Browsing by Author "Alonso, R."

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    Delfin plus plus : A Delaunay based algorithm for finding 3D polyhedral voids in galaxy surveys
    (2023) Guidotti, V.; Alonso, R.; Bravo, M.; Hitschfeld, N.; Marinello, G.; Hervias, C.; Campusano, L. E.
    Delfin++ (Delaunay Edge Void Finder) is a simple and time-efficient algorithm, with a single input variable, designed to find cosmological voids within a 3-dimensional distribution of galaxies by characterizing them as polyhedral regions from a Delaunay tessellation. Two density metrics are defined and used to search for density minima and construct polyhedra that represent the underdense zones. A density threshold is used to define the limit above which a galaxy will not be considered part of a void. This threshold is commonly defined as 0.2n over bar , where n over bar is the mean point density of the sample, whereas the values used in this work range from 0.2n over bar to 0.33n over bar . The algorithm is applied to artificial data, with different density contrasts, as well as to galaxy data from SDSS DR10. The detected voids are compared with voids that have been produced through the application of VIDE. Our algorithm detects roundish underdense regions in the galaxy samples, with differences and overlaps compared to the VIDE algorithm's results. Closer agreement is revealed when the edge length density metric is used over large galaxy samples, allowing for the detection of up to 90% of the largest VIDE voids. We measure ellipticities of Delfin++ detected voids and find that their distribution is shifted towards smaller values in comparison with VIDE's distribution, and with predictions from an analytical model. The voids found with Delfin++ are not intended to generate a catalog, but rather represent a proof of concept of a simpler algorithm or with fewer rules for further calibration and future production of a final catalog. Delfin++ performance tests suggest that enhanced characterization of voids can be achieved through (i) choice of other density threshold values, and (ii) early recognition and rejection of deformed polyhedra induced by missing data.& COPY; 2023 Elsevier B.V. All rights reserved.
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    The EBLM project - VIII. First results for M-dwarf mass, radius, and effective temperature measurements using CHEOPS light curves
    (2021) Swayne, M., I; Maxted, P. F. L.; Triaud, A. H. M. J.; Sousa, S. G.; Broeg, C.; Floren, H-G; Guterman, P.; Simon, A. E.; Boisse, I; Bonfanti, A.; Martin, D.; Santerne, A.; Salmon, S.; Standing, M. R.; Van Grootel, V.; Wilson, T. G.; Alibert, Y.; Alonso, R.; Anglada Escude, G.; Asquier, J.; Barczy, T.; Barrado, D.; Barros, S. C. C.; Battley, M.; Baumjohann, W.; Beck, M.; Beck, T.; Bekkelien, A.; Benz, W.; Billot, N.; Bonfils, X.; Brandeker, A.; Busch, M-D; Cabrera, J.; Charnoz, S.; Cameron, A. Collier; Csizmadia, Sz; Davies, M. B.; Deleuil, M.; Deline, A.; Delrez, L.; Demangeon, O. D. S.; Demory, B-O; Dransfield, G.; Ehrenreich, D.; Erikson, A.; Fortier, A.; Fossati, L.; Fridlund, M.; Futyan, D.; Gandolfi, D.; Gillon, M.; Guedel, M.; Hebrard, G.; Heidari, N.; Hellier, C.; Heng, K.; Hobson, M.; Hoyer, S.; Isaak, K. G.; Kiss, L.; Hodzic, V. Kunovac; Lalitha, S.; Laskar, J.; des Etangs, A. Lecavelier; Lendl, M.; Lovis, C.; Magrin, D.; Marafatto, L.; McCormac, J.; Miller, N.; Nascimbeni, V; Olofsson, G.; Ottensamer, R.; Pagano, I; Palle, E.; Peter, G.; Piotto, G.; Pollacco, D.; Queloz, D.; Ragazzoni, R.; Rando, N.; Rauer, H.; Ribas, I; Santos, N. C.; Scandariato, G.; Segransan, D.; Smith, A. M. S.; Steinberger, M.; Steller, M.; Szabo, Gy M.; Thomas, N.; Udry, S.; Walter, I; Walton, N. A.; Willett, E.
    The accuracy of theoretical mass, radius, and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue, we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius, and effective temperature of the M-dwarf star. Here, we present the analysis of three eclipsing binaries. We use the pycheops data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite - we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have similar to 24 new mass, radius, and effective temperature measurements for very low-mass stars within the next few years.