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1

Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris  

E-print Network

LETTERS Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris L. M Canis Majoris (VY CMa). A variety of unexpected chemical com- pounds have been identified, including Na is further modified by interstellar ultraviolet radiation3,4 . Chemical compounds in these shells apparently

Ziurys, Lucy M.

2

Detection of a weak surface magnetic field on Sirius A: are all tepid stars magnetic?  

NASA Astrophysics Data System (ADS)

Aims: We aim at a highly sensitive search for weak magnetic fields in main sequence stars of intermediate mass, by scanning classes of stars with no previously reported magnetic members. After detecting a weak magnetic field on the normal, rapidly rotating A-type star Vega, we concentrate here on the bright star Sirius A, taken as a prototypical, chemically peculiar, moderately rotating Am star. Methods: We employed the NARVAL and ESPaDOnS high-resolution spectropolarimeters to collect 442 circularly polarized spectra, complemented by 60 linearly polarized spectra. Using a list of about 1100 photospheric spectral lines, we computed a cross correlation line profile from every spectrum, leading to a signal-to-noise ratio of up to 30 000 in the polarized profile. Results: We report the repeated detection of circularly polarized, highly asymmetric signatures in the line profiles, interpreted as Zeeman signatures of a large-scale photospheric magnetic field, with a line-of-sight component equal to 0.2 ± 0.1 G. Conclusions: This is the first polarimetric detection of a surface magnetic field on an Am star. Using rough estimates of the physical properties of the upper layers of Sirius A, we suggest that a dynamo operating in the shallow convective envelope cannot account for the field strength reported here. Together with the magnetic field of Vega, this result confirms that a new class of magnetic objects exists among non Ap/Bp intermediate-mass stars, and it may indicate that a significant fraction of tepid stars are magnetic. Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Petit, P.; Lignières, F.; Aurière, M.; Wade, G. A.; Alina, D.; Ballot, J.; Böhm, T.; Jouve, L.; Oza, A.; Paletou, F.; Théado, S.

2011-08-01

3

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

This report summarizes the progress of the work conducted under the program "The Winds of B Supergiants," conducted by Raytheon STX Corporation. The report consists of a journal article "Wind variability in B supergiants III. Corotating spiral structures in the stellar wind of HD 64760." The first step in the project was the analysis of the 1996 time series of 2 B supergiants and an O star. These data were analyzed and reported on at the ESO workshop, "Cyclical Variability in Stellar Winds."

Fullerton, A. W.; Massa, D. L.; Prinja, R. K.; Owocki, S. P.; Cranmer, S. R.

1998-01-01

4

The chemistry of dust formation in red supergiants  

NASA Astrophysics Data System (ADS)

Massive stars in their late stages of evolution as Red Supergiants experience mass loss. The resulting winds show various degrees of dynamical and chemical complexity and produce molecules and dust grains. This review summarises our knowledge of the molecular and dust components of the wind of Red Supergiants, including VY CMa and Betelgeuse. We discuss the synthesis of dust as a non equilibrium process in stellar winds, and present the current knowledge of the chemistry involved in the formation of oxygen-rich dust such as silicates and metal oxides.

Cherchneff, I.

2013-05-01

5

The $^{13}$Carbon footprint of B[e] supergiants  

E-print Network

We report on the first detection of $^{13}$C enhancement in two B[e] supergiants in the Large Magellanic Cloud. Stellar evolution models predict the surface abundance in $^{13}$C to strongly increase during main-sequence and post-main sequence evolution of massive stars. However, direct identification of chemically processed material on the surface of B[e] supergiants is hampered by their dense, disk-forming winds, hiding the stars. Recent theoretical computations predict the detectability of enhanced $^{13}$C via the molecular emission in $^{13}$CO arising in the circumstellar disks of B[e] supergiants. To test this potential method and to unambiguously identify a post-main sequence B[e]SG by its $^{13}$CO emission, we have obtained high-quality $K$-band spectra of two known B[e] supergiants in the Large Magellanic Cloud, using the Very Large Telescope's Spectrograph for INtegral Field Observation in the Near-Infrared (VLT/SINFONI). Both stars clearly show the $^{13}$CO band emission, whose strength implies ...

Liermann, A; Schnurr, O; Fernandes, M Borges

2010-01-01

6

An investigation of the chemical composition of the atmospheres of the red giants Gamma And and Upsilon(2) CAS and the supergiant Epsilon Peg  

NASA Astrophysics Data System (ADS)

The method of curves is used in a quantitative analysis of spectrograms of these stars (dispersion, 6 A/mm). A table is included giving the equivalent line widths. The analysis yields atmospheric parameters and the relative abundances of the elements. The star Kappa Oph is used as a standard. It is found that Gamma And contains three to four times as much barium and certain other heavy elements as Kappa Oph. Upsilon(2) Cas is found to have a normal chemical composition and is not among the barium stars. A slight excess of heavy elements is detected in the atmosphere of Epsilon Peg.

Deinichenko, O. N.

7

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasises the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters, but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M (dot) q(sub i)) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in terms of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, D.; Oliversen, R. (Technical Monitor)

2002-01-01

8

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasizes the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M qi) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in turns of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, Derck; West, D. (Technical Monitor)

2002-01-01

9

The temperatures of Red Supergiants  

E-print Network

We present a re-appraisal of the temperatures of Red Supergiants (RSGs) using their optical and near-infrared spectral energy distributions (SEDs). We have obtained data of a sample of RSGs in the Magellanic Clouds using VLT+XSHOOTER, and we fit MARCS model atmospheres to different regions of the spectra, deriving effective temperatures for each star from (a) the TiO bands, (b) line-free continuum regions of the spectral energy distributions (SEDs), and (c) the integrated fluxes. We show that the temperatures derived from fits to the TiO bands are systematically {\\it lower} than the other two methods by several hundred Kelvin. The TiO fits also dramatically over-predict the flux in the near-IR, and imply extinctions which are anomalously low compared to neighbouring stars. In contrast, the SED temperatures provide good fits to the fluxes at all wavelengths other than the TiO bands, are in agreement with the temperatures from the flux integration method, and imply extinctions consistent with nearby stars. Afte...

Davies, Ben; Plez, Bertrand; Trager, Scott; Lancon, Ariane; Gazak, Zach; Bergemann, Maria; Evans, Chris; Chiavassa, Andrea

2013-01-01

10

Massive compact binaries hosting supergiant stars  

NASA Astrophysics Data System (ADS)

In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: i. Be circumstellar disk, ii. supergiant stellar wind, and iii. Roche lobe filling supergiants. I then report on the discovery of two new populations of HMXBs hosting supergiant stars, recently revealed by a wealth of new observations, coming from the high energy side (INTEGRAL, Swift, XMM, Chandra satellites), and complemented by multi-wavelength optical/infrared observations (mainly ESO facilities). The first population is constituted of obscured supergiant HMXBs, the second one of supergiant fast X-ray transients (SFXTs), exhibiting short and intense X-ray flares. I finally discuss the formation and evolution of HMXBs, constrain the accretion models (e.g. clumpy winds, transitory accretion disk, magneto-centrifugal barrier), show evidences suggesting the existence of an evolutionary link, include comparisons with population synthesis models, and finally build a consistent scenario explaining the various characteristics of these extreme celestial sources. Because they are the likely progenitors of Luminous Blue Variables (LBVs), and also of neutron star/black hole binary mergers, related to short/hard gamma-ray bursts, the knowledge of the nature, formation and evolution of these HMXB populations is of prime importance.

Chaty, Sylvain

2013-06-01

11

THE TEMPERATURES OF RED SUPERGIANTS  

SciTech Connect

We present a re-appraisal of the temperatures of red supergiants (RSGs) using their optical and near-infrared spectral energy distributions (SEDs). We have obtained data of a sample of RSGs in the Magellanic Clouds using VLT+XSHOOTER, and we fit MARCS model atmospheres to different regions of the spectra, deriving effective temperatures for each star from (1) the TiO bands, (2) line-free continuum regions of the SEDs, and (3) the integrated fluxes. We show that the temperatures derived from fits to the TiO bands are systematically lower than the other two methods by several hundred kelvin. The TiO fits also dramatically overpredict the flux in the near-IR, and imply extinctions which are anomalously low compared to neighboring stars. In contrast, the SED temperatures provide good fits to the fluxes at all wavelengths other than the TiO bands, are in agreement with the temperatures from the flux integration method, and imply extinctions consistent with nearby stars. After considering a number of ways to reconcile this discrepancy, we conclude that three-dimensional effects (i.e., granulation) are the most likely cause, as they affect the temperature structure in the upper layers where the TiO lines form. The continuum, however, which forms at much deeper layers, is apparently more robust to such effects. We therefore conclude that RSG temperatures are much warmer than previously thought. We discuss the implications of this result for stellar evolution and supernova progenitors, and provide relations to determine the bolometric luminosities of RSGs from single-band photometry.

Davies, Ben [Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)] [Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom); Kudritzki, Rolf-Peter; Gazak, Zach [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)] [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France)] [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France); Trager, Scott [Kapteyn Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands)] [Kapteyn Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands); Lancon, Ariane [Observatoire Astronomique and CNRS UMR 7550, Universite de Strasbourg, F-67000 Strasbourg (France)] [Observatoire Astronomique and CNRS UMR 7550, Universite de Strasbourg, F-67000 Strasbourg (France); Bergemann, Maria [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)] [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany); Evans, Chris [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)] [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Chiavassa, Andrea [CNRS Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, Observatoire de la Cote d'Azur, BP 4229, F-06304 Nice Cedex 4 (France)] [CNRS Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, Observatoire de la Cote d'Azur, BP 4229, F-06304 Nice Cedex 4 (France)

2013-04-10

12

Observations of emission lines in M supergiants  

NASA Technical Reports Server (NTRS)

Copernicus observations of Mg 2 h and k emission lines from M giants and supergiants are described. Supergiants with extensive circumstellar gas shells show an asymmetric k line. The asymmetry is ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width fit the Wilson-Bappu relation derived from observations of G and K Stars. Results of correlated ground-based observations include (1) the discovery of K 1 fluorescent emission from the Betelgeuse shell; (2) extimates of the mass-loss rates; and (3) the proposal that silicate dust grains must account for the major fraction of the Si atoms in the Betelgeuse shell.

Lambert, D. L.

1979-01-01

13

Multiple ring nebulae around blue supergiants  

Microsoft Academic Search

Context: In the course of the life of a massive star, wind-wind interaction can give rise to the formation of circumstellar nebulae which are both predicted and observed in nature. Aims: We present generic model calculations to predict the properties of such nebulae for blue supergiants. Methods: From stellar evolution calculations including rotation, we obtain the time dependence of the

S. M. Chita; N. Langer; A. J. van Marle; G. García-Segura; A. Heger

2008-01-01

14

Multiple ring nebulae around blue supergiants  

NASA Astrophysics Data System (ADS)

Context: In the course of the life of a massive star, wind-wind interaction can give rise to the formation of circumstellar nebulae which are both predicted and observed in nature. Aims: We present generic model calculations to predict the properties of such nebulae for blue supergiants. Methods: From stellar evolution calculations including rotation, we obtain the time dependence of the stellar wind properties and of the stellar radiation field. These are used as input for hydro-calculations of the circumstellar medium throughout the star's life. Results: Here, we present the results for a rapidly rotating 12 {M}_? single star. This star forms a blue loop during its post main sequence evolution, at the onset of which its contraction spins it up close to critical rotation. Due to the consequent anisotropic mass loss, the blue supergiant wind sweeps up the preceding slow wind into an hourglass structure. Its collision with the previously formed spherical red supergiant wind shell forms a short-lived luminous nebula consisting of two polar caps and a central inner ring. With time, the polar caps evolve into mid-latitude rings which gradually move toward the equatorial plane while the central ring fades. These structures are reminiscent of the observed nebulae around the blue supergiant Sher 25 and the supernova 1987A. Conclusions: The simple model of an hourglass colliding with a spherical shell reproduces most of the intriguing nebula geometries discovered around blue supergiants, and suggests that they form an evolutionary sequence. Our results indicate that a binary system is not required to obtain them. Appendix A is only available in electronic form at http://www.aanda.org

Chita, S. M.; Langer, N.; van Marle, A. J.; García-Segura, G.; Heger, A.

2008-09-01

15

RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES. II. NLTE EFFECTS IN J-BAND SILICON LINES  

SciTech Connect

Medium-resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star-forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE (NLTE) calculations are presented to investigate the influence of NLTE on the formation of silicon lines in the J-band spectra of red supergiants. Substantial effects are found resulting in significantly stronger absorption lines of neutral silicon in NLTE. As a consequence, silicon abundances determined in NLTE are significantly smaller than in local thermodynamic equilibrium (LTE) with the NLTE abundance corrections varying smoothly between -0.4 dex and -0.1 dex for effective temperatures between 3400 K and 4400 K. The effects are largest at low metallicity. The physical reasons behind the NLTE effects and the consequences for extragalactic J-band abundance studies are discussed.

Bergemann, Maria; Kudritzki, Rolf-Peter; Wuerl, Matthias [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str.1, D-85741 Garching (Germany)] [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str.1, D-85741 Garching (Germany); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France)] [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France); Davies, Ben [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 OHA (United Kingdom)] [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 OHA (United Kingdom); Gazak, Zach, E-mail: mbergema@mpa-garching.mpg.de, E-mail: Matthias.Wuerl@physik.uni-muenchen.de, E-mail: kud@ifa.hawaii.edu, E-mail: zgazak@ifa.hawaii.edu, E-mail: bertrand.plez@univ-montp2.fr, E-mail: bdavies@ast.cam.ac.uk [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)] [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2013-02-20

16

Non-LTE studies of A-type supergiants  

NASA Astrophysics Data System (ADS)

The tenuous atmospheres of A-type supergiants are good sources for studying non-LTE physics. We present an overview of recent achievements in quantitative analyses of high-resolution spectra of Galactic A-type supergiants at optical and near-IR wavelengths, focusing on the nature and extent of non-LTE effects. We discuss their impact on determinations of atmospheric and fundamental stellar parameters and element abundances, and draw some conclusions regarding the evolutionary status of A-type supergiants.

Przybilla, N.; Butler, K.; Firnstein, M.

2014-11-01

17

PACS and SPIRE spectroscopy of the red supergiant VY CMa  

NASA Astrophysics Data System (ADS)

With a luminosity >105 L? and a mass-loss rate of ~2 × 10-4 M? yr-1, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55-672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ~1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Royer, P.; Decin, L.; Wesson, R.; Barlow, M. J.; Polehampton, E. T.; Matsuura, M.; Agúndez, M.; Blommaert, J. A. D. L.; Cernicharo, J.; Cohen, M.; Daniel, F.; Degroote, P.; De Meester, W.; Exter, K.; Feuchtgruber, H.; Gear, W. K.; Gomez, H. L.; Groenewegen, M. A. T.; Hargrave, P. C.; Huygen, R.; Imhof, P.; Ivison, R. J.; Jean, C.; Kerschbaum, F.; Leeks, S. J.; Lim, T.; Lombaert, R.; Olofsson, G.; Posch, T.; Regibo, S.; Savini, G.; Sibthorpe, B.; Swinyard, B. M.; Vandenbussche, B.; Waelkens, C.; Witherick, D. K.; Yates, J. A.

2010-07-01

18

PACS and SPIRE Spectroscopy of the Red Supergiant VY CMa  

E-print Network

With a luminosity > 10^5 Lsun and a mass-loss rate of about 2.10-4 Msun/yr, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VYCMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55 to 672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as 1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.

Royer, P; Wesson, R; Barlow, M J; Polehampton, E T; Matsuura, M; Agundez, M; Blommaert, J A D L; Cernicharo, J; Cohen, M; Daniel, F; Degroote, P; De Meester, W; Exter, K; Feuchtgruber, H; Gear, W K; Gomez, H L; Groenewegen, M A T; Hargrave, P C; Huygen, R; Imhof, P; Ivison, R J; Jean, C; Kerschbaum, F; Leeks, S J; Lim, T; Lombaert, R; Olofsson, G; Posch, T; Regibo, S; Savini, G; Sibthorpe, B; Swinyard, B M; Vandenbussche, B; Waelkens, C; Witherick, D K; Yates, J A

2010-01-01

19

Red Supergiants and Post-Red Supergiants - the Evidence for High Mass Loss Events  

NASA Astrophysics Data System (ADS)

The complex circumstellar environments associated with several of the most luminous cool supergiants provide evidence for episodic high mass loss events. The origin of the high mass loss is not understood but circumstantial evidence strongly suggests that large scale surface activity and magnetic fields are responsible. I briefly review the observational evidence from multi-epoch imaging and spectroscopy for the high mass loss events and instabilities in these stars. New results from high-resolution AO near and mid-IR imaging of VY CMa, IRC +10420 and ? Cep is also presented.

Humphreys, R. M.

2013-05-01

20

Red supergiants around the obscured open cluster Stephenson 2  

NASA Astrophysics Data System (ADS)

Context. Several clusters of red supergiants have been discovered in a small region of the Milky Way close to the base of the Scutum-Crux Arm and the tip of the Long Bar. Population synthesis models indicate that they must be very massive to harbour so many supergiants. Amongst these clusters, Stephenson 2, with a core grouping of 26 red supergiants, is a strong candidate to be the most massive young cluster in the Galaxy. Aims: Stephenson 2 is located close to a region where a strong over-density of red supergiants had been found. We explore the actual cluster size and its possible connection to this over-density. Methods: Taking advantage of Virtual Observatory tools, we have performed a cross-match between the DENIS, USNO-B1 and 2MASS catalogues to identify candidate obscured luminous red stars around Stephenson 2, and in a control nearby region. More than 600 infrared bright stars fulfill our colour criteria, with the vast majority having a counterpart in the I band and >400 being sufficiently bright in I to allow observation with a 4-m class telescope. We observed a subsample of ~250 stars, using the multi-object, wide-field, fibre spectrograph AF2 on the WHT telescope in La Palma, obtaining intermediate-resolution spectroscopy in the 7500-9000 Å range. We derived spectral types and luminosity classes for all these objects and measured their radial velocities. Results: Our targets turned out to be G and K supergiants, late (? M4) M giants, and M-type bright giants (luminosity class II) and supergiants. We found ~35 red supergiants with radial velocities similar to Stephenson 2 members, spread over the two areas surveyed. In addition, we found ~40 red supergiants with radial velocities incompatible in principle with a physical association. Conclusions: Our results show that Stephenson 2 is not an isolated cluster, but part of a huge structure likely containing hundreds of red supergiants, with radial velocities compatible with the terminal velocity at this Galactic longitude (and a distance ~6 kpc). In addition, we found evidence of several populations of massive stars at different distances along this line of sight. Based on observations collected at the William Herschel Telescope (La Palma, Spain).Tables 2 and 3 are available in electronic form at http://www.aanda.org

Negueruela, I.; Marco, A.; González-Fernández, C.; Jiménez-Esteban, F.; Clark, J. S.; Garcia, M.; Solano, E.

2012-11-01

21

Spectral Classification of Cold IRAS Stars: Supergiants  

NASA Astrophysics Data System (ADS)

We have observed 72 stars with low resolution optical spectra (85 A/mm with 2.3 A/pixel) covering 6000 to 8800 A in an attempt to identify the spectral type and luminosity class of a number of dusty IRAS sources. These stars were chosen from region IIIa of the van der Veen & Habing color-color diagram, where infrared late-type stars are found with generally strong 10?m silicate emission and often OH maser emission. We present here initial classficiation results. These include the probable identification of 19 new M0--4 supergiants and the re-classification of 3 stars formerly categorized as S stars: IRC+70012 (M8 III), NSV12260 (M8 III) and IRC+60374 (M4 I). \\begin{tabular}{|l|c|c|c|l|} IRAS name & old type & new type & other name 03572+5509 & M4 & M4 I & AG Cam 05361+4644 & M6 & M3 I & IRC+50149 17360-3140 & M6,K5 & M2 I & IRC-30309 17513-2313 & M5 & M4 I & V774 Sgr 18025-2113 & M2 & M3-4 I & IRC-20427 18135-1740 & M3 & M2 I & IRC-20455 18522+0021 & M5 & M4 I & IRC+00392 18539+0026 & M & M4 I & IRC+00396 19229+1708 & M4e & M3-4 I & 19307+1338 & & M0 I & 19325+2346 & K5,M0 & M2-3 I & 20004+2955 & K8 & K2-4 I & V1027 Cyg 20015+3019 & M4 & M4 I & V719 Cyg 22048+5914 & & M4 I & RAFGL 4286 22480+6002 & & M0 I & IRC+60370 22512+6100 & S & M4 I & IRC+60374 23000+5932 & M3 & M3 I & AS Cep 23252+6010 & & M4 I & 23278+6000 & M4 & M4 I & IRC+60409

Winfrey, S.; Barnbaum, C.; Morris, M.; Omont, A.

1994-12-01

22

Magnetic Braking of Stellar Cores in Red Giants and Supergiants  

NASA Astrophysics Data System (ADS)

Magnetic configurations, stable on the long term, appear to exist in various evolutionary phases, from main-sequence stars to white dwarfs and neutron stars. The large-scale ordered nature of these fields, often approximately dipolar, and their scaling according to the flux conservation scenario favor a fossil field model. We make some first estimates of the magnetic coupling between the stellar cores and the outer layers in red giants and supergiants. Analytical expressions of the truncation radius of the field coupling are established for a convective envelope and for a rotating radiative zone with horizontal turbulence. The timescales of the internal exchanges of angular momentum are considered. Numerical estimates are made on the basis of recent model grids. The direct magnetic coupling of the core to the extended convective envelope of red giants and supergiants appears unlikely. However, we find that the intermediate radiative zone is fully coupled to the core during the He-burning and later phases. This coupling is able to produce a strong spin down of the core of red giants and supergiants, also leading to relatively slowly rotating stellar remnants such as white dwarfs and pulsars. Some angular momentum is also transferred to the outer convective envelope of red giants and supergiants during the He-burning phase and later.

Maeder, André; Meynet, Georges

2014-10-01

23

Unveiling supergiant fast X-ray transient sources with INTEGRAL  

E-print Network

Supergiant high mass X-ray binaries (SGXBs) are believed to be rare objects, as stars in the supergiant phase have a very short lifetime and to date only about a dozen of them have been discovered. They are known to be persistent and bright X-ray sources. INTEGRAL is changing this classical picture as its observations are revealing the presence of a new subclass of SGXBs which have been labelled as supergiant fast X-ray transients (SFXTs) as they are strongly characterized by fast X-ray outbursts lasting less than a day, typically a few hours. We report on IBIS detections of newly discovered fast X-ray outbursts from 10 sources, four of which have been recently optically identified as supergiant high mass X-ray binaries. In particular for one of them, IGR J11215-5952, we observe fast X-ray transient behaviour for the first time. The remaining six sources (IGR J16479-4514, IGR J16418-4532, XTE J1743-363, IGR J16195-4945=AX J161929-4945, AX J1749.1-2733, IGR J17407-2808) are still unclassified, however they can be considered as candidate SFXTs because of their similarity to the known SFXTs.

V. Sguera; A. Bazzano; A. J. Bird; A. J. Dean; P. Ubertini; E. J. Barlow; L. Bassani; D. J. Clark; A. B. Hill; A. Malizia; M. Molina; J. B. Stephen

2006-03-28

24

Red supergiants as tracers of Perseus Arm structure  

NASA Astrophysics Data System (ADS)

We have performed a systematic search for red supergiants in the Perseus Arm (from l = 95 degrees up to l = 150 degrees). For this purpose we made a selection of candidates through photometric criteria, using data from UCAC, USNO and 2MASS catalogs. 747 stars were observed in the spectral region around the infrared Ca triplet (8400-8900 Å) at R ~ 10000, using the Intermediate Dispersion Spectrograph (IDS) on the Isaac Newton Telescope (INT, Roque de los Muchachos Observatory). From these data we have obtained radial velocities, spectral type and luminosity class, finding 353 supergiants. Using them we have analysed the distribution in the radial velocity-galactic latitude diagram, tracing the young clusters and galactic structure in this region.

Dorda, Ricardo; Negueruela, Ignacio; Gonzalez-Fernandez, Carlos

2013-06-01

25

Yellow Hypergiants as Dynamically Unstable Post-Red-supergiant Stars  

NASA Technical Reports Server (NTRS)

According to recent theoretical studies, the majority of single stars more massive than 30 solar mass successfully evolve into red supergiants, but then lose most of their hydrogen envelopes and metamorphose into hot blue remnants. While they are cool, they become dynamically unstable as a result of high radiation pressure and partial ionization of the gases in their outer layers. It is shown here that these unstable red-supergiant models repeatedly shrink and re-expand on a thermal time scale when perturbed by heavy bursts of mass loss. Consequently, they fill up the domain of yellow hypergiants on the Hertzsprung-Russell diagram and display very fast rates of evolution there, as observed.

Stothers, Richard B.; Chin, Chao-wen; Hansen, James E. (Technical Monitor)

2001-01-01

26

The blue supergiant Sher 25 and its intriguing hourglass nebula  

E-print Network

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log[O/H] = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M_sun, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

M. A. Hendry; S. J. Smartt; E. D. Skillman; C. J. Evans; C. Trundle; D. J. Lennon; P. A. Crowther; I. Hunter

2008-03-29

27

The blue supergiant Sher 25 and its intriguing hourglass nebula  

NASA Astrophysics Data System (ADS)

The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher25, and of the background nebula of the host cluster NGC3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + logO/H = 8.61 +/- 0.13dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting that the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models, they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50Msolar, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

Hendry, M. A.; Smartt, S. J.; Skillman, E. D.; Evans, C. J.; Trundle, C.; Lennon, D. J.; Crowther, P. A.; Hunter, I.

2008-08-01

28

The blue supergiant Sher 25 and its intriguing hourglass nebula  

Microsoft Academic Search

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped\\u000acircumstellar nebula. Its structure and dynamics have been studied previously\\u000athrough high-resolution imaging and spectroscopy, and it appears dynamically\\u000asimilar to the ring structure around SN 1987A. Here we present long-slit\\u000aspectroscopy of the circumstellar nebula around Sher 25, and of the background\\u000anebula of the host cluster NGC

M. A. Hendry; S. J. Smartt; E. D. Skillman; C. J. Evans; C. Trundle; D. J. Lennon; P. A. Crowther; I. Hunter

2008-01-01

29

The blue supergiant Sher 25 and its intriguing hourglass nebula  

Microsoft Academic Search

The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher25, and of the background nebula of the host cluster NGC3603. We perform a

M. A. Hendry; S. J. Smartt; E. D. Skillman; C. J. Evans; C. Trundle; D. J. Lennon; P. A. Crowther; I. Hunter

2008-01-01

30

Far-infrared circumstellar 'debris' shell of red supergiant stars  

NASA Technical Reports Server (NTRS)

An examination of IRAS data of red supergiant stars in the field and in galactic OB star associations indicates the presence of substantial amounts of 60-micron emitting material extending several arcminutes around many such sources. The characteristics of these large shells are discussed in terms of remnants of ongoing mass loss, and a simple model developed for the case of Alpha Orionis, in particular.

Stencel, Robert E.; Pesce, Joseph E.; Hagen Bauer, Wendy

1988-01-01

31

Clump Accretion in Supergiant Fast X-Ray Transients  

NASA Astrophysics Data System (ADS)

Supergiant Fast X-Ray Transients (SFXTs) are a subclass of High-Mass X-Ray Binaries that consist of a neutron star and OB supergiant donor star. These systems display short, bright x-ray flares lasting a few minutes to a few hours with luminosities reaching 1036 erg/s, several orders of magnitude larger than the quiescent luminosities of 1032 erg/s. The clumpy wind hypothesis has been proposed as a possible mechanism for these transient flares; in this model, a portion of the stellar wind from the donor star forms into clumps and is accreted onto the neutron star, inducing flares. We use high-resolution 3D hydrodynamic simulations to test the clumpy wind hypothesis, tracking the mass and angular momentum accretion rates to infer properties of the resulting x-ray flare and secular evolution of the neutron star rotation. Our results are significantly different from the predictions of Hoyle-Lyttleton Accretion (HLA) theory, which assume steady, laminar, axisymmetric flow. For example, an off-axis clump initiated with an impact parameter greater than the clump radius (for which HLA predicts no effect) produces a small spike in mass accretion and induces a long period of disk-like flow that dramatically reduces the accretion rate below the steady HLA value. The result is a brief, weak flare with a net decrease in total accreted mass compared with steady wind accretion accompanied by a substantial accretion of angular momentum.

Chase, Eve; Raymer, E.; Blondin, J. M.

2014-01-01

32

Detection of a red supergiant progenitor star of a type II-plateau supernova.  

PubMed

We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion, and subsequent HST images confirm the positional coincidence of the supernova with a single resolved star that is a red supergiant of 8(+4)(-2) solar masses. This confirms both stellar evolution models and supernova theories predicting that cool red supergiants are the immediate progenitor stars of type II-plateau supernovae. PMID:14739452

Smartt, Stephen J; Maund, Justyn R; Hendry, Margaret A; Tout, Christopher A; Gilmore, Gerard F; Mattila, Seppo; Benn, Chris R

2004-01-23

33

NGC 7419 as a template for red supergiant clusters  

NASA Astrophysics Data System (ADS)

Context. The open cluster NGC 7419 is known to contain five red supergiants and a very high number of Be stars. However, there are conflicting reports about its age and distance that prevent a useful comparison with other clusters. Aims: We intend to obtain more accurate parameters for NGC 7419, using techniques different from those of previous authors, so that it may be used as a calibrator for more obscured clusters. Methods: We obtained Strömgren photometry of the open cluster NGC 7419, as well as classification spectroscopy of ~20 stars in the area. We then applied standard analysis and classification techniques. Results: We find a distance of 4 ± 0.4 kpc and an age of 14 ± 2 Myr for NGC 7419. The main-sequence turn-off is found at spectral type B1, in excellent agreement. We identify 179 B-type members, implying that there are more than 1200 M? in B stars at present. Extrapolating this to lower masses indicates an initial cluster mass of between 7000 and 10 000 M?, depending on the shape of the initial mass function. We find a very high fraction (?40%) of Be stars around the turn-off, but very few Be stars at lower masses. We also report for the first time a strong variability in the emission characteristics of Be stars. We verified that the parameters of the red supergiant members can be used to obtain accurate cluster parameters. Conclusions: NGC 7419 is sufficiently massive to serve as a testbed for theoretical predictions and as a template to compare more obscured clusters. The distribution of stars above the main-sequence turn-off is difficult to accommodate with current evolutionary tracks. Though the presence of five red supergiants is marginally consistent with theoretical expectations, the high number of Be stars and very low number of luminous evolved B stars hint at some unknown physical factor that is not considered in current synthesis models. Partially based on observations collected at the Nordic Optical Telescope and the William Herschel Telescope (La Palma) and at the 1.93-m telescope at Observatoire de Haute Provence (CNRS), France.Tables 1 and 2 are available in electronic form at http://www.aanda.orgTables 3, 4 and 7 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A92

Marco, A.; Negueruela, I.

2013-04-01

34

Elemental abundances of the supergiant stars ? Cygnus and ? Leonis  

NASA Astrophysics Data System (ADS)

This study aims to analyse the elemental abundances for the late B type supergiant star ? Cyg and the early A-type supergiant ? Leo using ATLAS9 (Kurucz, 1995; Sbordone et al., 2004), assuming local thermodynamic equilibrium (LTE). The spectra used in this study are obtained from Dominion Astrophysical Observatory and have high resolution and signal-to-noise ratios. The effective temperature and the surface gravity of ? Cyg are determined from the ionisation equilibria of Al I/II, Mg I/II, Fe I/II, Fe II/III, and by fitting to the wings of H? and H? profiles as Teff = 10388 K and log g = 1.80. The elemental abundances of ? Leo are determined using Teff = 9600 K and log g = 2.00, as reported by Przybilla et al. (2006). The ionisation equilibria of C I/II, N I/II, Mg I/II, Ca I/II, Cr I/II and Fe I/II/III are also satisfied in the atmosphere of ? Leo. The radial velocities of ? Cyg and ? Leo are -7.25 ± 7.57 km s-1 and 10.40 ± 13.37 km s-1, respectively. The derived projected rotational velocities vsini from synthetic spectra are 27 and 2 km s-1 for both stars, respectively. The macroturbulent velocities (?) are 24 ± 2 km s-1 and 14.5 ± 1.5 km s-1. Also, the microturbulent velocities (?) have been determined for both of stars as 3.5 km s-1. The CNO abundance results of ? Cyg and ? Leo show C deficiency, N overabundance and O in excess.

Tanr?verdi, Taner

2013-12-01

35

Investigating supergiant fast X-ray transients with LOFT  

NASA Astrophysics Data System (ADS)

Supergiant Fast X-ray Transients (SFXT) are a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. LOFT, the Large Observatory For X-ray Timing, with its coded mask Wide Field Monitor (WFM) and its 10 m2 class collimated X-ray Large Area Detector (LAD), will be able to dramatically deepen the knowledge of this class of sources. It will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states, and long term monitoring that will yield new determinations of orbital periods, as well as spin periods. We show the results of an extensive set of simulations performed using previous observational results on these sources obtained with Swift and XMM-Newton. The WFM will detect all SFXT flares within its field of view down to a 15-20 mCrab in 5 ks. Our simulations describe the outbursts at several intensities (F(2-10keV) = 5.9×10-9 to 5.5 × 10-10 erg cm-2 s-1), the intermediate and most common state (10-11 erg cm-2 s-1), and the low state (1.2 × 10-12 to 5 × 10-13 erg cm-2 s-1). We also considered large variations of NH and the presence of emission lines, as observed by Swift and XMM-Newton.

Romano, P.; Bozzo, E.; Esposito, P.; Ferrigno, C.; Mangano, V.

2012-12-01

36

An Observational Evaluation of Magnetic Confinement in the Winds of BA Supergiants  

E-print Network

Magnetic wind confinement has been proposed as one explanation for the complex wind structures of supergiant stars of spectral types B and A. Observational investigation of this hypothesis was undertaken using high-resolution ({\\lambda}/{\\Delta}{\\lambda} {\\sim} 65,000) circular polarization (Stokes V ) spectra of six late B and early A type supergiants ({\\beta} Ori, B8Iae; 4 Lac, B9Iab; {\\eta} Leo, A0Ib; HR1040, A0Ib; {\\alpha} Cyg, A2Iae; {\

Shultz, M; Petit, V; Grunhut, J; Neiner, C; Hanes, D

2013-01-01

37

THE DUSTY CIRCUMSTELLAR DISKS OF B[e] SUPERGIANTS IN THE MAGELLANIC CLOUDS  

SciTech Connect

To better ascertain the nature of the infrared excesses that are characteristic of B[e] supergiants, we obtained Spitzer IRS spectroscopy and IRAC/MIPS imaging for a sample of nine B[e] supergiant stars in the Magellanic Clouds. We find that all nine stars display mid- to far-IR spectral and spatial characteristics indicative of the presence of circumstellar dust disks. Several of the sample B[e] supergiants display crystalline silicate features in their IRS spectra, consistent with grain processing in long-lived (i.e., orbiting) disks. Although it is possible that these disks are primordial in origin, large shell structures (with size scales of tens of parsec) are associated with five of the nine B[e] supergiants, suggesting that mass loss has provided the circumstellar material now orbiting these stars. Hence-via analogy to the class of post-asymptotic giant branch stars with binary companions and dusty, circumbinary disks-we speculate that B[e] supergiant stars may be post-red supergiants in binary systems with orbiting, circumbinary disks that are derived from post-main-sequence mass loss.

Kastner, Joel H. [Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Buchanan, Catherine [School of Physics, University of Melbourne, Victoria, 3010 (Australia); Sahai, Raghvendra [NASA/JPL, 4800 Oak Grove Drive, Pasadena, CA 1109 (United States); Forrest, William J. [Department of Physics and Astronomy, University of Rochester, Bausch and Lomb Hall, P.O. Box 270171, Rochester, NY 14627-0171 (United States); Sargent, Benjamin A., E-mail: jhk@cis.rit.ed, E-mail: clb@unimelb.edu.a [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2010-05-15

38

HD 50975: a yellow supergiant in a spectroscopic binary system  

NASA Astrophysics Data System (ADS)

Context. Recent detection of a yellow supergiant star as a possible progenitor of a supernova has posed serious questions about our understanding of the evolution of massive stars. Aims: The spectroscopic binary star HD 50975 with an unseen hot secondary was studied in detail with the main goal of estimating fundamental parameters of both components and the binary system. Methods: A comprehensive analysis and modeling of collected long-term radial velocity measurements, photometric data, and spectra was performed to calculate orbital elements, atmospheric parameters, abundances, and luminosities. The spectrum in an ultraviolet region was studied to clarify the nature of an unseen companion star. Results: The orbital period was found to be 190.22 ± 0.01 days. The primary star (hereafter HD 50975A) is a yellow supergiant with an effective temperature Teff = 5900 ± 150 K and a surface gravity of log (g) = 1.4 ± 0.3 (cgs). The atmosphere of HD 50975 A is slightly metal deficient relative to solar, [Fe/H] = -0.26 ± 0.06 dex. Abundances of Si and Ca are close to the scaled solar composition. The r-process element europium is enhanced, [Eu/H] = + 0.61 ± 0.07. The bolometric magnitude of the primary was estimated to be Mbol = -5.5 ± 0.3 mag and its mass to be 10.7 ± 2.0 M?. The secondary (hereafter HD 50975B) is a hot star of spectral type ~B2 near ZAMS with an effective temperature of Teff ? 21 000 K and a mass M ? 8.6 M?. The distance between HD 50975A and B is about 370 R?. The binary star is near a semi-detached configuration with a radius, RA ? 107 R?, and a radius of Roche lobe of about 120 R? for the primary star. The reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A3

Sperauskas, J.; Za?s, L.; Raudeli?nas, S.; Musaev, F.; Puzin, V.

2014-10-01

39

The blue supergiant Sher 25 and its intriguing hourglass nebula  

E-print Network

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log[O/H] = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the ph...

Hendry, M A; Skillman, E D; Evans, C J; Trundle, C; Lennon, D J; Crowther, P A; Hunter, I

2008-01-01

40

The atmospheric structure and fundamental parameters of Red Supergiants  

NASA Astrophysics Data System (ADS)

We present studies of the atmospheric structure and fundamental properties of the red supergiants (RSGs) VY CMa, AH Sco, UY Sct, and KW Sgr based on near-infrared K-band interferometry obtained with the VLTI/AMBER instrument with a spectral resolution of 1500. In our visibility data, we observe the presence of molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases in the water band centered at 1.9 ?m and in the CO band at 2.3-2.5 ?m, with respect to the near-continuum bandpass (2.20-2.25 ?m). With our spectral resolution, we obtain diameters in the near-continuum, that are free from contamination by molecular layers. Using PHOENIX atmosphere models, we estimate Rosseland-mean photospheric angular diameters of VY CMa, AH Sco, UY Sct, and KW Sgr of 11.13 ± 0.3mas, 5.81 ± 0.15mas, 5.48 ± 0.10mas, and 3.91 ± 0.25mas, respectively. We estimate radii and effective temperatures, and place the stars in the HR diagram. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but do not predict the molecular layers visibility well: The model atmosphere is too compact when compared with the observations. This may be caused by pulsation and/or convection, which are not included in the models.

Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H.

2013-05-01

41

No stellar age gradient inside supergiant shell LMC 4  

E-print Network

The youngest stellar populations of a 'J'-shaped region (400 pc strip E-W across LH 77 and 850 pc S-N) inside the supergiant shell (SGS) LMC 4 (with a diameter of 1.4 kpc) have been analysed with CCD photometry in B,V passbands. Isochrone fitting to the colour-magnitude diagrams yields ages in the range from 9 Myr to 16 Myr without correlation with the distance to the LMC 4 centre. We construct the luminosity function and the mass function of five regions to ensure that projection effects don't mask the results. The slopes lie in the expected range (gamma in [0.22;0.41] and Gamma in [-1.3;-2.4] respectively, with the Salpeter value of Gamma = -1.35). After our calculations a total of 5-7 10^3 supernovae has dumped the energy of 10^54.5 erg over the past 10 Myr into LMC 4, in fact enough to tear the original star-forming cloud apart in the time span between 5 and 8 Myr after the starformation burst, initiated by a large scale triggering event. We conclude that LMC 4 can have been formed without a contribution from stochastic self-propagating star formation (SSPSF).

Jochen M. Braun; Dominik J. Bomans; Jean-Marie Will; Klaas S. de Boer

1997-08-08

42

THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR  

SciTech Connect

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R {approx} 200 R{sub Sun }-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be Almost-Equal-To 2 M{sub Sun }, the explosion energy to be E = (6-10) Multiplication-Sign 10{sup 50} erg, and the {sup 56}Ni mass to be approximately 0.06 M{sub Sun }. The progenitor star was composed of a helium core of 3-4 M{sub Sun} and a thin hydrogen-rich envelope of Almost-Equal-To 0.1M{sub Sun} with a main-sequence mass estimated to be in the range of 12-15 M{sub Sun }. Our models rule out progenitors with helium-core masses larger than 8 M{sub Sun }, which correspond to M{sub ZAMS} {approx}> 25M{sub Sun }. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

Bersten, Melina C.; Nomoto, Ken'ichi; Folatelli, Gaston; Maeda, Keiichi [Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583 (Japan); Benvenuto, Omar G. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, B1900FWA La Plata (Argentina); Ergon, Mattias; Sollerman, Jesper [The Oskar Klein Centre, Department of Astronomy, AlbaNova, SE-106 91 Stockholm (Sweden); Benetti, Stefano; Ochner, Paolo; Tomasella, Lina [INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy); Botticella, Maria Teresa [INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli (Italy); Fraser, Morgan; Kotak, Rubina, E-mail: melina.bersten@ipmu.jp [Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN (United Kingdom)

2012-09-20

43

Supergiant X-Ray Binaries Observed by Suzaku  

NASA Technical Reports Server (NTRS)

Suzaku observations are presented for the high-mass X-ray binaries IGR 116207-5129 and IGR 117391-3021. For IGR 116207-5129, we provide the first X-ray broadband (0.5-60 keV) spectrum from which we confirm a large intrinsic column density (N(sub H) = 1.6 x 10(exp 23)/sq cm), and we constrain the cutoff energy for the first time (E(sub cut) = 19 keV). A prolonged (> 30 ks) attenuation of the X-ray flux was observed which we tentatively attribute to an eclipse of the probable neutron star by its massive companion, in a binary system with an orbital period between 4 and 9 days, and inclination angles> 50 degrees. For IGRJ17391-3021, we witnessed a transition from quiescence to a low-activity phase punctuated by weak flares whose peak luminosities in the 0.5-10keV band are only a factor of 5 times that of the pre-flare emission. These micro flares are accompanied by an increase in NH which suggests the accretion of obscuring clumps of wind. We now recognize that these low-activity epochs constitute the most common emission phase for this system, and perhaps in other supergiant fast X-ray transients (SFXTs) as well. We close with an overview of our upcoming program in which Suzaku will provide the first ever observation of an SFXT (IGRJ16479-4514) during a binary orbit enabling us to probe the accretion wind at every phase.

Bodaghee, A.; Tomsick, J. A.; Rodriquez, J.; Chaty, S.; Pottschmidt, K.; Walter, R.; Romano, P.

2011-01-01

44

Near-infrared spectroscopy of candidate red supergiant stars in clusters  

E-print Network

Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks red supergiant stars with masses from 10 Msun to 15 Msun. Two red supergiants are located at Galactic coordinates (l,b)=(16.7deg,-0.63deg) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b)=(49.3deg,+0.72deg) and at a distance of ~7.0 kpc. Spectroscopic analysis of the brightest stars of detected overdensities and st...

Messineo, Maria; Ivanov, Valentin D; Figer, Donald F; Davies, Ben; Menten, Karl M; Kudritzki, Rolf P; Chen, C -H Rosie

2014-01-01

45

The galatic and LMC extreme line supergiants compared: IUE observations of the Henize-Carlson and Zoo star samples of massive supergiants. [Large Magellanic cloud (LMC)  

NASA Technical Reports Server (NTRS)

The Henize-Carlson sample of galactic massive supergiants, and a comparison between the Galactic and LMC samples are discussed. Several of the stars, notably He3-395 and S 127/LMC, have very similar shell characteristics. There appears to be little difference, other than luminosity, between the LMC and Galactic samples. One star, He3-1482, was detected with the Very Large Array at 6 cm. The UV data is combined with IRAS and optical information.

Shore, S. N.; Sanduleak, N.; Brown, D. N.; Sonneborn, G.; Bopp, B. W.; Robinson, C. R.

1988-01-01

46

SUPERNOVA 2008bk AND ITS RED SUPERGIANT PROGENITOR  

SciTech Connect

We have obtained limited photometric and spectroscopic data for supernova (SN) 2008bk in NGC 7793, primarily at {approx}> 150 days after explosion. We find that it is a Type II-Plateau (II-P) SN that most closely resembles the low-luminosity SN 1999br in NGC 4900. Given the overall similarity between the observed light curves and colors of SNe 2008bk and 1999br, we infer that the total visual extinction to SN 2008bk (A{sub V} = 0.065 mag) must be almost entirely due to the Galactic foreground, similar to what has been assumed for SN 1999br. We confirm the identification of the putative red supergiant (RSG) progenitor star of the SN in high-quality g'r'i' images we had obtained in 2007 at the Gemini-South 8 m telescope. Little ambiguity exists in this progenitor identification, qualifying it as the best example to date, next to the identification of the star Sk -69 Degree-Sign 202 as the progenitor of SN 1987A. From a combination of photometry of the Gemini images with that of archival, pre-SN, Very Large Telescope JHK{sub s} images, we derive an accurate observed spectral energy distribution (SED) for the progenitor. We find from nebular strong-intensity emission-line indices for several H II regions near the SN that the metallicity in the environment is likely subsolar (Z Almost-Equal-To 0.6 Z{sub Sun }). The observed SED of the star agrees quite well with synthetic SEDs obtained from model RSG atmospheres with effective temperature T{sub eff} = 3600 {+-} 50 K. We find, therefore, that the star had a bolometric luminosity with respect to the Sun of log (L{sub bol}/L{sub Sun} ) = 4.57 {+-} 0.06 and radius R{sub *} = 496 {+-} 34 R{sub Sun} at {approx}6 months prior to explosion. Comparing the progenitor's properties with theoretical massive-star evolutionary models, we conclude that the RSG progenitor had an initial mass in the range of 8-8.5 M{sub Sun }. This mass is consistent with, albeit at the low end of, the inferred range of initial masses for SN II-P progenitors. It is also consistent with the estimated upper limit on the initial mass of the progenitor of SN 1999br, and it agrees with the low initial masses found for the RSG progenitors of other low-luminosity SNe II-P.

Van Dyk, Schuyler D.; Elias-Rosa, Nancy [Spitzer Science Center/Caltech, Mailcode 220-6, Pasadena, CA 91125 (United States); Davidge, Tim J., E-mail: vandyk@ipac.caltech.edu, E-mail: tim.davidge@nrc.ca [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, B.C., V9E 2E7 (Canada); and others

2012-01-15

47

RED SUPERGIANTS IN THE ANDROMEDA GALAXY (M31)  

SciTech Connect

Red supergiants (RSGs) are a short-lived stage in the evolution of moderately massive stars (10-25 M{sub sun}), and as such their location in the H-R diagram provides an exacting test of stellar evolutionary models. Since massive star evolution is strongly affected by the amount of mass loss a star suffers, and since the mass-loss rates depend upon metallicity, it is highly desirable to study the physical properties of these stars in galaxies of various metallicities. Here we identify a sample of RSGs in M31, the most metal-rich of the Local Group galaxies. We determine the physical properties of these stars using both moderate resolution spectroscopy and broadband V - K photometry. We find that on average the RSGs of our sample are variable in V by 0.5 mag, smaller but comparable to the 0.9 mag found for Magellanic Cloud (MC) RSGs. No such variability is seen at K, also in accord with what we know of Galactic and MC RSGs. We find that there is a saturation effect in the model TiO band strengths with metallicities higher than solar. The physical properties we derive for the RSGs from our analysis with stellar atmosphere models agree well with the current evolutionary tracks, a truly remarkable achievement given the complex physics involved in each. We do not confirm an earlier result that the upper luminosities of RSGs depend upon metallicity; instead, the most luminous RSGs have log L/L{sub sun}{approx}5.2-5.3, broadly consistent but slightly larger than that recently observed by Smartt et al. as the upper luminosity limit to Type II-P supernovae, believed to have come from RSGs. We find that, on average, the RSGs are considerably more reddened than O and B stars, suggesting that circumstellar dust is adding a significant amount of extra extinction, {approx}0.5 mag, on average. This is in accord with our earlier findings on Milky Way and Magellanic Cloud stars. Finally, we call attention to a peculiar star whose spectrum appears to be heavily veiled, possibly due to scattering by an expanding dust shell.

