Gaia DR2 shows evidence of the freezing of white dwarfs.

1. Gaia and the white dwarf cooling track
Pier-Emmanuel Tremblay
Nicola Gentile Fusillo, Mark Hollands, Elena Cukanovaite,
Tim Cunningham, Jack McCleery, Boris Gänsicke, Tom Marsh

2. MWD ~ 0.2 - 1.3 Mʘ
log g = 5 - 9
g = GM
R2(M,Teff)
7% of local objects are white dwarfs but 95% will be…

3. Fraction: 75% 25% 0.1%
H (<10-4 MWD)
He (<10-2 MWD)
C/O (>99% MWD)
Except binary evolution and high-masses (O/Ne)

4. Manser et al. 2019, Science, press release

5. Modern evolution models:
cooling at near constant radius
MWD = 1.2 Mʘ
MWD = 0.4 Mʘ
Renedo et al. 2010

6. 1995-2018: cluster white dwarfs
(2013)
Age > 12 Gyr
it implies that white dwarfs
on the cooling track are all
MWD ~ 0.55 Mʘ
Minitial ~ 0.9 Mʘ
Other masses are at the
bottom.

7. DR2: 25 April 2018
(Gaia Collaboration Babusiaux et al. 2018)
~26,000 white dwarfs
0 < Age < 12 Gyr
Minitial ~ 0.9-8.0 Mʘ

8. 2019MNRAS.484.3544R Rowell & Kilic The kinematics of Galactic disc white dwarfs in Gaia DR2
2019arXiv190402022B Bergeron et al On the Measurement of Fundamental Parameters of White Dwarfs in the Gaia Era
2019MNRAS.tmp..778T Torres et al Thin disk, thick disk and halo Gaia-DR2 white dwarf population
2019MNRAS.483.3098S Salaris et al. Praesepe white dwarfs in Gaia DR2
2019A&A...623A.177S Serenelli et al. Nature of blackbody stars
2019NatAs...3..129V Van Horn The crystallization of white dwarf stars
2019MNRAS.483..901P Perpinyà-Vallès et al Discovery of the first resolved triple white dwarf
2019MNRAS.482.5222T Tremblay et al Fundamental parameter accuracy of DA and DB white dwarfs in Gaia Data Release 2
2019MNRAS.482.4570G Gentile Fusillo et al A Gaia Data Release 2 catalogue of white dwarfs and a comparison with SDSS
2019ApJ...871..169G Genest-Beaulieu & Bergeron A Comprehensive Analysis of DA and DB White Dwarfs from SDSS and Gaia
2019Natur.565..202T Tremblay et al Core crystallization and pile-up in the cooling sequence of evolving white dwarfs
2019MNRAS.482..965K Kilic et al The age of the Galactic stellar halo from Gaia white dwarfs
2019MNRAS.482..649O Ourique et al A study of cool white dwarfs in the Sloan Digital Sky Survey Data Release 12
2019A&A...621L...2R Röser et al Hyades tidal tails revealed by Gaia DR2
2018ApJS..239...26L Leggett et al Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample
2018A&A...620A.141R Ramsay et al. Physical properties of AM CVn stars: New insights from Gaia DR2
2018MNRAS.480.4884E El-Badry & Rix Imprints of white dwarf recoil in the separation distribution of Gaia wide binaries
2018MNRAS.480.4505J Jiménez-Esteban et al A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory
2018MNRAS.480.3942H Hollands et al The Gaia 20 pc white dwarf sample
2018MNRAS.480.3170S Salaris & Bedin A Gaia DR2 view of white dwarfs in the Hyades
2018A&A...619A..31S Scholz et al Spectroscopic classification and Gaia DR2 parallaxes of new nearby white dwarfs
2018MNRAS.479L.113K Kilic et al Gaia reveals evidence for merged white dwarfs
2018MNRAS.479L..96R Raddi et al Anatomy of the hyper-runaway star LP 40-365 with Gaia
2018MNRAS.479.1612J Joyce et al Testing the white dwarf mass-radius relation with Gaia DR2, HST, and FUSE
2018ApJ...865...15S Shen et al Three Hypervelocity White Dwarfs in Gaia DR2
2018ApJ...860L..17E El-Badry et al An Empirical Measurement of the Initial–Final Mass Relation with Gaia White Dwarfs

9. Gentile Fusillo et al. 2019
a catalogue of ~250,000 white dwarfs
parallax_over_error > 1

10. Gentile Fusillo et al. 2019
selection based on flags similar to Gaia Collaboration et al. but less restrictive
before
after

11. Hollands et al. 2018
completeness within 20 pc
Completeness for d < 100 pc
and G < 20 likely > 95% as well
99 %
at 20 pc
(G < 17)

12. Photometry + Parallax + Spectroscopy
• Teff
• Radius or Mass [Mass-Radius relation]
• Surface composition
-> Cooling age, Total age [Initial-to-final mass relation]
Gaia-data only fits already fairly precise (Hollands et al. 2018)
Bergeron et al. (2001)

13. Initial-to-final mass relation from Gaia DR2
El-Badry, Rix & Weisz 2018

14. 200 pc: ~3400 WDs in wide binaries in Gaia DR2
Alternative way of deriving initial-to-final relation
El-Badry & Rix (2018)
see also Hollands et al. (2018)

15. WD+MS binaries
Volume complete stellar evolution
Gaia + spectroscopy (4MOST + WEAVE + DESI + SDSS-V)
(total)
IMF
SFH
(Gaia volume complete)

16. About 4000 pure-H atmosphere WDs
(15 < G < 17), with reddening included
• Gaia Teff compatible with Pan-STARRS
and SDSS photometry (~ 2%)
• No corrections added to revised DR2 or
SDSS filters
• Gaia Teff has 5-10% offset with
spectroscopic values.
• Similar offset with HST/STIS
spectrophotometry
• Spectroscopic distances (Teff+radii)
agree very well with Gaia distances.
A Revise Gaia, SDSS, Pan-STARRS filters?
B Revise WD spectroscopy?
Gentile Fusillo et al. 2019
Tremblay et al. 2019b

17. 25 April 2018
(Gaia collaboration Babusiaux et al. 2018)

18. El-Badry et al. 2018, Gentile Fusillo et al. 2019, Bergeron et al. 2019
Gray = all 100 pc
A = hydrogen atmospheres
B = helium atmospheres

19. Gentile Fusillo et al. 2019
Gray = DA
A = hydrogen atmospheres
Q = also hydrogen atmospheres

21. Tremblay, Fontaine et al. 2019

22. Carbon phase diagram (terrestrial)
Temperature (1000 K)

23. Temperature (1000 K)
Pressure(Gpa)
1016
106
100,000100
solid
liquid
White dwarf evolution

24. 20% to 80% solid
0.6 Mʘ
1.1 Mʘ
0.9 Mʘ
Tremblay et al. 2019a
100 pc – 15,000 white dwarfs

25. Gaia DR2
No latent heat
C-core crystallization
C/O-core crystallization
10 Gyr
Tremblay et al. 2019a

26. Conclusions
• Galactic chronology is best with precise white dwarf ages.
• Up to 250,000 white dwarfs in Gaia DR2 with parallaxes.
• Spectroscopic follow-up with 4MOST, WEAVE, DESI, SDSS-V.
• 10 000 evolved planetary systems, 10 000 wide binaries including white dwarfs….