Aditional Ultra-High-Resolution Observations of Ca+ Ions in the Local Insterstellar Medium

We present ultra-high-resolution (0.35 km s−1 FWHM) observations of the interstellar Ca K line towards seven nearby stars. The spectral resolution was sufficient to resolve the line profiles fully, thereby enabling us to detect hitherto unresolved velocity components, and to obtain accurate measurements of the velocity dispersions (b values). Absorption components with velocities similar to those expected for the Local Interstellar Cloud (LIC) and the closely associated ‘G cloud’ were identified towards six of the seven stars. However, in most cases the b values deduced for these components were significantly larger than the b ≈ 2.2 km s−1 (i.e. Tk ≈ 7000 K, vt ≈ 1 km s−1) expected for the LIC, and it is argued that this results from the presence of additional, spectrally unresolved, components having similar velocities and physical conditions. For two stars (δ Vel and α Pav) we detect interstellar components with much smaller b values (1.1 ± 0.3 and 0.8 ± 0.1 km s−1, respectively) than are expected for low-density clouds within the Local Bubble. In the case of the narrow α Pav component, we also find an anomalously large Na i/Ca ii column density ratio, which is indicative of a relatively high density. Thus it is possible that, in addition to LIC-type clouds, the local interstellar medium contains a population of previously undetected cooler and denser interstellar clouds

δ Orionis: Further temporal variability and evidence for small-scale structure in the interstellar medium

We report here the detection of both spatial and temporal variations in interstellar absorption in the line of sight to δ Orionis. First, we present new high-resolution (R≈110 000) observations of the interstellar D lines of Na i towards both δ Ori A and C. Comparison of these spectra highlights variations in absorption between the two stars, indicative of small-scale spatial structure in the interstellar medium in this direction over distances of less than ≈15 000 au (the projected separation of the two stars). Components with the largest Na i column densities and lowest velocity dispersions are, in general, found to be subject to the greatest differences; in fact the narrowest component detected is only observed in one of the sightlines. This effect has also been reported by Meyer & Blades. Secondly, we present new ultra-high-resolution (R≈900 000) Na i D1 observations and high-resolution (R≈110 000) Ca ii H & K observations of δ Ori A which, through ultra-high-resolution work conducted between 1994 and 2000, has been shown to exhibit a time-variable interstellar Na i absorption component. These new observations, while revealing the further reduction in intensity of the time-variable Na i absorption, indicate constant Ca ii absorption over the same period. This results in a dramatic reduction in the Na°/Ca+ abundance ratio, perhaps indicating the line of sight to be gradually probing a less-dense outer region of an absorbing filament

κ Velorum: Another variable interstellar sightline?

We present ultra-high-resolution (R = 900 000) observations of interstellar Na i and K i absorption lines towards κ Vel (HD 81188) which show clear evidence for temporal variation between 1994 and 2000. Specifically, the column densities of K0 and Na0 in the main velocity component have increased by 40 and 16 per cent, respectively, over this period. Earlier work had suggested that this component actually consists of two unresolved sub-components; this result is confirmed here, and the overall line profile is found to be consistent with only one of these sub-components having increased in strength since 1994. We argue that this variation is consistent with the line of sight gradually probing a cold, dense interstellar filament of the kind recently proposed by Heiles to explain other observations of small-scale structure in the interstellar medium

Ultra-high-resolution observations of circumstellar K I and C2 around the post-AGB star HD 56126

We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s−1 (FWHM), to observe K I and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K I, two of which are also present in C2. We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions (b-values) of 0.2–0.3 km s−1 for the K I components, and 0.54 ± 0.03 km s−1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K I and 420 K for C2, although the b-value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures (Tk ≈10 K) and high densities (n ≈ 106 to 107 cm−3) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell

