Target selection for the SUNS and DEBRIS surveys for debris discs in the solar neighbourhood

Debris discs - analogous to the Asteroid and Kuiper-Edgeworth belts in the Solar system - have so far mostly been identified and studied in thermal emission shortward of 100 um. The Herschel space observatory and the SCUBA-2 camera on the James Clerk Maxwell Telescope will allow efficient photometric surveying at 70 to 850 um, which allow for the detection of cooler discs not yet discovered, and the measurement of disc masses and temperatures when combined with shorter wavelength photometry. The SCUBA-2 Unbiased Nearby Stars (SUNS) survey and the DEBRIS Herschel Open Time Key Project are complimentary legacy surveys observing samples of ~500 nearby stellar systems. To maximise the legacy value of these surveys, great care has gone into the target selection process. This paper describes the target selection process and presents the target lists of these two surveys.Comment: 67 pages with full tables, 7 figures, accepted to MNRA

Radial Distribution of Dust Grains Around HR 4796A

We present high-dynamic-range images of circumstellar dust around HR 4796A that were obtained with MIRLIN at the Keck II telescope at lambda = 7.9, 10.3, 12.5 and 24.5 um. We also present a new continuum measurement at 350 um obtained at the Caltech Submillimeter Observatory. Emission is resolved in Keck images at 12.5 and 24.5 um with PSF FWHM's of 0.37" and 0.55", respectively, and confirms the presence of an outer ring centered at 70 AU. Unresolved excess infrared emission is also detected at the stellar position and must originate well within 13 AU of the star. A model of dust emission fit to flux densities at 12.5, 20.8, and 24.5 um indicates dust grains are located 4(+3/-2) AU from the star with effective size, 28+/-6 um, and an associated temperature of 260+/-40 K. We simulate all extant data with a simple model of exozodiacal dust and an outer exo-Kuiper ring. A two-component outer ring is necessary to fit both Keck thermal infrared and HST scattered-light images. Bayesian parameter estimates yield a total cross-sectional area of 0.055 AU^2 for grains roughly 4 AU from the star and an outer-dust disk composed of a narrow large-grain ring embedded within a wider ring of smaller grains. The narrow ring is 14+/-1 AU wide with inner radius 66+/-1 AU and total cross-sectional area 245 AU^2. The outer ring is 80+/-15 AU wide with inner radius 45+/-5 AU and total cross-sectional area 90 AU^2. Dust grains in the narrow ring are about 10 times larger and have lower albedos than those in the wider ring. These properties are consistent with a picture in which radiation pressure dominates the dispersal of an exo-Kuiper belt.Comment: Accepted by Astrophysical Journal (Part1) on September 9, 2004. 13 pages, 10 figures, 2 table

Correlation Between the Deuteron Characteristics and the Low-energy Triplet np Scattering Parameters

The correlation relationship between the deuteron asymptotic normalization constant, $A_{S}$, and the triplet np scattering length, $a_{t}$, is investigated. It is found that 99.7% of the asymptotic constant $A_{S}$ is determined by the scattering length $a_{t}$. It is shown that the linear correlation relationship between the quantities $A_{S}^{-2}$ and $1/a_{t}$ provides a good test of correctness of various models of nucleon-nucleon interaction. It is revealed that, for the normalization constant $A_{S}$ and for the root-mean-square deuteron radius $r_{d}$, the results obtained with the experimental value recommended at present for the triplet scattering length $a_{t}$ are exaggerated with respect to their experimental counterparts. By using the latest experimental phase shifts of Arndt et al., we obtain, for the low-energy scattering parameters ($a_{t}$, $r_{t}$, $P_{t}$) and for the deuteron characteristics ($A_{S}$, $r_{d}$), results that comply well with experimental data.Comment: 19 pages, 1 figure, To be published in Physics of Atomic Nucle

