L. Rimoldini; B. Holl; M. Audard; N. Mowlavï; K. Nienartowicz; D. W. Evans; L. P. Guy; Lecoeur-Taïbi, I.; G. Jévardat de Fombelle; O. Marchal; M. Roelens; J. De Ridder; L. M. Sarro; S. Regibo; M. López; G. Clementini; V. Ripepi; R. Molinaro; A. Garofalo; L. Molnár; E. Plachy; Á. L. Juhász; L. Szabados; T. Lebzelter; D. Teyssier; L. Eyer
Repository of the Academy's Library (Library of the Hungarian Academy of Sciences) · DOI
More than half a million of the 1.69 billion sources in Gaia Data Release 2 (DR2) are published with photometric time series that exhibit light variations during the 22 months of observation. An all-sky classification of common high-amplitude pulsators (Cepheids, long-period variables, Delta Scuti / SX Phoenicis, and RR Lyrae stars) is provided for stars with brightness variations greater than 0.1 mag in G band. A semi-supervised classification approach was employed, firstly training multi-stage random forest classifiers with sources of known types in the literature, followed by a preliminary classification of the Gaia data and a second training phase that included a selection of the first classification results to improve the representation of some classes, before the improved classifiers were applied to the Gaia data. Dedicated validation classifiers were used to reduce the level of contamination in the published results. A relevant fraction of objects were not yet sufficiently sampled for reliable Fourier series decomposition, consequently classifiers were based on features derived from statistics of photometric time series in the G, BP, and RP bands, as well as from some astrometric parameters. The published classification results include 195,780 RR Lyrae stars, 150,757 long-period variables, 8550 Cepheids, and 8882 Delta Scuti / SX Phoenicis stars. All of these results represent candidates whose completeness and contamination are described as a function of variability type and classification reliability. Results are expressed in terms of class labels and classification scores, which are available in the vari_classifier_result table of the Gaia archive.
Gaia Collaboration; C. Babusiaux; F. van Leeuwen; M. A. Barstow; C. Jordi; A. Vallenari; D. Bossini; A. Bressan; T. Cantat-Gaudin; M. van Leeuwen; et al.
RECERCAT (Consorci de Serveis Universitaris de Catalunya) · DOI
We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.
M. Riello; F. De Angeli; D. W. Evans; G. Busso; N. C. Hambly; M. Davidson; P. W. Burgess; P. Montegriffo; P. Osborne; A. Kewley; J. M. Carrasco; C. Fabricius; C. Jordi; C. Cacciari; F. van Leeuwen; G. Holland
RECERCAT (Consorci de Serveis Universitaris de Catalunya) · DOI
CONTEXT. The second Gaia data release is based on 22 months of mission data with an average of 0.9 billion individual CCD observations per day. A data volume of this size and granularity requires a robust and reliable but still flexible system to achieve the demanding accuracy and precision constraints that Gaia is capable of delivering. AIMS. We aim to describe the input data, the treatment of blue photometer/red photometer (BP/RP) low–resolution spectra required to produce the integrated GBP and GRP fluxes, the process used to establish the internal Gaia photometric system, and finally, the generation of the mean source photometry from the calibrated epoch data for Gaia DR2. METHODS. The internal Gaia photometric system was initialised using an iterative process that is solely based on Gaia data. A set of calibrations was derived for the entire Gaia DR2 baseline and then used to produce the final mean source photometry. The photometric catalogue contains 2.5 billion sources comprised of three different grades depending on the availability of colour information and the procedure used to calibrate them: 1.5 billion gold, 144 million silver, and 0.9 billion bronze. These figures reflect the results of the photometric processing; the content of the data release will be different due to the validation and data quality filters applied during the catalogue preparation. The photometric processing pipeline, PhotPipe, implements all the processing and calibration workflows in terms of Map/Reduce jobs based on the Hadoop platform. This is the first example of a processing system for a large astrophysical survey project to make use of these technologies. RESULTS. The improvements in the generation of the integrated G–band fluxes, in the attitude modelling, in the cross–matching, and and in the identification of spurious detections led to a much cleaner input stream for the photometric processing. This, combined with the improvements in the definition of the internal photometric system and calibration flow, produced high-quality photometry. Hadoop proved to be an excellent platform choice for the implementation of PhotPipe in terms of overall performance, scalability, downtime, and manpower required for operations and maintenance.
