How do we observe AU-scale structure?
Pulsars, and optical depth imaging against extended radio
continuum sources….
CNM
Pulsar
V=5-50 AU/yr
*
Epoch 2
Epoch 1
1
Equivalent width variations
• EW = 0 within 2 for:
0823, 1133,1737, 2016
• EW0 for 1929
• TSAS: L=5-50AU, n~104 cm-4,
P~106 cm-3 K
Stanimirovic, Weisberg et al. (2010)
2
• Distance=350 pc, closest in the
sample
• ½ of LOS inside the Local Bubble.
• HD178125 and HD180555 show
NaI absorption as similar velocity
 TSAS is within the LB!
What’s going on
with B1929+10 ?
*
PSR at
~330pc
• LOS to B1929+10 pierces the LB
wall for 50-60 pc.
• Many diffuse clouds in this
direction (Aquila Rift) condensing
out of the LB wall or ablated
nearby molecular gas
• TSAS Tspin = 150-200 K
• CNM/WNM ratio = only 7%
 TSAS properties/production
influenced by the history/evolution
of the Local Bubble
Welsh et al. (2010)
3
High optical depth
Does the power
spectrum extend
down to AUscales?
Low optical depth
* : interferometric
other: pulsars
•
•
•
•
•
With different sources, essentially continuous coverage.
No observed power-law turbulent spectrum on scales: 1 to ~1000 AU.
Kendall’s tau test for censored data: P(no correlation) ~60%
Inhomogeneity in Galactic distribution of TSAS + v.f.f.<~1%
TSAS is not pervasive.
If TSAS is tracing the end-scales of turbulence then turbulence may dissipate
in bursts or active pockets, or it dissipates very fast.
4
Does the power
spectrum extend
down to AUscales?
* : interferometric
other: pulsars
•
•
•
•
•
With different sources, essentially continuous coverage.
No observed power-law turbulent spectrum on scales: 1 to ~1000 AU.
Kendall’s tau test for censored data: P(no correlation) ~60%
Inhomogeneity in Galactic distribution of TSAS + v.f.f.<~1%
TSAS is not pervasive.
If TSAS is tracing the end-scales of turbulence then turbulence may dissipate
in bursts or active pockets, or it dissipates very fast.
5