Heterodyne Data Analysis

CLASS is used at the CSO for analysis of heterodyne data. CLASS is part of the IRAM GILDAS package. The entire package is available on the CSO computers. You may also install GILDAS on your own computer. Please refer to the GILDAS documentation for installation instructions, tutorials, etc.

1. Connect to kilauea with X window transport
   mycomp> ssh -X user@kilauea.caltech.edu
   • Not necessary if you have installed GILDAS and transferred the data to your computer.
2. Move to your data directory
   kilauea> cd data_directory
3. Start CLASS
   kilauea> class
4. Open a graphics window, if necessary
   LAS> device image
5. Open the data file
   LAS> file in mydata.cso
6. List the contents
   LAS> list in
7. Choose a spectrum
   LAS> get N
8. Plot the spectrum
   LAS> plot

1. Access the CSO computer
   mycomp> sftp user@kilauea.caltech.edu
2. Move to your data directory
   sftp> cd data_directory
3. Transfer data to your computer
   sftp> get mydata.cso
4. End sftp session
   sftp> exit

Analyse simultaneous observations of ¹²CO, ¹³CO, and C¹⁸CO in IRC 40540, an evolved star, made on 2114-11-16. During the observations, the receiver was tuned for ¹²CO(2-1) but a tuning shift was deliberately introduced between between the first spectrum and the others. For the receiver tuning, see Wideband Observations, Example 1.

• Data overview
  • Notice the strong ¹²CO(2-1) line in the center and weaker ¹³CO(2-1) line on the left edge. C¹⁸CO(2-1) is not obvious.
  • Notice the shift of the ¹²CO(2-1) line.

file in 2014-11-16.cso                      ! open data file
list in                                     ! list contents
find /source IRC40540 /tel "CSO FFTS 1W"    ! select FFTS1 data
stamp /scan

• Analyse ¹²CO(2-1)
  • Because the receiver was tuned for ¹²CO(2-1), the sideband and reference information is correct for all four spectra. Hence the spectra may be averaged directly.

file in 2014-11-16.cso                      ! open data file
list in                                     ! list contents
find /source IRC40540 /tel "CSO FFTS 1W"    ! select FFTS1 data

set align v i                               ! select velocity alignment, intersect region 
average /resample                           ! average the spectra 
set unit v f                                ! set the display axes, velocity (bottom) and frequency (top)
set mode x -67 33                           ! set the display limits [km/s] 
plot

• Analyse ¹³CO(2-1)
  • Because ¹³CO(2-1) is in the image sideband, the reference information must be updated before the spectra may be averaged. This requires an intermediate, scratch file.

file in 2014-11-16.cso                      ! open data file
list in                                     ! list contents
find /source IRC40540 /tel "CSO FFTS 1W"    ! select FFTS1 data

set variable spectro write                  ! enable modification of reference information 
set variable calibration write
file out scratch1.cso multiple              ! open scratch file
for i 1 to found                            ! modify each spectrum
  get next
  let r%head%spe%line 13CO2-1               ! set line name
  @swap_sidebands 220398.6765               ! set reference info for 13CO(2-1)
  write 
next

file in scratch1.cso                        ! open scratch file
list in                                     ! list contents
find /source IRC40540 /tel "CSO FFTS 1W"    ! select FFTS1 data
set align v i                               ! select velocity alignment, intersect region 
average /resample                           ! average the spectra 
set unit v f                                ! set the display axes, velocity (bottom) and frequency (top)
set mode x -67 33                           ! set the display limits [km/s] 
plot

• Analyse C¹⁸O(2-1)
  • Because C¹⁸O(2-1) is also in the image sideband, the reference information must be updated before the spectra may be averaged. This requires an intermediate, scratch file. Moreover, C18O is only barely detected so the spectral resolution must be reduced to see the line.

file in 2014-11-16.cso                      ! open data file
list in                                     ! list contents
find /source IRC40540 /tel "CSO FFTS 1W"    ! select FFTS1 data

set variable spectro write                  ! enable modification of reference information 
set variable calibration write
file out scratch2.cso multiple              ! open scratch file
for i 1 to found                            ! modify each spectrum
  get next
  let r%head%spe%line C18O2-1               ! set line name
  @swap_sidebands 219560.3568               ! set reference info for C18O(2-1)
  write 
next

file in scratch2.cso                        ! open scratch file
list in                                     ! list contents
find /source IRC40540 /tel "CSO FFTS 1W"    ! select FFTS1 data
set align v i                               ! select velocity alignment, intersect region 
average /resample                           ! average the spectra 
set unit v f                                ! set the display axes, velocity (bottom) and frequency (top)
set mode x -67 33                           ! set the display limits [km/s] 
smooth                                      ! reduce spectral resolution by 2^6 = 64
smooth
smooth
smooth
smooth
smooth
plot