- ID:
- ivo://CDS.VizieR/J/MNRAS/313/43
- Title:
- OB association members in ACT+TRC Catalogs
- Short Name:
- J/MNRAS/313/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hipparcos Catalogue (Cat. I/239) contains members of nearby OB associations brighter than 12th magnitude in V. However, membership lists are complete only to magnitude V=7.3. In this paper we discuss whether proper motions listed in the `Astrographic Catalogue+Tycho' reference catalogue (ACT, Cat. I/246) and the Tycho Reference Catalogue (TRC, Cat. I/250), which are complete to V~10.5mag, can be used to find additional association members. Proper motions in the ACT/TRC have an average accuracy of ~3mas/yr. We search for ACT/TRC stars which have proper motions consistent with the spatial velocity of the Hipparcos members of the nearby OB associations already identified by de Zeeuw et al. (1999, Cat. J/AJ/117/354). These stars are first selected using a convergent-point method, and then subjected to further constraints on the proper-motion distribution, magnitude and colour to narrow down the final number of candidate members. Monte Carlo simulations show that the proper-motion distribution, magnitude, and colour constraints remove ~97% of the field stars, while at the same time retain more than 90% of the cluster stars. The procedure has been applied to five nearby associations: the three subgroups of Sco OB2, plus Per OB3 and Cep OB6. In all cases except Cep OB6, we find evidence for new association members fainter than the completeness limit of the Hipparcos Catalogue. However, narrow-band photometry and/or radial velocities are needed to pinpoint the cluster members, and to study their physical characteristics.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/117/354
- Title:
- OB associations from Hipparcos
- Short Name:
- J/AJ/117/354
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound "moving groups", which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V~<6mag), with spectral types earlier than ~B5. The Hipparcos measurements allow a major improvement in this situation. Moving groups are identified in the Hipparcos Catalog by combining de Bruijne's (1999MNRAS.306..394H) refurbished convergent point method with the "Spaghetti method" of Hoogerwerf & Aguilar (1999, MNRAS, in press). Astrometric members are listed for 12 young stellar groups, out to a distance of ~650pc. These are the three subgroups Upper Scorpius, Upper Centaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as Vel OB2, Tr 10, Col 121, Per OB2, {alpha} Persei (Per OB3), Cas-Tau, Lac OB1, Cep OB2, and a new group in Cepheus, designated as Cep OB6.
- ID:
- ivo://CDS.VizieR/J/A+A/502/1015
- Title:
- OB associations in IC 1613
- Short Name:
- J/A+A/502/1015
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determining the parameters of massive stars is crucial to understand many processes in galaxies and the Universe, since these objects are important sources of ionization, chemical enrichment and momentum. 10m class telescopes enable us to perform detailed quantitative spectroscopic analyses of massive stars in other galaxies, sampling areas of different metallicity. Relating the stars to their environment is crucial to understand the physical processes ruling their formation and evolution. In preparation for the new instrumentation planned for the Gran Telescopio CANARIAS (GTC), our goal is to build a list of massive star candidates in the metal-poor irregular galaxy IC 1613. The catalogue must have very high astrometric accuracy, suitable for the current generation of multi-object spectrographs. A census of OB associations in this galaxy is also needed, to provide important additional information about the age and environment of the candidate OB stars.
- ID:
- ivo://CDS.VizieR/J/A+A/440/783
- Title:
- OB associations in NGC 7793
- Short Name:
- J/A+A/440/783
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the results from application of an objective algorithm (PLC) to find OB associations, to B and V images of the Sculptor spiral galaxy NGC 7793, which were obtained with the ESO VLT and FORS instrument and basically cover the entire spatial extent of the galaxy. We detected 148 associations. Statistical tests show that less than 6 of these detections are caused by randomly concentrated blue stars. In the size distribution, a sharp peak is observed at a value of about 35 microradians, which corresponds to a linear diameter of 135pc, assuming a distance of 3.91Mpc to the galaxy. We also find 25 much larger objects. A second application of the PLC technique shows that 20 of them are stellar complexes consisting of multiple sub-associations with typical sizes on the order of 130pc. A comparison of the size distribution of the detected OB associations in NGC 7793 with observed distributions in other galaxies suggests that the conditions in two Sculptor Group galaxies (NGC 300 and NGC 7793) favour the formation of large associations. We provide a catalog giving coordinates and physical parameters for all the associations and stellar complexes we have found in our survey.
- ID:
- ivo://CDS.VizieR/J/A+A/371/497
- Title:
- OB associations in the spiral galaxy NGC 300
- Short Name:
- J/A+A/371/497
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a search for OB associations in NGC 300. Using an automatic and objective method (PLC technique) 117 objects were found. Statistical tests indicate that our sample is contaminated by less than 10 detections due to random concentrations of blue stars. Spatial distributions of detected associations and H II regions are strongly correlated. The size distribution reveals a significant peak at about 60{mu}rad which corresponds to 125 parsecs if a distance modulus of 26.66mag is assumed. Besides the objects with sizes corresponding to typical associations we also found several much larger objects. A second level application of our detection method revealed that most of these are composed of smaller subgroups, with sizes of about 100pc.
