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  • 1
    Electronic Resource
    Electronic Resource
    Quantitative Spectroscopy of Hot Stars (1990)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 28 (1990), S. 303-341 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.28.090190.001511
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  • 2
    Electronic Resource
    Electronic Resource
    Ionized Outflows of Hot Stars (1997)
    Springer
    Astrophysics and space science 255 (1997), S. 137-144 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001156028282
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  • 3
    Electronic Resource
    Electronic Resource
    Hubble Space Telescope spectroscopy of massive hot stars in the Magellanic Clouds and M31 (1993)
    Springer
    Space science reviews 66 (1993), S. 179-182 
    Details
    ISSN: 1572-9672
    Keywords: Hot stars ; extragalactic UV spectroscopy ; metallicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the Hubble Space Telescope (HST) and the Faint Object Spectrograph (FOS) high signal to noise spectrograms were obtained for 15 OB stars in the Magellanic Clouds***, three of which are of spectral type O3. The data cover the spectral region from 1150 A – 2300 A with a resolution of Δλ/λ≈1 A. One O8.5 supergiant, OB78#231, in M31
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00771060
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  • 4
    Electronic Resource
    Electronic Resource
    Shocks and shells in hot star winds (1995)
    Springer
    Astrophysics and space science 233 (1995), S. 293-299 
    Details
    ISSN: 1572-946X
    Keywords: Stars: early type ; Stars: winds ; Hydrodynamics ; Instabilities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Radiation-driven winds of hot, massive stars showvariability in UV and optical line profiles on time scales of hours to days.Shock heating of wind material is indicated by the observed X-ray emission. We present time-dependent hydrodynamical models of these winds, where flowstructures originate from a strong instability of the radiative driving. Recent calculations (Owocki 1992) of the unstable growth of perturbations were restricted by the assumptions of 1-D spherical symmetry and isothermality of the wind. We drop the latter assumption and include the energy transfer in the wind. This leads to a severe numerical shortcoming, whereby all radiative cooling zones collapse and the shocks become isothermal again. We propose a method to hinder this collapse. Calculations for dense supergiant winds then show: (1) The wind consists of a sequence of narrow and dense shells, which are enclosed by strong reverse shocks (with temperatures of 106 to 107 K) on their starward facing side. (2) Collisions of shells are frequent up to 6 to 7 stellar radii. (3) Radiative cooling is efficient only up to 4 to 6R *. Beyond these radii, cooling zones behind shocks become broad and alter the wind structure drastically: all reverse shocks disappear, leaving regions ofpreviously heated gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00627362
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  • 5
    Electronic Resource
    Electronic Resource
    O-star winds in the Magellanic Clouds and the Milky Way (1993)
    Springer
    Space science reviews 66 (1993), S. 187-190 
    Details
    ISSN: 1572-9672
    Keywords: Hot star winds ; UV P-Cygni profiles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract UV P-Cygni profiles of OB-stars in the Magellanic Clouds (observed with HST), and the galaxy (observed with IUE) are analyzed empirically using a line formation procedure similar to the one described by Lamers et al. (1987). The assumption of a constant microturbulencev turb throughout the wind is dropped and replaced by a radially increasing turbulence parameterv turb(v), thus improving the fit for the emission peaks substantially, and at the same time avoiding the need for a justification of extremely supersonic turbulence in the vicinity of the wind's sonic point. The Sobolev optical depth is determined interatively at fixed velocities in the wind, which removes the bias introduced by the choice of a specific parameterization function. Where it was possible and necessary a full photospheric spectrum was used to illuminate the wind line. The terminal velocitiesv ∞ are are found to be largest in the Galaxy, smallest in the Small Magellanic Cloud, and intermediate or similar to galactic in the Large Cloud.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00771062
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  • 6
    Electronic Resource
    Electronic Resource
    Radiation driven winds of hot stars: Theory of O-star atmospheres as a spectroscopic tool (1993)
    Springer
    Space science reviews 66 (1993), S. 105-125 
    Details
    ISSN: 1572-9672
    Keywords: stars: atmospheres ; early-type ; mass-loss ; X-rays ; fundamental parameters ; element abundances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The status of the continuing effort to construct radiation driven wind models for O-Stars atmospheres is reviewed. Emphasis is given to several problems relating to the fomation of UV line spectra the use of accurate atomic data, the inclusion of EUV radiation by shock heated matter, the simulation of photospheric line blocking. A new tool for O-star diagnostics is presented. This is based on the use of wind models to calculate synthetic high resolution spectra covering the observable UV region. A comparison with observed spectra then gives physical constraints on the properties of stellar winds and stellar parameters, additionally abundances can be determined. The astrophysical potential of this method is demonstrated by an application to two Of-stars, the galactic O4f-star ζ-Puppis and the LMC O3f-star Melnick 42. With regard to effective temperatures and gravities, the results from the application of classical methods to the analysis of photospheric lines are only partially verified. Explanations for the shortcomings of classical NLTE methods are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00771052
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  • 7
    Electronic Resource
    Electronic Resource
    The atmospheric composition, extinction and luminosity of the LBV R71 (1993)
