|Double Star Section Circulars|
There's been a change of date for the 2017 Annual Meeting in Cambridge. Please make sure that you have Saturday 3rd June 2017 in your diaries.
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.
September 2016 - Picture of the Month
IC 5332 in Sculptor
Back to the southern skies this month with data collected by The Star Shadows Remote Observatory (SSRO) at PROMPT2 - CTIO near La Serena in Chile. I also thought it was about time a galaxy appeared on the Picture of the Month and this is a real beauty, and its brought friends.
This image is provided with the kind permission of Warren A. Keller. The images were acquired by SSRO: Warren Keller, Steve Mazlin, Steve Menaker, Jack Harvey. Please click on the image to be taken to Warren's website for a higher resolution version, its really worth the effort.
In Warren's words
IC 5332 in Sculptor is a seldom seen Sc-type spiral galaxy. At a distance of 39,000,000 light-years, it is quite faint and considered 'unremarkable.' Sadly, precious little is written about it but I hope this image will spark some interest in IC 5332. There are numerous, fascinating galaxies surrounding the target, the most interesting of which, PGC 132690 appears at 4 o'clock.
September 2016 - Galaxy of the Month
NGC 741 in Pisces
The galaxy pair NGC 741 and 742 were first discovered by William Herschel in December 1784 using his large 20 foot telescope. They are part of a small group of galaxies listed as WBL 61 which, along with NGC 741 and 742, also contains the galaxies UGC 1425 and 1435 along with a couple of anonymous small galaxies.
The group does have some nomenclature confusion (as always) in the NGC/IC as a small galaxy close by the main pair is listed as IC 1751 and displayed as such in star charting programs such as Megastar and SkyTools. It is now known that in fact IC 1751 is a duplicate observation of NGC 741 and the galaxy formerly known as IC 1751 should now be called MCG 1-6-6. It is also part of the WBL 61 group.
The main pair of galaxies appear to be interacting and probably had a collision a few 10’s of million years ago. It is likely that this interaction between NGC 741 and NGC 742 took the form of an almost head on collision.
This close up of NGC 741 and NGC 742 was provided by the Sloan Digital Sky Survey.
NGC 741 would also appear to be an inactive AGN as it shows an old faint radio lobe. There appears to be both a radio and an X-Ray filament linking NGC 741 and NGC 742 as well as a hot gas bubble in the group. Both NGC 741 and 742 show point radio sources at their core which suggests the collision was not too disruptive. The results of the collision mirror the optical remnants of the more well-known Taffy Galaxies UGC 12914/12915.
In terms of group morphology NGC 741, NGC 742 and MCG 1-6-6 are all elliptical galaxies. UGC 1425’s type is unknown but it is probably either an elliptical or lenticular whilst UGC 1435 is probably a spiral galaxy. The interacting pair NGC 741/742 are also known as VV175. NGC 741 is a giant elliptical galaxy that appears to be the centre of a group of approximately 40 galaxies in total. The deep SDSS image shows a lot of faint galaxies in the area.
Visually NGC 741 should be seen in perhaps 20cm but to see NGC 742 will require probably 30cm and a high power to separate from NGC 741. To get the third member of the triplet MCG 1-6-6 will probably require a telescope in the 40cm class and good skies. The two fainter galaxies may just appear as stellar spots. NGC 741 is also part of the Herschel II list from the AL. I suspect that to pick up the UGC galaxies visually, especially from the UK, will require 50cm aperture or better.
Owen Brazell - Galaxy Section Director
A few of our members have provided observations for this field.
September 2016 - Double Star of the Month
Located in Cepheus, STT 461 = 15 Cephei (22 03 53.86 +59 48 52.5) offers a stellar grouping which more resembles an asterism than a multiple star. On the basis that a picture is worth a thousand words, an image from the POSS Quick V survey is appended showing the main components of the group.
This image was provided by the Digitized Sky Survey.
STT 461 is located close to the galactic equator and can be found about 2 degrees north-west of the orange supergiant zeta Cep. (mag. 3.4), the most south-easterly of the five bright stars in the pentangle of Cepheus. W. J. Hussey, who re-observed the complete STT catalogue using the Lick 36-in (1901) merely measured AB and the 9th magnitude companion C. The WDS lists eight stars to mag 14.3; the primary star is a hot B1 dwarf of magnitude 6.6 and has B (mag 11.4) 11" distant in PA 297. C which is a K0 giant is 90" away in PA 40. There is little relative motion in the group, which, if the stars are all at the same distance as A, lies about 1500 light years away.
One of S. W. Burnham's earlier discoveries (BU 172), made with the 6-inch Alvan Clark refractor, was 51 Aquarii (22 24 06.87 -04 50 13.2). At that time Burnham's telescope was not fitted with a micrometer so his friend and colleague, Baron Ercole Dembowski in Italy measured the pair for him. In 1875 the two stars were at PA 20 degrees and separated by 0".46 so offered a tough test for Dembowski's 7.5-inch refractor.
The pair then slowly closed through most of the last century, reaching a minimum distance of 0".11 around 1987 when the position angle was changing by 20 degs per year. A good set of speckle measures since then means that the orbit is now tolerably well-known. The period is 145 years and at the time of writing the separation was just under 0".5 and widening, with the companion almost at the point in the orbit where it was discovered last time around.
A good 20-cm should show the pair but its fairly low altitude means the air needs to be steady. On 1782 Oct 2, William Herschel noted three faint and distant companions to 51 Aqr, but the duplicity of the primary star, then close to its maximum separation of 0".6, escaped him.
Bob Argyle - Double Star Section Director
Object of the Season (Summer 2016)
Planetary Nebula NGC 7009 in Aquarius
This image was supplied by the Hubble Space Telescope (HST).
The planetary nebula NGC 7009 in Aquarius will be announced in DSO 172, and the results will be published in DSO 174.
Wolfgang Steinicke - Nebulae and Clusters Section Director