Isochronal age-mass discrepancy of young stars: SCExAO/CHARIS integral field spectroscopy of the HIP 79124 triple system

¹ Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
e-mail: ruben.torres@astro.su.se
² NASA-Ames Research Center, Moffett Field, California 94035, USA
³ National Astronomical Observatory of Japan, Subaru Telescope, National Institutes of Natural Sciences, Hilo, HI 96720, USA
⁴ Eureka Scientific, 2452 Delmer Street Suite 100. Oakland, CA 94602-3017, USA
⁵ INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁶ Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa Mitaka, Tokyo, Japan
⁷ National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
⁸ Institute for Astronomy, University of Hawaii, Hilo, HI, USA
⁹ Department of Physics, University of California-Santa Barbara, Santa Barbara, CA, USA
¹⁰ Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
¹¹ College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
¹² NASA-Goddard Space Flight Center, Greenbelt, MD, USA
¹³ Department of Mechanical Engineering, Princeton University, Princeton, NJ, USA
¹⁴ Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall Notre Dame, IN 46556, USA
¹⁵ Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁶ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
¹⁷ Center for Extrasolar Planetary Systems, Space Science Institute, 1120 Paxton Ave., Cincinnati, OH 45208, USA
¹⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁹ Institute for the Advancement of Higher Education, Hokkaido University, Kita 17, Nishi 8, Kita-ku, Sapporo 060-0817, Japan
²⁰ ISAS/JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
²¹ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²² Department of Astronomy, The Graduate University for Advanced Studies, National Astronomical Observatory of Japan, Japan
²³ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁴ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 20 November 2018
Accepted: 18 December 2018

Abstract

We present SCExAO/CHARIS 1.1–2.4 μm integral field direct spectroscopy of the young HIP 79124 triple system. HIP 79124 is a member of the Scorpius-Centaurus association, consisting of an A0V primary with two low-mass companions at a projected separation of < 1″. Thanks to the high quality wavefront corrections provided by SCExAO, both companions are decisively detected without the employment of any PSF-subtraction algorithm to eliminate quasi-static noise. The spectrum of the outer C object is very well matched by Upper Scorpius M4 ± 0.5 standard spectra, with a T_eff = 2945 ± 100 K and a mass of ∼350 M_Jup. HIP 79124 B is detected at a separation of only 180 mas in a highly-correlated noise regime, and it falls in the spectral range M6 ± 0.5 with T_eff = 2840 ± 190 K and ∼100 M_Jup. Previous studies of stellar populations in Sco-Cen have highlighted a discrepancy in isochronal ages between the lower-mass and higher-mass populations. This could be explained either by an age spread in the region, or by conventional isochronal models failing to reproduce the evolution of low-mass stars. The HIP 79124 system should be coeval, and therefore it provides an ideal laboratory to test these scenarios. We place the three components in a color–magnitude diagram and find that the models predict a younger age for the two low-mass companions (∼3 Myr) than for the primary star (∼6 Myr). These results imply that the omission of magnetic effects in conventional isochronal models inhibit them from reproducing early low-mass stellar evolution, which is further supported by the fact that new models that include such effects provide more consistent ages in the HIP 79124 system.