排序方式: 共有5条查询结果,搜索用时 78 毫秒
1
1.
Michael R. Line E.J. Mierkiewicz R.J. Oliversen J.K. Wilson L.M. Haffner F.L. Roesler 《Icarus》2012,219(2):609-617
The lunar sodium tail extends long distances due to radiation pressure on sodium atoms in the lunar exosphere. Our earlier observations measured the average radial velocity of sodium atoms moving down the lunar tail beyond Earth (i.e., near the anti-lunar point) to be ~12.5 km/s. Here we use the Wisconsin H-alpha Mapper to obtain the first kinematically resolved maps of the intensity and velocity distribution of this emission over a 15° × 15 ° region on the sky near the anti-lunar point. We present both spatially and spectrally resolved observations obtained over four nights bracketing new Moon in October 2007. The spatial distribution of the sodium atoms is elongated along the ecliptic with the location of the peak intensity drifting 3° east along the ecliptic per night. Preliminary modeling results suggest the spatial and velocity distributions in the sodium exotail are sensitive to the near surface lunar sodium velocity distribution. Future observations of this sort along with detailed modeling offer new opportunities to describe the time history of lunar surface sputtering over several days. 相似文献
2.
Harris Walter M. Morgenthaler Jeffrey P. Scherb Frank Anderson Christopher Oliversen Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):45-56
The comae of very active comets have a substantiallymore complex coma than their weaker cousins.The primary cause of this
is photolytic heating and collisionsthat occur over an ever-larger volume of the coma asQH
2O increases. Collisionswith the photochemical daughters ofwater in this regionmodify the radial distributions and outflowvelocity
of each species, excite and quench metastableemissions, and introduce velocity gradients from photolyticheating. Comet Hale–Bopp
was the first comet forwhich the collisional coma was both spatially resolvableand comparable in extent to the scale lengths
ofmajor coma species. In the case of this object,the classical assumptions that make it possible toinvert radial emission
line profiles, brightnesses, andlineshapes to production rate and velocity eitherdo not hold or require adjustment to work.Here
we describe how a large collision zone modifies thecoma, how it affects the classical methods for obtainingproduction rate
and velocity, and discuss how wide fieldimaging may be combined with modified versions ofsimple models to address the complications
and extract somestructural information. 相似文献
3.
Morgenthaler Jeffrey P. Harris Walter M. Scherb Frank Doane Nathaniel E. Oliversen Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):89-97
We present hydrogen Balmer-α spectra of comet C/1995 O1(Hale–Bopp) recorded on 5 nights from 1997 February 1 to April 19 by
ahigh-resolution (Δ v = 5 km s-1) Fabry–Pérot spectrometer for a4'.1 (∼2.7 × 105 km) FOV centered 5' sunwardof the nucleus. The Hα line profile is an important diagnostic ofphotolytic heating in cometary
atmospheres. Extraction of the spectrafrom the Fabry–Pérot ring images was complicated by obscuration of the telescope FOV
due to Hale–Bopp's low elevation, but the measuredH-α line widths of 11–13 km s-1 (FWHM) are insensitive to the spectral extraction technique. The line widths are consistent withestimates derived from a
successful model of Hale–Bopp's hydrogenLyman-α coma assuming the inner coma is opaque to Hα. Wediscuss methods for improving
the spectral extraction technique andderiving a precise instrument profile which will allow the detailedshape of the line
profile to constrain coma models. 相似文献
4.
Morgenthaler Jeffrey P. Harris Walter M. Roesler Frederick L. Scherb Frank Anderson Christopher M. Doane Nathaniel E. Oliversen Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):77-87
The University of Wisconsin–Madison and NASA–Goddard conducted acomprehensive multi-wavelength observing campaign of coma emissionsfrom comet Hale–Bopp, including OH 3080 Å, [O I] 6300 Å H2O+ 6158 Å, H Balmer-α 6563 Å, NH2 6330 Å, [C I] 9850 ÅCN 3879 Å, C2 5141 Å, C3 4062 Å,C I 1657 Å, and the UV and optical continua. In thiswork, we concentrate on the results of the H2O daughter studies.Our wide-field OH 3080 Å measured flux agrees with other, similarobservations and the expected value calculated from published waterproduction rates using standard H2O and OH photochemistry.However, the total [O I] 6300 Å flux determined spectroscopically overa similar field-of-view was a factor of 3-4 higher than expected.Narrow-band [O I] images show this excess came from beyond theH2O scale length, suggesting either a previously unknown source of[O I] or an error in the standard OH + ν→ O(1 D) + H branching ratio. The Hale–Bopp OH and[O I] distributions, both of which were imaged tocometocentric distances >1 × 106 km, were more spatiallyextended than those of comet Halley (after correcting for brightnessdifferences), suggesting a higher bulk outflow velocity. Evidence ofthe driving mechanism for this outflow is found in the Hα lineprofile, which was narrower than in comet Halley (though likelybecause of opacity effects, not as narrow as predicted by Monte-Carlomodels). This is consistent with greater collisional coupling betweenthe suprathermal H photodissociation products and Hale–Bopp's densecoma. Presumably because of mass loading of the solar wind by ionsand ions by the neutrals, the measured acceleration of H2O+ downthe ion tail was much smaller than in comet Halley. Tailwardextensions in the azimuthal distributions of OH 3080 Å,[O I], and [C I] , as well as a Doppler asymmetry in the[O I] line profile, suggest ion-neutral coupling. While thetailward extension in the OH can be explained by increased neutralacceleration, the [O I] 6300 Å and [C I] 9850 Å emissions show 13%and >200% excesses in this direction (respectively), suggesting anon-negligible contribution from dissociative recombination of CO+and/or electron collisional excitation. Thus, models including theeffects of photo- and collisional chemistry are necessary for the fullinterpretation of these data. 相似文献
5.
We analyze observations of Comet IRAS-Araki-Alcock taken on 1983 May 10 to determine the spatial molecular abundance of C2 in the inner coma via the Δν = +1 Swan band sequence near 4690 Å; total molecular abundance for C2 is ~6 × 1027 molecules across a projected linear diameter of ~9700 km centered on the nucleus. These observations show a deficiency of C2 emission across a projected diameter of ~2000 km centered on the peak of continuum emission. Comet imagery reveals a sunward-pointing coma suggestive of an outburst of subsurface volatile ices through a nonvolatile surface crust as predicted for periodic comets. Moreover, such imagery suggests that Haser model scale lengths for C2 and its parent molecule, as derived from our observations, do not fit the data very well. Our results are discussed in terms of the then-developing instrument and observational constraints which applied at the time. 相似文献
1