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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

THERMAL INFRARED IMAGING AND ATMOSPHERIC MODELING OF VHS J125601.92-125723.9 b: EVIDENCE FOR MODERATELY THICK CLOUDS AND EQUILIBRIUM CARBON CHEMISTRY IN A HIERARCHICAL TRIPLE SYSTEM

We present and analyze Subaru/IRCS L ′ and M ′ images of the nearby M dwarf VHS J125601.92-125723.9 (VHS 1256), which was recently claimed to have an ∼11 M {sub J} companion (VHS 1256 b) at ∼102 au separation. Our adaptive optics images partially resolve the central star into a binary, whose components are nearly equal in brightness and separated by 0.″106 ± 0.″001. VHS 1256 b occupies nearly the same near-infrared position in the color–magnitude diagram as HR 8799 bcde and has a comparable L ′ brightness. However, it has a substantially redder H – M ′ color, implying a relatively brighter M ′ flux density than for the planets of HR 8799 and suggesting that non-equilibrium carbon chemistry may be less significant in VHS 1256 b. We successfully match the entire spectral energy distribution (optical through thermal infrared) for VHS 1256 b to atmospheric models assuming chemical equilibrium, models that failed to reproduce HR 8799 b at 5 μ m. Our modeling favors slightly thick clouds in the companion's atmosphere, although perhaps not quite as thick as those favored recently for HR 8799 bcde. Combined with the non-detection of lithium in the primary, we estimate that the system is at least 200 Myr old and the masses of the stars comprising the central binary are at least 58 M {sub J} each. Moreover, we find that some of the properties of VHS 1256 are inconsistent with the recent suggestion that it is a member of the AB Dor moving group. Given the possible range in distance (12.7 pc versus 17.1 pc), the lower mass limit for VHS 1256 b ranges from 10.5 M {sub J} to 26.2 M {sub J} . Our detection limits rule out companions more massive than VHS 1256 b exterior to 6–8 au, placing significant limits on and providing some evidence against a second, more massive companion that may have scattered the wide-separation companion to its current location. VHS 1256 is most likely a very low-mass hierarchical triple system and could be the third such system in which all components reside in the mass regime of brown dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

An Empirical Determination of the Intergalactic Background Light Using Near-Infrared Deep Galaxy Survey Data Out to 5 Micrometers and the Gamma-Ray Opacity of the Universe

We extend our previous model-independent determination of the intergalactic background light, based purely on galaxy survey data, out to a wavelength of 5 micrometers. Our approach enables us to constrain the range of photon densities, based on the uncertainties from observationally determined luminosity densities and colors. We further determine a 68% confidence upper and lower limit on the opacity of the universe to gamma-rays up to energies of 1.6/(1 + z) terraelectron volts. A comparison of our lower limit redshift-dependent opacity curves to the opacity limits derived from the results of both ground-based air Cerenkov telescope and Fermi-LAT observations of PKS 1424+240 allows us to place a new upper limit on the redshift of this source, independent of IBL modeling.

BL Lacertae↗
DOE OSTI2019

Monopoles, strings, and necklaces in SO(10) and E 6

We employ a variety of symmetry breaking patterns in SO(10) and E 6 Grand Unified Theories to demonstrate the appearance of topological defects including magnetic monopoles, strings, and necklaces. We show that independent of the symmetry breaking pattern, a topologically stable superheavy monopole carrying a single unit of Dirac charge as well as color magnetic charge is always present. Lighter intermediate mass topologically stable monopoles carrying two or three quanta of Dirac charge can appear in SO(10) and E 6 models respectively. These lighter monopoles as well as topologically stable intermediate scale strings can survive an inflationary epoch. We also show the ap­pearance of a novel necklace configuration in SO(10) broken to the Standard Model via SU(4) c × SU(2) L × SU(2) R . It consists of SU(4) c and SU(2) R monopoles connected by flux tubes. Necklaces consisting of monopoles and antimonopoles joined together by flux tubes are also identified. Even in the absence of topologically stable strings, a monopole-string system can temporarily appear. This system decays by emitting gravity waves and we provide an example in which the spectrum of these waves is strongly peaked around 10 –4 Hz with Ω qw h 2 ≃10 –12 . This spectrum should be within the detection capability of LISA.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Rapid Identification of Calcium Aluminate Inclusions in Steels Using Cathodoluminescence Analysis

