{{Short description|Suspected binary star system in the constellation Camelopardalis}} {{Starbox begin}} {{Starbox image | image = {{Location mark |image=Camelopardalis constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=HD 42818 |x=400|y=685 }} | caption = Location of HD 42818 (circled in red) }} {{Starbox observe | epoch = J2000 | constell = Camelopardalis<ref name=Anderson2012/> | ra = {{RA|06|18|50.7809}}<ref name=Gaia2016/> | dec = {{DEC|+69|19|11.176}}<ref name=Gaia2016/> | appmag_v = +4.76<ref name=Anderson2012/> }} {{Starbox character | type = main sequence<ref name=zorec2012/> | class = A0 Vn<ref name=Cowley1969/> | b-v = {{Val|0.025|0.003}} | variable = }} {{Starbox astrometry | radial_v = {{Val|−7.0|7.4}}<ref name=deBruijne2012/> | prop_mo_ra = +0.686<ref name=Gaia2016/> | prop_mo_dec = −108.270<ref name=Gaia2016/> | parallax = 18.64 | p_error = 0.23 | parallax_footnote = <ref name=vanLeeuwen2007/> | absmag_v = +1.11<ref name=Anderson2012/> }} {{Starbox detail | source = | component1 = HD 42818 A | mass = 2.49<ref name=David2015/> | radius = 2.7<ref name=cadars/> | luminosity = 33.83<ref name=Anderson2012/> | gravity = {{Val|4.18|0.14}}<ref name=David2015/> | temperature = {{Val|10834|368|fmt=commas}}<ref name=David2015/> | metal_fe = 0.3<ref name=gebran2016/> | rotational_velocity = 255<ref name=David2015/> | age_myr = 99<ref name=David2015/> }} {{Starbox catalog | names = {{odlist | name=Shangwei | BD=+69°371 | FK5=234 | HD=42818 | HIP=29997 | HR=2209 | SAO=13788}}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = HD+42818 }} {{Starbox end}}
'''HD 42818''', also named '''Shangwei''',<ref name=IAU-CSN/> is a suspected astrometric binary<ref name=Eggleton2008/> star system in the northern circumpolar constellation of Camelopardalis. It is visible to the naked eye with an apparent visual magnitude of +4.76.<ref name=Anderson2012/> Based upon an annual parallax shift of {{Val|18.64|0.23|ul=mas}} as seen from Earth's orbit,<ref name=vanLeeuwen2007/> it is located some 175 light years away. The system appears to be moving closer with a heliocentric radial velocity of {{val|−7|u=km/s}}.<ref name=deBruijne2012/> As of 2012, it is estimated that the system will make its closest approach to the Sun in {{val|485,000|u=years|fmt=commas}} at a distance of around {{Convert|51.87|pc|ly|order=flip|abbr=on}}.<ref name=Anderson2012/>
The visible member, designated component A, is an A-type main-sequence star with a stellar classification of A0 Vn,<ref name=Cowley1969/> where the 'n' indicates "nebulous" absorption lines due to rotation. It is spinning rapidly with a projected rotational velocity of {{val|255|u=km/s}}<ref name=David2015/> (van Belle (2012) lists {{val|325|u=km/s}}), giving the star a pronounced equatorial bulge.<ref name=vanBelle2012/> 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.<ref name=Schroeder2007/>
The primary has an estimated 2.49 times the mass of the Sun<ref name=David2015/> and about 2.7 times the Sun's radius.<ref name=cadars/> 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 {{val|10,834|u=K|fmt=commas}}.<ref name=David2015/>
In Chinese astronomy, the fifth star in the right wall of the Purple Forbidden Enclosure is named ''Shàng Wèi'' (The Great Imperial Guard, {{lang|zh|上衛}}). Its identification has changed many times throughout history; it was identified as HD 42818 in the Yuan dynasty, but as 43 Camelopardalis in more recent sources.<ref name=ASE/> The IAU Working Group on Star Names approved the name Shangwei for HD 42818 on 25 December 2025, and it is now so entered in the IAU Catalog of Star Names.<ref name=IAU-CSN/>
==References== <references> <ref name=SIMBAD>{{cite simbad | title=HD 42818 | access-date=2018-06-05 }}</ref>
<ref name=zorec2012>{{cite journal |bibcode=2012A&A...537A.120Z |title=Rotational velocities of A-type stars. IV. Evolution of rotational velocities |last1=Zorec |first1=J. |last2=Royer |first2=F. |journal=Astronomy and Astrophysics |date=2012 |volume=537 |pages=A120 |doi=10.1051/0004-6361/201117691 |arxiv=1201.2052 }}</ref>
<ref name=vanLeeuwen2007>{{citation | title=Validation of the new Hipparcos reduction | last1=van Leeuwen | first1=F. | postscript=. | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | year=2007 | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | s2cid=18759600 }}</ref>
