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How to assemble a star?
sheding light on outbursts, mass
accretion and ejection
Dirk Froebrich
low mass star formation
(protostellar) luminosity problem
HR-diagram
HR-diagram
HR-diagram of NGC2264
(protostellar) luminosity problem
Young stars are fainter than expected
Young stars accrete not enough material
T-Tauri accretion rates are 10-7MSUN/yr or lower....
it would take 10 million years to assemble the Sun
Episodic/variable accretion can solve these problems!
YSO variability
one of the defining candidates of T-Tauri stars
present on all time scales
short time, mostly small changes:
rotation
ocultations from disk
‘flickering’
long time, larger amplitudes:
EX Lup (EXor)
FU Ori (FUor)
duration for FUor unclear, frequency 5-50kyr from infrared
monitoring with UKIDSS, VISTA, WISE vs Glimpse
Currently GAIA,
in future LSST, UoK Beacon Observatory …
Some Questions
What is the duration of the FUor bursts?
What fraction of time do YSOs spend in outburst (of what
strength and does it depend on mass, environment, etc)?
What mass fraction is accreted in the bursts?
YSO variability/outbursts
McNeil’s Nebula
YSO variability/outbursts
McNeil’s Nebula
YSO variability/outbursts
McNeil’s Nebula
YSO variability/outbursts
YSO variability/outbursts
YSO variability/outbursts
YSO variability/outbursts
YSO variability/outbursts
YSO variability/outbursts models
Some Questions
What is the duration of the FUor bursts?
What fraction of time do YSOs spend in outburst (of what
strength and does it depend on mass, environment, etc)?
What mass fraction is accreted in the bursts?
How to answer some of these?
Monitor the brightness of many YSOs over a long period
of time.
This does not have to be at regular intervals or specific
filters/wavelengths. EVERY image is helpful!
Young clusters are ideal as there are many YSOs in each
field of view and we know their age.
Can easily spot onset of eruption for detailed
investigations.