Delta Sagittae

Delta Sagittae (Delta Sge, δ Sagittae, δ Sge) is a binary star in the constellation of Sagitta, with an apparent magnitude of +3.68. The primary component is a red M-type bright giant, and the secondary is a B-type main-sequence star.[2] It is approximately 430 light years from Earth, based on its Gaia Data Release 2 parallax.[1]

δ Sagittae
Location of δ Sagittae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Sagitta
Right ascension 19h 47m 23.26653s[1]
Declination +18° 32′ 03.5203″[1]
Apparent magnitude (V) +3.82[2](3.91[3] / 6.64)[4]
Characteristics
Spectral type M2II + B9.5V[4]
U−B color index +0.98[5]
B−V color index +1.40[5]
Variable type LB?[6]
Astrometry
Radial velocity (Rv)2.5 ± 0.9[7] km/s
Proper motion (μ) RA: -6.514[1] mas/yr
Dec.: 0.849[1] mas/yr
Parallax (π)7.5299 ± 0.5044[1] mas
Distance430 ± 30 ly
(133 ± 9 pc)
Absolute magnitude (MV)−2.58[8]
Orbit[4]
Period (P)10.11 yr
Semi-major axis (a)0.051″
Eccentricity (e)0.44
Inclination (i)140.0°
Longitude of the node (Ω)170.2°
Periastron epoch (T)1979.93
Argument of periastron (ω)
(secondary)		257.7°
Details
δ Sge A
Mass3.35+0.335
−0.30[9] M☉
Radius108[10] R☉
Luminosity1,888 - 1,923[10] L☉
Surface gravity (log g)0.74 ± 0.10[9] cgs
Temperature3,660±170[10] K
δ Sge B
Mass2.9[4] M☉
Radius2.6[4] R☉
Luminosity63[4] L☉
Temperature10000[4] K
Other designations
δ Sagittae, 7 Sagittae, BD+18 4240, CCDM J19474+1832AB, FK5 743, GC 27391, HD 187076, HIP 97365, HR 7536, IDS 19429+1817 AB, PPM 136976, SAO 105259, WDS J19474+1832AB
Database references
SIMBADdata

Delta Sagittae is a spectroscopic binary with a composite spectrum, meaning that light from both stars can be detected. It has an orbital period of about 10 years and an eccentricity of about 0.44.[4] It is also a variable star, with its brightness changing between a maximum of magnitude 3.75 and a minimum of 3.83 in an unpredictable way.[6]

Delta Sagittae is moving through the Galaxy at a speed of 9.8 km/s relative to the Sun. Its projected Galactic orbit carries it between 23,800 and 35,300 light years from the center of the Galaxy.[11]

Naming

In Chinese, 左旗 (Zuǒ Qí), meaning Left Flag, refers to an asterism consisting of δ Sagittae, α Sagittae, β Sagittae, ζ Sagittae, γ Sagittae, 13 Sagittae, 11 Sagittae, 14 Sagittae and ρ Aquilae. Consequently, the Chinese name for δ Sagittae itself is 左旗三 (Zuǒ Qí sān, English: the Third Star of Left Flag.)[12]

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. "* del Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 23 February 2017.
  3. Calculated from subtracting magnitudes.
  4. Eaton, Joel A.; Hartkopf, William I.; McAlister, Harold A.; Mason, Brian D. (1995). "Winds and accretion in delta Sagittae". Astronomical Journal. 109 (4): 1856–1866. Bibcode:1995AJ....109.1856E. doi:10.1086/117412.
  5. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
  7. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  8. 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.
  9. Schröder, K.-P.; Cuntz, M. (2007). "A critical test of empirical mass loss formulas applied to individual giants and supergiants". Astronomy and Astrophysics. 465 (2): 593–601. arXiv:astro-ph/0702172. Bibcode:2007A&A...465..593S. doi:10.1051/0004-6361:20066633. S2CID 55901104.
  10. Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  11. "Delta Sagittae (HIP 97365)". Archived from the original on 2013-01-02. Retrieved 2012-09-17.
  12. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
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