Engineering topics

Luu, Jane

Publications and source records attributed to Luu, Jane.

7 records

NASA NTRS1997

A Search for 23rd Magnitude Kuiper Belt Comets

The goal of the project was to identify a statistically significant sample of large (200 km-sized) Kuiper Belt Objects (KBOs), by covering 10 sq. degrees of the sky to a red limiting magnitude m(sub R) = 23. This work differs from, but builds on, previous surveys of the outer solar system in that it will cover a large area to a limiting magnitude that is deep enough to guarantee positive results. The proposed work should provide us with a significant number of 200 km-size KBOs (approx. 20 are expected) for subsequent studies. Such a sample is crucial if we are to investigate the statistical properties of the Belt and its members. It was modified the original research strategy to accommodate unanticipated problems such as the urgent need for follow-up observations,the original goal was still reached: we have substantially increased the number of Kuiper Belt Objects brighter than 23rd mag.

Luu, Jane↗

NASA NTRS1994

Near-infrared spectroscopy of primitive solar system objects

We have obtained near-infrared (H and K band at lambda/Delta(lambda) is approximately 480 to 600) spectra of a sample of primitive objects including 2 Centaur objects (2060 Chiron and 5145 Pholus) and 16 P- and D-type asteroids. The spectra were obtained at the United Kingdom Infrared Telescope using the cooled grating spectrometer CGS4, and were used to search for chemically diagnostic vibrational features in these primitive objects. Pholus exhibits broad adsorption features at 2.07 and 2.27 micrometers, as well as a weak feature at 1.72 micrometers. The 1.72- and 2.27-micrometer features are similar to those seen in a laboratory tar sand sample. No distinct absorption features are found in other objects, including Chiron, which displays a spectrally neutral continuum. A comparison of the P- and D-type asteroid spectra with laboratory measurements of organic solids shows no compelling evidence for hydrocarbon overtones seen in terrestrial bituminous tar sands.

Luu, Jane↗

NASA NTRS1994

Comets disguised as asteroids

Comets and asteroids were previously thought to be two completely distinct groups of solar-system objects, with marked contrast in both physical and dynamical characteristics. A comet is operationally defined by the presence of a coma, while an asteroid has no coma. However, recent observations have shown that comets can sometimes take on asteroidal appearances and even asteroidal photometric behavior. Thus the observational distinction between comets and asteroids is not as clear cut as it once seemed. The possible presence of comets hidden among known asteroids forces us to reconsider the criterion by which we distinguish comets from asteroids and possibly our inventory of both comet and asteroid populations.

Luu, Jane↗

NASA NTRS1993

The new BL Lacertae objects discovered by an efficient X-ray/radio/optical technique

We report the recent discovery of ten BL Lac objects in the Einstein IPC Slew Survey by means of X-ray/radio versus X-ray/optical color-color diagrams and confirming optical spectroscopy. These ten BL Lac objects were discovered using a technique proposed by Stocke et al. (1989) which exploits the characteristic broad-band spectra of BL Lac objects. New VLA detections provide accurate fluxes (limiting f(6 cm) about 0.5 mJy) and about 1 arcsec positions, facilitating the determination of an optical counterpart. All ten new BL Lac objects show essentially featureless optical spectra and lie within the range of radio/X-ray/optical colors of known X-ray-selected BL Lac objects, when about 1 mag optical variability is included. We expect about 50 new BL Lac objects in total, from complete optical follow-up of our now completed VLA work and recent Australia Telescope observations, yielding a complete Slew Survey sample of about 90 BL Lac objects.

Schachter, Jonathan F.↗

NASA NTRS1993

Discovery of the candidate Kuiper belt object 1992 QB1

The discovery of a new faint object in the outer solar system, 1992 QB1, moving beyond the orbit of Neptune is reported. It is suggested that the 1992 QB1 may represent the first detection of a member of the Kuiper belt (Edgworth, 1949; Kuiper, 1951), the hypothesized population of objects beyond Neptune and a possible source of the short-period comets, as suggested by Whipple (1964), Fernandez (1980), and Duncan et al. (1988).

Jewitt, David↗

NASA NTRS1992

Thirteen new BL Lacertae objects discovered by an efficient x ray/radio/optical technique

The discovery of 13 serendipitous BL Lac objects in the Einstein IPC Slew Survey by means of x ray/radio vs. x ray/optical color-color diagrams and confirmation by optical spectroscopy are reported. These 13 BL Lacs were discovered using a technique which exploits the characteristic broad band spectra of BL Lacs. New VLA detections provide accurate fluxes (f(6 cm) is approximately 0.5 mJy) and 2 in. positions, facilitating the determination of an optical counterpart. All 13 new BL Lacs show essentially featureless optical spectra. Nine of these lie within the range of colors of known x ray selected BL Lacs. Of the remaining four, one is apparently x ray louder (by a factor of 1.5) or optically quieter (by 0.8 mags); and three are optically louder (by 1-1.3 mags) than x ray selected BL Lacs. Approximately 50 new BL Lacs in total are expected from VLA work and upcoming Australia Telescope observations, yielding a complete Slew Survey sample of approximately 90 BL Lacs.

Schachter, Jonathan F.↗

NASA NTRS1989

A CCD portrait of Comet P/Tempel 2

The development of activity in Comet P/Tempel 2 is studied from aphelion (R = 4 AU) to perihelion (R = 1.4 AU) using extensive time-series CCD photometry and CCD spectra. The comet undergoes a profound morphological change at R of about 2-2.5 AU, from a bare nucleus at larger distances to an active comet supporting a coma of gas and dust. Cyclic photometric variations with the period T = 8.95 + or - 0.01 hr. are present at all R, and are attributed to the rotation of the nucleus at this period. The nucleus is prolate (axes a:b:c = 1.9:1:1), a property shared with other nuclei studied using CCD photometry. Novel results include a limit on the bulk density of the nucleus, rho above 300 kg/cu m, and a 20-A-resolution CCD spectrum of the nucleus. Spatially and temporally resolved photometry is used to study the effects of nucleus rotation on the coma. The coma does not share the dramatic photometric variations shown by the nucleus. It possesses a steep surface-brightness distribution, which is attributable to progressive destruction of the coma grains with increasing space exposure.

Jewitt, David↗