Upsilon Sagittarii

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υ Sagittarii

Observation data Epoch J2000.0
Constellation (pronunciation)	Sagittarius
Right ascension	19h 21m 43.6s
Declination	-15° 57' 18"
Apparent magnitude (V)	+4.52
Absolute magnitude (V)	-4.03
Distance	1672 ± 618 ly (513 ± 189 pc)
Spectral type	B2Vpe+A2IaShell
Other designations
46 Sagittarii, HR 7342, HD 181615, SAO 162518, HIP 95176

Upsilon Sagittarii (υ Sgr / υ Sagittarii) is a spectroscopic binary star system in the constellation Sagittarius. Upsilon Sagittarii is the prototypical hydrogen-deficient binary (HdB), and one of only four such systems known. The unusual spectrum of hydrogen-deficient binaries has made stellar classification of Upsilon Sagittarii difficult.

The primary component, Upsilon Sagittarii A, is most likely an A type supergiant. The radius of the primary is estimated at 60 solar radii, and its mass is estimated to be between one and thirteen solar masses. A is classified as an irregular variable and experiences apparent magnitude fluctuations between +4.51 and +4.65 with a period of approximately 20 days. Its mean apparent magnitude is +4.52.

The companion, Upsilon Sagittarii B, is more massive, but so dim at visible frequencies as to be undetectable by optical telescopes. It is likely an O or B type main sequence dwarf, which has accreted much of the original mass of the primary. It is estimated to have a mass of three to eleven solar masses.

The binary system has an orbital period of 137.939 days and is approximately 1672 light years from Earth. It is predicted that Upsilon Sagittarii will end its life in a supernova.

[edit] References

Dudley, R. E., Jeffery, C. S., 1990. Mon. Not. R. astr. Soc. 247, 400