Gemini South Observatory

We present the first public version (v0.2) of the open-source and community-developed Python package, Astropy. This package provides core astronomy-related functionality to the community, including support for domain-specific file formats such as flexible image transport system (FITS) files, Virtual Observatory (VO) tables, and common ASCII table formats, unit and physical quantity conversions, physical constants specific to astronomy, celestial coordinate and time transformations, world coordinate system (WCS) support, generalized containers for representing gridded as well as tabular data, and a framework for cosmological transformations and conversions. Significant functionality is under activedevelopment, such as a model fitting framework, VO client and server tools, and aperture and point spread function (PSF) photometry tools. The core development team is actively making additions and enhancements to the current code base, and we encourage anyone interested to participate in the development of future Astropy versions.

Abstract The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of the Astropy Project is the core package astropy , which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package, as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of interoperable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy Project.

We present five new satellites of the Milky Way discovered in Sloan Digital Sky Survey (SDSS) imaging data, four of which were followed up with either the Subaru or the Isaac Newton Telescopes. They include four probable new dwarf galaxies-one each in the constellations of Coma Berenices, Canes Venatici, Leo, and Hercules-together with one unusually extended globular cluster, Segue 1. We provide distances, absolute magnitudes, half-light radii, and color-magnitude diagrams for all five satellites. The morphological features of the color-magnitude diagrams are generally well described by the ridge line of the old, metal-poor globular cluster M92. In the past two years, a total of 10 new Milky Way satellites with effective surface brightness muv>~28 mag arcsec-2 have been discovered in SDSS data. They are less luminous, more irregular, and apparently more metal-poor than the previously known nine Milky Way dwarf spheroidals. The relationship between these objects and other populations is discussed. We note that there is a paucity of objects with half-light radii between ~40 and ~100 pc. We conjecture that this may represent the division between star clusters and dwarf galaxies. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Merging neutron stars offer an excellent laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart (EM170817) with gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic data set, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultrarelativistic jets. Instead, we suggest that breakout of a wide-angle, mildly relativistic cocoon engulfing the jet explains the low-luminosity gamma rays, the high-luminosity ultraviolet-optical-infrared, and the delayed radio and x-ray emission. We posit that all neutron star mergers may lead to a wide-angle cocoon breakout, sometimes accompanied by a successful jet and sometimes by a choked jet.

The ACS Virgo Cluster Survey consists of HST ACS imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W and F850LP filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of ~23 Mpc and are members of the W' cloud. The remaining 79 galaxies have a narrow distribution around our adopted mean distance of 16.5+/-0.1 (random mean error) +/-1.1 Mpc (systematic). The rms distance scatter of this sample is 0.6+/-0.1 Mpc, with little dependence on morphological type or luminosity class (i.e., 0.7+/-0.1 and 0.5+/-0.1 Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of galaxies is 2.4+/-0.4 Mpc (i.e., +/-2sigma of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16.7+/-0.2 and 16.4+/-0.2 Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1:0.7:0.5). The principal axis of the best-fit ellipsoid is inclined ~20-40 deg. from the line of sight, while the galaxies belonging to the W' cloud lie on an axis inclined by ~10-15 deg.

Early results are reported from the SAURON survey of the kinematics and stellar populations of a representative sample of nearby E, S0 and Sa galaxies. The survey is aimed at determining the intrinsic shape of the galaxies, their orbital structure, the mass-to-light ratio as a function of radius, the age and metallicity of the stellar populations, and the frequency of kinematically decoupled cores and nuclear black holes. The construction of the representative sample is described, and its properties are illustrated. A comparison with long-slit spectroscopic data establishes that the SAURON measurements are comparable to, or better than, the highest-quality determinations. Comparisons are presented for NGC 3384 and 4365, where stellar velocities and velocity dispersions are determined to a precision of 6 km s 21 , and the h 3 and h 4 parameters of the line-of-sight velocity distribution to a precision of better than 0.02. Extraction of accurate gas emission-line intensities, velocities and linewidths from the data cubes is illustrated for NGC 5813. Comparisons with published line strengths for NGC 3384 and 5813 reveal uncertainties of & 0.1 A on the measurements of the Hb, Mg b and Fe5270 indices. Integral-field mapping uniquely connects measurements of the kinematics and stellar populations to the galaxy morphology. The maps presented here illustrate the rich stellar kinematics, gaseous kinematics, and line-strength distributions of early-type galaxies. The results include the discovery of a thin, edge-on, disc in NGC 3623, confirm the axisymmetric shape of the central region of M32, illustrate the LINER nucleus and surrounding counter-rotating star-forming ring in NGC 7742, and suggest a uniform stellar population in the decoupled core galaxy NGC 5813.

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10(-6) and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.

