Campaign: Doppler Shifts in X-ray Jets

Authors: D.E. Innes (SUMER), W. Curdt (SUMER), H. Warren (TRACE), D. McKenzie (Yohkoh), R.A. Harrison (CDS), J. Raymond (UVCS)

Version:  (4) May 2000

Objectives:

1. Obtain Doppler shifts in X-ray jets to test reconnection scenarios proposed to explain the X-ray structure.

2. To identify the origin and fate of high velocity, compact plasmoids that are seen as small regions of high Doppler shifted emission in the corona above active regions on the limb.

Secondary Objective: Investigate the association between hot X-ray jets, cold H I jets and coronal mass ejections.

Scientific Justification:

1. The X-ray jets seen with the soft X-ray telescope on Yohkoh, are seen as rapidly rising narrow toungues of X-ray emission. They are believed to be signatures of magnetic reconnection in the corona above the active region. Simulations based on reconnection between emerging flux and the original active region coronal field predict jet velocities of the order of several hundred km/s. The jet flow direction depends on the orientation of the overlying coronal field. For example, a field lying parallel to the solar surface, produces jets directed parallel to the surface and a field perpendicular to the surface produces perpendicular jets. By varying the orientation of the coronal field in the simulations, Yokoyama and Shibata (PASJ,48,353,96) can successfully model the X-ray emission structures seen. They also provide very definite predictions on the expected line-of-sight or Doppler shift velocities associated with each type of X-ray jet structure. So far there has been no co-ordinated effort to measure the Doppler shifts in X-ray jets on the limb. With the spectrometer SUMER it is possible to measure shifts in lines formed at temperatures up to 10^7 K and thereby test the Yokoyama and Shibata reconnection explanation.

2. SUMER observations of the corona above active regions have revealed what look like small compact plasmoids with high Doppler velocities (100 km/s). They have been seen in very high temperature lines such as Fe XVII and Fe XIX (Feldman et al; ApJ 503,467,98) and in low temperature lines such as N III (Innes et al; Sol. Phys. 181,103,88). There has been some speculation that the flows originate from reconnection sites in the corona but there is little really convincing evidence. The shifts could also be produced by internal or shear motion in plasmoids ejected from the chromosphere. To determine the origin of the high Doppler shift emission simultaneous high cadence images and SUMER spectra are required. To date, there have been only few co-ordinated observations of images at several temperatures together with SUMER spectra above active regions. 2ndary. In a recent analysis of the onset of a CME that occurred on the solar limb, it was concluded that multiple reconnection events occurring at the footpoints of a coronal arcade drove the release of arcade material into the corona (Innes et al, Sol. Phys, in press). Reconnection was diagnosed from what looked like hot, newly formed loop structures below and connecting two parallel X-ray jets. The CME cavity was concentrated in the 50 arcsec wide region between the two jets. Such an observation requires considerable luck and therefore it is not set as a primary goal for the observing proposal. However sequences designed to study the X-ray jets and activity in the corona above an active region on the limb would also provide excellent coverage of the CME onset if one occurred.

Hotshot: A nice movie explaining the scenario is available as SOHO hotshot at http://sohowww.nascom.nasa.gov/hotshot/1999_05_11/

Pointing: The target should be the an active region on the limb. In the study of X-ray jets by Shimojo et al. (PASJ 48,123,96), jets are found overwhelmingly on the leading edge of the active region. We therefore prefer the target to be an east limb active region so as not to lose the footpoints behind the limb.
SUMER - 1x300 slit will remain throughout the observation at a fixed position centered about 1.6 arcmin above the limb.
CDS - the FOV will be centred 0.5 arcmin off-limb.
UVCS - will observe at 1.6 Rsun.
TRACE - the FOV should centred on the active region limb area.
YOHKOH - the partial frame images will be centered on the active region limb area.
HESSI - will observe the hard X-ray flux from the sun.
MICA - during daylight hours in Argentina, obtains broad and narrow band coronagraph images around Fe XIV 5303 with a cadence between 15-40s.
HASTA - will obtain high cadence full-sun H-alpha images.
EIT - high cadence full-sun images.

Observing schedule: The high Doppler shift / plasmoid events, seen with SUMER are seen about once every 4 hours in the corona above active regions. The observations will have to wait for a suitable target. This requires a long period of continuous observation. The restrictions on the SUMER pointing put a constraint on the target selection and require a sit-and-stare position at the east limb without restrictions in elevation. In previous campaigns EIT 195 data have been used to show the long time evolution of the active region loops and thus made it possible to distinguish newly heated plasma from plasma cooling due to an earlier event. It would therefore be advantageous to observe at a time when EIT is taking the standard CME watch data. The best observing-season would be September to October: this is well before the TRACE eclipse-time and already the begin of the summer period of the southern hemisphere, although HESSI may not be available. Also the period around March seems to be a possible window.
Proposed dates for the first campaign: Sept 15 to Oct 27, 2000

Instruments:

SUMER Select a 40 A wavelength region that contains lines formed over a wide range of temperatures. There are many choices. For example we may select the 1109 - 1149 range which contains lines from Si III (5x10^4 K), Si IV (8x10^4 K), O IV (10^5 K), Ne V (3x10^5 K), Si VII (5x10^5 K), Ca X (6x10^5 K), Ca XIII (2x10^6 K), Al XI (2x10^6 K) and Fe XIX (8x10^6 K) and Fe XXIII (1x10^7 K). Another range lines covering a wide range in temperature is the 936-976 range which contains lines from H I (2x10^4 K), Ne VII (5x10^5 K), Si VIII (8x10^5 K), Si IX (10^6 K), Ca XIV (3x10^6 K) and Fe XVIII (6x10^6 K). There are several good hot plasma density diagnostics for example Fe XIX 1328/1118, Ar XII 1018/1054, Si XI 564/580, S X 624/649. Observations in these line pairs will be incorporated into the SUMER observing sequence. Exposure times will match the telemetry rate. When the high rate is available telemetry SUMER can transmit 8 windows of size 50x300 pixels in one min and we will therefore have 1 min exposures. When only the low rate is available, the exposure time will be 2 min.

Contact: Werner Curdt (curdt@linmpi.mpg.de; curdt@sumop1.nascom.nasa.gov)
         Davina Innes (innes@linmpi.mpg.de; innes@sumop1.nascom.de)

TRACE Trace will obtain images in 1600, 195 and 171. FOV 6.4x6.4 and cadence about 1 min.
 Contact: Jake Wolfson (wolfson@lmsal.com)
          Harry Warren (warren@cfa.harvard.edu)

CDS if TRACE is available: sit-and-stare taking high cadence spectra at a position near the SUMER slit in lines covering a wide temperature range
     else: CME onset programme, EJECT_V3 (4x12 arcmin 15 min rasters in Si X, FEXVI, MgIX, OV, HeI)
Contact: Richard Harrison (harrison@solg2.bnsc.rl.ac.uk)

UVCS  sit-and-stare in Ly alph, Ly Beta, C III, N III, O V, O VI, Mg X and Si XII
Contact: John Raymond (raymond@cfa.harvard.edu)

YOHKOH Contact: David McKenzie (mckenzie@isass0.solar.isas.ac .jp)
           &n bsp;    Lyndsay Fletcher (fletcher@sag.lmsal.com)

HESSI Contact: Richard Canfield (canfield@mithra.physics.mo ntana.edu)

EIT standard CME watch programme.

MICA/HASTA Contact: G. Stenborg (stenborg@linmpi.mpg.de)