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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Fringing Analysis and Simulation for the Vera C. Rubin Observatory’s Legacy Survey of Space and Time

Abstract The presence of fringing in astronomical Charge-Coupled Device (CCD) images will have an impact on photometric quality and measurements. Yet its impact on the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) has not been fully studied. We present a detailed study on fringing for CCDs already implemented on the Rubin Observatory LSST Camera’s focal plane. After making physical measurements and knowing the compositions, we developed a model for the e2v CCDs. We present a method to fit for the internal height variation of the epoxy layer within the sensors based on fringing measurements in a laboratory setting. This method is generic enough that it can be easily modified to work for other CCDs. Using the derived fringing model, we successfully reproduce comparable fringing amplitudes that match the observed levels in images taken by existing telescopes with different optical designs. This model is then used to forecast the expected level of fringing in a single LSST y -band sky background exposure with Rubin telescope optics in the presence of a realistic time-varying sky spectrum. The predicted fringing amplitude in LSST images ranges from 0.04% to 0.2% depending on the location of a CCD on the focal plane. We find that the predicted variation in surface brightness caused by fringing in LSST y -band sky background images is about 0.6 μ Jy arcsec − 2 , which is 40 times larger than the current measurement error. We conclude that it is necessary to include fringing correction in the Rubin’s LSST image processing pipeline.

Astronomy & Astrophysics↗
DOE OSTI2020

Estimating Atmospheric Parameters of DA White Dwarf Stars with Deep Learning

The determination of atmospheric parameters of white dwarf stars (WDs) is crucial for researches on them. Traditional methodology is to fit the model spectra to observed absorption lines and report the parameters with the lowest χ 2 error, which strongly relies on theoretical models that are not always publicly accessible. In this work, we construct a deep learning network to model-independently estimate T eff and log g of DA stars (DAs), corresponding to WDs with hydrogen-dominated atmospheres. The network is directly trained and tested on the normalized flux pixels of full optical wavelength range of DAs spectroscopically confirmed in the Sloan Digital Sky Survey. Experiments in test yield that the rms error for T eff and log g approaches 900 K and 0.1 dex, respectively. This technique is applicable for those DAs with T eff from 5000 to 40,000 K and log g from 7.0 to 9.0 dex. Furthermore, the applicability of this method is verified for the spectra with degraded resolution of ~200. So it is also practical for the analysis of DAs that will be detected by the Chinese Space Station Telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Chemical Inventory of the Planet-hosting Disk PDS 70

As host to two accreting planets, PDS 70 provides a unique opportunity to probe the chemical complexity of atmosphere-forming material. We present ALMA Band 6 observations of the PDS 70 disk and report the first chemical inventory of the system. With a spatial resolution of 0."4–0."5 (~50 au), 12 species are detected, including CO isotopologs and formaldehyde, small hydrocarbons, HCN and HCO{sup +} isotopologs, and S-bearing molecules. SO and CH{sub 3}OH are not detected. All lines show a large cavity at the center of the disk, indicative of the deep gap carved by the massive planets. The radial profiles of the line emission are compared to the (sub)millimeter continuum and infrared scattered light intensity profiles. Different molecular transitions peak at different radii, revealing the complex interplay between density, temperature, and chemistry in setting molecular abundances. Column densities and optical depth profiles are derived for all detected molecules, and upper limits obtained for the nondetections. Excitation temperature is obtained for H{sub 2}CO. Deuteration and nitrogen fractionation profiles from the hydrocyanide lines show radially increasing fractionation levels. Comparison of the disk chemical inventory to grids of chemical models from the literature strongly suggests a disk molecular layer hosting a carbon-to-oxygen ratio C/O > 1, thus providing for the first time compelling evidence of planets actively accreting high C/O ratio gas at present time.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2021

