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Obscured clusters. II. GLIMPSE-C02 - A new metal rich globular cluster in the Milky Way
Context: The estimated total number of Milky Way globulars is 160± 20. The question of whether there are any more undiscoveredglobular clusters in the Milky Way is particularly relevant withadvances in near and mid-IR instrumentation. Aims: Thisinvestigation is a part of a long-term project to search the inner MilkyWay for hidden star clusters and to study them in detail. GLIMPSE-C02(G02) is one of these objects, situated near the Galactic plane (l =14.129 deg, b = -0.644 deg). Methods: Our analysis is based onSOFI/NTT JHKS imaging and low resolution (R˜ 1400)spectroscopy of three bright cluster red giants in the K atmosphericwindow. We derived the metal abundance by analysis of these spectra andfrom the slope of the RGB. Results: The cluster is deeplyembedded in dust and undergoes a mean reddening of AV ~ 24.8± 3 mag. The distance to the object is D = 4.6 ± 0.7 kpc.The metal abundance of G02 is [Fe/H]H96 = -0.33± 0.14 and[Fe/H]CG = -0.16 ± 0.12 using different scales. The best fit tothe radial surface brightness profile with a single-mass King's modelyields a core radius rc = 0.70 arcmin (0.9 pc), tidal radiusrt = 15 arcmin (20 pc), and central concentration c = 1.33. Conclusions: We demonstrate that G02 is new Milky Way globularcluster, among the most metal rich globular clusters in the Galaxy. Theobject is physically located at the inner edge of the thin disk and thetransition region with the bulge, and also falls in the zone of the“missing” globulars toward the central region of the MilkyWay.Based on observations collected with the ESO New Technology Telescope,observing program 77.D-0089. Table with photometry is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/489/583
| Obscured clusters. I. GLIMPSE 30 - A young Milky Way star cluster hosting Wolf-Rayet stars
Context: Young massive clusters are usually deeply embedded in dust andgas. They represent excellent astrophysical laboratories for the studyof massive stars. Clusters with Wolf-Rayet (WR) stars are of specialimportance, since this enables us to study a coeval WR population at auniform metallicity and known age. Aims: We started a long-term projectto search the inner Milky Way for hidden star clusters and to study themin detail. GLIMPSE 30 (G30) is one of these clusters. It is situatednear the Galactic plane (l=298.756°, b=-0.408°) and we determineits physical parameters and investigate its high-mass stellar contentespecially WR stars. Methods: Our analysis is based on SOFI/NTTJ_SHKS imaging and low resolution (R˜2000) spectroscopyof the brightest cluster members in the K atmospheric window. For theage determination we applied isochrone fits for MS and Pre-MS stars. Wederived stellar parameters of the WR stars candidates using a fullnonLTE modeling of the observed spectra. Results: Using a variety oftechniques we found that G30 is very young cluster, with age t ≈ 4Myr. The cluster is located in the Carina spiral arm, it is deeplyembedded in dust and suffers reddening of AV ˜10.5± 1.1 mag. The distance to the object is d=7.2±0.9kpc. The mass of the cluster members down to 2.35 M_ȯ is 1600M_ȯ. The cluster's MF for the mass range of 5.6 to 31.6 {M_ȯ}shows a slope of Γ=-1.01± 0.03. The total mass of thecluster obtained by this MF down to 1 M_ȯ is about 3 ×103 M_ȯ. The spectral analysis and the models allow usto conclude that at least one Ofpe/WN and two WR stars can be found inG30. The WR stars are of the WN6-7 hydrogen rich type with progenitormasses of more than 60 M_ȯ. Conclusions: G30 is a new member ofthe family of young Galactic clusters hosting WR stars. It is a factorof two to three less massive than some of the youngest super-massivestar clusters like Arches, Quintuplet and the Central cluster and istheir smaller analog.Based on observations collected with the New Technology Telescope of theESO within observing program 77.D-0089.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Kentaur |
| Rektaszcenzió: | 12h13m52.77s |
| Deklináció: | -55°12'26.7" |
| Vizuális fényesség: | 8.433 |
| Távolság: | 56.211 parszek |
| RA sajátmozgás: | -95.9 |
| Dec sajátmozgás: | 27.6 |
| B-T magnitude: | 9.196 |
| V-T magnitude: | 8.496 |
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