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Sample records for o9 sub-giant star

  1. On the interpretation of sub-giant branch morphologies of intermediate-age star clusters with extended main sequence turnoffs

    NASA Astrophysics Data System (ADS)

    Goudfrooij, Paul; Girardi, Léo; Rosenfield, Philip; Bressan, Alessandro; Marigo, Paola; Correnti, Matteo; Puzia, Thomas H.

    2015-06-01

    High-quality photometry of many star clusters in the Magellanic Clouds with ages of 1-2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several 108 yr, challenging the traditional view of star clusters as being formed in a single star formation episode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC) that exhibit an eMSTO. They argued that the SGB of these star clusters can be explained only by an SSP. We study these and two other similar star clusters in the LMC, using extensive simulations of SSPs including unresolved binaries. We find that the shapes of the cross-SGB profiles of all star clusters in our sample are in fact consistent with their cross-MSTO profiles when the latter are interpreted as age distributions. Conversely, SGB morphologies of star clusters with eMSTOs are found to be inconsistent with those of simulated SSPs. Finally, we create PARSEC isochrones from tracks featuring a grid of convective overshoot levels and a very fine grid of stellar masses. A comparison of the observed photometry with these isochrones shows that the morphology of the red clump (RC) of such star clusters is also consistent with that implied by their MSTO in the age spread scenario. We conclude that the SGB and RC morphologies of star clusters featuring eMSTOs are consistent with the scenario in which the eMSTOs are caused by a distribution of stellar ages.

  2. A Spitzer Transit of the Most Inflated Planet Known, Around an Extremely Bright Sub-giant Star

    NASA Astrophysics Data System (ADS)

    Beatty, Thomas; Collins, Karen; Colon, Knicole; James, David; Kriedberg, Laura; Pepper, Joshua; Rodriguez, Joseph; Siverd, Robert; Stassun, Keivan; Stevens, Daniel

    2015-10-01

    KELT-11b is a newly discovered transiting Saturn-mass planet (Mp~0.22MJ) that promises to become a unique benchmark. KELT-11b orbits HD 93396,the second brightest star in the near-IR (K=6.122) and the third brightest star in the optical (V=8.04) to host a transiting giant planet. This makes KELT-11 comparable to the well-studied benchmarks HD 189733 and HD 209458. But unlike these other bright systems, KELT-11b's host star is a sub-giant, with log(g)~3.7. Thus KELT-11b is the first transiting giant planet known around a sub-giant star bright enough for precise follow-up observations. Furthermore, KELT-11b is the most inflated planet known, with the lowest surface gravity (log[g]~2.5) of any transiting planet. This makes it an exciting target for atmospheric characterization and studying the effect of post main-sequence evolution of a host star on a hot Jupiter. But to correctly interpret any follow-up observations, we will first need to measure accurate stellar and planetary parameters for the system via a precise transit observation. Unfortunately, this is effectively impossible to do from the ground. Spitzer's ability to provide high precision continuous photometry provides the only current way in which we may precisely observe a complete transit of KELT-11b. We therefore propose for 15.5 hours, to observe a single transit KELT-11b at 3.6um. This would reduce the uncertainties on the transit depth and stellar density by at least a factor of twenty, and will improve the model-derived stellar mass by at least a factor of ten, compared to ground-based observations. This will serve two goals. First, it will be a valuable legacy to the community, by providing a precise set of system parameters that will enable future observation and interpretation of this unique, bright, system. Second, an observation of a transit will allow us to strongly constrain the mass of KELT-11, and thus help resolve the disagreement over the true masses of the 'retired A stars' radial

  3. Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682

    NASA Astrophysics Data System (ADS)

    Grunhut, J. H.; Wade, G. A.; Sundqvist, J. O.; ud-Doula, A.; Neiner, C.; Ignace, R.; Marcolino, W. L. F.; Rivinius, Th.; Fullerton, A.; Kaper, L.; Mauclaire, B.; Buil, C.; Garrel, T.; Ribeiro, J.; Ubaud, S.

    2012-11-01

    The O9IV star HD 57682, discovered to be magnetic within the context of the Magnetism in Massive Stars (MiMeS) survey in 2009, is one of only eight convincingly detected magnetic O-type stars. Among this select group, it stands out due to its sharp-lined photospheric spectrum. Since its discovery, the MiMeS Collaboration has continued to obtain spectroscopic and magnetic observations in order to refine our knowledge of its magnetic field strength and geometry, rotational period and spectral properties and variability. In this paper we report new Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) spectropolarimetric observations of HD 57682, which are combined with previously published ESPaDOnS data and archival Hα spectroscopy. This data set is used to determine the rotational period (63.5708 ± 0.0057 d), refine the longitudinal magnetic field variation and magnetic geometry (dipole surface field strength of 880 ± 50 G and magnetic obliquity of 79° ± 4° as measured from the magnetic longitudinal field variations, assuming an inclination of 60°) and examine the phase variation of various lines. In particular, we demonstrate that the Hα equivalent width undergoes a double-wave variation during a single rotation of the star, consistent with the derived magnetic geometry. We group the variable lines into two classes: those that, like Hα, exhibit non-sinusoidal variability, often with multiple maxima during the rotation cycle, and those that vary essentially sinusoidally. Based on our modelling of the Hα emission, we show that the variability is consistent with emission being generated from an optically thick, flattened distribution of magnetically confined plasma that is roughly distributed about the magnetic equator. Finally, we discuss our findings in the magnetospheric framework proposed in our earlier study. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research

  4. B fields in OB stars (BOB). Detection of a strong magnetic field in the O9.7 V star HD 54879

    NASA Astrophysics Data System (ADS)

    Castro, N.; Fossati, L.; Hubrig, S.; Simón-Díaz, S.; Schöller, M.; Ilyin, I.; Carrol, T. A.; Langer, N.; Morel, T.; Schneider, F. R. N.; Przybilla, N.; Herrero, A.; de Koter, A.; Oskinova, L. M.; Reisenegger, A.; Sana, H.; BOB Collaboration

    2015-09-01

    The number of magnetic stars detected among massive stars is small; nevertheless, the role played by the magnetic field in stellar evolution cannot be disregarded. Links between line profile variability, enhancements/depletions of surface chemical abundances, and magnetic fields have been identified for low-mass B-stars, but for the O-type domain this is almost unexplored. Based on FORS 2 and HARPS spectropolarimetric data, we present the first detection of a magnetic field in HD 54879, a single slowly rotating O9.7 V star. Using two independent and different techniques we obtained the firm detection of a surface average longitudinal magnetic field with a maximum amplitude of about 600 G, in modulus. A quantitative spectroscopic analysis of the star with the stellar atmosphere code fastwind results in an effective temperature and a surface gravity of 33 000 ± 1000 K and 4.0 ± 0.1 dex. The abundances of carbon, nitrogen, oxygen, silicon, and magnesium are found to be slightly lower than solar, but compatible within the errors. We investigate line-profile variability in HD 54879 by complementing our spectra with spectroscopic data from other recent OB-star surveys. The photospheric lines remain constant in shape between 2009 and 2014, although Hα shows a variable emission. The Hα emission is too strong for a standard O9.7 V and is probably linked to the magnetic field and the presence of circumstellar material. Its normal chemical composition and the absence of photospheric line profile variations make HD 54879 the most strongly magnetic, non-variable single O-star detected to date. Based on observations made with ESO telescopes at the La Silla and Paranal observatories under programme ID 191.D-0255(C, F).Appendix A is available in electronic form at http://www.aanda.org

  5. Radial dependence of line profile variability in seven O9-B0.5 stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Marcolino, W.; Hillier, D. J.; Donati, J.-F.; Bouret, J.-C.

    2015-02-01

    Context. Massive stars show a variety of spectral variabilities: discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, and radial velocity modulations. Aims: Our goal is to study the spectral variability of single OB stars to better understand the relation between photospheric and wind variability. For that, we rely on high spectral resolution and on high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Télescope Bernard Lyot at Pic du Midi. Methods: We investigated the variability of twelve spectral lines by means of the temporal variance spectrum. The selected lines probe the radial structure of the atmosphere from the photosphere to the outer wind. We also performed a spectroscopic analysis with atmosphere models to derive the stellar and wind properties and to constrain the formation region of the selected lines. Results: We show that variability is observed in the wind lines of all bright giants and supergiants on a daily timescale. Lines formed in the photosphere are sometimes variable, sometimes not. The dwarf stars do not show any sign of variability. If variability is observed on a daily timescale, it can also (but not always) be observed on hourly timescales, albeit with lower amplitude. There is a very clear correlation between amplitude of the variability and fraction of the line formed in the wind. Strong anti-correlations between the different parts of the temporal variance spectrum are observed. Conclusions: Our results indicate that variability is stronger in lines formed in the wind. A link between photospheric and wind variability is not obvious from our study, since wind variability is observed regardless of the level of photospheric variability. Different photospheric lines also show different degrees of variability. Appendices are available in electronic form at http://www.aanda.org

  6. Observations of the He I 10830 A line in main-sequence O9-B6 stars and comparison with non-LTE predictions

    NASA Astrophysics Data System (ADS)

    Lennon, D. J.; Dufton, P. L.

    1989-11-01

    New high resolution CCD observations of the He I 10830 A line in O9-B6 main-sequence stars are presented and compared with previous non-LTE model atmosphere calculations. While good qualitative agreement with the results of Auer and Mihalas (1973) is found, the theoretical results tend to overestimate the line strength. This is particularly serious at the earliest spectral types where the observations imply that the line is either very weak in absorption or (for Tau Sco) very weak in emission. This line provides a stringent test of the validity of the model atmosphere calculations due to (1) its high sensitivity to non-LTE effects, (2) the transition between low lying levels leading to compact model atom and (3) reliable atomic data available for most processes involving helium atoms or ions. The difficulties inherent to modeling this line are discussed with particular attention being paid to the likely influence of line-blanketing.

  7. Chemical abundances in the multiple sub-giant branch of 47 Tucanae: insights on its faint sub-giant branch component

    NASA Astrophysics Data System (ADS)

    Marino, A. F.; Milone, A. P.; Casagrande, L.; Collet, R.; Dotter, A.; Johnson, C. I.; Lind, K.; Bedin, L. R.; Jerjen, H.; Aparicio, A.; Sbordone, L.

    2016-06-01

    The globular cluster 47 Tuc exhibits a complex sub-giant branch (SGB) with a faint-SGB comprising only about the 10 per cent of the cluster mass and a bright-SGB hosting at least two distinct populations. We present a spectroscopic analysis of 62 SGB stars including 21 faint-SGB stars. We thus provide the first chemical analysis of the intriguing faint-SGB population and compare its abundances with those of the dominant populations. We have inferred abundances of Fe, representative light elements C, N, Na, and Al, α elements Mg and Si for individual stars. Oxygen has been obtained by co-adding spectra of stars on different sequences. In addition, we have analysed 12 stars along the two main RGBs of 47 Tuc. Our principal results are (i) star-to-star variations in C/N/Na among RGB and bright-SGB stars; (ii) substantial N and Na enhancements for the minor population corresponding to the faint-SGB; (iii) no high enrichment in C+N+O for faint-SGB stars. Specifically, the C+N+O of the faint-SGB is a factor of 1.1 higher than the bright-SGB, which, considering random (±1.3) plus systematic errors (±0.3), means that their C+N+O is consistent within observational uncertainties. However, a small C+N+O enrichment for the faint-SGB, similar to what predicted on theoretical ground, cannot be excluded. The N and Na enrichment of the faint-SGB qualitatively agrees with this population possibly being He-enhanced, as suggested by theory. The iron abundance of the bright and faint-SGB is the same to a level of ˜0.10 dex, and no other significant difference for the analysed elements has been detected.

  8. HUBBLE SPACE TELESCOPE REVEALS MULTIPLE SUB-GIANT BRANCH IN EIGHT GLOBULAR CLUSTERS

    SciTech Connect

    Piotto, G.; Nascimbeni, V.; Milone, A. P.; Aparicio, A.; Anderson, J.; Bellini, A.; Bedin, L. R.; Cassisi, S.; Marino, A. F. E-mail: luigi.bedin@oapd.inaf.it E-mail: aparicio@iac.es E-mail: bellini@stsci.edu E-mail: amarino@MPA-Garching.MPG.DE

    2012-11-20

    In the last few years many globular clusters (GCs) have revealed complex color-magnitude diagrams, with the presence of multiple main sequences (MSs), broad or multiple sub-giant branches (SGBs) and MS turnoffs, and broad or split red giant branches (RGBs). After a careful correction for differential reddening, high-accuracy photometry with the Hubble Space Telescope (HST) presented in this paper reveals a broadened or even split SGB in five additional Milky Way GCs: NGC 362, NGC 5286, NGC 6656, NGC 6715, and NGC 7089. In addition, we confirm (with new and archival HST data) the presence of a split SGB in 47 Tuc, NGC 1851, and NGC 6388. The fraction of faint SGB stars with respect to the entire SGB population varies from one cluster to another and ranges from {approx}0.03 for NGC 362 to {approx}0.50 for NGC 6715. The average magnitude difference between the bright SGB and the faint SGB is almost the same at different wavelengths. This peculiarity is consistent with the presence of two groups of stars with either an age difference of about 1-2 Gyr or a significant difference in their overall C+N+O content.

  9. Infrared Teff calibration of late-O and early-B stars with ISO-SWS

    NASA Astrophysics Data System (ADS)

    de Koter, A.; Zaal, P. A.; Waters, L. B. F. M.; Lenorzer, A.

    2000-11-01

    We present observations of the bra, brb\\ and pfa\\ lines of 16 dwarf and (sub)giant stars in the spectral range O9-B3. The observations were done using SWS, and have a signal-to-noise of ~ 20 to >150 and a resolving power varying from ~ 1500 to 2000. We compare the equivalent widths of these lines with predictions using non-LTE model atmospheres to investigate to what extent these infrared lines can be used to derive effective temperatures. We find that pfa\\ is a sensitive Teff diagnostic for the range of spectral types investigated, and bra\\ for types O9-B2, yielding agreement with optical results to within 1-4 kK or one-three spectral sub-types. We find evidence for a gradient in the turbulent velocity in the atmospheres of these stars, increasing from <~ 5 kmsec\\ for the atmospheric region in which bra\\ is formed to ~ 15 kmsec\\ for the regime where pfa\\ originates. If this gradient is taken into account, the accuracy of the spectral type calibration is improved to ~ 1-2 kK or one to one and a half spectral sub-types.

  10. The morphology of the sub-giant branch and red clump reveal no sign of age spreads in intermediate-age clusters

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.

    2015-04-01

    A recent surprise in stellar cluster research, made possible through the precision of Hubble Space Telescope photometry, was that some intermediate-age (1-2 Gyr) clusters in the Large and Small Magellanic Clouds have main-sequence turn-off (MSTO) widths that are significantly broader than would be expected for a simple stellar population (SSP). One interpretation of these extended MSTOs (eMSTOs) is that age spreads of the order of ˜500 Myr exist within the clusters, radically redefining our view of stellar clusters, which are traditionally thought of as single-age, single-metallicity stellar populations. Here we test this interpretation by studying other regions of the CMD that should also be affected by such large age spreads, namely the width of the sub-giant branch (SGB) and the red clump (RC). We study two massive clusters in the LMC that display the eMSTO phenomenon (NGC 1806 and NGC 1846) and show that both have SGB and RC morphologies that are in conflict with expectations if large age spreads exist within the clusters. We conclude that the SGB and RC widths are inconsistent with extended star formation histories within these clusters, hence age spreads are not likely to be the cause of the eMSTO phenomenon. Our results are in agreement with recent studies that also have cast doubt on whether large age spreads can exist in massive clusters; namely the failure to find age spreads in young massive clusters, a lack of gas/dust detected within massive clusters, and homogeneous abundances within clusters that exhibit the eMSTO phenomenon.

  11. Stars

    NASA Astrophysics Data System (ADS)

    Capelato, Hugo Vicente

    1999-01-01

    We will begin our study with a more or less superficial inspection of the "forest" of stars that we see in the skies. The first thing we notice is that, as sources of light, they are much weaker than the Sun. Second, their apparent colors vary; from a bluish-white in most of them to a reddish-yellow, which is rarer. There is also a third aspect, though it is not very obvious to the naked eye: most of the stars group themselves in small families of two, three or more members. A good example is the Alpha Centauri, the closest star to us, which, in fact, is a triple system of stars. Another is the group of 7 stars that make up the Pleiades, which will be discussed later on. In fact, almost half of the stars are double systems with only two members, called binary stars. Most of these double stars, though together, are separated by several astronomical units (one astronomical unit, AU, is the distance from Earth to the sun: see Chapter 1), and revolve around each other over periods of several years. And yet the revolutions of some binary stars, separated by much smaller distances, occur in only a few hours! These stars are so close to each other that they can share enveloping material. Often this exchange occurs in a somewhat violent manner. Local explosions may occur, expelling matter away from the system. In other binary systems, where one of the components is a very compact, dense star, companion material flows more calmly, making up a light disk around the compact star.

  12. Anti-solar differential rotation on the active sub-giant HU Virginis

    NASA Astrophysics Data System (ADS)

    Harutyunyan, G.; Strassmeier, K. G.; Künstler, A.; Carroll, T. A.; Weber, M.

    2016-08-01

    Context. Measuring surface differential rotation (DR) on different types of stars is important when characterizing the underlying stellar dynamo. It has been suggested that anti-solar DR laws can occur when strong meridional flows exist. Aims: We aim to investigate the differential surface rotation on the primary star of the RS CVn binary, HU Vir, by tracking its starspot distribution as a function of time. We also aim to recompute and update the values for several system parameters of the triple system HU Vir (close and wide orbits). Methods: Time-series high-resolution spectroscopy for four continuous months was obtained with the 1.2-m robotic STELLA telescope. Nine consecutive Doppler images were reconstructed from these data, using our line-profile inversion code iMap. An image cross-correlation method was applied to derive the surface differential-rotation law for HU Vir. New orbital elements for the close and the wide orbits were computed using our new STELLA radial velocities (RVs) combined with the RV data available in the literature. Photometric observations were performed with the Amadeus Automatic Photoelectric Telescope (APT), providing contemporaneous Johnson-Cousins V and I data for approximately 20 yrs. This data was used to determine the stellar rotation period and the active longitudes. Results: We confirm anti-solar DR with a surface shear parameter α of -0.029 ± 0.005 and -0.026 ± 0.009, using single-term and double-term differential rotation laws, respectively. These values are in good agreement with previously claimed results. The best fit is achieved assuming a solar-like double-term law with a lap time of ≈400 d. Our orbital solutions result in a period of 10.387678 ± 0.000003 days for the close orbit and 2726 ± 7 d (≈7.5 yr) for the wide orbit. A Lomb-Scarge (L-S) periodogram of the pre-whitened V-band data reveals a strong single peak providing a rotation period of 10.391 ± 0.008 d, well synchronized to the short orbit. Based on

  13. The new silver borate Ag3B5O9

    NASA Astrophysics Data System (ADS)

    Sohr, Gerhard; Falkowski, Viktoria; Huppertz, Hubert

    2015-05-01

    Single crystals of Ag3B5O9 were obtained via high-pressure synthesis at 3 GPa and 600 °C, using a Walker-type multianvil high-pressure device. Ag3B5O9 crystalizes with a=674.7(2), b=943.5(2), c=1103.5(2) pm, V=0.7025(2) nm3, and Z=4 in the noncentrosymmetric space group P212121 (no. 19). The orthorhombic structure was refined from 3740 independent reflections with R1=0.0496 and wR2=0.587 (all data). It is built up from infinite corner-sharing chains of BO4 tetrahedra along the a axis, which are interconnected by BO3 groups to form a network. In the structure, three crystallographically independent sites are occupied with Ag+ cations exhibiting argentophillic interactions. The synthetic conditions as well as the results of the single crystal structure analysis are presented.

  14. Large magnetoelectric coupling in Co4Nb2O9

    PubMed Central

    Fang, Y.; Song, Y. Q.; Zhou, W. P.; Zhao, R.; Tang, R. J.; Yang, H.; Lv, L. Y.; Yang, S. G.; Wang, D. H.; Du, Y. W.

    2014-01-01

    Magnetoelectric materials which simultaneously exhibit electric polarization and magnetism have attracted more and more attention due to their novel physical properties and promising applications for next-generation devices. Exploring new materials with outstanding magnetoelectric performance, especially the manipulation of magnetization by electric field, is of great importance. Here, we demonstrate the cross-coupling between magnetic and electric orders in polycrystalline Co4Nb2O9, in which not only magnetic-field-induced electric polarization but also electric field control of magnetism is observed. These results reveal rich physical phenomenon and potential applications in this compound. PMID:24463631

  15. The weak magnetic field of the O9.7 supergiant ζOrionisA

    NASA Astrophysics Data System (ADS)

    Bouret, J.-C.; Donati, J.-F.; Martins, F.; Escolano, C.; Marcolino, W.; Lanz, T.; Howarth, I. D.

    2008-09-01

    We report here the detection of a weak magnetic field of 50-100G on the O9.7 supergiant ζOrionisA (ζOriA), using spectropolarimetric observations obtained with NARVAL at the 2-m Télescope Bernard Lyot atop Pic du Midi (France). ζOriA is the third O star known to host a magnetic field (along with θ1OriC and HD191612), and the first detection on a `normal' rapidly rotating O star. The magnetic field of ζOriA is the weakest magnetic field ever detected on a massive star. The measured field is lower than the thermal equipartition limit (about 100G). By fitting non-local thermodynamic equilibrium (NLTE) model atmospheres to our spectra, we determined that ζOriA is a 40Msolar star with a radius of 25Rsolar and an age of about 5-6Myr, showing no surface nitrogen enhancement and losing mass at a rate of about 2 × 10-6Msolaryr-1. The magnetic topology of ζOriA is apparently more complex than a dipole and involves two main magnetic polarities located on both sides of the same hemisphere; our data also suggest that ζOriA rotates in about 7.0d and is about 40° away from pole-on to an Earth-based observer. Despite its weakness, the detected magnetic field significantly affects the wind structure; the corresponding Alfvén radius is however very close to the surface, thus generating a different rotational modulation in wind lines than that reported on the two other known magnetic O stars. The rapid rotation of ζOriA with respect to θ1OriC appears as a surprise, both stars having similar unsigned magnetic fluxes (once rescaled to the same radius); it may suggest that the subequipartition field detected on ζOriA is not a fossil remnant (as opposed to that of θ1 OriC and HD191612), but the result of an exotic dynamo action produced through magnetohydrodynamics (MHD) instabilities. Based on observations obtained at the Télescope Bernard Lyot (TBL), operated by the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France

  16. Spectral atlas of O9.5-A1-Type supergiants

    NASA Astrophysics Data System (ADS)

    Chentsov, E. L.; Sarkisyan, A. N.

    2007-09-01

    High-resolution spectra of nine supergiants and three comparison stars taken with CCD echelle spectrographs in the coude’ foci of the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and 2-m telescope of Terskol Observatory (with R = 40000 and R = 45000, respectively) are reported in a tabular and graphic form. Two hundred ( α Cam, O9.5 Ia) to 1000 (HD 12953, A1 Ia-0) stellar and interstellar lines and bands are identified in the 3600 7800 ÅÅ wavelength interval and most of them have their central intensities and heliocentric radial velocities measured. A spectral classification based on weak photospheric absorptions is tested. This is actual for the brightest supergiants and hypergiants, where the formation regions of strong lines, which are traditionally used for classification, also include the bases of stellar winds. Radial gradients of velocity are revealed in the atmospheres of supergiants. The cases of the refinement of the effective wavelengths, analysis of blends, and revealing of wind anomalies in line profiles are illustrated. The atlas is used extensively as a teaching tool.

  17. Refinement of the α-U4O9 crystalline structure: new insight into the U4O9 → U3O8 transformation.

    PubMed

    Desgranges, L; Baldinozzi, G; Siméone, D; Fischer, H E

    2011-07-01

    The oxidation reaction of UO(2) into U(3)O(8) is studied as a function of the crystalline distortion of interstitial oxygen clusters, named cuboctahedra, which appear in U(4)O(9) and U(3)O(7) intermediate phases. For that purpose, the refinement of α-U(4)O(9) was performed because this phase undergoes a trigonal distortion from cubic β-U(4)O(9) when the temperature is decreased. In α-U(4)O(9), the cuboctahedra can be described as crumpled sheets taken from a fragment of U(3)O(8). The manner by which the accumulation of crumpled sheets can lead to the formation of U(3)O(8) is discussed. PMID:21634363

  18. Discovery of New Iron Oxide Fe7O9 and its Solid Solution, (Mg,Fe2+)3Fe3+4O9

    NASA Astrophysics Data System (ADS)

    Sinmyo, R.; Bykova, E.; Ovsyannikov, S. V.; McCammon, C. A.; Kupenko, I.; Ismailova, L.; Dubrovinsky, L. S.

    2015-12-01

    Iron oxides are fundamentally important compounds for Earth science. Particularly, the stability and properties of iron oxides are essential information to understand the structure and chemistry of the mantle. Here we report new high-pressure polymorphs of iron oxide Fe7O9 (Fe3+/Fe2+ = 4/3) and its Fe2+-Mg solid solution (Mg,Fe2+)3Fe3+4O9 that can be recovered at ambient conditions. We synthesized single crystals of the both compounds at about 24-26 GPa using a multi-anvil press. Single crystal X-ray diffraction (XRD) studies showed that the crystal structures of both Fe7O9 and (Mg,Fe2+)3Fe3+4O9 have monoclinic C2/m space groups, that differ from any other known lattices of iron oxides. Mössbauer spectra are in agreement with the crystal structure refined from single crystal XRD. This newly found Fe7O9 polymorph suggests that iron oxides may have more variable mixed valence state under high-pressure condition than previously thought. Based on analogy with Fe2+1+nFe3+2O4+n group, a Fe2+3±nFe3+4O9±n group might be also stable at certain high pressures and temperatures and oxygen fugacity.

  19. Tuning the giant magnetoelastic transition in Ba3BiIr2O9 and Ba3BiRu2O9.

    PubMed

    Huang, Zixin; Avdeev, Maxim; Kennedy, Brendan J; Knight, Kevin S; Zhou, Qingdi; Ling, Chris D

    2014-07-01

    We have experimentally investigated the effects of pressure on the magnetoelastic transitions associated with the opening of spin-gaps in Ba3BiIr2O9 and Ba3BiRu2O9. For both compounds, reducing the unit cell volume by either external physical and internal chemical pressure was found to reduce the temperature T(*) of the transition and, to a lesser extent, the magnitude of the associated negative thermal volume expansion. The results yield the latent heat associated with the transitions, -3.34(3) × 10(2) J mol(-1) for Ba3BiIr2O9 and -7.1(5) × 10(2) J mol(-1) for Ba3BiRu2O9. The transition in Ba3BiRu2O9 is significantly more robust than in Ba3BiIr2O9, requiring an order of magnitude higher pressures to achieve the same reduction in T(*). The differing responses of the two compounds points to differences between the 4d and 5d metals and hence to the importance of spin-orbit coupling, which is expected to be much stronger in the Ir compound. PMID:24935268

  20. Nearby Stars as Gravitational Wave Detectors

    NASA Astrophysics Data System (ADS)

    Lopes, Ilídio; Silk, Joseph

    2015-07-01

    Sun-like stellar oscillations are excited by turbulent convection and have been discovered in some 500 main-sequence and sub-giant stars and in more than 12,000 red giant stars. When such stars are near gravitational wave sources, low-order quadrupole acoustic modes are also excited above the experimental threshold of detectability, and they can be observed, in principle, in the acoustic spectra of these stars. Such stars form a set of natural detectors to search for gravitational waves over a large spectral frequency range, from {10}-7 to {10}-2 Hz. In particular, these stars can probe the {10}-6-{10}-4 Hz spectral window which cannot be probed by current conventional gravitational wave detectors, such as the Square Kilometre Array and Evolved Laser Interferometer Space Antenna. The Planetary Transits and Oscillations of State (PLATO) stellar seismic mission will achieve photospheric velocity amplitude accuracy of {cm} {{{s}}}-1. For a gravitational wave search, we will need to achieve accuracies of the order of {10}-2 {cm} {{{s}}}-1, i.e., at least one generation beyond PLATO. However, we have found that multi-body stellar systems have the ideal setup for this type of gravitational wave search. This is the case for triple stellar systems formed by a compact binary and an oscillating star. Continuous monitoring of the oscillation spectra of these stars to a distance of up to a kpc could lead to the discovery of gravitational waves originating in our galaxy or even elsewhere in the universe. Moreover, unlike experimental detectors, this observational network of stars will allow us to study the progression of gravitational waves throughout space.

  1. Magnetic and photoluminescence studies of electron irradiated Bi2Fe4O9 nanoparticles

    NASA Astrophysics Data System (ADS)

    Rao, Prashanth K. S.; Krishnan, Sheeja; Pattabi, Manjunatha; Sanjeev, Ganesh

    2016-03-01

    The effect of 8 MeV electron irradiation on the magnetic and photoluminescence properties of Bi2Fe4O9 has been investigated and reported in this paper. Magnetic parameters of unirradiated and irradiated Bi2Fe4O9 nanoparticles were investigated by Vibrating sample magnetometer (VSM). Modification in saturation magnetization, remanence magnetization and coercivity were observed after exposure of Bi2Fe4O9 nanoparticles to high energy electrons. A decrease in the intensity of photoluminescence (PL) spectra was observed in irradiated samples compared to the unirradiated samples.

  2. Stars and star systems

    NASA Astrophysics Data System (ADS)

    Martynov, D. Ia.

    Topics examined include close binary systems, supernovae and their remnants, variable stars, young star groups (e.g., clusters and associations), spherical star clusters, and planetary nebulae. Also considered are the interstellar medium and star formation, systems of galaxies, and current problems in cosmology.

  3. Dielectric properties of the low dimensional vanadium oxides Ba 2V 3O 9 and Sr 2V 3O 9

    NASA Astrophysics Data System (ADS)

    Bobnar, V.; Lunkenheimer, P.; Loidl, A.; Kaul, E. E.; Geibel, C.

    2002-06-01

    The dielectric response of the low-dimensional vanadium oxides Ba 2V 3O 9 and Sr 2V 3O 9 has been investigated in the frequency range of 20 Hz-1 MHz. At low frequencies the dielectric response is governed by strong relaxation-like features, which we attribute to Maxwell-Wagner type contact contributions. The analysis of the complex dielectric spectra in terms of an equivalent circuit revealed the intrinsic dielectric constant and dc conductivity of these systems. The frequency-dependent ac conductivity in both systems follows the universal dielectric response behaviour, clearly indicating that hopping of localised charge carriers is the dominating charge-transport process. Also, a newly observed dielectric relaxation process in both systems is reported and we find evidence for a phase transition close to 455 K in both materials.

  4. Enhanced dielectric, impedance and magnetic characteristics of Co doped multiferroic Bi2Fe4O9

    NASA Astrophysics Data System (ADS)

    Mohapatra, S. R.; Sahu, B.; Kaushik, S. D.; Singh, A. K.

    2016-05-01

    Multiferroic Bi2Fe4(1-x)Co4xO9 (x = 0, 0.05) were prepared by conventional solid state reaction route. X-ray diffraction (XRD) result indicated the decrease in lattice parameters due to 5% Co doping. Grain growth in the doped composition was confirmed from surface morphology characterization. Frequency dependent real part of dielectric constant (ɛ') at room temperature showed an enhancement of ~70% in doped sample at 1 kHz. A decrease in peak height with doping was noticed from the modulus study. Lastly, room temperature M-H measurement upto 9 T showed induced ferromagnetism in Bi2Fe4O9 due to 5% Co doping. The values of remnant magnetization (Mr) and coercive field (Hc) in Bi2Fe3.8Co0.2O9 was found to be 0.007 µB/f.u. and 0.295 kOe respectively.

  5. Photoluminescence of pyrochlore phase in SrBi2Ta2O9 thin films

    NASA Astrophysics Data System (ADS)

    Wang, Y. P.; Ning, H. F.; Zhou, L.; Shen, J. K.; Liu, Z. G.

    2003-07-01

    SrBi2Ta2O9 thin films were prepared by pulsed laser deposition at different substrate temperatures. Photoluminescence (PL) has been detected at room temperature from the pyrochlore phase in the SrBi2Ta2O9 film deposited at 850 °C. The PL shows five luminescence bands of 330, 365, 407, 490, and 600 nm. And the PL excitation shows six excitation bands of 278, 330, 365, 407, 490, and 600 nm. The one-to-one correspondence of PL and PL excitation spectra reveals a band-to-band excitation and a multienergy-gap structure in the pyrochlore phase in SrBi2Ta2O9 films.

  6. Wetting of microstructured alumina fabricated by epitaxial growth of Al4B2O9 whiskers

    NASA Astrophysics Data System (ADS)

    Wang, Yifeng; Feng, Jicai; Chen, Zhe; Song, Xiaoguo; Cao, Jian

    2015-12-01

    Topographical microstructures were fabricated on alumina by epitaxial growth of Al4B2O9 whiskers in air. The products were characterized via scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The whiskers were found to grow along the [0 0 1] crystallographic direction, and the lattice mismatch between Al2O3 and Al4B2O9 was determined to be 0.03%. The wetting of the Al4B2O9-whisker-coated surfaces by Ag-36.7Cu-8.0Ti at.% alloy was studied. The time needed to reach the equilibrium stage reduced as the temperature increased, and the final contact angle for liquid alloy on the rough surface was 27° at 880 °C. The wetting dynamics of the whiskers coated surfaces was investigated. After wetting, a whisker-interconnected region was formed between alumina and the alloy.

  7. Low Temperature Structural Phase Transition of Ba3NaIr2O9

    SciTech Connect

    Conrad, H.; Loye, Z; Kim, S; Macquart, R; Smith, M; Lee, Y; Vogt, T

    2009-01-01

    Single crystal X-ray and synchrotron X-ray powder diffraction have been used to probe the structure of Ba3NaIr2O9 from 300 K down to 20 K. Ba3NaIr2O9 is found to undergo a structural transition from hexagonal symmetry, P63/mmc, at ambient temperature to monoclinic symmetry, C2/c, at low temperature. The evolution of the unit cell volume upon cooling is indicative of a higher order structural transition, and the symmetry breaking becomes apparent as the temperature is decreased. The low temperature monoclinic structure of Ba3NaIr2O9 contains strongly distorted [NaO6] and [IrO6] octahedra in comparison to the room temperature hexagonal structure.

  8. Differential Astrometry to detect giant planets around A-stars

    NASA Astrophysics Data System (ADS)

    Monnier, John D.; Johnson, Keith; Swihart, Samuel; Ireland, Michael; Zhao, Ming; Ten Brummelaar, Theo

    2015-01-01

    The exoplanet field has remained vibrant and exciting due to the continuous development of new observing techniques and the refinement of older ones, both from the ground and from space. Here we propose to push the exoplanet frontier through the development of a new interferometric experiment that takes advantage of the Michigan Infrared Combiner (MIRC) on the CHARA Array, a visible and near-infrared interferometer boasting the longest baselines and finest angular resolution in the world. The ARMADA (ARrangement for Micro-Arcsecond Differential Astrometry) Project will search for astrometric wobble in a sample of hot stars (spectral type A,B) to search for giants planets in P<3 year orbits. Recent radial velocity (RV) work studying evolved sub-giants --``retired A stars" -- suggest up to a five-fold increase in the presence of massive gas giant planets in about 1 AU orbits compared to solar-type stars. Confirmation of this disputed result on A stars themselves would have profound effect on theories of planet formation but is difficult or impossible due to the broad, weak lines of hot stars. Using a novel etalon module already designed and fabricated to maintain precision wavelength calibration (Dl/l ~1x10-5), we aim to measure separations with <10 micro-arcsecond-level precision for binaries up to 0.25' separation.

  9. Structure modulations in nonlinear optical (NLO) materials Cs(2)TB4O9 (T = Ge, Si).

    PubMed

    Zhou, Zhengyang; Xu, Xiang; Fei, Rao; Mao, Jianggao; Sun, Junliang

    2016-04-01

    Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs(2)TB4O9 (T = Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace group I2(αβ0)0. The refinement results strongly suggest that the main structure modulation feature of Cs(2)TB4O9 is the ordering of the O atoms. With these modulated structure models, the unreasonable B-O distances in the average structures were explained as the ordering of BO4 and BO3. PMID:27048721

  10. Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure.

    PubMed

    Sinmyo, Ryosuke; Bykova, Elena; Ovsyannikov, Sergey V; McCammon, Catherine; Kupenko, Ilya; Ismailova, Leyla; Dubrovinsky, Leonid

    2016-01-01

    Iron oxides are fundamentally important compounds for basic and applied sciences as well as in numerous industrial applications. In this work we report the synthesis and investigation of a new binary iron oxide with the hitherto unknown stoichiometry of Fe7O9. This new oxide was synthesized at high-pressure high-temperature (HP-HT) conditions, and its black single crystals were successfully recovered at ambient conditions. By means of single crystal X-ray diffraction we determined that Fe7O9 adopts a monoclinic C2/m lattice with the most distorted crystal structure among the binary iron oxides known to date. The synthesis of Fe7O9 opens a new portal to exotic iron-rich (M,Fe)7O9 oxides with unusual stoichiometry and distorted crystal structures. Moreover, the crystal structure and phase relations of such new iron oxide groups may provide new insight into the cycling of volatiles in the Earth's interior. PMID:27605075

  11. Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure

    PubMed Central

    Sinmyo, Ryosuke; Bykova, Elena; Ovsyannikov, Sergey V.; McCammon, Catherine; Kupenko, Ilya; Ismailova, Leyla; Dubrovinsky, Leonid

    2016-01-01

    Iron oxides are fundamentally important compounds for basic and applied sciences as well as in numerous industrial applications. In this work we report the synthesis and investigation of a new binary iron oxide with the hitherto unknown stoichiometry of Fe7O9. This new oxide was synthesized at high-pressure high-temperature (HP-HT) conditions, and its black single crystals were successfully recovered at ambient conditions. By means of single crystal X-ray diffraction we determined that Fe7O9 adopts a monoclinic C2/m lattice with the most distorted crystal structure among the binary iron oxides known to date. The synthesis of Fe7O9 opens a new portal to exotic iron-rich (M,Fe)7O9 oxides with unusual stoichiometry and distorted crystal structures. Moreover, the crystal structure and phase relations of such new iron oxide groups may provide new insight into the cycling of volatiles in the Earth’s interior. PMID:27605075

  12. Chemical and orbital fluctuations in Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Yusuke; Nakajima, Daisuke; Ishiguro, Yuki; Kimura, Kenta; Kimura, Tsuyoshi; Tsutsui, Satoshi; Baron, Alfred Q. R.; Hayashi, Kouichi; Happo, Naohisa; Hosokawa, Shinya; Ohwada, Kenji; Nakatsuji, Satoru

    2016-06-01

    Structural fluctuation in Ba3CuSb2O9 , which is proposed to exhibit a spin-orbital entangled state, has been studied by diffuse x-ray scattering, x-ray fluorescence holography, and inelastic x-ray scattering. Two kinds of spatial fluctuations are observed: temperature-independent and temperature-dependent ones. The former is related to Cu/Sb arrangement. The short-range chemical correlation in Ba3CuSb2O9 is honeycomblike, whereas the correlation length is as short as the diameter of the honeycomb unit. The temperature variation of ferro- and antiferro-orbital correlations is extracted from Huang scattering intensity distributions. Both of these correlations increase with decreasing temperature down to 60 K, which corresponds to the energy of magnetic interaction of Ba3CuSb2O9 . A wide distribution of the characteristic time scale of the orbital motion is proposed from the spatial fluctuation of the ionic arrangement in Ba3CuSb2O9 .

  13. Differential Killing of Salmonella enterica Serovar Typhi by Antibodies Targeting Vi and Lipopolysaccharide O:9 Antigen

    PubMed Central

    Hart, Peter J.; O’Shaughnessy, Colette M.; Siggins, Matthew K.; Bobat, Saeeda; Kingsley, Robert A.; Goulding, David A.; Crump, John A.; Reyburn, Hugh; Micoli, Francesca; Dougan, Gordon; Cunningham, Adam F.; MacLennan, Calman A.

    2016-01-01

    Salmonella enterica serovar Typhi expresses a capsule of Vi polysaccharide, while most Salmonella serovars, including S. Enteritidis and S. Typhimurium, do not. Both S. Typhi and S. Enteritidis express the lipopolysaccharide O:9 antigen, yet there is little evidence of cross-protection from anti-O:9 antibodies. Vaccines based on Vi polysaccharide have efficacy against typhoid fever, indicating that antibodies against Vi confer protection. Here we investigate the role of Vi capsule and antibodies against Vi and O:9 in antibody-dependent complement- and phagocyte-mediated killing of Salmonella. Using isogenic Vi-expressing and non-Vi-expressing derivatives of S. Typhi and S. Typhimurium, we show that S. Typhi is inherently more sensitive to serum and blood than S. Typhimurium. Vi expression confers increased resistance to both complement- and phagocyte-mediated modalities of antibody-dependent killing in human blood. The Vi capsule is associated with reduced C3 and C5b-9 deposition, and decreased overall antibody binding to S. Typhi. However, purified human anti-Vi antibodies in the presence of complement are able to kill Vi-expressing Salmonella, while killing by anti-O:9 antibodies is inversely related to Vi expression. Human serum depleted of antibodies to antigens other than Vi retains the ability to kill Vi-expressing bacteria. Our findings support a protective role for Vi capsule in preventing complement and phagocyte killing of Salmonella that can be overcome by specific anti-Vi antibodies, but only to a limited extent by anti-O:9 antibodies. PMID:26741681

  14. Bright stars observed by FIMS/SPEAR

    NASA Astrophysics Data System (ADS)

    Jo, Young-Soo; Seon, Kwang-Il; Min, Kyoung-Wook; Choi, Yeon-Ju; Lim, Tae-Ho; Lim, Yeo-Myeong; Edelstein, Jerry; Han, Wonyong

    2016-02-01

    In this paper, we present a catalogue of the spectra of bright stars observed during the sky survey using the Far-Ultraviolet Imaging Spectrograph (FIMS), which was designed primarily to observe diffuse emissions. By carefully eliminating the contamination from the diffuse background, we obtain the spectra of 70 bright stars observed for the first time with a spectral resolution of 2-3 Å over the wavelength of 1370-1710 Å. The far-ultraviolet spectra of an additional 139 stars are also extracted with a better spectral resolution and/or higher reliability than those of the previous observations. The stellar spectral type of the stars presented in the catalogue spans from O9 to A3. The method of spectral extraction of the bright stars is validated by comparing the spectra of 323 stars with those of the International Ultraviolet Explorer (IUE) observations.

  15. New Wolf-Rayet stars in Galactic open clusters - Sher 1 and the giant H II region core Westerlund 2

    NASA Technical Reports Server (NTRS)

    Moffat, Anthony F. J.; Shara, Michael M.; Potter, Michael

    1991-01-01

    Two new Galactic Wolf-Rayet stars were found in open clusters: a WN4 star in the O9 cluster Sher 1 and a WN7 star in the O7 cluster Westerlund 2. This confirms a previous trend, namely that fainter, hotter WN stars tend to be older than brighter, cooler WN stars. This may be a consequence of evolution via extreme mass loss.

  16. Structural and dielectric properties of Sr3(MgTa2)O9 and Sr3(ZnTa2)O9

    NASA Astrophysics Data System (ADS)

    Hoque, Md. M.; Dutta, Alo; Kumar, S.; Sinha, T. P.

    2015-07-01

    Herein, we report the crystal structures and morphological properties of Sr3(MgTa2)O9 (SMT) and Sr3(ZnTa2)O9 (SZT) synthesized by solid state ceramic method along with the results of alternating current impedance spectroscopic (ACIS) study in a frequency range from 50 Hz to 1 MHz at selective temperatures between 393 and 573 K. The crystal structures of SMT and SZT have been determined by Rietveld refinement of powder X-ray diffraction pattern using an initial structural model developed on the basis of literature survey. The results indicate that both the samples possess hexagonal structure of trigonal P 3 bar m 1 space group. The lattice parameters of SMT are a=b=5.65162 Å, c=6.94440 Å, α=β=90° and γ=120° and those of SZT are a=b=5.65832 Å, c=6.95911 Å and α=β=90° and γ=120°. SMT and SZT are isostructural and they exhibit 2:1 B site ordering with the staking sequence of {-Ta-Ta-Mg (Zn)-} (Mg for SMT and Zn for SZT) layer repeat on (111) plane of the pseudocells. The characteristic vibrational bands due to Ta-O, Mg-O and Zn-O bonds have been observed in the FTIR spectra of the samples. The FESEM micrographs of the samples show that the grains size ranges between 0.40 and 3.65 μm and 0.9 to 4.2 μm for SMT and SZT, respectively. To account for the polydispersive nature of the dielectric relaxation mechanism along with the effects of dc conductivity and localized space charges the variation of real (ε‧) and imaginary (ε″) parts of dielectric constant with frequency has been analytically interpreted in the framework of modified Cole-Cole model. SMT and SZT having the activation energies of 0.35 eV and 0.33 eV, respectively (obtained from the Arrhenius plot of dc conductivity), are semiconducting in nature. The electrical current conduction in the samples occurs by polaron hopping process. Further, we have shown that chemical property of A site cations has significant role in determining the dielectric properties of A3B‧B″2O9 type perovskites

  17. Influence of P ion on Sr2B5O9Cl:Eu for TL dosimetry

    NASA Astrophysics Data System (ADS)

    Oza, Abha H.; Dhoble, N. S.; Dhoble, S. J.

    2015-02-01

    This paper investigates luminescence properties of Sr2B5O9Cl:Eu phosphor prepared by modified solid state diffusion. The influence of Phosphorous ion as codopant is also explained in detail. The structural confirmation of the sample was done using the XRD technique. SEM revealed the microcrystalline nature of the prepared phosphor. The characteristic Eu2+ emission at 437 nm and 423 nm was observed for Sr2B5O9Cl:Eu and Sr2B5O9Cl:P,Eu, respectively under 338 nm excitation. Samples in powder form were irradiated with different doses under γ-ray irradiation with 60Co source and the TL glow curves for both Sr2B5O9Cl:Eu and Sr2B5O9Cl:P,Eu samples were studied. In case of Sr2B5O9Cl:Eu phosphor, single glow curve nature centered on 260 °C with a shoulder peak around 144 °C was observed. However; Sr2B5O9Cl:P,Eu have shown slight different and broad glow curve nature. The TL sensitivity in both the cases was compared with CaSO4:Dy phosphor. Sr2B5O9Cl:Eu sample have shown 1.17 times less sensitivity than CaSO4:Dy and for Sr2B5O9Cl:P,Eu it was found to be equal to CaSO4:Dy and Sr2B5O9Cl:P,Eu is 1.21 times more sensitive than Sr2B5O9Cl:Eu. Other TL properties like dose response, fading and reusability were studied for both the samples. The trapping parameters for both the samples were calculated using computerized glow curve deconvolution and reported in this paper.

  18. AgNa2Mo3O9AsO4

    PubMed Central

    Hamza, Hamadi; Zid, Mohamed Faouzi; Driss, Ahmed

    2011-01-01

    The title compound, silver disodium trimolybdenum(VI) nonaoxide arsenate, AgNa2Mo3O9AsO4, was prepared by a solid-state reaction at 808 K. The structure consists of an infinite (Mo3AsO13)n ribbon, parallel to the c axis, composed of AsO4 tetra­hedra and MoO6 octa­hedra sharing edges and corners. The Na and Ag ions partially occupy several independent close positions, with various occupancies, in the inter-ribbon space delimited by the one-dimensional framework. The composition was refined to Ag1.06(1)Na1.94(1)Mo3O9AsO4. PMID:22219728

  19. Colossal magnetodielectric effect and spin flop in magnetoelectric Co4Nb2O9 crystal

    NASA Astrophysics Data System (ADS)

    Yin, L. H.; Zou, Y. M.; Yang, J.; Dai, J. M.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

    2016-07-01

    We have investigated the detailed magnetic, magnetoelectric (ME), magnetodielectric (MD) and thermal expansion properties in Co4Nb2O9 crystal. A magnetic-field-induced spin flop was observed below antiferromagnetic (AFM) transition temperature TN. Dielectric constant at applied magnetic field nearly diverges around the AFM transition, giving rise to a colossal MD effect as high as ˜138% around TN. Theoretical analysis of the ME and MD data revealed a major contribution of critical spin fluctuation to the colossal MD effect in Co4Nb2O9. These results suggest that linear ME materials with large ME coupling might be potentially used to realize large MD effect for future application.

  20. Optical conductivity of layered calcium cobaltate Ca3Co4O9.

    PubMed

    Tanabe, Kenji; Okazaki, Ryuji; Taniguchi, Hiroki; Terasaki, Ichiro

    2016-03-01

    We report the optical properties of layered calcium cobaltate, Ca3Co4O9, which is regarded as a promising candidate for use as a thermoelectric material. The optical conductivity shows three broad peaks related to the inter-band transition below 4 eV, which are quite similar to those in the spectra of Na x CoO2. This similarity implies that the CoO2 layer, which is an essential unit for both Ca3Co4O9 and Na x CoO2, is dominant in the energy band structure below 4 eV. In addition, we estimate the effective carrier number per Co site and find similarity between the CoO2 layers of Ca3Co4O9 and Na0.75CoO2, which is consistent with the similarity in their Seebeck coefficients. To discuss the contribution of the rocksalt-type Ca2CoO3 layer in Ca3Co4O9, we propose the concept of optical sheet conductivity in the layered materials and estimate its value in the Ca2CoO3 layer. A comparison with the spin-polarized band calculation of the LDA  +  Hubbard U formalism with U  =  5 eV suggests that the Ca2CoO3 layer has the inter-band transition of 2.6 eV in the spin-down band structure. Evaluation of the valences of Co 3d orbitals indicates the existence of charge transfer from the Ca2CoO3 layer to the CoO2 layer and mixing of Co(3+) and Co(4+) in the CoO2 layer, which may be the origin of the large thermoelectric effect. PMID:26823444

  1. Preparation and characterization of bioactive sol-gel-derived Na2Ca2Si3(O)9.

    PubMed

    Du, Ruilin; Chang, Jiang

    2004-12-01

    In this study, pure Na2Ca2Si3(O)9 was synthesized by a sol-gel method, and Na2Ca2Si3(O)9 cuboids and disks were prepared by uniaxial pressing and calcining at 700 degrees C. The porosity and mechanical strength of the Na2Ca2Si3(O)9 cuboids were measured, and the results showed that the Na2Ca2Si3(O)9 cuboids were porous with an average porosity of 44%, and the 3-point bending strength of the cuboids was 6.08 MPa. The in vitro bioactivity of Na2Ca2Si3(O)9 was carried out by soaking Na2Ca2Si3(O)9 disks in simulated body fluid (SBF). The results showed that hydroxyapatite (HA) formed on the surface of Na2Ca2Si3(O)9 samples after soaking for 1 day, which indicated good bioactivity of Na2Ca2Si3(O)9. PMID:15747180

  2. Synthesis and Luminescence Properties of La2W2O9:Eu3+ Micron-Crystals.

    PubMed

    Zhang, Jiao; Yang, Yanmin; Yu, Fang; Liu, Yanzhou; Han, Boning; Mi, Chao; Liu, Linlin

    2016-04-01

    La2W2O9:2%Eu3+ phosphors were synthesized by a typical hydrothermal procedure. The samples were characterized by X-ray diffraction and scanning electron microscope (SEM). X-ray diffraction analysis showed that a stock solution pH value equal to 9 is the ideal value, while the crystallization of the hydroxyl sodium yttrium tungstate crystal is improved by increasing the PH values of stock solution within limits. Meanwhile, SEMs of different pH values were recorded. Additionally, photo-luminescence excitation (PLE) and emission (PL) spectra were measured. It was found that this phosphor can be effectively excited by C-T band (266 nm) and ultraviolet light 342 nm. The wave-lengths at 342 nm fit in nicely with the whole visible region, thus the La2W2O9:2%Eu3+ phosphors emit white light. Furthermore, the annealing temperature's impact on PLE and PL spectra was also studied. The Eu3+-doped La2W2O9 phosphor may be a better candidate than current method for solid-state lighting applications. PMID:27451723

  3. Ga4B2O9: an efficient borate photocatalyst for overall water splitting without cocatalyst.

    PubMed

    Wang, Guangjia; Jing, Yan; Ju, Jing; Yang, Dingfeng; Yang, Jia; Gao, Wenliang; Cong, Rihong; Yang, Tao

    2015-03-16

    Borates are well-known candidates for optical materials, but their potentials in photocatalysis are rarely studied. Ga(3+)-containing oxides or sulfides are good candidates for photocatalysis applications because the unoccupied 4s orbitals of Ga usually contribute to the bottom of the conducting band. It is therefore anticipated that Ga4B2O9 might be a promising photocatalyst because of its high Ga/B ratio and three-dimensional network. Various synthetic methods, including hydrothermal (HY), sol-gel (SG), and high-temperature solid-state reaction (HTSSR), were employed to prepare crystalline Ga4B2O9. The so-obtained HY-Ga4B2O9 are micrometer single crystals but do not show any UV-light activity unless modified by Pt loading. The problem is the fast recombination of photoexcitons. Interestingly, the samples obtained by SG and HTSSR methods both possess a fine micromorphology composed of well-crystalline nanometer strips. Therefore, the excited e(-) and h(+) can move to the surface easily. Both samples exhibit excellent intrinsic UV-light activities for pure water splitting without the assistance of any cocatalyst (47 and 118 μmol/h/g for H2 evolution and 22 and 58 μmol/h/g for O2 evolution, respectively), while there is no detectable activity for P25 (nanoparticles of TiO2 with a specific surface area of 69 m(2)/g) under the same conditions. PMID:25714488

  4. Star Light, Star Bright.

    ERIC Educational Resources Information Center

    Iadevaia, David G.

    1984-01-01

    Presents a technique for obtaining a rough measure of the brightness among different stars. Materials needed include a standard 35-mm camera, a plastic ruler, and a photo enlarger. Although a telescope can be used, it is not essential. (JN)

  5. Enhanced magnetic and photocatalytic properties of Bi2Fe4O9 semiconductor with large exposed (001) surface

    NASA Astrophysics Data System (ADS)

    Wu, Tianli; Liu, Lin; Pi, Mingyu; Zhang, Dingke; Chen, Shijian

    2016-07-01

    Magnetic photocatalysts have attracted an increasing attention for photodegradation of organic containments and easy recycling. In this work, magnetic, single-crystalline Bi2Fe4O9 samples have been synthesized through a facile hydrothermal process and the morphologies were modulated by adjusting the Bi3+/Fe3+ precursor molar ratio and NaOH concentration. The most well crystalline Bi2Fe4O9 nanoplates were formed by self-assembled anisotropic growth along the (001) plane, with large exposed (001) surface. The Bi2Fe4O9 nanoplates exhibit excellent photocatalytic degradation of rhodamine b (RhB) under visible light irradiation with the assistant of a small amount of H2O2. The excellent photocatalytic performance of the Bi2Fe4O9 nanoplates was ascribed to the lower recombination rate of the photogenerated electrons and holes on the (001) surface, which was confirmed by detecting the hydroxyl radicals. In addition, Bi2Fe4O9 samples exhibit morphology-dependent magnetic properties. The mechanisms of morphology-dependent magnetic, photoadsorbing and photocatalytic properties of Bi2Fe4O9 crystals are discussed systematically. The magnetic Bi2Fe4O9 photocatalyst allows efficient utilization of solar energy and possible catalyst recovery via magnetically-enhanced gravity separation.

  6. Site Determination of Sr in Sr3YB3O9 Crystals by Anomalous X-ray Scattering

    NASA Astrophysics Data System (ADS)

    Simura, R.; Sugiyama, K.

    2014-04-01

    The distribution of Sr in Sr3YB3O9 crystals was determined by anomalous X-ray scattering. The Sr3YB3O9 sample was grown by the floating-zone method in dry air. The Sr3YB3O9 crystal has three cation sites (3a, 3b, and 18f). The results of single-crystal structural analysis using anomalous X-ray scattering at the Sr K-edge suggested that Sr is distributed at the 3a site as well as it is at the chemically disordered 18f site.

  7. Reversible phase transition and relaxor behavior in Te2V2O9 single crystals grown by Czochralski technique

    NASA Astrophysics Data System (ADS)

    Shet, Tukaram; Varma, K. B. R.

    2016-09-01

    Te2V2O9 single crystals were grown along the polar c-axis via the Czochralski crystal growth technique. Dielectric studies carried out along the polar axis in a wide temperature range at different frequencies confirmed the relaxor nature of the Te2V2O9 single crystals. Temperature dependent polarized light optical microscopy along a-axis established a reversible phase transition around 614 K. Relaxor nature of Te2V2O9 was attributed to the compositional heterogeneity at micro/nano scale within the grown crystal as vanadium was observed to be present in different oxidation states by X-ray photoelectron spectroscopic studies.

  8. A new high pressure form of Ba3NiSb2O9

    NASA Astrophysics Data System (ADS)

    Darie, Céline; Lepoittevin, Christophe; Klein, Holger; Kodjikian, Stéphanie; Bordet, Pierre; Colin, Claire V.; Lebedev, Oleg I.; Deudon, Catherine; Payen, Christophe

    2016-05-01

    In the search of an experimental realization of quantum spin liquid phases we have synthesized polycrystalline samples of Ba3NiSb2O9 under high pressure-high temperature conditions. Combining X-ray powder diffraction, neutron powder diffraction and precession electron diffraction we show that the obtained phase isn't hexagonal as reported in the literature, but trigonal. This new structure shows triangular Ni planes, but only in domains of sizes of the order of 10 nm. It therefore is still interesting as a potential candidate for a quantum spin liquid.

  9. Reduction Kinetics of La2Mo2O9 and Phase Evolution during Reduction and Reoxidation.

    PubMed

    Buvat, Gaëtan; Sellemi, Houssem; Ravella, Uday K; Barré, Maud; Coste, Sandrine; Corbel, Gwenaël; Lacorre, Philippe

    2016-03-01

    An amorphous reduced form of oxide ion conductor La2Mo2O9 had been proposed as sulfur-tolerant anode material for solid oxide fuel cell, but its oxygen content was not known. In this paper, we investigate the reduction kinetics by diluted hydrogen of La2Mo2O9 to amorphous, and the oxygen range of the amorphous form. The reduction kinetics is studied as a function of the powder specific surface area and of the temperature, on powders synthesized by solid state reaction and by polyol process using two different solvents. The reduction process was carried out by TGA under 10% H2 diluted in argon, and its kinetics is analyzed and modeled. As expected, small particles and high temperature lead to higher reduction rates. Several reduction steps were identified by XRD during the process. At 700 °C La2Mo2O9 is directly reduced into the amorphous phase La2Mo2O7-y, whereas at 760 °C reduction occurs through an intermediate crystallized La7Mo7O30 (≅ La2Mo2O8.57) phase before amorphization. In both cases, further reduction of La2Mo2O6.2 amorphous phase leads to an exsolution of metallic molybdenum and a molybdenum deficiency in the amorphous phase. Reoxidation of amorphous La2Mo2O7-y was studied by TGA, DTA and XRD. At low temperature in air, the reduced compounds are reoxidized while remaining amorphous. The annealing for 60 h at 350 °C in air of reduced La2Mo2O6.66, obtained beforehand by solid state reaction, gives an amorphous phase with composition La2Mo2O8.85. The existence domain of the reduced amorphous phase in terms of oxygen content therefore ranges at least from O6.2 to O8.85, thus including the composition La2Mo2O8.50 of the amorphous surface layer at the origin of a huge increase of ionic conductivity recently reported in nanowires of La2Mo2O9. PMID:26910206

  10. Kepler's first view of O-star variability: K2 data of five O stars in Campaign 0 as a proof of concept for O-star asteroseismology

    NASA Astrophysics Data System (ADS)

    Buysschaert, B.; Aerts, C.; Bloemen, S.; Debosscher, J.; Neiner, C.; Briquet, M.; Vos, J.; Pápics, P. I.; Manick, R.; Schmid, V. S.; Van Winckel, H.; Tkachenko, A.

