M. -I. Moretti

Publications (5)0 Total impact

• Article: The VMC Survey. V. First results for Classical Cepheids

  V. Ripepi, M. I. Moretti, M. Marconi, G. Clementini, M. R. Cioni, J. B. Marquette, L. Girardi, S. Rubele, M. A. T. Groenewegen, R. de Grijs, B. K. Gibson, J. M. Oliveira, J. Th. van Loon, J. P. Emerson
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  ABSTRACT: The VISTA Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted by the system formed by the two Magellanic Clouds (MCs) and the "bridge" connecting them. In this paper we present the first results for Classical Cepheids, from the VMC observations of two fields in the Large Magellanic Cloud (LMC). The VMC Ks-band light curves of the Cepheids are well sampled (12-epochs) and of excellent precision. We were able to measure for the first time the Ks magnitude of the faintest Classical Cepheids in the LMC (Ks\sim17.5 mag), which are mostly pulsating in the First Overtone (FO) mode, and to obtain FO Period-Luminosity (PL), Period-Wesenheit (PW), and Period-Luminosity-Color (PLC) relations, spanning the full period range from 0.25 to 6 day. Since the longest period Cepheid in our dataset has a variability period of 23 day, we have complemented our sample with literature data for brighter F Cepheids. On this basis we have built a PL relation in the Ks band that, for the first time, includes short period pulsators, and spans the whole range from 1.6 to 100 days in period. We also provide the first ever empirical PW and PLC relations using the (V-Ks) color and time-series Ks photometry. The very small dispersion (\sim0.07 mag) of these relations makes them very well suited to study the three-dimensional (3D) geometry of the Magellanic system. The use of "direct" (parallax- and Baade-Wesselink- based) distance measurements to both Galactic and LMC Cepheids, allowed us to calibrate the zero points of the PL, PW, and PLC relations obtained in this paper, and in turn to estimate an absolute distance modulus of (m-M)0=18.46\pm0.03 for the LMC. This result is in agreement with most of the latest literature determinations based on Classical Cepheids.
  04/2012;
• Source

  Available from: M. -R. Cioni

  Article: Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) Survey

  V. Ripepi, M. I. Moretti, G. Clementini, M. Marconi, M. R. Cioni, J. B. Marquette, P. Tisserand
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  ABSTRACT: The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting $K_S$-band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build $K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the $K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of $\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types of variables were used to derive $PLK_S$ relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.
  02/2012;
• Source

  Available from: R. Guandalini

  Article: The VMC Survey - I. Strategy and First Data

  M. -R. L. Cioni, G. Clementini, L. Girardi, R. Guandalini, M. Gullieuszik, B. Miszalski, M. -I. Moretti, V. Ripepi, S. Rubele, G. Bagheri, [......], C. Mastropietro, B. Moore, R. Napiwotzki, T. Naylor, J. M. Oliveira, M. Read, E. Sutorius, J. Th. van Loon, M. I. Wilkinson, P. R. Wood
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  ABSTRACT: The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations. Over its first five years it will be collecting data for six public surveys, one of these is the near-infrared YJKsVISTA survey of the Magellanic Clouds system (VMC). This survey comprises the LMC, the SMC, the Bridge connecting the two galaxies and two fields in the Stream. This paper provides an overview of the VMC survey strategy and presents first science results. The main goals of the VMC survey are the determination of the spatially resolved SFH and 3D structure of the Magellanic system. Therefore, the VMC survey is designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variable stars such as RR Lyrae stars and Cepheids. This paper focuses on observations of VMC fields in the LMC obtained between November 2009 and March 2010. These observations correspond to a 7% completeness of the LMC fields. The VMC observations consist of multi-epoch measurements organised following a specific structure. The data were reduced using the VISTA Data Flow System pipeline whose source catalogues were produced and made available via the VISTA Science Archive. The analysis of the data shows that the sensitivity in each wave band agrees with expectations. Uncertainties and completeness of the data are also derived. The first science results, aimed at assessing the science quality of the VMC data, include an overview of the distribution of stars in colour-magnitude and colour-colour diagrams, the detection of planetary nebulae and of stellar clusters, and the Ks band light-curve of variable stars. The VMC survey represents a tremendous improvement, in spatial resolution and sensitivity, on previous panoramic observations of the Magellanic system in the near-infrared and complements nicely the deep observations at other wavelengths. (Abridged)
  12/2010;
• Article: Stellar Archaeology in the Milky Way Halo: Variable Stars and Stellar Populations in the New Milky Way Satellites Discovered by the SDSS

