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

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At least 217 records · Page 12
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DOE OSTI2011

HIGH FILL-OUT, EXTREME MASS RATIO OVERCONTACT BINARY SYSTEMS. X. THE NEWLY DISCOVERED BINARY XY LEONIS MINORIS

The newly discovered short-period close binary star, XY LMi, has been monitored photometrically since 2006. Its light curves are typical EW-type light curves and show complete eclipses with durations of about 80 minutes. Photometric solutions were determined through an analysis of the complete B, V, R, and I light curves using the 2003 version of the Wilson-Devinney code. XY LMi is a high fill-out, extreme mass ratio overcontact binary system with a mass ratio of q = 0.148 and a fill-out factor of f = 74.1%, suggesting that it is in the late evolutionary stage of late-type tidal-locked binary stars. As observed in other overcontact binary stars, evidence for the presence of two dark spots on both components is given. Based on our 19 epochs of eclipse times, we found that the orbital period of the overcontact binary is decreasing continuously at a rate of dP/dt = -1.67 x 10{sup -7} days yr{sup -1}, which may be caused by mass transfer from the primary to the secondary and/or angular momentum loss via magnetic stellar wind. The decrease of the orbital period may result in the increase of the fill-out, and finally, it will evolve into a single rapid-rotation star when the fluid surface reaches the outer critical Roche lobe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

PHYSICAL STRUCTURE OF THE PLANETARY NEBULA NGC 3242 FROM THE HOT BUBBLE TO THE NEBULAR ENVELOPE

One key feature of the interacting stellar winds model of the formation of planetary nebulae (PNe) is the presence of shock-heated stellar wind confined in the central cavities of PNe. This so-called hot bubble should be detectable in X-rays. Here we present XMM-Newton observations of NGC 3242, a multiple-shell PN whose shell morphology is consistent with the interacting stellar winds model. Diffuse X-ray emission is detected within its inner shell with a plasma temperature of {approx}2.35 x 10{sup 6} K and an intrinsic X-ray luminosity of {approx}2 x 10{sup 30} erg s{sup -1} at the adopted distance of 0.55 kpc. The observed X-ray temperature and luminosity are in agreement with 'ad hoc' predictions of models including heat conduction. However, the chemical abundances of the X-ray-emitting plasma seem to imply little evaporation of cold material into the hot bubble, whereas the thermal pressure of the hot gas is unlikely to drive the nebular expansion as it is lower than that of the inner shell rim. These inconsistencies are compounded by the apparent large filling factor of the hot gas within the central cavity of NGC 3242.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A TWO-DIMENSIONAL MAP OF THE COLOR EXCESS IN NGC 3603

Using archival Hubble Space Telescope/Wide Field Camera 3 images centered on the young HD 97950 star cluster in the giant H II region NGC 3603, we computed the pixel-to-pixel distribution of the color excess, E(B - V){sub g}, of the gas associated with this cluster from its H{alpha}/Pa{beta} flux ratio. At the assumed distance of 6.9 kpc, the resulting median color excess within 1 pc from the cluster center is E(B - V){sub g} = 1.51 {+-} 0.04 mag. Outside the cluster (at r > 1 pc), the color excess is seen to increase with cluster-centric distance toward both north and south, reaching a value of about 2.2 mag at r = 2 pc from the cluster center. The radial dependence of E(B - V){sub g} westward of the cluster appears rather flat at about 1.55 mag over the distance range 1.2 pc <r < 3 pc. In the eastern direction, E(B - V){sub g} steadily increases from 1.5 mag at r = 1 pc to 1.7 mag at r = 2 pc and stays nearly constant at 1.7 mag for 2 pc <r < 3 pc. The different radial profiles and the pixel-to-pixel variations of E(B - V){sub g} clearly indicate the presence of significant differential reddening across the 4.9 pc x 4.3 pc area centered on the HD 97950 star cluster. We interpret the variations of E(B - V){sub g} as the result of stellar radiation and stellar winds interacting with an inhomogeneous dusty local interstellar medium whose density varies spatially. From the E(B - V){sub g} values measured along the rims of the prominent pillars MM1 and MM2 in the southwest and southeast of the HD 97950 cluster, we estimate an H{sub 2} column density of log{sub 10}(N{sub H{sub 2}})=21.7 and extrapolate it to log{sub 10}(N{sub H{sub 2}})=23 in the pillars' interior. We find the pillars to be closer to us than the central ionizing cluster and suggest that star formation may be occurring in the pillar heads.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

