COTM: Antlia

Steve Crouch

Antlia is a group of inconspicuous stars (alpha is 4th magnitude) between Hydra and Vela that was introduced by Lacaille in about 1752. It was originally known as Antlia Pneumatica (the air pump) but this name was mercifully dropped in favour of the shortened version in more recent times.

There are very few deep sky objects of note, Hartung only listing two double stars and a number of galaxies. As usual, I used my 36cm C14 and a 31mm Nagler to make these observations from my backyard in Theodore.

1. Double stars

The two double stars that I observed are both quite easy and are possibly the only worthwhile objects in Antlia for small telescopes unless you have a very dark sky. ?1 Ant (09 30.8, -31 53) has roughly equal (6.2 and 7.0) yellowish-white components separated by 8” while ? Ant (10 29.6, -30 36) has 5.6 and 9.6 magnitude white components separated by 11”. Both were of course easily split in the C14.

Editor’s note: For medium telescopes there are quite a few doubles in Antlia, some with primary stars of mag 7 or 8. Among those worth looking at are:

HJ 4224 (0936.1, -3114) Stars mag 8.3 and 8,8 at an easy 7.5” separation – colours are yellow and white.

BU 215 (0954.1, -2800) Stars are mags 7.0 and 9.0 at 1.7” separation.

I 209 (1024.4, -3835) Stars of mag 8.4 and 8.6 at 1.2” separation – a pale yellow pair that’s not difficult with 15cm at medium power.

BU 2001 (1040.9, -3544). A test object – The stars are mag 6.4 and 8.9 at only 0.7” separation. Because of the brightness difference I’d expect this one to need about 25cm aperture and good seeing. Good luck.

2. Galaxies

The only other objects in Antlia are galaxies and the best known and brightest of these is NGC 2997 (09 45 38.5, -31 11 25) having a magnitude of 10.3. It’s quite large (5’ x 4’) and the surface brightness is therefore fairly low so a dark sky is needed for the best view. The C14 showed a reasonably bright haze with a very prominent central condensation, the nucleus of the galaxy. Some hint of spiral structure is also visible.

There are a few faint galaxies in the vicinity of NGC 2997 that I didn’t attempt. IC 2507 (09 44 33.8, -31 47 25) at magnitude 13.3 shouldn’t be too hard in a moderately large scope. It has a 13.2 magnitude companion, UGCA 180 (09 44 46.7, -31 49 30) that would also be worth searching for. ESO 434-40 (9 47 39.9, -30 56 57) at magnitude 14.1 is the brightest of a nearby group of ESO galaxies.

The next galaxy is NGC 3271 (10 30 26.4, -35 21 34), the brightest member of the Antlia galaxy cluster. It would be a good idea to have a finder chart of this area available when you are observing because it’s quite cluttered. Galaxies visible include NGC 3267 (10 29 48.5, -35 19 20), NGC 3268 (10 30 00.5, -35 19 32), NGC 3269 (10 29 56.9, -35 13 28), NGC 3258 (10 28 53.3, -35 36 19), NGC 3260 (10 29 06.1, -35 35 47) and NGC 3281 (10 31 52.1, -34 51 17). These galaxies are generally in the 11-13 magnitude range and should therefore be accessible to 20cm apertures under a dark sky. ESO 375-41 (10 29 31.0, -35 15 38) is also worth a shot although I couldn’t see it given the fairly bright sky during my observing session. Most of these galaxies are spirals and show bright central condensations.

Finally we have three small galaxies in a line pointing roughly WSW. These are NGC 3347 (10 42 46.6, -36 21 46), NGC 3354 (10 43 02.8, -36 21 46) and NGC 3358 (10 43 32.9, -36 24 37). All of these seemed to show central condensations and NGC 3354 was the faintest.