|Double Star Section Circulars|
We have a date for your calendar! The 2016 Annual Meeting in Cambridge on Saturday the 18th June 2016.
The news section contains more detailed items. I try to post items that may be of interest to members there. If you have suggestions, please contact me.
April 2016 - Picture of the Month
M101 in the Constellation of Ursa Major
Image was provided courtesy of Bob and Janice Fera. Please click on the image to be taken to a much larger version on their website.
It's a challenge to pick a galaxy that Owen isn't going to use in the Galaxy of the Month. Fortunately he has a passion for the faint and obscure, so I thought I was on safe ground this month. That was until I read this month's Astronomy Now…
All the same I'm happy with my choice. M101 is not a particularly difficult object unless you have poor skies. That's exactly what I've got, so I've never seen more than a smudge of light under the best conditions, and that's reason enough to include this detail packed wide field image.
For those with small scopes or binoculars and skies like mine M101 can be an interesting hunt in itself. For something tougher why not go after its HII regions. It's also worth taking a look at the full size image on Bob and Janice's website, because there are plenty of other galaxies to chase in this field!
James Whinfrey - Website Administrator.
Object of the Season (Winter 2015)
Quasar 3C 273 in Virgo
Quasar 3C 273 in Virgo will be announced in DSO 170, and the results will be published in DSO 172.
This image was supplied by the Hubble Space Telescope (HST). Credit: ESA/Hubble & NASA
Quasar 3C 273
Wolfgang Steinicke - Nebulae and Clusters Section Director
April 2016 - Galaxy of the Month
NGC 3865 and NGC 3866 in Crater
This interactive image of the NGC 3865 was provided by the Digitised Sky Survey using Aladin Sky Atlas. You can download a finder chart for the area. There's a SkyTools chart for the position of NGC 3854. You're advised to read on to find out why that might be important!
The constellation of Crater is often ignored from mid-northern latitude because it never rises very high above the murk and is not a distinctive constellation like Corvus. There are however a number of interesting galaxies in this area.
The galaxy of the month this month is the pairing known as NGC 3865 and 3866. However as always in the NGC if only it was that easy as the pairing are also known as NGC 3854 and 3858 and the literature seems confused as to what designation to use for them. So for instance Megastar and NSOG use NGC 3865 and 3866 as the primary designation whilst SkyTools for instance uses NGC 3854 and 3858.
The galaxies were originally found visually in 1880 by Andrew Common using a 36” reflector and Dreyer uses the 3865 and 3866 numbers for that discovery. Common’s positions however were not very accurate so they were rediscovered in 1886 by Leavenworth using a 26” refractor. His positions were notoriously bad (at least in RA) so Dreyer added these as new objects in the NGC with the numbers 3854 and 3858.
The whole sorry story is described by Harold Corwin in his NGC notes (http://haroldcorwin.net/ngcic/) . The problem comes in deciding what NGC number to call the objects because as we have seen they are already mixed up. In theory as Common found them first they should be called by his numbers.
Interestingly there is some suggestion that this pair is part of a loose group of 18 galaxies, however this comes from a statistical study of galaxies from the 2MASS survey so the reality of this group may be questionable. The group is not listed in any of the other optical galaxy group catalogues.
NGC 3854 is a barred spiral but does have odd looking spiral arms, perhaps as a result of some form of interaction. It is also very prominent in both the 2MASS near IR images and the GALEX UV images. Hubble images show a very bright core with complex dust clouds.
NGC 3858 also looks like it may be distorted but the image is complicated by a second bright source near the nucleus which may be a superimposed star or perhaps part of the galaxy. Unfortunately, there are no detailed images of the galaxy to resolve this issue. NGC 3858 is also classified a type 2 Seyfert. It appears to be part of the group with 3854.
L&S suggest that 3854 (there listed as 3865) is barely visible in 15cm but visible in 30cm. They also suggest that 3866 is just visible in 30cm. Night Sky Observer's Guide (NSOG) suggest both are targets for 40-45cm telescopes and 3866 is tough. These observations will be from much further south than the UK so it will be interesting to see what can be seen from here.
Owen Brazell - Galaxy Section Director
April 2016 - Double Star of the Month
STF 1517 (11 13 41.22 +20 07 44.9) is very easy to find. It is about 30 arc minutes south and slightly west of the 3rd magnitude delta Leonis. Found by F. G. W. Struve at Dorpat, this binary appears to be moving in an orbit which is very highly inclined. Motion is therefore mostly in separation and between 1820 and the late 1890s the stars closed from more than 1 arc second to about one-quarter of an arc second. After that the quadrant changed and they began to separate. The proper motion of the system is large enough that we can say the system is definitely physical. The USNO Sixth Orbit Catalogue gives a period of 924 years which is highly speculative as the motion has been virtually linear since discovery.
The calculated position for early 2016 is 316° and 0".71 making it a good test for 20-cm. The stars are of similar brightness but a little on the faint side (mags 7.5 and 8.0). As part of his proper motion programme, Burnham added a star of mag 10.8 at 246" and 97° but the distance is increasing rapidly due to the proper motion of 0".4 annually in the bright pair.
BU 28 (12 30 04.93 -13 23 35.0) is one of Burnham's most interesting discoveries. Its low number tells us that it was in Burnham's first list of 81 new pairs which he published in MNRAS in 1873. Burnham often underestimated the magnitude of the fainter star in very close and unequal pairs and in this case he assigned a value of 12 to the magnitude of B, calling the pair
This is a pair with a period of 151 years and the separation ranges from less than 0".4 to 2".2 which, fortuitously, is where it is at present, so now is the very best opportunity to observe these stars. It is found 3 degrees due north of delta Corvi, but the low declination from the UK means that a good steady night is required. The writer has not yet looked at this system but will put it on his 'to do' list. BU 28 is 80 light years distant and moving across the sky at more than 0".25 per year. It is leaving behind two distant comites (mags 10.6 and 11.6) which are currently both 71" distant.
Bob Argyle - Double Star Section Director