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Browsing by Subject "Stars: atmospheres"

Browsing by Subject "Stars: atmospheres"

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  • Chemical composition of a sample of candidate post-asymptotic giant branch stars 
    Sumangala Rao, S; Giridhar, S; Lambert, D. L (Wiley-Blackwell, 2012-01)
    We have derived elemental abundances for a sample of nine IRAS sources with colours similar to those of post-asymptotic giant branch (post-AGB) stars. For IRAS 01259+6823, IRAS 05208−2035, IRAS 04535+3747 and IRAS 08187−1905, ...
  • A chemodynamical analysis of bright metal-poor stars from the HESP-GOMPA survey – indications of a non-prevailing site for light r-process elements 
    Bandyopadhyay, A; Beers, Timothy C; Ezzeddine, Rana; Sivarani, T; Nayak, Prasanta K; Pandey, Jeewan C; Saraf, Pallavi; Susmitha, A (Oxford University Press on behalf of Royal Astronomical Society, 2024-04)
    We present a comprehensive analysis of the detailed chemical abundances for a sample of 11 metal-poor, very metal-poor, and extremely metal-poor stars ([Fe/H] = −1.65 to [Fe/H] = −3.0) as part of the HESP-GOMPA (Galactic ...
  • Decoding the compositions of four bright r-process-enhanced stars 
    Saraf, Pallavi; Prieto, Carlos Allende; Sivarani, T; Bandyopadhyay, A; Beers, Timothy C.; Susmitha, A (Oxford University Press on behalf of Royal Astronomical Society, 2023-10)
    There has been a concerted effort in recent years to identify the astrophysical sites of the r-process that can operate early in the galaxy. The discovery of many r-process-enhanced (RPE) stars (especially by the R-process ...
  • First Steps with CO5BOLD Using HLLMHD and PP Reconstruction. 
    Steiner, O; Rajaguru, S. P; Vigeesh, G; Steffen, M; Schaffenberger, W; Freytag, B (Societa Astronomica Italiana, 2013)
    We report on first experiences with real-life applications using the MHD-module of CO5BOLD together with the piecewise parabolic reconstruction scheme and present preliminary results of stellar magnetic models with Teff = ...
  • The Hamburg/ESO R-process Enhanced Star survey (HERES) VIII. The r+s star HE 1405 0822 
    Cui, W. Y; Sivarani, T; Christlieb, N (EDP Sciences, 2013-10)
    Aims. The aim of this study is a detailed abundance analysis of the newly discovered r-rich star HE 1405−0822, which has [Fe/H] = −2.40. This star shows enhancements of both r- and s-elements, [Ba/Fe] = + 1.95 and [Eu/Fe] ...
  • High-resolution spectroscopy of extremely metal-poor stars from SDSS/SEGUE. I. Atmospheric parameters and chemical compositions 
    Aoki, W; Beers, T. C; Lee, Young Sun; Honda, S; Ito, H; Takada-Hidai, M; Frebel, A; Suda, T; Fujimoto, M. Y; Carollo, D; Sivarani, T (IOP Publishing, 2013-01)
    Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metalpoor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the ...
  • 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 ...
  • LAMOST J045019.27 + 394758.7, with peculiar abundances of N, Na, V, Zn, is possibly a Sculptor dwarf galaxy escapee 
    Meenakshi, P; Goswami, A; Shejeelammal, J; Sonamben, Mayani; Pawar, Ganesh; Mkrtichian, David; Doddamani, Vijayakumar H; Joshi, Santosh (Oxford University Press on behalf of Royal Astronomical Society, 2022-07)
    We present the results of the high-resolution (R ∼ 60 000) spectroscopic analysis of the star LAMOSTJ045019.27 + 394758.7 (hereafter J045) from the list of carbon stars of LAMOST DR2. From our analysis, we find that J045 ...
  • Line identification and photometric history of the hot post-AGB star Hen 3−1013 (IRAS 14331−6435) 
    Arkhipova, V. P; Parthasarathy, M; Ikonnikova, N. P; Ishigaki, M; Hubrig, S; Sarkar, G; Kniazev, A. Y (Oxford University Press on behalf of the Royal Astronomical Society, 2018-12)
