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.
F. van Leeuwen; D. W. Evans; F. De Angeli; C. Jordi; G. Busso; C. Cacciari; M. Riello; E. Pancino; G. Altavilla; A. G. A. Brown; et al.
Astronomy and Astrophysics · DOI
Context. This paper presents an overview of the photometric data that are part of the first Gaia data release.
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. 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
Context. Gaia is an ESA cornerstone mission launched on 19 December 2013 aiming to obtain the most complete and precise 3D map of our Galaxy by observing more than one billion sources. This paper is part of a series of documents explaining the data processing and its results for Gaia Data Release 1, focussing on the G band photometry.
Gerry Gilmore; F. van Leeuwen
Physics World · DOI
The Gaia spacecraft is conducting the most ambitious and thorough census of our galaxy ever attempted, gathering data on 100,000 stars every hour. With the mission's first major data release due this month, Gerry Gilmore and Floor van Leeuwen explain how the spacecraft works and assess its likely impact on the field of astrophysics
Camila Navarrete; Vasily Belokurov; S. E. Koposov; M. J. Irwin; M. Catelan; S. Duffau; A. J. Drake
Monthly Notices of the Royal Astronomical Society · DOI
We take advantage of the deep and wide coverage of the VLT Survey Telescope (VST) ATLAS survey to study the line-of-sight structure of the Sagittarius (Sgr) stellar stream in the Southern hemisphere, only ∼40° away from the progenitor. We use photometrically selected subgiant branch (SGB) stars to reveal a complex debris morphology of the trailing arm and detect at least two clear peaks in the SGB distance modulus distribution. The separation between the two line-of-sight components is at least 5 kpc at the edge of the VST ATLAS footprint, but appears to change along the stream, which allows us to conclude that these detections correspond to two physically independent stellar structures, rather than a mix of co-distant stellar populations within a single stream. Our discovery of a fork in the Sgr trailing arm is verified using blue horizontal branch stars, and our distance measurements are calibrated using RR Lyrae stars from the Catalina Real-Time Transient Survey. Comparing with numerical simulations of the Sgr dwarf disruption, the more distant of the two components in the fork matches perfectly with the track of the trailing debris. However, no obvious counterpart exists in the simulation for the closer line-of-sight component.
G. Torrealba; S. E. Koposov; Vasily Belokurov; M. J. Irwin; Michelle Collins; M. Spencer; Rodrigo Ibata; Mario Mateo; Ana Bonaca; Prashin Jethwa
Monthly Notices of the Royal Astronomical Society · DOI
We announce the discovery of the Aquarius 2 dwarf galaxy, a new distant satellite of the Milky Way, detected on the fringes of the VLT Survey Telescope (VST) ATLAS and the Sloan Digital Sky Survey (SDSS) surveys. The object was originally identified as an overdensity of red giant branch stars, but chosen for subsequent follow-up based on the presence of a strong blue horizontal branch, which was also used to measure its distance of ∼110 kpc. Using deeper imaging from the Inamori-Magellan Areal Camera and Spectrograph camera on the 6.5m Baade and spectroscopy with DEep Imaging Multi-Object Spectrograph on Keck, we measured the satellite's half-light radius 5.1 ± 0.8 arcmin, or ∼160 pc at this distance, and its stellar velocity dispersion of |$5.4^{+3.4}_{-0.9}$| km s−1. With μ = 30.2 mag arcsec−2 and MV = −4.36, the new satellite lies close to two important detection limits: one in surface brightness; and one in luminosity at a given distance, thereby making Aquarius 2 one of the hardest dwarfs to find.
J. Swan; Andrew A. Cole; Eline Tolstoy; M. J. Irwin
Monthly Notices of the Royal Astronomical Society · DOI
We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at ≈8500 Å was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line-of-sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be 〈vrad〉 = −52.8 ± 2.2 km s−1 with dispersion σv = 24.1 km s−1, in agreement with other studies. Ca ii triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was 〈[Fe/H]〉 = −0.84 ± 0.04 with dispersion σ = 0.31 dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars (|$\sigma _{v_{\rm MP}}=27.4$| km s−1; |$\sigma _{v_{\rm MR}}=21.1$| km s−1); combined with the age–metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars.. The low ratio vrot/σv suggests that within the inner 10 arcmin, NGC 6822's stars are dynamically decoupled from the H i gas, and possibly distributed in a thick disc or spheroid structure.
H. J. Farnhill; J. E. Drew; Geert Barentsen; Eduardo A. González-Solares
Monthly Notices of the Royal Astronomical Society · DOI
Following on from the second release of calibrated photometry from IPHAS, the INT/WFC Photometric Hα Survey of the Northern Galactic Plane, we present incompleteness-corrected stellar density maps in the r and i photometric bands. These have been computed to a range of limiting magnitudes reaching to 20th magnitude in r and 19th in i (Vega system), and with different angular resolutions – the highest resolution available being 1 arcmin2. The maps obtained cover 94 per cent of the 1800 square degree IPHAS footprint, spanning the Galactic latitude range, −5° < b < +5°, north of the celestial equator. The corrections for incompleteness, due to confusion and sensitivity loss at the faint limit, have been deduced by the method of artificial source injection. The presentation of this method is preceded by a discussion of other more approximate methods of determining completeness. Our method takes full account of position-dependent seeing and source ellipticity in the survey data base. The application of the star counts to testing reddened Galactic disc models is previewed by a comparison with predicted counts along three constant-longitude cuts at ℓ ≃ 30°, 90° and 175°: some overprediction of the most heavily reddened ℓ ≃ 30° counts is found, alongside good agreement at ℓ ≃ 90° and 175°.