Browsing by Author "Catelan, Marcio"

Now showing 1 - 20 of 174
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    A novel optimal transport-based approach for interpolating spectral time series
    (2024) Ramirez, Mauricio; Pignata, Giuliano; Forster, Francisco; Gonzalez-Gaitan, Santiago; Gutierrez, Claudia P.; Ayala, Bastian; Cabrera-Vives, Guillermo; Catelan, Marcio; Arancibia, Alejandra M. Munoz; Pineda-Garcia, Jonathan
    Context. The Vera C. Rubin Observatory is set to discover 1 million supernovae (SNe) within its first operational year. Given the impracticality of spectroscopic classification at such scales, it is mandatory to develop a reliable photometric classification framework. Aims. This paper introduces a novel method for creating spectral time series that can be used not only to generate synthetic light curves for photometric classification, but also in applications such as K-corrections and bolometric corrections. This approach is particularly valuable in the era of large astronomical surveys, where it can significantly enhance the analysis and understanding of an increasing number of SNe, even in the absence of extensive spectroscopic data. Methods. By employing interpolations based on optimal transport theory, starting from a spectroscopic sequence, we derive weighted average spectra with high cadence. The weights incorporate an uncertainty factor for penalizing interpolations between spectra that show significant epoch differences and lead to a poor match between the synthetic and observed photometry. Results. Our analysis reveals that even with a phase difference of up to 40 days between pairs of spectra, optical transport can generate interpolated spectral time series that closely resemble the original ones. Synthetic photometry extracted from these spectral time series aligns well with observed photometry. The best results are achieved in the V band, with relative residuals of less than 10% for 87% and 84% of the data for type Ia and II, respectively. For the B, g, R, and r bands, the relative residuals are between 65% and 87% within the previously mentioned 10% threshold for both classes. The worse results correspond to the i and I bands, where, in the case of SN Ia, the values drop to 53% and 42%, respectively. Conclusions. We introduce a new method for constructing spectral time series for individual SNe starting from a sparse spectroscopic sequence, and demonstrate its capability to produce reliable light curves that can be used for photometric classification.
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    A search for substructures near the Galactic plane and bulge using RR Lyrae stars as tracers
    (2024) Cristi Cambiaso, Nicolas Eduardo; Catelan, Marcio; Zoccali, Manuela; Pontificia Universidad Catolica de Chile. Faculty of Physics. Institute of Astrophysics
    Usando estrellas pulsantes de tipo RR Lyrae, hacemos una búsqueda de subestructuras Galácticas ("stellar streams" y cúmulos globulares) en la región del plano Galáctico. Construimos una muestra de estrellas RR Lyrae con valores de distancia y metalicidades. Estudiamos esta muestra con un algoritmo de "clustering" para encontrar grupos de estrellas cercanas y con propiedades similares. Mediante esta búsqueda, recuperamos estructuras conocidas y encontramos posibles nuevas estructuras.
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    A Study of Nine Extremely Low Mass Ratio-contact Binary Systems
    (IOP Publishing Ltd, 2024) Lalounta, Eleni; Christopoulou, Panagiota-Eleftheria; Papageorgiou, Athanasios; Ferreira Lopes, C. E.; Catelan, Marcio
    Low-mass ratio systems (LMR) are a very interesting class of contact eclipsing binaries challenging the theoretical models of stability. These systems are also considered possible progenitors of the rare low-mass optical transients called red novae. In this study, we present the identification of 7 new totally eclipsing LMR systems from Catalina Sky Surveys (CSS) and 77 LMR candidates from the All Sky Automated Survey. Using the available CSS light curves and new multiband observations for CSS_J210228.3-031048 and CSS_J231513.3+345335 with the 2.3 m Aristarchos telescope at Helmos Observatory, we estimate their physical and absolute parameters and investigate their stability and their progenitors. The light curves are analyzed by performing a two-dimensional scan on the mass-ratio inclination plane with Phoebe-0.31 scripter, while the errors are estimated using Monte Carlo simulations and heuristic scanning of the parameter space. Our analysis revealed that all 9 CSS systems have extreme mass ratios from 0.09 to 0.16. Our statistical analysis of well-studied LMR contact binaries shows that LMR systems tend to have warmer and more massive primaries. The investigation of the progenitors of both low and higher-mass-ratio systems reveals a trend for the former to originate from higher-mass ancestors. Finally, we investigate the stability condition by calculating the ratio of spin angular momentum to orbital angular momentum and other stability indicators in the context of the reliability of the solutions.
