Showing papers in "The Astronomical Journal in 2001"
Fermilab1, Pennsylvania State University2, University of Cincinnati3, Princeton University4, Johns Hopkins University5, University of Chicago6, Pontifical Catholic University of Chile7, University of Washington8, New Mexico State University9, California Institute of Technology10, University of Toulouse11, University of Pittsburgh12, Eötvös Loránd University13, University of Tokyo14, University of California, Berkeley15, University of Sussex16, Carnegie Mellon University17, United States Department of the Navy18, Rensselaer Polytechnic Institute19, University of Maryland, College Park20
TL;DR: In this article, a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS) was created, and the median composite covers a restwavelength range from 800 to 8555 A and reaches a peak signal-to-noise ratio of over 300 per 1 A resolution element in the rest frame.
Abstract: 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 A at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 A and reaches a peak signal-to-noise ratio of over 300 per 1 A 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 A. The frequency power-law index, αν, is -0.44 from ≈1300 to 5000 A and -2.45 redward of ≈5000 A. 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 A, 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.
1,973 citations
TL;DR: In this paper, the optical colors of 147,920 galaxies brighter than g* = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over ~100 deg2 of high Galactic latitude sky along the celestial equator.
Abstract: We study the optical colors of 147,920 galaxies brighter than g* = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over ~100 deg2 of high Galactic latitude sky along the celestial equator. The distribution of galaxies in the g*-r* versus u*-g* color-color diagram is strongly bimodal, with an optimal color separator of u*-r* = 2.22. We use visual morphology and spectral classification of subsamples of 287 and 500 galaxies, respectively, to show that the two peaks correspond roughly to early- (E, S0, and Sa) and late-type (Sb, Sc, and Irr) galaxies, as expected from their different stellar populations. We also find that the colors of galaxies are correlated with their radial profiles, as measured by the concentration index and by the likelihoods of exponential and de Vaucouleurs' profile fits. While it is well known that late-type galaxies are bluer than early-type galaxies, this is the first detection of a local minimum in their color distribution. In all SDSS bands, the counts versus apparent magnitude relations for the two color types are significantly different and demonstrate that the fraction of blue galaxies increases toward the faint end.
1,583 citations
TL;DR: In this article, transformation equations are presented to convert colors and magnitudes measured in the AAO, ARNICA, CIT, DENIS, ESO, LCO (Persson standards), MSSSO, SAAO, and UKIRT photometric systems to the photometric system inherent in the 2MASS Second Incremental Data Release.
Abstract: Transformation equations are presented to convert colors and magnitudes measured in the AAO, ARNICA, CIT, DENIS, ESO, LCO (Persson standards), MSSSO, SAAO, and UKIRT photometric systems to the photometric system inherent in the 2MASS Second Incremental Data Release. The transformations have been derived by comparing 2MASS photometry with published magnitudes and colors for stars observed in these systems. Transformation equations have also been derived indirectly for the Bessell & Brett and Koornneef homogenized photometric systems.
1,242 citations
University of Arizona1, University of Chicago2, Fermilab3, Princeton University4, Johns Hopkins University5, University of Pittsburgh6, Carnegie Mellon University7, Yale University8, University of Chile9, University of Tokyo10, New York University11, Space Telescope Science Institute12, California Institute of Technology13, Rochester Institute of Technology14, Pennsylvania State University15, Drexel University16, Ohio State University17
TL;DR: In this paper, the authors describe the target selection and resulting properties of a spectroscopic sample of luminous red galaxies (LRGs) from the imaging data of the Sloan Digital Sky Survey (SDSS).
Abstract: We describe the target selection and resulting properties of a spectroscopic sample of luminous red galaxies (LRGs) from the imaging data of the Sloan Digital Sky Survey (SDSS). These galaxies are selected on the basis of color and magnitude to yield a sample of luminous intrinsically red galaxies that extends fainter and farther than the main flux-limited portion of the SDSS galaxy spectroscopic sample. The sample is designed to impose a passively evolving luminosity and rest-frame color cut to a redshift of 0.38. Additional, yet more luminous red galaxies are included to a redshift of ~0.5. Approximately 12 of these galaxies per square degree are targeted for spectroscopy, so the sample will number over 100,000 with the full survey. SDSS commissioning data indicate that the algorithm efficiently selects luminous (M^+_g ≈ -21.4) red galaxies, that the spectroscopic success rate is very high, and that the resulting set of galaxies is approximately volume limited out to z = 0.38. When the SDSS is complete, the LRG spectroscopic sample will fill over 1 h^(-3) Gpc^3 with an approximately homogeneous population of galaxies and will therefore be well suited to studies of large-scale structure and clusters out to z = 0.5.
1,073 citations
TL;DR: The Washington Double Star Catalog (WDS) as mentioned in this paper contains positions, discoverer designations, epochs, position angles, separations, magnitudes, spectral types, proper motions, and, when available, Durchmusterung numbers and notes for the components of 84,486 systems based on 563,326 means.
Abstract: The Washington Double Star Catalog (WDS), maintained by the US Naval Observatory, is the world's principal database of astrometric double and multiple star information. The WDS contains positions (J2000), discoverer designations, epochs, position angles, separations, magnitudes, spectral types, proper motions, and, when available, Durchmusterung numbers and notes for the components of 84,486 systems based on 563,326 means. The current version, available on-line, is updated nightly. This catalog is one of four USNO double star catalogs to be included on a new CD-ROM. A brief summary and statistical analysis of the contents of the catalog are presented.
