JWST in the Age of Time Domain Astronomy: Understanding FU Orionis Phenomena Joel D. Green Space Telescope Science Institute
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Dissecting the Spectrum of a Low Mass Star Far-IR Submm Millimeter Modified from Hartmann & Kenyon, 1996, ARAA, /Jet 34, 207 X-ray Mid-IR UV Mass ~ < 2 М 8 Optical Near-IR Radio 4
How does this happen? Tightly collimated jet Quasi-periodic ejecta clumping HH30 jet HST/WFPC2; 1995-2000 (A. Watson) 5
Episodic Accretion & Outflow? 10 yr timescale 10 3 yr timescale 6
A Close Relationship Between Accretion and Outflow? Figure from Königl A et al. MNRAS 2011;416:757-766 -Accreting matter compresses the magnetosphere of the star -Field lines enhanced via differential rotation between disk and star -Conical winds & outflows twist from the inner disk Romanova et al., 2009, MNRAS, 399, 1802 Kurosawa and Romanova, 2012, MNRAS, 426, 2901 Disk–star interaction and the formation of a conical wind. The wind/outflow base originates very close to the stellar photosphere. 7
Potential Triggers of Burst Behavior • Intrinsic luminosity changes due to disk-related instabilities • Binarity: e.g, FU Ori (Reipurth & Aspin, 2004, ApJ, 608, 65) – Mass transfer? Instability triggered by perturbing the disk externally? • Variable extinction (flared disks, periodic obscuration); Morales- Calderón et al. 2012, ApJ, 733, 50 8
Magnetorotational + Gravitational Instability Model (MRI+GI) Armitage et al. 2001, MNRAS, 324, 705 Zhu et al. 2009, ApJ, 694, 1045 Zhu et al. 2010, ApJ, 714, 1143 Martin & Lubow 2011, AJ, 740, 6 Martin et al. 2012, MNRAS, 423, 2718 Bae et al. 2013, ApJ, 764, 141 GI: Outer Disk: Q = c s Ω / πGΣ ~ 1 MRI: Inner Disk (hot/highly ionized) Transition region: (1-10 AU) GI-MRI junction not smooth => episodic accretion Key zone is 1-10 AU Predicts correct outburst strength and timescale Single burst But the details of MRI triggering are uncertain 9
Empirical Prediction à New Accretion Paradigm Back of napkin Simulation Hartmann 1998, Camb. Astrophys. Ser., Vol. 32 From disk fragmentation model of Vorobyov & Basu 2010, ApJ, 719, 1896
Did it happen here? Clustered isotopic ratios of Fe and Al (G. MacPherson, priv. comm) Stardust mission reveals crystalline dust in comets (Brownlee et al. 2012) Depletion of certain volatiles in the inner solar system evidence of transient heating? (Hubbard & Ebel 2014) Outward transport of CAIs? Wurm & Haack (2009) FUors (may) anchor the fossil record of our Solar System to the protostellar development timescale 11
EXors and FUors are a Natural Laboratory for Accretion Physics Ábrahám et al., 2009, Nature, 459, 224 Courtesy: R. Hurt, SSC 12
Why study FUors and related outbursts? • Represent stages wherein most of the YSO mass may be accumulated, processed, ejected • Accretion mechanism may differ from the classical magnetospheric TTS accretion model: "new" accretion physics • Diagnostic for outburst triggering mechanisms, an important problem • Offer "unveiled" examples of YSOs with accretion rates comparable to embedded sources • Can look for signs of outburst in our solar system: clustered isotopic ratios representing system-wide events 13
Rapid Changes in Optical and NIR Hillenbrand+19 A p r M a y J un J u l A u g S e p O c t N o v D e c − 12 10 K - 1 H BC 722 8 H - 1 T = 4000 K J - 1 10 A V = 3.1 m a g − 13 10 I - 1 12 − 2 ] � F � [ W m M a g n i t u d e T a u r u s m e d i a n R 14 − 14 10 A V = 3.1 m a g Kospal+10 V + 1 16 − 15 10 18 B + 2 M ill e r e t a l . K ó s p á l e t a l . 20 H BC 722 ( li t e r a t u r e ) 1 10 100 H BC 722 ( t h i s w o r k ) W a v e l e n g t h [ ! m ] 22 300 350 400 450 500 550 J D ( 2,455,000 + ) 14
Key Questions • What is the triggering mechanism of these bursts? • What effect does a burst have on the protoplanetary system? • What is the connection between accretion and outflow? • Are (multiple) bursts common to most protostars? • Did it happen here in the Solar System? 15
