Observations of the Centaur 1999 UG 5 : Evidence of a Unique Outer Solar System Surface (original) (raw)
Related papers
Both Centaurs and trans-Neptunian objects (TNOs) are minor bodies found in the outer Solar Sys- tem. Centaurs are a transient population that moves between the orbits of Jupiter and Neptune, and they probably diffused out of the TNOs. TNOs move mainly beyond Neptune. Some of these objects display episodic cometary behaviour; a few percent of them are known to host binary companions. Here, we study the light- curves of two Centaurs —2060 Chiron (1977 UB) and 10199 Chariklo (1997 CU 26 )— and three TNOs —38628 Huya (2000 EB 173 ), 28978 Ixion (2001 KX 76 ), and 90482 Orcus (2004 DW)— and the colours of the Cen- taurs and Huya. Precise, ∼1%, R-band absolute CCD photometry of these minor bodies acquired between 2006 and 2011 is presented; the new data are used to in- vestigate the rotation rate of these objects. The colours of the Centaurs and Huya are determined using BV RI photometry. The point spread function of the five mi- nor bodies is analysed, searching for signs of a coma or close companions. Astrometry is also discussed. A periodogram analysis of the light-curves of these ob- jects gives the following rotational periods: 5.5±0.4 h for Chiron, 7.0±0.6 h for Chariklo, 4.45±0.07 h for Huya, 12.4±0.3 h for Ixion, and 11.9±0.5 h for Or- cus. The colour indices of Chiron are found to be B − V = 0.53 ± 0.05, V − R = 0.37 ± 0.08, and R − I = 0.36 ± 0.15. The values computed for Chariklo are V − R = 0.62 ± 0.07 and R − I = 0.61 ± 0.07. For Huya, we find V − R = 0.58 ± 0.09 and R − I = 0.64 ± 0.20. Our rotation periods are similar to and our colour val- ues are consistent with those already published for these objects. We find very low levels of cometary activity (if any) and no sign of close or wide binary companions for these minor bodies.
Visible and Infrared Photometry of Six Centaurs
Icarus, 1998
tune. They are believed to be objects which have been perturbed from the inner edge of what has become known We present infrared ( JHK ) and visible (VRI ) observations of the Centaurs 2060 Chiron, 5145 Pholus, 7066 Nessus, 1995 as the Kuiper Belt 3 by the gravitational influences of Nep-DW 2 , 1995 GO, and 1997 CU 26 . These are combined whenever tune and Uranus. Their properties have been reviewed by possible to derive relative reflectance spectra between 0.55 and Stern and Campins (1996) and in the introductions to re-2.2 m. The extreme visible to infrared color of Pholus found cent observational papers such as that of Romanishin et in 1992 is confirmed, as is the redness of 7066 Nessus. We al. (1997). Recently, Jedicke and Herron (1997) estimated refine the rotation period and lightcurve of 1995 GO and resolve that there must be fewer than ȁ2000 Centaurs of which ambiguous determinations of its V-R color. We find that 1997 only 3 would have diameters greater than about 200 km.
Compositional Variation on the Surface of Centaur 8405 Asbolus
The Astrophysical Journal, 2000
Near-infrared 1-2 mm spectra of the Centaur 8405 Asbolus (1995 GO) have been obtained using the Hubble Space Telescope near-infrared camera and multiobject spectrometer. Strong and variable absorption features indicate a significantly inhomogeneous surface characterized by water ice mixed with additional unknown constituents. Over a 1.7 hr interval, the observed spectra varied from a nearly featureless spectrum to a very complicated absorption spectrum, and the integrated flux varied in a manner consistent with previous light-curve observations. The accepted rotation period of 8.9351 hr assumes a shape-dominated light curve. Our observations indicate that the light curve may in fact be dominated by a relatively bright spot with a period of 4.47 hr, i.e., half the previous value.
