Colour and radial velocity variations in pulsating subluminous B stars (original) (raw)

Radial velocity variations of the pulsating subdwarf B star PG 1605+072

Monthly Notices of the Royal Astronomical Society, 2002

We present an analysis of high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Periodic radial motions are detected at frequencies similar to those reported for photometric variations in the star, with amplitudes of up to 6 km s −1 . Differences between relative strengths for given frequency peaks for our velocity data and previously measured photometry are probably a result of shifting of power between modes over time. Small differences in the detected frequencies may also indicate modeshifting. We report the detection of line-shape variations using the moments of the cross correlation function profiles. It may be possible to use the moments to identify the star's pulsation modes.

Synthetic photometry for non-radial pulsations in subdwarf B stars

Astronomy & Astrophysics, 2004

We describe a method for computing theoretical photometric amplitude ratios for a number of modes of nonradially pulsating subdwarf B stars in both SDSS and UBVR systems. In order to avoid costly solutions of the non-adiabatic nonradial pulsation equations, we have adopted the adiabatic approximation. We argue that this is a valid approach, at least for the V361 Hya stars, because observations show that the temperature perturbations dominate the radius perturbations in the flux variation. We find that for V361 Hya stars, low-degree (= 0, 1, 2) modes may be difficult to distinguish using optical photometry. However, the high degree modes (= 3, 4) are relatively well separated and may be distinguished more easily. We have also computed the amplitude ratios for a number of modes in PG 1716+426 stars. For these stars, the amplitude ratios for low degree modes (= 0, 1) are well resolved. For oscillations with periods ∼40 min, higher-degree modes (= 2−4) may also be identified easily from their amplitude ratios. However for longer period oscillations, the = 3 and the = 2, 4 modes approach the = 0 and = 1 modes respectively.

Pulsational properties of ten new slowly pulsating B stars

Astronomy & Astrophysics, 2019

Context. Slowly pulsating B (SPB) stars are upper main-sequence multi-periodic pulsators that show non-radial g-mode oscillations driven by the κ mechanism acting on the iron bump. These multi-periodic pulsators have great asteroseismic potential and can be employed for the calibration of stellar structure and evolution models of massive stars. Aims. We collected a sample of ten hitherto unidentified SPB stars with the aim of describing their pulsational properties and identifying pulsational modes. Methods. Photometric time series data from various surveys were collected and analyzed using diverse frequency search algorithms. We calculated astrophysical parameters and investigated the location of our sample stars in the log Teff vs. log L/L⊙ diagram. Current pulsational models were calculated and used for the identification of pulsational modes in our sample stars. An extensive grid of stellar models along with their g-mode eigenfrequencies was calculated and subsequently cross-mat...

New studies of a variety of Southern pulsating B stars

We present preliminary results of multi-colour photometry of Beta Cephei stars observed in the LMC and in NGC 6200. Tentative identifications of pulsation modes have been made, and a number of new B pulsators have been noted. Interesting features have also been discovered in the light curves of some of these stars.

Radial velocities of pulsating subdwarf B stars: KPD 2109+4401 and PB 8783

Monthly Notices of the Royal Astronomical Society, 2000

High-speed spectroscopy of two pulsating subdwarf B stars, KPD 210914401 and PB 8783, is presented. Radial motions are detected with the same frequencies as reported from photometric observations and with amplitudes of ,2 km s 21 in two or more independent modes. These represent the first direct observations of surface motion arising from multimode non-radial oscillations in subdwarf B stars. In the case of the sdB1F binary PB 8783, the velocities of both components are resolved; high-frequency oscillations are found only in the sdB star and not the F star. There also appears to be evidence for mutual motion of the binary components. If confirmed, it implies that the F-type companion is *1.2 times more massive than the sdB star, while the amplitude of the F-star acceleration over 4 h would constrain the orbital period to lie between 0.5 and 3.2 d.

Asteroseismic Analysis of Pulsating Subdwarf B Stars

International Astronomical Union Colloquium, 2002

We briefly present a method to perform detailed asteroseismological analyses of pulsating subdwarf B (sdB) stars (also referred to as the EC14026 stars). We use a forward approach based on the computation of large grids of sdB stellar models (each model being analyzed with a linear nonadiabatic pulsation code) to derive, in an objective way, the most appropriate set of model parameters that can best reproduce the observed period spectrum of a given sdB pulsator. We discuss an illustrative application of this method to the pulsating sdB star PG 1047+003, for which we derive the fundamental parameters Teff, logg, Mtot, and Menv.

