29 research outputs found
The space density of magnetic and non-magnetic cataclysmic variables, and implications for CV evolution
We present constraints on the space densities of both non-magnetic and
magnetic cataclysmic variables, and discuss some implications for models of the
evolution of CVs. The high predicted non-magnetic CV space density is only
consistent with observations if the majority of these systems are extremely
faint in X-rays. The data are consistent with the very simple model where
long-period IPs evolve into polars and account for the whole short-period polar
population. The fraction of WDs that are strongly magnetic is not significantly
higher for CV primaries than for isolated WDs. Finally, the space density of
IPs is sufficiently high to explain the bright, hard X-ray Galactic Centre
source population.Comment: Proceedings of the conferencs "The Golden Age of Cataclysmic
Variables and Related Objects II", Palermo, 9-14 September 2013. Accepted for
publication in Acta Polytechnica. 6 pages, 4 figure
Inflation after WMAP3
I discuss the current status of inflationary cosmology in light of the recent
WMAP 3-year data release. The basic predictions of inflation are all supported
by the data. Inflation also makes predictions which have not been well tested
by current data but can be by future experiments, most notably a deviation from
a scale-invariant power spectrum and the production of primordial gravitational
waves. A scale-invariant spectrum is disfavored by current data, but not
conclusively. Tensor modes are currently poorly constrained, and slow-roll
inflation does not make an unambiguous prediction of the expected amplitude of
primordial gravitational waves. A tensor/scalar ratio of is
within reach of near-future measurements.Comment: To appear in the proceedings of Colliders to Cosmic Rays 2007. 8
pages, 2 figures. (V2: Minor typo corrected
The influence of selection effects on the observed cataclysmic variable population: modelling and application to the Palomar-Green sample
Large differences between the properties of the known sample of cataclysmic
variable stars (CVs) and the predictions of the theory of binary star evolution
have long been recognised. However, because all existing CV samples suffer from
strong selection effects, observational biases must be taken into account
before it is possible to tell whether there is an inconsistency. In order to
address this problem, we have modelled the impact of selection effects on
observed CV samples using a Monte Carlo approach. By simulating the selection
criteria of the Palomar-Green (PG) Survey, we show that selection effects
cannot reconcile the predictions of standard CV evolution theory with the
observed sample. More generally, we illustrate the effect of the biases that
are introduced by magnitude limits, selection cuts in U-B, and restrictions in
galactic latitude.Comment: 12 pages, 11 figures, minor changes made to the text, accepted for
publication in MNRA
Cool Companions to White Dwarf Stars from the Two Micron All Sky Survey All Sky Data Release
We present the culmination of our near-infrared survey of the optically spectroscopically identified white dwarf stars from the McCook and Sion catalog, conducted using photometric data from the Two Micron All Sky Survey final All Sky Data Release. The color selection technique, which identifies candidate binaries containing a white dwarf and a low-mass stellar (or substellar) companion via their distinctive locus in the near-infrared color-color diagram, is demonstrated to be simple to apply and to yield candidates with a high rate of subsequent confirmation. We recover 105 confirmed binaries, and identify 27 firm candidates (19 of which are new to this work) and 21 tentative candidates (17 of which are new to this work) from the 2MASS data. Only a small number of candidates from our survey have likely companion spectral types later than M5, none of which is an obvious L-type (i.e., potential brown dwarf) companion. Only one previously known white dwarf + brown dwarf binary is detected. This result is discussed in the context of the 2MASS detection limits, as well as other recent observational surveys that suggest a very low rate of formation (or survival) for binary stars with extreme mass ratios
Statistical properties of dwarf novae-type cataclysmic variables: the outburst catalogue
The outburst catalogue contains a wide variety of observational properties for 722 dwarf nova (DN)-type cataclysmic variables (CVs) and 309 CVs of other types from the Catalina Real-time Transient Survey. In particular, it includes the apparent outburst and quiescent V-band magnitudes, duty cycles, limits on the recurrence time, upper and lower limits on the distance and absolute quiescent magnitudes, colour information, orbital parameters and X-ray counterparts. These properties were determined by means of a classification script presented in this paper. The DN in the catalogue show a correlation between the outburst duty cycle and the orbital period (and outburst recurrence time), as well as between the quiescent absolute magnitude and the orbital period (and duty cycle). This is the largest sample of DN properties collected to date. Besides serving as a useful reference for individual systems and a means of selecting objects for targetted studies, it will prove valuable for statistical studies that aim to shed light on the formation and evolution of cataclysmic variables
Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables -- VI. Spin rates, propellering, and coherence
We examine published observations of dwarf nova oscillations (DNOs) on the
rise and decline of outbursts and show that their rates of change are in
reasonable agreement with those predicted from the magnetic accretion model. We
find evidence for propellering in the late stages of outburst of several dwarf
novae, as shown by reductions in EUVE fluxes and from rapid increases of the
DNO periods. Reanalysis of DNOs observed in TY PsA, which had particularly
large amplitudes, shows that the apparent loss of coherence during late decline
is better described as a regular switching between two nearby periods. It is
partly this and the rapid deceleration in some systems that make the DNOs
harder to detect.
