In the last 30 days

• Open/close Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

  Adam G. Riess et al. 1998 The Astronomical Journal 116 1009 Tag this article

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  We present spectral and photometric observations of 10 Type Ia supernovae (SNe Ia) in the redshift range 0.16 ≤ z ≤ 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High- z Supernova Search Team and recent results by Riess et al., this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmological parameters: the Hubble constant ( H ₀), the mass density (Ω _M ), the cosmological constant (i.e., the vacuum energy density, Ω _Λ), the deceleration parameter ( q ₀), and the dynamical age of the universe ( t ₀). The distances of the high-redshift SNe Ia are, on average, 10%–15% farther than expected in a low mass density (Ω _M = 0.2) universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., Ω _Λ > 0) and a current acceleration of the expansion (i.e., q ₀ < 0). With no prior constraint on mass density other than Ω _M ≥ 0, the spectroscopically confirmed SNe Ia are statistically consistent with q ₀ < 0 at the 2.8 σ and 3.9 σ confidence levels, and with Ω _Λ > 0 at the 3.0 σ and 4.0 σ confidence levels, for two different fitting methods, respectively. Fixing a "minimal" mass density, Ω _M = 0.2, results in the weakest detection, Ω _Λ > 0 at the 3.0 σ confidence level from one of the two methods. For a flat universe prior (Ω _M + Ω _Λ = 1), the spectroscopically confirmed SNe Ia require Ω _Λ > 0 at 7 σ and 9 σ formal statistical significance for the two different fitting methods. A universe closed by ordinary matter (i.e., Ω _M = 1) is formally ruled out at the 7 σ to 8 σ confidence level for the two different fitting methods. We estimate the dynamical age of the universe to be 14.2 ± 1.7 Gyr including systematic uncertainties in the current Cepheid distance scale. We estimate the likely effect of several sources of systematic error, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination. Presently, none of these effects appear to reconcile the data with Ω _Λ = 0 and q ₀ ≥ 0.

• Open/close The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance

  Edward L. Wright et al. 2010 The Astronomical Journal 140 1868 Tag this article

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  The all sky surveys done by the Palomar Observatory Schmidt, the European Southern Observatory Schmidt, and the United Kingdom Schmidt, the InfraRed Astronomical Satellite, and the Two Micron All Sky Survey have proven to be extremely useful tools for astronomy with value that lasts for decades. The Wide-field Infrared Survey Explorer (WISE) is mapping the whole sky following its launch on 2009 December 14. WISE began surveying the sky on 2010 January 14 and completed its first full coverage of the sky on July 17. The survey will continue to cover the sky a second time until the cryogen is exhausted (anticipated in 2010 November). WISE is achieving 5σ point source sensitivities better than 0.08, 0.11, 1, and 6 mJy in unconfused regions on the ecliptic in bands centered at wavelengths of 3.4, 4.6, 12, and 22 μm. Sensitivity improves toward the ecliptic poles due to denser coverage and lower zodiacal background. The angular resolution is 6 1, 6 4, 6 5, and 12 0 at 3.4, 4.6, 12, and 22 μm, and the astrometric precision for high signal-to-noise sources is better than 0 15.

• Open/close Composite Quasar Spectra from the Sloan Digital Sky Survey

  Daniel E. Vanden Berk et al. 2001 The Astronomical Journal 122 549 Tag this article

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  We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ≤ z ≤ 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800–9200 Å at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 Å and reaches a peak signal-to-noise ratio of over 300 per 1 Å resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is 100 km s ^-1, compared with shifts of up to 550 km s ^-1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lyα emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at ≈5000 Å. The frequency power-law index, α _ν, is -0.44 from ≈1300 to 5000 Å and -2.45 redward of ≈5000 Å. The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500–3500 Å, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.

