The C/C isotopic ratio in Titan hydrocarbons from Cassini/CIRS infrared spectra

We have analyzed infrared spectra of Titan recorded by the Cassini Composite Infrared Spectrometer (CIRS) to measure the isotopic ratio ¹²C/¹³C in each of three chemical species in Titan's stratosphere: CH₄, C₂H₂ and C₂H₆. This is the first measurement of ¹²C/¹³C in any C₂ molecule on Titan, and the first measurement of ¹²CH₄/¹³CH₄ (non-deuterated) on Titan by remote sensing. Our spectra cover five widely-spaced latitudes, 65° S to 71° N and we have searched for both latitude variability of ¹²C/¹³C within a given species, and also for differences between the ¹²C/¹³C in the three gases. For CH₄ alone, we find (1-σ), essentially in agreement with the ¹²CH₄/¹³CH₄ measured by the Huygens Gas Chromatograph/Mass Spectrometer instrument (GCMS) [Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779-784]: 82.3±1.0, and also with measured values in H¹³CN and ¹³CH₃D by CIRS at lower precision [Bézard, B., Nixon, C., Kleiner, I., Jennings, D., 2007. Icarus 191, 397-400; Vinatier, S., Bézard, B., Nixon, C., 2007. Icarus 191, 712-721]. For the C₂ species, we find in C₂H₂ and 89.8±7.3 in C₂H₆, a possible trend of increasingly value with molecular mass, although these values are both compatible with the Huygens GCMS value to within error bars. There are no convincing trends in latitude. Combining all fifteen measurements, we obtain a value of , also compatible with GCMS. Therefore, the evidence is mounting that ¹²C/¹³C is some 8% lower on Titan than on the Earth (88.9, inorganic standard), and lower than typical for the outer planets (88±7 [Sada, P.V., McCabe, G.H., Bjoraker, G.L., Jennings, D.E., Reuter, D.C., 1996. Astrophys. J. 472, 903-907]). There is no current model for this enrichment, and we discuss several mechanisms that may be at work.     

Brightness profiles of C3 and NH3 in the atmosphere of P/Brorsen-Metcalf

Spectroscopic observations of Comet P/Brorsen-Metcalf were made on August 9–13, 1989. Spatial profiles extracted from long-slit spectra were analyzed to determine the lifetimes of C₃ and NH₂ radicals and their parents, as well as the tailward acceleration of these radicals. In our investigations we used a Monte Carlo model. The average lifetime for C₃ has been found to be 6.3 × 10⁴ s and that for the parent of C₃ to 6 × 10³ s. The spatial profiles of C₃ were almost symmetric and we need only 0.1 cm s⁻² as the tailward acceleration. According to our simulations, C₃H₄ (allene) can be considered as the parent for C₃. We obtained the average value 7.6 × 10⁴ s for the lifetime of NH₂ and 1.1 × 10⁴ s for the lifetime of the NH₂ parent. The tailward acceleration of NH₂ was not more than 0.1 cm s⁻². This result does not exceed the latest theoretical calculations of NH₂ and NH₃ lifetimes by a factor of 1.4. So, NH₃ may be considered as a parent for NH₂ in the atmosphere of P/Brorsen-Metcalf.     

Optical Spectroscopy of Comet C/2000 WM1 (LINEAR) at the Guillermo Harro Astrophysical Observatory in Mexico

We present a preliminary analysis of medium resolution optical spectra of comet C/2000 WM1 (LINEAR) obtained on 22 November 2001. Theemission lines of the molecules C₂, C₃, CN, NH₂,H₂O⁺ and presumably CO (Asundi and triplet bands) and C₂ ^-were identified in these spectra. By analysing the brightnessdistributions of the C₂, C₃, CN emission lines along theslit of the spectrograph we determined some physical parameters of theseneutrals, such as their lifetimes and expansion velocities inthe coma. The Franck–Condon factors for the CO Asundi bands and C₂ ^- bands were calculated using a Morse potential model.     

