Here are the PostScripts of some of my papers:
A set of color-color diagrams, histograms and cumulative probability functions are presented as a reference for further studies, and are discussed. In the color-color diagrams, most of the objects are located very close to the ``reddening line'' (corresponding to linear reflectivity spectra). A small but systematic deviation is observed toward the I band indicating a flattening of the reflectivity at longer wavelengths, as expected from laboratory spectra. A deviation from linear spectra is noticed toward the B for the bluer objects; this is not matched by laboratory spectra of fresh ices, possibly suggesting that these objects could be covered with extremely evolved/irradiated ices. Five objects (1995SM55, 1996TL66, 1999OY3, 1996TO66 and (2060)Chiron) have almost perfectly solar colors; as two of these are known or suspected to harbour cometary activity, the others should be searched for activity or fresh ice signatures. In the color-color diagrams, 1994ES2, 1994EV3, 1995DA2 and 1998HK151 are located very far from the main group of objects; it is suspected that this corresponds to inaccurate measurements and not intrinsically strange objects.
The color distributions were analyzed as functions of the orbital parameters of the objects and of their absolute magnitude. No significant correlation is observed, with the following exceptions: Cubewanos with low orbital excitation (low i, e and/or E = sqrt{e^2 + \sin^2 i), and therefore experiencing on average fewer and less violent collisions have significantly redder colors; Cubewanos with faint absolute magnitude M(1,1) tend to be redder than the others, while Plutinos present the opposite trend.
The color distribution of the various MBOSS classes are analyzed and compared using generic statistic tools. The comets were found to be significantly bluer than the other MBOSSes.
Finally, we compare the various 1D and 2D color distributions to simple models, in order to throw some light on the question of the bimodality of MBOSS color distributions. It is found that with the current data set, all color distributions are compatible with simple, continuous distribution models, while some color distributions are not compatible with simple bimodal distribution models.
The average magnitude (R = 21.15) was converted into a mean radius of 326+/-7km (assuming albedo p=0.04), making 1996 TO66 the largest known TNO after Pluto and Charon. The object is among the bluest in the outer Solar System and the colour, as measured at different epochs, shows marginally significant changes. Deep, composite images, totaling 13,500s integration time with the NTT and 4500s with the UH2.2m in the R filter, were searched for possible signatures of a faint coma. None were found and the photometric profile of 1996 TO66 perfectly matches a stellar one, down to the 29mag/sq.arcsec level. We also present an apparently featureless 8100s NTT +EMMI spectrum (6000-9100A) with a neutral reflectivity in the 6000--7600A range, and with a marginally significant red gradient S'=30+/-10%/1000A in the 7600--9000A range.
Note: this double nucleus has nothing to do with the "companion"
which is described on another page of this site.
)We present recovery observations of the parent of the Leonid meteor stream -- comet 55P/Tempel-Tuttle using the Keck II telescope. At recovery, the comet was at r = 4.5AU, with m_R = 22.6, and there was no indication of coma or activity. Pre- and post-recovery observations from 6 observing runs (1994--1997 June) are presented. From these measurements we estimate that the nucleus radius is R_N = 1.8 +/- 0.2 km with a nucleus axis ratio greater than 1.5. As of 6/97 (r = 3.5 AU), the comet activity had not yet started.
We have observed comet 46P/Wirtanen during 1996 June, August and November using the University of Hawai`i 2.2m telescope. At the time of the observations, the comet was at heliocentric distances, r = 2.99, 2.53 and 1.83 AU. During the August run observations were made in order to search for light curve variations due to rotational modulation of the nucleus. The comet was active for all runs, and during 1996 August the coma extended >16'' (1.8 10^4 km at the distance of the comet) at PA ~ 325deg, and during 1996 November the coma extended >20'' (2.5 10^4 km at the distance of the comet) at PA ~ 75deg. The surface brightness profile exhibited a gradient slope of -1.6 and -1.4 in August and November, respectively, only slightly steeper than that expected by radiation pressure and phase angle effects alone. Using a phase-dispersion minimization technique, we find a possible rotation period near 7.6 hours. The color of the nucleus plus dust is B-V = 0.756 +/- 0.009, V-R = 0.456 +/- 0.009 and R-I = 0.366 +/- 0.009 averaged over the three runs.
Asteroid 4 Vesta has been imaged in the Near-Infrared using the ESO 3.6~m telescope equipped with the Come-On-Plus adaptive optics system. The result of these observations is the first mineralogic map of a minor planet obtained from ground-based observations. We discuss the data acquisition and reduction techniques that we used and developed, and present our ground-based observational prospects.
Deep CCD observations have been performed with the 3.58m New Technology Telescope at La Silla in the direction of comet P/Halley on April 6, 1992, at heliocentric distance r=16.6AU and on January 11, 1994, at r = 18.8AU. In 1992, the comet could not be convincingly recorded; the limiting magnitude was V~25.8. In 1994, the image of the comet was clearly detected (at S/N = 7) as a V = 26.5 point-source, 0.9" from the predicted position. The identification is further strengthened by the observed motion, which is incompatible with that of more nearby minor bodies and perfectly matches that predicted for this comet. The observed brightness corresponds to that of the naked nucleus and no coma is detected at the 32 mag per square arcsecond level, indicating a complete lack of activity. The feasibility of continued monitoring of P/Halley during the next years is discussed.
