25 research outputs found
LSS 1135: an O-Type Spectroscopic Binary in the galactic OB association Bochum 7
From radial velocities derived from optical spectroscopic observations
performed at CTIO, Chile, and CASLEO, Argentina, we have discovered that LSS
1135 is a single--lined O-type binary system with an orbital period of 2.7532
days. We present an analysis of the orbital elements of this system based on
radial velocities of the He absorption lines. We classify the spectrum of LSS
1135 as O6.5V((f)). We also present spectral classifications and radial
velocities for other seven OB stars in the region of Bochum 7, an OB
association to which LSS 1135 belongs. Our data indicate a distance of 5.0 kpc
for this star group.Comment: 5 pages, 4 figures, many tables, uses aa.cls version 4.05. Accepted
for publication in A&
UBV-IR photometry and optical spectroscopy of the galactic OB association Bochum 7
The lack of tightly bound and easily identifiable young open clusters leads to the quest for OB associations as tracers of spiral arms. Massive stars are usually found in groups, and the presence of a WolfRayet star, WR12 in the catalogue of galactic WR stars (van der Hucht 2001), at α=8h44m47.2s , ÎŽ=â45âŠ58â55.5â (J2000.0), triggered the search for an surrounding OB association, now known as Bochum7 (Moffat & Vogt 1975)
Neutral Gas Bubbles Surrounding Southern Optical Ring Nebulae: Anon(WR23) and RCW52
Utilizando datos interferom Ă©tricos de la l Ănea de 21 cm del H I analizamos la distribuci Ăłn del hidr Ăłgeno neutroen la vecindad de las nebulosas anillo Ăłpticas alrededor de las estrellas WR23 (WC6) y LS 1887 (O8V). Identificamos sendas burbujas de gas neutro interestelar asociadas a las nebulosas anillo Anon(WR23) y RCW52.Based on interferometric H I 21 cm line data we analyze the distribution of the neutral hydrogen in the environsof the optical ring nebulae around WR23 (WC6) and LS 1887 (O8V). We identify the interstellar atomic gasbubbles associated with the optical ring nebulae Anon(WR23) and RCW52
Hubble Space Telescope Imaging of the WR 38/WR38a Cluster
We are conducting a high angular resolution imaging survey of Galactic
Wolf-Rayet stars using the Wide Field and Planetary Camera 2 aboard the Hubble
Space Telescope. We have found a small stellar cluster associated with the
faint, close pair WR 38 and WR 38a. We present astrometric measurements and
photometry in the wide-band F336W (U), F439W (B), and F555W (V) filter system
for these cluster and nearby stars. We compare their colors and magnitudes with
calibrated model results for reddened stars to identify seven probable main
sequence members of the cluster. A least-squares fit of the colors and
magnitudes of this set yields a cluster reddening of E(B-V) = 1.45 +/- 0.14 mag
and a distance of 3.7^{+3.8}_{-1.2} kpc. We discuss the relationship of this
cluster to other objects along the line of sight, and we argue that the
distance probably lies in the range 5 - 8 kpc (but is not as great as 14.5 kpc
distance recently advocated by Shorlin, Turner, & Pedreros). At a distance of 8
kpc, the cluster would reside in a dense region of the Carina spiral arm, close
to a giant molecular cloud and the starburst cluster NGC 3603.Comment: Submitted to AJ, 24 pages, 3 figures Content is significantly change
The highly polarized open cluster Trumpler 27
We have carried out multicolor linear polarimetry (UBVRI) of the brightest
stars in the area of the open cluster Trumpler 27. Our data show a high level
of polarization in the stellar light with a considerable dispersion, from to . The polarization vectors of the cluster members appear to be
aligned. Foreground polarization was estimated from the data of some non-member
objects, for which two different components were resolved: the first one
associated with a dust cloud close to the Sun producing
and degrees, and a second component, the main source of
polarization for the cluster members, originated in another dust cloud, which
polarizes the light in the direction of degrees. From a detailed
analysis, we found that the two components have associated values for the first one, and for the other. Due the
difference in the orientation of both polarization vectors, almost 90 degrees
(180 degrees at the Stokes representation), the first cloud (
degrees) depolarize the light strongly polarized by the second one ( degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in
A
Spatially resolved STIS spectra of WR+OB binaries with colliding winds
We present spatially resolved spectra of the visual WR+OB massive binaries
WR86, WR146, and WR147, obtained with the Space Telescope Imaging Spectrograph
on board the Hubble Space Telescope. The systems are classified as follows:
WR86 = WC7 + B0 III, WR146 = WC6 + O8 I-IIf, WR147 = WN8 + O5-7 I-II(f). Both
WR146 and WR147 are known to have strong non-thermal radio emission arising in
a wind-wind collision shock zone between the WR and OB components. We find that
the spectra of their O companions show Halpha profiles in emission, indicative
of large mass-loss rates, and consistent with the colliding-wind model. Our