Limits on the12C to13C isotopic ratio in two white dwarfs

A search for the molecular¹²C¹³C isotopic bands in two white dwarfs is described. Spectroscopic observations of the two carbon band white dwarfs, BPM 27606 (=2153-51) andL 879-14 (=0435-08) have been obtained. These data have a resolution slightly better than 2 Å, higher than usually employed for white dwarfs and cover the v=1 vibrational swan bands of the C₂ molecule where the isotopic shift is of order 8 Å. The isotopic bands have not been detected. However, upper limits to the¹²C:¹³C abundance ratio derived from the data yield¹²C:¹³C>40 for BPM 27606 and¹²C:¹³C>8 for L879-14. If these ratios are representative of the material in the interiors of the carbon band white dwarfs and taking the low upper limits on the N and O abundances relative to C, this is consistent with the carbon having been formed by the 3 process and not having undergone any subsequent mixing with H-rich material. In addition, the C₂ vibrational bandheads are blueshifted, most probably by pressure shifts. This shows that the employment of higher resolutions reveals additional physical effects in the spectra of the carbon band white dwarfs that may become important for interpreting the cool end of the helium rich white dwarf sequence.     

New C13N14 search regions in the solar spectrum

Ten new rotational line positions, due to the (0,0) red C¹³N¹⁴ band, are calculated to fall squarely within continuum regions 1–2 Å wide in the near infrared solar spectrum, , 10 990–11 630. Precision observations of the isotopic line strengths in this spectral region, albeit difficult, should resolve the present ambiguity in the blue-violet observations of whether or not the solar C¹²/C¹³ ratio is equal to or larger than the terrestrial ratio.     

The changing rotational excitation of C3 in comet 9P/Tempel 1 during Deep Impact

The 4050 Å band of C₃ was observed with Keck/HIRES echelle spectrometer during the Deep Impact encounter. We perform a 2-dimensional analysis of the exposures in order to study the spatial, spectral, and temporal changes in the emission spectrum of C₃. The rotational population distribution changes after impact, beginning with an excitation temperature of ～45 K at impact and increasing for 2 hr up to a maximum of 61±5 K. From 2 to 4 hours after impact, the excitation temperature decreases to the pre-impact value. We measured the quiescent production rate of C₃ before the encounter to be 1.0×10²³ s^?1, while 2 hours after impact we recorded a peak production rate of 1.7×10²³ s^?1. Whereas the excitation temperature returned to the pre-impact value during the observations, the production rate remained elevated, decreasing slowly, until the end of the 4 hr observations. These results are interpreted in terms of changing gas densities in the coma and short-term changes in the primary chemical production mechanism for C₃.     

Identification of C4H5, C4H4, C3H3 and CH3 radicals produced from the reaction of atomic carbon with propene: Implications for the atmospheres of Titan and giant planets and for the interstellar medium

We observed the products C₄H₅, C₄H₄, C₃H₃ and CH₃ of the C(³P) + C₃H₆ reaction using product time-of-flight spectroscopy and selective photoionization. The identified species arise from the product channels C₄H₅ + H, C₄H₄ + 2H and C₃H₃ + CH₃. Product isomers were identified via measurements of photoionization spectra and calculations of adiabatic ionization energy. Product C₄H₅ probably involves three isomers HCCCHCH₃, H₂CCCCH₃ and H₂CCCHCH₂. In contrast, products C₄H₄ and C₃H₃ involve exclusively HCCCHCH₂ and H₂CCCH, respectively. Reaction mechanisms are unraveled with crossed-beam experiments and quantum-chemical calculations. The ³P carbon atom attacks the π orbital of propene (C₃H₆) to form a cyclic complex c-H₂C(C)CHCH₃ that rapidly opens the ring to form H₂CCCHCH₃ followed by decomposition to HCCCHCH₃/H₂CCCCH₃/H₂CCCHCH₂ + H and H₂CCCH + CH₃; the corresponding branching ratios are 7:5:10:78 predicted with RRKM calculations at collision energy 4 kcal mol^?1. Nascent C₄H₅ with enough internal energy further decomposes to HCCCHCH₂ + H. Ratios of products C₄H₅, C₄H₄ and C₃H₃ are experimentally evaluated to be 17:8:75. This work provides a comprehensive look at product channels of the title reaction and gives implications for the formation of hydrocarbons in extra-terrestrial environments such as Titan and carbon-rich interstellar media. We suggest that the title reaction, hitherto excluded in any chemical networks, needs to be taken into account at least in the atmosphere of Titan and carbon-rich molecular clouds where rapid neutral–neutral reactions are dominant and carbon atoms and propene are abundant.     

