Last Update: 27th July 2020
The scan table prescribes the movement of the Nobeyama 45-m telescope. The Nobeyama 45-m telescope can observe the target object with 5 different scan patterns: Single Point, On-On, On-the-Fly, Cross Point, and Multi Point. The Scan Tab helps you to make the scan table easily.
Enter a name for the scan table. A configuration file will be saved under your working directory with the name of
<the name of the Scan Table you defined>.nscan
The limitations of a filename of the scan table are as follows:
NOTE: You can save the input parameters anytime you want (the nobs allows you to save the scan table even if some mandatory fields still blank). The nobs does not check whether these input parameters follow the rules at that time.
Click the Check button for a basic check of the parameters. This feature only checks for simple typos, and it is not meant for checking the details of the observational setup.
In order to check on-source positions for OTF mode, it is useful to utilise a tool named obspoint. This tool generates the positions of the on-source defined in your scan table.
You can use this space to leave any memo about the scan table. A character limit is 100, and a line break is prohibited.
There are 5 different scan patterns. Select the scan pattern you intend to use from the pull-down menu located at the upper-right corner or each tab. The scan tab will switch to the corresponding scan pattern.
'Single Point' scan is a standard single-point scan with a position-switch method.
Enter on-source integration time (in seconds). As integration time becomes long, nominal observing efficiency increases. The upper limit of the integration time is defined by the stability of the sky and the system. (if the integration time is too long, baseline gets worse). A recommended value is 10-20 seconds.
Beam Rotation Angle is applied to a multi-beam receiver. For most of the single-point observations, leave the beam rotation angle 0 degree. There is only one exception: single-point observation with all four beams of FOREST. The instruction on how to choose the 'beam rotation angle' in this case is written at the bottom of this page.
Define a way of observations: a pair of on-position (the on-source position) observation and off-position observations. The on-position is the position where you define in the source table, and the off-positions are what you describe in the reference table. You can select several off-positions in one sequence. The on-position observation is expressed '*' mark and off-positions are 1-9 (each number corresponds to (1)-(9) in the reference table). By default, the simplest sequence-pattern of one off-position which is written at (1) area in the reference position is set (i.e., '1*').
ex.) If you intend to perform a single-point observation with 2 off-positions, the sequence pattern becomes as follows:
'1*2*'
NOTE:
1. An off-position observation must come first.
2. The integration time for the off-position is the same as that of the on-position.
3. The sequence pattern must end with the on-position (i.e., '*').
Enter the total number of the sequence pattern you would like to repeat.
Total number of scans (i.e., On-position, Off-position, R, and Sky) is limited less than 1000.
For a rough estimation,
(total number of scans) ∼ (Sequence Pattern) x (Number of sequence).
In case that the sequence pattern is 1** and number of sequence is 300, total number of scans is roughly 900 (=3 x 300).
The Nobeyama 45-m telescope currently has two ways to perform absolute intensity calibration. Both of them utilize a standard room-temperature load. The 'R-SKY' method is the preferred way as the load, since the instrument is closer to the antenna cabin (and hence better temperature control), and the R-Sky switching is performed much quicker. Since FOREST owns a calibration system, LDM1-SKM1, you should use LDM1-SKM1 for FOREST.
| Receiver | Calibration Method |
|---|---|
This field sets the integration time for the absolute intensity calibration process. This value should be equal to the integration time used for the on-position.
This field defines how often the telescope performs the absolute intensity calibration. Set this value so that the interval is 10-15 minutes under typical weather conditions. Although frequent calibration makes observation efficiency low, a shorter interval may be better under highly variable weather conditions.
The On-On mode is a unique observing mode for multi-beam receiver.
Hence this mode must be used in conjunction with the FOREST receiver.
When the On-On observation is performed, the FOREST Beam 1 points to the on-position, while the other beam, the FOREST Beam 3, points to the off-position located 70" (corresponds to a beam separation of FOREST Beam 1 and Beam 3) away from the source coordinates.
When a single integration is done, then the telescope moves so that the FOREST Beam 3 is now pointed toward the on-position.
Thus, the user who is going to perform the On-On scan mode should previously know that the source is compact enough.
FOREST Beams used in the On-On mode
Schematic view of the sequence pattern and the observing positions in the On-On observation
Most of the items for the On-On mode are as same as what described in the Single Point section.
One important difference is that there is no choice for 'Beam Rotation Angle' (removed) and 'Calibration Mode'.
Therefore, these values are fixed as 0 degree and LDM1-SKYM1.
Note that off-position is automatically defined as 70" (the beam separation of the FOREST Beam 1 and 3) and rotates around the on-position depending on LST and EL, and is located both sides of the on-position).
The reference table for the On-On observing mode is used to define where is used for the absolute intensity calibration:
'Reference ID' refers to the position described in the Refernce Table and that position will be used as a blank sky.
'Number of Sequences' for On-On mode is defined by usual on-source scan number of one beam. The total on-source scan number with two beams is the double number entered here. The users should enter the value taking into account that 'Number of Sequences' in the scan table is a half number of "Scan number for one ON-point" in the results of the observing time estimator.
