A Large X-Ray Outburst in Mira A

Karovska, M.; Schlegel, Eric M.; Hack, W.; Raymond, J. C.; Wood, Brian E.

doi:10.1086/430111

Cited by 93 publications

(122 citation statements)

References 17 publications

(15 reference statements)

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“…2). Finally, an efficient mass transfer was also evidenced observationally for symbiotic stars Mira AB (Karovska et al 2005), SS Leporis (Blind et al 2011;Boffin et al 2014a), and FG Serpentis (Boffin et al 2014b).…”

Section: Introductionmentioning

confidence: 72%

Wind mass transfer in S-type symbiotic binaries

Shagatova

Skopal

Cariková

2016

A&A

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Context. The wind mass transfer from a giant to its white dwarf companion in symbiotic binaries is not well understood. For example, the efficiency of wind mass transfer of the canonical Bondi-Hoyle accretion mechanism is too low to power the typical luminosities of the accretors. However, recent observations and modelling indicate a considerably more efficient mass transfer in symbiotic binaries. Aims. We determine the velocity profile of the wind from the giant at the near-orbital-plane region of eclipsing S-type symbiotic binaries EG And and SY Mus, and derive the corresponding spherical equivalent of the mass-loss rate. With this approach, we indicate the high mass transfer ratio. Methods. We achieved this aim by modelling the observed column densities taking into account ionization of the wind of the giant, whose velocity profile is derived using the inversion of Abel's integral operator for the hydrogen column density function. Results. Our analysis revealed the spherical equivalent of the mass-loss rate from the giant to be a few times 10 −6 M yr −1 , which is a factor of > ∼ 10 higher than rates determined by methods that do not depend on the line of sight. This discrepancy rules out the usual assumption that the wind is spherically symmetric. As our values were derived from near-orbital-plane column densities, these values can be a result of focusing the wind from the giant towards the orbital plane. Conclusions. Our findings suggests that the wind from giants in S-type symbiotic stars is not spherically symmetric, since it is enhanced at the orbital plane and, thus, is accreted more effectively onto the hot component.

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Section: Introductionmentioning

confidence: 72%

Wind mass transfer in S-type symbiotic binaries

Shagatova

Skopal

Cariková

2016

A&A

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“…Despite theoretical predictions of possible dynamo operation on the asymptotic giant branch (AGB) (Blackman et al 2001;Soker & Zoabi 2002;Nordhaus et al 2008), actual evidence of magnetic activity in such evolved stars is sparse and indirect Karovska et al 2005;Herpin et al 2006). Hence, we here present a study of the variable magnetic field of the single M giant EK Boo.…”

Section: Introductionmentioning

confidence: 93%

Direct detection of a magnetic field in the photosphere of the single M giant EK Bootis

Konstantinova-Antova

Aurière

Charbonnel

et al. 2010

A&A

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Aims. We study the fast rotating M 5 giant EK Boo by means of spectropolarimetry to obtain direct and simultaneous measurements of both the magnetic field and activity indicators, in order to infer the origin of the activity in this fairly evolved giant. Methods. We used the new spectropolarimeter NARVAL at the Bernard Lyot Telescope (Observatoire du Pic du Midi, France) to obtain a series of Stokes I and Stokes V profiles for EK Boo. Using the least square deconvolution (LSD) technique we were able to detect the Zeeman signature of the magnetic field. We measured its longitudinal component by means of the averaged Stokes V and Stokes I profiles. The spectra also permitted us to monitor the Ca ii K&H chromospheric emission lines, which are well known as indicators of stellar magnetic activity. Results. From ten observations obtained between April 2008 and March 2009, we deduce that EK Boo has a magnetic field, which varied in the range of −0.1 to −8 G. On March 13, 2009, a complex structure of Stokes V was observed, which might indicate a dynamo. We also determined the initial mass and evolutionary stage of EK Boo, based on up-to-date stellar evolution tracks. The initial mass is in the range of 2.0−3.6 M , and EK Boo is either on the asymptotic giant branch (AGB), at the onset of the thermal pulse phase, or at the tip of the first (or red) giant branch (RGB). The fast rotation and activity of EK Boo might be explained by angular momentum dredge-up from the interior, or by the merging of a binary. In addition, we observed eight other M giants, which are known as X-ray emitters, or to be rotating fast for their class. For one of these, β And, presumably also an AGB star, we have a marginal detection of magnetic field, and a longitudinal component B l of about 1 G was measured. More observations like this will answer the question whether EK Boo is a special case, or whether magnetic activity is, rather, more common among M giants than expected.

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“…(1), is correct in the case of efficient accretion on the companion. Efficient accretion may already have been seen in systems such as Mira in which the stellar wind is channelled onto the companion star (Karovska et al 2005). Recent simulations of wind-RLOF hybrid mass transfer suggest accretion is indeed efficient (Mohamed & Podsiadlowski 2007).…”

Section: Mass Loss the Angular Momentum Budget And Miramentioning

confidence: 99%

White-dwarf kicks and implications for barium stars

Izzard

Dermine

Church

2010

A&A

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The formation mechanism of the barium stars is thought to be well understood. Barium-rich material, lost in a stellar wind from a thermally-pulsing asymptotic-giant branch star in a binary system, is accreted by its companion main-sequence star. Now, many millions of years later, the primary is an unseen white dwarf and the secondary has itself evolved into a giant which displays absorption lines of barium in its spectrum and is what we call a barium star. A similar wind-accretion mechanism is also thought to form the lowmetallicity CH and carbon-enhanced metal-poor stars. Qualitatively the picture seems clear but quantitatively it is decidedly murky: several key outstanding problems remain which challenge our basic understanding of binary-star physics. Barium stars with orbital periods less than about 4000 days should -according to theory -be in circular orbits because of tidal dissipation, yet they are often observed to be eccentric. Only one barium-star period longer than 10 4 days has been published although such stars are predicted to exist in large numbers. In this paper we attempt to shed light on these problems. First, we consider the impact of kicking the white dwarf at its birth, a notion which is supported by independent evidence from studies of globular clusters. Second, we increase the amount of orbital angular momentum loss during wind mass transfer, which shrinks barium-star binaries to the required period range. We conclude with a discussion of possible physical mechanisms and implications of a kick, such as the break up of wide barium-star binaries and the limits imposed on our models by observations.

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A Large X-Ray Outburst in Mira A

Cited by 93 publications

References 17 publications

Wind mass transfer in S-type symbiotic binaries

Wind mass transfer in S-type symbiotic binaries

Direct detection of a magnetic field in the photosphere of the single M giant EK Bootis

White-dwarf kicks and implications for barium stars

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