We investigate the proposed high-mass young stellar object ( YSO ) candidate CEN 34 , thought to be associated with the star forming region M 17 .
Its optical to near-infrared ( 550 - 2500 nm ) spectrum reveals several photospheric absorption features , such as H \alpha , the Ca ii triplet and the CO bandheads but lacks any emission lines .
The spectral features in the range 8375 - 8770 Å , showing the highest S/N ratio , are used to constrain an effective temperature T _ { \mathrm { eff } } = 5250 \pm 250 \mathrm { K } ( early-/mid-G ) and a \log g = 2.0 \pm 0.3 ( supergiant ) .
The spectral energy distribution displays a faint infrared excess that resembles the SED of a high-mass YSO or an evolved star of intermediate mass .
Moreover , the observed temperature and surface gravity are identical for high-mass YSOs and evolved stars .
The radial velocity relative to LSR ( V _ { 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 modeling yields \sim 10 ^ { -4 } M _ { \sun } of circumstellar material which contributes only a tiny fraction to the total visual extinction ( 11 mag ) .
The distance of CEN 34 is between 2.0 kpc and 4.5 kpc .
In the case of a YSO , a dynamical ejection process is proposed to explain the V _ { LSR } difference between CEN 34 and M 17 .
Additionally , to match the temperature and luminosity , we speculate that CEN 34 had accumulated the bulk of its mass with accretion rate > 4 \times 10 ^ { -3 } M _ { \sun } / yr in a very short time span ( \sim 10 ^ { 3 } yrs ) , and currently undergoes a phase of gravitational contraction without any further mass gain .
However , all the aforementioned characteristics of CEN 34 are compatible with an evolved star of 5 - 7 M _ { \sun } and an age of 50 - 100 Myrs , most likely a background post-AGB star with a distance between 2.0 kpc and 4.5 kpc .
We consider the latter classification as the more likely interpretation .
Further discrimination between the two possible scenarios should come from the more strict confinement of CEN 34 ’ s distance .