COORDINATED ANALYSES OF PRESOLAR GRAINS IN THE ALLAN HILLS 77307 AND QUEEN ELIZABETH RANGE 99177 METEORITES

We report the identification of presolar silicates ({approx}177 ppm), presolar oxides ({approx}11 ppm), and one presolar SiO{sub 2} grain in the Allan Hills (ALHA) 77307 chondrite. Three grains having Si-isotopic compositions similar to SiC X and Z grains were also identified, though the mineral phases are unconfirmed. Similar abundances of presolar silicates ({approx}152 ppm) and oxides ({approx}8 ppm) were also uncovered in the primitive CR chondrite Queen Elizabeth Range (QUE) 99177, along with 13 presolar SiC grains and one presolar silicon nitride. The O-isotopic compositions of the presolar silicates and oxides indicate that most of the grains condensed in low-mass red giant and asymptotic giant branch stars. Interestingly, unlike presolar oxides, few presolar silicate grains have isotopic compositions pointing to low-metallicity, low-mass stars (Group 3). The {sup 18}O-rich (Group 4) silicates, along with the few Group 3 silicates that were identified, likely have origins in supernova outflows. This is supported by their O- and Si-isotopic compositions. Elemental compositions for 74 presolar silicate grains were determined by scanning Auger spectroscopy. Most of the grains have non-stoichiometric elemental compositions inconsistent with pyroxene or olivine, the phases commonly used to fit astronomical spectra, and have comparable Mg and Fe contents. Non-equilibrium condensation and/or secondary alteration could produce the high Fe contents. Transmission electron microscopic analysis of three silicate grains also reveals non-stoichiometric compositions, attributable to non-equilibrium or multistep condensation, and very fine scale elemental heterogeneity, possibly due to subsequent annealing. The mineralogies of presolar silicates identified in meteorites thus far seem to differ from those in interplanetary dust particles.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MODELING BROADBAND X-RAY ABSORPTION OF MASSIVE STAR WINDS

We present a method for computing the net transmission of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming that the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes that all observed X-rays are emitted without attenuation from above the radius of optical depth unity. Our model is implemented in XSPEC as a pre-calculated table that can be coupled to a user-defined table of the wavelength-dependent wind opacity. We provide a default wind opacity model that is more representative of real wind opacities than the commonly used neutral interstellar medium (ISM) tabulation. Preliminary modeling of Chandra grating data indicates that the X-ray hardness trend of OB stars with spectral subtype can largely be understood as a wind absorption effect.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

SPECTROSCOPIC ANALYSIS OF HOT, HYDROGEN-RICH WHITE DWARFS: THE PRESENCE OF METALS AND THE BALMER-LINE PROBLEM

We present an analysis of optical spectra for 29 DAO white dwarfs. First, we present our new up-to-date model atmosphere grids computed without the assumption of local thermodynamic equilibrium in which we have included carbon, nitrogen, and oxygen at solar abundances. We demonstrate that the addition of these metals in the model atmospheres is essential in overcoming the Balmer-line problem, which manifests itself as an inability to fit all the Balmer lines simultaneously with consistent atmospheric parameters. We then present the spectroscopic analysis of our sample of DAO white dwarfs for which we determine the effective temperature, surface gravity, and helium abundance. We also present 18 hot DA white dwarfs that also suffer from the Balmer-line problem. We analyze these stars with models analogous to those for the DAO white dwarfs save for the presence of helium. Systematic differences between our newly determined atmospheric parameters with respect to previous determinations are explored. Far-ultraviolet spectra from the FUSE archive are then examined to demonstrate that there exists a correlation between higher metallic abundances and instances of the Balmer-line problem. The implications of these findings for all hot, hydrogen-rich white dwarfs are discussed. Specifically, the possible evolutionary scenario for DAO white dwarfs is revised and post-extreme horizontal branch evolution is no longer needed to explain the evolution for the majority of the DAO stars. Finally, we discuss how the presence of metals might drive a weak stellar wind which in turn could explain the presence of helium in DAO white dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

