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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Separation of Lanthanide Isotopes from Mixed Fission Product Samples

The measurement of radioactive fission products from nuclear events has important implications for nuclear data production, environmental monitoring, and nuclear forensics. In a previous paper, the authors reported the optimization of an intra-group lanthanide separation using LN extraction resin from Eichrom Technologies®, Inc. and a nitric acid gradient. In this work, the method was demonstrated for the separation and quantification of multiple short-lived fission product lanthanide isotopes from a fission product sample produced from the thermal irradiation of highly enriched uranium. The separations were performed in parallel in quadruplicate with reproducible results and high decontamination factors for 153 Sm, 156 Eu, and 161 Tb. Based on the results obtained here, the fission yields for 144 Ce, 153 Sm, 156 Eu, and 161 Tb are consistent with published fission yields. This work demonstrates the effectiveness of the separations for the intended application of short-lived lanthanide fission product analysis requiring high decontamination factors.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Identification of a Continuously Stable and Commercially Available Cell Line for the Identification of Infectious African Swine Fever Virus in Clinical Samples

African swine fever virus (ASFV) is causing outbreaks both in domestic pigs and wild boar in Europe and Asia. In 2018, the largest pig producing country, China, reported its first outbreak of African swine fever (ASF). Since then, the disease has quickly spread to all provinces in China and to other countries in southeast Asia, and most recently to India. Outbreaks of the disease occur in Europe as far west as Poland, and one isolated outbreak has been reported in Belgium. The current outbreak strain is highly contagious and can cause a high degree of lethality in domestic pigs, leading to widespread and costly losses to the industry. Currently, detection of infectious ASFV in field clinical samples requires accessibility to primary swine macrophage cultures, which are infrequently available in most regional veterinary diagnostic laboratories. Here, we report the identification of a commercially available cell line, MA-104, as a suitable substrate for virus isolation of African swine fever virus.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Identification of Possible Stellar Companions via Speckle Interferometry in a Sample of Be Stars

We present speckle interferometric measurements of Be stars made with the 1.60 m Perkin-Elmer telescope at the Pico dos Dias Observatory of the Laboratório Nacional de Astrofísica in Brazil. Using three different filters (V, R, and I), we obtained astrometric measurements for 23 stars, during three observing runs allocated in 2017 March, 2018 April, and 2019 July. We identified pairs with angular separation ranging from 0.″10 to 6.″69, including six systems with separations smaller than 1.″0. We estimated a mean error in separation of 15 mas, 1.°2 in position angle, and 0.29 mag for the magnitude difference. We discovered three new possible double systems that are not identified in the literature: HD 174886, HD 159032, and HD 168135 with an average angular separation of 0.″20, 3.″23, and 5.″41, respectively. In addition, we identified four new pairs in multiple systems previously known in the Washington Double Star Catalog. However, for 16 stars of our sample, we did not find evidence of binarity, based on the diffraction-limited resolution, the field of view, and/or the sensitivity of our observations. From the cross-match with data from Gaia Data Release 2, we verified the possibility of some of these systems be gravitationally bound or not.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Hot Degenerates in the MCT Survey. III. A Sample of White Dwarf Stars in the Southern Hemisphere

Here, we present optical spectra of 144 white dwarfs detected in the Montreal–Cambridge–Tololo colorimetric survey, including 120 DA, 12 DB, 4 DO, 1 DQ, and 7 DC stars. We also perform a model atmosphere analysis of all objects in our sample using the so-called spectroscopic technique, or the photometric technique in the case of DC white dwarfs. The main objective of this paper is to contribute to the ongoing effort of confirming spectroscopically all white dwarf candidates in the Gaia survey, in particular in the southern hemisphere. All our spectra are made available in the Montreal White Dwarf Database.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

