}}{{Starbox reference
| Simbad = HD+42818
}}{{Starbox end}}HD 42818 is a suspected astrometric binary[19] star system in the northern circumpolar constellation of Camelopardalis. It is visible to the naked eye with an apparent visual magnitude of +4.76.[3] Based upon an annual parallax shift of {{Val|18.64|0.23|ul=mas}} as seen from Earth's orbit,
[8] it is located some 175 light years away. The system appears to be moving closer with a heliocentric radial velocity of −7 km/s.[5] 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 {{Convert|51.87|pc|ly|order=flip|abbr=on}}.[3]The visible member, designated component A, is an A-type main-sequence star with a stellar classification of A0 Vn,[4] where the 'n' indicates "nebulous" absorption lines due to rotation. It is spinning rapidly with a projected rotational velocity of 255 km/s[10] (van Belle (2012) lists 325 km/s), giving the star a pronounced equatorial bulge.[26] 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 {{Val|120.4|e=20|u=W}}. This may be coming from a cooler, unseen companion.[27]
The primary has an estimated 2.49[10] times the mass of the Sun and about 2.7[11] times the Sun's radius. 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.[10]
References
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8. ^1 {{citation | last1=van Belle | first1=Gerard T. | title=Interferometric observations of rapidly rotating stars | journal=The Astronomy and Astrophysics Review | volume=20 | issue=1 | page=51 | date=March 2012 | doi=10.1007/s00159-012-0051-2 | bibcode=2012A&ARv..20...51V | postscript=. | arxiv=1204.2572 }}
9. ^1 {{citation | title=A new method for the inversion of atmospheric parameters of A/Am stars | display-authors=1 | last1=Gebran | first1=M. | last2=Farah | first2=W. | last3=Paletou | first3=F. | last4=Monier | first4=R. | last5=Watson | first5=V. | journal=Astronomy & Astrophysics | volume=589 | pages=A83 | year=2016 | bibcode=2016A&A...589A..83G | postscript=. | doi=10.1051/0004-6361/201528052 | arxiv=1603.01146 }}
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