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Using Gaia for Studying Milky Way Star Clusters

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Using Gaia for Studying Milky Way Star Clusters Using Gaia for studying Milky Way star clusters Eugene Vasiliev Institute of Astronomy, Cambridge Synopsis I Overview of the Gaia mission and DR2: scientific instruments, catalogue contents, measurement uncertainties, caveats and limitations. I Using Gaia astrometry for studying internal kinematics of globular clusters: sample cleaning, membership determination, measurement of velocity dispersion and rotation in the presence of correlated systematic errors. I Galactic population of globular clusters: distribution of clusters in 6d phase space, orbits, inference on the Milky Way potential. Overview of Gaia mission G I Scanning the entire sky every couple of weeks BP RP RVS I Astrometry for sources down to 21 mag I Broad-band photometry/low-res spectra I Radial velocity down to ∼ 15 mag (end-of-mission) [Source: ESA] Overview of Data Release 2 astrometry I Based on 22 months of data collection 9 I Total number of sources: 1:69 × 10 RV I Sources with full astrometry (parallax $, 9 proper motions µα∗; µδ): 1:33 × 10 9 I Colours (GBP ; GRP ): 1:38 × 10 6 I Radial velocities: 7:2 × 10 colours 6 108 I Effective temperature: 160 × 10 Teff ICRF3 prototype 107 vrad SSO Variable Gaia DR1 Gaia-CRF2 Gaia DR2 6 n 6 i 10 b I Stellar parameters (R ; L ): 77 × 10 g a 105 m 1 6 . 0 4 10 I Extinction and reddening: 88 × 10 r e p r 103 e 6 b Variable sources: 0:55 × 10 m I 2 u 10 N 101 100 5 10 15 20 25 Mean G [mag] [Brown+ 2018] Photometry G-band uncertainty [mag] 12 M 3 (NGC 5272), D=10 kpc 13 14 15 16 R-band uncertainty [mag] G 17 18 19 20 21 0.0 0.5 1.0 1.5 GBP GRP − [Evans+ 2018] Astrometry 10 parallax uncertainty [mas] 5 ] s a m 2 [ ) $ ¾ ( 1 x 12 a l l a 0:5 r M 3 (NGC 5272), D=10 kpc a p n i 0:2 y 13 t n i a t r 0:1 e c n u 0:05 14 d r a d n a 0 02 t : S systematic error 15 0:01 0:005 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 16 ] 10 1 G magnitude ¡ r y proper motion uncertainty [mas/yr] 5 s G a m [ 17 ) x a 2 m ; m p ¾ 1 ( 18 : m : 0:5 p n i e s p 0:2 i l 19 l e r o 0:1 r r e f o 0:05 20 s i x a systematic error r o j 0:02 a m 21 ¡ i 0:01 0.0 0.5 1.0 1.5 m e 1 mas/yr = 4:7 km/s × (D=1 Kpc) S 0:005 GBP GRP 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 − G magnitude [Lindegren+ 2018] Spectroscopy 12 RV measurements only for stars with M 3 (NGC 5272), D=10 kpc Teff 2 [3500 ÷ 6900] K and GRVS ≤ 12 13 14 15 radial velocity uncertainty [km/s] 16 G 17 18 19 20 systematic error 21 0.0 0.5 1.0 1.5 GBP GRP − [Katz+ 2018] Correlations and systematic errors correlations between parallax and PM (! Cen region) 1.0 1.0 1.0 1.0 µα µδ µα µδ ÷ ÷ ÷ 0.8 0.6 0.5 0.5 0.5 0.4 0.2 0.0 0.0 0.0 0.0 Y [deg] Y [deg] Y [deg] 0.2 0.4 0.5 0.5 0.5 0.6 0.8 1.0 1.0 1.0 1.0 1.0 0.5 0.0 0.5 1.0 1.0 0.5 0.0 0.5 1.0 1.0 0.5 0.0 0.5 1.0 X [deg] X [deg] X [deg] mean parallax and PM (Large Magellanic Cloud region) 0.10 0.05 0.00 0.05 0.10 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 8 8 8 µα µδ 6 6 6 4 ­ ® 4 ­ ® 4 ­ ® 2 2 2 0 0 0 Y [deg] Y [deg] Y [deg] 2 2 2 4 4 4 6 6 6 8 8 8 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 X [deg] X [deg] X [deg] Limitations I No special processing for binary stars (but a poor astrometric solution is marked clearly { astrometric excess noise) I Colour photometry has lower spatial resolution (a quality control flag is provided { phot bp rp excess factor) I Poor completeness at faint magnitudes in crowded regions I Need to apply various filters to clean up the sample (but do it wisely, e.g., don't just throw away stars with negative parallaxes $ < 0 [see Luri+ 2018 for a discussion]) I Should not generally use 1=$ as a proxy for distance (unless $=$ . 