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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Thermal emission measurements 2000-400 cm(exp -1) (5-25 microns) of Hawaiian palagonitic soils and their implications for Mars

The thermal emission of two palagonitic soils, common visible and near infrared spectral analogs for bright soils on Mars, was measured over the wavelength range of 5 to 25 microns (2000 to 400 cm(exp -1) for several particle size separates. All spectra exhibit emissivity features due to vibrations associated with H2O and SiO. The maximum variability of emissivity is approx. = 20% in the short wavelength region (5 to 6.5 microns, 2000 to 1500 cm(exp -1)), and is more subdued, < 4%, at longer wavelengths. The strengths of features present in infrared spectra of Mars cannot be solely provided by emissivity variations of palagonite; some other material or mechanism must provide additional absorption(s).

Roush, Ted L.↗
DOE OSTI2012

HOST GALAXY PROPERTIES OF THE SUBLUMINOUS GRB 120422A/SN 2012bz

GRB 120422A is a nearby (z = 0.283) long-duration gamma-ray burst (LGRB) detected by Swift with E {sub {gamma},iso} {approx} 4.5 Multiplication-Sign 10{sup 49} erg. It is also associated with the spectroscopically confirmed broad-lined Type Ic SN 2012bz. These properties establish GRB 120422A/SN 2012bz as the sixth and newest member of the class of subluminous GRBs supernovae (SNe). Observations also show that GRB 120422A/SN 2012bz occurred at an unusually large offset ({approx}8 kpc) from the host galaxy nucleus, setting it apart from other nearby LGRBs and leading to speculation that the host environment may have undergone prior interaction activity. Here, we present spectroscopic observations using the 6.5 m Magellan telescope at Las Campanas. We extract spectra at three specific locations within the GRB/SN host galaxy, including the host nucleus, the explosion site, and the 'bridge' of diffuse emission connecting these two regions. We measure a metallicity of log(O/H) + 12 = 8.3 {+-} 0.1 and a star formation rate (SFR) per unit area of 0.08 M {sub Sun} yr{sup -1} kpc{sup -2} at the host nucleus. At the GRB/SN explosion site we measure a comparable metallicity of log(O/H) + 12 = 8.2 {+-} 0.1 but find a much lower SFR per unit area of 0.01 M {sub Sun} yr{sup -1} kpc{sup -2}. We also compare the host galaxy of this event to the hosts of other LGRBs, including samples of subluminous LGRBs and cosmological LGRBs, and find no systematic metallicity difference between the environments of these different subtypes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE HISTORY AND ENVIRONMENT OF A FADED QUASAR: HUBBLE SPACE TELESCOPE OBSERVATIONS OF HANNY'S VOORWERP AND IC 2497

We present Hubble Space Telescope imaging and spectroscopy, along with supporting Galaxy Evolution Explorer and ground-based data, for the extended high-ionization cloud known as Hanny's Voorwerp, near the spiral galaxy IC 2497. Wide Field Camera 3 images show complex dust absorption near the nucleus of IC 2497. The galaxy core in these data is, within the errors, coincident with the very long baseline interferometry core component marking the active nucleus. Space Telescope Imaging Spectrograph (STIS) optical spectra show the active galactic nucleus (AGN) to be a type 2 Seyfert galaxy of rather low luminosity. The derived ionization parameter log U = -3.5 is in accordance with the weak X-ray emission from the AGN. We find no high-ionization gas near the nucleus, adding to the evidence that the AGN is currently at a low radiative output (perhaps with the central black hole having switched to a mode dominated by kinetic energy). The nucleus is accompanied by an expanding ring of ionized gas Almost-Equal-To 500 pc in projected diameter on the side opposite Hanny's Voorwerp. Where sampled by the STIS slit, this ring has Doppler offset Almost-Equal-To 300 km s{sup -1} from the nucleus, implying a kinematic age <7 Multiplication-Sign 10{sup 5} years. Narrowband [O III] and H{alpha}+[N II] Advanced Camera for Surveys images show fine structure in Hanny's Voorwerp, including limb-brightened sections suggesting modest interaction with a galactic outflow and small areas where H{alpha} is strong. We identify these latter regions as regions ionized by recent star formation, in contrast to the AGN ionization of the entire cloud. These candidate 'normal' H II regions contain blue continuum objects, whose colors are consistent with young stellar populations; they appear only in a 2 kpc region toward IC 2497 in projection, perhaps meaning that the star formation was triggered by compression from a narrow outflow. The ionization-sensitive ratio [O III]/H{alpha} shows broad bands across the object at a skew angle to the galaxy nucleus, and no discernible pattern near the prominent 'hole' in the ionized gas. The independence of ionization and surface brightness (SB) suggests that there is substantial spatial structure which remains unresolved, to such an extent that the SB samples the number of denser filaments rather than the characteristic density in emission regions; this might be a typical feature of gas in tidal tails, currently measurable only when such gas is highly ionized. These results fit with our picture of an ionization echo from an AGN whose ionizing luminosity has dropped by a factor >100 (and possibly much more) within the last (1-2) Multiplication-Sign 10{sup 5} years; we suggest a tentative sequence of events in IC 2497 and discuss implications of such rapid fluctuations in luminosity for our understanding of AGN demographics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Studies on nickel-tungsten oxide thin films

