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 * + L acc

ORION Spitzer 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 June 2011

Distance ~ 760 pc Age ~ 2-4 Myr Known members: ~ >3000 additional candidates Large photometric & spectroscopic database Many objects with disks Coordinated Synoptic Investigation of NGC 2264 IRAC/MIPS P. S. Teixeira

Variable young stars and their disks: A dynamic environment at many different wavelengths

Spitzer 0.75° 5.2’ d

Light curves display distinct patterns … “spotted multi- periodic” Spots + binary? Spots? “spotted” “spotted irregular” Rapidly evolving spots? 40d mag 0.04

“AA Tau” “accretor” Dust obscuration? Accretion bursts? 0.5 mag 0.2 mag d 30d 40d Light curves display distinct patterns …

Structure function analysis 176 candidate protostars in NGC 2264 Analysis of light curves for subset of 69 candidates with good light curves (I2<14) Similar statistics for Orion

Light curve What is the structure function? 0.1 mag

28 days 0.1 mag

Orion shows same structure function

Magnetic support near 0.1 AU V J o 0.8 AU Turner etal 2014

Accretion Luminosity L = L * + L acc L acc = 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 = P orbital Then R = 0.15 AU for M=0.5Msun

Conclusions The 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.