SIMULATIONS OF WINDS OF WEAK-LINED T TAURI STARS. II. THE EFFECTS OF A TILTED MAGNETOSPHERE AND PLANETARY INTERACTIONS

Based on our previous work, we investigate here the effects on the wind and magnetospheric structures of weak-lined T Tauri stars due to a misalignment between the axis of rotation of the star and its magnetic dipole moment vector. In such a configuration, the system loses the axisymmetry presented in the aligned case, requiring a fully three-dimensional (3D) approach. We perform 3D numerical magnetohydrodynamic simulations of stellar winds and study the effects caused by different model parameters, namely the misalignment angle {theta}{sub t}, the stellar period of rotation, the plasma-{beta}, and the heating index {gamma}. Our simulations take into account the interplay between the wind and the stellar magnetic field during the time evolution. The system reaches a periodic behavior with the same rotational period of the star. We show that the magnetic field lines present an oscillatory pattern. Furthermore, we obtain that by increasing {theta}{sub t}, the wind velocity increases, especially in the case of strong magnetic field and relatively rapid stellar rotation. Our 3D, time-dependent wind models allow us to study the interaction of a magnetized wind with a magnetized extrasolar planet. Such interaction gives rise to reconnection, generating electrons that propagate along the planet's magnetic field lines and produce electron cyclotron radiation at radio wavelengths. The power released in the interaction depends on the planet's magnetic field intensity, its orbital radius, and on the stellar wind local characteristics. We find that a close-in Jupiter-like planet orbiting at 0.05 AU presents a radio power that is {approx}5 orders of magnitude larger than the one observed in Jupiter, which suggests that the stellar wind from a young star has the potential to generate strong planetary radio emission that could be detected in the near future with LOFAR. This radio power varies according to the phase of rotation of the star. For three selected simulations, we find a variation of the radio power of a factor 1.3-3.7, depending on {theta} {sub t}. Moreover, we extend the investigation done in Vidotto et al. and analyze whether winds from misaligned stellar magnetospheres could cause a significant effect on planetary migration. Compared to the aligned case, we show that the timescale {tau}{sub w} for an appreciable radial motion of the planet is shorter for larger misalignment angles. While for the aligned case {tau}{sub w} {approx_equal} 100 Myr, for a stellar magnetosphere tilted by {theta}{sub t} = 30{sup 0}, {tau} {sub w} ranges from {approx}40 to 70 Myr for a planet located at a radius of 0.05 AU. Further reduction on {tau}{sub w} might occur for even larger misalignment angles and/or different wind parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

INTERACTION OF A MAGNETIZED SHELL WITH AN AMBIENT MEDIUM: LIMITS ON IMPULSIVE MAGNETIC ACCELERATION

The interaction of relativistic magnetized ejecta with an ambient medium is studied for a range of structures and magnetization of the unshocked ejecta. We particularly focus on the effect of the ambient medium on the dynamics of an impulsive, high-sigma shell. It is found that for sufficiently high values of the initial magnetization {sigma}{sub 0} the evolution of the system is significantly altered by the ambient medium well before the shell reaches its coasting phase. The maximum Lorentz factor of the shell is limited to values well below {sigma}{sub 0}; for a shell of initial energy E = 10{sup 52} E{sub 52} erg and size r{sub 0} = 10{sup 12} T{sub 30} cm expelled into a medium having a uniform density n{sub i} , we obtain {Gamma}{sub max} {approx_equal} 180(E{sub 52}/T {sup 3}{sub 30} n{sub i}){sup 1/8} in the high-sigma limit. The reverse shock and any internal shocks that might form if the source is fluctuating are shown to be very weak. The restriction on the Lorentz factor is more severe for shells propagating in a stellar wind. Intermittent ejection of small sub-shells does not seem to help, as the shells merge while still highly magnetized. Lower sigma shells start decelerating after reaching the coasting phase and spreading away. The properties of the reverse shock then depend on the density profiles of the coasting shell and the ambient medium. For a self-similar cold shell the reverse shock becomes strong as it propagates inward, and the system eventually approaches the self-similar solution recently derived by Nakamura and Shigeyama.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

