------------------------------------------------------------------------- CORONAL COUNTERPARTS TO HE I 1083 NM DYNAMIC EVENTS M. Penn, H. Jones ------------------------------------------------------------------------- Two joint observing runs, with the NSO Kitt Peak Vacuum Telescope (KPVT) and with the CDS and EIT instruments aboard SOHO will be made to correlate downflows observed in the chromosphere with KPVT (He~I rain) with coronal macrospicules or coronal loop interaction (CLI) events observed with SOHO. A statistical argument has been presented to show that He~I rain is likely to be correlated with either macrospicules or CLI events. Joint spectroscopic imaging with KPVT and with CDS and SUMER on SOHO, and imaging observations from EIT on SOHO will be used to directly determine which coronal events are correlated with He~I rain. KPVT will observe a region near the solar pole, collecting full spectral frames at a rapid cadence to measure downflow events in the He~I 1083~nm line. If correlated with macrospicules, these downflow events provide a key measure of the mass drain in the solar corona, and this will be important in the study of the mass flux budget of the solar wind. If correlated with CLI events, the observed birth rate of downflow events suggests that CLI events occur ten times more frequently than measured in previous studies, and this has important implications for heating of the solar corona. Understanding the solar wind mass flux and coronal heating are prime science goals of the SOHO mission. The SOHO observations required for this program will be scheduled simultaneously with KPVT observations. The SOHO spectrographs will each observe a field-of-view of about 200 x 240 arcsec. Imaging spectroscopy of 12 lines will be done with CDS to identify macrospicules, and to measure the temperature and electron density evolution of CLI events. EIT will image a 520 x 520 arcsec FOV to place the data in a more global frame. DETAILS OF KPVT/CDS/EIT OBSERVATIONS ------------------------------------------------------------------------- A simultaneous KPVT/SOHO observing run should be scheduled ASAP (as soon as is feasible during the grant period). The logistics of a joint observing run, combined with the statistics of weather conditions at Kitt Peak suggests that a hard observing date should be established, but a backup period during which the observations could be run instead of another program should also be established in the event of bad weather at KPVT during the primary period. The KPVT data would be similar to, though more extensive than previous He I 1083 nm observing campaigns. A 300 x 512 arcsec FOV, centered 240 arcsec inside the solar limb at the north or south pole would be scanned with a cadence of 310 seconds, and all spectral data from 1082 to 1084 nm will be saved to disk. The He I downflow events will be identified by line-of-sight velocities (the velocity resolution of the KPVT 1083 nm data in each pixel is 0.25 km per sec(0.1 spectral pixels), and p-mode oscillation amplitudes are expected to contribute a background noise of about 0.2 km per sec and transverse motions in the KPVT data, as originally done in Penn and Allen (1996). Using those observations of as a guide, data will be collected at 450 Mbytes per hour, and with 8 hours per day (other time must be allocated for synoptic observations) this results in 3.6 Gbytes of data per day. For a 7 day observing run over 25 Gbytes of ground-based data will be collected. Within the FOV of the KPVT data, imaging spectroscopic scans will be made with CDS. The CDS observing parameters are listed in Table 1. The exposure time, mainly driven by the telemetry rate, should give sufficient counts for each of the lines (Brekke, 1996). The lines are listed in Table 2; the lines for CDS cover cool lines (for detection of macrospicules, via intensity evolution) and include higher temperature lines up to coronal temperatures. CLI events will be detected as coronal brightenings which cascade through lower temperatures matching the cooling rates observed by Smartt et al. (1993). A density sensitive pair of hot Fe XIII lines is included to search for density evolution in CLI events. The CDS data also includes a He I line to locate He I downflow events using transverse velocities, and to exactly co-align the CDS data with KPVT data. Using the size of the scan area, event birth rates and lifetime, 5 CLI events, 35 He I downflow events, and 1400 macrospicules will be observed in each 8 hours sequence of the CDS data. Seven days of 8 hours during each of two observing runs are requested to build a statistically significant event base. --------------------------------------------------------- Table 1 -- CDS Observing Details --------------------------------------------------------- Spectrometer - Normal Incidence Slit - 4 x 240 arcsec Raster Area - 200 x 240 arcsec Step (DX, DY) - (4, 0) arcsec Raster Locations - 50 x 1 Exposure Time - 6.2 sec Duration of Raster - 310 sec Number of Rasters - 93 Total Duration - 8 hours Line Selections - 12 lines from Line List Bins Across Line - 4 Compression - 12 bits Telemetry - 1.4 kbytes per sec Pointing - TBD; quiet Sun coincident with KPVT Flags - N/A Solar Tracking - No --------------------------------------------------------- --------------------------------------------------------- Table 2 -- CDS Line List --------------------------------------------------------- Ion - Wavelength [nm] - Temperature [MK] --------------------------------------------------------- Si VIII - 31.983 - 7.9 Fe XIII - 32.080 - 16.0 Fe XIII - 34.818 - 16.0 Si IX - 34.987 - 10.0 Fe XVI - 36.076 - 25.0 Fe XII - 36.447 - 15.0 Si XII - 52.067 - 11.1 O III - 52.580 - 0.9 O IV - 55.452 - 1.1 Si XI - 58.090 - 10.0 He I - 58.433 - 0.1 O III - 59.959 - 0.9 O V - 62.973 - 1.2 --------------------------------------------------------- EIT images will put the CDS, SUMER and KPVT data into a more global context. Sequences of He II 30.4 nm images and Fe XII 19.5 nm images will show alternatively the time evolution of macrospicules and CLI events. A series of exposures, once per CDS/SUMER scan (310~s) will be taken during the 8 hours run, with 4 continuous hours of data at each wavelength. The 0.12 kbyte per sec normal telemetry rate from EIT with square-root image compression will allow a 200 x 200 pixel region to be readout and transmitted. The resulting 520 x 520 square arcsec field-of-view will cover four times the area of the CDS and KPVT spectroscopy FOVs. -------------------------------------------------------------------------