The impact and rotational lightcurves of Comet 9P/Tempel 1

UVES and HIRES high-resolution spectra of comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C3, CH, C2, NH2 and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact lightcurves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The rotational light curve for each species is explained in terms of a single model with three sources.Comment: 34 pages, 11 figures Accepted for publication in the special issue of Icarus associated with the Deep Impact mission to Comet 9P/Tempel

A study of molecular and physical processes in comets

The rotational structure of the violet CN (0, 0) band in cometary spectra is investigated from a new point of view. The usual assumption of a Boltzmann distribution of populations of the rotational levels in the ground state is abandoned. These populations are determined by solving the system of steady-state equations which describes the resonance-fluorescence of the CN band. As expected, it is possible in this way to reproduce the observed profile more satisfactorily than in the case when a Boltzmann distribution is used. Furthermore, it is shown that the Swings effect (presence of absorption lines in the solar exciting light) has to be taken into account from the beginning in the resolution of the system of the steady-state equations, to achieve complete agreement between observed and computed profiles. The Greenstein effect (differences in relative intensities of rotational lines in different regions of the comet) has been studied in high-resolution spectrograms of Comet Seki-Lines (1962c). The observations can be interpreted partly by means of either of two simple models for the comet's head (uniform, isotropic expansion, or "fountain model"). In addition there are random motions of the order of a few km/sec. A detailed analysis of spectra of Comet Humason (1961e) has furnished the following results: a) The CO+ comet-tail bands are excited by the same resonance-fluorescence mechanism known to be responsible for the emissions of the neutral molecules observed in the head. b) The continuum is of the pure reflection type: there is no detectable selective scattering. c) Molecular abundances are estimated (at 10[superscript 4] km from the nucleus) N(CO+)=10[superscript 13] cm[superscript -2] N(N2+)=10[superscript 11] cm[superscript -2] N(CN) = 5X10[superscript 10] cm[superscript -2] The probable error on these estimates corresponds to a factor of 2 or 3. d) The infra-red surface brightness produced by the CO+ ions in pure vibration transitions v" = 1 -> v" = 0([lambda] approx.= 4.6 [mu]) is found to be rather large: approx.= 0.001 erg cm[superscript -2] sec[superscript -1]. e) The radial distributions of the various molecules are discussed. While CN follows the usual l/[rho] law ([rho] being the projected distance from the nucleus), it is suggested that the remarkable flatness of the ion distributions might be explained in terms of a "magnetic model." A critical discussion of some physical and chemical characteristics of comets is presented in the last chapter. In particular, the results of a number of abundance determinations are tabulated. (Photographic material on page 46 will not reproduce clearly on Xerox copies)

The Al/Mg abundance ratio in halo stars

The Al to Mg abundance ratio is redetermined in two extreme metal-poor stars, HD 19445 and HD 140283, on the basis of accurate spectral material. It is found that: (1) one of the two lines used for the Al abundance determination is blended by CH lines; (2) no anomalous difference appears between the hotter and the cooler star, both showing an Al overdeficiency; (3) the observations are in fair agreement with predictions from the theory of explosive carbon burning

Pre- and postperihelion photometry of Comet Halley from several observatories

Photoelectric observations of P/Halley were carried out during several weeks between 15 Sept. 1985 and 25 June 1986. All measurements were made using the standard IAU/IHW cometary filters. Large amplitude night-to-night changes over periods of several days superimposed on the general trend of slow brightness variation were seen. Smooth and irregular variations with a range up to 0.2 mag on time scales of several hours were observed. Present photometric scans of comet Halley through the various filters are presented. Successive integrations were made every 5 arc sec, radially from the center out to a distance of 5 arcmin, essentially along the sunward-antisunward direction and in the direction perpendicular to it

Photometry of p/ Halley 1982I

Abstract image available at: http://cdsads.u-strasbg.fr/abs/1987A&A...187..523

Production and kinematics of sodium atoms in the coma of comet Hale-Bopp

High-resolution spectra of sodium D line emission in comet Hale-Bopp (C/1995 O1) were obtained at the Observatoire de Haute-Provence, France, on 25-27 March and on 15-17 April, 1997. The observations have been used to measure the velocity of sodium atoms in the coma within 2 10(5) km from the nucleus. A comparison between the March and April data provides an illustration of the influence of the heliocentric radial velocity on the strength of the fluorescence (Swings effect), and on the velocity of Na atoms achieved by solar radiation pressure acceleration. Evidence for the presence of a distributed source in the coma is found from the relatively high tailward velocities on the sunward side of the coma, in addition to the sunward extent of sodium emission up to 1.4 10(5) km in April. Based on observations secured at OHP (France

Photoelectric scans of comet Halley.

The authors compare radial photometric scans of comet Halley obtained in April 1986 at the European Southern Observatory, La Silla, Chile, with theoretical profiles derived from Haser's model

New constraints on the delivery of cometary water and nitrogen to Earth from the 15N/14N isotopic ratio

New independent constraints on the amount of water delivered to Earth by comets are derived using the [SUP]15[/SUP]N/[SUP]14[/SUP]N isotopic ratio, measured to be roughly twice as high in cometary CN and HCN as in the present Earth. Under reasonable assumptions, we find that no more than a few percent of Earthâ s water can be attributed to comets, in agreement with the constraints derived from D/H. Our results also suggest that a significant part of Earthâ s atmospheric nitrogen might come from comets. Since the [SUP]15[/SUP]N/[SUP]14[/SUP]N isotopic ratio is not different in Oort-cloud and Kuiper-belt comets, our estimates apply to the contribution of both types of objects