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The STIS NUV-MAMA objective prism … … and looking beyond for HST UV slitless spectroscopy

The STIS NUV-MAMA objective prism … … and looking beyond for HST UV slitless spectroscopy. Jes ú s Ma í z Apell á niz HST Calibration worskhop 26 October 2005. Outline. The STIS objective prism Description Calibration problems MULTISPEC Calibration Flux calibration

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The STIS NUV-MAMA objective prism … … and looking beyond for HST UV slitless spectroscopy

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  1. The STIS NUV-MAMA objective prism……and looking beyond for HST UV slitless spectroscopy Jesús Maíz Apellániz HST Calibration worskhop 26 October 2005

  2. Outline • The STIS objective prism • Description • Calibration problems • MULTISPEC • Calibration • Flux calibration • Time-dependent sensitivity • Slitless UV spectroscopy with HST

  3. The STIS objective prism NUV FUV

  4. The standard star HS 2027 +0651 with the STIS objective prism 1200 2125

  5. A crowded field with the STIS objective prism

  6. Calibration issues • Sources • Difficulty of wavelength calibration • Lack of “repeatability” (~10%) • Diagnostic • Coupling between wavelength and flux calibration: positioning and geometric distortion are crucial • Strong count gradient @ 3300 Å: PSF effects • TDS effects • Solution • Flux recalibration and geometric distortion solution • Ad-hoc solution for  > 3000 Å • TDS correction

  7. Flux calibration of the objective prism

  8. Calibration issues • Sources • Difficulty of wavelength calibration • Lack of “repeatability” (~10%) • Diagnostic • Coupling between wavelength and flux calibration: positioning and geometric distortion are crucial • Strong count gradient @ 3300 Å: PSF effects • TDS effects • Solution • Flux recalibration, separation by settings (1200 and 2125), and geometric distortion solution • Ad-hoc solution for  > 3000 Å (low precision) • TDS correction

  9. MULTISPEC • Slitless-spectra automatic-extraction IDL code • Profile fitting (with or without residuals) • Requires: • Spectral exposure (objective prism, grism, grating) • Image of the field (two filters) • Image photometry (using e.g. DAOPHOT) • Optional multiple orientations • Calibration files (ready for STIS objective prism) • See http://www.stsci.edu/~jmaiz

  10. Original measured/reference values

  11. Sensitivity correction and TDS solution

  12. New measured/reference values

  13. Summary of precisions • Fit to centered isolated stars: 1 % ( < 3000 Å) 10 % ( > 3000 Å) • Flat-field and variations of the intensity profile across the detector: 3-5 % (lower for isolated stars and dithered data) • Detector: only Poisson (no read noise) • Background: case-dependent but negligible for bright stars • Contamination from nearby spectra: case-dependent

  14. Slitless UV spectroscopy with HST • STIS: • Slitless and 52x2 datasets in the archive (prism, G140L, G230L) • Will STIS become a born-again instrument? • ACS: • HRC (1 objective prism): PR200L • SBC (2 objective prisms): PR110L + PR130L • Possible problems: • Wavelength and flux calibration: yes for prisms (especially PR200L) • Strong count gradient: minor issue for PR200L • TDS effects: yes for SBC, not for HRC (but CTE) • Ongoing calibration programs: • Observations of standard stars with very different spectral slopes and emission line objects (10391,10743) • Observations of crowded, UV-bright clusters (10722, 10736)

  15. A crowded field with ACS/SBC PR130L

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