Showing papers in "Publications of the Astronomical Society of the Pacific in 1993"
TL;DR: In this article, the authors discuss progress in application of the reverberation mapping technique and describe the underlying assumptions and limitations of the method, discuss how the results obtained to date are changing our understanding of active nuclei, and outline several new questions that might be addressed through further reverberational mapping programs.
Abstract: The broad emission lines in the spectra of active galactic nuclei respond to variations in the luminosity of the central continuum source with a delay due to light-travel time effects within the emission-line region. It is therefore possible through the process of 'reverberation mapping' to determine the geometry and kinematics of the emission-line region by careful monitoring of the continuum variations and the resulting emission-line response. In this review, I will discuss progress in application of the reverberation mapping technique. I will describe the underlying assumptions and limitations of the method, discuss how the results obtained to date are changing our understanding of active nuclei, and outline several new questions that might be addressed through further reverberation mapping programs.
973 citations
TL;DR: In this article, a point-spread function (PSF) fitting photometry program, DOPHOT, is described and the quality of the resulting photometry is assessed via reductions of an 'artificial' globular cluster generated from a list of stars with known magnitudes and colors.
Abstract: The design considerations and operational features of DOPHOT, a point-spread function (PSF) fitting photometry program, are described. Some relevant details of the PSF fitting are discussed. The quality of the photometry returned by DOPHOT is assessed via reductions of an 'artificial' globular cluster generated from a list of stars with known magnitudes and colors. Results from comparative tests between DOPHOT and DAOPHOT using this synthetic cluster and real data are also described.
896 citations
TL;DR: Close binaries are defined as systems in which at least one of the components has filled or will fill its Roche lobe and attempt to transfer matter to its companion; some of the orbital energy helps drive matter from the common envelope (CE) into interstellar space as mentioned in this paper.
Abstract: The characteristics of many close, evolved binaries can be understood most easily if there exists some agency that can abstract angular momentum or mass, or both, from the precursor system. Close binaries may be defined as systems in which at least one of the components has filled or will fill its Roche lobe and attempt to transfer matter to its companion. If the timescale for mass transfer is considerablyy shorter than the timescale on which the accretor can adjust thermally to the proferred mass, the accreted layer will heat up, expand, and fill the Roche lobe of the accretor. The mass lost by the donor thereafter flows into a "common envelope" (CE) which encomapsses both stars. The frictional interaction between this common envelope and the stellar cores produces drag forces that cause the cores to spiral in toward one another; some of the orbital energy helps drive matter from the CE into interstellar space. Examples of the systems which are experiencing or have experienced this process include some planetary nebulae, cataclysmic variables, and close binary degenerate stars. Similar situations can arise if one of the components can support, of its own accord, a dense wind that flows out of the system; the drag luminosity produced by interaction between the companion and the wind may intensify the wind and contribute tot eh mass loss from the donor. Systems undergoing this "wind-CE" process include novae and close binaries containing a Wolf-Rayet star. Planetary nebulae with close binary central stars are actually ejected CEs, and precursors of many cataclysmic variables were once the central stars of planetary nebulae formed in a CE event. In this review, we (1) describe various initial configurations which will produce a CE, (2) discuss the physics of the CE event, (3) describe attempts to model the event quantiatively, and (4) apply what we have learned to describe, in several real situations, the tarnsformations wrought by evolution through a CE phase.
526 citations
TL;DR: The structure of the mm-array database and the implementation of a data analysis program are described, both of which make extensive use of Sybase, a commercial database management system with application development software.
Abstract: A relational database management system has been implemented on the Caltech millimeter-wave array for both real-time astronomical engineering data and post-processing calibration and analysis This system provides high storage-efficiency for the data and on-line access to data from multiple observing seasons The ability to access easily the full database enables more accurate calibration of the raw data and greatly facilitates the calibration process In this article we describe both the structure of the mm-array database and the implementation of a data analysis program, both of which make extensive use of Sybase, a commercial database management system with application development software This use of relational database technology in real-time astronomical data storage and calibration may serve as a prototype for similar systems at other observatories
307 citations
TL;DR: Denisenkov and Denisenkova as mentioned in this paper explored and extended the conjecture that 23Na might be produced in the interior of an evolving low-mass globular cluster giant and mixed to the surface.
