We present the latest results of the Meudon Multicolor Survey. This survey is aimed at characterizing the color properties and trends of Centaurs and trans-Neptunian objects. We report IJHK ...photometry of objects obtained with CFHT-IR at the 3.6 m Canada-France-Hawaii Telescope (Hawaii), JHK photometry with INGRID at the 4.2 m William Hershel Telescope (La Palma), and BVRI photometry with OIG at the 3.6 m Telescopio Nazionale Galileo Telescope (La Palma). We present visible-near-IR colors for 38 objects. Either these were acquired simultaneously, or the new near-IR photometry was tied to previously published visible measurements using the I magnitude measured in both sets. This large sample allows an extended characterization of the color properties of these primitive objects over the B (0.4 mm) to K (2.2 mm) wavelength range. We performed a detailed statistical analysis of all available IR colors in order to search for significant trends. The most relevant conclusion about visible and near-IR color-color correlations is that, basically, JHK bands alone do not show evidence of correlations, either between them or with BVRIJ bands. Only Centaurs show an anticorrelation between visible colors and H - K. Colors within each dynamical family compare very similarly.
We present here the latest
B
−
V
,
V
−
R
, and
R
−
I
color measurements obtained with the CFH12K mosaic camera of the 3.6-m Canada–France–Hawaii Telescope (CFHT). This work is the latest extension of ...the Meudon Multicolor Survey (2MS) and extends the total number of Centaurs and trans-neptunian objects (TNOs) in the dataset to 71. With this large and homogeneous dataset, we performed relevant statistical analyses to search for correlations with physical and orbital parameters and interrelations with related populations (cometary nuclei and irregular satellites). With a larger dataset, we confirm the correlations found for the Classical TNOs in our previous survey: some colors are significantly correlated with perihelion distance and inclination. The only exception is with the eccentricity. However, results strongly depend on which objects are considered Classicals, and with a dynamically more restricted definition these correlations are no longer present. We also find that strongly significant trends with orbital parameters are not detected for Centaurs, Plutinos or scattered disk objects (SDOs). We also make for the first time reliable statistical comparison between TNOs and related populations (e.g., Centaurs, irregular satellites, short period comets—i.e., SPCs). We find that (1) the colors of SPCs do not match either their TNO or Centaur precursors, and this suggests that some process modifies the surface of SPCs at entry into the inner Solar System. The only exception concerns colors of SDOs from which we could statistically assess that SPCs and SDOs could be drawn from a same single parent distribution. (2) Not surprisingly, Centaurs are compatible with each of the Edgeworth–Kuiper belt dynamical groups at a highly significant level except with the SDOs. (3) Centaurs' colors still present a strong dichotomy between a neutral/slightly red group (e.g., Chiron) and a very red group (e.g., Pholus). (4) The irregular satellite population is not compatible with any of the Centaur, Plutino or Classical populations; however, the similarity of their color properties with SDOs suggests that both groups can be extracted from the same parent distribution. However, due to the small number of Centaurs and SDOs these conclusions cannot be taken as definitive.
This study presents an alternative approach for the absorption of impact energy that uses the internal pressurization of structures in the framework of a crash‐adaptive response. Numerical ...simulations were conducted on axial impact of thin‐walled tubular structures with circular cross section that serve as an approximation to a front crash box of a motor vehicle. The main objective of this work consists in studying the effect of internal pressurization of tubular structures in a crashworthiness application, as well as the possibility to obtain a reduction in wall thickness thus improving weight efficiency. A numerical study is presented for an internal pressure of 20 bar and tubular structures of circular section and 1.14 mm thickness. Numerical simulations were performed recurring to LS‐DYNA explicit dynamics software while considering for the material a stainless steel alloy that is a material with interest for crashworthiness applications and manufacturing requisites due to its balance between strength, ductility and energy absorption. The results obtained allow concluding that recurring to internal pressurization it is feasible to reduce the wall thickness and have an impact resistance identical to the original while improving overall efficiency.