    2015-10-01

    We present high-precision photometric light curves of five O-type stars observed with the refurbished Kepler satellite during its Campaign 0. For one of the stars, we also assembled high-resolution ground-based spectroscopy with the HERMES spectrograph attached to the 1.2 m Mercator telescope. The stars EPIC 202060097 (O9.5V) and EPIC 202060098 (O7V) exhibit monoperiodic variability due to rotational modulation with an amplitude of 5.6 and 9.3 mmag and a rotation period of 2.63 and 5.03 d, respectively. EPIC 202060091 (O9V) and EPIC 202060093 (O9V:pe) reveal variability at low frequency but the cause is unclear. EPIC 202060092 (O9V:p) is discovered to be a spectroscopic binary with at least one multiperiodic β Cep-type pulsator whose detected mode frequencies occur in the range [0.11, 6.99] d-1 and have amplitudes between 0.8 and 2.0 mmag. Its pulsation spectrum is shown to be fully compatible with the ones predicted by core-hydrogen burning O-star models. Despite the short duration of some 33 d and the limited data quality with a precision near 100 μmag of these first K2 data, the diversity of possible causes for O-star variability already revealed from campaigns of similar duration by the MOST and CoRoT satellites is confirmed with Kepler. We provide an overview of O-star space photometry and give arguments why future K2 monitoring during Campaigns 11 and 13 at short cadence, accompanied by time-resolved high-precision high-resolution spectroscopy, opens up the possibility of in-depth O-star seismology.

  11. Suppressed phase transition and giant ionic conductivity in La2Mo2O9 nanowires

    PubMed Central

    Liu, Wei; Pan, Wei; Luo, Jian; Godfrey, Andy; Ou, Gang; Wu, Hui; Zhang, Wei

    2015-01-01

    Improving the ionic conductivity of solid electrolytes at low temperatures represents a major challenge and an opportunity for enabling a variety of solid-state ionic devices for energy conversion and storage, as well as for environmental protection. Here we report a giant ionic conductivity of 0.20 Scm−1, achieved at 500 °C, in the La2Mo2O9 nanowires with a bamboo-wire morphology, corresponding to a 1000-fold enhancement in conductivity over conventional bulk material. Stabilization of the high-temperature phase is observed to account for about a 10-fold increase in the conductivity. We further demonstrate that fast surface conduction in ∼3 nm thick, partially ordered, surface ‘amorphous' films, under strain on the curved surfaces of the nanowires (as a non-autonomous surface phase or complexion), contributes to an enhancement of the conductivity by another two orders of magnitude. Exemplified here by the study of the La2Mo2O9 nanowires, new possibilities for improvement of conductivity and for miniaturization of solid-state ionic devices by the careful use of one-dimensional nanomaterials can be envisioned. PMID:26380943

  12. Crystallographic and Electronic Structure of the Sr3Sb2CoO9 Triple Perovskite

    NASA Astrophysics Data System (ADS)

    González, W.; Cardona, R.; Landínez Téllez, D. A.; Roa-Rojas, J.

    2014-04-01

    Compounds The perovskites are materials with physical and chemical characteristics that make them optimal for application in the technological and scientist. When the ideal formula of perovskite ABO3 is modified by introducing a special structural arrangement can get to get triple perovskites, which correspond to the formula A3B2B'O9. In this work we report the synthesis process and the study of electronic structure and crystal Sr3Sb2CoO9 new triple perovskite. From the experiments of X-ray Diffraction and the application of the Rietveld refinement method was revealed that the system crystallizes in a perovskite structure with a characteristic triple given by the space group Immm (#71) and lattice parameters a=9.791(9) Å, b=5.656(7) Å and c=16.957(8) Å. Ab initio calculations of density of states (DOS) and electronic structure were carried out for this perovskite-like system by using the Quantum EXPRESSO code. The exchange-correlation potential was treated using the Generalized Gradient Approximation (GGA). All calculations were carried-out using spin polarization. ©2013 Elsevier Science. All rights reserved.

  13. Magnetoelectric coupling in the honeycomb antiferromagnet Co4Nb2O9

    NASA Astrophysics Data System (ADS)

    Khanh, N. D.; Abe, N.; Sagayama, H.; Nakao, A.; Hanashima, T.; Kiyanagi, R.; Tokunaga, Y.; Arima, T.

    2016-02-01

    The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet Co4Nb2O9 . Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. Co2 + magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to C 2 /c' with the propagation vector k =0 . Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below Néel temperature TN with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in Co4Nb2O9 . Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.

  14. Thermoelectric transport in the layered Ca3Co4-xRhxO9 single crystals

    NASA Astrophysics Data System (ADS)

    Ikeda, Yusuke; Saito, Kengo; Okazaki, Ryuji

    2016-06-01

    We have examined an isovalent Rh substitution effect on the transport properties of the thermoelectric oxide Ca3Co4O9 using single-crystalline form. With increasing Rh content x, both the electrical resistivity and the Seebeck coefficient change systematically up to x = 0.6 for Ca3Co4-xRhxO9 samples. In the Fermi-liquid regime where the resistivity behaves as ρ = ρ 0 + A T 2 around 120 K, the A value decreases with increasing Rh content, indicating that the correlation effect is weakened by Rh 4d electrons with extended orbitals. We find that, in contrast to such a weak correlation effect observed in the resistivity of Rh-substituted samples, the low-temperature Seebeck coefficient is increased with increasing Rh content, which is explained with a possible enhancement of a pseudogap associated with the short-range order of spin density wave. In high-temperature range above room temperature, we show that the resistivity is largely suppressed by Rh substitution while the Seebeck coefficient becomes almost temperature-independent, leading to a significant improvement of the power factor in Rh-substituted samples. This result is also discussed in terms of the differences in the orbital size and the associated spin state between Co 3d and Rh 4d electrons.

  15. Strange stars

    NASA Technical Reports Server (NTRS)

    Alcock, Charles; Farhi, Edward; Olinto, Angela

    1986-01-01

    Strange matter, a form of quark matter that is postulated to be absolute stable, may be the true ground stage of the hadrons. If this hypothesis is correct, neutron stars may convert to 'strange stars'. The mass-radius relation for strange stars is very different from that of neutron stars; there is no minimum mass, and for mass of 1 solar mass or less, mass is proportional to the cube of the radius. For masses between 1 solar mass and 2 solar masses, the radii of strange stars are about 10 km, as for neutron stars. Strange stars may have an exposed quark surface, which is capable of radiating at rates greatly exceeding the Eddington limit, but has a low emissivity for X-ray photons. The stars may have a thin crust with the same composition as the preneutron drip outer layer of a conventional neutron star crust. Strange stars cool efficiently via neutrino emission.

  16. Stars and Star Myths.

    ERIC Educational Resources Information Center

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  17. Be Stars

    NASA Astrophysics Data System (ADS)

    Peters, G.; Murdin, P.

    2000-11-01

    A Be star (pronounced `bee-ee' star) is a non-supergiant B-type star whose spectrum displays or has displayed one or more Balmer lines in emission and Be is the notation for the spectral classification of such a star (see also CLASSIFICATION OF STELLAR SPECTRA). `Classical' Be stars are believed to have acquired the circumstellar (CS) material that produces the Balmer emission through ejection of...

  18. Comparison of Cytokine Immune Responses to Brucella abortus and Yersinia enterocolitica Serotype O:9 Infections in BALB/c Mice

    PubMed Central

    Gu, Wenpeng; Wang, Xin; Qiu, Haiyan; Cui, Buyun; Zhao, Shiwen; Zheng, Han; Xiao, Yuchun; Liang, Junrong; Duan, Ran

    2013-01-01

    Brucella abortus and Yersinia enterocolitica serotype O:9 serologically cross-react in the immune response with the host; therefore, our aim was to compare the immune responses to these two pathogens. We selected typical B. abortus and Y. enterocolitica O:9 strains to study the cytokine immune response and the histopathological changes in livers and spleens of BALB/c mice. The data showed the cytokine responses to the two strains of pathogens were different, where the average levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), gamma interferon (IFN-γ), interleukin-12 (IL-12), and tumor necrosis factor alpha (TNF-α) were higher with B. abortus infections than with Y. enterocolitica O:9 infections, especially for IFN-γ, while the IL-10 level was lower and the levels of IL-1β, IL-4, IL-5, and IL-6 were similar. The histopathological effects in the livers and spleens of the BALB/c mice with B. abortus and Y. enterocolitica O:9 infections were similar; however, the pathological changes in the liver were greater with B. abortus infections, while damage in the spleen was greater with Y. enterocolitica O:9 infections. These observations show that different cytokine responses and histopathological changes occur with B. abortus and Y. enterocolitica O:9 infections. PMID:24042115

  19. Asteroseismic analysis of two α-enhanced stars KIC 7976303 and KIC 8694723

    NASA Astrophysics Data System (ADS)

    Shuai Ge, Zhi

    2015-08-01

    We intent to use stellar models with and without α-enhancement, as well as asteroseismic analysis, to study twoα-enhanced stars, KIC 7976303 and KIC 8694723. For the α-enhanced models, we adopt [α/Fe] = 0.2, and 0.4. For the evolved sub-giant KIC 7976303 with mixed-modes, we find thatα-enhanced models fit the mixed-modes better than the models withoutα-enhancement. For the post turn-off star KIC 8694723, we find models fitting observations well in all three cases ([α/Fe] = 0.0, 0.2, 0.4). According to the observed metal abundances, only α-enhanced models are used to estimate the stellar parameters. We then derive the fundamental properties of these two stars.Our α-enhanced models indicate KIC 7976303 with larger mass and younger age than the previous works based on standard models. Furthermore, the differences of estimated mass and age between the three cases are ˜ 0.1 M⊙ and ˜ 0.5 - 1.3 Gyr. These results suggest including α-enhancement in the modeling of α-enhanced stars, such as members of GCs (Globular Clusters), metal-poor stars in the disk and in the halo.

  20. Revised physical elements of the astrophysically important O9.5+O9.5V eclipsing binary system Y Cygni

    NASA Astrophysics Data System (ADS)

    Harmanec, P.; Holmgren, D. E.; Wolf, M.; Božić, H.; Guinan, E. F.; Kang, Y. W.; Mayer, P.; McCook, G. P.; Nemravová, J.; Yang, S.; Šlechta, M.; Ruždjak, D.; Sudar, D.; Svoboda, P.

    2014-03-01

    Context. Rapid advancements in light-curve and radial-velocity curve modelling, as well as improvements in the accuracy of observations, allow more stringent tests of the theory of stellar evolution. Binaries with rapid apsidal advance are particularly useful in this respect since the internal structure of the stars can also be tested. Aims: Thanks to its long and rich observational history and rapid apsidal motion, the massive eclipsing binary Y Cygrepresents one of the cornerstones of critical tests of stellar evolutionary theory for massive stars. Nevertheless, the determination of the basic physical properties is less accurate than it could be given the existing number of spectral and photometric observations. Our goal is to analyse all these data simultaneously with the new dedicated series of our own spectral and photometric observations from observatories widely separated in longitude. Methods: We obtained new series of UBV observations at three observatories separated in local time to obtain complete light curves of Y Cygfor its orbital period close to 3 days. This new photometry was reduced and carefully transformed to the standard UBV system using the HEC22 program. We also obtained new series of red spectra secured at two observatories and re-analysed earlier obtained blue electronic spectra. Reduction of the new spectra was carried out in the IRAF and SPEFO programs. Orbital elements were derived independently with the FOTEL and PHOEBE programs and via disentangling with the program KOREL . The final combined solution was obtained with the program PHOEBE . Results: Our analyses provide the most accurate value of the apsidal period of (47.805 ± 0.030) yr published so far and the following physical elements: M1 = 17.72 ± 0.35 M⊙, M2 = 17.73 ± 0.30 M⊙, R1 = 5.785 ± 0.091 R⊙, and R2 = 5.816 ± 0.063 R⊙. The disentangling thus resulted in the masses, which are somewhat higher than all previous determinations and virtually the same for both stars

  1. Comparison Study of Transition Temperature between the Superconducting Compounds Tl0.9 Pb0.1 Ba2Ca2Cu3O9-δ, Tl0.9Sb0.1Ba2Ca2Cu3O9-δ and Tl0.9Cr0.1Ba2Ca2Cu3O9

    NASA Astrophysics Data System (ADS)

    Jasim, Kareem Ali; Makki, Sameer Atta; Almohsin, Alia abud

    Three high temperature superconductors namely Tl0.9Pb0.1Ba2Ca2Cu3O9-δ, Tl0.9Sb0.1Ba2Ca2Cu3O9-δ and Tl0.9Cr0.1Ba2Ca2Cu3O9-δ have been successfully prepared by three-step solid state reaction method. The sintering was within (1128-1133) K. Electrical resistively, using four probe techniques, is used to find the transition temperature Tc. The transition temperature at zero resistivity Tc(offset) were 110, 115 and 118K, onset superconducting transition temperature Tc(onset) were 128, 131 and 132 K for Tl0.9Cr0.1Ba2Ca2Cu3O9-δ, Tl0.9Sb0.1Ba2Ca2Cu3O9-δ and Tl0.9Cr0.1Ba2Ca2Cu3O9-δ respectively. All samples preparation with O2 flow. X-ray diffraction (XRD) analysis showed a pesudotetragonal structure with changes of lattice parameters for these samples.

  2. Laser site-selective spectroscopy of Eu3+ ions doped Y4Al2O9

    NASA Astrophysics Data System (ADS)

    Kaczkan, M.; Turczyński, S.; Pawlak, D. A.; Wencka, M.; Malinowski, M.

    2016-08-01

    Eu3+ doped Y4Al2O9 (YAM) crystals were prepared by the micro-pulling down method. Optical-absorption and laser-selective-excitation techniques along with the luminescence decays have been used to reveal that Eu3+ ions in YAM occupy three distinct sites, which were characterized and discussed. The Stark energy levels of Eu3+ at three different sites in YAM were assigned from selectively excited emission spectra at 10 K. The intensity ratio of forced electric dipole (5D0 → 7F2) and magnetic dipole (5D0 → 7F1) transitions was discussed in order to obtain information about the degree of asymmetry of the luminescent centers. These results were confirmed by the luminescence lifetime measurements. The temperature dependent photo-luminescence spectra indicated that there is no energy transfer between different sites in the 10-300 K range.

  3. Modeling the Thermoelectric Properties of Ti5O9 Magnéli Phase Ceramics

    NASA Astrophysics Data System (ADS)

    Pandey, Sudeep J.; Joshi, Giri; Wang, Shidong; Curtarolo, Stefano; Gaume, Romain M.

    2016-07-01

    Magnéli phase Ti5O9 ceramics with 200-nm grain-size were fabricated by hot-pressing nanopowders of titanium and anatase TiO2 at 1223 K. The thermoelectric properties of these ceramics were investigated from room temperature to 1076 K. We show that the experimental variation of the electrical conductivity with temperature follows a non-adiabatic small-polaron model with an activation energy of 64 meV. In this paper, we propose a modified Heikes-Chaikin-Beni model, based on a canonical ensemble of closely spaced titanium t 2g levels, to account for the temperature dependency of the Seebeck coefficient. Modeling of the thermal conductivity data reveals that the phonon contribution remains constant throughout the investigated temperature range. The thermoelectric figure-of-merit ZT of this nanoceramic material reaches 0.3 K at 1076 K.

  4. Time-resolved spectroscopy of Bi3+ centers in Y4Al2O9

    NASA Astrophysics Data System (ADS)

    Babin, V.; Lipińska, L.; Mihokova, E.; Nikl, M.; Shalapska, T.; Suchocki, A.; Zazubovich, S.; Zhydachevskii, Ya

    2015-08-01

    Steady-state and time-resolved emission and excitation spectra as well as luminescence decay kinetics are studied at 4.2-400 K under excitation in the 3-6 eV energy range for Bi3+ ions substituting for Y3+ ions in four inequivalent crystal lattice sites of Y4Al2O9:Bi ceramics. Luminescence characteristics of Bi3+ centers of all the four types are identified and are shown to arise from the radiative decay of the triplet relaxed excited state (RES) of Bi3+ ions. The parameters of the triplet RES, namely, probabilities of the radiative and nonradiative transitions from the metastable and emitting levels as well as the energy distance between these levels, are determined. The influence of the nearest surroundings of Bi3+ ions on the luminescence characteristics and the parameters of the triplet RES of Bi3+ centers is discussed.

  5. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  6. Structure cristalline de K 3NbAs 2O 9

    NASA Astrophysics Data System (ADS)

    Zid, Mohamed Faouzi; Jouini, Tahar; Jouini, Noureddine; Omezzine, Mohamed

    1989-09-01

    K 3NbAs 2O 9 is a new compound of Mr = 503.4: orthorhombic, Pnma, a = 22.389(6), b = 5.436(1), c = 7.870(2) Å, V = 957.8 Å 3, Z = 4, ρ = 3.495 g/cm 3, AgK overlineα, λ = 0.5608 Å, μ = 97.6 cm -1, F(000) = 1287, R = 0.050, w R = 0.046 for 661 independent reflections. The structure contains chains of AsO 4 tetrahedra and NbO 6 octahedra sharing corners. They are staggered and connected by NbO(5)As bridges to form «puckeredå layers parallel to the bc plane. The K + ions, located in channels communicating by the interlayer spaces, contribute mainly by holding together chains belonging to the same layer. Although the niobium atom is off-center in an "O 6" octahedron and forms a short NbO axial(1) distance and a long NbO axial(5) distance, the hypothesis of square pyramidal coordination is rejected by showing indirectly the influence of the Nb atom on O(5) from a comparison between the AsO equatorial and the AsO(5) distances in the NbOAs bridges. The structure of β-TaH(PO 4) 2 (three-dimensional anion) derives from that of K 3NbAs 2O 9 (two-dimensional) through the sharing of the homolog of O(1) between successive layers, thus locking the communication between the channels containing the H + ions.

  7. Synthesis, crystal structure and electrical proprieties of new phosphate KCoP3O9

    NASA Astrophysics Data System (ADS)

    Ben Smida, Y.; Guesmi, A.; Georges, S.; Zid, M. F.

    2015-01-01

    Crystals of new tricyclophosphate KCoP3O9 have been grown from solid state reaction and characterized by single crystal X-ray diffraction. KCoP3O9 crystallizes in the hexagonal system, space group P 6 barc2, with a=6.616 (7) Å; c=9.788 (3) Å; V=371.06 (13) Å3, Z=2. The final agreement factors are R=0.014, ωR=0.038, S(F2)=1.231. The structure of the title compound can be described as a three-dimensional framework built up of corner sharing CoO6 and PO4 polyhedra containing wide tunnels oriented along [001] direction and others, less broad, along [100] and [010] directions. The structural model was validated by bond valence sum (BVS) and charge distribution (CD) methods. Ball milling was used to reduce the particles sizes of the synthesized powder. At the optimal sintering temperature of 800 °C, a relative density of 85% was obtained. The microstructure was characterized by scanning electron microscopy. The electrical conductivity was 8.4×10-7 S cm-1 and 1.7×10-4 S cm-1 at 480 °C and 680 °C respectively. The activation energy deduced from the slope is 2.2 eV at low temperature region and 1.2 eV at high temperature region. The BVS model is extended to simulate the ionic migration pathways of alkali cations in the anionic framework. The BVS calculation shows one-dimensional pathways migration along c-axis.

  8. Successive magnetic phase transitions and multiferroicity in quasi-two-dimensional triangular lattice Heisenberg antiferromagnets Ba3CoNb2O9 and Ba3MnNb2O9

    NASA Astrophysics Data System (ADS)

    Lee, M.; Hwang, J.; Choi, E. S.; Ma, J.; Dela Cruz, C. R.; Zhu, M.; Ke, X.; Dun, Z. L.; Zhou, H. D.

    2014-03-01

    We have measured magnetic, dielectric and thermodynamic properties of quasi-two-dimensional triangular lattice antiferromagnet (TLAF), Ba3CoNb2O9 (S = 1/2) and Ba3MnNb2O9 (S = 3/2). At zero magnetic field, Ba3CoNb2O9 undergoes a two-step transition at 1.36 K and 1.10 K and enters a 120 degree ordered state. By applying magnetic fields, a series of magnetic phases with fractional saturation magnetization (1/3, 1/2, 2/3 (or √{ 3}/3Ms) are observed. The collinear spin phase with 1/3 Ms becomes more robust at lower temperatures due to quantum fluctuations. For Ba3MnNb2O9, the 120 degree ordered state is stabilized below 3.10 K at zero field. Under the magnetic field, successive magnetic phase transitions are observed with fractional magnetization 1/3 and 1/2 Ms. The 1/3 Ms phase becomes more stable at higher temperatures due to thermal fluctuations. The ferroelectricity emerges in all spin states in both compounds regardless of the spin chirality. Therefore, Ba3CoNb2O9andBa3MnNb2O9 are unique TLAFs exhibiting not only a series of magnetic phase transitions but also multiferroicity. NHMFL is supported by NSF, the State of Florida and US DOE. ORNL HFIR was sponsored by U.S. DOE.

  9. Massive Stars

    NASA Astrophysics Data System (ADS)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  10. STAR System.

    ERIC Educational Resources Information Center

    Doverspike, James E.

    The STAR System is a developmental guidance approach to be used with elementary school children in the 5th or 6th grades. Two basic purposes underlie STAR: to increase learning potential and to enhance personal growth and development. STAR refers to 4 basic skills: sensory, thinking, adapting, and revising. Major components of the 4 skills are:…

  11. STUDY ON SYNTHESIS AND EVOLUTION OF NANOCRYSTALLINE Mg4Ta2O9 BY AQUEOUS SOL-GEL PROCESS

    NASA Astrophysics Data System (ADS)

    Wu, H. T.; Yang, C. H.; Wu, W. B.; Yue, Y. L.

    2012-06-01

    Nanosized and highly reactive Mg4Ta2O9 were successfully synthesized by aqueous sol-gel method compared with conventional solid-state method. Ta-Mg-citric acid solution was first formed and then evaporated resulting in a dry gel for calcination in the temperature ranging from 600°C to 800°C for crystallization in oxygen atmosphere. The crystallization process from the gel to crystalline Mg4Ta2O9 was identified by thermal analysis and phase evolution of powders was studied using X-ray diffraction (XRD) technique during calcinations. Particle size and morphology were examined by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HR-SEM). The results revealed that sol-gel process showed great advantages over conventional solid-state method and Mg4Ta2O9 nanopowders with the size of 20-30 nm were obtained at 800°C.

  12. Luminescence properties of Ba3Si6O9N4:Eu2+ green-emitting phosphors for white LEDs

    NASA Astrophysics Data System (ADS)

    Yu, Lanlan; Hua, Youjie; Chen, Hong; Deng, Degang; Wang, Huanping; Ma, Hongping; Xu, Shiqing

    2014-03-01

    A green-emitting phosphor, Eu2+-activated Ba3Si6O9N4 phosphor, was synthesized by a conventional solid state reaction method. X-ray diffraction patterns showed that the synthesized phosphor sintered at 1300 °C for 6 h was a Ba3Si6O9N4 pure phase. It could be efficiently excited by UV-blue light (280-500 nm) and showed a single intense broad emission band (470-625 nm). Suitable excitation range makes it match well with the emission of near-UV or blue LEDs. Concentration quenching of the doped-Eu2+ ions occurred at x=0.15, and the critical distance is calculated to be about 1.807 nm by theory of energy transfer. The result indicates that Ba3Si6O9N4:Eu2+ is a promising green-emitting phosphor for white LEDs.

  13. CH Stars and Barium Stars

    NASA Astrophysics Data System (ADS)

    Bond, H.; Sion, E.; Murdin, P.

    2000-11-01

    The classical barium (or `Ba II') stars are RED GIANT STARS whose spectra show strong absorption lines of barium, strontium and certain other heavy elements, as well as strong features due to carbon molecules. Together with the related class of CH stars, the Ba II stars were crucial in establishing the existence of neutron-capture reactions in stellar interiors that are responsible for the synt...

  14. Enhancement of hydrocarbon waste biodegradation by addition of a biosurfactant from Bacillus subtilis O9.

    PubMed

    Morán, A C; Olivera, N; Commendatore, M; Esteves, J L; Siñeriz, F

    2000-01-01

    A non-sterile biosurfactant preparation (surfactin) was obtained from a 24-h culture of Bacillus subtilis O9 grown on sucrose and used to study its effect on the biodegradation of hydrocarbon wastes by an indigenous microbial community at the Erlenmeyer-flask scale. Crude biosurfactant was added to the cultures to obtain concentrations above and below the critical micelle concentration (CMC). Lower concentration affected neither biodegradation nor microbial growth. Higher concentration gave higher cell concentrations. Biodegradation of aliphatic hydrocarbons increased from 20.9 to 35.5% and in the case of aromatic hydrocarbons from nil to 41%, compared to the culture without biosurfactant. The enhancement effect of biosurfactant addition was more noticeable in the case of long chain alkanes. Pristane and phytane isoprenoids were degraded to the same extent as n-C17 and n-C18 alkanes and, consequently, no decrease in the ratios n-C17/pri and n-C18/phy was observed. Rapid production of surfactin crude preparation could make it practical for bioremediation of ship bilge wastes. PMID:11194975

  15. Strain Engineered CaBi2Nb2O9 Thin Films with Enhanced Electrical Properties.

    PubMed

    Zhang, Yunxiang; Ouyang, Jun; Zhang, Jincan; Li, Yao; Cheng, Hongbo; Xu, Huiwen; Liu, Menglin; Cao, Zhao-Peng; Wang, Chun-Ming

    2016-07-01

    In this work, strain engineered polycrystalline thin films (∼250 nm) of bismuth layer-structured ferroelectric (BLSF) CaBi2Nb2O9 (CBNO) were prepared by using a radio frequency (RF) magnetron sputtering technique. XRD analysis revealed that the films were (200)/(020) and (00l) textured with a large in-plane tensile stress. Cross-sectional TEM analyses confirmed the bismuth layered-structure, as well as crystalline orientations and a strain-controlled growth mode of the grains. Result of a quantitative XPS analysis revealed that the composition of the film is close to the chemical stoichiometry. Excellent electrical properties were achieved in the CBNO films, including a high dielectric constant (∼280 @5 kHz), a small dielectric loss (tgδ ≤ 1.6% up to an applied electric field of ∼1200 kV/cm) and a large polarization (Pr ≈ 14 μC/cm(2) @ 1 kHz). PMID:27294811

  16. High-throughput synthesis of thermoelectric Ca3Co4O9 films

    NASA Astrophysics Data System (ADS)

    Pravarthana, D.; Lebedev, O. I.; Hebert, S.; Chateigner, D.; Salvador, P. A.; Prellier, W.

    2013-09-01

    Properties of complex oxide thin films can be tuned over a range of values as a function of mismatch, composition, orientation, and structure. Here, we report a strategy for growing structured epitaxial thermoelectric thin films leading to improved Seebeck coefficient. Instead of using single-crystal sapphire substrates to support epitaxial growth, Ca3Co4O9 films are deposited, using the Pulsed Laser Deposition technique, onto Al2O3 polycrystalline substrates textured by spark plasma sintering. The structural quality of the 2000 Å thin film was investigated by transmission electron microscopy, while the crystallographic orientation of the grains and the epitaxial relationships were determined by electron backscatter diffraction. The use of a polycrystalline ceramic template leads to structured films that are in good local epitaxial registry. The Seebeck coefficient is about 170 μV/K at 300 K, a typical value of misfit material with low carrier density. This high-throughput process, called combinatorial substrate epitaxy, appears to facilitate the rational tuning of functional oxide films, opening a route to the epitaxial synthesis of high quality complex oxides.

  17. Vaporization behaviour and Gibbs' energy of formation of UTeO 5 and UTe 3O 9 by transpiration

    NASA Astrophysics Data System (ADS)

    Mishra, R.; Namboodiri, P. N.; Tripathi, S. N.; Bharadwaj, S. R.; Dharwadkar, S. R.

    1998-08-01

    Vapour pressures of UTeO 5 and UTe 3O 9 were determined by a transpiration technique employing their incongruent vaporization represented by the reactions: 3< UTeO5>→< U3O8>+1/2( O2)+3( TeO2) and < UTe3O9>→< UTeO5>+2( TeO2). Standard Gibbs energies of formation of UTeO 5 and UTe 3O 9 were derived from the vapour pressures of TeO 2 measured in the temperature ranges of 1107-1217 and 947-1011 K, respectively, and could be represented by the equations Δ fG°< UTeO5>/ kJ/mol(±0.72)=-1614.17+0.450 T (1107⩽ T/K⩽1217) and Δ fG°< UTe3O9>/ kJ/mol(±1.31)=-2313.12+0.868 T (947⩽ T/K⩽1011)

  18. Reversible photoresponsive switching in Bi(2.5)Na(0.5)Nb(2)O(9)-based luminescent ferroelectrics.

    PubMed

    Zhang, Qiwei; Sun, Haiqin; Li, Hao; Wang, Xusheng; Hao, Xihong; Song, Jinling; An, Shengli

    2015-11-25

    Reversible luminescence modulation upon photochromic reactions with excellent reproducibility was achieved from Eu(3+) doped Bi2.5Na0.5Nb2O9 multifunctional ferroelectrics. The material exhibits strong sensitivity to visible light or sunlight with fast response time without inducing any structural changes. PMID:26390220

  19. No evidence of disk destruction by OB stars

    NASA Astrophysics Data System (ADS)

    Richert, Alexander J. W.; Feigelson, Eric

    2015-01-01

    It has been suggested that the hostile environments observed in massive star forming regions are inhospitable to protoplanetary disks and therefore to the formation of planets. The Orion Proplyds show disk evaporation by extreme ultraviolet (EUV) photons from Theta1 Orionis C (spectral type O6). In this work, we examine the spatial distributions of disk-bearing and non-disk bearing young stellar objects (YSOs) relative to OB stars in 17 massive star forming regions in the MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey. Any tendency of disky YSOs, identified by their infrared excess, to avoid OB stars would reveal complete disk destruction.We consider a sample of MYStIX that includes 78 O3-O9 stars, 256 B stars, 5,606 disky YSOs, and 5,794 non-disky YSOs. For each OB star, we compare the cumulative distribution functions of distances to disky and non-disky YSOs. We find no significant avoidance of OB stars by disky YSOs. This result indicates that OB stars are not sufficiently EUV-luminous and long-lived to completely destroy a disk within its ordinary lifetime. We therefore conclude that massive star forming regions are not clearly hostile to the formation of planets.

  20. Search for OB stars running away from young star clusters. I. NGC 6611

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Bomans, D. J.

    2008-11-01

    N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young (⪉several Myr) clusters and OB associations. We discovered dozens of bow shocks generated by OB stars running away from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper, we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC 6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested to be one of “the best examples for isolated Galactic high-mass star formation” (de Wit et al. 2005, A&A, 437, 247). Possible implications of our results for the origin of field OB stars are discussed.

  1. Manipulating Thermal Conductivity by Interfacial Modification of Misfit-Layered Cobaltites Ca3Co4O9

    NASA Astrophysics Data System (ADS)

    Fujii, Susumu; Yoshiya, Masato

    2016-03-01

    The phonon thermal conductivities of misfit-layered Ca3Co4O9, Sr3Co4O9, and Ba3Co4O9 were calculated using the perturbed molecular dynamics method to clarify the impact of lattice misfit on the phonon thermal conduction in misfit-layered cobaltites. Substitution of Sr and Ba for Ca substantially modified the magnitude of the lattice misfit between the CoO2 and rock salt (RS) layers, because of the different ionic radii, increasing overall phonon thermal conductivity. Further analyses with intentionally changed atomic masses of Ca, Sr, or Ba revealed that smaller ionic radius at the Ca site in the RS layer, instead of heavier atomic mass, is a critical factor suppressing the overall thermal conductivity of Ca3Co4O9, since it determines not only the magnitude of lattice misfit but also the dynamic interference between the two layers, which governs the phonon thermal conduction in the CoO2 and RS layers. This concept was demonstrated for Sr-doped Ca3Co4O9 as an example of atomistic manipulation for better thermoelectric properties. Phonon thermal conductivities not only in the RS layer but also in the CoO2 layer were reduced by the substitution of Sr for Ca. These results provide another strategy to improve the thermal conductivity of this class of misfit cobaltites, that is, to control the thermal conductivity of the CoO2 layer responsible for electronic and thermal conductivity by atomistic manipulation in the RS layer adjacent to the CoO2 layer.

  2. Star Polymers.

    PubMed

    Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

    2016-06-22

    Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings. PMID:27299693

  3. Radio stars.

    PubMed

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars. PMID:17836594

  4. Effects of BaBi2Ta2O9 thin buffer layer on crystallization and electrical properties of CaBi2Ta2O9 thin films on Pt-coated silicon

    NASA Astrophysics Data System (ADS)

    Kato, Kazumi; Suzuki, Kazuyuki; Nishizawa, Kaori; Miki, Takeshi

    2001-05-01

    Non-c-axis oriented CaBi2Ta2O9 (CBT) thin films have been successfully deposited via the triple alkoxide solution method on Pt-coated Si substrates by inserting BaBi2Ta2O9 (BBT) thin buffer layers. The BBT thin buffer layer, which was prepared on Pt-coated Si, was a key material for suppression of the nonpolar c-axis orientation and promoting the ferroelectric structure perpendicular to the in-plane direction of CBT thin film. The annealing temperature and thickness of the BBT thin buffer layers affected the dielectric, ferroelectric, and fatigue properties of the stacked CBT/BBT thin films. The resultant 650 °C annealed CBT/BBT(30 nm) thin film exhibited good P-E hysteresis properties and fatigue behaviors.

  5. On the distance to Cygnus X-1. [extrapolation from nearby stars

    NASA Technical Reports Server (NTRS)

    Margon, B.; Bowyer, S.; Stone, R. P. S.

    1973-01-01

    Interstellar extinction of 50 stars in the immediate vicinity of Cyg X-1 is compared with color excess of HDE 226868. The fact that HDE 226868 has extinction drastically exceeding that of all stars in the field at less than 1 kpc is believed to be in conflict with the model of Trimble et al. (1973) in which the primary is a luminous undermassive star and with other similar models. Uniform extrapolation of the reddening yields a distance estimate of (2.5 plus or minus 0.4) kpc for Cygnus X-1, in agreement with the spectroscopic modulus for an O9 star.

  6. A comparison of lyman alpha and HeI lambda 10830 line structure and variations in early-type star atmospheres

    NASA Technical Reports Server (NTRS)

    Meisel, D. D.

    1977-01-01

    Fabry-Perot interferometric profiles for fifty of the early-type stars including supergiants, eclipsing binaries, Bp and Ap stars, Be and shell stars, and variable stars have been obtained. Results for beta Persei (Algol) just before primary and secondary eclipses show strong emission profiles lasting about 0.1 phase. An absorption line was seen during secondary eclipse. Bright supergiant stars (O9-A2) show time-variable, complicated absorption/emission profiles similar to those obtained for the Be/shell stars.

  7. Influence of composition nonstoichiometry on the electrical conductivity of LiNaGe4O9 crystals

    NASA Astrophysics Data System (ADS)

    Volnyanskii, M. D.; Trubitsyn, M. P.; Bibikova, O. A.

    2014-06-01

    The electrical conductivity σ of Li2 - x Na x Ge4O9 ( x = 1, 0.5, 0.2) crystals in an alternating-current electric field has been investigated at a frequency of 1 kHz in the temperature range of 300-800 K. A considerable anisotropy of the electrical conductivity has been revealed for crystals with a sodium concentration x = 1 at T > 500 K. It has been shown that the electrical conductivity σ along certain crystallographic directions increases by more than three orders of magnitude with a change in the sodium concentration from x = 1 to x = 0.2. The results have been discussed taking into account the specific features of the structure of the crystals under investigation. Presumably, the major charge carriers are interstitial Li ions migrating along channels of the framework structure of the Li2 - x Na x Ge4O9 crystals.

  8. Effects of Lu and Ni Substitution on Thermoelectric Properties of Ca3Co4O9+ δ

    NASA Astrophysics Data System (ADS)

    Yang, Wenchao; Qian, Haoji; Gan, Jinyu; Wei, Wei; Wang, Zhihe; Tang, Guodong

    2016-08-01

    Effects of (Lu, Ni) co-doping on the thermoelectric properties of Ca3Co4O9+ δ (CCO) have been systematically investigated from 20 K to 350 K. The electrical resistivity and thermopower of (Lu, Ni) co-doped samples increase, while their thermal conductivity is significantly depressed as compared to that of pristine CCO. The figure of merit ( ZT) of co-doped samples is higher than those of Lu-doped samples and pristine CCO. A maximum ZT of 0.0185 is achieved at 350 K for Ca2.9Lu0.1Co3.9Ni0.1O9+ δ . We demonstrate that the simultaneous increase of spin entropy and phonon scattering induced by (Lu, Ni) co-doping boosts ZT of CCO. This study indicates that (Lu, Ni) co-doping may promise an effective way to improve thermoelectric properties of the CCO system.

  9. High-quality single crystal growth and spin flop of multiferroic Co4Nb2O9

    NASA Astrophysics Data System (ADS)

    Cao, Yiming; Yang, Yali; Xiang, Maolin; Feng, Zhenjie; Kang, Baojuan; Zhang, Jincang; Ren, Wei; Cao, Shixun

    2015-06-01

    A single crystal of Co4Nb2O9 about 7 mm in diameter and 55 mm in length was successfully grown by an optical floating zone method. X-ray powder diffraction (XRD) indicates that it has a single phase corundum-type structure. Clear Laue spots and sharp XRD peaks confirm the good quality and crystallographic orientations. Below TN, magnetization of Co4Nb2O9 along a axis shows dramatically different behaviors between H=1 kOe and 20 kOe, suggesting a spin flop occurs along a axis. Ma(H) curve at 5 K shows a change of slope at a critical magnetic field of 7.5 kOe for triggering the spin flip.

  10. Effect of RF power on structural and magnetic properties of La doped Bi2Fe4O9 thin films

    NASA Astrophysics Data System (ADS)

    Santhiya, M.; Pugazhvadivu, K. S.; Balakrishnan, L.; Tamilarasan, K.

    2016-05-01

    Effect of RF power on structural and magnetic properties of lanthanum (La3+) doped Bi2Fe4O9 thin films grown on p-Si substrates by radio frequency (RF) magnetron sputtering has studied in this investigation. It is observed that the sputtering power affects the crystalline nature and magnetic properties of grown thin films. X-ray diffraction and Raman spectrum confirms that the Bi2Fe4O9 (BFO) thin films were crystallized well with orthorhombic structure. The BFO thin films which was prepared at sputtering power of 100 W have good crystallinity than those prepared at 40 W. The magnetic properties are investigated by vibrating sample magnetometer. The magnetic hysteresis perceptive loop shows that the anti-ferromagnetic behavior of the sample at room temperature. These results confirms that the crystallinity and magnetic properties of the BFO thin films were enhanced at the higher sputtering power (100 W).

  11. Effects of Lu and Ni Substitution on Thermoelectric Properties of Ca3Co4O9

    NASA Astrophysics Data System (ADS)

    Yang, Wenchao; Qian, Haoji; Gan, Jinyu; Wei, Wei; Wang, Zhihe; Tang, Guodong

    2016-06-01

    Effects of (Lu, Ni) co-doping on the thermoelectric properties of Ca3Co4O9+δ (CCO) have been systematically investigated from 20 K to 350 K. The electrical resistivity and thermopower of (Lu, Ni) co-doped samples increase, while their thermal conductivity is significantly depressed as compared to that of pristine CCO. The figure of merit (ZT) of co-doped samples is higher than those of Lu-doped samples and pristine CCO. A maximum ZT of 0.0185 is achieved at 350 K for Ca2.9Lu0.1Co3.9Ni0.1O9+δ . We demonstrate that the simultaneous increase of spin entropy and phonon scattering induced by (Lu, Ni) co-doping boosts ZT of CCO. This study indicates that (Lu, Ni) co-doping may promise an effective way to improve thermoelectric properties of the CCO system.

  12. Plasmids in Yersinia enterocolitica serotypes O:3 and O:9: correlation with epithelial cell adherence in vitro.

    PubMed Central

    Vesikari, T; Nurmi, T; Mäki, M; Skurnik, M; Sundqvist, C; Granfors, K; Grönroos, P

    1981-01-01

    Human isolates of Yersinia enterocolitica serotypes O:3 (biotype 4) and O:9 (biotype 3) harbored plasmids sized approximately 47 and 44 megadaltons, respectively. No such plasmids were found in "apathogenic" strains of Y. enterocolitica belonging to biotype 1. There was a positive correlation among the presence of plasmid, autoagglutination, and adherence to and toxicity for HEp-2 cell cultures; all of these properties were lost by culturing at 37 degrees C in the absence of calcium. Strains of Y. enterocolitica O:3 and O:9 cured of the plasmids showed increased invasiveness in the HEp-2 cell culture model, but no invasiveness in guinea pig eye. It is suggested that the plasmids of Y. enterocolitica primarily determine epithelial cell adherence, but may also be associated with other pathogenic properties. Images PMID:7287174

  13. Muon spin rotation study of spin dimers on a triangular lattice in Ba3 MRu2 O9

    NASA Astrophysics Data System (ADS)

    Ziat, Djamel; Verrier, Aimé; Quilliam, Jeffrey; Aczel, Adam; Sinclair, Ryan; Chen, Qiang; Zhou, Haidong

    The family of hexagonal perovskites, Ba3 MA2 O9 has recently been proven to be fertile ground for the discovery of new, exotic magnetic phases, including several quantum spin liquid candidates. The 6H-perovskites can also accommodate spin dimers on a triangular lattice, as in the ruthenate materials Ba3MRu2O9. We will present measurements on materials containing M3 + (M = Y, La, Lu, In), which give rise to mixed valence Ru4.5 + ions wherein the orbital and charge degrees of freedom must also be considered. In particular, muon spin rotation (µSR) experiments, have allowed us to probe the nature of the magnetically ordered ground state of these materials at low temperatures.

  14. Discovering Massive Runaway Stars with Infrared Bow Shock Nebulae: Four New OB Runaway Candidate Stars Found in WISE Atlas Images

    NASA Astrophysics Data System (ADS)

    Olivier, Grace M.; Kobulnicky, Henry A.; Povich, Matthew S.; Chick, William T.; Dale, Daniel A.; Andrews, Julian E.; Munari, Stephan; Schurhammer, Danielle; Sorber, Rebecca; Wernke, Heather N.

    2016-01-01

    Determining the mass loss rates of massive stars is an important unsolved problem in astronomy because mass loss dictates the evolutionary track of the star and its fate. One way to measure mass loss rates is through studying the infrared bow shocks from massive O and B type stars. These stars form bow shocks because they have been expelled from their birth regions and are moving at high velocities through the ISM. The stars we studied in this project were discovered by searching the Wide-Field Infrared Survey Explorer (WISE) 22 μm atlas. Using the Longslit Spectrograph at the Wyoming Infrared Observatory (WIRO) we observed each star to obtain a spectrum. Spectral types were then fit to these stars, the stars: G073.6200+1.8522 (B0V), G074.3117+1.0041 (O9V), G059.9225-1.9671 (B3V), and G063.1263+0.3327 (B5V). The spectral types of these stars agree with the predicted range of late-O to early-B type stars. These spectral types will be used to determine temperature, stellar wind velocities, space velocities, and other fundamental quantities that can be used to study stellar mass loss. This work is supported by the National Science Foundation under grants AST-1063146 (REU), AST-1411851 (RUI), and AST-1412845.

  15. Collective versus local Jahn-Teller distortion in Ba3CuSb2O9 : Raman scattering study

    NASA Astrophysics Data System (ADS)

    Drichko, Natalia; Broholm, Collin; Kimura, K.; Ishii, R.; Nakasutji, Satoru

    2016-05-01

    We present temperature dependent Raman spectra of single crystals of two different samples of the spin-orbital liquid candidate Ba3CuSb2O9 . The "hexagonal" sample is known to show no magnetic order down to low temperatures, while the "orthorhombic" sample undergoes a crossover into an orthorhombic crystal structure below TJT of approximately 200 K and shows spin freezing at 110 μ K . Our Raman scattering results demonstrate a strong influence of disorder in both samples. The frequencies of stretching vibrations of oxygens associated with CuSbO9 octahedra indicate a difference in the crystal structure between the hexagonal and orthorhombic samples even at room temperature. On cooling below TJT we observe new bands in the spectra of the orthorhombic sample due to a lowering of symmetry of the unit cell and a collective Jahn-Teller distortion. The spectra of the hexagonal sample show that average hexagonal symmetry is maintained at least down to 20 K. An analysis of the band shape of stretching oxygen vibrations suggests a weak disordered local Jahn-Teller distortion in the hexagonal sample of Ba3CuSb2O9 which increases slightly on cooling. This Jahn-Teller distortion is either static or dynamic with a frequency below 1.5 THz.

  16. Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9

    NASA Astrophysics Data System (ADS)

    Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang

    2015-12-01

    We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

  17. Optical Properties of Blue-Light-Emitting (Ca,Sr)Mg2Si3O9:Eu2+ Phosphor

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Ju; Choi, Sung Hwan; Kim, Kyung Pil; Shin, Hyun Ho; Yoo, Jae Soo

    2010-10-01

    For light-emitting diode (LED) excitation at 400 nm, the optical properties of a Eu2+-activated CaO-SrO-MgO-SiO2 material system were investigated. All the materials were synthesized by solid state reaction. In particular, (Ca,Sr)Mg2Si3O9:Eu2+, which has the same crystal structure as CaMgSi2O6, was found to be promising as a blue-light-emitting phosphor for near UV LED application. The luminance intensity was optimized by controlling the Eu2+ concentration and the composition of the host lattice. The ratio of calcium ions to strontium ions was a convenient parameter for adjusting the maximum excitation peak to 400 nm, which is favorable for near UV LED excitation. The highest luminance intensity of Ca1-x-ySryMg2Si3O9:Eux2+ under 405 nm excitation was achieved at the Eu2+ concentration of x=0.01 and a Sr2+ concentration of y=0.3. The luminance intensity of (Ca,Sr)Mg2Si3O9:Eu2+ was found to be superior to that of a commercial blue-light-emitting BaMgAl10O17:Eu2+ phosphor, which is used for near-UV LED excitation.

  18. Hypervelocity Stars

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.

    2015-08-01

    Hypervelocity stars (HVSs) travel with such extreme velocities that dynamical ejection via gravitational interaction with a massive black hole (MBH) is their most likely origin. Observers have discovered dozens of unbound main-sequence stars since the first in 2005, and the velocities, stellar nature, spatial distribution, and overall numbers of unbound B stars in the Milky Way halo all fit an MBH origin. Theorists have proposed various mechanisms for ejecting unbound stars, and these mechanisms can be tested with larger and more complete samples. HVSs' properties are linked to the nature and environment of the Milky Way's MBH, and, with future proper motion measurements, their trajectories may provide unique probes of the dark matter halo that surrounds the Milky Way.

  19. STARS no star on Kauai

    SciTech Connect

    Jones, M.

    1993-04-01

    The island of Kuai, home to the Pacific Missile Range Facility, is preparing for the first of a series of Star Wars rocket launches expected to begin early this year. The Strategic Defense Initiative plans 40 launches of the Stategic Target System (STARS) over a 10-year period. The focus of the tests appears to be weapons and sensors designed to combat multiple-warhead ICBMs, which will be banned under the START II Treaty that was signed in January. The focus of this article is to express the dubious value of testing the STARS at a time when their application will not be an anticipated problem.

  20. YSOVAR: The Age of the Cepheus C Star Cluster

    NASA Astrophysics Data System (ADS)

    Luna, Jessica; Covey, K.; YSOVAR

    2014-01-01

    We constructed a spectroscopic Hertzsprung-Russell diagram for the Cepheus C (Ceph C) sub-cluster, which we use to generate the first quantitative measurement of this young cluster’s age. Using two TripleSpec spectrographs, on the 3.5m telescope at Apache Point Ob- servatory and the 200” telescope at Palomar Observatory, we obtained near infrared (NIR) spectra for 31 candidate Ceph C members. By comparing our target spectra to a large library of dwarf, sub-giant, and giant star templates, we measured spectral types for candidate Ceph C members ranging from F2 to M2.5. We converted each YSO’s ST into a Teff estimate using the ST to Teff relation recently published by Pecaut et al. (2013). Using our spectroscopically derived extinction estimates to deredden spectral energy distributions constructed from 2MASS and Spitzer photometry, we measured each YSO’s bolometric luminosity. Placing each candidate Ceph C member on an HR Dia- gram, we used Dartmouth pre-main sequence evolutionary tracks to estimate the mass and age of each YSO. We measure a median stellar age for the Ceph C cluster of ˜10 Myrs or less. We also detect a large systematic effect in our ages, however, such that cooler, low mass mem- bers have substantially smaller inferred ages than their higher mass counterparts. We are working to understand the root cause of this systematic effect, but this first estimate of Ceph C’s age will advance our understanding of the cluster’s relationship to other sub clusters in Cepheus, and place the Ceph C cluster in context among other local star forming regions. This research was funded by the NSF through grant number AST-1004107.

  1. Symbiotic stars

    NASA Technical Reports Server (NTRS)

    Kafatos, M.; Michalitsianos, A. G.

    1984-01-01

    The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

  2. Binary star orbits from speckle interferometry. 5: A combined speckle/spectroscopic study of the O star binary 15 Monocerotis

    NASA Technical Reports Server (NTRS)

    Gies, Douglas R.; Mason, Brian D.; Hartkopf, William I.; Mcalister, Harold A.; Frazin, Richard A.; Hahula, Michael E.; Penny, Laura R.; Thaller, Michelle L.; Fullerton, Alexander W.; Shara, Michael M.

    1993-01-01

    We report on the discovery of a speckle binary companion to the O7 V (f) star 15 Monocerotis. A study of published radial velocities in conjunction with new measurements from Kitt Peak National Observatory (KPNO) and IUE suggests that the star is also a spectroscopic binary with a period of 25 years and a large eccentricity. Thus, 15 Mon is the first O star to bridge the gap between the spectroscopic and visual separation regimes. We have used the star's membership in the cluster NGC 2264 together with the cluster distance to derive masses of 34 and 19 solar mass for the primary and secondary, respectively. Several of the He I line profiles display a broad shallow component which we associate with the secondary, and we estimate the secondary's classification to be O9.5 Vn. The new orbit leads to several important predictions that can be tested over the next few years.

  3. First-Principles Investigations of the Structure, Electronic, and Optical Properties of Mullite-Type Orthorhombic Bi2M4O9 (M = Al(3+), Ga(3+)).

    PubMed

    Zahedi, Ehsan; Xiao, Bing; Shayestefar, Mohadese

    2016-05-16

    The structure, electronic band structure, density of state, projected wave function, and optical properties of mullite-type orthorhombic Bi2M4O9 (M = Al(3+), Ga(3+)) crystals have been studied by applying density functional theory based on the Vanderbilt ultrasoft pseudopotential in the frame of the generalized gradient approximation as an exchange-correlation function. Satisfactory agreement between experimental and theoretical results indicates that the used method and conditions are suitable. M-O bonds in tetrahedral MO4 environments are stronger and more covalent with respect to octahedral MO6; also Bi-O bonds in both studied structures are almost ionic in nature. The photocatalytic activity of Bi2Al4O9 and Bi2Ga4O9 is enhanced due to unequal values of Mulliken charges on the O atoms in MO4, MO6, and BiO6E groups. Bi2Al4O9 and Bi2Ga4O9 are direct and indirect band gap semiconductors with band gaps of 2.71 and 2.86 eV, respectively. Higher photocatalytic activity of Bi2Al4O9 is inferable from the lower effective masses of photogenerated carriers around the conduction band minimum and valence band maximum, in comparison with Bi2Ga4O9. The presence of M and O orbitals in the valence and conduction bands reveals that symmetry breaking in the MO4 and MO6 units has an important role in separating charges and increasing photocatalytic activity. Photocatalytic activities of Bi2Al4O9 and Bi2Ga4O9 for decomposition of organic pollutants and generation of hydrogen from water splitting are confirmed from band edge potentials. PMID:27139249

  4. Properties of two-dimensional insulators: A DFT study of bimetallic oxide CrW2O9 clusters adsorption on MgO ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhu, Jia; Zhang, Hui; Zhao, Ling; Xiong, Wei; Huang, Xin; Wang, Bin; Zhang, Yongfan

    2016-08-01

    Periodic density functional theory calculations have been performed to study the electronic properties of bimetallic oxide CrW2O9 clusters adsorbed on MgO/Ag(001) ultrathin films (<1 nm). Our results show that after deposition completely different structures, electronic properties and chemical reactivity of dispersed CrW2O9 clusters on ultrathin films are observed compared with that on the thick MgO surface. On the thick MgO(001) surface, adsorbed CrW2O9 clusters are distorted significantly and just a little electron transfer occurs from oxide surface to clusters, which originates from the formation of adsorption dative bonds at interface. Whereas on the MgO/Ag(001) ultrathin films, the resulting CrW2O9 clusters keep the cyclic structures and the geometries are similar to that of gas-phase [CrW2O9]-. Interestingly, we predicted the occurrence of a net transfer of one electron by direct electron tunneling from the MgO/Ag(001) films to CrW2O9 clusters through the thin MgO dielectric barrier. Furthermore, our work reveals a progressive Lewis acid site where spin density preferentially localizes around the Cr atom not the W atoms for CrW2O9/MgO/Ag(001) system, indicating a potentially good bimetallic oxide for better catalytic activities with respect to that of pure W3O9 clusters. As a consequence, present results reveal that the adsorption of bimetallic oxide CrW2O9 clusters on the MgO/Ag(001) ultrathin films provide a new perspective to tune and modify the properties and chemical reactivity of bimetallic oxide adsorbates as a function of the thickness of the oxide films.

  5. Atomic-resolution study of charge transfer and structural disorder in thermoelectric Ca3Co4O9

    NASA Astrophysics Data System (ADS)

    Klie, Robert

    2010-03-01

    Thermoelectric oxides have attracted increasing attention due to their high thermal power and temperature stability. In particular, Ca3Co4O9, a misfit layered structure consisting of single layer hole-doped CoO2 sandwiched between insulating Ca2CoO3 rocksalt layers, exhibits figure of merit (ZT) of >1 at 1000 K.^1 It was suggested that the Seebeck-coefficient can be further increased by controlling the spin- and valence-state of the Co-ions in the CoO2 layers. This study combines aberration-corrected scanning transmission electron microscopy with electron energy loss spectroscopy (EELS) to examine the atomic and electronic structures of Ca3Co4O9. Using annular dark and bright field imaging, it will be demonstrated that the CoO2 layers are ordered, while the CoO columns in the Ca2CoO3 layer exhibit a modulation along (010). Atomic-column resolved EELS reveals that the Ca2CoO3 layers act as charge reservoirs providing mobile holes to the CoO2 layers; the structural disorder in Ca2CoO3 is responsible for the low in-plane thermal conductivity. The temperature dependence of the Co-ion spin-state as the origin for the unusually high Seebeck coefficient of Ca3O4O9 will be examined.^2 ^1 K. Fujita, et al., Jpn. J. Appl. Phys. 40 (2001), 4644--47^ ^2 Funded by: NSF CAREER Award DMR-0846748

  6. Epitaxial growth of (001)-oriented and (110)-oriented SrBi2Ta2O9 thin films

    NASA Astrophysics Data System (ADS)

    Lettieri, J.; Jia, Y.; Urbanik, M.; Weber, C. I.; Maria, J.-P.; Schlom, D. G.; Li, H.; Ramesh, R.; Uecker, R.; Reiche, P.

    1998-11-01

    Epitaxial SrBi2Ta2O9 thin films have been grown with (001) and (110) orientations by pulsed laser deposition on (001) LaAlO3-Sr2AlTaO6 and (100) LaSrAlO4 substrates, respectively. Four-circle x-ray diffraction and transmission electron microscopy reveal nearly phase pure epitaxial films. Minimization of surface mesh mismatch between the film and substrate (i.e., choice of appropriate substrate material and orientation) was used to stabilize the desired orientations and achieve epitaxial growth.

  7. Serological relationship between cattle exposed to Brucella abortus, Yersinia enterocolitica O:9 and Escherichia coli O157:H7.

    PubMed

    Nielsen, K; Smith, P; Widdison, J; Gall, D; Kelly, L; Kelly, W; Nicoletti, P

    2004-05-20

    Sera from cattle naturally infected with Brucella abortus (n = 160), vaccinated with B. abortus S19 (n = 88) or immunized with Yersinia enterocolitica O:9 (n = 25) or Escherichia coli O157:H7 (n = 80) were collected. The sera were compared for antibody content to the same bacteria by indirect enzyme immunoassay (IELISA), fluorescence polarization assay (FPA) and competitive enzyme immunoassay (CELISA). Cattle sera (n = 523) collected randomly from across Canada were tested in the same tests. Sera from the B. abortus infected group reacted positively in the brucellosis IELISA (IELISA(Br)), CELISA and FPA (FPA(Br)) and the Y. enterocolitica IELISA (IELISA(Ye)) while the Y. enterocolitica FPA (FPA(Ye)) detected antibody in 93.8% and the E. coli IELISA (IELISA(Ec)) 86.9% and the E. coli FPA (FPA(Ec)) 48.1%. About 70% of the sera from B. abortus S19 vaccinated animals reacted in the three IELISAs, 45% in the CELISA, and 37.7% in the FPA(Ec), 21.6% in the FPA(Br) and 5.7% in the FPA(Ye). Sera from E. coli O:157 exposed cattle reacted mainly in the IELISA(Ec) and FPA(Ec) although surprisingly 87.5% reacted in the IELISA(Ye) and only 3.8% in the IELISA(Br). No reactions were observed with these sera in the FPA(Br) and FPA(Ye) but one serum gave a low positive reaction in the CELISA. All sera from Y. enterocolitica O:9 exposed cattle reacted in the IELISA(Br) and IELISA(Ye) and 80% in the IELISA(Ec). In the CELISA, 44% gave a positive reaction and 64% were positive in the FPA(Br), 28% in the FPA(Ye) and 12% in the FPA(Ec). Of the 523 Canadian sera, about 50% reacted in the E. coli tests with only minor reactions in the Y. enterocolitica O:9 and B. abortus assays. From the data, the cross reaction between E. coli O157:H7, Y. enterocilitica O:9 and B. abortus is dependent on the test used. Thus, extensive cross reaction was observed with the IELISA with much less reactivity in the FPA and the CELISA. PMID:15135510

  8. Direct Observation of Pressure-Driven Valence Electron Transfer in Ba3BiRu2O9, Ba3BiIr2O9, and Ba4BiIr3O12.

    PubMed

    Blanchard, Peter E R; Chapman, Karena W; Heald, Steve M; Zbiri, Mohamed; Johnson, Mark R; Kennedy, Brendan J; Ling, Chris D

    2016-06-01

    The hexagonal perovskites Ba3BiIr2O9, Ba3BiRu2O9, and Ba4BiIr3O12 all undergo pressure-induced 1% volume collapses above 5 GPa. These first-order transitions have been ascribed to internal transfer of valence electrons between bismuth and iridium/ruthenium, which is driven by external applied pressure because the reduction in volume achieved by emptying the 6s shell of bismuth upon oxidation to Bi(5+) is greater in magnitude than the increase in volume by reducing iridium or ruthenium. Here, we report direct observation of these valence transfers for the first time, using high-pressure X-ray absorption near-edge spectroscopy (XANES) measurements. Our data also support the highly unusual "4+" nominal oxidation state of bismuth in these compounds, although the possibility of local disproportionation into Bi(3+)/Bi(5+) cannot be definitively ruled out. Ab initio calculations reproduce the transition, support its interpretation as a valence electron transfer from Bi to Ir/Ru, and suggest that the high-pressure phase may show metallic behavior (in contrast to the insulating ambient-pressure phase). PMID:27187072

  9. Chameleon stars

    SciTech Connect

    Dzhunushaliev, Vladimir; Folomeev, Vladimir; Singleton, Douglas

    2011-10-15

    We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.

  10. The friendly stars

    NASA Astrophysics Data System (ADS)

    Martin, Martha Evans

    Describes prominent stars such as Vega, Arcturus, and Antares and means of identifying them, discusses the constellations in which they are located, and explains star names, stellar light, distances between stars, and types of stars.

