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.