Physical survey of 24 Centaurs with visible photometry

We present optical observations of 24 Centaurs performed between 1998 and 2002 with the University of Hawaii 2.2-m telescope. This is the largest such Centaur survey to date. We report colors for all objects, and show that they cover a continuum with mean V–R color of 0.58±0.01 and standard deviation 0.15. The color distribution fits between those of the Kuiper Belt and the cometary nuclei, and seems consistent with the dynamical concept of the majority of Centaurs originating from the Kuiper Belt. We find no strong correlation between a Centaur's color and its orbital elements; there is at best a <3−σ correlation with semimajor axis, with redder Centaurs being farther from the Sun. We have calculated the phase-darkening slope parameters G for 5 Centaurs, 4 of which are reported for the first time. They range from −0.18 to 0.13. We have sufficient data to constrain the rotation periods of two Centaurs, 1999 UG₅ (which we reported earlier) and 1998 SG₃5. We performed a comparison of the surface brightness profiles of 10 apparently-inactive Centaurs with point sources. We found no coma around these 10 objects, including C/LINEAR (2000 B4), and generally the upper limits to the dust mass loss rates are below 0.05 kg s⁻¹.     

Project Pan-STARRS and the Outer Solar System

Pan-STARRS, a funded project to repeatedly survey the entire visiblesky to faint limiting magnitudes (m_R～ 24), will have asubstantial impact on the study of the Kuiper Belt and outer solarsystem. We briefly review the Pan-STARRS design philosophy and sketchsome of the planetary science areas in which we expect this facility tomake its mark. Pan-STARRS will find ～20,000 Kuiper Belt Objectswithin the first year of operation and will obtain accurate astrometryfor all of them on a weekly or faster cycle. We expect that it willrevolutionise our knowledge of the contents and dynamical structure ofthe outer solar system.     

Physical Characterization of the Binary Edgeworth–Kuiper Belt Object 2001 QT 297

Following our discovery of 2001 QT₂₉₇ as the second knownbinary Edgeworth–Kuiper Belt Object (EKBO) in October of 2001 [IAUC 7733], we havecarried out additional high spatial resolution ground based imaging in October andNovember of 2001 and July, August, and September of 2002. Using the Raymond andBeverly Sackler Magellan Instant Camera (MagIC) on the Baade and Clay 6.5 m telescopesat Las Campanas Observatory in Chile, we have obtained accurate astrometric and photometricmeasurements in the Sloan r’ i’ and g’ filters. Superb seeing conditions andPSF fitting allow an accurate determination of the binary component separation and positionangle over time as well as a detailed study of color and temporal variability of the individualcomponents. Here we present a physical characterization of the individual componentsof 2001 QT₂₉₇ based on these astrometric, color and variability measurements. We findthe primary to exhibit colors about 0.3 magnitudes redder than solar with no evidencefor variability. The secondary component, however, exhibits strong variability(～0.6 magnitudes) with a best fit period of 4.7526 ± 0.0007 h for a single peaklightcurve or 9.505 ± 0.001 h for a dual peaked lightcurve. The colors measured for thesecondary also suggest variability. Based on a preliminary orbit fit for thepair using observations spanning a one year arc, we are able to estimate a system mass of～ 3.2 × 10¹⁸ kg and provide constraints to the surface albedo of 9–14% for assumeddensities between 1 and 2 g/cm³.     

The Common Origin of the High Inclination TNO's

Numerical integrations of the four major planets orbits inside a primordialplanetesimals disk show that a fraction of Neptune primordial scatteredobjects are deposited into the classical Kuiper Belt at Solar System age. Theseobjects exhibit inclinations as high as 40° and can account forpresent high inclinations population in the classical Kuiper Belt. The samemechanism can also originate high perihelion scattered objects like 2000 CR₁₀₅. The process that in the end produced such objects can be divided into two phases, a migration phase where nonconservative dynamics acted to producesome stable objects already at 10⁸ years and a nonmigrating phase that helped to establish some other objects as stable TNO's. Low inclination CKBO's have inprinciple an origin through the resonance sweeping process, although someresults from numerical integrations at least suggest a possible origin also fromthe primordial Neptune scattered population.     

