Showing papers by "Mike Irwin published in 2017"
University of Leicester1, University of Warwick2, University of Cambridge3, Los Alamos National Laboratory4, University of Birmingham5, Stockholm University6, University of Copenhagen7, INAF8, Space Telescope Science Institute9, Spanish National Research Council10, Liverpool John Moores University11, Instituto Politécnico Nacional12, Cardiff University13, University of St Andrews14, Nagoya University15, Max Planck Society16, University of Iceland17, Pontifical Catholic University of Chile18, Monash University19, University of Amsterdam20, ASTRON21, Weizmann Institute of Science22
TL;DR: In this article, the authors reported the discovery and monitoring of the near-infrared counterpart (AT2017gfo) of a binary neutron-star merger event detected as a gravitational wave source by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo (GW170817) and as a short gamma-ray burst by Fermi Gamma-ray Burst Monitor (GBM) and Integral SPI-ACS (GRB 170817A).
Abstract: We report the discovery and monitoring of the near-infrared counterpart (AT2017gfo) of a binary neutron-star merger event detected as a gravitational wave source by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo (GW170817) and as a short gamma-ray burst by Fermi Gamma-ray Burst Monitor (GBM) and Integral SPI-ACS (GRB 170817A). The evolution of the transient light is consistent with predictions for the behavior of a "kilonova/macronova" powered by the radioactive decay of massive neutron-rich nuclides created via r-process nucleosynthesis in the neutron-star ejecta. In particular, evidence for this scenario is found from broad features seen in Hubble Space Telescope infrared spectroscopy, similar to those predicted for lanthanide-dominated ejecta, and the much slower evolution in the near-infrared ${K}_{{\rm{s}}}$-band compared to the optical. This indicates that the late-time light is dominated by high-opacity lanthanide-rich ejecta, suggesting nucleosynthesis to the third r-process peak (atomic masses $A\approx 195$). This discovery confirms that neutron-star mergers produce kilo-/macronovae and that they are at least a major—if not the dominant—site of rapid neutron capture nucleosynthesis in the universe.
600 citations
TL;DR: In this article, the authors reported the discovery and monitoring of the near-infrared counterpart (AT2017gfo) of a binary neutron-star merger event detected as a gravitational wave source by Advanced LIGO/Virgo (GW170817) and as a short gamma-ray burst by Fermi/GBM and Integral/SPI-ACS (GRB 170817A), which is consistent with predictions for the behaviour of a "kilonova/macronova", powered by the radioactive decay of massive neutron-rich nucl
Abstract: We report the discovery and monitoring of the near-infrared counterpart (AT2017gfo) of a binary neutron-star merger event detected as a gravitational wave source by Advanced LIGO/Virgo (GW170817) and as a short gamma-ray burst by Fermi/GBM and Integral/SPI-ACS (GRB170817A). The evolution of the transient light is consistent with predictions for the behaviour of a "kilonova/macronova", powered by the radioactive decay of massive neutron-rich nuclides created via r-process nucleosynthesis in the neutron-star ejecta. In particular, evidence for this scenario is found from broad features seen in Hubble Space Telescope infrared spectroscopy, similar to those predicted for lanthanide dominated ejecta, and the much slower evolution in the near-infrared Ks-band compared to the optical. This indicates that the late-time light is dominated by high-opacity lanthanide-rich ejecta, suggesting nucleosynthesis to the 3rd r-process peak (atomic masses A~195). This discovery confirms that neutron-star mergers produce kilo-/macronovae and that they are at least a major - if not the dominant - site of rapid neutron capture nucleosynthesis in the universe.
436 citations
TL;DR: In this article, the first parallax measurements of the primary standard candles of the cosmological distance ladder, that involve astrometry collected by Gaia during the initial 14 months of science operation, are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS).
Abstract: Parallaxes for 331 classical Cepheids, 31 Type II Cepheids and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, that involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity ($PL$), period-Wesenheit ($PW$) relations for classical and Type II Cepheids and infrared $PL$, $PL$-metallicity ($PLZ$) and optical luminosity-metallicity ($M_V$-[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS. The new relations were computed using multi-band ($V,I,J,K_{\mathrm{s}},W_{1}$) photometry and spectroscopic metal abundances available in the literature, and applying three alternative approaches: (i) by linear least squares fitting the absolute magnitudes inferred from direct transformation of the TGAS parallaxes, (ii) by adopting astrometric-based luminosities, and (iii) using a Bayesian fitting approach. TGAS parallaxes bring a significant added value to the previous Hipparcos estimates. The relations presented in this paper represent first Gaia-calibrated relations and form a "work-in-progress" milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia's Data Release 2 (DR2) in 2018.