D. W. Evans; M. Riello; F. De Angeli; J. M. Carrasco; P. Montegriffo; C. Fabricius; C. Jordi; L. Palaversa; C. Diener; G. Busso; C. Cacciari; E. Pancino; F. van Leeuwen
Proceedings of the International Astronomical Union · DOI
Abstract Gaia DR2 was released in April 2018 and contains a photometric catalogue of more than 1 billion sources. This release contains colour information in the form of integrated BP and RP photometry in addition to the latest G-band photometry. The level of uncertainty can be as good as 2 mmag with some residual systematics at the 10 mmag level. The addition of colour information greatly enhances the value of the photometric data for the scientific community. A high level overview of the photometric processing, with a focus on the improvements with respect to Gaia DR1, was given. The definition of the Gaia photometric system, a crucial part of the calibration of the photometry, was also explained. Finally, some of the photometric improvements expected for the next data release were described.
Z. Kostrzewa-Rutkowska; P. G. Jonker; S. T. Hodgkin; Ł. Wyrzykowski; M. Fraser; D. L. Harrison; G. Rixon; A. Yoldaş; F. van Leeuwen; A. Delgado; M. van Leeuwen; S. E. Koposov
Monthly Notices of the Royal Astronomical Society · DOI
The high spatial resolution and precise astrometry and photometry of the Gaia mission should make it particularly apt at discovering and resolving transients occurring in, or near, the centres of galaxies. Indeed, some nuclear transients are reported by the Gaia Science Alerts (GSA) team, but not a single confirmed Tidal Disruption Event has been published. In order to explore the sensitivity of GSA, we performed an independent and systematic search for nuclear transients using Gaia observations. Our transient search is driven from an input galaxy catalogue (derived from the Sloan Digital Sky Survey Release 12). We present a candidate detection metric which is independent from the existing GSA methodology, to see if Gaia Alerts are biased against the discovery of nuclear transients, and in particular which steps may have an impact. Our technique does require significant manual vetting of candidates, making implementation in the GSA system impractical for daily operations, although it could be run weekly, which for month-to-year long transients would make a scientifically valuable addition. Our search yielded ~480 nuclear transients, 5 of which were alerted and published by GSA. The list of (in some cases ongoing) transients includes candidates for events related to enhanced accretion onto a super-massive black hole and TDEs. An implementation of the detection methodology and criteria used in this paper as an extension of GSA could open up the possibility for Gaia to fulfil the role as a main tool to find transient nuclear activity as predicted in the literature.
S. Feltzing; T. Bensby; M. Bergemann; C. Chiappini; N. Christlieb; Cioni, M.; A. Helmi; M. J. Irwin; Ivan Minchev; Else Starkenburg; Roelof de Jong
MPG.PuRe (Max Planck Society)
4MOST is a new wide-field, high-multiplex spectroscopic survey facility for the VISTA telescope of ESO. Starting in 2022, 4MOST will deploy 2400 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. In this contribution we give an outline of the major science goals we wish to achieve with 4MOST in the area of Galactic Archeology. The 4MOST Galactic Archeology surveys have been designed to address long-standing and far-reaching problems in Galactic science. They are focused on four major themes: 1) Near-field cosmology tests, 2) Chemo-dynamical characterisation of the major Milky Way stellar components, 3) The Galactic Halo and beyond, and 4) Discovery and characterisation of extremely metal-poor stars. In addition to a top-level description of the Galactic surveys we provide information about how the community will be able to join 4MOST via a call for Public Spectroscopic Surveys that ESO will launch.