Evidence for an Extended Scattered Disk

By telescopic tracking, we have established that the transneptunian object (TNO) 2000 CR₁₀₅ has a semimajor axis of 220±1 AU and perihelion distance of 44.14±0.02 AU, beyond the domain which has heretofore been associated with the “scattered disk” of Kuiper Belt objects interacting via gravitational encounters with Neptune. We have also firmly established that the TNO 1995 TL₈ has a high perihelion (of 40.08±0.02 AU). These objects, and two other recent discoveries which appear to have perihelia outside 40 AU, have probably been placed on these orbits by a gravitational interaction which is not strong gravitational scattering off of any of the giant planets on their current orbits. Their existence may thus have profound cosmogonic implications for our understanding of the formation of the outer Solar System. We discuss some viable scenarios which could have produced these objects, including long-term diffusive chaos and scattering off of other massive bodies in the outer Solar System. This discovery implies that there must be a large population of TNOs in an “extended scattered disk” with perihelia above the previously suggested 38 AU boundary. The total population is difficult to estimate due to the ease with which such objects would have been lost. This illustrates the great value of frequent and well time-sampled recovery observations of trans-neptunian objects within their discovery opposition.     

Masses of the Main Asteroid Belt and the Kuiper Belt from the Motions of Planets and Spacecraft

Dynamicalmass estimates for the main asteroid belt and the trans-Neptunian Kuiper belt have been found from their gravitational influence on the motion of planets. Discrete rotating models consisting ofmovingmaterial points have been used tomodel the total attraction fromsmall or as yet undetected bodies of the belts. The masses of the model belts have been included in the set of parameters being refined and determined and have been obtained by processing more than 800 thousand modern positional observations of planets and spacecraft. We have processed the observations and determined the parameters based on the new EPM2017 version of the IAA RAS planetary ephemerides. The large observed radial extent of the belts (more than 1.2 AU for the main belt and more than 8 AU for the Kuiper belt) and the concentration of bodies in the Kuiper belt at a distance of about 44 AU found from observations have been taken into account in the discrete models. We have also used individual mass estimates for large bodies of the belts as well as for objects that spacecraft have approached and for bodies with satellites. Our mass estimate for the main asteroid belt is (4.008 ± 0.029) × 10^?4/m_⊕ (3σ). The bulk of the Kuiper belt objects are in the ring zone from 39.4 to 47.8 AU. The estimate of its total mass together with the mass of the 31 largest trans-Neptunian Kuiper belt objects is (1.97 ± 0.30) × 10^?2m_⊕ (3σ), which exceeds the mass of the main asteroid belt almost by a factor of 50. The mass of the 31 largest trans-Neptunian objects (TNOs) is only about 40% of the total one.     

Long-Term Evolution of Objects in the Kuiper Belt Zone—Effects of Insolation and Radiogenic Heating

The Kuiper Belt zone is unique insofar as the major heat sources of objects a few tens of kilometers in size—solar radiation on the one hand and radioactive decay on the other—have comparable power. This leads to unique evolutionary patterns, with heat waves propagating inward from the irradiated surface and outward from the radioactively heated interior. A major radioactive source that is considered in this study is ²⁶Al. The long-term evolution of several models with characteristics typical of Kuiper Belt objects is followed by means of a 1-D numerical code that solves the heat and mass balance equations on a spherically symmetric grid. The free parameters considered are radius (10-500 km), heliocentric distance (30-120 AU), and initial ²⁶Al content (0-5×10⁻⁸ by mass). The initial composition assumed is a porous mixture of ices (H₂O, CO, and CO₂) and dust. Gases released in the interior are allowed to escape to the surface. It is shown that, depending on parameters, the interior may reach quite high temperatures (up to 180 K). The models suggest that Kuiper Belt objects are likely to lose the ices of very volatile species during early evolution; ices of less volatile species are retained in a surface layer, about 1 km thick. The models indicate that the amorphous ice crystallizes in the interior, and hence some objects may also lose part of the volatiles trapped in amorphous ice. Generally, the outer layers are far less affected than the inner part, resulting in a stratified composition and altered porosity distribution. These changes in structure and composition should have significant consequences for the short-period comets, which are believed to be descendants of Kuiper Belt objects.     