105 citations
University of Cambridge1, University of Barcelona2, INAF3, Instituto Politécnico Nacional4, Leiden University5, University of Edinburgh6, Rutherford Appleton Laboratory7, University of Copenhagen8, University of Leicester9, University of Warsaw10, Open University11, University of Bordeaux12, Serco Group13, Notre Dame University – Louaize14, University of Geneva15, University of Lisbon16, Kapteyn Astronomical Institute17, University of Rome Tor Vergata18, Radboud University Nijmegen19
TL;DR: In this article, the authors present an overview of the photometric data that are part of the first Gaia data release, and the overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases.
Abstract: Context. This paper presents an overview of the photometric data that are part of the first Gaia data release. Aims. The principles of the processing and the main characteristics of the Gaia photometric data are presented. Methods. The calibration strategy is outlined briefly and the main properties of the resulting photometry are presented. Results. Relations with other broadband photometric systems are provided. The overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases.
75 citations
TL;DR: The work in this paper was partially financially supported by a 2015 ESO DGDF grant, which was used for a three-week visit to the Institute of Astronomy of the Netherlands.
Abstract: This study
was partially financially supported by a 2015 ESO DGDF
grant. NK acknowledges financial support from IAC for a
three-weeks visit to the institute. GB gratefully acknowledges
support through a Marie- Curie action Intra European Fellowship, funded by the European Union Seventh
Framework Program (FP7/2007-2013) under Grant agreement
number PIEF-GA-2010-274151, as well as the financial
support by the Spanish Ministry of Economy and Competitiveness
(MINECO) under the Ramon y Cajal Programme
(RYC-2012-11537). AC was supported by a fellowship from
the Netherlands Research School for Astronomy (NOVA).
This work made extensive use of the NASA Astrophysics
Data System bibliographic services. This research used the
facilities of the Canadian Astronomy Data Centre operated
by the National Research Council of Canada with the support
of the Canadian Space Agency.
73 citations
University of Minnesota1, University of La Laguna2, University of Washington3, University of Texas at Austin4, University of Tasmania5, Raytheon6, Space Telescope Science Institute7, University of Cambridge8, Centre national de la recherche scientifique9, Max Planck Society10, University of Zurich11, ETH Zurich12, National Research Council13, University of Victoria14
TL;DR: In this article, the Initial Star formation and Lifetimes of Andromeda Satellites (ISLAndS) project employed Hubble Space Telescope imaging to study a representative sample of six Andromeda dSph satellite companion galaxies.
Abstract: The Initial Star formation and Lifetimes of Andromeda Satellites (ISLAndS) project employs Hubble Space Telescope imaging to study a representative sample of six Andromeda dSph satellite companion galaxies. Our main goal is to determine whether the star formation histories (SFHs) of the Andromeda dSph satellites demonstrate significant statistical differences from those of the Milky Way (MW). Our deep observations yield a time resolution at the oldest ages of ∼1 Gyr, allowing meaningful comparisons to the MW satellites. The six dSphs present a variety of SFHs (e.g., a significant range in quenching times, τq, from 9 to 6 Gyr ago) that are not strictly correlated with luminosity or present distance from M31. In agreement with observations of MW companions of similar mass, there is no evidence of complete quenching of star formation by the cosmic UV background responsible for reionization, but the possibility of a degree of quenching at reionization cannot be ruled out. We do not find significant differences between the SFHs of the members and non-members of the vast, thin plane of satellites. The SFHs of the ISLAndS M31 dSphs appear to be more uniform than those of the MW dSphs. Specifically, the primary difference between the SFHs of the ISLAndS dSphs and MW dSph companions of similar luminosities and host distances is the absence of late-quenching (τq ⩽ 5 Gyr) dSphs in the ISLAndS sample. Thus, models that can produce satellite populations with and without late-quenching satellites are of extreme interest.
