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The HST/STIS Next Generation Spectral Library

The HST/STIS Next Generation Spectral Library. Michael Gregg, U.C. Davis/IGPP-LLNL David Silva, ESO (NOAO) John Rayner, IfA Guy Worthey, Washington State F. Valdes, A. Pickles, J. Rose, B. Carney, W. Vacca. NGSL Proposed:.

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The HST/STIS Next Generation Spectral Library

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  1. The HST/STISNext Generation Spectral Library • Michael Gregg, U.C. Davis/IGPP-LLNL • David Silva, ESO (NOAO) • John Rayner, IfA • Guy Worthey, Washington State • F. Valdes, A. Pickles, J. Rose, B. Carney, W. Vacca

  2. NGSL Proposed: • Snapshot program to produce a UV/Optical stellar spectral atlas of 600 stars • STIS Low Resolution modes: G230LB, G430L, G750L • High S/N • Stable HST calibration • Good coverage of L, Teff, log(g) with 150 stars in each of 4 abundance intervals: [Fe/H] < -1.5 -1.5 < [Fe/H] < -0.5 -0.3 < [Fe/H] < 0.1 [Fe/H] > 0.2

  3. NGSL Realized: • Cycle 10: 300 snapshots, 156 observed • Cycle 12: 450 snapshots, 208 observed • Cycle 13: 450 snapshots, 17 observed • Total of 380 targets

  4. Final Sample

  5. Example NGSL Spectra

  6. Metallicity Comparison

  7. NGSL Calibration Challenges • No Wavecals (on purpose) • E1 Aperture, 0.2” slit • Fringing • G230LB Red Light Contamination • $%&# Fits Table Format

  8. No Wavecals • All targets have known V_rad • Cross correlate to find SHIFTA1 • Shift to published V_rad • De-redshift • $%&# Fits Table Format

  9. E1 Aperture, 0.2” slit • Absolute calibration • Relative calibration between gratings • Mis-centered observations • $%&# Fits Table Format

  10. Flux Calibration Comparison

  11. Flat Fielding / Fringing • Modified versions of CALSTIS routines • Flux calibration would be improved by using flats to take out high order response at blue end of G750L • Fringe removal is improved by subtracting scattered light from fringe flat

  12. G230LB Red Light Contamination • Zeroth order image wings overlap G230LB blue end • FOS had similar (but different) trouble • Affects bright red targets the most

  13. Rising red light contamination

  14. Example correction

  15. G230LB Contamination: • Not a DC correction as for FOS • Contamination increases to the red => important components besides zero order image • Sloping straight line scaled to V magnitude works over limited color range • Need to develop sophisticated correction

  16. What’s Coming... • G430L + G750L release • UV addition • Fill out red giants & dwarfs from HST archive • Add far UV from HST & IUE archive • VLT/UVES extension • IRTF/SPEX extension • Interpolated, semi-empirical spectral library

  17. Text

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