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- ID:
- ivo://CDS.VizieR/J/MNRAS/472/4634
- Title:
- Large perihelion dist. Oort spike comets
- Short Name:
- J/MNRAS/472/4634
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The complete sample of large-perihelion nearly-parabolic comets discovered during the period 1901-2010 is studied, starting with their orbit determination. Next, an orbital evolution that includes three perihelion passages (previous-observed-next) is investigated in which a full model of Galactic perturbations and perturbations from passing stars is incorporated. We show that the distribution of planetary perturbations suffered by actual large-perihelion comets during their passage through the Solar system has a deep, unexpected minimum around zero, which indicates a lack of 'almost unperturbed' comets. Using a series of simulations we show that this deep well is moderately resistant to some diffusion of the orbital elements of the analysed comets. It seems reasonable to assert that the observed stream of these large perihelion comets experienced a series of specific planetary configurations when passing through the planetary zone. An analysis of the past dynamics of these comets clearly shows that dynamically new comets can appear only when their original semimajor axes are greater than 20000au. On the other hand, dynamically old comets are completely absent for semimajor axes longer than 40000au. We demonstrate that the observed 1/a_ori_-distribution exhibits a local minimum separating dynamically new from dynamically old comets. Long-term dynamical studies reveal a wide variety of orbital behaviour. Several interesting examples of the action of passing stars are also described, in particular the impact of Gliese 710, which will pass close to the Sun in the future. However, none of the obtained stellar perturbations is sufficient to change the dynamical status of the analysed comets.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/L25
- Title:
- Li-Be-B measurements using SIMS
- Short Name:
- J/ApJ/748/L25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Beryllium-10 is a short-lived radionuclide (t_1/2_=1.4Myr) uniquely synthesized by spallation reactions and inferred to have been present when the solar system's oldest solids (calcium-aluminum-rich inclusions, CAIs) formed. Yet, the astrophysical site of ^10^Be nucleosynthesis is uncertain. We report Li-Be-B isotope measurements of CAIs from CV chondrites, including CAIs that formed with the canonical ^26^Al/^27^Al ratio of ~5x10^-5^ (canonical CAIs) and CAIs with Fractionation and Unidentified Nuclear isotope effects (FUN-CAIs) characterized by ^26^Al/^27^Al ratios much lower than the canonical value. Our measurements demonstrate the presence of four distinct fossil ^10^Be/^9^Be isochrons, lower in the FUN-CAIs than in the canonical CAIs, and variable within these classes. Given that FUN-CAI precursors escaped evaporation-recondensation prior to evaporative melting, we suggest that the ^10^Be/^9^Be ratio recorded by FUN-CAIs represents a baseline level present in presolar material inherited from the protosolar molecular cloud, generated via enhanced trapping of galactic cosmic rays. The higher and possibly variable apparent ^10^Be/^9^Be ratios of canonical CAIs reflect additional spallogenesis, either in the gaseous CAI-forming reservoir, or in the inclusions themselves: this indicates at least two nucleosynthetic sources of ^10^Be in the early solar system. The most promising locale for ^10^Be synthesis is close to the proto-Sun during its early mass-accreting stages, as these are thought to coincide with periods of intense particle irradiation occurring on timescales significantly shorter than the formation interval of canonical CAIs.
- ID:
- ivo://CDS.VizieR/J/A+AS/103/83
- Title:
- Line identifications in a fireball spectrum
- Short Name:
- J/A+AS/103/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 305 emission lines were found in a spectrum of a fireball of -9th magnitude. The identification of most of the lines is given. Also a detailed tracing of the spectrum in the range 3600-6600{AA} is presented. The tracing contains also computed synthetic spectrum and both spectra can be easily compared. The following species were found in the spectrum: Fe I, Na I, Mg I, Al I, Ca I, Ti I, Cr I, Mn I, Ni I, Mg II, Si II, Ca II, Fe II, FeO, probably also Si I, Ba II, C_2_, and possibly V I, Co I, Cu I, Ti II. The presence of other chemical elements in meteor spectra is discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A87
- Title:
- Local production rates of 67P/CG from MIRO
- Short Name:
- J/A+A/603/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using spectroscopic and continuum data measured by the MIRO instrument on board Rosetta of comet 67P/Churyumov-Gerasimenko, it is possible to derive and track the change in the water production rate, to learn how the outgassing evolves with heliocentric distance. The MIRO data are well suited to investigate the evolution of 67P, in unprecedented spatial and temporal detail. To obtain estimates of the local effective Haser production rates we developed an efficient and reliable retrieval approach with precalculated lookup tables. We employed line area ratios (H_2_^16^O/H_2_^18^O) from pure nadir observations as the key variable, along with the Doppler shift velocity, and continuum temperature. This method was applied to the MIRO data from August 2014 until April 2016. Perihelion occurred on August 13, 2015 when the comet was 1.24AU from the Sun. During the perihelion approach, the water production rates increased by an order of magnitude, and from the observations, the derived maximum for a single observation on August 29, 2015 is (1.42+/-0.51)x10^28^. Modelling the data indicates that there is an offset in the peak outgassing, occurring 34+/-10 days after perihelion. During the pre-perihelion phase, the production rate changes with heliocentric distance as r_h_^-3.8+/-0.2^; during post- perihelion, the dependence is r_h_^-4.3+/-0.2^. The comet is calculated to have lost 0.12+/-0.06% of its mass during the perihelion passage, considering only water ice sublimation. Additionally, this method provides well- sampled data to determine the spatial distribution of outgassing versus heliocentric distance. The time evolution is definitely not uniform across the surface. Pre- and post-perihelion, the surface temperature on the southern hemisphere changes rapidly, as does the sublimation rate with an exponent of ~-6. There is a strong latitudinal dependence on the r_h_ exponent with significant variation between northern and southern hemispheres, and so the average over the comet surface may only be of limited importance. We present more detailed regional variation in the outgassing, thereby demonstrating that the highest derived production rates originate from the Wosret, Neith, and Bes regions during perihelion.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A80
- Title:
- 122 long-period comets non-gravitational param.
