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)

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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