandling (129)
visa fler...
bokkapitel (96)
konstnärligt arbete (54)
rapport (43)
bok (25)
samlingsverk (redaktörskap) (13)
recension (9)
proceedings (redaktörskap) (8)
visa färre...
Typ av innehåll
refereegranskat (10256)
övrigt vetenskapligt/konstnärligt (1210)
populärvet., debatt m.m. (92)
Författare/redaktör
Reimer, O. (282)
Reimer, A. (266)
Aalto, Susanne, 1964 (224)
Ackermann, M. (207)
Becherini, Yvonne (206)
Quirrenbach, A. (199)
visa fler...
Bregeon, J. (195)
Sollerman, Jesper (190)
Vlemmings, Wouter, 1 ... (189)
Katz, U. (186)
Funk, S. (186)
Conrad, Jan (185)
Lemoine-Goumard, M. (183)
Grondin, M. -H (177)
Longo, F. (176)
Wolke, Magnus (176)
Kupsc, Andrzej (175)
Lohse, T. (173)
Bulik, T. (173)
Johansson, Tord (171)
Fontaine, G. (169)
Mizuno, T. (167)
Boisson, C. (166)
Hofmann, W. (165)
Khelifi, B. (165)
Kluzniak, W. (165)
Moulin, E. (164)
Giglietto, N. (164)
Ablikim, M. (164)
Glicenstein, J. F. (162)
de Naurois, M. (162)
Stawarz, L. (162)
Wagner, S. J. (162)
Mazziotta, M. N. (162)
Kosack, K. (161)
Moderski, R. (161)
Venter, C. (161)
Lenain, J. -P (160)
Niemiec, J. (160)
Rudak, B. (160)
Zdziarski, A. A. (160)
Morselli, A. (160)
Schönning, Karin, 19 ... (160)
Rieger, F. (159)
Aharonian, F. (158)
Ohm, S. (158)
Ostrowski, M. (158)
Santangelo, A. (158)
Schwanke, U. (158)
Zech, A. (158)
visa färre...
Lärosäte
Stockholms universitet (3551)
Chalmers tekniska högskola (2656)
Uppsala universitet (2655)
Lunds universitet (1922)
Kungliga Tekniska Högskolan (1800)
Linnéuniversitetet (408)
visa fler...
Göteborgs universitet (281)
Luleå tekniska universitet (201)
Umeå universitet (173)
Malmö universitet (154)
Högskolan i Halmstad (79)
Högskolan Dalarna (29)
Högskolan Kristianstad (24)
Karlstads universitet (24)
Linköpings universitet (20)
RISE (18)
Jönköping University (16)
Örebro universitet (11)
Mittuniversitetet (7)
Högskolan Väst (3)
Karolinska Institutet (3)
Blekinge Tekniska Högskola (3)
Mälardalens universitet (2)
Naturhistoriska riksmuseet (2)
Sveriges Lantbruksuniversitet (2)
Högskolan i Gävle (1)
Konstfack (1)
visa färre...
Språk
Engelska (11392)
Svenska (154)
Danska (5)
Odefinierat språk (3)
Tyska (2)
Spanska (1)
visa fler...
Kinesiska (1)
visa färre...
Forskningsämne (UKÄ/SCB)
Naturvetenskap (11557)
Teknik (378)
Samhällsvetenskap (63)
Humaniora (48)
Medicin och hälsovetenskap (19)
Lantbruksvetenskap (2)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy