Magnetic Stars

Oct. 14, 2013 C. Neiner & W. W. Weiss: Impact of space based instruments 1

Magnetic Starsand

Space Instruments


©Townsend

Magnetic Fields

& Stars

& Environment

Variations in the ...


... Visual (flux, lines): -- Periodic –> surface properties-- Vibration –> stellar structure-- “Flares” –> interaction with B

f(n)




... UV (lines):-- wind confined by oblique magnetic field

f(n)




... UV (lines):-- wind confined by oblique magnetic field

... X-ray (emission):-- shocks in magnetosphere at

magnetic equator

f(n)

One Example:


NGC 1624-2 (O*, largest known Bp~20 kG)

The high X-ray luminosity, its variation

with stellar rotation, and its large

attenuation are all consistent with a

large dynamical magnetosphere with

magnetically confined wind shocks.

70-95% of X-ray emission produced by

magnetically confined X-ray wind

shocks is absorbed before it escapes

the magnetosphere.

Wade et al. 2012 MNRAS 425, 1278

Petit et al. 2015 MNRAS 453, 3288

.... Chandra

non-periodic Variations


• straylight

• cosmics

• aging (detector, ACS, ...)

• communication gaps

• ...

Challenge for instrumentation:

Instrumental effect

or

real activity?

8Oct. 14, 2013 C. Neiner & W. W. Weiss: Impact of space based instruments

Space Bonus

Atmospheric Windows


this overview


Space Bonus


O. Kochukhov: ... In particular, adding

linear polarisation to modelling led in

many (but not all!) cases to finding

considerably more complex field

structures than simple oblique dipoles.

(e.g. 2014MNRAS.440..182S

2017arXiv170609196S)

13

Space Malus

Oct. 14, 2013 C. Neiner & W. W. Weiss: Impact of space based instruments

Range of Scale


Canada’s “Humble” Space Telescope

2.500 M€ 8 M€

Small is Beautiful … and Bright !

< 1 M€HUBBLE MOST BRITE

X-ray satellitesXMM-Newton Chandra

1999 –

Diameter = 0.7 m

0.15 – 15 keV

ESA

1999 –

Diameter = 1.2 m

0.1 – 10 keV

NASA


• Magnetically confined winds are X-ray sources. We

have analyzed a large series of Chandra and XMM-

Newton observations of massive magnetic stars:

X-ray luminosity is strongly correlated with the

stellar wind mass-loss-rate.

Nazé et al. 2014 ApJS 215, 10

• First detailed study of wind-wind collision

dynamics and X-ray and radio emission utilizing

three-dimensional hydrodynamic models and radiative

transfer, with an analysis of multiple epoch data.

Parkin et al. 2014 A&A 570, 10


• X-ray spectroscopy of stars

Güdel et al. 2009, A&ARv 17, 309

• Chandra Carina Complex

Gagné et al. 2011 ApJS 194,5

• The mystery of Of?p stars is solved.

All of them are magnetic.

Grunhut et al. 2017 MNRAS

UV satellitesIUE HST

1990 – 2020?Diameter = 2.4 m

STIS: 114-318 nm

COS: 90-320 nm

→ mostly snapshots

1978 – 1996Diameter = 0.45 m

115-325 nm

→ long base archival data


V 2052 Oph (B2IV-V, b Cep) is the second discovered

magnetic pulsating B star, after β Cep. UV delivered a

very precise value of the rotation period. Star has no

extra internal mixing due to the presence of the magnetic

field which inhibits mixing.

Briquet et al. 2012

More recent magnetic analysis of this star in:

Neiner et al. 2012


Ori (B3Ve):

The first classical Be star showing indirect magnetic

indicators

Neiner et al. 2009 A&A 409. 275


HD 1933793 (WC7+O4.5)Gunawan et al. 2001

A&A 376,460


The first magnetic fields in O-

and B-type stars that do not

belong to the Bp-star class, have

been discovered.

Strong fields are not wide spread

and are either weak (few hundred

G) or localised.

The cyclic UV wind-line variability is

likely to be related to magnetic

fields.

Schnerr et al. 2008 A&A 483, 857

10 Lac (O9V)

Space Telescopes – Visible


BRITE-Constellation / A, CN, PL 2013-14

CoRoT / CNES & ESA 2006

GAIA / ESA 2013

Kepler / NASA 2009

MOST / CSA 2003

NEOSSat / CSA & DRDC 2013

SWIFT / NASA 2004

MOST (2003 – ...)


https://science.ubc.ca/feature/MOST

• x Per (B1Ib): This is the first convincing case ... with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.

