1. Science with the new HST after SM4 WFC3 slitless spectroscopy Harald Kuntschner Martin Kümmel, Jeremy R. Walsh (ST-ECF) WFC3-team at STScI and NASA

2. Science with the new HST after SM4 WFC3 Grism Parameters Disperser Channel Wavelength Resolution* Å/pixel Tilt X Length range (Å) (deg.) (pix) G280 UVIS 2000-4000 70@3000 Å 13 -2.8 250 G102 IR 7800-10700 + 210@10000 Å 25 +0.6 210 G141 IR 10500-17000 + 130@14000 Å 47 +0.3 130 *Resolution based on FWHM of Gaussian core in cross-dispersion direction X Tilt to positive X axis + Limits at 2% transmission

3. Science with the new HST after SM4 WFC3-IR G141 Ground calibration; simulated single point source 1014 pixel (full size) ~130 arcsec detector defects Combined white light + direct image Target position on direct image 0th order +1st order Science 1.1 -1.7mu +2nd order+3rd order

4. Science with the new HST after SM4 WFC3-IR G141 trace and dispersion calibration Linear trace solutions (but 2-dim variations) Linear dispersion solutions with rms < 5 Å Dispersion: 46.9 Å/pixel (130 pixel length) 2-dim solution varies from 45 to 48 Å/pixel * Data points omitted in fit due to wavelength shift caused by steep sensitivity decline dispersion

5. Science with the new HST after SM4 WFC3-IR G141 Throughput +1st order –Peak efficiency of ~40% at 1420 - 1640nm –Good sensitivity range: 1120 - 1660nm +2nd order –Efficiency < 6% 0th order –Efficiency < 1.5% 0th +1st +2nd +3rd

6. Science with the new HST after SM4 WFC3-IR G102 Ground calibration; simulated point source Target position on direct image 0th order +1st order Science 0.8 - 1.1mu +2nd order 1014 pixel (full size) ~130 arcsec detector defects Combined white light + direct image

7. Science with the new HST after SM4 WFC3 G102 Trace and Dispersion Similar to G141 linear trace and dispersion relations well reproduced by a simple 2-dim solution Dispersion 24.6 Å/pixel (210 pixel length in +1st order) 2-dim solution ranging from 24.0 - 25.5 Å/pixel

8. Science with the new HST after SM4 WFC3-IR G102 Throughput +1st order –Peak efficiency of ~30% at 960 - 1120nm –Good sensitivity range: 840 - 1140nm +2nd order –Efficiency < 5% 0th order –Efficiency < 1.5% 0th +1st +2nd

9. Science with the new HST after SM4 WFC3-UV G280 0th order +1st -1st 4096 pixel (full size) 160 arcsec +2nd -2nd Combined monochromator steps +1st +2nd +3rd Order overlap Higher orders 200nm 330nm 0th

10. Science with the new HST after SM4 WFC3-UV G280 Trace: 5th order polynomial fits Dispersion: 4th order polynomial needed to achieve good fit (rms ~ 0.2 pixel) ~13 Å per pixel At least +8 to -8 orders visible Order overlap between +1st and +2nd beyond ~380nm Heavy order overlap for > +2 orders Trace

11. Science with the new HST after SM4 WFC3-UV G280 Throughput 1st order –Peak efficiency of 24% at 240nm –'Good' sensitivity range: 200 - 330nm 2nd order –Efficiency < 2% 0th order –Efficiency equal to first order at 330nm and rising +2nd +1st 0th -1st -2nd 0th order dominates

12. Science with the new HST after SM4 Limiting magnitudes V-band detection limits for point source, 1-hour exposure and S/N=5 See Instrument Handbook See also posters by Kümmel et al. and Pirzkal et al.

13. Science with the new HST after SM4 How to design observations? F150W and IR G141 with M51 image, galaxy images and Gaussians (for HII regions and stars) Simulated direct image Simulated dispersed image

14. Science with the new HST after SM4 See poster by Kümmel et al. The simulation package aXeSIM PYRAF package (ST-ECF Webpage, STSDAS in ~Jul ‘08) designed and supported at ST-ECF One command to run full multi-object simulation – simdata Simple object shape and spectra as built-in defaults Produces associated direct image (opt.) Performs default extraction of simulated spectra (opt.) Adds noise (opt.)

15. Science with the new HST after SM4 UDF simulations Direct image Dispersed image F160W < 23.0, “noise free” simulation to show 2-dim distribution UV G280 - subarray, not to scale

16. Science with the new HST after SM4 Extraction software ST-ECF offers a semi-automatic extraction software (aXe) to extract fully calibrated 1-dim spectra from WFC3 grism observations; including contamination estimates The software is already successfully being used for ACS grisms since 2003 Available as part of STSDAS and from ST- ECF Web pages http://www.stecf.org/

17. Science with the new HST after SM4 Summary Highly efficient and well behaved IR grisms Open up wavelength not accessible from the ground! Challenging UV grism (order overlap, bent traces, strong 0th order…) Software support with 2-dim simulation and data extraction packages, as well as general user support and calibration reference files available from ST-ECF (http://www.stecf.org/) Existing, good experience with ACS grisms and NICMOS HLA project