Precision Thermal Control (PTC) Technology to Enable Thermally Stable Telescopes

The Precision Thermal Control (PTC) project was a multiyear effort initiated in Fiscal Year 2017 to mature the Technology Readiness Level (TRL) of technologies required to enable ultra-thermally stable ultraviolet/ optical/infrared (UVOIR) space telescope primary-mirror (PM) assemblies for ultra-high-contrast observations of exoplanets. PTC had three objectives: (1) validate thermal optical performance models, (2) derive thermal system stability specifications, and (3) demonstrate multi-zonal active thermal control. PTC successfully achieved its objectives and matured active thermal control technology to at least TRL 5. PTC’s key accomplishments are a demonstration of better than 2-mK root-mean-square (rms) stable thermal control of the 1.5-m ultra-low-expansion (ULE®) Advanced Mirror Technology Development-2 (AMTD-2) mirror when exposed to thermal disturbances in a relevant thermal/vacuum environment, and the ability to shape the 1.5-m AMTD-2 mirror to picometer precision.

thermal control↗
NASA NTRS1984

Conceptual design of a hybrid Ge:Ga detector array

For potential applications in space infrared astronomy missions such as the Space Infrared Telescope Facility and the Large Deployable Reflector, integrated arrays of long-wavelength detectors are desired. The results of a feasibility study which developed a design for applying integrated array techniques to a long-wavelength (gallium-doped germanium) material to achieve spectral coverage between 30 and 200 microns are presented. An approach which builds up a two-dimensional array by stacking linear detector modules is presented. The spectral response of the Ge:Ga detectors is extended to 200 microns by application of uniaxial stress to the stack of modules. The detectors are assembled with 1 mm spacing between the elements. Multiplexed readout of each module is accomplished with integration sampling of a metal-oxide-semiconductor (MOS) switch chip. Aspects of the overall design, including the anticipated level of particle effects on the array in the space environment, a transparent electrode design for 200 microns response, estimates of optical crosstalk, and mechanical stress design calculations are included.

Parry, C. M.↗
DOE OSTI2020

Utilizing a Database of Simulated Geometric Albedo Spectra for Photometric Characterization of Rocky Exoplanet Atmospheres

In anticipation of future flagship missions focused on the goal of achieving direct imaging of rocky exoplanets, we have developed a database of models to help the community examine the potential spectral characteristics of a broad range of rocky planet atmospheres. Using the publicly available Planetary Spectrum Generator, we have computed a grid of 141,600 rocky exoplanet geometric albedo spectra across a seven-dimensional parameter space. Using this grid, we have performed a color–color analysis seeking to identify the most useful near-UV and red or near-infrared photometric follow-up channels to combine with a green-optical (discovery) spectral channel. We found that a combination of filters at 0.4, 0.58, and ∼0.8 μm were able to distinguish between atmospheres with moderate-to-high concentrations of four different dominant absorbing constituents, given at least 10 hr of observation on a star at 10 parsec with a 15 m class space telescope; however, more moderate abundances similar to those of solar system rocky bodies would be more challenging to detect. We recommend that future missions seeking to characterize directly imaged rocky exoplanets by colors alone further consider multiband photometry as a first discriminator for planetary characteristics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Gravitational wave modes in matter

Here, a general linear gauge-invariant equation for dispersive gravitational waves (GWs) propagating in matter is derived. This equation describes, on the same footing, both the usual tensor modes and the gravitational modes strongly coupled with matter. It is shown that the effect of matter on the former is comparable to diffraction and therefore negligible within the geometrical-optics approximation. However, this approximation is applicable to modes strongly coupled with matter due to their large refractive index. GWs in ideal gas are studied using the kinetic average-Lagrangian approach and the gravitational polarizability of matter that we have introduced earlier. In particular, we show that this formulation subsumes the kinetic Jeans instability as a collective GW mode with a peculiar polarization, which is derived from the dispersion matrix rather than assumed a priori. This forms a foundation for systematically extending GW theory to GW interactions with plasmas, where symmetry considerations alone are insufficient to predict the wave polarization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Apparent superluminality of lensed gravitational waves