SDSS-IV MaNGA: The MaNGA Dwarf Galaxy Sample Presentation

We present the MaNGA Dwarf galaxy (MaNDala) Value Added Catalog (VAC), from the final release of the Sloan Digital Sky Survey-IV program. MaNDala consists of 136 randomly selected bright dwarf galaxies with M * < 10 9.1 M ⊙ and M g > -18.5, making it the largest integral field spectroscopy homogeneous sample of dwarf galaxies. We release a photometric analysis of the g, r, and z broadband imaging based on the DESI Legacy Imaging Surveys, as well as a spectroscopic analysis based on the Pipe3D SDSS-IV VAC. Our release includes the surface brightness (SB), geometric parameters, and color profiles, Sérsic fits as well as stellar population properties (such as stellar ages, metallicities, and star formation histories), and emission lines' fluxes within the FOV and the effective radii of the galaxies. We find that the majority of the MaNDala galaxies are star-forming late-type galaxies with $\langle$n Sersic,r $\rangle$ ~ 1.6 that are centrals (central/satellite dichotomy). MaNDala covers a large range of SB values (we find 11 candidate ultra-diffuse galaxies and three compact ones), filling the gap between classical dwarfs and low-mass galaxies in the Kormendy Diagram and in the size–mass/luminosity relation, which seems to flatten at 10 8 < M * /M ⊙ < 10 9 with $\langle$R e,r $\rangle$ ~ 2.7 kpc. A large fraction of MaNDala galaxies formed from an early low-metallicity burst of SF, but also from late SF events from more metal-enriched gas: half of the MaNDala galaxies assembled 50% of their mass at $\langle$z$\rangle$ > 2, while the last 20% was at $\langle$z$\rangle$ < 0.3. Finally, a bending of the sSFR-M * relation at M * ~ 10 9 M ⊙ for the main-sequence galaxies seems to be supported by MaNDala.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Searching in H I for Massive Low Surface Brightness Galaxies: Samples from HyperLeda and the UGC

A search has been made for 21 cm H I line emission in a total of 350 unique galaxies from two samples whose optical properties indicate they may be massive. The first consists of 241 low surface brightness (LSB) galaxies of morphological type Sb and later selected from the HyperLeda database and the second consists of 119 LSB galaxies from the UGC with morphological types Sd-m and later. Of the 350 unique galaxies, 239 were observed at the Nançay Radio Telescope, 161 at the Green Bank Telescope, and 66 at the Arecibo telescope. A total of 295 (84.3%) were detected, of which 253 (72.3%) appear to be uncontaminated by any other galaxies within the telescope beam. Finally, of the total detected, uncontaminated galaxies, at least 31 appear to be massive LSB galaxies, with a total H I mass ≥ 10 10 M ⊙ , for H 0 = 70 kms -1 Mpc -1 . If we expand the definition to also include galaxies with significant total (rather than just gas) mass, i.e., those with an inclination-corrected H I line width W 50,cor > 500 km s -1 , this brings the total number of massive LSB galaxies to 41. There are no obvious trends between the various measured global galaxy properties, particularly between mean surface brightness and galaxy mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Measurements of Effective Optical Depth in the Lyα Forest from the BOSS DR12 Quasar Sample

We measure the effective optical depth in the Lyα forest using 40,035 quasar spectra from the Twelfth Data Release (DR12) of the Baryon Oscillation Spectroscopic Survey of Sloan Digital Sky Survey IV. A rigorous selection based on spectral index and the equivalent width of the C iv emission line is applied to choose seven uniform samples with minimal intrinsic variations across redshifts. Modeling the redshift evolution of the effective optical depth with a power law, ${\tau }_{\mathrm{eff}}={\tau }_{0}{(1+z)}^{\gamma },$ produces ${\tau }_{0}=(5.54\pm 0.64)\times {10}^{-3}$ and $\gamma =3.182\pm 0.074$. The 2.2% precision estimate on γ is dominated by systematic errors, likely arising from the bias and uncertainties in spectral index estimates. Even after incorporating the systematic errors, this work provides the most precise estimates of optical depth parameters to date. Finally, using the reconstructed Lyα forest continuum to directly measure the transmitted flux ratio as a function of redshift, we find deviations of less than 2.5% from the predictions from the global model and no convincing evidence for signal associated with He ii reionization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The 100 pc White Dwarf Sample in the SDSS Footprint