62 citations
TL;DR: In this paper, the authors used the Vista Variables in Via Lactea (VVV) survey data to study the structure of the inner Milky Way using the latest data release of the VVV survey.
Abstract: We study the structure of the inner Milky Way using the latest data release of the Vista Variables in Via Lactea (VVV) survey. The VVV is a deep near-infrared, multi-colour photometric survey with a coverage of 300 square degrees towards the Bulge/Bar. We use Red Clump (RC) stars to produce a high-resolution dust map of the VVV's field of view. From de-reddened colour-magnitude diagrams we select Red Giant Branch stars to investigate their 3D density distribution within the central 4 kpc. We demonstrate that our best-fit parametric model of the Bulge density provides a good description of the VVV data, with a median percentage residual of 5$\%$ over the fitted region. The strongest of the otherwise low-level residuals are overdensities associated with a low-latitude structure as well as the so-called X-shape previously identified using the split RC. These additional components contribute only $\sim5\%$ and $\sim7\%$ respectively to the Bulge mass budget. The best-fit Bulge is `boxy' with an axis ratio of [1:0.44:0.31] and is rotated with respect to the Sun-Galactic Centre line by at least $20^{\circ}$. We provide an estimate of the total, full sky, mass of the Bulge of $M_\mathrm{Bulge}^{\mathrm{Chabrier}} = 2.36 \times 10^{10} M_{\odot}$ for a Chabrier initial mass function. We show there exists a strong degeneracy between the viewing angle and the dispersion of the Red Clump absolute magnitude distribution. The value of the latter is strongly dependent on the assumptions made about the intrinsic luminosity function of the Bulge.
58 citations
Andrés Bello National University1, Heidelberg University2, Pontifical Catholic University of Chile3, European Southern Observatory4, University of Antofagasta5, University of La Serena6, University of São Paulo7, Universidade Federal do Rio Grande do Sul8, Valparaiso University9, National University of Cordoba10, University of Concepción11, Queen Mary University of London12, University of Kent13, University of Leeds14, University of Cambridge15, University of Hertfordshire16, Mount Saint Vincent University17, Saint Mary's University18, Catholic University of the North19, Universidade Federal de Santa Catarina20
TL;DR: In this article, Minniti et al. presented a study of the evolution of the Earth's magnetic field in the context of Cordoba Astronomical Observatorio Astronomico de Cordoba.
Abstract: Fil: Minniti, Dante. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina
58 citations
TL;DR: In this article, the authors used deep multi-epoch near-IR images of the VISTA Variables in the Via Lactea (VVV) Survey to search for RR Lyrae stars towards the Southern Galactic plane.
Abstract: We use deep multi-epoch near-IR images of the VISTA Variables in the Via Lactea (VVV) Survey to search for RR Lyrae stars towards the Southern Galactic plane. Here we report the discovery of a group of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster, that matches the position of the previously known star cluster FSR\,1716. The stellar density map of the field yields a $>100$ sigma detection for this candidate globular cluster, that is centered at equatorial coordinates $RA_{J2000}=$16:10:30.0, $DEC_{J2000}=-$53:44:56; and galactic coordinates $l=$329.77812, $b=-$1.59227. The color-magnitude diagram of this object reveals a well populated red giant branch, with a prominent red clump at $K_s=13.35 \pm 0.05$, and $J-K_s=1.30 \pm 0.05$. We present the cluster RR Lyrae positions, magnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with age $>10$ Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, $ =0.540$ days, and argue that this is a relatively metal-poor cluster with $[Fe/H] = -1.5 \pm 0.4$ dex. The mean extinction and reddening for this cluster are $A_{K_s}=0.38 \pm 0.02$, and $E(J-K_s)=0.72 \pm 0.02$ mag, respectively, as measured from the RR Lyrae colors and the near-IR color-magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is $(m-M)_0 = 14.38 \pm 0.03$ mag, implying a distance $D = 7.5 \pm 0.2$ kpc, and a Galactocentric distance $R_G=4.3$ kpc.
51 citations
Heidelberg University1, Saint Mary's University2, Mount Saint Vincent University3, Andrés Bello National University4, European Southern Observatory5, University of Antofagasta6, Pontifical Catholic University of Chile7, University of Edinburgh8, University of Cambridge9, University of Hertfordshire10, Universidade Federal de Santa Catarina11
TL;DR: In this article, an author created, un-copyedited version of an article published in The Astronomical Journal was published under embargo, under the name of "The Version of Record".
