439 research outputs found
Automated Classification of Periodic Variable Stars detected by the Wide-field Infrared Survey Explorer
We describe a methodology to classify periodic variable stars identified
using photometric time-series measurements constructed from the Wide-field
Infrared Survey Explorer (WISE) full-mission single-exposure Source Databases.
This will assist in the future construction of a WISE Variable Source Database
that assigns variables to specific science classes as constrained by the WISE
observing cadence with statistically meaningful classification probabilities.
We have analyzed the WISE light curves of 8273 variable stars identified in
previous optical variability surveys (MACHO, GCVS, and ASAS) and show that
Fourier decomposition techniques can be extended into the mid-IR to assist with
their classification. Combined with other periodic light-curve features, this
sample is then used to train a machine-learned classifier based on the random
forest (RF) method. Consistent with previous classification studies of variable
stars in general, the RF machine-learned classifier is superior to other
methods in terms of accuracy, robustness against outliers, and relative
immunity to features that carry little or redundant class information. For the
three most common classes identified by WISE: Algols, RR Lyrae, and W Ursae
Majoris type variables, we obtain classification efficiencies of 80.7%, 82.7%,
and 84.5% respectively using cross-validation analyses, with 95% confidence
intervals of approximately +/-2%. These accuracies are achieved at purity (or
reliability) levels of 88.5%, 96.2%, and 87.8% respectively, similar to that
achieved in previous automated classification studies of periodic variable
stars.Comment: 48 pages, 17 figures, 1 table, accepted by A
Non-conservative evolution in Algols: where is the matter?
There is gathering indirect evidence suggesting non-conservative evolutions
in Algols. However, the systemic mass-loss rate is poorly constrained by
observations and generally set as a free parameter in binary-star evolution
simulations. Moreover, systemic mass loss may lead to observational signatures
that are still to be found. We investigate the impact of the outflowing gas and
the possible presence of dust grains on the spectral energy distribution (SED).
We used the 1D plasma code Cloudy and compared the results with the 3D
Monte-Carlo radiative transfer code Skirt for dusty simulations. The
circumbinary mass-distribution and binary parameters are computed with
state-of-the-art binary calculations done with the Binstar evolution code. The
outflowing material reduces the continuum flux-level of the stellar SED in the
optical and UV. Due to the time-dependence of this effect, it may help to
distinguish between different ejection mechanisms. Dust, if present, leads to
observable infrared excesses even with low dust-to-gas ratios and traces the
cold material at large distances from the star. By searching for such dust
emission in the WISE catalogue, we found a small number of Algols showing
infrared excesses, among which the two rather surprising objects SX Aur and CZ
Vel. We find that some binary B[e] stars show the same strong Balmer continuum
as we predict with our models. However, direct evidence of systemic mass loss
is probably not observable in genuine Algols, since these systems no longer
eject mass through the hotspot mechanism. Furthermore, owing to its high
velocity, the outflowing material dissipates in a few hundred years. If hot
enough, the hotspot may produce highly ionised species such as SiIV and
observable characteristics that are typical of W Ser systems.Comment: Accepted for piblications in A&A; 21 pages, 19 figure
Implementation of a Scientific Subset of Algol 68
Computing and Information Science
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