Young Stellar Object VARiability (YSOVAR): Long Timescale Variations in the Mid-infrared

Author(s)

L. M. Rebull, A. M. Cody, K. R. Covey, H. M. Günther, L. A. Hillenbrand, P. Plavchan, K. Poppenhaeger, J. R. Stauffer, S. J. Wolk, R. Gutermuth, M. Morales-Calderón, I. Song, D. Barrado, A. Bayo, David J. James, J. L. Hora, F. J. Vrba, C. Alves de Oliveira, J. Bouvier, S. J. Carey, J. M. Carpenter, F. Favata, K. Flaherty, J. Forbrich, J. Hernandez, M. J. McCaughrean, S. T. Megeath, G. Micela, H. A. Smith, S. Terebey, N. Turner, L. Allen, D. Ardila, H. Bouy, S. Guieu

Abstract

The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope

observing program obtained the first extensive mid-infrared (3.6 and 4.5

μm) time series photometry of the Orion Nebula Cluster plus smaller

footprints in 11 other star-forming cores (AFGL 490, NGC 1333, Mon R2,

GGD 12-15, NGC 2264, L1688, Serpens Main, Serpens South, IRAS

20050+2720, IC 1396A, 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 roughly twice per day for

~40 days. 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 χ2

fit to a flat light curve, and significant periodicity. We also

identified variables on the longest timescales possible of six to seven

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 set; out of members and field objects combined,

at most 0.02% may have transient IR excesses.

Organisation(s)

Department of Astrophysics

External organisation(s)

Harvard-Smithsonian Center for Astrophysics, Lowell Observatory, INAF Osservatorio Astronomico di Palermo, University of Massachusetts, Amherst, University of Georgia, California State University, Los Angeles, Centro de Investigaciones de Astronomía, Venezuela, California Institute of Technology (Caltech), Missouri State University, National Aeronautics & Space Administration (NASA), Universidad de Valparaíso, Cerro Tololo InterAmerican Observatory (CTIO), US Naval Observatory, Flagstaff Station, Centre National De La Recherche Scientifique (CNRS), Science and Operations Department - Science Division (SCI-SC), Wesleyan University, University of Toledo, National Optical Astronomy Observatory, Tucson, European Space Astronomy Centre (ESA)

Journal

The Astronomical Journal

Volume

148

Pages

46

No. of pages

46

ISSN

0004-6256

DOI

https://doi.org/10.1088/0004-6256/148/5/92

Publication date

11-2014

Peer reviewed

Yes

Austrian Fields of Science 2012

103003 Astronomy, 103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/young-stellar-object-variability-ysovar-long-timescale-variations-in-the-midinfrared(90f67545-4f9c-4f48-83c1-ae576397bcd4).html