285 research outputs found
KIC 4768731: a bright long-period roAp star in theKeplerfield
We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff = 8100 ± 200 K, log g = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i = 14.8 ± 1.6 km s−1.
Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr
Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants
Context : We still do not know which mechanisms are responsible for the
transport of angular momentum inside stars. The recent detection of mixed modes
that contain the signature of rotation in the spectra of Kepler subgiants and
red giants gives us the opportunity to make progress on this issue.
Aims: Our aim is to probe the radial dependance of the rotation profiles for
a sample of Kepler targets. For this purpose, subgiants and early red giants
are particularly interesting targets because their rotational splittings are
more sensitive to the rotation outside the deeper core than is the case for
their more evolved counterparts.
Methods: We first extract the rotational splittings and frequencies of the
modes for six young Kepler red giants. We then perform a seismic modeling of
these stars using the evolutionary codes CESAM2k and ASTEC. By using the
observed splittings and the rotational kernels of the optimal models, we
perform inversions of the internal rotation profiles of the six stars.
Results: We obtain estimates of the mean rotation rate in the core and in the
convective envelope of these stars. We show that the rotation contrast between
the core and the envelope increases during the subgiant branch. Our results
also suggest that the core of subgiants spins up with time, contrary to the RGB
stars whose core has been shown to spin down. For two of the stars, we show
that a discontinuous rotation profile with a deep discontinuity reproduces the
observed splittings significantly better than a smooth rotation profile.
Interestingly, the depths that are found most probable for the discontinuities
roughly coincide with the location of the H-burning shell, which separates the
layers that contract from those that expand. These results will bring
observational constraints to the scenarios of angular momentum transport in
stars.Comment: Accepted in A&A, 27 pages, 18 figure
Overview of the LAMOST- project
The NASA mission obtained long-term high-quality photometric
observations for a large number of stars in its original field of view from
2009 to 2013. In order to provide reliable stellar parameters in a homogeneous
way, the LAMOST telescope began to carry out low-resolution spectroscopic
observations for as many stars as possible in the field in 2012. By
September 2018, 238,386 low-resolution spectra with SNR had been
collected for 155,623 stars in the field, enabling the determination
of atmospheric parameters and radial velocities, as well as spectral
classification of the target stars. This information has been used by
astronomers to carry out research in various fields, including stellar
pulsations and asteroseismology, exoplanets, stellar magnetic activity and
flares, peculiar stars and the Milky Way, binary stars, etc. We summarize the
research progress in these fields where the usage of data from the
LAMOST- (LK) project has played a role. In addition, time-domain
medium-resolution spectroscopic observations have been carried out for about
12,000 stars in four central plates of the field since 2018. The
currently available results show that the LAMOST- medium resolution
(LK-MRS) observations provide qualified data suitable for research in
additional science projects including binaries, high-amplitude pulsating stars,
etc. As LAMOST is continuing to collect both low- and medium-resolution spectra
of stars in the field, we expect more data to be released continuously
and new scientific results to appear based on the LK project data.Comment: 15 pages, 9 figures, 1 table, RAA accepte
Lamost observations in the kepler field. I. Database of low-resolution spectra*
The nearly continuous light curves with micromagnitude precision provided by the space mission Kepler are revolutionizing our view of pulsating stars. They have revealed a vast sea of low-amplitude pulsation modes that were undetectable from Earth. The long time base of Kepler light curves allows for the accurate determination of the frequencies and amplitudes of pulsation modes needed for in-depth asteroseismic modeling. However, for an asteroseismic study to be successful, the first estimates of stellar parameters need to be known and they cannot be derived from the Kepler photometry itself. The Kepler Input Catalog provides values for the effective temperature, surface gravity, and metallicity, but not always with sufficient accuracy. Moreover, information on the chemical composition and rotation rate is lacking. We are collecting low-resolution spectra for objects in the Kepler field of view with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, Xinglong observatory, China). All of the requested fields have now been observed at least once. In this paper, we describe those observations and provide a useful database for the whole astronomical communit
