AV Microscopii

AV Microscopii is a variable star in the southern constellation of Microscopium. It is a dim, red-hued star near the lower limit of visibility to the naked eye with a baseline apparent visual magnitude of 6.28.[2] The star is located approximately 740 light years away from the Sun, based on parallax,[1] but is moving closer with a radial velocity of −23 km/s.[2] It is a member of the Milky Way's old disk population.[6]

AV Microscopii

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Microscopium
Right ascension	20^h 41^m 24.66513^s[1]
Declination	−42° 08′ 01.6196″[1]
Apparent magnitude (V)	6.28[2] (6.25 – 6.35)[3]
Characteristics
Spectral type	M4 III[4]
B−V color index	1.584±0.019[2]
Variable type	LC:[3]
Astrometry
Radial velocity (Rv)	−22.9±0.9[2] km/s
Proper motion (μ)	RA: +46.627[1] mas/yr Dec.: −32.891[1] mas/yr
Parallax (π)	4.3815 ± 0.1715[1] mas
Distance	740 ± 30 ly (228 ± 9 pc)
Absolute magnitude (MV)	−1.40[2]
Details
Radius	77.5+3.2 −16.4[1] R☉
Luminosity	849±38[1] L☉
Temperature	3,539+448 −70[1] K
Other designations
AV Mic, CD−42°15034, HD 196829, HIP 102096, SAO 230323[5]
Database references
SIMBAD	data

Based upon a stellar classification of M4 III,[4] this is an aging red giant star,[4] having exhausted the supply of hydrogen at its core then expanded to around 78[1] times the Sun's radius. Earlier it had been classed as M3 II,[7] with the luminosity class of a bright giant. Samus et al. (2017) have it tentatively classified as an irregular variable of subtype LC, suggesting this is a supergiant star.[3] It is a pulsating variable with multiple periods discovered,[8] ranging in apparent visual magnitude between 6.25 and 6.35.[3][9] The star radiates 849 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 3,539 K.[1]

Pulsation periods[8]

Period (days)	22.3	23.3	30.3	31.0	32.3	45.0	110.7
Amplitude (mag.)	0.038	0.050	0.017	0.027	0.019	0.025	0.018

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
3. Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S.
4. Houk, Nancy (1978). "Michigan catalogue of two-dimensional spectral types for the HD stars". 2. Ann Arbor: Dept. of Astronomy, University of Michigan. Bibcode:1978mcts.book.....H. Cite journal requires |journal= (help)
5. "AV Mic". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-08-11.
6. Eggen, O. J. (August 1976). "A sample of old-disk-population red giants". Publications of the Astronomical Society of the Pacific. 88: 426–443. Bibcode:1976PASP...88..426E. doi:10.1086/129965.
7. Evans, David S.; et al. (1959). "Fundamental data for southern stars (Second List)". Monthly Notices of the Royal Astronomical Society. 119: 638. Bibcode:1959MNRAS.119..638E. doi:10.1093/mnras/119.6.638.
8. Tabur, V.; et al. (December 2009). "Long-term photometry and periods for 261 nearby pulsating M giants". Monthly Notices of the Royal Astronomical Society. 400 (4): 1945–1961. arXiv:0908.3228. Bibcode:2009MNRAS.400.1945T. doi:10.1111/j.1365-2966.2009.15588.x.
9. Watson, Christopher (28 September 2009). "AV Microscopii". AAVSO Website. American Association of Variable Star Observers. Retrieved 20 March 2015.