Elena Schilbach

THE PPMXL CATALOG OF POSITIONS AND PROPER MOTIONS ON THE ICRS. COMBINING USNO-B1.0 AND THE TWO MICRON ALL SKY SURVEY (2MASS)

USNO-B1.0 and the Two Micron All Sky Survey (2MASS) are the most widely used all-sky surveys. However, 2MASS has no proper motions at all, and USNO-B1.0 published only relative, not absolute (i.e., on the International Celestial Reference Frame (ICRS), proper motions. We performed a new determination of mean positions and proper motions on the ICRS system by combining USNO-B1.0 and 2MASS astrometry. This catalog is called PPMXL (VO access to the catalog is possible via http://vo.uni-hd.de/ppmxl), and it aims to be completed from the brightest stars down to about V ≈ 20 all sky. PPMXL contains about 900 million objects, some 410 million with 2MASS photometry, and is the largest collection of ICRS proper motions at present. As representative for the ICRS, we chose PPMX. The recently released UCAC3 could not be used because we found plate-dependent distortions in its proper motion system north of –20° declination. UCAC3 served as an intermediate system for δ ≤ –20°. The resulting typical individual mean errors of the proper motions range from 4 mas yr–1 to more than 10 mas yr–1 depending on observational history. The mean errors of positions at epoch 2000.0 are 80-120 mas, if 2MASS astrometry could be used, 150-300 mas else. We also give correction tables to convert USNO-B1.0 observations of, e.g., minor planets to the ICRS system.

The radial velocity experiment (RAVE): First data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, and surface gravity) of up to one million stars using the Six Degree Field multiobject spectrograph on the 1.2 m UK Schmidt Telescope of the Anglo-Australian Observatory. The RAVE program started in 2003, obtaining medium-resolution spectra (median R 1⁄4 7500) in the Ca-triplet region (8410–8795 8) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9 < I < 12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including reobservations). Those data were obtained on 67 nights between 2003 April 11 and 2004 April 3. The total sky coverage within this data release is 4760 deg. The average signal-to-noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km s . Combining internal errors and zero-point errors, the mode is found to be 2 km s . Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km s . We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal-to-noise ratio. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2, and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS, and the TwoMicron All Sky Survey). The data release can be accessed via the RAVE Web site.

Astrophysical parameters of galactic open clusters

We present a catalogue of astrophysical data for 520 Galactic open clusters. These are the clusters for which at least three most probable members (18 on average) could be identified in the ASCC-2.5, a catalogue of stars based on the Tycho-2 observations from the Hipparcos mission. We applied homogeneous methods and algorithms to determine angular sizes of cluster cores and coronae, heliocentric distances, mean proper motions, mean radial velocities, and ages. For the first time we derive distances for 200 clusters, radial velocities for 94 clusters, and ages of 196 clusters. This homogeneous new parameter set is compared with earlier determinations, where we find, in particular, that the angular sizes were systematically underestimated in the literature.

Global survey of star clusters in the Milky Way - II. The catalogue of basic parameters

Context. Although they are the main constituents of the Galactic disk population, for half of the open clusters in the Milky Way reported in the literature nothing is known except the raw position and an approximate size. Aims. The main goal of this study is to determine a full set of uniform spatial, structural, kinematic, and astrophysical param eters for as many known open clusters as possible. Methods. On the basis of stellar data from PPMXL and 2MASS, we used a dedicated data-processing pipeline to determine kinematic and photometric membership probabilities for stars in a cluster region. Results. For an input list of 3784 targets from the literature, we confi rm that 3006 are real objects, the vast majority of them are open clusters, but associations and globular clusters are also p resent. For each confirmed object we determined the exact pos ition of the cluster centre, the apparent size, proper motion, distance , colour excess, and age. For about 1500 clusters, these basic astrophysical parameters have been determined for the first time. For the bu lk of the clusters we also derived the tidal radius. We estimated additionally average radial velocities for more than 30% of the confirmed clusters. The present sample (called MWSC) reaches both the central parts of the Milky Way and its outer regions. It is almost complete up to 1.8 kpc from the Sun and also covers neighbouring spiral arms. However, for a small subset of the oldest open clusters (log t & 9) we found some evidence of incompleteness within about 1 kpc from the Sun.

The Radial Velocity Experiment (RAVE)

We present the second data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity, and rotational velocity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution specUniversity of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia Astrophysikalisches Institut Potsdam, Potsdam, Germany Observatoire de Strasbourg, Strasbourg, France INAF, Osservatorio Astronomico di Padova, Sede di Asiago, Italy RSAA, Australian national University, Canberra, Australia Anglo Australian Observatory, Sydney, Australia Johns Hopkins University, Baltimore MD, USA Macquarie University, Sydney, Australia Institute of Astronomy, University of Cambridge, UK e2v Centre for Electronic Imaging, School of Engineering and Design, Brunel University, Uxbridge, UK Astronomisches Rechen-Institut, Center for Astronomy of the University of Heidelberg, Heidelberg, Germany Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands University of Victoria, Victoria, Canada Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Australia Rudolf Pierls Center for Theoretical Physics, University of Oxford, UK Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia Sterrewacht Leiden, University of Leiden, Leiden, the Netherlands University of Leicester, Leicester, UK MPI fuer extraterrestrische Physik, Garching, Germany University of Central Lancashire, Preston, UK University of Rochester, Rochester NY, USA University of Edinburgh, Edinburgh, UK

109 new Galactic open clusters

We present a list of 130 Galactic Open Clusters, found in the All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5). For these clusters we determined a homogeneous set of astrophysical parameters such as size, membership, motion, distance and age. In a previous work, 520 already-known open clusters out of a sample of 1700 clusters from the literature were confirmed in the ASCC-2.5 using independent, objective methods. Using these methods the whole sky was systematically screened for new clusters. The newly detected clusters show the same distribution over the sky as the known ones. It is found that without the a priori knowledge about existing clusters our search lead to clusters which are, on average, brighter, have more members and cover larger angular radii than the 520 previously-known ones.

