Leibnitz Institute For Astrophysik Potsdam

Neustadt an der Weinstraße, Germany

Leibnitz Institute For Astrophysik Potsdam

Neustadt an der Weinstraße, Germany

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Ripepi V.,National institute for astrophysics | Cignoni M.,US Space Telescope Science Institute | Cignoni M.,National institute for astrophysics | Tosi M.,National institute for astrophysics | And 25 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guaranteed Time Observation survey being performed at the VST (the ESO VLT Survey Telescope). STEP will image an area of 74 deg2 covering the main body of the Small Magellanic Cloud (32 deg2), the Bridge that connects it to the Large Magellanic Cloud (30 deg2) and a small part of the Magellanic Stream (2 deg2). Our g, r, i, Hα photometry is able to resolve individual stars down to magnitudes well below the main-sequence turn-off of the oldest populations. In this first paper, we describe the observing strategy, the photometric techniques and the upcoming data products of the survey. We also present preliminary results for the first two fields for which data acquisition is completed, including some detailed analysis of the two stellar clusters IC 1624 and NGC 419. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ripepi V.,National institute for astrophysics | Marconi M.,National institute for astrophysics | Moretti M. I.,National institute for astrophysics | Clementini G.,National institute for astrophysics | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The VISTA near-infrared YJKs survey of the Magellanic Clouds System (VMC, PI M.-R. L. Cioni) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we present for the first time Ks-band light curves for anomalous Cepheid (AC) variables. In particular, we have analysed a sample of 48 Large Magellanic Cloud ACs, for which identification and optical magnitudes were obtained from the OGLE III and IV catalogues. The VMC Ks-band light curves for ACs are well sampled, with the number of epochs ranging from 8 to 16, and allowing us to obtain very precise mean Ks magnitudes with errors on average of the order of 0.01 mag. The (Ks) values were used to build the first period-luminosity and period-Wesenheit relations in the near-infrared for fundamental mode and first overtone ACs. At the same time we exploited the optical (V, I) OGLE data to build accurate period-luminosity, period-luminosity-colour and period-Wesenheit relations both for fundamental mode and first overtone ACs. For the first time, these relations were derived from a sample of pulsators which uniformly cover the whole AC instability strip. The application of the optical period-Wesenheit relation to a sample of dwarf galaxies hosting a significant population of ACs revealed that this relation is a valuable tool for deriving distances within the Local Group. Due to its lower dispersion, we expect the Ks period- Wesenheit relations first derived in this paper to represent a valuable tool for measuring accurate distances to galaxies hosting ACs when more data in near-infrared filters become available. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Moretti M.I.,University of Bologna | Moretti M.I.,National institute for astrophysics | Clementini G.,University of Bologna | Muraveva T.,University of Bologna | And 14 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The VISTA near-infrared Y, J, Ks survey of the Magellanic System (VMC) survey is obtaining multi-epoch photometry in the Ks band of theMagellanic System down to a limiting magnitude of Ks ~ 19.3 for individual epoch data. The observations are spaced in time such as to provide optimal sampling of the light curves for RR Lyrae stars and for Cepheids with periods up to 20-30 d.We present examples of the Ks-band light curves of Classical Cepheids and RR Lyrae stars we are obtaining from the VMC data and outline the strategy we put in place to measure distances and infer the System three-dimensional geometry from the variable stars. For this purpose, the near-infrared Period-Luminosity, Period-Wesenheit and Period-Luminosity- Colour relations of the system RR Lyrae stars and Cepheids are used. We extensively exploit the catalogues of the Magellanic Clouds' variable stars provided by the EROS-2 and OGLE III/IV microlensing surveys. By combining these surveys, we present the currently widest-area view of the Large Magellanic Cloud as captured by the galaxy Cepheids, RR Lyrae stars and binaries. This reveals the full extent of the main structures (bar/s - spiral arms) that have only been vaguely guessed before. Our work strengthens the case for a detailed study of the Large Magellanic Cloud three-dimensional geometry. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Li C.,Peking University | Li C.,CAS National Astronomical Observatories | De Grijs R.,Peking University | Deng L.,CAS National Astronomical Observatories | And 17 more authors.
Astrophysical Journal | Year: 2014

We present a deep near-infrared color-magnitude diagram of the Galactic globular cluster 47 Tucanae, obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA) as part of the VISTA near-infrared Y, J, K s survey of the Magellanic System (VMC). The cluster stars comprising both the subgiant and red giant branches exhibit apparent, continuous variations in color-magnitude space as a function of radius. Subgiant branch stars at larger radii are systematically brighter than their counterparts closer to the cluster core; similarly, red-giant-branch stars in the cluster's periphery are bluer than their more centrally located cousins. The observations can very well be described by adopting an age spread of 0.5 Gyr as well as radial gradients in both the cluster's helium abundance (Y) and metallicity (Z), which change gradually from (Y = 0.28, Z = 0.005) in the cluster core to (Y = 0.25, Z = 0.003) in its periphery. We conclude that the cluster's inner regions host a significant fraction of second-generation stars, which decreases with increasing radius; the stellar population in the 47 Tuc periphery is well approximated by a simple stellar population. © 2014. The American Astronomical Society. All rights reserved..


