Preparation for Lab

You should have with you a sheet with important observing information needed to setup the UMRAO sun-mapping program.

Running SunMap program at 85-ft UMRAO Telescope

(These instructions have been transcribed from Prof. Aller's 1992 Mar 04 Instructions, with minor modifications for clarity.)

1. First, the SunMap program must be loaded into the control computer by the telescope operator (G.Latimer), Example: 'load p d:list\mapra.txt'

2. This program makes a raster scan of a region of the sky that is specified by the user in terms of the half-height and half-width of the region (both in arcminutes and seconds). Before starting the program, the user must determine the current position of the sun (RA/Dec) and its rate of motion in RA/Dec.

3. To start program enter (this part is typically done by operator also):

4. The user is then asked to enter a series of parameters. Please pay very careful attention to the data format, since an incorrect response has dire consequences on the system. If you make a mistake, a lengthy restart process must be done. Thus, always double check each parameter you enter to be sure its appropriate and compare with 'example answer' in the table. Please record the parameters you use, since these will be needed again when making the map.

5. This program will then start the map, consisting of the following steps:

• The telescope moves to the edge of the map region (see accompanying sheet which explain raster scans geometry).
• A Test Signal Sequence is done to calibrate receiver
• Starting at the SW corner of the map, the telescope stars its scans in Right Ascension. Observe changing flux on the digital chart recorder. At the end of each scan, the Declination is incremented and a scan in the opposite direction is started.
• When the specified range in Dec has been covered, a second Test Signal is taken.

6. At this point, the program asks for the next source to observe. Let the next group take over the controls. To terminate the observing session, ask operator to put up "Sense Switch 1" on the control program computer.

Lab Writeup

Due to the fact that this lab takes place on the last day of the semester, the Lab Writeup will be relatively simple. Please give Prof. Monnier the observing parameters you entered into the SunMap program and he will generate an ASCII file containing the map data using existing Fortran code written by Prof. Aller.

For the lab writeup:

A. Give brief description of this experiment, including the mapping method, the observing wavelength/frequency, and the expected resolution of our map given the diffraction-limited beamsize of the UMRAO at this wavelength.

B. Make a figure showing the map of the Sun, with appropriate axes labels, etc. I have included some tools you can use to make this straightforward. Using the IDL program 'read_umrao' in the 'ay361 materials' directory of astroclass (windows network), you can read the ASCII map file (Example Syntax: IDL> read_umrao, im, ra_offset, dec_offset ; returns ra/dec offsets in arcminutes) . The program 'imcont' is also included and is very useful to overlay contours on an image and label axes (based on image_cont). (Syntax: IDL> imcont, im, xv=ra_offset,yv=dec_offset, xtitle="xaxis label",ytitle="yaxis label"). Remember to compile/run the idl_startup.pro to setup the IDL environment correctly.

C. Please comment on the antenna temperature measured for the Sun at this wavelength. Remember to multiple the temperatures in the ASCII file by 100 to account for the 20dB attenuator in the feed horn. Extra Credit: Include a figure with 1-D scans across the solar disk showing how the temperature profile changes.

D. Please discuss in a paragraph or two the image morphology. How does the radio size of the Sun compare to the known visible-wavelength size? If you see any structure on the solar surface, where does it come from? How does the temperature from part C compare to the Black Body temperature at visible wavelength? at 21cm measured by SRT Lab #1? Any other comments?