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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

The CRISPR effector Cam1 mediates membrane depolarization for phage defence

Prokaryotic type III CRISPR–Cas systems provide immunity against viruses and plasmids using CRISPR-associated Rossman fold (CARF) protein effectors. Recognition of transcripts of these invaders with sequences that are complementary to CRISPR RNA guides leads to the production of cyclic oligoadenylate second messengers, which bind CARF domains and trigger the activity of an effector domain. Whereas most effectors degrade host and invader nucleic acids, some are predicted to contain transmembrane helices without an enzymatic function. Whether and how these CARF–transmembrane helix fusion proteins facilitate the type III CRISPR–Cas immune response remains unknown. Here we investigate the role of cyclic oligoadenylate-activated membrane protein 1 (Cam1) during type III CRISPR immunity. Structural and biochemical analyses reveal that the CARF domains of a Cam1 dimer bind cyclic tetra-adenylate second messengers. In vivo, Cam1 localizes to the membrane, is predicted to form a tetrameric transmembrane pore, and provides defence against viral infection through the induction of membrane depolarization and growth arrest. These results reveal that CRISPR immunity does not always operate through the degradation of nucleic acids, but is instead mediated via a wider range of cellular responses.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Nanoporous Cu-C composites based on carbon-nanotube aerogels

Current synthesis methods of nanoporous Cu–C composites offer limited control of the material composition, structure, and properties, particularly for large Cu loadings of ≳20 wt%. Here, we describe two related approaches to realize novel nanoporous Cu–C composites based on the templating of recently developed carbon-nanotube aerogels (CNT-CAs). Our first approach involves the trapping of Cu nanoparticles while CNT-CAs undergo gelation. This method yields nanofoams with relatively high densities of ≳65 mg cm -3 for Cu loadings of ≳10 wt%. Our second approach overcomes this limitation by filling the pores of undoped CNT-CA monoliths with an aqueous solution of CuSO 4 followed by (i) freeze-drying to remove water and (ii) thermal decomposition of CuSO 4 . With this approach, we demonstrate Cu–C composites with a C matrix density of -25 mg cm -3 and Cu loadings of up to 70 wt%. These versatile methods could be extended to fabricate other nanoporous metal–carbon composite materials geared for specific applications.

Charnvanichborikarn, S.↗
DOE OSTI2025

Effect of growth dynamics on the structural, photophysical and pseudocapacitance properties of famatinite copper antimony sulphide colloidal nanostructures (including nanosheets)

Facile phase selective synthesis of copper antimony sulphide (CAS) nanostructures is important because of their tunable photoconductive and electrochemical properties. In this study, off-stoichiometric famatinite phase CAS (fCAS) quasi-spherical and quasi-hexagonal colloidal nanostructures (including nanosheets) of sizes, 2.4–18.0 nm were grown under variable conditions of temperature (60–200 °C), time and oleylamine capping ligand concentration using copper(II) acetylacetonate and antimony(III) diethyldithiocarbamate precursors. Data from powder X-ray diffraction, Raman spectroscopy and high-resolution scanning/transmission electron microscopy confirm the tetragonal structure of the famatinite phase. X-ray photoelectron spectroscopy, transmission electron microscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy data suggest a correlation of particle size, morphology and composition of the off-stoichiometric fCAS nanostructures with growth temperature and time, and oleylamine concentration. The off-stoichiometric Cu 3-a Sb 1+b S 4±c (a, b, c – mole fractions) nanostructures being severely copper-deficient and antimony-rich, exhibit shallow-lying acceptor copper vacancy states, deep-lying donor states of antimony interstitials, sulphur vacancies and antimony-copper antisites and shallow-lying acceptor surface trapping states. Further, these electronic states are likely implicated in tunable UV-visible absorption and bandgaps between 2.3 and 2.8 eV, and broad visible-NIR photoluminescence with fast recombination of radiative lifetimes between 0.2 and 6.2 ns, confirmed from absorption, steady-state and time-resolved photoluminescence spectroscopies. Additionally, cyclic voltammetry and electrochemical impedance spectroscopy confirm that electrodes of the fCAS nanostructures display slightly variable pseudocapacitance of charge-storage primarily via possible sodium ion intercalation with a high specific capacitance of ~84 F g -1 obtained at a scan rate of 5 mV s -1 . Overall, these results show the influence of composition, in particular point defects, phase quality and morphology on the optical and pseudocapacitance properties of fCAS nanostructures, suitable as solar absorbers or electrodes for energy storage devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Communication: Multireference equation of motion coupled cluster: A transform and diagonalize approach to electronic structure