Massey, Philip [Lowell Observatory, 1400 West Mars Hill Rd., Flagstaff, AZ 86001 (United States); Silva, David R.; Olsen, Knut A. G. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85748 (United States); Levesque, Emily M. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Plez, Bertrand [GRAAL, Universite Montpellier II, CNRS, 34095 Montpellier (France); Clayton, Geoffrey C. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Meynet, Georges; Maeder, Andre, E-mail: phil.massey@lowell.ed, E-mail: dsilva@noao.ed, E-mail: kolsen@noao.ed, E-mail: emsque@ifa.hawaii.ed, E-mail: bertrand.plez@graal.univ-montp2.f, E-mail: gclayton@fenway.phys.lsu.ed, E-mail: georges.meynet@unige.c, E-mail: andre.maeder@unige.c [Geneva University, Geneva Observatory, CH-1290 Versoix (Switzerland)

2009-09-20

48

RAPIDLY ACCRETING SUPERGIANT PROTOSTARS: EMBRYOS OF SUPERMASSIVE BLACK HOLES?  

SciTech Connect

Direct collapse of supermassive stars (SMSs) is a possible pathway for generating supermassive black holes in the early universe. It is expected that an SMS could form via very rapid mass accretion with M-dot{sub *} {approx} 0.1-1 M{sub Sun} yr{sup -1} during the gravitational collapse of an atomic-cooling primordial gas cloud. In this paper, we study how stars would evolve under such extreme rapid mass accretion, focusing on the early evolution until the stellar mass reaches 10{sup 3} M{sub Sun }. To this end, we numerically calculate the detailed interior structure of accreting stars with primordial element abundances. Our results show that for accretion rates higher than 10{sup -2} M{sub Sun} yr{sup -1}, stellar evolution is qualitatively different from that expected at lower rates. While accreting at these high rates, the star always has a radius exceeding 100 R{sub Sun }, which increases monotonically with the stellar mass. The mass-radius relation for stellar masses exceeding {approx}100 M{sub Sun} follows the same track with R{sub *}{proportional_to}M {sup 1/2}{sub *} in all cases with accretion rates {approx}> 10{sup -2} M{sub Sun} yr{sup -1}; at a stellar mass of 10{sup 3} M{sub Sun }, the radius is {approx_equal} 7000 R{sub Sun} ({approx_equal} 30 AU). With higher accretion rates, the onset of hydrogen burning is shifted toward higher stellar masses. In particular, for accretion rates exceeding M-dot{sub *}{approx}>0.1 M{sub Sun} yr{sup -1}, there is no significant hydrogen burning even after 10{sup 3} M{sub Sun} have accreted onto the protostar. Such 'supergiant' protostars have effective temperatures as low as T{sub eff} {approx_equal} 5000 K throughout their evolution and because they hardly emit ionizing photons, they do not create an H II region or significantly heat their immediate surroundings. Thus, radiative feedback is unable to hinder the growth of rapidly accreting stars to masses in excess of 10{sup 3} M{sub Sun} as long as material is accreted at rates M-dot{sub *}{approx}>10{sup -2} M{sub Sun} yr{sup -1}.

Hosokawa, Takashi; Yorke, Harold W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Omukai, Kazuyuki, E-mail: Takashi.Hosokawa@jpl.nasa.gov, E-mail: hosokwtk@gmail.com, E-mail: omukai@tap.scphys.kyoto-u.ac.jp [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

2012-09-01

49

X-ray Spectroscopy of O Supergiant Winds: Shock Physics, Clumping, and Mass-Loss Rates  

E-print Network

X-ray Spectroscopy of O Supergiant Winds: Shock Physics, Clumping, and Mass-Loss Rates David Cohen-ray emission: wind shocks 1. X-ray constraints on the shocked wind plasma 2. X-ray absorption as a mass. Adiabatic shocks Open questions: very dense winds (WR stars); low density winds (B stars); magnetic OB stars

Cohen, David

50

Water vapor on supergiants. The 12 micron TEXES spectra of mu Cephei  

E-print Network

Several recent papers have argued for warm, semi-detached, molecular layers surrounding red giant and supergiant stars, a concept known as a MOLsphere. Spectroscopic and interferometric analyses have often corroborated this general picture. Here, we present high-resolution spectroscopic data of pure rotational lines of water vapor at 12 microns for the supergiant mu Cephei. This star has often been used to test the concept of molecular layers around supergiants. Given the prediction of an isothermal, optically thick water-vapor layer in Local Thermodynamic Equilibrium around the star (MOLsphere), we expected the 12 micron lines to be in emission or at least in absorption but filled in by emission from the molecular layer around the star. Our data, however, show the contrary; we find definite absorption. Thus, our data do not easily fit into the suggested isothermal MOLsphere scenario. The 12 micron lines, therefore, put new, strong constraints on the MOLsphere concept and on the nature of water seen in signatures across the spectra of early M supergiants. We also find that the absorption is even stronger than that calculated from a standard, spherically symmetric model photosphere without any surrounding layers. A cool model photosphere, representing cool outer layers is, however, able to reproduce the lines, but this model does not account for water vapor emission at 6 microns. Thus, a unified model for water vapor on mu Cephei appears to be lacking. It does seem necessary to model the underlying photospheres of these supergiants in their whole complexity. The strong water vapor lines clearly reveal inadequacies of classical model atmospheres.

N. Ryde; M. J. Richter; G. M. Harper; K. Eriksson; D. L. Lambert

2006-03-15

51

The Red and Yellow Supergiants in M33: Kinematics and Massive Star Evolution  

NASA Astrophysics Data System (ADS)

Massive star evolution is hard to model, owing to the complications of mass-loss, uncertainties over mixing and convection, the effects of rotation, and so on. It is generally agreed that the most massive stars spend their He-burning lives as Wolf-Rayet stars. Stars of slightly smaller masses spend most of their He-burning phase as red supergiants, after briefly passing through a yellow supergiant phase. We are interested in identifying the numbers and physical properties of these stars throughout the star-forming galaxies of the Local Group in an effort to test stellar evolutionary models at varying metallicities. However, foreground contamination by Milky Way dwarfs is severe for both the yellow supergiants (YSGs) and red supergiants (RSGs). Using the photometry of the Local Group Galaxy Survey, we have used two-color information (B-V vs V-R) to separate likely foreground dwarfs from bona fide RSGs in M33, and obtained radial velocities with Hectospec on the 6.5-m MMT. The radial velocities refine the rotation curves of previous studies, and demonstrate that the rotation curve is quite flat. With the new velocity data we then separate the yellow supergiant population from the foreground using radial velocities as well. Since the number of Wolf-Rayet stars is now known to a few percent in M33 (Neugent et al. 2011, ApJ, in press, as well as poster at this meeting) it is now possible to compare the numbers of RSGs, YSGs, and WRs in this nearby spiral. This work is supported by the National Science Foundation through AST-1008020.

Massey, Philip; Drout, M.; Tokarz, S.; Caldwell, N.

2011-05-01

52

Discovery of the First B[e] Supergiants in M 31  

NASA Astrophysics Data System (ADS)

B[e] supergiants (B[e]SGs) are transitional objects in the post-main sequence evolution of massive stars. The small number of B[e]SGs known so far in the Galaxy and the Magellanic Clouds indicates that this evolutionary phase is short. Nevertheless, the strong aspherical mass loss occurring during this phase, which leads to the formation of rings or disk-like structures, and the similarity to possible progenitors of SN1987 A emphasize the importance of B[e]SGs for the dynamics of the interstellar medium as well as stellar and galactic chemical evolution. The number of objects and their mass-loss behavior at different metallicities are essential ingredients for accurate predictions from stellar and galactic evolution calculations. However, B[e]SGs are not easily identified, as they share many characteristics with luminous blue variables (LBVs) in their quiescent (hot) phase. We present medium-resolution near-infrared K-band spectra for four stars in M 31, which have been assigned a hot LBV (candidate) status. Applying diagnostics that were recently developed to distinguish B[e]SGs from hot LBVs, we classify two of the objects as bonafide LBVs; one of them currently in outburst. In addition, we firmly classify the two stars 2MASS J00441709+4119273 and 2MASS J00452257+4150346 as the first B[e]SGs in M 31 based on strong CO band emission detected in their spectra, and infrared colors typical for this class of stars. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), under program ID GN-2013B-Q-10.

Kraus, M.; Cidale, L. S.; Arias, M. L.; Oksala, M. E.; Borges Fernandes, M.

2014-01-01

53

The population of M-type supergiants in the starburst cluster Stephenson 2  

NASA Astrophysics Data System (ADS)

The open cluster Stephenson 2 contains the largest collection of red supergiants known in the Galaxy, and at present is the second most massive young cluster known in the Milky Way. We have obtained multi-epoch, intermediate-resolution spectra around the Ca ii triplet for more than 30 red supergiants in Stephenson 2 and its surroundings. We find a clear separation between a majority of RSGs having spectral types M0-M2 and the brightest members in the NIR, which have very late spectral types and show strong evidence for heavy mass loss. The distribution of spectral types is similar to that of RSGs in other clusters, such as NGC 7419, or associations, like Per OB1. The cluster data strongly support the idea that heavy mass loss and maser emission is preferentially associated with late-M spectral types, suggesting that they represent an evolutionary phase.

Negueruela, I.; González-Fernández, C.; Dorda, R.; Marco, A.; Clark, J. S.

2013-05-01

54

Properties of the CO and H$_2$O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations  

E-print Network

Context. Betelgeuse is the closest red supergiant (RSG), therefore it is well suited to study the complex processes in its atmosphere that lead to the chemical enrichment of the interstellar medium. Aims. We intend to investigate the shape and composition of the close molecular layer (also known as the MOLsphere) that surrounds the star. This analysis is part of a wider program that aims at understanding the dynamics of the circumstellar envelope of Betelgeuse. Methods. On January and February 2011, Betelgeuse was observed using the VLTI/AMBER interferometer in the H and K bands. Using the medium spectral resolution of the instrument ($R \\sim 1500$), we were able to investigate the carbon monoxide band heads and the water-vapor bands. We used two different approaches to analyse our data: model fitting both in the continuum and absorption lines and then fit with a RHD simulation. Results. Using the continuum data we derive a uniform disk diameter of $41.01 \\pm 0.41$ mas, a power law type limb-darkened disk dia...

Montargès, Miguel; Perrin, Guy; Ohnaka, Keiichi; Chiavassa, Andrea; Ridgway, Stephen T; Lacour, Sylvestre

2014-01-01

55

A Transient Supergiant X-Ray Binary in IC 10: An Extragalactic SFXT?  

NASA Astrophysics Data System (ADS)

We report the discovery of a large amplitude (factor of ~100) X-ray transient (IC 10 X-2, CXOU J002020.99+591758.6) in the nearby dwarf starburst galaxy IC 10 during our Chandra monitoring project. Based on the X-ray timing and spectral properties, and an optical counterpart observed with Gemini, the system is a high-mass X-ray binary consisting of a luminous blue supergiant and a neutron star. The highest measured luminosity of the source was 1.8 × 1037 erg s-1during an outburst in 2003. Observations before, during, and after a second outburst in 2010 constrain the outburst duration to be less than 3 months (with no lower limit). The X-ray spectrum is a hard power law (? = 0.3) with fitted column density (NH = 6.3 × 1021 atom cm-2), consistent with the established absorption to sources in IC 10. The optical spectrum shows hydrogen Balmer lines strongly in emission at the correct blueshift (-340 km s-1) for IC 10. The N III triplet emission feature is seen, accompanied by He II [4686] weakly in emission. Together these features classify the star as a luminous blue supergiant of the OBN subclass, characterized by enhanced nitrogen abundance. Emission lines of He I are seen, at similar strength to H?. A complex of Fe II permitted and forbidden emission lines are seen, as in B[e] stars. The system closely resembles galactic supergiant fast X-ray transients, in terms of its hard spectrum, variability amplitude, and blue supergiant primary.

Laycock, Silas; Cappallo, Rigel; Oram, Kathleen; Balchunas, Andrew

2014-07-01

56

LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX  

NASA Astrophysics Data System (ADS)

In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV~-7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 271 days, and the light curve is well fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed of two yellow supergiants (V-I~=1 mag, Teff~=4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however, note a second example. The SMC F0 supergiant R47 is a bright (MV~-7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well fit as a contact binary with a 181 day period. We propose that these systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage. We also discuss the possibility of this variable being a long-period Cepheid. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

Prieto, J. L.; Stanek, K. Z.; Kochanek, C. S.; Weisz, D. R.; Baruffolo, A.; Bechtold, J.; Burwitz, V.; De Santis, C.; Gallozzi, S.; Garnavich, P. M.; Giallongo, E.; Hill, J. M.; Pogge, R. W.; Ragazzoni, R.; Speziali, R.; Thompson, D. J.; Wagner, R. M.

2008-01-01

57

Near-infrared spectroscopy of candidate red supergiant stars in clusters  

NASA Astrophysics Data System (ADS)

Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims: We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods: We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks< 7 mag) in GLIMPSE and 2MASS images. Results: A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M? to 15 M?. Two red supergiants are located at Galactic coordinates (l,b) = (16.°7, -0.°63) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b) = (49.°3, + 0.°72) and at a distance of ~7.0 kpc. Conclusions: Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. Based on observations collected at the European Southern Observatory (ESO Programme 60.A-9700(E), and 089.D-0876), and on observations collected at the UKIRT telescope (programme ID H243NS).MM is currently employed by the MPIfR. Part of this work was performed at RIT (2009), at ESA (2010), and at the MPIfR.Tables 3, 4, and 6 are available in electronic form at http://www.aanda.org

Messineo, Maria; Zhu, Qingfeng; Ivanov, Valentin D.; Figer, Donald F.; Davies, Ben; Menten, Karl M.; Kudritzki, Rolf P.; Chen, C.-H. Rosie

2014-11-01

58

Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei  

E-print Network

We report a detection of water in emission in the spectrum of the M2 supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer (SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO Archives. The emission first appears in the 6 micron region (nu2 fundamental) and then in the 40 micron region (pure rotation lines) despite the rather strong dust emission. The intensity ratios of the emission features are far from those of the optically thin gaseous emission. Instead, we could reproduce the major observed emission features by an optically thick water sphere of the inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) = 3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission provides strong constraints on the nature of water in the early M supergiant stars, and especially its origin in the outer atmosphere is confirmed against other models such as the large convective cell model. We finally confirm that the early M supergiant star is surrounded by a huge optically thick sphere of the warm water vapor, which may be referred to as MOLsphere for simplicity. Thus, the outer atmosphere of M supergiant stars should have a complicated hierarchical and/or hybrid structure with at least three major constituents including the warm MOLsphere (T about 1.0E+3K) together with the previously known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope (T about 1.0E+2K).

T. Tsuji

2000-08-03

59

An observational evaluation of magnetic confinement in the winds of BA supergiants  

NASA Astrophysics Data System (ADS)

Magnetic wind confinement has been proposed as one explanation for the complex wind structures of supergiant stars of spectral types B and A. Observational investigation of this hypothesis was undertaken using high-resolution (?/?? ˜ 65 000) circular polarization (Stokes V) spectra of six late B- and early A-type supergiants (? Ori, B8Iae; 4 Lac, B9Iab; ? Leo, A0Ib; HR1040, A0Ib; ? Cyg, A2Iae; ? Cep, A2Iab), obtained with the instruments ESPaDOnS and Narval at the Canada-France-Hawaii Telescope and the Bernard Lyot Telescope. Least-squares deconvolution (LSD) analysis of the Stokes V spectra of all stars yields no evidence of a magnetic field, with best longitudinal field 1? error bars ranging from ˜0.5 to ˜4.5 G for most stars. Spectrum synthesis analysis of the LSD profiles using Bayesian inference yields an upper limit with 95.4 per cent credibility on the polar strength of the (undetected) surface dipole fields of individual stars ranging from 3 to 30 G. These results strongly suggest that magnetic wind confinement due to organized dipolar magnetic fields is not the origin of the wind variability of BA supergiant stars. Upper limits for magnetic spots may also be inconsistent with magnetic wind confinement in the limit of large spot size and filling factor, depending on the adopted wind parameters. Therefore, if magnetic spots are responsible for the wind variability of BA supergiant stars, they likely occupy a small fraction of the photosphere.

Shultz, M.; Wade, G. A.; Petit, V.; Grunhut, J.; Neiner, C.; Hanes, D.; MiMeS Collaboration

2014-02-01

60

Systematic detection of magnetic fields in massive, late-type supergiants  

NASA Astrophysics Data System (ADS)

We report the systematic detection of magnetic fields in massive (M > 5Msolar) late-type supergiants, using spectropolarimetric observations obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations reveal detectable Stokes V Zeeman signatures in least-squares deconvolved mean line profiles in one-third of the observed sample of more than 30 stars. The signatures are sometimes complex, revealing multiple reversals across the line. The corresponding longitudinal magnetic field is seldom detected, although our longitudinal field error bars are typically 0.3 G (1?). These characteristics suggest topologically complex magnetic fields, presumably generated by dynamo action. The Stokes V signatures of some targets show clear time variability, indicating either rotational modulation or intrinsic evolution of the magnetic field. We also observe a weak correlation between the unsigned longitudinal magnetic field and the CaII K core emission equivalent width of the active G2Iab supergiant ? Dra and the G8Ib supergiant ? Gem. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii. E-mail: Jason.Grunhut@rmc.ca

Grunhut, J. H.; Wade, G. A.; Hanes, D. A.; Alecian, E.

2010-11-01

61

Detection of a 1.59h Period in the B Supergiant Star HD 202850  

NASA Astrophysics Data System (ADS)

Photospheric lines of B-type supergiants show variability in their profile shapes. In addition, their widths are much larger than purely due to stellar rotation. This excess broadening is often referred to as macroturbulence. Both effects have been linked to stellar oscillations, however B supergiants have not been systematically searched yet for the presence of especially short-term variability caused by stellar pulsations. We obtained four time-series of high-quality optical spectra for the Galactic B supergiant HD 202850 with Ond?ejov 2-m telescope. The spectral coverage of about 500Å, around H_? encompasses the Si II (6347, 6371 Å) and He I (6678 Å) photospheric lines. Their time-series display a simultaneous, periodic variability in their profile shapes. Proper analysis using the moment method revealed a period of 1.59 hours in all three lines. This period is found to be stable with time over the observed span of 19 months. This period is much shorter than the rotation period of the star and might be ascribed to stellar oscillations. Since the star seems to fall outside the currently known pulsational instability domains, the nature of the discovered oscillation remains unclear.

Tomic, S.; Kraus, M.; Oksala, M.; Smole, M.

2013-05-01

62

Spectral atlas of O9.5-A1-Type supergiants  

NASA Astrophysics Data System (ADS)

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 ( ? 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.

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

2007-09-01

63

SUPERGIANT SHELLS AND MOLECULAR CLOUD FORMATION IN THE LARGE MAGELLANIC CLOUD  

SciTech Connect

We investigate the influence of large-scale stellar feedback on the formation of molecular clouds in the Large Magellanic Cloud (LMC). Examining the relationship between H I and {sup 12}CO(J = 1-0) in supergiant shells (SGSs), we find that the molecular fraction in the total volume occupied by SGSs is not enhanced with respect to the rest of the LMC disk. However, the majority of objects ({approx}70% by mass) are more molecular than their local surroundings, implying that the presence of a supergiant shell does on average have a positive effect on the molecular gas fraction. Averaged over the full SGS sample, our results suggest that {approx}12%-25% of the molecular mass in supergiant shell systems was formed as a direct result of the stellar feedback that created the shells. This corresponds to {approx}4%-11% of the total molecular mass of the galaxy. These figures are an approximate lower limit to the total contribution of stellar feedback to molecular cloud formation in the LMC, and constitute one of the first quantitative measurements of feedback-triggered molecular cloud formation in a galactic system.

Dawson, J. R.; Dickey, John M. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia)] [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); McClure-Griffiths, N. M. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield NSW 2122 (Australia)] [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield NSW 2122 (Australia); Wong, T. [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States)] [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States); Hughes, A. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany)] [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Fukui, Y. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan)] [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan); Kawamura, A., E-mail: joanne.dawson@utas.edu.au [National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan)

2013-01-20

64

Interacting supernovae from photoionization-confined shells around red supergiant stars  

E-print Network

Betelgeuse, a nearby red supergiant, is a runaway star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have significantly more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas...

Mackey, Jonathan; Gvaramadze, Vasilii V; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M -A; Moriya, Takashi J; Neilson, Hilding R

2014-01-01

65

Interacting supernovae from photoionization-confined shells around red supergiant stars.  

PubMed

Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction. PMID:25119040

Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M-A; Moriya, Takashi J; Neilson, Hilding R

2014-08-21

66

Quantitative spectroscopy of Galactic BA-type supergiants. I. Atmospheric parameters  

NASA Astrophysics Data System (ADS)

Context. BA-type supergiants show a high potential as versatile indicators for modern astronomy. This paper constitutes the first in a series that aims at a systematic spectroscopic study of Galactic BA-type supergiants. Various problems will be addressed, including in particular observational constraints on the evolution of massive stars and a determination of abundance gradients in the Milky Way. Aims: The focus here is on the determination of accurate and precise atmospheric parameters for a sample of Galactic BA-type supergiants as prerequisite for all further analysis. Some first applications include a recalibration of functional relationships between spectral-type, intrinsic colours, bolometric corrections and effective temperature, and an exploration of the reddening-free Johnson Q and Strömgren [c1] and ?-indices as photometric indicators for effective temperatures and gravities of BA-type supergiants. Methods: An extensive grid of theoretical spectra is computed based on a hybrid non-LTE approach, covering the relevant parameter space in effective temperature, surface gravity, helium abundance, microturbulence and elemental abundances. The atmospheric parameters are derived spectroscopically by line-profile fits of our theoretical models to high-resolution and high-S/N spectra obtained at various observatories. Ionization equilibria of multiple metals and the Stark-broadened hydrogen and the neutral helium lines constitute our primary indicators for the parameter determination, supplemented by (spectro-)photometry from the UV to the near-IR. Results: We obtain accurate atmospheric parameters for 35 sample supergiants from a homogeneous analysis. Data on effective temperatures, surface gravities, helium abundances, microturbulence, macroturbulence and rotational velocities are presented. The interstellar reddening and the ratio of total-to-selective extinction towards the stars are determined. Our empirical spectral-type-Teff scale is steeper than reference relations from the literature, the stars are significantly bluer than usually assumed, and bolometric corrections differ significantly from established literature values. Photometric Teff-determinations based on the reddening-free Q-index are found to be of limited use for studies of BA-type supergiants because of large errors of typically ±5% (1? statistical) ±3% (1? systematic), compared to a spectroscopically achieved precision of 1-2% (combined statistical and systematic uncertainty with our methodology). The reddening-free [c1] -index and ? on the other hand are found to provide useful starting values for high-precision/accuracy analyses, with uncertainties of ±1% ± 2.5% in Teff, and ±0.04 ± 0.13 dex in log g (1?-statistical, 1?-systematic, respectively). Based on observations collected at the Centro Astronómico Hispano Alemán at Calar Alto (CAHA), operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), proposals H2001-2.2-011 and H2005-2.2-016.Based on observations obtained at the European Southern Observatory, proposals 62.H-0176 and 079.B-0856(A). Additional data were adopted from the UVES Paranal Observatory Project (ESO DDT Program ID 266.D-5655).

Firnstein, M.; Przybilla, N.

2012-07-01

67

XTE J1739-302 as a Supergiant Fast X-ray Transient  

E-print Network

XTE J1739-302 is a transient X-ray source with unusually short outbursts, lasting on the order of hours. Here we give a summary of X-ray observations we have made of this object in outburst with the Rossi X-ray Timing Explorer (RXTE) and at a low level of activity with the Chandra X-ray Observatory, as well as observations made by other groups. Visible and infrared spectroscopy of the mass donor of XTE J1739-302 are presented in a companion paper. The X-ray spectrum is hard both at low levels and in outburst, but somewhat variable, and there is strong variability in the absorption column from one outburst to another. Although no pulsation has been observed, the outburst data from multiple observatories show a characteristic timescale for variability on the order of 1500-2000 s. The Chandra localization (right ascension 17h 39m 11.58s, declination -30o 20' 37.6'', J2000) shows that despite being located less than 2 degrees from the Galactic Center and highly absorbed, XTE J1739-302 is actually a foreground object with a bright optical counterpart. The combination of a very short outburst timescale and a supergiant companion is shared with several other recently-discovered systems, forming a class we designate as Supergiant Fast X-ray Transients (SFXTs). Three persistently bright X-ray binaries with similar supergiant companions have also produced extremely short, bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.

D. M. Smith; W. A. Heindl; C. B. Markwardt; J. H. Swank; I. Negueruela; T. E. Harrison; L. Huss

2005-10-21

68

On the possible existence of brightness spots on the Cyg X-1 supergiant  

NASA Astrophysics Data System (ADS)

A magnetic field was recently detected on the O9.7 Iab supergiant component of the Cyg X-1 X-ray binary system. This paper considers its impact upon the star's atmosphere. We have used the simple model of a unipolar cylindrically symmetric circumpolar magnetic spot in static approximation with the parallel magnetic force lines. In that model the Lorentz-force component related to the force line curvature can be neglected and the equation of hydrostatic equilibrium is nabla (P_{g}+P_{r}+{B^2}/{8?}) = ?{g} , where P_{g} and P_{r} are the gaseous and radiative pressures, respectively, B^2/8? is the isotropic magnetic pressure, g is the gravitation acceleration, and ? is the gas density. In the frame of this model, and of the model atmosphere that we calculated for the Cyg X-1 O-supergiant te{skb}, the magnetic pressure was found to be comparable with the model atmosphere gas and radiative pressures, and exceeded them in the area surrounding the magnetic poles. That condition should lead to the formation of circumpolar bright spots on the stellar surface. We estimate their brightness contrast to be 25 A dipolar or quadrupolar magnetic field can create large bright spots, which can be studied by ground-based optical photometry. If the magnetic field is inclined to the stellar rotation axis, the anticipated variability may reach about 1% can form spots of lesser size, and those may be revealed only by space telescopes. The spots may also be revealed through variability in spectral line profiles. The observation of spots can be considered an independent instrument for the analysis of magnetic fields in O-type supergiants such as that in Cyg X-1. The full text of this contribution has been published in te{kb}.

Karitskaya, E. A.; Bochkarev, N. G.

2014-11-01

69

Properties of the CO and H2O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations  

NASA Astrophysics Data System (ADS)

Context. Betelgeuse is the closest red supergiant (RSG); therefore, it is well suited for studying the complex processes in its atmosphere that lead to the chemical enrichment of the interstellar medium. Aims: We intend to investigate the shape and composition of the close molecular layer (also known as the MOLsphere) that surrounds the star. This analysis is part of a wider program that aims at understanding the dynamics of the circumstellar envelope of Betelgeuse. Methods: On January and February 2011, Betelgeuse was observed using the Astronomical Multi-BEam combineR (AMBER) instrument of the Very Large Telescope Interferometer (VLTI) in the H and K bands. Using the medium spectral resolution of the instrument (R ~ 1500), we were able to investigate the carbon monoxide band heads and the water-vapor bands. We used two different approaches to analyse our data: a model fit in both the continuum and absorption lines and then a fit with a radiative hydrodynamics (RHD) simulation. Results: Using the continuum data, we derive a uniform disk diameter of 41.01 ± 0.41 mas, a power law type limb-darkened disk diameter of 42.28 ± 0.43 mas and a limb-darkening exponent of 0.155 ± 0.009. Within the absorption lines, using a single layer model, we obtain parameters of the MOLsphere. Using a RHD simulation, we unveil the convection pattern in the visibilities. Conclusions: We derived a new value of the angular diameter of Betelgeuse in the K band continuum. Our observations in the absorption lines are well reproduced by a molecular layer at 1.2 stellar radii containing both CO and H2O. The visibilities at higher spatial frequencies are matching a convection pattern in a RHD simulation. Based on AMBER observations made with ESO Telescopes at the Paranal Observatory under programmes ID 086.D-0351 and 286.D-5036(A).Table 1 is available in electronic form at http://www.aanda.org

Montargès, M.; Kervella, P.; Perrin, G.; Ohnaka, K.; Chiavassa, A.; Ridgway, S. T.; Lacour, S.

2014-12-01

70

DOUBLE BOW SHOCKS AROUND YOUNG, RUNAWAY RED SUPERGIANTS: APPLICATION TO BETELGEUSE  

SciTech Connect

A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent three-dimensional simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a constant wind, indicate that the bow shock is very young (<30, 000 years old), hence Betelgeuse may have only recently become an RSG. To test this possibility, we have calculated stellar evolution models for single stars which match the observed properties of Betelgeuse in the RSG phase. The resulting evolving stellar wind is incorporated into two-dimensional hydrodynamic simulations in which we model a runaway blue supergiant (BSG) as it undergoes the transition to an RSG near the end of its life. We find that the collapsing BSG wind bubble induces a bow shock-shaped inner shell around the RSG wind that resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We suggest that this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.

Mackey, Jonathan; Mohamed, Shazrene; Neilson, Hilding R.; Langer, Norbert; Meyer, Dominique M.-A., E-mail: jmackey@astro.uni-bonn.de [Argelander-Institut fuer Astronomie, Auf dem Huegel 71, D-53121 Bonn (Germany)

2012-05-20

71

The 100-month Swift Catalogue of Supergiant Fast X-ray Transients  

NASA Astrophysics Data System (ADS)

We present the 100-month Swift Catalogue of Supergiant Fast X-ray Transients, a collection of over a thousand Swift/BAT flares from 11 Supergiant Fast X-ray Transients (SFXT), complete down to 15-150 keV fluxes of about ˜6×10^{-10} erg cm^{-2} s^{-1} (daily timescale) and about ˜ 1.5×10^{-9} erg cm^{-2} s^{-1} (orbital timescale, averaging about 800 s). This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100 mCrab, 15-50 keV) events, lasting much less than a day in the hard X-rays. The outbursts are a much longer phenomenon however, as testified by the clustering of flares in orbital phase-space. They last up to a few days, as previously discovered from Swift deeper soft X-ray observations. We use this large dataset to probe the properties of the high and intermediate emission states in SFXTs, and to infer the properties of these binary systems. We also present preliminary results from our analysis of spectral evolution dependent flux light curves and broad-band spectroscopy of the outbursts. Finally, we provide a recipe to estimate the number of flares per year each source is likely to produce as a function of the detection threshold and limiting flux.

Romano, P.; Ducci, L.; Krimm, H.; Palmer, D.; Esposito, P.; Vercellone, S.; Evans, P.; Guidorzi, C.; Mangano, V.; Kennea, J.

2014-07-01

72

The 100-month Swift Catalogue of Supergiant Fast X-ray Transients  

NASA Astrophysics Data System (ADS)

The 100-month Swift Catalogue of Supergiant Fast X-ray Transients, collects over a thousand Swift/BAT flares from 11 Supergiant Fast X-ray Transients (SFXTs), and is complete down to fluxes of about 6x1E-10 erg/cm2/s (daily timescale) and about 1.5x1E-9 erg/cm2/s (orbital timescale, averaging about 800 s) in the 15-150 keV energy band. These hard X-ray flares typically last a few hundred seconds, reach fluxes in excess of 100 mCrab (15-50 keV), and last much less than a day. Their clustering in orbital phase-space,however, demonstrates that the outbursts are a much longer phenomenon, lasting up to a few days, as previously observed in deeper Swift soft X-ray observations. This large dataset is used to probe the properties of the high and intermediate emission states in SFXTs, and to infer the properties of these binary systems, as well as to estimate the number of flares per year each source is likely to produce as a function of the detection threshold and limiting flux. We also present preliminary results from our analysis of spectral evolution-dependent flux light curves and broad-band spectroscopy of the outbursts.

Romano, Patrizia; Krimm, Hans A.; Palmer, David; Ducci, Lorenzo; Esposito, Paolo; Vercellone, Stefano; Evans, Phil; Guidorzi, Cristiano; Mangano, Vanessa; Kennea, Jamie A; Barthelmy, Scott Douglas; Burrows, David N.; Gehrels, Neil

2014-08-01

73

The red supergiant and supernova rate problems: implications for core-collapse supernova physics  

NASA Astrophysics Data System (ADS)

Mapping supernovae to their progenitors is fundamental to understanding the collapse of massive stars. We investigate the red supergiant problem, which concerns why red supergiants with masses ˜16-30 M? have not been identified as progenitors of Type IIP supernovae, and the supernova rate problem, which concerns why the observed cosmic supernova rate is smaller than the observed cosmic star formation rate. We find key physics to solving these in the compactness parameter, which characterizes the density structure of the progenitor. If massive stars with compactness above ?2.5 ˜ 0.2 fail to produce canonical supernovae, (i) stars in the mass range 16-30 M? populate an island of stars that have high ?2.5 and do not produce canonical supernovae, and (ii) the fraction of such stars is consistent with the missing fraction of supernovae relative to star formation. We support this scenario with a series of two- and three-dimensional radiation hydrodynamics core-collapse simulations. Using more than 300 progenitors covering initial masses 10.8-75 M? and three initial metallicities, we show that high compactness is conducive to failed explosions. We then argue that a critical compactness of ˜0.2 as the divide between successful and failed explosions is consistent with state-of-the-art three-dimensional core-collapse simulations. Our study implies that numerical simulations of core collapse need not produce robust explosions in a significant fraction of compact massive star initial conditions.

Horiuchi, S.; Nakamura, K.; Takiwaki, T.; Kotake, K.; Tanaka, M.

2014-11-01

74

The progenitor of supernova 1993J - A stripped supergiant in a binary system?  

NASA Technical Reports Server (NTRS)

Supernova 1993J in the spiral galaxy M81 is the brightest supernova since SN1987A and, like the latter, appears to be another 'peculiar' type II supernova. The available photometry of the supernova region before the explosion requires the presence of at least two supergiants (one of early spectral type and the other of late type), but the actual progenitor has yet to be identified. We show that the explosion of a late-type supergiant can explain the initial sharp peak in the supernova light curve, provided that the star had lost almost all of its hydrogen-rich envelope before the explosion. In our model, the secondary brightening of the supernova, about 10 days later, is then a consequence of the radioactive decay of Ni-56 (and subsequently Co-56) produced in the explosion. The progenitor could have lost its hydrogen-rich envelope either in a strong stellar wind or, as seems more likely, through mass transfer to a companion star. In the latter case, the companion should reappear after the supernova photosphere has receded, the system having become a binary composed of a neutron star with a massive stellar companion.

Podsiaklowski, PH.; Hsu, J. J. L.; Joss, P. C.; Ross, R. R.

1993-01-01

75

X-RAY PHOTOIONIZED BUBBLE IN THE WIND OF VELA X-1 PULSAR SUPERGIANT COMPANION  

SciTech Connect

Vela X-1 is the archetype of high-mass X-ray binaries (HMXBs), composed of a neutron star and a massive B supergiant. The supergiant is a source of a strong radiatively driven stellar wind. The neutron star sweeps up this wind and creates a huge amount of X-rays as a result of energy release during the process of wind accretion. Here, we provide detailed NLTE models of the Vela X-1 envelope. We study how the X-rays photoionize the wind and destroy the ions responsible for the wind acceleration. The resulting decrease of the radiative force explains the observed reduction of the wind terminal velocity in a direction to the neutron star. The X-rays create a distinct photoionized region around the neutron star filled with a stagnating flow. The existence of such photoionized bubbles is a general property of HMXBs. We unveil a new principle governing these complex objects, according to which there is an upper limit to the X-ray luminosity the compact star can have without suspending the wind due to inefficient line driving.

Krticka, Jiri; Skalicky, Jan [Ustav teoreticke fyziky a astrofyziky, Masarykova univerzita, Kotlarska 2, CZ-611 37 Brno (Czech Republic); Kubat, Jiri [Astromomicky ustav Akademie ved Ceske republiky, Fricova 298, CZ-251 65 Ondrejov (Czech Republic)

2012-10-01

76

Spectroscopic and Temporal Properties of Supergiant Fast X-ray Transients with Swift  

NASA Astrophysics Data System (ADS)

We present a review of the Swift Supergiant Fast X-ray Transients (SFXT) project. Swift has recently opened a brand new way of investigating this class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. Thanks to its scheduling flexibility, Swift has allowed us to regularly monitor a small sample of SFXTs with 2-3 observations per week (1-2 ks) with the X-Ray Telescope (XRT) over their entire visibility period (9 months/year) for over 2 years. This intense monitoring has allowed us to study them throughout all phases of their lives (outbursts, intermediate level, and quiescence) and to determine the long-term properties and their duty cycles, through very sensitive and non-serendipitous observations. We also monitored one source along its whole orbital period. Furthermore, thanks to its autonomous and rapid repointing, Swift has allowed us for the first time to catch and study, from optical to hard X-ray, the bright outbursts, and to follow them in the X-ray for days, thus determining the actual duration of the outburst episodes and the shape of their X-ray spectra through simultaneous broadband spectroscopy. We acknowledge financial contribution from the agreement ASI-INAF I/009/10/0.

Romano, Patrizia; Kennea, J. A.; Vercellone, S.; Burrows, D. N.; Cusumano, G.; Esposito, P.; Farinelli, R.; Krimm, H. A.; La Parola, V.; Mangano, V.; Pagani, C.; Gehrels, N.

2011-09-01

77

IUE observations of the Henize-Carlson sample of peculiar emission line supergiants: The galactic analogs of the Magellanic Zoo  

NASA Technical Reports Server (NTRS)

Some 15 stars from the Carlson-Henize survey of southern peculiar emission line stars were studied. From both the optical and UV spectra, they appear to be galactic counterparts of the most extreme early-type emission line supergiants of the Magellanic Clouds.

Shore, Steven N.; Brown, Douglas N.; Sanduleak, N.

1986-01-01

78

The early-type strong emission-line supergiants of the Magellanic Clouds - A spectroscopic zoology  

NASA Technical Reports Server (NTRS)

The results of a spectroscopic survey of 21 early-type extreme emission line supergiants of the Large and Small Magellanic Clouds using IUE and optical spectra are presented. The combined observations are discussed and the literature on each star in the sample is summarized. The classification procedures and the methods by which effective temperatures, bolometric magnitudes, and reddenings were assigned are discussed. The derived reddening values are given along with some results concerning anomalous reddening among the sample stars. The derived mass, luminosity, and radius for each star are presented, and the ultraviolet emission lines are described. Mass-loss rates are derived and discussed, and the implications of these observations for the evolution of the most massive stars in the Local Group are addressed.

Shore, S. N.; Sanduleak, N.

1984-01-01

79

Narrow polarized components in the OH 1612-MHz maser emission from supergiant OH-IR sources  

NASA Technical Reports Server (NTRS)

High-resolution (300 Hz) OH 1612-MHz spectra of the supergiant OH-IR sources VY CMa, VX Sgr, IRC 10420, and NML Cyg are presented. Linewidths as small as 550 Hz (0.1 km/s) are found for narrow components in the spectra. The present results are consistent with current models for maser line-narrowing and for the physical properties in the OH maser regions. A significant degree of circular polarization is noted in many of the narrow components. The circular polarization suggests the presence of magnetic fields of about 1 mG in the circumstellar envelopes which would be strong enough to influence the outflow from the stars, and which may explain asymmetries found in the circumstellar envelopes.

Cohen, R. J.; Downs, G.; Emerson, R.; Grimm, M.; Gulkis, S.; Stevens, G.

1987-01-01

80

Physical conditions near red giant and supergiant stars - An interpretation of SiO VLBI maps  

NASA Technical Reports Server (NTRS)

Understanding the dynamical structure of circumstellar envelopes around cool giant and supergiant stars depends critically on the knowledge of what happens in the 'near zone' of the envelope, within a few stellar radii of the star. One probe with adequate angular resolution to study the near zone is VLBI observation of the SiO masers. It is shown that VLBI maps of VX Sgr establish that the particle density in the SiO masers is very high (about 10 to the 12th/cu cm), indicating that the masers form in dense cloudlets and not in a spherically expanding wind. The implications of these results for the mechanism of mass loss are discussed.

Alcock, Charles; Ross, Randy R.

1986-01-01

81

THE RED SUPERGIANT PROGENITOR OF SUPERNOVA 2012aw (PTF12bvh) IN MESSIER 95  

SciTech Connect

We report on the direct detection and characterization of the probable red supergiant (RSG) progenitor of the intermediate-luminosity Type II-Plateau (II-P) supernova (SN) 2012aw in the nearby (10.0 Mpc) spiral galaxy Messier 95 (M95; NGC 3351). We have identified the star in both Hubble Space Telescope images of the host galaxy, obtained 17-18 yr prior to the explosion, and near-infrared ground-based images, obtained 6-12 yr prior to the SN. The luminous supergiant showed evidence for substantial circumstellar dust, manifested as excess line-of-sight extinction. The effective total-to-selective ratio of extinction to the star was R'{sub V} Almost-Equal-To 4.35, which is significantly different from that of diffuse interstellar dust (i.e., R{sub V} = 3.1), and the total extinction to the star was therefore, on average, A{sub V} Almost-Equal-To 3.1 mag. We find that the observed spectral energy distribution for the progenitor star is consistent with an effective temperature of 3600 K (spectral type M3), and that the star therefore had a bolometric magnitude of -8.29. Through comparison with recent theoretical massive-star evolutionary tracks we can infer that the RSG progenitor had an initial mass 15 {approx}< M{sub ini}(M{sub Sun }) < 20. Interpolating by eye between the available tracks, we surmise that the star had initial mass {approx}17-18 M{sub Sun }. The circumstellar dust around the progenitor must have been destroyed in the explosion, as the visual extinction to the SN is found to be low (A{sub V} = 0.24 mag with R{sub V} = 3.1).

Van Dyk, Schuyler D. [Spitzer Science Center/Caltech, Mailcode 220-6, Pasadena, CA 91125 (United States); Cenko, S. Bradley; Filippenko, Alexei V., E-mail: vandyk@ipac.caltech.edu, E-mail: cenko@berkeley.edu, E-mail: afilippenko@berkeley.edu [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); and others

2012-09-10

82

Young red supergiants and the near infrared light appearance of disk galaxies  

E-print Network

Disk galaxies often show prominent nonaxisymmetric features at near-infrared wavelengths. Such features may indicate variations in the surface density of stellar mass, contributions from young red supergiants in star forming regions, or substantial dust obscuration. To distinguish among these possibilities, we have searched for spatial variations in the 2.3 micron photometric CO index within the disks of three nearby galaxies (NGC 278, NGC 2649, & NGC 5713). This index measures the strength of the absorption bands of molecular CO in stellar atmospheres, and is strong in cool, low surface-gravity stars, reaching the largest values for red supergiants. We observe significant spatial CO index variations in two galaxies (NGC 278 & NGC 5713), indicating that the dominant stellar population in the near-infrared is not everywhere the same. Central CO index peaks are present in two galaxies; these could be due to either metallicity gradients or recent star formation activity. In addition, significant azimuthal CO index variations are seen in NGC 278. Because strong azimuthal metallicity gradients are physically implausible in disk galaxies, these features are most naturally explained by the presence of a young stellar population. The fraction of 2 micron light due to young stellar populations in star forming regions can be calculated from our data. Overall, young stellar populations can contribute ~3% of a (normal) galaxy's near infrared flux. Locally, this fraction may rise to ~33%. Thus, young stars do not dominate the total near infrared flux, but can be locally dominant in star forming regions, and can bias estimates of spiral arm amplitude or other nonaxisymmetric structures in galaxies' mass distributions.

James E. Rhoads

1997-10-17

83

Supergiant Fast X-ray Transients: A Case Study for LOFT  

NASA Astrophysics Data System (ADS)

LOFT, the Large Observatory For X-ray Timing, is a new space mission concept selected by ESA in February 2011 and currently competing for a launch of opportunity in 2022. LOFT will carry a coded mask Wide Field Monitor (WFM) and a 10-m^2 class collimated X-ray Large Area Detector (LAD) operating in the energy range 2-80 keV. The instruments on-board LOFT will dramatically deepen our knowledge of Supergiant Fast X-ray Transients, a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state. The LAD and the WFM will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states, long term monitoring that will yield new determinations of orbital periods, as well as spin periods. We show the results of an extensive set of simulations based on the Swift broad-band and detailed XMM-Newton observations we collected up to now. Our simulations describe the outbursts at several intensities (F(2-10 keV)=5.9E-9 to 5.5E-10 erg cm-2 s-1), the intermediate and most common state (1E-11 erg cm-2 s-1), and the low state (1.2E-12 to 5E-13 erg cm-2 s-1). We also considered large variations of NH and the presence of emission lines, as observed by Swift and XMM-Newton. We acknowledge financial contribution from ASI-INAF I/004/11/0 and I/021/12/0.

Romano, Patrizia; Mangano, V.; Bozzo, E.; Esposito, P.; Ferrigno, C.

2013-04-01

84

The ring nebula around the blue supergiant SBW1: pre-explosion snapshot of an SN 1987A twin  

NASA Astrophysics Data System (ADS)

SBW1 is a B-type supergiant surrounded by a ring nebula that is a nearby twin of SN 1987A's progenitor and its circumstellar ring. We present images and spectra of SBW1 obtained with the Hubble Space Telescope (HST), the Spitzer Space Telescope and Gemini South. HST images of SBW1 do not exhibit long Rayleigh-Taylor (RT) fingers, which are presumed to cause the `hotspots' in the SN 1987A ring when impacted by the blast wave, but instead show a geometrically thin (?R/R ? 0.05) clumpy ring. The radial mass distribution and size scales of inhomogeneities in SBW1's ring closely resemble those in the SN 1987A ring, but the more complete disc expected to reside at the base of the RT fingers is absent in SBW1. This structure may explain why portions of the SN 1987A ring between the hotspots have not yet brightened, more than 15 years after the first hotspots appeared. The model we suggest does not require a fast wind colliding with a previous red supergiant wind, because a slowly expanding equatorial ring may be ejected by a rotating blue supergiant star or in a close binary system. More surprisingly, high-resolution images of SBW1 also reveal diffuse emission filling the interior of the ring seen in H? and in thermal-infrared (IR) emission; ˜190 K dust dominates the 8-20 ?m luminosity (but contains only 10-5 M? of dust). Cooler (˜85 K) dust resides in the equatorial ring itself (and has a dust mass of at least 5 × 10-3 M?). Diffuse emission extends inward to ˜1 arcsec from the central star, where a paucity of H? and IR emission suggests an inner hole excavated by the B-supergiant wind. We propose that diffuse emission inside the ring arises from an ionized flow of material photoevaporated from the dense ring, and its pressure prevents the B-supergiant wind from advancing in the equatorial plane. This inner emission could correspond to a structure hypothesized to reside around Sk-69°202 that was never directly detected. If this interpretation is correct, it would suggest that photoionization can play an important dynamical role in shaping the ring nebula, and we speculate that this might help explain the origin of the polar rings around SN 1987A. In effect, the photoevaporative flow shields the outer bipolar nebula at low latitudes, whereas the blue supergiant wind expands freely out the poles and clears away the polar caps of the nebula; the polar rings reside at the intersection of these two zones.

Smith, Nathan; Arnett, W. David; Bally, John; Ginsburg, Adam; Filippenko, Alexei V.

2013-02-01

85

Long-period variables in the Magellanic Clouds: Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium  

Microsoft Academic Search

Infrared JHK magnitudes and low-dispersion red spectra have been obtained for 90 long-period variables (LPVs) in the Small and Large Magellanic Clouds. The LPVs fall into two distinct groups, core helium (or carbon) burning supergiants and stars on the asymptotic giant branch (AGB). The supergiants have small pulsation amplitudes in K (<0.25 mag) whereas the AGB stars have typical amplitudes

P. R. Wood; M. S. Bessell; M. W. Fox

1983-01-01

86

Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta  

Microsoft Academic Search

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the ``yellow void.'' We report

Roberta M. Humphreys; Kris Davidson; Nathan Smith

2002-01-01

87

INTEGRAL Long-Term Monitoring of the Supergiant Fast X-Ray Transient XTE J1739-302  

NASA Technical Reports Server (NTRS)

Context. In the past few years, a new class of High Mass X-Ray Binaries (HMXRB) has been claimed to exist, the Supergiant Fast X-ray Transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds. Aims. Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind. Methods. We have used INTEGRAL and RXTE/PCA observations in order to obtain broad band (1 - 200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability. Results. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.

Blay, P.; Martinez-Nunez, S.; Negueruela, I.; Pottschmidt, K.; Smith, D. M.; Torrejon, J. M.; Reig, P.; Kretschmar, P.; Kreykenbohm, I.

2008-01-01

88

Isolated Wolf-Rayet Stars and O Supergiants in the Galactic Center Region Identified via Paschen-alpha Excess  

E-print Network

We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-alpha emission-line excess, following a narrowband imaging survey of the central 0.65 x 0.25 degress (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include 6 carbon-type (WC) and 5 nitrogen-type (WN) Wolf-Rayet stars, 6 O supergiants, and 2 Be supergiants. Two of the O supergiants have X-ray counterparts having properties consistent with solitary O stars and colliding-wind binaries. The infrared photometry of 17 stars is consistent with the Galactic center distance, but 2 of them are located in the foreground. Several WC stars exhibit a relatively large infrared excess, which is possibly thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may ...

