OR 3: GSSP and Sierra Buttes (Globs)

by Steve Gottlieb

Steve

Palomar 5
15 16 05.3 -00 06 41
V = 11.8; Size 6.9'
18" (7/14/07): the best view of this low surface brightness globular was at 225x. Appeared as a very faint, round glow, ~3' diameter and involving a mag 13.5 star. Could hold continuously with averted vision, though the surface brightness is very low and even with no central condensation. The mag 13 star is offset to the west side of the glow and a mag 15 star 1' due east is also superimposed or a resolved member. Located 2.3 degrees NNW of M5 and 30' south of 5.6-mag 4 Serpentis.

NGC 5897
15 17 24.3 -21 00 36
V = 8.6; Size 12.6'
18" (7/11/07): this low surface brightness globular was easily picked up 12.5x in the 80mm finder as a small, faint, hazy knot. Excellent view at 225x in the 18" which showed 60-70 stars with a very weak concentration and no distinct core. At 325x, 90-100 stars were resolved over an 11' diameter though the halo does not have a well defined edge so the count is somewhat arbitrary. The hazy background glow of unresolved star is quite lively and irregular in surface brightness.

M4
16 23 35.3 -26 31 32
V = 5.9; Size 26.3'
18" (7/12/07): at 225x, the remarkable 10' central region is bounded by a nearly complete ring of stars with a prominent string (bar) of brighter stars oriented SSW-NNE nearly bisecting the central region. The center of this ridge of stars is intersected by a dense, elongated ring of stars with major axis E-W, with the majority of the stars to the east of the bar. A wide, brighter pair of stars (10.8/10.9 at 17") to the SE of the bar has an orange tint. Sprays of stars appear to emanate from the bar in all directions with a beautiful arc of stars curving along the entire north side of the core. The outer halo is relatively sparce but includes a number of brighter stars and appears to extend 15'-18' in diameter.

M12
16 47 14.5 -01 56 52
V = 6.8; Size 14.5
18" (7/11/07): at 325x this globular nearly fills the field and extends roughly 11' in diameter. Contains a very bright 3.5'x2.5' oval core, extended WNW-ESE. A mag 10 star with an orange tint is just south of the core, 2' from the center. Two other mag 10-11 stars lie 4' N and 5' ENE of center in the halo. The core is plastered with an immense number of mag 12.5-13.5 stars and in the central 2' is an incredibly dense mat of mag 13.5 and fainter stars. Very irregular sprays of stars emanate from the central region and form part of the very scraggly outer halo.hundred fainter stars in the central 8' over unresolved haze. The outline is very irregular and there are distinctive star-poor areas in the outer halo.

M10
16 57 08.9 -04 05 58
V = 6.6; Size 15.1'
18" (7/14/07): large, gorgeous GC at 225x, extends ~15' in diameter and fills most of the field. The cluster is sharply concentrated with an intense 5' core containing a huge number of resolved mag 13-15 stars over an unresolved background glow and beautiful strings of stars in the halo. At 323x the core is slightly elongated SW-NE, ~5'x4' in size. Strings of stars crisscross the core with a very small triangle of stars at the geometric center. At 393x, one of the 3 stars in this central triangle is a very close double. The core is pretty uniformly rich and evenly resolved and does not compress towards the center.

NGC 6284
17 04 28.8 -24 45 53v V = 9.0; Size 5.6'
18" (7/12/07): easily picked up at 25x in the 80mm finder with a very bright core and fainter halo. At 220x, this globular is sharply concentrated with an intense core that increases to the center. The 2' halo is very lively and several very faint stars are just visible. Clouds then interrupted this observation and I wasn't able to use high power.

Djorgovski 2
18 01 49 -27 49.6
V = 9.9; Size 3.5'
18" (7/11/07): easily picked up at 115x as a 2' round, hazy spot centered within a small trapezoid or"Keystone" asterism of stars. At 225x the cluster is very lively with several extremely faint stars briefly popping in and out as well as two brighter stars at the SW and N edges. At 325x the cluster is irregular in outline and a number of extremely faint stars are barely resolved, particularly on the north side. The brighter star at the NNW vertex of the Keystone is a striking double star.

NGC 6540 = Djorgovski 3
18 06 08.5 -27 45 55, Size 1'
18" (7/11/07): very unusual globular that is buried within a small asterism and requires careful viewing. At 325x a very distinctive 1.5' string or shallow arc of stars is oriented E-W and contains 6 stars (possible cluster members). Within this shallow arc is a 20" knot just east of the midpoint and this may be the core of the globular. The entire string is superimposed on a rich Milky Way background and it was very difficult to determine the diameter of the outer halo.

NGC 6642
18 31 54.2 -23 28 34
V = 9.4; Size 4.5'
18" (7/14/07): at 393x appears as a fairly small but fairly bright globular with a very bright 30" core and 2' halo. The small core is very mottled and partially resolved into 2 or 3 clumps. Roughly 15-20 mag 14.5-16 stars are just visible in the halo including a very close pair on the NNE edge. Located just 1.1 degrees NW of M22.

Palomar 8
18 41 29.9 -19 49 33
V = 11.2; Size 4.7'
18" (7/14/07): this moderately bright Palomar was immediately visible at 174x as a 3' disc with a slightly uneven surface brightness, with no visible core. At 280x, the central 2' is clearly slightly brighter and the 3.5' halo is very irregular or scraggly. Perhaps a dozen very faint stars are resolved over the face of the cluster. At 393x, a brighter star at the south edge of the core is a very close double and cluster is quite clumpy, although there was no additional resolution.

Palomar 9 = NGC 6717
18 55 06.0 -22 42 06
V = 9.2; Size 3.9
18" (7/15/07): at 280x, stands out prominently just 2' S of mag 5 Nu2 Sagittarii. The globular appears as an unconcentrated, low surface brightness hazy glow just 1' in diameter but with 5 likely field stars superimposed, giving the appearance of a small open cluster over unresolved background haze. At 393x, the five mag 13 and fainter stars are grouped into two close pairs with roughly similar separations and orientations. One pair is near the center (oriented ~N-S) and another is at the NE edge oriented NNW-SSE (catalogued as IC 4802) while another is at the WNW edge. The glow of the cluster is irregularly round (slightly elongated E-W) and has a well-defined edge, unusual for a globular.

Palomar 11
19 45 14.4 -08 00 26
V = 9.8; Size 8
18" (7/14/07): swept up at 150x as a very low surface brightness hazy region, ~3' in diameter with a few mag 15+ stars superimposed. Cradled by three mag 13 stars close SW, E and NE. A 22" pair of mag 11.5/12 stars lie ~3.5' N. The observation was interrupted before I could use higher power to resolve.

M2
21 33 27.2 -00 49 23
V = 6.6; Size 16
18" (7/17/07): overfills the 8' field at 393x with resolved stars from edge to edge. M2 contains a very bright 3' core that increases to a very intense 1' nucleus. The halo is very symmetric and thins out fairly evenly. A few hundred stars were resolved in the cluster with the central region extremely densely packed.