JOP166 OSCILLATIONS IN CORONAL BRIGHT POINTS ============================================ AUTHORS: J.G. Doyle, I. Ugarte-Urra & M.S. Madjarska (Armagh Observatory) INSTRUMENTS : CDS, MDI (SOHO); TRACE RECEIVED: 21 April 2003 MODIFIED (SOC): 22 April 2003 - XBP to be selected within TRACE FOV SCIENTIFIC OBJECTIVE AND JUSTIFICATION ====================================== In recent studies, the time evolution of a X-ray/EUV coronal bright point (XBP) was investigated using CDS, EIT and MDI. Two different time sequences were run with the CDS spectrometer with exposure times of 30 and 81 sec., allowing us to find that there are correlated intensity oscillations in the transition region (TR) lines O V (629.73 A) and O III (599.6 A) and the optically thick He I (584.33) chromospheric line with characteristic periods of 400-600 sec. and 1000 sec. Same periods have been found sporadicly for the Mg IX (368.07 A) line, but not correlated with the TR lines. The intensity fluctuations seem to be correlated as well with the electron density changes as determined with the O IV (625.8/608.4) density sensitive ratio. A comparison of the total magnetic flux in the bipolarity with the intensity fluctuations has also been done and as a result no correspondence between the changes in both quantities has been found. Finally a single TRACE image available in the 171 A passband allowed us to distinguish the fine structure of the fuzzy brightening seen in the 195 A EIT images. The XBP consists of a set of at least four loops with a foot-point separation of ~8-10 Mm. Here we propose to extend this study via simultaneous CDS, MDI & TRACE observations. The comparison of EIT and TRACE images shows that the diffuse cloud appearance of the XBP in EIT images can be resolved as a loop structure in TRACE images (also noted by Frank & Slater 2002AAS...201.8304). A comparison of CDS, MDI and TRACE, with the highest spatial resolution, is required in order to discriminate the processes that could be responsible for these short scale fluctuations in the intensity seen in spectral lines (by both CDS & SUMER). Reconnection processes taking place at/between the coronal loops that form the XBP have been proposed as a possible explanation. MDI magnetograms with a cadence of 1 minute are then required in order to inspect whether these oscillations are related to changes in the magnetic strength or configuration. The 1 minute cadence is justified considering that the shorter periods that we have found with CDS are of the order of 400 sec. and sampling with several points is required. TRACE high cadence imaging is needed in order to compare the evolution in time of the fine structure of the XBP, consisting of loops connecting opposite polarities, to the spectroscopic changes obtained from CDS, basically intensity for different lines at different temperatures (see line list), electron density and velocities. POINTING ======== Last minute pointing (i.e. final coords. given just before upload), to be selected within a predetermined TRACE FOV, due to technical constraints. We have been successful getting the right pointing for several XBP observed with CDS using as a reference, EIT images of the preceding hour. The last minute pointing is required to follow the appearance and/or evolution of possible targets, considering that the average lifetime is around 20 h. DURATION ======== 1 XBP per day. 8 hr 10 min per day, i.e per XBP 4 days TIMING ====== 15, 16, 17 & 18 July 2003 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CDS (SOHO) ~~~~~~~~~~~~ ================================ Use existing NIS & GIS sequences with some small changes Acronym Study: ID Var BP_W_1 13 22 BP_W_2 266 1 BP_W_3 267 1 SPECT_1 G2AL BP_W_1: context rasters at beginning, middle and end of the time series. Exp. time: 35 sec. Total duration per raster: 10 minutes Lines Wavelength Pixels: wavelength x y ------------------------------------------------------------- Mg IX 368.07 80 15 143 He I 584.33 80 15 143 O V 629.73 53 15 143 BP_W_2: time series (v1) with wide spectral windows (to extract continuum level) Lines: wide range of lines in NIS 1 and NIS 2. See spectral range. Exp. time: 81 sec. Total duration per raster: 15 min 30 sec Center Wavelength Pixels: wavelength x y t ------------------------------------------------------------------- Mg V 353.3 550 (333.9 - 372.6 A) 1 71 10 O III 599.6 545 (567.5 - 631.3 A) 1 71 10 BP_W_3: time series (v2) for selected spectral windows Exp. time: 30 sec. Total duration per raster: 15 min Lines Wavelength Pixels: wavelength x y t ------------------------------------------------------------------- Mg IX 368.07 80 1 95 25 He I 584.33 80 1 95 25 O III 599.6 80 1 95 25 O V 629.73 53 1 95 25 SPECT_1 & G2AL .. we plan to change these GIS sequences as outlined below. Sequences to be run and their duration ====================================== ======================================== BP_W_1 x 2 Context image: == 21 min. BP_W_2 x 8 Time series v1: == 2 hr 5 min. BP_W_1 x 2 Context image: == 21 min. SPECT_1 x 1 Raster == 37 min. G2AL_v3 x12 Raster == 1 hr 1 min. BP_W_1 x 2 Context image: == 21 min. BP_W_3 x 8 Time series v2: == 2 hr BP_W_1 x 2 Context image: == 21 min G2AL_v4 x60 Time series == 1 hr Total: 8 h 15 min Modifications to the above sequences: ===================================== BP_W_1: Increase window size to 95 pixels .. (i.e. in order to include the line Mg X 624.94 A [alignment NIS1 and NIS2]). BP_W_2: Increase window to 570 pixels, central windows at wavelengths 352.300 A & 598,597 A (i.e. decrease wavelength by 1A from presebt value .. this will allow us to include the line Fe XIV 334.2 A density diagnostic). BP_W_3: Increase window size to 95 pixels .. (i.e. in order to include the line Mg X 624.94 A [alignment NIS1 and NIS2]). SPECT_1 change to 4x4 slit, change to 60 sec interg., change to 4 arcsec step with 6 x 6 M/S scan posn. G2AL_v3 change G2AL to 60 sec. interg., 5 M/S scan posn. G2AL_v4 change G2AL to 60 sec. interg., 1 M/S scan posn. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MDI (SOHO) ~~~~~~~~~~~~ 1 MINUTE cadence FULL-DISK MAGNETOGRAMS simultaneous to the TRACE and CDS observation in order to follow the evolution of the magnetic field below the coronal brightening (XBP)s. For two of the days we request the HIGH RESOLUTION mode. Our only reason for not requesting it for all four days it that it restricts the pointings and therefore the selection of the best BP. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ TRACE ~~~~~~~ 30-60 sec. cadence in the Fe IX/X 171 A BANDPASS simultaneous to the CDS time series.