A semi-automatic procedure for abundance determination of A- and F-type stars
A variety of physical processes leading to different types of pulsations and
chemical compositions is observed among A- and F-type stars. To investigate the
underlying mechanisms responsible for these processes in stars with similar
locations in the H-R diagram, an accurate abundance determination is needed,
among others. Here, we describe a semi-automatic procedure developed to
determine chemical abundances of various elements ranging from helium to
mercury for this type of stars. We test our procedure on synthetic spectra,
demonstrating that our procedure provides abundances consistent with the input
values, even when the stellar parameters are offset by reasonable observational
errors. For a fast-rotating star such as Vega, our analysis is consistent with
those carried out with other plane-parallel model atmospheres. Simulations show
that the offsets from the input abundances increase for stars with low
inclination angle of about 4 degrees. For this inclination angle, we also show
that the distribution of the iron abundance found in different regions is
bimodal. Furthermore, the effect of rapid rotation can be seen in the peculiar
behaviour of the H_beta line.Comment: accepted for publication in MNRAS, contains 6 tables and 8 figure
Catalog of Galactic Beta Cephei Stars
We present an extensive and up-to-date catalog of Galactic Beta Cephei stars.
This catalog is intended to give a comprehensive overview of observational
characteristics of all known Beta Cephei stars. 93 stars could be confirmed to
be Beta Cephei stars. For some stars we re-analyzed published data or conducted
our own analyses. 61 stars were rejected from the final Beta Cephei list, and
77 stars are suspected to be Beta Cephei stars. A list of critically selected
pulsation frequencies for confirmed Beta Cephei stars is also presented. We
analyze the Beta Cephei stars as a group, such as the distributions of their
spectral types, projected rotational velocities, radial velocities, pulsation
periods, and Galactic coordinates. We confirm that the majority of these stars
are multiperiodic pulsators. We show that, besides two exceptions, the Beta
Cephei stars with high pulsation amplitudes are slow rotators. We construct a
theoretical HR diagram that suggests that almost all 93 Beta Cephei stars are
MS objects. We discuss the observational boundaries of Beta Cephei pulsation
and their physical parameters. We corroborate that the excited pulsation modes
are near to the radial fundamental mode in frequency and we show that the mass
distribution of the stars peaks at 12 solar masses. We point out that the
theoretical instability strip of the Beta Cephei stars is filled neither at the
cool nor at the hot end and attempt to explain this observation
Light therapy as a treatment for sexual dysfunctions -beyond a pilot study
Summary Aim. Seasonal trends were demonstrated in reproduction and sexual activity. Through the secretion of melatonin the pineal gland plays an important role, in the neuroendocrine control of sexual function and reproductive physiology. We hypothesized that inhibition of the pineal gland activity through a light treatment may favorably affect sexual function. Method. We recruited 24 subjects with a diagnosis of hypoactive sexual desire disorder and / or primary sexual arousal disorder. The subjects were randomly assigned to either active light treatment (ALT) or placebo light treatment (L-PBO). Participants were assessed during the first evaluation and after 2 weeks of treatment, using the Structured Clinical Interview for Sexual Disorders DSM-IV (SCID-S) and a self-administered rating scale of the level of sexual satisfaction (1 to 10). Repeated measures ANOVA were performed to compare the two groups of patients. Post-hoc analysis was performed by Holm-Sidak test for repeated comparisons. Results. At baseline the two groups were comparable. After 2 weeks the group treated with Light Therapy showed a significant improvement in sexual satisfaction, about 3 times higher than the group that received placebo, while no significant improvement was observed in the group L-PBO. Conclusions. Our results confirm a potentially beneficial effect of Light Therapy on primary sexual dysfunction. In the future, we propose to correlate clinical findings with testosterone levels pre / post treatment
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