80 research outputs found
Photometry of two unusual A supergiant systems in the Small Magellanic Cloud
We present multiwavelength broadband photometry and V, I time resolved
photometry for two variable bright stars in the SMC, OGLE004336.91-732637.7
(SMC-SC3) and OGLE004633.76-731204.3 (SMC-SC4). The light curves span 12 years
and show long-term periodicities (SMC-SC3) and modulated eclipses (SMC-SC4)
that are discussed in terms of wide-orbit intermediate mass interacting
binaries and associated envelopes. SMC-SC3 shows a primary period of 238.1 days
along with a complicated waveform suggesting ellipsoidal variablity influenced
by an eccentric orbit. This star also shows a secondary variability with an
unstable periodicity that has a mean value of 15.3 days. We suggest this could
be associated with nonradial pulsations.Comment: To be published in Publications of the Astronomical Society of the
Pacific (PASP)
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
A CCD Search for Variable Stars in the Open Cluster NGC 6611
We present the results of the variability survey in the young open
cluster NGC 6611 based on observations obtained during 34 nights spanning one
year. In total, we found 95 variable stars. Most of these stars are classified
as periodic and irregular pre-main sequence (PMS) stars. The analysis of the
2MASS photometry and four-colour IRAC photometry revealed 165 Class II
young stellar sources, 20 of which are irregular variables and one is an
eclipsing binary. These classifications, complemented by UKIDSS
photometry and VPHAS photometry, were used to identify 24
candidates for classical T Tauri stars and 30 weak-lined T Tauri stars. In
addition to the PMS variables, we discovered eight Scuti candidates.
None of these were previously known. Furthermore, we detected 17 eclipsing
binaries where two were previously known. Based on the proper motions provided
by the Gaia EDR3 catalogue, we calculated the cluster membership probabilities
for 91 variable stars. For 61 variables, a probability higher than 80% was
determined, which makes them cluster members. Only 25 variables with a
probability less than 20% were regarded to be non-members.Comment: 30 pages, 31 figure
KIC 8410637: a 408-day period eclipsing binary containing a pulsating red giant
Detached eclipsing binaries (dEBs) are ideal targets for accurate measurement
of masses and radii of ther component stars. If at least one of the stars has
evolved off the main sequence (MS), the masses and radii give a strict
constraint on the age of the stars. Several dEBs containing a bright K giant
and a fainter MS star have been discovered by the Kepler satellite. The mass
and radius of a red giant (RG) star can also be derived from its asteroseismic
signal. The parameters determined in this way depend on stellar models and may
contain systematic errors. It is important to validate the asteroseismically
determined mass and radius with independent methods. This can be done when
stars are members of stellar clusters or members of dEBs. KIC 8410637 consists
of an RG and an MS star. The aim is to derive accurate masses and radii for
both components and provide the foundation for a strong test of the
asteroseismic method and the accuracy of the deduced mass, radius and age. We
analyse high-resolution spectra from three different spectrographs. We also
calculate a fit to the Kepler light curve and use ground-based photometry to
determine the flux ratios between the component stars in the BVRI passbands. We
measured the masses and radii of the stars in the dEB, and the classical
parameters Teff, log g and [Fe/H] from the spectra and ground-based photometry.
The RG component of KIC 8410637 is most likely in the core helium-burning red
clump phase of evolution and has an age and composition very similar to the
stars in the open cluster NGC 6819. The mass of the RG in KIC 8410637 should
therefore be similar to the mass of RGs in NGC 6819, thus lending support to
the most up-to-date version of the asteroseismic scaling relations. This is the
first direct measurement of both mass and radius for an RG to be compared with
values for RGs from asteroseismic scaling relations.Comment: Accepted 20.6.2013 for publication in Astronomy and Astrophysic
A cyclic bipolar wind in the interacting binary V393 Scorpii
V393 Scorpii is a Double Periodic Variable characterized by a relatively
stable non-orbital photometric cycle of 253 days. Mennickent et al. argue for
the presence of a massive optically thick disc around the more massive B-type
component and describe the evolutionary stage of the system. In this paper we
analyze the behavior of the main spectroscopic optical lines during the long
non-orbital photometric cycle. We study the radial velocity of the donor
determining their orbital elements and find a small but significant orbital
eccentricity (e = 0.04). The donor spectral features are modeled and removed
from the spectrum at every observing epoch using the light-curve model given by
Mennickent et al. We find that the line emission is larger during eclipses and
mostly comes from a bipolar wind. We find that the long cycle is explained in
terms of a modulation of the wind strength; the wind has a larger line and
continuum emissivity on the high state. We report the discovery of highly
variable chromospheric emission in the donor, as revealed by Doppler maps of
the emission lines MgII 4481 and CI 6588. We discuss notable and some novel
spectroscopic features like discrete absorption components, especially visible
at blue-depressed OI 7773 absorption wings during the second half-cycle, Balmer
double emission with V/R-curves showing "Z-type" and "S-type" excursions around
secondary and main eclipse, respectively, and H_beta emission wings extending
up to +- 2000 km/s. We discuss possible causes for these phenomena and for
their modulations with the long cycle.Comment: 19 pages, 22 figures, accepted for publication in MNRA
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