Visible and infrared photometry of Kuiper Belt objects: searching for evidence of trends

We present new visible-infrared (V−J) observations of 17 Kuiper Belt objects, of which 14 were observed in the visible and infrared wavebands simultaneously to limit the effects of lightcurve variations. Combining these data with our previously published visible-infrared data provides a dataset of 29 objects, 25 of which offer simultaneous V−J colors. We examine the resulting dataset for evidence of relationships between physical properties and orbital characteristics. We find no evidence of a color-size relationship (as previously suspected), at least over the size range sampled. The dataset supports the trend, reported elsewhere, that there is a predominance of red material on the surfaces of objects having perihelia beyond 40 AU. Our data are also supportive, albeit weakly, of a reported correlation between inclination and color in the classical Kuiper Belt — although it is perhaps more correct to say that our data show that there appears to be a lack of low inclination blue objects. Our V−J colors appear broadly correlated with published optical colors, thus suggesting that the surfaces of Kuiper Belt objects are subject to a single reddening agent.     

Orbital eccentricity of the symbiotic star MWC 560

We present projected rotational velocity measurements of the red giant in the symbiotic star MWC 560, using the high‐resolution spectroscopic observations with the FEROS spectrograph. We find that the projected rotational velocity of the red giant is v sin i = 8.2 ± 1.5 km s^–1, and estimate its rotational period tobe P_rot = 144–306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e = 0.68–0.82. We briefly discuss the connection of our results with the photometric variability of the object (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the <Emphasis Type="Italic">Z</Emphasis> and <Emphasis Type="Italic">Y</Emphasis> Filters of the Vista Sky Surveys and the <Emphasis Type="Italic">IRAC</Emphasis> Filters of the Spitzer Sky Surveys

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] μm bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: M _Z = ?0.20 ± 0.04, M _Y = ?0.470 ± 0.045, M_[3.6] = ?1.70 ± 0.03, M_[4.5] = ?1.60 ± 0.03, M_[5.8] = ?1.67 ± 0.03, and M_[8.0] = ?1.70 ± 0.03. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [M/H] ? 0.40 (Z ? 0.038) with an error of [M/H] ? 0.1 dex, while the effective temperature is 4250± 150 K. Stars with an age of 9–10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of ~8 Gyr can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200–8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.     

Searching for stars closely encountering with the solar system

Based on a new version of the Hipparcos catalog and currently available radial velocity data, we have searched for stars that either have encountered or will encounter the solar neighborhood within less than 3 pc in the time interval from −2 Myr to +2 Myr. Nine new candidates within 30 pc of the Sun have been found. To construct the stellar orbits relative to the solar orbit, we have used the epicyclic approximation. We show that, given the errors in the observational data, the probability that the well-known star HIP 89 825 (GL 710) encountering with the Sun most closely falls into the Oort cloud is 0.86 in the time interval 1.45 ± 0.06 Myr. This star also has a nonzero probability, 1 × 10⁻⁴, of falling into the region d < 1000 AU, where its influence on Kuiper Belt objects becomes possible.     

A rotational light curve for the Kuiper belt object 1997 CV29

We present R- and V-band rotational light curves for classical Kuiper belt object 1997 CV₂₉. The imaging data was obtained from the Canada-France-Hawaii Telescope (CFHT) archive located at the Canadian Astronomical Data Center (CADC). The data consist of one nights observations of a series of 42, 8 minute exposures in R band followed by 33, 8 minute exposures in V band acquired on the following night. Using relative photometry we determined a highly significant variation in the brightness of 1997 CV₂₉. Using phase-dispersion-minimization we find 8.0, 11.2, and 15.8 hrs to be the most likely, periods of rotation and we argue that the ∼16 hr period is the most likely based on our limited observing window. The phased light curve has a peak-to-peak range of Δm?0.4±0.1 mag suggesting an axial ratio of a/b?1.45.     