Abstract: We explore and extend the suggstion that 23Na might be produced in the interior of an evolving low-mass globular cluster giant and mixed to the surface (Kudryashov & Tutukov 1988, Denisenkov & Denisenkova 1990). The reaction rates alone show that sodium will be produced by proton captures on 22Ne in the region of a globulr cluster giant in which oxygen is being depleted. A more detailed calculation shows that significant amounts of the much more abundant 20Ne can be transformed into 23Na on somewhat longer timescales. Atmospheric oxygen depletions that are the result of very deep mixing are bound to be accompanied by sodium enhancements due to 22Ne(p,gamma)23Na reactions; they are quite likely to be accopanied by larger sodium enhancements that begin with proton captures on 20Ne. One cannot argue that a Na-O anticorrelation is strong evidence for a primordial account of the observed variations in O and Na. We find that 27Al can also be produced by very deep mixing and that the aluminum enhancements that would result are likely to be smaller than the sodium enhancements. Finally, we suggest a number of ways in which the consequences of this sort of very deep mixing might be distinguished from primordial variations in oxygen, sodium and aluminum.
246 citations
TL;DR: In this article, a flexure-compensated Cassegrain echelle spectrograph for the 2.1 m (82-inch) Struve reflector at McDonald Observatory is described.
Abstract: We describe the design, construction, and performance of an efficient new flexure-compensated Cassegrain echelle spectrograph for the 2.1 m (82-inch) Struve reflector at McDonald Observatory. The instrument has a resolving power R = lambda/Delta-lambda of 60,000 for two CCD pixels (for a reciprocal velocity dispersion of 2.5 km s-1 per pixel) and provides continuous wavelength coverage for lambda < 8000 A using a thinned backside illuminated Reticon 1200 X 400 CCD detector. Total wavelength coverage in a single exposure varies from roughly 500 A at lambda = 4400 A (range 4200 - 4700 A) to 2500 A at lambda = 7500 A (range 6500 - 9000 A), and the total system efficiency at lambda = 6000 A from the top of the atmosphere through the telescope, spectrograph, and CCD detector is 10 percent or more. The mechanical design of the Cassegrain-mounted spectrograph incorporates a unique cantilevered counterweight system designed to drastically reduce the effects of gravitational flexure. In spite of the large physical size of the Cassegrain instrument, worst case flexure shifts over 60-degrees (4 hours) of telescope motion are less than 1/2-pixel and are typically on the order of 0.2 pixels or less from all sources. A subsequent paper will describe the CCD and associated electronics in detail.
148 citations
TL;DR: It is shown how an optimal basis for image representation can be selected and in doing so, the concept of the "pixon" which is a generalized image cell from which this basis is constructed is developed.
Abstract: In this paper we describe the optimal image model, maximum residual likelihood method (OptMRL) for image reconstruction. OptMRL is a Bayesian image reconstruction technique for removing point-spread function blurring. OptMRL uses both a goodness-of-fit criterion (GOF) and an 'image prior', i.e., a function which quantifies the a priori probability of the image. Unlike standard maximum entropy methods, which typically reconstruct the image on the data pixel grid, OptMRL varies the image model in order to find the optimal functional basis with which to represent the image. We show how an optimal basis for image representation can be selected and in doing so, develop the concept of the 'pixon' which is a generalized image cell from which this basis is constructed. By allowing both the image and the image representation to be variable, the OptMRL method greatly increases the volume of solution space over which the image is optimized. Hence the likelihood of the final reconstructed image is greatly increased. For the goodness-of-fit criterion, OptMRL uses the maximum residual likelihood probability distribution introduced previously by Pina and Puetter (1992). This GOF probability distribution, which is based on the spatial autocorrelation of the residuals, has the advantage that it ensures spatially uncorrelated image reconstruction residuals.