941 citations
Princeton University1, University of California, Davis2, Lawrence Livermore National Laboratory3, Space Telescope Science Institute4, Max Planck Society5, University of Hawaii at Manoa6, Pennsylvania State University7, University of Washington8, New Mexico State University9, University of Pittsburgh10, Eötvös Loránd University11, Johns Hopkins University12, University of Tokyo13, University of Chicago14, United States Department of the Navy15, Carnegie Mellon University16, Spanish National Research Council17
TL;DR: In this article, the authors present the results from a survey of i-dropout objects selected from ~1550 deg2 of multicolor imaging data from the Sloan Digital Sky Survey to search for luminous quasars at z 5.8.
Abstract: We present the results from a survey of i-dropout objects selected from ~1550 deg2 of multicolor imaging data from the Sloan Digital Sky Survey to search for luminous quasars at z 5.8. Objects with i*-z* > 2.2 and z* 0.90. The ARC 3.5 m spectrum of SDSSp J103027.10+052455.0 shows that over a range of ~300 A immediately blueward of the Lyα emission, the average transmitted flux is only 0.003 ± 0.020 times that of the continuum level, consistent with zero flux over a ~300 A range of the Lyα forest region and suggesting a tentative detection of the complete Gunn-Peterson trough. The existence of strong metal lines in the quasar spectra suggests early metal enrichment in the quasar environment. The three new objects, together with the previously published z = 5.8 quasar SDSSp J104433.04-012502.2, form a complete color-selected flux-limited sample at z 5.8. We estimate the selection function of this sample, taking into account the estimated variations in the quasar spectral energy distribution, as well as observational photometric errors. We find that at z = 6, the comoving density of luminous quasars at M1450 < -26.8 (H0 = 50 km s-1 Mpc-1, Ω = 1) is 1.1 × 10-9 Mpc-3. This is a factor of ~2 lower than that at z ~ 5 and is consistent with an extrapolation of the observed quasar evolution at z < 5. Using the current sample, we discuss the constraint on the shape of the quasar luminosity function and the implications for the contribution of quasars to the ionizing background at z ~ 6. The luminous quasars discussed in the paper have central black hole masses of several times 109 M⊙ by the Eddington argument, with likely dark halo masses on the order of 1013 M⊙. Their observed space density provides a sensitive test of models of quasar and galaxy formation at high redshift.
924 citations
University of California, Davis1, Lawrence Livermore National Laboratory2, Space Telescope Science Institute3, Princeton University4, Fermilab5, New Mexico State University6, University of Pittsburgh7, Johns Hopkins University8, Eötvös Loránd University9, University of Tokyo10, University of Chicago11, University of Michigan12, United States Department of the Navy13, Carnegie Mellon University14, Pennsylvania State University15
TL;DR: In this paper, the authors present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS).
Abstract: We present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Ly? absorption in the spectra of these quasars evolves strongly with redshift. To z ~ 5.7, the Ly? absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest-redshift object, SDSSp J103027.10+052455.0 (z = 6.28), the average transmitted flux is 0.0038 ? 0.0026 times that of the continuum level over 8450 ? 20, on the optical depth to Ly? absorption at z = 6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Ly? forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z ~ 5 to 6, and the universe is approaching the reionization epoch at z ~ 6.
900 citations
TL;DR: In this paper, an unsupervised software robot that automatically and robustly reduces and analyzes CCD observations of photometric standard stars is described; the robot measures extinction coefficients and other photometric parameters in real time and, more carefully, on the next day.
Abstract: An unsupervised software robot that automatically and robustly reduces and analyzes CCD observations of photometric standard stars is described. The robot measures extinction coefficients and other photometric parameters in real time and, more carefully, on the next day. It also reduces and analyzes data from an all-sky 10 μm camera to detect clouds; photometric data taken during cloudy periods are automatically rejected. The robot reports its findings to observers and data analysts via the World Wide Web. It can be used to assess photometricity and to build data on site conditions. The robot's automated and uniform site monitoring represents a minimum standard for any observing site with queue scheduling, a public data archive, or likely participation in any future National Virtual Observatory.
769 citations
Fermilab1, University of Washington2, University of Chicago3, University of Sussex4, Princeton University5, Ohio State University6, New Mexico State University7, California Institute of Technology8, Paul Sabatier University9, University of Pittsburgh10, Johns Hopkins University11, University of Tokyo12, University of California, Berkeley13, University of Michigan14, University of Edinburgh15, Carnegie Mellon University16, Space Telescope Science Institute17, Pennsylvania State University18, University of Maryland, College Park19, Leibniz Institute for Astrophysics Potsdam20, Drexel University21, National Institutes of Natural Sciences, Japan22
TL;DR: In this article, the luminosity function of galaxies in the r* band over a range (for h \ 1) was computed using a Schechter function with parameters [23 \ M rp \ [16 h3 Mpc~3,
Abstract: In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced one of the largest redshift samples of galaxies selected from CCD images. Using 11,275 galaxies complete to r* \ 17.6 over 140 deg2, we compute the luminosity function of galaxies in the r* band over a range (for h \ 1). The result is well-described by a Schechter function with parameters [23 \ M rp \ [16 h3 Mpc~3,
693 citations
TL;DR: Brown dwarfs are assumed to be stellar embryos for which the star formation process was aborted before the hydrostatic cores could build up enough mass to eventually start hydrogen burning as discussed by the authors, which explains the rarity of brown dwarfs as close companions to normal stars, the absence of wide brown dwarf binaries, and the flattening of the low mass end of the initial mass function.
