GR Muscae

{{Short description|Star in the constellation Musca}}

{{starbox short

|constell= Musca

|name= GR Muscae

|type=

|ra= {{RA|12|57|37.153}}{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=GR+Mus&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = GR Muscae – Low Mass X-ray Binary |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |accessdate = 9 March 2014}}

|dec= {{DEC|-69|17|18.98}}

|appmag_v= 19.1

|Simbad=GR+Mus

}}

File:GRMusLightCurve.png light curves for GR Muscae, adapted from Cornelisse et al. (2013).]]

GR Muscae, also known as 2S 1254-690 is a binary star system in the constellation Musca composed of a neutron star of between 1.2 and 1.8 times the mass of the Sun and a low-mass star likely to be around the mass of the Sun in close orbit.{{cite journal|author1=Cornelisse, R. |author2=Kotze, M.M. |author3=Casares, J. |author4=Charles, P.A. |author5=Hakala, P.J. |date=2013|title=The Origin of the Tilted Disc in the Low-mass X-ray Binary GR Mus (XB 1254-690)|journal=Monthly Notices of the Royal Astronomical Society|volume=436|issue=1|pages=910–20|arxiv=1309.4972|bibcode = 2013MNRAS.436..910C |doi = 10.1093/mnras/stt1654 |doi-access=free |s2cid=119242800 }} A magnitude 19 blue star was pinpointed as the optical counterpart of the X-ray source in 1978.{{cite journal|author1=Griffiths, R.E. |author2=Gursky, H. |author3=Schwartz, D.A. |author4=Schwarz, J. |author5=Bradt, H. |author6=Doxsey, R.E. |author7=Charles, P.A. |author8=Thorstensen, J. R. |date=1978|title=Positions and Identifications for Galactic X-ray Sources 2A1822-371 and 2S1254-690|journal=Nature|volume=276|issue=16|pages=247–49|bibcode = 1978Natur.276..247G |doi = 10.1038/276247a0 |s2cid=4372341 }} Its apparent magnitude varies from 18 to 19.1 over a period of 0.16 days.{{Cite web | url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=19876 | title=VSX : Detail for GR Mus |work=The International Variable Star Index |publisher=AAVSO}}

While the optical counterpart to the X-ray source was identified in 1978, optical variability was not detected until 1980, when a bright flare was seen that increased the white-light flux by a factor of two in a time interval of about 1.7 seconds.{{cite journal |last1=Mason |first1=K. O. |last2=Middleditch |first2=J. |last3=Nelson |first3=J. E. |last4=White |first4=N. E. |title=An optical burst from the star identified with the X-ray source 2S1254-690 |journal=Nature |date=9 October 1980 |volume=287 |issue=5782 |pages=516-518 |bibcode=1980Natur.287..516M |doi=10.1038/287516a0 |url=https://www.nature.com/articles/287516a0 |access-date=8 October 2024|url-access=subscription }} GR Muscae received its variable star designation in 1985.{{cite journal |last1=Kholopov |first1=P. N. |last2=Samus |first2=N. N. |last3=Kazarovets |first3=E. V. |last4=Perova |first4=N. B. |title=The 67th Name-List of Variable Stars |journal=Information Bulletin on Variable Stars |date=March 1985 |volume=2681 |bibcode=1985IBVS.2681....1K |url=https://ibvs.konkoly.hu/pub/ibvs/2601/2681.pdf |access-date=8 October 2024}}

The neutron star has an accretion disk that takes around 6.74 days to complete a revolution, and is inclined at an angle to the incoming stream of material from the donor star.