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A. Moitinho

Publications and source records attributed to A. Moitinho.

At least 37 records · Page 2Linked to original sources
arXiv2017

Gaia Data Release 1: The archive visualisation service

Context: The first Gaia data release (DR1) delivered a catalogue of astrometry and photometry for over a billion astronomical sources. Within the panoply of methods used for data exploration, visualisation is often the starting point and even the guiding reference for scientific thought. However, this is a volume of data that cannot be efficiently explored using traditional tools, techniques, and habits. Aims: We aim to provide a global visual exploration service for the Gaia archive, something that is not possible out of the box for most people. The service has two main goals. The first is to provide a software platform for interactive visual exploration of the archive contents, using common personal computers and mobile devices available to most users. The second aim is to produce intelligible and appealing visual representations of the enormous information content of the archive. Methods: The interactive exploration service follows a client-server design. The server runs close to the data, at the archive, and is responsible for hiding as far as possible the complexity and volume of the Gaia data from the client. This is achieved by serving visual detail on demand. Levels of detail are pre-computed using data aggregation and subsampling techniques. For DR1, the client is a web application that provides an interactive multi-panel visualisation workspace as well as a graphical user interface. Results: The Gaia archive Visualisation Service offers a web-based multi-panel interactive visualisation desktop in a browser tab. It currently provides highly configurable 1D histograms and 2D scatter plots of Gaia DR1 and the Tycho-Gaia Astrometric Solution (TGAS) with linked views. An innovative feature is the creation of ADQL queries from visually defined regions in plots. [abridged]

astro-ph.IM↗
arXiv2017

Gaia Data Release 1: The variability processing & analysis and its application to the south ecliptic pole region

The ESA Gaia mission provides a unique time-domain survey for more than one billion sources brighter than G=20.7 mag. Gaia offers the unprecedented opportunity to study variability phenomena in the Universe thanks to multi-epoch G-magnitude photometry in addition to astrometry, blue and red spectro-photometry, and spectroscopy. Within the Gaia Consortium, Coordination Unit 7 has the responsibility to detect variable objects, classify them, derive characteristic parameters for specific variability classes, and provide global descriptions of variable phenomena. We describe the variability processing and analysis that we plan to apply to the successive data releases, and we present its application to the G-band photometry results of the first 14 months of Gaia operations that comprises 28 days of Ecliptic Pole Scanning Law and 13 months of Nominal Scanning Law. Out of the 694 million, all-sky, sources that have calibrated G-band photometry in this first stage of the mission, about 2.3 million sources that have at least 20 observations are located within 38 degrees from the South Ecliptic Pole. We detect about 14% of them as variable candidates, among which the automated classification identified 9347 Cepheid and RR Lyrae candidates. Additional visual inspections and selection criteria led to the publication of 3194 Cepheid and RR Lyrae stars, described in Clementini et al. (2016). Under the restrictive conditions for DR1, the completenesses of Cepheids and RR Lyrae stars are estimated at 67% and 58%, respectively, numbers that will significantly increase with subsequent Gaia data releases. Data processing within the Gaia Consortium is iterative, the quality of the data and the results being improved at each iteration. The results presented in this article show a glimpse of the exceptional harvest that is to be expected from the Gaia mission for variability phenomena. [abridged]

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arXiv2017

Gaia Data Release 1: Catalogue validation

Before the publication of the Gaia Catalogue, the contents of the first data release have undergone multiple dedicated validation tests. These tests aim at analysing in-depth the Catalogue content to detect anomalies, individual problems in specific objects or in overall statistical properties, either to filter them before the public release, or to describe the different caveats of the release for an optimal exploitation of the data. Dedicated methods using either Gaia internal data, external catalogues or models have been developed for the validation processes. They are testing normal stars as well as various populations like open or globular clusters, double stars, variable stars, quasars. Properties of coverage, accuracy and precision of the data are provided by the numerous tests presented here and jointly analysed to assess the data release content. This independent validation confirms the quality of the published data, Gaia DR1 being the most precise all-sky astrometric and photometric catalogue to-date. However, several limitations in terms of completeness, astrometric and photometric quality are identified and described. Figures describing the relevant properties of the release are shown and the testing activities carried out validating the user interfaces are also described. A particular emphasis is made on the statistical use of the data in scientific exploitation.