In this work, we present follow-up spectroscopy of 711 white dwarfs within 100 pc, and we present a detailed model atmosphere analysis of the 100 pc white dwarf sample in the Sloan Digital Sky Survey footprint. Our spectroscopic follow-up is complete for 83% of the white dwarfs hotter than 6000 K, where the atmospheric composition can be constrained reliably. We identify 1508 DA white dwarfs with pure hydrogen atmospheres. The DA mass distribution has an extremely narrow peak at 0.59 M ⊙ and reveals a shoulder from relatively massive white dwarfs with M = 0.7–0.9 M ⊙. Comparing this distribution with binary population synthesis models, we find that the contribution from single stars that form through mergers cannot explain the overabundance of massive white dwarfs. In addition, the mass distribution of cool DAs shows a near absence of M > 1 M ⊙ white dwarfs. The pile-up of 0.7–0.9 M ⊙ and the disappearance of M > 1 M ⊙ white dwarfs is consistent with the effects of core crystallization. Even though the evolutionary models predict the location of the pile-up correctly, the delay from the latent heat of crystallization by itself is insufficient to create a significant pile-up, and additional cooling delays from related effects like phase separation are necessary. We also discuss the population of infrared-faint (ultracool) white dwarfs and demonstrate for the first time the existence of a well-defined sequence in color and magnitude. Curiously, this sequence is connected to a region in the color–magnitude diagrams where the number of white dwarfs with a helium-dominated atmosphere is low. This suggests that the infrared-faint white dwarfs likely have mixed H/He atmospheres.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Zwicky Transient Facility Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics

Here we present a public catalog of transients from the Zwicky Transient Facility (ZTF) Bright Transient Survey, a magnitude-limited ( m < 19 mag in either the g or r filter) survey for extragalactic transients in the ZTF public stream. We introduce cuts on survey coverage, sky visibility around peak light, and other properties unconnected to the nature of the transient, and show that the resulting statistical sample is spectroscopically 97% complete at <18 mag, 93% complete at <18.5 mag, and 75% complete at <19 mag. We summarize the fundamental properties of this population, identifying distinct duration–luminosity correlations in a variety of supernova (SN) classes and associating the majority of fast optical transients with well-established spectroscopic SN types (primarily SN Ibn and II/IIb). We measure the Type Ia SN and core-collapse (CC) SN rates and luminosity functions, which show good consistency with recent work. About 7% of CC SNe explode in very low-luminosity galaxies ( M i > –16 mag), 10% in red-sequence galaxies, and 1% in massive ellipticals. We find no significant difference in the luminosity or color distributions between the host galaxies of SNe Type II and SNe Type Ib/c, suggesting that line-driven wind stripping does not play a major role in the loss of the hydrogen envelope from their progenitors. Future large-scale classification efforts with ZTF and other wide-area surveys will provide high-quality measurements of the rates, properties, and environments of all known types of optical transients and limits on the existence of theoretically predicted but as yet unobserved explosions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The SAGA Survey. II. Building a Statistical Sample of Satellite Systems around Milky Way–like Galaxies

In this work, we present the Stage II results from the ongoing Satellites Around Galactic Analogs (SAGA) Survey. Upon completion, the SAGA Survey will spectroscopically identify satellite galaxies brighter than M r,o = -12.3 around 100 Milky Way (MW) analogs at z ~ 0.01. In Stage II, we have more than quadrupled the sample size of Stage I, delivering results from 127 satellites around 36 MW analogs with an improved target selection strategy and deep photometric imaging catalogs from the Dark Energy Survey and the Legacy Surveys. We have obtained 25,372 galaxy redshifts, peaking around z = 0.2. These data significantly increase spectroscopic coverage for very low redshift objects in 17 < r o < 20.75 around SAGA hosts, creating a unique data set that places the Local Group in a wider context. The number of confirmed satellites per system ranges from zero to nine and correlates with host galaxy and brightest satellite luminosities. We find that the number and luminosities of MW satellites are consistent with being drawn from the same underlying distribution as SAGA systems. The majority of confirmed SAGA satellites are star-forming, and the quenched fraction increases as satellite stellar mass and projected radius from the host galaxy decrease. Overall, the satellite quenched fraction among SAGA systems is lower than that in the Local Group. We compare the luminosity functions and radial distributions of SAGA satellites with theoretical predictions based on cold dark matter simulations and an empirical galaxy–halo connection model and find that the results are broadly in agreement.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Rare Event Sampling Improves Mercury Instability Statistics

