Sub-millimeter images of a dusty Kuiper belt around eta Corvi

We present sub-millimeter and mid-infrared images of the circumstellar disk around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size of ~100AU. At 450um the emission is found to be extended at all position angles, with significant elongation along a position angle of 130+-10deg; at the highest resolution (9.3") this emission is resolved into two peaks which are to within the uncertainties offset symmetrically from the star at 100AU projected separation. Modeling the appearance of emission from a narrow ring in the sub-mm images shows the observed structure cannot be caused by an edge-on or face-on axisymmetric ring; the observations are consistent with a ring of radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are possible if the dust distribution includes two clumps similar to Vega; we show how such a clumpy structure could arise from the migration over 25Myr of a Neptune mass planet from 80-105AU. The inner 100AU of the system appears relatively empty of sub-mm emitting dust, indicating that this region may have been cleared by the formation of planets, but the disk emission spectrum shows that IRAS detected an additional hot component with a characteristic temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the emission to be unresolved with no background sources which could be contaminating the fluxes measured by IRAS. The age of this star is estimated to be ~1Gyr. It is very unusual for such an old main sequence star to exhibit significant mid-IR emission. The proximity of this source makes it a perfect candidate for further study from optical to mm wavelengths to determine the distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February 2005 issu

CO emission from discs around isolated HAeBe and Vega-excess stars

We describe results from a survey for J=3-2 12CO emission from visible stars with an infrared excess. The line is clearly detected in 21 objects, with molecular gas (>10^-3 Jupiter masses) common in targets with infrared excesses >0.01 (>56% of objects). Such high excesses indicate the presence of a disc of opening angle >12 degrees; within this, the optically thick disc prevents CO photodissociation. Two or three stars with associated CO have an excess <0.01, implying a disc opening angle <1 degree. Most line profiles are double-peaked or relatively broad. Model fits, assuming a Keplerian disc, indicate outer radii, R_out, of ~20-300 au. As many as 5 discs have outer radii smaller than the Solar System (50 au), and a further 4 have gas at radii <20 au. R_out is independent of the stellar spectral type (from K through to B9), but is correlated with total dust mass. R_out appears to decrease with time: discs around stars of age 3-7 Myr have a mean radius of ~210 au, whereas discs of age 7-20 Myr are a factor of 3 smaller. The only bona fide debris disc with detected CO is HD9672; this has a double peaked line profile and is the most compact gas disc observed, with a modelled radius 17 au). A fit to HD141569 suggests the gas lies in two rings of radii 90 and 250 au, similar to the scattered light structure. In both AB Aur and HD163296 the sizes of the molecular and dust scattering discs are also similar, suggesting that the gas and small dust grains are co-located.Comment: 16 pages, 5 figures MNRAS - accepte

Auxetic regions in large deformations of periodic frameworks

In materials science, auxetic behavior refers to lateral widening upon stretching. We investigate the problem of finding domains of auxeticity in global deformation spaces of periodic frameworks. Case studies include planar periodic mechanisms constructed from quadrilaterals with diagonals as periods and other frameworks with two vertex orbits. We relate several geometric and kinematic descriptions.Comment: Presented at the International Conference on "Interdisciplinary Applications of Kinematics" (IAK18), Lima, Peru, March 201

CN and HCN in Dense Interstellar Clouds

We present a theoretical investigation of CN and HCN molecule formation in dense interstellar clouds. We study the gas-phase CN and HCN production efficiencies from the outer photon-dominated regions (PDRs) into the opaque cosmic-ray dominated cores. We calculate the equilibrium densities of CN and HCN, and of the associated species C+, C, and CO, as functions of the far-ultraviolet (FUV) optical depth. We consider isothermal gas at 50 K, with hydrogen particle densities from 10^2 to 10^6 cm^-3. We study clouds that are exposed to FUV fields with intensities 20 to 2*10^5 times the mean interstellar FUV intensity. We assume cosmic-ray H2 ionization rates ranging from 5*10^-17 s^-1, to an enhanced value of 5*10^-16 s^-1. We also examine the sensitivity of the density profiles to the gas-phase sulfur abundance.Comment: Accepted for publication in ApJ, 33 pages, 8 figure

