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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 709680.0, MPI für Astronomie / Publikationen_mpia
Spectroscopic follow-up of L- and T-type proper-motion member candidates in the Pleiades
Authors:Zapatero Osorio, M. R.; Béjar, V. J. S.; Martín, E. L.; Gálvez Ortiz, M. C.; Rebolo, R.; Bihain, G.; Henning, T.; Boudreault, S.; Goldman, B.; Mundt, R.; Caballero, J. A.; Miles-Páez, P. A.
Date of Publication (YYYY-MM-DD):2014
Title of Journal:Astronomy and Astrophysics
Start Page:id. A67 (6 pp)
Audience:Not Specified
Abstract / Description:We report on the near-infrared (JHK-bands) low-resolution spectroscopy and red optical (Z-band) photometry of seven proper-motion, very low-mass substellar member candidates of the Pleiades cluster with magnitudes in the interval J = 17.5-20.8 and K = 16.1-18.5 mag. Spectra were acquired for six objects with the LIRIS and NIRSPEC instruments mounted on the 4.2-m William Herschel and the 10-m Keck II telescopes, respectively. Z-band images of two of the faintest candidates were collected with the ACAM instrument on the WHT. The new data confirm the low temperatures of all seven Pleiades proper motion candidates. From the imaging observations, we find extremely red Z - J and Z - K colors that suggest that the faintest target, Calar Pleiades 25, has a Galactic rather than extragalactic nature. We tentatively classify the spectroscopic targets from early-L to ~T0 and suggest that the L/T transition, which accounts for the onset of methane absorption at 2.1 mum, may take place at J &ap; 20.3 and K &ap; 17.8 mag in the Pleiades (absolute values of MJ &ap; 14.7 and MK &ap; 12.2 mag). We find evidence of likely low-gravity atmospheres based on the presence of triangular-shape H-band fluxes and the high flux ratio K/H (compatible with red H - K colors) of Calar Pleiades 20, 21, and 22, which is a feature also seen in field low-gravity dwarfs. Weak K i absorption lines at around 1.25 mum are probably seen in two targets. These observations add support to the cluster membership of all seven objects in the Pleiades. The trend delineated by the spectroscopic sequence of Pleiades late-M and L dwarfs resembles that of the field. With masses estimated at 0.012-0.015 M&sun; (solar metallicity and 120 Myr), Calar Pleiades 20 (L6±1), 21 (L7±1), and 22 (L/T) may become the coolest and least massive Pleiades members that are corroborated with photometry, astrometry, and spectroscopy. Calar Pleiades 25 (<0.012 M&sun;) is a firm free-floating planetary-mass candidate in the Pleiades. Appendix A is available in electronic form at <A href=""></A>The final reduced spectra (in FITS format) are only available at the CDS via anonymous ftp to <A href=""></A> ( or via <A href=""></A>
Free Keywords:stars: low-mass; brown dwarfs; stars: late-type; open clusters and associations: individual: Pleiades
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-6361 %R 10.1051/0004-6361/201424634
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