21 research outputs found
On the Hardness of a New Boron Phase, Orthorhombic {\gamma}-B28
Measurements of the hardness of a new high-pressure boron phase, orthorhombic
{\gamma}-B28, are reported. According to the data obtained, {\gamma}-B28 has
the highest hardness (~50 GPa) of all known crystalline modifications of boron
A Search for Rapid Photometric Variability in Symbiotic Binaries
We report on our survey for rapid (time scale of minutes) photometric
variability in symbiotic binaries. These binaries are becoming an increasingly
important place to study accretion onto white dwarfs since they are candidate
Type Ia supernovae progenitors. Unlike in most cataclysmic variables, the white
dwarfs in symbiotics typically accrete from a wind, at rates greater than or
equal to 10^{-9} solar masses per year. In order to elucidate the differences
between symbiotics and other white dwarf accretors, as well as search for
magnetism in symbiotic white dwarfs, we have studied 35 primarily northern
symbiotic binaries via differential optical photometry. Our study is the most
comprehensive to date of rapid variability in symbiotic binaries. We have found
one magnetic accretor, Z And, previously reported by Sokoloski & Bildsten
(1999). In four systems (EG And, BX Mon, CM Aql, and BF Cyg), some evidence for
flickering at a low level (roughly 10 mmag) is seen for the first time. These
detections are, however, marginal. For 25 systems, we place tight upper limits
(order of mmag) on both aperiodic and periodic variability, highlighting a
major difference between symbiotics and cataclysmic variables. The remaining
five of the objects included in our sample (the 2 recurrent novae RS Oph and T
CrB, plus CH Cyg, o Ceti, and MWC 560) had previous detections of
large-amplitude optical flickering, and we present our extensive observations
of these systems in a separate paper. We discuss the impact of our results on
the ``standard'' picture of wind-fed accretion, and speculate on the
possibility that in most symbiotics, light from quasi-steady nuclear burning on
the surface of the white dwarf hides the fluctuating emission from accretion.Comment: 24 pages, 17 figures. Submitted to MNRAS (12/21/00), and revised in
response to referee comments (3/30/01
Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review)
The basic known and hypothetic one- and two-element phases of the B-C-N-O
system (both superhard phases having diamond and boron structures and
precursors to synthesize them) are described. The attention has been given to
the structure, basic mechanical properties, and methods to identify and
characterize the materials. For some phases that have been recently described
in the literature the synthesis conditions at high pressures and temperatures
are indicated.Comment: Review on superhard B-C-N-O phase