Theta Herculis

Theta Herculis

Historical view of the Hercules constellation showing Rukbalgethi Genubi (θ Her) as the "southern knee", right of center
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 17h 56m 15.18054s[1]
Declination 37° 15′ 01.9343″[1]
Apparent magnitude (V) 3.851[2]
Characteristics
Spectral type K1IIaCN2[3]
U−B color index +1.40 [4]
B−V color index +1.35[4]
R−I color index +0.63[5]
Variable type Irregular (suspected)[6]
Astrometry
Radial velocity (Rv)–28.32[7] km/s
Proper motion (μ) RA: 2.67[1] mas/yr
Dec.: 6.47[1] mas/yr
Parallax (π)4.33 ± 0.13 mas[1]
Distance750 ± 20 ly
(231 ± 7 pc)
Absolute magnitude (MV)−2.71+0.26
−0.23[8]
Details
Mass4.94[9] M☉
Radius89.97[9] R☉
Luminosity2,405.7[9] L☉
Surface gravity (log g)1.24[9] cgs
Temperature4,266[9] K
Metallicity [Fe/H]−0.11[9] dex
Rotational velocity (v sin i)3.4 ± 0.6[8] km/s
Age130[9] Myr
Other designations
Rukbalgethi Genubi, θ Her, 91 Her, BD+37°2982, FK5 672, GC 24415, HD 163770, HIP 87808, HR 6695, SAO 66485[10]
Database references
SIMBADdata

Theta Herculis is a single,[11] variable star in the northern constellation of Hercules. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 3.851.[2] Based upon parallax measurements, it is located around 750 light years away from the Sun. The star is advancing toward the Earth with a heliocentric radial velocity of –28 km/s.[7]

This is an aging K-type bright giant with a stellar classification of K1IIaCN2,[3] where the suffix notation indicates a strong overabundance of CN in the spectrum. The brightness variations of this star was first noticed in 1935 by M. Fedtke and confirmed by Erich Przybyllok and Kurt Walter the same year.[12] French astronomer Paul Muller then classified Theta Herculis as an irregular variable with a range of magnitudes between 3.7 and 4.1 and a periodicity of roughly 8–9 days.[6]

The star is about 130[9] million years old with 4.94[9] times the mass of the Sun. With the hydrogen at its core exhausted, the star has expanded to 90[9] times the Sun's radius. It is radiating 2,406[9] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,266 K.[9]

  1. ^ a b c d e Cite error: The named reference hipparcos was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference MCWILLIAM was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference mk was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference MERMILLIOD was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference HR1 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference MULLER was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference rv was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference aj135_3_892 was invoked but never defined (see the help page).
  9. ^ a b c d e f g h i j k l Cite error: The named reference reffert was invoked but never defined (see the help page).
  10. ^ "tet Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-05-31.
  11. ^ Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Shapiro1972 was invoked but never defined (see the help page).