2016
Until now, rings have been detected in the Solar System exclusively around the four giant planets 1. Here we report the discovery of the first minor-body ring system around the Centaur object (10199) Chariklo, a body with equivalent radius 2 124±9 km. A multi-chord stellar occultation revealed the presence of two dense rings around Chariklo, with widths of about 7 km and 3 km, optical depths 0.4 and 0.06, and orbital radii 391 and 405 km, respectively. The present orientation of the ring is consistent with an edge-on geometry in 2008, thus providing a simple explanation for the dimming of Chariklo's system between 1997 and 2008 3 , and for the gradual disappearance of ice and other absorption features in its spectrum over the same period 4, 5. This implies that the rings are partially composed of water ice. These rings may be the remnants of a debris disk, which were possibly confined by embedded kilometre-sized satellites. Chariklo is the largest known Centaur object orbiting in a region between Saturn and Uranus with orbital eccentricity 0.171 and semi-major axis 15.8 astronomical units (1AU is the Earth-Sun distance). It may be a former transneptunian object that has been recently (less than 10 Myr) scattered by gravitational perturbations from Uranus 6. No clear detection of Chariklo's rotation has been made so far. Its surface is very dark with a geometric albedo 2 0.035±0.011, and it is subject to long-term spectral and photometric variabilities 3, 4, 5 , although no cometary activity has ever been reported. An occultation of an R=12.4 magnitude star by Chariklo was predicted 7 to cross South America on June 3, 2013; see Extended Data Figures 1 and 2. We obtained data from sites distributed in Brazil, Argentina, Uruguay and Chile (Extended Data Table 1). While the occultation by Chariklo itself was recorded at three sites in Chile, seven sites detected a total of thirteen rapid stellar flux interruptions (secondary events), two of them being resolved into two sub-events by the Danish 1.54m telescope at the European Southern Observatory (ESO) at La Silla (Figure 1).
Photometry of Active Centaurs: Colors of Dormant Active Centaur Nuclei
The Astronomical Journal
We present multiband photometric observations of nine Centaurs. Five of the targets are known active Centaurs (167P/CINEOS, 174P/Echeclus, P/2008 CL94, P/2011 S1, and C/2012 Q1), and the other four are inactive Centaurs belonging to the redder of the two known color subpopulations (83982 Crantor, 121725 Aphidas, 250112 2002 KY14, and 281371 2008 FC76). We measure the optical colors of eight targets and carry out a search for cometary activity. In addition to the four inactive Centaurs, three of the five active Centaurs showed no signs of activity at the time of observation, yielding the first published color measurements of the bare nuclei of 167P and P/2008 CL94 without possible coma contamination. Activity was detected on P/2011 S1 and C/2012 Q1, yielding relatively high estimated mass loss rates of 140 ± 20 and 250 ± 40 kg/s, respectively. The colors of the dormant nuclei are consistent with the previously-published colors, indicating that any effect of non-geometric scattering from Centaur dust or blanketing debris on the measured colors is minimal. The results of our observations are discussed in the context of the cause of Centaur activity and the color distributions of active and inactive Centaurs. We suggest that the relative paucity of red Centaurs with low-perihelion orbits may not be directly due to the blanketing of the surface by unweathered particulates, but could instead be a result of the higher levels of thermal processing on low-perihelion Centaurs in general.
Physical properties of centaur (54598) Bienor from photometry
Monthly Notices of the Royal Astronomical Society, 2016
We present time series photometry of Bienor in four observation campaigns from 2013 to 2016 and compare them with previous observations in the literature dating back to 2000. The results show a remarkable decline in the amplitude of the rotational light curve and in the absolute magnitude. This suggests that the angle between the rotation axis and the line of sight has changed noticeably during the last 16 yr as Bienor orbits the Sun. From the light-curve amplitude data, we are able to determine the orientation of the rotation axis of Bienor (β p = 50 ± 3 • , λ p = 35 ± 8 •). We are also able to constrain the b/a axial ratio of a triaxial Jacobi ellipsoidal body (with semi-axis a > b > c). The best fit is for b/a = 0.45 ± 0.05, which corresponds to a density value of 594 +47 −35 kg m −3 under the usual assumption of hydrostatic equilibrium and given that Bienor's rotational period is 9.17 h. However, the absolute magnitude of Bienor at several epochs is not well reproduced. We tested several explanations such as relaxing the hydrostatic equilibrium constraint, a large north-south asymmetry in the surface albedo of Bienor or even a ring system. When a ring system of similar characteristics to those of Chariklo and Chiron is included, we can fit both the lightcurve amplitude and absolute magnitude. In this case, the derived axial ratio is modified to b/a = 0.37 ± 0.10. The implied density is 678 +209 −100 kg m −3. Also, the existence of a ring is consistent with the spectroscopic detection of water ice on Bienor. Nevertheless, the other explanations cannot be discarded.
