Submm- and FIR-observations of the S106 Photon Dominated Region

N. Schneider ^1,2, C. Kramer ¹, R. Simon ¹, J. Stutzki ¹, & G. Winnewisser ¹

¹ I. Physik. Institut, Universität zu Köln, Köln ² Observatoire de Grenoble, l'Universite Joseph Fourier, Grenoble

The HII region S106 in Cygnus is a prominent bipolar emission nebula, associated with a molecular cloud. The optical and radio emission of the nebula is formed in two lobes with a linear extent of 3', seperated by a dark bar which is devoid of optical and radio continuum emission. The nebula is excited by a single O9 star, referred to as S106 IR, which created a bright Photon Dominated Region (Tielens et al. 1985). But though S106 has been extensively studied in various optical and radio lines as well as in continuum emission, there are only few observations of typical PDR tracers as well as extended molecular line maps at higher angular resolution. Therefore, we started a multiwavelength study of S106 in various fine structure lines, using the Kuiper Airborne Observatory (KAO) and the Infrared Space Observatory (ISO) for these observations, and molecular lines, using the IRAM 30m and KOSMA 3m radio telescopes.

We observed S106 in the [CII] 158  and [OI] 63 and 145  fine structure lines with the MPE/UCB Fabry-Perot Interferometer FIFI (Poglitsch et al. 1991) onboard the KAO. The [CII] 158  map at an angular resolution of 55'' covers an area of with peak emission at the exciting star S106 IR at and .

The overall structure is similar to the 25 resolution map obtained by Harris et al. (1987), indicating that the PDR extends deep into the molecular cloud. The higher angular resolution [OI] observations at 22 show more structure, a pronounced peak of [OI] emission is located 20 east of S106 IR. The [CII] 158 /[OI] 63  line ratio in a 55 beam centering S106 IR is 0.1, which accounts for a gas temperature of 500 K and a density around (Tielens et al. 1985).

The ISO observations concentrate on two positions within the PDR region. The observations constitute an LWS01 scan between 45 and 195 , including the [CII] and [OI] lines obtained with the KAO, and SWS data on the H₂ S(0), S(1) and S(2) lines at 28, 17 and 12 , the SiII line at 34.8 , the FeII and SI lines between 25 and 26  and OIII between 52 and 88 .

The extend of the warm, molecular gas component of the PDR was determined by observations of the 13CO 6-5 line at the KOSMA 3m-telescope in February 1998. The observatory has recently been equipped with a new telescope (including pedestal, backstructure, main reflector and wobbling secondary) with a surface accuracy of about 30 mu to date for the main dish (Kramer et al. 1998). A total of 37 positions, centering on S106 IR, was mapped fully sampled. The HPBW was 48 and the main beam efficiency 0.48 at 660 GHz. A prelimary analysis indicates that the 6-5 emission is extended on a (main beam brightness) temperature scale of 5 to 15 K.

The cooler gas, constituting the interior of the molecular cloud clumps, was traced by isotomoperic ¹²CO, ¹³CO and C¹⁸O J=2-1 and J=1-0 observations, using the IRAM 30m telescope. An area of about was covered in the new 'on-the-fly'-mapping modus.