ON HIGHLY CLUMPED MAGNETIC WIND MODELS FOR COOL EVOLVED STARS

Recently, it has been proposed that the winds of non-pulsating and non-dusty K and M giants and supergiants may be driven by some form of magnetic pressure acting on highly clumped wind material. While many researchers believe that magnetic processes are responsible for cool evolved stellar winds, existing MHD and Alfven wave-driven wind models have magnetic fields that are essentially radial and tied to the photosphere. The clumped magnetic wind scenario is quite different in that the magnetic flux is also being carried away from the star with the wind. We test this clumped wind hypothesis by computing continuum radio fluxes from the {zeta} Aur semiempirical model of Baade et al., which is based on wind-scattered line profiles. The radio continuum opacity is proportional to the electron density squared, while the line scattering opacity is proportional to the gas density. This difference in proportionality provides a test for the presence of large clumping factors. We derive the radial distribution of clump factors (CFs) for {zeta} Aur by comparing the nonthermal pressures required to produce the semiempirical velocity distribution with the expected thermal pressures. The CFs are {approx}5 throughout the sub-sonic inner wind region and then decline outward. These implied clumping factors lead to excess radio emission at 2.0 cm, while at 6.2 cm it improves agreement with the smooth unclumped model. Smaller clumping factors of {approx}2 lead to better overall agreement but also increase the discrepancy at 2 cm. These results do not support the magnetic clumped wind hypothesis and instead suggest that inherent uncertainties in the underlying semiempirical model probably dominate uncertainties in predicted radio fluxes. However, new ultraviolet line and radio continuum observations are needed to test the new generations of inhomogeneous magnetohydrodynamic wind models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

CHANDRA HETG OBSERVATIONS OF THE COLLIDING STELLAR WIND SYSTEM WR 147

We present an extended analysis of deep Chandra HETG observations of the WR+OB binary system WR 147 that was resolved into a double X-ray source (Zhekov and Park). Our analysis of the profiles of strong emission lines shows that their centroids are blueshifted in the spectrum of the northern X-ray source. We find no suppressed forbidden line in the He-like triplets which indicates that the X-ray emitting region is not located near enough to the stars in the binary system to be significantly affected by their UV radiation. The most likely physical picture that emerges from the entire set of HETG data suggests that the northern X-ray source can be associated with the colliding stellar wind region in the wide WR+OB binary system, while the X-rays of its southern counterpart, the WN8 star, result from stellar wind shocking onto a close companion (a hypothesized third star in the system).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE MOUSE THAT ROARED: A SUPERFLARE FROM THE dMe FLARE STAR EV LAC DETECTED BY SWIFT AND KONUS-WIND

We report on a large stellar flare from the nearby dMe flare star EV Lac observed by the Swift and Konus-Wind satellites and the Liverpool Telescope. It is the first large stellar flare from a dMe flare star to result in a Swift trigger based on its hard X-ray intensity. Its peak f{sub X} from 0.3 to 100 keV of 5.3 x 10{sup -8} erg cm{sup -2} s{sup -1} is nearly 7000 times larger than the star's quiescent coronal flux, and the change in magnitude in the white filter is {>=}4.7. This flare also caused a transient increase in EV Lac's bolometric luminosity (L{sub bol}) during the early stages of the flare, with a peak estimated L{sub X}/L{sub bol} {approx} 3.1. We apply flare loop hydrodynamic modeling to the plasma parameter temporal changes to derive a loop semi-length of l/R{sub *} = 0.37 {+-} 0.07. The soft X-ray spectrum of the flare reveals evidence of iron K{alpha} emission at 6.4 keV. We model the K{alpha} emission as fluorescence from the hot flare source irradiating the photospheric iron, and derive loop heights of h/R{sub *} = 0.1, consistent within factors of a few with the heights inferred from hydrodynamic modeling. The K{alpha} emission feature shows variability on timescales of {approx}200 s which is difficult to interpret using the pure fluorescence hypothesis. We examine K{alpha} emission produced by collisional ionization from accelerated particles, and find parameter values for the spectrum of accelerated particles which can accommodate the increased amount of K{alpha} flux and the lack of observed nonthermal emission in the 20-50 keV spectral region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

