13 research outputs found
Near-Ultraviolet Spectra of Flares on YZ CMi
Near-ultraviolet spectroscopic data obtained with the HST STIS instrument on
the dMe flare star YZ Canis Minoris (YZ CMi) were analyzed. Flare and quiet
intervals were identified from the broadband near-UV light curve, and the
spectrum of each flare was separately extracted. Mg II and Fe II line profiles
show similar behavior during the flares. Two large flares allowed time-resolved
spectra to be analyzed, revealing a very broad component to the Mg II k line
profile in at least one flare spectrum (F9b). If interpreted as a velocity,
this component requires chromospheric material to be moving with FWHM ~ 250
km/sec, implying kinetic energy far in excess of the radiative energy. The Mg
II k flare line profiles were compared to recent radiative hydrodynamic models
of flare atmospheres undergoing electron beam heating. The models successfully
predict red enhancements in the line profile with typical velocity of a few
km/sec, but do not reproduce the flares showing blue enhancements, or the
strongly broadened line observed in flare F9b. A more complete calculation of
redistribution into the line wings, including the effect of collisions with the
electron beam, may resolve the origin of the excess line broadening.Comment: 29 pages, 12 figures; accepted to PAS
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 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 erg
cm s. 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 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-
Discovery of 1-(3-{2-[4-(2-Methyl-5-quinolinyl)-1-piperazinyl]ethyl}phenyl)-2-imidazolidinone (GSK163090), a Potent, Selective, and Orally Active 5-HT(1A/B/D) Receptor Antagonist.
In an effort to identify selective drug like pan-antagonists of the 5-HT(1) autoreceptors, studies were conducted to elaborate a previously reported dual acting 5-HT(1) antagonist/SSRI structure. A novel series of compounds was identified showing low intrinsic activities and potent affinities across the 5-HT(1A), 5-HT(1B), and 5-HT(1D) receptors as well as high selectivity against the serotonin transporter. From among these compounds, 1-(3-{2-[4-(2-methyl-5-quinolinyl)-1-piperazinyl]ethyl}phenyl)-2-imidazolidinone (36) was found to combine potent in vivo activity with a strong preclinical developability profile, and on this basis it was selected as a drug candidate with the aim of assessing its potential as a fast-onset antidepressant/anxiolytic