|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.
October 2016 - Picture of the Month
NGC 7023 in the Constellation of Cepheus
Image was provided courtesy of Bill Snyder. Please click on the image to be taken to a much larger version on his website. He has much more detail about the image itself.
So after a brief sojourn to galaxies I'm back to a couple of favourites: Cepheus and nebulous open clusters.
The Iris nebula ticks those boxes very nicely, except NGC 7023 is a reflection nebulae surrounding that bright 7th magnitude star in the middle. According to Archinal and Hynes (Star Clusters) there is an open cluster, but it has nothing to do with the nebula.
Collinder 427 is just to the right of NGC 7023 itself in this fabulous image, but that's close enough for me to mention it, though as a poorly detached cluster with relatively few stars it isn't really the highlight here.
However with the advent of the Caldwell Catalogue (NGC7023 is No. 4) it seems that the supposed open cluster surrounding that central star (Collinder 429) might be real again! All very confusing as usual and I'm not going to pretend that I have an answer.
NGC 7023 is frequently imaged, but I think that Bill has framed this subject extremely well and the dust clouds lend great depth. Well worth observing visual with any aperture.
James Whinfrey - Website Administrator.
October 2016 - Double Star of the Month
STF3050 (23 59 29.33 +33 43 26.9) is a beautiful pair of white stars forming a long period binary system to the north of the Square of Pegasus. More specifically, it is 5 degrees north of and 2 degrees preceding Alpheratz (alpha And).
The components are mags 6.4 and 6.8 and the spectral type of star A is F8V, whilst that of B is likely to be similar. The first observation in the WDS is for 1777 representing the discovery of the system by Christian Mayer. It is the 80th and last entry in his pioneering double star catalogue. William Herschel later recovered it on December 13, 1787 and called it H N 58.
Thomas Lewis in his book on the Struve stars published in 1906 said it was
Lewis noted that both stars were yellowish.
Beta PsA, (22 31 30.33 -32 20 45.9) bemoans Jim Kaler on his Stars website, is a neglected object
Beta is certainly a fine double star and worth a visit, and the question of whether it is binary or not can be settled by considering the proper motions of the two stars.
The Hipparcos satellite reveals than A (mag. 4.3) is 143 light years away and moves across the sky, mostly to the east, at about 60 milliarcseconds per year. Star B has an almost identical proper motion and radial velocity and so is physically connected to A. Over the last 200 years the separation has reduced from 35".3 to 30".6 and the PA is almost fixed at 172 degrees.
The SIMBAD spectral types of A1 and G1 might suggest stars of white and pale yellow when in fact the observed colours (by Hartung) are given as pale yellow and white, although he notes that B sometimes appears reddish.
Bob Argyle - Double Star Section Director
October 2016 - Galaxy of the Month
NGC 7046 in Equuleus
Equuleus is not a constellation often thought of in deep sky circles, with good reason as there is really nothing of note in the constellation. It does however boast one reasonably bright galaxy in NGC 7046.
First discovered by William Herschel in October 1790, NGC 7046 is a barred spiral galaxy with a listed magnitude of 14. The core of the galaxy is probably all that will be seen, except with the largest scopes, of this object. It does have a fainter halo with some structure.
NGC 7046 is listed as part of a small group of galaxies including IC 1364 and IC 1368. The group is at a distance of perhaps 55 Mpc and appears fairly isolated. There is no evidence of any interactions in the group.
NSOG suggests 30cm is probably needed to see NGC 7046 and to use a relatively high power in which case more detail than just the core may be seen. L&S suggests 25cm will show it but 30cm is needed to see much detail. Although there are a number of IC objects in the general area of NGC 7046 most were found with a 30” reflector, however two, IC 1365 and IC 1368, were found by the 16-year-old Edward Swift using the 16” refractor that his father Lewis also used. As such these should be visible in larger modern telescopes (say 40cm+) from a good sky.
IC 1365 is interesting because it is also included in the VV catalogue of interacting galaxies as VV 508. In NED IC 1365 is given as a designation not to one object but to a group of galaxies closely packed together, it was probably the fact that they are so close that it was thought to be an interacting galaxy.
This close up of the group around IC 1365 was provided by the Sloan Digital Sky Survey.
The central galaxy in the group has a classification of cD i.e. a giant amorphous elliptical of a type normally found at the centre of clusters. It appears to have several other galaxies superimposed on its halo. It will be interesting to see if any of the large telescope owners can separate the galaxies. The group appears to be at a distance of about 207 Mpc.
The other Swift discovery, IC 1368, is actually over the border in Aquarius and quite a distance (40.8’) from NGC 7046. It appears to be quiet a nice edge on spiral galaxy. There are no visual observations I can find for IC 1365 or IC 1368.
Owen Brazell - Galaxy 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