[ Japanese | English ]

Prev: How to Determine Parameters | Index | Next: Data Reduction

Observations

Getting Observation/Reduction Account

Before visiting the observatory, submit an Observing Plan Sheet to obtain an observation/reduction account (see Proposal Information: If your proposal is approved). Caution: "Observation mode" must be "OTF". If you choose others, you cannot execute OTF observations. Observation account (GROUP) is named as an alphabetical character ("z" in general) + 4 digits + 2 alphabetical characters (observer's initial): e.g., z6500hg. If the second digit is "5", it is an account for OTF.

The observatory does not backup data in OTF reduction accounts. And 6 months after the observations the raw data and intermediate data in the OTF reduction account will be deleted. Please be advised to bring a storage media whose capacity is large enough for your raw data and their outgrowth. If you use BEARS receiver array, the raw data rate may reach 1GB/hr.

Making "Observe Table"

To prepare "Observe Table", use obstable. The basic instruction for obstable is written in obstable manual. Here we describe OTF-specific settings.

#Hereafter parameters derived in An Example of Parameters in the previous section are used in obstable and obspointotf screen dumps.

Source Table

Same as normal observations. Refer to Source Table in the obstable manual. Please contact us if you intend to observe the solar system objects.

Fig. 3-1: Source Table window of obstable.

Scan Table

Open "Line (OTF)" (Fig. 3-2). See also Scan Table (Line) in the obstable manual.

• Scan pattern: A window to specify a scan pattern opens (Fig. 3-3, described later).
• Off/Calib Positions: position(s) to obtain OFF and R-SKY.
  • Coordinate System: Specify a coordinate system. Please set the same coordinate system as the "Scan pattern".
  • Coordinate Mode: Offset from center (the position specified in the Source Table), or absolute value.
  • Coordinate Values: Position(s) of the OFF point(s). Specify as offset from the center or absolute coordinates, depending on the above "Coordinate Mode". For RA as "absolute value", the format is "hh mm ss.s". Otherwise "ddd mm ss.s".
  • Integration Time: OFF-point integration time (t_OFF).
• Frequency Switch: Used for frequency-swithed observations (Fig. 3-4, described later).
• Sequence: Specify observation sequence. If "0" is used as the OFF point symbol, the starting point of the next approach-run is used as an OFF (effective in frequency-switch observations).
• Calibration: Parameters for R-SKY intensity calibration.
  • Calibration Mode: Select a calibration system for intensity calibration. "LDM2-SKYM2" for BEARS, otherwise "R-SKY".
  • Integration Time: Integration time for R and SKY. In general, it is set to be the same as t_OFF.
  • Interval: Number of sequences between R-SKY calibrations. Typically R-SKY must be done at every 10--20 minutes (depending on weather condition).
• Digital BE Option: Some (OTF-specific) settings of the spectrometer.
  • Channel Range: Channel range specified here (out of 1--1024) is written in the raw data. We strongly recommend to set the range as narrow as possible because of the following two reasons: (1) increase of noises at band edges may heavily affect the data, and (2) smaller data are much easier to deal with. (On the other hand --needless to say-- it must be wide enough to cover a sufficient baseline range.)
  • Channel Bind: Width of channel binning. The output from the spectrometer in the "Channel Range" are binned by "Channel Bind", and then written into the raw data file.
  • Integration time for qlook: Spectra averaged in this duration is displayed in QLOOK. Must be 1 second to 10 seconds.
  • Dump Time: Data dump time of the spectrometer t_dump (0.1 times N seconds: N is an integer between 1 and 10). See How to Determine Parameters. Reconfirm that t_dump v_scan is smaller enough than the HPBW.

Fig. 3-2: Scan Table window.

In the scan pattern window (Fig. 3-3), specify parameters listed below. See also Scan Table (Cont) of the obstable manual.