Nickel-Tungsten oxide (95:5) thin films were prepared by rf sputtering at 200W rf power with various substrate temperatures. X-ray diffraction study reveals the amorphous nature of films. The substrate temperature induced decrease in energy band gap with a maximum transmittance of 71%1 was observed. The Micro-Raman study shows broad peaks at 560 cm{sup −1} and 1100 cm{sup −1} correspond to Ni-O vibration and the peak at 860 cm{sup −1} can be assigned to the vibration of W-O-W bond. Photoluminescence spectra show two peaks centered on 420 nm and 485 nm corresponding to the band edge emission and vacancies created due to the addition of tungsten, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The photoluminescence and structural properties of (Ce, Yb) co-doped silicon oxides after high temperature annealing

We studied the photoluminescence (PL) and structural properties of Ce and Yb co-doped silicon oxide films after high temperature annealing. The PL spectra of Ce{sup 3+} and Yb{sup 3+} ions were sensitive to the structural variation of the films, and the Yb PL intensities were significantly enhanced especially upon 1200 °C annealing. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, indicated that rare earth silicates and the CeO{sub 2} phase had formed in the oxides. The proportions of the phases varied with the “nominal Si-richness” of the films. Energy transfer from the excited Ce{sup 3+} to Yb{sup 3+} can be inferred from both PL excitation and decay spectra.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

PROPER MOTIONS OF THE HH 110/270 SYSTEM

We present a study of the HH 110/270 system based on three sets of optical images obtained with the ESO New Technology Telescope, the Subaru Telescope, and the Hubble Space Telescope (HST). The ground-based observations are made in the H{alpha} and [S II] emission lines and the HST observations are made in the H{alpha} line only. Ground-based observations reveal the existence of nine knots, which have not been previously discussed and offer some important insight into the HH 110/270 history. We perform a kinematic study of the HH 110/270 system and an analysis of its emission properties. We measure proper motions of all the knots in the system. Four of the newly identified knots belong to the HH 270 jet. Their positions indicate that the jet's axis changed its direction in the past. We speculate that similar changes may have occurred many times in the past and this could be part of the reason for the unusual structure of the HH 110 jet. The HST observations allow us to resolve individual knots into their substructures and to measure their proper motions. These measurements show that the knots are highly turbulent structures. Finally, we report the discovery of four new Herbig-Haro (HH) objects located near the HH 110/270 system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DISCOVERY OF A WOLF-RAYET STAR THROUGH DETECTION OF ITS PHOTOMETRIC VARIABILITY

