22 research outputs found
Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system
Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the
youngest and nearest high-mass stars (O5-O7) and also known to be a close
binary system. Using new multi-epoch visual and near-infrared bispectrum
speckle interferometric observations obtained at the BTA 6 m telescope, and
IOTA near-infrared long-baseline interferometry, we trace the orbital motion of
the Theta 1 Ori C components over the interval 1997.8 to 2005.9, covering a
significant arc of the orbit. Besides fitting the relative position and the
flux ratio, we apply aperture synthesis techniques to our IOTA data to
reconstruct a model-independent image of the Theta 1 Ori C binary system.
The orbital solutions suggest a high eccentricity (e approx. 0.91) and
short-period (P approx. 10.9 yrs) orbit. As the current astrometric data only
allows rather weak constraints on the total dynamical mass, we present the two
best-fit orbits. From these orbital solutions one can be favoured, implying a
system mass of 48 M_sun and a distance to the Trapezium cluster of 434 pc. When
also taking the measured flux ratio and the derived location in the HR-diagram
into account, we find good agreement for all observables, assuming a spectral
type of O5.5 for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun).
We find indications that the companion C2 is massive itself, which makes it
likely that its contribution to the intense UV radiation field of the Trapezium
cluster is non-negligible. Furthermore, the high eccentricity of the
preliminary orbit solution predicts a very small physical separation during
periastron passage (approx. 1.5 AU, next passage around 2007.5), suggesting
strong wind-wind interaction between the two O stars.Comment: 13 pages, 9 figures, Accepted for publication in Astronomy &
Astrophysic
Chandra Observations of Variable Embedded X-ray sources in Orion. Paper I: Resolving Orion Trapezium
We used the High Energy Transmission Grating Spectrometer (HETGS) onboard the
Chandra X-ray Observatory to perform two observations, separated by three
weeks, of the Orion Trapezium region. The zeroth order images on the Advanced
CCD Imaging Spectrometer (ACIS) provide spatial resolution of 0.5" and moderate
energy resolution. Within a 160"x140" region around the Orion Trapezium we
resolve 111 X-ray sources with luminosities between 7x10^{28} ergs/s and
2x10^{32} ergs/s. We do not detect any diffuse emission. Many sources appear
much more heavily absorbed, with N_H in the range of 10^22 to 10^23 cm^-2. The
main objective of this paper is to study the Orion Trapezium and its close
vicinity. Most spectra of the very early type members can be fit with a
two-temperature thermal spectrum with a soft component of kT ~ 0.8 keV and a
hard component of kT ~ 2 to 3 keV. We discuss these results in the context of
stellar wind models. We detect eight additional, mostly variable X-ray sources
in the close vicinity of the Trapezium. Five of these X-rays sources are
identified with proplyds and we argue that the X-ray emission originates from
class I, II and III protostars at the cores of the proplyds.Comment: 12 pages, 3 figures, accepted for publication in The Astrophysical
Journa
Preliminary results of the alignment and Hartmann tests of the AZT-22 telescope
The AZT-22 telescope installed in Turkey (Antalia) was aligned and tested on stars by the Hartmann method. The rms normal deviation of an equivalent optical system is 0.040 ± 0.016 μm. The circle of confusion is 0.40 ± 0.04 arcsec in diameter at a 50% energy level. © 2001 MAIK "Nauka/Interperiodica"
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