Pang, K. D.; Rhoads, J. W.; Hanover, G. A.; Lumme, K.; Bowell, E.
Small scale surface features of the moons Deimos and Phobos were studied using star tracker observations made by the Mariner 9 and Viking orbiters. The whole-disk brightness/solar phase angle phase curves were developed out to a phase angle of 125 deg. An analysis was undertaken according to Lumme-Bowell theory to obtain accurate phase integrals zero-phase geometric albedos, and Bond albedos. The microstructural and particulate surface properties of the two moons were found to be very similar, as were the whole-body densities and the microphysical makeup, thereby suggesting a common origin. However, the presence of streamers on Deimos and the relatively smooth surfaces of both moons indicates a long-term influence of Mars producing surface morphologies different from what would occur with asteroids.
Pang, K. D.; Lumme, K.; Bowell, E.
The phase curves of Io and Ganymede between 0 and 40 deg solar phase angle have been compiled from Voyager photopolarimeter and ground-based observations. Modeling the data with the Lumme-Bowell theory made it possible to determine improved estimates of the surface texture and particulate properties. Accurate V-band zero-phase geometric albedos, phase integrals, and Bond albedos are also obtained. The properties of the particles on Io's surface appear to be different from those of other solar system objects whose surfaces are totally controlled by impact cratering processes. Sulfur and SO2 frost, previously identified by spectral analysis, seem to exist in a physical form not commonly found on earth. The agglomeration of volcanic ash into aggregates on Io's surface is postulated.
Carvano, J. M.
Aims: In this first paper we investigate the dependence of the geometric albedo on the phase function of the particles that cover it, and derive the expected geometric albedo of bodies for a given mineralogy, taking into account the constraints imposed by the observed phase functions of the asteroids. Methods: A genetic fitting algorithm is used to fit Hapke integral phase functions to Lumme-Bowell integral phase functions described by values of the slope parameter G of the IAU HG system. The resulting geometric albedo of laboratory samples are then compared to the observed values of asteroids with assumed similar mineralogy. Results: Because of the weak dependence of barθ on the integral phase functions it is not possible to find a unique set of Hapke parameters that fit the Lumme-Bowell function for a given value of G, at least for phase angles <60°. Instead, unique solutions can be found if we leave barθ as a free parameter. It is shown that the laboratory derived scattering parameters in general fail to match the geometric albedo and slope parameter of asteroids of presumed equal mineralogy. It is also shown that a given value of the single scatter albedo can lead to very different values of p_v, depending on G and barθ. The methodology developed is used to compare the observed pv and G of the asteroids (4) Vesta and (21) Lutetia with laboratory measurements of materials with suposedly similar compositions. As expected, it is found that the albedo and slope parameter of Vesta are compatible with measurements of unweathered terrestrial basalts with grain sizes <= 250 μm. The albedo and slope parameter of Lutetia are found to be compatible with samples of the Allende CV3 meteorite for grain sizes <500 μm. The routines that allow the conversion between w and pV (and vice-versa) are available at http://funk.on.br/ carvano/albedo/albedo.html
Slivan, Stephen M.; Binzel, Richard P.; Kaasalainen, Mikko; Hock, Andrew N.; Klesman, Alison J.; Eckelman, Laura J.; Stephens, Robert D.
We recorded 101 new rotation lightcurves of five Koronis family members, and then combined the new observations with previous data to determine the objects' sidereal rotation periods, spin vector orientations, and model shape solutions. The observing program was tailored specifically for spin vector analyses by determining single-apparition Lumme-Bowell solar phase coefficients, and by measuring synodic rotation periods precisely enough to unambiguously count the rotations between two consecutive oppositions, which is a prerequisite for identifying the correct sidereal period. The new data make possible first pole and shape determinations for (263) Dresda, (462) Eriphyla, and (1289) Kutaïssi, and they improve the models for (277) Elvira and (534) Nassovia, two objects previously studied by Slivan et al. [Slivan, S.M., Binzel, R.P., Crespo da Silva, L.D., Kaasalainen, M., Lyndaker, M.M., Krčo, M., 2003. Icarus 162, 285-307]. Our results increase the number of Koronis family spin vectors reported in the literature to fourteen, a sample which now includes the seven largest family members. The spin properties of Eriphyla (rotation period P=8.66h, spin vector obliquity ɛ=51°) and Kutaïssi ( P=3.62 h, ɛ=165°) are consistent with the markedly nonrandom distribution reported by Slivan [Slivan, S.M., 2002. Nature 419, 49-51], and explained by Vokrouhlický et al. [Vokrouhlický, D., Nesvorný, D., Bottke, W.F., 2003. Nature 425, 147-151] as the result of the effects of thermal "YORP" torques combined with solar and planetary gravitational torques. Dresda ( P=16.81 h, ɛ=16°) is the first prograde Koronis member whose spin obliquity and spin rate significantly differ from the clustered spin properties previously found for other prograde Koronis members; nevertheless, its spin vector is consistent with several of the spin evolution possibilities that were identified in the YORP modeling.