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On-the-Fly mapping method is available for all receivers.
Required parameters can be derived with Time Estimator for On-The-Fly Observations
(also see A Guide to OTF Observations with 45-m).
A window to specify a scan pattern. Some symbols used below are as same as in Time Estimator for OTF.
Schematic view of OTF parameters
Specify a reference coordinate system from 'Equatorial (J2000)', 'Equatorial (B1950)', 'Galactic' and 'Horizontal'.
The direction of the scans.
Scan direction for position angle of 0 deg.
The relative coordinate of a start position of the first scan (Row 1). Note that this position is difined in the XY coordinate (not in the reference coordinates).
Length: Length along the scan direction
Spacing: Spacing between each scan
We recommend setting this value to be about 1/3 of HPBW in order to fulfil the Nyquist sampling.
Position angle of the map (XY coordinates) from the reference coordinate.
Position angle of the map (XY coordinates) from the reference coordinate.
Describe number of scans in one block.
Note that length perpendicular to the scan direction becomes (Number of Scan - 1) x Spacing.
Define number of blocks.
Since only one block is available for the 2017-2018 observing season, number of blocks is set to 1.
The separation between blocks in the unit of the arcsecond.
Since only one block is available for 2017-2018 observing season, block spacing is set to none.
Begin and end number of scan rows. In general, Begin=1 and End=Nrow.
Specify observation sequence. '*' mark indicates the on-position (scan), while 1~9 represent off-positions.
NOTE:
1. Scan must start with the off-point (i.e., numbers, which is defined in the reference table)
2. The sequence pattern must end with the on-scan (i.e., '*').
Duration of approach-run (tapp).
Duration of the scan (main-run) (tscan). A recommended value is 10-20 seconds.
Integration time for Off-point.
Duration of transit-run (ttran).
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.
Set how often the data is obtained during the scan.
For the observatory's data storage policy, data-dump time is set to 0.1 seconds.
Number of repeats of the scan.
In order to keep the pointing of the telescope accurate, total observation time with one observe table should be shorter than 1-1.5 hours.
Total number of scans (i.e., On-position, Off-position, R, and Sky) is limited less than 1000.
The total number of scans can be estimated as follws:
(total number of scans) ∼ (Sequence Pattern) x (Number of scan) x (Number of blocks) x (Number of Maps).
For example, assume that the sequence pattern, number of scans, number of blocks, and number of maps are 1**, 30, 1, and 2, respectively.
The total number of scans is roughly 180 (=3 x 30 x 1 x 2).
Parameters for absolute intensity calibration.
Select a calibration system for the absolute intensity calibration. "LDM1-SKYM1" for FOREST, otherwise "R-SKY".
The integration time for the absolute intensity calibration. In general, it is set to be the same as tOFF.
Number of sequences between the absolute intensity calibrations. The absolute intensity calibration must be done at every 10--20 minutes (depending on weather condition).
Users must carefully make the scan table when observing with the FOREST receiver since the FOREST has the asymmetric beam alignment to the rotation centre of the dewar. An optical axis of the FOREST receiver is designed to be along the Beam 1. This changes the beam alignment due to a declination of a target. If users intend to observe an area of 2A [arcsec] x 2B [arcsec] with a position angle of 0 [degree] using OTF scan mode, the parameters for the scan table should be as follows:
| Declination > (+35d56m40s.17)? | Beam Rotation Angle [deg.]* | start position X and Y | Spacing (d), Number of Scan (Nrow) |
|---|---|---|---|
| d x (Nrow-1) = 2B + BS** | |||
| d x (Nrow-1) = 2B + BS** | |||
| d x (Nrow-1) = 2B + BS** | |||
| d x (Nrow-1) = 2B + BS** | |||
| d x (Nrow-1) = 2B + BS** | |||
| d x (Nrow-1) = 2B + BS** |
The following figures illustrate a mapping area with the beam alignment of the FOREST based on a declination of a target(> or < the latitude of the observatory[+35d56m40s.17]) and the Beam Rotation Angle (0, +90, and -90 deg.).
The area overlapped with four beams is shown as a filled blue box.
Case 1: Decl. > +35d56m40s.17, Beam Rotation Angle = 0 deg.
Case 2: Decl. > +35d56m40s.17, Beam Rotation Angle = 90 deg.
Case 3: Decl. > +35d56m40s.17, Beam Rotation Angle = -90 deg.
Case 4: Decl. < +35d56m40s.17, Beam Rotation Angle = 0 deg.
Case 5: Decl. < +35d56m40s.17, Beam Rotation Angle = 90 deg.
Case 6: Decl. < +35d56m40s.17, Beam Rotation Angle = -90 deg.
After making observing scripts, please confirm that the observing region is as same as you intend to with ''obspoint.py''.
| Introduction | Project Tab | Source Tab | Reference Tab | Scan Tab | Device Tab |
This mode allows the user to create an observing script for a pointing observation (a 5-point cross-scan).
Many of the items here are the same as the Single Point mode, and the user should consult the items described the Single Point mode.