- ID:
- ivo://CDS.VizieR/J/ApJ/454/151
- Title:
- OB Associations of the Northern Milky Way
- Short Name:
- J/ApJ/454/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the massive star content of Milky Way clusters and OB associations in order to answer three questions: (1) How coeval is star formation? (2) How constant is the initial mass function (IMF)? (3) What is the progenitor mass of Wolf-Rayet stars? Our sample includes NGC 6823/Vul OB1, NGC 6871/Cyg OB3, Berkeley 86/Cyg OB1, NGC 6913/Cyg OB1, NGC 7235, NGC 7380/Cep OB1, Cep OB5, IC 1805/Cas OB6, NGC 1893/Aur OB2, and NGC 2244/Mon OB2. Large-field CCD imaging and multiobject, fiber spectroscopy has resulted in UBV photometry for >10,000 stars and new spectral types for ~200 stars. These data are used to redetermine distances and reddenings for these regions and to help exclude probable nonmembers in constructing the H-R diagrams. We reanalyze comparable data previously published on Cyg OB2, Tr 14/16, and NGC 6611 and use all of these to paint a picture of star formation and to measure the IMFs. We find the following: (1) Most of the massive stars are born during a period Delta(Tau) < 3 Myr in each association. Some star formation has clearly preceded this event, as evidenced by the occasional presence of evolved (Tau ~ 10 Myr) 15 Msun stars despite a typical age Tau ~ 2 Myr for the more massive population. However, all these regions also show evidence of 5-10 Msun pre-main-sequence stars (Tau < 1 Myr), demonstrating that some star formation at lower masses does continue for at least 1 Myr after the formation of high-mass stars. (2) There is no statistically significant difference in IMF slopes among these clusters, and the average value is found to be Gamma = -1.1 +/- 0.1 for stars with masses > 7 Msun. A comparison with similarly studied OB associations in the Magellanic Clouds reveals no difference in IMF slope, and hence we conclude that star formation of massive stars in clusters proceeds independently of metallicity, at least between z = 0.02 and z = 0.002. The masses of the highest mass stars are approximately equal in the Milky Way, LMC, and SMC associations, contrary to the expectation that this value should vary by a factor of 3 over this metallicity range. We conclude that radiation pressure on grains must not limit the mass of the highest mass star that can form, in accord with the suggestion of Wolfire & Cassinelli that the mere existence of massive stars suggests that shocks or other mechanisms have disrupted grains in star-forming events. (3) The four Wolf-Rayet stars in our sample have come from stars more massive than 40 Msun; one WC star and one late-type WN star each appear to have come from very massive (~100 Msun) progenitors.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A101
- Title:
- OB stars in Cygnus OB2 association
- Short Name:
- J/A+A/543/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Cygnus OB2 association and its surroundings display the richest collection of massive stars in our nearby Galactic environment and a wealth of signposts of the interaction between these stars and the interstellar gas. We perform a magnitude-limited, homogeneous census of O and early B-type stars with accurate spectral classifications in the blue, in a 6{deg}x4{deg} region centered on Cygnus OB2 that includes most of the Cygnus X complex, a sizeable fraction of the adjacent Cygnus OB9 association, and a large area of the field surrounding these complexes
- ID:
- ivo://CDS.VizieR/J/AcA/50/337
- Title:
- OGLE LMC star clusters
- Short Name:
- J/AcA/50/337
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of age determination based on the standard procedure of isochrone fitting for about 600 star clusters younger than about 1.2Gyr from the central parts of the LMC. Comparison of age distributions of star clusters from the LMC and the SMC shows that cluster formation histories are different in these galaxies. The age distribution of the LMC clusters reveals bursty nature of cluster formation in this galaxy, with contrast to the relatively uniform distribution of cluster ages in the SMC. We detected three extended peaks in the distribution of ages of LMC clusters, located at about 7Myr, 125Myr and 0.8Gyr. All detected peaks have complex structure. While the structure of the youngest and the oldest peaks may be spurious due to accuracy of age determination, in the middle peak two evident sub-peaks at 100Myr and 160Myr are clearly seen. Similar peaks are seen in the distribution of ages of clusters from the SMC, which indicates that increased cluster formation ratio during these periods might be caused by the last encounter between the Magellanic Clouds. The sample of clusters from the LMC is overabundant in very young (<10Myr) anal old (>400Myr) clusters, and underabundant in clusters having ages in the range from 80 to 15Myr with respect to the studied sample of clusters from the SMC.
- ID:
- ivo://CDS.VizieR/J/AcA/49/521
- Title:
- OGLE LMC star clusters BVI photometry
- Short Name:
- J/AcA/49/521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the catalog of star clusters found in the area of about 5.8 square degree in the central regions of the Large Magellanic Cloud. It contains data for 745 clusters. 126 of them are new objects. For each cluster equatorial coordinates, radius, approximate number of members and cross-identification are provided. Photometric data for all clusters presented in the catalog and Atlas consisting of finding charts and color-magnitude diagrams are available electronically from the OGLE Internet archive at URL: ftp://sirius.astrouw.edu.pl/ogle/ogle2/clusters/lmc
- ID:
- ivo://CDS.VizieR/J/AcA/50/355
- Title:
- OGLE Multiple Cluster Candidates in LMC
- Short Name:
- J/AcA/50/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 100 multiple cluster candidates selected from the OGLE catalog of star clusters in the Large Magellanic Cloud. Statistical analysis shows that the significant fraction of these objects may constitute physical systems. Coeval ages of 102 components of multiple objects suggest their common origin. 53 components have very different ages. The comparison of the population of multiple clusters candidates from the SMC and the LMC shows that: a) distributions of sizes and ages of multiple and single clusters from the Magellanic Clouds are very similar, b) the difference of sizes of components of a given system is small, c) in both distributions of separation of multiple clusters from the LMC and SMC two peaks are seen at about 9pc and 15pc, d) both age distributions reveal peaks around 100Myr, which may be connected with the last encounter of the LMC and the SMC.
