314 research outputs found
Spectrum Analysis of Bright Kepler late B- to early F- Stars
The Kepler satellite mission delivers single band-pass light curves of a huge
number of stars observed in the Cygnus-Lyra region opening a new window for
asteroseismology. In order to accomplish one of the preconditions for the
asteroseismic modelling of the stars, we aim to derive fundamental parameters
and individual abundances for a sample of 18 Gamma Dor (GD)/Delta Sct (DSct)
and 8 SPB/beta Cep candidate stars in the Kepler satellite field of view. We
use the spectral synthesis method to model newly obtained, high-resolution
spectra of 26 stars in order to derive their fundamental parameters and
individual abundances. The stars are then placed into the log(Teff)-log(g)
diagram and the obtained spectroscopic classification is compared to the
existing photometric one. For hot stars, the KIC temperatures appear to be
systematically underestimated, in agreement with previous findings. We also
find that the temperatures derived from our spectra agree reasonably well with
those derived from the SED fitting. According to their position in the
log(Teff)-log(g) diagram, two stars are expected GD stars, four stars are
expected DSct stars, and four stars are possibly DSct stars at the blue edge of
the instability strip. Two stars are confirmed SPB variables, and one star
falls into the SPB instability region but its parameters might be biased by
binarity. Two of the four stars that fall into the DSct instability region show
GD-type oscillation in their light curves implying that GD-like oscillations
are much more common among the DSct stars than is theoretically expected.
Moreover, one of the stars located at the hot border of the DSct instability
strip is classified as DSct-GD hybrid pulsator from its light curve analysis.
Given that these findings are fully consistent with recent investigations, we
conclude that a revision of the GD and DSct instability strips is essential.Comment: 14 pages, 14 figures, 6 tables; accepted for publication in MNRA
The orbit of the close spectroscopic binary epsilon Lupi and the intrinsic variability of its early B-type components
We subjected 106 new high-resolution spectra of the double-lined
spectroscopic close binary epsilon Lupi, obtained in a time-span of 17 days
from two different observatories, to a detailed study of orbital and intrinsic
variations. We derived accurate values of the orbital parameters. We refined
the sidereal orbital period to 4.55970 days and the eccentricity to e=0.277. By
adding old radial velocities, we discovered the presence of apsidal motion with
a period of the rotation of apses of about 430 years. Such a value agrees with
theoretical expectations. Additional data is needed to confirm and refine this
value. Our dataset did not allow us to derive the orbit of the third body,
which is known to orbit the close system in approximately 64 years. We present
the secondary of epsilon Lupi as a new beta Cephei variable, while the primary
is a beta Cephei suspect. A first detailed analysis of line-profile variations
of both primary and secondary led to detection of one pulsation frequency near
10.36 c/d in the variability of the secondary, while no clear periodicity was
found in the primary, although low-amplitude periodicities are still suspected.
The limited accuracy and extent of our dataset did not allow any further
analysis, such as mode-identification.Comment: 13+3 pages, 20 figures. Astronomy and Astrophysics, accepte
Interpretation of the variability of the <i>β</i> Cephei star <i>λ</i> Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binary β Cephei star λ Scorpii. Moreover, we present the first determination of the properties of the triple system to which λ Scorpii belongs. Our analysis is based on a time series of 815 high-resolution spectra, covering a timespan of 14 years. We find a close orbit of 5d.9525days (e=0.26) and a wide orbit of approximately 1082d days (e=0.23). The orbital parameters of the triple star and a spectrum synthesis lead us to conclude that the system is composed of two early-type B stars and a low-mass pre-main-sequence star rather than containing an ultra-massive white dwarf as claimed before. Our proposed configuration is compatible with population synthesis. The radial velocity variations of the primary allow us to confirm the presence of at least one pulsation mode with frequency 4.679410 c d-1 which is subject to the light-time effect in the triple system. A detailed analysis of the complex line-profile variations is described in a subsequent paper
Observational evidence for a correlation between macroturbulent broadening and line-profile variations in OB Supergiants
The spectra of O and B supergiants are known to be affected by a significant
form of extra line broadening (usually referred to as macroturbulence) in
addition to that produced by stellar rotation. Recent analyses of high
resolution spectra have shown that the interpretation of this line broadening
as a consequence of large scale turbulent motions would imply highly supersonic
velocity fields in photospheric regions, making this scenario quite improbable.
