HD 42818

HD 42818 is a suspected astrometric binary^[10] star system in the northern circumpolar constellation of Camelopardalis. It is visible to the naked eye with an apparent visual magnitude of +4.76.^[2] Based upon an annual parallax shift of 18.64±0.23 mas as seen from Earth's orbit,^[5] it is located some 175 light years away. The system appears to be moving closer with a heliocentric radial velocity of −7 km/s.^[4] As of 2012, it is estimated that the system will make its closest approach to the Sun in 485,000 years at a distance of around 169.2 ly (51.87 pc).^[2]

HD 42818

Observation data Epoch J2000      Equinox J2000
Constellation	Camelopardalis
Right ascension	06h 18m 50.7809s[1]
Declination	+69° 19′ 11.176″[1]
Apparent magnitude (V)	+4.76[2]
Characteristics
Spectral type	A0 Vn[3]
B−V color index	0.025±0.003
Astrometry
Radial velocity (Rv)	−7.0±7.4[4] km/s
Proper motion (μ)	RA: +0.686[1] mas/yr Dec.: −108.270[1] mas/yr
Parallax (π)	18.64 ± 0.23 mas[5]
Distance	175 ± 2 ly (53.6 ± 0.7 pc)
Absolute magnitude (MV)	+1.11[2]
Details
HD 42818 A
Mass	2.49[6] M☉
Radius	2.7[7] R☉
Luminosity	33.83[2] L☉
Surface gravity (log g)	4.18±0.14[6] cgs
Temperature	10,834±368[6] K
Metallicity [Fe/H]	0.3[8] dex
Rotational velocity (v sin i)	255[6] km/s
Age	99[6] Myr
Other designations
BD+62°628, FK5 234, HD 42818, HIP 29997, HR 2209, SAO 13788[9]
Database references
SIMBAD	data

The visible member, designated component A, is an A-type main-sequence star with a stellar classification of A0 Vn,^[3] where the 'n' indicates "nebulous" absorption lines due to rotation. It is spinning rapidly with a projected rotational velocity of 255 km/s^[6] (van Belle (2012) lists 325 km/s), giving the star a pronounced equatorial bulge.^[11] Although spectral type A stars are not expected to emit X-rays, the coordinates of this star is a source of X-ray emission with a luminosity of 120.4×10²⁰ W. This may be coming from a cooler, unseen companion.^[12]

The primary has an estimated 2.49 times the mass of the Sun^[6] and about 2.7 times the Sun's radius.^[7] It is a relatively young star, about 99 million years old. The star is radiating 34 times the Sun's luminosity from its photosphere at an effective temperature of 10,834 K.^[6]

References

1. Brown, A. G. A.; et al. (2016), "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties", Astronomy and Astrophysics, 595, A2, arXiv:1609.04172, Bibcode:2016A&A...595A...2G, doi:10.1051/0004-6361/201629512, S2CID 1828208.
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. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
5. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
6. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
7. Pasinetti Fracassini, L. E.; et al. (2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy & Astrophysics, 367 (Third ed.): 521–24, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
8. Gebran, M.; et al. (2016), "A new method for the inversion of atmospheric parameters of A/Am stars", Astronomy & Astrophysics, 589: A83, arXiv:1603.01146, Bibcode:2016A&A...589A..83G, doi:10.1051/0004-6361/201528052, S2CID 118549566.
9. "HD 42818". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-06-05.
10. 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.
11. van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
12. Schröder, C.; Schmitt, J. H. M. M. (November 2007), "X-ray emission from A-type stars", Astronomy and Astrophysics, 475 (2): 677–684, Bibcode:2007A&A...475..677S, doi:10.1051/0004-6361:20077429.