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CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I. Time resolved X-ray spectral analysis during optical dips and accretion bursts in stars with disks

Guarcello, M. G. and Flaccomio, E. and Micela, G. and Argiroffi, C. and Sciortino, S. and Venuti, L. and Stauffer, J. and Rebull, L. and Cody, A. M. (2017) CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I. Time resolved X-ray spectral analysis during optical dips and accretion bursts in stars with disks. Astronomy and Astrophysics, 602 . Art. No. A10. ISSN 0004-6361. https://resolver.caltech.edu/CaltechAUTHORS:20170928-132408868

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Abstract

Context. Pre-main sequence stars are variable sources. The main mechanisms responsible for their variability are variable extinction, unsteady accretion, and rotational modulation of both hot and dark photospheric spots and X-ray-active regions. In stars with disks, this variability is related to the morphology of the inner circumstellar region (≤0.1 AU) and that of the photosphere and corona, all impossible to be spatially resolved with present-day techniques. This has been the main motivation for the Coordinated Synoptic Investigation of NGC 2264, a set of simultaneous observations of NGC 2264 with 15 different telescopes. Aims. In this paper, we focus on the stars with disks. We analyze the X-ray spectral properties extracted during optical bursts and dips in order to unveil the nature of these phenomena. Stars without disks are studied in a companion paper. Methods. We analyze simultaneous CoRoT and Chandra/ACIS-I observations to search for coherent optical and X-ray flux variability in stars with disks. Then, stars are analyzed in two different samples. In stars with variable extinction, we look for a simultaneous increase of optical extinction and X-ray absorption during the optical dips; in stars with accretion bursts, we search for soft X-ray emission and increasing X-ray absorption during the bursts. Results. We find evidence for coherent optical and X-ray flux variability among the stars with variable extinction. In 9 of the 24 stars with optical dips, we observe a simultaneous increase of X-ray absorption and optical extinction. In seven dips, it is possible to calculate the N_H/A_V ratio in order to infer the composition of the obscuring material. In 5 of the 20 stars with optical accretion bursts, we observe increasing soft X-ray emission during the bursts that we associate to the emission of accreting gas. It is not surprising that these properties are not observed in all the stars with dips and bursts, since favorable geometric configurations are required. Conclusions. The observed variable absorption during the dips is mainly due to dust-free material in accretion streams. In stars with accretion bursts, we observe, on average, a larger soft X-ray spectral component not observed in non-accreting stars.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1051/0004-6361/201629983DOIArticle
https://www.aanda.org/articles/aa/abs/2017/06/aa29983-16/aa29983-16.htmlPublisherArticle
https://arxiv.org/abs/1701.04842arXivDiscussion Paper
ORCID:
AuthorORCID
Guarcello, M. G.0000-0002-3010-2310
Stauffer, J.0000-0003-3595-7382
Rebull, L.0000-0001-6381-515X
Cody, A. M.0000-0002-3656-6706
Additional Information:© 2017 ESO. Article published by EDP Sciences. Received 31 October 2016; Accepted 13 January 2017; Published online 24 May 2017. We thank the referee for his/hers comments and suggestions that helped us to improve our manuscript. M.G.G., E.F. and G.M. acknowledge the grant PRIN-INAF 2012 (P.I. E. Flaccomio). This research has made use of data from the Chandra X-ray Observatory and the CoRoT satellite. This research also made extensive use of Xspec software and the NASA’s Astrophysics Data System and Vizier databases, operated at CDS, Strasbourg, France.
Funders:
Funding AgencyGrant Number
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:circumstellar matter – stars: pre-main sequence – stars: rotation – stars: variables: T Tauri, Herbig Ae/Be
Record Number:CaltechAUTHORS:20170928-132408868
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170928-132408868
Official Citation:CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars - I. Time resolved X-ray spectral analysis during optical dips and accretion bursts in stars with disks M. G. Guarcello, E. Flaccomio, G. Micela, C. Argiroffi, S. Sciortino, L. Venuti, J. Stauffer, L. Rebull and A. M. Cody A&A, 602 (2017) A10 DOI: https://doi.org/10.1051/0004-6361/201629983
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81902
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:28 Sep 2017 20:56
Last Modified:03 Oct 2019 18:48

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