  11. Star Power

    SciTech Connect

    2014-10-17

    The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

  12. Star Power

    ScienceCinema

    None

    2014-11-18

    The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

  13. Electrical properties of ferroelectric-gate FETs with SrBi2Ta2O9 formed using MOCVD technique

    NASA Astrophysics Data System (ADS)

    Yan, Kang; Takahashi, Mitsue; Sakai, Shigeki

    2012-09-01

    Ferroelectric-gate field-effect transistors (FeFETs) with a Pt/SrBi2Ta2O9/Hf-Al-O/Si gate stack were fabricated using the metal-organic chemical vapor deposition (MOCVD) technique to prepare the SrBi2Ta2O9 (SBT) ferroelectric layer. A good threshold voltage ( V th) distribution was found for more than 90 n-channel FeFETs in one chip with a 170 nm SBT layer owing to the good film uniformity of the SBT layer deposited by MOCVD. The average memory window (Vw^{av}) and the standard deviations ( σ thl, σ thr) of the left- and right-side branches of the drain-gate voltage curves of the FeFETs yielded a Vw^{av}/(σ_{thl} + σ_{thr}) value of 5.45, indicating that the FeFETs can be adapted for large-scale-integration. The electric field, the energy band profile in the gate stack, and the gate leakage current were also investigated at high gate voltages. We found that the effect of Fowler-Nordheim tunneling appeared under these conditions. Because of the tunneling injection and trapping of electrons into the gate insulators, the operation voltage ranges of the FeFETs were limited by this tunneling.

  14. Synthesis and thermoluminescence characterizations of Sr2B5O9Cl:Dy3+ phosphor for TL dosimetry.

    PubMed

    Oza, Abha H; Dhoble, N S; Park, K; Dhoble, S J

    2015-09-01

    The photoluminescence (PL) and thermoluminescence (TL) displayed by Dy-activated strontium haloborate (Sr2 B5 O9 Cl) were studied. A modified solid-state reaction was employed for the preparation of the phosphor. Photoluminescence spectra showed blue (484 nm) and yellow (575 nm) emissions due to incorporation of Dy(3+) into host matrix. The Dy-doped (0.5 mol%) Sr2 B5 O9 Cl was studied after exposure to γ-irradiation and revealed a prominent glow curve at 261°C with a small hump around 143°C indicating that two types of traps were generated. The glow peak at the higher temperature side (261°C) was more stable than the lower temperature glow peak. The TL intensity was 1.17 times less than that of the standard CaSO4 :Dy thermoluminescence dosimetry (TLD) phosphor, the phosphor showed a linear dose-response curve for different γ-ray irradiation doses (0.002-1.25 Gy) and fading of 5-7% was observed for higher temperature peaks upon storage. Trapping parameters and their estimated error values have been calculated by Chen's peak shape method and by the initial rise method. Values of activation energies estimated by both these techniques were comparable. The slight difference in activation energy values calculated by Chen's peak shape method indicated the formation of two kinds of traps Furthermore, slight differences in frequency values are due to various escaping and retrapping probabilities. PMID:25428207

  15. Giant magnetoelastic effect at the opening of a spin-gap in Ba3BiIr2O9.

    PubMed

    Miiller, Wojciech; Avdeev, Maxim; Zhou, Qingdi; Kennedy, Brendan J; Sharma, Neeraj; Kutteh, Ramzi; Kearley, Gordon J; Schmid, Siegber; Knight, Kevin S; Blanchard, Peter E R; Ling, Chris D

    2012-02-15

    As compared to 3d (first-row) transition metals, the 4d and 5d transition metals have much more diffuse valence orbitals. Quantum cooperative phenomena that arise due to changes in the way these orbitals overlap and interact, such as magnetoelasticity, are correspondingly rare in 4d and 5d compounds. Here, we show that the 6H-perovskite Ba(3)BiIr(2)O(9), which contains 5d Ir(4+) (S = 1/2) dimerized into isolated face-sharing Ir(2)O(9) bioctahedra, exhibits a giant magnetoelastic effect, the largest of any known 5d compound, associated with the opening of a spin-gap at T* = 74 K. The resulting first-order transition is characterized by a remarkable 4% increase in Ir-Ir distance and 1% negative thermal volume expansion. The transition is driven by a dramatic change in the interactions among Ir 5d orbitals, and represents a crossover between two very different, competing, ground states: one that optimizes direct Ir-Ir bonding (at high temperature), and one that optimizes Ir-O-Ir magnetic superexchange (at low temperature). PMID:22296219

  16. Enhanced electrical transport by texture modulation and co-doping for Ca3Co4O9+δ materials

    NASA Astrophysics Data System (ADS)

    Liu, Z. Y.; Zhang, F. P.; Zhang, J. X.; Zhang, X.; Lu, Q. M.; Yang, X. Y.

    The powders as well as the texture modulated Ca2.8BaxPryCo4O9+δ (x, y = 0, 0.05, 0.1, 0.15 and 0.2) bulk materials are prepared via solid state reaction, sol-gel and spark plasma sintering method. The powder and bulk materials are analyzed with regard to their phase composition and microscopic character by X-ray diffraction (XRD) and scanning electron microscope (SEM). The thermoelectric transport properties of the bulk materials are measured and investigated. The results show that the plate-like powders with uniform particle size tend to align regularly rather than the powders with anomaly shape and particle size distribution by spark plasma sintering method. The bulk materials co-doped by elements with lower electronegativity tend to form better texture rather than that of the bulk materials co-doped by elements with higher electronegativity via spark plasma sintering method. The resistivities and Seebeck coefficients are in negative accordance to the bulk material texture as a whole, and the carrier transport mechanism is not influenced. The electrical performance is tuned with optimized power factor 462 μW m-1 K-2 at 973 K for Ca2.8BaxPryCo4O9+δ (x = y = 0.1) bulk materials.

  17. Tunning of microstructure and thermoelectric properties of Ca3Co4O9 ceramics by high-magnetic-field sintering

    NASA Astrophysics Data System (ADS)

    Huang, Yanan; Zhao, Bangchuan; Fang, Jun; Ang, Ran; Sun, Yuping

    2011-12-01

    The structural, magnetic, electrical, and thermal transport properties of Ca3Co4O9 ceramics sintered under high magnetic field were investigated. Crystal grain texturing and densification were achieved through cold-pressing and high-magnetic-field sintering techniques. The c-axis of the layered crystal grain was partly oriented along the c-axis of the pressed samples via a cold-pressing technique, and the degree of orientation was further increased while applying the magnetic field in the sample sintering progress. The easy magnetization axis of Ca3Co4O9 polycrystalline ceramics was found to be the c-axis. The room-temperature resistivity along the ab-plane of the sample sintered under 8 T magnetic field was about 30% smaller than that of the sample sintered without magnetic field, and the Seebeck coefficient of the former reached 177.7 μV/K at the room temperature, which is about 50% larger than that of the latter. Consequently, for the sample sintered at 8 T magnetic field, the power factor along the ab-plane was enhanced by about 1.8 times compared to the sample without magnetic field sintering. The obtained result is suggested to originate from the variations of the carrier mobility and spin-orbital degeneracy due to high-magnetic-field sintering in the progress of the sample preparation.

  18. Disorder-Driven Spin-Orbital Liquid Behavior in the Ba3X Sb2O9 Materials

    NASA Astrophysics Data System (ADS)

    Smerald, Andrew; Mila, Frédéric

    2015-10-01

    Recent experiments on the Ba3X Sb2O9 family have revealed materials that potentially realize spin- and spin-orbital liquid physics. However, the lattice structure of these materials is complicated due to the presence of charged X2 +-Sb5 + dumbbells, with two possible orientations. To model the lattice structure, we consider a frustrated model of charged dumbbells on the triangular lattice, with long-range Coulomb interactions. We study this model using Monte Carlo simulation, and find a freezing temperature, Tfrz , at which the simulated structure factor matches well to low-temperature x-ray diffraction data for Ba3 CuSb2 O9 . At T =Tfrz we find a complicated "branching" structure of superexchange-linked X2 + clusters, which form a fractal pattern with fractal dimension df=1.90 . We show that this gives a natural explanation for the presence of orphan spins. Finally we provide a plausible mechanism by which such dumbbell disorder can promote a spin-orbital resonant state with delocalized orphan spins.

  19. Chiral separation of acidic compounds using an O-9-(tert-butylcarbamoyl)quinidine functionalized monolith in micro-liquid chromatography.

    PubMed

    Wang, Qiqin; Zhu, Peijie; Ruan, Meng; Wu, Huihui; Peng, Kun; Han, Hai; Somsen, Govert W; Crommen, Jacques; Jiang, Zhengjin

    2016-04-29

    An O-9-(tert-butylcarbamoyl) quinidine (t-BuCQD) functionalized polymeric monolithic capillary column was prepared by the in situ copolymerization method. The physicochemical properties of the optimized monolithic column were characterized by scanning electron microscopy and micro-LC. Satisfactory column permeability, efficiency, stability and reproducibility were obtained for this monolithic column. The chiral recognition ability of the resulting monolith was also evaluated using 47 N-derivatized amino acids, eight N-derivatized dipeptides, and two herbicides. Under the selected conditions, the enantiomers of all chiral analytes were baseline separated with exceptionally high selectivity and resolution using micro-LC. It is worth noting that this chiral stationary phase (CSP) containing quinidine with a tert-butyl carbamate residue as chiral selector exhibits much higher enantioselectivity and diastereoselectivity than the previously developed O-9-[2-(methacryloyloxy)-ethylcarbamoyl]-10,11-dihydroquinidine (MQD) based CSP for N-derivatized amino acids and dipeptides. These results indicate that this novel quinidine-based polymeric monolith can be used as an effective tool for the enantioseparation of chiral acidic compounds. PMID:27038701

  20. Structure and microstructure of hexagonal Ba3Ti2RuO9 by electron diffraction and microscopy.

    PubMed

    Maunders, Christian; Etheridge, Joanne; Wright, Natasha; Whitfield, Harold J

    2005-04-01

    We have used electron microscopy and diffraction to refine the structure and investigate the microstructure of Ba(3)Ti(2)RuO(9). The parent compound is hexagonal BaTiO(3) with the space group P6(3)/mmc. Using convergent-beam electron diffraction (CBED) combined with electron-sensitive image plates we have found that the space group of Ba(3)Ti(2)RuO(9) is the non-centrosymmetric group P6(3)mc at room temperature and at approximately 110 K. This is consistent with the Ru and Ti atoms occupying alternate face-sharing octahedral sites in the 0001 direction. This maintains the c-glide, but breaks the mirror normal to the c axis and consequently removes the centre of symmetry. Using powder X-ray diffraction, we have measured the lattice parameters from polycrystalline samples to be a = 5.7056 +/- 0.0005, c = 14.0093 +/- 0.0015 A at room temperature. Using high-resolution electron microscopy (HREM) we observed highly coherent, low-strain {10\\bar 10} grain boundaries intersecting at 60 and 120 degrees . From CBED we deduce that adjacent grains are identical but for the relative phase of the Ti and Ru atom ordering along the c axis. HREM also revealed occasional stacking faults, normal to the c-axis. PMID:15772447

  1. BaTi4O9 thin films for high-performance metal-insulator-metal capacitors

    NASA Astrophysics Data System (ADS)

    Jang, Bo-Yun; Kim, Beom-Jong; Lee, Suk-Jin; Lee, Kyong-Jae; Nahm, Sahn; Sun, Ho-Jung; Lee, Hwack-Joo

    2005-09-01

    The dielectric and electrical properties of a BaTi4O9 film were investigated in order to evaluate its potential use in metal-insulator-metal (MIM) capacitors for rf/mixed signal integrated circuits. A high capacitance density of 4.62fF/μm2 along with a low tanδ of 0.0025 were obtained at 100 kHz. A high capacitance density of 4.12fF /μm2 and a high quality factor of 322 were also achieved at 2 GHz. The leakage current density was approximately 1nA/cm2 at ±2V. Small linear and quadratic voltage coefficients of capacitance of 110ppm/V and 40.05ppm/V2, respectively, and a small temperature coefficient of capacitance of -92.157ppm/°C at 100 kHz were obtained. These results demonstrate that the BaTi4O9 film is a good candidate material for MIM capacitors.

  2. Nanoscale heterogeneity in thermoelectrics: the occurrence of phase separation in Fe-doped Ca3Co4O9.

    PubMed

    Xu, Wei; Butt, Sajid; Zhu, Yingcai; Zhou, Jing; Liu, Yong; Yu, Meijuan; Marcelli, Augusto; Lan, Jinle; Lin, Yuan-Hua; Nan, Ce-Wen

    2016-06-01

    The misfit layered cobaltate thermoelectrics are good candidates for high temperature thermoelectric applications. Ca3Co4O9 is a typical compound of this family, which consists of rock salt Ca2CoO3 slabs alternating with hexagonal CoO2 slabs with a large lattice mismatch along the b axis. Each slab is 0.3-0.5 nm thick and shows an inherent structural heterogeneity at the nanoscale. The latter is a key parameter that affects the electrical transport and the heat flow in these misfit structured thermoelectrics. To clarify the physical origin of the thermoelectric performance of iron doped Ca3Co4O9 we combined X-ray near-edge absorption spectroscopy (XANES) and quantum modeling using density functional theory. In contrast to single-site doping, the iron doping first occurs at the Co1 site of the rock salt slab at low doping while at higher doping it prefers the Ca1 site of the rock salt slab. Doping at the Ca1 site modifies the electronic structure tuning the nanoscale structural heterogeneity. This mechanism may open a new route to optimizing the thermoelectric performance of misfit layered thermoelectrics. PMID:27181423

  3. Growth of thin, c-axis oriented Sr-doped LaP3O9 electrolyte membranes in condensed phosphoric acid solutions

    NASA Astrophysics Data System (ADS)

    Hatada, Naoyuki; Takahashi, Kota; Adachi, Yoshinobu; Uda, Tetsuya

    2016-08-01

    Proton-conducting Sr-doped LaP3O9 has potential application as electrolytes in intermediate temperature fuel cells, but reduction of the electrical resistance of the electrolyte membranes is necessary for practical applications. In this study, we focused on reducing the resistance by reducing the electrolyte thickness, while maintaining a preferable microstructure for proton conduction (c-axis orientation and absence of the small-crystal layer). Thin, c-axis oriented Sr-doped LaP3O9 membranes were successfully obtained in condensed phosphoric acid solutions by a novel "two-step precipitation method". In this method, Sr-doped LaP3O9 powder was artificially deposited on the surface of the carbon paper supports as seeds, and then columnar crystals were grown "downward" in the solutions. We expect that this method will be utilized to produce LaP3O9 electrolyte membranes with lower electrical resistance.

  4. Star Numbers and Constellations.

    ERIC Educational Resources Information Center

    Francis, Richard L.

    1993-01-01

    A number for which the number of digits categorizes the number is called a star number. A set of star numbers having a designated property is called a constellation. Discusses nature and cardinality of constellations made up of star square, star prime, star abundant, and star deficient numbers. Presents five related problems for exploration. (MDH)

  5. Point Defects and Protonic Conduction in A(3)(B'B"(2))O(9) Perovskite-Type Compounds

    NASA Astrophysics Data System (ADS)

    Du, Yang

    The defect structure and protonic transport properties of a number of rm A_3(B^' Nb_2)O_9 perovskite-type oxides, with A and B^' cations being alkaline earth elements, are investigated. The oxygen vacancies, V_sp{rm o}{ ^ddot}, are generated by nonstoichiometry which replaces a fraction of Nb^{5+ } ions by B^{'2+ } ions. Protons are then incorporated into the structure through the exchange reaction,. rm H_2O + V_sp {rm o}{^ddot} to O_sp{o}{x} + 2H^{.} by annealing the materials in moistened atmosphere. The protons can be removed by high temperature annealing in vacuum or in dry atmospheres. Impedance analysis is employed to extract the bulk electrical conductivity, sigma. The conductivity, sigma_{rm H}, of proton charged samples is more than an order of magnitude higher than samples without protons. Among the compounds studied, the H^+ charged samples of rm Ba_3(Ca_{1+3x }Nb_{2-3x})O_{9-delta } and rm Sr_3(Ca_ {1+3x}Nb_{2-3x})O_{9 -delta} show activation energy, E _{rm H}, of 0.52 ~ 0.55 eV and 0.64 ~ 0.66 eV, respectively, with sigma_ {rm H} comparable to those of the well-studied Nd^{3+}-doped BaCeO_3 and Yb^{3+ }-doped SrCeO_3. Without protons, the materials studied here are oxygen ion conductors with activation energy and conductivity compatible to Y -stablized ZrO_2. The ionic character of the dry samples is stable in a range of P_{o_2} over 18 orders of magnitude. As the number ratio of B site cations, B ^'/Nb, increases from 1/2, 1-1 ordered domains with B^'/Nb ~ 1 are created. The size and volume fraction of 1-1 ordered domains increases as B ^'/Nb approaches unity. The domain regions are rich in B^' and require positive ions, e.g. H^+ and V_sp{o}{2+}, for compensation. Internal friction peaks related to protons are observed in Nd^{3+}-doped BaCeO_3 but not in rm A_3(B^' Nb_2)O_9 compounds. Then pair-wise association of H ^+ or V_sp{o}{2+ } to specific sites in rm A_3(B ^' Nb_2)O_9 should not be considered. All compounds, showing considerable enhancement of

  6. Tomographic separation of composite spectra - The components of the O-star spectroscopic binary AO Cassiopeiae

    NASA Technical Reports Server (NTRS)

    Bagnuolo, William G., Jr.; Gies, Douglas R.

    1991-01-01

    The UV photospheric lines of the short-period, double-lined O-star spectroscopic binary AO Cas are analyzed. Archival data from IUE (16 spectra uniformly distributed in orbital phase) were analyzed with a tomography algorithm to produce the separate spectra of the two stars in six spectral regions. The spectral classifications of the primary and secondary, O9.5 III and O8 V, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. An intensity ratio of 0.5-0.7 (primary brighter) at 1600 A is compatible with the data.

  7. A novel tunable white light emitting multiphase phosphor obtained from Ba2TiP2O9 by introducing Eu3+

    NASA Astrophysics Data System (ADS)

    Zhou, Zhenzhen; Liu, Guanghui; Wan, Jieqiong; Ni, Jia; Lu, Zhouguang; Ma, Ruguang; Zhou, Yao; Wang, Jiacheng; Liu, Qian

    2016-04-01

    Tunable white light was realized in samples Ba2(1- x)TiP2O9:2 xEu ( x = 0-0.80) by introducing orange-red light emitting Eu3+ in self-activated blue-green light emitting matrix Ba2TiP2O9. The sample Ba2(1- x)TiP2O9:2 xEu is a multiphase system consisting of Ba2TiP2O9, EuPO4 and TiO2 when x is greater than or equal to 0.20. The tunable light from blue-green to bluish-white, to white, and eventually to pinky-white of samples Ba2(1- x)TiP2O9:2 xEu under UV light excitation is attributed to the light mixture of tunable blue-green light from Ti4+-O2- charge transfer transition in Ba2TiP2O9 and orange-red light from Eu3+ 4f-4f transition mostly in EuPO4. The Commission International de l'Eclairage chromaticity coordinates, correlated color temperature and color rendering index were tuned from (0.262, 0.339), 9492 K and 74 for matrix sample Ba2TiP2O9 to (0.324, 0.346), 5876 K and 87 for sample Ba2(1- x)TiP2O9:2 xEu ( x = 0.40) under UV light excitation. Therefore, a kind of promising UV-excited white light emitting multiphase phosphor was obtained.

  8. Sol-gel syntheses, luminescence, and energy transfer properties of α-GdB5O9:Ce(3+)/Tb(3+) phosphors.

    PubMed

    Sun, Xiaorui; Gao, Wenliang; Yang, Tao; Cong, Rihong

    2015-02-01

    Sol-gel method was applied to prepare homogenous and highly crystalline phosphors with the formulas α-GdB5O9:xTb(3+) (0 ≤ x ≤ 1), α-Gd1-xCexB5O9 (0 ≤ x ≤ 0.40), α-GdB5O9:xCe(3+), 0.30Tb(3+) (0 ≤ x ≤ 0.15) and α-GdB5O9:0.20Ce(3+), xTb(3+) (0 ≤ x ≤ 0.10). The success of the syntheses was proved by the linear shrinkage or expansion of the cell volumes against the substitution contents. In α-GdB5O9:xTb(3+), an efficient energy transfer from Gd(3+) to Tb(3+) was observed and there was no luminescence quenching. The exceptionally high efficiency of the f-f excitations of Tb(3+) implies that these phosphors may be good green-emitting UV-LED phosphors. For α-Gd1-xCexB5O9, Ce(3+) absorbs the majority of the energy and transfers it to Gd(3+). Therefore, the co-doping of Ce(3+) and Tb(3+) leads to a significant enhancement in the green emission of Tb(3+). Our current results together with the study on α-GdB5O9:xEu(3+) in the literature indicate that α-GdB5O9 is a good phosphor host with advantages including controllable preparation, diverse cationic doping, the absence of concentration quenching, and effective energy transfer. PMID:25532125

  9. Local Jahn-Teller distortions and orbital ordering in Ba3Cu1+xSb2-xO9 investigated by neutron scattering

    DOE PAGESBeta

    Li, Bing; Feygenson, Mikhail; Brown, Craig M.; Copley, John R. D.; Iida, Kazuki

    2016-01-15

    In this study, a spin-orbital quantum liquid state is theoretically proposed in the honeycomb lattice of Ba3CuSb2O9, enabled by dynamic short-range correlations between the spin and orbital degrees of freedom. Using neutron diffraction, the local atomic structure of Ba3Cu1+xSb2-xO9 at x = 0 and 0.1 is obtained via the pair density function analysis. The results indicate that both compositions exhibit local Jahn-Teller (JT) distortions with the elongated CuO3 octahedral configuration. In Ba3Cu1.1Sb1.9O9, JT ordering of the distorted CuO3 octahedra gives rise to the orthorhombic symmetry with ferro-orbital order. On the other hand, in Ba3CuSb2O9, even though the CuO3 octahedra aremore » JT distorted, there is no long-range ordering hence the symmetry is hexagonal. Furthermore, the local singlet excitation at 5.8 meV observed in Ba3CuSb2O9 below 50 K is absent in Ba3Cu1.1Sb1.9O9. Instead, an excitation at 2.5 meV is observed in the latter, which is likely associated with short-range spin order.« less

  10. Local Jahn-Teller distortions and orbital ordering in Ba3Cu1 +xSb2 -xO9 investigated by neutron scattering

    NASA Astrophysics Data System (ADS)

    Li, Bing; Louca, Despina; Feygenson, Mikhail; Brown, Craig M.; Copley, John R. D.; Iida, Kazuki

    2016-01-01

    A spin-orbital quantum liquid state is theoretically proposed in the honeycomb lattice of Ba3CuSb2O9 , enabled by dynamic short-range correlations between the spin and orbital degrees of freedom. Using neutron diffraction, the local atomic structure of Ba3Cu1 +xSb2 -xO9 at x =0 and 0.1 is obtained via the pair density function analysis. The results indicate that both compositions exhibit local Jahn-Teller (JT) distortions with the elongated CuO3 octahedral configuration. In Ba3Cu1.1Sb1.9O9 , JT ordering of the distorted CuO3 octahedra gives rise to the orthorhombic symmetry with ferro-orbital order. On the other hand, in Ba3CuSb2O9 , even though the CuO3 octahedra are JT distorted, there is no long-range ordering hence the symmetry is hexagonal. Furthermore, the local singlet excitation at 5.8 meV observed in Ba3CuSb2O9 below 50 K is absent in Ba3Cu1.1Sb1.9O9 . Instead, an excitation at 2.5 meV is observed in the latter, which is likely associated with short-range spin order.

  11. Local Jahn-Teller distortions and orbital ordering in Ba3Cu1+xSb2-xO9 investigated by neutron scattering

    SciTech Connect

    Li, Bing; Feygenson, Mikhail; Brown, Craig; Copley, John R. D.; Iida, Kazuki

    2016-01-01

    A spin-orbital quantum liquid state is theoretically proposed in the honeycomb lattice of Ba3CuSb2O9, enabled by dynamic short-range correlations between the spin and orbital degrees of freedom. Using neutron diffraction, the local atomic structure of Ba3Cu1+xSb2-xO9 at x = 0 and 0.1 is obtained via the pair density function analysis. The results indicate that both compositions exhibit local Jahn-Teller (JT) distortions with the elongated CuO3 octahedral configuration. In Ba3Cu1.1Sb1.9O9, JT ordering of the distorted CuO3 octahedra gives rise to the orthorhombic symmetry with ferro-orbital order. On the other hand, in Ba3CuSb2O9, even though the CuO3 octahedra are JT distorted, there is no long-range ordering hence the symmetry is hexagonal. Furthermore, the local singlet excitation at 5.8 meV observed in Ba3CuSb2O9 below 50 K is absent in Ba3Cu1.1Sb1.9O9. Instead, an excitation at 2.5 meV is observed in the latter, which is likely associated with short-range spin order.

  12. THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS). II. BRIGHT SOUTHERN STARS

    SciTech Connect

    Sota, A.; Apellániz, J. Maíz; Alfaro, E. J.; Barbá, R. H.; Arias, J. I.; Walborn, N. R.; Gamen, R. C.

    2014-03-01

    We present the second installment of GOSSS, a massive spectroscopic survey of Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ∼ 2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog (GOSC). In this paper we include bright stars and other objects drawn mostly from the first version of GOSC, all of them south of δ = –20°, for a total number of 258 O stars. We also revise the northern sample of Paper I to provide the full list of spectroscopically classified Galactic O stars complete to B = 8, bringing the total number of published GOSSS stars to 448. Extensive sequences of exceptional objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is also discussed. The magnitude and spatial distributions of the observed sample are analyzed. We also present new results from OWN, a multi-epoch high-resolution spectroscopic survey coordinated with GOSSS that is assembling the largest sample of Galactic spectroscopic massive binaries ever attained. The OWN data combined with additional information on spectroscopic and visual binaries from the literature indicate that only a very small fraction (if any) of the stars with masses above 15-20 M {sub ☉} are born as single systems. In the future we will publish the rest of the GOSSS survey, which is expected to include over 1000 Galactic O stars.

  13. Converting neutron stars into strange stars

    NASA Technical Reports Server (NTRS)

    Olinto, A. V.

    1991-01-01

    If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

  14. Christmas star.

    NASA Astrophysics Data System (ADS)

    Biała, J.

    There are continuous attempts to identify the legendary Christmas Star with a real astronomical event accompanying the birth of Jesus from Nazareth. Unfortunately, the date of birth is difficult to establish on the basis of historical records with better accuracy than a few years. During that period a number of peculiar astronomical events were observed and it seem to be impossible to identify the right one unambiguously.

  15. Symbiotic Stars

    NASA Astrophysics Data System (ADS)

    Munari, U.

    2012-06-01

    Symbiotic stars are interacting binary systems composed of a white dwarf (WD) accreting at high rate from a cool giant companion, which frequently fills its Roche lobe. The WD usually is extremely hot and luminous, and able to ionize a sizeable fraction of the cool giant wind, because it is believed the WD undergoes stable hydrogen nuclear burning on its surface of the material accreted from the companion. This leads to consider symbiotic stars as good candidates for the yet-to-be-identified progenitors of type Ia supernovae. Symbiotic stars display the simultaneous presence of many different types of variability, induced by the cool giant, the accreting WD, the circumstellar dust and ionized gas, with time scales ranging from seconds to decades. The long orbital periods (typically a couple of years) and complex outburst patterns, lasting from a few years to a century, make observations from professionals almost impossible to carry out, and open great opportunities to amateur astronomers to contribute fundamental data to science.

  16. Exceptional Stars

    NASA Astrophysics Data System (ADS)

    Kulkarni, S. R.; Hansen, B.; van Kerkwijk, M.; Phinney, E. S.

    2005-12-01

    As part of our Interdisciplinary Scientist effort (PI, Kulkarni) for the Space Interferometry Mission (SIM) we proposed an investigation with SIM of a number of exceptional stars. With SIM we plan to observe dozens of nearby white dwarfs and search for planets surviving the evolution away from the main sequence as well as (newly formed) planets formed in the circumbinary disks of post-AGB binaries or as a result of white dwarf mergers. We propose to measure the proper motion of a sample of X-ray binaries and Be star binaries with the view of understanding the originof high latitude objects and inferring natal kicks and pre-supernova orbits. We plan to observe several compact object binaries to determine the mass of the compact star. Of particular importance is the proposed observation of SS 433 (for which we propose to use the spectrometer on SIM to measure the proper motion of the emission line clumps embedded in the relativistic jets). Separately we are investigating the issue of frame tie between SIM and the ecliptic frame (by observing binary millisecond pulsars with SIM; the position of these objects is very well determined by pulsar timing) and the degree to which highly precise visibility amplitude measurements can be inverted to infer binary parameters.

  17. A facile approach to pure-phase Bi2Fe4O9 nanoparticles sensitive to visible light

    NASA Astrophysics Data System (ADS)

    Wang, X.; Zhang, M.; Tian, P.; Chin, W. S.; Zhang, C. M.

    2014-12-01

    Pure-phase Bi2Fe4O9 nanoparticles with mullite-type structure were successfully fabricated through a facile and environmentally benign sol-gel process. According to the UV-Vis diffuse reflection spectrum, the multiband structure and the band edge position of the nanoparticles were confirmed, indicating the prominent absorption in the expanded visible-light region. As compared to the bulk, the visible-light-driven photocatalytic activity of the obtained nanoparticles was improved by 30-fold. The much improved photocatalytic efficiency of the sample mainly owed to the small crystal size and the multiband characteristic as well as the adding of H2O2 as electron scavenger and a source of hydroxide free radicals instead of Fenton-like reaction, leading to a low recombination of the photogenerated e-/h+ pairs.

  18. Highly localized strain fields due to planar defects in epitaxial SrBi2Nb2O9 thin films

    NASA Astrophysics Data System (ADS)

    Boulle, A.; Guinebretière, R.; Dauger, A.

    2005-04-01

    Thin films of (00l) oriented SrBi2Nb2O9 epitaxially grown on SrTiO3 by sol-gel spin coating have been studied by means of high-resolution x-ray diffraction reciprocal space mapping. It is shown that these materials contain highly localized heterogeneous strain fields due to imperfect stacking faults (i.e., faults that do not propagate throughout the crystallites building up the film). In the film plane, the strain fields are confined to 11 nm wide regions and characterized by a vertical displacement of 0.18c (where c is the cell parameter) showing that the stacking faults are mainly composed of one additional (or missing) perovskite layer. Prolonged thermal annealing at 700 °C strongly reduces the density of stacking faults and yields a more uniform strain distribution within the film volume without inducing significant grain growth.

  19. Efficient Microwave-Assisted Functionalization of the Aurivillius-Phase Bi2SrTa2O9.

    PubMed

    Wang, Yanhui; Delahaye, Emilie; Leuvrey, Cédric; Leroux, Fabrice; Rabu, Pierre; Rogez, Guillaume

    2016-04-18

    A new method of acidification and subsequent functionalization of the Aurivillius-phase Bi2SrTa2O9 (BST), using microwave irradiation, was developed. This method enables to obtain hybridized phases from layered BST. Functionalization of BST by various kinds of amines and diamines can be achieved in a few hours only, compared to much longer time (over a week) using conventional heating. Good crystallinity of the compounds is kept. In addition, a microwave-assisted preintercalation strategy was developed, allowing inserting new amines (bearing cyclic or aromatic groups) between the oxide layers previously unseen in this type of compound. This work opens new perspectives for the fast and easy functionalization of layered oxides with more elaborated molecules. PMID:27042754

  20. Ferroelectric properties of lead-free polycrystalline CaBi2Nb2O9 thin films on glass substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Jang, Joonkyung; Son, Jong Yeog

    2016-03-01

    CaBi2Nb2O9 (CBNO) thin film, a lead-free ferroelectric material, was prepared on a Pt/Ta/glass substrate via pulsed laser deposition. The Ta film was deposited on the glass substrate for a buffer layer. A (115) preferred orientation of the polycrystalline CBNO thin film was verified via X-ray diffraction measurements. The CBNO thin film on a glass substrate exhibited good ferroelectric properties with a remnant polarization of 4.8 μC/cm2 (2Pr ˜9.6 μC/cm2), although it had lower polarization than the epitaxially c-oriented CBNO thin film reported previously. A mosaic-like ferroelectric domain structure was observed via piezoresponse force microscopy. Significantly, the polycrystalline CBNO thin film showed much faster switching behavior within about 100 ns than that of the epitaxially c-oriented CBNO thin film.

  1. Ordering of calcium and vacancies in calcium catapleiite CaZr[Si3O9] • 2H2O

    NASA Astrophysics Data System (ADS)

    Aksenov, S. M.; Portnov, A. M.; Chukanov, N. V.; Rastsvetaeva, R. K.; Nelyubina, Yu. V.; Kononkova, N. N.; Akimenko, M. I.

    2016-05-01

    A sample of holotypic calcium catapleiite from the Burpala alkaline massif (Northern Baikal, Russia) is studied by single crystal X-ray analysis at 120 K and IR spectroscopy. The empirical formula of calcium catapleiite is Ca0.97Na0.02Zr1.01Si3O9 • 2H2O ( Z = 4). The X-ray diffraction study confirms the orthorhombic unit cell with the following parameters: a = 7.406(1), b = 12.687(1), and c = 10.112(1) Å; V = 950.1(2) Å3; space group Pbnn. The crystal structure is refined in the anisotropic approximation of atomic displacement parameters using 1177 reflections with I > 2σ( I) to the final R = 2.91%. The structure of calcium catapleiite under study is based on the microporous heteropolyhedral framework formed by ZrO6 octahedra and threemembered silicon-oxygen rings [Si3O9]. It is on the whole analogous to the structures of the samples studied earlier, but differs from them by a high degree of ordering of calcium and vacancies at extraframework positions. The distribution of calcium over Ca1 and Ca2 positions in the calcium catapleiite structure leads to the formation of zigzag chains of the …Ca1-Zr-Ca1-Zr… and …Ca2-h-Ca2-□… types. Low occupancy of the Ca2 position and its alternation with the vacancy are prerequisites for potential Ca2+ cationic conduction.

  2. Star ratings. Stars of wonder.

    PubMed

    Dawes, David

    2002-09-12

    Analysis of trusts that changed their star-rating over the past two years indicates that a change of chief executive was not a significant factor. The length of time in post and the experience of the chief executive were also insignificant. This has serious implications for the theory behind franchising and the evaluation of franchised trusts. Holding chief executives to account for the organisation's performance within their first 12 months is unlikely to be effective. PMID:12357738

  3. Biaxial crystal α-BaTeMo(2)O(9): theory study of large birefringence and wide-band polarized prisms design.

    PubMed

    Gao, Z L; Wu, Q; Liu, X T; Sun, Y X; Tao, X T

    2015-02-23

    α-BaTeMo(2)O(9) is a novel biaxial crystal with wide-band transmittance spectrum. The refractive index dispersion curves and birefringence of the α-BaTeMo(2)O(9) crystal were obtained in spectral range of 0.4~5 μm. The origin of the birefringence for the crystal has been calculated and interpreted on the basis of the crystal structure combined with theoretical studies. The polarized directions and formulations of refractive index of optical waves in biaxial α-BaTeMo(2)O(9) were investigated by solving the refractive index ellipsoid equations. Furthermore, polarized prisms based on the α-BaTeMo(2)O(9) crystal used in spectral ranges of 0.4~2.7 μm and 0.48~4.5 μm were designed and characterized. The extinction ratios of both prisms were determined to be larger than 10000:1, which would satisfy the practical requirements. The impacts on extinction ratio for biaxial and uniaxial crystals were also discussed. To our knowledge, it is the first report about biaxial crystals for the polarized prisms, and the results show that the α-BaTeMo(2)O(9) crystal is a promising material for polarized optical components, especially in the range of 3~5 μm. PMID:25836424

  4. One-step preparation of carbon nanotubes doped mesoporous birnessite K2Mn4O9 achieving 77% of theoretical capacitance by a facile redox reaction

    NASA Astrophysics Data System (ADS)

    Kang, Litao; Li, Peiyang; Tao, Keyu; Wang, Xiaomin; Liang, Wei; Gao, Yanfeng

    2016-01-01

    A facile, scalable and cost-efficient redox reaction is developed to prepare micro-powders of a quasi-crystallised, mesoporous birnessite-type manganese oxide, K2Mn4O9. In 1 M KOH electrolyte, the K2Mn4O9 powder shows a high specific capacitance of 754 F g-1 at 1 A g-1 (calculated with the net weight of K2Mn4O9 micro-powder only). Meanwhile, the electrode retains 91% of its initial capacitance after 5000 cycles at a high current density of 5 A g-1. By simply adding carbon nanotubes (CNTs) into the reaction system, the specific capacitances of as-prepared K2Mn4O9/CNTs composites are further increased to 929 and 1055 F g-1 at 1 A g-1 in 1 and 6 M KOH electrolyte (corresponding to 69 and 77% of the theoretical capacitance of MnO2), or 600 and 674 F g-1 at 5 A g-1, respectively. Significantly, a maximum energy density of 62 Wh kg-1 at a power density of 852 W kg-1 could be achieved based on a K2Mn4O9/CNTs//activated carbon asymmetric supercapacitor (ASC). At the same time, the ASC device exhibits a decent long cycle life with 85% specific capacitance retained after 1000 cycles, suggesting its wide application potential in low-cost high energy density storage systems.

  5. A novel hexanuclear titanium(iv)-oxo-iminodiacetate cluster with a Ti6O9 core: single-crystal structure and photocatalytic activities.

    PubMed

    Ni, Lubin; Liang, Dashuai; Cai, Yin; Diao, Guowang; Zhou, Zhaohui

    2016-05-01

    A new family of hexanuclear titanium(iv)-oxo-carboxylate cluster K7H[Ti6O9(ida)6]Cl2·13H2O {Ti6O9} has been synthesized via the H2O2-assisted reaction between TiCl4 and iminodiacetate ligands. This cluster was fully characterized by single-crystal X-ray diffraction and a wide range of analytical methods, including FT-IR, UV/vis spectroscopy as well as electrochemistry and thermogravimetric analysis. As a new type of carboxylate substituted Ti-oxo-cluster, the structural motif of the {Ti6O9} cluster consists of one symmetric {Ti6O6} hexagonal prism with two staggered triangular {Ti3O3} subunits linked by three μ2-O bridges. The {Ti6O9} polyanions are linked by K(+) cations to form a novel 3D architecture. The structural information and stability of the {Ti6O9} polyanion in aqueous solution were thoroughly investigated by solid-state/solution NMR, ESI-MS spectroscopy. Moreover, this Ti-oxo cluster exhibits remarkable potential as a visible-light homogeneous photocatalyst for degradation of rhodamine B (RhB). Finally, a proposed peroxotitanium(iv)-mediated photocatalytic pathway involved is illustrated by spectroscopic data. PMID:26857945

  6. Binary stars.

    PubMed

    Paczynacuteski, B

    1984-07-20

    Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars. PMID:17749544

  7. Eutactic star closest to a given star

    SciTech Connect

    Gomez, A.; Torres, M.; Aragon, J. L.

    2007-05-15

    A eutactic star is a set of M vectors in R{sup n} (M>n) that are projections of M orthogonal vectors in R{sup M}. Eutactic stars have remarkable properties that have been exploited in several fields such as crystallography, graph theory, wavelets, and quantum measurement theory. In this work we show that given an arbitrary star of vectors, there exists a closest eutactic star in the Frobenius norm. An algorithm for calculating this star is presented. Additionally, the distance between both stars provides a new measure of eutacticity.

  8. Lighting up stars in chemical evolution models: the CMD of Sculptor

    NASA Astrophysics Data System (ADS)

    Vincenzo, F.; Matteucci, F.; de Boer, T. J. L.; Cignoni, M.; Tosi, M.

    2016-08-01

    We present a novel approach to draw the synthetic color-magnitude diagram of galaxies, which can provide - in principle - a deeper insight in the interpretation and understanding of current observations. In particular, we `light up' the stars of chemical evolution models, according to their initial mass, metallicity and age, to eventually understand how the assumed underlying galaxy formation and evolution scenario affects the final configuration of the synthetic CMD. In this way, we obtain a new set of observational constraints for chemical evolution models beyond the usual photospheric chemical abundances. The strength of our method resides in the very fine grid of metallicities and ages of the assumed database of stellar isochrones. In this work, we apply our photo-chemical model to reproduce the observed CMD of the Sculptor dSph and find that we can reproduce the main features of the observed CMD. The main discrepancies are found at fainter magnitudes in the main sequence turn-off and sub-giant branch, where the observed CMD extends towards bluer colors than the synthetic one; we suggest that this is a signature of metal-poor stellar populations in the data, which cannot be captured by our assumed one-zone chemical evolution model.

  9. Lighting up stars in chemical evolution models: the CMD of Sculptor

    NASA Astrophysics Data System (ADS)

    Vincenzo, F.; Matteucci, F.; de Boer, T. J. L.; Cignoni, M.; Tosi, M.

    2016-08-01

    We present a novel approach to draw the synthetic colour-magnitude diagram (CMD) of galaxies, which can provide - in principle - a deeper insight in the interpretation and understanding of current observations. In particular, we `light up' the stars of chemical evolution models, according to their initial mass, metallicity and age, to eventually understand how the assumed underlying galaxy formation and evolution scenario affects the final configuration of the synthetic CMD. In this way, we obtain a new set of observational constraints for chemical evolution models beyond the usual photospheric chemical abundances. The strength of our method resides in the very fine grid of metallicities and ages of the assumed data base of stellar isochrones. In this work, we apply our photochemical model to reproduce the observed CMD of the Sculptor dSph and find that we can reproduce the main features of the observed CMD. The main discrepancies are found at fainter magnitudes in the main sequence turn-off and sub-giant branch, where the observed CMD extends towards bluer colours than the synthetic one; we suggest that this is a signature of metal-poor stellar populations in the data, which cannot be captured by our assumed one-zone chemical evolution model.

  10. On the kinematic separation of field and cluster stars across the bulge globular NGC 6528

    SciTech Connect

    Lagioia, E. P.; Bono, G.; Buonanno, R.; Milone, A. P.; Stetson, P. B.; Prada Moroni, P. G.; Dall'Ora, M.; Aparicio, A.; Monelli, M.; Calamida, A.; Ferraro, I.; Iannicola, G.; Gilmozzi, R.; Matsunaga, N.; Walker, A.

    2014-02-10

    We present deep and precise multi-band photometry of the Galactic bulge globular cluster NGC 6528. The current data set includes optical and near-infrared images collected with ACS/WFC, WFC3/UVIS, and WFC3/IR on board the Hubble Space Telescope. The images cover a time interval of almost 10 yr, and we have been able to carry out a proper-motion separation between cluster and field stars. We performed a detailed comparison in the m {sub F814W}, m {sub F606W} – m {sub F814W} color-magnitude diagram with two empirical calibrators observed in the same bands. We found that NGC 6528 is coeval with and more metal-rich than 47 Tuc. Moreover, it appears older and more metal-poor than the super-metal-rich open cluster NGC 6791. The current evidence is supported by several diagnostics (red horizontal branch, red giant branch bump, shape of the sub-giant branch, slope of the main sequence) that are minimally affected by uncertainties in reddening and distance. We fit the optical observations with theoretical isochrones based on a scaled-solar chemical mixture and found an age of 11 ± 1 Gyr and an iron abundance slightly above solar ([Fe/H] = +0.20). The iron abundance and the old cluster age further support the recent spectroscopic findings suggesting a rapid chemical enrichment of the Galactic bulge.

  11. Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba_{3}ZnIr_{2}O_{9}.

    PubMed

    Nag, Abhishek; Middey, S; Bhowal, Sayantika; Panda, S K; Mathieu, Roland; Orain, J C; Bert, F; Mendels, P; Freeman, P G; Mansson, M; Ronnow, H M; Telling, M; Biswas, P K; Sheptyakov, D; Kaushik, S D; Siruguri, Vasudeva; Meneghini, Carlo; Sarma, D D; Dasgupta, Indra; Ray, Sugata

    2016-03-01

    We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba_{3}ZnIr_{2}O_{9} is a realization of a novel spin-orbital liquid state. Our results reveal that Ba_{3}ZnIr_{2}O_{9} with Ir^{5+} (5d^{4}) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J=0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir_{2}O_{9} dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK. PMID:26991199

  12. Origin of the Spin-Orbital Liquid State in a Nearly J =0 Iridate Ba3ZnIr2O9

    NASA Astrophysics Data System (ADS)

    Nag, Abhishek; Middey, S.; Bhowal, Sayantika; Panda, S. K.; Mathieu, Roland; Orain, J. C.; Bert, F.; Mendels, P.; Freeman, P. G.; Mansson, M.; Ronnow, H. M.; Telling, M.; Biswas, P. K.; Sheptyakov, D.; Kaushik, S. D.; Siruguri, Vasudeva; Meneghini, Carlo; Sarma, D. D.; Dasgupta, Indra; Ray, Sugata

    2016-03-01

    We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5 + (5 d4) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J =0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

  13. Star formation - An overview

    NASA Technical Reports Server (NTRS)

    Evans, N. J., II

    1985-01-01

    Methods for studying star formation are reviewed. Stellar clusters and associations, as well as field stars, provide a fossil record of the star formation process. Regions of current star formation provide a series of snapshots of different epochs of star formation. A simplified picture of individual star formation as it was envisioned in the late 1970s is contrasted with the results of recent observations, in particular the outflow phenomenon.

  14. Center-to-limb variation of intensity and polarization in continuum spectra of FGK stars for spherical atmospheres

    NASA Astrophysics Data System (ADS)

    Kostogryz, N. M.; Milic, I.; Berdyugina, S. V.; Hauschildt, P. H.

    2016-02-01

    Aims: One of the necessary parameters needed for the interpretation of the light curves of transiting exoplanets or eclipsing binary stars (as well as interferometric measurements of a star or microlensing events) is how the intensity and polarization of light changes from the center to the limb of a star. Scattering and absorption processes in the stellar atmosphere affect both the center-to-limb variation of intensity (CLVI) and polarization (CLVP). In this paper, we present a study of the CLVI and CLVP in continuum spectra, taking into consideration the different contributions of scattering and absorption opacity for a variety of spectral type stars with spherical atmospheres. Methods: We solve the radiative transfer equation for polarized light in the presence of a continuum scattering, taking into consideration the spherical model of a stellar atmosphere. To cross-check our results, we developed two independent codes that are based on Feautrier and short characteristics methods, respectively, Results: We calculate the center-to-limb variation of intensity (CLVI) and polarization (CLVP) in continuum for the Phoenix grid of spherical stellar model atmospheres for a range of effective temperatures (4000-7000 K), gravities (log g = 1.0-5.5), and wavelengths (4000-7000 Å), which are tabulated and available at the CDS. In addition, we present several tests of our codes and compare our calculations for the solar atmosphere with published photometric and polarimetric measurements. We also show that our two codes provide similar results in all considered cases. Conclusions: For sub-giant and dwarf stars (log g = 3.0-4.5), the lower gravity and lower effective temperature of a star lead to higher limb polarization of the star. For giant and supergiant stars (log g = 1.0-2.5), the highest effective temperature yields the largest polarization. By decreasing the effective temperature of a star down to 4500-5500 K (depending on log g), the limb polarization decreases and

  15. Near-infrared luminescence and color tunable chromophores based on Cr(3+)-doped mullite-type Bi2(Ga,Al)4O9 solid solutions.

    PubMed

    Liu, Chengyin; Xia, Zhiguo; Chen, Mingyue; Molokeev, Maxim S; Liu, Quanlin

    2015-02-16

    Cr(3+)-activated mullite-type Bi2Ga(4-x)Al(x)O9 (x = 0, 1, 2, 3, and 4) solid solutions were prepared by the solid state reaction, and their spectroscopic properties were investigated in conjunction with the structural evolution. Under excitation at 610 nm, Bi2[Ga(4-y)Al(y)]3.97O9:0.03Cr(3+) (y = 0, 1, 2, 3, and 4) phosphors exhibited broad-band near-infrared (NIR) emission peaking at ∼710 nm in the range 650-850 nm, and the optimum Cr(3+) concentrations and concentration quenching mechanism were determined. Except for the interesting NIR emission, the body color changed from white (at x = 0) to green (at x = 0.08) for Bi2Ga(4-x)O9:xCr(3+), and from light yellow (at x = 0) to deep brown (at x = 0.08) for Bi2Al(4-x)O9:xCr(3+), respectively. Moreover, as a result of variable Al/Ga ratio, the observed body color for Bi2[Ga(4-y)Al(y)]3.97O9:0.03Cr(3+) (y = 0, 1, 2, 3, and 4) varied from deep brown to green. The relationship between the observed colors and their diffuse reflectance spectra were also studied for the understanding of the different absorption bands. The results indicated that Cr(3+)-doped Bi2Ga(4-x)Al(x)O9 solid solutions appeared as the bifunctional materials with NIR phosphors and color-tunable pigments. PMID:25622046

  16. Asteroseismic Fundamental Properties of Solar-type Stars Observed by the NASA Kepler Mission

    NASA Astrophysics Data System (ADS)

    Chaplin, W. J.; Basu, S.; Huber, D.; Serenelli, A.; Casagrande, L.; Silva Aguirre, V.; Ball, W. H.; Creevey, O. L.; Gizon, L.; Handberg, R.; Karoff, C.; Lutz, R.; Marques, J. P.; Miglio, A.; Stello, D.; Suran, M. D.; Pricopi, D.; Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Molenda-Żakowicz, J.; Appourchaux, T.; Christensen-Dalsgaard, J.; Elsworth, Y.; García, R. A.; Houdek, G.; Kjeldsen, H.; Bonanno, A.; Campante, T. L.; Corsaro, E.; Gaulme, P.; Hekker, S.; Mathur, S.; Mosser, B.; Régulo, C.; Salabert, D.

    2014-01-01

    We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental properties of more than 500 main-sequence and sub-giant stars. Data obtained during the first 10 months of Kepler science operations were used for this work, when these solar-type targets were observed for one month each in survey mode. Stellar properties have been estimated using two global asteroseismic parameters and complementary photometric and spectroscopic data. Homogeneous sets of effective temperatures, T eff, were available for the entire ensemble from complementary photometry; spectroscopic estimates of T eff and [Fe/H] were available from a homogeneous analysis of ground-based data on a subset of 87 stars. We adopt a grid-based analysis, coupling six pipeline codes to 11 stellar evolutionary grids. Through use of these different grid-pipeline combinations we allow implicitly for the impact on the results of stellar model dependencies from commonly used grids, and differences in adopted pipeline methodologies. By using just two global parameters as the seismic inputs we are able to perform a homogenous analysis of all solar-type stars in the asteroseismic cohort, including many targets for which it would not be possible to provide robust estimates of individual oscillation frequencies (due to a combination of low signal-to-noise ratio and short dataset lengths). The median final quoted uncertainties from consolidation of the grid-based analyses are for the full ensemble (spectroscopic subset) approximately 10.8% (5.4%) in mass, 4.4% (2.2%) in radius, 0.017 dex (0.010 dex) in log g, and 4.3% (2.8%) in mean density. Around 36% (57%) of the stars have final age uncertainties smaller than 1 Gyr. These ages will be useful for ensemble studies, but should be treated carefully on a star-by-star basis. Future analyses using individual oscillation frequencies will offer significant improvements on up to 150 stars, in particular for estimates of the ages, where having the

  17. [Study on the Preparation of Ba3Si6O9N4 : Eu(2+) Phosphor and the Characterization of Their Luminescence Properties].

    PubMed

    Pan, Hua-yan; Wang, Le; Luo, Dong; Li, Yang-hui; Zhang, Hong; Shen, Ye

    2016-03-01

    Ba3Si6O9N4 : Eu(2+) phosphors were synthesized by two-step synthesis processes based on high temperature solid phase using BaSiO3 as a precursor. The influence mechanism of the Eu(2+) doping concentration to the luminescence properties of Ba3Si6O9N4 : Eu(2+) phosphors were mainly investigated. This paper made a comparison between the luminescence properties of Ba3Si6ON4 : Eu(2+) phosphors prepared by two-step processes and solid- state reaction method. The results showed that the Ba3Si6O9N4 : Eu(3+) phosphors synthesized by two-step processes had higher purity and higher crystallinity. There exists concentration quenching in Ba3Si6O9N4 : Eu(2+) phosphors for both two-step processes and solid-state reaction when the doping concentration x is more than 9%. Both the concentration quenching mechanism of Ba3 Si 09 N4 : EuI+ phosphor prepared by solid-state reaction and two-step processes is electric dipole-dipole interaction. The emission peak of Ba3Si6O9N4 : Eu(2+) phosphors (peak 489 nm) prepared by two-step processes had a blue shift compared to the emission peak of Ba3Si6O9N4 : Eu2+ phosphors (peak 512nm) prepared by solid-state reaction. The emission peak of Ba3Si6O9N4 : Eu2+ phosphors prepared by two-step processes relatively close to the theoretical value (480 nm). The spectrum analysis result showed that the element component of Ba3Si6O3N4 : Eu2+ phosphors prepared by two-step processes was closer to the theoretical value, it means that the two-step processes can effectively reduce the lattice defects. The Ba3Si6O9N4 : Eu(2+) phosphors synthesized by two-step processes had better thermal stability, which demonstrates to be a highly promising phosphor for white-LED applications. PMID:27400500

  18. Studies of dielectric characteristics of BaBi 2Nb 2O 9 ferroelectrics prepared by chemical precursor decomposition method

    NASA Astrophysics Data System (ADS)

    Debasis, Dhak; Tanmay, Ghorai K.; Panchanan, Pramanik

    2007-01-01

    BaBiNb 2O 9 (BBN) powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). TG-DTA showed that precursor sample got freed from organic contaminants at 575 °C. XRD showed that a single phase with the layered perovskite structure of BBN was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size ( D) and the effective strain ( η) were found to be 26 nm and 0.000867, respectively, while the particle size obtained from TEM was 28 ± 2 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was ˜1.67 μm. A relative density of ˜93% was obtained using a two-step sintering process at moderate pressure. Dielectric and ferroelectric properties were investigated in the temperature range 50-500 °C and frequencies from 1 kHz to 5 MHz. Strong dispersion of the complex relative dielectric constant was observed including typical relaxor features such as shift of permittivity maximum with frequency and broadening of the peak maximum. The high dielectric constant of 545 measured at 100 kHz and other properties of BBN ceramics were compared to that of BBN prepared by other conventional methods and found to be superior.

  19. Model experiments to establish behaviour of Yersinia enterocolitica O: 9 strains in various types of fresh dry sausage.

    PubMed

    Kleemann, J; Bergann, T

    1996-01-01

    In model experiments different kinds of raw sausages were inoculated with liquid cultures of virulent-plasmid-carrying clinical Yersinia (Y.) enterocolitica (e.) strains of the O: 9 serotype, doses being between 10(4) and 10(5) cfu g-1. The sausage samples were stored at 3-5 degrees C and 13-16 degrees C. During the first 10 d of storage the Y.e. plate count was detected with Desoxycholate-Citrate-Lactose-Sucrose Agar every day, later on in addition to it with phosphate buffer-enrichment and with enrichment according to Schiemann (1982) in intervals of several days' duration. The pH and aw values, the contents of salt and water were detected. The multitude of complexly acting factors and substances prevents obviously the proliferation of Y.e. in fresh dry sausages. Decay dynamics of Y.e. were found to be considerably affected by storage temperature. Cold storage, basically, had a conservation effect and thus delayed the dying process of model strains. Yersinia enterocolitica-contaminated fresh dry sausage may cause potential danger to consumers, because of relatively extended survival periods of the pathogen. Therefore, manufacturers are expected to observe most stringent hygienic rules of Good Manufacturing Practice. PMID:8698649

  20. Ionic conductivity and dielectric relaxation in Y doped La2Mo2O9 oxide-ion conductors

    NASA Astrophysics Data System (ADS)

    Paul, T.; Ghosh, A.

    2014-10-01

    In this work, we have studied electrical conductivity and dielectric properties of polycrystalline La2-xYxMo2O9 (0.05 ≤ x ≤ 0.3) compounds in the temperature range from 358 K to 1088 K and the frequency range from 10 Hz to 3 GHz. The bulk and grain boundary contributions to the overall conductivity of these compounds show Arrhenius type behavior at low temperatures. The random free-energy barrier model has been used to analyze the frequency dependence of the conductivity. The charge carrier relaxation time and its activation energy have been determined from the analysis of the conductivity spectra using this model. The results obtained from the random free-energy barrier model satisfy Barton-Nakajima-Namikawa relation. The conduction mechanism has been also predicted using random free-energy barrier model and the scaling formalism. We have observed that the dielectric relaxation peaks arise from the diffusion of oxygen ions via vacancies.

  1. Magnetic and ESR studies in a Quasi-two-dimensional Triangular magnet Ba3MnNb2O9

    NASA Astrophysics Data System (ADS)

    Tian, Zhaoming; Guo, Qian; Ouyang, Zhongwen; Du, Guihuan; Tong, Wei; Wang, Junfeng; Yuan, Songliu

    2014-08-01

    We report the magnetic, specific heat and electron spin resonance (ESR) studies on Ba3MnNb2O9, as one of quasi-two-dimensional triangula-lattice magnet. The magnetic susceptibility and specific heat measurement show that it undergoes an magnetic transition at TN=3.2 K. The magnetic capacity (Cmag) follows T2 dependence, and magnetic entropy (Smag) reaching to 14.5 J K-1mol-1 at 32 K satisfactorily agrees with the theoretical estimations of Mn2+ ion in high-spin configuration with S=5/2. From the ESR spectra, the Landé factor (geff), the linewidth (ΔHpp) and the ESR intensity (I) are derived and analyzed as a function of temperature. As temperature decreases to T*~18 K, the g-factor shows a minima with geff=1.984(2) before shifts to larger value at lower temperatures, and the ESR intensity starts to be suppressed below this temperature. This anomalous phenomenon is explained in terms of the establishment of short-range AFM spin correlations at much higher temperatures above TN.

  2. Electronic structure and spin-orbit driven magnetism in d4.5 insulator Ba3YIr2O9

    NASA Astrophysics Data System (ADS)

    Panda, S. K.; Bhowal, S.; Li, Ying; Ganguly, S.; Valentí, Roser; Nordström, L.; Dasgupta, I.

    2015-11-01

    We have carried out a detailed first-principles study of a d4.5 quaternary iridate Ba3YIr2O9 both in its 6H-perovskite-type ambient pressure (AP) phase and also for the high pressure (HP) cubic phase. Our analysis reveals that the AP phase belongs to the intermediate spin-orbit coupling (SOC) regime. This is further supported by the identification of the spin moment as the primary order parameter (POP) obtained from a magnetic multipolar analysis. The large t2 g bandwidth renormalizes the strength of SOC and the Ir intersite exchange interaction dominates resulting in long-range magnetic order in the AP phase. In addition to SOC and Hubbard U , strong intradimer coupling is found to be crucial for the realization of the insulating state. At high pressure (HP) the system undergoes a structural transformation to the disordered cubic phase. In sharp contrast to the AP phase, the calculated exchange interactions in the HP phase are found to be much weaker and SOC dominates leading to a quantum spin-orbital liquid (SOL) state.

  3. Magnetoelectric Coupling, Ferroelectricity, and Magnetic Memory Effect in Double Perovskite La3Ni2NbO9.

    PubMed

    Dey, K; Indra, A; De, D; Majumdar, S; Giri, S

    2016-05-25

    We observe ferroelectricity in an almost unexplored double perovskite La3Ni2NbO9. Ferroelectricity appears below ∼60 K, which is found to be correlated with the significant magnetostriction. A reasonably large value of spontaneous electric polarization is recorded to be ∼260 μC/m(2) at 10 K for E = 5 kV/cm, which decreases signifi- cantly upon application of a magnetic field (H), suggesting considerable magnetoelectric coupling. The dielectric permittivity is also influenced by H below the ferroelectric transition. The magnetodielectric response scales linearly to the squared magnetization, as described by the Ginzburg-Landau theory. Meticulous studies of static and dynamic features of dc magnetization and frequency dependent ac susceptibility results suggest spin-glass state below 29 K. Intrinsic magnetic memory effect is observed from zero-field cooled magnetization and isothermal remanent magnetization studies, also pointing spin-glass state below 29 K. Appearance of ferroelectricity together with a significant magnetoelectric coupling in absence of conventional long-range magnetic order is promising for searching new magnetoelectric materials. PMID:27136317

  4. O stars and Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

    Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

  5. Origins of the thick disk of the Milky Way Galaxy as traced by the elemental abundances of metal-poor stars

    NASA Astrophysics Data System (ADS)

    Ruchti, Gregory Randal

    2010-12-01

    Understanding the formation and evolution of disks in galaxies in the early universe is very important for understanding the forms of galaxies today. Recent studies of the Milky Way Galaxy, an ideal galaxy for analyzing individual stars within its disk, indicate that the formation of the Galactic disk is very complex. Most of these studies, however, contain very few stars at low metallicities. Metal-poor stars are important, because they are potential survivors of the earliest star formation in the disk of the Milky Way Galaxy. I therefore measured elemental abundances of a statistically significant sample of metal-poor ([Fe/H] ≲ - 1.0) stars in the disk of the Galaxy, chosen from the RAVE survey in order to study the early formation history of the Galactic disk. I report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 dwarf/sub-giant metal-poor thick-disk candidate stars. I found that the [alpha/Fe] ratios are enhanced implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the interstellar medium prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star initial mass function. I further looked for radial or vertical gradients in metallicity or alpha-enhancement for the metal-poor thick disk, never before done for such a sample. I found no radial gradient and a moderate vertical gradient in my derived iron abundance, and only minimal-amplitude gradients in [alpha/Fe]. In addition, I show that the distribution of orbital eccentricities for my metal-poor thick-disk stars requires that the thick disk was formed primarily in situ, with direct accretion being extremely minimal. I conclude that the alpha-enhancement of the metal-poor thick disk, and the lack of obvious radial or

  6. Lifestyles of the Stars.

    ERIC Educational Resources Information Center

    National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

    Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)

  7. Egyptian "Star Clocks"

    NASA Astrophysics Data System (ADS)

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  8. Computational study on the molecular structures and photoelectron spectra of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta).

