ROSAT view of the ISM in the Large Magellanic Cloud

Science.gov (United States)

Chu, You-Hua

1996-01-01

Rosat observations of the Large Magellanic Cloud (LMC) show a large scale unbounded diffuse X-ray emission, as well as an enhanced emission within large shell structures. These observations allow the distribution of hot ionized medium in the LMC to be examined. Moreover, the hot interior of supernova shells and superbubbles, supernova remnants and the multi-phase structure of the interstellar medium (ISM) can be investigated.

Hydrodynamics and stellar winds an introduction

CERN Document Server

Maciel, Walter J

2014-01-01

Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

The SILCC (SImulating the LifeCycle of molecular Clouds) project - I. Chemical evolution of the supernova-driven ISM

Czech Academy of Sciences Publication Activity Database

Walch, S.; Girichidis, P.; Naab, T.; Gatto, A.; Glover, S.C.O.; Wünsch, Richard; Klessen, R.S.; Clark, P.C.; Peters, T.; Derigs, D.; Baczynski, C.

2015-01-01

Roč. 454, č. 1 (2015), s. 238-268 ISSN 0035-8711 R&D Projects: GA ČR GAP209/12/1795 Institutional support: RVO:67985815 Keywords : magnetodydrodynamics * ISM clouds * ISM evolution Subject RIV: BN - Astronomy , Celestial Mechanics, Astrophysics Impact factor: 4.952, year: 2015

The influence of Oort clouds on the mass and chemical balance of the interstellar medium

International Nuclear Information System (INIS)

Stern, S.A.; Shull, J.M.

1990-01-01

The contribution of stellar encounters and interstellar erosion to comet cloud mass injection to the ISM is calculated. It is shown that evaporative mass loss from passing stars and SNe results in an average Galactic mass injection rate of up to 10 to the -5th solar mass/yr if such clouds are frequent around solar-type stars. Cometary erosion by interstellar grains produces an injection rate of 10 to the -5th to 10 to the -4th solar mass/yr. An injection rate of 2 x 10 to the -5th solar mass/yr is calculated. Each of these rates could be increased by a factor of about 15 if the comet clouds contain a significant amount of smaller debris. It is concluded that the total mass injection rate of material to the ISM by comet clouds is small compared to other ISM mass injection sources. Comet cloud mass loss to the ISM could be responsible for a sizeable fraction of the metal and dust abundances of the ISM if Oort clouds are common. 50 refs

EVIDENCE FOR CLOUD-CLOUD COLLISION AND PARSEC-SCALE STELLAR FEEDBACK WITHIN THE L1641-N REGION

Energy Technology Data Exchange (ETDEWEB)

Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Miura, Tomoya; Nishi, Ryoichi [Department of Physics, Niigata University, 8050 Ikarashi-2, Niigata 950-2181 (Japan); Kitamura, Yoshimi; Akashi, Toshiya; Ikeda, Norio [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan); Shimajiri, Yoshito; Kawabe, Ryohei [Nobeyama Radio Observatory, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305 (Japan); Tsukagoshi, Takashi [Department of Astronomy, School of Science, University of Tokyo, Bunkyo, Tokyo 113-0033 (Japan); Momose, Munetake [Institute of Astrophysics and Planetary Sciences, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512 (Japan); Li Zhiyun, E-mail: fumitaka.nakamura@nao.ac.jp [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States)

2012-02-10

We present high spatial resolution {sup 12}CO (J = 1-0) images taken by the Nobeyama 45 m telescope toward a 48' Multiplication-Sign 48' area, including the L1641-N cluster. The effective spatial resolution of the maps is 21'', corresponding to 0.04 pc at a distance of 400 pc. A recent 1.1 mm dust continuum map reveals that the dense gas is concentrated in several thin filaments. We find that a few dust filaments are located at the parts where {sup 12}CO (J = 1-0) emission drops sharply. Furthermore, the filaments have two components with different velocities. The velocity difference between the two components is about 3 km s{sup -1}, corresponding to a Mach number of 10, significantly larger than the local turbulent velocity in the cloud. These facts imply that the collision of the two components (hereafter, the cloud-cloud collision) possibly contributed to the formation of these filaments. Since the two components appear to overlap toward the filaments on the plane of the sky, the collision may have occurred almost along the line of sight. Star formation in the L1641-N cluster was probably triggered by such a collision. We also find several parsec-scale CO shells whose centers are close to either the L1641-N cluster or the V 380 Ori cluster. We propose that these shells were created by multiple winds and/or outflows from cluster young stellar objects, i.e., 'protocluster winds'. One exceptional dust filament located at the western cloud edge lies along a shell; it is presumably part of the expanding shell. Both the cloud-cloud collision and protocluster winds are likely to influence the cloud structure and kinematics in this region.

Molecular Line Studies of Ballistic Stellar Interlopers Burrowing through Dense Interstellar Clouds

Science.gov (United States)

Rosen, Anna; Sahai, R.; Claussen, M.; Morris, M.