Due to the chaotic nature of planetary dynamics, there is a non-zero probability that Mercury's orbit will become unstable in the future. Previous efforts have estimated the probability of this happening between 3 and 5 billion years in the future using a large number of direct numerical simulations with an N-body code, but were not able to obtain accurate estimates before 3 billion years in the future because Mercury instability events are too rare. In this paper we use a new rare-event sampling technique, Quantile Diffusion Monte Carlo (QDMC), to estimate that the probability of a Mercury instability event in the next 2 billion years is approximately 10 –4 in the REBOUND N-body code. We show that QDMC provides unbiased probability estimates at a computational cost of up to 100 times less than direct numerical simulation. QDMC is easy to implement and could be applied to many problems in planetary dynamics in which it is necessary to estimate the probability of a rare event.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The Environments of Green Pea Galaxies. I. The KISS Sample

We present environmental analyses for 13 KPNO International Spectroscopic Survey Green Pea (GP) galaxies. These galaxies were discovered via their strong [O ιιι] emission in the redshift range 0.29 < z < 0.42, and they are undergoing a major burst of star formation. A primary goal of this study is to understand what role the environment plays in driving the current star formation activity. By studying the environments around these extreme star-forming galaxies, we can learn more about what triggers their star formation processes and how they fit into the narrative of galaxy evolution. Using the Hydra multifiber spectrograph on the WIYN 3.5 m telescope, we mapped out the galaxy distribution around each of the GPs (out to ~15 Mpc at the redshifts of the targets). Using three density analysis methodologies chosen for their compatibility with the geometry of our redshift survey, we categorized the galaxian densities of the GPs into different density regimes. We find that the GPs in our sample tend to be located in low-density environments. We find no correlation between the density and the SFRs seen in the GPs. We conclude that the environments the GPs are found in are likely not the driving factor behind their extreme star formation activity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The SDSS-HET Survey of Kepler Eclipsing Binaries. A Sample of Four Benchmark Binaries

The purpose of this work is to extend a sample of accurately modeled, benchmark-grade eclipsing binaries (EBs) with accurately determined masses and radii. We select four "well-behaved" Kepler binaries, KIC 2306740, KIC 4076952, KIC 5193386 and KIC 5288543, each with at least eight double-lined spectra from the Apache Point Observatory Galactic Evolution Experiment instrument that is part of the Sloan Digital Sky Surveys III and IV, and from the Hobby–Eberly High Resolution Spectrograph. We obtain masses and radii with uncertainties of 2.5% or less for all four systems. Three of these systems have orbital periods longer than 9 days, and thus populate an undersampled region of the parameter space for extremely well-characterized detached EBs. We compare the derived masses and radii against MESA MIST isochrones to determine the ages of the systems. All systems were found to be coeval, showing that the results are consistent across MESA MIST and PHOEBE .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Palomar Transient Factory Core-collapse Supernova Host-galaxy Sample. I. Host-galaxy Distribution Functions and Environment Dependence of Core-collapse Supernovae

Several thousand core-collapse supernovae (CCSNe) of different flavors have been discovered so far. However, identifying their progenitors has remained an outstanding open question in astrophysics. Studies of SN host galaxies have proven to be powerful in providing constraints on the progenitor populations. In this paper, we present all CCSNe detected between 2009 and 2017 by the Palomar Transient Factory. This sample includes 888 SNe of 12 distinct classes out to redshift z ≈ 1. We present the photometric properties of their host galaxies from the far-ultraviolet to the mid-infrared and model the host-galaxy spectral energy distributions to derive physical properties. The galaxy mass function of Type Ic, Ib, IIb, II, and IIn SNe ranges from 105 to 1011.5 M o˙, probing the entire mass range of star-forming galaxies down to the least-massive star-forming galaxies known. Moreover, the galaxy mass distributions are consistent with models of star-formation-weighted mass functions. Regular CCSNe are hence direct tracers of star formation. Small but notable differences exist between some of the SN classes. Type Ib/c SNe prefer galaxies with slightly higher masses (i.e., higher metallicities) and star formation rates than Type IIb and II SNe. These differences are less pronounced than previously thought. H-poor superluminous supernovae (SLSNe) and SNe Ic-BL are scarce in galaxies above 1010 M o˙. Their progenitors require environments with metallicities of < 0.4 and < 1 solar, respectively. In addition, the hosts of H-poor SLSNe are dominated by a younger stellar population than all other classes of CCSNe. Our findings corroborate the notion that low metallicity and young age play an important role in the formation of SLSN progenitors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The Milky Way Revealed by Variable Stars. I. Sample Selection of RR Lyrae Stars and Evidence for Merger History

