S. Fabbro

Cea Leti, Grenoble, Rhône-Alpes, France

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Publications (84)222.29 Total impact

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    ABSTRACT: We present cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The data set includes several low-redshift samples (z<0.1), all 3 seasons from the SDSS-II (0.05 < z < 0.4), and 3 years from SNLS (0.2 <z < 1) and totals \ntotc spectroscopically confirmed type Ia supernovae with high quality light curves. We have followed the methods and assumptions of the SNLS 3-year data analysis except for the following important improvements: 1) the addition of the full SDSS-II spectroscopically-confirmed SN Ia sample in both the training of the SALT2 light curve model and in the Hubble diagram analysis (\nsdssc SNe), 2) inter-calibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis, and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN Ia light-curves. We produce recalibrated SN Ia light-curves and associated distances for the SDSS-II and SNLS samples. The large SDSS-II sample provides an effective, independent, low-z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low-z SN sample. For a flat LCDM cosmology we find Omega_m=0.295+-0.034 (stat+sys), a value consistent with the most recent CMB measurement from the Planck and WMAP experiments. Our result is 1.8sigma (stat+sys) different than the previously published result of SNLS 3-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark-energy equation of state parameter w=-1.018+-0.057 (stat+sys) for a flat universe. Adding BAO distance measurements gives similar constraints: w=-1.027+-0.055.
    Astronomy and Astrophysics 01/2014; 568. · 5.08 Impact Factor
  • S. Fabbro, S. Goliath
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    ABSTRACT: We present an approach to deliver astronomy processing software using virtualization and a network file system. User-requested astronomy software applications are built and tested on a dedicated server, and distributed on-demand to cloud-based worker clients using a fast HTTP read-only cache file system. The worker clients are light virtual machines which keep overheads to processing resources very small, while still ensuring the portability of all software applications. The goal is to limit the need for astronomers to carry out software maintenance tasks and to keep consistency between batch processing and interactive analysis sessions. We describe the design and infrastructure of the system, the software building process on the server, and show an application with a multi-frame automated transient detection on a wide field survey, with a batch processing on a cloud infrastructure.
    10/2013;
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    ABSTRACT: We report the discovery of two possible supernovae within a projected distance of <1 Mpc of rich galaxy clusters by the Survey at Intermediate Redshift for Cluster and Lensed Supernovae (SIRCLS).
    The Astronomer's Telegram. 09/2013;
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    ABSTRACT: We present a technique to measure lightcurves of time-variable point sources on a spatially structured background from imaging data. The technique was developed to measure light curves of SNLS supernovae in order to infer their distances. This photometry technique performs simultaneous PSF photometry at the same sky position on an image series. We describe two implementations of the method: one that resamples images before measuring fluxes, and one which does not. In both instances, we sketch the key algorithms involved and present the validation using semi-artificial sources introduced in real images in order to assess the accuracy of the supernova flux measurements relative to that of surrounding stars. We describe the methods required to anchor these PSF fluxes to calibrated aperture catalogs, in order to derive SN magnitudes. We find a marginally significant bias of 2 mmag of the after-resampling method, and no bias at the mmag accuracy for the non-resampling method. Given surrounding star magnitudes, we determine the systematic uncertainty of SN magnitudes to be less than 1.5 mmag, which represents about one third of the current photometric calibration uncertainty affecting SN measurements. The SN photometry delivers several by-products: bright star PSF flux mea- surements which have a repeatability of about 0.6%, as for aperture measurements; we measure relative astrometric positions with a noise floor of 2.4 mas for a single-image bright star measurement; we show that in all bands of the MegaCam instrument, stars exhibit a profile linearly broadening with flux by about 0.5% over the whole brightness range.
