Transcript Document

HIGH-PRECISION PHOTOMETRY
OF ECLIPSING BINARY STARS
John Southworth
+ Hans Bruntt + Pierre Maxted + many others
Eclipsing binary stars:
why bother?
Eclipsing binary stars:
why bother?
• Light curve and radial velocity analysis:
get masses and radii of two stars to 1%
– where else could we get this from?
Eclipsing binary stars:
why bother?
• Light curve and radial velocity analysis:
get masses and radii of two stars to 1%
– where else could we get this from?
• Accurate mass, radius, Teff, luminosity
– use as high-precision distance indicators
– check that theoretical models work
Eclipsing binary stars:
why bother?
• Light curve and radial velocity analysis:
get masses and radii of two stars to 1%
– where else could we get this from?
• Accurate mass, radius, Teff, luminosity
– use as high-precision distance indicators
– check that theoretical models work
• Comparison with theoretical models
– get metal abundance and age
– investigate overshooting, mixing length, helium
abundance, diffusion
Eclipsing binary stars: how?
WW Aurigae – Southworth et al. (2005)
Eclipsing binary stars: how?
• Light curve analysis gives:
– rA rB
–e ω
–P i
radii as fraction of orbital separation
orbital eccentricity and periastron longitude
orbital period and inclination
Eclipsing binary stars: how?
WW Aurigae – Southworth et al. (2005)
Eclipsing binary stars: how?
• Light curve analysis gives:
– rA
rB e
ω
P
i
• Radial velocity analysis gives:
– MA sin3 i
– MB sin3 i
– a sin i
P e ω
minimum mass of star A
minimum mass of star B
projected orbital separation
Eclipsing binary stars: how?
• Light curve analysis gives:
– rA
rB e
ω
P
i
• Radial velocity analysis gives:
– MA sin3 i
MB sin3 i
a sin i
P
e
• Combine quantities:
– MA MB RA RB log gA log gB
– get the masses and radii of both stars
ω
Eclipsing binary stars: how?
• Light curve analysis gives:
– rA
rB e
ω
P
i
• Radial velocity analysis gives:
– MA sin3 i
MB sin3 i
a sin i
P
e
ω
• Combine quantities:
– MA MB RA RB log gA log gB
– get the masses and radii of both stars
• Spectral modelling or photometric colours:
– get effective temperatures
– get luminosities
– get distance
The WIRE satellite
• Launched in 1999 for
an IR galaxy survey
– electronics problem caused
loss of coolant
The WIRE satellite
• Launched in 1999 for
an IR galaxy survey
– electronics problem caused
loss of coolant
• Star tracker used since
1999 as a high-speed
photometer
– aperture: 5 cm
– cadence: 2 Hz
– 5 targets at once
Eclipsing binaries with WIRE. I. ψ Centauri
• V = 4.0
spectral type = B9 V + A2 V
• Known spectroscopic binary
• WIRE light curve: 41 000 points with 2 mmag scatter
Interlude 1: JKTEBOP
• Based on EBOP model (Paul Etzel, 1975)
– stars treated as biaxial spheroids
– numerical integration includes LD and GD
Interlude 1: JKTEBOP
• Based on EBOP model (Paul Etzel, 1975)
– stars treated as biaxial spheroids
– numerical integration includes LD and GD
• JKTEBOP retains original model
– new input / output
– Levenberg-Marquardt optimisation algorithm
– bootstrapping and Monte Carlo simulations to find
parameter uncertainties
http://www.astro.keele.ac.uk/~jkt/codes.html
FORTRAN77
Eclipsing binaries with WIRE. I. ψ Centauri
• JKTEBOP fit to the eclipses
Eclipsing binaries with WIRE. I. ψ Centauri
• Best fit and Monte Carlo
simulation results:
–
–
–
–
rA = 0.043984 ± 0.000045
rB = 0.021877 ± 0.000032
e = 0.55408 ± 0.00024
P = 38.81252 ± 0.00029
• And limb darkening too:
– uA = 0.256 ± 0.009
– uB = 0.362 ± 0.041
Eclipsing binaries with WIRE. I. ψ Centauri
• Best fit and Monte Carlo
simulation results:
–
–
–
–
rA = 0.043984 ± 0.000045
rB = 0.021877 ± 0.000032
e = 0.55408 ± 0.00024
P = 38.81252 ± 0.00029
• And limb darkening too:
– uA = 0.256 ± 0.009
– uB = 0.362 ± 0.041
• See Bruntt et al. (2006, A&A, 456, 651)
• We are currently working on new spectroscopy
Eclipsing binaries with WIRE. II. AR Cas
• P = 6.07 days
B4 V + A6 V
V = 4.9
– variation at primary star rotation period
– several pulsation frequencies
Eclipsing binaries with WIRE. III. β Aurigae
• V = 1.9
P = 3.960 days
A1m + A1m
• First known double-lined binary: 1889 (Maury)
• First known double-lined eclipsing binary: Stebbins (1911)
• WIRE light curve: 30 000 points; 0.3 mmag scatter
Interlude 2: more JKTEBOP