Rubio-Godoy, Miguel; Paladini, Giuseppe; Freeman, Mark A; García-Vásquez, Adriana; Shinn, Andrew P
Gyrodactylus salmonis (Yin et Sproston, 1948) isolates collected from feral rainbow trout, Oncorhynchus mykiss (Walbaum) in Veracruz, southeastern Mexico are described. Morphological and molecular variation of these isolates to G. salmonis collected in Canada and the U.S.A. is characterised. Morphologically, the marginal hook sickles of Mexican isolates of G. salmonis closely resemble those of Canadian specimens - their shaft and hook regions align closely with one another; only features of the sickle base and a prominent bridge to the toe permit their separation. The 18S sequence determined from the Mexican specimens was identical to two variable regions of SSU rDNA obtained from a Canadian population of G. salmonis. Internal transcribed spacer (ITS) regions (spanning ITS1, 5.8S and ITS2) of Mexican isolates of G. salmonis are identical to ITS sequences of an American population of G. salmonis and to Gyrodactylus salvelini Kuusela, Ziętara et Lumme, 2008 from Finland. Analyses of the ribosomal RNA gene of Mexican isolates of G. salmonis show 98-99% similarity to those of Gyrodactylus gobiensis Gläser, 1974, Gyrodactylus salaris Malmberg, 1957, and Gyrodactylus rutilensis Gläser, 1974. Mexican and American isolates of G. salmonis are 98% identical, as assessed by sequencing the mitochondrial cox1 gene. Oncorhynchus mykiss is one of the most widely-dispersed fish species in the world and has been shown to be an important vector for parasite/disease transmission. Considering that Mexican isolates of G. salmonis were collected well outside the native distribution range of all salmonid fish, we discuss the possibility that the parasites were translocated with their host through the aquacultural trade. In addition, this study includes a morphological review of Gyrodactylus species collected from rainbow trout and from other salmonid fish of the genus Oncorhynchus which occur throughout North America.
Slivan, Stephen M.; Binzel, Richard P.; Boroumand, Shaida C.; Pan, Margaret W.; Simpson, Christine M.; Tanabe, James T.; Villastrigo, Rosalinda M.; Yen, Lesley L.; Ditteon, Richard P.; Pray, Donald P.; Stephens, Robert D.
We report the results of an observational survey of rotation lightcurves for members of the Koronis asteroid family that we conducted using CCD imaging cameras at seven different observatories during the period 1998-2005. A total of 375 individual lightcurves yield new or refined rotation periods for the 24 survey objects (658) Asteria, (761) Brendelia, (811) Nauheima, (975) Perseverantia, (1029) La Plata, (1079) Mimosa, (1100) Arnica, (1245) Calvinia, (1336) Zeelandia, (1350) Rosselia, (1423) Jose, (1482) Sebastiana, (1618) Dawn, (1635) Bohrmann, (1725) CrAO, (1741) Giclas, (1742) Schaifers, (1848) Delvaux, (1955) McMath, (2123) Vltava, (2144) Marietta, (2224) Tucson, (2729) Urumqi, and (2985) Shakespeare. Most of the data have been calibrated to standard magnitudes. Several previously unpublished lightcurves recorded using a photoelectric photometer during the period 1987-1989 are also reported here. We present composite lightcurves and report derived synodic rotation periods. For those objects with sufficient coverage in solar phase angle we also determined Lumme-Bowell solar phase parameters, and for four objects we obtained V-R colors. Our results reduce selection biases among known rotation lightcurve parameters for Koronis family members by completing the sample down to H≈11.2, and they lay the foundation for future spin vector and shape determinations. The distribution of rotation rates in the available sample of N=40 Koronis members is non-Maxwellian at a confidence level of 99%. It also seems to be qualitatively consistent with the effects of long-term modification by thermal YORP torques, as proposed by Vokrouhlický et al. [Vokrouhlický, D., Nesvorný, D., Bottke, W.F., 2003. Nature 425, 147-151] to explain the distribution of the ten Koronis member spin vectors that have already been determined [Slivan, S.M., 2002. Nature 419, 49-51; Slivan, S.M., Binzel, R.P., Crespo da Silva, L.D., Kaasalainen, M., Lyndaker, M.M., Krčo, M., 2003. Icarus 162, 285-307].
Muinonen, K.; Wilkman, O.; Wang, X.; Cellino, A.
The rotational period, pole orientation, and convex three-dimensional shape of an asteroid can be derived from photometric lightcurves observed in a number of apparitions with varying illumination and observation geometries (e.g., Kaasalainen et al. 2001, Torppa et al. 2008, Durech et al. 2009). It is customary to estimate the rotational period with a simplified shape model and a small number of trial pole orientations. Once the period is available, the pole orientation can be refined with a general convex shape model represented by the spherical harmonics expansion for the Gaussian surface density. Once the Gaussian surface density is available, the actual convex shape is constructed as a solution of the Minkowski problem. We focus on the initial derivation of the rotational period and pole orientation with the help of the Lommel-Seeliger ellipsoid (LS-ellipsoid), a triaxial ellipsoid with a Lommel-Seeliger surface scattering law. The disk-integrated photometric brightness for the LS-ellipsoid is available in a closed form (Muinonen and Lumme, in preparation), warranting efficient direct computation of lightcurves. With modern computers and the LS-ellipsoid, the rotation period, pole orientation, and ellipsoidal shape can be derived, in principle, simultaneously (see Cellino et al., present meeting). However, here we choose to proceed systematically as follows. First, the rotation period is scanned systematically across its relevant range with a resolution of P_0^2/2T dictated by a tentative period estimate P_0 and the time interval spanned by the photometric data T. This is typically carried out for a small number of pole orientations distributed uniformly on a unit sphere. For each pole orientation, the ellipsoid pole orientation, rotational phase, and axial ratios are optimized with the help of the Nelder-Mead downhill simplex method. Although the shape optimization can suffer from getting stuck in local minima, overall, the rotation period is fairly accurately