Search results for "Brown dwarf"
showing 10 items of 26 documents
X-ray emission from young brown dwarfs in the Orion Nebula Cluster
2005
We use the sensitive X-ray data from the Chandra Orion Ultradeep Project (COUP) to study the X-ray properties of 34 spectroscopically-identified brown dwarfs with near-infrared spectral types between M6 and M9 in the core of the Orion Nebula Cluster. Nine of the 34 objects are clearly detected as X-ray sources. The apparently low detection rate is in many cases related to the substantial extinction of these brown dwarfs; considering only the BDs with $A_V \leq 5$ mag, nearly half of the objects (7 out of 16) are detected in X-rays. Our 10-day long X-ray lightcurves of these objects exhibit strong variability, including numerous flares. While one of the objects was only detected during a sho…
Astrometric detection of a low-mass companion orbiting the star AB Doradus
1997
International audience; We report submilliarcsecond-precise astrometric measurements for the late-type star AB Doradus via a combination of VLBI (very long baseline interferometry) and HIPPARCOS data. Our astrometric analysis results in the precise determination of the kinematics of this star, which reveals an orbital motion readily explained as caused by gravitational interaction with a low-mass companion. From the portion of the reÑex orbit covered by our data and using a revised mass of the primary star (0.76 M _) derived from our new value of the parallax (66.3 mas \ n \ 67.2 mas), we Ðnd the dynamical mass of the newly discovered companion to be between 0.08 and 0.11 If accurate photom…
X-shooter spectroscopy of young stars with disks. The TW Hydrae association as a probe of the final stages of disk accretion
2019
We investigate ongoing accretion activity in young stars in the TW Hydrae association (TWA, ~8-10 Myr), an ideal target to probe the final stages of disk accretion down to brown dwarf masses. Our sample comprises eleven TWA members with infrared excess, amounting to 85% of the total TWA population with disks, with spectral types between M0 and M9, and masses between 0.58 and 0.02 Msol. We employed homogeneous spectroscopic data from 300 to 2500 nm, obtained with X-shooter, to derive individual extinction, stellar parameters, and accretion parameters simultaneously. We then examined Balmer lines and forbidden emission lines to probe the physics of the star-disk interaction environment. We de…
XMM-Newton detection of the 2.1 ms coherent pulsations from IGR J17379-3747
2018
We report on the detection of X-ray pulsations at 2.1 ms from the known X-ray burster IGR J17379-3747 using XMM-Newton. The coherent signal shows a clear Doppler modulation from which we estimate an orbital period of ~1.9 hours and a projected semi-major axis of ~8 lt-ms. Taking into account the lack of eclipses (inclination angle of < 75 deg) and assuming a neutron star mass of 1.4 Msun, we estimated a minimum companion star of ~0.06 Msun. Considerations on the probability distribution of the binary inclination angle make less likely the hypothesis of a main-sequence companion star. On the other hand, the close correspondence with the orbital parameters of the accreting millisecond puls…
A brown dwarf orbiting an M-dwarf:MOA 2009-BLG-411L
2012
Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted.Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit.Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties b…
MILES extended: Stellar population synthesis models from the optical to the infrared
2016
We present the first single-burst stellar population models which covers the optical and the infrared wavelength range between 3500 and 50000 Angstrom and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical with our new infrared models that are based on the IRTF (Infrared Telescope Facility) library. The latter are available only for a limited range in terms of both age and metallicity. Our combined single-burst stellar population models were calculated for ages larger than 1 Gyr, for metallicities between [Fe/H] = -0.40 and 0.26, for initial mass functions of various types and slopes, and on the basis …
The brown dwarf population in the Chamaeleon I cloud
2003
We present the results of a multiband survey for brown dwarfs in the Chamaeleon I dark cloud with the Wide Field Imager (WFI) camera at the ESO/MPG 2.2-m telescope on La Silla (Chile). The survey has revealed a substantial population of brown dwarfs in this southern star forming region. Candidates were selected from R, I and H-alpha imaging observations. We also observed in two medium-band filters, M855 and M915, for the purpose of spectral type determination. The former filter covers a wavelength range containing spectral features characteristic of M-dwarfs, while the latter lies in a relatively featureless wavelength region for these late-type objects. A correlation was found between spec…
Radio emission in ultracool dwarfs: the nearby substellar triple system VHS 1256$-$1257
2018
Aims. With the purpose of investigating the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92-125723.9 (hereafter VHS 1256-1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8 pc. Methods. We observed in phase-reference mode the system VHS 1256-1257 with the Karl G. Jansky Very Large Array at X band and L band and with the European VLBI Network at L band in several epochs during 2015 and 2016. Results. We discovered radio emission at X band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 μJy. We determined a spectral index α …
Characterizing Lenses and Lensed Stars of High-magnification Single-lens Gravitational Microlensing Events with Lenses Passing over Source Stars
2012
We present the analysis of the light curves of 9 high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For 7 events, we measure the Einstein radii and the lens-source relative proper motions. Among the…
Quiescent X-ray emission from an evolved brown dwarf ?
2004
I report on the X-ray detection of Gl569Bab. During a 25ksec Chandra observation the binary brown dwarf is for the first time spatially separated in X-rays from the flare star primary Gl569A. Companionship to Gl569A constrains the age of the brown dwarf pair to ~300-800 Myr. The observation presented here is only the second X-ray detection of an evolved brown dwarf. About half of the observing time is dominated by a large flare on Gl569Bab, the remainder is characterized by weak and non-variable emission just above the detection limit. This emission -- if not related to the afterglow of the flare -- represents the first detection of a quiescent corona on a brown dwarf, representing an impor…