PCTR Physics and “Chewy Nougats*” SSL, UC Berkeley * This nomenclature due either to Greg Slater or Sam Freeland, SXT data pioneers (most likely Greg)

ISSI Jan. 14, 2009 What is the prominence-corona transition region (PCTR)? Analogous (?) with the horizontally stratified ordinary TR, it separates the cold prominence from the hot corona It must be closely aligned with the separatrix between filament fields and cavity fields There are several approaches to understanding it: DEM, radio, filaments, hydrodynamic, MHD, each seemingly with its own literature

ISSI Jan. 14, 2009 Vernazza, Avrett & Loeser 1981 Behind the DEM approach

ISSI Jan. 14, 2009 Different views of the prominence- corona transition region Kucera & Landi, 2008 Cirigliano et al Antiochos & Klimchuk 1991 Heinzel et al. 2008

ISSI Jan. 14, 2009 “Chewy Nougat” There is a hot (soft X-ray) brightening around the cold prominence Hudson et al. 1999

ISSI Jan. 14, 2009 The original nougat as seen on the disk Some polar nougats found by Okumura

ISSI Jan. 14, 2009 EIT 284EIT 304EIT 195 (Aulanier) cavity prominence cavity Filament material in dips of magnetic field lines Multiwavelength Nougat (thanks, Brigitte!)

ISSI Jan. 14, 2009 Nougats and flares?

ISSI Jan. 14, 2009 The Nougat’s basic messages If the PCTR is hotter than the corona surrounding it, the PCTR is unlikely to depend on static conduction as in normal TR models. -We don’t really know if the nougats observed by SXT were hotter than the cavity, since the cavity temperature is hard to determine A filamentary (Chiuderi-type) PCTR would need to extend to heights well above the cold prominence material The PCTR is likely not to be a TR at all, just loops

ISSI Jan. 14, 2009 Is a “PCTR” as such observable or even relevant? Transport perpendicular to the field may be negligible; “conductive heating is completely insignificant”* If so the TR-temperature regions may be physically separated from the prominence Large perpendicular gradients of gas pressure would be expected even at low plasma beta *Anzer & Heinzel 2008

ISSI Jan. 14, 2009 Is “magnetic reconnection” observable or even relevant? The boundary between corona and prominence should correspond to a current system, which can support instabilities The standard reconnection model of a flare/CME involves shocks and jets, whose heating is not local

ISSI Jan. 14, 2009 Conclusions The “Nougat” signature may just be space-filling hot branches of the actual prominence fields Need a proper electrodynamic theory to understand the true (perpendicular) boundary structure in the corona Need high resolution and sensitivity to understand how hot loops relate to prominence-bearing fields The term “PCTR” is probably misleading, except to a spectroscopist* *n.b. PCTR ≈ PETR

ISSI Jan. 14, 2009 Challenge Is it possible to show that the cavity itself does not consist of just the hot branches of the prominence field?