69 research outputs found
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
Alone but not lonely: Observational evidence that binary interaction is always required to form hot subdwarf stars
Hot subdwarfs are core-helium burning stars that show lower masses and higher
temperatures than canonical horizontal branch stars. They are believed to be
formed when a red giant suffers an extreme mass-loss episode. Binary
interaction is suggested to be the main formation channel, but the high
fraction of apparently single hot subdwarfs (up to 30%) has prompted single
star formation scenarios to be proposed. If such formation scenarios without
interaction were possible, that would also imply the existence of hot subdwarfs
in wide binaries that have undergone no interaction. We probe the existence of
these systems by analysing light curves from the Transiting Exoplanet Survey
Satellite (TESS) for all known hot subdwarfs with a main sequence wide binary
companion, and by searching for common proper motion pairs to spectroscopically
confirmed hot subdwarfs. We find that (i) the companions in composite hot
subdwarfs show short rotation periods when compared to field main sequence
stars. They display a triangular-shaped distribution with a peak around 2.5
days, similar to what is observed for young open clusters. This observed
distribution of rotation rates for the companions in known wide hot subdwarf
binaries provides evidence of previous interaction causing spin-up. We also
report (ii) a shortage of hot subdwarfs with candidate common proper motion
companions, considering the frequency of such systems among progenitors. We
identify only 16 candidates after probing 2938 hot subdwarfs with good
astrometry. Out of those, at least six seem to be hierarchical triple systems,
in which the hot subdwarf is part of an inner binary. These results suggest
that binary interaction is always required for the formation of hot subdwarfs.Comment: 17 pages, 11 figures, 5 tables. Accepted for publication in A&
Constraining the degree of the dominant mode in QQ Vir
We present early results of the application of a method which uses multicolor
photometry and spectroscopy for \ell discrimination. This method has been
successfully applied to the pulsating hot subdwarf Balloon 090100001. Here we
apply the method to QQ Vir (PG1325+101). This star was observed
spectroscopically and photometrically in 2008. Details on spectroscopy can be
found in Telting et al. (2010) while photometry and preliminary results on \ell
discrimination are provided here. The main aim of this work was to compare the
value of the \ell parameter derived for the main mode in QQ Vir to previously
published values derived by using different methods.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 and Space Scienc
Short-period pulsating hot-subdwarf stars observed by TESS: I. Southern ecliptic hemisphere
We present results of a Transiting Exoplanet Survey Satellite (TESS) search for short-period pulsations in compact stellar objects
observed in years 1 and 3 of the TESS mission, during which the southern ecliptic hemisphere was targeted. We describe the TESS
data used and the details of the search method. For many of the targets, we use unpublished spectroscopic observations to classify the
objects. From the TESS photometry, we clearly identify 43 short-period hot-subdwarf pulsators, including 32 sdB stars, eight sdOB
stars, two sdO stars, and, significantly, one He-sdOB star, which is the first of this kind to show short-period pulsations. Eight stars
show signals at both low and high frequencies, and are therefore “hybrid” pulsators. We report the list of prewhitened frequencies and
we show the amplitude spectra calculated from the TESS data. We make an attempt to identify possible multiplets caused by stellar
rotation, and we select four candidates with rotation periods between 1 and 12.9 days. The most interesting targets discovered in this
survey should be observed throughout the remainder of the TESS mission and from the ground. Asteroseismic investigations of these
data sets will be invaluable in revealing the interior structure of these stars and will boost our understanding of their evolutionary
history. We find three additional new variable stars but their spectral and variability types remain to be constrained
GALEX J201337.6+092801: The lowest gravity subdwarf B pulsator
We present the recent discovery of a new subdwarf B variable (sdBV), with an
exceptionally low surface gravity. Our spectroscopy of J20136+0928 places it at
Teff = 32100 +/- 500, log(g) = 5.15 +/- 0.10, and log(He/H) = -2.8 +/- 0.1.
With a magnitude of B = 12.0, it is the second brightest V361 Hya star ever
found. Photometry from three different observatories reveals a temporal
spectrum with eleven clearly detected periods in the range 376 to 566 s, and at
least five more close to our detection limit. These periods are unusually long
for the V361 Hya class of short-period sdBV pulsators, but not unreasonable for
p- and g-modes close to the radial fundamental, given its low surface gravity.
