Eta Herculis

Eta Herculis (η Her, η Herculis) is a fourth-magnitude star in the constellation Hercules.

Eta Herculis
Location of η Herculis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 16h 42m 53.7653s[1]
Declination 38° 55′ 20.116″[1]
Apparent magnitude (V) 3.487[1]
Characteristics
Spectral type G7.5 IIIb[1]
U−B color index +0.61[2]
B−V color index +0.92[2]
Astrometry
Radial velocity (Rv)8.3[1] km/s
Proper motion (μ) RA: 35.58[1] mas/yr
Dec.: -84.98[1] mas/yr
Parallax (π)29.11 ± 0.52 mas[3]
Distance112 ± 2 ly
(34.4 ± 0.6 pc)
Absolute magnitude (MV)+0.84[4]
Details
Mass2.13[4] M☉
Radius8.9 ± 0.3[5] R☉
Luminosity50[6] L☉
Temperature4,900[6] K
Metallicity [Fe/H]-0.28[7] dex
Rotational velocity (v sin i)8[8] km/s
Age1[6] Gyr
Other designations
η Her, 44 Her, HR 6220, BD -39° 3029, HD 150997, FK5 626, HIP 81833, SAO 65504, GC 22502, CCDM J16428+3855A
Database references
SIMBADdata

Properties

Eta Herculis is a G-type star. With a stellar classification G7.5IIIb, it is considerably larger than the Sun, having a mass that is 2.3 times solar and a radius 9.8 times.[6] Though it only shines with an apparent magnitude of 3.48, it is part of the "Keystone" asterism, visible overhead in the mid-summer night sky to northern observers, allowing it to be easily recognized. Eta Herculis is 50 times more luminous than the Sun.[6] The Hipparcos satellite mission estimated its distance at roughly 34.4 parsecs[3] from Earth, or 112 light years away.

If one follows the line connecting Eta Herculis with Zeta Herculis one comes across one of the earliest and most stunning globular clusters in the nighttime sky, M13, discovered in 1714 by Edmond Halley.

Eta Herculis is a double star once thought to be part of a binary star system.[6]

References
  1. "* eta Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-06-09.
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; et al. (July 1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P.
  4. Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P
  5. Nordgren, Tyler E.; et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal, 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114{{citation}}: CS1 maint: multiple names: authors list (link)
  6. Kaler, James B. "ETA HER (Eta Herculis)". Stars. University of Illinois. Retrieved 2010-06-09.
  7. Soubiran, C.; Bienaymé, O.; Mishenina, T. V.; Kovtyukh, V. V. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics. 480 (1): 91–101. arXiv:0712.1370. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. S2CID 16602121.
  8. Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago. 239. Bibcode:1970CoAsi.239....1B.
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