- ID:
- ivo://CDS.VizieR/B/comets
- Title:
- Database of the orbital elements of comets
- Short Name:
- B/comets
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- comets.dat is an ASCII file of cometary orbital elements prepared at the "Institut de Mecanique Celeste et de Calcul des Ephemerides" (related to the Bureau des Longitudes, Paris). The research and computing needed to generate comets.dat are funded by the French Ministry of Education. The data can be freely used, provided that their origin (Bureau des longitudes) and the author (P. Rocher) are properly cited. User feed-back is encouraged. Unless otherwise specified, send comments and bug reports to: E-mail : stc@imcce.fr Fax : (33) 1 46 33 28 34 Postal mail : IMCCE - Observatoire de Paris 77 avenue Denfert Rochereau F-75014 PARIS
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/733/L31
- Title:
- Distribution of ^26^Al in the solar system
- Short Name:
- J/ApJ/733/L31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is believed that ^26^Al, a short-lived (t_1/2_=0.73Ma) and now extinct radionuclide, was uniformly distributed in the nascent solar system (SS) with the initial ^26^Al/^27^Al ratio of ~5.2x10^-5^, suggesting an external, stellar origin rather than local, solar source. However, the stellar source of ^26^Al and the manner in which it was injected into the SS remain controversial: the ^26^Al could have been produced by an asymptotic giant branch star, a supernova, or a Wolf-Rayet star and injected either into the protosolar molecular cloud, protosolar cloud core, or protoplanetary disk. Corundum (Al_2_O_3_) is predicted to be the first condensate from a cooling gas of solar composition. Here we show that micron-sized corundum condensates from ^16^O-rich ({Delta}^17^O~-25%) gas of solar composition recorded heterogeneous distribution of ^26^Al at the birth of the SS: the inferred initial ^26^Al/^27^Al ratio ranges from ~6.5x10^-5^ to <2x10^-6^; 52% of corundum grains measured are ^26^Al-poor. Abundant ^26^Al-poor, ^16^O-rich refractory objects include grossite- and hibonite-rich calcium-aluminum-rich inclusions (CAIs) in CH (high metal abundance and high iron concentration) chondrites, platy hibonite crystals in CM (Mighei-like) chondrites, and CAIs with fractionation and unidentified nuclear effects CAIs chondrites. Considering the apparently early and short duration (<0.3Ma) of condensation of refractory ^16^O-rich solids in the SS, we infer that ^26^Al was injected into the collapsing protosolar molecular cloud and later homogenized in the protoplanetary disk. The apparent lack of correlation between ^26^Al abundance and O-isotope composition of corundum grains constrains the stellar source of ^26^Al in the SS.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A153
- Title:
- EMCCD observations of the 2018 Draconids
- Short Name:
- J/A+A/635/A153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several authors predicted an outburst of the Draconid meteor shower in 2018, but with an uncertain level of activity. Optical meteor observations were used to derive the population and mass indices, flux, and radiant positions of Draconid meteors. We performed 90 minutes of multi-station observations after the predicted peak of activity were performed using highly sensitive Electron Multiplying Charge Coupled Device (EMCCD) cameras. The data calibration is discussed in detail. A novel maximum likelihood estimation method of computing the population and mass index with robust error estimation was developed. We apply the method to observed Draconids and use the values to derive the flux. Meteor trajectories are computed and compared to predicted radiant positions from meteoroid ejection models. We find a mass index of 1.74+/-0.18 in the 30 min bin after the predicted peak, and 2.32+/-0.27 in the subsequent 60 min. The location and the dispersion of the radiant are a good match to modeled values, but there is an offset of 0.4{deg} in solar longitude.
