Gaia's view of star clusters - @Jos_de_Bruijne European Space Agency 15 November 2017 @ESAGaia #GaiaMission - cosmos.esa.int
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Gaia’s view of star clusters
@Jos_de_Bruijne
European Space Agency
15 November 2017
@ESAGaia
#GaiaMission Figure courtesy ESA/Gaia/DPAC
Gaia’s first sky map
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPAC
Gaia’s first sky map
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPAC
Promises
q No equations
q Light on acronyms
q Watch a video
q Quiz
q Reveal secret
q Lots of data (April 2018)
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPAC
Contents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPAC
Contents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPAC
A Milky Way look-alike
Sebastien: “We study comets
because they have preserved
the original building blocks of
the Solar system”
Gaia’s main aim: unravel the structure, formation,
composition, and evolution of our Galaxy
Key: stars, through their motions and chemical composition,
contain a fossil record of the Galaxy’s past evolution
7
Figure courtesy European Southern Observatory (NGC1232)
The need for Gaia
q Archaeological studies of the Galaxy require:
q Distances and motions, combined with physical properties of stars
(temperature, gravity, extinction, chemical composition, mass, age, ….)
q For a representative, complete sample of stars
(1+ billion objects ≈ 0.5% of the stars in the Milky Way)
q This can only be achieved from space, by collecting:
q Astrometry (3D positions and 2D velocities; Astrometric Field = AF)
q Photometry (spectro-photometry; Blue and Red Photometers = BP and RP)
q Spectroscopy (150 million brightest stars; Radial Velocity Spectrograph = RVS)
q This precisely is Gaia!
8
The reach of Gaia
Our Sun
Figures courtesy NASA/JPL-Caltech/R. Hurt and DPAC/X. Luri
The reach of Gaia
Figures courtesy NASA/JPL-Caltech/R. Hurt and DPAC/X. LuriOne billion stars in 3D will provide …
• ... in our Galaxy …
– the spatial and velocity distributions of all stellar populations
– the formation history and past evolution of bulge, disk, and halo
– a rigorous framework for stellar structure and evolution theories
– a large-scale survey of double and multiple stars (~100,000,000)
– a large-scale survey of extra-solar planets (~7,000)
– a large-scale survey of solar-system bodies (~350,000)
• … and beyond ...
– supernovae and burst sources (~6,000)
– local-group galaxies, including the Magellanic Clouds (~20)
– resolved galaxies (~1,000,000) plus quasars and redshifts (~500,000)
– relativistic light bending, microlensing, gravitational waves (upper limits), ...
Posters Timo and11UweGaia in one viewgraph
X
q Who: European, ESA-only mission
q When: launch 19 December 2013 for a
nominal 5-year mission (+ extension)
q Where: L2 (1.5 million km from Earth)
q What: positions, parallaxes, proper motions for
1+ billion stars (2016, 2018, 2020, 2022)
X
q Data processing: 430 scientists (DPAC)
q Software: 3 million lines of code (Java)
q Data collected so far: 47 terabyte with 90
billion star transits (and counting ...)
q First data
X release: 14 September 2016 with 2
Figure courtesy Jane Douglas (ESA)
Figure courtesy ESA million positions, parallaxes, proper motionsRoutine operations
q In five-year routine phase since 25 July 2014
q Data collected so far (cosmos.esa.int/web/gaia/mission-numbers):
q 891 billion astrometric measurements (AF)
q 180 billion low-resolution photometric measurements (BP/RP)
q 17 billion high-resolution spectra (RVS)
q Magnitude limits:
q Astrometry and photometry down to G = 20.7 mag
q Spectra down to GRVS = 16.2 mag Posters
Natalia and
q Special data:
Johannes
q Sky-Mapper imaging for stars brighter than G = 3 mag
q Sky-Mapper imaging of Baade’s Window, ω Cen, etc.
q Special data not (yet) processed in the standard pipelinesContents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACData Release 1 (DR1) – 14 September 2016
q Based (only) on 14 months of input data
q Astrometry
q Position for ~1.1 billion sources (epoch J2015.0)
q Parallax and proper motion for ~2 million Hipparcos and Tycho-2 stars
(V < 11 mag; Tycho-Gaia Astrometric Solution – TGAS)
q Covariance matrix (standard errors and correlations)
q Reference frame aligned to ICRS using ~2000 QSOs
q Photometry
q Mean G-band flux and error for all sources
q Photometric zero-point (VEGAMAG and AB)
q Transformations to other photometric systems (e.g., Sloan, Johnson-Cousins)
q Light curve and classification for ~3000 selected RR-Lyraes and Cepheids
q Data, documentation, and visualisation
q archives.esac.esa.int/gaia (plus ESASky!)Data Release 1 (DR1) – 14 September 2016
x 2 million d
x 1 billion
x 3000
Brightness
Figure (idea) courtesy Anthony Brown
TimeContents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACGaia’s first sky map
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACM4 in ESASky with DR1 positions
Globular clusters and Gaia
Watkins & Van der Marel (2017) Total number ... globular
of stars in ... clusters
Milky Way GC catalogue (Harris 1996 + updates) Many 157
Search DR1-TGAS within 2 tidal radii 4268 142
Check magnitude (tip RGB and fainter) 967 30
Retain if proper motion and parallax agree with HST 64 15
Add radial velocity from literature 59 15
Retain if on evolutionary CMD sequence 48 11
Check with field-star model 20 5
Wait for (at least) DR2 ...
