Active Region Loops - Observational Constraints on Heating from Hinode/EIS Observations

Helen E. Mason DAMTP, Centre for Mathematical Sciences,University of Cambridge

Cristina Chifor, DAMTP, Giulio Del Zanna, DAMTP, Brendan O’Dwyer, DAMTP, Durgesh Tripathi, DAMTP, Peter Young, NRL

Solar Cycle 24, Napa, December 2008

Photo: Giulio Del Zanna

Active Region loops: Open questions

• Are quiescent (1MK) loops isothermal or multi-thermal along the line of sight?

• Is there a weak high temperature component for all AR loops?• Loop structures appear fuzzier at higher temperatures: is this

real or just the matter of spatial resolution?• What are the values of densities and the filling factors of a

coronal loop? How do they vary along the loop length?• How does the temperature vary along the loop length?• What are the plasma flow in the active region loops? • What are the physical properties of the ‘moss’? • Do the hot, dense core loops interact with the larger, cooler

1MK loops?

Hinode/EIS: Intensity, velocity and line width maps Young, 2007 Doschek et al, 2008

• Active region map– Fe XII 195.12 Å– Dec 2, 2006

Intensity

Velocity

Width

For the first time, using Hinode/EIS, we are able to derived detailedmaps of electron density, temperature, flows, non-thermal broadenings, and fill factors.

However, rastering can be slow, so carefully designed EIS sequences are needed to obtain observations with a good cadence.

Flow patterns are different at different temperatures and persist for several days.

Active region flows at different temperaturesDel Zanna, 2007, 2008HEALTH WARNING! Several of the EIS spectral lines are blended – dealing with the blends is difficult. There are several papers, eg led by Young, Del Zanna and others to aid identifications. Resolving idividual lines, especially weak ones is tricky. Deriving velocity shifts is even more ‘tricky’!! Seek advice from the EIS team.

EIS observations: May 19, 2007, Tripathi et al, 2008Ion /

wavelengthlog T[MK]

log Ne(cm-3)

Fe VIII (185) 5.6

Mg VII (278) 5.8

Mg VIII (280) 5.8

Si VIII (275) 5.8

Fe X (184) 6.0

Fe XII (195) 6.1

Fe XII (186) 6.1

Si X (258) 6.1

Si X (261) 6.1

Fe XIII (202) 6.2

Fe XIII (203) 6.2

Fe XIV (264) 6.3

Fe XIV (274) 6.3

Fe XV (284) 6.4

7.0 – 12.0

8.0 – 9.8

8.0 – 10.5

8.5 – 11.0

8.0 – 10.5

1 arcsec slitExp time=40s

Obs seq: “AR_velocity_

maps”

11:41:2316:35:01

Flows in individual structures Tripathi et al, 2008

With EIS, we can measure flows with a precision of ±3 km/s in spatially resolved coronal structures.

We can measure flows simultaneously at different temperatures from:log T = 5.6 MK (Fe VIII) to log T = 6.4 (Fe XV).

Velocity flows are seen along the AR loops, predominantly red-shifted at cool temperatures (see Si VII, left).

Blue-shifted flows are seen in other parts of the AR particularly at higher temperatures.

Flows near loop footpoints at different temperatures

The foot point regions show red-shifted emission at lower temperatures. However, blue shifts dominate at high temperatures.

Intensity variation across loop structureslog T = 5.8 log T = 6.0 log T = 6.1 log T = 6.2 log T = 6.3 log T = 6.4

Intensity cut across a loop (between the two white lines). At low temperatures the loops are sharp, at higher temperatures they become diffuse.

Temperature along the loop: EM-LociEM [Te ]= Iobs /[A (b) G(Ne,Te)] Iobs = Background removed observed intensities

A(b) = Abundances (Coronal Abundance)G (Ne, Te) = Contribution function

Temperature rises from 0.8MK at base to 1.5MK at the loop top. Mildly multi-thermal?

Height (Mm)

Lo

g N

e (c

m -3

)

Mg VIISi X

Fe XII

Electron density along loop A

Electron densities are 1010 cm-3 at the base of the loop and fall to 108.5 cm-3 higher up (Background has been subtracted). MgVII densities seem lower that FeXII and SiX. We obtained a low value of filling factor (0.02 – 0.05) at log T = 6.1 MK and a filling factor close to 1 at log T = 5.8 MK towards the foot point of the loop.

