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Register a new userNew members of Datura family
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Added by
Eva Pl\\'avalov\\'a PhD.
Publication date
2015
fields
Physics
and research's language is
English
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Asteroid families are groups of minor planets which have a common origin in catastrophic disruptions. Young asteroid families are very interesting because they represent the product of their parent bodys fragmentation before orbital and physical evolutionary processes could have changed them. A group of minor asteroids associated with the largest body Datura(1270) is of particular interest because it has enough known members and resides in the inner part of the main asteroid belt and is easy to observe. Up to now, 7 members of this family are known. Here we discuss three new members of the Datura Family: 338309(2002 VR17), 2002 RH291 and 2014 OE206. To prove that these recently-discovered members belong to the Datura family, we conducted numeric integration with all gravitational perturbation over the last 800 kyrs. In the results, we have found that 338309(2002 VR17) and 2002 RH291 are very close to the mean orbit of this family throughout the calculation. In the case of 2014 OE206, it has a strongly chaotic orbit. The possible explanation of this is in the resonance character of its orbit.
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We present a search for new planetary-mass members of nearby young moving groups (YMGs) using astrometry for 694 T and Y dwarfs, including 447 objects with parallaxes, mostly produced by recent large parallax programs from UKIRT and Spitzer. Using the BANYAN $Sigma$ and LACEwING algorithms, we identify 30 new candidate YMG members, with spectral types of T0$-$T9 and distances of $10-43$ pc. Some candidates have unusually red colors and/or faint absolute magnitudes compared to field dwarfs with similar spectral types, providing supporting evidence for their youth, including 4 early-T dwarfs. We establish one of these, the variable T1.5 dwarf 2MASS J21392676$+$0220226, as a new planetary-mass member ($14.6^{+3.2}_{-1.6}$ M$_{rm Jup}$) of the Carina-Near group ($200pm50$ Myr) based on its full six-dimensional kinematics, including a new parallax measurement from CFHT. The high-amplitude variability of this object is suggestive of a young age, given the coexistence of variability and youth seen in previously known YMG T dwarfs. Our four latest-type (T8$-$T9) YMG candidates, WISE J031624.35$+$430709.1, ULAS J130217.21$+$130851.2, WISEPC J225540.74$-$311841.8, and WISE J233226.49$-$432510.6, if confirmed, will be the first free-floating planets ($approx2-6$ M$_{rm Jup}$) whose ages and luminosities are compatible with both hot-start and cold-start evolutionary models, and thus overlap the properties of the directly-imaged planet 51 Eri b. Several of our early/mid-T candidates have peculiar near-infrared spectra, indicative of heterogenous photospheres or unresolved binarity. Radial velocity measurements needed for final membership assessment for most of our candidates await upcoming 20$-$30 meter class telescopes. In addition, we compile all 15 known T7$-$Y1 benchmarks and derive a homogeneous set of their effective temperatures, surface gravities, radii, and masses.
From 1996 to 2015 sixteen main belt asteroids were discovered exhibiting cometary activity (less than one per year), all of them during searches at the telescope. In this work we will explore another way to discover them. We reduced 192016 magnitude observations of 165 asteroids of the Themis family, using data from the astrometric-photometric database of the Minor Planet Center, MPCOBS, and measuring the absolute magnitudes from the phase plots. 25 objects of 165 (15.2%), exhibited bumps or enhancements in brightness that might indicate low level cometary activity. Since activity repeats at the same place in different orbits and in many occasions is centered at perihelion, activity might be due to water ice sublimation. As of September 2016, there are 717768 asteroids listed in the MPC files. If we assume that we do not have any false positives and the above percentage can be extrapolated to the whole Main Belt, the number of potentially active asteroid gets to the very large number of ~111.000. This number is much larger than the ones predicted in previous surveys and indicates one of three scenarios: A) there are many false positives in our detections and the real number of active asteroid is much smaller than we found, implying that the MPC astrometric-photometric database is only astrometric and not photometric. B) The location of active asteroids is restricted to the Themis family and an extrapolation to the whole belt is not possible. Or C) there are few false positives in our candidates and the main belt actually contains many low level active asteroids undetected by current surveys. Case C) would imply that the main belt is not a field of bare rocks but a graveyard of extinct comets, changing our current paradigm of the main belt. So it is of the outmost importance to verify observationally our candidates, and determine which of these scenarios is valid.