We present the stellar kinematics of 48 representative elliptical and lenticular galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data were homogeneously processed through a dedicated reduction and analysis pipeline. All resulting SAURON datacubes were spatially binned to a constant minimum signal-to-noise. We have measured the stellar kinematics with an optimized (penalized pixel-fitting) routine which fits the spectra in pixel space, via the use of optimal templates, and prevents the presence of emission lines to affect the measurements. We have thus generated maps of the mean stellar velocity, the velocity dispersion, and the Gauss-Hermite moments h3 and h4 of the line-of-sight velocity distributions. The maps extend to approximately one effective radius. Many objects display kinematic twists, kinematically decoupled components, central stellar disks, and other peculiarities, the nature of which will be discussed in future papers of this series.

We present 0.6-2.5 mum, Rgreater than or similar to400 spectra of 27 cool, low-luminosity stars and substellar objects. Based on these and previously published spectra, we develop a preliminary spectral classification system for L and T dwarfs. For late L and T types the classification system is based entirely on four spectral indices in the 1-2.5 mum interval. Two of these indices are derived from water absorption bands at 1.15 and 1.4 km, the latter of which shows a smooth increase in depth through the L and T sequences and can be used to classify both spectral types. The other two indices make use of methane absorption features in the H and K bands, with the K-band index also applicable to mid-to-late L dwarfs. Continuum indices shortward of 1 mum used by previous authors to classify L dwarfs are found to be useful only through mid-L subclasses. We employ the 1.5 mum water index and the 2.2 mum methane index to complete the L classification through L9.5 and to link the new system with a modified version of the 2MASS "color-d" index. By correlating the depths of the methane and water absorption features, we establish a T spectral sequence from T0 to T8, based on all four indices, that is a smooth continuation of the L sequence. We reclassify two 2MASS L8 dwarfs as L9 and L9.5 and identify one SDSS object as L9. In the proposed system methane absorption appears in the K band approximately at L8, two subclasses earlier than its appearance in the H band. The L and T spectral classes are distinguished by the absence and presence, respectively, of H-band methane absorption.

Abstract We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey. This subsample includes six detected planets and three brown dwarfs; from these detections and our contrast curves we infer the underlying distributions of substellar companions with respect to their mass, semimajor axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M * > 1.5 M ⊙ more likely to host planets with masses between 2 and 13 M Jup and semimajor axes of 3–100 au at 99.92% confidence. We fit a double power-law model in planet mass ( m ) and semimajor axis ( a ) for planet populations around high-mass stars ( M * > 1.5 M ⊙ ) of the form , finding α = −2.4 ± 0.8 and β = −2.0 ± 0.5, and an integrated occurrence rate of % between 5–13 M Jup and 10–100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with % of stars hosting a brown dwarf companion between 13–80 M Jup and 10–100 au. Brown dwarfs also appear to be distributed differently in mass and semimajor axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semimajor axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the radial velocity method, our results are consistent with a peak in occurrence of giant planets between ∼1 and 10 au. We discuss how these trends, including the preference of giant planets for high-mass host stars, point to formation of giant planets by core/pebble accretion, and formation of brown dwarfs by gravitational instability.

Context. The ESO public survey VISTA variables in the Vía Láctea (VVV) started in 2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane region and is expected to run for about five years.

To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L $ 0:1Y10 L ) using 3Y38 m Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L $ 10 5 L ). The long-known 6.0 and 6.85 m bands are detected toward all sources, with the Class 0Y type YSOs showing the deepest bands ever observed. The 6.0 m band is often deeper than expected from the bending mode of pure solid H 2 O. The additional 5Y7 m absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%Y30% for CH 3 OH, 3%Y8% for NH 3 , 1%Y5% for HCOOH, $6% for H 2 CO, and $0.3% for HCOO relative to solid H 2 O. The 6.85 m band has one or two carriers, of which one may be less volatile than H 2 O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH 4 -containing salt is the carrier, its abundance relative to solid H 2 O is $7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-rayYinduced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8 m. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution.

With a combination of adaptive optics imaging and a multi-epoch common proper motion search, we have conducted a large volume-limited (D ≤ 75 pc) multiplicity survey of Atype stars, sensitive to companions beyond 30 au. The sample for the Volume-limited

The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy’s early star formation and its entire merging history. We present specific frequencies, luminosities, andmass fractions for the globular cluster systems of 100 early-type galaxies in the ACSVirgo Cluster Survey, the largest homogeneous catalog of its kind.We find the following: (1) GCmass fractions can be high in both giants and dwarfs but are universally low in galaxies with intermediate luminosities. (2) The be-havior of specific frequency across galaxy mass is dominated by the blue GCs. (3) GC fractions of low-mass galaxies exhibit a dependence on environment. Nearly all dwarf galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarfs is biased toward dense environments. (4) GC formation in central dwarfs is biased because their stars form earliest and most intensely. Comparisons to the

Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January -April and August -December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5 m for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 between 3345-9995 . A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935-2.53 m and resolutions 23-33 ) and imaging with broadband JHK s filters. Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012(April -2013)). A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically 15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHK s imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey.

