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  • 1
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 625 ( 2019-5), p. A42-
    Abstract: Context. The tenuous nitrogen (N 2 ) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. Aims. The main goals of this study are ( i ) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and ( ii ) to constrain the structure of the lower atmosphere using a central flash observed in 2015. Methods. Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 μ bar to 10 nbar). Results. ( i ) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N 2 ice are derived. ( ii ) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4–7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2019
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 2
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 670 ( 2023-2), p. A159-
    Abstract: Context. Hyperactive comets are a small group of comets whose activity is higher than expected. They seem to emit more water than would normally be expected given the size of their nucleus. Comet 46P/Wirtanen (hereafter, 46P) is among these objects of interest. Investigating its activity and composition evolution could provide clues about its origins and its formation region in the Solar nebulae. Aims. Given the exceptional close approach of comet 46P to the Earth in 2018, we aim to study the evolution of its activity and composition as a function of heliocentric distances before and after perihelion. Methods. We used both TRAPPIST telescopes to monitor the comet for almost a year with broad and narrow-band filters. We derived the production rates of five gaseous species (OH, NH, CN, C 3 , and C 2 ) using a Haser model as well as the A( θ )f ρ dust proxy parameter. The comet was also observed with the two optical high-resolution spectrographs UVES and ESPRESSO, mounted on the 8-m ESO VLT, to measure the isotopic ratios of C and N, along with the oxygen forbidden-line ratios and the NH 2 ortho-to-para ratios. Results. Over nearly a year, we followed the rise and decline of the production rates of different species as well as the dust activity of 46P on both pre- and post-perihelion. Relative abundances with respect to CN and OH along the orbit of the comet show constant and symmetric abundance ratios and a typical coma composition. We determined the rotation period of the nucleus using high-cadence observations and long series of CN images on several nights. We obtained a value of (9.18±0.05) hours at perihelion. Using the high-resolution spectra of 46P coma, we derived C and N isotopic ratios of 100±20 and 150±30 as well as a green-to-red forbidden oxygen [OI] line ratio of 0.23±0.02. We measured a NH 2 ortho-to-para ratio of 3.31 ±0.03 and derived an ammonia ratio of 1.19±0.03, corresponding to a spin temperature of 27±1 K. Conclusions. Narrow-band observations show that comet 46P is a hyperactive comet for which 40% of its nucleus surface is active. It has a typical composition, similar to other normal comets; however, an asymmetric behavior with respect to perihelion has been seen in its activity, which is typical of seasonal effects. Photometric measurements show no evidence for a change in the rotation period of the nucleus during this apparition. High-resolution spectra show that 46P has typical NH 2 ortho-to-para, [OI] lines ratios, and C and N isotopic ratios.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 3
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 640 ( 2020-8), p. A54-
    Abstract: We report on photometry and high-resolution spectroscopy of the chemically peculiar Jupiter-family comet (hereafter JFC) 21P/Giacobini-Zinner. Comet 21P is a well-known member of the carbon-chain-depleted family, but also displays a depletion of amines. We continuously monitored the comet over more than seven months with the two TRAPPIST telescopes (TN and TS), covering a wide heliocentric distance range from 1.60 au inbound to 2.10 au outbound with a perihelion at 1.01 au on September 10, 2018. We computed and followed the evolution of the dust- (represented by Afρ ) and gas-production rates of the daughter species OH, NH, CN, C 3 , and C 2 and their relative abundances to OH and to CN over the cometary orbit. We compared them to those measured in the previous apparitions. The activity of the comet and its water production rate reached a maximum of (3.72 ± 0.07) × 10 28 mol s −1 on August 17, 2018 ( r h = 1.07 au), 24 days before perihelion. The peak value of A (0) fρ was reached on the same date (1646 ± 13) cm in the red filter. Using a sublimation model for the nucleus, we constrained the active surface of the nucleus using the slow-rotator model. The abundance ratios of the various species are remarkably constant over a wide range of heliocentric distances before and after perihelion, showing a high level of homogeneity of the ices in the surface of the nucleus. The behaviour and level of the activity of the comet is also remarkably similar over the last five orbits. In the coma dust colour, 21P shows reflective gradients similar to JFCs. We obtained a high-resolution spectrum of 