Molecular gas towards G18.8+1.8

J. VASQUEZ , M. RUBIO , C.E. CAPPA1 , AND N. U. DURONEA

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2012 vol. 545 p. 89 - 101

0004-6361

    This work aims at investigating the characteristics of the molecular gas associated with the nebula G18.8+1.8, linked to the Wolf-Rayet star HD 168206 (WR 113), ant its relation to other components of its local interstellar medium.     We carried out molecular observations of the  ^{12}CO(J=1-0) and (J=2-1) lines with angular resolution of 44 arcsec and 22 arcsec using the SEST telescope. Complementary NANTEN data of the ^{12}CO(1-0) line were also used. The dust emission was analyzed using Spitzer-IRAC images at 8.0 microns, and WISE data at 3.4 microns, 4.6 microns, and 12.0 microns.     The SEST data allowed us to identify a molecular component (Cloud 3) having velocities in the  interval from aprox.  +30 to +36 km/seg    which is most probably linked to the nebula. Morphological and kinematical properties suggest that Cloud 3 constitute a wind-blown molecular half shell, which expands around WR 113. The ratio R_{2-1/1-0} and excitation temperatures  indicate that the molecular gas is being irradiated by strong  UV radiation. The location of the inner optical ring in the outer  edge of Cloud 3 suggests that the stars SerOB2-1, -2, -3, -63, and -64 are  responsables for the ionization of Cloud 3 and the inner ring nebula. A comparison between the spatial distribution of the molecular gas and the PAH emission at microns indicates the existence of  a PDR between the ionized and the molecular gas. A search for candidate  young stellar objects (YSOs) in the region around G18.8+1.8 based on available 2MASS, MSX, IRAS, and {it Spitzer}-IRAC  catalogs resulted in the detection of about  sixty sources, some of them projected onto Cloud 3. Two small spots of clustered candidates YSOs are projected near the outer border of Cloud 3, although a triggered stellar formation scenario is doubtful.  }