Title: Structure and dynamics of the complete lifetime 
       of coronal X-ray bright points

Short title: Structure and Dynamics of Coronal XRBPs

Lead Author: D.S. Brown (Aberystwyth)
             dob@aber.ac.uk

Co-Authors: K. Schrijver (LMSAL/TRACE)
            D. Bewsher (UCLAN/CDS)
            S. Gregory (MDI)

Participating Instruments: MDI, CDS

Participating S/C: TRACE

Observing Period: 20-24 October  2005   (current target date)

History
-------
 8 Jul 2005: 1st draft written
26 Jul 2005: 2nd draft with modified TRACE requests after 
             consultation with TRACE team

Scientific Objective
--------------------

The aim of this study is to observe the structure of coronal (X-ray)
bright points over their complete lifespan. By studying TRACE EUV/UV
images and high-resolution MDI magnetograms we can deduce how bright
point are born, how they evolve, whether they erupt and how they
eventually disappear. This study aims to capture several instances of
the complete lifetime of an X-ray bright point.

CDS observations will be used to study portions of the lifespan of
bright points. The temperature and density structure of different
phases of a bright points life will be analysed and the flows within
bright points will be deduced.


Scientific Justification
------------------------

The structure of the complete lifespan of a coronal bright point has
been studied Brown et al (2001) using TRACE and high-resolution MDI
magnetograms. In this example, the bright point exhibited several
distinct phases including an unstressed bud phase and a twisted
sigmoidal phase which led to an eruptive phase.

Analysis of the magnetograms showed distinct magnetic footpoint
behaviour to correspond to the different phases observed by
TRACE. During the bud phase, there was fragmentation and coalescence
of the footpoints that would be consistent with the occurrence of
magnetic separators and heating by separator reconnection. During the
sigmoid phase, there were only two distinct footpoints, but they were
each observed to rotate giving a total injected twist of 200 degrees.

Magnetic footpoint behaviour was also studied in the run up to the
appearance of the bright point. Rather than the traditional theories
of either an emerging or cancelling bipole, the bright point is
activated by coalescence of magnetic flux at a pair of downflow
regions on either side of a supergranular cell. The initially weak
bipole pair is supplemented by small concentration of flux migrating
into these downflow regions.

This study aims to find several examples of the complete lifetime of
an X-ray bright point (the aim is to find at least 10 cases). From
these cases, the different phases that can occur during the life of a
bright point will be studied, paying particular attention to behaviour
exhibited by multiple bright points. The study will also investigate
eruptive phases, how frequently they occur and what is the magnetic
behaviour leading up to an eruptive phase. Do eruptive phases signal
the demise of a bright point?

The MDI magnetograms will also be used to investigate the appearance
of bright points and find out what footpoint dynamics lead to the
birth of bright points. Whether the traditional emerging/cancelling
magnetic features are the norm, or if interacting footpoints are more
likely to produce bright points.

CDS observations will be used to investigate the diagnostics of
portions of the life of bright points. A sequence of fixed position
rasters will capture bright points as they rotate into the field of
view. The captured bright points can then be analysed to determine the
temperatures, densities and flows within the different phases. This
will identify the evolution of the dynamics and heating mechanisms in
the different phases


Operational Considerations
--------------------------

This campaign requires relatively continuous observations from TRACE
and MDI over 4-5 days. It is appreciated that there is likely to be
some gaps when instruments perform synoptic duties and maintenance,
etc, but it is hoped that this will be kept to a minimum.

The observation target is a region of quiet Sun at, or close to, disk
centre. The TRACE field of view should be kept within the
high-resolution MDI fov as much as possible and CDS observations
should be well within the TRACE and MDI fov.


Detailed Observing Sequences
----------------------------

1. MDI 

High-resolution (0.625 arcsec) magnetograms with a cadence of 1
minute, continuous for 4-5 days. The field of view must be the full 10
arcmin in the E-W direction (so magnetic footpoints can be tracked
before the bright point appears and after its demise). It should also
be at least 8.5 arcmin in the N-S direction to encompass the TRACE fov.

The hr_m1_v2 campaign may be a possibility.

*** Extra DSN coverage for the dates requested may be required ***


2. TRACE

Pointing should be within the MDI fov. Imaging should be for the full
8.5 arcmin x 8.5 arcmin fov. Ideal pointing is centre of MDI fov with
no change during 5 days. However, pointing may start towards the
eastern edge of the MDI fov and track slowly westwards if this helps
avoid incoming/outgoing active regions.

The passband sequence should be as follows. TRACE will predominantly
observe in the 195 Angstrom band with an exposure of around 30-40
seconds. Approximately every 10 minutes, TRACE will also image in the
171 (30-40 second exposures) and 1600 (exposure times to be decided)
Angstrom bands to provide context images. All image will preferably at
0.5 arcsec pixels (at least for the 195 A). This sequence will be
repeated for the duration of the campaign (excluding times when TRACE
must perform synoptic duties).


3. CDS

The CDS studies that will be used will raster over a fixed
position. The fov should be completely contained within the TRACE fov,
probably near the centre of the TRACE fov, but if TRACE is pointing
slightly off disk centre (due to slow tracking to avoid active
regions) then CDS should point to as close to disk centre as possible
while remaining in the TRACE fov.

Exact studies are tbd, but discussions have started with Peter Young
at RAL involving the design of 2 new studies. Studies will contain a
variety of lines spread over chromospheric, transition region and
coronal temperatures. Coronal temperature and density diagnostic lines
that are suitable for use with post-recovery profiles will be
included.

Rasters will be approximately 60"x240" in size, using the 4"x240"
slit. Double binning in solar-y may be used to save on
telemetry. Exposure time will be approximately 30 seconds at each slit
position. Cadence of the rasters will be as close to the cadence of
the TRACE cycles as possible.