Pancino et al. (2017): “The astrometry will be only marginally affected by
crowding, even for the most field-contaminated bulge GCs” Figure courtesy ESA/Gaia/DPACReally wait for DR2?
q Massari et al. (2017) combined
HST and Gaia DR1 positions in
NGC2419 (d ~ 87.5 kpc)
q Relative proper motions over
12.27 year for 366 members
q Made absolute using a (I mean
one ) background galaxy
q Derive orbit in Milky Way halo
(pericentre ~ 53 kpc, apocentre ~
98 kpc)
q Possibly associated to Sgr dwarf
spheroidalContents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACOpen clusters Talks Antonella,
Anthony, and
Danny
q How / when / where / why do clusters form?
q Internal structure, mass segregation, flattening, mass & luminosity function, ...
q How / when / where / why do clusters evaporate and populate the field?
q How do galactic disks evolve?
q Trace stars / streams back to original cluster / association (+ runaway stars)
q Milky Way disk tracers (migration, resonances, heating, chemical evolution)
q Test stellar structure and evolution models across the mass spectrum
q Variability (Cepheids, RR Lyraes, ...) and multiplicity (incl. planets)
q ...
Figure courtesy Roth RitterOpen clusters before Gaia
q Karchenko et al. (2013)
q Some 3006 clusters* known
q Knowledge heavily biased
q Most are nearby
q Only complete to ~1.5 kpc(?)
q Size of nucleus depends on
distance (detection bias)
q Some 100,000 could exist ...
*Actually includes asterisms,
remnants, associations, ...
Figure courtesy NASA/JPL-Caltech/R. HurtOpen clusters and Gaia
q End-of-mission astrometric accuracy rule of thumb at 15th magnitude
q 1% accuracy at 1 kpc
q 5% accuracy at 5 kpc
Type Number known < 1 kpc < 5 kpc
Globular clusters 157 0 15
Open clusters 3006 370 ~2630
q Detection of clusters (all sky, faint, complete, accurate, precise, unbiased)
q Determination of members (astrometry + photometry + spectroscopy)
q Characterisation of clusters (distances, motions, orbits, ages, metallicities)
q Characterisation of cluster members (binaries, variables, abundances)
Figure courtesy ESA/Gaia/DPACGaia Collaboration et al. (2017) q Validation of TGAS using 19 clusters within ~500 pc q Some ~15-150 members q Find members out to ~15 pc (which is selected field size) q Distances in line with literature, with one exception (see later) q Narrow main sequences, for instance Hyades (see later) q TGAS = tip of the iceberg ...
Gaia Collaboration et al. (2017) q Validation of TGAS using 19 NGC 2516: Jeffries et al. (2001) clusters within ~500 pc q Some ~15-150 members q Find members out to ~15 pc (which is selected field size) q Distances in line with literature, with one exception (see later) q Narrow main sequences, for instance Hyades (see later) q TGAS = tip of the iceberg ...
Gaia reveals cluster existence
q Koposov et al. (2017) systematically
searched the DR1 position
catalogue for position overdensities
q Known dwarf galaxies show up
q Note: Antoja et al. (2015) predict
new ultra-faint dwarf galaxy
detections!
q “These examples demonstrate the
incredible purity and quality of the
Gaia Catalogue, and highlight
Gaia’s superb satellite discovery
capabilities even without colour
information”Gaia reveals cluster existence q Koposov et al. (2017) discovered a new cluster ~11’ from Sirius (“Gaia 1”) q A 10σ detection, actually also seen in WISE star counts
Gaia reveals cluster existence q Koposov et al. (2017) discovered a new cluster ~11’ from Sirius (“Gaia 1”) q A 10σ detection, actually also seen in WISE star counts q Spectroscopic confirmation by Simpson et al. (2017)
Gaia reveals cluster existence
q Koposov et al. (2017)
discovered a new cluster ~11’
from Sirius (“Gaia 1”)
q A 10σ detection, actually also
seen in WISE star counts
q Spectroscopic confirmation by
Simpson et al. (2017)
q Old (3 Gyr), thick-disk cluster
(zmax ~ 1.1 kpc) at ~4.5 kpc
q Did it survive ~30 galactic-
plane passages?!