    PubMed

    Chen, Wen-Jie; Zhang, Chang-Fu; Zhang, Xian-Hui; Zhang, Yong-Fan; Huang, Xin

    2013-05-15

    Density functional theory (DFT) and coupled cluster theory (CCSD(T)) calculations are carried out to investigate the electronic and structural properties of a series of bimetallic oxide clusters MW2O9(-/0) (M=V, Nb, Ta). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES). Theoretical calculations at the B3LYP level yield singlet and doublet ground states for the bimetallic anionic and neutral clusters, respectively. All the clusters present the six-membered ring structures with different symmetries, except that the TaW2O9(-) cluster shows a chained style with a penta-coordinated tantalum atom. Spin density analyses reveal oxygen radical species in all neutral clusters, consistent with their structural characteristics. Moreover, additional calculations are performed to study the oxidation reaction of CO molecule with the W3O9(+) cation and the isoelectronic VW2O9 cluster, and results indicate that the introduction of vanadium at tungsten site can efficiently improve the oxidation reactivity. PMID:23523755

  9. Excellent stability of plasma-sprayed bioactive Ca 3ZrSi 2O 9 ceramic coating on Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Liang, Ying; Xie, Youtao; Ji, Heng; Huang, Liping; Zheng, Xuebin

    2010-05-01

    In this work, novel zirconium incorporated Ca-Si based ceramic powder Ca 3ZrSi 2O 9 was synthesized. The aim of this study was to fabricate Ca 3ZrSi 2O 9 coating onto Ti-6Al-4V substrate using atmospheric plasma-spraying technology and to evaluate its potential applications in the fields of orthopedics and dentistry. The phase composition, surface morphologies of the coating were examined by XRD and SEM, which revealed that the Ca 3ZrSi 2O 9 coating was composed of grains around 100 nm and amorphous phases. The bonding strength between the coating and the substrate was 28 ± 4 MPa, which is higher than that of traditional HA coating. The dissolution rate of the coating was assessed by monitoring the ions release and mass loss after immersion in the Tris-HCl buffer solution. The in vitro bioactivity of the coating was determined by observing the formation of apatite on its surface in simulated body fluids. It was found that the Ca 3ZrSi 2O 9 coating possessed both excellent chemical stability and good apatite-formation ability, suggesting its potential use as bone implants.

  10. Ultrahigh temperature Bi3Ti0.96Sc0.02Ta0.02NbO9-based piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Gai, Zhi-Gang; Wang, Jin-Feng; Sun, Wen-bin; Wang, Chun-Ming; Zhao, Ming-Lei; Sun, Shang-Qian; Ming, Bao-Quan; Qi, Peng; Zheng, Li-mei; Du, Juan; Zhang, Shujun; Shrout, Thomas R.

    2008-07-01

    The effect of (Sc,Ta,Ce) doping on the properties of Bi3TiNbO9 (BTNO)-based ceramics was investigated. The cerium modification greatly improves the piezoelectric activity of Bi3(Ti0.96Sc0.02Ta0.02)NbO9-based ceramics and significantly decreases the dielectric dissipation. The d33 of Bi3Ti0.96Sc0.02Ta0.02NbO9+x wt %CeO2 (x =0.35) was found to be 18 pC/N, the highest value among the BTNO-based ceramics and almost three times as much as the reported d33 values of the pure BTNO ceramics (˜6 pC/N). The modification increased the resistivity ρ of the samples extremely, resolving the low resistivity problem for high temperature applications. The dielectric spectroscopy shows that the TC for all the ceramics is higher than 900 °C. The mechanical quality factor Q and planar coupling factors kp and kt of Bi3Ti0.96Sc0.02Ta0.02NbO9+0.35 wt %CeO2 ceramic were found to be 2835, 9%, and 23%, respectively, and it has high TC and stable piezoelectric properties, demonstrating that the (Sc,Ta,Ce) modified BTNO-based material is a wonderful candidate for high temperature applications.

  11. Domain Motion of Ferroelectricity of Bi2SrTa2O9 Single Crystals under an AC-Voltage Electric Field

    NASA Astrophysics Data System (ADS)

    Machida, Akio; Nagasawa, Naomi; Ami, Takaaki; Suzuki, Masayuki

    1999-02-01

    A novel phenomenon, which increases the remanent polarization of Bi2SrTa2O9 single crystals, a promising candidate for ferroelectric random access memories (FeRAM), has been identified. The single crystals, grown in vapor phases using the self-flux method, have a composition characterized asBixSryTa2O9 (x=2.08±0.09, y=1.04±0.06). Incontrast to BixSryTa2O9 (x=1.91±0.05, y=1.27±0.08) single crystals grown by the self-flux method, the coercive field of the present single crystals is smaller. Observing optical anisotropy in the c-plane, we found that this material has a paraelectric phase, which might originate from the partial distortion of the crystal. After voltage was applied, the paraelectric phase disappeared and the crystal became a ferroelectric domain structure. Measuring the electrical properties in the c-plane, the remanent polarization of the Bi2SrTa2O9 single crystal was increased by applying ac-voltage. One-hour annealing over the Curie temperature also produced a paraelectric phase in the crystal but it was confirmed that this paraelectric phase can also be decreased by applying ac-voltage. Using this ac-voltage application, we can clearly observe the domain structure of BiSTa single crystal for the first time.

  12. Magnetic phase diagram and multiferroicity of Ba3MnNb2O9: A spin-5/2 triangular lattice antiferromagnet with weak easy-axis anisotropy

    NASA Astrophysics Data System (ADS)

    Lee, M.; Choi, E. S.; Huang, X.; Ma, J.; Dela Cruz, C. R.; Matsuda, M.; Tian, W.; Dun, Z. L.; Dong, S.; Zhou, H. D.

    2015-03-01

    We have performed magnetic, electric, thermal, and neutron powder diffraction (NPD) experiments as well as density functional theory (DFT) calculations on Ba3MnNb2O9. All results suggest that Ba3MnNb2O9 is a spin-5/2 triangular lattice antiferromagnet (TLAF) with weak easy-axis anisotropy. At zero field, we observed a narrow two-step transition at TN 1 = 3.4 K and TN 2 = 3.0 K. The neutron diffraction measurement and the DFT calculation indicate a 120° spin structure in the ab plane with out-of-plane canting at low temperatures. With increasing magnetic field, the 120° spin structure evolves into up-up-down (uud) and oblique phase showing successive magnetic phase transitions, which fits well to the theoretical prediction for the 2D Heisenberg TLAF with classical spins. Multiferroicity is observed when the spins are not collinear but suppressed in the uud and the oblique phase. We discuss the results in comparison with our previous works on its sister compounds with small spins, Ba3NiNb2O9 (S = 1) (J. Hwang et al ., Phys. Rev. Lett. 109, 257205 (2012) and Ba3CoNb2O9 (S = 1/2) (M. Lee et al ., Phys. Rev. B 89, 104420 (2014)). NHMFL is supported by NSF, the state of Florida and US DOE. ORNL HFIR was sponsored by U.S. DOE.

  13. Integration of SrBi2Ta2O9 thin films for high density ferroelectric random access memory

    NASA Astrophysics Data System (ADS)

    Wouters, D. J.; Maes, D.; Goux, L.; Lisoni, J. G.; Paraschiv, V.; Johnson, J. A.; Schwitters, M.; Everaert, J.-L.; Boullart, W.; Schaekers, M.; Willegems, M.; Vander Meeren, H.; Haspeslagh, L.; Artoni, C.; Caputa, C.; Casella, P.; Corallo, G.; Russo, G.; Zambrano, R.; Monchoix, H.; Vecchio, G.; Van Autryve, L.

    2006-09-01

    Ferroelectric random access memory (FeRAM) is an attractive candidate technology for embedded nonvolatile memory, especially in applications where low power and high program speed are important. Market introduction of high-density FeRAM is, however, lagging behind standard complementary metal-oxide semiconductor (CMOS) because of the difficult integration technology. This paper discusses the major integration issues for high-density FeRAM, based on SrBi2Ta2O9 (strontium bismuth tantalate or SBT), in relation to the fabrication of our stacked cell structure. We have worked in the previous years on the development of SBT-FeRAM integration technology, based on a so-called pseudo-three-dimensional (3D) cell, with a capacitor that can be scaled from quasi two-dimensional towards a true three-dimensional capacitor where the sidewalls will importantly contribute to the signal. In the first phase of our integration development, we integrated our FeRAM cell in a 0.35μm CMOS technology. In a second phase, then, possibility of scaling of our cell is demonstrated in 0.18μm technology. The excellent electrical and reliability properties of the small integrated ferroelectric capacitors prove the feasibility of the technology, while the verification of the potential 3D effect confirms the basic scaling potential of our concept beyond that of the single-mask capacitor. The paper outlines the different material and technological challenges, and working solutions are demonstrated. While some issues are specific to our own cell, many are applicable to different stacked FeRAM cell concepts, or will become more general concerns when more developments are moving into 3D structures.

  14. Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal.

    PubMed

    Katayama, Naoyuki; Kimura, Kenta; Han, Yibo; Nasu, Joji; Drichko, Natalia; Nakanishi, Yoshiki; Halim, Mario; Ishiguro, Yuki; Satake, Ryuta; Nishibori, Eiji; Yoshizawa, Masahito; Nakano, Takehito; Nozue, Yasuo; Wakabayashi, Yusuke; Ishihara, Sumio; Hagiwara, Masayuki; Sawa, Hiroshi; Nakatsuji, Satoru

    2015-07-28

    With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose-Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Moreover, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc2S4. To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn-Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn-Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. We discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state. PMID:26170280

  15. Crystallization, dehydration and experimental phasing of WbdD, a bifunctional kinase and methyltransferase from Escherichia coli O9a

    SciTech Connect

    Hagelueken, Gregor; Huang, Hexian; Harlos, Karl; Clarke, Bradley R.; Whitfield, Chris; Naismith, James H.

    2012-10-01

    The optimization of WbdD crystals using a novel dehydration protocol and experimental phasing at 3.5 Å resolution by cross-crystal averaging followed by molecular replacement of electron density into a non-isomorphous 3.0 Å resolution native data set are reported. WbdD is a bifunctional kinase/methyltransferase that is responsible for regulation of lipopolysaccharide O antigen polysaccharide chain length in Escherichia coli serotype O9a. Solving the crystal structure of this protein proved to be a challenge because the available crystals belonging to space group I23 only diffracted to low resolution (>95% of the crystals diffracted to resolution lower than 4 Å and most only to 8 Å) and were non-isomorphous, with changes in unit-cell dimensions of greater than 10%. Data from a serendipitously found single native crystal that diffracted to 3.0 Å resolution were non-isomorphous with a lower (3.5 Å) resolution selenomethionine data set. Here, a strategy for improving poor (3.5 Å resolution) initial phases by density modification and cross-crystal averaging with an additional 4.2 Å resolution data set to build a crude model of WbdD is desribed. Using this crude model as a mask to cut out the 3.5 Å resolution electron density yielded a successful molecular-replacement solution of the 3.0 Å resolution data set. The resulting map was used to build a complete model of WbdD. The hydration status of individual crystals appears to underpin the variable diffraction quality of WbdD crystals. After the initial structure had been solved, methods to control the hydration status of WbdD were developed and it was thus possible to routinely obtain high-resolution diffraction (to better than 2.5 Å resolution). This novel and facile crystal-dehydration protocol may be useful for similar challenging situations.

  16. Neutron Stars and NuSTAR

    NASA Astrophysics Data System (ADS)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses

  17. The Cambridge Double Star Atlas

    NASA Astrophysics Data System (ADS)

    MacEvoy, Bruce; Tirion, Wil

    2015-12-01

    Preface; What are double stars?; The binary orbit; Double star dynamics; Stellar mass and the binary life cycle; The double star population; Detecting double stars; Double star catalogs; Telescope optics; Preparing to observe; Helpful accessories; Viewing challenges; Next steps; Appendices: target list; Useful formulas; Double star orbits; Double star catalogs; The Greek alphabet.

  18. Oral vaccination of calves with an aromatic-dependent Salmonella dublin (O9,12) hybrid expressing O4,12 protects against S. dublin (O9,12) but not against Salmonella typhimurium (O4,5,12).

    PubMed Central

    Segall, T; Lindberg, A A

    1993-01-01

    Three groups of six calves each, 5 to 7 weeks old, were orally vaccinated with the live aromatic-dependent delta aroA Salmonella dublin (O9,12) hybrid strain SL7103 with the O4,12-specifying rfb gene cluster from Salmonella typhimurium. SL7103 was given in three weekly doses, increasing from 2 x 10(9) to 1 x 10(11) bacteria per ml, was well tolerated, and caused mild, short-term temperature increases which diminished with each immunization. The strain was shed for up to 1 week. Strain SL7103 elicited significant (P < 0.001) and equal anti-S. dublin and -S. typhimurium lipopolysaccharide serum antibody responses and skin delayed-type hypersensitivity immune responses. Six vaccinated calves orally challenged with 10(10) CFU (equivalent to 1,000 50% lethal doses) of the virulent parent strain S. dublin SVA47 were protected and experienced only transient fever and mild mucoid diarrhea. However, six vaccinated calves orally challenged with 3 x 10(9) CFU and another six challenged with 3 x 10(8) CFU (equivalent to 1,000 50% lethal doses) of the virulent S. typhimurium SVA44 became bacteremic with a profuse hemorrhagic diarrhea and had to be sacrificed within 2 to 7 days. The results suggest that the S. typhimurium antilipopolysaccharide immunity was insufficient to provide a solid protective efficacy against oral S. typhimurium infection. The immunohistopathological examination revealed that S. typhimurium SVA44 could be found in all layers of the intestinal mucosa and the lymphatic tissues of the Peyer's patches. In contrast, S. dublin SVA47 was found predominantly in the columnar enterocytes of the jejunum and ileum and the follicle-associated epithelium over the Peyer's patches. In addition, SVA47 was found in the glandular tissues of the duodenal and tonsillar areas and in the lungs. This suggests that the S. typhimurium and S. dublin strains have different virulence traits determining their tissue localization and dissemination. Images PMID:7681042

  19. MGB and the new Galactic O-Star Spectroscopic Survey spectral classification standard grid

    NASA Astrophysics Data System (ADS)

    Maíz Apellániz, J.; Alfaro, E. J.; Arias, J. I.; Barbá, R. H.; Gamen, R. C.; Herrero, A.; Leão, J. R. S.; Marco, A.; Negueruela, I.; Simón-Díaz, S.; Sota, A.; Walborn, N. R.

    2015-05-01

    In this poster we present three developments related to the Galactic O-Star Spectroscopic Survey (http://adsabs.harvard.edu/abs/2011hsa6.conf..467M{GOSSS}). First, we are making public the first version of MGB, an IDL code that allows the user to compare oberved spectra to a grid of spectroscopic standards to measure spectral types, luminosity classes, rotation indexes, and spectral qualifiers. Second, we present the associated grid of standard stars for the spectral types O2 to O9.7, with several improvements over the original GOSSS grid of http://adsabs.harvard.edu/abs/2011ApJS..193...24S {Sota et al. (2011)}. Third, we present a list of egregious classification errors in http://simbad.u-strasbg.fr/simbad/{ SIMBAD}: stars that are or have been listed there as being of O type but that in reality are late-type stars.

  20. The Millennium Star Atlas

    NASA Astrophysics Data System (ADS)

    Sinnott, R. W.

    1997-08-01

    Derived from Hipparcos and Tycho observations, the Millennium Star Atlas is a set of 1548 charts covering the entire sky to about magnitude 11. It stands apart from all previous printed atlases in completeness to magnitude 10 and in uniformity around the sky. The generous chart scale has made possible a number of innovations never before seen in a star atlas: arrows on high-proper-motion stars, double-star ticks conveying separation and position angle for a specific modern epoch, distance labels for nearby stars, and variable stars coded by amplitude, period, and type. Among the nonstellar objects plotted, more than 8000 galaxies are shown with aspect ratio and orientation.

  1. The Pistol Star

    NASA Astrophysics Data System (ADS)

    Najarro, F.; Figer, D. F.

    1998-06-01

    Results of an spectroscopic investigation of the Pistol star are presented. The near-infrared spectra and photometry data are fit with stellar wind models to find that the star is extraordinarily luminous, L = 106.7±0.5 L⊙, making it one of the most luminous stars known. Coupled with the relatively cool temperature, Teff = 10^{4.17_{ - 0.06}^{ + 0.19} } K, the star is clearly in violation of the Humphreys-Davidson limit. The derived line of sight velocity of the star assures its membership in the Quintuplet cluster. This, along with the inferred extinction, places the star at the Galactic Center.

  2. Effect of cation substitution on structural transition: synthesis, characterization and theoretical studies of NaCa4B3O9, NaCaBO3, NaSrBO3 and Li4CaB2O6.

    PubMed

    Yang, Yun; Su, Xin; Pan, Shilie; Yang, Zhihua

    2015-10-21

    Single crystals of NaCa4B3O9, NaCaBO3, NaSrBO3 and Li4CaB2O6 have been successfully synthesized through conventional high-temperature solid-state reactions. They are structurally characterized by single crystal X-ray diffraction and exhibit three-dimensional crystal structures consisting of isolated planar BO3 as fundamental building blocks. Interestingly, for the centrosymmetric crystal structure of NaCaBO3 (Na3Ca3B3O9), as 2/3 of the Na(+) ions are substituted by Ca(2+) ions, NaCa4B3O9 is obtained and crystallizes in the noncentrosymmetric space group Ama2 (crystal class mm2). A second harmonic generation (SHG) test of the title compound by the Kurtz-Perry method shows that NaCa4B3O9 can be phase matchable with an effective SHG coefficient approximately one-half that of KH2PO4 (KDP). Studies of their optical properties as well as band structure calculations based on density functional theory methods have been also performed. NaCa4B3O9 possesses a moderate birefringence of about 0.05 at 1064 nm. To explain the difference in optical nonlinearity we compared the electronic structures of NaCa4B3O9, KCa4B3O9 and KSr4B3O9 crystals, in particular at the bottom of the conduction band (CB) and the top of the valence band (VB), since they are known to play a primary role in SHG. These electronic structures are responsible for the optical-nonlinearity of NaCa4B3O9, KCa4B3O9 and KSr4B3O9 crystals. PMID:26387438

  3. NaKV4O9·2H2O: a new 2D magnetic compound with a 1/5-depleted square lattice.

    PubMed

    Cui, Meiyan; He, Zhangzhen; Wang, Nannan; Tang, Yingying; Guo, Wenbin; Zhang, Suyun; Wang, Lin; Xiang, Hongping

    2016-03-15

    A new vanadate compound NaKV4O9·2H2O is successfully synthesized by a conventional hydrothermal method. This compound crystallizes in the monoclinic system with the space group C2/c, showing a typical 2D layered structure built from VO5 pyramids, in which the layers are separated by Na(+), K(+), and H2O. The topology structure of magnetic V(4+) ions shows a quite interesting 1/5-depleted square lattice, which is quite similar to that of a famous low-dimensional quantum spin system CaV4O9. A structural and magnetic comparison confirmed that the title compound may exhibit a more pronounced 2D character with a large spin gap. PMID:26892907

  4. K[AsW2O9], the first member of the arsenate-tungsten bronze family: Synthesis, structure, spectroscopic and non-linear optical properties

    NASA Astrophysics Data System (ADS)

    Alekseev, Evgeny V.; Felbinger, Olivier; Wu, Shijun; Malcherek, Thomas; Depmeier, Wulf; Modolo, Giuseppe; Gesing, Thorsten M.; Krivovichev, Sergey V.; Suleimanov, Evgeny V.; Gavrilova, Tatiana A.; Pokrovsky, Lev D.; Pugachev, Alexey M.; Surovtsev, Nikolay V.; Atuchin, Victor V.

    2013-08-01

    K[AsW2O9], prepared by high-temperature solid-state reaction, is the first member of the arsenate-tungsten bronze family. The structure of K[AsW2O9] is based on a 3-dimensional (3D) oxotungstate-arsenate framework with the non-centrosymmetric P212121 space group, a=4.9747(3) Å, b=9.1780(8) Å, c=16.681(2) Å. The material was characterized using X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman and infrared (IR) spectroscopic techniques. The results of DSC demonstrate that this phase is stable up to 1076 K. Second harmonic generation (SHG) measurements performed on a powder sample demonstrate noticeable (0.1 of LiIO3) non-linear optical (NLO) activity.

  5. Magnetized Neutron Stars

    NASA Astrophysics Data System (ADS)

    Liebling, Steven; Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Tohline, Joel

    2008-04-01

    Magnetized neutron stars, whether considered individually or within compact binary systems, demonstrate a number of interesting dynamical effects. Using a distributed adaptive mesh refinement (AMR) code, we evolve such stars and study their dynamics.

  6. Intrinsically variable stars

    NASA Technical Reports Server (NTRS)

    Bohm-Vitense, Erika; Querci, Monique

    1987-01-01

    The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.

  7. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  8. Rare-earth-free red-emitting K2Ge4O9:Mn(4+) phosphor excited by blue light for warm white LEDs.

    PubMed

    Ding, Xin; Wang, Qian; Wang, Yuhua

    2016-03-01

    A series of novel K2Ge4O9:Mn(4+) phosphors with red emission under blue light excitation have been synthesized successfully by traditional high-temperature solid-state reaction. The structure of K2Ge4O9 has been investigated by high-resolution transmission electron microscopy, scanning electron microscopy and X-ray powder diffraction with Rietveld refinement. The PL properties have been investigated by measuring diffuse reflection spectra, emission spectra, excitation spectra, decay curves and temperature-dependent spectra. The KGO:0.1% Mn(4+) phosphor can emit red light peaking at 663 nm under UV or blue light excitation. The critical quenching concentration of Mn(4+) was about 0.1 mol%. The concentration quenching mechanism could be a d-d interaction for the Mn(4+) center. The CIE chromaticity coordinates and FWHM are (0.702, 0.296) and 20 nm, which demonstrated that the K2Ge4O9:Mn(4+) has a high color purity. By tuning the weight ratio of yellow and red phosphors, the fabricated white LEDs, using a 455 nm InGaN blue chip combined with a blend of the yellow phosphor YAG:Ce(3+) and the red-emitting KGO:Mn(4+) phosphor driven by a 40 mA current, can get white light with chromaticity coordinates (0.405, 0.356) and CCT 3119 K. These results indicated that K2Ge4O9:Mn(4+) is a potential red phosphor to match blue LED chips to get warm white light. PMID:26923078

  9. Synthesis, structure and magnetic ordering of the mullite-type Bi2Fe(4-x)CrxO9 solid solutions with a frustrated pentagonal Cairo lattice.

    PubMed

    Rozova, M G; Grigoriev, V V; Bobrikov, I A; Filimonov, D S; Zakharov, K V; Volkova, O S; Vasiliev, A N; Antipov, E V; Tsirlin, A A; Abakumov, A M

    2016-01-21

    Highly homogeneous mullite-type solid solutions Bi2Fe(4-x)CrxO9 (x = 0.5, 1, 1.2) were synthesized using a soft chemistry technique followed by a solid-state reaction in Ar. The crystal structure of Bi2Fe3CrO9 was investigated using X-ray and neutron powder diffraction, transmission electron microscopy and (57)Fe Mössbauer spectroscopy (S.G. Pbam, a = 7.95579(9) Å, b = 8.39145(9) Å, c = 5.98242(7) Å, RF(X-ray) = 0.022, RF(neutron) = 0.057). The ab planes in the structure are tessellated with distorted pentagonal loops built up by three tetrahedrally coordinated Fe sites and two octahedrally coordinated Fe/Cr sites, linked together in the ab plane by corner-sharing forming a pentagonal Cairo lattice. Magnetic susceptibility measurements and powder neutron diffraction show that the compounds order antiferromagnetically (AFM) with the Néel temperatures decreasing upon increasing the Cr content from TN ∼ 250 K for x = 0 to TN ∼ 155 K for x = 1.2. The magnetic structure of Bi2Fe3CrO9 at T = 30 K is characterized by a propagation vector k = (1/2,1/2,1/2). The tetrahedrally coordinated Fe cations form singlet pairs within dimers of corner-sharing tetrahedra, but spins on the neighboring dimers are nearly orthogonal. The octahedrally coordinated (Fe,Cr) cations form antiferromagnetic up-up-down-down chains along c, while the spin arrangement in the ab plane is nearly orthogonal between nearest neighbors and collinear between second neighbors. The resulting magnetic structure is remarkably different from the one in pure Bi2Fe4O9 and features several types of spin correlations even on crystallographically equivalent exchange that may be caused by the simultaneous presence of Fe and Cr on the octahedral site. PMID:26661379

  10. Synthesis, characterization, temperature dependent electrical and magnetic properties of Ca3Co4O9 by a starch assisted sol-gel combustion method

    NASA Astrophysics Data System (ADS)

    Agilandeswari, K.; Ruban Kumar, A.

    2014-09-01

    In this present work we discussed the synthesis of pure Ca3Co4O9 ceramic powder by a starch assisted sol-gel combustion method. The products were characterized by powder X-ray diffraction (XRD), thermogravimetric and differential thermal analyses (TGA-DTA), Fourier transformation infrared spectroscopy (FTIR), scanning electron microscope (SEM) and UV-visible diffuse reflectance spectroscopy (DRS). X-ray diffraction pattern confirmed the formation of single phase Ca3Co4O9 at a sintering temperature of 1073 K, and it is also confirmed in the thermal analysis. SEM images indicate the presence of diffused microporous sphere like morphology and the grain sizes are in the range of 150-300 nm. Optical properties of Ca3Co4O9 ceramic show a band gap at an energy level of 2.10 eV. A maximum electrical resistivity of 0.002 mΩ cm was exhibited by Ca3Co4O9 that was decreased to 0.0012 mΩ cm, when the temperature increased from 300 K to 473 K. Dielectric studies were conducted at various temperatures from room temperature to 673 K and the results indicate that the space charge polarization contributes to the conduction mechanism. It also shows that the dielectric relaxation with activation energy is 0.96 eV. The magnetic properties as a function of temperature represent the ferri-paramagnetic phase transition at above 50 K. M-H curve shows the hysteresis loop with saturation magnetization (Ms) and confirms the presence of soft magnetic materials.

  11. QCD in Neutron Stars and Strange Stars

    SciTech Connect

    Weber, Fridolin; Negreiros, Rodrigo

    2011-05-24

    This paper provides an overview of the possible role of Quantum Chromo Dynamics (QCD) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than even the most stable atomic nucleus, {sup 56}Fe. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

  12. Dibaryons in neutron stars

    NASA Technical Reports Server (NTRS)

    Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.

    1991-01-01

    The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.

  13. Chromospheres of Coronal Stars

    NASA Technical Reports Server (NTRS)

    Linsky, Jeffrey L.; Wood, Brian E.

    1996-01-01

    We summarize the main results obtained from the analysis of ultraviolet emission line profiles of coronal late-type stars observed with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. The excellent GHRS spectra provide new information on magnetohydrodynamic phenomena in the chromospheres and transition regions of these stars. One exciting new result is the discovery of broad components in the transition region lines of active stars that we believe provide evidence for microflare heating in these stars.

  14. Wolf-Rayet Stars

    NASA Astrophysics Data System (ADS)

    Hillier, D.; Murdin, P.

    2000-11-01

    Wolf-Rayet (W-R) stars are a class of peculiar stars first identified in 1867 by C J E WOLF and G RAYET. Unlike the spectra of most stars, which are dominated by narrow absorption lines, the spectra of W-R stars show broad emission lines. The rich emission line spectrum makes them easy to identify, by spectroscopic observations, even at large distances....

  15. Synthesis, characterization and theoretical studies of nonlinear optical crystal Sr2B5O9(OH)·H2O.

    PubMed

    Zhang, Fangyuan; Zhang, Fangfang; Qun, Jing; Pan, Shilie; Yang, Zhihua; Jia, Dianzeng

    2015-04-28

    Strontium borate Sr2B5O9(OH)·H2O (space group C2, No. 5) has been synthesized in high yields using a facile hydrothermal method. The UV-Vis-NIR diffuse reflectance spectrum shows that it has a wide transparency range extending from UV to NIR with the short-wavelength cut off edge below 190 nm. Second-harmonic generation (SHG) has been measured with a 1064 nm laser using the Kurtz and Perry technique, which shows that Sr2B5O9(OH)·H2O is phase matchable and the powder SHG effect is approximately 3 times that of KDP. It also has a high thermal stability up to 500 °C which has been identified by TG, DSC and variable-temperature PXRD. These properties make it possible for application as a UV nonlinear optical (NLO) material. Based on the electronic band structure, the optical refractive indices, birefringence, and SHG coefficients of Sr2B5O9(OH)·H2O are calculated, which are consistent with experiments. In addition, the electronic structure, SHG-weighted electron density and real-space atom-cutting analyses are performed to elucidate the origin of its NLO properties. PMID:25803617

  16. Comparison of the virulence of O:9,12 and O:4,5,12 Salmonella typhimurium his+ transductants for mice.

    PubMed Central

    Lyman, M B; Stocker, B A; Roantree, R J

    1977-01-01

    The purpose of these experiments was to determine whether qualitative differences in the O repeat unit of the lipopolysaccharide of pathogenic Salmonella species affected virulence for mice. O:4,5,12 and O:9,12 sister his+ transductants were derived from a virulent Salmonella typhimurium. Fermentation markers were introduced by transduction to differentiate these strains, and the strains were used as mixed challenge to CF1 and C57B1/6J mice. Liver and spleen cultures of the mice of various intervals after challenge indicated that the O:4,5,12 member of the nearly isogenic pair regularly multiplied to a greater extent than the O:9,12 after intraperitoneal challenge for both strains of mice. After oral challenge, there was little difference in the amount of multiplication of the O:4,5,12 and O:9,12 strains in CF1 mice, but the O:4,5,12 was the predominant strain recovered in 8 of 10 instances in the C57B1/6J mice. PMID:321351

  17. Ferroelectric domain structures in SrBi2Nb2O9 epitaxial thin films: Electron microscopy and phase-field simulations

    NASA Astrophysics Data System (ADS)

    Li, Y. L.; Chen, L. Q.; Asayama, G.; Schlom, D. G.; Zurbuchen, M. A.; Streiffer, S. K.

    2004-06-01

    Ferroelectric domain structures of (001)SrBi2Nb2O9 epitaxial films, investigated using both transmission electron microscopy and phase-field simulations, are reported. Experiment and numerical simulation both reveal that the domain structures consist of irregularly shaped domains with curved domain walls. It is shown that the elastic contribution to domain structures can be neglected in SrBi2Nb2O9 due to its small ferroelastic distortion, less than 0.0018%. Two-beam dark-field imaging using reflections unique to domains of each of the two 90° polarization axes reveal the domain structure. Phase-field simulation is based on the elastic and electrostatic solutions obtained for thin films under different mechanical and electric boundary conditions. The effects of ferroelastic distortion and dielectric constant on ferroelectric domains are systematically analyzed. It is demonstrated that electrostatic interactions which favor straight domain walls are not sufficient to overcome the domain wall energy which favors curved domains in SrBi2Nb2O9.

  18. Effects of Sr2+ substitution on photoluminescence characteristics of Ba1-x-ySryZrSi3O9:xEu2+ phosphors

    NASA Astrophysics Data System (ADS)

    Chiang, Chung-Hao; Gong, Syuan-Jhih; Lin, Han-Yu; Zhan, Ting-Shi; Chu, Sheng-Yuan

    2014-12-01

    In this work, single-phase Ba1-x-ySryZrSi3O9:xEu2+ phosphors were synthesized via the solid-state reaction method. The crystal structure and luminescence properties were investigated using X-ray diffraction and photoluminescence measurements, respectively. An increase of the dopant Sr2+ increased the emission intensity of the phosphors. The peak intensity of the samples was at y = 0.4 under near-ultraviolet light excitation (397 nm). The wavelength of the emission peaks red-shifts slightly from 477 to 483 nm due to the splitting of the 5d energy level. Sr2+ ions have a smaller ionic radius than that of Ba2+ ions, and thus the dopant changes the crystal structure, improving the energy transfer efficiency between luminescence centers. More Eu2+ solid solubility was found in Ba0.6-xSr0.4ZrSi3O9:xEu2+ phosphors (10 mol. %) than in the host BaZrSi3O9 (6 mol. %), which enhanced the emission intensity. In addition, the thermal reliability of the phosphors was studied.

  19. Electron diffraction and microscopy study of the structure and microstructure of the hexagonal perovskite Ba3Ti2MnO9.

    PubMed

    Maunders, Christian; Whitfield, Harold J; Hay, David G; Etheridge, Joanne

    2007-06-01

    This paper reports a structural and microstructural investigation of the hexagonal perovskite Ba(3)Ti(2)MnO(9) using electron microscopy and diffraction. Convergent-beam electron diffraction (CBED) revealed the structure has the non-centrosymmetric space group P6(3)mc (186) at room temperature and at approximately 110 K. Compared with the centrosymmetric parent structure BaTiO(3), with space group P6(3)/mmc, this represents a break in mirror symmetry normal to the c axis. This implies the Ti and Mn atoms are ordered on alternate octahedral sites along the 0001 direction in Ba(3)Ti(2)MnO(9). Using high-resolution electron microscopy (HREM), we observed occasional 6H/12R interfaces on (0001) planes, however, no antiphase boundaries were observed, as were seen in Ba(3)Ti(2)RuO(9). Using powder X-ray Rietveld refinement we have measured the lattice parameters from polycrystalline samples to be a = 5.6880 +/- 0.0005, c = 13.9223 +/- 0.0015 A at room temperature. PMID:17507751

  20. Series of phase transitions and multiferroicity in the quasi-two-dimensional spin-1/2 triangular-lattice antiferromagnet Ba3CoNb2O9

    NASA Astrophysics Data System (ADS)

    Lee, M.; Hwang, J.; Choi, E. S.; Ma, J.; Dela Cruz, C. R.; Zhu, M.; Ke, X.; Dun, Z. L.; Zhou, H. D.

    2014-03-01

    We have investigated the magnetic and electric ground states of a quasi-two-dimensional triangular lattice antiferromagnet (TLAF), Ba3CoNb2O9, in which the effective spin of Co2+ is 1/2. At zero field, the system undergoes a two-step transition upon cooling at TN2=1.36 K and TN1=1.10 K and enters a 120∘ ordered state. By applying magnetic fields, a series of spin states with fractions of the saturation magnetization Ms are observed. They are spin states with 1/3, 1/2, 2/3 (or √3 /3) Ms. The ferroelectricity emerges in all spin states, either with collinear or noncollinear spin structure, which makes Ba3CoNb2O9 another unique TLAF exhibiting both a series of magnetic phase transitions and multiferroicity. We discuss the role of quantum fluctuations and magnetic anisotropy in contributing more complex phase diagram compared to its sister multiferroic TLAF compound Ba3NiNb2O9 [J. Hwang et al., Phys. Rev. Lett. 109, 257205 (2012), 10.1103/PhysRevLett.109.257205].

  1. Pathogenic Yersinia enterocolitica 2/O:9 and Yersinia pseudotuberculosis 1/O:1 strains isolated from human and non-human sources in the Plateau State of Nigeria.

    PubMed

    Okwori, Ameh E J; Martínez, Pilar Ortiz; Fredriksson-Ahomaa, Maria; Agina, Samuel E; Korkeala, Hannu

    2009-12-01

    Foodborne yersiniosis, caused by enteropathogenic Yersinia, especially Yersinia enterocolitica, is an important cause of diarrhea in developed countries, especially in temperate zones. Since studies concerning the presence of enteropathogenic Yersinia in humans and foods are rare in developing countries and tropical areas, human and non-human samples were studied in Plateau state of Nigeria to obtain information on the epidemiology of Y. enterocolitica and Yersinia pseudotuberculosis. Surprisingly, ail-positive Y. enterocolitica and inv-positive Y. pseudotuberculosis were isolated in Plateau state of Nigeria from several samples of human and non-human origin. Bioserotype 1/O:1 was the only Y. pseudotuberculosis type found. Y. enterocolitica belonging to bioserotype 2/O:9 was the dominating type found in most samples. Bioserotype 4/O:3 was isolated only from one pig and one sheep. Using PFGE, 5 genotypes were obtained among 45 Y. enterocolitica 2/O:9 strains with NotI, ApaI and XhoI enzymes and 3 among 20 Y. pseudotuberculosis 1/O:1 strains with NotI and SpeI enzymes. All human Y. pseudotuberculosis 1/O:1 strains were indistinguishable from pig, sheep or food strains. The dominating genotype of Y. enterocolitica 2/O:9 strains among humans was also found among strains isolated from pig, fermented cow milk and traditional intestine pepper soap samples. PMID:19835774

  2. America's Star Libraries

    ERIC Educational Resources Information Center

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  3. Managing the star performer.

    PubMed

    Hills, Laura

    2013-01-01

    Our culture seems to be endlessly fascinated with its stars in entertainment, athletics, politics, and business, and holds fast to the idea that extraordinary talent accounts for an individual's extraordinary performance. At first glance, managing a star performer in your medical practice may seem like it would be an easy task. However, there's much more to managing a star performer than many practice managers realize. The concern is how to keep the star performer happy and functioning at a high level without detriment to the rest of the medical practice team. This article offers tips for practice managers who manage star performers. It explores ways to keep the star performer motivated, while at the same time helping the star performer to meld into the existing medical practice team. This article suggests strategies for redefining the star performer's role, for holding the star performer accountable for his or her behavior, and for coaching the star performer. Finally, this article offers practical tips for keeping the star performer during trying times, for identifying and cultivating new star performers, and for managing medical practice prima donnas. PMID:23767124

  4. Strange Quark Star Crusts

    SciTech Connect

    Steiner, Andrew W.

    2007-02-27

    If strange quark matter is absolutely stable, some neutron stars may be strange quark stars. Strange quark stars are usually assumed to have a simple liquid surface. We show that if the surface tension of droplets of quark matter in the vacuum is sufficiently small, droplets of quark matter on the surface of a strange quark star may form a solid crust on top of the strange quark star. This solid crust can significantly modify the predictions for the photon emission for the surface in an observable way.

  5. Transiting exoplanets from the CoRoT space mission. XXIII. CoRoT-21b: a doomed large Jupiter around a faint subgiant star

    NASA Astrophysics Data System (ADS)

    Pätzold, M.; Endl, M.; Csizmadia, Sz.; Gandolfi, D.; Jorda, L.; Grziwa, S.; Carone, L.; Pasternacki, T.; Aigrain, S.; Almenara, J. M.; Alonso, R.; Auvergne, M.; Baglin, A.; Barge, P.; Bonomo, A. S.; Bordé, P.; Bouchy, F.; Cabrera, J.; Cavarroc, C.; Cochran, W. B.; Deleuil, M.; Deeg, H. J.; Díaz, R.; Dvorak, R.; Erikson, A.; Ferraz-Mello, S.; Fridlund, M.; Gillon, M.; Guillot, T.; Hatzes, A.; Hébrard, G.; Léger, A.; Llebaria, A.; Lammer, H.; MacQueen, P. J.; Mazeh, T.; Moutou, C.; Ofir, A.; Ollivier, M.; Parviainen, H.; Queloz, D.; Rauer, H.; Rouan, D.; Santerne, A.; Schneider, J.; Tingley, B.; Weingrill, J.; Wuchterl, G.

    2012-09-01

    CoRoT-21, a F8IV star of magnitude V = 16 mag, was observed by the space telescope CoRoT during the Long Run 01 (LRa01) in the first winter field (constellation Monoceros) from October 2007 to March 2008. Transits were discovered during the light curve processing. Radial velocity follow-up observations, however, were performed mainly by the 10-m Keck telescope in January 2010. The companion CoRoT-21b is a Jupiter-like planet of 2.26 ± 0.33 Jupiter masses and 1.30 ± 0.14 Jupiter radii in an circular orbit of semi-major axis 0.0417 ± 0.0011 AU and an orbital period of 2.72474 ± 0.00014 days. The planetary bulk density is (1.36 ± 0.48) × 103 kg m-3, very similar to the bulk density of Jupiter, and follows an M1/3 - R relation like Jupiter. The F8IV star is a sub-giant star of 1.29 ± 0.09 solar masses and 1.95 ± 0.2 solar radii. The star and the planet exchange extremetidal forces that will lead to orbital decay and extreme spin-up of the stellar rotation within 800 Myr if the stellar dissipation is Q∗/k2∗ ≤ 107. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain.

  6. Stars and their Spectra

    NASA Astrophysics Data System (ADS)

    Kaler, James B.

    1997-03-01

    This unique and informative text describes how stars are classified according to their spectral qualities and temperature. James Kaler explains the alphabet of stellar astronomy, running from cool M stars to hot O stars, and tells the story of their evolution. Before embarking on a voyage of cosmic discovery, the author discusses the fundamental properties of stars, their atomic structure and the formation of spectra. Then, Kaler considers each star type individually and explores its spectra in detail. A review of unusual, hard-to-classify stars, and a discussion of data related to the birth, life and death of stars round out the text. This book is an important resource for all amateur astronomers and students of astronomy. Professionals will find it a refreshing read as well.

  7. Ponderable soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

  8. Massive Compact Stars as Quark Stars

    NASA Astrophysics Data System (ADS)

    Rodrigues, Hilário; Barbosa Duarte, Sérgio; de Oliveira, José Carlos T.

    2011-03-01

    High-mass compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultra dense matter beyond the saturation nuclear density. In view of these results, the calculations of quark star or hybrid star equilibrium structure must be compatible with the provided observational data. But since the equations of state used in describing quark matter are in general too soft in comparison with the equation of states used to describe the hadronic or nuclear matter, the calculated quark star models presented in the literature are in general not suitable to explain the stability of highly-compact massive objects. In this work, we present the calculations of a spherically symmetric quark star structure by using an equation of state that takes into account the superconducting color-flavor locked phase of the strange quark matter. In addition, some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, the density-dependent quark mass model. The quark matter behavior introduced by this model stiffens the corresponding equation of state. We thus investigate the influence of this model on the mass-radius diagram of quark stars. We obtain massive quark stars due to the stiffness of the equation of state, when a reasonable parameterization of the color superconducting gap is used. Models of quark stars enveloped by a nucleonic crust composed of a nuclear lattice embedded in an electron gas, with nuclei close to neutron drip line, are also discussed.

  9. Dark stars: a review

    NASA Astrophysics Data System (ADS)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼1{{M}ȯ} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}ȯ} and luminosities  >{{10}10}{{L}ȯ} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  10. Dark stars: a review.

    PubMed

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars. PMID:27214049

  11. A classification system for O-B2 stars based on the Si IV and C IV resonance lines

    NASA Technical Reports Server (NTRS)

    Henize, K. G.; Wray, J. D.; Parsons, S. B.

    1981-01-01

    Low-dispersion ultraviolet spectra from Skylab Experiment S-019 are used to explore the variations of Si IV and C IV line strengths with temperature and luminosity. These considerations lead to a classification system in which the Si/C ratio is used to discriminate luminosity among the O stars and temperature among the O9-B2 stars of lower luminosity. Stars falling in these two regimes may be distinguished either by the presence of C IV emission or on the basis of C IV absorption strength. The log(Si IV/C IV) vs C IV diagram is proposed as a primary tool in such a classification system. The rapid variation in the Si IV/C IV ratio from less than 1/10 at O9 to greater than 10 at B1.5 for luminosity class III-V stars appears to be an especially useful criterion for the temperature classification of stars in this spectral range.

  12. Density functional theory calculations of UO2 oxidation: evolution of UO(2+x), U4O(9-y), U3O7, and U3O8.

    PubMed

    Andersson, D A; Baldinozzi, G; Desgranges, L; Conradson, D R; Conradson, S D

    2013-03-01

    Formation of hyperstoichiometric uranium dioxide, UO2+x, derived from the fluorite structure was investigated by means of density functional theory (DFT) calculations. Oxidation was modeled by adding oxygen atoms to UO2 fluorite supercells. For each compound ab initio molecular dynamics simulations were performed to allow the ions to optimize their local geometry. A similar approach was used for studying the reduction of U3O8. In agreement with the experimental phase diagram we identify stable line compounds at the U4O9-y and U3O7 stoichiometries. Although the transition from fluorite to the layered U3O8 structure occurs at U3O7 (UO2.333) or U3O7.333 (UO2.444), our calculated low temperature phase diagram indicates that the fluorite derived compounds are favored up to UO2.5, that is, as long as the charge-compensation for adding oxygen atoms occurs via formation of U(5+) ions, after which the U3O8-y phase becomes more stable. The most stable fluorite UO2+x phases at low temperature (0 K) are based on ordering of split quad-interstitial oxygen clusters. Most existing crystallographic models of U4O9 and U3O7, however, apply the cuboctahedral cluster. To better understand these discrepancies, the new structural models are analyzed in terms of existing neutron diffraction data. DFT calculations were also performed on the experimental cuboctahedral based U4O9-y structure, which enable comparisons between the properties of this phase with the quad-interstitial ones in detail. PMID:23406007

  13. Microstructural evolution and electrical properties of base-metal electroded BaTi4O9 materials with B-Si-Ba-Zn-O glass system.

    PubMed

    Chou, Chen-Chia; Su, Yu-Hsuan; Liu, Ze-Ming; Utami, Brianti Satrianti; Chen, Cheng-Sao; Chu, Li-Wen

    2012-09-01

    Barium titanate-based microwave dielectrics usually require relatively high temperatures to sinter, which prevents the use of base metals such as copper for electrodes. In this work, BaTi(4)O(9) microwave dielectric ceramics co-fired with copper electrodes are made possible by adding B-Si-Ba- Zn-O glass to induce liquid-phase sintering at sufficiently low temperature and in reduced atmosphere. The microstructures and electric properties of the BaTi(4)O(9) ceramics thus obtained are carefully examined and studied. Proper glass composition may significantly facilitate mass transportation in the low-temperature co-fired ceramic (LTCC) material, resulting in better densification without serious degradation of electric properties. Although the B2O3/SiO2 ratio enhances the glass mobility during sintering, the BaO/ZnO ratio contributes to the chemical affinity of glass to BaTi(4)O(9) ceramics. In addition, various Ba-Ti-O phases with different Ba/Ti ratios may be found in the specimen through the X-ray diffraction patterns when the BaO/ZnO ratio is varied. If the BaO/ZnO ratio is high and the glass flows easily in the material, the Ba(4)Ti(13)O(30) phase is formed. If the BaO/ZnO ratio is low and the glass flows easily in the material, the BaTi(6)O(13) phase appears. We find that glass-induced Ba(4)Ti(13)O(30) transformation may significantly decrease Qxf values in the BT4-BSBZ materials. Therefore, the appropriate glass composition must be selected to ensure the phase stability of dielectrics to achieve the best performance possible. PMID:23007760

  14. Phase compatibilities of YBa2Cu3O(9-delta) type structure in quintenary systems Y-Ba-Cu-O-X (impurity)

    NASA Technical Reports Server (NTRS)

    Karen, P.; Fjellvag, H.; Kjekshus, A.

    1990-01-01

    Electrical transport properties of the oxidic high T(sub c) superconductors are significantly affected by the presence of minor amounts of various elements adventing as impurities, e.g., from the chemical environment during manufacturing. YBa2Cu3O(9-delta) is prone to an extinction of the superconductivity on (partial) substitution of all four elemental components. E.g., Pr (for Y), La (for Ba), Zn (for Cu) or peroxygroup (for O) substituents will alter some of the superconductivity preconditions, like mixed valence state in Cu3O7/O(9-delta) network or structural distortion of the network. Although various pseudoternary chemical equilibrium phase diagrams of the Y(O)-Ba(O)-Cu(O) system now are available, no consensus is generally shown, however, this is partly due to lack of compatible definitions of the equilibrium conditions. Less information is available about the phase compatibilities in the appropriate quaternary phase diagram (including oxygen) and virtually no information exists about any pentenary phase diagrams (including one impurity). Unfortunately, complexity of such systems, stemming both from number of quaternary or pentenary compounds and from visualizing the five-component phase system, limits this presentation to more or less close surroundings of the YBa2Cu3O(9-delta) type phase in appropriate pseudoquaternary or pseudopseudoternary diagrams, involving Y-Ba-Cu and O, O-CO2, alkaline metals, Mg and alkaline earths, and Sc and most of the 3-d and 4-f elements. The systems were investigated by means of x ray diffraction, neutron diffraction and chemical analytical methods on samples prepared by sol-gel technique from citrates. The superconductivity was characterized by measuring the diamagnetic susceptibility by SQUID.

  15. The TUBEX typhoid test based on particle-inhibition immunoassay detects IgM but not IgG anti-O9 antibodies.

    PubMed

    Tam, Frankie Chi Hang; Lim, Pak Leong

    2003-11-01

    A serological test kit (TUBEX, IDL Biotech, Sweden) developed recently for the diagnosis of typhoid fever detects antibodies to the Salmonella enterica serovar Typhi lipopolysaccharide (LPS) O9 antigen. The antibodies are detected by their ability to inhibit the interaction between two types of reagent particles: (a). indicator latex microspheres sensitized with an anti-O9 monoclonal antibody, and (b). magnetic microspheres sensitized with S. typhi LPS. Following rapid mixing of the serum with these reagents and sedimentation of the magnetic particles by magnetic force, the concentration of indicator particles left in suspension provides a measure of the inhibition. Whereas it was previously assumed that both IgM and IgG antibodies could inhibit in the system, the present study reveals, surprisingly, that only the IgM antibodies do. It is not clear why IgG anti-O9 antibodies, both of mouse and human origin, do not inhibit, although these can bind to the LPS-sensitized magnetic particles as efficiently as the IgM antibodies. In addition, they can also inhibit very well in another detection system (ELISA) which uses a similar assay format and the same antibody and antigen reagents. Increasing the size of the LPS-sensitized microspheres made no difference; microscopic analysis of the TUBEX reaction mixture revealed that while the indicator particles bound abundantly to the IgG-aggregated LPS-sensitized particles, forming large clumps, these only formed a very light decoration on the IgM-aggregated particles. Thus, the TUBEX system is ideally suited for use in the diagnosis of infections as it allows IgM antibodies to be detected easily and rapidly from whole sera. PMID:14604543

  16. VizieR Online Data Catalog: Colour indices of selected OB stars (Krelowski+, 2012)

    NASA Astrophysics Data System (ADS)

    Krelowski, J.; Strobel, A.

    2012-01-01

    Tables contain V magnitudes and colour indices: (B-V), (U-V), (1500-V), (1800-V), (2200-V), (3300-V), (J-V), (H-V) and (K-V) of selected stars of spectral types: O9V, B0V, B1V, B1Ve, B2V and B3V. Spectral type of each star is according to SIMBAD. The stars are identified with their HD/BD numbers or names. The used photometry was taken from: U,B,V (in the Johnson System) from SIMBAD magnitudes at 5 ANS passbands (15, 18, 22, 25, 33) from Wesselius et al. (1982, Cat. II/97) J, H, K from IR 2MASS Catalog (Kleinmann et al., 1994Ap&SS.217...11K). (6 data files).

  17. First Circumstellar Disk around a Massive Star

    NASA Astrophysics Data System (ADS)

    1998-06-01

    arrow). Earlier observations with radio telescopes of the object G339.88-1.26 , deeply embedded in an interstellar nebula, had been interpreted in terms of the possible existence of a circumstellar disk around a high-mass star. It was concluded that the star responsible for heating the surrounding gas must be very hot and also that it must be intrinsically very bright. The star, most likely of spectral type O9, would have a luminosity 10,000 times higher than that of the Sun and a mass of about 20 times that of the Sun. From the measured velocity, the likely distance of this object is about 10,000 light-years. The object is associated with several "spots" of very strong radio emission from methanol molecules (methanol masers). Interestingly, they form a chain in the sky and the measured velocities of the individual spots are indicative for orbital motion in a rotating disk around the central star. The circumstellar disk ESO PR Photo 22/98 ESO PR Photo 22b/98 [JPEG, 640k] The TIMMI 10 µm image of the inclined dust disk around a hot O9 star at the G339.88-1.26 radio source. The diameter of the disk is of the order of 5 arcsec, i.e. at the most probable distance to the object (10,000 lightyears) it is 20,000 times larger than the diameter of the Earth's orbit around the Sun. The new TIMMI observations of G339.88-1.26 showed an elliptical object with strong infrared radiation. The peak of this radiation (as seen in the sky) coincides with the peak of the radio emission. Furthermore, the apparent orientation of the disk is well aligned with that of the methanol maser "spots". There is little doubt that this object is indeed the infrared image of a circumstellar disk, viewed at an angle. As far as known, this is the first direct image of a disk around a very massive star. At a wavelength of 10 µm, however, the central star that is responsible for heating the dust disc, cannot be seen in spite of its rather high luminosity. This is because it radiates mostly in the ultra

  18. Effect of annealing on the charge-voltage characteristics of SrBi2(TaxNb1-x)2O9 films

    NASA Astrophysics Data System (ADS)

    Morozovsky, N. V.; Semchenko, A. V.; Sidsky, V. V.; Kolos, V. V.; Turtsevich, A. S.; Eliseev, E. A.; Morozovska, A. N.

    2015-05-01

    The effect of changes of the Nb content and annealing on charge-voltage and current-voltage characteristics of film structures Pt/SrBi2(Ta1-xNbx)2O9/Pt/TiO2/SiO2/Si-substrate with х=0, 0.1, 0.2 was studied theoretically and experimentally. Theoretical modeling, which takes into account the mobile charged donors impact on the features of charge-voltage and current-voltage characteristics of ferroelectric-semiconductor films, revealed the changes of conductivity value and ferroelectric parameters. The results of theoretical analysis and experimental results are in qualitative agreement.

  19. Compatibilities of YBa2Cu3O(9-delta) type phase in quintenary systems Y-Ba-Cu-O-X (impurity)

    NASA Technical Reports Server (NTRS)

    Karen, P.; Braaten, O.; Fjellvag, H.; Kjekshus, A.

    1991-01-01

    Isothermal phase diagrams at various oxygen pressures were studied by powder diffraction and chemical analytical methods. The components, Y, Ba, Cu, and O (specifically O2, O2-, and O2 sup 2-) are treated, together with C (specifically CO2 and CO2 sup 2-), alkaline metals, Mg, alkaline earths, Sc, 3-d and 4-f elements. Effects of the substitutions at the structural sites of YBa2Cu3O(9-delta) on T sub c are discussed with respect to changes in crystallochemical characteristics of the substituted phase and to the nature of the substituents.

  20. Neutron powder diffraction study of Ba3ZnRu2-xIrxO9 (x = 0, 1, 2) with 6H-type perovskite structure

    NASA Astrophysics Data System (ADS)

    Beran, P.; Ivanov, S. A.; Nordblad, P.; Middey, S.; Nag, A.; Sarma, D. D.; Ray, S.; Mathieu, R.

    2015-12-01

    The triple perovskites Ba3ZnRu2-xIrxO9 with x = 0, 1, and 2 are insulating compounds in which Ru(Ir) cations form a dimer state. Polycrystalline samples of these materials were studied using neutron powder diffraction (NPD) at 10 and 295 K. No structural transition nor evidence of long range magnetic order was observed within the investigated temperature range. The results from structural refinements of the NPD data and its polyhedral analysis are presented, and discussed as a function of Ru/Ir content.

  1. Hydrothermal synthesis and characterization of the first mixed alkali borate-nitrate K3Na[B6O9(OH)3]NO3

    NASA Astrophysics Data System (ADS)

    Ortner, Teresa S.; Wurst, Klaus; Perfler, Lukas; Tribus, Martina; Huppertz, Hubert

    2015-01-01

    The first mixed alkali borate-nitrate K3Na[B6O9(OH)3]NO3 was synthesized under hydrothermal conditions from Na2B4O7·10H2O and K2B4O7·4H2O using KNO3 as a nitrate source. The compound crystallizes in the space group Pnnm (no. 58) with the lattice parameters a=1320.8(3), b=910.7(2), and c=1232.5(3) pm (Z=4). Isolated Sechserrings formed by BO4 and BO3 groups are linked through hydrogen bridges to form a three-dimensional network.

  2. Characteristic length scale dependence on conductivity for La2-xErxMo2O9 (0.05 ≤ x ≤ 0.3) oxide ion conductors

    NASA Astrophysics Data System (ADS)

    Paul, T.; Ghosh, A.

    2016-05-01

    Structural property of polycrystalline La2-xErxMo2O9 has been investigated. Rietveld refinements at room temperature of the materials suggest a single phase nature with cubic symmetry (space group P213). The electron density contour plot confirms the nature of different cation-oxygen bonds. Time dependent mean square displacement (√) and the spatial extent of the sub-diffusive motion (√) are evaluated using the linear response theory. The localized hop at O2 and O3 sites is found to be favorable for oxygen ion migration for these systems.

  3. The First Stars

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2010-10-01

    The standard cosmological model predicts that the first cosmological objects are formed when the age of the universe is a few hundred million years. Recent theoretical studies and numerical simulations consistently suggest that the first objects are very massive primordial stars. We introduce the key physics and explain why the first stars are thought to be massive, rather than to be low-mass stars. The state-of-the-art simulations include all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to very high ``stellar'' densities. Evolutionary calculations of the primordial stars suggest the formation of massive blackholes in the early universe. Finally, we show the results from high-resolution simulations of star formation in a low-metallicity gas. Vigorous fragmentation is triggered in a star-forming gas cloud at a metallicity of as low as Z = 10-5Zsolar.

  4. Cooling of dense stars

    NASA Technical Reports Server (NTRS)

    Tsuruta, S.

    1972-01-01

    Cooling rates were calculated for neutron stars of about one solar mass and 10 km radius, with magnetic fields from zero to about 10 to the 14th power gauss, for extreme cases of maximum and zero superfluidity. The results show that most pulsars are so cold that thermal ionization of surface atoms would be negligible. Nucleon superfluidity and crystallization of heavy nuclei were treated quantitatively, and more realistic hadron star models were chosen. Cooling rates were calculated for a stable hyperon star near the maximum mass limit, a medium weight neutron star, and a light neutron star with neutron-rich heavy nuclei near the minimum mass limit. Results show that cooling rates are a sensitive function of density. The Crab and Vela pulsars are considered, as well as cooling of a massive white dwarf star.

  5. Activity in F stars

    NASA Technical Reports Server (NTRS)

    Wolff, Sidney C.; Boesgaard, Ann Merchant; Simon, Theodore

    1986-01-01

    Measurements of He I 5876 A and IUE measurements of chromospheric and transition region lines in a large sample of F-type stars are presented. The data show that activity is detectable in nearly all early F-type stars and differs in several of its characteristics from that typically seen in cooler stars with slow rotation and fully developed convective zones. The onset of activity occurs near B-V = 0.28, which corresponds approximately to spectral type F0 and T(eff) = 7300 K. There is no correlation between the level of activity and the abundances of lithium and beryllium in F stars hotter than T(eff) = 6600 K. All but one of the stars in the 6600-7300 K temperature interval are active. The levels of activity in these stars are independent of Rossby number.

  6. Intelligent star tracker

    NASA Astrophysics Data System (ADS)

    Clark, Natalie

    2001-11-01

    Current state-of-the-art commercial star sensors typically weigh 15 pounds, attain 5 to 10 arc-second accuracy, and use roughly 10 watts of power. Unfortunately, the current state-of-the-art commercial star sensors do not meet many of NASA's next-generation spacecraft and instrument needs. Nor do they satisfy Air Force's needs for micro/nano-satellite systems. In an effort to satisfy micro/nano satellite mission needs the Air Force Research Laboratory is developing an intelligent star Tracker, called IntelliStar, which incorporates several novel technologies including Silicon carbide optical housing, MEMs based adaptive optic technologies, smart active pixels, and algebraic coding theory. The design considerations associated with the development of the IntelliStar system are presented along with experimental results which characterize each technologies contribution to overall system performance. In addition to being light weight, the IntelliStar System offers advantages in speed, size, power consumption, and radiation tolerance.

