87 research outputs found
Unexpected series of regular frequency spacing of delta Scuti stars in the non-asymptotic regime -- I. The methodology
A sequence search method was developed to search regular frequency spacing in
delta Scuti stars by visual inspection and algorithmic search. We searched for
sequences of quasi-equally spaced frequencies, containing at least four members
per sequence, in 90 delta Scuti stars observed by CoRoT. We found an
unexpectedly large number of independent series of regular frequency spacing in
77 delta Scuti stars (from 1 to 8 sequences) in the non-asymptotic regime. We
introduce the sequence search method presenting the sequences and echelle
diagram of CoRoT 102675756 and the structure of the algorithmic search. Four
sequences (echelle ridges) were found in the 5-21 d^{-1} region, where the
pairs of the sequences are shifted (between 0.5-0.59 d^{-1}) by twice the value
of the estimated rotational splitting frequency (0.269 d^{-1}). The general
conclusions for the whole sample are also presented in this paper. The
statistics of the spacings derived by the sequence search method, by FT and
that of the shifts are also compared. In many stars, more than one almost
equally valid spacing appeared. The model frequencies of FG Vir and their
rotationally split components were used to reveal a possible explanation that
one spacing is the large separation, while the other is a sum of the large
separation and the rotational frequency. In CoRoT 102675756, the two spacings
(2.249 and 1.977 d^{-1}) agree better with the sum of a possible 1.710 d^{-1}
large separation and two or one times, respectively, the value of the
rotational frequency.Comment: 12 pages, 10 figures, accepted for publication in Ap
A new eclipsing binary system with a pulsating component detected by CoRoT
We report the discovery of CoRoT 102980178 (R.A.= 06:50:12.10, Dec.=
-02:41:21.8, J2000) an Algol-type eclipsing binary system with a pulsating
component (oEA). It was identified using a publicly available 55 day long
monochromatic lightcurve from the CoRoT initial run dataset (exoplanet field).
Eleven consecutive 1.26m deep total primary and the equal number of 0.25m deep
secondary eclipses (at phase 0.50) were observed. The following light elements
for the primary eclipse were derived: HJD_MinI= 2454139.0680 + 5.0548d x E. The
lightcurve modeling leads to a semidetached configuration with the photometric
mass ratio q=0.2 and orbital inclination i=85 deg. The out-of-eclipse
lightcurve shows ellipsoidal variability and positive O'Connell effect as well
as clear 0.01m pulsations with the dominating frequency of 2.75 c/d. The
pulsations disappear during the primary eclipses, which indicates the primary
(more massive) component to be the pulsating star. Careful frequency analysis
reveals the second independent pulsation frequency of 0.21 c/d and numerous
combinations of these frequencies with the binary orbital frequency and its
harmonics. On the basis of the CoRoT lightcurve and ground based multicolor
photometry, we favor classification of the pulsating component as a gamma
Doradus type variable, however, classification as an SPB star cannot be
excluded.Comment: 16 pages, 7 figures, 3 tables, accepted to Communications in
Asteroseismolog
Report on the third and last run of the ESO LP 182.D-0356 ([email protected])
The ESO Large Programme 182.D-0356 ended with the two runs of December 2009 with the HARPS instrument at the 3.6m ESO telescope. The log of these observations, the prob- lems encountered and solved in the spectra reduction, some tips, the situation of the publications, and a look to the future are given
Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
A precise characterisation of the red giants in the seismology fields of the
CoRoT satellite is a prerequisite for further in-depth seismic modelling.
