Delta Sagittae

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)5.9674 ± 0.2597 mas[8]
Distance550 ± 20 ly
(168 ± 7 pc)
Absolute magnitude (MV)−2.58[9]
Orbit[4]
Period (P)10.15[10] yr
Semi-major axis (a)0.051″
Eccentricity (e)0.453[10]
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
Mass4.073[10] M☉
Radius223 – 267[10] R☉
Surface gravity (log g)0.74 ± 0.10[11] cgs
Temperature3,660±170[12] K
δ Sge B
Mass3.611[10] M☉
Radius3.3 – 4.7[10] 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 (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]

A visual band light curve for Delta Sagittae, plotted from data published by Tabur et al. (2009)[13]

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.[14][better source needed]

  1. ^ a b c d e Cite error: The named reference DR2 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference calc was invoked but never defined (see the help page).
  4. ^ a b c d e f Cite error: The named reference Eaton was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference EgUBV was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference gcvs was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference GCRV was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Gaia3 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  10. ^ a b c d e f Eggleton, Peter P.; Yakut, Kadri (2017). "Models for 60 double-lined binaries containing giants". Monthly Notices of the Royal Astronomical Society. 468 (3): 3533–3556. arXiv:1611.05041. doi:10.1093/mnras/stx598.
  11. ^ Cite error: The named reference Schroeder was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference messinio was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Tabur was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference astrostudio was invoked but never defined (see the help page).