Informing the development of online weight management interventions:a qualitative investigation of primary care patient perceptions

Background: The internet is a potentially promising medium for delivering weight loss interventions. The current study sought to explore factors that might influence primary care patients’ initial uptake and continued use (up to four-weeks) of such programmes to help inform the development of novel, or refinement of existing, weight management interventions.Methods: Semi-structured interviews were conducted with 20 patients purposively sampled based on age, gender and BMI from a single rural general practice. The interviews were conducted 4 weeks after recruitment at the general practice and focused on experiences with using one of three freely available weight loss websites. Thematic Analysis was used to analyse the data.Results: Findings suggested that patients were initially motivated to engage with internet-based weight loss programmes by their accessibility and novelty. However, continued use was influenced by substantial facilitators and barriers, such as time and effort involved, reaction to prompts/reminders, and usefulness of information. Facilitation by face-to-face consultations with the GP was reported to be helpful in supporting change.Conclusions: Although primary care patients may not be ready yet to solely depend on online interventions for weight loss, their willingness to use them shows potential for use alongside face–to-face weight management advice or intervention. Recommendations to minimise barriers to engagement are provided

Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+

Using an absorption line from the metastable (J, K) = (3, 3) level of H3+ together with other lines of H3+ and CO observed along several sightlines, we have discovered a vast amount of high temperature (T ~ 250 K) and low density (n ~ 100 cm-3) gas with a large velocity dispersion in the Central Molecular Zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately three fourths of the H3+ along the line of sight to the brightest source we observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the remaining H3+ located in intervening spiral arms. About half of H3+ in the CMZ has velocities near ~ - 100 km s-1 indicating that it is associated with the 180 pc radius Expanding Molecular Ring which approximately forms outer boundary of the CMZ. The other half, with velocities of ~ - 50 km s-1 and ~ 0 km s-1, is probably closer to the center. CO is not very abundant in those clouds. Hot and diffuse gas in which the (3, 3) level is populated was not detected toward several dense clouds and diffuse clouds in the Galactic disk where large column densities of colder H3+ have been reported previously. Thus the newly discovered environment appears to be unique to the CMZ. The large observed H3+ column densities in the CMZ suggests an ionization rate much higher than in the diffuse interstellar medium in the Galactic disk. Our finding that the H3+ in the CMZ is almost entirely in diffuse clouds indicates that the reported volume filling factor (f &#8805; 0.1) for n &#8805; 104 cm-3 clouds in the CMZ is an overestimate by at least an order of magnitude.Comment: 33 pages, 5 figures, 3 table

HCO+ detection of dust-depleted gas in the inner hole of the LkCa 15 pre-transitional disk

LkCa 15 is an extensively studied star in the Taurus region, known for its pre-transitional disk with a large inner cavity in the dust continuum and normal gas accretion rate. The most popular hypothesis to explain the LkCa 15 data invokes one or more planets to carve out the inner cavity, while gas continues to flow across the gap from the outer disk onto the central star. We present spatially unresolved HCO+ J = 4 → 3 observations of the LkCa 15 disk from the James Clerk Maxwell telescope (JCMT) and model the data with the ProDiMo code. We find that: (1) HCO+ line-wings are clearly detected, certifying the presence of gas in the cavity within ≲50 au of the star. (2) Reproducing the observed line-wing flux requires both a significant suppression of cavity dust (by a factor ≥ 104 compared to the interstellar medium (ISM)) and a substantial increase in the gas scale-height within the cavity (H0/R0 ∼ 0.6). An ISM dust-to-gas ratio (d:g = 10-2) yields too little line-wing flux, regardless of the scale-height or cavity gas geometry, while a smaller scale-height also under-predicts the flux even with a reduced d:g. (3) The cavity gas mass is consistent with the surface density profile of the outer disk extended inwards to the sublimation radius (corresponding to mass Md ∼ 0.03 M⊙), and masses lower by a factor ≥10 appear to be ruled out.Publisher PDFPeer reviewe

A multi-wavelength analysis for interferometric (sub-)mm observations of protoplanetary disks: radial constraints on the dust properties and the disk structure