Mauerhan, Jon; Dong, Hui; Morris, Mark; Wang, Daniel; Stolovy, Susan; Lang, Cornelia

2010-01-01

89

The impact of mass-loss on the evolution and pre-supernova properties of red supergiants  

E-print Network

The post main-sequence evolution of massive stars is very sensitive to many parameters of the stellar models. Key parameters are the mixing processes, the metallicity, the mass-loss rate and the effect of a close companion. We study how the red supergiant lifetimes, the tracks in the Hertzsprung-Russel diagram (HRD), the positions in this diagram of the pre-supernova progenitor as well as the structure of the stars at that time change for various mass-loss rates during the red supergiant phase (RSG), and for two different initial rotation velocities. The surface abundances of RSGs are much more sensitive to rotation than to the mass-loss rates during that phase. A change of the RSG mass-loss rate has a strong impact on the RSG lifetimes and therefore on the luminosity function of RSGs. At solar metallicity, the enhanced mass-loss rate models do produce significant changes on the populations of blue, yellow and red supergiants. When extended blue loops or blue ward excursions are produced by enhanced mass-loss...

Meynet, G; Ekström, S; Georgy, C; Granada, A; Groh, J; Maeder, A; Eggenberger, P; Levesque, E; Massey, P

2014-01-01

90

An HST COS "SNAPshot" Spectrum of the K Supergiant ? Vel (K4Ib-II)  

NASA Astrophysics Data System (ADS)

We present a far-ultraviolet spectrum of the K4 Ib-II supergiant ? Vel obtained with the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) as a part of the SNAPshot program "SNAPing coronal iron" (GO 11687). The observation covers a wavelength region (1326-1467 Å) not previously recorded for ? Vel at a spectral resolving power of R ~ 20,000 and displays strong emission and absorption features, superposed on a bright chromospheric continuum. Fluorescent excitation is responsible for much of the observed emission, mainly powered by strong H I Ly? and the O I (UV 2) triplet emission near ?1304. The molecular CO and H2 fluorescences are weaker than in the early-K giant ? Boo while the Fe II and Cr II lines, also pumped by H I Ly?, are stronger in ? Vel. This pattern of relative line strengths between the two stars is explained by the lower iron-group element abundance in ? Boo, which weakens that star's Fe II and Cr II emission without reducing the molecular fluorescences. The ? Vel spectrum shows fluorescent Fe II, Cr II, and H2 emission similar to that observed in the M supergiant ? Ori, but more numerous well-defined narrow emissions from CO. The additional CO emissions are visible in the spectrum of ? Vel since that star does not have the cool, opaque circumstellar shells that surround ? Ori and produce broad circumstellar CO (A-X) band absorptions that hide those emissions in the cooler star. The presence of Si IV emission in ? Vel indicates a ~8 × 104 K plasma that is mixed into the cooler chromosphere. Evidence of the stellar wind is seen in the C II ??1334,1335 lines and in the blueshifted Fe II and Ni II wind absorption lines. Line modeling using Sobolev with Exact Integration for the C II lines indicates a larger terminal velocity (~45 versus ~30 km s-1) and turbulence (~27 versus <21 km s-1) with a more quickly accelerating wind (? = 0.35 versus 0.7) at the time of this COS observation in 2010 than derived from Goddard High Resolution Spectrograph data obtained in 1994. The Fe II and Ni II absorptions are blueshifted by 7.6 km s-1 relative to the chromospheric emission, suggesting formation in lower levels of the accelerating wind and their widths indicate a higher turbulence in the ? Vel wind compared to ? Ori. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

Carpenter, Kenneth G.; Ayres, Thomas R.; Harper, Graham M.; Kober, Gladys; Nielsen, Krister E.; Wahlgren, Glenn M.

2014-10-01

91

Stochastic accretion and the variability of supergiant fast X-ray transients  

E-print Network

In this paper we consider the variability of the luminosity of a compact object (CO) powered by the accretion of an extremely inhomogeneous ("clumpy") stream of matter. The accretion of a single clump results in an X-ray flare: we adopt a simple model for the response of the CO to the accretion of a single clump, and derive a stochastic differential equation (SDE) for the accretion powered luminosity $L(t)$. We put the SDE in the equivalent form of an equation for the flares' luminosity distribution (FLD), and discuss its solution in the stationary case. As a case study, we apply our formalism to the analysis of the FLDs of Super-Giant Fast X-ray Transients (SFXTs), a peculiar sub-class of High Mass X-ray Binary Systems (HMXBs). We compare our theoretical FLDs to the distributions observed in the SFXTs IGR J16479-4514, IGR J17544-2619 and XTE J1739-302. Despite its simplicity, our model fairly agrees with the observed distributions, and allows to predict some properties of the stellar wind. Finally, we discus...

Pizzolato, Fabio

2012-01-01

92

THE ULTRA-LONG GAMMA-RAY BURST 111209A: THE COLLAPSE OF A BLUE SUPERGIANT?  

SciTech Connect

We present optical, X-ray and gamma-ray observations of GRB 111209A, observed at a redshift of z = 0.677. We show that this event was active in its prompt phase for about 25000 s, making it the longest burst ever observed. This rare event could have been detected up to z {approx} 1.4 in gamma-rays. Compared to other long gamma-ray bursts (GRBs), GRB 111209A is a clear outlier in the energy-fluence and duration plane. The high-energy prompt emission shows no sign of a strong blackbody component, the signature of a tidal disruption event, or a supernova shock breakout. Given the extreme longevity of this event, and lack of any significant observed supernova signature, we propose that GRB 111209A resulted from the core-collapse of a low-metallicity blue supergiant star. This scenario is favored because of the necessity to supply enough mass to the central engine over a duration of thousands of seconds. Hence, we suggest that GRB 111209A could have more in common with population III stellar explosions, rather than those associated with normal long GRBs.

Gendre, B.; Cutini, S.; D'Elia, V. [ASI Science Data Center, via Galileo Galilei, I-00044 Frascati (Italy)] [ASI Science Data Center, via Galileo Galilei, I-00044 Frascati (Italy); Stratta, G. [Osservatorio Astronomico di Roma, OAR-INAF, via Frascati 33, I-00040, Monte Porzio Catone (Italy)] [Osservatorio Astronomico di Roma, OAR-INAF, via Frascati 33, I-00040, Monte Porzio Catone (Italy); Atteia, J. L.; Klotz, A. [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France)] [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France); Basa, S. [Aix Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France)] [Aix Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille (France); Boeer, M. [CNRS, ARTEMIS, UMR 7250, Boulevard de l'Observatoire, BP 4229, F-06304 Nice Cedex 4 (France)] [CNRS, ARTEMIS, UMR 7250, Boulevard de l'Observatoire, BP 4229, F-06304 Nice Cedex 4 (France); Coward, D. M.; Howell, E. J [University of Western Australia, School of Physics, University of Western Australia, Crawley WA 6009 (Australia)] [University of Western Australia, School of Physics, University of Western Australia, Crawley WA 6009 (Australia); Piro, L., E-mail: bruce.gendre@gmail.com [Istituto di Astrofisica e Planetologia Spaziali di Roma, INAF, via fosso del cavaliere 100, I-00133 Roma (Italy)

2013-03-20

93

Quantitative Spectroscopic J-band study of Red Supergiants in Perseus OB-1  

NASA Astrophysics Data System (ADS)

We demonstrate how the metallicities of red supergiant (RSG) stars can be measured from quantitative spectroscopy down to resolutions of ?3000 in the J-band. We have obtained high resolution spectra on a sample of the RSG population of h and ? Persei, a double cluster in the solar neighborhood. We show that careful application of the MARCS model atmospheres returns measurements of Z consistent with solar metallicity. Using two grids of synthetic spectra-one in pure LTE and one with non-LTE (NLTE) calculations for the most important diagnostic lines-we measure Z = +0.04 ± 0.10 (LTE) and Z = -0.04 ± 0.08 (NLTE) for the sample of eleven RSGs in the cluster. We degrade the spectral resolution of our observations and find that those values remain consistent down to resolutions of less than ?/?? of 3000. Using measurements of effective temperatures we compare our results with stellar evolution theory and find good agreement. We construct a synthetic cluster spectrum and find that analyzing this composite spectrum with single-star RSG models returns an accurate metallicity. We conclude that the RSGs make ideal targets in the near infrared for measuring the metallicities of star forming galaxies out to 7-10 Mpc and up to 10 times farther by observing the integrated light of unresolved super star clusters. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Gazak, J. Zachary; Davies, Ben; Kudritzki, Rolf; Bergemann, Maria; Plez, Bertrand

2014-06-01

94

The superimposed photospheric and stellar wind variability of the O-type supergiant alpha Cam  

E-print Network

(Abridged) We provide empirical constraints on the different physical components that can act to yield temporal variability in predominantly or partially wind-formed optical lines of luminous OB stars, and thus potentially affect the reliable determination of fundamental parameters, including mass-loss rates via clumped winds. Using time-series spectroscopy from epochs spread over $\\sim$ 4 years, a case study of the O9.5 supergiant $\\alpha$ Cam is presented. We demonstrate that the He I 5876 (2$^3$P$^0$--3$^3$D) line is an important diagnostic for photospheric and wind variability in this star. The optical line profiles of $\\alpha$ Cam are affected by (i) deep-seated fluctuations close to, or at, the photosphere, (ii) atmospheric velocity gradients, and (iii) large-scale stellar wind structure. This study provides new empirical perspectives on accurate line-synthesis modelling of stellar wind signatures in massive luminous stars. Using a pure Halpha line-synthesis code we interpret maximum changes in the red-ward and peak emission of $\\alpha$ Cam in terms of mass-loss rate differences in the range $\\sim$ 5.1 $\\times$ 10$^{-6}$ to 6.5 $\\times$ 10$^{-6}$ M$_\\odot$ yr$^{-1}$. However, the models generally fail to reproduce the morphology of blueward (possibly absorptive) regions of the profiles.

R. K. Prinja; N. Markova; S. Scuderi; H. Markov

2006-06-29

95

STOCHASTIC ACCRETION AND THE VARIABILITY OF SUPERGIANT FAST X-RAY TRANSIENTS  

SciTech Connect

In this paper, we consider the variability of the luminosity of a compact object (CO) powered by the accretion of an extremely inhomogeneous (clumpy) stream of matter. The accretion of a single clump results in an X-ray flare; we adopt a simple model for the response of the CO to its arrival, and derive a stochastic differential equation (SDE) for the accretion-powered luminosity L(t). We set the SDE in the equivalent form of an equation for the flare luminosity distribution (FLD) and discuss its solution in the stationary case. We apply our formalism to the analysis of the FLDs of supergiant fast X-ray transients (SFXTs), a peculiar sub-class of high-mass X-ray binary (HMXB) systems. We compare our theoretical FLDs to the distributions observed in the SFXTs IGR J16479-4514, IGR J17544-2619, and XTE J1739-302. Despite its simplicity, our model agrees well with the observed distributions and allows us to predict some properties of the stellar wind. Finally, we discuss how our model may explain the difference between the broad FLDs of SFXTs and the much narrower FLDs of persistent HMXBs.

Pizzolato, Fabio; Sidoli, Lara, E-mail: fabio@iasf-milano.inaf.it, E-mail: sidoli@iasf-milano.inaf.it [INAF-IASF Milano, Via Bassini No. 15, I-20133 Milano (Italy)] [INAF-IASF Milano, Via Bassini No. 15, I-20133 Milano (Italy)

2013-01-10

96

Neutral and ionized gas around the post-Red Supergiant IRC+10420 at au size scales  

E-print Network

IRC +10420 is one of the few known massive stars in rapid transition from the Red Supergiant phase to the Wolf-Rayet or Luminous Blue Variable phase. The star has an ionised wind and using the Br gamma hydrogen recombination emission we assess the mass-loss on spatial scales of order 1 au. We present new VLT Interferometer AMBER data which are combined with all other AMBER data in the literature. The final dataset covers a position angle range of 180 degrees and baselines up to 110 meters. The spectrally dispersed visibilities, differential phases and line flux are conjointly analyzed and modelled. We also present AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na I doublet at 2.2 micron. The data are complemented by X-Shooter data, which provide a higher spectral resolution view. The Brackett gamma line and the Na I doublet are both spatially resolved. After correcting the AMBER data for the fact that the lines are not spectrally resolved, we find that Br gamma tra...

Oudmaijer, Rene

2012-01-01

97

The stars near the centre of supergiant shell LMC4: Further constraints on triggering scenarios  

E-print Network

The huge supergiant shell (SGS) LMC4, next to the giant HII region 30 Doradus the second most impressive feature of the Large Magellanic Cloud (LMC), has been the subject of many studies and was used to test various models of star forming mechanisms. In this paper we present a B, V photometry of the very centre of this SGS. The new data yield an age of 11(2)Myr and a colour excess E(B-V) = 0.10(3)mag. Additionally, the two clusters near the geometric centre are too old to be related to the formation of LMC4: HS343 being ~0.1Gyr and KMHK1000 being ~0.3Gyr of age. This and existing photometries support that the young stellar population covering the entire inner region is nearly coeval. We compare these findings with predictions of models proposed for the creation mechanism of SGSs. We conclude that the large-scale trigger, necessary to explain the observations, comes from hydrodynamic interaction of the galactic halo with gas in the leading edge of the moving LMC.

Jochen M. Braun; Klaas S. de Boer; Martin Altmann

2000-06-05

98

X-RAY EMISSION FROM THE SUPERGIANT SHELL IN IC 2574  

SciTech Connect

The M81 group member dwarf galaxy IC 2574 hosts a supergiant shell of current and recent star formation activity surrounding a 1000 Multiplication-Sign 500 pc hole in the ambient H I gas distribution. Chandra X-ray Observatory imaging observations reveal a luminous, L{sub X} {approx} 6.5 Multiplication-Sign 10{sup 38} erg s{sup -1} in the 0.3-8.0 keV band, point-like source within the hole but offset from its center and fainter diffuse emission extending throughout and beyond the hole. The star formation history at the location of the point source indicates a burst of star formation beginning {approx}25 Myr ago and currently weakening and there is a young nearby star cluster, at least 5 Myr old, bracketing the likely age of the X-ray source at between 5 and {approx}25 Myr. The source is thus likely a bright high-mass X-ray binary-either a neutron star or black hole accreting from an early B star undergoing thermal-timescale mass transfer through Roche lobe overflow. The properties of the residual diffuse X-ray emission are consistent with those expected from hot gas associated with the recent star formation activity in the region.

Yukita, Mihoko [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL (United States); Swartz, Douglas A. [Universities Space Research Association, NASA Marshall Space Flight Center, ZP12 Huntsville, AL 35812 (United States)

2012-05-01

99

Investigating the Powering Sources of Expanding Supergiant Shells in the Nearby Dwarf Galaxy IC 2574  

NASA Astrophysics Data System (ADS)

Using the unique resolving capability of the Hubble Space Telescope {HST} and the wide-field imaging capabilities of the ACS, we propose to perform a stellar population study of two prominent supergiant shells {SGS} in the nearby dwarf galaxy IC2574. By constructing the star formation history for those SGSs we will for the first time be able to test if past star formation created these impressive structures, as suggested by theory. We have carefully selected 2 SGSs; one is young {age: few 10^7yr, exhibiting a prominent central stellar association and the other is older {few 10^8yr}, with no obvious optical counterpart. The aim of this proposal is to determine the age and SF history of the central stellar associations of both SGSs by B, V, and I band imaging using HST's ACS. A primary goal is the comparison of the stellar ages with the age estimates from the HI kinematics. Using color magnitude diagrams, we will also estimate how many stars have evolved off the main sequence and exploded as SN, giving an estimate for the total mechanical energy deposited. A comparison with the values derived in other wavelengths is not only important for understanding these particular SGSs but will also set strong timing as well as energy constraints on the physical mechanisms which lie at the origin of SGSs in general.

Walter, Fabian

2003-07-01

100

Pulsations of red supergiant pair-instability supernova progenitors leading to extreme mass loss  

E-print Network

Recent stellar evolution models show consistently that very massive metal-free stars evolve into red supergiants shortly before they explode. We argue that the envelopes of these stars, which will form pair-instability supernovae, become pulsationally unstable, and that this will lead to extreme mass-loss rates even though the metal content of the envelopes is very small. We investigate the pulsational properties of such models, and derive pulsationally induced mass-loss rates which take the damping effects of the mass loss on the pulsations selfconsistently into account. We find that the pulsations may induce mass-loss rates of ~ 1e-4 - 1e-2 Msun/yr shortly before the explosions, which may create a dense circumstellar medium. Our results show that very massive stars with dense circumstellar media may originate from a wider initial mass range than that of pulsational-pair instability supernovae. The extreme mass loss will cease when so much of the hydrogen-rich envelope is lost that the star becomes more comp...

Moriya, Takashi J

2014-01-01

101

Dense Molecular Clumps Associated with the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5  

NASA Astrophysics Data System (ADS)

We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. 12CO (J = 3-2, 1-0) and 13CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H2)) of the clumps are distributed from low to high density (103-105 cm–3) and their kinetic temperatures (T kin) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of H?, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H2) and T kin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

Fujii, Kosuke; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Kawamura, Akiko; Muller, Erik; Dawson, Joanne; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie E.; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Ezawa, Hajime; Fukui, Yasuo

2014-12-01

102

Swift observations of two supergiant fast X-ray transient prototypes in outburst  

NASA Astrophysics Data System (ADS)

We report on the results from observations of the most recent outbursts of XTE J1739-302 and IGR J17544-2619, which are considered to be the prototypes of the supergiant fast X-ray transient class. They triggered the Swift/Burst Alert Telescope on 2011 February 22 and March 24, respectively, and each time a prompt Swift slew allowed us to obtain the rich broad-band data we present. The X-ray Telescope light curves show the descending portion of very bright flares that reached luminosities of ˜2 × 1036 and ˜5 × 1036 erg s-1. The broad-band spectra, when fitted with the usual phenomenological models adopted for accreting neutron stars, yield values of both high-energy cut-off and e-folding energy consistent with those obtained from previously reported outbursts from these sources. In the context of more physical models, the spectra of both sources can be well fitted either with a two-blackbody model or with a single unsaturated Comptonization model. In the latter case, the model can be either a classical static Comptonization model, such as COMPTT, or the recently developed COMPMAG model, which includes thermal and bulk Comptonization for cylindrical accretion on to a magnetized neutron star. We discuss the possible accretion scenarios derived by the different models, and we also emphasize the fact that the electron density derived from the Comptonization models, in the regions where the X-ray spectrum presumably forms, is lower than that estimated using the continuity equation at the magnetospheric radius and the source X-ray luminosity, and we give some possible explanations.

Farinelli, R.; Romano, P.; Mangano, V.; Ceccobello, C.; Ducci, L.; Vercellone, S.; Esposito, P.; Kennea, J. A.; Burrows, D. N.

2012-08-01

103

A FEROS spectroscopic study of the extreme O supergiant He 3-759  

NASA Astrophysics Data System (ADS)

We present a study of the extreme O-type supergiant He 3-759 using new high-resolution FEROS data, revealing that it is a near spectroscopic twin of HD 151804 (O8 Iaf). We investigate the extinction towards He 3-759 using a variety of methods, revealing AV ˜ 4.7^m. If we assume He 3-759 has an identical absolute K-band magnitude to HD 151804 we find that it lies in the Sagittarius-Carina spiral arm at a distance of 6.5 kpc. We derive the physical and wind properties for He 3-759, revealing Tast = 30.5 kK, log L/L? = 5.9 and dot{M} = 10-5.17 M? yr-1 for a clumped wind whose terminal velocity is estimated at 1000 km s-1. The atmosphere of He 3-759 is enriched in helium (X_He = 49%) and nitrogen (XN = 0.3%). A reanalysis of HD 151804 and HD 152408 (WN9ha) reveals similar parameters except that the WN9ha star possesses a stronger wind and reduced surface hydrogen content. HD 151804 and HD 152408 lie within the Sco OB1 association, with initial masses of 60 M? and ages 2.7 Myr, consistent with NGC 6231 cluster members using standard Geneva isochrones. Improved agreement with observed surface abundances are obtained for similar initial masses with more recent Geneva group predictions from which higher ages of 3.75 Myr are obtained. No young, massive star cluster is known to be associated with He 3-759. Based on observations made with ESO telescopes at the La Silla observatory under program ID 082-D.0136.

Crowther, P. A.; Evans, C. J.

2009-09-01

104

Spatially resolved dusty torus toward the red supergiant WOH G64 in the Large Magellanic Cloud  

E-print Network

We present N-band spectro-interferometric observations of the red supergiant WOH G64 in the Large Magellanic Cloud (LMC) using MIDI at the Very Large Telescope Interferometer (VLTI). The location of WOH G64 on the H-R diagram based on the previously estimated luminosities is in serious disagreement with the current stellar evolution theory. The dust envelope around WOH G64 has been spatially resolved with a baseline of ~60 m--the first MIDI observations to resolve an individual stellar source in an extragalactic system. The observed N-band visibilities show a slight decrease from 8 to 10 micron and a gradual increase longward of 10 micron, reflecting the 10 micron silicate feature in self-absorption. The visibilities measured at four position angles differing by ~60 degrees but at approximately the same baseline length (~60 m) do not show a noticeable difference, suggesting that the object appears nearly centrosymmetric. The observed N-band visibilities and spectral energy distribution can be reproduced by an optically and geometrically thick silicate torus model viewed close to pole-on. The luminosity of the central star is derived to be 2.8 x 10^5 Lsun, which is by a factor of 2 lower than the previous estimates based on spherical models. The lower luminosity newly derived from our MIDI observations and two-dimensional modeling brings the location of WOH G64 on the H-R diagram in much better agreement with theoretical evolutionary tracks for a 25 Msun star. We also identify the H2O absorption features at 2.7 and 6 micron in the spectra obtained with the Infrared Space Observatory and the Spitzer Space Telescope. The 2.7 micron feature originates in the photosphere and/or the extended molecular layers, while the 6 micron feature is likely to be of circumstellar origin.

Keiichi Ohnaka; Thomas Driebe; Karl-Heinz Hofmann; Gerd Weigelt; Markus Wittkowski

2008-03-26

105

Three-micron spectra of AGB stars and supergiants in nearby galaxies  

E-print Network

The dependence of stellar molecular bands on the metallicity is studied using infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB stars. The equivalent width of acetylene is found to be high even at low metallicity. The high C2H2 abundance can be explained with a high carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast, the HCN equivalent width is low: fewer than half of the extra-galactic carbon stars show the 3.5micron HCN band, and only a few LMC stars show high HCN equivalent width. HCN abundances are limited by both nitrogen and carbon elemental abundances. The amount of synthesized nitrogen depends on the initial mass, and stars with high luminosity (i.e. high initial mass) could have a high HCN abundance. CH bands are found in both the extra-galactic and Galactic carbon stars. None of the oxygen-rich LMC stars show SiO bands, except one possible detection in a low quality spectrum. The limits on the equivalent widths of the SiO bands are below the expectation of up to 30angstrom for LMC metallicity. Several possible explanations are discussed. The observations imply that LMC and SMC carbon stars could reach mass-loss rates as high as their Galactic counterparts, because there are more carbon atoms available and more carbonaceous dust can be formed. On the other hand, the lack of SiO suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich stars. The effect on the ISM dust enrichment is discussed.

M. Matsuura; A. A. Zijlstra; J. Th. van Loon; I. Yamamura; A. J. Markwick; P. A. Whitelock; P. M. Woods; J. R. Marshall; M. W. Feast; L. B. F. M. Waters

2005-01-13

106

V838 Mon and the new class of stars erupting into cool supergiants (SECS)  

NASA Astrophysics Data System (ADS)

V838 Mon has undergone one of the most mysterious stellar outbursts on record. The spectrum at maximum closely resembled a cool AGB star, evolving toward cooler temperatures with time, never reaching optically thin conditions or showing increasing ionization and a nebular stage. The latest spectral type recorded is M8-9. The amplitude peaked at ?V=9 mag, with the outburst evolution being characterized by a fast rise, three maxima over four months, and a fast decay (possibly driven by dust condensation). BaII, LiI and s-element lines were prominent in the outburst spectra. Strong and wide (500 km/sec) P-Cyg profiles affected low ionization species, while Balmer lines emerged to modest emission only during the central phase of the outburst. A light-echo discovered expanding around the object constrains its distance to 790+/-30 pc, providing MV = +4.45 in quiescence and MV = -4.35 at optical maximum (dependent on the still uncertain EB-V=0.5 reddening). The visible progenitor resembles a somewhat under-luminous F0 main sequence star, that did not show detectable variability over the last half century. V838 Mon together with M31-RedVar and V4332 Sgr seems to define a new class of astronomical objects, Stars that Erupt into Cool Supergiants (SECS). They do not develop optically thin or nebular phases, and deep P-Cyg profiles denounce large mass loss at least in the early outburst phases. Their progenitors are photometrically located close to the Main Sequence, away from the post-AGB region. After the outburst, the remnants still closely resemble the precursors (same brightness, same spectral type). Many more similar objects could be buried among poorly studied variable stars that have been classified as Miras or SemiRegulars on the base of a single spectrum at maximum brightness.

Munari, U.; Henden, A.; Corradi, R. M. L.; Zwitter, T.

2002-11-01

107

A NEW DISTANCE TO M33 USING BLUE SUPERGIANTS AND THE FGLR METHOD  

SciTech Connect

The quantitative spectral analysis of medium resolution optical spectra of A and B supergiants obtained with DEIMOS and ESI at the Keck Telescopes is used to determine a distance modulus of 24.93 +- 0.11 mag (968 +- 50 kpc) for the Triangulum Galaxy M33. The analysis yields stellar effective temperatures, gravities, interstellar reddening, and extinction, the combination of which provides a distance estimate via the flux-weighted gravity-luminosity relationship (FGLR). This result is based on an FGLR calibration that is continually being polished. An average reddening of (E(B - V)) approx 0.08 mag is found, with a large variation ranging from 0.01 to 0.16 mag, however, demonstrating the importance of accurate individual reddening measurements for stellar distance indicators in galaxies with evident signatures of interstellar absorption. The large-distance modulus found is in good agreement with recent work on eclipsing binaries, planetary nebulae, long-period variables, RR Lyrae stars, and also with Hubble Space Telescope (HST) observations of Cepheids, if reasonable reddening assumptions are made for the Cepheids. Since distances based on the tip of the red giant branch (TRGB) method found in the literature give conflicting results, we have used HST Advanced Camera for Surveys V- and I-band images of outer regions of M33 to determine a TRGB distance of 24.84 +- 0.10 mag, in basic agreement with the FGLR result. We have also determined stellar metallicities and discussed the metallicity gradient in the disk of M33. We find metallicity of Z {sub sun} at the center and 0.3 Z {sub sun} in the outskirts at a distance of one isophotal radius. The average logarithmic metallicity gradient is -0.07 +- 0.01 dex kpc{sup -1}. However, there is a large scatter around this average value, very similar to what has been found for the H II regions in M33.

U, Vivian; Urbaneja, Miguel A.; Kudritzki, Rolf-Peter; Jacobs, Bradley A.; Bresolin, Fabio [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Przybilla, Norbert, E-mail: vivian@ifa.hawaii.ed, E-mail: urbaneja@ifa.hawaii.ed, E-mail: kud@ifa.hawaii.ed, E-mail: bjacobs@ifa.hawaii.ed, E-mail: bresolin@ifa.hawaii.ed, E-mail: przybilla@sternwarte.uni-erlangen.d [Dr. Remeis-Sternwarte Bamberg, Sternwartstrasse 7, D-96049 Bamberg (Germany)

2009-10-20

108

ASPHERICAL CORE-COLLAPSE SUPERNOVAE IN RED SUPERGIANTS POWERED BY NONRELATIVISTIC JETS  

SciTech Connect

We explore the observational characteristics of jet-driven supernovae (SNe) by simulating bipolar-jet-driven explosions in a red supergiant (RSG) progenitor. We present results of four models in which we hold the injected kinetic energy at a constant 10{sup 51} erg across all jet models but vary the specific characteristics of the jets to explore the influence of the nature of jets on the structure of the SN ejecta. We evolve the explosions past shock-breakout and into quasi-homologous expansion of the SN envelope into a RSG wind. The simulations have sufficient numerical resolution to study the stability of the flow. Our simulations show the development of fluid instabilities that produce pristine helium clumps in the hydrogen envelope. The oppositely directed, nickel-rich jets give a large-scale asymmetry that may account for the nonspherical excitation and substructure of spectral lines such as H{alpha} and He I 10830 A. Jets with a large fraction of kinetic to thermal energy punch through the progenitor envelope and give rise to explosions that would be observed to be asymmetric from the earliest epochs, inconsistent with spectropolarimetric measurements of Type II SNe. Jets with higher thermal energy fractions result in explosions that are roughly spherical at large radii but are significantly elongated at smaller radii, deep inside the ejecta, in agreement with the polarimetric observations. We present shock-breakout light curves that indicate that strongly aspherical shock breakouts are incompatible with recent Galaxy Evolution Explorer observations of shock breakout from RSG stars. Comparison with observations indicates that jets must deposit their kinetic energy efficiently throughout the ejecta while in the hydrogen envelope. Thermal-energy-dominated jets satisfy this criterion and yield many of the observational characteristics of Type II SNe.

Couch, Sean M.; Wheeler, J. Craig; Milosavljevic, Milos [Department of Astronomy, University of Texas, Austin, TX 78712 (United States)], E-mail: smc@astro.as.utexas.edu

2009-05-01

109

Geological and geochemical controls on the formation and distribution of supergiant gas fields in the Russian sedimentary basins  

SciTech Connect

The West Siberian, Barents Sea and Northern Caspian sedimentary basins are the most prolific Russian gas producing regions and include 15 supergiant gas fields each of them content identified gas reserves between 1 x 10[sup 12] m[sup 3] to 11 x 10[sup 12] m[sup 3]. They are Urengoi, Yarnburg, Bovanenkov, Zapoljarnoye, Medvezhie, Charasavey, Kruzenshtern, N.Urengoi, S.Tambey, S.Russkoye, Rusanov, Shtockmanov, Lunin, Astrachan and Orenburg. The gas reserves in these basins exceed 70 x 10[sup 12] m[sup 3] and about 65% of them concentrated in supergiant fields. Among the geological prerequisites for largest gas accumulations note big size of trap (Urengoi 40x300 km[sup 2]; Astrachan l80x200 km[sup 2]), anticline type of tectonic structure (swell, megaswell, dome, arch) with amplitude from 110 m to 800 in. These tectonic structure were active long time include the latest period. The main gas productive reservoirs are slightly consulted non-marine sandstones of Cenomanian or Middle Jurassic ages (West Siberia and Barents Sea) or Middle Carboniferous reef carbonate buildups (Northern Caspian basin). The next geochemical parameters controlled of the gas accumulation histories: (1) West Siberia and Barents Sea regions gas genetically connect with dispersed or concentrated non-marine coal type kerogen distributed into productive complex under lower maturity conditions (before or early oil window zone). This is dry gas almost pure methane with [delta][sup 13] C[sub 1] between -44,40[per thousand]. In this case we observe widely distributed mainly sandstones reservoirs at same time gas source rocks also; (2) the Northern Caspian basin found supergiant wet gas-condensate accumulations into local distributed reef carbonate buildups. Gas source rocks is marine kerogen type II, which has a low concentration in marlaceous facies. It is gas high maturity zone.

Lopatin, N. (VNIIgeosystem, Moscow (Russian Federation))

1996-01-01

110

Geological and geochemical controls on the formation and distribution of supergiant gas fields in the Russian sedimentary basins  

SciTech Connect

The West Siberian, Barents Sea and Northern Caspian sedimentary basins are the most prolific Russian gas producing regions and include 15 supergiant gas fields each of them content identified gas reserves between 1 x 10{sup 12} m{sup 3} to 11 x 10{sup 12} m{sup 3}. They are Urengoi, Yarnburg, Bovanenkov, Zapoljarnoye, Medvezhie, Charasavey, Kruzenshtern, N.Urengoi, S.Tambey, S.Russkoye, Rusanov, Shtockmanov, Lunin, Astrachan and Orenburg. The gas reserves in these basins exceed 70 x 10{sup 12} m{sup 3} and about 65% of them concentrated in supergiant fields. Among the geological prerequisites for largest gas accumulations note big size of trap (Urengoi 40x300 km{sup 2}; Astrachan l80x200 km{sup 2}), anticline type of tectonic structure (swell, megaswell, dome, arch) with amplitude from 110 m to 800 in. These tectonic structure were active long time include the latest period. The main gas productive reservoirs are slightly consulted non-marine sandstones of Cenomanian or Middle Jurassic ages (West Siberia and Barents Sea) or Middle Carboniferous reef carbonate buildups (Northern Caspian basin). The next geochemical parameters controlled of the gas accumulation histories: (1) West Siberia and Barents Sea regions gas genetically connect with dispersed or concentrated non-marine coal type kerogen distributed into productive complex under lower maturity conditions (before or early oil window zone). This is dry gas almost pure methane with {delta}{sup 13} C{sub 1} between -44,40{per_thousand}. In this case we observe widely distributed mainly sandstones reservoirs at same time gas source rocks also; (2) the Northern Caspian basin found supergiant wet gas-condensate accumulations into local distributed reef carbonate buildups. Gas source rocks is marine kerogen type II, which has a low concentration in marlaceous facies. It is gas high maturity zone.

Lopatin, N. [VNIIgeosystem, Moscow (Russian Federation)

1996-12-31

111

MOST Detects g- and p-Modes in the B Supergiant HD 163899 (B2 Ib/II)  

NASA Astrophysics Data System (ADS)

The Microvariability and Oscillations of Stars (MOST) satellite observed the B supergiant HD 163899 (B2 Ib/II) for 37 days as a guide star and detected 48 frequencies <~2.8 cycles day-1 with amplitudes of a few millimagnitudes (mmag) and less. The frequency range embraces g- and p-mode pulsations. It was generally thought that no g-modes are excited in less luminous B supergiants because strong radiative damping is expected in the core. Our theoretical models, however, show that such g-modes are excited in massive post-main-sequence stars, in accordance with these observations. The nonradial pulsations excited in models between 20 Msolar at logTeff~4.41 and 15 Msolar at logTeff~4.36 are roughly consistent with the observed frequency range. Excitation by the Fe bump in opacity is possible because g-modes can be partially reflected at a convective zone associated with the hydrogen-burning shell, which significantly reduces radiative damping in the core. The MOST light curve of HD 163899 shows that such a reflection of g-modes actually occurs and reveals the existence of a previously unrecognized type of variable, slowly pulsating B supergiants (SPBsg) distinct from ? Cyg variables. Such g-modes have great potential for asteroseismology. Based on data from the MOST satellite, a Canadian Space Agency mission, operated jointly by Dynacon, Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia, with the assistance of the University of Vienna.

Saio, H.; Kuschnig, R.; Gautschy, A.; Cameron, C.; Walker, G. A. H.; Matthews, J. M.; Guenther, D. B.; Moffat, A. F. J.; Rucinski, S. M.; Sasselov, D.; Weiss, W. W.

2006-10-01

112

X-ray Constraints on Magnetic Activity and Star Formation Associated with the Red Supergiant VY CMa  

NASA Astrophysics Data System (ADS)

Magnetic field strengths inferred from maser observations of the optically thick circumstellar envelope enshrouding the red supergiant VY CMa indicate that its stellar surface fields may be capable of producing coronal X-ray emission. Evidence for episodic yet randomly directed mass ejections from VY CMa, coupled with the magnetism inferred from maser emission, further suggests that magnetic surface activity may play a fundamental role in mass loss from the red supergiant. Motivated by this evidence, we obtained X-ray observations of a field centered on VY CMa with the XMM-Newton X-ray Observatory in May of 2012. VY CMa is not detected in the ~20 ks XMM exposure. We have determined the upper limit on the X-ray flux of VY CMa as a function of assumed source plasma temperature and intervening absorption, and we use these results to constrain the level of surface magnetic activity on VY CMa at the epoch of the XMM observation. We also detected over a hundred X-ray emitting field sources within ~15' of VY CMa. Via cross-correlation of these sources with optical and infrared catalogs, we identify a few dozen X-ray sources that have stellar counterparts. Comparison with theoretical pre-main sequence (pre-MS) isochrones suggests most of these newly discovered X-ray-emitting stars in the immediate vicinity of VY CMa may be late-type, pre-MS stars at the approximate distance of the famous supergiant itself. We consider whether these stars may constitute a loose association that is coeval with VY CMa, and we discuss the potential relationship of this putative "VY CMa Association" to other nearby regions of recent star formation, including the young cluster NGC 2362.

Montez, Rodolfo; Humphreys, R. M.; Kastner, J. H.; Turok, R. L.

2014-01-01

113

ISOLATED WOLF-RAYET STARS AND O SUPERGIANTS IN THE GALACTIC CENTER REGION IDENTIFIED VIA PASCHEN-{alpha} EXCESS  

SciTech Connect

We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-{alpha} (P{alpha}) emission-line excess, following a narrowband imaging survey of the central 0.{sup 0}65 x 0.{sup 0}25 (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include six carbon-type (WC) and five nitrogen-type (WN) Wolf-Rayet stars, six O supergiants, and two B supergiants. Two of the O supergiants have X-ray counterparts having properties consistent with solitary O stars and colliding-wind binaries. The infrared photometry of 17 stars is consistent with the Galactic center distance, but 2 of them are located in the foreground. Several WC stars exhibit a relatively large infrared excess, which is possibly thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may have originated within one of these systems. The results of this work bring the total sample of Wolf-Rayet (WR) stars in the GCR to 88. All sources of strong P{alpha} excess have been identified in the area surveyed with HST, which implies that the sample of WN stars in this region is near completion, and is dominated by late (WNL) types. The current WC sample, although probably not complete, is almost exclusively dominated by late (WCL) types. The observed WR subtype distribution in the GCR is a reflection of the intrinsic rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is driven by metallicity.

Mauerhan, J. C.; Stolovy, S. R. [Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 220-6, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Cotera, A. [SETI Institute, 515 North Whisman Road, Mountain View, CA 94043 (United States); Dong, H.; Wang, Q. D. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Morris, M. R. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Lang, C., E-mail: mauerhan@ipac.caltech.edu [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States)

2010-12-10

114

DISCOVERY OF A POSSIBLY SINGLE BLUE SUPERGIANT STAR IN THE INTRA-CLUSTER REGION OF VIRGO CLUSTER OF GALAXIES  

SciTech Connect

IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated H II region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.

Ohyama, Youichi; Hota, Ananda [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China)

2013-04-20

115

VizieR Online Data Catalog: Nature of the peculiar supergiant HD 101584 (Bakker+, 1996)  

NASA Astrophysics Data System (ADS)

We present a study of low- and high-resolution ultraviolet, high-resolution optical CAT/CES spectra and ultraviolet, optical and infrared photometry of the peculiar supergiant HD 101584. From the photometry we learn that the ultraviolet and optical energy distribution cannot be fitted in a consistent way and we need a model in which the UV and optical energy distribution are formed by different gas. The Geneva photometry is best fitted to a B9II Kurucz model, Teff=12000+/-1000K and logg=3.0+/-1.0, with an extinction of E(B-V)=0.49+/-0.05. The observed spectral features in the spectrum of HD 101584 are classified in eight different categories based on the velocity, shape of profile and the identification. The high-excitation HeI (?=20.87eV), NII (?=18.40eV), CII (?=14.39eV) and NI (?=10.29eV) optical absorption lines are formed in the photosphere of a late B-star (e.g. B8-9I-II). These absorption lines show radial velocity variations which are attributed to binary motion, with the secondary being a white dwarf or a low-mass main sequence object. The low-excitation P-Cygni lines in the optical and UV are formed in the wind. The number density of absorption lines in the UV is so large that the wind spectrum acts as an iron curtain in front of the B-star. The terminal velocity of the wind of v{infinity}=100+/-30km/s is consistent with the star being a low-mass post-AGB star and the low effective gravity is attributed to the presence of a nearby, unseen, secondary. We estimate a mass-loss rate of M?=~10-8M?/yr. Narrow absorption and emission lines are observed which are formed in a circumsystem disk with a typical radius of 102R*. (2 data files).

Bakker, E. J.; Lamers, H. J. G. L. M.; Waters, L. B. F. M.; Waelkens, C.; Trams, N. R.; van Winckel, H.

1995-07-01

116

Two years of monitoring supergiant fast X-ray transients with Swift  

NASA Astrophysics Data System (ADS)

We present results based on 2 yr of intense Swift monitoring of three supergiant fast X-ray transients (SFXTs), IGR J16479-4514, XTE J1739-302 and IGR J17544-2619, which we started in 2007 October. Our out-of-outburst intensity-based X-ray (0.3-10 keV) spectroscopy yields absorbed power laws characterized by hard photon indices (?˜ 1 -2). The broad-band (0.3-150 keV) spectra of these sources, obtained while they were undergoing new outbursts observed during the second year of monitoring, can be fitted well with models typically used to describe the X-ray emission from accreting neutron stars in high-mass X-ray binaries. We obtain an assessment of how long each source spends in each state using a systematic monitoring with a sensitive instrument. By considering our monitoring as a casual sampling of the X-ray light curves, we can infer that the time these sources spend in bright outbursts is between 3 and 5 per cent of the total. The most probable X-ray flux for these sources is ˜(1 -2) × 10-11 erg cm-2 s-1 (2-10 keV, unabsorbed), corresponding to luminosities of the order of a few 1033 to a few 1034 erg s-1 (two orders of magnitude lower than the bright outbursts). In particular, the duty-cycle of inactivity is ˜19, 39 and 55 per cent (˜5 per cent uncertainty) for IGR J16479-4514, XTE J1739-302 and IGR J17544-2619, respectively. We present a complete list of BAT onboard detections, which further confirm the continued activity of these sources. This demonstrates that true quiescence is a rare state and that these transients accrete matter throughout their life at different rates. Variability in the X-ray flux is observed at all time-scales and intensity ranges we can probe. Superimposed on the day-to-day variability is intraday flaring, which involves flux variations up to one order of magnitude that can occur down to time-scales as short as ˜1 ks, and which can be naturally explained by the accretion of single clumps composing the donor wind with masses Mcl˜ (0.3 -2) × 1019 g. Thanks to the Swift observations, the general picture we obtain is that, despite individual differences, common X-ray characteristics of this class are now well defined, such as outburst lengths well in excess of hours, with a multiple peaked structure, and a high dynamic range (including bright outbursts), up to approximately four orders of magnitude.

Romano, P.; La Parola, V.; Vercellone, S.; Cusumano, G.; Sidoli, L.; Krimm, H. A.; Pagani, C.; Esposito, P.; Hoversten, E. A.; Kennea, J. A.; Page, K. L.; Burrows, D. N.; Gehrels, N.

2011-01-01

117

Wind Variability of B Supergiants. No. 2; The Two-component Stellar Wind of gamma Arae  

NASA Technical Reports Server (NTRS)

The stellar wind of the rapidly rotating early-B supergiant, gamma Ara, is studied using time series, high-resolution IUE spectroscopy secured over approx. 6 days in 1993 March. Results are presented based on an analysis of several line species, including N(N), C(IV), Si(IV), Si(III), C(II), and Al(III). The wind of this star is grossly structured, with evidence for latitude-dependent mass loss which reflects the role of rapid rotation. Independent, co-existing time variable features are identified at low-velocity (redward of approx. -750 km/s) and at higher-speeds extending to approx. -1500 km/s. The interface between these structures is 'defined' by the appearance of a discrete absorption component which is extremely sharp (in velocity space). The central velocity of this 'Super DAC' changes only gradually, over several days, between approx. -400 and -750 km/s in most of the ions. However, its location is shifted redward by almost 400 km/s in Al(III) and C(II), indicating that the physical structure giving rise to this feature has a substantial velocity and ionization jump. Constraints on the relative ionization properties of the wind structures are discussed, together with results based on SEI line-profile-fitting methods. The overall wind activity in gamma Ara exhibits a clear ion dependence, such that low-speed features are promoted in low-ionization species, including Al(III), C(II), and Si(III). We also highlight that - in contrast to most OB stars - there are substantial differences in the epoch-to-epoch time-averaged wind profiles of gamma Ara. We interpret the results in terms of a two-component wind model for gamma Ara, with an equatorially compressed low ionization region, and a high speed, higher-ionization polar outflow. This picture is discussed in the context of the predicted bi-stability mechanism for line-driven winds in rapidly rotating early-B type stars, and the formation of compressed wind regions in rapidly rotating hot stars. The apparent absence of a substantial shift in the wind ionization mixture of gamma Ara, and the normal nature of its photospheric spectrum, suggests wind-compression as the likely dominant cause for the observed equatorial density enhancements.

Prinja, R. K.; Massa, D.; Fullerton, A. W.; Howarth, I. D.; Pontefract, M.

1996-01-01

118

Unveiling Type IIb Supernova Progenitors: SN 2011hs from a Supergiant Star  

NASA Astrophysics Data System (ADS)

Type IIb Supernovae are the final evolutionary stage of massive stars that were able to retain only a thin (lesssim 1 M_{odot}) H/He external envelope at the time of the explosion. The mechanism of mass-loss that made such final structure possible and the nature of such progenitor stars are still open issues. We present the results obtained from the study of a sample of Type IIb SNe, in particular, of SN 2011hs (Bufano et al., 2013, MNRAS submitted). SN 2011hs was a relatively faint (M_{B} = -15.6 mag) and red Type IIb SN, characterized by a narrow light curve shape. Its spectral evolution showed the metamorphosis typical of this class of SN, from spectra dominated by H I lines to spectra where He I features dominate, but with broad absorption line profiles indicating high expansion velocities. Modeling the light curve of SN 2011hs and its velocity evolution with hydrodynamical calculations, we estimated that the SN is consistent with the explosion of a 3-4 M_{odot} He-core star, from a main sequence mass of 12-15 M_{odot}, ejecting a ^{56}Ni mass equal to 0.04 M_{odot} and characterized by an explosion energy of E? 8.5× 10^{50} erg s^{-1}. Based on the light curve evolution, we assumed that the explosion occurred 6 days before the discovery (2,455,872 ± 4 JD), resulting in an adiabatic cooling phase lasting 8 days, similarly to SN 1993J. Since the duration and the decreasing rate of the cooling branch depends mainly on the progenitor size, we could infer from it a progenitor radius of ? 500-600 R_{odot}, like a supergiant star. Our modeling rules out models with He core mass >5 M_{odot}, i.e. main sequence masses above 20 M_{odot}. Such a lower limit for the progenitor mass could indicate the possibility of a binary origin, although the radio light curve does not show strong deviations, typically signature of the presence of a companion star.

Bufano, F.

2014-10-01

119

Long-period variables in the Magellanic Clouds - Supergiants, AGB stars, supernova precursors, planetary nebula precursors, and enrichment of the interstellar medium  

Microsoft Academic Search

IR JHK magnitudes and low dispersion red spectra for 90 long period variables (LPVs) in the Magellanic Clouds show the LPVs to fall into distinct groups of core He or C burning supergiants and asymptotic giant branch (AGB) stars. The existence of stars at the AGB limit provides direct evidence that the more massive AGB stars produce supernovae. Carbon star

P. R. Wood; M. S. Bessell; M. W. Fox

1983-01-01

120

INTEGRAL and Swift observations of the supergiant fast X-ray transient AXJ1845.0-0433=IGRJ18450-0435  

E-print Network

Context: AXJ1845.0-0433 was discovered by ASCA in 1993 during fast outburst activity characterized by several flares on short timescales. Up to now, the source was not detected again by any X-ray mission. Its optical counterpart is suggested to be an O9.5I supergiant star, which is the only remarkable object found inside the ASCA error box. Aims: To detect and characterize new fast outbursts of AXJ1845.0-0433 and confirm its supergiant HMXB nature, using INTEGRAL and archival Swift XRT observations. Methods: We performed an analysis of INTEGRAL IBIS and JEM-X data with OSA 5.1 as well as an analysis of archive Swift XRT data. Results: We report on fast flaring activity from the source on timescales of a few tens of minutes, the first to be reported since its discovery in 1993. Two outbursts have been detected by INTEGRAL (Apr 2005 and Apr 2006) with similar peak fluxes and peak luminosities of 80 mCrab and 9.3X10^35 erg s^-1 (20--40 keV), respectively. Two other outbursts were detected by Swift XRT on Nov 2005 and Mar 2006. The refined Swift XRT position of AXJ1845.0-0433 confirms its association with the supergiant star previously proposed as optical counterpart. Conclusions: Our INTEGRAL and Swift results fully confirm the supergiant HMXB nature of AXJ1845.0-0433 which can therefore be classified as a supergiant fast X-ray transient. Moreover they provide for the first time evidence of its recurrent fast transient behaviour.