Optical Spectroscopy and Near-Infrared Observations of Comet C/2000 Wm1 (Linear) in December 2001 from Chile and Brazil

We report on the preliminary analysis of the high-resolution spectrum of CometC/2000 WM1 (LINEAR), obtained on Dec. 1, 2001 with the Fiber fed ExtendedRange Optical Spectrograph (FEROS) installed on the 1.52-m telescope of ESO(Chile). Many emission lines of the molecules C₂, C₃, CN, CH, CH⁺,NH₂, CO, CO⁺, H₂O⁺ and, presumably, C₂ ^- were identifiedin the spectral range 400–900 nm. Also, near-infrared photometry was performed on Dec. 2 and 3, with the infraredcamera (CamIV) attached to the 0.60-m Boller and Chivens telescope of the Picodos Dias Observatory (LNA/MCT), Brazil. We report the preliminary and comparativeanalysis of the I-J and J-H color indices.     

Comet C/2010X1 (Elenin). Unrealized expectations

We present the analysis of the photometric and spectroscopic data obtained for comet C/2010 X1 (Elenin) when it was at a distance of 2.92 AU from the Sun. The observations were made at the prime focus of the 6-m BTA telescope with the SCORPIO focal reducer. The magnitude of the comet, measured in the R _c -band with an 9?? aperture radius amounted to 16?8 ± 0?1. The computed dust production rate was estimated to be about 6 kg/s. The cometary coma manifested the emissions in the (0?C0) band of the CN molecule violet system, and a number of emission band heads of the C₃ molecule. The gas production rate of the molecules is determined using the Haser model and amounts to 1.41 × 10²⁴ and 4.20 × 10²³ molecules per second for CN and C₃, respectively. The ratio of gas production rates log[Q(C₃)/Q(CN)] is equal to ?0.85, which is close to the mean value, determined for a significant number of comets. A normalized gradient of the cometary dust reflectivity, calculated for the 4430?C6840 ? spectral range amounts to 14.3 ± 1.2%.     

Spectra Of Split Comet C/1999 S4 (Linear)

We obtained spectra of comet C/1999 S4 (LINEAR) with the UAGS spectrograph(long slit and CCD) installed on the 1-m Zeiss reflector of the SAO of the RAS(Northern Caucuses, Nizhny Arkhyz) on July 23/24, 26/27 and 27/28, 2000. OnJuly 22/23, before the splitting of the cometary nucleus, several emission lines,such as C₂, C₃, CN, NH, CH, NH₂, CO⁺, H₂O⁺ wereclearly identified in the spectra. The inspections of the CCD spectra obtainedon July 27/28, 2000 reveals only very weak emission lines superimposed on thesolar reflection spectrum. From analyzing the surface brightness profile of C₂ along the slit the velocity of separation of two secondary fragments (V = 10 km/h) and the energy of the fragment separation (E = 8.7 × 10¹⁵ erg) were estimated. A luminescence cometary continuum of 26% of the total continuum level is detected in the spectra of the comet at 5000 Å. Possible mechanisms of nucleus splitting are discussed.     

Spectral studies of comet C/2001 Q4 (NEAT)

The paper presents the results of the spectral observations of comet C/2001 Q4 (NEAT) acquired with the Zeiss-600 telescope of the Andrushevka astronomical observatory in May 2004. The spectrum of the comet was obtained in the range of 3600–8200 Å. We identified a number of emission features in the spectrum of comet C/2001 Q4 (NEAT). The emission bands of C₂, C₃, CN, CH, NH₂, H₂O⁺ were detected in the spectrum of the comet, and their intensities were determined. The ratios of gas-production rates Q(C₂)/Q(CN) = 0.23, Q(C₃)/Q(CN) = ?0.79, and Q(NH₂)/Q(CN) = ?0.029 were determined with the Haser model.     

