|Double Star Section Circulars|
Thank you to everyone that attended our Annual Meeting. As requested, Owen and David have given me their presentations which can be downloaded from the meeting archive page.
Someone in the US would like to know if anyone with a copy of "Astronomy Delights" by Magda Streicher might be interested in selling. If you would please contact me so I can put you in touch.
June 2016 - Picture of the Month
The Region surrounding Antares in Scorpio
This outstanding image is here this month because I spotted it on www.capella-observatory.com and was stunned by the colour and how many deep-sky objects it contains.
There are no less than three large globular clusters, a mass of bright nebulae with a few dark ones thrown in, and too many double stars for me to count! I haven't spotted any galaxies though 😉
But my ulterior motive is that this is a composite of images taken on film. I'm still a film photographer in the daylight, and the detail and vibrancy of this image leaves me stunned. Please click on the image above to view its larger brother it's well worth it.
It's not the easiest region of the sky to observe from the UK, because it's low and the skies are always bright, but those further south may have more success in June.
James Whinfrey - Website Administrator.
Oh, and there are also a couple of planets nearby this year, but we don't speak of them.
Object of the Season (Spring 2016)
Dark nebula B 86 and open cluster NGC 6520 in Sagittarius
Dark nebula B 86 and open cluster NGC 6520 in Sagittarius will be announced in DSO 171, and the results will be published in DSO 173.
This interactive image of the NGC 6520 and B86 was provided by the Digitised Sky Survey using Aladin Sky Atlas.
Wolfgang Steinicke - Nebulae and Clusters Section Director
June 2016 - Galaxy of the Month
NGC 6702 in Lyra
Summer nights in northern climes are not very good for any form of deep sky observing, let alone hunting galaxies and I had debated whether or not to have a GOM for June and July. However just to keep the sequence going for June I decided to add a couple of galaxies in Lyra to the list, NGC 6703 and 6702.
Although NED suggests that they are a physical pair the fact that the recession velocity for NGC 6702 is 4727 km/s and NCG 6703 has a recession velocity is 2365 km/s suggests that they are not in fact physically associated but may be separated by 30 Mpc.
Visually they are challenging enough objects that they were not discovered by either of the Herschel’s but had to wait until 1863 when they were found by d’Arrest using an 11” refractor.
NGC 6702 is classified as an elliptical galaxy (E3) whilst 6703 is a lenticular (S0/E). Images from the DSS show that NGC 6703 appears to have a bright core and then a much fainter halo whilst NGC 6702 appears to be elongated and with a much fainter extension. For owners of larger telescopes there is also an interesting edge on galaxy UGC 11357 close by as well, although this is very much fainter.
NGC 6702 shows the attributes of a LINER galaxy, one that shows emission lines and probably a sign of a mild AGN or enhanced star formation. NGC 6703 is about 26 Mpc from us whilst NGC 6702 would appear to be nearer 60 Mpc distant. It is possible that NGC 6702 may have undergone a merger on a relatively recent (2 Gyr) timescale from both the colour and the fact it has two distinct globular cluster systems. This would also be borne out by the fact that deep images show a dust lane near the centre of the galaxy.
NGC 6702 was also the source of a recent supernova 2002cs which was discovered by the amateur astronomer Mark Armstrong and appeared to be a Type Ia, typical for an elliptical galaxy. Both of these galaxies may be seen with a 20cm telescope, although NGC 6702 will be tough to find and will require averted vison at the very least.
Owen Brazell - Galaxy Section Director
June 2016 - Double Star of the Month
16/17 Dra (16 36 13.72 +52 55 27.8) is a 90" binocular pair to be found about 15 degrees preceding the head of Draco and the stars are of magnitude 5.4 and 5.5. William Herschel noted that A itself was a rather unequal but easy pair 4" apart, and he included it is his 1782 catalogue as H I 4. He reported that
COO 197 (16 25 17.59 - 49 08 52.2) is a rather faint pair (mags 8.1 and 8.2) in southern Norma, near the border with TrA, which appeared in the catalogues of stars compiled at Cordoba Observatory.
It was first measured as double by R. P. Sellors at Sydney in 1895 using the 11.5-inch refractor. It was found to be in slow direct orbital motion and in 1977 an orbit was calculated with a period of 311 years. In 2008 the writer observed it with the large refractor in Johannesburg and at that time the observed position angle and the calculated value differed by more than 20 degrees. Andreas Alzner then performed a re-calculation of the elements of apparent orbit and found that the period was much longer (1132 years). In mid-2016 the stars will be found at 93 degs and 2".3.
In recent years, observations of this system with high resolution techniques and large telescopes have revealed that it is quite a complex multiple star. Using the NACO infra-red camera on one of the 8.2-metre VLT telescopes in 2004, Chauvin and colleagues found that B was again double at a distance of 0".1. The image in the journal shows the two stars clearly separated, but nearby star A appeared single. However, in 2014 Andrei Tokovinin also resolved A into two unequally bright stars separated by 0".1. It appears likely that there is also a spectroscopic sub-system in either Aa or Ab but which of the stars it can be pinned to is not yet determined. A 12th mag star now at 77 degs and 20" is being left behind.
Bob Argyle - Double Star Section Director