We report the serendipitous discovery of a heavily reddened Wolf-Rayet star that we name WR 142b. While photometrically monitoring a cataclysmic variable, we detected weak variability in a nearby field star. Low-resolution spectroscopy revealed a strong emission line at 7100 A, suggesting an unusual object and prompting further study. A spectrum taken with the Hobby-Eberly Telescope confirms strong He II emission and an N IV 7112 A line consistent with a nitrogen-rich Wolf-Rayet star of spectral class WN6. Analysis of the He II line strengths reveals no detectable hydrogen in WR 142b. A blue-sensitive spectrum obtained with the Large Binocular Telescope shows no evidence for a hot companion star. The continuum shape and emission line ratios imply a reddening of E(B - V) = 2.2-2.6 mag. We estimate that the distance to WR 142b is 1.4 {+-} 0.3 kpc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

METALLICITIES, DUST, AND MOLECULAR CONTENT OF A QSO-DAMPED Ly{alpha} SYSTEM REACHING log N(H I) = 22: AN ANALOG TO GRB-DLAs

We present the elemental abundance and H{sub 2} content measurements of a damped Ly{alpha} (DLA) system with an extremely large H I column density, log N(H I) (cm{sup -2}) = 22.0 {+-} 0.10, at z{sub abs} = 3.287 toward the QSO SDSS J081634+144612. We measure column densities of H{sub 2}, C I, C I*, Zn II, Fe II, Cr II, Ni II, and Si II from a high signal-to-noise and high spectral resolution VLT-UVES spectrum. The overall metallicity of the system is [Zn/H] = -1.10 {+-} 0.10 relative to solar. Two molecular hydrogen absorption components are seen at z = 3.28667 and 3.28742 (a velocity separation of Almost-Equal-To 52 km s{sup -1}) in rotational levels up to J = 3. We derive a total H{sub 2} column density of log N(H{sub 2}) (cm{sup -2}) = 18.66 and a mean molecular fraction of f = 2N(H{sub 2})/[2N(H{sub 2}) + N(H I)] = 10{sup -3.04{+-}0.37}, typical of known H{sub 2}-bearing DLA systems. From the observed abundance ratios we conclude that dust is present in the interstellar medium of this galaxy, with an enhanced abundance in the H{sub 2}-bearing clouds. However, the total amount of dust along the line of sight is not large and does not produce any significant reddening of the background QSO. The physical conditions in the H{sub 2}-bearing clouds are constrained directly from the column densities of H{sub 2} in different rotational levels, C I and C I*. The kinetic temperature is found to be T Almost-Equal-To 75 K and the particle density lies in the range n{sub H} = 50-80 cm{sup -3}. The neutral hydrogen column density of this DLA is similar to the mean H I column density of DLAs observed at the redshift of {gamma}-ray bursts (GRBs). We explore the relationship between GRB-DLAs and the high column density end of QSO-DLAs finding that the properties (metallicity and depletion) of DLAs with log N(H I) > 21.5 in the two populations do not appear to be significantly different.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z {approx} 2-3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY

We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and intergalactic baryons within the same survey volumes, focusing particularly on scales from {approx}50 kpc to a few Mpc. The KBSS is optimized for the redshift range z {approx} 2-3, combining S/N {approx}100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z {approx_equal} 2.5-2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H I) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 {approx}< z {approx}< 2.8 and with projected distances {<=}3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Ly{alpha} forest region of all 15 QSO spectra, we compiled a catalog of {approx}6000 individual absorbers in the redshift range of interest, with 12 {<=} log (N{sub HI}) {<=}21. These are used to measure H I absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalactic medium (IGM) within the survey volume. We find that N{sub HI} and the multiplicity of velocity-associated H I components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H I absorbers within {approx_equal} 100 physical kpc of galaxies have N{sub HI} {approx}3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H I absorption is found within transverse distances of {approx}< 300 kpc and within {+-}300 km s{sup -1} of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(N{sub HI}) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N{sub HI} remain significantly elevated to transverse distances of {approx}2 physical Mpc from galaxies in our sample. Absorbers with N{sub HI} >10{sup 14.5} cm{sup -2} are tightly correlated with the positions of galaxies, while absorbers with lower N{sub HI} are correlated with galaxy positions only on {approx}>Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of {approx}100 physical kpc peculiar velocities of {Delta}v {approx_equal} {+-}260 km s{sup -1} with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 r{sub vir} of galaxies are larger by {approx_equal} 50% than randomly chosen absorbers of the same N{sub HI}, suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with M{sub halo} {approx_equal} 10{sup 12} M{sub Sun} at z {approx} 2-3.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CHARGE-EXCHANGE LIMITS ON LOW-ENERGY {alpha}-PARTICLE FLUXES IN SOLAR FLARES