523676 (2013 UL10): the first active red centaur
Astronomy & Astrophysics, 2018
Aims. We present observations of 523676 (2013 UL10), a centaur orbiting between Jupiter and Uranus that is dynamically similar to the few tens of active centaurs that are currently known. Methods. We analysed visible BVR images of the centaur obtained at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain) to investigate the weak comet-like activity and to derive information on the nucleus surface colours and size. Results. Centaur 523676 (2013 UL10) is the only centaur known so far that has both comet-like activity and red surface colours: its nucleus has a colour index [B – R] = 1.88 ± 0.11. The nucleus R magnitude (R = 20.93 ± 0.09) allowed us to derive an upper limit for its nucleus size of D ≤ 10 km. We estimated its dust production rate to be Qd ~ 10 kg s−1 at 6.2 au (just after its perihelion passage), resulting in a timescale for the surface blanketing process τB of approximately tens of years, which is very short with respect to typical dynamical lifetime insi...
The Composition of Centaur 5145 Pholus
Icarus, 1998
The short dynamical lifetime of Pholus in its present orbit (e.g., Levison and Duncan 1993), plus its red color We present a new spectrum of the Centaur object 5145 Pholus between 1.15 and 2.4 m. We model this, and the previously and spectral properties, strongly suggest that it recently published (0.4-to 1.0-m) spectrum, using Hapke scattering entered the planetary zone from the Kuiper Disk of planetheory. Seen in absorption are the 2.04-m band of H 2 O ice tesimals. Because the Kuiper Disk is the source of the and a strong band at 2.27 m, interpreted as frozen methanol low-inclination comets, and because of the compositional and/or a photolytic product of methanol having small molecular similarities of Pholus to comets, it is reasonable to conclude weight. The presence of small molecules is indicative of a chemithat Pholus is a primitive body that has not experienced cally primitive surface, since heating and other processes relarge-scale sublimation or chemical processing through move the light hydrocarbons in favor of macromolecular carbon heating by the Sun. Instead, it has spent all but the past of the kind found in carbonaceous meteorites. The unusually 10 6 to 10 7 years of its existence in the frozen state beyond red slope of Pholus' spectrum is matched by fine grains of a about 30 AU from the Sun. refractory organic solid (tholin), as found previously by M. While the orbit of Pholus is comet-like, its dimensions Hoffmann et al. (1993, J. Geophys. Res. 98, 7403-7407) and P. D. Wilson et al. (1994, Icarus 107, 288-303). Olivine (which are an order of magnitude greater than those of a typical we model with Fo 82) also appears to be present on Pholus. comet nucleus and are more similar to many asteroids. We present a five-component model for the composite spectrum Pholus does not clearly fall into either classification. Inof all spectroscopic and photometric data available for 5145 deed, both classifications have become rather indistinct in Pholus and conclude that this is a primitive object which has not recent years, with the realization from orbital dynamics yet been substantially processed by solar heat. The properties of that some objects long considered asteroids are inactive Pholus are those of the nucleus of a large comet that has never comets (e.g., Hartmann et al. 1986) and the detection of been active.
Photometric and spectroscopic evidence for a dense ring system around Centaur (10199) Chariklo
2014
Context. A stellar occultation observed on 3rd June 2013 revealed the presence of two dense and narrow rings separated by a small gap around the Centaur object (10 199) Chariklo. The composition of these rings is not known. We suspect that water ice is present in the rings, as is the case for Saturn and other rings around the giant planets. Aims. In this work, we aim to determine if the variability in the absolute magnitude of Chariklo and the temporal variation of the spectral ice feature, even when it disappeared in 2007, can be explained by an icy ring system whose aspect angle changes with time. Methods. We explained the variations on the absolute magnitude of Chariklo and its ring by modeling the light reflected by a system as the one described above. Using X-shooter at VLT, we obtained a new reflectance spectra. We compared this new set of data with the ones available in the literature. We showed how the water ice feature is visible in 2013 in accordance with the ring configuration, which had an opening angle of nearly 34 • in 2013. Finally, we also used models of light scattering to fit the visible and near-infrared spectra that shows different characteristics to obtain information on the composition of Chariklo and its rings. Results. We showed that absolute photometry of Chariklo from the literature and new photometric data that we obtained in 2013 can be explained by a ring of particles whose opening angle changes as a function of time. We used the two possible pole solutions for the ring system and found that only one of them, α = 151.30 ± 0.5, δ = 41.48 ± 0.2 • (λ = 137.9 ± 0.5, β = 27.7 ± 0.2 •), provides the right variation of the aspect angle with time to explain the photometry, whereas the other possible pole solution fails to explain the photometry. From spectral modeling, we derived the composition of the Chariklo surface and that of the rings using the result on the pole solution. Chariklo surface is composed with about 60% of amorphous carbon, 30% of silicates and 10% of organics; no water ice was found on the surface. The ring, on the other hand, contains 20% of water ice, 40−70% of silicates, and 10−30% of tholins and small quantities of amorphous carbon.