The novel multireference equation-of-motion coupled-cluster (MREOM-CC) approaches provide versatile and accurate access to a large number of electronic states. The methods proceed by a sequence of many-body similarity transformations and a subsequent diagonalization of the transformed Hamiltonian over a compact subspace. The transformed Hamiltonian is a connected entity and preserves spin- and spatial symmetry properties of the original Hamiltonian, but is no longer Hermitean. The final diagonalization spaces are defined in terms of a complete active space (CAS) and limited excitations (1h, 1p, 2h, …) out of the CAS. The methods are invariant to rotations of orbitals within their respective subspaces (inactive, active, external). Applications to first row transition metal atoms (Cr, Mn, and Fe) are presented yielding results for up to 524 electronic states (for Cr) with an rms error compared to experiment of about 0.05 eV. The accuracy of the MREOM family of methods is closely related to its favorable extensivity properties as illustrated by calculations on the O{sub 2}–O{sub 2} dimer. The computational costs of the transformation steps in MREOM are comparable to those of closed-shell Coupled Cluster Singles and Doubles (CCSD) approach.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Structural and electronic modification of photovoltaic SnS by alloying

Emergence of a terawatt scalable photovoltaic (PV) thin film technology is currently impeded by the limited supply of relatively rare elements like In or Te, which has spurred active research in recent years on earth-abundant PV materials. Instead of searching for alternative PV materials, we approach the problem here by structural modification through alloying of a known PV material, namely, tin sulfide. Although SnS is a strong visible light absorber that is naturally p-doped, its indirect band gap reduces the open circuit voltage of SnS-based solar cells. The anisotropic crystal structure results in undesirable anisotropic transport properties. Based on the observation that the isoelectronic sulfides MgS, CaS, and SrS assume the rock-salt structure, we use ab initio calculations to explore the structure and electronic properties of metastable Sn{sub 1−x}(II){sub x}S (II = Mg, Ca, Sr) alloys, finding that the isotropic rock-salt phase is stabilized above x = 0.2–0.3, and predicting direct band gaps in the range of interest for PV applications, i.e., 0.6–1.5 eV for Ca and Sr alloying. We subsequently synthesized such Sn{sub 1−x}(Ca){sub x}S films by pulsed laser deposition, confirmed the cubic rock-salt structure, and observed optical band gaps between 1.1 and 1.3 eV. These results highlight the potential of structural modification by alloying as a route to widen the otherwise limited materials base for promising earth-abundant materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A fixed-node Diffusion Monte Carlo study of the 1,2,3-tridehydrobenzene triradical

The electronic structure of 1,2,3-tridehydrobenzene was investigated using quantum Monte Carlo methods. The radical contains two low-lying electronic states that are nearly degenerate adiabatically (within 2 kcal/mol separation), according to previous coupled cluster calculations. We performed Diffusion Monte Carlo (DMC) calculations starting from Multi-Reference Configuration Interaction (MRCI) trial wavefunctions, with a complete active space (CAS) containing 9 electrons in 9 orbitals, CAS(9,9). Our converged DMC results are in close agreement with the best coupled-cluster results, and further strengthen the assignment of a {sup 2}A{sub 1} ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Synthesis of the unmanned aerial vehicle remote control augmentation system

