February 17, 2010: Touring the Celestial Zoo

Steve Gottlieb

Last Sunday night (2/14/10) I decided to take a chance on the fickle weather and headed down to Willow Springs. When I arrived there was a mix of haze and jet contrails criss-crossing the sky. Soon after it darkened, low clouds started drifting over and obscured most of the sky. Yuck. I patiently waited for conditions to improve while observing bright eye-candy and double stars. By 11:00 I was ready to call it a night and started putting my gear away as it looked like another lost winter night. But right on cue the skies started clearing as a cooler breeze came up and by 11:30 I was looking up at a perfectly clear, dark canopy. Conditions were cold and somewhat dewy but pretty dark with an SQM average of 21.58. Kevin Ritschel came out around midnight and we observed together until after 4:00AM when Omega Cen, Cen A (NGC 5128) and M83 were crossing the meridian.

Here's a potpourri of the evening's samplings:

Double Stars - When there were only sucker holes to look through in the sky, I decided to observe double stars instead of getting frustrated looking for faint fuzzies that always seem to lose the battle with gaps in the clouds. Here are a few that caught my attention in Lepus -

Kappa Leporis
05 13 13.9 -12 56 29
V = 4.4/7.4; Size 2.6"
Challenging, 2.6" pair with a large mag contrast. Cleanly split at 300x and just resolved at 175x when the seeing was steady. The primary was a pale yellow and the fainter companion a very light blue, though the contrast was not strong.

South 476
05 19 17.4 -18 31 12
V = 6.3/6.5; Size 39"
Very wide, matching pair of mag 6.5 white stars at 39". Easily split in the 80mm finder at 25x and also cleanly split using my handheld 15x50 IS binoculars.

h3752
05 21 46.3 -24 46 23
V = 5.5/6.7; Size 3.4"
Beautiful, 3.4" colored pair at 175x with a mag 5.5 orange primary and a mag 6.7 bluish companion. A mag 9.2 star is about 1' E and nearly collinear with the pair

A High Surface Brightness Planetary - compact planetaries under 10" are among the easiest deep sky objects to view in small scopes and under compromised sky conditions (though sometimes difficult to locate). The fun comes in jacking up the magnification to 500x or higher and looking for hidden structure. Williamina Fleming discovered IC 2149 in 1906 on a Harvard College Observatory plate.

IC 2149
05 56 23.9 +46 06 17
V = 10.6; Size 15"x10"
Easily picked up at 175x as a fuzzy bluish "star, typical of high surface brightness compact planetaries. At 450x, the bright. 11.6-magnitude central star was encased in a high surface brightness elongated halo, extending ~14"x8" E-W. The following end is a bit tapered and the halo on this side appeared brighter with the impression of a very tiny embedded knot. At 568x (8mm Ethos + 2x Powermate), a virtually stellar knot was definitely visible just a few arc seconds following the central star.

Low Surface Brightness Abell Planetary - one of my favorite early spring planetaries is Abell 33 in Hydra, a 4 arc-minute bubble that is adorned with a 7th magnitude on the southwest edge of the rim. It's easy to see how the Herschels would have missed this faint diamond ring, but it's an easy object with an OIII filter in 10" and larger scopes.

Abell 33
09 39 09.0 -02 48 33
V = 12.9; Size 275"x260"
Using 73x and OIII filter, Abell 33 was immediately visible with direct vision as a very large, well-defined 4' disc, attached to a 7.2-magnitude star at the SW edge. The rim is slightly brighter, noticeably along a 120 degree arc on the western side, giving a mild annular or bubble appearance. Removing the filter and upping the magnification to 280x, the planetary was still faintly visible and a 12" pair of stars was embedded at the NNW edge of the rim. At this power, the 15.5-magnitude central star was faintly visible (collinear with the double star).

Sharpless HII region - Stewart Sharpless' 1959 catalogue lists 313 HII regions, many of which are not plotted on standard sky atlases, so are often overlooked as deep sky targets. Auriga is home to several Sharpless objects, from the high surface brightness NGC 1931 (Sh 2-237) to the low surface brightness supernova remnant Sh 2-224 (anyone observe this one??)

Sharpless 2-217
04 58 45 +47 59.6
Easily picked up unfiltered at 175x as a large, roundish glow of low surface brightness with a diameter of at least 5'. A mag 9.4 star is at the E end and a group of four mag 11 stars are superimposed. The nebulosity is a little more extensive or brighter to the south of these four stars and is also slightly elongated E-W. There was no response using an OIII filter and only a very weak response to an H-beta filter.

While observing Sh 2-217 I noticed a fuzzy mag 12 "star" or very small knot on the SW end that would not focus cleanly and was clearly non-stellar at 275x. Checking later, I discovered this is an ultra-compact star cluster (resolved on infrared images) and HII knot at the SW edge of the ionization front of Sh 2-217 and it corresponds with the position of IRAS 04547+4753. The discovery article with an image of the cluster was published in A&A 399, 1135-1145 (2003) or tinyurl.com/ye58ywo.