We propose a method to identify calcium aluminate inclusions in calcium-treated aluminum-killed steels (Ca{sub 12}Al{sub 14}O{sub 33}, CaAl{sub 4}O{sub 7}, CaAl{sub 12}O{sub 19}, and Al{sub 2}O{sub 3}) using cathodoluminescence (CL) analysis. Such inclusions result in nozzle clogging and melting of the stopper rod during continuous casting. We obtain CL images and CL spectra of calcium aluminate inclusions in model samples of calcium-treated aluminum-killed steel. The model samples are prepared by heating mixtures of Fe powder, Al powder, and Ca shot at 1550 °C in an argon atmosphere. On the basis of the CL colors and CL spectra of the calcium aluminate inclusions, we demonstrate that it is possible to distinguish Ca{sub 12}Al{sub 14}O{sub 33}, CaAl{sub 4}O{sub 7}, CaAl{sub 12}O{sub 19}, and Al{sub 2}O{sub 3} inclusions from CaAl{sub 2}O{sub 4} and Ca{sub 3}Al{sub 10}O{sub 18} inclusions, which do not cause nozzle clogging and melting of the stopper rod, by comparing CL images obtained using digital cameras with and without a built-in filter. The acquisition times for the CL images are less than 10 seconds. Thus, the method we present here can be applied for the rapid detection of harmful calcium aluminate inclusions during continuous casting. The CL spectra also provide basic information to specify compositions in agglomerated calcium aluminate inclusions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Analysis of broad-lined Type Ic supernovae from the (intermediate) Palomar Transient Factory

Here, we study 34 Type Ic supernovae that have broad spectral features (SNe Ic-BL). This is the only SN type found in association with long-duration gamma-ray bursts (GRBs). We obtained our photometric data with the Palomar Transient Factory (PTF) and its continuation, the intermediate PTF (iPTF). This is the first large, homogeneous sample of SNe Ic-BL from an untargeted survey. Furthermore, given the high observational cadence of iPTF, most of these SNe Ic-BL were discovered soon after explosion. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We analyzed the shape of the r-band light curves, finding a correlation between the decline parameter Δm 15 and the rise parameter Δm -10 . We studied the SN colors and, based on g-r, we estimated the host-galaxy extinction for each event. Peak r-band absolute magnitudes have an average of -18.6 ± 0.5 mag. We fit each r-band light curve with that of SN 1998bw (scaled and stretched) to derive the explosion epochs. We computed the bolometric light curves using bolometric corrections, r-band data, and g-r colors. Expansion velocities from Fe II were obtained by fitting spectral templates of SNe Ic. Bolometric light curves and velocities at peak were fitted using the semianalytic Arnett model to estimate ejecta mass Mej, explosion energy E K and 56Ni mass M(56Ni) for each SN. We find average values of M ej = 4 ± 3 M ⊙ , E K = (7 ± 6)×10 51 erg, and M( 56 Ni)=0.31 ± 0.16 M ⊙ . The parameter distributions were compared to those presented in the literature and are overall in agreement with them. We also estimated the degree of 56 Ni mixing using scaling relations derived from hydrodynamical models and we find that all the SNe are strongly mixed. The derived explosion parameters imply that at least 21% of the progenitors of SNe Ic-BL are compatible with massive (> 28 M ⊙ ), possibly single stars, whereas at least 64% might come from less massive stars in close binary systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

