Eliminating Noise at the Box-fitting Spectrum

AbstractNon gaussian sources of erros need to be taken into consideration when searching for planetary transits. Such phenomena are mostly caused by the impact of high energetic particles on the detector (Pinheiro da Silva et al. 2008). The detection efficiency of transits, therefor, depend significantly on the data quality and the algorithms utilized to deal with these errors sources. In this work we show that a modified detrend algorithm CDA (CoRoT Detrend Algorithm; Mislis et al. 2010) using a robust statistics and an empirical fit, instead of a polynomial one, can eliminate more efficiently gaps in the data and other long-term trends from the light-curve. Using this algorithm enables us to obtain a reconstructed light-curve with better signal-to-noise ratio that allows to improve the detection of exoplanet transits, although long term signals are destroyed. The results show that these modifications lead to an improved BLS (Box-fitting Least Squares; Kovács, Zucker & Mazeh 2002) algorithm spectrum. At the end we have compared our planetary search results with CoRoT (Convection, Rotation and planetary Transits) satellite chromatic light-curves available in the literature.

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Long-term Photometric Monitoring of FUor and FUor-like Objects

Communications of the Byurakan Astrophysical Observatory ◽

10.52526/25792776-2018.2.2-240 ◽

2018 ◽

pp. 240-248

Author(s):

E. Semkov ◽

S. Ibryamov ◽

S. Peneva ◽

A. Mutafov

Keyword(s):

Light Curve ◽

Significant Role ◽

Stellar Evolution ◽

Photographic Plate ◽

Light Curves ◽

Curve Shape ◽

Rate Of Increase ◽

Fu Ori ◽

Photometric Monitoring

A phenomenon with a significant role in stellar evolution is the FU Orionis (FUor) type of outburst. The first three (classical) FUors (FU Ori, V1515 Cyg and V1057 Cyg) are well-studied and their light curves are published in the literature. But recently, over a dozen new objects of this type were discovered, whose photometric history we do not know well. Using recent data from photometric monitoring and data from the photographic plate archives we aim to study, the long-term photometric behavior of FUor and FUor-like objects. The construction of the historical light curves of FUors could be very important for determining the beginning of the outburst, the time to reach the maximum light, the rate of increase and decrease in brightness, the pre-outburst variability of the star. So far we have published our results for the light curves of V2493 Cyg, V582 Aur, Parsamian 21 and V1647 Ori. In this paper we present new data that describe more accurate the photometric behavior of these objects. In comparing our results with light curves of the well-studied FUors (FU Ori, V1515 Cyg and V1057 Cyg), we conclude that every object shows different photometric behavior. Each known FUor has a different rate of increase and decrease in brightness and a different light curve shape.

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The impact of non-ideality on reconstructing spatial and temporal variations of aerosol acidity with multiphase buffer theory

10.5194/egusphere-egu21-9292 ◽

2021 ◽

Author(s):

Yafang Cheng ◽

Guangjie Zheng ◽

Hang Su ◽

Siwen Wang ◽

Andrea Pozzer

Keyword(s):

Molar Fraction ◽

Temporal Variations ◽

Spatial Variations ◽

Acid Dissociation ◽

Acid Dissociation Constant ◽

Aerosol Acidity ◽

Long Term Trends ◽

Factor C ◽

The Impact

Aerosol acidity is a key parameter in atmospheric aqueous chemistry and strongly influence the interactions of air pollutants and ecosystem. The recently proposed multiphase buffer theory provides a framework to reconstruct long-term trends and spatial variations of aerosol pH based on the effective acid dissociation constant of ammonia (Ka,NH3*). However, non-ideality in aerosol droplets is a major challenge limiting its broad applications. Here, we introduced a non-ideality correction factor (cni) and investigated its governing factors. We found that besides relative humidity (RH) and temperature, cni is mainly determined by the molar fraction of NO3- in aqueous-phase anions, due to different NH4+ activity coefficients between (NH4)2SO4- and NH4NO3-dominated aerosols. A parameterization method is thus proposed to estimate cni at given RH, temperature and NO3- fraction, and is validated against long-term observations and global simulations. In the ammonia-buffered regime, with cni correction the buffer theory can well reproduce the Ka,NH3* predicted by comprehensive thermodynamic models, with root-mean-square deviation ~0.1 and correlation coefficient ~1. Note that, while cni is needed to predict Ka,NH3* levels, it is usually not the dominant contributor to its variations, as ~90% of the temporal or spatial variations in Ka,NH3* is due to variations in aerosol water and temperature.

