Discovery of new Milky Way star cluster candidates in the 2MASS point source catalog (original) (raw)
Astronomy and Astrophysics, 2003
Three new obscured Milky Way clusters were detected as surface density peaks in the 2MASS point source catalog during our on-going search for hidden globular clusters and massive Arches-like star clusters. One more cluster was discovered serendipitously during a visual inspection of the candidates. The first deep J, H, and K s imaging of the cluster [IBP 2002] CC 01 is presented. We estimated a cluster age of ∼1-3 Myr, distance modulus of (m-M) 0 =12.56±0.08 mag (D=3.5 Kpc), and extinction of A V ∼7.7 mag. We also derived the initial mass function slope for the cluster: Γ=−2.23±0.16 (Γ Salpeter =−2.35). The integration over the initial mass function yielded a total cluster mass M total ≤1800±200M ⊙ . CC 01 appears to be a regular, not very massive star cluster, whose formation has probably been induced by the shock front from the nearby H region Sh 2-228.
Infrared surveys of Galactic star clusters
Proceedings of the International Astronomical Union, 2009
Many attempts have been made to carry out a complete observational census of Milky Way star clusters based on recent near- and mid-infrared surveys. However, more clusters are still being discovered, indicating that existing catalogs are incomplete. We attempt to estimate the total number of supermassive (SM; Mcl ≥ 104 M⊙) clusters in the Galaxy, and to improve the yield from the automated cluster searches. Assuming that the ‘local’ census of SM clusters is complete, and that their surface density accross the disk follows that of the stars, we predict that the Milky Way contains ≥81 ± 21 SM clusters. We apply a cluster-detection algorithm to the 2mass Point Source Catalog after a preliminary color and/or magnitude selection of the point sources to improves the surface-density cluster-to-field contrast. Our algorithm identified 94 new candidates, and re-identified 34 known clusters. During the visual inspection, we detected an additional 41 new candidates, and re-identified 32 known ...
Near-infrared spectroscopy of candidate red supergiant stars in clusters
Astronomy & Astrophysics, 2014
Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims. We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (K s < 7 mag) in GLIMPSE and 2MASS images. Results. A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M to 15 M. Two red supergiants are located at Galactic coordinates (l, b) = (16. • 7, −0. • 63) and at a distance of about ∼3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l, b) = (49. • 3, +0. • 72) and at a distance of ∼7.0 kpc. Conclusions. Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps.
The young Galactic star cluster [DBS2003] 179
Astronomy and Astrophysics, 2008
Context. Recent near-and mid-infrared surveys have brought evidence that the Milky Way continues to form massive clusters. Aims. We carry out a program to determine the basic physical properties of the new massive cluster candidate [DBS2003] 179. Methods. Medium-resolution K-band spectra and deep near-infrared images of [DBS2003] 179 were used to derive the spectral types of eight member stars, and to estimate the distance and reddening to the cluster. Results. Seven of ten stars with spectra show emission lines. Comparison with template spectra indicated that they are early O-type stars. The mean radial velocity of the cluster is V rad = −77 ± 6 km s −1. Knowing the spectral types of the members and the color excesses, we determined extinction A V ∼ 16.6 and distance modulus (m − M) 0 ∼ 14.5 mag (D ∼ 7.9 Kpc). The presence of early O-stars and a lack of red supergiants suggests a cluster age of 2-5 Myr. The total cluster mass is approximated to 0.7 × 10 4 M and it is not yet dynamically relaxed. Conclusions. The candidate [DBS2003] 179 further increases the family of the massive young clusters in the Galaxy, although it appears less massive than the prototypical starburst clusters.