This paper reports on a search for flare emission via charge-exchange radiation in the wings of the Ly{alpha} line of He II at 304 A, as originally suggested for hydrogen by Orrall and Zirker. Via this mechanism a primary {alpha} particle that penetrates into the neutral chromosphere can pick up an atomic electron and emit in the He II bound-bound spectrum before it stops. The Extreme-ultraviolet Variability Experiment on board the Solar Dynamics Observatory gives us our first chance to search for this effect systematically. The Orrall-Zirker mechanism has great importance for flare physics because of the essential roles that particle acceleration plays; this mechanism is one of the few proposed that would allow remote sensing of primary accelerated particles below a few MeV nucleon{sup -1}. We study 10 events in total, including the {gamma}-ray events SOL2010-06-12 (M2.0) and SOL2011-02-24 (M3.5) (the latter a limb flare), seven X-class flares, and one prominent M-class event that produced solar energetic particles. The absence of charge-exchange line wings may point to a need for more complete theoretical work. Some of the events do have broadband signatures, which could correspond to continua from other origins, but these do not have the spectral signatures expected from the Orrall-Zirker mechanism.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

INCLINATION-DEPENDENT ACTIVE GALACTIC NUCLEUS FLUX PROFILES FROM STRONG LENSING OF THE KERR SPACETIME

Recent quasar microlensing observations have constrained the X-ray emission sizes of quasars to be about 10 gravitational radii, one order of magnitude smaller than the optical emission sizes. Using a new ray-tracing code for the Kerr spacetime, we find that the observed X-ray flux is strongly influenced by the gravity field of the central black hole, even for observers at moderate inclination angles. We calculate inclination-dependent flux profiles of active galactic nuclei in the optical and X-ray bands by combining the Kerr lensing and projection effects for future reference. We further study the dependence of the X-ray-to-optical flux ratio on the inclination angle caused by differential lensing distortion of the X-ray and optical emission, assuming several corona geometries. The strong lensing X-ray-to-optical magnification ratio can change by a factor of {approx}10 for normal quasars in some cases, and a further factor of {approx}10 for broad absorption line (BAL) quasars and obscured quasars. Comparing our results with the observed distributions in normal and BAL quasars, we find that the inclination angle dependence of the magnification ratios can significantly change the X-ray-to-optical flux ratio distributions. In particular, the mean value of the spectrum slope parameter {alpha}{sub ox}, 0.3838log F {sub 2keV}/F {sub 2500A}, can differ by {approx}0.1-0.2 between normal and BAL quasars, depending on corona geometries, suggesting larger intrinsic absorptions in BAL quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES AT z {approx} 3: A TEST FOR STELLAR FEEDBACK, GALACTIC OUTFLOWS, AND COLD STREAMS

