Shoemaker-Levy 9 impact with Jupiter: Spectral peculiarities of the impact sites H,K, L,N, and D + G + S + R group

Long-slit CCD spectra of the impact parallel of Jupiter were obtained on July 20–21, 1994. Observations were made at Nasmith focus of the 2.6 m Shajn telescope of the Crimean Astrophysical Observatory. Observed spectra covered 4600–10,250 Å at a resolution of 4.5 Å.Combined investigations of the Nasmith spectra, both the spatial profiles for different spectral regions and extracted spectra for different sites of the crash latitude, show that the impact spots have some spectral peculiarities. Detectable absorption in the observed wavelength region is the general peculiarity of the observed impact sites, except for CH₄ bands at 8900 Å and 1 m, where methane absorption was weakened. Also, our analysis evidenced that there are two types of the spectral peculiarities. One of them, related to the great spots D + G + R + S, K, and L, shows that the absorption in the impact sites is increasing gradually to the blue with respect to the unaffected sites. The other, related to the medium-sized spots, H and N, shows no obvious changes in the gradient of the spots' spectra over a wide wavelength region, except that for the green region, where absorption is slightly weakened.     

Comet Hale-Bopp (C/1995 O1): UVSTAR-FUV Spectroscopy from the Space Shuttle

We report here on unique post-perihelion (2.3 AU) measurements of Comet Hale-Bopp in the FUV-range (950–1250 Å) by means of the UVSTAR spectrometer from the space shuttle with the main purpose of searching for argon and other FUV emitters. New methods for separating the strong airglow emission at shuttle altitudes are here discussed in detail. Due to our low resolution (15 Å) and S/N ratio the possible rocket-borne detection of argon near perihelion (0.9 AU) could not be confirmed. New species as N₂ are suspected but difficult to separate from the strong airglow emission at shuttle altitudes. From the Lyα brightness (1.30± 0.08 kRy) a water production rate Q = 5.9 ± 0.4 × 10²⁹ molecules s^?1 could be derived and compared with other post-perihelion observations.     

Comment on “Is the D/H ratio in the comet coma equal to the D/H ratio in the comet nucleus?” by M. Podolak, Y. Mekler, and D. Prialnik—rebuttal

We defend the position taken in our earlier note that under certain conditions the D/H ratio measured in the coma of a comet can be much higher that the D/H ratio in to cometary ice itself.     

IRAS 02232+6138的13CO、C18O、HCO+和N2H+的观测研究

利用中国科学院紫金山天文台德令哈观测站13．7米望远镜在IRAS 02232 6138方向进行了13CO,C18O,HCO 和N2H 的观测．随着探针分子的激发密度从13CO到N2H 逐渐增加, IRAS02232 6138云核的尺度从13CO的2．40 pc减小到N2H 的0．54pc,云核的维里质量从13CO的2．2×103M⊙减小到N2H 的5．1×102M⊙．研究发现,该方向区域内存在双极分子外流．对云核的空间密度结构用幂函数n(r)αr-α的形式进行拟合分析,得到α=2．3-1．2;随着探测密度的增加,该指数逐渐变平．分析得到, 13CO／C18O分子丰度比值为12．4±6．9,与暗云的11．8±5．9及大质量核的9．0-15．6值一致;N2H 丰度是3．5±2．5×10-10,与暗云核的1．0-5．0×10-10和大质量核的1．2-12．8×10-10值一致;HCO 丰度为0．9±0．5×10-9,接近大质量核的1．6-2．4×10-9值,没有发现HCO 丰度增长．结合IRAS数据,得到云核的光度质量比范围为37-163(L／M)⊙,由IRAS光度估计, IRAS 02232 6138方向云核内嵌埋的大约是一颗主序O7．5星．     

D/O and D/H ratios in the local interstellar medium from FUSE observations

Since HI, OI, and DI have nearly the same ionization potential, the deuterium-to-oxygen ratio (D/O) is an important tracer of the D/H ratio and of its putative spatial variations. D/O is indeed very sensitive to astration, both because of deuterium destruction and oxygen production. Moreover, D/O measurements are less subject to systematic errors than D/H.A survey of D/O in the interstellar medium is performed by the Deuterium Working Group of the FUSE PI Team. The first results show that D/O is a better D/H proxy than D/N, and that D/O is homogeneous in the local interstellar medium, at least within about 100pc. The stability of D/O appears as a strong argument which supports both D/H and O/H spatial stability in the local interstellar medium.     