Some of the items listed in the 'Scan Parameters', however, are unique to the Cross Point mode.
The best way to prepare a scan table for a pointing observation is to use a sample file, which can be accessed by pushing the "Sample" button.
Naming rules of sample files for the pointing observation are as follows:
pt[frequency in GHz]_[integration time in seconds]([receiver]).nscan
The observatory prepared 22 GHz, 43 GHz and 86 GHz sample files which correspond H2O maser, SiO(J = 1-0) maser, and SiO(J = 2-1) maser, respectively.
T70 and FOREST receiver can observe SiO(J = 2-1) maser at 86 GHz, although the absolute intensity calibration systems are different each other.
When you use FOREST for pointing observation, please use one of sample files with a name of
pt86_~f.nscan.
If you find that the pointing source is too strong or weak to observe with default integration time,
please modify the integration time in 'Scan Parameters' and 'Calibration' section.
This defines the coordinate system used for the scan; i.e. if you chose a grid spacing of 20" along with 'Horizontal', then the telescope will scan along the AZ-EL direction with a separation of 20" among the points. Grid spacing = 20", and Coordinate System = Horizontal are recommended for 40 GHz pointing.
This scan mode should be selected when the user would like to observe multiple points during one observing script.
The Single Point section may help you to make 'Multi Point' scan table.
Select the coordinate system. 'Equatorial (J2000)', 'Equatorial (B1950)', 'Galactic', and 'Horizontal' are available.
Enter on-source integration time per one on-position (in seconds). A recommended value is 10-20 seconds.
Unless users who intend to use the FOREST receiver as a frontend, leave this field 0 degree. For FOREST, please see the explanation which treats the beam alignment and the relationship of the beam rotation angle.
Enter the offset coordinates in (dd mm ss) form. The points should be defined as offsets from the source coordinate (defined in the source table). The user needs to express the offset angle at the great circle (a correction of cos(lat) effect must be considered). Up to 26 points can be defined. If the desired position has a negative value, the negative sign must be placed at the beginning (e.g., -40 min 10 sec should be written as -0 40 10).
The user can specify the desired sequence pattern by listing the on-point (in alphabetical characters) and the off-point (in numbers, which are defined in the reference table). A sequence pattern must be started from the off-position. For example, if the user has four different on-points and two off-points, the user can arrange the sequence pattern in any of (but not limited to) the following ways.
| Sequence Pattern | Actual Observing Sequence |
|---|---|
NOTE: The sequence pattern must end with the on-scan (i.e., '*').
Enter the total number of times you would like the above sequence to be repeated.
As other scan methods, the total number of scans (i.e., On-position, Off-position, R, and Sky) is limited less than 1000.
You can estimate the total number of scans as the following way:
(total number of scans) ∼ (Sequence Pattern) x (Number of sequence).
In case that the sequence pattern is 1abc2abc and number of sequence is 100, total number of scans is roughly 600 (=6 x 100).
The Nobeyama 45-m telescope currently has two ways to perform absolute intensity calibration. Both of them utilize a standard room-temperature load. The 'R-SKY' method is the preferred way as the load, since the instrument is closer to the antenna cabin (and hence better temperature control), and the R-Sky switching is performed much quicker. Since FOREST owns a calibration system, LDM1-SKM1, you should use LDM1-SKM1 for FOREST.
| Receiver | Calibration Method |
|---|---|
This field sets the integration time for the absolute intensity calibration process. This value should be equal to the integration time used for the on-position.
This field defines how often the telescope performs the absolute intensity calibration. Set this value so that the interval is 10-15 minutes under typical weather conditions. Although frequent calibration makes observation efficiency low, a shorter interval may be better under highly variable weather conditions.
For a multi-beam receiver, positions of beams rotate on the celestial sphere along time.
FOREST equips a rotator in order to avoid a rotation of beams.
Since the rotator has a limitation on rotation angle (from -100 degrees to 100 degrees), users need to set a beam rotation angle.
The following figures represent the beam alignment of the FOREST based on a declination of a target(> or < the latitude of the observatory[+35d56m40s.17]) and the Beam Rotation Angle (0, +90, and -90 deg.).
Note that the Beam 1 is always centred on the map coordinate (XY coordinate) unless users explicitly shift start position (for OTF) or observing positions (for Multi Point mode).
In order to check whether or when the rotator of FOREST reaches the limitation of the rotation angle with the initial rotation angle you specified,
please use a python tool the observatory offers "multpa.py".
The usage is explained here.
Case 1: Decl. > +35d56m40s.17, Beam Rotation Angle = 0 deg.
Case 2: Decl. > +35d56m40s.17, Beam Rotation Angle = 90 deg.
Case 3: Decl. > +35d56m40s.17, Beam Rotation Angle = -90 deg.
Case 4: Decl. < +35d56m40s.17, Beam Rotation Angle = 0 deg.
Case 5: Decl. < +35d56m40s.17, Beam Rotation Angle = 90 deg.
Case 6: Decl. < +35d56m40s.17, Beam Rotation Angle = -90 deg.
