The magnetic personalities of stars revealed by MOST
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Transcript of The magnetic personalities of stars revealed by MOST
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The magnetic personalitiesof stars revealed by MOST
Jaymie MatthewsUniv. of British Columbia
VancouverCanada
Ap star impersonatorB ≈ 500 G age ≈ 1 Gyr
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The magnetic personalitiesof stars revealed by MOST
Jaymie MatthewsUniv. of British Columbia
VancouverCanada
CP2 star impersonator B ≈ 500 G age ≈ 1 Gyr
CP2 = (Crazy Person)2
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The magnetic personalitiesof stars revealed by MOST
Jaymie MatthewsUniv. of British Columbia
VancouverCanada
Ap star impersonatorB ≈ 300 G age ≈ 60 Myr
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The magnetic personalitiesof stars revealed by MOST
Jaymie MatthewsUniv. of British Columbia
VancouverCanada
Ap star impersonatorB ≈ 20 kG age ≈ 10 Gyr
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Evolution of space telescopes
HST
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Evolution of space telescopes
MOST
HST
to scale
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“Suitcase” in space
MOST
HST
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Happy
Birthday!
MOST
HST
10 years in space!
launchedfrom
Plesetsk30 June 2013
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Evolution of space telescopes
MOST
HST
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Evolution of space telescopes
MOST
BRITE
HST
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Evolution of space telescopes
MOST
BRITEConstellation
Canada 2 nanosatsAustria 2 nanosatsPoland 2 nanosats
HST
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Evolution of space telescopes
MOST
BRITEConstellation
Canada 2 nanosatsAustria 2 nanosatsPoland 2 nanosats
launch25 Feb
2013
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MOST
BRITEConstellation
Canada 2 nanosatsAustria 2 nanosatsPoland 2 nanosats
launch25 Feb
2013
Constellation
Evolution of space telescopes
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Constellation
Car battery in space
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HST
MOST
Evolution of space telescopes
BRITEConstellation
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MOST
BRITEConstellation
Evolution of stars
HST
“retired”A-type
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MOST
Evolution of stars
HST
K giant
BRITEConstellation
“retired”A-type
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MOST
Evolution of stars
HST
“retired” B-type
BRITEConstellation
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MOST
BRITEConstellation
Evolution of stars
HST
“retired” B-type
rapidrotation+ densewinds
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MOST
BRITEConstellation
Evolution of stars
HST
“retired” B-type
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MOST, CoRoT and Kepler give ultra-precision and are being joined by BRITE Constellation
to extend coverage of stellar parameter space
CoRoT BRITEMOST
not to scale
Kepler
Photometry of stars from space
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The magnetic personalitiesof stars revealed by MOST
Jaymie MatthewsUniv. of British Columbia
VancouverCanada
Ap star impersonatorB ≈ 500 G age ≈ 1 Gyr
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The nonmagnetic personality...of an A star revealed by MOST
Jaymie MatthewsUniv. of British Columbia
VancouverCanada
David MkrtichianNational Astronomical
Research Institute ofThailand
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A bright, rapidly rotating A5 star (HD 15082) with a transiting gas giant planet in a 1.22-day retrograde orbit – 5.5 stellar radii from the star’s photosphere
WASP-33
Trailed spectrum of rotation profilefrom the HERMES spectrograph
(MERCATOR, La Palma) covering the transit on 26 October 2010
The longest high-resolution spectral time series of this system
Several pulsation modes are seenPlanet's spectral silhouette seen travelling in retrograde direction
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A bright, rapidly rotating A5 star (HD 15082) with a transiting gas giant planet in a 1.22-day retrograde orbit – 5.5 stellar radii from the star’s photosphere
WASP-33
Trailed spectrum of rotation profilefrom the HERMES spectrograph
(MERCATOR, La Palma) covering the transit on 26 October 2010
The longest high-resolution spectral time series of this system
Several pulsation modes are seenPlanet's spectral silhouette seen travelling in retrograde direction
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A bright, rapidly rotating A5 star (HD 15082) with a transiting gas giant planet in a 1.22-day retrograde orbit – 5.5 stellar radii from the star’s photosphere
WASP-33
Trailed spectrum of rotation profilefrom the HERMES spectrograph
(MERCATOR, La Palma) covering the transit on 26 October 2010
The longest high-resolution spectral time series of this system
Several pulsation modes are seenPlanet's spectral silhouette seen travelling in retrograde direction
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MOST light curve
45615 observationsover 24 days in October 2010
V = 8.3
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Phased to the orbital period
f = 9.84 cycles per daya = 0.001 mag
P = 1.22 dayretrograde orbit
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Pulsation frequencies
hybrid?