Comment on “Comparison of the composition of the Tempel 1 ejecta to the dust in Comet C/Hale-Bopp 1995 O1 and YSO HD 100546” by C.M. Lisse, K.E. Kraemer, J.A. Nuth III, A. Li, D. Joswiak [2007. Icarus 187, 69-86]

Lisse et al. [Lisse, C.M., Kraemer, K.E., Nuth III, J.A., Li, A., Joswiak, D., 2007. Icarus 187, 69-86] recently presented a new analysis of an ISO spectrum of Comet C/1995 O1 (Hale-Bopp), from which they claimed the identification of many new dust species. Among them are PAHs, which were not found in our first analysis of the ISO spectra. We present here a re-examination of the ISO observations of Comet Hale-Bopp. From the absence of PAHs features in the 5.25-8.5 μm region, we infer that PAHs are at least twice less abundant than derived by Lisse et al. The carbonate feature at 7.00 μm is marginally present, but lower by a factor 2 to 3 than predicted by the model of Lisse et al.     

Chemical and physical properties of gas jets in comets: II. Modeling OH, CN and C2 jets in Comet C/1995 O1 (Hale-Bopp) one month after perihelion

We present an analysis of OH, CN, and C₂ jets observed in Comet Hale-Bopp during April 22-26, 1997. We conclude that an extended source, which peaks in productivity after a certain amount of time has passed after being released from the nucleus (8.5, 2.5, and 42.6×¹⁰⁴ s, respectively) is responsible for the observed coma jet morphology in all three species. Sub-micron organic grains are the favored explanation for the extended source. Our models indicate that this extended source produces approximately 40% of the OH, 50% of the C₂, and 75% of the CN. The balance for each species is created by a diffuse nuclear gas source. Compared with the nuclear gas source and normalized to the CN abundance, the composition of the extended source is depleted in OH by a factor of ∼6, and depleted in C₂ by a factor of ∼2. The existence of anti-sunward jets do not require production of radicals throughout the cometary night. Instead, our model demonstrates that active areas exposed to near-twilight conditions throughout the comet's rotational period can produce the observed anti-sunward morphology.     

Laboratory measurements of the association rate coefficients of NO+, O+2, N+, and N+2 ions with N2 and CO2 at temperatures between 100 k and 400 k

Rate coefficients for the association reactions of NO⁺ ions with N₂ and CO₂, O₂⁺ with N₂, and N⁺ and N₂⁺ with N₂ have been determined as a function of gas temperature in a laboratory experiment employing a variable-temperature drift-tube apparatus. The measured rate coefficients were fitted to power laws of the form $\text{k = C}\text{(}\text{T}\text{300}\text{)}{}^{\mathrm{x}}$ where the exponents x ranged from 2.2 to 4.3. The strong temperature dependence observed in the case of the reaction of NO⁺ with N₂ (x = 4.3) supports the thesis by Arnold et al. (1979) that the temperature variability of D-region ion densities is a result of this reaction step in the ion clustering sequence.     

Deep Impact, Stardust-NExT and the behavior of Comet 9P/Tempel 1 from 1997 to 2010

We present observational data for Comet 9P/Tempel 1 taken from 1997 through 2010 in an international collaboration in support of the Deep Impact and Stardust-NExT missions. The data were obtained to characterize the nucleus prior to the Deep Impact 2005 encounter, and to enable us to understand the rotation state in order to make a time of arrival adjustment in February 2010 that would allow us to image at least 25% of the nucleus seen by the Deep Impact spacecraft to better than 80 m/pixel, and to image the crater made during the encounter, if possible. In total, ∼500 whole or partial nights were allocated to this project at 14 observatories worldwide, utilizing 25 telescopes. Seventy percent of these nights yielded useful data. The data were used to determine the linear phase coefficient for the comet in the R-band to be 0.045 ± 0.001 mag deg⁻¹ from 1° to 16°. Cometary activity was observed to begin inbound near r ∼ 4.0 AU and the activity ended near r ∼ 4.6 AU as seen from the heliocentric secular light curves, water-sublimation models and from dust dynamical modeling. The light curve exhibits a significant pre- and post-perihelion brightness and activity asymmetry. There was a secular decrease in activity between the 2000 and 2005 perihelion passages of ∼20%. The post-perihelion light curve cannot be easily explained by a simple decrease in solar insolation or observing geometry. CN emission was detected in the comet at 2.43 AU pre-perihelion, and by r = 2.24 AU emission from C₂ and C₃ were evident. In December 2004 the production rate of CN increased from 1.8 × 10²³ mol s⁻¹ to Q_CN = 2.75 × 10²³ mol s⁻¹ in early January 2005 and 9.3 × 10²⁴ mol s⁻¹ on June 6, 2005 at r = 1.53 AU.     

