Transcript Moscow A Stars

The magnetic personalities
of stars revealed by MOST
Jaymie Matthews
Univ. of British Columbia
Vancouver
Canada
Ap star impersonator
B ≈ 500 G age ≈ 1 Gyr
The magnetic personalities
of stars revealed by MOST
Jaymie Matthews
Univ. of British Columbia
Vancouver
Canada
CP2 star impersonator
B ≈ 500 G age ≈ 1 Gyr
CP2 = (Crazy Person)2
The magnetic personalities
of stars revealed by MOST
Jaymie Matthews
Univ. of British Columbia
Vancouver
Canada
Ap star impersonator
B ≈ 300 G age ≈ 60 Myr
The magnetic personalities
of stars revealed by MOST
Jaymie Matthews
Univ. of British Columbia
Vancouver
Canada
Ap star impersonator
B ≈ 20 kG age ≈ 10 Gyr
Evolution of space telescopes
HST
Evolution of space telescopes
MOST
to scale
HST
“Suitcase” in space
MOST
HST
10 years in space!
MOST
launched
from
Plesetsk
HST
30 June 2013
Evolution of space telescopes
MOST
HST
Evolution of space telescopes
MOST
BRITE
HST
Evolution of space telescopes
MOST
BRITE
Constellation
HST
Canada 2 nanosats
Austria 2 nanosats
Poland 2 nanosats
Evolution of space telescopes
MOST
BRITE
Constellation
launch
25 Feb
2013
Canada 2 nanosats
Austria 2 nanosats
Poland 2 nanosats
Evolution of space telescopes
MOST
BRITE
Constellation
launch
25 Feb
2013
Canada 2 nanosats
Austria 2 nanosats
Poland 2 nanosats
Car battery in space
Constellation
Evolution of space telescopes
MOST
BRITE
Constellation
HST
Evolution of stars
MOST
BRITE
Constellation
HST
“retired”
A-type
Evolution of stars
MOST
BRITE
Constellation
HST
“retired”
A-type
K giant
Evolution of stars
MOST
BRITE
Constellation
HST
“retired”
B-type
Evolution of stars
MOST
BRITE
Constellation
HST
“retired”
B-type
rapid
rotation
+ dense
winds
Evolution of stars
MOST
BRITE
Constellation
HST
“retired”
B-type
Photometry of stars from space
MOST, CoRoT and Kepler give ultra-precision
and are being joined by BRITE Constellation
to extend coverage of stellar parameter space
MOST
not to scale
CoRoT
Kepler
BRITE
The magnetic personalities
of stars revealed by MOST
Jaymie Matthews
Univ. of British Columbia
Vancouver
Canada
Ap star impersonator
B ≈ 500 G age ≈ 1 Gyr
The nonmagnetic personality...
of an A star revealed by MOST
David Mkrtichian
Jaymie
Matthews
Univ.
National
of British
Astronomical
Columbia
Research Institute
Vancouver
of
Thailand
Canada
WASP-33
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
Trailed spectrum of rotation profile
from 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 seen
Planet's spectral silhouette seen
travelling in retrograde direction
WASP-33
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
Trailed spectrum of rotation profile
from 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 seen
Planet's spectral silhouette seen
travelling in retrograde direction
WASP-33
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
Trailed spectrum of rotation profile
from 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 seen
Planet's spectral silhouette seen
travelling in retrograde direction
MOST light curve
45615 observations
over 24 days in October 2010
V = 8.3
Phased to the orbital period
P = 1.22 day
retrograde orbit
f = 9.84 cycles per day
a = 0.001 mag
Pulsation frequencies
hybrid?
The magnetic personalities
of stars revealed by MOST
MOST and magnetic stars
Target
Type
Main objective
HR 1217
γ Equ
10 Aql
HD 9289
HD 99563
HD 134214
roAp
roAp
roAp
roAp
roAp
roAp
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
σ Ori E
B2Vpe
HR 5907 B2Vpe
wind physics
wind physics
exoplanet systems
star-planet
magnetospheric interactions
MOST and magnetic stars
Target
Type
Main objective
HR 1217
γ Equ
10 Aql
HD 9289
HD 99563
HD 134214
roAp
roAp
roAp
roAp
roAp
roAp
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
σ Ori E
B2Vpe
HR 5907 B2Vpe
wind physics
wind physics
exoplanet systems
