FG Sagittae

FG Sagittae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagitta
Right ascension 20h 11m 56.05947s[1]
Declination +20° 20′ 04.3672″[1]
Apparent magnitude (V) 8.7 - 23.0[2]
Characteristics
Spectral type (O3[3] -) B4Ieq - K2Ib[4]
U−B color index +0.75[5]
B−V color index +1.21[5]
Astrometry
Parallax (π)0.7630 ± 0.2302 mas[6]
Distanceapprox. 4,000 ly
(approx. 1,300 pc)
Details
Mass0.8[3] M☉
Radius0.9 - 184[3] R☉
Luminosity2,692- 12,000[3] L☉
Surface gravity (log g)0.2 - 2.2[3] cgs
Temperature4,467 - 45,000[3] K
Other designations
FG Sge, HIP 99527, PN ARO 169, ALS 10924, IRAS 20097+2010, PN G060.3-07.3, AN 377.1943, Hen 3-1844, JP11 5474, CSI+20-20097, Hen 2-457, LS II +20 19, TYC 1626-619-1, CSV 5066, Hen 1-5, 2MASS J20115606+2020044, UBV M 50884, PK 060-07 1, AAVSO 2007+20
Database references
SIMBADdata

FG Sagittae is a supergiant star in the constellation Sagitta at a distance of 4000 light-years. When first noted in 1943, it was identified to be a variable star, and it was found to be a hot, blue star of stellar spectral type B in 1955. Since then it has expanded and cooled, becoming a yellow G-type star by 1991,[7] and then further cooling to become an orange K-type star. It started to pulsate when becoming an A-type star with a period of 15 days. This period later increased to over 100 days.[citation needed]

Since 1992 the star has exhibited fadings and recoveries similar to that of a R Coronae Borealis variable star; this behavior is emphasized by a hydrogen deficiency typical for this class of stars.[8] It has been proposed that this star has undergone a late thermal pulse (LTP) of helium fusion after having left the asymptotic giant branch (AGB) to move towards the hottest end of the "white dwarf cooling track". This thermal pulse is believed to have revived this aged star to once again, for a short time, behave as an AGB star.[8]

FG Sagittae is the central star of the planetary nebula Henize 1-5.

  1. ^ a b Cite error: The named reference hipparcos was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference vsx was invoked but never defined (see the help page).
  3. ^ a b c d e f Cite error: The named reference vangenderen1995 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference shenavrin was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference ducati was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference dr2 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference newscientist was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference lawnald was invoked but never defined (see the help page).