Progress on the Front of Pulsating Subdwarf B Stars

Astrophysics and Space Science, 2000

We briefly review the recent advances that have been made on the front of pulsating subdwarf B (sdB) stars. The first family of sdB pulsators, the EC 14026 stars, was discovered a few years ago and consists of short-period (∼100−200 s) p-mode variables. The second type of pulsating sdB's consists of the PG 1716+426 stars, a group of variables showing long-period (∼1 h) g-mode pulsations. The existence of the latter was first reported less than a year ago. While the two types of sdB pulsators differ markedly in their observational characteristics, we recently found a unifying property in the sense that the observed modes in these objects are excited through the same driving process, a classic kappa mechanism associated with the radiative levitation of iron in the stellar envelope.

Adiabatic Survey of Subdwarf B Star Oscillations. II. Effects of Model Parameters on Pulsation Modes

Astrophysical Journal Supplement Series, 2002

We present the Ðrst results of a large, systematic adiabatic survey of the pulsation properties of models of subdwarf B (sdB) stars. This survey is aimed at providing the most basic theoretical data with which to analyze the asteroseismological properties of the recently discovered class of pulsating sdB stars (the EC 14026 stars). Such a theoretical framework has been lacking up to now. In this paper, the Ðrst of a series of three, an adiabatic pulsation code is used to compute, in the 80È1500 s period window, the radial (l \ 0) and nonradial (from l \ 1 up to l \ 3) oscillation modes for a representative evolutionary model of subdwarf B stars. Quantities such as the periods, kinetic energies, Ðrst-order rotational splitting coefficients, eigenfunctions, and weight functions are given by the code, providing a complete set of very useful diagnostic tools with which to study the mode properties. The main goal is to determine how these quantities relate to the internal structure of B subdwarfs, a crucial and necessary step if one wants to eventually apply the tools of asteroseismology to EC 14026 stars. All modes (p, f, and g) were considered in order to build the most complete picture we can have on pulsations in these stars. In that context, we show that g-modes are essentially deep interior modes oscillating mainly in the radiative helium-rich core (but not in the convective nucleus), while p-modes are shallower envelope modes. We demonstrate that g-modes respond to a trapping/conÐnement phenomenon induced mainly by the He/H chemical transition between the H-rich envelope and the He-rich core of subdwarf B stars. This phenomenon is very similar in nature to the g-mode trapping and conÐnement mechanisms observed in pulsating white dwarf models. We emphasize that p-modes may also experience distortions of their period distribution due to this He/H transition, although these are not as pronounced as in the g-mode case. These phenomena are of great interest as they can potentially provide powerful tools for probing the internal structure of these objects, in particular, with respect to constraining the mass of their H-rich envelope. The results given in this Ðrst paper form the minimal background on pulsation mode characteristics in sdB stars. Upcoming discussions on additional mode properties in subdwarf B star models (Paper II and Paper III of this series) will strongly rely on these basic results since they provide essential guidance in understanding mode period behaviors as functions of B subdwarf stellar parameters and/or evolution.

Multicolour high-speed photometry of pulsating subdwarf B stars with ULTRACAM

Monthly Notices of the Royal Astronomical Society, 2004

High-speed multicolour photometry is presented for two pulsating subdwarf B stars, KPD 2109+4401 and HS 0039+4302. The observations were obtained using the high-speed multichannel photometer ULTRACAM on the 4.2-m William Herschel Telescope with a sampling interval of 1 and 4 s, respectively, for the two targets. Both targets show multiperiodic oscillations, generally considered to be due to p-mode pulsations. The frequency spectra are similar to those observed previously, although the amplitudes of some modes have altered. The observations are compared with theoretical multicolour light curves for non-radially oscillating extreme horizontal branch stars using the amplitude ratio method. The radial and spherical degrees n and l of all unambiguously identified frequencies have been determined. In general, n 3 and l 2, but both stars show one l = 4 mode. The spectra of frequency versus spherical degree are compared with models for evolved extended horizontal branch stars. These confirm that KPD 2109+4401 has a post-zero-age horizontal branch age of approximately 47 Myr and an envelope mass ∼0.0002 M. HS 0039+4302 lies on the upper edge of the horizontal branch and hence its envelope mass and age are less well determined spectroscopically. The pulsation properties suggest a more massive envelope and evolved structure. In both stars, the frequencies of the radial (l = 0) modes, if correctly identified, do not match the selected models well, suggesting that the density structure or opacity in the stellar envelopes may be incorrect.