21P with UVES at ESO Very Large Telescope one week after perihelion. Using the CN B-X (0, 0) violet band, we measured 12 C/ 13 C and 14 N/ 15 N isotopic ratios of 100 ± 10 and 145 ± 10, respectively, both in very good agreement with the ratios commonly found in comets. We measured an ortho-para abundance ratio of NH 3 of 1.16 ± 0.02, corresponding to a nuclear spin temperature of T spin = 27 ± 1 K, which is similar to other comets. While the abundance ratios in the gaseous coma reveal a peculiar composition, the isotopic and ortho-to-para ratios appear entirely normal. We performed a dynamical simulation of 21P and found that it is likely a young member of the JFC population. We favour a pristine composition scenario to explain the chemical peculiarities of this comet.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    IOP Publishing ; 2020
    In:  Journal of Physics: Conference Series Vol. 1412, No. 17 ( 2020-01-01), p. 172005-
    In: Journal of Physics: Conference Series, IOP Publishing, Vol. 1412, No. 17 ( 2020-01-01), p. 172005-
    Abstract: We will present our recent results in the study of electron-induced reactivity of ionized and neutral molecules. The Configuration Interaction method and the Multichannel Quantum Defect Theory have been employed in order to obtain cross sections for collisions of electrons with ArH + , HD + , N 2 and CO 2 .
    Type of Medium: Online Resource
    ISSN: 1742-6588 , 1742-6596
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 2166409-2
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  • 5
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 676 ( 2023-8), p. A105-
    Abstract: Aims. We report on the composition of comet C/2021 A1 (Leonard) as measured by CRIRES + , the upgraded high resolution infrared echelle spectrometer of VLT/ESO. We compare our results with those obtained in the near-UV-visible using TRAPPIST-South. Methods. C/2021 A1 (Leonard) was observed with CRIRES + on December 29, 2021 and January 1–3, 2022, and monitored almost daily using TRAPPIST-South from about mid-December 2021 to the end of January 2022. During the TRAPPIST observations the comet showed (almost) periodic outbursts, with an estimated interval of about 4.4 days. One of these outbursts occurred close in time with our CRIRES + observations on January 1, allowing us to investigate fresh material released from the nucleus. Both data sets were reduced using established algorithms tailored for each telescope and instrument. The obtained results in the two spectral ranges were searched for correlations and similarities to compare the primary and secondary species in the coma. Results. The abundance ratios (with respect to water) of CH 3 OH, C 2 H 6 , and CH 4 in C/2021 A1, as measured in the infrared with CRIRES + , are lower than the average values measured in other comets, suggesting a depletion in organics for this comet. On the contrary, measurements in the near UV-Visible spectral region obtained close in time with TRAPPIST-South show a C 2 /CN ratio that falls in the typical range. The different conclusions that can be reached observing the same comet in different spectral ranges (organic depleted vs. organic typical) open a series of questions on the processes occurring in the coma. Their comprehensive interpretation requires deeper investigations in future studies.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 6
    Online Resource
    Online Resource
    EDP Sciences ; 2018
    In:  Astronomy & Astrophysics Vol. 615 ( 2018-7), p. A53-
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 615 ( 2018-7), p. A53-
    Abstract: Context. In order to improve our understanding of the kinetics of the cometary coma, theoretical studies of the major reactive collisions in these environments are needed. Deep in the collisional coma, inelastic collisions between thermal electrons and molecular ions result in recombination and vibrational excitation, the rates of these processes being particularly elevated due to the high charged particle densities in the inner region. Aims. This work addresses the dissociative recombination, vibrational excitation, and vibrational de-excitation of electrons with CO + molecular cations. The aim of this study is to understand the importance of these reactive collisions in producing carbon and oxygen atoms in cometary activity. Methods. The cross-section calculations were based on multichannel quantum defect theory. The molecular data sets, used here to take into account the nuclear dynamics, were based on ab initio R-matrix approach. Results. The cross-sections for the dissociative recombination, vibrational excitation, and vibrational de-excitation processes, for the six lowest vibrational levels of CO + – relevant for the electronic temperatures observed in comets – are computed, as well as their corresponding Maxwell rate coefficients. Moreover, final state distributions for different dissociation pathways are presented. Conclusions. Among all reactive collisions taking place between low-energy electrons and CO + , the dissociative recombination is the most important process at electronic temperatures characterizing the comets. We have shown that this process can be a major source of O( 3 P), O( 1 D), O( 1 S), C( 3 P) and C( 1 D) produced in the cometary coma at small cometocentric distances.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 7
