The non-convex shape of (234) Barbara, the first Barbarian (original) (raw)
Related papers
Shape and spin determination of Barbarian asteroids
2017
Context. The so-called Barbarian asteroids share peculiar, but common polarimetric properties, probably related to both their shape and composition. They are named after (234) Barbara, the first on which such properties were identified. As has been suggested, large scale topographic features could play a role in the polarimetric response, if the shapes of Barbarians are particularly irregular and present a variety of scattering/incidence angles. This idea is supported by the shape of (234) Barbara, that appears to be deeply excavated by wide concave areas revealed by photometry and stellar occultations. Aims. With these motivations, we started an observation campaign to characterise the shape and rotation properties of Small Main-Belt Asteroid Spectroscopic Survey (SMASS) type L and Ld asteroids. As many of them show long rotation periods, we activated a worldwide network of observers to obtain a dense temporal coverage. Methods. We used light-curve inversion technique in order to d...
Shapes and rotational properties of thirty asteroids from photometric data
Icarus, 2003
We have analyzed photometric lightcurves of 30 asteroids, and present here the obtained shapes, rotational periods and pole directions. We also present new photometric observations of five asteroids. The shape models indicate the existence of many features of varying degrees of irregularity. Even large main-belt asteroids display such features, so the resulting poles and periods are more consistent than those obtained by simple ellipsoid-like models. In some cases the new rotational parameters are rather different from those obtained previously, and in a few cases there were no proper previous estimates at all. and 694 Ekard. New observations of 21 Lutetia, 37 Fides, 85 Io, 129 Antigone, and 135 Hertha are presented in Section 4. In Section 5 we sum up the paper and discuss some future prospects of the analysis of photometric and complementary data.
Polarimetry of the Asteroid (599) Luisa: a New Barbarian
Solar System Research, 2020
The results of polarimetric observations of the asteroid (599) Luisa carried out on the same type of aperture photoelectric polarimeters of the 2.6-m reflector of the Crimean Astrophysical Observatory and the Zeiss 2000 telescope of the Terskol Peak Observatory in November 2018 and February 2019 are presented. Based on these and available literature data, the parameters of the composite phase dependence of the polarization degree are obtained: P min =-1.68%, α min = 14.7°, α inv = 29.2°, which indicates that the asteroid belongs to the class of "Barbarians". The absolute value of the negative polarization degree of the asteroid in the range of the BVRI photometric bands is shown to increase with wavelength, which contradicts the data of Bagnulo et al. (2015) but is consistent with the spectral polarization behavior of other silicate S-, K-, and Ltype asteroids, including well-known Barbarians. Possible causes of differences in the spectral behavior of the polarization degree of this asteroid are discussed. The properties of the asteroid (599) Luisa are unique in that it combines spectral properties of silicate L-type asteroids and polarization properties (P min and the slope h) of low-albedo C and Ch asteroids.
Radar observations of Asteroids 64 Angelina and 69 Hesperia
Icarus, 2011
Context. In the past decade, more than one hundred asteroid models were derived using the lightcurve inversion method. Measured by the number of derived models, lightcurve inversion has become the leading method for asteroid shape determination. Aims. Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population. Methods. We use sparse photometry from selected observatories from the AstDyS database (Asteroids-Dynamic Site), either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We investigate various correlations between several asteroid parameters and characteristics such as the rotational state and diameter or family membership. We focus on the distribution of ecliptic latitudes of pole directions. We create a synthetic uniform distribution of latitudes, compute the method bias, and compare the results with the distribution of known models. We also construct a model for the long-term evolution of spins. Results. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. For another 30 asteroids we present their partial models, i.e., an accurate period value and an estimate of the ecliptic latitude of the pole. The addition of new models increases the total number of models derived by the lightcurve inversion method to ∼200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D < 30 km) is clustered towards ecliptic poles and can be explained by the YORP thermal effect while the latitude distribution of larger asteroids (D > 60 km) exhibits an evident excess of prograde rotators, probably of primordial origin.