Piatti A.E.,National University of Cordoba | Piatti A.E.,CONICET | Ivanov V.D.,European Southern Observatory | Rubele S.,National institute for astrophysics | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We report the first search for new star clusters performed using the VISTA near-infrared YJKs Magellanic Clouds survey (VMC) data sets. We chose a pilot field of ~0.4 deg2 located in the South-west of the Small Magelllanic Cloud bar, where the star field is among the densest and highest reddened region in the galaxy. In order to devise an appropriate automatic procedure we made use of dimensions and stellar densities observed in the VMC data sets of the known clusters in this area. We executed different kernel density estimations over a sample of more than 358 000 stars with magnitudes measured in the three YJKs filters. We analysed the new cluster candidates whose colour-magnitude diagrams (CMDs), cleaned from field star contamination, were used to assess the clusters' reality and estimate reddenings and ages of the genuine systems. As a result 38 objects (≈ a 55 per cent increase in the known star clusters located in the surveyed field) of 0.15-0.40 arcmin (2.6-7.0 pc) in radius resulted to have near-infrared CMD features which resemble those of star clusters of young to moderate intermediate age (log(t yr-1) ~7.5-9.0). Most of the new star cluster candidates are hardly recognizable in optical images without the help of a sound star field decontaminated CMD analysis. For highly reddened star cluster candidates (E(B-V) ≥ 0.6 mag) the VMC data sets were necessary in order to recognize them. © 2016 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society.


Cioni M.-R.L.,Leibnitz Institute For Astrophysik Potsdam | Cioni M.-R.L.,Ludwig Maximilians University of Munich | Cioni M.-R.L.,University of Hertfordshire | Girardi L.,National institute for astrophysics | And 10 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Proper motion (PM) studies are fundamental ingredients in the understanding of the orbital history of galaxies. Current measurements do not yet provide a satisfactory answer to the possible scenarios for the formation and evolution of the Magellanic Clouds and of the Bridge and Stream that link them with each other and with our Galaxy. Aims. We use multi-epoch near-infrared observations from the VISTA survey of the Magellanic Cloud system (VMC) to measure the PM of stars of the Large Magellanic Cloud (LMC), in one tile of 1.5 deg2 centred at (α,δ) = (05:59:23.136, -66:20:28.68) and including the south ecliptic pole, with respect to their Two Micron All Sky Survey (2MASS) position over a time baseline of about 10 years. Proper motions from VMC observations only, spanning a time range of about 1 year, are also derived. Methods. Stars of different ages are selected from the colour-magnitude diagram, (J - Ks) vs. Ks, and their average coordinate displacement is computed from the difference between Ks band observations from VMC and 2MASS or among VMC data alone for stars as faint as Ks = 19 mag. Proper motions are derived by averaging up to seven 2MASS-VMC combinations in the first case and from the slope of the best-fit line among the seven VMC epochs in the second case. Separate PM values are obtained for Cepheids, RR Lyrae stars, long period variables, and eclipsing binary stars in the field. Results. The PM of ~40 000 LMC stars in the tile, with respect to ~8000 background galaxies, obtained from VMC data alone, is μ αcos (δ) = +2.20 ± 0.06 (stat) ±0.29 (sys) and μδ = +1.70 ± 0.06 (stat) ±0.30 (sys) mas yr-1. This value agrees with recent ground-based determinations, but is larger than studies with the Hubble Space Telescope; this discrepancy may be due to additional systematic errors in the data. Our result implies either higher tangential motion or higher internal motion, or a combination of these, although we cannot discuss these possibilities quantitatively based on one field. The PM of the LMC is also clearly distinct from the PM derived for stars in the Milky Way foreground. The relative PM between the foreground stars and the LMC stars is ~5 mas yr-1. Furthermore, we measure a decrease in the PM with increasing logarithm of stellar age for LMC stars. Conclusions. This study, based on just one VMC tile, shows the potential of the 2MASS-VMC and VMC-VMC combinations for a comprehensive investigation of PM across the Magellanic system. © ESO, 2014.