0:2) [Arenou+ 2018] Example: NGC 5139 (! Cen) 40 10 Sky map PM map All stars 30 5 20 10 ] r 0 y / s 0 a m [ δ Y [arcmin] 5 10 µ 20 10 N=248494 30 40 15 100 101 102 103 40 30 20 10 0 10 20 30 40 20 15 10 5 0 5 X [arcmin] µα [mas/yr] 10 10 10 Color - magnitude diagram Magnitude vs. distance from center Magnitude vs. PM error 12 12 12 14 14 14 16 16 16 G [mag] G [mag] G [mag] 18 18 18 20 20 20 0.0 0.5 1.0 1.5 2.0 0 5 10 15 20 25 30 35 40 0.05 0.1 0.2 0.5 1 2 4 BP-RP [mag] R [arcmin] δµα [mas/yr] Example: NGC 5139 (! Cen) 40 10 Sky map PM map 30 Stars with full astrometry 5 20 ($; µα; µδ) 10 ] r 0 y / s 0 a m [ δ Y [arcmin] 5 10 µ 20 10 N=156227 30 40 15 100 101 102 103 40 30 20 10 0 10 20 30 40 20 15 10 5 0 5 X [arcmin] µα [mas/yr] 10 10 10 Color - magnitude diagram Magnitude vs. distance from center Magnitude vs. PM error 12 12 12 14 14 14 16 16 16 G [mag] G [mag] G [mag] 18 18 18 20 20 20 0.0 0.5 1.0 1.5 2.0 0 5 10 15 20 25 30 35 40 0.05 0.1 0.2 0.5 1 2 4 BP-RP [mag] R [arcmin] δµα [mas/yr] Example: NGC 5139 (! Cen) 40 10 Sky map PM map 30 5 Parallax cut: 20 $ − $0 < 3 δ$, 10 ] r 0 y / s $0 = 0:2 mas 0 a m [ δ Y [arcmin] 5 10 µ 20 10 N=146313 30 40 15 100 101 102 103 40 30 20 10 0 10 20 30 40 20 15 10 5 0 5 X [arcmin] µα [mas/yr] 10 10 10 Color - magnitude diagram Magnitude vs. distance from center Magnitude vs. PM error 12 12 12 14 14 14 16 16 16 G [mag] G [mag] G [mag] 18 18 18 20 20 20 0.0 0.5 1.0 1.5 2.0 0 5 10 15 20 25 30 35 40 0.05 0.1 0.2 0.5 1 2 4 BP-RP [mag] R [arcmin] δµα [mas/yr] Example: NGC 5139 (! Cen) 40 10 Sky map PM map 30 Cut on astrometric quality: 5 20 astrometric excess noise < 1 mas 10 ] r 0 y / s renormalized unit weight error < 1:4 0 a m [ δ Y [arcmin] 5 10 µ 20 10 N=111336 30 40 15 100 101 102 103 40 30 20 10 0 10 20 30 40 20 15 10 5 0 5 X [arcmin] µα [mas/yr] 10 10 10 Color - magnitude diagram Magnitude vs. distance from center Magnitude vs. PM error 12 12 12 14 14 14 16 16 16 G [mag] G [mag] G [mag] 18 18 18 20 20 20 0.0 0.5 1.0 1.5 2.0 0 5 10 15 20 25 30 35 40 0.05 0.1 0.2 0.5 1 2 4 BP-RP [mag] R [arcmin] δµα [mas/yr] Example: NGC 5139 (! Cen) 40 10 Sky map PM map 30 Cut on photometric quality: 5 20 phot bp rp excess factor < 10 ] r 0 y / 2 s 1:3 + 0:06 (GBP − GRP ) 0 a m [ δ Y [arcmin] 5 10 µ 20 10 N=47857 30 40 15 100 101 102 103 40 30 20 10 0 10 20 30 40 20 15 10 5 0 5 X [arcmin] µα [mas/yr] 10 10 10 Color - magnitude diagram Magnitude vs. distance from center Magnitude vs. PM error 12 12 12 14 14 14 16 16 16 G [mag] G [mag] G [mag] 18 18 18 20 20 20 0.0 0.5 1.0 1.5 2.0 0 5 10 15 20 25 30 35 40 0.05 0.1 0.2 0.5 1 2 4 BP-RP [mag] R [arcmin] δµα [mas/yr] Example: NGC 5139 (! Cen) 40 10 Sky map PM map 30 Cut on proper motions: 5 20 2 2 2 (µα − µα,0) + (µδ − µδ;0) < ∆µ , 10 ] r 0 y / s µα,0 = −3:2 mas/yr, 0 a m [ δ µδ;0 = −6:7 mas/yr, Y [arcmin] 5 10 µ ∆µ = 2 mas/yr 20 10 N=22865 30 40 15 100 101 102 103 40 30 20 10 0 10 20 30 40 20 15 10 5 0 5 X [arcmin] µα [mas/yr] 10 10 10 Color - magnitude diagram Magnitude vs.
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