Young Stellar Object Variability (YSOVAR): Long Timescale Variations in the Mid-Infrared

Abstract

The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (3.6 & 4.5 um) time-series photometry of the Orion Nebula Cluster plus smaller footprints in eleven other star-forming cores (AFGL490, NGC1333, MonR2, GGD 12-15, NGC2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC1396A, and Ceph C). There are ~29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. We present the data collection and reduction for the Spitzer and ancillary data, and define the "standard sample" on which we calculate statistics, consisting of fast cadence data, with epochs about twice per day for ~40d. We also define a "standard sample of members", consisting of all the IR-selected members and X-ray selected members. We characterize the standard sample in terms of other properties, such as spectral energy distribution shape. We use three mechanisms to identify variables in the fast cadence data--the Stetson index, a chi^2 fit to a flat light curve, and significant periodicity. We also identified variables on the longest timescales possible of ~6 years, by comparing measurements taken early in the Spitzer mission with the mean from our YSOVAR campaign. The fraction of members in each cluster that are variable on these longest timescales is a function of the ratio of Class I/total members in each cluster, such that clusters with a higher fraction of Class I objects also have a higher fraction of long-term variables. For objects with a YSOVAR-determined period and a [3.6]-[8] color, we find that a star with a longer period is more likely than those with shorter periods to have an IR excess. We do not find any evidence for variability that causes [3.6]-[4.5] excesses to appear or vanish within our data; out of members and field objects combined, at most 0.02% may have transient IR excesses.

Accepted to AJ; 38 figures, 93 pages

References in corpus (26)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The distance to the Orion Nebula
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• Measuring the rotation period distribution of field M-dwarfs with Kepler
• Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster
• Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e
• Lithium depletion and the rotational history of exoplanet host stars
• A Spitzer census of the IC 348 nebula
• The Spitzer Gould Belt Survey of Large Nearby Interstellar Clouds: Discovery of a Dense Embedded Cluster in the Serpens-Aquila Rift
• A Combined Spitzer and Chandra Survey of Young Stellar Objects in the Serpens Cloud Core
• A Correlation Between Pre-Main Sequence Stellar Rotation Rates and IRAC Excesses in Orion
• Spitzer/IRAC and ISOCAM/CVF insights on the origin of the Near to Mid-IR Galactic diffuse emission
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• Near-Infrared Variability in the 2MASS Calibration Fields: A Search for Planetary Transit Candidates
• The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS
• ACIS-I observations of NGC2264. Membership and X-ray properties of PMS stars
• Variability of the Infrared Excess of Extreme Debris Disks
• The Orbit and Occultations of KH 15D
• The onset of X-ray emission in young stellar objects: a Chandra observation of the Serpens star-forming region
• A Simultaneous Optical and X-ray Variability Study of the Orion Nebula Cluster. I. Incidence of Time-Correlated X-ray/Optical Variations
• Deep near-IR variability survey of pre-main-sequence stars in Rho Ophiuchi
• The Monitor project: JW 380 -- a 0.26, 0.15 Msol pre main sequence eclipsing binary in the Orion Nebula Cluster
• The Peculiar Periodic YSO WL 4 in Rho Ophiuchus
• Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. II. Temporal evolution of the eruptive source
• Pre-Main Sequence variables in the VMR-D : identification of T Tauri-like accreting protostars through Spitzer-IRAC variability
• The Diskionary: A Glossary of Terms Commonly Used for Disks and Related Objects, First Edition

Cited by in corpus (9)

• CSI 2264: Probing the inner disks of AA Tau-like systems in NGC 2264
• IN-SYNC II: Virial Stars from Sub-Virial Cores -- The Velocity Dispersion of Embedded Pre-Main-Sequence Stars in NGC 1333
• HOPS 383: An Outbursting Class 0 Protostar in Orion
• Molecule sublimation as a tracer of protostellar accretion: Evidence for accretion bursts from high angular resolution C18O images
• Planetary Collisions outside the Solar System: Time Domain Characterization of Extreme Debris Disks
• Chemical tracers of episodic accretion in low-mass protostars
• YSOVAR: Mid-IR variability in the star forming region Lynds 1688
• 1D accretion discs around eccentric planets: observable near-infrared variability
• Circumstellar Disks revealed by $H$/$K$ Flux Variation Gradients