scholarly journals Adaptive elliptical aperture photometry: A software package for high-cadence ground-based photometry

2019 ◽  
Vol 629 ◽  
pp. A21 ◽  
Author(s):  
Dominic M. Bowman ◽  
Daniel L. Holdsworth
Keyword(s):  
High Frequency ◽  
Software Package ◽  
Variable Stars ◽  
Light Curves ◽  
Series Data ◽  
Rapid Variability ◽  
Period Variability ◽  
Short Period ◽  
Ap Stars ◽  
High Cadence

Context. Modern space telescopes are currently providing high-precision light curves for a large fraction of the sky, such that many new variable stars are being discovered. However, some stars have periodic variability with periods on the order of minutes and require high-cadence photometry to probe the physical mechanisms responsible. A cadence of less than a minute is often required to remove Nyquist ambiguities and confirm rapid variability, which forces observers to obtain high-cadence ground-based photometry. Aims. We aim to provide a modern software package to reduce ground-based photometric time series data and deliver optimised (differential) light curves. To produce high-quality light curves, which maximise the amplitude signal-to-noise ratio of short-period variability in a Fourier spectrum, we require adaptive elliptical aperture photometry as this represents a significant advantage compared to aperture photometry using circular apertures of fixed radii. Methods. The methodology of our code and its advantages are demonstrated using high-cadence ground-based photometry from the South African Astronomical Observatory (SAAO) of a confirmed rapidly oscillating Ap (roAp) star. Furthermore, we employed our software package to search for rapid oscillations in three candidate roAp stars. Results. We demonstrate that our pipeline represents a significant improvement in the quality of light curves, and we make it available to the community for use with different instruments and observatories. We search for and demonstrate the lack of high-frequency roAp pulsations to a limit of ∼1 mmag using B data in the three Ap stars HD 158596, HD 166542, and HD 181810. Conclusions. We demonstrate the significant improvement in the extraction of short-period variability caused by high-frequency pulsation modes, and discuss the implication of null detections in three Ap stars.

scholarly journals Confirmation of monoperiodicity above 20 s for two blue large-amplitude pulsators

2020 ◽  
Vol 496 (2) ◽  
pp. 1105-1114 ◽  
Author(s):  
Paul Ross McWhirter ◽  
Marco C Lam ◽  
Iain A Steele
Keyword(s):  
Gravitational Lensing ◽  
Large Amplitude ◽  
Variable Stars ◽  
Light Curves ◽  
Driving Mechanism ◽  
New Class ◽  
Pulsating Variable Stars ◽  
Short Period ◽  
Filter Frequency ◽  
High Cadence

ABSTRACT Blue large-amplitude pulsators (BLAPs) are a new class of pulsating variable stars. They are located close to the hot subdwarf branch in the Hertzsprung–Russell diagram and have spectral classes of late O or early B. Stellar evolution models indicate that these stars are likely radially pulsating, driven by iron group opacity in their interiors. A number of variable stars with a similar driving mechanism exist near the hot subdwarf branch with multiperiodic oscillations caused by either pressure (p) or gravity (g) modes. No multiperiodic signals were detected in the OGLE (Optical Gravitational Lensing Experiment) discovery light curves since it would be difficult to detect short-period signals associated with higher order p modes with the OGLE cadence. Using the RISE instrument on the Liverpool Telescope, we produced high-cadence light curves of two BLAPs, OGLE-BLAP-009 (mv = 15.65 mag) and OGLE-BLAP-014 (mv = 16.79 mag), using a 720 nm longpass filter. Frequency analysis of these light curves identifies a primary oscillation with a period of 31.935 ± 0.0098 min and an amplitude from a Fourier series fit of 0.236 mag for BLAP-009. The analysis of BLAP-014 identifies a period of 33.625 ± 0.0214 min and an amplitude of 0.225 mag. Analysis of the residual light curves reveals no additional short-period variability down to an amplitude of 15.20 ± 0.26 mmag for BLAP-009 and 58.60 ± 3.44 mmag for BLAP-014 for minimum periods of 20 and 60 s, respectively. These results further confirm that the BLAPs are monoperiodic.

scholarly journals SuperWASP variable stars: classifying light curves using citizen science