Abstract: We conjecture that brown dwarfs are substellar objects because they have been ejected from small newborn multiple systems that have decayed in dynamical interactions. In this view, brown dwarfs are stellar embryos for which the star formation process was aborted before the hydrostatic cores could build up enough mass to eventually start hydrogen burning. The disintegration of a small multiple system is a stochastic process, which can be described only in terms of the half-life of the decay. A stellar embryo competes with its siblings in order to accrete infalling matter, and the one that grows slowest is most likely to be ejected. With better luck, a brown dwarf would therefore have become a normal star. This interpretation of brown dwarfs readily explains the rarity of brown dwarfs as close companions to normal stars, the absence of wide brown dwarf binaries, and the flattening of the low-mass end of the initial mass function. Possible observational tests of this scenario include statistics of brown dwarfs near Class 0 sources and the kinematics of brown dwarfs in star-forming regions, while they still retain a kinematic signature of their expulsion. Because the ejection process limits the amount of gas brought along in a disk, it is predicted that substellar equivalents to the classical T Tauri stars should be rather short-lived.
624 citations
TL;DR: In this article, the authors investigated the dynamical family relations and dark halo properties of 21 mostly luminous, slowly rotating, and nearly round elliptical galaxies and found that they follow a Tully-Fisher (TF) relation with marginally shallower slope than spiral galaxies.
Abstract: Based on a uniform dynamical analysis of the line-pro—le shapes of 21 mostly luminous, slowly rotating, and nearly round elliptical galaxies, we have investigated the dynamical family relations and dark halo properties of ellipticals. Our results include: (i) The circular velocity curves (CVCs) of elliptical galaxies are —at to within ^10% for (ii) Most ellipticals are moderately radially anisotropic; R Z 0.2R e . their dynamical structure is surprisingly uniform. (iii) Elliptical galaxies follow a Tully-Fisher (TF) relation with marginally shallower slope than spiral galaxies, and km s~1 for an galaxy. At
TL;DR: In this article, the authors presented a panoramic image of the entire Galactic plane within 5° in four mid-infrared spectral bands between 6 and 25 μm at a spatial resolution of ~183, which was redundant within |b| ≤ 45 with fourfold coverage over two-thirds of the area.
Abstract: The Midcourse Space Experiment (MSX) surveyed the entire Galactic plane within |b| ≤ 5° in four mid-infrared spectral bands between 6 and 25 μm at a spatial resolution of ~183. The survey was redundant within |b| ≤ 45 with four-fold coverage over two-thirds of the area. These survey data were combined to create 1680 15 × 15 images that cover the region with 6'' pixel spacing in each of the spectral bands. The images preserve the inherent resolution of the data but have up to twice the sensitivity of a single scan. The individual survey observations had to be extensively conditioned to achieve the co-add advantage. The noise equivalent radiance (NER) at 8.3 μm, the most sensitive MSX mid-infrared spectral band, varies from ~1.3 MJy sr-1 in the inner Galaxy to 3 times that at the latitude limits in the outer Galaxy; the sensitivities of the other MSX mid-infrared bands are 10–25 times less. Additionally, 36 lower resolution 10° × 10° images were generated in each band that span the full latitude and longitude range of the survey. These panoramic images have a resolution of ~12 with 36'' pixel spacing and a six-fold improvement in NER, making them an ideal product for comparison with radio surveys of the Galactic plane. An ancillary set of images has been created from other MSX astronomy experiments that lie within 10° of the Galactic plane. These images either extend the latitude coverage of the survey or provide deeper probes of Galactic structure either by themselves or when added to the survey images.
Princeton University1, University of Washington2, Lawrence Livermore National Laboratory3, University of Hawaii at Manoa4, United States Department of the Navy5, University of Chicago6, Pennsylvania State University7, Fermilab8, New Mexico State University9, Eötvös Loránd University10, Johns Hopkins University11, United States Naval Research Laboratory12, University of Michigan13, University of Wyoming14, Ames Research Center15
TL;DR: In this article, measurements of the properties of D13,000 asteroids detected in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data were discussed.
Abstract: We discuss measurements of the properties of D13,000 asteroids detected in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 \ r* \ 21.5, with a baseline of D5 minutes, resulting in typical velocity errors of D3%. Extensive tests show that the sample is at least 98% complete, with a contamination rate of less than 3%. We —nd that the size distribution of asteroids resembles a broken power law, independent of the heliocentric distance: D~2.3 for 0.4 km, and D~4 for 5
TL;DR: In this paper, a search of the literature up to 2001 May, the number of known variable stars in Galactic globular clusters is approximately 3000, of which more than 2200 have known periods and the majority (approximately 1800) are of the RR Lyrae type.
