Vatican City, Italy
Vatican City, Italy

Time filter

Source Type

Minniti D.,University of Santiago de Chile | Minniti D.,Vatican Observatory | Minniti D.,European Southern Observatory | Saito R.K.,University of Santiago de Chile | And 3 more authors.
Astrophysical Journal Letters | Year: 2011

We use the clump giants of the disk as standard candles calibrated from Hipparcos parallaxes in order to map their distribution with two new near-infrared surveys of the Galactic plane: UKIDSS-GPS and VISTA Variables in the Vía Lctea (VVV). We explore different selection cuts of clump giants. We conclude that there is an edge of the stellar disk of the Milky Way at R = 13.9 0.5kpc along various lines of sight across the Galaxy. The effect of the warp is considered, taking fields at different longitudes and above and below the plane. We demonstrate that the edge of the stellar disk of the Milky Way can now be mapped in the near-infrared in order to test different models, and to establish our own place within the Galaxy. © 2011. The American Astronomical Society. All rights reserved.


News Article | October 26, 2016
Site: spaceref.com

Our Milky Way has a densely populated centre -- a feature common to many galaxies, but unique in that it is close enough to study in depth. A team led by Dante Minniti (Universidad Andrés Bello, Santiago, Chile) and Rodrigo Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile) used observations from the VISTA infrared survey telescope, as part of the Variables in the Via Lactea (VVV) ESO public survey, to carefully search the central part of the Milky Way. By observing infrared light, which is less affected by cosmic dust than visible light, and exploiting the excellent conditions at ESO's Paranal Observatory, the team was able to get a clearer view of this region than ever before. They found a dozen ancient RR Lyrae stars at the heart of the Milky Way that were previously unknown. Our Milky Way has a densely populated centre -- a feature common to many galaxies, but unique in that it is close enough to study in depth. This discovery of RR Lyrae stars provides compelling evidence that helps astronomers decide between two main competing theories for how these bulges form. RR Lyrae stars are typically found in dense globular clusters. They are variable stars, and the brightness of each RR Lyrae star fluctuates regularly. By observing the length of each cycle of brightening and dimming in an RR Lyrae, and also measuring the star's brightness, astronomers can calculate its distance [1]. Unfortunately, these excellent distance-indicator stars are frequently outshone by younger, brighter stars and in some regions they are hidden by dust. Therefore, locating RR Lyrae stars right in the extremely crowded heart of the Milky Way was not possible until the public VVV survey was carried out using infrared light. Even so, the team described the task of locating the RR Lyrae stars in amongst the crowded throng of brighter stars as "daunting". Their hard work was rewarded, however, with the identification of a dozen RR Lyrae stars. Their discovery indicate that remnants of ancient globular clusters are scattered within the centre of the Milky Way's bulge. Rodrigo Contreras Ramos elaborates: "This discovery of RR Lyrae Stars in the centre of the Milky Way has important implications for the formation of galactic nuclei. The evidence supports the scenario in which the bulge was originally made out of a few globular clusters that merged." The theory that galactic bulges form through the merging of globular clusters is contested by the competing hypothesis that these bulges are actually due to the rapid accretion of gas. The unearthing of these RR Lyrae stars -- almost always found in globular clusters -- isvery strong evidence that the Milky Way bulge did in fact form through merging. By extension, all other similar galactic bulges may have formed the same way. Not only are these stars powerful evidence for an important theory of galactic evolution, they are also likely to be over 10 billion years old -- the dim, but dogged survivors of perhaps the oldest and most massive star cluster within the Milky Way. [1] RR Lyrae stars, like some other regular variables such as Cepheids, show a simple relationship between how quickly they change in brightness and how luminous they are. Longer periods mean brighter stars. This period-luminosity relationship can be used to deduce the distance of a star from its period of variation and its apparent brightness. This research was presented in a paper to appear in The Astrophysical Journal Letters. The team is composed of D. Minniti (Instituto Milenio de Astrofísica, Santiago, Chile; Departamento de Física, Universidad Andrés Bello, Santiago, Chile; Vatican Observatory, Vatican City State, Italy; Centro de Astrofisica y Tecnologias Afines - CATA), R. Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile), M. Zoccali (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile), M. Rejkuba (European Southern Observatory, Garching bei München, Germany; Excellence Cluster Universe, Garching, Germany), O.A. Gonzalez (UK Astronomy Technology Centre, Royal Observatory, Edinburgh, UK), E. Valenti (European Southern Observatory, Garching bei München, Germany), F. Gran (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile) ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky". * Variables in the Via Lactea (VVV) - https://vvvsurvey.org/ ESO public survey Please follow SpaceRef on Twitter and Like us on Facebook.


