CD –27°11535: Evidence for a Triple System in the β Pictoris Moving Group

Creators: Thomas, Andrew D.^{1, 2}; Nielsen, Eric L.^{1, 3}; De Rosa, Robert J.⁴; Peck, Anne E.³; Macintosh, Bruce^{1, 5}; Chilcote, Jeffrey⁶; Kalas, Paul⁷; Wang, Jason J.^{8, 9}; Blunt, Sarah^{8, 9}; Greenbaum, Alexandra^{10, 9}; Konopacky, Quinn M.¹¹; Ireland, Michael J.¹²; Tuthill, Peter¹³; Ward-Duong, Kimberly¹⁴; Hirsch, Lea A.¹⁵; Czekala, Ian^{16, 7, 17}; Marchis, Franck¹⁸; Marois, Christian^{19, 20}; Millar-Blanchaer, Max A.²¹; Roberson, William¹; Smith, Adam³; Gallamore, Hannah³; Klusmeyer, Jessica³

1. Kavli Institute for Particle Astrophysics and Cosmology
2. Seattle Sounders FC, 800 Occidental Avenue S, Seattle, WA 98134, USA
3. New Mexico State University
4. European Southern Observatory
5. University of California, Santa Cruz
6. University of Notre Dame
7. University of California, Berkeley
8. Northwestern University
9. California Institute of Technology
10. Infrared Processing and Analysis Center
11. University of California, San Diego
12. Australian National University
13. University of Sydney
14. Smith College
15. University of Toronto
16. Pennsylvania State University
17. NASA Hubble Fellowship Program Sagan Fellow.
18. Search for Extraterrestrial Intelligence
19. National Research Council Canada
20. University of Victoria
21. University of California, Santa Barbara

Abstract

We present new spatially resolved astrometry and photometry of the CD –27°11535 system, a member of the β Pictoris moving group consisting of two resolved K-type stars on a ∼20 yr orbit. We fit an orbit to relative astrometry measured from NIRC2, GPI, and archival NaCo images, in addition to literature measurements. However, the total mass inferred from this orbit is significantly discrepant from that inferred from stellar evolutionary models using the luminosity of the two stars. We explore two hypotheses that could explain this discrepant mass sum: a discrepant parallax measurement from Gaia due to variability, and the presence of an additional unresolved companion to one of the two components. We find that the ∼20 yr orbit could not bias the parallax measurement, but that variability of the components could produce a large-amplitude astrometric motion, an effect that cannot be quantified exactly without the individual Gaia measurements. The discrepancy could also be explained by an additional star in the system. We jointly fit the astrometric and photometric measurements of the system to test different binary and triple architectures for the system. Depending on the set of evolutionary models used, we find an improved goodness of fit for a triple system architecture that includes a low-mass (M = 0.177 ± 0.055 M ⊙) companion to the primary star. Further studies of this system will be required in order to resolve this discrepancy, either by refining the parallax measurement with a more complex treatment of variability-induced astrometric motion or by detecting a third companion.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

This work was supported in part by NASA grants NNX14AJ80G, 80NSSC21K0958 (E.L.N. and A.E.P.), and 21-ADAP21-0130 (E.L.N. and A.S.) and authored by employees of Caltech/IPAC under contract No. 80GSFC21R0032 with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work is partially based on observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This research has also made use of the VizieR catalog access tool, CDS, Strasbourg, France (DOI :10.26093/cds/vizier) and the SIMBAD database, operated at the same location. The original description of the VizieR service was published in 2000, A&AS 143, 23. Further, this work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia. Finally, this publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Funding

This work was supported in part by NASA grants NNX14AJ80G, 80NSSC21K0958 (E.L.N. and A.E.P.), and 21-ADAP21-0130 (E.L.N. and A.S.) and authored by employees of Caltech/IPAC under contract No. 80GSFC21R0032 with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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