The Cygnus complex is one of the most powerful star forming regions at a close distance from the Sun (~1.4 kpc). Its richest OB association Cygnus OB2 is known to harbor many tens of O-type stars and hundreds of B-type stars, providing a large homogeneous population of OB stars that can be analyzed. Many studies of its massive population have been developed in the last decades, although the total number of OB stars is still incomplete. Our aim is to increase the sample of O and B members of Cygnus OB2 and its surroundings by spectroscopically classifying 61 candidates as possible OB-type members of Cygnus OB2. We have obtained new blue intermediate-resolution spectra suitable for spectral classification of the 61 candidates in Cygnus OB2 and surroundings. We thus performed a spectral classification of the sample using He I-II and metal lines rates, as well as the Marxist Ghost Buster (MGB) software for O-type stars and the IACOB standards catalog for B-type stars. Out of the 61 candidates, we have classified 42 stars as new massive OB-type stars, earlier than B3, in Cygnus OB2 and surroundings, including 11 O-type stars. The other candidates are discarded as they display later spectral types inconsistent with membership in the association. However, the magnitude cutoff and dust extinction introduce an incompleteness. Many O and early B stars at B > 16 mag are still undiscovered in the region. Finally, we have studied the age and extinction distribution of our sample within the region, placing them in the Hertzsprung-Russell Diagram using different stellar models in order to assess age uncertainties. Massive star formation in Cygnus OB2 seems to have proceeded from lower to higher Galactic longitudes, regardless of the details of the models used. The correlation between age and Galactic longitude previously found in the region is now confirmed.
All asteroids are currently classified as either family, originating from the disruption of known bodies, or non-family. An outstanding question is the origin of these non-family asteroids. Were they formed individually, or as members of known families but with chaotically evolving orbits, or are they members of old ghost families, that is, asteroids with a common parent body but with orbits that no longer cluster in orbital element space? Here, we show that the sizes of the non-family asteroids in the inner belt are correlated with their orbital eccentricities and anticorrelated with their inclinations, suggesting that both non-family and family asteroids originate from a small number of large primordial planetesimals. We estimate that ~85% of the asteroids in the inner main belt originate from the Flora, Vesta, Nysa, Polana and Eulalia families, with the remaining ~15% originating from either the same families or, more likely, a few ghost families. These new results imply that we must seek explanations for the differing characteristics of the various meteorite groups in the evolutionary histories of a few, large, precursor bodies. Our findings also support the model that asteroids formed big through the gravitational collapse of material in a protoplanetary disk.
We demonstrate, using the high resolution spectra from the ESPADONS spectrograph, fed with the 3.6m CFH telescope, that the strength ratios of the strong--to--weak spectral features, attributed to C$_{60}^+$, are variable. We found that in the range of expected 9366~AA C$_{60}^+$ feature there are two diffuse bands centered at 9362.0$pm$0.1 and 9365.3$pm$0.1 AA with variable intensity ratio. We confidently confirm the lack of 9428~AA feature which, in the laboratory spectra of C$_{60}^+$, is stronger than 9366~AA. The weakest laboratory feature, near 9348.4~AA, remains below the level of detection in all spectra. The intensity ratio 9577/9365 is variable. These facts contradict to their common origin and so -- the identification of some interstellar spectral features as being carried by the cation of the soccer ball. We also refined the rest wavelength position of the strongest diffuse band in this range: it is 9576.8$pm$0.1~AA.
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