    Astronomy and Astrophysics 06/2013; · 5.08 Impact Factor
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    ABSTRACT: The New Horizons spacecraft will fly past Pluto in July 2015 and then continue deeper into the Kuiper Belt, providing an opportunity to encounter one or more small ( 50 km) KBOs. This first flyby of a typical KBO would revolutionize our understanding of these bodies, providing information that can be extrapolated to hundreds of thousands of similar objects in the Kuiper Belt. Statistically, we expect several KBOs with ground based V magnitude less than 26.0 to be accessible with the delta-V available onboard New Horizons. At this point, however, no known KBOs are reachable by the spacecraft. We have therefore begun a dedicated search for suitable targets, using the Subaru, Magellan, and CFHT telescopes. The search is complicated by the fact that targetable objects are currently in the Milky Way, so search depth is limited by confusion with background stars unless seeing is exceptional. As of mid-2012, we have discovered 24 KBOs near the spacecraft trajectory, none of which are accessible to the spacecraft. Several of the targets could be reached with less than twice the available delta-V, and much of the accessible volume has not yet been searched to sufficient depth. Several objects already discovered will be observable at long range from New Horizons, providing opportunities for (for example) searches for binarity with much higher spatial resolution than is possible from Earth. The search has already yielded the second known trailing Neptune Trojan (Parker et al., this conference).
    10/2012;
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    ABSTRACT: After its encounter with Pluto in July of 2015, New Horizons will be capable of performing a course change to target a more distant Kuiper Belt Object. We are currently engaged in a search for one or more candidate Kuiper Belt Objects for New Horizons to visit. In the course of this search, we identified a new L5 Neptune Trojan. This Trojan is as bright as the largest L5 Jupiter Trojan (H 8.2), and has an inclination higher than any other known Neptune Trojan, at 29.4 degrees. We have performed numerical integrations of its orbit and confirmed that it is stably resonant for a large fraction of the age of the Solar System, making it only the second stable L5 Neptune Trojan known. Given our survey's characteristics, the detection of this object confirms that the L5 Neptune Trojans are a large, highly excited population. In addition, we have obtained its photometric colors, a first for an L5 Neptune Trojan, and confirmed that it has a moderately-red color similar to the L4 Neptune Trojan cloud, which are similar to the Jupiter Trojan colors. In late 2013 this object passes within approximately 1.2 AU of the New Horizons spacecraft, and may be within the limits of detection of the LORRI imager. We present the discovery circumstances and our characterization of this Neptune Trojan, and its implications for the Neptune Trojan population. We also introduce a novel statistical technique for debiasing the Neptune Trojan orbit distribution, and compare these debiased orbit distributions to those of other minor planet populations.
    10/2012;
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    ABSTRACT: We present a summary of current efforts to find a Kuiper Belt Object that is within reach of the New Horizons spacecraft after its encounter with Pluto.
    LPI Contributions. 05/2012;
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    ABSTRACT: Our ability to study the most remote supernova explosions, crucial for the understanding of the evolution of the high-redshift universe and its expansion rate, is limited by the light collection capabilities of telescopes. However, nature offers unique opportunities to look beyond the range within reach of our unaided instruments thanks to the light-focusing power of massive galaxy clusters. Here we report on the discovery of one of the most distant supernovae ever found, at redshift z = 1.703. Due to a lensing magnification factor of 4.3 ± 0.3, we are able to measure a light curve of the supernova, as well as spectroscopic features of the host galaxy with a precision comparable to what would otherwise only be possible with future generation telescopes.
    The Astrophysical Journal Letters 10/2011; 742(1):L7. · 6.35 Impact Factor
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    ABSTRACT: The Canadian Advanced Network For Astronomical Research (CANFAR) is an operational system for the delivery, processing, storage, analysis, and distribution of very large astronomical datasets. CANFAR combines the Canadian national research network (CANARIE), grid processing and storage resources (Compute Canada) and a data center (CADC) into a unified Platform-as-a-service (PaaS) cyberinfrastructure supporting Canadian astronomy projects. The CANFAR processing service is based on virtualization and combines features of the grid and cloud processing models to provide a self-configuring virtual cluster deployed on multiple cloud clusters. The service makes use of many technologies from the grid, cloud and Virtual Observatory communities.
