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Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension 17h 56m 20.7s
Declination −28° 47′ 42″
Apparent magnitude (V)  ?
Distance ~10,000 ly
(3,100 pc)
Spectral type M / M
Other designations
MACHO 402.47862.1576, MACHO 402.47862.1576

MACHO-1997-BLG-41, commonly abbreviated as 97-BLG-41 or MACHO-97-BLG-41, was a gravitational microlensing event located in Sagittarius which occurred in July 1999. The source star is likely a giant or subgiant star of spectral type K located at a distance of around 8 kiloparsecs (26,000 light years). The lens star is a binary system approximately 10,000 light years away in the constellation Sagittarius. The two stars are separated from each other by about 0.9 AU and have an orbital period of around 1.5 years. The most likely mass of the system is about 0.3 times that of our Sun. Star A and star B are both red dwarfs.[1]

The first published model of the MACHO-1997-BLG-41 event using data from Mount Stromlo Observatory, Cerro Tololo Inter-American Observatory and Wise Observatory show the lens system as being located in the galactic bulge at a distance of 6.3 kiloparsecs (21,000 light years), a total system mass of about 0.8 times that of the Sun and a separation of 1.8 AU (the most likely value given a random orientation of the system). The individual components were assigned masses 0.6 and 0.16 times that of our Sun, making them an orange dwarf of spectral class K and a class M red dwarf respectively. According to this model, a planet with around 3.5 times the mass of Jupiter orbits in a circumbinary orbit around the two stars at a distance of around 7 AU (assuming random orientation of the system).[2]

Subsequently, an independent analysis with data from five different observatories revealed that the microlensing event could be interpreted as being caused by a low-mass binary system of two red dwarf stars located in the galactic disk if one considers their orbital motion, without the need to invoke a planetary mass.[1] A further study combining both datasets confirmed this finding. The planet is thus considered disproven.[3]

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  1. ^ a b Albrow, M. D.; et al. (2000). "Detection of Rotation in a Binary Microlens: PLANET Photometry of MACHO 97-BLG-41". The Astrophysical Journal. 534 (2): 894–906. arXiv:astro-ph/9910307Freely accessible. Bibcode:2000ApJ...534..894A. doi:10.1086/308798. 
  2. ^ Bennett, D. P.; et al. (1999). "Discovery of a planet orbiting a binary star system from gravitational microlensing". Nature. 402 (6757): 57–59. arXiv:astro-ph/9908038Freely accessible. Bibcode:1999Natur.402...57B. doi:10.1038/46990. 
  3. ^ Jung, Youn Kil; et al. (2013). "Reanalysis of the Gravitational Microlensing Event MACHO-97-BLG-41 Based on Combined Data". The Astrophysical Journal Letters. 768 (1). L7. arXiv:1303.0952Freely accessible. Bibcode:2013ApJ...768L...7J. doi:10.1088/2041-8205/768/1/L7. 

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