Browsing by Author "Bayo A."

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    ATAT: Astronomical Transformer for time series and Tabular data
    (EDP Sciences, 2024) Cabrera-Vives G.; Moreno-Cartagena D.; Astorga N.; Reyes-Jainaga I.; Forster F.; Huijse P.; Arredondo J.; Munoz Arancibia A.M.; Bayo A.; Catelan, Marcio; Estevez P.A.; Sanchez-Saez P.; Alvarez A.; Castellanos P.; Gallardo P.; Moya A.; Rodriguez-Mancini D.
    The advent of next-generation survey instruments, such as the Vera C. Rubin Observatory and its Legacy Survey of Space and Time (LSST), is opening a window for new research in time-domain astronomy. The Extended LSST Astronomical Time-Series Classification Challenge (ELAsTiCC) was created to test the capacity of brokers to deal with a simulated LSST stream. Aims. Our aim is to develop a next-generation model for the classification of variable astronomical objects. We describe ATAT, the Astronomical Transformer for time series And Tabular data, a classification model conceived by the ALeRCE alert broker to classify light curves from next-generation alert streams. ATAT was tested in production during the first round of the ELAsTiCC campaigns. Methods. ATAT consists of two transformer models that encode light curves and features using novel time modulation and quantile feature tokenizer mechanisms, respectively. ATAT was trained on different combinations of light curves, metadata, and features calculated over the light curves. We compare ATAT against the current ALeRCE classifier, a balanced hierarchical random forest (BHRF) trained on human-engineered features derived from light curves and metadata. Results. When trained on light curves and metadata, ATAT achieves a macro F1 score of 82.9 ± 0.4 in 20 classes, outperforming the BHRF model trained on 429 features, which achieves a macro F1 score of 79.4 ± 0.1. Conclusions. The use of transformer multimodal architectures, combining light curves and tabular data, opens new possibilities for classifying alerts from a new generation of large etendue telescopes, such as the Vera C. Rubin Observatory, in real-world brokering scenarios.
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    Physical parameters of late M-type members of Chamaeleon I and TW Hydrae Association: Dust settling, age dispersion and activity
    (2017) Bayo A.; Barrado, D.; Allard, F.; Henning, T.; Comerón, F.; Morales-Calderón, M.; Rajpurohit, A.S.; Peña Ramírez, Karla Yulien; Beamín, J.C.; Beamín, J.C.
    Although mid-to-late type M dwarfs are the most common stars in our stellar neighbourhood, our knowledge of these objects is still limited. Open questions include the evolution of their angular momentum, internal structures, dust settling in their atmospheres and age dispersion within populations. In addition, at young ages, late-type Ms have masses below the hydrogen burning limit and therefore are key objects in the debate on the brown dwarf mechanism of formation. In this work, we determine and study in detail the physical parameters of two samples of young, late M-type sources belonging to either the Chamaeleon I dark cloud or the TW Hydrae Association and compare them with the results obtained in the literature for other young clusters and also for older, field, dwarfs. We used multiwavelength photometry to construct and analyse SEDs to determine general properties of the photosphere and disc presence. We also used low-resolution optical and near-infrared spectroscopy to study activity, accretion, gravity and effective temperature sensitive indicators.We propose a Virtual Observatory-based spectral index that is both temperature and age sensitive.We derived physical parameters using independent techniques confirming the already common feature/problem of the age/luminosity spread. In particular, we highlight two brown dwarfs showing very similar temperatures but clearly different surface gravity (explained invoking extreme early accretion). We also show how, despite large improvement in the dust treatment in theoretical models, there is still room for further progress in the simultaneous reproduction of the optical and near-infrared features of these cold young objects.