Shape, size and multiplicity of main-belt asteroidsI. Keck Adaptive Optics survey
Icarus, 2006
This paper presents results from a high spatial resolution survey of 33 main-belt asteroids with diameters >40 km using the Keck II Adaptive Optics (AO) facility. Five of these () were confirmed to have satellite. Assuming the same albedo as the primary, these moonlets are relatively small (∼5% of the primary size) suggesting that they are fragments captured after a disruptive collision of a parent body or captured ejecta due to an impact. For each asteroid, we have estimated the minimum size of a moonlet that can positively detected within the Hill sphere of the system by estimating and modeling a 2-σ detection profile: in average on the data set, a moonlet located at 2/100 × R Hill (1/4 × R Hill ) with a diameter larger than 6 km (4 km) would have been unambiguously seen. The apparent size and shape of each asteroid was estimated after deconvolution using a new algorithm called AIDA. The mean diameter for the majority of asteroids is in good agreement with IRAS radiometric measurements, though for asteroids with a D < 200 km, it is underestimated on average by 6-8%. Most asteroids had a size ratio that was very close to those determined by lightcurve measurements. One observation of 104 Klymene suggests it has a bifurcated shape. The bi-lobed shape of 121 Hermione described in Marchis et al. [Marchis, F., Hestroffer, D., Descamps, P., Berthier, J., Laver, C., de Pater, I., 2005c. Icarus 178, 450-464] was confirmed after deconvolution. The ratio of contact binaries in our survey, which is limited to asteroids larger than 40 km, is surprisingly high (∼6%), suggesting that a non-single configuration is common in the main-belt. Several asteroids have been analyzed with lightcurve inversions. We compared lightcurve inversion models for plane-of-sky predictions with the observed images (9 Metis, 52 Europa, 87 Sylvia, 130 Elektra, 192 Nausikaa, and 423 Diotima, 511 Davida). The AO images allowed us to determine a unique photometric mirror pole solution, which is normally ambiguous for asteroids moving close to the plane of the ecliptic (e.g., 192 Nausikaa and 52 Europa). The photometric inversion models agree well with the AO images, thus confirming the validity of both the lightcurve inversion method and the AO image reduction technique.
Figure of the double Asteroid 90 Antiope from adaptive optics and lightcurve observations
Icarus, 2007
A long-term adaptive optics (AO) campaign of observing the double Asteroid (90) Antiope has been carried out in 2003–2005 using 8–10-m class telescopes, allowing prediction of the circumstances of mutual events occurring during the July 2005 opposition [Marchis, F., Descamps, P., Hestroffer, D., Berthier, J., de Pater, I., 2004. Bull. Am. Astron. Soc. 36, 1180]. This is the first opportunity to use complementary lightcurve and AO observations to extensively study the (90) Antiope system, an interesting visualized binary doublet system located in the main belt. The orbital parameters derived from the AO observations have served as input quantities for the derivation of a whole set of other physical parameters (namely shapes, surface scattering, bulk density, and internal properties) from analysis of collected lightcurves. To completely model the observed lightcurves, we employed Roche figures to construct an overall shape solution. The combination of these complementary observations has enabled us to derive a reliable physical and orbital solution for the system. Our model is consistent with a system of slightly non-spherical components, having a size ratio of 0.95 (with Ravg=42.9±0.5 kmRavg=42.9±0.5 km, separation=171±1 km=171±1 km), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves suggests that the real shapes of the components do not depart from Roche equilibrium figures by more than 10%. The J2000 ecliptic coordinates of the pole of the system are λn=200°±2°λn=200°±2° and αn=38°±2°αn=38°±2°. The orbital period was refined to P=16.5051±0.0001 hP=16.5051±0.0001 h, and the density is found to be slightly lower than previous determinations, with a value of 1.25±0.05 g/cm31.25±0.05 g/cm3, leading to a significant macro-porosity of 30%. Possible scenarios for the origin of the system are also discussed.