Abstract: This is an author created, un-copyedited version of an article published in The Astronomical Journal. Under embargo. Embargo end date: 27 March 2018. IOP Publishing is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi: https://doi.org/10.3847/1538-3881/aa5be4.
37 citations
TL;DR: Lymphocyte density in pre-treatment biopsies was validated as an independent predictor of pCR in breast cancer and Computational pathology is emerging as a viable and objective means of identifying predictive biomarkers for cancer patients.
Heidelberg University1, Mount Saint Vincent University2, Saint Mary's University3, Andrés Bello National University4, European Southern Observatory5, University of Antofagasta6, Pontifical Catholic University of Chile7, University of Edinburgh8, University of Cambridge9, University of Hertfordshire10, Universidade Federal de Santa Catarina11
TL;DR: In this article, a sample of 404 RR Lyrae of type ab stars was identified across a thin slice of the 4$^{\rm th}$ Galactic quadrant, and the sample's spatial distribution presented evidence of density enhancements and substructure that warrants further investigation.
Abstract: Deep near-IR images from the VISTA Variables in the Via Lactea (VVV) Survey were used to search for RR Lyrae stars in the Southern Galactic plane. A sizable sample of 404 RR Lyrae of type ab stars was identified across a thin slice of the 4$^{\rm th}$ Galactic quadrant ($295°< l < 350°$, $-2.24°< b < -1.05°$). The sample's distance distribution exhibits a maximum density that occurs at the bulge tangent point, which implies that this primarily Oosterhoff type I population of RRab stars does not trace the bar delineated by their red clump counterparts. The bulge RR Lyrae population does not extend beyond $l \sim340 °$, and the sample's spatial distribution presents evidence of density enhancements and substructure that warrants further investigation. Indeed, the sample may be employed to evaluate Galactic evolution models, and is particularly lucrative since half of the discovered RR Lyrae are within reach of Gaia astrometric observations.
TL;DR: In this paper, the deep and wide V and I-c photometry of the Sextans dwarf spheroidal galaxy (dSph) was presented by the Suprime-Cam imager on the Subaru Telescope, which extends out to the tidal radius.
Abstract: We present the deep and wide V and I-c photometry of the Sextans dwarf spheroidal galaxy (dSph) taken by the Suprime-Cam imager on the Subaru Telescope, which extends out to the tidal radius. The colour-magnitude diagram (CMD) reaches two magnitudes below the main-sequence (MS) turn-off, showing a steep red giant branch, a blue and a red horizontal branch (BHB and RHB, respectively), a sub-giant branch (SGB), an MS and blue stragglers (BSs). We construct the radial profile of each evolutionary phase and demonstrate that blue HB stars are more spatially extended, while red HB stars are more centrally concentrated than the other components. The colour distribution of SGB stars also varies with the galactocentric distance; the inner SGB stars shift bluer than those in the outskirts. The radial differences in the CMD morphology indicate the existence of the age gradient. The relatively younger stars (similar to 10 Gyr) are more centrally concentrated than the older ones (similar to 13 Gyr). The spatial contour maps of stars in different age bins also show that the younger population has a higher concentration and higher ellipticity than the older one. We also detect the centrally concentrated bright BS stars, the number of which is consistent with the idea that a part of these stars belongs to the remnant of a disrupted star cluster discovered in the previous spectroscopic studies.
TL;DR: In this article, the authors used integral field spectroscopic (IFS) observations from the Gemini North Multi-Object Spectrograph (GMOS-N) to study the central H II region in a nearby blue compact dwarf (BCD) galaxy NGC 4449.