S. Pasetto; E. K. Grebel; C. Chiosi; Denija Crnojević; Peter Zeidler; G. Busso; L. P. Cassará; L. Piovan; Rosaria Tantalo; Claudio Brogliato
The Astrophysical Journal · DOI
Abstract We present a new Galaxy population synthesis Model, GalMod. GalMod is a star-count model featuring an asymmetric bar/bulge as well as spiral arms and related extinction. The model, initially introduced in Pasetto et al., has been here completed with a central bar, a new bulge description, new disk vertical profiles, and several new bolometric corrections. The model can generate synthetic mock catalogs of visible portions of the Milky Way, external galaxies like M31, or N -body simulation initial conditions. At any given time, e.g., at a chosen age of the Galaxy, the model contains a sum of discrete stellar populations, namely the bulge/bar, disk, and halo. These populations are in turn the sum of different components: the disk is the sum of the spiral arms, thin disks, a thick disk, and various gas components, while the halo is the sum of a stellar component, a hot coronal gas, and a dark-matter component. The Galactic potential is computed from these population density profiles and used to generate detailed kinematics by considering up to the first four moments of the collisionless Boltzmann equation. The same density profiles are then used to define the observed color–magnitude diagrams in a user-defined field of view (FoV) from an arbitrary solar location. Several photometric systems have been included and made available online, and no limits on the size of the FoV are imposed thus allowing full-sky simulations, too. Finally, we model the extinction by adopting a dust model with advanced ray-tracing solutions. The model's Web page (and tutorial) can be accessed at www.GalMod.org and support is provided at Galaxy.Model@yahoo.com.
P. Cruz; Marcos P. Diaz; Jayne Birkby; D. Barrado; Brigitta Sipőcz; S. T. Hodgkin
Monthly Notices of the Royal Astronomical Society · DOI
We present the characterization of 5 new short-period low-mass eclipsing binaries from the WFCAM Transit Survey. The analysis was performed by using the photometric WFCAM J-mag data and additional low-and intermediate-resolution spectroscopic data to obtain both orbital and physical properties of the studied sample. The light curves and the measured radial velocity curves were modeled simultaneously with the JKTEBOP code, with Markov chain Monte Carlo simulations for the error estimates. The best-model fit have revealed that the investigated detached binaries are in very close orbits, with orbital separations of 2.9 a 6.7 R and short periods of 0.59 P orb 1.72 d, approximately. We have derived stellar masses between 0.24 and 0.72 M and radii ranging from 0.42 to 0.67 R . The great majority of the LMEBs in our sample has an estimated radius far from the predicted values according to evolutionary models. The components with derived masses of M < 0.6 M present a radius inflation of 9% or more. This general behavior follows the trend of inflation for partiallyradiative stars proposed previously. These systems add to the increasing sample of low-mass stellar radii that are not well-reproduced by stellar models. They further highlight the need to understand the magnetic activity and physical state of small stars. Missions like TESS will provide many such systems to perform high-precision radius measurements to tightly constrain low-mass stellar evolution models.
A. B. Higgins; K. Wiersema; S. Covino; R. L. C. Starling; H. F. Stevance; Ł. Wyrzykowski; S. T. Hodgkin; Justyn R. Maund; P. T. O’Brien; N. R. Tanvir
Monthly Notices of the Royal Astronomical Society · DOI
We present SPLOT, a small scale pilot survey to test the potential of snapshot (single epoch) linear imaging polarimetry as a supplementary tool to traditional transient follow-up. Transients exist in a vast volume of observational parameter space and polarimetry has the potential to highlight sources of scientific interest and add value to near real-time transient survey streams. We observed a sample of $\sim 50$ randomly selected optical transients with the EFOSC2 and SofI instruments, on the 3.6m New Technology Telescope (NTT) to test the feasibility of the survey. Our sample contained a number of interesting individual sources: a variety of supernovae, X-ray binaries, a tidal disruption event, blazar outbursts, and, by design, numerous transients of unknown nature. We discuss the results, both for the individual sources and the survey in detail. We provide an overview on the success and limitations of SPLOT and also describe a novel calibration method for removing instrumental polarisation effects from Nasymth-mounted telescopes. We find that a SPLOT-like survey would be a benefit to the large scale future transient survey streams such as LSST. The polarimetric measurements have added scientific value to a significant number of the sources and, most importantly, has shown the potential to highlight unclassified transient sources of scientific interest for further study.
