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Binarity at the L/T brown dwarf transition
B. Goldman, H. Bouy, M. R. Zapatero Osorio +3
Current atmospheric models cannot reproduce some of the characteristics of the transition between the L dwarfs with cloudy atmospheres and the T dwarfs with dust-depleted photosphe…
Chemical abundances of late-type pre-main sequence stars in the -Orionis cluster
J. I. González Hernández, J. A. Caballero, R. Rebolo +4
The young -Orionis cluster is an important location for understanding the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although b…
Eight new T4.5-T7.5 dwarfs discovered in the UKIDSS Large Area Survey Data Release 1
N. Lodieu, D. J. Pinfield, S. K. Leggett +4
We present eight new T4.5-T7.5 dwarfs identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) Data Release 1 (DR1). In addition we have recovered the T4.5…
The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
J. A. Caballero, V. J. S. Béjar, R. Rebolo +8
We investigate the mass function in the substellar domain down to a few Jupiter masses in the young sigma Orionis open cluster (3+/-2 Ma, d = 360^+70_-60 pc). We have performed a d…
Spectroscopic rotational velocities of brown dwarfs
M. R. Zapatero Osorio, E. L. Martin, H. Bouy +3
We have obtained projected rotation velocities (vsini) of a sample of 19 ultracool dwarfs with spectral types in the interval M6.5-T8 using high-resolution, near-infrared spectra o…
S Ori J053825.4-024241: A Classical T Tauri-like object at the substellar boundary
J. A. Caballero, E. L. Martín, M. R. Zapatero Osorio +4
We present a spectrophotometric analysis of S Ori J053825.4-024241, a candidate member close to the substellar boundary of the young (1-8 Myr), nearby (~360 pc) sigma Orionis star…
Optical and infrared photometry of new very low-mass stars and brown dwarfs in the Sigma Orionis cluster
V. J. S. Bejar, M. R. Zapatero Osorio, R. Rebolo
We present an RI photometric survey covering an area of 430 arcmin^2 around the multiple star Sigma Orionis. The observations were conducted with the 0.8 m IAC-80 Telescope at the…
A Methane Isolated Planetary Mass Object in Orion
M. R. Zapatero Osorio, V. J. S. Bejar, E. L. Martin +5
We report on the discovery of a free-floating methane dwarf toward the direction of the young star cluster sigma Orionis. Based on the object's far-red optical and near-infrared ph…
Lithium and Halpha in stars and brown dwarfs of sigma Orionis
M. R. Zapatero Osorio, V. J. S. Bejar, Ya. Pavlenko +4
We present intermediate- and low-resolution optical spectra around Halpha and LiI 6708 A for a sample of 25 low mass stars and 2 brown dwarfs with confirmed membership in the pre-m…
Optical spectroscopy of isolated planetary mass objects in the sigma Orionis cluster
D. Barrado-y-Navascués, M. R. Zapatero-Osorio, V. J. S. Béjar +5
We have obtained low resolution optical spectra of 15 isolated planetary mass objects (IPMOs) in the sigma Orionis cluster, and derived spectral types by comparison with nearby M a…
Keck NIRC Observations of Planetary-mass Candidate Members in the sigma Orionis Open Cluster
E. L. Martin, M. R. Zapatero Osorio, D. Barrado y Navascues +2
We present K-band photometry and low-resolution near-infrared spectroscopy from 1.44 to 2.45 micron of isolated planetary-mass candidate members in the sigma Orionis cluster found…
The orbit of the brown dwarf binary Gl 569B
B. F. Lane, M. R. Zapatero Osorio, M. C. Britton +2
We present photometric, astrometric and spectroscopic observations of the nearby (9.8 pc) low-mass binary Gl 569Bab (in turn being a companion to the early-M star Gl 569A), made wi…