Astrophysics Hundreds of new cluster candidates in the VISTA Variables in the Vía Láctea survey DR1
Context. VISTA variables in the Vía Láctea is an ESO Public survey dedicated to scanning the bulge and an adjacent portion of the Galactic disk in the fourth quadrant using the VISTA telescope and its near-infrared camera VIRCAM. One of the leading goals of the VVV survey is to contribute to knowledge of the star cluster population of the Milky Way. Aims. To improve the census of Galactic star clusters, we performed a systematic and careful scan of the JHK s images of the Galactic plane section of the VVV survey. Methods. Our detection procedure is based on a combination of stellar density maps and visual inspection of promising features in the J-, Hand nd K S-band images. The material examined are VVV JHK S color-composite images corresponding to Data Release 1 of VVV. Results. We report the discovery of 493 new infrared star cluster candidates. The analysis of the spatial distribution show that the clusters are very concentrated in the Galactic plane, presenting some local maxima around the position of large star-forming complexes, such as G305, RCW 95, and RCW 106. The vast majority of the new star cluster candidates are quite compact and generally surrounded by bright and/or dark nebulosities. IRAS point sources are associated with 59% of the sample, while 88% are associated with MSX point sources. GLIMPSE 8 μm images of the cluster candidates show a variety of morphologies, with 292 clusters dominated by knotty sources, while 361 clusters show some kind of nebulosity in this wavelength regime. Spatial cross-correlation with young stellar objects, masers, and extended green-object catalogs suggest that a large sample of the new cluster candidates are extremely young. In particular, 104 star clusters associated with methanol masers are excellent candidates for ongoing massive star formation. Also, there is a special set of sixteen cluster candidates that present clear signposts of star-forming activity having associated simultaneosly dark nebulae, young stellar objects, extended green objects, and masers.
Discovery of an Extraordinarily Massive Cluster of Red Supergiants
Astrophysical Journal, 2006
We report the discovery of an extraordinarily massive young cluster of stars in the Galaxy, having an inferred total initial cluster mass comparable to the most massive young clusters in the Galaxy. Using IRMOS, 2MASS, and Spitzer observations, we conclude that there are 14 red supergiants in the cluster, compared with five, in what was previously thought to be the richest Galactic cluster of such stars. We infer spectral types from near-infrared spectra that reveal deep CO bandhead absorption that can only be fit by red supergiants. We identify a gap of ∆K s ∼4 magnitudes between the stars and the bulk of the other stars in the region that can only be fit by models if the brightest stars in the cluster are red supergiants. We estimate a distance of 5.8 kpc to the cluster by associating an OH maser with the envelope of one of the stars. We also identify a "yellow" supergiant of G6 I type in the cluster. Assuming a Salpeter IMF, we infer an initial cluster mass of 20,000 to 40,000 M ⊙ for cluster ages of 7-12 Myr. Continuing with these assumptions, we find 80% of the intial mass and 99% of the number of stars remain at the present time. We associate the cluster with an x-ray source (detected by ASCA and Einstein), a recently discovered very high energy γ-ray source (detected by INTEGRAL and HESS), and several non-thermal radio sources, finding that these objects are likely related to recent supernovae in the cluster. In particular, we claim that the cluster has produced at least one recent -2supernova remnant with properties similar to the Crab nebula. It is not unlikely to find such a source in this cluster, given our estimated supernova rate of one per 40,000 to 80,000 yr.
A newly discovered young massive star cluster at the far end of the Galactic Bar
Monthly Notices of the Royal Astronomical Society, 2011
We present a near-infrared study of the candidate star cluster Mercer 81, located at the centre of the G338.4+0.1 H II region and close to the TeV gamma-ray source HESS 1640-465. Using Hubble Space Telescope/NICMOS imaging and VLT/ISAAC spectroscopy, we have detected a compact and highly reddened cluster of stars, although the bright stars in the centre of the field are in fact foreground objects. The cluster contains nine stars with strong Pα emission, one of which we identify as a Wolf-Rayet (WR) star, as well as an A-type supergiant. The line-of-sight extinction is very large, A V ∼ 45, illustrating the challenges of locating young star clusters in the Galactic plane. From a quantitative analysis of the WR star, we argue for a cluster age of 3.7 +0.4 −0.5 Myr, and, assuming that all emission-line stars are WR stars, a cluster mass of 10 4 M. A kinematic analysis of the cluster's surrounding H II region shows that the cluster is located in the Galactic disc at a distance of 11 ± 2 kpc. This places the cluster close to where the far end of the Bar intersects the Norma spiral arm. This cluster, as well as the nearby cluster [DBS2003]179, represents the first detections of active star cluster formation at this side of the Bar, in contrast to the near side which is well known to have recently undergone a ∼10 6 M starburst episode.
