Doppler shift of hot coronal lines in a moss area of an active region

Abstract

The moss is the area at the footpoint of the hot (3 to 5 MK) loops forming the core of the active region where emission is believed to result from the heat flux conducted down to the transition region from the hot loops. Studying the variation of Doppler shift as a function of line formation temperatures over the moss area can give clues on the heating mechanism in the hot loops in the core of the active regions. We investigate the absolute Doppler shift of lines formed at temperatures between 1 MK and 2 MK in a moss area within active region NOAA 11243 using a novel technique that allows determining the absolute Doppler shift of EUV lines by combining observations from the SUMER and EIS spectrometers. The inner (brighter and denser) part of the moss area shows roughly constant blue shift (upward motions) of 5 km s −1 in the temperature range of 1 MK to 1.6 MK. For hotter lines the blue shift decreases and reaches 1 km s −1 for Fe xv 284 Å (∼2 MK). The measurements are discussed in relation to models of the heating of hot loops.The results for the hot coronal lines seem to support the quasi-steady heating models for nonsymmetric hot loops in the core of active regions.

Coronal Loops: Observations and Modeling of Confined Plasma

“…The redshift peak increases to 15 km s −1 in an active region at temperature of 10 5 K, while the redshifts were found to turn into blueshifts at temperatures above 5 × 10 5 K (Teriaca et al , 1999 ). The trend from redshift to blueshift also applies to active region moss, but the transition from red to blue appears to occur at a higher temperature in the moss (∼ 1 MK versus 0.5 MK in the quiet Sun) (Dadashi et al , 2012 ; Tripathi et al , 2012b ).…”

“…No strong flows were found in an active region core in the Hinode/EIS Fe xii 195 Å line (Brooks and Warren, 2009 ). In the core of moss regions SUMER and EIS data show some blueshifts of a few km s −1 at low coronal temperatures, decreasing at higher temperatures (Dadashi et al , 2012 ). Specific studies of coronal loops in an active region show mostly blue-shifted emission at coronal temperatures, with speed of about 20 km s −1 at the footpoints (Tripathi et al , 2012a ).…”

The evolution of the emission measure distribution in the core of an active region

“…The heating of the hot loops in the core of the active regions has been, however, a matter of much debate (see e.g. Tripathi et al 2010bTripathi et al ,a, 2011Tripathi et al , 2012Warren et al 2010Warren et al , 2011Warren et al , 2012Winebarger et al 2011Winebarger et al , 2013Viall & Klimchuk 2011;Dadashi et al 2012;Schmelz & Pathak 2012;Ugarte-Urra & Warren 2012). One issue that is still not clear is the amount of hot plasma above 3 MK; EUV and X-ray spectroscopic observations indicate that the cores of quiescent ARs have very little hot plasma (see Del Zanna 2013b; Del Zanna & Mason 2014 and references therein), a topic that we do not discuss here.…”

“…Warren et al 2003, Warren et al 2008, Tripathi et al 2009, Ugarte-Urra et al 2009, Klimchuk 2009. The heating of the hot loops in the core of the active regions has been, however, a matter of much debate (see e.g., Tripathi et al 2010b, Warren et al 2010, Tripathi et al 2010a, Tripathi et al 2011, Viall & Klimchuk 2011, Dadashi et al 2012 This paper instead focuses on the slopes in the 1-3 MK temperature range. Recent studies used Hinode EIS observations of the cores of active regions, avoiding moss emission.…”

Ανάδυση Μαγνητικής Ροής Στον Ήλιο, Ηλιακοί Πίδακες Και Στεμματικές Εκτινάξεις Μάζας

“…Εργασίες πάνω σε απόλυτες ταχύτητες (στην περίπτωση του moss μιας ενεργού περιοχής (Dadashi et al, 2012), στον ήρεμο ήλιο και σε κέντρα δράσης (Teriaca et al, 1999) και σε σαρώσεις ολόκληρου του ηλιακού δίσκου (Peter and Judge, 1999)), δείχνουν ότι οι γραμμές με θερμοκρασίες σχηματισμού μεγαλύτερες των T ≈ 10 6 K είναι εν γένει μετατοπισμένες προς το κυανό (blueshifted). Οι Dadashi et al (2012) βρήκαν ότι οι ταχύτητες φθίνουν από 5 km s −1 (1-1.5MK γραμμές σιδήρου) σε 1 km s −1 (Fe XV 284Å, log T=6.4). Οι Teriaca et al (1999) μέτρησαν μετατοπίσεις προς το κυανό τάξης 10km s −1 στην γραμμή Fe XII 1242Å (logT=6.12).…”