Of the ~50 short period sdB pulsators known to date, only a single one has been
found to have comparable spectroscopic parameters to J20136+0928. This is the
enigmatic high-amplitude pulsator V338 Ser, and we conclude that J20136+0928 is
the second example of this rare subclass of sdB pulsators located well above
the canonical extreme horizontal branch in the HR diagram.Comment: 5 pages, accepted for publication in ApJ Letter
Neutron halos in heavy nuclei -- relativistic mean field approach
Assuming a~simple spherical relativistic mean field model of the nucleus, we
estimate the width of the antiproton--neutron annihilation () and the
width of antiproton--proton () annihilation, in an antiprotonic atom
system. This allows us to determine the halo factor , which is then
discussed in the context of experimental data obtained in measurements recently
done on LEAR utility at CERN. Another quantity which characterizes the
deviation of the average nuclear densities ratio from the corresponding ratio
of the homogeneous densities is introduced too. It was shown that it is also a
good indicator of the neutron halo. The results are compared to experimental
data as well as to the data of the simple liquid droplet model of the nuclear
densities. The single particle structure of the nuclear density tail is
discusssed also.Comment: revtex, 12 pages + 6 postscript figure
Variable Blue Straggler Stars in Open Cluster NGC 6819 Observed in the Kepler 'Superstamp' Field
NGC 6819 is an open cluster of age 2.4 Gyr that was in the NASA Kepler
spacecraft field of view from 2009 to 2013. The central part of the cluster was
observed in a 200 x 200 pixel `superstamp' during these four years in 30-minute
cadence photometry, providing a unique long time-series high-precision data
set. The cluster contains 'blue straggler' stars, i.e., stars on the main
sequence above the cluster turnoff that should have left the main sequence to
become red giants. We present light curves and pulsation frequency analyses
derived from custom photometric reductions for five confirmed cluster
members--four blue stragglers and one star near the main-sequence turnoff. Two
of these stars show a rich spectrum of Scuti pulsation modes, with 236
and 124 significant frequencies identified, respectively, while two stars show
mainly low-frequency modes, characteristic of Doradus variable stars.
The fifth star, a known active x-ray binary, shows only several harmonics of
two main frequencies. For the two Scuti stars, we use a frequency
separation--mean-density relation to estimate mean density, and then use this
value along with effective temperature to derive stellar mass and radius. For
the two stars showing low frequencies, we searched for period-spacing sequences
that may be representative of gravity-mode or Rossby-mode sequences, but found
no clear sequences. The common age for the cluster members, considered along
with the frequencies, will provide valuable constraints for asteroseismic
analyses, and may shed light on the origin of the blue stragglers.Comment: Accepted for publication in The Astronomical Journal February 23,
2023. 36 pages, 14 figures, 4 tables in text, 5 in Appendi
A review of seismic observations of Kepler and K2-Observed sdBV stars
This paper reviews recent seismic findings from Kepler and K2 data. Using three years of short cadence Kepler (K1) data, it is possible to examine time evolution of pulsations in an unprecedented way. While K2 observations are shorter, only three months, they are important as they are finding more sdBV stars than K1 did. Most importantly, K2 is discovering more p-mode pulsators with coverage not possible to get from the ground
Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS: I. Asteroseismology of the GW Vir stars RX J2117+3412, HS 2324+3944, NGC 6905, NGC 1501, NGC 2371, and K 1-16
In this paper, we present a detailed asteroseismological analysis of six GW
Vir stars including the observations collected by the TESS mission. We
processed and analyzed TESS observations of RX J2117+3412, HS 2324+3944, NGC
6905, NGC 1501, NGC 2371, and K 1-16. We carried out a detailed
asteroseismological analysis of these stars on the basis of PG 1159
evolutionary models that take into account the complete evolution of the
progenitor stars. In total, we extracted 58 periodicities from the TESS light
curves using a standard pre-whitening procedure to derive the potential
pulsation frequencies. All the oscillation frequencies that we found are
associated with g-mode pulsations with periods spanning from s to
s. We find constant period spacings for all but one star, which
allowed us to infer their stellar masses and constrain the harmonic degree
of the modes. We performed period-to-period fit analyses on five of the
six analyzed stars. For four stars, we were able to find an asteroseismological
model with masses in agreement with the stellar-mass values inferred from the
period spacings, and generally compatible with the spectroscopic masses. We
estimated the seismological distance and compared it with the precise
astrometric distance measured with GAIA. Finally, we find that the period
spectrum of K 1-16 exhibits dramatic changes in frequency and amplitude. The
high-quality data collected by the TESS space mission, considered
simultaneously with ground-based observations, are able to provide a very
valuable input to the asteroseismology of GW Vir stars, similar to the case of
other classes of pulsating white-dwarf stars. The TESS mission, in conjunction
with future space missions and upcoming surveys, will make impressive progress
in white-dwarf asteroseismology.Comment: 34 pages, 33 figures, 21 tables. Accepted for publication in
Astronomy and Astrophysic
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