Neptune Trojans and Plutinos are two subpopulations of trans-Neptunian objects located in the 1:1 and the 3:2 mean motion resonances with Neptune, respectively, and therefore protected from close ...encounters with the planet. However, the orbits of these two kinds of objects may cross very often, allowing a higher collisional rate between them than with other kinds of trans-Neptunian objects, and a consequent size distribution modification of the two subpopulations. Observational colors and absolute magnitudes of Neptune Trojans and Plutinos show that i) there are no intrinsically bright (large) Plutinos at small inclinations; ii) there is an apparent excess of blue and intrinsically faint (small) Plutinos; and iii) Neptune Trojans possess the same blue colors as Plutinos within the same (estimated) size range do. For the present subpopulations we analyzed the most favorable conditions for close encounters/collisions and address any link there could be between those encounters and the sizes and/or colors of Plutinos and Neptune Trojans. We also performed a simultaneous numerical simulation of the outer Solar System over 1 Gyr for all these bodies in order to estimate their collisional rate. We conclude that orbital overlap between Neptune Trojans and Plutinos is favored for Plutinos with large libration amplitudes, high eccentricities, and small inclinations. Additionally, with the assumption that the collisions can be disruptive creating smaller objects not necessarily with similar colors, the present high concentration of small Plutinos with small inclinations can thus be a consequence of a collisional interaction with Neptune Trojans and such hypothesis should be further analyzed.
Observability of comets with Gaia Tozzi, G.P.; Dell'Oro, A.; Peixinho, N.
Planetary and space science,
December 2012, 2012-12-00, 20121201, Letnik:
73, Številka:
1
Journal Article
Recenzirano
The Gaia mission is a precious opportunity to collect a large amount of interesting data about the dynamical and physical properties of the minor bodies of our Solar System. About a quarter of ...million of asteroids will be detected by Gaia, but likely a number of active and non-active comets will cross the fields of view of its telescopes. Gaia's 20 magnitude limit for detection represents, on one hand, a critical factor for the completeness of the sample of the observed cometary bodies. On the other hand, the particular scanning mode of the sky specifically designed for Gaia will provide a good time and sky coverage reducing the effects of the observational bias. In any case it is difficult to predict a definitive statistics of the detections of comets. In this paper we discuss the features of the signal of comets we expect when they will be detected by Gaia. In particular, we show how the dust coma has a prominent role for the final output CCD signal, according to the instrument consolidated specifications, affecting the shape and extension of the instrument point spread function in a different way respect to the case of the asteroids. These conclusions should be taken into account for the development of software for the mission data processing.
► Gaia will observe different kinds of minor bodies. ► Detectability of comets by Gaia. ► Peculiar observational features of the comets. ► For the Gaia detector the major contribution is from nucleus and dust coma.
We report 43 new visible colors of Centaurs and TNOs, obtained at NTT and VLT telescopes under the “ESO large program on physical properties of Centaurs and TNOs.” Merging these new measurements with ...those obtained during the first part of the program (Boehnhardt et al., 2002, Astron. Astrophys. 395, 297–303) and the “Meudon Multicolor Survey” (Doressoundiram et al., 2002, Astron. J. 124, 2279–2296) we have a unique dataset of 109 objects. We checked for correlations and trends between colors, physical and orbital parameters, carrying out an analysis based on Monte Carlo simulation to account for observational error bars. Centaurs show no evidence for correlation between
V−
R vs.
R−
I colors which raises the hypothesis that more than one single coloring process might be acting on their surfaces. Classical objects seem to be composed of two different color populations: objects with
i<4.5° display only red colors while those with
i>4.5° display the whole range of colors from blue to very red. The possibility that the low inclined population is misguiding global conclusions is analyzed. Classical objects also show a stronger color–perihelion correlation for intrinsically brighter objects, corresponding to critical estimated sizes of different formation/evolutionary histories. Scattered disk objects show color resemblances with the classical objects at
i>12°, hence surface reflectivities resemblances, pointing to a common origin. No color–aphelion trend is found for SDOs, as expected from the intense irradiation by galactic cosmic-rays beyond the solar wind termination shock. Plutinos show a color–absolute magnitude trend, in which all the intrinsically faintest objects are blue. We see many red Plutinos in highly inclined and highly eccentric orbits, that should have originated in a primordial inner disk under Gomes (2003, Icarus 161, 404–418) migration scenario. This seems to invalidate the assumption that objects originated in this inner disk are mainly blue. Finally, we also find six candidates for light–curve studies: four objects (1998 WU
31, 1999 OE
4, 1999 OX
3, and 2001 KP
77) present significant short term
R-magnitude variability, and two objects (1999 XX
143 and 2000 GP
183) evidence possible color variations with rotation.
