Hinode observations AST2210 Autumn 2014 1 Introduction The Japanese solar satellite Hinode was launched in September 2006. Before launch it was called Solar-B. Hinode is equipped with three solar telescopes: a 50 cm opti- cal telescope (Solar Optical Telscope, SOT), an ultraviolet spectrograph (Extreme ultraviolet Imaging Spectrograph, EIS) and an X-ray telescope (XRT). The satellite is in a near polar orbit, a special orbit (called Sun synchroneous orbit) that is above the day-night line on Earth permitting observations of the Sun 24 hours a day most of the year. The orbit is such that the precession of the orbit is once per year, keeping the orbital plane perpendicular to the direction to the Sun all the time. Because of the Earth's elliptical orbit, there are eclipse periods where the Sun is hidden for parts of the orbit (end of May to beginning of August). The Institute of Theoretical Astrophysics at the University of Oslo runs the Hinode Science Data Centre Europe. All the data collected by Hinode is thus available locally on servers at the Institute through a fast web interface. For more information on the data centre and Hinode, see http://www.sdc.uio.no/sdc. 2 Goal This lab will take you through the various stages of data reduction, going from find- ing relevant data through compensating for instrument artifacts to science analysis. The tools will be the Hinode Science Data Centre Europe search engine and IDL using routines in the Solarsoft package. 3 Finding data Go to the Hinode Science Data Centre Europe search page (http://www.sdc.uio.no/search/API) Exercise 1 Find out what Hinode was observing with the various instruments during your time on La Palma. By clicking on the thumb-nail image you can see it enlarged. Read about the five instruments on the web and compare the images. Detailed information about each image can be found in the FITS header. This is available through the first field in the result screen. Exercise 2 Search results are sorted in groups. Set the Grouping to \by OBSTITLE,PROG VER. The prog ver is a number assigned to a particular observing sequence. Search for SOT/BFI images in prog ver 52 taken in the period 01-Apr-2007 to 30-Apr-2007. Prog ver is under \More search criteria", SOT as SX PROG VER. Prog ver 52 is a synoptic program run every day (often several times) with one image in each of the 1 six broad-band filters (plus a special image from programmatic reasons). Expand one of the groups (click on the expand symbol in the first column, just before the number 7). Example of appearance in Fig. 1 4 Reading images into IDL In order to work with Hinode images in IDL we have to include the Solarsoft package. This is done by setting up a few environment variables. Solarsoft needs to be run under c-shell or a derivative thereof (csh, tcsh). At the unix prompt you therefore need to start tcsh (by typing tcsh). You should do this on a institute machine like nekkar/papsukal/achernar/aramec (ssh -Y [email protected]) and in the directory your source code is in. Thereafter you setup the environment variables by executing: tcsh source ~haaksk/csh-ast2210 sswidl Once you have started IDL with Solarsoft included (with the command sswidl above) you have access to all IDL capabilities and in addition a large number of routines made for solar data reductions. You first need to get an array with the file-names for the files you want to work with. The Hinode SDC Europe search result page includes the IDL code you need to get the same files as in the web interface. The above example of SOT/BFI synoptic files can thus be returned as an array with the IDL commands: o=obj_new('osdc') o->show,'INSTRUME,DATE_OBS,SX__PROG_VER,THUMBS' o->page,1 o->limit,50 ;; Use o->limit,0 to get all! o->order,'DATE_OBS',/DESCENDING o->condition,'INSTRUME: ,SOT/WB o->condition,'EPOCH_START: 01-Apr-2007 o->condition,'EPOCH_END: 30-Apr-2007 o->condition,'SS_L1LEAD: y' o->condition,'SX__PROG_VER: 52 o->condition,'SQ_OBSTITLE_PROG_VER: FG20070429_182200.6 o->search,out paths = o->paths(out,/fetch) ;; /unzip has been deprecated Use the mouse to cut the text from the web-browser into the window where IDL is run. Beware that on some systems when copying text the quotation marks may change into 0, which is not a valid symbol in IDL. After executing the above commands, you have the file-names in the array paths. Exclude the first image before proceeding with reading the images using the Solarsoft routine read sot: paths=paths[1:*] read_sot,paths,index,data You can verify the output by using the help command: help,index,data which should give the following output: 2 Hinode SDC Europe - Search results - Searching... 