An all sky survey of 1.7 billion point like sources (V<20):
— Position & brightness: 1.7 billion
— Color: 1.4 billion; distance & proper motion: 1.3 billion
— Surface temperature: 161 million
— Radius & luminosity: 77 million
— Radial velocity: 7 million
Scanning:
each object 10-250 times (ave=80)
Hipparcos: 0.7-0.9 mas
(1mas = 0.001’’)
Slide 6
Slide 6 text
Astrometry the Ancient Technique
Proper Motion: angular motion across the sky of nearby stars with
respect to distant stars. At same Vt, the further, the smaller μ.
Cumulative.
Slide 7
Slide 7 text
Proper Motion: angular motion across the sky of nearby stars with
respect to distant stars. At same Vt, the further, the smaller μ.
Cumulative.
Parallax: the displacement in the apparent position viewed along
two different lines of sight. Only along the direction of earth’s motion.
Go back and forth.
Astrometry the Ancient Technique
Slide 8
Slide 8 text
Proper Motion: angular motion across the sky of nearby stars with
respect to distant stars. At same Vt, the further, the smaller μ.
Cumulative.
Parallax: the displacement in the apparent position viewed along
two different lines of sight. Only along the direction of earth’s motion.
Go back and forth.
Astrometry the Ancient Technique
0GGF$C[GUKCP/GVJQFŎ
Slide 9
Slide 9 text
Science Instruments
Two telescopes
One focal plane
)NQDCN#UVTQOGVTKE+PVGTHGTQOGVGTQH#UVTQRJ[UKEU
Slide 10
Slide 10 text
The Focal Plane
wave front sensor
basic angle monitor
The sky
Mappers Astrometric Field 2
Slide 11
Slide 11 text
The Focal Plane
BP (blue photometer):
330-680nm
RP (red photometer):
640-1050nm
two low resolution spectra — color
R = 20-100
Slide 12
Slide 12 text
The Focal Plane
doppler shift of absorption lines
in a high-resolution spectrum
845-872nm CaT
R = 11500
Vr, classification,
Teff, logg, [Fe/H], E…
Slide 13
Slide 13 text
• Stellar Physics: CMD ( WD Population + Variable Stars)
• Kinematics of the Milky Way & the Solar Neighborhood
Science
Slide 14
Slide 14 text
Composite HRD of
32 Open Cluster
Young
Old
Slide 15
Slide 15 text
Globular Cluster
Slide 16
Slide 16 text
Solar neighborhood HRD
Gaia
Hipparcos
(<200pc)
Slide 17
Slide 17 text
Hipparcos Gaia
blue: median fiducial
green: the same fiducial -0.753 mag,
corresponding to an unresolved
binary system of two identical stars.
Gaia
age
binary
Solar neighborhood HRD
Slide 18
Slide 18 text
Gaia
Gaia
age
binary
RC
Solar neighborhood HRD
Hipparcos
Red Clump Stars
White Dwarfs
blue: median fiducial
green: the same fiducial -0.753 mag,
corresponding to an unresolved
binary system of two identical stars.
Slide 19
Slide 19 text
Local WD Population
DA: hydrogen
atmosphere WDs
DB: helium
atmosphere WDs
Slide 20
Slide 20 text
Local WD Population
Slide 21
Slide 21 text
Local WD Population
36% DB
not due to different
atmospheric composition
Fit Gaia CMD with DA/DB
mass distribution
Slide 22
Slide 22 text
Local WD Population
DA
DA
DB
low mass
WDs require
binary evolution
second peak
contributes ~25%
WDs (0.65-0.9 Msun)
predicted frequency of
single WDs that form
through mergers.
Slide 23
Slide 23 text
Variable Stars
Slide 24
Slide 24 text
Pulsating Stars on the CMD
Slide 25
Slide 25 text
Motions on the CMD
Pulsating Stars:
brightness variations dominated by
changes in temperature (not radius)
Slide 26
Slide 26 text
Pulsating Stars:
brightness variations dominated by
changes in temperature (not radius)
Eclipsing Variables:
EW type — similar mass (color)
— nearly vertical path
Motions on the CMD
Slide 27
Slide 27 text
Pulsating Stars:
brightness variations dominated by
changes in temperature (not radius)
Eclipsing Variables:
EW type — similar mass (color)
— nearly vertical path
Rotationally induced Variables:
cold star-spots, absorb light in blue,
re-emit in red.
Broad band G, horizontal.
Motions on the CMD
Slide 28
Slide 28 text
Pulsating Stars:
brightness variations dominated by
changes in temperature (not radius)
Eclipsing Variables:
EW type — similar mass (color)
— nearly vertical path
Rotationally induced Variables:
cold star-spots, absorb light in blue,
re-emit in red.
Broad band G, horizontal.
Eruptive Stars:
additional extinction during eruptive
phases — redder when brighter.
Motions on the CMD
Slide 29
Slide 29 text
The story just begins…
Slide 30
Slide 30 text
No content
Slide 31
Slide 31 text
azimuth -30~30 deg
inertial frame: clockwise
Slide 32
Slide 32 text
Radial Velocity Gradient in the MW Disk
Median Galactic Vr of the giant sample as a function of galactic radius for 2 azimuth slices.
The curves correspond to different Z layers.
A pattern of oscillation.
Confirmed galactocentric radial velocity gradients in the inner / outer disk.
Slide 33
Slide 33 text
Median velocities in the disk plane
Complexity and richness of the galactic velocity fields.
Streaming motions could be produced by:
(i) internal mechanisms (response of the stars to the bar or spiral structure)
(ii) external perturber: e.g. satellite accretion, impact of low-mass dark matter halos.
of the giant sample.
semi-circular geometry,
with a small pitch angle.
red circular arcs,
large-scale variation
gradient outwards
Velocity distribution of the Solar Neighborhood
away from galactic center towards galactic center
slower than
the sun
faster than
the sun
Most stars
at Sun’s location:
V=-20
U=0
W=0
Slide 36
Slide 36 text
Velocity distribution of the Solar Neighborhood
Velocity plane of stars in the solar neighborhood, 2D histogram of the velocity with a sbin of 1km/s.
away from galactic center towards galactic center
slower than
the sun
faster than
the sun
Arch-like structure; Hercules stream — 2 branches? Hyades, Pleiades…
Slide 37
Slide 37 text
Velocity plane of stars in several distant regions in a ring between 0.5 and 1 kpc from the Sun.
Velocity distribution in the Solar Outskirts
Galactic Center
Arch-like structure; great change in galactic radius (than in azimuth);
Hercules gap variations (right to left: 200 - 240 km/s); 2nd gap…
Slide 38
Slide 38 text
Future of Astrometry
•Relative Astrometry (Pointed Mission) in the Sub-μas Regime
•Global astrometry in sub-μas or even nano-arcsec regime
•Global astrometry in the near-infrared (NIR)
•Global astrometry in the optical in a new Gaia-like mission
6JCPMUHQTNKUVGPKPI