Interpreting the line-profile variations of subdwarf B pulsators: the case of PG 1336-018 (NY Virginis)

Abstract

Aims. We analyze the high-resolution time-resolved VLT/uves spectra of PG 1336−018, a rapidly pulsating subdwarf B (sdB) primary in a close orbit with an M5 companion, with the aim to detect the pulsational signal of the primary in line-profile variations. Methods. After removing the dominant radial-velocity component inherent to the orbital motion and taking only out-of-eclipse data we computed cross-correlation functions (CCFs) for each individual spectrum and assumed these to approximate the average line profile. We computed predictions of line-profile variations for pulsating sdB stars and present their diagnostic value for mode identification. Results. We detect the pulsation mode at 5435 μHz in the line-profile variations of the CCFs which allows us to characterize the detected pulsation mode of PG 1336−018. Conclusions. We model the pulsational perturbations of synthetic spectra for a star with physical parameters like PG 1336−018 and confront them with the observed spectra. We find that low order Balmer lines can be used as diagnostic tool to identify pulsation modes. A detailed line-profile analysis of the perturbed time-series spectra excludes the = |m| = (3, 3), (1, 0), (2, 1) and (2, 0) modes, but does not allow a unique mode identification among the radial or sectoral dipole or quadrupole modes.

Third generation stellar models for asteroseismology of hot B subdwarf stars

“…Their detailed line-profile analysis excluded the ( , |m|) = (3,3), (1,0), (2,1), or (2,0) modes for the 5435 μHz pulsation ( f 5 in Table A.1), although data were too noisy to uniquely identify this pulsation with the radial or sectoral dipole/quadrupole modes. The 5435 μHz f 5 pulsation is identified as the fundamental radial mode (k, , m) = (0, 0, 0) in Table A.1, which is consistent with the results of Vučković et al 2009 (see in particular their Fig. 13).…”

“…On average, the relative dispersion between the observed and theoretical periods is 0.18%, which is similar to the best-fit model of second generation uncovered by Charpinet et al (2008b) that led to 0.17%. Independent constraints on the mode identification in PG 1336−018 exist from time-resolved spectroscopy (Vučković et al 2009). Their detailed line-profile analysis excluded the ( , |m|) = (3,3), (1,0), (2,1), or (2,0) modes for the 5435 μHz pulsation ( f 5 in Table A.1), although data were too noisy to uniquely identify this pulsation with the radial or sectoral dipole/quadrupole modes.…”

A new HW Vir binary from the Palomar Transient Factory

“…Their detection would make PTF0724 an ideal target for asteroseismolgy similar to the enigmatic NY Vir (Vučković et al 2007(Vučković et al , 2009, providing two independent tools of mass determination to be combined (Van Grootel et al 2013 …”

Mode identification from monochromatic amplitude and phase variations for the rapidly pulsating subdwarf B star EC 20338−1925

“…Other, more universally applicable methods rely on the wavelength-dependent behaviour of the target flux during a pulsation cycle. Several recent projects have focussed on the interpretation of line profile variations observed in EC 14026 stars from high-resolution time-series spectroscopy (Telting et al 2008;Vučković et al 2009;Telting et al 2010), but these efforts were always hampered by the low S /N of the data. Indeed, the relative faintness of subdwarf B stars (V > ∼ 12) coupled with the short exposure times acceptable ( < ∼ 30 s) for these fast pulsators make this type of study a challenge even when granted access to the world's largest telescopes, and none of the observations obtained to date were of sufficient quality to yield a unique identification of .…”