Cours M1 Signal et Bruit en Astronomie Rodrigo Ibata

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Cours M1

Signal et Bruit en Astronomie

Rodrigo Ibata

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demandes de temps télescope...

Date: September

21, 2006Category : Structure and

Dynamics of Gala xies

Proposal: F1738

OBSERVING CFHT

TIME REQUEST Semester: 2006 A

Agency: France

1. Title of the Program

(may be made publicly available for accepted proposals):

The extended

disks of galaxie s: a new galact ic component?

2. Principal InvestPostal address:igator:

Observatoire Rodrigo Ibata

de Strasbourg,

11, rue de l’Univ

ersite, F-67000

Strasbourg, France

Fax: +33 3 90 24 24 32

Phone: +33 3 90 24 23 91E-mail:

ibata@astro.u-strasbg.fr 3. Co-Investigators:

Scott Chapman

Institute: Caltech

E-mail: schapman@astro.caltech.edu Annette Ferguson

Institute: Royal Observatory Edinburgh

E-mail: ferguson@roe.ac.uk Michael Irwin

Institute: Institute of Astronomy, Cmabridge E-mail: mike@ast.cam.ac.uk Geraint Lewis

Institute: University of Sydney

E-mail: gfl@physics.usyd.edu.au Nicolas Martin

Institute: Observatoire de Strasbourg

E-mail: martin@astro.u-strasbg.fr Mustapha Mouchine Institute:

John Moore’s Univeristy, Liverpool E-mail: mm@astro.livjm.ac.uk Nial Tanvir

Institute: University of Hartfordshre

E-mail: nrt@ast.cam.ac.uk 4. Summary of the Program

(may be made pu

blicly available for accepted proposals):

We propose to use

MegaCam to obse rve M81, the near est giant spiral ga

laxy beyond the L ocal Group, reach ing

∼ 2 magnitudes belo

w the red giant b ranch (RGB) tip

to probe the stella

r populations bey ond the end of th e thin disk. If this galaxy is similar

to the Milky Way

and M31, we will uncover an inhom

ogenous, low-surfa ce brightness, exten

ded disk-like stru cture, a previous ly unknown com

ponent of galaxie s. This would have profound implicat ions for our under standing of galax y formation. How

ever, if this struct

ure is not present, we will be able to in terpret the Milky

Way and M31 de tections as being

due to their pecu liar accretion hist ory;

the requested M

egaCam data will then serve as an

excellent probe o f the halo compon ent of M81, impro ving significantly on ex tant studies of th

e large-scale struc ture of the halos of giant spirals.

5. Summary of th^Instrument e Observing RunDetector Moon (d)Requested:

Filters

Grisms

MegaPrime N/A 6

g, i

Time Req.

Service/Queue?

Queue Mode

Image Quality

Opt. LST

Min. LST

Max. LST

8 hours Queue

Regular

0.65” < IQ < 0.80”

10:00

05:00

15:00 6a. Is this a joint proposal?

NO

6b. If yes, total number of nights or hours requested

from all agencies?

—

7a. Is this a Thesis Project?

NO

7b. If yes, indicate supervisor:

—

8. Special instrum

ent or telescope requirements:

9. Scheduling constraints:

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demandes de temps télescope...

9. Justific ation of requeste d observing time an d luna r phas e Lunar Phase Justification:

Grey timeor bright time is adequate to observe these relatively bright sources.

Time J ustification : (inclu ding se eing overh ead)

^{Using th}

e Version2.9.4 ETCfor FLAMES-GIRAFFE, when

observing the CaII triplet of a template K7V star at I ∼ 16.5 with the HR21 setting (8484–9001˚A, R=16200), 31 minutesare necessary toreach S/N= 20in normalobservingconditions(seeing0^!!.8; airmass 1.3, 10days from

new moon). Thisis sufficient tomeasure velocities to an accuracy of 2 km/s and determine the intrinsic velocity dispersion of the CMa population as well as derive metallicities from the Ca tripletobservations. Including the

overheads, this means that the single MEDUSA configuration requested for eight fields correspond to 0.7 h of exposure for each field, including the overhead. The three last fields we wish to observe will require a second

MEDUSA configuration, and will therefore need 1.5 h of exposure time.

Thus, the total observation time adds up to 10.0 hours.

Calibra tion Re quest:

^Standard

Calibration

10.Rep ort on the use of ESO facilities during the last 2 years

No observing time was previously allocated.

