Image of the Week

A new heart for the Gaia Object Generator

   
  The new Galactic Thin Disc Hess Diagram ready to be integrated in the Gaia Object Generator (Luri et al. 2014). It shows the stellar density in the Solar Neighbourhood distributed in temperature and brightness, and split in age intervals from 0 to 10 Gyrs. The signature of the stellar evolution can be clearly seen. The diagram was simulated using the Besançon Galaxy Model (Robin et al. 2003) with the Galactic Thin Disc treatment from Czekaj et al. (2014). It represents a big improvement in the generation of important Galaxy tracers, such as giant stars at different stages of evolution (i.e., Red Clump), and also in pre-main sequence stars at low masses for the youngest populations. White Dwarfs are treated separately and thus not included here.  
 

The first Gaia data release, scheduled for end of the summer 2016, is going to revolutionise the study of Galactic structure and evolution. As part of its preparation, the Data Processing and Analysis Consortium (DPAC) Coordination Unit 9 is in charge of guaranteeing that the data has passed a set of quality tests. These tests ensure that the published data are valid for scientific exploitation. The Besançon Galaxy Model (Robin et al. 2003, 2012), which is integrated in the Gaia Object Generator (GOG, Luri et al. 2014), is being used as a tool for Gaia data validation tests. A new run of GOG, to be executed by the Barcelona team, is expected for February 2016. It will provide a simulation of the full sky as seen by Gaia, using, at its heart, the new Galactic Thin Disc Hess Diagram presented in the above figure. This simulation will be used for Gaia data validation, in the data archive, and for scientific exploitation.  

Thanks to the very precise distances that Gaia will provide, the physical parameters of the stars, such as brightness or temperature, will be better determined. Thus, stellar evolution will be better understood. The evolution of a star, over time, depends on its nature. During its life, a star's brightness and temperature change, and as a consequence its position in the Hess Diagram changes too. Notice that the diagram x-axis makes reference to the star temperature, and the y-axis makes reference to its brightness. The animated view shows, for each age interval, the number of stars per cubic parsec in the Solar Neighbourhood. Notice that the signatures of stellar evolution can be clearly seen. The presented diagram was simulated using the Besançon Galaxy Model (Robin et al. 2003) with the Galactic Thin Disc component from Czekaj et al. (2014). The model machinery incorporates spatial density distributions to extend the stellar population densities in the Solar Neighbourhood through the whole galaxy. It translates the Hess Diagram for each Galactic component (thin disc, thick disc, halo, etc.) to a full-sky simulation with its Gaia observables (parallax, apparent magnitude, and colours). These simulations, together with the first Gaia data release, will provide an excellent tool to test key hypotheses on fundamental Galactic parameters. As an example, notice how the shifting of the Turn Off with age can be clearly seen. Its study, related to the Galactic Thin Disc age and stellar formation bursts, is one of the challenges of Gaia.

This Hess Diagram represents a big improvement in the generation of important Galaxy tracers, such as giant stars at different stages of evolution (i.e., Red Clump), and also in pre-main sequence stars at low masses for the youngest stellar populations. White Dwarfs are treated separately and thus not included here. The above mentioned diagram areas are statistically robust thanks to the rescale of 400 runs of the Solar Neighbourhood Sphere, with a total of about 925 million simulated stars.

By improving the stellar population synthesis of the Milky Wayin such a way, we are striking double: we have a better tool to validate Gaia data releases (specially the Tycho-Gaia Astrometric Solution) and a valuable starting point for the scientific exploitation of the Gaia data. 

Note: DPAC will be releasing its own estimates of stellar parameters, starting in Gaia-DR2 (see CU8 paper by Bailer-Jones et al. 2013).

Credits: ESA/Gaia/DPAC/CU2/R. Mor (ICCUB-IEEC, Barcelona University), A.C. Robin (OSU THETA and Institut UTINAM, Besançon), F. Figueras (ICCUB-IEEC, Barcelona University)

[Published: 11/02/2016]

 

Image of the Week Archive

2017
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
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
2016
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
2015
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
2014
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
2013
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
2012
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
2011
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
2010
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.