Medium size Unmanned Aerial Vehicle (UAV) usually flies as an autonomous aircraft including automatic take-off and landing phases. However in the case of the on-board control system failure, the remote steering is using as an emergency procedure. In this reason, remote manual control of unmanned aerial vehicle is used more often during take-of and landing phases. Depends on UAV take-off mass and speed (total energy) the potential crash can be very danger for airplane and environment. So, handling qualities of UAV is important from pilot-operator point of view. In many cases the dynamic properties of remote controlling UAV are not suitable for obtaining the desired properties of the handling qualities. In this case the control augmentation system (CAS) should be applied. Because the potential failure of the on-board control system, the better solution is that the CAS algorithms are placed on the ground station computers. The method of UAV handling qualities shaping in the case of basic control system failure is presented in this paper. The main idea of this method is that UAV reaction on the operator steering signals should be similar - almost the same - as reaction of the 'ideal' remote control aircraft. The model following method was used for controller parameters calculations. The numerical example concerns the medium size MP-02A UAV applied as an aerial observer system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak

The time and position behavior of runaway electrons at the Parail–Pogutse instability moments has been investigated using experimental observations in plasma current, loop voltage, the Hard X-ray (HXR) radiations, and 18 poloidal pickup coils signals received by data acquisition system simultaneously. The conditional average sampling (CAS) method was used to analyze the output data. Moreover, a filament current code was modified to study the runaway electrons beam movement in the event of instabilities. The results display a rapid drift of runaway beam toward the inner wall of the vacuum vessel and the collision with the wall components at the instability moments. The existence of the collisions in these experiments is evident in the HXR bursts which are considered as the main trigger for CAS Analysis. Also, the variation of HXR bursts with the toroidal magnetic field shows that the hard X-ray bursts drop with increase in the toroidal magnetic field and runaway electrons confinement quality.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Potent CRISPR-Cas9 inhibitors from Staphylococcus genomes

Anti-CRISPRs (Acrs) are small proteins that inhibit the RNA-guided DNA targeting activity of CRISPR-Cas enzymes. Encoded by bacteriophage and phage-derived bacterial genes, Acrs prevent CRISPR-mediated inhibition of phage infection and can also block CRISPR-Cas-mediated genome editing in eukaryotic cells. To identify Acrs capable of inhibiting Staphylococcus aureus Cas9 (SauCas9), an alternative to the most commonly used genome editing protein Streptococcus pyogenes Cas9 (SpyCas9), we used both self-targeting CRISPR screening and guilt-by-association genomic search strategies. Here we describe three potent inhibitors of SauCas9 that we name AcrIIA13, AcrIIA14, and AcrIIA15. These inhibitors share a conserved N-terminal sequence that is dispensable for DNA cleavage inhibition and have divergent C termini that are required in each case for inhibition of SauCas9-catalyzed DNA cleavage. In human cells, we observe robust inhibition of SauCas9-induced genome editing by AcrIIA13 and moderate inhibition by AcrIIA14 and AcrIIA15. We also find that the conserved N-terminal domain of AcrIIA13–AcrIIA15 binds to an inverted repeat sequence in the promoter of these Acr genes, consistent with its predicted helix-turn-helix DNA binding structure. These data demonstrate an effective strategy for Acr discovery and establish AcrIIA13–AcrIIA15 as unique bifunctional inhibitors of SauCas9.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Crystal Structure of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated Csn2 Protein Revealed Ca[superscript 2+]-dependent Double-stranded DNA Binding Activity

Clustered regularly interspaced short palindromic repeats (CRISPR) and their associated protein genes (cas genes) are widespread in bacteria and archaea. They form a line of RNA-based immunity to eradicate invading bacteriophages and malicious plasmids. A key molecular event during this process is the acquisition of new spacers into the CRISPR loci to guide the selective degradation of the matching foreign genetic elements. Csn2 is a Nmeni subtype-specific cas gene required for new spacer acquisition. Here we characterize the Enterococcus faecalis Csn2 protein as a double-stranded (ds-) DNA-binding protein and report its 2.7 {angstrom} tetrameric ring structure. The inner circle of the Csn2 tetrameric ring is {approx}26 {angstrom} wide and populated with conserved lysine residues poised for nonspecific interactions with ds-DNA. Each Csn2 protomer contains an {alpha}/{beta} domain and an {alpha}-helical domain; significant hinge motion was observed between these two domains. Ca{sup 2+} was located at strategic positions in the oligomerization interface. We further showed that removal of Ca{sup 2+} ions altered the oligomerization state of Csn2, which in turn severely decreased its affinity for ds-DNA. In summary, our results provided the first insight into the function of the Csn2 protein in CRISPR adaptation by revealing that it is a ds-DNA-binding protein functioning at the quaternary structure level and regulated by Ca{sup 2+} ions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