Context. Centaurs are the transitional population between trans-Neptunian objects (TNOs) and Jupiter-family comets. Their physical properties provide an insight into TNO properties, but only under ...restricted conditions since Centaurs are closer to the Sun and Earth. For this reason it is possible to access the smaller ones, which is more difficult to do with the TNO population. Aims. The goal of this work is to characterize a set of 16 Centaurs in terms of their size, albedo, and thermal properties. We study the correlations, for a more extended sample obtained from the literature, of diameter, albedo, orbital parameters, and spectral slopes. Methods. We performed three-band photometric observations using Herschel-PACS and used a consistent method for the data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70, 100, and 160 μm. Additionally, we used Spitzer-MIPS flux densities at 24 and 70 μm when available. We also included in our Centaur sample scattered disk objects, a dynamical family of TNOs, using results previously published by our team, and some Centaurs observed only with the Spitzer-MIPS instrument. Results. We have determined new radiometric sizes and albedos of 16 Centaurs. The first conclusion is that the albedos of Centaur objects are not correlated with their orbital parameters. Similarly, there is no correlation between diameter and orbital parameters. Most of the objects in our sample are dark (pv< 7%) and most of them are small (D< 120 km). However, there is no correlation between albedo and diameter, in particular for the group of small objects as albedo values are homogeneously distributed between 4 to 16%. The correlation with the color of the objects showed that red objects are all small (mean diameter 65 km), while the gray ones span a wide range of sizes (mean diameter 120 km). Moreover, the gray objects tend to be darker, with a mean albedo of 5.6%, compared with a mean of 8.5% (ranging from 5 to 15%) for the red objects.
Context. The Kuiper belt is formed of planetesimals which failed to grow to planets and its dynamical structure has been affected by Neptune. The classical Kuiper belt contains objects both from a ...low-inclination, presumably primordial, distribution and from a high-inclination dynamically excited population. Aims. Based on a sample of classical trans-Neptunian objects (TNOs) with observations at thermal wavelengths we determine radiometric sizes, geometric albedos and thermal beaming factors for each object as well as study sample properties of dynamically hot and cold classicals. Methods. Observations near the thermal peak of TNOs using infrared space telescopes are combined with optical magnitudes using the radiometric technique with near-Earth asteroid thermal model (NEATM). We have determined three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and 160.0 μm and Spitzer/MIPS at 23.68 and 71.42 μm when available. We use reexamined absolute visual magnitudes from the literature and ground based programs in support of Herschel observations. Results. We have analysed 18 classical TNOs with previously unpublished data and re-analysed previously published targets with updated data reduction to determine their sizes and geometric albedos as well as beaming factors when data quality allows. We have combined these samples with classical TNOs with radiometric results in the literature for the analysis of sample properties of a total of 44 objects. We find a median geometric albedo for cold classical TNOs of 0.14-0.07+0.09 and for dynamically hot classical TNOs, excluding the Haumea family and dwarf planets, 0.085-0.045+0.084. We have determined the bulk densities of Borasisi-Pabu (2.1-1.2+2.6 g cm-3), Varda-Ilmarë (1.25-0.43+0.40 g cm-3) and 2001 QC298 (1.14-0.30+0.34 g cm-3) as well as updated previous density estimates of four targets. We have determined the slope parameter of the debiased cumulative size distribution of dynamically hot classical TNOs as q = 2.3 ± 0.1 in the diameter range 100 < D < 500 km. For dynamically cold classical TNOs we determine q = 5.1 ± 1.1 in the diameter range 160 < D < 280 km as the cold classical TNOs have a smaller maximum size.
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