• Open/close Simple, Regular, and Efficient Numerical Integration of Rotational Motion

  Toshio Fukushima 2008 The Astronomical Journal 135 2298 Tag this article

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  Among various formulations to integrate rotational motions numerically, we recommend the integration of the combination of Euler parameters and the angular velocity components referred to the body-fixed reference frame with the renormalization of the Euler parameters at every integration step. This is because the formulation proposed is not only simple and regular, but also stable and precise in studying rotational motions numerically. Its efficiency is not degraded even for almost uniform rotations if their nominal uniform part is separated by Encke's method.

• Open/close A New VLA-Hipparcos Distance to Betelgeuse and its Implications

  Graham M. Harper et al. 2008 The Astronomical Journal 135 1430 Tag this article

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  The distance to the M supergiant Betelgeuse is poorly known, with the Hipparcos parallax having a significant uncertainty. For detailed numerical studies of M supergiant atmospheres and winds, accurate distances are a prerequisite to obtaining reliable estimates for many stellar parameters. New high spatial resolution, multiwavelength, NRAO ³3The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Very Large Array (VLA) radio positions of Betelgeuse have been obtained and then combined with Hipparcos Catalogue Intermediate Astrometric Data to derive new astrometric solutions. These new solutions indicate a smaller parallax, and hence greater distance (197 ± 45 pc), than that given in the original Hipparcos Catalogue (131 ± 30 pc) and in the revised Hipparcos reduction. They also confirm smaller proper motions in both right ascension and declination, as found by previous radio observations. We examine the consequences of the revised astrometric solution on Betelgeuse's interaction with its local environment, on its stellar properties, and its kinematics. We find that the most likely star-formation scenario for Betelgeuse is that it is a runaway star from the Ori OB1 association and was originally a member of a high-mass multiple system within Ori OB1a.

• Open/close The Two Micron All Sky Survey (2MASS)

  M. F. Skrutskie et al. 2006 The Astronomical Journal 131 1163 Tag this article

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  Between 1997 June and 2001 February the Two Micron All Sky Survey (2MASS) collected 25.4 Tbytes of raw imaging data covering 99.998% of the celestial sphere in the near-infrared J (1.25 μm), H (1.65 μm), and K _s (2.16 μm) bandpasses. Observations were conducted from two dedicated 1.3 m diameter telescopes located at Mount Hopkins, Arizona, and Cerro Tololo, Chile. The 7.8 s of integration time accumulated for each point on the sky and strict quality control yielded a 10 σ point-source detection level of better than 15.8, 15.1, and 14.3 mag at the J, H, and K _s bands, respectively, for virtually the entire sky. Bright source extractions have 1 σ photometric uncertainty of <0.03 mag and astrometric accuracy of order 100 mas. Calibration offsets between any two points in the sky are <0.02 mag. The 2MASS All-Sky Data Release includes 4.1 million compressed FITS images covering the entire sky, 471 million source extractions in a Point Source Catalog, and 1.6 million objects identified as extended in an Extended Source Catalog.

• Open/close ALFALFA Discovery of the Nearby Gas-rich Dwarf Galaxy Leo P. II. Optical Imaging Observations

  Katherine L. Rhode et al. 2013 The Astronomical Journal 145 149 Tag this article

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  We present results from ground-based optical imaging of a low-mass dwarf galaxy discovered by the ALFALFA 21 cm H I survey. Broadband ( BVR) data obtained with the WIYN 3.5 m telescope at Kitt Peak National Observatory (KPNO) are used to construct color-magnitude diagrams of the galaxy's stellar population down to V _o ~ 25. We also use narrowband Hα imaging from the KPNO 2.1 m telescope to identify a H II region in the galaxy. We use these data to constrain the distance to the galaxy to be between 1.5 and 2.0 Mpc. This places Leo P within the Local Volume but beyond the Local Group. Its properties are extreme: it is the lowest-mass system known that contains significant amounts of gas and is currently forming stars.

