A Caltech Library Service

Evidence That the Directly Imaged Planet HD 131399 Ab Is a Background Star

Nielsen, Eric L. and Jensen-Clem, Rebecca (2017) Evidence That the Directly Imaged Planet HD 131399 Ab Is a Background Star. Astronomical Journal, 154 (6). Art. No. 218. ISSN 1538-3881.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We present evidence that the recently discovered, directly imaged planet HD 131399 Ab is a background star with nonzero proper motion. From new JHK1L' photometry and spectroscopy obtained with the Gemini Planet Imager, VLT/SPHERE, and Keck/NIRC2, and a reanalysis of the discovery data obtained with VLT/SPHERE, we derive colors, spectra, and astrometry for HD 131399 Ab. The broader wavelength coverage and higher data quality allow us to reinvestigate its status. Its near-infrared spectral energy distribution excludes spectral types later than L0 and is consistent with a K or M dwarf, which are the most likely candidates for a background object in this direction at the apparent magnitude observed. If it were a physically associated object, the projected velocity of HD 131399 Ab would exceed escape velocity given the mass and distance to HD 131399 A. We show that HD 131399 Ab is also not following the expected track for a stationary background star at infinite distance. Solving for the proper motion and parallax required to explain the relative motion of HD 131399 Ab, we find a proper motion of 12.3 mas yr^(−1). When compared to predicted background objects drawn from a galactic model, we find this proper motion to be high but consistent with the top 4% fastest-moving background stars. From our analysis, we conclude that HD 131399 Ab is a background K or M dwarf.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Nielsen, Eric L.0000-0001-6975-9056
Jensen-Clem, Rebecca0000-0003-0054-2953
Additional Information:© 2017 The American Astronomical Society. Received 2017 May 18; revised 2017 August 30; accepted 2017 September 1; published 2017 November 8. This work is based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). 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 based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO program 098.C-0864(A) and based on data obtained from the ESO Science Archive Facility. SPHERE is an instrument designed and built by a consortium consisting of IPAG (Grenoble, France), MPIA (Heidelberg, Germany), LAM (Marseille, France), LESIA (Paris, France), Laboratoire Lagrange (Nice, France), INAFOsservatorio di Padova (Italy), Observatoire de Genve (Switzerland), ETH Zurich (Switzerland), NOVA (Netherlands), ONERA (France), and ASTRON (Netherlands) in collaboration with ESO. SPHERE was funded by ESO, with additional contributions from CNRS (France), MPIA (Germany), INAF (Italy), FINES (Switzerland), and NOVA (Netherlands). SPHERE also received funding from the European Commission Sixth and Seventh Framework Programmes as part of the Optical Infrared Coordination Network for Astronomy (OPTICON) under grant number RII3-Ct-2004-001566 for FP6 (20042008), grant number 226604 for FP7 (20092012), and grant number 312430 for FP7 (20132016). This research has made use of the SIMBAD and VizieR databases, operated at CDS, Strasbourg, France, the Database of Ultracool Parallaxes maintained by Trent Dupuy, and the Washington Double Star Catalog maintained by the U.S. Naval Observatory at This research has benefited from the SpeX Prism Library (or SpeX Prism Library Analysis Toolkit), maintained by Adam Burgasser at, the IRTF Spectral Library, maintained by Michael Cushing, and the Montreal Brown Dwarf and Exoplanet Spectral Library, maintained by Jonathan Gagné. J.R., R.D., and D.L. acknowledge support from the Fonds de Recherche du Québec. J.R.M.'s work was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Support for M.M.B.'s work was provided by NASA through Hubble Fellowship grant #51378.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Researchers were supported by NSF grants AST-1411868 (K.B.F., B.M., and J.P.), AST-141378 (G.D.), and AST-1518332 (R.D.R., J.J.W., T.M.E., J.R.G., P.G.K.). Researchers were supported by NASA grants NNX14AJ80G (E.L.N., S.C.B., B.M., F.M., and M.P.), NNX15AC89G and NNX15AD95G (B.M., J.E.W., T.M.E., R.J.D.R., G.D., J.R.G., P.G.K.) and NNX16AD44G (K.M.M.). K.W.D. is supported by an NRAO Student Observing Support Award SOSPA3-007. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work benefited from the NASA Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by the NASA Science Mission Directorate. Facilities: Gemini:South (GPI) - , VLT:Melipal (SPHERE) - , Keck:II (NIRC2) - . Software: Astropy (Astropy Collaboration et al. 2013), emcee (Foreman-Mackey et al. 2013), GPI DRP (Perrin et al. 2016), IDL Astronomy Library (Landsman 1993), pyKLIP (Wang et al. 2015), SPHERE DRH (Pavlov et al. 2008), SPHERE IFS (Vigan et al. 2015).
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
European Southern Observatory (ESO)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Max Planck Institute for Astronomy (MPIA)UNSPECIFIED
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Nederlandse Onderzoekschool Voor Astronomie (NOVA)UNSPECIFIED
European CommissionRII3-Ct-2004-001566
European Research Council (ERC)226604
European Research Council (ERC)312430
Fonds de Recherche du QuébecUNSPECIFIED
NASA Hubble Fellowship51378.01-A
National Radio Astronomy ObservatorySOSPA3-007
Department of Energy (DOE)DE-AC52-07NA27344
Subject Keywords:astrometry – instrumentation: adaptive optics – planets and satellites: detection – stars: individual (HD 131399) – techniques: image processing – techniques: spectroscopic
Issue or Number:6
Record Number:CaltechAUTHORS:20171107-141250262
Persistent URL:
Official Citation:Eric L. Nielsen et al 2017 AJ 154 218
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83039
Deposited By: Tony Diaz
Deposited On:07 Nov 2017 23:09
Last Modified:03 Oct 2019 19:01

Repository Staff Only: item control page