Photometry and spectroscopy of the new sdBV CS 1246

Abstract

We report the discovery of a large-amplitude oscillation in the hot subdwarf B star CS 1246 and present multi-colour photometry and time-resolved spectroscopy supporting this discovery. We used the 0.41-m PROMPT array to acquire data in the u', g', r', and i' filters simultaneously over 3 consecutive nights in 2009 April. These data reveal a single oscillation mode with a period of 371.707 +/- 0.002 s and an amplitude dependent upon wavelength, with a value of 34.5 +/- 1.6 mma in the u' filter. We detected no additional frequencies in any of the light curves. Subsequently, we used the 4.1-m SOAR telescope to acquire a time-series of 248 low-resolution spectra spanning 6 hrs to look for line profile variations. Models fits to the spectra give mean atmospheric values of Teff = 28450 +/- 700 K and log g = 5.46 +/- 0.11 undergoing variations with semi-amplitudes of 507 +/- 55 K and 0.034 +/- 0.009 dex, respectively. We also detect a radial velocity oscillation with an amplitude of 8.8 +/- 1.1 km/s. The relationship between the angular and physical radii variations shows the oscillation is consistent with a radial mode. Under the assumption of a radial pulsation, we compute the stellar distance, radius, and mass as d = 460 +/- 140 pc, R = 0.19 +/- 0.08 Rsun, and M = 0.39 +/- 0.22 Msun, respectively, using the Baade-Wesselink method.Comment: 12 pages, 11 figures, 3 tables. Accepted for publication in MNRA

Fortnightly fluctuations in the O−C diagram of CS 1246★

“…Each of the individual 89 light curves is dominated by the 371.7‐s pulsation mode (hereinafter f 1 ) reported by Barlow et al (2010) and shows no other significant signals in the p‐mode range of the amplitude spectrum (1600–14 000 Hz) after pre‐whitening the signal. Low‐amplitude signals appear in some of the nightly Fourier transforms (FTs) at frequencies near the g‐mode regime, but we hesitate to claim these signals as real since 1/ f noise and improperly removed extinction effects could easily account for those structures.…”

“…CS 1246, a recently discovered sdBV r star (Barlow et al 2010), is a prime target for an extended O−C diagram study since it exhibits a single, large‐amplitude pulsation mode. Using the 0.41‐m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) array, we monitored the pulse timings for 14 months by collecting nearly 400 h of time‐series photometry.…”

A survey for pulsating subdwarf B stars with the Nordic Optical Telescope

“…Together with the two new pulsators presented by Kilkenny et al (2009), another two recently found by Barlow et al (2009Barlow et al ( , 2010, and HE 0230-4323 5 , our latest tally brings the total up to 49. Our effort to implement an efficient system for CCD photometry at the not has certainly been fruitful, producing on average one new pulsator for every three nights of observations.…”

Concluding remarks

“…Baade's [53] pulsation test shows [54] that the sdB star CS 1246 is a radial pulsator; given its T eff , log g and period, tables by Charpinet et al [55] do not exclude pulsation in the fundamental mode. The secular decrease in the CS 1246 pulsation amplitude which Barlow et al [56] report is understood by them to be a consequence of structural changes as a consequence of stellar evolution.…”