Upsilon Sagittarii

Not to be confused with the Cepheid variable U Sagittarii.
Upsilon Sagittarii
Location of υ Sgr (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 19h 21m 43.62284s[1]
Declination −15° 57′ 18.0625″[1]
Apparent magnitude (V) 4.61[2]
Characteristics
Spectral type A2 Ia + B2 Vpe[3]
U−B color index −0.53[2]
B−V color index +0.10[2]
Variable type PV Tel[4] (β Lyr?[5])
Astrometry
Radial velocity (Rv)8.9[6] km/s
Proper motion (μ) RA: 1.34[1] mas/yr
Dec.: −6.25[1] mas/yr
Parallax (π)1.83 ± 0.23 mas[1]
Distanceapprox. 1,800 ly
(approx. 550 pc)
Absolute magnitude (MV)−4.73 / −1.14[7]
Orbit[8]
Period (P)137.9 days
Semi-major axis (a)270.8 R☉
Eccentricity (e)0
Inclination (i)50[9]°
Semi-amplitude (K1)
(primary)		49.6[10] km/s
Semi-amplitude (K2)
(secondary)		29.7[10] km/s
Details
"visible"
Mass2.5 + 4[11] M☉
Radius23[12] R☉
Luminosity4,700[12] L☉
Surface gravity (log g)1.2[12] cgs
Temperature12,300[3] K
Metallicity [Fe/H]−0.2[3] dex
Rotational velocity (v sin i)≤10[12] km/s
Age52[11] Myr
"invisible"
Mass6.2[7] M☉
Radius2.2[12] R☉
Luminosity1,300[12] L☉
Surface gravity (log g)1.0[12] cgs
Temperature23,000[12] K
Rotational velocity (v sin i)250[12] km/s
Other designations
υ Sagittarii, υ Sgr, Upsilon Sgr, 46 Sagittarii, BD−16°5283, FK5 727, GC 26697, HD 181615, HD 181616, HIP 95176, HR 7342, PPM 235885, SAO 162518
Database references
SIMBADdata

Upsilon Sagittarii (Upsilon Sgr, υ Sagittarii, υ Sgr) 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.

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