Characteristic UV spectra from stellar accretion

Fabio Reale Dipartimento di Fisica e Chimica Universita` di Palermo fabio.reale@unipa.it

Bright hot impacts by erupted fragments falling back on the Sun: 1)  a template for stellar accretion (Science, 2013)

2)  UV redshifts in stellar accretion (ApJL 2014) Fabio Reale (Univ. Palermo) Salvatore Orlando (INAF-OAPa) Paola Testa (Harvard CfA, USA) Giovanni Peres (Univ. Palermo) Enrico Landi (Univ. Michigan, USA) Carolus (Karel) J. Schrijver (LMSAL, USA)

Accretion flows on young stars (T Tauri)

T Tauri stars: C IV 1550A doublet

!  Magnetic geometry? !  Turbulence?

Ardila et al. 2013

Broad redshifted component

The UV emission: The impact

We focus on the impact at 7:27 UT (second arrow)

193A Magnetogram

1600A

UV emission: SDO/AIA 1600 A !  Before impact, absorbed in

171A, not in 1600A

!  Bright impacts both in 171A and 1600A

!  The 171A emission peaks later than the 1600 A 171A

1600 A

Light curves of the impact: peak delay

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New Hydrodynamic simulations (Reale et al. 2014) !  2D cartesian !  20 random droplets:

!  Radius: 1.4 < R < 2.6 108 cm !  Avg. separation: ~109 cm !  V=400 km/s !  Density: 5 x1010 cm-3

!  Oblique trajectory (75o)

New hydrodynamic simulations (Reale et al. 2014): free-falling random dense fragments

!  Asymmetric surge !  Next falling

fragments hit by the surge

!  Structured temperature

Temperature

Hydrodynamic simulation: the density

!  Dense (RED) shells BEFORE impacts

Density

The EUV emission: mostly from the surge

Emission absorbed below the line

The UV emission: mostly from thin shells of still downfalling fragments

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1600A 171A

UV emission: the fragments shells

-2 -1 0 1 2x [109 cm]

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t = 96 s

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Log nH [cm-3]

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SDO/AIA 1600 A

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.]

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Observed

Simulated

UV emission: synthesis of C IV doublet profile

!  Intense redshifted component (~ 350 km/s)

!  Single accretion flow

UV emission: C IV broadening

!  Many flows, different orientations -> broadening

Comparison with observation

Conclusions

!  This model naturally reproduces the observed high-speed UV redshift in a new way: fragments while they are still falling

!  Presence or absence connected to fragmented or continuous flows

!  Distributed flows? !  Importance of fragmentation: instabilities or since

the beginning? !  Coronal rain?