CSI 2264: SIMULTANEOUS OPTICAL AND INFRARED LIGHT CURVES OF YOUNG DISK-BEARING STARS IN NGC 2264 WITH<i>CoRoT</i>and<i>SPITZER</i>—EVIDENCE FOR MULTIPLE ORIGINS OF VARIABILITY

Context. The accretion process has a central role in the formation of stars and planets. Aims. We aim at characterizing the accretion properties of several hundred members of the star-forming cluster NGC 2264 (3 Myr).Methods. We performed a deep ugri mapping as well as a simultaneous u-band+r-band monitoring of the star-forming region with CFHT/MegaCam in order to directly probe the accretion process onto the star from UV excess measurements. Photometric properties and stellar parameters are determined homogeneously for about 750 monitored young objects, spanning the mass range ∼0.1-2 M . About 40% of the sample are classical (accreting) T Tauri stars, based on various diagnostics (H α , UV and IR excesses). The remaining non-accreting members define the (photospheric + chromospheric) reference UV emission level over which flux excess is detected and measured. Results. We revise the membership status of cluster members based on UV accretion signatures, and report a new population of 50 classical T Tauri star (CTTS) candidates. A large range of UV excess is measured for the CTTS population, varying from a few times 0.1 to ∼3 mag. We convert these values to accretion luminosities and accretion rates, via a phenomenological description of the accretion shock emission. We thus obtain mass accretion rates ranging from a few 10 −10 to ∼10 −7 M /yr. Taking into account a mass-dependent detection threshold for weakly accreting objects, we find a >6σ correlation between mass accretion rate and stellar mass. A power-law fit, properly accounting for censored data (upper limits), yieldsṀ acc ∝ M 1.4±0.3 * . At any given stellar mass, we find a large spread of accretion rates, extending over about 2 orders of magnitude. The monitoring of the UV excess on a timescale of a couple of weeks indicates that its variability typically amounts to 0.5 dex, i.e., much smaller than the observed spread in accretion rates. We suggest that a non-negligible age spread across the star-forming region may effectively contribute to the observed spread in accretion rates at a given mass. In addition, different accretion mechanisms (like, e.g., short-lived accretion bursts vs. more stable funnel-flow accretion) may be associated to differentṀ acc regimes. Conclusions. A huge variety of accretion properties is observed for young stellar objects in the NGC 2264 cluster. While a definite correlation seems to hold between mass accretion rate and stellar mass over the mass range probed here, the origin of the large intrinsic spread observed in mass accretion rates at any given mass remains to be explored.

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“…(1) Object identifiers adopted within the CSI 2264 project (see Cody et al 2014). A full version of the Table is available at the CDS.…”

Section: Ngc 2264 Members In the Cfht Survey: Individual Extinction Amentioning

confidence: 99%

Mapping accretion and its variability in the young open cluster NGC 2264: a study based onu-band photometry

Venuti

Bouvier

Flaccomio

et al. 2014

A&A

132

261

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“…Besides the variability caused by the presence of cold spots, the most common sources of variability in CTTS are: obscuration by circumstellar material, accretion driven variability (like the presence of hot spots and variable mass accretion rates), and instabilities in the accretion disk (e.g. Carpenter et al 2001;Cody et al 2014;Stauffer et al 2014;Rice et al 2015;McGinnis et al 2015;Sousa et al 2016;Roquette 2017). While sometimes a single physical process may dominate the star's light curve, the existence of several concurrent variability sources is often the case.…”

