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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Accurate atmospheric parameters at moderate resolution using spectral indices: Preliminary application to the marvels survey

Studies of Galactic chemical, and dynamical evolution in the solar neighborhood depend on the availability of precise atmospheric parameters (effective temperature T {sub eff}, metallicity [Fe/H], and surface gravity log g) for solar-type stars. Many large-scale spectroscopic surveys operate at low to moderate spectral resolution for efficiency in observing large samples, which makes the stellar characterization difficult due to the high degree of blending of spectral features. Therefore, most surveys employ spectral synthesis, which is a powerful technique, but relies heavily on the completeness and accuracy of atomic line databases and can yield possibly correlated atmospheric parameters. In this work, we use an alternative method based on spectral indices to determine the atmospheric parameters of a sample of nearby FGK dwarfs and subgiants observed by the MARVELS survey at moderate resolving power (R ∼ 12,000). To avoid a time-consuming manual analysis, we have developed three codes to automatically normalize the observed spectra, measure the equivalent widths of the indices, and, through a comparison of those with values calculated with predetermined calibrations, estimate the atmospheric parameters of the stars. The calibrations were derived using a sample of 309 stars with precise stellar parameters obtained from the analysis of high-resolution FEROS spectra, permitting the low-resolution equivalent widths to be directly related to the stellar parameters. A validation test of the method was conducted with a sample of 30 MARVELS targets that also have reliable atmospheric parameters derived from the high-resolution spectra and spectroscopic analysis based on the excitation and ionization equilibria method. Our approach was able to recover the parameters within 80 K for T {sub eff}, 0.05 dex for [Fe/H], and 0.15 dex for log g, values that are lower than or equal to the typical external uncertainties found between different high-resolution analyses. An additional test was performed with a subsample of 138 stars from the ELODIE stellar library, and the literature atmospheric parameters were recovered within 125 K for T {sub eff}, 0.10 dex for [Fe/H], and 0.29 dex for log g. These precisions are consistent with or better than those provided by the pipelines of surveys operating with similar resolutions. These results show that the spectral indices are a competitive tool to characterize stars with intermediate resolution spectra.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

INSIGHTS INTO THE CEPHEID DISTANCE SCALE

We present a detailed investigation of the Cepheid distance scale by using both theory and observations. Through the use of pulsation models for fundamental mode Cepheids, we found that the slope of the period-luminosity (P-L) relation covering the entire period range (0.40 {<=} log P {<=} 2.0) becomes steeper when moving from optical to near-infrared (NIR) bands, and that the metallicity dependence of the slope decreases from the B- to the K band. The sign of the metallicity dependence for the slopes of the P-L{sub V} and P-L{sub I} relation is at odds with some recent empirical estimates. We determined new homogeneous estimates of V- and I-band slopes for 87 independent Cepheid data sets belonging to 48 external galaxies with nebular oxygen abundance 7.5 {<=} 12 + log (O/H) {<=} 8.9. By using Cepheid samples including more than 20 Cepheids, the {chi}{sup 2} test indicates that the hypothesis of a steepening of the P-L{sub V,I} relations with increased metal content can be discarded at the 99% level. On the contrary, the observed slopes agree with the metallicity trend predicted by pulsation models, i.e., the slope is roughly constant for galaxies with 12+log (O/H) < 8.17 and becomes shallower in the metal-rich regime, with confidence levels of 62% and 92%, respectively. The {chi}{sup 2} test concerning the hypothesis that the slope does not depend on metallicity gives confidence levels either similar (PL{sub V} , 62%) or smaller (PL{sub I} , 67%). We investigated the dependence of the period-Wesenheit (P-W) relations on the metal content and we found that the slopes of optical and NIR P-W relations in external galaxies are similar to the slopes of Large Magellanic Cloud (LMC) Cepheids. They also agree with the theoretical predictions suggesting that the slopes of the P-W relations are independent of the metal content. On this ground, the P-W relations provide a robust method to determine distance moduli relative to the LMC, but theory and observations indicate that the metallicity dependence of the zero point in the different passbands has to be taken into account. To constrain this effect, we compared the independent set of galaxy distances provided by Rizzi et al. using the tip of the red giant branch with our homogeneous set of extragalactic Cepheid distances based on the P-W relations. We found that the metallicity correction on distances based on the P-WBV relation is {gamma}{sub B,V} = -0.52 mag dex{sup -1}, whereas it is vanishing for the distances based on the P-WVI and on the P-WJK relations. These findings fully support Cepheid theoretical predictions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

