Query : 2015A&A...577L...4V

2015A&A...577L...4V - Astronomy and Astrophysics, volume 577, L4-4 (2015/5-1)

Resolving the stellar activity of the Mira AB binary with ALMA.


Abstract (from CDS):

We present the size, shape, and flux densities at millimeter continuum wavelengths, based on ALMA science verification observations in Band 3 (∼94.6GHz) and Band 6 (∼228.7GHz), from the binary Mira A (omicron Ceti) and Mira B. The Mira AB system was observed with ALMA at a spatial resolution down to ∼25mas. The extended atmosphere of Mira A and the wind around Mira B sources were resolved, and we derived the sizes of Mira A and of the ionized region around Mira B. The spectral indices within Band 3 (between 89-100GHz) and between Bands 3 and 6 were also derived. The spectral index of Mira A is found to change from 1.71±0.05 within Band 3 to 1.54±0.04 between Bands 3 and 6. The spectral index of Mira B is 1.3±0.2 in Band 3, in good agreement with measurements at longer wavelengths; however, it rises to 1.72±0.11 between the bands. For the first time, the extended atmosphere of a star is resolved at these frequencies, and for Mira A the diameter is ∼3.8x3.2AU in Band 3 (with brightness temperature Tb∼5300K) and ∼4.0x3.6AU in Band 6 (Tb∼2500K). Additionally, a bright hotspot ∼0.4AU, with Tb∼10000K, is found on the stellar disk of Mira A. The size of the ionized region around the accretion disk of Mira B is found to be ∼2.4AU. The emission around Mira B is consistent with emission from a partially ionized wind of gravitationally bound material from Mira A close to the accretion disk of Mira B. The Mira A atmosphere does not fully match predictions with brightness temperatures in Band 3 significantly higher than expected, potentially owing to shock heating. The hotspot is very likely due to magnetic activity and could be related to the previously observed X-ray flare of Mira A.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - stars: atmospheres - binaries: close - stars: individual: Mira AB

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 * omi Cet Mi* 02 19 20.79210 -02 58 39.4956   7.63 6.53 5.03   M5-9IIIe+DA 1486 0
2 * omi Cet B WD* 02 19 20.80 -02 58 40.0           DA 46 1
3 QSO B0235+1624 BLL 02 38 38.9300958576 +16 36 59.276150136   16.46 15.50 15.92   ~ 1450 2
4 QSO B0332-403 BLL 03 34 13.6546782528 -40 08 25.399790304 18.54 18.35 17.87 17.5   ~ 291 1
5 ICRF J225805.9-275821 Sy1 22 58 05.9627218728 -27 58 21.258376248   17.34 16.77 17.20   ~ 322 1

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