2010/09/13 by J. L. Sokoloski, Lars Bildsten · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/723/2/1188
Accepted for publication in ApJ
arxiv created 2010/09/13 · openalex publication_date 2010/10/19 · arxiv updated 2015/05/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
The nature of the accreting companion to Mira—the prototypical pulsating asymptotic giant branch star—has been a matter of debate for more than 25 years. Here, we use a quantitative analysis of the rapid optical brightness variations from this companion, Mira B, which we observed with the Nickel Telescope at Lick Observatory, to show that it is a white dwarf (WD). The amplitude of aperiodic optical variations on timescales of minutes to tens of minutes (≈0.2 mag) is consistent with that of accreting WDs in cataclysmic variables on these same timescales. It is significantly greater than that expected from an accreting main-sequence star. With Mira B identified as a WD, its ultraviolet (UV) and optical luminosities, along with constraints on the WD effective temperature from the UV, indicate that it accretes at ∼10 −10 M ☉ yr -1 . This accretion rate is lower than that predicted by Bondi–Hoyle theory. The accretion rate is high enough, however, to explain the weak X-ray emission, since the accretion-disk boundary layer around a low-mass WD accreting at this rate is likely to be optically thick and therefore to emit primarily in the far or extreme UV. Furthermore, the finding that Mira B is a WD means that it has experienced, and will continue to experience, nova explosions, roughly every 10 6 years. It also highlights the similarity between Mira AB and other jet-producing symbiotic binaries such as R Aquarii, CH Cygni, and MWC 560, and therefore raises the possibility that Mira B launched the recently discovered bipolar streams from this system.