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arXiv2015

Insights into the properties of the Local (Orion) spiral arm. NGC 2302: First results and description of the program

The spiral structure of the Milky Way is highly uncertain and is the subject of much discussion nowadays. We present the first result from a program that determines the properties of the Local spiral arm (LOA), together with a full description of the program. In this context we have made a comprehensive study of the young LOA open cluster NGC 2302, which includes a UBVRI photometric analysis and determination of its kinematic properties - proper motion and radial velocity - and of its orbital parameters. We determined the mean PM of NGC 2302 relative to the local field of disk stars, and, through a comparison with the UCAC4 catalog, we transformed this relative PM into an absolute one. Using medium-resolution spectroscopy of 26 stars in the field of NGC 2302, we derived its mean RV. Isochrone fits to the photometric diagrams allowed us to determine the fundamental parameters of NGC 2302, including reddening, distance, and age. The kinematic data and derived distance allowed us to determine the space motion of NGC 2302. This was done by adopting a time-independent, axisymmetric, and fully analytic gravitational potential for the MW. We obtained an absolute PM for NGC 2302 of ($μ_α \cosδ,μ_δ) = (-2.09,-2.11)$ mas/yr, with standard errors of 0.410 and 0.400 mas/yr. The mean RV of NGC 2302 turned out to be 31.2 km/sec with a standard error of 0.7 km/sec. Isochrone fits displaced for this reddening and for a distance modulus of (m-M)o = 10.69 indicate an age of log(t) = 7.90-8.00 with a slight tendency toward the younger age. Inspection of the shape of the orbit of NGC 2302 and the resulting orbital parameters indicate that it is a typical population I object.

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arXiv2015

Evidence of tidal distortions and mass loss from the old open cluster NGC 6791

We present the first evidence of clear signatures of tidal distortions in the density distribution of the fascinating open cluster NGC 6791. We used deep and wide-field data obtained with the Canada-France-Hawaii-Telescope covering a 2x2 square degrees area around the cluster. The two-dimensional density map obtained with the optimal matched filter technique shows a clear elongation and an irregular distribution starting from ~300" from the cluster center. At larger distances, two tails extending in opposite directions beyond the tidal radius are also visible. These features are aligned to both the absolute proper motion and to the Galactic center directions. Moreover, other overdensities appear to be stretched in a direction perpendicular to the Galactic plane. Accordingly to the behaviour observed in the density map, we find that both the surface brightness and the star count density profiles reveal a departure from a King model starting from ~600" from the center. These observational evidence suggest that NGC 6791 is currently experiencing mass loss likely due to gravitational shocking and interactions with the tidal field. We use this evidence to argue that NGC 6791 should have lost a significant fraction of its original mass. A larger initial mass would in fact explain why the cluster survived so long. Using available recipes based on analytic studies and N-body simulations, we derived the expected mass loss due to stellar evolution and tidal interactions and estimated the initial cluster mass to be M_ini=(1.5-4) x 10^5 M_sun.

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arXiv2013

UPMASK: unsupervised photometric membership assignment in stellar clusters

We develop a method for membership assignment in stellar clusters using only photometry and positions. The method, UPMASK, is aimed to be unsupervised, data driven, model free, and to rely on as few assumptions as possible. It is based on an iterative process, principal component analysis, clustering algorithm, and kernel density estimations. Moreover, it is able to take into account arbitrary error models. An implementation in R was tested on simulated clusters that covered a broad range of ages, masses, distances, reddenings, and also on real data of cluster fields. Running UPMASK on simulations showed that it effectively separates cluster and field populations. The overall spatial structure and distribution of cluster member stars in the colour-magnitude diagram were recovered under a broad variety of conditions. For a set of 360 simulations, the resulting true positive rates (a measurement of purity) and member recovery rates (a measurement of completeness) at the 90% membership probability level reached high values for a range of open cluster ages ($10^{7.1}-10^{9.5}$ yr), initial masses ($0.5-10\times10^3$M$_{\sun}$) and heliocentric distances ($0.5-4.0$ kpc). UPMASK was also tested on real data from the fields of the open cluster Haffner~16 and of the closely projected clusters Haffner~10 and Czernik~29. These tests showed that even for moderate variable extinction and cluster superposition, the method yielded useful cluster membership probabilities and provided some insight into their stellar contents. The UPMASK implementation will be available at the CRAN archive.