Kuiper Belt structure as a reflection of the migration process of a planet

One of the main particular features of the structure of the Kuiper Belt is that it contains clusters of objects of small orbital eccentricity and inclination (“cold population”). In order to solve the problem of the origin of the objects, we considered the process of the gravitational interaction of a comparatively small-mass planet with a planetesimal disk. We found that one particular property of the process is that the planet changes its direction of migration. The interaction with the planet results in the transportation of a considerable portion of planetesimals from the inner zone out to the Kuiper Belt. After such a transition of the objects, the planet returns to the inner regions of the planetesimal disk. Numerical simulations show that the reversible migration of a planet of a mass similar to that of the Earth can explain the main properties of the Kuiper Belt’s cold population orbit distribution.     

The period of rotation, shape, density, and homogeneous surface color of the Centaur 5145 Pholus

We present optical photometry of the Centaur 5145 Pholus during 2003 May and 2004 April using the facility CCD camera on the 1.8-m Vatican Advanced Technology Telescope on Mt. Graham, Arizona. We derive a double-peaked lightcurve and a rotation period of 9.980±0.002 h for Pholus, consistent with periods of 9.9825±0.004 and 9.9823±0.0012 h by Buie and Bus (1992, Icarus 100, 288-294) and Farnham (2001, Icarus 152, 238-245). We find a lightcurve peak-to-peak amplitude of 0.60 mag, significantly larger than peak-to-peak amplitude determinations of 0.15 and 0.39 mag by Buie and Bus and Farnham. We use the three observed amplitudes and an amplitude-aspect model to derive four possible rotational pole positions as well as axial ratios of a/b=1.9 and c/b=0.9. If we assume an albedo of 0.04, we find Pholus has dimensions of 310×160×150 km. If we assume Pholus is a strengthless rubble-pile and its non-spherical shape is due to rotational distortion, our axial ratios and period measurements indicate Pholus has a density of 0.5 g cm⁻³, suggestive of an ice-rich, porous interior. By combining B-band and R-band lightcurves, we find B−R=1.94±0.01 and any B−R color variation over the surface of Pholus must be smaller than 0.06 mag (i.e., much smaller than the 1.0<B−R<2.0 range seen among the Centaur and Kuiper belt object populations). By combining our V−R measurements with values in the literature, we find no evidence for any color variegation between the northern and southern hemispheres of Pholus. Observations of the Kuiper belt object 2004 DW (90482) over a time interval of seven hours show no color variation Our observations add to the growing body of evidence that individual Centaurs and KBOs exhibit homogeneous surface colors and hence gray impact craters on radiation reddened crusts are probably not responsible for the surprising range of colors seen among the Centaur and Kuiper belt object populations.     

The Substellar Population in the Young σ Orionis Cluster, Spatial Distribution

We review different surveys, in the optical and infrared, conducted in the very young (age 1–8 Myr), nearby (d ～ 350 pc) σ Orionis cluster aimed to characterize the substellar population. We describe spectral characteristics of very low mass stars, brown dwarfs and planetary mass objects in the cluster with spectral types from K7 to T6. We study the spatial distribution of the substellar population detected in a IZJ survey covering an area of 1.12 deg.² We find that the radial distribution of substellar objects can be well fitted by an exponential law (ρ = ρ_o e ^?r/ro ), with a central density (ρ _o ) of 0.26 ± 0.03 objects/arcmin² and a characteristic radius (r _o) of 8.8 arcmin ± 0.6 (equivalent to 0.90 ± 0.06 pc at the distance of the cluster). We discuss the presence of possible inhomogeneities in this distribution due to the existence of subclustering. We also compare the spatial distribution of the substellar population with previously known stars in the cluster. We report the initial mass spectrum in the substellar domain.     

The Shape Distribution Of Kuiper Belt Objects

If we assume that the periodic brightness variations ina Kuiper Belt lightcurve are determined only by theiraspherical shapes and the observing geomtry, the fractionof detectable Kuiper Belt lightcurves and the lightcurveamplitude distribution can be used to constrain the shapesof Kuiper Belt objects. The results indicate that most KuiperBelt objects (～85%) have shapes that are close to spherical(a/b ≤ 1.5$), but there is a small but significant fraction(～12%) possessing highly aspherical shapes (a/b ≥ 1.7).The distribution cannot be well fitted by a gaussian and is betterapproximated by a power law.     

