Examinando por Autor "Monelli, M."

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    Chemical Compositions of Field and Globular Cluster RR Lyrae Stars. I. NGC 3201
    (Institute of Physics Publishing, 2018-09) Magurno, D.; Sneden, C.; Braga, V.F.; Bono, G.; Mateo, M.; Persson, S.E.; Dall'Ora, M.; Marengo, M.; Monelli, M.; Neeley, J.R.
    We present a detailed spectroscopic analysis of horizontal branch stars in the globular cluster NGC 3201. We collected optical (4580-5330), high-resolution (∼34,000), high signal-to-noise ratio (∼200) spectra for 11 RR Lyrae stars and one red horizontal branch star with the multifiber spectrograph M2FS with the 6.5 m Magellan telescope at the Las Campanas Observatory. From measured equivalent widths, we derived atmospheric parameters and abundance ratios for (Mg, Ca, and Ti), iron-peak (Sc, Cr, Ni, and Zn), and s-process (Y) elements. We found that NGC 3201 is a homogeneous, monometallic ([Fe/H] = -1.47 ± 0.04), enhanced ([/Fe] = 0.37 ± 0.04) cluster. The relative abundances of the iron-peak and s-process elements were found to be consistent with solar values. In comparison with other large stellar samples, NGC 3201 RR Lyraes have similar chemical enrichment histories as do those of other old (t ≥ 10 Gyr) Halo components (globular clusters; red giants; blue and red horizontal branch stars; and RR Lyraes). We also provided a new average radial velocity estimate for NGC 3201 by using a template velocity curve to overcome the limit of single-epoch measurements of variable stars: Vrad = 494 ± 2 km s-1 (σ = 8 km s-1). © 2018. The American Astronomical Society. All rights reserved.
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    Multiband study of RX J0838-2827 and XMM J083850.4-282759: A new asynchronous magnetic cataclysmic variable and a candidate transitional millisecond pulsar
    (Oxford University Press, 2017-11) Rea, N.; Coti Zelati, F.; Esposito, P.; D'Avanzo, P.; de Martino, D.; Israel, G.L.; Torres, D.F.; Campana, S.; Belloni, T.M.; Papitto, A.; Masetti, N.; Carrasco, L.; Possenti, A.; Wieringa, M.; De Oña Wilhelmi, E.; Li, J.; Bozzo, E.; Ferrigno, C.; Linares, M.; Tauris, T.M.; Hernanz, M.; Ribas, I.; Monelli, M.; Borghese, A.; Baglio, M.C.; Casares, J.
    In a search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multiwavelength campaign: in the X-ray band with Swift and XMM-Newton; in the infrared and optical with OAGH, ESO-NTT and IAC80; and in the radio with ATCA observations. We also used archival hard X-ray data obtained by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source.We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827 is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as being caused by the binary system orbital period of ~1.64 h and the white dwarf spin period of ~1.47 h. A strong flux modulation at ~15 h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hß, He I and He II emission lines that are Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827 accretes through a disc-less configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system on its way to reaching synchronism. Regarding the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting for ~600 s, similar to what is observed in transitional millisecond pulsars during the subluminous disc state: this observation possibly means that this source can be associated with the Fermi-LAT source. © 2017 The Authors.
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    On a New Method to Estimate the Distance, Reddening, and Metallicity of RR Lyrae Stars Using Optical/Near-infrared (B, V, I, J, H, K ) Mean Magnitudes: ω Centauri as a First Test Case
    (Astrophysical Journal, 2019-01-10) Bono, G.; Iannicola, G.; Braga, V. F.; Ferraro, I.; Stetson, P. B.; Magurno, D.; Matsunaga, N.; Beaton, R. L.; Buonanno, R.; Chaboyer, B.; Dall’Ora, M.; Fabrizio, M.; Fiorentino, G.; Freedman, W. L.; Gilligan, C. K.; Madore, B. F.; Marconi, M.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Mateo, M.; Monelli, M.; Neeley, J. R.; Nonino, M.; Sneden, C.; Thevenin, F.; Valenti, E.; Walker, A. R.
