Authors: V. Hansteen, University of Oslo and P. Judge, HAO
Scientific Justification:
We propose to look for evidence of downwardly propagating, nano-flare generated compressive waves in the corona and transition region. As a secondary goal we would consider the fate of the upwardly propagating acoustic waves that presumably heat the chromospheric cell centres.
In the first picture, the sudden deposition of energy in the corona from a nano-flare event will lead to the generation of MHD waves propagating along the magnetic field lines and towards the transition region. The waves will, on reaching the transition region, compress the material. Since the intensity of an allowed optically thin emission line scales roughly with the (electron) density squared, emission will be enhanced as the transition region is pushed downward. Hansteen (1993) has shown quantitatively that the net effect of this process is on average a redshifted line profile when one integrates the emission over the full wave cycle.
In the second picture, the upwardly propagating wave field that is heating the chromospheric cell centers would be expected to produce components in the lower transition region emission lines that are, on average, blueshifted.
Current line shift observations indicate that the nano-flare picture is more important in the lower transition region, but it is neither adequately tested by observations nor can the prescence of upwardly propagting acoustic modes be ruled out. Therefore we propose two observing sequences with CDS and SUMER to test directly these alternatives. We also hope to elicit supporting observations from EIT (high ~90s cadence picures in the Fe IX/Fe X band) and MDI (high resolution magnetograms) of the region concerned.
The first sequence would monitor a small quiet Sun region in lines spanning a large range of temperatures with CDS looking for brightenings in the high temperature lines. Concurrently we would observe the same region at much higher spectral resolution with SUMER in lines typical of the transition region such as C IV, N V or O V expecting to see enhanced emission and (red-) shifts delayed in time from the CDS brightening by some few seconds in case of fast mode disturbances to some tens of seconds for slow mode disturbances, assuming that loop lengths are on the order of 10 000km.
The second sequence would use CDS in the same manner as above but with SUMER observing density dependent lines from O IV], S IV] as well as Si IV at a high signal to noise ratio without the need for high temporal resolution, but instead attempting to extract densities as a function of projected Doppler velocity from the monochromatic intensities of density sensitive lines. This method was successfully applied to high quality data from the Hubble Space Telescope by Judge (1994) to argue that outward propagating shock waves do not heat the chromosphere of a typical giant star. Applied to the O IV] and S IV] lines, the method (taking into account blended features following Judge's analysis) will provide a direct, unambiguous test of the upward or downward propagation of compressive waves since a correlation between high electron density and redshift is required in order for the proposed mechanism to be active. The CDS portion of this experiment would reveal the level of activity in the field of view during our exposure.
The region of the Sun studied is tailored to minimize the cycle time while ensuring that the SUMER and CDS fields overlap; a 20 x 120 arcsecond field should be sufficient. We have set up a nominal time span for each combination of CDS and SUMER sequences to cover approximately one hour. It may, however, be of interest to run the sequences over longer timespans, where possible, in order to isolate lower-frequency information such as the expected 3 minute oscillations.
Since the coronal heating mechanisms apparently differ inside and outside of coronal holes, an important experiment is to run these sequences both inside and outside of a coronal hole.
References
Hansteen V. H.: 1993 ``A New Interpretation of the Red-Shift Observed in Optically Thin Transition Region Lines'', ApJ 402 741.
Judge P. G.: 1994 ``The `Monochromatic Density Diagnositic' Technique: First Density Components in the Chromosphere of Alpha Tauri'', ApJ 430, 351.
The CDS Part of the Investigation
Sequence reference: CDS Blue Book NFCTR
We select a set of bright lines with good temperature coverage (20 000K to 2.5MK). We require fast rastering and good spectral resolution; we will therefore use the NIS with a 2 x 240 arcsecond slit. To cover our 20 x 120 arcsecond field we need 10 slit positions to the raster -- the CDHS will read out only the central 2 arcmin of the slit. We believe that, say, 11 pixels across each of 8 lines will give us adequate coverage of line shifts. This corresponds to velocities on the order of 300km/s.
Spectrometer: Normal Incidence
Slit 2 x 240 arcseconds
Raster Area 20 x 120 arcseconds
Step (DX,DY) 2 arcsecond, 0 arcsecond
Raster Locations 10
Dwell Time 5s
Duration of Raster 84s
Number of Rasters 130
Total Duration 182 minutes
Line Selection He I 584.33E, O IV 554.52E, O V 629.73E,
Mg IX 368.06E, Fe XIV 334.17E, Fe XII 364.438E,
Fe XVI 360.76E, Mg X 624.94E
Bins Across Line 11
Telemetry/Compression compression by 1.24 required
Pointing To pre-planned location (Quiet Sun or Coronal Hole)
No repointing necessary
Solar Feature Tracking
may be used if the study is performed over long periods
Frequency Preferably several times to establish
lower - frequency information
The SUMER Part of the Investigation:
Sequence reference: Sumer Red Book 8.1.2.43
For operational sequence 1 we have selected two possible line lists; both with good temperature coverage of the transition region. The first line list has the advantages of better count rates and of sharing a line with the CDS portion of the experiment.
