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Astrometry of Binary Stars:What Are We Waiting For?
Elliott Horch, Southern Connecticut State University
9/21/2008 1Stars in Motion
BU 151AB
1 arcsec
AndoriXon
PI PIXIS
9/21/2008 2
High Resolution Imaging and Binary Stars
Stellar Masses.
Mass-Luminosity Relation (MLR) Initial Mass Function (IMF) Statistics of binaries as clues to star formation and
galactic evolution. Ghez et al, Leinert et al. Recent models of Bate, etc. Duquennoy & Mayor and updates. Post-formation environment.
Future projects such as SIM, GAIA: a very important development for binary star research.
Stars in Motion
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Orbits and masses.
Binary stars. Gravitation --> orbit.
Traditionally very hard to get good masses.
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Need SIZE of orbit, which means we need the distance.
Hipparcos Satellite has done that job reasonably well … Gaia, SIM will do much better!
Stars in Motion
Example: Burnham 151AB
An exquisite orbit! P/P = 0.00041 a/a = 0.00137 Hipparcos distance
~30 pc = 0.02628 Gaia: ~ 0.0006.
Then you’ll get great masses!
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BU 151AB Continued…
H-R diagram with Y2 isochrones at right.
Speckle binaries with good magnitude/ color information of components can be excellent tests of stellar evolution.
We want to make many plots like this!
With evolved components, one can derive good ages.
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Speckle: What’s New? Instrumentation/Data Analysis
• CCDs for good differential photometry (and of course astrometry too!)
• EMCCDs: near photon-counting performance at >90% QE• Linear detectors mean more possibilities in terms of
reduction algorithms.
Science• Hipparcos doubles Hipparcos BINARIES!• Many tests of stellar evolution: put COMPONENTS of
binaries on the H-R diagram.• Evolved Components.
9/21/2008 6Stars in Motion
9/21/2008 7
Solving the m problem with CCDs.
CCD Array
Tip-Tilt Mirror
Telescope Optics
SpeckleImages
(b)
CCD Array
“Tip” Mirror
Telescope Optics
SpeckleImages
Row Shifts
(a)
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9/21/2008 8
DSSI: The latest project…
Stars in Motion
The Differential Speckle Survey Instrument (DSSI) Two channel CCD-based
speckle camera, completed in August, 2008
Observe two colors at the same time (dichroic beamsplitter inside).
Differential refraction
9/21/2008 9Stars in Motion
DSSI@WIYN
DSSI Raw Frames, HIP 15737
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692 nm562 nm
Color Differences
9/21/2008 11Stars in Motion
HIP 15737(Primary isK3III)
HIP 101958(Primary is B9IV)
1 arcsec
McAlister 40 Below the Diffraction Limit CCDs: good
photometry -> speckle shapes.
Elongated speckles: Could be refraction, could be a component below the diff. lim.
Two colors can tell you which.
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DSSI Result: Analytic Continuation
562 nm 692 nm
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1 arcsec 1 arcsec
HIP 6966 = A 1910AB Separation = 0.175 arcsec, position angle = 187o, V=6.77,Spectral Type = A0
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Wavelet-Based Image Reconstruction
We can see fainter companion stars!
Stars in Motion
iXon EMCCD Camera
512x512 pixels 1,3,5 MHz
full frame ~17Hz
128x128 sub- array, use 33 Hz.
9/21/2008 Stars in Motion 15
Near Photon-Counting Performance at >90% QE!!
iXon@WIYN
A sample result: RYTSI+iXon @ WIYN LP 439-387
Primary Mag. =15.7
Secondary Mag. =16.0
Sep ~ 0.8” About 40
seconds of data.
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iXon and Kepler
Kepler: Satellite to detect Earthlike exoplanets through transits.
iXon set-up is helping to screen targets of interest to Kepler for binarity.
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11.5-mag Kepler comparisonstar shown to be binary at WIYN,June 2008.
Conclusions
What are we waiting for? We’ve got great instrumentation for speckle
that is significantly more capable than in the past!
We can’t yet reap all the astrophysical benefits of these observations. We still need better distances, even to many “nearby” systems.
Bill van Altena has been a tireless supporter, advocate, and all-around cheerleader of this work.
Thank you Bill!!
9/21/2008 Stars in Motion 18