q Links to extra-galactic origin
discussion ...Open clusters beyond the Milky Way
q JdB & De Marchi (2011)
simulated Gaia’s view of R136
in the LMC
q Even a density of ~1.5 million
stars deg-2 is “no problem” for
on-board detection
q Obviously, crowding causes
window truncation and blending
q Crowded regions therefore sub-
optimally covered in DR2
Figure courtesy NASA/ESAContents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACThe Hyades
q Nearby (~45 pc), intermediate age (~700 Myr), not reddened, huge
area on sky (60° × 60°), large (peculiar) proper motion (110 mas yr-1),
large (peculiar) radial velocity (40 km s-1)
q Reino et al. (in prep.) use TGAS data (+ Hipparcos stars as needed
to complement bright end)
q Start with 2296 stars in field
q Add 908 literature radial velocities (vr)
q Determine membership only based on kinematics
q Find 251 candidate members (200 with vr)
q Past members demoted: 15
q New members with vr: 18
Figure courtesy Airbus DSTGAS entries in 10-pc-radius sphere @ 45 pc
TGAS entries in 10-pc-radius sphere @ 45 pc
Principal axes of the moment-of-inertia matrix
q TGAS data confirm
Major axis
Hipparcos findings
Intermediate axis
q Cluster roughly Minor axis
spherical in core
(rc ~ 3 pc) but
flattened at larger
radii (rt ~ 10 pc)
q Cluster flattened
along galactic plane
q Naturally expected
from tidal evolution
over ~700 MyrStars colour coded with distance to centre
q Clear, dense core
with significant
spread of members
Distance to cluster centre [pc]
out to large radiiStars colour coded with member likelihood
lower-probability member
q Clear, dense core
with significant
spread of members
out to large radii
q Some corona / halo
stars are high-fidelity
members
Highest-probability memberProjections of the three principal axes added
lower-probability member
q Clear, dense core
with significant
spread of members
out to large radii
q Some corona / halo
stars are high-fidelity
members
Highest-probability member
q Cluster is resolved:
spread reflects
internal structure +
projection
q “Soft edge” / gradual
transition into fieldColour vs absolute-magnitude diagram
lower-probability member
q Smooth main sequence
over ~10 magnitudes Main and binary
q Messy turn-off (rotation, sequence from
binarity, Am stars, Smith (2012)
magnetic mixing, ...)
q Four (known) giants
q Binary sequence visible
Highest-probability member
q Photometric errors in
B-V dominate over
absolute-magnitude
errors(!)Colour vs absolute-magnitude diagram
lower-probability member
q Kinematic modelling:
assume stars share 3D Padova isochrone (675 Myr)
cluster space motion but
allow for dispersion σv
q Use maximum likelihood
method to fit 3D space
motion, σv, and individual
Highest-probability member
parallaxes, given the
proper motions + errors
q Iterate: reject outliers
(binaries, escapers, ...)
q Improved parallaxes for
187 stars and
σv ~ 0.25 km s-1Colour vs absolute-magnitude diagram q Substructure in main sequence around B-V ~ 0.4 q Effects of convection in atmospheres and envelope (Böhm-Vitense gap) q D’Antona et al. (2002) show that isochrones are sensitive to convection treatment: mixing-length theory (MLT) versus full-spectrum turbulence (FST) q Work in progress ...
Colour vs absolute-magnitude diagram q Substructure in main sequence around B-V ~ 0.4 q Effects of convection in atmospheres and envelope (Böhm-Vitense gap) q D’Antona et al. (2002) show that isochrones are sensitive to convection treatment: mixing-length theory (MLT) versus full-spectrum FST turbulence (FST) MLT q Work in progress ...
Moving the Hyades 0.450 Myr into the future
Movie courtesy JdBThe Pleiades cluster
Images courtesy Anthony Ayiomamitis and Gaia CollaborationThe Pleiades cluster
Images courtesy Anthony Ayiomamitis and Gaia CollaborationThe Pleiades cluster
Images courtesy Anthony Ayiomamitis and Gaia CollaborationContents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACData Release 2 (Gaia DR2) – April 2018
q Based on 21 months of data
q Position, parallax, and proper motion for ~1 billion sources (epoch J2015.5) with
full covariance matrix (standard errors & correlations)
“Gaia DR2 will not be perfect but it will be
q Typical parallax standard errors: 30 µas (Contents
q Gaia
q Gaia DR1
q Globular clusters
q Open clusters(+ dwarf galaxies)
q The Hyades
q Gaia DR2
q Conclusions
Figure courtesy ESA/Gaia/DPAC
Figure courtesy ESA/Gaia/DPACConclusion
q Gaia = U3
q Unique mission aimed at
q Unfolding the structure and evolution of the Milky Way through
q Ultra-precise, multi-epoch observations of 1+ billion stars
q Two+ million stars “teaser release” September 2016
q One+ billion stars “bomb release” April 2018
q Since I started talking, Gaia collected
q 7,577,189 astrometric observations
q 996,170 photometric observations
q 155,411 spectroscopic observations
Figure courtesy Airbus DSYou can also read