131 citations
TL;DR: In this article, a complete atlas of optical spectra of white dwarf stars is presented, and the variation of the dominant spectra features as a function of effective temperature and abundance is documented.
Abstract: We present a complete atlas of optical spectra of white dwarf stars. Spectra for all major spectral classes and subclasses are illustrated, and the variation of the dominant spectra features as a function of effective temperature and abundance is documented. We present, as well, spectra of several peculiar or rare types of degenerate stars.
118 citations
TL;DR: In this article, the J-and H-bands were observed for the purpose of determining the line widths, the precise wavelengths of individual lines, and also the continuum emission level between lines.
Abstract: The OH airglow emission in the J- and H-bands was observed for the purpose of determining the line widths, the precise wavelengths of individual lines, and also the continuum emission level between lines. The lines were not resolved with a resolving power of about 17000. Wavelengths and intensities were measured for approximately 120 lines from 1.1 to 1.8 microns. The continuum emission intensity was also measured on a dark night and was as low as 590 photons s-1m-2 arcsec-2 um-1 at 1.665 um. The level is about one fiftieth the average of the OH airglow emission in the H-band.
102 citations
TL;DR: In this paper, a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994 was presented, showing a clear break in the rotation-activity relation around P approximately 6-7 days.
Abstract: We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several show rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleiades stars with photometric periods together with current X-ray flux measurements, we illustrate the X-ray activity/rotation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P approximately 6-7 days -- in general accordance with previous results using more heterogeneous samples of G/K stars.
81 citations
TL;DR: In this article, the effect of the redshift on the observed B and V magnitudes of type Ia supernovae has been investigated using the best spectra of SNe 1990N, 1991T, and 1992A covering from day 14 to day +76.
Abstract: The usefulness of type Ia supernovae as distance indicators is a metter of current study and discussion. The avaialbel data suggest that the intrinsic dispersion in the absolute B magnitudes of SNe Ia at maximum light is less than 0.4 mag. Hence, SNe Ia offer considerable potential for cosmological studies out to redshifts of z~0.1 or greater. At these distances, however, the effects of the redshift on the observed magnitudes are not negligible and must be taken into account in order to compare the magnitudes and light curves of objects of different redshifts. In this paper we make use of the best spectra avaialbe for type Ia supernovae in order to calculate the effect of theredshift on the observed B and V magnitudes. We present K-temrs in the redshift range z=0.005-0.50 from a collection of spectra of SNe 1990N, 1991T, and 1992A covering from day -14 to day +76, counted from the time of maximum light in the blue band. The K-terms calculated for the V band from the different spectra show a well defined trend as a function of time. In the B band the K-terms show some scatter before maximum light due to the spectroscopic differences displayed by the trhee SNe selected. These spectral differences tend ti disappear for later epochs and, consequently the K-term curves in the B band after maximum light are much tighter. Our calculations enable us to interpolate K-terms for SNe Ia at maximum light, which should prove useful to study the Hubble diagram for these objects.
TL;DR: In this article, the authors describe the operation of the APS and the scanning procedures and parameters for the POSS I. The database, including the cataloged objects and the pixel data for the non-stellar images, will be available to the scientific community on-line via Internet.
Abstract: We have just completed scanning glass copies of the blue and red plates in the original Palomar Observatory - National Geographic Sky Survey (POSS I) for the fields with b >/= |20 deg.|. All of the detected images are being cataloged with positions, shapes, magnitudes and colors. The stellar and non-stellar images are separated using a neural network approach. We estimate that there will be nearly a billion stellar objects and image data for several million galaxies in the finished database. The database, including the cataloged objects and the pixel data for the non-stellar images, will be available to the scientific community on-line via Internet. This paper is the first of a series describing the APS Catalog of the POSS I. In this first paper we describe the operation of the APS and the scanning procedures and parameters for the POSS I.
TL;DR: The General Catalog of Variable Stars contains information necessary for obtaining observaitons of variable stars, and in particular, cataclysmic variables as discussed by the authors, but the references to finding charts are often to journals not easily accessible to some astronomers.