Salvatore Taibi; G. Battaglia; N. Kacharov; M. Rejkuba; M. J. Irwin; Ryan Leaman; M. Zoccali; Eline Tolstoy; P. Jablonka
Springer Link (Chiba Institute of Technology) · DOI
Context. The great majority of early-type dwarf galaxies, in the Local Group as well as in other galaxy groups, are found in the vicinity of much larger galaxies, making it hard to disentangle the role of internal versus external effects in driving their evolution. &lt;BR /&gt; Aims: In order to minimize environmental effects and gain an insight into the internal mechanisms that shape the properties of these systems, we study one of the few dwarf spheroidal galaxies of the Local Group found in isolation: Cetus. This system is of particular interest since it does not follow the Local Group morphology-density relation. &lt;BR /&gt; Methods: We obtained Very Large Telescope (VLT) FORS2 spectra (R ̃ 2600) in the region of the nIR CaII triplet lines for 80 candidate red giant branch (RGB) stars. The analysis yielded line-of-sight velocities and metallicities ([Fe/H]) for 54 bona fide member stars. &lt;BR /&gt; Results: The kinematic analysis shows that Cetus is a mainly pressure-supported (σ&lt;SUB&gt;v&lt;/SUB&gt; = 110&lt;SUB&gt;-1.3&lt;/SUB&gt;&lt;SUP&gt;+1.6&lt;/SUP&gt; km s&lt;SUP&gt;-1&lt;/SUP&gt;), dark-matter-dominated system (M&lt;SUB&gt;1/2&lt;/SUB&gt;/L&lt;SUB&gt;V&lt;/SUB&gt; = 23.9&lt;SUB&gt;-8.9&lt;/SUB&gt;&lt;SUP&gt;+9.7&lt;/SUP&gt; M&lt;SUB&gt;☉&lt;/SUB&gt;/L&lt;SUB&gt;☉&lt;/SUB&gt;) with no significant signs of internal rotation. We find Cetus to be a metal-poor system with a significant metallicity spread (median [Fe/H]= - 1.71 dex, median-absolute-deviation = 0.49 dex), as expected for its stellar mass. We report the presence of a mild metallicity gradient compatible with those found in other dwarf spheroidals of the same luminosity; we trace the presence of a stellar population gradient also in the spatial distribution of stars in different evolutionary phases in ancillary SuprimeCam photometric data. There are tentative indications of two chemo-kinematically distinct sub-populations, with the more metal-poor stars showing a hotter kinematics than the metal-richer ones. Furthermore, the photometric dataset reveals the presence of a foreground population that most likely belongs to the Sagittarius stream. &lt;BR /&gt; Conclusions: This study represents an important step forward in assessing the internal kinematics of the Cetus dwarf spheroidal galaxy as well as the first wide-area spectroscopic determination of its metallicity properties. With our analysis, Cetus adds to the growing scatter in stellar-dark matter halo properties in low-mass galactic systems. The presence of a metallicity gradient akin to those found in similarly luminous and pressure-supported systems inhabiting very different environments may hint at metallicity gradients in Local Group early-type dwarfs being driven by internal mechanisms. Based on observations made with ESO telescopes at the La Silla Paranal Observatory as part of the program 090.B-0284(B)The averaged spectra (FITS files) are only available at the CDS via anonymous ftp to &lt;A href="http://cdsarc.u-strasbg.fr"&gt;http://cdsarc.u-strasbg.fr&lt;/A&gt; (&lt;A href="http://130.79.128.5"&gt;http://130.79.128.5&lt;/A&gt;) or via &lt;A href="http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/618/A122"&gt;http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/618/A122&lt;/A&gt;
Alan W. McConnachie; Rodrigo Ibata; Nicolas F. Martin; A. M. N. Ferguson; Michelle Collins; Stephen Gwyn; M. J. Irwin; Geraint F. Lewis; Dougal Mackey; T. J. Davidge; Verónica Arias; A. R. Conn; Patrick Côté; Denija Crnojević; Avon Huxor; Jorge Peñarrubia; Chelsea Spengler; N. R. Tanvir; D. Valls‐Gabaud; Arif Babul; P. Barmby; N. F. Bate; Edouard J. Bernard; S. C. Chapman; Aaron Dotter; William E. Harris; B. McMonigal; Julio F. Navarro; Thomas H. Puzia; R. Michael Rich; Guillaume F. Thomas; Lawrence M. Widrow
The Astrophysical Journal · DOI
Abstract The Pan-Andromeda Archaeological Survey is a survey of &gt;400 square degrees centered on the Andromeda (M31) and Triangulum (M33) galaxies that has provided the most extensive panorama of an L ⋆ galaxy group to large projected galactocentric radii. Here, we collate and summarize the current status of our knowledge of the substructures in the stellar halo of M31, and discuss connections between these features. We estimate that the 13 most distinctive substructures were produced by at least 5 different accretion events, all in the last 3 or 4 Gyr. We suggest that a few of the substructures farthest from M31 may be shells from a single accretion event. We calculate the luminosities of some prominent substructures for which previous estimates were not available, and we estimate the stellar mass budget of the outer halo of M31. We revisit the problem of quantifying the properties of a highly structured data set; specifically, we use the OPTICS clustering algorithm to quantify the hierarchical structure of M31's stellar halo and identify three new faint structures. M31's halo, in projection, appears to be dominated by two “mega-structures,” which can be considered as the two most significant branches of a merger tree produced by breaking M31's stellar halo into increasingly smaller structures based on the stellar spatial clustering. We conclude that OPTICS is a powerful algorithm that could be used in any astronomical application involving the hierarchical clustering of points. The publication of this article coincides with the public release of all PAndAS data products.