V. Sguera; A. J. Bird; A. J. Dean; A. Bazzano; P. Ubertini; R. Landi; A. Malizia; E. J. Barlow; D. J. Clark; A. B. Hill; M. Molina

2006-10-30

121

Statistical properties of a sample of periodically variable B-type supergiants. Evidence for opacity-driven gravity-mode oscillations  

NASA Astrophysics Data System (ADS)

Aims:We have studied a sample of 28 periodically variable B-type supergiants selected from the HIPPARCOS mission and 12 comparison stars covering the whole B-type spectral range. Our goal is to test if their variability is compatible with opacity-driven non-radial oscillations. Methods: We have used the NLTE atmosphere code FASTWIND to derive the atmospheric and wind parameters of the complete sample through line profile fitting. We applied the method to selected H, He, and Si line profiles, measured with the high resolution CES spectrograph attached to the ESO CAT telescope in La Silla, Chile. Results: From the location of the stars in the (log T_eff, log g) diagram, we suggest that variability of our sample supergiants is indeed due to the gravity modes resulting from the opacity mechanism. We find nine of the comparison stars to be periodically variable as well, and suggest them to be new ? Cyg variables. We find marginal evidence of a correlation between the amplitude of the photometric variability and the wind density. We investigate the wind momentum-luminosity relation for the whole range of B spectral type supergiants, and find that the later types (>B5) perfectly follow the relation for A supergiants. Additionally, we provide a new spectral type - T_eff calibration for B supergiants. Conclusions: .Our results imply the possibility of probing internal structure models of massive stars of spectral type B through seismic tuning of gravity modes. Figures of the spectral line fits and discussion of the individual objects, Appendices A, B and Table 6 are only available in electronic form at http://www.aanda.org

Lefever, K.; Puls, J.; Aerts, C.

2007-03-01

122

Monitoring supergiant fast X-ray transients with Swift: results from the first year  

NASA Astrophysics Data System (ADS)

The advent of Swift has allowed, for the first time, the possibility to give supergiant fast X-ray transients (SFXTs), the new class of high-mass X-ray binaries discovered by the International Gamma-Ray Astrophysics Laboratory, non-serendipitous attention throughout most phases of their life. In this paper, we present our results based on the first year of intense Swift monitoring of four SFXTs, IGR J16479-4514, XTE J1739-302, IGR J17544-2619 and AX J1841.0-0536. We obtain the first assessment of how long each source spends in each state using a systematic monitoring with a sensitive instrument. The duty-cycle of inactivity is ~17, 28, 39 and 55 per cent (~5per cent uncertainty), for IGR J16479-4514, AX J1841.0-0536, XTE J1739-302 and IGR J17544-2619, respectively, so that true quiescence, which is below our detection ability even with the exposures we collected in 1 yr, is a rare state, when compared with estimates from less sensitive instruments. This demonstrates that these transients accrete matter throughout their lifetime at different rates. AX J1841.0-0536 is the only source which has not undergone a bright outburst during our monitoring campaign. Although individual sources behave somewhat differently, common X-ray characteristics of this class are emerging, such as outburst lengths well in excess of hours, with a multiple peaked structure. A high dynamic range (including bright outbursts) of ~4 orders of magnitude has been observed in IGR J17544-2619 and XTE J1739-302, of ~3 in IGR J16479-4514 and of about 2 in AX J1841.0-0536 (this lowest range is due to the lack of bright flares). We also present a complete list of Burst Alert Telescope (BAT) on-board detections, which complements our previous work, and further confirms the continuous activity of these sources. We performed out-of-outburst intensity-based spectroscopy. In particular, spectral fits with an absorbed blackbody always result in blackbody radii of a few hundred metres, consistent with being emitted from a small portion of the neutron star surface, very likely the neutron star polar caps. We used the whole BAT data set, since the beginning of the mission, to search for periodicities due to orbital motion and found Porb = 3.32d for IGR J16479-4514, confirming previous findings. We also present the Ultraviolet/Optical Telescope (UVOT) data of these sources; we show the UVOT light curves of AX J1841.0-0536 and the ones of XTE J1739-302 before, during and after the outbursts.

Romano, P.; Sidoli, L.; Cusumano, G.; La Parola, V.; Vercellone, S.; Pagani, C.; Ducci, L.; Mangano, V.; Cummings, J.; Krimm, H. A.; Guidorzi, C.; Kennea, J. A.; Hoversten, E. A.; Burrows, D. N.; Gehrels, N.

2009-11-01

123

Einstein Observatory magnitude-limited X-ray survey of late-type giant and supergiant stars  

NASA Technical Reports Server (NTRS)

Results are presented of an extensive X-ray survey of 380 giant and supergiant stars of spectral types from F to M, carried out with the Einstein Observatory. It was found that the observed F giants or subgiants (slightly evolved stars with a mass M less than about 2 solar masses) are X-ray emitters at the same level of main-sequence stars of similar spectral type. The G giants show a range of emissions more than 3 orders of magnitude wide; some single G giants exist with X-ray luminosities comparable to RS CVn systems, while some nearby large G giants have upper limits on the X-ray emission below typical solar values. The K giants have an observed X-ray emission level significantly lower than F and F giants. None of the 29 M giants were detected, except for one spectroscopic binary.

Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.; Bookbinder, J.

1990-01-01

124

BROADBAND ESO/VISIR-SPITZER INFRARED SPECTROSCOPY OF THE OBSCURED SUPERGIANT X-RAY BINARY IGR J16318-4848  

SciTech Connect

A new class of X-ray binaries has recently been discovered by the high-energy observatory INTEGRAL. It is composed of intrinsically obscured supergiant high-mass X-ray binaries, unveiled by means of multi-wavelength X-ray, optical, near- and mid-infrared observations, in particular, photometric and spectroscopic observations using ESO facilities. However, the fundamental questions about these intriguing sources, namely, their formation, evolution, and the nature of their environment, are still unsolved. Among them, IGR J16318-4848, a compact object orbiting around a supergiant B[e] star, seems to be one of the most extraordinary celestial sources of our Galaxy. We present here new ESO/Very Large Telescope (VLT) VISIR mid-infrared (MIR) spectroscopic observations of this source. First, line diagnostics allow us to confirm the presence of absorbing material (dust and cold gas) enshrouding the whole binary system, and to characterize the nature of this material. Second, by fitting broadband near- to mid-infrared spectral energy distribution, including ESO NTT/SofI, VLT/VISIR, and Spitzer data, with a phenomenological model for sgB[e] stars, we show that the star is surrounded by an irradiated rim heated to a temperature of {approx}3800-5500 K, along with a viscous disk component at an inner temperature of {approx}750 K. VISIR data allow us to exclude the spherical geometry for the dust component. This detailed study will allow us in the future to get better constraints on the formation and evolution of such rare and short-living high-mass X-ray binary systems in our Galaxy.

Chaty, S.; Rahoui, F., E-mail: sylvain.chaty@cea.fr, E-mail: frahoui@cfa.harvard.edu [AIM (UMR-E 9005 CEA/DSM-CNRS-Universite Paris Diderot) Irfu/Service d'Astrophysique, Centre de Saclay, FR-91191 Gif-sur-Yvette Cedex (France)

2012-06-01

125

On the magnetic structure and wind parameter profiles of Alfven wave driven winds in late-type supergiant stars  

E-print Network

Cool stars at giant and supergiant evolutionary phases present low velocity and high density winds, responsible for the observed high mass-loss rates. Although presenting high luminosities, radiation pressure on dust particles is not sufficient to explain the wind acceleration process. Among the possible solutions to this still unsolved problem, Alfven waves are, probably, the most interesting for their high efficiency in transfering energy and momentum to the wind. Typically, models of Alfven wave driven winds result in high velocity winds if they are not highly damped. In this work we determine self-consistently the magnetic field geometry and solve the momentum, energy and mass conservation equations, to demonstrate that even a low damped Alfven wave flux is able to reproduce the low velocity wind. We show that the magnetic fluxtubes expand with a super-radial factor S>30 near the stellar surface, larger than that used in previous semi-empirical models. The rapid expansion results in a strong spatial dilution of the wave flux. We obtained the wind parameter profiles for a typical supergiant star of 16 M_sun. The wind is accelerated in a narrow region, coincident with the region of high divergence of the magnetic field lines, up to 100 km/s. For the temperature, we obtained a slight decrease near the surface for low damped waves, because the wave heating mechanism is less effective than the radiative losses. The peak temperature occurs at 1.5 r_0 reaching 6000 K. Propagating outwards, the wind cools down mainly due to adiabatic expansion.

D. Falceta-Goncalves; A. A. Vidotto; V. Jatenco-Pereira

2006-02-14

126

QUANTITATIVE SPECTROSCOPY OF BLUE SUPERGIANT STARS IN THE DISK OF M81: METALLICITY, METALLICITY GRADIENT, AND DISTANCE  

SciTech Connect

The quantitative spectral analysis of low-resolution ({approx}5 A) Keck LRIS spectra of blue supergiants in the disk of the giant spiral galaxy M81 is used to determine stellar effective temperatures, gravities, metallicities, luminosities, interstellar reddening, and a new distance using the flux-weighted gravity-luminosity relationship. Substantial reddening and extinction are found with E(B - V) ranging between 0.13 and 0.38 mag and an average value of 0.26 mag. The distance modulus obtained after individual reddening corrections is 27.7 {+-} 0.1 mag. The result is discussed with regard to recently measured tip of the red giant branch and Cepheid distances. The metallicities (based on elements such as iron, titanium, magnesium) are supersolar ( Almost-Equal-To 0.2 dex) in the inner disk (R {approx}< 5 kpc) and slightly subsolar ( Almost-Equal-To - 0.05 dex) in the outer disk (R {approx}> 10 kpc) with a shallow metallicity gradient of 0.034 dex kpc{sup -1}. The comparison with published oxygen abundances of planetary nebulae and metallicities determined through fits of Hubble Space Telescope color-magnitude diagrams indicates a late metal enrichment and a flattening of the abundance gradient over the last 5 Gyr. This might be the result of gas infall from metal-rich satellite galaxies. Combining these M81 metallicities with published blue supergiant abundance studies in the Local Group and the Sculptor Group, a galaxy mass-metallicity relationship based solely on stellar spectroscopic studies is presented and compared with recent studies of Sloan Digital Sky Survey star-forming galaxies.

Kudritzki, Rolf-Peter; Urbaneja, Miguel A.; Gazak, Zachary; Bresolin, Fabio [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Przybilla, Norbert [Dr. Remeis-Sternwarte Bamberg and ECAP, D-96049 Bamberg (Germany); Gieren, Wolfgang; Pietrzynski, Grzegorz, E-mail: kud@ifa.hawaii.edu, E-mail: urbaneja@ifa.hawaii.edu, E-mail: zgazak@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: przybilla@sternwarte.uni-erlangen.de, E-mail: wgieren@astro-udec.cl, E-mail: pietrzyn@astrouw.edu.pl [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)

2012-03-01

127

High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR  

NASA Astrophysics Data System (ADS)

Context. The mass-loss mechanism in red giants and red supergiants is not yet understood well. The SiO fundamental lines near 8 ?m are potentially useful for probing the outer atmosphere, which is essential for clarifying the mass-loss mechanism. However, these lines have been little explored until now. Aims: We present high spectral resolution spectroscopic observations of the SiO fundamental lines near 8.1 ?m in 16 bright red giants and red supergiants. Our sample consists of seven normal (i.e., non-Mira) K-M giants (from K1.5 to M6.5), three Mira stars, three optically bright red supergiants, two dusty red supergiants, and the enigmatic object GCIRS3 near the Galactic center. Methods: Our program stars were observed between 8.088 ?m and 8.112 ?m with a spectral resolution of 30 000 using VLT/VISIR. Results: We detected SiO fundamental lines in all of our program stars except for GCIRS3. The SiO lines in normal K and M giants as well as optically bright (i.e., not dusty) red supergiants do not show P-Cyg profiles or blueshifts, which means the absence of systematic outflows in the SiO line forming region. We detected P-Cyg profiles in the SiO lines in the dusty red supergiants VY CMa and VX Sgr, with the latter object being a new detection. These SiO lines originate in the outflowing gas with the thermal dust continuum emission seen as the background. The outflow velocities of the SiO line forming region in VY CMa and VX Sgr are estimated to be 27 km s-1 and 17 km s-1, respectively. We derived basic stellar parameters (effective temperature, surface gravity, luminosity, and mass) for the normal K-M giants and optically bright red supergiants in our sample and compared the observed VISIR spectra with synthetic spectra predicted from MARCS photospheric models. Most of the SiO lines observed in the program stars warmer than ~3400 K are reasonably reproduced by the MARCS models, which allowed us to estimate the silicon abundance as well as the 28Si/29Si and 28Si/30Si ratios. However, we detected possible absorption excess in some SiO lines. Moreover, the SiO lines in the cooler red giants and red supergiant cannot be explained by the MARCS models at all, even if the dust emission is taken into account. This disagreement may be a signature of the dense, extended molecular outer atmosphere. Based on VISIR observations made with the Very Large Telescope of the European Southern Observatory. Program ID: 087.D-0522(A).Reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A47

Ohnaka, K.

2014-01-01

128

Hunting for Magnetars in High Mass X-ray Binaries. The Case of SuperGiant Fast X-Ray Transients  

E-print Network

In this paper we summarize some aspects of the wind accretion theory in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. In particular, we concentrate on the different types of interaction between the inflowing wind matter and the neutron star magnetosphere that are relevant when accretion of matter onto the neutron star surface is largely inhibited; these include inhibition by the centrifugal and magnetic barriers. We show that very large luminosity swings (~10^4 or more on time scales as short as hours) can result from transitions across different regimes. This scenario is then applied to the activity displayed by supergiant fast X-ray transients (SFXTs), a new class of high mass X-ray binaries in our galaxy recently discovered with INTEGRAL. According to this interpretation we argue that SFXTs which display very large luminosity swings and host a slowly spinning neutron star are expected to be characterized by magnetar-like fields. Supergiant fast X-ray transients might thus provide a unique opportunity to detect and study accreting magnetars in binary systems.

E. Bozzo; M. Falanga; L. Stella

2008-11-06

129

Short time-scale spectral variability in the A0 supergiant HD 92207 and the importance of line profile variations for the interpretation of FORS 2 spectropolarimetric observations  

NASA Astrophysics Data System (ADS)

Our recent search for the presence of a magnetic field in the bright early A-type supergiant HD 92207 using FOcal reducer low dispersion spectrograph (FORS) 2 in spectropolarimetric mode indicated the presence of a longitudinal magnetic field of the order of a few hundred gauss. Assuming the ideal case of a non-variable star, this discovery has recently been questioned in one work trying to demonstrate the importance of non-photon noise in FORS 2 observations. The assumption of non-variability of HD 92207 can, however, not be held since substantial profile variations of diverse lines on a time-scale of minutes or maybe even a fraction of a minute are detected in FORS 2 spectra. The presence of short-term spectral variability in blue supergiants, which are considered as Type II supernova progenitors, has not been a subject of systematic studies before and is critical for the current theoretical understanding of their physics. Given the detected short-term variability, the question of the presence of a magnetic field cannot be answered without proper modelling of the impact of such a variability on the measurements of the magnetic field. Since the short-term periodicity does not fit into the currently known domain of non-radially pulsating supergiants, its confirmation is of great importance for models of stellar evolution.

Hubrig, S.; Schöller, M.; Kholtygin, A. F.

2014-05-01

130

Clumped stellar winds in supergiant high-mass X-ray binaries: X-ray variability and photoionization  

NASA Astrophysics Data System (ADS)

The clumping of massive star winds is an established paradigm, which is confirmed by multiple lines of evidence and is supported by stellar wind theory. The purpose of this paper is to bridge the gap between detailed models of inhomogeneous stellar winds in single stars and the phenomenological description of donor winds in supergiant high-mass X-ray binaries (HMXBs). We use the results from time-dependent hydrodynamical models of the instability in the line-driven wind of a massive supergiant star to derive the time-dependent accretion rate on to a compact object in the Bondi-Hoyle-Lyttleton approximation. The strong density and velocity fluctuations in the wind result in strong variability of the synthetic X-ray light curves. The model predicts a large-scale X-ray variability, up to eight orders of magnitude, on relatively short time-scales. The apparent lack of evidence for such strong variability in the observed HMXBs indicates that the details of the accretion process act to reduce the variability resulting from the stellar wind velocity and density jumps. We study the absorption of X-rays in the clumped stellar wind by means of a two-dimensional stochastic wind model. The monochromatic absorption in the cool stellar wind, depending on the orbital phase, is computed for realistic stellar wind opacity. We find that the absorption of X-rays changes strongly at different orbital phases. The degree of the variability resulting from the absorption in the wind depends on the shape of the wind clumps, and this is stronger for oblate clumps. We address the photoionization in the clumped wind, and we show that the degree of ionization is affected by the wind clumping. We derive a correction factor for the photoionization parameter, and we show that the photoionization parameter is reduced by a factor ? compared to the smooth wind models with the same mass-loss rate, where ? is the wind inhomogeneity parameter. We conclude that wind clumping must also be taken into account when comparing the observed and model spectra of the photoionized stellar wind.

Oskinova, L. M.; Feldmeier, A.; Kretschmar, P.

2012-04-01

131

Herschel SPIRE and PACS observations of the red supergiant VY CMa: analysis of the molecular line spectra  

NASA Astrophysics Data System (ADS)

We present an analysis of the far-infrared and submillimetre molecular emission-line spectrum of the luminous M-supergiant VY CMa, observed with the Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer for Herschel spectrometers aboard the Herschel Space Observatory. Over 260 emission lines were detected in the 190-650 ?m SPIRE Fourier Transform Spectrometer spectra, with one-third of the observed lines being attributable to H2O. Other detected species include CO, 13CO, H_2^{18}O, SiO, HCN, SO, SO2, CS, H2S and NH3. Our model fits to the observed 12CO and 13CO line intensities yield a 12C/13C ratio of 5.6 ± 1.8, consistent with measurements of this ratio for other M-supergiants, but significantly lower than previously estimated for VY CMa from observations of lower-J lines. The spectral line energy distribution for 20 SiO rotational lines shows two temperature components: a hot component at ˜1000 K, which we attribute to the stellar atmosphere and inner wind, plus a cooler ˜200 K component, which we attribute to an origin in the outer circumstellar envelope. We fit the line fluxes of 12CO, 13CO, H2O and SiO, using the SMMOL non-local thermodynamic equilibrium (LTE) line transfer code, with a mass-loss rate of 1.85 × 10-4 M? yr-1 between 9R* and 350R*. We also fit the observed line fluxes of 12CO, 13CO, H2O and SiO with SMMOL non-LTE line radiative transfer code, along with a mass-loss rate of 1.85 × 10-4 M? yr-1. To fit the high rotational lines of CO and H2O, the model required a rather flat temperature distribution inside the dust condensation radius, attributed to the high H2O opacity. Beyond the dust condensation radius the gas temperature is fitted best by an r-0.5 radial dependence, consistent with the coolant lines becoming optically thin. Our H2O emission-line fits are consistent with an ortho:para ratio of 3 in the outflow.

Matsuura, Mikako; Yates, J. A.; Barlow, M. J.; Swinyard, B. M.; Royer, P.; Cernicharo, J.; Decin, L.; Wesson, R.; Polehampton, E. T.; Blommaert, J. A. D. L.; Groenewegen, M. A. T.; Van de Steene, G. C.; van Hoof, P. A. M.

2014-01-01

132

Revised Stellar Temperatures for Magellanic Cloud O Supergiants from Far Ultraviolet Spectroscopic Explorer and Very Large Telescope UV-Visual Echelle Spectrograph Spectroscopy  

NASA Astrophysics Data System (ADS)

We have undertaken quantitative analysis of four LMC and SMC O4-9.7 extreme supergiants using far-ultraviolet FUSE, ultraviolet IUE/Hubble Space Telescope, and optical Very Large Telescope UV-Visual Echelle Spectrograph spectroscopy. Extended, non-LTE model atmospheres that allow for the consistent treatment of line blanketing, developed by Hillier & Miller, are used to analyze wind and photospherics spectral features simultaneously. Using H? to constrain mass-loss rates, He I-He II photospheric lines reveal stellar temperatures that are systematically (5-7.5 kK) and substantially (15%-20%) lower than previously derived from unblanketed, plane-parallel, non-LTE photospheric studies. We have confidence in these revisions since derived temperatures generally yield consistent fits across the entire 912-7000 Å observed spectral range. In particular, we are able to resolve the UV-optical temperature discrepancy identified for AzV 232 (O7 Iaf+) in the SMC by Fullerton and coworkers. The temperature and abundance sensitivity of far-ultraviolet, UV, and optical lines are discussed. ``Of'' classification criteria are directly linked to (strong) nitrogen enrichment (via N III ?4097) and (weak) carbon depletion (via C III ??4647-4651), providing evidence for mixing of unprocessed and CNO-processed material at their stellar surfaces. Oxygen abundances are more difficult to constrain, except via O II lines in the O9.7 supergiant, for which it is also found to be somewhat depleted. Unfortunately, He/H is very difficult to determine in individual O supergiants because of uncertainties in microturbulence and the atmospheric scale height. The effect of wind clumping is also investigated, for which P V ??1118-1128 potentially provides a useful diagnostic in O star winds, unless phosphorus can be independently demonstrated to be underabundant relative to other heavy elements. Revised stellar properties affect existing calibrations of (1) Lyman continuum photons-a factor of 2 lower for the O4 supergiant-and (2) kinetic energy released into the ISM by O supergiants. Our results also have importance for the calibration of the wind momentum-luminosity relationship for OB stars, particularly since the stars studied here are among the visually brightest OB stars in external galaxies. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by Johns Hopkins University under NASA contract NAS 5-32985. Also based in part on observations collected at the European Southern Observatory Very Large Telescopes in programs 65.H-0705 and 67.D-0238, plus archival data obtained with the NASA-ESA Hubble Space Telescope and NASA-ESA-PPARC International Ultraviolet Explorer.

Crowther, P. A.; Hillier, D. J.; Evans, C. J.; Fullerton, A. W.; De Marco, O.; Willis, A. J.

2002-11-01

133

ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY CMa  

E-print Network

The processes leading to dust formation and the subsequent role it plays in driving mass-loss in cool evolved stars is an area of intense study. Here, we present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, allowing us to trace dust on spatial scales down to 11 R$_{\\star}$ (71 AU). Two prominent dust components are detected and resolved. The brightest dust component, C, is located 334 mas (61 R$_{\\star}$) south-east of the star and has a dust mass of at least $2.5\\times 10^{-4} $M$_{\\odot}$. It has an emissivity spectral index of $\\beta =-0.1$ at its peak, implying that it is either optically thick at these frequencies with a cool core of $T_{d}\\lesssim 100$ K, and/or contains very large dust grains. Interestingly, not a single molecule in the ALMA data has emission close to th...

O'Gorman, E; Richards, A M S; Baudry, A; De Beck, E; Decin, L; Harper, G M; Humphreys, E M; Kervella, P; Khouri, T; Muller, S

2014-01-01

134

IGR J17354-3255 as bench test for investigation of ?-ray emission from Supergiant Fast X-ray Transients  

NASA Astrophysics Data System (ADS)

Among the different types of sources shining in the high energy sky, gamma-ray binaries are rapidly becoming the subject of major interest. In fact, in the last few years a number of High Mass X-ray Binaries (HMXBs) have been firmly detected from MeV to TeV energies, providing secure evidences that particles can be efficiently accelerated up to very high energies in such galactic systems. Similarly to this general and emerging class of gamma-ray binaries, in principle Supergiant Fast X-ray Transients (SFXTs) have all the "ingredients" to be transient high energy emitters. In this context, the SFXT IGR J17354-3255 is a good bench test and we present intriguing hints likely suggesting that it is a transient gamma-ray source flaring on short timescales. If fully confirmed by further studies, the implications stemming are huge, both theoretically and observationally, and would add a further extreme characteristic to the already extreme class of SFXTs.

Sguera, V.

2013-06-01

135

RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES: NLTE EFFECTS IN J-BAND IRON AND TITANIUM LINES  

SciTech Connect

Detailed non-LTE (NLTE) calculations for red supergiant (RSG) stars are presented to investigate the influence of NLTE on the formation of atomic iron and titanium lines in the J band. With their enormous brightness at J band RSG stars are ideal probes of cosmic abundances. Recent LTE studies have found that metallicities accurate to 0.15 dex can be determined from medium-resolution spectroscopy of individual RSGs in galaxies as distant as 10 Mpc. The NLTE results obtained in this investigation support these findings. NLTE abundance corrections for iron are smaller than 0.05 dex for effective temperatures between 3400 K and 4200 K and 0.1 dex at 4400 K. For titanium the NLTE abundance corrections vary smoothly between -0.4 dex and +0.2 dex as a function of effective temperature. For both elements, the corrections also depend on stellar gravity and metallicity. The physical reasons behind the NLTE corrections and the consequences for extragalactic J-band abundance studies are discussed.

Bergemann, Maria; Kudritzki, Rolf-Peter; Lind, Karin [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str.1, D-85741 Garching (Germany); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS, F-34095 Montpellier (France); Davies, Ben [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Gazak, Zach, E-mail: mbergema@mpa-garching.mpg.de, E-mail: klind@mpa-garching.mpg.de, E-mail: kud@ifa.hawaii.edu, E-mail: zgazak@ifa.hawaii.edu, E-mail: bertrand.plez@univ-montp2.fr, E-mail: bdavies@ast.cam.ac.uk [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2012-06-01

136

Sharpest views of Betelgeuse reveal how supergiant stars lose mass-Unveiling the true face of a behemoth  

NASA Astrophysics Data System (ADS)

Using different state-of-the-art techniques on ESO's Very Large Telescope, two independent teams of astronomers have obtained the sharpest ever views of the supergiant star Betelgeuse. They show that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. These discoveries provide important clues to help explain how these mammoths shed material at such a tremendous rate. Betelgeuse - the second brightest star in the constellation of Orion (the Hunter) - is a red supergiant, one of the biggest stars known, and almost 1000 times larger than our Sun [1]. It is also one of the most luminous stars known, emitting more light than 100000 Suns. Such extreme properties foretell the demise of a short-lived stellar king. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight. Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material - about the mass of the Sun - in only 10 000 years. Two teams of astronomers have used ESO's Very Large Telescope (VLT) and the most advanced technologies to take a closer look at the gigantic star. Their combined work suggests that an answer to the long-open mass-loss question may well be at hand. The first team used the adaptive optics instrument, NACO, combined with a so-called "lucky imaging" technique, to obtain the sharpest ever image of Betelgeuse, even with Earth's turbulent, image-distorting atmosphere in the way. With lucky imaging, only the very sharpest exposures are chosen and then combined to form an image much sharper than a single, longer exposure would be. The resulting NACO images almost reach the theoretical limit of sharpness attainable for an 8-metre telescope. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground. "Thanks to these outstanding images, we have detected a large plume of gas extending into space from the surface of Betelgeuse," says Pierre Kervella from the Paris Observatory, who led the team. The plume extends to at least six times the diameter of the star, corresponding to the distance between the Sun and Neptune. "This is a clear indication that the whole outer shell of the star is not shedding matter evenly in all directions," adds Kervella. Two mechanisms could explain this asymmetry. One assumes that the mass loss occurs above the polar caps of the giant star, possibly because of its rotation. The other possibility is that such a plume is generated above large-scale gas motions inside the star, known as convection - similar to the circulation of water heated in a pot. To arrive at a solution, astronomers needed to probe the behemoth in still finer detail. To do this Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues used interferometry. With the AMBER instrument on ESO's Very Large Telescope Interferometer, which combines the light from three 1.8-metre Auxiliary Telescopes of the VLT, the astronomers obtained observations as sharp as those of a giant, virtual 48-metre telescope. With such superb resolution, the astronomers were able to detect indirectly details four times finer still than the amazing NACO images had already allowed (in other words, the size of a marble on the ISS, as seen from the ground). "Our AMBER observations are the sharpest observations of any kind ever made of Betelgeuse. Moreover, we detected how the gas is moving in different areas of Betelgeuse's surface ? the first time this has been done for a star other than the Sun", says Ohnaka. The AMBER observations revealed that the gas in Betelgeuse's atmosphere is moving vigorously up and down, and that these bubbles are as large as the supergiant star itself. Their unrivalled observations have led

2009-07-01

137

CHARA/MIRC Observations of Two M Supergiants in Perseus OB1: Temperature, Bayesian Modeling, and Compressed Sensing Imaging  

NASA Astrophysics Data System (ADS)

Two red supergiants (RSGs) of the Per OB1 association, RS Per and T Per, have been observed in the H band using the Michigan Infra-Red Combiner (MIRC) instrument at the CHARA array. The data show clear evidence of a departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. The stellar surfaces are first modeled as limb-darkened disks based on SATLAS models that fit both MIRC interferometric data and publicly available spectrophotometric data. Bayesian model selection is then used to determine the most probable number of spots. The effective surface temperatures are also determined and give further support to the recently derived hotter temperature scales of RSGs. The stellar surfaces are reconstructed by our model-independent imaging code SQUEEZE, making use of its novel regularizer based on Compressed Sensing theory. We find excellent agreement between the model-selection results and the reconstructions. Our results provide evidence for the presence of near-infrared spots representing about 3%-5% of the stellar flux.

Baron, F.; Monnier, J. D.; Kiss, L. L.; Neilson, H. R.; Zhao, M.; Anderson, M.; Aarnio, A.; Pedretti, E.; Thureau, N.; ten Brummelaar, T. A.; Ridgway, S. T.; McAlister, H. A.; Sturmann, J.; Sturmann, L.; Turner, N.

2014-04-01

138

The Orbit and Position of the X-ray Pulsar XTE J1855-026: An Eclipsing Supergiant System  

NASA Technical Reports Server (NTRS)

A pulse timing orbit has been obtained for the X-ray binary XTEJ1855-026 using observations made with the Proportional Counter Array on board the Rossi X-ray Timing Explorer. The mass function obtained of approximately 16 solar mass together with the detection of an extended near-total eclipse confirm that the primary star is supergiant as predicted. The orbital eccentricity is found to be very low with a best fit value of 0.04 +/- 0.02. The orbital period is also refined to be 6.0724 +/- 0.0009 days using an improved and extended light curve obtained with RXTE's All Sky Monitor. Observations with the ASCA satellite provide an improved source location of R.A.= 18 hr 55 min 31.3 sec, decl.= -02 deg 36 min 24.0 sec (2000) with an estimated systematic uncertainty of less than 12 min. A serendipitous new source, AX J1855.4-0232, was also discovered during the ASCA observations.

Corbet, Robin H. D.; Mukai, Koji; White, Nicholas E. (Technical Monitor)

2002-01-01

139

The supergiant shell with triggered star formation in the dwarf irregular galaxy IC 2574: neutral and ionized gas kinematics  

NASA Astrophysics Data System (ADS)

We analyse the ionized gas kinematics in the star formation regions of the supergiant shell (SGS) of the IC 2574 galaxy using observations made with the Fabry-Perot interferometer at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences; the data of the H I Nearby Galaxy Survey (THINGS) are used to analyse the neutral gas kinematics in the area. We perform the `derotation' of the H? and H I data cubes and show its efficiency in the kinematics analysis. We confirm the SGS expansion velocity of 25 km s-1 obtained previously and conclude that the SGS is located at the far side of the galactic disc plane. We determine the expansion velocities, kinematic ages and the required mechanical energy input rates for four star formation complexes in the walls of the SGS; for those remaining, we give the limiting values of the above parameters. A comparison with the age and energy input of the stellar population of the complexes shows that sufficient energy is fed to all H II regions except one. We discuss in detail the possible nature of this region and that of another region, which was believed to be a supernova remnant, according to radio observations. We have measured the expansion velocity of the latter and we can confirm its identification as an old supernova remnant. Our observations have allowed us to identify a faint diffuse H? emission inside the SGS, which was not been previously observed.

Egorov, O. V.; Lozinskaya, T. A.; Moiseev, A. V.; Smirnov-Pinchukov, G. V.

2014-10-01

140

MASER OBSERVATIONS OF WESTERLUND 1 AND COMPREHENSIVE CONSIDERATIONS ON MASER PROPERTIES OF RED SUPERGIANTS ASSOCIATED WITH MASSIVE CLUSTERS  

SciTech Connect

We report the results of Australia Telescope Compact Array observations of the Westerlund 1 (Wd1) region in the SiO v = 1, J = 1-0, and H{sub 2}O 6{sub 16}-5{sub 23} maser lines, and we also report the analysis of maser properties of red supergiants (RSGs) associated with six massive clusters including Wd1. The primary purpose of this research is to explore possibilities of using maser emission for investigating the nature of massive clusters and associated RSGs. The SiO v = 1, J = 1-0, and H{sub 2}O 6{sub 16}-5{sub 23} maser lines are detected toward two of four known RSGs in Wd1. The large velocity ranges of maser emission are consistent with the RSG status. RSGs with maser emission tend to exhibit redder log (F {sub 21}/F {sub 12}) and [K-12.13] colors compared to RSGs with no maser emission. The mass-loss rates derived from dust radiative transfer modeling suggest that RSGs with maser emission tend to exhibit larger mass-loss rates compared to RSGs with no maser emission. In an extended sample of 57 RSGs in six massive clusters, detections in the SiO line tend to homogeneously distribute in absolute luminosity L, whereas those in the H{sub 2}O line tend to distribute in a region with large L values.

Fok, Thomas K. T.; Nakashima, Jun-ichi; Yung, Bosco H. K.; Hsia, Chih-Hao [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Deguchi, Shuji, E-mail: junichi@hku.hk [Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)

2012-11-20

141

Low-amplitude rotational modulation rather than pulsations in the CoRoT B-type supergiant HD 46769  

NASA Astrophysics Data System (ADS)

Aims: We aim to detect and interpret photometric and spectroscopic variability of the bright CoRoT B-type supergiant target HD 46769 (V = 5.79). We also attempt to detect a magnetic field in the target. Methods: We analyse a 23-day oversampled CoRoT light curve after detrending and spectroscopic follow-up data using standard Fourier analysis and phase dispersion minimization methods. We determine the fundamental parameters of the star, as well as its abundances from the most prominent spectral lines. We perform a Monte Carlo analysis of spectropolarimetric data to obtain an upper limit of the polar magnetic field, assuming a dipole field. Results: In the CoRoT data, we detect a dominant period of 4.84 d with an amplitude of 87 ppm and some of its (sub-)multiples. Given the shape of the phase-folded light curve and the absence of binary motion, we interpret the dominant variability in terms of rotational modulation, with a rotation period of 9.69 d. Subtraction of the rotational modulation signal does not reveal any sign of pulsations. Our results are consistent with the absence of variability in the Hipparcos light curve. The spectroscopy leads to a projected rotational velocity of 72 ± 2 km s-1 and does not reveal periodic variability or the need to invoke macroturbulent line broadening. No signature of a magnetic field is detected in our data. A field stronger than ~500 G at the poles can be excluded, unless the possible non-detected field were more complex than dipolar. Conclusions: The absence of pulsations and macroturbulence of this evolved B-type supergiant is placed into the context of instability computations and of observed variability of evolved B-type stars. Based on CoRoT space-based photometric data; the CoRoT space mission was developed and operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. Based on observations collected at La Silla Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6 m telescope, under programme LP185.D-0056. Based on observations obtained with the HERMES spectrograph attached to the 1.2 m Mercator telescope, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of KU Leuven, Belgium, the Fonds National de la Recherche Scientific (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Genève, Switzerland, and the Thüringer Landessternwarte Tautenburg, Germany. Based on observations obtained with the Narval spectropolarimeter at the Observatoire du Pic du Midi (France), which is operated by the Institut National des Sciences de l'Univers (INSU).

Aerts, C.; Simón-Díaz, S.; Catala, C.; Neiner, C.; Briquet, M.; Castro, N.; Schmid, V. S.; Scardia, M.; Rainer, M.; Poretti, E.; Pápics, P. I.; Degroote, P.; Bloemen, S.; Østensen, R. H.; Auvergne, M.; Baglin, A.; Baudin, F.; Michel, E.; Samadi, R.

2013-09-01

142

Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta  

NASA Astrophysics Data System (ADS)

IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his collaborators have called the ``yellow void.'' We report HST/STIS spatially resolved spectroscopy of IRC +10420 and its reflection nebula with some surprising results. Long-slit spectroscopy of the reflected spectrum allows us to effectively view the star from different directions. Measurements of the double-peaked H? emission profile show a uniform outflow of gas in a nearly spherical distribution, contrary to previous models with an equatorial disk or bipolar outflow. Based on the temperature and mass-loss rate estimates that are usually quoted for this object, the wind is optically thick to the continuum at some and possibly all wavelengths. Consequently, the observed variations in apparent spectral type and inferred temperature are changes in the wind and do not necessarily mean that the underlying stellar radius and interior structure are evolving on such a short timescale. To explain the evidence for simultaneous outflow and infall of material near the star, we propose a ``rain'' model, in which blobs of gas condense in regions of lowered opacity outside the dense wind. With the apparent warming of its wind, the recent appearance of strong emission, and a decline in the mass-loss rate, IRC +10420 may be about to shed its opaque wind, cross the yellow void, and emerge as a hotter star. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Humphreys, Roberta M.; Davidson, Kris; Smith, Nathan

2002-08-01

143

Blue Supergiant Model for Ultra-long Gamma-Ray Burst with Superluminous-supernova-like Bump  

NASA Astrophysics Data System (ADS)

Long gamma-ray bursts (LGRBs) have a typical duration of ~30 s, and some of them are associated with hypernovae, such as Type Ic SN 1998bw. Wolf-Rayet stars are the most plausible LGRB progenitors, since the free fall time of the envelope is consistent with the duration, and the natural outcome of the progenitor is a Type Ic SN. While a new population of ultra-long GRBs (ULGRBs), GRB 111209A, GRB 101225A, and GRB 121027A, has a duration of ~104 s, two of them are accompanied by superluminous-supernova-like (SLSN-like) bumps, which are <~ 10 times brighter than typical hypernovae. Wolf-Rayet progenitors cannot explain ULGRBs because of durations that are too long and SN-like bumps that are too bright. A blue supergiant (BSG) progenitor model, however, can explain the duration of ULGRBs. Moreover, SLSN-like bumps can be attributed to the so-called cocoon fireball photospheric emissions (CFPEs). Since a large cocoon is inevitably produced during the relativistic jet piercing though the BSG envelope, this component can be smoking gun evidence of the BSG model for ULGRBs. In this paper, we examine u-, g-, r-, i-, and J-band light curves of three ULGRBs and demonstrate that they can be fitted quite well by our BSG model with the appropriate choices of the jet opening angle and the number density of the ambient gas. In addition, we predict that for 121027A, SLSN-like bump could have been observed for ~20-80 days after the burst. We also propose that some SLSNe might be CFPEs of off-axis ULGRBs without visible prompt emissions.

Nakauchi, Daisuke; Kashiyama, Kazumi; Suwa, Yudai; Nakamura, Takashi

2013-11-01

144

An Upper Mass Limit on a Red Supergiant Progenitor for the Type II-Plateau Supernova SN 2006my  

E-print Network

We analyze two pre-supernova (SN) and three post-SN high-resolution images of the site of the Type II-Plateau supernova SN 2006my in an effort to either detect the progenitor star or to constrain its properties. Following image registration, we find that an isolated stellar object is not detected at the location of SN 2006my in either of the two pre-SN images. In the first, an I-band image obtained with the Wide-Field and Planetary Camera 2 on board the Hubble Space Telescope, the offset between the SN 2006my location and a detected source ("Source 1") is too large: > 0.08", which corresponds to a confidence level of non-association of 96% from our most liberal estimates of the transformation and measurement uncertainties. In the second, a similarly obtained V-band image, a source is detected ("Source 2") that has overlap with the SN 2006my location but is definitively an extended object. Through artificial star tests carried out on the precise location of SN 2006my in the images, we derive a 3-sigma upper bound on the luminosity of a red supergiant that could have remained undetected in our pre-SN images of log L/L_Sun = 5.10, which translates to an upper bound on such a star's initial mass of 15 M_Sun from the STARS stellar evolutionary models. Although considered unlikely, we can not rule out the possibility that part of the light comprising Source 1, which exhibits a slight extension relative to other point sources in the image, or part of the light contributing to the extended Source 2, may be due to the progenitor of SN 2006my. Only additional, high-resolution observations of the site taken after SN 2006my has faded beyond detection can confirm or reject these possibilities.

Douglas C. Leonard; Avishay Gal-Yam; Derek B. Fox; P. B. Cameron; Erik M. Johansson; Adam L. Kraus; David Le Mignant; Marcos A. van Dam

2008-09-10

145

Soft X-ray characterisation of the long-term properties of supergiant fast X-ray transients  

NASA Astrophysics Data System (ADS)

Context. Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) that are characterised by a hard X-ray (? 15 keV) flaring behaviour. These flares reach peak luminosities of 1036-1037 erg s-1 and last a few hours in the hard X-rays. Aims: We investigate the long-term properties of SFXTs by examining the soft (0.3-10 keV) X-ray emission of the three least active SFXTs in the hard X-ray and by comparing them with the remainder of the SFXT sample. Methods: We performed the first high-sensitivity soft X-ray long-term monitoring with Swift/XRT of three relatively unexplored SFXTs, IGR J08408-4503, IGR J16328-4726, and IGR J16465-4507, whose hard X-ray duty cycles are the lowest measured among the SFXT sample. We assessed how long each source spends in each flux state and compared their properties with those of the prototypical SFXTs. Results: The behaviour of IGR J08408-4503 and IGR J16328-4726 resembles that of other SFXTs, and it is characterised by a relatively high inactivity duty cycle (IDC) and pronounced dynamic range (DR) in the X-ray luminosity. We found DR ~ 7400, IDC ~ 67% for IGR J08408-4503, and DR ~ 750, IDC ~ 61% for IGR J16328-4726 (in all cases the IDC is given with respect to the limiting flux sensitivity of XRT, that is 1-3 × 10-12 erg cm-2 s-1). In common with all the most extreme SFXT prototypes (IGR J17544-2619, XTE J1739-302, and IGR J16479-4514), IGR J08408-4503 shows two distinct flare populations. The first one is associated with the brightest outbursts (X-ray luminosity LX ? 1035 - 36 erg s-1), while the second comprises dimmer events with typical luminosities of LX ? 1035 erg s-1. This double-peaked distribution of the flares as a function of the X-ray luminosity seems to be a ubiquitous feature of the extreme SFXTs. The lower DR of IGR J16328-4726 suggests that this is an intermediate SFXT. IGR J16465-4507 is characterised by a low IDC ~ 5% and a relatively narrow DR ~ 40, reminiscent of classical supergiant HMXBs. The duty cycles measured with XRT are found to be comparable with those reported previously by BAT and INTEGRAL, when the higher limiting sensitivities of these instruments are taken into account and sufficiently long observational campaigns are available. By making use of these new results and those we reported previously, we prove that no clear correlation exists between the duty cycles of the SFXTs and their orbital periods. Conclusions: The unique sensitivity and scheduling flexibility of Swift/XRT allowed us to carry out an efficient long-term monitoring of the SFXTs, following their activity across more than 4 orders of magnitude in X-ray luminosity. While it is not possible to exclude that particular distributions of the clump and wind parameters may produce double-peaked differential distributions in the X-ray luminosities of the SFXTs, the lack of a clear correlation between the duty cycles and orbital periods of these sources make it difficult to interpret their peculiar variability by only using arguments related to the properties of supergiant star winds. Our findings favour the idea that a correct interpretation of the SFXT phenomenology requires a mechanism to strongly reduce the mass accretion rate onto the compact object during most of its orbit around the companion, as proposed in a number of theoretical works. Tables 1-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A55

Romano, P.; Ducci, L.; Mangano, V.; Esposito, P.; Bozzo, E.; Vercellone, S.

2014-08-01

146

IGR J17544-2619 in Depth With Suzaku: Direct Evidence for Clumpy Winds in a Supergiant Fast X-ray Transient  

NASA Astrophysics Data System (ADS)

We present direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544-2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 104 in luminosity and gives a detailed look at SFXT behavior.

Rampy, Rachel A.; Smith, David M.; Negueruela, Ignacio

2009-12-01

147

Magnetic confinement, Alfven wave reflection, and the origins of X-ray and mass-loss 'dividing lines' for late-type giants and supergiants  

NASA Technical Reports Server (NTRS)

A simple qualitative model for the origin of the coronal and mass-loss dividing lines separating late-type giants and supergiants with and without hot, X-ray-emitting corona, and with and without significant mass loss is discussed. The basic physical effects considered are the necessity of magnetic confinement for hot coronal material on the surface of such stars and the large reflection efficiency for Alfven waves in cool exponential atmospheres. The model assumes that the magnetic field geometry of these stars changes across the observed 'dividing lines' from being mostly closed on the high effective temperature side to being mostly open on the low effective temperature side.

Rosner, R.; An, C.-H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T.

1991-01-01

148

A Suzaku X-ray Observation of One Orbit of the Supergiant Fast X-ray Transient IGR J16479-4514  

NASA Technical Reports Server (NTRS)

We report on a 250 ks long X-ray observation of the supergiant fast X-ray transient (SFXT) IGR J16479-4514 performed with Suzaku in 2012 February. During this observation, about 80% of the short orbital period (P(sub orb) approximates 3.32 days) was covered as continuously as possible for the first time. The source light curve displays variability of more than two orders of magnitude, starting with a very low emission state (10(exp -13) erg / sq cm/s; 1-10 keV) lasting the first 46 ks, consistent with being due to the X-ray eclipse by the supergiant companion. The transition to the uneclipsed X-ray emission is energy dependent. Outside the eclipse, the source spends most of the time at a level of 6-7X10)(exp-12) erg/sq. cm/s) punctuated by two structured faint flares with a duration of about 10 and 15 ks, respectively, reaching a peak flux of 3-4X10(exp -11) erg/sq. cm./S, separated by about 0.2 in orbital phase. Remarkably, the first faint flare occurs at a similar orbital phase of the bright flares previously observed in the system. This indicates the presence of a phase-locked large scale structure in the supergiant wind, driving a higher accretion rate onto the compact object. The average X-ray spectrum is hard and highly absorbed, with a column density, NH, of 10*exp 23)/sq cm, clearly in excess of the interstellar absorption. There is no evidence for variability of the absorbing column density, except that during the eclipse, where a less absorbed X-ray spectrum is observed. A narrow Fe K-alpha emission line at 6.4 keV is viewed along the whole orbit, with an intensity which correlates with the continuum emission above 7 keV. The scattered component visible during the X-ray eclipse allowed us to directly probe the wind density at the orbital separation, resulting in rho(sub w)=7X10(exp -14) g/cubic cm. Assuming a spherical geometry for the supergiant wind, the derived wind density translates into a ratio M(sub w)/v(sub infinity) = 7X10(exp -17) Solar M/km which, assuming terminal velocities in a large range 500-3000 km/s, implies an accretion luminosity two orders of magnitude higher than that observed. As a consequence, a mechanism should be at work reducing the mass accretion rate. Different possibilities are discussed.

Sidoli, L.; Esposito, P.; Sguera, V.; Bodaghee, A.; Tomsick, J. A.; Pottschmidt, K.; Rodriguez, J.; Ramano, P.; Wilms, J.

2013-01-01

149

A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL {alpha} CYGNI VARIABLE AND A-TYPE SUPERGIANT STAR DENEB  

SciTech Connect

Deneb is often considered the prototypical A-type supergiant and is one of the visually most luminous stars in the Galaxy. A-type supergiants are potential extragalactic distance indicators, but the variability of these stars needs to be better characterized before this technique can be considered reliable. We analyzed 339 high-resolution echelle spectra of Deneb obtained over the five-year span of 1997 through 2001 as well as 370 Stroemgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the H{alpha} profile, H{alpha} equivalent widths, and radial velocities measured from Si II {lambda}{lambda} 6347, 6371. Time-series analysis reveals no obvious cyclic behavior that proceeds through multiple observing seasons, although we found a suspected 40 day period in two, non-consecutive observing seasons. Some correlations are found between photometric and radial velocity data sets and suggest radial pulsations at two epochs. No correlation is found between the variability of the H{alpha} profiles and that of the radial velocities or the photometry. Lucy found evidence that Deneb was a long-period single-lined spectroscopic binary star, but our data set shows no evidence for radial velocity variations caused by a binary companion.

Richardson, N. D. [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Morrison, N. D.; Kryukova, E. E. [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft, Toledo, OH 43606 (United States); Adelman, S. J., E-mail: richardson@chara.gsu.edu, E-mail: nmorris@utnet.utoledo.edu, E-mail: eallga@physics.utoledo.edu, E-mail: adelmans@citadel.edu [Department of Physics, The Citadel, 171 Moultrie Street, Charleston, SC 29409 (United States)

2011-01-15

150

GALEX AND PAN-STARRS1 DISCOVERY OF SN IIP 2010aq: THE FIRST FEW DAYS AFTER SHOCK BREAKOUT IN A RED SUPERGIANT STAR  

SciTech Connect

We present the early UV and optical light curve of Type IIP supernova (SN) 2010aq at z = 0.0862, and compare it to analytical models for thermal emission following SN shock breakout in a red supergiant star. SN 2010aq was discovered in joint monitoring between the Galaxy Evolution Explorer (GALEX) Time Domain Survey (TDS) in the NUV and the Pan-STARRS1 Medium Deep Survey (PS1 MDS) in the g, r, i, and z bands. The GALEX and Pan-STARRS1 observations detect the SN less than 1 day after the shock breakout, measure a diluted blackbody temperature of 31, 000 {+-} 6000 K 1 day later, and follow the rise in the UV/optical light curve over the next 2 days caused by the expansion and cooling of the SN ejecta. The high signal-to-noise ratio of the simultaneous UV and optical photometry allows us to fit for a progenitor star radius of 700 {+-} 200R {sub sun}, the size of a red supergiant star. An excess in UV emission two weeks after shock breakout compared with SNe well fitted by model atmosphere-code synthetic spectra with solar metallicity is best explained by suppressed line blanketing due to a lower metallicity progenitor star in SN 2010aq. Continued monitoring of PS1 MDS fields by the GALEX TDS will increase the sample of early UV detections of Type II SNe by an order of magnitude and probe the diversity of SN progenitor star properties.

