5 Attachment(s)
Object of the Week, September 29, 2013 – NGC 7250
Object of the Week, September 29, 2013 – NGC 7250
NGC 7250
Lacerta
Position
RA 22 18 17.8
DEC +40 33’ 45”
Size: 1.7’ x 0.8’
Mag: 12.6 (V)
Type: Starburst Galaxy / Possible Double Galaxy
The recent supernova SN 2013DY in Lacerta was one of the highlights of this past summer, but not for its own merit: Rather, it was the reason for “discovering” NGC 7250, a little known gem of a galaxy in the usually neglected constellation of Lacerta, the Lizard. Lacerta culminates during fall evenings, so now it’s the ideal time to observe NGC 7250.
This little galaxy sits just to the north of the middle star of a distinctive asterism (made of 10th and 11th magnitude stars) shaped like a bent arrow, making it a snap to identify the correct field. I first observed NGC7250 (when I heard of SN2013DY) on July 29th, 2013, from a rural site (SQM averaging 20.9 at the zenith) with my 6” achromatic refractor. Although some observing reports I had read described NGC7250 as “very faint” in 10” instruments, both the supernova AND the galaxy were readily visible in my 6” refractor, provided I used rather high power (129X was ideal). The galaxy was distinctly lens shaped with a steady brightness profile, but at the time it was a bit overwhelmed by the light of the 11th magnitude supernova on one side and of the 11th magnitude field star on its other side.
Attachment 900
The tiny galaxy seemed like an ideal candidate target for my 18” dob, and I re-observed it on August 8, 2013, from a much darker mountain locality with the lightbucket. Using a power of 276x I logged a distinctly elongated 3:1 shape for the galaxy, with a brighter core area that was even more elongated (4:1) than the outer halo. What piqued my interest though was that this inner, brighter area seemed “split”, especially with averted vision. It sort of reminded me of a tiny “M82” contained within the halo of NGC7250. After finishing the observation, while driving back, I kept thinking whether this split was real, or whether my mind was playing games – could it be that the light of the nearby supernova was creating contrast effects?
Attachment 901
The next day, I found out that what I was seeing was real. Not only that, but actually the second brightening to the north of the nucleus is actually further split in three sections! In addition, there is a debate about what this collection of bright knots might be. The only piece of information that seemed to be available on the web is Courtney Seligman’s website (http://cseligman.com/text/atlas/ngc72a.htm) which mentions that this group of (at least!) three bluish bright knots are listed as the galaxy PGC 214816 in LEDA catalogs but he doubts about their galactic nature! I have also located a report where the author considers this “cosmic mess” as he calls it the result of a galaxy merger (http://cosmoquest.org/forum/showthre...warf-galaxies&). Amazingly, this galaxy was not listed by Arp in his famous catalog of Peculiar Galaxies, nor has it ever received (it seems) any distinct fame in the amateur astronomer circles! I have found very few observational reports for this galaxy, which is surprising as the second brightening is distinctly visible (but not split in three parts) in DSS photographs. The only report that mentions an observation of the second brightening was by Steve Gottlieb in his NGC Observations, made with his 17.5” dob.
Attachment 902Attachment 903
Needless to say, I impatiently waited for another observing opportunity. Now that I knew that the second brightening was real, I wanted to examine it as much as I could. On September 5, I was again at my usual mountain site with quite steady conditions, which allowed me to push the magnification of my 18” dob to 552X. I could hold steady the second brightening with direct vision, and I could detect that it seemed triangular, but I was unable to further split it in three sections. The dimming of the supernova certainly helped my observation. The galaxy has quite a high surface brightness, so it can take magnification well. After my last observing session, I thought that I should check the galaxy with OIII or H-beta filters. Maybe the brightening could be extensive hydrogen clouds with star-forming regions. Seems far-fetched, but who knows?
Attachment 904
So, NGC7250 can give us a nice set of challenges: What is the smallest aperture through which this galaxy can be seen? It was not hard in my 6” on a good night, and I think that it might be detected even with 4”. What is the minimum aperture and magnification required to “split” the galaxy and get that “M82 within galaxy halo” effect?What are the prerequisites for splitting “PGC 214816” into the three knots? Magnification, steadiness of seeing, or transparency? Does this “second brightening / “galaxy” respond to nebula filters? And, of course, there are the astrophysical questions: Are these really two superimposed galaxies? Are we watching the merger of two galaxies? Or, are the second group of knots mere starburst regions within NGC 7250?
I know for sure that I will be soon returning to NGC7250. And don’t forget,
“Give it a go and let us know!”
Good luck and great viewing!