Detection of C2HD and the D/H ratio on Titan

We report here the first detection of mono-deuterated acetylene (acetylene-d1, C₂HD) in Titan's atmosphere from the presence of two of its emission bands at 678 and 519 cm⁻¹ as observed in CIRS spectral averages of nadir and limb observations taken between July 2004 and mid-2007. By using new laboratory spectra for this molecule, we were able to derive its abundance at different locations over Titan's disk. We find the C₂HD value () to be roughly constant with latitude from the South to about 45° N and then to increase slightly in the North, as is the case for C₂H₂. Fitting the 678 cm⁻¹ν₅ band simultaneously with the nearby C₂H₂ 729 cm⁻¹ν₅ band, allows us to infer a D/H ratio in acetylene on Titan with an average of the modal values of 2.09±0.45×¹⁰⁻⁴ from the nadir observations, the uncertainties being mainly due to the vertical profile used for the fit of the acetylene band. Although still subject to significant uncertainty, this D/H ratio appears to be significantly larger than the one derived in methane from the CH₃D band (upper limit of 1.5×¹⁰⁻⁴; Bézard, B., Nixon, C.A., Kleiner, I., Jennings, D.E., 2007. Icarus, 191, 397-400; Coustenis, A., Achterberg, R., Conrath, B., Jennings, D., Marten, A., Gautier, D., Bjoraker, G., Nixon, C., Romani, P., Carlson, R., Flasar, M., Samuelson, R.E., Teanby, N., Irwin, P., Bézard, B., Orton, G., Kunde, V., Abbas, M., Courtin, R., Fouchet, Th., Hubert, A., Lellouch, E., Mondellini, J., Taylor, F.W., Vinatier, S., 2007. Icarus 189, 35-62). From the analysis of limb data we infer D/H values of (at 54° S), (at 15° S), (at 54° N) and (at 80° N), which average to a mean value of 1.63±0.27×¹⁰⁻⁴.     

2D and 3D Polar Plume Analysis from the Three Vantage Positions of STEREO/EUVI A, B, and SOHO/EIT

Polar plumes appear as elongated objects starting at the solar polar regions. Here we analyze these objects from a sequence of images taken simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and SOHO/EIT. We establish a method capable of automatically identifying plumes in solar EUV images close to the limb at 1.01?–?1.39?R _⊙ in order to study their temporal evolution. This plume-identification method is based on a multiscale Hough-wavelet analysis. Then two methods to determine the 3D localization and structure of the plumes are discussed: first, tomography using filtered back-projection and including the differential rotation of the Sun and, second, conventional stereoscopic triangulation. We show that tomography and stereoscopy are complementary for studying polar plumes. We also show that this systematic 2D identification and the proposed methods of 3D reconstruction are well suited to identify plumes individually and also to analyze the distribution of plumes and inter-plume regions. Finally, the results are discussed, focusing on plume position and cross-sectional area.     

A model for the molecular accretion disk and H2O maser in the nucleus of the galaxy NGC 4258

A model is developed for the H₂O maser source observed in the circumnuclear region of the galaxy NGC 4258. The maser emission originates at distances of 0.15–0.29 pc from the center in a thin, cold accretion disk (gas-dust torus) rotating around a supermassive black hole of mass 4 × 10⁷ M _⊙. The conditions for the emergence of an inverse population of the signal 6₁₆?5₂₃ levels in ortho-H₂O working molecules are simulated numerically. The complex line profile, which includes both central and high-velocity components, is calculated. A comparison of the calculations with radiointerferometric and spectrophotometric observations allowed the physical conditions in the emitting region to be determined.     

