 The red giant starMira (right), and its companion Mira B on the left. Taken on December 11, 1995, by theHubble Space Telescope using theFaint Object Camera. | |
| Observation data EpochJ2000 EquinoxJ2000 | |
|---|---|
| Constellation | Cetus |
| Right ascension | 02h 19m 20.80s[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 asVZ Ceti, is the companionstar to thevariable starMira, separated by around100 AU. Suspected as early as 1918, it was visually confirmed in 1923 byRobert Grant Aitken, and has been observed more or less continually since then, most recently by theChandra X-Ray Observatory.[5]
Long known to be erratically variable itself, its fluctuations seem to be related to itsaccretion ofmatter from Mira'sstellar wind, which makes it asymbiotic star.[6]
Itsorbit around Mira is poorly known; the most recent estimate listed in theSixth Catalog of Orbits of Visual Binary Stars gives anorbital period of roughly 500 years, with aperiastron around the year 2285. Assuming the distance in theHipparcos catalog and orbit are correct, Mira A and B are separated by an average of 100AU.[7]
In January 2007, astronomers at theKeck Observatory announced the discovery of aprotoplanetary disk around Mira B. Discovered viainfrared 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 itsred giant phase and becomes awhite dwarf remnant.[9]
Several factors, such as low x-ray luminosity, suggest that Mira B is actually a normalmain-sequence star ofspectral type K and roughly 0.7solar mass, rather than awhite 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]
