Post on 21-Apr-2020
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"
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
Peter et al. bomb spectra"
missing O IV lines!
optically thin!“Effectively” thin!
1 UV spectra & solar atmosphere!Philip Judge!
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
1 UV spectra & solar atmosphere!Philip Judge!
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?!
1 UV spectra & solar atmosphere!Philip Judge!
Summary"
7!
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!
1 UV spectra & solar atmosphere!Philip Judge!
-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!
1 UV spectra & solar atmosphere!Philip Judge!
stratification"
9!
p dyne/cm2!
400!
1000!2500!
G star: Lots of UV opacity (≅ Lyman continuum)!
Si I and C I photoionization!
1 UV spectra & solar atmosphere!Philip Judge!
Puzzle: How do 140nm photons escape from regions with pressures > 550 dyn cm-2?"
10!
1 UV spectra & solar atmosphere!Philip Judge!
Summary"
11!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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
1 UV spectra & solar atmosphere!Philip Judge!
Electron density diagnosis"
15!
1 UV spectra & solar atmosphere!Philip Judge!
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
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
Summary"
20!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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?!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
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!
1 UV spectra & solar atmosphere!Philip Judge!
Peter et al. average plage spectrum"