THREE NEW GALACTIC CENTER X-RAY SOURCES IDENTIFIED WITH NEAR-INFRARED SPECTROSCOPY

We have conducted a near-infrared spectroscopic survey of 47 candidate counterparts to X-ray sources discovered by the Chandra X-Ray Observatory near the Galactic center (GC). Though a significant number of these astrometric matches are likely to be spurious, we sought out spectral characteristics of active stars and interacting binaries, such as hot, massive spectral types or emission lines, in order to corroborate the X-ray activity and certify the authenticity of the match. We present three new spectroscopic identifications, including a Be high-mass X-ray binary (HMXB) or a γ Cassiopeiae (Cas) system, a symbiotic X-ray binary, and an O-type star of unknown luminosity class. The Be HMXB/γ Cas system and the symbiotic X-ray binary are the first of their classes to be spectroscopically identified in the GC region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

COLDER AND HOTTER: INTERFEROMETRIC IMAGING OF {beta} CASSIOPEIAE AND {alpha} LEONIS

Near-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star {beta} Cas (F2IV) and a hotter one {alpha} Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting a solid-body rotation model with a simple gravity darkening prescription, we modeled the stellar geometric properties and surface temperature distributions, confirming that both stars are rapidly rotating and show gravity darkening anomalies. We estimate the masses and ages of these rapid rotators on L-R{sub pol} and H-R diagrams constructed for non-rotating stars by tracking their non-rotating equivalents. The unexpected fast rotation of the evolved sub-giant {beta} Cas offers a unique test of the stellar core-envelope coupling, revealing quite efficient coupling over the past {approx}0.5 Gyr. Lastly, we summarize all our interferometric determinations of the gravity darkening coefficient for rapid rotators, finding that none match the expectations from the widely used von Zeipel gravity darkening laws. Since the conditions of the von Zeipel law are known to be violated for rapidly rotating stars, we recommend using the empirically derived {beta} = 0.19 for such stars with radiation-dominated envelopes. Furthermore, we note that no paradigm exists for self-consistently modeling heavily gravity-darkened stars that show hot radiative poles with cool convective equators.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

EFFECTS OF A COMPANION STAR ON SLOW NOVA OUTBURSTS-TRANSITION FROM STATIC TO WIND EVOLUTIONS

Two types of nova evolutions can occur in low-mass white dwarfs of {approx}0.5-0.7 M{sub Sun }, i.e., an evolution with optically thick winds like in usual classical novae, or an another type of evolution without them like in the symbiotic nova PU Vul. The latter type is characterized by spectra with no indication of strong winds as well as a long-lasting flat optical peak in its light curve. We propose a transition from evolution with no optically thick wind to usual evolution with optically thick winds as a new outburst model for slow novae that show a relatively long-lasting multipeak phase followed by a wind phase like in the slow novae V723 Cas, HR Del, and V5558 Sgr. We calculated nova envelopes with one-dimensional approximation of the companion's effects and found that when the companion star is deeply embedded in the extended nova envelope, the structure of the static envelope approaches that of the optically thick wind solution. Thus, the transition from static to wind solution is triggered by the effect of the companion. The transition occurs in a close binary nova like V723 Cas, but is not triggered in a long-period binary like PU Vul. We reconfirm our previous results that the frictional energy deposition is negligibly small in almost all hydrogen/helium novae because of the low envelope density at the orbit.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE STRUCTURES AND TOTAL (MINOR + MAJOR) MERGER HISTORIES OF MASSIVE GALAXIES UP TO z {approx} 3 IN THE HST GOODS NICMOS SURVEY: A POSSIBLE SOLUTION TO THE SIZE EVOLUTION PROBLEM

