APPLICATIONS OF ARTIFICIAL INTELLIGENCE TECHNIQUES TO REMOTE SENSING*

Remote sensing is a geographic analysis tool capable of producing large quantities of data in the spectral, temporal and spatial domains. Techniques for automating the image analysis process would be advanced by the inclusion of artificial intelligence techniques in the design of image processing systems. The remote sensing application which show promise for successful implementation of artificial intelligence techniques are intelligent onboard processing, advanced database interrogation, and the automated analysis of multispectral imagery.     

The intermediate-age brown dwarf LP 944-20

Observations are presented which show that Li  I  λ 6708 is detected with an equivalent width of 0.53 ± 0.05Å in the proper-motion object LP 944-20 (which is also known as BRI 0337-3535). Hα is detected in emission at an equivalent width of 1.2 ± 0.5Å. The detection of Li implies a mass less than 0.065 M⊙, making this object a brown dwarf. Moreover, the relative weakness of this Li detection (compared to the equivalent widths of 1–2Å seen in objects of similar spectral type in the Pleiades) implies that Li has been somewhat depleted. This, together with the precisely determined luminosity of LP 944-20, implies a mass between 0.056 and 0.064 M⊙, and age between 475 and 650 Myr. This makes it the first brown dwarf to have a well-constrained mass and age determined.     

Spectral evolution of the peculiar Ic Supernova 1998bw

Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ -ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 d after V -band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.     

High-resolution spectra of very low-mass stars

We present the results of high-resolution (1–0.4 Å) optical spectroscopy of a sample of very low-mass stars. These data are used to examine the kinematics of the stars at the bottom of the hydrogen-burning main sequence. No evidence is found for a significant difference between the kinematics of the stars in our sample with I  −  K  > 3.5 ( M _bol ≳ 12.8) and those of more massive M dwarfs ( M _bol ≈ 7–10). A spectral atlas at high (0.4-Å) resolution for M8–M9+ stars is provided, and the equivalent widths of Cs  I , Rb  I and Hα lines present in our spectra are examined. We analyse our data to search for the presence of rapid rotation, and find that the brown dwarf LP 944-20 is a member of the class of 'inactive, rapid rotators'. Such objects seem to be common at and below the hydrogen-burning main sequence. It seems that in low-mass/low-temperature dwarf objects either the mechanism that heats the chromosphere, or the mechanism that generates magnetic fields, is greatly suppressed.