Abstract: Based on a search of the literature up to 2001 May, the number of known variable stars in Galactic globular clusters is approximately 3000. Of these, more than 2200 have known periods and the majority (approximately 1800) are of the RR Lyrae type. In addition to the RR Lyrae population, there are approximately 100 eclipsing binaries, 120 SX Phoenicis variables, 60 Cepheids (including Population II Cepheids, anomalous Cepheids and RV Tauri), and 120 SR/red variables. The mean period of the fundamental mode RR Lyrae variables is 0.585 days, for the overtone variables it is 0.342 days (0.349 days for the first-overtone pulsators and 0.296 days for the second-overtone pulsators) and approximately 30% are overtone pulsators. These numbers indicate that about 65% of RR Lyrae variables in Galactic globular clusters belong to Oosterhoff type I systems. The mean period of the RR Lyrae variables in the Oosterhoff type I clusters seems to be correlated with metal abundance in the sense that the periods are longer in the more metal poor clusters. Such a correlation does not exist for the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue horizontal branches.
TL;DR: In this article, the authors used pseudoisothermal (core dominated) and cold dark matter (CDM; cusp dominated) models for a sample of 30 high-resolution rotation curves of low surface brightness galaxies.
Abstract: We present mass models for a sample of 30 high-resolution rotation curves of low surface brightness galaxies. We fit both pseudoisothermal (core dominated) and cold dark matter (CDM; cusp dominated) halos for a wide variety of assumptions about the stellar mass-to-light ratio. We find that the pseudoisothermal model provides superior fits. CDM fits show systematic deviations from the data and often have a small statistical likelihood of being the appropriate model. The distribution of concentration parameters is too broad, and has too low a mean, to be explained by low-density, flat CDM (ΛCDM). This failing becomes more severe as increasing allowance is made for stellar mass: Navarro, Frenk, & White (NFW) model fits require uncomfortably low mass-to-light ratios. In contrast, the maximum disk procedure does often succeed in predicting the inner shape of the rotation curves, but it requires uncomfortably large stellar mass-to-light ratios. The data do admit reasonable stellar population mass-to-light ratios if halos have cores rather than cusps.
TL;DR: In this article, a study of globular clusters (GCs) in 17 relatively nearby early-type galaxies, based on deep F555W and F814W images from the Wide Field Planetary Camera 2, on board the Hubble Space Telescope, was performed and compared with GCs in the Milky Way.
Abstract: We present a study of globular clusters (GCs) in 17 relatively nearby early-type galaxies, based on deep F555W and F814W images from the Wide Field Planetary Camera 2, on board the Hubble Space Telescope. A detailed analysis of color distributions, cluster sizes, and luminosity functions is performed and compared with GCs in the Milky Way. In nearly all cases, a KMM test returns a high confidence level for the hypothesis that a sum of two Gaussians provides a better fit to the observed color distribution than a single Gaussian, although histograms of the (V-I)0 distribution are not always obviously bimodal. The blue and red peak colors returned by the KMM test are both found to correlate with absolute host galaxy B-band magnitude and central velocity dispersion (at about the 2–3 σ level). Red GCs are generally smaller than blue GCs by about 20%. The size difference is seen at all radii at least out to 4' and within sub-bins in (V-I)0 color, and exists also in the Milky Way and Sombrero (M104) spiral galaxies. Fitting t5 functions to the luminosity functions of blue and red GC populations separately, we find that the V-band turnover of the blue GCs is brighter than that of the red ones by about 0.3 mag on the average, as expected if the two GC populations have similar ages and mass distributions but different metallicities. Brighter than the turnover at MV ~ -7.5, the luminosity functions (LFs) are well approximated by power laws with an exponent of about -1.75. This is similar to the LF for young star clusters, suggesting that young and old globular clusters form by the same basic mechanism. We discuss scenarios for GC formation and conclude that our data appear to favor in situ models in which all GCs in a galaxy formed after the main body of the protogalaxy had assembled into a single potential well.
Princeton University1, Pennsylvania State University2, University of California, Davis3, University of California, Berkeley4, University of Chicago5, Space Telescope Science Institute6, Fermilab7, California Institute of Technology8, Johns Hopkins University9, United States Naval Research Laboratory10, University of Tokyo11, University of Michigan12, United States Department of the Navy13
TL;DR: In this article, the authors used the color-selected sample of 39 luminous high-redshift quasars presented in Paper III to derive the evolution of the quasar luminosity function over the range 3.6 < z < 5.5 (? = 1, H0 = 50 km s-1 Mpc-1).
Abstract: This is the fourth paper in a series aimed at finding high-redshift quasars from five-color (u'g'r'i'z') imaging data taken along the celestial equator by the Sloan Digital Sky Survey during its commissioning phase. In this paper, we use the color-selected sample of 39 luminous high-redshift quasars presented in Paper III to derive the evolution of the quasar luminosity function over the range 3.6 < z < 5.0 and -27.5 < M1450 < -25.5 (? = 1, H0 = 50 km s-1 Mpc-1). We use the selection function derived in Paper III to correct for sample incompleteness. The luminosity function is estimated using three different methods: (1) the 1/Va estimator; (2) a maximum likelihood solution, assuming that the density of quasars depends exponentially on redshift and as a power law in luminosity; and (3) Lynden-Bell's nonparametric C- estimator. All three methods yield consistent results. The luminous quasar density decreases by a factor of ~6 from z = 3.5 to z = 5.0, consistent with the decline seen from several previous optical surveys at z < 4.5. The luminosity function follows ?(L) ? L-2.5 for z ~ 4 at the bright end, significantly flatter than the bright-end luminosity function ?(L) ? L-3.5 found in previous studies for z < 3, suggesting that the shape of the quasar luminosity function evolves with redshift as well, and that the quasar evolution from z = 2 to z = 5 cannot be described as pure luminosity evolution. Possible selection biases and the effect of dust extinction on the redshift evolution of the quasar density are also discussed.