• Coordinate System: Specify reference coordinate system. Equatorial (RA,DEC) or Galactic (L,B). (AZ,EL) does not work.
• Map Position Angle: Position angle of the map (XY coordinates) from the reference coodinates.
• Scan Positions: Parameters on the scan coordinates.
  • dX0, dY0: Relative coordinate of start position of the first scan.
  • Length: Length of scans (l₁).
  • Spacing: Spacing between the scans (5l for BEARS, otherwise l).
  • Directions: Direction of the scans.
  • Begin - End: Begin and end number of scan rows. In general Begin=1, End=N_row.
• Time
  • Approach: Duration of approach-run (t_app).
  • Scan: Duration of scan (main-run) (t_scan).
  • Transient: Duration of transit-run (t_tran).
  • Return: Duration of return-run from the end point of the last scan to the start point of the first scan. In general set to 1 second.
  • Number of Maps: Number of repeat of the scan.

Fig. 3-3: Scan Pattern window.

In the frequency switch windo (Fig. 3-4), specify parameters listed below. "Frequency switching" for OTF is implemented in a different way from normal observations: throws the LO frequency only at OFF positions.

• Throw Rate: amount of LO frequency throw. Each receiver is connected with one of 4 synthesizers (No. 1--4): see Device Table section of the obstable manual, and set the frequency throw for the synthesizer you are going to use. See a report on Frequency Switch to determine appropriate amount of throw.
• Modulation Rate: set the direction of frequency throw, etc.
  • Single, Single(+-), Double: direction of LO frequency throw.
    • "Single" --- always throws frequency toward positive direction (i.e., increases LO frequency if you specified positive Throw Rate) to obtain OFF data.
    • "Single(+-)" --- throws toward positive and negative directions by turns (i.e., positive for an OFF, then negative for the next OFF).
    • "Double" --- throws toward positive and negative successively, and the average of them is used as an OFF. Accordingly, OFF-point integration time becomes twice of the one specified in the Scan Table.
  • time per phase: leave it to be "0.5 s".

Fig. 3-4: Frequency Switch window.

Device Table

Same as normal observations. Refer to Device Table (Line)/ Device Table (BEARS) in the obstable manual.

The inclination of BEARS, , is specified in "RX Init Angle". If you will execute scans inclined with respect to the (RA,Dec) or (l,b) coordinates (i.e., if the "Map Position Angle" in the Scan Pattern Window is not 0), the position angle should be added to the "RX Init Angle". If necessary, you have to add +-90 (or 180) degrees to avoid the BEARS rotation stage exceeding the limit (within +-138 degrees: see Mult PA).

Fig. 3-5: Device Table (BEARS) window.

Verifying the Table

There is a utility "Obs Point" to verify observe tables, but it cannot be used for OTF tables (we apologize for the inconvenience). Instead, a command named obspointotf is designed for OTF scans. Usage is as follows:

obspointotf [-center/-all] [-ps/-cps] [-out] [-lp] [-xr Xblc:Xtrc] [-yr Yblc:Ytrc] infile1 [infile2 ...]

When you "Save&Send" an observe table, a file TableName.start is created in the directory /home/GROUP/PROJECT/obstable/work/ . Specify this ".start" file (or files) as an argument of obspointotf to plot scan paths. You can close the plot window by typing "q" key when the window is focused.

cd /home/GROUP/PROJECT/obstable/work
obspointotf hoge.start fuga.start

For BEARS, paths of 4 beams at the corners of the array are drawn. If you use -center option only the central beam is plotted; with -all option all the 25 beams are plotted. (Of course these options does not make any difference for single-beam receivers).

obspointotf -center hoge.start
obspointotf -all hoge.start

Another option -ps is used to write monochrome PostScript onto the standard output. Use -cps for color PostScript.

obspointotf -ps hoge.start | lpr
obspointotf -cps hoge.start > hoge.ps

With the -out option, a temporal file "_ObsPointOtf_tmp_file.dat" is retained in the current directory. The "with linespoints" style of gnuplot is applied by setting the -lp option, otherwise "with lines" style is used.

Using -xr and/or -yr, a region to be plotted can be specified.

obspointotf -xr 10:5 -yr -10:-5 hoge.start

Fig. 3-6: An example of obspointotf result.

Executing Observations

Just like as normal observations, select a observe table and press "Start Observation" to run the observation.

A line profile averaged in a specified duration ("Integration time for qlook" in the Scan Table) is displayed in QLOOK. QLOOK works in the same way as normal line observations ("Integration mode" does not work).

Fig. 3-7: OTF QLOOK.

Prev: How to Determine Parameters | Index | Next: Data Reduction