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Welcome to the Exposure Time Calculator for the HabEx coronagraph and starshade.  The Habitable Exoplanet Observatory (HabEx) is a concept for a mission to directly characterize planetary systems around nearby Sun-like stars, and enable a broad range of general astrophysics and solar system science in the UV through near-IR.   HabEx is one of four mission concepts currently being studied in preparation for the 2020 Astrophysics Decadal Survey.

(Skip this introductory material and go straight to the ETC interface here.)

A noise model for the HabEx coronagraph and starshade instruments has been developed for studying the potential of spectroscopic observations of exoplanets, with characteristics representable by various Solar System planet templates.   The noise model adopts a set of parameters for the instruments and the 4-m diameter telescope under study, which is described at JPL's HabEx mission pages.  Access to the ETCs for the UV Spectrograph (UVS) and HabEx Workhorse Camera (HWC) can be found at JPL's HabEx Instruments page.

The noise model is described by Robinson, Stapelfeldt, & Marley (2016).

For questions about the ETC, contact us here.  For questions about HabEx science or mission design, study scientists can be contacted here

 

HabEx Exposure Time Calculator

Run the time estimator

1.  Select between the Coronagraph or Starshade,  and available planetary albedo and host star templates.  Additional spectra will be added.  (Contact us for urgent requests.)

2.  Set the desired values for each of the planetary radius, stellar effective temperature (if using the blackbody representation) and radius, orbital seperation, distance to the system, exozodiacal emission level (a scaling of the solar zodiacal emission assumed to have a constant V-band surface brightness of 23 mag arcsec-2), and the desired signal-to-noise ratio.  SNRs is the spectroscopic SNR that is used to calculate the integration time per resolution bin; SNRb is a visible-range SNR for broad-band detection.

Tips:

  • The radiation incident on the planet includes a solar equivalent flux scaling for the host star templates by spectral type.  This effectively scales the input planetary distance from the star Rp(eff) = Rp (L*/Lsun)½ so that the planet receives the solar constant 1361 W m–2 of normal-incidence flux.  Bolometric luminosities L* are from Pecaut & Mamajek (2013, ApJS, 208, 9).
  • If "Blackbody" is selected for the host star, the SED is computed using a Planck function at the temperature Tbb, radius Rs, and distance d.  The parameters Tbb and Rs have no effect when a stellar template is selected.   No solar equivalent flux correction is applied to the blackbody curve.
  • The integration times are computed at the baseline instrument spectral resolutions: 
    • 0.2 - 0.45 µm:  R(NUV) = 7 (starshade only)
    • 0.45 - 1.0 µm:  R(VIS) = 140 (both instruments)
    • 0.975 - 1.8 µm:  R(NIR) = 40 (both instruments)
  • The planet-star phase angle is currently fixed to quadrature.
  • Hovering with your mouse over the parameter text will bring up a tooltip indicating the allowable ranges. 

View the results

When your configuration is submitted, the planetary albedo and the amount of time required to reach the desired SNRs are plotted with wavelength.  The integration time needed for broad-band detection at SNRb is indicated on the integration time plot.

Tips:

  • Excessively high exposure times can result from absorption or "black" regions of the input planetary albedo spectrum.  When this happens, the ordinate is set to a default maxiumum of 2500 hours but can be zoomed out.
  • Some configurations can lead to a portion of the spectrum falling inside the inner working angle (IWA) or outside the outer working angle (OWA) of the instrument (see JPL's instrument page).  A warning will appear when this occurs.
  • Exposure times will be plotted as zero when speckle subtraction is ineffective (the system background is high compared to the planet count rate), or the SNR goal is too high, and the planet cannot be detected regardless of integration time.  (See Sec. 2 in Nemati, Krist, & Mennesson 2017).
  • Hovering with your mouse on the plots will bring up a set of tools near the top of the plot space, allowing you to pan and zoom, or send the plot to the cloud in the Plotly package by clicking on the disk icon to edit the contents, scale the axes, and so on.

Save the output

The output can be downloaded as a CSV file to your disk.   The table columns appear as follows:

column name explanation unit
A Planetary albedo at the instrument resolution n/a
csp speckle count rate s–1
cT telescope thermal count rate s–1
ctot total count rate s–1
cR read noise count rate s–1
cC charge count rate s–1
Fs Stellar flux at the instrument resolution W m–2 µm–1
cRatio planet/star contrast ratio n/a
cD dark current count rate s–1
lam wavelength µm
cp planet count rate s–1
cz solar zodiacal emission count rate s–1
cez exozodiacal emission count rate s–1
dlam wavelength bin interval µm
DtSNR exposure time required to reach goal SNR per spectral resolution bin h
cnoise noise count rate s–1

The integration time for broad-band detection at SNRb is reported on the integration time plot, but is not saved in the CSV file. 

You can also save and edit the plot on the cloud using the disk icon that will appear when you hover your mouse over the plot. 

Last update:  noise model v2.2  11 Dec 2018.