Alphard/ˈælfɑːrd/,[9] designated Alpha Hydrae (α Hydrae, abbreviated Alpha Hya, α Hya), is the brightest
star in the
constellation of
Hydra. It is a single
giant star, cooler than the
Sun but larger and more luminous. It is about 177
light-years away.
The traditional name Alphard is from the
Arabicالفرد (al-fard), "the individual", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the
Arabs. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, it was designated Soheil al Fard, which was translated into
Latin as Soheil Solitarius, meaning the bright solitary one.[10] In 2016, the
International Astronomical Union organized a
Working Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[12] included a table of the first two batches of names approved by the WGSN; which included Alphard for this star. It is now so entered in the IAU Catalog of Star Names.[13]
The European astronomer
Tycho Brahe dubbed it Cor Hydræ, Latin for 'the heart of Hydra'.[14]
Precise radial velocity measurements have shown variations in the stellar
radial velocities and
spectral line profiles. The
oscillations are multi-periodic with periods from several hours up to several days. The short-term oscillations were assumed to be a result of stellar
pulsations, similar to the solar ones. A correlation between the variations in the asymmetry of the spectral line profile and the radial velocity has also been found. The multi-periodic oscillations make HD 81797 (Alphard) an object of interest for
asteroseismologic investigations.[19]
^
abPfleiderer, J.; Mayer, U. (October 1971). "Near-ultraviolet surface photometry of the southern Milky Way". Astronomical Journal. 76: 691–700.
Bibcode:
1971AJ.....76..691P.
doi:
10.1086/111186.
^Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto:
International Astronomical Union.
Bibcode:
1967IAUS...30...57E.
^
abSetiawan, J.; et al. (July 2004), "Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch", Astronomy and Astrophysics, 421: 241–254,
Bibcode:
2004A&A...421..241S,
doi:10.1051/0004-6361:20041042-1
^Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub.
ISBN978-1-931559-44-7.