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تسجيل مستخدم جديدObscured clusters.I. GLIMPSE30 - Young Milky Way Star Cluster Hosting Wolf-Rayet Stars
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R. Kurtev
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Young massive clusters are perfect astrophysical laboratories for study of massive stars. Clusters with Wolf-Rayet (WR) stars are of special importance, since this enables us to study a coeval WR population at a uniform metallicity and known age. GLIMPSE30 (G30) is one of them. The cluster is situated near the Galactic plane (l=298.756deg, b=-0.408deg) and we aimed to determine its physical parameters and to investigate its high-mass stellar content and especially WR stars. Our analysis is based on SOFI/NTT JsHKs imaging and low resolution (R~2000) spectroscopy of the brightest cluster members in the K atmospheric window. For the age determination we applied isochrone fits for MS and Pre-MS stars. We derived stellar parameters of the WR stars candidates using a full nonLTE modeling of the observed spectra. Using a variety of techniques we found that G30 is very young cluster, with age t~4Myr. The cluster is located in Carina spiral arm, it is deeply embedded in dust and suffers reddening of Av~10.5+-1.1mag. The distance to the object is d=7.2+-0.9kpc. The mass of the cluster members down to 2.35Msol is ~1600Msol. Clusters MF for the mass range of 5.6 to 31.6Msol shows a slope of Gamma=-1.01+-0.03. The total mass of the cluster obtained by this MF down to 1Msol is about 3x10^3Msol. The spectral analysis and the models allow us to conclude that in G30 are at least one Ofpe/WN and two WR stars. The WR stars are of WN6-7 hydrogen rich type with progenitor masses more than 60Msol. G30 is a new member of the exquisite family of young Galactic clusters, hosting WR stars. It is a factor of two to three less massive than some of the youngest super-massive star clusters like Arches, Quintuplet and Central cluster and is their smaller analog.
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ry. When beginning our WR searches using infrared techniques it was not clear whether WR number predictions were too optimistic or whether there was more hidden behind interstellar and circumstellar extinction. During the last decade we pioneered a technique of exploiting the near- and mid-infrared continuum colours for individual point sources provided by large-format surveys of the Galaxy, including 2MASS and Spitzer/GLIMPSE, to pierce through the dust and reveal newly discovered WR stars throughout the Galactic Plane. The key item to the colour discrimination is via the characteristic infrared spectral index produced by the strong winds of the WR stars, combined with dust extinction, which place WR stars in a relatively depopulated area of infrared colour-colour diagrams. The use of the Spitzer/GLIMPSE 8$mu$m and, more recently, WISE 22$mu$m fluxes together with cross-referencing with X-ray measurements in selected Galactic regions have enabled improved candidate lists that increased our confirmation success rate, achieved via follow-up infrared and optical spectroscopy. To date a total of 102 new WR stars have been found with many more candidates still available for follow-up. This constitutes an addition of $sim$16% to the current inventory of 642 Galactic WR stars. In this talk we review our methods and provide some new results and a preliminary review of their stellar and interstellar medium environments. We provide a roadmap for the future of this search, including statistical modeling, and what we can add to star formation and high mass star evolution studies.
We report the discovery of a new transition type Wolf-Rayet (WR) WN/C star in the Galaxy. According to its coordinates (R.A., Dec)J2000 = 18h51m39.7s, -05d34m51.1s, and the distance (7.11 kpc away from Earth) inferred from the second Gaia, data relea
se, its found that WR 121-16 is located in the Far 3 kpc Arm, and it is 3.75 kpc away from the Galactic Center. The optical spectra obtained by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and the 2.16 m telescope, both located at the Xinglong Observatory in China, indicate that this is a WR star of the transitional WN7o/WC subtype. A current stellar mass of about 7.1 M_solar, a mass-loss rate of M_dot = 10^(-4.97) M_solar/yr, a bolometric luminosity of log L/L_solar = 4.88, and a stellar temperature of T_* = 47 kK are derived, by fitting the observed spectrum with a specific Potsdam Wolf-Rayet (PoWR) model. The magnitude in V-band varies between 13.95 and 14.14 mag, while no period is found. Based on the optical spectra, the time domain data, and the indices of the astrometric solution of the Gaia data, WR 121-16 is likely a transitional WN/C single star rather than a WN+WC binary.
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pc. Our goal in this work is a systematic search for young, massive star candidates throughout the entire region within R ~ 2.5 pc of the black hole. Methods. The main criterion for the photometric identification of young, massive early-type stars is the lack of CO-absorption in the spectra. We used narrow-band imaging with VLT/ISAAC to search for young, massive stars within ~2.5 pc of Sgr A*. Results. We have found 63 early-type star candidates at R < 2.5 pc, with an estimated erroneous identification rate of only about 20%. Considering their K-band magnitudes and interstellar extinction, they are candidates for Wolf-Rayet stars, supergiants, or early O-type stars. Of these, 31 stars are so far unknown young, massive star candidates, all of which lie at R>0.5pc. The surface number density profile of the young, massive star candidates can be well fit by a single power-law, with Gamma = 1.6 +- 0.17 at R < 2.5 pc, which is significantly steeper than that of the late-type giants that make up the bulk of the observable stars in the NSC. Intriguingly, this power-law is consistent with the power-law that describes the surface density of young, massive stars in the same brightness range at R < 0.5 pc. Conclusions. The finding of a significant number of newly identified early-type star candidates at the Galactic center suggests that young, massive stars can be found throughout the entire cluster which may require us to modify existing theories for star formation at the Galactic center. Follow-up studies are needed to improve the existing data and lay the foundations for a unified theory of star formation in the Milky Ways NSC.
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