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arXiv2012

Comments on the "Monoceros" affair

This is a brief note to comment on some recent papers addressing the Monoceros ring. In our view, nothing new was delivered on the matter: No new evidence or arguments are presented which lead to think that the over-densities in Monoceros must not be due to the flared thick disc of the Milky Way. Again, we restate that extrapolations are easily misleading and that a model of the Galaxy is not the Galaxy. Raising and discussing exciting possibilities is healthy. However, enthusiasm should not overtake and produce strong claims before thoroughly checking simpler and more sensible possibilities within their uncertainties. In particular, claiming that a reported structure, such as the Monoceros Ring, is not Galactic (an exciting scenario) should not be done without rejecting the possibility of being due to the well established warped and flared disc of the Milky Way (simpler).

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arXiv2011

G0.253+0.016: a molecular cloud progenitor of an Arches-like cluster

Young massive clusters (YMCs) with stellar masses of 10^4 - 10^5 Msun and core stellar densities of 10^4 - 10^5 stars per cubic pc are thought to be the `missing link' between open clusters and extreme extragalactic super star clusters and globular clusters. As such, studying the initial conditions of YMCs offers an opportunity to test cluster formation models across the full cluster mass range. G0.253+0.016 is an excellent candidate YMC progenitor. We make use of existing multi-wavelength data including recently available far-IR continuum (Herschel/Hi-GAL) and mm spectral line (HOPS and MALT90) data and present new, deep, multiple-filter, near-IR (VLT/NACO) observations to study G0.253+0.016. These data show G0.253+0.016 is a high mass (1.3x10^5 Msun), low temperature (T_dust~20K), high volume and column density (n ~ 8x10^4 cm^-3; N_{H_2} ~ 4x10^23 cm^-2) molecular clump which is close to virial equilibrium (M_dust ~ M_virial) so is likely to be gravitationally-bound. It is almost devoid of star formation and, thus, has exactly the properties expected for the initial conditions of a clump that may form an Arches-like massive cluster. We compare the properties of G0.253+0.016 to typical Galactic cluster-forming molecular clumps and find it is extreme, and possibly unique in the Galaxy. This uniqueness makes detailed studies of G0.253+0.016 extremely important for testing massive cluster formation models.

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arXiv2009

UBV(RI)_C photometry of the open clusters Be 15, Be 80, and NGC 2192

The three open clusters Be 15, Be 80, and NGC 2192 have been observed using CCD UBV(RI)_C photometry at the San Pedro Mártir Observatory, México within the framework of our open-cluster survey. The fundamental parameters of interstellar reddening, distance, and age have been derived, and also the metallicity for NGC 2192 (solar metallicity has been assumed for the other two). By shifting the colours of Schmidt-Kaler in the (U-B, B-V) two-colour diagram along the appropriate reddening vector, the interstellar reddenings have been derived as E(B-V)=0.23+/-0.03 mag for Be 15, 1.31+/-0.05 for Be 80, and 0.16+/-0.03 for NGC 2192. Evidence is shown for a variable interstellar extinction across the cluster Be 80. For NGC 2192 a nicely consistent fit is obtained for both the interstellar reddening and the metallicity ([Fe/H]=-0.31) using simultaneously the F-type and red-clump stars. By fitting isochrones to the observed sequences of these three clusters in various colour-magnitude diagrams of different colour indices, (B-V, V-I, or V-R) the averages of distance moduli and heliocentric distances ((V-M_V)_o (mag); d(pc)) are the following: (10.74+/-0.01; 1202) for Be 15, (10.75+/-0.01; 1413) for Be 80, and (12.7+/-0.01; 3467) for NGC 2192, and the averages of the inferred best ages (log(age); age (Gyr)) are (8.6+/-0.05; 0.4) for Be 80, and (9.15+/-0.05; 1.4) for NGC 2192; for Be 15 there are two distinct possibilities for the age fit, depending on the membership of three brighter stars, (9.35 or 9.95+/-0.05; 2.2 or 8.9). The need for spectroscopic observations in Be 15 is emphasized to select between alternate reddening and age solutions, and for deeper UBV observations in Be 80 to study in greater detail the variable interstellar, or intracluster, reddening across this cluster.