VISIR/VLT AND VLA JOINT IMAGING ANALYSIS OF THE CIRCUMSTELLAR NEBULA AROUND IRAS 18576+0341

High spatial and sensitivity images of the Luminous Blue Variable IRAS 18576+0341 were obtained using the mid-infrared imager VISIR at the Very Large Telescope and the Very Large Array interferometer. The resulting mid-infrared continuum maps show a similar clumpy and approximately circular symmetric nebula, which contrasts sharply with the asymmetry that characterizes the ionized component of the envelope, as evidenced from the radio and [Ne II] line images obtained with comparable spatial resolution. In particular, there is excellent overall agreement between the 12.8 {mu}m map and the radio images, consistent with free-free emission from circumstellar ionized material surrounding a central stellar wind. The color temperature and optical depth maps obtained from mid-infrared images show only slight fluctuations, suggesting quite uniform dust characteristics over the dust shell. We explore various possibilities to understand the cause of the different morphology of the dusty and gaseous component of the circumstellar envelope which are compatible with the observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MASS TRANSFER, TRANSITING STREAM, AND MAGNETOPAUSE IN CLOSE-IN EXOPLANETARY SYSTEMS WITH APPLICATIONS TO WASP-12

We study mass transfer by Roche lobe overflow in close-in exoplanetary systems. The planet's atmospheric gas passes through the inner Lagrangian point and flows along a narrow stream, accelerating to 100-200 km s{sup -1} velocity before forming an accretion disk. We show that the cylinder-shaped accretion stream can have an area (projected in the plane of the sky) comparable to that of the planet and a significant optical depth to spectral line absorption. Such a 'transiting cylinder' may produce an earlier ingress of the planet transit, as suggested by recent Hubble Space Telescope observations of the WASP-12 system. The asymmetric disk produced by the accretion stream may also lead to time-dependent obscuration of the starlight and apparent earlier ingress. We also consider the interaction of the stellar wind with the planetary magnetosphere. Since the wind speed is subsonic/sub-Alfvenic and comparable to the orbital velocity of the planet, the head of the magnetopause lies eastward relative to the substellar line (the line joining the planet and the star). The gas around the magnetopause may, if sufficiently compressed, give rise to asymmetric ingress/egress during the planet transit, although more works are needed to evaluate this possibility.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

CHARACTERIZING THE THERMOSPHERE OF HD209458b WITH UV TRANSIT OBSERVATIONS

Transmission spectroscopy at UV wavelengths is a rich and largely unexplored source of information about the upper atmospheres of extrasolar planets. So far, UV transit observations have led to the detection of atomic hydrogen, oxygen, and ionized carbon in the upper atmosphere of HD209458b. The interpretation of these observations is controversial-it is not clear if the absorption arises from an escaping atmosphere interacting with the stellar radiation and stellar wind, or from the thermosphere inside the Roche lobe. In this paper, we introduce an empirical model that can be used to analyze UV transit depths of extrasolar planets. We use this model to interpret the transits of HD209458b in the H I 1216 and the O I 1304 triplet emission lines. The results indicate that the mean temperature of the thermosphere is T = 8000-11,000 K and that the H{sub 2}/H dissociation front is located at pressures between p = 0.1 and 1 {mu}bar, which correspond to a distance r{approx} 1.1 R{sub p} from the center of the planet. The upper boundary of the model thermosphere is located at r = 2.7-3 R{sub p} , above which the atmosphere is mostly ionized. We find that the H I transit depth in the wings of the H Ly{alpha} line reflects the optical depth of the thermosphere, but that the atmosphere also overflows the Roche lobe. By assuming a solar mixing ratio of oxygen, we obtain an O I transit depth that is statistically consistent with the observations. An O I transit depth comparable to the H I transit depth is possible if the atmosphere is undergoing fast hydrodynamic escape, the O/H ratio is supersolar, or if a significant quantity of neutral oxygen is found outside the Roche lobe. We find that the observations can be explained solely by absorption in the upper atmosphere and extended clouds of energetic neutral atoms or atoms strongly perturbed by radiation pressure are not required. Due to the large uncertainty in the data, repeated observations are necessary to better constrain the O I transit depths and thus the composition of the thermosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

WINDS FROM LUMINOUS LATE-TYPE STARS. II. BROADBAND FREQUENCY DISTRIBUTION OF ALFVEN WAVES

We present the numerical simulations of winds from evolved giant stars using a fully nonlinear, time-dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully nonlinear MHD wind simulations to include a broadband frequency spectrum of Alfven waves that drive winds from red giant stars. We calculated four Alfven wind models that cover the whole range of the Alfven wave frequency spectrum to characterize the role of freely propagated and reflected Alfven waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate that, unlike linear Alfven wave-driven wind models, a stellar wind model based on plasma acceleration due to broadband nonlinear Alfven waves can consistently reproduce the wide range of observed radial velocity profiles of the winds, their terminal velocities, and the observed mass-loss rates. Comparison of the calculated mass-loss rates with the empirically determined mass-loss rate for {alpha} Tau suggests an anisotropic and time-dependent nature of stellar winds from evolved giants.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

