Long-term EXOTIME photometry and follow-up spectroscopy of the sdB pulsator HS 0702+6043

Pulsating subdwarf B (sdB) stars oscillate in short-period p-modes or long-period g-modes. HS0702+6043 (DW Lyn) is one of a few objects to show characteristics of both types and is hence classified as hybrid pulsator. It is one of our targets in the EXOTIME program to search for planetary companions around extreme horizontal branch objects. In addition to the standard exercise in asteroseismology to probe the instantaneous inner structure of a star, measured changes in the pulsation frequencies as derived from an O-C diagram can be compared to theoretical evolutionary timescales. Based on the photometric data available so far, we are able to derive a high-resolution frequency spectrum and to report on our efforts to construct a multi-season O-C diagram. Additionally, we have gathered time-resolved spectroscopic data in order to constrain stellar parameters and to derive mode parameters as well as radial and rotational velocities.Comment: 2 pages, JENAM 2008 proceedings, to be published in 'Communications in Asteroseismology', 15

Search for sdB/WD pulsators in the Kepler FOV

In this article we present the preliminary results of an observational search for subdwarf B and white dwarf pulsators in the Kepler field of view, performed using the DOLORES camera attached to the 3.6m Telescopio Nazionale Galileo (TNG).Comment: Communications in Asteroseismology, in press; 2 pages, 1 figur

Multicolour photometry of Balloon 090100001: linking the two classes of pulsating hot subdwarfs

We present results of the multicolour UBVR photometry of the high-amplitude EC14026-type star, Balloon 090100001. The data span over a month and consist of more than a hundred hours of observations. Fourier analysis of these data led us to the detection of at least 30 modes of pulsation of which 22 are independent. The frequencies of 13 detected modes group in three narrow ranges, around 2.8, 3.8 and 4.7 mHz, where the radial fundamental mode, the first and second overtones are likely to occur. Surprisingly, we also detect 9 independent modes in the low-frequency domain, between 0.15 and 0.4 mHz. These modes are typical for pulsations found in PG1716+426-type stars, discovered recently among cool B-type subdwarfs. The modes found in these stars are attributed to the high-order g modes. As both kinds of pulsations are observed in Balloon 090100001, it represents a link between the two classes of pulsating hot subdwarfs. At present, it is probably the most suitable target for testing evolutionary scenarios and internal constitution models of these stars by means of asteroseismology. Three of the modes we discovered form an equidistant frequency triplet which can be explained by invoking rotational splitting of an $\ell$ = 1 mode. The splitting amounts to about 1.58 $\mu$Hz, leading to a rotation period of 7.1 $\pm$ 0.1 days.Comment: 12 pages, 14 figures, accepted for publication in MNRAS. For full-resolution postscript file, visit http://www.as.wsp.krakow.pl/~andy/balloon.ps.g

Time-resolved spectroscopy of the planet-hosting sdB pulsator V391 Pegasi

The subdwarf B (sdB) star V391 Peg oscillates in short-period p modes and long-period g modes, making it one of the three known hybrids among sdBs. As a by-product of the effort to measure secular period changes in the p modes due to evolutionary effects on a time scale of almost a decade, the O-C diagram has revealed an additional sinusoidal component attributed to a periodic shift in the light travel time caused by a planetary-mass companion around the sdB star in a 3.2 yr orbit. In order to derive the mass of the companion object, it is necessary to determine the orbital inclination. One promising possibility to do this is to use the stellar inclination as a primer for the orbital orientation. The stellar inclination can refer to the rotational or the pulsational axis, which are assumed to be aligned, and can in turn then be derived by combining measurements of v_(rot) and v_(rot)sin i. The former is in principle accessible through rotational splitting in the photometric frequency spectrum (which has however not been found for V391 Peg yet), while the projected rotational velocity can be measured from the rotational broadening of spectral lines. The latter must be deconvolved from the additional pulsational broadening caused by the surface radial velocity variation in high S/N phase averaged spectra. This work gives limits on pulsational radial velocities from a series of phase resolved spectra. Phase averaged and phase resolved high resolution echelle spectra were obtained in May and September 2007 with the 9m-class Hobby-Eberly Telescope (HET), and one phase averaged spectrum in May 2008 with the 10m-Keck 1 telescope.Comment: 3 pages, JENAM 2008 proceedings, to be published in 'Communications in Asteroseismology', 15

Finding binaries among Kepler pulsating stars from phase modulation of their pulsations

We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire 4 yr light curves to accurately measure the frequencies of the strongest pulsation modes, and then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the parameters of the orbit, including the period, eccentricity, angle of ascending node, and time of periastron passage. Differentiating the time-delay curve yields the full radial-velocity curve directly from the Kepler photometry, without the need for spectroscopy.We showexamples with δ scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightforward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone