Post-main-sequence and POST red giant branch variables with pulsation periods less than one day

Abstract

view Abstract Citations (16) References (81) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Post-Main-Sequence and POST Red Giant Branch Variables With Pulsation Periods Less Than One Year Eggen, Olin J. Abstract Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5 to 1 solar mass) pulsators are discussed on the basis of four color and H beta light curves published elsewhere. The post-main-sequence variables, called ultrashort period cepheid (USPC) (delta Sct), pulsate in the fundamental and first harmonic modes of radial pulsation and, in many cases, in nonradial modes. The variables for which photometry allows accurate, luminosity estimates and are known to pulsate simultaneously in the fundamental and first harmonic or in the fundamental mode alone, define a PL relation (MV = -2.80 log P - 0.60, fundamental). It is notable that the slope of this relation is in the range of slopes found for classical cepheids. Accurate V photometry is lacking for many of the variables known as 'anomalous cepheids', but the available data divide them into low mass, pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC (delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, for which accurate photometry is available, give remarkably consistent moduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for the clusters, in which they are blue stragglers similar to SX Phe in Kapteyn's star group. The assumption that the four post-giant branch variables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn's star group and RR Lyr in the Groombridge 1830 group, are physical members of these groups and share their V-velocities, leads to a calibration of the photometry for the derivation of reddening, luminosity, and heavy element abundance of 45 field variables. The resulting reddenings are consistent with values obtained by other methods and the metallicities are consistent with the most accurately available spectroscopic determinations of delta S and of Ca II K. The luminosities of the bulk of the variables confirm Sandage's (1993) relation between MV and (Fe/H). Four or five of the field variables are probably binary, including BB Vir which Kinman & Carreta (1992) have independently noted as double. The PL relation for USPC (delta Sct) variables intersects the horizontal branch (HB) near P = 0.3d and at least two field very short period cepheid (VSPC) (RR Lyr) star, FW Lup (0.484 d) and ST Pic (0.486 d) may be first overtone pulsators of the USPC (delta Sct) variety. A dozen field VSPC (RR Lyr) stars populate a (Fe/H), MV relation with the same slope as the other stars but displaced 0.7 mag toward higher luminosities. The only cluster variable found to populate this diplaced relation is No. 9 in 47 Tuc, although ST Vir, which may be a member of the Arcturus group, should also be considered. The elevated luminosities are unlikely to be caused by either evolution or errors in the photometric indices. A possible source of these apparently young VSPC(RR Lyr) variables with halo metallicity is in second (or third) generation globular clusters formed during an episodic collapse of the galaxy that produced metal poor stars but in a dynamical situation that hastened the disruption of the clusters, currently formed, before the still older globular clusters, created under conditions that have kept them in a more disruptive free environment. Publication: The Astronomical Journal Pub Date: June 1994 DOI: 10.1086/117024 Bibcode: 1994AJ....107.2131E Keywords: Globular Clusters; Main Sequence Stars; Star Distribution; Variable Stars; Radial Velocity; Stellar Magnitude; Astrophysics; STARS: OSCILLATIONS full text sources ADS | data products SIMBAD (98)