The Chemical Compositions of the Type II Cepheids -- The BL Her and W Vir Variables

Abstract

Abundance analyses from high-resolution optical spectra are presented for 19 Type II Cepheids in the Galactic field. The sample includes both short-period (BL Her) and long-period (W Vir) stars. This is the first extensive abundance analysis of these variables. The C, N, and O abundances with similar spreads for the BL Her and W Vir show evidence for an atmosphere contaminated with $3\alpha$-process and CN-cycling products. A notable anomaly of the BL Her stars is an overabundance of Na by a factor of about five relative to their presumed initial abundances. This overabundance is not seen in the W Vir stars. The abundance anomalies running from mild to extreme in W Vir stars but not seen in the BL Her stars are attributed to dust-gas separation that provides an atmosphere deficient in elements of high condensation temperature, notably Al, Ca, Sc, Ti, and $s$-process elements. Such anomalies have previously been seen among RV Tau stars which represent a long-period extension of the variability enjoyed by the Type II Cepheids. Comments are offered on how the contrasting abundance anomalies of BL Her and W Vir stars may be explained in terms of the stars' evolution from the blue horizontal branch.

41 pages including 11 figures and 4 tables; Accepted for publication in ApJ

References in corpus (7)

• Elemental Abundance Survey of The Galactic Thick Disk
• The Chemical Compositions of Galactic Disk F and G Dwarfs
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• Using Cepheids to determine the galactic abundance gradient I. The solar neighbourhood
• Chemical Abundances and Rotation Velocities of Blue Horizontal-Branch Stars in Six Globular Clusters
• 3D Numerical Experimentation on the Core Helium Flash of low-mass Red Giants
• Abundance Analyses of Field RV Tauri Stars, VI: An Extended Sample

Cited by in corpus (25)

• The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees
• Post-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators
• The Luminosities and Distance Scales of Type II Cepheid and RR Lyrae variables
• Distance Scale Zero-Points from Galactic RR Lyrae Star Parallaxes
• Old-Aged Stellar Population Distance Indicators
• The WISE View of RV Tauri Stars
• Variable stars in Local Group Galaxies - II. Sculptor dSph
• A population of transition disks around evolved stars: Fingerprints of planets? Catalog of disks surrounding Galactic post-AGB binaries
• New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue
• Chemical abundances of solar neighborhood RR Lyrae stars
• High-precision distance measurements with classical pulsating stars
• Modelling depletion by re-accretion of gas from a dusty disc in post-AGB stars
• Evolutionary and pulsation properties of Type II Cepheids
• On the separation between RR Lyrae and Type II Cepheids and their importance for distance determination: the case of $\omega$ Cen
• High Resolution Optical Spectroscopy of the F Supergiant Proto-Planetary Nebula V887 Her=IRAS 18095+2704
• A Spectroscopic and Photometric Study of the Metal-Poor, Pulsating, Post-AGB Binary HD 46703
• An absolute calibration of the near-infrared Period-Luminosity Relations of Type II Cepheids in the Milky Way and in the Large Magellanic Cloud
• KP Cyg: an Unusual Metal-rich RR Lyr Type Star of Long Period
• Metal-Poor Type II Cepheids with Periods Less Than Three Days
• New classical Cepheids in the inner part of the northern Galactic disk and their kinematics
• High-resolution spectroscopy of the extremely iron-poor post-AGB star CC Lyr
• Kinematics of Type II Cepheids of the Galactic Halo
• A new method of measuring center-of-mass velocities of radially pulsating stars from high-resolution spectroscopy
• On the evolutionary status of high-latitude variable V534 Lyr
• AU Pegasi revisited: period evolution and orbital elements of a peculiar Type II Cepheid