Gaia - High Energy Astrophysics Group

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G
aia


A Stereoscopic Census of our Galaxy

&
Czech Participation


http://www.rssd.esa.int/Gaia

IBWS October 25
-
28,

2006



2

Gaia













Unraveling the chemical and dynamical

history of our Galaxy

3

Gaia: Design Considerations


Astrometry (V < 20):


completeness to 20 mag (
on
-
board detection)


10
9

stars


accuracy: 10

25
μ
arcsec at 15 mag (Hipparcos: 1 milliarcsec at 9 mag)


scanning satellite, two viewing directions



global accuracy, with optimal use of observing time


principles: global astrometric reduction (as for Hipparcos)



Photometry (V < 20):


astrophysical diagnostics (low
-
dispersion photometry) + chromaticity



T
eff

~ 200 K, log g, [Fe/H] to 0.2 dex, extinction



Radial velocity (V < 16

17):


application:


third component of space motion, perspective acceleration



dynamics, population studies, binaries


spectra: chemistry, rotation


principles: slitless spectroscopy using Ca triplet (847

874 nm)

4

G
aia
: Complete, Faint, Accurate



Hipparcos

Gaia

Magnitude limit

12

20 mag

Completeness

7.3

9.0

20 mag

Bright limit

0

6 mag

Number of objects

120 000

26 million to V = 15



250 million to V = 18



1000 million to V = 20

Effective distance
limit

1 kpc

1 Mpc

Quasars

None

5
x
10
5

Galaxies

None

10
6


10
7

Accuracy

1 milliarcsec

7 µarcsec at V = 10



10
-
25 µarcsec at V = 15



300 µarcsec at V = 20

Photometry
photometry

2
-
colour (B and V)

Low
-
res.
spectra to V = 20

Radial velocity

None

15 km/s to V = 16
-
17

Observing
progr
amme

Pre
-
selected

Complete and unbiased



5

Stellar Astrophysics



Comprehensive luminosity calibration, for example:


distances to 1% for ~10 million stars to 2.5 kpc


distances to 10% for ~100 million stars to 25 kpc


rare stellar types and rapid evolutionary phases in large numbers


parallax calibration of all distance indicators



e.g. Cepheids and RR Lyrae to LMC/SMC


Physical properties, for example:


clean Hertzsprung

Russell
diagrams

throughout the Galaxy


solar neighbourhood mass function and luminosity function



e.g. white dwarfs (~200,000) and brown dwarfs (~50,000)


initial mass and luminosity functions in star forming regions


luminosity function for pre main
-
sequence stars


detection and dating of all spectral types and Galactic populations


detection and characterisation of variability for all spectral types

6

One Billion Stars in 3
-
d will Provide …


in our Galaxy …


the distance and velocity distributions of all stellar populations


the spatial and dynamic structure of the disk and halo


its formation history


a rigorous framework for stellar structure and evolution theories


a large
-
scale survey of extra
-
solar planets (~10

20,000)


a large
-
scale survey of Solar System bodies (~100,000)


support to developments such as VLT, JWST, etc.



… and beyond


definitive distance standards out to the LMC/SMC


rapid reaction alerts for supernovae and burst sources (~20,000)


QSO detection, redshifts, microlensing structure (~500,000)


fundamental quantities to unprecedented accuracy:


to 10
-
7
(10
-
5
present)

7

0
0.2
0.4
0.6
0.8
1
1.2
a
cos
d
(")
1/01/00
1/01/01
1/01/02
1/01/03
1/07/00
1/07/01
1/07/02
d
(")
0
0.2
0.4
0.6
0.8
1.0
Planète :
r
= 100 mas P = 18 mois
Exo
-
Planets: Expected Discoveries


Astrometric survey:


monitoring of hundreds of thousands of FGK stars to ~200 pc


detection limits: ~1M
J

and P < 10 years


complete census of all stellar types, P = 2

9 years


masses, rather than lower limits (m sin i)


multiple systems measurable, giving relative inclinations



Results expected:


10

2
0,000 exo
-
planets (~10 per day)


displacement for 47 UMa = 360
μ
as


orbits for ~5000 systems


masses down to 10 M
Earth

to 10 pc



Photometric transits:
~5000?

