相关论文: Discovery of a very cool object with extraordinari…

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=20.53, Bejar et al. 1999). Its very red (I-J)=3.3+/-0.1 color…

We report very intense and variable Halpha emission (pseudo-equivalent widths of ~180, 410 A) of S Ori 55, a probable free-floating, M9-type substellar member of the young sigma Orionis open star cluster. After comparison with…

(Abridged) The nature of S Ori 70, a faint mid-T type object found towards the direction of the young sigma Orionis cluster, is still under debate. We intend to disentangle whether it is a field brown dwarf or a 3-Myr old planetary-mass…

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 photometry and spectroscopy, we conclude that it is a possible…

Time series spectrophotometry of the L5 dwarf 2MASS 01443536-0716142 showed strong H\alpha emission which declined by nearly 75% in four consecutive exposures. The line was not detected in emission on a spectrum obtained eleven months…

We report differential I-band and J-band photometry of S Ori 45, a cool (M8.5), young (1-8 Myr) brown dwarf of the sigma Orionis cluster with a likely mass estimated at around 20 times the mass of Jupiter. We detect variability (amplitudes…

By collecting optical and infrared photometry and low resolution spectroscopy, we have identified a large number of low mass stars and brown dwarf candidates belonging to the young cluster (~5 Myr) associated with the binary star lambda…

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 cluster. Our optical and near-infrared photometry and…

Intermediate resolution (R=7000) spectroscopy is presented for 76 photometrically selected very low mass (0.04<M<0.3M_{sun}) candidate members of the Sigma Orionis cluster. More than two thirds appear to be genuine cluster members on the…

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-main sequence stellar sigma Orionis cluster. Our observations…

In this paper I show that the coolest $\sigma$Orionis cluster planet S Ori 70 is still a strong candidate member despite recent claims by Burgasser et al. that it could be a brown dwarf interloper. The main point of my argument is that the…

Because of the intense brightness of the OB-type multiple star system sigma Ori, the low-mass stellar and substellar populations close to the centre of the very young sigma Orionis cluster is poorly know. I present an IJHKs survey in the…

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 magnitudes are 23.2, 21.8, and 21.0, respectively. From our…

Context. Intrinsic H$\alpha$ emission can be advantageously used to detect substellar companions because it improves contrasts in direct imaging. Characterising this emission from accreting exoplanets allows for the testing of planet…

We present the results of optical spectroscopy of 139 stars obtained with the Hydra multi-object spectrograph. The objects extend over a 1.3 square degree area surrounding the main cloud of the rho Oph complex. The objects were selected…

We use high time cadence, high spectral resolution optical observations to detect excess H-alpha emission from the 2 - 3 Myr old weak lined T Tauri star PTFO8-8695. This excess emission appears to move in velocity as expected if it were…

In Hall (2002) I reported that 2MASSI J1315309-264951 is an L dwarf with strong H-alpha emission. Two spectroscopic epochs appeared to show that the H-alpha was variable, decreasing from 121 Angstroms to 25 Angstroms EW, which I interpreted…

The properties of accretion disks around stars and brown dwarfs in the SOri cluster (age 3 Myr) are studied based on NIR time series photometry supported by MIR spectral energy distributions. We monitor ~30 young low-mass sources over 8…

We report optical and infrared imaging spectroscopy observations of the young binary object Sigma Orionis IRS1 A/B. The brighter component (Sigma Ori IRS1 A) of this binary system has M1 spectral type and a mass in the range of 0.3 to 0.8…

We report the discovery of twenty-one hitherto unknown bright southern ultracool dwarfs with spectral types in the range M7 to L5.5, together with new observations of a further three late M dwarfs previously confirmed. Three more objects…