GT Muscae

GT Muscae, also known as 12 Muscae, is a variable star about 400 light years from the Earth, in the constellation Musca.[3] It is a 5th magnitude star, so it should be faintly visible to the naked eye of an observer far from city lights.[3] It is a quadruple star system, consisting of a spectroscopic binary containing an RS Canum Venaticorum variable (RS CVn) star (HD 101379), orbiting an eclipsing binary (HD 101380).[1] It varies in brightness from magnitude 4.96 to 5.23.[4] GT Muscae is a very active X-ray source.[9]

GT Muscae

Light curves for GT Muscae. The upper panel (adapted from Murdoch et al.[1]) shows the long-term variability after a model of the eclipsing binary variability has been removed. The orbital period of HD 101379 is shown in red. The lower panel shows TESS data,[2] in which the eclipses (both primary and secondary) are clearly visible. The orbital period of HD 101380 is shown in red.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Musca
Right ascension 11h 39m 29.56610s[3]
Declination −65° 23′ 52.0995″[3]
Apparent magnitude (V) 4.96 - 5.23[4]
Characteristics
Spectral type A: G5/8III+F, B: A0V+A2V[4]
Variable type Algol + RS CVn[5]
Astrometry
Proper motion (μ) RA: −29.762±0.561[3] mas/yr
Dec.: 5.783±0.504[3] mas/yr
Parallax (π)8.3972 ± 0.5075 mas[3]
Distance390 ± 20 ly
(119 ± 7 pc)
Orbit[6]
PrimaryA (HD 101379)
CompanionB (HD 101380)
Period (P)96.8±2.4 yr
Semi-major axis (a)0.276″±0.004″
Eccentricity (e)0.634±0.015
Inclination (i)60.9±2°
Longitude of the node (Ω)259.8±1.5°
Periastron epoch (T)2452778±110
Argument of periastron (ω)
(secondary)		92.4±1.5°
Orbit[1]
PrimaryAa
CompanionAb
Period (P)61.448±0.007 d
Eccentricity (e)0.032±0.013
Periastron epoch (T)2444929±6
Argument of periastron (ω)
(secondary)		238±24°
Semi-amplitude (K1)
(primary)		12.7±0.2 km/s
Orbit[4]
PrimaryBa
CompanionBb
Period (P)2.75459 d
Other designations
12 Muscae, HD 101379, HD 101380, HIP 56862, HR 4492, SAO 251522, WDS J11395-6524AB,[7] B 1705 AB[8]
Database references
SIMBADdata

In 1929, Willem van den Bos discovered that GT Muscae is a visual double star, whose A (HD 101379) and B (HD 101380) components were separated by 0.2 arc seconds at the time he observed it.[8] Examining photographic plates in 1964, Wolfgang Strohmeier et al. discovered that GT Muscae is a variable star.[10] In 1979, based on spectroscopic features, Edward Weiler and Robert Stencel listed GT Muscae as a likely RS CVn variable.[11] Eclipses of the HD 101380 pair were first reported by Andrew Collier Cameron in his 1982 PhD thesis, in which he also determined that pair's orbital period.[12] The entire star system was given the variable star designation GT Muscae in 1988.[13]

Strong, variable, 5 GHz radio emission from GT Muscae, indicative of flares, was detected in 1982 and was interpreted as indicating high levels of chromospheric and coronal activity.[14]

GT Muscae was detected in the early observations of the Uhuru X-ray satellite, originally denoted as 2U 1134–161, later renamed 4U 1137–65.[15][16] Michael Garcia et al. identified HD 101379 as the source seen by Uhuru, in 1980.[17] During the 2010-2019 decade, GT Muscae showed the most X-ray flare activity of any star in the sky, producing flares with energies as high as ~1038 ergs.[9]

