342 research outputs found
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
The eclipsing LMC star OGLE 05155332-6925581: a clue for double periodic variables
We investigate the nature of OGLE05155332-6925581, one of the brightest members of the enigmatic group of double periodic variables (DPVs) recently found in the Magellanic Clouds. The modelling of archival orbital light curves (LCs), along with the analysis of the radial velocities (RVs) suggest that this object is a semidetached binary with the less massive star transferring matter to the more massive and less evolved star, in an Algol-like configuration. We find evidence for additional orbital variability and Hα emission, likely caused by an accretion disc around the primary star. As in the case of β Lyr the circumprimary disc seems to be more luminous than the primary, but we do not detect orbital period changes. We find that the LC follows a loop in the colour-magnitude diagram during the long cycle; the system is redder when brighter and the rising phase is bluer than during decline. Infrared excess is also present. The source of the long-term periodicity is not eclipsed, indicating its circumbinary origin. Strong asymmetries, discrete absorption components (DACs) and a γ shift are new and essential observational properties in the infrared HI lines. The DACs strength and RV follow a saw-teeth pattern during the orbital cycle. We suggest that the system experiences supercycles of mass outflow feeding a circumbinary disc. Mass exchange and mass loss could produce comparable but opposite effects in the orbital period on a long time-scale, resulting in a quasi-constancy of this parameter.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
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 evolution stage and massive disc of the interacting binary V393 Scorpii
V393 Scorpii is a bright Galactic Double Periodic Variable showing a long
photometric cycle of approx. 253 days. We present new VIJK photometric time
series for V393 Scorpii along with the analysis of ASAS V-band photometry. We
disentangled all light curves into the orbital and long cycle components. The
ASAS V-band orbital light curve was modeled with two stellar components plus a
circumprimary optically thick disc assuming a semidetached configuration. We
present the results of this calculation, giving physical parameters for the
stars and the disc, along with general system dimensions. Our results are in
close agreement with those previously found by Mennickent et al. (2010) from IR
spectroscopy and the modeling of the spectral energy distribution. The
stability of the orbital light curve suggests that the stellar + disc
configuration remains stable during the long cycle. Therefore, the long cycle
should be produced by an additional variable and not-eclipsed emitting
structure. We discuss the evolutionary stage of the system finding the best
match with one of the evolutionary models of van Rensbergen et al. (2008).
According to these models, the system is found to be after an episode of fast
mass exchange that transferred 4 M_sun from the donor to the gainer in a period
of 400.000 years. We argue that a significant fraction of this mass has not
been accreted by the gainer but remains in an optically thick massive (about 2
M_sun) disc-like surrounding pseudo-photosphere whose luminosity is not driven
by viscosity but probably by reprocessed stellar radiation. Finally, we provide
the result of our search for Galactic Double Periodic Variables and briefly
discuss the outliers beta Lyr and RX Cas.Comment: 10 pages, 5 tables, 6 figures, accepted for publication in MNRAS main
journa
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
The eclipsing LMC star OGLE05155332--6925581: a clue for Double Periodic Variables
We investigate the nature of OGLE05155332-6925581, one of the brightest
members of the enigmatic group of Double Periodic Variables (DPVs) recently
found in the Magellanic Clouds. The modeling of archival orbital light curves
(LCs), along with the analysis of the radial velocities suggest that this
object is a semi--detached binary with the less massive star transferring
matter to the more massive and less evolved star, in an Algol--like
configuration. We find evidence for additional orbital variability and
H emission, likely caused by an accretion disc around the primary star.
As in the case of the circumprimary disc seems to be more luminous
than the primary, but we do not detect orbital period changes. We find that the
LC follows a loop in the color--magnitude diagram during the long cycle; the
system is redder when brighter and the rising phase is bluer than during
decline. Infrared excess is also present. The source of the long--term
periodicity is not eclipsed, indicating its circumbinary origin. Strong
asymmetries, discrete absorption components (DACs) and a shift are new
and essential observational properties in the infrared H I lines. The DACs
strength and RV follow a saw--teeth pattern during the orbital cycle. We
suggest that the system experiences supercycles of mass outflow feeding a
circumbinary disc. Mass exchange and mass loss could produce comparable but
opposite effects in the orbital period on a long time scale, resulting in a
quasi--constancy of this parameter.Comment: submitted to MNRA
Comparison of Urinary Neopterin and Pseudouridine in Patients with Malignant Proliferative Diseases
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