UV spectra, bombs and the solar atmosphere · UV spectra, bombs and the solar atmosphere " 1!...

1 UV spectra & solar atmosphere!Philip Judge!

UV spectra, bombs and the solar atmosphere"

1!

Philip Judge, "

High Alitude Observatory, "

NCAR"

Some comments on IRIS spectroscopy "of the solar atmosphere with special"reference to Peter et al 2014 Science"


Summary"

2!

1.  Bombs- IRIS observations of Peter et al 2014!

2.  Stratification!

3.  Densities!1.  Si and O!2.  Si IV and O IV!3.  Line ratios!4.  Atomic and plasma processes!5.  Results!

4.  Ramifications!


Peter et al. emerging AR: IRIS & SDO"

three bright features!with lifetimes of > 5 min!

Si IV spectroheliogram"

IRIS 1400 Å"

AIA 171 Å"

AIA 304 Å"

AIA 1600 Å"HMI Blos"

70” x 35”!

Lyman continuum!invoked to explain!lack of EUV!


Peter et al. bomb spectra"

missing O IV lines!

optically thin!“Effectively” thin!


Peter et al: electron densities"

Doppler shift relative to target line rest wavelength [km/s] !

spec

tral

radi

ance

[DN

/ p

ixel

] !

O IV!1401.16!

Si IV!1403.77!

Si IV 1394!O IV 1401! > 700!

no O IV lines!upper limit:!

→ density Si IV: >5 x 1013 cm-3 Pe > 550 dyne cm-2!

→ total pressure of T mimimum


Peter et al. B1 highest density case"

Si IV 1394!O IV 1401! > 700!

I examine B1, which has the highest!density, pressure!

I assume, as do Peter et al, that the bomb forms!without expansion or compression !from pre-existing dense material deep in the !atmosphere.!

Is it formed in out of photospheric plasma?!


Summary"

7!






-1000 0 1000 2000 3000Height km

-2

0

2

4

6

log

pres

sure

cgs

-1000 0 1000 2000 3000

-2

0

2

4

6

0.0

0.2

0.4

0.6

0.8

1.0

1 minus PDF

BifrostVAL3C

-1000 0 1000 2000 30000

200

400

600

800

1000

pres

sure

sca

le h

eigh

t

stratification"

8!

p=1000 ! dyne cm-2!

On average, the atmosphere below the corona is!hydrostatically stratified, especially the dense, heavy stuff!

~ Hydrostatic stratification!


stratification"

9!

p dyne/cm2!

400!

1000!2500!

G star: Lots of UV opacity (≅ Lyman continuum)!

Si I and C I photoionization!


Puzzle: How do 140nm photons escape from regions with pressures > 550 dyn cm-2?"

10!


Summary"

11!






Si vs O "

12!

•  FIP bias (factor 3-4 possible)!•  Widing & Feldman (1995 ApJ):!•  !

Bombs:!

Si might be stronger!by factor 1-4 only !because of !abundances!


Si IV vs O IV"

13!

•  Emission measure analysis ! disk integrated EUV data! Judge et al 1995 apj !

•  Li and Na-like ions too strong!

•  Si IV 2.3x too strong!

Si IV!

O IV!


Electron density diagnosis"

14!

•  Under-determined (2 lines, 2 different temperatures) !

•  Assumptions determine solution. Standard assumptions plus!

•  Explicit: sources are bi-isothermal, isobaric!•  Implicit: !

•  sources are equal strength (no “DEM” specified)!•  low ne calculations ion balance are valid (CHIANTI)!

a/b fixes the “DEM” shape!extra degree of freedom


Electron density diagnosis"

15!


density-dependent dielectronic recombination (DR)"

16!

Silicon IV

4.2 4.4 4.6 4.8 5.0 5.2 5.4Log Te

0.2

0.4

0.6

0.8

1.0

Ion

fract

ion

p0104p0

No DR104p0 LTE

p0= 1015 cm-3K

Oxygen IV

4.2 4.4 4.6 4.8 5.0 5.2 5.4


Accompanying free-free emission (LTE)"

17!

1320 1340 1360 1380 1400 1420 1440Wavelength Angstrom

103

104

105In

tens

ity e

rg c

m-2s-1

sr-1A-1

IRIS B-1100x B(4600K)

Free-free

Predicted from Si IV ξ(T)!

Discrepancy x3!


134.3 nm O IV multiplet in IRIS range"

18!

2p2p

2p22p22p2

2p22p2

2p22p22p2

2p32p32p3

1401.157

1343.514

4S4So

4P4Po

4D4Do 4Fo 3Po

2S2So

2P2Po

2D2Do

2F2Fo

1S

eV!

1343 multiplet would have helped!constrain plasma thermal properties!

Feldman et al!1998 flare!SUMER!


Electron density diagnosis- results"

19!

Peter et al. over-estimate ne:!

•  Previous work on Li and Na-like ions: factor 2.5!

•  Possible FIP effect in flaring plasma: factor 1-4!

•  Finite density dielectronic recombination: factor 2!•  Free-free emission: factor ≥ 3!

Pressures over estimated by factors between 5 and 20.!

Lower pressures are consistent with the stratification and opacity of the lower!solar atmosphere: Peter et al. H < 500 km, here H > 550 km, probably >> 550 km!

Lower densities lead to higher Alfvén speeds in better agreement!with dynamics!

This is a chromospheric phenomenon!


Summary"

20!






Ramifications"

21!

• Reminders !•  stratification and opacity interlinked. UV mfp’s tiny in photosphere!•  most “ionization equilibrium” calculations apply ne < 108 cm-3!

•  analyze all relevant lines and continua!

•  What is a photosphere?!•  Physical: !

•  99.9% of stellar flux is radiated to space: τ500 < 0.001, H < 450 km!•  Radiative heating only!•  dynamics (granulation below ~ 300 km, e.g. Cheung et al 2007)! (reverse granulation < 650 km, Kostik et al. 2009)!•  => H below ~ 450 km!•  semanticism? I think not… !

•  Empirical: All cool material above τ500 = 1 independent of H?!


density-dependent dielectronic recombination (DR)"

22!

Silicon p(QS)

0.1

1.0 II III IVV VI

SI IV <F>= 0.12 TMAX= 4.76

Silicon104 x p(QS)

0.1

1.0 II III IV V VISI IV <F>= 0.17 TMAX= 4.72

Silicon No DR QS

4.5 5.0 5.5Log Te

0.1

1.0

Ion

fract

ion

II III IV V VISI IV <F>= 0.22 TMAX= 4.67

Oxygen p(QS)

II III IV VVI

VIIO IV <F>= 0.20 TMAX= 5.14

Oxygen104 x p(QS)

II III IV VVI

VIIO IV <F>= 0.14 TMAX= 5.03

Oxygen No DR QS

4.5 5.0 5.5

II III IV V VI VIIO IV <F>= 0.17 TMAX= 4.98

Si IV <F> ÷ O IV <F>!

0.6!

1.2!

1.3!


Stratification& dynamics: HRTS (Dere et al 1983)"

23!

C I lines: RMS chromospheric doppler shifts ~ 1-2 km/s, subsonic!! Widths 0.08 Å = instrumental (2x IRIS), turbulence < 10 km/s!


Peter et al. average plage spectrum"

UV spectra, bombs and the solar atmosphere · UV spectra, bombs and the solar atmosphere " 1!...

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