In order to study the Milky Way, RR Lyrae (RRL) variable stars identified by Gaia, ASAS-SN, and ZTF sky survey projects have been analyzed as tracers in this work. Photometric and spectroscopic information of 3417 RRLs including proper motions, radial velocity, and metallcity are obtained from observational data of Gaia, LAMOST, GALAH, APOGEE, and RAVE. Precise distances of RRLs with typical uncertainties less than 3% are derived by using a recent comprehensive period–luminosity–metallicity relation. Our results from kinematical and chemical analysis provide important clues for the assembly history of the Milky Way, especially for the Gaia–Sausage ancient merger. The kinematical and chemical trends found in this work are consistent with those of recent simulations that indicated that the Gaia–Sausage merger had a dual origin in the Galactic thick disk and halo. As recent similar works have found, the halo RRL sample in this work contains a subset of radially biased orbits besides a more isotropic component. This higher orbital anisotropy component amounts to β ≃ 0.8, and it contributes between 42% and 83% of the halo RRLs at 4 < R( kpc) < 20.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Hard X-Ray to Radio Multiwavelength SED Analysis of Local U/LIRGs in the GOALS Sample with a Self-consistent AGN Model including a Polar-dust Component

We conduct hard X-ray to radio multiwavelength spectral energy distribution (SED) decomposition for 57 local luminous and ultraluminous infrared galaxies observed with the Nuclear Spectroscopic Telescope Array and/or Swift/Burst Alert Telescope in the GOALS sample. We modify the latest SED-fitting code X-CIGALE by implementing the infrared (IR) CLUMPY model, allowing us to conduct the multiwavelength study with the X-ray torus model XCLUMPY self-consistently. Adopting the torus parameters obtained by the X-ray fitting, we estimate the properties of the host galaxies, active galactic nucleus (AGN) tori, and polar dust. The star formation rates (SFRs) become larger with merger stage and most of them are above the main sequence. The SFRs are correlated with radio luminosity, indicating starburst emission is dominant in the radio band. Although polar-dust extinction is much smaller than torus extinction, the UV-to-IR (mainly IR) polar dust luminosities are ~2 times larger than the torus ones. The polar-dust temperature decreases while the physical size, estimated by the temperature and dust sublimation radius, increases with AGN luminosity from a few tens of parsec (early mergers) to kiloparsec scales (late mergers), where the polar dust likely comes from expanding (i.e., evolving) dusty outflows. A comparison between the SFRs and intrinsic AGN luminosities suggests that starbursts occur first and AGNs arise later, and overall their growth rates follow the simultaneous coevolution local galaxy–SMBH mass relation. We confirm the coexistence of intense starbursts, AGNs, and large-scale outflows in late mergers, supporting a standard AGN feedback scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Preliminary Target Selection for the DESI Emission Line Galaxy (ELG) Sample

DESI will precisely constrain cosmic expansion and the growth of structure by collecting ~35 million redshifts across ~80% of cosmic history and one third of the sky to study Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD). In this work, we present a preliminary target selection for an Emission Line Galaxy (ELG) sample, which will comprise about half of all DESI tracers. The selection consists of a g-band magnitude cut and a (g – r) versus (r – z) color box, which we validate using HSC/PDR2 photometric redshifts and DEEP2 spectroscopy. The ELG target density should be ~2400 deg –2 , with ~65% of ELG redshifts reliably within a redshift range of 0.6 < z < 1.6. ELG targeting for DESI will be finalized during a "Survey Validation" phase.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Preliminary Target Selection for the DESI Luminous Red Galaxy (LRG) Sample

The DESI survey will observe more than 8 million candidate luminous red galaxies (LRGs) in the redshift range 0.3 < z < 1.0. In this work, we present a preliminary version of the DESI LRG target section developed using Legacy Surveys Data Release 8 g, r, z and W1 photometry. This selection yields a sample with a uniform surface density of ~600 deg –2 and very low predicted stellar contamination and redshift failure rates. During DESI Survey Validation, updated versions of this selection will be tested and optimized.

79 ASTRONOMY AND ASTROPHYSICS↗