- ID:
- ivo://CDS.VizieR/J/A+A/639/A11
- Title:
- Exocomets. A Spectroscopic Survey
- Short Name:
- J/A+A/639/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be exocomets (falling evaporating bodies) around beta Pic in the early 1980s, Monly 20 stars have been reported to host exocomet-like events. We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity. We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the CaII K&H and NaI D lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies. We detected non-photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the CaII and/or NaI lines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the CaII K line are similar to those observed in beta^L Pic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with larger vsini is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (lambda Boo-like) abundances, but this would require confirmation by expanding the sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/727/91
- Title:
- Fluorescence excitation models in comets
- Short Name:
- J/ApJ/727/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ammonia is a major reservoir of nitrogen atoms in cometary materials. However, detections of ammonia in comets are rare, with several achieved at radio wavelengths. A few more detections were obtained through near-infrared observations (around the 3um wavelength region), but moderate relative velocity shifts are required to separate emission lines of cometary ammonia from telluric absorption lines in the 3um wavelength region. On the other hand, the amidogen radical (NH_2_, a photodissociation product of ammonia in the coma) also shows rovibrational emission lines in the 3um wavelength region. Thus, gas production rates for ammonia can be determined from the rovibrational emission lines of ammonia (directly) and amidogen radical (indirectly) simultaneously in the near-infrared. In this article, we present new fluorescence excitation models for cometary ammonia and amidogen radical in the near-infrared, and we apply these models to the near-infrared high-dispersion spectra of comet C/2004 Q2 (Machholz) to determine the mixing ratio of ammonia to water in the comet. Based on direct detection of NH_3_ lines, the mixing ratio of NH_3_/H_2_O is 0.46%+/-0.03% in C/2004 Q2 (Machholz), in agreement with other results. The mixing ratio of ammonia determined from the NH_2_ observations (0.31%-0.79%) is consistent but has relatively larger error, owing to uncertainty in the photodissociation rates of ammonia. At the present level of accuracy, we confirm that NH_3_ could be the sole parent of NH_2_ in this comet.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A92
- Title:
- Global plasma parameter simulation of Comet 67P
- Short Name:
- J/A+A/520/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of the plasma environment of comet 67P/Churyumov-Gerasimenko (CG) the target comet of the European Space Agency's (ESA) Rosetta mission is investigated as the comet approaches the Sun. The plasma environment is calculated in three dimensions with a hybrid plasma model. The model treats the dynamics of the solar wind protons and the cometary ions in the framework of the macroparticle approach while the electrons are treated as a massless, charge-neutralizing fluid. The simulation starts at 4.2AU and finishes at 1.3AU, when the comet is at its perihelion position. Two dimensional contour plots of the absolute value of the cometary ion mass flux and the magnetic field in the orthogonal plane of the interplanetary magnetic field are shown. The undisturbed solar wind flows from left to right. The convective electric field points downwards. The nucleus is in the middle of the simulation box. The coma is assumed to consist of water vapor and it increases by several orders of magnitude as the comet approaches the Sun. Therefore, the size of the simulation box is adapted as an animation above the contour plots shows.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/458
- Title:
- Highly excited H2 in Comets
- Short Name:
- J/ApJS/169/458
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotationally resolved molecular hydrogen transitions originating from excitation of highly excited rovibrational levels of the X^1^{SIGMA}^+^_g_ state have been systematically identified for the first time in the Far Ultraviolet Spectroscopic Explorer (FUSE) observation of comets C/2000 WM1 (LINEAR) and C/2001 A2 (LINEAR). Spectral assignments for the observed lines of H_2_ and other atomic and molecular species are given. All observed H_2_ transitions belong to the Lyman (B^1^{SIGMA}^+^_u_-X^1^{sigma}^+^_g_) and Werner (C^1^{PI}_u_-X^1^{SIGMA}^+^_g_) band systems. Resonant excitation of H_2_ by Ly{beta} and other solar lines is very limited.
- ID:
- ivo://CDS.VizieR/VII/91
- Title:
- IRAS Asteroid and Comet Survey
- Short Name:
- VII/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The main purpose of the Infrared Astronomical Satellite (IRAS) was to survey the sky in four infrared wavelength bands centered at 12, 25, 60 and 100 um. Data for 25 comets, 1811 known asteroids and ~TBD asteroids without orbits were obtained and accepted into this IRAS asteroid and comet catalog, which is the largest, least biased and most uniform survey of asteroids and comets. For the IRAS Asteroid Survey, 7,015 sightings from 1,811 individual asteroids that were of sufficient quality have been accepted into the asteroid catalog. Diameters, albedos and various technical parameters have been derived for these minor planet. The IRAS comet catalog contains the detection history for each comet reliably detected in the ADAS search. Positions were searched for all periodic comets that passed near the sun or earth during the period from 1982 to 1985 plus all comets that were observed during that period.
- 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.
