• HighFrequencyDataCalibrationandImaging

High frequency data tutorial

• F.Gueth

Dataset

The data to be calibrated/imaged in this tutorial is the IRAM Plateau de Bure G067 project: observations of the HCO+ 1-0 line at 89.2 GHz, the 13 CO 2-1 line at 220.4 GHz, and the 3.4 mm and 1.3 mm continuum emission in the circumstellar disk of the pre-main-sequence star GG Tau. This dataset has been published by Guilloteau et al. in Astronomy & Astrophysics 348 570 (1999).

/home/user/eris05 contains subdirectories:

The rawdata directory will be used during the tutorial. Since it is very unlikely that people manage to calibrate the whole project, the (calibrated) uv tables are available in the uvtables directory, to be used for the imaging. The other directories are there mostly for reference.

Observations

The dual-channel receivers were used to observe simulataneously two frequency bands:

• 3 mm receivers:
  • tuned at 89.188523 GHz LSB (HCO+ 1-0)
  • 1 correlator unit of 160 MHz, to provide continuum measurement
  • 1 correlator unit of 8 MHz centered on the line (160 channels,
    • 60 kHz resolution = 0.2 km/s)
  1.3 mm receivers:
  • tuned at 220.398686 GHz LSB (13CO 2-1)
  • 3 correlator units of 160 MHz each, to provide continuum measurement over ~500 MHz.
  • 1 correlator unit of 20 MHz centered on the line (256 channels,
    • 120 kHz resolution = 0.16 km/s)

Four or five antennas were used in this project, and three different configuration were observed (D=conpact to A=extended):

Baselines ranged from 24 to 408 m, giving a final angular resolution of 0.85 x 0.6" at 1.3 mm (natural weighting). Excellent weather conditions gave phase rms below 30 deg even on the longest baselines.

• === GILDAS ===

GILDAS is a collection of softwares oriented toward (sub-)millimeter radioastronomical applications, either single-dish or interferometry observations. It is daily used to reduce all data acquired with the IRAM 30m telescope and the Plateau de Bure Interferometer (except VLBI observations). The single-dish software (CLASS) was/is also used at several cm- to sub-mm facilities, such as Effelsberg, the CSO, the SMT, the SEST, or APEX.

GILDAS includes the following softwares:

• GREG graphical displys, astronomical images manipulation
• ASTRO ephemeris and observation preparation
• CLASS calibration of single-dish spectral observations
• CLIC calibration of interferometric observations
• MAPPING aperture synthesis, deconvolution, ALMA simulator

These are installed at ERIS in /home/user/GILDAS

• ==== PdBI calibration (CLIC) ====

To setup the GILDAS software please run

source /home/user/gildasnew/gildas-exe-jul05a/pc-debian3.1-g95/etc/bash_profile

See http://www.iram.fr/IRAMFR/IS/presentations/gueth-23nov04.pdf for a description of the calibration procedures.

The following steps must be followed:

• 1 Create and enter a directory for the calibration, e.g. 'calib' (the
  • procedures create many files).
  2 Open a clic session, just by typing CLIC at the shell prompt. A GUI
  • is created, giving access to various menus. The CLIC menu is used for the calibration.
  3 Raw data file selection. The raw data directory is /home/user/eris05/rawdata
  • In the CLIC menu, select "Raw data file directories". A widget is created, allowing the user to enter up to 10 directories in which CLIC will search for the raw data (.IPB) files - the directory is /home/user/eris05/rawdata. Then clic on "GO".
  4 Creation of the header file.
  • The "Open a raw data file" widget is created by GO in the previous step, or by selecting it in the CLIC menu. Select your raw data file and clic on "Create header file". This will create a .hpb file, in which all calibration curves will be stored (the raw data file is in read-only mode). The hpb filename convention is dd-mmm-yyy-ppp.hpb, ppp being the project id (G067 in our case).
  5 Getting the observing conditions.
  • In the main CLIC widget, select the CLIC menu and then "First look". In the widget that is created, one should clic on each button in a row (SELECT, METEO, etc). Each of them runs a procedure that plots various quantities. If the prompt is CLIC_#, then you should type "continue" (or simply C, or clic on CONTINUE in the main menu) to proceed. The GO button runs all buttons in a pipeline mode. A report is created (show-filename.ps) with all relevant information and plots. This procedures does not affect the data and is only aims at providing informations on the observing conditions (weather, pointing accuracy, system temperature, etc.)
  6 Calibration.
  • In the main CLIC widget, select the CLIC menu and then "Standard calibration". This is the key procedure that performs the whole calibration. Each button runs a procedure:

    SELECT	open the files, find sources/calibrators, check for receiver tunings, select RF calibrator
    AUTOFLAG	check for (known) instrumental problems and flag the corrupted scans if any
    PHCORR	check the validity of the real-time atmospheric phase correction
    RF	RF bandpass calibration (amplitude + phase)
    PHASE	temporal phase fluctuation calibration
    FLUXR1	flux scale calibration (= find the flux of the calibrators!)
    FLUXR2	idem for receiver 2
    AMPL.	temporal amplitude fluctuation calibration
    PRINT	create a calibration report (filename.ps)

  7 Continuation
  • Start again at step 4 with the next data file. Each data file is to be calibrated independently. However, if the observing dates are reasonably close in time (i.e. within 1 or 2 weeks), the flux scale calibration can be performed on the best dataset and then used for the other(s) date(s). The file calibration/calibration-tutorial.txt contains some notes on the calibration of the G067 project.
  ==== Imaging (MAPPING) ====

Imaging is performed in the MAPPING software. It reads as input the uv tables and performs the inversion (FFT) and deconvolution (CLEAN).