XMM-NEWTON AND FUSE TENTATIVE EVIDENCE FOR A WHIM FILAMENT ALONG THE LINE OF SIGHT TO PKS 0558-504

We present a possible O VIII X-ray absorption line at z = 0.117 {+-} 0.001 which, if confirmed, will be the first one associated with a broad H I Ly{beta} (BLB: FWHM = 160{sup +50} {sub -30} km s{sup -1}) absorber. The absorber lies along the line of sight to the nearby (z = 0.1372) Seyfert 1 galaxy PKS 0558-504, consistent with being a WHIM filament. The X-ray absorber is marginally detected in two independent XMM-Newton spectra of PKS 0558-504, a long {approx}600 ks guest-observer observation and a shorter, {approx}300 ks total, calibration observation, with a combined single line statistical significance of 2.8{sigma} (2.7{sigma} and 1.2{sigma} in the two spectra, respectively). When fitted with our self-consistent hybrid-photoionization WHIM models, the combined XMM- Newton spectrum is consistent with the presence of O VIII K{alpha} at z = (0.117 {+-} 0.001). This model gives best-fitting temperature and equivalent H column density of the absorber of log T = 6.56{sup +0.19} {sub -0.17} K, and log N{sub H} = (21.5 {+-} 0.3)(Z/Z {sub 0.01sun}){sup -1} cm{sup -2}, and predicts the marginal contribution of only two more lines within the XMM- Newton Reflection Grating Spectrometer band pass, Ne IX K{alpha} ({lambda} = 13.45 A) and Fe XVII L ({lambda} = 15.02 A), both with equivalent widths well within the 1{sigma} sensitivity of the combined XMM-Newton spectrum of PKS 0558-504 (EW{sup 1}{sigma} < 3 mA). The lack of detection of associated O VI in the archival FUSE spectrum of PKS 0558-504 allows us to infer a tighter lower limit on the temperature, of log T>6.52 K (at 1{sigma}). The statistical significance of this single X-ray detection is increased by the detection of BLB and complex H I Ly{beta} absorption in archival FUSE spectra of PKS 0558-504, at redshifts z = 0.1183 {+-} 0.0001 consistent with the best-fitting redshift of the X-ray absorber. The FUSE spectrum shows a broad (FWHM = 160{sup +50} {sub -30} km s{sup -1}) absorption complex, which we identify as H I Ly{beta} z {sub BLB} = (0.1183 {+-} 0.0001). The single line statistical significance of this line is 4.1{sigma} (3.7{sigma} if systematics are considered). A possible H I Ly{alpha} is marginally hinted in an archival low-resolution ({Delta}{lambda} {approx} 6 A) International Ultraviolet Explorer (IUE) spectrum of PKS 0558-504, at a redshift of z = (0.119 {+-} 0.001) and with single line significance of 1.7{sigma}. Thus, the combined significance of the three (XMM- Newton, FUSE, and IUE) independent tentative detections, is 5.2{sigma} (5.0{sigma} if the H I Ly{alpha} is not considered, and 4.6{sigma} if the systematics in FUSE are considered). The detection of both metal and H lines at a consistent redshift, in this hot absorbing system, allows us to speculate on its metallicity. By associating the bulk of the X-ray absorber with the BLB line detected in the FUSE spectrum at z {sub BLB} = 0.1183 {+-} 0.0001, we obtain a metallicity of 1%-4% Solar. Although the absorber is only blueshifted by {approx}-6000 km s{sup -1} from the systemic redshift of PKS 0558-504, the identification of the absorbing gas with a high velocity nuclear ionized outflow, is unlikely. The physical, chemical, and dynamical properties of the detected absorber are all quite different from those typically found in the warm absorber (WA) outflows, commonly detected in Seyferts and higher luminosity quasars. WA outflow velocities typically span a range of few hundreds to {approx}1-2 thousands km s{sup -1}; WA metallicities, when measured, are typically found to be at least Solar; high-ionization WAs are virtually always found to coexist with lower-ionization X-ray and UV phases. All this strongly suggests that the absorber, if confirmed, is an intervening WHIM system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE LICK AGN MONITORING PROJECT: THE M {sub BH}-{sigma}{sub *} RELATION FOR REVERBERATION-MAPPED ACTIVE GALAXIES

