Transcript Dynamite Diameters

Dynamite
Diameters
Observations of main sequence stars with
long baseline optical/infrared
interferometry
Tabetha Boyajian (Georgia State University / CHARA)
Hubble Fellow Symposium
March 8-11, 2010
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Big Picture:
Empirically determined H-R diagram from interferometric measurements
Spica

An interferometer
measure the angular
diameter (θ) of a star.
(yields the effective
temperature and L with
distance and flux)

Important issues at
hand:
 Calibration of
temperature
scales established
through less direct
methods
 Discrepancies
between theory
and observations
Hyades Giants
Regulus
Vega
Procyon
Altair
Sun
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α Cen A,B
61 Cyg A,B
Interferometers today
 Direct methods to
Current and Future
Optical / Infrared Interferometers
measure stellar
sizes:
 Long baseline
optical
interferometry
 Eclipsing binaries
 Occultation
(Planetary and
Lunar)
 Speckle
interferometry
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a) Closed 2006, b) closed 2009, c) under construction
The CHARA Array
 Six 1 meter telescopes
with maximum
baseline of 330 meters
 Longest optical
interferometer in the
world
 Five beam combiners
available (2,3, and 4
telescope modes)
 Accommodates
remote and parallel
observing modes
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The First
Diameters
 1921
 Michelson and Pease measure the diameter
of Betelgeuse
 20-foot interferometer mounted on the 100inch Hooker telescope
 1950-1972
 Narrabri Stellar Intensity Interferometer
 32 diameters of stars measured in the visible
 Empirical temperature scale for stars hotter
than our Sun is based upon this data
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Code et al. 1976
Progress
Total # of stars with angular
diameter measurement
Stars with σθ < 5%
Stars with σθ < 5% and on
main-sequence
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1997
2004
145
458
(~3)
45
242
(~5.5)
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Source:
Davis 1997
(4)
Source:
Richichi et al. 2005
(CHARM2 Catalogue)
Census 2009
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*Measurements outlined in black are from the CHARA Array.
Does not include new results presented here on K-M dwarfs.
How do direct measurements compare
to semi-empirical values?
APL99=Allende Prieto and Lambert 1999; GCS07=Holmberg 2007; Tak07=Takeda 2007
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Boyajian et al. 2009, 2010, in
Inconsistencies and
their implications
 Y2 isochrones fit to empirically
determined T and L to determine M
and age
 Results agree well will eclipsing
binaries
 If temperature is over-estimated:
 Gravity (log g) is over-estimated
 e.g.: if you use spectroscopic log g
and interferometric radius to derive
a mass, then the star appears too
massive
 Radius is under-estimated
 Age is under-estimated
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Boyajian et al. 2009, 2010, in prep
Metallicity effects on temperature
A0
K0
A0
K0
Effective temperature calibrations
 Calibrations used for transforming
observed colors and metallicity to
temperatures
 Solution finds coefficients to polynomial
where θ=5040/T, X is color index and [Fe/H]
is metallicity of object (Alonso et al. 1996)
 Spread in temperatures of different scales is
up to 300K
 At [Fe/H]=-1.5, the empirical scale is ~200K
cooler for all stars in other relations
compared here
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 EFF  a0  a1 X  a2 X 2  a3 X[Fe/H]  a4 [Fe/H]  a5[Fe/H]2
Observations of
late-type dwarfs
 K-M stars with
diameters
measured to
better than 5%
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Theory versus
observation: I
 Masses for single stars are
derived from the K-band
mass-luminosity relationship
from Delfosse et al. 2000, and
assume a 10% error.
 (TOP) The solid black line is a
5 Gyr isochrone from the
BCAH98 models (Baraffe et
al. 1998) for Lmix=Hp, the
dotted and dashed lines are
Lmix=1.5 and 1.9 Hp,
respectively.
 (BOTTOM) dotted line
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signifies zero deviation
between observation and
model.
Theory versus observation: II
López-Morales 2007
 More data makes these plots
look a little different
 A new explanation is needed
to explain offset in single stars
Demory et al. 2009 (Includes Mass<.9 M)
Berger et al. 2006
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Theory versus observation: III
 ll
The KINK
and
The GAP
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 Interferometry allows us to empirically determine
fundamental properties of stars in order to provide the
foundation for calibrating the effective temperature scales
and testing model atmosphere and evolution calculations
 For main sequence stars, the temperature is often
overestimated while the radius is underestimated
compared to observations
 Thank you for your interference!
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