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Warning : talk deals with bottom rungs of Drake’s Ladder, where, sadly, sexiness is low

STIS N eutral D ensity Filters: Bridging STIS’s ND Desert T.R. Ayres (CASA) C.R. Proffitt (CSC). Warning : talk deals with bottom rungs of Drake’s Ladder, where, sadly, sexiness is low. The Cosmic Sexiness Ladder.

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Warning : talk deals with bottom rungs of Drake’s Ladder, where, sadly, sexiness is low

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  1. STIS Neutral Density Filters:Bridging STIS’s ND Desert T.R. Ayres (CASA) C.R. Proffitt (CSC)

  2. Warning:talk deals with bottomrungs of Drake’s Ladder, where, sadly, sexiness is low The Cosmic Sexiness Ladder However, nothing on upper rungs would get done without good instrument calibrations CALIBRATION

  3. ND Desert Project STIS MAMA Global Count Rate ceiling (200,000 cps) imposes severe caps on S/N of bright objects: <10 cps resol-1 vs. 700 for Local Count Rate limit 0.2x0.2 0.2x0.09 0.2x0.06 0.1x0.03 ND DESERT 0.2x0.05ND 0.3x0.05ND Worse, if echelle setting just exceeds GCR limit w/ smallest clear aperture, have to use 0.2x0.05ND2: 50xexposure time penalty

  4. l l l l l l l l l l l * (105 cps)

  5. STIS “Hidden” Options to Rescue Usefully, there are three “available, but unsupported” aper’s in STIS slit wheel that cover the intermediate Neutral Density range: NDA (0.6), NDB (1.0), and NDC (1.3) These slits are tall: 31”x0.05”; normal echelleaper’s are only 0.1”-0.3” high

  6. Cycle 19 Observing Program • Use DA-WD G191B2B to validate slit throughputs for 31x0.05NDA,B,C relative to PHOT aperture (0.2x0.2) • Take high-res (E140H) spectra of bright UV source Vega (αLyrae: A0V) to evaluate any side effects from tall slits compared w/ short 0.2x0.05ND2

  7. PHOT NDA NDB NDC Lower: Transmissions from flux ratios of spliced spectra (error bars) or total cnts order-by-order (open symbols) [connected dots: earlier estimates] ND0.6 ND1.0 ND1.4 ND2.0 Upper: E140M+E230M spectra of G191B2B with PHOT (upper curve) and NDA,B,C (lower curves)

  8. (105 cps)

  9. l l l l l l l l l l l * (105 cps)

  10. Red: ND2 (2990s) Black: NDC ( 850s) 10σ noise E140H spectra of Vega taken w/ NDC and ND2both are identical:tall slits OK for echelles(thanks to excellent image quality of STIS)

  11. OUTCOME Validation of ND tall slits for STIS echelles enabled Cycle 21 Large Treasury Project Advanced Spectral Library: Hot Stars (ASTRAL-II: 230 orbits; half completed 8/2014) and hopefully many more STIS echelle programs in future Thanks Bruce!

  12. ISSUES • ND throughputs sometimes below predictions even following peak-ups (“Breathing” effects compounded by unevenness of slit width along length?) • How to accommodate in STIS ETC, given lack of reproducibility? • Refined throughput curves based on higher S/N sources?

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