SOHO-JOP038 : Diagnostic of Coronal Bright Points. ------------------------------------------------------------------------ Last update: 30 March 2000 (+ THEMIS) Scientific justification Propagating waves are good candidates to provide energy and heat the corona. But to ascertain the viability of a wave theory of coronal heating, we still have to check if the energy is actually deposited by the travelling waves in the time interval corresponding to the crossing of the corona by the wave itself. The dissipation properties of MHD waves are governed by equations where the coefficients of dissipative terms are very small. Therefore the rate of dissipation of MHD waves is strongly related to the existence of small scales (Malara et al., 1992). These small scales are not observable, but could have signatures such as small and intermittent energetic bursts, like bright points. These elementary small magnetic structures (size between 10" and 30") can be observed in the network boundaries, in the quiet Sun or in coronal holes, and evolve on timescale of several minutes. Such a signature could be characterized by an intensity distribution that follows a power-law, as obtained in SOC and MHD statistics models (Einaudi et al.). (update) The very small scales are favourable for magnetic reconnection whose the possible source could be magnetic flux emergence. The aims of the program are: A/ to derive a diagnostic (Temperature, densities, etc) of the bright points using different lines formed a different altitudes, and ratios of lines sensitive to the temperature and density; the observing profiles will be compared with theoretical ones computed from the thermodynamical parameters provided by the numerical code developed at the University of Pisa. B/ to perform a statistical study IN bright points as a function of the integrated intensity in several wavelengths (Bocchialini et al., Regnier et al.). SUMER and CDS spatial resolution allows the computation of the intensity distribution over a large amount of pixels inside a selected bright point. C/ to perform a statistical study of a collection of bright points as a function of the integrated intensity in several wavelengths (Aletti et al.). D/ (update) to take profit of the possibility of putting together chromosphere-transition region-corona observations with SOHO with photospheric-chromospheric magnetic studies with THEMIS. References : Malara, Veltri, Chiuderi, Einaudi, 1992, ApJ, 396, 297 Einaudi, Velli, Politano, Pouquet, 1996, ApJ, 457, L-1113 Bocchialini, Vial, Einaudi, 5th SOHO Workshop, Oslo, ESA series SP-404, p 211 Regnier, Bocchialini, Vial, et al., 1998, CRAS, t. 326, Serie II b, p. 211 Aletti et al., 1999, A&A, submitted ------------------------------------------------------------------------- Observing program The program requires the cooperation of EIT, MDI, SUMER, CDS, TRACE and THEMIS. It is based on independent sequences: Sequence 1- requires 2 steps: a/ The disk target of SUMER and CDS is selected using one EIT image in Fe XV, in one region (5x5 blocks) such as quiet Sun, coronal hole (polar and equatorial). MDI provides the corresponding magnetogram (11'x11'). Total Duration: 5 minutes b/ CDS pointing is predefined as EIT pointing in step a/. SUMER fine pointing is defined in real time, from the selection of a bright point in the EIT f.o.v. of step a/. CDS study is a part of BRPNT (see the details at the end). SUMER follows the selected bright point (thanks to the compensation of the rotation). Two modes are proposed : the transmission of the spectral window (i) or the transmission of the 4 moments (ii), (see the details at the end). EIT continues to provide 5x5 blocks Fe XV images (10 images with a 5 minute cadence) MDI continues to provide the corresponding magnetograms. Total Duration: 45 minutes Sequence 2- The idea is here to accumulate a large number of bright points from EIT and TRACE images (subfields), to have enough events on a statistical point of view. The filling factor will be provided by CDS in a large f.o.v. (240"x240"). TRACE provides subfields of 8x8 arcmin: - alternatively 171 and 195 with the best cadence. EIT provides subfield images: - 10 images in 304 A, to compare the field of view with CDS, 5x5 blocks - Duration 15 minutes. - then alternatively in 171 and 195 (NRT required) with a 2 minute cadence (5x5 blocks). MDI provides the corresponding magnetograms at the best cadence. Total duration for TRACE, EIT and MDI : ~2 hours. CDS studies are: HEII2P - it begins with a He sequence, that will allow us to compare with EIT f.o.v. Duration 15 minutes. The f.o.v is here 240"x240" FILLFACN - v8 Several lines sensitive to the density are observed, in order to derive the filling factor useful for the energy computation. The f.o.v is here 240"x240"- Duration 1h47. Total duration for CDS : ~2 hours THEMIS (update): Instrument : MTR (4 Stokes parameters) ---------------------------------------------- DETAILS FOR INSTRUMENTS: * SUMER Sequence 1- step b/ i) line selection : Lbeta (1025 Å), O VI (1032 Å) on KBr slit : 1" x 120" exposure time : 1 s format : 25 x 120 total duration : 44 mn compression rate: sqrt OR ii) line selection : O VI (1032 and 1037 Å) on MCP bare, Lbeta (1025 Å), Si II(1020.699 Å), and Ne VI (1006 and 1010 Å) on KBr slit : 1" x 120" exposure time : 1 s format : 4 x 120 total duration : 44 mn compression rate: Gauss B4 * CDS : Sequence 1- step b/ (part of the BRPNT study) spectrometer : GIS slit : 4" x 4" scan area: 24" x 24" step: 4" x 4" raster locations: 6 x 6 exposure time: 15 s Duration of raster: 540 s Number of raster: 5 Total duration : 45 mn Sequence 2- (update) Studies to be run: HEII2P STUDY_ID : 11 TITLE_ID : 129 DURATION : 15 minutes 240"x240" FILLFACN / v8 STUDY_ID : 10 TITLE_ID : 96 DURATION : 1h47 240" x 240" * MDI: Sequence 1- magnetograms - high resolution observed area: 11' x 11' step a/ duration 5 minutes, 1 magnetogram step b/ duration 45 minutes Sequence 2- 11' x 11' magnetograms 2 hours with the best cadence * EIT: Sequence 1- 284 A - 5x5 blocks step a/ 1 image step b/ 10 images (5 minute cadence) Sequence 2- subfields: 5x5 blocks 304 A : 10 images at the beginning of the sequence. Then, alternatively 171/195 A with a 2 minute cadence (NRT required). Total Duration: 2 hours. * TRACE: Sequence 2- 8x8 arcmin, 171 and 195 alternatively, at the best cadence. Total duration: 2 hours. * THEMIS: (update) Sequence 1 or 2- MTR : 4 Stokes Parameters 5 lines: Mg (b2) 5173 A; Fe I 5225 A; Fe I 5250 A; Na (D2) 5890 A; Fe I 6302 A. exposure time: 300 ms ; step: 1" every 3 s; fov: 2x2' total duration of scan 6 minutes Field images, alternating G-band and Halpha every 6 minutes. Total duration : 4 hours in order to see the full life of a few BPs. Good seeing imperative. !! FOR ALL INSTRUMENTS!! : (update) Period requested: Early morning for the best seeing at THEMIS. ------------------------------------------------------------------------