TL;DR: In this article, a detailed study of the viewing angles of the LMC disk plane is presented, which has important implications for the structure and shape of the disk and reveals that the intrinsic shape is not circular but elliptical.
Abstract: We present a detailed study of the viewing angles of the LMC disk plane. We find that our viewing direction differs considerably from the commonly accepted values, which has important implications for the structure of the LMC. The discussion is based on an analysis of spatial variations in the apparent magnitude of features in the near-IR color-magnitude diagrams extracted from the Deep Near-Infrared Southern Sky Survey (DENIS) and Two Micron All-Sky Survey (2MASS). Sinusoidal brightness variations with a peak-to-peak amplitude of ~0.25 mag are detected as a function of position angle. The same variations are detected for asymptotic giant branch stars (using the mode of their luminosity function) and for red giant branch stars (using the tip of their luminosity function), and these variations are seen consistently in all of the near-IR photometric bands in both DENIS and 2MASS data. The observed spatial brightness variations are naturally interpreted as the result of distance variations because of one side of the LMC plane being closer to us than the opposite side. There is no evidence that any complicating effects, such as possible spatial variations in dust absorption or the age/metallicity of the stellar population, cause large-scale brightness variations in the near-IR at a level that exceeds the formal errors (~0.03 mag). The best-fitting geometric model of an inclined plane yields an inclination angle i = 347 ? 62 and line-of-nodes position angle ? = 1225 ? 83. The quoted errors are conservative estimates that take into account the possible influence of systematic errors; the formal errors are much smaller, 07 and 16, respectively. There is tentative evidence for variations of ~10? in the viewing angles with distance from the LMC center, suggesting that the LMC disk plane may be warped. Traditional methods to estimate the position angle of the line of nodes have used either the major-axis position angle ?maj of the spatial distribution of tracers on the sky or the position angle ?max of the line of maximum gradient in the velocity field, given that for a circular disk ?maj = ?max = ?. The present study does not rely on the assumption of circular symmetry and is considerably more accurate than previous studies of its kind. We find that the actual position angle of the line of nodes differs considerably from both ?maj and ?max, for which measurements have fallen in the range 140??190?. This indicates that the intrinsic shape of the LMC disk is not circular but elliptical. Paper II of this series explores the implications of this result through a detailed study of the shape and structure of the LMC. The inclination angle inferred here is consistent with previous estimates, but this is to some extent a coincidence, given that also for the inclination angle most previous estimates were based on the incorrect assumption of circular symmetry.
TL;DR: An extremely deep X-ray survey of the Hubble Deep Field North (HDF-N) and its environs (≈450 arcmin2) has been performed with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory.
Abstract: An extremely deep X-ray survey (≈1 Ms) of the Hubble Deep Field North (HDF-N) and its environs (≈450 arcmin2) has been performed with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. This is one of the two deepest X-ray surveys ever performed; for point sources near the aim point, it reaches 0.5–2.0 and 2–8 keV flux limits of ≈3 × 10-17 and ≈2 × 10-16 ergs cm-2 s-1, respectively. Here we provide source catalogs, along with details of the observations, data reduction, and technical analysis. Observing conditions, such as background, were excellent for almost all of the exposure. We have detected 370 distinct point sources: 360 in the 0.5–8.0 keV band, 325 in the 0.5–2.0 keV band, 265 in the 2–8 keV band, and 145 in the 4–8 keV band. Two new Chandra sources in the HDF-N itself are reported and discussed. Source positions are accurate to within 06–17 (at ≈90% confidence), depending mainly on the off-axis angle. We also detect two highly significant extended X-ray sources and several other likely extended X-ray sources. We present basic number count results for sources located near the center of the field. Source densities of 7100 deg-2 (at 4.2 × 10-17 ergs cm-2 s-1) and 4200 deg-2 (at 3.8 × 10-16 ergs cm-2 s-1) are observed in the soft and hard bands, respectively.
TL;DR: In this article, an analysis of J, H, and K_s time-series photometry obtained with the southern 2MASS telescope over a 0.°84 × 6° region centered near the Trapezium region of the Orion Nebula cluster is presented.