Gezari, S.; Huber, M. E.; Grav, T. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Rest, A.; Narayan, G. [Department of Physics, Harvard University, Cambridge, MA 20138 (United States); Forster, K.; Neill, J. D.; Martin, D. C. [California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125 (United States); Valenti, S.; Smartt, S. J. [Astrophysics Research Centre, School of Maths and Physics, Queen's University, BT7 1NN, Belfast (United Kingdom); Chornock, R.; Berger, E.; Soderberg, A. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Mattila, S.; Kankare, E. [Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Fl-21500, Piikkioe (Finland); Burgett, W. S.; Chambers, K. C.; Dombeck, T.; Heasley, J. N.; Hodapp, K. W., E-mail: suvi@pha.jhu.ed [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

2010-09-01

151

Detection of the radial velocity curve of the B5-A0 supergiant companion star of Cir X-1?  

NASA Astrophysics Data System (ADS)

In this paper, we report on phase-resolved I-band optical spectroscopic and photometric observations of Cir X-1 obtained with the Very Large Telescope. The spectra are dominated by Paschen absorption lines at nearly all orbital phases except near phase zero (coinciding with the X-ray dip) when the absorption lines are filled in by broad Paschen emission lines. The radial velocity curve of the absorption lines corresponds to an eccentric orbit (e = 0.45) whose period and time of periastron passage are consistent with the period and phase predicted by the most recent X-ray dip ephemeris. We found that the I-band magnitude decreases from 17.6 to ~16.8 near phase 0.9-1.0 this brightening coincides in phase with the X-ray dip. Even though it is likely that the absorption-line spectrum is associated with the companion star of Cir X-1, we cannot exclude the possibility that the spectrum originates in the accretion disc. However, if the spectrum belongs to the companion star, it must be a supergiant of spectral type B5-A0. If we assume that the compact object does not move through the companion star at periastron, the companion star mass is constrained to <~10 Msolar for a 1.4-Msolar neutron star, whereas the inclination has to be . Alternatively, the measured absorption lines and their radial velocity curve can be associated with the accretion disc surrounding a 1.4-Msolar neutron star and its motion around the centre of mass. An absorption-line spectrum from an accretion disc is typically found when our line of sight passes through the accretion disc rim implying a high inclination. In this scenario, the companion star mass is found to be ~0.4 Msolar. However, from radio observations it was found that the angle between the line of sight and the jet axis is smaller than 5°. This would mean that the jet ploughs through the accretion disc in this scenario, making this solution less probable.

Jonker, P. G.; Nelemans, G.; Bassa, C. G.

2007-01-01

152

The circumstellar environment and evolutionary state of the supergiant B[e] star Wd1-9  

NASA Astrophysics Data System (ADS)

Context. Historically, supergiant (sg)B[e] stars have been difficult to include in theoretical schemes for the evolution of massive OB stars. Aims: The location of Wd1-9 within the coeval starburst cluster Westerlund 1 means that it may be placed into a proper evolutionary context and we therefore aim to utilise a comprehensive multiwavelength dataset to determine its physical properties and consequently its relation to other sgB[e] stars and the global population of massive evolved stars within Wd1. Methods: Multi-epoch R- and I-band VLT/UVES and VLT/FORS2 spectra are used to constrain the properties of the circumstellar gas, while an ISO-SWS spectrum covering 2.45-45 ?m is used to investigate the distribution, geometry and composition of the dust via a semi-analytic irradiated disk model. Radio emission enables a long term mass-loss history to be determined, while X-ray observations reveal the physical nature of high energy processes within the system. Results: Wd1-9 exhibits the rich optical emission line spectrum that is characteristic of sgB[e] stars. Likewise its mid-IR spectrum resembles those of the LMC sgB[e] stars R66 and 126, revealing the presence of equatorially concentrated silicate dust, with a mass of ~10-4 M?. Extreme historical and ongoing mass loss (?10-4 M? yr-1) is inferred from the radio observations. The X-ray properties of Wd1-9 imply the presence of high temperature plasma within the system and are directly comparable to a number of confirmed short-period colliding wind binaries within Wd1. Conclusions: The most complete explanation for the observational properties of Wd1-9 is that it is a massive interacting binary currently undergoing, or recently exited from, rapid Roche-lobe overflow, supporting the hypothesis that binarity mediates the formation of (a subset of) sgB[e] stars. The mass loss rate of Wd1-9 is consistent with such an assertion, while viable progenitor and descendent systems are present within Wd1 and comparable sgB[e] binaries have been identified in the Galaxy. Moreover, the rarity of sgB[e] stars - only two examples are identified from a census of ~68 young massive Galactic clusters and associations containing ~600 post-Main Sequence stars - is explicable given the rapidity (~104 yr) expected for this phase of massive binary evolution. This work is based on observations collected at the European Southern Observatory, Paranal (programme IDs ESO 087.D-0355, 087.D-0440, 087.D-0673, and 073.D-0327) and uses the ISO-SWS database of Sloan et al. (2003).Table 1 and Appendix A are available in electronic form at http://www.aanda.org

Clark, J. S.; Ritchie, B. W.; Negueruela, I.

2013-12-01

153

NuSTAR Detection Of A Cyclotron Line In The Supergiant Fast X-ray Transient IGR J17544-2619  

E-print Network

We present NuSTAR spectral and timing studies of the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619. The spectrum is well-described by a ~1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a cyclotron line at 17 keV, confirming that the compact object in IGR J17544-2619 is indeed a neutron star. This is the first measurement of the magnetic field in a SFXT. The inferred magnetic field strength, B = (1.45 +/- 0.03) * 10^12 G * (1+z) is typical of neutron stars in X-ray binaries, and rules out a magnetar nature for the compact object. We do not find any significant pulsations in the source on time scales of 1-2000 s.

Bhalerao, Varun; Tomsick, John; Natalucci, Lorenzo; Smith, David M; Bellm, Eric; Boggs, Steven E; Chakrabarty, Deepto; Christensen, Finn E; Craig, William W; Fuerst, Felix; Hailey, Charles J; Harrison, Fiona A; Krivonos, Roman A; Lu, Ting-Ni; Madsen, Kristin; Stern, Daniel; Younes, George; Zhang, William

2014-01-01

154
155

Chemical Mechanical Planarization- Chemical  

NSDL National Science Digital Library

This website includes an animation which illustrates the chemical action of slurry in the chemical-mechanical planarization process. Objective: Explain the mechanical and chemical steps in the CMP process. This simulation is from Module 068 of the Process & Equipment III Cluster of the MATEC Module Library (MML). Find this animation under the section "Process & Equipment III." To view other clusters or for more information about the MML visit http://matec.org/ps/library3/process_I.shtmlKey Phrase: MATEC Animation

2012-12-07

156

Dust Production Factories in the Early Universe: Formation of Carbon Grains in Red-supergiant Winds of Very Massive Population III Stars  

E-print Network

We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with the zero-age main sequence mass of 500 M_sun. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condense into dust for wide ranges of the mass-loss rate ((0.1-3)x10^{-3} M_sun yr^{-1}) and wind velocity (1-100 km s^{-1}). We also find that the acceleration of the wind driven by newly formed dust suppresses the grain growth but still allows more than half of gas-phase carbon to be finally locked up in dust grains. These results indicate that at most 1.7 M_sun of carbon grains can form in total during the RSG phase of 500 M_sun Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top...

Nozawa, Takaya; Maeda, Keiichi; Kozasa, Takashi; Nomoto, Ken'ichi; Langer, Norbert

2014-01-01

157

SUZAKU OBSERVES WEAK FLARES FROM IGR J17391-3021 REPRESENTING A COMMON LOW-ACTIVITY STATE IN THIS SUPERGIANT FAST X-RAY TRANSIENT  

SciTech Connect

We present an analysis of a 37 ks observation of the supergiant fast X-ray transient IGR J17391-3021 (= XTE J1739-302) gathered with Suzaku. The source evolved from quiescence to a low-activity level culminating in three weak flares lasting {approx}3 ks each in which the peak luminosity is only a factor of five times that of the pre-flare luminosity. The minimum observed luminosity was 1.3 x 10{sup 33} erg s{sup -1}(d/2.7 kpc){sup 2} in the 0.5-10 keV range. The weak flares are accompanied by significant changes in the spectral parameters including a column density (N{sub H} =(4.1{sup +0.4}{sub -0.5}) x 10{sup 22} cm{sup -2}) that is {approx}2-9 times the absorption measured during quiescence. Accretion of obscuring clumps of stellar wind material can explain both the small flares and the increase in N{sub H}. Placing this observation in the context of the recent Swift monitoring campaign, we find that weak-flaring episodes, or at least epochs of enhanced activity just above the quiescent level but well below the moderately bright or high-luminosity outbursts, represent more than 60% {+-} 5% of all observations in the 0.5-10 keV energy range making this the most common state in the emission behavior of IGR J17391-3021.

Bodaghee, A.; Tomsick, J. A. [Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720 (United States); Rodriguez, J.; Chaty, S. [Laboratoire AIM, CEA/IRFU-Universite Paris Diderot-CNRS/INSU, CEA DSM/IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette (France); Pottschmidt, K. [CRESST and NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771 (United States); Walter, R. [INTEGRAL Science Data Centre, Universite de Geneve, Chemin d'Ecogia 16, CH-1290 Versoix (Switzerland); Romano, P., E-mail: bodaghee@ssl.berkeley.edu [INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via U. La Malfa 153, I-90146 Palermo (Italy)

2011-01-20

158

Long-Lasting X-Ray Emission from Type IIb Supernova 2011dh and Mass-Loss History of The Yellow Supergiant Progenitor  

E-print Network

Type IIb Supernova (SN) 2011dh, with conclusive detection of an unprecedented Yellow Supergiant (YSG) progenitor, provides an excellent opportunity to deepen our understanding on the massive star evolution in the final centuries toward the SN explosion. In this paper, we report on detection and analyses of thermal X-ray emission from SN IIb 2011dh at ~500 days after the explosion on Chandra archival data, providing a solidly derived mass loss rate of an YSG progenitor for the first time. We find that the circumstellar media (CSM) should be dense, more than that expected from a Wolf-Rayet (WR) star by one order of magnitude. The emission is powered by a reverse shock penetrating into an outer envelope, fully consistent with the YSG progenitor but not with a WR progenitor. The density distribution at the outermost ejecta is much steeper than that expected from a compact WR star, and this finding must be taken into account in modeling the early UV/optical emission from SNe IIb. The derived mass loss rate is 3 x ...

Maeda, Keiichi; Bamba, Aya; Terada, Yukikatsu; Fukazawa, Yasushi

2014-01-01

159

High spectral resolution imaging of the dynamical atmosphere of the red supergiant Antares in the CO first overtone lines with VLTI/AMBER  

NASA Astrophysics Data System (ADS)

Aims: We present aperture-synthesis imaging of the red supergiant Antares (? Sco) in the CO first overtone lines. Our goal is to probe the structure and dynamics of the outer atmosphere. Methods: Antares was observed between 2.28 ?m and 2.31 ?m with VLTI/AMBER with spectral resolutions of up to 12 000 and angular resolutions as high as 7.2 mas at two epochs with a time interval of one year. Results: The reconstructed images in individual CO lines reveal that the star appears differently in the blue wing, line center, and red wing. In 2009, the images in the line center and red wing show an asymmetrically extended component, while the image in the blue wing shows little trace of it. In 2010, however, the extended component appears in the line center and blue wing, and the image in the red wing shows only a weak signature of the extended component. Our modeling of these AMBER data suggests that there is an outer atmosphere (MOLsphere) extending to 1.2-1.4 R? with CO column densities of (0.5-1) × 1020 cm-2 and a temperature of ~2000 K. The CO line images observed in 2009 can be explained by a model in which a large patch or clump of CO gas is infalling at only 0-5 km s-1, while the CO gas in the remaining region is moving outward much faster at 20-30 km s-1. The images observed in 2010 suggest that a large clump of CO gas is moving outward at 0-5 km s-1, while the CO gas in the remaining region is infalling much faster at 20-30 km s-1. In contrast to the images in the CO lines, the AMBER data in the continuum show only a slight deviation from limb-darkened disks and only marginal time variations. We derive a limb-darkened disk diameter of 37.38 ± 0.06 mas and a power-law-type limb-darkening parameter of (8.7 ± 1.6) × 10-2 (2009) and 37.31 ± 0.09 mas and (1.5 ± 0.2) × 10-1 (2010). We also obtain an effective temperature of 3660 ± 120 K (the error includes the effects of the temporal flux variation that is assumed to be the same as Betelgeuse) and a luminosity of log L?/L? = 4.88 ± 0.23. Comparison with theoretical evolutionary tracks suggests a mass of 15 ± 5 M? with an age of 11-15 Myr, which is consistent with the recently estimated age for the Upper Scorpius OB association. Conclusions: The properties of the outer atmosphere of Antares are similar to those of another well-studied red supergiant, Betelgeuse. The density of the extended outer atmosphere of Antares and Betelgeuse is higher than predicted by the current 3D convection simulations by at least six orders of magnitude, implying that convection alone cannot explain the formation of the extended outer atmosphere. Based on AMBER observations made with the Very Large Telescope Interferometer of the European Southern Observatory. Program ID: 083.D-0333(A/B) (AMBER guaranteed time observation), 085.D-0085(A/B).Appendices are available in electronic form at http://www.aanda.orgMovies of data cube are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A24

Ohnaka, K.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Baffa, C.; Chelli, A.; Petrov, R.; Robbe-Dubois, S.

2013-07-01

160

APERTURE SYNTHESIS OBSERVATIONS OF CO, HCN, AND 89 GHz CONTINUUM EMISSION TOWARD NGC 604 IN M33: SEQUENTIAL STAR FORMATION INDUCED BY A SUPERGIANT H II REGION  

SciTech Connect

We present the results from new Nobeyama Millimeter Array observations of CO(1-0), HCN(1-0), and 89 GHz continuum emission toward NGC 604, known as the supergiant H II region in the nearby galaxy M33. Our high spatial resolution images (4.''2 x 2.''6, corresponding to 17 pc x 11 pc physical size) of CO emission allowed us to uncover 10 individual molecular clouds that have masses of (0.8-7.4) x10{sup 5} M{sub sun} and sizes of 5-29 pc, comparable to those of typical Galactic giant molecular clouds. Moreover, we detected for the first time HCN emission in the two most massive clouds and 89 GHz continuum emission at the rims of the 'H{alpha} shells'. The HCN and 89 GHz continuum emission are offset from the CO peak and are distributed in the direction of the central cluster. Three out of ten CO clouds are well correlated with the H{alpha} shells both in spatial and velocity domains, implying an interaction between molecular gas and the expanding H II region. The CO clouds show varieties in star formation efficiencies (SFEs), which are estimated from the 89 GHz emission and combination of H{alpha} and Spitzer 24 {mu}m data. Furthermore, we found that the SFEs decrease with increasing projected distance measured from the heart of the central OB star cluster in NGC 604, suggesting radial changes in the evolutionary stages of the molecular clouds in the course of stellar cluster formation. Our results provide further support to the picture of sequential star formation in NGC 604 initially proposed by Tosaki et al. with the higher spatially resolved molecular clouds, in which an isotropic expansion of the H II region pushes gases outward, which accumulates to form dense molecular clouds, and then induces massive star formations.

Miura, Rie; Okumura, Sachiko K.; Kurono, Yasutaka; Nakanishi, Kouichiro [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Tosaki, Tomoka [Joetsu University of Education, Yamayashiki-machi, Joetsu, Niigata 943-8512 (Japan); Tamura, Yoichi [Department of Astronomy, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 133-0033 (Japan); Kuno, Nario; Kawabe, Ryohei [Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1805 (Japan); Sakamoto, Seiichi [Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara-shi, Kanagawa 252-5210 (Japan); Hasegawa, Takashi, E-mail: rie.miura@nao.ac.j [Gunma Astronomical Observatory, Nakayama, Takayama, Agatsuma, Gunma 377-0702 (Japan)

2010-12-01

161

Carbon stars as possible members of open clusters. VII - The carbon star MZ CEP and the M-type supergiant MY CEP in the cluster NGC 7419 = C22252 + 605  

NASA Astrophysics Data System (ADS)

Two cool variable stars situated in the sky in or near the open cluster NGC 7419 have been photographically monitored in R(0,63)-, V- and B-passbands. Tables show individual magnitudes of both stars. The carbon star MZ Cep has irregular light variations with the V-amplitude of 0m.5 while the late-M-type supergiant shows semiregular light variations with the mean cycle length of about 395 days and the V-amplitude of more than 1m.1. The R(0,63)- and V-light curves for the two variables are shown in figures.

Alksne, Z.; Alksnis, A.

162

1-D Imaging of the Dynamical Atmosphere of the Red Supergiant Betelgeuse in the CO First Overtone Lines with VLTI/AMBER  

NASA Astrophysics Data System (ADS)

We present high-spatial and high-spectral resolution observations of the red supergiant Betelgeuse in the CO first overtone lines near 2.3?m with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Our AMBER observations in 2008 spatially resolved the gas motions in a stellar atmosphere (photosphere and extended molecular outer atmosphere) for the first time other than the Sun. From our second observations one year later, we have reconstructed 1-D images in the individual CO lines with an angular resolution of 9.8 mas and a spectral resolution of 6000 by applying the self-calibration technique to restore the Fourier phase from the differential phase measurements. The reconstructed 1-D images reveal that the star appears different in the blue and red wing of the individual CO lines. In the blue wing, the star shows a pronounced, asymmetrically extended component at least up to 1.3 R?, while such a component does not appear in the red wing 1-D image. This can be explained by a model in which the CO gas patch (or clump) more than half as large as the star is moving slightly outward with 0–5 km s-1, while the gas in the remaining region is infalling fast with 20–30 km s-1. Comparison between the CO line data taken in 2008 and 2009 shows a significant time variation in the dynamics of the photosphere and outer atmosphere. However, the 1-D images in the continuum show only a slight deviation from a limb-darkened disk with an angular diameter of 42.49±0.06 mas, which leads to an effective temperature of 3690± 54 K. Moreover, the continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulation. The derived continuum diameter also shows that the near-IR size of Betelgeuse has been nearly constant over the last 18 years, in marked contrast to the recently reported noticeable decrease in the mid-IR size.

Ohnaka, K.

2014-09-01

163

Red-Eye Astronomy: 15 Years of V-band and Near-IR Tio Photometry of the Red Supergiants Alpha Orionis And TV Geminorum.  

NASA Astrophysics Data System (ADS)

V-band and narrow to intermediate-band Wing TiO-band (719 nm, 754 nm), and near-IR 1024 nm pseudo-bolometric photometric observations of the SRc M2 Iab supergiants Alpha Orionis and TV Geminorum have been conducted for the past 15 years. The goals are to monitor brightness and temperature-dependent TiO-band variations, ascertain any resulting periodicities and amplitudes, and estimate variations of basic stellar parameters such as temperature, luminosity, and radius. Preliminary results for both stars indicate similar long-term V-mag periods of 6.5 years with imposed shorter-term V-mag periods of 1.2 years. The V-magnitude amplitudes were 0.8 for Alpha Ori and 1.3 for TV Gem. For both stars the temperature and luminosity variations correlate well with the V-mag changes. However, inverse radii correlations with respect to temperature and luminosity variations were not seen in either star. In Alpha Ori the the radii changes were approximately in direct correlation with the temperature and luminosity changes. In TV Gem there was a combination of correlation/inverse correlation effects. Causes for these variations are speculative, but may be due to highly convective super-granulations occurring at irregular intervals rather than fundamental mode pulsation or harmonic oscillations. Based in part on an updated RSG temperature scale and a new VLA/Hipparchos distance estimate (197 PC), the Alpha Ori temperatures ranged from 3550 K to 3730 K, with ranges in solar luminosities and radii of L = 90,000 to 115,000 and R = 760 to 820, respectively. The slightly more dynamical TV Gem underwent temperature variations from 3500 K to 3850 K with ranges in solar luminosity and radii of L = 65,000 to 90,000 and R = 620 to 720 respectively. Discussions of the observations, data reduction methods, and analysis of the data will be presented. This research is supported by NASA grant NNX10AI85G and NSF grants AST 10-09903 and AST 05-07542.

Wasatonic, Richard P.; Guinan, E.; Engle, S.

2011-05-01

164

Chemical Communication  

NSDL National Science Digital Library

A concise lesson about chemical communication in insects covering both semio and info chemicals. The site includes a short video of grape root borer moths using sex pheromone. Further links on the take the user to visual and auditory communication.

0002-11-30

165

Home Chemicals  

NSDL National Science Digital Library

This lesson provides an introduction to the occurrence and possible risks of household chemical products. Topics include some basic chemistry (how elements combine to form compounds), how chemicals are classified, and the idea of natural, as opposed to synthetic, chemicals. The lesson includes an activity in which students take an inventory of chemical products in their homes and research the possible hazards of some of them using an online resource developed by the National Institutes of Health (NIH).

Fox, Chris

166

Chemical sensor  

NASA Technical Reports Server (NTRS)

A sensor for detecting a chemical substance includes an insertion element having a structure which enables insertion of the chemical substance with a resulting change in the bulk electrical characteristics of the insertion element under conditions sufficient to permit effective insertion; the change in the bulk electrical characteristics of the insertion element is detected as an indication of the presence of the chemical substance.

Rauh, R. David (Inventor)

1990-01-01

167

Chemical microsensors  

NASA Astrophysics Data System (ADS)

Recent developments are discussed in the field of chemical microsensors that attempt to marry physical transducers based on microelectronic and optoelectronic technologies with thin films and coatings that serve as chemical transducers. Microelectronic silicon chemical sensors, acoustic wave sensors, microsensors based on optical fibers, and electrochemical microsensors are considered. Both technological achievements and problems that remain to be solved are addressed.

Hughes, R. C.; Ricco, A. J.; Butler, M. A.; Martin, S. J.

1991-10-01

168

[Chemical weapons and chemical terrorism].  

PubMed

Chemical Weapons are kind of Weapons of Mass Destruction (WMD). They were used large quantities in WWI. Historically, large quantities usage like WWI was not recorded, but small usage has appeared now and then. Chemical weapons are so called "Nuclear weapon for poor countrys" because it's very easy to produce/possession being possible. They are categorized (1) Nerve Agents, (2) Blister Agents, (3) Cyanide (blood) Agents, (4) Pulmonary Agents, (5) Incapacitating Agents (6) Tear Agents from the viewpoint of human body interaction. In 1997 the Chemical Weapons Convention has taken effect. It prohibits chemical weapons development/production, and Organization for the Prohibition of Chemical Weapons (OPCW) verification regime contributes to the chemical weapons disposal. But possibility of possession/use of weapons of mass destruction by terrorist group represented in one by Matsumoto and Tokyo Subway Sarin Attack, So new chemical terrorism countermeasures are necessary. PMID:16296384

Nakamura, Katsumi

2005-10-01

169

The 100-month Swift catalogue of supergiant fast X-ray transients. I. BAT on-board and transient monitor flares  

NASA Astrophysics Data System (ADS)

Context. Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) that are defined by their hard X-ray flaring behaviour. During these flares they reach peak luminosities of 1036-1037 erg s-1 for a few hours (in the hard X-ray), which are much shorter timescales than those characterizing Be/X-ray binaries. Aims: We investigate the characteristics of bright flares (detections in excess of 5?) for a sample of SFXTs and their relation to the orbital phase. Methods: We have retrieved all Swift/BAT Transient Monitor light curves and collected all detections in excess of 5? from both daily- and orbital-averaged light curves in the time range of 2005 February 12 to 2013 May 31 (MJD 53 413-56 443). We also considered all on-board detections as recorded in the same time span and selected those in excess of 5? and within 4 arcmin of each source in our sample. Results: We present a catalogue of over a thousand BAT flares from 11 SFXTs, down to 15-150 keV fluxes of ~6 × 10-10 erg cm-2 s-1 (daily timescale) and ~1.5 × 10-9 erg cm-2 s-1 (orbital timescale, averaging ~800 s); the great majority of these flares are unpublished. The catalogue spans 100 months. This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100 mCrab, 15-50 keV) events. In the hard X-ray, these flares last generally much less than a day. Clustering of hard X-ray flares can be used to indirectly measure the length of an outburst, even when the low-level emission is not detected. We construct the distributions of flares, of their significance (in terms of ?), and of their flux as a function of orbital phase to infer the properties of these binary systems. In particular, we observe a trend of clustering of flares at some phases as Porb increases, which is consistent with a progression from tight circular or mildly eccentric orbits at short periods to wider and more eccentric orbits at longer orbital periods. Finally, we estimate the expected number of flares for a given source for our limiting flux and provide the recipe for calculating them for the limiting flux of future hard X-ray observatories. Project web page: http://www.ifc.inaf.it/sfxt/Full Table 4 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/562/A2

Romano, P.; Krimm, H. A.; Palmer, D. M.; Ducci, L.; Esposito, P.; Vercellone, S.; Evans, P. A.; Guidorzi, C.; Mangano, V.; Kennea, J. A.; Barthelmy, S. D.; Burrows, D. N.; Gehrels, N.

2014-02-01

170

AMBER/VLTI and MIDI/VLTI spectro-interferometric observations of the B[e] supergiant CPD-57°2874. Size and geometry of the circumstellar envelope in the near- and mid-IR  

NASA Astrophysics Data System (ADS)

We present the first high spatial and spectral resolution observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD-57°2874), performed with the Very Large Telescope Interferometer (VLTI). Spectra, visibilities and closure phase were obtained using the beam-combiner instruments AMBER (near-IR interferometry with three 8.3 m Unit Telescopes or UTs) and MIDI (mid-IR interferometry with two UTs). The interferometric observations of the CSE are well fitted by an elliptical Gaussian model with FWHM diameters varying linearly with wavelength. Typical diameters measured are ?1.8×3.4 mas or ?4.5×8.5 AU (adopting a distance of 2.5 kpc) at 2.2 ?m, and ?12×15 mas or ?30×38 AU at 12 ?m. The size of the region emitting the Br? flux is ?2.8×5.2 mas or ?7.0×13.0 AU. The major-axis position angle of the elongated CSE in the mid-IR (?144°) agrees well with previous polarimetric data, hinting that the hot-dust emission originates in a disk-like structure. In addition to the interferometric observations we also present new optical (UBVR_cI_c) and near-IR (JHKL) broadband photometric observations of CPD-57°2874. Our spectro-interferometric VLTI observations and data analysis support the non-spherical CSE paradigm for B[e] supergiants. Based on observations collected at the European Southern Observatory, Paranal, Chile, within the AMBER science demonstration time programme 074.A-9026 and the MIDI open time programme 074.D-0101.

Domiciano de Souza, A.; Driebe, T.; Chesneau, O.; Hofmann, K.-H.; Kraus, S.; Miroshnichenko, A. S.; Ohnaka, K.; Petrov, R. G.; Preisbisch, T.; Stee, P.; Weigelt, G.; Lisi, F.; Malbet, F.; Richichi, A.

2007-03-01

171

Chemical Reactions  

NSDL National Science Digital Library

We don't often stop to think about it, but underlying many of our everyday activities are chemical reactions. From the cooking of an egg to the growth of a child, chemical reactions make things happen. Although many of the reactions that support our lives

National Science Teachers Association (NSTA)

2009-05-01

172

Chemical sensors  

DOEpatents

Sensors responsive to small changes in the concentration of chemical species are disclosed, comprising (a) a mechanochemically responsive polymeric film capable of expansion or contraction in response to a change in its chemical environment, operatively coupled to (b) a transducer capable of directly converting said expansion or contraction to a measurable electrical response.

Lowell, Jr., James R. (Bend, OR); Edlund, David J. (Bend, OR); Friesen, Dwayne T. (Bend, OR); Rayfield, George W. (Bend, OR)

1991-01-01

173

Chemical sensors  

DOEpatents

Sensors responsive to small changes in the concentration of chemical species are disclosed. The sensors comprise a mechanochemically responsive polymeric film capable of expansion or contraction in response to a change in its chemical environment. They are operatively coupled to a transducer capable of directly converting the expansion or contraction to a measurable electrical response. 9 figures.

Lowell, J.R. Jr.; Edlund, D.J.; Friesen, D.T.; Rayfield, G.W.

1991-07-02

174

Chemical peels.  

PubMed

Chemical peels are a method of resurfacing with a long-standing history of safety in the treatment of various skin conditions. This article reviews the classification of different chemical agents based on their depth of injury. The level of injury facilitates cell turnover, epidermal thickening, skin lightening, and new collagen formation. Preprocedural, periprocedural, and postprocedural skin care are briefly discussed. To select the appropriate chemical peel, the provider should evaluate the patient's expectations, medical history, skin type, and possible complications to determine the best chemical peel to achieve the desired results. Patients with Fitzpatrick skin types IV to VI have increased risk of dyspigmentation, hypertrophic, and keloid scarring. These individuals respond well to superficial and medium-depth chemical peels. Advances in the use of combination peels allow greater options for skin rejuvenation with less risk of complications. PMID:24488634

Jackson, Adrianna

2014-02-01

175

Chemical threats.  

PubMed

The use of chemical agents as military weapons has been recognized for many centuries but reached the most feared and publicized level during World War I. Considerable political effort has been exercised in the twentieth century to restrict military strategies with chemicals. However, considerable concern currently exists that chemical weapons may be used as agents in civilian terrorism. The distribution of acetaminophen tablets contaminated with potassium cyanide and the release of sarin in the Tokyo sub-way system show that larger-scale deployment of chemical agents can be a reality. This reality makes it necessary for civilian disaster-planning strategies to incorporate an understanding of chemical agents, their effects, and the necessary treatment. PMID:16781273

Fry, Donald E

2006-06-01

176

Unnecessary Chemicals  

ERIC Educational Resources Information Center

Discusses the health hazards resulting from chemical additions of many common products such as cough syrups, food dyes, and cosmetics. Steps being taken to protect consumers from these health hazards are included. (MDR)

Johnson, Anita

1978-01-01

177

Chemical Analyses.  

National Technical Information Service (NTIS)

As a preliminary study on the effects of chemical aging of polymer materials MERL and TRI have examined two polymeric materials that are typically used for offshore umbilical applications. These two materials were Tefzel, a copolymer of ethylene and tetra...

J. W. Bulluck, R. A. Rushing

1994-01-01

178

Chemical sensors  

DOEpatents

Sensors responsive to small changes in the concentration of chemical species are disclosed, comprising a mechanicochemically responsive polymeric film capable of expansion or contraction in response to a change in its chemical environment, either operatively coupled to a transducer capable of directly converting the expansion or contraction to a measurable electrical or optical response, or adhered to a second inert polymeric strip, or doped with a conductive material.

Lowell, Jr., James R. (Bend, OR); Edlund, David J. (Bend, OR); Friesen, Dwayne T. (Bend, OR); Rayfield, George W. (Eugene, OR)

1992-01-01

179

Chemical sensors  

DOEpatents

Sensors responsive to small changes in the concentration of chemical species are disclosed, comprising a mechanicochemically responsive polymeric film capable of expansion or contraction in response to a change in its chemical environment, either operatively coupled to a transducer capable of directly converting the expansion or contraction to a measurable electrical or optical response, or adhered to a second inert polymeric strip, or doped with a conductive material. 12 figs.

Lowell, J.R. Jr.; Edlund, D.J.; Friesen, D.T.; Rayfield, G.W.

1992-06-09

180

Chemical sensors  

SciTech Connect

The revolution in analytical chemistry promised by recent developments in the field of chemical sensors has potential for significant positive impact on both research and production activities conducted by and for the Department of Energy. Analyses which were, in the past, performed only with a roomful of expensive equipment can now be performed with miniature solid-state electronic devices or small optical probes. Progress in the development of chemical sensors has been rapid, and the field is currently growing at a great rate. In accordance, Pacific Northwest Laboratory initiated a survey of recent literature so that contributors to active programs in research on analytical methods could be made aware of principles and applications of this new technology. This report presents the results of that survey. The sensors discussed here are divided into three types: micro solid-state devices, optical sensors, and piezoelectric crystal devices. The report is divided into three corresponding sections. The first section, ''Micro Solid-State Devices,'' discusses the design, operation, and application of electronic sensors that are produced in much the same way as standard solid-state electronic devices. The second section, ''Optrodes,'' covers the design and operation of chemical sensors that use fiber optics to detect chemically induced changes in optical properties. The final section, ''Piezoelectric Crystal Detectors,'' discusses two types of chemical sensors that depend on the changes in the properties of an oscillating piezoelectric crystal to detect the presence of certain materials. Advantages and disadvantages of each type of sensor are summarized in each section.

Hubbard, C.W.; Gordon, R.L.

1987-05-01

181

Chemical Mahjong  

ERIC Educational Resources Information Center

An open-access, Web-based mnemonic game is described whereby introductory chemistry knowledge is tested using mahjong solitaire game play. Several tile sets and board layouts are included that are themed upon different chemical topics. Introductory tile sets can be selected that prompt the player to match element names to symbols and metric…

Cossairt, Travis J.; Grubbs, W. Tandy

2011-01-01

182

Delicious Chemicals.  

ERIC Educational Resources Information Center

This paper presents an approach to chemistry and nutrition that focuses on food items that people consider delicious. Information is organized according to three categories of food chemicals that provide energy to the human body: (1) fats and oils; (2) carbohydrates; and (3) proteins. Minerals, vitamins, and additives are also discussed along with…

Barry, Dana M.

183

Chemical Evolution  

E-print Network

In this series of lectures we first describe the basic ingredients of galactic chemical evolution and discuss both analytical and numerical models. Then we compare model results for the Milky Way, Dwarf Irregulars, Quasars and the Intra-Cluster- Medium with abundances derived from emission lines. These comparisons allow us to put strong constraints on the stellar nucleosynthesis and the mechanisms of galaxy formation.

Francesca Matteucci

2007-04-05

184

Chemical Wonders  

NSDL National Science Digital Library

Students are introduced to chemical engineering and learn about its many different applications. They are provided with a basic introduction to matter and its different properties and states. An associated hands-on activity gives students a chance to test their knowledge of the states of matter and how to make observations using their five senses: touch, smell, sound, sight and taste.

Integrated Teaching And Learning Program

185

Chemical Changes  

NSDL National Science Digital Library

This is an excellent resource for teachers and students. It offers countless lab ideas for teaching chemical and physical changes and is geared for fifth through eighth grade. It also gives interactive web addresses for students and includes PowerPoint presentations on this topic.

can't tell- a science educator- not affiliated with any specific organization

2011-10-10

186

Chemical peel.  

PubMed

Chemical face peeling as described in this article produces gross and microscopic changes in the skin which are permanent. The most important aspect in assuring the success of this procedure is the proper selection of patients. The primary use of this procedure is for the purpose of eliminating wrinkles, whether as the primary or ancillary procedure, such as regional peeling. Chemical peeling of the face is a valuable adjunct in the treatment of the aging face and can produce some rather dramatic results with the careful selection of patients and meticulous attention to detail in carrying out the peel, as well as the exact adherence to the post peel instructions by the patient. PMID:639446

Mosienko, P; Baker, T J

1978-01-01

187

Chemical warfare  

PubMed Central

Leaf-cutting ants are well known for their highly complex social organization, which provides them with a strong defense against parasites invading their colonies. Besides this attribute, these insects have morphological, physiological and structural characteristics further reinforcing the defense of their colonies. With the discovery of symbiotic bacteria present on the integument of leaf-cutting ants, a new line of defense was proposed and considered to be specific for the control of a specialized fungal parasite of the ants’ fungus gardens (Escovopsis). However, recent studies have questioned the specificity of the integumental bacteria, as they were also found to inhibit a range of fungi, including entomopathogens. The microbiota associated with the leaf-cutting ant gardens has also been proposed as another level of chemical defense, protecting the garden from parasite invasion. Here we review the chemical defense weaponry deployed by leaf-cutting ants against parasites of their fungus gardens and of the ants themselves. PMID:23795235

Samuels, Richard Ian; Mattoso, Thalles Cardoso; Moreira, Denise D.O.

2013-01-01

188

Chemical Reactions  

NSDL National Science Digital Library

We are going go over a general view of reactions to prepare us for our unit on Chemical Reactions! Have fun learning! WARNING: If you are caught looking at ANY other site, without permission, you will be sent to the ALC, and you will not participate in any other computer activities for the rest of the year. Get your worksheet and begin! Overview Take this quiz and have me come over and sign off on your worksheet when you have completed the quiz! Overview Quiz Next let's take a look at what effect the rate of a chemical reaction. Rates of Reactions Another quiz, another check off by me! Rates of Reactions Quiz Now how do we measure how fast a ...

Hicken, Mrs.

2009-05-04

189

Chemical lasers  

NASA Astrophysics Data System (ADS)

The application and the advances of quantum electronics, specifically, of optical quantum generators lasers is reviewed. Materials are cut, their surfaces are machined, chemical transformations of substances are carried out, surgical operations are performed, data are transmitted, three dimensional images are produced and the content of microimpurities, in the atmosphere, are analyzed by use of a beam. Laser technology is used in conducting investigations in the most diverse fields of the natural and technical sciences from controlled thermonuclear fusion to genetics. Many demands are placed on lasers as sources of light energy. The importance of low weight, compactness of the optical generator and the efficiency of energy conversion processes is emphasized.

Khariton, Y.

1984-08-01

190

Chemical Separations  

NSDL National Science Digital Library

This site contains complete notes in a PowerPoint-like presentation for a chemical separations course. It covers a wide variety of topics, including distillation, extraction, gas chromatography, liquid chromatograpy, chromatography theory, instrumentation, electrophoresis, field flow fractionation, and affinity chromatography. It covers these topics thoroughly using a clear, consistent, and simple presentation style. Links to major topics like GC, LC, and electrophoresis provide specific information about the theory, instrumentation, and practice related to these techniques. The site also contains many annimations illustrating important separation processes.

2011-05-18

191

Chemical Analyses  

NASA Technical Reports Server (NTRS)

As a preliminary study on the effects of chemical aging of polymer materials MERL and TRI have examined two polymeric materials that are typically used for offshore umbilical applications. These two materials were Tefzel, a copolymer of ethylene and tetrafluoroethylene, and Coflon, polyvinylidene fluoride. The Coflon specimens were cut from pipe sections and exposed to H2S at various temperatures and pressures. One of these specimens was tested for methane permeation, and another for H2S permeation. The Tefzel specimens were cut from .05 mm sheet stock material and were exposed to methanol at elevated temperature and pressure. One of these specimens was exposed to methanol permeation for 2 days at 100 C and 2500 psi. An additional specimen was exposed to liquid methanol for 3 days at 150 C and 15 Bar. Virgin specimens of each material were similarly prepared and tested.

Bulluck, J. W.; Rushing, R. A.

1994-01-01

192

Chemical Accelerators The phrase "chemical accelerators"  

E-print Network

Meetings Chemical Accelerators The phrase "chemical accelerators" is scarcely older than for one or two dozen people grew to include nearly a hundred. Chemical accelerators is a name sug- gested by one of us for devices that produce beams of chemically interesting species at relative kinetic

Zare, Richard N.

193

Nature's chemicals and synthetic chemicals: Comparative toxicology  

Microsoft Academic Search

The toxicology of synthetic chemicals is compared to that of natural chemicals, which represent the vast bulk of the chemicals to which humans are exposed. It is argued that animals have a broad array of inducible general defenses to combat the changing array of toxic chemicals in plant food (nature's pesticides) and that these defenses are effective against both natural

B. N. Ames; M. Profet; L. S. Gold

1990-01-01

194

Chemical composition and origin of nebulae around Luminous Blue Variables  

E-print Network

We use the analysis of the heavy element abundances (C, N, O, S) in circumstellar nebulae around Luminous Blue Variables to infer the evolutionary phase in which the material has been ejected. (1) We discuss the different effects that may have changed the gas composition of the nebula since it was ejected (2) We calculate the expected abundance changes at the stellar surface due to envelope convection in the red supergiant phase. If the observed LBV nebulae are ejected during the RSG phase, the abundances of the LBV nebulae require a significantly smaller amount of mass to be lost than assumed in evolutionary models. (3) We calculate the changes in the surface composition during the main sequence phase by rotation induced mixing. If the nebulae are ejected at the end of the MS-phase, the abundances in LBV nebulae are compatible with mixing times between 5 x 10^6 and 1 x 10^7 years. The existence of ON stars supports this scenario. (4) The predicted He/H ratio in the nebulae are significantly smaller than the current observed photospheric values of their central stars. Combining various arguments we show that the LBV nebulae are ejected during the blue SG phase and that the stars have not gone through a RSG phase. The chemical enhancements are due to rotation induced mixing, and the ejection is possibly triggered by near-critical rotation. During the ejection, the outflow was optically thick, which resulted in a large effective radius and a low effective temperature. This also explains the observed properties of LBV dust.

Henny J. G. L. M. Lamers; Antonella Nota; Nino Panagia; Linda J. Smith; Norbert Langer

2001-03-28

195

Modern Chemical Technology, Guidebook for Chemical Technicians.  

ERIC Educational Resources Information Center

This volume is a part of the ACS "Modern Chemical Technology" (ChemTeC) curriculum that is developed for chemical technicians. It is intended as a handbook that will be used throughout the instruction. Safety is stressed in eight of the ten chapters under the headings: safety in the chemical laboratory, personal protective equipment, fire safety…

Pecsok, Robert L.; Chapman, Kenneth

196

Chemical and Biomolecular Engineering  

E-print Network

Chemical and Biomolecular Engineering Combining theory and neutron scattering to understand molecular diffusion in porous materials David Sholl School of Chemical & Biomolecular Engineering Georgia Institute of Technology #12;Chemical and Biomolecular Engineering Porous materials www

Pennycook, Steve

197

CHEMICALS IN PROGRESS BULLETIN  

EPA Science Inventory

Chemicals in Progress Bulletin is a quarterly newsletter which highlights regulatory and program activities of the Office of Pollution Prevention and Toxics. Regular features and news items include the existing chemicals program, new chemicals program, pollution prevention activi...

198

Microfluidic chemical reaction circuits  

DOEpatents

New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

Lee, Chung-cheng (Irvine, CA); Sui, Guodong (Los Angeles, CA); Elizarov, Arkadij (Valley Village, CA); Kolb, Hartmuth C. (Playa del Rey, CA); Huang, Jiang (San Jose, CA); Heath, James R. (South Pasadena, CA); Phelps, Michael E. (Los Angeles, CA); Quake, Stephen R. (Stanford, CA); Tseng, Hsian-rong (Los Angeles, CA); Wyatt, Paul (Tipperary, IE); Daridon, Antoine (Mont-Sur-Rolle, CH)

2012-06-26

199

Nature's chemicals and synthetic chemicals: Comparative toxicology  

SciTech Connect

The toxicology of synthetic chemicals is compared to that of natural chemicals, which represent the vast bulk of the chemicals to which humans are exposed. It is argued that animals have a broad array of inducible general defenses to combat the changing array of toxic chemicals in plant food (nature's pesticides) and that these defenses are effective against both natural and synthetic toxins. Synthetic toxins such as dioxin are compared to natural chemicals, such as indole carbinol (in broccoli) and ethanol. Trade-offs between synthetic and natural pesticides are discussed. The finding that in high-dose tests, a high proportion of both natural and synthetic chemicals are carcinogens, mutagens, teratogens, and clastogens (30-50{percent} for each group) undermines current regulatory efforts to protect public health from synthetic chemicals based on these tests.

Ames, B.N.; Profet, M.; Gold, L.S. (Univ. of California, Berkeley (USA))

1990-10-01

200

The elusive chemical potential  

Microsoft Academic Search

This paper offers some qualitative understanding of the chemical potential, a topic that students invariably find difficult. Three ``meanings'' for the chemical potential are stated and then supported by analytical development. Two substantial applications-depression of the melting point and batteries-illustrate the chemical potential in action. The origin of the term ``chemical potential'' has its surprises, and a sketch of the

Ralph Baierlein

2001-01-01

201

Chemical engineers design, control and optimize large-scale chemical,  

E-print Network

38 Chemical engineers design, control and optimize large-scale chemical, physicochemical and electronics fields. Chemical Engineers are employed in areas as diverse as the chemical, pharmaceutical, petrochemical and environmental industries. Emerging fields in chemical engineering include biotechnology

Rohs, Remo

202

CHEMICAL ENGINEERING AND MANUFACTURING CHEMICAL ENGINEERING  

E-print Network

, completion, attention to detail, etc. Materials 1. Cookies 2. Frosting 3. Food coloring 4. Sprinkles 5 are involved in the production of food, cosmetics, fuels, and anything else that requires the mixing of chemicals. This lesson introduces students to one component of chemical engineering: food processing

Provancher, William

203

Red supergiants around Stephenson 2 (Negueruela+, 2012)  

NASA Astrophysics Data System (ADS)

Observations were carried out with the AutoFib2+WYFFOS (AF2) multi-object, wide-field, fibre spectrograph mounted on the Prime Focus of the 4.2m William Herschel Telescope (WHT), in La Palma, Spain. The observations were taken on the nights of 2009, June 5th (in service mode) and June 6th-7th (in visitor mode). (2 data files).

Negueruela, I.; Marco, A.; Gonzalez-Fernandez, C.; Jimenez-Esteban, F.; Clark, J. S.; Garcia, M.; Solano, E.

2013-01-01

204

The Chemical Heritage Foundation  

NASA Astrophysics Data System (ADS)

This first in a series of articles on the Chemical Heritage Foundation will outline a brief history of the foundation and give an overview of its present programs, with emphasis on the Othmer Library of Chemical History. The Chemical Heritage Foundation (CHF) is a unique asset and unique partnership of the chemical community. It had its origins in a simple written agreement some 15 years ago, in January 1982. CHF's mission of recording, preserving, and making known the heritage of chemical achievement does not reflect the concerns of the chemical corporations or of anyone directly concerned with the "image" or economic and political future of the chemical sciences. Rather, it was an idea of academics and professional scientists. Thus it was appropriate that the three founding organizations were the American Chemical Society, the American Institute of Chemical Engineers and the University of Pennsylvania.

Orna, Mary Virginia

1998-04-01

205

Components in Chemical Thermodynamics  

NASA Astrophysics Data System (ADS)

Chemical equations are actually matrix equations, and this has important implications for their thermodynamic treatment. The fundamental equation for chemical thermodynamics for a chemical reaction system can be written in terms of species, but at chemical equilibrium, it has to be written in terms of components. The number of components is equal to the number of species minus the number of independent chemical reactions. The fundamental equation for the Gibbs energy of a system containing ethylene, methane, ethane, and propane is discussed. At chemical equilibrium there are two components, which can be taken to be carbon and hydrogen or ethylene and methane. There are advantages in using matrix notation.

Alberty, Robert A.

1995-09-01

206

Advanced chemical lasers  

Microsoft Academic Search

A review of recent advances in chemical laser technology is presented. New technology and concepts related to the Chemical Oxygen Iodine Laser (COIL), All Gas-phase Iodine Laser (AGIL), and HF Overtone Laser are discussed.

Gerald C. Manke II; Kevin B. Hewett; Timothy J. Madden; John E. McCord; Charles F. Wisniewski; Gordon D. Hager

2004-01-01

207

Children and Dairy Chemicals  

MedlinePLUS

Children & Dairy Chemicals Chemicals used to clean dairy facilities and equipment, especially dairy pipeline cleaners, pose a special risk for children. Rapid medical assessment and treatment is critical in preventing long ...

208

DTP - Chemical Biology Consortium  

Cancer.gov

Chemical Biology Consortium Home Discovery Development Pathways Grants/Contracts Books/Publications Site Search Data Search What's New Chemical Biology Consortium (CBC) Division of Cancer Treatment and Diagnosis To download Adobe Reader for documents

209

Chemistry 455 Chemical Nanotechnology  

E-print Network

Chemistry 455 Chemical Nanotechnology 4 units Prof. Richard Brutchey, Fall 2014 (Lecture = 12:00�12:50 pm MWF) CHEM 455 is an upper-division undergraduate course in Chemical Nanotechnology. The intent

Rohs, Remo

210

PhD Chemical Engineering MS Chemical Engineering  

E-print Network

1 PhD Chemical Engineering MS Chemical Engineering Bylaws Gene and Linda Voiland School of ChemicalD Chemical Engineering, MS Chemical Engineering B. Discipline: Edgar, et al.1 provide a succinct description of chemical engineering: "chemical engineers seek to understand, manipulate, and control the molecular basis

Collins, Gary S.