To investigate the black hole mass versus stellar velocity dispersion (M {sub BH}-{sigma}{sub *}) relation of active galaxies, we measured the velocity dispersions of a sample of local Seyfert 1 galaxies, for which we have recently determined black hole masses using reverberation mapping. For most objects, stellar velocity dispersions were measured from high signal-to-noise ratio optical spectra centered on the Ca II triplet region ({approx}8500 A), obtained at the Keck, Palomar, and Lick Observatories. For two objects, in which the Ca II triplet region was contaminated by nuclear emission, the measurement was based on high-quality H-band spectra obtained with the OH-Suppressing Infrared Imaging Spectrograph at the Keck-II telescope. Combining our new measurements with data from the literature, we assemble a sample of 24 active galaxies with stellar velocity dispersions and reverberation-based black hole mass measurements in the range of black hole mass 10{sup 6} < M {sub BH}/M {sub sun} < 10{sup 9}. We use this sample to obtain reverberation-mapping constraints on the slope and intrinsic scatter of the M {sub BH}-{sigma}{sub *} relation of active galaxies. Assuming a constant virial coefficient f for the reverberation-mapping black hole masses, we find a slope {beta} = 3.55 {+-} 0.60 and the intrinsic scatter {sigma}{sub int} = 0.43 {+-} 0.08 dex in the relation log(M {sub BH}/M {sub sun}) = {alpha} + {beta} log({sigma}{sub *}/200 km s{sup -1}), which are consistent with those found for quiescent galaxies. We derive an updated value of the virial coefficient f by finding the value which places the reverberation masses in best agreement with the M {sub BH}-{sigma}{sub *} relation of quiescent galaxies; using the quiescent M {sub BH}-{sigma}{sub *} relation determined by Gueltekin et al., we find log f = 0.72{sup +0.09} {sub -0.10} with an intrinsic scatter of 0.44 {+-} 0.07 dex. No strong correlations between f and parameters connected to the physics of accretion (such as the Eddington ratio or line-shape measurements) are found. The uncertainty of the virial coefficient remains one of the main sources of the uncertainty in black hole mass determinations using reverberation mapping, and therefore also in single-epoch spectroscopic estimates of black hole masses in active galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MULTIWAVELENGTH OBSERVATIONS OF THE HOT DB STAR PG 0112+104

We present a comprehensive multiwavelength analysis of the hot DB white dwarf PG 0112+104. Our analysis relies on newly acquired FUSE observations, on medium-resolution FOS and GHRS data, on archival high-resolution GHRS observations, on optical spectrophotometry both in the blue and around H{alpha}, as well as on time-resolved photometry. From the optical data, we derive a self-consistent effective temperature of 31,300 {+-} 500 K, a surface gravity of log g = 7.8 {+-} 0.1 (M = 0.52 M{sub sun}), and a hydrogen abundance of log N(H)/N(He)< -4.0. The FUSE spectra reveal the presence of C II and C III lines that complement the previous detection of C II transitions with the GHRS. The improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 {+-} 0.23. No photospheric features associated with other heavy elements are detected. We reconsider the role of PG 0112+104 in the definition of the blue edge of the V777 Her instability strip in light of our high-speed photometry and contrast our results with those of previous observations carried out at the McDonald Observatory.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

