11 research outputs found
TFAW: wavelet-based signal reconstruction to reduce photometric noise in time-domain surveys
There have been many efforts to correct systematic effects in astronomical
light curves to improve the detection and characterization of planetary
transits and astrophysical variability. Algorithms like the Trend Filtering
Algorithm (TFA) use simultaneously-observed stars to remove systematic effects,
and binning is used to reduce high-frequency random noise. We present TFAW, a
wavelet-based modified version of TFA. TFAW aims to increase the periodic
signal detection and to return a detrended and denoised signal without
modifying its intrinsic characteristics. We modify TFA's frequency analysis
step adding a Stationary Wavelet Transform filter to perform an initial noise
and outlier removal and increase the detection of variable signals. A wavelet
filter is added to TFA's signal reconstruction to perform an adaptive
characterization of the noise- and trend-free signal and the noise contribution
at each iteration while preserving astrophysical signals. We carried out tests
over simulated sinusoidal and transit-like signals to assess the effectiveness
of the method and applied TFAW to real light curves from TFRM. We also studied
TFAW's application to simulated multiperiodic signals, improving their
characterization. TFAW improves the signal detection rate by increasing the
signal detection efficiency (SDE) up to a factor ~2.5x for low SNR light
curves. For simulated transits, the transit detection rate improves by a factor
~2-5x in the low-SNR regime compared to TFA. TFAW signal approximation performs
up to a factor ~2x better than bin averaging for planetary transits. The
standard deviations of simulated and real TFAW light curves are ~40x better
than TFA. TFAW yields better MCMC posterior distributions and returns lower
uncertainties, less biased transit parameters and narrower (~10x) credibility
intervals for simulated transits. We present a newly-discovered variable star
from TFRM.Comment: Accepted for publication by A&A. 13 pages, 16 figures and 5 table
TFAW: Wavelet-based signal reconstruction to reduce photometric noise in time-domain surveys
Context. There have been many efforts to correct systematic effects in astronomical light curves to improve the detection and characterization of planetary transits and astrophysical variability. Algorithms such as the trend filtering algorithm (TFA) use simultaneously-observed stars to measure and remove systematic effects, and binning is used to reduce high-frequency random noise. Aims: We present TFAW, a wavelet-based modified version of TFA. First, TFAW aims to increase the periodic signal detection and second, to return a detrended and denoised signal without modifying its intrinsic characteristics. Methods: We modified TFA's frequency analysis step adding a stationary wavelet transform filter to perform an initial noise and outlier removal and increase the detection of variable signals. A wavelet-based filter was added to TFA's signal reconstruction to perform an adaptive characterization of the noise- and trend-free signal and the underlying noise contribution at each iteration while preserving astrophysical signals. We carried out tests over simulated sinusoidal and transit-like signals to assess the effectiveness of the method and applied TFAW to real light curves from TFRM. We also studied TFAW's application to simulated multiperiodic signals. Results: TFAW improves the signal detection rate by increasing the signal detection efficiency (SDE) up to a factor Ì2.5Ă for low S/R light curves. For simulated transits, the transit detection rate improves by a factor Ì2 - 5Ă in the low-S/R regime compared to TFA. TFAW signal approximation performs up to a factor Ì2Ă better than bin averaging for planetary transits. The standard deviations of simulated and real TFAW light curves are Ì40% better compared to TFA. TFAW yields better MCMC posterior distributions and returns lower uncertainties, less biased transit parameters and narrower (by approximately ten times) credibility intervals for simulated transits. TFAW is also able to improve the characterization of multiperiodic signals. We present a newly-discovered variable star from TFRM
Optical microflares in LS I +61 303 and the search for their multiwavelength counterpart
Stellar sources of gamma rays are one of the front lines in modern
astrophysics whose understanding can benefit from observational tools not
originally designed for their study. We take advantage of the high precision
photometric capabilities of present-day space facilities to obtain a new
perspective on the optical behavior of the X-ray and gamma-ray binary LS I +61
303. Previously unknown phenomena whose effects manifest with amplitudes below
0.01 magnitude can now be clearly observed and studied. Our work is mainly
based on the analysis of optical and gamma-ray archival data and uses the tools
recommended by the different collaborations that provide these valuable
observational resources (in particular, the TESS and Fermi orbiting
observatories). In addition, complementary ground-based optical spectroscopy
has also been conducted. We report the discovery of small-amplitude optical
flares on timescales of a day in the LS I +61 303 light curve. Different
alternative scenarios to explain their origin are tentatively proposed.Comment: In press in Astronomy & Astrophysics. 6 pages, 5 figure