  7. V 3903 Sagittarii: a massive main-sequence (O7V+O9V) detached eclipsing binary

    NASA Astrophysics Data System (ADS)

    Vaz, L. P. R.; Cunha, N. C. S.; Vieira, E. F.; Myrrha, M. L. M.

    1997-11-01

    We present for the first time an analysis based on uvby light curves, Hβ indices and on new spectroscopic data of the massive detached double-lined O-type eclipsing binary V 3903Sgr. The uvby light curves are analysed with the WINK (initial solutions) and the Wilson-Devinney (WD, final solution) programs. Both codes were used in their extended versions, with stellar atmospheres and taking into account the geometric distortions and photometric effects caused by proximity of the components. The spectroscopic CCD observations were analysed with the harmonic ``Wilsing-Russell'' and the ``Lehman-Filhes'' methods. We conclude that V 3903Sgr is one of the rare O-type detached systems where both components are still on the initial phases of the main sequence, with an age of either 1.6x10(6) yrs or 2.5x10(6) yrs (depending on the evolutionary model adopted) at a distance of ~1500pc, the same as for the Lagoon Nebula (Messier8) complex, of which the system is probably a member. We determine the absolute dimensions: M_A=27.27+/-0.55, R_A=8.088+/-% 0.086, M_B=19.01+/-0.44 and R_B=6.125+/-0.060 (solar units). There is no evidence of mass transfer and the system is detached. The orbit is circular, and both components show synchronous rotation, despite their early evolutionary stage. The absolute dimensions determined should be representative for normal single stars. Amongst the massive systems (M>17Msun) with precise absolute dimensions (errors <2%), V 3903Sgr is that with the most massive primary, with the largest mass difference between the components, and it is the youngest one. Based on data collected with the 60$\\,$cm and 1.6$\\,$m telescopes at the Pico dos Dias Observatory, Na\\-tional Laboratory of Astrophysics, LNA-CNPq, Bra\\-só\\-polis, MG, Brazil and with the Danish 50$\\,$cm telescope (SAT) at the European Southern Observatory (ESO), La Silla, Chile

  8. The MiMeS survey of magnetism in massive stars: CNO surface abundances of Galactic O stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Hervé, A.; Bouret, J.-C.; Marcolino, W.; Wade, G. A.; Neiner, C.; Alecian, E.; Grunhut, J.; Petit, V.

    2015-03-01

    Context. The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss, and rotation are the main drivers of stellar evolution. Binarity and the magnetic field may also significantly affect the fate of massive stars. Aims: Our goal is to investigate the evolution of single O stars in the Galaxy. Methods: For that, we used a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We relied on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We performed spectral modelling with the code CMFGEN. We determined the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen, and oxygen. Results: Most of our sample stars have initial masses in the range of 20 to 50 M⊙. We show that nitrogen is more enriched and carbon and oxygen are more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More massive stars, within a given luminosity class, appear to be more chemically enriched than lower mass stars. We compare our results with predictions of three types of evolutionary models and show that for two sets of models, 80% of our sample can be explained by stellar evolution including rotation. The effect of magnetism on surface abundances is unconstrained. Conclusions: Our study indicates that in the 20-50 M⊙ mass range, the surface chemical abundances of most single O stars in the Galaxy are fairly well accounted for by stellar evolution of rotating stars. Based on observations obtained at 1) the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique of France; 2) at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut

  9. Strange Nonchaotic Stars

    NASA Astrophysics Data System (ADS)

    Lindner, John F.; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G.; Ditto, William L.

    2015-02-01

    The unprecedented light curves of the Kepler space telescope document how the brightness of some stars pulsates at primary and secondary frequencies whose ratios are near the golden mean, the most irrational number. A nonlinear dynamical system driven by an irrational ratio of frequencies generically exhibits a strange but nonchaotic attractor. For Kepler's "golden" stars, we present evidence of the first observation of strange nonchaotic dynamics in nature outside the laboratory. This discovery could aid the classification and detailed modeling of variable stars.

  10. Nagyszombat and the stars

    NASA Astrophysics Data System (ADS)

    Zsoldos, E.

    Péter Pázmány, founder of the University of Nagyszombat, considered stars in terms inherited from medieval times. The theses, connected to the university graduation, soon left this definition, and imagined stars as made from sublunar elements. The 1753 decree of the Empress Maria Theresia ordered university professors to publish textbooks. These textbooks, together with the theses showed a definite improvement, defining stars according to contemporary knowledge.

  11. CSTAR star catalogue development

    NASA Technical Reports Server (NTRS)

    Uhde-Lacovara, J. A.

    1986-01-01

    The Continuous Stellar Tracking Attitude Reference (CSTAR) system is an in-house project for the Space Station to provide high accuracy, drift free attitude and angular rate information for the GN&C system. Constraints exist on the star catalogue incorporated in the system. These constraints include the following: mass memory allocated for catalogue storage, star tracker imaging sensitivity, the minimum resolvable separation angle between stars, the width of the field of view of the star tracker, and the desired number of stars to be tracked in a field of view. The Smithsonian Astrophysical Observatory (SAO) catalogue is the basis reference for this study. As it stands, the SAO does not meet the requirements of any of the above constraints. Star selection algorithms have been devised for catalogue optimization. Star distribution statistics have been obtained to aid in the development of these rules. VAX based software has been developed to implement the star selection algorithms. The software is modular and provides a design tool to tailor the catalogue to available star tracker technology. The SAO catalogue has been optimized for the requirements of the present CSTAR system.

  12. Introduction to neutron stars

    SciTech Connect

    Lattimer, James M.

    2015-02-24

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  13. Delta Scuti stars: Theory

    SciTech Connect

    Guzik, J.A.

    1998-03-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one`s understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying {delta} Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for {delta} Scuti stars, using FG Vir, {delta} Scuti, and CD-24{degree} 7599 as examples.

  14. Strange Nonchaotic Stars

    NASA Astrophysics Data System (ADS)

    Lindner, John F.; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G.; Ditto, William L.

    2015-08-01

    Exploiting the unprecedented capabilities of the planet-hunting Kepler space telescope, which stared at 150 000 stars for four years, we discuss recent evidence that certain stars dim and brighten in complex patterns with fractal features. Such stars pulsate at primary and secondary frequencies whose ratios are near the famous golden mean, the most irrational number. A nonlinear system driven by an irrational ratio of frequencies is generically attracted toward a “strange” behavior that is geometrically fractal without displaying the “butterfly effect” of chaos. Strange nonchaotic attractors have been observed in laboratory experiments and have been hypothesized to describe the electrochemical activity of the brain, but a bluish white star 16 000 light years from Earth in the constellation Lyra may manifest, in the scale-free distribution of its minor frequency components, the first strange nonchaotic attractor observed in the wild. The recognition of stellar strange nonchaotic dynamics may improve the classification of these stars and refine the physical modeling of their interiors. We also discuss nonlinear analysis of other RR Lyrae stars in Kepler field of view and discuss some toy models for modeling these stars.References: 1) Hippke, Michael, et al. "Pulsation period variations in the RRc Lyrae star KIC 5520878." The Astrophysical Journal 798.1 (2015): 42.2) Lindner, John F., et al. "Strange nonchaotic stars." Phys. Rev. Lett. 114, 054101 (2015)

  15. Massive soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  16. Combinations of 148 navigation stars and the star tracker

    NASA Technical Reports Server (NTRS)

    Duncan, R.

    1980-01-01

    The angular separation of all star combinations for 148 nav star on the onboard software for space transportation system-3 flight and following missions is presented as well as the separation of each pair that satisfies the viewing constraints of using both star trackers simultaneously. Tables show (1) shuttle star catalog 1980 star position in M 1950 coordinates; (2) two star combination of 148 nav stars; and (3) summary of two star-combinations of the star tracker 5 deg filter. These 148 stars present 10,875 combinations. For the star tracker filters of plus or minus 5 deg, there are 875 combinations. Formalhaut (nav star 26) has the best number of combinations, which is 33.

  17. VizieR Online Data Catalog: Far-UV spectral atlas of O-type stars (Smith, 2012)

    NASA Astrophysics Data System (ADS)

    Smith, M. A.

    2012-10-01

    In this paper, we present a spectral atlas covering the wavelength interval 930-1188Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. (4 data files).

  18. Magnetic phase diagram and multiferroicity of Ba3MnNb2O9 : A spin -52 triangular lattice antiferromagnet with weak easy-axis anisotropy

    DOE PAGESBeta

    Lee, M.; Choi, E. S.; Huang, X.; Ma, J.; Dela Cruz, C. R.; Matsuda, M.; Tian, W.; Dun, Z. L.; Dong, S.; Zhou, H. D.

    2014-12-01

    Here we have performed magnetic, electric, thermal and neutron powder diffraction (NPD) experiments as well as density functional theory (DFT) calculations on Ba3MnNb2 O9. All results suggest that Ba3MnNb2 O9 is a spin-5/2 triangular lattice antiferromagnet (TLAF) with weak easy-axis anisotropy. At zero field, we observed a narrow two-step transition at TN1 = 3.4 K and TN2 = 3.0 K. The neutron diffraction measurement and the DFT calculation indicate a 120 spin structure in ab plane with out-of-plane canting at low temperatures. With increasing magnetic field, the 120 spin structure evolves into up-up-down (uud) and oblique phases showing successive magneticmore » phase transitions, which fits well to the theoretical prediction for the 2D Heisenberg TLAF with classical spins. Ultimately, multiferroicity is observed when the spins are not collinear but suppressed in the uud and oblique phases.« less

  19. Electronic structure of alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4 single crystal: DFT approach

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Kamarudin, H.; Auluck, S.

    2015-10-01

    The electronic band structure, total and angular momentum resolved projected density of states for NaSr3Be3B3O9F4 are calculated using the all-electron full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) method. The calculations are performed within four exchange correlations namely; local density approximation (LDA), general gradient approximation (PBE-GGA), Engel-Vosko generalized gradient approximation (EVGGA) and the recently modified Becke-Johnson potential (mBJ). Calculations suggest that NaSr3Be3B3O9F4 is a direct wide band gap semiconductor. The exchange correlations potentials exhibit significant influence on the value of the energy gap being about 4.82 eV (LDA), 5.16 eV (GGA), 6.20 (EVGGA) and 7.20 eV (mBJ). The mBJ approach succeed by large amount in bringing the calculated energy gap closer to the experimental one (7.28 eV). The angular momentum resolved projected density of states shows the existence of a strong hybridization between the various orbitals. In additional we have calculated the electronic charge density distribution in two crystallographic planes namely (1 0 1) and (0 0 -1) to visualized the chemical bonding characters.

  20. Magnetic phase diagram and multiferroicity of Ba3MnNb2O9: A spin-5/2 triangular lattice antiferromagnet with weak easy-axis anisotropy

    NASA Astrophysics Data System (ADS)

    Lee, M.; Choi, E. S.; Huang, X.; Ma, J.; Dela Cruz, C. R.; Matsuda, M.; Tian, W.; Dun, Z. L.; Dong, S.; Zhou, H. D.

    2014-12-01

    We have performed magnetic, electric, thermal, and neutron powder diffraction (NPD) experiments as well as density functional theory (DFT) calculations on Ba3MnNb2O9 . All results suggest that Ba3MnNb2O9 is a spin-5/2 triangular lattice antiferromagnet (TLAF) with weak easy-axis anisotropy. At zero field, we observed a narrow two-step transition at TN 1=3.4 K and TN 2=3.0 K. The neutron diffraction measurement and the DFT calculation indicate a 120∘ spin structure in the a b plane with out-of-plane canting at low temperatures. With increasing magnetic field, the 120∘ spin structure evolves into up-up-down (u u d ) and oblique phases showing successive magnetic phase transitions, which fits well to the theoretical prediction for the 2D Heisenberg TLAF with classical spins. Multiferroicity is observed when the spins are not collinear but suppressed in the u u d and oblique phases.

  1. Oxygen-vacancy-related dielectric relaxation in SrBi2Ta1.8V0.2O9 ferroelectrics

    NASA Astrophysics Data System (ADS)

    Wu, Yun; Forbess, Mike J.; Seraji, Seana; Limmer, Steven J.; Chou, Tammy P.; Cao, Guozhong

    2001-05-01

    The strontium bismuth tantalate vanadate, SrBi2Ta1.8V0.2O9, (SBTV) layered perovskite ferroelectrics were made by solid state powder sintering. It was found that the SBTV ferroelectrics had the same crystal structure as that of strontium bismuth tantalate, SrBi2Ta2O9 (SBT), but an increased paraferroelectric transition temperature at ˜360 °C as compared to 305 °C for SBT. In addition, SBTV ferroelectrics showed a frequency dispersion at low frequencies and broadened dielectric peaks at the paraferroelectric transition temperature that shifted to a higher temperature with a reduced frequency. However, after a postsintering annealing at 850 °C in air for 60 h, SBTV ferroelectrics showed reduced dielectric constants and tangent loss, particularly at high temperatures. In addition, no frequency dependence of paraferroelectric transition was found in the annealed SBTV ferroelectrics. Furthermore, there was a significant reduction in dc conductivity with annealing. The prior results implied that the dielectric relaxation in the as-sintered SBTV ferroelectrics was most likely due to the oxygen-vacancy-related dielectric relaxation instead of relaxor ferroelectric behavior.

  2. Oriented Nucleation of both Ge-Fresnoite and Benitoite/BaGe4O9 during the Surface Crystallisation of Glass Studied by Electron Backscatter Diffraction

    PubMed Central

    Wisniewski, Wolfgang; Patschger, Marek; Murdzheva, Steliana; Thieme, Christian; Rüssel, Christian

    2016-01-01

    Two glasses of the compositions 2 BaO - TiO2 - 2.75 GeO2 and 2 BaO – TiO2 –3.67 GeO2 (also known as BTG55) are annealed at temperatures from 680 to 970 °C to induce surface crystallization. The resulting samples are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). Ge-Fresnoite (Ba2TiGe2O8, BTG) is observed at the immediate surface of all samples and oriented nucleation is proven in both compositions. After a very fast kinetic selection, the crystal growth of BTG into the bulk occurs via highly oriented dendrites where the c-axes are oriented perpendicular to the surface. The growth of this oriented layer is finally blocked by dendritc BTG originating from bulk nucleation. The secondary phases BaTiGe3O9 (benitoite) and BaGe4O9 are also identified near the surface by XRD and localized by EBSD which additionally indicates orientation preferences for these phases. This behaviour is in contrast with previous reports from the Ba2TiSi2O8 as well as the Sr2TiSi2O8 systems. PMID:26853738

  3. Dilute ferrimagnetism of ilmenites Mn3FeTiSbO9 and Mn4FeTi2SbO12

    NASA Astrophysics Data System (ADS)

    Bazuev, G. V.; Korolev, A. V.; Golovkin, B. G.

    2016-07-01

    Metastable solid solutions (SS) Mn3FeTiSbO9 and Mn4FeTi2SbO12 with the ilmenite structure (space group R bar 3) have been prepared by quenching at normal conditions. The compositions of the compounds have been justified using EDX spectroscopy and X-ray diffraction. The magnetic properties of SSs have been analyzed by comparison with ferrimagnetic ilmenite Mn2FeSbO6 ( T N = 269 K) as a natural mineral and ceramics obtained at high pressure and high temperature. The solid solutions have been characterized as dilute magnetic systems formed as a result of substitution of nonmagnetic cations Ti4+ for a part of Fe3+ and Sb5+ cations. Mn3FeTiSbO9 is considered as a ferromagnetic with T N = 171 K and Mn4FeTi2SbO12 as a magnetic with the concentration of magnetic clusters below the percolation threshold.

  4. Oriented Nucleation of both Ge-Fresnoite and Benitoite/BaGe4O9 during the Surface Crystallisation of Glass Studied by Electron Backscatter Diffraction.

    PubMed

    Wisniewski, Wolfgang; Patschger, Marek; Murdzheva, Steliana; Thieme, Christian; Rüssel, Christian

    2016-01-01

    Two glasses of the compositions 2 BaO - TiO2 - 2.75 GeO2 and 2 BaO - TiO2 -3.67 GeO2 (also known as BTG55) are annealed at temperatures from 680 to 970 °C to induce surface crystallization. The resulting samples are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). Ge-Fresnoite (Ba2TiGe2O8, BTG) is observed at the immediate surface of all samples and oriented nucleation is proven in both compositions. After a very fast kinetic selection, the crystal growth of BTG into the bulk occurs via highly oriented dendrites where the c-axes are oriented perpendicular to the surface. The growth of this oriented layer is finally blocked by dendritc BTG originating from bulk nucleation. The secondary phases BaTiGe3O9 (benitoite) and BaGe4O9 are also identified near the surface by XRD and localized by EBSD which additionally indicates orientation preferences for these phases. This behaviour is in contrast with previous reports from the Ba2TiSi2O8 as well as the Sr2TiSi2O8 systems. PMID:26853738

  5. Identifying Young, Nearby Stars

    NASA Technical Reports Server (NTRS)

    Webb, Rich; Song, Inseok; Zuckerman, Ben; Bessell, Mike

    2001-01-01

    Young stars have certain characteristics, e.g., high atmospheric abundance of lithium and chromospheric activity, fast rotation, distinctive space motion and strong X-ray flux compared to that of older main sequence stars. We have selected a list of candidate young (<100Myr) and nearby (<60pc) stars based on their space motion and/or strong X-ray flux. To determine space motion of a star, one needs to know its coordinates (RA, DEC), proper motion, distance, and radial velocity. The Hipparcos and Tycho catalogues provide all this information except radial velocities. We anticipate eventually searching approx. 1000 nearby stars for signs of extreme youth. Future studies of the young stars so identified will help clarify the formation of planetary systems for times between 10 and 100 million years. Certainly, the final output of this study will be a very useful resource, especially for adaptive optics and space based searches for Jupiter-mass planets and dusty proto-planetary disks. We have begun spectroscopic observations in January, 2001 with the 2.3 m telescope at Siding Spring Observatory (SSO) in New South Wales, Australia. These spectra will be used to determine radial velocities and other youth indicators such as Li 6708A absorption strength and Hydrogen Balmer line intensity. Additional observations of southern hemisphere stars from SSO are scheduled in April and northern hemisphere observations will take place in May and July at the Lick Observatory of the University of California. AT SSO, to date, we have observed about 100 stars with a high resolution spectrometer (echelle) and about 50 stars with a medium spectral resolution spectrometer (the "DBS"). About 20% of these stars turn out to be young stars. Among these, two especially noteworthy stars appear to be the closest T-Tauri stars ever identified. Interestingly, these stars share the same space motions as that of a very famous star with a dusty circumstellar disk--beta Pictoris. This new finding better

  6. Extreme horizontal branch stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    A review is presented on the properties, origin and evolutionary links of hot subluminous stars which are generally believed to be extreme Horizontal Branch stars or closely related objects. They exist both in the disk and halo populations (globular clusters) of the Galaxy. Amongst the field stars a large fraction of sdBs are found to reside in close binaries. The companions are predominantly white dwarfs, but also low mass main sequence stars are quite common. Systems with sufficiently massive white dwarf companions may qualify as Supernova Ia progenitors. Recently evidence has been found that the masses of some unseen companions might exceed the Chandrasekhar mass, hence they must be neutron stars or black holes. Even a planet has recently been detected orbiting the pulsating sdB star V391 Peg. Quite to the opposite,in globular clusters, only very few sdB binaries amongst are found indicating that the dominant sdB formation processes is different in a dense environment. Binary population synthesis models identify three formation channels, (i) stable Roche lobe overflow, (ii) one or two common envelope ejection phases and (iii) the merger of two helium white dwarfs. The latter channel may explain the properties of the He-enriched subluminous O stars, the hotter sisters of the sdB stars, because their binary fraction is lower than that of the sdBs by a factor of ten or more. The rivaling ''late hot flasher'' scenario is also discussed. Pulsating subluminous B (sdB) stars play an important role for asteroseismology as this technique has already led to mass determinations for a handful of stars. A unique hyper-velocity sdO star moving so fast that it is unbound to the Galaxy has probably been ejected by the super-massive black hole in the Galactic centre.

  7. GLOBAL STAR FORMATION REVISITED

    SciTech Connect

    Silk, Joseph; Norman, Colin E-mail: norman@stsci.edu

    2009-07-20

    A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

  8. The Pistol Star

    NASA Astrophysics Data System (ADS)

    Figer, Donald F.; Najarro, Francisco; Morris, Mark; McLean, Ian S.; Geballe, Thomas R.; Ghez, Andrea M.; Langer, Norbert

    1998-10-01

    We present new near-infrared data and analysis, which indicate that the Pistol Star is one of the most luminous stars known, adding another test point for massive star formation and stellar evolution theories. We estimate an extinction of AK = 3.2 +/- 0.5 using the near-infrared colors of the star and of surrounding stars in the young Quintuplet cluster. Using our wind/atmosphere code, we find two families of models that fit the spectral energy distribution and detailed line profiles. The lower luminosity models give L = 106.6+/-0.2 L⊙ and Teff = 104.15+/-0.01 K, while the higher luminosity models give L = 107.2+/-0.2 L⊙ and Teff = 104.33+/-0.01 K; the error in luminosity assumes an uncertainty of +/-0.5 in AK, while the error in Teff is constrained by detailed line modeling. The models also reveal a helium enriched surface. As previously existing stellar evolution models do not extend to such high luminosities, we employ new evolutionary tracks for very massive stars to determine the initial mass and age of the Pistol Star, and estimate Minitial = 200-250 M⊙ and an age of 1.7-2.1 Myr. The inferred luminosity and temperature place the star in a sparsely populated zone in the H-R diagram where luminous blue variables (LBVs) are often found. This is consistent with our evolutionary models, which predict that the star is in an unstable evolutionary stage. We interpret the star and its surrounding nebula as an LBV that has recently ejected large amounts of material. Our K-band speckle-imaging data reveal the star to be single down to a projected separation of 110 AU.

  9. Neutron Star Compared to Manhattan

    NASA Video Gallery

    A pulsar is a neutron star, the crushed core of a star that has exploded. Neutron stars crush half a million times more mass than Earth into a sphere no larger than Manhattan, as animated in this s...

  10. Stars and Flowers, Flowers and Stars

    NASA Astrophysics Data System (ADS)

    Minti, Hari

    2012-12-01

    The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

  11. Zn(1,3-DAP)[B4O7]: a rare chiral zeolitic framework constructed of four-connected [B4O9] clusters with a single-stranded helical channel.

    PubMed

    Pan, Chun-Yang; Zhong, Li-Juan; Zhao, Feng-Hua; Yang, Hong-Mei; Zhou, Jian

    2015-01-14

    A zinc borate Zn(1,3-DAP)[B4O7] (1) was prepared. 1 was revealed to be a rare chiral zeolitic framework based on a [B4O9] cluster. The combination of a [B4O9] cluster and Zn(1,3-DAP)O3 chain produced a helical ribbon motif and gave rise to a single-stranded helical channel. PMID:25421529

  12. Modeling rapidly rotating stars

    NASA Astrophysics Data System (ADS)

    Rieutord, M.

    2006-06-01

    We review the quest of modeling rapidly rotating stars during the past 40 years and detail the challenges to be taken up by models facing new data from interferometry, seismology, spectroscopy... We then present the progress of the ESTER project aimed at giving a physically self-consistent model for the structure and evolution of rapidly rotating stars.

  13. Party with the Stars.

    ERIC Educational Resources Information Center

    Blaine, Lloyd

    1997-01-01

    Describes a Star Party which involves comparing the different colors of the stars, demonstrating how astronomers measure the sky with degrees, determining the cardinal direction, discussing numerous stories that ancient civilizations gave to constellations, exercising science process skills, and using science instruments. (JRH)

  14. Neutron star models

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Bowers, R. L.

    1981-01-01

    The current state of neutron star structure calculations is reviewed. Uncertainties in the equation of state for matter at and above nuclear density remain. The role of the delta resonance, pion condensates, and quark matter is reviewed. It is found that recent models yield stable neutron star masses which are consistent with observational estimates.

  15. Observing Double Stars

    NASA Astrophysics Data System (ADS)

    Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

    2012-05-01

    Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

  16. Science Through ARts (STAR)

    NASA Technical Reports Server (NTRS)

    Kolecki, Joseph; Petersen, Ruth; Williams, Lawrence

    2002-01-01

    Science Through ARts (STAR) is an educational initiative designed to teach students through a multidisciplinary approach to learning. This presentation describes the STAR pilot project, which will use Mars exploration as the topic to be integrated. Schools from the United Kingdom, Japan, the United States, and possibly eastern Europe are expected to participate in the pilot project.

  17. Populations of Carbon Stars

    NASA Astrophysics Data System (ADS)

    Lloyd Evans, T.

    2011-09-01

    Carbon stars in the Galaxy do not constitute a single family, but may be divided over several types with distinctive spectroscopic and photometric properties. A subtype of the N stars, characterised by high velocities and weak CN bands, may have been captured by the Milky Way from a cannibalised dwarf galaxy.

  18. Science through ARts (STAR)

    ERIC Educational Resources Information Center

    Densmore, Marycay; Kolecki, Joseph C.; Miller, Allan; Petersen, Ruth; Terrell, Mike

    2005-01-01

    Science Through ARts (STAR) is a free, international, cross-curricular program thematically aligned with "The Vision for Space Exploration," a framework of goals and objectives published by NASA in February 2004. Through the STAR program, students in grades 5 through 12 are encouraged to apply their knowledge in creative ways as they approach a…

  19. First detections of FS Canis Majoris stars in clusters. Evolutionary state as constrained by coeval massive stars

    NASA Astrophysics Data System (ADS)

    de la Fuente, D.; Najarro, F.; Trombley, C.; Davies, B.; Figer, D. F.

    2015-03-01

    Context. FS CMa stars are low-luminosity objects showing the B[e] phenomenon whose evolutionary state remains a puzzle. These stars are surrounded by compact disks of warm dust of unknown origin. Hitherto, membership of FS CMa stars to coeval populations has never been confirmed. Aims: The discovery of low-luminosity line emitters in the young massive clusters Mercer 20 and Mercer 70 prompts us to investigate the nature of such objects. We intend to confirm membership to coeval populations in order to characterize these emission-line stars through the cluster properties. Methods: Based on ISAAC/VLT medium-resolution spectroscopy and NICMOS/HST photometry of massive cluster members, new characterizations of Mercer 20 and Mercer 70 are performed. Coevality of each cluster and membership of the newly-discovered B[e] objects are investigated using our observations as well as literature data of the surroundings. Infrared excess and narrow-band photometric properties of the B[e] stars are also studied. Results: We confirm and classify 22 new cluster members, including Wolf-Rayet stars and blue hypergiants. Spectral types (O9-B1.5 V) and radial velocities of B[e] objects are compatible with the remaining cluster members, while emission features of Mg ii, Fe ii], and [Fe ii] are identified in their spectra. The ages of these stars are 4.5 and 6 Myr, and they show mild infrared excesses. Conclusions: We confirm the presence of FS CMa stars in the coeval populations of Mercer 20 and Mercer 70. We discuss the nature and evolutionary state of FS CMa stars, discarding a post-AGB nature and introducing a new hypothesis about mergers. A new search method for FS CMa candidates in young massive clusters based on narrow-band Paschen-α photometry is proposed and tested in photometric data of other clusters, yielding three new candidates. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under program IDs 083.D

  20. Producing Runaway Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    How are the hypervelocity stars weve observed in our galaxy produced? A recent study suggests that these escapees could be accelerated by a massive black hole in the center of the Large Magellanic Cloud.A Black Hole SlingshotSince their discovery in 2005, weve observed dozens of candidate hypervelocity stars stars whose velocity in the rest frame of our galaxy exceeds the local escape velocity of the Milky Way. These stars present a huge puzzle: how did they attain these enormous velocities?One potential explanation is known as the Hills mechanism. In this process, a stellar binary is disrupted by a close encounter with a massive black hole (like those thought to reside at the center of every galaxy). One member of the binary is flung out of the system as a result of the close encounter, potentially reaching very large velocities.A star-forming region known as LHA 120-N 11, located within the LMC. Some binary star systems within the LMC might experience close encounters with a possible massive black hole at the LMCs center. [ESA/NASA/Hubble]Blame the LMC?Usually, discussions of the Hills mechanism assume that Sagittarius A*, the supermassive black hole at the center of the Milky Way, is the object guilty of accelerating the hypervelocity stars weve observed. But what if the culprit isnt Sgr A*, but a massive black hole at the center of the Large Magellanic Cloud (LMC), one of the Milky Ways satellite galaxies?Though we dont yet have evidence of a massive black hole at the center of the LMC, the dwarf galaxy is large enough to potentially host one as large as 100,000 solar masses. Assuming that it does, two scientists at the University of Cambridge, Douglas Boubert and Wyn Evans, have now modeled how this black hole might tear apart binary star systems and fling hypervelocity stars around the Milky Way.Models for AccelerationBoubert and Evans determined that the LMCs hypothetical black hole could easily eject stars at ~100 km/s, which is the escape velocity of the

  1. Activity Cycles in Stars

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    2009-01-01

    Starspots and stellar activity can be detected in other stars using high precision photometric and spectrometric measurements. These observations have provided some surprises (starspots at the poles - sunspots are rarely seen poleward of 40 degrees) but more importantly they reveal behaviors that constrain our models of solar-stellar magnetic dynamos. The observations reveal variations in cycle characteristics that depend upon the stellar structure, convection zone dynamics, and rotation rate. In general, the more rapidly rotating stars are more active. However, for stars like the Sun, some are found to be inactive while nearly identical stars are found to be very active indicating that periods like the Sun's Maunder Minimum (an inactive period from 1645 to 1715) are characteristic of Sun-like stars.

  2. Neutron stars - General review

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.; Canuto, V.

    1974-01-01

    A review is presented of those properties of neutron stars upon which there is general agreement and of those areas which currently remain in doubt. Developments in theoretical physics of neutron star interiors are summarized with particular attention devoted to hyperon interactions and the structure of interior layers. Determination of energy states and the composition of matter is described for successive layers, beginning with the surface and proceeding through the central region into the core. Problems encountered in determining the behavior of matter in the ultra-high density regime are discussed, and the effects of the magnetic field of a neutron star are evaluated along with the behavior of atomic structures in the field. The evolution of a neutron star is outlined with discussion centering on carbon detonation, cooling, vibrational damping, rotation, and pulsar glitches. The role of neutron stars in cosmic-ray propagation is considered.

  3. Star spot location estimation using Kalman filter for star tracker.

    PubMed

    Liu, Hai-bo; Yang, Jian-kun; Wang, Jiong-qi; Tan, Ji-chun; Li, Xiu-jian

    2011-04-20

    Star pattern recognition and attitude determination accuracy is highly dependent on star spot location accuracy for the star tracker. A star spot location estimation approach with the Kalman filter for a star tracker has been proposed, which consists of three steps. In the proposed approach, the approximate locations of the star spots in successive frames are predicted first; then the measurement star spot locations are achieved by defining a series of small windows around each predictive star spot location. Finally, the star spot locations are updated by the designed Kalman filter. To confirm the proposed star spot location estimation approach, the simulations based on the orbit data of the CHAMP satellite and the real guide star catalog are performed. The simulation results indicate that the proposed approach can filter out noises from the measurements remarkably if the sampling frequency is sufficient. PMID:21509065

  4. Catch a Star!

    NASA Astrophysics Data System (ADS)

    2006-11-01

    ESO and the European Association for Astronomy Education are launching today the 2007 edition of 'Catch a Star!', their international astronomy competition for school students. Now in its fifth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. Students are invited to 'become astronomers' and embark on a journey to explore the Universe. ESO PR Photo 42/06 The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. For the artistically minded, 'Catch a Star!' also includes an artwork competition, 'Catch a Star Artists'. "'Catch a Star!' offers a unique opportunity for students to learn more about astronomy and about the methods scientists use to discover new things about the Universe", said Douglas Pierce-Price, Education Officer at ESO. In teams, students choose an astronomical topic to study and produce an in-depth report. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes or a telescope of the future can contribute to their investigations of the subject. As well as the top prize - a trip to one of ESO's observatory sites in Chile - visits to observatories in Germany, Austria and Spain, and many other prizes are also available to be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners chosen with the help of a public online vote. The first editions of 'Catch a Star!' have attracted several hundred entries from more than 25 countries worldwide. Previous winning entries have included "Star clusters and the structure of the Milky Way" (Budapest, Hungary), "Vega" (Acqui Terme, Italy) and "Venus

  5. Making star teams out of star players.

    PubMed

    Mankins, Michael; Bird, Alan; Root, James

    2013-01-01

    Top talent is an invaluable asset: In highly specialized or creative work, for instance, "A" players are likely to be six times as productive as "B" players. So when your company has a crucial strategic project, why not multiply all that firepower and have a team of your best performers tackle it? Yet many companies hesitate to do this, believing that all-star teams don't work: Big egos will get in the way. The stars won't be able to work with one another. They'll drive the team Leader crazy. Mankins, Bird, and Root of Bain & Company believe it's time to set aside that thinking. They have seen all-star teams do extraordinary work. But there is a right way and a wrong way to organize them. Before you can even begin to assemble such a team, you need to have the right talent management practices, so you hire and develop the best people and know what they're capable of. You have to give the team appropriate incentives and leaders and support staffers who are stars in their own right. And projects that are ill-defined or small scale are not for all-star teams. Use them only for critical missions, and make sure their objectives are clear. Even with the right setup, things can still go wrong. The wise executive will take steps to manage egos, prune non-team-players, and prevent average coworkers from feeling completely undervalued. She will also invest a lot of time in choosing the right team Leader and will ask members for lots of feedback to monitor how that leader is doing. PMID:23390743

  6. Pseudosynchronization of Heartbeat Stars

    NASA Astrophysics Data System (ADS)

    Zimmerman, Mara; Thompson, Susan E.; Hambleton, Kelly; Fuller, Jim; Shporer, Avi; Isaacson, Howard T.; Howard, Andrew; Kurtz, Donald

    2016-01-01

    A type of eccentric binary star that undergoes extreme dynamic tidal forces, known as Heartbeat stars, were discovered by the Kepler Mission. As the two stars pass through periastron, the tidal distortion causes unique brightness variations. Short period, eccentric binary stars, like these, are theorized to pseudosynchronize, or reach a rotational frequency that matches the weighted average orbital angular velocity of the system. This pseudosynchronous rate, as predicted by Hut (1981), depends on the binary's orbital period and eccentricity. We tested whether sixteen heartbeat stars have pseudosynchronized. We measure the rotation rate from obvious spot signatures in the light curve. We measure the eccentricity by fitting the light curve using PHOEBE and are actively carrying out a radial velocity monitoring program with Keck/HIRES in order to improve these orbital parameters. Our initial results show that while most heartbeat stars appear to have pseudosynchronized we find stars with rotation frequencies both longer and shorter than this rate. We thank the SETI Institute REU program, the NSF, and the Kepler Guest Observer Program for making this work possible.

  7. Measuring stars with Gaia

    NASA Astrophysics Data System (ADS)

    Thévenin, F.

    2013-12-01

    Beyond the extraordinary three dimensional map that Gaia will create for a billion of stars, it will reveal the origin and history of the Milky Way as the major goal. This does not weakness the fantastic impact of Gaia on the stellar physic. It will put constraints on the modeling of stars to an extreme that consequently new input physics will be mandatory to understand a Gaia HR diagram. Stars are formed in populations and evolve as collection of objects revealing important clues on how they formed, what kind of mass function is active during the star formation, how frequent is the star formation, all of this is imprinted in the intrinsic properties of stars that large surveys combined together like Gaia, Kepler, PLATO will revealed. The characterization of stars hosting planets is also a goal of such combination of large surveys and in particular of the measure of distances in the Galaxy. The launch of Gaia is for November of 2013 and the output catalogue is expected for 2020. Then will start the beginning of a new Astrophysics touching so many topics that a new age of astrophysics is then foreseen.

  8. Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Mendez-Abreu, Jairo; Gallagher, John S.; Rafelski, Marc; Filho, Mercedes; Ceverino, Daniel

    2016-07-01

    The tadpole galaxy Kiso 5639 has a slowly rotating disk with a drop in metallicity at its star-forming head, suggesting that star formation was triggered by the accretion of metal-poor gas. We present multi-wavelength Hubble Space Telescope Wide Field Camera 3 images of UV through I band plus Hα to search for peripheral emission and determine the properties of various regions. The head has a mass in young stars of ∼ {10}6 {M}ȯ and an ionization rate of 6.4× {10}51 s‑1, equivalent to ∼2100 O9-type stars. There are four older star-forming regions in the tail, and an underlying disk with a photometric age of ∼1 Gyr. The mass distribution function of 61 star clusters is a power law with a slope of ‑1.73 ± 0.51. Fourteen young clusters in the head are more massive than {10}4 {M}ȯ , suggesting a clustering fraction of 30%–45%. Wispy filaments of Hα emission and young stars extend away from the galaxy. Shells and holes in the head H ii region could be from winds and supernovae. Gravity from the disk should limit the expansion of the H ii region, although hot gas might escape through the holes. The star formation surface density determined from Hα in the head is compared to that expected from likely pre-existing and accreted gas. Unless the surface density of the accreted gas is a factor of ∼3 or more larger than what was in the galaxy before, the star formation rate has to exceed the usual Kennicutt–Schmidt rate by a factor of ≥slant 5.

  9. A new Wolf-Rayet star and its circumstellar nebula in Aquila

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Kniazev, A. Y.; Hamann, W.-R.; Berdnikov, L. N.; Fabrika, S.; Valeev, A. F.

    2010-04-01

    We report the discovery of a new Wolf-Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR121b). We analysed the spectrum of WR121b by using the Potsdam Wolf-Rayet model atmospheres, obtaining a stellar temperature of ~=50kK. The stellar wind composition is dominated by helium with ~20 per cent of hydrogen. The stellar spectrum is highly reddened [E(B - V) = 2.85mag]. Adopting an absolute magnitude of Mv = -5.7, the star has a luminosity of logL/Lsolar = 5.75 and a mass-loss rate of 10-4.7Msolaryr-1, and resides at a distance of 6.3kpc. We searched for a possible parent cluster of WR121b and found that this star is located at ~=1° from the young star cluster embedded in the giant HII region W43 (containing a WN7+a/OB? star - WR121a). We also discovered a bow shock around the O9.5III star ALS9956, located at from the cluster. We discuss the possibility that WR121b and ALS9956 are runaway stars ejected from the cluster in W43. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); wrh@astro.physik.uni-potsdam.de (WRH); berdnik@sai.msu.ru (LNB); fabrika@sao.ru (SF); azamat@sao.ru (AFV)

  10. Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Mendez-Abreu, Jairo; Gallagher, John S.; Rafelski, Marc; Filho, Mercedes; Ceverino, Daniel

    2016-07-01

    The tadpole galaxy Kiso 5639 has a slowly rotating disk with a drop in metallicity at its star-forming head, suggesting that star formation was triggered by the accretion of metal-poor gas. We present multi-wavelength Hubble Space Telescope Wide Field Camera 3 images of UV through I band plus Hα to search for peripheral emission and determine the properties of various regions. The head has a mass in young stars of ˜ {10}6 {M}ȯ and an ionization rate of 6.4× {10}51 s‑1, equivalent to ˜2100 O9-type stars. There are four older star-forming regions in the tail, and an underlying disk with a photometric age of ˜1 Gyr. The mass distribution function of 61 star clusters is a power law with a slope of ‑1.73 ± 0.51. Fourteen young clusters in the head are more massive than {10}4 {M}ȯ , suggesting a clustering fraction of 30%–45%. Wispy filaments of Hα emission and young stars extend away from the galaxy. Shells and holes in the head H ii region could be from winds and supernovae. Gravity from the disk should limit the expansion of the H ii region, although hot gas might escape through the holes. The star formation surface density determined from Hα in the head is compared to that expected from likely pre-existing and accreted gas. Unless the surface density of the accreted gas is a factor of ˜3 or more larger than what was in the galaxy before, the star formation rate has to exceed the usual Kennicutt–Schmidt rate by a factor of ≥slant 5.

  11. Structure and magnetism in hexagonal tungsten bronze metal oxides AM1/3W8/3O9 (A-K, Rb, Cs; M-Cr, Fe)

    NASA Astrophysics Data System (ADS)

    Ivanov, S. A.; Sahu, J. R.; Voronkova, V. I.; Mathieu, R.; Nordblad, P.

    2015-02-01

    The structure and magnetic properties of hexagonal tungsten bronzes AM1/3W8/3O9 (A-K+, Rb+, Cs+; M- Cr3+, Fe3+) have been investigated. Pure ceramic samples were synthesized by solid-state reaction. The samples have been studied by X-ray powder diffraction in combination with magnetic measurements. The compounds crystallize in hexagonal space group P63/mcm. The substitution of magnetic ions into the WO6 octahedra yields dilute antiferromagnetic Cr3+-O2--Cr3+ (or Fe3+-O2--Fe3+) superexchange interaction causing the appearance of short-range magnetic order at low temperatures. The antiferromagnetic character of the interaction is supported by negative values of the derived Curie-Weiss temperatures, θCW. The magnitude of θCW is found to decrease with increasing ionic radius of the A cation.

  12. Bright green upconversion emission and enhanced ferroelectric polarization in Sr1-1.5xErxBi2Nb2O9

    NASA Astrophysics Data System (ADS)

    Wei, T.; Zhao, C. Z.; Zhou, Q. J.; Li, Z. P.; Wang, Y. Q.; Zhang, L. S.

    2014-05-01

    Upconversion (UC) luminescence and ferroelectric (FE) polarization properties were first investigated in polycrystalline Er3+-doped SrBi2Nb2O9 (SBN:xEr3+) samples. Bright UC green and weak UC red emission, originating from (2H11/2, 4S3/2)-4I15/2 and 4F9/2-4I15/2 transitions, respectively, was confirmed to be a two-photon energy transfer process. The UC green luminescence can be seen by the naked eye at room temperature. The optimal UC green emission was obtained when x = 5 mol.% in SBN:xEr3+. Furthermore, it is surprisingly found that a proper Er3+ doping can also remarkably enhance the FE polarization of SBN:xEr3+.

  13. Debye’s temperature and heat capacity for Sr0.15Ba0.85Bi2Nb2O9 relaxor ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Peláiz-Barranco, A.; González-Abreu, Y.; Saint-Grégoire, P.; Guerra, J. D. S.; Calderón-Piñar, F.

    2016-02-01

    A lead-free relaxor ferroelectric, Sr0.15Ba0.85Bi2Nb2O9, was synthesized via solid-state reaction and the temperature-dependence of the heat capacity was measured in a wide temperature range. The dielectric permittivity was also measured between 500Hz and 5MHz in the same temperature range. No anomaly has been detected in the heat capacity curve for the whole temperature range covered in the present experiments, while broad peaks have been observed in the dielectric permittivity with high frequency dispersion. A typical relaxor behavior has been observed from the dielectric analysis. The Debye’s temperature has showed a minimum value near the freezing temperature. The results are discussed considering the spin-glass model and the high frequency dispersion, which has been observed for the studied relaxor system.

  14. Static and Dynamical Properties of the Spin-1/2 Equilateral Triangular-Lattice Antiferromagnet Ba_{3}CoSb_{2}O_{9}.

    PubMed

    Ma, J; Kamiya, Y; Hong, Tao; Cao, H B; Ehlers, G; Tian, W; Batista, C D; Dun, Z L; Zhou, H D; Matsuda, M

    2016-02-26

    We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba_{3}CoSb_{2}O_{9}. Besides confirming that the Co^{2+} magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Thus, our results call for a new theoretical framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects. PMID:26967439

  15. Improved ferroelectric property and domain structure of highly a-oriented polycrystalline CaBi2Nb2O9 thin film

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Son, Jong Yeog

    2015-12-01

    A Lead-free ferroelectric CaBi2Nb2O9 (CBNO) thin film was deposited on Si substrate by pulsed laser deposition. TiO2 buffer layer was employed and Pt electrode was used for nano-scale capacitor. The x-ray diffraction reveals that the CBNO thin film has highly a-oriented polycrystalline structure. The highly a-oriented polycrystalline CBNO thin film significantly exhibit the enhanced ferroelectric property with a remnant polarization of 10 μC/cm2 compared to other values reported previously. In particular, the highly a-oriented polycrystalline CBNO thin film show faster ferroelectric switching characteristics than the epitaxially c-oriented CBNO thin film.

  16. Gapless quantum spin liquid ground state in the spin-1 antiferromagnet 6HB-Ba3NiSb2O9

    NASA Astrophysics Data System (ADS)

    Quilliam, J. A.; Bert, F.; Manseau, A.; Darie, C.; Guillot-Deudon, C.; Payen, C.; Baines, C.; Amato, A.; Mendels, P.

    2016-06-01

    We present an in-depth study of the magnetic properties of the spin-1 antiferromagnet 6HB-Ba3NiSb2O9 . μ SR measurements demonstrate that this material shows no static magnetism down to temperatures as low as 20 mK, making it a likely candidate for a quantum spin liquid state. 121Sb NMR shift measurements show that the local, intrinsic susceptibility levels off at temperatures below ˜60 K. The NMR spin-lattice relaxation rate 1 /T1 is essentially constant in temperature and the muon relaxation rate exhibits a low-temperature relaxation plateau, all indications of gapless spin excitations. Our local probe measurements are discussed in the context of several theories proposed for this material.

  17. Local structural distortion induced by antiferromagnetic ordering in Bi2Fe4O9 studied by using a neutron total scattering analysis

    NASA Astrophysics Data System (ADS)

    Jeong, I.-K.; Hur, N.

    2016-07-01

    To unravel the origin of the dielectric anomaly at the antiferromagnetic ordering of magnetoelectric Bi2Fe4O9, we performed neutron powder diffraction measurements at temperatures across the Néel temperature, T N. Both local structures and long-range symmetry were studied by using the complementary analyses of atomic pair distribution function (PDF) and Rietveld methods at temperatures of 300 K, 250 K, and 200 K. We found that the PDF peaks that reflected local atomic arrangements exhibited a noticeable variation at temperature below T N without long-range symmetry change. The implication of the PDF evolution is discussed in view of a local structural distortion at the onset of antiferromagnetic ordering.

  18. Enhanced thermoelectric performance in c-axis oriented Ca3Co4O9 films by Ag addition through multiple annealing

    NASA Astrophysics Data System (ADS)

    Liu, Shengman; Zhu, Caixia; Ge, Xianghong; Wang, Tingtai; Feng, Junlan; Yang, Linfeng

    2016-06-01

    The c-axis oriented Ca3Co4O9 (CCO) films without and with 5 wt.% Ag addition were prepared by chemical solution deposition (CSD) through multiple annealing processing on single crystal LaAlO3 (001) substrates. With Ag addition, the resistivity at 300 K is decreased to 2.25 mΩṡcm, the Seebeck coefficient at 300 K is enhanced to 106 μV/K and the power factor at 300 K can reach as high as 0.5 mWṡK‑1ṡm‑2, which is the highest value among CCO films prepared by CSD. The results suggest that Ag addition is a very effective route to improve the thermoelectric properties of CCO films through multiple annealing processing.

  19. Lead-nano-dopings effects on the structural, microstructural, vibrational and thermal properties of Bi 2- xPb xSrV 2O 9 layered perovskite

    NASA Astrophysics Data System (ADS)

    Elsabawy, Khaled M.; Abou Sekkina, Morsy M.; Asker, Mohamed A.; El-Newehy, Mohamed H.

    2010-07-01

    The sample with in the general formula Bi 2-xPb xSrV 2O 9, where x = 0.0, 0.05, 0.1, 0.2, 0.3, and 0.6 mol were synthesized by the high temperature solid state reaction and firing method. The X-ray diffractograms confirmed the formation of single phased layered perovskite in all samples. TGA and DTA thermal analyses on the green samples included steps of thermal analysis of strontium carbonate, bismuth carbonate, ammonium vanadate, lead oxide and finally on the high temperature solid state formation. The effect of lead dopings on the sintering, structural and micro-structure, properties of 212BiSrV-ceramics were investigated. The infrared absorption spectra show a series of vibrational modes within the range of 400-1600 cm -1.

  20. Static and dynamical properties of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9

    DOE PAGESBeta

    Ma, Jie; Kamiya, Yoshitomo; Hong, Tao; Cao, H. B.; Ehlers, Georg; Tian, Wei; Batista, C. D.; Dun, Z. L.; Zhou, H. D.; Matsuda, Masaaki

    2016-02-24

    We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9. Besides confirming that the Co2+ magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Hence, our results call for a new theoreticalmore » framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.« less

  1. Vibrational spectroscopy of the borate mineral tunellite SrB6O9(OH)2·3(H2O) - Implications for the molecular structure

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; López, Andrés; Scholz, Ricardo; Xi, Yunfei

    2014-02-01

    Tunellite is a strontium borate mineral with formula: SrB6O9(OH)2·3(H2O) and occurs as colorless crystals in the monoclinic pyramidal crystal system. An intense Raman band at 994 cm-1 was assigned to the BO stretching vibration of the B2O3 units. Raman bands at 1043, 1063, 1082 and 1113 cm-1 are attributed to the in-plane bending vibrations of trigonal boron. Sharp Raman bands observed at 464, 480, 523, 568 and 639 cm-1 are simply defined as trigonal and tetrahedral borate bending modes. The Raman spectrum clearly shows intense Raman bands at 3567 and 3614 cm-1, attributed to OH units. The molecular structure of a natural tunellite has been assessed by using vibrational spectroscopy.

  2. Infrared spectroscopy of stars

    NASA Technical Reports Server (NTRS)

    Merrill, K. M.; Ridgway, S. T.

    1979-01-01

    This paper reviews applications of IR techniques in stellar classification, studies of stellar photospheres, elemental and isotopic abundances, and the nature of remnant and ejected matter in near-circumstellar regions. Qualitative IR spectral classification of cool and hot stars is discussed, along with IR spectra of peculiar composite star systems and of obscured stars, and IR characteristics of stellar populations. The use of IR spectroscopy in theoretical modeling of stellar atmospheres is examined, IR indicators of stellar atmospheric composition are described, and contributions of IR spectroscopy to the study of stellar recycling of interstellar matter are summarized. The future of IR astronomy is also considered.

  3. Strange nonchaotic stars.

    PubMed

    Lindner, John F; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G; Ditto, William L

    2015-02-01

    The unprecedented light curves of the Kepler space telescope document how the brightness of some stars pulsates at primary and secondary frequencies whose ratios are near the golden mean, the most irrational number. A nonlinear dynamical system driven by an irrational ratio of frequencies generically exhibits a strange but nonchaotic attractor. For Kepler's "golden" stars, we present evidence of the first observation of strange nonchaotic dynamics in nature outside the laboratory. This discovery could aid the classification and detailed modeling of variable stars. PMID:25699444

  4. STARs in the CNS.

    PubMed

    Ehrmann, Ingrid; Fort, Philippe; Elliott, David J

    2016-08-15

    STAR (signal transduction and activation of RNA) proteins regulate splicing of target genes that have roles in neural connectivity, survival and myelination in the vertebrate nervous system. These regulated splicing targets include mRNAs such as the Neurexins (Nrxn), SMN2 (survival of motor neuron) and MAG (myelin-associated glycoprotein). Recent work has made it possible to identify and validate STAR protein splicing targets in vivo by using genetically modified mouse models. In this review, we will discuss the importance of STAR protein splicing targets in the CNS (central nervous system). PMID:27528753

  5. Vidicon star tracker.

    PubMed

    Schuck, W H

    1966-04-01

    In many applications of star trackers, extremely short acquisition times, as well as accuracy and sensitivity, are required. Tracking systems employing the vidicon as a radiation sensor have been shown to provide the necessary speed of acquisition for such applications. This paper discusses the various theoretical and practical considerations involved in using the vidicon as a sensor in a star tracking system. A typical system configuration including telescope, sensor, and processing electronics is presented. The various optical and sensor parametric relationships required in the design of a vidicon star tracker are fully discussed and analyzed. PMID:20048884

  6. Chromium substitution in mullite type bismuth aluminate: Bi2CrxAl4-xO9 with 0≤x≤2.0

    NASA Astrophysics Data System (ADS)

    Debnath, Tapas; Ullah, Ahamed; Rüscher, Claus H.; Hussain, Altaf

    2014-12-01

    Nominal compositions Bi2CrxAl4-xO9 with 0.0≤x≤2.0 (Δx=0.2) were prepared using appropriate amounts of nitrates dissolved in glycerine and heated at 800 °C for 24 h as we previously used for the preparation of solid solution series Bi2Mx/M‧4-xO9 (M/M‧=Fe/Al, Ga/Al and Fe/Ga). The samples were characterized using XRD, FTIR and optical microscopic techniques. Analyses of XRD data show mullite type single phase can be prepared up to x=1.2. The lattice parameters (a, b and c) increases with increasing Cr content. Further increase in x (i.e., x≥1.4) show the presence of some additional phases indicating a limiting value for Cr doping is in the range of 1.2≤x<1.4. The effect of Cr incorporation could also be observed in the infrared absorption spectra via systematic hard mode shifts of certain lattice modes, e.g. the Bi-O related vibration changes from 96 cm-1 to 93 cm-1 with increasing x up to 1.2 and certain intensity changes together with shift in peak positions. Interestingly, the absence of any splitting and shift of the high energy IR absorption peak at 821 cm-1 as assigned to the characteristic tetrahedral type dimer, Al2O7, indicate that the Cr thus partially substitutes only the octahedrally coordinated Al. This is confirmed by Rietveld structure refinements, too.

  7. Ba4KFe3O9: A Novel Ferrite Containing Discrete Six-member Rings of Corner-sharing FeO4 Tetrahedra

    PubMed Central

    Zhao, Qingbiao; Nellutla, Saritha; Son, Won-Joon; Vaughn, Shae A.; Ye, Longfei; Smith, Mark D.; Caignaert, Vincent; Lufaso, Michael; Pekarek, Thomas M.; Smirnov, Alex I.; Whangbo, Myung-Hwan

    2011-01-01

    Single crystals of a new iron containing oxide, Ba4KFe3O9, were grown from a hydroxide melt and the crystal structure was determined by single crystal x-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-member rings of corner sharing FeO4 tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe3+ coordination environments. The observed magnetic moment (~3.9 BM) at 400 K is significantly lower than the calculated spin-only (~5.2 BM) value indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional calculations confirm the strong antiferromagnetic coupling between adjacent Fe3+ sites within each 6-member ring and estimate the nearest neighbor spin exchange integral as ~200 K; next nearest neighbor interactions are shown to be negligible. The lower than expected effective moment for Ba4KFe3O9 calculated from χT data is explained as resulting from the occupation of lower lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of powder sample consist of a single line at g~2.01 that is characteristic of Fe3+ ions in a tetrahedral environment, thus, confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe6 magnetic species with an intensity ratio of ~1:9. Both species have Lorentzian line shapes and indistinguishable g-factors but differ in the peak-to-peak line widths (δBpp). The line width ratio δBpp(major)/δBpp(minor) ~ 3.6 correlates well with the ratio of the Weiss constants, θminor/θmajor ~ 4. PMID:21905756

  8. Comparative analysis of Brucella serotype A and M and Yersinia enterocolitica O:9 polysaccharides for serological diagnosis of brucellosis in cattle, sheep, and goats.

    PubMed Central

    Díaz-Aparicio, E; Aragón, V; Marín, C; Alonso, B; Font, M; Moreno, E; Pérez-Ortiz, S; Blasco, J M; Díaz, R; Moriyón, I

    1993-01-01

    Hapten polysaccharides of Brucella smooth M and A serotypes were prepared from Brucella sp. and Yersinia enterocolitica O:9 by previously described hydrolytic (O chain) or nonhydrolytic (native hapten [NH]) procedures. The purified polysaccharides differed only in the presence (O chain) or absence (NH) of lipopolysaccharide core sugars. The polysaccharides were compared by reverse radial immunodiffusion for the diagnosis of brucellosis in cattle (Brucella abortus biotype 1 [A serotype] and Brucella melitensis biotype 3 [AM serotype]), sheep (B. melitensis biotypes 1 [M serotype] and 3), and goats (B. melitensis biotype 1). The reverse radial immunodiffusion test with the NH from B. melitensis 16 M (serotype M) showed the highest sensitivity (89.6 to 97.3%), regardless of the host species and the serotype of the infecting Brucella sp. Y. enterocolitica O:9 NH (A serotype) was useful for diagnosing disease in cattle infected with B. abortus biotype 1, but not in cattle infected with B. melitensis biotype 3, sheep, or goats. The different results obtained with the serotype M and A polysaccharides and the sera from animals infected with M, A, and AM serotypes of Brucella spp. showed that in naturally infected animals, a large proportion of the antibodies are directed to or react with a previously defined common epitope(s) (J. T. Douglas and D. A. Palmer, J. Clin. Microbiol. 26:1353-1356, 1988) different from the A or M epitopes. By using the radial immunodiffusion test with B. melitensis 16M NH, it was possible to differentiate infected from vaccinated cattle, sheep, and goats with a sensitivity and specificity similar to that of the complement fixation test. PMID:8308104

  9. Surface and finite size effects impact on the phase diagrams, polar, and dielectric properties of (Sr,Bi)Ta2O9 ferroelectric nanoparticles

    NASA Astrophysics Data System (ADS)

    Eliseev, E. A.; Semchenko, A. V.; Fomichov, Y. M.; Glinchuk, M. D.; Sidsky, V. V.; Kolos, V. V.; Pleskachevsky, Yu. M.; Silibin, M. V.; Morozovsky, N. V.; Morozovska, A. N.

    2016-05-01

    In the framework of the thermodynamic approach Landau-Ginzburg-Devonshire (LGD) combined with the equations of electrostatics, we investigated the effect of polarization surface screening on finite size effects of the phase diagrams, polar, and dielectric properties of ferroelectric nanoparticles of different shapes. We obtained and analyzed the analytical results for the dependences of the ferroelectric phase transition temperature, critical size, spontaneous polarization, and thermodynamic coercive field on the shape and size of the nanoparticles. The pronounced size effect of these characteristics on the scaling parameter, the ratio of the particle characteristic size to the length of the surface screening, was revealed. Also our modeling predicts a significant impact of the flexo-chemical effect (that is a joint action of flexoelectric effect and chemical pressure) on the temperature of phase transition, polar, and dielectric properties of nanoparticles when their chemical composition deviates from the stoichiometric one. We showed on the example of the stoichiometric nanosized SrBi2Ta2O9 particles that except the vicinity of the critical size, where the system splitting into domains has an important role, results of analytical calculation of the spontaneous polarization have a little difference from the numerical ones. We revealed a strong impact of the flexo-chemical effect on the phase transition temperature, polar, and dielectric properties of SryBi2+xTa2O9 nanoparticles when the ratio Sr/Bi deviates from the stoichiometric value of 0.5 within the range from 0.35 to 0.65. From the analysis of experimental data, we derived the parameters of the theory, namely, the coefficients of expansion of the LGD functional, the contribution of flexo-chemical effect, and the length of the surface screening.

  10. A Detailed Far-ultraviolet Spectral Atlas of O-type Stars

    NASA Astrophysics Data System (ADS)

    Smith, Myron A.

    2012-10-01

    In this paper, we present a spectral atlas covering the wavelength interval 930-1188 Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188 Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas, to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. We discuss the statistics of line populations among the various elemental ionization states. Also, as an aid to users we list those isolated lines that can be used to determine stellar temperatures and the presence of possible chemical anomalies. Finally, we have prepared FITS files that give pairs of merged spectra for

  11. A DETAILED FAR-ULTRAVIOLET SPECTRAL ATLAS OF O-TYPE STARS

    SciTech Connect

    Smith, Myron A.

    2012-10-15

    In this paper, we present a spectral atlas covering the wavelength interval 930-1188 A for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188 A. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of 'missed' features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas, to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. We discuss the statistics of line populations among the various elemental ionization states. Also, as an aid to users we list those isolated lines that can be used to determine stellar temperatures and the presence of possible chemical anomalies. Finally, we have prepared FITS files that give pairs of merged spectra for

  12. On the conversion of neutron stars into quark stars

    NASA Astrophysics Data System (ADS)

    Pagliara, Giuseppe

    2014-03-01

    The possible existence of two families of compact stars, neutron stars and quark stars, naturally leads to a scenario in which a conversion process between the two stellar objects occurs with a consequent release of energy of the order of 1053 erg. We discuss recent hydrodynamical simulations of the burning process and neutrino diffusion simulations of cooling of a newly formed strange star. We also briefly discuss this scenario in connection with recent measurements of masses and radii of compact stars.