PHYSICAL CONDITIONS IN A YOUNG, UNREDDENED, LOW-METALLICITY GALAXY AT HIGH REDSHIFT

Increasingly large samples of galaxies are now being discovered at redshifts z {approx} 5-6 and higher. Many of these objects are inferred to be young, low in mass, and relatively unreddened, but detailed analysis of their high quality spectra will not be possible until the advent of future facilities. In this paper, we shed light on the physical conditions in a plausibly similar low-mass galaxy by presenting the analysis of the rest-frame optical and UV spectra of Q2343-BX418, an L* galaxy at z = 2.3 with a very low mass-to-light ratio and unusual properties: BX418 is young (<100 Myr), low mass (M {sub *} {approx} 10{sup 9} M{sub sun}), low in metallicity (Z {approx} 1/6 Z{sub sun}), and unreddened (E(B - V) {approx_equal} 0.02, UV continuum slope {beta} = -2.1). We infer a metallicity 12 + log(O/H) = 7.9 {+-} 0.2 from the rest-frame optical emission lines. We also determine the metallicity via the direct, electron temperature method, using the ratio O III] {lambda}{lambda}1661, 1666/[O III] {lambda}5007 to determine the electron temperature and finding 12 + log(O/H) = 7.8 {+-} 0.1. These measurements place BX418 among the most metal-poor galaxies observed in emission at high redshift. The rest-frame UV spectrum, which represents {approx}12 hr of integration with the Keck telescope, contains strong emission from Ly{alpha} (with rest-frame equivalent width 54 A), He II {lambda}1640 (both stellar and nebular), C III] {lambda}{lambda}1907, 1909 and O III] {lambda}{lambda}1661, 1666. The C IV/C III] ratio indicates that the source of ionization is unlikely to be an active galactic nucleus. Analysis of the He II, O III], and C III] line strengths indicates a very high ionization parameter log U {approx} -1, while Ly{alpha} and the interstellar absorption lines indicate that outflowing gas is highly ionized over a wide range of velocities. It remains to be determined how many of BX418's unique spectral features are due to its global properties, such as low metallicity and dust extinction, and how many are indicative of a short-lived phase in the early evolution of an otherwise normal star-forming galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

O VI ABSORBERS TRACING HOT GAS ASSOCIATED WITH A PAIR OF GALAXIES AT z = 0.167

High signal-to-noise observations of the QSO PKS 0405-123 (z {sub em} = 0.572) with the Cosmic Origins Spectrograph from 1134 to 1796 A with a resolution of {approx}17 km s{sup -1} are used to study the multi-phase partial Lyman limit system (LLS) at z = 0.16716, which has previously been studied using relatively low signal-to-noise spectra from STIS and FUSE. The LLS and an associated H I-free broad O VI absorber likely originate in the circumgalactic gas associated with a pair of galaxies at z = 0.1688 and 0.1670 with impact parameters of 116 h {sup -1} {sub 70} and 99 h {sup -1} {sub 70}. The broad and symmetric O VI absorption is detected in the z = 0.16716 rest frame with v = -278 {+-} 3 km s{sup -1}, log N(O VI) = 13.90 {+-} 0.03, and b = 52 {+-} 2 km s{sup -1}. This absorber is not detected in H I or other species with the possible exception of N V. The broad, symmetric O VI profile and the absence of corresponding H I absorption indicate that the circumgalactic gas in which the collisionally ionized O VI arises is hot (log T {approx} 5.8-6.2). The absorber may represent a rare but important new class of low-z intergalactic medium absorbers. The LLS has strong asymmetrical O VI absorption with log N(O VI) = 14.72 {+-} 0.02 spanning a velocity range from -200 to +100 km s{sup -1}. The high and low ions in the LLS have properties resembling those found for Galactic highly ionized high-velocity clouds where the O VI is likely produced in the conductive and turbulent interfaces between cool and hot gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE MID-INFRARED PERIOD-LUMINOSITY RELATIONS FOR THE SMALL MAGELLANIC CLOUD CEPHEIDS DERIVED FROM SPITZER ARCHIVAL DATA

