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Towards absolute scales for the radii and masses of open clusters
Aims. In this paper we derive tidal radii and masses of open clusters inthe nearest kiloparsecs around the Sun. Methods: For each cluster, themass is estimated from tidal radii determined from a fitting ofthree-parameter King profiles to the observed integrated densitydistribution. Different samples of members are investigated. Results:For 236 open clusters, all contained in the catalogue ASCC-2.5, weobtain core and tidal radii, as well as tidal masses. The distributionsof the core and tidal radii peak at about 1.5 pc and 7-10 pc,respectively. A typical relative error of the core radius lies between15% and 50%, whereas, for the majority of clusters, the tidal radius wasdetermined with a relative accuracy better than 20%. Most of theclusters have tidal masses between 50 and 1000 m_ȯ, and for abouthalf of the clusters, the masses were obtained with a relative errorbetter than 50%.Full Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/468/151
| Revisiting the population of Galactic open clusters
We present results of a study of the galactic open cluster populationbased on the all-sky catalogue ASCC-2.5 (I/280A) compiled from Tycho-2,Hipparcos and other catalogues. The sample of optical clusters fromASCC-2.5 is complete up to about 850 pc from the Sun. The symmetry planeof the clusters' distribution is determined to be at Z_0=-22±4pc, and the scale height of open clusters is only 56±3 pc. Thetotal surface density and volume density in the symmetry plane areΣ= 114 kpc-2 and D(Z_0)=1015 kpc-3,respectively. We find the total number of open clusters in the Galacticdisk to be of order of 105 at present. Fluctuations in thespatial and velocity distributions are attributed to the existence offour open cluster complexes (OCCs) of different ages containing up to afew tens of clusters. Members in an OCC show the same kinematicbehaviour, and a narrow age spread. We find, that the youngest clustercomplex, OCC 1 (log t<7.9), with 19 deg inclination to the Galacticplane, is apparently a signature of Gould's Belt. The most abundant OCC2 complex has moderate age (log t≈8.45). The clusters of thePerseus-Auriga group, having the same age as OCC 2, but differentkinematics are seen in breaks between Perseus-Auriga clouds. The oldest(log t≈8.85) and sparsest group was identified due to a large motionin the Galactic anticentre direction. Formation rate and lifetime ofopen clusters are found to be 0.23±0.03 kpc-2Myr-1 and 322±31 Myr, respectively. This implies atotal number of cluster generations in the history of the Galaxy between30 to 40. We estimate that less than about 10% of the total Galacticstellar disk population has ever passed an open cluster membership.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| Galactic B-supergiants. II - Line strengths in the visible: Evidence for evolutionary effects?
Following the discovery by Lennon et al. (1992) of anomalously weakcarbon lines in the Galactic B-supergiants, a search was conducted forthe signatures of CNO processed material in the atmospheres of thesestars. It was found that the NII line strengths around spectral type B2correlate with luminosity, but exhibit a clear anticorrelation with theCII lines. It is suggested that this trend may be evidence for CNOprocessed material contaminating the atmospheres of the most luminousstars. The CNO processing signature was found to be most pronounced inthe more luminous supergiants, in qualitative agreement with stellarevolution calculations (provided that such stars have passed through aprevious red-supergiant phase of evolution).
| Galactic B-supergiants. I - an atlas of O9-B9 supergiant spectra from 3950 A to 4950 A
CCD spectra are presented for supergiants of spectral types O9-B9 andluminosity subclasses Ia and Ib. They cover the wavelength region fromapproximately 3950 A to 4950 A at a resolution of 0.8 A, and normallyhave a signal-to-noise in excess of 150 at 4600 A. The spectra arediscussed in respect to their classification. A number of stars showclear evidence of the 'filling in' of hydrogen lines by emission fromthe stellar wind, while HD 190603, a B1.5 Ia(+) hypergiant, exhibits anH-beta P-Cygni type line-profile. Also reported is the finding of a newnitrogen weak star, HD 13866, in the Per OB1 association which isclassified here as BC2 Ib.
| The determination of kinematic parameters of extremely young stars in the solar neighborhood using radial-velocity data and accounting for random errors in their photometric distances
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| Atlas of the wavelength dependence of ultraviolet extinction in the Galaxy
The paper presents a collection of 115 extinction curves derived fromlow-dispersion IUE spectra. The spectra have been reduced with the useof techniques designed to reduce the effects of random noise and theinfluence of residual spectral features due to classification mismatch.The magnitudes of other instrumental and interpretational uncertaintiesare estimated. The extinction curves are presented with normalization toE(B-V) = 1 and the FUV portion (below 170 nm) is also shown for E(13-17)= 1. The atlas includes examples of extinction originating in thediffuse medium and several major nebulae and dense clouds.
| A study of UV extinction towards OB associations and star-forming regions based on IUE data
Extinction curves for 115 stars were derived using the IUE data bank:70% of them belong to OB associations. The sample provides good coverageof the galactic plane including objects located as far as 4 kpc from theSun. The sample covers a variety of different areas includinginteresting objects such as the Carina Nebula and the Rho Ophiuchi DarkCloud. While the older associations and field stars show extinctioncurves very close to the MIEC, younger objects show strong variations ofthe amount of the extinction in the far UV and, in some cases, also inthe hump region.
| Structure and origin of the Cygnus superbubble
Data from radio, optical, IR, and X-ray observations of the region ofthe Cyg superbubble are compiled in tables, maps, and graphs andanalyzed in detail. It is shown that the outline of the X-raysuperbubble is reproduced by eight OB associations at distances 0.5-2.5kpc containing 110 high-luminosity stars (40 of Wolf-Rayet or Of type)which can account for 50-75 percent of the X-ray emission of thesuperbubble. The remaining emission is attributed to 100-pc-diametercoronal-gas regions formed by set stellar winds or supernova explosionsin the associations.
| La constel lacio del cigne.
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