We present new results on the kinematics, thermal and ionization state, and spatial distribution of metal-enriched gas in the circumgalactic medium (CGM) of massive galaxies at redshift {approx}3, using the Eris suite of cosmological hydrodynamic ''zoom-in'' simulations. The reference run adopts a blastwave scheme for supernova feedback that produces large-scale galactic outflows, a star formation recipe based on a high gas density threshold, metal-dependent radiative cooling, and a model for the diffusion of metals and thermal energy. The effect of the local UV radiation field is added in post-processing. The CGM (defined as all gas at R > 0.2 R{sub vir} = 10 kpc, where R{sub vir} is the virial radius) contains multiple phases having a wide range of physical conditions, with more than half of its heavy elements locked in a warm-hot component at T > 10{sup 5} K. Synthetic spectra, generated by drawing sightlines through the CGM, produce interstellar absorption-line strengths of Ly{alpha}, C II, C IV, Si II, and Si IV as a function of the galactocentric impact parameter (scaled to the virial radius) that are in broad agreement with those observed at high redshift by Steidel et al. The covering factor of absorbing material declines less rapidly with impact parameter for Ly{alpha} and C IV compared to C II, Si IV, and Si II, with Ly{alpha} remaining strong (W{sub Ly{alpha}} > 300 mA) to {approx}> 5 R{sub vir} = 250 kpc. Only about one third of all the gas within R{sub vir} is outflowing. The fraction of sightlines within one virial radius that intercept optically thick, N{sub H{sub I}}>10{sup 17.2} cm{sup -2} material is 27%, in agreement with recent observations by Rudie et al. Such optically thick absorption is shown to trace inflowing ''cold'' streams that penetrate deep inside the virial radius. The streams, enriched to metallicities above 0.01 solar by previous episodes of star formation in the main host and in nearby dwarfs, are the origin of strong (N{sub C{sub II}}>10{sup 13} cm{sup -2}) C II absorption with a covering factor of 22% within R{sub vir} and 10% within 2 R{sub vir}. Galactic outflows do not cause any substantial suppression of the cold accretion mode. The central galaxy is surrounded by a large O VI halo, with a typical column density N{sub O{sub VI}} {approx}> 10{sup 14} cm{sup -2} and a near unity covering factor maintained all the way out to 150 kpc. This matches the trends recently observed in star-forming galaxies at low redshift by Tumlinson et al. Our zoom-in simulations of this single system appear then to reproduce quantitatively the complex baryonic processes that determine the exchange of matter, energy, and metals between galaxies and their surroundings.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Effect of transverse electric field and temperature on light absorption in GaAs/AlGaAs tunnel-coupled quantum wells

The photoluminescence and intersubband absorption spectra are studied in GaAs/AlGaAs tunnel- coupled quantum well structures. The peak positions in the photoluminescence and absorption spectra are consistent with the theoretically calculated energies of optical carrier transitions. The effect of a transverse electric field and temperature on intersubband light absorption is studied. It is caused by electron redistribution between the size-quantization levels and a variation in the energy spectrum of quantum wells. The variation in the refractive index in the energy region of observed intersubband transitions is estimated using Kramers–Kronig relations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Modulation of intersubband light absorption and interband photoluminescence in double GaAs/AlGaAs quantum wells under strong lateral electric fields

The effect of a lateral electric field on the mid-infrared absorption and interband photoluminescence spectra in double tunnel-coupled GaAs/AlGaAs quantum wells is studied. The results obtained are explained by the redistribution of hot electrons between quantum wells and changes in the space charge in the structure. The hot carrier temperature is determined by analyzing the intersubband light absorption and interband photoluminescence modulation spectra under strong lateral electric fields.

36 MATERIALS SCIENCE↗
NASA NTRS1984

An optical investigation of the peculiar supernova remnant CTB 80

Interference-filter photographs and optical spectrophotometry are used to investigate the optical emission associated with the peculiar supernova remnant CTB 80. Optically, the remnant consists of outlying diffuse and filamentary emission surrounding a small, central ring of filaments which are coincident with the central radio emission peak. Spectra of two filaments in the southwestern part of the remnant show strong forbidden S II emission relative to H-alpha; in conjunction with the nonthermal radio emission in this region, this suggests that the filaments are shock heated. Filaments outside the radio structure in the northeast show a similar optical spectrum and may also be a part of CTB 80. The central filaments form a well-defined shell structure in the light of forbidden O III emission 5007 A but are irregular in H-alpha showing both knots and diffuse emission.

