308 research outputs found
Properties and nature of Be stars: 29. Orbital and long-term spectral variations of \gamma\ Cassiopei\ae
A detailed analysis of more than 800 electronic high-resolution spectra of
gamma Cas, which were obtained during a time interval of over 6000 days (16.84
yrs) at several observatories, documents the smooth variations in the density
and/or extend of its circumstellar envelope. We found a clear anticorrelation
between the peak intensity and FWHM of the H alpha emission, which seems to
agree with recent models of such emission lines. The main result of this study
is a confirmation of the binary nature of the object, determination of a
reliable linear ephemeris T_{min.RV} = HJD (2452081.90.6) +
(203.520.08)*E, and a rather definitive set of orbital elements. We
clearly demonstrated that the orbit is circular within the limits of accuracy
of our measurements and has a semi-amplitude of radial-velocity curve of
4.300.09 (km/s). No trace of the low-mass secondary was found. The time
distribution of our spectra does not allow a reliable investigation of rapid
spectral variations, which are undoubtedly present in the spectra. We postpone
this investigation for a future study, based on series of dedicated whole-night
spectral observations
V2368 Oph: An eclipsing and double-lined spectroscopic binary used as a photometric comparison star for U Oph
The A-type star HR 6412 = V2368 Oph was used by several investigators as a
photometric comparison star for the known eclipsing binary U Oph but was found
to be variable by three independent groups, including us. By analysing series
of new spectral and photometric observations and a critical compilation of
available radial velocities, we were able to find the correct period of light
and radial-velocity variations and demonstrate that the object is an eclipsing
and double-lined spectroscopic binary moving in a highly eccentric orbit. We
derived a linear ephemeris T min.I = HJD (2454294.67 +/- 0.01) + (38.32712 +/-
0.00004)d x E and estimated preliminary basic physical properties of the
binary. The dereddened UBV magnitudes and effective temperatures of the primary
and secondary, based on our light- and velocity-curve solutions, led to
distance estimates that agree with the Hipparcos distance within the errors. We
find that the mass ratio must be close to one, but the limited number and
wavelength range of our current spectra does not allow a truly precise
determination of the binary masses. Nevertheless, our results show convincingly
that both binary components are evolved away from the main sequence, which
makes this system astrophysically very important. There are only a few
similarly evolved A-type stars among known eclipsing binaries. Future
systematic observations and careful analyses can provide very stringent tests
for the stellar evolutionary theory.Comment: 10 pages, 7 figs, in press 2011 A&
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
High-precision elements of double-lined spectroscopic binaries from combined interferometry and spectroscopy. Application to the beta Cephei star beta Centauri
We present methodology to derive high-precision estimates of the fundamental
parameters of double-lined spectroscopic binaries. We apply the methods to the
case study of the double-lined beta Cephei star beta Centauri. We also present
a detailed analysis of beta Centauri's line-profile variations caused by its
oscillations. We point out that a systematic error in the orbital amplitudes,
and any quantities derived from them, occurs if the radial velocities of
blended component lines are computed without spectral disentangling. This
technique is an essential ingredient in the derivation of the physical
parameters if the goal is to obtain a precision of only a few percent. We have
devised iteration schemes to obtain the orbital elements for systems whose
lines are blended throughout the orbital cycle. We find the following
parameters for beta Cen: and , an age of years. We deduce two oscillation
frequencies for the broad-lined primary of beta Centauri with degrees higher
than 2. We propose that our iteration schemes be used in any future derivations
of the spectroscopic orbital parameters of double-lined binaries with blended
component lines to which disentangling can be successfully applied.Comment: 12 pages, 13 figures, accepted for publication in A&
A unified solution for the orbit and light-time effect in the V505 Sgr system
The multiple system V505 Sagittarii is composed of at least three stars: a
compact eclipsing pair and a distant component, which orbit is measured
directly using speckle interferometry. In order to explain the observed orbit
of the third body in V505 Sagittarii and also other observable quantities,
namely the minima timings of the eclipsing binary and two different radial
velocities in the spectrum, we thoroughly test a fourth-body hypothesis - a
perturbation by a dim, yet-unobserved object. We use an N-body numerical
integrator to simulate future and past orbital evolution of 3 or 4 components
in this system. We construct a suitable chi^2 metric from all available
speckle-interferometry, minima-timings and radial-velocity data and we scan a
part of a parameter space to get at least some of allowed solutions. In
principle, we are able to explain all observable quantities by a presence of a
fourth body, but the resulting likelihood of this hypothesis is very low. We
also discuss other theoretical explanations of the minima timings variations.
