Object of the Week, April 12, 2015 – NGC 5248

Object of the Week, April 12, 2015 – NGC 5248

Aliases: UGC 8616 = MCG +02-35-015 = CGCG 073-054 = PGC 48130
Galaxy Type: SAB(rs)bc
RA: 13h 37m 32s Dec: +08° 53’ 07”
Size: 6.2'x4.5'
Mag: 10.3V, 11.0B
Surface Brightness: 13.8 mag/sq. arcmin

The Atlas of Universe lists it as the main galaxy of a small subgroup of the Virgo III Group, at the extreme eastern end of Virgo -- not far from M5.


NGC 5248 was discovered by -- you guessed it -- William Herschel on 15 Apr 1784 (sweep 194). Who knows, perhaps he had just finished doing his taxes! ;) He recorded H. I 34 as "vB, nearly R and cometic but the nucleus is large and seems to consist of bright close stars, resolvable." He made a second observation on 1 May 1786 (sweep 560) and logged "vB, cL, E from np to sf, a small bright nucleus."

John Herschel made a slightly more detailed observation on 18 Jan 1828 (sweep 120) and noted "pB; vL; E 60° np to sf; psbM; 3' long, 2' broad." The spiral structure was discovered in 1855 using Lord Rosse's 72-inch.

On 19 Apr 1855, observing assistant R.J. Mitchell, reported "Large and pretty bright, Bright nucleus. Seen as in sketch, but not certain whether the lower branch joins the nucleus or is only the continuation of the upper curve." On 29 March 1856 he recorded "The preceding arm does appear to originate from the nucleus, which is very bright and oval shaped." Here's the page, including his notes and a rough sketch, from Lord Rosse's 1861 publication. The two brightest spiral arms are clearly shown in more detail on Plate XXVIII, fig 29 (does someone have a good photocopy of that page?)

Attachment 1601

Of course, it doesn't require a 72-inch to resolve the two main arms. Here are my notes with my 18-inch --

18" (6/7/08): bright, large, elongated NW-SE, 3.5'x2.4', sharply concentrated with a very bright, round 25" core. At 200x, two spiral arms extend out from the central region. The brightest and longest arm is attached at the west side of the core and gradually sweeps to the north. A couple of very faint, very small knots are embedded in this arm including one due west of the core. On the east end of the core a matching arm is attached that curves a bit more as it swings towards the south in a counter clockwise orientation. A faint star is just north of the central region and a brighter star is 1.7' S of center.

Images reveal numerous pink HII regions and blue OB-stellar associations in the two high surface brightness spiral arms as well as the low surface brightness outer arms. A few were noted above. But the 1983 Hodge-Kennicutt "An Atlas of H II regions in 125 galaxies" lists nearly a 100 regions.

Attachment 1604

I picked off a number of these knots through Jimi's 48-inch three years back -- quite an impressive view!

48" (5/15/12): beautiful two-armed spiral, very large, elongated ~3:2 SW-NE. The brightest portion is ~3.8'x2.5' but the faint, outer spiral arms increase the diameter to at least 5'. The galaxy is sharply concentrated with an intense oval core. The brighter spiral arm is attached to the north of the core, wrapping counterclockwise around the east and southeast side and is lit up by several fairly prominent knots. The arm dims fairly abruptly on the southeast side but continues unwrapping to the south, extending outside and just beyond a mag 13.5-14 star 1.7' SSW of center. A mag 15.3 star is 0.6' N of center, just outside where the arm emerges on the north side.

At least four distinct HII knots are in or near this arm, along with brighter segments. The following designations are from the 1983 Hodge-Kennicutt "An Atlas of H II regions in 125 galaxies". A faint knot, [HK 83] 26/28 is between this star and the core. The arm brightens along the east side of the core and include the faint knots [HK 83] 13/15, 28" NE of center, and [HK 83] 5/6 1.0' ESE of center. The most prominent knot along with this arm is [HK 83] 5/6, 1.2' SE of center.

Along the western arm, the first knot is [HK 83] 63, 0.8' W of center. A large brighter knot or arc ~1.1' NW of center includes [HK 83] 74/77/81. A faint knot, [HK 83] 66/71, is near the tip of this arm 1.5' NNW of center. A similar knot, [HK 83] 53, is 25" SE, on line with the core.

Attachment 1603

As always, “GIVE IT A GO AND LET US KNOW”

Nice OOTW Steve. One of the easiest spiral in the sky. Below some better copies of the historic 72" observation.

rough sketch
Attachment 1605

finer sketch - fig 29
Attachment 1606

My observation and sketch with 16" shows the two bright inner arms with a prominent HII region at the end of the SE arm.

16", 257x, NELM 7m+, Seeing III
Attachment 1607

Thanks for posting copies of the Rosse observations, Uwe. As you mention, this is one of the best non-NGC spirals to resolve, so I'm surprised it's not better known.

This is definitely a nice spiral. I looked at it last week with my 22":

There is an oval bright core surrounded by a large oval halo (axes of the ovals not in line). In this halo structure the spiral arms are visible as brighter edges of the oval structure. The W arm of the spiral is easy to see, the E arm is more difficult and not as well defined, but is appears to be somewhat longer than the W arm. The W arm also appears to be a bit straighter than the E one, which is more inward bent.

I took a look at this beautiful barred spiral at the end of my observing run this new moon, the last object of March 25th night in western Arizona. Here's what I logged:

"Fantastic barred spiral, perhaps a northern exemplar of the class. The structure is apparent even at low power. Round suddenly brighter core, two prominent arms emerge from the bar."

I also made the following rough sketch:
Attachment 5088

For some reason, I saw the western arm thicken at the junction with the bar, as I have sketched it. I was also unable to perfectly identify which feature on the image the knot I was seeing corresponded to. Reading Steve's 48" report makes me believe it must be the region composed of [HK 83] 5/6, which he considered the brightest in the 48".