Abstract: We use integral field spectroscopic (IFS) observations from the Gemini North Multi-Object Spectrograph (GMOS-N) to study the central H II region in a nearby blue compact dwarf (BCD) galaxy NGC 4449. The IFS data enable us to explore the variation of physical and chemical conditions of the star-forming region and the surrounding gas on spatial scales as small as 5.5 pc. Our kinematical analysis shows possible signatures of shock ionisation and shell structures in the surroundings of the star-forming region. The metallicity maps of the region, created using direct T$_e$ and indirect strong line methods (R$_{23}$, O3N2 and N2), do not show any chemical variation. From the integrated spectrum of the central H II region, we find a metallicity of 12 + log(O/H) = 7.88 $\pm$ 0.14 ($\sim$ 0.15$^{+0.06}_{-0.04}$ Z$_{\odot}$) using the direct method. Comparing the central H II region metallicity derived here with those of H II regions throughout this galaxy from previous studies, we find evidence of increasing metallicity with distance from the central nucleus. Such chemical inhomogeneities can be due to several mechanisms, including gas-loss via supernova blowout, galactic winds, or metal-poor gas accretion. However, we find that the localised area of decreased metallicity aligns spatially with the peak of star-forming activity in the galaxy, suggesting that gas-accretion may be at play here. Spatially-resolved IFS data for the entire galaxy is required to confirm the metallicity inhomogeneity found in this study, and determine its possible cause.
TL;DR: In this paper, Majewski et al. examined the SDSS-III APOGEE DR12 database for new candidates of the young star cluster Palomar 1, a system with previously reported tidal tails.
Abstract: The SDSS-III APOGEE DR12 is a unique resource to search for stars beyond the tidal radii of star clusters. We have examined the APOGEE DR12 database for new candidates of the young star cluster Palomar 1, a system with previously reported tidal tails (Niederste-Ostholt et al. 2010). The APOGEE ASPCAP database includes spectra and stellar parameters for two known members of Pal 1 (Stars I and II), however these do not agree with the stellar parameters determined from optical spectra by Sakari et al. (2011). We find that the APOGEE analysis of these two stars is strongly affected by the known persistence problem (Majewski et al. 2015; Nidever et al. 2015). By re-examining the individual visits, and removing the blue (and sometimes green) APOGEE detector spectra affected by persistence, then we find excellent agreement in a re-analysis of the combined spectra. These methods are applied to another five stars in the APOGEE field with similar radial velocities and metallicities as those of Pal 1. Only one of these new candidates, Star F, may be a member located in the tidal tail based on its heliocentric radial velocity, metallicity, and chemistry. The other four candidates are not well aligned with the tidal tails, and comparison to the Besancon model (Robin et al. 2003) suggests that they are more likely to be non-members, i.e. part of the Galactic halo. This APOGEE field could be re-examined for other new candidates if the persistence problem can be removed from the APOGEE spectral database.
TL;DR: In this article, the authors confirm the reality of the recently discovered Milky Way stellar cluster Gaia 1 using spectra acquired with the HERMES and AAOmega spectrographs of the Anglo-Australian Telescope.
Abstract: We confirm the reality of the recently discovered Milky Way stellar cluster Gaia 1 using spectra acquired with the HERMES and AAOmega spectrographs of the Anglo-Australian Telescope. This cluster had been previously undiscovered due to its close angular proximity to Sirius, the brightest star in the sky at visual wavelengths. Our observations identified 41 cluster members, and yielded an overall metallicity of [{Fe}/{H}]=-0.13± 0.13 and barycentric radial velocity of vr = 58.30 ± 0.22 km s-1. These kinematics provide a dynamical mass estimate of 12.9^{+4.6}_{-3.9}× 10^3 M_{⊙}. Isochrone fits to Gaia, 2MASS, and Pan-STARRS1 photometry indicate that Gaia 1 is an intermediate age (˜3 Gyr) stellar cluster. Combining the spatial and kinematic data we calculate Gaia 1 has a circular orbit with a radius of about 12 kpc, but with a large out of plane motion: z_{max}=1.1^{+0.4}_{-0.3} kpc. Clusters with such orbits are unlikely to survive long due to the number of plane passages they would experience.
29 Aug 2017
TL;DR: 4MOST is a new wide-field, high-multiplex spectroscopic survey facility for the VISTA telescope of ESO, which will deploy 2400 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle as mentioned in this paper.
Abstract: 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. (Less)
TL;DR: 4MOST is a new wide-field, high-multiplex spectroscopic survey facility for the VISTA telescope of ESO, which will deploy more than 2400 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle.
Abstract: 4MOST is a new wide-field, high-multiplex spectroscopic survey facility for the VISTA telescope of ESO. Starting in 2022, 4MOST will deploy more than 2400 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. In this ontribution 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 our 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.