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    A Superwind from Early Post-Red Giant Stars?
    (2001) Soker, Noam; Catelan, Marcio; Rood, Robert T.; Harpaz, Amos
    We suggest that the gap observed at ~20,000 K in the horizontal branches of several Galactic globular clusters is caused by a small amount of extra mass loss that occurs when stars start to ``peel off'' the red giant branch (RGB), i.e., when their effective temperature starts to increase, even though they may still be on the RGB. We show that the envelope structure of RGB stars that start to peel off is similar to that of late asymptotic giant branch stars known to have a superwind phase. An analogous superwind in the RGB peel-off stars could easily lead to the observed gap in the distribution of the hottest horizontal-branch stars....
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    Alert Classification for the ALeRCE Broker System: The Anomaly Detector
    (IOP Publishing Ltd, 2023) Pérez-Carrasco, Manuel; Cabrera-Vives, Guillermo; Hernández-García, Lorena; Forster, F.; Sanchez-Saez, Paula; Muñoz Arancibia, Alejandra M.; Arredondo, Javier; Astorga, Nicolas; Bauer, Franz Erik; Bayo, Amelia; Catelan, Marcio; Dastidar, Raya; Estevez, P. A.; Lira, Paulina; Pignata, Giuliano
    Astronomical broker systems, such as Automatic Learning for the Rapid Classification of Events (ALeRCE), are currently analyzing hundreds of thousands of alerts per night, opening up an opportunity to automatically detect anomalous unknown sources. In this work, we present the ALeRCE anomaly detector, composed of three outlier detection algorithms that aim to find transient, periodic, and stochastic anomalous sources within the Zwicky Transient Facility data stream. Our experimental framework consists of cross-validating six anomaly detection algorithms for each of these three classes using the ALeRCE light-curve features. Following the ALeRCE taxonomy, we consider four transient subclasses, five stochastic subclasses, and six periodic subclasses. We evaluate each algorithm by considering each subclass as the anomaly class. For transient and periodic sources the best performance is obtained by a modified version of the deep support vector data description neural network, while for stochastic sources the best results are obtained by calculating the reconstruction error of an autoencoder neural network. Including a visual inspection step for the 10 most promising candidates for each of the 15 ALeRCE subclasses, we detect 31 bogus candidates (i.e., those with photometry or processing issues) and seven potential astrophysical outliers that require follow-up observations for further analysis.
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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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    Impact of Current Uncertainties in the 12C+12C Nuclear Reaction Rate on Intermediate-mass Stars and Massive White Dwarfs
    (2024) De Geronimo, Francisco C.; Bertolami, Marcelo M. Miller; Battich, Tiara; Tang, Xiaodong; Catelan, Marcio; Corsico, Alejandro H.; Li, Yunjun; Fang, Xiao; Althaus, Leandro G.
    Recent determinations of the total rate of the 12C+12C nuclear reaction show non-negligible differences with the reference reaction rate commonly used in previous stellar simulations. In addition, the current uncertainties in determining each exit channel constitute one of the main uncertainties in shaping the inner structure of super asymptotic giant branch stars that could have a measurable impact on the properties of pulsating ultramassive white dwarfs (WDs). We explore how new determinations of the nuclear reaction rate and its branching ratios affect the evolution of WD progenitors. We show that the current uncertainties in the branching ratios constitute the main uncertainty factor in determining the inner composition of ultramassive WDs and their progenitors. We found that the use of extreme branching ratios leads to differences in the central abundances of 20Ne of at most 17%, which are translated into differences of at most 1.3% and 0.8% in the cooling times and size of the crystallized core, respectively. However, the impact on the pulsation properties is small, less than 1 s for the asymptotic period spacing. We found that the carbon burns partially in the interior of ultramassive WD progenitors within a particular range of masses, leaving a hybrid CONe-core composition in their cores. The evolution of these new kinds of predicted objects differs substantially from the evolution of objects with pure CO cores. Differences in the size of the crystallized core and cooling times of up to 15% and 6%, respectively, lead to distinct patterns in the period spacing distribution.
