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

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Outline

•Physics Motivation•The Instrument•The Method•La Silla/Alma Datasets•In retrospective

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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 ?!

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The Instrument / Telescope

Custom Newtonian 10” Optical Guidance SystemsOptical Guidance Systems

F/4 UV custom coated

mirrors Takahashi EMT-200

mount CCD ST7-XME SBIG FOV 22x15arcmin 1.7arcsec/pixel (9m) Johnson UBV filter set. Transportable (45kilos)

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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

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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

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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)

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The ALMA Site / APEX (5062m)

Source

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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

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The data

Standard stars used as reference

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The data

Extinction Parameter Calculation for LaSilla and Alma

Preliminary analysis shows Preliminary analysis shows ~0.1mag/airmass increase in ~0.1mag/airmass increase in detected light between 2400 detected light between 2400

and 4000 mand 4000 m

(slope of Bouguer Curve)(slope of Bouguer Curve)

Slopes : 0.43 and 0.33 mag/airmass

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The data

Preliminary analysis shows a net Preliminary analysis shows a net benefit in detected light between benefit in detected light between

2450m and 5000m for any air 2450m and 5000m for any air mass (close to a magnitude for mass (close to a magnitude for

high airmass)high airmass)

LaSilla : 0.43 mag/airmass

Alma4K : 0.33

Alma5K : 0.26

Transparency figure

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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.