• Open/close K-Corrections and Filter Transformations in the Ultraviolet, Optical, and Near-Infrared

  Michael R. Blanton and Sam Roweis 2007 The Astronomical Journal 133 734 Tag this article

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  Template fits to observed galaxy fluxes allow calculation of K-corrections and conversions among observations of galaxies at various wavelengths. We present a method for creating model-based template sets given a set of heterogeneous photometric and spectroscopic galaxy data. Our technique, nonnegative matrix factorization, is akin to principal component analysis (PCA), except that it is constrained to produce nonnegative templates, it can use a basis set of models (rather than the delta-function basis of PCA), and it naturally handles uncertainties, missing data, and heterogeneous data (including broadband fluxes at various redshifts). The particular implementation we present here is suitable for ultraviolet, optical, and near-infrared observations in the redshift range 0 < z < 1.5. Since we base our templates on stellar population synthesis models, the results are interpretable in terms of approximate stellar masses and star formation histories. We present templates fitted with this method to data from Galaxy Evolution Explorer, Sloan Digital Sky Survey spectroscopy and photometry, the Two Micron All Sky Survey, the Deep Extragalactic Evolutionary Probe, and the Great Observatories Origins Deep Survey. In addition, we present software for using such data to estimate K-corrections.

• Open/close High-Resolution Rotation Curves and Galaxy Mass Models from THINGS

  W. J. G. de Blok et al. 2008 The Astronomical Journal 136 2648 Tag this article

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  We present rotation curves of 19 galaxies from The H I Nearby Galaxy Survey (THINGS). The high spatial and velocity resolution of THINGS make these the highest quality H I rotation curves available to date for a large sample of nearby galaxies, spanning a wide range of H I masses and luminosities. The high quality of the data allows us to derive the geometric and dynamical parameters using H I data alone. We do not find any declining rotation curves unambiguously associated with a cut-off in the mass distribution out to the last measured point. The rotation curves are combined with 3.6 μm data from the Spitzer Infrared Nearby Galaxies Survey to construct mass models. Our best-fit dynamical disk masses, derived from the rotation curves, are in good agreement with photometric disk masses derived from the 3.6 μm images in combination with stellar population synthesis arguments and two different assumptions for the stellar initial mass function (IMF). We test the cold dark matter (CDM) motivated cusp model, and the observationally motivated central density core model and find that (independent of IMF) for massive, disk-dominated galaxies, all halo models fit apparently equally well; for low-mass galaxies, however, a core-dominated halo is clearly preferred over a cusp-like halo. The empirically derived densities of the dark matter halos of the late-type galaxies in our sample are half of what is predicted by CDM simulations, again independent of the assumed IMF.

• Open/close The Sloan Digital Sky Survey Quasar Catalog. V. Seventh Data Release

  Donald P. Schneider et al. 2010 The Astronomical Journal 139 2360 Tag this article

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  We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which contains 105,783 spectroscopically confirmed quasars, represents the conclusion of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS objects that have luminosities larger than M _i = –22.0 (in a cosmology with H ₀ = 70 km s ^–1 Mpc ^–1, Ω _M = 0.3, and Ω _Λ = 0.7), have at least one emission line with FWHM larger than 1000 km s ^–1 or have interesting/complex absorption features, are fainter than i 15.0, and have highly reliable redshifts. The catalog covers an area of 9380 deg ². The quasar redshifts range from 0.065 to 5.46, with a median value of 1.49; the catalog includes 1248 quasars at redshifts greater than 4, of which 56 are at redshifts greater than 5. The catalog contains 9210 quasars with i < 18; slightly over half of the entries have i < 19. For each object the catalog presents positions accurate to better than 0 1 rms per coordinate, five-band ( ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 Å at a spectral resolution of 2000; the spectra can be retrieved from the SDSS public database using the information provided in the catalog. Over 96% of the objects in the catalog were discovered by the SDSS. We also include a supplemental list of an additional 207 quasars with SDSS spectra whose archive photometric information is incomplete.