Comoving Stars in Gaia DR1

Princeton thunch talk - please see https://arxiv.org/abs/1709.05344 for the updated writeup of Kronos-Krios.

Transcript

1. Comoving Stars Semyeong Oh (Princeton) 2017-05-11 Thunch Gaia DR1 in
2. I acknowledge help from David N. Spergel (Princeton, CCA) Adrian M. Price-Whelan (Princeton) David W. Hogg (NYU, CCA, MPIA) Tim D. Morton (Princeton) John M. Brewer (Yale) Keith A. Hawkins (Columbia) Nathan W. C. Leigh (AMNH)
3. I will talk about Searching for comoving pairs in Gaia DR1 Kronos & Krios (HD 240429 & HD 240430) Intro: what and why Summary
4. What are comoving stars?
5. Comoving stars are any number of stars roughly co-located and on a scale smaller than galactic scale sharing very similar space velocity with dispersions smaller than that of field stars
6. Comoving stars are wide binaries
 (triples, multiples) moving groups open clusters
7. Example 1: wide binaries triples, multiples ?
8. Example 2. Moving Groups • clumps of stars with the same velocity • anomaly from smooth velocity distribution origin still under debate • remnants of clusters? • transient phenomena? Bovy et al. 2009
9. Example 3. Open Clusters • hundreds to thousands stars • loosely gravitationally bound • σ < 1 km/s M44 (Beehive), credit: Bob Franke M45 (Pleiades), credit: Robert Gendler
10. Why are they interesting?
11. Comoving stars are tracers of Galactic tidal field.
12. Some binaries are more valuable for calibrating/testing stellar models • F/G/K - M binaries provides anchors for calibrating M dwarf properties. • Giant-Main Sequence pairs are useful for testing consistency between stellar atmospheric models. Wide separation ensures no interaction since birth.
13. Young moving groups are interesting places to search planets and brown dwarfs. Credit: ESO/A.-M. Lagrange et al. debris disk (1996) β Pic b (2008) β Pic Age:12Myr
14. Gaia opens a new era for studying the Milky Way. from M. Perryman’s Spitzer lecture (2013)
15. Gaia maps a billion stars. HIPPARCOS Gaia mission date 1989-1993 2013-2018 # sources 100,000 100,000,000 magnitude limit 12 20 parallax accuracy ~ 1 mas 7 µas at V=10 25 µas at V=15 300 µas at V=20 effective distance limit 1 kph 1 Mpc
16. Many spectroscopic surveys will complement the Gaia data. Name Number of sources Product Status RAVE 483k stars RV + Teff, logg, Z 2003-2013 DR5 Sep 2016 GALAH 1M stars RV + 15 abundances late 2013- DR1 Sep 2016 Gaia-ESO ≥100k stars RV + ≥12 abundances Dec 2011- DR2 July 2015 APOGEE (-2) 100k giants (300k stars) RV + 15 abundances 1: 2011-2014 (2: 2014-2020)
17. Gaia first data release on Sep 14, 2016
18. Tycho-Gaia Astrometric Solution (TGAS) provides proper motions for 2M stars Credit: Michalik & Lindegren
19. Tycho-Gaia Astrometric Solution (TGAS) provides proper motions for 2M stars Credit: Michalik & Lindegren
20. Tycho-Gaia Astrometric Solution (TGAS) provides proper motions for 2M stars Credit: Michalik & Lindegren
21. Tycho-Gaia Astrometric Solution (TGAS) provides proper motions for 2M stars Credit: Michalik & Lindegren
22. Searching for comoving pairs in Gaia DR1 Oh et al. 2017 (in press) arxiv:1612.02440
23. We pose the discovery as a model selection problem. Case 1 Case 2
24. We build a probabilistic model for the data on assumptions of space velocities. Case 1 Case 2
25. parallax [mas] position [deg] proper motion [mas/yr] We build a probabilistic model for the data on assumptions of space velocities.
