Analysis of the Type IIn Supernova 1998S: Effects of Circumstellar Interaction on Observed Spectra

We present spectral analysis of early observations of the Type IIn supernova 1998S using the general non-local thermodynamic equilibrium atmosphere code \tt PHOENIX}. We model both the underlying supernova spectrum and the overlying circumstellar interaction region and produce spectra in good agreement with observations. The early spectra are well fit by lines produced primarily in the circumstellar region itself, and later spectra are due primarily to the supernova ejecta. Intermediate spectra are affected by both regions. A mass-loss rate of order $\dot M \sim 0.0001-0.001$\msol yr$^{-1}$ is inferred for a wind speed of 100-1000 \kmps. We discuss how future self-consistent models will better clarify the underlying progenitor structure.Comment: to appear in ApJ, 2001, 54

Quantitative analysis of cell types during growth and morphogenesis in Hydra

Tissue maceration was used to determine the absolute number and the distribution of cell types in Hydra. It was shown that the total number of cells per animal as well as the distribution of cells vary depending on temperature, feeding conditions, and state of growth. During head and foot regeneration and during budding the first detectable change in the cell distribution is an increase in the number of nerve cells at the site of morphogenesis. These results and the finding that nerve cells are most concentrated in the head region, diminishing in density down the body column, are discussed in relation to tissue polarity

Surface heat flux variability over the northern California shelf

Surface heat flux components are estimated at a midshelf site over the northern California shelf using moored measurements from the 1981-1982 Coastal Ocean Dynamics Experiment (CODE) and the 1988-1989 Shelf Mixed Layer Experiment (SMILE). Time series of estimated fluxes extend from early winter through summer upwelling conditions, allowing examination of seasonal variations as well as synoptic events. On a seasonal timescale, the surface heat flux is strongly influenced net surface heat flux are the annual variation in incident shortwave solar radiation (insolation) and the atmospheric spring transition. Between mid-November 1988 and late February 1989, insolation is weak and the Mean daily averaged heat flux is nearly zero (absolute value less than 10W m¯²), with a standard deviation of ~50 W m¯². Beginning in March, insolation increases markedly, and typical daily-average heat fluxes increase to greater than 100W m¯² by the spring transition in April or May. In June and July, the average heat flux is near 200 W m¯², with a standard deviation of ~90 W m¯². In winter, the daily-averaged heat flux varies on periods of several days. Net heat flux losses can range up to 130W m¯². These losses are not identified with any one type of event. For example, comparable heat flux losses can occur for very low relative humidities (RHs), moderate winds, and clear skies, and for high RHs, high winds, and cloudy skies. In summer, surface heat flux variability is strongly influenced by upwelling and relaxation events. Upwelling is characterized by clear skies and high equatorward winds, while relaxation is characterized by the presence of clouds and low or northward winds. These conditions lead to opposing changes in insolation and in longwave radiative cooling and latent heat flux. Variability in insolation dominates, and the daily-averaged heat flux into the ocean is greatest during upwellineg vents (up to 350W m¯² or more) and least during relaxation events (sometimes less than 100W m¯²)

PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae

Aim: We present new extraction and identification techniques for supernova (SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration. Method: The new spectral extraction method takes full advantage of photometric information from the Canada-France-Hawai telescope (CFHT) discovery and reference images by tracing the exact position of the supernova and the host signals on the spectrogram. When present, the host spatial profile is measured on deep multi-band reference images and is used to model the host contribution to the full (supernova + host) signal. The supernova is modelled as a Gaussian function of width equal to the seeing. A chi-square minimisation provides the flux of each component in each pixel of the 2D spectrogram. For a host-supernova separation greater than <~ 1 pixel, the two components are recovered separately and we do not use a spectral template in contrast to more standard analyses. This new procedure permits a clean extraction of the supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra of the SNLS. A new supernova identification method is also proposed. It uses the SALT2 spectrophotometric template to combine the photometric and spectral data. A galaxy template is allowed for spectra for which a separate extraction of the supernova and the host was not possible. Result: These new techniques have been tested against more standard extraction and identification procedures. They permit a secure type and redshift determination in about 80% of cases. The present paper illustrates their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&

