Lambda Cancri is a blue-white-hued spectroscopic binary star in the zodiac constellation of Cancer. Its name is a Bayer designation that is Latinized from λ Cancri, and abbreviated Lambda Cnc or λ Cnc. With a combined apparent visual magnitude of +5.93, it is faintly visible to the naked eye. Based upon parallax measurements obtained during the Gaia mission, it is approximately distant from the Sun. The system is drifting further away with a line of sight velocity of around +23 km/s.
The two components are designated Lambda Cancri A (formally named Piautos ) and B. The position of this system near the ecliptic means it is subject to lunar occultation.
Nomenclature
λ Cancri (Latinised to Lambda Cancri) is the binary's Bayer designation. The designations of the two components as Lambda Cancri A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
The system occurs in the lunar station that was given the name πιαυτος piautos in a Coptic manuscript list of lunar stations, nearly all of which were in "debased" Greek. Walter Crum was of the opinion that Piautos is formed from the Greek word autos "self" and the Coptic determiner pi- "that", which is automatically tacked onto Greek nouns. The combination would (in Greek) mean "the same, the very one". Given that the Greeks are not known to have used lunar stations, the origin of the names is unknown.See station 10 in footnote 12 in Stefan Weinstock, "Lunar Mansions and Early Calendars", Journal of Hellenic Studies, Volume 69, November 1949, pp. 48-69.
In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name Piautos for Lambda Cancri on 1 June 2018 and it is now so included in the List of IAU-approved Star Names. The WGSN had previously stated that where a component letter (from e.g. Washington Double Star Catalog) is not explicitly listed, that the name should be understood to be attributed to the brightest component by visual brightness (Lambda Cancri A in this case).
In Chinese, (), meaning Beacon Fire, refers to an asterism consisting of Lambda Cancri and Psi, Phi1 and 15 Cancri. 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, . Consequently, Lambda Cancri itself is known as (, ). AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 27 日 From this Chinese name, the name Kwan Wei meaning "the bright fire" was given.
Properties
The binary nature of this system was announced by K. Gullikson and associates in 2016. The primary, Lambda Cancri A, is a B-type main-sequence star with a stellar classification of B9.5 V. This star is roughly 105 million years old and is spinning rapidly with a projected rotational velocity of 188 km/s. It has 2.6 times the mass of the Sun and 3.7 times the Sun's radius. The star radiates 131 times the Sun's luminosity from its photosphere at an effective temperature of roughly . Its close companion, Lambda Cancri B, has 80% of the mass of the Sun.
References See SAO 80113 on p. 396.