Mira’s Wind Explored in Scattering Infrared CO Lines

Ryde, Nils; Gustafsson, B.; Eriksson, K.; Hinkle, K. H.

doi:10.1086/317832

Cited by 21 publications

(25 citation statements)

References 32 publications

(52 reference statements)

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“…Comparison of the observed line positions with the laboratory data results in a heliocentric velocity of 24 km s −1 . This value agrees with the velocity range 17−27 km s −1 derived from the visible and IR atomic and molecular lines, as well as the mm CO lines (e.g., Brooke et al 1974;Huggins 1987;Smith et al 1989;Huggins et al 1994;Ryde et al 1999). Figure 3a shows the visibilities observed on the three baselines.…”

Section: Resultssupporting

confidence: 85%

Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

Ohnaka¹,

Hofmann²,

Benisty

et al. 2009

A&A

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Aims. We present spatially resolved, high-spectral resolution K-band observations of the red supergiant Betelgeuse (α Ori) using AMBER at the Very Large Telescope Interferometer (VLTI). Our aim is to probe inhomogeneous structures in the dynamical atmosphere of Betelgeuse. Methods. Betelgeuse was observed in the wavelength range between 2.28 and 2.31 μm with VLTI/AMBER using baselines of 16, 32, and 48 m. The spectral resolutions of 4800−12 000 allow us to study inhomogeneities seen in the individual CO first overtone lines. Results. Spectrally dispersed interferograms have been successfully obtained in the second, third, and fifth lobes, which represents the highest spatial resolution (9 mas) achieved for Betelgeuse. This corresponds to five resolution elements over its stellar disk. The AMBER visibilities and closure phases in the K-band continuum can be reasonably fitted by a uniform disk with a diameter of 43.19 ± 0.03 mas or a limb-darkening disk with 43.56 ± 0.06 mas and a limb-darkening parameter of (1.2 ± 0.07) × 10 −1 . These AMBER data and the previous K-band interferometric data taken at various epochs suggest that Betelgeuse seen in the K-band continuum shows much smaller deviations from the above uniform disk or limb-darkened disk than predicted by recent 3-D convection simulations for red supergiants. On the other hand, our AMBER data in the CO lines reveal salient inhomogeneous structures. The visibilities and phases (closure phases, as well as differential phases representing asymmetry in lines with respect to the continuum) measured within the CO lines show that the blue and red wings originate in spatially distinct regions over the stellar disk, indicating an inhomogeneous velocity field that makes the star appear different in the blue and red wings. Our AMBER data in the CO lines can be roughly explained by a simple model, in which a patch of CO gas is moving outward or inward with velocities of 10−15 km s −1 , while the CO gas in the remaining region in the atmosphere is moving in the opposite direction at the same velocities. Also, the AMBER data are consistent with the presence of warm molecular layers (so-called MOLsphere) extending to ∼1.4−1.5 R with a CO column density of ∼1 × 10 20 cm −2 . Conclusions. Our AMBER observations of Betelgeuse are the first spatially resolved study of the so-called macroturbulence in a stellar atmosphere (photosphere and possibly MOLsphere as well) other than the Sun. The spatially resolved CO gas motion is likely to be related to convective motion in the upper atmosphere or intermittent mass ejections in clumps or arcs.

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Section: Resultssupporting

confidence: 85%

Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

Ohnaka¹,

Hofmann²,

Benisty

et al. 2009

A&A

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“…Our conclusion that Mira B is a WD accreting atṀ ∼ 10 −10 M yr −1 has implications for the mode and efficiency of mass transfer in wide binaries. Although Mohamed & Podsiadlowski (2007) and de Val-Borro et al (2009) have suggested that a focused wind could enable up to tens of percent of the donor wind to be captured, the accretion rate needed to produce Mira B's luminosity and effective temperature is just 0.1% of the RG wind mass-loss rate (Ryde et al 2000). It is also below the Bondi-Hoyle accretion rate ofṀ BH ≈ 10 −8 M yr −1 (M/0.6 M ) 2 (7 km s −1 /v ∞ ) 3 , where v ∞ is the relative velocity of the wind at Mira B.…”

Section: Discussionmentioning

confidence: 99%

Evidence for the White Dwarf Nature of Mira B

Sokoloski

Bildsten

2010

ApJ

229

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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.

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“…3 # 10 M , s Ϫ1 . These are based on observations of the CO lines (Ryde et al 2000). An unphysical temperature of K was used for the 4 10 temperature of the wind as the cooling curves extend no further, but this does not affect the overall result (Wareing et al 2006b).…”

Section: Simulationsmentioning

confidence: 99%

It's a Wonderful Tail: The Mass-Loss History of Mira

Wareing

Zijlstra

O’Brien

et al. 2007

ApJ

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Recent observations of the Mira AB binary system have revealed a surrounding arclike structure and a stream of material stretching 2Њ away in opposition to the arc. The alignment of the proper motion vector and the arclike structure shows the structures to be a bow shock and accompanying tail. We have successfully hydrodynamically modeled the bow shock and tail as the interaction between the asymptotic giant branch (AGB) wind launched from Mira A and the surrounding interstellar medium. Our simulations show that the wake behind the bow shock is turbulent; this forms periodic density variations in the tail similar to those observed. We investigate the possibility of mass-loss variations but find that these have limited effect on the tail structure. The tail is estimated to be approximately 450,000 yr old and is moving with a velocity close to that of Mira itself. We suggest that the duration of the high mass-loss phase on the AGB may have been underestimated. Finally, both the tail curvature and the rebrightening at large distance can be qualitatively understood if Mira recently entered the Local Bubble. This is estimated to have occurred 17 pc downstream from its current location.

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Mira’s Wind Explored in Scattering Infrared CO Lines

Cited by 21 publications

References 32 publications

Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER

Evidence for the White Dwarf Nature of Mira B

It's a Wonderful Tail: The Mass-Loss History of Mira

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