362 research outputs found
BE Ursae Majoris: A detached binary with a unique reprocessing spectrum
New infrared photometry, optical and UV spectrophotometry, and a photographic ephemeris are presented for the detached binary BE UMa. Results show the primary to be a DO white dwarf with an effective temperature of 80,000 + or - 15,000 K and a mass of 0.6 + or - 0.1 solar masses. No evidence is found for variability of the primary. The main sequence secondary star is shown to be of early M spectral type, with a formal range of M1 to M5 being possible. A reflection effect in reprocessed line and continuum radiation is produced by EUV radiation from the primary incident on the secondary atmosphere. It is suggested that the temperature of the reprocessed component of the secondary's atmosphere is in the 5000 to 8500 K range, and that emission lines of decreasing ionization form deeper in the irradiated envelope. Relatively narrow He II and high excitation metal lines are formed from recombination and continuum fluorescence processes
Curriculum Data Deep Dive: Identifying Data Literacies in the Disciplines
Objective: Evaluate and examine Data Literacy (DL) in the supported disciplines of four liaison librarians at a large research university.
Methods: Using a framework developed by Prado and Marzal (2013), the study analyzed 378 syllabi from a two-year period across six departmentsâCriminal Justice, Geography, Geology, Journalism, Political Science, and Sociologyâto see which classes included DLs.
Results: The study was able to determine which classes hit on specific DLs and where those classes might need more support in other DLs. The most common DLs being taught in courses are Reading, Interpreting, and Evaluating Data, and Using Data. The least commonly taught are Understanding Data and Managing Data skills.
Conclusions: While all disciplines touched on data in some way, there is clear room for librarians to support DLs in the areas of Understanding Data and Managing Data
A search for the Perseus flasher and the limits on optical burst rates
We conducted a study of the error box of the possible optical burster, reported by Katz et al. (1986). This âPerseus Flasherâ was subsequently identified with satellite glints by Maley (1987), a conclusion with which we fully concur. Our study, completed before Maleyâs report, involved a search for highly-variable objects on archival and newly-taken plates, with a total integration time of about 260 hours, a proper-motion survey of the area, deep optical imaging with a CCD, and a single-dish radio monitoring. We found no optical or radio bursts or any other unusual objects in this area. Our upper limit to the optical flash rate from the error box of the flash photographed by Katz et al. is at least 20 times lower than the flash rate reported by those authors. Similar negative results were achieved independently by other groups; like them, we conclude that the photographed flash was most likely caused by an Earth-orbiting artifact and that most of the remaining, visually-detected flashes were spurious. From our data, we derive limits on the optical flash rates from astrophysically-interesting sources
A Unique Concept for Liquid Level and Void Fraction Detection in Severe Fuel Damage Tests
This report describes a direct-contacting liquid level and void fraction detection system that is being developed by Pacific Northwest Laboratory. The measurement technique could be used in the severe fuel damage tests that will be conducted at the Power Burst Facility, Idaho Falls, Idaho, and at the ESSOR reactor, Ispra, Italy. The detection system could also be retrofitted for commercial operating reactors to provide definitive thermal-hydraulic information. The technique can provide unambiguous, real-time data on liquid level and void fraction during normal reactor operation as well as during shutdown and accident conditions
A Machine Learning Method to Infer Fundamental Stellar Parameters from Photometric Light Curves
A fundamental challenge for wide-field imaging surveys is obtaining follow-up
spectroscopic observations: there are > photometrically cataloged
sources, yet modern spectroscopic surveys are limited to ~few x targets.
