The Three-Dimensional Morphology of VY Canis Majoris. II. Polarimetry and the Line-of-Sight Distribution of the Ejecta

Jones, T. J.; Humphreys, R. M.; Helton, L. A.; Gui, Changfeng; Huang, Xue

doi:10.1086/517610

Cited by 31 publications

(33 citation statements)

References 28 publications

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“…This southwest clump is already detected in other molecules (CS, SiS, NS, and H 2 S) with the SMA (Kamiński et al 2013a) and in TiO 2 with ALMA (De Beck et al 2015) and is aligned with the southwest extension seen in dust scattered light (Smith et al 2001) and other near-infrared and polarimetric data (e.g. Monnier et al 1999;Jones et al 2007). …”

Section: Discussionsupporting

confidence: 78%

“…Images, polarimetric data and radial velocity measurements (Smith 2004;Humphreys et al 2007;Jones et al 2007) show evidence that the arcs and knots in the ejecta are not only spatially distinct features, but are also kinematically separate from the surrounding diffuse material representing the steady wind Smith et al 2009). The current understanding is that VY CMa went through a series of episodic mass ejections with dense cloudlets moving at ∼35 km s −1 that produced a very high mass-loss rate of ∼ 2 × 10 −3 M yr −1 between a few hundred and 1 000 year ago.…”

Section: The Red Supergiant Vy Cmamentioning

confidence: 99%

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ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Decin

Richards

Millar

et al. 2016

A&A

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Context. At the end of their lives, most stars lose a significant amount of mass through a stellar wind. The specific physical and chemical circumstances that lead to the onset of the stellar wind for cool luminous stars are not yet understood. Complex geometrical morphologies in the circumstellar envelopes prove that various dynamical and chemical processes are interlocked and their relative contributions are not easy to disentangle. Aims. We aim to study the inner-wind structure (R < 250 R ) of the well-known red supergiant VY CMa, the archetype for the class of luminous red supergiant stars suffering high mass loss. Specifically, the objective is to unravel the density structure in the inner envelope and to examine the chemical interaction between some gas and dust species. Methods. We analyse high spatial resolution (∼ 0 . 24 × 0 . 13) ALMA Science Verification (SV) data in band 7 in which four thermal emission lines of gaseous sodium chloride (NaCl) are present at high signal-to-noise ratio. Results. For the first time, the NaCl emission in the inner wind region of VY CMa is spatially resolved. The ALMA observations reveal the contribution of up to four different spatial regions. The NaCl emission pattern is different compared to the dust continuum and TiO2 emission already analysed from the ALMA SV data. The emission can be reconciled with an axisymmetric geometry, where the lower density polar/rotation axis has a position angle of ∼50• measured from north to east. However, this picture can not capture the full morphological diversity, and discrete mass ejection events need to be invoked to explain localized higher-density regions. The velocity traced by the gaseous NaCl line profiles is significantly lower than the average wind terminal velocity, and much slower than some of the fastest mass ejections, signalling a wide range of characteristic speeds for the mass loss. Gaseous NaCl is detected far beyond the main dust condensation region. Realising the refractory nature of this metal halide, this hints at a chemical process preventing all NaCl from condensing onto dust grains. We show that in the case of the ratio of the surface binding temperature to the grain temperature being ∼50, only some 10% of NaCl remains in gaseous form, while for lower values of this ratio thermal desorption efficiently evaporates NaCl. Photodesorption by stellar photons seems not to be a viable explanation for the detection of gaseous NaCl at 220 R from the central star, and instead, we propose shock-induced sputtering driven by localized mass ejection events as alternative. Conclusions. The analysis of the NaCl lines demonstrate the capabilities of ALMA to decode the geometric morphologies and chemical pathways prevailing in the winds of evolved stars. These early ALMA results prove that the envelopes surrounding evolved stars are far from homogeneous, and that a variety of dynamical and chemical processes dictate the wind structure.

