23 research outputs found
Probing the centre of the large circumstellar disc in M17
We investigated the nature of the hitherto unresolved elliptical infrared
emission in the centre of the ~20000 AU disc silhouette in M 17. We combined
high-resolution JHKsL'M' band imaging carried out with NAOS/CONICA at the VLT
with [Fe II] narrow band imaging using SOFI at the NTT. The analysis is
supported by Spitzer/GLIMPSE archival data and by already published SINFONI/VLT
Integral Field Spectroscopy data. For the first time, we resolve the elongated
central infrared emission into a point-source and a jet-like feature that
extends to the northeast in the opposite direction of the recently discovered
collimated H2 jet. They are both orientated almost perpendicular to the disc
plane. In addition, our images reveal a curved southwestern emission nebula
whose morphology resembles that of the previously detected northeastern one.
Both nebulae are located at a distance of 1500 AU from the disc centre. We
describe the infrared point-source in terms of a protostar that is embedded in
circumstellar material producing a visual extinction of 60 <= Av <= 82. The
observed Ks band magnitude is equivalent to a stellar mass range of 2.8 Msun <=
Mstar <= 8 Msun adopting conversions for a main-sequence star. Altogether, we
suggest that the large M 17 accretion disc is forming an intermediate to
high-mass protostar. Part of the accreted material is expelled through a
symmetric bipolar jet/outflow.Comment: 6 pages, 3 figures, accepted by MNRAS (16 May 2008
2.3 micron CO emission and absorption from young high-mass stars in M17
We are studying the extremely young cluster of M17 to investigate the birth
of high-mass stars and the initial mass function. Deep JHKL imaging and K-band
spectroscopy from the VLT of 201 stars toward the cluster is presented. The
majority of 104 stars show the CO band-head in absorption. Half of them emit
X-rays and/or have infrared excess, indicative of very young objects. Their
intrinsic IR luminosity is compatible with intermediate and high-mass pre-main
sequence stars. Nine additional stars have the CO feature in emission, while
sixty sources are lacking any stellar spectral feature due to veiling by
circumstellar dust. We suggest that CO absorption is - as in the case of
low-mass stars - also a common feature during the early evolution of stars with
higher masses. According to model calculations the observed CO absorption is
most likely a sign of heavily accreting protostars with mass accretion rates
above 10^-5 solar masses/yr.Comment: 4 pages, 3 figure + 1 online figure, accepted for publication in A&