O. Fors

Universitat de Barcelona

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Xavier Otazu

Universitat Autònoma de Barcelona

J. Núñez

National Institute for Space Research

María González-Audícana

Universidad Publica de Navarra

Román Arbiol

Institut Cartogràfic i Geològic de Catalunya

Stephen Walser

Virginia Tech

Raül Orús‐Pérez

European Space Research and Technology Centre

Enric Monte-Moreno

Universitat Politècnica de Catalunya

Hank Corbett

University of North Carolina at Chapel Hill

Kyle A. Corcoran

University of Virginia

Daniel del Ser

Reial Acadèmia de Ciències i Arts de Barcelona

Cooperative Institutions

Universitat Politècnica de Catalunya

University of North Carolina at Chapel Hill

FC Barcelona

Institut d'Estudis Espacials de Catalunya

Universitat de Barcelona

Embry–Riddle Aeronautical University

European Space Research and Technology Centre

Universidad Publica de Navarra

University of Toronto

Lowell Observatory

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Evryscope Observations of Post-Common-Envelope Hot Subdwarf Systems

AAS (2019)

Kyle A. Corcoran B. N. Barlow Stephen Walser Sam Mycroft John Aube

Subdwarf

Envelope (radar)

Source

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New observational techniques and analysis tools for wide field CCD surveys and high resolution astrometry

arXiv (Cornell University) (2006)

O. Fors

(Abridged) In the first part of this thesis, a general methodology for applying image deconvolution to wide-field CCD imagery. Results show that wavelet-based deconvolution can increase limiting magnitude up to 0.6 mag and improve limiting resolution 1 pixel with respect to original image with no astrometric accuracy degradation. In the second part, a new observational technique based on CCD fast drift scanning has been proposed for lunar occultations (LO) and speckle interferometry. This enables all kind of professional and high-end amateur observatories to perform such kind of observations. For LO, 16 new binaries up to 2mas of projected separation were detected and stellar diameters measurements in the 7 mas regime were obtained with that CCD and IR subarray based techniques. A new wavelet-based LO reduction pipeline was implemented. For speckle, CCD fast drift scanning technique was validated with the observation of four binary systems with well determined orbits. The results of separation, position angle and magnitude difference are in accordance with published measurements. A new approach for calibrating speckle transfer function from the binary power spectrum itself has been introduced. It does not require point source observations, which gives a more effective use of observation time.

Limiting magnitude

Astrometry

10.48550/arxiv.astro-ph/0604150

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Lunar occultations events from the Earth-Moon equilateral Lagrangian point: Simulations and scientific potential

Monthly Notices of the Royal Astronomical Society (2023)

A. Richichi O. Fors David Canales Kamal Patel Luis E. Mendoza Zambrano

ABSTRACT Recently, a novel idea has been proposed to use a spacecraft orbiting closely around the L4 or L5 Lagrangian points of the Earth–Moon system as a vantage location for astronomical observations under unique and advantageous conditions, e.g. to investigate the Solar corona or Kordylewski clouds. In this paper, we explore the scientific advantages of this configuration to observe lunar occultations. By using simulations based on actual orbital parameters and detector performance, we find that even a telescope as small as 10 cm in a L4 orbit would enable better light-curve sampling and higher angular resolution than from ground, and open up at the same time new spectral windows such as e.g. in the UV. We focus in particular on angular diameter measurements, which we find would be possible at the 100 $\mu$as level even at magnitudes normally considered faint in the context of ground-based LOs. Considerable benefits would also be afforded in the area of small separation binary objects, not just in terms of angular resolution but also by the capability of L4-based observations to repeat an LO scan of a source at multiple different position angles. Additional science cases would be made possible by the high time resolution intrinsic to the LO technique and the access to UV wavelengths. On-board data pipeline codes already exist, greatly simplifying the automatic pre-processing and the data transfer requirements.

