Nicholas Fantin NGVS Meeting September 22 nd 2016 Outline Motivation Selecting White Dwarf Candidates Photometric and Kinematic Properties Halo White Dwarfs Next Steps Summary Motivation ID: 932241
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Slide1
Characterizing the Galactic White Dwarf Population
Nicholas Fantin
NGVS Meeting,
September 22
nd
, 2016
Slide2Outline
Motivation
Selecting White Dwarf Candidates
Photometric and Kinematic Properties
Halo White Dwarfs
Next Steps
Summary
Slide3Motivation
Despite their importance to Galactic formation and evolutionary models, halo white dwarfs are one of the least studied populations of stars
They provide boundary conditions for stellar evolutionary
models
White dwarfs can be used to estimate the age of the Milky
Way and it’s components
Slide4Halo White Dwarfs
Pauli et al. (2006) studied 398 DAs and found 7 Halo Candidates (to R~18)
Kalirai
(2012) classified these objects as ‘Inner Halo’ WDs by comparing them with those in the globular cluster M4
They have temperatures between 14,000 and 20,000 K
These represent the newest white dwarfs in the Galactic halo
Slide5Proper Motions
Proper Motions were calculated using the difference between SDSS and NGVS positions and epochs
Uncertainties were estimated using QSOs
Slide6Candidate Selection
Slide7Magnitude Distribution
The magnitude distribution highlights the depth of the NGVS and
GUViCS
data compared to Bianchi et al. (2011) (B11) and the SDSS Spectroscopic form
Kleinman
et al. (2013) (K13).
Slide8Photometric Distances
Photometric distances were calculated using a colour-absolute magnitude relation from Bianchi et al. (2011)
Slide9Disk or Halo WD?
Galactic Space Velocities were calculated following the Johnson & Soderblom (1987) method
Velocity ellipses from Chiba & Beers (2000) were used to separate the disk and halo populations
Slide10Reduced Proper Motion Diagram
H = m + 5logμ + 5 = M + 5logv
t
– 3.379
Slide11Results
120:20
Disk:Halo
ratio
20 Halo White Dwarf Candidates:
Distances ranging from 1-3
kpc
Tangential velocities > 150 kms-1
Galactic Space velocities which place them outside the 2σ velocity ellipsoid for the thick disk
Slide12Next Steps
1. Select cooler white dwarfs
Slide13Next steps (cont’d)
2. Using Proper Motions to improve candidate selection
3. Investigate whether using just NGVS magnitudes for candidate selection yields better results
4. Estimate space density for disk and halo white dwarfs and compare to previous studies
5. Form a luminosity function for both components and compare to previous results
Slide14Summary
White dwarf candidates were selected using the NGVS and
GUViCS
(GALEX) colours
White dwarfs were characterized as disk or halo white dwarfs using kinematics
Future work will use this catalog to obtain a space density and produce a luminosity function
F
eedback welcome!
Slide15