  13. Mass loss of massive stars

    NASA Astrophysics Data System (ADS)

    Martins, F.

    2015-12-01

    In this contribution we review the properties of the winds of massive stars. We focus on OB stars, red supergiants, Luminous Blue Variables (LBVs) and Wolf-Rayet stars. For each type of star, we summarize the main wind properties and we give a brief description of the physical mechanism(s) responsible for mass loss.

  14. Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars

    NASA Astrophysics Data System (ADS)

    Pecaut, Mark J.; Mamajek, Eric E.

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVIC , 2MASS JHKS and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T eff) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T eff and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T eff scale for pre-MS stars is within sime100 K of dwarfs at a given spectral type for stars stars are ~250 K cooler than their MS counterparts. Lastly, we present (1) a modern T eff, optical/IR color, and BC sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  15. INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS

    SciTech Connect

    Pecaut, Mark J.; Mamajek, Eric E.

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVI{sub C} , 2MASS JHK{sub S} and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T {sub eff}) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T {sub eff} and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T {sub eff} scale for pre-MS stars is within ≅100 K of dwarfs at a given spectral type for stars stars are ∼250 K cooler than their MS counterparts. Lastly, we present (1) a modern T {sub eff}, optical/IR color, and BC sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  16. Ultrabass Sounds of the Giant Star xi Hya

    NASA Astrophysics Data System (ADS)

    2002-05-01

    then represented by "ξ" . [3]: In astrophysical terms, xi Hya is currently in the hydrogen shell-burning phase, having left the main sequence some time ago and now near the sub-giant/giant border.

  17. Cosmology with hypervelocity stars

    SciTech Connect

    Loeb, Abraham

    2011-04-01

    In the standard cosmological model, the merger remnant of the Milky Way and Andromeda (Milkomeda) will be the only galaxy remaining within our event horizon once the Universe has aged by another factor of ten, ∼ 10{sup 11} years after the Big Bang. After that time, the only extragalactic sources of light in the observable cosmic volume will be hypervelocity stars being ejected continuously from Milkomeda. Spectroscopic detection of the velocity-distance relation or the evolution in the Doppler shifts of these stars will allow a precise measurement of the vacuum mass density as well as the local matter distribution. Already in the near future, the next generation of large telescopes will allow photometric detection of individual stars out to the edge of the Local Group, and may target the ∼ 10{sup 5±1} hypervelocity stars that originated in it as cosmological tracers.

  18. Finding New Variable Stars

    NASA Astrophysics Data System (ADS)

    Joner, M. D.

    2016-06-01

    (Abstract only) Initial findings are presented for several new variable stars that have been identified using CCD photometry done with the 0.9-meter telescope located at the BYU West Mountain Observatory.

  19. Women and the Stars.

    ERIC Educational Resources Information Center

    Spradley, Joseph L.

    1990-01-01

    Described are the contributions of 15 women astronomers to the modern understanding of the stars. Discussed are early women pioneers, early spectrographic studies, and recent women astronomers. A list of 29 references is included. (CW)

  20. The Auger Star Monitor

    NASA Astrophysics Data System (ADS)

    Diaz, Johana; Nitz, David; Fick, Brian

    2006-04-01

    The Auger Star Monitor (ASM) is designed to automatically measure the total vertical atmospheric extinction above the Auger Observatory. The system continually takes wide-field CCD images of the night sky through a Johnson U-Band filter. Photometry is performed on the star images. The change in recorded star brightness as a function of zenith angle is used to obtain values for the integrated density of atmospheric scattering components. The MTU group has installed two ASMs; one at the Southern Observatory atop the Los Leones Fluorescence Detector building and one at the future site of the Northern Observatory in Colorado. Both of these units have been routinely operating during the past year. Much of our effort has turned to developing better data-reduction algorithms and automated software. Significant work has done to perfect the algorithms for image processing, star identification and photometry. Partial results of extinction coefficients obtained by the ASM will be presented.

  1. The Oldest Stars

    NASA Astrophysics Data System (ADS)

    Beers, T. C.

    I review the techniques used to identify the oldest "living" stars in the Universe, concentrating on two large modern surveys: the HK survey of Beers and colleagues and the Hamburg/ESO survey of Christlieb and collaborators. I then consider the knowledge that has been gained recently concerning the the distribution of measured stellar metallicities from these samples, the so-called Metallicity Distribution Function of the halo of the Milky Way. A summary of some of the most exciting results from recent high-resolution spectroscopy of very metal-poor stars identified in these samples is provided. Special attention is given to the nature of r-process-enhanced metal-poor stars, and what they reveal about the operation and possible astrophysical site(s) of the r-process in the early Universe. Finally, I discuss plans for next-generation surveys for extremely metal-poor stars.

  2. Molecules in star formation.

    NASA Astrophysics Data System (ADS)

    Shu, F. H.

    The author reviews current ideas and models in the problem of star formation from molecular cloud cores that are relatively isolated from the influences of other forming stars. He discusses the time scales, flow dynamics, and density and temperature structures applicable to each of the four stages of the entire process: (1) formation of a magnetized cloud core by ambipolar diffusion and evolution to a pivotal state of gravomagneto catastrophe; (2) self-similar collapse of the pivotal configuration and the formation of protostars, disks, and pseudo-disks; (3) onset of a magnetocentrifugally driven, lightly ionized wind from the interaction of an accretion disk and the magnetosphere of the central star, and the driving of bipolar molecular outflows; (4) evolution of pre-main-sequence stars surrounded by dusty accretion disks. For each of these stages and processes, he considers the characteristics of the molecular diagnostics needed to investigate the crucial aspects of the observational problem.

  3. Discovery of variable stars

    NASA Technical Reports Server (NTRS)

    Kurochkin, N. Y.

    1973-01-01

    Instrumented methods of discovering variable stars are reviewed, specifically the blink comparator, color contrast method, positive-negative method, and television method. Among the empirical methods discussed, the Van Gent method is the most important.

  4. Cooling of neutron stars

    NASA Technical Reports Server (NTRS)

    Pethick, C. J.

    1992-01-01

    It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.

  5. Variable star data online

    NASA Astrophysics Data System (ADS)

    Pickard, Roger; Wilson, Andy; Poyner, Gary

    2012-06-01

    Roger Pickard, Andy Wilson and Gary Poyner describe the online database of the British Astronomical Association Variable Star Section, a treasure trove of observations stretching back nearly 125 years.

  6. Planets Around Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wolszczan, Alexander; Kulkarni, Shrinivas R; Anderson, Stuart B.

    2003-01-01

    The objective of this proposal was to continue investigations of neutron star planetary systems in an effort to describe and understand their origin, orbital dynamics, basic physical properties and their relationship to planets around normal stars. This research represents an important element of the process of constraining the physics of planet formation around various types of stars. The research goals of this project included long-term timing measurements of the planets pulsar, PSR B1257+12, to search for more planets around it and to study the dynamics of the whole system, and sensitive searches for millisecond pulsars to detect further examples of old, rapidly spinning neutron stars with planetary systems. The instrumentation used in our project included the 305-m Arecibo antenna with the Penn State Pulsar Machine (PSPM), the 100-m Green Bank Telescope with the Berkeley- Caltech Pulsar Machine (BCPM), and the 100-m Effelsberg and 64-m Parkes telescopes equipped with the observatory supplied backend hardware.

  7. Catch a Star 2008!

    NASA Astrophysics Data System (ADS)

    2007-10-01

    ESO and the European Association for Astronomy Education have just launched the 2008 edition of 'Catch a Star', their international astronomy competition for school students. Now in its sixth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. CAS logo The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. In teams, students investigate an astronomical topic of their choice and write a report about it. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes such as the Very Large Telescope (VLT) or future telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Extremely Large Telescope (E-ELT) could contribute to investigations of the topic. Students may also include practical activities such as observations or experiments. For the artistically minded, 'Catch a Star' also offers an artwork competition, 'Catch a Star Artists'. Last year, hundreds of students from across Europe and beyond took part in 'Catch a Star', submitting astronomical projects and artwork. "'Catch a Star' gets students thinking about the wonders of the Universe and the science of astronomy, with a chance of winning great prizes. It's easy to take part, whether by writing about astronomy or creating astronomically inspired artwork," said Douglas Pierce-Price, Education Officer at ESO. As well as the top prize - a trip to ESO's Very Large Telescope in Chile - visits to observatories in Austria and Spain, and many other prizes, can also be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners

  8. Sounds of a Star

    NASA Astrophysics Data System (ADS)

    2001-06-01

    Acoustic Oscillations in Solar-Twin "Alpha Cen A" Observed from La Silla by Swiss Team Summary Sound waves running through a star can help astronomers reveal its inner properties. This particular branch of modern astrophysics is known as "asteroseismology" . In the case of our Sun, the brightest star in the sky, such waves have been observed since some time, and have greatly improved our knowledge about what is going on inside. However, because they are much fainter, it has turned out to be very difficult to detect similar waves in other stars. Nevertheless, tiny oscillations in a solar-twin star have now been unambiguously detected by Swiss astronomers François Bouchy and Fabien Carrier from the Geneva Observatory, using the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory. This telescope is mostly used for discovering exoplanets (see ESO PR 07/01 ). The star Alpha Centauri A is the nearest star visible to the naked eye, at a distance of a little more than 4 light-years. The new measurements show that it pulsates with a 7-minute cycle, very similar to what is observed in the Sun . Asteroseismology for Sun-like stars is likely to become an important probe of stellar theory in the near future. The state-of-the-art HARPS spectrograph , to be mounted on the ESO 3.6-m telescope at La Silla, will be able to search for oscillations in stars that are 100 times fainter than those for which such demanding observations are possible with CORALIE. PR Photo 23a/01 : Oscillations in a solar-like star (schematic picture). PR Photo 23b/01 : Acoustic spectrum of Alpha Centauri A , as observed with CORALIE. Asteroseismology: listening to the stars ESO PR Photo 23a/01 ESO PR Photo 23a/01 [Preview - JPEG: 357 x 400 pix - 96k] [Normal - JPEG: 713 x 800 pix - 256k] [HiRes - JPEG: 2673 x 3000 pix - 2.1Mb Caption : PR Photo 23a/01 is a graphical representation of resonating acoustic waves in the interior of a solar-like star. Red and blue

  9. The Pistol Star

    NASA Astrophysics Data System (ADS)

    Figer, D. F.; Morris, M.; McLean, I. S.; Ghez, A. M.; Najarro, F.; Geballe, T. R.; Serabyn, E.; Rich, R. M.

    1998-01-01

    We present near-infrared spectra, photometry (JHK(') nbL), and Keck K-band speckle images of the ``Pistol Star.'' We also present HST/NICMOS Paschen-alpha images and near-infrared spectra of the surrounding HII region (G0.15-0.05), the ``Pistol.'' The stellar spectra cover the J, H, and K bands at low resolution, and between 1.80 to 1.96 \\micron, 2.10 to 2.26 \\micron, and 4.02 to 4.08 \\micron\\ at moderate resolution. The spectra of the Pistol cover the K-band at low resolution and 1.80 to 1.96 \\micron\\ at moderate resolution. The stellar data are fit with wind/atmosphere models to find that the star is extraordinarily luminous, having L = 10(6.7({+0.5}_{-0.5})) L_sun, making it one of the most luminous stars known; the range in luminosity is primarily due to uncertainties in extinction and intrinsic spectral energy distribution of the star. Coupled with the relatively cool temperature, T_eff = 10(4.17({+0.19}_{-0.06})) K, the star is clearly in violation of the Humphreys-Davidson limit. The line of sight velocity of the star is confirmed to be ~ 130 kms(-1) , assuring membership in the Quintuplet cluster. This, along with the inferred extinction, places the star at the Galactic Center. The spectra of the Pistol confirm that the ionized gas has smoothly varying velocity gradients superposed on a bulk velocity of 130 kms(-1) . Radio and near-infrared hydrogen-to-helium line ratios suggest that the Pistol may have extrasolar helium abundance and that it must be excited, in part, by a star which is hotter than the Pistol Star. The morphology of the gas, the velocities in the gas, and the location of the star in the HR diagram suggest that the gas in G0.15-0.05 is matter which was ejected from the star.

  10. Star of Bethlehem

    NASA Astrophysics Data System (ADS)

    Hughes, D.; Murdin, P.

    2001-07-01

    The biblical Star of Bethlehem, which heralded the birth of Jesus Christ, is only mentioned in the Gospel of St Matthew 2. The astrologically significant 7 bc triple conjunction of Jupiter and Saturn in the constellation of Pisces is the most likely candidate, although a comet/nova in 5 bc and a comet in 4 bc cannot be ruled out. There is also the possibility that the star was simply fictitious....

  11. Chaotic Star Birth

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset

    Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives.

    The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region.

    The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333.

    In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.

  12. Cold Hybrid Star Properties

    SciTech Connect

    Moshfegh, H. R.; Darehmoradi, M.; Mojarrad, M. Ghazanfari

    2011-10-28

    Properties of neutron stars with quark core are investigated. The equation of state of hadronic matter is calculated using Myers and Swiatecki two nucleon interaction within Thomas-Fermi semiclassical approximation (TF). For quark matter we employ The MIT bag model with constant and density dependent bag parameter. With use of the obtained equation of states we have calculated mass-radius relation of such hybrid stars.

  13. Bubbly Little Star

    NASA Technical Reports Server (NTRS)

    2007-01-01

    In this processed Spitzer Space Telescope image, baby star HH 46/47 can be seen blowing two massive 'bubbles.' The star is 1,140 light-years away from Earth.

    The infant star can be seen as a white spot toward the center of the Spitzer image. The two bubbles are shown as hollow elliptical shells of bluish-green material extending from the star. Wisps of green in the image reveal warm molecular hydrogen gas, while the bluish tints are formed by starlight scattered by surrounding dust.

    These bubbles formed when powerful jets of gas, traveling at 200 to 300 kilometers per second, or about 120 to 190 miles per second, smashed into the cosmic cloud of gas and dust that surrounds HH 46/47. The red specks at the end of each bubble show the presence of hot sulfur and iron gas where the star's narrow jets are currently crashing head-on into the cosmic cloud's gas and dust material.

    Whenever astronomers observe a star, or snap a stellar portrait, through the lens of any telescope, they know that what they are seeing is slightly blurred. To clear up the blurring in Spitzer images, astronomers at the Jet Propulsion Laboratory developed an image processing technique for Spitzer called Hi-Res deconvolution.

    This process reduces blurring and makes the image sharper and cleaner, enabling astronomers to see the emissions around forming stars in greater detail. When scientists applied this image processing technique to the Spitzer image of HH 46/47, they were able to see winds from the star and jets of gas that are carving the celestial bubbles.

    This infrared image is a three-color composite, with data at 3.6 microns represented in blue, 4.5 and 5.8 microns shown in green, and 24 microns represented as red.

  14. Spectroscopic Binary Stars

    NASA Astrophysics Data System (ADS)

    Batten, A.; Murdin, P.

    2000-11-01

    Historically, spectroscopic binary stars were binary systems whose nature was discovered by the changing DOPPLER EFFECT or shift of the spectral lines of one or both of the component stars. The observed Doppler shift is a combination of that produced by the constant RADIAL VELOCITY (i.e. line-of-sight velocity) of the center of mass of the whole system, and the variable shift resulting from the o...

  15. Matter accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

    Some of the fundamental neutron star parameters, such as the mass and the magnetic field strength, were experimentally determined in accreting neutron star systems. Some of the relevant data and the models used to derive useful information from them, are reviewed concentrating mainly on X-ray pulsars. The latest advances in our understanding of the radiation mechanisms and the transfer in the strongly magnetized polar cap regions are discussed.

  16. Massive Stars: Stellar Populations

    NASA Astrophysics Data System (ADS)

    Bianchi, Luciana

    2007-07-01

    Massive stars dominate the chemical and dynamical evolution of the ISM, and ultimately of their parent galaxy and the universe, because of their fast evolution and intense supersonic winds. Four decades ago, the first rocket UV spectra of massive stars revealed the importance of mass loss and began to change our understanding of their evolution. Recently, advances in stellar modeling, and the observation of crucial ions in the far-UV spectral range, led to the resolution of long-standing issues in our understanding of massive star atmospheres. A revised (downwards) calibration of Teff for early spectral types is emerging as a result. Meanwhile, HST imaging, and large ground-based telescopes with multislit spectroscopic capabilities, had opened the possibility of resolved studies of stellar populations in Local Group galaxies, which sample a variety of metallicity and environment conditions. More recently, GALEX is providing a global, deep view of the young stellar populations for hundreds of nearby galaxies, revealing their recent star-formation history and modalities. The wide-field coverage and sensitivity of the GALEX UV imaging, easily detecting extremely low levels of star formation, is again changing some of our views on massive star formation in galaxies.

  17. Seeing Stars in Serpens

    NASA Technical Reports Server (NTRS)

    2006-01-01

    Infant stars are glowing gloriously in this infrared image of the Serpens star-forming region, captured by NASA's Spitzer Space Telescope.

    The reddish-pink dots are baby stars deeply embedded in the cosmic cloud of gas and dust that collapsed to create it. A dusty disk of cosmic debris, or 'protoplanetary disk,' that may eventually form planets, surrounds the infant stars.

    Wisps of green throughout the image indicate the presence of carbon rich molecules called polycyclic aromatic hydrocarbons. On Earth, these molecules can be found on charred barbecue grills and in automobile exhaust. Blue specks sprinkled throughout the image are background stars in our Milky Way galaxy.

    The Serpens star-forming region is located approximately 848 light-years away in the Serpens constellation.

    The image is a three-channel, false-color composite, where emission at 4.5 microns is blue, emission at 8.0 microns is green, and 24 micron emission is red.

  18. Star formation around isolated T Tauri stars?

    NASA Astrophysics Data System (ADS)

    Hoff, W.; Pfau, W.; Henning, T.

    1996-02-01

    The authors want to present their search for young stellar objects around the two isolated T Tau stars TW Hya (Rucinski and Krautter 1983) and CoD -29°8887 (de la Reza et al. 1989). From the known spectroscopic features of these objects, TW Hya is to be classified as a classical T Tau star (CTTS), but it is not associated with a dark cloud region like all other known CTTSs. The same situation turns out for the weak-line T Tau star (WTTS) CoD -29°8887. One possible explanation for their isolated position is that they have formed from small dark clouds or globules, which were later destroyed. The authors carried out two ROSAT PSPC observations pointing at TW Hya and CoD -29°8887 and used a source detection procedure considering all the standard ROSAT energy bands to test this hypothesis. Spectroscopic follow-up observations were made for 24 possible T Tauri candidates, but there are no further low-mass young stellar objects in the vicinity of the two targets. The study shows that the objects are definitely not formed in a cluster at the positions of the objects.

  19. Tuning the charge states of CrW2O9 clusters deposited on perfect and defective MgO(001) surfaces with different color centers: A comprehensive DFT study

    NASA Astrophysics Data System (ADS)

    Zhu, Jia; Zhang, Hui; Tong, Yawen; Wang, Chengxing; Wang, Bin; Huang, Xin; Zhang, Yongfan

    2016-05-01

    The structures and electronic properties of bimetallic oxide CrW2O9 clusters supported on the perfect and defective MgO(001) surfaces with three different color centers, FS0, FS+, and FS2+ centers, respectively, have been investigated by density functional theory calculations. Our results show that the configurations, adsorption energies, charge transfers, and bonding modes of dispersed CrW2O9 clusters are sensitive to the charge states of the FS centers. Compared with the gas-phase configuration, the CrW2O9 clusters supported on the defective surfaces are distorted dramatically, which exhibit different chain structures. On the perfect MgO surface, the depositions of clusters do not involve obvious charge transfer, while the situation is quite different on the defective MgO(001) surfaces in which significant electron transfer occurs from the surface to the cluster. Interestingly, this effect becomes more remarkable for electron-rich oxygen vacancies (FS0 center) than that for electron-poor oxygen vacancies (FS+ and FS2+ centers). Furthermore, our work reveals a progressive Brønsted acid sites where spin density preferentially localized around the Cr atoms not the W atoms for all kinds of FS-centers, indicating the better catalytic activities can be expected for CrW2O9 cluster on defective MgO(001) surfaces with respect to the W3O9 cluster.

  20. K2NaOsO5.5 and K3NaOs2O9: The first osmium perovskites containing alkali cations at the “A” site

    NASA Astrophysics Data System (ADS)

    Mogare, Kailash M.; Klein, Wilhelm; Jansen, Martin

    2012-07-01

    K2NaOsO5.5 and K3NaOs2O9 were obtained from solid-state reactions of potassium superoxide, sodium peroxide and osmium metal at elevated oxygen pressures. K2NaOsO5.5 crystallizes as an oxygen-deficient cubic double perovskite in space group Fm3¯m with a=8.4184(5) Å and contains isolated OsO6 octahedra. K3NaOs2O9 crystallizes hexagonally in P63/mmc with a=5.9998(4) Å and c=14.3053(14) Å. K3NaOs2O9 consists of face sharing Os2O9 pairs of octahedra. According to magnetic measurements K2NaOsO5.5 is diamagnetic, whereas K3NaOs2O9 displays strong antiferromagnetic coupling (TN=140 K), indicating enhanced magnetic interactions within the octahedral pair.

  1. Collapsing Enormous Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-09-01

    One of the big puzzles in astrophysics is how supermassive black holes (SMBHs) managed to grow to the large sizes weve observed in the very early universe. In a recent study, a team of researchers examines the possibility that they were formed by the direct collapse of supermassive stars.Formation MysterySMBHs billions of times as massive as the Sun have been observed at a time when the universe was less than a billion years old. But thats not enough time for a stellar-mass black hole to grow to SMBH-size by accreting material so another theory is needed to explain the presence of these monsters so early in the universes history. A new study, led by Tatsuya Matsumoto (Kyoto University, Japan), poses the following question: what if supermassive stars in the early universe collapsed directly into black holes?Previous studies of star formation in the early universe have suggested that, in the hot environment of these primordial times, stars might have been able to build up mass much faster than they can today. This could result in early supermassive stars roughly 100,000 times more massive than the Sun. But if these early stars end their lives by collapsing to become massive black holes in the same way that we believe massive stars can collapse to form stellar-mass black holes today this should result in enormously violent explosions. Matusmoto and collaborators set out to model this process, to determine what we would expect to see when it happens!Energetic BurstsThe authors modeled the supermassive stars prior to collapse and then calculated whether a jet, created as the black hole grows at the center of the collapsing star, would be able to punch out of the stellar envelope. They demonstrated that the process would work much like the widely-accepted collapsar model of massive-star death, in which a jet successfully punches out of a collapsing star, violently releasing energy in the form of a long gamma-ray burst (GRB).Because the length of a long GRB is thought to

  2. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung–Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  3. An Introduction to the Sun and Stars

    NASA Astrophysics Data System (ADS)

    Green, Simon F.; Jones, Mark H.

    2015-02-01

    Introduction; 1. Seeing the Sun; 2. The working Sun; 3. Measuring stars; 4. Comparing stars; 5. The formation of stars; 6. The main sequence life of stars; 7. The life of stars beyond the main sequence; 8. The death of stars; 9. The remnants of stars; Conclusion; Answers and comments; Appendices; Glossary; Further reading; Acknowledgements; Figure references; Index.

  4. Spectra of hot stars

    NASA Astrophysics Data System (ADS)

    Hillier, D. John

    2015-08-01

    Non-LTE modeling is essential for interpreting the spectra of O stars and their decendents, and much progress has been made. The major uncertainty associated with analyzing photospheric spectra of O stars arises from issues related to microturbulence and macroturbulence. Many supergiants, for example, have microturbulent velocities that approach the sound speed, while macroturbulent velocities are often several times the sound speed. The cause of this turbulence is unknown, but may be related to pulsation, an underlying convection zone associated with the Fe opacity bump, or feedback from the stellar wind. Determining accurate abundances in O stars is hampered by the lack of lines belonging to low-z elements. Many species only have a few observable lines, and some of these are subject to complex non-LTE effects. A characteristic of massive stars is the existence of a stellar wind which is driven by radiation pressure. Radiation driving is inherently unstable, and this leads to winds with an inhomogeneous structure. Major issues that are still unresolved include: How are winds driven through the sonic point? What is the nature of the inhomogeneities, and how do the properties of these inhomogeneities change with density and velocity? How important is spatial porosity, and porosity in velocity space? What is the structure of the shocks, and in what stars do the shocks fail to cool? With Wolf-Rayet (W-R) stars the major uncertainty arises because the classic spectroscopic radius (i.e., the location where τ = 2/3) often refers to a location in the wind — not necessarily the stellar radius associated with stellar evolution models. Derived radii are typically several times those predicted by stellar evolution calculations, although for strong-lined W-R stars it is possible to construct models that are consistent with evolution calculations. The driving of the winds in these stars is strongly coupled to the closeness of the stars to the Eddington limit and to their

  5. Wolf-Rayet Stars

    NASA Astrophysics Data System (ADS)

    Hamann, Wolf-Rainer; Sander, Andreas; Todt, Helge

    Nearly 150 years ago, the French astronomers Charles Wolf and Georges Rayet described stars with very conspicuous spectra that are dominated by bright and broad emission lines. Meanwhile termed Wolf-Rayet Stars after their discoverers, those objects turned out to represent important stages in the life of massive stars. As the first conference in a long time that was specifically dedicated to Wolf-Rayet stars, an international workshop was held in Potsdam, Germany, from 1.-5. June 2015. About 100 participants, comprising most of the leading experts in the field as well as as many young scientists, gathered for one week of extensive scientific exchange and discussions. Considerable progress has been reported throughout, e.g. on finding such stars, modeling and analyzing their spectra, understanding their evolutionary context, and studying their circumstellar nebulae. While some major questions regarding Wolf-Rayet stars still remain open 150 years after their discovery, it is clear today that these objects are not just interesting stars as such, but also keystones in the evolution of galaxies. These proceedings summarize the talks and posters presented at the Potsdam Wolf-Rayet workshop. Moreover, they also include the questions, comments, and discussions emerging after each talk, thereby giving a rare overview not only about the research, but also about the current debates and unknowns in the field. The Scientific Organizing Committee (SOC) included Alceste Bonanos (Athens), Paul Crowther (Sheffield), John Eldridge (Auckland), Wolf-Rainer Hamann (Potsdam, Chair), John Hillier (Pittsburgh), Claus Leitherer (Baltimore), Philip Massey (Flagstaff), George Meynet (Geneva), Tony Moffat (Montreal), Nicole St-Louis (Montreal), and Dany Vanbeveren (Brussels).

  6. Models of symbiotic stars

    NASA Technical Reports Server (NTRS)

    Friedjung, Michael

    1993-01-01

    One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical

  7. Life Cycle of Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  8. ON THE MULTIPLICITY OF THE ZERO-AGE MAIN-SEQUENCE O STAR HERSCHEL 36

    SciTech Connect

    Arias, Julia I.; Barba, Rodolfo H.; Gamen, Roberto C.; Apellaniz, Jesus MaIz; Alfaro, Emilio J.; Sota, Alfredo; Bidin, Christian Moni

    2010-02-10

    We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 {+-} 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.

  9. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung–Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  10. Pulsating Star Mystery Solved

    NASA Astrophysics Data System (ADS)

    2010-11-01

    By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. Up to now astronomers had two incompatible theoretical predictions of Cepheid masses. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations. The new results, from a team led by Grzegorz Pietrzyński (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the 25 November 2010 edition of the journal Nature. Grzegorz Pietrzyński introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct." Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun [1]. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe [2]. Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20-30% less than predictions from the theory of the

  11. Synthesis, structural elucidation, and catalytic properties in olefin epoxidation of the polymeric hybrid material [Mo3O9(2-[3(5)-pyrazolyl]pyridine)]n.

    PubMed

    Amarante, Tatiana R; Neves, Patrícia; Gomes, Ana C; Nolasco, Mariela M; Ribeiro-Claro, Paulo; Coelho, Ana C; Valente, Anabela A; Paz, Filipe A Almeida; Smeets, Stef; McCusker, Lynne B; Pillinger, Martyn; Gonçalves, Isabel S

    2014-03-01

    The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)]n (2) as a microcrystalline powder in yields of 72–79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)2(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl4(2–) anion, and the tetranuclear compound [Mo4O12(pzpy)4] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O2)2(pzpy)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic–inorganic one-dimensional (1D) polymer, ∞(1)[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction. PMID:24520803

  12. Regulatory Protein OmpR Influences the Serum Resistance of Yersinia enterocolitica O:9 by Modifying the Structure of the Outer Membrane

    PubMed Central

    Skorek, Karolina; Raczkowska, Adrianna; Dudek, Bartłomiej; Miętka, Katarzyna; Guz-Regner, Katarzyna; Pawlak, Aleksandra; Klausa, Elżbieta; Bugla-Płoskońska, Gabriela; Brzostek, Katarzyna

    2013-01-01

    The EnvZ/OmpR two-component system constitutes a regulatory pathway involved in bacterial adaptive responses to environmental cues. Our previous findings indicated that the OmpR regulator in Yersinia enterocolitica O:9 positively regulates the expression of FlhDC, the master flagellar activator, which influences adhesion/invasion properties and biofilm formation. Here we show that a strain lacking OmpR grown at 37°C exhibits extremely high resistance to the bactericidal activity of normal human serum (NHS) compared with the wild-type strain. Analysis of OMP expression in the ompR mutant revealed that OmpR reciprocally regulates Ail and OmpX, two homologous OMPs of Y. enterocolitica, without causing significant changes in the level of YadA, the major serum resistance factor. Analysis of mutants in individual genes belonging to the OmpR regulon (ail, ompX, ompC and flhDC) and strains lacking plasmid pYV, expressing YadA, demonstrated the contribution of the respective proteins to serum resistance. We show that Ail and OmpC act in an opposite way to the OmpX protein to confer serum resistance to the wild-type strain, but are not responsible for the high resistance of the ompR mutant. The serum resistance phenotype of ompR seems to be multifactorial and mainly attributable to alterations that potentiate the function of YadA. Our results indicate that a decreased level of FlhDC in the ompR mutant cells is partly responsible for the serum resistance and this effect can be suppressed by overexpression of flhDC in trans. The observation that the loss of FlhDC enhances the survival of wild-type cells in NHS supports the involvement of FlhDC regulator in this phenotype. In addition, the ompR mutant exhibited a lower level of LPS, but this was not correlated with changes in the level of FlhDC. We propose that OmpR might alter the susceptibility of Y. enterocolitica O:9 to complement-mediated killing through remodeling of the outer membrane. PMID:24260242

  13. Condensate dark matter stars

    SciTech Connect

    Li, X.Y.; Harko, T.; Cheng, K.S. E-mail: harko@hkucc.hku.hk

    2012-06-01

    We investigate the structure and stability properties of compact astrophysical objects that may be formed from the Bose-Einstein condensation of dark matter. Once the critical temperature of a boson gas is less than the critical temperature, a Bose-Einstein Condensation process can always take place during the cosmic history of the universe. Therefore we model the dark matter inside the star as a Bose-Einstein condensate. In the condensate dark matter star model, the dark matter equation of state can be described by a polytropic equation of state, with polytropic index equal to one. We derive the basic general relativistic equations describing the equilibrium structure of the condensate dark matter star with spherically symmetric static geometry. The structure equations of the condensate dark matter stars are studied numerically. The critical mass and radius of the dark matter star are given by M{sub crit} ≈ 2(l{sub a}/1fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2}M{sub s}un and R{sub crit} ≈ 1.1 × 10{sup 6}(l{sub a}/1 fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2} cm respectively, where l{sub a} and m{sub χ} are the scattering length and the mass of dark matter particle, respectively.

  14. Star Caught Smoking

    NASA Astrophysics Data System (ADS)

    2007-08-01

    VLTI Snapshots Dusty Puff Around Variable Star Using ESO's Very Large Telescope Interferometer, astronomers from France and Brazil have detected a huge cloud of dust around a star. This observation is further evidence for the theory that such stellar puffs are the cause of the repeated extreme dimming of the star. ESO PR Photo 34a/07 ESO PR Photo 34a/07 Dust Cloud in a R CrB Star (Artist's Impression) R Coronae Borealis stars are supergiants exhibiting erratic variability. Named after the first star that showed such behaviour [1], they are more than 50 times larger than our Sun. R Coronae Borealis stars can see their apparent brightness unpredictably decline to a thousandth of their nominal value within a few weeks, with the return to normal light levels being much slower. It has been accepted for decades that such fading could be due to obscuration of the stellar surface by newly formed dusty clouds. This 'Dust Puff Theory' suggests that mass is lost from the R Coronae Borealis (or R CrB for short) star and then moves away until the temperature is low enough for carbon dust to form. If the newly formed dust cloud is located along our line-of-sight, it eclipses the star. As the dust is blown away by the star's strong light, the 'curtain' vanishes and the star reappears. RY Sagittarii is the brightest member in the southern hemisphere of this family of weird stars. Located about 6,000 light-years away towards the constellation of Sagittarius (The Archer), its peculiar nature was discovered in 1895 by famous Dutch astronomer Jacobus Cornelius Kapteyn. In 2004, near-infrared adaptive optics observations made with NACO on ESO's Very Large Telescope allowed astronomers Patrick de Laverny and Djamel Mékarnia to clearly detect the presence of clouds around RY Sagittarii. This was the first direct confirmation of the standard scenario explaining the light variations of R CrB stars by the presence of heterogeneities in their envelope surrounding the star. ESO PR Photo 32e

  15. Origin of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Brecher, K.

    1999-12-01

    The origin of the concept of neutron stars can be traced to two brief, incredibly insightful publications. Work on the earlier paper by Lev Landau (Phys. Z. Sowjetunion, 1, 285, 1932) actually predated the discovery of neutrons. Nonetheless, Landau arrived at the notion of a collapsed star with the density of a nucleus (really a "nucleus star") and demonstrated (at about the same time as, and independent of, Chandrasekhar) that there is an upper mass limit for dense stellar objects of about 1.5 solar masses. Perhaps even more remarkable is the abstract of a talk presented at the December 1933 meeting of the American Physical Society published by Walter Baade and Fritz Zwicky in 1934 (Phys. Rev. 45, 138). It followed the discovery of the neutron by just over a year. Their report, which was about the same length as the present abstract: (1) invented the concept and word supernova; (2) suggested that cosmic rays are produced by supernovae; and (3) in the authors own words, proposed "with all reserve ... the view that supernovae represent the transitions from ordinary stars to neutron stars (italics), which in their final stages consist of extremely closely packed neutrons." The abstract by Baade and Zwicky probably contains the highest density of new, important (and correct) ideas in high energy astrophysics ever published in a single paper. In this talk, we will discuss some of the facts and myths surrounding these two publications.

  16. Nursery of New Stars

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This is a Hubble Space Telescope image (right) of a vast nebula called NGC 604, which lies in the neighboring spiral galaxy M33, located 2.7 million light-years away in the constellation Triangulum. This is a site where new stars are being born in a spiral arm of the galaxy. Though such nebulae are common in galaxies, this one is particularly large, nearly 1,500 light-years across. The nebula is so vast it is easily seen in ground-based telescopic images (left). At the heart of NGC 604 are over 200 hot stars, much more massive than our Sun (15 to 60 solar masses). They heat the gaseous walls of the nebula making the gas fluoresce. Their light also highlights the nebula's three-dimensional shape, like a lantern in a cavern. By studying the physical structure of a giant nebula, astronomers may determine how clusters of massive stars affect the evolution of the interstellar medium of the galaxy. The nebula also yields clues to its star formation history and will improve understanding of the starburst process when a galaxy undergoes a 'firestorm' of star formation. The image was taken on January 17, 1995 with Hubble's Wide Field and Planetary Camera 2. Separate exposures were taken in different colors of light to study the physical properties of the hot gas (17,000 degrees Fahrenheit, 10,000 degrees Kelvin

  17. Young Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gieles, Mark

    2010-09-01

    Young massive clusters (YMCs) are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few YMCs that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. YMCs are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in YMCs, although their older cousins, the globular clusters, are unusually rich in stellar exotica. In this review, we focus on star clusters younger than ˜100 Myr, more than a few current crossing times old, and more massive than ˜104M⊙; the size of the cluster and its environment are considered less relevant as distinguishing parameters. We describe the global properties of the currently known young massive star clusters in the Local Group and beyond, and discuss the state of the art in observations and dynamical modeling of these systems. In order to make this review readable by observers, theorists, and computational astrophysicists, we also review the cross-disciplinary terminology.

  18. Circulation of Stars

    NASA Astrophysics Data System (ADS)

    Boitani, P.

    2016-01-01

    Since the dawn of man, contemplation of the stars has been a primary impulse in human beings, who proliferated their knowledge of the stars all over the world. Aristotle sees this as the product of primeval and perennial “wonder” which gives rise to what we call science, philosophy, and poetry. Astronomy, astrology, and star art (painting, architecture, literature, and music) go hand in hand through millennia in all cultures of the planet (and all use catasterisms to explain certain phenomena). Some of these developments are independent of each other, i.e., they take place in one culture independently of others. Some, on the other hand, are the product of the “circulation of stars.” There are two ways of looking at this. One seeks out forms, the other concentrates on the passing of specific lore from one area to another through time. The former relies on archetypes (for instance, with catasterism), the latter constitutes a historical process. In this paper I present some of the surprising ways in which the circulation of stars has occurred—from East to West, from East to the Far East, and from West to East, at times simultaneously.

  19. Crystal growth of incommensurate members of 2H-hexagonal perovskite related oxides: Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt)

    NASA Astrophysics Data System (ADS)

    Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho; zur Loye, Hans-Conrad

    2016-04-01

    Millimeter sized crystals of six oxides of approximate composition Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt) were grown from molten K2CO3 fluxes and found to crystallize in a 2H hexagonal perovskite-related structure type. The compositions of these incommensurate structures, which belong to the A3n+3mA‧nB3m+nO9m+6n family of 2H hexagonal perovskite related oxides, were characterized by X-ray diffraction, energy dispersive spectroscopy, and magnetic susceptibility measurements. The specific synthetic considerations, crystal growth conditions, and magnetic susceptibility measurements are discussed.

  20. Blurred Star Image Processing for Star Sensors under Dynamic Conditions

    PubMed Central

    Zhang, Weina; Quan, Wei; Guo, Lei

    2012-01-01

    The precision of star point location is significant to identify the star map and to acquire the aircraft attitude for star sensors. Under dynamic conditions, star images are not only corrupted by various noises, but also blurred due to the angular rate of the star sensor. According to different angular rates under dynamic conditions, a novel method is proposed in this article, which includes a denoising method based on adaptive wavelet threshold and a restoration method based on the large angular rate. The adaptive threshold is adopted for denoising the star image when the angular rate is in the dynamic range. Then, the mathematical model of motion blur is deduced so as to restore the blurred star map due to large angular rate. Simulation results validate the effectiveness of the proposed method, which is suitable for blurred star image processing and practical for attitude determination of satellites under dynamic conditions. PMID:22778666

  1. GRACE star camera noise

    NASA Astrophysics Data System (ADS)

    Harvey, Nate

    2016-08-01

    Extending results from previous work by Bandikova et al. (2012) and Inacio et al. (2015), this paper analyzes Gravity Recovery and Climate Experiment (GRACE) star camera attitude measurement noise by processing inter-camera quaternions from 2003 to 2015. We describe a correction to star camera data, which will eliminate a several-arcsec twice-per-rev error with daily modulation, currently visible in the auto-covariance function of the inter-camera quaternion, from future GRACE Level-1B product releases. We also present evidence supporting the argument that thermal conditions/settings affect long-term inter-camera attitude biases by at least tens-of-arcsecs, and that several-to-tens-of-arcsecs per-rev star camera errors depend largely on field-of-view.

  2. Heavy Metal Stars

    NASA Astrophysics Data System (ADS)

    2001-08-01

    La Silla Telescope Detects Lots of Lead in Three Distant Binaries Summary Very high abundances of the heavy element Lead have been discovered in three distant stars in the Milky Way Galaxy . This finding strongly supports the long-held view that roughly half of the stable elements heavier than Iron are produced in common stars during a phase towards the end of their life when they burn their Helium - the other half results from supernova explosions. All the Lead contained in each of the three stars weighs about as much as our Moon. The observations show that these "Lead stars" - all members of binary stellar systems - have been more enriched with Lead than with any other chemical element heavier than Iron. This new result is in excellent agreement with predictions by current stellar models about the build-up of heavy elements in stellar interiors. The new observations are reported by a team of Belgian and French astronomers [1] who used the Coude Echelle Spectrometer on the ESO 3.6-m telescope at the La Silla Observatory (Chile). PR Photo 26a/01 : A photo of HD 196944 , one of the "Lead stars". PR Photo 26b/01 : A CES spectrum of HD 196944 . The build-up of heavy elements Astronomers and physicists denote the build-up of heavier elements from lighter ones as " nucleosynthesis ". Only the very lightest elements (Hydrogen, Helium and Lithium [2]) were created at the time of the Big Bang and therefore present in the early universe. All the other heavier elements we now see around us were produced at a later time by nucleosynthesis inside stars. In those "element factories", nuclei of the lighter elements are smashed together whereby they become the nuclei of heavier ones - this process is known as nuclear fusion . In our Sun and similar stars, Hydrogen is being fused into Helium. At some stage, Helium is fused into Carbon, then Oxygen, etc. The fusion process requires positively charged nuclei to move very close to each other before they can unite. But with increasing

  3. Lowered operation voltage in Pt/SBi2Ta2O9/HfO2/Si ferroelectric-gate field-effect transistors by oxynitriding Si

    NASA Astrophysics Data System (ADS)

    Horiuchi, Takeshi; Takahashi, Mitsue; Li, Qiu-Hong; Wang, Shouyu; Sakai, Shigeki

    2010-05-01

    Oxynitrided Si (SiON) surfaces show smaller subthreshold swings than do directly nitrided Si (SiN) surfaces when used in ferroelectric-gate field-effect transistors (FeFETs) having the following stacked-gate structure: Pt/SrBi2Ta2O9(SBT)/HfO2/Si. SiON/Si substrates for FeFETs were prepared by rapid thermal oxidation (RTO) in O2 at 1000 °C and subsequent rapid thermal nitridation (RTN) in NH3 at various temperatures in the range 950-1150 °C. The electrical properties of the Pt/SBT/HfO2/SiON/Si FeFET were compared with those of reference FETs, i.e. Pt/SBT/HfO2 gate stacks formed on Si substrates subjected to various treatments: SiNx/Si formed by RTN, SiO2/Si formed by RTO and untreated Si. The Pt/SBT/HfO2/SiON/Si FeFET had a larger memory window than all the other reference FeFETs, particularly at low operation voltages when the RTN temperature was 1050 °C.

  4. Structural properties, electric response and magnetic behaviour of La2SrFe2CoO9 triple complex perovskite

    NASA Astrophysics Data System (ADS)

    Casallas, F.; Vera, E.; Landínez, D.; Parra, C.; Roa, J.

    2016-02-01

    The triple perovskite La2SrFe2CoO9 was prepared by the solid state reaction method from the high purity precursor powders La2O3, SrCO3, Fe2O3, Co2O3 (99.9%). The crystalline structure was studied by X-ray diffraction experiments and Rietveld refinement analysis. Results reveal that this material crystallizes in an orthorhombic triple perovskite belonging to the space group Pnma (#62) with lattice constants a=5.491978(2)Ǻ, b=7.719842(2)Ǻ and c=5.436260(3)Ǻ. The granular surface morphology was studied from images of Scanning Electron Microscopy. The electric response was studied by the Impedance Spectroscopy technique from 10.0mHz up to 0.1MHz, at different temperatures (77-300K). Measurements of magnetization as a function of temperature permitted to determine the occurrence of a paramagnetic - ferromagnetic transition for a Curie temperature of 280K, which suggests it application in nanoelectronic devices. From the fit of the magnetic response with the Curie- Weiss equation it was concluded that the effective magnetic moment is particularly large due to the contribution of La, Fe and Co cations.

  5. Cooperativity among defect sites in AO2+x and A4O9 (A=U,Np,Pu) : Density functional calculations

    NASA Astrophysics Data System (ADS)

    Andersson, D. A.; Lezama, J.; Uberuaga, B. P.; Deo, C.; Conradson, S. D.

    2009-01-01

    Actinide dioxides derived from the AO2 fluorite lattice are of high technological relevance due to their application in nuclear reactor fuels. In this paper we use density functional theory calculations to study the oxidation of uranium, neptunium and plutonium dioxides, AO2 ( A=U , Np, or Pu), in O2 and O2/H2O environments. We pay particular attention to the formation of oxygen clusters (cooperativity) in AO2+x and how this phenomenon governs oxidation thermodynamics and the development of ordered A4O9 compounds. The so-called split di-interstitial, composed of two nearest-neighbor octahedral oxygen interstitials that dislocate one regular fluorite lattice oxygen ion to form a cluster of triangular geometry, is predicted to be the fundamental building block of the most stable cluster configurations. We also identify how the formation of oxygen defect clusters and the degree of oxidation in AO2+x are both governed by the ability of the O2p orbitals of the interstitial-like (+x) ions to hybridize with regular fluorite lattice ions.

  6. Reduction of the hydrogen degradation in SrBi2(Ta1-xNbx)2O9 by TiN barrier metal

    NASA Astrophysics Data System (ADS)

    Furuya, Akira; Cuchiaro, J. D.

    2000-11-01

    The use of ferroelectric SrBi2(Ta1-xNbx)2O9 (SBTN) as a mainstream form of nonvolatile memory requires that the degradation of its electrical qualities that is caused by annealing in a hydrogen atmosphere be reduced. Titanium nitride (TiN) is a candidate for use as a barrier-metal layer against hydrogen diffusion. The relationship between the degradation in the qualities of SBTN and the quality of the TiN barrier metal has been investigated. TiN when sputtered onto SBTN capacitors creates a good barrier under all sputtering conditions, and maintains the electrical characteristics of the SBTN through annealing in an atmosphere of H2. Higher density TiN films provide more effective protection. The characteristics of the degraded capacitor were investigated in terms of its current-voltage characteristic. Remanent polarization can be recovered from, at least partially, by applying a series of bipolar pulses. This rejuvenation of the electrical qualities indicates that degradation arises from a combination of electrical and structural faults.

  7. Electrical properties and water incorporation in A-site deficient perovskite La1-xBaxNb3O9-0.5x

    NASA Astrophysics Data System (ADS)

    Animitsa, I.; Iakovleva, A.; Belova, K.

    2016-06-01

    Barium doped A-site deficient perovskites La1-xBaxNb3O9-0.5x (x=0-0.05) were synthesized by the solid state method, their structure, electrical properties and state of oxygen-hydrogen groups have been investigated. These phases were found to be able to incorporate water from the gas phase and to exhibit proton transport. Hydration is accompanied by the formation of different forms of oxygen-hydrogen groups: OH- - groups and H3O+ - ions. The total conductivities of doped samples increased in a wet atmosphere due to the appearance of proton current carriers (at the temperatures below 700 °C), but the conductivity increased insignificantly (~0.25 order of magnitude) because of a low doping level and, consequently, small concentration of protons. TG-measurements confirmed relatively low water content (below 0.2%). The total conductivity depends substantially on x and exhibits a minimum on σ-f(x) dependencies. It has been suggested that such behavior is a manifestation of a mixed cation effect.

  8. Recent progress in oxide thermoelectric materials: p-type Ca3Co4O9 and n-type SrTiO3(-).

    PubMed

    Ohta, Hiromichi; Sugiura, Kenji; Koumoto, Kunihito

    2008-10-01

    Thermoelectric energy conversion technology to convert waste heat into electricity has received much attention. In addition, metal oxides have recently been considered as thermoelectric power generation materials that can operate at high temperatures on the basis of their potential advantages over heavy metallic alloys in chemical and thermal robustness. We have fabricated high-quality epitaxial films composed of oxide thermoelectric materials that are suitable for clarifying the intrinsic "real" properties. This review focuses on the thermoelectric properties of two representative oxide epitaxial films, p-type Ca 3Co 4O 9 and n-type SrTiO 3, which exhibit the best thermoelectric figures of merit, ZT (= S (2)sigma Tkappa (-1), S = Seebeck coefficient, sigma = electrical conductivity, kappa = thermal conductivity, and T = absolute temperature) among oxide thermoelectric materials reported to date. In addition, we introduce the recently discovered giant S of two-dimensional electrons confined within a unit cell layer thickness ( approximately 0.4 nm) of SrTiO 3. PMID:18821809

  9. Remarkable enhancement in the Kapitza resistance and electron potential barrier of chemically modified In2O3(ZnO)9 natural superlattice interfaces.

    PubMed

    Liang, Xin

    2015-11-28

    Superlattice interfaces can efficiently scatter phonons and filter low-energy electrons, thereby reducing the thermal conductivity to the "alloy limit" of crystalline solids and increasing the Seebeck coefficient substantially. In this paper, we report a two-fold reduction in the thermal conductivity and an improvement of about 170% in the Seebeck coefficient of an existing In2O3(ZnO)9 superlattice by chemically modifying the interface with small additions of aluminum. Using a classical model for the interface transport, we attribute such significant changes to the increase in both the Kapitza (thermal) resistance and the electron potential barrier height of the InO2(-) superlattice interfaces that are modified by Al(3+). The present work opens a new avenue of research showing that the superlattice interfaces can be chemically tuned for specific properties, which can be investigated in both experimental and computational ways, and also suggests a new route for material design for applications in areas like thermoelectrics. PMID:26477746

  10. Spin-orbital short-range order in the honeycomb-based quantum magnet Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Nakatsuji, Satoru

    2013-03-01

    The realization of quantum correlated matter beyond one dimension has been vigorously pursued in geometrically frustrated spin systems for decades. In frustrated magnetic materials, however, symmetry breaking of orbital and chemical origin is usually found to induce semi-classical spin freezing. In this talk, I present a contrast case where spins and possibly orbitals remain in a liquid state down to low temperature even in a highly disordered structure of 6H-perovskite Ba3CuSb2O9. Our comprehensive experimental analysis indicates that the geometrical frustration of Wannier's Ising antiferromagnet on a triangular lattice can be exploited to build a nano-structured bipartite honeycomb lattice from electric dipolar spin-1/2 molecules. Despite a strong local Jahn-Teller distortion about the Cu2+ ion, the resulting spin-orbital random bond lattice not only retains hexagonal symmetry averaged over time and space, but it supports a gapless excitation spectrum without spin freezing down to ultralow temperatures. This is the work based on the collaboration with K. Kuga, K. Kimura, R. Satake, N. Katayama, E. Nishibori, H. Sawa, R. Ishii, M. Hagiwara, F. Bridges, T. U. Ito, W. Higemoto, Y. Karaki, M. Halim, A. A. Nugroho, J. A. Rodriguez-Rivera, M. A. Green, C. Broholm. This work is partially supported by Grant-in-Aid for Scientific Research (No. 20340089,21684019) from JSPS, by Grant-in-Aid for Scientific Research on Priority Areas (No. 1951010,19052003) from MEXT, Japan.

  11. Magnetic phase diagram of the S =1/2 triangular-lattice antiferromagnet Ba3CoSb2O9

    NASA Astrophysics Data System (ADS)

    Kamiya, Yoshitomo; Batista, Cristian

    2015-03-01

    To explain the recently reported magnetic phase diagram of the spin-1/2 triangular-lattice compound Ba3CoSb2O9, we present a semiclassical mean-field theory for the easy-plane XXZ model on the stacked triangular-lattice with a small inter-layer coupling. Quantum effects are incorporated by deriving effective interactions from the linear spin-wave analysis of the two-dimensional model. This analysis reproduces the main experimental observations, such as the 1/3-magnetization plateau (B || a) , a cusp near 1/3 of the saturated moment (B || c) , and a small step anomaly in the high field regime. The predicted spin configurations are compared against the NMR measurements on this compound. This work was done in collaboration with G. Koutroulakis (Los Alamos), T. Zhou (UCLA), J. D. Thompson (Los Alamos), H. D. Zhou (Univ. of Tennessee), and S. E. Brown (UCLA). Y.K. acknowledges financial support from the RIKEN iTHES Project.

  12. General Relativity&Compact Stars

    SciTech Connect

    Glendenning, Norman K.

    2005-08-16

    Compact stars--broadly grouped as neutron stars and white dwarfs--are the ashes of luminous stars. One or the other is the fate that awaits the cores of most stars after a lifetime of tens to thousands of millions of years. Whichever of these objects is formed at the end of the life of a particular luminous star, the compact object will live in many respects unchanged from the state in which it was formed. Neutron stars themselves can take several forms--hyperon, hybrid, or strange quark star. Likewise white dwarfs take different forms though only in the dominant nuclear species. A black hole is probably the fate of the most massive stars, an inaccessible region of spacetime into which the entire star, ashes and all, falls at the end of the luminous phase. Neutron stars are the smallest, densest stars known. Like all stars, neutron stars rotate--some as many as a few hundred times a second. A star rotating at such a rate will experience an enormous centrifugal force that must be balanced by gravity or else it will be ripped apart. The balance of the two forces informs us of the lower limit on the stellar density. Neutron stars are 10{sup 14} times denser than Earth. Some neutron stars are in binary orbit with a companion. Application of orbital mechanics allows an assessment of masses in some cases. The mass of a neutron star is typically 1.5 solar masses. They can therefore infer their radii: about ten kilometers. Into such a small object, the entire mass of our sun and more, is compressed.

  13. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  14. Chemical Evolution of Binary Stars

    NASA Astrophysics Data System (ADS)

    Izzard, R. G.

    2013-02-01

    Energy generation by nuclear fusion is the fundamental process that prevents stars from collapsing under their own gravity. Fusion in the core of a star converts hydrogen to heavier elements from helium to uranium. The signature of this nucleosynthesis is often visible in a single star only for a very short time, for example while the star is a red giant or, in massive stars, when it explodes. Contrarily, in a binary system nuclear-processed matter can captured by a secondary star which remains chemically polluted long after its more massive companion star has evolved and died. By probing old, low-mass stars we gain vital insight into the complex nucleosynthesis that occurred when our Galaxy was much younger than it is today. Stellar evolution itself is also affected by the presence of a companion star. Thermonuclear novae and type Ia supernovae result from mass transfer in binary stars, but big questions still surround the nature of their progenitors. Stars may even merge and one of the challenges for the future of stellar astrophysics is to quantitatively understand what happens in such extreme systems. Binary stars offer unique insights into stellar, galactic and extragalactic astrophysics through their plethora of exciting phenomena. Understanding the chemical evolution of binary stars is thus of high priority in modern astrophysics.

  15. Weighing the Smallest Stars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    VLT Finds Young, Very Low Mass Objects Are Twice As Heavy As Predicted Summary Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be. This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. PR Photo 03/05: Near-infrared image of AB Doradus A and its companion (NACO SDI/VLT) A winning combination A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter. This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or "failed stars", are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior. To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called "Kepler's Third Law"). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time - one year - it takes our planet to make a tour around the Sun. The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed

  16. American Urban Star Fest

    NASA Astrophysics Data System (ADS)

    Pazmino, John

    2003-12-01

    Over the last couple of decades New York City implemented, and continues to carry out, several schemes of eradicating luminous graffiti. One result has been the gradual recovery of the natural night sky. By 1994 the normal clear sky transparency over Manhattan deepened to fourth magnitude and has been slowly creeping deeper, until in 2002 it is at magnitude 4 to 4.5. In the spring of 1995, during some lazing on a Manhattan rooftop under a sky full of stars, several New York astronomers hatched the idea of letting the whole people celebrate the renewed starry sky. In due course they, through the Amateur Astronomers Association, engaged the New York City Parks Department and the Urban Park Rangers in an evening of quiet picnicking to enjoy the stars in their natural sky. Thus the Urban Star Fest was born. The event thrilled about 3,000 visitors in Central Park's Sheep Meadow on Saturday 30 September 1995. This year's Fest, the eighth in the series demonstrated the City's upper skyline of stars on Saturday 5 October 2002 to about 2,200 enthused visitors. Although the Fest is always noted as cancelable for inclement weather, so far, it has convened every year, with attendance ranging from 4,000 down to a mere 1,000, this latter being under the smoke plume of the World Trade Center in 2001. Despite this swing in attendance, the American Urban Star Fest is America's largest regularly scheduled public astronomy event. Of course, special occasions, like comets or eclipses, can and do attract far larger interest both in the city and elsewhere. The presentation shows the setup and program of the American Urban Star Fest, to illustrate how the general public can actively become aware of the night sky and see for themselves the result of their very own efforts at removing light pollution--and note where improvement is yet to come.

  17. High mass stars: starbursts

    NASA Astrophysics Data System (ADS)

    González Delgado, R. M.

    2006-08-01

    Starbursts are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. Starbursts are bright at ultraviolet (UV) wavelengths, and after the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues: a) The determination of the initial mass function in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments. b) The modes of star formation: Starburst clusters are an important mode of star formation. c) The role of starbursts in AGN. d) The interaction between massive stars and the interstellar and intergalactic media. e) The contribution of starbursts to the reionization of the universe. Despite the very significant progress obtained over the past two decades of UV observations of starbursts, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. Thus, a new UV mission furnished with an intermediate spectral resolution long-slit spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.

  18. JetStar

    NASA Technical Reports Server (NTRS)

    1982-01-01

    In this photo of the C-140 JetStar on the Dryden Ramp, a subscale propeller has been fitted to the upper fuselage of the aircraft. NASA's Dryden Flight Research Facility, in co-operation with the Lewis Research Center, investigated the acoustic characteristics of a series of subscale advanced design propellors in the early eighties. These propellors were designed to rotate at a tip speed faster than the speed of sound. They are, in effect, a 'swept back wing' version of a propellor. The tests were conducted on Dryden's C-140 Jetstar, seen here on the ramp at Dryden in Edwards, California. The JetStar was modified with the installation of an air turbine drive system. The drive motor, with a 24 inch test propellor, was mounted in a pylon atop the JetStar. The JetStar was equipped with an array of 28 microphones flush-mounted in the fuselage of the aircraft beneath the propellor. Microphones mounted on the wings and on accompanying chase aircraft provided far-field acoustic data. In the 1960s, the same JetStar was equipped with an electronic variable stability flight control system. Called then a General Purpose Airborne Simulator (GPAS), the aircraft could duplicate the flight characteristics of a wide variety of advanced aircraft and was used for supersonic transport and general aviation research and as a training and support system for Space Shuttle Approach and Landing Tests at Dryden in 1977. In 1985, the JetStar's wings were modified with suction and spray devices in a laminar (smooth) air flow program to study ways of improving the flow of air over the wings of airliners. The program also studied ways of reducing the collection of ice and insects on airliner wings.

  19. Detection of a large sample of γ Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy

    NASA Astrophysics Data System (ADS)

    Tkachenko, A.; Aerts, C.; Yakushechkin, A.; Debosscher, J.; Degroote, P.; Bloemen, S.; Pápics, P. I.; de Vries, B. L.; Lombaert, R.; Hrudkova, M.; Frémat, Y.; Raskin, G.; Van Winckel, H.

    2013-08-01

    Context. The launches of the MOST, CoRoT, and Kepler missions opened up a new era in asteroseismology, the study of stellar interiors via interpretation of pulsation patterns observed at the surfaces of large groups of stars. These space missions deliver a huge amount of high-quality photometric data suitable to study numerous pulsating stars. Aims: Our ultimate goal is a detection and analysis of an extended sample of γ Dor-type pulsating stars with the aim to search for observational evidence of non-uniform period spacings and rotational splittings of gravity modes in main-sequence stars typically twice as massive as the Sun. This kind of diagnostic can be used to deduce the internal rotation law and to estimate the amount of rotational mixing in the near core regions. Methods: We applied an automated supervised photometric classification method to select a sample of 69 Gamma Doradus (γ Dor) candidate stars. We used an advanced method to extract the Kepler light curves from the pixel data information using custom masks. For 36 of the stars, we obtained high-resolution spectroscopy with the HERMES spectrograph installed at the Mercator telescope. The spectroscopic data are analysed to determine the fundamental parameters like Teff, log g, vsini, and [M/H]. Results: We find that all stars for which spectroscopic estimates of Teff and log g are available fall into the region of the HR diagram, where the γ Dor and δ Sct instability strips overlap. The stars cluster in a 700 K window in effective temperature; log g measurements suggest luminosity class IV-V, i.e. sub-giant or main-sequence stars. From the Kepler photometry, we identify 45 γ Dor-type pulsators, 14 γ Dor/δ Sct hybrids, and 10 stars, which are classified as "possibly γ Dor/δ Sct hybrid pulsators". We find a clear correlation between the spectroscopically derived vsini and the frequencies of independent pulsation modes. Conclusions: We have shown that our photometric classification based on the

  20. Plastic star coupler

    NASA Astrophysics Data System (ADS)

    Yuuki, Hayato; Ito, Takeharu; Sugimoto, Tetsuo

    1991-12-01

    We applied an ultrasonic welding method for the bonding of plastic fibers, and obtained many types of optical star couplers for optical communication systems. It enables the manufacturing of optical components with low loss without damaging the clad layer except for the welding surface. Therefore, they have some merits, such as low loss, small size, light weight, and low cost. The 4-ports (2 X 2) star coupler of 1000 micrometers diam APF has 0.7 dB excess loss at most, and the welding length is 20 mm.

