possible incorrect sdfits headers

[Andrew Walsh <andrew.walsh@…>]

I am trying to process Parkes mosaicing data partially through ASAP. The standard route is to use livedata, then gridzilla. But ASAP is preferred partially due to the superior baseline fitter (there are other reasons). I have tried two methods to reduce the data, whose steps are outlined below:

Method1:

1. Livedata - read in rpfits, flag off-source data, quotient, baseline, write sdfits
2. Gridzilla - read in sdfits, map, write fits data cube

Method2:

1. Livedata - read in rpfits, flagg off-source data, write sdfits
2. ASAP - remove RFI, quotient, baseline, write sdfits
3. Gridzilla - read in sdfits, map, write fits data cube

The problem is that the resultant cubes for the two methods are offset in velocity by about 1.18km/s. I suspect that the ASAP stage is either incorrectly writing header information or writing it in a format that subsequent gridzilla processing does not recognise. I come to this conclusion partly because in the output sdfits header from ASAP (Method2), one line says:

SPECSYS = 'TOPOCENT' / Doppler reference frame (transformed)

whilst the sdfits output from livedata (Method1) says:

SPECSYS = 'LSRK ' / Doppler reference frame (transformed)

Note that manually editing the sdfits file from ASAP to read "LSRK" does NOT change the final data cube, and it is still offset in velocity.

I have attached the following files:

raw rpfits file (2012-05-13_1506-P817_G335.0-1.0_lon_dfb4.rpf)

sdfits file made using livedata in step 1 of Method1 (method1.sdfits)

sdfits file made using livedata in step 1 of Method2 (2012-05-13_1506-P817_G335.0-1.0_lon_dfb4.sdfits)

sdfits file made using ASAP in step 2 of Method2 (1506.sdfits)

ASAP script used to produce 1506.sdfits above (red.py)

I have included the files in a tar file.

Later. Andrew xxx

[Malte Marquarding]

I had a look at the writer source code and the write by default frequency aligns the data if the two frames are different. By default asap loads "freqframe" from .asaprc or if that is not present sets it to "LSRK". So If you don't want to align on write you have to call

scantable.set_freqframe("TOPO")

or at the top of the script

from asap import rcParams

rcParams['scantable.freqframe'] = "TOPO"

Could you try this please.

[Malte Marquarding]

Another note. I assume that setting it to "TOPO" in ASAP then editing it to "LSRK" before livedata, will give you the 'expected' result.