We consider gravitational wave (GW) sources with an associated electromagnetic (EM) counterpart, and analyze the time delay between both signals in the presence of lensing. If GWs have wavelengths comparable to the Schwarzschild radius of astrophysical lenses, they must be treated with wave optics, whereas EM waves are typically well within the approximation of geometric optics. Here, with concrete examples, we confirm that the GW signal never arrives before its EM counterpart, if both are emitted at the same time. However, during the inspiral of a binary, peaks of the GW waveform can arrive before their EM counterpart. We stress this is only an apparent superluminality since the GW waveform is both distorted and further delayed with respect to light. In any case, measuring the multi-messenger time delay and correctly interpreting it has important implications for unveiling the distribution of lenses, testing the nature of gravity, and probing the cosmological expansion history.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Improved limits on the tensor-to-scalar ratio using BICEP and P l a n c k data

In this study, we present constraints on the tensor-to-scalar ratio r using a combination of BICEP/Keck 2018 (BK18) and Planck PR4 data allowing us to fit for r consistently with the six parameters of the Λ CDM model. We discuss the sensitivity of constraints on r to uncertainties in the Λ CDM parameters as defined by the Planck data. In particular, we are able to derive a constraint on the reionization optical depth τ and thus propagate its uncertainty into the posterior distribution for r . While Planck sensitivity to r is slightly lower than the current ground-based measurements, the combination of Planck with BK18 and baryon-acoustic-oscillation data yields results consistent with r = 0 and tightens the constraint to r < 0.032 at 95% confidence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Distant, Galaxy Cluster Environment of the Short GRB 161104A at $z\sim 0.8$ and a Comparison to the Short GRB Host Population

We present optical observations of the Swift short-duration gamma-ray burst (GRB) GRB 161104A and its host galaxy at z = 0.793 ± 0.003. We model the multiband photometry and spectroscopy with the stellar population inference code Prospector and explore the posterior using nested sampling. We find a mass-weighted age of $t_m = 2.12^{+0.23}_{-0.21}$ Gyr, stellar mass of log(M/M ⊙ ), metallicity of log(Z/Z ⊙ ), dust extinction of $A_V = 0.08^{+0.08}_{-0.05}$, and low star formation rate of 9.9 × 10 -2 M ⊙ yr -1 . These properties, along with a prominent 4000 Å break and optical absorption lines, classify this host as an early-type, quiescent galaxy. Using Dark Energy Survey galaxy catalogs, we demonstrate that the host of GRB 161104A resides on the outskirts of a galaxy cluster at z ≈ 0.8, situated ≈1 Mpc from the likely brightest cluster galaxy. We also present new modeling for 20 additional short GRB hosts (≈33% of which are early-type galaxies), finding population medians of and $t_m = 1.07^{+1.98}_{-0.67}$ Gyr (68% confidence). We further find that the host of GRB 161104A is more distant, less massive, and younger than the four other short GRB hosts known to be associated with galaxy clusters. Cluster short GRBs have faint afterglows, in the lower ≈11% (≈30%) of observed X-ray (optical) luminosities. We place a lower limit on the fraction of short GRBs in galaxy clusters versus those in the field of ≈5%–13%, consistent with the fraction of stellar mass of ≈10%–20% in galaxy clusters at redshifts 0.1 ≤ z ≤ 0.8. Future studies that take advantage of wider-field and deeper cluster surveys are needed to understand the true rate of short GRBs in clusters and their effect on heavy-element enrichment in the intracluster medium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves. II. Period–Fourier–Metallicity Relations for First Overtone RR Lyrae

We present new period-$\phi$ 31 -[Fe/H] relations for first-overtone RRL stars (RRc), calibrated over a broad range of metallicities (–2.5 ≲ [Fe/H] ≲ 0.0) using the largest currently available set of Galactic halo field RRL with homogeneous spectroscopic metallicities. Our relations are defined in the optical (ASAS-SN V band) and, inaugurally, in the infrared (WISE W1 and W2 bands). Our V-band relation can reproduce individual RRc spectroscopic metallicities with a dispersion of 0.30 dex over the entire metallicity range of our calibrator sample (an rms smaller than what we found for other relations in literature including nonlinear terms). Our infrared relation has a similar dispersion in the low- and intermediate-metallicity range ([Fe/H] ≲ –0.5), but tends to underestimate the [Fe/H] abundance around solar metallicity. We tested our relations by measuring both the metallicity of the Sculptor dSph and a sample of Galactic globular clusters, rich in both RRc and RRab stars. The average metallicity we obtain for the combined RRL sample in each cluster is within ±0.08 dex of their spectroscopic metallicities. The infrared and optical relations presented in this work will enable deriving reliable photometric RRL metallicities in conditions where spectroscopic measurements are not feasible; e.g., in distant galaxies or reddened regions (observed with upcoming Extremely Large Telescopes and the James Webb Space Telescope), or in the large sample of new RRL that will be discovered in large-area time-domain photometric surveys (such as the LSST and the Roman space telescope).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