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    Informative regularization for a multi-layer perceptron RR Lyrae classifier under data shift
    (2023) Perez-Galarce, Francisco; Pichara, Karim; Huijse, Pablo; Catelan, Marcio; Mery Quiroz, Domingo Arturo
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    Properties of RR Lyrae variables in binary systems: towards a first-time mass measurement
    (2022) Hajdu, Gergely; Pietrzyński, Grzegorz; Catelan, Marcio; Jurcsik, Johanna; Karczmarek, Paulina; Pilecki, Bogumił; Thompson, Ian
    Despite their general usefulness as distance indicators and tracers of old stellar populations, several properties of RR Lyrae variable stars remain poorly understood. Crucially, the most basic stellar parameter, the stellar mass, has never been measured for any member of this class. We performed a new search for RR Lyrae variables in binary systems, looking for the light travel-time effect in the long-term light curves obtained by the OGLE project toward the Galactic bulge, finding 87 high-confidence candidates. The distributions of the inferred properties of these binary systems are quite peculiar: no system has a binary period below 1000d, and their frequency peaks between 3000 and 4000d; their eccentricities are strongly concentrated around 0.27; and their mass functions are apparently trimodal. Supposing an isotropic inclination distribution, and a mass of 0.65 times solar for a typical RR Lyrae, these three modes point to typical companion masses of ~0.6, ~0.2 and ~0.067 solar masses. These can be attributed to a combination of main sequence and white dwarf, red dwarf, and brown dwarf companions, respectively. As RR Lyrae variables are evolved from (close to) solar mass, Population II main sequence stars, their binary parameters provide a unique glimpse into the binary properties of the old stellar population. These properties seem to be wildly different from those of Population I binaries. The difference in the distribution of binary periods can be explained tentatively by binary stellar evolution and selection effects. However, the distribution of eccentricities, and especially the trimodal companion mass distribution is in stark contrast to Population I binary parameters of solar-type stars, requiring further observations to confirm, and theoretical efforts to explain them. Finally, the observed binary properties inform us on the prospects of both finding and RR Lyrae variable in an eclipsing binary system, as well as on the possibility of obtaining an astrometric mass measurement using observations of the Gaia satellite....
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    Pulsating Stars
    (2015) Catelan, Marcio; Smith, H. A.
    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail....
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    Pulsating stars in ω Centauri. Near-IR properties and period-luminosity relations
    (2017) Navarrete, Camila; Catelan, Marcio; Contreras Ramos, Rodrigo; Alonso-García, Javier; Gran, Felipe; Dékány, István; Minniti, Dante
    ω Centauri (NGC 5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of ω Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete J and KS near-IR catalog of variable stars in the field of ω Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands....
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    Relative ratios and radial distributions of the multiple populations in the Galactic globular clusters
    (2015) Alonso-Garcia, Javier; Catelan, Marcio; Amigo, Pía; Contreras Ramos, Rodrigo; Cortés, Cristián; Kuehn, Charles; Grundahl, Frank; López, Graciela; Salinas, Ricardo; Smith, Horace; Stetson, Peter; Sweigart, Allen; Valcarce, Aldo A. R.; Zoccali, Manuela
    Recently, the long-standing paradigm that globular clusters are close approximations to simple stellar populations, with all stars formed at precisely the same time from populations having precisely the same chemical composition, has been shattered by a series of photometric and spectroscopic observations that reveal that these objects are more complex than we once thought . In this poster, we present the first results of a survey we are conducting among the Galactic globular clusters using the Strömgren photometric system. We show that the bluest Strömgren filters reveal broadenings or splits in the stellar sequences in the color-magnitude diagrams of the sampled clusters. These features allow us to disentangle successfully the different stellar populations in a given globular cluster, which let us measure their relative ratios, and explore their radial trends and gradients from the cluster center out to its tidal radius....
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    Results from the Catalina Real-time Transient Survey
    (2009) Drake, Andrew J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M.; Williams, R.; Catelan, Marcio; Beshore, E.; Larson, S.; Christensen, E.