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arXiv2008

VSI: the VLTI spectro-imager

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13 will be imaged without requiring a brighter nearby reference object. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysic including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return.

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arXiv2008

Blue Straggler Stars in Galactic Open Clusters and the effect of field star contamination

We investigate the distribution of Blue Straggler stars in the field of three open star clusters. The main purpose is to highlight the crucial role played by general Galactic disk fore-/back-ground field stars, which are often located in the same region of the Color Magnitude Diagram as Blue Straggler stars. We analyze photometry taken from the literature of 3 open clusters of intermediate/old age rich in Blue Straggler stars, and which are projected in the direction of the Perseus arm, and study their spatial distribution and the Color Magnitude Diagram. As expected, we find that a large portion of the Blue Straggler population in these clusters are simply young field stars belonging to the spiral arm. This result has important consequences on the theories of the formation and statistics of Blue Straggler stars in different population environments: open clusters, globular clusters or dwarf galaxies. As previously emphasized by many authors, a detailed membership analysis is mandatory before comparing the Blue Straggler population in star clusters against theoretical models. Moreover, these sequences of young field stars (blue plumes) are potentially powerful tracers of Galactic structure which require further consideration.

astro-ph↗
arXiv2008

Milli-arcsecond astrophysics with VSI, the VLTI spectro-imager in the ELT era

Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain. This instrument will provide information complementary to what is obtained at the same time with ALMA at different wavelengths and the extreme large telescopes.

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arXiv2006

On the difference between nuclear and contraction ages

Context:Ages derived from the low mass stars still contracting onto the main sequence often differ from ages derived from the high mass ones that have already evolved away from it. Aims:We investigate the general claim of disagreement between these two independent age determinations by presenting UBVRI photometry of the young galactic open clusters NGC 2232, NGC 2516, NGC 2547 and NGC 4755, spanning the age range ~10-150 Myr Methods: We derive reddenings, distances and nuclear ages by fitting ZAMS and isochrones to color-magnitudes and color-color diagrams. To derive contraction ages, we use four different pre-main sequence models, with an empirically calibrated color-temperature relation to match the Pleiades cluster sequence. Results: When using exclusively the V vs. V-I color-magnitude diagram and empirically calibrated isochrones, there is consistency between nuclear and contraction ages for the studied clusters. Although the contraction ages seem systematically underestimated, in none of cases they deviate by more than one standard deviation from the nuclear ages.

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arXiv2006

Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate

With the discovery of the Sagittarius dwarf spheroidal (Ibata et al. 1994), a galaxy caught in the process of merging with the Milky Way, the hunt for other such accretion events has become a very active field of astrophysical research. The identification of a stellar ring-like structure in Monoceros, spanning more than 100 degrees (Newberg et al. 2002), and the detection of an overdensity of stars in the direction of the constellation of Canis Major (CMa, Martin et al. 2004), apparently associated to the ring, has led to the widespread belief that a second galaxy being cannibalised by the Milky Way had been found. In this scenario, the overdensity would be the remaining core of the disrupted galaxy and the ring would be the tidal debris left behind. However, unlike the Sagittarius dwarf, which is well below the Galactic plane and whose orbit, and thus tidal tail, is nearly perpendicular to the plane of the Milky Way, the putative CMa galaxy and ring are nearly co-planar with the Galactic disk. This severely complicates the interpretation of observations. In this letter, we show that our new description of the Milky Way leads to a completely different picture. We argue that the Norma-Cygnus spiral arm defines a distant stellar ring crossing Monoceros and the overdensity is simply a projection effect of looking along the nearby local arm. Our perspective sheds new light on a very poorly known region, the third Galactic quadrant (3GQ), where CMa is located.

