Signatures of magnetic activity in very low mass stars and brown dwarfs
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Signatures of Magnetic Activity in Very Low Mass Stars and Brown Dwarfs. Rachel Osten Hubble Fellows Symposium. Collaborators. Suzanne HawleyUniversity of Washington Tim BastianNRAO Neill ReidSTScI Ray JayawardhanaU. Toronto. Sun M dwarf L dwarf T dwarf Jupiter.

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Signatures of Magnetic Activity in Very Low Mass Stars and Brown Dwarfs

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Signatures of magnetic activity in very low mass stars and brown dwarfs

Signatures of Magnetic Activity in Very Low Mass Stars and Brown Dwarfs

Rachel Osten

Hubble Fellows Symposium


Collaborators

Collaborators

Suzanne HawleyUniversity of Washington

Tim BastianNRAO

Neill ReidSTScI

Ray JayawardhanaU. Toronto


Signatures of magnetic activity in very low mass stars and brown dwarfs

Sun M dwarf L dwarf T dwarf Jupiter

  • Transition to completely convective interior happens at ~M3

  •  Should expect a changeover in magnetic activity observables, since

  • no aw dynamo can operate; not observed

  •  See same manifestations of magnetic activity (Ha, X-ray, radio emission) in some late M/L objects as in solar-like active stars

  • Cool, neutral, high density atmospheres have large resistivity, magnetic fields and matter are decoupled


Activity signatures are seen sporadically in late m l dwarfs

Activity Signatures Are Seen (Sporadically) in Late-M/L Dwarfs

steady

and

variable (flaring)

levels of emission

X-ray emission

Stelzer (2004)

BD pair:

Ba 55-87 Mjup

Bb 34-70 Mjup

 Ha emission

2MASS 0144-0716 (L5V; Liebert et al. 2003)

Radio emission

Berger 2002; 2MASS 0036+18 (L3.5)


How common is radio emission in late m l t field dwarfs

How common is radio emission in late M, L, T field dwarfs?

Not Very:

only a handful of detections, all earlier than L4V

Consistent with Ha, X-ray decline in emission with decreasing Teff

Average radio properties

Osten et al. 2006


T eff more important than mass age in controlling x ray properties

Teff more important than mass, age in controlling X-ray properties

Field objects

t>500 MYr

BDs in Orion t~1 MYr

Preibisch et al. 2005


Signatures of magnetic activity in very low mass stars and brown dwarfs

No dramatic changes in magnetic activity observables, despite large differences in stellar properties

West et al. 2004


Detailed investigation of radio properties tvlm513 46456 m9 v

Detailed Investigation of Radio Properties: TVLM513-46456 (M9 V)

Osten et al. 2006

Radio spectral properties consistent with behavior of earlier spectral type active M stars: magnetic activity present at levels comparable with extrapolations


Detailed investigation of radio properties compare with ev lac dm3e

Detailed Investigation of Radio Properties: Compare with EV Lac (dM3e)

Osten et al. 2006, ApJ, accepted


Radio emission from young brown dwarfs

Radio Emission from Young Brown Dwarfs

Tsuboi et al. 2003

TWA 5B; ~10 Myr old

Fossil magnetic fields probably play a significant role in X-ray activity (Feigelson et al. 2002).


Radio emission from young brown dwarfs1

Radio Emission from Young Brown Dwarfs

Radio upper limits on all 4 substellar members of the nearest youngest association TW Hydrae (Burgasser & Putman 2005, Osten & Jayawardhana 2006)


Radio emission from young brown dwarfs2

Radio Emission from Young Brown Dwarfs

Lr/Lx of TWA 5B

anomalous behavior

compared to field brown dwarfs

TWA 5B

Caution: Lx/Lr relationship for active stars still not well understood

Berger 2005


Signatures of magnetic activity in very low mass stars and brown dwarfs

Why is this so difficult?

age

Some possibly important

measurable parameters

Mass, temperature

(Spectral type)

rotation

Radio

Ha

UV

X-ray

Steady

Flaring

Consistent behavior?


Future work

Future Work

  • What kind of magnetic activity survives in ultracool objects, and how cool?

     transient Ha emission out to L5

     to date, no X-ray detection of L dwarfs,

     radio detections up to L4

    is plasma heating to chromospheric temps. easier than to coronal temps?

    relative ease/efficiency of particle acceleration vs. plasma heating?

  • What is the systematic behavior of magnetic activity as a function of age, mass, temperature, rotation?

     Need large samples with known properties

  • What do the different activity observables tell us about the nature of the activity?

     In-depth investigation of magnetic activity properties to discern differences from active stars


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