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64 Publications visible to you, out of a total of 64
Probabilistic Modelling of Time Series for explorative Big Data Analysis in Astronomy

Abstract

Not specified

Author: Fenja Schweder

Date Published: 1st Feb 2023

Publication Type: Master's Thesis

Accretion disks, quasars and cosmology: meandering towards understanding

Abstract (Expand)

Abstract As Setti and Woltjer noted back in 1973, one can use quasars to construct the Hubble diagram; however, the actual application of the idea was not that straightforward. It took years to implement …It took years to implement the proposition successfully. Most ways to employ quasars for cosmology now require an advanced understanding of their structure, step by step. We briefly review this progress, with unavoidable personal biases, and concentrate on bright unobscured sources. We will mention the problem of the gas flow character close to the innermost stable circular orbit near the black hole, as discussed five decades ago. This problem later led to the development of the slim disk scenario and is recently revived in the context of Magnetically Arrested Disks (MAD) and Standard and Normal Evolution (SANE) models. We also discuss the hot or warm corona issue, which is still under debate and complicates the analysis of X-ray reflection. We present the scenario of the formation of the low ionization part of the Broad Line Region as a failed wind powered by radiation pressure acting on dust (Failed Radiatively Driven Dusty Outflow – FRADO). Next, we examine the cosmological constraints currently achievable with quasars, primarily concentrating on light echo methods (continuum time delays and spectral-line time delays to the continuum) that are (or should be) incorporating the progress mentioned above. Finally, we briefly discuss prospects in this lively subject area.

Authors: Bożena Czerny, Shulei Cao, Vikram Kumar Jaiswal, Vladimír Karas, Narayan Khadka, Mary Loli Martínez-Aldama, Mohammad Hassan Naddaf, Swayamtrupta Panda, Francisco Pozo Nuñez, Raj Prince, Bharat Ratra, Marzena Sniegowska, Zhefu Yu, Michal Zajaček

Date Published: 1st Feb 2023

Publication Type: Journal

The EURONEAR Lightcurve Survey of Near Earth Asteroids 2017–2020

Abstract

Not specified

Authors: O. Vaduvescu, A. Aznar Macias, T. G. Wilson, T. Zegmott, F. M. Pérez Toledo, M. Predatu, R. Gherase, V. Pinter, F. Pozo Nunez, K. Ulaczyk, I. Soszyński, P. Mróz, M. Wrona, P. Iwanek, M. Szymanski, A. Udalski, F. Char, H. Salas Olave, G. Aravena-Rojas, A. C. Vergara, C. Saez, E. Unda-Sanzana, B. Alcalde, A. de Burgos, D. Nespral, R. Galera-Rosillo, N. J. Amos, J. Hibbert, A. López-Comazzi, J. Oey, M. Serra-Ricart, J. Licandro, M. Popescu

Date Published: 1st Oct 2022

Publication Type: Journal

Innovative Tools Fostered by the HiPS Ecosystem

Abstract (Expand)

Over the past 10 years HiPS (Hierarchical Progressive Surveys) has evolved from an experiment led by CDS to an ecosystem supported by more than 20 data centers exposing their own HiPS node. This trend … has been pushed by advanced and simple clients (Aladin Desktop, Aladin Lite) or portals (ESASky, ESO Science Portal) and thanks to Hipsgen. Today the HiPS ecosystem gathers 900 HiPS datasets published by 20+ HiPS nodes. We describe a selection of different tools and services that benefit from having a large collection of multi-wavelength datasets available in the same format: hips2fits, on-the-fly generation of RGB tiles from pre-existing HiPS, HiPS as a container for 1d and 2d histograms, CatTiler, computation on the HiPS grid, generation of Spectral Energy Distribution from FITS tiles.

