Sky Background Measurements at Los Leones

C.B.Bonifazi1,3, D.V.Camin 6, P.F.Gomez Vitale 4, V.Grassi6, M.Lantz 3, M.Lapolla 6, M. Santander 2,5, M.Santarrosa 2,5,

A.Risi 2,5, D.Rodriguez 3, V.Scherini6, G.Sequeiros 5

1-Laboratorio Tandar, CNEA

2-Museo de Ciencias Naturales de San Rafael

3-Universidad Nacional de Buenos Aires

4-Universidad Tecnologica de Mendoza

5-Universidad Tecnologica de San Rafael

6-Universita’ di Milano/INFN

Instrumentation

• Two PMT’s XP2012 + Head Electronics

• High resolution volmeter HP34401 + GPIB bus

• Lab View software driver + DAQ on laptop

• Telescope with 15 cm diam. mirror - f/8

• MUG2 and HiRes UV Filters

Measurements done at :

• Buenos Aires (Top of Tandar Lab building)

• San Rafael (Observatory of Natural Science Museum)

• Auger site, at Los Leones

Targets

• A star (Alfa Centauro)and its nearby background in three different places: BsAs, SR, Los Leones

• Background, looking NO at Los Leones• Zenit with the telescope and with an open PMT.

Scaling our measurements to actual FD size

Auger:

• FD mirror area - camera area = 3 m2

• Aperture 2.25 deg2

Telescope:

• Mirror area = 1.77 10-2 m2

• Aperture 2.34 deg2

Scaling factor: 163

Scaling the directly exposed PMT

• Photocathode area : 8.10- 4m2

• Scaling Factor :

3m2 x5.38 10-4str / 8 10-4 m2 / 2.37sr

SF= FD/PMT = 0.85

103 deg

PM

T+

HE

Square wave on LED illuminating the PMT

400 450 500 550 6001.6330

1.6335

1.6340

1.6345

1.6350

0.035 phel/100ns=56fA

Vou

t [V

] 0.

5mV

/div

Time [sec]

The following measurements were taken at Pino Torinese Astronomical Observatory using the 1.05 m REOSC telescope. The two graphs show the different response of the PMT to orange, white and blue stars.

Telescope data:

primary mirror diameter 1050 mm focal lenght 9943 mm image scale 20.7 arcsec./mmlinear obstruction 60% http://www.to.astro.it/Services/services.html

PMT

FILTER WHEEL

Preliminary measurements at Torino Astronomical Observatory

The UV filter was provided by the observatory in the filter wheel, it is a U band filter from the UBVRI system made of 3 filters superimposed.The spectral response is given below.

U filter

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200 300 400 500 600 700 800nm

tra

sm

iss

ion

UG1

BG18WG225

Total

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

-1.00.01.02.03.04.05.06.0

Visual magnitude

rela

tiv

e m

ag

nit

ud

e (

Ve

ga

=0

)Pino Torinese no filter

Star spectra:blue (B)white (A)orange (K)red (M)

Relative mag.= -2.5log(i/i0) i0: PMT current from Vega

Note that the departure from the straight line is due to the higher weight of the background for fainter stars.

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

-1.00.01.02.03.04.05.0

Visual magnitude

rela

tiv

e m

ag

nit

ud

e (

Ve

ga

=0

)

A0

A0

B3

A0

B5 Star spectra:blue (B)white (A)

Pino Torinese U filter

Orange and red stars give too low signals to be measured

Preparing Telescope, PMT and Filter adapters, etc...

Alfa Centauro - MUG2 Filter - Los LeonesTelescope Measurement

0 100 200 300 400 500

1.856

1.857

1.858

1.859

1.860

1.861

1.862

Vou

t [vo

lt] 1

mV

/div

.

Time [sec]

Star ( 0.253 phel/100ns = 405 fA)

Background(0.044 phel/100ns = 70 fA)

Alfa Centauro - MUG2 Filter - Los LeonesSignal scaled to Auger

0 100 200 300 400 5000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Vou

t [vo

lt]

Time [sec]

Background

Star

Dark level

Alfa Centauro - HiRes Filter - Los Leones

-50 0 50 100 150 200 250 300 350

1.856

1.857

1.858

1.859

1.860

1.861

1.862

1.863

1.864

1.865

1.866

Vou

t [vo

lt] 1

mV

/div

.

Time [sec]

Star (0.252 phel/100ns = 403 fA)

Background (0.039 phel/100ns = 62 fA)

Zenit - MUG2 Filter - Los LeonesPMT directly exposed

0 50 100 150 200 2500.6

0.8

1.0

1.2

1.4

1.6

1.8

Vou

t [vo

lt]

Time [sec]

Background (10 phel/100ns)Auger scaled: 8.5 phel/100ns

No Filter

MUG2 Filter - Alfa Centauro and Background Different places

-100 0 100 200 300 400 5001.880

1.885

1.890

1.895

Los Leones San Rafael Buenos Aires

Vou

t [V

],0.5

8 ph

el/1

00 n

s/ d

iv

Time [sec]

Results scaled to Auger FD prototype[phel/100 ns]

Alfa Centauro - Background

Without Filter MUG2 Filter HiRes Filter

Mean Sigma Mean Sigma Mean Sigma

Buenos Aires 585 18 31 3 - -

San Rafael 505 45 37 4 44 4

Los Leones 385 28 34 3 35 4

Background

Without Filter MUG2 Filter HiRes Filter

Mean Sigma Mean Sigma Mean Sigma

Buenos Aires 1471 45 200 10 - -

San Rafael 120 12 26 2 32 3

Los Leones:

- near -Centauro

- Zenit

- NO, 30 deg

- open PMT to Zenit

35

92

-

117

2.4

9

-

4

7.1

3.7

6.9

8.5

0.8

0.4

0.7

0.5

6.3

4.3

6.3

-

0.3

0.4

0.4

-

Background results scaled to Auger FD prototype[ph/s/m2/deg2]

( quantum efficiency = 20 %)conservative value

Without Filter MUG2 Filter HiRes Filter

Mean Sigma Mean Sigma Mean Sigma

Buenos Aires 11000 330 1500 75 - -

San Rafael 890 90 250 25 260 26

Los Leones:

- near -Centauro

- Zenit

- NO, 30 deg

- open PMT to Zenit

260

680

-

870

18

68

-

30

53 *

27

51*

63

6

3

5

4

47

32

47

-

2

3

3

-

*) Most significative values for Auger.

- 30 % larger than HiRes’ 40 ph/us/m2/deg2.- 14 % larger noise.

Background results scaled to Auger FD prototype[ph/s/m2/deg2]

( quantum efficiency = 25 %)acccording to Philips data sheet

Without Filter MUG2 Filter HiRes Filter

Mean Sigma Mean Sigma Mean Sigma

Buenos Aires 8800 264 1200 60 - -

San Rafael 712 72 200 20 208 21

Los Leones:

- near -Centauro

- Zenit

- NO, 30 deg

- open PMT to Zenit

208

544

-

696

14

54

-

24

42 *

22

41*

50

5

2.5

4

3

38

26

38

-

1.5

2.5

2.5

-

*) Most significative values for Auger.

- confirms HiRes’ 40 ph/us/m2/deg2 alsofor the southern site.