gaia commissioning update and flux calibration by elena pancino

GaiaCommissioning update

and flux calibration

by Elena Pancino

Gaia timeline

Gaia at HST Calibration Workshop Elena PancinoBaltimore August 2014 INAF- Bologna Observatory

• Launch 19 Dec 2013• L2 orbit insertion 1-15 Jan 2014• Commissioning until 18 Jul 2014• EPSL will last 28 days• NSL from then on (5 years)

The Gaia mission• All Sky – 109 point-like sources – few μas astrometry• 6D phase space sampling – SEDs – Astrophysical parameters• Focused on Galactic Science – but huge discovery space

Encased view Two telescopes inside


All-sky scanning• Each object observed 10-250 times (average ≈70-80)• Maximum number of passages around ±45° from EP

Nominal Scanning Law Sky Coverage Map


Astrometry principle

Sky scans (highest accuracy along scan)

Scan width: 0.7°

1. Object matching in successive scans2. Attitude and calibrations are updated3. Objects positions etc. are solved4. Higher terms are solved5. More scans are added6. System is iterated (Global Iterative Solution - GIS)


To give you the feeling…

Distance to the Pleiades attainable by Gaia: tiny errorbars and a large sample of starsEach plotted star will also have a radial velocity, magnitude, color, andastrophysical parameters by means of high-resolution spectroscopy in the CaT region


Science possibilities• Focus on the Milky Way• Solar system objects• Distant galaxies and QSO• Fundamental physics• Transients & variables• Distance scale


Focal plane & instruments• Sky mappers (SM) • Astrometric field (AF)

• Spectro-photometers (BP & RP)• Radial velocity spectrometer (RVS)


Sky Mappers & object detectionBright stars (V<13 mag)

Intermediate stars(13 <V<16 mag)squares for Gaia spin ratemeasurements

Faint stars(16<V<20 mag)1D profile only

Each detectedobject is assigneda 2D window


Astrometric field

First images: Sadalmelik (α Aqr)Telescope not aligned nor focused then

• White light (G-band ≈ V band)• Photometry and astrometryAstrometric performance (G2V)

• 3<V<12 mag: 5-14 μas• V=15 mag: 24 μas• V=20 mag: 540 μas

• NGC 2516, commissioning image• Later 1 star = 1 little window


Tuning Gaia

First images: Cat’s eye nebula before and after spin rate adjustmentThis might be one of the last images – Gaia is not an imaging mission!

Spin

rate

adj

ustm

ent

(Telescope focus & alignment) Courtesy of SOC calibration team


BP/RP dispersed images

First images: NGC 1818 in the LMC2.85 sec integration, 212 x 212 arcsec2

• Blue and red channels• R≈100 dispersed images• Color-correction for AF• SEDs for:

• Classification• Parametrization

Courtesy of Jordi & Carrasco


Gaia integrated magnitudes• Four bands (G, BP, RP, RVS)• Four integrated magnitudes• One important colour (GBP-GRP)

G band performance (G2V)• V=15 mag, 1 mmag• V=18 mag, 2 mmag• V=20 mag, 6 mmagBP performance (G2V)• V=15 mag, 4 mmag• V=18 mag, 13 mmag• V=20 mag, 80 mmagRP performance (G2V)• V=15 mag, 4 mmag• V=18 mag, 11 mmag• V=20 mag, 59 mmag


RVS spectra

First spectra: the bright star HIP 86564Courtesy of Katz, Marchal, & Soubiran

Pre-launch simulations

• R≈10000 CaT spectra• Down to V ≈ 16.5 mag• Full object parametrization• Chemical abundancesRVS performances (GV2)• V=12 mag, 1 km/s• V=15 mag, 15 km/s


Second part:Commissioning update

(1) Gaia brightness

Gaia seen by ESO-VST, image courtesy ESO

• Optical tracking necessary for attaining max performance• Gaia is 3 mags fainter than expected (V≈20.5 mag)• The GBOT group negotiated time at 2-4m telescopes


(2) L2 environment

Micro-meteoroid hit, courtesy van Leeuwen

• Large hits ok, small hits orders of mag more frequent than expected• Attitude control system copes very well with this dusty environment• Attitude modeling more complex – some noise at bright end


(3) Stray light

SAA = 45° (nominal operation angle)SAA = 0° (commissioning maneuver)

Sun light dominates

night sky dominates

• Higher than expected backround levels, varying with time • Caused by scattered sunlight, affecting mostly faint sources• The solution is a redesign of the background treatment software

Figures byDavidson


(4) Contamination

1st decontamination

2nd decontamination

• Response loss (water ice) – heating to decontaminate• Unintended outgassing path from service to payload module

Figure byFabricius


(5) BAM variations• The BAM measures 6h variations - some are confirmed – open issue

BAM measurements

1 day astro solution

Figure by First Look Team


Gaia status summary• Five unexpected issues emerged after commissioning

• Two are minor (GBOT and L2 dust)• Three have an impact on Gaia performances

• Stray light, contamination, BAM variations

• Excellent maneuvers from launch to L2 orbit insertion• We have a good propellant reservoir for the future• Some minor micro-thruster problems

• Service module commissioning ok• The downlink allows for high data rate• The rubidium clock and GB phased array antennaes are ok

• Payload module works well (Electronics, CCDs, optics)• Gaia -> ESOC -> DPAC chain working excellently so far


Third part:Flux calibration

Gaia flux calibration


On-board pre-processing

Ground processing

Internal Calibration(internal standards)

External Calibration(external standards)

External calibration model


Gaia obs SED Instrument LSF

Sam

ple

Wavelength

In matricial form:Sobs = D x Strue

Strue = D-1 x Sobs

Two problems:• Matrix is rectangular• Stars ≠ orthogonal set

You need many (200) stars of different spectral types

with <1% calibration wrt Vega

SPSS observing campaign


450 nights at 6 telescopes,started in 2006 (end 2015)

Four campaigns• Spectroscopy (R≈2000)• Absolute photometry• Constancy monitoring (>10 mmag)

• Short term (2 h)• Long term (3 yrs)

215 remaining candidates• From CALSPEC & literature• One CALSPEC variable found• Preliminary results published (Pancino et al., 2012)

BFOSC@Cassini, Loiano EFOSC2@NTT, La Silla

[email protected], San Pedro Martir

ROSS@REM, La Silla

Dolores@TNG, La [email protected], Calar Alto

Data analysis


The pre-launch (internal) release


October 2013• 94 SPSS• Photometric sky• Pipeline testingQuality• <1% central• Red: fringing (10%)• Blue: noisy (3-5%)To do for borders• 330-1050 nm• More S/N• Models extension

Next steps


• First Gaia release expected 2017 – SPSS release in 2016• Will build on the best 94 SPSS increasing their quality• Later releases will expand on the number of SPSS as well• Data will be available @ ASDC archive (under works)

• 100000 raw frames + 3000 calibration masterframes

That’s all,Thank you!

gaia commissioning update and flux calibration by elena pancino

Documents

inaf bologna observatory

elena pancino slide

gaia timeline gaia

gaia mission

flux calibration

gaia commissioning update

cat region gaia

objects positions