arXiv subjects

J. D. Smith

Publications and source records attributed to J. D. Smith.

94 records · Page 6Linked to original sources

arXiv2000

Discovery of a Bright Field Methane (T-type) Brown Dwarf by 2MASS

We report the discovery of a bright (J = 13.83$\pm$0.03) methane brown dwarf, or T dwarf, by the Two Micron All Sky Survey. This object, 2MASSI J0559191-140448, is the first brown dwarf identified by the newly commissioned CorMASS instrument mounted on the Palomar 60-inch Telescope. Near-infrared spectra from 0.9 - 2.35 $\micron$ show characteristic CH$_4$ bands at 1.1, 1.3, 1.6, and 2.2 $\micron$, which are significantly shallower than those seen in other T dwarfs discovered to date. Coupled with the detection of an FeH band at 0.9896 $\micron$ and two sets of K I doublets at J-band, we propose that 2MASS J0559-14 is a warm T dwarf, close to the transition between L and T spectral classes. The brightness of this object makes it a good candidate for detailed investigation over a broad wavelength regime and at higher resolution.

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arXiv1999

A Multi-Component Measurement of the Cosmic Ray Composition Between 10^{17} eV and 10^{18} eV

The average mass composition of cosmic rays with primary energies between $10^{17}$eV and $10^{18}$eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum, $X_{max}$, and in the change in the muon density at a fixed core location, $ρ_μ(600m)$, as a function of energy. The composition has also been evaluated in terms of the combination of $X_{max}$ and $ρ_μ(600m)$. The results show that the composition is changing from a heavy to lighter mix as the energy increases.

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arXiv1999

Mid-Infrared Spectra of Be Stars

We present the first medium-resolution ($R\sim 600$) mid-infrared (8-13.3\micron) spectra of 11 Be stars. A large number of lines are observed and identified in these spectra, including, as an example, 39 hydrogen recombination lines in the spectrum of $γ$ Cas. In the majority of our spectra, all of the observed lines are attributable to hydrogen recombination. Two of the sources, $β$ Lyr and MWC 349 also show emission from other species. Both of these objects show evidence of [Ne II] emission, and $β$ Lyr also shows evidence of He I emission. We tabulate the effective line strength and line widths for the observed lines, and briefly discuss the physical implications of the observed line series. We also use a simple model of free-free emission to characterize the disks around these sources.

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arXiv1998

Study of Broad Scale Anisotropy of Cosmic Ray Arrival Directions from $2\times 10^{17} eV$ to $10^{20} eV$ from Fly's Eye Data

We report results on the broad scale anisotropy of cosmic ray arrival directions in the energy rage from $2 \times 10^{17} eV$ to $10^{20} eV$. The data was taken by the Fly's Eye detector in both monocular and stereo modes of operation. We look for dependence on galactic latitude or supergalactic latitude by fitting the data to a Wdowczyk and Wolfendale plane enhancement function and a N-S gradient functional form. We report a small but statistically significant galactic plane enhancement in the energy range between $2\times 10^{17}eV$ and $3.2 \times 10^{18} eV$. The probability that this anisotropy is due to fluctuations of an isotropic distribution is less than 0.06%. The most significant galactic plane enhancement factor $f_{E} = 0.104 \pm 0.036$ is in the energy range $0.4-1.0 \times 10^{18} eV$. No statistically significant evidence for a N-S gradient is found. There is no sign of significant deviation from isotropic background when the data is analyzed in terms of supergalactic latitude distributions

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