BG Background

Electron number densities along a loop

Active Region Observation – focus on ‘core’Tripathi et al, 2008

EIS FOV

MAY 01, 2007

MOSS

LOOPS

SUNSPOT

Active Regions Observations – focus on core

EIS Fe XII 195

• EIS sequence(cam_artb_cds_a)• Raster using 2 arcsec slit• Total time 20 minutes• Exposure time 10 sec• FOV 200 X 200 arcsec

Active region Moss at different temperatures

The TRACE emission is similar to EIS SiVIII and the XRT to EIS FeXV

Density map derived from Fe XII (186.88+186.85/195.12+195.17)

The density in the core of the active region can be as high as 1010.5 cm-3

The density is highest at a temperature of Log T = 6.1

Note that the high densities are in +ve polarity regions not the sunspot side. The density correlates well with the strength of the +ve magnetic field.

EIS: Comparison of density map with magnetic field

Limb Active Region - EIS ObservationsO’Dwyer, Mason, Del Zanna, Tripathi and Young, 2009, unpublished

Dec 17, 2007

Target of OpportunityAR close to the limb,but with core still on disk

Hinode Joint ObservingSequence -+ Alphonse Stirling

CAM_AR_LIMB_v12" slit45sec exposurefull length slit 6' wide raster run time: 2.5 hours

Intensity variation for some EIS lines

These observations can be used to determine line blends, average temperature and density along the line of site, across and above the AR .

Average density along the line of sight

The electron density measured from the FeXII 203/202 diagnostic ratio. The average density peaks in the core of the AR.

Average temperature and density maps for the AR

Average electron density map from FeXIII lines

Temperature map from FeXVI/FeXVRed is Log T = 6.7, yellow is Log T= 6.5

Hot, dense AR cores are clearly seen with EIS. XRT shows ‘dynamic’ activity.These data confirm earlier results with CDS (Mason et al, 1999), but are much better.

Summary and Conclusions

At T around 1MK, red-shifts in loops are ubiquitous.

Blue-shifts are present in higher temperature emission.

Smoking gun! Multi-strands – heating, evaporating and condensing?

Non-thermal broadening associated with blue-shifts.

Density in 1MK loop is 1010 cm-3 at the base and falls to 108.5 cm-3 higher up.

Temperature in the loop rises from 0.7MK at base to 1.5MK higher up.

Could be mildly ‘multi-thermal? Jury is still out! High temperature emission

is predicted by nano-flare models (eg EBTEL). It is very difficult to analyse

EIS high temperature lines (because of line blending).

EIS density and temperature maps show great detail (much better than CDS).

The temperature in the hot, dense core exceeds log T = 6.7, and the

density exceeds 1010 cm-3 .

The ‘moss’ regions have a high densities as high as 1010.5 cm-3 at Log T of 6.1.

The density is correlated with the magnetic field (on the non-sunspot side)

Possible Scenario?

Zwaan 1985

Flux emergence and braiding could cause reconnection at the boundaries as the active region grows.

This could cause a turbulent regime with evaporation strongest at higher temperatures.

Cool loops are mainly radiatively cooling, so we see predominant red-shifts (downward flowing plasma). Definitely need multi-strand models.

What about the hot dynamic cores? Could the flux be submerging again in the core?

Are we in equilibrium?! Recent (independent)work by Bradshaw and Serio discuss the need for time dependent ionisation calculations.

Need good atomic data - CHIANTI v6 – to be released soon, includes ionisation and recombination rates.

Next few years should be reallyexciting. So far we’ve just hada taster of AR observations!!

The Future?

EIS has already provided some fascinating and new observations of active regions. This talk has outlined work led by Cambridge.

Active regions are very dynamic. Work by other members ofthe EIS team, eg Harry Warren, Ignatio Ugarte-Urra, Dochek

et al studying dynamic activity was discussed yesterday.

EIS sequences are being devised to optimise the diagnosticsand to track the dynamics of active region structures –

this balance is perhaps the most difficult to achieve.

A carefully designed combination of different EIS and Hinode -wideobserving modes is needed.

So far, we have just had a ‘taster’, hopefully there will be a lotmore EIS data to analyse once solar cycle 24 gets going..

IT’S A VERY EXCITING TIME...!!