Abstract: The General Catalog of Variable Stars contains information necessary for obtaining observaitons of variable stars, and in particular, cataclysmic variables. However, the coordinates presented are not accurate enough for observatories such as the Hubble Space Telescope, and the references to finding charts are often to journals not easily accessible to some astronomers. We have therefore created a catalog of all cataclysmic variables (known to us as of 1992 February) which contains coordinates (measured in the reference frame of the Hubble Space Telescope Guide Star Survey for the non-novae, and obtained from the literature for the novae), the variability type, the magnitude range, and references to both finding charts and spectroscopy. The atlas contains finding charts for the dwarf novae, novalike variables, and objects classified only as cataclysmic variables, for which we could obtain valid identifications; a similar catalog and atlas for novae has been published by Duerbeck (1987a).
TL;DR: In this paper, the authors presented spectra of O to M stars, luminosity classes V, III, and Ib in the wavelength range 5800-8900 A, at approxiamtely 15 A resolution.
Abstract: We present spectra of O to M stars, luminosity classes V, III, and Ib in the wavelength range 5800-8900 A, at approxiamtely 15 A resolution. We give identifications of the main spectral features and show that the stars follow well defined morphological sequences in both temperature and luminosity. This wavelength region and resolution, combined with the high sensitivity of silicon-based detectors, are very useful for spectral classification.
TL;DR: The spectral classification of the red carbon stars has been brought into the Revised MK system by combining some of the features of the old R, N, and C classifications, as modified by Yamashita, and adding numerical abundance indices as discussed by the authors.
Abstract: The spectral classification of the red carbon stars has been brought into the Revised MK system by combining some of the features of the old R, N, and C classifications, as modified by Yamashita, and adding numerical abundance indices. The new types are intended to: (1) Define the population to which the star belongs. (2) Allow quick interpolation between the detailed atmospheric analyses of individual stars. (3) Indicate the differences between carbon stars in different parts of our galaxy, and in other galaxies. It is the flexibility of the notation, allowing the incorporation of improved criteria, that should make the new system useful.
TL;DR: Fourier cosine coefficients a1 to a6 are tabulated and shown graphically for light curves of contact binary stars of one (solar) effective temperature, with orbital inclinations, 30 degrees, mass-ratios, 0.05, and three values of the degree of contact.
Abstract: Fourier cosine coefficients a1 to a6 are tabulated and shown graphically for light curves of contact binary stars of one (solar) effective temperature, with orbital inclinations, 30 degrees
TL;DR: In this paper, the authors present a review of the improvements that have been found to result in more reliable and detailed maps in all aspects of surface imaging of stars from the profiles of spectral lines.
Abstract: Surface imaging of stars from the profiles of spectral lines, has become an important tool in modern astrophysics. It is presently used for mapping the distribution of chemical elements on Ap stars and the variation in temperature over the surface of late-type stars. Magnetic field maps will be produced as soon as high quality polarization observations are available. Recently imaging techniques have been developed for application to eclipsing binary stars. In this paper we review the improvements we have found to result in more reliable and detailed maps in all aspects of surface imaging.
TL;DR: In this paper, the first observations of central velocity dispersions are presented for galaxies in the rich cluster Abell 665 at z = 0.18, and the measurements result in a well defined Faber Jackson relation for the red cluster members.
Abstract: There is significant evidence that galaxy evolution is a complex process, in which mass accretion, mergers, and star bursts play an important role. This complex evolution adds significant freedom to the modeling of observations of high redshift galaxies. Additional constraints are necessary. Such constraints may come from measurements of circular velocities, or velocity dispersions of galaxies at intermediate redshift. The first observations of central velocity dispersions are presented for galaxies in the rich cluster Abell 665 at z=0.18. Full curves of radial velocity dispersion of cluster members are presented. The measurements result in a well defined Faber Jackson relation for the red cluster members. A blue galaxy is lying 2.2 mag off the relation, and has an "E+A" spectrum. This "Butcher Oemler" galaxy is rotating rapidly, which is indicative of a strong disk. The observations show that measurements of central velocity dispersions are possible with current telescope capabilities. Observaitons at higher redshifts will lead to new constraints on both galaxy evolution and cosmology.
