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Browsing by Subject "Stars: Atmospheres"

Browsing by Subject "Stars: Atmospheres"

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  • Convective Intensification of Magnetic Flux Tubes in Stellar Photospheres 
    Rajaguru, S. P; Kurucz, R. L; Hasan, S. S (The American Astronomical Society, 2002-02)
    The convective collapse of thin magnetic flux tubes in the photospheres of Sun-like stars is investigated using realistic models of the superadiabatic upper convection zone layers of these stars. The strengths of convectively ...
  • Elemental Abundances and Atmospheric Parameters of Seven F-G Supergiants 
    Giridhar, S; Ferro, A; Parrao, L (Astronomical Society of the Pacific, 1997-10)
    Spectroscopic abundance determinations for a sample of seven F-G stars have been carried out. The majority of them have large galactic latitudes. One objective in deriving spectroscopic abundances is to differentiate evolved ...
  • Explaining the Observed Polarization from Brown Dwarfs by Single Dust Scattering 
    Sengupta, S (The American Astronomical Society, 2003-03)
    Recent observation of linear optical polarization from brown dwarfs confirms the dust hypothesis in the atmospheres of brown dwarfs with effective temperature higher than 1400 K. The observed polarization could arise because ...
  • High-resolution spectroscopy of R CrB - pulsations, shells and mass loss 
    Kameswara Rao, N; Lambert, D. L (The Royal Astronomical Society, 1997-01)
    High spectral resolution observations obtained in 1994 and spanning three pulsation cycles of R CrB are discussed along with available UBV photometric observations for the same epochs. Model atmosphere based analyses of ...
  • Low resolution spectroscopy of hot post-AGB candidates 
    Parthasarathy, M; Vijapurkar, J; Drilling, J. S (EDP Sciences, 2000-08)
    Spectral types are determined from low resolution optical spectra of 40 IRAS sources with far-infrared colours similar to planetary nebulae. The presence of circumstellar dust, high galactic latitude, and early supergiant ...
  • Multiple scattering polarization of substellar-mass objects: T dwarfs 
    Sengupta, S; Marley, M. S (American Astronomical Society, 2009-12-10)
    While there have been multiple observational programs aimed at detecting linear polarization of optical radiation emitted by ultracool dwarfs, there has been comparatively less rigorous theoretical analysis of the problem. ...
  • An operator perturbation method for polarized line transfer. I. Non-magnetic regime in 1D media. 
    Faurobert-Scholl, M; Frisch, H; Nagendra, K. N (European Southern Observatory, 1997-06)
    In this paper we generalize an Approximate Lambda Iteration (ALI) technique developed for scalar transfer problems to a vectorial transfer problem for polarized radiation. Scalar ALI techniques are based on a suitable ...
  • Origin of Lithium Enrichment in K Giants 
    Bharat Kumar, Y; Reddy, B. E; Lambert, D. L (Institute of Physics Publishing, 2011-03-20)
    In this Letter, we report on a low-resolution spectroscopic survey for Li-rich K giants among 2000 low-mass (M ≤ 3 M sun) giants spanning the luminosity range from below to above the luminosity of the clump. Fifteen new ...
  • Oxygen isotopic ratios in cool R coronae borealis stars 
    Garcia-Hernandez, D. A; Lambert, D. L; Kameswara Rao, N; Hinkle, K. H; Eriksson, K (Institute of Physics, 2010-05)
    We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for five cool RCB stars. The 16O/18O ratios are derived by spectrum ...
  • Probing Dust in the Atmosphere of Brown Dwarfs through Polarization 
    Sengupta, S; Krishan, V (The American Astronomical Society, 2001-11)
    The theoretical analysis and observational evidence indicate that a brown dwarf with an effective temperature greater than 1300 K would have a dust cloud in its atmosphere. In this Letter, we show that dust scattering ...
  • The R Coronae Borealis stars: carbon abundances from forbidden carbon lines 
    Pandey, G; Lambert, D. L; Kameswara Rao, N; Gustafsson, B; Ryde, N; Yong, D (Royal Astronomical Society, 2004-09)
    Spectra of several R Coronae Borealis (RCB) stars at maximum light have been examined for the [CI] 9850- and 8727-Åabsorption lines. The 9850-Åline is variously blended with an FeII and CN lines, but positive identifications ...
  • Resonance line polarization in the presence of wave motion 
    Rangarajan, K. E (European Southern Observatory, 1997-04)
    The effect of wave velocity on resonance line polarization is studied. We assumed a photosphere - chromosphere type of temperature structure for the atmosphere with plane parallel symmetry. The "Discrete Space Theory ...
  • Searching for the metal-weak thick disc in the solar neighbourhood 
    Reddy, B. E; Lambert, D. L (Royal Astronomical Society, 2008-11)
    An abundance analysis is presented of 60 metal-poor stars drawn from catalogues of nearby stars provided by Arifyanto et al. and Schuster et al. In an attempt to isolate a sample of metal-weak thick disc stars, we applied ...
  • Study of Compton broadening due to electron-photo scattering 
    Srinivasa Rao, M (Astronomical Observatory, Serbia, 2010-06)
    SUMMARY: We have investigated the effects of Compton broadening due to electron-photon scattering in hot stellar atmospheres. A purely electron-photon scattering media is assumed to have plane parallel geometry with an ...

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