Processes with Potentially Observable Signatures Herczeg, Calvet, & Hartmann 2016 16
Disk Chemistry: Temperature and Wavelength Green et al. 2019; 2020 Decadal Survey Whitepaper 17
So all we have to do… • Observe objects repeatedly before, during, and after outburst – Using tracers that provide accretion rate, temperature, kinematics, chemical pathway alterations, and radial profiles – At radio, mm, IR, optical, UV, and X-ray, including spectroscopy of R~ 100-100,000 – In tracers of gas, ice, and dust – On objects that are typically 400-4000 pc distant – Waiting for sources to go into outburst, and return to quiescence (~ 100 yr) – While rapidly surveying the sky 18
Where can we progress? • Time domain • X-ray, MIR, FIR, submm, and radio large sensitivity improvements • Spatial resolution in radio, MIR, FIR • Survey speeds, area coverage • High spectral resolution • Space-accessible bands 19
Or in summary • High (v < 10 km/s for survey; v < 1 km/s for followup) spectral resolution capabilities with relatively rapid response times in the IR (3-500 μm), X-ray (0.1-10 keV), and radio (cm) are critical to follow the course of accretion and outflow during an outburst. Complementary, AU-scale radio observations are needed to probe the disk accretion zone, and 10 AU-scale to probe chemical and kinematic structures of the disk- forming regions, and track changes in the dust, ice, and gas within protostellar envelopes. 20
FUors and X-rays FUors are X-ray bright, • compared to X-ray active T Tauri stars, but not relative to the total system output Multiple (hard and soft) X-ray • components sometimes seen but can be attributed to binaries? Chandra/XMM studies ongoing • to track emission during burst – accretion column obscuration (in prep.)? Hard X-rays = magnetically-driven Soft X-rays = accretion processes e.g. Grosso et al. 2010, A&A 522, A56 Skinner et al., AJ, 2006, 643, 995; Skinner et al. 2009, ApJ, 696, 766 21
The Burst of FUor HBC 722 – optical, near-IR, and X-ray monitoring, 2010-2013 Lee+15 22
Diary of a Burst 2010: 400 km/s outflow/wind • 2011-2012: luminosity & accretion rate decreases, but wind • remains strong. Hot inner disk dominated rotation profiles as central star fades. – X-rays indicate accretion onto central star activated 2013-14: Disk heat moves outward (viscous dissipation?) as profiles • narrow (IGRINS). – X-rays indicate large column of dust-depleted absorbing material Outer disks affected on longer timescales (years) • Envelope chemistry, ice composition are affected (years to • decades…) if envelopes are still present 23
How does line emission evolve during the burst, and what is it tracing? How does the disk change during a burst? 24
FUor silicate dust is amorphous 50-90% of T Tauri stars show crystalline features Spitzer Water vapor (abs) – disk photosphere? Amorphous silicate emission 25 Green+06
IR Spectroscopy Traces Rapid Changes in Dust and Gas Does dust processing from flash heating (or vertical transport and stirring of dust grains) occur on few month timescales? Ábraham et al., 2009, Nature, 459, 224 26
FU Orionis in Outburst circa 2004 circa 2016 Black model = Red model x 0.88 SOFIA- FORCAST Spitzer-IRS 2016 2004 Green+16c <=7% % Change 2004-16: -12% -7% Green+06 27 Overall uncertainty ~ 4.2%
No change in solid state features Dust Hot gas H 2 O? H 2 O? Silicates Green+16c Green+06 28
Depletion of the innermost disk regions? Cooling? Next up, V1057 Cyg! 29
JWST-MIRI and NIRSpec can track FUors during burst 30
Multi-wavelength Analysis Chandra/Swift ToO and ALMA, Herschel – e.g. VLTI/MIDI, Spitzer, SOFIA/HIRMES; Monitoring – Liebhart+14, Green+13,16, Cieza+16, JWST, SphereX – Origins Space Telescope; Pooley+18 Hales+16, Lee+18; e.g. Kospal+18, e.g., Logan+19 Johnstone+16, Green+16 Molyarova+18 Optical/IR Monitoring: e.g., Hillenbrand+18,+19; Fischer+19 New transient surveys (PTF, LSST; WFIRST, Euclid) will provide “early warning” with more systematics 31
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