    The Catalina Real-time Transient Survey (CRTS) is a collaborative effort between Caltech and LPL that uses data from Catalina Sky Survey's 0.7m Schmidt telescope to search for optical transients. This survey currently covers a total of 26,000 square degrees on the sky between declinations -30 and 70. Observations covering 1200 square degrees are taken 21 nights per lunation and reach magnitudes of 19 to 20. CRTS is sensitive to transients with timescales from minutes to years since images are taken in sequences separated by 10 minutes and past observations date back over four years. Transient classification is performed using follow up imaging and spectroscopy in combination with VO-enabled archival analysis of CSS and Palomar Quest synoptic datasets and DSS, 2MASS, SDSS, GALEX and UKIDSS surveys. To date more than 600 unique transients have been identified by CRTS. These include more than 200 newly discovered Supernovae, Cataclysmic Variables and Blazars. Initial results of note include in the discovery of hyper-luminous supernovae, as well as a high rate of supernovae associated with intrinsically faint galaxies. In the near future we expect to expand the survey area and depth by utilizing data from two additional operational Catalina Sky Survey telescopes. All CRTS transients are discovered and distributed openly within minutes of observation using VOEvent technology as well as html tables, RSS feeds and GoogleSky (from VOEventNet.org). Astronomers will soon be able to automatically select transients of particular interest by using the personalized event selection available via the SkyAlert system....
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    Results From The First Year Of The Catalina Real-time Transient Survey
    (2009) Drake, Andrew J.; Djorgovski, S. G.; Mahabal, A.; Graham, M. J.; Williams, R.; Catelan, Marcio; Beshore, E.; Larson, S.; Christensen, E.
    The Catalina Real-time Transient Survey (CRTS) is a collaborative effort between Caltech and LPL that uses data from Catalina Sky Survey's 0.76m Schmidt telescope to search for optical transients (OTs) varying by more than two magnitudes between past and current data. The survey covers 26,000 square degrees on the sky between declination -30 and 70 at Galactic latitudes |b| > 10 deg. Sequences of four observations are taken separated by 10 minutes and cover 1200 square degrees each night for 21 nights per lunation. Observations reach transients at unfiltered magnitudes of 19 to 20. To date more than 400 unique OTs have been identified by CRTS. These transients include more than 150 supernovae and dwarf novae, as well as UV Ceti flares, high proper motion stars, comets, Miras and currently unidentified transients. Classification is carried out using follow up imaging and spectroscopy in combination with VO-enabled archival analysis of CSS and Palomar Quest synoptic datasets and DSS, 2MASS, SDSS, GALEX and UKIDSS surveys. All candidate OTs are published within 5 mins of observation and are openly accessible as VOEvents, html tables and RSS feeds (from VOEventNet.org). As part of our public outreach program, the CRTS event stream is also published in the event layer of Google Sky....
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    RR Lyrae binary systems in the Galactic bulge
    (2017) Hajdu, Gergely; Catelan, Marcio
    The possibility of a direct mass measurement of RR Lyrae variable stars in binary systems has remained elusive for many years, due to the apparent paucity of such systems. Motivated by our recent success of finding a population of high confidence candidates, we have been continuing the search for RR Lyrae variables in binary systems towards the Galactic bulge. We describe the preliminary results of our project in these proceedings....
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    RR Lyrae in LMC Globular Clusters
    (2009) Kuehn, Charles A., III; Smith, H. A.; Taylor, L.; McClellan, R. E.; Catelan, Marcio; Looper, K.; Pritzl, B. J.; De Lee, N.
    We present preliminary results from a study of five globular clusters located in the Large Magellanic Cloud. The goal of this project is to carry out a large, systematic study of the behavior of RR Lyrae stars in Oosterhoff-intermediate globular clusters. The LMC is an ideal target for a study of this sort as it contains Oosterhoff-intermediate clusters as well as Oo-I/II clusters. We seek to answer three main questions. 1.) Are there double-mode RR Lyrae stars (RRd) in Oo-intermediate clusters and if so how do their properties compare to RRd stars in Oo-I/II clusters? 2.) How do the positions of RR Lyrae stars on the Bailey diagram differ between stars in Oo-intermediate clusters compared to those in Oo-I/II clusters? 3.) How do the Fourier decomposition parameters of RR Lyrae stars change when going from Oo-I/II clusters to Oo-intermediate ones? We present Oosterhoff classifications and sample light curves for some of the clusters in our study and discuss their Fourier parameters and resulting physical properties. We also discuss the implications of our findings on the nature of the Oosterhoff dichotomy and what that implies about Milky Way formation....