  V. Ripepi, G. Clementini, M. Dall’Ora, K. Kinemuchi, I. Musella, M. Marconi, C. Greco, L. Di Fabrizio, M. I. Moretti, H. A. Smith, C. Kuehn, C. T. Rodgers, T. C. Beers, M. Catelan, B. J. Pritzl
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  ABSTRACT: We present results of a project devoted to the extensive survey of the ultra‐faint Milky Way dwarf spheroidal satellites recently discovered by the SDSS (Bootes I, Ursa Major II, Coma, Hercules, Canes Venatici I, Canes Venatici II, Leo IV), that we are monitoring for variability using time‐series multiband observations collected at a variety of telescopes from the 1.5 to the 4.3 m size, and reaching each galaxy’s main sequence turnoff In particular, we present results on the pulsation properties and “Oosterhoff type” of the RR Lyrae stars detected in two of the newly discovered dwarf spheroidals, namely Leo IV and Ursa Major II. The variable stars and the stellar populations of these two galaxies are discussed in light of the insight they can provide to reconstruct the star formation history and the merging episodes that led to the early assembly of the Galactic halo.
  AIP Conference Proceedings. 09/2009; 1170(1):200-202.
• Source

  Available from: M. Dall'Ora

  Article: The Leo IV dwarf spheroidal galaxy: color-magnitude diagram and pulsating stars

  M. -I. Moretti, M. Dall'Ora, V. Ripepi, G. Clementini, L. Di Fabrizio, H. Smith, N. De Lee, C. Kuehn, M. Catelan, M. Marconi, I. Musella, T. Beers, K. Kinemuchi
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  ABSTRACT: We present the first V, B-V color-magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B,V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V= 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental-mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period-amplitude diagram the Leo IV RR Lyrae stars are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. However, their mean pulsation period, $<P{\rm ab}>$=0.655 days, would suggest an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy's horizontal branch, setting its average magnitude at $<V_{\rm RR}>= 21.48 \pm 0.03$ mag (standard deviation of the mean). This leads to a distance modulus of $\mu_{0}=20.94 \pm 0.07$ mag, corresponding to a distance of $154 \pm 5$ kpc, by adopting for the Leo IV dSph a reddening $E(B-V) = 0.04 \pm 0.01$ mag and a metallicity of [Fe/H] = -2.31 $\pm$ 0.10. Comment: 14 pages, 4 figures, accepted for publication on The Astrophysical Journal Letters
  06/2009;
• Article: The VISTA Near-infrared YJKs Public Survey of the Magellanic Clouds System (VMC)

  M.-R. Cioni, G. Clementini, L. Girardi, R. Guandalini, M. Gullieuszik, B. Miszalski, M.-I. Moretti, V. Ripepi, S. Rubele, G. Bagheri, K. Bekki, N. Cross
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  ABSTRACT: The VISTA public survey project VMC targets the Large Magellanic Cloud, the Small Magellanic Cloud, the Bridge and two fields in the Stream. The VMC survey is a uniform and homogeneous survey in the Y, J and Ks near-infrared filters. The main goals are the determination of the star formation history and the three-dimensional structure of the Magellanic system. The survey is therefore designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variable stars such as RR Lyrae and Cepheids. We provide a brief overview of the survey strategy and first science results. Further details are given in Cioni et al. (2011).