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The magnetic personalitiesof stars revealed by MOST
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Target Type Main objectiveHR 1217 roAp asteroseismologyγ Equ roAp asteroseismology10 Aql roAp asteroseismologyHD 9289 roAp asteroseismologyHD 99563 roAp asteroseismologyHD 134214 roAp asteroseismologyσ Ori E B2Vpe wind physicsHR 5907 B2Vpe wind physicsexoplanet systems star-planet magnetospheric interactions
MOST and magnetic stars
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Target Type Main objectiveHR 1217 roAp asteroseismologyγ Equ roAp asteroseismology10 Aql roAp asteroseismologyHD 9289 roAp asteroseismologyHD 99563 roAp asteroseismologyHD 134214 roAp asteroseismologyσ Ori E B2Vpe wind physicsHR 5907 B2Vpe wind physicsexoplanet systems star-planet magnetospheric interactions
MOST and magnetic stars
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rapidly oscillating Ap
discovered by Don Kurtz in 1978 ~45 members of the class periods: 6 ~ 21 minutes amplitudes: few mmag and less p-modes of low-degree, high-overtone global magnetic fields: B ~ 1 - 35 kG
roAp stars
but see SuperWASP posterby Holdsworth & Smalley
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models by Hideyuki Saio roAp starsfreq. vs. T
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models by Hideyuki Saioshaded region is
where κ mechanism in H ionisation zone
can excite high-order
p-modes
Z = 0.02 Bpolar = 0
He-depleted He I ionisation zoneℓ = 1 modesboundary condition at log τ = −6running wavefor ω > ωc
roAp starsexcitation
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models by Hideyuki Saioshaded region is
where κ mechanism in H ionisation zone
can excite high-order
p-modes
The preliminary models suggest that a mechanism other than H ionisation is needed to excite most roAp pulsations
roAp starsexcitation
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ν1 – ν6MOST photometryMichael Gruberbauer
(Mk1 – 1 c/d); Mk2radial velocity dataDavid Mkrtichian
gamma Equulei
echelle diagram of modes roAp starsexcitation
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ν1 – ν6MOST photometryMichael Gruberbauer
(Mk1 – 1 c/d); Mk2radial velocity dataDavid Mkrtichian
Model frequencies agree with observation but none are excited
gamma Equulei
roAp starsexcitation
echelle diagram of modes
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Target Type Main objectiveHR 1217 roAp asteroseismologyγ Equ roAp asteroseismology10 Aql roAp asteroseismologyHD 9289 roAp asteroseismologyHD 99563 roAp asteroseismologyHD 134214 roAp asteroseismologyσ Ori E B2Vpe wind physicsHR 5907 B2Vpe wind physicsexoplanet systems star-planet magnetospheric interactions
MOST and magnetic stars
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1
23
45
6
residuals
spectralwindow
50 µmag
Kurtz et al. 2002, MNRAS 330, L57 Kurtz, Cameron et al. 2005, MNRAS
rapidly oscillating Ap star periods near 6 min
0 < B field < 1.2 kG P = 12.45877(16) d
discovered by Kurtz (1982)
Ryabchikova et al. (2005) rot
Rich p-mode spectrum 6 dominant modes + 1 anomalous one
1 2 3 4 5 6 7 7
window
HR 1217 = HD 24712
2000 WET campaign
p-modes in magnetic stars
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HR 1217
Chris CameronPhD thesis, 2010, UBC
3 gapsdue to charged
particle hits
12.5 d = Prot’n
MOST photometryNov-Dec 2004 666 hr over 29 days duty cycle = 96% 30-sec integrations
custom optical filter
p-modes in magnetic stars
2004 MOST campaign
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34 frequencies
p-modes in magnetic starsHR 1217
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105 YREC modelsYale Rotating
Evolution Code
M = 1.3 → 1.8 Mʘ
in steps of 0.05 Mʘ
Z = 0.008 → 0.022in steps of 0.002
X = 0.70, 0,72, 0.74
569 modelsin error box used for
pulsation modeling values of large frequency spacing Δν
Z ↑X ↑
α = 1.4, 1.6, 1.8
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HR 1217
smal
l spa
cing
s of m
odel
s
observedsmall spacing
~ 2.5 μHz
This value consistent with models of low metallicity Z < 0.01 mass M ~ 1.5 Mʘ
age t > 1 Gyr
p-modes in magnetic stars
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Kurtz 1982 MNRAS 200, 807
pulsation amplitudes & phases modulated with magnetic (= rotation) period
Oblique Pulsator Model
