TIC 137608661 is a new sdBV+dM reflection-effect binary discovered by the TESS space mission with an orbital period of 7.21 hours. In addition to the detailed study of this system that was recently ...published (Silvotti et al., 2022), this article contains a further discussion on its inclination. Moreover, from the 3D space velocities of the binary obtained from the system’s radial velocity and from the Gaia DR3 proper motion, it is shown that TIC 137608661 belongs to the galactic thin disk population.
The Transiting Exoplanet Survey Satellite (TESS) will be conducting a nearly all-sky photometric survey over two years, with a core mission goal to discover small transiting exoplanets orbiting ...nearby bright stars. It will obtain 30 minute cadence observations of all objects in the TESS fields of view, along with two-minute cadence observations of 200,000-400,000 selected stars. The choice of which stars to observe at the two-minute cadence is driven by the need to detect small transiting planets, which leads to the selection of primarily bright, cool dwarfs. We describe the catalogs assembled and the algorithms used to populate the TESS Input Catalog (TIC), including plans to update the TIC with the incorporation of the Gaia second data release in the near future. We also describe a ranking system for prioritizing stars according to the smallest transiting planet detectable, and assemble a Candidate Target List (CTL) using that ranking. We discuss additional factors that affect the ability to photometrically detect and dynamically confirm small planets, and we note additional stellar populations of interest that may be added to the final target list. The TIC is available on the STScI MAST server, and an enhanced CTL is available through the Filtergraph data visualization portal system at the URL http://filtergraph.com/tess_ctl.
Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through ...emission lines. We report a stable 123.4-minute periodic variation in the strength and shape of the Ca ii emission line profiles originating from the debris disc around the white dwarf SDSS J122859.93+104032.9. We interpret this short-period signal as the signature of a solid-body planetesimal held together by its internal strength.
Abstract Stellar flares are critical phenomena on stellar surfaces, which are closely tied to stellar magnetism. While extensively studied in main-sequence (MS) stars, their occurrence in evolved ...compact stars, specifically hot subdwarfs and white dwarfs (WDs), remains scarcely explored. Based on Cycles 1–5 of TESS photometry, we conducted a pioneering survey of flare events in ∼12,000 compact stars, corresponding to ∼38,000 light curves with a 2 minute cadence. Through dedicated techniques for detrending light curves, identifying preliminary flare candidates, and validating them via machine learning, we established a catalog of 1016 flares from 193 compact stars, including 182 from 58 sdB/sdO stars and 834 from 135 WDs, respectively. However, all flaring compact stars showed signs of contamination from nearby objects or companion stars, preventing sole attribution of the detected flares. For WDs, it is highly probable that the flares originated from their cool MS companions. In contrast, the higher luminosities of sdB/sdO stars diminish companion contributions, suggesting that detected flares originated from sdB/sdO stars themselves or through close magnetic interactions with companions. Focusing on a refined sample of 23 flares from 13 sdB/sdO stars, we found their flare frequency distributions were slightly divergent from those of cool MS stars; instead, they resemble those of hot B/A-type MS stars having radiative envelopes. This similarity implies that the flares on sdB/sdO stars, if these flares did originate from them, may share underlying mechanisms with hot MS stars, which warrants further investigation.
TIC 033834484 and TIC 309658435 are long-period pulsating subdwarf B stars, which were observed extensively (675 and 621 days, respectively) by the Transiting Exoplanet Survey Satellite (TESS). The ...high-precision photometric light curve reveals the presence of more than 40 pulsation modes including both stars. All the oscillation frequencies that we found are associated with gravity (g)-mode pulsations, with frequencies spanning from ∼80 µHz (2 500 s) to ∼400 µHz (12 000 s). We utilize the asteroseismic tools including asymptotic period spacings and rotational frequency multiplets in order to identify the pulsational modes. We found dipole (l = 1) mode sequences for both targets and calculate the mean period spacing of dipole modes (ΔPl=1), which allows us to identify the modes. Frequency multiplets provide a rotation period of ∼64 d for TIC 033834484. From follow-up ground-based spectroscopy, we find that TIC 033834484 has an effective temperature of 24 210 K (140), a surface gravity of log g/cms-2 = 5.28 (03) and TIC 309658435 has an effective temperature of 25 910 K (150), a surface gravity of log g/cms-2 = 5.48 (03).
Hot subdwarf B (sdB) stars are evolved, subluminous, helium-burning stars that most likely form when red giant stars loose their hydrogen envelope via interactions with close companions. They play an ...important role in our understanding of binary evolution, stellar atmospheres, and interiors. Only a small fraction of the sdB population is known to exhibit pulsations. Pulsating sdBs have typically been discovered serendipitously in various photometric surveys because specific selection criteria for the sample are lacking. Consequently, while individual properties of these stars are well known, a comprehensive understanding of the entire population remains elusive, and many related questions remain unanswered. The Gaia mission has presented an exceptional chance to create an unbiased sample by employing precise criteria and ensuring a high degree of completeness. The progression of high-precision and high-duty cycle photometric monitoring facilitated by space missions such as Kepler/K2 and the Transiting Exoplanet Survey Satellite (TESS) has yielded an unparalleled wealth of data for pulsating sdBs. We created a dataset of confirmed pulsating sdB stars by combining information from various ground- and space-based photometric surveys. With this dataset, we present a thorough approach to search for pulsating sdB stars based on the current Gaia DR3 sample. Based on TESS photometry, we discovered 61 new pulsating sdB stars and 20 variable sdBs whose source of variability remains to be determined through future spectroscopic follow-up observations.
