High-precision determination of transition amplitudes of principal transitions in Cs from van der Waals coefficient C_6

A method for determination of atomic dipole matrix elements of principal transitions from the value of dispersion coefficient C_6 of molecular potentials correlating to two ground-state atoms is proposed. The method is illustrated on atomic Cs using C_6 deduced from high-resolution Feshbach spectroscopy. The following reduced matrix elements are determined < 6S_{1/2} || D || 6P_{1/2} > =4.5028(60) |e| a0 and =6.3373(84) |e| a0 (a0= 0.529177 \times 10^{-8} cm.) These matrix elements are consistent with the results of the most accurate direct lifetime measurements and have a similar uncertainty. It is argued that the uncertainty can be considerably reduced as the coefficient C_6 is constrained further.Comment: 4 pages; 3 fig

New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation

(abridged) The heating mechanism at high densities during M dwarf flares is poorly understood. Spectra of M dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive phase: 1) an energetically dominant blackbody component with a color temperature of T $\sim$ 10,000 K in the blue-optical, 2) a smaller amount of Balmer continuum emission in the near-ultraviolet at lambda $<$ 3646 Angstroms and 3) an apparent pseudo-continuum of blended high-order Balmer lines. These properties are not reproduced by models that employ a typical "solar-type" flare heating level in nonthermal electrons, and therefore our understanding of these spectra is limited to a phenomenological interpretation. We present a new 1D radiative-hydrodynamic model of an M dwarf flare from precipitating nonthermal electrons with a large energy flux of $10^{13}$ erg cm$^{-2}$ s$^{-1}$. The simulation produces bright continuum emission from a dense, hot chromospheric condensation. For the first time, the observed color temperature and Balmer jump ratio are produced self-consistently in a radiative-hydrodynamic flare model. We find that a T $\sim$ 10,000 K blackbody-like continuum component and a small Balmer jump ratio result from optically thick Balmer and Paschen recombination radiation, and thus the properties of the flux spectrum are caused by blue light escaping over a larger physical depth range compared to red and near-ultraviolet light. To model the near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer lines, we include the extra Balmer continuum opacity from Landau-Zener transitions that result from merged, high order energy levels of hydrogen in a dense, partially ionized atmosphere. This reveals a new diagnostic of ambient charge density in the densest regions of the atmosphere that are heated during dMe and solar flares.Comment: 50 pages, 2 tables, 13 figures. Accepted for publication in the Solar Physics Topical Issue, "Solar and Stellar Flares". Version 2 (June 22, 2015): updated to include comments by Guest Editor. The final publication is available at Springer via http://dx.doi.org/10.1007/s11207-015-0708-

Studies of Dense Cores with ALMA

Dense cores are the simplest star-forming sites that we know, but despite their simplicity, they still hold a number of mysteries that limit our understanding of how solar-type stars form. ALMA promises to revolutionize our knowledge of every stage in the life of a core, from the pre-stellar phase to the final disruption by the newly born star. This contribution presents a brief review of the evolution of dense cores and illustrates particular questions that will greatly benefit from the increase in resolution and sensitivity expected from ALMAComment: 6 pages, 2 figures, to appear in Astrophysics and Space Science, special issue of "Science with ALMA: a new era for Astrophysics" conference, ed. Dr. Bachille

