HOP 0045

abstract of observational proposal

Waves play an important role in the heating of the corona and in the acceleration of the fast solar wind from Coronal Holes (CHs). Thus far, only long period (10-70 min) radiance fluctuations have been detected in plumes and inter-plume regions, but nothing is known about higher frequency and/or lower amplitude variations and, whether or not these waves have also a signature in line-widths and line-shifts of emission lines. During April 2007, a previous version of this study has shown some evidence of radiance fluctuations propagating outward with a speed of about 60 km/s. The fluctuations seem to show a periodicity of 7 to 8 min.

Based on that experience we would like to apply for one or two additional runs of a modified version of the study. The modifications are based on the analysis of the April 2007 data. The study duration is of about 5 hours, to be executed one or two times during the campaign. Because of the requested VTT support (important but not indispensable to achieve the proposed science goals), we would request observing time during the 08:00 to 14:00 UT time frame (VTT prime time 08:00 to 11:00 UT). VTT observing time ends on November 2, so we would like to allocate our observations in the 30 Oct_ 02 Nov 2007 timeframe, if possible.

request to EIS

Time series of slot images in strong isolated lines to study radiance
oscillations at different temperatures. Exposure times of about 60
seconds. Context raster images are foreseen for context and for
co-alignment with the other instruments. The slit will be centred at
the north (south) limb, observing up to 256 above the limb.

Estimated Study duration: about 5 h. The new study will be a modification of study CH_SUM_EIS, ID 000118

Lines
Fe XI______ 180.40
Fe X_______ 184.54__ + OVI__ 184.12
Fe VIII____ 185.25
Fe VIII____ 186.60
Fe XI______ 188.23
Fe X_______ 190.13
Ca XVII____ 192.82
Fe XII_____ 193.71
Fe XII_____ 195.12
Fe XIII____ 202.04
O V________ 248.46
He II______ 256.32
Fe X_______ 257.26
Mg VI______ 270.40
Si X_______ 272.01
Si VII_____ 275.35
Mg VII_____ 276.99
Mg VII_____ 278.39
O IV_______ 279.93
Fe XV______ 284.16

other participating instruments

SUMER:
Use the 1"120" slit centred on the limb in a Northern or Southern coronal hole (the best defined one at the time of observation). This way, part of the slit is on-disk and part off-disk.

Observations need to be run on an inter-plume region and in a plume region to see what difference this makes to the measured oscillations.

Main lines to be used Ne VIII 77 nm and O VI 103.2 nm and 103.7 nm. The Ne VIII line is formed at the base of the corona at a temperature (about 0.6 MK) where there still is enough plasma to in coronal holes to yieldspectra with a good signal to noise. This line is unique of SUMER and it is perhaps the best diagnostic to study coronal holes. An additional line will be the O IV 79 nm, probing the transition region. The O VI lines have a measurable radiatively excited component that can be modulated by the outflow speed velocity. We plan to add these lines to verify whether the observed fluctuations are due to a modulation of the radiatively excited component by the out-flowing wind.

Obtain spectra of each target region with an exposure time of about 20s.
Each sit-and-stare sequence is to be preceded by a small context raster
(50120) to co-align with EIS. Total duration of the sequence is between
4 and 5 hours.

VTT_ TIP-2:
Repeated rasters in the He I multiplet at 1083 nm, recovering the four
Stokes profiles. The data will be taken with the slit tangent to the limb, over a FOV of +/- 15 from the limb. The exposure time will be around 10 seconds, allowing a raster cadence of less than 10 minutes. Sit and stare sequences at given heights above the limb may be also added.

TRACE:
Images in the 171 band at 30s cadence. On-board 22 binning.