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arXiv2005

NGC 2401: A template of the Norma-Cygnus Arm's young population in the Third Galactic Quadrant

Based on a deep optical CCD (UBV(RI)_C) photometric survey and on the Two-Micron All-Sky-Survey (2MASS) data we derived the main parameters of the open cluster NGC 2401. We found this cluster is placed at 6.3 $\pm$ 0.5 kpc (V_O - M_V = 14.0 \pm 0.2) from the Sun and is 25 Myr old, what allows us to identify NGC 2401 as a member of the young population belonging to the innermost side of the extension of the Norma-Cygnus spiral--arm in the Third Galactic Quadrant. A spectroscopic study of the emission star LSS 440 that lies in the cluster area revealed it is a B0Ve star; however, we could not confirm it is a cluster member. We also constructed the cluster luminosity function (LF) down to $V \sim 22$ and the cluster initial mass function (IMF) for all stars with masses above $M \sim 1-2 M_{\sun}$. It was found that the slope of the cluster IMF is $x \approx 1.8 \pm 0.2$. The presence of a probable PMS star population associated to the cluster is weakly revealed.

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arXiv2005

uvby-βphotometry of high-velocity and metal-poor stars XI. Ages of halo and old disk stars

New uvby-βdata are provided for 442 high-velocity and metal-poor stars; 90 of these stars have been observed previously by us, and 352 are new. When combined with our previous two photometric catalogues, the data base is now made up of 1533 high-velocity and metal-poor stars, all with uvby-βphotometry and complete kinematic data, such as proper motions and radial velocities taken from the literature. Hipparcos, plus a new photometric calibration for M_v also based on the Hipparcos parallaxes, provide distances for nearly all of these stars; our previous photometric calibrations give values for E(b-y) and [Fe/H]. The [Fe/H],V(rot) diagram allows us to separate these stars into different Galactic stellar population groups, such as old-thin-disk, thick-disk, and halo. The X histogram, where X is our stellar-population discriminator combining V(rot) and [Fe/H], and contour plots for the [Fe/H],V(rot) diagram both indicate two probable components to the thick disk. These population groups and Galactic components are studied in the (b-y)_o,M_v diagram, compared to the isochrones of Bergbusch & VandenBerg (2001), to derive stellar ages. The two thick-disk groups have the mean characteristics: ([Fe/H], V(rot), Age, σ_W') ~ (-0.7 dex, 120 km/s, 12.5 Gyr, 62.0 km/s), and ~(-0.4, 160, 10.0, 45.8). The seven most metal-poor halo groups, -2.31 <= [Fe/H] <= -1.31, show a mean age of 13.0 +/-0.2 (mean error) Gyr, giving a mean difference from the WMAP results for the age of the Universe of 0.7 +/- 0.3 Gyr. These results for the ages and components of the thick disk and for the age of the Galactic halo field stars are discussed in terms of various models and ideas for the formation of galaxies and their stellar populations.

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arXiv2005

Open clusters in the Third Galactic Quadrant. II. The intermediate age open clusters NGC 2425 and NGC 2635

We analyse CCD broad band (UBV(RI)c) photometric data obtained in the fields of the poorly studied open clusters NGC 2425 and NGC 2635. Both clusters are found to be of intermediate age thus increasing the population of open clusters known to be of the age of, or older than, the Hyades. More explicitly, we find that NGC 2425 is a 2.2 Gyr old cluster, probably of solar metallicity, located at 3.5 kpc from the Sun. NGC 2635 is a Hyades age (600 Myr) cluster located at a distance of 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that it is extremely metal poor for its age and position, thus making it a very interesting object in the context of Galactic Disk chemical evolution models.

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