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  • 1
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    The Beta Pictoris circumstellar disk. XV - Highly ionized species near Beta Pictoris (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Temporal variations of the Fe II, Mg II, and Al III circumstellar lines towards Beta Pictoris have been detected and monitored since 1985. However, the unusual presence of Al III ions is still puzzling, since the UV stellar flux from an A5V star such as Beta Pic is insufficient to produce such an ion. In order to better define the origin of such a phenomenon, new observations have been carried out to detect faint signatures of other highly ionized species in the short UV wavelength range, where the stellar continuum flux is low. These observations reveal variations not only near the C IV doublet lines, but also in C I and Al II lines, two weakly ionized species, not clearly detectable until now. In the framework of an infalling body scenario, highly ionized species would be created in the tail, far from the comet head, by collisions with ambient gas surrounding the star, or a weak stellar wind. Spectral changes have also been detected near a CO molecular band location, which, if confirmed, would provide the first molecular signature around Beta Pictoris.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 267; 1; p. 187-193.
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  • 2
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    The composition of comets (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Questions concerning the origin of comets are considered. It is pointed out that the molecular composition of a dense interstellar cloud appears to have exactly the composition needed to produce the observed features of the visible cometary spectrum, which consists mainly of emission bands of unstable free radicals. A working model of cometary structure is discussed together with the classical observations which have led to it. The discussed model was originally described by Whipple (1951). It is emphasized that the model can serve only as a rough guide in efforts to interpret the evolution of cometary behavior. A survey is provided of new techniques which have only recently been applied to cometary observations, taking into account the spectrum of a comet, radio observations, and ultraviolet observations.
    Keywords: ASTROPHYSICS
    Type: American Scientist; 65; May-June
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  • 3
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    The grains and gas in Comet Bowell 1980b (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The importance of coordinating different types of observations of a comet is illustrated in terms of spectral data on Comet Bowell. Photometric data in 1980 indicated that OH emissions were occurring when the comet was still more than 4 AU from the sun. Further measurements were arranged with the IUE satellite, the photoelectric scanner at Cerro Tololo and the IR telescope on Mauna Kea. Several sizes of diaphragms were used in order to estimate variations with respect to aperture. Calculations were made to quantify the wavelengths observed as a function of the grains' cross-sections. The OH emission was confirmed by the spectrographic and photometric data. It is suggested that sufficient dark materials are present on the cometary surface to have enhanced the absorption of solar radiation to levels sufficient for heating and dissociating surface ice particles.
    Keywords: ASTROPHYSICS
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  • 4
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    IUE observations of comet Austin (1989c1) (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Observations of comet Austin (1989c1) were made using the International Ultraviolet Explorer (IUE) satellite on December 22, 1989 (preperihelion) and on nine dates between 7 and 24 May, 1990 (postperihelion). A summary of observation dates and parameters is given. The ultraviolet spectrum is characteristic of that of non-dusty comets. Some preliminary results are presented for OH and CS production rates and dust-reflected solar continuum emission based upon the long wavelength, low resolution mode spectra; photometry using the IUE Fine Error Sensor; a detection of the CO fourth positive system in the short wavelength, low dispersion spectra; and an upper limit on S2.
    Keywords: ASTROPHYSICS
    Type: Southwest Research Inst., Workshop on Observations of Recent Comets (1990); p 64-68
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  • 5
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    Rocket observations of the ultraviolet spectrum of comet Austin (1989c1) (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Long slit ultraviolet spectra of Comet Austin (1989c1) were obtained from a sounding rocket experiment launched from White Sands Missile Range, New Mexico, on 21 April 1990 at 1015 UT. The instrument, known as the Faint Object Telescope, consisted of f/15.5 Dall-Kirkham telescope, a Rowland Circle spectrograph and a microchannel plate intensifier coupled to a Reticon diode array. An onboard television camera transmitted images to the ground during flight, which permitted real-time maneuvers in order to center the comet in the entrance slit. The comet was held near the center of the slit for approximately 270 seconds by sending six pointing corrections, all but one of which was less than 30 arcseconds. The comet's parameters at the time of observation, along with the characteristics of the instrument, are given.
