Ysovar: The First Sensitive, Wide-Area, Mid-Infrared Photometric Monitoring of the Orion Nebula Cluster

Abstract

We present initial results from time-series imaging at infrared wavelengths of 0.9 deg 2 in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 μm data over 40 consecutive days. We extracted light curves with ∼3% photometric accuracy for ∼2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (I c ) and/or near-infrared (JK s ) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5 μm variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs-YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.

The identification of 93 day periodic photometric variability for YSO YLW 16A

“…This could be due to long-term evolution in primordial disk structure. Follow-up observations with the Spitzer Space Telescope and the YSOVAR program will further constrain the long-term stability of the observed periodic variability (Morales-Calderon et al 2011). …”

“…YSOVAR has also obtained photometric time-series of YLW 16A at 3.6 and 4.5 μm during the Spitzer Space Telescope warm mission, which will be part of a separate future publication (Morales-Calderon et al 2011).…”

“…The observed variability is generally attributed to the rotational modulation of large cold spots, hot spots, accretion and disk veiling. Photometric variability driven by rotational modulation of the proto-star are less pronounced at infrared wavelengths, thus improving sensitivity to variability driven by disk-related processes and the subject of many recent near-infrared (NIR) and Spitzer Space Telescope studies such as YSOVAR (Morales-Calderon et al 2011;Flaherty et al 2012;Flaherty & Muzerolle 2010;Faesi et al 2012). …”

Chemical tracers of episodic accretion in low-mass protostars

“…The spacings between periodic shocks in jets and outflows support quiescent intervals anywhere from 10 4 yr down to 10 yr, separating bursts with an unknown range of accretion rates (Devine et al 1997;Raga et al 2002;Arce et al 2013). Highcadence photometric surveys show luminosity variations at the 5-50% level on timescales of hours to weeks (Billot et al 2012;Stauffer et al 2014), though only some of that may be related to accretion variability (Morales-Calderón et al 2011;Rebull et al 2014). Despite the incomplete statistics, it appears that stronger accretion bursts occur less frequently than weaker ones.…”

Near-infrared variability in the star-forming region RCW 38

“…Using the 2MASS south telescope, Carpenter et al (2001Carpenter et al ( , 2002 performed widefield near infrared (NIR) variability studies of stars towards the Orion A and Chamaeleon I star-forming regions. More recently, Rice et al (2012) have monitored the dark cloud L 1003 in Cygnus OB7 at NIR wavelengths with UKIRT over a time span of 1.5 years, and Morales et al (2011Morales et al ( , 2012 collected multi-epoch, multi-color light curves of candidate members of the Orion nebular cluster region during their dedicated Warm Spitzer Exploration Science Program YSOVAR (complemented by UKIRT and CFHT data). Likewise, a comprehensive longterm (meanwhile spanning 8 yrs) monitoring campaign of NIR variability in a large sample of brown dwarfs and T Tauri stars has been carried out by Scholz and collaborators (Scholz et al 2009;Scholz 2012).…”