discussion of atomic data for O IV and Si OV
see especially the appendix. We need to update this once the dust settles.
Density diagnostics derived from the O iv and S iv intercombination lines observed by IRIS
Polito, V., Del Zanna, G., Dud\ik, J., Mason, H. E., Giunta, A., & Reeves, K. K.
2016, \aap, 594, A64
ABSTRACT: The intensity of the O iv 2s2 2p 2P-2s2p24P and S iv 3 s2 3p 2P-3s
3p24 P intercombination lines around 1400 Å observed with the Interface Region
Imaging Spectrograph (IRIS) provide a useful tool to diagnose the electron
number density (Ne) in the solar transition region plasma. We measure the
electron number density in a variety of solar features observed by IRIS, including
an active region (AR) loop, plage and brightening, and the ribbon of the 22-June-
2015 M 6.5 class flare. By using the emissivity ratios of O iv and S iv lines, we find
that our observations are consistent with the emitting plasma being near
isothermal (logT[K] ? 5) and iso-density (Ne ? 1010.6 cm-3) in the AR loop.
Moreover, high electron number densities (Ne ? 1013 cm-3) are obtained during
the impulsive phase of the flare by using the S iv line ratio. We note that the S iv
lines provide a higher range of density sensitivity than the O iv lines. Finally, we
investigate the effects of high densities (Ne ? 1011 cm-3) on the ionization
balance. In particular, the fractional ion abundances are found to be shifted
towards lower temperatures for high densities compared to the low density case.
We also explored the effects of a non-Maxwellian electron distribution on our
diagnostic method. The movie associated to Fig. 3 is available at
http://www.aanda.org
KEYWORDS: Sun: transition region, Sun: UV radiation, techniques: spectroscopic, atomic data
NOTE:
REMOTE URL : http://dx.doi.org/10.1051/0004-6361/201628965
REMOTE URL : http://arxiv.org/abs/1607.05072
REMOTE URL : http://adsabs.harvard.edu/abs/2016A%26A...594A..64P
ADS URL : http://adsabs.harvard.edu/abs/2016A%26A...594A..64P