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Title: Spectroscopic Comparison of Metal-rich RRab Stars of the Galactic Field with their Metal-poor Counterparts

Abstract

We investigate atmospheric properties of 35 stable RRab stars that possess the full ranges of period, light amplitude, and metal abundance found in Galactic RR Lyrae stars. Our results are derived from several thousand echelle spectra obtained over several years with the du Pont telescope of Las Campanas Observatory. Radial velocities of metal lines and the H α line were used to construct curves of radial velocity versus pulsation phase. From these we estimated radial velocity amplitudes for metal lines (formed near the photosphere) and H α Doppler cores (formed at small optical depths). We also measured H α emission fluxes when they appear during primary light rises. Spectra shifted to rest wavelengths, binned into small phase intervals, and co-added were used to perform model atmospheric and abundance analyses. The derived metallicities and those of some previous spectroscopic surveys were combined to produce a new calibration of the Layden abundance scale. We then divided our RRab sample into metal-rich (disk) and metal-poor (halo) groups at [Fe/H] = −1.0; the atmospheres of RRab families, so defined, differ with respect to (a) peak strength of H α emission flux, (b) H α radial velocity amplitude, (c) dynamical gravity, (d) stellar radius variation,more » (e) secondary acceleration during the photometric bump that precedes minimum light, and (f) duration of H α line-doubling. We also detected H α line-doubling during the “bump” in the metal-poor family, but not in the metal-rich one. Although all RRab probably are core helium-burning horizontal branch stars, the metal-rich group appears to be a species sui generis.« less

Authors:
 [1];  [2];  [3]
  1. Université Nice Sophia–Antipolis, Observatoire de la Côte dAzur, UMR 7293, Parc Valrose, F-06108, Nice Cedex 02 (France)
  2. Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712 (United States)
  3. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
Publication Date:
OSTI Identifier:
22663949
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ACCELERATION; AMPLITUDES; BALMER LINES; CALIBRATION; DOPPLER EFFECT; EMISSION; GRAVITATION; HELIUM BURNING; METALLICITY; METALS; PHOTOSPHERE; PULSATIONS; RADIAL VELOCITY; SPECTRA; STARS; TELESCOPES; VISIBLE RADIATION; WAVELENGTHS

Citation Formats

Chadid, Merieme, Sneden, Christopher, and Preston, George W., E-mail: chadid@unice.fr, E-mail: chris@verdi.as.utexas.edu, E-mail: gwp@obs.carnegiescience.edu. Spectroscopic Comparison of Metal-rich RRab Stars of the Galactic Field with their Metal-poor Counterparts. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/187.
Chadid, Merieme, Sneden, Christopher, & Preston, George W., E-mail: chadid@unice.fr, E-mail: chris@verdi.as.utexas.edu, E-mail: gwp@obs.carnegiescience.edu. Spectroscopic Comparison of Metal-rich RRab Stars of the Galactic Field with their Metal-poor Counterparts. United States. doi:10.3847/1538-4357/835/2/187.
Chadid, Merieme, Sneden, Christopher, and Preston, George W., E-mail: chadid@unice.fr, E-mail: chris@verdi.as.utexas.edu, E-mail: gwp@obs.carnegiescience.edu. Wed . "Spectroscopic Comparison of Metal-rich RRab Stars of the Galactic Field with their Metal-poor Counterparts". United States. doi:10.3847/1538-4357/835/2/187.
@article{osti_22663949,
title = {Spectroscopic Comparison of Metal-rich RRab Stars of the Galactic Field with their Metal-poor Counterparts},
author = {Chadid, Merieme and Sneden, Christopher and Preston, George W., E-mail: chadid@unice.fr, E-mail: chris@verdi.as.utexas.edu, E-mail: gwp@obs.carnegiescience.edu},
abstractNote = {We investigate atmospheric properties of 35 stable RRab stars that possess the full ranges of period, light amplitude, and metal abundance found in Galactic RR Lyrae stars. Our results are derived from several thousand echelle spectra obtained over several years with the du Pont telescope of Las Campanas Observatory. Radial velocities of metal lines and the H α line were used to construct curves of radial velocity versus pulsation phase. From these we estimated radial velocity amplitudes for metal lines (formed near the photosphere) and H α Doppler cores (formed at small optical depths). We also measured H α emission fluxes when they appear during primary light rises. Spectra shifted to rest wavelengths, binned into small phase intervals, and co-added were used to perform model atmospheric and abundance analyses. The derived metallicities and those of some previous spectroscopic surveys were combined to produce a new calibration of the Layden abundance scale. We then divided our RRab sample into metal-rich (disk) and metal-poor (halo) groups at [Fe/H] = −1.0; the atmospheres of RRab families, so defined, differ with respect to (a) peak strength of H α emission flux, (b) H α radial velocity amplitude, (c) dynamical gravity, (d) stellar radius variation, (e) secondary acceleration during the photometric bump that precedes minimum light, and (f) duration of H α line-doubling. We also detected H α line-doubling during the “bump” in the metal-poor family, but not in the metal-rich one. Although all RRab probably are core helium-burning horizontal branch stars, the metal-rich group appears to be a species sui generis.},
doi = {10.3847/1538-4357/835/2/187},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}