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

Transcript of Gaia Commissioning update and flux calibration by Elena Pancino.