Gonzalez O.A.,European Southern Observatory | Rejkuba M.,European Southern Observatory | Zoccali M.,University of Chile | Valent E.,European Southern Observatory | And 4 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. We investigate the large-scale metallicity distribution in the Galactic bulge using large spatial coverage to constrain the bulge formation scenario. Methods. We use the VISTA variables in the Via Lactea (VVV) survey data and 2MASS photometry, which cover 320 sqdeg of the Galactic bulge, to derive photometric metallicities by interpolating the (J - Ks)0 colors of individual red giant branch stars based on a set of globular cluster ridge lines. We then use this information to construct the first global metallicity map of the bulge with a resolution of 30′ × 45′. Results. The metallicity map of the bulge revealed a clear vertical metallicity gradient of ∼0.04 dex/deg (∼0.28 dex/kpc), with metal-rich stars ([Fe/H] ∼ 0) dominating the inner bulge in regions closer to the Galactic plane (|b| < 5). At larger scale heights, the mean metallicity of the bulge population becomes significantly more metal poor. Conclusions. This fits in the scenario of a boxy bulge originating from the vertical instability of the Galactic bar, formed early via secular evolution of a two-component stellar disk. Older metal-poor stars dominate at higher scale heights due to the non-mixed orbits of originally hotter thick disk stars. © 2013 ESO.


Macke R.J.,University of Central Florida | Consolmagno G.J.,Vatican Observatory | Britt D.T.,University of Central Florida | Hutson M.L.,Portland State University
Meteoritics and Planetary Science | Year: 2010

As part of our continuing survey of meteorite physical properties, we measured grain and bulk density, porosity, and magnetic susceptibility for 41 stones from 23 enstatite chondrites (ECs), all with masses greater than 10-g, representing the majority of falls and a significant percentage of all available non-Antarctic EC meteorites. Our sampling included a mix of falls and finds. For falls, grain densities range from 3.45 to 4.17-g-cm -3, averaging 3.66-g-cm -3; bulk densities range from 3.15 to 4.10-g-cm -3, averaging 3.55-g-cm -3; porosities range from 0 to 12% with the majority less than 7%, and magnetic susceptibilities (in log units of 10 -9-m 3-kg -1) from 5.30 to 5.64, with an average of 5.47. For finds, weathering reduces both grain and bulk densities as well as magnetic susceptibilities. On average, finds have much higher porosity than falls. The two EC subgroups EH and EL, nominally distinguished by total iron content, exhibit similar values for all of the properties measured, indicating similar metallic iron content in the bulk stones of both subgroups. We also observed considerable intra-meteorite variation, with inhomogeneities in bulk and grain densities at scales up to approximately 40-g (approximately 12-cm 3). © The Meteoritical Society, 2010.


Heller M.,The Interdisciplinary Center | Heller M.,Vatican Observatory
Annalen der Physik (Leipzig) | Year: 2010

The closed Friedman cosmological model, based on noncommutative geometry, is presented. Two global effects exhibited by the model are discussed. The first effect is the "generation of matter out of geometry". Gravitational field equation in this model has the form of the eigenvalue equation for the Einstein operator.It turns out that the eigenvalues of this operator reproduce components of the energy-momentum tensor. Thesecond effect concerns the existence of the initial and final singularities. Because of the strongly probabilistic character of the noncommutative dynamics on the fundamental level, although singularities do exist, they are probabilistically irrelevant. © 2010 WILEY-VCH Verlag GmbH & Co.


Romanishin W.,University of Oklahoma | Tegler S.C.,Northern Arizona University | Consolmagno G.J.,Vatican Observatory
Astronomical Journal | Year: 2010

We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the ten inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper Belt Objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper Belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and/or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects. © 2010. The American Astronomical Society. All rights reserved.


Gonzalez O.A.,European Southern Observatory | Rejkuba M.,European Southern Observatory | Zoccali M.,University of Santiago de Chile | Zoccali M.,National institute for astrophysics | And 6 more authors.
Astronomy and Astrophysics | Year: 2012

Context. The Milky Way bulge is the nearest galactic bulge and the most readily accessible laboratory for studies of stellar populations in spheroids based on individual stellar abundances and kinematics. These studies are challenged by the strongly variable and often large extinction on a small spatial scale. Aims. We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution. Methods. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J-K s) color of red clump giants in small subfields of 2′ × 2′ to 6′ × 6′ in the following bulge area:-10.3° ≤ b ≤ +5.1° and-10.0° ≤ l ≤ +10.4°. To determine the reddening values E(J-K s) for each region, we measure the RC color and compare it to the (J-K s) color of RC stars measured in Baade's Window, for which we adopt E(B-V) = 0.55. This allows us to construct a reddening map sensitive to small-scale variations minimizing the problems arising from differential extinction. Results.The significant reddening variations are clearly observed on spatial scales as small as 2′. We find good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are unreliable for regions within |b| ≈ 6. In the inner regions, we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map is of higher quality owing to both its higher resolution and a more complete spatial coverage of the bulge. We investigate the importance of differential reddening and demonstrate the need for high spatial resolution extinction maps for detailed studies of bulge stellar populations and structure. Conclusions. We present the first extinction map covering uniformly ∼315 sq. deg. of the Milky Way bulge at high spatial resolution. We consider a 30 arcmin window at a latitude of b =-4°, which corresponds to a frequently studied low extinction window, the so-called Baade's Window, and find that its AK s values can vary by up to 0.1 mag. Larger extinction variations are observed at lower Galactic latitudes. The extinction variations on scales of up to 2′-6′ must be taken into account when analyzing the stellar populations of the Galactic bulge. © 2012 ESO.


