Resolving the hot atmospheres of evolved stars with ALMA LBs. Wouter Vlemmings, Chalmers Univ. of Technology w. Theo Khouri, Eamon O Gorman et al.

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1 Resolving the hot atmospheres of evolved stars with ALMA LBs Wouter Vlemmings, Chalmers Univ. of Technology w. Theo Khouri, Eamon O Gorman et al.

2 AGB mass loss

3 (before) dust formation Ballistic motions from pulsations Convection Freytag et al. (2017)

4 Radio/submm stellar surface observations Unique probes of temperature profile through the atmosphere free-free optical depth changes with observing frequency (Reid & Menten 1997) direct probe of temperature within 1-4 R star resolution improvements with ALMA allow resolving structures much less line confusion lines allow for probes of the dynamics Trace e.g. convective motions, shocks, stellar (magnetic) activity within wind acceleration zone chromospheres? e.g. Betelgeuse (O Gorman et al. 2015)

5 W Hya size & dust W Hya Teff L D dm/dt 2500 K 5400 Lsun 98 pc 1.3x10-7 Msun/yr Zhao-Geisler et al R *,1μm~2 AU (20mas) Ohnaka et al. 2016

6 Radio ~7 mm W ~1 ~1.2 cm Reid & Menten 1997, 2007 Matthews et al. 2015

7 W 338 GHz Observed Dec 2015 With 8 km baselines robust weighting: 38x31 mas beam Vlemmings et al. 2017

8 W 338 GHz Observed Dec 2015 With 8 km baselines robust weighting: 38x31 mas beam uniform weighting: 17x24 mas beam (restored with 17 mas circular beam) Vlemmings et al. 2017

9 W 338 GHz Observed Dec 2015 With 8 km baselines robust weighting: 38x31 mas beam uniform weighting: 17x24 mas beam (restored with 17 mas circular beam) Residuals after subtracting best fit disk 56.5 x degrees Vlemmings et al. 2017

10 Hotspots and inhomogenieties Significant structure seen on the stellar disk Average disk temperature ~2500 K, similar to photosphere Unresolved features lower limits on temperature

11 Hotspots and inhomogenieties Significant structure seen on the stellar disk brightest hotspot < 2x3 mas (5 σ) > K! other spots of several K as well as colder spots (larger optical depth) few 100 K below disk temp.

12 Result summary ~7 mm W ~1 μm Chromosphere average T~2500 K non-uniform disk with mottled surface and compact hotspot area filling factor <0.1% up to > K Change of dynamics across the star infall and outflow up to ~20 km/s hot region lower infall ~1.2 cm

13 Model comparison W Hya Freytag et al. (2017)

14 Result Summary II Shock heating non-instantaneous radiation of shock energy Low filling factor chromosphere origin of UV emission? >65% of all AGB stars are UV active (Montez et al. 2017) contribution of magnetic activity? gas mass >> mass lost per year all expelled gas will experience shock heating shock chemistry unavoidable

15 0.4 deltamodel Outlook gaussmodel Offset [arcsec] B ig. 1. example caption Offset [arcsec] East offset [arcsec] ~1500 K A Mira A&B A B Offset [arcsec] Offset [arcsec] ~3000 K To map temperature East offset [arcsec] deltamodel Offset [arcsec] structure we need: multi-band obs resolving power (>4 beams across) continuum sensitivity not very crucial, SNR>100 gaussmodel requires Tb,rms<30 K practically ~1 hr per source self-calibration! Offset [arcsec] East offset [arcsec] -0.4 Vlemmings et al East offset [arcsec] white dwarf companion East offset [arcsec] East offset [arcsec]

16 5 Dec 2015 Outlook II max 345 GHz nr. of stars notes Current ~16 mas ~5 oxygen-rich! x2 ~8 mas ~20 x3 ~5 mas ~100 oxygen-rich dominated optical/nir interferometryy synergy W Hya (scattered) dust polarisation VLT Sphere (Khouri et al. in prep) for >4 beams across briggs (0.5) weighting R Dor VLT Sphere (Khouri et al. in prep) VLTI (Wittkowski et al. 2017)

17 Conclusions ALMA long baselines provide unique capability to characterise the extended atmospheres of evolved stars Only probe of temperature structure together with dynamics! (next talk) (non-thermal processes with full polarisation) Avoid line opacity sources affecting most other wavelengths important synergy with optical/(n)ir observations The required model constraints for the study of dust formation and wind driving (ISM replenishment) Direct probes of astrophysical dust (seed) formation only possible around evolved stars!