Magnetoasteroseismology
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Cunha & Gough 2002
Bigot & Dziembowski 2002, A&A 391, 235
Kurtz 1982 MNRAS 200, 807
Cunha 2006
Dziembowski & Goode 1996
Saio & Gautschy 2004, Saio 2005
eigenfunction expanded with Yℓm
(θ,φ)variational principle and WKB approximation
including rotation
pulsation amplitudes & phases modulated with magnetic (= rotation) period
Oblique Pulsator Model
magneto-acoustic coupling
Magnetoasteroseismology
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magneticslowwave
acoustic wave
phasedifference
surface
vA > cs
vA << cs
0.95 R
δP = 0 × B’ = 0
∆
Magnetoasteroseismology
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Re ( shift )
nS B
Jumps in frequency depend on model structure and on pulsation mode & magnetic field geometries
Cunha 2006
Magnetoasteroseismology
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SaioExpands magnetic contribution to hydrostatic equation in spherical harmonics
CunhaEstimates magnetic contributionvia a variational principle
Qualitative agreement between both approaches
Magnetoasteroseismology
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Magnetic fields shift pulsation frequencies The frequency shift changes depending on
the structure of the stellar envelope Magnetic fields tend to damp pulsations
This effect seems strong enough to damp low-overtone p-modes in roAp stars Magnetic fields modify the latitudinal
distribution of pulsation amplitude
Amplitude confined to polar regions, as in HR 3831
Theoretical models for Przybylski's Star, γ Equ,
and 10 Aql agree with observed frequencies but required Bp might be too big
Magnetoasteroseismology
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HR 1217 models of magnetic perturbations
M = 1.7 MM = 1.6 M
B = 10 kG
B = 5 kG
B = 1 kG
log L/Lʘ → log L/Lʘ →
frequ
ency
shift
→Magnetoasteroseismology
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HR 1217
νB0.75
frequencyreal imaginary shifts
Frequencyperturbations
are cyclic
52,000 magnetic
dipole models in grid
B = 1 → 10 kG (steps of 0.1 kG)
Magnetoasteroseismology
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HR 1217 Only half of
52,000 ..models match even ..only one frequency
Only 0.5% of models ..have a fit probability ..within a factor of 100 ..of the model with the ..highest probability
→ only a few × 100 …...models give a …..“good” match
A magnetohydrodynamic lab
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HR 1217 Magnetic fields essential
to model observed very rich roAp eigenspectra
… but parameter space is very complex
with many local false minima
Interpolations of limited model grids are dangerous
A magnetohydrodynamic lab
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What if there are no p-modes?
his pet puppy “Spot”?
Luis Balona
Luis’ dream
woman????????
next to Mrs. Balona
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MOST photometryRotational modulation of spots
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rapidly oscillating Ap
discovered by Don Kurtz in 1978 ~45 members of the class periods: 6 ~ 21 minutes amplitudes: few mmag and less p-modes of low-degree, high-overtone global magnetic fields: B ~ 1 - 35 kG
roAp stars
but see SuperWASP posterby Holdsworth & Smalley
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He-strong stars with magnetospheric winds ~40 members of the class include HR 7355, HR 5907 delta Ori C, sigma Ori E variability in
photometric indices Hα and radio emission UV wind absorption lines linear continuum &
circular line polarisation
massive magnetic fast rotators
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Magnetospheres of OB stars magnetic OB stars → structured magnetospheres interaction between B field & radiatively-driven winds → wind confinement and rotation systematic investigation
optical, UV, X-ray observations 2D and 3D, static and dynamic models highly precise photometry constrains
rotation period, geometry rotational evolution (braking) plasma density and distribution
GreggWade
RMC Canada
massive magnetic fast rotators
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Magnetospheres of OB stars
Rigidly-Rotating Magnetosphere model of σ Ori E
massive magnetic fast rotators
Recall Zdenek Mikulasek’s talk
this morning
Rich TownsendWisconsin .