Figure courtesy Fran
ç
ois Mignard

8


Asteroids etc.:


d
eep and uniform (20 mag) detection of all moving objects


10
5

10
6

new objects expected (340,000 presently)


taxonomy/mineralogical composition versus heliocentric distance


diameters for ~1000, masses for ~100


orbits: 30 times better than present, even after 100 years


Trojan

companions of Mars, Earth and Venus


Kuiper Belt objects: ~300 to 20 mag (binarity, Plutinos)



Near
-
Earth Objects
:


Amors, Apollos and Atens (1775, 2020, 336 known today)


~1600 Earth
-
crossers >1 km predicted (100 currently known)


detection limit: 260

590 m at 1 AU, depending on albedo

G
aia
: Studies of the Solar System

9

Light Bending in Solar System

Movie courtesy Jos de Bruijne

10

Satellite and System



ESA
-
only mission



Launch date: 201
1



Lifetime: 5 years



Launcher: Soyuz

Fregat from CSG



Orbit: L2



Ground station: New Norcia and/or Cebreros



Downlink rate: 4

8 Mbps



Mass: 2030 kg (payload 690 kg)



Power: 1720 W (payload 830 W)

Figures courtesy EADS
-
Astrium

11

Payload and Telescope

Two SiC primary mirrors

1.45


0.50 m
2

at 106.5
°

SiC toroidal

structure

(optical bench)

Basic angle

monitoring system

Combined

focal plane

(CCDs)

Rotation axis (6 h)

Figure courtesy EADS
-
Astrium

Superposition of
two Fields of View
(FoV)

12

Focal Plane

Star motion in 10 s

Total field:


-

active
area: 0.75 deg
2


-

CCDs:

14 + 62
+ 14 + 12


-

4500 x 1966 pixels (TDI)


-

pixel size = 10 µm x 30
µm



= 59 mas
x

177 mas

Astrometric Field CCDs

Blue Photometer CCDs

Sky Mapper
CCDs

104.26cm

Red Photometer CCDs

Radial
-
Velocity
Spectrometer
CCDs

Basic
Angle
Monitor

Wave
Front
Sensor

Basic
Angle
Monitor

Wave
Front
Sensor

Sky mapper:


-

detects all objects to 20 mag


-

rejects cosmic
-
ray events


-

FoV discrimination

Astrometry:


-

total
detection

noise: 6

e
-

Photometry:


-

two
-
channel photometer


-

blue and red CCDs

Spectroscopy:


-

high
-
resolution spectra


-

red CCDs

42.35cm

Figure courtesy Alex Short

13

On
-
Board Object Detection


Requirements:


unbiased sky sampling (mag, colour, resolution)


no all
-
sky catalogue at Gaia resolution (0.1 arcsec) to V~20



Solution: on
-
board detection:


no input catalogue or observing programme


good detection efficiency to V~21 mag


low false
-
detection rate, even at high star densities



Will therefore detect:


variable stars (eclipsing binaries, Cepheids, etc.)


supernovae: 20,000


microlensing events: ~1000 photometric; ~100 astrometric


Solar System objects, including near
-
Earth asteroids and KBOs

14

Sky Scanning Principle

Spin axis 45
o

to Sun

Scan rate: 60 arcsec/s

Spin period: 6 hours

45
o

Figure courtesy Karen O’Flaherty

15

Comments on Astrometric Accuracy


Massive leap from Hipparcos to Gaia:


accuracy: 2 orders of magnitude (1 milliarcsec to 7 microarcsec)


limiting sensitivity: 4 orders of magnitude (~10 mag to 20 mag)


number of stars: 4 orders of magnitude (10
5

to 10
9
)



Measurement principles identical:


two viewing directions (absolute parallaxes)


sky scanning over 5 years


parallaxes and proper motions



Instrument improvement:


larger primary mirror: 0.3


0.3 m
2



1.45


0.50 m
2
,




D
-
(3/2)



improved detector (IDT


CCD): QE, bandpass, multiplexing



Control of all associated error sources:


aberrations, chromaticity, solar system ephemerides, attitude control …

16

Photometry Measurement Concept (1/2)