Total internal partition sums to support planetary remote sensing

Total internal partition sums are determined from 65 to 3010 K for ¹³C¹⁸O₂, ¹³C¹⁸O¹⁷O, ¹²CH₃D, ¹³CH₃D, H¹²C¹²CD, ¹³C¹²CH₆, ¹²CH₃⁷⁹Br, ¹²CH₃⁸¹Br, ¹²CF₄, H¹²C¹²C¹²C¹²CH, H¹²C¹²C¹²C¹⁴N, H¹²C¹²C¹³C¹⁴N, H¹²C¹³C¹²C¹⁴N, H¹³C¹²C¹²C¹⁴N, H¹²C¹²C¹²C¹⁵N, D¹²C¹²C¹²C¹⁴N, ¹⁴N¹²C¹²C¹⁴N, ¹⁵N¹²C¹²C¹⁵N, ¹²C³²S, ¹²C³³S, ¹²C³⁴S, ¹³C³²S, H₂, HD, ³²S¹⁶O, ³²S¹⁸O, ³⁴S¹⁶O, ¹²C₃H₄, ¹²CH₃, ¹²C³²S₂, ³²S¹²C³⁴S, ¹³C³²S₂, and ³²S¹²C³³S. These calculations complete the partition sum data needed for additional isotopologues in HITRAN2008 and also extend the partition sums to molecules of astrophysical interest. These data, at 25 K steps, are incorporated into a FORTRAN code (TIPS_2011.for) that can be used to rapidly generate the data at any temperature in the range 70-3000 K.     

Absolute redshifts in the C iv 1548 Å line in the transition region of the quiet Sun

Observations with the UVSP instrument on the SMM spacecraft were made at the polar limb and disk center for the accurate determination of Doppler shifts of the Civ 1548 Å emission line formed at 10⁵ K in the transition region of the quiet Sun. Individual data points representing 3 arc sec square pixels yield both redshifts and blueshifts, but the mean values from four different days of observations are toward the red. The mean redshifts are in the range 4–8 km s^-1 and are produced by nearly vertically directed flows; the uncertainty associated with the mean values correspond to ±0.5 km s^-1. The redshift increases with brightness of the Civ line.     

The C+, C,CO network in interstellar clouds

A chemical network determining the formation and destruction of C⁺, C, and CO and other species is set up and applied to spherical clouds in the normal interstellar radiation field. The spherical geometry adopted gives results which are different from those for slab models. The sensitivity of chemical species to chemical and astronomical parameters is explored. The relevance of this work to the observations is discussed.     

Infrared measurements of the chemical composition of C/2006 P1 McNaught

C/2006 P1 McNaught is a dynamically new comet from the Oort cloud that passed very close to the Sun, driving overall volatile production rates up to about 10³¹ molecules s⁻¹. Post-perihelion observations were obtained in a target-of-opportunity campaign using the CSHELL instrument at the NASA Infrared Telescope Facility atop Mauna Kea, Hawaii, on UT 2007 January 27 and 28. Eight parent volatiles (H₂O, CH₄, C₂H₂, C₂H₆, HCN, CO, NH₃, H₂CO) and two daughter fragments (OH and NH₂) were detected, enabling the determination of a rotational temperature and production rate for H₂O on UT January 27 and absolute and relative production rates for all the detected parent species on UT January 28. The chemical composition measured in the coma suggests that this close perihelion passage stripped off processed outer surface layers, likely exposing relatively fresh primordial material during these observations. The post-perihelion abundances we measure for CO and CH₄ (relative to H₂O) are slightly depleted while C₂H₂, NH₂ and possibly NH₃ are enhanced when compared to the overall comet population. Measured abundances for other detected molecular species were within the range typically observed in comets.     