Abstract: We present an analysis of J, H, and K_s time-series photometry obtained with the southern 2MASS telescope over a 0.°84 × 6° region centered near the Trapezium region of the Orion Nebula cluster. These data are used to establish the near-infrared variability properties of pre–main-sequence stars in Orion on timescales of ~1–36 days, ~2 months, and ~2 years. A total of 1235 near-infrared variable stars are identified, ~93% of which are likely associated with the Orion A molecular cloud. The variable stars exhibit a diversity of photometric behavior with time, including cyclic fluctuations with periods up to 15 days, aperiodic day-to-day fluctuations, eclipses, slow drifts in brightness over 1 month or longer, colorless variability (within the noise limits of the data), stars that become redder as they fade, and stars that become bluer as they fade. The mean peak-to-peak amplitudes of the photometric fluctuations are ~0.2 mag in each band, and 77% of the variable stars have color variations less than 0.05 mag. The more extreme stars in our sample have amplitudes as large as ~2 mag and change in color by as much as ~1 mag. The typical timescale of the photometric fluctuations is less than a few days, indicating that near-infrared variability results primarily from short-term processes. We examine rotational modulation of cool and hot starspots, variable obscuration from an inner circumstellar disk, and changes in the mass accretion rate and other physical properties in a circumstellar disk as possible physical origins of the near-infrared variability. Cool spots alone can explain the observed variability characteristics in ~56%–77% of the stars, while the properties of the photometric fluctuations are more consistent with hot spots or extinction changes in at least 23% of the stars, and with variations in the disk mass accretion rate or inner disk radius in ~1% of our sample. However, differences between the details of the observations and the details of variability predicted by hot-spot, extinction, and accretion disk models suggest either that another variability mechanism not considered here may be operative or that the observed variability represents the net results of several of these phenomena. Analysis of the star-count data indicates that the Orion Nebula cluster is part of a larger area of enhanced stellar surface density that extends over a 0.°4 × 2.°4 (3.4 pc × 20 pc) region containing ~2700 stars brighter than Ks = 14 mag.
TL;DR: In this paper, a general method for determining the unbiased inclination distribution of the Kuiper belt using only the inclination and latitude of discovery of known KBOs (KBOs) was developed.
Abstract: We develop a general method for determining the unbiased inclination distribution of the Kuiper belt using only the inclination and latitude of discovery of known Kuiper belt objects (KBOs). These two parameters are well determined for each discovered object, so we can use all 379 known KBOs (as of 2001 January 1)—without knowing the object's precise orbit, area, detection efficiency, or the latitudinal coverage of the survey that found the object—to determine the inclination distribution. We find that a natural analytic form for the inclination distribution is a sine of the inclination multiplied by a Gaussian. The inclination distribution of all KBOs is well fitted by sin i multiplied by a sum of two Gaussians with widths 2°.6^(+.8)_(-.2) and 15° ± 1°. For this inclination distribution, the Kuiper belt has an effective area of 8100^(+1500)-(-1100) deg^2 and a FWHM of 12.5° ± 3.5° in latitude. The inclination distribution of the different dynamical classes appear different. The Plutinos are well fit by sin i mulitplied by a single Gaussian of width 10°.2^(+2.5)_(-1.8), the classical KBOs cannot be fit to a single Gaussian but are well fit by sin i multiplied by the sum of two Gaussians of widths 2°.2^(+.2)_(-.6) and 17° ± 3°, and the scattered KBOs are poorly fit by sin i multiplied by a single Gaussian of width 20° ± 4°. The poor fit of the scattered objects is possibly a result of limitations of the method in dealing with large eccentricities. The effective areas of the Plutinos, classical KBOs, and scattered KBOs are 9300 ± 1800, 6100 ± 2100, and 17000 ± 3000 deg^2, respectively. The FWHMs are 23° ± 5°, 6°.8^(+2.0)_(-3.6), and 44° ± 10°, respectively. In all cases, the inclinations of the Kuiper belt objects appear larger than expected from dynamical simulations of possible perturbations.
TL;DR: In this paper, the authors present an analysis of the globular cluster systems of 28 elliptical galaxies using archival WFPC2 images in the V and I bands, showing that at least 50% of the galaxies appear to be bimodal at the present level of photometric accuracy.
Abstract: We present an analysis of the globular cluster systems of 28 elliptical galaxies using archival WFPC2 images in the V and I bands. The V-I color distributions of at least 50% of the galaxies appear to be bimodal at the present level of photometric accuracy. We argue that this is indicative of multiple epochs of cluster formation early in the history of these galaxies, possibly due to mergers. We also present the first evidence of bimodality in low-luminosity galaxies and discuss its implication on formation scenarios. The mean color of the 28 cluster systems studied by us is V-I = 1.04 ± 0.04 (0.01) mag corresponding to a mean metallicity of Fe/H = -1.0 ± 0.19 (0.04). We find that the turnover magnitudes of the globular cluster luminosity functions (GCLF) of our sample are in excellent agreement with the distance measurements using other methods and conclude that the accuracy of the GCLF is at least as good as the surface brightness fluctuation method. The absolute magnitude of the turnover luminosity of the GCLF is M = -7.41 (0.03) in V and M = -8.46 (0.03) in I. The mean local specific frequency of our sample of elliptical galaxies within the WFPC2 field-of-view is 2.4 ± 1.8 (0.4), considerably higher than the 1.0 ± 0.6 (0.1) derived for a comparable sample of S0s in a similar analysis. It shows no obvious correlation with metallicity, host galaxy mass or membership in a galaxy cluster. The median size of clusters in all galaxies appears to be remarkably constant at ~2.4 pc. We suggest that in the future it might be possible to use the sizes of clusters in the inner regions of galaxies as a simple geometrical distance indicator.
TL;DR: In this article, the authors examined the statistical properties of color indices, scale lengths, and concentration indices as functions of morphology for the SDSS photometric system, and found that u-,g', g'-r', and r'-i' colors of SDSs galaxies match well with those expected from the synthetic calculation of spectroscopic energy distribution of template galaxies and with those transformed from UBVRCIC color data of nearby galaxies.
