Confirming the least massive members of the Pleiades star cluster

Abstract

We present optical photometry (i- and Z-band) and low-resolution spectroscopy (640-1015 nm) of very faint candidate members (J = 20.2-21.2 mag) of the Pleiades star cluster (120 Myr). The main goal is to address their cluster membership via photometric, astrometric, and spectroscopic studies, and to determine the properties of the least massive population of the cluster through the comparison of the data with younger and older spectral counterparts and state-of-the art model atmospheres. We confirm three bona-fide Pleiades members that have extremely red optical and infrared colors, effective temperatures of ~1150 K and ~1350 K, and masses in the interval 11-20 Mjup, and one additional likely member that shares the same motion as the cluster but does not appear to be as red as the other members with similar brightness. This latter object requires further near-infrared spectroscopy to fully address its membership in the Pleiades. The optical spectra of two bona-fide members were classified as L6-L7 and show features of KI, a tentative detection of CsI, hydrides and water vapor with an intensity similar to high-gravity dwarfs of related classification despite their young age. The properties of the Pleiades L6-L7 members clearly indicate that very red colors of L dwarfs are not a direct evidence of ages younger than ~100 Myr. We also report on the determination of the bolometric corrections for the coolest Pleiades members. These data can be used to interpret the observations of the atmospheres of exoplanets orbiting stars.

Accepted for publication in MNRAS (17 pages)

References in corpus (36)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• The Star-formation History and Accretion-Disk Fraction Among the K-Type Members of the Scorpius-Centaurus OB Association
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Population Properties of Brown Dwarf Analogs to Exoplanets
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9
• A search for binary systems among the nearest L dwarfs
• A VLBI Resolution of the Pleiades Distance Controversy
• Characterizing 51 Eri b from 1-5 $\mu$m: a partly-cloudy exoplanet
• A Census of Young Stars and Brown Dwarfs in IC 348 and NGC 1333
• The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties
• Discovery of a T Dwarf Binary with the Largest Known J-Band Flux Reversal
• A Survey for New Members of the Taurus Star-Forming Region with the Sloan Digital Sky Survey
• Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses
• Cloud Atlas: Discovery of Patchy Clouds and High-amplitude Rotational Modulations In a Young, Extremely Red L-type Brown Dwarf
• HST Rotational Spectral Mapping of Two L-Type Brown Dwarfs: Variability In and Out of Water Bands Indicates High-Altitude Haze Layers
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
• Proper motion L and T dwarf candidate members of the Pleiades
• On the common origin of the AB Dor moving group and the Pleiades cluster
• Pleiades low-mass brown dwarfs: the cluster L dwarf sequence
• The substellar companion in the eclipsing white dwarf binary SDSS J141126.20+200911.1
• The optical+infrared L dwarf spectral sequence of young planetary-mass objects in the Upper Scorpius association
• A 2MASS/AllWISE Search for Extremely Red L Dwarfs -- The Discovery of Several Likely L Type Members of $\beta$ Pic, AB Dor, Tuc-Hor, Argus, and the Hyades
• Planets Around Low-Mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-Mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425
• A Survey For Planetary-mass Brown Dwarfs in the Taurus and Perseus Star-forming Regions
• Optical and Near-Infrared Spectra of sigma Orionis Isolated Planetary-mass Objects
• The low mass star and sub-stellar populations of the 25 Orionis group
• A revised moving cluster distance to the Pleiades open cluster
• Spectroscopic follow-up of L- and T-type proper-motion member candidates in the Pleiades
• A new L5 brown dwarf member of the Hyades cluster with chromospheric activity
• Thermal Infrared Imaging and Atmospheric Modeling of VHS J125601.92-125723.9 b: Evidence for Moderately Thick Clouds and Equilibrium Carbon Chemistry in a Hierarchical Triple System
• Photospheric carbon and oxygen abundances of F-G type stars in the Pleiades cluster

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