    We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period-luminosity-metallicity relations (IJHK) and absolute mean magnitude-metallicity relations (BV). We obtained solutions for three different RRL samples in ω Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at [Fe/H]∼-1.98 and a standard deviation of σ = 0.54 dex. The spread is, as expected, metal-poor ([Fe/H] ≤ -2.3) objects. The current metallicity distribution is ∼0.3 dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by -0.06/-0.07 mag in true distance modulus. We also found a cluster true distance modulus of μ = 13.720 ±0.002 ±0.030 mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of E(B - V) = 0.132 ±0.002 ±0.028 mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1σ. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.
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    On the Chemical Abundances of Miras in Clusters: V1 in the Metal-rich Globular NGC 5927
    (Institute of Physics Publishing, 2018-03) D'Orazi, V.; Magurno, D.; Bono, G.; Matsunaga, N.; Braga, V.F.; Elgueta, S.S.; Fukue, K.; Hamano, S.; Inno, L.; Kobayashi, N.; Kondo, S.; Monelli, M.; Nonino, M.; Przybilla, N.; Sameshima, H.; Saviane, I.; Taniguchi, D.; Thevenin, F.; Urbaneja-Perez, M.; Watase, A.; Arai, A.; Bergemann, M.; Buonanno, R.; Dall'Ora, M.; Da Silva, R.; Fabrizio, M.; Ferraro, I.; Fiorentino, G.; Francois, P.; Gilmozzi, R.; Iannicola, G.; Ikeda, Y.; Jian, M.; Kawakita, H.; Kudritzki, R.P.; Lemasle, B.; Marengo, M.; Marinoni, S.; Martínez-Vázquez, C.E.; Minniti, D.; Neeley, J.; Otsubo, S.; Prieto, J.L.; Proxauf, B.; Romaniello, M.; Sanna, N.; Sneden, C.; Takenaka, K.; Tsujimoto, T.; Valenti, E.; Yasui, C.; Yoshikawa, T.; Zoccali, M.
    We present the first spectroscopic abundance determination of iron, α-elements (Si, Ca, and Ti), and sodium for the Mira variable V1 in the metal-rich globular cluster NGC 5927. We use high-resolution (R ∼ 28,000), high signal-to-noise ratio (∼200) spectra collected with WINERED, a near-infrared (NIR) spectrograph covering simultaneously the wavelength range 0.91-1.35 μm. The effective temperature and the surface gravity at the pulsation phase of the spectroscopic observation were estimated using both optical (V) and NIR time-series photometric data. We found that the Mira is metal-rich ([Fe/H] = -0.55 ± 0.15) and moderately α-enhanced ([α/Fe] = 0.15 ± 0.01, σ = 0.2). These values agree quite well with the mean cluster abundances based on high-resolution optical spectra of several cluster red giants available in the literature ([Fe/H] = - 0.47 ± 0.06, [α/Fe] = + 0.24 ± 0.05). We also found a Na abundance of +0.35 ±0.20 that is higher than the mean cluster abundance based on optical spectra (+0.18 ± 0.13). However, the lack of similar spectra for cluster red giants and that of corrections for departures from local thermodynamical equilibrium prevents us from establishing whether the difference is intrinsic or connected with multiple populations. These findings indicate a strong similarity between optical and NIR metallicity scales in spite of the difference in the experimental equipment, data analysis, and in the adopted spectroscopic diagnostics. © 2018. The American Astronomical Society. All rights reserved.
