mid-infrared variability and mass accretion toward ngc2264 protostars susan terebey csula dept of...
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Mid-Infrared Variability and Mass Accretion Toward NGC2264 Protostars
Susan Terebey
CSULA Dept of Physics & Astronomy
Ann Marie Cody, Luisa M. Rebull, John R. Stauffer, YSOVAR Science Team
Workshop on Dense Cores; Monterey July 2014
Premise: in protostar regime
Mass accretion -> accretion luminosity
Motivation
Protostar mass and mass accretion rates have been difficult to determine. We are in better shape with older class II YSOs.
Variability provides new view of mass accretion
L = L* + Lacc
ORIONSpitzer data
~250 hours of our observing time ~ 1 square degree region of the Orion Nebula cluster Cadence: 40 days, with 2 ∼epochs each day.~1400 Class I and II Orion YSOs with good quality time series (1-2% accuracy)more than half of them show significant variability. period Sep 2009 -- June 2011
• Distance ~ 760 pc• Age ~ 2-4 Myr• Known members: ~2000 + >3000 additional candidates• Large photometric & spectroscopic database• Many objects with disks
Coordinated Synoptic Investigation of NGC 2264
IRAC/MIPSP. S. Teixeira
Variable young stars and their disks:
A dynamic environment at many different wavelengths
Spitzer0.75°
5.2’
0.1
0.1
0.1
0.1
30d
Light curves display distinct patterns…
“spotted multi-periodic”
Spots + binary?
Spots?
“spotted”
“spotted irregular”
Rapidly evolving spots?
40d
0.02
0.1 mag
0.04
“AA Tau”
“accretor”
Dust obscuration?
Accretion bursts?
0.5 mag
0.2 mag
0.1
40d
30d
40d
Light curves display distinct patterns…
Structure function analysis
• 176 candidate protostars in NGC 2264
• Analysis of light curves for subset of69 candidates with good light curves (I2<14)
• Similar statistics for Orion
Light curve
What is the structure function?
0.1 mag
0.1 mag
28 days
0.1 mag
Orion shows same structure function
Magnetic support near 0.1 AU
V J
3.6
60o
0.8 AU
Turner etal 2014
Accretion LuminosityL = L* + Lacc
Lacc = ε GM⁄R *dM/dt
Characteristic 0.1 mag variability Suggests 10% or more accretion luminosity
Characteristic 30 day time scale for accretion events. If 30day = Porbital
Then R = 0.15 AU for M=0.5Msun
ConclusionsThe CSI2264 and YSOVAR Spitzer campaigns produced high quality multi-wavelength light curves for thousands of young stars. Emission at 4.5um is sensitive to the inner regions of young star disks.
Results for class I protostars in NGC2264 and Orion. • Light curve morphology of Class I protostars suggests accretion (variable
but not periodic).
Structure Function (SF) analysis shows characteristic• magnitude difference of 0.1 mag at 4.5 micron• timescale of T ~ 30 days• Power-law behavior for <30 day• Same structure function for protostars in Orion and NGC 2264
turbulent mass-accretion can lead to power-laws.