EMIR ETC GUI Manual 

Tips

Examples:

J-band for YJ grism and Ks-band for HK

Y-band for Y filter

 

Intput

ETC has a simple structure, its interface it is divided into 4 main areas:

Source Configuration

Here you must input the observed magnitude (in the Vega system or AB system) in the selected band.

In addition, you must specify the target is a point source or an extended source. If the latter, all the derived S/N will be PER PIXEL, while for a point source the S/N will be estimated over the whole aperture (considering an optimal aperture of 1.2*FWHM) and of course the size is influenced by the image quality.

The Seasons button simply alters the sky brightness magnitude. The only function of this button thus far is to change the K-band sky brightness from 12.5 (summer) to 13.0 (winter) mag/arcsec2. The sky brightness value used is specified in the Telescope and Instrument section of the output.

Spectral Template

Here you need to choose what kind of SED you will use to simulate your observations. Currently, 4 modes are allowed:

Wavelength Flux
micron(default) perone
ang percent
nm W/m2/nm
  W/m2/micron
  photon/s/m2/micron/arcsec2
  photon/s/m2/nm/arcsec2
  normal_flux
  normal_photon (default)

The first line should always be wavelength and the second flux. normal_flux and normal_photon are useful for normalized spectra, either in  photons/electrons/ADUs per pixel or in energy units. An example of a possible input file:

ang
normal_flux
#iRMS=2.231515282e-05 0
#    lk   ukf_b0v   uks_b0v        fh       fse        fd         fl
# Any line that begins with # will be ignored
# Any data after the first two columns will be ignored
 1150.0 168.676208 25.963779 168.676208  0.000000  0.000000  0.000000
 1155.0 133.073959  8.482157  133.073959  0.000000  0.000000  0.000000
 1160.0 113.737320  8.189384  113.737320  0.000000  0.000000  0.000000
 1165.0 111.826813  9.793808  111.826813  0.000000  0.000000  0.000000
 1170.0   99.958008  5.583178   99.958008  0.000000  0.000000  0.000000
 1175.0   79.515594  2.369892   79.515594  0.000000  0.000000  0.000000
 1180.0   86.660614 11.841807  86.660614  0.000000  0.000000  0.000000
 1185.0   96.530807  7.990627   96.530807  0.000000  0.000000  0.000000
 1190.0   89.222694  1.723856   89.222694  0.000000  0.000000  0.000000
 1195.0  79.401352   5.760297   79.401352  0.000000  0.000000  0.000000
 1200.0  79.882309   1.469236   79.882309  0.000000  0.000000  0.000000
[....]
 

N.B: if you want to taking into account the redshift, you must introduce your SED already redshifted.

A Black Body (BB) SED will be used. The temperature, in Kelvin, will be specified in the BB temperature text field.

In this case the source is a single emission line, and a Gaussian is generated with a specified  center (in µm), FWHM (in arcseconds) and peak flux (in 10-16 ergs/s/cm2 units). For each filter/grism the central value of the line center is selected as default. You can choose another value in the given range.

 

Observation Configuration

These parameters are related to the observation conditions: airmass and seeing.  The latter is specified as the FWHM, in arcseconds.

Operation

Photometry

These parameters are only relevant for an estimation of the S/N expected for photometry. The exposure time can be input as a single number, in  which case a single calculation of the S/N for this time will be performed or as a range (for example, 10-100) in which case the S/N will be calculated for the whole range and a S/N vs. time plot produced. In both cases, a pop-up window will be produced with summary of the results.
Once all the previous parameters, including exposure time and filter, have been specified or selected, you can press the "Calculate" button, that will launch the calculation itself and present the results. Depending on your OS, you might need to close the pop-up windows to perform another calculation.

The number of sky frames affects the final S/N estimate. The noise in the sky is calculated as a function of the square root of the number of sky frames i.e

sky_noise_final = sky_noise / sqrt(Nsky)

The total noise is then the quadrature sum of the sky noise and object noise. Which is essentially like saying, the more skies you observe, the better you will be able to remove the sky.

No sky frame implies that reduction is as good as taking one single sky frame.

 

Spectroscopy

These parameters are only relevant for an estimation of the S/N expected for a  spectroscopy measurement. The exposure time can be input as a single number, in which case a single calculation of the S/N for this time will be performed or as  a range (for example, 10-100) in which case the S/N will be calculated for the  whole time range, as the median S/N over the whole spectra. In both cases, a pop-up window will be produced with a summary of the results, along with a plot of S/N vs. wavelength and normalized flux vs. wavelength. The slit width must be input in arcseconds.
 
Once all the previous parameters, including exposure time and filter, have been specified or selected, you can press the "Calculate" button, that will launch the calculation itself and present the results. Depending on your OS, you might need to close the pop-up windows to perform another calculation.
The number of sky and object frames are the number of on and off target images taken, using the exposure time provided. It is assumed that the frames are averaged.
The number of sky frames affects the final S/N estimate. The
noise in the sky is calculated as a function of the square root of the number of sky frames i.e

sky_noise_final = sky_noise / sqrt(Nsky)

The total noise is then the quadrature sum of the sky noise and object noise. Which can be essentially summarised as: the more skies you observe, the better you will be able to remove the sky.

No sky frame implies that reduction is as good as taking one single sky frame.

N.B: Resolutions for the different filters: Res(J)=5000, Res(H)=4500, Res(K)=4000

 

Output

The results of the ETC are split up into 5 sections. The first three (Source, Observation and Observing Conditions) summarise what you have put into the ETC.

The Telescope and Instrument section detail some of the useful parameters that the ETC uses in its calculations.

The Results section details the S/N of the input. In photometry, three S/N calculations are displayed:

  1. S/N per pixel
  2. S/N within an aperture of 1.2*seeing
  3. S/N within an aperture of 2.0*seeing

In spectroscopy mode, the S/N is calculated per pixel and per resolution element (which is defined in the Telescope and Instrument section). In addition the median counts per resolution element for the object and sky are also returned.

There are various figures returned in spectroscopy mode:

  1. S/N per pixel as a function of wavelength [um] with the median S/N highlighted in Red
  2. Source counts (blue) and sky counts (green) as a function of wavelength [um]. Note that one of these spectra is sometimes not visible. In addition, the counts that are displayed here is the sum over several spatial pixels (within the seeing line spread function) and hence, although it may appear initially that these pixels are saturated (given the large counts), no individual pixel is actually saturated.
  3. Normalised flux as a function of wavelength [um]
  4. Response curves for the different optical systems as a function of wavelength [um]
  5. A zoom in of the overall response curve as a function of wavelength [um]
  6. A zoom out of the response curves for the different optical systems as a function of wavelength [um]