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Section: Discussionsupporting

confidence: 78%

Section: The Red Supergiant Vy Cmamentioning

confidence: 99%

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

Decin

Richards

Millar

et al. 2016

A&A

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“…This assumed value of θ max is 2.5σ away from our scaled MW dust model, but the actual function depends on the composition of the dust that is probably different in the Homunculus and the average MW interstellar medium. The massive nebula surrounding the red supergiant VY CMa was observed in polarimetric imaging by Jones et al (2007) using HST/WFPC2 and the F550M and F658N (Hα) filters. The measured p L values reach 75%, with an assumed p L (θ) function peaking around θ max = 100…”

Section: Polarization Models From the Literaturementioning

confidence: 99%

The long-period Galactic Cepheid RS Puppis

Kervella

Bond

Cracraft

et al. 2014

A&A

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As one of the most luminous Cepheids in the Milky Way, the 41.5-day RS Puppis is an analog of the long-period Cepheids used to measure extragalactic distances. An accurate distance to this star would therefore help anchor the zero-point of the bright end of the period-luminosity relation. But, at a distance of about 2 kpc, RS Pup is too far away for measuring a direct trigonometric parallax with a precision of a few percentage points with existing instrumentation. RS Pup is unique by being surrounded by a reflection nebula whose brightness varies as pulses of light from the Cepheid propagate outward. We present new polarimetric imaging of the nebula obtained with HST/ACS. The derived map of the degree of linear polarization p L allows us to reconstruct the three-dimensional structure of the dust distribution. To retrieve the scattering angle from the p L value, we consider two different polarization models, one based on a Milky Way dust mixture and one assuming Rayleigh scattering. Considering the derived dust distribution in the nebula, we adjust a model of the phase lag of the photometric variations over selected nebular features to retrieve the distance of RS Pup. We obtain a distance of 1910 ± 80 pc (4.2%), corresponding to a parallax of π = 0.524 ± 0.022 mas. The agreement between the two polarization models that we considered is good, but the final uncertainty is dominated by systematics in the adopted model parameters. The distance we obtain is consistent with existing measurements from the literature, but light echoes provide a distance estimate that is not subject to the same systematic uncertainties as other estimators (e.g., the Baade-Wesselink technique). RS Pup therefore provides an important fiducial for calibrating the systematic uncertainties of the long-period Cepheid distance scale.

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“…For some RSGs and post-RSGs, we find evidence of discrete, episodic mass loss. For example, high-resolution optical imaging and spectroscopy of the warm OH/IR post-red supergiant (RSG) IRC +10420 and the peculiar OH/IR M-type supergiant VY CMa have yielded surprising results about their complex circumstellar environments, with evidence for asymmetric ejections and multiple high mass-loss events (Smith et al 2001;Humphreys et al 2005Humphreys et al , 2007Jones et al 2007;Tiffany et al 2010;Shenoy et al 2013).…”

Section: Introductionmentioning

confidence: 99%

SEARCHING FOR COOL DUST IN THE MID-TO-FAR INFRARED: THE MASS-LOSS HISTORIES OF THE HYPERGIANTS μ Cep, VY CMa, IRC+10420, AND ρ Cas*

Shenoy

Humphreys

Jones

et al. 2016

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We present mid-and far-IR imaging of four famous hypergiant stars: the red supergiants μ Cep and VY CMa, and the warm hypergiants IRC +10420 and ρ Cas. Our 11-37 μm SOFIA/FORCAST imaging probes cool dust not detected in visual and near-IR imaging studies. Adaptive optics 8-12 μm imaging of μ Cep and IRC +10420 with MMT/MIRAC reveals extended envelopes that are the likely sources of these stars' strong silicate emission features. We find μ Cep's mass-loss rate to have declined by about a factor of five over a 13,000 year history, ranging from 5×10 −6 down to ∼1× 10 −6 M e yr −1 . The morphology of VY CMa indicates a cooler dust component coincident with the highly asymmetric reflection nebulae seen in the visual and near-IR. The lack of cold dust at greater distances around VY CMa indicates that its mass-loss history is limited to the last ∼1200 years, with an average rate of 6×10 −4 M e yr −1 . We find two distinct periods in the mass-loss history of IRC +10420 with a high rate of 2×10 −3 M e yr −1 until approximately 2000 years ago, followed by an order of magnitude decrease in the recent past. We interpret this change as evidence of its evolution beyond the RSG stage. Our new infrared photometry of ρ Cas is consistent with emission from the expanding dust shell ejected in its 1946 eruption, with no evidence of newer dust formation from its more recent events.

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The Three-Dimensional Morphology of VY Canis Majoris. II. Polarimetry and the Line-of-Sight Distribution of the Ejecta

Cited by 31 publications

References 28 publications

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

ALMA-resolved salt emission traces the chemical footprint and inner wind morphology of VY Canis Majoris

The long-period Galactic Cepheid RS Puppis

SEARCHING FOR COOL DUST IN THE MID-TO-FAR INFRARED: THE MASS-LOSS HISTORIES OF THE HYPERGIANTS μ Cep, VY CMa, IRC+10420, AND ρ Cas*

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