Browsing by Author "Cassisi, Santi"

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    PERIOD CHANGE SIMILARITIES AMONG THE RR LYRAE VARIABLES IN OOSTERHOFF I AND OOSTERHOFF II GLOBULAR SYSTEMS
    (2011) Kunder, Andrea; Walker, Alistair; Stetson, Peter B.; Bono, Giuseppe; Nemec, James M.; de Propris, Roberto; Monelli, Matteo; Cassisi, Santi; Andreuzzi, Gloria; Dall'Ora, Massimo; Di Cecco, Alessandra; Zoccali, Manuela
    We present period change rates (dP/dt) for 42 RR Lyrae variables in the globular cluster IC 4499. Despite clear evidence of these period increases or decreases, the observed period change rates are an order of magnitude larger than predicted from theoretical models of this cluster. We find that there is a preference for increasing periods, a phenomenon observed in most RR Lyrae stars in Milky Way globular clusters. The period change rates as a function of position in the period-amplitude plane are used to examine possible evolutionary effects in OoI clusters, OoII clusters, field RR Lyrae stars, and the mixed-population cluster. Centauri. It is found that there is no correlation between the period change rate and the typical definition of Oosterhoff groups. If the RR Lyrae period changes correspond with evolutionary effects, this would be in contrast to the hypothesis that RR Lyrae variables in OoII systems are evolved horizontal-branch stars that spent their zero-age horizontal-branch phase on the blue side of the instability strip. This may suggest that age may not be the primary explanation for the Oosterhoff types.
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    Stellar Astrophysics and Exoplanet Science with the Maunakea Spectroscopic Explorer (MSE)
    (2019) Bergemann, Maria; Huber, Daniel; Adibekyan, Vardan; Angelou, George; Barría, Daniela; Beers, Timothy C.; Beck, Paul G.; Bellinger, Earl P.; Bestenlehner, Joachim M.; Bitsch, Bertram; Burgasser, Adam; Buzasi, Derek; Cassisi, Santi; Catelan, Marcio; Escorza, Ana; Fleming, Scott W.; Gänsicke, Boris T.; Gandolfi, Davide; García, Rafael A.; Gieles, Mark; Karakas, Amanda; Lebreton, Yveline; Lodieu, Nicolas; Melis, Carl; Merle, Thibault; Mészáros, Szabolcs; Miglio, Andrea; Molaverdikhani, Karan; Monier, Richard; Morel, Thierry; Neilson, Hilding R.; Oshagh, Mahmoudreza; Rybizki, Jan; Serenelli, Aldo; Smiljanic, Rodolfo; Szabó, Gyula M.; Toonen, Silvia; Tremblay, Pier-Emmanuel; Valentini, Marica; Van Eck, Sophie; Zwintz, Konstanze; Bayo, Amelia; Cami, Jan; Casagrande, Luca; Gabdeev, Maksim; Gaulme, Patrick; Guiglion, Guillaume; Handler, Gerald; Hillenbrand, Lynne; Yildiz, Mutlu; Marley, Mark; Mosser, Benoit; Price-Whelan, Adrian M.; Prsa, Andrej; Hernández Santisteban, Juan V.; Silva Aguirre, Victor; Sobeck, Jennifer; Stello, Dennis; Szabo, Robert; Tsantaki, Maria; Villaver, Eva; Wright, Nicholas J.; Xu, Siyi; Zhang, Huawei; Anguiano, Borja; Bedell, Megan; Chaplin, Bill; Collet, Remo; Kamath, Devika; Martell, Sarah; Sousa, Sérgio G.; Ting, Yuan-Sen; Venn, Kim
    The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture facility with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. A rebirth of the 3.6m Canada-France-Hawaii Telescope on Maunakea, MSE will use 4332 fibers operating at three different resolving powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with dynamical fiber positioning that allows fibers to match the exposure times of individual objects. MSE will enable spectroscopic surveys with unprecedented scale and sensitivity by collecting millions of spectra per year down to limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100 m/s in high-resolution mode. This white paper describes science cases for stellar astrophysics and exoplanet science using MSE, including the discovery and atmospheric characterization of exoplanets and substellar objects, stellar physics with star clusters, asteroseismology of solar-like oscillators and opacity-driven pulsators, studies of stellar rotation, activity, and multiplicity, as well as the chemical characterization of AGB and extremely metal-poor stars....
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    The GeMS/GSAOI galactic globular cluster survey (G4CS). I. A pilot study of the stellar populations in NGC 2298 and NGC 3201
    (2018) Monty, Stephanie; Puzia, Thomas H.; Miller, Bryan W.; Carrasco, Eleazar R.; Simunovic, Mirko; Schirmer, Mischa; Stetson, Peter B.; Cassisi, Santi; Venn, Kim A.; Dotter, Aaron
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    The GeMS/GSAOI Galactic Globular Cluster Survey (G4CS). II. Characterization of 47 Tuc with Bayesian Statistics
    (2023) Simunovic, Mirko; Puzia, Thomas H. H.; Miller, Bryan; Carrasco, Eleazar R. R.; Dotter, Aaron; Cassisi, Santi; Monty, Stephanie; Stetson, Peter
    We present a photometric analysis of globular cluster 47 Tuc (NGC 104) using near-IR imaging data from the GeMS/ GSAOI Galactic Globular Cluster Survey (G4CS), which is in operation at Gemini-South telescope. Our survey is designed to obtain AO-assisted deep imaging with near diffraction-limited spatial resolution of the central fields of MilkyWay globular clusters. The G4CS near-IR photometry was combined with an optical photometry catalog that was obtained from Hubble Space Telescope survey data to produce a high-quality color-magnitude diagram that reaches down to K-s approximate to 21 Vega mag. We used the software suite BASE-9, which uses an adaptive Metropolis sampling algorithm to perform a Markov chain Monte Carlo Bayesian analysis, and obtained probability distributions and precise estimates for the age, distance, and extinction cluster parameters. Our best estimate for the age of 47 Tuc is 12.42(-0.05)(+0.05)+/- 0.08 Gyr and our true distance modulus estimate is (m-M)0= 13.250-(+ 0.003)(-0.003) +/- 0.028 mag, which are in tight agreement with previous studies using Gaia DR2 parallax and detached eclipsing binaries.