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Stellar Rotation: A Clue to the Origin of High-Mass Stars?
We present the results of a study aimed at assessing whether low- andhigh-mass stars form similarly. Our approach is (1) to examine theobserved projected rotational velocities among a large sample of newlyformed stars spanning a range in mass between 0.2 and 50Msolar and (2) to search for evidence of a discontinuity inrotational properties that might indicate a difference in the stellarformation process at some characteristic mass. Our database includesrecently published values of vsini for young intermediate- and low-massstars in Orion, as well as new observations of O stars located in youngclusters and OB associations. We find that the median of the quantityvobs/vc (observed rotational speed divided byequatorial breakup velocity) is typically about 0.15 and shows noevidence of a discontinuity over the full range of stellar masses, whilethe quantity Jsini/M (derived angular momentum per unit mass) exhibits aslow, monotonic rise (J/M~M0.3) with increasing mass with noevidence of a discontinuity. We suggest that these observations are mostsimply interpreted as indicative of a single stellar formation andangular momentum regulation mechanism, one that results in rotationrates well below breakup and angular momenta per unit mass that differsystematically by no more than a factor of 3-4 over a mass rangespanning a factor of 250.
| 10 MK Gas in M17 and the Rosette Nebula: X-Ray Flows in Galactic H II Regions
We present the first high spatial resolution X-ray images of twohigh-mass star forming regions, the Omega Nebula (M17) and the RosetteNebula (NGC 2237-2246), obtained with the Chandra X-Ray ObservatoryAdvanced CCD Imaging Spectrometer instrument. The massive clusterspowering these H II regions are resolved at the arcsecond level intomore than 900 (M17) and 300 (Rosette) stellar sources similar to thoseseen in closer young stellar clusters. However, we also detect softdiffuse X-ray emission on parsec scales that is spatially and spectrallydistinct from the point-source population. The diffuse emission hasluminosity LX~=3.4×1033 ergs s-1in M17 with plasma energy components at kT~=0.13 and ~=0.6 keV (1.5 and7 MK), while in Rosette it has LX~=6×1032ergs s-1 with plasma energy components at kT~=0.06 and ~=0.8keV (0.7 and 9 MK). This extended emission most likely arises from thefast O star winds thermalized either by wind-wind collisions or by atermination shock against the surrounding media. We establish that onlya small portion of the wind energy and mass appears in the observeddiffuse X-ray plasma; in these blister H II regions, we suspect thatmost of it flows without cooling into the low-density interstellarmedium. These data provide compelling observational evidence that strongwind shocks are present in H II regions.
| On the eclipsing nature of CPD-59degr2628
The spectroscopic binary CPD -59°2628 (Sp = O9.5V) has been discovered to be a detached eclipsing binary, and we presentan analysis based on new light curves, published spectroscopy and twonew high-resolution spectra. uvby light curves from more than 2000observations are analysed with the WINK and the Wilson-Devinney (WD)programs. Geometric distortions and photometric effects from theproximity of the components are included in the computations. Thedetached system has a close circular orbit of high inclination and highmaximum projected velocities. We find a photometric period P=1fd47 whichis consistent with the spectroscopy-binary period by Solivella &Niemela (\cite{solivella&niemela99}). We use this period to rematchthe misidentified radial velocities from Levato et al.(\cite{levato&al91}) and apply them in an analysis using the methodof Lehmann-Filhes. We find that CPD -59°2628 is ayoung system close to the ZAMS. Its distance is 2.6+/-0.1 kpc and it hasa systemic velocity of -19 km s-1, confirming its membershipin the cluster Trumpler 16 (radial velocity -23.5 kms-1). The temperatures are 32 000 K for the hotter star (A)and 30 000 K for the cooler (B). We determine the absolute dimensions(solar units): M_A=14.0+/-2.0, R_A=5.29+/-0.26, M_B=11.7+/-1.8 andR_B=4.38+/-0.22. By adopting E(b-y)=0.306, we get M_{bol,A}=-6.3+/-0.1,MV,A=-3.2+/-0.1, M_{bol,B}=-5.6+/-0.1 andMV,B=-2.7+/-0.1. Theoretical stellar models from Claret(\cite{claret95}), including convective-core overshooting and mass lossfor a composition (X=0.70, Z=0.02), appear to fit the components at anage of ~ 2 Myr. Based on observations obtained at the European SouthernObservatory at La Silla, Chile (Applications 62H-0110, 62H-0110 and64.L-0031) and the South African Astronomical Observatory, Sutherland,South Africa.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| The Initial Mass Function and Massive Star Evolution in the OB Associations of the Northern Milky Way
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...454..151M&db_key=AST
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| The Einstein X-ray Observatory Catalog of O-type stars
A catalog of X-ray count rates for all O-type stars surveyed by theEinstein Observatory is presented. The procedures by which the IPC andHigh Resolution Imager rates are converted to emitted X-ray luminositiesare discussed in detail. The catalog contains 289 stars with 89detections and 176 upper bounds for the observed count rates. Precisepositions for 43 O-type stars are given whose previously known locationswere unknown or erroneous. It is argued that most O-type stars are X-raypoint sources, but some are possibly embedded in extended nebulae and/orbubbles. The X-ray spectra of O-type stars are discussed briefly, and itis argued that their mean spectrum can reasonably be taken as an 0.5 keVthermal bremsstrahlung model. It is argued that at least 30 percent ofall O-type stars are variable in X-rays.
| Catalog of BV magnitudes and spectral classes of 6000 stars
The present catalog, compiled at the Abastumani Observatory, contains BVmagnitudes and spectral classes of about 6000 stars up to V(lim) = 13.0min five circular areas of 18 sq deg located near the salactic-equatorplane. The catalog is intended for star-statistics studies ofstar-formation regions.
| UBV Photometry of NGC2244
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981PASJ...33..149O&db_key=AST
| The value of R in Monoceros
Recent photometric and spectroscopic observations are used inconjunction with other data for early-type stars in northern Monocerosin order to investigate the local value of R (the ratio of total toselective extinction). From a variable-extinction analysis, it isconcluded that a ratio of approximately 3.2 is appropriate for thegeneral interstellar extinction in this region and that there is noevidence here for the existence of local anomalies. The two majorassociations Mon OB 1 and Mon OB 2 are clearly delineated and are foundto exhibit properties typical of such young stellar groups. Derivedproperties for a few interesting stars are presented.
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| Сазвежђа: | Једнорог |
| Ректацензија: | 06h30m33.31s |
| Deклинација: | +04°41'27.6" |
| Apparent магнитуда: | 9.757 |
| Proper motion RA: | -0.9 |
| Proper motion Dec: | 0.8 |
| B-T magnitude: | 10.286 |
| V-T magnitude: | 9.801 |
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