211

The elusive chemical potential  

NSDL National Science Digital Library

The author offers some qualitative understanding of the chemical potential, a topic that students invariably find difficult. Three "meanings" for the chemical potential are stated and then supported by analytical development. Two substantial applications â depression of the melting point and batteries â illustrate the chemical potential in action. The origin of the term "chemical potential" has its surprises, and a sketch of the history is given.variable particle number.

Baierlein, Ralph

2011-08-31

212

Chemical Synthesis Database  

NSDL National Science Digital Library

This database provides information on thousands of chemical compounds, including synthesis references and physical properties. The database is searchable by keyword and browseable by journal title. For each compound, the information includes molecular formula and weight, Chemical Abstracts Service (CAS) numbers, International Chemical Identifier (InChIKey), and Simplified Molecular Input Line Entry System (SMILES) notation. There is also information on synonyms, physical properties (boiling and melting points, density), an illustration of chemical structure, spectral data, and links to additional data.

213

Chemical of the Week  

NSDL National Science Digital Library

Professor Bassam Z. Shakhashiri at the University of Wisconsin-Madison adds a new chemical to this page every week. The site was created for his general chemistry courses, Chem 103 and Chem 104, to increase students' knowledge about various chemicals and their use. Users can view featured chemicals from the currently updated fall course (103) or from the spring course (104). The chemicals featured thus far include: lime, methane, uranium, the chemistry of autumn colors, and gases that emit light.

Shakhashiri, Bassam Z.

2007-05-30

214

Chemicals for worldwide aquaculture  

USGS Publications Warehouse

Regulations and therapeutants or other safe chemicals that are approved or acceptable for use in the aquaculture industry in the US, Canada, Europe and Japan are presented, discussing also compounds that are unacceptable for aquaculture. Chemical use practices that could affect public health are considered and details given regarding efforts to increase the number of registered and acceptable chemicals.

Schnick, R.A.

1991-01-01

215

Toxicology and Chemical Safety.  

ERIC Educational Resources Information Center

Topics addressed in this discussion of toxicology and chemical safety include routes of exposure, dose/response relationships, action of toxic substances, and effects of exposure to chemicals. Specific examples are used to illustrate the principles discussed. Suggests prudence in handling any chemicals, whether or not toxicity is known. (JN)

Hall, Stephen K.

1983-01-01

216

Chemical and Environmental Technology.  

ERIC Educational Resources Information Center

The two-year curriculum in chemical technology presented in the document is designed to prepare high school graduates for technical positions in the chemical industry. Course outlines are given for general chemistry, chemical calculations, quantitative analysis, environmental chemistry, organic chemistry 1 and 2, instrumental analysis, and…

Sheather, Harry

217

Chemical Reactions at Surfaces  

Microsoft Academic Search

Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The

Nancy Ryan Gray Michael Henderson

2010-01-01

218

More on Chemical Changes  

NSDL National Science Digital Library

The phenomenon is a series of chemical reactions and observation of signs of a chemical change. The laboratory activities can be done by students or as a teacher demonstration. They involve mixing chemicals and noting color change, formation of a precipitate, and production of a gas.

219

AGRICULTURAL CHEMICAL USAGE DATA  

EPA Science Inventory

This report, which summarizes the use of agricultural chemicals is issued by the National Agricultural Statistics Service (NASS) as part of its series on Agricultural Chemical Usage. Other publications in the series present statistics for on-farm agricultural chemical usage for f...

220

Make a Chemical Clock  

NSDL National Science Digital Library

This lesson for Grades 6-8 combines a short video with three experiments to observe and record chemical changes. The experiments use common household materials to demonstrate chemical reaction -- a change that leads to a transformation of one substance into another substance. In the 3rd experiment, there are two chemical reactions happening at the same time. Through careful observation, learners see that the 3rd reaction represents a "chemical clock", because the time it takes the chemicals to react happens very predictably, like a regular clock. Talking Science is part of National Public Radio's Science Friday initiative.

2011-08-18

221

Chemical Synthesis of Proteins  

PubMed Central

Proteins have become accessible targets for chemical synthesis. The basic strategy is to use native chemical ligation, Staudinger ligation, or other orthogonal chemical reactions to couple synthetic peptides. The ligation reactions are compatible with a variety of solvents and proceed in solution or on a solid support. Chemical synthesis enables a level of control on protein composition that greatly exceeds that attainable with ribosome-mediated biosynthesis. Accordingly, the chemical synthesis of proteins is providing previously unattainable insight into the structure and function of proteins. PMID:15869385

Nilsson, Bradley L.; Soellner, Matthew B.; Raines, Ronald T.

2010-01-01

222

Chemical exchange program analysis.  

SciTech Connect

As part of its EMS, Sandia performs an annual environmental aspects/impacts analysis. The purpose of this analysis is to identify the environmental aspects associated with Sandia's activities, products, and services and the potential environmental impacts associated with those aspects. Division and environmental programs established objectives and targets based on the environmental aspects associated with their operations. In 2007 the most significant aspect identified was Hazardous Materials (Use and Storage). The objective for Hazardous Materials (Use and Storage) was to improve chemical handling, storage, and on-site movement of hazardous materials. One of the targets supporting this objective was to develop an effective chemical exchange program, making a business case for it in FY07, and fully implementing a comprehensive chemical exchange program in FY08. A Chemical Exchange Program (CEP) team was formed to implement this target. The team consists of representatives from the Chemical Information System (CIS), Pollution Prevention (P2), the HWMF, Procurement and the Environmental Management System (EMS). The CEP Team performed benchmarking and conducted a life-cycle analysis of the current management of chemicals at SNL/NM and compared it to Chemical Exchange alternatives. Those alternatives are as follows: (1) Revive the 'Virtual' Chemical Exchange Program; (2) Re-implement a 'Physical' Chemical Exchange Program using a Chemical Information System; and (3) Transition to a Chemical Management Services System. The analysis and benchmarking study shows that the present management of chemicals at SNL/NM is significantly disjointed and a life-cycle or 'Cradle-to-Grave' approach to chemical management is needed. This approach must consider the purchasing and maintenance costs as well as the cost of ultimate disposal of the chemicals and materials. A chemical exchange is needed as a mechanism to re-apply chemicals on site. This will not only reduce the quantity of unneeded chemicals and the amount spent on new purchases, but will also avoid disposal costs. If SNL/NM were to realize a 5 percent reduction in chemical inventory and a 10 percent reduction in disposal of unused chemicals the total savings would be $189, 200 per year.

Waffelaert, Pascale

2007-09-01

223

Chemical Hygiene Plan i January 2013 Chemical Hygiene Plan  

E-print Network

Chemical Hygiene Plan i January 2013 Chemical Hygiene Plan (CHP) (Appendix C in Lab Safety Manual........................................................................................................................1-1 Chapter 2: Chemical Hazard Communication....................................................................................2-1 Chapter 3: Classes of Hazardous Chemicals

Nizkorodov, Sergey

224

Journal of Chemical Education: Chemical Resource Shelf  

NSDL National Science Digital Library

Produced under the auspices of the Journal of Chemical Education Online, this site is the basis for that journal's "Book Buyer's Guide." It provides high school and college-level chemistry educators with various teaching resources, including a comprehensive index to chemistry textbooks in print. The index is arranged by subject, under which entries are listed in chronological order, from newest to oldest. Subjects covered range from Biochemistry and Computers in Chemistry to Quantum Chemistry and Writing in Science. In addition to basic bibliographic information, when available, each entry includes citations of reviews and links to publishers' online catalogs. Another feature is "Hal's Picks of the Month," a growing archive of over 30 "books and recent articles for teachers of chemistry and related sciences" as recommended and reviewed by Professor Harold (Hal) Harris of the University of Missouri - St. Louis Chemistry Department. "Journals of Interest to Chemical Educators" and "Suppliers of Software for Chemical Education" are two other lists available at this site.

1995-01-01

225

Chemical evolution STRUCTURE OF GALAXIES  

E-print Network

Outline Absorption Chemical evolution STRUCTURE OF GALAXIES 8. Absorption; chemical evolution Piet Piet van der Kruit, Kapteyn Astronomical Institute Absorption; chemical evolution #12;Outline Absorption Chemical evolution Outline Absorption Holmberg's analysis Analysis of Disney et al. Edge

Kruit, Piet van der

226

Chemically pumped iodine laser  

Microsoft Academic Search

McDermott et al. (1978) have developed a practical O2(1 Delta) generator based on bubbling Cl2 in alkaline H2O2. In the work described in the present paper, it proved possible to convert a transverse-flow mixing chemical laser, originally designed as a CO chemical laser, to a chemical iodine-atom laser by installing a version of the McDermott generator on the laser. The

R. J. Richardson; C. E. Wiswall

1979-01-01

227

Insect Chemical Warfare  

NSDL National Science Digital Library

Discussion of the Bombardier beetle's chemical defense, detailing the explosive qualities of the chemicals, where the beetle is found, a bit about distribution, and what the chemicals do to people. There's also a bit about insects in the news detailing the beetle's role in the ongoing religious debate as it pertains to how such an animal might evolve, with an aside about a Richard Dawkin's demonstration.

0002-11-30

228

Chemical spill exposure assessment  

Microsoft Academic Search

POSSM, the PCB On-Site Spill Model, is a contaminant transport model developed to predict environmental concentrations associated with a chemical spill. The model predicts daily changes in chemical concentrations on a spill site (e.g., in soil and on vegetation) and losses of chemical due to volatilization, surface runoff\\/soil erosion, and leaching to groundwater. Spill areas consisting of soil\\/vegetation and\\/or an

Stuart M. Brown; Abraham Silvers

1986-01-01

229

Multivariate Quantitative Chemical Analysis  

NASA Technical Reports Server (NTRS)

Technique of multivariate quantitative chemical analysis devised for use in determining relative proportions of two components mixed and sprayed together onto object to form thermally insulating foam. Potentially adaptable to other materials, especially in process-monitoring applications in which necessary to know and control critical properties of products via quantitative chemical analyses of products. In addition to chemical composition, also used to determine such physical properties as densities and strengths.

Kinchen, David G.; Capezza, Mary

1995-01-01

230

Chemically Layered Porous Solids  

NASA Technical Reports Server (NTRS)

Aerogels and other porous solids in which surfaces of pores have chemical properties varying with depth below macroscopic surfaces prepared by sequences of chemical treatments. Porous glass or silica bead treated to make two depth zones having different chemical properties. Beads dropped along tube filled with flowing gas containing atomic oxygen, generated in microwave discharge. General class of materials treatable include oxides of aluminum, silicon, zirconium, tin, titanium, and nickel, and mixtures of these oxides. Potential uses of treated materials include chromatographic separations, membrane separations, controlled releases of chemicals, and catalysis.

Koontz, Steve

1991-01-01

231

Physical and Chemical Changes  

NSDL National Science Digital Library

Physical and chemical changes in matter affect us every day. Use the following resources to help you understand these changes more completely. Read this document to help you understand the difference between physical and chemical changes in matter. definitions Watch this! It illustrates the physical change of matter. physical change video Now, watch this! It illustrates the chemical change of matter. chemical change video Click on this link to read and explore the Utah Science Sci-ber Site. It will help you to ...

Holly, Mrs.

2010-11-15

232

310 Facility chemical specifications  

SciTech Connect

The 300 area Treated Effluent Disposal Facility (TEDF) was designed and built to treat the waste water from the 300 area process sewer system. Several treatment technologies are employed to remove the trace quantities of contaminants in the stream, including iron coprecipitation, clarification, filtration, ion exchange, and ultra violet light/hydrogen peroxide oxidation of organics. The chemicals that will be utilized in the treatment process are hydrogen peroxide, sulfuric acid, sodium hydroxide, and ferric chloride. This document annotates the required chemical characteristics of TEDF bulk chemicals as well as the criteria that were used to establish these criteria. The chemical specifications in appendix B are generated from this information.

Hagerty, K.J.

1997-05-21

233

Apparatus for chemical synthesis  

DOEpatents

A method and apparatus for forming a chemical hydride is described and which includes a pseudo-plasma-electrolysis reactor which is operable to receive a solution capable of forming a chemical hydride and which further includes a cathode and a movable anode, and wherein the anode is moved into and out of fluidic, ohmic electrical contact with the solution capable of forming a chemical hydride and which further, when energized produces an oxygen plasma which facilitates the formation of a chemical hydride in the solution.

Kong, Peter C. (Idaho Falls, ID); Herring, J. Stephen (Idaho Falls, ID); Grandy, Jon D. (Idaho Falls, ID)

2011-05-10

234

Predicting Chemical Toxicity Effects Based on Chemical-Chemical Interactions  

PubMed Central

Toxicity is a major contributor to high attrition rates of new chemical entities in drug discoveries. In this study, an order-classifier was built to predict a series of toxic effects based on data concerning chemical-chemical interactions under the assumption that interactive compounds are more likely to share similar toxicity profiles. According to their interaction confidence scores, the order from the most likely toxicity to the least was obtained for each compound. Ten test groups, each of them containing one training dataset and one test dataset, were constructed from a benchmark dataset consisting of 17,233 compounds. By a Jackknife test on each of these test groups, the 1st order prediction accuracies of the training dataset and the test dataset were all approximately 79.50%, substantially higher than the rate of 25.43% achieved by random guesses. Encouraged by the promising results, we expect that our method will become a useful tool in screening out drugs with high toxicity. PMID:23457578

Zhang, Jian; Feng, Kai-Rui; Zheng, Ming-Yue; Cai, Yu-Dong

2013-01-01

235

Great Lakes: Chemical Monitoring  

ERIC Educational Resources Information Center

The Tenth Great Lakes Regional Meeting of the American Chemical Society met to assess current Chemical Research activity in the Great Lakes Basin, and addressed to the various aspects of the theme, Chemistry of the Great Lakes. Research areas reviewed included watershed studies, atmospheric and aquatic studies, and sediment studies. (BT)

Delfino, Joseph J.

1976-01-01

236

Chemically pumped iodine laser  

Microsoft Academic Search

A chemically pumped iodine-atom laser is described based on electronic energy transfer to atomic iodine from chemically generated O2(1?). The total extracted power (10 W) is approximately 3% of the power contained in the O2(1?) flow.

R. J. Richardson; C. E. Wiswall

1979-01-01

237

Chemical carcinogens. Second edition  

SciTech Connect

This book looks at the latest research in chemical carcinogenic agents. To gain an understanding these agents and their importance in identifying the occupational and environmental causes of cancer. Included are studies in soots, tars, and oils; DNA interaction of reactive intermediates; mineral fiber carcinogenesis; carcinogens in foods and medicine; and laboratory chemicals as carcinogens.

Searle, C.E.

1984-01-01

238

Chemical Effects of Ultrasonics  

Microsoft Academic Search

The present work was undertaken with the purpose of considering why and how reaction takes place in an ultrasonic field, rather than studying the chemical kinetics of such reactions. Experimental evidence is presented which supports the conclusions that chemical processes brought about by ultrasonics require cavitation. Furthermore, the experiments were planned so as to show whether the reactions take place

Mary Evelyn Fitzgerald; Virginia Griffing; James Sullivan

1956-01-01

239

Chemical and Physical Changes  

NSDL National Science Digital Library

The phenomenon is a chemical reaction between sugar and sulfuric acid. The demonstration (a discrepant event) compares the way sugar and water interact when combined (physical change) to the way sugar and sulfuric acid interact when combined (chemical change). In part II, students are given additional substances and changes to observe.

240

Chemical Biology Consortium Agreement  

Cancer.gov

NCI_CBC v.1.2 9/2009 The National Cancer Institute’s Chemical Biology Consortium Participants Agreement Mission: The mission of the National Cancer Institute’s (“NCI”) Chemical Biology Consortium (“CBC”) is to increase the flow of early

241

Chemical Process Synthesis.  

ERIC Educational Resources Information Center

Process synthesis is the specification of chemical and physical operations and the selection and interconnection of equipment to implement these operations to effect desired chemical processing transformations. Optimization and evolutionary and systematic generation process synthesis approaches are described. (Author/SK)

Siirola, J. J.

1982-01-01

242

Geothermal chemical engineering  

Microsoft Academic Search

Programs, projects, and research for utilization of geothermal energy are reviewed from a chemical engineering vantage point, with attention given to costs, proved resources, reservoir models, applications, and environmental impact. Neglect of crucial chemical reactions occurring in geothermal systems impair the usefulness of existing models constructed for hydrothermal reservoirs. Currently entertained models, studies of reservoir mechanics and ground water hydrology,

R. C. Axtmann; L. B. Peck

1976-01-01

243

Chemical Kinetics: Isolation Method  

NSDL National Science Digital Library

This site offers an interactive tutorial that guides the student through the Method of Isolation used for the determination of chemical reaction rate laws and rate constants. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

244

Forward chemical genetic screening.  

PubMed

Chemical genetics utilizes small molecules to perturb biological processes. Unlike conventional genetics methods, which involve the alteration of genetic information mostly with lasting effects, chemical genetics allows temporary and reversible alterations of biological processes. Furthermore, it enables the alteration of biological processes in a dose-dependent manner, providing an advantage over conventional genetics. In the present chapter, the general procedures of forward chemical genetic screening are described. Forward chemical genetic screening can be performed in three steps. The first step involves the identification of small molecules that induce phenotypic or physiological changes in a biological system from a chemical library. In the second step, cellular targets that interact with the isolated chemical, which are mostly proteins, are identified. Although several methods can be applied in the second step, the most common one is affinity pull-down assay using a target protein that binds to the isolated compound. However, affinity pull-down of a target protein is a formidable barrier in forward chemical genetics. We introduced a tagged chemical library approach that significantly facilitates the identification of target proteins. The third step consists of the validation of the target protein, which should include the assessment of target specificity. This step is critical because small molecules often show pleiotropic effects due to low specificity. The specificity test may include a competition assay using cold competitors and a genetic study using mutants or transgenic lines modified for the cellular target. PMID:24057378

Choi, Hyunmo; Kim, Jun-Young; Chang, Young Tae; Nam, Hong Gil

2014-01-01

245

Elemental Chemical Puzzlers  

ERIC Educational Resources Information Center

This paper provides nine short chemically based puzzles or problems extensible for use with students from middle school to college. Some of these will strengthen students' recognition of individual elements and element names. Others require students to focus on the salient properties of given chemical elements.

Thomas, Nicholas C.

2009-01-01

246

On tropospheric chemical oscillations  

Microsoft Academic Search

Tropospheric chemical mechanisms can generate oscillations in which the concentrations of all reactive chemical species oscillate on timescales ranging from days to years, depending on certain parameter ranges of specified sources for NOx and a reduced species (e.g., carbon monoxide, isoprene, or methane). A simple carbon monoxide oxidation mechanism is presented that exhibits oscillatory solutions qualitatively similar to those found

Peter G. Hess; Sasha Madronich

1997-01-01

247

Chemical cloud tracking systems  

NASA Astrophysics Data System (ADS)

This paper describes the Chemical Cloud Tracking System (CCTS) which has been installed at Dugway Proving Ground. The CCTS allows mapping of chemical clouds in real time from a safe standoff distance. The instruments used are passive standoff chemical agent detectors (FTIRs). Each instrument individually can only measure the total of all the chemical in its line-of-site; the distance to the cloud is unknown. By merging data from multiple vantage points (either one instrument moving past the cloud or two or more instruments spaced so as to view the cloud from different directions) a map of the cloud locations can be generated using tomography. To improve the sensitivity and accuracy of the cloud map, chemical point sensors can be added to the sensor array being used. The equipment required for the CCTS is commercially available. Also, the data fusion techniques (tomography) have been demonstrated previously in the medical field. The Chemical Cloud Tracking System can monitor the movement of many chemical clouds of either military or industrial origin. Since the technique is standoff, the personnel are not exposed to toxic hazards while they follow the cloud. Also, the equipment works on-the-move which allows rapid response to emergency situations (plant explosions, tanker car accidents, chemical terrorism, etc.).

Grim, Larry B.; Gruber, Thomas C., Jr.; Marshall, Martin; Rowland, Brad

2002-02-01

248

Microorganisms and Chemical Pollution  

ERIC Educational Resources Information Center

Discusses the importance of microorganisms in chemical pollution and pollution abatement. Selected chemical pollutants are chosen to illustrate that microorganisms synthesize hazardous substances from reasonably innocuous precursors, while others act as excellent environmental decontaminating agents by removing undesirable natural and synthetic…

Alexander, M.

1973-01-01

249

The Chemical Abstract Machine  

Microsoft Academic Search

We introduce a new kind of abstract machine based on the chemical metaphor used in the ? language of Banâtre & al. States of a machine are chemical solutions where floating molecules can interact according to reaction rules. Solutions can be stratified by encapsulating subsolutions within membranes that force reactions to occur locally. We illustrate the use of this model

Gérard Berry; Gérard Boudol

1990-01-01

250

Hazardous chemicals desk reference  

Microsoft Academic Search

This book supplies instant-access data on nearly 4,700 of the most dangerous chemicals and compounds used in the workplace. It alerts readers to potential short- and long-term hazards by providing for each chemical a 1 to 3 hazard rating ... CAS, NIOSH, and DOT numbers ... concise descriptions of physical properties ... synonyms ... and current standards for exposure limits.

N. I. Sax; R. J. Sr. Lewis

1987-01-01

251

Chemical recognition software  

SciTech Connect

We have developed a capability to make real time concentration measurements of individual chemicals in a complex mixture using a multispectral laser remote sensing system. Our chemical recognition and analysis software consists of three parts: (1) a rigorous multivariate analysis package for quantitative concentration and uncertainty estimates, (2) a genetic optimizer which customizes and tailors the multivariate algorithm for a particular application, and (3) an intelligent neural net chemical filter which pre-selects from the chemical database to find the appropriate candidate chemicals for quantitative analyses by the multivariate algorithms, as well as providing a quick-look concentration estimate and consistency check. Detailed simulations using both laboratory fluorescence data and computer synthesized spectra indicate that our software can make accurate concentration estimates from complex multicomponent mixtures, even when the mixture is noisy and contaminated with unknowns.

Wagner, J.S.; Trahan, M.W.; Nelson, W.E.; Hargis, P.H. Jr.; Tisone, G.C.

1994-06-01

252

Tortuous path chemical preconcentrator  

DOEpatents

A non-planar, tortuous path chemical preconcentrator has a high internal surface area having a heatable sorptive coating that can be used to selectively collect and concentrate one or more chemical species of interest from a fluid stream that can be rapidly released as a concentrated plug into an analytical or microanalytical chain for separation and detection. The non-planar chemical preconcentrator comprises a sorptive support structure having a tortuous flow path. The tortuosity provides repeated twists, turns, and bends to the flow, thereby increasing the interfacial contact between sample fluid stream and the sorptive material. The tortuous path also provides more opportunities for desorption and readsorption of volatile species. Further, the thermal efficiency of the tortuous path chemical preconcentrator is comparable or superior to the prior non-planar chemical preconcentrator. Finally, the tortuosity can be varied in different directions to optimize flow rates during the adsorption and desorption phases of operation of the preconcentrator.

Manginell, Ronald P. (Albuquerque, NM); Lewis, Patrick R. (Albuquerque, NM); Adkins, Douglas R. (Albuquerque, NM); Wheeler, David R. (Albuquerque, NM); Simonson, Robert J. (Cedar Crest, NM)

2010-09-21

253

Chemical engineers design, control and optimize large-scale chemical,  

E-print Network

- and nanomaterials. Chemical engineers are uniquely qualified to provide solutions to many pressing problems38 Chemical engineers design, control and optimize large-scale chemical, physicochemical and electronics fields. Chemical Engineers are employed in areas as diverse as the chemical, pharmaceutical

Rohs, Remo

254

Chemical engineers design, control and optimize large-scale chemical,  

E-print Network

materials including bio- and nanomaterials. Chemical engineers are uniquely qualified to provide solutions38 Chemical engineers design, control and optimize large-scale chemical, physicochemical and electronics fields. Chemical Engineers are employed in areas as diverse as the chemical, materials, energy

Rohs, Remo

255

Chemical Heritage Foundation  

NSDL National Science Digital Library

"The Chemical Heritage Foundation (CHF) is dedicated to preserving and sharing the history and heritage of the chemical and molecular sciences, technologies, and allied industries." This Web site illustrates how chemistry has shaped our world. Students can discover the chemical history of Innovations and Industry, Ancients and Alchemists, and much more. Through the Online Exhibits, visitors can view the pictures of Walter J. Hamer's collection of early batteries. In the Classroom Resources, educators will find online tools discussing molecular science and pharmaceutical achievers and many Chemistry Web Quests including Evidence for Atoms and The Great MTBE Controversy. Graduate students may want to take advantage of the many fellowships offered on the site.

2003-01-01

256

Selecting chemical treatment programs  

SciTech Connect

Many process equipment performance and reliability problems can be solved economically by the proper selection and application of chemical treatment programs. It is important to choose an experienced chemical vendor and to work closely with the vendor to develop a good chemical treatment program. This requires devoting sufficient manpower to ensure that the treatment program development is thorough and timely. After the treatment program is installed, the system operation and performance should be routinely monitored to ensure that expected benefits are achieved and unexpected problems do not develop.

Miller, J.E. (TOSCO Corp., Avon Refinery, Martinez, CA (US))

1988-09-01

257

Chemical warfare agents  

PubMed Central

Among the Weapons of Mass Destruction, chemical warfare (CW) is probably one of the most brutal created by mankind in comparison with biological and nuclear warfare. Chemical weapons are inexpensive and are relatively easy to produce, even by small terrorist groups, to create mass casualties with small quantities. The characteristics of various CW agents, general information relevant to current physical as well as medical protection methods, detection equipment available and decontamination techniques are discussed in this review article. A brief note on Chemical Weapons Convention is also provided. PMID:21829312

Ganesan, K.; Raza, S. K.; Vijayaraghavan, R.

2010-01-01

258

Chemical Educators Ponder Innovations  

ERIC Educational Resources Information Center

Discusses topics presented at the Fourth Biennial Conference on Chemical Education, which included curriculum and course design, pedagogical methodology, computers, instructional aids, the environment and the history of chemistry. (MLH)

Worthy, Ward

1976-01-01

259

Chemical burn or reaction  

MedlinePLUS

... the skin has come in contact with the toxic substance Rash , blisters , burns on the skin Unconsciousness ... locked cabinet. Avoid mixing different products that contain toxic chemicals such as ammonia and bleach. The mixture ...

260

Chemical Emergencies Overview  

MedlinePLUS

... Metals Nerve Agents Pulmonary Agents Riot Control Agents Toxic Alcohols Vesicants Chemical-Specific Fact Sheets Toxicology FAQs Case Definitions Toxic Syndrome Descriptions Toxicological Profiles Training First Responders Medical ...

261

Chemical Principles Exemplified  

ERIC Educational Resources Information Center

Collection of two short descriptions of chemical principles seen in life situations: the autocatalytic reaction seen in the bombardier beetle, and molecular potential energy used for quick roasting of beef. Brief reference is also made to methanol lighters. (PS)

Plumb, Robert C.

1972-01-01

262

STP Chemical Demon Program  

NSDL National Science Digital Library

The STP ChemicalDemon program displays a histogram of the energy of a demon that exchanges energy and particles with a one-dimensional lattice of particles. The purpose of this simulation is to understand how the demon acts as an ideal thermometer and ideal measurement of the chemical potential. The default system is a lattice of length L = 100 with N = 100 particles, an energy E = 200 and non interacting particles. STP ChemicalDemon is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double-clicking the stp_ChemicalDemon.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2009-03-06

263

Advanced Chemical Propulsion  

NASA Technical Reports Server (NTRS)

Design, propellant selection, and launch assistance for advanced chemical propulsion system is discussed. Topics discussed include: rocket design, advance fuel and high energy density materials, launch assist, and criteria for fuel selection.

Bai, S. Don

2000-01-01

264

Safer Science: Chemical Storage  

NSDL National Science Digital Library

Using chemicals safely requires a number of things, including current inventory control, appropriate labeling and storage segregation, ongoing inspections, and more. How can a science teacher find the appropriate storage information? Read on. This month's

Roy, Ken

2009-10-01

265

Crop Protection Chemical Safety  

MedlinePLUS

... use of the chemical; its proper handling, safe storage and first aid information. • Obtain Material Safety Data ... sure to keep a set separate from the storage area. • Have on hand and wear the personal ...

266

The Chemical Batch Reactor  

Microsoft Academic Search

\\u000a This chapter faces the description of the main object of the book, namely, the chemical batch reactor. First, the batch reactor\\u000a is compared to the continuous reactors in the light of ideal physical models, the main ideas of chemical kinetics are reviewed,\\u000a and the relevant modeling of the isothermal batch reactor is developed. Then, the heat balance introduces elements of

Fabrizio Caccavale; Mario Iamarino; Francesco Pierri; Vincenzo Tufano

267

Chemical Communication in Lobsters  

Microsoft Academic Search

\\u000a Lobsters are fascinating animals that use chemicals as messages regarding their sexual status, their standing in a social\\u000a hierarchy, and whether they affiliate with or avoid conspecifics. This, plus their economic importance, makes them important\\u000a models for the study of intraspecific chemical communication. Our chapter is an overview of these processes, including the\\u000a types of interactions between lobsters influenced by

Juan Aggio; Charles D. Derby

268

Quality of Chemical Measurements  

NSDL National Science Digital Library

The International Union of Pure and Applied Chemistry's online newsletter, Chemistry International, posts this article about the problem of wide variation in chemical trace and catalyst measurements. This is important because such data are increasingly used in industry decision-making. In the words of the authors, "This article provides 'snapshot' pictures of chemical measurement (un)reliability, with many practical, societal implications." All text is in HTML.

1997-01-01

269

Chemical and Biological Disarmament  

NSDL National Science Digital Library

This online directory from the University of Michigan Documents Center provides annotated links to materials related to chemical and biological warfare and disarmament. Included here are resources for background information, related international organizations, and subject-specific sites on chemical and biological warfare, Iraq, peace and conflict studies, as well as pertinent treaties and organizations. The site was created by librarian Susan Wright at the University of Michigan Residential College.

270

Quality of Chemical Measurements  

NSDL National Science Digital Library

The International Union of Pure and Applied Chemistry's online newsletter, Chemistry International, posts this article about the problem of wide variation in chemical trace and catalyst measurements. This is important because such data are increasingly used in industry decision-making. In the words of the authors, "This article provides 'snapshot' pictures of chemical measurement (un)reliability, with many practical, societal implications." All text is in HTML.

2005-11-01

271

Sonifying Chemical Evolution  

Microsoft Academic Search

This presentation-demonstration discusses the creation of FIRST LIFE, a75-minute mixed media performance for string quartet, live audio processing,live motion capture video, and audience participation utilizing stochasticmodels of chemical data provided by Martha Grover's Research Group at theSchool of Chemical and Biomolecular Engineering at Georgia Institute ofTechnology. Each section of this work is constructed from contingent outcomesdrawn from biochemical research exploring

Steve Everett

2013-01-01

272

Chemical flame heights  

Microsoft Academic Search

A “chemical” flame height has been defined from the ratio of CO to CO2 yields, yCO\\/yCO2, and has been shown to be functionally identical with previous results based on flame luminosity. The chemical flame heights have been determined for propane and acetylene data for fire Froude numbers, Q*, ranging from 0.1 to 60,000. The functional dependence of Zf\\/D on Q*

Jeffrey S Newman; Christopher J Wieczorek

2004-01-01

273

Chemical shifts in biomolecules  

PubMed Central

Summary NMR chemical shifts are sensitive probes of stucture and dynamics in proteins. Empirical models, based on a large database of measured shifts, take an input structure and provide increasingly accurate estimates of the corresponding shifts. Quantum chemical calculations can provide the same information, with greater generality but (currently) with less accuracy. These methods are now providing new ways to approach NMR structure determination, and new insights into the conformational dynamics of proteins. PMID:23422068

Case, David A.

2013-01-01

274

Computational Systems Chemical Biology  

PubMed Central

There is a critical need for improving the level of chemistry awareness in systems biology. The data and information related to modulation of genes and proteins by small molecules continue to accumulate at the same time as simulation tools in systems biology and whole body physiologically-based pharmacokinetics (PBPK) continue to evolve. We called this emerging area at the interface between chemical biology and systems biology systems chemical biology, SCB (Oprea et al., 2007). The overarching goal of computational SCB is to develop tools for integrated chemical-biological data acquisition, filtering and processing, by taking into account relevant information related to interactions between proteins and small molecules, possible metabolic transformations of small molecules, as well as associated information related to genes, networks, small molecules and, where applicable, mutants and variants of those proteins. There is yet an unmet need to develop an integrated in silico pharmacology / systems biology continuum that embeds drug-target-clinical outcome (DTCO) triplets, a capability that is vital to the future of chemical biology, pharmacology and systems biology. Through the development of the SCB approach, scientists will be able to start addressing, in an integrated simulation environment, questions that make the best use of our ever-growing chemical and biological data repositories at the system-wide level. This chapter reviews some of the major research concepts and describes key components that constitute the emerging area of computational systems chemical biology. PMID:20838980

Oprea, Tudor I.; May, Elebeoba E.; Leitão, Andrei; Tropsha, Alexander

2013-01-01

275

Environmental/chemical thesaurus  

SciTech Connect

The Environmental/Chemical Thesaurus approaches scientific language control problems from a multidisciplinary view. The Environmental/Biomedical Terminology Index (EBTI) was used as a base for the present thesaurus. The Environmental/Chemical Thesaurus, funded by the Environmental Protection Agency, used as its source of new terms those major terms found in 13 Environmental Protection Agency data bases. The scope of this thesaurus includes not only environmental and biomedical sciences, but also the physical sciences with emphasis placed on chemistry. Specific chemical compounds are not included; only classes of chemicals are given. To adhere to this level of classification, drugs and pesticides are identified by class rather than by specific chemical name. An attempt was also made to expand the areas of sociology and economics. Terminology dealing with law, demography, and geography was expanded. Proper names of languages and races were excluded. Geographic terms were expanded to include proper names for oceans, continents, major lakes, rivers, and islands. Political divisions were added to allow for proper names of countries and states. With such a broad scope, terminology for specific sciences does not provide for indexing to the lowest levels in plant, animal, or chemical classifications.

Shriner, C.R.; Dailey, N.S.; Jordan, A.C.; Miller, K.C.; Owens, E.T.; Rickert, L.W.

1978-06-01

276

Chemical information systems  

SciTech Connect

The growing number of Federal and State regulations today from EPA to OSHA is putting a large burden on organizations to comply with regard to chemicals in the work place. The cornerstone of chemical information is the Material Safety Data Sheet (MSDS). The MSDS has been a requirement for chemical manufacturers for over fifteen years. Manufacturers of hazardous materials must provide MSDSs to purchasers. However, recent additional regulations from OSHA, in particular the Right To Know and the Hazard Communication Standard (Haz-Com) require that employers who use chemicals must be capable of providing an MSDS to every employee that requests one for a material that they work with. Paper filing systems to managing MSDSs are hard to maintain, costly, and inefficient. In multifacility organizations this can result in delays in distributions of those MSDSs to employees. At AT and T Bell Laboratories the Environmental Health and Safety Center has invested over a decade of development work into producing an integrated Chemical Inventory System/MSDS System. That system meets the requirements discussed in this paper and serves six major R and D laboratory facilities in three states. The system resides on a desktop personal computer. Operation of the system relies on teamwork between several diverse organizations which are involved in management of chemical safety at AT and T Bell Laboratories. The departments represented on that team are Industrial Hygiene and Safety, Environmental Management, Facilities Operations, Purchasing, Health Services, Research, and Environmental Data Management Services.

Zebora, M. [AT and T Bell Labs., Murray Hill, NJ (United States). Environmental Health and Safety Center

1994-12-31

277

Protein Chemical Shift Prediction  

E-print Network

The protein chemical shifts holds a large amount of information about the 3-dimensional structure of the protein. A number of chemical shift predictors based on the relationship between structures resolved with X-ray crystallography and the corresponding experimental chemical shifts have been developed. These empirical predictors are very accurate on X-ray structures but tends to be insensitive to small structural changes. To overcome this limitation it has been suggested to make chemical shift predictors based on quantum mechanical(QM) calculations. In this thesis the development of the QM derived chemical shift predictor Procs14 is presented. Procs14 is based on 2.35 million density functional theory(DFT) calculations on tripeptides and contains corrections for hydrogen bonding, ring current and the effect of the previous and following residue. Procs14 is capable at performing predictions for the 13CA, 13CB, 13CO, 15NH, 1HN and 1HA backbone atoms. In order to benchmark Procs14, a number of QM NMR calculatio...

Larsen, Anders S

2014-01-01

278

The chemical wars.  

PubMed

The culture of economic growth and rapid innovation has led the chemical industry to contaminate tens of thousands of locales with hazardous chemicals that are poorly understood. As a result, the chemical industry finds itself at war with citizens who are troubled by the widespread dissemination of industrial poisons and alarmed by the power and unaccountability of the corporations themselves. The current chemical regulatory system has not provided an effective or reassuring restraint on chemical contamination because it relies heavily on a technique called risk assessment instead of the newer approach being tried now in Europe and elsewhere, the precautionary principle. Here's a riddle to keep you up at night: How come, at a time when the environmental movement is stronger and richer than ever, our most pressing ecological problems just get worse? It's as though the planet has hit a Humpty-Dumpty moment in which unprecedented amounts of manpower and money are unable to put the world back together again. PMID:17208883

Montague, Peter

2004-01-01

279

Porphyria and chemicals.  

PubMed

Porphyria is a genetic family of diseases that is most frequently described as neuropsychiatric or toxogenetic. It is well known to be initiated by drugs, infections, heavy metals, hormones, chemicals and fasting. There are extensive lists of drugs that have been known to cause attacks. Others are thought to be likely to cause attacks on the basis of animal studies or in vitro studies. It has become obvious that lists of chemicals capable of causing illness in porphyrics are sorely lacking. Chemicals that have the same base as drugs that are labeled in the PDR (Physicians Desk Reference) as porphyrogenic have no such labeling in their MSDS (Material Safety Data Sheet). This article is intended to point out why porphyria needs to be considered when illness occurs after chemical exposure. The capability of testing enzymes in the porphyrin pathway allows us to evaluate these patients more thoroughly, for we are now aware that the standard measures for recognizing these diseases are often inadequate. Three examples where illness has occurred after environmental exposure to chemicals will serve as illustrations. One, a documented porphyria, is the Turkish porphyria. The other two are not yet documented as porphyria, but may be some day. One is Agent Orange which caused illness in Vietnam, and the other is exposure to unknown sources of what has been named the Gulf War syndrome. PMID:10532713

Downey, D C

1999-08-01

280

Appendix G. Chemicals Appendix G. Chemicals G-3  

E-print Network

), not a comprehensive discussion of chemicals and their effects on the environment and biological systems. G.1 in apple seeds. However, exposures to many more hazardous chemicals result from the direct or indirect exposure to the public. G.3 Definitions G.3.1 Toxicity Chemicals have varying types of effects. Chemical

Pennycook, Steve

281

Appendix G. Chemicals Appendix G. Chemicals G-3  

E-print Network

), not a comprehensive discussion of chemicals and their effects on the environment and biological systems. G.1 in apple seeds. However, exposures to many more hazardous chemicals result from the direct or indirect to the public. G.3 Definitions G.3.1 Toxicity Chemicals have varying types of effects. Chemical health effects

Pennycook, Steve

282

Appendix G: Chemicals Appendix G: Chemicals G-3  

E-print Network

), not a comprehensive discussion of chemicals and their effects on the environment and biological systems. PERSPECTIVE in apple seeds. However, exposures to many more hazardous chemicals result fromthe direct or indirect exposure to the public. DEFINITIONS Toxicity Chemicals have varying types of effects. Chemical health

Pennycook, Steve

283

Chemical inhomogeneities and pulsation  

E-print Network

Major improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and lambda Bootis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.

S. Turcotte

2001-11-08

284

The renewable chemicals industry.  

PubMed

The possibilities for establishing a renewable chemicals industry featuring renewable resources as the dominant feedstock rather than fossil resources are discussed in this Concept. Such use of biomass can potentially be interesting from both an economical and ecological perspective. Simple and educational tools are introduced to allow initial estimates of which chemical processes could be viable. Specifically, fossil and renewables value chains are used to indicate where renewable feedstocks can be optimally valorized. Additionally, C factors are introduced that specify the amount of CO2 produced per kilogram of desired product to illustrate in which processes the use of renewable resources lead to the most substantial reduction of CO2 emissions. The steps towards a renewable chemicals industry will most likely involve intimate integration of biocatalytic and conventional catalytic processes to arrive at cost-competitive and environmentally friendly processes. PMID:18605090

Christensen, Claus Hviid; Rass-Hansen, Jeppe; Marsden, Charlotte C; Taarning, Esben; Egeblad, Kresten

2008-01-01

285

Chemical spill exposure assessment  

SciTech Connect

POSSM, the PCB On-Site Spill Model, is a contaminant transport model developed to predict environmental concentrations associated with a chemical spill. The model predicts daily changes in chemical concentrations on a spill site (e.g., in soil and on vegetation) and losses of chemical due to volatilization, surface runoff/soil erosion, and leaching to groundwater. Spill areas consisting of soil/vegetation and/or an impervious surface (e.g., asphalt and concrete) can be analyzed, as can different spill cleanup practices. POSSM is used to analyze exposure levels associated with a hypothetical capacitor spill. While the model was developed for PCB spills, it is generally applicable to a number of organic compounds.

Brown, S.M.; Silvers, A.

1986-09-01

286

Chemical spill exposure assessment.  

PubMed

POSSM, the PCB On-Site Spill Model, is a contaminant transport model developed to predict environmental concentrations associated with a chemical spill. The model predicts daily changes in chemical concentrations on a spill site (e.g., in soil and on vegetation) and losses of chemical due to volatilization, surface runoff/soil erosion, and leaching to groundwater. Spill areas consisting of soil/vegetation and/or an impervious surface (e.g., asphalt and concrete) can be analyzed, as can different spill cleanup practices. POSSM is used to analyze exposure levels associated with a hypothetical capacitor spill. While the model was developed for PCB spills, it is generally applicable to a number of organic compounds. PMID:3110872

Brown, S M; Silvers, A

1986-09-01

287

Advanced Chemical Propulsion Study  

NASA Technical Reports Server (NTRS)

A study was performed of advanced chemical propulsion technology application to space science (Code S) missions. The purpose was to begin the process of selecting chemical propulsion technology advancement activities that would provide greatest benefits to Code S missions. Several missions were selected from Code S planning data, and a range of advanced chemical propulsion options was analyzed to assess capabilities and benefits re these missions. Selected beneficial applications were found for higher-performing bipropellants, gelled propellants, and cryogenic propellants. Technology advancement recommendations included cryocoolers and small turbopump engines for cryogenic propellants; space storable propellants such as LOX-hydrazine; and advanced monopropellants. It was noted that fluorine-bearing oxidizers offer performance gains over more benign oxidizers. Potential benefits were observed for gelled propellants that could be allowed to freeze, then thawed for use.

Woodcock, Gordon; Byers, Dave; Alexander, Leslie A.; Krebsbach, Al

2004-01-01

288

National Historic Chemical Landmarks  

NSDL National Science Digital Library

The American Chemical Society (ACS) displays the key roles chemists played in "expanding the frontiers of knowledge, advancing medicine and industry, and creating products from aspirin to zippers" at this website. Users can find clear summaries and images of the places, discoveries, and achievements that have been designated landmarks by ACS members and an international committee. Within many of the biographies, educators can find links to teaching guides and activities. Individuals that know of an unrecognized important element of the chemical heritage can learn how to nominate the site, artifact, or collection.

2007-05-18

289

Laboratory Safety and Chemical Hazards.  

ERIC Educational Resources Information Center

Toxicology/chemical hazards, safety policy, legal responsibilities, adequacy of ventilation, chemical storage, evaluating experimental hazards, waste disposal, and laws governing chemical safety were among topics discussed in 10 papers presented at the Seventh Biennial Conference on Chemical Education (Stillwater, Oklahoma 1982). Several topics…

Journal of Chemical Education, 1983

1983-01-01

290

Chemical carcinogenesis: nature's metabolic mistake  

Microsoft Academic Search

The normal biochemical defense against toxic chemicals, such as polyaromatic hydrocarbons, is to attach functional groups, such as hydroxyl, glucuronic acid, glutathione, etc. that tend to make the chemicals more water-soluble and readily excretable as harmless derivatives. However, chemical carcinogens form highly reactive intermediates on the path to final detoxification. These chemically unstable compounds, once formed, can readily attack cellular

James K. Selkirk; Michael C. MacLeod

1982-01-01

291

Chemical power sources  

Microsoft Academic Search

The working principles of chemical power sources are considered along with cell types, aspects of cell performance, the electrochemical aspects of cell operation, the porous systems used for real electrodes, questions of design and technology, operational problems, and applications of cells. Various cell systems are discussed, taking into account manganese-zinc cells with salt solution electrolyte, lead acid storage cells, nickel-cadmium

V. S. Bagotskii; A. M. Skundin

1980-01-01

292

Prioritizing Industrial Chemical Hazards  

Microsoft Academic Search

This article describes the approach used to develop a prioritized list of toxic and hazardous industrial chemical hazards considered to pose substantial risk to deployed troops and military operations. The U.S. Army Center for Health Promotion and Preventive Medicine published the prioritized list in November 2003. The work was performed as part of a multinational military effort supported by Canada,

Veronique D. Hauschild; Gary M. Bratt

2005-01-01

293

NETL - Chemical Looping Reactor  

SciTech Connect

NETL's Chemical Looping Reactor unit is a high-temperature integrated CLC process with extensive instrumentation to improve computational simulations. A non-reacting test unit is also used to study solids flow at ambient temperature. The CLR unit circulates approximately 1,000 pounds per hour at temperatures around 1,800 degrees Fahrenheit.

None

2013-07-24

294

Endocrine disrupting chemicals  

PubMed Central

In the past 200 years, an enormous number of synthetic chemicals with diverse structural features have been produced for industrial, medical and domestic purposes. These chemicals, originally thought to have little or no biological toxicity, are widely used in our daily lives as well as are commonly present in foods. It was not until the first World Wildlife Federation Wingspread Conference held in 1994 were concerns about the endocrine disrupting (ED) effects of these chemicals articulated. The potential hazardous effects of endocrine disrupting chemicals (EDCs) on human health and ecological well-being are one of the global concerns that affect the health and propagation of human beings. Considerable numbers of studies indicated that endocrine disruption is linked to “the developmental basis of adult disease,” highlighting the significant effects of EDC exposure on a developing organism, leading to the propensity of an individual to develop a disease or dysfunction in later life. In this review, we intend to provide environmental, epidemiological and experimental data to associate pollutant exposure with reproductive disorders, in particular on the development and function of the male reproductive system. Possible effects of pollutant exposure on the processes of embryonic development, like sex determination and masculinization are described. In addition, the effects of pollutant exposure on hypothalamus-pituitary-gonadal axis, testicular signaling, steroidogenesis and spermatogenesis are also discussed. PMID:22319671

Yeung, Bonnie HY; Wan, Hin T; Law, Alice YS

2011-01-01

295

Chemical process simulation  

SciTech Connect

This book offers a guide to simulation techniques for chemical engineering. It covers flowsheeting, partitioning and tearing a set of equations and networks of process units, maintaining sparsity of matrices, convergence promotion methods, and available data banks of properties. The book reviews background information on model formulation and numerical methods, and applications of graph theory in synthesising networks.

Husain, A.

1986-01-01

296

Green Chemical Processing with  

E-print Network

(biologics) · Commodity chemicals production ­ 1,3 propanediol, lysine, succinic acid, more · Specialty Anaplerotic reactions TCA cycle Biosynthesis of serine family amino acids Biosynthesis of alanine family amino acids Biosynthesis of histidine Biosynthesis of aromatic family amino acids ... Catabolism of amino

Su, Xiao

297

Risks and Chemical Substances.  

ERIC Educational Resources Information Center

Examines exposure to chemicals within the home and three important ways in which hazardous substances can be identified and evaluated. Suggests a rational picture of human health risks and contains an introductory discussion of reasons for exposure, epidemiology, cancer causes and patterns, animal testing, toxins, and risk. (LZ)

Blumberg, Avrom A.

1994-01-01

298

CHAPTER XVII CHEMICAL COMPOSITION  

E-print Network

L___________________________________________ 382 Inorganic constltuents____________ __ __ ___ _ __ __ _ 383 Iodine the tissues and organs, exclusive of skeleton or shells, consists of three major groups of organic eompounds is blown through it to remove grit, pieces of broken shell, and mud. The pro- cedure affects the chemical

299

Evolution was Chemically Constrained  

Microsoft Academic Search

The objective of this paper is to present a systems view of the major features of biological evolution based upon changes in internal chemistry and uses of cellular space, both of which it will be stated were dependent on the changing chemical environment. The account concerns the major developments from prokaryotes to eukaryotes, to multi-cellular organisms, to animals with nervous

R. J. P. WILLIAMS; J. J. R. FRAÚSTO DA SILVA

2003-01-01

300

Chemical Principles Exemplified  

ERIC Educational Resources Information Center

This is the first of a new series of brief ancedotes about materials and phenomena which exemplify chemical principles. Examples include (1) the sea-lab experiment illustrating principles of the kinetic theory of gases, (2) snow-making machines illustrating principles of thermodynamics in gas expansions and phase changes, and (3) sunglasses that…

Plumb, Robert C.

