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Browsing by Author "Lambert, D. L"

Browsing by Author "Lambert, D. L"

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  • 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)
  • The Spectrum of the Cool R Coronae Borealis Variable S Apodis in a Deep Decline 
    Goswami, A; Kameswara Rao, N; Lambert, D. L; Smith, V. V (Astronomical Society of the Pacific, 1997-03)
    A high resolution spectrum (5575 - 8875\AA) of the cool R Coronae Borealis variable S Apodis in its 1993 deep decline is discussed. Narrow or chromospheric emission lines of Na I, K I, Ca II, and Ba II and broad emission ...
  • The spectrum of the cool R Coronae Borealis variable Z Ursae Minoris at minimum 
    Goswami, A; Kameswara Rao, N; Lambert, D. L (The Observatory, 1999-02)
  • A stellar endgame - the born-again Sakurai's object 
    Asplund, M; Gustafsson, B; Lambert, D. L; Kameswara Rao, N (European Southern Observatory, 1997-05)
    The surface chemical composition of this remarkable star shows that it is hydrogen-deficient, carbon-rich and enriched in the light s-process elements. Spectra taken in May and October 1996 indicate a decrease in the surface ...

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