Metal-Rich SX Phe stars in the Kepler Field

TL;DR

This study provides a detailed spectroscopic and photometric analysis of 32 SX Phe variable stars in the Kepler field, revealing their metallicities, kinematics, rotation, and binary status, with implications for their population origins.

Contribution

It presents the first comprehensive spectroscopic and kinematic characterization of SX Phe stars in the Kepler field, highlighting their metal-rich nature and binary characteristics.

Findings

Most stars are metal-rich compared to typical halo stars.

Two-thirds of stars are fast rotators with v sin i > 50 km/s.

At least one-third are in binary or multiple systems.

Abstract

A spectroscopic and photometric analysis has been carried out for thirty-two candidate SX_Phe variable blue straggler stars in the Kepler-field (Balona & Nemec 2012). Radial velocities (RVs), space motions (U,V,W), projected rotation velocities (v sin i), spectral types, and atmospheric characteristics (T_eff, log g, [Fe/H], xi_t, zeta_RT, etc.) are presented for 30 of the 32 stars. Although several stars are metal-weak with extreme halo orbits, the mean [Fe/H] of the sample is near solar, thus the stars are more metal-rich than expected for a typical sample of Pop.II stars, and more like halo metal-rich A-type stars (Perry 1969). Two thirds of the stars are fast rotators with v sin i > 50 km/s, including four stars with v sin i > 200 km/s. Three of the stars have (negative) RVs > 250 km/s, five have retrograde space motions, and 21 have total speeds (relative to the LSR) > 400 km/s. All but one of the 30 stars have positions in a Toomre diagram consistent with the kinematics of bona fide halo stars (the exception being a thick-disk star). Observed Roemer time delays, pulsation frequency modulations and light curves suggest that at least one third of the stars are in binary (or triple) systems with orbital periods ranging from 2.3 days to more than four years.