Title: Temperature, density and 3-D structure of active region loops 

Authors: D.E. Innes, R. Attie, B. Inhester, S.K Solanki, D. Tothova

Intruments and POCs
SOHO/SUMER: D.E. Innes
SOHO/CDS: A. Fludra
SOHO/MDI: TBD
HINODE/SOT: H. Isobe
HINODE/EIS: H. Mason
HINODE/XRT: TBD
TRACE: TBD
STEREO: B. Inhester
VTT (Tenerife): A. Lagg
Huairou (China): H. Zhang


Scientific Objectives:

The aim is to simultaneously determine the 3-D geometric structure,
temperature, density and flows of active region loops. This will be
possible for a few months near the end of 2007 when the two STEREO
spacecraft are at an optimum separation for loop stereoscopy. Later, when
the spacecraft are further apart, we expect there will be more confusion in
identifying the same loops from the two different perspectives.

For an unambiguous reconstruction of loops, extrapolation of vector
magnetic fields is very helpful. Hinode/SOT provides high resolution vector
fields and will be essential. We also put a lot of weight on simultaneous
ground-based observations. These provide the magnetic vector near the base
of the corona, and display cool loops to complement the hotter loops seen
by other instruments.

The spectrograph Hinode/EIS observes lines from Fe VIII-XXIV, thus
providing good temperature resolution for the main structure and flows in
the loop.  In addition line intensity ratios of Fe XII, Fe XIII, Fe XIV
provide density diagnostics of the coronal plasma.

The SOHO/SUMER wavelength has many strong lines coming from the
chromosphere and transition region, and can be used to obtain details of
the structure and flows at the base of the corona.

As a secondary objective, we will be hoping to capture microflares
triggering Doppler shift oscillation. The Doppler shift oscillations are
thought to be signatures of magnetoacoustic standing waves in coronal
loops. As such, their oscillation period is determined by the wave time
along the loop. This depends on loop length, loop magnetic field, plasma
density and temperature. The temperature and density can be obtained to
better than 20% by spectroscopy.  Previously we have used circular loops
models to estimate the loop length and derive the magnetic field. The loop
length is the most critical parameter in the equation for loop magnetic
field. With STEREO we will be able to obtain a much better picture of the
loop, and so for the first time be able to derive realistic magnetic field
strengths in loops exhibiting Doppler shift oscillation.


Target:

Active region observed at several positions, 6 hours per position, as it
crosses the disk.


Proposed dates:

2007 Oct 22 - Nov 2. We have been allocated observing time with the VTT on
Tenerife and SUMER is planning a campaign to run at the same time.
 

Detailed Observing sequences:

STEREO: Stereoscopic high cadence 304, 171, 195, 284 images

SOHO/SUMER: map connection to chromosphere, pick up transition region and
lower coronal flows and Doppler shift oscillations.  Observations in one
band C I, N I, Si III, Ne V, Ne VI, Ca X, Ca XIII, Fe XIX
         
SOHO/CDS: Temperature and density diagnostic of the loop plasma 

SOHO/MDI: High Res when possible

Hinode/SOT: magnetic field, Ca II, blue continuum + SP scan 

Hinode/EIS: Wide range of temperature and density diagnostics

Hinode/XRT:  Structure and dynamics of hot loops

TRACE: 171 and 195 interleaved, with 1600 for coalignment

VTT: Chromospheric flows and vector fields

Huairou: Vector magnetic fields