H{alpha} EMISSION VARIABILITY IN THE {gamma}-RAY BINARY LS I +61 303

LS I +61 303 is an exceptionally rare example of a high-mass X-ray binary that also exhibits MeV-TeV emission, making it one of only a handful of '{gamma}-ray binaries'. Here we present H{alpha} spectra that show strong variability during the 26.5 day orbital period and over decadal timescales. We detect evidence of a spiral density wave in the Be circumstellar disk over part of the orbit. The H{alpha} line profile also exhibits a dramatic emission burst shortly before apastron, observed as a redshifted shoulder in the line profile, as the compact source moves almost directly away from the observer. We investigate several possible origins for this red shoulder, including an accretion disk, mass-transfer stream, and a compact pulsar wind nebula that forms via a shock between the Be star's wind and the relativistic pulsar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE NATURE OF STARBURSTS. II. THE DURATION OF STARBURSTS IN DWARF GALAXIES

The starburst phenomenon can shape the evolution of the host galaxy and the surrounding intergalactic medium. The extent of the evolutionary impact is partly determined by the duration of the starburst, which has a direct correlation with both the amount of stellar feedback and the development of galactic winds, particularly for smaller mass dwarf systems. We measure the duration of starbursts in twenty nearby, ongoing, and 'fossil' starbursts in dwarf galaxies based on the recent star formation histories derived from resolved stellar population data obtained with the Hubble Space Telescope. Contrary to the shorter times of 3-10 Myr often cited, the starburst durations we measure range from 450to650 Myr in fifteen of the dwarf galaxies and up to 1.3 Gyr in four galaxies; these longer durations are comparable to or longer than the dynamical timescales for each system. The same feedback from massive stars that may quench the flickering star formation does not disrupt the overall burst event in our sample of galaxies. While five galaxies present fossil bursts, fifteen galaxies show ongoing bursts and thus the final durations may be longer than we report here for these systems. One galaxy shows a burst that has been ongoing for only 20 Myr; we are likely seeing the beginning of a burst event in this system. Using the duration of the starbursts, we calculate that the bursts deposited 10{sup 53.9}-10{sup 57.2} erg of energy into the interstellar medium through stellar winds and supernovae, and produced 3%-26% of the host galaxy's mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

A CRITICAL EXAMINATION OF THE X-WIND MODEL FOR CHONDRULE AND CALCIUM-RICH, ALUMINUM-RICH INCLUSION FORMATION AND RADIONUCLIDE PRODUCTION

Meteoritic data, especially regarding chondrules and calcium-rich, aluminum-rich inclusions (CAIs), and isotopic evidence for short-lived radionuclides (SLRs) in the solar nebula, potentially can constrain how planetary systems form. Interpretation of these data demands an astrophysical model, and the 'X-wind' model of Shu et al. and collaborators has been advanced to explain the origin of chondrules, CAIs, and SLRs. It posits that chondrules and CAIs were thermally processed <0.1 AU from the protostar, then flung by a magnetocentrifugal outflow to the 2-3 AU region to be incorporated into chondrites. Here we critically examine key assumptions and predictions of the X-wind model. We find a number of internal inconsistencies: theory and observation show no solid material exists at 0.1 AU; particles at 0.1 AU cannot escape being accreted into the star; particles at 0.1 AU will collide at speeds high enough to destroy them; thermal sputtering will prevent growth of particles; and launching of particles in magnetocentrifugal outflows is not modeled, and may not be possible. We also identify a number of incorrect predictions of the X-wind model: the oxygen fugacity where CAIs form is orders of magnitude too oxidizing, chondrule cooling rates are orders of magnitude lower than those experienced by barred olivine chondrules, chondrule-matrix complementarity is not predicted, and the SLRs are not produced in their observed proportions. We conclude that the X-wind model is not relevant to chondrule and CAI formation and SLR production. We discuss more plausible models for chondrule and CAI formation and SLR production.

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