26. with uncertainties We build a probabilistic model for the data on assumptions of space velocities.
27. L(~ µ |~ v, r) p(~ v) p(r | $) We build a probabilistic model for the data on assumptions of space velocities.
28. Case 1 Case 2 We build a probabilistic model for the data on assumptions of space velocities.
29. We build a probabilistic model for the data on assumptions of space velocities.
30. We marginalize over unknown distances and 3D velocities. L1 L2 = R L(~ µ1 |~ v, r1) L(~ µ2 |~ v, r2) p(~ v) p(r1 | $1) p(r2 | $2)drd3~ v ⇧i=1,2 R L(~ µi |~ v, r) p(~ v) p(r | $i) dr d3~ v We use the ratio of fully marginalized likelihoods (“Bayes factor”) as the quantity to select co-moving stars.
31. We examine 271k pairs with [S/N]ϖ > 8, |∆x| < 10 pc, |∆vt | < 10 km/s.
32. We select pairs with as candidate co-moving pairs ln L1/L2 > 6 random pairs
33. Of 271k pairs, we find 13,058 candidate comoving pairs among 10,606 stars.
35. Of 271k pairs, we find 13,058 candidate comoving pairs among 10,606 stars, resulting in 4,555 connected components.
36. Size of connected components varies from 2 to 151.
37. Largest connected component: 151 stars, 3465 edges “Pleiades”
39. NCC > 5
40. Melotte 111 (Coma) Melotte 25 (Hyades) Alessi 13 NGC 2632
 beehive Explore yourself at smoh.space/vis/gaia-comoving-stars
42. The number of very wide separation co-moving pairs increases at > 1pc. 10 2 10 1 100 101 separation [pc] 10 1 100 101 102 103 104 count all size=2 (mutually exclusive) size>2
43. 10 5 0 5 10 vr / vr size=2 (mutually exclusive) size>2 10 1 100 101 separation [pc] 0.0 0.2 0.4 0.6 0.8 1.0 f (| vr / vr | < 3) 283 pairs with RAVE RV
44. Jiang & Tremaine (2010) predicted these wide separation co-moving pairs. Jacobi radius rJ = 1.7 pc Jiang & Tremaine (2010)
45. 0.0 0.5 1.0 1.5 2.0 2.5 G J [mag] 2 0 2 4 6 8 10 G + 5(log ˆ d + 1) [mag] separation < 1 pc (N=297) 0.0 0.5 1.0 1.5 2.0 2.5 G J [mag] 2 0 2 4 6 8 10 separation > 1 pc (N=3939) mutually exclusive pairs
46. Krios & Kronos HD 240429 & HD 240430 work in progress
48. HD 240429 & HD 240430 Name HD 240429 HD 240430 Sun Sp Type G2 G0 G2 Teff 5878 5803 5777 log(g) 4.43 4.33 4.44 vsin(i) 1.1 2.5 2 [Fe/H] 0.01 0.20 0.00 Krios Kronos
49. Krios and Kronos are comoving. Name HD 240429 HD 240430 9.35 ± 0.24 9.41 ± 0.25 89.25 ± 0.66 89.41 ± 0.69 -29.68 ± 0.54 -30.12 ± 0.69 vr -21.2 -21.2 Krios Kronos
50. Krios & Kronos are coeval. 4.00+1.51 -1.56 Gyr 4.28+1.11 -1.05 Gyr
51. Yet, Krios and Kronos have
 very different abundances.
52. Condensation temperature for solar abundance
 from Lodders et al. 2003
53. Kronos is enhanced
 in only high-TC elements.
54. Krios and Kronos show
 anomalously high surface Li abundance. Name Krios Kronos [Fe/H] 0.01 0.20 A(Li) 2.25 2.75 Melendez et al. 2017
55. Kronos probably engulfed rocky planet(s)? • Two stars are comoving and coeval, most likely in wide binary system. • Yet, they have different abundance patterns strongly dependent on TC . • Metal enrichment of convective zone from rocky planets provides an explanation. Francisco Goya,
 Saturn Devouring His Son, c. 1819–1823
56. Hom much mass of metals is needed? ZfCZM ⇥ 0.6 = 65 M fraction of mass in convection zone 0.02 0.2 dex increment in [Fe/H] mass fraction in metals 0.01631
57. Summary • Comoving stars are interesting for studying the Milky Way, stars, and planets. • We made a catalog of comoving pairs using model selection. • We discovered a pair of comoving stars with very different abundances, suggesting heavy rocky planet accretion.