|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.
August 2016 - Picture of the Month
The Veil Nebula
This image was provided courtesy of Sara Wager. Please visit her website for much detail about the image and a far better version.
Nights are getting darker at northern latitudes, astronomical darkness has returned to the UK, and Cygnus is overhead. I have a bit of a mission at this time of year: to explore the Veil Nebula.
I've heard that its visible with the naked eye with the help of a good O-III narrowband filter from really dark skies, but it certainly isn't from any sky I've experienced.
There aren't all that many supernova remnants accessible to my small scopes which makes the Veil a bit of a seasonal treat. Especially since the whole complex favours a short focal length due to its huge size. However, the individual NGC objects can be explored in detail with a bigger aperture. So the Veil has something for everyone.
I love the visual challenge of trying to pull detail from the background glow, but as Sara has shown with this wonderful wide-field mosaic, it responds really well the narrowband imaging. Her web page highlights the Eastern and Western Veil where I've had visual success… albeit somewhat less well defined.
James Whinfrey - Website Administrator.
August 2016 - Double Star of the Month
STF 2690 (20 31 11.94 +11 15 37.7) was found by William Herschel in 1779 and he called it H III 16. Since that time the position angle has reduced 26° to 255° and the separation has increased from 15" to 17".6.
Located in Delphinus it can be found just 30 arc mins preceding epsilon Del. Also in a low power field is 1 Del (BU 63) an unequal close pair which is a test for 15-cm.
The components of STF 2690 are mags 7.1 and 7.4 and Sissy Haas called them both 'peach-white'. Whilst observing at George Bishop's observatory, at South Villa in Regent's Park, London, W. R. Dawes noted
DA 1, as the close pair became known, has a highly eccentric orbit and the separation ranges from 0".55 to 0".02, a distance which it attained in the last years of the previous century. It is now widening and in mid-2016, the separation is expected to be 0".34. The stars are mags 7.9 and 8.0 so this will be a severe test for 30-cm. A is also a very close pair being found in speckle survey of B stars in 1983. Motion appears slow and the period is likely to be a century or more.
Rho Capricorni (SHJ 323 - 20 28 52.19 -17 48 49.2) is the northernmost of a bright triangle of naked-eye stars about 5 degrees south-south-east of beta Capricorni. Of the other two, omicron featured in this column in 2015, and pi will appear in 2017.
Although discovered by the elder Herschel the pair now has the moniker SHJ attached to it - the name for stars catalogued by James South and Sir John Herschel.
This is a binary of period 278 years which is now widening but will remain quite a difficult object for the northern observer. The writer has not yet observed it but with a magnitude difference of 2 between the brightest components and a separation of 1".8 then it requires a good night to be seen.
There is a 13.3 star at 55" (distance increasing) and a 6.7 mag star some 259" away (and increasing) has, in turn, a companion of mag 10.6 at 54" and is catalogued as DOB 13DE.
Sissy Haas notes that A and D are pretty -
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
August 2016 - Galaxy of the Month
NGC 7727 in Aquarius
NGC 7727, also known as Arp 222, is a face on spiral galaxy in Aquarius.
First discovered by William Herschel in 1785, the galaxy has numerous star streams and plumes associated with it which are probably the result of a merger with another spiral galaxy about 1 billion years ago. It may take another billion years for this merger to settle down. It was this odd shape that led to its inclusion in Arp’s catalogue of peculiar galaxies. The support for the merger scenario comes from the fact that there are two star like objects near the core of NGC 7727, one of which may be the core of the merging galaxy and the other the main core of NGC 7727.
NGC 7727 does not seem to have a large reservoir of hydrogen gas to form new stars so it is probably going to become an elliptical galaxy in the future. Images from GALEX, an ultraviolet satellite, show very little star formation going on at the current time in NGC 7727 compared to its neighbour NGC 7724.
Deep images such as those at Kent Biggs' website, the Sedona Stargazer Observatory gallery and captured by the Chilean Advanced Robotic Telescope 32 inch show the tails and plumes in the galaxy very well. The second link also shows an enhanced version of the core area which shows the dual cores as well.
NGC 7727’s classification of SAB(s)a pec also gives an idea of its jumbled state. The globular cluster system of NGC 7727 is also strange and it appears to contain 25 young globular star clusters which also support the merger hypothesis. Deep Hubble images show a string of dust clouds, perhaps remnants of spiral arms, in projection across the front of the galaxy. Hubble legacy images can be obtained from their website if you want to do your own processing.
NGC 7727 is also potentially part of a small group of galaxies listed as LGG 480, which also includes the nearby NGC galaxies 7723 and 7724, along with a couple of MCG galaxies, MCG-2-60-7 and MCG-2-60- 10. The reason I suggest that this group assignment may not be correct is that although NGC 7727 and 7723 are at approximately the same distance of 27 Mpc, NGC 7724 is listed at 37 Mpc in NED. The recession velocities however are fairly close.
The Night Sky Observer's Guide (NSOG) reports all the galaxies should be visible in a 20-22cm telescope but to see detail you may need 35cm telescope. NGC 7727 is also in the Herschel 400 list from the AL. A medium power field, say 200x centred on NGC 7727 should show NGC 7724 as well using a modern hyperwide eyepiece (100 AFOV). Modern visual observations of the galaxy can also be found on the Deep Sky Observer's Companion – the online database (DOCdb).
Owen Brazell - Galaxy Section Director