Lagrangian point

Position (finance)

Orbital mechanics

10.1093/mnras/stad3473

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A Wavelet-Based Method for the Determination of the Relative Resolution Between Remotely Sensed Images

IEEE Transactions on Geoscience and Remote Sensing (2006)

J. Núñez O. Fors Xavier Otazu Vicenç Palà Román Arbiol

Spatial resolution is a key parameter of all remote sensing satellites and platforms. The nominal spatial resolution of satellites is a well-known characteristic because it is directly related to the area in ground that represents a pixel in the detector. Nevertheless, in practice, the actual resolution of a specific image obtained from a satellite is difficult to know precisely because it depends on many other factors such as atmospheric conditions. However, if one has two or more images of the same region, it is possible to compare their relative resolutions. In this paper, a wavelet-decomposition-based method for the determination of the relative resolution between two remotely sensed images of the same area is proposed. The method can be applied to panchromatic, multispectral, and mixed (one panchromatic and one multispectral) images. As an example, the method was applied to compute the relative resolution between SPOT-3, Landsat-5, and Landsat-7 panchromatic and multispectral images taken under similar as well as under very different conditions. On the other hand, if the true absolute resolution of one of the images of the pair is known, the resolution of the other can be computed. Thus, in the last part of this paper, a spatial calibrator that is designed and constructed to help compute the absolute resolution of a single remotely sensed image is described, and an example of its use is presented

10.1109/tgrs.2006.875359

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Citations (9)

GNSS Astronomy: a new field of synergestic research facilitated by the response of the Earth's ionosphere to solar flares and stellar superflares

Manuel Hernández Pajares David Moreno‐Borràs O. Fors Liu Qi Alberto Garcıa Rigo

Solar flare

10.46620/ursigass.2023.1960.msdr8934

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Enhancing the detection of low-energy M dwarf flares: wavelet-based denoising of CHEOPS data

arXiv (Cornell University) (2024)

Juan F. Poyatos O. Fors José María Gómez I. Ribas

Stellar flares are powerful bursts of electromagnetic radiation triggered by magnetic reconnection in the chromosphere of stars, occurring frequently and intensely on active M dwarfs. While missions like TESS and Kepler have studied regular and super-flares, their detection of flares with energies below $10^{30}$ erg remains incomplete. Extending flare studies to include these low-energy events could enhance flare formation models and provide insight into their impacts on exoplanetary atmospheres. This study investigates CHEOPS's capacity to detect low-energy flares in M dwarf light curves. Using CHEOPS's high photometric precision and observing cadence, along with a tailored wavelet-based denoising algorithm, we aim to improve detection completeness and refine flare statistics for low-energy events. We conducted a flare injection and recovery process to optimise denoising parameters, applied it to CHEOPS light curves to maximise detection rates, and used a flare breakdown algorithm to analyse complex structures. Our analysis recovered 349 flares with energies ranging from $2.2\times10^{26}$ to $8.1\times10^{30}$ erg across 63 M dwarfs, with $\sim$40% exhibiting complex, multi-peaked structures. The denoising algorithm improved flare recovery by $\sim$34%, though it marginally extended the lower boundary of detectable energies. For the full sample, the power-law index $\alpha$ was $1.92\pm0.07$, but a log-normal distribution fit better, suggesting multiple flare formation scenarios. While CHEOPS's observing mode is not ideal for large-scale surveys, it captures weaker flares than TESS or Kepler, expanding the observed energy range. Wavelet-based denoising enhances low-energy event recovery, enabling exploration of the micro-flaring regime. Expanding low-energy flare observations could refine flare generation models and improve the understanding of their role in star-planet interactions.