• Problem: linear limb darkening law too simple
– Solution: add log, sqrt, quad, cubic LD laws
Interlude 2: more JKTEBOP
• Problem: linear limb darkening law too simple
– Solution: add log, sqrt, quad, cubic LD laws
• Problem: ratio of the radii poorly determined
– Solution: allow spectroscopic light ratio to be
included directly as another observation
http://www.astro.keele.ac.uk/~jkt/codes.html
FORTRAN77
Interlude 2: more JKTEBOP
• Problem: linear limb darkening law too simple
– Solution: add log, sqrt, quad, cubic LD laws
• Problem: ratio of the radii poorly determined
– Solution: allow spectroscopic light ratio to be
included directly as another observation
• Problem: difficult to get good times of
minimum light from the WIRE data
– Solution: include old times of minimum light
directly as additional observations
http://www.astro.keele.ac.uk/~jkt/codes.html
FORTRAN77
Eclipsing binaries with WIRE. III. β Aurigae
• rA = 0.1569 ± 0.0008
• rB = 0.1460 ± 0.0008
P = 3.96004673 (17)
e = 0.0018 ± 0.0004
Eclipsing binaries with WIRE. III. β Aurigae
• Combine light curve result with spectroscopic
orbit of Smith (1948):
–
–
–
–
MA = 2.376 ± 0.027 M
MB = 2.291 ± 0.027 M
RA = 2.762 ± 0.017 R
RB = 2.568 ± 0.017 R
Eclipsing binaries with WIRE. III. β Aurigae
• Combine light curve result with spectroscopic
orbit of Smith (1948):
–
–
–
–
MA = 2.376 ± 0.027 M
MB = 2.291 ± 0.027 M
RA = 2.762 ± 0.017 R
RB = 2.568 ± 0.017 R
• Distance to system:
– Hipparcos parallax: 25.2 ± 0.5 pc
– Orbital parallax:
24.8 ± 0.8 pc
– Surface brightness:
25.0 ± 0.4 pc
– Bolometric corrections:
24.8 ± 0.3 pc
• Southworth, Bruntt & Buzasi (2007, A&A, 467, 1215)
Eclipsing binaries: why bother?
• Get mass and radius to 1%
– accurate distance indicators
– compare to theoretical models: get precise age
and metal abundance
Eclipsing binaries: why bother?
• Get mass and radius to 1%
– accurate distance indicators
– compare to theoretical models: get precise age
and metal abundance
• Now apply to EBs in open clusters
– get accurate distance
– get precise age and metallicity
– no need for MS fitting
Eclipsing binaries: why bother?
• Get mass and radius to 1%
– accurate distance indicators
– compare to theoretical models: get precise age
and metal abundance
• Now apply to EBs in open clusters
– get accurate distance
– get precise age and metallicity
– no need for MS fitting
• Combined study of cluster and binary
– stronger test of theoretical models
Eclipsing binaries in open
clusters. I. V615 and V618 Per
• Both members of the
young h Per cluster
– have same age and
chemical composition
– compare all four stars
to models using a
mass-radius diagram
• h Per has low metal
abundance: Z = 0.01
Eclipsing binaries in open
clusters. II. V453 Cyg
• Member of sparse young cluster NGC 6871
• Comparison to theoretical models:
– age = 10.0 ± 0.2 Myr
– metal abundance Z ≈ 0.01 (half solar – maybe)
Eclipsing binaries in open clusters.
III. The distance to the Pleiades
• Surface brightness method gives good results
– Use zeroth-magnitude angular diameter Φ(m=0)
– Kervella et al (2004) give Φ(m=0) - Teff calibrations
– Just need RA and RB and apparent magnitudes
• See Southworth, Maxted & Smalley (2005, A&A, 429, 645)
Eclipsing binaries in open clusters.
III. HD 23642 in the Pleiades
• V = 6.8
P = 2.46
AO Vp (Si) + Am
• Light curves from Munari et al. (2004)
• We find distance = 139.1 ± 3.5 pc
Eclipsing binaries in open clusters:
what next?
• V1481 Cyg and V2263 Cyg in NGC 7128
– 14 nights of INT / WFC photometry
– 7 nights of INT / IDS spectroscopy
– watch this space
JKTEBOP and HD 209458
• JKTEBOP very good for transiting exoplanets
– fast and accurate
– lots of different limb
darkening laws
JKTEBOP and HD 209458
• JKTEBOP very good for transiting exoplanets
– fast and accurate
– lots of different limb
darkening laws
• Results for HD 209458
– rA = 0.11405 ± 0.00042
– rB = 0.01377 ± 0.00008
– gB = 9.28 ± 0.15 m s-2
Southworth et al. (2007, MNRAS, 379, L)
Extrasolar planet surface gravity
• The known transiting
extrasolar planets
have a significant
correlation between
orbital period and
suface gravity
– the closer planets
are more bloated
Southworth et al. (2007, MNRAS, 379, L)
John Southworth
[email protected]
University of Warwick, UK