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 < z < 6.5 quasars with zAB < 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.
A. Keivani; Douglas Cowen; D. B. Fox; J. A. Kennea; G. Tešić; Colin Turley; P. A. Evans; J. P. Osborne; F. E. Marshall
Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017) · DOI ↗
We present results of the first four Swift satellite follow-up campaigns seeking to identify transient or variable X-ray or UV/optical sources that might be associated with individual candidate high-energy cosmic muon neutrinos detected by the IceCube Neutrino Observatory. Real-time public alerts providing coordinates and arrival times of likely-cosmic neutrinos have been provided by IceCube, via the Astrophysical Multimessenger Observatory Network, since April 2016. Subsequent Swift X-ray observations of four likely-cosmic neutrinos (events 160731A, 161103A, 170312A, and 170321A) reveal multiple X-ray sources in the targeted 90%-containment regions, most of which have been previously identified, and none of which are considered likely sources of high-energy neutrinos. Observations exclude association with the brightest 30% to 65% of Swift-type gamma-ray burst X-ray afterglows over the observed regions. Contemporaneous Swift UV/optical observations, providing reduced coverage of the event localizations, also reveal no candidate transient or variable UV/optical counterparts. We discuss the results of these campaigns and our plans for further follow-up of likely-cosmic high-energy neutrinos from IceCube.
J. M. Carrasco; D. W. Evans; P. Montegriffo; C. Jordi; F. van Leeuwen; M. Riello; H. Voss; F. De Angeli; G. Busso; C. Fabricius; C. Cacciari; M. Weiler; E. Pancino; A. G. A. Brown; G. Holland; P. W. Burgess; P. Osborne; G. Altavilla; M. Gebran; S. Ragaini; S. Galleti; G. Cocozza; S. Marinoni; M. Bellazzini; A. Bragaglia; L. Federici; L. Balaguer-Núñez
Astronomy and Astrophysics · DOI ↗
D. W. Evans; M. Riello; F. De Angeli; G. Busso; F. van Leeuwen; C. Jordi; C. Fabricius; Brown, A. G. A.; J. M. Carrasco; H. Voss; M. Weiler; P. Montegriffo; C. Cacciari; P. W. Burgess; P. Osborne
arXiv (Cornell University) · DOI ↗
Aims. The photometric validation of the Gaia DR1 release of the ESA Gaia mission is described and the quality of the data shown. Methods. This is carried out via an internal analysis of the photometry using the most constant sources. Comparisons with external photometric catalogues are also made, but are limited by the accuracies and systematics present in these catalogues. An analysis of the quoted errors is also described. Investigations of the calibration coefficients reveal some of the systematic effects that affect the fluxes. Results. The analysis of the constant sources shows that the early-stage photometric calibrations can reach an accuracy as low as 3 mmag.
D. W. Evans; M. Riello; F. De Angeli; G. Busso; F. van Leeuwen; L. Eyer; C. Jordi; C. Fabricius; J. M. Carrasco; M. Weiler; P. Montegriffo; C. Cacciari; E. Pancino
Proceedings of the International Astronomical Union · DOI ↗
Abstract Gaia DR1 was released in September 2016 and contained a photometric catalogue of over 1 billion sources. At this stage, this only included mean G-band photometry and an estimate of the error. Even though this may sound limited in nature, interesting science can still be achieved with this data thanks to its quality. A high level overview of the photometric processing and some validation results will be presented. Additionally, epoch photometry in the G-band was released in Gaia DR1 for a small number of variable sources in the South Ecliptic Pole which covers the LMC. The second data release (Gaia DR2) is currently being prepared and, if available, some preliminary validation results will be presented. It is planned that this release will contain colour information in the form of integrated BP and RP photometry in addition to the latest G-band photometry.
Marco Delbò; L. Galluccio; F. De Angeli; F. Mignard; A. Cellino; P. Tanga
HAL (Le Centre pour la Communication Scientifique Directe)
International audience
A. G. Butkevich; Sergei A. Klioner; L. Lindegren; D. Hobbs; F. van Leeuwen
Springer Link (Chiba Institute of Technology) · DOI ↗
Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as H<ns0:sc>ipparcos </ns0:sc>or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims. We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods. The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results. In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If these kinds of perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than H<ns0:sc>ipparcos</ns0:sc>. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.
Ł. Wyrzykowski; Krzysztof A. Rybicki; K. Kruszyńska; M. Gromadzki; P. Zieliski; Z. Kostrzewa-Rutkowska; S. T. Hodgkin
Proceedings of the International Astronomical Union · DOI ↗
Abstract As shown by recent gravitational wave detections, galaxies harbour an unknown population of black holes at high masses. In our Galaxy such dark objects can be found and studied solely via gravitational microlensing methods. This paper described our search for black-hole lenses both in archived OGLE data and among on-going microlensing events found by OGLE and Gaia . That combination of superb time-domain astrometry and photometry will enable us to derive masses and distances to these dark lenses uniquely, and to describe the demographics of the unseen component of the Milky Way.
