April 2015 - Double Star of the Month
STF1555 (11 36 17.94 +27 46 52.7) is in Ursa Major in a fairly sparse part of the constellation down by the Bear's front foot. It is perhaps most eassily found by moving 5 degrees south-east from the bright binary xi UMa (STF1523). This was an easy pair for the small aperture at discovery at 1".4 but during the next one hundred years the two stars approached each other until minimum separation of about 0".1 was reached in the 1930s and since then they have been separating. The nature of this system is a little unclear but observations over the next decade or so will show whether it is an optical pair (as classified in the WDS, or a highly inclined binary system, as suggested by Docobo in 2007 when he derived an orbit of 916 years for it. The orbit predicts star B beginning to turn back towards A with the separation slowly decreasing again. In spring 2015 B can be found at 150°, 0".67. The stars are magnitudes 6.4 and 6.8, and a third component of magnitude 11.2 which is listed as HJ 503, can be seen at 158° 22".5, both values are slowly increasing.
RMK 14 (12 14 02.71 -45 43 26.1) can also be found by reference to a nearby bright binary star. It forms an isoceles triangle of side about 5 degrees with gamma and delta Centauri to the south. Unfortunately, as of early 2015, gamma is near closest separation and needs a large aperture to resolve but RMK 14 (D Cen) is a beautiful pair which is worth searching out. The primary is a K3 giant of visual magnitude 5.8 and is also known to be a spectroscopic binary. The companion can be found at 243° and 2".7 having closed up from 4" at discovery. This is a distant pair - Hipparcos lists the parallax as 5.71 mas which, as it happens, translates to 571 light years. The colours seem to be well determined. E. J. Hartung gives orange and white whilst more recently, Richard Jaworski finds yellowish-orange and white. Sissy Haas notes it as a
Bob Argyle - Double Star Section Director
April 2015 - Galaxy of the Month
NGC 4330 in Virgo
This interactive image of NGC 4330 was provided by the Sloan Sky Survey using Aladin Sky Atlas.
This finder chart should help you locate this galaxy, and a few others too.
As spring rolls around it would be remiss not to choose the galaxy of the month from the Virgo cluster. As always with such a well-known cluster most people have their favourite galaxies but for this month I have chosen the little observed edge on galaxy NGC 4330.
Situated in a nice field of galaxies NGC 4330 was first discovered by Bindon Stoney is 1852 using Lord Rosse’s 72" at Birr. It was later independently rediscovered by d’Arrest using a 15.4" refractor. The other galaxies in the field NGC 4294, 4299 and 4313 were all discovered by William Herschel so this suggests that NGC 4330 is not going to be any easy target.
The galaxy itself is a late type spiral galaxy with a small bulge that is currently falling in towards the centre of the Virgo cluster as defined by M87. Because of this it is undergoing ram stripping of its gas, a process whereby the gas in the galaxy is stripped out by the interaction with the intra-cluster medium. As such NGC 4330 would appear to be transforming from a spiral galaxy into a lenticular galaxy. NGC 4330 appears to have a bright UV tail consisting of neutral Hydrogen (HI) gas which points directly away from M87. Currently NGC 4330 only appears to have about 15% of the expected HI mass of a similar field spiral which suggests that it is well on the way to becoming a lenticular. Although it is relatively close in spatial terms to the larger spiral galaxy NGC 4313 the stellar component of NGC 4330 does not look like it has been disturbed by gravitational interaction with it.
Observationally all four galaxies NGC 4294, 4299, 4313 and 4330 should fit in the same field of view of a medium power hyper wide field (100 degree field) eyepiece. For those with larger telescopes it may be possible to pick up the very much fainter galaxy IC 3209 near NGC 4313. IC3209 was discovered visually by Frost using a 24" refractor so it should be visible to observers with dark skies and a 20" telescope. It may also be picked up by those using electronic assistance.
Interestingly NGC 4330 is not mentioned in either the NSOG or L&S so a new challenge out there.
Owen Brazell - Galaxy Section Director