    07/2011;
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    ABSTRACT: We present observational constraints on the nature of dark energy using the Supernova Legacy Survey three year sample (SNLS3) of Guy et al. (2010) and Conley et al. (2011). We use the 472 SNe Ia in this sample, accounting for recently discovered correlations between SN Ia luminosity and host galaxy properties, and include the effects of all identified systematic uncertainties directly in the cosmological fits. Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan Digital Sky Survey luminous red galaxy power spectrum, and a prior on the Hubble constant H0 from SHOES, in a flat universe we find omega_m=0.269+/-0.015 and w=-1.061+0.069-0.068 -- a 6.5% measure of the dark energy equation-of-state parameter w. The statistical and systematic uncertainties are approximately equal, with the systematic uncertainties dominated by the photometric calibration of the SN Ia fluxes -- without these calibration effects, systematics contribute only a ~2% error in w. When relaxing the assumption of flatness, we find omega_m=0.271+/-0.015, omega_k=-0.002+/-0.006, and w=-1.069+0.091-0.092. Parameterizing the time evolution of w as w(a)=w_0+w_a(1-a), gives w_0=-0.905+/-0.196, w_a=-0.984+1.094-1.097 in a flat universe. All of our results are consistent with a flat, w=-1 universe. The size of the SNLS3 sample allows various tests to be performed with the SNe segregated according to their light curve and host galaxy properties. We find that the cosmological constraints derived from these different sub-samples are consistent. There is evidence that the coefficient, beta, relating SN Ia luminosity and color, varies with host parameters at >4sigma significance (in addition to the known SN luminosity--host relation); however this has only a small effect on the cosmological results and is currently a sub-dominant systematic.
    The Astrophysical Journal 04/2011; 737(2). · 6.73 Impact Factor
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    ABSTRACT: We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = –0.91+0.16 –0.20(stat)+0.07 –0.14(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems.
    The Astrophysical Journal Supplement Series 12/2010; 192(1):1. · 16.24 Impact Factor
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    ABSTRACT: We present photometric properties and distance measurements of 252 high redshift Type Ia supernovae (0.15 < z < 1.1) discovered during the first three years of the Supernova Legacy Survey (SNLS). These events were detected and their multi-colour light curves measured using the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four one-square degree fields in four bands. Follow-up spectroscopy was performed at the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and to measure their redshifts. Systematic uncertainties arising from light curve modeling are studied, making use of two techniques to derive the peak magnitude, shape and colour of the supernovae, and taking advantage of a precise calibration of the SNLS fields. A flat LambdaCDM cosmological fit to 231 SNLS high redshift Type Ia supernovae alone gives Omega_M = 0.211 +/- 0.034(stat) +/- 0.069(sys). The dominant systematic uncertainty comes from uncertainties in the photometric calibration. Systematic uncertainties from light curve fitters come next with a total contribution of +/- 0.026 on Omega_M. No clear evidence is found for a possible evolution of the slope (beta) of the colour-luminosity relation with redshift. Comment: (The SNLS Collaboration) 40 pages, 32 figures, Accepted in A&A
    10/2010;
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    ABSTRACT: The Canadian Advanced Network For Astronomical Research (CANFAR) is a 2 1/2-year project that is delivering a network-enabled platform for the accessing, processing, storage, analysis, and distribution of very large astronomical datasets. The CANFAR infrastructure is being implemented as an International Virtual Observatory Alliance (IVOA) compliant web service infrastructure. A challenging feature of the project is to channel all survey data through Canadian research cyberinfrastructure. Sitting behind the portal service, the internal architecture makes use of high-speed networking, cloud computing, cloud storage, meta-scheduling, provisioning and virtualisation. This paper describes the high-level architecture and the current state of the project.