A catalog of visual double and multiple stars with eclipsing components

A new catalog of visual double systems containing eclipsing binaries as one component is presented. The main purpose of this catalog is to compile a complete list of all known multiples of this variety, both for current analysis and to highlight those in need of additional observations. All available photometric and astrometric data were analyzed, resulting in new orbits for eight systems and new times of minimum light for a number of the eclipsing binaries. Some of the systems in the catalog have acceptable solutions for their visual orbits, although in most cases their orbital periods are too long for simultaneous analysis. Also included, however, are a number of systems which currently lack an orbital solution but which may be suitable for simultaneous analysis in the future.Comment: 15 pages, 8 figures, 4 tables, published in A

Transits across a Cyclopentadienyl: Organic and Organometallic Haptotropic Shifts

references cited therein. (13) Electron acceptors which are also conjugated with the alkene r system will polarize the HOMO in the same directions as, but to a smaller extent than, Inductive acceptors.8 (14) There has been a suggestion that Me is an acceptor relative to H when attached to an sp3 carbon [C. A. Grob, Angew. Chem. lnt. Ed. Engl., 15, 569 (1976), and references cited therein]. The product ratio discussed here reflect this, but the IP changes do not. A subtle role of solvent may be involved. (15) J. Bastideand J. P. Maier, Chem. Phys., 12, 144 (1976 Li+, CUR+), the e component of which greatly stabilizes the most symmetrical q5 coordination. The lower the energy of the e acceptor set and the better the overlap with its Cp counterpart, the more are q2 and q5 stabilized relative to 7'. In the case of XH3+ (X = C, Si, Ge, Sn) an e acceptor orbital moves to lower energy as one proceeds down the group, and this is responsible for the decreasing barrier for sigmatropic shifts in CpXH3. The XH2 case, which yields a number of interesting collapse structures, is analyzed in detail for X, a main group center. Contrast the interaction of a cyclopentadienide anion and a proton with the interaction of the same anion and a Mn(CO)3+ fragment. Both result in stable molecules: cyclopentadiene (1) and V~-C~M~( C O )~ (2). But what a difference in the equilibrium geometries of these end products of the interaction! If we focus our attention on the cyclopentadienide site where the interacting partner settles down, then the proton chooses a position near to one carbon of the ring, but the Mn(C0)3+ fragment sits directly over the center of the ring. The ramifications of this differential are the concern of this paper. We will examine the interaction of a cyclopentadienide (CsHs-, Cp) ion with an interacting group X, X = H+, CH3+, SiR3+, Mn(C0)3+, CH22f, CH2. The result will consist of some conclusions concerning the equilibrium geometry of CpX as well as the relative energetics of the various haptotropic reactions of this Consider the passage of the interacting group X across the face of a Cp molecule, moving as indicated in 3 in a plane parallel to the Cp ring. Let the distance d be a separation at which there is sizable interaction between the frontier orbitals of X and the Cp a system. For a surface so constrained the asymmetric unit that need be calculated consists of the shaded area in 4, and two of the three boundaries of that area are contained in a transit along a line shown in projection in 5. Mirror symmetry is maintained at all points. The numbers nq shown along that line are convenient labels invoking a connection to the inorganic 7" notation* for denoting an approximate coordination geometry. In order to avoid confusion with structure numbers and ring carbon numbers, we have labeled the various sites along the transit line as 17, 217, . . . , 57. The site labeled 17, or some geometry near it, corresponds to or simple u interaction, such as we have in the collapse product cyclopentadiene. The 7IS site 57 is where one better come up with maximum stabilization for X = Mn(C0)3+. The site labeled 27 positions X over the center of a bond, and obviously will describe the important transition state region for a sigmatropic shift of a system like cyclopentadiene. 37 and 47 are not so easily defined. Experimentally, slippage of Cp rings from q5 coordination is often observed and q3 or q4 coordination may or may not be invoked. Somewhat arbitrarily we define 317 at the intersection of the transit line with the line joining C-2 and C-5 projected on the transit plane. The tetrahapto coordination site is most ambiguous (it could be near 37 or near 57), and SO we will not label any position as such. The analysis will consist of an inspection of interaction diagrams for the orbitals of Cp and X, as the ligand X and its position along the transit are varied. The qualitative arguments based on symmetry and overlap are supported by extended Huckel calculations whose details are given in the Appendix. The reader should be aware that this is an approximate metho

