Other
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997dps....29.3711c&link_type=abstract
American Astronomical Society, DPS meeting #29, #37.11; Bulletin of the American Astronomical Society, Vol. 29, p.1048
Other
1
Scientific paper
Very high resolution (R=200,000) and high signal-to-noise echelle spectra were obtained of comet C/Hyakutake 1996 B2 using the 2DCoude spectrograph on the 2.7 m telescope at McDonald Observatory during late March and early April 1996. Doppler resolved profiles are presented for individual lines of most of the major optical neutral species: CN, C_2, O((1) D) at 6300{ Angstroms}, O((1) S) at 5577{ Angstroms} , NH_2, and H Balmer-alpha at 6563{ Angstroms}. These may be the first ever to be published for CN, C_2, and O((1) S). In all cases the instrument spectral function is smaller than the intrinsic line widths of the individual cometary lines, so the observations provide clear signatures of lines which are Doppler broadened by different combinations of the coma expansion, exothermic photochemical ejection speeds, and collisional thermalization. For modeling analysis of these data we have used a hybrid fluid/kinetic Monte Carlo approach which can realistically include all of the relevant physical/chemical processes important for shaping the spectral lines. Because of the very short lifetime of the NH_2 parent (NH_3), the NH_2 is collisionally thermalized and provides an excellent probe of the outflow of the expanding coma. Because O((1) D) atoms in the region sampled are produced mainly by the photodissociation of water and the resulting photon is a prompt emission, the line retains signatures of both the basic coma expansion velocity and the 1.6 km s(-1) ejection speed of the O({(1}) D) atoms. The O((1) S) profile is consistent with that for the O((1) D). The profiles of CN and C_2 are somewhat broadened (CN more so than C_2), compared with NH_2, and seem to require a combination of coma expansion and the exothermic ejection speed they receive upon their production. Although the H Balmer-alpha line is complicated by a chance coincidence of an H_2O(+) line and optical depth effects in the solar Lyman-beta which pumps the Balmer-alpha emission, the spread of the wings of the line is consistent with other observations of past comets and the production by dissociation of H_2O and OH, and subsequent partial thermalization. %Replace this paragraph with your abstract; use two returns (i.e., one %return and then one blank line) to signify breaks between paragraphs, %as opposed to the usual new line command (two backslashes), and try %to limit your line length to 72 characters including spaces (this %paragraph is a good example of the line length you should use). Your %word limit is approximately 300 words (this is for the text of the %abstract only); keep in mind that if your author list is unusually long, %you will need to shorten your abstract accordingly. If your abstract %exceeds the limit, you will get an ``overfill'' error message when you %compile your abstract. Remember that if you use any punctuation marks %that LaTeX considers to be special characters (&, \$, %, #, _), you must %put a backslash in front of them. This is particularly important in the %case of the percent sign; if you don't use the backslash, LaTeX will %drop the rest of your text on that line, because it thinks you are %inserting a comment.
Cochran Anita L.
Combi Michael R.
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