HOP 0193

abstract of observational proposal

Following observations in earlier SUMER campaigns, a short joint SUMER/EIS observation is proposed for the period 4th to 8th July when SUMER will be briefly operational.

In 2007, during the first campaign, SUMER and EIS observations of the quiet Sun were made to determine the average Doppler shift vs. temperature up to 2 MK. Before the launch of Hinode and the possibility of recording coronal line profiles with high spectral resolution with EIS, our knowledge was limited to temperatures up to 1 MK. At this temperature modest blueshifts of few km/s are observed, in contrast to the substantial redshifts, up to 10 km/s observed in the transition region. The extension to higher temperatures and the determination of whether increasing blueshifts or a return towards zero velocities is observed, allows us to probe the bulk of the coronal emission and, thus, to provide an important global observable to be matched by models of the solar corona (e.g., the 3-D models developed by Hansteen et al. 2010).

This study is based on a new technique to obtain absolute velocities by combining the on-disk observations with off-limb data and with calibrated SUMER spectra of at least one coronal line. Above the limb, in areas without prominent loops or prominences, mass flows are expected to cancel out on average. Thus, off-limb spectra can be used to determine the wavelength separation at rest between spectral lines and a line assumed as reference. Then, the measurement of the same quantities on the disk and the knowledge of the average velocity of the ion forming the reference line, allow a reliable and robust determination of the absolute Doppler velocity in all the observed EIS lines. SUMER spectra, for which a wavelength calibration is possible (see, e.g., Teriaca et al. 1999), provide the absolute Doppler velocity of the Mg X line at 62.5 nm that is taken as proxy of the Doppler velocity in EIS lines from Fe X.

This work is part of the PhD thesis of Neda Dadashi, supervised by Teriaca and Solanki at MPS in Katlenburg-Lindau. A paper on this topic has been submitted to A&A and the referee responses are expected shortly.

As a next step in this project we would like to repeat the observations and related analysis for a full active region. Although a possible active area was also observed briefly in April 2007, assessment of this second dataset suggests that the activity level was so low that the region could at best be considered to be a slightly active part of the Quiet Sun. We are, therefore, seeking a joint EIS/SUMER observation for an approximately four hour slot to observe an AR, preferably close to disk centre, to enable good velocity measurements. Two already existing EIS studies have been selected that would be suitable for this observation.

request to EIS

The sequence would consist of one run of:
HPW018AR300x400_30s2_HOT_CA_LINES_V2 (study ID #356)
on the target AR (FOV 300"x400", duration 2h47m19s)

This should be followed by a repointing to about 50" above the limb - either West or East, to an area free of Active Regions. At this position there should be one run of:
HPW017AR_30x400_30s2_HOT_CA_LINES_V2 (study ID #355)
This is identical to the previous study except for a narrow FOV (30”x400”).
A good reference spectrum (full detector read-out) with the same slit just before or after the AR raster would be very useful.
EIS Study Detail
HPW018AR300x400_30s2_HOT_CA_LINES_V2 (study ID #356)
TARGET: Active Region
EXPOSURE TIME: 30s
RASTER: Scanning
SLIT: 1"
STEP SIZE: 1"
FOV: 300"x400"
RASTER DURATION: 2h47m19s
VOLUME: 496 Mbits (after DPCM compression)
RATE: 49.4 kbits/s

LINE LIST (ID #356 and #355)
181.90 16 # Ca XV 181.900
184.33 32 # O VI 184.117, Fe X 184.536
186.75 32 # Fe VIII 186.601, (Ca XIV 186.610), Fe XII 186.880
188.40 32 # Fe XI 188.216, Fe XI 188.299, Fe IX 188.497, S XI 188.675
192.20 32 # Fe XXIV 192.04, Fe XII 192.394
192.82 24 # Fe XI 192.813, Ca XVII 192.858
194.10 40 # Ca XIV 193.874, Ar XIV 194.396
195.12 24 # Fe XII 195.119, Fe XII 195.180
201.05 24 # Ca XV 200.972, Fe XIII 201.121
202.04 24 # Fe XIII 202.044
203.83 24 # Fe XII 203.720, Fe XIII 203.826
208.50 32 # Ca XV 208.324, Ca XVI 208.604, (Fe XIII 208.679, Ca XV 208.722)
255.00 32 # Fe XVII 254.87, Fe XXIV 255.10
256.48 32 # He II 256.317, Si X 256.366, S XIII 256.686
262.98 24 # Fe XVI 262.984
263.98 40 # Fe XXIII 263.76, S X 264.233
270.52 24 # Mg VI 270.394, Fe XIV 270.519
275.40 24 # Si VII 275.352, Fe XVII 275.54
276.30 40 # Mg VII 276.153, Mg V 276.579
278.40 32 # Mg VII 278.402, Si VII 278.445
280.74 24 # Mg VII 280.737
284.16 24 # (Al IX 284.015), Fe XV 284.160