String-Breaking Dynamics in Quantum Adiabatic and Diabatic Processes

Confinement prohibits isolation of color charges, e.g., quarks, in nature via a process called string breaking : the separation of two charges results in an increase in the energy of a color flux, visualized as a string, connecting those charges. Eventually, creating additional charges is energetically favored, hence breaking the string. Such a phenomenon can be probed in simpler models, including quantum spin chains, enabling enhanced understanding of string-breaking dynamics. A challenging task is to understand how string breaking occurs as time elapses, in an out-of-equilibrium setting. This work establishes the phenomenology of dynamical string breaking induced by a gradual increase of string tension over time. It, thus, goes beyond instantaneous quench processes and enables tracking the real-time evolution of strings in a more controlled setting. We focus on domain-wall confinement in a family of quantum Ising chains. Our results indicate that, for sufficiently short strings and slow evolution, string breaking can be described by the transition dynamics of a two-state quantum system akin to a Landau-Zener process. For longer strings, a more intricate spatiotemporal pattern emerges: the string breaks by forming a superposition of bubbles (domains of flipped spins of varying sizes), which involve highly excited states. We finally demonstrate that string breaking driven only by quantum fluctuations can be realized in the presence of sufficiently long-ranged interactions. This work holds immediate relevance for studying string breaking in quantum-simulation experiments.

Ising model↗
DOE OSTI2026

Using Gravitational Lensing to Probe for Candidate Quintessential Galaxies in the Epoch of Reionization

Abstract Understanding the properties of the first generation of galaxies is an ongoing challenge in observational astrophysics. James Webb Space Telescope deep-field observations have led to the identification of large numbers of galaxies within the Epoch of Reionization (EoR); however, it remains observationally challenging to study the detailed properties of the most numerous, faint high- z galaxies without strong gravitational lensing. To this end, we present five m AB ≃ 24 galaxies, all projected behind the cores of massive clusters where high lensing magnifications significantly (≳1.5 mag) boost their observed brightness. These galaxies are each characterized by a drop-off in their spectra between the near-IR and optical wavelengths, suggesting the presence of a Lyman break at z > 6. The bright sources enable precise dropout color constraints. We combine the dropout data with follow-up imaging to constrain continuum slopes redward of their breaks. Using the open-source spectral energy distribution modeling software Prospector , we characterize two of these galaxies as probable high- z ( z ∼ 6.5–7) and three as probable low- z ( z ∼ 2) sources, demonstrating that for very bright ( m AB < 24) dropout candidates even limited photometric data have good power to distinguish between high- z galaxies and red or dusty low- z galaxies. The two candidate high- z dropouts are comparably bright to the brightest galaxies identified at such redshifts in deep fields, but due to lensing magnifications are intrinsically fainter by at least 1.5 mag. If confirmed, these galaxies represent exciting laboratories for performing detailed follow-up studies of galaxy properties within the EoR.

Roberson, Joshua [University of Cincinnati] (ORCID↗
NASA NTRS1977

The upper Jovian atmosphere aerosol content determined from a satellite eclipse observation

An eclipse of Ganymede observed in 30 colors with a multichannel spectrometer and the 5-m Hale telescope is analyzed to determine the aerosol content of the upper Jovian atmosphere. Contemporary radiative-equilibrium atmospheric models are used, and less restrictive a priori assumptions about the aerosol distribution are made than in previous studies. Preliminary processing of the raw data to correct for telescope aperture change and to remove scattered light is described, eclipse light-curve theory is reviewed, and light-curve features are examined. The primary 'cloudy' atmospheric model employed is outlined along with the computational method, and results are presented on aerosol profiles, the upper limit of the aerosol region, the aerosol structure, the sensitivity of the aerosol profiles to various parameters, and the stratospheric aerosol distribution. The aerosol profiles are found to indicate a very dilute stratospheric haze overlying a tenuous tropopause cloud or cloud top.

Smith, D. W.↗
NASA NTRS1981

IUE observations of eight OB stars in NGC 2244 - Ultraviolet continua and extinction

Low-resolution IUE ultraviolet continuum observations of O and B stars in the young open cluster NGC 2244 are presented. When only relative energy distributions are considered, thereby eliminating any dependence on reddening corrections or absolute energy calibrations, it is found that the ultraviolet energy distributions of the O stars have significantly cooler ultraviolet color temperatures than the cluster early B stars. The effect is not considered a property of the B stars because their observed continua can be well represented by model atmospheres and ultraviolet extinction characteristic of the local interstellar medium. The effect is thus thought to originate with the O star continua and can be due to either interstellar effects (the cluster O stars suffer additional extinction which has an anomalous wavelength dependence) or stellar effects (the physics incorporated into current O star model atmospheres is inadequate). It is noted that current data do not allow a definitive distinction to be made between these two alternatives, and the possible origins and consequences of each are considered.

