170 research outputs found
Notes on the disentangling of spectra I. Enhancement in precision
Context: The technique of disentangling has been applied to numerous
high-precision studies of spectroscopic binaries and multiple stars. Although,
its possibilities have not yet been fully understood and exploited. Aims:
Theoretical background aspects of the method, its latest improvements and hints
for its use in practice are explained in this series of papers. Methods: In
this first paper of the series, we discuss spectral-resolution limitations due
to a discrete representation of the observed spectra and introduce a new method
how to achieve a precision higher than the step of input-data binning. Results:
Based on this principle, the latest version of the KOREL code for Fourier
disentangling achieves an increase in precision for an order of magnitude.Comment: 2 figure
Disentangling telluric lines in stellar spectra
The use of a method of spectra disentangling for telluric lines is explained
in detail, with a particular emphasis on high-precision radial-velocity
measurements for the search for extrasolar planets. New improvements to the
method are introduced.Comment: Accepted for publication in Astronomy and Astrophysic
Notes on disentangling of spectra II. Intrinsic line-profile variability due to Cepheid pulsations
The determination of pulsation velocities from observed spectra of Cepheids
is needed for the Baade-Wesselink calibration of these primary distance
markers. The applicability of the Fourier-disentangling technique for the
determination of pulsation velocities of Cepheids and other pulsating stars is
studied. The KOREL-code was modified to enable fitting of free parameters of a
prescribed line-profile broadening function corresponding to the radial
pulsations of the stellar atmosphere. It was applied to spectra of delta Cep in
the H-alpha region observed with the Ondrejov 2-m telescope. The telluric lines
were removed using template-constrained disentangling, phase-locked variations
of line-strengths were measured and the curves of pulsational velocities
obtained for several spectral lines. It is shown that the amplitude and phase
of the velocities and line-strength variations depend on the depth of line
formation and the excitation potential. The disentangling of pulsations in the
Cepheid spectra may be used for distance determination
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&
A naked-eye triple system with a nonaccreting black hole in the inner binary
Several dozen optical echelle spectra demonstrate that HR 6819 is a
hierarchical triple. A classical Be star is in a wide orbit with an
unconstrained period around an inner 40 d binary consisting of a B3 III star
and an unseen companion in a circular orbit. The radial-velocity semi-amplitude
of 61.3 km/s of the inner star and its minimum (probable) mass of 5.0 Msun (6.3
+- 0.7 Msun) imply a mass of the unseen object of >= 4.2 Msun (>= 5.0 +- 0.4
Msun), that is, a black hole (BH). The spectroscopic time series is stunningly
similar to observations of LB-1. A similar triple-star architecture of LB-1
would reduce the mass of the BH in LB-1 from ~70 Msun to a level more typical
of Galactic stellar remnant BHs. The BH in HR 6819 probably is the closest
known BH to the Sun, and together with LB-1, suggests a population of quiet
BHs. Its embedment in a hierarchical triple structure may be of interest for
models of merging double BHs or BH + neutron star binaries. Other triple stars
with an outer Be star but without BH are identified; through stripping, such
systems may become a source of single Be stars.Comment: Accepted as Letter to the Editor for A&
Really focused stellar winds in X-ray binaries
We investigate the anisotropy of stellar winds in binaries to improve the
models of accretion in high-mass X-ray binaries. We model numerically the
stellar wind from a supergiant component of a binary in radial and
three-dimensional radiation hydrodynamic approximation taking into account the
Roche potential, Coriolis force, and radiative pressure in the continuum and
spectral lines. The Coriolis force influences substantially the mass loss and
thus also the accretion rate. The focusing of the stellar wind by the
gravitational field of the compact companion leads to the formation of a
gaseous tail behind the companion.Comment: 10 figure
First detailed analysis of multiple system V2083 Cyg
Main aim of this paper is the first detailed analysis of multiple system
V2083 Cyg and to reveal its basic physical properties. The system was studied
by method of the light and radial velocity curves analysis, together with the
interferometric data of the visual pair obtained during a last century. There
was found that the close subsystem contains two very similar stars of spectral
type A7-8. Moreover, the third body is orbiting around this pair with period of
about 177 years. Due to the discrepancy of total mass as derived from two
methods, there arises that the third body is maybe also a binary, or some
object with lower luminosity but higher mass than normal main-sequence star.
Another explanation is that the Hipparcos value of parallax is incorrect and
the system is much closer to the Sun.Comment: 6 pages, 4 figures, published in 2012MNRAS.421.1196
CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Mon
Analyses of very accurate CoRoT space photometry, past Johnson V
photoelectric photometry and high-resolution \'echelle spectra led to the
determination of improved and consistent fundamental stellar properties of both
components of AU Mon. We derived new, accurate ephemerides for both the orbital
motion (with a period of 11.113d) and the long-term, overall brightness
variation (with a period of 416.9d) of this strongly interacting Be + G
semi-detached binary. It is shown that this long-term variation must be due to
attenuation of the total light by some variable circumbinary material. We
derived the binary mass ratio = 0.17\p0.03 based on the
assumption that the G-type secondary fills its Roche lobe and rotates
synchronously. Using this value of the mass ratio as well as the radial
velocities of the G-star, we obtained a consistent light curve model and
improved estimates of the stellar masses, radii, luminosities and effective
temperatures. We demonstrate that the observed lines of the B-type primary may
not be of photospheric origin. We also discover rapid and periodic light
changes visible in the high-quality residual CoRoT light curves. AU Mon is put
into perspective by a comparison with known binaries exhibiting long-term
cyclic light changes.Comment: Accepted for publication in MNRA
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