HD 181720

HD 181720 / Sika
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius[1]
Right ascension 19h 22m 52.985s[2]
Declination –32° 55′ 08.59″[2]
Apparent magnitude (V) 7.84[3]
Characteristics
Evolutionary stage main sequence
Spectral type G1V[3]
Apparent magnitude (B) 8.44[1]
Apparent magnitude (J) 6.652±0.019[1]
Apparent magnitude (H) 6.346±0.029[1]
Apparent magnitude (K) 6.294±0.034[1]
B−V color index 0.599±0.019[1]
V−R color index 0.599[3]
Astrometry
Radial velocity (Rv)−45.404±0.0006[4] km/s
Proper motion (μ) RA: 88.036 mas/yr[2]
Dec.: −415.197 mas/yr[2]
Parallax (π)16.6766 ± 0.0273 mas[2]
Distance195.6 ± 0.3 ly
(59.96 ± 0.10 pc)
Absolute magnitude (MV)4.10[3]
Details
Mass0.87±0.01[5] M☉
Radius1.42±0.02[5] R☉
Luminosity2.112±0.003[5] L☉
Surface gravity (log g)4.06±0.02[5] cgs
Temperature5,781±18[3] K
Metallicity [Fe/H]−0.53±0.02[3] dex
Rotation47 days[citation needed]
Rotational velocity (v sin i)1.5[3] km/s
Age12.4±0.5[5] Gyr
Other designations
CD–33°14164, Gaia DR2 6745589980571162752, HIP 95262, SAO 211218, PPM 298918, LTT 7666, NLTT 47718, GCRV 69331, 2MASS J19225298-3255079[6]
Database references
SIMBADdata
Exoplanet Archivedata

HD 181720 is star with an orbiting substellar companion in the southern constellation of Sagittarius. It is located at a distance of 196 light years from the Sun based on parallax measurements,[2] but is drifting closer with a radial velocity of −45.4 km/s.[4] The star has an absolute magnitude of 4.10,[3] but at that distance it has an apparent visual magnitude of 7.84,[3] which is too faint to be seen with the naked eye. It shows a high proper motion, traversing the celestial sphere at an angular rate of 0.444 arcsec yr−1.[7]

The spectrum of HD 181720 presents as an ordinary G-type main-sequence star with a stellar classification of G1V.[3] It is an older star with an estimated age of roughly 12 billion years[5] and a minimal level of magnetic activity in its chromosphere.[3] The star has 87% of the mass of the Sun but the radius is now 42% larger than the Sun's.[5] Its metallicity content, as measured by the abundance of iron, is three-tenths as much as in the Sun. HD 181720 is radiating more than double the luminosity of the Sun from its photosphere at an effective temperature of 5,781 K.[3]

The star HD 181720 is named Sika. The name was selected in the NameExoWorlds campaign by Ghana, during the 100th anniversary of the IAU. Sika means gold in the Ewe language.[8][9]

  1. ^ a b c d e f Cite error: The named reference Anderson_Francis_2012 was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference GaiaDR3 was invoked but never defined (see the help page).
  3. ^ a b c d e f g h i j k l Cite error: The named reference santos2010 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Soubiran_et_al_2018 was invoked but never defined (see the help page).
  5. ^ a b c d e f g Cite error: The named reference Bonfanti_et_al_2016 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Luyten1995 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference exoworld was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference iau was invoked but never defined (see the help page).