References
  1. Murdoch, K. A.; Hearnshaw, J. B.; Kilmartin, P. M.; Gilmore, A. C. (October 1995). "A photometric and orbital analysis of GT Muscae". Monthly Notices of the Royal Astronomical Society. 276 (3): 836–846. Bibcode:1995MNRAS.276..836M. doi:10.1093/mnras/276.3.836. Retrieved 26 January 2023.
  2. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 24 January 2023.
  3. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  4. "GT Mus". The International Variable Star Index. AAVSO. Retrieved 26 January 2023.
  5. Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  6. "11395-6524 B 1705AB (GT Mus)". Washington Double Star Catalog. US Naval Observatory. Retrieved 28 January 2023.
  7. "12 Mus -- RS CVn Variable". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-01-26.
  8. van den Bos, W. H. (October 1929). "New southern double stars, ninth list". Bulletin of the Astronomical Institutes of the Netherlands. 5: 125–134. Bibcode:1929BAN.....5..125V. Retrieved 27 January 2023.
  9. Sasaki, Ryo; Tsuboi, Yohko; Iwakiri, Wataru; Nakahira, Satoshi; Maeda, Yoshitomo; Gendreau, Keith; Corcoran, Michael F.; Hamaguchi, Kenji; Arzoumanian, Zaven; Markwardt, Craig B.; Enoto, Teruaki; Sato, Tatsuki; Kawai, Hiroki; Mihara, Tatehiro; Shidatsu, Megumi; Negoro, Hitoshi; Serino, Motoko (March 2021). "The RS CVn-type Star GT Mus Shows Most Energetic X-Ray Flares Throughout the 2010s". The Astrophysical Journal. 910 (1): 25. arXiv:2103.16822. Bibcode:2021ApJ...910...25S. doi:10.3847/1538-4357/abde38. S2CID 232427851. Retrieved 28 January 2023.
  10. Strohmeier, W.; Knigge, R.; Ott, H. (September 1964). "Bright Southern BV-Stars". Information Bulletin on Variable Stars. 66 (1): 1. Bibcode:1964IBVS...66....1S. Retrieved 27 January 2023.
  11. Weiler, E. J.; Stencel, R. E. (September 1979). "Southern RS CVn systems. Candidate list". Astronomical Journal. 84: 1372–1373. Bibcode:1979AJ.....84.1372W. doi:10.1086/112553. Retrieved 27 January 2023.
  12. Collier Cameron, Andrew (1982). Late-type Ca II emission-line stars in the Southern Hemisphere. University of Canterbury. Bibcode:1982PhDT.......163C. doi:10.26021/7260. Retrieved 28 January 2023.
  13. Kholopov, P. N.; Samus, N. N.; Kazarovets, B. V.; Frolov, M. S.; Kireeva, N. N. (April 1989). "The 69th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 3323 (1): 1. Bibcode:1989IBVS.3323....1K. Retrieved 27 January 2023.
  14. Collier, A. C.; Haynes, R. F.; Slee, O. B.; Wright, A. E.; Hillier, D. J. (September 1982). "A coordinated radio and Half survey of southern RS CVn systems and related objects". Monthly Notices of the Royal Astronomical Society. 200 (4): 869–880. Bibcode:1982MNRAS.200..869C. doi:10.1093/mnras/200.4.869. Retrieved 28 January 2023.
  15. Giacconi, R.; Murray, S.; Gursky, H.; Kellogg, E.; Schreier, E.; Tananbaum, H. (December 1972). "The Uhuru catalog of X-ray sources". Astrophysical Journal. 178: 281–308. Bibcode:1972ApJ...178..281G. doi:10.1086/151790. Retrieved 27 January 2023.
  16. Forman, W.; Jones, C.; Cominsky, L.; Julien, P.; Murray, S.; Peters, G.; Tananbaum, H.; Giacconi, R. (December 1978). "The fourth Uhuru catalog of X-ray sources". Astrophysical Journal Supplement Series. 38: 357–412. Bibcode:1978ApJS...38..357F. doi:10.1086/190561. Retrieved 28 January 2023.
  17. Garcia, M.; Baliunas, S. L.; Conroy, M.; Johnston, M. D.; Ralph, E.; Roberts, W.; Schwartz, D. A.; Tonry, J. (September 1980). "Optical identification of H 0123+07.5 and 4U 1137-65 : hard X-ray emission from RS CVn systems". Astrophysical Journal. 240: L107–L110. Bibcode:1980ApJ...240L.107G. doi:10.1086/183334. Retrieved 28 January 2023.
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