Lightcurve Analysis of Five Taxonomic A-class Asteroids
2011
All observations reported here were made at the Xuyi Observatory (D29) in China where the equipment consists of a 0.4-m f/10 Meade LX200 Schmidt-Cassegrain (SCT), Apogee Alta U6 CCD camera without shutter, and a clear filter. The image scale was 1.3 arcseconds per pixel. Exposure time was 90 seconds. Because there was no shutter, we took a light frame and then a bias frame by removing smear caused by the stars moving through the field during the exposure. Calibration of these images was done by using master twilight flats or a supersky flat frame. All calibration frames were created using IDL. MPO Canopus was used to measure the processed images and do the period analysis of the lightcurve. 121 Hermione. This 209 km C-type asteroid is a binary system (Marchis, 2005) belonging to the Cybele family. In all, 272 images were taken on 2011 March 7 and covered one synodic period (5.55128 h, JPL Solar System Dynamics website). The resulting lightcurve shows an amplitude of 0.08 ± 0.01 mag. 620 Drakonia. Images were taken on 2011 Feb 24 and Mar 8. There were not enough data to form a complete curve. Assuming a period near that reported by Warner (2002), we found a good fit with P = 5.480 ± 0.003 h and A = 0.65 ± 0.01 mag. 877 Walkure. Rene Roy (Behrend 2010) reported a period of 17.436 h. New observations on seven nights from 2011 Jan 3 to March 26 indicate a period of 17.424 ± 0.004 h with an amplitude of 0.44 ± 0.02 mag. 933 Susi. Data were collected from 2011 Mar 7 to 9. A period of 4.621 ± 0.002 h was determined with an amplitude of 0.52 ± 0.01 mag. The results are consistent with that reported by Higgins (2011). 2903 Zhuhai. This S-type asteroid belonging to the Maria family was worked by Alvarez et al. (2004), who were looking for possible correlations between rotational periods, amplitudes, and sizes. Based on their observations, they reported a period of 6.152 h. Our new observations on two nights (2010 Dec 28 and 29) show a period of 5.27 ± 0.01 h with amplitude 0.55 ± 0.02 mag. The data were checked against the period of 6.152 h reported by Alvarez but this produced a very unconvincing fit.
Astronomy & Astrophysics, 2007
Context. For a large group of post-AGB binaries, the presence of a stable reservoir of dust is postulated. Although this reservoir will influence the final evolution stages of these objects significantly, its actual geometry and structure remains largely unknown. Aims. We aim at determining the dust morphology of a member of this group, IRAS 08544-4431. Methods. We use the interferometric capabilities of the AMBER and MIDI instruments, operating in the K and N-band respectively. The high spatial resolution measurements are used in conjunction with the broad band spectral characteristics to determine the dust geometry, based on self consistent 2D radiative transfer models. Results. We resolve the object in both K and N. Moreover, using the closure phase capabilities of AMBER, we measure in the K-band a large asymmetry of the dusty environment. The interferometric data are clearly incompatible with a spherical outflow. We model the dusty environment with a passive irradiated dusty disc model. Although this model is constrained mainly on the basis of the spectral energy distribution, it reproduces simultaneously the amplitude and closure phase of the visibilities, in both wavelength bands. Conclusions. Our model of a passive, irradiated disc in equilibrium gives an excellent fit to both the K and N-band visibilities and closure phase. The dust around this evolved binary star is indeed locked in a circumbinary disc with a significant scale height. Grain growth, settling, radial mixing and crystallization are efficient in such an environment. We conclude that the circumbinary disc of this evolved object, is governed by the same physical processes that govern the proto-planetary discs around young stellar objects.
Lightcurves of the Karin Family Asteroids
Advances in Geosciences, 2006
The Karin family is a young asteroid family formed by an asteroid breakup 5.8 Myr ago. Since the members of this family probably have not experienced significant orbital or collisional evolution yet, it is possible that they still preserve properties of the original family-forming event in terms of their spin state. We carried out a series of photometric observations of the Karin family asteroids, and here we report on the analysis of the lightcurves including the rotation period of eleven members. The mean rotation rate of the Karin family members turned out to be much lower than those of near-Earth asteroids or small main belt asteroids (diameter D < 12 km), and even lower