Image of the Week

100 Weeks of Trouble-Chasing


Figure 1: Important daily work reported on a weekly basis: DPAC First-Look Scientists and Payload Experts celebrate the 100th issue of their Weekly Report today. 10 reports had been issued during pre-launch Operations Rehearsals which is why this week's document carries the running number 110.


Since early January 2014, the Gaia First-Look Scientists (FLS) team and the Payload Experts (PE) group, in co-operation with the Gaia Mission Operations Centre at ESOC, Darmstadt, have been checking Gaia's instrument health and its scientific data quality on a daily basis. All findings of problems and oddities as well as their resolution are continuously reported in FLS & PE Weekly Reports, internal documents for the people working on Gaia. Today the 100th report has been released (Figure 1), exactly two years after the first one appeared after the switch-on of Gaia's science instruments.

Tasked with detecting issues and sub-optimal conditions of diverse sorts and importance, the FLS team and PE group prompt actions to improve the performance of Gaia and of the data processing on ground whenever necessary. While Gaia is working very well and produces vast amounts of astrometric data in unprecedented quality and quantity, the task of the FLS team and PE group is to find and act on any and all troubles, however small they may be. This trouble-chasing will continue as deeper understanding of Gaia allows finding smaller and smaller effects. Yet for the final catalogue accuracies even the tiniest issues have to be understood. In the past two years of Gaia operations, including commissioning and nominal operations, 104 different problems and oddities were spotted in the data, out of which 89 have been resolved already. About half of the issues were linked to the spacecraft and the other half to the ground-processing software. Figure 2 gives one spacecraft-related example of an on-board optimisation achieved in this process, and also illustrates how the process of First-Look works.

One among the thousands of diagnostic quantities checked every day is a measure of the sharpness of the star images produced by Gaia's two telescopes (in fact this one consists of several such measures, for different parts of the Gaia focal plane). In early July 2015 the First-Look team identified the potential to improve the image sharpness in the astrometric section for one of Gaia's fields of view. The Payload Experts group discussed the matter in its weekly teleconference to be sure that a corrective action for the astrometric field would not reduce the image quality in the photometric and spectroscopic parts of the fields of view. In this case the group gave the green light for a refocussing recommendation from the science point of view. Subsequently, following Mission Manager approval, members of the Gaia Science Operations Centre at ESAC, Villafranca, worked out the details of the needed mirror movement in Telescope 1, and the Mission Operations Center at Darmstadt conducted the actual re-focussing in early August 2015 after having checked it for correctness, for possible risks, and for possible interference with other planned spacecraft operations. As can be seen in Figure 2, the refocussing activity improved the image sharpness, in other words the angular resolution of the telescope, by roughly 8%.


Figure 2: Time series of the image width measurements, derived by the First Look data processing chain nominally once a day. The data points show the so-called Cramer-Rao criterion for Gaia's Telescope 1 as a function of the DPAC-internal time scale OBMT (one rev equals six hours). The smaller the value, the better the image sharpness. The planned re-focussing took place on 3 August 2015 (OBMT rev. 2574.7). For completely unrelated technical reasons, the First Look's image sharpness diagnostic could not be run for about 10 days shortly after the refocussing, producing a data gap in this plot.


Credits: ESA/Gaia/DPAC/CU3/M. Biermann (ARI, Heidelberg)



Image of the Week Archive

24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
Please note: Entries from the period 2003-2010 are available in this PDF document.