    Proc SPIE 07/2010;
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    ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z > 1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation. The flat concordance ΛCDM model remains an excellent fit to the Union2 data with the best-fit constant equation-of-state parameter w = –0.997+0.050 –0.054(stat)+0.077 –0.082(stat + sys together) for a flat universe, or w = –1.038+0.056 –0.059(stat)+0.093 –0.097(stat + sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depends strongly on redshift. In particular, at z 1, the existence and nature of dark energy are only weakly constrained by the data.
    The Astrophysical Journal 05/2010; 716(1):712. · 6.73 Impact Factor
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    ABSTRACT: Spectroscopy of SNLS SN candidates was performed on several 8 to 10-m class telescopes in both hemispheres, namely the VLT, Gemini-N and S, Keck I and II. During the first large program (2003-2005), we performed long slit spectroscopy (LSS) of SN candidates on FORS1 for a total of 60h of dark/grey time per semester. During the second large program (2005-2007), we observed using both FORS1 and FORS2 with the standard collimator in LSS and multi object spectroscopy (MOS) mode. (2 data files).
    VizieR Online Data Catalog. 02/2010;
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    ABSTRACT: We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy Survey and catalogs of galaxies with photometric redshifts, Very Large Array 1.4 GHz radio sources, and Spitzer infrared sources. We present eight SNe Ia in early-type host galaxies which have counterparts in the radio and infrared source catalogs. We find the SN Ia rate in subsets of radio and infrared early-type galaxies is ~1-5 times the rate in all early-type galaxies, and that any enhancement is always 2σ. Rates in these subsets are consistent with predictions of the two-component "A+B" SN Ia rate model. Since infrared properties of radio SN Ia hosts indicate dust-obscured star formation, we incorporate infrared star formation rates into the "A+B" model. We also show the properties of SNe Ia in radio and infrared galaxies suggest the hosts contain dust and support a continuum of delay time distributions (DTDs) for SNe Ia, although other DTDs cannot be ruled out based on our data.
    The Astronomical Journal 01/2010; 139(2):594. · 4.97 Impact Factor
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    ABSTRACT: We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy Survey and catalogs of galaxies with photometric redshifts, VLA 1.4 GHz radio sources, and Spitzer infrared sources. We present eight SNe Ia in early-type host galaxies which have counterparts in the radio and infrared source catalogs. We find the SN Ia rate in subsets of radio and infrared early-type galaxies is ~1-5 times the rate in all early-type galaxies, and that any enhancement is always <~ 2 sigma. Rates in these subsets are consistent with predictions of the two component "A+B" SN Ia rate model. Since infrared properties of radio SN Ia hosts indicate dust obscured star formation, we incorporate infrared star formation rates into the "A+B" model. We also show the properties of SNe Ia in radio and infrared galaxies suggest the hosts contain dust and support a continuum of delay time distributions for SNe Ia, although other delay time distributions cannot be ruled out based on our data. Comment: 14 pages, 6 figures, 7 tables, accepted for publication in AJ
    12/2009;
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    ABSTRACT: Aims. We present 139 spectra of 124 Type Ia supernovae (SNe Ia) that were observed at the ESO/VLT during the first three years of the Canada-France-Hawaï Telescope (CFHT) supernova legacy survey (SNLS). This homogeneous data set is used to test for redshift evolution of SN Ia spectra, and will be used in the SNLS 3rd year cosmological analyses.Methods. Spectra have been reduced and extracted with a dedicated pipeline that uses photometric information from deep CFHT legacy survey (CFHT-LS) reference images to trace, at sub-pixel accuracy, the position of the supernova on the spectrogram as a function of wavelength. It also separates the supernova and its host light in ~60% of cases. The identification of the supernova candidates is performed using a spectrophotometric SN Ia model. Results. A total of 124 SNe Ia, roughly 50% of the overall SNLS spectroscopic sample, have been identified using the ESO/VLT during the first three years of the survey. Their redshifts range from $z = 0.149$ to $z = 1.031$. The average redshift of the sample is $z$ = 0.63$\pm$0.02. This constitutes the largest SN Ia spectral set to date in this redshift range. The spectra are presented along with their best-fit spectral SN Ia model and a host model where relevant. In the latter case, a host subtracted spectrum is also presented. We produce average spectra for pre-maximum, maximum and post-maximum epochs for both $z < 0.5$ and $z$ $\geq$ 0.5 SNe Ia. We find that $z < 0.5$ spectra have deeper intermediate mass element absorptions than $z$ $\geq$ 0.5 spectra. The differences with redshift are consistent with the selection of brighter and bluer supernovae at higher redshift.

