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Browsing by Author "Lambert, D. L"

Browsing by Author "Lambert, D. L"

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  • Infrared Space Observatory Spectra of R Coronae Borealis Stars. I. Emission Features in the Interval 3-25 Microns 
    Lambert, D. L; Kameswara Rao, N; Pandey, G; Ivans, I. I (American Astronomical Society, 2001-07)
    Infrared Space Observatory 3-25 μm spectra of the R Coronae Borealis stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp emission features coincident in wavelength with the well-known unidentified emission ...
  • Is DZ Andromedae an R Coronae Borealis variable? 
    Goswami, A; Kameswara Rao, N; Lambert, D. L (The Observatory, 1998-08)
    The variable star DZ Andromedae has been suspected to be an R Coronae Borealis variable. Our analysis of a high-resolution spectrum shows that the star has been misclassified: the spectrum resembles that of a K giant. We ...
  • Is LR SCO and RCB star? 
    Giridhar, S; Kameswara Rao, N; Lambert, D. L (The Observatory, 1990-08)
  • Is the Post-AGB Star SAO 40039 Mildly Hydrogen-Deficient? 
    Sumangala Rao, S; Pandey, G; Lambert, D. L; Giridhar, S (IOP Publishing, 2011-08-10)
    We have conducted an LTE abundance analysis for SAO 40039, a warm post-AGB star whose spectrum is known to show surprisingly strong He I lines for its effective temperature and has been suspected of being H-deficient and ...
  • Li Abundance Survey in Galactic Thin Disk 
    Lambert, D. L; Reddy, B. E (Astronomical Society of the Pacific, 2005-09)
    Lithium abundances for a sample of 451 F and G dwarfs including 181 new stars all belonging to the Galactic thin disk are discussed. Lithium abundances, metallicities ([Fe/H]), masses, and ages are determined (Lambert & ...
  • Lithium abundances and asteroseismology of red giants: understanding the evolution of lithium in giants based on asteroseismic parameters 
    Deepak; Lambert, D. L (Oxford University Press on behalf of the Royal Astronomical Society, 2021-07)
    In this study, we explore the evolution of lithium in giant stars based on data assembled from the literature on asteroseismology and Li abundances for giants. Our final sample of 187 giants consists of 44 red giant branch ...
  • Lithium abundances in the α Per cluster 
    Balachandran, S. C; Mallik, S. G. V; Lambert, D. L (Wiley Blackwell, 2011-02)
    Lithium (Li) abundances are presented and discussed for 70 members of the 50-Myr-old open cluster α Per. More than half of the abundances are from new high-resolution spectra. The Li abundance in the F-type stars is equal ...
  • Lithium abundances in the α Per cluster 
    Mallik, S. G. V; Balachandran, S. C; Lambert, D. L (Cambridge University Press, 2010-04)
    As a sequel to the Li observations by Balachandran, Lambert & Stauffer (1988, 1996) in 35 stars of the 50 Myr old cluster α Persei, we have obtained and analyzed high resolution spectra of another 51 stars. Following a ...
  • Lithium abundances of the local thin disc stars 
    Lambert, D. L; Reddy, B. E (Royal Astronomical Society, 2004-04-01)
    Lithium abundances are presented for a sample of 181 nearby F and G dwarfs with accurate Hipparcos parallaxes. The stars are on circular orbits about the Galactic centre and, hence, are identified as belonging to the thin ...
  • Lithium in red giants: the roles of the He-core flash and the luminosity bump 
    Deepak; Lambert, D. L (Oxford University Press on behalf of the Royal Astronomical Society, 2021-10)
    Lithium abundances for red giants in the GALAH DR3 survey are studied. The rare examples of Li-enriched stars with abundances A(Li) ≥1.5 are confirmed to be He-core burning stars belonging to or evolved from the red clump ...
  • 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 ...

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