The processing of raw data from modern astronomical instruments is often carried out nowadays using dedicated software, known as pipelines, largely run in automated operation. In this paper we describe the data reduction pipeline of the Multi Unit Spectroscopic Explorer (MUSE) integral field spectrograph operated at the ESO Paranal Observatory. This spectrograph is a complex machine: it records data of 1152 separate spatial elements on detectors in its 24 integral field units. Efficiently handling such data requires sophisticated software with a high degree of automation and parallelization. We describe the algorithms of all processing steps that operate on calibrations and science data in detail, and explain how the raw science data is transformed into calibrated datacubes. We finally check the quality of selected procedures and output data products, and demonstrate that the pipeline provides datacubes ready for scientific analysis.

International audience

We present the results of the Gemini Deep Planet Survey, a near-infrared adaptive optics search for giant planets and brown dwarfs around 85 nearby young stars. The observations were obtained with the Altair adaptive optics sys- tem at the Gemini North telescope, and angular differential imaging was used to suppress the speckle noise of the central star. Typically, the observations are sensitive to angular separations beyond 0.5″ with 5 σ contrast sensitivities in magnitude difference at 1.6 μm of 9.5 at 0.5″, 12.9 at 1″, 15.0 at 2″, and 16.5 at 5″. These sensitivities are sufficient to detect planets more massive than 2 MJ with a projected separation in the range 40-200 AU around a typical target. Second-epoch observations of 48 stars with candidates (out of 54) have confirmed that all candidates are unrelated background stars. A detailed statistical analysis of the survey results is presented. Assuming a planet mass distribution dn/dm oc m-1.2 anda semimajor-axis distribution dn/da ∝ a-1, the 95% credible upper limits on the fraction of stars with at least one planet of mass 0.5-13 MJ are 0.28 for the range 10-25 AU, 0.13 for 25-50 AU, and 0.093 for 50-250 AU; this result is weakly dependent on the semimajor-axis distribution power-law index. The 95% credible interval for the fraction of stars with at least one brown dwarf companion having a semimajor axis in the range 25-250 AU is 0.019-0.015+0.083 irrespective of any assumption on the mass and semimajor-axis distributions. The observations made as part of this survey have resolved the stars HD 14802, HD 166181, and HD 213845 into binaries for the first time. © 2007. The American Astronomical Society. All rights reserved.

We present ZJHKL'M' photometry of a sample of 58 late-M, L, and T dwarfs, most of which are identified from the Sloan Digital Sky Survey and the Two Micron All-Sky Survey. Near-infrared spectra and spectral classifications for most of this sample are presented in a companion paper by Geballe et al. We derive the luminosities of 18 dwarfs in the sample and the results imply that the effective temperature range for the L dwarfs in our sample is approximately 2200-1300 K and for the T dwarfs 1300-800 K. We obtained new photometric data at the United Kingdom Infrared Telescope for: 42 dwarfs at Z, 34 dwarfs at JHK, 21 dwarfs at L', as well as M' data for two L dwarfs and two T dwarfs. The M' data provide the first accurate photometry for L and T dwarfs in this bandpass - for a T2 and a T5 dwarf, we find K-M'=1.2 and 1.6, respectively. These colors are much bluer than predicted by models suggesting that CO may be more abundant in these objects than expected, as has been found for the T6 dwarf Gl 229B. We also find that K-L' increases monotonically through most of the M, L, and T subclasses, but it is almost constant between types L6 and T5. The degeneracy is probably due to the onset of methane absorption at the blue edge of the L' bandpass. The JHK colors of L dwarfs show significant scatter, suggesting that the fluxes in these bandpasses are sensitive to variations in photospheric dust properties. The H-K colors of the later T dwarfs also show some scatter which we suggest is due to variations in pressure-induced molecular hydrogen opacity, which is sensitive to gravity and metallicity.

We present near-infrared observations of 71 newly discovered L and T dwarfs, selected from imaging data of the Sloan Digital Sky Survey (SDSS) using the i-dropout technique. Sixty-five of these dwarfs have been classified spectroscopically according to the near-infrared L dwarf classification scheme of Geballe et al. and the unified T dwarf classification scheme of Burgasser et al. The spectral types of these dwarfs range from L3 to T7, and include the latest types yet found in the SDSS. Six of the newly identified dwarfs are classified as early- to mid-L dwarfs according to their photometric near-infrared colors, and two others are classified photometrically as M dwarfs. We also present new near-infrared spectra for five previously published SDSS L and T dwarfs, and one L dwarf and one T dwarf discovered by Burgasser et al. from the Two Micron All Sky Survey. The new SDSS sample includes 27 T dwarfs and 30 dwarfs with spectral types spanning the complex L-T transition (L7-T3). We continue to see a large (~0.5 mag) spread in J-H for L3 to T1 types, and a similar spread in H-K for all dwarfs later than L3. This color dispersion is probably due to a range of grain sedimentation properties, metallicity, and gravity. We also find L and T dwarfs with unusual colors and spectral properties that may eventually help to disentangle these effects.