Massive planets in FU Orionis objects Giuseppe Lodato Institute of Astronomy, Cambridge In collaboration with Cathie Clarke (IoA)

FU Orionis objects Large outbursts:  L≈ 2-3 orders fo magnitude Sudden increase in the mass accretion rate in the circumstellar disc –Accretion disc SED fit the observation for <10  m Kenyon & Hartmann 1991 –Double peaked optical - near IR line profiles Rise timescale: t rise ≈ 1 yr (FU Ori and V1057 Cyg) t rise ≈ 20 yr (V1515 Cyg) Decay timescale: t decay ≈ 10 yr (V1057 Cyg) t decay ≈ yr (FU Ori and V1515 Cyg)

Outburst mechanism Tidal interaction with a companion star Bonnel & Bastien 1992 Gravitational instability in a massive disc Armitage, Livio & Pringle 2001 Thermal instability Clarke, Lin & Papaloizou 1989 Bell & Lin 1994, Bell et al 1995

Limit cycle instability  Stable branches Unstable branch Outwardly propagating front: slow Inwardly propagating front: fast

Time-scale problem for thermal instability models Bell & Lin (1994): accurate vertical structure calculations  A and  B are strongly increasing function of R: instability triggered close to the inner edge Slow rise timescale: t rise ≈ 10 yr A fast rise time would be achieved if R trig ≈ 10 R o

A massive planet in FU Orionis discs Periodic modulation of the line profiles: the signature of a massive planet? (Clarke & Armitage 2003) Accretion onto the embedded planet Hot spot in the disc at the instantaneous position of the planet Observational evidence (Herbig et al. 2003) Herbig et al Clarke & Armitage 2003

Influence of the planet on the outburst Gap formation: rapid draining of the inner disc Planet migration (Type II) : if the planet is massive enough, it is slower than the viscous evolution Banking up of  upstream of the planet position Triggered instability at planet position R s Clarke & Syer 1996

Coupled planet-disc evolution The disc  =  =M/3 .  eq define the S-curve: analytical approximation from the Bell & Lin (1994) results

Coupled planet-disc evolution Planet migration Analytic prediction from Ivanov et al Banking up

Planet induced outbursts: the "reference" case M in = M o /yr. M s = 15 M Jupiter

Details of the planet induced outburst Trigger radius: R trig ≈ 11 R o Mass accretion rate in the inner disc during the outburst: M out ≈ M o /yr Peak luminosity ≈ 400 L o Outer propagation radius of the instability R lim ≈ 50 R o.

Light curves Rise time: t rise ≈ 2yr Peak luminosity: 400 L o

Long term evolution Radial migration of the planet significantly slowed down. Residual migration causes R trig to decrease Most outburst features determined by R trig Subsequent outbursts have: –Smaller amplitude (by a factor 2, after 10 outbursts) –Shorter recurrence time (by a factor 3, after 10 outbursts) –Longer rise time

Dependence on planet mass As planet mass increases, outbursts are triggered at progressively larger radii

Summary of results Massive planet (with M ≈ M Jupiter ) able to trigger FU Orionis outbursts at R≈ 10 R o Outbursts properties (amplitude, duration, rise time) depend on the location where the outburst is triggered Fast rise time (1-2 yr) if M s ≈ M Jupiter Radial migration of the planet significantly slowed down by the occurence of the outbursts

Remaining issues and fututre developments Steadiness of FU Orionis: t decay < yr in our models. All thermal instability models suffer from this problem. What happens to the planet during the outburst? Both dynamically and physically Long term evolution and planet migration Triggered outburst for lower feeding rates?