I have a short paper on electron temperature measurements using emission lines. I thought the loops group may find it of interest.
It will soon become available on http://arxiv.org/abs/0911.4085
It can also be found at
http://download.hao.ucar.edu/pub/judge/thermometer.pdf
It will appear in apj.
best wishes
philip judge
Dear all,
if you go to http://solar.physics.montana.edu/cgi-bin/eprint/index.pl
you will find three papers relevant to the last two loop workshop meetings.
Those of you present during my talk at the loop meeting in Santorini might recall the Hinode EIS observations which I used to cross-calibrate EIS with the TRACE 195 A band. I made the point that at upper transition region temperatures there is a host of lines, many still not identified, and which can become important in any modelling of this TRACE band. After two years I finally finished the `preliminary' work, and identified a large number of lines [the TRACE calibration work has been postponed for now].
A nice by-product of this work is the fact that with newly-identified lines from Fe VII and Fe VIII (together with lines from Fe IX, X), it is in principle possible to provide good constraints on the electron temperatures in the `upper transition region'. I say in principle because I think that the radiometric calibration of the EIS instrument needs some revisions. And because a lot more work still needs to be done on the atomic data [I found some surprising results which need to be confirmed]. In all the `leg' of loops I looked at, I found `near-isothermal' emission measures (confirming my SOHO CDS results), and electron temperatures far off from those where ions have peak abundance [not surprisingly].
I fully agree on the word of caution given recently by Phil Judge, however combining different diagnostics can provide reliable measurements. When I first applied the `good old' EM Loci method to AR loops in 2003, I did it to show that AR plasma is composed of near-isothermal structures, and not of multi-thermal ones as many people still think. However, I have always warned that better direct temperature measurements are needed and large uncertainties are present in any EM technique.
Finally, those of you present at the Florence meeting might recall me saying that most Hinode/XRT filters in AR observations would be dominated by Fe XVII emission lines, and that a host of Fe XVII lines are present in the Hinode EIS spectra, so some direct cross-calibration is in principle possible. Well again after a number of years I have finally finished the identification work for the Fe XVII EUV lines. Results on the XRT calibration will follow at some point. The Fe XVII lines, once blends and various problems are taken into account, can also be used to constrain emission measures in an interesting temperature region.
cheers
loops@solar.physics.montana.edu