2021 ◽  
Vol 502 (1) ◽  
pp. 1299-1311
Author(s):  
Heidi B Thiemann ◽  
Andrew J Norton ◽  
Hugh J Dickinson ◽  
Adam McMaster ◽  
Ulrich C Kolb
Keyword(s):  
Variable Stars ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Data Set ◽  
Resultant Data ◽  
Sky Survey ◽  
Short Period ◽  
Contact Binaries ◽  
Analysis Of Results

ABSTRACT We present the first analysis of results from the SuperWASP variable stars Zooniverse project, which is aiming to classify 1.6 million phase-folded light curves of candidate stellar variables observed by the SuperWASP all sky survey with periods detected in the SuperWASP periodicity catalogue. The resultant data set currently contains >1 million classifications corresponding to >500 000 object–period combinations, provided by citizen–scientist volunteers. Volunteer-classified light curves have ∼89 per cent accuracy for detached and semidetached eclipsing binaries, but only ∼9 per cent accuracy for rotationally modulated variables, based on known objects. We demonstrate that this Zooniverse project will be valuable for both population studies of individual variable types and the identification of stellar variables for follow-up. We present preliminary findings on various unique and extreme variables in this analysis, including long-period contact binaries and binaries near the short-period cut-off, and we identify 301 previously unknown binaries and pulsators. We are now in the process of developing a web portal to enable other researchers to access the outputs of the SuperWASP variable stars project.

The High-Cadence Transient Survey (HiTS): Early Supernova Light-Curves

2017 ◽  
Vol 14 (S339) ◽  
pp. 66-66
Author(s):  
F. Förster
Keyword(s):  
Interdisciplinary Approach ◽  
Early Time ◽  
Small Region ◽  
Variable Stars ◽  
Machine Learning Algorithms ◽  
Light Curves ◽  
Physical Parameters ◽  
Physical Mechanisms ◽  
Cosmic Explosions ◽  
High Cadence

AbstractSupernovae (SNe) are cosmic explosions which are usually represented in a small region of the luminosity–time-scale diagram when discussing the variable sky. However, there are different time-scales involved in the evolution of SNe that are not reflected by that representation. This talk reviewed some of the physical mechanisms driving the SN light-curve diversity, especially at early times. It then discussed our efforts in the astroinformatics laboratory at CMM and at MAS to discover very young SNe using large etendue telescopes such as Blanco/DECam; those efforts led to the real-time discovery of more than one hundred SNe, some of them very young, under the High cadence Transient Survey (HiTS). We showed that, by comparing hydrodynamical models in the literature with HiTS SNe using Markov Chain Monte Carlo to sample from the posterior in a Bayesian approach, we can constrain the physical parameters that are driving the early time-evolution of these events. We also discussed how these data are being used for different projects, such as the discovery of asteroids and variable stars, and for testing different machine-learning algorithms in an interdisciplinary approach.

scholarly journals Flickering around the outburst cycle in Kepler dwarf novae

2021 ◽  
Author(s):  
Albert Bruch
Keyword(s):  
Spectral Index ◽  
High Frequency ◽  
Power Spectra ◽  
Light Curves ◽  
Dwarf Novae ◽  
Dwarf Nova ◽  
New Feature ◽  
Nova Outbursts ◽  
High Cadence

Abstract Taking advantage of the unparallel quantity and quality of high cadence Kepler light curves of several dwarf novae, the strength of the flickering and the high frequency spectral index of their power spectra are investigated as a function of magnitude around the outburst cycle of these systems. Previous work suggesting that the flickering strength (on a magnitude scale) is practically constant above a given brightness threshold and only rises at fainter magnitudes is confirmed for most of the investigated systems. As a new feature, a hysteresis in the flickering strength is seen in the sense that at the same magnitude level flickering is stronger during decline from outburst than during the rise. A similar hysteresis is also seen in the spectral index. In both cases, it can qualitatively be explained under plausible assumptions within the DIM model for dwarf nova outbursts.

scholarly journals Photometry and Multipolar Magnetic Field Modeling of Polars: BY Camelopardalis and FL Ceti

2015 ◽  
Vol 2 (1) ◽  
pp. 71-75 ◽  
Author(s):  
P. A. Mason ◽  
A. G. Zhilkin ◽  
D. V. Bisikalo ◽  
S. Gomez ◽  
J. Morales ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Broad Band ◽  
Cataclysmic Variables ◽  
Variable Stars ◽  
Field Structure ◽  
Light Curves ◽  
Optical Photometry ◽  
Quadrupole Field ◽  
Short Period ◽  
Mhd Modeling