The imaging-tutorial.map file should be copied from /home/user/eris05/procedures/imaging-tutorial.map to /home/user, then when in /home/user type
mapping
and then enter
@ imaging-tutorial

• === Calibration tutorial ===

for IRAM MIS4 Nov. 2004 - J.Pety

• Updated for ERIS05 Sept. 2005 - F.Gueth ==== Calibration notes ====

07-feb-1997-g067:

• 7h observation with 4 antennas in configuration A from 17h to 24h UT.
• Observing conditions:
  • Elevation tracking errors on ant.3 before 19h UT.
  • Tsys at 3mm: about 130 to 160 K (note: SSB LSB tuning)
  • Tsys at 1mm: about 300 to 400 K (note DSB tuning)
  • Water vapor content: about 3 mm
• Calibration:
  • Autoflag:
    • Timing error in scan 934 ... duration 61 sec
    • Timing error in scan 1300 ... duration 65 sec
  • Bandpass calibration:
    • There is an absorption line for calibrator 0415+379 at 355 MHz LSB at 3mm. Nothing to be done if the fit is not affected.
  • Phase calibration:
    • Probably small baseline determination error (see phase difference
    • between the two calibrators on some baseline). Phase rms is
    • however excellent (this is the extended configuration A!).
    • Note: the phase plots have different Y range for each baseline;

    • try CLIC_4> SET Y PHASE /LIMIT -180 180

      • CLIC_4> PLOT /ID COL

      • CLIC_4> SOLVE PHASE /PLOT

    • to have all plots on the same scale (and enjoy the phase
    • stability over 7h!).
  • Flux calibration (see section below)

10-feb-1997-g067:

• 4h observation with 4 antennas in configuration A from 18h to 22h UT.
• Observing conditions:
  • Tsys at 3mm: about 130 K (note: SSB LSB tuning)
  • Tsys at 1mm: about 220 K (note: DSB tuning)
  • Water vapor content: about 1.5 mm
• Calibration:
  • Autoflag:
    • Timing error in scan 4950 ... duration 61 sec
  • Bandpass calibration:

    • Wrong first flux estimation => wrong bandpass calibrator automatic selection. You may select the right one by entering (before clicking on RF):

      • CLIC> let band_source 0415+379

  • Phase calibration:
    • Phase noise increasing after 21h30 UT. Data could be flagged out.
  • Flux calibration (see section below):
    • At 1mm: Had to push twice SOLVE because of a numerical instability.

20-feb-1997-g067:

• 9h observation with 5 antennas in configuration B from 13h to 20h and from 21h to 23h UT.
• Observing conditions:
  • Elevation tracking errors:
    • on ant.1 between 17h and 20h UT.
    • on ant.3 before 19h UT.
  • 180deg cable phase jump on receiver 2 of ant. 3 around 15h30 UT.
  • Tsys at 3mm: about 130 K (note: SSB LSB tuning)
  • Tsys at 1mm: about 275 K (note: DSB tuning)
  • Water vapor content: about 1.5 mm
• Calibration:
  • Autoflag:
    • Timing error in scan 9586 ... duration 62 sec
  • Bandpass calibration:

    • Wrong first flux estimation => wrong bandpass calibrator automatic selection. You may select the right one by entering (before clicking on RF):

      • CLIC> let band_source 0415+379

  • Phase calibration:
    • At 1mm: Phase jump on antenna 3 (maybe linked to cable phase jump)

      • CLIC_4> plot /id col

      • CLIC_4> solve phase /plot /break 1 13.5

  • Flux calibration (see section below)

31-mar-1997-g067:

• 10h observation with 5 antennas in configuration D from 10h to 20h UT.
• Observing conditions:
  • Tsys at 3mm: about 140 K (note: SSB LSB tuning)
  • Tsys at 1mm: about 400 K (note: DSB tuning)
  • Water vapor content: 3 to 4.5 mm
• Calibration:
  • Autoflag:
    • Timing error in scan 2078 ... duration 61 sec
    • Timing error in scan 2124 ... duration 66 sec
  • Flux calibration (see section below)
  • Amplitude calibration:
    • At 1mm:

      • CLIC_4> plot /id col

      • CLIC_4> solve amplitude /plot /break 1 12

Table of fluxes

3 mm:

1 mm:

• === Tutorial procedure about imaging for IRAM === MIS4 Nov. 2004 - J.Pety

Adapted for ERIS 05 Sept. 2005 - F.Gueth

IRAM GILDAS Imaging Procedure