mercredi 3 septembre 2008

Ara 3

Ara commemorates the altar on which sacrifices were made to the gods, in both Greek and Roman times. The Romans called it Ara Centauri, considering it to represent the altar Centaurus used (perhaps to sacrifice Lupus, the Wolf).
The constellation is nearly out of sight from North America and Europe, as its stars extend from -46º to -60º. (In fact it goes much further south, however except for a faint globular cluster there's nothing of interest south of delta Ara.)
And yet this rather obscure constellation has a number of rather interesting deep sky objects.

Double stars:
Gamma Arae is a fixed binary with rather faint companion: 3.5, 10; PA 328, separation 18". A second companion is twelfth magnitude: PA 66º, separation 41.6". (Burnham questions whether these form a true binary.)
h4876 is a pleasant multiple in the star cluster NGC 6193 (see below): 6.6, 8.5; 14º, 1.6"; there is a seventh magnitude companion at PA 266º and 9.6".
h4866, better known as R Arae (see below): 6.0, 8.5; PA 123º, 3.6".

Variable stars:
The only variable of any interest in Ara is R Arae, an eclipsing binary which changes from 6.0 to 7.0 every 4.4 days.

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