Surprising detection of an equatorial dust lane on the AGB star IRC+10216

The Atacama Large Millimeter/submillimeter Array (ALMA) is allowing us to study the innermost regions of the circumstellar envelopes of evolved stars with precision and sensitivity. Key processes in the ejection of matter and dust from these objects occur in their inner zones. In this work, we present sub-arcsecond interferometric maps of transitions of metal-bearing molecules towards the prototypical C-rich evolved star IRC +10216. While Al-bearing molecules seem to be present as a roughly spherical shell, the molecular emission from the salts NaCl and KCl presents an elongation in the inner regions, with a central minimum. In order to accurately analyze the emission the NaCl rotational lines, we present new calculations of the collisional rates for this molecule based on new spectroscopic constants. The most plausible interpretation for the spatial distribution of the salts is a spiral with a NaCl mass of 0.08. Alternatively, a torus of gas and dust would result in similar structures as those observed. ~ 1.1 × 10 In both cases, the spiral and the torus, the NaCl structure presents an inner minimum of 27 AU. In the case of the torus, the outer radius is 73 AU. The kinematics of both the spiral and the torus suggests that they are slowly expanding and rotating. Alternative explanations for the presence of the elongation are explored. The presence of only in KCl and NaCl might be a result of their comparatively high dipole moment with respect to the Al-bearing species.

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“…However, this P.A. is not compatible with the dust lane observed by Tuthill et al (2000) or Jeffers et al (2014) which presents a P.A. of ~ 120°.…”

Section: Spatial Distribution Of the Molecular Emissioncontrasting

confidence: 92%

Hints of a Rotating Spiral Structure in the Innermost Regions Around Irc +10216

Quintana-Lacaci

Cernicharo

Agúndez

et al. 2016

ApJ

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“…∼°80 ) and connects the brightest parts in the two lobes of polarized optical light. The width of our elongated structure is ∼10-20 AU (or 5-10 stellar radii with the photospheric radius of IRC+10216 ∼2 AU suggested by Menten et al 2012), which is similar to the radius of a dust formation zone or the inner radii used in the torus and ring models of Jeffers et al (2014). The elongated structure could be caused by either an illumination or a confined outflow through the central hole of a dense equatorial torus.…”

Section: Optical Identification Of Central Starsupporting

confidence: 70%

“…This source is projected within the dust lane of Jeffers et al (2014). The FWHM of its profile, 0″ .15, is within the range of 0″ .09-0″ .17 measured for 10 unsaturated images of isolated stars.…”

Section: Candidate For Companion Of Irc+10216supporting

confidence: 54%

“…A dust lane of IRC+10216, extending up to ″ 4 in the eastwest direction, is recently presented by Jeffers et al (2014) in a linearly polarized optical intensity map. By placing the brightest peak in the HST 2011 image at their suggested location of the central star in the dust lane, we noticed that our elongated structure (P.A.…”

Section: Optical Identification Of Central Starmentioning

confidence: 95%

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HST IMAGES REVEAL DRAMATIC CHANGES IN THE CORE OF IRC+10216

Kim

Lee

Mauron

et al. 2015

ApJ

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IRC+10216 is the nearest carbon star with a very high mass-loss rate. The existence of a binary companion has been hinted at by indirect observational evidence, such as the bipolar morphology of its nebula and a spiral-like pattern in its circumstellar material; however, to date, no companion has been identified. We have examined archival Hubble Space Telescope images of IRC+10216, and find that the images taken in 2011 exhibit dramatic changes in its innermost region from those taken at earlier epochs. The scattered light is more spread out in 2011. After proper motion correction, the brightest peak in 2011 is close to, but not coincident with, the dominant peak in previous epochs. A fainter point-like object was revealed at ∼0″ .5 from this brightest peak. We suggest that these changes at the core of IRC+10216 are caused by dissipation of intervening circumstellar dust, as indicated by the brightening trend in the light curve extracted from the Catalina photometric survey. We tentatively identify the brightest peak in 2011 as the primary star of IRC+10216 and the fainter point-like source as a companion. The cause of non-detections of the companion candidate in earlier epochs is uncertain. These identifications need to be verified by monitoring the core of IRC+10216 at high resolution in the future.

