Radial velocity variations of the pulsating subdwarf B star PG 1605+072 (original) (raw)
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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.
The Astrophysical Journal, 2005
We report the detection of three discrete pulsation frequencies in the long-period variable subdwarf B star PG 0101+039 on the basis of $400 hr of MOST wide-band photometry. The periodicities uncovered lie at 7235, 5227, and 2650 s, respectively, and are associated with amplitudes between 0.03% and 0.06% of the mean brightness, lower than those measured in any other variable of this kind. We also find evidence for luminosity variations consistent with an ellipsoidal deformation of the subdwarf in the rotationally locked short-period binary system predicted from radial velocity measurements and evolutionary models. Our atmospheric modeling of two independent time-averaged optical spectra of PG 0101+039 yields T eA ' 28;300 K and log g ' 5:52, making it one of the hottest long-period variable subdwarf B stars known. The fact that we nevertheless detect brightness variations in the data is in conflict with predictions from current models, which place the theoretical blue edge for observable long-period instabilities at a temperature around 4000 K cooler than that of PG 0101+039.
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.
The Astrophysical Journal, 2006
In the first spectroscopic campaign for a PG 1716 variable (or long-period pulsating subdwarf B star), we succeeded in detecting velocity variations due to g-mode pulsations at a level of 1.0-1.5 km s −1 , just above our detection limit. The observations were obtained during 40 nights on 2 m class telescopes in Arizona, South Africa, and Australia. The target, PG 1627+017, is one of the brightest (V = 12.9) and largest amplitude (∼0.03 mag) stars in its class. It is also the visible component of a post-common envelope binary. Our final radial velocity data set includes 84 hours of time-series spectroscopy over a time baseline of 53 days, with typical errors of 5-6 km s −1 per spectrum. We combined the velocities with previously existing data to derive improved orbital parameters. Unexpectedly, the velocity power spectrum clearly shows an additional component at twice the orbital frequency of PG 1627+017, supporting Edelmann et al.'s recent results for several other short-period subdwarf B stars, which they claim to be evidence for slightly elliptical orbits. Our derived radial velocity amplitude spectrum, after subtracting the orbital motion, shows three potential pulsational modes 3-4σ above the mean noise level of 0.365 km s −1 , at 7201.0 s (138.87 µHz), 7014.6 s (142.56 µHz) and 7037.3 s (142.10 µHz). Only one of the features is statistically 1 Observations reported here were obtained at the MMT Observatory, a joint facility of the Univerity of Arizona and the Smithsonian Institution.
Colour and radial velocity variations in pulsating subluminous B stars
Astrophysics and Space Science, 2004
The utility of pulsations for the investigation of the structure and evolution of subdwarf B stars is considerable. However, the small number of detected modes generally limits the potential for a traditional seismological analysis such as that carried out for the Sun. Therefore, it is crucial to acquire additional primary data to characterise the stellar oscillations more completely. We review recent studies of radial velocity amplitudes and introduce new multi-colour photometry of smallamplitude sdBV stars. We also discuss a set of models for radial velocity and colour variations and demonstrate how these may be used to infer the spherical and azimuthal degrees of observed pulsations.
O-C analysis of the pulsating subdwarf B star PG 1219 + 534
2017
PG 1219 + 534 (KY Uma) is a subdwarf B pulsating star with multiple periodicities between 120 – 175 s. PG 1219 + 534 was monitored for 90 hours during 2010-1 and 2016 using the 0.9m SARA-KP telescope at Kitt Peak National Observatory (KPNO) in Arizona and the 0.8 m Ortega telescope at Florida Institute of Technology in Melbourne, Florida. So far, the most promising theory for the origin of subdwarf B (sdB) stars is that they result from binary mass transfer near the Helium Flash stage of evolution. The observations of PG 1219+534 reported here are part of our program to constrain this evolutional theory by searching for companions and determining orbital separations around sdB pulsators using the Observed-minus-Calculated (O-C) method. A star’s position in space will wobble due to the gravitational forces of any companion or planet. If the star emits periodic signal like pulsations, its orbital motion around the system’s center of mass causes periodic changes in the light pulse arri...
Discovery of Gravity‐Mode Pulsators among Subdwarf B Stars: PG 1716+426, the Class Prototype
The Astrophysical Journal, 2004
A new class of pulsating subdwarf B stars has recently been announced by Green and coworkers. Here we present a follow-up paper describing our observations and the pulsation structure of the class prototype PG 1716+426. The oscillations are multiperiodic with periods between 0.8 and 1.4 hr (180-340 Hz) and semiamplitudes less than 0.2%. We also observe that the periods and amplitudes appear variable, making the pulsation structure of PG 1716 complicated. The periods are an order of magnitude longer than those seen in EC 14026 (sdBV) stars, implying that they are gravity modes rather than pressure modes. As such, they represent a new class of variable star. Subject headings: stars: individual (PG 1716+426) -stars: oscillations -subdwarfs 2. CCD PHOTOMETRY The discovery light curve was obtained on the 2.3 m Steward telescope at Kitt Peak while searching for eclipses, reflection, and/or ellipsoidal effects in sdB stars. Additional CCD photometry was obtained at Mount Bigelow, the Nordic Optical Telescope (NOT), Calar Alto, and Fick Observatories. The specific runs are listed in .
Multisite spectroscopic and photometric observations of the pulsating sdB star PG 1605+072
International Astronomical Union Colloquium, 2004
We present the first results from the MultiSite Spectroscopic Telescope (MSST) observations of the sdBV star PG 1605+072. Pulsating sdB stars (V361 Hya stars) offer the chance to gain new insights into the formation and evolution of extreme Horizontal Branch stars using the tools of asteroseismology. PG 1605+072 is an outstanding object in its class, with the richest frequency spectrum, the longest periods, and the largest variations. The MSST campaign took place in 2002 May/June and we present here the massive data set, made up of 399 hr of photometry and 151 hr of spectroscopy. The overall aims of the project are to examine light/velocity amplitude ratios and phase differences, changes in equivalent width/line index, and λ-dependence of photometric amplitudes, and to use these properties for mode identification.
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...