C. Gónzalez-Fernández; S. T. Hodgkin; M. J. Irwin; E. González-Solares; S. E. Koposov; James R. Lewis; Jim Emerson; P. C. Hewett; A. Yoldaş; M. Riello
Apollo (University of Cambridge) · DOI
In this paper, we describe the routine photometric calibration of data taken with the VISTA infrared camera (VIRCAM) instrument on the ESO Visible and Infrared Survey Telescope for Astronomy (VISTA) telescope. The broad-band ZYJHKs data are directly calibrated from Two Micron all Sky Survey (2MASS) point sources visible in every VISTA image. We present the empirical transformations between the 2MASS and VISTA, and Wide-Field Camera and VISTA, photometric systems for regions of low reddening. We investigate the long-term performance of VISTA+VIRCAM. An investigation of the dependence of the photometric calibration on interstellar reddening leads to these conclusions: (1) For all broad-band filters, a linear colour-dependent correction compensates the gross effects of reddening where E(B − V) &lt; 5.0. (2) For Z and Y, there is a significantly larger scatter above E(B − V) = 5.0, and insufficient measurements to adequately constrain the relation beyond this value. (3) The JHKs filters can be corrected to a few per cent up to E(B − V) = 10.0. We analyse spatial systematics over month-long time-scales, both inter- and intradetector and show that these are present only at very low levels in VISTA. We monitor and remove residual detector-to-detector offsets. We compare the calibration of the main pipeline products: pawprints and tiles. We show how variable seeing and transparency affect the final calibration accuracy of VISTA tiles, and discuss a technique, grouting, for mitigating these effects. Comparison between repeated reference fields is used to demonstrate that the VISTA photometry is precise to better than ≃ 2 per cent for the YJHKs bands and 3 per cent for the Z bands. Finally, we present empirically determined offsets to transform VISTA magnitudes into a true Vega system.
S. Pasetto; Denija Crnojević; G. Busso; C. Chiosi; L. P. Cassará
New Astronomy · DOI
We aim to investigate the connections existing between the density profiles of the stellar populations used to define a gravitationally bound stellar system and their star formation history: we do this by developing a general framework accounting for both classical stellar population theory and classical stellar dynamics. We extend the work of Pasetto et al. (2012) on a single composite-stellar population (CSP) to multiple CSPs, including also a phase-space description of the CSP concept. In this framework, we use the concept of distribution function to define the CSP in terms of mass, metallicity, and phase-space in a suitable space of existence E of the CSP. We introduce the concept of foliation of E to describe formally any CSP as sum of disjointed Simple Stellar Populations (SSP), with the aim to offer a more general formal setting to cast the equations of stellar populations theory and stellar dynamics theory. In doing so, we allow the CSP to be object of dissipation processes thus developing its dynamics in a general non-Hamiltonian framework. Furthermore, we investigate the necessary and sufficient condition to realize a multiple CSP consistent with its mass-metallicity and phase-space distribution function over its temporal evolution, for a collisionless CSP. Finally, analytical and numerical examples show the potential of the result obtained.