<ref name=Anderson2012>{{cite XHIP|29997}}</ref>
<ref name=cadars>{{citation | display-authors=1 | last1=Pasinetti Fracassini | first1=L. E. | last2=Pastori | first2=L. | last3=Covino | first3=S. | last4=Pozzi | first4=A. | title=Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) | edition=Third | journal=Astronomy & Astrophysics | volume=367 | pages=521–24 | date=2001 | bibcode=2001A&A...367..521P | doi=10.1051/0004-6361:20000451 | arxiv=astro-ph/0012289 | s2cid=425754 | postscript=. }}</ref>
<ref name=Eggleton2008>{{citation | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=2 | pages=869–879 | date=September 2008 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | bibcode=2008MNRAS.389..869E | postscript=. | arxiv=0806.2878 | s2cid=14878976 }}</ref>
<ref name=Schroeder2007>{{citation | title=X-ray emission from A-type stars | last1=Schröder | first1=C. | last2=Schmitt | first2=J. H. M. M. | journal=Astronomy and Astrophysics | postscript=. | volume=475 | issue=2 | date=November 2007 | pages=677–684 | doi=10.1051/0004-6361:20077429 | bibcode=2007A&A...475..677S | doi-access=free }}</ref>
<ref name=Cowley1969>{{citation | display-authors=1 | last1=Cowley | first1=A. | last2=Cowley | first2=C. | last3=Jaschek | first3=M. | last4=Jaschek | first4=C. | title=A study of the bright A stars. I. A catalogue of spectral classifications | journal=Astronomical Journal | postscript=. | volume=74 | pages=375–406 | date=April 1969 | doi=10.1086/110819 | bibcode=1969AJ.....74..375C }}</ref>
<ref name=deBruijne2012>{{citation | last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C. | title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project | journal=Astronomy & Astrophysics | volume=546 | id=A61 | pages=14 | date=October 2012 | doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D | arxiv=1208.3048 | s2cid=59451347 | postscript=. }}</ref>
<ref name=vanBelle2012>{{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 | s2cid=119273474 }}</ref>
<ref name=gebran2016>{{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 | s2cid=118549566 }}</ref>
<ref name=Gaia2016>{{citation | title=Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties | last1=Brown | first1=A. G. A. | last2=Vallenari | first2=A. | last3=Prusti | first3=T. | last4=De Bruijne | first4=J. H. J. | last5=Mignard | first5=F. | last6=Drimmel | first6=R. | last7=Babusiaux | first7=C. | last8=Bailer-Jones | first8=C. A. L. | last9=Bastian | first9=U. | last10=Biermann | first10=M. | last11=Evans | first11=D. W. | last12=Eyer | first12=L. | last13=Jansen | first13=F. | last14=Jordi | first14=C. | last15=Katz | first15=D. | last16=Klioner | first16=S. A. | last17=Lammers | first17=U. | last18=Lindegren | first18=L. | last19=Luri | first19=X. | last20=o'Mullane | first20=W. | last21=Panem | first21=C. | last22=Pourbaix | first22=D. | last23=Randich | first23=S. | last24=Sartoretti | first24=P. | last25=Siddiqui | first25=H. I. | last26=Soubiran | first26=C. | last27=Valette | first27=V. | last28=Van Leeuwen | first28=F. | last29=Walton | first29=N. A. | last30=Aerts | first30=C. | display-authors=1 | journal=Astronomy and Astrophysics | volume=595 | at=A2 | year=2016 | arxiv=1609.04172 | bibcode=2016A&A...595A...2G | doi=10.1051/0004-6361/201629512 | s2cid=1828208 | postscript=. }}</ref>
<ref name=David2015>{{citation | title=The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets | last1=David | first1=Trevor J. | last2=Hillenbrand | first2=Lynne A. | journal=The Astrophysical Journal | volume=804 | issue=2 | pages=146 | year=2015 | bibcode=2015ApJ...804..146D | doi=10.1088/0004-637X/804/2/146 | arxiv=1501.03154 | s2cid=33401607 | postscript=. }}</ref>
<ref name=ASE>{{cite web |title=Shangwei (上衛) |url=https://ase.exopla.net/index.php/Shangwei |website=All Skies Encyclopaedia |publisher=IAU Working Group on Star Names |access-date=28 December 2025}}</ref>
<ref name=IAU-CSN>{{cite web |title=IAU Catalog of Star Names |url=https://exopla.net/star-names/modern-iau-star-names/ |access-date=28 December 2025}}</ref> </references>
{{Stars of Camelopardalis}}
Category:A-type main-sequence stars Category:Astrometric binaries Category:Camelopardalis BD+69 0371 042818 029997 2209 Shangwei