HD 172991

HD 172991/172992
Location of HD 172991 (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Australis
Right ascension 18h 44m 57.15228s[1]
Declination −39° 41′ 10.2781″[1]
Apparent magnitude (V) 5.44±0.01[2]
Characteristics
A
Spectral type K1/2III[3]
B−V color index +0.87[4]
B
Spectral type B9/A1V[3]
Astrometry
Radial velocity (Rv)−17.4±0.8[5] km/s
Proper motion (μ) RA: +9.815 mas/yr[1]
Dec.: −6.261 mas/yr[1]
Parallax (π)2.6806 ± 0.1453 mas[1]
Distance1,220 ± 70 ly
(370 ± 20 pc)
Absolute magnitude (MV)−2.56[6]
Details
A
Mass4.98±0.05[7] M☉
Radius53.9±3.0[8] R☉
Luminosity1,750+188
−154[1] L☉
Surface gravity (log g)1.03[9] cgs
Temperature4,990±123[10] K
Metallicity [Fe/H]−0.41[9] dex
Rotational velocity (v sin i)3.9±2[11] km/s
Other designations
20 G. Coronae Australis[12], CD−39°12864, CPD−39°8163, GC 25628, HD 172991, 172992, HIP 91989, HR 7031, SAO 210518[13]
Database references
SIMBADdata

HD 172991, also known as HR 7031 or rarely 20 G. Coronae Australis, is a binary star[14] located in the southern constellation Corona Australis. It has a combined apparent magnitude of 5.44,[2] making it faintly visible to the naked eye. The system is located relatively far at a distance of 1,220 light years based on Gaia DR3 parallax measurements[1] but is receding with a heliocentric radial velocity of −17.4 km/s.[5] At its current distance HD 172991's brightness is diminished by magnitudes due to interstellar dust and it has an absolute magnitude of −2.56.[6]

HD 172991 has a stellar classification of K1/2 III,[3] indicating that it is an evolved red giant. The companion, HD 172992, is a B-type star with a stellar classification of B9/A1 V.[3] Although the two components can be resolved in the spectrum, they cannot be observed in telescopes, making observation difficult.[15]

HD 172991 has 4.98 times the mass of the Sun[7] but it has expanded to 53.9 times the Sun's radius.[8] It radiates 1,750 times the luminosity of the Sun[1] from its enlarged photosphere at an effective temperature of 4,990 K,[10] giving it a yellowish-orange hue. It is metal deficient with an iron abundance 39% of the Sun's ([Fe/H] = −0.41)[9] and spins modestly with a projected rotational velocity of 3.9 km/s.[11]

  1. ^ a b c d e f g Cite error: The named reference GaiaDR3 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference Tycho2000 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference houk1982 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Corben1968 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Gontcharov2006 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Hohle2010 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Kervella2004 was invoked but never defined (see the help page).
  9. ^ a b c Cite error: The named reference Anders2019 was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference Stassun2019 was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference De Medeiros2014 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Gould1879 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Bonneau1980 was invoked but never defined (see the help page).