Magnetic Flares on Asymptotic Giant Branch Stars

Abstract

We investigate the consequences of magnetic flares on the surface of asymptotic giant branch (AGB) and similar stars. In contrast to the solar wind, in the winds of AGB stars the gas cooling time is much shorter than the outflow time. As a result, we predict that energetic flaring will not inhibit, and may even enhance, dust formation around AGB stars. If magnetic flares do occur around such stars, we expect some AGB stars to exhibit X-ray emission; indeed certain systems including AGB stars, such as Mira, have been detected in X-rays. However, in these cases, it is difficult to distinguish between potential AGB star X-ray emission and, e.g., X-ray emission from the vicinity of a binary companion. Analysis of an archival ROSAT X-ray spectrum of the Mira system suggests an intrinsic X-ray luminosity 2x10^{29} erg/sec and temperature 10^7 K. These modeling results suggest that magnetic activity, either on the AGB star (Mira A) or on its nearby companion (Mira B), is the source of the X-rays, but do not rule out the possibility that the X-rays are generated by an accretion disk around Mira B.

ApJ, Accepted; revised version of astro-ph/0209236

References in corpus (5)

• Circular Polarization of Water Masers in the Circumstellar Envelopes of Late Type Stars
• Analysis of H2 Emission from Mira B in UV Spectra from HST
• The Effects of Alfven Waves and Radiation Pressure in Dust Winds of Late-type Stars
• Models of Planets and Brown Dwarfs in Mira Winds
• The Structure of Winds in AGB Stars

Cited by in corpus (23)

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• X-ray Outburst in Mira A
• A Compact X-ray Source and Possible X-ray Jets within the Planetary Nebula Menzel 3
• Magnetic activity in late-type giant stars: Numerical MHD simulations of non-linear dynamo action in Betelgeuse
• s-Processing in AGB Stars Revisited. III. Neutron captures from MHD mixing at different metallicities and observational constraints
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• Multi-epoch imaging polarimetry of the SiO masers in the extended atmosphere of the Mira variable TX Cam
• Searching for X-ray emission from AGB stars
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• Magnetic Activity in Stellar Merger Products
• Activity cycle of the giant star of Z Andromedae and its spin period
• Strong Variable Ultraviolet Emission from Y Gem: Accretion Activity in an AGB Star with a Binary Companion?
• Filaments as Possible Signatures of Magnetic Field Structure in Planetary Nebulae
• Constraining the X-ray Luminosities of Asymptotic Giant Branch Stars: TX Cam and T Cas
• X-rays from the Mira AB Binary System
• A Phenomenological Model for the Extended Zone Above AGB Stars
• A hybrid steady-state magnetohydrodynamic dust-driven stellar wind model for AGB stars
• The giant star of the symbiotic system YY Her: Rotation, Tidal wave, Solar-type cycle and Spots
• Is Mira a magneto-dusty rotator?
• Production of n-rich nuclei in red giant stars