La Silla - Science Operation Department

A QUICK LOOK TOOL FOR EFOSC2

A quick look tool for EFOSC2 long-slit spectroscopy

The tool is based on the context/long of Midas. A basic knowledge of the context would thus be helpful in case of trouble. In any case, it's good to know that the current setup can be inspected with show/long, and parameters values (both variables and the software behaviour) can be changed with set/long parameter=xxx

The software should be as much non-interactive as possible, so it assumes that you have a guess session for the wavelength calibration. The guess sessions can be downloaded from

efosc2_guess.tgz (5.7 MB)

Currently, the package contains sessions for grisms 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 16.

The tool is described here below, and in more detail in a short Manual in PDF format.

Installation

Cookbook

0 Prerequisites
1 Start MIDAS
2 Getting some help
3 Prepare the images
4 Apply the wavelength calibration
5 Extract the spectrum
6 Create the response function
7 Apply the flux calibration

Installation

Download efosc2_qlook.tgz (7KB), and put all the *.prg in ~/midwork. Even better, put the files in a subdirectory (e.g. call it EFOSC2) and create symlinks in ~/midwork, so things are cleaner this way.

Put the tables of the guess sessions in ~/midwork and convert them into MIDAS tables, with a command like indisk/fits initial_xxx.tbl.fits initial_xxx.tbl.

That's all!

Cookbook

0) The tool will work if:

Arc line lists are stored in:

/scisoft/midas/calib/data/spec/line/

The atmospheric extinction curve is stored in

/scisoft/midas/calib/data/spec/exti/

The standard stars flux tables are stored in

/scisoft/midas/calib/data/spec/flux/

/scisoft/midas/calib/data/spec/ctio/

(The links above will give you the file list if you are browsing your local copy of this cookbook)

You have a guess session for your grism, so tables like the following exist (for example these are for grism 11):

$HOME/midwork/initial_11.tbl

$HOME/midwork/initial_11COE.tbl

The names of the frames have the following form

BIASes are called : *Dark*
FFs are called : *FlatSpec*
Arcs are called : *HeAr*
Science spectra are called : *EFOSC_Spectrum*obj*

1) Start MIDAS

@@ inmidas !! of course

2) Getting some help

The following command will give you the list of available prg's

Midas xxx> @@ readme

3) Do the image preparation and find the wavelength solution (in the afternoon)

Midas xxx> @@ prepare

The program does:

Initialize default parameters for EFOSC2
Convert FITS into BDF
Rotate to have wavelength running "from left to right"
Set the O_AIRM descriptor (it is not set automatically)
Create the median BIAS frame and subtract from all images
Create the master FF frame (the interpolation along the dispersion is done with a polynomial of degree 'fdeg', and 'fdeg' is set at the beginning
divide each frame by the master FF
create master HeAr frame
Calibrate in wavelength, based on a guess session

The program calls two more macros: the initialization is done by:

@@ defaultpars

And the wavelength calibration is done by:

@@ waveguess

In turn, waveguess displays the solution using

@@ plodist

Now during the night, each time you get a new spectrum, you can go ahead with the following steps.

4) Apply the wavelength calibration

@@ calib xxx.fits:

Of course, this will first subtract the BIAS, divide by FF, trim the image, etc. (all the stuff that was done for the calib images).

The wavelength calibration also corrects for the distortions in the cross-dispersion direction, so you can now extract the spectrum.
The name of the new 2-d spectrum will be xxx.bdf

5) Extract the spectrum of the object

@@ exsingle xxx.bdf

The spectrum is extracted taking the extraction windows for the object and the sky from the file obdef.dat (a template is created by @@ defaultpars). The file looks like this:

--- obdef.dat ---
change these values if you wish
skydown_y1: 100
skydown_y2: 150
obj_y1: 191
obj_y2: 210
skyup_y1: 250
skyup_y2: 300
object_nr: 1
-----------------

From top to bottom, the numbers are the lower sky window, the object window, and the upper sky window. The possibility of extracting more than one object from the 2D spectrum is forseen, so an object nr. can be specified with the last parameter, and it will be used to name the extracted spectrum, which will be called like 2D_spectrum_name_objnnn.bdf, where nnn is the object number defined by 'object_nr' in obdef.dat.

The spectrum is extracted by

@@ subext

which uses the plain average method. If you wish to use the optimal extraction, please see EXTRACT/LONG.

Now you could be satisfied with the extracted spectrum, but in case you observed a standard, you can flux-calibrate the extracted spectrum.

6) Create the response function (after observing a std star)

If you have a standard star spectrum, then first apply the wavelength calibration and then extract its spectrum, as you did for all the other spectra (so do @@ calib and @@ exsingle in sequence). After this execute

@@ resplong

Which will find the response curve. By default, the response function is fitted with a polynomial of degree 12.

7) Apply flux calibration to your object

@@ fluxlong xxx_obj1.bdf

La Silla - Science Operation Department A QUICK LOOK TOOL FOR EFOSC2