Alpha Sagittae, formally named Sham/ˈʃæm/,[11][12] is a single[13]star in the northern
constellation of
Sagitta. Alpha Sagittae is the
Bayer designation, which is
latinized from α Sagittae and abbreviated Alpha Sge or α Sge. It is visible to the naked eye as a yellow-hued star with an
apparent visual magnitude of +4.38.[2] Despite the name, this is not the brightest star in the constellation – that distinction belongs to
Gamma Sagittae. Based upon
parallax measurements, Alpha Sagittae is approximately 382
light-years from the
Sun. It is moving further away from the Earth with a heliocentric
radial velocity of 1.7 km/s.[5]
The evolutionary state of Alpha Sagittae is unclear. Its temperature and luminosity place it within the
Hertzsprung gap, a region of the
H-R diagram where stars more massive than the sun are evolving rapidly away from the
main sequence towards becoming red giants. However, the chemical composition of its surface indicates that it has already experienced the first
dredge-up of fusion products that occurs soon after a star reaches the
red giant branch. It also lies within the
Cepheid instability strip, but is not a
Cepheid variable.[15] It belongs to a small group of known stars that have been called carbon-deficient red giants and may have experienced binary mass exchanges.[16]
Nomenclature
This star bore the traditional name Sham (or Alsahm), which derives from the
Arabic word سهم sahm, meaning "arrow", the name formerly having been applied to the whole constellation. In 2016, the
International Astronomical Union organized a
Working Group on Star Names (WGSN)[17] to catalogue and standardize proper names for stars. The WGSN approved the name Sham for this star on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[12]
^
abHøg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30.
Bibcode:
2000A&A...355L..27H.
^
abcdefgMallik, Sushma V. (December 1999). "Lithium abundance and mass". Astronomy and Astrophysics. 352: 495–507.
Bibcode:
1999A&A...352..495M.
^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.