Evidence for Asphericity in the Type IIn Supernova 1998S

We present optical spectropolarimetry obtained at the Keck-II 10-m telescope on 1998 March 7 UT along with total flux spectra spanning the first 494 days after discovery (1998 March 2 UT) of the peculiar type IIn supernova (SN) 1998S. The SN is found to exhibit a high degree of linear polarization, implying significant asphericity for its continuum-scattering environment. Prior to removal of the interstellar polarization, the polarization spectrum is characterized by a flat continuum (at p ~ 2%) with distinct changes in polarization associated with both the broad (FWZI >= 20,000 km/s) and narrow (unresolved, FWHM < 300 km/s) line emission seen in the total flux spectrum. When analyzed in terms of a polarized continuum with unpolarized broad-line recombination emission, an intrinsic continuum polarization of p ~ 3% results (the highest yet found for a SN), suggesting a global asphericity of >= 45% from the oblate, electron-scattering dominated models of Hoflich (1991). The smooth, blue continuum evident at early times is shown to be inconsistent with a reddened, single-temperature blackbody, instead having a color temperature that increases with decreasing wavelength. Broad emission-line profiles with distinct blue and red peaks are seen in the total flux spectra at later times, perhaps suggesting a disk-like or ring-like morphology for the dense (n_e ~ 10^7 cm^{-3}) circumstellar medium. Implications of the circumstellar scattering environment for the spectropolarimetry are discussed, as are the effects of uncertain removal of interstellar polarization.Comment: 25 pages + 2 tables + 14 figures, Submitted to The Astrophysical Journa

Impact of Temporal Features of Cattle Exchanges on the Size and Speed of Epidemic Outbreaks

International audienceDatabases recording cattle exchanges offer unique opportunities for a better understanding and fighting of disease spreading. Most studies model contacts with (sequences of) networks, but this approach neglects important dynamical features of exchanges, that are known to play a key role in spreading. We use here a fully dynamic modeling of contacts and empirically compare the spreading outbreaks obtained with it to the ones obtained with network approaches. We show that neglecting time information leads to significant overestimates of actual sizes of spreading cascades, and that these sizes are much more heterogeneous than generally assumed. Our approach also makes it possible to study the speed of spreading, and we show that the observed speeds vary greatly, even for a same cascade size

The 1995 Georges Bank Stratification Study and moored array measurements

The 1995 Geoges Bank Stratification Study (GBSS) was the first intensive process study conducted as part of the U.S. GLOBEC Northwest Atlantic/Georges Bank field program. The GBSS was designed to investigate the physical processes which control the seasonal development of stratification along the southern flank of Georges Bank during spring and summer. Past work suggested that during this period, larval cod and haddock tended to aggregate to the thermocline on the southern flank where higher concentrations of their copepod prey were found. A moored array was deployed as part of GBSS to observe the onset and evolution of sesonal stratification over the southern flank with sufficient vertical and horizontal resolution that key physical processes could be identified and quantified. Moored current, temperature, and conductivity (salinity) measurements were made at three sites along the southern flank, one on the crest, and one on the northeast peak of the bank. Moored surface meteorological measurements were also made at one southern flank site to determine the surface wind stress and heat and moisture fluxes. The oceanographic and meteorological data collected with the GBSS array during January-August 1995 are presented in this report. Meteorological data collected on National Data Buoy Center environmental buoys 44011 (Georges Bank), 44008 (Nantucket Shoals), and 44005 (Gulf of Maine) are included in this report for completeness and comparison with the GBSS southern flank meteorological measurements.Funding was provided by the National Science Foundation under Grant Numbers OCE-98-06379 and OCE-98-06445

Northern Monterey Bay upwelling shadow front : observations of a coastally and surface-trapped buoyant plume

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C12013, doi:10.1029/2009JC005623.During the upwelling season in central California, northwesterly winds along the coast produce a strong upwelling jet that originates at Point Año Nuevo and flows southward across the mouth of Monterey Bay. A convergent front with a mean temperature change of 3.77 ± 0.29°C develops between the warm interior waters and the cold offshore upwelling jet. To examine the forcing mechanisms driving the location and movement of the upwelling shadow front and its effects on biological communities in northern Monterey Bay, oceanographic conditions were monitored using cross-shelf mooring arrays, drifters, and hydrographic surveys along a 20 km stretch of coast extending northwestward from Santa Cruz, California, during the upwelling season of 2007 (May–September). The alongshore location of the upwelling shadow front at the northern edge of the bay was driven by: regional wind forcing, through an alongshore pressure gradient; buoyancy forces due to the temperature change across the front; and local wind forcing (the diurnal sea breeze). The upwelling shadow front behaved as a surface-trapped buoyant current, which is superimposed on a poleward barotropic current, moving up and down the coast up to several kilometers each day. We surmise that the front is advected poleward by a preexisting northward barotropic current of 0.10 m s−1 that arises due to an alongshore pressure gradient caused by focused upwelling at Point Año Nuevo. The frontal circulation (onshore surface currents) breaks the typical two-dimensional wind-driven, cross-shelf circulation (offshore surface currents) and introduces another way for water, and the material it contains (e.g., pollutants, larvae), to go across the shelf toward shore.Funded primarily by the Gordon and Betty Moore Foundation and the David and Lucile Packard Foundation