Geology of the Barossa Valley

Lower Tertiary deltaic and lacustrine sediments at the southern margin of the Barossa Valley are designated at the Rowlands Flat Sands and the name Rowlands Flat Sands Conglomeratic Lens is proposed for a transgressive deltaic conglomerate near the base of the formation. Mineralogical composition of the sediments indicates a derivation by prolonged weathering on a fairly mature surface and dispositional structures and the abundance of staurolite at the type locality point to the Marinoan schists north of Nuriootpa as the source of part of the early sediment. The climate of the Lower Tertiary is judged to have been humid and a Cinnamomum flora is recorded from the late Eocene of Bakers Gully, near Clarendon. Fossiliferous deposits along the Para Scarp near Gawler and sands and conglomerates which extend several miles to the east are grouped together as an unnamed Middle Tertiary fluviatile and littoral sequence which has been correlated with the Port Willunga Beds. Upper Tertiary deposits include outwash clays and conglomerates in the Barossa Valley, Mount Crawford and Gawler areas. The basal Tertiary surface is known in the western part of the Murray Basin, in the Barossa Valley, the Golden Grove-One Tree Hill area and about the margins of the St. Vincent Basin. It shows slight to moderate relief. Uplift of the surface formed after the accumulation of the Lower Tertiary sands is inferred near Gawler where Middle Tertiary deposits blanket an eroded surface with local highs west of elevated residuals of the Lower Tertiary. The pre-Pliocene surface recognized in the hills west of Adelaide extends along the Para Block and may also be represented by the dissected plateau near Eden Valley and Gomersal. The Barossa Valley is interpreted as a shallow, asymmetrical syncline with a Tertiary fault of flexure, unrelated to any pre-existing structure, inferred along the steep south-eastern flank. No Tertiary movement is indicated on the Kitchener and Bremer Faults in this vicinity and part of the relief of the Barossa Ranges is attributed to differential erosion consequent upon general uplift of the Ranges. Within the Ranges broad warping along prominent zones of flexure has occurred throughout the Tertiary but dating of the movements and measurements of differential displacement are only possible about the margins of the Murray and St. Vincent Basins where well dated Tertiary deposits are affected. Three main phases of terrestrial deposits are postulated for the western margin of the Mount Lofty Ranges, the two most important being in the late Eocene and late Pliocene to Pleistocene.Thesis (M.Sc.) -- University of Adelaide, Dept. of Geology, 196

Lateral facies variability along the margin of an outcropping salt-withdrawal minibasin, South Australia

Many aspects of depositional processes adjacent to exposed evaporite diapirs are not well understood, yet these processes are key to understanding sediments that are part of economically important hydrocarbon systems around the world. In the Adelaide Rift Complex of South Australia, diapirs intersected the seafloor and land surface during the Ediacaran–Cambrian at the same time as sediment was being deposited. Excellent exposures of these diapirs and their associated minibasins allow the character and distribution of these deposits to be studied in detail; this study examines the interaction between a diapir body and minibasin sediments from a sedimentological perspective. Numerous sections were measured along the minibasin margin, allowing the sedimentary facies, lateral sediment variability, and depositional processes to be determined. Deposition took place in a variety of environments, ranging from carbonate shelves to subaerially exposed tidal flats and alluvial fans. Minibasin sedimentation adjacent to the diapir is characterized by an abundance of gravity-flow deposits, including turbidites and debrites. These deposits often contain extraformational conglomerates brought to the surface by the diapir and redeposited into the minibasin depocenter. Within the minibasin fill, sedimentary facies are unevenly distributed, and sedimentary character is most affected by the diapir in areas where depositional thinning, onlap, and growth faulting are most common. Comparison of our observations with other localities where salt bodies intersect the surface show that syndepositional salt–sediment interaction results in a recurring set of features that can be useful in predicting the sedimentary character of these deposits. This study is one of relatively few to examine the sedimentology of an outcropping minibasin in detail and to describe lateral variability of sedimentary facies along an outcropping minibasin margin. The deposits discussed here therefore provide a valuable analogue for subsurface and seafloor deposits elsewhere where salt–sediment interactions cannot be studied in detail.John W. Counts, Charles R. Dalgarno, Kathryn J. Amos, and Stephen T. Hasioti

The Cambrian System in the Arrowie Basin, Flinders Ranges, South Australia

The lower to ?middle Cambrian rocks (Terreneuvian, Series 2 and possibly Miaolingian) of the Arrowie Basin are exposed superbly in the Flinders Ranges of South Australia. They comprise two major sedimentary packages: a lower carbonate-rich succession (Hawker Group and correlates) and an upper siliciclastic-dominated succession (Billy Creek Formation, Wirrealpa Limestone and Lake Frome Group). These rocks form one of the most complete lower Cambrian (Terreneuvian and Series 2) successions globally. They contain one of the most diverse known early Cambrian biotas in the world, with trilobites, archaeocyaths, bradoriides, brachiopods, some of the earliest known coralomorphs, small shelly fossils, molluscs, hyoliths, acritarchs and trace fossils. Series divisions, based on ranges of shelly fossils and archaeocyath biostratigraphy are currently being established. Ancient reef structures are prominent in several areas. Syndepositional faulting and diapiric activity affected sedimentation in places. The global significance of the region is enhanced by the presence of tuff horizons at some levels, which provide the opportunity to link the biostratigraphic zones with radiometric dates and carbon isotope curves.J. B. Jago, J. G. Gehling, M. J. Betts, G. A. Brock, C. R. Dalgarno, D. C. García-Bellido, P. G. Haslett, S. M. Jacquet, P. D. Kruse, N. R. Langsford, T. J. Mount, J. R. Paterso