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Issue A&A
Volume 375, Number 2, August IV 2001
Page(s) 359 - 365
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010716



A&A 375, 359-365 (2001)
DOI: 10.1051/0004-6361:20010716

WFPC2 observations of two dwarf spheroidal galaxies in the M 81 group

I. D. Karachentsev1, M. E. Sharina1, 2, A. E. Dolphin3, D. Geisler4, E. K. Grebel5, 6, P. Guhathakurta7, P. W. Hodge6, V. E. Karachentseva8, A. Sarajedini9 and P. Seitzer10

1  Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR, 369167, Russia
2  Isaac Newton Institute, SAO Branch Chile
3  Kitt Peak National Observatory, National Optical Astronomy Observatories, PO Box 26732, Tucson, AZ 85726, USA
4  Departamento de Fisica, Grupo de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile
5  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6  Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA
7  UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
8  Astronomical Observatory of Kiev University, 04053, Observatorna 3, Kiev, Ukraine
9  Astronomy Department, Wesleyan University, Middletown, CT 06459, USA
10  Department of Astronomy, University of Michigan, 830 Dennison Building, Ann Arbor, MI 48109, USA

(Received 27 November 2000 / Accepted 17 May 2001 )

Abstract
We have obtained HST WFPC2 and ground-based images of two low surface brightness dwarf spheroidal galaxies in the M 81 group, FM1 and KKH57. Their colour-magnitude diagrams show red giant branches with tips at $I = 23.77 \pm 0.14$ and $I = 23.97 \pm0.17$, respectively. The derived true distance moduli, $27.66 \pm 0.16$ and $27.96 \pm 0.19$, agree well with the mean distance modulus of the M 81 group, $27.84 \pm 0.05$. Absolute V magnitudes of the galaxies (-11.46 and -10.85), their colours ( (B-V) = 0.88 and 0.80), and central surface brightnesses ( $\Sigma_{0,V}$ = 24.8 and 24.4 mag/ $\sq\arcsec$) are in the range of other dSph companions of M 81, M 31, and Milky Way. With two new objects the maximum projected radius of the dwarf spheroidal subsystem around M 81 is 380 kpc.


Key words: galaxies: dwarf -- galaxies: stellar content -- galaxies: distances -- galaxies: M 81 group: FM1 and KKH57

Offprint request: I. D. Karachentsev, ikar@luna.sao.ru

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© ESO 2001


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