Massa, D.↗
NASA NTRS1983

Heterogeneous shock-induced thermal radiation in minerals

A 500-channel optical imaging intensifying and spectral digital recording system is used for recording the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. The initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range reveal grey-body emission spectra corresponding to temperatures in the 3000 to 4000 K range and emissivities ranging from 0.003 to 0.02. With gypsum and calcite, distinctive line spectra are superimposed on the thermal radiation. The observed color temperatures are greater than the Hugoniot temperature by a factor of 2 to 10; this is calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are thought to be real. It is concluded that a large number of closed spaced high temperature shear-band regions are being detected immediately behind the shock front.

Kondo, K.-I.↗
NASA NTRS1987

The moderately interacting Algol-type eclipsing binary RY Geminorum

Ultraviolet spectra of the Algol-type semidetached system RY Geminorum, whose components can be described as A0 V and K0 IV, have been matched to the ultraviolet spectrum by Kurucz (1979) model atmospheres, and a best fit is found for T(eff) = 9150 K. Comparison with standard star spectra requires that this value be raised to 9400 K. The color excess of the system is determined to be no more than E(B-V) = 0.03 mag; the distance to the system is about 360 pc. The masses are approximately 2.36 and 0.38 solar masses, and the radii are 2.5 and 5.8 solar radii, respectively. The separation of the two centers is 26 solar radii. Evidence for a circumstellar line absorption is found in optical and ultraviolet spectrograms, and evidence is found in IUE spectra taken in partial eclipse for circumstellar emission lines of the type detected previously in the WS Serpentis stars and in several semidetected systems of the Algol type.

Plavec, Mirek J.↗
NASA NTRS1991

Evolutionary models of halo stars with rotation. I - Evidence for differential rotation with depth in stars

Evolutionary models of metal-poor stars are computed including the effects of rotation, and their properties are compared with observations. The models rotate slowly at the surface, in agreement with the observed upper limits on the rotation velocity at main-sequence turnoff; they also have substantial differential rotation with depth. This differential rotation preserves a sufficient amount of internal angular momentum to explain the rapid rotation of evolved horizontal-branch stars. These results hold for a wide range of angular momentum loss and transport parameter values. Differences and similarities between the surface and internal rotation of solar metallicity and metal-poor models are discussed. Rigidly rotating models are found to be incompatible with the observations once giant branch mass loss is taken into account. Horizontal-branch rotation velocity measurements as a function of color are proposed as a test of the rotation law enforced in convection zones, and their dependence on cluster age and metallicity are discussed.

Pinsonneault, Marc H.↗
NASA NTRS1992

Atmospheric correction of AVIRIS data in ocean waters

Hyperspectral data offers unique capabilities for characterizing the ocean environment. The spectral characterization of the composition of ocean waters can be organized into biological and terrigenous components. Biological photosynthetic pigments in ocean waters have unique spectral ocean color signatures which can be associated with different biological species. Additionally, suspended sediment has different scattering coefficients which result in ocean color signatures. Measuring the spatial distributions of these components in the maritime environments provides important tools for understanding and monitoring the ocean environment. These tools have significant applications in pollution, carbon cycle, current and water mass detection, location of fronts and eddies, sewage discharge and fate etc. Ocean color was used from satellite for describing the spatial variability of chlorophyll, water clarity (K(sub 490)), suspended sediment concentration, currents etc. Additionally, with improved atmospheric correction methods, ocean color results produced global products of spectral water leaving radiance (L(sub W)). Ocean color results clearly indicated strong applications for characterizing the spatial and temporal variability of bio-optical oceanography. These studies were largely the results of advanced atmospheric correction techniques applied to multispectral imagery. The atmosphere contributes approximately 80 percent - 90 percent of the satellite received radiance in the blue-green portion of the spectrum. In deep ocean waters, maximum transmission of visible radiance is achieved at 490nm. Conversely, nearly all of the light is absorbed by the water at wavelengths greater than about 650nm and thus appears black. These spectral ocean properties are exploited by algorithms developed for the atmospheric correction used in satellite ocean color processing. The objective was to apply atmospheric correction techniques that were used for procesing satellite Coastal Zone Color Scanner (CZCS) data to AVIRIS data. Quantitative measures of L(sub W) from AVIRIS are compared with ship ground truth data and input into bio-optical models.

