Preparing Observing Scripts

Observing with DECam is quite simple, straightforward and very efficient. Every exposure sequence will perform every step in the process automatically, from moving the telescope and dome, setting up the filter, focusing, finding suitable guiding stars and start the guiding, taking the exposure, building the images and finally, storing of the data. The preparation of observing scripts will make a night with DECam efficient, and hence, more relaxed. 

N.B. Please take into account that you can not point anywhere with the Blanco telescope (equatorial mounting), there are forbidden limits. See here the horizon limits of the Blanco telescope.

 
For preparing the scripts there is a convenient, stand-alone software (python based) which can be downloaded and installed in any computer. The tarball of the ScriptsEditor software and full documentation can be downloaded here.

Are you sharing your nights with other projects? Read This about Prop-ID!

ScriptsEditor is also available at the computers in the control room (observer2) in case that modification or creation of scripts during the night is needed.

Depending on your python distribution, you may need to install the modules TKinter, json and pyephem to make ScriptsEditor work on your computer.

Note: ScriptsEditor runs under python 2. If you get an error of the type "SyntaxError: invalid syntax", you may be using python 3.

Screenshot of the ScriptEditor interface

ScriptEditor allows to easily plan observations with different dithering patterns or centering objects on a particular CCD, among other features.

The DECam observing system expects scripts to be written in .json format (a text file with special formatting). ScriptsEditor takes care of that. However, some people feel more comfortable working on simple text scripts. Scripts in .txt format are possible but they will need to be loaded anyway to the ScriptsEditor and saved in .json format. A .txt script is made of a set of exposures, each exposure in a single line, with the observing parameters separated by a comma.

This is an example of a .txt script which makes sets of 3x60s exposures in bands g, r and i, with no dithering:

ExpType = object, ra= 281.0, dec=-29.866, filter = g, expTime = 60, object = Sgr, count = 3
ExpType = object, ra= 281.0, dec=-29.866, filter = r, expTime = 60, object = Sgr, count = 3
ExpType = object, ra= 281.0, dec=-29.866, filter = i, expTime = 60, object = Sgr, count = 3

The same script will look this way in .json format:

[
 {
  "count": 3,
  "expType": "object",
  "object": "Sgr",
  "filter": "g",
  "RA": 281.0,
  "dec": -29.866,
  "expTime": 60
 },
 {
 "count": 3,
 "expType": "object",
 "object": "Sgr",
 "filter": "r",
 "RA": 281.0,
 "dec": -29.866,
 "expTime": 60
 },
 {
 "count": 3,
 "expType": "object",
 "object": "Sgr",
 "filter": "i",
 "RA": 281.0,
 "dec": -29.866,
 "expTime": 60
 }
]

 

The possible parameters for defining an exposure are the following:

Parameters related with the Exposures

Keyword

Sample value

Explanation

expTime

12.54

Exposure time in seconds

object

Moon

Observer selected identifier for the object/field

filter

r

Allowed names include: u, g, r, i, z, Y, VR, N964, block, pinhole

 

2

or the cassette number: 1, 2, 3, ...8

 

 

you can choose more than one (is allowed by FCM mechanic):

 

[1, 3, 5]

or [u,Y] or [r,pinhole]

count

25

Instruct SISPI to repeat the same exposure N times

focus

-23.5

Force hexapod position. A single float is the z axis (all others remain unchanged)

 

[1.0, 1.4, 2.0, 1.0, 0.8, 0.0]

Or a list of 6 floats (6th value will be forced to 0.0)

 

[1.0, None, None, 2.3, 4.3, 0.0]

Use None for hexapod coordinates you do not want to adjust

comment

Last exposure of night

User comment (will be copied to FITS header)

earlyTime

<YYYY-MM-DD HH:MM:SS>

Don't take exposure before this time. Wait if too early

lateTime

<YYYY-MM-DD HH:MM:SS>

Don't take exposure after this time. Discard if too late

epoch

2000.0

Specify an epoch

exclude

[bcam, aos, guider]

Exclude selected DECam components from this exposure

calmode

 

Calibration mode (DECal use)

 

Parameters related with the Input Coordinates

Keyword

Sample value

Explanation

ra

17:32:12.032

Right ascension in HH:MM:SS.xxx or

 

123.54

float degrees format

dec

-54:43:5.22

Declination in DD:MM:SS.xxx or

 

-30.221

float degrees format

deltaRA

-3.9

RA offset (float arcsec)

 

W3.9

Use of E/W instead of +/- is allowed

deltaDEC

8.2

DEC offset (float arcsec)

 

N8.2

Use of N/S instead of +/- is allowed

ha

8:12:43.21

Hour angle in HH:MM:SS.xxx or

 

43.211

float degrees format

az

54.000

Azimuth (float degrees)

el

32.1

Elevation (float degrees)

 

Parameters related with Sequences

Keyword

Sample value

Explanation

seqid

twilight darks

Exposure sequence identifier

seqtot

23

Total number of exposures in sequence

seqnum

17

Number of current exposure in sequence

multiexposure

start

This request starts a multiexposure frame

 

cont

This request continues the multiexposure frame

 

end

This request ends the multiexposure frame

multiid

focus

Name of multiexposure frame

multitot

10

Number of exposures in frame

You can specify the requested telescope position in a number of different systems: ra and dec, ha and dec, az and el. You can also specify an offset relative to the current telescope pointing using the deltaRA and deltaDEC keywords. In most cases both sexagesimal and float degrees formats are supported. If you do not specify coordinates in your exposure request the image will be take at the current telescope position.

Additional explanations on the exposure parameters can be found in the ScriptsEditor documentation included in the tarball.

Special tools to prepare observing scripts for standard stars are described here.

Notice that the community pipeline will automatically ignore images with any of these words in the title (i.e. in the parameter object): junk, pointing, focus and donut. These images will still be stored at the NOAO science archive but they won't be processed. More details here.

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The propid keyword

Image headers will contain your Prop-ID (your project number, for example 2016A-0343) under keyword "propid". It is very important to setup the right propid since the access to your data through the NOAO Science Archive depends on it. During proprietary time only you and your collaborators will have access to the data taken under your Prop-id.

In normal circumstances (observing only one project in a night) the exposures will take the Prop-ID from the setup information entered every afternoon. However, it has become more and more common to share time with other projects. In those cases, it is convenient to incorporate the keyword "propid" in your observing scripts. Unfortunately, this is something that the ScriptsEditor software is not currently handling, and thus it must be incorporated by hand or using your own script. The extra keywords have to be incorporated as strings, for example:

"propid" : "2016A-9999",

"proposer" : "Smith",

"program" : "The title of my program"