TL;DR: In this article, the authors present observations obtained both in quiescence and eruption that emphasize the great similarity of the star to well-credentialed dwarf novae like WZ Sagittae.
Abstract: For many years VY Aquarii has been regarded as a charter member of the class fo recurrent novae, because it erupted several times, with outburst amplitudes of ~8 mag, exceeding those normally attributed to dwarf novae. We present observations obtained both in quiescence and eruption that emphasize the great similarity of the star to well-credentialed dwarf novae like WZ Sagittae. Long-term visual and photographic coverage shows two types of eruptions, differing in brightness and timescale by a factor of ~5. A transient wave in the quiescent light curve suggests a period in the range 80-120 minutes, which could be the orbital period of the underlying binary. Photometry during a long eruption in 1986 showed a large-amplitude modulation ("superhump") with a period of 92.7 (or possibly 99.1) minutes, which slowly decreased during the eruption. These are normal signatures of SU Ursae Majoris stars, a subclass of dwarf novae. The superhumps observed in SU UMa stars appear to show a similar degree of period instability, such that P ~ -(3-10)X10-5. Perhaps a more physically significant expression of this is a period-magnitude law: the periods decrease by 0.64±0.10% per magnitude of decline,_ at least during the early decline. This is a plausible decrease to expect from the precessing-disk model for the origin of superhumps, assuming the disk to be largest near maximum light.
TL;DR: In this article, the main beam efficiency measurements at 211-365 GHz of the Caltech Submillimeter Observatory (OSO) were reported based on antenna temperature measurements of Mars, Jupiter, Saturn, and the Moon.
Abstract: We report main beam efficiency measurements at 211-365 GHz of the Caltech Submillimeter Observatory (OSO). These calculations are based on antenna temperature measurements of Mars, Jupiter, Saturn, and the Moon. We also present an analysis and review of the broadband millimeter and submillimeter continuum emission properties of Mars, Jupiter, Saturn, and the Moon. Through this analysis we establish a set of recommended main beam efficiencies for the facility receivers at the CSO.
TL;DR: In this paper, an objective-prism H-alpha survey of star-forming regions using the CIDA 1 m Schmidt Camera was carried out for selected areas of the Taurus-Auriga molecular clouds.
Abstract: We have begun an objective-prism H-alpha survey of star-forming regions using the CIDA 1 m Schmidt Camera, with a limiting magnitude of V ~ 18. We report here first results for selected areas of the Taurus-Auriga molecular clouds. Of the list of candidates found in the objective-prism plates, 12 stars have been confirmed as pre-main sequence by the detection of the Li I 6707 A absorption line. Five of these stars are in the dark cloud L1544, where only one T Tauri star was previously known. The new stars have very late spectral types and most have estimated masses between 0.2 M and 0.3 M.
TL;DR: In this paper, moderate resoluiton CCD spectra for giants in six old open clusters in the direction of the galactic anti-center (NGC 188, 6705 (M11), 6819, 6940, and IC 4756) were obtinaed.
Abstract: We have obtinaed moderate resoluiton CCD spectra for giants in six old open clusters in the direction of the galactic anti-center (NGC 188, 6705 (M11), 6819, 6940, and IC 4756). Using cross correlation techniques, we determined radial velocities for stars in each cluster and used these values to compute a cluster mean accurate to ~10 km s-1. These means agree quite well with published values. We then used between 4 and 6 spectroscopic indices to measure the metallicity of each star and produce a mean cluster metallicity. Following the Galactic metallicity gradient, more distant clusters are metal poor compared with clusters closer to the solar neighborhood. We used our data, which is centered around the solar radius, to supplement published results by Friel and Janes (1993), and used the combined data set to better define the Galactic metallicity gradient. We found that delta[Fe/H]/deltaRgc = -0.097 ± 0.017 dex/kpc for Rgc > 7 kpc. This result agrees quite well with that of Friel and Janes and with that of other authors. We discuss a possible correlation between age and Mg-enhancement which is indicated by the differences between Fe and Mg line strength among cluster giants. We also briefly consider metallicity dependencies with age and height above the Galactic plane.