- Short Name:
- J/A+A/633/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The original 1/a-distribution is the only observational basis for the origin of long-period comets (LPCs) and the dynamical properties of the Oort Cloud. Although they are very subtle in the motion of these comets, non-gravitational effects can cause major changes in the original semimajor axis, 1/a_ori_ We obtained reliable non-gravitational orbits for as many LPCs with small perihelion distances of q<3.1au as possible, and determined the corresponding shape of the Oort spike. We determined the osculating orbits of each comet using several data-processing methods, and selected the preferred orbit using a few specific criteria. The distribution of 1/a_ori_ for the whole comet sample was constructed using the individual Gaussian distribution we obtained for the preferred solution of each comet. The derived distribution of 1/a_ori_ for almost all known small-perihelion Oort spike comets was based on 64% of the non-gravitational orbits. This was compared with the distribution based on purely gravitational orbits, as well as with 1/a_ori_ constructed earlier for LPCs with q>3.1 au. We present a statistical analysis of the magnitudes of the non-gravitational acceleration for about 100~LPCs. The 1/a_ori_-distribution, which is based mainly on the non-gravitational orbits of small-perihelion Oort spike comets, is shifted by about 10x10^-6^au^-1^ to higher values of 1/a_ori_ compared with the distribution that is obtained when the non-gravitational effects on comet motion are ignored. We show the differences in the 1/a_ori_-distributions between LPCs with q<3.1au and those with q>3.1au. These findings indicate the important role of non-gravitational~acceleration in the motion and origin of LPCs and in the formation of the Oort Cloud.
- ID:
- ivo://CDS.VizieR/J/A+A/287/990
- Title:
- Meteor stream activity.
- Short Name:
- J/A+A/287/990
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/629/A71
- Title:
- mm-dm-sized meteoroids spectral & orbital survey
- Short Name:
- J/A+A/629/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the spectra, material properties and orbital distribution of mid-sized meteoroids. Our study aims to distinguish characteristics of different size populations of meteoroids and reveal the heterogeneity of identified meteoroid streams. The emission spectra and multi-station meteor trajectories were collected within the AMOS network observations. The sample is based on 202 meteors of -1 to -14 magnitude, corresponding to meteoroids of mm-dm in size. Overall increase of Na content compared to the population of mm-sized meteoroids was detected, reflecting weaker effects of space weathering processes on larger meteoroids. We report on very low ratio of pure iron meteoroids and the discovery of a new spectral group of Fe-rich meteors. The majority of meteoroids on asteroidal orbits were found to be chondritic. Thermal processes causing Na depletion and physical processes resulting in Na-rich spectra are described and linked to characteristically increased material strengths. Numerous major and minor shower meteors were identified in our sample, revealing various degrees of heterogeneity within Halley-type, ecliptical and sungrazing meteoroid streams.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A48
- Title:
- Mm-spectra of comets C/2001 Q2 and C/2002 T7
- Short Name:
- J/A+A/559/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical composition of comets can be inferred using spectroscopic observations in submillimeter and radio wavelengths. We aim to compare the production rates ratio of several volatiles in two comets, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), which are generally regarded as dynamically new comets likely to originate in the Oort cloud. This type of comets is considered to be composed of primitive material that has not undergone considerable thermal processing. The line emission in the coma was measured in the comets, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), that were observed on five consecutive nights, 7-11 May 2004, at heliocentric distances of 1.0 and 0.7AU, respectively, by means of high resolution spectroscopic observations using the 10-m Submillimeter Telescope (SMT) at the Arizona Radio Observatory (ARO). Both objects became very bright and reached naked-eye visibility during their perihelion passage in the spring of 2004.
- ID:
- ivo://CDS.VizieR/J/ApJ/792/30
- Title:
- NEOWISE magnitudes for near-Earth objects
- Short Name:
- J/ApJ/792/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft has been brought out of hibernation and has resumed surveying the sky at 3.4 and 4.6 {mu}m. The scientific objectives of the NEOWISE reactivation mission are to detect, track, and characterize near-Earth asteroids and comets. The search for minor planets resumed on 2013 December 23, and the first new near-Earth object (NEO) was discovered 6 days later. As an infrared survey, NEOWISE detects asteroids based on their thermal emission and is equally sensitive to high and low albedo objects; consequently, NEOWISE-discovered NEOs tend to be large and dark. Over the course of its three-year mission, NEOWISE will determine radiometrically derived diameters and albedos for ~2000 NEOs and tens of thousands of Main Belt asteroids. The 32 months of hibernation have had no significant effect on the mission's performance. Image quality, sensitivity, photometric and astrometric accuracy, completeness, and the rate of minor planet detections are all essentially unchanged from the prime mission's post-cryogenic phase.
