Euclid slitless calibrations

Jeremy R. WalshHarald Kuntschner

Martin KümmelSpace Telescope European Co-ordinating Facility, ESO

Slitless Spectroscopy• HST NICMOS, ACS and most recently WFC3

provided slitless spectroscopy• WFC3 has similar λ coverage to Euclid 0.8-1.7µm• Typical features: • Spectra of all objects in field → contamination• Multiple orders • Individual λ zero points → require direct image to

determine

WFC3 G141 (1.1-1.7µm) slitless image

WFC3 G141 point source spectrum

Calibrations for slitless spectroscopy

1. Wavelength – dispersion and zero point2. λ-dependent flat field 3. Sensitivity (flux calibration)4. Dispersed sky background

Wavelength calibration• Compact Galactic planetary nebulae provide

excellent sky wavelength calibration sources• Expect that dispersion solution varies across field

→ calibrate with multiple sources• Map transfer of zero point

Wavelength error budget• In order to achieve Δλ/λ ≤ 0.001 for measurement

of emission lines. Following systematics to control:• Dispersion solution variation across field• Estimation of object positions on direct image • Transfer of wavelength zero point to grism image• Determination of emission line position

Flat fielding

• Any pixel can receive any λ so require a flat field cube

• On ground construct mono-chromatic flat fields then fits as function of λ for flat field cube

• In-orbit correct for large scale illumination with rastered star field (L-flat)