star-planet
magnetospheric interactions
rapidly oscillating Ap
roAp stars
 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
but see SuperWASP poster
by Holdsworth & Smalley
 global magnetic fields:
B ~ 1 - 35 kG
models by Hideyuki Saio
25
HD42659
20
HD99563
33Lib
AlpCir
HD134214
15
HD24712
BetCrB
HD60435
10
10Aql
HR3831
GamEq
HD116114
HD154708
HD101065
HD122970
HD217522
HD185256
5
3.95
3.9
3.85
3.8
roAp stars
freq. vs. T
models by Hideyuki Saio
25
shaded region is
where κ mechanism in
H ionisation zone
can excite
highorder
p-modes
HD42659
20
HD99563
33Lib
AlpCir
HD134214
15
roAp stars
excitation
Z = 0.02 Bpolar = 0
He-depleted
He I ionisation zone
HD24712
BetCrB
HD60435
10
10Aql
HR3831
GamEq
HD116114
HD154708
HD101065
HD122970
HD217522
HD185256
5
3.95
3.9
3.85
3.8
ℓ = 1 modes
boundary condition
at log τ = −6
running wave
for ω > ωc
models by Hideyuki Saio
25
shaded region is
where κ mechanism in
H ionisation zone
can excite
highorder
p-modes
HD42659
20
HD99563
33Lib
AlpCir
HD134214
15
HD24712
BetCrB
HD60435
10
10Aql
HR3831
GamEq
HD116114
HD154708
HD101065
HD122970
HD217522
HD185256
5
3.95
3.9
3.85
3.8
roAp stars
excitation
The preliminary
models suggest
that a mechanism
other than
H ionisation
is needed to
excite most
roAp pulsations
echelle diagram of modes
roAp stars
excitation
gamma Equulei
ν1 – ν6
MOST photometry
Michael Gruberbauer
(Mk1 – 1 c/d); Mk2
radial velocity data
David Mkrtichian
echelle diagram of modes
roAp stars
excitation
gamma Equulei
ν1 – ν6
MOST photometry
Michael Gruberbauer
(Mk1 – 1 c/d); Mk2
radial velocity data
David Mkrtichian
Model frequencies
agree with observation
but none are excited
MOST and magnetic stars
Target
Type
Main objective
HR 1217
γ Equ
10 Aql
HD 9289
HD 99563
HD 134214
roAp
roAp
roAp
roAp
roAp
roAp
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
σ Ori E
B2Vpe
HR 5907 B2Vpe
wind physics
wind physics
exoplanet systems
star-planet
magnetospheric interactions
p-modes in magnetic stars
HR 1217 = HD 24712
 rapidly oscillating Ap star
50 µmag
residuals
 periods near 6 min
discovered by Kurtz (1982)
 0 < B field < 1.2 kG
 P rot = 12.45877(16) d
Ryabchikova et al. (2005)
1
2
2
1
33
4
4
55
6 7 7
6
spectral
window
window
Rich p-mode spectrum
2000 WET campaign
 6 dominant modes
Kurtz et al. 2002, MNRAS 330, L57
+ 1 anomalous one
Kurtz, Cameron et al. 2005, MNRAS
p-modes in magnetic stars
HR 1217
MOST photometry
Nov-Dec 2004
 666 hr over 29 days
 duty cycle = 96%
 30-sec integrations
custom optical filter
3 gaps
due to charged
particle hits
12.5 d = Prot’n
2004 MOST campaign
Chris Cameron
PhD thesis, 2010, UBC
p-modes in magnetic stars
HR 1217
34 frequencies
105 YREC models
Yale Rotating
Evolution Code
M = 1.3 → 1.8 Mʘ
in steps of 0.05 Mʘ
Z = 0.008 → 0.022
in steps of 0.002
X = 0.70, 0,72, 0.74
α = 1.4, 1.6, 1.8
569 models
in error box used for
pulsation modeling
values of large frequency spacing Δν
HR 1217
observed
small spacing
~ 2.5 μHz
This value consistent
with models of
 low metallicity
Z < 0.01
 mass M ~ 1.5 Mʘ
 age
t > 1 Gyr
small spacings of models
p-modes in magnetic stars
Magnetoasteroseismology
pulsation amplitudes &
phases modulated with
magnetic (= rotation) period
Oblique Pulsator Model
Kurtz 1982 MNRAS 200, 807
Magnetoasteroseismology
pulsation amplitudes &
phases modulated with
magnetic (= rotation) period
Oblique Pulsator Model
Kurtz 1982 MNRAS 200, 807
magneto-acoustic coupling
Dziembowski & Goode 1996
eigenfunction expanded with Yℓm (θ,φ)
Cunha & Gough 2002 Cunha 2006
variational principle and WKB approximation
Saio & Gautschy 2004, Saio 2005
Bigot & Dziembowski 2002, A&A 391, 235
including rotation
Magnetoasteroseismology

vA > cs
∆
δP = 0
× B’ = 0
surface
phase
difference

0.95 R
vA << cs
acoustic
wave
magnetic
slow
wave
Magnetoasteroseismology

S B
n

Re (  shift )

