magnetic fields of protostars & accretion discs
credit: Mark Garlick
origin & impact on star / planet formation
✵ STAR / PLANET FORMATION ✵ key role of magnetic fields in star / planet formation comparable to turbulence next to gravitation ✒ inhibits fragmentation / hampers formation of a Keplerian disc ✒ generate jets / outflows / evacuate angular momentum
✵ STAR / PLANET FORMATION ✵ key role of magnetic fields in star / planet formation
Machida et al
2007
comparable to turbulence next to gravitation ✒ inhibits fragmentation / hampers formation of a Keplerian disc ✒ generate jets / outflows / evacuate angular momentum
✵ STAR / PLANET FORMATION ✵ key role of magnetic fields in star / planet formation comparable to turbulence next to gravitation ✒ inhibits fragmentation / hampers formation of a Keplerian disc ✒ generate jets / outflows / evacuate angular momentum
collapsing pre-stellar cores
Girart et al 2006
mass to flux ratio close to critical ✒ confirm key role of magnetic fields
✵ STAR / PLANET FORMATION ✵ key role of magnetic fields in star / planet formation comparable to turbulence next to gravitation ✒ inhibits fragmentation / hampers formation of a Keplerian disc ✒ generate jets / outflows / evacuate angular momentum
collapsing pre-stellar cores mass to flux ratio close to critical ✒ confirm key role of magnetic fields
class I-III PMS stars central engine of star / planet formation class-I protostars < 0.5 Myr cTTSs : classical / accreting T Tauri stars wTTSs : weak-line / non-accreting T Tauri stars FU Ori : accretion discs in outbursts
✵ Main Questions ✵
magnetic topologies of protostars & accretion discs ? fields detected for a few tens of TTSs and a few accretion discs ✒ origin on these fields, fossil vs dynamo ✒ evolution of fields as stars contract to the MS
✵ Main Questions ✵
magnetic topologies of protostars & accretion discs ? fields detected for a few tens of TTSs and a few accretion discs ✒ origin on these fields, fossil vs dynamo ✒ evolution of fields as stars contract to the MS
impact on star / planet formation ? alter disc dynamics, accretion & outflows ✒ carve magnetospheric gap in inner disc ✒ evacuate angular momentum through magnetic winds / jets / ejections ✒ modify stellar structure, planet formation / migration / survival ? ✒ when is the field dissipated ?
✵ Magnetic FIELDS of ACCRETION DISCS ✵ direct: polarized Zeeman signatures from cores & protostars at cm wavelengths (H, OH, CN) for cold diffuse pre-stellar cores (10-100 µG) shock-induced masers (H2O, OH) for denser high-mass protostars (10-100 mG) at optical wavelengths for the warm dense PMS disc FU Ori, kG ✒ field ~10 µG for n < 300 cm-3 then B ∝ n0.65±0.05 (Crutcher 2012) ✒ pre-stellar cores slightly supercritical (relative M/Φ > 1) AA50CH02-Crutcher
ARI
27 July 2012
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Crutcher 2012
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12.50:29-63. Downloaded from www.annualreviews.org louse 3 -Paul Sabatier on 10/06/16. For personal use only.
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✵ Magnetic FIELDS of ACCRETION DISCS ✵ direct: polarized Zeeman signatures from cores & protostars at cm wavelengths (H, OH, CN) for cold diffuse pre-stellar cores (10-100 µG) shock-induced masers (H2O, OH) for denser high-mass protostars (10-100 mG) at optical wavelengths for the warm dense PMS disc FU Ori, kG ✒ field ~10 µG for n < 300 cm-3 then B ∝ n0.65±0.05 (Crutcher 2012) ✒ pre-stellar cores slightly supercritical (relative M/Φ > 1)
indirect: polarisation of dust emission at mm & sub-mm wavelength for class-0 & class-I protostars field strength from dispersion of orientation (Chandrasekhar Fermi) ✒ hourglass shape of field lines confirming key role of fields ✒ fields ~mG & clouds slightly supercritical contamination from scattering by dust grains (Kataoka et al 2015,Yang et al 2016)
✵ Magnetic FIELDS of ACCRETION DISCS ✵
magnetic field of pre-stellar core NGC 1333 - IRAS 4A
Girart et al 2006
~1.2 M class-0 core viewed edge-on ✒ field ~5 mG (n ~4 107 cm-3) slightly super critical (relative M/Φ ~1.7) ✒ field stronger than turbulence (ß ~0.02) ✒ magnetic tension / gravity ~0.2 ✒ but scattering likely playing a role (Yang et al 2016)
pinch
Rao et al.
twist?
magnetic field of pre-stellar core NGC 1333 - IRAS 4A
~1.2 M class-0 core viewed edge-on ✒ field ~5 mG (n ~4 107 cm-3) slightly super critical (relative M/Φ ~1.7) ✒ field stronger than turbulence (ß ~0.02) ✒ magnetic tension / gravity ~0.2 ✒ but scattering likely playing a role (Yang et al 2016)
(a)
magnetic field of protostar IRAS 16293−2422 B ~0.3 M class-0-I young protostar viewed face-on ✒ field ~5 mG (n ~8 107 cm-3) slightly super critical (maser 110 mG nearby) ✒ turbulent to magnetic energy ratio ß~0.32 ✒ radial field twisted by Keplerian disc ? ✒ impact of scattering unclear (Yang et al 2016)
Rao et al 2014
✵ Magnetic FIELDS of ACCRETION DISCS ✵
The Astrophysical Journal Letters, 780:L6 (5pp), 2014 January 1
✵ Magnetic FIELDS of ACCRETION DISCS ✵ magnetic fields in outer disc of HL Tau ?
