Sigma Puppis

Sigma Puppis, Latinized from σ Puppis, is a binary star system in the southern constellation Puppis. It has an apparent visual magnitude of 3.25,^[2] which is bright enough to be visible to the naked eye at night from the Southern Hemisphere. Through a telescope, it appears as a bright, orange-hued star with a nearby white companion.^[10] Parallax measurements indicate this star is located at a distance of about 192 light-years (59 parsecs) from Earth.^[1]

A light curve for Sigma Puppis, adapted from Otero (2007)^[11]

Sigma Puppis

Location of σ Puppis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Puppis
Right ascension	07h 29m 13.83263s[1]
Declination	−43° 18′ 05.1674″[1]
Apparent magnitude (V)	3.25[2]
Characteristics
Spectral type	K5 III[3]
U−B color index	+1.77[2]
B−V color index	+1.52[2]
Astrometry
Radial velocity (Rv)	+87.3[4] km/s
Proper motion (μ)	RA: +199.39 mas/yr[1] Dec.: −61.828 mas/yr[1]
Parallax (π)	17.0234±0.5614 mas[1]
Distance	192 ± 6 ly (59 ± 2 pc)
Absolute magnitude (MV)	−0.50[5]
Orbit[6]
Period (P)	257.8 days
Eccentricity (e)	0.17
Periastron epoch (T)	20418.6
Argument of periastron (ω) (secondary)	349.3°
Semi-amplitude (K1) (primary)	18.6 km/s
Details
σ Pup A
Mass	1.65[7] M☉
Radius	43.7[4] R☉
Luminosity	344[7] L☉
Surface gravity (log g)	1.51[7] cgs
Temperature	4,077±4[7] K
Rotational velocity (v sin i)	3.0[8] km/s
Other designations
σ Pup, Sigma Pup, CD−43 3260, CPD−43 1499, FK5 1194, GC 10040, HD 59717, HIP 36377, HR 2878, SAO 218755, WDS J07292-4318A[9]
Database references
SIMBAD	data

This is a spectroscopic binary system,^[9] consisting of an orbiting pair of stars that have not been individually resolved with a telescope. Their orbital period is 257.8 days and the eccentricity is 0.17.^[6] The pair form an eclipsing binary of the Beta Lyrae type and a period of 130.5 days, or one half of their orbital period. The eclipse of the primary component causes a decline of 0.04 of a magnitude, while the secondary eclipse reduces the magnitude by 0.03.^[11][12]

The combined stellar classification is K5 III,^[3] which matches the spectrum of a giant star. The primary is 44 times larger than the Sun^[4] and 340 times more luminous. Its surface has an effective temperature of 4,077 K,^[7] giving it the orange hue of a K-type star.^[13] It shows the behavior of a slow irregular variable.^[11][12]

In addition to its binary components, Sigma Puppis has a more distant companion that has a matching proper motion, suggesting that it may be gravitationally bound to the binary. This magnitude 8.5^[10] star is at an angular separation of 22.4 arcseconds with a position angle of 74° from Sigma Puppis, which is equivalent to a projected separation of 1,200 AU.^[14] In 1970, American astronomer Olin J. Eggen suggested that Sigma Puppis belonged to a moving group of stars that share a similar motion through space, and thereby a common origin. It served as the eponym for this, the σ Puppis group.^[15] The existence of this group was later brought into question.^[16]

The SIMBAD database lists the name "Hadir" for this star, of unclear origin.^[9]