Magnetic loops above a small flux-emerging region observed by IRIS, Hinode and SDO

Abstract

I report on observations of a set of magnetic loops above a region with late-phase flux emergence taken by IRIS, Hinode and SDO. The loop system consists of many transition region loop threads with size of 5--12\arcsec\ in length and $\sim 0.5$\arcsec in width and coronal loops with similar length and $\sim 2$\arcsec width. Although the loop system consists of threads with different temperatures, most individual loop thread have temperature in a narrow range. In the middle of the loop system, it shows clear systematic blue-shifts of about 10\,\kms\ in the transition region that is consistent with a flux emerging picture, while red-shifts of about 10\,\kms\ in the corona is observed. The nonthermal velocity of the loop system are smaller than the surrounding region in the transition region but are comparable in the corona. The electron densities of the coronal counterpart of the loop system range from $1\times 10^9$\,cm${}^{-3}$ to $4\times 10^9$\,cm${}^{-3}$. Electron density of a transition region loop is also measured and found to be about $5\times 10^{10}$\,cm${}^{-3}$, a magnitude larger than that in the coronal loops. In agreement with imaging data, the temperature profiles derived from the differential emission measurement technique confirms that some of the loops have been heated to corona. Our observations indicate that the flux emergence in its late phase is much different from that at the early stage. While the observed transition region is dominated by emerging flux, these emerging loops could be heated to corona and the heatings (if via nonthermal processes) most likely take place only after they reaching the transition region or lower corona.

Accepted for publication in ApJ

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