1. G.Vasileiadis, CTA Meeting 4-5 May-2006 High Altitude UBV Observations E.Giraud, I.Toledo, P.Valvin & G.Vasileiadis LPTA/Montpellier, Un.Cath Chile

2. G.Vasileiadis, CTA Meeting 4-5 May-2006 2 Outline Physics Motivation The Instrument The Method La Silla/Alma Datasets In retrospective

3. G.Vasileiadis, CTA Meeting 4-5 May-2006 3 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 ?!

4. G.Vasileiadis, CTA Meeting 4-5 May-2006 4 The Instrument / Telescope Optical Guidance Systems  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 (9  m)  Johnson UBV filter set.  Transportable (45kilos)

5. G.Vasileiadis, CTA Meeting 4-5 May-2006 5 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

6. G.Vasileiadis, CTA Meeting 4-5 May-2006 6 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

7. G.Vasileiadis, CTA Meeting 4-5 May-2006 7 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)

8. G.Vasileiadis, CTA Meeting 4-5 May-2006 8 The ALMA Site / APEX (5062m) Source 

9. G.Vasileiadis, CTA Meeting 4-5 May-2006 9 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

10. G.Vasileiadis, CTA Meeting 4-5 May-2006 10 The data  Standard stars used as reference

11. G.Vasileiadis, CTA Meeting 4-5 May-2006 11 The data  Extinction Parameter Calculation for LaSilla and Alma 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

12. G.Vasileiadis, CTA Meeting 4-5 May-2006 12 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) LaSilla : 0.43 mag/airmass Alma4K : 0.33 Alma5K : 0.26 Transparency figure

13. G.Vasileiadis, CTA Meeting 4-5 May-2006 13 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.