Eamon O'GormanOnsala Space Observatory

Why Galaxies Care About AGB Stars III2014 July

The Wind Acceleration Region of Betelgeuse: Resolved at Centimeter Wavelengths

Image courtesy of NRAO/AUI and NRAO

Mass-loss in Late-K & Early-M Supergiants

2014 July Why Galaxies Care About AGB Stars III

Problem: Small pulsation amplitudes (Smith et al., 1989)Dust observed too far away (many R

*; Danchi et al., 1994) (Talk by Xavier Haubois)

Convection? (“Unlikely” Talk by Ohnaka)

Mass-loss in Late-K & Early-M Supergiants

2014 July Why Galaxies Care About AGB Stars III

Problem: Small pulsation amplitudes (Smith et al., 1989)Dust observed too far away (many R

*; Danchi et al., 1994) (Talk by Xavier Haubois)

Wind acceleration region:

Betelgeuse: 1D: Harper et al., 2001

Kervella et al., 2009

VLT/NACO (1.04–2.17 μm)

Convection? (“Unlikely” Talk by Ohnaka)

Mass-loss in Late-K & Early-M Supergiants

Problem: Small pulsation amplitudes (Smith et al., 1989)Dust observed too far away (many R

*; Danchi et al., 1994) (Talk by Xavier Haubois)

Wind acceleration region:

Betelgeuse: 1D: Harper et al., 2001

Kervella et al., 2009

Winds are partially ionized (free-free)Thermal continuum radio opacity is proportional to ~ λ2.1 n

en

ion

λ = wavelengthn

e = electron density

nion

= ion density

VLT/NACO (1.04–2.17 μm)

2014 July Why Galaxies Care About AGB Stars III

Antares (M1.5 Iab) and Betelgeuse (M2 Iab)

Distance 197 ± 45 pcAngular Diameter 42.49 mas (940 Rʘ)

Herschel/PACS

150 R*

Distance 185 ± 44 pcAngular Diameter 37.38 mas (740 Rʘ)

(Hjellming and Newell, 1983)

Antares at 6 cm

2014 July Why Galaxies Care About AGB Stars III

Betelgeuse: Flux Density Variability

λ

Multi-wavelength VLA studiesStochastic variabilityα = 1.32 (i.e., > 0.6)

Warm (~104 K) & partially ionized wind acceleration region

Good agreement with Alfven wave models to follow (e.g., Hartmann & Avrett, 1984)

2014 July Why Galaxies Care About AGB Stars III

Betelgeuse: Wind Acceleration Region Resolved

Brightness Temperature (K)

Angular Diameter

2014 July Why Galaxies Care About AGB Stars III

(Lim et al., 1998, Nature)

Betelgeuse: Wind Acceleration Region Resolved

Brightness Temperature (K)

Angular Diameter

Alfven waves, acoustic shocks

Convection?

2014 July Why Galaxies Care About AGB Stars III

(Lim et al., 1998, Nature)

Betelgeuse: Wind Acceleration Region Resolved

Brightness Temperature (K)

Angular Diameter

Alfven waves, acoustic shocks

Convection?

2014 July Why Galaxies Care About AGB Stars III

Betelgeuse: 2012 e-MERLIN (5.2 cm)

2014 July Why Galaxies Care About AGB Stars III

(Richards et al., 2013)

Betelgeuse: 2012 e-MERLIN (5.2 cm)

Two radio 'hotspots': Te >3800 ± 500 K, 5400 ± 600 K (T

eff = 3690 K)

Projected separation: 90 mas (4 R*)

2014 July Why Galaxies Care About AGB Stars III

Astrometric solution of Harper et al., (2008)Uncertainty ± 5 mas

(Richards et al., 2013)

Betelgeuse: 2012 e-MERLIN (5.2 cm)

Two radio 'hotspots': Te >3800 ± 500 K, 5400 ± 600 K (T

eff = 3690 K)

Projected separation: 90 mas (4 R*)

Hottest source at 4 R*.

At least ~3 times the predicted Te.

2014 July Why Galaxies Care About AGB Stars III

Betelgeuse with VLA + Pie Town

w/l (cm) Resolution ('')0.7 40 x 251.3 80 x 402.0 120 x 90

3.5 200 x 130

6.2 380 x 270

w/l (cm) Resolution ('')5.2 80 x 60

e-MERLIN

VLA + Pie Town

+ =

VLA

Pie Town Antenna

VLA – 1996 (Lim et al., 1998, Nature)

VLA + Pie Town – 2000,2001,2002,2003,2004

2014 July Why Galaxies Care About AGB Stars III

Betelgeuse with VLA – Pie Town: Images

0.7 cm Maps (Superior resolution to e-MERLIN)

Dec 1996 Dec 2000 Oct 2004

Q band: Tropospheric phase fluctuations

→ Short cycle times

2014 July Why Galaxies Care About AGB Stars III

Betelgeuse with VLA – Pie Town: Visibilities20

0 4

2014 July Why Galaxies Care About AGB Stars III

Mean Thermal Profile

Betelgeuse with VLA – Pie Town: Visibilities20

0 4

2014 July Why Galaxies Care About AGB Stars III

Mean Thermal Profile

Betelgeuse with VLA – Pie Town: Visibilities20

0 4

2014 July Why Galaxies Care About AGB Stars III

A Tale of Two Telescopes

e-MERLIN

Two radio hot spots separated by 90 mas (4 R*) in plane of sky

At least one has a chromospheric temperature

VLA + Pie Town

No radio hot spots

Cool (but variable) extended atmosphere

Sufficient sensitivity and resolution

0.09" at 197 pc and 10 km s-1: possible evolution

2014 July Why Galaxies Care About AGB Stars III

Prospectives (cm observations)

Multi-epoch e-MERLIN 5.2 cm Cycle 2 submittedFollow the motion of 'ejections'Velocity in the plane of skyTime-scales

Co-ordinated JVLA effort 0.7 (Q band) and 0.9 (Ka band)Spectral index

5.2 cm

2014 July Why Galaxies Care About AGB Stars III

Prospectives (ALMA)

Cycle 1 time awarded (Kervella, P., Decin L., et al.,)

Band 9: CO(J=6-5) , most extended configuration

Dynamics, structure and clumpiness in the inner envelope

Spatial scales: 0.1” → 3” (~4.5 → 130 R*)

Spatially resolve dust condensation radius: 0.5” → 1” (~20 → 40 R*)

VLT/VISIR image at 10.49 μm (Kervella et al. 2011)

2014 July Why Galaxies Care About AGB Stars III

Prospectives (ALMA)

Cycle 1 time awarded (Kervella, P., Decin L., et al.,)

Band 9: CO(J=6-5) , most extended configuration

Dynamics, structure and clumpiness in the inner envelope

Spatial scales: 0.1” → 3” (~4.5 → 130 R*)

Spatially resolve dust condensation radius: 0.5” → 1” (~20 → 40 R*)

cm hotspots: future ALMA cycles? e-MERLIN? Jansky VLA?

VLT/VISIR image at 10.49 μm (Kervella et al. 2011)

2014 July Why Galaxies Care About AGB Stars III

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