Spatially resolved absolute spectral reflectivity of Jupiter: 3390–8400 Å

Observational determinations of the absolute spectral reflectivities of visually distinct regions of Jupiter are presented. The observations cover the 3390–8400 Å region at 10 Å resolution, and they are compared with observations using 150–200 Å filters in the 3400–6400 Å range. The effective reflectivities for several regions (on the meridian) in the 3400–8400 Å range are: South Tropical Zone, 0.76±0.05; North Tropical Zone, 0.68±0.08; South Equatorial Belt, 0.63±0.08; North Equatorial Belt, 0.62±0.04; and the Great Red Spot, 0.64±0.09. Reflectivities near the limb are also observed. The appropriate blue and red reflectivities are tabulated in support of the Pioneer 10 and 11 imaging photopolarimeter experiments. For the regions listed above, equivalent widths of molecular bands vary as: CH₄ (6190 Å), 14–16 Å; CH₄ (7250 Å), 77–86 Å; and NH₃ (7900 Å), 87–95 Å. Significant differences from the results of C. B. Pilcher, R. G. Prinn, and T. B. McCord (“Spectroscopy of Jupiter: 3200 to 11200 Å,” J. Atmos. Sci.30, 302–307.)     

Four-color photometry of the Galilean satellites

Photometry obtained in 1973 on the uvby system yields high-precision rotational light curves for Io, Europa, and Ganymede at a mean phase angle of ～6°. By combining our observations with photometry obtained by others over a broader range of phase angle, we alsi derive improved values for the phase coefficients and opposition surges of the four Galilean satellites. The values of V(1, 0) obtained by linear extrapolation to zero phase are accurate to ±0.03 magnitudes. We also derive the colors of the sun of the uvby system and use these to obtain albedos of the satellites in four colors.     

BVR broadband photometry of comets 1P/Halley and 4P/Faye

We analyzed the visible broadband photometric data of comets 1P/Halley and 4P/Faye, obtained during their perihelion passages of 1986 and 1991, respectively at the Sanglokh Observatory (Tajikistan) and the European Southern Observatory (Chile). Applying the Lomb-Scargle periodogram in the V-band magnitudes and B-V color index, we find that the most probable periodicities are 79 ± 6 and 7.36 ± 0.04 days for 1P, and 6.1 ± 0.3 days for 4P. After comparing results of color and magnitude periodograms, we argue there is a systematic difference in the number of signals identified and the level of confidence of the same periodicity in the periodograms. Our results suggest the quest for periodicities in the color of the coma of active comets should be complementary to ones in magnitudes. We have verified that the distribution of the color B-V of Faye’s coma was invariable during and after the possible occurrence of a post-perihelion outburst. We verify a symmetry in the pre- and post-perihelion H₀ photoelectric absolute magnitude of the comet Halley. The same issues were not observed in the B-V color index. We verify that the absolute magnitude H₀ of the comet Halley differs from each other when calculated from the visual or photoelectric magnitudes, due to the section of the coma used to estimate these magnitudes. We also verified that this difference in the photometric aperture can compromise comparisons of B-V color distributions between active comets.     

Occultations of stars brighter than 15<Superscript>m</Superscript> by the largest trans-Neptunian objects in 2004–2014

We computed the occultations of stars brighter than 15^m by the largest trans-Neptunian objects (TNOs) for the next ten years. In our search, we used the following catalogs: Hipparcos; Tycho2 with the coordinates of 2838666 stars taken from UCAC2 (Herald 2003); and UCAC2 (Zacharias et al. 2003) with 16356096 stars between \(12\mathop .\limits^m 00\) and \(14\mathop .\limits^m 99\) north of ?45° declination. We predicted the occultations of stars by the seventeen largest numbered TNOs, the recently discovered 2004 DW, and four known binary Kuiper Belt objects. We selected 64 events at solar elongations of no less than 30°, including the extremely rare occultation of a \(6\mathop .\limits^m 5\) star by the double asteroid (66652) 1999 RZ₂₅₃ on October 4, 2007. Observations of these events by all available means are extremely important, since they can provide unique information about the sizes of TNOs and improve our knowledge of their orbits dramatically.