Terrie, Gregory↗
NASA NTRS2010

Mini-TES Observations of Comanche Carbonate and Its Distribution

The discovery by the Spirit rover of outcrops rich in Mg-Fe carbonate [Morris et al., 2010] represents another manifestation of a diverse aqueous history in Gusev crater. In 2005, observations by the Moessbauer spectrometer (MB) on outcrops dubbed Comanche provided initial indication of Fe-Mg carbonate that was subsequently supported by analysis of elemental data from the Alpha Particle X-ray Spectrometer (APXS). The recognition of a carbonate component in thermal infrared spectra measured by the Miniature Thermal Emission Spectrometer (Mini-TES) was significantly delayed due to dust contamination of the instrument's optics. With the implementation of a viable dust correction, the Comanche spectra were revisited and presented clear and compelling evidence for a Mg-Fe carbonate component that could be as much as a third of the total mineral abundance. The data from all three instruments in combination are best matched by Mg-Fe carbonate with an abundance of 16-34 wt%. Mini-TES spectra were acquired for 12 targets at various locations on the Comanche (4-5 m long) and Comanche Spur (1-2 m long) outcrops, the latter being the location of the MB and APXS measurements. The two outcrops are spectrally comparable and share similar morphology and texture based on color images from the Panoramic Camera (Pancam). The highest quality Mini-TES spectrum comes from the larger Comanche outcrop on a target named Saupitty. Linear least squares modeling of the Saupitty spectrum employed a library of laboratory spectra tailored for consistency with the APXS and MB data and included spectra representing Martian dust, a slope spectrum to account for any temperature determination errors, and a blackbody spectrum to account for differences in spectral contrast between the laboratory and Mini-TES spectrum. Successful modeling of the Comanche Saupitty spectrum required one or more carbonate phases to obtain a good fit. Excluding all carbonates from the full starting library more than doubled the root-mean-squared error of the model fit (0.147% vs. 0.299%). Because Mg-Fe carbonate and Ca-Mg carbonate (dolomite) are so spectrally similar over the range used for modeling, both provide a comparable fit. However, Carich carbonates like dolomite are precluded based on APXS data and are inconsistent with MB results. The Comanche carbonate rocks are stratigraphically above a set of olivine-rich volcaniclastic rocks known as Algonquin class that mantle the Haskin Ridge feature of the Columbia Hills. Based on ~50 Mini-TES observations, the Comanche outcrops are the only rocks that host abundant carbonate. However, a target at the base of the larger Comanche outcrop appears spectrally transitional between the carbonate and olivine units. This transitional spectral character applies to additional outcrops a few 10s of meters away from Comanche that also appear stratigraphically transitional. Additional work will attempt to establish whether we are seeing an alteration horizon or depositional unit associated with the emplacement Comanche carbonate.

Ruff, Steven W.↗
NASA NTRS2019

Analysis of Broad-Lined Type Ic Supernovae From the (Intermediate) Palomar Transient Factory

