Tau Herculis

Tau Herculis

Historical depiction of the constellation Hercules with τ, bottom left, as the "northern knee"
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 16h 19m 44.43666s[1]
Declination 46° 18′ 48.1123″[1]
Apparent magnitude (V) 3.91[2] 3.83 to 3.86[3]
Characteristics
Evolutionary stage Main sequence[4]
Spectral type B5 IV[5]
U−B color index −0.569[2]
B−V color index −0.151±0.009[2]
Variable type SPB[3]
Astrometry
Radial velocity (Rv)−15.5±0.5[2] km/s
Proper motion (μ) RA: −13.33[1] mas/yr
Dec.: 38.48[1] mas/yr
Parallax (π)10.61 ± 0.11 mas[1]
Distance307 ± 3 ly
(94.3 ± 1.0 pc)
Absolute magnitude (MV)−0.96[2]
Details
Mass4.01[6] M☉
Radius3.55±0.19 R☉[7]
3.80±0.25[8] R☉
Luminosity574[2] L☉
Surface gravity (log g)4.02±0.05[7] cgs
Temperature15,615±301[7] K
Metallicity [Fe/H]0.15[9] dex
Rotational velocity (v sin i)32[6] km/s
Age26[6] Myr
Other designations
Rukbalgethi Shemali, τ Her, 22 Her, BD+46°2169, FK5 608, GC 21987, HD 147394, HIP 79992, HR 6092, SAO 46028, CCDM J16197+4619A[10]
Database references
SIMBADdata

Tau Herculis, a name Latinized from τ Herculis, is a variable star in the northern constellation of Hercules. It has a blue-white hue and is visible to the naked eye at night with an apparent visual magnitude that fluctuates around 3.91.[2] The star is located at a distance of approximately 307 light years from the Sun based on parallax,[1] but it is drifting closer with a radial velocity of −16 km/s.[2]

A light curve for Tau Herculis, plotted from TESS data[11]

The stellar classification of Tau Hercules is B5 IV,[5] and it serves as a standard spectrum in the modern Morgan–Keenan (MK) classification.[12] It is estimated to be just 26 million years old with a relatively low projected rotational velocity of 32 km/s.[6] Slowly rotating B-type stars are often chemically peculiar, so the mostly normal spectra of this star suggests we may be viewing it from near pole-on.[13] The abundance of most heavier elements in this star are about 85% of those in the Sun.[14] The star has four times the mass of the Sun[6] and around 3.8[8] times the Sun's radius. On average, it is radiating 574[2] times the luminosity of the Sun from its photosphere at an effective temperature of 15,615 K.[7]

During the Hipparcos mission,[4] Tau Hercules was discovered to be a variable star of the slowly pulsating B-type. These are mid-B main sequence stars that vary with a period of about a day;[4] the brightness of Tau Hercules varies by 0.03 magnitude[3] over a period of 1.24970±0.00008 days. The radial velocity of the star varies at a different rate than the photometric period, with the object showing both radial and non-radial pulsation modes.[4][15]

  1. ^ a b c d e f Cite error: The named reference van_Leeuwen_2007 was invoked but never defined (see the help page).
  2. ^ a b c d e f g h i Cite error: The named reference Anderson_Francis_2012 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference Masuda_Hirata_2000 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Morgan_Keenan1973 was invoked but never defined (see the help page).
  6. ^ a b c d e Cite error: The named reference David_Hillenbrand_2015 was invoked but never defined (see the help page).
  7. ^ a b c d Cite error: The named reference aj129_3_1642 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Gordon_et_al_2019 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference aaa480 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Garcia1989 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference KALER was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Adelman_et_al_2001 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Briquet_et_al_2003 was invoked but never defined (see the help page).