    Astronomy and Astrophysics 11/2009; · 5.08 Impact Factor
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    ABSTRACT: We use three years of data from the Supernova Legacy Survey (SNLS) to study the general properties of core-collapse and type Ia supernovae. This is the first such study using the "rolling search" technique which guarantees well-sampled SNLS light curves and good efficiency for supernovae brighter than $i^\prime\sim24$. Using host photometric redshifts, we measure the supernova absolute magnitude distribution down to luminosities $4.5 {\rm mag}$ fainter than normal SNIa. Using spectroscopy and light-curve fitting to discriminate against SNIa, we find a sample of 117 core-collapse supernova candidates with redshifts $z<0.4$ (median redshift of 0.29) and measure their rate to be larger than the type Ia supernova rate by a factor $4.5\pm0.8(stat.) \pm0.6 (sys.)$. This corresponds to a core-collapse rate at $z=0.3$ of $[1.42\pm 0.3(stat.) \pm0.3(sys.)]\times10^{-4}\yr^{-1}(h_{70}^{-1}\Mpc)^{-3}$. Comment: accepted Astronomy and Astrophysics
    Astronomy and Astrophysics 04/2009; · 5.08 Impact Factor
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    ABSTRACT: We report measurements of the mass density, ΩM, and cosmological-constant energy density, ΩΛ, of the universe based on the analysis of 42 type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these supernovae, at redshifts between 0.18 and 0.83, are fitted jointly with a set of supernovae from the Calán/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All supernova peak magnitudes are standardized using a SN Ia light-curve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8ΩM-0.6ΩΛ≈-0.2±0.1 in the region of interest (ΩM1.5). For a flat (ΩM+ΩΛ=1) cosmology we find ΩMflat=0.28+0.09-0.08 (1 σ statistical) +0.05-0.04 (identified systematics). The data are strongly inconsistent with a Λ=0 flat cosmology, the simplest inflationary universe model. An open, Λ=0 cosmology also does not fit the data well: the data indicate that the cosmological constant is nonzero and positive, with a confidence of P(Λ>0)=99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t0flat=14.9+1.4-1.1(0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calán/Tololo sample and our high-redshift sample. Excluding those few supernovae that are outliers in color excess or fit residual does not significantly change the results. The conclusions are also robust whether or not a width-luminosity relation is used to standardize the supernova peak magnitudes. We discuss and constrain, where possible, hypothetical alternatives to a cosmological constant.
    The Astrophysical Journal 01/2009; 517(2):565. · 6.73 Impact Factor

Publication Stats

5k Citations
222.29 Total Impact Points

Institutions

  • 2011
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 2010–2011
    • University of Victoria
      • Department of Physics and Astronomy
      Victoria, British Columbia, Canada
  • 2006–2009
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
  • 2007–2008
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
    • Centra Health
      Lynchburg, Virginia, United States
    • University of Lisbon
      • Departamento de Física
      Lisbon, Lisbon, Portugal
    • Technical University of Lisbon
      • Department of Physics (DF)
      Lisboa, Lisbon, Portugal