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“…Models exist for more evolved systems (e.g. Jeffers et al 2014;Kervella et al 2015) However, a disk around a first-ascent giant must have formed very recently, which makes our knowledge on the large scale geometry of such systems very uncertain. Therefore, we do not consider a comparison of this system to AGB disk models as a viable option.…”

Section: Modeling the Diskmentioning

confidence: 99%

BP Piscium: its flaring disc imaged with SPHERE/ZIMPOL

Boer

Girard

Cánovas

et al. 2016

Monthly Notices of the Royal Astronomical Society: Letters

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Whether BP Piscium (BP Psc) is either a pre-main sequence T Tauri star at d ≈ 80 pc, or a post-main sequence G giant at d ≈ 300 pc is still not clear. As a first-ascent giant, it is the first to be observed with a molecular and dust disc. Alternatively, BP Psc would be among the nearest T Tauri stars with a protoplanetary disc (PPD). We investigate whether the disc geometry resembles typical PPDs, by comparing polarimetric images with radiative transfer models. Our Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)/Zurich IMaging Polarimeter (ZIMPOL) observations allow us to perform polarimetric differential imaging, reference star differential imaging, and Richardson-Lucy deconvolution. We present the first visible light polarization and intensity images of the disc of BP Psc. Our deconvolution confirms the disc shape as detected before, mainly showing the southern side of the disc. In polarized intensity the disc is imaged at larger detail and also shows the northern side, giving it the typical shape of high-inclination flared discs. We explain the observed disc features by retrieving the large-scale geometry with MCMAX radiative transfer modelling, which yields a strongly flared model, atypical for discs of T Tauri stars.Key words: polarization -techniques: high angular resolution -techniques: polarimetricprotoplanetary discs -circumstellar matter -stars: evolution. deconvolving Keck H-and K -band images they detected a dust disc at high inclination (i = 75 ± 10 • , with i = 0 • for a face-on disc) and position angle PA = 118 ± 5 • . Since no reliable parallax has been determined, the distance (d) to the star is highly uncertain. For two possible evolutionary scenarios with an effective temperature T eff ∼ 5000 K, the luminosities are matched to observations by varying d. Z08 propose two possible evolutionary scenarios for BP Psc: (1) at a distance d ≈ 80 pc, it is one of the nearest pre-main-sequence Classical T Tauri Stars (CTTSs) with an age ≈10 Myr; or (2) at d ≈ 300 pc, BP Psc is a post-main-sequence star of a few Gyr at its first-ascent, or hydrogen shell burning phase. A more luminous (therefore d ∼ 5000 pc) (post-) AGB (helium shell burning) star is ruled out due to its large Tycho 2 proper motion ( RA = 44.4 ± 4.1 mas yr −1 , Dec. = −26.3 ± 4.3 mas yr −1 , Høg et al. 2000). For a star on the first-ascent giant branch, the associated molecular disc, accretion and Herbig Haro objects would be the first ever to be detected. The growing primary star would have recently enveloped a previous companion, hence creating the disc. Z08 favour the G giant scenario for BP Psc, mainly because of low C I N T RO D U C T I O N

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Surprising detection of an equatorial dust lane on the AGB star IRC+10216

Cited by 15 publications

References 35 publications

Hints of a Rotating Spiral Structure in the Innermost Regions Around Irc +10216

Hints of a Rotating Spiral Structure in the Innermost Regions Around Irc +10216

HST IMAGES REVEAL DRAMATIC CHANGES IN THE CORE OF IRC+10216

BP Piscium: its flaring disc imaged with SPHERE/ZIMPOL

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