Stephens et al 2014
0.55 M star, 0.14 M disc, angular momentum gain + contraction exerted along the field lines connected to the disk. Because of the stellar wind would require a considerable driving good agreement with existing observations the ✒ large amount of angular momentum extracted by the magne- even during the phases during which the disk is not ac tospheric ejections, both the accretion disk and the MEs rotate On the other hand, in this case the role played by the stell observed vs predicted accretion modes more slowly than the central star, even in the subcorotation re- can be neglected, since the torque exerted by the star-dis ✒ stable accretion when spun-down Ω★/ΩK > along 0.6 the interaction is generally sufficient to brake the stellar r gion. Therefore the star can be efficiently ✒ unstable magnetic surfaces directlychaotic connectedaccretion with the diskotherwise and the MEs. Even neglecting the stellar wind torque, we can estima During the high-accretion phases, the disk can deposit its angular momentum along the funnel flows, exerting a small but
on average, the characteristic spin-down timescale in ca is approximately equal to 8 × 105 yr.
between Stable and Unstable M. Romanova, Boundary R. V. E. Lovelace
5
star / disc magnetospheric interaction 2D & 3D simulations of accretion along magnetic funnels ✒ simulations for realistic large-scale fields ✒ estimate angular momentum loss
ordered
control angular momentum evolution
Blinova et al 2015
✵ Magnetospheric accretion ✵
chaotic
atter flow magnetosphere in a in case chaotic accretion in multiple tongues dominates, mod ered accretion twowhere tongues dominates, model µ0.5c3⇥5a0.02, at time t = 14. extending beyond co-rotation, i.e. Ω★/ΩK > 1 hown in color, selected linesregime are shown in red. Middle panel: Same b ✒ CME-likemagnetic ejections infield propeller ✒ angular momentum loss > angular momentum gain + contraction ensity distribution is shown in color. ✒ good agreement with existing observations observed vs predicted accretion modes ✒ stable accretion when Ω★/ΩK > 0.6 ✒ unstable chaotic accretion otherwise
✵ IMPACT on CLOSE-IN Planets ✵
close-in planets stellar-mass dependent drop in occurence rates of inner planets ✒ corotation radius better than planet / stellar tides & dust / viscous sublimation ✒ planet formation / migration stopped at magnetospheric boundary ? Mulders, Pascucci, & Apai
Mulders et al 2015
The Astrophysical Journal, 798:112 (18pp), 2015 January 10
close-in planets stellar-mass dependent drop in occurence rates of inner planets ✒ corotation radius better than planet / stellar tides & dust / viscous sublimation ✒ planet formation / migration stopped at magnetospheric boundary ?
newborn close-in giant planets recently detected hot Jupiter orbiting in 4.93 d (0.057 AU) around the 2 Myr-old wTTS V830 Tau eclipsing hot Neptune around the 5-10 Myr wTTS K2-33 candidate hot Jupiter around 2-Myr cTTS CI Tau ? ✒ close-in giant planet likely generated through migration ✒ avoided falling into the host star thanks to the large-scale field ✒ viable for all magnetospheric configurations ? ✒ detect planet magnetic field with LOFAR ?
credit: Mark Garlick
✵ IMPACT on CLOSE-IN Planets ✵
✵ conclusions & perspectives ✵ growing body of magnetic field observations for dense cores and class-0 protostars / discs ✒ field slightly super critical, playing a key role in collapse first exploration of large-scale magnetic fields of TTS ✒ field relates to internal structure ✒ impacts angular momentum evolution, affects convection zone
✵ conclusions & perspectives ✵ growing body of magnetic field observations for dense cores and class-0 protostars / discs ✒ field slightly super critical, playing a key role in collapse first exploration of large-scale magnetic fields of TTS ✒ field relates to internal structure ✒ impacts angular momentum evolution, affects convection zone
multiple detections of newborn planets including close-in giants that survived migration ✒ role of large-scale stellar fields ? ✒ estimate fields of close-in giants ?
✵ conclusions & perspectives ✵ growing body of magnetic field observations for dense cores and class-0 protostars / discs ✒ field slightly super critical, playing a key role in collapse first exploration of large-scale magnetic fields of TTS ✒ field relates to internal structure ✒ impacts angular momentum evolution, affects convection zone
multiple detections of newborn planets including close-in giants that survived migration ✒ role of large-scale stellar fields ? ✒ estimate fields of close-in giants ?
lots of progress expected soon on disc magnetic fields thanks to SPIRou & ALMA more spectropolarimetry :)
