SINFONI Exposure Time Calculator
Important notes and bug reports
Note: These tools are only provided for the technical assessment of feasibility of the observations. Variations
of the atmospheric conditions can strongly affect the required observation time. Calculated exposure times do not
take into account instrument and telescope overheads. Users are advised to exert caution in the interpretation
of the results and kindly requested to report any result which may appear inconsistent.
The SINFONI ETC is an exposure time calculator for the ESO Spectrograph for INtegral Field Observations in the Near
Infrared, SINFONI, which uses the SINFONI AO module. The HTML/Java based interface allows to set the simulation
parameters and examine interactively the model generated graphs.
The ETC programs allow easy comparison of the different options
relevant to an observing program, including target information, instrument configuration, variable
atmospheric conditions and observing parameters. The ETCs are maintained on the ESO web servers to
always provide up-to-date information reflecting the known performance of ESO instruments.
These programs provide an HTML/Java based interface and consist of two
pages. The observation parameters page presents the entry fields and
widgets for the target and reference source information, expected atmospheric conditions,
instrument configuration, observation parameters such as exposure time
or signal-to-noise, and results selection. An "Apply"
button submits the parameters to the model executed on the ESO Web server.
The results page presents the computed results, including number of counts
for the object and the sky, signal-to-noise ratios, instrument efficiencies,
PSF size etc.. The optional graphs are displayed within Java applets allowing
interactive manipulation. The results are also provided in ASCII and GIF
formats for further analysis and printing. Finally, a summary of the input
parameters is appended to the result page.
In the Target Input Flux Distribution field, you can select a spectral type and filter magnitude for the target.
Alternatively, you can choose to specify the target with a blackbody temperature (and a filter magnitude). In both
cases, the flux will be scaled to the specified magnitude in the selected band.
You can also choose to specify a single emission line instead; an analytic Gaussian, centered
on the wavelength parameter, defined by its total flux and full-width at half-maximum (FWHM) width.
The target model can be defined by the target's spectral type.
It uses a template spectrum, which is scaled to the provided magnitude and
filter. The spectral type is used to make the color correction.
All magnitudes are in the Vega system - unless otherwise indicated.
You must select the filter and filter magnitude for proper scaling of the template spectrum. Available
filters are V, J, H and K. For extended sources, the magnitude must be given per square arc second.
The geometry of the target will affect the signal to noise, since extended sources will cover a wider area of the
detector. You can either select:
If point source is chosen, the target object is assumed to be an emitter with negligible angular size. This can be
selected for objects with an angular radius of much less than the sky-projected pixel size. The reference area for
the S/N depends on the configuration:
The target object is assumed to have a uniform intensity and the S/N on the result page is given per 2 pixels of the
detector. (We use 2 pixels to obtain a square area on the sky). Note that the magnitude (or the flux for an emission
line) is always given per arcsec2 for extended sources.
- In the AO/25 mas case, the reference area is the diffraction limited core of the PSF; a disk with
radius=1.22 lambda/D, which is 70 mas for an 8 m diameter telescope observing in the K band.
- In the AO/100 mas and AO/250 mas cases, the reference area is to a disk with a radius that
encloses 50% of the object's total flux.
- In the non-AO case, the reference area is the seeing disk at the wavelength of observation. This
effective seeing is computed from the given seeing value (which refer to FWHM in the V band), using Roddier's
Extended Source (with a given area)
The source is assumed to have a uniform intensity over the given area (Ω) on the sky. Since we use 2 pixels to
obtain a square area on the sky, in this case the number of pixels in the S/N area is 2 × Ω / pixelScale2.
To obtain the S/N per arcsec2, enter Ω=1 here. Note that the magnitude (or the flux for an emission
line) is always given per arcsec2 for extended sources.
The entered separation between target and reference star refers to the value at Zenith. The ETC will scale the
given separation d(Zenith) to an effective separation d(X) at the given airmass X, using different formulas for
NGS and LGS:
Note that the AO-performance model is currently limited to effective separations d(X)≤30" in NGS mode and d(X)≤60"
in LGS mode.
Choose a value from the drop-down menu. Stars brighter than 10th mag will be dimmed to 10th mag with a neutral
density filter. Stars fainter than 17th mag do not provide significant AO correction.
- NGS: d(X) = d(Zenith) * X8/5 , d(X)≤30"
- LGS: d(X) = d(Zenith) * X3/2 , d(X)≤60"
Seeing conditions. The value refers to the FWHM of the seeing disk in V band, at observed airmass.
The seeing FWHM in V-band.
Seeing(airmass=X) is the seeing at the airmass at which the observation is performed. Use this seeing in the
phase I proposal and the OB constraints.
The values in the two seeing fields are mutually updated when one of the values changes. The field "Seeing(at
Zenith)" also depends dynamically on the airmass value. The seeing is assumed to scale with the airmass X like
this: Seeing(X) = Seeing(Zenith) * X3/5.
Angular Resolution Scale
Choose one of the three available spatial scales. Note that a pixel projects to a non-square area on the sky,
namely for pixelscale x, the size of the projection is x*x/2.
This refers to the combination of filter and grating determining the (fixed) wavelength range of observations.
The entire J, H, K or H+K band is fit onto the detector, respectively.
You must supply information about the total observation time. This can be done
in terms of DIT (Detector Integration Time), which is the duration of individual exposures,
and NDIT (Number of DIT's), which is the number of exposures. The total exposure time
is the product of DIT times NDIT. This exposure time does not take into account
instrument and telescope overheads.
Alternatively, you can specify a signal to noise ratio, in which case the ETC will compute the minimal number of
individual exposures (each of duration DIT) required to reach the requested S/N ratio.
The Signal to Noise Ratio (SNR or S/R) is defined for a point-like source
at the central observation wavelength. Indicate here a value
and choose a DIT, to get an estimate on how many exposures (NDIT) will be needed to achieve it.
The Exposure Time is the product of DIT and NDIT.
- DIT is the detector integration time (in seconds)
- NDIT is the number of exposures of duration DIT.
- INT is the total exposure time (excluding overheads). INT = DIT x NDIT
- Encircled Energy on Target:
This is the fraction of the object's total flux contained in those pixels over which the S/N is calculated, i.e.
"Number of Pixels in PSF spatial profile" on the results page.
- Strehl Ratio:
This is the peak intensity of the observed PSF to that of a perfect diffraction limited PSF.
- Version 5.1.0 (April 9, 2014)
Detector parameters updated as given in the User manual P94. The detector RON now depends on the DIT.
Added an warning appering if any pixels in the resulting spectrum exceeds the level at which
persistence may occur, see sec. 2.6 of the User Manual.
- Version 5.0.0 (July 1, 2013)
All ETC version numbers have been aligned at 5.0.0 as the ETC system infrastructure was re-factored and
installed on a new web server. Please report significant discrepancies to the ESO user support group email@example.com