    Springer
    Space science reviews 66 (1993), S. 207-210 
    Details
    ISSN: 1572-9672
    Keywords: stars:R71 ; stars:LBV ; stars:abundances ; stars:extinction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract ESO 3.6m Caspec spectra of the LMC luminous blue variable (LBV) taken at minimum have been analysed using NLTE model atmospheres and line formation calculations to derive atmospheric parameters and chemical composition. Using the silicon ionization balance and the hydrogen Balmer lines we deriveT eff =17250, log g=1.80 and a microturbulent velocity of 15–20 km/s. The analysis yields abundance ratios by number of approximately 0.43 for He/H, 0.03 for C/N and 0.14 for O/N, implying that enrichment of the atmosphere by processed material has taken place. We have re-evaluated the reddening of R71 using IUE low resolution data and published UBVRIJHKL photometry and derive a value for A V of 0.63. We also construct an extinction curve using archive IUE data for mid-B LMC supergiants and show that the extinction is anomalous; the 2175A bump being almost absent and the far UV rise very pronounced. A comparison of our model flux in theV-band with the observed (dereddened)V magnitude and the D.M. of the LMC (18.45), implies that the bolometric magnitude or R71 is −9.9. This is significantly higher than the value of −9.0 usually adopted for R71 and suggests that this object may not in fact be a ‘subluminous’ LBV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00771067
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  • 8
    Electronic Resource
    Electronic Resource
    NLTE analysis of massive ob stars in open clusters (1990)
    Springer
    Astrophysics and space science 169 (1990), S. 7-13 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a new method for deriving stellar masses and distances using the theory of radiatively driven winds as presented by Kudritzkiet al. (1989) and the stellar parameters derived from NLTE spectroscopic analysis. We illustrate the procedure with five stars observed in three open clusters and show that the method can be advantageous against the more usual of using the expression for the gravity. The comparison with evolutionary tracks indicates a possible discrepancy between the masses and helium abundances (when enhanced) derived from these tracks and those obtained by the other methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00640677
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  • 9
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    The chemical evolution of local star-forming galaxies: radial profiles of ISM metallicity, gas mass, and stellar mass and constraints on galactic accretion and winds (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-18
    Description: The radially averaged metallicity distribution of the interstellar medium (ISM) and the young stellar population of a sample of 20 disc galaxies is investigated by means of an analytical chemical evolution model which assumes constant ratios of galactic wind mass-loss and accretion mass gain to star formation rate. Based on this model, the observed metallicities and their gradients can be described surprisingly well by the radially averaged distribution of the ratio of stellar mass to ISM gas mass. The comparison between observed and model-predicted metallicity is used to constrain the rate of mass-loss through galactic wind and accretion gain in units of the star formation rate. Three groups of galaxies are found: galaxies with either mostly winds and only weak accretion, or mostly accretion and only weak winds, and galaxies where winds are roughly balanced by accretion. The three groups are distinct in the properties of their gas discs. Galaxies with approximately equal rates of mass-loss and accretion gain have low metallicity, atomic-hydrogen-dominated gas discs with a flat spatial profile. The other two groups have gas discs dominated by molecular hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential decline, which is on average steeper for the galaxies with small accretion rates. The rates of accretion ( 1.0 x SFR) and outflow ( 2.4 x SFR) are relatively low. The latter depend on the calibration of the zero-point of the metallicity determination from the use of H  ii region strong emission lines.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The superluminous supernova PS1-11ap: bridging the gap between low and high redshift (2013)
    Oxford University Press
    Details
    Publication Date: 2013-12-06
    Description: We present optical photometric and spectroscopic coverage of the superluminous supernova (SLSN) PS1-11ap, discovered with the Pan-STARRS1 Medium Deep Survey at z  = 0.524. This intrinsically blue transient rose slowly to reach a peak magnitude of M u  = –21.4 mag and bolometric luminosity of 8 10 43 erg s –1 before settling on to a relatively shallow gradient of decline. The observed decline is significantly slower than those of the SLSNe-Ic which have been the focus of much recent attention. Spectroscopic similarities with the lower redshift SN2007bi and a decline rate similar to 56 Co decay time-scale initially indicated that this transient could be a candidate for a pair instability supernova (PISN) explosion. Overall the transient appears quite similar to SN2007bi and the lower redshift object PTF12dam. The extensive data set, from 30 d before peak to 230 d after, allows a detailed and quantitative comparison with published models of PISN explosions. We find that the PS1-11ap data do not match these model explosion parameters well, supporting the recent claim that these SNe are not pair instability explosions. We show that PS1-11ap has many features in common with the faster declining SLSNe-Ic, and the light-curve evolution can also be quantitatively explained by the magnetar spin-down model. At a redshift of z  = 0.524, the observer-frame optical coverage provides comprehensive rest-frame UV data and allows us to compare it with the SLSNe recently found at high redshifts between z  = 2 and 4. While these high- z explosions are still plausible PISN candidates, they match the photometric evolution of PS1-11ap and hence could be counterparts to this lower redshift transient.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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