We investigate the total major (>1:4 by stellar mass) and minor (>1:100 by stellar mass) merger history of a population of 80 massive (M{sub *} > 10{sup 11} M{sub Sun }) galaxies at high redshifts (z = 1.7-3). We utilize extremely deep and high-resolution Hubble Space Telescope H-band imaging from the GOODS NICMOS Survey, which corresponds to rest-frame optical wavelengths at the redshifts probed. We find that massive galaxies at high redshifts are often morphologically disturbed, with a CAS (concentration, C; asymmetry, A; clumpiness, S) deduced merger fraction f{sub m} = 0.23 {+-} 0.05 at z = 1.7-3. We find close accord between close pair methods (within 30 kpc apertures) and CAS methods for deducing major merger fractions at all redshifts. We deduce the total (minor + major) merger history of massive galaxies with M{sub *} > 10{sup 9} M{sub Sun} galaxies, and find that this scales roughly linearly with log-stellar-mass and magnitude range. We test our close pair methods by utilizing mock galaxy catalogs from the Millennium Simulation. We compute the total number of mergers to be (4.5 {+-} 2.9)/({tau}{sub m}) from z = 3 to the present, to a stellar mass sensitivity threshold of {approx}1:100 (where {tau}{sub m} is the merger timescale in Gyr which varies as a function of mass). This corresponds to an average mass increase of (3.4 {+-} 2.2) Multiplication-Sign 10{sup 11} M{sub Sun} over the past 11.5 Gyr due to merging. We show that the size evolution observed for these galaxies may be mostly explained by this merging.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

TINY SCALE OPACITY FLUCTUATIONS FROM VLBA, MERLIN, AND VLA OBSERVATIONS OF H I ABSORPTION TOWARD 3C 138

The structure function of opacity fluctuations is a useful statistical tool to study tiny scale structures of neutral hydrogen. Here we present high-resolution observation of H I absorption toward 3C 138, and estimate the structure function of opacity fluctuations from the combined VLA, MERLIN, and VLBA data. The angular scales probed in this work are {approx}10-200 mas (about 5-100 AU). The structure function in this range is found to be well represented by a power law S{sub {tau}}(x) {approx} x{sup {beta}} with index {beta} {approx} 0.33 {+-} 0.07 corresponding to a power spectrum P{sub {tau}}(U) {approx} U{sup -2.33}. This is slightly shallower than the earlier reported power-law index of {approx}2.5-3.0 at {approx}1000 AU to few pc scales. The amplitude of the derived structure function is a factor of {approx}20-60 times higher than the extrapolated amplitude from observation of Cas A at larger scales. On the other hand, extrapolating the AU scale structure function for 3C 138 predicts the observed structure function for Cas A at the pc scale correctly. These results clearly establish that the atomic gas has significantly more structures in AU scales than expected from earlier pc scale observations. Some plausible reasons are identified and discussed here to explain these results. The observational evidence of a shallower slope and the presence of rich small-scale structures may have implications for the current understanding of the interstellar turbulence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CHANDRA AND SUZAKU OBSERVATIONS OF THE Be/X-RAY STAR HD110432

