Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1H039

CEN34 -- high-mass YSO in M17 or background post-AGB star ?

Chen, Zhiwei (Purple Mountain Observatory, Chinese Academy of Sciences)
Nuernberger, Dieter E. A. (Astronomy Institute of Ruhr-University Bochum)
Chini, Rolf (Astronomy Institute of Ruhr-University Bochum)
Liu, Yao (Purple Mountain Observatory, Chinese Academy of Sciences)
Fang, Min (Purple Mountain Observatory, Chinese Academy of Sciences)
Jiang, Zhibo (Purple Mountain Observatory, Chinese Academy of Sciences)

Abstract:
We investigate a high-mass YSO candidate (CEN 34) embedded in the star forming region M 17. Its optical to near-infrared (550 - 2500 nm) spectrum reveals several photospheric absorption features, such as H alpha, Ca II triplet and K-band CO bandheads but lacks any emission lines. The spectral features in the range 8375 - 8770 angstrom, showing the highest S/N ratio, are used to constrain an effective temperature T= 5250 K and a log g = 2.0. The radial velocity relative to LSR of CEN 34 as obtained from various photospheric lines is of the order of -60 km/s and thus distinct from the +25 km/s found for several OB stars in the cluster and for the associated molecular cloud. The SED displays a faint infrared excess that resembles the SED of a high-mass YSO or an evolved star of intermediate-mass. If CEN 34 is a high-mass YSO, the radial velocity of CEN 34 not comparable with M 17 could only be explained by an ejection mechanism in which O stars kicked out CEN 34. On the other hand, the radial velocity discrepancy is naturally understandable if CEN 34 is an evolved intermediate-mass star located just behind M 17. Therefore, we suggest that CEN 34 is more likely an evolved intermediate-mass star (e.g., AGB/post-AGB) unrelated with M 17 rather than a high-mass YSO as a member of M 17.

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