spectra indicate that the B component in WR86 has a low mass-loss rate, which
possibly explains the fact that WR86, despite being a long period WR+OB binary,
was not found to be a strong non-thermal radio emitter. Because of the small
mass-loss rate of the B star component in WR86, the wind collision region must
be closer to the B star and smaller in effective area, hence generating smaller
amounts of non-thermal radio emission. Absolute magnitudes for all the stars
are estimated based on the spectral types of the components (based on the
tables by Schmidt-Kaler for OB stars, and van der Hucht for WR stars), and
compared with actual, observed magnitude differences. While the derived
luminosities for the WC7 and B0 III stars in WR86 are consistent with the
observed magnitude difference, we find a discrepancy of at least 1.5 magnitudes
between the observed luminosities of the components in each of WR146 and WR147
and the absolute magnitudes expected from their spectral types. In both cases,
it looks as though either the WR components are about 2 magnitudes too bright
for their spectral types, or that the O components are about 2 magnitudes too
faint. We discuss possible explanations for this apparent discrepancy.Comment: Accepted for publication in the Astronomical Journa
A short history and other stories of binary stars
Se presenta una corta historia de estrellas binarias desde los primeros descubrimientos. Se discuten ejemplos actualmente conocidos de sistemas con componentes de temperatura y masas mas altas.A short history of binary stars from the first discoveries is presented. Exam- ples of currently known binary Systems with components of highest temperature and mass are discussed
Magellanic Cloud WC/WO Wolf-Rayet stars : II. Colliding winds in binaries
A search for evidence of colliding winds is undertaken among the four certain Magellanic Cloud WC/WO spectroscopic binaries found in the companion Paper I, as well as among two Galactic WC/WO binaries of very similar subtype. Two methods of analysis, which allow the determination of orbital inclination and parameters relating to the shock cone from spectroscopic studies of colliding winds, are attempted. In the first method, LĂŒhrsâ spectroscopic model is fitted to the moderately strong C iii 5696-Ă
excess line emission arising in the shock cone for the stars Br22 and WR 9. The four other systems show only very weak C iii 5696-Ă
emission. LĂŒhrsâ model follows well the mean displacement of the line in velocity space, but is unable to reproduce details in the line profile and fails to give a reliable estimate of the orbital inclination. In the second method, an alternative attempt is also made to fit the variation of more global quantities, full width at half-maximum and radial velocity of the excess emission, with phase. This method also gives satisfactory results in a qualitative way, but shows numerical degeneracy with orbital inclination. Colliding wind effects on the very strong C iv 5808-Ă
WolfâRayet emission line, present in all six binaries, are also found to behave qualitatively as expected. After allowing for line enhancement in colliding wind binaries, it now appears that all Magellanic Cloud WC/WO stars occupy a very narrow range in spectral subclass: WC4/WO3.Facultad de Ciencias AstronĂłmicas y GeofĂsica
Magellanic Cloud WC/WO Wolf-Rayet stars : I. Binary frequency and Roche lobe overflow formation
A nearly complete sample of 24 Magellanic Cloud WC/WO subclass WolfâRayet stars is studied spectroscopically and photometrically to determine its binary frequency. Theory predicts the Roche lobe overflow produced WolfâRayet binary frequency to be 52±14 per cent in the Large Magellanic Cloud and 100 per cent in the Small Magellanic Cloud, not counting non-Roche lobe overflow WolfâRayet binaries. Lower ambient metallicity (Z) leads to lower opacity, preventing all but the most massive (hence luminous) single stars from reaching the WolfâRayet stage. However, theory predicts that Roche lobe overflow even in binaries of modest mass will lead to WolfâRayet stars in binaries with periods below approximately 200 d, for initial periods below approximately 1000 d, independent of Z. By examining their absolute continuum magnitudes, radial velocity variations, emission-line equivalent widths and full widths at half-maximum, a WC/WO binary frequency of only 13 per cent, significantly lower than the prediction, is found in the Large Magellanic Cloud. In the unlikely event that all of the cases with a less certain binary status actually turn out to be binary, current theory and observation would agree. (The Small Magellanic Cloud contains only one WC/WO star, which happens to be a binary.) The three WC+O binaries in the Large Magellanic Cloud all have periods well below 1000 d. The large majority of WC/WO stars in such environments apparently can form without the aid of a binary companion. Current evolutionary scenarios appear to have difficulty explaining either the relatively large number of WolfâRayet stars in the Magellanic Clouds, or the formation of WolfâRayet stars in general.Facultad de Ciencias AstronĂłmicas y GeofĂsica