A closer look at the footpoints of coronal loops rooted in ... · coronal loop diagnostics ... The...

A closer look at the footpoints of coronalloops rooted in a sunspot umbra

Pradeep Chitta, Hardi Peter and Peter Young (GMU)

Solar Group Seminar14 July 2015

Coronal loops

Composite image of SDO/HMI magnetogram and AIA 171 A channel

Coronal loops

coronal loop diagnostics – flows, temperature, density,non-thermal velocity – key to understand coronal heating

mechanism

Coronal loop diagnostics – SOHO/SUMER era

Dammasch et al. (2008)

Coronal loop diagnostics – Hinode/EIS era

Del Zanna (2008)

Coronal loop diagnostics – Hinode/EIS era

Young et al. (2007)

Hara et al. (2008)

Coronal loop diagnostics – Hinode/EIS era

Young et al. (2007) Hara et al. (2008)

Supersonic downflows – IRIS era

Kleint et al. (2014)

Supersonic downflows – IRIS era

Kleint et al. (2014)

Bright dots in the TR – IRIS era

Tian et al. (2014)

Footpoints rooted in a sunspot umbra

• The footpoints of loops appear as isolated bright dots in Si1400 slit-jaw observations.• Weak or little background emission from umbra allows us toclearly detect and associate the loops and their footpoints

Observational context

Spatial maps in various lines

Average O IV and Si IV spectra

Connecting footpoint to its loop!

Doppler maps at the footpoint

• Footpoint in O IV showsdownflows at ≈15 kms−1.

• Spatially resolvedDoppler maps offootpoints havepotential information toplace bounds on thenon-thermal velocityand constraints on theprocesses

O IV and Si IV spectra vs. time

C II and Mg II k spectra vs. time

Distribution of emission

Discussion – Heating

Hansteen et al. (2010)

• “ downflows in TR lines naturally produced by rapid,episodic heating, at low heights of the upperchromospheric plasma to coronal temperatures”

• “heating by stressing of the magnetic field by photosphericand convection zone dynamics”

Conclusions and tasks to be completed

• Isolated coronal loops identified in a sunspot umbra• Footpoint in O IV shows a strong flow component at 10-15

km s−1, and a weak ≈ 100 km s−1 redshifted component• The origin of redshifted component can be traced to the

strong downflows observed in the loop (issues with masssupply – Siphon flows due to asymmetric heating?)

• Downflows at TR temperatures show acceleration• Preliminary density analysis with different O IV line

pair ratios shows some inconsistencies – to becompleted

• Deriving and comparing non-thermal velocities at thefootpoint and its loop – to be completed

Thank you!