A Multi-band Catalog of 10978 Star Clusters, Associations, and Candidates in the Milky Way
The Astronomical Journal, 2018
We present a catalog of Galactic star clusters, associations and candidates with 10978 entries. This multi-band catalog was constructed over 20 years, starting with visual inspections on the Digital Sky Survey and incremented with the 2MASS, WISE, VVV, Spitzer, and Herschel surveys. Large and small catalogs, as well as papers on individual objects have been systematically cross-identified. The catalog provides Galactic and equatorial coordinates, angular diameters, and chronologically ordered designations, making it simple to assign discoveries and verify how often the objects were cataloged by different authors, search methods, and/or surveys. Detection in a single band is the minimum constraint to validate an entry. About 3200 objects have measured parameters in the literature. A fundamental contribution of the present study is to present an additional ≈7700 objects for the first analyses of nature, photometry, spectroscopy and structure. The present focus is not to compile or determine fundamental parameters, but to provide a catalog uniformly characterizing the entries. A major result is that now 4234 embedded clusters are cataloged, a factor of ≈1.5 larger than open clusters. In addition to crossidentifications in different references and wavelength domains, we also communicate the discovery of 638 star clusters and similar objects. The present general catalog provides previously studied objects and thousands of additional entries in a homogeneous way, a timely contribution to Gaia-related works.
Young star clusters and the structure of the second Galactic quadrant
Monthly Notices of the Royal Astronomical Society, 2018
Aiming to improve the knowledge of the Galactic structure in the second Galactic quadrant, we selected 10 young open clusters from a sample of more than 200 covered by the SDSS. Our study was based on a photometric data set provided by SDSS and APASS in the visible and by 2MASS and WISE in the infrared. We also carried out spectroscopic observations with GMOS/GEMINI and made use of spectroscopic information available in the literature. The analysis was performed with a suite of tools developed by us to systematically determine the main parameters of the studied clusters, and to identify possible pre-main-sequence populations. We obtained novel parameters and found that the studied clusters are scattered at distances ranging from 1.7 to 8.8 kpc, covering three spiral arms. In particular, we located two of the clusters over the 'Outer Arm' and other two probably belong to the more distant 'New Arm'. Hence, it was possible to get a better picture of the structure of the outer part of the Galaxy. We also obtained traces of coeval star formation processes in all of the selected clusters with a pre-main-sequence population and identified young stellar object candidates in one of them. Regarding the most massive members of the clusters, we discovered 14 B-type stars, eight of them earlier than B3 and another one was identified as a Be star.
New Galactic embedded clusters and candidates from a WISE Survey
New Astronomy, 2015
We carried out a search for new infrared star clusters, stellar groups and candidates using WISE images, which are very sensitive to dust emission nebulae. We report the discovery of 437 embedded clusters and stellar groups that show a variety of structures, both in the stellar and nebular components. Pairs or small groupings of clusters are observed, suggesting multiple generations at the early formation stages. The resulting catalogue provides Galactic and equatorial coordinates, together with angular sizes for all objects. The nature of a representative test sub-sample of 14 clusters is investigated in detail by means of 2MASS photometry. The colour magnitude diagrams and radial density distributions characterize them as stellar clusters. The 437 new objects were found in the ranges 145 • ≤ ℓ ≤ 290 • and −25 • ≤ b ≤ 20 • , and they appear to be a major object source for future studies of star cluster formation and their early evolution. WISE is a powerful tool to further probe for very young clusters throughout the disk.