GR 8

Irregular Galaxy GR 8 (UGC 8091, DDO 155), type Im V, in Virgo

Imprint of a Foot Galaxy, Footprint Galaxy

[GR 8 image, D.A. Hunter]

12 : 58.7
+14 : 13
Im V
+165 km/sec
7900 kly :
Apparent Dimension:
1.2 x 1.1 arc min
1.5 kly
14.5 mag ph
Abs. Mag:
This dwarf irregular galaxy was first photographically captured within a supernova survey with the photographically-corrected Ross lens of Lick Observatory's 20-inch astrograph on 8x10-inch Eastman 103a-O plates, exposed for two hours, under the direction of C.D. Shane, performed 1946-47 and 1951 at Lick Observatory. Shane noted some nebulae of abnormally low surface brightness on these plates and suspected they might be dwarf galaxies like some then-known Local Group galaxies. Gibson Reaves investigated these photographic plates of the Virgo Cluster of Galaxies within his Ph.D. thesis, and discovered a number of candidate Virgo dwarf galaxies, including our dwarf galaxy, and compiled the "GR" catalog (Gibson-Reeves 1956), and our dwarf became No. 8. GR 8 appeared as a footprint-shaped, tiny, irregular smudge.

A few years after its discovery, another Lick astronomer observed GR 8 with the 120-inch telescope at Lick Observatory, and was surprised that he could recognize the brightest individual stars of GR8 visually. Therefore, it must be much closer to us than the Virgo Cluster's distance (some 60 million light years) or even our closest neighboring galaxy groups such as the M81 group. Because of this reason, it was very probable that GR8 was a new member galaxy of the Local Group. For years, this galaxy was searched for Cepheid variables without success - simply it seemed to have none at this time.

It was finally confirmed as a very nearby galaxy and possible Local Group member by measuring its radial velocity. Hodge (1974) found a velue of +181 km/s, and from various mathods, estimated the distance at between 1.5 and 5 million lightyears. Later investigations lead to estimates typically between 3 and 5 million lightyears.

Nevertheless, the Sky Catalog 2000.0 still suspects that this galaxy might be a Virgo Cluster member which is peculiarly moving toward us and thus has only small redshift or recession velocity. Newer catalogs assume it may be a Local Group member (e.g., Tully's Nearby Galaxies Catalog, Hodge 1986). In the latter reference, Paul Hodge tells the story of GR8 as of 1986.

Eventually, Tolstoy (1995) discovered one single Cepheid variable, together with 5 red, probable long-period variables of Mira type. From the Cepheid, they were able to derive a distance of 7.3 million lightyears, which will get slightly greater when the Hipparcos correction of 1997 is applied, perhaps about 7.9 million light years. Then its apparent extension corresponds to about 2,400 lightyears.

GR8 is now placed well at the border of the gravitationally bound Local Group with the membership question open, as e.g. Mike Irwin and his coworkers have pointed out. Thus the membership of GR8 to the Local Group is still doubtful, and it may be a nearby nonmember instead.

The photograph of GR8 in this page was obtained by Deidre A. Hunter of Lowell Observatory. It is a so-called UBV image, i.e. a combination of images obtained in the U-band (UV), B-band (blue) and V-band (visible light), and assigned blue to U-band, green to B-band and red to V-band. It was taken from D.A. Hunter's UBV collection.

  • HST image of GR8


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    Hartmut Frommert
    Christine Kronberg

    Last Modification: October 31, 2001