Image of the Week

Pulsating stars to study galactic structures


Figure 1: Colour-(apparent) magnitude diagram, in Gaia passbands of known fundamental mode (ab-type) RR Lyrae stars. Magnitudes and colours are not corrected for extinction. The colours indicate the other surveys that have identified these RR Lyrae stars. (Image credit: ESA/Gaia/DPAC)

Pulsating stars can and have been used to study galactic structures. One group of pulsating variable stars are the RR Lyrae stars, which have been studied in various surveys such as OGLE (Soszyńcski et al. 2014, 2016), Catalina (Torrealba at al. 2015, Drake et al. 2013a, 2013b, 2014), and LINEAR (Palaversa et al. 2013).

In Figure 1 a colour-(apparent) magnitude diagram of 71 464 known RR Lyrae stars (Bailey's ab-type) is shown. Data on these RR Lyrae stars can also be found in the Gaia DR1 Catalogue, although colours will only be available from Gaia DR2 onwards (and are here with a preliminary reduction). The OGLE, Catalina and LINEAR surveys have been cross-matched with the Gaia catalogue allowing us to obtain a homogeneous set of magnitudes and colours from G, BP, and RP photometry.

As RR Lyrae variables can be used as standard candles, interesting structures are revealed in this diagram of apparent magnitude versus colour. First of all, it can be seen that the black and brown points, corresponding to the Catalina and LINEAR surveys respectively, produce a vertical structure that traces the Galactic halo. In the diagram some over-densities are discerned. Following the release of Gaia DR2 it would be most interesting to see if these over-densities are due to streams or are spatially clumped structures.

Looking in more detail at the data available from the OGLE survey, three groups are distinguished and shown in red, green and blue. The diagonal structure in red is caused by interstellar extinction, which attenuates and reddens the light of (RR Lyrae) stars in the direction of the Bulge.

The small clump in red (with G ~ 18 mag) includes primarily RR Lyrae stars from the Sagittarius dwarf spheroidal galaxy at a heliocentric distance of about 25kpc.

Finally the blue and green points correspond to the RR Lyrae stars in the Large and Small Magellanic Clouds (LMC and SMC). Notice that the LMC is closer than the SMC, with a difference in distance modulus of about 0.5 magnitude, and both galaxies show a much larger spread in colour indices than the halo ones.

Figure 2: Sky distribution in Galactic coordinates of the cross-matched RR Lyrae stars, colour-coded with apparent magnitude, as with distance (though not accounting for extinction) (Image credit: ESA/Gaia/DPAC)

In Figure 2 the Magellanic clouds (high-density red points in the southern Galactic hemisphere), the Sagittarius tidal streams (extended structures with low-density red points), and the Sagittarius dwarf spheroidal galaxy (yellow points around Galactic latitude -14 degrees and longitude +6 degrees) are clearly visible.

Credits: ESA/Gaia/DPAC, Lorenzo Rimoldini, Laurent Eyer, Gisella Clementini, Vincenzo Ripepi, Marco Riello, Dafydd W. Evans and the whole CU7/DPCG team.

[Published: 24/03/2017]


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.