644 research outputs found
Near-Infrared Constraints on the Presence of Warm Dust at Metal-Rich, Helium Atmosphere White Dwarfs
Here, we present near-infrared spectroscopic observations of 15 helium
atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope
Facility. While a connection has been demonstrated between the most highly
polluted, hydrogen atmosphere white dwarfs and the presence of warm
circumstellar dust and gas, their frequency at the helium atmosphere variety is
poorly constrained. None of our targets show excess near-infrared radiation
consistent with warm orbiting material. Adding these near-infrared constraints
to previous near- and mid-infrared observations, the frequency of warm
circumstellar material at metal-bearing white dwarfs is at least 20% for
hydrogen-dominated photospheres, but could be less than 5% for those
effectively composed of helium alone. The lower occurrence of dust disks around
helium atmosphere white dwarfs is consistent with Myr timescales for
photospheric metals in massive convection zones. Analyzing the mass
distribution of 10 white dwarfs with warm circumstellar material, we search for
similar trends between the frequency of disks and the predicted frequency of
massive planets around intermediate mass stars, but find the probability that
disk-bearing white dwarfs are more massive than average is not significant.Comment: AJ, in pres
Roles of Fukutin, the Gene Responsible for Fukuyama-Type Congenital Muscular Dystrophy, in Neurons: Possible Involvement in Synaptic Function and Neuronal Migration
Fukutin is a gene responsible for Fukuyama-type congenital muscular dystrophy (FCMD), accompanying ocular and brain malformations represented by cobblestone lissencephaly. Fukutin is related to basement membrane formation via the glycosylation of α-dystoglycan (α-DG), and astrocytes play a crucial role in the pathogenesis of the brain lesion. On the other hand, its precise function in neurons is unknown. In this experiment, the roles of fukutin in mature and immature neurons were examined using brains from control subjects and FCMD patients and cultured neuronal cell lines. In quantitative PCR, the expression level of fukutin looked different depending on the region of the brain examined. A similar tendency in DG expression appears to indicate a relation between fukutin and α-DG in mature neurons. An increase of DG mRNA and core α-DG in the FCMD cerebrum also supports the relation. In immunohistochemistry, dot-like positive reactions for VIA4-1, one of the antibodies detecting the glycosylated α-DG, in Purkinje cells suggest that fukutin is related to at least a post-synaptic function via the glycosylation of α-DG. As for immature neurons, VIA4-1 was predominantly positive in cells before and during migration with expression of fukutin, which suggest a participation of fukutin in neuronal migration via the glycosylation of α-DG. Moreover, fukutin may prevent neuronal differentiation, because its expression was significantly lower in the adult cerebrum and in differentiated cultured cells. A knockdown of fukutin was considered to induce differentiation in cultured cells. Fukutin seems to be necessary to keep migrating neurons immature during migration, and also to support migration via α-DG
Seismology Of A Massive Pulsating Hydrogen Atmosphere White Dwarf
We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1 m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1 m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M-star = 0.88 +/- 0.02 M-circle dot and T-eff = 12,100 +/- 140 K. These values are consistent with those derived from the the optical spectra and photometric colors.CNPqFAPERGS/PronexUS National Science Foundation AST-0909107Norman Hackerman Advanced Research Program 003658-0252-2009MICINN grant AYA08-1839/ESPESF EUROCORES Program EuroGENESIS (MICINN grant) EUI2009-04170Generalitat de Catalunya 2009SGR315EU-FEDER fundsAGENCIA through the Programa de Modernizacion Tecnologica BID 1728/OC-ARCONICET PIP 112-200801-00940Astronom
Effects of Elaborate Feedback During Practice Tests:Costs and Benefits of Retrieval Prompts
This study explores the effect of feedback with hints on students’ recall of words. In three classroom experiments, high school students individually practiced vocabulary words through computerized retrieval practice with either standard show-answer feedback (display of answer) or hints feedback after incorrect responses. Hints feedback gave students a second chance to find the correct response using orthographic (Experiment 1), mnemonic (Experiment 2), or cross-language hints (Experiment 3). During practice, hints led to a shift of practice time from further repetitions to longer feedback processing but did not reduce (repeated) errors. There was no effect of feedback on later recall except when the hints from practice were also available on the test, indicating limited transfer of practice with hints to later recall without hints (in Experiments 1 and 2). Overall, hints feedback was not preferable over show-answer feedback. The common notion that hints are beneficial may not hold when the total practice time is limited
Rotational spectroscopy of the thioformaldehyde isotopologues HCS and HCS in four interacting excited vibrational states and an account on the rotational spectrum of thioketene, HCCS
An investigation of the rotational spectrum of the interstellar molecule
thioformaldehyde between 110 and 377 GHz through a pyrolysis reaction revealed
a multitude of absorption lines assignable to HCS and HCS in
their lowest four excited vibrational states besides lines of numerous
thioformaldehyde isotopologues in their ground vibrational states reported
earlier as well as lines pertaining to several by-products. Additional
transitions of HCS in its lowest four excited vibrational states were
recorded in selected regions between 571 and 1386 GHz. Slight to strong
Coriolis interactions occur between all four vibrational states with the
exception of the two highest lying states because both are totally symmetric
vibrations. We present combined analyses of the ground and the four interacting
states for our rotational data of HCS and HCS. The HCS data
were supplemented with two sets of high-resultion IR data in two separate
analyses. The state has been included in analyses of Coriolis
interactions of low-lying fundamental states of HCS for the first time and
this improved the quality of the fits substantially. We extended furthermore
assignments in of transition frequencies of thioketene in its ground
vibrational state.Comment: 23 pages including figures, tables, and references; Mol. Phys.,
accepted (for the Tim Lee memorial issue
A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4
We present a catalog of 9316 spectroscopically confirmed white dwarfs from
the Sloan Digital Sky Survey Data Release 4. We have selected the stars through
photometric cuts and spectroscopic modeling, backed up by a set of visual
inspections. Roughly 6000 of the stars are new discoveries, roughly doubling
the number of spectroscopically confirmed white dwarfs. We analyze the stars by
performing temperature and surface gravity fits to grids of pure hydrogen and
helium atmospheres. Among the rare outliers are a set of presumed helium-core
DA white dwarfs with estimated masses below 0.3 Msun, including two candidates
that may be the lowest masses yet found. We also present a list of 928 hot
subdwarfs.Comment: Accepted by the Astrophysical Journal Supplements, 25 pages, 24
figures, LaTeX. The electronic catalog, as well as diagnostic figures and
links to the spectra, is available at http://das.sdss.org/wdcat/dr4
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