Jumps in frequency  depend on model structure
and on pulsation mode & magnetic field geometries
Cunha 2006
Magnetoasteroseismology
Saio
Expands magnetic contribution
to hydrostatic equation in
spherical harmonics
Cunha
Estimates magnetic contribution
via a variational principle
Qualitative agreement between both approaches
Magnetoasteroseismology
 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
frequency shift →
HR 1217
models of magnetic perturbations
log L/Lʘ →
log L/Lʘ →
B = 10 kG
B = 5 kG
B = 1 kG
M = 1.6 M
M = 1.7 M
Magnetoasteroseismology
HR 1217
real
frequency
shifts
Frequency
perturbations
are cyclic
52,000
magnetic
dipole models
in grid
B = 1 → 10 kG
(steps of 0.1 kG)
νB0.75
imaginary
A magnetohydrodynamic lab
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
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
What if there are no p-modes?
Luis
Balona
Luis’
dream
woman
????????
next to Mrs. Balona
his pet puppy
“Spot”?
Rotational modulation of spots
MOST photometry
rapidly oscillating Ap
roAp stars
 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
but see SuperWASP poster
by Holdsworth & Smalley
 global magnetic fields:
B ~ 1 - 35 kG
massive magnetic fast rotators
 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
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
Gregg
Wade
RMC Canada
massive magnetic fast rotators
Magnetospheres of OB stars
Rigidly-Rotating
Magnetosphere
model of σ Ori E
Rich Townsend
Wisconsin
Recall Zdenek
Mikulasek’s talk
this morning
.
massive magnetic fast rotators
σ Ori E
B2Vpe
vsini ~ 165 km/s
Mstar ~ 7 Mʘ
Prot ~ 1.1908 d
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
Ω rotation frequency
σ Ori E
Ω rotation frequency
MOST and magnetic stars
Target
Type
Main objective
HR 1217
γ Equ
10 Aql
HD 9289
HD 99563
HD 134214
roAp
roAp
roAp
roAp
roAp
roAp
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
asteroseismology
σ Ori E B2Vpe
HR 5907 B2Vpe
wind physics
wind physics
exoplanet systems
star-planet
magnetospheric interactions
massive magnetic fast rotators
σ Ori E
21 days of
MOST photometry
in Nov – Dec 2007
→ 21 rotations
massive magnetic fast rotators
σ Ori E
21 days of
MOST photometry
in Nov – Dec 2007
→ 21 rotations
New rotation period
1.190847±0.000015 d
matches ephemeris
– confirming that star’s
rotation is slowing due
to magnetic braking
massive magnetic fast rotators
σ Ori E
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)
massive magnetic fast rotators
σ Ori E
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 cycle
were predicted from such centrifugal breakout episodes
massive magnetic fast rotators
σ Ori E
21 days of
MOST photometry
in Nov – Dec 2007
Analyses of depths of
light curve minima
and residuals show
no evidence for abrupt
centrifugal breakout
of plasma from the
magnetosphere
depths of primary (filled symbols)
and secondary (open symbols)
minima as a function of time
massive magnetic fast rotators
σ Ori E
Townsend & Owocki (2005) proposed “breakouts”
→ stress on and eventual breaking of magnetic loops by
centrifugal force, growing in strength as plasma accumulates
Analyses of depths of
light curve minima
and residuals show
no evidence for abrupt
centrifugal breakout
of 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
Ω rotation frequency
HR 5907
Ω rotation frequency
massive magnetic fast rotators
HR 5907
B2Vpe
vsini ~ 280 km/s
RKeplerian ~ 1.4 Rstar
Prot ~ 0.508 d
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
HR 5907
 observed by MOST during April/May 2011
for 18 days ≈ 35 rotations
11 rotations
massive magnetic fast rotators
HR 5907
phase diagram
1σ error bars
0.01 cycle bins
red squares
Hipparcos
measurements
rescaled to
MOST fluxes
Magnetohydrodynamic labs
sigma Ori E
HR 5907
Thanks
for listening
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