Wieslaw Z. Wisniewski

Physical studies of small asteroids: I. Lightcurves and taxonomy of 10 asteroids

Abstract A program of physical studies (lightcurves and taxonomy) of asteroids with diameters near 10 km or less has been conducted with the use of 1.5- and 2.3-m telescopes. The detectors used were: a Varian 159A photomultiplier and RCA and TI CCD cameras. A total of 21 lightcurves for 10 asteroids were obtained, and rotational periods were determined. For 9 of the asteroids the lightcurves were observed for the first time. Half of the objects for which taxonomy is reported in this paper are of class S. The colors for Apollo asteroid 3361 Orpheus are best represented by the rare class V.

Photometry of six radar target asteroids

Abstract Photoelectric photometry of six Earth-approaching asteroids is presented. The selection criterion was that they were close enough in 1986 to be observed by radar. Rotation periods were obtained for 1986 DA, 3199, 3103, and 1983 RD. 1986 JK and 1986 RA showed no detectable brightness variations during the monitoring time on several nights each, and therefore were either seen pole-on or have long rotation periods. Asteroids 1986 JK and 1986 RA are of taxonomic class C, 1986 DA and 3103 of class X, 1983 RD of class Q, and only 3199 of the class S that was previously believed to be predominant among Earth-approaching asteroids.

Spectrophotometry and UBVRI photometry of Eros

Spectrophotometric and broad-band photoelectric observations of Eros are reported. No existing meteorite spectrum matches the asteroid data directly. Assemblages of iron or stony-iron with ordinary-chondrite material generate the best match for the reflectivity curve of Eros. Variability was found in the 0.6 micron band and V-R and V-I colors.

The rotational poles and shapes of 1580 Betulia and 3908 (1980PA) from one apparition

Abstract The rotational poles, triaxial ellipsoid shapes, absolute magnitudes, and phase functions of two Amor asteroids have been calculated from lightcurves obtained in a single apparition. The lightcurves of 1580 Betulia were obtained in 1976, and the present analysis gives a preferred pole within 9° of Ecliptic coordinates (212; −5), with triaxial ellipsoid ratios of a b = 1.62±.20 and b c = 1.39±.09 . Its orbital inclination of 52°, the fourth highest among asteroids to date, makes it a strong defunct comet candidate. Asteroid 3908 (1980PA) is the second most accessible asteroid to the Earth in terms of relative velocity, making it a good candidate for a return sample mission. Its preferred rotational pole, lying within 10° of (312; +61), and its triaxial ellipsoid ratios of a b = 1.36±.03 and b c = 1.27 ± .03 were determined from eight lightcurves obtained in its 1988 apparition, and make this the fastest such calculation ever. Its spectrum, albedo, and phase functions are similar to Vesta, Dembowska, and another Amor 3551 (1983RD), all being reddish and bright. The orbits of 3908 and 3551 are similar to each other and to at least two photographic meteors and one fireball from the Prairie Network. All five objects may be pieces of the eucrite parent body, and the radiants indicate that eucrite falls may peak between late August and late November.

0.35-3.5 MICRON PHOTOMETRY OF POLARIZED QSOS.

Visual and infrared photometry of strongly polarized QSOs (BL Lacertae objects) is reported. Spectral flux distributions of these objects are discussed in combination with results from earlier studies. With the exception of the well-resolved galaxies Mkn 421 and Mkn 501 only one object (1218 + 304) has a change in spectral index easily explained by the presence of an underlying galaxy. Six other sources appear to have either a break in their spectra near about 1 micron or a smoother general steepening of their spectra at shorter wavelengths. A spectral break at this wavelength may be attributed to a low flux of nonthermal radiation superimposed on a stellar energy distribution or by nonthermal electron energy losses.

Asteroid 951 Gaspra - Pre-Galileo physical model

Abstract Prior to the October 1991 encounter of 951 Gaspra, asteroids were the only class of Solar System objects not resolved by spacecraft images. Analysis of the data returned by the Galileo spacecraft will apply critical tests to many techniques developed during the past 50 years for deriving physical properties for several hundred asteroids. As a benchmark for comparison, we have applied these techniques to establish in advance our best estimates for Gaspras properties. We estimate it has an elongated shape with a ratio between equatorial axes of about 1.5–1.7. Further, we derive its sidereal rotation period to be 0.2934197 ± 0.0000010 days with its spin vector pointing toward ecliptic coordinates λ 0 = 20° ± 5°, β 0 = +22° ± 5° (or less likely λ 0 = 198° ± 5°, β 0 = +13° ± 5°).

Rotation of comet p/Tempel 2 from CCD and photoelectric photometry

Abstract Taking advantage of its favorable opposition, periodic comet Tempel 2 was extensively monitored during May and June 1988. Two lightcurves were obtained with a CCD camera on the 2.3-m telescope of the Steward Observatory on Kitt Peak, and five light-curves were obtained with the photoelectric photometer on the 1.5-m NASA telescope on Mt. Lemmon. The lightcurve amplitude (12-arcsec diaphragm) was nearly 0.5 mag and the synodic period of rotation was 8 hr 55.8 min. On each occasion two uneven maxima were observed, leading to the conclusion that a lightcurve is not a product of an active spot on the comet, but is caused by a true reflection from an elongated rotating nucleus seen through a transparent yet underdeveloped coma. A comparison is made of CCD and photoelectric photometry.

EMISSION LINES IN THE SPECTRUM OF VEGA.

The infrared lines of Ca II and O I in the spectrum of Vega are found to have small violet-shifted emission satellites. It is therefore suggested that Vega has a relatively thin, extended atmosphere, which may be expanding. The measured equivalent widths of the emission satellites range from 0.02 A to 0.07 A, averaging about 0.05 A. It is the very high photometric precision of the spectra produced by an advanced Michelson spectrophotometer system which makes possible the detection and measurement of such minute details.

The complex lightcurve of 1992 NA

Abstract Amor asteroid 1992 NA was monitored during three nights at a large phase angle of −65°. The lightcurves obtained did not reveal a repeatable curve with two maxima and two minima. However, some features suggested a periodicity with three maxima and three minima. A satisfactory composite lightcurve of this form was obtained by means of an “eyeball” fit and by Fourier analysis. Individual and composite lightcurves are presented. The observed colors are consistent with the C class.

Standard stars for cometary photometry

Abstract Five narrowband interference filters centered at wavelengths 0.365, 0.387, 0.406, 0.484, and 0.514 μm have been selected by the International Astronomical Union to represent ultraviolet continuum, CN emission, C 3 emission, blue continuum, and C 2 emission in the spectra of comets, respectively. We present adopted magnitudes and colors in this filter system for 50 standard stars ranging in blue magnitude 4 to 12, in spectral type from O to K, and mostly distributed around equatorial regions of the sky. Tabulated uncertainties are generally on the order of 0.02 mag or smaller. The zero points of the photometric system are chosen such that blue-continuum magnitudes are approximately equivalent to Johnson B, and such that color indices average zero for solar analog stars.