New studies of a variety of Southern pulsating B stars (original) (raw)
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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...
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.
New Opacities and the Beta Cephei Stars
International Astronomical Union Colloquium
The recent revision of metal opacities has opened up the possibility that the long-sought mechanism for driving pulsations in these stars has at last, been found. This hypothesis makes a testable prediction — that no β Cep variables should exist among metal-poor B-type stars. We report on the results of an intensive CCD monitoring campaign to test this prediction. The question of the pulsation mode of β Cep stars and the consequence of a revision of the absolute magnitudes to accommodate the fundamental radial mode among these stars is also discussed. Pulsational instability due to driving by ionization of metals has many other repercussions for the incidence of pulsation among the B-type stars. A classification scheme for other intrinsically variable B-type stars is suggested. It is shown that if, as generally supposed, pulsation is common among B-type stars then at least two different mechanisms must be in operation.
Monthly Notices of The Royal Astronomical Society, 2006
We report a multisite photometric campaign for the β Cephei star 12 Lacertae. 750 h of high-quality differential photoelectric Strömgren, Johnson and Geneva time-series photometry were obtained with nine telescopes during 190 nights. Our frequency analysis results in the detection of 23 sinusoidal signals in the light curves. Ten of those correspond to independent pulsation modes, and the remainder are combination frequencies. We find some slow aperiodic variability such as that seemingly present in several β Cephei stars. We perform mode identification from our colour photometry, derive the spherical degree ℓ for the five strongest modes unambiguously and provide constraints on ℓ for the weaker modes. We find a mixture of modes of 0 ≤ℓ≤ 4. In particular, we prove that the previously suspected rotationally split triplet within the modes of 12 Lac consists of modes of different ℓ; their equal frequency splitting must thus be accidental.One of the periodic signals we detected in the light curves is argued to be a linearly stable mode excited to visible amplitude by non-linear mode coupling via a 2:1 resonance. We also find a low-frequency signal in the light variations whose physical nature is unclear; it could be a parent or daughter mode resonantly coupled. The remaining combination frequencies are consistent with simple light-curve distortions.The range of excited pulsation frequencies of 12 Lac may be sufficiently large that it cannot be reproduced by standard models. We suspect that the star has a larger metal abundance in the pulsational driving zone, a hypothesis also capable of explaining the presence of β Cephei stars in the Large Magellanic Cloud.
Pulsating B and Be stars in the Small Magellanic Cloud
Astronomy & Astrophysics, 2008
Context. Stellar pulsations in main-sequence B-type stars are driven by the κ-mechanism due to the Fe-group opacity bump. The current models do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the SMC is lower than Z = 0.005, it constitutes a very suitable object to test these predictions. Aims. The main objective is to investigate the existence of B-type pulsators at low metallicities, searching for short-term periodic variability in absorption-line B and Be stars in the SMC. The analysis has been performed in a sample of 313 B and Be stars with fundamental astrophysical parameters accurately determined from high-resolution spectroscopy. Methods. Photometric light curves of the MACHO project have been analyzed using standard Fourier techniques and linear and nonlinear least squares fitting methods. The position of the pulsating stars in the HR diagram has been used to ascertain their nature and to map the instability regions in the SMC. Results. We have detected 9 absorption-line B stars showing short-period variability, two among them being multiperiodic. One star is most likely a β Cephei variable and the remaining 8 are SPB stars. The SPB instability strip in the SMC is shifted towards higher temperatures than the Galaxy. In the Be star sample, 32 stars are short-period variables, 20 among them multiperiodic. 4.9% of B stars and 25.3% of Be stars are pulsating stars. Conclusions. β Cephei and SPB stars do exist at the SMC metallicity. The fractions of SPB stars and pulsating Be stars in the SMC are lower than in the Galaxy. The fraction of pulsating Be stars in the SMC is much higher than the fraction of pulsating absorption-line B stars, as in the Galaxy.
2004
We undertook a multisite photometric campaign for the β Cephei star ν Eridani. More than 600 h of differential photoelectric uvyV photometry were obtained with 11 telescopes during 148 clear nights. The frequency analysis of our measurements shows that the variability of ν Eri can be decomposed into 23 sinusoidal components, eight of which correspond to independent pulsation frequencies between 5 and 8 cd −1. Some of these are arranged in multiplets, which suggests rotational m-mode splitting of non-radial pulsation modes as the cause. If so, the rotation period of the star must be between 30 and 60 d. One of the signals in the light curves of ν Eri has a very low frequency of 0.432 cd −1. It can be a high-order combination frequency or, more likely, an independent pulsation mode. In the latter case, ν Eri would be both a β Cephei star and a slowly pulsating B (SPB) star. The photometric amplitudes of the individual pulsation modes of ν Eri appear to have increased by about 20 per cent over the last 40 years. So have the amplitudes of the dominant combination frequencies of the star. Among the latter, we could only identify sum frequencies with certainty, not difference frequencies, which suggests that neither light-curve distortion in its simplest form nor resonant mode coupling is their single cause. One of our comparison stars, µ Eridani, turned out to be variable with a dominant timescale of 1.62 d. We believe either that it is an SPB star just leaving its instability strip or that its variations are of rotational origin.
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.