GRB 110213A: A Study of Afterglow Electromagnetic Cascade Radiation

We obtained well-sampled optical photometry of GRB 110213A, including Swift/UVOT and XRT. Combining our data from those of other ground-based telescopes, we present 15 optical multicolor light curves showing similar shapes with two peaks. In contrast, in the X-ray band, only a single peak is observed between the two optical peaks. Temporal and spectral analysis of GRB 110213A shows that the X-rays differ from the optical for Phases I–III (before the second peak of the optical band at ~5.6 ks). Moreover, they have the same spectral behavior at late times (Phases IV–VI). These data indicate that the optical and X-ray emission are dominated by different components. The synchrotron-supported pair cascade emission is included in the standard external forward-shock model, which is dominated by synchrotron radiation and synchrotron self-Compton (SSC). We find that the optical bands of GRB 110213A are dominated by the cascade emission from synchrotron radiation + SSC at the early stage, while the primary synchrotron + SSC radiation dominates the X-ray band. At late stages, both the X-ray and optical bands are dominated by emission from primary synchrotron + SSC radiation. The cascade component can reasonably explain the first optical peak. In contrast, the primary synchrotron + SSC emission mainly contributes to the second peak.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

A transmission hologram for slitless spectrophotometry on a convergent telescope beam. 1. Focus and resolution

We report in this paper the test of a plane holographic optical element to be used as an aberration-corrected grating for a slitless spectrograph, inserted in a convergent telescope beam. Our long-term objective is the optimization of a specific hologram to switch the auxiliary telescope imager of the Vera Rubin Observatory into an accurate slitless spectrograph, dedicated to the atmospheric transmission measurement. We present and discuss here the promising results of tests performed with prototype holograms at the CTIO $0.9\,$m telescope during a run of 17 nights in 2017 May–June. After their on-sky geometrical characterization, the performances of the holograms as aberration-balanced dispersive optical elements have been established by analysing spectra obtained from spectrophotometric standard stars and narrow-band emitter planetary nebulae. Thanks to their additional optical function, our holographic disperser prototypes allow us to produce significantly better focused spectra within the full visible wavelength domain $[370,1050]\,$nm than a regular grating, which suffers from strong defocusing and aberrations when used in similar conditions. We show that the resolution of our slitless on-axis spectrograph equipped with the hologram approaches its theoretical performance. While estimating the benefits of a hologram for the spectrum resolution, the roadmap to produce a competitive holographic element for the Vera Rubin Observatory auxiliary telescope has been established.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Quantifying the poor purity and completeness of morphological samples selected by galaxy colour

The galaxy population is strongly bimodal in both colour and morphology, and the two measures correlate strongly, with most blue galaxies being late-types (spirals) and most early-types, typically ellipticals, being red. This observation has led to the use of colour as a convenient selection criterion to make samples that are then labelled by morphology. Such use of colour as a proxy for morphology results in necessarily impure and incomplete samples. In this paper, we make use of the morphological labels produced by Galaxy Zoo to measure how incomplete and impure such samples are, considering optical (ugriz), near-ultraviolet (NUV), and near-infrared (NIR; JHK) bands. The best single colour optical selection is found using a threshold of g - r = 0.742, but this still results in a sample where only 56 per cent of red galaxies are smooth and 56 per cent of smooth galaxies are red. Use of the NUV gives some improvement over purely optical bands, particularly for late-types, but still results in low purity/completeness for early-types. No significant improvement is found by adding NIR bands. With any two bands, including NUV, a sample of early-types with greater than two-thirds purity cannot be constructed. In conclusion, advances in quantitative galaxy morphologies have made colour–morphology proxy selections largely unnecessary going forward; where such assumptions are still required, we recommend studies carefully consider the implications of sample incompleteness/impurity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Does the Sun have a dark disk?

