JOP145 Active Region Irradiance Study Version: 16.01.2001 Contributors: E.O'Shea, B.Fleck - ESA Space Science Department K. Muglach - AIP Potsdam C. Schrijver - LMSAL Participating instruments: SOHO/CDS, TRACE, SOHO/MDI Observation dates: July 23 - August 6, 2001, 2 weeks continous POC: First week: E.O'Shea (at GSFC, CDS planner) Second week: K. Muglach (at AIP) Target: well developed AR, to be followed from east to west limb Scientific Objective and Justification: We will measure, the EUV irradiance variability from an active region as it rotates across the Sun. It is known that magnetic features (dark sunspots, bright faculae, hot coronal loops) are the primary sources of irradiance variability. By measuring the irradiance variability from the area of an active region (a large magnetic feature) it will be possible to quantify its effect on the total solar irradiance. To calculate the irradiances it will be necessary to obtain a number of spectral lines over a wide range of temperatures in order to contruct the differential emission measures from which the irradiances can then be estimated. In the case of CDS we will obtain rasters in the active region so as to then be able to construct the emission measures. A similar procedure was carried out recently by O'Shea et al. (A&A, 2000, 358, 741) on a CDS dataset obtained in the quiet Sun. We will run these observations as part of a JOP together with CDS, TRACE and MDI. MDI will provide information on the underlying magnetic structure and TRACE will complement the raster images of CDS. By using TRACE, CDS and MDI together it will also be possible to provide estimates of the fraction volume of the different emitting features present in the CDS field of view. In addition, by using both the CDS NIS Mg VI 349 and Ne VI 562 lines as part of the raster observations it will also be possible to measure the variation (if any) in time the FIP effect in the observed active regions. References: O'Shea, E., Gallagher, P. T., Mathioudakis, M., Phillips, K. J. H., Keenan, F. P., Katsiyannis, A. C.: 2000, A&A 358, 741 ---------------------------------------------------------------- Detailed instrument plans: CDS: Operational Sequence: Initial Pointing Active region Spectrometer NIS Slit 4 x 240 arcsec (Reduce slit height, by windowing, to 200 arcsec) Steps 50 (to build up raster of 200"x200") Exposure Time 35s Total Duration 3672s Line Selection (20 lines) Si XII 521.3 pixel posn. 83 Mg VIII 315.013 pixel posn. 112 Mg VIII 317.03 pixel posn. 149 Ne IV 543.89 pixel posn. 277 Al XI 549.75 pixel posn. 327 O IV 554.1 pixel posn. 364 Ca X 558.4 pixel posn. 401 Ne VI 562.70 pixel posn. 438 Ne V 572.331 pixel posn. 520 Si IX 344.40 pixel posn. 532 Si X 347.003 pixel posn. 569 Si XI 580.91 pixel posn. 594 Mg VI 349.65 pixel posn. 606 He I 584.327 pixel posn. 623 Si X 356.212 pixel posn. 700 O III 599.59 pixel posn. 753 Fe XVI 360.76 pixel posn. 764 Mg IX 368.07 pixel posn. 868 Mg X 624.94 pixel posn. 969 O V 629.505 pixel posn. 1008 Spectral window width 40 pixels Binning Binning by 2 along the slit ---------------------------------------------------------------- TRACE Operational Sequence: primary filter: 171 full field and full res. context filters: 1600 or 1700 512x512 cutout WL 512x512 cutout Quadrant shutter permitting: also 195 and 284 (2x2 summed) in context. ---------------------------------------------------------------- MDI: data from the standard synoptic program will be used for this (I-grams, Doppler-grams and magnetograms every 96 min) ---------------------------------------------------------------- EIT: Standard synoptic sets every 6 hours.