Stellar oscillations have been proposed as a likely alternative explanation. As
part of a long term observational project, we are investigating the
macroturbulent broadening in O and B supergiants and its possible connection
with spectroscopic variability phenomena and stellar oscillations. In this
letter, we present the first encouraging results of our project, namely firm
observational evidence for a strong correlation between the extra broadening
and photospheric line-profile variations in a sample of 13 supergiants with
spectral types ranging from O9.5 to B8.Comment: 8 pages, 3 figures, accepted for publication in ApJ
New ground-based observational methods and instrumentation for asteroseismology
Space instrumentation like SOHO, MOST, CoRoT and Kepler has been and is being
built to attain very high precision data to be used for asteroseismic analysis.
Nonetheless, there is a very strong need for providing additional information,
especially on mode identification. With this contribution I will review the
efforts been put on new ground-based instrumentation and the methodology that
can be used to achieve this aim.Comment: 6 pages. Review contribution to be published in Astrophysics and
Space Science Proceedings series (ASSP), in the proceedings of "20th Stellar
Pulsation Conference Series: Impact of new instrumentation and new insights
in stellar pulsations", 5-9 September 2011, Granada, Spai
Time-scales of Line-broadening Variability in OB Supergiants
Several works have recently shown that there is an important extra
line-broadening (usually called ) affecting the spectra of O
and B Supergiants that adds to stellar rotation. So far, the only (very recent)
physical explanation for the appearance of relates to
oscillations. This is a plausible explanation, but no direct evidence
confirming its validity has been presented yet. We recently started an
observational project to obtain constraints on the time-scales of variability
associated to this extra line-broadening and its possible origin. Our
observational strategy consists of the study of a well selected group of O and
B stars, for which we obtain time series of high-quality spectra. We present
some preliminary results from our first campaign with [email protected]: 3 pages, 3 figures, 2 tables, Proceeding of the conference "Stellar
pulsation: Challenges for theory and Observations" held in Santa Fe, New
Mexico (May 31-June 5, 2009
The classification of frequencies in the {\gamma} Doradus / {\delta} Scuti hybrid star HD 49434
Hybrid stars of the {\gamma} Doradus and {\delta} Scuti pulsation types have
great potential for asteroseismic analysis to explore their interior structure.
To achieve this, mode identi- fications of pulsational frequencies observed in
the stars must be made, a task which is far from simple. In this work we begin
the analysis by scrutinizing the frequencies found in the CoRoT photometric
satellite measurements and ground-based high-resolution spectroscopy of the
hybrid star HD 49434. The results show almost no consistency between the
frequencies found using the two techniques and no characteristic period
spacings or couplings were identified in either dataset. The spectroscopic data
additionally show no evidence for any long term (5 year) variation in the
dominant frequency. The 31 spectroscopic frequencies identified have standard
deviation profiles suggesting multiple modes sharing (l, m) in the {\delta}
Scuti frequency region and several skewed modes sharing the same (l, m) in the
{\gamma} Doradus frequency region. In addition, there is a clear frequency in
the {\gamma} Doradus frequency region that appears to be unrelated to the
others. We conclude HD 49434 remains a {\delta} Scuti/ {\gamma} Doradus
candidate hybrid star but more sophisticated models dealing with rotation are
sought to obtain a clear picture of the pulsational behaviour of this star.Comment: Accepted for publication in MNRAS December 201
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