TL;DR: In this paper, the IRAS data base at the positions of the 1808 O6-B9.5 stars in The Bright Star Catalog for extended objects with excess emission at 60 microns, indicating the presence of interstellar dust at the location of the star.
Abstract: We surveyed the IRAS data base at the positions of the 1808 O6-B9.5 stars in The Bright Star Catalog for extended objects with excess emission at 60 microns, indicating the presence of interstellar dust at the location of the star. Within 400 pc the filling factor of the interstellar medium, for dust clouds with a density greater than 0.5/cu cm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the density distribution function appears to follow a power law index - 1.25. When the dust clouds are mapped onto the galactic plane, the sun appears to be located in a low-density region of the interstellar medium of width about 60 pc extending at least 500 pc in the direction of longitudes 80 deg - 260 deg, a feature we call the 'local trough'.
TL;DR: The design and control system of the Berkeley Automatic Imaging Telescope (BAIT), an observatory that performs all its tasks with minimal human intervention, is described and an analysis of its performance during its first eight months is presented.
Abstract: We describe the design and control system of the Berkeley Automatic Imaging Telescope (BAIT), an observatory that performs all its tasks with minimal human intervention. We concentrate on the system's software, especially that which communicates with astronomers at remote sites and that which schedules targets during the night. BAIT has been in nearly continuous operation since January, 1992; we present an analysis of its performance during its first eight months.
TL;DR: In this article, high-resolution, very high signal-to-noise echelle spectra of the diffuse interstellar bands (DIBs) have been obtained in the wavelength range 5760-5830 A and 6100-6200 A in selected lightly-tomoderately reddened stars.
Abstract: New high resolution, very high signal-to-noise echelle spectra of the diffuse interstellar bands (DIBs) have been obtained in the wavelength range 5760-5830 A and 6100-6200 A in selected lightly-to-moderately reddened stars. These spectra have been used to search for the existence of substructures in the so-called 5778 band (first suggested by Herbig 1975) and to identify similar features in another wavelength range. We have detected many weak absorptions in these two spectral regions, and we show that these features are not spectrograph artifacts, are not telluric (H2O) lines, and are not absorption features in the atmospheres of the background stars. Thus they must arise in interstellar medium clouds. The spectra of dark interstellar clouds are much more complex than imagined until very recently. The pattern of weak features changes as the intensity ratio of the major DIBs at 5780 and 5797 A varies, which suggests that many strong and weak features may belong to the same carrier species.
TL;DR: In this paper, the authors obtained low-dispersion IUE spectra of the late-type stars HD 15638 (F3 V), HR 1608 (=63 Eridani, KO IV), and HR 8210 (A8m) and fit the Lyman-alpha profile and UV continuum of each white dwarf using pure hydrogen models.
Abstract: We have obtained low-dispersion IUE spectra of the late-type stars HD 15638 (F3 V), HR 1608 (=63 Eridani, KO IV), and HR 8210 (A8m). Each of these stars had been detected as a strong EUV source with the Wide Field Camera aboard the ROSAT satellite. The short-wavelength IUE spectrum of each star reveals the presence of a hot white-dwarf companion. We have fit the Lyman-alpha profile and UV continuum of each white dwarf using pure hydrogen models. The excellent fit of the data to the models provides confirmation of the Finley and Koester absolute calibration of the SWP camera of IUE. The UV data alone are insufficient to constrain the model gravity, but an additional constraint is provided by the photometric distance to the late-type primary. The most interesting of the three white dwarfs is the companion to HR 8210 for which our results imply a mass of 1.15 +0.05/-0.15 solar mass. This result is in good agreement with the lower limit on the mass derived from the spectroscopic orbit (greater than 1.1 solar mass), provided that the inclination is close to 90 deg.
