ASPH 611 Term Project
A University of Calgary Department of Physics and Astronomy
Graduate Course in Radio Astronomy
Julie Grant, December 12, 2005
Conducted by: Annalisa De Cia, Jeff Dever, Dave Gibson, Julie Grant, Nicole Kaiser
During the first two weeks of December, 2005 we pointed the telescope to observe Cassiopeia A, Cygnus Region, Virgo A, the Sun and the Moon. Below you will find the observations of these areas with our 21cm Radio Telescope.
The data was processed in the following matter. It was first run through Jeff's SPEC2FITS program which converted the outputted data to FITS format. From there is was run through Julie's BANDCORR program which averaged the bandshape of the hot loads taken before and after each observation. It was then run through Julie's DATACORR and Dave's temperature conversion which removed the bandshape and converted the voltages to Kelvins. It should be noted that the DATACORR did not completely remove the background level and should be dealt with in the future if more observations are to be made.
The hot load is the observation of the sky with the microwave absorber attached to the feed horn, see Figure 1. The absorber was left outside to adjust to the outside temperature. This allowed us to get a measurement of the system at the same temperature as the temperature that the observations were taken at. The hot load observations were made before and after the observations of the source we were observing. This allowed us to track the temperature change of the system while the observations were taken. By averaging the two hot load observations we were able to create a measurement of the system without any interference from outside sources thus allowing for the removal of the bandshape from our observations of the source.
Cas A was observed on December 6, 2005 and was expected to cross the meridian at 6:55pm MST. The spectral line observations, Figure 3, show data corresponding to the HI line which, upon closer look at Figure 4, show a broad line spanning a few hundred channels of the spectrometer. However, Cas A is a continuum source and we wanted to use it as a calibration source. In order to detect Cas A a total power plot, Figure 5 was made. Knowing the transit time of Cas A we should be able to observe a change in the total power output. There was no detectable change in the total power near transit time. A reasonable explaination of this is due to the pointing. The higher the altitude that the telescope points to increases the pointing error (pointing explanation) thus Cas A could be outside our beam area.
Figure 5: Total power plot of the observations of Cas A. Cas A was to transit around 6:55pm MST (18:55 hours) thus a noticable increase in the total power should be present here. The is no shift in total power thus indicating that Cas A was not in our beam upon observation.
Virgo A was observed on December 7, 2005 at 8:01am MST. The first image displays the spectral data taken on that day and the RFI of another frequency has been alisaed up to the 1420 MHZ area and has covered our potential HI data. Upon further investigation of this RFI, it was noted that it is potentially due to geosynchronus satelittes which ordbit at an altitude of 40o. Thus we have considered this region a bad region to look at during our observing run due to this RFI.
As you can see, RFI is a huge problem for us. A proper filter for this has yet to be installed, but it is currently in the process of being added to the system. The largest problem was in the Virgo A region where it was determined that the geosynchrous satellites play a huge role. These satellites are located around 40o altitude, and as such we stopped observing this area of the sky. This included the Origon Region as well as the Virgo A region. For more information on the problems of RFI please visit the RFI page.
Figure 8: Total power plot of the Sun during transit on December 8, 2005. A sidelobe of our beam is visable at a time of 13 hours.
The Sun was observed on December 8, 2005 and was used to try to correct our pointing error. The Sun was to transit at 12:28pm MST and at this time we positioned the telescope so that the shadow of the Sun was in the centre of the dish. We were aquiring data during this whole time. In order to identify the Sun we need to look at the Total Power plot, Figure 8. On this plot, all the data prior to 12.5 hours was obtained while moving the dish around while all the data from 12.5 hours onwards is when the dish is sationary and the Sun went through the centre of the beam. From 12.5 hours onwards, the peak of the Sun as well as a sidelobe of the beam are visible.
Last modified: 10:22 am July 17, 2014