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Astron. Astrophys. 363, 755-766 (2000)

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1. Introduction

This paper is part of an extensive multiwavelength survey of low mass clouds (LDN 1235, LDN 1251, LDN 1274 (Nikoli et al. 2000, in prep.), Kh 20, etc.) in the Cep-Cas void (Grenier et al. 1989). Our main aims are to derive distances and investigate the differences in the morphology, chemical composition and physical properties of these clouds.

It is likely that molecular clouds interact with at least one shock front during their lifetime and form cores due to this trigger. Compression by stellar or supernova (SN) winds forms molecular clouds, triggers cloud collapse or may act indirectly speeding up the diffusion of the magnetic field (see e.g. Heathcote & Brand 1983). Several papers (see e.g. Kun & Prusti 1993; Sato et al. 1994; Tóth & Walmsley 1996) reported triggered star formation in the Upper Cepheus-Cassiopeia (UCC) region, the three main parts of which are: the Cepheus Flare giant molecular cloud (Hubble 1934; Lebrun 1986), the Cep-Cas void (a SN bubble; Grenier et al. 1989) and the Cassiopeia giant molecular cloud (Grenier et al. 1989). The latter CO survey was followed by the Nagoya 13CO (1-0) survey (Yonekura et al. 1997), which revealed a large number of small clouds in the UCC region. Distances to the clouds inside the 15o [FORMULA] 15o Cep-Cas void were not estimated so far. Tóth & Horváth (1996) investigated the morphology of 7 dark clouds towards the UCC region and found examples of slow shock-cloud interactions.

Kh 15 (Khavtassi 1955), located at [FORMULA] [FORMULA] is one of these head-tail clouds found in the Cep-Cas void. It appears as an elongated opaque spot (with a size of [FORMULA]) on the POSS image (see Fig. 5) near another dark cloud, LDN 1308 (Lynds 1962). In the Atlas of Galactic Dark Clouds (Khavtassi 1960) no. 216 appears as an E-W elongated banjo-shaped feature which includes LDN 1308 and Kh 15. We investigated the most opaque western part, and the catalogue number, 15, is used accordingly.

The cloud is visible on the Dame et al. (1987) 12CO integrated intensity map as a small bright spot. It was also detected in the 12CO and 13CO (J=1-0) survey of Taylor et al. (1987), where it is listed as TDS 473. In the Nagoya 13CO (1-0) survey of the Cepheus-Cassiopeia region the cloud has been listed as no. 137 by Yonekura et al. (1997). Kh 15 has also been included in the Catalogue of Infrared Excess Clouds (Désert et al. 1988) with the number 169.

We report the results of a multiwavelength study of Kh 15, including optical and infrared data and radio spectral line measurements in Sects. 2 and 3. We provide distance and optical extinction estimations derived by our new algorithm in Sect. 4, investigate the velocity distribution and calculate the molecular gas mass. In Sect. 5 we analyse the stability using the virial theorem. The distributions of the emission of dust and gas are also compared in this section.

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© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000