Abstract: We investigate the photometric properties of 456 bright galaxies using imaging data recorded during the commissioning phase of the Sloan Digital Sky Survey (SDSS). Morphological classification is carried out by correlating results of several human classifiers. Our purpose is to examine the statistical properties of color indices, scale lengths, and concentration indices as functions of morphology for the SDSS photometric system. We find that u'-g', g'-r', and r'-i' colors of SDSS galaxies match well with those expected from the synthetic calculation of spectroscopic energy distribution of template galaxies and with those transformed from UBVRCIC color data of nearby galaxies. The agreement is somewhat poor, however, for the i'-z' color band, with a discrepancy of 0.1?0.2 mag. With the aid of the relation between surface brightness and radius obtained by Kent in 1985, we estimate the averages of the effective radius of early-type galaxies and the scale length of exponential disks both to be 2.6 kpc for L* galaxies. We find that the half-light radius of galaxies depends slightly on the color bands, consistent with the expected distribution of star-forming regions for late-type galaxies and with the known color gradient for early-type galaxies. We also show that the (inverse) concentration index, defined by the ratio of the half-light Petrosian radius to the 90% light Petrosian radius, correlates tightly with the morphological type; this index allows us to classify galaxies into early (E/S0) and late (spiral and irregular) types, allowing for a 15%?20% contamination from the opposite class compared with eye-classified morphology.
TL;DR: In this paper, the authors developed a methodology to "k-correct" the implied prompt energy release of a gamma-ray burst (GRB) to a fixed comoving bandpass.
Abstract: The fluences of gamma-ray bursts (GRBs) are measured with a variety of instruments in different detector energy ranges. A detailed comparison of the implied energy releases of the GRB sample requires then an accurate accounting of this diversity in fluence measurements that properly corrects for the redshifting of GRB spectra. Here we develop a methodology to "k-correct" the implied prompt energy release of a GRB to a fixed comoving bandpass. This allows us to homogenize the prompt energy release of 17 cosmological GRBs (using published redshifts, fluences, and spectra) to two common comoving bandpasses: 20–2000 keV and 0.1 keV–10 MeV ("bolometric"). While the overall distribution of GRB energy releases does not change significantly by using a k-correction, we show that uncorrected energy estimates systematically undercount the bolometric energy by ~5% to 600%, depending on the particular GRB. We find that the median bolometric isotropic equivalent prompt energy release is 2.19 × 1053 ergs, with an rms scatter of 0.80 dex. The typical estimated uncertainty on a given k-corrected energy measurement is ~20%.
TL;DR: In this article, the authors investigated the unusual structures in the stellar body and ionized gas in and around the Perseus Cluster central galaxy NGC 1275 using the WIYN 3.5 m telescope.
Abstract: Subarcsecond images, taken in B, R, and Hα filters, and area spectroscopy obtained with the WIYN 3.5 m telescope provide the basis for an investigation of the unusual structures in the stellar body and ionized gas in and around the Perseus Cluster central galaxy NGC 1275. Our Hα filter is tuned to gas at the velocity of NGC 1275, revealing complex, probably unresolved, small-scale features in the extended ionized gas, located up to 50 h kpc from NGC 1275. The mean Hα surface brightness varies little along the outer filaments; this, together with the complex excitation state demonstrated by spectra, imply that the filaments are likely to be tubes, or ribbons, of gas. The morphology, location, and inferred physical parameters of the gas in the filaments are consistent with a model, whereby the filaments form through compression of the intracluster gas by relativistic plasma emitted from the active nucleus of NGC 1275. Imaging spectroscopy with the DensePak fiber array on WIYN suggests partial rotational support of the inner component of low-velocity ionized gas. Our broadband data is used to derive color maps of the stellar distribution and also to investigate asymmetries in the stellar surface brightness. We confirm and extend evidence for features in the stellar body of NGC 1275 and identify outer stellar regions containing very blue, probably very young, star clusters. We interpret these as evidence for recent accretion of a gas-rich system, with subsequent star formation. Other star clusters are identified, some of which are possibly associated with the high-velocity 8200 km s-1 emission-line system being in the same projected location. We suggest that two main processes, which may be causally connected, are responsible for the rich phenomenology of the NGC 1275 system—NGC 1275 experienced a recent merger and/or interaction with a group of gas-rich galaxies, and recent outflows from its AGN have compressed the intracluster gas and perhaps the gas in the infalling galaxies to produce a complex web of filaments.
National Institutes of Natural Sciences, Japan1, University of Tokyo2, Princeton University3, Ohio State University4, University of Sussex5, Fermilab6, New Mexico State University7, California Institute of Technology8, University of Pittsburgh9, Johns Hopkins University10, Tohoku University11, University of Chicago12, University of Michigan13, United States Department of the Navy14, Carnegie Mellon University15, Pennsylvania State University16, Leibniz Institute for Astrophysics Potsdam17, Drexel University18
TL;DR: In this paper, the galaxy number counts were derived from two independent stripes of imaging scans along the celestial equator, one each toward the northern and the southern Galactic cap, covering about 230 and 210 deg2, respectively.
