Examinando por Autor "Iannicola, G."
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Ítem GRAWITA: VLT Survey Telescope observations of the gravitational wave sources GW150914 and GW151226(Oxford University Press, 2018-02) Brocato, E.; Branchesi, M.; Cappellaro, E.; Covino, S.; Grado, A.; Greco, G.; Limatola, L.; Stratta, G.; Yang, S.; Campana, S.; D'Avanzo, P.; Getman, F.; Melandri, A.; Nicastro, L.; Palazzi, E.; Pian, E.; Piranomonte, S.; Pulone, L.; Rossi, A.; Tomasella, L.; Amati, L.; Antonelli, L.A.; Ascenzi, S.; Benetti, S.; Bulgarelli, A.; Capaccioli, M.; Cella, G.; Dadina, M.; De Cesare, G.; D'Elia, V.; Ghirlanda, G.; Ghisellini, G.; Giuffrida, G.; Iannicola, G.; Israel, G.; Lisi, M.; Longo, F.; Mapelli, M.; Marinoni, S.; Marrese, P.; Masetti, N.; Patricelli, B.; Possenti, A.; Radovich, M.; Razzano, M.; Salvaterra, R.; Schipani, P.; Spera, M.; Stamerra, A.; Stella, L.; Tagliaferri, G.; Testa, V.We report the results of deep optical follow-up surveys of the first two gravitational-wave sources, GW150914 and GW151226, done by the GRAvitationalWave Inaf TeAm Collaboration (GRAWITA). The VLT Survey Telescope (VST) responded promptly to the gravitational wave alerts sent by the LIGO and Virgo Collaborations, monitoring a region of 90 and 72 deg 2 for GW150914 and GW151226, respectively, and repeated the observations over nearly two months. Both surveys reached an average limiting magnitude of about 21 in the r band. The paper describes the VST observational strategy and two independent procedures developed to search for transient counterpart candidates in multi-epoch VST images. Several transients have been discovered but no candidates are recognized to be related to the gravitational wave events. Interestingly, among many contaminant supernovae, we find a possible correlation between the supernova VSTJ57.77559-59.13990 and GRB150827A detected by Fermi-GBM. The detection efficiency of VST observations for different types of electromagnetic counterparts of gravitational wave events is evaluated for the present and future follow-up surveys. © 2017 The Author(s).Ítem 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.Ítem 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.Ítem 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.