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    RR Lyrae in LMC Globular Clusters: Insights into the Oosterhoff Phenomenon and Milky Way Formation
    (2011) Kuehn, Charles A., III; Smith, H. A.; Catelan, Marcio; Taylor, L.; McClellan, R. E.; Looper, K.; DeLee, N.; Pritzl, B. J.
    We present results from a study of RR Lyrae stars in five globular clusters located in the Large Magellanic Cloud. The goal of this study was to look at the behavior and properties of RR Lyrae stars in Oosterhoff-intermediate globular clusters and compare them to RR Lyrae in Oosterhoff I and II clusters. New BVI photometric observations of these clusters were obtained with the SMARTS consortium telescopes and with the SOAR 4-meter telescope. We present light curves and Fourier properties for the RR Lyrae stars in our study as well as physical properties for these stars derived from their Fourier parameters. We compare these physical properties to those of RR Lyrae in Milky Way halo globular clusters and discuss implications for Milky Way halo formation....
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    RR Lyrae in the Large Magellanic Cloud: New Insights Into Oosterhoff Intermediate Globular Clusters
    (2013) Kuehn, Charles A.; Smith, H. A.; Catelan, Marcio; Pritzl, B. J.; De Lee, N. M.; Borissova, J.
    Current models suggest that the Milky Way halo was formed through the accretion of objects similar to the present day nearby dwarf galaxies. The ancient nature of RR Lyrae stars make them ideal tracers of stellar populations that can be used to determine how similar the present day dwarf galaxies are to the objects that were accreted to form the Milky Way halo. Globular clusters in the halo can be divided into two groups based on the properties of their RR Lyrae stars, called Oosterhoff groups, with a zone of avoidance between these groups. Nearby dwarf galaxies and their globular clusters fall not only in the Oosterhoff I and II groups, like in the Milky Way, but also in the zone of avoidance between these groups. These Oosterhoff intermediate objects, as the objects that fall in the zone of avoidance are called, present a challenge to the current theories of Milky Way halo formation. We present results of a recent study of globular clusters in the Large Magellanic Cloud which focused on the behavior of individual RR Lyrae stars in Oosterhoff intermediate objects and how this behavior compares to RR Lyrae stars in the other Oosterhoff groups. We discuss how these results demonstrate that Oosterhoff intermediate objects should not be thought of as one homogenous group. We also discuss how these results suggest that the traditional dividing lines between the Oosterhoff groups may need to be revised....
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    RR Lyrae in the LMC: Insights Into the Oosterhoff Phenomenon
    (2013) Kuehn, Charles A; Smith, Horace A.; Catelan, Marcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Dame, Kyra; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura
    Although more than eight decades have passed since P. Th. Oosterhoff drew attention to differences in the properties of RR Lyrae variables in globular clusters, the origin and significance of the Oosterhoff groups remain unclear. Nonetheless, the accumulation of extensive new observations of RR Lyrae stars in globular clusters of the Milky Way and Local Group galaxies allows a fresh look at the phenomenon. Insights come not only from surveys of variables within the original Oosterhoff groups I and II but also from recent observations of the Oosterhoff-intermediate systems found especially in smaller Local Group galaxies. We will compare properties of RR Lyrae in several systems to investigate what they reveal about system-to-system differences of transition temperature between fundamental-mode and first overtone pulsators and of horizontal branch luminosity. Both transition temperature and horizontal branch luminosity have at various times been credited as playing roles in the creation of the Oosterhoff dichotomy....
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    RR Lyrae Period-Amplitude Diagrams: From Bailey to Today
    (2011) Smith, Horace A.; Catelan, Marcio; Kuehn, Charles
    More than a century ago, Solon Bailey's pioneering investigations of the variable stars in globular clusters allowed the first period-amplitude diagrams to be constructed for their RR Lyrae stars. These diagrams differ from cluster to cluster, and there has been debate as to whether these differences are correlated mainly with [Fe/H] or with Oosterhoff type. It is clear now that a cluster's Oosterhoff type plays an important role in determining its period-amplitude relation, although the Oosterhoff dichotomy itself is correlated with metallicity. Not all clusters follow the usual patterns, however. The globular clusters NGC 6388 and NGC 6441 have period-amplitude diagrams similar to those of metal-poor Oosterhoff type II globular clusters, but they themselves are comparatively metal-rich. The period-amplitude diagrams of Oosterhoff-intermediate systems are discussed....