Proposers to the NOAO call for NEID should use this calculator to estimate
the exposure times for their observations given a target SNR or RV precision,
and the inverse of those functions. This exposure time calculator was written
by the NEID Science Team and is based on current best-estimates for the total
system throughput as a function of wavelength, precision from the default data
pipeline, and based on template stellar spectra at vsini = 2 km/s and solar
metallicity. All throughput estimates are deliberately conservative, and there is an additional 30% margin built-in on top of this conservatism.
This calculator will be updated as better estimates of system performance
become available, and as on-sky performance is measured during commissioning.
About the NEID Exposure Time Calculator
This calculator is based on precomputed grids with parameter bounds of:
2700 K < Teff < 6600 K
3 < V-mag < 17
10 s < exptime < 3600 s
Interpolating beyond these bounds will result in errors in the returned RV values.
All calculations are based on BT-Settl synthetic stellar spectra (with
logg = 4.5 and solar metallicity), available at:
The grids use the latest NEID throughput model (R ~ 95,000 and 380 nm -
930 nm spectral coverage) and a median KPNO atmospheric transmission curve.
For RV precision estimates, we exclude regions of the spectrum with 1% or
deeper telluric features (based on TelFit model for WIYN observatory). The calculator assumes airmass 1.1 and median WIYN seeing.
SNR is reported per 1D extracted pixel. The NEID resolution element is approximately
5 pixels wide.
Note that this exposure time calculator reports only the photon noise contribution to the RV precision. This contribution must be added in quadrature to the 27 cm/s instrumental floor to determine the total measurement precision.
A python implementation of the NEID Exposure Time Calculator is available here. (https://bitbucket.org/erik_timmermann_noao/neid-etc)