Weak capture of protons by protons

The cross section for the proton weak capture reaction $^1H(p,e^+\nu_e)^2H$ is calculated with wave functions obtained from a number of modern, realistic high-precision interactions. To minimize the uncertainty in the axial two-body current operator, its matrix element has been adjusted to reproduce the measured Gamow-Teller matrix element of tritium $\beta$ decay in model calculations using trinucleon wave functions from these interactions. A thorough analysis of the ambiguities that this procedure introduces in evaluating the two-body current contribution to the pp capture is given. Its inherent model dependence is in fact found to be very weak. The overlap integral $\Lambda^2(E=0)$ for the pp capture is predicted to be in the range 7.05--7.06, including the axial two-body current contribution, for all interactions considered.Comment: 17 pages RevTeX (twocolumn), 5 postscript figure

The high-precision, charge-dependent Bonn nucleon-nucleon potential (CD-Bonn)

We present a charge-dependent nucleon-nucleon (NN) potential that fits the world proton-proton data below 350 MeV available in the year of 2000 with a chi^2 per datum of 1.01 for 2932 data and the corresponding neutron-proton data with chi^2/datum = 1.02 for 3058 data. This reproduction of the NN data is more accurate than by any phase-shift analysis and any other NN potential. The charge-dependence of the present potential (that has been dubbed `CD-Bonn') is based upon the predictions by the Bonn Full Model for charge-symmetry and charge-independence breaking in all partial waves with J <= 4. The potential is represented in terms of the covariant Feynman amplitudes for one-boson exchange which are nonlocal. Therefore, the off-shell behavior of the CD-Bonn potential differs in a characteristic and well-founded way from commonly used local potentials and leads to larger binding energies in nuclear few- and many-body systems, where underbinding is a persistent problem.Comment: 69 pages (RevTex) including 20 tables and 9 figures (ps files

Post-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators

While the first binary post-AGB stars were serendipitously discovered, the distinct characteristics of their Spectral Energy Distribution (SED) allowed us to launch a more systematic search for binaries. We selected post-AGB objects which show a broad dust excess often starting already at H or K, pointing to the presence of a gravitationally bound dusty disc in the system. We started a very extensive multi-wavelength study of those systems and here we report on our radial velocity and photometric monitoring results for six stars of early F type, which are pulsators of small amplitude. To determine the radial velocity of low signal-to-noise time-series, we constructed dedicated auto-correlation masks. The radial velocity variations were subjected to detailed analysis to differentiate between pulsational variability and variability due to orbital motion. Finally orbital minimalisation was performed to constrain the orbital elements. All of the six objects are binaries, with orbital periods ranging from 120 to 1800 days. Five systems have non-circular orbits. The mass functions range from 0.004 to 0.57 solar mass and the companions are likely unevolved objects of (very) low initial mass. We argue that these binaries must have been subject to severe binary interaction when the primary was a cool supergiant. Although the origin of the circumstellar disc is not well understood, the disc is generally believed to be formed during this strong interaction phase. The eccentric orbits of these highly evolved objects remain poorly understood. With the measured orbits and mass functions we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems.Comment: 13 pages, 15 figures, accepted for Astronomy and Astrophysic

A promiscuous cytochrome P450 aromatic O-demethylase for lignin bioconversion

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOMicrobial aromatic catabolism offers a promising approach to convert lignin, a vast source of renewable carbon, into useful products. Aryl-O-demethylation is an essential biochemical reaction to ultimately catabolize coniferyl and sinapyl lignin-derived a9FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2013/08293-72014/10448-12016/22956-7We acknowledge funding from NSF grants to J.L.D. (MCB-1715176), K.N.H. (CHE-1361104), and E.L.N. (DEB-1556541 and MCB-1615365) and BBSRC grants to J.E.M. (BB/P011918/1, BB/L001926/1 and a studentship to S.J.B.M.). G.T.B., M.M.M., C.W.J., M.F.C., E.L.N.,