In this paper, we derive the Spitzer IRAC band period-luminosity (P-L) relations for the Small Magellanic Cloud (SMC) Cepheids, by matching the Spitzer archival SAGE-SMC data with the OGLE-III SMC Cepheids. We find that the 3.6 {mu}m and 4.5 {mu}m band P-L relations can be better described using two P-L relations with a break period at log(P) = 0.4: this is consistent with similar results at optical wavelengths for SMC P-L relations. The 5.8 {mu}m and 8.0 {mu}m band P-L relations do not extend to sufficiently short periods to enable a similar detection of a slope change at log(P) = 0.4. The slopes of the SMC P-L relations, for log(P) > 0.4, are consistent with their Large Magellanic Cloud counterparts that were derived from a similar data set. They are also in agreement with those obtained from a small sample of Galactic Cepheids with parallax measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MULTI-STRANDED AND MULTI-THERMAL SOLAR CORONAL LOOPS: EVIDENCE FROM HINODE X-RAY TELESCOPE AND EUV IMAGING SPECTROMETER DATA

Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS) on the Japanese/USA/UK Hinode spacecraft were used to investigate the spatial and thermal properties of an isolated quiescent coronal loop. We constructed differential emission measure (DEM) curves using Monte Carlo based, iterative forward fitting algorithms. We studied the loop as a whole, in segments, in transverse cuts, and point-by-point, always with some form of background subtraction, and find that the loop DEM is neither isothermal nor extremely broad, with approximately 96% of the EM between 6.2 {<=}log T{<=} 6.7, and an EM-weighted temperature of log T = 6.48 {+-} 0.16. We find evidence for a gradual change in temperature along the loop, with log T increasing only by {approx}0.1 from the footpoints to the peak. The combine XRT-EIS data set does a good job of constraining the temperature distribution for coronal loop plasma. Our studies show that the strong constraints at high and low temperatures provided by the combined data set are crucial for obtaining reasonable solutions. These results confirm that the observations of at least some loops are not consistent with isothermal plasma, and therefore cannot be modeled with a single flux tube and must be multi-stranded.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

AN EXTRAGALACTIC {sup 12}CO J = 3-2 SURVEY WITH THE HEINRICH HERTZ TELESCOPE

We present results of a {sup 12}CO J = 3-2 survey of 125 nearby galaxies obtained with the 10 m Heinrich Hertz Telescope, with the aim to characterize the properties of warm and dense molecular gas in a large variety of environments. With an angular resolution of 22'', {sup 12}CO 3-2 emission was detected in 114 targets. Based on 61 galaxies observed with equal beam sizes the {sup 12}CO 3-2/1-0 integrated line intensity ratio R{sub 31} is found to vary from 0.2 to 1.9, with an average value of 0.81. No correlations are found for R{sub 31} to Hubble-type and far-infrared luminosity. Possible indications for a correlation with inclination angle and the 60 {mu}m/100 {mu}m color temperature of the dust are not significant. Higher R{sub 31} ratios than in 'normal' galaxies, hinting at enhanced molecular excitation, may be found in galaxies hosting active galactic nuclei. Even higher average values are determined for galaxies with bars or starbursts, the latter being identified by the ratio of infrared luminosity versus isophotal area, log [(L{sub FIR}/L{sub sun})/(D {sup 2}{sub 25}/kpc{sup 2})] > 7.25. (U)LIRGs are found to have the highest averaged R{sub 31} value. This may be a consequence of particularly vigorous star formation activity, triggered by galaxy interaction and merger events. The nuclear CO luminosities are slightly sublinearly correlated with the global FIR luminosity in both the {sup 12}CO J = 3-2 and the 1-0 lines. The slope of the log-log plots rises with compactness of the respective galaxy sub-sample, indicating a higher average density and a larger fraction of thermalized gas in distant luminous galaxies. While linear or sublinear correlations for the {sup 12}CO J = 3-2 line can be explained, if the bulk of the observed J = 3-2 emission originates from the molecular gas with densities below the critical one, the case of the {sup 12}CO J = 1-0 line with its small critical density remains a puzzle.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE UNUSUAL VARIABLE HOT B SUBDWARF LS IV-14{sup 0}116