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    On the RR Lyrae Stars in Globulars. V. the Complete Near-infrared (JHK s) Census of ω Centauri RR Lyrae Variables
    (nstitute of Physics Publishing, 2018-03) Braga, V.F.; Stetson, P.B.; Bono, G.; Dall'Ora, M.; Ferraro, I.; Fiorentino, G.; Iannicola, G.; Marconi, M.; Marengo, M.; Monson, A.J.; Neeley, J.; Persson, S.E.; Beaton, R.L.; Buonanno, R.; Calamida, A.; Castellani, M.; Carlo, E.D.; Fabrizio, M.; Freedman, W.L.; Inno, L.; Madore, B.F.; Magurno, D.; Marchetti, E.; Marinoni, S.; Marrese, P.; Matsunaga, N.; Minniti, D.; Monelli, M.; Nonino, M.; Piersimoni, A.M.; Pietrinferni, A.; Prada-Moroni, P.; Pulone, L.; Stellingwerf, R.; Tognelli, E.; Walker, A.R.; Valenti, E.; Zoccali, M.
    We present a new complete near-infrared (NIR, JHK s) census of RR Lyrae stars (RRLs) in the globular ω Cen (NGC 5139). We collected 15,472 JHK s images with 4-8 m class telescopes over 15 years (2000-2015) covering a sky area around the cluster center of 60 ×34 arcmin2. These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with 10 to 60 measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 (J), 176 (H) and 174 (K s) RRLs. These data were supplemented with single-epoch JK s magnitudes from VHS and with single-epoch H magnitudes from 2MASS. Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide JHK s magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed-mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (P > 0.7 days) fundamental RRLs. Using predicted period-luminosity-metallicity relations, we derive a true distance modulus of 13.674 ± 0.008 ±0.038 mag (statistical error and standard deviation of the median) based on spectroscopic iron abundances, and of 13.698 ±0.004 ±0.048 mag based on photometric iron abundances. We also found evidence of possible systematics at the 5%-10% level in the zero-point of the period-luminosity relations based on the five calibrating RRLs whose parallaxes had been determined with the HST. © 2018. The American Astronomical Society. All rights reserved.
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    The Gaia EDR3 view of Johnson-Kron-Cousins standard stars: the curated Landolt and Stetson collections
    (EDP Sciences, 2022-08) Pancino, E.; Marrese, P.M.; Marinoni, S.; Sanna, N.; Turchi, A.; Tsantaki, M.; Rainer, M.; Altavilla, G; Monelli, M.; Monaco, L.
    Context. In the era of large surveys and space missions, it is necessary to rely on large samples of well-characterized stars for inter-calibrating and comparing measurements from different surveys and catalogues. Among the most employed photometric systems, the Johnson-Kron-Cousins has been used for decades and for a large amount of important datasets. Aims. Our goal is to profit from the Gaia EDR3 data, Gaia official cross-match algorithm, and Gaia-derived literature catalogues, to provide a well-characterized and clean sample of secondary standards in the Johnson-Kron-Cousins system, as well as a set of transformations between the main photometric systems and the Johnson-Kron-Cousins one. Methods. Using Gaia as a reference, as well as data from reddening maps, spectroscopic surveys, and variable stars monitoring surveys, we curated and characterized the widely used Landolt and Stetson collections of more than 200 000 secondary standards, employing classical as well as machine learning techniques. In particular, our atmospheric parameters agree significantly better with spectroscopic ones, compared to other machine learning catalogues. We also cross-matched the curated collections with the major photometric surveys to provide a comprehensive set of reliable measurements in the most widely adopted photometric systems. Results. We provide a curated catalogue of secondary standards in the Johnson-Kron-Cousins system that are well-measured and as free as possible from variable and multiple sources. We characterize the collection in terms of astrophysical parameters, distance, reddening, and radial velocity. We provide a table with the magnitudes of the secondary standards in the most widely used photometric systems (ugriz, grizy, Gaia, HIPPARCOS, Tycho, 2MASS). We finally provide a set of 167 polynomial transformations, valid for dwarfs and giants, metal-poor and metal-rich stars, to transform UBVRI magnitudes in the above photometric systems and vice-versa. © E. Pancino et al. 2022.