The scanning in this sequence run asynchronously with the CDS scans.
Parameter List for SUMER Study: STUDY_8_1_2_43_0
Item # 0
-------------------------------------------------
You have selected (Irrelevant points are not listed.):
1. Interruption or flag mode: No interruption.
2. Slit 4 (centred) with 1*120 arcsec^2.
3. Initial pointing: (x_ii) = 2000.00 arcsec
(y_ii) = 2000.00 arcsec
SOHO roll angle: 0.00000 deg
4. Solar rotation: Standard compensation.
5. Binning (spectral) = 1
(spatial) = 1
6. Compression: 5. Quasilog_min_max (0.92 s).
7. Reference pixel 1: 425 on detector A
Flat-field correction: OFF
Ion(s) in band 1:
FE XII .... 1242.01 Angstroem
Spectral window(s) (pixel): 1024
8. Image format: Format #4 (1024*120, B1); 1 time(s)
9. Spectrohelio mode: Spectrohelio 3
Integration time: 100.000 s
Step size: 0.00000 arcsec or 0 units.
Image number: 1.00000
17. Your selection requires
a mean telemetry rate of: 9.83040 kbit/s
Available bitrate: 10.0000 kbit/s
This item will run
for approximately: 1.68480 minutes
and will cover a solar area defined by
120 px time(s) 0.00000 arcsec
Note that the memory monitoring and the run times are not very
accurate. The run times just give the total exposure times with
a margin of 1%, but the grating focus adjust time is included.
More detailed information can be provided by the SUMER Simulator.
All items up to now will run
for approximately: 1.68480 minutes
You will use for this item: 0.122966 MB
out of which 0.00000 MB are for uncompressed images.
You will have used in total: 0.122966 MB
out of which 0.00000 MB are for uncompressed images.
Parameter List for SUMER Study: STUDY_8_1_2_43_0
Item # 1
-------------------------------------------------
You have selected (Irrelevant points are not listed.):
1. Interruption or flag mode: No interruption.
2. Slit 4 (centred) with 1*120 arcsec^2.
3. Initial pointing: (x_ii) = 2000.00 arcsec
(y_ii) = 2000.00 arcsec
SOHO roll angle: 0.00000 deg
4. Solar rotation: Standard compensation.
5. Binning (spectral) = 1
(spatial) = 1
6. Compression: 5. Quasilog_min_max (0.92 s).
7. Reference pixel 1: 425 on detector A
Flat-field correction: OFF
Ion(s) in band 1:
FE XII .... 1242.01 Angstroem
N V .... 1238.82 Angstroem
MG X .... 609.794 Angstroem
Spectral window(s) (pixel): 25
8. Image format: Format #14 (25*120, B1); 3 time(s)
9. Spectrohelio mode: Spectrohelio 3
Scans back and forth.
Integration time: 7.50000 s
Step size: 0.760000 arcsec or 2 units.
Step number: 0
Step mode: Normal steps
Repetition number: 480
Staggering: 1
17. Your selection requires
a mean telemetry rate of: 9.60000 kbit/s
Available bitrate: 10.0000 kbit/s
This item will run
for approximately: 61.3030 minutes
and will cover a solar area defined by
120 px time(s) 0.00000 arcsec
Note that the memory monitoring and the run times are not very
accurate. The run times just give the total exposure times with
a margin of 1%, but the grating focus adjust time is included.
More detailed information can be provided by the SUMER Simulator.
All items up to now will run
for approximately: 62.9878 minutes
You will use for this item: 0.00000 MB
out of which 0.00000 MB are for uncompressed images.
You will have used in total: 0.00000 MB
out of which 0.00000 MB are for uncompressed images.
Parameter List for SUMER Study: STUDY_8_1_2_43_0
Item # 2
-------------------------------------------------
You have selected (Irrelevant points are not listed.):
1. Interruption or flag mode: No interruption.
2. Slit 4 (centred) with 1*120 arcsec^2.
3. Initial pointing: (x_ii) = 2000.00 arcsec
(y_ii) = 2000.00 arcsec
SOHO roll angle: 0.00000 deg
4. Solar rotation: Standard compensation.
5. Binning (spectral) = 1
(spatial) = 1
6. Compression: 5. Quasilog_min_max (0.92 s).
7. Reference pixel 1: 300 on detector A
Flat-field correction: OFF
Ion(s) in band 1:
C IV .... 1548.20 Angstroem
Spectral window(s) (pixel): 1024
8. Image format: Format #4 (1024*120, B1); 1 time(s)
9. Spectrohelio mode: Spectrohelio 3
Integration time: 100.000 s
Step size: 0.00000 arcsec or 0 units.
