Image of the Week

Eclipsing binary light curves fitted with DPAC code


In the course of its mission, Gaia is expected to obtain multicolour epoch photometry ("light curves") for at least several hundred thousand, and possibly up to several million, eclipsing binaries, most of them previously unknown. Spectroscopic data (radial velocity curves) are also expected to be available for a subset of these systems.

The Eclipsing Binaries Development Unit is responsible for processing the light and radial velocity curves of systems identified as eclipsing binaries upstream in the pipeline (mainly by CU7). The aim is to extract as much useful information about the physical parameters of these systems as allowed by the quality of the data, the requirement for an automatic processing, and infrastructure constraints (e.g., the availability of CPU resources). This task is accomplished by comparing the observables (photometry and spectroscopy) with model light curves of known physical parameters, and picking the model that "best" fits the observables in a maximum-likelihood (least squares) sense.

In general, finding the best model is not a trivial task because the least-squares function is not quadratic in the model parameters. For this reason, a two-step procedure is followed. First, the observations are compared to a database of precalculated models spanning a wide range in parameter space in order to find the model closest to the observations. The parameters of this model are then used as initial estimates for a least-squares optimization that homes in on the nearest minimum. This approach improves the chances of finding the globally best solution, rather than falling into a local minimum "trap".

The four figures shown here, provided by DU436FirstPublicLight (2010), illustrate some early results from this endeavour. The blue circles with associated error bars represent simulated observations of eclipsing binaries in the G band, generated by CU2. The fluxes are scaled so that the brightest datapoint in each curve correspond to a flux of one. The size of the error bars varies depending on the apparent G magnitude of each binary, with smaller error bars implying a brighter system. Phases are calculated from transit times assuming that the period of variability is known (as provided by CU2). Transit times were sampled according to the Gaia scanning law, resulting in between 68 and 89 transits. Finally, the red squares represent the flux predictions of the best-fit model for the same times. The dashed lines are straight-line segments that simply connect the red squares.

The quality of the fits is overall quite good. However, work is under way to improve on several aspects of the procedure. The current priorities are (i) to incorporate multicolour photometry and radial velocity information in the fitting procedure (currently only the G-band photometry is fit); (ii) to make a number of performance improvements, for example in the calculation of models with elliptical orbits which is time-consuming because of the need to recalculate the Roche geometry as the distance between the two stars varies; (iii) to optimize the parameter coverage of the model database; and (iv) to implement an intelligent way of dealing with errors in period determination, and in particular with period aliasing, which will become issues when the period is calculated from the data. Because the period will be an output of CU7 and, sometimes, of the Spectroscopic Binaries Development Unit as well, the Eclipsing Binaries Development Unit is in collaboration with these Units to ensure an efficient handling of the problem.

[Published: 27/10/2010]


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.