Training Materials

CASA Sit­-together session 6

Solar continuum data at 20 cm from VLA

29th October 2010, ARC Czech Node at Astronomical Institute in Ondřejov

Introduction – Specifics of solar radio astronomy

The Sun is our closest star and this simple fact has a few consequences for its observations, also on the radio waves:

1. Its is bright, in fact on many wavelengths much brighter than other sources usually observed. This has both pros and cons – shorter integration time is sufficient, on the other hand one can get into problems with calibration.
2. Linear scales (in km) which we can resolve are many orders of magnitude smaller than for the remote radio sources. Having a speed at which disturbances propagate in the source (typically Alfven speed) this also means that the resolved sources at the Sun can be much more variable than usually – ­ source dynamics does matter and we are frequently interested in time evolution.

Second peculiar feature of solar radio emission is the specific emission mechanism that applies mainly on lower frequencies (<5GHz): so called plasma emission. It can produce very bright non­thermal (T_b up to 10¹⁵ K while coronal temperature is 2MK), rather narrow-­band (∆f/f < 0.001) and highly time-­varying radiation at plasma frequency or its harmonics. In addition to that, also "standard" emission mechanisms (brehmstrahlung, gyro­synchrotron and in the lowest­temperature regions also molecular transitions) occur.

The data, script, scan descriptions, and a few notes (readme.pdf) are available at:
http://www.asu.cas.cz/~barta/CASA/sit-together6/