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  The GRAVITY young stellar object survey - V. The orbit of the T Tauri binary star WW Cha

Eupen, F., Labadie, L., Grellmann, R., Perraut, K., Brandner, W., Duchêne, G., et al. (2021). The GRAVITY young stellar object survey - V. The orbit of the T Tauri binary star WW Cha. Astronomy and Astrophysics, 648: A37. doi:10.1051/0004-6361/202039599.

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Eupen, F., Author
Labadie, L., Author
Grellmann, R., Author
Perraut, K., Author
Brandner, W., Author
Duchêne, G., Author
Köhler, R., Author
Sanchez-Bermudez, J., Author
Lopez, R. Garcia, Author
Garatti, A. Caratti o, Author
Benisty, M., Author
Dougados, C., Author
Garcia, P., Author
Klarmann, L., Author
Amorim, A., Author
Bauböck, M.1, Author           
Berger, J. P., Author
Caselli, P.2, Author           
Clénet, Y., Author
du Foresto, V. Coudé, Author
de Zeeuw, P. T.1, Author           Drescher, A.1, Author           Duvert, G., AuthorEckart, A., AuthorEisenhauer, F.1, Author           Filho, M., AuthorGanci, V., AuthorGao, F.1, Author           Gendron, E., AuthorGenzel, R.1, Author           Gillessen, S.1, Author           Heissel, G., AuthorHenning, Th., AuthorHippler, S., AuthorHorrobin, M., AuthorHubert, Z., AuthorJiménez-Rosales, A.1, Author           Jocou, L., AuthorKervella, P., AuthorLacour, S., AuthorLapeyrère, V., AuthorLe Bouquin, J. B., AuthorLéna, P., AuthorOtt, T.1, Author           Paumard, T., AuthorPerrin, G., AuthorPfuhl, O., AuthorRodríguez-Coira, G., AuthorRousset, G., AuthorScheithauer, S., AuthorShangguan, J.1, Author           Shimizu, T.1, Author           Stadler, J.1, Author           Straub, O.1, Author           Straubmeier, C., AuthorSturm, E.1, Author           Van Dishoeck, E.1, Author           Vincent, F., AuthorFellenberg, Sebastiano D. von1, Author           Widmann, F.1, Author           Woillez, J., AuthorWojtczak, A., Author more..
1Infrared and Submillimeter Astronomy, MPI for Extraterrestrial Physics, Max Planck Society, ou_159889              
2Center for Astrochemical Studies at MPE, MPI for Extraterrestrial Physics, Max Planck Society, ou_1950287              


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 Abstract: Context. Close young binary stars are unique laboratories for the direct measurement of pre-main-sequence (PMS) stellar masses and their comparison to evolutionary theoretical models. At the same time, a precise knowledge of their orbital parameters when still in the PMS phase offers an excellent opportunity for understanding the influence of dynamical effects on the morphology and lifetime of the circumstellar as well as circumbinary material.
Aims. The young T Tauri star WW Cha was recently proposed to be a close binary object with strong infrared and submillimeter excess associated with circum-system emission, which makes it dynamically a very interesting source in the above context. The goal of this work is to determine the astrometric orbit and the stellar properties of WW Cha using multi-epoch interferometric observations.
Methods. We derive the relative astrometric positions and flux ratios of the stellar companion in WW Cha from the interferometric model fitting of observations made with the VLTI instruments AMBER, PIONIER, and GRAVITY in the near-infrared from 2011 to 2020. For two epochs, the resulting uv-coverage in spatial frequencies permits us to perform the first image reconstruction of the system in the K band. The positions of nine epochs are used to determine the orbital elements and the total mass of the system. Combining the orbital solution with distance measurements from Gaia DR2 and the analysis of evolutionary tracks, we constrain the mass ratio.
Results. We find the secondary star orbiting the primary with a period of T = 206.55 days, a semimajor axis of a = 1.01 au, and a relatively high eccentricity of e = 0.45. The dynamical mass of Mtot = 3.20 M can be explained by a mass ratio between ∼0.5 and 1, indicating an intermediate-mass T Tauri classification for both components. The orbital angular momentum vector is in close alignment with the angular momentum vector of the outer disk as measured by ALMA and SPHERE, resulting in a small mutual disk inclination. The analysis of the relative photometry suggests the presence of infrared excess surviving in the system and likely originating from truncated circumstellar disks. The flux ratio between the two components appears variable, in particular in the K band, and may hint at periods of triggered higher and lower accretion or changes in the disks’ structures.
Conclusions. The knowledge of the orbital parameters, combined with a relatively short period, makes WW Cha an ideal target for studying the interaction of a close young T Tauri binary with its surrounding material, such as time-dependent accretion phenomena. Finding WW Cha to be composed of two (probably similar) stars led us to reevaluate the mass of WW Cha, which had been previously derived under the assumption of a single star. This work illustrates the potential of long baseline interferometry to precisely characterize close young binary stars separated by a few astronomical units. Finally, when combined with radial velocity measurements, individual stellar masses can be derived and used to calibrate theoretical PMS models.


Language(s): eng - English
 Dates: 2021-04-09
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1051/0004-6361/202039599
 Degree: -



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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
Publ. Info: France : EDP Sciences S A
Pages: - Volume / Issue: 648 Sequence Number: A37 Start / End Page: - Identifier: ISSN: 1432-0746
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1