The isolated embedded cluster IRAS 17136-3617 (GM24) revisited

M. TAPIA, P. PERSI, M. ROTH, M. GOMEZ

Heidelberg

Congreso; Massive Star Formation: Observations confront Theory; 2007

Max Planck Institutes and ESO

We present new infrared observations of the very young embedded cluster GM 24, which at its core (Irs 3) has a proto-trapezium stellar system, IRAS 17136-3617. Images in the wavelength range 1.2 to 20 micron are analysed. In an area of 111 arcsec x 111 arcsec, a total of 619 sources were detected in K, 296 in HK and 119 in JHK.  Of these, 54 were also measured at 3.6 and 4.5 microns and only 10 at 5.8 microns. By means of source counts, a circle of radius 38 arcsec was found to contain most of the cluster. The number of sources belonging to the cluster is found to decrease abruptly at K > 14.5,corresponding to a 2 M_Sun ZAMS, although the completeness limit of the survey is two magnitudes fainter. Only Irs 3 and Irs 27 and, marginally Irs 17, were measurable in the ground-based mid-infrared images. The Class I source Irs 3, which dominates the emission at lambda > 8 microns and is responsible for the ionization of the associated compact H II region, is found to be composed of at least four near-infrared components within a 3 arc circle. Its luminosityand number of UV photons imply the presence of at least one late O-type star. Irs 17 appears to be an extended spherical mid-IR source with a near-infrared bipolar reflection nebula. A long bar of diffuseemission seen at wavelengths 2.2 to 8.9 micron near the centre of the cluster may be a photodissociation front. The considerable fraction of stars with infrared excess, including two Class I objects associated with a compact radio H II region and the presence of an H_2O maser source with a faint mid-IR counterpart, provide evidence of the extreme youth of the isolated cluster, with age probably < 10^5 years.