Abstract: We present bright galaxy number counts in five broad bands (u', g', r', i', z') from imaging data taken during the commissioning phase of the Sloan Digital Sky Survey (SDSS). The counts are derived from two independent stripes of imaging scans along the celestial equator, one each toward the northern and the southern Galactic cap, covering about 230 and 210 deg2, respectively. A careful study is made to verify the reliability of the photometric catalog. For galaxies brighter than r* = 16, the catalog produced by automated software is examined against eye inspection of all objects. Statistically meaningful results on the galaxy counts are obtained in the magnitude range 12 ≤ r* ≤ 21, using a sample of 900,000 galaxies. The counts from the two stripes differ by about 30% at magnitudes brighter than r* = 15.5, consistent with a local 2 σ fluctuation due to large-scale structure in the galaxy distribution. The shape of the number counts–magnitude relation brighter than r* = 16 is well characterized by N ∝ 100.6m, the relation expected for a homogeneous galaxy distribution in a "Euclidean" universe. In the magnitude range 16 < r* < 21, the galaxy counts from both stripes agree very well and follow the prediction of the no-evolution model, although the data do not exclude a small amount of evolution. We use empirically determined color transformations to derive the galaxy number counts in the B and I814 bands. We compute the luminosity density of the universe at zero redshift in the five SDSS bands and in the B band. We find B = 2.4 ± 0.4 × 108 L⊙ h Mpc-3, for a reasonably wide range of parameters of the Schechter luminosity function in the B band.
TL;DR: The Fifth catalog of Orbits of Visual Binary Stars as mentioned in this paper contains 1465 orbits of 1430 visual binary stars from the 1930s to the 1980s, with the same grading scheme as in earlier catalogs, although the grading scheme was modified to be more objective.
Abstract: The Fifth Catalog of Orbits of Visual Binary Stars continues the series of compilations of visual binary star orbits published by Finsen, Worley, and Heintz from the 1930s to the 1980s. As of 2001 January 1, the new catalog includes 1465 orbits of 1430 systems. All orbits have been graded as in earlier catalogs, although the grading scheme has been modified to be more objective. Ephemerides are given for all orbits, as are plots including all associated data in the Washington Double Star 2001.0 database. A subset of orbits useful for scale calibration is also presented. This catalog is one of four USNO double star catalogs to be included on a new CD-ROM.
TL;DR: The size distribution in the Kuiper Belt records physical processes operating during the formation and subsequent evolution of the solar system was studied in this paper, showing that the entire range of observed objects (magnitudes) is well represented by an unbroken power law with the number of objects per m R D 20¨27) square degree brighter than magnitude R being of the form with a
Abstract: The size distribution in the Kuiper Belt records physical processes operating during the formation and subsequent evolution of the solar system. This paper reports a study of the apparent magnitude distribution of faint objects in the Kuiper Belt, obtained via deep imaging on the Canada-France-Hawaii Telescope and the ESO Very Large Telescope UT1. We —nd that the entire range of observed objects (magnitudes is well represented by an unbroken power law, with the number of objects per m R D 20¨27) square degree brighter than magnitude R being of the form with a \ 0.69 and &(m R \ R) \ 10a(R~R0),
TL;DR: In this article, it was shown that supermassive black holes are associated only with galaxy bulges and not with their disks, and that no corresponding relationship applies in the pure disk galaxy M33.
Abstract: Galaxies that contain bulges appear to contain central black holes whose masses correlate with the velocity dispersion of the bulge. We show that no corresponding relationship applies in the pure disk galaxy M33. Three-integral dynamical models fit Hubble Space Telescope WFPC2 photometry and Space Telescope Imaging Spectrograph spectroscopy best if the central black hole mass is zero. The upper limit is 1500 M⊙. This is significantly below the mass expected from the velocity dispersion of the nucleus and far below any mass predicted from the disk kinematics. Our results suggest that supermassive black holes are associated only with galaxy bulges and not with their disks.
TL;DR: The results of new spectroscopic analyses of 20 recently reported extrasolar planet parent stars are presented in this article, showing that the most massive stars with planets are systematically more metal-rich than field stars of the same mass.
Abstract: The results of new spectroscopic analyses of 20 recently reported extrasolar planet parent stars are presented. The companion of one of these stars, HD 10697, has recently been shown to have a mass in the brown dwarf regime; we find [Fe/H] = +0.16 for it. For the remaining sample, we derive [Fe/H] estimates ranging from -0.41 to +0.37, with an average value of +0.18 ± 0.19. If we add the 13 stars included in the previous papers of this series and six other stars with companions below the 11 MJ limit from the recent studies of Santos et al., we derive [Fe/H] = +0.17 ± 0.20. Among the youngest stars with planets with F or G0 spectral types, [Fe/H] is systematically larger than young field stars of the same Galactocentric distance by 0.15 to 0.20 dex. This confirms the recent finding of Laughlin that the most massive stars with planets are systematically more metal-rich than field stars of the same mass. We interpret these trends as supporting a scenario in which these stars accreted high-Z material after their convective envelopes shrunk to near their present masses. Correcting these young star metallicities by 0.15 dex still does not fully account for the difference in mean metallicity between the field stars and the full parent stars sample. The stars with planets appear to have smaller [Na/Fe], [Mg/Fe], and [Al/Fe] values than field dwarfs of the same [Fe/H]. They do not appear to have significantly different values of [O/Fe], [Si/Fe], [Ca/Fe], or [Ti/Fe], though. The claim made in Paper V that stars with planets have low [C/Fe] is found to be spurious, due to unrecognized systematic differences among published studies. When corrected for these differences, they instead display slightly enhanced [C/Fe] (but not significantly so). If these abundance anomalies are due to the accretion of high-Z matter, it must have a composition different from that of the Earth.