We present new broad band optical photometry of two magnetic cataclysmic variable stars, the asynchronous polar BY Camelopardalis and the short period polar FL Ceti. Observations were obtained at the 2.1-m Otto Struve Telescope of McDonald Observatory with 3s and 1s integration times respectively. In an attempt to understand the observed complex changes in accretion flow geometry observed in BY Cam, we performed full 3D MHD simulations assuming a variety of white dwarf magnetic field structures. We investigate fields with increasing complexity including both aligned and non-aligned dipole plus quadrupole field components. We compare model predictions with photometry at various phases of the beat cycle and find that synthetic light curves derived from a multipolar field structure are broadly consistent with optical photometry. FL Ceti is observed to have two very small accretion regions at the foot-points of the white dwarf’s magnetic field. Both accretion regions are visible at the same time in the high state and are about 100 degrees apart. MHD modeling using a dipole plus quadrupole field structure yields quite similar accretion regions as those observed in FL Ceti. We conclude that accretion flows calculated from MHD modeling of multi-polar magnetic fields produce synthetic light curves consistent with photometry of these magnetic cataclysmic variables.

scholarly journals Microlensing of radially pulsating stars

2020 ◽  
Vol 494 (2) ◽  
pp. 1735-1743
Author(s):  
Sedighe Sajadian ◽  
Richard Ignace
Keyword(s):  
Finite Size ◽  
Variable Stars ◽  
Light Curves ◽  
Finite Size Effect ◽  
Magnification Factor ◽  
Variable Source ◽  
Pulsating Stars ◽  
Source Radius ◽  
Source Distance ◽  
High Cadence

ABSTRACT In this paper, we study the microlensing of radially pulsating stars. It is possible to discern and characterize the properties of distant, faint pulsating stars using high-cadence microlensing observations. By combining the stellar variability period with microlensing, we can obtain the source distance, type and radius, and we can better determine the lens parameters. Considering the variations in the radius and surface temperature of radially pulsating stars periodically, their microlensing light curves can be obtained by multiplying the magnification factor with a variable finite size effect by the intrinsic brightness curves of the pulsing source. The variable finite size of the source due to pulsation can be significant for transit and single microlensing with caustic-crossing features. This type of deviation in the magnification factor is considerable when the ratio of the source radius to the projected lens–source distance is in the range of ρ⋆/u ∈ [0.4, 10] and when its duration is short and of the same order as the time of crossing the source radius. Other deviations due to variable source intensity and its area make coloured and periodic deviations, which are asymmetric with respect to the signs of the pulsation phase. The positive phase makes deviations with larger amplitude than the negative phase. These deviations dominate in filters with short wavelengths (e.g. the B band). The position of the magnification peaks in the microlensing of variable stars varies and this displacement differs in different filters.

scholarly journals PRELIMINARY RESULTS FOR SHORT-PERIOD VARIABILITY SURVEY (SPVS) : NEW FIELD VARIABLE STARS

2007 ◽  
Vol 22 (4) ◽  
pp. 141-149 ◽  
Author(s):  
Young-Beom Jeon ◽  
Ki-Hyung Nam ◽  
Yoon-Ho Park ◽  
Kyung-Hoon Lee
Keyword(s):  
Variable Stars ◽  
Field Variable ◽  
Preliminary Results ◽  
Period Variability ◽  
Short Period

scholarly journals CCD Photometry of Variable Stars in the Galactic Open Cluster NGC 7419

2002 ◽  
Vol 185 ◽  
pp. 150-151 ◽  
Author(s):  
Z. Kołaczkowski ◽  
A. Pigulski ◽  
G. Kopacki
Keyword(s):  
Time Scales ◽  
Open Cluster ◽  
Variable Stars ◽  
Be Stars ◽  
Ccd Photometry ◽  
Period Variability ◽  
Short Period ◽  
Young Open Cluster ◽  
Almost All ◽  
Different Time Scales

AbstractWe present results of a CCD variability search in the field of the young open cluster NGC 7419. This cluster contains a large number of Be stars and almost all of them turned out to be variable. They show mostly irregular variations on different time-scales with ranges up to 0.4 mag in the IC band. The most interesting result is the discovery of short-period variability in some of the Be stars.

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