Astrophysical supplements to the ASCC‐2.5: Ia. Radial velocities of ∼55000 stars and mean radial velocities of 516 Galactic open clusters and associations

We present the 2nd version of the Catalogue of Radial Velocities with Astrometric Data (CRVAD-2). This is the result of the cross-identification of stars from the All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5) with the General Catalogue of Radial Velocities and with other recently published radial velocity lists and catalogues. The CRVAD-2 includes accurate J2000 equatorial coordinates, proper motions and trigonometric parallaxes in the Hipparcos system, B, V photometry in the Johnson system, spectral types, radial velocities (RVs), multiplicity and variability flags for 54907 ASCC-2.5 stars. We have used the CRVAD-2 for a new determination of mean RVs of 363 open clusters and stellar associations considering their established members from proper motions and photometry in the ASCC-2.5. For 330 clusters and associations we compiled previously published mean RVs from the literature, critically reviewed and partly revised them. The resulting Catalogue of Radial Velocities of Open Clusters and Associations (CRVOCA) contains about 460 open clusters and about 60 stellar associations in the Solar neighbourhood. These numbers still represent less than 30% of the total number of about 1820 objects currently known in the Galaxy. The mean RVs of young clusters are generally better known than those of older ones. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tidal radii and masses of open clusters

Context. In a previous paper we obtained King’s parameters for 236 of 650 Galactic open clusters identified in the ASCC-2.5. Aims. Estimating tidal radii by use of observable parameters available for all clusters. Bias-free results are required. Methods. We use methods of stellar statistics and develop a semi-empirical model of open clusters. Results. We check two effects impacting the determination of tidal radii from a fitting of King’s profiles to the observed density distribution, i.e., ellipticity of open clusters and a bias depending on distances. Though a typical cluster has an elliptical form, the effect is rather weak to produce a prominent bias in the resulting tidal radii. In contrast, a distance dependent bias is not negligible and can cause a systematic underestimation of tidal radii computed with ASCC-2.5 data by a factor of two for the most distant clusters of our sample. This finding is used to correct the original results for 236 clusters and to extend the system of tidal radii and masses to all 650 clusters. We found that the semi-major axis of the projected distribution of cluster members on the sky is a parameter suited to estimate tidal radii of open clusters of our sample. No systematic differences are found between measured and calibrated tidal radii. From the comparison with mass estimates based on star counts and on the assumption of the Salpeter IMF, empirical evidence is obtained for an evolution of cluster mass functions starting in young clusters. Conclusions. The set of homogeneous parameters available for all clusters of our sample is extended by tidal radius and mass. Within 850 pc where our sample is complete, the distributions of tidal radii and masses peak at rt ≈ 6p c and logMc/m� ≈ 2.5, respectively. In young open clusters, the mass distributions show differences to the Salpeter IMF, and this discrepancy increases with cluster age.

On the origin of field O-type stars

Aims. We aim to identify the origins of field O-stars in the nearest 2 to 3 kpc around the Sun using the best presently available kinematic data on O-stars and on young open clusters. We investigate the question of whether the present-day data are consistent with the assumption that O-stars have formed in groups (clusters, associations), or in isolation. Methods. We apply the epicycle theory to back-trace the orbits of O-type stars and of candidate parent open clusters. Results. From the 370 O-stars in the “Galactic O star catalog v 2.0” (GOSV2) we have investigated 93 stars classified as field ,a nd found the origin for 73 of them in 48 open clusters younger than 30 Myr. Only for 32 stars or about 9% of all O-stars from this catalogue is the question of their origin in groups not solved; some of them may have originated in isolation or may have disintegrated the group in which they formed. Fifty percent of the young open clusters (age < 30 Myr) in the “Catalogue of Open Cluster Data” (COCD) have O-stars as members, or have ejected at least one O-star in the first 10 Myr of their life, or both. During this period the

Towards absolute scales for the radii and masses of open clusters

Aims. In this paper we derive tidal radii and masses of open clusters in the nearest kiloparsecs around the Sun. Methods. For each cluster, the mass is estimated from tidal radii determined from a fitting of three-parameter King profiles to the observed integrated density distribution. Different samples of members are investigated. Results. For 236 open clusters, all contained in the catalogue ASCC-2.5, we obtain core and tidal radii, as well as tidal masses. The distributions of 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 between 15% and 50%, whereas, for the majority of clusters, the tidal radius was determined with a relative accuracy better than 20%. Most of the clusters have tidal masses between 50 and 1000 m� , and for about half of the clusters, the masses were obtained with a relative error better than 50%.