Alpha Sagittae

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]

α Sagittae

Location of α Sagittae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Sagitta
Right ascension	19h 40m 05.7918540977s[1]
Declination	+18° 00′ 50.004597761″[1]
Apparent magnitude (V)	+4.38[2]
Characteristics
Evolutionary stage	bright giant
Spectral type	G1 II[3]
B−V color index	0.777±0.014[4]
Astrometry
Radial velocity (Rv)	1.72 ± 0.16[5] km/s
Proper motion (μ)	RA: 14.630 ± 0.257[1] mas/yr Dec.: -20.160 ± 0.276[1] mas/yr
Parallax (π)	8.5307 ± 0.1848 mas[1]
Distance	382 ± 8 ly (117 ± 3 pc)
Absolute magnitude (MV)	−0.96[6]
Details
Mass	4.11[7] M☉
Radius	21±2[8] R☉
Luminosity	340[3] L☉
Surface gravity (log g)	3.11[3] cgs
Temperature	5,333[3] K
Metallicity [Fe/H]	−0.15[3] dex
Rotational velocity (v sin i)	10[9] km/s
Age	151[7] Myr
Other designations
Sham, Alsahm, α Sge, 5 Sagittae, BD+17°4042, FK5 1133, GC 27215, HD 185758, HIP 96757, HR 7479, SAO 105120, PPM 136737, CCDM J19401+1801A, WDS J19401+1801A[10]
Database references
SIMBAD	data

This is an evolved bright giant with a stellar classification of G1 II.^[3] It is 151^[7] million years old with 4^[7] times the mass of the Sun and has expanded to around 21^[8] times the Sun's radius. It is radiating 340 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 5,333 K.^[3] There is an X-ray source within 12″ of these coordinates.^[14]

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]

In Chinese, 左旗 (Zuǒ Qí), meaning Left Flag, refers to an asterism consisting of Alpha Sagittae, Beta Sagittae, Delta Sagittae, Zeta Sagittae, Gamma Sagittae, 13 Sagittae, 11 Sagittae, 14 Sagittae and Rho Aquilae. Consequently, the Chinese name for Alpha Sagittae itself is 左旗一 (Zuǒ Qí yī, English: the First Star of Left Flag).^[18]

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. Høg, 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.
3. Mallik, Sushma V. (December 1999). "Lithium abundance and mass". Astronomy and Astrophysics. 352: 495–507. Bibcode:1999A&A...352..495M.
4. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
5. Soubiran, C.; Bienaymé, O.; Mishenina, T. V.; Kovtyukh, V. V. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics. 480 (1): 91–101. arXiv:0712.1370. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. S2CID 16602121.
6. Kovtyukh, V. V.; Gorlova, N. I.; Belik, S. I. (2012). "Accurate luminosities from the oxygen λ7771-4 Å triplet and the fundamental parameters of F-G supergiants". Monthly Notices of the Royal Astronomical Society. 423 (4): 3268. arXiv:1204.4115. Bibcode:2012MNRAS.423.3268K. doi:10.1111/j.1365-2966.2012.21117.x. S2CID 118683158.
7. Takeda, Yoichi; Sato, Bun'ei; Murata, Daisuke (2008). "Stellar Parameters and Elemental Abundances of Late-G Giants". Publications of the Astronomical Society of Japan. 60 (4): 781. arXiv:0805.2434. Bibcode:2008PASJ...60..781T. doi:10.1093/pasj/60.4.781. S2CID 16258166.
8. van Belle, G. T.; et al. (2009). "Supergiant temperatures and linear radii from near-infrared interferometry". Monthly Notices of the Royal Astronomical Society. 394 (4): 1925. arXiv:0811.4239. Bibcode:2009MNRAS.394.1925V. doi:10.1111/j.1365-2966.2008.14146.x. S2CID 118372600.
9. Böhm-Vitense, Erika (November 2004). "Rotation and Lithium Surface Abundances, Revisited". The Astronomical Journal. 128 (5): 2435−2442. Bibcode:2004AJ....128.2435B. doi:10.1086/425053.
10. "5 Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-30.
11. 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. ISBN 978-1-931559-44-7.
12. "Naming Stars". IAU.org. Retrieved 16 December 2017.
13. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
14. Greiner, J.; Richter, G. A. (March 2015). "Optical counterparts of ROSAT X-ray sources in two selected fields at low vs. high Galactic latitudes". Astronomy & Astrophysics. 575: 67. arXiv:1408.5529. Bibcode:2015A&A...575A..42G. doi:10.1051/0004-6361/201322844. S2CID 59501196. A42.
15. Vanture, Andrew D.; Wallerstein, George (1999). "Carbon, Nitrogen, and Oxygen Abundances of Selected Stars in the Hertzsprung Gap". Publications of the Astronomical Society of the Pacific. 111 (755): 84. Bibcode:1999PASP..111...84V. doi:10.1086/316306.
16. Bond, Howard E. (2019). "Carbon-deficient Red Giants". The Astrophysical Journal. 887 (1): 12. arXiv:1910.06256. Bibcode:2019ApJ...887...12B. doi:10.3847/1538-4357/ab4e13. S2CID 204512549.
17. "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Retrieved 22 May 2016.
18. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日 Archived 2011-05-21 at the Wayback Machine