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, storaging of the data. The preparation of observing scripts will make a night with DECam efficient, and hence, more relaxed.

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 found here [1].

ScriptsEditor is also available at the computers in the control room (observer1 and 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.

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, 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
exclude	[bcam, aos, guider]	Exclude selected DECam components from this exposure
calmode		Calibration mode (DECal use)

Parameters related with the Input Coordinates


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


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 documentation of ScriptsEditor (pdf file) [2].