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Proposal ID Venkatakrishnan_76

Date of Proposal
97/02/16

firstname
P.

lastname
Venkatakrishnan

institute
Indian Institute of Astrophysics

address
Sarjapur Road, Bangalore 560034 INDIA

email
pvk@iiap.ernet.in

phone
(91)-80-533-0672

fax
(91)-80-533-4043

proposal
Motivation:
In an attempt to understand the excitation of HeI 1083 nm line
in the solar chromosphere, Venkatakrishnan et al. (PASJ, 48, L1,
1996) found enhanced HeI absorption at the feet of Yohkoh X-ray
loops. This was explained as due to enhanced excitation of the
3S lower state of the HeI transition by enhanced exciting EUV
emission at the feet of X-ray loops by conduction of heat down
the legs of the loops. Support for this explanation was drawn
from the similarity of texture of transition region (TR) images
seen in the Skylab Atlas with that of HeI 1083 nm pictures. A
proper comparison of TR pictures (e.g. HeII 30.4 nm) with pictures
taken in coronal lines (hot coronal loops) will confirm this
scenario and provide a breakthrough in the understanding of the
mechanism of HeI excitation.

Data Required:
Simultaneous pictures in TR emission and coronal emission of
active regions.

Method to be adopted:
Every pair of TR and coronal images must be spatially registered.
The contours of equal brightness of TR emission must be overlaid
on the coronal images. Any preference for TR emission to be enhanced
at the feet of the hot loops can be clearly seen.

inside_collab
1. Dr D.M. Zarro
2. Dr J. Gurman

consortium
no

topic
Active Regions

topic

title
Search for Enhanced TR Emission at Feet of Hot Coronal Loops

update added on 1997/10/15 at 01:02:56

update added on 1997/10/15 at 08:49:14
PRELIMINARY RESULTS:

1) HeII pictures look different from coronal pictures in certain details.

2) Short bright loops in FeXV and FeXII emission show less HeII emission
beneath the body of the loops compared to the feet.

3) A faint loop system in coronal emission seems to connect patches of
HeII emission which have "filled in" emission in the interior of the
network cells.

4) There is almost no HeII emission beneath the body of these faint
coronal loop systems.

VERY PRELIMINARY INFERENCES:

1) Coronal EUV radiation does not seem to excite HeII in the regions
beneath the body of the loops.

2) HeII could be excited by heat conduction into feet of loops.

3) Co-existence of 30.4 nm emission with 29.5 or 28.4 nm emission
at feet of loops implies that either plasma at FeXV/FeXII
temperatures co-exists with HeII temperature or there are
other sources of radiation at 28.4 nm and 29.5 nm.

update added on 1998/07/28 at 04:51:15
The work has been completed and a paper entitled, Comparative
Morphology of EIT/SOHO Images and HeII Excitation'' has been
submitted to SOLAR PHYSICS. The preprint can be obtained by
contacting the author at pvk@iiap.ernet.in.


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