Photometric Variability in the Ultracool Dwarf BRI 0021-0214: Possible Evidence for Dust Clouds
E. L. Martin, M. R. Zapatero Osorio, H. J. Lehto
We report CCD photometric monitoring of the nonemission ultracool dwarf BRI 0021-0214 (M9.5) obtained during 10 nights in 1995 November and 4 nights in 1996 August, with CCD camera…
The Substellar Mass Function in sigma Orionis
V. J. S. Bejar, E. L. Martin, M. R. Zapatero Osorio +7
We combine results from imaging searches for substellar objects in the sigma Orionis cluster and follow-up photometric and spectroscopic observations to derive a census of the brow…
CCD-based observations of PG 0856+121 and a theoretical analysis of its oscillation modes
A. Ulla, M. R. Zapatero Osorio, F. Perez Hernandez +1
BVRI CCD-based and near-IR (J) imaging, together with unfiltered photometry of the hot subdwarf B star PG 0856+121 are reported. Two close, faint, red, point-like sources are resol…
An Early-Time Infrared and Optical Study of the Type Ia Supernova 1998bu in M96
M. Hernandez, W. P. S. Meikle, A. Aparicio +22
We present first-season infrared (IR) and optical photometry and spectroscopy of the Type Ia Supernova 1998bu in M96. We also report optical polarimetry of this event. SN1998bu is…
Optical and Infrared photometry of the type IIn SN 1998S:Days 11-146
A. Fassia, W. P. S. Meikle, W. D. Vacca +1
We present contemporaneous optical and infrared photometric observations of the type IIn SN 1998S covering the period between 11 and 146 days after discovery. The infrared data con…
Membership and Multiplicity among Very Low-Mass Stars and Brown Dwarfs in the Pleiades Cluster
E. L. Martin, W. Brandner, J. Bouvier +4
We present near-infrared photometry and optical spectroscopy of very low-mass stars and brown dwarf candidates in the Pleiades open cluster. The membership status of these objects…
An L-type substellar object in Orion: reaching the mass boundary between brown dwarfs and giant planets
M. R. Zapatero Osorio, V. J. S. Bejar, R. Rebolo +2
We present J-band photometry and low-resolution optical spectroscopy (600-1000 nm) for one of the faintest substellar member candidates in the young sigma Ori cluster, SOri 47 (I=2…
A Search for Very Low-mass Stars and Brown Dwarfs in the Young sigma Orionis Cluster
V. J. S. Bejar, M. R. Zapatero Osorio, R. Rebolo
We present a CCD-based photometric survey covering 870 sq. arcmin in a young stellar cluster around the young multiple star sigma Orionis. Our survey limiting R, I, and Z magnitude…
Brown Dwarfs in the Pleiades Cluster. III. A deep IZ survey
M. R. Zapatero Osorio, R. Rebolo, E. L. Martin +5
We present the results of a deep CCD-based IZ photometric survey of a ~1 sq. deg area in the central region of the Pleiades Galactic open cluster. The magnitude coverage of our sur…
The First L-type Brown Dwarf in the Pleiades
E. L. Martin, G. Basri, M. R. Zapatero Osorio +2
We have obtained low-resolution optical spectra of three faint brown dwarf candidates in the Pleiades open cluster. The objects observed are Roque 12 (I=18.5), Roque 5 (I=19.7) and…
A brown dwarf candidate in the Praesepe Open Cluster
A. Magazzu, R. Rebolo, M. R. Zapatero Osorio +2
We present optical and infrared observations of RPr1, a faint (I = 21.01) and very red object (I - K = 4.57) discovered in a deep CCD survey, covering an area of 800 square arcmin…
New Brown Dwarfs in the Pleiades Cluster
M. R. Zapatero Osorio, R. Rebolo, E. L. Martin +5
We present intermediate and low resolution optical spectroscopy (650-915 nm) of seven faint, very red objects (20 > I >= 17.8, I-Z >= 0.5) discovered in a CCD-based IZ survey cover…