Blair, W. P.↗
NASA NTRS1985

Emission features in the 4-13 micron spectra of the reflection nebulae NGC 7023 and NGC 2023

Spectroscopy from 4 to 13 microns of the visual reflection nebulae NGC 7023 and NGC 2023 has been obtained. These data, together with previous work from 1 to 4 microns, show that the spectra of these sources consist of a relatively flat continuum from 1 to 13 microns and six emission features at 3.3, 3.4, 6.2, 7.7, 8.6, and 11.3 microns. The observations rule out equilibrium thermal emission for the features and continuum in reflection nebulae, and point toward a nonequilibrium emission mechanism such as thermal emission from thermally fluctuating small grains or fluorescence from large molecules. The similarity of the emission feature spectra in reflection nebulae to those in other sources suggests a universal emission mechanism, thus implying nonequilibrium emission mechanisms in other sources.

Sellgren, K.↗
NASA NTRS2010

High-Resolution X-Ray Spectra of the Symbiotic Star SS73 17

SS73 17 was an innocuous Mira-type symbiotic star until the International Gamma-Ray Astrophysics Laboratory and Swift discovered its bright hard X-ray emission, adding it to the small class of "hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it emits three bright iron lines as well, with little to no emission in the 0.3-2.0 keV bandpass. We present here follow-up observations with the Chandra High Energy Transmission Grating and Suzaku that confirm the earlier detection of strong emission lines of Fe K(alpha) fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray emission. The high-resolution spectrum also shows emission lines of other highly ionized ions as Si xiv and possibly S XVI. In addition, a re-analysis of the 2006 Suzaku data using the latest calibration shows that the hard (15-50 keV) X-ray emission is brighter than previously thought and remains constant in both the 2006 and 2008 data. The G ratio calculated from the Fe xxv lines shows that these lines are thermal, not photoionized, in origin.With the exception of the hard X-ray emission, the spectra from both epochs can be fit using thermal radiation assuming a differential emission measure based on a cooling-flow model combined with a full and partial absorber. We show that acceptable fits can be obtained for all the data in the 1-10 keV band varying only the partial absorber. Based on the temperature and accretion rate, the thermal emission appears to be arising from the boundary layer between the accreting white dwarf and the accretion disk.

Eze, R. N. C.↗
DOE OSTI2012

THE SIZES OF THE NEAREST YOUNG STARS

We present moderate resolution (R {approx} 3575) optical spectra of 19 known or suspected members of the AB Doradus and {beta} Pictoris Moving Groups, obtained with the DeVeny Spectrograph on the 72 inch Perkins telescope at Lowell Observatory. For four of five recently proposed members, signatures of youth such as Li I 6708 A absorption and H{alpha} emission further strengthen the case for youth and membership. The lack of detected lithium in the proposed {beta} Pic member TYC 2211-1309-1 implies that it is older than all other K-type members and weakens the case for membership. Effective temperatures are determined via line ratio analyses for the 11 F, G, and early-K stars observed, and via spectral comparisons for the eight late-K and M stars observed. We assemble updated candidate membership lists for these moving groups that account for known binarity. Currently, the AB Dor Moving Group contains 127 proposed members and the {beta} Pic Moving Group holds 77 proposed members. We then use temperature, luminosity, and distance estimates to predict angular diameters for these stars; the motivation is to identify stars that can be spatially resolved with long-baseline optical/infrared interferometers in order to improve age estimates for these groups and to constrain evolutionary models at young ages. Considering the portion of the sky accessible to northern hemisphere facilities (decl. > - 30), six stars have diameters large enough to be spatially resolved ({theta} > 0.4 mas) with the CHARA Array, which currently has the world's longest baseline of 331 m; this subsample includes the low-mass M2.5 member of AB Dor, GJ 393, which is likely to still be pre-main sequence. For southern hemisphere facilities (decl. < + 30), 18 stars have diameters larger than this limiting size, including the low-mass debris disk star AU Mic (0.72 mas). However, the longest baselines of southern hemisphere interferometers (160 m) are only able to resolve the largest of these, the B6 star {alpha} Gru (1.17 mas); proposed long-baseline stations may alleviate the current limitations.

79 ASTRONOMY AND ASTROPHYSICS↗