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Measurements of the Diffuse night sky brightness

Measurements of the Diffuse night sky brightness

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Measurements of the Diffuse night sky brightness

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  1. Measurements of moonless night sky brightness Measurements of background pointing to a mountain IASF/CNR Palermo Research staff Mechanical and electronics staff G. Agnetta B. Biondo G. Gugliotta A. Mangano F. Russo. O. CatalanoG. Cusumano T. Mineo Measurementsof theDiffuse night sky brightness

  2. The experiment • 4 cylindrical aluminium cases • 2 PMTs per cylindrical aluminium case • 1 filter per each couple of PMTs • 1 light collimator for each PMT giving 5.7° of angular aperture. • Single photoelectron counting and charge integration • < 15 ns double pulse resolution

  3. PMT • 8 PMTs R3878 Hamamatsu • QE ~ 16 %at 400 nm • Sensitive area ~ 38 mm2 • Effective solid angle 4.3°

  4. Filters • Narrow band @ 337 nm ~ 30 % of transmitting efficiency • Narrow band @ 391 nm ~ 40 % of transmitting efficiency • Wide band BG1 (280-500nm) ~ 80 % of transmitting efficiency • Narrow band @ 357 nm ~ 30 % of transmitting efficiency • Wide band U300 (250-400 nm) ~ 80 % of transmitting efficiency

  5. U300 391 nm 337 nm BG1 357 nm Filter transmission efficiency

  6. The Situs: Piano Battaglia Observing level 1500 m a.s.l. Mountain distance 700 m

  7. Measurements with narrow band filters • For measurements with a narrow-band filter the measured count rate is directly converted into a photon flux by: • F(l)= R / (A eff T(l) ePMT (l) dl) • where : R = measured counting rate • A = photocatode entrance area • eff = effective solid angle of the baffled tube • T(l) =filter transmission • ePMT (l) = photomultiplier efficiency Assuming the spectral distribution of the light is constant over the width of the filter response

  8. Measurements with wide band filters and no filter For measurements over a wide wavelength interval, the count rate is converted into a photon flux by: F(l)= R / (A eff< eDet >) where : < eDet > is the efficiency of the detector, weightd with the input spectrum S(l ): < eDet > = l1, l2S(l )T(l)ePMT(l)dl withl1, l2S(l )dl = 1

  9. S(l ) is the spectrum of night sky in arbitrary units

  10. Measured Flux (ph m-2 s-1 sr-1)

  11. 0.39 Mountain / sky ratio 0.27 0.35 337 nm 357nm 391 nm Narrow band Filters

  12. 0.68 No Filter (300-650 nm) Mountain / sky ratio 0.48 BG1 (300-500 nm) 0.22 U300 (300-450 nm) 300 450 500 600 (nm) Wide Band Filters