We first present the results of follow-up photometric observations of the He-rich hot B subdwarf LS IV-14{sup 0}116, which confirm the presence of multiperiodic luminosity variations in the light curve of this star. Rather surprisingly, no other follow-up observations of this kind seem to have been published after the initial suggestion in 2005 that LS IV-14{sup 0}116 could be a pulsating star of a new kind. We were able to extract from our data at least six significant periodicities ranging from 1954 s to 5084 s, including the two oscillations uncovered previously. We also present the results of an analysis combining a high signal-to-noise optical spectrum of LS IV-14{sup 0}116 with recently developed non-local thermodynamic equilibrium model atmospheres and synthetic spectra. Our best estimates of the atmospheric parameters of this star are T{sub eff} = 34950 {+-} 250 K, log g = 5.93 {+-} 0.04, and log N(He)/N(H) = -0.62 {+-} 0.03 (formal fitting errors only). These place LS IV-14{sup 0}116 very near the region of maximum instability in the T{sub eff}-log g plane for short-period p-mode pulsators of the hot subdwarf type. If the luminosity variations are indeed due to pulsations, then LS IV-14{sup 0}116 poses a real challenge to current theory: how can such long observed periods (which would have to be associated with medium- to high-order g-modes) be excited at such a high effective temperature and surface gravity, while the short-period p-modes, more typically excited in this domain, are not observed in this particular star?

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE DISTRIBUTION OF THERMAL PRESSURES IN THE DIFFUSE, COLD NEUTRAL MEDIUM OF OUR GALAXY. II. AN EXPANDED SURVEY OF INTERSTELLAR C I FINE-STRUCTURE EXCITATIONS

We analyzed absorption features arising from interstellar neutral carbon that appeared in the UV spectra of 89 stars recorded in the highest resolution echelle modes of the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope so that we could determine the relative populations of collisionally excited fine-structure levels in the atom's electronic ground state. From this information, in combination with molecular hydrogen rotation temperatures, we derive the distribution of thermal pressures in the diffuse, cold neutral medium (CNM). We find a lognormal pressure distribution (weighted by mass) with a mean in log (p/k) equal to 3.58 and an rms dispersion of at least 0.175 dex that plausibly arises from turbulence with a characteristic Mach number in the range 1 < M < 4. The extreme tails in the distribution are, however, above the lognormal function. Overall, pressures are well correlated with local starlight intensities and extreme kinematics, and they show some anticorrelation with kinetic temperatures. A subsample restricted to low ambient UV intensities reveals a mode in the distribution of log (p/k) that is nearly the same as the complete sample, but with a strong negative skewness created by a near absence of a tail at high pressures. Approximately 23% of this gas is at a pressure that is below that which is allowed for a static CNM. Accompanying nearly all of the gas is a small fraction ({approx}0.05%) that has an extraordinarily large pressure, log (p/k) > 5.5, and this condition is more prevalent at high velocities or for regions with enhanced starlight densities. This survey suggests that the dispersion of thermal pressures in the CNM is predominantly governed by microscopic turbulence driven by star-forming regions, with some additional effects from macroscopic events (e.g., supernova explosions), and these measurements provide constraints for future studies of the broader impact of turbulence on the ISM and star formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE XMM-NEWTON WIDE FIELD SURVEY IN THE COSMOS FIELD: REDSHIFT EVOLUTION OF AGN BIAS AND SUBDOMINANT ROLE OF MERGERS IN TRIGGERING MODERATE-LUMINOSITY AGNs AT REDSHIFTS UP TO 2.2

We present a study of the redshift evolution of the projected correlation function of 593 X-ray selected active galactic nuclei (AGNs) with I{sub AB} < 23 and spectroscopic redshifts z < 4, extracted from the 0.5-2 keV X-ray mosaic of the 2.13 deg{sup 2} XMM- Cosmic Evolution Survey (COSMOS). We introduce a method to estimate the average bias of the AGN sample and the mass of AGN hosting halos, solving the sample variance using the halo model and taking into account the growth of the structure over time. We find evidence of a redshift evolution of the bias factor for the total population of XMM-COSMOS AGNs from b-bar (z-bar =0.92)=2.30{+-}0.11 to b-bar (z-bar =1.94)=4.37{+-}0.27 with an average mass of the hosting dark matter (DM) halos log M{sub 0}(h{sup -1} M{sub sun}) {approx} 13.12 {+-} 0.12 that remains constant at all z < 2. Splitting our sample into broad optical line AGNs (BL), AGNs without broad optical lines (NL), and X-ray unobscured and obscured AGNs, we observe an increase of the bias with redshift in the range z-bar = 0.7-2.25 and z-bar = 0.6-1.5 which corresponds to a constant halo mass of log M{sub 0}(h{sup -1} M{sub sun}) {approx} 13.28 {+-} 0.07 and log M{sub 0}(h{sup -1} M{sub sun}) {approx} 13.00 {+-} 0.06 for BL/X-ray unobscured AGNs and NL/X-ray obscured AGNs, respectively. The theoretical models, which assume a quasar phase triggered by major mergers, cannot reproduce the high bias factors and DM halo masses found for X-ray selected BL AGNs with L{sub BOL} {approx} 2 x 10{sup 45} erg s{sup -1}. Our work extends up to z {approx} 2.2 the z {approx}< 1 statement that, for moderate-luminosity X-ray selected BL AGNs, the contribution from major mergers is outnumbered by other processes, possibly secular ones such as tidal disruptions or disk instabilities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. II. NGC 346 IN THE SMALL MAGELLANIC CLOUD