1970-01-01

301

Computational Chemical Materials Engineering  

E-print Network

: Thermal barrier coatings, wear resistance coatings, radiation resistant materials · Materials for optical with usable ­ Chemical ­ Electronic ­ Optical ­ Magnetic ­ Transport, thermal and mechanical properties storage, conversion, transport: Catalysts, Thermoelectrics, polymer/solid oxide membranes · Coatings

302

Chemical reacting flows  

NASA Technical Reports Server (NTRS)

Future aerospace propulsion concepts involve the combination of liquid or gaseous fuels in a highly turbulent internal air stream. Accurate predictive computer codes which can simulate the fluid mechanics, chemistry, and turbulence combustion interaction of these chemical reacting flows will be a new tool that is needed in the design of these future propulsion concepts. Experimental and code development research is being performed at Lewis to better understand chemical reacting flows with the long term goal of establishing these reliable computer codes. The approach to understanding chemical reacting flows is to look at separate simple parts of this complex phenomena as well as to study the full turbulent reacting flow process. As a result research on the fluid mechanics associated with chemical reacting flows was initiated. The chemistry of fuel-air combustion is also being studied. Finally, the phenomena of turbulence-combustion interaction is being investigated. This presentation will highlight research, both experimental and analytical, in each of these three major areas.

Mularz, Edward J.; Sockol, Peter M.

1987-01-01

303

Chemical modification of biocatalysts  

Microsoft Academic Search

Although several powerful methods exist for the redesign of enzyme structure and function these are typically limited to the 20 most abundant proteinogenic amino acids. The use of chemical modification overcomes this limitation to allow virtually unlimited alteration of amino acid sidechain structures. If heterogeneous mixtures of enzyme products are to be avoided, however, the required chemistry should be efficient,

Benjamin G Davis

2003-01-01

304

Advanced Chemical Propulsion  

NASA Technical Reports Server (NTRS)

Advanced Chemical Propulsion (ACP) provides near-term incremental improvements in propulsion system performance and/or cost. It is an evolutionary approach to technology development that produces useful products along the way to meet increasingly more demanding mission requirements while focusing on improving payload mass fraction to yield greater science capability. Current activities are focused on two areas: chemical propulsion component, subsystem, and manufacturing technologies that offer measurable system level benefits; and the evaluation of high-energy storable propellants with enhanced performance for in-space application. To prioritize candidate propulsion technology alternatives, a variety of propulsion/mission analyses and trades have been conducted for SMD missions to yield sufficient data for investment planning. They include: the Advanced Chemical Propulsion Assessment; an Advanced Chemical Propulsion System Model; a LOx-LH2 small pumps conceptual design; a space storables propellant study; a spacecraft cryogenic propulsion study; an advanced pressurization and mixture ratio control study; and a pump-fed vs. pressure-fed study.

Alexander, Leslie, Jr.

2006-01-01

305

NETL - Chemical Looping Reactor  

ScienceCinema

NETL's Chemical Looping Reactor unit is a high-temperature integrated CLC process with extensive instrumentation to improve computational simulations. A non-reacting test unit is also used to study solids flow at ambient temperature. The CLR unit circulates approximately 1,000 pounds per hour at temperatures around 1,800 degrees Fahrenheit.

None

2014-06-26

306

Chemical Aspects of Dentistry.  

ERIC Educational Resources Information Center

Dental caries (tooth decay) and periodontal (gum) disease are treated/prevented by procedures utilizing chemical expertise. Procedures and suggestions on how they might be incorporated into the high school chemistry curriculum are described. Specific topics discussed include dental caries, fluoride, diet, tooth decay prevention, silver amalgan,…

Helfman, Murry

1982-01-01

307

Categorizing Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the second of four Science Objects in the Chemical Reactions SciPack. It provides an

National Science Teachers Association (NSTA)

2009-07-10

308

Rates of Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the third of four Science Objects in the Chemical Reactions SciPack. It demonstrates

National Science Teachers Association (NSTA)

1900-01-01

309

Making a Chemical Rainbow  

ERIC Educational Resources Information Center

In this laboratory experiment, high school students are challenged to prepare a six-layered chemical "rainbow" in a test tube. Students start with six unknown, colorless liquids and six pigments ranging from violet to red. The experiment is problem based and forces the students to apply their knowledge of solubility and density and combine it with…

Angelin, Marcus; Ramstrom, Olof

2010-01-01

310

Great Lakes: chemical monitoring  

Microsoft Academic Search

The article discusses a symposium sponsored by the 10th Great Lakes Regional Meeting of the American Chemical Society (ACS) that addressed various aspects of the theme ''Chemistry of the Great Lakes''. The symposium attempted to gather together environmental information produced by chemists, and included: watershed studies, involving investigation of the sources, transport, and fate of sterols in the Menomonee River;

Joseph J. Delfino

1976-01-01

311

Proton Chemical Shifts  

NSDL National Science Digital Library

Created by Hans Reich, professor of organic chemistry at the Uiversity of Wisconsin-Madison, this site contains a compilation of proton chemical shifts and coupling constants. This is an excellent resource for providing students familiarity with Nuclear Magnetic Resonance (NMR) Spectroscopy Data.

Reich, Hans J.

2007-11-16

312

Global chemical pollution  

SciTech Connect

Over the past decade, public and governmental awareness of environmental problems has grown steadily, with an accompanying increase in the regulation of point sources of pollution. As a result, great strides have been made in cleaning polluted rivers and decreasing air pollution near factories. However, traditional regulatory approaches to environmental pollution have focused primarily on protecting the maximally exposed individual located in the immediate vicinity of the pollution source. Little attention has been given to the global implications of human production and use of synthetic chemicals. A consensus is emerging that even trace levels of environmental contamination can have potentially devastating environmental consequences. The authors maintain that ambient levels of pollution have risen to the point where human health is being affected on a global scale. Atmospheric transport is recognized as the primary mode of global distribution and entry into the food chain for organic chemicals. The following are examples of global chemical pollutants that result in human exposure of significant proportions: PCBs, dioxins, benzene, mercury and lead. Current regulatory approaches for environmental pollution do not incorporate ways of dealing with global pollution. Instead the major focus has been on protecting the maximally exposed individual. If we do not want to change our standard of living, the only way to reduce global chemical pollution is to make production and consumption processes more efficient and to lower the levels of production of these toxic chemicals. Thus the only reasonable solution to global pollution is not increased regulation of isolated point sources, but rather an increased emphasis on waste reduction and materials recycling. Until we focus on these issues, we will continue to experience background cancer risk in the 10{sup {minus}3} range.

Travis, C.C.; Hester, S.T. (Oak Ridge National Lab., TN (United States))

1991-05-01

313

Chemical Debridement of Burns  

PubMed Central

The development of effective, non-toxic (local and systemic) methods for the rapid chemical (enzymatic and non-enzymatic) debridement of third degree burns would dramatically reduce the morbidity and mortality of severely burned patients. Sepsis is still the major cause of death of patients with extensive deep burns. The removal of the devitalized tissue, without damage to unburned skin or skin only partially injured by burning, and in ways which would permit immediate (or very prompt) skin grafting, would lessen substantially the problems of sepsis, speed convalescence and the return of these individuals to society as effective human beings, and would decrease deaths. The usefulness and limitations of surgical excision for patients with extensive third degree burns are discussed. Chemical debridement lends itself to complementary use with surgical excision and has the potential advantage over surgical excision in not requiring anesthesia or a formal surgical operation. The authors' work with the chemical debridement of burns, in particular the use of Bromelain, indicates that this approach will likely achieve clinical usefulness. The experimental studies indicate that rapid controlled debridement, with minimal local and systemic toxicity, is possible, and that effective chemotherapeutic agents may be combined with the Bromelain without either interfering with the actions of the other. The authors believe that rapid (hours) debridement accomplished by the combined use of chemical debriding and chemotherapeutic agents will obviate the possibility of any increase in infection, caused by the use of chemical agents for debridement, as reported for Paraenzyme21 and Travase.39,48 It is possible that the short term use of systemic antibiotics begun just before and continued during, and for a short time after, the rapid chemical debridement may prove useful for the prevention of infection, as appears to be the case for abdominal operations of the clean-contaminated and contaminated types. ImagesFigs. 1a-c.Fig. 1b.Fig. 1c.Fig. 2.Fig. 3.Fig. 4.Fig. 5.Fig. 6.Fig. 7.Fig. 8.Fig. 9a.Fig. 9B.Fig. 10.Fig. 11.Figs. 12a-c.Fig. 12b.Fig. 12c.Figs. 14a-c.Fig. 14b.Fig. 14c.Figs. 15a-c.Fig. 15b.Fig. 15c. PMID:4606330

Levenson, Stanley M.; Kan, Dorinne; Gruber, Charles; Crowley, Leo V.; Lent, Richard; Watford, Alvin; Seifter, Eli

1974-01-01

314

Planetary nebulae as observational constraints in chemical evolution models for NGC 6822  

NASA Astrophysics Data System (ADS)

Aims: Chemical evolution models are useful for understanding the formation and evolution of stars and galaxies. Model predictions will be more robust when more observational constraints are used. We present chemical evolution models for the dwarf irregular galaxy NGC 6822 using chemical abundances of old and young planetary nebulae (PNe) and H ii regions as observational constraints. We use two sets of chemical abundances, one derived from collisionally excited lines (CELs) and one from recombination lines (RLs). We use our models as a tool to distinguish between both procedures for abundance determinations. Methods: In our chemical evolution code the chemical contribution of low and intermediate mass stars is time-delayed, while for the massive stars the chemical contribution follows the instantaneous recycling approximation. Our models have two main free parameters: the mass-loss rate of a well-mixed outflow and the upper mass limit, Mup, of the initial mass function (IMF). To reproduce the gaseous mass and the present-day O/H value we need to vary the outflow rate and the Mup value. Results: We calculate two models with different Mup values that reproduce the constraints adequately. The abundances of old PNe agree with our models and support the star-formation history derived independently from photometric data. Both require an early well-mixed wind, lasting 5.3 Gyr, to reproduce the observed gaseous mass in the galaxy. In addition, by assuming a fraction of binaries producing SNIa of 1%, the models fit the Fe/H abundance ratio as derived from A supergiants. The first model (M4C), which assumes Mup = 40 M?, fits within errors smaller than 2? the O/H, Ne/H, S/H, Ar/H and Cl/H abundances obtained from CELs for old and young PNe and H ii regions. The second model (M1R), which adopts Mup = 80 M?, reproduces within 2? errors the O/H, C/H, Ne/H and S/H abundances adopted from RLs. Both models reproduce the increase of the O, Ne, S, and Ar elements during the last 6 Gyr. We are not able to match the observed N/O ratios in either case, which suggests that the N yields of LIMS need to be improved. Model M1R does not provide a good fit to the Cl/H and Ar/H ratios, because the SN yields of those elements for m > 40 M? are not adequate and need to be improved (two sets of yields were tried). From these results we are unable to conclude which set of abundances (the one from CELs or the one from RLS) represents the real abundances in the ISM better. We discuss the predicted ?Y/?O values, finding that the value from model M1R agrees better with data for other galaxies from the literature than the value from model M4C.

Hernández-Martínez, L.; Carigi, L.; Peña, M.; Peimbert, M.

2011-11-01

315

Interactive chemical reactivity exploration.  

PubMed

Elucidating chemical reactivity in complex molecular assemblies of a few hundred atoms is, despite the remarkable progress in quantum chemistry, still a major challenge. Black-box search methods to find intermediates and transition-state structures might fail in such situations because of the high-dimensionality of the potential energy surface. Here, we propose the concept of interactive chemical reactivity exploration to effectively introduce the chemist's intuition into the search process. We employ a haptic pointer device with force feedback to allow the operator the direct manipulation of structures in three dimensions along with simultaneous perception of the quantum mechanical response upon structure modification as forces. We elaborate on the details of how such an interactive exploration should proceed and which technical difficulties need to be overcome. All reactivity-exploration concepts developed for this purpose have been implemented in the samson programming environment. PMID:25205397

Haag, Moritz P; Vaucher, Alain C; Bosson, Maël; Redon, Stéphane; Reiher, Markus

2014-10-20

316

COOEE bitumen: chemical aging  

E-print Network

We study chemical aging in "COOEE bitumen" using molecular dynamic simulations. The model bitumen is composed of four realistic molecule types: saturated hydrocarbon, resinous oil, resin, and asphaltene. The aging reaction is modelled by the chemical reaction: "2 resins $\\rightarrow$ 1 asphaltene". Molecular dynamic simulations of four bitumen compositions, obtained by a repeated application of the aging reaction, are performed. The stress autocorrelation function, the fluid structure, the rotational dynamics of the plane aromatic molecules, and the diffusivity of each molecule, are determined for the four different compositions. The aging reaction causes a significant dynamics slowdown, which is correlated to the aggregation of asphaltene molecules in larger and dynamically slower nanoaggregates. Finally, a detailed description of the role of each molecule types in the aggregation and aging processes is given.

Lemarchand, Claire A; Dyre, Jeppe C; Hansen, Jesper S

2013-01-01

317

Chemical Engineering in Space  

NASA Technical Reports Server (NTRS)

The aerospace industry has long been perceived as the domain of both physicists and mechanical engineers. This perception has endured even though the primary method of providing the thrust necessary to launch a rocket into space is chemical in nature. The chemical engineering and chemistry personnel behind the systems that provide access to space have labored in the shadows of the physicists and mechanical engineers. As exploration into the cosmos moves farther away from Earth, there is a very distinct need for new chemical processes to help provide the means for advanced space exploration. The state of the art in launch systems uses chemical propulsion systems, primarily liquid hydrogen and liquid oxygen, to provide the energy necessary to achieve orbit. As we move away from Earth, there are additional options for propulsion. Unfortunately, few of these options can compare to the speed or ease of use provided by the chemical propulsion agents. It is with great care and significant cost that gaseous compounds such as hydrogen and oxygen are liquefied and become dense enough to use for rocket fuel. These low-temperature liquids fall within a specialty area known as cryogenics. Cryogenics, the science and art of producing cold operating conditions for use on Earth, in orbit, or on some other nonterrestrial body, has become increasingly important to our ability to travel within our solar system. The production of cryogenic fuels and the long-term storage of these fluids are necessary for travel. As our explorations move farther away from Earth, we need to address how to produce the necessary fuels to make a round-trip. The cost and the size of these expeditions are extreme at best. If we take everything necessary for our survival for the round-trip, we invalidate any chance of travel in the near future. As with the early explorers on Earth, we need to harvest much of our energy and our life support from the celestial bodies. The in situ production of these energy sources is paramount to success. We are currently working on several processes to produce the propellants that would allow us to visit and explore the surface of Mars. The capabilities currently at our disposal for launching and delivering equipment to another planet or satellite dictate that the size and scale of any hardware must be extremely small. The miniaturization of the processes needed to prepare the in situ propellants and life support commodities is a real challenge. Chemical engineers are faced with the prospect of reproducing an entire production facility in miniature so the complex can be lifted into space and delivered to our destination. Another area that does not normally concern chemical engineers is the extreme physical aspects payloads are subjected to with the launch of a spacecraft. Extreme accelerations followed by the sudden loss of nearly all gravitational forces are well outside normal equipment design conditions. If the equipment cannot survive the overall trip, then it obviously will not be able to yield the needed products upon arrival. These launch constraints must be taken into account. Finally, we must consider both the effectiveness and efficiencies of the processes. A facility located on the Moon or Mars will not have an unlimited supply of power or other ancillary utilities. For a Mars expedition, the available electric power is severely limited. The design of both the processes and the equipment must be considered. With these constraints in mind, only the most efficient designs will be viable. Cryogenics, in situ resource utilization, miniaturization, launchability, and power/process efficiencies are only a few of the areas that chemical engineers provide support and expertise for the exploration of space.

Lobmeyer, Dennis A.; Meneghelli, Barry; Steinrock, Todd (Technical Monitor)

2001-01-01

318

Cooee bitumen: Chemical aging  

NASA Astrophysics Data System (ADS)

We study chemical aging in ``Cooee bitumen'' using molecular dynamic simulations. This model bitumen is composed of four realistic molecule types: saturated hydrocarbon, resinous oil, resin, and asphaltene. The aging reaction is modelled by the chemical reaction: ``2 resins --> 1 asphaltene.'' Molecular dynamic simulations of four bitumen compositions, obtained by a repeated application of the aging reaction, are performed. The stress autocorrelation function, the fluid structure, the rotational dynamics of the plane aromatic molecules, and the diffusivity of each molecule are determined for the four different compositions. The aging reaction causes a significant dynamics slowdown, which is correlated to the aggregation of asphaltene molecules in larger and dynamically slower nanoaggregates. Finally, a detailed description of the role of each molecule types in the aggregation and aging processes is given.

Lemarchand, Claire A.; Schrøder, Thomas B.; Dyre, Jeppe C.; Hansen, Jesper S.

2013-09-01

319

Chemical Sensing with Nanowires  

NASA Astrophysics Data System (ADS)

Transformational advances in the performance of nanowire-based chemical sensors and biosensors have been achieved over the past two to three years. These advances have arisen from a better understanding of the mechanisms of transduction operating in these devices, innovations in nanowire fabrication, and improved methods for incorporating receptors into or onto nanowires. Nanowire-based biosensors have detected DNA in undiluted physiological saline. For silicon nanowire nucleic acid sensors, higher sensitivities have been obtained by eliminating the passivating oxide layer on the nanowire surface and by substituting uncharged protein nucleic acids for DNA as the capture strands. Biosensors for peptide and protein cancer markers, based on both semiconductor nanowires and nanowires of conductive polymers, have detected these targets at physiologically relevant concentrations in both blood plasma and whole blood. Nanowire chemical sensors have also detected several gases at the parts-per-million level. This review discusses these and other recent advances, concentrating on work published in the past three years.

Penner, Reginald M.

2012-07-01

320

Chemical Education Xchange  

NSDL National Science Digital Library

The JCE Chemical Education Exchange serves as the website of the Journal of Chemical Education. It is committed to providing helpful resources for educators working at two-year colleges. In the Navigation area, visitors can get started with their journey through the site by looking over Activities, Blogs, Picks, and Popular Content. The Activities area features dynamic and interactive activities that deal with writing formulas of ionic compounds, the organization of the periodic table, and a fun one that relates the solubility of gas to the boiling of eggs. The Picks area includes thoughtful meditations on thermodynamic sinks, the use of social media in organic chemistry labs, and how to address climate change in the classroom through small discussion groups.

321

Chemical Modification of Polysaccharides  

PubMed Central

This review covers methods for modifying the structures of polysaccharides. The introduction of hydrophobic, acidic, basic, or other functionality into polysaccharide structures can alter the properties of materials based on these substances. The development of chemical methods to achieve this aim is an ongoing area of research that is expected to become more important as the emphasis on using renewable starting materials and sustainable processes increases in the future. The methods covered in this review include ester and ether formation using saccharide oxygen nucleophiles, including enzymatic reactions and aspects of regioselectivity; the introduction of heteroatomic nucleophiles into polysaccharide chains; the oxidation of polysaccharides, including oxidative glycol cleavage, chemical oxidation of primary alcohols to carboxylic acids, and enzymatic oxidation of primary alcohols to aldehydes; reactions of uronic-acid-based polysaccharides; nucleophilic reactions of the amines of chitosan; and the formation of unsaturated polysaccharide derivatives. PMID:24151557

Cumpstey, Ian

2013-01-01

322

Chemical Process Systems: A Second Course in Chemical Engineering.  

ERIC Educational Resources Information Center

Describes an undergraduate chemical engineering course which was designed at North Carolina State University to introduce the experimental side of chemical process technology. The course lectures, experiments, objectives, evaluation and information sources are also discussed. (HM)

Felder, Richard M.; Marsland, David B.

1979-01-01

323

Chemical Terrorism: US Policies to Reduce the Chemical Terror Threat.  

National Technical Information Service (NTIS)

This study recognizes significant US government progress in detecting and mitigating chemical terror threats, including enhancements in interagency coordination. It finds similarly noteworthy progress in elimination of military chemical stockpiles, though...

M. E. Kosal

2008-01-01

324

Chemical and Biological Engineering Department of Chemical and Biological Engineering  

E-print Network

Issues Particle Processing Pharmaceutical Engineering Polymer Science and Engineering Process Operation Hybrid Systems Biological Engineering Molecular Modeling Diabetes Biomedical and Pharmaceutical EngineeriChemical and Biological Engineering Department of Chemical and Biological Engineering 127 Perlstein

Heller, Barbara

325

Chemical Peeling of Tomatoes.  

E-print Network

desired scalding treatments ac- ,, ,& cording to variety and chemical in terms of percent; 3. peel removed and percent weight lost. 4 , " Both NaOH and CaC12 solutions were more - : effective for peeling tomatoes than the standard% .? water... treatment. More complete peel removal was j.' obtained with equal or less weight loss and the ' fruits generally were firmer and possessed a more% attractive red color. The CaCktreated fruits were_ . particularly firm and attractive after thermal...

Heddins, Gerald C.; Burns, E. E.

1965-01-01

326

Insect Chemical Defense  

Microsoft Academic Search

Research on the defensive chemistry of insects during the last decade is reviewed, with special emphasis on non-volatile compounds. The isolation and structure determination of defensive chemicals, of glandular and non-glandular origins, are first discussed, followed by an overview of the synthesis and biological\\/pharmacological activities of some of them. Biosynthesis has been largely omitted since this topic has been addressed

Pascal Laurent; Jean-Claude Braekman; Désiré Daloze

327

All about Chemical Bonding  

NSDL National Science Digital Library

Stephen Lower, a retired professor at Simon Fraser University, created this expansive and instructive website as a supplement to formal chemistry education for undergraduate students. Visitors will find in-depth descriptions along with several diagrams dealing with chemical bonding issues including their properties, shared-electron covalent bonds, hybrid orbitals, coordination complexes, and metals and semiconductors. General chemistry students looking for assistance should visit this well-developed educational site.

Lower, Stephen

328

Chemical constituents of Asparagus  

PubMed Central

Asparagus species (family Liliaceae) are medicinal plants of temperate Himalayas. They possess a variety of biological properties, such as being antioxidants, immunostimulants, anti-inflammatory, antihepatotoxic, antibacterial, antioxytocic, and reproductive agents. The article briefly reviews the isolated chemical constituents and the biological activities of the plant species. The structural formula of isolated compounds and their distribution in the species studied are also given. PMID:22228964

Negi, J. S.; Singh, P.; Joshi, G. P.; Rawat, M. S.; Bisht, V. K.

2010-01-01

329

Chemical sensor system  

NASA Technical Reports Server (NTRS)

A chemical sensing apparatus and method for the detection of sub parts-per-trillion concentrations of molecules in a sample by optimizing electron utilization in the formation of negative ions is provided. A variety of media may be sampled including air, seawater, dry sediment, or undersea sediment. An electrostatic mirror is used to reduce the kinetic energy of an electron beam to zero or near-zero kinetic energy.

Darrach, Murray R. (Inventor); Chutjian, Ara (Inventor)

2008-01-01

330

Chemical bonding technology  

NASA Technical Reports Server (NTRS)

Primers employed in bonding together the various material interfaces in a photovoltaic module are being developed. The approach develops interfacial adhesion by generating actual chemical bonds between the various materials bonded together. The current status of the program is described along with the progress toward developing two general purpose primers for ethylene vinyl acetate (EVA), one for glass and metals, and another for plastic films.

Plueddemann, E.

1986-01-01

331

LEGO® Chemical Reactions  

NSDL National Science Digital Library

This activity uses LEGO® bricks to represent atoms bonding into molecules and crystals. The lesson plan is for a 2.5 hour workshop (or four 45-minute classes). There is a "wet lab" chemistry experiment (mixing baking soda and calcium chloride with phenol red indicator), followed by a "LEGO lab" modeling phase that includes writing formulas using chemical notation. This lesson is also offered as a 2.5 hour field trip lesson at the MIT Edgerton Center.

Vandiver, Kathleen M.

2009-01-01

332

Micromachined chemical jet dispenser  

SciTech Connect

Goal is to develop a multi-channel micromachined chemical fluid jet dispenser that is applicable to prototype tests with biological samples that demonstrate its utility for molecular biology experiments. Objective is to demonstrate a new device capable of ultrasonically ejecting droplets from 10-200 {mu}m diameter capillaries that are arranged in an array that is linear or focused. The device is based on several common fabrication procedures used in MEMS (micro electro mechanical systems) technology: piezoelectric actuators, silicon, etc.

Swierkowski, S.; Ciarlo, D.

1996-05-13

333

The Chemical Scorecard  

NSDL National Science Digital Library

An information service provided by the Environmental Defense Fund, The Chemical Scorecard allows the general population easy access to the Environmental Protection Agency's (EPA) Toxic Release Inventory (TRI). The TRI is a compilation of all self-reported releases of toxic substances into the environment. Visitors can search for pollution reports via a map interface or by specifying the desired state. Reports are available for states, counties, cities, and companies. Each report includes maps of manufacturing facilities, chemical releases or waste generation for 1995, TRI pollution releases and data summaries. At the end of each report, visitors are provided with ways to voice their concern about toxic releases. In addition to the reports, the Scorecard contains rankings of toxic releases by state, county, zip code, and facility. The rankings are ordered based on a variety of criteria, including carcinogens, different toxicants, and cancer and non-cancer hazards. The Scorecard also provides information on over 5,000 chemicals included in the TRI, their health effects, and a glossary of commonly used terminology.

1998-01-01

334

Chemical Industry Archives  

NSDL National Science Digital Library

In March 2001, PBS aired a disturbing two-hour special hosted by Bill Moyers that explores the history of the chemical revolution of the past 50 years and how companies have long sought to withhold information from the public and their employees about the safety of many substances. The program draws on a large collection of previously secret industry documents unearthed during a ten-year lawsuit by the family of a man who died from a rare brain cancer after working at a vinyl-chloride plant. The family's lawyer eventually charged all vinyl-chloride-producing companies with conspiracy, and the discovery process brought to light hundreds of thousands of pages of documents which reveal a closely planned and well-executed campaign to limit regulation of toxic chemicals and the liability of manufacturers and to withhold important health information from all parties. A large selection of these internal documents, over 37,000 pages, is available at the Chemical Industry Archives, created by the Environmental Working Group. The site offers several essays on the archive and the industry, including a selection of some egregious examples of companies hiding or denying known health risks of their products. The archive itself may be searched by keyword with several modifiers. The documents are presented in .pdf format. This site is sure to become an extremely important resource for health activists, journalists, and the concerned public.

2001-01-01

335

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Thermal decomposition activation energies have been determined using two methods of Thermogravimetric Analysis (TGA), with good correlation being obtained between the two techniques. Initial heating curves indicated a two-component system for Coflon (i.e. polymer plus placticizer) but a single component system for Tefzel. Two widely differing activation energies were for Coflon supported this view, 15 kcl/mol being associated with plasticizer, and 40 kcal/mol with polymer degradation. With Tefzel, values were 40-45 kcal/mol, the former perhaps being associated with a low molecular weight fraction. Appropriate acceleration factors have been determined. Thermomechanical Analysis (TMA) has shown considerable dimensional change during temperature cycles. For unaged pipe sections heating to 100 C and then holding the temperature resulted in a stable thickness increase of 2%, whereas the Coflon thickness decreased continuously, reaching -4% in 2.7 weeks. Previously strained tensile bars of Tefzel expanded on cooling during TMA. SEM performed on H2S-aged Coflon samples showed significant changes in both physical and chemical nature. The first may have resulted from explosive decompression after part of the aging process. Chemically extensive dehydrofluorination was indicated, and sulfur was present as a result of the aging. These observations indicate that chemical attack of PVDF can occur in some circumstances.

Bulluck, J. W.; Rushing, R. A.

1994-01-01

336

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Work has included significant research in several areas aimed at further clarification of the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. Among the areas investigated were the crystallinity changes associated with both the Coflon and Tefzel after various simulated environmental exposures using X-Ray diffraction analysis. We have found that significant changes in polymer crystallinity levels occur as a function of the exposures. These crystallinity changes may have important consequences on the fracture, fatigue, tensile, and chemical resistance of the materials. We have also noted changes in the molecular weight distribution of the Coflon material using a dual detector Gel Permeation Analysis. Again these changes may result in variation in the mechanical and chemical properties in the material. We conducted numerous analytical studies with methods including X-Ray Diffraction, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, and Differential Scanning Calorimetry. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. Pressurized tests were performed in a modified Fluid G, which we will call G2. In this case the ethylene diamine concentration was increased to 3 percent in methanol. Coflon pipe sections and powdered Coflon were exposed in pressure cells at 1700 psi at three separate test temperatures, 70 C, 110 C, and 130 C. The primary purpose of the pressure tests in Fluid G2 was to further elucidate the aging mechanism of PVDF degradation.

Bulluck, J. W.; Rushing, R. A.; Thornton, C. P.

1996-01-01

337

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Work during the past three years has included significant research in several areas aimed at further clarification of the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. Among the areas investigated were the crystallinity changes associated with both the Coflon and Tefzel after various simulated environmental exposures using X-Ray diffraction analysis. We have found that significant changes in polymer crystallinity levels occur as a function of the exposures. These crystallinity changes may have important consequences on the fracture, fatigue, tensile, and chemical resistance of the materials. We have also noted changes in the molecular weight distribution and the increased crosslinking of the Coflon material using Gel Permeation Chromatographic Analysis. Again these changes may result in variations in the mechanical and chemical properties in the material. We conducted numerous analytical studies with methods including X-ray Diffraction, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, and Differential Scanning Calorimetry. We investigated a plethora of aged samples of both Tefzel and Coflon that were forwarded from MERL. Pressurized tests were performed on powdered PVDF in a modified Fluid A, which we will call A-2. In this case the ethylene diamine concentration was increased to 3 percent in methanol. Coflon pipe sections and powdered Coflon were exposed in pressure cells at 1700 psi at three separate test temperatures.

Bulluck, J. W.; Rushing, R. A.

1997-01-01

338

Appendix B: Chemicals Appendix B: Chemicals B-3  

E-print Network

of chemicals, we can increase food production, cure diseases, build more efficient houses, and send people of metals such as selenium, arsenic, or molybdenum, which may be hazardous to humans or animals. However health. Not all chemicals are toxic: every day we ingest chemicals in the form of food, water

Pennycook, Steve

339

Appendix B: Chemicals Appendix B: Chemicals B-3  

E-print Network

of chemicals, we can increase food production, cure diseases, build more efficient houses, and send people of metals such as selenium, arsenic, or molybdenum, which may be hazardous to humans or animals. However we ingest chemicals in the form of food, water, and sometimes medications. Even those chemicals

Pennycook, Steve

340

CHEMICALS IN THE ENVIRONMENT: OPPT CHEMICAL FACT SHEETS  

EPA Science Inventory

The OPPT Chemical Fact Sheets are produced by the Office of Pollution, Prevention and Toxics to provide a brief summary of information on selected chemicals. The Fact Sheets cover each chemicals identity, production and use, environmental fate, and health and environmental effect...

341

Appendix H: Chemicals Appendix H: Chemicals H-3  

E-print Network

), not a comprehensive discussion of chemicals and their effects on the environment and biological systems. PERSPECTIVE in apple seeds. However, exposures to many more hazardous chemicals result from the direct or indirect have varying types of effects. Generally, when considering human health, chemicals are divided into two

Pennycook, Steve

342

Appendix G: Chemicals Appendix G: Chemicals G-3  

E-print Network

), not a comprehensive discussion of chemicals and their effects on the environment and biological systems. PERSPECTIVE in apple seeds. However, exposures to many more hazardous chemicals result fromthe direct or indirect exposure to the public. DEFINITIONS Toxicity Chemicals have varying types of effects. Generally, when

Pennycook, Steve

343

Devices for collecting chemical compounds  

DOEpatents

A device for sampling chemical compounds from fixed surfaces and related methods are disclosed. The device may include a vacuum source, a chamber and a sorbent material. The device may utilize vacuum extraction to volatilize the chemical compounds from a fixed surface so that they may be sorbed by the sorbent material. The sorbent material may then be analyzed using conventional thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS) instrumentation to determine presence of the chemical compounds. The methods may include detecting release and presence of one or more chemical compounds and determining the efficacy of decontamination. The device may be useful in collection and analysis of a variety of chemical compounds, such as residual chemical warfare agents, chemical attribution signatures and toxic industrial chemicals.

Scott, Jill R; Groenewold, Gary S

2013-12-24

344

Control in the Chemical Industry  

ERIC Educational Resources Information Center

Discusses various control techniques used in chemical processes, including measuring devices, controller functions, control valves, and feedforward and feedback actions. Applications of control to a real chemical plant are exemplified. (CC)

Jones, R. G.

1974-01-01

345

ChemTeacher: Chemical Changes  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Chemical Changes page includes resources for teaching students about properties and examples of chemical changes.

2011-01-01

346

Information extraction from chemical patents  

E-print Network

, Chemical Markup Language and the software libraries that operate on it and the tools OSCAR3, ChemicalTagger and OSRA. 2.1 Availability of Documents Crucial to the success of this work is the availability and usability of suitable source documents... .................................................................... 211 Figure 6-2: Diagrammatic illustration of PatentEye Repository RDF .................................................. 212 ix Glossary API Application Programming Interface CAS Chemical Abstracts Service ChEBI Chemical Entities...

Jessop, David M

2011-03-15

347

Canadian Society for Chemical Technology  

NSDL National Science Digital Library

The Canadian Society for Chemical Technology (CSCT) is dedicated to "the advancement of chemical technology, the maintenance and improvement of standards of practitioners and educators, and the continual evaluation of chemical technology in Canada." Users can learn about the Society's many activities including certifying chemical technologists and supporting student endeavors. The site features upcoming workshops and events held in Europe and North America. Visitors can learn about student and regional chapters.

2005-11-07

348

LLNL Chemical Kinetics Modeling Group  

SciTech Connect

The LLNL chemical kinetics modeling group has been responsible for much progress in the development of chemical kinetic models for practical fuels. The group began its work in the early 1970s, developing chemical kinetic models for methane, ethane, ethanol and halogenated inhibitors. Most recently, it has been developing chemical kinetic models for large n-alkanes, cycloalkanes, hexenes, and large methyl esters. These component models are needed to represent gasoline, diesel, jet, and oil-sand-derived fuels.

Pitz, W J; Westbrook, C K; Mehl, M; Herbinet, O; Curran, H J; Silke, E J

2008-09-24

349

Hazards in the chemical laboratory  

SciTech Connect

The contents of this book are: Preface; Introduction; Health and Safety at Work Act 1974; Safety Planning and Management; Fire Protection; Reactive Chemical Hazards; Chemical Hazards and Toxicology; Health Care and First Aid; Hazardous Chemicals; Precautions against Radiations; and An American View.

Bretherick, L.

1987-01-01

350

CHEMICAL LABORATORY SAFETY AND METHODOLOGY  

E-print Network

CHEMICAL LABORATORY SAFETY AND METHODOLOGY MANUAL August 2013 #12;ii Emergency Numbers UNBC Prince-Emergency Numbers UNBC Prince George Campus Chemstores 6472 Chemical Safety 6472 Radiation Safety 6472 Biological the safe use, storage, handling, waste and emergency management of chemicals on the University of Northern

Northern British Columbia, University of

351

High energy chemical laser system  

Microsoft Academic Search

A high energy chemical laser system is described wherein explosive ; gaseous mixtures of a reducing agent providing hydrogen isotopes and interhalogen ; compounds are uniformly ignited by means of an electrical discharge, flash-; photolysis or an electron beam. The resulting chemical explosion pumps a lasing ; chemical species, hydrogen fluoride or deuterium fluoride which is formed in the ;

D. W. Gregg; R. K. Pearson

1975-01-01

352

Chemical ecology of bark beetles  

Microsoft Academic Search

Summary The purview of chemical ecology and the recent criticisms of improper application of theory to bark beetle phenomena is briefly discussed. Seven levels of research in chemical ecology are presented as well as their relationship to research on bark beetles. The biology and chemical ecology of several pest bark beetles from North America and Europe are discussed in regard

J. A. Byers

1989-01-01

353

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The stoichiometric coefficients for a chemical equation are determined by comparing the slopes of concentration-time plots for the reactants and products. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

354

Green chemistry for chemical synthesis.  

PubMed

Green chemistry for chemical synthesis addresses our future challenges in working with chemical processes and products by inventing novel reactions that can maximize the desired products and minimize by-products, designing new synthetic schemes and apparati that can simplify operations in chemical productions, and seeking greener solvents that are inherently environmentally and ecologically benign. PMID:18768813

Li, Chao-Jun; Trost, Barry M

2008-09-01

355

Green chemistry for chemical synthesis  

PubMed Central

Green chemistry for chemical synthesis addresses our future challenges in working with chemical processes and products by inventing novel reactions that can maximize the desired products and minimize by-products, designing new synthetic schemes and apparati that can simplify operations in chemical productions, and seeking greener solvents that are inherently environmentally and ecologically benign. PMID:18768813

Li, Chao-Jun; Trost, Barry M.

2008-01-01

356

AUV guidance with chemical signals  

Microsoft Academic Search

A great variety of marine animals navigate using chemical signals to locate food sources, mates and spawning grounds. The sensory systems and behaviors exhibited by these animals are well adapted for robust operations in turbulent and chemically complex environments. The algorithms used by an animal to rapidly extract guidance information from a discontinuous and complex chemical signal are presently unknown

T. R. Consi; J. Atema; C. A. Goudey; J. Cho; C. Chryssostomidis

1994-01-01

357

ANALYTICAL METHODS in CHEMICAL ECOLOGY  

E-print Network

ANALYTICAL METHODS in CHEMICAL ECOLOGY a post graduate course (doktorandkurs) when: February 10 ­ 28, 2014 where: Chemical Ecology, Plant Protection Biology, Swedish University of Agriculture (SLU to modern analytical methods used in Chemical Ecological and Ecotoxicological research, such as: methods

358

Mass Transfer with Chemical Reaction.  

ERIC Educational Resources Information Center

Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

DeCoursey, W. J.

1987-01-01

359

Physical and Chemical Changes Paper  

NSDL National Science Digital Library

In this activity you will write a paper explaining Physical and Chemical Changes. Follow the instructions below to show what you know about Physical and Chemical Changes. Create a word document titled "Physical and Chemical Changes". Put a heading on it that includes your name, number, date, and class period in the upper right corner. Your document should be double spaced, 12 point Times ...

Wall, Mr.

2008-10-28

360

48 Chemical Engineering Education Incorporating  

E-print Network

these to fields such as specialty chemical manufacture, green engineering, bio/pharmaceutical manufac- ture48 Chemical Engineering Education Incorporating GREEN ENGINEERING Into a Material and Energy prob- lems in chemical engineering. Problems of the type that can be used to motivate the student

Hesketh, Robert

361

Assimilating chemical compound with a regional chemical model  

NASA Astrophysics Data System (ADS)

To constrain the sink and source of the chemical compounds at surface during model simulation, chemical compound assimilation with Local Ensemble Transform Kalman Filter has been implemented for the WRFChemT model. The WRFChemT model has the chemical components coupled with the regional meteorological model with specified surface fluxes of the chemical compounds. Previous related studies on chemical assimilation have been focusing on the impact on the global atmospheric models (Kang et al. 2010 and Liu et al. 2010). In this study, we investigate the regional impact of the chemical compounds. Different from the applications of EnKF to weather prediction, the interactions between meteorological variables and surface emission of the chemical compounds are indirect and bridged through the tracer variables. How to construct the coupled atmospheric-chemical multi-variate error covariance based on the ensemble becomes the challenge of this new assimilation system. In this work, we perform OSSE experiments to evaluate the performance of the new assimilation system and also to investigate the strategies for assimilating the chemical compounds with LETKF. Corrections for surface flux can be obtained from adequately using observations of meteorology and chemical compounds with the ensemble-based multivariable covariance. Results suggest that meteorological dynamics plays a crucial role in adjusting the total mass of the chemical compounds, which in turns affect the retrieval of the surface emission.

Yang, S.; Liang, M.; Tseng, Y.

2011-12-01

362

Areawide chemical contamination  

SciTech Connect

Nine case histories illustrate the mounting problems owing to chemical contamination that often extends beyond the workplace into the community. The effects include not only carcinogenesis and teratogenesis, so much in the public's mind, but also severe neurological and gonadal disabilities immediately after exposure. Recognition of causal relationships is often made by astute clinicians. The experience of the Atomic Bomb Casualty Commission in studying Japanese survivors in Hiroshima and Nagasaki serves as a model for future studies of communities exposed to unusual environmental contamination.

Miller, R.W.

1981-04-17

363

Chemical sensor system  

DOEpatents

An implantable chemical sensor system for medical applications is described which permits selective recognition of an analyte using an expandable biocompatible sensor, such as a polymer, that undergoes a dimensional change in the presence of the analyte. The expandable polymer is incorporated into an electronic circuit component that changes its properties (e.g., frequency) when the polymer changes dimension. As the circuit changes its characteristics, an external interrogator transmits a signal transdermally to the transducer, and the concentration of the analyte is determined from the measured changes in the circuit. This invention may be used for minimally invasive monitoring of blood glucose levels in diabetic patients.

Darrow, Christopher B. (Pleasanton, CA); Satcher, Jr., Joe H. (Modesto, CA); Lane, Stephen M. (Oakland, CA); Lee, Abraham P. (Walnut Creek, CA); Wang, Amy W. (Berkeley, CA)

2002-01-01

364

Chemically rechargeable battery  

NASA Technical Reports Server (NTRS)

Batteries (50) containing oxidized, discharged metal electrodes such as an iron-air battery are charged by removing and storing electrolyte in a reservoir (98), pumping fluid reductant such as formalin (aqueous formaldehyde) from a storage tank (106) into the battery in contact with the surfaces of the electrodes. After sufficient iron hydroxide has been reduced to iron, the spent reductant is drained, the electrodes rinsed with water from rinse tank (102) and then the electrolyte in the reservoir (106) is returned to the battery. The battery can be slowly electrically charged when in overnight storage but can be quickly charged in about 10 minutes by the chemical procedure of the invention.

Graf, James E. (Inventor); Rowlette, John J. (Inventor)

1984-01-01

365

Sirtuin Chemical Mechanisms  

PubMed Central

Sirtuins are ancient proteins widely distributed in all lifeforms of earth. These proteins are universally able to bind NAD+, and activate it to effect ADP-ribosylation of cellular nucleophiles. The most commonly observed sirtuin reaction, is the ADPribosylation of acetyllysine, which leads to NAD+-dependent deacetylation. Other types of ADP-ribosylation have also been observed, including protein ADP-ribosylation, NAD+ solvolysis and ADP-ribosyltransfer to 5,6-dimethylbenzimidazole, a reaction involved in eubacterial cobalamin biosynthesis. This review broadly surveys the chemistries and chemical mechanisms of these enzymes. PMID:20132909

Sauve, Anthony A.

2010-01-01

366

Chemical kinetics modeling  

SciTech Connect

This project emphasizes numerical modeling of chemical kinetics of combustion, including applications in both practical combustion systems and in controlled laboratory experiments. Elementary reaction rate parameters are combined into mechanisms which then describe the overall reaction of the fuels being studied. Detailed sensitivity analyses are used to identify those reaction rates and product species distributions to which the results are most sensitive and therefore warrant the greatest attention from other experimental and theoretical research programs. Experimental data from a variety of environments are combined together to validate the reaction mechanisms, including results from laminar flames, shock tubes, flow systems, detonations, and even internal combustion engines.

Westbrook, C.K.; Pitz, W.J. [Lawrence Livermore National Laboratory, CA (United States)

1993-12-01

367

Selective chemical protein modification.  

PubMed

Chemical modification of proteins is an important tool for probing natural systems, creating therapeutic conjugates and generating novel protein constructs. Site-selective reactions require exquisite control over both chemo- and regioselectivity, under ambient, aqueous conditions. There are now various methods for achieving selective modification of both natural and unnatural amino acids--each with merits and limitations--providing a 'toolkit' that until 20 years ago was largely limited to reactions at nucleophilic cysteine and lysine residues. If applied in a biologically benign manner, this chemistry could form the basis of true Synthetic Biology. PMID:25190082

Spicer, Christopher D; Davis, Benjamin G

2014-01-01

368

Adapting Chemical Mixture Risk Assessment Methods to Assess Chemical and Non-Chemical Stressor Combinations  

EPA Science Inventory

Presentation based on the following abstract: Chemical mixtures risk assessment methods are routinely used. To address combined chemical and nonchemical stressors, component-based approaches may be applicable, depending on the toxic action among diverse stressors. Such methods a...

369

Chemical toxins that cause seizures.  

PubMed

Seizurogenic chemicals include a variety of toxic agents, including chemical warfare agents, toxic industrial chemicals, and natural toxins. Chemical weapons such as sarin and VX, and pesticides such as parathion and carbaryl cause hyperstimulation of cholinergic receptors and an increase in excitatory neurotransmission. Glutamatergic hyperstimulation can occur after exposure to excitatory amino acid toxins such as the marine toxin domoic acid. Other pesticides such as lindane and strychnine do not affect excitatory neurotransmission directly, but rather, they block the inhibitory regulation of neurotransmission by antagonism of inhibitory GABA and glycine synapses. In this paper, chemicals that cause seizures by a variety of molecular mechanisms and pathways are discussed. PMID:23085523

Jett, David A

2012-12-01

370

Chemical Health and Safety Data  

NSDL National Science Digital Library

These Chemical Health and Safety Data are an excellent resource for reliable, no-frills information from the National Toxicology Program (NTP). Data from "over 2000 chemicals studied by the NTP" are made available here, and users have a couple of different options for retrieving information. They may simply view a list of chemicals or search the Health and Safety database. Information on each chemical includes physical chemical data (like solubilities, solvents, volatility, flammability, and reactivity), toxicity data, handling procedures, emergency procedures, and a bibliographic list of sources for the information collected. Archived data may be downloaded (.sea, .zip).

371

Chemical Reactions in DSMC  

SciTech Connect

DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

Bird, G. A. [GAB Consulting Pty Ltd, 144/110 Sussex Street, Sydney NSW 2000 (Australia)

2011-05-20

372

The chemical peel.  

PubMed

Chemical peeling of facial skin has become a valuable adjunct in the armamentarium of the facial aesthetic surgeon. Among the various techniques available, phenol solutions are the most commonly used. Peeling produces a controlled, partial-thickness chemical burn of the epidermis and the outer dermis. Several techniques are available to "fine tune" the depth of the peel. Regeneration of peeled skin results in a fresh, orderly, organized epidermis. In the dermis, a new 2- to 3-mm band of dense, compact, orderly collagen is formed between the epidermis and the underlying damaged dermis, which results in effective ablation of the fine wrinkles in the skin and a reduction of pigmentation. These clinical and histological changes are long lasting (15-20 years) and may be permanent in some patients. Because of the metabolism and systemic complications of phenol, patient selection should involve systemic evaluation of liver, renal, and cardiac function, as well as an evaluation of the skin quality and medication status of the patient. Because of potential cardiac arrhythmias, peeling must be performed in a medically supervised environment, with continuous cardiac monitoring. The local complications of peeling include pigmentation changes, scarring, milia, ectropion, infection, activation of herpes simplex, and toxic shock syndrome. PMID:1883165

Peters, W

1991-06-01

373

Aqueous chemical wash compositions  

SciTech Connect

This patent describes an aqueous, substantially unfoamed chemical wash composition having properties making it suitable for use as a pre-flush in well cementing operations and/or for removal of drilling mud from a borehole at a temperature of from about 150/sup 0/F to about 270/sup 0/F, the wash a. being predominantly composed of water, b. containing an active surfactant component comprising a combination of (1) from about 0.1 to about 1.5 weight percent (total weight basis) of a water soluble anionic surfactant; (2) from about 0.1 to about 1.5 weight percent (total weight basis) of a nonionic surfactant; and (3) from about 0.05 to about 0.54 weight percent (total weight basis) of at least one water soluble amphoteric surfactant, and c. having dispersed therein a heterogeneous mixture of distinct particles comprising both a first particulate oil soluble resin which is friable and a second particulate oil soluble resin which is pliable and where the size of the friable resin particles ranges from about 0.5 to about 300 microns and the size of the pliable resin particles ranges from about 0.05 to about 30 microns. The amount of the friable-pliable resin mixture is sufficient to impart effective fluid loss control to the chemical wash composition.

Bannister, C.E.

1987-07-21

374

Wearable Optical Chemical Sensors  

NASA Astrophysics Data System (ADS)

Wearable sensors can be used to provide valuable information about the wearer's health and/or monitor the wearer's surroundings, identify safety concerns and detect threats, during the wearer's daily routine within his or her natural environment. The "sensor on a textile", an integrated sensor capable of analyzing data, would enable early many forms of detection. Moreover, a sensor connected with a smart delivery system could simultaneously provide comfort and monitoring (for safety and/or health), non-invasive measurements, no laboratory sampling, continuous monitoring during the daily activity of the person, and possible multi-parameter analysis and monitoring. However, in order for the technology to be accessible, it must remain innocuous and impose a minimal intrusion on the daily activities of the wearer. Therefore, such wearable technologies should be soft, flexible, and washable in order to meet the expectations of normal clothing. Optical chemical sensors (OCSs) could be used as wearable technology since they can be embedded into textile structures by using conventional dyeing, printing processes and coatings, while fiber-optic chemical sensors (FOCSs) as well as nanofiber sensors (NFSs) can be incorporated by weaving, knitting or laminating. The interest in small, robust and sensitive sensors that can be embedded into textile structures is increasing and the research activity on this topic is an important issue.