    We present a study of the high-resolution optical spectrum for the hot post-asymptotic giant branch (post-AGB) star, Hen 3−1013, identified as the optical counterpart of the infrared source IRAS 14331−6435. For the first ...
  • Line identification and photometric history of the hot post-AGB star Hen 3−1013 (IRAS 14331−6435) 
    Arkhipova, V. P; Parthasarathy, M; Ikonnikova, N. P; Ishigaki, M; Hubrig, S; Sarkar, G; Kniazev, A. Y (Oxford University Press on behalf of the Royal Astronomical Society, 2018-12)
    We present a study of the high-resolution optical spectrum for the hot post-asymptotic giant branch (post-AGB) star, Hen 3−1013, identified as the optical counterpart of the infrared source IRAS 14331−6435. For the first ...
  • 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 ...
  • Observation of R-Band Variability of L Dwarfs 
    Maiti, M; Sengupta, S; Parihar, P. S; Anupama, G. C (University of Chicago Press, 2005-02)
    We report, for the first time, photometric variability of L dwarfs in the R band. Out of three L1 dwarfs (2MASS 1300+19, 2MASS 1439+19, and 2MASS 1658+70) observed, we have detected R-band variability in 2MASS 1300+19 and ...
  • 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 ...
  • Polarized line formation in moving atmospheres with partial frequency redistribution and a weak magnetic field 
    Sampoorna, M; Nagendra, K. N (IOP Publishing, 2015-10-10)
    The dynamical state of the solar and stellar atmospheres depends on the macroscopic velocity fields prevailing within them. The presence of such velocity fields in the line formation regions strongly affects the polarized ...
  • Polarized Line Formation in Non-Monotonic Velocity Fields 
    Sampoorna, M; Nagendra, K. N (IOP Publishing, 2016-12-10)
    For a correct interpretation of the observed spectro-polarimetric data from astrophysical objects such as the Sun, it is necessary to solve the polarized line transfer problems taking into account a realistic temperature ...
  • Polarized resonance line transfer in a spherically symmetric medium with angle-dependent partial frequency redistribution 
    Sampoorna, M; Supriya, H. D (Oxford University Press on behalf of Royal Astronomical Society, 2023-12)
    In a stellar atmosphere, the resonance line polarization arises from scattering of limb-darkened radiation field by atoms. This spectral line polarization gets affected particularly in the wings, when the line photons ...
  • Properties of small-scale magnetism of stellar atmospheres 
    Steiner, O; Salhab, R; Freytag, B; Rajaguru, S. P; Schaffenberger, W; Steffen, M (Published by Oxford University Press on behalf of the Astronomical Society of Japan, 2014-12)
    The magnetic field outside of sunspots is concentrated in the intergranular space, where it forms a delicate filigree of bright ribbons and dots as seen on broad band images of the Sun. We expect this small-scale magnetic ...
  • Simulation of the small-scale magnetism in main-sequence stellar atmospheres 
    Salhab, R. G; Steiner, O; Berdyugina, S. V; Freytagz, B; Rajaguru, S. P; Steffen, M (EDP Sciences, 2018-06)
    Context. Observations of the Sun tell us that its granular and subgranular small-scale magnetism has significant consequences for global quantities such as the total solar irradiance or convective blueshift of spectral ...
  • Spectroscopic study of two new super Li-rich red clump K giants 
    Raghubar, Singh; Reddy, B. E; Bharat Kumar, Y (Oxford University Press on behalf of the Royal Astronomical Society, 2019-01)
    In this paper, we report the discovery of two new super Li-rich K giants: HD 24960 and TYC 1751-1713-1. Based on high-resolution (R ≈ 60 000) spectroscopy, we have derived Li abundance of A(Li) ≈ 4.0 dex for both ...

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