The Sun is not quite a perfect sphere, and its oblateness, thought to be induced through its rotation, has been measured using optical observations of its radius. Its gravitational quadrupole moment can then be deduced using solar models, or through helioseismology, and it can also be determined from measurements of its gravitational effects on Mercury’s orbit. The various assessments do not appear to agree, with the most complete and precise orbital assessments being in slight excess of other determinations. This may speak to the existence of a nonluminous disk or ring, where we also note evidence for a circumsolar dust ring within Mercury’s orbit from the Solar TErrestrial RElations Observatory (STEREO) mission. Historically, too, a protoplanetary disk may have been key to reconciling the Sun’s metallicity with its neutrino yield. The distribution of the nonluminous mass within Mercury’s orbit can modify the relative size of the optical and orbital quadrupole moments in different ways. We develop how we can use these findings to limit the mass of a dark disk, ring, or halo in the immediate vicinity of the Sun, and we note how future observational studies of the inner Solar System can not only refine these constraints but can also help to identify and to assess the mass of its dark-matter component. Published by the American Physical Society 2025

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Status of the Dark Energy Spectroscopic Instrument (DESI) and Year 1 Cosmology results

The Dark Energy Spectroscopic Instrument (DESI) will measure the effect of dark energy on the expansion of the universe. It will obtain optical spectra for tens of millions of galaxies and quasars, constructing a 3D map spanning the nearby universe to 11 billion light years. The DESI Survey is being conducted on the Mayall 4-meter telescope at Kitt Peak National Observatory. DESI is supported by the Department of Energy Office of Science to perform this Stage IV dark energy measurement using baryon acoustic oscillations and other techniques that rely on spectroscopic measurements. I will discuss the status of the Dark Energy Spectroscopic Instrument (DESI) survey and present our Year 1 Baryon Acoustic Oscillation measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

The Peculiar Variable X-Ray Spectrum of the Active Galactic Nucleus PKS 2005–489

PKS 2005-489 is a well-known, bright southern BL Lac object that has been detected up to TeV energies. In a low-flux state it exhibits the expected multiwavelength double-peaked spectrum in the radio- γ -ray band. The high-flux state shows extreme flux variations in the X-ray band with a hardening as well as a peculiar curved feature in the spectrum. Thus far, PKS 2005-489 is the only source to exhibit such a feature. To study the X-ray variability further, we obtained the first hard X-ray spectrum of the source with the Nuclear Spectroscopic Telescope Array. We compare quasi-simultaneous radio, optical, UV, soft and hard X-ray, and γ -ray data of PKS 2005-489 to archival data in order to study its broadband behavior. We find a very consistent quiet state in the spectral energy distribution, with little variation in spectral shape or flux between the 2012 and 2020 data. A possible explanation for the peculiar X-ray spectrum in the flaring state is an additional component in the jet, possibly accelerated via magnetic reconnection, that is not co-spatial to the low-flux state emission region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Synchrotron-driven Instabilities in Relativistic Plasmas of Arbitrary Opacity

Recent work has shown that synchrotron emission from relativistic plasmas leads the electron distribution to form an anisotropic ring in momentum space, which can be unstable to both kinetic and hydrodynamic instabilities. Fundamental to these works was the assumption that the plasma was optically thin, allowing all emitted radiation to escape. Here, we examine the behavior of these instabilities as the plasma becomes more optically thick. To do this, we extend a recently developed Fokker–Planck operator for synchrotron emission and absorption in mildly relativistic plasmas to ultrarelativistic plasmas. For a given set of plasma parameters, photons emitted by higher-energy electrons tend to be higher frequency, and thus more easily escape the plasma. As a result, the ratio of the photon emission rate (radiative drag) to absorption rate (radiative diffusion) for a given electron is extremely energy dependent. Given this behavior, we determine the critical parameters that control the opacity, and show how the plasma gradually transitions to become more isotropic and stable at higher opacity.

79 ASTRONOMY AND ASTROPHYSICS↗