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Astron. Astrophys. 342, L9-L12 (1999)

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1. Introduction

Until recently, only three dwarf spheroidal (dSph) companions of M31 were known, namely And I, II, and III while no less than 9 such systems are associated with the Milky Way Galaxy (MWG). The M31 companions have been known since 1972 and were found by a visual inspection of the (old) Palomar Sky Survey by van den Bergh (1972). Recently, new searches were initiated based on the new, deeper plates of the POSS II. Armandroff et al. (1998) found and confirmed a new M31 companion which they named And V. Karachentsev & Karachentseva (1998) announced the finding of two low surface brightness objects, namely the Cassiopeia Dwarf of B[FORMULA]16 and the Pegasus Dwarf of B[FORMULA]14.5. The Pegasus dwarf was meanwhile found independently by Armandroff et al. (1999), they called it And VI. According to the location in the sky and the morphology, both newly identified dwarf candidates might be additional M31 companions. As argued by Armandroff et al., the new survey plates are not only more sensitive than those available to van den Bergh, but were searched also to larger M31-centric distances, since the MWG companions implied larger dimensions of the companion systems. We here present ground-based CCD observations done with the Calar Alto 2.2m telescope of the later candidate in constellation Pegasus and will show that it is indeed a dSph companion to M31. Therefore, one might prefer Armandroff 's et al. designation as And VI. In the following, we will use this later name which refers (as the name Pegasus dwarf) to a faint, low surface brightness object at RA 23h 49.2m DEC +24o 19' (1950), see Table 1. The name And VI avoids confusion with the Pegasus irregular dwarf galaxy and outlines that the new dwarf galaxy belongs to the M31 system.


Table 1. Overall properties of And VI from the literature and as derived in this paper. Absolute magnitudes are corrected for galactic reddening with the given extinction value from Burstein & Heiles (1978), distance depend values are converted with the new distance estimate of 795 kpc.

The observations are briefly presented in Sect. 2 of this letter and discussed in Sect. 3. We conclude on the distance and thus on the satellite nature of the And VI galaxy in Sect. 4, while all other aspects which can be derived from our data are postponed to a later paper.

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998