{{short description|White dwarf system in the constellation Coma Berenices}} {{Sky|13|05|42.4008|+|18|01|03.7653}} {{Starbox begin}} {{Starbox image | image = [[Image:GPComLightCurve.png|250px]] | caption = An [[Photometric_system#Photometric_letters|ultraviolet band]] [[light curve]] for GP Comae Berenices, adapted from Smak (1975).<ref name="Smak"/> The error bar shown on the leftmost point applies to all points. }} {{Starbox observe | constell = [[Coma Berenices]] | epoch = J2000 | ra = {{RA|13|05|42.401}}<ref name=EDR3/> | dec = {{DEC|+18|01|03.76}}<ref name=EDR3/> | appmag_v = 15.69<ref name=gcvs>{{cite journal |bibcode=2017ARep...61...80S |title=General catalogue of variable stars: Version GCVS 5.1 |last1=Samus' |first1=N. N. |last2=Kazarovets |first2=E. V. |last3=Durlevich |first3=O. V. |last4=Kireeva |first4=N. N. |last5=Pastukhova |first5=E. N. |journal=Astronomy Reports |year=2017 |volume=61 |issue=1 |page=80 |doi=10.1134/S1063772917010085 |s2cid=125853869 }}</ref> }} {{Starbox character | type = [[White dwarf]] | class = DBe<ref name=burbridge1971>{{citation |bibcode=1971ApJ...170L..39B |title=G61 - 29, a Helium Emission-Line Star |last1=Burbidge |first1=E. M. |last2=Strittmatter |first2=P. A. |journal=The Astrophysical Journal |year=1971 |volume=170 |pages=L39 |doi=10.1086/180836 }}</ref> | appmag_1_passband = g | appmag_1 = 15.929<ref name=EDR3/> | variable = [[AM Canum Venaticorum star|AM CVn]] }} {{Starbox astrometry | radial_v = | prop_mo_ra = {{val|-344.92|0.06}} | prop_mo_dec = {{val|34.85|0.06}} | pm_footnote=<ref name=EDR3/> | parallax = 13.7306 | p_error = 0.0452 | parallax_footnote = <ref name=EDR3/> | absmag_v = }} {{Starbox detail |source=<ref name=Sion2011>{{citation|arxiv=1108.1388|year=2011|title=THE HOT COMPONENTS OF AM CVN HELIUM CATACLYSMICS|doi=10.1088/0004-637X/741/1/63|last1=Sion|first1=Edward M.|last2=Linnell|first2=Albert P.|last3=Godon|first3=Patrick|last4=Ballouz|first4=Ronald-Louis|journal=The Astrophysical Journal|volume=741|issue=1|page=63|bibcode=2011ApJ...741...63S|s2cid=119284962}}</ref> | 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 }}<ref name=SIMBAD/> }} {{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.<ref name=Zhang2018/> 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<ref>{{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}}</ref> to be a low-activity [[AM Canum Venaticorum star|AM CVn star]].<ref name=Zhang2018/><ref name=Sion2011/> The star system is showing signs of a high abundance of [[Ionization|ionized]] nitrogen from the [[accretion disk]] around the primary.<ref name=Kupfer2016>{{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 }} </ref>
In 1971, Brian Warner discovered that the star, then known as G61-29, is a [[variable star]].<ref name="Warner1971"/><ref name="Warner1972"/> it was given its [[variable star designation]], GP Comae Berenices, in 1975.<ref name="Kukarkin1975"/>
== Planetary system== The material emitted from the substellar 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.<ref>{{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}}</ref> Approximately half of the luminosity of the system comes from the accretion disk.<ref name=Sion2011/> The planetary object is suspected to contain a [[Strange matter|strange quark matter]] core due to its unusually high density, which must be above {{val|187.5|u=g/cm3}} to prevent [[Tidal force|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.<ref name=Kuerban2019>{{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 }}</ref>
{{OrbitboxPlanet begin | name = GP Com | table_ref = <ref name=Sion2011/> | period_unit = second }} {{OrbitboxPlanet | exoplanet = b | mass = 10.5{{±|1.5}} | radius = ≤ {{val|0.420|0.020}} | semimajor = 0.0014<ref name=Kuerban2019/> | period = 2794 | eccentricity = 0 | inclination = 59.5{{±|14.5}}<ref name=Kupfer2016/> }} {{orbitbox end}}
== References == {{Reflist|refs=
<ref name=EDR3>{{cite Gaia EDR3|3938156295111047680}}</ref>
<ref name=SIMBAD>{{cite simbad |title=G 61-29|access-date=2021-12-09}}</ref>
<ref name=Zhang2018>{{citation|arxiv=1801.03196|year=2018|title=The double helium-white dwarf channel for the formation of AM CVN binaries|doi=10.1088/1674-4527/18/1/9|last1=Zhang|first1=Xian-Fei|last2=Liu|first2=Jin-Zhong|last3=Jeffery|first3=C. Simon|last4=Hall|first4=Philip D.|last5=Bi|first5=Shao-Lan|journal=Research in Astronomy and Astrophysics|volume=18|issue=1|page=009|bibcode=2018RAA....18....9Z|s2cid=73586281}}</ref>
<ref name="Warner1971">{{cite journal |last1=Warner |first1=B. |title=Helium emission white dwarfs |journal=IAU Circular |date=1971 |volume=2374 |page=1 |bibcode=1971IAUC.2374....1W }}</ref>
<ref name="Kukarkin1975">{{cite journal |last1=Kukarkin |first1=B. V. |last2=Kholopov |first2=P. N. |last3=Kukarkina |first3=N. P. |last4=Perova |first4=N. B. |title=60th Name-List of Variable Stars |journal=Information Bulletin on Variable Stars |date=January 1975 |volume=961 |pages=1–15 |bibcode=1975IBVS..961....1K |url=https://ibvs.konkoly.hu/pub/ibvs/0901/0961.pdf |access-date=29 January 2025}}</ref>
<ref name="Warner1972">{{cite journal |last1=Warner |first1=B. |title=Observations of rapid blue variables - X. G61-29 |journal=Monthly Notices of the Royal Astronomical Society |date=1972 |volume=159 |issue=3 |pages=315–319 |bibcode=1972MNRAS.159..315W |doi=10.1093/mnras/159.3.315 |doi-access=free |url=https://articles.adsabs.harvard.edu/pdf/1972MNRAS.159..315W |access-date=29 January 2025}}</ref>
<ref name="Smak">{{cite journal |last1=Smak |first1=J. |title=The helium emission-line object G 61-29 |journal=Acta Astronomica |date=January 1975 |volume=25 |pages=227–233 |bibcode=1975AcA....25..227S |url=https://ui.adsabs.harvard.edu/abs/1975AcA....25..227S |access-date=12 December 2021}}</ref> }}
{{Coma Berenices}} <!-- Properties --> [[Category:AM CVn stars]] [[Category:White dwarfs]] [[Category:Planetary systems with one confirmed planet]] <!-- Location/catalogues --> [[Category:Coma Berenices]] [[Category:Objects with variable star designations|Comae Berenices, GP]]