Authors: Thomas Boch, Mark Allen, Caroline Bot, Pierre Fernique, Matthieu Baumann, Mihaela Buga, Francois Bonnarel, Daniel Durand, Kai Polsterer

Date Published: 1st Jul 2022

Publication Type: InProceedings

Interactive Exploration Framework for Big Data Sets

Abstract (Expand)

Big data issues are the order of the day for many researchers in astronomy. In the past, several machine learning methods were proposed to organize, classify, or condense big data sets. However, this … is not the end of the road. In most cases, researchers need to take further analysis by hand on automatically preprocessed data to gather valuable conclusions. To facilitate the pipeline of data analysis, we suggest a generic front-end framework allowing the user not only to process the data automatically, but also to interactively explore and investigate the results of machine learning procedures. A compact visualization gives an initial overview and can be adjusted to point out the parts of interest. By providing abstract accommodation functions such as zooming, scrolling, filtering, and labeling, crucial data fragments can be found and marked in an intuitive way.

Authors: Fenja Kollasch, Kai Polsterer

Date Published: 1st Jul 2022

Publication Type: InProceedings

Convolutional autoencoders for spatially-informed ensemble post-processing

Abstract (Expand)

Ensemble weather predictions typically show systematic errors that have to be corrected via post-processing. Even state-of-the-art post-processing methods based on neural networks often solely rely on … location-specific predictors that require an interpolation of the physical weather model's spatial forecast fields to the target locations. However, potentially useful predictability information contained in large-scale spatial structures within the input fields is potentially lost in this interpolation step. Therefore, we propose the use of convolutional autoencoders to learn compact representations of spatial input fields which can then be used to augment location-specific information as additional inputs to post-processing models. The benefits of including this spatial information is demonstrated in a case study of 2-m temperature forecasts at surface stations in Germany.

Authors: Sebastian Lerch, Kai L. Polsterer

Date Published: 25th Apr 2022

Publication Type: InProceedings

An Absolute Calibration of the Near-infrared Period–Luminosity Relations of Type II Cepheids in the Milky Way and in the Large Magellanic Cloud

Abstract (Expand)

Abstract We present time-series photometry of 21 nearby type II Cepheids in the near-infrared J , H , and K s passbands. We use this photometry, together with the Third Gaia Early Data Release parallaxes, … K s passbands. We use this photometry, together with the Third Gaia Early Data Release parallaxes, to determine for the first time period–luminosity relations (PLRs) for type II Cepheids from field representatives of these old pulsating stars in the near-infrared regime. We found PLRs to be very narrow for BL Herculis stars, which makes them candidates for precision distance indicators. We then use archival photometry and the most accurate distance obtained from eclipsing binaries to recalibrate PLRs for type II Cepheids in the Large Magellanic Cloud (LMC). Slopes of our PLRs in the Milky Way and in the LMC differ by slightly more than 2 σ and are in a good agreement with previous studies of the LMC, Galactic bulge, and Galactic globular cluster type II Cepheids samples. We use PLRs of Milky Way type II Cepheids to measure the distance to the LMC, and we obtain a distance modulus of 18.540 ± 0.026(stat.) ± 0.034(syst.) mag in the W JK Wesenheit index. We also investigate the metallicity effect within our Milky Way sample, and we find a rather significant value of about −0.2 mag dex −1 in each band meaning that more metal-rich type II Cepheids are intrinsically brighter than their more metal-poor counterparts, in agreement with the value obtained from type II Cepheids in Galactic globular clusters. The main source of systematic error on our Milky Way PLRs calibration, and the LMC distance, is the current uncertainty of the Gaia parallax zero-point.

Authors: Piotr Wielgórski, Grzegorz Pietrzyński, Bogumił Pilecki, Wolfgang Gieren, Bartłomiej Zgirski, Marek Górski, Gergely Hajdu, Weronika Narloch, Paulina Karczmarek, Radosław Smolec, Pierre Kervella, Jesper Storm, Alexandre Gallenne, Louise Breuval, Megan Lewis, Mikołaj Kałuszyński, Dariusz Graczyk, Wojciech Pych, Ksenia Suchomska, Mónica Taormina, Gonzalo Rojas Garcia, Aleksandra Kotek, Rolf Chini, Francisco Pozo Nũnez, Sadegh Noroozi, Catalina Sobrino Figaredo, Martin Haas, Klaus Hodapp, Przemysław Mikołajczyk, Krzysztof Kotysz, Dawid Moździerski, Piotr Kołaczek-Szymański

Date Published: 8th Mar 2022

Publication Type: Journal

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