اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدFirst Kepler results on compact pulsators V: Slowly pulsating subdwarf B stars in short-period binaries
119
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The survey phase of the Kepler Mission includes a number of hot subdwarf B (sdB) stars to search for nonradial pulsations. We present our analysis of two sdB stars that are found to be g-mode pulsators of the V1093 Her class. These two stars also display the distinct irradiation effect typical of sdB stars with a close M-dwarf companion with orbital periods of less than half a day. Because the orbital period is so short, the stars should be in synchronous rotation, and if so, the rotation period should imprint itself on the multiplet structure of the pulsations. However, we do not find clear evidence for such rotational splitting. Though the stars do show some frequency spacings that are consistent with synchronous rotation, they also display multiplets with splittings that are much smaller. Longer-duration time series photometry will be needed to determine if those small splittings are in fact rotational splitting, or caused by slow amplitude or phase modulation. Further data should also improve the signal-to-noise, perhaps revealing lower amplitude periodicities that could confirm the expectation of synchronous rotation. The pulsation periods seen in these stars show period spacings that are suggestive of high-overtone g-mode pulsations.
قيم البحث
اقرأ أيضاً
We investigate the possibility of nearly-equally spaced periods in 13 hot subdwarf B (sdB) stars observed with the Kepler spacecraft and one observed with CoRoT. Asymptotic limits for gravity (g-)mode pulsations provide relationships between equal pe
riod spacings of modes with differing degrees and relationships between periods of the same radial order but differing degrees. Period transforms, Kolmogorov-Smirnov tests, and linear least-squares fits have been used to detect and determine the significance of equal period spacings. We have also used Monte Carlo simulations to estimate the likelihood that the detected spacings could be produced randomly. Period transforms for nine of the Kepler stars indicate ell=1 period spacings, with five also showing peaks for ell=2 modes. 12 stars indicate ell=1 modes using the Kolmogorov-Smirnov test while another shows solely ell=2 modes. Monte Carlo results indicate that equal period spacings are significant in 10 stars above 99% confidence and 13 of the 14 are above 94% confidence. For 12 stars, the various methods find consistent regular period spacing values to within the errors, two others show some inconsistencies, likely caused by binarity, and the last has significant detections but the mode assignment disagrees between methods. We find a common ell=1 period spacing spanning a range from 231 to 272 s allowing us to correlate pulsation modes with 222 periodicities and that the ell=2 period spacings are related to the ell=1 spacings by the asymptotic relationship $1/sqrt{3}$. We briefly discuss the impact of equal period spacings which indicate low-degree modes with a lack of significant mode trappings.
We present the discovery of nonradial pulsations in five hot subdwarf B (sdB) stars based on 27 days of nearly continuous time-series photometry using the Kepler spacecraft. We find that every sdB star cooler than $approx 27,500,$K that Kepler has ob
served (seven so far) is a long-period pulsator of the V1093~Her (PG~1716) class or a hybrid star with both short and long periods. The apparently non-binary long-period and hybrid pulsators are described here. The V1093~Her periods range from one to 4.5~h and are associated with $g-$mode pulsations. Three stars also exhibit short periods indicative of $p-$modes with periods of 2 to 5~m and in addition, these stars exhibit periodicities between both classes from 15 to 45~m. We detect the coolest and longest-period V1093~Her-type pulsator to date, KIC010670103 ($T_effapprox 20,900,$K, $P_maxapprox 4.5$~h) as well as a suspected hybrid pulsator, KIC002697388 which is extremely cool ($T_{rm eff}approx 23,900,$K) and for the first time hybrid pulsators which have larger $g-$mode amplitudes than $p-$mode ones. All of these pulsators are quite rich with many frequencies and we are able to apply asymptotic relationships to associate periodicities with modes for KIC010670103. Kepler data are particularly well-suited for these studies as they are long-duration, extremely high duty cycle observations with well-behaved noise properties.
We present the discovery of nonradial pulsations in a hot subdwarf B star based on 30.5 days of nearly continuous time-series photometry using the emph{Kepler} spacecraft. KIC 010139564 is found to be a short-period pulsator of the V361 Hya (EC 14026
) class with more than 10 independent pulsation modes whose periods range from 130 to 190 seconds. It also shows one periodicity at a period of 3165 seconds. If this periodicity is a high order g-mode, then this star may be the hottest member of the hybrid DW Lyn stars. In addition to the resolved pulsation frequencies, additional periodic variations in the light curve suggest that a significant number of additional pulsation frequencies may be present. The long duration of the run, the extremely high duty cycle, and the well-behaved noise properties allow us to explore the stability of the periodic variations, and to place strong constraints on how many of them are independent stellar oscillation modes. We find that most of the identified periodicities are indeed stable in phase and amplitude, suggesting a rotation period of 2-3 weeks for this star, but further observations are needed to confirm this suspicion.
Massive stars are important building blocks of the Universe, and their stellar structure and evolution models are fundamental cornerstones of various fields in modern astrophysics. The precision of these models is limited by our lack of understanding
of various internal mixing processes that significantly influence the lifetime of these objects (e.g. core overshoot, chemical mixing, or the internal differential rotation). Our goal is to calibrate models by extending the sample of available seismic studies of slowly pulsating B (SPB) stars, providing input for theoretical modelling efforts that will deliver precise constraints on the parameters describing the internal mixing processes in these objects. We used spectral synthesis and disentangling techniques to derive fundamental parameters and to determine precise orbital parameters from high-resolution spectra. We employed custom masks to construct light curves from the Kepler pixel data and used standard time-series analysis tools to construct a set of significant frequencies for each target. These sets were first filtered from combination frequencies, and then screened for period spacing patterns. We detect gravity mode period series of modes of the same degree l with consecutive radial order n in four new and one revisited SPB star. These predominantly prograde dipole series (covering ~10-40 radial orders) are influenced by rotation and carry signatures of chemical mixing processes. Our spectroscopic analysis, in addition to placing each object inside the SPB instability strip and identifying KIC 4930889 as an SB2 binary, reveals that KIC 11971405 is a fast rotator that shows very weak Be signatures. Together with the observed photometric outbursts this illustrates that this Be star is a fast rotating SPB star. We hypothesise that the outbursts might be connected to its very densely compressed oscillation spectrum.
We present results from the final six months of a survey to search for pulsations in white dwarfs and hot subdwarf stars with the Kepler spacecraft. Spectroscopic observations are used to separate the objects into accurate classes, and we explore the
physical parameters of the subdwarf B (sdB) stars and white dwarfs in the sample. From the Kepler photometry and our spectroscopic data, we find that the sample contains 5 new pulsators of the V1093 Her type, one AM CVn type cataclysmic variable, and a number of other binary systems. This completes the survey for compact pulsators with Kepler. No V361 Hya type of short-period pulsating sdB stars were found in this half, leaving us with a total of one single multiperiodic V361 Hya and 13 V1093 Her pulsators for the full survey. Except for the sdB pulsators, no other clearly pulsating hot subdwarfs or white dwarfs were found, although a few low-amplitude candidates still remain. The most interesting targets discovered in this survey will be observed throughout the remainder of the Kepler Mission, providing the most long-term photometric datasets ever made on such compact, evolved stars. Asteroseismic investigations of these datasets will be invaluable in revealing the interior structure of these stars, and will boost our understanding of their evolutionary history.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
