Sky Background Measurements atLos 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 backgroundin 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 toactual 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 degP

MT

+H

E

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

] 0.5

mV

/div

Time [sec]

The following measurements were taken at PinoTorinese Astronomical Observatory using the 1.05 mREOSC telescope. The two graphs show the differentresponse of the PMT to orange, white and blue stars.

Telescope data:

primary mirror diameter 1050 mmfocal lenght 9943 mmimage 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

200 300 400 500 600 700 800

nm

tras

mis

sio

nUG1

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

tive

mag

nit

ud

e (V

ega=

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

tive

mag

nit

ud

e (V

ega

=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 Filteradapters, 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

2.0V

out [

volt]

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

1.866V

out [

volt]

1m

V/d

iv.

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

1.8V

out [

volt]

Time [sec]

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

No Filter

MUG2 Filter - Alfa Centauro and BackgroundDifferent 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 α-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/µs/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 α-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/µs/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 α-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.