We suggest that the 28.95 s periodicity in WZ Sge, which has long been a
puzzle, is caused by heated regions in the disc, just beyond the corotation
radius, which are a consequence of magnetic coupling between the primary and
gas in the accretion disc. This leads to a possible new interpretation of the
`longer period DNOs' (lpDNOs) commonly observed in dwarf novae and nova-like
variables.Comment: 9 pages, 3 figure, accepted for publication in MNRA
High speed photometry of faint Cataclysmic Variables: IV. V356 Aql, Aqr1, FIRST J1023+0038, Ha 0242-2802, GI Mon, AO Oct, V972 Oph, SDSS 0155+00, SDSS 0233+00, SDSS 1240-01, SDSS 1556-00, SDSS 2050-05, FH Ser
We present results from high speed photometry of a further thirteen faint
cataclysmic variables. V356 Aql (Nova Aql 1936) shows flare-like outbursts with
recurrence time scales ~ 3000 s, but no coherent periodicities. Aqr1 is an
intermediate polar with a spin period of 6.7284 min and a probable orbital
period P(orb) = 3.226 h derived from orbital sidebands. Its orbital sideband
frequencies show very variable amplitudes. The published spectroscopic period
of 2.0 h suggests that Aqr1 is similar to GW Lib and FS Aur in having an
additional periodicity of unknown origin. FIRST J1023+0038 has P(orb) = 4.7548
h with an orbital modulation of range 0.45 mag, probably caused by reflection
effect from a hot white dwarf primary; as such it may have been a nova sometime
in the past few decades. Ha 0242 is a deeply eclipsing very low mass-transfer
rate system, probably a dwarf nova of very long outburst interval, with P(orb)
= 1.792 h. GI Mon, an old nova, has optical modulations at 4.325 h and possibly
also at 48.6 min and is thus a candidate intermediate polar. AO Oct, an SU UMa
type dwarf nova, shows orbital modulation at quiescence with P(orb) = 94.097
min. V972 Oph (Nova Ophiuchi 1957) showed no flickering activity during one set
of observations, but did so at a later time, confirming the correctness of the
identification of this object, but it shows no orbital modulation. SDSS 0155 is
a deeply eclipsing polar with an orbital period of 87.13 min. SDSS 0233 shows
flaring activity but no discernible periodicity. No periodicity was found in
the new AM CVn candidate SDSS 1240. SDSS 1556 shows a periodic modulation at
1.778 h which is possibly due to orbital motion. SDSS 2050 is an eclipsing
polar with P(orb) = 1.5702 h. FH Ser (Nova Serpentis 1970) has strong
flickering activity but no detectable orbital modulation.Comment: 12 pages, 22 figures (Figs. 1, 2, 5 and 6 are available at higher
resolution upon request). Accepted for publication in MNRA