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Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-Mass Star-Forming Regions
In this paper, we present VLT/SINFONI integral field spectroscopy of RCW34 along with Spitzer/IRAC photometry of the surroundings. RCW 34consists of three different regions. A large bubble has been detected inthe IRAC images in which a cluster of intermediate- and low-mass classII objects is found. At the northern edge of this bubble, an H II regionis located, ionized by 3 OB stars, of which the most massive star hasspectral type O8.5V. Intermediate-mass stars (2-3 M sun) aredetected of G- and K-spectral type. These stars are still in thepre-main-sequence (PMS) phase. North of the H II region, aphoton-dominated region is present, marking the edge of a densemolecular cloud traced by H2 emission. Several class 0/Iobjects are associated with this cloud, indicating that star formationis still taking place. The distance to RCW 34 is revised to 2.5 ±0.2 kpc and an age estimate of 2 ± 1 Myr is derived from theproperties of the PMS stars inside the H II region. Between the class IIsources in the bubble and the PMS stars in the H II region, no agedifference could be detected with the present data. The presence of theclass 0/I sources in the molecular cloud, however, suggests that theobjects inside the molecular cloud are significantly younger. The mostlikely scenario for the formation of the three regions is that starformation propagated from south to north. First the bubble is formed,produced by intermediate- and low-mass stars only, after that, the H IIregion is formed from a dense core at the edge of the molecular cloud,resulting in the expansion similar to a champagne flow. More recently,star formation occurred in the rest of the molecular cloud. Twodifferent formation scenarios are possible. (1) The bubble with thecluster of low- and intermediate-mass stars triggered the formation ofthe O star at the edge of the molecular cloud, which in its turn inducesthe current star formation in the molecular cloud. (2) An externaltriggering is responsible for the star formation propagating from southto north.Based on observations collected at the European Southern Observatory atParanal, Chile (ESO program 078.C-0780).
| The young, tight, and low-mass binary TWA22AB: a new calibrator for evolutionary models?. Orbit, spectral types, and temperature
Context: Tight binaries discovered in young, nearby associations areideal targets for providing dynamical mass measurements to test thephysics of evolutionary models at young ages and very low masses. Aims: We report the binarity of TWA22 for the first time. We aim atmonitoring the orbit of this young and tight system to determine itstotal dynamical mass using an accurate distance determination. We alsointend to characterize the physical properties (luminosity, effectivetemperature, and surface gravity) of each component based onnear-infrared photometric and spectroscopic observations. Methods: We used the adaptive-optics assisted imager NACO to resolvethe components, to monitor the complete orbit and to obtain the relativenear-infrared photometry of TWA22 AB. The adaptive-optics assistedintegral field spectrometer SINFONI was also used to obtainmedium-resolution (R?=1500-2000) spectra in JHK bands.Comparison with empirical and synthetic librairies were necessary forderiving the spectral type, the effective temperature, and the surfacegravity for each component of the system. Results: Based on anaccurate trigonometric distance (17.5 ± 0.2 pc) determination, weinfer a total dynamical mass of 220 ± 21 MJup for thesystem. From the complete set of spectra, we find an effectivetemperature T_eff=2900+200-200 K for TWA22 A andT_eff=2900+200-100 K for TWA22 B and surfacegravities between 4.0 and 5.5 dex. From our photometry and an M6± 1 spectral type for both components, we find luminosities oflog(L/L?) = -2.11 ± 0.13 dex andlog(L/L?) = -2.30 ± 0.16 dex for TWA22 A and B,respectively. By comparing these parameters with evolutionary models, wequestion the age and the multiplicity of this system. We also discuss apossible underestimation of the mass predicted by evolutionary modelsfor young stars close to the substellar boundary.Based on service-mode observations (072.C-0644, 073.C-0469, 075.C-0521,076.C-0554, 078.C-0510, 080.C-0581) collected at the EuropeanOrganisation for Astronomical Research in the Southern Hemisphere,Chile.
| The Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/523
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. III. Carina Spiral Feature
Strömgren and Hβ photometry of O and B type stars, generallybrighter than 9.5 mag is reported for the field of the Carina SpiralFeature. The observations are based on the PPM catalogue identificationsand are designed to improve the completeness of the existing uvbybetadata for the bright early-type stars in the field. We present new uvbyphotometry for 283 stars and Hβ photometry for 225 of them. Theseobservations are part of an ongoing effort to study the structure ofselected star-forming regions in the Milky Way by means of uvbybetaphotometry. A comparison of the new data to other uvbybeta data sets forthis field is presented. Based on data from the Strömgren AutomaticTelescope of the Copenhagen University Observatory, La Silla. Tables 1and 2 are only available in electronic form at the CDS via anonymous ftpto 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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