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High Altitude UBV Observations E.Giraud, I.Toledo, P.Valvin & G.Vasileiadis LPTA/Montpellier, Un.Cath Chile G.Vasileiadis, CTA Meeting 4-5 May-2006 Outline •Physics Motivation •The Instrument •The Method •La Silla/Alma Datasets •In retrospective G.Vasileiadis, CTA Meeting 4-5 May-2006 2 Physics Motivation • Measure Night Sky Parameters relevant to Cherenkov Telescopes • • Extinction Parameter Night Sky Background • Photometry of Night Sky at High Altitude (4-5Km) • • • Thinner Atmosphere Clearer skies LaSilla/Hawaiian reference measurements (4300m) • U,B and V measurements Whats the gain for going higher ?! G.Vasileiadis, CTA Meeting 4-5 May-2006 3 The Instrument / Telescope Custom Newtonian 10” Optical Guidance Systems F/4 UV custom coated mirrors Takahashi EMT-200 mount CCD ST7-XME SBIG FOV 22x15arcmin 1.7arcsec/pixel (9mm) Johnson UBV filter set. Transportable (45kilos) G.Vasileiadis, CTA Meeting 4-5 May-2006 4 The Method / Photometry Photometry Using known Luminosity stars as reference Landolt Photometric Star Fields used Standard Johnson U, B, V Filters Choice Calibrate on a well-known site (La Silla ) Measure the extinction as a function of azimuth angle during photometric nights, mainly in U Measure the sky background, mainly in U, directly on standard fields G.Vasileiadis, CTA Meeting 4-5 May-2006 5 La Silla Datasets La Silla Site at 2400m. Camped outside EROS-II Telescope. Extinction Dataset using a standard star. Luminosity measurements using U V and B filters. ( 8 nights) Dataset using two distinctive Landault star fields for Color equations and Sky Background. All Data used as “Calibration” Comparison with known measurements G.Vasileiadis, CTA Meeting 4-5 May-2006 6 ALMA Site Whatever follows done with the ALMA Logistics Support. Medical Support All Night Radio Connection Escorted to and from Site area Jacques Lasalle (Site Security Manager) G.Vasileiadis, CTA Meeting 4-5 May-2006 7 The ALMA Site / APEX (5062m) a Source G.Vasileiadis, CTA Meeting 4-5 May-2006 8 The Alma Site 4000m and 5000m •Two periods Nov 2005 and April 2006 •4 nighs at 4000m •4 nights at 5000m • -8 degrees temperatures •Almost safe conditions •All battery Operated •UBV using std Landolt Star fields •Direct comparison with La Silla G.Vasileiadis, CTA Meeting 4-5 May-2006 9 The data Standard stars used as reference G.Vasileiadis, CTA Meeting 4-5 May-2006 10 The data Preliminary analysis shows ~0.1mag/airmass increase in detected light between 2400 and 4000 m (slope of Bouguer Curve) Slopes : 0.43 and 0.33 mag/airmass Extinction Parameter Calculation for LaSilla and Alma G.Vasileiadis, CTA Meeting 4-5 May-2006 11 The data Preliminary analysis shows a net benefit in detected light between 2450m and 5000m for any air mass (close to a magnitude for high airmass) Transparency figure LaSilla : 0.43 mag/airmass Alma4K : 0.33 Alma5K : 0.26 G.Vasileiadis, CTA Meeting 4-5 May-2006 12 In Perspective • Succeed on having good data on La Silla and some nights at 4000m and 5000m (ALMA site) • Promising Results • Net Gain on Extinction Parameters for the U • NSB comes in the near future – Already we see the limit of our CCD ( square star pattern) • Keep Contact with ESO-ELT and Univ.Catholica Santiago/Chile. G.Vasileiadis, CTA Meeting 4-5 May-2006 13