Galactic, stellar (and planetary) archaeology with Gaia: The galactic white dwarf population Boris Gänsicke & Roberto Raddi Richard Ashley Jay Farihi Nicola Gentile Fusillo Mark Hollands Paula Izquierdo Matthew Hoskin Alberto Rebassa Mansergas Tom Marsh Pablo Rodríguez Gil Pier-Emmanuel Tremblay Silvia Toonen
95% 5%
B2 35Myr A0 250Myr 10Gyr
Gaia and the Solar neighbourhood 300.000 white dwarfs with G 20 350.000 stars within 100pc
White Dwarf Luminosity Function Cut-off at faintest, coolest, oldest white dwarfs Cut-off in the white dwarf luminosity function due to the limited age of the Galaxy Even the oldest white dwarfs (9-11 Gyrs) are still visible in the solar neighborhood bright hot young faint cool old Measure the age of the Galaxy (e.g. Oswalt et al. 1996, Nature 382, 692)
Tentative evidence of enhance star formation over the past ~5Gyr 117 white dwarfs Teff, log g, masses Distances Ages Initial mass function Star formation rate / history Initial-to-final mass relation Tremblay et al. 2014, ApJ 791, 92
Many (most?) stars are in binaries Binary fraction Initial mass ratio distribution Initial period (& eccentricity) distribution Interactions (common envelope) using again the 20pc white dwarf sample Toonen et al. 2017, A&A 602, 16
Supernova Type Ia progenitors SN Ia progenitors need M 1 +M 2 1.4M So far... Zero known Silvia Toonen
3x20min sensitive to massive short period DDs
Many planetary systems will survive into the white dwarf phase
Photospheric metal pollution by planetary debris Jura & Young 2014, ARE&PS 42, 45 Fe Mg Ca
Planetary archaeology = bulk composition Raddi et al. 2015, MNRAS 450, 2083 Hollands et al. 2017, MNRAS 467, 4970
Flux calibration with white dwarfs - Only two free parameters (Teff, log g), no metallicity. - Fit is done to the normalised Balmer lines, Stark broadening is sensitive to both temperature and surface gravity. cool hot
Flux calibration with white dwarfs - Only two free parameters (Teff, log g), no metallicity. - Fit is done to the normalised Balmer lines, Stark broadening is sensitive to both temperature and surface gravity. - Balmer lines go through max. equivalent width near ~15000K, hot & cold solution, selection (now) based on χ 2 cool hot
Flux calibration with white dwarfs - Only two free parameters (Teff, log g), no metallicity. - Fit is done to the normalised Balmer lines, Stark broadening is sensitive to both temperature and surface gravity. - Balmer lines go through max. equivalent width near ~15000K, hot & cold solution, unambiguous selection based on Gaia parallax (April 2018) cool hot
Flux calibration with white dwarfs - Best fit & count rate spectrum response function
Flux calibration with white dwarfs - Works also at relatively low S/N
Flux calibrations from OpR2 & residuals in OpR2.5
OpR2.5: Gp=19.2 S/N=17
OpR2.5: Gp=19.4 S/N=7
OpR2.5: Input vs output (Gaia π, Gp, Rp, Bp not used as constraints!)
White dwarf selection April 2018 Gaia Data Release 2 - Prediction from the GUMS-10 simulation (Robin et al. 2012) - G 20 500.000 white dwarfs all-sky, probably over-estimated by x2 Absolute magnitude giants main sequence halo/thick disc white dwarfs
White dwarf selection April 2018 Gaia Data Release 2 - Prediction from the GUMS-10 simulation (Robin et al. 2012) - G 20 500.000 white dwarfs all-sky, probably over-estimated by x2 - Adding 2-year-into-mission uncertainties using PyGaia - pseudo absolute magnitude using π instead of distance giants main sequence white dwarfs 100 deg 2 l=180, b=45
White dwarf selection April 2018 Gaia Data Release 2 - Prediction from the GUMS-10 simulation (Robin et al. 2012) - G 20 500.000 white dwarfs all-sky, probably over-estimated by x2 - Adding 2-year-into-mission uncertainties using PyGaia - pseudo absolute magnitude using π instead of distance giants main sequence white dwarfs reddening! 100 deg 2 l=100, b=0
White dwarf selection April 2018 G + 5log(π) + 5 > 2.8 x (BP-RP) + 8 && (BP-RP) < 2.3 white dwarfs
White dwarf selection April 2018 - G 20 250.000 500.000 white dwarfs all-sky 6-12 white dwarfs deg -2 / 18-36 per WEAVE field
Why observe ~150000 with WEAVE? Gaia - First unbiased sample Accurate mass-dependent luminosity function as tracer of galactic SFR Sample thick disc & halo population (~1%) Initial-to-final mass relation in HD Huge resource for stellar, binary & planetary evolution Rare (few %) WDs provide important link to supernovae, planets, gravitational waves sources, strong magnetic fields etc. and if you don t care about any of the above, we ll flux calibrate your spectra
White dwarf selection now Gentile-Fusillo et al. 2015, MNRAS 448, 2260: - SDSS colours + SDSS vs USNO proper motions - Probability of being a white dwarf (Pwd) spectroscopically calibrated - Largest, most reliable white dwarf catalogue - g 19, SDSS imaging footprint, 23.000 white dwarfs, 9000 with spectra DA / non-da white dwarfs, hot stars, QSO