Morphology of HCN and CN in Comet Hale-Bopp (1995 O1)

We compare images of Comet Hale-Bopp (1995 O1) in HCN and CN taken near perihelion (April 1, 1997) to determine the origin of CN in comets. We imaged the J=1→0 transition of HCN at λ=3 mm with the BIMA Array. Data from two weeks around perihelion were summed within four phase bins based on the rotational period of the comet. This increases both the signal-to-noise ratio and the u-v coverage while decreasing the smearing of the spatial features. The similarly phased narrowband CN images were taken at Lowell Observatory within the same range of dates as the HCN images. We find that there is a better correlation between HCN and CN than between HCN and the optically dominant dust. If the CN in jets does have a dust source it would have to have a very low albedo and/or small particle size. The production rates are consistent with HCN being a primary parent of CN, although there are discrepancies between the HCN destruction scalelength and the CN production scalelength which we discuss.     

Small hypervelocity particles captured in aerogel collectors: Location,extraction, handling and storage

Abstract— It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit.     

Simulations of baryon oscillations

The coupling of photons and baryons by Thomson scattering in the early universe imprints features in both the cosmic microwave background (CMB) and matter power spectra. The former have been used to constrain a host of cosmological parameters, the latter have the potential to strongly constrain the expansion history of the universe and dark energy. Key to this program is the means to localize the primordial features in observations of galaxy spectra which necessarily involve galaxy bias, non-linear evolution and redshift space distortions. We present calculations, based on mock catalogs produced from high-resolution N-body simulations, which show the range of behaviors we might expect of galaxies in the real universe. We investigate physically motivated fitting forms which include the effects of non-linearity, galaxy bias and redshift space distortions and discuss methods for analysis of upcoming data. In agreement with earlier work, we find that a survey of several Gpc³ would constrain the sound horizon at z  1 to about 1%.     

Why chromatic imaging matters

During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u ? v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, we present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix we include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, we recovered chromatic images, from simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.     

Jet Deflection by a Quasi-Steady-State Side Wind in the Laboratory

We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium.     

40Ar‐39Ar studies of whole rock nakhlites: Evidence for the timing of formation and aqueous alteration on Mars

Abstract— 20–25 mg whole rock samples of the nakhlites Lafayette and Nakhla have been analyzed via the ⁴⁰Ar‐³⁹Ar technique, in part to verify their formation ages, but primarily, in an attempt to determine the timing of aqueous alteration in these martian meteorites. As in previous studies, plateaus in apparent age are observed at about 1300 Ma (1322 ± 10 for Lafayette, 1332 ± 10 and 1323 ± 11 for Nakhla), presumably corresponding to crystallization ages. The plateaus are not entirely flat, perhaps reflecting the effects of recoil during creation of ³⁹Ar in the nuclear irradiation. The first 5–20% of the K‐derived Ar released from all three samples give apparent ages <1300 Ma. Coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance, we believe the low temperature pattern represents more recent (than 1300 Ma) formation of martian aqueous alteration products such as iddingsite. No low temperature plateaus are observed. This is consistent with petrographic evidence for multiple formation events, although the lack of low temperature plateaus is far from conclusive. On the other hand, if there was a single time of alteration, we believe that it will be difficult, if not impossible, to determine it using the K‐Ar system.     

Discrete calculations of interstellar migration and settlement

Monte Carlo calculations of the expansion of space-faring civilizations are presented for a wide range of values of the population growth coefficient (α) and emigration coefficient (γ). Even for the very low values proposed by Newman and Sagan (α = 10^?4per year; γ = 10^?8per year) the migration wavefront expands at 1.4 × 10^?5 pc per year. Even with this low expansion velocity, such a civilization would fill the Galaxy in about 10⁹ years. Filling times of the order of 60 million years seem probable. The wavefront velocity is approximated by $\text{υ =}\text{Δr}\text{[(}\text{Δx}\text{υ}{}_{\mathrm{<mtext>s</mtext>}}\text{)}\text{+ (}\text{1}\text{α}\text{)}\text{ln}\text{(}\text{2α}\text{γ}\text{)]}$, where $\text{Δr}$ is the average radial distance traveled, $\text{δx}$ the average distance traveled, and υ_s the ship speed. This approximation was derived by Newman.