EVIDENCE FOR THE WHITE DWARF NATURE OF MIRA B

Journal Article · Wed Nov 10 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/723/2/1188· OSTI ID:21471283

Sokoloski, J L ^[1]; Bildsten, Lars ^[2]

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1. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
2. Kavli Institute for Theoretical Physics and Department of Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)

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 ({approx}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 {approx}10{sup -10} M{sub sun} yr{sup -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{sup 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.

• OSTI ID: 21471283
• Journal Information: Astrophysical Journal, Vol. 723, Issue 2; Other Information: DOI: 10.1088/0004-637X/723/2/1188; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
BRIGHTNESS
LUMINOSITY
MAIN SEQUENCE STARS
NICKEL
NOVAE
TELESCOPES
ULTRAVIOLET RADIATION
WHITE DWARF STARS
X RADIATION
BINARY STARS
DWARF STARS
ELECTROMAGNETIC RADIATION
ELEMENTS
ERUPTIVE VARIABLE STARS
IONIZING RADIATIONS
METALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
STARS
TRANSITION ELEMENTS
VARIABLE STARS