25.8.08 15:12 Hinode SDC Europe - Search results Search completed in 0.26 sec. Showing 7 matching files (0% of all files). Retrieve selected files Summarise search Modify search Retrieve all files Add : Common fields N-valued fields EIS fields XRT fields SOT fields SOT/FG fields SOT/SP fields SOT/XRT fields Rows/page: 50 Group: Thumbnails Select Actions FILE INSTRUME DATE_OBS SX__PROG_VER FOV/data images All: FG20070429_182254.8 SOT/WB 2007-04-29 18:22:54 52 FG20070429_182245.3 SOT/WB 2007-04-29 18:22:45 52 FG20070429_182235.7 SOT/WB 2007-04-29 18:22:35 52 FG20070429_182226.1 SOT/WB 2007-04-29 18:22:26 52 FG20070429_182214.9 SOT/WB 2007-04-29 18:22:14 52 FG20070429_182205.4 SOT/WB 2007-04-29 18:22:05 52 FG20070429_182200.6 SOT/WB 2007-04-29 18:22:00 52 Retrieve selected files Summarise search Modify search Retrieve all files Add : Common fields N-valued fields EIS fields XRT fields SOT fields SOT/FG fields SOT/SP fields SOT/XRT fields Rows/page: 50 Group: Thumbnails o=obj_new('osdc') o->show,'FILE,INSTRUME,DATE_OBS,SX__PROG_VER,THUMBS' o->page,1 o->limit,50 ;; Use o->limit,0 to get all! o->order,'DATE_OBS',/DESCENDING o->condition,'INSTRUME: ,SOT/NB,SOT/WB,SOT/SP o->condition,'EPOCH_START: 01-apr-2007 o->condition,'EPOCH_END: 30-apr-2007 o->condition,'SX__PROG_VER: 52 o->condition,'SQ_OBSTITLE_PROG_VER: FG20070429_182200.6 o->search,out paths = o->paths(out,/fetch) ;; /unzip has been deprecated Search statistics: *** Ran 110 queries. *** 4 queries used more than 0.01 seconds. *** Total query time: 0.219 seconds. *** Total elapsed time: 1.165 seconds. Problems, questions, suggestions and comments to: [email protected] http://sdc.uio.no/search/process5?INSTRUME=,SOT%2FNB,SOT%2FWB…G_VER=52;G=;SQ_OBSTITLE_PROG_VER=FG20070429_182200.6;P=1;th=y Page 1 of 1 Figure 1: Example of a result page, exact appearance depends on web-browser 3 INDEX STRUCT = -> MS_273579585001 Array[6] DATA INT = Array[4096, 2048, 6] index is thus a structure containing the header information and data contains the six images, each 4096x2048 pixels large. You can get a listing of all the tags in the index structure with the IDL command help,index,/structure and inspect an individual value using array indexing: for i=0,5 do print,index[i].date_obs,' ',index[i].wave prints the date/time of the observation and the wave ID of the filter. The Solarsoft routine plot image can be used to look at the images. Note that these are raw- images. Exercise 3: Read into IDL the SOT/BFI synoptic images from Exercise 2. Compare the images in the various wavelengths. Look for image artifacts. List the minimum value, maximum value, mean and standard deviation of each image. 5 Basic corrections for instrumental artifacts The CCD images need to be corrected for dark current and for variations of sensi- tivity from pixel to pixel (flat-fielding). In addition there is an error in the middle of the detector (actually in the border between the two 2048x2048 CCD detectors) that needs correcting. This is done by the Solarsoft routine fg prep. Normally you do these corrections in one step for all images but here we will only do one image in order to inspect the dark current image and the flat-field image. Exercise 4: Perform the reductions for only one image with fg_prep,index[0],data[*,*,0],index2,data2,dark_image=dark_image,flat_image=flat_image What are the statistics of the dark image? flat image? Use plot image to look at a part of dark image. Do you see any patterns? Describe the properties of dark image. Do the same for flat image. Look at dark image and flat image for all six wavelenghts and describe the differences (change the 0 in the statement above to 1,2,3,4,5). You can change the contrast with the plot image command by adding keywords min and max, e.g. plot image,flat image,min=0.9,max=1.1. You can plot a part of the image by giving subranges to the array to be displayed, e.g. plot image,dark image[2:2000,*] Exercise 5: Do the corrections for all images in one command: fg_prep,index,data,index2,data2 Compare the images before and after corrections for CCD artifacts. List the contrast in the corrected images in percent (defined as stdev(image)/mean(image)*100). 6 Analysis of Spicules We will now apply these techniques to analyze observations of spicules. Spicules are fingers of cool gas (around 10000 K) that extend above the solar limb into the corona. They are very dynamic. With Hinode they are best seen in SOT/BFI data in the calcium H-line.