Organic matter responses to radiation under lunar conditions

Large bodies, such as the Moon, which have remained relatively unaltered for long periods of time have the potential to preserve a record of organic chemical processes from early in the history of the solar system. A record of volatiles and impactors may be preserved in buried lunar regolith layers that have been capped by protective lava flows. Of particular interest is the possible preservation of prebiotic organic materials delivered by ejected fragments of other bodies, including those originating from the surface of the early Earth. Lava flow layers would shield the underlying regolith and any carbon-bearing materials within them from most of the effects of space weathering, but the encapsulated organic materials would still be subject to irradiation before they were buried by regolith formation and capped with lava. We have performed a study to simulate the effects of solar radiation on a variety of organic materials mixed with lunar and meteorite analogue substrates. A fluence of ~3 x 1013 protons cm-2 at 4-13 MeV, intended to be representative of solar energetic particles, has little detectable effect on low molecular weight (≤C30) hydrocarbon structures that can be used to indicate biological activity (biomarkers) or the high molecular weight hydrocarbon polymer poly(styrene-co-divinylbenzene), and has little apparent effect on a selection of amino acids (≤C9). Inevitably, more lengthy durations of exposure to solar energetic particles may have more deleterious effects and rapid burial and encapsulation will always be more favourable to organic preservation. Our data indicate that biomarker compounds that may be used to infer biological activity on their parent planet can be relatively resistant to the effects of radiation, and may have a high preservation potential in paleoregolith layers on the Moon

Ultra-high-resolution measurements of the intrinsic line profiles of interstellar C-2 towards zeta Ophiuchi and HD 169454

We have used the Ultra-High-Resolution Facility at the Anglo-Australian Telescope (AAT), operating at a resolution of 0.35 km s−1 (FWHM), to measure the intrinsic profiles of the Q(2) and Q(4) lines of the (2-0) Phillips band of interstellar C2 towards ζ Oph and HD 169454. The C2 lines were found to be very narrow, with intrinsic velocity dispersions (b-values) in the range 0.25−0.71 km s−1. In the case of ζ Oph, two velocity components (separation 1.10 ± 0.17 km s−1) have been resolved, and found to have rather different linewidths and rotational excitation temperatures. In the case of HD 169454, the data are consistent with a single velocity component, but the well-defined b-value (0.59 + 0.04 km s−1) and low kinetic temperature would then imply supersonic turbulent velocities. One way to avoid this conclusion is to postulate the existence of unresolved velocity structure (or a velocity gradient) within the cloud

Detection of a variable interstellar absorption component towards δ Orionis A

Observations of δ Ori A made with the UHRF in its highest resolution mode (R≈900 000) have revealed the presence of a cool (Tk⩽350 K) variable absorption component at a heliocentric velocity of +21.3 km s−1. The component is detected in Na I D1, where clear hyperfine splitting is seen, and Ca II K. Comparison of our data with existing spectra suggests that the component has consistently increased in strength from 1966 to 1994, and subsequently reduced in intensity by 1999. Following a discussion of the possible origins of this component it is concluded that an interstellar, rather than circumstellar, origin is most likely. This is one of very few detections of variable interstellar absorption reported in the literature, and we suggest an origin within filamentary material associated with the expanding H I shell surrounding the Orion-Eridanus superbubble

High-Resolution Observations of Interstellar NA i and CA II Absorption Lines toward the Scorpius OB1 Association

Observations of Na I and Ca II in absorption toward 22 stars in the Sco OB1 region, obtained at resolution R = 100,000 with a coude echelle spectrograph and 3.3-m camera on the 1.9-m telescope at Mt. Stromlo Observatory during 1986, are reported. The data are presented in extensive tables and graphs and analyzed in detail. Features discussed include (1) strong absorption at heliocentric velocities between 0 and -20 km/sec, (2) sharp discrete components with blueshifted velocities of up to -50 km/sec, and (3) some absorption at positive heliocentric velocities up to +20 km/sec. The (Na I)/(Ca II) ratios are found to be 4-200 for component (1), near 1 for component (2), and 0.4 or less for component (3)

An ultra-high-resolution study of the interstellar medium towards Orion

We report ultra-high-resolution observations graphic of Na I, Ca II, K I, CH and CH+ for interstellar sightlines towards 12 bright stars in Orion. These data enable the detection of many more absorption components than previously recognized, providing a more accurate perspective on the absorbing medium. This is especially so for the line of sight to the Orion nebula, a region not previously studied at very high resolution. Model fits have been constructed for the absorption-line profiles, providing estimates for the column density, velocity dispersion and central velocity for each constituent velocity component. A comparison between the absorption occurring in sightlines with small angular separations has been used, along with comparisons with other studies, to estimate the line-of-sight velocity structures. Comparisons with earlier studies have also revealed temporal variability in the absorption-line profile of ζ Ori, highlighting the presence of small-scale spatial structure in the interstellar medium on scales of ≈10 au. Where absorption from both Na0 and K0 is observed for a particular cloud, a comparison of the velocity dispersions measured for each of these species provides rigorous limits on both the kinetic temperature and turbulent velocity prevailing in each cloud. Our results indicate the turbulent motions to be subsonic in each case. graphic abundance ratios are derived for individual clouds, providing an indication of their physical state