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Expected performances of the Characterising Exoplanet Satellite (CHEOPS)

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935977 ◽

2020 ◽

Vol 635 ◽

pp. A22 ◽

Cited By ~ 3

Author(s):

A. Deline ◽

D. Queloz ◽

B. Chazelas ◽

M. Sordet ◽

F. Wildi ◽

...

Keyword(s):

Light Curve ◽

High Precision ◽

Background Level ◽

Monte Carlo Algorithm ◽

Complete Analysis ◽

Transiting Planets ◽

End To End ◽

Set Up ◽

The Impact

Context. The characterisation of Earth-size exoplanets through transit photometry has stimulated new generations of high-precision instruments. In that respect, the Characterising Exoplanet Satellite (CHEOPS) is designed to perform photometric observations of bright stars to obtain precise radii measurements of transiting planets. The CHEOPS instrument will have the capability to follow up bright hosts provided by radial-velocity facilities. With the recent launch of the Transiting Exoplanet Survey Satellite (TESS), CHEOPS may also be able to confirm some of the long-period TESS candidates and to improve the radii precision of confirmed exoplanets. Aims. The high-precision photometry of CHEOPS relies on careful on-ground calibration of its payload. For that purpose, intensive pre-launch campaigns of measurements were carried out to calibrate the instrument and characterise its photometric performances. This work reports on the main results of these campaigns. It provides a complete analysis of data sets and estimates in-flight photometric performance by means of an end-to-end simulation. Instrumental systematics were measured by carrying out long-term calibration sequences. Using an end-to end model, we simulated transit observations to evaluate the impact of in-orbit behaviour of the satellite and to determine the achievable precision on the planetary radii measurement. Methods. After introducing key results from the payload calibration, we focussed on the data analysis of a series of long-term measurements of uniformly illuminated images. The recorded frames were corrected for instrumental effects and a mean photometric signal was computed on each image. The resulting light curve was corrected for systematics related to laboratory temperature fluctuations. Transit observations were simulated, considering the payload performance parameters. The data were corrected using calibration results and estimates of the background level and position of the stellar image. The light curve was extracted using aperture photometry and analysed with a transit model using a Markov chain Monte Carlo algorithm. Results. In our analysis, we show that the calibration test set-up induces thermally correlated features in the data that can be corrected in post-processing to improve the quality of the light curves. We find that on-ground photometric performances of the instrument measured after this correction is of the order of 15 parts per million over five hours. Using our end-to-end simulation, we determine that measurements of planet-to-star radii ratio with a precision of 2% for a Neptune-size planet transiting a K-dwarf star and 5% for an Earth-size planet orbiting a Sun-like star are possible with CHEOPS. These values correspond to transit depths obtained with signal-to-noise ratios of 25 and 10, respectively, allowing the characterisation and detection of these planets. The pre-launch CHEOPS performances are shown to be compliant with the mission requirements.

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Long rotation period main-sequence stars from Kepler SAP light curves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2432 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5513-5529 ◽

Cited By ~ 3

Author(s):

Kaiming Cui ◽

Jifeng Liu ◽

Shuhong Yang ◽

Qing Gao ◽

Huiqin Yang ◽

...

Keyword(s):

Light Curve ◽

Main Sequence ◽

Rotation Period ◽

Light Curves ◽

Stellar Rotation ◽

Main Sequence Stars ◽

Found Objects ◽

Period Detection ◽

Search Data

ABSTRACT Stellar rotation plays a key role in stellar activity. The rotation period could be detected through light curve variations caused by star-spots. Kepler provides two types of light curves: one is the Pre-search Data Conditioning (PDC) light curves, and the other is the Simple Aperture Photometer (SAP) light curves. Compared with the PDC light curves, the SAP light curves keep the long-term trend, relatively suitable for searches of long-period signals. However, SAP data are inflicted by some artefacts such as quarterly rolls and instrumental errors, making it difficult to find the physical periods in the SAP light curves. We explore a systematic approach based on the light curve pre-processing, period detection, and candidate selection. We also develop a simulated light curve test to estimate our detection limits for the SAP-like LCs. After applying our method to the raw SAP light curves, we found more than 1000 main-sequence stars with periods longer than 30 d; 165 are newly discovered. Considering the potential flaw of the SAP, we also inspect the newly found objects with photometry methods, and most of our periodical signals are confirmed.

