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UV variability and accretion dynamics in the young open cluster NGC 2264

Venuti, L. and Bouvier, J. and Irwin, J. and Stauffer, J. R. and Hillenbrand, L. A. and Rebull, L. M. and Cody, A. M. and Alencar, S. H. P. and Micela, G. and Flaccomio, E. and Peres, G. (2015) UV variability and accretion dynamics in the young open cluster NGC 2264. Astronomy and Astrophysics, 581 . Art. No. A66. ISSN 0004-6361. https://resolver.caltech.edu/CaltechAUTHORS:20151103-102001817

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Abstract

Context. Photometric variability is a distinctive feature of young stellar objects; exploring variability signatures at different wavelengths provides insight into the physical processes at work in these sources. Aims. We explore the variability signatures at ultraviolet (UV) and optical wavelengths for several hundred accreting and non-accreting members of the star-forming region NGC 2264 (~3 Myr). Methods. We performed simultaneous monitoring of u- and r-band variability for the cluster population with CFHT/MegaCam. The survey extended over two full weeks, with several flux measurements per observing night. A sample of about 750 young stars is probed in our study, homogeneously calibrated and reduced, with internally consistently derived stellar parameters. Objects span the mass range 0.1–2 M⊙; about 40% of them show evidence for active accretion based on various diagnostics (H_α, UV, and IR excesses). Results. Statistically distinct variability properties are observed for accreting and non-accreting cluster members. The accretors exhibit a significantly higher level of variability than the non-accretors, in the optical and especially in the UV. The amount of u-band variability is found to correlate statistically with the median amount of UV excess in disk-bearing objects, which suggests that mass accretion and star-disk interaction are the main sources of variability in the u band. Spot models are applied to account for the amplitudes of variability of accreting and non-accreting members, which yields different results for each group. Cool magnetic spots, several hundred degrees colder than the stellar photosphere and covering from 5 to 30% of the stellar surface, appear to be the leading factor of variability for the non-accreting stars. In contrast, accretion spots with a temperature a few thousand degrees higher than the photospheric temperature and that extend over a few percent of the stellar surface best reproduce the variability of accreting objects. The color behavior is also found to be different between accreting and non-accreting stars. While objects commonly become redder when fainter, typical amplitudes of variability for accreting members rapidly increase from the r to the u band, which indicates a much stronger contrast at short wavelengths; a lower color dependence in the photometric amplitudes is instead measured for diskless stars. Finally, we compare the u-band variability monitored here on two-week timescales with that measured on both shorter (hours) and longer (years) timescales. We find that variability on timescales of hours is typically ~10% of the peak-to-peak variability on day timescales, while longer term variability on a timescale of years is consistent with amplitudes measured over weeks. Conclusions. We conclude that for both accreting and non-accreting stars, the mid-term rotational modulation by hot and cold spots is the leading timescale for a variability of up to several years. In turn, this suggests that the accretion process is essentially stable over years, although it exhibits low-level shorter term variations in single accretion events.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1051/0004-6361/201526164DOIArticle
http://www.aanda.org/articles/aa/abs/2015/09/aa26164-15/aa26164-15.htmlPublisherArticle
http://arxiv.org/abs/1506.06858arXivDiscussion Paper
ORCID:
AuthorORCID
Bouvier, J.0000-0002-7450-6712
Stauffer, J. R.0000-0003-3595-7382
Rebull, L. M.0000-0001-6381-515X
Cody, A. M.0000-0002-3656-6706
Micela, G.0000-0002-9900-4751
Flaccomio, E.0000-0002-3638-5788
Additional Information:© 2015 ESO. Article published by EDP Sciences. Received 23 March 2015; Accepted 16 June 2015; Published online 03 September 2015. We thank the anonymous referee for useful comments. This publication makes use of data products from the Sloan Digital Sky Survey. This project was in part supported by the grant ANR 2011 Blanc SIMI5-6 020 01. L.V. acknowledges partial funding for this work from program LLP Erasmus 2011/2012 at Università degli Studi di Palermo. S.H.P.A. acknowledges financial support from CNPq, CAPES and Fapemig.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
Agence Nationale pour la Recherche (ANR)SIMI5-6 020 01
Università degli Studi di PalermoUNSPECIFIED
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)UNSPECIFIED
Fundação de Amparo à Pesquisa do estado de Minas Gerais (FAPEMIG)UNSPECIFIED
Subject Keywords:accretion, accretion disks – stars: low-mass – stars: pre-main sequence – stars: variables: T Tauri, Herbig Ae/Be –open clusters and associations: individual: NGC 2264 – ultraviolet: stars
Record Number:CaltechAUTHORS:20151103-102001817
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20151103-102001817
Official Citation:UV variability and accretion dynamics in the young open cluster NGC 2264 L. Venuti, J. Bouvier, J. Irwin, J. R. Stauffer, L. A. Hillenbrand, L. M. Rebull, A. M. Cody, S. H. P. Alencar, G. Micela, E. FlaccomioL. Venuti, J. Bouvier, J. Irwin, J. R. Stauffer, L. A. Hillenbrand, L. M. Rebull, A. M. Cody, S. H. P. Alencar, G. Micela, E. Flaccomio and G. Peres A&A, 581 (2015) A66 DOI: http://dx.doi.org/10.1051/0004-6361/201526164
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:61793
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Nov 2015 19:06
Last Modified:09 Mar 2020 13:19

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