Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation

High-resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over six pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least 2 at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km s−1 (depending how measured) and at least 10 times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 kms−1 on a time-scale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra

Towards asteroseismology of the non-radial pulsating sdB star PG 1605+072

The recently discovered new class of sdB pulsators (sdBV) offers a powerful possibility for the investigation of their interior and thus their evolutionary history. The first step towards applying asteroseismologic tools is the identification of pulsation modes. We reoport on simultaneous spectroscopic and multi-band photometric time series observations of PG 1605+072 and analyse its radial velocity and light curve.Comment: 4 pages, 3 figures, Proc. XIII Workshop on White Dwarfs, eds. D. de Martino, R. Kalytis, R. Silvotti, J.E. Solheim, Kluwe

RAT0455+1305: another pulsating hybrid sdB star

RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in finding any variability on timescales of a few minutes to several hours. The star was found to be another sdBV star with one high amplitude mode and relatively long period. These features along with estimation of T_eff and log g makes this star very similar to Balloon 090100001. Encouraged by prominent results obtained for the latter star we have decided to perform white light photometry on RAT0455+1305. In 2009 we used the 1.5m telescope located in San Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant mode found in the discovery data, uncovered another peak close to the dominant one, and three peaks in the low frequency region. This shows that RAT0455+1305 is another hybrid sdBV star pulsating in both p- and g-modes.Comment: Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related Objects held in China, 20-24 July 2009. Accepted for publication in Astrophysics & Space Scienc

Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)

Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion (O'Donoghue et al. 1997), however the period and the orbit semi-major axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P = 792.3 days) and the light-travel time amplitude (A = 468.9 s). This binary shows no significant orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3 $\sigma$ as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was $\dot{P}$ = 5.4 ($\pm$0.7) $\times$ $10^{-14}$ d d$^{-1}$, which shows that the sdB is just before the end of the core helium-burning phase

EC03089−6421: A new, very rapidly pulsating sdO star

EC 03089−6421, classified sdO in the Edinburgh-Cape (EC) blue object survey, is shown to have unusually rapid pulsations with a dominant frequency near 32 mHz (amplitude ∼0.02 mag; period 31.1 s) – which appears to be strongly variable in amplitude on time-scales of hours and days – and a generally weaker frequency near 29 mHz (amplitude ∼0.004 mag; period 34.2 s), which is also variable in amplitude. This star varies at twice the frequency of any known hot subdwarf pulsator. Although the low-resolution EC spectrogram appears very similar to those of DAO stars, our analysis derives T eff = 40 200 ± 1600 K; log g = 6.25 ± 0.23 and log N(He)/N(H) = −1.63 ± 0.55; more recent spectrograms give T eff = 37 400 ± 1000 K; log g = 5.70 ± 0.13 and log N(He)/N(H) = −2.02 ± 0.17, both of which indicate that the gravity is too low for a white dwarf star, although the low temperature derived from the Balmer lines is at odds with the absence of neutral Helium and the strength of He II 4686. It is possible that EC 03089−6421 is a field analogue of the ω Cen sdO variables

The Solar Neighborhood. XIX. Discovery and Characterization of 33 New Nearby White Dwarf Systems

We present spectra for 33 previously unclassified white dwarf systems brighter than V = 17 primarily in the southern hemisphere. Of these new systems, 26 are DA, 4 are DC, 2 are DZ, and 1 is DQ. We suspect three of these systems are unresolved double degenerates. We obtained VRI photometry for these 33 objects as well as for 23 known white dwarf systems without trigonometric parallaxes, also primarily in the southern hemisphere. For the 56 objects, we converted the photometry values to fluxes and fit them to a spectral energy distribution using the spectroscopy to determine which model to use (i.e. pure hydrogen, pure helium, or metal-rich helium), resulting in estimates of effective temperature and distance. Eight of the new and 12 known systems are estimated to be within the NStars and Catalogue of Nearby Stars (CNS) horizons of 25 pc, constituting a potential 18% increase in the nearby white dwarf sample. Trigonometric parallax determinations are underway via CTIOPI for these 20 systems. One of the DCs is cool so that it displays absorption in the near infrared. Using the distance determined via trigonometric parallax, we are able to constrain the model-dependent physical parameters and find that this object is most likely a mixed H/He atmosphere white dwarf similar to other cool white dwarfs identified in recent years with significant absorption in the infrared due to collision-induced absorptions by molecular hydrogen.Comment: 33 pages, 10 figures, accepted for publication in the Astronomical Journa