Section: Does Cygob2 Corroborate the Disk-locking Scenario?mentioning

confidence: 99%

Near-infrared time-series photometry in the field of Cygnus OB2 association

Roquette

Bouvier

Alencar

et al. 2017

A&A

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Context. In the last decades, the early pre main sequence stellar rotational evolution picture has been constrained by studies targetting different regions at a variety of ages with respect to young star formation. Observational studies suggest a dependence of rotation with mass, and for some mass ranges a connection between rotation and the presence of a circumstellar disk. Not still fully explored, though, is the role of environmental conditions on the rotational regulation.Aims. We investigate the rotational properties of candidate members of the young massive association Cygnus OB2. By evaluating their rotational properties, we address questions regarding the effect of environment properties on PMS rotational evolution.Methods. We studied JHK-band variability in 5083 candidate members (24% of them are diskbearing stars). The selection of variable stars was done using Stetson variability index, and period search was performed using Lomb-Scargle periodogram for periods between 0.83-45 days. Period detections were verified by using False Alarme Probability levels, the Saunders statistics, string/rope length method, and visual verification of folded light curves.Results. We identified 1224 periodic variable stars (24% of the candidate member sample, 8% of the disk-bearing sample, and 28% of the non-disked sample). Monte Carlo simulations were performed in order to evaluate completeness and contamination of the periodic sample, out of which 894 measured periods were considered reliable. Our study was considered reasonably complete for periods between 2 and 30 days. Conclusions. The general scenario for the rotational evolution of young stars seen in other regions is confirmed by Cygnus OB2 period distributions, with disked stars rotating on average slower than non-disked stars. A mass-rotation dependence was also verified, but as in NGC 6530, very low mass stars (M ≤ 0.4M ) are rotating on average slower than higher mass stars (0.4 M < M ≤ 1.4M ). We observed an excess of slow rotators among the lower mass population. The disk and mass-rotation connection was also analysed by taking into account the incident UV radiation arising from O stars in the association. Results compatible with the disk-locking scenario were verified for stars with low UV incidence, but no statistical significant relation between rotation and disk presence was verified for stars with high UV incidence suggesting that massive stars can have an important role on regulating the rotation of nearby low mass stars.Key words. infrared: stars -stars: variables: T Tauri -stars: low-mass -stars: formation -stars: pre main sequence -stars: rotation Use \titlerunning to supply a shorter title and/or \authorrunning to supply a shorter list of authors.

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“…A detailed description of the photometric data we collected in our 2008 and 2011 observing campaigns for the NGC 2264 star-forming region is provided in Cody et al (2014). 21 The subset of the data sources that we use here includes several sets of time-series, photometric monitoring data (the first four items below) plus additional single-epoch ancillary photometry (the last two items).…”

Section: Observational Datamentioning

confidence: 99%

“…Figure 2(a) is the light curve for Mon-256, a dM-dM binary member of NGC 2264 (Gillen et al 2014) that is a borderline CTTS (broad and structured Hα profile; modest IR excess); this is the only EB in NGC 2264 with an IR excess presumably due to circumstellar Cody et al (2014) and the Appendix for the sources of the spectral type and Hα equivalent width (EW) data. Here we use the convention that negative values are in emission, which is opposite to the convention in Cody et al (2014). e FR4.5 is an estimate of the ratio of the flux from the disk to the flux from the stellar photosphere at 4.5 μm, based on all the available broad band photometry and the published spectral types.…”

Section: Aperiodic Extinctors (Examples Illustrated Inmentioning

confidence: 99%

Csi 2264: Characterizing Young Stars in NGC 2264 With Short-Duration Periodic Flux Dips in Their Light Curves

Stauffer

Cody

McGinnis

et al. 2015

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We identify nine young stellar objects (YSOs) in the NGC 2264 star-forming region with optical CoRoT light curves exhibiting short-duration, shallow periodic flux dips. All of these stars have infrared excesses that are consistent with their having inner disk walls near the Keplerian co-rotation radius. The repeating photometric dips have FWHMs generally less than 1 day, depths almost always less than 15%, and periods (3 < P < 11 days) consistent with dust near the Keplerian co-rotation period. The flux dips vary considerably in their depth from epoch to epoch, but usually persist for several weeks and, in two cases, were present in data collected in successive years. For several of these stars, we also measure the photospheric rotation period and find that the rotation and dip periods are the same, as predicted by standard "disk-locking" models. We attribute these flux dips to clumps of material in or near the inner disk wall, passing through our line of sight to the stellar photosphere. In some cases, these dips are also present in simultaneous Spitzer IRAC light curves at 3.6 and 4.5 microns. We characterize the properties of these dips, and compare the stars with light curves exhibiting this behavior to other classes of YSOs in NGC 2264. A number of physical mechanisms could locally increase the dust scale height near the inner disk wall, and we discuss several of those mechanisms; the most plausible mechanisms are either a disk warp due to interaction with the stellar magnetic field or dust entrained in funnel-flow accretion columns arising near the inner disk wall.

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CSI 2264: SIMULTANEOUS OPTICAL AND INFRARED LIGHT CURVES OF YOUNG DISK-BEARING STARS IN NGC 2264 WITHCoRoTandSPITZER—EVIDENCE FOR MULTIPLE ORIGINS OF VARIABILITY

Cited by 344 publications

References 97 publications

Mapping accretion and its variability in the young open cluster NGC 2264: a study based onu-band photometry

Mapping accretion and its variability in the young open cluster NGC 2264: a study based onu-band photometry

Near-infrared time-series photometry in the field of Cygnus OB2 association

Csi 2264: Characterizing Young Stars in NGC 2264 With Short-Duration Periodic Flux Dips in Their Light Curves

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