Stellar Photometry of the Globular Cluster NGC 6229. I. Data Reduction and Morphology of the Brighter Part of the CMD

BV CCD photometry of the central (1.5 arcmin x 2.0 arcmin) part of the mildly concentrated outer-halo globular cluster NGC 6229 is presented. The data reduction in such a crowded field was based on a wavelet transform analysis. Our larger dataset extends the previous results by Carney et al. (1991, AJ, 101, 1699) for the outer and less crowded fields of the cluster, and confirms that NGC 6229 has a peculiar color-magnitude diagram for its position in the Galaxy. In particular, NGC 6229's horizontal branch (HB) presents several interesting features, among which stand out: a well populated and very extended blue tail; a rather blue overall morphology, with (B-R)/(B+V+R) = 0.24+/-0.02; a bimodal color distribution, resembling those found for NGC 1851 and NGC 2808; and gaps on the blue HB. NGC 6229 is the first bimodal-HB cluster to be identified in the Galactic outer halo. A low value of the R parameter is confirmed, suggestive of a low helium abundance or of the presence of a quite substantial population of extreme HB stars fainter than our photometric limit (~ 2.5 mag below the RR Lyrae level in V). Twelve new possible variable stars were found in the central part of the cluster. The morphology of the red giant branch (RGB) also seems to be peculiar. In particular, the RGB luminosity function ``bump'' is not a prominent feature and has only been tentatively identified, on the basis of a comparison with a previously reported detection for M3 (NGC 5272). Finally, we compare the properties of NGC 6229 with those for other outer-halo globular clusters, and call attention to what appears to be a bimodal HB distribution for the outer-halo cluster population, where objects with very red or very blue HB types are much more frequently found than clusters with intermediate HB types.Comment: 31 pages, LaTeX, uses AASTeX v4.0, 11 postscript figures and 7 postscript tables pasted into text. To appear in The Astronomical Journal (Feb. 1997 issue

A not so massive cluster hosting a very massive star

We present the first physical characterization of the young open cluster VVV CL041. We spectroscopically observed the cluster main-sequence stellar population and a very-massive star candidate: WR62-2. CMFGEN modeling to our near-infrared spectra indicates that WR62-2 is a very luminous (10$^{6.4\pm0.2} L_{\odot}$) and massive ($\sim80 M_{\odot}$) star.Comment: 1 page, 1 figure, to be published in the "International Workshop on Wolf-Rayet Stars conference proceedings" by Universit\"atsverlag Potsdam (editors: W.-R. Hamann, A. Sander, and H. Todt

New Metallicities of RR Lyrae Stars in omega Centauri: Evidence for a Non He-Enhanced Metal-Intermediate Population

We present new spectroscopic metal abundances for 74 RR Lyrae stars in omega Cen obtained with FLAMES. The well-known metallicity spread is visible among the RR Lyrae variables. The metal-intermediate (MInt) RR Lyrae stars ([Fe/H] ~ -1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H] ~ -1.7), in good agreement with the corresponding zero-age horizontal branch models with cosmological helium abundance Y = 0.246. This result conflicts with the hypothesis that the progenitors of the MInt RR Lyrae stars correspond to the anomalous blue main-sequence stars, which share a similar metallicity but whose properties are currently explained by assuming for them a large helium enhancement. Therefore, in this scenario, the coexistence within the cluster of two different populations with similar metallicities ([Fe/H] ~ -1.2) and different helium abundances has to be considered.Comment: 9 pages, 4 figures, accepted for publication by ApJ

The embedded clusters DBS 77, 78, 102, and 160-161 and their link with the interstellar medium

Aims. We report a study of the global properties of some embedded clusters placed in the fourth quadrant of the Milky Way to clarify some issues related with their location into the Galaxy and their stellar formation processes. Methods. We performed BVI photometric observations in the region of DBS 77, 78, 102, 160, and 161 clusters and infrared spectroscopy in DBS 77 region. They were complemented with JHK data from VVV survey combined with 2MASS catalogue, and used mid-infrared information from GLIMPSE catalogue. We also searched for HI data from SGPS and PMN radio surveys, and previous spectroscopic stellar classification. The spectroscopic and photometric information allowed us to estimate the spectral classification of the brightest stars of each studied region. On the other hand, we used the radio data to investigate the interstellar material parameters and the continuum sources probably associated with the respective stellar components. Results. We estimated the basic physical parameters of the clusters (reddening, distance, age, and initial mass function). We searched for HII regions located near to the studied clusters and we analyzed the possible link between them. In the particular case of DBS 160-161 clusters, we identified the HI bubble B332.5-0.1-42 located around them. We found that the mechanical energy injected to the interstellar medium by the more massive stars of this couple of clusters was enough to generate the bubble.Comment: 15 pages, 14 figures, 6 tables, accepted for publication in A&

Obscured clusters.IV. The most massive stars in [DBS2003]179

Aims. We report new results for the massive evolved and main sequence members of the young galactic cluster DBS2003 179. We determine the physical parameters and investigate the high-mass stellar content of the cluster, as well as of its close vicinity. Methods. Our analysis is based on ISAAC/VLT moderate-resolution (R\approx4000) infrared spectroscopy of the brightest cluster members. We derive stellar parameters for sixteen of the stellar members, using full non-LTE modeling of the obtained spectra. Results. The cluster contains three late WN or WR/LBV stars (Obj 4, Obj 15, and Obj 20:MDM32) and at least 5 OIf and 5 OV stars. According to the Hertzsprung-Russell diagram for DBS2003 179, the WR stars show masses above 85Msun, the OIf stars are between 40 and 80Msun, and the main sequence O stars are >20Msun. There are indications of binarity for Obj 4 and Obj 11, and Obj 3 shows a variable spectrum. The cluster is surrounded by a continuous protostar formation region most probably triggered by DBS2003 179. Conclusions. We confirm that DBS2003 179 is young massive cluster (2.5 10^4Msun) very close to the Galactic center at the distance of 7.9+-0.8 kpc.Comment: 14 pages, 16 figures, accepted in A&