mardi 8 juillet 2008

Aquarius 9

Aquarius has a few nice binaries, a unique variable, and a few deep sky objects of some interest (but the Messiers here are generally sub-par). The stars are generally fourth magnitude.

The most notable asterism is of the water jug itself, tipped and pouring water. This small asterism, which fits nicely into a binocular field of view, is just west of alpha Aquarii and made up of zeta Aqr and three other stars.

Double stars in Aquarius:
Zeta2 Aquarii and zeta1 Aquarii form a binary of two equal white stars with an orbit of 760 years.
Zeta2 Aquarii is the primary: 4.4, 4.6; current PA 266º and separation: 2.3".
Struve 2944 is a nice triple system, with all three in a neat line.
AB: 7.0, 7.5; PA 276º, separation 2.5".C: 8.4; PA 106º, separation 50".
The binary is 2º due east of kappa Aquarii.
Struve 2988 is a very attractive pair of equal stars: 7.2, 7.2; PA 101º, separation 3.5".
The binary is 3º SW of psi1 Aquarii.

Variable stars in Aquarius:

The most remarkable variable in the constellation is R Aquarii, usually listed as a "Mira variable". Yet this red giant isn't your normal long-period variable; it is a 'symbiotic star', resembling Z Andromedae.
"Z Andromedae" stars are those which show two separate spectra, indicating two quite different temperatures, one cool, the other very hot. This phenomenon is caused by a very close binary system, which the larger star the cooler one, the small star(perhaps a white dwarf) the hot one.

And in fact, R Aquarii has a small blue companion, which is encircled by a gas cloud. When this small star eclipses the giant, the visual magnitude of the primary drops several degrees.
The star has a period of 386.96 days and a range from 5.8 to 12.4; the best time to view this star after the year 2000 is in 2005, in the first week of September.

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