982 research outputs found
RX J2115-5840: confirmation of a new near-synchronous polar
Schwope et al (1997) suggested that the newly discovered Polar RX J2115-5840
is a near-synchronous system. We have obtained circular polarisation
observations of RX J2115-5840 which show that the spin and orbital periods
differ by 1.2%. We find the first direct evidence of `pole-switching' in a
near-synchronous Polar. Further our data requires that the accretion flow must
be directed onto the same magnetic field line at all spin-orbit beat phases
implying that at some phases the flow must follow a path around the white dwarf
before accreting.Comment: To be published in Proc Annapolis workshop on magnetic CVs, held in
July 199
UBVRI photopolarimetry of the long period eclipsing AM Herculis binary V1309
We report simultaneous UBVRI photo-polarimetric observations of the long
period (7.98 h) AM Her binary V1309 Ori. The length and shape of the eclipse
ingress and egress varies from night to night. We suggest this is due to the
variation in the brightness of the accretion stream. By comparing the phases of
circular polarization zero-crossovers with previous observations, we confirm
that V1309 Ori is well synchronized, and find an upper limit of 0.002 percent
for the difference between the spin and orbital periods. We model the
polarimetry data using a model consisting of two cyclotron emission regions at
almost diametrically opposite locations, and centered at colatitude 35 (deg)
and 145 (deg) on the surface of the white dwarf. We also present archive X-ray
observations which show that the negatively polarised accretion region is X-ray
bright.Comment: 11 pages, 12 figures (2 colour), Fig1 and Fig 4 are in lower
resolution than in original paper, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Infrared spectroscopy of cataclysmic variables: III. Dwarf novae below the period gap and novalike variables
We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, BK
Lyn, T Leo, SW UMa and WZ Sge, the novalike variables DW UMa, V1315 Aql, RW
Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral
types ranging from K2-M6.
The spectra of the dwarf novae are dominated by emission lines of HI and HeI.
The large velocity and equivalent widths of these lines, in conjunction with
the fact that the lines are double-peaked in the highest inclination systems,
indicate an accretion disc origin. In the case of YZ Cnc and T Leo, for which
we obtained time-resolved data covering a complete orbital cycle, the emission
lines show modulations in their equivalent widths which are most probably
associated with the bright spot (the region where the gas stream collides with
the accretion disc). There are no clear detections of the secondary star in any
of the dwarf novae below the period gap, yielding upper limits of 10-30% for
the contribution of the secondary star to the observed K-band flux. In
conjunction with the K-band magnitudes of the dwarf novae, we use the derived
secondary star contributions to calculate lower limits to the distances to
these systems.
The spectra of the novalike variables are dominated by broad, single-peaked
emission lines of HI and HeI - even the eclipsing systems we observed do not
show the double-peaked profiles predicted by standard accretion disc theory.
With the exception of RW Tri, which exhibits NaI, CaI and 12CO absorption
features consistent with a M0V secondary contributing 65% of the observed
K-band flux, we find no evidence for the secondary star in any of the novalike
variables. The implications of this result are discussed.Comment: 13 pages, 5 figures, to appear in MNRA
Accretion stream mapping with genetically modified "fire-flies"
We apply an eclipse mapping technique using `genetically modified fire-flies'
to the eclipse light curves of HU Aqr and EP Dra. The technique makes as few
assumptions as possible about the location of accretion stream material,
allowing the emission to be located anywhere within the Roche lobe of the white
dwarf. We model two consecutive eclipses in the UBVR_c band for HU Aqr, and
four consecutive `white'-light eclipses for EP Dra, to determine the changing
brightness distribution of stream material. We find fire-fly distributions
which are consistent with accretion through a curtain of material in both HU
Aqr and EP Dra, and show that the previously assumed two part ballistic and
magnetic trajectory is a good approximation for polars. Model fits to the
colour band data of HU Aqr indicate that the material confined to the magnetic
field lines is brightest, and most of the emission originates from close to the
white dwarf. There is evidence for emission from close to a calculated
ballistic stream in both HU Aqr and EP Dra.We propose that a change in the
stream density causes a change in the location of the bright material in the
accretion stream in EP Dra.Comment: accepted for publication in MNRA
Kinetic Resolution in Asymmetric Epoxidation using Iminium Salt Catalysis
The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes
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