Image number: 1.00000
17. Your selection requires
a mean telemetry rate of: 9.83040 kbit/s
Available bitrate: 10.0000 kbit/s
This item will run
for approximately: 1.68480 minutes
and will cover a solar area defined by
120 px time(s) 0.00000 arcsec
Note that the memory monitoring and the run times are not very
accurate. The run times just give the total exposure times with
a margin of 1%, but the grating focus adjust time is included.
More detailed information can be provided by the SUMER Simulator.
All items up to now will run
for approximately: 64.6726 minutes
You will use for this item: 0.122966 MB
out of which 0.00000 MB are for uncompressed images.
You will have used in total: 0.122966 MB
out of which 0.00000 MB are for uncompressed images.
Parameter List for SUMER Study: STUDY_8_1_2_43_0
Item # 3
-------------------------------------------------
You have selected (Irrelevant points are not listed.):
1. Interruption or flag mode: No interruption.
2. Slit 4 (centred) with 1*120 arcsec^2.
3. Initial pointing: (x_ii) = 2000.00 arcsec
(y_ii) = 2000.00 arcsec
SOHO roll angle: 0.00000 deg
4. Solar rotation: Standard compensation.
5. Binning (spectral) = 1
(spatial) = 1
6. Compression: 5. Quasilog_min_max (0.92 s).
7. Reference pixel 1: 300 on detector A
Flat-field correction: OFF
Ion(s) in band 1:
C IV .... 1548.20 Angstroem
SI II .... 1533.43 Angstroem
NE VIII .... 770.409 Angstroem
N IV .... 765.143 Angstroem
Spectral window(s) (pixel): 25
8. Image format: Format #14 (25*120, B1); 4 time(s)
9. Spectrohelio mode: Spectrohelio 3
Scans back and forth.
Integration time: 10.0000 s
Step size: 0.760000 arcsec or 2 units.
Step number: 0
Step mode: Normal steps
Repetition number: 360
Staggering: 1
17. Your selection requires
a mean telemetry rate of: 9.60000 kbit/s
Available bitrate: 10.0000 kbit/s
This item will run
for approximately: 61.1272 minutes
and will cover a solar area defined by
120 px time(s) 0.00000 arcsec
Note that the memory monitoring and the run times are not very
accurate. The run times just give the total exposure times with
a margin of 1%, but the grating focus adjust time is included.
More detailed information can be provided by the SUMER Simulator.
All items up to now will run
for approximately: 125.800 minutes
You will use for this item: 0.00000 MB
out of which 0.00000 MB are for uncompressed images.
You will have used in total: 0.00000 MB
out of which 0.00000 MB are for uncompressed images.
Parameter List for SUMER Study: STUDY_8_1_2_43_0
Item # 4
-------------------------------------------------
You have selected (Irrelevant points are not listed.):
1. Interruption or flag mode: No interruption.
2. Slit 2 with 1*300 arcsec^2.
3. Initial pointing: (x_ii) = 2000.00 arcsec
(y_ii) = 2000.00 arcsec
SOHO roll angle: 0.00000 deg
4. Solar rotation: Standard compensation.
5. Binning (spectral) = 1
(spatial) = 1
6. Compression: 5. Quasilog_min_max (0.92 s).
7. Reference pixel 1: 511 on detector A
Flat-field correction: OFF
Ion(s) in band 1:
SI IV .... 1403.00 Angstroem
Spectral window(s) (pixel): 512
8. Image format: Format #37 (512*360); 1 time(s)
9. Spectrohelio mode: Spectrohelio 3
Scans back and forth.
Integration time: 150.0000 s
Step size: 0.760000 arcsec or 2 units.
Step number: 0
Step mode: Normal steps
Repetition number: 22
Staggering: 1
17. Your selection requires
a mean telemetry rate of: 0.00000 kbit/s
Available bitrate: 10.0000 kbit/s
This item will run
for approximately: 56.8784 minutes
and will cover a solar area defined by
120 px time(s) 0.00000 arcsec
Note that the memory monitoring and the run times are not very
accurate. The run times just give the total exposure times with
a margin of 1%, but the grating focus adjust time is included.
More detailed information can be provided by the SUMER Simulator.
All items up to now will run
for approximately: 182.678 minutes
You will use for this item: 0.00000 MB
out of which 0.00000 MB are for uncompressed images.
You will have used in total: 0.00000 MB
out of which 0.00000 MB are for uncompressed images.
This study ends in a wavelength range (converted to 1st order)
longer than Lyman alpha.
The EIT and MDI parts of the Investigation:
EIT should cover a region centered on that observed by CDS roughly of size 500"x500". We hope for observations in the Fe IX/X 171/305 band at a cadence of not much more than 2.5minutes. If instrumental concerns (i.e. temperature) render it possible it would be nice to also cover the Fe XII 195/305 band simultaniously.
In check for any correlation with the photospheric magnetic field MDI could supply high resoultion magnetograms of the region concerned taken at a cadence and with a size deemed meaningful by a member of the MDI team.
Last revised: April 24, 1996