We present 81 photometric lightcurves of 36 minor planets observed in the V and B bands at the ESO 50cm telescope at La Silla (Chile). These asteroids were selected preferentially in order to improve their ecliptic longitude coverage in view of pole determinations and lightcurve inversions. We also give some first photometric observations and/or rotational period for several asteroids.
We describe experimental observations and reduction techniques used to image sky fields around three extremely distant comets (Shoemaker 1984~XV at heliocentric distance r=17AU, Bowell 1982I at 23AU and Schuster 1975II at 31AU) during a pilot programme (3 half-nights) at the 3.5-metre ESO New Technology Telescope. Very deep upper brightness limits could be set (V >~ 27m), consistent with their nuclei now being quiescent and implying unexpectedly small upper limits for their radii, 3.4km, 5.4km and 10.3km, respectively. We address in some detail the important problem of determining objectively the ``limiting magnitude'' actually achieved during CCD imaging of a moving object. We also discuss some of the specific problems related to observations of very faint, moving objects with the currently available instrumentation, and we make predictions about observational possibilities with the new generation of giant telescopes.
We observed comets P/Faye 1991 XXI and Zanotta-Brewington 1992 III from the ESO La Silla Observatory (Chile) with photoelectric photometry and CCD techniques. We used narrow-band filters to calculate the Afr parameter and gas production rates for both comets. P/Faye has a low Q(CN)/Afr of 14 1021 molec.s-1.cm-1 at perihelion, but a typical reddening between 11 and 15 %/1000 A (between 4845 and 6840 A). Furthermore, CCD imaging revealed a faint and diffuse asymmetry attributed to anisotropic outgassing. As expected for a newly injected comet, Zanotta-Brewington has a high Q(CN)/Afr of more than 110 1021 molec.s-1.cm-1, which decreased with CN activity in March 1992. No reddening is measured from the continuum filters.
Images of the Pluto-Charon system were obtained with the Faint Object Camera (FOC) of the Hubble Space Telescope (HST) after the refurbishment of the telescope. The images are of superb quality, allowing the determination of radii, fluxes, and albedos. Attempts were made to improve the resolution of the already diffraction limited images by image restoration. These yielded indications of surface albedo distributions qualitatively consistent with models derived from observations of Pluto-Charon mutual eclipses.
Using a collection of deep CCD high-resolution images obtained in February--March 1991 at the European Southern Observatory, we investigate the properties and evolution of the major outburst experienced by Halley's comet at 14 AU from the Sun, some 5 years after perihelion. It is found that the observed crescent-shaped halo represents a segment of a conical surface populated by particulate ejecta that had been released from a suddenly activated source on the sunlit hemisphere of the comet's rotating nucleus. It is shown that the ejecta's total mass was at least ~10^12g and that carbon monoxide was the most likely prime driver, accelerating the smallest grains (~1micron across) to a terminal velocity of ~45 m/s. The mass loading of the gas flow by the particulate matter (which includes water ice) is found to be enormous, its mass production rate exceeding the expected production rate of carbon monoxide by a factor of several tens. The derived particle size distribution function of the ejecta, g(a)da, appears to be relatively flat, a^-3.7da for larger grains and a^-2.3da for smaller grains, the dividing radius of ~14micron in one particular scenario corresponding to particles populating the area of the secondary peak seen about midway from the nucleus to the halo's boundary. For the adopted rotation model, the production rate of the solids peaks shortly before the source's local noon, but the integrated contribution from the afternoon ejecta slightly exceeds that from the morning ejecta. The problem of this event's triggering mechanism is also addressed.
Very deep CCD observations have been made of P/Halley in Feb.1990 at heliocentric distance r = 12.5 AU and in Feb.-Apr.1991 at r = 14.3 - 14.6 AU. In 1990, the image of the comet was stellar-like and no coma was detected at the 29 mag/arcsec^2 level, but the mean brightness was= 24.34 +/- 0.08 (variations between 23.9 and 24.9), or 0.43 mag brighter than predicted for the nucleus alone, indicating the presence of an unresolved coma with the same brightness as the nucleus and a modest level of activity. Contrarily, in Feb.1991 the comet was found to have undergone a major outburst; the nucleus is located in a diffuse, central condensation with FWHM = 1.8" (projected 1.7 * 10^4 km) and V = 21.4 mag (5" diaphragm), situated about 2" NW of the centre of an elliptically shaped, diffuse coma measuring ~38.5" * 27.7" (3.74 x 2.69 10^5 km) at the 28.3 mag/"^2 level and with V_tot = 18.9 mag. No evidence is seen of a break-up of the nucleus. Superimposed upon this component, there is an outward moving, curved structure of higher surface brightness; a linear extrapolation of the temporal, radial displacement of the maximum allows to determine the epoch of origin as Dec.17 +/- 4, 1990, and a projected expansion rate 14.5 +/- 0.9 m/s. A low-dispersion, low-S/N spectrum shows a solar-type continuum with no gaseous emission lines, while the colour of the central condensation, (V-R) = 0.55 +/- 0.05, is nearly solar, i.e. the coma mainly consists of dust grains. Assuming particle size 1micron and density 1 g/cm^3, the observed dust mass is ~10^8 kg, or ~10^-6 of the estimated mass of the nucleus. This is the first time a cometary outburst has been observed at such a large distance.
(2.4Mo). Note that the papers annexed in the thesis are not in this file).Load
to disk and use gunzip to decompress (do you need the GnuZip
compression software?)
2004-05-06T03:20:28 Thu