L. Cicuéndez; G. Battaglia; M. J. Irwin; J. R. Bermejo-Climent; B. McMonigal; N. F. Bate; Geraint F. Lewis; A. R. Conn; de Boer, TJL; Carme Gallart; Magda Guglielmo; Rodrigo Ibata; Alan W. McConnachie; Eline Tolstoy; Nuwanthika Fernando
Springer Link (Chiba Institute of Technology) · DOI
Aims. We present results from deep and very spatially extended CTIO/DECam g and r photometry (reaching out to ~2 mag below the oldest main-sequence turn-off and covering ~20 deg 2 ) around the Sextans dwarf spheroidal galaxy. We aim to use this dataset to study the structural properties of Sextans overall stellar population and its member stars in different evolutionary phases, as well as to search for possible signs of tidal disturbance from the Milky Way, which would indicate departure from dynamical equilibrium. Methods. We performed the most accurate and quantitative structural analysis to-date of Sextans’ stellar components by applying Bayesian Monte Carlo Markov chain methods to the individual stars’ positions. Surface density maps are built by statistically decontaminating the sample through a matched filter analysis of the colour-magnitude diagram, and then analysed for departures from axisymmetry. Results. Sextans is found to be significantly less spatially extended and more centrally concentrated than early studies suggested. No statistically significant distortions or signs of tidal disturbances were found down to a surface brightness limit of ~31.8 mag/arcsec 2 in V -band. We identify an overdensity in the central regions that may correspond to previously reported kinematic substructure(s). In agreement with previous findings, old and metal-poor stars such as Blue Horizontal Branch stars cover a much larger area than stars in other evolutionary phases, and bright Blue Stragglers (BSs) are less spatially extended than faint ones. However, the different spatial distribution of bright and faint BSs appears consistent with the general age and metallicity gradients found in Sextans’ stellar component. This is compatible with Sextans BSs having formed by evolution of binaries and not necessarily due to the presence of a central disrupted globular cluster, as suggested in the literature. We provide structural parameters for the various populations analysed and make publicly available the photometric catalogue of point-sources as well as a catalogue of literature spectroscopic measurements with updated membership probabilities.
A. Lähteenmäki; E. Järvelä; T. Hovatta; M. Tornikoski; D. L. Harrison; M. López-Caniego; W. Max-Moerbeck; М. Г. Мингалиев; T. J. Pearson; Venkatessh Ramakrishnan; A. C. S. Readhead; R. Reeves; J. L. Richards; Yu. V. Sotnikova; J. Tammi
Astronomy and Astrophysics · DOI
Observations performed at Metshovi Radio Observatory at 37 GHz are presented for a sample of 78 radio-loud and radio-quiet narrow-line Seyfert 1 (NLS1) galaxies, together with additional lower and higher frequency radio data from RATAN-600, Owens Valley Radio Observatory, and the Planck satellite. Most of the data have been gathered between February 2012 and April 2015 but for some sources even longer light curves exist. The detection rate at 37 GHz is around 19%, which is comparable to other populations of active galactic nuclei presumed to be faint at radio frequencies, such as BL Lac objects. Variability and spectral indices are determined for sources with enough detections. Based on the radio data, many NLS1 galaxies show a blazar-like radio spectra exhibiting significant variability. The spectra at a given time are often inverted or convex. The source of the high-frequency radio emission in NLS1 galaxies, detected at 37 GHz, is most probably a relativistic jet rather than star formation. Jets in NLS1 galaxies are therefore expected to be a much more common phenomenon than earlier assumed.
F. van Leeuwen; A. Vallenari; C. Jordi; L. Lindegren; U. Bastian; T. Prusti; J. H. J. de Bruijne; A. G. A. Brown; C. Babusiaux; C. A. L. Bailer-Jones; et al.
Astronomy and Astrophysics · DOI
Context. The first Gaia Data Release contains the Tycho - Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using H ipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier H ipparcos -based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the H ipparcos data, with clearly increased luminosities for older A and F dwarfs.
D. W. Evans; M. Riello; F. De Angeli; G. Busso; F. van Leeuwen; C. Jordi; C. Fabricius; A. G. A. Brown; J. M. Carrasco; H. Voss; M. Weiler; P. Montegriffo; C. Cacciari; P. W. Burgess; P. Osborne
Astronomy and Astrophysics · DOI
Aims. The photometric validation of the Gaia DR1 release of the ESA Gaia mission is described and the quality of the data shown.
