42 Herculis

42 Herculis is a single^[6] star located around 450^[1] light years away from the Sun in the northern constellation of Hercules.^[5] It is visible to the naked eye as a faint, red-hued star with an apparent visual magnitude of 4.86.^[2] The star is moving closer to the Earth with a heliocentric radial velocity of −56 km/s.^[2]

42 Herculis

42 Herculis in optical light
Observation data Epoch J2000      Equinox J2000
Constellation	Hercules
Right ascension	16h 38m 44.84465s[1]
Declination	+48° 55′ 42.0160″[1]
Apparent magnitude (V)	4.86[2]
Characteristics
Evolutionary stage	asymptotic giant branch[3]
Spectral type	M2.5III[3]
B−V color index	1.562±0.011[2]
Astrometry
Radial velocity (Rv)	−55.74±0.33[2] km/s
Proper motion (μ)	RA: −47.768[1] mas/yr Dec.: +27.349[1] mas/yr
Parallax (π)	7.2737 ± 0.1764 mas[1]
Distance	450 ± 10 ly (137 ± 3 pc)
Absolute magnitude (MV)	−0.65[2]
Details
Radius	63.81+5.20 −7.75[1] R☉
Luminosity	733.6±20.5[1] L☉
Surface gravity (log g)	1.50[4] cgs
Temperature	3,760.5+251.5 −144.5[1] K
Other designations
42 Her, NSV 7896, BD+49°2531, FK5 1434, HD 150450, HIP 81497, HR 6200, SAO 46210, WDS J16387+4856[5]
Database references
SIMBAD	data

This is an aging red giant star on the asymptotic giant branch with a stellar classification of M2.5III.^[3] It has been catalogued as a suspected variable star,^[5] although a 1992 photometric survey found the brightness to be constant.^[7] Having exhausted the supply of hydrogen at its core, the star has expanded to 64 times the Sun's radius. It is radiating 734 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 3761 K.^[1]

There is an unknown source of X-ray and far ultraviolet emission originating from a location offset by more than one arcsecond from the star.^[8] This may indicate there is an undetected main sequence companion.^[4]

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
3. Eggen, Olin J. (July 1992), "Asymptotic giant branch stars near the sun", Astronomical Journal, 104 (1): 275–313, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
4. Ortiz, Roberto; Guerrero, Martín A. (September 2016), "Ultraviolet emission from main-sequence companions of AGB stars", Monthly Notices of the Royal Astronomical Society, 461 (3): 3036, arXiv:1606.09086, Bibcode:2016MNRAS.461.3036O, doi:10.1093/mnras/stw1547, S2CID 118619933.
5. "42 Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-06-13.
6. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
7. Percy, J. R.; Shepherd, C. W. (October 1992), "Photometric Survey of Small-Amplitude Red Variables", Information Bulletin on Variable Stars, 3792: 1, Bibcode:1992IBVS.3792....1P.
8. Famaey, B.; et al. (2009), "Spectroscopic binaries among Hipparcos M giants. I. Data, orbits, and intrinsic variations", Astronomy and Astrophysics, 498 (2): 627–640, arXiv:0901.0934, Bibcode:2009A&A...498..627F, doi:10.1051/0004-6361/200810698, S2CID 18739721.