Gamma Virginis

Gamma Virginis (γ Virginis, abbreviated Gamma Vir, γ Vir), officially named Porrima Template:IPAc-en,<ref name="Kunitzsch" /><ref name="IAU-CSN" /> is a binary star system in the constellation of Virgo. It consists of two almost identical main sequence stars at a distance of about 38 light-years.

Name

γ Virginis (Latinised to Gamma Virginis) is the star's Bayer designation.

The traditional name Porrima derives from Ancient Rome: Porrima, also known as Antevorta, was one of the Camenae or goddesses of prophecy.<ref name="Allen1963" /> In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN" /> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1" /> included a table of the first two batches of names approved by the WGSN; which included Porrima for this star.

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Laouiyet al Aoua, which was translated into Latin as Angulus Latratoris, meaning 'the angle of the barker'.<ref name="knobel" /> This star, along with Beta Virginis (Zavijava), Eta Virginis (Zaniah), Delta Virginis (Minelauva) and Epsilon Virginis (Vindemiatrix), were Al ʽAwwāʼ, the Barker.<ref name="Allen1963" />

In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Left Wall of Supreme Palace Enclosure, refers to an asterism consisting of Gamma Virginis, Eta Virginis, Delta Virginis, Epsilon Virginis and Alpha Comae Berenices.<ref name="dLvJ8" /> Consequently, the Chinese name for Gamma Virginis itself is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx.),<ref name="d3vs6" /> representing {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning The First Eastern Minister.<ref name="jplsC" /> 東上相 (Dōngshǎngxiāng), westernized into Shang Seang by R. H. Allen and the meaning is "the High Minister of State".<ref name="Allen1963" />

Properties

Gamma Virginis is a binary star, consisting of two stars of nearly equal apparent magnitudes 3.65 and 3.56, and of spectral type F0V.<ref name="cayrel" /> With an orbital period of 168.93 years,<ref name="mason" /><ref name="scardia" /> it was an easy object for amateur astronomers until the beginning of the 1990s, but in 2011 the smaller apparent distance between the stars requires a larger telescope or special techniques such as speckle interferometry,<ref name="mason" /><ref name="scardia" /> adaptive optics<ref name="riddle" /> or optical interferometry<ref name="hutter" /> to resolve the individual components. The last time they were at periapsis was in 1836. The distance became wide enough in 2020 to view with a small telescope. The star system has a combined apparent magnitude of 2.9. The system is 39 light-years away from the Sun.

Gamma Virginis has been reported to be slightly variable,<ref name=gcvs/> but this is now considered unlikely.<ref name=vsx/>

At 2.8 degrees north of the ecliptic, Gamma Virginis it can be occulted by the Moon and (rarely) by planets. In June 2011 Saturn passed a quarter of a degree south of Porrima.

Based upon X-ray emissions—an indicator of the strength of the stellar magnetic field—this system has an estimated age of 1.14 billion years.<ref name="vican" />

Changes of distance and position angle

This table shows the apparent distance between the two stars and their relative position angle: the first three columns show data predicted from an orbit calculated in 1937, the next two columns show in 2006,<ref name="pipGh" /> the next three columns show observations reported by the Hanwell Community Observatory.<ref name="hanwellobservatory" />

Predicted from 1937 Strand orbit			Predicted from 2006 Docobo orbit		Observations 2003 to 2005
Year	distance	position angle	distance	position angle	Date	distance	position angle
1995	2.5″	280	2.25″	277.6
2000	1.8″	267	1.50″	260.9
2002	1.5″	259	1.13″	247.5
2003			0.92″	236.6	2003 Dec.	0.6″	219°
2004	1.2″	246	0.68″	218.4	2004 Dec.	0.4″	177°
2005			0.44″	179.8	2005 April	0.27–0.29″	161±0.6°
2006	0.8″	221	0.41″	103.5
2008	0.4″	126	0.93″	41.0
2010	0.9″	44	1.39″	23.6