We study 34 Type Ic supernovae that have broad spectral features (SNe Ic-BL). This is the only SN type found in association with long duration gamma-ray bursts (GRBs).We obtained our photometric data with the Palomar Transient Factory (PTF) and its continuation, the intermediate PTF (iPTF). This is the first large, homogeneous sample of SNe Ic-BL from an untargeted survey. Furthermore, given the high observational cadence of iPTF, most of these SNe Ic-BL were discovered soon after explosion. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We analyzed the shape of the r-band light curves, finding a correlation between the decline parameter delta m15 and the rise parameter delta m-10. We studied the SN colors and, based on g - r, we estimated the host-galaxy extinction for each event. Peak r-band absolute magnitudes have an average of -18:6 +- 0:5 mag. We fit each r-band light curve with that of SN 1998bw (scaled and stretched) to derive the explosion epochs. We computed the bolometric light curves using bolometric corrections, r-band data, and g - r colors. Expansion velocities from Fe ii were obtained by fitting spectral templates of SNe Ic. Bolometric light curves and velocities at peak were fitted using the semianalytic Arnett model to estimate ejecta mass Mej, explosion energy EK and 56Ni mass M(56Ni) for each SN. We find average values of Mej = 4 +- 3 M sun, EK = (7 +- 6) x 1051 erg, and M(56Ni) = 0:31 +- 0:16 M . The parameter distributions were compared to those presented in the literature and are overall in agreement with them. We also estimated the degree of 56Ni mixing using scaling relations derived from hydrodynamical models and we find that all the SNe are strongly mixed. The derived explosion parameters imply that at least 21% of the progenitors of SNe Ic-BL are compatible with massive (>28 M ), possibly single stars, whereas at least 64% might come from less massive stars in close binary systems.

Supernovae↗
DOE OSTI2014

A classification scheme for young stellar objects using the wide-field infrared survey explorer AllWISE catalog: revealing low-density star formation in the outer galaxy

We present an assessment of the performance of WISE and the AllWISE data release for a section of the Galactic Plane. We lay out an approach to increasing the reliability of point-source photometry extracted from the AllWISE catalog in Galactic Plane regions using parameters provided in the catalog. We use the resulting catalog to construct a new, revised young star detection and classification scheme combining WISE and 2MASS near- and mid-infrared colors and magnitudes and test it in a section of the outer Milky Way. The clustering properties of the candidate Class I and II stars using a nearest neighbor density calculation and the two-point correlation function suggest that the majority of stars do form in massive star-forming regions, and any isolated mode of star formation is at most a small fraction of the total star forming output of the Galaxy. We also show that the isolated component may be very small and could represent the tail end of a single mechanism of star formation in line with models of molecular cloud collapse with supersonic turbulence and not a separate mode all to itself.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Hubble Space Telescope Medium Deep Survey. 2: Deconvolution of Wide Field Camera field galaxy images in the 13 hour + 43 deg field

We present isophotal profiles of six faint field galaxies from some of the first deep images taken for the Hubble Space Telescope (HST) Medium Deep Survey (MDS). These have redshifts in the range z = 0.126 to 0.402. The images were taken with the Wide Field Camera (WFC) in `parallel mode' and deconvolved with the Lucy method using as the point-spread function nearby stars in the image stack. The WFC deconvolutions have a dynamic range of 16 to 20 dB (4 to 5 mag) and an effective resolution approximately less than 0.2 sec (FWHM). The multiorbit HST images allow us to trace the morphology, light profiles, and color gradients of faint field galaxies down to V approximately equal to 22 to 23 mag at sub-kpc resolution, since the redshift range covered is z = 0.1 to 0.4. The goals of the MDS are to study the sub-kpc scale morphology, light profiles, and color gradients for a large samole of faint field galaxies down to V approximately equal to 23 mag, and to trace the fraction of early to late-type galaxies as function of cosmic time. In this paper we study the brighter MDS galaxies in the 13 hour + 43 deg MDS field in detail, and investigate to what extent model fits with pure exponential disks or a(exp 1/4) bulges are justified at V approximately less than 22 mag. Four of the six field galaxies have light profiles that indicate (small) inner bulges following r(exp 1/4) laws down to 0.2 sec resolution, plus a dominant surrounding exponential disk with little or no color gradients. Two occur in a group at z = 0.401, two are barred spiral galaxies at z = 0.179 and z = 0.302, and two are rather subluminous (and edge-on) disk galaxies at z = 0.126 and z = 0.179. Our deep MDS images can detect galaxies down to V, I approximately less than 25 to 26 mag, and demonstrate the impressive potential of HST--even with its pre-refurbished optics--to resolve morphological details in galaxies at cosmologically significant distances (v approximately less than 23 mag). Since the median redshift of these galaxies is approximately less than 0.4, the HST resolution allows us to study sub kpc size scales at the galaxy, which cannot be done with stable images over wide fields from the best ground-based sites.

Windhorst, R. A.↗