Hot subdwarf B (sdB) stars are evolved, subluminous, helium-burning stars that most likely form when red giant stars loose their hydrogen envelope via interactions with close companions. They play an ...important role in our understanding of binary evolution, stellar atmospheres, and interiors. Only a small fraction of the sdB population is known to exhibit pulsations. Pulsating sdBs have typically been discovered serendipitously in various photometric surveys because specific selection criteria for the sample are lacking. Consequently, while individual properties of these stars are well known, a comprehensive understanding of the entire population remains elusive, and many related questions remain unanswered. The Gaia mission has presented an exceptional chance to create an unbiased sample by employing precise criteria and ensuring a high degree of completeness. The progression of high-precision and high-duty cycle photometric monitoring facilitated by space missions such as Kepler /K2 and the Transiting Exoplanet Survey Satellite (TESS) has yielded an unparalleled wealth of data for pulsating sdBs. We created a dataset of confirmed pulsating sdB stars by combining information from various ground- and space-based photometric surveys. With this dataset, we present a thorough approach to search for pulsating sdB stars based on the current Gaia DR3 sample. Based on TESS photometry, we discovered 61 new pulsating sdB stars and 20 variable sdBs whose source of variability remains to be determined through future spectroscopic follow-up observations.
The Observed-minus-Calculated diagram shows a stability of a period being analyzed. In case of binary system, any nonlinear O − C variation indicates an orbital period variation that can be caused by ...e.g., mass loss or mass transfer between components (physical change), additional component(s) to the system (apparent change only). Baran et al. reported a sinusoidal variation of the O − C of 2M 1938+4603 and interpreted it as a circumbinary planet. We analyzed the newest and most reliable release of the Kepler data of 2M 1938+4603 and by using our newest approach we removed two main sources that could cause the variation not to be intrinsic to 2M 1938+4603. We removed significant signal not associated with binarity and folded eclipses to increase their cadences. Consequently, we lowered rms of the O − C diagram by a factor of six confirming the sinusoidal variation reported by Baran et al. and making it even more convincing now.
Planets that orbit their parent star at less than about one astronomical unit (1 AU is the Earth-Sun distance) are expected to be engulfed when the star becomes a red giant. Previous observations ...have revealed the existence of post-red-giant host stars with giant planets orbiting as close as 0.116 AU or with brown dwarf companions in tight orbits, showing that these bodies can survive engulfment. What has remained unclear is whether planets can be dragged deeper into the red-giant envelope without being disrupted and whether the evolution of the parent star itself could be affected. Here we report the presence of two nearly Earth-sized bodies orbiting the post-red-giant, hot B subdwarf star KIC 05807616 at distances of 0.0060 and 0.0076 AU, with orbital periods of 5.7625 and 8.2293 hours, respectively. These bodies probably survived deep immersion in the former red-giant envelope. They may be the dense cores of evaporated giant planets that were transported closer to the star during the engulfment and triggered the mass loss necessary for the formation of the hot B subdwarf, which might also explain how some stars of this type did not form in binary systems.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Context.
We present photometric and spectroscopic analyses of gravity (
g
-mode) long-period pulsating hot subdwarf
B
(sdB) stars, also called V1093 Her stars, observed by the TESS space telescope in ...both 120 s short-cadence and 20 s ultra-short-cadence mode during the survey observation and the extended mission of the southern ecliptic hemisphere.
Aims.
We performed a detailed asteroseismic and spectroscopic analysis of five pulsating sdB stars observed with TESS in order to compare the observations with model predictions based on our stellar evolution computations coupled with adiabatic pulsation computations.
Methods.
We processed and analyzed TESS observations of long-period pulsating hot subdwarf
B
stars. We used standard pre-whitening techniques on the datasets to extract the pulsation periods from the TESS light curves. We applied standard seismic tools for mode identification, including asymptotic period spacings and rotational frequency multiplets. Based on the values obtained from Kolmogorov-Smirnov and Inverse Variance tests, we searched for a constant period spacing for dipole (
l
= 1) and quadrupole (
l
= 2) modes. We calculated the mean period spacing for
l
= 1 and
l
= 2 modes and estimated the errors by means of a statistical resampling analysis. For all stars, atmospheric parameters were derived by fitting synthetic spectra to the newly obtained low-resolution spectra. We computed stellar evolution models using the
LPCODE
stellar evolution code, and computed
l
= 1
g
-mode frequencies with the adiabatic nonradial pulsation code
LP-PUL
. Derived observational mean period spacings were then compared to the mean period spacings from detailed stellar evolution computations coupled with the adiabatic pulsation computations of
g
-modes.
Results.
We detect 73 frequencies, most of which are identified as dipole and quadrupole
g
-modes with periods spanning from ∼3000 s to ∼14 500 s. The derived mean period spacing of dipole modes is concentrated in a narrow region ranging from 251 s to 256 s, while the mean period spacing for quadrupole modes spans from 145 s to 154 s. The atmospheric parameters derived from spectroscopic data are typical of long-period pulsating sdB stars with an effective temperature ranging from 23 700 K to 27 600 K and surface gravity spanning from 5.3 dex to 5.5 dex. In agreement with the expectations from theoretical arguments and previous asteroseismological works, we find that the mean period spacings obtained for models with small convective cores, as predicted by a pure Schwarzschild criterion, are incompatible with the observations. We find that models with a standard, modest convective boundary mixing at the boundary of the convective core are in better agreement with the observed mean period spacings and are therefore more realistic.
Conclusions.
Using high-quality space-based photometry collected by the TESS mission coupled with low-resolution spectroscopy from the ground, we provide a global comparison of the observations with model predictions by means of a robust indicator such as the mean period spacing. All five objects that we analyze in this work show remarkable homogeneity in both seismic and spectroscopic properties.
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