Ramiaramanantsoa et al. 2014, MNRAS 441, 910

• HR 5907 (B2V): detection of a large-scale polar surface magnetic field with 10-16 kG. Longitudinal magnetic field and Hα variations are consistent with an oblique rotator, -> shortest period (0.51d), non-degenerate, magnetic massive star (5.5 M

) known. %

Grunhut et al. 2012 MNRAS 419, 1610)

MOST


Inset: expansion of the HR 5907 MOST-data over a few nights to

highlight the cycle to cycle variability and the clear periodicity. The red

curve corresponds to a best fit to the phased data.

MOST - II


• WR 110 has revealed properties of the corotating inter-action region (CIR) with MOST photometry during a month. This allows probing the mysterious origin of the CIR phenomenon rooted at the stellar surface, e.g. as a phenomenon related to magnetism or pulsations. Chené et al. 2011 ApJ 735, 34

• roAp stars HD 9289, HD 99563 & HD 134214: All three MOST data sets have revealed previously unknown features, and helped to clarify ambiguities that could not be resolved from the ground.

Gruberbauer et al. 2011 A&A 530,135

MOST - III


• 10 Aql (A7VpSrEu): Evidence for finite mode lifetimes in roAp stars has been found.

Huber et al. 2008 A&A 483, 239

• k1 Cet (G5V): All of the photometric periods found to date can be explained by spots appearing at different lati- tudes. The apparent persistence of this period for some 35 years, corresponding to spot latitude-ranges of 50◦ to 60◦, might be due to large scale magnetic structures with solar-like differential rotation. %

Walker et al. 2007 ApJ 659, 1611

MOST


Likelihood contours for the latitude and spot period are

shown by dots for each spot – 2003 (green), 2004 (blue)

and 2005 (pink). The central red curve is the solar-period,

latitude relation -> observed differential rotation is

closely solar.

k1 Cet

CoRoT (2006 – 2012)

https://corot.cnes.fr/en/COROT/index.htm

• HD 49310 (A0pSi): A comprehensive analysis, preferably from space missions, would contribute significantly to our understanding of CP stars and their evolution.

Paunzen et al. 2015 A&A 547, 57

• HD 43317 (B3IV): Photometric data of unprecedented precision, complemented by ground-based spectro-scopy & polarimetry, allow to study the effect of magnetism in the mixing processes inside the star.

Briquet et al., A&A 2013, 557, 16)


C. Neiner & W. W. Weiss: Impact of space based instruments

CoRoT – II• Close-in massive planets interact with their host stars

through tidal and magnetic mechanisms, possibly related with hot Jupiters. The unique advantages of CoRoT and Kepler observations to test these models are pointed out.

Lanza 2011, Ap&SS 336, 303

• HD 49933 (F3V): Observed variations in mode frequencies are related to its magnetic activity. HD 49933 is thus the second star after the Sun for which the frequency dependence of the p-mode frequency shifts with magnetic activity has been measured. %

Salabert et al. 2011 A&A 530, 127

Oct. 14, 2013 30


Smoothed power spectra of the 90-day period of low stellar activity

(black) and of the 47-day period of high activity (red) of the analyzed

observations of HD 49933 represented over the frequency range

between 1440 and 2170 μHz.

Non-Stable Magnetic Field

Kepler (2009 – 2013)

• Surprising picture: beyond middle-age the efficiency of magnetic braking is dramatically reduced, implying a fundamental change in angular momentum loss beyond a critical Rossby number.

Metcalf et al. 2016 ApJ 826, 2

but:

• K2 is the first opportunity to measure rotation periods (P rot) for many Hyads simultaneously while also being sensitive to fully convective M dwarf members. The deficit of single rapid rotators more massive than ≈0.3 M ⊙ indicates that magnetic braking is more efficient than previously thought, and that age-rotation studies must account for multiplicity. %

Douglas et al. 2016 ApJ 822, 47



Mass-period distribution

for all Hyads with measured

periods.

- Grey symbols represent literature

Prot,

- Red symbols denote new Prot

measured from K2 data.

Kepler – II

• The asteroseismology of red giant stars has continued to yield surprises. The observed suppression of dipole oscillation modes in red giants can be used to detect strong magnetic fields in the stellar cores.

Stello et al. 2016 PASA 33,11

• The interpretation of superflares promotes understanding of extreme processes on the Sun and how effective particle acceleration can be on stars in the lower MS.

Katsova et al. 2015 SoPh 290. 3663


Kepler – III

• HD 188774 (A7.5 IV-III) is the first known magnetic main-sequence δ Sct star. This challenges analysis and interpretation of the Kepler results for the class of A-type stars. Neiner et al. 2015 MNRAS 454 86


Stokes V (top),

N (middle),

I (bottom)

LSD profiles of HD 188774

for the first (black) and

second (red)

measurements.

