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Exposure Time Calculator

Exposure Time Calculator. Perry Gee UC Davis August 13, 2007. Changes this year in the ETC . C call interface using an anonymous pipe Modifications to the sky brightness model New dark sky magnitudes Model of lunar effect on sky brightness Effects of OH emissions in Y band

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Exposure Time Calculator

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  1. Exposure Time Calculator Perry Gee UC Davis August 13, 2007

  2. Changes this year in the ETC • C call interface using an anonymous pipe • Modifications to the sky brightness model • New dark sky magnitudes • Model of lunar effect on sky brightness • Effects of OH emissions in Y band • On-going work to study the signal-to-noise properties of different filter and detector designs

  3. C and Shell calling interfaces • The ETC was written as a java servlet • ETC can now be called from a shell • Output either HTML or plain text • ETC can also be called from C through an anonymous pipe. • C interface sets the ETC parameters for each run and allows individual result values to be fetched.

  4. Study of sky dark sky brightness at various sites

  5. Study of CTIO sky brightness • We used data .9m CTIO data (ugriz) from Smith & Tucker to study sky brightness at CTIO • Data was taken at various times of the year from 2001-2005 • Around 1400 sky measurements, not taken independently. • Looked at the variation in dark sky brightness with airmass. • Studied lunar effect on sky brightness (phase, elevation, separation)

  6. Fit of sky brightness using the model from Krisciunas & Schafer 1991

  7. Fit of sky brightness as a function of lunar phase (2nd order polynomial (as in Kriciunas & Schafer 1991)

  8. UKIDDS Y data • Sky data from the UKIRT telescope was used to study Y band • Data was taken in 2005-2006 • Over 4000 sky measurements, not taken independently • Data was corrected to LSST Y1 and Y2

  9. Y dark sky vs. airmass

  10. Y sky brightness vs. lunar phase

  11. Study of signal-to-noise in Y band • The ETC is being used to study the SNR properties of different Y filter designs • OH emission in the upper atmosphere • Sky absorption in the 900-1000 nm range • Detector cutoff near 1100 nm.

  12. Proposed LSST filter set

  13. Alternative designs for Y

  14. SNR, 24 y mag AB source galaxy 400 15 sec. Exposures, sky subtracted, 1” seeing source z Y1 Y2 Y3 elliptical 0 8.42 7.20 8.42 elliptical 1 8.44 7.23 8.54 elliptical 2 8.09 7.15 8.64 spiral 0 8.43 7.21 8.40 spiral 1 7.82 7.29 7.56 spiral 2 8.34 7.20 8.45 G5V 0 8.49 7.24 8.28 G5V 1 8.42 7.21 8.44 G5V 2 7.95 7.11 8.78

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