Further observations of the minima timings during the next decade or
high-resolution spectroscopic data can significantly constrain the model
Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri
Radial-velocity variations of the H-alpha emission measured on the steep
wings of the H-alpha line, prewhitened for the long-time changes, vary
periodically with a period of (218.025 +/- 0.022)d, confirming the suspected
binary nature of the bright Be star Pleione, a member of the Pleiades cluster.
The orbit seems to have a high eccentricity over 0.7, but we also briefly
discuss the possibility that the true orbit is circular and that the
eccentricity is spurious owing to the phase-dependent effects of the
circumstellar matter. The projected angular separation of the spectroscopic
orbit is large enough to allow the detection of the binary with large optical
interferometers, provided the magnitude difference primary - secondary is not
too large. Since our data cover the onset of a new shell phase up to
development of a metallic shell spectrum, we also briefly discuss the recent
long-term changes. We confirm the formation of a new envelope, coexisting with
the previous one, at the onset of the new shell phase. We find that the full
width at half maximum of the H-alpha profile has been decreasing with time for
both envelopes. In this connection, we briefly discuss Hirata's hypothesis of
precessing gaseous disk and possible alternative scenarios of the observed
long-term changes
UX Monocerotis as a W Serpentis binary
Using our new photometric and spectroscopic observations as well as all
available published data, we present a new interpretation of the properties of
the peculiar emission-line binary UX Mon. We conclude that this binary is in a
rare phase of fast mass transfer between the binary components prior to the
mass ratio reversal. We firmly establish that the orbital period is secularly
decreasing at a rate of seconds per year. From several lines
of reasoning, we show that the mass ratio of the component losing mass to the
mass-gaining component must be larger than 1 and find our most probable
value to be . The BINSYN suite of programs and the steepest
descent method were used to perform the final modeling. We modeled the star as
a W Ser star with a thick disk around its primary. Although the remaining
uncertainties in some of the basic physical elements describing the system in
our model are not negligible, the model is in fair agreement with available
observations. Only the nature of the light variations outside the primary
eclipse remains unexplained
The orbital elements and physical properties of the eclipsing binary BD+36 3317, a probable member of Lyr cluster
Context. The fact that eclipsing binaries belong to a stellar group is
useful, because the former can be used to estimate distance and additional
properties of the latter, and vice versa. Aims. Our goal is to analyse new
spectroscopic observations of BD along with the photometric
observations from the literature and, for the first time, to derive all basic
physical properties of this binary. We aim to find out whether the binary is
indeed a member of the Lyr open cluster. Methods. The spectra were
reduced using the IRAF program and the radial velocities were measured with the
program SPEFO. The line spectra of both components were disentangled with the
program KOREL and compared to a grid of synthetic spectra. The final combined
radial-velocity and photometric solution was obtained with the program PHOEBE.
Results. We obtained the following physical elements of BD: , , , , ,
. We derived the effective temperatures
K, K. Both components
are located close to ZAMS in the Hertzsprung-Russell (HR) diagram and their
masses and radii are consistent with the predictions of stellar evolutionary
models. Our results imply the average distance to the system d = pc.
We re-investigated the membership of BD in the Lyr
cluster and confirmed it. The distance to BD, given above,
therefore represents an accurate estimate of the true distance for Lyr
cluster. Conclusions. The reality of the Lyr cluster and the cluster
membership of BD have been reinforced.Comment: 10 pages, 7 figures. Accepted for publication in A&
A new study of the spectroscopic binary 7 Vul with a Be star primary
We confirmed the binary nature of the Be star 7~Vul, derived a~more accurate
spectroscopic orbit with an orbital period of (69.4212+/-0.0034) d, and
improved the knowledge of the basic physical elements of the system. Analyzing
available photometry and the strength of the \ha emission, we also document the
long-term spectral variations of the Be primary. In addition, we confirmed
rapid light changes with a~period of 0.5592 d, which is comparable to the
expected rotational period of the Be primary, but note that its amplitude and
possibly its period vary with time. We were able to disentangle only the He I
6678 A line of the secondary, which could support our tentative conclusion that
the secondary appears to be a hot subdwarf. A search for this object in
high-dispersion far-UV spectra could provide confirmation. Probable masses of
the binary components are ()~Mnom \ and ()~Mnom. If the
presence of a hot subdwarf is firmly confirmed, 7 Vul might be identified as a
rare object with a B4-B5 primary; all Be + hot subdwarf systems found so far
contain B0-B3 primaries.Comment: 17 pages, 23 figures, accepted for publication in Astronomy and
Astrophysic
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