As we approach the Large Synoptic Survey Telescope (LSST) era, new algorithmic
solutions are required to cope with the data deluge. Here we report the
development of a machine-learning framework capable of inferring fundamental
stellar parameters (Teff, log g, and [Fe/H]) using photometric-brightness
variations and color alone. A training set is constructed from a systematic
spectroscopic survey of variables with Hectospec/MMT. In sum, the training set
includes ~9000 spectra, for which stellar parameters are measured using the
SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest
algorithm to perform a non-parametric regression that predicts Teff, log g, and
[Fe/H] from photometric time-domain observations. Our final, optimized model
produces a cross-validated root-mean-square error (RMSE) of 165 K, 0.39 dex,
and 0.33 dex for Teff, log g, and [Fe/H], respectively. Examining the subset of
sources for which the SSPP measurements are most reliable, the RMSE reduces to
125 K, 0.37 dex, and 0.27 dex, respectively, comparable to what is achievable
via low-resolution spectroscopy. For variable stars this represents a ~12-20%
improvement in RMSE relative to models trained with single-epoch photometric
colors. As an application of our method, we estimate stellar parameters for
~54,000 known variables. We argue that this method may convert photometric
time-domain surveys into pseudo-spectrographic engines, enabling the
construction of extremely detailed maps of the Milky Way, its structure, and
history
Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC 5548
We present the results of three years of ground-based observations of the
Seyfert 1 galaxy NGC 5548, which combined with previously reported data, yield
optical continuum and broad-line H-beta light curves for a total of eight
years. The light curves consist of over 800 points, with a typical spacing of a
few days between observations. During this eight-year period, the nuclear
continuum has varied by more than a factor of seven, and the H-beta emission
line has varied by a factor of nearly six. The H-beta emission line responds to
continuum variations with a time delay or lag of 10-20 days, the precise value
varying somewhat from year to year. We find some indications that the lag
varies with continuum flux in the sense that the lag is larger when the source
is brighter.Comment: 29 pages, 6 figures. Accepted for publication in ApJ (1999 Jan 10
Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A Thirteen-Year Study of Spectral Variability in NGC 5548
We present the final installment of an intensive 13-year study of variations
of the optical continuum and broad H-beta emission line in the Seyfert 1 galaxy
NGC 5548. The data base consists of 1530 optical continuum measurements and
1248 H-beta measurements. The H-beta variations follow the continuum variations
closely, with a typical time delay of about 20 days. However, a year-by-year
analysis shows that the magnitude of emission-line time delay is correlated
with the mean continuum flux. We argue that the data are consistent with the
simple model prediction that the size of the broad-line region is proportional
to the square root of the ionizing luminosity. Moreover, the apparently linear
nature of the correlation between the H-beta response time and the nonstellar
optical continuum arises as a consequence of the changing shape of the
continuum as it varies, specifically with the optical (5100 A) continuum
luminosity proportional to the ultraviolet (1350 A) continuum luminosity to the
0.56 power.Comment: 20 pages plus 4 figures. Accepted for publication in The
Astrophysical Journa
Engineering characterization of ground motion. Task I. Effects of characteristics of free-field motion on structural response
This report presents the results of the first task of a two-task study on the engineering characterization of earthquake ground motion for nuclear power plant design. The overall objective of this study is to develop recommendations for methods for selecting design response spectra or acceleration time histories to be used to characterize motion at the foundation level of nuclear power plants. Task I of the study develops a basis for selecting design response spectra, taking into account the characteristics of free-field ground motion found to be significant in causing structural damage
The Updated Zwicky Catalog (UZC)
The Zwicky Catalog of galaxies (ZC), with m_Zw<=15.5mag, has been the basis
for the Center for Astrophysics (CfA) redshift surveys. To date, analyses of
the ZC and redshift surveys based on it have relied on heterogeneous sets of
galaxy coordinates and redshifts. Here we correct some of the inadequacies of
previous catalogs by providing: (1) coordinates with <~2 arcsec errors for all
of the Nuzc catalog galaxies, (2) homogeneously estimated redshifts for the
majority (98%) of the data taken at the CfA (14,632 spectra), and (3) an
estimate of the remaining "blunder" rate for both the CfA redshifts and for
those compiled from the literature. For the reanalyzed CfA data we include a
calibrated, uniformly determined error and an indication of the presence of
emission lines in each spectrum. We provide redshifts for 7,257 galaxies in the
CfA2 redshift survey not previously published; for another 5,625 CfA redshifts
we list the remeasured or uniformly re-reduced value. Among our new
measurements, Nmul are members of UZC "multiplets" associated with the original
Zwicky catalog position in the coordinate range where the catalog is 98%
complete. These multiplets provide new candidates for examination of tidal
interactions among galaxies. All of the new redshifts correspond to UZC
galaxies with properties recorded in the CfA redshift compilation known as
ZCAT. About 1,000 of our new measurements were motivated either by inadequate
signal-to-noise in the original spectrum or by an ambiguous identification of
the galaxy associated with a ZCAT redshift. The redshift catalog we include
here is ~96% complete to m_Zw<=15.5, and ~98% complete (12,925 galaxies out of
a total of 13,150) for the RA(1950) ranges [20h--4h] and [8h--17h] and
DEC(1950) range [-2.5d--50d]. (abridged)Comment: 34 pp, 7 figs, PASP 1999, 111, 43
- âŠ