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Influence of macroclumping on type II supernova light curves

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935794 ◽

2019 ◽

Vol 629 ◽

pp. A17

Author(s):

Luc Dessart ◽

Edouard Audit

Keyword(s):

Light Curve ◽

Early Time ◽

Radiation Energy ◽

Mean Free Path ◽

Light Curves ◽

Type Ii ◽

Different Temperatures ◽

Curve Modeling ◽

2D And 3D ◽

The Impact

Core-collapse supernova (SN) ejecta are probably structured on both small and large scales, with greater deviations from spherical symmetry nearer the explosion site. Here, we present 2D and 3D gray radiation hydrodynamics simulations of type II SN light curves from red and blue supergiant star explosions to investigate the impact of inhomogeneities in density or composition on SN observables, with a characteristic scale set to a few percent of the local radius. Clumping is found to hasten the release of stored radiation, boosting the early time luminosity and shortening the photospheric phase. Around the photosphere, radiation leaks between the clumps where the photon mean free path is greater. Since radiation is stored uniformly in volume, a greater clumping can increase this leakage by storing more and more mass into smaller and denser clumps containing less and less radiation energy. An inhomogeneous medium in which different regions recombine at different temperatures can also impact the light curve. Clumping can thus be a source of diversity in SN brightness. Clumping may lead to a systematic underestimate of ejecta masses from light curve modeling, although a significant offset seems to require a large density contrast of a few tens between clumps and interclump medium.

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Long term trends in the 3.5 μ light curve of RX Puppis

International Astronomical Union Colloquium ◽

10.1017/s0252921100097736 ◽

1982 ◽

Vol 70 ◽

pp. 207-208

Author(s):

Patricia A. Whitelock ◽

R.M. Catchpole

Keyword(s):

Infrared Spectrum ◽

Light Curve ◽

Variable Component ◽

Mira Variable ◽

Long Term Trends

SAAO photometry of RX Pup at 3.5 μ between 1972 and 1981 shows a very well defined period of 580 days with an amplitude of 0.35 mag, which is attributed to a Mira variable component. The infrared variability of RX Pup was demonstrated by Feast, Robertson and Catchpole (1977), who also pointed out that the infrared colours were indicative of the presence of a Mira variable with a dust excess. Further evidence for the Mira comes from the observations of H2O in the infrared spectrum by Barton, Phillips and Allen (1979).

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Evaluating the impact of ballast undercutting on the roughness of track geometry over different subgrade conditions

Proceedings of the Institution of Mechanical Engineers Part F Journal of Rail and Rapid Transit ◽

10.1177/0954409717720347 ◽

2017 ◽

Vol 232 (5) ◽

pp. 1266-1276

Author(s):

Kirk M Scanlan ◽

Michael T Hendry ◽

C Derek Martin

Keyword(s):

Surface Roughness ◽

Organic Soils ◽

Western Canada ◽

Railway Ballast ◽

Track Geometry ◽

Track Maintenance ◽

Heavy Haul ◽

Long Term Trends ◽

The Impact

The progressive degradation of railway ballast is often cited as a primary factor that contributes to the development of track roughness, while ballast renewal (undercutting) attempts to manage its long-term development. Soft subgrades have been shown to strongly influence track geometry and are a contributing factor that has not been considered during conventional track maintenance. This study evaluated the impact of undercutting on long-term trends in track geometry roughness, and what impact softer subgrades had on the effectiveness of undercutting. A combined 6.90 km of Class II–IV heavy-haul track in Western Canada (undercut in 2010 and 2011) formed the basis for this analysis. Annual traffic on these sections typically totals 50 million gross tonnes. Long-term trends in the track crosslevel, alignment, and surface roughness after ballast renewal were derived from 50 track geometry surveys carried out over a five-year period (2010–2015). The results showed that undercutting significantly reduced track roughness over sand, silt, clay, or till subgrades; however, it was often ineffective when used over soft organic subgrades. Thus, while ballast degradation is the primary cause of track roughness in segments constructed on mineral subgrades, it is not a mechanism that results in track geometry roughness over soft organic soils.