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2018
    In:  Monthly Notices of the Royal Astronomical Society Vol. 479, No. 2 ( 2018-09-11), p. 2415-2420
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 479, No. 2 ( 2018-09-11), p. 2415-2420
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2018
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 8
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 615 ( 2018-07), p. A154-
    Abstract: Context . Thanks to the Rosetta mission, our understanding of comets has greatly improved. A very good opportunity to apply this knowledge appeared in early 2017 with the appearance of the Jupiter family comet 41P/Tuttle–Giacobini–Kresak. The comet was only 0.15 au from the Earth as it passed through perihelion on April 12, 2017. We performed an observational campaign with the TRAPPIST telescopes that covered almost the entire period of time when the comet was active. Aims . In this work we present a comprehensive study of the evolution of the dust environment of 41P based on observational data from January to July, 2017. In addition, we performed numerical simulations to constrain its origin and dynamical nature. Methods . To model the observational data set we used a Monte Carlo dust tail model, which allowed us to derive the dust parameters that best describe its dust environment as a function of heliocentric distance: its dust production rate, the size distribution and ejection velocities of the dust particles, and its emission pattern. In order to study its dynamical evolution, we completed several experiments to evaluate the degree of stability of its orbit, its life time in its current region close to Earth, and its future behaviour. Results . From the dust analysis, we found that comet 41P is a dust-poor comet compared to other comets of the same family, with a complex emission pattern that shifted from full isotropic to anisotropic ejection sometime during February 24–March 14 in 2017, and then from anisotropic to full isotropic again between June 7 and 28. During the anisotropic period, the emission was controlled by two strongly active areas, where one was located in the southern and one in the northern hemisphere of the nucleus. The total dust mass loss is estimated to be ~7.5 × 10 8 kg. From the dynamical simulations we estimate that ~3600 yr is the period of time during which 41P will remain in a similar orbit. Taking into account the estimated mass loss per orbit, after 3600 yr, the nucleus may lose about 30% of its mass. However, based on its observed dust-to-water mass ratio and its propensity to outbursts, the lifetime of this comet could be much shorter.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 9
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 652 ( 2021-08), p. L1-
    Abstract: FeI and NiI emission lines have recently been found in the spectra of 17 Solar System comets observed at heliocentric distances between 0.68 and 3.25 au and in the interstellar comet 2I/Borisov. The blackbody equilibrium temperature at the nucleus surface is too low to vaporize the refractory dust grains that contain metals, making the presence of iron and nickel atoms in cometary atmospheres a puzzling observation. Moreover, the measured NiI/FeI abundance ratio is on average one order of magnitude larger than the solar photosphere value. We report new measurements of FeI and NiI production rates and abundance ratios for the Jupiter-family comet (JFC) 46P/Wirtanen in its 2018 apparition and from archival data of the Oort-cloud comet (OCC) C/1996 B2 (Hyakutake). The comets were at geocentric distances of 0.09 au and 0.11 au, respectively. The emission line surface brightness was found to be inversely proportional to the projected distance to the nucleus, confirming that FeI and NiI atoms are ejected from the surface of the nucleus or originate from a short-lived parent. Considering the full sample of 20 comets, we find that the range of NiI/FeI abundance ratios is significantly larger in JFCs than in OCCs. We also unveil significant correlations between NiI/FeI and C 2 /CN, C 2 H 6 /H 2 O, and NH/CN. Carbon-chain- and NH-depleted comets show the highest NiI/FeI ratios. The existence of such relations suggests that the diversity of NiI/FeI abundance ratios in comets could be related to the cometary formation rather than to subsequent processes in the coma.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 10
    Online Resource
    Online Resource
    IOP Publishing ; 2017
    In:  Journal of Physics: Conference Series Vol. 869 ( 2017-06), p. 012079-
    In: Journal of Physics: Conference Series, IOP Publishing, Vol. 869 ( 2017-06), p. 012079-
    Type of Medium: Online Resource
    ISSN: 1742-6588 , 1742-6596
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 2166409-2
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