GP Comae Berenices
{{short description|White dwarf system in the constellation Coma Berenices}}
{{Sky|13|05|42.4008|+|18|01|03.7653}}
{{Starbox begin}}
{{Starbox image
| image = 250px
| caption = An ultraviolet band light curve for GP Comae Berenices, adapted from Smak (1975). The error bar shown on the leftmost point applies to all points.
}}
{{Starbox observe
| constell = Coma Berenices
| epoch = J2000
}}
{{Starbox character
| type = White dwarf
| appmag_1_passband = g
| variable = AM CVn
}}
{{Starbox astrometry
| radial_v =
| prop_mo_ra = {{val|-344.92|0.06}}
| prop_mo_dec = {{val|34.85|0.06}}
| parallax = 13.7306
| p_error = 0.0452
| absmag_v =
}}
{{Starbox detail
| mass = {{val|0.59|0.09}}
| radius =
| temperature = {{val|14800|500|fmt=commas}}
| gravity=
| luminosity =
| rotation=
| age_myr =
}}
{{Starbox catalog
| names = {{odlist | 2MASS=J13054243+1801039 | G=61-29 | LTT=18284 | WD=1303+18 | Gaia DR2=3938156295111047680 }}
}}
{{Starbox reference
| Simbad = G+61-29
}}
{{Starbox end}}
GP Comae Berenices, abbreviated to GP Com and also known as G 61-29, is a star system composed of a white dwarf orbited by a planetary mass object, likely the highly eroded core of another white dwarf star. The white dwarf is slowly accreting material from its satellite at a rate of {{solar mass|{{val|3.5|0.5|e=−11}}}}/year and was proven{{citation|arxiv=astro-ph/0304265|year=2003|title=New results on GP Com|doi=10.1051/0004-6361:20030552|last1=Morales-Rueda|first1=L.|last2=Marsh|first2=T. R.|last3=Steeghs|first3=D.|last4=Unda-Sanzana|first4=E.|last5=Wood|first5=J. H.|last6=North|first6=R. C.|journal=Astronomy & Astrophysics|volume=405|pages=249–261|bibcode=2003A&A...405..249M|s2cid=119033361}} to be a low-activity AM CVn star. The star system is showing signs of a high abundance of ionized nitrogen from the accretion disk around the primary.{{citation |bibcode=2016MNRAS.457.1828K |title=UVES and X-Shooter spectroscopy of the emission line AM CVN systems GP Com and V396 Hya |last1=Kupfer |first1=T. |last2=Steeghs |first2=D. |last3=Groot |first3=P. J. |last4=Marsh |first4=T. R. |last5=Nelemans |first5=G. |last6=Roelofs |first6=G. H. A. |journal=Monthly Notices of the Royal Astronomical Society |year=2016 |volume=457 |issue=2 |page=1828 |doi=10.1093/mnras/stw126 |doi-access=free |arxiv=1601.02841 }}
In 1971, Brian Warner discovered that the star, then known as G61-29, is a variable star. it was given its variable star designation, GP Comae Berenices, in 1975.
Planetary system
The material emitted from the planetary mass companion is mostly helium, with a molar ratio of nitrogen up to 1.7%, very low neon levels and other elements not detectable at all.{{citation|arxiv=0909.3376|year=2009|title=The chemical composition of donors in AM CVN stars and ultracompact X-ray binaries: Observational tests of their formation|doi=10.1111/j.1365-2966.2009.15731.x|last1=Nelemans|first1=G.|last2=Yungelson|first2=L. R.|last3=Sluys|first3=M. V. van der|last4=Tout|first4=Christopher A.|journal=Monthly Notices of the Royal Astronomical Society|volume=401|issue=2|pages=1347–1359|doi-access=free |s2cid=2716902}} Approximately half of the luminosity of the system comes from the accretion disk. The planetary object is suspected to contain a strange quark matter core due to its unusually high density, which must be above {{val|187.5|u=g/cm3}} to prevent tidal disruption; the theoretical bound for planets composed solely of ordinary matter is on the order of {{val|30|u=g/cm3}}. The object's orbit is expected to decay within 100 million years due to gravitational wave emission.{{citation|arxiv=1908.11191|year=2020|title=Close-in Exoplanets as Candidates for Strange Quark Matter Objects|doi=10.3847/1538-4357/ab698b|last1=Kuerban|first1=Abudushataer|last2=Geng|first2=Jin-Jun|last3=Huang|first3=Yong-Feng|last4=Zong|first4=Hong-Shi|last5=Gong|first5=Hang|journal=The Astrophysical Journal|volume=890|issue=1|page=41|bibcode=2020ApJ...890...41K|s2cid=201671383 |doi-access=free }}
{{OrbitboxPlanet begin
| name = GP Com
| period_unit = second
}}
{{OrbitboxPlanet
| exoplanet = b
| mass = 10.5{{±|1.5}}
| radius = ≤ {{val|0.420|0.020}}
| period = 2794
| eccentricity = 0
| inclination = 59.5{{±|14.5}}
}}
{{orbitbox end}}
References
{{Reflist|refs=
{{cite Gaia EDR3|3938156295111047680}}
{{cite simbad |title=G 61-29|access-date=2021-12-09}}
}}
{{Coma Berenices}}