Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1107.1316

Is the post-AGB star SAO 40039 mildly H-deficient?

S. Sumangala Rao·Gajendra Pandey·David L. Lambert·Sunetra Giridhar
View original source ↗Read source document ↗Export metadata ↓

Abstract

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 He-rich. High-resolution optical spectra are analyzed using a family of model atmospheres with different He/H ratios. Atmospheric parameters are estimated from the ionization equilibrium set by neutral and singly ionized species of Fe and Mg, the excitation of Fe I and Fe II lines and the wings of the Paschen lines. On the assumption that the He I lines are of photospheric and not chromospheric in origin, a He/H ratio of approximately unity is found by imposing the condition that the adopted He/H ratio of the model atmosphere must equal the ratio derived from the observed He I triplet lines at 5876, 4471 and 4713 Angstrom, and singlet lines at 4922 and 5015 Angstrom. Using the model with the best-fitting atmospheric parameters for this He/H ratio, SAO 40039 is confirmed to exhibit mild dust-gas depletion, i.e., the star has an atmosphere deficient in elements of high condensation temperature. The star appears to be moderately metal-deficient with [Fe/H]=-0.4 dex. But the star's intrinsic metallicty as estimated from Na, S and Zn, elements of a low condensation temperature, is [Fe/H]_o {[Fe/H]_o refers to the star's intrinsic metallicity} ~ -0.2. The star is enriched in N and perhaps O too, changes reflecting the star's AGB past and the event that led to He enrichment.

Explore related subjects

astro-ph.SR

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

S. Sumangala Rao, Gajendra Pandey, David L. Lambert, Sunetra Giridhar. 2011-07-07. Is the post-AGB star SAO 40039 mildly H-deficient?. https://doi.org/10.1088/2041-8205%2F737%2F1%2Fl7

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Solar Wind Proton Heating and its Effect on Temperature Anisotropy Evolution between 0.05 and 1 au

This study focuses on the radial evolution of the solar wind proton adiabatic invariants and temperature anisotropies in the inner heliosphere. More specifically, we study in-situ measurements provided by the Parker Solar Probe, between 0.05 au and 0.25 au from the Sun, and Solar Orbiter spacecraft between 0.3 au and 1 au. Throughout the studied range of radial distances, we observe a significant average heating in the direction perpendicular to the local magnetic field for both fast and slow solar wind populations. On the other hand, there is no clear deviation from adiabaticity in the parallel direction regardless of the wind speed. The perpendicular heating is enough to significantly reduce the generation of the temperature anisotropy expected from a double adiabatic evolution. Despite the heating, an important portion of the solar wind (especially the slower wind streams) develops substantial anisotropies with higher parallel temperatures, which eventually become constrained by kinetic firehose instabilities.

astro-ph.SR↗
arXiv2026

MEGARA Stellar Spectral Library. Second Release

We present the second release of the MEGARA spectral library, MEGASTAR, which now includes all spectra collected during ten observing semesters at the Gran Telescopio CANARIAS. This new release supersedes our first release and incorporates a substantial number of additional observations (2000 new spectra), obtained at high spectral resolution, R(FWHM)$\sim$20000, in two wavelength ranges centred on H$α$ (6420 - 6790 A) and on the CaII triplet (8370 - 8885 A). The aim of this paper is to introduce MEGASTAR DR2 to the community as its high-resolution spectra can serve as a valuable resource for numerous types of research. In particular, we will use MEGASTAR spectra to construct SSP blocks within the HR-PyPopStar evolutionary synthesis models. The stars were observed using the integral field spectroscopy mode of the instrument. We process the data in a uniform way with the MEGARA data reduction pipeline. We estimate the stellar flux by adding the spectra from 37 spaxels, centred on the spaxel with the highest flux in the IFU reconstructed image. This approach guarantees that the effective slit width, and therefore the spectral resolution, are the same for all spectra. The second MEGASTAR release consists of 2838 spectra corresponding to 1408 stars, providing a better coverage of the stellar parameter space than the first release. The spectra were acquired with an average continuum S/N of about 215. This second release meets the standards of a modern empirical library: it offers reliable calibrations, data free from slit effects, observations of a large number of stars, and provides high spectral resolution to model both individual stellar clusters and entire galaxies observed with MEGARA.

astro-ph.SR↗
arXiv2026

SPAMMS: 3D spectroscopic modeling of stellar surfaces. II. Implementation of Kurucz and TLUSTY model atmospheres

Context. Accurate stellar spectra are essential to derive stellar properties. Traditional model atmospheres often oversimplify phenomena that break spherical symmetry, such as rotational deformation or multiplicity. The Spectroscopic PAtch Model for Massive Stars (SPAMMS) accounts for these effects, but its applicability has been limited by the spectral types covered by its model atmosphere grids. Aims. We aim to extend the parameter space of the model atmosphere grids available to SPAMMS, enabling spectral synthesis across a broader range of stellar types. Methods. We computed specific intensities, $I\left(λ,μ\right)$, for $101$ emergent angles using PRISMAS (Pipeline of Radiative Intensity Synthesis for Meshed Atmospheric Surfaces), and pre-computed LTE and non-LTE atmospheres from two ATLAS9-Kurucz grids and the TLUSTY-based OSTAR2002 and BSTAR2006 models. Results. The intensity grids cover effective temperatures from $3500$ to $55000\,\mathrm{K}$ and surface gravities from $0.0$ to $5.0\,\mathrm{dex}$, spanning O- to K-type stars. They include metallicities from $0$ to $30\,\mathrm{Z_\odot}$ and microturbulent velocities of $1$, $3$, $5$, and $10\,\mathrm{km\,s^{-1}}$. The spectral range extends from $3000$ to $9000\,\mathring{\mathrm{A}}$ with $Δλ=0.01\,\mathring{\mathrm{A}}$. As a proof of concept, we modelled with SPAMMS a rapidly rotating B-type star and an eclipsing Algol-type binary. Conclusions. The new LTE-Kurucz and NLTE-TLUSTY grids substantially expand the parameter space accessible to SPAMMS. The code can now generate synthetic spectra for a broader range of stellar types and geometries, including rapidly rotating and multiple systems -- providing a more comprehensive framework for modelling non-spherical stellar surfaces.

astro-ph.SR↗