10.48550/arxiv.2412.15297

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Evryscope Photometry of the New Hot Subdwarf Reflection Effect Binary EC 01578-1743

AAS (2019)

Stephen Walser Kyle A. Corcoran B. N. Barlow Sam Mycroft John Aube

Subdwarf

Reflection

Source

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Multiresolution-based image fusion with additive wavelet decomposition

IEEE Transactions on Geoscience and Remote Sensing (1999)

J. Núñez Xavier Otazu O. Fors Albert Prades Vicenç Palà

The standard data fusion methods may not be satisfactory to merge a high-resolution panchromatic image and a low-resolution multispectral image because they can distort the spectral characteristics of the multispectral data. The authors developed a technique, based on multiresolution wavelet decomposition, for the merging and data fusion of such images. The method presented consists of adding the wavelet coefficients of the high-resolution image to the multispectral (low-resolution) data. They have studied several possibilities concluding that the method which produces the best results consists in adding the high order coefficients of the wavelet transform of the panchromatic image to the intensity component (defined as L=(R+G+B)/3) of the multispectral image. The method is, thus, an improvement on standard intensity-hue-saturation (IHS or LHS) mergers. They used the "a trous" algorithm which allows the use of a dyadic wavelet to merge nondyadic data in a simple and efficient scheme. They used the method to merge SPOT and LANDSAT/sup TM/ images. The technique presented is clearly better than the IHS and LHS mergers in preserving both spectral and spatial information.

Panchromatic film

Multispectral pattern recognition

Multiresolution analysis

Merge (version control)

10.1109/36.763274

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Citations (1,097)

TFAW survey II: six newly validated planets and 13 planet candidates fromK2

Monthly Notices of the Royal Astronomical Society (2022)

Daniel del Ser O. Fors M. del Alcázar V. V. Dyachenko Elliott P. Horch

ABSTRACT Searching for Earth-sized planets in data from Kepler’s extended mission (K2) is a niche that still remains to be fully exploited. The TFAW survey is an ongoing project that aims to re-analyse all light curves in K2 C1–C8 and C12–C18 campaigns with a wavelet-based detrending and denoising method, and the period search algorithm TLS to search for new transit candidates not detected in previous works. We have analysed a first subset of 24 candidate planetary systems around relatively faint host stars (10.9 < Kp < 15.4) to allow for follow-up speckle imaging observations. Using vespa and TRICERATOPS, we statistically validate six candidates orbiting four unique host stars by obtaining false-positive probabilities smaller than 1 per cent with both methods. We also present 13 vetted planet candidates that might benefit from other, more precise follow-up observations. All of these planets are sub-Neptune-sized with two validated planets and three candidates with sub-Earth sizes, and have orbital periods between 0.81 and 23.98 d. Some interesting systems include two ultra-short-period planets, three multiplanetary systems, three sub-Neptunes that appear to be within the small planet Radius Gap, and two validated and one candidate sub-Earths (EPIC 210706310.01, K2-411 b, and K2-413 b) orbiting metal-poor stars.

Orbital period

10.1093/mnras/stac3087

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GNSS Solar Astronomy in real-time during more than one solar cycle

Advances in Space Research (2023)

Manuel Hernández Pajares Alberto Garcıa Rigo Enric Monte-Moreno Qi Liu David Roma-Dollase

This work presents a summary of the continuous non-stop (hereinafter 24/7) real-time measurement and warning system for EUV solar activity, which is based on worldwide multifrequency Global Navigation Satellite Systems (GNSS) observations. The system relies on continuous tracking of the intensity of expected global patterns in the Earth's ionosphere's free electron distribution, which are associated with solar flares. The paper includes a discussion on the foundations of GNSS Solar Astronomy, along with details on its real-time implementation that began in 2011. Furthermore, a summary of the corresponding validation is provided, comparing it to external and direct solar EUV flux measurements obtained from SOHO-SEM. Finally, there will be a brief mention of the ongoing efforts to extend this technique to detect huge extra-solar sources.

Extreme Ultraviolet Lithography

Space Weather

Solar flare

Solar maximum

10.1016/j.asr.2023.12.016

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Citations (1)