Comparison of X-rays from Comets LINEAR (C/1999 S4) and McNaught-Hartley (C/1999 T1)

The Chandra X-ray Observatory (CXO) observations of Comets McNaught-Hartley (MH) and LINEAR S4 (S4) have been processed in the same way to compare X-rays from those comets. The X-ray isophotes are crescent-like in S4 and more circular in MH because of the different phase angles (98° and 44°, respectively). The peak X-ray brightness is greater in S4 than that in MH by a factor of 1.5 and smaller by a factor of 1.7 after the correction for heliocentric distance. The X-ray luminosities of MH and S4 are equal to 8.6 and 1.4×10¹⁵ erg s⁻¹ inside the apertures of ρ=1.5 and 0.5×10⁴ km, respectively. (Brightness is 20% of the peak value at these ρ.) Efficiencies of X-ray excitation corrected to the solar wind flow are similar and equal to 4.3×10⁻¹⁴ erg AU^3/2 in both comets. This confirms the solar wind excitation of X-rays in comets. Spectra of the comets were extracted with a special care of the background correction and using an energy-dependent spectral resolution code. The MH spectrum consists of ten emissions instead of nine emissions in the previously published spectrum. The new emission at 307 eV fills in a strong minimum in the previous spectrum and removes the major difference between that spectrum and the synthetic spectrum. This emission is assigned to the C⁺⁴ and Mg⁺⁹ lines. The positions of the other emissions and their identification are similar to those in the previous spectrum. The S4 spectrum consists of eight emissions, and four emissions are the same as in MH. The line identification is given. Ion ratios in the solar wind have been extracted from the spectra. O⁺⁸/O⁺⁷ is equal to 0.29±0.04 and 0.14±0.02 in MH and S4, and this difference correlates with the higher solar wind speed in S4. Ne⁺⁹/O⁺⁷ is (15±6)×10⁻³ and (19±7)×10⁻³, and these are the first data on Ne⁺⁹ in the solar wind. C⁺⁶/O⁺⁷ is 0.7±0.2 in both MH and S4. X-ray spectroscopy of comets may be used as a diagnostic tool to study the solar wind composition.     

Neutral-neutral reactions for the formation of C3O and C3S

We investigate, neutral-neutral radiative association reactions (C₂+CO) and (C₂+CS) for the formation of C₃O and C₃S respectively by DFT. Both the reactions are spin allowed and found to be exothermic and barrierless in nature. The product of these reactions are perfectly linear and the calculated rotational transitions are in good agreement with earlier published data. At the DFT/TZ2P level, the difference between the calculated rotational constant and experimental one is 0.064 % for C₃O and 0.16 % for C₃S. We also discussed the intrinsic and relative stability of these molecules.     

Presence of C2 molecular Lines in Sunspot Umbral Spectra

The C₂ molecule is well known for its astrophysical importance. The radiative transition parameters that include Franck-Condon (FC) factor, r-centroid, electronic transition moment, Einstein coefficient, absorption band oscillator strength, effective temperatures and radiative life time have been estimated for the Swan band $(d^3{\Pi }_g-a^3{\Pi }_u)$ system of C₂ molecule for experimentally observed vibrational levels using RKR (Rydberg–Klein–Rees) potential energy curve. The lifetime for the d³Π_g state of C₂ molecule was found to be 82.36 ns for the $v^{\prime }=0$ level. A reliable numerical integration method has been used to solve the radial Schrödinger equation for the vibrational wave functions of upper and lower electronic states based on the latest available spectroscopic data and known wavelengths. The estimated radiative transition parameters are tabulated. The effective vibrational temperature of Swan band system of C₂ molecule is found agreed with the effective rotational temperature from photosphere spectrum. Hence, the radiative transition parameters and effective temperatures help us to ascertain the presence of C₂ molecule in the interstellar medium, photosphere and sunspots.     

Haser model CN,C2 and C3 production rates in some comets

Emission fluxes of CN, C₂ and C₃ species observed in the coma of some comets are analysed in the framework of Haser model. CN, C₂ and C₃ production rates are determined using recently derived fluorescence efficiencies and dependence of CN, C₂ and C₃ production rates on the heliocentric distance is studied. Evidence for a burst type activity around January 15, 1974 in the post-perihelion period of comet Kohoutek (1973f) is observed.     

Ubv(Ri)C Photometry of the Contact W Uma Binary Bd + 14∘5016

New UBV(RI)_C observations and radial velocities of the W UMa-type system BD + 14^∘5016 were collected. Changes of the properties of a hot spot, located on the surface of the primary component, have been noticed.