AST460: Assignment 6
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(Oct 19 2012)
Follow the instructions in the Project Introduction document
(Section 5) to process your SRT observations. In particular,
- Read your specific data file in IDL and place data in a 2-dimensional array
representing a stack of spectra (each row of the array will be a single
HI spectrum).
- To convert from artificial telescope units to brightness temperature, multiply
each intensity element of each HI spectrum by 0.1. (Ideally we would
run a calibration procedure with our observations but let's try to simplify the process.)
- Average all HI spectra to produce a single HI spectrum. Your y-axis
is now Brightness Temperature in units of Kelvin.
- Using the information provided in your data file, build a frequency array for your observations.
Use the Doppler equation to convert from Frequency to Topocentric Radial Velocity.
To convert from Topocentric to LSR Velocity you will need to add a correction factor
to your velocity array.
For observations on Oct 19 2012, the correction factor is:
(l,b) = (75,0) 1.48 km/s
(l,b) = (70,0) 0.04 km/s
(l,b) = (65,0) -1.40 km/s
(l,b) = (60,0) -2.83 km/s
(l,b) = (55,0) -4.24 km/s
(l,b) = (50,0) -5.62 km/s
(l,b) = (45,0) -6.95 km/s
(l,b) = (40,0) -8.23 km/s
(l,b) = (35,0) -9.45 km/s
(l,b) = (30,0) -10.60 km/s
(l,b) = (25,0) -11.66 km/s
If your observations were obtained on a different day, please contact me and I will calculate
your correction factor.
- Fit a polynomial function to the portion of the spectrum unaffected by HI emission
to remove the contribution from the electronics noise and blank sky.
- Make a nice plot of the resultant HI spectrum, with the LSR velocity on the x-axis and
Brightness temperature (in K) on the y-axis.
The assignment is due at the next class meeting.