The signature of Ca II K grains in the Transition Region and Corona ___________________________________________________________________ Authors: B. Fleck, S. Steffens, F.-L. Deubner, R. Rutten, ________ K. Wilhelm (SUMER), R. Harrison (CDS), O. Kjeldseth-Moe (CDS), J. Gurman (EIT) Progress: _________ Discussion at SPWG August 25, 1995 First Draft Scheme 9 May, 1996 1st Revision 12 July, 1996 Scientific Case: ________________ Ca II K ``grains'', sometimes also referred to as ``intranetwork bright points'', were discovered early in this century by Hale and Ellerman (1904) who called them ``minute bright calcium flocculi''. They appear on Ca II H and K filtergrams and spectroheliograms as bright roundish dots of approximately 1 to 2 arcsec. They occur within cell interiors in quiet areas of the solar surface, they are short lived, and they come and go with 2-5 min intervals (for a comprehensive review of the Ca II K literature see Rutten and Uitenbroek, 1991). Recent investigations seem to converge towards a consistent picture in which the K-grains (or K_2v "flashes") are interpreted as the most prominent effects (``tops of the icebergs'') of chromospheric shocks governed by the p-mode interference pattern (Rutten and Uitenbroek, 1991; von Uexkuell and Kneer, 1995; Steffens et al., 1995). As such, the K grains are the signature of one of the most dynamic phenomena in the solar atmosphere. The observed K_3 Doppler shifts often reveal a highly non-linear wave form with amplitudes approaching the sound speed of 7 km/s (e.g. Hofmann et al., 1996), in good agreement with the self-consistent radiation hydrodynamic calculations of Carlsson and Stein (1994). From these calculations the latter authors conclude that the Sun may not have a classical chromosphere in magnetic field-free regions (cf. also Carlsson and Stein, 1995). They showed that enhanced chromospheric emission, which corresponds to an outwardly increasing semiempirical temperature structure, can be reproduced by non-linear wave motions without any increase in the mean gas temperature. They therefore concluded that the semiempirical chromospheric temperature rise may be an artifact of temporal averaging of the highly nonlinear UV Planck function. High resolution UV emission line observations should provide a clear answer to the questions of whether a non-magnetic chromosphere does exist or not. Here we propose a study of the Ca K grain phenomenon and its impact on the higher atmospheric layers by coordinated observations of the Ca II K line from ground (Vacuum Tower Telescope (VTT) at Izana, Tenerife) and selected UV lines from SUMER, CDS, and EIT. How do these highly dynamic events show up in optically thin UV lines? How do they affect the transition region. Are they related to the C I jets (Dere et al., 1983, 1986). Do they affect the high temperature corona? We hope to find some answers to these and related questions by analyzing simultaneous, co-spatial high-resolution Ca K and UV line observations, formed at different levels in the solar atmosphere, from the chromosphere up to the transition region and hot corona. References: ___________ Carlsson, Stein: 1994, Oslo Mini Workshop, p.47 Carlsson, Stein: 1995, ApJ 440, L29 Dere, Bartoe, Brueckner: 1983, ApJ 267, L65 Dere, Bartoe, Brueckner: 1986, ApJ 305, 947 Hale, Ellerman: 1904, ApJ 19, 41 Hofmann, Steffens, Deubner: A&A 308, 192 Rutten, Uitenbroek: 1991, Solar Phys. 134, 15 Steffens, Hofmann, Deubner: 1995, A&A 302,277 von Uexkuell, Kneer: 1995, A&A 294, 252 Observing Scheme: _________________ Pointing: - Quiet sun disk center. - Fixed slit position. - Rotation compensation ON. SUMER: ______ JOP026a: ======== Slit: 1*120 arcsec Exposure time: 14.5 s Number of frames: 512 Compression: 5. Quasilog_min_max Lines: O I 1302.17 A O I 1306.03 A Si II 1309.28 A C I 1311.36 A C II 1334.53 A C II 1335.71 A JOP026b: ======== Slit: 1*360 arcsec Exposure time: 14.5 s Number of frames: 512 Compression: 5. Quasilog_min_max Lines: Si I 1256.49 A N V 1242.80 A O V 629.73 A JOP026c: ======== Slit: 1*120 arcsec Exposure time: 7.25 s Number of frames: 1024 Compression: 5. Quasilog_min_max Lines: He I 584.33 A C III 1175.59 A O I 1152.15 A JOP026d: ======== Slit: 1*120 arcsec Exposure time: 7.25 s Number of frames: 1024 Compression: 5. Quasilog_min_max Lines: H I 1025.72 A O VI 1031.91 A O VI 1037.61 A JOP026e: ======== Slit: 1*120 arcsec Exposure time: 7.25 s Number of frames: 1024 Compression: 5. Quasilog_min_max Lines: Si III 1298.96 A S I 1300.91 A O I 1304.87 A O I 1306.03 A Each of these 5 sequences (A to E) consists of 3 items: - #0 raster scan with 80 smear steps of 1.52" at beginning - #1 actual run - #2 full spectrum for calibration purposes (120*1024 px, 98s). CDS: ____ TEST6_1: (for context) ======== - 2x240 arcsec slit - 120 steps (-> 240x240" raster) - Exposure time: 30 sec - Compression scheme: truncate to 12 bits - Lines: Si XII 520.67 He I 537.03 Fe XIV 334.20 Fe XVI 335.40 Ne VI 562.83 Mg VI 349.10 He I 584.33 O III 599.59 Mg IX 368.10 Mg X 624.90 O V 629.73 CA_STUDY: ========= - 2x240 arcsec slit - Exposure time: 15 sec - Compression scheme: truncate to 12 bits - Lines: O VI 554.52 He I 584.33 He II 607.56 Mg IX 368.06 O V 629.73 MOVIE_CA: ========= - 90x240 arcsec slit - Exposure time: 15 sec - Compression scheme: truncate to 12 bits - Lines: He I 584.33 Mg IX 368.06 O V 629.73 Each day run subsequently: TEST6_1, CA_STUDY, MOVIE_CA. EIT: ____ Run #1: He 304 high time resolution sequences in a 3x3 block (250x250 arcsec^2), centered on disk center. Temporal resolution: approx. 30 sec Ground-based (VTT Tenerife): ____________________________ 1.) Simultaneous filtergram series with a FOV of 120x120 arcsec^2 in a) Ca K_2V b) Mg b_2 c) H-alpha Temporal resolution: approx. 4 sec 2.) Simultaneous time series (scans) in Ca K + Mg b2 (+ slit jaw images).