TL;DR: The velocity field of the ionized gas has been determined over most of the optical disk at an angular resolution of 2-8" and a realtive velocity accuracy of 1-2 km s-1 rms as discussed by the authors.
Abstract: The Maryland-Caltech wide-field Fabry-Perot camera has been used to image H-alpha emission in the grand design spiral galaxy M51. The velocity field of the ionized gas has been determined over most of the optical disk at an angular resolution of 2-8" and a realtive velocity accuracy of 1-2 km s-1 rms. The well-known kinematic perturbations due to density wave streaming are clearly resolved in both arm and interarm regions. Determination of the radius at which the gas and spiral pattern corotate using reversals in the streaming direction, frequently proposed as the preferred method of locating the corotation resonance, is hampered by the observed complexity of the density wave response. Nonetheless, new evidence is presented that supports previous determinations using other methods that corotation of the inner spiral is located near a glactocentric radius of 6 kpc, and that the outer optical arms cannot be part of the same spiral pattern as the inner arms.
TL;DR: In this paper, the radial velocity data for the six brightest members of the open cluster Tr 14 is presented based on high dispersion spectra obtained over a five-night interval, and it is shown that none of these O-type stars appear to be spectroscopic binaries with periods of the order of a week or less.
Abstract: We present radial velocity data for the six brightest members of the open cluster Tr 14 based on high dispersion spectra obtained over a five night interval. None of these O-type stars appear to be spectroscopic binaries with periods of the order of a week or less, and none are speckle binaries. This binary fraction is low for O-type stars, and we suggest that the lack of primoridal hard binaries and their dynamical interactiosn may explain how the cluster has maintained a high spatial density even after several cluster crossing times.
TL;DR: In this article, a set of neural network image classifiers are used to automatically perform star galaxy discrimination to an imposed O magnitude limit of 20.0, and the efficiency of image classification and sample completeness through comparisons with a variety of independent studies of the NGP area is assessed.
Abstract: A two color survey of 9 fileds of the first epoch Palomar Sky Survey, centered on the North Galactic Pole, has been performed with the Minnesota Automated Plate Scanner. A set of neural network image classifiers are used to automatically perform star galaxy discrimination to an imposed O magnitude limit of 20.0. We assess the efficiency of image classification and sample completeness through comparisons with a variety of independent studies of the NGP area.
TL;DR: A general Bayesian iterative algorithm with entropy prior for image reconstruction that solves the cases of both pure Poisson data and PoissonData with Gaussian readout noise and it is shown that ground based images can be reconstructed successfully with the algorithm.
Abstract: This paper describes a general Bayesian iterative algorithm with entropy prior for image reconstruction. It solves the cases of both pure Poisson data and Poisson data with Gaussian readout noise. The algorithm maintains positivity of the solution; it includes case-specific prior information (default map) and flatfield corrections; it removes background and can be acclerated to be faster than the Richardson-Lucy algorithm. In order to determine the hyperparameter that balances the entropy and likelihood terms in the Bayesian approach, we have used a likeliehood cross-validation technique. Cross-validation is more robust than other methods because it is less demanding in terms of the knowledge of exact data characteristics and of the point spread function. We have used the algorithm to reconstruct successfully images obtained in different space and ground based imaging situations. It has been possible to recover most of the original intended capabilities of the Hubble Space Telescope Wide Field and Planetary Camera and Faint Object Camera from images obtained in their present state. Semi-real situations for the future Wide Field Planetary Camera 2 show that even after the repair of the spherical aberration problem, image reconstruction can play a key role in improving the resolution of the cameras, well beyond the design of the Hubble instruments. We also show that ground based images can be reconstructed successfully with the algorithm. A technique which consists of dividing the CCD observations into two frames, with one half the exposure time each, emerges as a recommended procedure for the utilization of the described algorithms. We have compared our technique with two commonly used reconstruction algorithms: the Richardson-Lucy and the Cambridge Maximum Entropy algorithms.