Jeffrey D. Simpson; G. M. De Silva; Sarah L. Martell; D. B. Zucker; A. M. N. Ferguson; Edouard J. Bernard; M. J. Irwin; Jorge Peñarrubia; Eline Tolstoy
Monthly Notices of the Royal Astronomical Society · DOI ↗
International audience
T. Wevers; P. G. Jonker; S. T. Hodgkin; Z. Kostrzewa-Rutkowska; D. L. Harrison; Guy Rixon; G. Nelemans; M. Roelens; L. Eyer; F. van Leeuwen; Abdullah Yoldaş
Monthly Notices of the Royal Astronomical Society · DOI ↗
The ESA Gaia satellite scans the whole sky with a temporal sampling ranging from seconds and hours to months. Each time a source passes within the Gaia field of view, it moves over 10 charge coupled devices (CCDs) in 45 s and a light curve with 4.5 s sampling (the crossing time per CCD) is registered. Given that the 4.5 s sampling represents a virtually unexplored parameter space in optical time domain astronomy, this data set potentially provides a unique opportunity to open up the fast transient sky. We present a method to start mining the wealth of information in the per CCD Gaia data. We perform extensive data filtering to eliminate known onboard and data processing artefacts, and present a statistical method to identify sources that show transient brightness variations on 2 h time-scales. We illustrate that by using the Gaia photometric CCD measurements, we can detect transient brightness variations down to an amplitude of 0.3 mag on time-scales ranging from 15 s to several hours. We search an area of 23.5 deg 2 on the sky and find four strong candidate fast transients. Two candidates are tentatively classified as flares on M-dwarf stars, while one is probably a flare on a giant star and one potentially a flare on a solar-type star. These classifications are based on archival data and the time-scales involved. We argue that the method presented here can be added to the existing Gaia Science Alerts infrastructure for the near real-time public dissemination of fast transient events.
S. Dye; A. Lawrence; Mike Read; Xiaohui Fan; Tom Kerr; W. P. Varricatt; K Furnell; A. C. Edge; M. J. Irwin; N. C. Hambly; P. W. Lucas; O. Almaini; K. C. Chambers; R. Green; P. C. Hewett; Michael C. Liu; Ian D. McGreer; William M. J. Best; Zhoujian Zhang; E. Sutorius; D. Froebrich; E. A. Magnier; G. Hasinger; Susan M. Lederer; Matthew Bold; Jonathan Tedds
Monthly Notices of the Royal Astronomical Society · DOI ↗
This paper defines the UK Infra-Red Telescope (UKIRT) Hemisphere Survey (UHS) and release of the remaining ∼12 700 deg2 of J-band survey data products. The UHS will provide continuous J- and K-band coverage in the Northern hemisphere from a declination of 0° to 60° by combining the existing Large Area Survey, Galactic Plane Survey and Galactic Clusters Survey conducted under the UKIRT Infra-red Deep Sky Survey (UKIDSS) programme with this new additional area not covered by UKIDSS. The released data include J-band imaging and source catalogues over the new area, which, together with UKIDSS, completes the J-band UHS coverage over the full ∼17 900 deg2 area. 98 per cent of the data in this release have passed quality control criteria. The remaining 2 per cent have been scheduled for re-observation. The median 5σ point source sensitivity of the released data is 19.6 mag (Vega). The median full width at half-maximum of the point spread function across the data set is 0.75 arcsec. In this paper, we outline the survey management, data acquisition, processing and calibration, quality control and archiving as well as summarizing the characteristics of the released data products. The data are initially available to a limited consortium with a world-wide release scheduled for 2018 August.
C. Gónzalez-Fernández; S. T. Hodgkin; M. J. Irwin; E. González-Solares; S. E. Koposov; J. R. Lewis; J. P. Emerson; P. C. Hewett; A. Yoldaş; M. Riello
Monthly Notices of the Royal Astronomical Society · 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) < 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.
A. Cellino; P. Tanga; Marco Delbò; L. Galluccio; Philippe Bendjoya; F. De Angeli
Proceedings of the International Astronomical Union · DOI ↗
Abstract A new asteroid taxonomy will be an important result of Gaia observations of Solar System objects. Since Gaia observes asteroids in observing conditions and in an interval of wavelength which are slightly different with respect to normal ground-based observations, a dedicated observing campaign has been carried out at the Telescopio Nazionale Galileo in La Palma (Canary Islands, Spain). The obtained spectra have been used to generate a large number of synthetic clones, each one having slight changes with respect to its parent spectrum. These synthetic spectra are then used to feed the algorithm of taxonomic classification developed to reduce Gaia asteroid spectra. Processing of these data is in progress.
N. A. Walton; M. Rejkuba; J. R. Walsh; Albert A. Zijstra
Proceedings of the International Astronomical Union · DOI ↗
Abstract This paper comments on the use Gaia in studying the internal dynamics and morphologies of Planetary Nebulae (PN). It is noted that the second and subsequent releases of Gaia data, will have significant potential in unravelling PN morphologies.