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Browsing by Author "Lambert, D. L"

Browsing by Author "Lambert, D. L"

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  • Mid-infrared variations of R Coronae Borealis stars 
    Kameswara Rao, N; Lambert, D. L (Oxford University Press on behalf of the Royal Astronomical Society, 2015-03-11)
    Mid-infrared (IR) photometry of R Coronae Borealis stars obtained from various satellites from Infrared Astronomical Satellite (IRAS) to Wide-field Infrared Survey Explorer (WISE) has been utilized in studying the ...
  • Neon and CNO Abundances for Extreme Helium Stars—A Non-LTE Analysis 
    Pandey, G; Lambert, D. L (IOP Publishing, 2011-02)
    A non-LTE (NLTE) abundance analysis was carried out for three extreme helium stars (EHes): BD+10° 2179, BD–9° 4395, and LS IV+6° 002, from their optical spectra with NLTE model atmospheres. NLTE TLUSTY model atmospheres ...
  • A New Near-IR C2 Linelist for an Improved Chemical Analysis of Hydrogen-deficient, Carbon-rich Giants\unboldmath 
    Garcia-Hernandez, D. A; Masseron, T; Zamora, O; Manchado, A; Rao, N. K; Reddy, A. B. S; Lambert, D. L; Yurchenko, S; Tennyson, J (Astronomical Society of the Pacific, 2019)
    Diatomic carbon (C2) is ubiquitous in astronomical environments, from comets and stars to translucent clouds and the interstellar medium. In particular, the C2 bands (mainly the Ballik-Ramsay and Phillips transitions) are ...
  • Non-local Thermodynamic Equilibrium Abundance Analyses of the Extreme Helium Stars V652Her and HD144941 
    Pandey, G; Lambert, D. L (IOP Publishing, 2017-10)
    Optical high-resolution spectra of V652 Her and HD 144941, the two extreme helium stars with exceptionally low C / He ratios, have been subjected to a non-LTE abundance analysis using the tools TLUSTY and SYNSPEC. De fi ning ...
  • On the absolute magnitude of V482 Cygni, an R Coronae Borealis star 
    Kameswara Rao, N; Lambert, D. L (Astronomical Society of the Pacific, 1993-06)
    An identification of V482 Cygni, a R Coronae Borealis star, with a quadruple system containing a K5 III star is rejected. High-resolution spectra show that the radial velocity of V482 Cyg and the K5 III star differ by 35 ...
  • On the Binary Helium Star DY Centauri: Chemical Composition and Evolutionary State 
    Pandey, G; Kameswara Rao, N; Jeffery, C. S; Lambert, D. L (IOP Publishing, 2014-10-01)
    DY Cen has shown a steady fading of its visual light by about one magnitude in the last 40 yr, suggesting a secular increase in its effective temperature. We have conducted non-local thermodynamic equilibrium (LTE) and LTE ...
  • On the hydrogen-deficient nature of Z Ursae Minoris 
    Goswami, A; Kameswara Rao, N; Lambert, D. L; Gonzalez, G (The Astronomical Society of the Pacific, 1997-05)
    Z Ursa Minoris was classified by Benson et al. (1994) a a R Coronae Borealis (RCB) variable star from its light variations. Hydrogen deficiency, which is a defining feature of RCB stars, was not established. To investigate ...
  • Optical Emission Bands in the Spectrum of the R-Coronae and V854-CENTAURI at Minimum 
    Kameswara Rao, N; Lambert, D. L (Royal Astronomical Society, 1993-08-01)
    Several unidentified broad emission features, previously seen only in the spectrum of the nebulosity in the Red Rectangle, have been observed in a spectrum of the R CrB star V854 Cen taken in a deep minimum. Similarities ...
  • 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 ...
  • R Coronae Borealis at the 2003 light minimum 
    Kameswara Rao, N; Lambert, D. L; Shetrone, M. D (Blackwell Publishing, 2006-08)
    A set of five high-resolution optical spectra of R CrB obtained in 2003 March is discussed. At the time of the first spectrum (March 8), the star was at V = 12.6, a decline of more than six magnitudes. By March 31, the ...
  • The R Coronae Borealis stars - A few mere facts 
    Lambert, D. L; Kameswara Rao, N (Indian Academy of Sciences, 1994-03)
    This review presents a selection of recent highlights of observations of R Coronae Borealis (RCB) variables. Emphasis is placed on an abundance analysis of a complete sample (18 stars) of the warm galactic RCBs. It is shown ...
  • The R Coronae Borealis stars - atmospheres and abundances 
    Asplund, M; Gustafsson, B; Lambert, D. L; Kameswara Rao, N (European Southern Observatory, 2000-01)
    An abundance analysis of the H-deficient and He- and C-rich R Coronae Borealis (R CrB) stars has been undertaken to examine the ancestry of the stars. The investigation is based on high-resolution spectra and line-blanketed ...
  • R Coronae Borealis stars at minimum light - UW Cen 
    Kameswara Rao, N; Reddy, B. E; Lambert, D. L (Blackwell Publishing, 2004-12)
    Two high-resolution optical spectra of the R Coronae Borealis (R CrB) star UW Cen in decline are discussed. A spectrum from mid-1992 when the star had faded by 3 mag shows just a few differences with the spectrum at maximum ...
  • 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 ...
  • SALT revisits DY Cen: a rapidly evolving strontium-rich single helium star 
    Jeffery, C. S; Kameswara Rao, N; Lambert, D. L (Oxford University Press on behalf of the Royal Astronomical Society, 2020-04)
    The hydrogen-deficient star DY Cen has been reported as an R CrB-type variable, an extreme helium star (with some hydrogen), and as a single-lined spectroscopic binary. It has been associated with a dramatic change in ...
  • 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 ...
  • A Spectral Analysis of HD 165553 
    Goswami, A; Kameswara Rao, N; Lambert, D. L (Astronomical Society of India, 2003)
    High resolution spectra of HD 165553, a star reported to be a spectroscopic binary of spectral type F8 Ib are analysed. The stellar parameters - effective temperature, surface gravity and microturbulence are determined ...
  • Spectral Variations of DY Cen 
    Giridhar, S; Kameswara Rao, N; Lambert, D. L (Indaian Academy of Sciences, 1996-06)
    Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines show a radial velocity variation of 12 km s(sup -1) between 1989 July and 1992 May. Emission components ...
  • Spectrum of S Aps at deep minimum 
    Kameswara Rao, N; Goswami, A; Smith, V. V; Lambert, D. L (Astronomical Society of the Pacific, 1996)

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