S Antliae

S Antliae is a W Ursae Majoris-type eclipsing binary star in Antlia.

S Antliae

The blue light curve of S Antliae, adapted from Hogg & Bowe (1950)[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Antlia[2]
Right ascension	09h 32m 18.38648s[3]
Declination	−28° 37′ 39.9685″[3]
Apparent magnitude (V)	6.27 to 6.83[4]
Characteristics
Spectral type	A9V
B−V color index	0.33
Variable type	Eclipsing binary W UMa type
Astrometry
Proper motion (μ)	RA: −89.375 mas/yr[3] Dec.: +44.049 mas/yr[3]
Parallax (π)	12.6116±0.0203 mas[3]
Distance	258.6 ± 0.4 ly (79.3 ± 0.1 pc)
Absolute magnitude (MV)	1.963[5] (2.25 + 3.42)[6]
Orbit[7]
Period (P)	0.59145447(30) days
Semi-major axis (a)	3.82±0.02 R☉
Inclination (i)	74.02±0.14°
Semi-amplitude (K1) (primary)	75±1 km/s
Semi-amplitude (K2) (secondary)	234±1 km/s
Details[6]
A
Mass	1.66±0.10 M☉
Radius	2.09±0.11 R☉
Luminosity	10.0±2.2 L☉
Surface gravity (log g)	4.02±0.03 cgs
Temperature	7,100±200 K
B
Mass	0.55±0.05 M☉
Radius	1.31±0.06 R☉
Luminosity	3.4±0.7 L☉
Temperature	6,859±200 K
Age	1.9[7] Gyr
Other designations
CD-28°7373, HD 82610, SAO 177619, HIP 46810, HR 3798.
Database references
SIMBAD	data

Characteristics

S Antiliae is classed as an A-type W Ursae Majoris variable, since the primary is hotter than the secondary and the drop in magnitude is caused by the latter passing in front of the former. S Antiliae varies in apparent magnitude from 6.27 to 6.83 over a period of 15.6 hours.^[4] The system shines with a combined spectrum of A9V.^{[citation needed]}

The system's orbital period is about 0.591 days. The stars' centres are an average of 3.82 times the Sun's radius apart. The system will evolve into an Algol variable.^[6]

Calculating the properties of the component stars indicates that the primary star has a mass 1.66 times and a diameter 2.09 times that of the Sun, and the secondary has a mass 0.55 times and a diameter 1.31 times that of the Sun. The primary has a surface temperature of 7,100 K, while the secondary is a little cooler at 6,859 K.^[6] The two stars have similar luminosity and spectral type as they have a common envelope and share stellar material.^{[citation needed]} The system is thought to be around two billion years old.^[7]

Based upon an annual parallax shift of 12.6116 milliarc seconds as measured by the Gaia satellite,^[3] this system is 259 light-years (79.3 parsecs) from Earth. Analysing and recalibrating yields a parallax of 13.30 and hence a distance of 250 light-years (76 parsecs).^[5]

History

The star's variability was first recorded in 1888 by H.M. Paul,^[8] when it had the shortest known period of any variable star. It was initially thought to be an Algol-type eclipsing binary, but this was discounted by E.C. Pickering on account of it lacking a shallow minimum in its maximum and the width of its minimum period. Alfred H. Joy noted the similarity of its light curve to W Ursae Majoris in 1926, concluding the system was indeed an eclipsing binary with two stars of spectral type A8.^[9]