    Keywords: ASTROPHYSICS
    Type: Southwest Research Inst., Workshop on Observations of Recent Comets (1990); p 55-58
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  • 6
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    IUE observations of comets P/Brorsen-Metcalf and Okazaki-Levy-Rudenko (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Comet P/Brorsen-Metcalf (1989c) was observed with the International Ultraviolet Explorer (IUE) on several dates from 27 July 1989 through 5 August 1989; comet Okazaki-Levy-Rudenko (1989r) was observed in low dispersion with IUE on 2 and 22 December 1989. The water production rates for P/Brorsen-Metcalf were derived from OH measurements using the vectorial model of Festou (1981). Included also are the water production rates for Okazaki-Levy-Rudenko. Two estimates of the water production rate from the O I emission around 1304 A(octogons) are included. The ultraviolet continuum was not reliably measurable in comet P/Brorsen-Metcalf in most of the spectra, but Afp is approximately 30 cm for 2 August. For the comet Okazaki-Levy-Rudenko, an Afp = 50 cm was derived for 22 December. Both comets have very little dust compared to other recently observed comets. The ratio of CS to water production rates are presented. Relative to water, both comets had less CS than P/Halley in the same range of heliocentric distances. The CS production rates were obtained from a Haser model, assuming a short-lived parent (CS2). Because the dynamic range of the IUE spectrographs are limited, not all species can be measured in each spectrum. The P/Brorsen-Metcalf spectra from 31 July and 3 August were obtained from the NSSDC Archives. Due to the observing technique used for these spectra, the exposure time and hence, the brightnesses and derived quantities have a small uncertainty associated with them.
    Keywords: ASTROPHYSICS
    Type: Southwest Research Inst., Workshop on Observations of Recent Comets (1990); p 59-63
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  • 7
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    Carbon monoxide in cometary ice (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Carbon monoxide has been positively identified by means of ultraviolet fluorescence in the Fourth Positive System in two comets, West (1976 VI) and Bradfield (1979 X). In both cases, the spatial distribution of the emission is consistent with the CO being a 'parent' molecule, present in the cometary ice, rather than a dissociation product of a polyatomic species such as CO2 or HCOH. However, the abundance of CO relative to that of H2O is more than an order of magnitude smaller for comet Bradfield than for comet West. Further data on CO are expected with the use of more sensitive ultraviolet instruments such as the ASTRO spectrographs which will observe P/Halley in March 1986.
    Keywords: ASTROPHYSICS
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  • 8
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    The atomic carbon distribution in the coma of Comet Halley (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The radial distribution of CO, OI, Ci, and CII emissions in the coma of comet Halley were measured by a long-slit far ultraviolet spectrograph aboard a sounding rocket on 26 Feb. and 13 Mar. 1986. While the CO profiles strongly suggest that CO is vaporized directly from the nucleus, the observed carbon distribution is not consistent with a radial outflow model of CO, suggesting an additional source of atomic carbon in the inner coma. Based on the in situ plasma measurements from the Vega and Giotto spacecraft, it is possible that this additional source of carbon could be the recombination of ionized CO in the inner coma.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 431-435
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  • 9
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    IUE observations of Comet Halley: Evolution of the UV spectrum between September 1985 and July 1986 (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The ultraviolet spectrum of comet P/Halley was monitored with the IUE between 12 September 1985 and 8 July 1986 (r 〈2.6 AU pre and post-perihelion) at regular time intervals except for a two-month period around the time of perihelion. A complete characterization of the UV spectrum of the comet was obtained to derive coma abundances and to study the light emission mechanisms of the observed species. The Fine Error Sensor (FES) camera of the IUE was used to photometrically investigate the coma brightness variation on time scales of the order of hours. Spectroscopic observations as well as FES measurements show that the activity of the nucleus is highly variable, particularly at the end of December 1985 and during March and April 1986. The production rates of OH, CS and dust are derived for the entire period of the observations. The total water loss rate for this period is estimated to be 150 million metric tons.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 325-328
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  • 10
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    IUE observations of Comet Halley: Evolution of the UV spectrum between September 1985 and June 1986 (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The UV spectrum of comet P/Halley (1982 i) was monitored with the IUE at regular time intervals. A complete characterization of the UV spectrum of the comet was obtained to derive coma abundances and to study the light emission mechanisms of the observed species. The Fine Error Sensor (FES) camera of the IUE was used to investigate the coma brightness variability on short time scales. Spectroscopic observations as well as FES measurements show that the comet nucleus activity was highly variable.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of an International Symposium on New Insights in Astrophysics. Eight Years of UV Astronomy with IUE; p 39-42
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