270 research outputs found
Photometric and spectroscopic variability of 53 Per
A new investigation of the variability of the SPB-type star 53 Per is
presented. The analysis of the BRITE photometry allowed us to determine eight
independent frequencies and the combination one. Five of these frequencies and
the combination one were not known before. In addition, we gathered more than
1800 new moderate and high-resolution spectra of 53 Per spread over
approximately six months. Their frequency analysis revealed four independent
frequencies and the combination one, all consistent with the BRITE results.Comment: 2 pages, accepted for publication in the Proceedings of the PAS
(Proc. of the 2nd BRITE Science conference, Innsbruck
Spectroscopic Study of the Open Cluster NGC 6811
The NASA space telescope Kepler has provided unprecedented time-series
observations which have revolutionised the field of asteroseismology, i.e. the
use of stellar oscillations to probe the interior of stars. The Kepler-data
include observations of stars in open clusters, which are particularly
interesting for asteroseismology. One of the clusters observed with Kepler is
NGC 6811, which is the target of the present paper. However, apart from
high-precision time-series observations, sounding the interiors of stars in
open clusters by means of asteroseismology also requires accurate and precise
atmospheric parameters as well as cluster membership indicators for the
individual stars. We use medium-resolution (R~25,000) spectroscopic
observations, and three independent analysis methods, to derive effective
temperatures, surface gravities, metallicities, projected rotational velocities
and radial velocities, for 15 stars in the field of the open cluster NGC 6811.
We discover two double-lined and three single-lined spectroscopic binaries.
Eight stars are classified as either certain or very probable cluster members,
and three stars are classified as non-members. For four stars, cluster
membership could not been assessed. Five of the observed stars are G-type
giants which are located in the colour-magnitude diagram in the region of the
red clump of the cluster. Two of these stars are surely identified as red clump
stars for the first time. For those five stars, we provide chemical abundances
of 31 elements. The mean radial-velocity of NGC 6811 is found to be
+6.680.08 km s and the mean metallicity and overall abundance
pattern are shown to be very close to solar with an exception of Ba which we
find to be overabundant.Comment: 18 pages, 11 tables, 7 figures, accepted for MNRA
A Spectroscopic and Photometric Investigation of the Mercury-Manganese Star KIC 6128830
The advent of space-based photometry provides the opportunity for the first
precise characterizations of variability in Mercury-Manganese (HgMn/CP3) stars,
which might advance our understanding of their internal structure. We have
carried out a spectroscopic and photometric investigation of the candidate CP3
star KIC 6128830. A detailed abundance analysis based on newly-acquired
high-resolution spectra was performed, which confirms that the star's abundance
pattern is fully consistent with its proposed classification. Photometric
variability was investigated using four years of archival Kepler data. In
agreement with results from the literature, we have identified a single
significant and independent frequency =0.2065424 d with a
peak-to-peak amplitude of 3.4 mmag and harmonic frequencies up to .
Drawing on the predictions of state-of-the-art pulsation models and information
on evolutionary status, we discuss the origin of the observed light changes.
Our calculations predict the occurrence of g-mode pulsations at the observed
variability frequency. On the other hand, the strictly mono-periodic nature of
the variability strongly suggests a rotational origin. While we prefer the
rotational explanation, the present data leave some uncertainty.Comment: 13 pages, 13 figures, accepted for publication in MNRA
Fundamental stellar and accretion disc parameters of the eclipsing binary DQ Velorum
To add to the growing collection of well-studied double periodic variables
(DPVs) we have carried out the first spectroscopic and photometric analysis of
the eclipsing binary DQ Velorum to obtain its main physical stellar and orbital
parameters. Combining spectroscopic and photometric observations that cover
several orbital cycles allows us to estimate the stellar properties of the
binary components and the orbital parameters. We also searched for
circumstellar material around the more massive star. We separated DQ Velorum
composite spectra and measured radial velocities with an iterative method for
double spectroscopic binaries. We obtained the radial velocity curves and
calculated the spectroscopic mass ratio. We compared our single-lined spectra
with a grid of synthetic spectra and estimated the temperature of the stars. We
modeled the V-band light curve with a fitting method based on the simplex
algorithm, which includes an accretion disc. To constrain the main stellar
parameters we fixed the mass ratio and donor temperature to the values obtained
by our spectroscopic analysis. We obtain donor and gainer masses, the radii,
and temperatures for the stellar components. We find that DQ Vel is a
semi-detached system consisting of a B3V gainer and an A1III donor star plus an
extended accretion disc around the gainer. The disc is filling 89% of the
gainer Roche lobe and it has a concave shape that is thicker at its edge than
at its centre. We find a significant sub-orbital frequency of 0.19 d^{-1} in
the residuals of the V-band light curve, which we interpret as a pulsation of
an slowly pulsating B-type (SPB) of a gainer star. We also estimate the
distance to the binary (3.1 kpc) using the absolute radii, apparent magnitudes,
and effective temperatures of the components found in our study.Comment: 12 pages, 13 Postscript figure
Optical spectroscopy of DPVs and the case of LP Ara
We present preliminary results of our spectroscopic campaign of a group of
intermediate mass interacting binaries dubbed "Double Periodic Variables"
(DPVs), characterized by orbital light curves and additional long photometric
cycles recurring roughly after 33 orbital periods (Mennickent et al. 2003,
2005). They have been interpreted as interacting, semi-detached binaries
showing cycles of mass loss into the interstellar medium (Mennickent et al.
2008, Mennickent & Kolaczkowski 2009). High resolution Balmer and helium line
profiles of DPVs can be interpreted in terms of mass flows in these systems. A
system solution is given for LP Ara, based on modeling of the ASAS V-band
orbital light curve and the radial velocity of the donor star.Comment: To be published in the proceedings book of the IAUS 272, Cambridge
University Press. Editors C. Neiner, G. Wade, G. Meynet and G. Peter
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