Kiefer W.S.,Lunar and Planetary Institute | MacKe R.J.,University of Central Florida | MacKe R.J.,Boston College | Britt D.T.,University of Central Florida | And 2 more authors.
Geophysical Research Letters | Year: 2012

Accurate lunar rock densities are necessary for constructing gravity models of the Moon's crust and lithosphere. Most Apollo-era density measurements have errors of 2-5% or more and few include porosity measurements. We report new density and porosity measurements using the bead method and helium pycnometry for 6 Apollo samples and 7 lunar meteorites, with typical grain density uncertainties of 10-30kgm -3 (0.3-0.9%) and porosity uncertainties of 1-3%. Comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space. Basalt grain densities are a strong function of composition, varying over at least 3270 kg m -3 (high aluminum basalt) to 3460 kg m -3 (high titanium basalt). Feldspathic highland crust has a bulk density of 2200-2600 kg m -3 and porosity of 10-20%. Impact basin ejecta has a bulk density of 2350-2600 kg m -3 and porosity of ∼20%. Copyright 2012 by the American Geophysical Union.


Gonzalez O.A.,European Southern Observatory | Rejkuba M.,European Southern Observatory | Zoccali M.,University of Santiago de Chile | Valenti E.,European Southern Observatory | And 3 more authors.
Astronomy and Astrophysics | Year: 2011

Context. The Milky Way bulge is the nearest galactic bulge and the best laboratory for studies of stellar populations in spheroids based on individual stellar abundances and kinematics. The observed properties point to a very complex nature, which is hard to extrapolate from a few fields. Aims. We present a method of obtaining reddening maps and tracing structure and metallicity gradients of the bulge using data from the recently started ESO public survey Vista Variables in the Via Lactea (VVV). The method is used to derive properties of the fields along the minor axis. Methods. We derived the mean J-K s color of the red clump (RC) giants in 1835 subfields in the bulge region with-8° < b <-0.4° and 0.2° < l < 1.7°, and compare it to the color of RC stars in Baade's window, for which we adopt E(B-V) = 0.55. This allows us to derive the reddening map on a small enough scale to minimize the problems arising from differential extinction. The dereddened magnitudes were then used to build the bulge luminosity function in regions of ~0.4° × 0.4° to obtain the mean RC magnitudes. These were used as distance indicator in order to trace the bulge structure. Finally, for each subfield the derived distance and extinction values were used to obtain photometric metallicities through interpolation of red giant branch colors on a set of empirical ridge lines. The photometric metallicity distributions were compared to metallicity distributions obtained from high-resolution spectroscopy in the same regions. Results. The reddening determination is sensitive to small-scale variations, which are clearly visible in our maps. Our results agree within the errors with literature values based on different methods, although our maps have much higher resolution and more complete coverage. The luminosity function clearly shows the double RC recently discovered in 2MASS and OGLE III datasets, thereby allowing the X-shape morphology of the bulge to be traced. Finally, the mean of the derived photometric metallicity distributions are in remarkable agreement with those obtained from spectroscopy. Conclusions. The VVV survey is a unique tool for mapping the bulge properties by means of the consistent method presented here. The remarkable agreement between our results and those presented in literature for the minor axis allows us to safely extend our method to the whole region covered by the survey. © 2011 ESO.


Saito R.K.,University of Santiago de Chile | Zoccali M.,University of Santiago de Chile | McWilliam A.,Observatories of the Carnegie Institute of Washington | Minniti D.,University of Santiago de Chile | And 4 more authors.
Astronomical Journal | Year: 2011

We analyzed the distribution of the red clump (RC) stars throughout the Galactic bulge using Two Micron All Sky Survey data. We mapped the position of the RC in 1deg2 fields within the area |l| ≤ 85 and 35 ≤ |b| ≤ 85, for a total of 170deg2. The single RC seen in the central area splits into two components at high Galactic longitudes in both hemispheres, produced by two structures at different distances along the same line of sight. The X-shape is clearly visible in the Z-X plane for longitudes close to the l = 0° axis. Crude measurements of the space densities of RC stars in the bright and faint RC populations are consistent with the adopted RC distances, providing further supporting evidence that the X-structure is real, and that there is approximate front-back symmetry in our bulge fields. We conclude that the Milky Way bulge has an X-shaped structure within |l| ≲ 2°, seen almost edge-on with respect to the line of sight. Additional deep near-infrared photometry extending into the innermost bulge regions combined with spectroscopic data is needed in order to discriminate among the different possibilities that can cause the observed X-shaped structure. © 2011. The American Astronomical Society. All rights reserved..

Loading Vatican Observatory collaborators
Loading Vatican Observatory collaborators