arXiv subjects

H. Bouy

Publications and source records attributed to H. Bouy.

130 records · Page 8Linked to original sources

arXiv2004

First determination of the dynamical mass of a binary L dwarf

We present here the results of astrometric, photometric and spectroscopic observations leading to the determination of the orbit and dynamical masses of the binary L dwarf 2MASSW J0746425+2000321. High angular resolution observations spread over almost 4 years and obtained with the Hubble Space Telescope (HST), the ESO Very Large Telescope (VLT), and a the W. M. Keck Observatory (Keck) allow us to cover 36% of the period, corresponding to 60% of the orbit, and, for the first time, to derive a precise estimate of the total and individual masses of such a late-type object. We find an orbital period of 3850.9$^{+904}_{-767}$ days. The corresponding total mass is 0.146$^{+0.016}_{-0.006}$ M$_{\sun}$, with uncertainties depending on the distance. Spatially resolved low resolution optical (550--1025 nm) spectra have been obtained with HST/STIS, allowing us to measure the spectral types of the two components (L0$\pm$0.5 for the primary and L1.5$\pm$0.5 for the secondary). We also present precise photometry of the individual components measured on the high angular resolution images obtained with HST/ACS and WFPC2 (visible), VLT/NACO (J, H and Ks bands) and Keck I (Ks) band). These spectral and photometric measurements enable us to estimate their effective temperatures and mass ratio, and to place the object accurately in a H--R diagram. The binary system is most likely formed by a primary with a mass of 0.085$\pm$0.010 M$_{\sun}$ and a secondary with a mass of 0.066$\pm$0.006 M$_{\sun}$, thus clearly substellar, for an age of approximately 300$\pm$150 Myr. H$α$ variability indicates chromospheric and/or magnetic activity.

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arXiv2004

X-ray Detections of Two Young Bona-Fide Brown Dwarfs

I report here the detection of two bona-fide brown dwarfs by XMM-Newton: [GY92] 141 in the rho-Ophiuchus star forming region and DENIS-P J155601-233809 in the Upper Scorpius OB association. The two objects have been detected with luminosities of Lx=8.35\pm2.86*10^28 erg/s and Lx=6.54\pm1.35*10^28 erg/s respectively, corresponding to luminosity ratios of log(Lx/Lbol)= -2.07 and log(Lx/Lbol)= -2.69. The two sources were close to the limit of detection of the instruments at only 2~3-sigma above the background level, and no significant flare or variation could be detected during the 48.3ks and 33.9ks observations. [GY92] 141 had already been observed 10 months earlier with Chandra (see 2001 ApJ, 563, 361) with a luminosity ~14 times fainter than the one I report here, meaning that the X-ray emission of this object is strongly variable.

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arXiv2004

A young binary Brown Dwarf in the R-CrA star formation region

We present imaging and spectroscopic observations with HST (WFPC2, ACS/HRC and STIS), VLT (FORS2) and Keck (HIRES) of the dM8 ultra-cool dwarf DENIS-P J185950.9-370632, located in the R-CrA region. The presence of lithium absorption at 670.8 nm and the strong Halpha emission indicate a young age and a sub-stellar mass. Our diffraction-limited images resolve a companion at the separation limit of HST/ACS (~0.06"). The 2.1 mJy flux in the LW2 filter (5.0-8.5 microns) of the Infrared Space Observatory (see 1999A&A...350..883) likely corresponds to an infrared excess, suggesting the presence of circumstellar material. Proper motion and photometric measurements, as well as the Halpha activity, confirm membership in the R-CrA star forming region. If confirmed by further observations, DENIS-P J185950.9-370632 would be the first accreting sub-stellar multiple system observed to date.

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arXiv2003

First NACO observations of the Brown Dwarf LHS 2397aB

Observations of the standard late type M8 star LHS 2397aA were obtained at the ESO-VLT 8m telescope ``Yepun'' using the NAOS/CONICA Adaptive Optics facility. The observations were taken during the NACO commissioning, and the infrared standard star LHS 2397aA was observed in the H, and Ks broad band filters. In both bands the brown dwarf companion LHS2397aB was detected. Using a program recently developed (Bouy et al., 2003) for the detection of stellar binaries we calculated the principal astrometric parameters (angular binary separation and position angle P.A.) and the photometry of LHS 2397aA and LHS 2397aB. Our study largely confirms previous results obtained with the AO-Hokupa'a facility at Gemini-North (Freed et al., 2003); however a few discrepancies are observed.

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