761 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
Binaries with total eclipses in the LMC: potential targets for spectroscopy
35 Eclipsing binaries presenting unambiguous total eclipses were selected
from a subsample of the list of Wyrzykowski et al. (2003). The photometric
elements are given for the I curve in DiA photometry, as well as approximate
Teff and masses of the components. The interest of these systems is stressed in
view of future spectroscopic observations.Comment: 4 pages, 1 figure; poster presented at the conference "Close binaries
in the 21st Century: new opportunities and challenges", Syros, 27-30 June
200
Adaptive Horizon Model Predictive Control and Al'brekht's Method
A standard way of finding a feedback law that stabilizes a control system to
an operating point is to recast the problem as an infinite horizon optimal
control problem. If the optimal cost and the optmal feedback can be found on a
large domain around the operating point then a Lyapunov argument can be used to
verify the asymptotic stability of the closed loop dynamics. The problem with
this approach is that is usually very difficult to find the optimal cost and
the optmal feedback on a large domain for nonlinear problems with or without
constraints. Hence the increasing interest in Model Predictive Control (MPC).
In standard MPC a finite horizon optimal control problem is solved in real time
but just at the current state, the first control action is implimented, the
system evolves one time step and the process is repeated. A terminal cost and
terminal feedback found by Al'brekht's methoddefined in a neighborhood of the
operating point is used to shorten the horizon and thereby make the nonlinear
programs easier to solve because they have less decision variables. Adaptive
Horizon Model Predictive Control (AHMPC) is a scheme for varying the horizon
length of Model Predictive Control (MPC) as needed. Its goal is to achieve
stabilization with horizons as small as possible so that MPC methods can be
used on faster and/or more complicated dynamic processes.Comment: arXiv admin note: text overlap with arXiv:1602.0861
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 Îł 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 AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
Detached binaries in the Large Magellanic Cloud. A selection of binaries suitable for distance determination
As a result of a careful selection of eclipsing binaries in the Large
Magellanic Cloud using the OGLE-II photometric database, we present a list of
98 systems that are suitable targets for spectroscopic observations that would
lead to the accurate determination of the distance to the LMC. For these
systems we derive preliminary parameters combining the OGLE-II data with the
photometry of MACHO and EROS surveys. In the selected sample, 58 stars have
eccentric orbits. Among these stars we found fourteen systems showing apsidal
motion. The data do not cover the whole apsidal motion cycle, but follow-up
observations will allow detailed studies of these interesting objects.Comment: 15 pages, 6 figures, accepted for publication in A&
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
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