  1. The Drifting Star

    NASA Astrophysics Data System (ADS)

    2008-04-01

    By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way. ESO PR Photo 09a/08 ESO PR Photo 09a/08 Iota Horologii The yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction. Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days (ESO 12/99). But until now, all studies were unable to pinpoint the exact characteristics of the star, and hence to understand its origin. A team of astronomers, led by Sylvie Vauclair from the University of Toulouse, France, therefore decided to use the technique of 'asteroseismology' to unlock the star's secrets. "In the same way as geologists monitor how seismic waves generated by earthquakes propagate through the Earth and learn about the inner structure of our planet, it is possible to study sound waves running through a star, which forms a sort of large, spherical bell," says Vauclair. The 'ringing' from this giant musical instrument provides astronomers with plenty of information about the physical conditions in the star's interior. And to 'listen to the music', the astronomers used one of the best instruments available. The observations were conducted in November 2006 during 8 consecutive nights with the state-of-the-art HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla. Up to 25 'notes' could be identified in the unique dataset, most of them corresponding to waves having a period of about 6.5 minutes. These observations allowed the astronomers to obtain a very precise portrait of Iota Horologii: its

  2. The neutron star zoo

    NASA Astrophysics Data System (ADS)

    Harding, Alice K.

    2013-12-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission.

  3. The DQ Herculis stars

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph

    1994-01-01

    We review the properties of the DQ Herculis stars: cataclysmic variables containing an accreting, magnetic, rapidly rotating white dwarf. These stars are characterized by strong X-ray emission, high-excitation spectra, and very stable optical and X-ray pulsations in their light curves. There is considerable resemblance to their more famous cousins, the AM Herculis stars, but the latter class is additionally characterized by spin-orbit synchronism and the presence of strong circular polarization. We list eighteen stars passing muster as certain or very likely DQ Her stars. The rotational periods range from 33 s to 2.0 hr. Additional periods can result when the rotating searchlight illuminates other structures in the binary. A single hypothesis explains most of the observed properties: magnetically channeled accretion within a truncated disk. Some accretion flow still seems to proceed directly to the magnetosphere, however. The white dwarfs' magnetic moments are in the range 10(sup 32) - 10(sup 34) G cc, slightly weaker than in AM Her stars but with some probable overlap. The more important reason why DQ Hers have broken synchronism is probably their greater accretion rate and orbital separation. The observed L(sub x)/L(sub V) values are surprisingly low for a radially accreting white dwarf, suggesting that most of the accretion energy is not radiated in a strong shock above the magnetic pole. The fluxes can be more satisfactorily explained if most of the radial infall energy manages to bypass the shock and deposit itse lf directly in the white dwarf photosphere, where it should emerge as extreme ultraviolet (EUV) radiation. This also provides an adequate source of ionizing photons to power the high-excitation optical and UV emission lines. This is probably the DQ Her analog to the famous 'soft X-ray excess' in AM Her stars. However, unlike the AM Her case, this radiation has not been directly observed, so the analogy must not (yet) be embraced too firmly. There is

  4. GeoSTAR

    NASA Astrophysics Data System (ADS)

    Lambrigtsen, B.; Gaier, T.; Tanner, A.; Kangaslahti, P.; Brown, S.

    2006-12-01

    The Geostationary Synthetic Thinned Aperture Radiometer, GeoSTAR, is a new concept for a microwave atmospheric sounder intended for geostationary satellites such as the GOES weather satellites operated by NOAA. A small but fully functional prototype has recently been developed at the Jet Propulsion Laboratory to demonstrate the feasibility of using aperture synthesis in lieu of the large solid parabolic dish antenna that is required with the conventional approach. Spatial resolution requirements dictate such a large aperture in GEO that the conventional approach has not been feasible, and it is only now with the GeoSTAR approach that a GEO microwave sounder can be contemplated. Others have proposed GEO microwave radiometers that would operate at sub-millimeter wavelengths to circumvent the large-aperture problem, but GeoSTAR is the only viable approach that can provide full sounding capabilities equal to or exceeding those of the AMSU systems now operating on LEO weather satellites and which have had tremendous impact on numerical weather forecasting. GeoSTAR will satisfy a number of important measurement objectives, many of them identified by NOAA as unmet needs in their GOES-R pre-planned product improvements (P3I) lists and others by NASA in their research roadmaps and as discussed in a white paper submitted to the NRC Decadal Survey. The performance of the prototype has been outstanding, and this proof of concept represents a major breakthrough in remote sensing capabilities. The GeoSTAR concept is now at a stage of development where an infusion into space systems can be initiated either on a NASA sponsored research mission or on a NOAA sponsored operational mission. GeoSTAR is an ideal candidate for a joint "research to operations" mission, and that may be the most likely scenario. Additional GeoSTAR related technology development and other risk reduction activities are under way, and a GeoSTAR mission is feasible in the GOES-R/S time frame, 2014-2016. This

  5. Mesopotamian Star Lists

    NASA Astrophysics Data System (ADS)

    Horowitz, Wayne

    Sumerian and Akkadian names of stars and constellations occur in cuneiform texts for over 2,000 years, from the third millennium BC down to the death of cuneiform in the early first millennium AD, but no fully comprehensive list was ever compiled in antiquity. Lists of stars and constellations are available in both the lexical tradition and astronomical-astrological tradition of the cuneiform scribes. The longest list in the former is that in the series Urra = hubullu, in the latter, those in Mul-Apin.

  6. A Star on Earth

    ScienceCinema

    Prager, Stewart; Zwicker, Andrew; Hammet, Greg; Tresemer, Kelsey; Diallo, Ahmed

    2014-06-06

    At the Energy Department's Princeton Plasma Physics Lab, scientists are trying to accomplish what was once considered the realm of science fiction: create a star on Earth. The National Spherical Torus Experiment (NSTX) is a magnetic fusion device that is used to study the physics principles of spherically shaped plasmas -- hot ionized gases in which, under the right conditions, nuclear fusion will occur. Fusion is the energy source of the sun and all of the stars. Not just limited to theoretical work, the NSTX is enabling cutting-edge research to develop fusion as a future energy source.

  7. Neutrinos from neutron stars

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.

    1979-01-01

    A calculation of the flux of ultra-high energy neutrinos from galactic neutron stars is presented. The calculation is used to determine the number of point sources detectable at the sensitivity threshold of a proposed deep underwater muon and neutrino detector array. The detector array would have a point source detection threshold of about 100 eV/sq cm-sec. Analysis of neutrino luminosities and the number of detectable sources suggests that the deep underwater detector may make a few discoveries. In particular, a suspected neutron star in the Cyg X-3 source seems a promising target for the deep underwater array.

  8. Chaplygin dark star

    SciTech Connect

    Bertolami, O.; Paramos, J.

    2005-12-15

    We study the general properties of a spherically symmetric body described through the generalized Chaplygin equation of state. We conclude that such an object, dubbed generalized Chaplygin dark star, should exist within the context of the generalized Chaplygin gas (GCG) model of unification of dark energy and dark matter, and derive expressions for its size and expansion velocity. A criteria for the survival of the perturbations in the GCG background that give origin to the dark star are developed, and its main features are analyzed.

  9. Synthetic guide star generation

    DOEpatents

    Payne, Stephen A [Castro Valley, CA; Page, Ralph H [Castro Valley, CA; Ebbers, Christopher A [Livermore, CA; Beach, Raymond J [Livermore, CA

    2008-06-10

    A system for assisting in observing a celestial object and providing synthetic guide star generation. A lasing system provides radiation at a frequency at or near 938 nm and radiation at a frequency at or near 1583 nm. The lasing system includes a fiber laser operating between 880 nm and 960 nm and a fiber laser operating between 1524 nm and 1650 nm. A frequency-conversion system mixes the radiation and generates light at a frequency at or near 589 nm. A system directs the light at a frequency at or near 589 nm toward the celestial object and provides synthetic guide star generation.

  10. Synthetic guide star generation

    DOEpatents

    Payne, Stephen A.; Page, Ralph H.; Ebbers, Christopher A.; Beach, Raymond J.

    2004-03-09

    A system for assisting in observing a celestial object and providing synthetic guide star generation. A lasing system provides radiation at a frequency at or near 938 nm and radiation at a frequency at or near 1583 nm. The lasing system includes a fiber laser operating between 880 nm and 960 nm and a fiber laser operating between 1524 nm and 1650 nm. A frequency-conversion system mixes the radiation and generates light at a frequency at or near 589 nm. A system directs the light at a frequency at or near 589 nm toward the celestial object and provides synthetic guide star generation.

  11. Isolating Triggered Star Formation

    SciTech Connect

    Barton, Elizabeth J.; Arnold, Jacob A.; Zentner, Andrew R.; Bullock, James S.; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC

    2007-09-12

    Galaxy pairs provide a potentially powerful means of studying triggered star formation from galaxy interactions. We use a large cosmological N-body simulation coupled with a well-tested semi-analytic substructure model to demonstrate that the majority of galaxies in close pairs reside within cluster or group-size halos and therefore represent a biased population, poorly suited for direct comparison to 'field' galaxies. Thus, the frequent observation that some types of galaxies in pairs have redder colors than 'field' galaxies is primarily a selection effect. We use our simulations to devise a means to select galaxy pairs that are isolated in their dark matter halos with respect to other massive subhalos (N= 2 halos) and to select a control sample of isolated galaxies (N= 1 halos) for comparison. We then apply these selection criteria to a volume-limited subset of the 2dF Galaxy Redshift Survey with M{sub B,j} {le} -19 and obtain the first clean measure of the typical fraction of galaxies affected by triggered star formation and the average elevation in the star formation rate. We find that 24% (30.5 %) of these L* and sub-L* galaxies in isolated 50 (30) h{sup -1} kpc pairs exhibit star formation that is boosted by a factor of {approx}> 5 above their average past value, while only 10% of isolated galaxies in the control sample show this level of enhancement. Thus, 14% (20 %) of the galaxies in these close pairs show clear triggered star formation. Our orbit models suggest that 12% (16%) of 50 (30) h{sup -1} kpc close pairs that are isolated according to our definition have had a close ({le} 30 h{sup -1} kpc) pass within the last Gyr. Thus, the data are broadly consistent with a scenario in which most or all close passes of isolated pairs result in triggered star formation. The isolation criteria we develop provide a means to constrain star formation and feedback prescriptions in hydrodynamic simulations and a very general method of understanding the importance of

  12. A Real Shooting Star

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Click on the image for movie of A Real Shooting Star

    This artist's animation illustrates a star flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake. The star, named Mira (pronounced my-rah) after the latin word for 'wonderful,' sheds material that will be recycled into new stars, planets and possibly even life. NASA's Galaxy Evolution Explorer discovered the long trail of material behind Mira during its survey of the entire sky in ultraviolet light.

    The animation begins by showing a close-up of Mira -- a red-giant star near the end of its life. Red giants are red in color and extremely bloated; for example, if a red giant were to replace our sun, it would engulf everything out to the orbit of Mars. They constantly blow off gas and dust in the form of stellar winds, supplying the galaxy with molecules, such as oxygen and carbon, that will make their way into new solar systems. Our sun will mature into a red giant in about 5 billion years.

    As the animation pulls out, we can see the enormous trail of material deposited behind Mira as it hurls along between the stars. Like a boat traveling through water, a bow shock, or build up of gas, forms ahead of the star in the direction of its motion. Gas in the bow shock is heated and then mixes with the cool hydrogen gas in the wind that is blowing off Mira. This heated hydrogen gas then flows around behind the star, forming a turbulent wake.

    Why does the trailing hydrogen gas glow in ultraviolet light? When it is heated, it transitions into a higher-energy state, which then loses energy by emitting ultraviolet light - a process known as fluorescence.

    Finally, the artist's rendering gives way to the actual ultraviolet image taken by the Galaxy Evolution Explorer

    Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira

  13. The DQ Herculis stars

    NASA Astrophysics Data System (ADS)

    Patterson, Joseph

    1994-03-01

    We review the properties of the DQ Herculis stars: cataclysmic variables containing an accreting, magnetic, rapidly rotating white dwarf. These stars are characterized by strong X-ray emission, high-excitation spectra, and very stable optical and X-ray pulsations in their light curves. There is considerable resemblance to their more famous cousins, the AM Herculis stars, but the latter class is additionally characterized by spin-orbit synchronism and the presence of strong circular polarization. We list eighteen stars passing muster as certain or very likely DQ Her stars. The rotational periods range from 33 s to 2.0 hr. Additional periods can result when the rotating searchlight illuminates other structures in the binary. A single hypothesis explains most of the observed properties: magnetically channeled accretion within a truncated disk. Some accretion flow still seems to proceed directly to the magnetosphere, however. The white dwarfs' magnetic moments are in the range 1032 - 1034 G cc, slightly weaker than in AM Her stars but with some probable overlap. The more important reason why DQ Hers have broken synchronism is probably their greater accretion rate and orbital separation. The observed Lx/LV values are surprisingly low for a radially accreting white dwarf, suggesting that most of the accretion energy is not radiated in a strong shock above the magnetic pole. The fluxes can be more satisfactorily explained if most of the radial infall energy manages to bypass the shock and deposit itse lf directly in the white dwarf photosphere, where it should emerge as extreme ultraviolet (EUV) radiation. This also provides an adequate source of ionizing photons to power the high-excitation optical and UV emission lines. This is probably the DQ Her analog to the famous 'soft X-ray excess' in AM Her stars. However, unlike the AM Her case, this radiation has not been directly observed, so the analogy must not (yet) be embraced too firmly. There is some conventional wisdom

  14. A Star on Earth

    SciTech Connect

    Prager, Stewart; Zwicker, Andrew; Hammet, Greg; Tresemer, Kelsey; Diallo, Ahmed

    2014-03-05

    At the Energy Department's Princeton Plasma Physics Lab, scientists are trying to accomplish what was once considered the realm of science fiction: create a star on Earth. The National Spherical Torus Experiment (NSTX) is a magnetic fusion device that is used to study the physics principles of spherically shaped plasmas -- hot ionized gases in which, under the right conditions, nuclear fusion will occur. Fusion is the energy source of the sun and all of the stars. Not just limited to theoretical work, the NSTX is enabling cutting-edge research to develop fusion as a future energy source.

  15. Finding Planets around other stars

    NASA Video Gallery

    Just as the Earth revolves around the sun, our closest star, other planets might orbit the stars you see in the night sky. Think of all the planets in the universe that may be just the right distan...

  16. The Death of a Star

    ERIC Educational Resources Information Center

    Thorne, Kip S.

    1971-01-01

    Theories associated with the gravitational collapse of a star into black holes" are described. Suggests that the collapse and compression might go through the stages from white dwarf star to neutron core to black hole." (TS)

  17. Star Formation in Irregular Galaxies.

    ERIC Educational Resources Information Center

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  18. Photographic photometry of variable stars

    NASA Technical Reports Server (NTRS)

    Kholopov, P. N.

    1973-01-01

    Photographic methods of determining stellar magnitude and measuring brightness of variable stars on negatives include the photoelectric method and the contascope. Calibration curves are usually plotted by the UBV method. Magnitudes of comparison stars can be determined from photographs.

  19. A Vanishing Star Revisited

    NASA Astrophysics Data System (ADS)

    1999-07-01

    VLT Observations of an Unusual Stellar System Reinhold Häfner of the Munich University Observatory (Germany) is a happy astronomer. In 1988, when he was working at a telescope at the ESO La Silla observatory, he came across a strange star that suddenly vanished off the computer screen. He had to wait for more than a decade to get the full explanation of this unusual event. On June 10-11, 1999, he observed the same star with the first VLT 8.2-m Unit Telescope (ANTU) and the FORS1 astronomical instrument at Paranal [1]. With the vast power of this new research facility, he was now able to determine the physical properties of a very strange stellar system in which two planet-size stars orbit each other. One is an exceedingly hot white dwarf star , weighing half as much as the Sun, but only twice as big as the Earth. The other is a much cooler and less massive red dwarf star , one-and-a-half times the size of planet Jupiter. Once every three hours, the hot star disappears behind the other, as seen from the Earth. For a few minutes, the brightness of the system drops by a factor of more than 250 and it "vanishes" from view in telescopes smaller than the VLT. A variable star named NN Serpentis ESO PR Photo 30a/99 ESO PR Photo 30a/99 [Preview - JPEG: 400 x 468 pix - 152k] [Normal - JPEG: 800 x 936 pix - 576k] [High-Res - JPEG: 2304 x 2695 pix - 4.4M] Caption to ESO PR Photo 30a/99 : The sky field around the 17-mag variable stellar system NN Serpentis , as seen in a 5 sec exposure through a V(isual) filter with VLT ANTU and FORS1. It was obtained just before the observation of an eclipse of this unsual object and served to centre the telescope on the corresponding sky position. The field shown here measures 4.5 x 4.5 armin 2 (1365 x 1365 pix 2 ; 0.20 arcsec/pix). The field is somewhat larger than that shown in Photo 30b/99 and has the same orientation to allow comparison: North is about 20° anticlockwise from the top and East is 90° clockwise from that direction. The

  20. X-ray diagnostics of massive star winds

    NASA Astrophysics Data System (ADS)

    Oskinova, Lidia M.

    2016-09-01

    Nearly all types of massive stars with radiatively driven stellar winds are X-ray sources that can be observed by the presently operating powerful X-ray telescopes. In this review I briefly address recent advances in our understanding of stellar winds obtained from X-ray observations. X-rays may strongly influence the dynamics of weak winds of main sequence B-type stars. X-ray pulsations were detected in a β Cep type variable giving evidence of tight photosphere-wind connections. The winds of OB dwarfs with subtypes later than O9V may be predominantly in a hot phase, and X-ray observations offer the best window for their studies. The X-ray properties of OB supergiants are largely determined by the effects of radiative transfer in their clumped stellar winds. The recently suggested method to directly measure mass-loss rates of O stars by fitting the shapes of X-ray emission lines is considered but its validity cannot be confirmed. To obtain robust quantitative information on stellar wind parameters from X-ray spectroscopy, a multiwavelength analysis by means of stellar atmosphere models is required. Independent groups are now performing such analyses with encouraging results. Joint analyses of optical, UV, and X-ray spectra of OB supergiants yield consistent mass-loss rates. Depending on the adopted clumping parameters, the empirically derived mass-loss rates are a factor of a few smaller or comparable to those predicted by standard recipes (Vink et al., 2001). All sufficiently studied O stars display variable X-ray emission that might be related to corotating interaction regions in their winds. In the latest stages of stellar evolution, single red supergiants (RSG) and luminous blue variable (LBV) stars do not emit observable amounts of X-rays. On the other hand, nearly all types of Wolf-Rayet (WR) stars are X-ray sources. X-ray spectroscopy allows a sensitive probe of WR wind abundances and opacities.

  1. Identification of Galactic Bulge Survey X-Ray Sources with Tycho-2 Stars

    NASA Astrophysics Data System (ADS)

    Hynes, Robert I.; Wright, N. J.; Maccarone, T. J.; Jonker, P. G.; Greiss, S.; Steeghs, D.; Torres, M. A. P.; Britt, C. T.; Nelemans, G.

    2012-12-01

    We identify 69 X-ray sources discovered by the Galactic Bulge Survey (GBS) that are coincident with or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-ray-to-optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also examine Two Micron All Sky Survey colors, variability information from the All-Sky Automated Survey, and X-ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very mixed selection, ranging in spectral class from O9 to M3. In some cases, the X-ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these exhibit redder near-IR colors than expected for their spectral type and/or variability, and it is likely that the X-rays originate from a late-type companion star in most or all of these objects.

  2. IDENTIFICATION OF GALACTIC BULGE SURVEY X-RAY SOURCES WITH TYCHO-2 STARS

    SciTech Connect

    Hynes, Robert I.; Britt, C. T.; Wright, N. J.; Jonker, P. G.; Steeghs, D.; Torres, M. A. P.; Maccarone, T. J.; Greiss, S.; Nelemans, G.

    2012-12-20

    We identify 69 X-ray sources discovered by the Galactic Bulge Survey (GBS) that are coincident with or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-ray-to-optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also examine Two Micron All Sky Survey colors, variability information from the All-Sky Automated Survey, and X-ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very mixed selection, ranging in spectral class from O9 to M3. In some cases, the X-ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these exhibit redder near-IR colors than expected for their spectral type and/or variability, and it is likely that the X-rays originate from a late-type companion star in most or all of these objects.

  3. The evolution of massive stars

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The hypotheses underlying theoretical studies of the evolution of massive model stars with and without mass loss are summarized. The evolutionary tracks followed by the models across theoretical Hertzsprung-Russell (HR) diagrams are compared with the observed distribution of B stars in an HR diagram. The pulsational properties of models of massive star are also described.

  4. Young Stars in IC 2118

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Rebull, Luisa; Daou, Doris; Maranto, Tony; Roelofsen, Theresa; Sepulveda, Babs; Weehler, Cynthia

    2005-02-01

    IC 2118, the Witch Head Nebula (~210 parsecs), is region forming stars located near the supergiant star Rigel in the constellation Orion. Kun et al. (2004, A&A, 418, 89) have determined that IC 2118 is on the near side of the Orion-Eridanus Super Bubble and that stellar winds from the Orion OB1 association may be triggering new star formation in the nebula. We propose using IRAC and MIPS to reexamine a small dense region of this nebula where Kun et al. have spectroscopically identified three 2MASS sources as T Tauri stars embedded in the cloud. Previous all-sky surveys, including both IRAS and 2MASS, have included this region, but not to the resolution that Spitzer can provide, and there are few studies of this particular region in the literature. Our team proposes to use IRAC and MIPS observations to (1) investigate star formation, (2) look for likely cluster member stars with infrared excesses, and characterize this young star population by obtaining their colors and therefore estimates of masses and ages, (3) study the distribution of stars, their relationship to the ISM, and the possibilities of triggered star formation, (4) compare the young star population, distribution, and age to other similar sites of star formation, e.g., IC 1396 and (5) produce a dramatic image of the interstellar medium in the region surrounding IC 2118. Since this region is in the Orion constellation near the bright star Rigel, it provides additional appeal to students and the general public.

  5. Physics of the Stars

    ERIC Educational Resources Information Center

    Haig, G. Y.

    1974-01-01

    Describes how astrophysics can be a do-it-yourself project within a school boy's budget and background, by giving detailed instruction on equipment construction. In addition, this article describes many experiments to undertake, with the equipment, such as determining color temperature, star spectra, chemical composition and others. (BR)

  6. Reaching for the Stars.

    ERIC Educational Resources Information Center

    Roper-Davis, Sharon

    1999-01-01

    Describes "Reaching for the Stars," a program which develops teaming and mentoring skills in senior physics students. Phase 1 requires student pairs to design a rocket; Phase 2 pairs seniors with gifted second graders who build the rocket from written instructions; and in Phase 3, pairs of seniors create a children's storybook explaining one of…

  7. Pygmy stars: first pair.

    PubMed

    Zwicky, F

    1966-07-01

    The binary LP 101-15/16 having the proper motion of 1.62 seconds of arc per year has been studied with the prime-focus spectrograph of the 200-inch (508 cm) telescope. Indications are that LP 101-15/16 is the first pair of pygmy stars ever discovered. One of its components, LP 101-16, is probably a blue pygmy star which is at least four magnitudes fainter than the ordinary white dwarfs. Also, two of the Balmer lines in absorption appear to be displaced toward the red by amounts which indicate the existence of an Einstein gravitational red shift corresponding to about 1000 km sec-1. On the other hand LP 101-15 is red and shows an entirely new type of spectrum, which suggests that it may be a first representative of a type of red pygmy star which is 2.5 magnitudes fainter than the M-type dwarf stars of the main sequence. PMID:17730606

  8. The Astounding Stars.

    ERIC Educational Resources Information Center

    Montgomery, Angela; And Others

    1983-01-01

    Studying about stellar constellations provides children with an opportunity to learn about ancient myths and mathematics at the same time. An interdisciplinary teaching unit combines information about myths associated with the zodiac signs and instructions for plotting the coordinates of stars. (PP)

  9. Trek to the Stars

    ERIC Educational Resources Information Center

    Rubinstein, Robert E.

    1977-01-01

    "Star Trek", which was aired on television for three years, brought the creatures and conflicts of the "outer reaches" of space into our living rooms. Here its new episodes and reruns are analyzed by elementary students as part of a social studies/elementary science curriculum. (Author/RK)

  10. Housing Star Schools Reforms.

    ERIC Educational Resources Information Center

    Tushnet, Naida C.

    The Star Schools Program has funded projects to explore innovative educational applications of technology in distance education. Funded projects have applied a variety of technologies, including videodisks, compressed data transmission, fiber optic technology, and computer networks. Program evaluation is a mandated aspect of the program. This…

  11. Chemical Compositions of Stars

    NASA Astrophysics Data System (ADS)

    Leckrone, D.; Murdin, P.

    2000-11-01

    In 1835, in a famously inaccurate forecast, the French philosopher Auguste Comte wrote of stars that, `We understand the possibility of determining their shapes, their distances, their sizes and their movements; whereas we would never know how to study by any means their chemical composition…'. At the close of the 20th century the accurate measurement of the abundances of the chemical elements in...

  12. Multipath star switch controller

    NASA Technical Reports Server (NTRS)

    Anderson, T. O.

    1980-01-01

    Device concept permits parallel computers to scan several commonnetwork-connected data stations at maximum rate. Sequencers leap-frog to bypass ports already being serviced by another computer. Two-path system for 16-port star switch controller is cost effective if added bandwidth or increased reliability is desired. Triple-path system would be cost effective for 32-port controller.

  13. NuStar

    Integrated Risk Information System (IRIS)

    NuStar ; CASRN 85509 - 19 - 9 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic Effects

  14. Molecules between the Stars.

    ERIC Educational Resources Information Center

    Verschuur, Gerrit L.

    1987-01-01

    Provides a listing of molecules discovered to date in the vast interstellar clouds of dust and gas. Emphasizes the recent discoveries of organic molecules. Discusses molecular spectral lines, MASERs (microwave amplification by stimulated emission of radiation), molecular clouds, and star birth. (TW)

  15. Insight into star death

    SciTech Connect

    Talcott, R.

    1988-02-01

    Nineteen neutrinos, formed in the center of a supernova, became a theorist's dream. They came straight from the heart of supernova 1987A and landed in two big underground tanks of water. Suddenly a new chapter in observational astronomy opened as these two neutrino telescopes gave astronomers their first look ever into the core of a supernova explosion. But the theorists' dream almost turned into a nightmare. Observations of the presupernova star showed conclusively that the star was a blue supergiant, but theorists have long believed only red supergiant stars could explode as supernovae. Do astronomers understand supernovae better now than when supernova 1987A exploded in the Large Magellanic Cloud (LMC) one year ago Yes. The observations of neutrinos spectacularly confirmed a vital aspect of supernova theory. But the observed differences between 1987A and other supernovae have illuminated and advanced our perception of how supernovae form. By working together, observers and theorists are continuing to hone their ideas about how massive stars die and how the subsequent supernovae behave.

  16. Stabilizing Star Wars

    SciTech Connect

    Weinberg, A.M.; Barkenbus, J.N.

    1984-01-01

    An orderly replacement of offensive with defensive nuclear weapons is part of the defense-protected build-down (DPB) strategy described by Weinberg and Barkenbus. Differing from the administration's Star Wars approach by relying on interceptor missiles rather than costly and unproven lasers and particle beams, the plan also calls for a simultaneous freeze on offensive weapons. (DCK)

  17. Reaching for the Stars

    ERIC Educational Resources Information Center

    Terry, Dorothy Givens

    2012-01-01

    Dr. Mae Jemison is the world's first woman astronaut of color who continues to reach for the stars. Jemison was recently successful in leading a team that has secured a $500,000 federal grant to make interstellar space travel a reality. The Dorothy Jemison Foundation for Excellence (named after Jemison's mother) was selected in June by the Defense…

  18. StarLogo TNG

    NASA Astrophysics Data System (ADS)

    Klopfer, Eric; Scheintaub, Hal; Huang, Wendy; Wendel, Daniel

    Computational approaches to science are radically altering the nature of scientific investigatiogn. Yet these computer programs and simulations are sparsely used in science education, and when they are used, they are typically “canned” simulations which are black boxes to students. StarLogo The Next Generation (TNG) was developed to make programming of simulations more accessible for students and teachers. StarLogo TNG builds on the StarLogo tradition of agent-based modeling for students and teachers, with the added features of a graphical programming environment and a three-dimensional (3D) world. The graphical programming environment reduces the learning curve of programming, especially syntax. The 3D graphics make for a more immersive and engaging experience for students, including making it easy to design and program their own video games. Another change to StarLogo TNG is a fundamental restructuring of the virtual machine to make it more transparent. As a result of these changes, classroom use of TNG is expanding to new areas. This chapter is concluded with a description of field tests conducted in middle and high school science classes.

  19. Sleeping under the stars

    NASA Astrophysics Data System (ADS)

    Zirkel, Jack

    Sherlock Holmes and Dr. Watson went on a camping trip. As they lay down for the night, Holmes said, “Watson, look up at the sky and tell me what you see.”Watson:“! see millions and millions of stars.”

  20. THE STAR OFFLINE FRAMEWORK.

    SciTech Connect

    FINE,V.; FISYAK,Y.; PEREVOZTCHIKOV,V.; WENAUS,T.

    2000-02-07

    The Solenoidal Tracker At RHIC (STAR) is a-large acceptance collider detector, commissioned at Brookhaven National Laboratory in 1999. STAR has developed a software framework supporting simulation, reconstruction and analysis in offline production, interactive physics analysis and online monitoring environments that is well matched both to STAR's present status of transition between Fortran and C++ based software and to STAR's evolution to a fully OO software base. This paper presents the results of two years effort developing a modular C++ framework based on the ROOT package that encompasses both wrapped Fortran components (legacy simulation and reconstruction code) served by IDL-defined data structures, and fully OO components (all physics analysis code) served by a recently developed object model for event data. The framework supports chained components, which can themselves be composite subchains, with components (''makers'') managing ''data sets'' they have created and are responsible for. An St-DataSet class from which data sets and makers inherit allows the construction of hierarchical organizations of components and data, and centralizes almost all system tasks such as data set navigation, I/O, database access, and inter-component communication. This paper will present an overview of this system, now deployed and well exercised in production environments with real and simulated data, and in an active physics analysis development program.

  1. Reading Stars. 2013 Report

    ERIC Educational Resources Information Center

    National Literacy Trust, 2013

    2013-01-01

    The National Literacy Trust's Premier League Reading Stars has now been running for 10 years. During this time, hundreds of thousands of children and families have been inspired by the power of football to develop a love of reading. Although the programme has grown and evolved over this period, the premise remains the same: harnessing the…

  2. Magnetic Dynamos and Stars

    SciTech Connect

    Eggleton, P P

    2007-02-15

    Djehuty is a code that has been developed over the last five years by the Lawrence Livermore National Laboratory (LLNL), from earlier code designed for programmatic efforts. Operating in a massively parallel environment, Djehuty is able to model entire stars in 3D. The object of this proposal was to continue the effort to introduce magneto-hydrodynamics (MHD) into Djehuty, and investigate new classes of inherently 3D problems involving the structure, evolution and interaction of stars and planets. However, towards the end of the second year we discovered an unexpected physical process of great importance in the evolution of stars. Consequently for the third year we changed direction and concentrated on this process rather than on magnetic fields. Our new process was discovered while testing the code on red-giant stars, at the 'helium flash'. We found that a thin layer was regularly formed which contained a molecular-weight inversion, and which led therefore to Rayleigh-Taylor instability. This in turn led to some deeper-than-expected mixing, which has the property that (a) much {sup 3}He is consumed, and (b) some {sup 13}C is produced. These two properties are closely in accord with what has been observed over the last thirty years in red giants, whereas what was observed was largely in contradiction to what earlier theoretical models predicted. Thus our new 3D models with Djehuty explain a previously-unexplained problem of some thirty years standing.

  3. Study on luminescent properties of Eu3+ doped Gd2WO6, Gd2W2O9 and Gd2(WO4)3 nanophosphors prepared by co-precipitation.

    PubMed

    Meng, Qingyu; Hua, Ruinian; Chen, Baojiu; Tian, Yue; Lu, Shuchen; Sun, Linan

    2011-01-01

    Eu3+ doped Gd2WO6, Gd2W2O9 and Gd2(WO4)3 nanophosphors with different concentrations have been prepared by co-precipitation. XRD (X-ray diffraction) and SEM (scanning electron microscopy) were used to investigate the structure and morphology. The emission spectra, excitation spectra and fluorescence decay curves were measured, and partial J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated. Furthermore, concentration quenching curves of Eu3+ in different hosts were drawn. The photoluminescent properties of Eu3+ doped Gd2WO6, Gd2W2O9 and Gd2(WO4)3 nanophosphors have been studied. The results indicate that Eu3+ 5D0-7F2 red luminescence can be effectively excited by 395 nm and 465 nm in Gd2WO6 and Gd2W2O9 hosts, similar to the familiar Gd2(WO4)3:Eu. Especially Gd2W2O9:Eu has strong red emission and high quenching concentration, so it has potential applications for trichromatic white LED as red fluorescent materials. PMID:21446424

  4. Stabilization of the previously unknown tautomer HP(OH)2 of hypophosphorous acid as ligand; preparation of [W3(Ni(HP(OH)2))Q4(H2O)9]4+ (Q = S, Se) complexes.

    PubMed

    Sokolov, Maxim N; Hernández-Molina, Rita; Clegg, William; Fedin, Vladimir P; Mederos, Alfredo

    2003-01-01

    Bis(hydroxy)phosphine, the isomer of hypophosphorous acid which remained elusive for a long time, coordinates to the Ni site of heterometallic clusters with a W3NiQ4 core (Q = S, Se) to give [W3(Ni(HP(OH)2))Q4(H2O)9]4+ (Q = S, Se). PMID:12611005

  5. Multiple star formation

    NASA Astrophysics Data System (ADS)

    Kraus, Adam L.

    2010-11-01

    In this thesis, I present a study of the formation and evolution of stars, particularly multiple stellar systems. Binary stars provide a key constraint on star formation because any successful model should reproduce the mass-dependent frequency, distribution of separations, and distribution of mass ratios. I have pursued a number of surveys for different ranges of parameter space, all yielding one overarching conclusion: binary formation is fundamentally tied to mass. Solar-mass stars have a high primordial binary frequency (50%--75%) and a wide range of separations (extending to >10,000 AU), but as the system mass decreases, the frequency and separation distribution also decrease. For brown dwarfs, binaries are rare (~10%--15%) and have separations of <5 AU. Inside of this outer separation cutoff, the separation distribution appears to be log-flat for solar-mass stars, and perhaps for lower-mass systems. Solar-mass binary systems appear to have a flat mass ratio distribution, but for primary masses <0.3 Msun, the distribution becomes increasingly biased toward similar-mass companions. My results also constrain the binary formation timescale and the postformation evolutionary processes that sculpt binary populations. The dynamical interaction timescale in sparse associations like Taurus and Upper Sco is far longer than their ages, which suggests that those populations are dynamically pristine. However, binary systems in denser clusters undergo significant dynamical processing that strips outer binary companions; the difference in wide binary properties between my sample and the field is explained by the composite origin of the field population. I also have placed the individual components of young binary systems on the HR diagram in order to infer their coevality. In Taurus, binary systems are significantly more coeval (Δτ~0.5 Myr) than the association as a whole (Δτ~3--5 Myr). Finally, my survey of young very-low-mass stars and brown dwarfs found no planetary

  6. H-cluster stars

    NASA Astrophysics Data System (ADS)

    Lai, X. Y.; Gao, C. Y.; Xu, R. X.

    2013-06-01

    The study of dense matter at ultrahigh density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. It is well known that the state of cold matter at supranuclear density depends on the non-perturbative nature of quantum chromodynamics (QCD) and is essential for modelling pulsars. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other there. That might render quarks grouped in clusters, although the hypothetical quark clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we therefore consider here a possible kind of quark clusters, H-clusters, that could emerge inside compact stars during their initial cooling as the dominant components inside (the degree of freedom could then be H-clusters there). Taking into account the in-medium stiffening effect, we find that at baryon densities of compact stars H-cluster matter could be more stable than nuclear matter. We also find that for the H-cluster matter with lattice structure, the equation of state could be so stiff that it would seem to be `superluminal' in the most dense region. However, the real sound speed for H-cluster matter is in fact difficult to calculate, so at this stage we do not put constraints on our model from the usual requirement of causality. We study the stars composed of H-clusters, i.e. H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M⊙ as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general

  7. Halo Star Lithium Depletion

    SciTech Connect

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-12-10

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  8. White Dwarf Stars

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.

    2014-10-01

    White dwarfs are the evolutionary endpoint for nearly 95% of all stars born in our Galaxy, the final stages of evolution of all low- and intermediate mass stars, i.e., main sequence stars with masses below (8.5± 1.5) M_{odot}, depending on metallicity of the progenitor, mass loss and core overshoot. Massive white dwarfs are intrinsically rare objects, tand produce a gap in the determination of the initial vs. final mass relation at the high mass end (e.g. Weidemann 2000 A&A, 363, 647; Kalirai et al. 2008, ApJ, 676, 594; Williams, Bolte & Koester 2009, ApJ, 693, 355). Main sequences stars with higher masses will explode as SNII (Smartt S. 2009 ARA&A, 47, 63), but the limit does depend on the metallicity of the progenitor. Massive white dwarfs are probably SNIa progenitors through accretion or merger. They are rare, being the final product of massive stars (less common) and have smaller radius (less luminous). Kepler et al. 2007 (MNRAS, 375, 1315), Kleinman et al. 2013 (ApJS, 204, 5) estimate only 1-2% white dwarfs have masses above 1 M_{odot}. The final stages of evolution after helium burning are a race between core growth and loss of the H-rich envelope in a stellar wind. When the burning shell is exposed, the star rapidly cools and burning ceases, leaving a white dwarf. As they cool down, the magnetic field freezes in, ranging from a few kilogauss to a gigagauss. Peculiar type Ia SN 2006gz, SN 2007if, SN 2009dc, SN 2003fg suggest progenitors in the range 2.4-2.8 M_{odot}, and Das U. & Mukhopadhyay B. (2012, Phys. Rev. D, 86, 042001) estimate that the Chandrasekhar limit increases to 2.3-2.6 M_{odot} for extremely high magnetic field stars, but differential rotation induced by accretion could also increase it, according to Hachisu I. et al. 2012 (ApJ, 744, 69). García-Berro et al. 2012, ApJ, 749, 25, for example, proposes double degenerate mergers are the progenitors of high-field magnetic white dwarfs. We propose magnetic fields enhance the line broadening in

  9. Weighing the Smallest Stars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    VLT Finds Young, Very Low Mass Objects Are Twice As Heavy As Predicted Summary Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be. This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. PR Photo 03/05: Near-infrared image of AB Doradus A and its companion (NACO SDI/VLT) A winning combination A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter. This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or "failed stars", are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior. To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called "Kepler's Third Law"). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time - one year - it takes our planet to make a tour around the Sun. The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed

  10. Synthesis and Thermodynamic Stability of Ba2B‧B″O6 and Ba3B*B″2O9 Perovskites Using the Molten Salt Method

    NASA Astrophysics Data System (ADS)

    Meng, Wei; Virkar, Anil V.

    1999-12-01

    A number of mixed perovskites of the types Ba2B‧B″O6 (BaB‧1/2B″1/2O3) and Ba3B*B″2O9 (BaB*1/3B″2/3O3) where B‧=Gd, La, Nd, Sm, or Y; B″=Nb and B*=Ca were synthesized by a conventional calcination process, as well as by the molten salt method. The former consists of calcining appropriate mixtures of oxide or carbonate precursors in air at elevated temperatures (∼1250°C). The latter method consists of adding appropriate mixtures of oxide or carbonate precursors to a molten salt bath at relatively low temperatures (on the order of 300 to 500°C) so that the requisite compound is formed by dissolution-reprecipitation. X-ray diffraction confirmed the formation of a single-phase perovskite in each case with calcination at 1250°C. In a molten salt bath, however, all except Ba2LaNbO6 and Ba2NdNbO6 formed the perovskite structure. On the contrary, powders of Ba2LaNbO6 and Ba2NdNbO6 formed by a high-temperature calcination process readily decomposed when introduced into the molten salt bath. The formation of the requisite perovskite at a temperature as low as 350°C in a molten salt suggests that: (a) The perovskite is stable at 350°C. (b) The molten salt exhibits sufficient precursor solubility for the dissolution-reprecipitation process to occur in a reasonable time. Similarly, the decomposition of Ba2LaNbO6 and Ba2NdNbO6 in a molten salt bath shows that these materials are thermodynamically unstable at the temperature of the molten salt bath.

  11. The mechanisms of complement activation in normal bovine serum and normal horse serum against Yersinia enterocolitica O:9 strains with different outer membrane proteins content.

    PubMed

    Miętka, K; Brzostek, K; Guz-Regner, K; Bugla-Płoskońska, G

    2016-01-01

    Yersinia enterocolitica is a common zoonotic pathogen and facultative intracellular bacterium which can survive within blood cells. Cattle and horses are considered a reservoir of Y. enterocolitica which often causes several serious syndromes associated with yersiniosis such as abortions, premature births or infertility. The aim of our investigation was to determine the vitality of Y. enterocolitica O:9 strains (Ye9) in bovine and horse sera (NBS and NHrS) and explain the role of outer membrane proteins (OMPs) in serum resistance of these bacteria. Our previous studies demonstrated moderate human serum (NHS) resistance of the wild type Ye9 strain, whereas mutants lacking YadA, Ail or OmpC remained sensitive to the bactericidal activity of NHS. The present study showed that the wild type of Ye9 strain was resistant to the bactericidal activity of both NHrS and NBS, while Ye9 mutants lacking the YadA, Ail and OmpC proteins were sensitive to NHrS and NBS as well as to NHS. The mechanisms of complement activation against Ye9 strains lacking Ail and YadA were distinguished, i.e. activation of the classical/lectin pathways decisive in the bactericidal mechanism of complement activation of NBS, parallel activation of the classical/lectin and alternative pathways of NHrS. In this research the mechanism of independent activation of the classical/lectin or the alternative pathway of NBS and NHrS against Ye9 lacking OmpC porin was also established. The results indicate that serum resistance of Ye9 is multifactorial, in which extracellular structures, i.e. outer membrane proteins (OMPs) such as Ail, OmpC or YadA, play the main role. PMID:27096793

  12. A Vanishing Star Revisited

    NASA Astrophysics Data System (ADS)

    1999-07-01

    VLT Observations of an Unusual Stellar System Reinhold Häfner of the Munich University Observatory (Germany) is a happy astronomer. In 1988, when he was working at a telescope at the ESO La Silla observatory, he came across a strange star that suddenly vanished off the computer screen. He had to wait for more than a decade to get the full explanation of this unusual event. On June 10-11, 1999, he observed the same star with the first VLT 8.2-m Unit Telescope (ANTU) and the FORS1 astronomical instrument at Paranal [1]. With the vast power of this new research facility, he was now able to determine the physical properties of a very strange stellar system in which two planet-size stars orbit each other. One is an exceedingly hot white dwarf star , weighing half as much as the Sun, but only twice as big as the Earth. The other is a much cooler and less massive red dwarf star , one-and-a-half times the size of planet Jupiter. Once every three hours, the hot star disappears behind the other, as seen from the Earth. For a few minutes, the brightness of the system drops by a factor of more than 250 and it "vanishes" from view in telescopes smaller than the VLT. A variable star named NN Serpentis ESO PR Photo 30a/99 ESO PR Photo 30a/99 [Preview - JPEG: 400 x 468 pix - 152k] [Normal - JPEG: 800 x 936 pix - 576k] [High-Res - JPEG: 2304 x 2695 pix - 4.4M] Caption to ESO PR Photo 30a/99 : The sky field around the 17-mag variable stellar system NN Serpentis , as seen in a 5 sec exposure through a V(isual) filter with VLT ANTU and FORS1. It was obtained just before the observation of an eclipse of this unsual object and served to centre the telescope on the corresponding sky position. The field shown here measures 4.5 x 4.5 armin 2 (1365 x 1365 pix 2 ; 0.20 arcsec/pix). The field is somewhat larger than that shown in Photo 30b/99 and has the same orientation to allow comparison: North is about 20° anticlockwise from the top and East is 90° clockwise from that direction. The

  13. Theoretical Modelling of Hot Stars

    NASA Astrophysics Data System (ADS)

    Najarro, F.; Hillier, D. J.; Figer, D. F.; Geballe, T. R.

    1999-06-01

    Recent progress towards model atmospheres for hot stars is discussed. A new generation of NLTE wind blanketed models, together with high S/N spectra of the hot star population in the central parsec, which are currently being obtained, will allow metal abundance determinations (Fe, Si, Mg, Na, etc). Metallicity studies of hot stars in the IR will provide major constraints not only on the theory of evolution of massive stars but also on our efforts to solve the puzzle of the central parsecs of the Galaxy. Preliminary results suggest that the metallicity of the Pistol Star is 3 times solar, thus indicating strong chemical enrichment of the gas in the Galactic Center.

  14. IUE observations of central stars

    NASA Technical Reports Server (NTRS)

    Heap, S. R.

    1983-01-01

    IUE satellite data on sixty galactic planetary nebulae (PN) and three PNs in the Magellanic clouds are examined to establish a mass distribution among the central star types. An evolutionary lineage was determined for the observed central stars, based on UV magnitudes, demonstrating that central stars in optically thin nebulae have a narrow distribution around 0.58 solar mass, whereas stars in optically thick nebulae exhibited the highest masses of the sample, implying that highest mass stars in PN are the most difficult to detect. No definitive correlation was found between the mass of an object and its spectral type.

  15. Disk Dispersal Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    We first review the evidence pertaining to the lifetimes of planet-forming disks of gas and dust around young stars and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation caused by the heating of the disk surface by ultraviolet radiation. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks, and this talk focuses on the evaporation caused by the presence of a nearby, luminous star rather than the central star itself. We also focus on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We find a possible explanation for the differences between Neptune and Jupiter, and make a prediction concerning recent searches for giant planets in large clusters. We discuss recent models of the infrared spectra from gaseous disks around young stars.

  16. Young Stars in IC 2118

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Sepulveda, Babs; Maranto, Tony; Weehler, Cynthia; Roelofsen, Theresa; Rebull, Luisa

    2006-02-01

    IC 2118, the Witch Head Nebula (~210 parsecs), is a region of star formation located near the supergiant star Rigel in the constellation Orion. Last year, we observed the head of the nebula and approximately QUADRUPLED the number of young stars known here. We propose using IRAC and MIPS to continue our investigation by observing the densest part of the rest of the cloud. Our team proposes to use IRAC and MIPS observations to (1) investigate star formation, (2) look for likely cluster member stars with infrared excesses, and characterize this young star population by obtaining their colors and therefore estimates of masses and ages, (3) study the distribution of stars, their relationship to the ISM, and the possibilities of triggered star formation, (4) compare the young star population, distribution, and age to other similar sites of star formation, e.g., IC 1396 and (5) produce a dramatic image of the interstellar medium in the region surrounding IC 2118. Since this region is in the Orion constellation near the bright star Rigel, it provides additional appeal to students and the general public.

  17. VizieR Online Data Catalog: Spectroscopy of standard stars (Joner+, 2015)

    NASA Astrophysics Data System (ADS)

    Joner, M. D.; Hintz, E. G.

    2016-06-01

    Between 2005 and 2015, spectroscopic data were obtained using the 1.2-m McKellar Telescope of the Dominion Astrophysical Observatory (DAO). In total, data were secured on 153 nights using the telescope in robotic mode. Observations were made using the Coude spectrograph with the 3231 grating, which provided 40.9Å/mm. Using the Site4 CCD with 15μm pixels gives 0.614Å/pixel. With 4096 pixels along the dispersion axis, this provided a total coverage of approximately 2500Å. Aligning the grating to give a central wavelength of 5710Å allowed a spectral coverage from 4450 to 6970Å, which provided coverage of both Hα and Hβ. In total we examined 75 field stars (table2), 12 stars from the Coma star cluster (table3), 24 from the Hyades (table4), 17 from the Pleiades (table5), and 8 from NGC 752 (table6). These stars cover a spectral type range from O9 to K2. (5 data files).

  18. Massive stars: Starbursts

    NASA Astrophysics Data System (ADS)

    González Delgado, Rosa María

    2007-07-01

    Starbursts are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. Starbursts are bright at ultraviolet (UV) wavelengths, and after the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues: a) The determination of the initial mass function (IMF) in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments: A Salpeter IMF with high-mass stars constrains well the UV properties. b) Stellar clusters are an important mode of star formation in starbursts. c) The role of starbursts in AGN: Nuclear starbursts can dominate the UV light in Seyfert 2 galaxies, having bolometric luminosities similar to the estimated bolometric luminosities of the obscured AGN. d) The interaction between massive stars and the interstellar medium: Outflows in cold, warm and coronal phases leave their imprints on the UV interstellar lines. Outflows of a few hundred km s%u22121 are ubiquitous phenomena in starbursts. Despite the very significant progress obtained over the past two decades of UV observations of starbursts, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. High-spatial resolution spectra are also needed to isolate the light from the center to the disk in UV luminous galaxies found by GALEX. Thus, a new UV mission furnished with an intermediate spectral resolution spectrograph with high spatial

  19. Dead Star Rumbles

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Composite of Supernova Remnant Cassiopeia A This Spitzer Space Telescope composite shows the supernova remnant Cassiopeia A (white ball) and surrounding clouds of dust (gray, orange and blue). It consists of two processed images taken one year apart. Dust features that have not changed over time appear gray, while those that have changed are colored blue or orange. Blue represents an earlier time and orange, a later time.

    These observations illustrate that a blast of light from Cassiopeia A is waltzing outward through the dusty skies. This dance, called an 'infrared echo,' began when the remnant erupted about 50 years ago.

    Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion 325 years ago. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. This remnant is located 10,000 light-years away in the northern constellation Cassiopeia.

    An infrared echo is created when a star explodes or erupts, flashing light into surrounding clumps of dust. As the light zips through the dust clumps, it heats them up, causing them to glow successively in infrared, like a chain of Christmas bulbs lighting up one by one. The result is an optical illusion, in which the dust appears to be flying outward at the speed of light. This apparent motion can be seen here by the shift in colored dust clumps.

    Echoes are distinct from supernova shockwaves, which are made up material that is swept up and hurled outward by exploding stars.

    This infrared echo is the largest ever seen, stretching more than 50 light-years away from Cassiopeia A. If viewed from Earth, the entire movie frame would take up the same amount of space as two full moons.

    Hints of an older infrared echo from Cassiopeia A's supernova explosion hundreds of years ago can also be seen.

    The earlier Spitzer image was taken on November 30

  20. JetStar

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The Dryden C-140 JetStar during testing of advanced propfan designs. Dryden conducted flight research in 1981-1982 on several designs. The technology was developed under the direction of the Lewis Research Center (today the Glenn Research Center, Cleveland, OH) under the Advanced Turboprop Program. Under that program, Langley Research Center in Virginia oversaw work on accoustics and noise reduction. These efforts were intended to develop a high-speed and fuel-efficient turboprop system. NASA's Dryden Flight Research Facility (later the Dryden Flight Research Center, Edwards, CA), in co-operation with the Lewis Research Center, investigated the acoustic characteristics of a series of subscale advanced design propellors in the early eighties. These propellors were designed to rotate at a tip speed faster than the speed of sound. They are, in effect, a 'swept back wing' version of a propellor. The tests were conducted on Dryden's C-140 Jetstar, seen here on a research flight over the Mojave desert. The JetStar was modified with the installation of an air turbine drive system. The drive motor, with a 24 inch test propellor, was mounted in a pylon atop the JetStar. The JetStar was equipped with an array of 28 microphones flush-mounted in the fuselage of the aircraft beneath the propellor. Microphones mounted on the wings and on accompanying chase aircraft provided far-field acoustic data. In the 1960s, the same JetStar was equipped with an electronic variable stability flight control system. Called the General Purpose Airborne Simulator (GPAS), the aircraft could duplicate the flight characteristics of a wide variety of advanced aircraft and was used for supersonic transport and general aviation research and as a training and support system for Space Shuttle Approach and Landing Tests at Dryden in 1977. In 1985, the JetStar's wings were modified with suction and spray devices in a laminar (smooth) air flow program to study ways of improving the flow of air over the

  1. Gaining Insight into Star Formation: Resolved Star Formation Laws

    NASA Astrophysics Data System (ADS)

    Liebst, Kelley; Scowen, Paul A.

    2014-06-01

    Until recently astronomers have used star formation laws to measure the star formation rate and star formation efficiency of galaxies only on global scales because of the poor resolution of available data. What I am now capable of producing is a spatially resolved star formation law that can provide direct insight into the physical processes that govern star formation and assess the short-term nature of bursts of star formation and the longer-term nature of larger-scale events that can dictate the global distribution of stars and the ultimate fate of a galaxy as a whole. I am using exquisite narrowband optical data from a variety of sources, including the Hubble Space Telescope, and Kitt Peak National Observatory, etc., in conjunction with infrared data from the Spitzer Infrared Nearby Galaxy Survey and the Spitzer Local Volume Legacy survey, neutral gas data from The HI Nearby Galaxy Survey, and molecular gas data from the Berkeley-Illinois-Maryland Association Survey of Nearby Galaxies, to provide star formation rates and star formation efficiencies on previously inaccessible small spatial scales across a suite of galaxies that represent a range of star formation environments and scales. My sample includes 18 spiral galaxies ranging from 2.1 to 15.1 Mpc in distance and offers a large range of morphological types (i.e. a large range of star formation environments). I am using these data to test different models of star formation modes under a variety of physical conditions and relate the variations I observe to the known local physical conditions and the associated star formation histories for each locale within each galaxy.This is the heart of the matter - that the nature and evolution of the local physical environment intimately influences how stars can form, how quickly and how massive those stars are allowed to form, and as a result how they shape the local conditions for subsequent star formation. It is this tracking of the stellar ecology that is vital for

  2. Neutron Star Science with the NuSTAR

    SciTech Connect

    Vogel, J. K.

    2015-10-16

    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

  3. Flattest Star Ever Seen

    NASA Astrophysics Data System (ADS)

    2003-06-01

    VLT Interferometer Measurements of Achernar Challenge Stellar Theory Summary To a first approximation, planets and stars are round. Think of the Earth we live on. Think of the Sun, the nearest star, and how it looks in the sky. But if you think more about it, you realize that this is not completely true. Due to its daily rotation, the solid Earth is slightly flattened ("oblate") - its equatorial radius is some 21 km (0.3%) larger than the polar one. Stars are enormous gaseous spheres and some of them are known to rotate quite fast, much faster than the Earth. This would obviously cause such stars to become flattened. But how flat? Recent observations with the VLT Interferometer (VLTI) at the ESO Paranal Observatory have allowed a group of astronomers [1] to obtain by far the most detailed view of the general shape of a fast-spinning hot star, Achernar (Alpha Eridani) , the brightest in the southern constellation Eridanus (The River). They find that Achernar is much flatter than expected - its equatorial radius is more than 50% larger than the polar one! In other words, this star is shaped very much like the well-known spinning-top toy, so popular among young children. The high degree of flattening measured for Achernar - a first in observational astrophysics - now poses an unprecedented challenge for theoretical astrophysics . The effect cannot be reproduced by common models of stellar interiors unless certain phenomena are incorporated, e.g. meridional circulation on the surface ("north-south streams") and non-uniform rotation at different depths inside the star. As this example shows, interferometric techniques will ultimately provide very detailed information about the shapes, surface conditions and interior structure of stars . PR Photo 15a/03 : The VLT Interferometer configuration for the Achernar measurements PR Photo 15b/03 : Achernar's "profile" , as measured by the VLTI. PR Photo 15c/03 : Models of Achernar's spatial shape. VLTI observations of Achernar

  4. Jets from young stars

    NASA Astrophysics Data System (ADS)

    Bally, John

    2007-10-01

    Most stars produce spectacular jets during their formation. There are thousands of young stars within 500 pc of the Sun and many power jets. Thus protostellar jets may be the most common type of collimated astrophysical outflow. Shocks powered by outflows excite many emission lines, exhibit a rich variety of structure, and motions with velocities ranging from 50 to over 500 km s-1. Due to their relative proximity, proper motions and structural changes can be observed in less than a year. I review the general properties of protostellar jets, summarize some results from recent narrow-band imaging surveys of entire clouds, discuss irradiated jets, and end with some comments concerning outflows from high-mass young stellar objects. Protostellar outflows are ideal laboratories for the exploration of the jet physics.

  5. Star formation in Taurus

    NASA Technical Reports Server (NTRS)

    Beichman, C. A.; Jarrett, Tom

    1994-01-01

    Data with the Two Micron All Sky Survey (2MASS) prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from Infrared Astronomy Satellite (IRAS) observations to contain a number of very young solar type stars. Data at 1.25 (J), 1.65 (H), and 2.2 (K(sub s)) micrometers are presented. These data are representative of the type and quality of data expected from the planned near-IR surveys, 2MASS and Deep Near-Infrared Survey (DENIS). Near-IR surveys will be useful for determining the large scale variation of extinction with clouds, for determining the luminosity function in nearby clouds down to ranges of 0.1-1.0 solar luminosity, and for finding highly extincted T Tauri stars missed by IRAS because the bulk of their luminosity is emitted shortward of 12 micrometers.

  6. White Dwarf Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe.

    Located in the globular cluster M4, these small, burned-out stars -- called white dwarfs -- are about 12 to 13 billion years old. By adding the one billion years it took the cluster to form after the Big Bang, astronomers found that the age of the white dwarfs agrees with previous estimates that the universe is 13 to 14 billion years old.

    The images, including some taken by Hubble's Wide Field and Planetary Camera 2, are available online at

    http://oposite.stsci.edu/pubinfo/pr/2002/10/ or

    http://www.jpl.nasa.gov/images/wfpc .

    The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's .9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope.

    The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles indicate the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars.

    Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the

  7. Flare Activity on Stars

    NASA Astrophysics Data System (ADS)

    Oskanian, V. S.

    A review of the existing flare data analyses indicates that most probably the flare phenomenon should be considered as one of the manifestation forms of solar-type chromospheric activity on stars and therefore has to be investigated in common with other phenomena specifying this activity. In order to estimate the reliability of such an approach different types of observational data are discussed. It could be shown that most of the phenomena specifying the solar chromospheric activity (BY Dra syndrome, indicating the spottedness of the stellar surface, long-term cyclic variations of emission line intensities, variable local magnetic fields, flares, coronal phenomena, etc.) are observable on a constantly growing number of stars of almost all spectral types and luminosity classes. This fact indicates that the proposed approach could be the right way to solve the problem of the flare phenomenon.