BRITE-Constellation (2013 - ...) http://www.brite-constellation.at

BRITE spectropolarimetric survey !! Neiner et al. 2016, 2nd BRITE Science Conf. Proceedings

• r Pup (F5IIkF2IImF5II): 2nd confirmed magnetic d Scuti star

Neiner et al. 2017 MNRAS 468, 46

• z Ori Aa (O9.7 Ib): no pulsation detected -> Absorption Components variability due to NRP beating is questionable %

Buysschaert et al. 2017 A&A 602, 918


Oct. 14, 2013 W. W. Weiss: BRITE-Constellation 37

Comparison between the

simultaneous CHIRON

spectroscopy and the

BRITE photometry.

Left: Superimposed red

and blue BRITE

photometry.

Right: Dynamical

representation of different

lines from the CHIRON

spectroscopy taken

simultaneously with the

BRITE campaign.

BRITE-Constellation – II

• g Gem (A1.5 IV): BRITE spectropolarimetric survey: first detection of a Zeeman pattern in an Am star(Bl ~ 5.5 G).

Blazere et al. 2016 MNRAS 459, 81

• I Car (F3V) & 27 Tau (B8 III): Combining magnetic and seismic information is the only way to probe the impact of magnetism on the physics of non-standard mixing processes inside hot stars.

Neiner et al. 2015 MNRAS 454, 56


... and the future

Oct. 14, 2013 C. Neiner & W. W. Weiss: BRITE-Constellation 39

Arago

UV & visible

spectropolarimetry

PI: C. Neiner

ESA M candidate

Instrument:

1.3-m telescope & spectropolarimeter

UV: 119–320 nm with R=25000

visible: 355–888 nm with R=35000

Rotating plates in MgF2 as spectropolarimetric technology

Goal:

life cycle of matterISM, stars of all types at all evolutionary stages, magnetism, ...

star-planet interactionsUV irradiation, emergence of life,...

Status:

studied by CNES & European consortium,

proposed for M5 but rejected based on cost, likely

to be re-proposed for M6 (launch in 2032)

UV spectropolarimetry will allow to measure, for

the first time, the magnetic fields in the wind, i.e. in

the

circumstellar environment

Visible spectropolarimetry allows to measure the

magnetic fields at the surface of a star

Links circumstellar events to surface structures

Strategy:

long-term monitoring,

e.g. 3D mapping of the star & surroundings

large statistical samples

Targets of Opportunity (ToO)

Targets: all kind of stars, including massive

stars, PMS stars, supernovae,...

LUVOIRNASA’s Large UV/Optical/IR Surveyor

15-m telescope

with a

suite of instruments

Status: NASA Flagship mission, will be evaluated at

the 2020 Decadal survey (launch in 2035)

POLLUX:UV spectropolarimeter

PIs: C. Neiner and J.-C. Bouret

Design: FUV (90 – 123 nm) or MUV+NUV (119 – 220 &

210 – 390 nm), linear & circular polarisation with R = 120.000,

mirrors for FUV, rotating plates in MgF2 for MUV+NUV

Goal: star and planet formation, stellar magnetism, wind and

outflows, white dwarfs, supernovae, exoplanets, ISM, IGM,

cosmology, galaxy evolution, solar system,...

Status: under study by CNES and a European consortium,

will be evaluated with LUVOIR and its other instruments

at the 2020 NASA Decadal survey

FAASTnanosat for UV spectropolarimetry

CNES – PI: P.-J. Hebert

Nanosat with 12-cm telescope,

l=170-320 nm, R=10000

Birefringent wedges, no moving

parts, all Stokes parameters at once

Pertenais et al. 2016

Also available for amateurs

with pointing through a website

AthenaX-ray mission

ESA – PI: P. Nandra

Instrument:X-IFU for high-spectral resolution imaging, 0.2-12 keV

WFI for high count rate, mid-resolution spectroscopy

over a large FoV, 0.2-15 keV

Goal: map hot gas structures in the Universe, determine their physical

properties, track their evolution, find and study

supermassive black holes,... and can be used to study

magnetospheres!

Status: L2 mission by ESA, launch in 2028

The advent of the new X-ray mission Athena+ (Nandra et al., 2013) may notably enable us

to study confined winds in radically different environments like low-metallicity galaxies such

as the Magellanic Clouds, where massive stars are known to display weaker stellar winds.

Such new data would allow to test our current models on vastly different cases, thus

improving their reliability.

ud-Doula et al. 2016 AdSpR 58, 680


Understanding of magnetic fields in stars and their environment has gained much from observations

in space .....

and more will come !

an outsiders view...

Magnetic Stars

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