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

Abstract

(abreviated) We aim to study the inner-wind structure (R<250 Rstar) of the well-known red supergiant VY CMa. We analyse high spatial resolution (~0".24x0".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. 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 degrees 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 Rstar from the central star, and instead, we propose shock-induced sputtering driven by localized mass ejection events as alternative.

arXiv comment17 pages, Astronomy & Astrophysics

References in corpus (26)

• Formation rates of complex organics in UV irradiated CH3OH-rich ices I: Experiments
• Photodesorption of Ices II: H2O and D2O
• Dust formation in the oxygen-rich AGB star IK Tau
• Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• Molecular abundances in the inner layers of IRC +10216
• Atmospheric dynamics and the mass loss process in red supergiant stars
• High-resolution imaging of dust shells using Keck aperture masking and the IOTA Interferometer
• The 3D Morphology of VY Canis Majoris. I The Kinematics of the Ejecta
• Pure rotational spectra of TiO and TiO_2 in VY Canis Majoris
• The last gasps of VY CMa: Aperture synthesis and adaptive optics imagery
• Distance to VY Canis Majoris with VERA
• Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry
• Modelling the Hubble Space Telescope Ultraviolet and Optical Spectrum of Spot 1 on the Circumstellar Ring of SN 1987A
• An Interferometric Spectral-Line and Imaging Survey of VY Canis Majoris in the 345 GHz Band
• High velocity bipolar outflow and disk-like envelope in the carbon star V Hya
• ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris
• ALMA sub-mm maser and dust distribution of VY Canis Majoris
• The molecular envelope around the red supergiant VY CMa
• ALMA observations of TiO${}_2$ around VY Canis Majoris
• Photodesorption of H2O, HDO, and D2O ice and its impact on fractionation
• Water in Low-Mass Star-Forming Regions with Herschel: The Link Between Water Gas and Ice in Protostellar Envelopes
• The 3D Morphology of VY Canis Majoris II: Polarimetry and the Line-of-Sight Distribution of the Ejecta
• Spatially extended K I 7699 emission in the nebula of VY CMa: Kinematics and geometry
• Adaptive Optics Imaging of VY Canis Majoris at 2 - 5 micron with LBT/LMIRCam
• The Magnetised Bellows of Betelgeuse

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