Browsing by Author "Piotto, G."

Now showing 1 - 8 of 8
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    A double stellar generation in the globular cluster NGC 6656 (M 22) Two stellar groups with different iron and s-process element abundances
    (2009) Marino, A. F.; Milone, A. P.; Piotto, G.; Villanova, S.; Bedin, L. R.; Bellini, A.; Renzini, A.
    We present a chemical abundance analysis based on high resolution UVES spectra of seventeen bright giant stars in the Globular Cluster (GC) M 22. We obtained an average iron abundance of [Fe/H] = -1.76 +/- 0.02 (internal errors only) and an alpha enhancement of 0.36 +/- 0.04 (internal errors only). Na and O, and Al and O follow the well known anticorrelations found in many other GCs. We identified two groups of stars with significantly different abundances of the s-process elements Y, Zr, and Ba. The relative numbers of the two group members are very similar to the ratio of the number of stars in the two sub giant branches (SGB) of M 22. Y and Ba abundances do not correlate with Na, O, and Al. The s-element rich stars are also richer in iron and have higher Ca abundances. The results from high resolution spectra were confirmed by analyses of lower resolution GIRAFFE spectra of fourteen additional M 22 stars. The analyses of the GIRAFFE spectra also show that the Eu - a pure r-process element - abundance is not related to the iron content. We discuss the chemical abundance pattern of M 22 stars in the context of GC multiple stellar populations phenomenon.
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    A HOT HORIZONTAL BRANCH STAR WITH A CLOSE K-TYPE MAIN-SEQUENCE COMPANION
    (2015) Bidin, C. Moni; Momany, Y.; Montalto, M.; Catelan, Márcio; Villanova, S.; Piotto, G.; Geisler, D.
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    High-precision astrometry with VVV – I. An independent reduction pipeline for VIRCAM@VISTA
    (2015) Libralato, M.; Bellini, A.; Bedin, L.; Anderson, J.; Piotto, G.; Nascimbeni, V.; Platais, I.; Minniti, D.; Zoccali, Manuela
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    MULTIPLE STELLAR POPULATIONS IN THE GALACTIC GLOBULAR CLUSTER NGC 6752
    (2010) Milone, A. P.; Piotto, G.; King, I. R.; Bedin, L. R.; Anderson, J.; Marino, A. F.; Momany, Y.; Malavolta, L.; Villanova, S.
    We have carried out high-precision photometry on a large number of archival Hubble Space Telescope images of the Galactic globular cluster NGC 6752, to search for signs of multiple stellar populations. We find a broadened main sequence (MS) and demonstrate that this broadening cannot be attributed either to binaries or to photometric errors. There is also some indication of an MS split. No significant spread could be found along the sub-giant branch, however. Ground-based photometry reveals that in the U versus (U - B) color-magnitude diagram the red-giant branch (RGB) exhibits a clear color spread, which we have been able to correlate with variations in Na and O abundances. In particular, the Na-rich, O-poor stars identified by Carretta et al. define a sequence on the red side of the RGB, while Na-poor, O-rich stars populate a bluer, more dispersed portion of the RGB.
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    THE ACS SURVEY OF GLOBULAR CLUSTERS. XIII. PHOTOMETRIC CALIBRATION IN COMPARISON WITH STETSON STANDARDS
    (2014) Hempel, Maren; Sarajedini, A.; Anderson, J.; Aparicio Alonso, Andrés; Bedin, L. R.; Chaboyer, B.; Majewski, S. R.; Marín, A.; Milone, A.; Paust, N.; Piotto, G.; Reid, I.; Rosenberg, A.; Siegel, M.
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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.
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    The Hubble Space Telescope UV Legacy Survey of galactic globular clusters - II. The seven stellar populations of NGC 7089 (M2)
    (2015) Milone, A. P.; Marino, A. F.; Piotto, G.; Bedin, L. R.; Anderson, J.; Renzini, A.; King, I. R.; Bellini, A.; Brown, T. M.; Zoccali, Manuela
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    The Hubble Space Telescope UV legacy survey of galactic globular clusters. I. Overview of the project and detection of multiple stellar populations
    (2015) Piotto, G.; Milone, A. P.; Bedin, L. R.; Anderson, J.; King, I. R.; Marino, A. F.; Nardiello, D.; Aparicio Alonso, Andrés; Barbuy, B.; Zoccali, Manuela