We have studied the properties of the stellar populations in the field of the NGC 346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to identify all stars with excess H{alpha} emission and derive the accretion luminosity L{sub acc} and mass accretion rate M-dot{sub acc} for all of them. The application of this method to existing Hubble Space Telescope (HST)/Advanced Camera for Surveys photometry of the NGC 346 field has allowed us to identify and study 680 bona fide PMS stars with masses from {approx}0.4 M{sub sun} to {approx}4 M{sub sun} and ages in the range from {approx}1 Myr to {approx}30 Myr. Previous investigations of this region, based on the same data, had identified young ({approx}3 Myr old) candidate PMS stars on the basis of their broadband colors. In this study, we show that there are at least two, almost equally numerous, young populations with distinct ages of, respectively, {approx}1 and {approx}20 Myr. We provide accurate physical parameters for all of them. We take advantage of the unprecedented size of our PMS sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters. We find that, regardless of stellar mass, the mass accretion rate decreases with roughly the square root of the age, or about three times slower than predicted by current models of viscous disk evolution, and that more massive stars systematically have a higher mass accretion rate in proportion to their mass. A multivariate linear regression fit reveals that log M-dot{sub acc}{approx_equal}-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a quantity that is higher at lower metallicity. This result is consistent with measurements of the mass accretion rate in the 30 Dor region and in the Milky Way and suggests that the longer duration for mass accretion could be related to lower metallicity. The high-mass accretion rates that we find suggest that a considerable amount of mass is accreted during the PMS phase, of order {approx}0.2 M{sub sun} or possibly {approx}20% of the final mass for stars with mass m < 1 M{sub sun} if their disks are eroded by 20 Myr, i.e., before they reach the main sequence. Therefore, PMS evolutionary models that do not account for this effect will systematically underestimate the true age when compared with the observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A VIEW OF THE NARROW-LINE REGION IN THE INFRARED: ACTIVE GALACTIC NUCLEI WITH RESOLVED FINE-STRUCTURE LINES IN THE SPITZER ARCHIVE

We queried the Spitzer archive for high-resolution observations with the Infrared Spectrograph of optically selected active galactic nuclei (AGNs) for the purpose of identifying sources with resolved fine-structure lines that would enable studies of the narrow-line region (NLR) at mid-infrared wavelengths. By combining 298 Spitzer spectra with 6 Infrared Space Observatory spectra, we present kinematic information of the NLR for 81, z {approx}< 0.3 AGNs. We used the [Ne V], [O IV], [Ne III], and [S IV] lines, whose fluxes correlate well with each other, to probe gas photoionized by the AGN. We found that the widths of the lines are, on average, increasing with the ionization potential of the species that emit them. No correlation of the line width with the critical density of the corresponding transition was found. The velocity dispersion of the gas, {sigma}, is systematically higher than that of the stars, {sigma}{sub *}, in the AGN host galaxy, and it scales with the mass of the central black hole, M{sub BH}. Further correlations between the line widths and luminosities L, and between L and M{sub BH}, are suggestive of a three-dimensional plane connecting log(M{sub BH}) to a linear combination of log ({sigma}) and log (L). Such a plane can be understood within the context of gas motions that are driven by AGN feedback mechanisms, or virialized gas motions with a power-law dependence of the NLR radius on the AGN luminosity. The M{sub BH} estimates obtained for 35 type 2 AGNs from this plane are consistent with those obtained from the M{sub BH{sup -{sigma}}} relation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

