Image of the Week

Hertzsprung-russell Diagram Using Gaia DR1

 

Figure 1: Hertzsprung-Russell diagram, Gaia absolute magnitude versus G-Ks colour, using Gaia DR1 with relative standard uncertainty better than 10%, 2MASS high photometric quality and low extinction stars (E(B-V)<0.015). This selection leads to 149226 stars located within 400 pc of the Sun. Note that the top of the red giant branch is absent from this diagram due to the fact that those very bright and red stars are saturated in 2MASS.

Trigonometric parallaxes allow to directly estimate distances in astronomy, but their relative precision decrease with distance. To go further with high precision we need to use standard candles, like solar neighbourhood Red Clump stars whose luminosity is hardly dependent on colour, age and stellar composition.

While Hipparcos giants are close enough to suffer only mildly from extinction, this is not the case anymore for the Gaia giants, even for the bright Tycho-Gaia astrometric solution (TGAS) stars of Gaia DR1. To be able to derive a Gaia Hertzsprung-Russell diagram one needs intrinsic magnitudes and colours, e.g. with a small foreground extinction or an accurate correction for this extinction.

We used here the most up-to-date local 3D extinction map of Capitanio et al. (2017), built using the TGAS parallaxes, to select only low extinction stars (E(B-V)<0.015). We selected stars with relative standard uncertainties on the parallax less than 10% and good 2MASS photometry to derive the Gaia Hertzsprung-Russell diagram shown in Figure 1. This selection leads to 149 226 stars located within 400 pc of the Sun. Note that the top of the red giant branch is absent from this diagram due to the fact that those very bright and red stars are saturated in 2MASS.

In the global Gaia DR1 Hertzsprung-Russell diagram presented in Brown et al. (2016), one can find a well defined lower part as here, including the binary sequence parallel to the main sequence and a few white dwarfs on the bottom left, but the upper main sequence and the red giants were spread by the extinction (the more luminous the stars the more distant and the more extincted). With a selection of low extinction stars only, the upper main sequence is narrower in colour and the red giant branch shows substructures.

Figure 2 presents a zoom on the Red Clump. The Red Clump absolute magnitude, slightly dependent on the colour (temperature), produces the elongated and slightly inclined main feature (in yellow). It corresponds to cool horizontal branch stars, burning helium in their cores. On the blue side of the main Red Clump, the luminosity is fainter: it is the Secondary Red Clump (in blue). This feature is made of stars just massive enough to have ignited helium in non-degenerate conditions.

Figure 2: Zoom on the Red Clump region. In blue: the Secondary Red Clump. In red: the Red Giant Branch Bump. The yellow line corresponds to the obtained calibration of the Gaia absolute magnitude versus colour.

Fainter than the Red Clump extending to the red side is the Red Giant Branch Bump (in red). This bump is caused by a discontinuity in hydrogen abundance which briefly interrupts the luminosity increase of the star during its ascent of the RGB, causing an excess of stars at that point. All those features are typical of a young metal-rich population.

In Ruiz-Dern et al. (2017) complete and robust photometric empirical calibrations are provided for the Gaia Red Clump stars, through colour-colour, effective temperature-colour and absolute magnitude-colour relations, from the Gaia, Johnson, 2MASS, Hipparcos, Tycho-2, APASS-Sloan and WISE photometric systems, and the APOGEE DR13 spectroscopic temperatures.

This was performed by using the high quality of the Gaia DR1 data. Now those calibrations are in turn being used for the validation of the Gaia DR2. Indeed, Red Clump stars may be used to check the zero point of the Gaia parallaxes and their precision if we choose them distant enough so that their estimated distance uncertainty is better than the Gaia parallax precision (Arenou et al, 2017). Within the Gaia Data Release 2 DPAC CU9 validation process this is already being applied.

Credits: ESA/Gaia/DPAC, L. Ruiz-Dern, C. Babusiaux, F. Arenou, C. Turon, R. Lallement (GEPI, Observatoire de Paris)

[Published: 20/10/2017]

 

Image of the Week Archive

2017
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
31/08: Close stellar encounters from the first Gaia data release
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.