  8. Hyperons in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Vidaña, Isaac

    2016-01-01

    In this work I briefly review some of the effects of hyperons on the properties of neutron and proto-neutron stars. In particular, I revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a puzzle which has become more intringuing and difficult to solve because of the recent measurements of the unusually high masses of the millisecond pulsars PSR J1903+0327 (1.667 ± 0.021M⊙), PSR J1614-2230 (1.97 ± 0.04M⊙), and PSR J0348+0432 (2.01 ± 0.04M⊙). Some of the solutions proposed to tackle this problem are discussed. Finally, I re-examine also the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

  9. Shooting Star Experiment

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Shooting Star Experiment (SSE) is designed to develop and demonstrate the technology required to focus the sun's energy and use the energy for inexpensive space Propulsion Research. Pictured is an engineering model (Pathfinder III) of the Shooting Star Experiment (SSE). This model was used to test and characterize the motion and deformation of the structure caused by thermal effects. In this photograph, alignment targets are being placed on the engineering model so that a theodolite (alignment telescope) could be used to accurately measure the deformation and deflections of the engineering model under extreme conditions, such as the coldness of deep space and the hotness of the sun as well as vacuum. This thermal vacuum test was performed at the X-Ray Calibration Facility because of the size of the test article and the capabilities of the facility to simulate in-orbit conditions

  10. Hyperons and neutron stars

    SciTech Connect

    Vidaña, Isaac

    2015-02-24

    In this lecture I will briefly review some of the effects of hyperons on the properties of neutron and proto-neutron stars. In particular, I will revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a puzzle which has become more intringuing and difficult to solve due the recent measurements of the unusually high masses of the millisecond pulsars PSR J1903+0327 (1.667±0.021M{sub ⊙}), PSR J1614–2230 (1.97±0.04M{sub ⊙}), and PSR J0348+0432 (2.01±0.04M{sub ⊙}). Finally, I will also examine the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

  11. Gravitoastronomy with neutron stars

    NASA Astrophysics Data System (ADS)

    Woan, Graham

    2004-09-01

    Recent advances in gravitational wave detectors mean that we can start to make astrophysically important statements about the physics of neutron stars based on observed upper limits to their gravitational luminosity. Here we consider statements we can already make about a selection of known radio pulsars, based on data from the LIGO and GEO600 detectors, and look forward to what could be learned from the first detections.

  12. The Physics of Stars

    NASA Astrophysics Data System (ADS)

    Arnett, W. David

    2009-05-01

    John von Neumann speculated that computers might become sufficiently powerful that they could be used to solve analytically intractable problems numerically (he gave turbulence as an example), and that those ``numerical experiments'' could be used to provide the insight necessary to develop analytic solutions. A case study will be presented in which we attempt in this way to use computer simulations of 3D turbulent flow in presupernova stars. We find that we can reproduce the simulations surprisingly well---on average---if we replace the viscous term with an effective damping which turns out to be similar to that inferred by Kolmogorov for a turbulent cascade. Stars are gravitationally-controlled thermonuclear reactors. Abundance change (and hence evolution) occurs because of nuclear burning, and mixing. It is now possible to treat this coupled problem in a self-consistent way, free of astronomically calibrated parameters. Implications for stellar evolution, nucleosynthesis yields, core collapse, supernova explosions, helio-seismology, and solar neutrinos will be discussed. It is argued that advances in the treatment of stellar fluid dynamics, along with new developments in laboratory astrophysics, now allow far more reliable predictions of how stars behave.

  13. Flares on Mira stars?

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.

    1991-01-01

    Fourteen cases of flares reported on Mira type stars have been collected. These flares typically have an amplitude of over half a magnitude, a rise time of minutes, and a duration of tens of minutes. Nine of the 11 stars represent a normal cross section of the Mira population, while the remaining two are in symbiotic systems (CH Cyg and RX Pup). The flares were observed photographically (five cases), photometrically (three cases), visually (three cases), and with radio telescopes (two cases), while CH Cyg has had flares observed by many techniques. The evidence for the existence of flares on Miras is strong but not definitive. It is possible to hypothesize a variety of background or instrumental effects that could explain all 14 events; however, there is no evidence that suggests the data should be taken at other than face value, and there are good arguments for rejecting the possibility of artifacts. It is felt that the current data warrant systematic observational and theoretical investigation of the possibility of flares on Mira stars.

  14. Photoevaporating Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    Ultraviolet radiation from the central star or from a nearby massive star heats the surfaces of protoplanetary disks and causes the outer, less gravitationally bound part of the disks, to photoevaporate into interstellar space. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks. We focus in this talk on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We discuss recent models of the effects of the radiation from the central low mass star including both the predicted infrared spectra from the heated disks as well as preliminary results on the photoevaporation rates.

  15. Runaway Stars in Supernova Remnants

    NASA Astrophysics Data System (ADS)

    Pannicke, Anna; Neuhaeuser, Ralph; Dinçel, Baha

    2016-07-01

    Half of all stars and in particular 70 % of the massive stars are a part of a multiple system. A possible development for the system after the core collapse supernova (SN) of the more massive component is as follows: The binary is disrupted by the SN. The formed neutron star is ejected by the SN kick whereas the companion star either remains within the system and is gravitationally bounded to the neutron star, or is ejected with a spatial velocity comparable to its former orbital velocity (up to 500 km/s). Such stars with a large peculiar space velocity are called runaway stars. We present our observational results of the supernova remnants (SNRs) G184.6-5.8, G74.0-8.5 and G119.5+10.2. The focus of this project lies on the detection of low mass runaway stars. We analyze the spectra of a number of candidates and discuss their possibility of being the former companions of the SN progenitor stars. The spectra were obtained with INT in Tenerife, Calar Alto Astronomical Observatory and the University Observatory Jena. Also we investigate the field stars in the neighborhood of the SNRs G74.0-8.5 and G119.5+10.2 and calculate more precise distances for these SNRs.

  16. Contamination: Tie SMOV Stars to Cycle 7 Star

    NASA Astrophysics Data System (ADS)

    Bohlin, Ralph

    1997-07-01

    Because of the lack of a perfect flat field correction and because of positioning differences on the CCD in SMOV, apparent changes in sensitivity appear in the response to the fundamental pure hydrogen WD standard stars G191B2B and GD153. Now that the pointing procedures and thermal conditions have stabilized, observation of these stars are needed to tie the SMOV calibration to the GO era and to the new cycle7 monitoring star AGK+81D266.

  17. RR Lyrae Stars, Metal-Poor Stars, and the Galaxy

    NASA Astrophysics Data System (ADS)

    McWilliam, Andrew

    2011-08-01

    This online book contains the proceedings of a meeting on "RR Lyrae Stars, Metal-Poor Stars, and the Galaxy" held at the Carnegie Observatories, Pasadena, California, in January 2011, to honor the 80th year of George W. Preston III. The book comprises the 5th volume of the Carnegie Observatories Astrophysics Series, and contains reviews and research articles on recent developments in the area of RR Lyrae stars, including results from the Kepler space mission. Review and research articles on metal-poor stars and Galactic structure are also included.

  18. Triggered star formation in the environment of young massive stars

    NASA Astrophysics Data System (ADS)

    Gritschneder, Matthias; Naab, T.; Heitsch, F.; Burkert, A.

    Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (VINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula (M16) or the Horsehead Nebula B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

  19. Spectropolarimetry of hot, luminous stars

    NASA Technical Reports Server (NTRS)

    Schulte-Ladbeck, Regina E.

    1994-01-01

    I review polarimetric observations of presumably single, hot luminous stars. The stellar types discussed are OB stars. B(e) supergiants, Luminous Blue Variables (LBV), Wolf-Rayet (W-R) stars, and type II supernovae (SN). It is shown that variable, intrinsic polarization is a common phenomenon in that part of the Hertzsprung-Russell (HR) diagram which these stars occupy. However, much observational work remains to be done before we can answer the most basic, statistical questions about the polarimetric properties of different groups of hot, luminous stars. Insight into the diagnostic power of polarization observations has been gained, but cannot be exploited without detailed models. Thus, while polarimetric observations do tell us that the mass-loss processes of all types of massive stars are time-dependent and anisotropic, the significance that this might have for the accuracy of their stellar parameters and evolutionary paths remains elusive.

  20. Chinese Constellations and Star Maps

    NASA Astrophysics Data System (ADS)

    Sun, Xiaochun

    Star observations can be traced back to as early as the twenty-third century BC in ancient China. By the fifth century BC, the Chinese had named the 28 asterisms that formed the basic reference points for the Chinese equatorial coordinate system. By the first century BC, the Chinese had developed a unique system of constellations that reflected Chinese cosmological ideas with the central theme of the correlation between Heaven and Man. Star charts have been discovered on tomb ceilings dating back to Han times. But most of them are illustrative in their presentation of stars. The Dunhuang star maps from the ninth century, the star maps in the Xin yixiang fa yao of the eleventh century, and the Suzhou Astronomical Planisphere of the thirteenth century are examples of precise star maps from ancient China.

  1. The physics of neutron stars.

    PubMed

    Lattimer, J M; Prakash, M

    2004-04-23

    Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics, and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near 10(10) kelvin, opaqueness to neutrinos, and magnetic fields in excess of 10(13) Gauss. Here, we describe the formation, structure, internal composition, and evolution of neutron stars. Observations that include studies of pulsars in binary systems, thermal emission from isolated neutron stars, glitches from pulsars, and quasi-periodic oscillations from accreting neutron stars provide information about neutron star masses, radii, temperatures, ages, and internal compositions. PMID:15105490

  2. The Birth of Stars and Planets

    NASA Astrophysics Data System (ADS)

    Bally, John; Reipurth, Bo

    2006-08-01

    Part I. Stars and Clusters: 1. Our Cosmic Backyard; 2. Looking up at the night sky; 3. The dark clouds of the Milky Way; 4. Infant stars; 5. Companions in birth: binary stars; 6. Outflows from young stars; 7. Towards adulthood; 8. The social life of stars: stellar groups; 9. Chaos in the nest: The brief lives of massive stars. Part II. Planetary Systems: 10. Solar systems in the making; 11. Messengers from the past; 12. Hazards to planet formation; 13. Planets around other stars; Part III. The Cosmic Context: 14. Cosmic cycles; 15. Star formation in galaxies; 16. The first stars and galaxies; 17. Astrobiology, origins, and SETI.

  3. Star names - Origins and misconceptions

    NASA Astrophysics Data System (ADS)

    Heuter, Gwyneth

    The sources of present day star names used in the western world are examined. Particular interest is shown in the meanings of the most popular names and those whose meanings have proved difficult to trace. A classification of star names is made and attention is drawn to the errors introduced in translation from one language to another. In particular an in-depth study of pre-Ptolemaic Arabic star names is given.

  4. Reinvestigating the Lambda Boo Stars

    NASA Astrophysics Data System (ADS)

    Cheng, Kwang-Ping; Corbally, C. J.; Gray, R. O.; Murphy, S.; Neff, J. E.; Desai, A.; Newsome, I.; Steele, P.

    2014-01-01

    The peculiar nature of Lambda Bootis was first introduced in 1943. Subsequently, Lambda Boo stars have been slowly recognized as a group of A-type Population I dwarfs that show mild to extreme deficiencies of iron-peak elements, although C, N, O, and S can be near solar. MK classification criteria include broad hydrogen lines, a weak metallic-line spectrum compared to MK standards, coupled with a particularly weak Mg II 4481 line. This intriguing stellar class has recently regained the spotlight because of the directly imaged planets around a confirmed Lambda Boo star-HR 8799 and a probable Lambda Boo star-Beta Pictoris. The possible link between Lambda Boo stars and planet-bearing stars motivates us to study Lambda Boo stars systematically. However, Lambda Boo candidates published in the literature have been selected using widely different criteria. The Lambda Boo class has become somewhat of a "grab bag" for any peculiar A-type stars that didn't fit elsewhere. In order to determine the origin of Lambda Boo stars’ low abundances and to better discriminate between theories explaining the Lambda Boo phenomenon, a refined working definition of Lambda Boo stars is needed. We have re-evaluated all published Lambda Boo candidates and their existing spectra. After applying a consistent set of optical/UV classification criteria, we identified over 60 confirmed and over 20 probable Lambda Boo stars among all stars that have been suggested as Lambda Boo candidates. We are obtaining new observations for those probable Lambda Boo stars. We also have explored the possible link between debris disks and Lambda Boo Stars.

  5. The Orion nebula star cluster

    NASA Technical Reports Server (NTRS)

    Panek, R. J.

    1982-01-01

    Photography through filters which suppress nebular light reveal a clustering of faint red stars centered on the Trapezium, this evidences a distinct cluster within the larger OB1 association. Stars within about 20 ft of trapezium comprise the Orion Nebula star cluster are considered. Topics discussed re: (1) extinction by dust grains; (2) photometric peculiarities; (3) spectroscopic peculiarities; (4) young variables; (5) the distribution and motion of gas within the cluster.

  6. The influence of microscopic parameters on the ionic conductivity of SrBi2(Nb1-xVx)2O9-δ(0≤x≤0.3) ceramics

    NASA Astrophysics Data System (ADS)

    Harihara Venkataraman, B.; Varma, K. B. R.

    2005-10-01

    Layered SrBi2(Nb1-xVx)2O9-δ (SBVN) ceramics with x lying in the range 0 0.3 (30 mol%) were fabricated by the conventional sintering technique. The microstructural studies confirmed the truncating effect of V2O5 on the abnormal platy growth of SBN grains. The electrical conductivity studies were centred in the 573 823 K as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D0) and the mean free path (a) were calculated by using Rice and Roth formalism. The conductivity parameters such as ion-hopping rate (ωp) and the charge carrier concentration (K‧) term have been calculated using Almond and West formalism. The aforementioned microscopic parameters were found to be V2O5 content dependent on SrBi2(Nb1-xVx)2O9-δ ceramics.

  7. Space Science in Action: Stars [Videotape].

    ERIC Educational Resources Information Center

    1999

    This videotape recording shows students the many ways scientists look at the stars and how they can use what they see to answer questions such as What are stars made of?, How far away are they?, and How old are the stars? Students learn about the life span of stars and the various stages they pass through from protostar to main sequence star to…

  8. Spectroscopic Binary Frequency among CNO Stars

    NASA Astrophysics Data System (ADS)

    Levato, H.; Malaroda, S.; Garcia, B.; Morell, N.

    1987-05-01

    ABSTRACT. Radial velocity variations are- analyzed through a sample of 35 OB stars with CH anomalies.Bolton and Rogers' proposal (1978) is con- firmed in the sense that the OBN stars appear preferably in short-period binary systems, in contrast to OBC stars. : STARS-BINARY - STARS-EARLY TYPE

  9. Population synthesis of massive stars

    NASA Astrophysics Data System (ADS)

    Vanbeveren, Dany

    2014-09-01

    This review deals with massive star population synthesis with a realistic population of binaries. We focus on the comparison between observed star numbers (as a function of metallicity) and theoretically predicted numbers of stellar populations in regions of continuous star formation and in starburst regions. Special attention is given to the O-type/WR/red supergiant stellar population, the population of blue supergiants, the pulsar and binary pulsar population, and the supernova rates. Finally, we consider massive double compact star mergers and the link with gravitational wave sources (the advanced LIGO II) and r-process element production sites.

  10. QPO Constraints on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Miller, M. Coleman

    2005-01-01

    The kilohertz frequencies of QPOs from accreting neutron star systems imply that they are generated in regions of strong gravity, close to the star. This suggests that observations of the QPOs can be used to constrain the properties of neutron stars themselves, and in particular to inform us about the properties of cold matter beyond nuclear densities. Here we discuss some relatively model-insensitive constraints that emerge from the kilohertz QPOs, as well as recent developments that may hint at phenomena related to unstable circular orbits outside neutron stars.

  11. Optical filtering for star trackers

    NASA Technical Reports Server (NTRS)

    Wilson, R. E.

    1973-01-01

    The optimization of optical filtering was investigated for tracking faint stars, down to the fifth magnitude. The effective wavelength and bandwidth for tracking pre-selected guide stars are discussed along with the results of an all-electronic tracker with a star tracking photomultiplier, which was tested with a simulated second magnitude star. Tables which give the sum of zodiacal light and galactic background light over the entire sky for intervals of five degrees in declination, and twenty minutes in right ascension are included.

  12. Thermal instability in DAV stars

    NASA Astrophysics Data System (ADS)

    Labrador, J.; Falcon, N.

    2008-01-01

    The short period of the fluctuations of stars DAV, in the order of the hun dreds of seconds; the modes of luminosity oscillation's to constant radio, and the non existence of fusion processes in such stars invite elaboration of models in the formalism of Mixing Length Theory of Convection(MLT). In the present work a mechanism of luminosity variation in DAV stars based on thermodynamic processes of non balance with homogenous convection. The results of the model allow satisfactorily reproducing the light curves of DAV classic stars: G29- 38, GD 358, HL Tau- 76 and WD1647+1591.

  13. The Uhuru star aspect sensor.

    NASA Technical Reports Server (NTRS)

    Jagoda, N.; Austin, G.; Mickiewicz, S.; Goddard, R.

    1972-01-01

    Description of the star sensor used in the spin-stabilized Uhuru satellite for the purpose of detecting and locating stellar X-ray sources. The star sensor had the capability of detecting fourth-magnitude stars to within 1 arc minute of azimuth and 2 arc minutes of elevation. This was achieved with the aid of a slightly modified 76-mm, f/0.87 Super Farron lens, an 'n' shaped reticle located in the focal plane, and an RCA CF70114F photomultiplier serving as the detection element. The star sensor is composed of three major components - a high-voltage power supply, the photomultiplier, and an amplifier.

  14. Apple Valley Double Star Workshop

    NASA Astrophysics Data System (ADS)

    Brewer, Mark

    2015-05-01

    The High Desert Astronomical Society hosts an annual double star workshop, where participants measure the position angles and separations of double stars. Following the New Generation Science Standards (NGSS), adopted by the California State Board of Education, participants are assigned to teams where they learn the process of telescope set-up and operation, the gathering of data, and the reduction of the data. Team results are compared to the latest epoch listed in the Washington Double Star Catalog (WDS) and papers are written for publication in the Journal of Double Star Observations (JDSO). Each team presents a PowerPoint presentation to their peers about actual hands-on astronomical research.

  15. Stars with Extended Atmospheres

    NASA Astrophysics Data System (ADS)

    Sterken, C.

    2002-12-01

    This Workshop consisted of a full-day meeting of the Working Group "Sterren met Uitgebreide Atmosferen" (SUA, Working Group Stars with Extended Atmospheres), a discussion group founded in 1979 by Kees de Jager, Karel van der Hucht and Pik Sin The. This loose association of astronomers and astronomy students working in the Dutch-speaking part of the Low Countries (The Netherlands and Flanders) organised at regular intervals one-day meetings at the Universities of Utrecht, Leiden, Amsterdam and Brussels. These meetings consisted of the presentation of scientific results by junior as well as senior members of the group, and by discussions between the participants. As such, the SUA meetings became a forum for the exchange of ideas, and for asking questions and advice in an informal atmosphere. Kees de Jager has been chairman of the WG SUA from the beginning in 1979 till today, as the leading source of inspiration. At the occasion of Prof. Kees de Jager's 80th birthday, we decided to collect the presented talks in written form as a Festschrift in honour of this well-respected and much beloved scientist, teacher and friend. The first three papers deal with the personality of Kees de Jager, more specifically with his role as a supervisor and mentor of young researchers and as a catalyst in the research work of his colleagues. And also about his remarkable role in the establishment of astronomy education and research at the University of Brussels. The next presentation is a very detailed review of solar research, a field in which Cees was prominently active for many years. Then follow several papers dealing with stars about which Kees is a true expert: massive stars and extended atmospheres.

  16. The Double Star mission

    NASA Astrophysics Data System (ADS)

    Liu, Z. X.; Escoubet, C. P.; Pu, Z.; Laakso, H.; Shi, J. K.; Shen, C.; Hapgood, M.

    2005-11-01

    The Double Star Programme (DSP) was first proposed by China in March, 1997 at the Fragrant Hill Workshop on Space Science, Beijing, organized by the Chinese Academy of Science. It is the first mission in collaboration between China and ESA. The mission is made of two spacecraft to investigate the magnetospheric global processes and their response to the interplanetary disturbances in conjunction with the Cluster mission. The first spacecraft, TC-1 (Tan Ce means "Explorer"), was launched on 29 December 2003, and the second one, TC-2, on 25 July 2004 on board two Chinese Long March 2C rockets. TC-1 was injected in an equatorial orbit of 570x79000 km altitude with a 28° inclination and TC-2 in a polar orbit of 560x38000 km altitude. The orbits have been designed to complement the Cluster mission by maximizing the time when both Cluster and Double Star are in the same scientific regions. The two missions allow simultaneous observations of the Earth magnetosphere from six points in space. To facilitate the comparison of data, half of the Double Star payload is made of spare or duplicates of the Cluster instruments; the other half is made of Chinese instruments. The science operations are coordinated by the Chinese DSP Scientific Operations Centre (DSOC) in Beijing and the European Payload Operations Service (EPOS) at RAL, UK. The spacecraft and ground segment operations are performed by the DSP Operations and Management Centre (DOMC) and DSOC in China, using three ground station, in Beijing, Shanghai and Villafranca.

  17. Gravitational Condensate Stars

    NASA Astrophysics Data System (ADS)

    Mazur, P.; Mottola, E.

    The issue of the final state of the gravitational collapse will be addressed. Ishall present physical arguments to the effect that the remnant of the gravitationalcollapse of super-massive stars is a cold and dark super-dense object which isthermodynamically and dynamically stable: a Gravitational Condensate Star orQuasi Black Hole (QBH). A QBH is characterized by a huge, but not an infinite,surface redshift. This surface redshift depends universally on the total mass of aQBH and the proper thickness of a thin shell of an exotic matter described bythe Zel'dovich equation of state p = c2 . The velocity of sound in a thin shell isequal to the velocity of light. Hence, this thin shell replaces the event horizon of amathematical black hole ( = 0). Inside a thin shell the zero entropy gravitationalcondensate characterized by the cosmological equation of state p = -c2 resides.A QBH is described by a new static and spherically symmetric solution of Ein-stein's equations supplemented with the proper boundary conditions based on mi-crophysics considerations. The new solution has no singularities and no eventhorizons. Its entropy is maximized under small fluctuations and is given by thestandard hydrodynamic entropy of the thin shell which is proportional to the to-tal mass instead of the Bekenstein-Hawking entropy which is proportional to thesquare of the total mass. This resolves the paradox of an excessively high en-tropy of black holes as compared to their progenitors. The formation of such acold gravitational condensate stellar remnant very likely would require a violentcollapse process with an explosive output of energy. Some observational conse-quences of the formation of gravitational condensate stars will be described.

  18. Rotation of Giant Stars

    NASA Astrophysics Data System (ADS)

    Kissin, Yevgeni; Thompson, Christopher

    2015-07-01

    The internal rotation of post-main sequence stars is investigated, in response to the convective pumping of angular momentum toward the stellar core, combined with a tight magnetic coupling between core and envelope. The spin evolution is calculated using model stars of initial mass 1, 1.5, and 5 {M}⊙ , taking into account mass loss on the giant branches. We also include the deposition of orbital angular momentum from a sub-stellar companion, as influenced by tidal drag along with the excitation of orbital eccentricity by a fluctuating gravitational quadrupole moment. A range of angular velocity profiles {{Ω }}(r) is considered in the envelope, extending from solid rotation to constant specific angular momentum. We focus on the backreaction of the Coriolis force, and the threshold for dynamo action in the inner envelope. Quantitative agreement with measurements of core rotation in subgiants and post-He core flash stars by Kepler is obtained with a two-layer angular velocity profile: uniform specific angular momentum where the Coriolis parameter {Co}\\equiv {{Ω }}{τ }{con}≲ 1 (here {τ }{con} is the convective time), and {{Ω }}(r)\\propto {r}-1 where {Co}≳ 1. The inner profile is interpreted in terms of a balance between the Coriolis force and angular pressure gradients driven by radially extended convective plumes. Inward angular momentum pumping reduces the surface rotation of subgiants, and the need for a rejuvenated magnetic wind torque. The co-evolution of internal magnetic fields and rotation is considered in Kissin & Thompson, along with the breaking of the rotational coupling between core and envelope due to heavy mass loss.

  19. Intense violet-blue-emitting Ba(2)AlB(4)O(9)Cl:Eu(2+) phosphors for applications in fluorescent lamps and ultraviolet-light-emitting diodes.

    PubMed

    Kuo, Te-Wen; Huang, Chien-Hao; Chen, Teng-Ming

    2010-08-01

    We synthesized a violet-blue phosphor Ba(2)AlB(4)O(9)Cl:Eu(2+) with a solid-state reaction. The excitation and emission spectra of this phosphor showed that all were broadband due to 4f(7)-4f(6)d(1) transitions of Eu(2+). The phosphors with different Eu(2+) concentrations presented violet-blue luminescence for ultraviolet [(UV) 250-390nm] excitation. The optimum concentration of Eu(2+) in Ba(2)AlB(4)O(9)Cl:Eu(2+) is determined to be 6mol.%. The luminous efficiency was found to be 8.1lm/W for the violet-blue fluorescent lamp and 3.2lm/W for the violet-blue phosphor-converted light-emitting diode, respectively. Ba(2)AlB(4)O(9)Cl:Eu(2+) would be a promising phosphor for converting the UV radiation to violet-blue emission for a novel high light-conversion efficiency phototherapy illuminator. PMID:20676174

  20. Solid-State Synthesis and Structure of the Enigmatic Ammonium Octaborate: (NH4)2[B7O9(OH)5]·3/4B(OH)3·5/4H2O.

    PubMed

    Neiner, Doinita; Sevryugina, Yulia V; Schubert, David M

    2016-09-01

    The compound known since the 19th century as ammonium octaborate was structurally characterized revealing the ammonium salt of the ribbon isomer of the heptaborate anion, [B7O9(OH)5](2-), with boric acid and water molecules. Of composition (NH4)2B7.75O12.63·4.88H2O, it approximates the classical ammonium octaborate composition (NH4)2B8O13·6H2O and has the structural formula {(NH4)2[B7O9(OH)5]}4·3B(OH)3·5H2O. It spontaneously forms at room temperature in solid-state mixtures of ammonium tetraborate and ammonium pentaborate. It crystallizes in the monoclinic space group P21/c with a = 11.4137(2) Å, b = 11.8877(2) Å, c = 23.4459(3) Å, β = 90.092(1)°, V = 3181.19(8) Å(3), and Z = 2 and contains well-ordered ammonium cations and [B7O9(OH)5](2-) anions and disordered B(OH)3 and H2O molecules linked by extensive H bonding. Expeditious solid-state formation of the heptaborate anion under ambient conditions has important implications for development of practical syntheses of industrially useful borates. PMID:27513178

  1. Star Atlases and Software

    NASA Astrophysics Data System (ADS)

    Brazell, Owen; Argyle, R. W.

    In the 7 years or so that have passed since the first edition of this book was published perhaps one of the areas that has changed the most has been in the area of charts and software. The realm of the paper chart has pretty much been taken over by software in all its guises. It would perhaps not have been possible to have foreseen 10 years ago that one could look up double stars and their information on your phone as you can do on many of today's smart phones. The popularity of tablets and netbooks also means that much more information is now available in the field that it was before.

  2. O3 stars

    SciTech Connect

    Walborn, N.R.

    1982-03-01

    A brief review of the 10 known objects in this earliest spectral class is presented. Two new members are included: HD 64568 in NGC 2467 (Puppis OB2), which provides the first example of an O3 V((f*)) spectrum; and Sk -67/sup 0/22 in the Large Magellanic Cloud, which is intermediate between types O3 If* and WN6-A. In addition, the spectrum of HDE 269810 in the LMC is reclassified as the first of type O3 III (f*). The absolute visual magnitudes of these stars are rediscussed.

  3. OGLE and pulsating stars

    NASA Astrophysics Data System (ADS)

    Udalski, A.

    2016-05-01

    OGLE-IV is currently one of the largest sky variability surveys worldwide, focused on the densest stellar regions of the sky. The survey covers over 3000 square degrees and monitors regularly over a billion sources. The main targets include the inner Galactic bulge and the Magellanic System. Supplementary shallower Galaxy Variability Survey covers the extended Galactic bulge and 2/3 of the whole Galactic disk. The current status, prospects, and the latest results of the OGLE-IV survey focused on pulsating stars, in particular RR Lyrae variables, are presented.

  4. TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

    SciTech Connect

    Liu Tie; Wu Yuefang; Zhang Huawei; Qin Shengli

    2012-05-20

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10{sup 3} cm{sup -3} and kinematic temperature {approx}20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

  5. Star-forming galaxy models: Blending star formation into TREESPH

    NASA Technical Reports Server (NTRS)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  6. Mendigite, Mn2Mn2MnCa(Si3O9)2, a new mineral species of the bustamite group from the Eifel volcanic region, Germany

    NASA Astrophysics Data System (ADS)

    Chukanov, N. V.; Aksenov, S. M.; Rastsvetaeva, R. K.; Van, K. V.; Belakovskiy, D. I.; Pekov, I. V.; Gurzhiy, V. V.; Schüller, W.; Ternes, B.

    2015-12-01

    A new mineral, mendigite (IMA no. 2014-007), isostructural with bustamite, has been found in the In den Dellen pumice quarry near Mendig, Laacher Lake area, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. Associated minerals are sanidine, nosean, rhodonite, tephroite, magnetite, and a pyrochlore-group mineral. Mendigite occurs as clusters of long-prismatic crystals (up to 0.1 × 0.2 × 2.5 mm in size) in cavities within sanidinite. The color is dark brown with a brown streak. Perfect cleavage is parallel to (001). D calc = 3.56 g/cm3. The IR spectrum shows the absence of H2O and OH groups. Mendigite is biaxial (-), α = 1.722 (calc), β = 1.782(5), γ = 1.796(5), 2 V meas = 50(10)°. The chemical composition (electron microprobe, mean of 4 point analyses, the Mn2+/Mn3+ ratio determined from structural data and charge-balance constraints) is as follows (wt %): 0.36 MgO, 10.78 CaO, 37.47 MnO, 2.91 Mn2O3, 4.42 Fe2O3, 1.08 Al2O3, 43.80 SiO2, total 100.82. The empirical formula is Mn2.00(Mn1.33Ca0.67) (Mn0.50 2+ Mn0.28 3+ Fe0.15 3+ Mg0.07)(Ca0.80 (Mn0.20 2+)(Si5.57 Fe0.27 3+ Al0.16O18). The idealized formula is Mn2Mn2MnCa(Si3O9)2. The crystal structure has been refined for a single crystal. Mendigite is triclinic, space group Pbar 1; the unit-cell parameters are a = 7.0993(4), b = 7.6370(5), c = 7.7037(4) Å, α = 79.58(1)°, β = 62.62(1)°, γ = 76.47(1)°; V = 359.29(4) Å3, Z = 1. The strongest reflections on the X-ray powder diffraction pattern [ d, Å ( I, %) ( hkl)] are: 3.72 (32) (020), 3.40 (20) (002, 021), 3.199 (25) (012), 3.000 (26), (01bar 2, 1bar 20), 2.885 (100) (221, 2bar 11, 1bar 21), 2.691 (21) (222, 2bar 10), 2.397 (21) (02bar 2, 21bar 1, 203, 031), 1.774 (37) (412, 3bar 21). The type specimen is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4420/1.

  7. Stars For Citizens With Urban Star Parks and Lighting Specialists

    NASA Astrophysics Data System (ADS)

    Grigore, Valentin

    2015-08-01

    General contextOne hundred years ago, almost nobody imagine a life without stars every night even in the urban areas. Now, to see a starry sky is a special event for urban citizens.It is possible to see the stars even inside cities? Yes, but for that we need star parks and lighting specialists as partners.Educational aspectThe citizens must be able to identify the planets, constellations and other celestial objects in their urban residence. This is part of a basic education. The number of the people living in the urban area who never see the main constellations or important stars increase every year. We must do something for our urban community.What is an urban star park?An urban public park where we can see the main constellations can be considered an urban star park. There can be organized a lot of activities as practical lessons of astronomy, star parties, etc.Classification of the urban star parksA proposal for classification of the urban star parks taking in consideration the quality of the sky and the number of the city inhabitants:Two categories:- city star parks for cities with < 100.000 inhabitants- metropolis star parks for cities with > 100.000 inhabitantsFive levels of quality:- 1* level = can see stars of at least 1 magnitude with the naked eyes- 2* level = at least 2 mag- 3* level = at least 3 mag- 4* level= at least 4 mag- 5* level = at least 5 magThe urban star urban park structure and lighting systemA possible structure of a urban star park and sky-friend lighting including non-electric illumination are descripted.The International Commission on IlluminationA description of this structure which has as members national commissions from all over the world.Dark-sky activists - lighting specialistsNational Commissions on Illumination organize courses of lighting specialist. Dark-sky activists can become lighting specialists. The author shows his experience in this aspect as a recent lighting specialist and his cooperation with the Romanian National

  8. Al-Sufi's Investigation of Stars, Star Clusters and Nebulae

    NASA Astrophysics Data System (ADS)

    Hafez, Ihsan; Stephenson, F. R.; Orchiston, W.

    2011-01-01

    The distinguished Arabic astronomer, Al-Sufi (AD 903-986) is justly famous for his Book of the Fixed Stars, an outstanding Medieval treatise on astronomy that was assembled in 964. Developed from Ptolemy's Algamest, but based upon al-Sufi's own stellar observations, the Book of the Fixed Stars has been copied down through the ages, and currently 35 copies are known to exist in various archival repositories around the world. Among other things, this major work contains 55 astronomical tables, plus star charts for 48 constellations. For the first time a long-overdue English translation of this important early work is in active preparation. In this paper we provide biographical material about Al-Sufi and the contents of his Book of the Fixed Stars, before examining his novel stellar magnitude system, and his listing of star clusters and nebulae (including the first-ever mention of the Great Nebula in Andromeda).

  9. Recovery Ship Freedom Star

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Freedom Star, one of NASA's two solid rocket booster recovery ships, is towing a barge containing the third Space Shuttle Super Lightweight External Tank (SLWT) into Port Canaveral. This SLWT was slated for use to launch the orbiter Discovery on mission STS-95 in October 1998. This first time towing arrangement, part of a cost saving plan by NASA to prudently manage existing resources, began June 12 from the Michoud Assembly Facility in New Orleans where the Shuttle's external tanks were manufactured. The barge was transported up Banana River to the LC-39 turn basin using a conventional tug boat. Previously, NASA relied on an outside contractor to provide external tank towing services at a cost of about $120,000 per trip. The new plan allowed NASA's Space Flight Operations contractor, United Space Alliance (USA), to provide the same service to NASA using the recovery ships during their downtime between Shuttle launches. Studies showed a potential savings of about $50,000 per trip. The cost of the necessary ship modifications would be paid back by the fourteenth tank delivery. The other recovery ship, Liberty Star, also underwent deck strengthening enhancements and had the necessary towing wench installed.

  10. Stars and Planets

    NASA Astrophysics Data System (ADS)

    Neta, Miguel

    2014-05-01

    'Estrelas e Planetas' (Stars and Planets) project was developed during the academic year 2009/2010 and was tested on three 3rd grade classes of one school in Quarteira, Portugal. The aim was to encourage the learning of science and the natural and physical phenomena through the construction and manipulation of materials that promote these themes - in this case astronomy. Throughout the project the students built a small book containing three themes of astronomy: differences between stars and planets, the solar system and the phases of the Moon. To each topic was devoted two sessions of about an hour each: the first to teach the theoretical aspects of the theme and the second session to assembly two pages of the book. All materials used (for theoretical sessions and for the construction of the book) and videos of the finished book are available for free use in www.miguelneta.pt/estrelaseplanetas. So far there is only a Portuguese version but soon will be published in English as well. This project won the Excellency Prize 2011 of Casa das Ciências, a portuguese site for teachers supported by the Calouste Gulbenkian Fundation (www.casadasciencias.org).

  11. Starspots on flare stars

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1974-01-01

    Sizes of starspots on flare stars can be derived from the author's convection-cell hypothesis. The sizes are in fair agreement with those observed on YY Gem, CC Eri, and BY Dra by Bopp and Evans (1973). The hypothesis predicts that periodic brightness variations due to starspots are restricted to stars brighter than a critical absolute visual magnitude. A convective model of a starspot on YY Gem has been computed, assuming that the missing flux is in the form of Alfven waves. It is found that the surface field must exceed 10,000 G, and is probably less than about 30,000 G. With a surface field of 20,000 G, the effective temperature of the spot is in the range from 1590 to 1890 K, depending on the field gradient. These figures are to be compared with an effective temperature of 2000 K estimated from observations by Bopp and Evans. Efficient dynamo action is shown to be a possible mechanism for generating such large surface fields. There is a possibility that tidal effects may influence starspot formation.

  12. The Stars of Heaven

    NASA Astrophysics Data System (ADS)

    Pickover, Clifford A.

    2004-05-01

    Do a little armchair space travel, rub elbows with alien life forms, and stretch your mind to the furthest corners of our uncharted universe. With this astonishing guidebook, you don't have to be an astronomer to explore the mysteries of stars and their profound meaning for human existence. Clifford A. Pickover tackles a range of topics from stellar evolution to the fundamental reasons why the universe permits life to flourish. He alternates sections that explain the mysteries of the cosmos with sections that dramatize mind-expanding concepts through a fictional dialog between futuristic humans and their alien peers (who embark on a journey beyond the reader's wildest imagination). This highly accessible and entertaining approach turns an intimidating subject into a scientific game open to all dreamers. Told in Pickover's inimitable blend of fascinating state-of-the-art science and whimsical science fiction, and packed with numerous diagrams and illustrations, The Stars of Heaven unfolds a world of paradox and mystery, one that will intrigue anyone who has ever pondered the night sky with wonder.

  13. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  14. Multistate boson stars

    SciTech Connect

    Bernal, A.; Barranco, J.; Alic, D.; Palenzuela, C.

    2010-02-15

    Motivated by the increasing interest in models which consider scalar fields as viable dark matter candidates, we have constructed a generalization of relativistic boson stars (BS) composed of two coexisting states of the scalar field, the ground state and the first excited state. We have studied the dynamical evolution of these multistate boson stars (MSBS) under radial perturbations, using numerical techniques. We show that stable MSBS can be constructed, when the number of particles in the first excited state, N{sup (2)}, is smaller than the number of particles in the ground state, N{sup (1)}. On the other hand, when N{sup (2)}>N{sup (1)}, the configurations are initially unstable. However, they evolve and settle down into stable configurations. In the stabilization process, the initially ground state is excited and ends in a first excited state, whereas the initially first excited state ends in a ground state. During this process, both states emit scalar field radiation, decreasing their number of particles. This behavior shows that even though BS in the first excited state are intrinsically unstable under finite perturbations, the configuration resulting from the combination of this state with the ground state produces stable objects. Finally we show in a qualitative way, that stable MSBS could be realistic models of dark matter galactic halos, as they produce rotation curves that are flatter at large radii than the rotation curves produced by BS with only one state.

  15. Modeling Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Park, Conner; Read, Jocelyn; Flynn, Eric; Lockett-Ruiz, Veronica

    2016-03-01

    Gravitational waves, predicted by Einstein's Theory of Relativity, are a new frontier in astronomical observation we can use to observe phenomena in the universe. Laser Interferometer Gravitational wave Observatory (LIGO) is currently searching for gravitational wave signals, and requires accurate predictions in order to best extract astronomical signals from all other sources of fluctuations. The focus of my research is in increasing the accuracy of Post-Newtonian models of binary neutron star coalescence to match the computationally expensive Numerical models. Numerical simulations can take months to compute a couple of milliseconds of signal whereas the Post-Newtonian can generate similar signals in seconds. However the Post-Newtonian model is an approximation, e.g. the Taylor T4 Post-Newtonian model assumes that the two bodies in the binary neutron star system are point charges. To increase the effectiveness of the approximation, I added in tidal effects, resonance frequencies, and a windowing function. Using these observed effects from simulations significantly increases the Post-Newtonian model's similarity to the Numerical signal.

  16. A Star on the Run

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    Usually stars that are born together tend to move together but sometimes stars can go rogue and run away from their original birthplace. A pair of astronomers have now discovered the first runaway red supergiant (RSG) ever identified in another galaxy. With a radial velocity discrepancy of 300 km/s, its also the fastest runaway massive star known. Discrepant Speeds: When massive stars form in giant molecular clouds, they create what are known as OB associations: groups of hot, massive, short-lived stars that have similar velocities because theyre moving through space together. But sometimes stars that appear to be part of an OB association dont have the same velocity as the rest of the group. These stars are called runaways.What causes an OB star to run away is still debated, but we know that a fairly significant fraction of OB stars are runaways. In spite of this, surprisingly few runaways have been found that are evolved massive stars i.e., the post-main-sequence state of OB stars. This is presumably because these evolved stars have had more time to move away from their birthplace, and its more difficult to identify a runaway without the context of its original group. An Evolved Runaway: Difference between observed velocity and expected velocity, plotted as a function of expected velocity. The black points are foreground stars. The red points are expected RSGs, clustered around a velocity difference of zero. The green pentagon is the runaway RSG J004330.06+405258.4. [Evans Massey 2015]Despite this challenge, a recent survey of RSGs in the galaxy M31 has led to the detection of a massive star on the run! Kate Evans (Lowell Observatory and California Institute of Technology) and Philip Massey (Lowell Observatory and Northern Arizona University) discovered that RSG J004330.06+405258.4 is moving through the Andromeda Galaxy with a radial velocity thats off by about 300 km/s from the radial velocity expected for its location.Evans and Massey discovered this rogue star

  17. Stars in the Tarantula Nebula

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In the most active starburst region in the local universe lies a cluster of brilliant, massive stars, known to astronomers as Hodge 301. Hodge 301, seen in the lower right hand corner of this image, lives inside the Tarantula Nebula in our galactic neighbor, the Large Magellanic Cloud. This star cluster is not the brightest, or youngest, or most populous star cluster in the Tarantula Nebula, that honor goes to the spectacular R136. In fact, Hodge 301 is almost 10 times older than the young cluster R136. But age has its advantages; many of the stars in Hodge 301 are so old that they have exploded as supernovae. These exploded stars are blasting material out into the surrounding region at speeds of almost 200 miles per second. This high speed ejecta are plowing into the surrounding Tarantula Nebula, shocking and compressing the gas into a multitude of sheets and filaments, seen in the upper left portion of the picture. Hodge 301 contains three red supergiants - stars that are close to the end of their evolution and are about to go supernova, exploding and sending more shocks into the Tarantula. Also present near the center of the image are small, dense gas globules and dust columns where new stars are being formed today, as part of the overall ongoing star formation throughout the Tarantula region.

  18. Dust near luminous ultraviolet stars

    NASA Technical Reports Server (NTRS)

    Henry, Richard C.

    1993-01-01

    This report describes research activities related to the Infrared Astronomical Satellite (IRAS) sky survey. About 745 luminous stars were examined for the presence of interstellar dust heated by a nearby star. The 'cirrus' discovered by IRAS is thermal radiation from interstellar dust at moderate and high galactic latitudes. The IRAS locates the dust which must (at some level) scatter ultraviolet starlight, although it was expected that thermal emission would be found around virtually every star, most stars shown no detectable emission. And the emission found is not uniform. It is not that the star is embedded in 'an interstellar medium', but rather what is found are discrete clouds that are heated by starlight. An exception is the dearth of clouds near the very hottest stars, implying that the very hottest stars play an active role with respect to destroying or substantially modifying the dust clouds over time. The other possibility is simply that the hottest stars are located in regions lacking in dust, which is counter-intuitive. A bibliography of related journal articles is attached.

  19. Stars get dizzy after lunch

    SciTech Connect

    Zhang, Michael; Penev, Kaloyan

    2014-06-01

    Exoplanet searches have discovered a large number of {sup h}ot Jupiters{sup —}high-mass planets orbiting very close to their parent stars in nearly circular orbits. A number of these planets are sufficiently massive and close-in to be significantly affected by tidal dissipation in the parent star, to a degree parameterized by the tidal quality factor Q {sub *}. This process speeds up their star's rotation rate while reducing the planet's semimajor axis. In this paper, we investigate the tidal destruction of hot Jupiters. Because the orbital angular momenta of these planets are a significant fraction of their star's rotational angular momenta, they spin up their stars significantly while spiraling to their deaths. Using the Monte Carlo simulation, we predict that for Q {sub *} = 10{sup 6}, 3.9 × 10{sup –6} of stars with the Kepler Target Catalog's mass distribution should have a rotation period shorter than 1/3 day (8 hr) due to accreting a planet. Exoplanet surveys such as SuperWASP, HATnet, HATsouth, and KELT have already produced light curves of millions of stars. These two facts suggest that it may be possible to search for tidally destroyed planets by looking for stars with extremely short rotational periods, then looking for remnant planet cores around those candidates, anomalies in the metal distribution, or other signatures of the recent accretion of the planet.

  20. STARS: A Year in Review

    ERIC Educational Resources Information Center

    Association for the Advancement of Sustainability in Higher Education, 2011

    2011-01-01

    The Sustainability Tracking, Assessment & Rating System[TM] (STARS) is a program of AASHE, the Association for the Advancement of Sustainability in Higher Education. AASHE is a member-driven organization with a mission to empower higher education to lead the sustainability transformation. STARS was developed by AASHE with input and insight from…

  1. Mathematics Teaching with the Stars

    ERIC Educational Resources Information Center

    McKinney, Sueanne E.; Bol, Linda; Berube, Clair

    2010-01-01

    The mathematics instructional approaches of effective elementary teachers in urban high- poverty schools were investigated. Approximately 99 urban elementary teachers were administered the Star Teacher Selection Interview; a total of 31 were identified as star teachers. These teachers were then administered the Instructional Practices…

  2. Comparable Habitable Zones of Stars

    NASA Video Gallery

    The habitable zone is the distance from a star where one can have liquid water on the surface of a planet. If a planet is too close to its parent star, it will be too hot and water would have evapo...

  3. Star formation in the multiverse

    SciTech Connect

    Bousso, Raphael; Leichenauer, Stefan

    2009-03-15

    We develop a simple semianalytic model of the star formation rate as a function of time. We estimate the star formation rate for a wide range of values of the cosmological constant, spatial curvature, and primordial density contrast. Our model can predict such parameters in the multiverse, if the underlying theory landscape and the cosmological measure are known.

  4. Star formation in Galactic flows

    NASA Astrophysics Data System (ADS)

    Smilgys, Romas; Bonnell, Ian A.

    2016-06-01

    We investigate the triggering of star formation in clouds that form in Galactic scale flows as the interstellar medium passes through spiral shocks. We use the Lagrangian nature of smoothed particle hydrodynamics simulations to trace how the star-forming gas is gathered into self-gravitating cores that collapse to form stars. Large-scale flows that arise due to Galactic dynamics create shocks of the order of 30 km s-1 that compress the gas and form dense clouds (n > several × 102 cm-3) in which self-gravity becomes relevant. These large-scale flows are necessary for creating the dense physical conditions for gravitational collapse and star formation. Local gravitational collapse requires densities in excess of n > 103 cm-3 which occur on size scales of ≈1 pc for low-mass star-forming regions (M < 100 M⊙), and up to sizes approaching 10 pc for higher mass regions (M > 103 M⊙). Star formation in the 250 pc region lasts throughout the 5 Myr time-scale of the simulation with a star formation rate of ≈10-1 M⊙ yr-1 kpc-2. In the absence of feedback, the efficiency of the star formation per free-fall time varies from our assumed 100 per cent at our sink accretion radius to values of <10-3 at low densities.

  5. Physics of primordial star formation

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2012-09-01

    The study of primordial star formation has a history of nearly sixty years. It is generally thought that primordial stars are one of the key elements in a broad range of topics in astronomy and cosmology, from Galactic chemical evolution to the formation of super-massive blackholes. We review recent progress in the theory of primordial star formation. The standard theory of cosmic structure formation posits that the present-day rich structure of the Universe developed through gravitational amplification of tiny matter density fluctuations left over from the Big Bang. It has become possible to study primordial star formation rigorously within the framework of the standard cosmological model. We first lay out the key physical processes in a primordial gas. Then, we introduce recent developments in computer simulations. Finally, we discuss prospects for future observations of the first generation of stars.

  6. A Swarm of Ancient Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This stellar swarm is M80 (NGC 6093), one of the densest of the 147 known globular star clusters in the Milky Way galaxy. Located about 28,000 light-years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives.

  7. The R Coronae Borealis Stars

    NASA Astrophysics Data System (ADS)

    Clayton, Geoffrey C.

    1996-03-01

    This year marks the bicentennial of the discovery of the variability of R Coronae Borealis. The R Coronae Borealis (RCB) stars are distinguished from other hydrogen-deficient objects by their spectacular dust formation episodes. They may decline by up to 8 magnitudes in a few weeks revealing a rich emission-line spectrum. Their atmospheres have unusual abundances with very little hydrogen and an overabundance of carbon and nitrogen. The RCB stars are thought to be the product of a final helium shell flash or the coalescence of a binary white-dwarf system. Dust may form in non-equilibrium conditions created behind shocks caused by pulsations in the atmospheres of these stars. The RCB stars are interesting and important, first because they represent a rare, or short-lived stage of stellar evolution, and second because these stars regularly produce large amounts of dust so they are laboratories for the study of dust formation and evolution. (SECTION: Invited Review Paper)

  8. Grand unification of neutron stars

    PubMed Central

    Kaspi, Victoria M.

    2010-01-01

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical “grand unification” of this wealth of observational phenomena, and comment on possibilities for Chandra’s next decade in this field. PMID:20404205

  9. Binary Stars in SBS Survey

    NASA Astrophysics Data System (ADS)

    Erastova, L. K.

    2016-06-01

    Thirty spectroscopic binary stars were found in the Second Byurakan Survey (SBS). They show composite spectra - WD(DA)+dM or dC (for example Liebert et al. 1994). They may have red color, if the radiation of the red star dominates, and blue one, if the blue star is brighter and have peculiar spectrum in our survey plate. We obtained slit spectra for most of such objects. But we often see the spectrum of one component, because our slit spectra did not cover all optical range. We examine by eye the slit spectra of all SBS stellar objects (˜700) in SDSS DR7, DR8 or DR9 independent on our observations. We confirmed or discovered the duplicity of 30 stars. Usually they are spectroscopic binaries, where one component is WD (DA) and the second one is a red star with or without emission. There also are other components combinations. Sometimes there are emission lines, probably, indicating variable ones.

  10. Magnetic Field Generation in Stars

    NASA Astrophysics Data System (ADS)

    Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan

    2015-10-01

    Enormous progress has been made on observing stellar magnetism in stars from the main sequence (particularly thanks to the MiMeS, MAGORI and BOB surveys) through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence, in the generation and stability of neutron star fields.

  11. Asteroseismology of Exoplanet Host Stars

    NASA Astrophysics Data System (ADS)

    Kayhan, Cenk; Çelik Orhan, Zeynep; Yildiz, Mutlu

    2016-07-01

    Exoplanet studies are one of the most interesting and attractive topics in astrophysics. Besides of ground-based observations, Kepler and CoRoT space missions improved our knowledge by providing unprecedented data of exoplanets and host stars. Precise determination of basic properties of planets depends on how we accurately determine fundamental properties of host stars. Asteroseismology is a powerful tool to study stellar structure and evolution and provides us radius, mass and age of the host stars. In this study, we construct stellar interior models of these stars with the MESA evolution code and compare model frequencies with the oscillation frequencies derived from Kepler data. Then, we obtain fundamental parameters of the host stars. Finally, fundamental parameters of exoplanets are reevaluated.

  12. Kicked Neutron Stars and Microlensing

    NASA Astrophysics Data System (ADS)

    Mollerach, Silvia; Roulet, Esteban

    1997-04-01

    Because of the large kick velocities with which neutron stars are born in supernova explosions, their spatial distribution is more extended than that of their progenitor stars. The large scale height of the neutron stars above the disk plane makes them potential candidates for microlensing of stars in the Large Magellanic Cloud. Adopting for the distribution of kicks the measured velocities of young pulsars, we obtain a microlensing optical depth of τ ~ 2N10 × 10-8 (where N10 is the total number of neutron stars born in the disk in units of 1010). The event duration distribution has the interesting property of being peaked at T ~ 60-80 days, but for the rates to be relevant for the present microlensing searches, it would require N10 >~ 1, a value larger than the usually adopted ones (N10 ~ 0.1-0.2).

  13. Improved autonomous star identification algorithm

    NASA Astrophysics Data System (ADS)

    Luo, Li-Yan; Xu, Lu-Ping; Zhang, Hua; Sun, Jing-Rong

    2015-06-01

    The log-polar transform (LPT) is introduced into the star identification because of its rotation invariance. An improved autonomous star identification algorithm is proposed in this paper to avoid the circular shift of the feature vector and to reduce the time consumed in the star identification algorithm using LPT. In the proposed algorithm, the star pattern of the same navigation star remains unchanged when the stellar image is rotated, which makes it able to reduce the star identification time. The logarithmic values of the plane distances between the navigation and its neighbor stars are adopted to structure the feature vector of the navigation star, which enhances the robustness of star identification. In addition, some efforts are made to make it able to find the identification result with fewer comparisons, instead of searching the whole feature database. The simulation results demonstrate that the proposed algorithm can effectively accelerate the star identification. Moreover, the recognition rate and robustness by the proposed algorithm are better than those by the LPT algorithm and the modified grid algorithm. Project supported by the National Natural Science Foundation of China (Grant Nos. 61172138 and 61401340), the Open Research Fund of the Academy of Satellite Application, China (Grant No. 2014_CXJJ-DH_12), the Fundamental Research Funds for the Central Universities, China (Grant Nos. JB141303 and 201413B), the Natural Science Basic Research Plan in Shaanxi Province, China (Grant No. 2013JQ8040), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130203120004), and the Xi’an Science and Technology Plan, China (Grant. No CXY1350(4)).

  14. A Multi-wavelength Study of Star Formation Activity in the S235 Complex

    NASA Astrophysics Data System (ADS)

    Dewangan, L. K.; Ojha, D. K.; Luna, A.; Anandarao, B. G.; Ninan, J. P.; Mallick, K. K.; Mayya, Y. D.

    2016-03-01

    We have carried out an extensive multi-wavelength study to investigate the star formation process in the S235 complex. The S235 complex has a spherelike shell appearance at wavelengths longer than 2 μm and harbors an O9.5V type star approximately at its center. A near-infrared extinction map of the complex traces eight subregions (having AV > 8 mag), and five of them appear to be distributed in an almost regularly spaced manner along the spherelike shell surrounding the ionized emission. This picture is also supported by the integrated 12CO and 13CO intensity maps and by Bolocam 1.1 mm continuum emission. The position-velocity analysis of CO reveals an almost semi-ringlike structure, suggesting an expanding H ii region. We find that the Bolocam clump masses increase as we move away from the location of the ionizing star. This correlation is seen only for those clumps that are distributed near the edges of the shell. Photometric analysis reveals 435 young stellar objects (YSOs), 59% of which are found in clusters. Six subregions (including five located near the edges of the shell) are very well correlated with the dust clumps, CO gas, and YSOs. The average values of Mach numbers derived using NH3 data for three (East 1, East 2, and Central E) out of these six subregions are 2.9, 2.3, and 2.9, indicating these subregions are supersonic. The molecular outflows are detected in these three subregions, further confirming the ongoing star formation activity. Together, all these results are interpreted as observational evidence of positive feedback of a massive star.

  15. Neutron stars, strange stars, and the nuclear equation of state

    SciTech Connect

    Weber, F.; Glendenning, N.K.

    1992-11-02

    This article consists of three parts. In part one we review the present status of dense nuclear matter calculations, and introduce a representative collection of realistic nuclear equations of state which are derived for different assumptions about the physical behavior of dense matter (baryon population, pion condensation,.possible transition of baryon matter to quark matter). In part two we review recently performed non-rotating and rotating compact star calculations performed for these equations of state. The minimum stable rotational periods of compact stars, whose knowledge is of decisive importance for the interpretation of rapidly rotating pulsars, axe determined. For this purpose two different limits on stable rotation are studied: rotation at the general relativistic Kepler period (below which mass shedding at the star`s equator sets in), and, secondly, rotation at the gravitational radiation-reaction instability (at which emission of gravitational waves set in which slows the star down). Part three of this article deals with the properties of hypothetical strange stars. Specifically we investigate the amount of nuclear solid crust that can be carried by a rotating strange star, and answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

  16. Shooting Star Experiment

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Shooting Star Experiment (SSE) is designed to develop and demonstrate the technology required to focus the Sun's energy and use the energy for inexpensive space propulsion research. Pictured is an engineering model (Pathfinder III) of SSE and its thermal vacuum test to simulate in-orbit conditions at the X-Ray Calibration Facility at the Marshall Space Flight Center (MSFC). This model was used to test and characterize the motion and deformation of the structure caused by thermal effects. In this photograph, alignment targets are being placed on the engineering model so that a theodolite (alignment telescope) could be used to accurately measure the deformation and deflection of the engineering model under extreme condition, such as the coldness of deep space and the hotness of the Sun, as well as vacuum.

  17. Nonassociative Weyl star products

    NASA Astrophysics Data System (ADS)

    Kupriyanov, V. G.; Vassilevich, D. V.

    2015-09-01

    Deformation quantization is a formal deformation of the algebra of smooth functions on some manifold. In the classical setting, the Poisson bracket serves as an initial conditions, while the associativity allows to proceed to higher orders. Some applications to string theory require deformation in the direction of a quasi-Poisson bracket (that does not satisfy the Jacobi identity). This initial condition is incompatible with associativity, it is quite unclear which restrictions can be imposed on the deformation. We show that for any quasi-Poisson bracket the deformation quantization exists and is essentially unique if one requires (weak) hermiticity and the Weyl condition. We also propose an iterative procedure that allows one to compute the star product up to any desired order.

  18. Modes of clustered star formation

    NASA Astrophysics Data System (ADS)

    Pfalzner, S.; Kaczmarek, T.; Olczak, C.

    2012-09-01

    Context. The recent realization that most stars form in clusters, immediately raises the question of whether star and planet formation are influenced by the cluster environment. The stellar density in the most prevalent clusters is the key factor here. Whether dominant modes of clustered star formation exist is a fundamental question. Using near-neighbour searches in young clusters, Bressert and collaborators claim this not to be the case. They conclude that - at least in the solar neighbourhood - star formation is continuous from isolated to densely clustered environments and that the environment plays a minor role in star and planet formation. Aims: We investigate under which conditions near-neighbour searches in young clusters can distinguish between different modes of clustered star formation. Methods: Model star clusters with different memberships and density distributions are set up and near-neighbour searches are performed. We investigate the influence of the combination of different cluster modes, observational biases, and types of diagnostic on the results. Results: We find that the specific cluster density profile, the relative sample sizes, the limitations of the observation, and the choice of diagnostic method decide, whether modelled modes of clustered star formation are detected by near-neighbour searches. For density distributions that are centrally concentrated but span a wide density range (for example, King profiles), separate cluster modes are only detectable under ideal conditions (sample selection, completeness) if the mean density of the individual clusters differs by at least a factor of ~65. Introducing a central cut-off can lead to an underestimate of the mean density by more than a factor of ten especially in high density regions. The environmental effect on star and planet formation is similarly underestimated for half of the population in dense systems. Conclusions: Local surface-density distributions are a very useful tool for single

  19. Surface abundances of ON stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Simón-Díaz, S.; Palacios, A.; Howarth, I.; Georgy, C.; Walborn, N. R.; Bouret, J.-C.; Barbá, R.

    2015-06-01

    Context. Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient or when mass transfer in binary systems occurs, chemically processed material is observed at the surface of O and B stars. Aims: ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence of material processed through the CNO cycle is not known. Our goal is to answer this question. Methods: We performed a spectroscopic analysis of a sample of ON stars with atmosphere models. We determined the fundamental parameters as well as the He, C, N, and O surface abundances. We also measured the projected rotational velocities. We compared the properties of the ON stars to those of normal O stars. Results: We show that ON stars are usually rich in helium. Their CNO surface abundances are fully consistent with predictions of nucleosynthesis. ON stars are more chemically evolved and rotate - on average - faster than normal O stars. Evolutionary models including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members of binary systems, but others are single stars as indicated by stable radial velocities. Mass transfer is therefore not a simple explanation for the observed chemical properties. Conclusions: We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through the CNO cycle. Its origin is not clear at present. Based on observations obtained 1) at the Anglo-Australian Telescope; 2) at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii; 3) at the ESO/La Silla Observatory under programs 081.D-2008, 083.D-0589, 086.D-0997; 4) the Nordic Optical Telescope, operated on the island of La

  20. Neutron Star Mass Distribution in Binaries

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hwan; Kim, Young-Min

    2016-05-01

    Massive neutron stars with ∼ 2Mʘ have been observed in neutron star-white dwarf binaries. On the other hand, well-measured neutron star masses in double-neutron-star binaries are still consistent with the limit of 1.5Mʘ. These observations raised questions on the neutron star equations of state and the neutron star binary evolution processes. In this presentation, a hypothesis of super-Eddington accretion and its implications are discussed. We argue that a 2Mʘ neutron star is an outcome of the super-Eddington accretion during the evolution of neutron star-white dwarf binary progenitors. We also suggest the possibility of the existence of new type of neutron star binary which consists of a typical neutron star and a massive compact companion (high-mass neutron star or black hole) with M ≥ 2Mʘ.