11.Applican t’s publication

s relat ed to th e subje ct of th is application

during the last 2 years

Martin N., Ibata R., Bellazzini M., Irwin M., Lewis G., Dehnen W., 2004a, MNRAS 398, 12: A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion onto the Milky Way.

Martin N., Ibata R., Conn B., Lewis G., Bellazzini M., Irwin M., McConnachie A., 2004b, MNRAS 355, L33:

Why the Canis Major overdensity is not due to the Warp: analysis of its radial profile and velocities.

Martin N., Ibata R., Conn B., Irwin M., Lewis G., 2005a, PASA, submitted: Correcting the influence of an asymmetric line spread function in the 2-degree Field spectrograph.

MartinN., Ibata R., Conn B., Lewis G.,Bellazzini M., Irwin M., 2005b, MNRAS,submitted: A radial velocity survey of low Galactic

latitude structures: I. Kinematics of the Canis Major dwarf galaxy.

Lewis G., Ibata R., Irwin M., Martin N., Bellazzini M., Conn B., 2004, PASA 21, 371: The Canis Major dwarf galaxy.

Bellazzini M., Ibata R.,Monaco L., Martin N., Irwin M.,Lewis G, 2004, MNRAS 354, 1263: The Moon behind the finger: detection of the Canis Major galaxy in the background of Galactic open clusters.

Bellazzini M., Ibata R., Martin N., Lewis G, Conn B., Irwin M., 2005, MNRAS submitted: The core of the Canis Major structure as traced by Red Clump stars.

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Presque tous les spectrographes...

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(spectre “echelle” du Soleil)

plus rouge

plus bleu

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et les cameras...

Filtre

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...utilisent les cameras CCD...

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Les cameras CCD

Très efficaces!!!

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Les cameras CCD

Puce silicium

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Propriétés des CCDs

• CCDs optiques faites sur puce de Silicium

• ΔE = 1.2 eV entre bandes de valence et conduction

• h ν / λ > ΔE λ < 1 μm

• CCDs “minces” et “épaisses”

• Grand avantage: détecteurs à réponse linéaire et très sensibles

• Problèmes:

– bruit de lecture / temps de lecture

– difficile de fabriquer des grands détecteurs – pixels “chauds”

– “fringing”

– “traps” (pièges)

– “dead pixels” et “dead columns”

– saturation (typiquement à valeurs de 2

¹⁶

=65536) – “video pattern noise”

– “charge transfer efficiency”

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Calibration des images CCD

bias

flat

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Défauts typiques

Lignes mortes

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Défauts des CCDs

Poussière

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Rayons cosmiques

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Rayons cosmiques

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Défauts typiques

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Saturation et diffraction

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“Fringing”

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PSF (point spread function)

• PSF idéal est un disque d’Airy:

• Les obstructions dans l’instrument et l’optique rendent la PSF plus complexe

• résolution angulaire:

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“Seeing” aux télescopes ESO

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Réduction des données CCD

raw = (obj + sky x (1 + fringe)) x QE + dark + flash + bias Correction for Zero exposure Additive Systematics:

<dark> = dark + flash + bias

“Overscan” region to remove DC bias variations:

raw - <dark> - (overscn - <overscn>) = obj +sky x (1+fringe)) x QE Correction for Multiplicative Spatial Systematics (flat-fielding):

<flat> = QE + dark + flash + bias

const x (raw - <dark>) / (<flat> - <dark>) = obj + sky x (1 + fringe) Correction for Additive Spatial Systematics:

<sky> = sky x (1+fringe)

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Définition du système de magnitudes AB:

• F ν (mag=0) = 3631 Jy (pour toutes les ν)

• = 3631 x 10 ^-26 W / Hz / m ²

• F λ (mag=0) = 5.48 x 10 ⁶ /(λ[Å]) ph/s/Å/cm ²

• F λ ≈ 1000 x 10 ^{-0.4 V} ph/s/Å/cm ² (en V)

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Brillance du ciel (mag arcsec ² )

U B V R I J H K

Ciel obscur 22.8 22.5 21.5 20.8 19.3 6 nuits 21.3 20.8 20.4 19.2 Pleine

Lune

18.8 18.5 18.9 18.2 13.7 13.7 12.5

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Les CCDs comptent des photons

Distribution de Poisson

• f(k, λ) = e ^-λ λ ^k / k!

• moyenne = λ

• variance = λ

k

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Calcul du Signal sur Bruit

• Autres:

– Bruit de lecture =

– Bruit de “flat-fielding” = facteur x N sig

– Bruit de “fringing” = facteur x N ciel

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