54 research outputs found
Characterization of Kepler targets based on medium-resolution LAMOST spectra analyzed with ROTFIT
In this work we present the results of our analysis of 16,300
medium-resolution LAMOST spectra of late-type stars in the Kepler field with
the aim of determining the stellar parameters, activity level, lithium
atmospheric content, and binarity. We have used a version of the code ROTFIT
specifically developed for these spectra. We provide a catalog with the
atmospheric parameters (Teff, log(g), and [Fe/H]), radial velocity (RV), and
projected rotation velocity (vsini). For cool stars (Teff < 6500 K), we also
calculated the H-alpha and LiI-6708 equivalent width, which are important
indicators of chromospheric activity and evolutionary stage, respectively. We
have derived the RV and atmospheric parameters for 14,300 spectra of 7443
stars. Literature data were used for a quality control of the results. The Teff
and log(g) values are in good agreement with the literature. The [Fe/H] values
appear to be overestimated for metal-poor stars. We propose a relation to
correct the [Fe/H] values derived with ROTFIT. We were able to identify
double-lined binaries, stars with variable RVs, lithium-rich giants, and
emission-line objects. Based on the H-alpha flux, we found 327 active stars. We
detected the LiI-6708 line and measure its equivalent width for 1657 stars,
both giants and stars on the main sequence. Regarding the latter, we performed
a discrete age classification based on the atmospheric lithium abundance and
the upper envelopes of a few open clusters. Among the giants, we found 195
Li-rich stars, 161 of which are reported here for the first time. No
relationship is found between stellar rotation and lithium abundance, which
allows us to rule out merger scenarios as the predominant explanation of the
enrichment of Li in our sample. The fraction of Li-rich giants, about 4%, is
higher than expected.Comment: 32 pages, 34 figures; accepted for publication in Astronomy &
Astrophysic
UVSat: a concept of an ultraviolet/optical photometric satellite
Time-series photometry from space in the ultraviolet can be presently done
with only a few platforms, none of which is able to provide wide-field
long-term high-cadence photometry. We present a concept of UVSat, a twin space
telescope which will be capable to perform this kind of photometry, filling an
observational niche. The satellite will host two telescopes, one for
observations in the ultraviolet, the other for observations in the optical
band. We also briefly show what science can be done with UVSat.Comment: 6 pages, 2 figures, accepted for publication in the Proceedings of
the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck
The 2003-4 multisite photometric campaign for the Beta Cephei and eclipsing star 16 (EN) Lacertae with an Appendix on 2 Andromedae, the variable comparison star
A multisite photometric campaign for the Beta Cephei and eclipsing variable
16 Lacertae is reported. 749 h of high-quality differential photoelectric
Stromgren, Johnson and Geneva time-series photometry were obtained with ten
telescopes during 185 nights. After removing the pulsation contribution, an
attempt was made to solve the resulting eclipse light curve by means of the
computer program EBOP. Although a unique solution was not obtained, the range
of solutions could be constrained by comparing computed positions of the
secondary component in the Hertzsprung-Russell diagram with evolutionary
tracks.
For three high-amplitude pulsation modes, the uvy and the Geneva UBG
amplitude ratios are derived and compared with the theoretical ones for
spherical-harmonic degrees l <= 4. The highest degree, l = 4, is shown to be
incompatible with the observations. One mode is found to be radial, one is l =
1, while in the remaining case l = 2 or 3.
The present multisite observations are combined with the archival photometry
in order to investigate the long-term variation of the amplitudes and phases of
the three high-amplitude pulsation modes. The radial mode shows a
non-sinusoidal variation on a time-scale of 73 yr. The l = 1 mode is a triplet
with unequal frequency spacing, giving rise to two beat-periods, 720.7 d and
29.1 yr. The amplitude and phase of the l = 2 or 3 mode vary on time-scales of
380.5 d and 43 yr.
The light variation of 2 And, one of the comparison stars, is discussed in
the Appendix.Comment: 18 pages, 19 figures, accepted for publication in MNRA
Characterizing two solar-type Kepler subgiants with asteroseismology: KIC10920273 and KIC11395018
Determining fundamental properties of stars through stellar modeling has
improved substantially due to recent advances in asteroseismology. Thanks to
the unprecedented data quality obtained by space missions, particularly CoRoT
and Kepler, invaluable information is extracted from the high-precision stellar
oscillation frequencies, which provide very strong constraints on possible
stellar models for a given set of classical observations. In this work, we have
characterized two relatively faint stars, KIC10920273 and KIC11395018, using
oscillation data from Kepler photometry and atmospheric constraints from
ground-based spectroscopy. Both stars have very similar atmospheric properties;
however, using the individual frequencies extracted from the Kepler data, we
have determined quite distinct global properties, with increased precision
compared to that of earlier results. We found that both stars have left the
main sequence and characterized them as follows: KIC10920273 is a
one-solar-mass star (M=1.00 +/- 0.04 M_sun), but much older than our Sun
(t=7.12 +/- 0.47 Gyr), while KIC11395018 is significantly more massive than the
Sun (M=1.27 +/- 0.04 M_sun) with an age close to that of the Sun (t=4.57 +/-
0.23 Gyr). We confirm that the high lithium abundance reported for these stars
should not be considered to represent young ages, as we precisely determined
them to be evolved subgiants. We discuss the use of surface lithium abundance,
rotation and activity relations as potential age diagnostics.Comment: 12 pages, 3 figures, 5 tables. Accepted by Ap
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