The magnetic personalities of stars revealed by MOST

The magnetic personalitiesof stars revealed by MOST

Jaymie MatthewsUniv. of British Columbia

VancouverCanada

Ap star impersonatorB ≈ 500 G age ≈ 1 Gyr



VancouverCanada

CP2 star impersonator B ≈ 500 G age ≈ 1 Gyr

CP2 = (Crazy Person)2



VancouverCanada

Ap star impersonatorB ≈ 300 G age ≈ 60 Myr



VancouverCanada

Ap star impersonatorB ≈ 20 kG age ≈ 10 Gyr

Evolution of space telescopes

HST


MOST

HST

to scale

“Suitcase” in space

MOST

HST

Happy

Birthday!

MOST

HST

10 years in space!

launchedfrom

Plesetsk30 June 2013


MOST

HST


MOST

BRITE

HST


MOST

BRITEConstellation

Canada 2 nanosatsAustria 2 nanosatsPoland 2 nanosats

HST


MOST

BRITEConstellation


launch25 Feb

2013

MOST

BRITEConstellation


launch25 Feb

2013

Constellation


Constellation

Car battery in space

HST

MOST


BRITEConstellation

MOST

BRITEConstellation

Evolution of stars

HST

“retired”A-type

MOST

Evolution of stars

HST

K giant

BRITEConstellation

“retired”A-type

MOST

Evolution of stars

HST

“retired” B-type

BRITEConstellation

MOST

BRITEConstellation

Evolution of stars

HST


rapidrotation+ densewinds

MOST

BRITEConstellation

Evolution of stars

HST


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



VancouverCanada

Ap star impersonatorB ≈ 500 G age ≈ 1 Gyr

The nonmagnetic personality...of an A star revealed by MOST


VancouverCanada

David MkrtichianNational Astronomical

Research Institute ofThailand

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


WASP-33






WASP-33





MOST light curve

45615 observationsover 24 days in October 2010

V = 8.3

Phased to the orbital period

f = 9.84 cycles per daya = 0.001 mag

P = 1.22 dayretrograde orbit

Pulsation frequencies

hybrid?


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



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

models by Hideyuki Saio roAp starsfreq. vs. T

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

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


ν1 – ν6MOST photometryMichael Gruberbauer

(Mk1 – 1 c/d); Mk2radial velocity dataDavid Mkrtichian

gamma Equulei

echelle diagram of modes roAp starsexcitation

ν1 – ν6MOST photometryMichael Gruberbauer

(Mk1 – 1 c/d); Mk2radial velocity dataDavid Mkrtichian

Model frequencies agree with observation but none are excited

gamma Equulei


echelle diagram of modes



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

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


2004 MOST campaign

34 frequencies

p-modes in magnetic starsHR 1217

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

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


Kurtz 1982 MNRAS 200, 807

pulsation amplitudes & phases modulated with magnetic (= rotation) period

Oblique Pulsator Model

Magnetoasteroseismology

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


magneticslowwave

acoustic wave

phasedifference

surface

vA > cs

vA << cs

0.95 R

δP = 0 × B’ = 0

∆


Re ( shift )

nS B

Jumps in frequency depend on model structure and on pulsation mode & magnetic field geometries

Cunha 2006


SaioExpands magnetic contribution to hydrostatic equation in spherical harmonics

CunhaEstimates magnetic contributionvia a variational principle

Qualitative agreement between both approaches


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


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

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)


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

A magnetohydrodynamic lab

What if there are no p-modes?

his pet puppy “Spot”?

Luis Balona

Luis’ dream

woman????????

next to Mrs. Balona

MOST photometryRotational modulation of spots

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

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

GreggWade

RMC Canada


Magnetospheres of OB stars

Rigidly-Rotating Magnetosphere model of σ Ori E


Recall Zdenek Mikulasek’s talk

this morning

Rich TownsendWisconsin .

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


Ω rotation frequency

σ Ori E


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

σ Ori E 21 days of

MOST photometry in Nov – Dec 2007

→ 21 rotations


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


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)



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

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 breakoutof plasma from the

magnetosphere

depths of primary (filled symbols) and secondary (open symbols)

minima as a function of time


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



HR 5907


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


HR 5907 observed by MOST during April/May 2011 for 18 days ≈ 35 rotations

11 rotations


HR 5907

phase diagram

1σ error bars 0.01 cycle bins

red squaresHipparcos measurements rescaled to MOST fluxes


Magnetohydrodynamic labs

sigma Ori EHR 5907

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I’m afraidI may nothave lefttime for

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The magnetic personalities of stars revealed by MOST