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I. Becker

Publications and source records attributed to I. Becker.

5 recordsLinked to original sources

Multiband Embeddings of Light Curves

In this work, we propose a novel ensemble of recurrent neural networks (RNNs) that considers the multiband and non-uniform cadence without having to compute complex features. Our proposed model consists of an ensemble of RNNs, which do not require the entire light curve to perform inference, making the inference process simpler. The ensemble is able to adapt to varying numbers of bands, tested on three real light curve datasets, namely Gaia, Pan-STARRS1, and ZTF, to demonstrate its potential for generalization. We also show the capabilities of deep learning to perform not only classification, but also regression of physical parameters such as effective temperature and radius. Our ensemble model demonstrates superior performance in scenarios with fewer observations, thus providing potential for early classification of sources from facilities such as Vera C. Rubin Observatory's LSST. The results underline the model's effectiveness and flexibility, making it a promising tool for future astronomical surveys. Our research has shown that a multitask learning approach can enrich the embeddings obtained by the models, making them instrumental to solve additional tasks, such as determining the orbital parameters of binary systems or estimating parameters for object types beyond periodic ones.

astro-ph.IM

ASTROMER: A transformer-based embedding for the representation of light curves

Taking inspiration from natural language embeddings, we present ASTROMER, a transformer-based model to create representations of light curves. ASTROMER was pre-trained in a self-supervised manner, requiring no human-labeled data. We used millions of R-band light sequences to adjust the ASTROMER weights. The learned representation can be easily adapted to other surveys by re-training ASTROMER on new sources. The power of ASTROMER consists of using the representation to extract light curve embeddings that can enhance the training of other models, such as classifiers or regressors. As an example, we used ASTROMER embeddings to train two neural-based classifiers that use labeled variable stars from MACHO, OGLE-III, and ATLAS. In all experiments, ASTROMER-based classifiers outperformed a baseline recurrent neural network trained on light curves directly when limited labeled data was available. Furthermore, using ASTROMER embeddings decreases computational resources needed while achieving state-of-the-art results. Finally, we provide a Python library that includes all the functionalities employed in this work. The library, main code, and pre-trained weights are available at https://github.com/astromer-science

astro-ph.IM

The VVV survey: Long-period variable stars I. Photometric catalog of ten VVV/OGLE tiles

Long-period variable stars (LPVs) are pulsating red giants, primarily in the asymptotic giant branch phase, and they include both Miras and semi-regular variables (SRVs). Their period-age and period-luminosity relations enable us to trace different stellar populations, as they are intrinsically very bright and cover a wide range in distances and ages. The purpose of this study is to establish a census of LPV stars in a region close to the Galactic center, using the six-year database of the Vista Variables in the V\'ia L\'actea (VVV) ESO Public Survey, as well as to describe the methodology that was employed to search for and characterize LPVs using VVV data. Near-IR surveys such as VVV provide a unique opportunity to probe the high-extinction innermost regions of the Milky Way. The detection and analysis of the intrinsically bright Miras in this region could provide us with an excellent probe of the properties of the Milky Way far behind its bulge. We used point-spread function photometry for all available $K_{s}$-band images in ten VVV tiles, covering $16.4~\deg^2$ in total, overlapping fields observed in the course of the Optical Gravitational Lensing Experiment (OGLE)-III survey. We designed a method to select LPV candidates, and we used the known variables from OGLE-III and other known variables from the literature to test our approach. The reduced $\chi^2$ statistic, along with the flux-independent index $K_{(fi)}$, were used in our analysis. The Lomb-Scargle period search method, Fourier analysis, template fitting, and visual inspection were then performed to refine our sample and characterize the properties of the stars included in our catalog. A final sample of 130 Mira candidates, of which 129 are new discoveries, was thus obtained, with periods in the range between about 80 and 1400~days.

astro-ph.SR

Vaccination with Leishmania mexicana LPG induces PD-1 in CD8+ and PD-L2 in macrophages thereby suppressing the immune response: A model to assess vaccine efficacy

Leishmania lipophosphoglycan is a molecule that has been used as a vaccine candidate, with contradictory results. Since unsuccessful protection could be related to suppressed T cell responses, we analyzed the expression of inhibitory receptor PD-1 in CD8+ and CD4+ lymphocytes and it is ligand PD-L2 in macrophages of BALB/c mice immunized with various doses of Leishmania mexicana LPG and re-stimulated in vitro with different concentrations of LPG. Vaccination with LPG enhanced the expression of PD-1 in CD8+ cells. Activation molecules CD137 were reduced in CD8+ cells from vaccinated mice. In vitro re-stimulation enhanced PD-L2 expression in macrophages of healthy mice in a dose-dependent fashion. The expression of PD-1, PD-L2, and CD137 is modulated according to the amount of LPG used during immunization and in vitro re-stimulation. We analyzed the expression of these molecules in mice infected with 1 x 10'4 or 1 x 10'5 L. mexicana promastigotes and re-stimulated in vitro with LPG. Infection with 1 x 10'5 parasites increased the PD-1 expression in CD8+ and diminished PD-L2 in macrophages. When these CD8+ cells were re-stimulated in vitro with LPG, simulating a second exposure to parasite antigens, PD-1 expression increased significantly more, in a dose-dependent fashion. We conclude that CD8+ T lymphocytes and macrophages express inhibition molecules according to the concentrations of Leishmania LPG and to the parasite load. Vaccination with increased amounts of LPG or infections with higher parasite numbers induces enhanced expression of PD-1 and functional inactivation of CD8+ cells, which can have critical consequences in leishmaniasis since these cells are crucial for disease control.

q-bio.CB

New variable Stars from the Photographic Archive: Semi-automated Discoveries, Attempts of Automatic Classification, and the New Field 104 Her

Using 172 plates taken with the 40-cm astrograph of the Sternberg Astronomical Institute (Lomonosov Moscow University) in 1976-1994 and digitized with the resolution of 2400 dpi, we discovered and studied 275 new variable stars. We present the list of our new variables with all necessary information concerning their brightness variations. As in our earlier studies, the new discoveries show a rather large number of high-amplitude Delta Scuti variables, predicting that many stars of this type remain not detected in the whole sky. We also performed automated classification of the newly discovered variable stars based on the Random Forest algorithm. The results of the automated classification were compared to traditional classification and showed that automated classification was possible even with noisy photographic data. However, further improvement of automated techniques is needed, which is especially important having in mind the very large numbers of new discoveries expected from all-sky surveys.

astro-ph.SR