Challenging Abell Galaxy Cluster - AGC 1377 (also known as Ursa Major I) is a fairly remote and difficult galaxy cluster. With a redshift of z = .051 it resides at a distance of 700 million light years but the kicker is that the rich cluster is located in the same field as a 5th magnitude star! The nearest member I viewed to this star was MCG +09-19-181, just 4.8' northeast of the glare. Here are the brightest two members -

PGC 36774
11 47 21.4 +55 43 49
V = 14.7; Size 0.7'x0.6'
This member of AGC 1377 appeared very faint, small, round, 20" diameter. The glare from mag 5.3 HD 102328 just 7' SW hampered the observation, but the galaxy was not very difficult if the star was kept out of the field. PGC 36805 lies 5.7' ENE.

PGC 36805
11 48 00.8 +55 45 41
V = 14.7; Size 0.8'x0.6'
At 280x appeared very faint, fairly small, slightly elongated, 30"x25", low fairly even surface brightness. Located 12' NE of the 5.3-magnitude star.

Naked-eye Messier Cluster - At mag 4.5, M41 is easily visible to the naked-eye in a dark sky, just 4 degrees below Sirius. Although it was likely noticed as a fuzzy patch in the sky in antiquity, the telescopic discovery generally goes to Hodierna in 1654 and rediscovered by Flamsteed in 1702.

M41 was perfectly framed at 73x with a 31mm Nagler (67' field). M41 extends roughly 35' in diameter though many of the brighter mag 7 and 8 stars are in a smaller central region. The cluster includes roughly a dozen brighter stars, many forming a large central oval ~15'-20' diameter and elongated W-E or SW-NE. Near the center is a richer grouping with a number of fainter stars and two bright stars including 6.9-magnitude orange HD 49091 (brightest member).

A number of loops and chains appear to spin out from the central grouping. One long chain extends NNW to the edge of the cluster and a shorter nearby chain heads WNW and includes a pretty pair (h2341) before bending abruptly SW. Two other chains extend from the center to the SW and ENE. About 20' SE of the center of the cluster is mag 6.1 HD 49333, the brightest star in the field though not a member.

NGC Asterism - NGC 2248 was found in 1853 at the private observatory of Edward Cooper in Ireland with a 13" refractor and listed as a nebulous object in the "Catalogue of Stars Near the Ecliptic Observed at Markree". In my 18", this object looks like a poor version of M73!

NGC 2248
06 34 35.7 +26 18 16
At 175x a small clump of 4 stars was resolved. The brightest two are a 16" pair of mag 12/13 stars, while the fainter two are probably mag 15-15.5.

Bright NGC Galaxy - NGC 2903 is one of the brightest non-Messier galaxies (V = 9.0) and leads the pack (at the western side of Leo) for the springtime parade of galaxies.

NGC 2903 - 175x provided a beautiful view of this barred spiral. The galaxy extends 2:1 SSW-NNE, roughly 8'x4', with a slightly brighter bar running through the major axis. The center is sharply concentrated with a very bright clumpy core. At the SSW end of the main body a faint arm emerges and sweeps around to the east. Near the NNE of the central bar is a brighter knot with its own NGC designation (NGC 2905) and beyond the knot is a fainter, less defined arm that curves around a short way to the west.

Exotic Blazar - OJ 287 is a well-studied blazar (quasar at z = .306 with an powerful jet pointing directly towards us) that displays extremely large and rapid variations at both radio and optical wavelengths with timescales varying from minutes to years. It was discovered in radio observations in 1967 and first identified on Palomar Sky Survey prints in 1968. The optical variation of this blazar is roughly 6 magnitudes! (mag 12.5-18 in the B band)

The April '08 S&T mentioned this object may harbor the most massive black hole known with 18 billion solar masses. A smaller black hole with 100 million solar masses apparently whips around it once every 12 years causing a 12-year periodicity in brightness.

OJ 287 was easily identified at 175x using a detailed chart of the field. This distant blazar appeared as a mag 14-14.5 "star". At 280x, I carefully compared the brightness of OJ 287 to three nearby mag 14.2, 14.6 and 14.9 stars that closely follow this highly variable blazar and the current magnitude appeared to be 14.2-14.3. You'll need a detailed finder chart to track down this stellar object but the position is 08 54 48.9 +20 06 31 (J2000), about 15' NE of a 6.6-magnitude star.

I wrote an article that will appear in next month's S&T (April) about observing blazars (several reach 14 magnitude or brighter), though this object is not discussed. Several blazars were originally discovered as variable "stars" as they appear virtually stellar and the concept of a variable galaxy was unimaginable. So, these objects are known by their variable star designations (AP Librae, W Comae, BW Tauri and BL Lacertae).

Steve