The formation and aqueous alteration of CM2 chondrites and their relationship to CO3 chondrites: A fresh isotopic (O,Cd, Cr,Si, Te,Ti, and Zn) perspective from the Winchcombe CM2 fall

As part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements of the Winchcombe CM2 meteorite. δ⁶⁶Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The difference between these analyses likely reflects sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data. δ¹¹⁴Cd for a single Winchcombe aliquot is +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison. δ¹³⁰Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰ (2SD) and are essentially identical to published values for CM2s. ε⁵³Cr and ε⁵⁴Cr for Winchcombe are 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE), respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites. ε⁵⁰Ti and ε⁴⁶Ti values for Winchcombe are 3.21 ± 0.09 (2SE) and 0.46 ± 0.08 (2SE), respectively, and are in line with recently published data for CM2s. The δ³⁰Si composition of Winchcombe is −0.50 ± 0.06‰ (2SD, n = 11) and is essentially indistinguishable from measurements obtained on other CM2 chondrites. In conformity with petrographic observations, oxygen isotope analyses of both bulk and micromilled fractions from Winchcombe clearly demonstrate that its parent body experienced extensive aqueous alteration. The style of alteration exhibited by Winchcombe is consistent with relatively closed system processes. Analysis of different fractions within Winchcombe broadly support the view that, while different lithologies within an individual CM2 meteorite can be highly variable, each meteorite is characterized by a predominant alteration type. Mixing of different lithologies within a regolith environment to form cataclastic matrix is supported by oxygen isotope analysis of micromilled fractions from Winchcombe. Previously unpublished bulk oxygen isotope data for 12 CM2 chondrites, when combined with published data, define a well-constrained regression line with a slope of 0.77. Winchcombe analyses define a more limited linear trend at the isotopically heavy, more aqueously altered, end of the slope 0.77 CM2 array. The CM2 slope 0.77 array intersects the oxygen isotope field of CO3 falls, indicating that the unaltered precursor material to the CMs was essentially identical in oxygen isotope composition to the CO3 falls. Our data are consistent with earlier suggestions that the main differences between the CO3s and CM2s reflect differing amounts of water ice that co-accreted into their respective parent bodies, being high in the case of CM2s and low in the case of CO3s. The small difference in Si isotope compositions between the CM and CO meteorites can be explained by different proportions of matrix versus refractory silicates. CMs and COs may also be indistinguishable with respect to Ti and Cr isotopes; however, further analysis is required to test this possibility. The close relationship between CO3 and CM2 chondrites revealed by our data supports the emerging view that the snow line within protoplanetary disks marks an important zone of planetesimal accretion.     

Observation and Study of the CO, CO, HCO and N2H Molecular Lines Towards IRAS 02232+6138

Using the 13.7 m millimeter-wave telescope at the Qinghai Station of Purple Mountain Observatory, we have made observations of ¹³CO, C¹⁸O, HCO⁺ and N₂H⁺ molecular lines towards IRAS 02232+6138. As the excitation density of the probe molecule increases from ¹³CO to HCO⁺, the size of the cloud core associated with IRAS 02232+6138 decreases from 2.40 pc to 0.54 pc, and the virial mass of the cloud core decreases from 2.2 × 10³M to 5.1 × 10²M. A bipolar molecular outflow is found towards IRAS 02232+6138. Using the power function n(r) ∝ r⁻ to fit the spatial density structure of the cloud core, we obtain the power-law index  = 2.3 − 1.2; and we find that, as the probed density increases, the power function becomes more flat. The abundance ratio of ¹³CO to C¹⁸O is 12.4 ± 6.9, comparable with the values 11.8 ± 5.9 for dark clouds and the values 9.0–15.6 for massive cores. The abundance of N₂H⁺ molecules is 3.5 ± 2.5 × 10⁻¹⁰, consistent with the value 1.0 − 5.0 × 10⁻¹⁰ for dark cloud cores and the value 1.2 − 12.8 × 10⁻¹⁰ for massive cores. The abundance of HCO⁺ molecules is 0.9 ± 0.5 × 10⁻⁹, close to the value 1.6 − 2.4 × 10⁻⁹ for massive cores. An increase of HCO⁺ abundance in the outflow region was not found. Combining with the IRAS data, the luminosity-mass ratio of the cloud core is obtained in the range 37–163(L/M). Based on the IRAS luminosity, it is estimated that a main-sequence O7.5 star is probably embedded in the IRAS 02232+6138 cloud core.