IDL Data Analysis Package for Single Dish Radioastronomy

The NRAO Robert C. Byrd Green Bank Telescope (GBT)


Motivated by the failure of AIPS++ DISH to accomodate the data analysis needs of his 3-Helium research, Tom Bania has written a data analysis package for single dish radioastronomy in IDL which has all of the functionality of the old NRAO UniPOPS program. Since it is written as a suite of IDL procedures, this package is far more powerful than UniPOPS ever was. It is completely extensible; those familiar with IDL will immediately be able to write powerful, new procedures for their specific needs.

The package description and procedure documentation can be found here. The package is available as a gzipped tar file download here: gbtidl.tar.gz (7.2 Mbyte). This is the entire v3.2 package without any data. Unpacking the tar file creates an empty data/ directory. You can get some test GBT total power data here: LFeb04.avg.acs.fits (19 Mbyte).

If you have any questions please contact Tom Bania directly:

The initial package implementation has been made to accomodate GBT data. The current v3,2 release expects input data to be in NRAO SDFITS v1.1 format. That is, the package is nominally tuned to analyze GBT autocorrelation spectrometer (acs) and digital continuum receiver (dcr) data. Nonetheless, importing *any* single dish radioastronomical data into the package is very straightforward. Instructions on how to do this can be found in the IMPORT_DATA file at the link cited above. Bania has successfully imported data from the FCRAO 12 meter and Arecibo. Any CLASS .fits format data should be straightforward to import.

Below we give some examples of data products from this package. All the examples are from GBT data taken in June 2004 for Bania's 3-Helium project. Each spectrum sampled 50 MHz total bandwidth with 4096 channels. Data were taken as position switched total power observations toward a sample of Galactic HII regions and planetary nebulae (PNe).

Fig. 1

Raw spectrum of the S209 HII region after a 14.5 receiver hour integration (average of two polarizations at 7.25 hr each). Various recombination line transitions are flagged together with that of the 3-He+ transition. Note the excellent quality of the GBT X-band baselines in this calibrated, but otherwise unprocessed, spectrum.

Fig. 2

Zoom in of the 3-He+ spectral region for the fig. 1 data after a polynomial baseline model has been subtracted and the spectrum smoothed to 5 km/sec resolution. Emission lines from the H171eta recombination (left) and 3-He+ spin-flip (right) transitions are obvious. This is a GBT confirmation of a previous 3He+ detection made in this source by the 3-He team using the NRAO 140 foot telescope.

Fig. 3

GBT 3-He+ spectrum for a composite average of a sample of Galactic planetary nebulae. Shown is the average of spectra taken toward NGC 3242 + NGC 6543 + NGC 6826 + NGC 7009 aligned to a common LSR velocity. Both the H171 eta recombination (left) and 3-He+ spin-flip (right) transitions are clearly seen in this composite spectrum. Although we do not yet have sufficient signal-to-noise to detect 3-He+ in an individual PN, this 125.7 receiver hour integration clearly shows that PNe contain 3-He. This GBT result confirms our conclusions based on a similar, but not identical, composite PNe sample spectrum made with the MPIfR 100 meter telescope (Balser et al. 1997, ApJ 483, 320-334). (Note that the composite spectrum here is in antenna temperature whereas that of the MPIfR result is in brightness temperature.)

This GBT spectrum is, however, an integration that is 1/4 that of the MPIfR spectrum! We have achieved the same result in 1/4 the observing time. This strongly suggests that the GBT spectral baselines are MUCH better than the MPIfR 100 meter.