95 research outputs found
IPHAS J062746.41+014811.3: a deeply eclipsing intermediate polar
We present time-resolved photometry of a cataclysmic variable discovered in
the Isaac Newton Telescope Photometric Halpha Survey of the northern galactic
plane, IPHAS J062746.41+014811.3 and classify the system as the fourth deeply
eclipsing intermediate polar known with an orbital period of Porb=8.16 h, and
spin period of Pspin=2210 s. The system shows mild variations of its
brightness, that appear to be accompanied by a change in the amplitude of the
spin modulation at optical wavelengths, and a change in the morphology of the
eclipse profile. The inferred magnetic moment of the white dwarf is mu_wd = 6-7
x 10^33 Gcm^3, and in this case IPHAS J0627 will either evolve into a
short-period EX Hya-like intermediate polar with a large Pspin\Porb ratio, or,
perhaps more likely, into a synchronised polar. Swift observations show that
the system is an ultraviolet and X-ray source, with a hard X-ray spectrum that
is consistent with those seen in other intermediate polars. The ultraviolet
light curve shows orbital modulation and an eclipse, while the low
signal-to-noise ratio X-ray light curve does not show a significant modulation
on the spin period. The measured X-ray flux is about an order of magnitude
lower than would be expected from scaling by the optical fluxes of well-known
X-ray selected intermediate polars.Comment: 34 pages, 9 figures, accepted for publication in Ap
Transition-metal interactions in aluminum-rich intermetallics
The extension of the first-principles generalized pseudopotential theory
(GPT) to transition-metal (TM) aluminides produces pair and many-body
interactions that allow efficient calculations of total energies. In
aluminum-rich systems treated at the pair-potential level, one practical
limitation is a transition-metal over-binding that creates an unrealistic TM-TM
attraction at short separations in the absence of balancing many-body
contributions. Even with this limitation, the GPT pair potentials have been
used effectively in total-energy calculations for Al-TM systems with TM atoms
at separations greater than 4 AA. An additional potential term may be added for
systems with shorter TM atom separations, formally folding repulsive
contributions of the three- and higher-body interactions into the pair
potentials, resulting in structure-dependent TM-TM potentials. Towards this
end, we have performed numerical ab-initio total-energy calculations using VASP
(Vienna Ab Initio Simulation Package) for an Al-Co-Ni compound in a particular
quasicrystalline approximant structure. The results allow us to fit a
short-ranged, many-body correction of the form a(r_0/r)^{b} to the GPT pair
potentials for Co-Co, Co-Ni, and Ni-Ni interactions.Comment: 18 pages, 5 figures, submitted to PR
Discovery of Negative Superhumps during a Superoutburst of January 2011 in ER Ursae Majoris
We report on a discovery of "negative" superhumps during the 2011 January
superoutburst of ER UMa. During the superoutburst which started on 2011 January
16, we detected negative superhumps having a period of 0.062242(9) d, shorter
than the orbital period by 2.2%. No evidence of positive superhumps was
detected during this observation. This finding indicates that the disk
exhibited retrograde precession during this superoutburst, contrary to all
other known cases of superoutbursts. The duration of this superoutburst was
shorter than those of ordinary superoutbursts and the intervals of normal
outbursts were longer than ordinary ones. We suggest a possibility that such
unusual outburst properties are likely a result of the disk tilt, which is
supposed to be a cause of negative superhumps: the tilted disk could prevent
the disk from being filled with materials in the outmost region which is
supposed to be responsible for long-duration superoutbursts in ER UMa-type
dwarf novae. The discovery signifies the importance of the classical prograde
precession in sustaining long-duration superoutbursts. Furthermore, the
presence of pronounced negative superhumps in this system with a high
mass-transfer rate favors the hypothesis that hydrodynamical lift is the cause
of the disk tilt.Comment: 8 pages, 3 figures, Accepted for publication in PASJ Lette
Close binary stars in the solar-age Galactic open cluster M67
We present multi-colour time-series CCD photometry of the solar-age galactic
open cluster M67 (NGC 2682). About 3600 frames spread over 28 nights were
obtained with the 1.5 m Russian-Turkish and 1.2 m Mercator telescopes.
High-precision observations of the close binary stars AH Cnc, EV Cnc, ES Cnc,
the Scuti type systems EX Cnc and EW Cnc, and some long-period
variables belonging to M67 are presented. Three full multi-colour light curves
of the overcontact binary AH Cnc were obtained during three observing seasons.
Likewise we gathered three light curves of EV Cnc, an EB-type binary, and two
light curves of ES Cnc, a blue straggler binary. Parts of the light change of
long-term variables S1024, S1040, S1045, S1063, S1242, and S1264 are obtained.
Period variation analysis of AH Cnc, EV Cnc, and ES Cnc were done using all
times of mid-eclipse available in the literature and those obtained in this
study. In addition, we analyzed multi-colour light curves of the close binaries
and also determined new frequencies for the Scuti systems. The
physical parameters of the close binary stars were determined with simultaneous
solutions of multi-colour light and radial velocity curves. Finally we
determined the distance of M67 as 857(33) pc via binary star parameters, which
is consistent with an independent method from earlier studies.Comment: 12 pages, 9 Figures, 13 Table
The helium-rich cataclysmic variable SBSS 1108+574
We present time-resolved spectroscopy and photometry of the dwarf nova SBSS 1108+574, obtained during the 2012 outburst. Its quiescent spectrum is unusually rich in helium, showing broad, double-peaked emission lines from the accretion disc. We measure a line flux ratio He I 5875/Hα = 0.81 ± 0.04, a much higher ratio than typically observed in cataclysmic variable stars (CVs). The outburst spectrum shows hydrogen and helium in absorption, with weak emission of Hα and He I 6678, as well as strong He II emission.
From our photometry, we find the superhump period to be 56.34 ± 0.18 min, in agreement with the previously published result. The spectroscopic period, derived from the radial velocities of the emission lines, is found to be 55.3 ± 0.8 min, consistent with a previously identified photometric orbital period, and significantly below the normal CV period minimum. This indicates that the donor in SBSS 1108+574 is highly evolved. The superhump excess derived from our photometry implies a mass ratio of q = 0.086 ± 0.014. Our spectroscopy reveals a grazing eclipse of the large outbursting disc. As the disc is significantly larger during outburst, it is unlikely that an eclipse will be detectable in quiescence. The relatively high accretion rate implied by the detection of outbursts, together with the large mass ratio, suggests that SBSS 1108+574 is still evolving towards its period minimum
A Variable Star Census in a Perseus Field
The Berlin Exoplanet Search Telescope is a small-aperture, wide-field
telescope dedicated to time-series photometric observations. During an initial
commissioning phase at the Thueringer Landessternwarte Tautenburg, Germany, and
subsequent operations at the Observatoire de Haute-Provence, France, a 3.1
{\deg} x 3.1 {\deg} circumpolar field close to the galactic plane centered at
({\alpha}, {\delta}) = (02h 39m 23s, +52{\deg} 01' 46") (J 2000.0) was observed
between 2001 August and 2006 December during 52 nights. From the 32129 stars
observed, a subsample of 145 stars with clear stellar variability was detected
out of which 125 are newly identified variable objects. For five bright
objects, the system parameters were derived by modeling the light curve.Comment: 8 pages, 5 figures, 3 table
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