Figures courtesy EADS
-
Astrium

Blue

photometer:

330

680 nm


Red

photometer:

640

1000 nm



17

Photometry Measurement Concept (2/2)

Figures courtesy Anthony Brown

Blue photometer
300
350
400
450
500
550
600
650
700
0
5
10
15
20
25
30
35
AL pixels
wavelength (nm)
0
5
10
15
20
25
30
35
40
spectral dispersion per pixel (nm) .
Red photometer
600
650
700
750
800
850
900
950
1000
1050
0
5
10
15
20
25
30
35
AL pixels
wavelength (nm)
0
2
4
6
8
10
12
14
16
18
spectral dispersion per pixel (nm) .
RP spectrum of M dwarf (V=17.3)

Red box: data sent to ground

White contour: sky
-
background level

Colour coding: signal intensity

18

Figures courtesy EADS
-
Astrium

Spectroscopy:

847

874 nm

(resolution 11,500)




Radial Velocity Measurement Concept (1/2)

19

Radial Velocity Measurement Concept (2/2)

RVS spectra of F3 giant (V=16)


S/N = 7 (single measurement)

S/N = 130 (summed over mission)

Field of view

RVS spectrograph

CCD detectors

Figures courtesy David Katz

20

Data Reduction Principles

Sky scans

(highest accuracy

along scan)

Scan width: 0.7
°

1. Object matching in successive scans

2. Attitude and calibrations are updated

3. Objects positions etc. are solved

4. Higher terms are solved

5. More scans are added

6. System is iterated

Figure courtesy Michael Perryman

21

Scientific Organisation


Gaia Science Team (GST):


12 members + ESA Project Scientist



Scientific community:


organised in Data Processing and Analysis Consortium (DPAC)


~270 scientists active at some level



Community is active and productive:


regular science team/DPAC meetings


growing archive of scientific reports


advance of simulations, algorithms, accuracy models, etc.



Data distribution policy:


final catalogue ~201
9

20


intermediate catalogues as appropriate


science alerts data released immediately


no proprietary data rights

22

Ingestion, preprocessing,

data base + versions,

astrometric iterative solution

ESAC (+ Barcelona + OATo)

Object processing

(shell tasks)

+ Classification

CNES, Toulouse

Photometry

Cambridge (IOC)

+ Variability

Geneva (ISDC)

Spectroscopic

processing

CNES, Toulouse

Overall system

architecture

ESAC

Data simulations

Barcelona

From ground station

Community access

Data Processing Concept (simplified)

Status and contributions to be confirmed

23

Status and Schedule


Prime contractor: EADS
-
Astrium


implementation phase started early 2006



Main activities and challenges:


CCDs and FPA (including PEM electronics)


SiC primary mirror


high
-
stability optical bench


payload data handling electronics


phased
-
array antenna


micro
-
propulsion


scientific calibration of CCD radiation
-
damage effects



Schedule:


no major identified uncertainties to affect cost or launch schedule


launch in 2011


technology/science ‘window’: 2010

12

24

Schedule

Catalogue

2000

2004

2008

2012

2016

2020

ESA acceptance

Technology
Development

Design, Build,
Test

Launch

Observations

Data
Analysis

Early Data

Concept & Technology Study

(ESA)

R
e
-
assessment
:

Ariane
-
5



卯S畺

Cruise t
o L2

25


Participation

of Ondrejov HEA team

Focuses on Gaia CU7 Variability Processing

Natural Extension of Czech participation in
INTEGRAL ISDC

Two work

packages accepted on CVs and
Optical counterparts of High energy sources

Additional participation in image processing


recently algorithms designed of scanned
Schmidt spectral plates


simulation of Gaia
data

26

Simulated low dispersion Gaia spectrum

Real low dispersion spectrum from digitised Schmidt spectral plate

27

Czech Participation II


another part of the Czech Gaia participation
will focus on direct participation in Gaia
CU7 DPC Data Processing Center


Participation in software development in a
team, Java, object oriented programming

28

The End