Theoretical models of grain growth predict dust properties to change as a function of protoplanetary disk radius, mass, age and other physical conditions. We lay down the methodology for a multi-wavelength analysis of (sub-)mm and cm continuum interferometric observations to constrain self-consistently the disk structure and the radial variation of the dust properties. The computational architecture is massively parallel and highly modular. The analysis is based on the simultaneous fit in the uv-plane of observations at several wavelengths with a model for the disk thermal emission and for the dust opacity. The observed flux density at the different wavelengths is fitted by posing constraints on the disk structure and on the radial variation of the grain size distribution. We apply the analysis to observations of three protoplanetary disks (AS 209, FT Tau, DR Tau) for which a combination of spatially resolved observations in the range ~0.88mm to ~10mm is available (from SMA, CARMA, and VLA), finding evidence of a decreasing maximum dust grain size (a_max) with radius. We derive large a_max values up to 1 cm in the inner disk between 15 and 30 AU and smaller grains with a_max~1 mm in the outer disk (R > 80AU). In this paper we develop a multi-wavelength analysis that will allow this missing quantity to be constrained for statistically relevant samples of disks and to investigate possible correlations with disk or stellar parameters.Comment: 19 pages, 15 figures, accepted for publication in A&

Southwest Pacific deep-water carbonate chemistry during the Mid-Pleistocene Transition

After more than 40 years of research, there is still wide disagreement in defining when the Mid-Pleistocene Transition (MPT) occurred, with climate reconstructions ranging from an abrupt versus gradual transition that began as early as 1500 ka and ended as late as 600 ka. Our recent work in the Southwest Pacific (Ocean Drilling Program Site 1123) has provided some evidence for a rapid transition, suggesting that the MPT was initiated by an abrupt increase in global ice volume 900 thousand years ago [1]. This study uses shallow-infaunal benthic foraminifera Uvigerina spp. to disentangle the contributions of deep-water temperature (using Mg/Ca ratios) and ice volume to the oxygen isotopic composition of foraminiferal calcite over the last 1.5 Ma. The resulting sea-level reconstruction across the MPT shows that the critical step in ice-volume variation was associated with the suppression of melting in Marine Isotope Stage (MIS) 23, followed by renewed ice growth in MIS 22 to yield a very large ice sheet with 120 m of sea level lowering. Here, we built on this work with the aim to investigate further the abrupt event centered on MIS 24 to 22 (the ‘900-ka event’) and try to shed some light on the processes and mechanisms that caused the MPT. Different hypotheses account for the origin of the MPT as a response to long-term ocean cooling, perhaps because of lowering CO2. To better quantify the role of the carbon system during the MPT, we reconstruct past changes in bottom water inorganic carbon chemistry from the trace element (B/Ca) and stable isotopic composition of calcite shells of the infaunal benthic foraminifera Uvigerina spp. from 1100 ka to 350 ka at ODP Site 1123. This site was retrieved from Chatham Rise, east of New Zealand in the Southwest Pacific Ocean (41º47.2’S, 171º 29.9’ W, 3290 m water depth) and lies under the Deep Western Boundary Current (DWBC) that flows into the Pacific Ocean, and is responsible for most of the deep water in that ocean; DWBC strength is directly related to processes occurring around Antarctica. The ratio of boron to calcium (B/Ca) in benthic foraminifer shells has proven to be a reliable indicator of the calcite saturation state of ocean bottom waters. The comparison between benthic foraminifera δ18O and δ13C shows a similar trend at ODP Site 1123, implying a close relationship between these climate and carbon cycle signals, and we use our B/Ca record reconstructed from the same samples to explore the potential processes behind this tight coupling. These results permit preliminary discussion on the deep-water carbonate saturation state during glacial/interglacial cycles. Deep-water temperatures estimates using Mg/Ca and oxygen isotopic composition of seawater (δ18Osw) are available from Site 1123 for the last 1.5 million years [1] and the phase relationship between the different signals is tentatively assessed for the early/middle Pleistocene, when different patterns of climate variability have been inferred from marine and ice cores records. [1] Elderfield et al. (2012). Evolution of ocean temperature and ice volume through the Mid Pleistocene Climate Transition. Science, vol. 337, 6095, 704-70