In this practical section we are going to learn to use the IDL routines included in the SIR distribution (reading and writting model and profile files). In addition, we will perform spectral syntheses and simple inversions, to find out about the strengths and limitations of the standard SIR code. Exercise 1: Spectral synthesis ------------------------------ In IDL, open the HSRA model (hsra.mod) with leemod,'hsra.mod',tau,t,p,mic,strength,vel,gamma,phi,mac,filling,stray Look at the model with graphics.pro. Note that this model is a quiet Sun model with no magnetic fields. Add a magnetic field whose strength changes linearly with optical depth (say, 1500 G at log tau=0 and 500 G at log tau =-3) and whose inclination changes linearly with optical depth (from 20 deg at log tau=0 to 50 deg at log tau=-3). Use a constant field azimuth of, say, 20 deg. Write the new model atmosphere with escribemod,NEWFILENAME,tau,t,p,mic,strength,vel,gamma,phi,mac,filling,stray Prepare a control file to synthesize the Fe I lines at 6301.5 and 6302.5 using the LINES, THEVENIN and sp.psf files provided in the directory /home/lbellot/sir_course/1st_session/. For the moment, do not include a stray light profile. Run the SIR code and visualize with graphics the output profiles. If you want to play with the code, you can perform additional spectral synthesis with the same model, changing the inclination and azimuth values, to see how Q, U and V change. Don't forget to rename the output files (they will be used in Exersi Exercise 2: Inversion of the synthetic profiles. ----------------------------------------------- We will try to invert the profiles synthesized in the previous exercise. First of all, we need to create an initial guess model atmosphere. We can use the same hsra.mod, but with different (constant) values for the field strength, field inclination, field azimuth, LOS velocity, and temperature. Use the leemod.pro routine to create the initial guess model you prefer. You may modify the hsra.mod thermal stratification in a simple way changing the slope of the stratification (do not use more complex modifications!!!) Now prepare a sir.trol file to run an inversion of the profiles with three cycles. In the first cycle, use two nodes for temperature and one node for all the other atmospheric parameters. In the second cycle, use two nodes for all the atmospheric parameters. In the third cycle, increase the nodes for field strength and LOS velocity to 10 (just to see what happens). Run the inversion and visualize the results with graphics.pro. How would you interpret the results?? Exercise 3: Inversion of umbral profiles observed with SOT/SP ------------------------------------------------------------- The profiles "umbra_mu84.per" and "umbra_mu47.per" can be found in the directory /home/lbellot/sir_course/1st_session and have been prepared by Jan-san. The image "map_umbra.png" shows the location in the umbra where these profiles come from. Note that they correspond to a region very close to the inner penumbral region. Look at the profiles with graphics.pro. Which model would you use to invert these profiles? Once you have decided about the model, create an initial guess atmosphere (you may use the intial guess model you prepared in the previous exercises, if you like) with leemod.pro and escribemod.pro. Create a sir.trol file to perform the inversion. How many cycles are you going to use? How many nodes for each atmospheric parameter? Include the instrumental PSF of the SP in the inversion (sp.pdf). Look at the best-fit profiles with graphics.pro. Are they reasonable? Are the main fetures of the observed profiles reproduced? Exercise 4: Inversion of pore profiles observed with SOT/SP ----------------------------------------------------------- The profiles "asterisk329_262.per" and "plus401_255.per" were observed in a pore region (map_pore.png). They have been prepared by Morinaga-san. Examine the profiles and start with the simplest one. Which model will you use for the inversion? Create an initial guess model and a sir.trol file and perform the inversion. Do the best-fit profiles look reasonable? Are more complex geometries needed?