Lobnik, Aleksandra

375

a Submillimeter Chemical Sensor  

NASA Astrophysics Data System (ADS)

Rotational spectroscopy has been recognized a potentially powerful tool for chemical analysis since the very beginnings of the field. A typical rotational fingerprint consists of 10^5 resolvable spectral channels, leading to `absolute' specificity, even in complex mixtures. Furthermore, rotational spectroscopy requires very small amounts of sample with detection limits as low as picograms. Nevertheless, this technique has not yet been widely applied to analytical science because of the size, cost, and complexity of traditional spectrometers. A resurgence of interest in spectroscopic sensors has been fueled by increases in performance made possible by advances in laser systems and applications in medicine, environmental monitoring, and national security. Most of these new approaches make use of the optical/infrared spectral regions and their well established, but still rapidly evolving technology base. The submillimeter (SMM) spectral region, while much less well known, has also seen significant technological advances, allowing the design of powerful spectroscopic sensors. Using modern solid-state multiplier technology we have built a small bench top SMM spectrometer designed for use as a chemical sensor. This spectrometer includes a sample acquisition system including the vacuum equipment to provide the ideal pressures (1--10 mtorr) for SMM spectroscopy and a sorbent tube for analyte collection and preconcentration. The entire spectrometer, including power supplies, frequency synthesizers, a 1.2 m folded sample cell, and a computer for data analysis fits into a cubic foot box.

Neese, Christopher F.; Medvedev, Ivan R.; De Lucia, Frank C.; Plummer, Grant M.; Ball, Christopher D.; Frank, Aaron J.

2010-06-01

376

Chemical shift imaging: a review.  

PubMed

Chemical shift is the phenomenon that is seen when an isotope possessing a nuclear magnetic dipole moment resonates at a spectrum of resonance frequencies in a given magnetic field. These resonance frequencies, or chemical shifts, depend on the chemical environments of particular nuclei. Mapping the spatial distribution of nuclei associated with a particular chemical shift (e.g., hydrogen nuclei associated with water molecules or with lipid groups) is called chemical shift imaging. Several techniques of proton chemical shift imaging that have been applied in vivo are presented, and their clinical findings are reported and summarized. Acquiring high-resolution spectra for large numbers of volume elements in two or three dimensions may be prohibitive because of time constraints, but other methods of imaging lipid of water distributions (i.e., selective excitation, selective saturation, or variations in conventional magnetic resonance imaging pulse sequences) can provide chemical shift information. These techniques require less time, but they lack spectral information. Since fat deposition seen by chemical shift imaging may not be demonstrated by conventional magnetic resonance imaging, certain applications of chemical shift imaging, such as in the determination of fatty liver disease, have greater diagnostic utility than conventional magnetic resonance imaging. Furthermore, edge artifacts caused by chemical shift effects can be eliminated by certain selective methods of data acquisition employed in chemical shift imaging. PMID:3008543

Brateman, L

1986-05-01

377

Natural chemicals, synthetic chemicals, risk assessment, and cancer  

SciTech Connect

The administration of chemicals at the maximum tolerated dose (MTD) in standard animal cancer tests is postulated to increase cell division (mitogenesis), which in turn increases rates of mutagenesis and thus carcinogenesis. The animal data are consistent with this mechanism, because a high proportion of all chemicals tested are indeed rodent carcinogens. We conclude that at the low doses of most human exposures, where cell killing does not occur, the hazards to humans of rodent carcinogens may be much lower than is commonly assumed. The toxicological significance of exposures to synthetic chemicals is examined in the context of exposures to naturally occurring chemicals. We calculate that 99.99% of the pesticides in the American diet are chemicals that plants produce to defend themselves. Only 52 natural pesticides have been tested in high-dose animal cancer tests, and about half (27) are rodent carcinogens; these 27 are shown to be present in many common foods. We conclude that natural and synthetic chemicals are equally likely to be positive in animal cancer tests. The toxicology of synthetic chemicals is compared to that of natural chemicals, which represent the vast bulk of the chemicals to which humans are exposed. It is argued that animals have a broad array of inducible general defenses to combat the changing array of toxic chemicals in plant food (nature's pesticides) and that these defenses are effective against both natural and synthetic toxins. Synthetic toxins such as dioxin are compared to natural chemicals, such as indole carbinol and ethanol. The finding that in high-dose tests, a high proportion of both natural and synthetic chemicals are carcinogens, mutagens, teratogens, and clastogens (30-50% for each group) undermines current regulatory effects based on these tests to protect public health from low doses of synthetic chemicals.

Ames, B.N.; Gold, L.S. (Division of Biochemistry and Molecular Biology, University of California, Berkeley (United States))

1990-01-01

378

Gas phase chemical detection with an integrated chemical analysis system  

SciTech Connect

Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample preconcentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described.

CASALNUOVO,STEPHEN A.; FRYE-MASON,GREGORY CHARLES; KOTTENSTETTE,RICHARD; HELLER,EDWIN J.; MATZKE,CAROLYN M.; LEWIS,PATRICK R.; MANGINELL,RONALD P.; BACA,ALBERT G.; HIETALA,VINCENT M.

2000-04-12

379

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

During the past six months we have conducted significant research in several domains in order to clarify and understanding the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. We organized numerous analytical studies with methods including Fourier Transform Infrared Spectroscopy, Dynamic Mechanical Analysis, Differential Scanning Calorimetry, and Stress Relaxation experiments. In addition we have reanalyzed previous thermogravimetric data concerning the rate of deplasticization of Coflon pipe. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. We conducted stress relaxation experiments of Coflon pipe at several temperatures and determined an activation energy. We also examined the dynamic mechanical response PVDF during deplasticization and during methanol plasticization. We performed numerous DSC analyses to research the changing crystalline morphology. We have noted significant changes in crystallinity upon aging for both PVDF and Tefzel. Little variation in elemental composition was noted for many of the aged Coflon and Tefzel samples tested.

Bulluck, J. W.; Rushing, R. A.

1995-01-01

380

Groundwater and organic chemicals  

SciTech Connect

Groundwater is a major source of drinking water for many communities. Unfortunately, organic chemicals such as dry cleaning fluids, solvent, fuels, and pesticides have contaminated groundwater in many areas, rendering the groundwater useless as a drinking water resource. In many cases, the groundwater cannot be cleaned up with current technologies, particularly if the groundwater has been contaminated with immiscible (low solubility) organic liquids. In this talk, I will describe the path I have followed from geologist to geochemist and finally to environmental engineer. As a geologist, I studied the chemistry of rock metamorphosis. As a geochemist, I explored for gold and other metals. Now as an environmental engineer, I investigate the behavior of organic liquids in the subsurface. While these fields all appear very different, in reality I have always focused on the interaction of rocks or sediments with the fluids with which they come in contact.

Dawson, H.E. [Colorado School of Mines, Golden, CO (United States)

1995-12-01

381

Chemical Comic Relief  

NSDL National Science Digital Library

John Selegue and James Holler at the University of Kentucky have provided this ingenious learning resource, Chemical Comic Relief. Visitors to the site click on an element on the periodic table to see a list of comic pages involving that element. For example, clicking on Oxygen brings up a list of comics including Four Color: Ricky Nelson, which shows Ricky discussing oxygen to attempt (unsuccessfully) to impress a girl. Some pages include a summary discussing both the comic as well as the element it features, and the site also offers a chronological History of Chemistry in the Comics -- an album of comic pages from the 1930s to the present. To gain a greater understanding of the technical aspects (atomic weight, key data and description, and history) of each element, the user can link to the WebElements Website.

382

Chemical composition of patikaraparpam.  

PubMed

Patikaraparpam, a Siddha formulation in prepared by trituration of potash alum with egg albumin followed by calcinatin. The three authentic laboratories made parpams as well as six commercial samples have been examined for their chemical composition. The analytical data that emerged from the analysis of the above samples showed that seven parpams contained only aluminium sulphate and they did respond to tests for potassium. An inspection of the crude drugs patikaram' available in the market established that potash alum and ammonia alum are indiscriminateldy taken for use, according to literature, only potash alum should be used in Indian system of medicine. Patikarapparapam is indicated in urinary inflammations and obstructions and is a reputed diuretic. Potassium salts are established diuretic. These studies show that the raw drugs sellers, the pharamaceutists or manufacturers of medicine and the physician as well should make sure that only potash alum is used in Indian medicine. PMID:22556804

Saraswathy, A; Rani, M G; Susan, T; Purushothaman, K K

1997-04-01

383

Chemical heat pump  

DOEpatents

A chemical heat pump system is disclosed for use in heating and cooling structures such as residences or commercial buildings. The system is particularly adapted to utilizing solar energy, but also increases the efficiency of other forms of thermal energy when solar energy is not available. When solar energy is not available for relatively short periods of time, the heat storage capacity of the chemical heat pump is utilized to heat the structure as during nighttime hours. The design also permits home heating from solar energy when the sun is shining. The entire system may be conveniently rooftop located. In order to facilitate installation on existing structures, the absorber and vaporizer portions of the system may each be designed as flat, thin wall, thin pan vessels which materially increase the surface area available for heat transfer. In addition, this thin, flat configuration of the absorber and its thin walled (and therefore relatively flexible) construction permits substantial expansion and contraction of the absorber material during vaporization and absorption without generating voids which would interfere with heat transfer. The heat pump part of the system heats or cools a house or other structure through a combination of evaporation and absorption or, conversely, condensation and desorption, in a pair of containers. A set of automatic controls change the system for operation during winter and summer months and for daytime and nighttime operation to satisfactorily heat and cool a house during an entire year. The absorber chamber is subjected to solar heating during regeneration cycles and is covered by one or more layers of glass or other transparent material. Daytime home air used for heating the home is passed at appropriate flow rates between the absorber container and the first transparent cover layer in heat transfer relationship in a manner that greatly reduce eddies and resultant heat loss from the absorbant surface to ambient atmosphere.

Greiner, Leonard (2750-C Segerstrom Ave., Santa Ana, CA 92704)

1980-01-01

384

Gas Phase Chemical Detection with an Integrated Chemical Analysis System  

SciTech Connect

Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample concentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described. The design and performance of novel micromachined acoustic wave devices, with the potential for improved chemical sensitivity, are also described.

Baca, Albert G.; Casalnuovo, Stephen A.; Frye-Mason, Gregory C.; Heller, Edwin J.; Hietala, Susan L.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carloyn M.; Reno, John L.; Sasaki, Darryl Y.; Schubert, W. Kent

1999-07-08

385

CHEMICAL ENGINEERING 2012-2014 CATALOG  

E-print Network

CHEMICAL ENGINEERING 2012-2014 CATALOG (catalog valid until August 2020) Suggested Arrangement 204, Introduction to Chemical Practice............................2 CHE 102, Introduction to Chemical ..............................1 CHE 317, Intro to Chemical Engineering Analysis...................3 CH 353, Physical Chemistry

Texas at Austin, University of

386

CHEMICAL SENSORS School of Chemistry and Biochemistry  

E-print Network

CHEMICAL SENSORS CHEM 6282 School of Chemistry and Biochemistry Chemical sensors physics and electronics or a chemical instrumentation course. The topics covered will include general theory of chemical recognition, electrochemical, optical, mass sensors and data reduction. Text: J

Sherrill, David

387

Chemical engineers design, control and optimize large-scale chemical, physicochemical and  

E-print Network

40 Chemical engineers design, control and optimize large-scale chemical, physicochemical and electronics fields. Chemical Engineers are employed in areas as diverse as the chemical, pharmaceutical, petrochemical and environmental industries. Emerging fields in chemical engineering include biotechnology

Rohs, Remo

388

Chemical engineers design, control and optimize large-scale chemical, physicochemical and  

E-print Network

38 Chemical engineers design, control and optimize large-scale chemical, physicochemical and electronics fields. Chemical Engineers are employed in areas as diverse as the chemical, pharmaceutical, petrochemical and environmental industries. Emerging fields in chemical engineering include biotechnology

Rohs, Remo

389

46 CFR 190.05-20 - Segregation of chemical laboratories and chemical storerooms.  

Code of Federal Regulations, 2010 CFR

... Segregation of chemical laboratories and chemical storerooms...CONTINUED) OCEANOGRAPHIC RESEARCH VESSELS CONSTRUCTION AND... Segregation of chemical laboratories and chemical storerooms...hazard area. (d) Chemical laboratories shall not be located...

2010-10-01

390

Chemical evolution of dense clouds  

NASA Technical Reports Server (NTRS)

Chemical processes that could determine the molecular composition of the cloud during the several stages of its evolution are considered. Reactions at the relatively interstellar densities are emphasized.

Chappelle, E. W.; Donn, B. D.; Payne, W. A., Jr.; Stief, L. J.

1972-01-01

391

Bright Ideas for Chemical Biology  

PubMed Central

Small-molecule fluorescent probes embody an essential facet of chemical biology. Although numerous compounds are known, the ensemble of fluorescent probes is based on a modest collection of modular “core” dyes. The elaboration of these dyes with diverse chemical moieties is enabling the precise interrogation of biochemical and biological systems. The importance of fluorescence-based technologies in chemical biology elicits a necessity to understand the major classes of small-molecule fluorophores. Here, we examine the chemical and photophysical properties of oft-used fluorophores, and highlight classic and contemporary examples in which utility has been built upon these scaffolds. PMID:18355003

Lavis, Luke D.; Raines, Ronald T.

2009-01-01

392

A Chemical Technology Program Partnership  

NASA Astrophysics Data System (ADS)

Brazosport College would be the first to admit that they owe the success of their Chemical Technology Program to the partnership that was developed between the college and the surrounding chemical industry. The college is a two-year institution located near the Texas Gulf Coast with more than twelve chemical companies in the immediate area. Dow Chemical is the largest, employing more than 5,000. Currently, the Science Department at Brazosport College offers associate of science degrees in biology, chemistry, and physics, and associate of applied science degrees in chemical technology and instrumentation technology to meet the needs of these industries. In addition, many students enroll in classes to prepare for specific occupations or to build their skills for employment. This may only require the student to take a few courses. The current Chemical Technology Program addresses skills needed for both laboratory and process technician jobs in the chemical industry. An Associate of Applied Science Degree in Chemical Technology is offered with either a laboratory or a process option. These programs were developed with input from the chemical industry, and the college trains all new process employees for BASF and Dow. Additionally, the college does customized flexible-entry training in process operations and laboratory analysis for these and several other companies.

Hicks, Gary

1998-01-01

393

Counterexamples in Chemical Ring Perception  

E-print Network

Counterexamples in Chemical Ring Perception Franziska Berger # , Christoph Flamm + , Petra M. Gleiss + , Josef Leydold ¶ , Peter F. Stadler #,+,#,# # Zentrum Mathematik, TU MË?unchen, Boltzmannstrasse

Stadler, Peter F.

394

Chemical substructure analysis in toxicology  

SciTech Connect

A preliminary examination of chemical-substructure analysis (CSA) demonstrates the effective use of the Chemical Abstracts compound connectivity file in conjunction with the bibliographic file for relating chemical structures to biological activity. The importance of considering the role of metabolic intermediates under a variety of conditions is illustrated, suggesting structures that should be examined that may exhibit potential activity. This CSA technique, which utilizes existing large files accessible with online personal computers, is recommended for use as another tool in examining chemicals in drugs. 2 refs., 4 figs.

Beauchamp, R.O. Jr. [Center for Information on Toxicology and Environment, Raleigh, NC (United States)

1990-12-31

395

Light with nonzero chemical potential  

NSDL National Science Digital Library

Thermodynamic states and processes involving light are discussed in which the chemical potential of light is nonzero. Light with nonzero chemical potential is produced in photochemical reactions, for example, in a light emitting diode. The chemical potential of black-body radiation becomes negative upon a Joule expansion. The isothermal diffusion of light is driven by the gradient in the chemical potential. These and other examples support the idea that light can be interpreted as a gas of photons, with properties similar to a material gas.

Herrmann, F.; Wurfel, P.

2011-08-30

396

Chemical Engineering in Space  

NASA Technical Reports Server (NTRS)

The state of the art in launch systems uses chemical propulsion systems, primarily liquid hydrogen and liquid oxygen, to provide the energy necessary to achieve orbit and escape the bonds of Earth's gravity. In the future there may be other means available; however, currently few of these alternatives can compare to the speed or the ease of use provided by cryogenic chemical propulsion agents. Cryogenics, the science and art of producing cold operating conditions, has become increasingly important to our ability to travel within our solar system. The production and transport of cryogenic fuels as well as the long-term storage of these fluids are necessary for mankind to travel within our solar system. It is with great care and at a significant cost that gaseous compounds such as hydrogen and oxygen are liquified and become dense enough to use for rocket fuel. As our explorations move farther away from Earth, we need to address how to produce the necessary fuels to make a complete round-trip. The cost and the size of any expedition to another celestial body are extreme. If we are constrained by the need to take everything necessary (fuel, life support, etc.) for our survival and return, we greatly increase the risk of being able to go. As with the early explorers on Earth, we will need to harvest much of our energy and our life support from the celestial bodies. The in situ production of these energy sources is paramount to success. Due to the current propulsion system designs, the in-situ processes will require liquefaction and the application of cryogenics. The challenge we face for the near future is to increase our understanding of cryogenic long-term storage and off-world production of cryogenic fluids. We must do this all within the boundaries of very restricted size, weight, and robustness parameters so that we may launch these apparatus from Earth and utilize them elsewhere. Miniaturization, efficiency, and physically robust systems will all play a part in making space exploration possible; however, it is cryogenics that will enable all of this to occur.

Lobmeyer, Dennis A.; Meneghelli, Barry J.

2001-01-01

397

Appendix G. Chemicals Appendix G. Chemicals G-3  

E-print Network

. Through the use of chemicals, we can increase food production, cure diseases, build more efficient houses to humans or animals. Even some of the foods we eat contain natural tox- ins. Aflatoxin is a known toxin (noncarcinogens) and cancer (carcinogens). Sometimes a chemical can have both a toxic and a carcinogenic effect

Pennycook, Steve

398

Appendix H. Chemicals Appendix H. Chemicals H-3  

E-print Network

. Through the use of chemicals, we can increase food production, cure diseases, build more efficient houses to humans or animals. Even some of the foods we eat contain natural tox- ins. Aflatoxin is a known toxin (noncarcinogens) and cancer (carcinogens). Sometimes a chemical can have both a toxic and a carcinogenic effect

Pennycook, Steve

399

Chemical Mixtures: Considering the Evolution of Toxicology and Chemical Assessment  

PubMed Central

The assessment of chemical mixtures is a complex topic for toxicologists, regulators, and the public. In this article the linkage between the science of toxicology and the needs of governmental regulatory agencies in the United States is explored through an overview of environmental regulations enacted over the past century and a brief history of modern toxicology. One of the goals of this overview is to encourage both regulators and scientists to consider the benefits and limitations of this science–regulatory relationship as they tackle existing issues such as chemical mixtures. It is clear that a) over the past 100 years chemical regulation and toxicologic research, have in large part, shared a common emphasis on characterization and regulation of individual chemicals. But chemical mixtures have been, and continue to be, evaluated at hazardous waste sites around the United States. For this reason the current U.S. Environmental Protection Agency guidelines for chemical mixtures assessment are also reviewed. These guidelines highlight the current practice of mixtures assessment, which relies primarily on the existing single-chemical database. It is also clear that b) the science and assessment of chemical mixtures are moving forward through the combined efforts of regulatory agencies and scientists from a broad range of disciplines, including toxicology. Because toxicology is at this exciting crossroads, particular attention should be paid to the forces (e.g., public demands, regulatory needs, funding, academic interests) that both promote and limit the growth of this expanding discipline. PMID:15811826

Monosson, Emily

2005-01-01

400

Chemical Biology Chemical Screening for Hair Cell Loss and Protection  

E-print Network

degeneration and to regenerate new hair cells, replacing those that are lost due to aging, disease information for hearing and balance, respectively, to the brain. The mechanosensory hair cells of the innerChemical Biology Chemical Screening for Hair Cell Loss and Protection in the Zebrafish Lateral Line

Rubel, Edwin

401

Chemically Driven Spinodal Decomposition  

NASA Astrophysics Data System (ADS)

Thermally driven spinodal decomposition in polymer/polymer systems is often observed through the growth of a peak in the small-angle light scattering pattern. Phase growth is related to an increase in intensity with time following Cahn-Hillard theory. Latter stage deviations from this thermodynamic prediction are described by Oswald ripening mechanisms. A parallel to thermally driven phase separation is seen in some systems where miscibility is governed not by a thermal driving force but by a chemical reaction which leads to immiscibility of a reaction product and a polymer phase. In this study hydroxyl terminated, low molecular weight polydimethyl siloxane is reacted with multi-functional silicon based crosslinking agents to form a two phase rubber with silica-like inclusions. By varying the molecular weight of the PDMS precursor, the catalyst type and other reaction conditions the phase separation process can be drastically altered. A modified Cahn-Hillard approach is described where extent of reaction substitutes for the thermal driving force in conventional spinodal decomposition.

Sukumaran, S.; Beaucage, G.; Viers, B.; Mark, J. E.; Saraf, M.

1997-03-01

402

Chemical Sensors in Oceanography  

NASA Astrophysics Data System (ADS)

About 40 years ago, I served as graduate student labor on the International Indian Ocean Expedition, where I carried out what seemed to be vast numbers of routine chemical analyses of sea water. I vowed, as have many others, that on my return I would find a better way. From this effort, the first uses of “autoanalyzers” for sea water emerged. Over the years, the demand for fundamental scientific data from the oceans has increased enormously, as has the range of properties and the need for precision and rapidity. The recent global ocean survey of carbon dioxide and related properties carried out by the Joint Global Ocean Flux Study, and World Ocean Circulation Experiment, cruises is but one example of the huge effort involved. There has long been a desire for a set of sophisticated yet robust sensors that would do the job with minimum labor and produce data of maximum quality in environments ranging from the sea surface to the ocean floor. This is quite a tall order!

Brewer, Peter G.

403

CHEMICAL TRANSMISSION AND ADAPTATION  

PubMed Central

Acetylcholine and factor I appear to be transmitter substances of excitatory and inhibitory regulatory nerve fibers supplying the sensory neurons of stretch receptor organs of the crayfish. Sudden application of a low concentration of acetylcholine causes the impulse frequency to jump to a peak value. But immediately the frequency falls again and gradually reaches a steady state which is not far above the previous frequency level. If the acetylcholine is now withdrawn there follows a silent period after which the frequency returns to its original level. The time course of these events is identical with that of adaptations to sudden increase or decrease of stretch. Factor I in sufficiently low concentrations causes an immediate fall in impulse frequency (silent period) which is followed by a return to a value near the previous frequency level. Withdrawal of factor I is followed by excitation and again return of the frequency to the rate measured before the application of factor I. The time course of these phenomena is identical with that of adaptations to sudden decrease and increase of stretch. It is suggested that adaptation may be a property not only of sensory neurons but of neurons in general and that even central neurons may be considered as receptor neurons inasmuch as they respond to chemically transmitted excitatory and inhibitory stimuli. PMID:13416529

Florey, Ernst

1957-01-01

404

Chemical Stockpile Disposal Program  

SciTech Connect

As part of the Chemical Stockpile Disposal Program mandated by Public Law 99--145 (Department of Defense Authorization Act), an independent review is presented of the US Army Phase I environmental report for the disposal program at the Pine Bluff Arsenal (PBA) in Arkansas. The Phase I report addressed new and additional concerns not incorporated in the final programmatic environmental impact statement (FPEIS). Those concerns were addressed by examining site-specific data for the PBA and by recommending the scope and content of a more detailed site- specific study. This dependent review evaluates whether the new site-specific data presented in the Phase I report would alter the decision in favor of on-site disposal that was reached in the FPEIS, and whether the recommendations for the scope and content of the site-specific study are adequate. Based on the methods and assumptions presented in the FPEIS, the inclusion of more detailed site-specific data in the Phase I report does not change the decision reached in the FPEIS (which favored on-site disposal at PBA). It is recommended that alternative assumptions about meteorological conditions be considered and that site-specific data on water, ecological, socioeconomic, and cultural resources, and emergency planning and preparedness be considered explicitly in the site-specific EIS decision-making process. 13 refs., 1 fig.

Krummel, J.R.; Policastro, A.J.; Olshansky, S.J.; McGinnis, L.D.

1990-10-01

405

Strength of Chemical Bonds  

NASA Technical Reports Server (NTRS)

Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

Christian, Jerry D.

1973-01-01

406

Chemical vapor deposition growth  

NASA Technical Reports Server (NTRS)

The objective was to investigate and develop chemical vapor deposition (CVD) techniques for the growth of large areas of Si sheet on inexpensive substrate materials, with resulting sheet properties suitable for fabricating solar cells that would meet the technical goals of the Low Cost Silicon Solar Array Project. The program involved six main technical tasks: (1) modification and test of an existing vertical-chamber CVD reactor system; (2) identification and/or development of suitable inexpensive substrate materials; (3) experimental investigation of CVD process parameters using various candidate substrate materials; (4) preparation of Si sheet samples for various special studies, including solar cell fabrication; (5) evaluation of the properties of the Si sheet material produced by the CVD process; and (6) fabrication and evaluation of experimental solar cell structures, using impurity diffusion and other standard and near-standard processing techniques supplemented late in the program by the in situ CVD growth of n(+)/p/p(+) sheet structures subsequently processed into experimental cells.

Ruth, R. P.; Manasevit, H. M.; Campbell, A. G.; Johnson, R. E.; Kenty, J. L.; Moudy, L. A.; Shaw, G. L.; Simpson, W. I.; Yang, J. J.

1978-01-01

407

Modern Chemical Technology, Volume 9.  

ERIC Educational Resources Information Center

This volume is one of the series for the Chemical Technician Curriculum Project (ChemTeC) of the American Chemical Society funded by the National Science Foundation. It consists of discussions, exercises, and experiments on the following topics: ion exchange, electrphoresis, dialysis, electrochemistry, corrosion, electrolytic cells, coulometry,…

Pecsok, Robert L.; Chapman, Kenneth

408

Sensors for chemical weapons detection  

Microsoft Academic Search

Many methods can sense and respond to chemical agent release. We evaluate current and near-term sensor options for detecting the most likely threats, currently sarin, cyanide, and pesticides. We also identify sensor technologies that may be capable of responding to additional chemical threats and biological agents and provide options for coping with new threats as they develop. We collate previous

G. M. Murray; G. E. Southard

2002-01-01

409

The electromagnetic chemical propulsion concept  

Microsoft Academic Search

A new concept of propulsion to high velocities is presented. It combines the strong points of electrothermal chemical and electromagnetic methods. The projectile is accelerated by electromagnetic forces. Similar to other methods of electromagnetic propulsion, this overcomes the common limitations of conventional and electrothermal guns, caused by limited expansion speed of hot gases at acceptable temperatures. As with electrothermal chemical

Yuri A. Dreizin

1995-01-01

410

Safety in the Chemical Laboratory  

ERIC Educational Resources Information Center

The author discusses a system for establishing the relative potential of a chemical to release energy suddenly and to indicate release. This system is applicable to chemical storage and transportation. The system is based upon three simple tests requiring a minimum sample (1 go or 1 ml): (1) computation, (2) impact sensitivity, and (3) thermal…

Coffee, Robert D.

1972-01-01

411

Chemical evolution: The first stages  

Microsoft Academic Search

The available data on the syntheses of critically important precursor molecules for chemical evolution are reviewed and problems of rates of production versus rates of destruction in the primitive ocean are discussed. It is concluded that many global chemical syntheses would have been improbable in the Earth's oceans and that more attention should be paid to specific environments which would

Alan W. Schwartz

1983-01-01

412

Chemical generation of iodine atoms  

Microsoft Academic Search

The chemical generation of atomic iodine using a chemical combustor to generate the atomic fluorine intermediate, from the reaction of F2 + H2, followed by the production of atomic iodine, from the reaction of F + HI, was investigated. The maximum conversion efficiency of HI into atomic iodine was observed to be approximately 75%, which is in good agreement with

Kevin B. Hewett; Gordon D. Hager; Peter G. Crowell

2005-01-01

413

CHEMICAL HYGIENE LAB SPECIFIC INFORMATION  

E-print Network

___________________________ 7 MRI and NMR Laboratory__________________________ 10 IR/Raman and QCM-D Laboratory____________________19 #12;3 Introduction 12/4/2013 This is the Chemical Hygiene Plan (CHP) for the Materials Research;7 Materials Research Laboratory University of California at Santa Barbara Spectroscopy Department Chemical

Sideris, Thomas C.

414

CHEMICAL PROTECTION AGAINST IONIZING RADIATION  

Microsoft Academic Search

Recent work on chemical protection against radiation effects in mammals ; is reviewed, especially with respect to whole-body exposure to external radiation. ; This survey shows that many explanations are being offered to account for the ; action of radioprotective agents. In general, the proposed mechanisms are ; concerned with inactivation of radicals and other chemical intermediates, ; depletion of

R. L. Straube; H. M. Patt

1963-01-01

415

Chemicals, Health, Environment, and Me.  

ERIC Educational Resources Information Center

The CHEM (Chemicals, Health, Environment, and Me) Project is a series of 10 units designed to provide experiences for fifth and sixth graders that help them to accomplish an understanding of: (1) the nature of chemicals and how they interact with the environment; (2) how to collect, process, and analyze information; (3) how to use scientific…

California Univ., Berkeley. Lawrence Hall of Science.

416

Toolbox Safety Talk Chemical Labeling  

E-print Network

effective means of communicating chemical hazards. DEFINITIONS · Pictogram: a symbol plus other graphic in the workplace to be clearly labeled with the appropriate identification and warnings. A label may be affixed to to be taken to minimize or prevent adverse effects resulting from exposure to a hazardous chemical, improper

Pawlowski, Wojtek

417

Chemical Control of Plant Growth.  

ERIC Educational Resources Information Center

Seven experiments are presented in this Science Study Aid to help students investigate the control of plant growth with chemicals. Plant growth regulators, weed control, and chemical pruning are the topics studied in the experiments which are based on investigations that have been and are being conducted at the U. S. Agricultural Research Center,…

Agricultural Research Center (USDA), Beltsville, MD.

418

Chemical Evolution in Omega Centauri  

E-print Network

The globular cluster Omega Centauri displays evidence of a complex star formation history and peculiar internal chemical evolution, setting it apart from essentially all other globular clusters of the Milky Way. In this review we discuss the nature of the chemical evolution that has occurred within Omega Cen and attempt to construct a simple scenario to explain its chemistry.

Verne V. Smith

2003-10-22

419

Teaching Chemical Engineers about Teaching  

ERIC Educational Resources Information Center

The Chemical and Biomolecular Engineering Department at The Ohio State University in collaboration with the University Center for the Advancement of Teaching developed the Chemical Engineering Mentored Teaching Experience. The Mentored Teaching Experience is an elective for Ph.D. students interested in pursuing faculty careers. Participants are…

Heath, Daniel E.; Hoy, Mary; Rathman, James F.; Rohdieck, Stephanie

2013-01-01

420

Chemical deposition of conducting polymers  

Microsoft Academic Search

The coating of different materials with conducting electroactive polymers (CEP), i.e. polyaniline, polypyrrole, polythiophene, and their derivatives, provided by means of chemical polymerization, is briefly reviewed. The topics covered include the deposition of CEP (i) by bulk oxidative chemical polymerization, (ii) by surface-located polymerization, and (iii) by coating of micro- and nanoparticles. The coating of different materials like polymers, polymer

A. Malinauskas

2001-01-01

421

âChemical Changes: Burningâ  

NSDL National Science Digital Library

This lesson demonstrates how students can apply the process of identifying main idea and supporting details to show the different ways burning can chemically change matter. The students can identify these changes and discuss the details that support these changes, which will help them further understand how burning matter is considered a chemical change.

Ryan, Kris

2012-07-25

422

Chemical quality of Michigan streams  

USGS Publications Warehouse

Concentrations of chemical constituents of Michigan streams exhibit regional patterns that are primarily a function of geology and evapotranspiration. However, in some areas waste disposal by municipal and industrial organizations has altered the natural distribution and concentrations of dissolved material. Concentration and areal distribution of chemical constitutents were found to change very little from high spring to low summer flow conditions.

Wood, Warren W.

1970-01-01

423

CHEMICAL ENGINEERING Program of Study  

E-print Network

CHEMICAL ENGINEERING Program of Study Research Facilities Financial Aid Applying Correspondence, general pilot plant facilities, and specific project units. In addition, the Department has excellent experimental apparatus. There are state-of-the-art units for basic studies utilizing chemical analysis, surface

Thomas, Andrew

424

AGRI-SCIENCE CHEMICAL BIOLOGY  

E-print Network

be applied across the agri-sciences, (defined in this context as plant, fungal and insect sciences through translation of chemical biology tools and technologies Control weeds, disease and pests Minimise photosynthetic efficiency Improve chemical agronomic and agro-ecological control measures Modelling

425

Indiana University: Chemical Information Sources  

NSDL National Science Digital Library

This fantastic Indiana University website helps individuals "find and learn how to use chemical information resources on the Internet and elsewhere." Users can find two types of resource guides. The first, SIRCh (Selected Internet Resources for Chemistry) offers numerous links to educational websites where users can find answers to many of their chemistry questions. The second, CCIIM (Clearinghouse for Chemical Information Instructional Materials), is a collection of items created by chemistry and science librarians, chemists, and publishers to help visitors learn how to use chemical information sources. Users can find links to four databases providing information on publications, references, acronyms, and crystallography. The website offers archives of the University's Chemical Information Sources Discussion List and materials on chemical information classes taught at Indiana University.

2007-05-05

426

Chemical earth models  

NASA Astrophysics Data System (ADS)

This article presents a critical review of method, concepts and prejudices used bv modelists of the Earth's chemical composition over approximate the last fifty years and of the resulting compositions. Brief descriptions are given of admitted accretion mechanisms, of the starting materials most often considered and of the major parameters and recurrent concepts: 'reduced" state, mantle homogeneity vs heterogeneity, 'low pressure' core formation, 'great impact', refractory, lithophile, siderophile, compatible, incompatible character of elements, depleted and degassed mantle, Urey ratio, as well as the description of a commonly-used instrument, possibly harmful to Iogic, the famous Ockham's razor. Differences between models are now restricted to the lower mantle composition:the 'primary' (before crust differentiation) upper mentle varies little from model to model and the idea of a 10-15% combined Si-O-S concentration as representing the necessary light elements in the core is gaining more and more ground. The dominant type of model derives more or less directly from the CI cabonaceous composition by complete devolatilization and reduction. Its mantle is homogeneous and convecting mainly in a one-level mode, in accordence with dominant geophysicists' views but in rather strong disagreement with geochemical data and models which insist on the strong decoupling between lower and upper mantle. Its low Si excess is generally supposed to have been absorbed by the core, whereas its high refractory lithophile element (RLE) content creates mass balance problems relative to presently observed mantle and crust concentrations. The alternative type is a two-lavel mantle with a Si and Fe-rich, RLE-poor, lower mantle, previously based mainly on seismic and mineral physics data, and now also on geochemical and cosmochemical arguments.

Javoy, Marc

1999-10-01

427

Titan's chemical complexity  

NASA Astrophysics Data System (ADS)

We review here our current knowledge of Titan's gas phase chemistry. We base our discussion on photochemical models as well as on laboratory experiments. We identify the lower mass positive [1,2] and negative [3] ions detected in the upper atmosphere and we show that their formation is a direct consequence of the presence of heavy neutrals. We demonstrate that the observed densities of CO, CO2 and H2O can be explained by a combination of exogenous O, and OH/H2O input [4]. We argue that benzene [5] and ammonia [6] are created in the upper atmosphere through complex chemical processes involving both neutral and ion chemistry. These species diffuse downward where they are at the origin of heavier aromatics and amines, respectively. Finally, we discuss the impact on hydrocarbon densities of recent theoretical calculations of the rate constants of association reactions [7]. [1] V. Vuitton, R. V. Yelle and V. G. Anicich, Astrophys. J., 647, L175 (2006). [2] V. Vuitton, R. V. Yelle and M. J. McEwan, Icarus, 191, 722 (2007). [3] V. Vuitton, P. Lavvas, R. V. Yelle, M. Galand, A. Wellbrock, G. R. Lewis, A. J. Coates and J.-E. Wahlund, Planet. Space Sci., 57, 1558 (2009). [4] S. M. Hörst, V. Vuitton, and R. V. Yelle, J. Geophys. Res., 113, E10006 (2008). [5] V. Vuitton, R. V. Yelle and J. Cui, J. Geophys. Res., 113, E05007 (2008). [6] R. V. Yelle, V. Vuitton, P. Lavvas, S. J. Klippenstein, M. A. Smith, S. M. Hörst and J. Cui, Faraday Discuss., 147, 31 (2010). [7] V. Vuitton, R. V. Yelle, S. J. Klippenstein and P. Lavvas, Astrophys. J., in press.

Vuitton, Veronique

2012-04-01

428

Chemical Soil Physics Phenomena for Chemical Sensing of Buried UXO  

SciTech Connect

Technology development efforts are under way to apply chemical sensors to discriminate inert ordnance and clutter from live munitions that remain a threat to reutilization of military ranges. However, the chemical signature is affected by multiple environmental phenomena that can enhance or reduce its presence and transport behavior, and can affect the distribution of the chemical signature in the environment. For example, the chemical can be present in the vapor, aqueous, and solid phases. The distribution of the chemical among these phases, including the spatial distribution, is key in designing appropriate detectors, e.g., gas, aqueous or solid phase sampling instruments. A fundamental understanding of the environmental conditions that affect the chemical signature is needed to describe the favorable and unfavorable conditions of a chemical detector based survey to minimize the consequences of a false negative. UXO source emission measurements are being made to estimate the chemical flux from a limited set of ordnance items. Phase partitioning analysis has been completed to show what the expected concentrations of chemical analytes would be fi-om total concentrations measured in the soil. The soil moisture content in the dry region has been shown to be critical in the attenuation of soil gas concentrations by increased sorption to soil particles. Numerical simulation tools have been adapted to include surface boundary conditions such as solar radiation, surface boundary layer (which is a function of wind speed), precipitation and evaporation, and plant cover/root density to allow transport modeling and evaluate long term processes. Results of this work will provide performance targets for sensor developers and support operational decisions regarding field deployments.

Phelan, James, M.; Webb, Stephen W.

1999-06-14

429

Method of forming a chemical composition  

DOEpatents

A method of forming a chemical composition such as a chemical hydride is described and which includes the steps of selecting a composition having chemical bonds and which is capable of forming a chemical hydride; providing a source of hydrogen; and exposing the selected composition to an amount of ionizing radiation to encourage the changing of the chemical bonds of the selected composition, and chemically reacting the selected composition with the source of hydrogen to facilitate the formation of a chemical hydride.

Bingham, Dennis N. (Idaho Falls, ID); Wilding, Bruce M. (Idaho Falls, ID); Klingler, Kerry M. (Idaho Falls, ID); Zollinger, William T. (Idaho Falls, ID); Wendt, Kraig M. (Idaho Falls, ID)

2007-10-09

430

THE JOURNAL OF CHEMICAL PHYSICS 135, 084103 (2011) How accurate are the nonlinear chemical Fokker-Planck and chemical  

E-print Network

THE JOURNAL OF CHEMICAL PHYSICS 135, 084103 (2011) How accurate are the nonlinear chemical Fokker-Planck and chemical Langevin equations? Ramon Grima,1,a) Philipp Thomas,1,2 and Arthur V. Straube2 1 School August 2011) The chemical Fokker-Planck equation and the corresponding chemical Langevin equation are com

Straube, Arthur V.

431

Chemical Mapping of Vesta  

NASA Technical Reports Server (NTRS)

Vesta s surface mineralogy and composition have been studied for decades via telescopic spectroscopy and laboratory analyses of the howardite, eucrite, and diogenite (HED) meteorites, which are thought to originate from Vesta. Visible and infrared reflectance measurements by Dawn have broadly confirmed the paradigm established by Earth-based work, strengthening the Vesta-HED connection. The Dawn mission has achieved a milestone by completing the first chemical measurements of a main-belt asteroid using nuclear spectroscopy. Dawn s Gamma Ray and Neutron Detector (GRaND) has globally mapped the composition of Vesta, including the portions of the northern hemisphere not illuminated by solar radiation. GRaND is sensitive to the composition of the bulk regolith to depths of several decimeters. Abundances and/or detection limits for specific elements and elemental ratios, such as H, Fe, Si, Fe/O, Fe/Si, and K, have been measured. Variations in the average atomic mass and neutron macroscopic absorption cross section have been characterized. The measurements constrain the relative proportions of HED whole-rock end-members, providing measurements of the pyroxene and plagioclase content of the regolith, thereby constraining the processes underlying Vesta s differentiation and crustal evolution. The spatial resolution of GRaND is sufficient to determine basin-average compositions of Veneneia and Rheasilvia, which may contain outcrops of Vesta s olivine-rich mantle. While the elemental composition of Vesta s regolith is similar to the meteorites, there are notable departures from HED whole-rock compositions. While these differences are not sufficient to topple the Vesta-HED paradigm, they provide insight into global-scale processes that have shaped Vesta s surface. Questions addressed by the analysis of GRaND data include: (i) Is Vesta the source of the Fe-rich mesosiderites? (ii) Are evolved, igneous lithologies present on Vesta s surface? (iii) What are the origins of exogenic materials found in Vesta s regolith? (iv) Is the vestan mantle exposed within the southern basins?

Prettyman, Thomas H.; Mittlefehldt, D. W.; Yamashita, N.; Lawrence, D. J.; Beck, A. W.; McSween, H. Y.; Feldman, W. C.; McCoy, T. J.; Titus, T. N.; Toplis, M. J.; Reedy, R. C.; Forni, O.; Mizzon, H.; Peplowski, P. N.; Raymond, C. A.; Russell, C. T.

2012-01-01

432

Chemical detection of buried landmines  

SciTech Connect

Of all the buried landmine identification technologies currently available, sensing the chemical signature from the explosive components found in landmines is the only technique that can classify non-explosive objects from the real threat. In the last two decades, advances in chemical detection methods has brought chemical sensing technology to the foreground as an emerging technological solution. In addition, advances have been made in the understanding of the fundamental transport processes that allow the chemical signature to migrate from the buried source to the ground surface. A systematic evaluation of the transport of the chemical signature from inside the mine into the soil environment, and through the soil to the ground surface is being explored to determine the constraints on the use of chemical sensing technology. This effort reports on the results of simulation modeling using a one-dimensional screening model to evaluate the impacts on the transport of the chemical signature by variation of some of the principal soil transport parameters.

Phelan, J.M.; Webb, S.W.

1998-03-01

433

Experimental characterization and chemical kinetics study of chemical looping combustion  

E-print Network

Chemical looping combustion (CLC) is one of the most promising technologies to achieve carbon capture in fossil fuel power generation plants. A novel rotary-bed reactor concept was proposed by Zhao et. al. [1] in 2013. It ...

Chen, Tianjiao, S.M. Massachusetts Institute of Technology

2014-01-01

434

Prioritization methodology for chemical replacement  

NASA Technical Reports Server (NTRS)

Since United States of America federal legislation has required ozone depleting chemicals (class 1 & 2) to be banned from production, The National Aeronautics and Space Administration (NASA) and industry have been required to find other chemicals and methods to replace these target chemicals. This project was initiated as a development of a prioritization methodology suitable for assessing and ranking existing processes for replacement 'urgency.' The methodology was produced in the form of a workbook (NASA Technical Paper 3421). The final workbook contains two tools, one for evaluation and one for prioritization. The two tools are interconnected in that they were developed from one central theme - chemical replacement due to imposed laws and regulations. This workbook provides matrices, detailed explanations of how to use them, and a detailed methodology for prioritization of replacement technology. The main objective is to provide a GUIDELINE to help direct the research for replacement technology. The approach for prioritization called for a system which would result in a numerical rating for the chemicals and processes being assessed. A Quality Function Deployment (QFD) technique was used in order to determine numerical values which would correspond to the concerns raised and their respective importance to the process. This workbook defines the approach and the application of the QFD matrix. This technique: (1) provides a standard database for technology that can be easily reviewed, and (2) provides a standard format for information when requesting resources for further research for chemical replacement technology. Originally, this workbook was to be used for Class 1 and Class 2 chemicals, but it was specifically designed to be flexible enough to be used for any chemical used in a process (if the chemical and/or process needs to be replaced). The methodology consists of comparison matrices (and the smaller comparison components) which allow replacement technology to be quantitatively compared in several categories, and a QFD matrix which allows process/chemical pairs to be rated against one another for importance (using consistent categories). Depending on the need for application, one can choose the part(s) needed or have the methodology completed in its entirety. For example, if a program needs to show the risk of changing a process/chemical one may choose to use part of Matrix A and Matrix C. If a chemical is being used, and the process must be changed; one might use the Process Concerns part of Matrix D for the existing process and all possible replacement processes. If an overall analysis of a program is needed, one may request the QFD to be completed.

Cruit, Wendy; Goldberg, Ben; Schutzenhofer, Scott

1995-01-01

435

Non-planar chemical preconcentrator  

DOEpatents

A non-planar chemical preconcentrator comprises a high-surface area, low mass, three-dimensional, flow-through sorption support structure that can be coated or packed with a sorptive material. The sorptive material can collect and concentrate a chemical analyte from a fluid stream and rapidly release it as a very narrow temporal plug for improved separations in a microanalytical system. The non-planar chemical preconcentrator retains most of the thermal and fabrication benefits of a planar preconcentrator, but has improved ruggedness and uptake, while reducing sorptive coating concerns and extending the range of collectible analytes.

Manginell, Ronald P. (Albuquerque, NM); Adkins, Douglas R. (Albuquerque, NM); Sokolowski, Sara S. (Albuquerque, NM); Lewis, Patrick R. (Albuquerque, NM)

2006-10-10

436

Chemical processing of lunar materials  

NASA Technical Reports Server (NTRS)

The paper highlights recent work on the general problem of processing lunar materials. The discussion covers lunar source materials, refined products, motivations for using lunar materials, and general considerations for a lunar or space processing plant. Attention is given to chemical processing through various techniques, including electrolysis of molten silicates, carbothermic/silicothermic reduction, carbo-chlorination process, NaOH basic-leach process, and HF acid-leach process. Several options for chemical processing of lunar materials are well within the state of the art of applied chemistry and chemical engineering to begin development based on the extensive knowledge of lunar materials.

Criswell, D. R.; Waldron, R. D.

1979-01-01

437

Development of a chemical vision spectrometer to detect chemical agents.  

SciTech Connect

This paper describes initial work in developing a no-moving-parts hyperspectral-imaging camera that provides both a thermal image and specific identification of chemical agents, even in the presence of nontoxic plumes. The camera uses enhanced stand-off chemical agent detector (ESCAD) technology based on a conventional thermal-imaging camera interfaced with an acousto-optical tunable filter (AOTF). The AOTF is programmed to allow selected spectral frequencies to reach the two dimensional array detector. These frequencies are combined to produce a spectrum that is used for identification. If a chemical agent is detected, pixels containing the agent-absorbing bands are given a colored hue to indicate the presence of the agent. In test runs, two thermal-imaging cameras were used with a specially designed vaporizer capable of controlled low-level (low ppm-m) dynamic chemical releases. The objective was to obtain baseline information about detection levels. Dynamic releases allowed for realistic detection scenarios such as low sky, grass, and wall structures, in addition to reproducible laboratory releases. Chemical releases consisted of dimethylmethylphosphonate (DMMP) and methanol. Initial results show that the combination of AOTF and thermal imaging will produce a chemical image of a plume that can be detected in the presence of interfering substances.

Demirgian, J.

1999-02-23

438

Daily Chemical Bulk Storage Inspection Form  

E-print Network

Daily Chemical Bulk Storage Inspection Form Chemical Bulk Storage Form Approved by: Paul Jennette, CVM Last revised by: Barbara English Revision date: 3/19/14 Daily_Chemical://sp.ehs.cornell.edu/env/bulk-material-storage/chemical-bulk- storage/Documents/Daily_Chemical

Pawlowski, Wojtek

439

Coatings with controlled porosity and chemical properties  

DOEpatents

Coatings and sensors having both steric and chemical selectivity. Controlled porosity provides the steric selectivity, whereas chemically tailored film properties, using controlled composition or modification by coupling agents, chemical species replacement, or chemical species within pores, provide the chemical selectivity. Single or multiple layers may be provided.

Frye, Gregory C. (Bernalillo County, NM); Brinker, C. Jeffrey (Albuquerque, NM); Doughty, Daniel H. (Albuquerque, NM); Bein, Thomas (Albuquerque, NM); Moller, Karin (Albuquerque, NM)

1996-01-01

440