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The Impact of Improved Thermistor Calibration on the Expendable Bathythermograph Profile Data

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-17-0024.1 ◽

2017 ◽

Vol 34 (9) ◽

pp. 1947-1961 ◽

Cited By ~ 2

Author(s):

Marlos Goes ◽

Elizabeth Babcock ◽

Francis Bringas ◽

Peter Ortner ◽

Gustavo Goni

Keyword(s):

Small Sample Size ◽

Heat Content ◽

Small Sample ◽

Profile Data ◽

Expendable Bathythermograph ◽

Different Types ◽

Long Term Trends ◽

The Mean ◽

The Impact

AbstractExpendable bathythermograph (XBT) data provide one of the longest available records of upper-ocean temperature. However, temperature and depth biases in XBT data adversely affect estimates of long-term trends of ocean heat content and, to a lesser extent, estimates of volume and heat transport in the ocean. Several corrections have been proposed to overcome historical biases in XBT data, which rely on constantly monitoring these biases. This paper provides an analysis of data collected during three recent hydrographic cruises that utilized different types of probes, and examines methods to reduce temperature and depth biases by improving the thermistor calibration and reducing the mass variability of the XBT probes.The results obtained show that the use of individual thermistor calibration in XBT probes is the most effective calibration to decrease the thermal bias, improving the mean thermal bias to less than 0.02°C and its tolerance from 0.1° to 0.03°C. The temperature variance of probes with screened thermistors is significantly reduced by approximately 60% in comparison to standard probes. On the other hand, probes with a tighter weight tolerance did not show statistically significant reductions in the spread of depth biases, possibly because of the small sample size or the sensitivity of the depth accuracy to other causes affecting the analysis.

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Identifying outliers of non-Gaussian groundwater state data based on ensemble estimation for long-term trends

Journal of Hydrology ◽

10.1016/j.jhydrol.2017.02.058 ◽

2017 ◽

Vol 548 ◽

pp. 135-144 ◽

Cited By ~ 7

Author(s):

Jina Jeong ◽

Eungyu Park ◽

Weon Shik Han ◽

Kueyoung Kim ◽

Sungwook Choung ◽

...

Keyword(s):

State Data ◽

Ensemble Estimation ◽

Long Term Trends ◽

Non Gaussian

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The Impact of Non-uniform Sampling on Stratospheric Ozone Trends Derived from Occultation Instruments

10.5194/acp-2017-575 ◽

2017 ◽

Author(s):

Robert P. Damadeo ◽

Joseph M. Zawodny ◽

Ellis E. Remsberg ◽

Kaley A. Walker

Keyword(s):

Stratospheric Ozone ◽

Primary Source ◽

Data Sets ◽

Sampled Data ◽

Uniform Sampling ◽

Ozone Trends ◽

Long Term Trends ◽

Non Uniform Sampling ◽

The Impact

Abstract. This paper applies a recently developed technique for deriving long-term trends in ozone from sparsely sampled data sets to multiple occultation instruments simultaneously without the need for homogenization. The technique can compensate for the non-uniform temporal, spatial, and diurnal sampling of the different instruments and can also be used to account for biases and drifts between instruments. These problems have been noted in recent international assessments as being a primary source of uncertainty that clouds the significance of derived trends. Results show potential recovery trends of ~ 2–3 %/decade in the upper stratosphere at mid-latitudes, which are similar to other studies, and also how sampling biases present in these data sets can create differences in derived "recovery" trends of up to ~ 1 %/decade if not properly accounted for. Limitations inherent to all techniques (e.g., relative instrument drifts) and their impacts (e.g., trend differences up to ~ 2 %/decade) are also described and a potential path forward towards resolution is presented.

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