REJUVENATING THE MATTER POWER SPECTRUM. III. THE COSMOLOGY SENSITIVITY OF GAUSSIANIZED POWER SPECTRA

It was recently shown that applying a Gaussianizing transform, such as a logarithm, to the nonlinear matter density field extends the range of useful applicability of the power spectrum by a factor of a few smaller. Such a transform dramatically reduces nonlinearities in both the covariance and the shape of the power spectrum. Here, analyzing Coyote Universe real-space dark-matter density fields, we investigate the consequences of these transforms for cosmological parameter estimation. The power spectrum of the log-density provides the tightest cosmological parameter error bars (marginalized or not), giving a factor of 2-3 improvement over the conventional power spectrum in all five parameters tested. For the tilt, n{sub s} , the improvement reaches a factor of five. Similar constraints are achieved if the log-density power spectrum and conventional power spectrum are analyzed together. Rank-order Gaussianization seems just as useful as a log transform to constrain n{sub s} , but not other parameters. Dividing the overdensity by its dispersion in few-Mpc cells, while it diagonalizes the covariance matrix, does not seem to help with parameter constraints. We also provide a code that emulates these power spectra over a range of concordance cosmological models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

COS OBSERVATIONS OF METAL LINE AND BROAD LYMAN-{alpha} ABSORPTION IN THE MULTI-PHASE O VI AND Ne VIII SYSTEM AT z = 0.20701 TOWARD HE 0226-4110

Observations of the QSO HE 0226-4110 (z{sub em} = 0.495) with the Cosmic Origins Spectrograph (COS) from 1134 to 1796 A with a resolution of {approx}17 km s{sup -1} and signal-to-noise ratio (S/N) per resolution element of 20-40 are used to study the multi-phase absorption system at z = 0.20701 containing O VI and Ne VIII. The system was previously studied with lower S/N observations with Far-Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS). The COS observations provide more reliable measures of the H I and metal lines present in the system and reveal the clear presence of broad Ly{alpha} (BLA) absorption with b = 72(+13, -6) km s{sup -1} and log N(H I) = 13.87 {+-} 0.08. Detecting BLAs associated with warm gas absorbers is crucial for determining the temperature, metallicity, and total baryonic content of the absorbers. The BLA is probably recording the trace amount of thermally broadened H I in the collisionally ionized plasma with log T {approx} 5.7 that also produces the O VI and Ne VIII absorption. The total hydrogen column in the collisionally ionized gas, log N(H) {approx} 20.1, exceeds that in the cooler photoionized gas in the system by a factor of {approx}22. The oxygen abundance in the collisionally ionized gas is [O/H] = -0.89 {+-} 0.08 {+-} 0.07. The absorber probably occurs in the circumgalactic environment (halo) of a foreground L = 0.25L{sub *} disk galaxy with an impact parameter of 109 h{sub 70}{sup -1} kpc identified by Mulchaey and Chen.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A REVISED ASTEROID POLARIZATION-ALBEDO RELATIONSHIP USING WISE/NEOWISE DATA

We present a reanalysis of the relationship between asteroid albedo and polarization properties using the albedos derived from the Wide-field Infrared Survey Explorer. We find that the function that best describes this relation is a three-dimensional linear fit in the space of log (albedo)-log (polarization slope)-log (minimum polarization). When projected to two dimensions, the parameters of the fit are consistent with those found in previous work. We also define p* as the quantity of maximal polarization variation when compared with the albedo and present the best-fitting albedo-p* relation. Some asteroid taxonomic types stand out in this three-dimensional space, notably the E, B, and M Tholen types, while others cluster in clumps coincident with the S- and C-complex bodies. We note that both low albedo and small (D < 30 km) asteroids are underrepresented in the polarimetric sample, and we encourage future polarimetric surveys to focus on these bodies.

79 ASTRONOMY AND ASTROPHYSICS↗