We present an analysis of a pointed 141 ks Chandra high-resolution transmission gratings observation of the Be X-ray emitting star HD110432, a prominent member of the {gamma} Cas analogs. This observation represents the first high-resolution spectrum taken for this source as well as the longest uninterrupted observation of any {gamma} Cas analog. The Chandra light curve shows a high variability but its analysis fails to detect any coherent periodicity up to a frequency of 0.05 Hz. Hardness ratio versus intensity analyses demonstrate that the relative contributions of the [1.5-3] A, [3-6] A, and [6-16] A energy bands to the total flux change rapidly in the short term. The analysis of the Chandra High Energy Transmission Grating (HETG) spectrum shows that, to correctly describe the spectrum, three model components are needed. Two of those components are optically thin thermal plasmas of different temperatures (kT Almost-Equal-To 8-9 and 0.2-0.3 keV, respectively) described by the models vmekal or bvapec. The Fe abundance in each of these two components appears equal within the errors and is slightly subsolar with Z Almost-Equal-To 0.75 Z{sub Sun }. The bvapec model better describes the Fe L transitions, although it cannot fit well the Na XI Ly{alpha} line at 10.02 A, which appears to be overabundant. Two different models seem to describe well the third component. One possibility is a third hot optically thin thermal plasma at kT = 16-21 keV with an Fe abundance Z Almost-Equal-To 0.3 Z{sub Sun }, definitely smaller than for the other two thermal components. Furthermore, the bvapec model describes well the Fe K shell transitions because it accounts for the turbulence broadening of the Fe XXV and Fe XXVI lines with a v{sub turb} Almost-Equal-To 1200 km s{sup -1}. These two lines, contributed mainly by the hot thermal plasma, are significantly wider than the Fe K{alpha} line whose FWHM < 5 mA is not resolved by Chandra. Alternatively, the third component can be described by a power law with a photon index of {Gamma} = 1.56. In either case, the Chandra HETG spectrum establishes that each one of these components must be modified by distinct absorption columns. The analysis of a noncontemporaneous 25 ks Suzaku observation shows the presence of a hard tail extending up to at least 33 keV. The Suzaku spectrum is described with the sum of two components: an optically thin thermal plasma at kT Almost-Equal-To 9 keV and Z Almost-Equal-To 0.74 Z{sub Sun }, and a very hot second plasma with kT Almost-Equal-To 33 keV or, alternatively, a power law with photon index of {Gamma} = 1.58. In either case, each one of the two components must be affected by different absorption columns. Therefore, the kT = 8-9 keV component is definitely needed while the nature of the harder emission cannot be unambiguously established with the present data sets. The analysis of the Si XIII and S XV He-like triplets present in the Chandra spectrum points to a very dense (n{sub e} {approx} 10{sup 13} cm{sup -3}) plasma located either close to the stellar surface (r < 3R{sub *}) of the Be star or, alternatively, very close (r {approx} 1.5R{sub WD}) to the surface of a (hypothetical) white dwarf companion. We argue, however, that the available data support the first scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

LATE-TIME OPTICAL EMISSION FROM CORE-COLLAPSE SUPERNOVAE

Ground-based optical spectra and Hubble Space Telescope images of 10 core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and the progenitor star's circumstellar material. The most distinct trend is an increase in the strength of [O III]/([O I]+[O II]) with age, and a decline in H{alpha}/([O I]+[O II]) which is broadly consistent with the view that the reverse shock has passed through the H envelope of the ejecta in many of these objects. We also present a spatially integrated spectrum of the young Galactic supernova remnant Cassiopeia A (Cas A). Similarities observed between the emission line profiles of the Almost-Equal-To 330 yr old Cas A remnant and decades old CCSNe suggest that observed emission line asymmetry in evolved CCSN spectra may be associated with dust in the ejecta, and that minor peak substructure typically interpreted as 'clumps' or 'blobs' of ejecta may instead be linked with large-scale rings of SN debris.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

YELLOW HYPERGIANTS SHOW LONG SECONDARY PERIODS?

There is observational evidence that intermittent long secondary periods of {approx}1000 days are present in the well-observed yellow hypergiants {rho} Cas and HR 8752. The long secondary period is interpreted here as the turnover time of giant convection cells in the convective envelope, as has been already suggested in the case of red giants and supergiants of high luminosity. The observed secondary periods and surface radial velocities of {rho} Cas and HR 8752 agree with the theoretical predictions, within the expected errors. These results support a theoretical interpretation that now covers the entire initial mass range from 1 to 50 M{sub Sun} for luminous cool stars.

79 ASTRONOMY AND ASTROPHYSICS↗