Mira B

Mira B

The red giant star Mira (right), and its companion Mira B on the left. Taken on December 11, 1995, by the Hubble Space Telescope using the Faint Object Camera.
Observation data Epoch J2000      Equinox J2000
Constellation	Cetus
Right ascension	02^h 19^m 20.80^s[1]
Declination	−02° 58′ 40.0″[1]
Apparent magnitude (V)	9.5 - 12.0[2]
Characteristics
Spectral type	DA[3]
Astrometry
Distance	approx. 300[4] ly (approx. 90 pc)
Other designations
VZ Cet, ο Cet B, WDS J02193-0259Ab, CCDM J02194-0258P, WD 0216-032
Database references
SIMBAD	data

Mira B, also known as VZ Ceti, is the companion star to the variable star Mira, separated by around 100 AU. Suspected as early as 1918, it was visually confirmed in 1923 by Robert Grant Aitken, and has been observed more or less continually since then, most recently by the Chandra X-Ray Observatory.^[5]

Long known to be erratically variable itself, its fluctuations seem to be related to its accretion of matter from Mira's stellar wind, which makes it a symbiotic star.^[6]

Orbit

Its orbit around Mira is poorly known; the most recent estimate listed in the Sixth Catalog of Orbits of Visual Binary Stars gives an orbital period of roughly 500 years, with a periastron around the year 2285. Assuming the distance in the Hipparcos catalog and orbit are correct, Mira A and B are separated by an average of 100 AU.^[7]

Current research

Blue band light curves for Mira B (VZ Ceti), adapted from Sokoloski and Bildsten (2010)^[8]

In January 2007, astronomers at the Keck Observatory announced the discovery of a protoplanetary disk around Mira B. Discovered via infrared data, the disk is apparently derived from captured material from Mira itself; Mira B accretes as much as one percent of the matter lost by its primary. Though planetary formation is perhaps unlikely as long as the disk is in active accretion, it may proceed apace once Mira A completes its red giant phase and becomes a white dwarf remnant.^[9]

Several factors, such as low x-ray luminosity, suggest that Mira B is actually a normal main-sequence star of spectral type K and roughly 0.7 solar mass, rather than a white dwarf as first envisioned. However, a 2010 analysis of rapid optical brightness variations has indicated that Mira B is, in fact, a white dwarf.^[8]

External links

• From the AAVSO Variable Star of the Month: Mira Archived 2003-07-05 at the Wayback Machine
• Sixth Orbit Catalog
• Chandra Photo Album, Mira press release
• Born Again Protoplanetary Disk Around Mira B

References

1. Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications". VizieR On-line Data Catalog. 1. Bibcode:2014yCat....1.2023S.
2. Samus', N. N.; et al. (2003). "An Electronic Version of the Second Volume of the General Catalogue of Variable Stars with Improved Coordinates". Astronomy Letters. 29 (7): 468–479. Bibcode:2003AstL...29..468S. doi:10.1134/1.1589864. S2CID 16299532.
3. Warner, B. (1972). "Observations of rapid blue variables - VIII. The companion to Mira". Monthly Notices of the Royal Astronomical Society. 159: 95–100. Bibcode:1972MNRAS.159...95W. doi:10.1093/mnras/159.1.95.
4. van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
5. Robert Burnham (15 April 2013). Burnham's Celestial Handbook, Volume One: An Observer's Guide to the Universe Beyond the Solar System. Courier Corporation. ISBN 978-0-486-31902-5.
6. James B. Kaler (7 May 2006). The Hundred Greatest Stars. Springer Science & Business Media. ISBN 978-0-387-21625-6.
7. "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 21 June 2017.
8. J. L. Sokoloski; Lars Bildsten (2010). "Evidence for the White Dwarf Nature of Mira B". The Astrophysical Journal. 723 (2): 1188–1194. arXiv:1009.2509. Bibcode:2010ApJ...723.1188S. doi:10.1088/0004-637X/723/2/1188. S2CID 119247560.
9. Ireland, M. J; Monnier, J. D; Tuthill, P. G; Cohen, R. W; De Buizer, J. M; Packham, C; Ciardi, D; Hayward, T; Lloyd, J. P (2007). "Born-Again Protoplanetary Disk around Mira B". The Astrophysical Journal. 662 (1): 651–657. arXiv:astro-ph/0703244. Bibcode:2007ApJ...662..651I. doi:10.1086/517993. S2CID 16694.