High-resolution FEROS and HARPS spectra were obtained as part of the
ground-based follow-up campaigns for 19 targets holding great asteroseismic
potential. These data are used to accurately estimate their fundamental
parameters and the abundances of 16 chemical species in a self-consistent
manner. Some powerful probes of mixing are investigated (the Li and CNO
abundances, as well as the carbon isotopic ratio in a few cases). The
information provided by the spectroscopic and seismic data is combined to
provide more accurate physical parameters and abundances. The stars in our
sample follow the general abundance trends as a function of the metallicity
observed in stars of the Galactic disk. After an allowance is made for the
chemical evolution of the interstellar medium, the observational signature of
internal mixing phenomena is revealed through the detection at the stellar
surface of the products of the CN cycle. A contamination by NeNa-cycled
material in the most massive stars is also discussed. With the asteroseismic
constraints, these data will pave the way for a detailed theoretical
investigation of the physical processes responsible for the transport of
chemical elements in evolved, low- and intermediate-mass stars.Comment: Accepted for publication in A&A, 25 pages, 13 colour figures (revised
version after language editing
Photometric variability of the Herbig Ae star HD 37806
The more massive counterparts of T Tauri stars, Herbig Ae/Be stars, are known
to vary in a complex way with no variability mechanism clearly identified. We
attempt to characterize the optical variability of HD~37806 (MWC 120) on time
scales ranging between minutes and several years. A continuous, one-minute
resolution, 21 day-long sequence of MOST (Microvariability & Oscillations of
STars) satellite observations has been analyzed using wavelet, scalegram and
dispersion analysis tools. The MOST data have been augmented by sparse
observations over 9 seasons from ASAS (All Sky Automated Survey), by previously
non-analyzed ESO (European Southern Observatory) data partly covering 3 seasons
and by archival measurements dating back half a century ago. Mutually
superimposed flares or accretion instabilities grow in size from about 0.0003
of the mean flux on a time scale of minutes to a peak-to-peak range of <~0.05
on a time scale of a few years. The resulting variability has properties of
stochastic "red" noise, whose self-similar characteristics are very similar to
those observed in cataclysmic binary stars, but with much longer characteristic
time scales of hours to days (rather than minutes) and with amplitudes which
appear to cease growing in size on time scales of tens of years. In addition to
chaotic brightness variations combined with stochastic noise, the MOST data
show a weakly defined cyclic signal with a period of about 1.5 days, which may
correspond to the rotation of the star.Comment: Accepted for publication by Astron. & Astroph. 8 pages, 9 figures.
For some reason Fig.5 incorrectly shows in arXiv: Contours OK, gray scale no
Report on the third run of the ESO LP 185.D-0056 ([email protected])
The ESO Large Programme 185.D-0056 ([email protected]) continued in June and July 2011, with the first radial velocity survey of red giants. The log of the the observations, the problems encountered, some tips in the use of HARPS in the HAM mode, the situation of the publications, and a look to the future are given
Quantitative spectroscopy of close binary stars
The method of spectral disentangling has now created the opportunity for
studying the chemical composition in previously inaccessible components of
binary and multiple stars. This in turn makes it possible to trace their
chemical evolution, a vital aspect in understanding the evolution of stellar
systems. We review different ways to reconstruct individual spectra from
eclipsing and non-eclipsing systems, and then concentrate on some recent
applications to detached binaries with high-mass and intermediate-mass stars,
and Algol-type mass-transfer systems.Comment: To appear in the Proceedings of IAU Symposium 282 'From Interacting
Binaries to Exoplanets: Essential Modeling Tools
Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints
Context. The availability of asteroseismic constraints for a large sample of
red giant stars from the CoRoT and Kepler missions paves the way for various
statistical studies of the seismic properties of stellar populations.
Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant
stars (Morel et al 2014) to compare theoretical stellar evolution models to
observations of the open cluster NGC 6633 and field stars.
Methods. In order to explore the effects of rotation-induced mixing and
thermohaline instability, we compare surface abundances of carbon isotopic
ratio and lithium with stellar evolution predictions. These chemicals are
sensitive to extra-mixing on the red-giant branch.
Results. We estimate mass, radius, and distance for each star using the
seismic constraints. We note that the Hipparcos and seismic distances are
different. However, the uncertainties are such that this may not be
significant. Although the seismic distances for the cluster members are self
consistent they are somewhat larger than the Hipparcos distance. This is an
issue that should be considered elsewhere. Models including thermohaline
instability and rotation-induced mixing, together with the seismically
determined masses can explain the chemical properties of red-giants targets.
However, with this sample of stars we cannot perform stringent tests of the
current stellar models. Tighter constraints on the physics of the models would
require the measurement of the core and surface rotation rates, and of the
period spacing of gravity-dominated mixed modes. A larger number of stars with
longer times series, as provided by Kepler or expected with Plato, would help
for ensemble asteroseismology.Comment: Accepted 03/05/201
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