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σ Ori E B2Vpe vsini ~ 165 km/s Prot ~ 1.1908 dMstar ~ 7 Mʘ Bdipole ~ 11 kG magnetic He-strong star
rotation period is gradually lengthening due to magnetic braking Townsend et al. 2010 variability originates from a combination of surface abundance inhomogeneities and wind-originated plasma trapped in a circumstellar, co-rotating, Townsend et al. 2005 centrifugally supported magnetosphere
massive magnetic fast rotators
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Ω rotation frequency
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σ Ori E
Ω rotation frequency
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MOST and magnetic starsTarget Type Main objectiveHR 1217 roAp asteroseismologyγ Equ roAp asteroseismology10 Aql roAp asteroseismologyHD 9289 roAp asteroseismologyHD 99563 roAp asteroseismologyHD 134214 roAp asteroseismologyσ Ori E B2Vpe wind physicsHR 5907 B2Vpe wind physicsexoplanet systems star-planet magnetospheric interactions
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σ Ori E 21 days of
MOST photometry in Nov – Dec 2007
→ 21 rotations
massive magnetic fast rotators
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σ Ori E massive magnetic fast rotators
New rotation period 1.190847±0.000015 d matches ephemeris
– confirming that star’s rotation is slowing due
to magnetic braking
21 days of MOST photometry in Nov – Dec 2007
→ 21 rotations
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σ Ori E massive magnetic fast rotators
Townsend & Owocki (2005) proposed “breakouts”→ stress on and eventual breaking of magnetic loops by centrifugal force, growing in strength as plasma accumulates
MHD simulations by Owocki (2007) showing logarithmic density and temperature T in a meridional plane. The darkest areas represent gas with T ~ 107 K, hot enough to produce relatively hard X-ray emission (few keV)
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σ Ori E massive magnetic fast rotators
Townsend & Owocki (2005) proposed “breakouts”→ stress on and eventual breaking of magnetic loops by centrifugal force, growing in strength as plasma accumulates
MHD simulations by ud-Doula et al. (2006) also supported this centrifugal breakout hypothesis, suggesting that reconnection heating from breakout episodes could explain the X-ray flares seen in σ Ori E (Groote & Schmitt 2004 & Sanz-Forcada et al. 2004)
Sharp changes n the light curve from rotational cycle to cyclewere predicted from such centrifugal breakout episodes
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σ Ori E 21 days of
MOST photometry in Nov – Dec 2007
massive magnetic fast rotators
Analyses of depths of light curve minima
and residuals show no evidence for abrupt
centrifugal breakoutof plasma from the
magnetosphere
depths of primary (filled symbols) and secondary (open symbols)
minima as a function of time
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σ Ori E massive magnetic fast rotators
Analyses of depths of light curve minima
and residuals show no evidence for abrupt
centrifugal breakoutof plasma from the
magnetosphere
Together with a demonstration that the mass in the magnetosphere is 100 times less than the theoretical asymptotic mass, these findings suggest that breakout episodes do not play a major role in setting a star’s magnetospheric mass budget
Townsend & Owocki (2005) proposed “breakouts”→ stress on and eventual breaking of magnetic loops by centrifugal force, growing in strength as plasma accumulates
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Ω rotation frequency
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HR 5907
Ω rotation frequency
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HR 5907 B2Vpe vsini ~ 280 km/s Prot ~ 0.508 dRKeplerian ~ 1.4 Rstar RAlfven ~ 32 Rstar
Bdipole ~ 12 – 17 kG
the most rapidly rotating known magnetic star discovered in 2010 by the MiMeS collaboration (Magnetism in Massive Stars) Grunhut et al. 2012
massive magnetic fast rotators
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HR 5907 observed by MOST during April/May 2011 for 18 days ≈ 35 rotations
11 rotations
massive magnetic fast rotators
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HR 5907
phase diagram
1σ error bars 0.01 cycle bins
red squaresHipparcos measurements rescaled to MOST fluxes
massive magnetic fast rotators
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Magnetohydrodynamic labs
sigma Ori EHR 5907
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