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 , δ=−45◦58’55.5” (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 étricos de la l ínea de 21 cm del H I analizamos la distribuci ón del hidr ógeno neutroen la vecindad de las nebulosas anillo ópticas 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 $P = 4$ to $P = 9.5$. 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 $P_{\lambda max}=1.3$ and $\theta=146$ 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 $\theta= 29.5$ degrees. From a detailed analysis, we found that the two components have associated values $E_{B-V} < 0.45$ for the first one, and $E_{B-V} > 0.75$ 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 ($\theta \sim 146$ degrees) depolarize the light strongly polarized by the second one ($\theta \sim 29.5$ 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

Optical Spectroscopy of X-Mega Targets in Carina Nebula

Optical spectroscopy of CPD-59° 2635, one of the O-type stars in the open cluster Trumpler 16 in the Carina Nebula, reveals this star to be a double-lined binary system. We have obtained the first radial velocity orbit for this system, consisting of a circular solution with a period of 2.2999 d and semi-amplitudes of 208 and 273 km s−1. This results in minimum masses of 15 and 11 M? for the binary components of CPD-59° 2635, which we classified as O8V and O9.5V, although spectral type variations of the order of 1 subclass, which we identify as the Struve–Sahade effect, seem to be present in both components. From ROSAT HRI observations of CPD −59° 2635 we determine a luminosity ratio log(Lx/Lbol)≈−7, which is similar to that observed for other O-type stars in the Carina Nebula region. No evidence of light variations is present in the available optical or X-ray data sets

HI bubbles surrounding southern optical ring nebulae: Anon(WR 23) and RCW 52

We analyze the interstellar medium in the environs of two hot and massive stars, HD 92809 (= WR 23, WC6) and LSS 1887 (O8V), which ionize the optical ring nebulae Anon(WR 23) and RCW 52, respectively. Our analysis is based on neutral hydrogen (Hi) 21cm line data, which reveal interstellar bubbles surrounding the massive stars and their optical ring nebulae. The Hi bubble related to WR 23 is 13.3 pc in radius and is expanding at 10 km s −1 . The associated atomic neutral mass amounts to 830 M . The Hi structure related to LSS 1887 is about 6.3 pc in radius, has an expansion velocity of 7 km s −1 and an associated atomic neutral mass of 100 M . These Hi features are the neutral counterparts of the optical ring nebulae and were mainly created by the action of the stellar winds of the massive stars on their environs. The dynamical age of the Hi bubble around WR 23 (7×105 yr) suggests that it was created during the WR phase of stellar evolution. However, the large tangential motions of WR 23 and LSS 1887 suggest that part of the observed optical and Hi structures may be due to a bow shock. The analysis of the distribution of emission in the far infrared and in the CO(1-0) molecular line in the environs of WR 23 and LSS 1887, reveals that there are also infrared and molecular counterparts of the detected Hi bubbles.Fil: Cappa, Cristina Elisabeth. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Niemela, Virpi S.. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Martin, Maria Cristina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: McClure Griffiths, Naomi M.. Australia Telescope National Facility; Australi