Cioni M.-R.L.,University of Potsdam | Cioni M.-R.L.,Leibnitz Institute For Astrophysik Potsdam | Cioni M.-R.L.,University of Hertfordshire
Astrophysics and Space Science Proceedings | Year: 2016

The VISTA survey of the Magellanic Clouds system (VMC) is a public survey project of ESO. It is collecting near-infrared data across large areas of the Large and Small Magellanic Clouds, the Bridge and a few fields in the Stream. The combination of great sensitivity to stars below the old main sequence turn off, and the multiplicity at Ks band (at least 12 epochs) make VMC highly suitable for the determination of the spatially resolved star formation history and three-dimensional geometry, using variable stars such as Cepheids and RR Lyrae stars. The VMC observations, to be completed in 2018, have a high legacy value and many science results have already been published while others are in preparation. © Springer International Publishing Switzerland 2016.


Ripepi V.,National institute for astrophysics | Moretti M.I.,National institute for astrophysics | Moretti M.I.,Normal School of Pisa | Marconi M.,National institute for astrophysics | And 11 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The VISTA (Visible and Infrared Survey Telescope for Astronomy) survey of the Magellanic Clouds System (VMC) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near-complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III (Optical Gravitational Lensing Experiment) survey. We present J and Ks light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW Vir) and 27 RV Tau variables. We complement our near-infrared photometry with the V magnitudes from the OGLE III survey, allowing us to build a variety of period-luminosity (PL), period-luminosity-colour (PLC) and period-Wesenheit (PW) relationships, including any combination of the V, J, Ks filters and valid for BL Her and W Vir classes. These relationships were calibrated in terms of the LMC distance modulus, while an independent absolute calibration of the PL(Ks) and the PW(Ks, V) was derived on the basis of distances obtained from Hubble Space Telescope parallaxes and Baade-Wesselink technique. When applied to the LMC and to the Galactic globular clusters hosting T2CEPs, these relations seem to show that (1) the two Population II standard candles RR Lyrae and T2CEPs give results in excellent agreement with each other; (2) there is a discrepancy of ~0.1 mag between Population II standard candles and classical Cepheids when the distances are gauged in a similar way for all the quoted pulsators. However, given the uncertainties, this discrepancy is within the formal 1s uncertainties. © 2014 The Authors.


Rubele S.,National institute for astrophysics | Girardi L.,National institute for astrophysics | Kerber L.,University Estadual Of Santa Cruz | Cioni M.-R.L.,University of Hertfordshire | And 19 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJKs filters, covering 14 deg2 (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour-magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68 per cent confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39°, although deviations of up to ±3 kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age-metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2 Gyr and the peak of star formation in the SMC Bar at ~40 Myr. We clearly detect periods of enhanced star formation at 1.5 and 5 Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1 Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages. © 2015 The Authors.


Romita K.,University of Florida | Lada E.,University of Florida | Cioni M.-R.,University of Potsdam | Cioni M.-R.,Leibnitz Institute For Astrophysik Potsdam | Cioni M.-R.,University of Hertfordshire
Astrophysical Journal | Year: 2016

We present initial results of the first large-scale survey of embedded star clusters in molecular clouds in the Large Magellanic Cloud (LMC) using near-infrared imaging from the Visible and Infrared Survey Telescope for Astronomy Magellanic Clouds Survey. We explored a ∼1.65 deg2 area of the LMC, which contains the well-known star-forming region 30 Doradus as well as ∼14% of the galaxy's CO clouds, and identified 67 embedded cluster candidates, 45 of which are newly discovered as clusters. We have determined the sizes, luminosities, and masses for these embedded clusters, examined the star formation rates (SFRs) of their corresponding molecular clouds, and made a comparison between the LMC and the Milky Way. Our preliminary results indicate that embedded clusters in the LMC are generally larger, more luminous, and more massive than those in the local Milky Way. We also find that the surface densities of both embedded clusters and molecular clouds is ∼3 times higher than in our local environment, the embedded cluster mass surface density is ∼40 times higher, the SFR is ∼20 times higher, and the star formation efficiency is ∼10 times higher. Despite these differences, the SFRs of the LMC molecular clouds are consistent with the SFR scaling law presented in Lada et al. This consistency indicates that while the conditions of embedded cluster formation may vary between environments, the overall process within molecular clouds may be universal. © 2016. The American Astronomical Society. All rights reserved.

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