Carlos González Fernández; M. Irwin; JP Lewis; E. González-Solares
Zenodo (CERN European Organization for Nuclear Research) · DOI
"In this talk I will review the strategies in CASU to calibrate wide field surveys, in particular applied to data taken with the VISTA telescope. These include traditional night-by-night calibrations along with the search for a global, coherent calibration of all the data once observations are finished. The difficulties of obtaining photometric accuracy of a few percent and a good \nabsolute calibration will also be discussed."
Sophie L. Reed; R. G. McMahon; Paul Martini; M. Banerji; Matthew W. Auger; P. C. Hewett; S. E. Koposov; S. L. J. Gibbons; E. González-Solares; F. Ostrovski; Suk Sien Tie; F. B. Abdalla; S. Allam; A. Benoit-Lévy; E. Bertin; D. Brooks; E. Buckley‐Geer; D. L. Burke; A. Carnero Rosell; M. Carrasco Kind; J. Carretero; L. N. da Costa; D. L. DePoy; S. Desai; H. T. Diehl; P. Doel; A. E. Evrard; D. A. Finley; B. Flaugher; P. Fosalba; J. Frieman; J. García-Bellido; E. Gaztañaga; D. A. Goldstein; D. Gruen; R. A. Gruendl; G. Gutiérrez; D. J. James; K. Kuehn; N. Kuropatkin; O. Lahav; M. Lima; M. A. G. Maia; J. L. Marshall; P. Melchior; C. J. Miller; R. Miquel; B. Nord; R. L. C. Ogando; A. A. Plazas; A. K. Romer; E. Sánchez; V. Scarpine; M. Schubnell; I. Sevilla-Noarbe; R. C. Smith; F. Sobreira; E. Suchyta; M. E. C. Swanson; G. Tarlé; D. L. Tucker; A. R. Walker; W. C. Wester
Monthly Notices of the Royal Astronomical Society · DOI
We present the discovery and spectroscopic confirmation with the European Southern Observatory New Technology Telescope (NTT) and Gemini South telescopes of eight new, and the rediscovery of two previously known, 6.0 &lt; z &lt; 6.5 quasars with zAB &lt; 21.0. These quasars were photometrically selected without any morphological criteria from 1533 deg2 using spectral energy distribution (SED) model fitting to photometric data from Dark Energy Survey (g, r, i, z, Y), VISTA Hemisphere Survey (J, H, K) and Wide-field Infrared Survey Explorer (W1, W2). The photometric data were fitted with a grid of quasar model SEDs with redshift-dependent Ly α forest absorption and a range of intrinsic reddening as well as a series of low-mass cool star models. Candidates were ranked using an SED-model-based χ2-statistic, which is extendable to other future imaging surveys (e.g. LSST and Euclid). Our spectral confirmation success rate is 100 per cent without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants, the method allows large data sets to be processed without human intervention and without being overrun by spurious false candidates. We also present a robust parametric redshift estimator that gives comparable accuracy to Mg ii and CO-based redshift estimators. We find two z ∼ 6.2 quasars with H ii near zone sizes ≤3 proper Mpc that could indicate that these quasars may be young with ages ≲ 106-107 years or lie in over dense regions of the IGM. The z = 6.5 quasar VDES J0224−4711 has JAB = 19.75 and is the second most luminous quasar known with z ≥ 6.5.
Pieter Gruyters; L. Casagrande; A. P. Milone; S. T. Hodgkin; Aldo Serenelli; S. Feltzing
Springer Link (Chiba Institute of Technology) · DOI
Spectroscopic studies have demonstrated that nearly all Galactic globular clusters (GCs) harbour multiple stellar populations with different chemical compositions. Moreover, colour-magnitude diagrams based exclusively on Strömgrem photometry have allowed us to identify and characterise multiple populations along the RGB of a large number of clusters. In this paper we show for the first time that Strömgren photometry is also very efficient at identifying multiple populations along the AGB, and demonstrate that the AGB of M 3, M 92, NGC 362, NGC 1851, and NGC 6752 are not consistent with a single stellar population. We also provide a catalogue of RGB and AGB stars photometrically identified in these clusters for further spectroscopic follow-up studies. We combined photometry and elemental abundances from the literature for RGB and AGB stars in NGC 6752 where the presence of multiple populations along the AGB has been widely debated. We find that, while the MS, SGB, and RGB host three stellar populations with different helium and light element abundances, only two populations of AGB stars are present in the cluster. These results are consistent with standard evolutionary theory.