Image of the Week

Validation of GAia DR1: How Faint are the faintest Gaia Stars

 

Figure 1: Limiting magnitude: 99th percentile of the G distribution in ecliptic coordinates: a) TGAS; b) full Gaia DR1 Catalogue (Image credit: ESA/Gaia/DPAC)

Gaia observes sources until magnitude 20.7 and sometimes even a bit fainter. In the first data release, Gaia DR1, only sources fulfilling a number of criteria were included, e.g., they should all have a certain minimum number of observations. Especially faint sources and sources in very dense fields did not always reach this minimum, and many sources will therefore only appear in later data releases.

The given images show the 99th percentile of the Gaia magnitude in 49152 regions of the sky, each covering 0.84 square degrees. This means that in each region we show the magnitude where 99% of the sources are brighter than that magnitude and the remaining 1% are fainter. In that way we get a good impression of how deep Gaia DR1 goes without the confusion of a few unusually faint cases.

Gaia observations are carried out along great circles maintaining a certain distance from the Sun. For this reason the images are arranged in Ecliptic coordinates. The bottom panel is for the full Gaia DR1 and clearly shows the imprint of the observational pattern. The six big loops are narrow areas where particularly many observations were made and where Gaia therefore could go deeper. There, the faintest Gaia sources may exceed the 21st magnitude at the end of mission.

Inside the loops, in contrast, is where fewer observations were made. The brightest point inside the second loop from the right is the Galactic centre, where we are up against both a very high star density and a relatively low number of observations, leading to a decrease of more than one magnitude for the faintest stars in this area.

The upper panel shows in a similar way the faint limit of the Tycho Gaia Astrometric Solution (TGAS). This solution, which is included in Gaia DR1, combines the Tycho-2 catalogue from the Hipparcos mission with the Gaia observations. Tycho-2 is almost complete until V ~ 11.5 mag and has only few stars fainter than 12 mag. The much more complex pattern in this diagram is a reflexion of the limitations of a long series of processes, starting decades ago with the Hipparcos observational strategy and with the construction of the input star list for Tycho-2, and ending with some specific issues for stars near 11th magnitude for Gaia DR1.

Both figures illustrate the complexity of the statistical analysis of the Gaia Catalogue content, which will improve in future releases with a larger number of observations. The diagrams were made at the Institute of Cosmos Sciences, University of Barcelona, for the paper on the catalogue validation of Gaia DR1 by Arenou, Luri, Babusiaux et al. published in Astronomy & Astrophysics.

Credits: ESA/Gaia/DPAC/CU9, Sergio Soria, Claus Fabricius (IEEC-ICCUB, Barcelona), Frédéric Arenou (Observatoire de Paris-Meudon)

[Published: 07/04/2017]

 

Image of the Week Archive

2017
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.