TY - JOUR
T1 - Young stellar object variability (YSOVAR)
T2 - Long timescale variations in the mid-infrared
AU - Rebull, L. M.
AU - Cody, A. M.
AU - Covey, K. R.
AU - Günther, H. M.
AU - Hillenbrand, L. A.
AU - Plavchan, P.
AU - Poppenhaeger, K.
AU - Stauffer, J. R.
AU - Wolk, S. J.
AU - Gutermuth, R.
AU - Morales-Calderón, M.
AU - Song, I.
AU - Barrado, D.
AU - Bayo, A.
AU - Hora, J. L.
AU - Vrba, F. J.
AU - Alves De Oliveira, C.
AU - Bouvier, J.
AU - Carey, S. J.
AU - Carpenter, J. M.
AU - Favata, F.
AU - Flaherty, K.
AU - Forbrich, J.
AU - Hernandez, J.
AU - McCaughrean, M. J.
AU - Megeath, S. T.
AU - Micela, G.
AU - Terebey, S.
AU - Turner, N.
AU - Allen, L.
AU - Ardila, D.
AU - Bouy, H.
AU - Guieu, S.
PY - 2014/11/1
Y1 - 2014/11/1
N2 - 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.
AB - 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.
KW - circumstellar matter
KW - stars: pre-main sequence
KW - stars: protostars
KW - stars: variables: general
UR - http://www.scopus.com/inward/record.url?scp=84908179489&partnerID=8YFLogxK
U2 - 10.1088/0004-6256/148/5/92
DO - 10.1088/0004-6256/148/5/92
M3 - Article
AN - SCOPUS:84908179489
VL - 148
JO - The Astronomical Journal
JF - The Astronomical Journal
SN - 0004-6256
IS - 5
M1 - 92
ER -