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. Exercise 6: Use Hinode SDC Europe to find a timeseries of SOT/BFI data taken on the limb with a cadence (time-distance between exposures) less than 18s and a duration of at least 20 minutes. Use search criteria CEN RADIUS and SOT

4 search criterium S WAVE to isolate limb observations in the Ca II H line, Make sure the files are sorted in ascending time by setting ”Sort prder” to DATE OBS Ascending. Click on the arrows in the DATE OBS colum in the search result to find cadence and duration (these quantities are not searchable in the database at the moment since they involve combinations of several files). Try to find a series with not too many exposures (100-300) in order to cut down on the reduction times. Once you have the paths in an array in IDL (see above) you should use a wrapper routine around read sot and fg prep to avoid memory problems and to get data organized in a form that allows easy manipulation afterwards. This is done by using the routine mfg mkcube: mfg_mkcube,paths,id where id is a string that identifies the time-series for you and is used in file-names afterwards. As an example here we use the string ’cah’ such that the above call is mfg_mkcube,paths,’cah’ This call will create two files: one file with the index data called cah.idl and one file with the data called cah.icube. You can read in the index data with the command restore,’cah.idl’,/verbose As you see from the screen printout, the index structure array is called hdr. This file is in IDL machine-independent binary form and was created with the command save,hdr,file=’cah.idl’ This is a practical way of saving data in machine independent form for later use in IDL. One can also save the complete content of an IDL session (variables, compiled routines etc), see the help page for details. You manipulate the data array with a series of routines: crispex,’cah.icube’, /single ; play the cube as a movie image=lp_get(’cah.icube’,20) ; read image number 20 from the timeseries Use crispex to look at the timeseries. Use the widget buttons to change the contrast to highlight specific parts of the image (disk part or limb part). You can change the size of the plotting window by using the mouse and you can start a new session with a subpart of the image by using the cursor. Experiment with the widget control buttons to explore the capabilities of this tool. The Hinode satellite is three-axis stabilized but there is still significant jitter left uncompensated. The SOT instruments have a tip-tilt mirror to make such compensations. This unit uses cross-correlation between images to detect jitter and feeds the signal to a tip-tilt mirror that compensates for this motion. The result is less jitter and a compensation for solar rotation at the field-of-view of this correlation tracker. This last compensation is not wanted for these limb observations - the consequence is that the limb moves in the timeseries. Exercise 7: Extract a few images from the timeseries and determine the average motion of the limb. Store the average displacement per timestep in the variables dx and dy. Make an array with this information and correct the time-series for this drift: lp_header,’cah.icube’,nt=nt ; determine the number of images dxy=fltarr(2,nt) ; make a dxy-array filled with zeroes dxy[0,*]=dx ; average displacement per timestep in x direction dxy[1,*]=dy ; average displacement per timestep in y direction mfg_shift,’cah.icube’,dxy ; compensate for the drift

5 There is normally only motion in x, in such a case the last dxy statement above is not needed. The output is written to the file cah align.icube and this cube can be analyzed with crispex. Exercise 8: Spicules have an apparent motion outwards. Find a good example in the cube cah align.icube and measure the outward velocity.

7 Report

The report should contain the answers and explanations on how you did exercise 3, 7 and 8. In addition the source code should be attached.

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