2010-01-01

When an intermediate-mass star speeds through a dense interstellar cloud at a high velocity, it can produce a cometary or bow shock structure due to the cloud being impacted by the intense stellar wind. This class of objects, recently discovered in an HST imaging survey, has been dubbed "ballistic stellar interlopers" (Sahai et al. 2009). Using the ARO's 12m and SMT 10m millimeter-wave dishes, we have obtained molecular line emission data towards 10 stellar interloper sources, in order to identify and characterize the dense clouds with which the interlopers are interacting. We have made small "on-the-fly" maps in the 12CO (J=2-1) and 13CO (J=2-1) lines for each cloud, and obtained spectra of high-density tracers such as N2H+ (J=3-2), HCO+ (J=3-2), CN(N=2-1), and SO(J=5-4), which probe a range of physical conditions in the interstellar clouds being impacted by the interlopers. The data have been reduced and analyzed, and preliminary estimates of the cloud temperatures (9-22 K) and 13CO optical depths (0.18-0.37) have been made. The maps, which show the emission as a function of radial velocity and spatial offset from the location of the interlopers, have helped us distinguish between the clouds interacting with the interlopers, and those which are unrelated but happen to lie along the line of sight. These data will now enable us to carry out high-resolution mm-wave interferometric observations of the interlopers in the future. This research was performed at JPL under the Minority Education Initiatives program. RS and MM were funded by a Long Term Space Astrophysics award from NASA for this work. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Special thanks goes to John Bieging and Bill Peters of the Arizona Radio Observatory.

The Contribution of Stellar Winds to Cosmic Ray Production

Science.gov (United States)

Seo, Jeongbhin; Kang, Hyesung; Ryu, Dongsu

2018-04-01

Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The wind mechanical energy of a massive star deposited to the interstellar medium can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity by all massive stars in the Galaxy is about Lw ≈ 1.1×1041 ergs, which is about 1/4 of the power of supernova explosions, LSN ≈ 4.8×1041 ergs. If we assume that ˜1-1% of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds are expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

AXISYMMETRIC SIMULATIONS OF HOT JUPITER–STELLAR WIND HYDRODYNAMIC INTERACTION

International Nuclear Information System (INIS)

Christie, Duncan; Arras, Phil; Li, Zhi-Yun

2016-01-01

Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point

AXISYMMETRIC SIMULATIONS OF HOT JUPITER–STELLAR WIND HYDRODYNAMIC INTERACTION

Energy Technology Data Exchange (ETDEWEB)

Christie, Duncan; Arras, Phil; Li, Zhi-Yun [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)

2016-03-20

Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point.

The Local ISM and its Interaction with the Winds of Nearby Late-type Stars

Science.gov (United States)

Wood, Brian E.; Linsky, Jeffrey L.

1998-01-01

We present new Goddard High-Resolution Spectrograph (GHRS) observations of the Ly-alpha and Mg II absorption lines seen toward the nearby stars 61 Cyg A and 40 Eri A. We use these data to measure interstellar properties along these lines of sight and to search for evidence of circumstellar hydrogen walls, which are produced by collisions between the stellar winds and the Local InterStellar Medium (LISM). We were able to model the Ly-alpha lines of both stars without hydrogen-wall absorption components, but for 61 Cyg A the fit required a stellar Ly-alpha, line profile with an improbably deep self-reversal, and for 40 Eri A the fit required a very low deuterium-to-hydrogen ratio that is inconsistent with previous GHRS measurements. Since these problems could be rectified simply by including stellar hydrogen-wall components with reasonable attributes, our preferred fits to the data include these components. We have explored several ways in which the hydrogen-wall properties measured here and in previous work can be used to study stellar winds and the LISM. We argue that the existence of a hydrogen wall around 40 Eri A and a low H I column density along that line of sight imply that either the interstellar density must decrease toward 40 Eri A or the hydrogen ionization fraction (chi) must increase. We find that hydrogen-wall temperatures are larger for stars with faster velocities through the LISM. The observed temperature-velocity relation is consistent with the predictions of hydromagnetic shock jump conditions. More precise comparison of the data and the jump conditions suggests crude upper limits for both chi and the ratio of magnetic to thermal pressure in the LISM (alpha): chi less than 0.6 and alpha less than 2. The latter upper limit corresponds to a limit on the LISM magnetic field of B less than 5 micro G. These results imply that the plasma Mach number of the interstellar wind flowing into the heliosphere is M(sub A) greater than 1.3, which indicates that

Stellar Wind Retention and Expulsion in Massive Star Clusters

Science.gov (United States)

Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

2018-05-01

Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

CubeSat Constellation Cloud Winds(C3Winds) A New Wind Observing System to Study Mesoscale Cloud Dynamics and Processes

Science.gov (United States)

Wu, D. L.; Kelly, M.A.; Yee, J.-H.; Boldt, J.; Demajistre, R.; Reynolds, E. L.; Tripoli, G. J.; Oman, L. D.; Prive, N.; Heidinger, A. K.;

Cosmic-ray-modified stellar winds. III. A numerical iterative approach

International Nuclear Information System (INIS)

Ko, C.M.; Jokipii, J.R.; Webb, G.M.

1988-01-01

A numerical iterative method is used to determine the modification of a stellar wind flow with a termination shock by the galactic cosmic rays. A two-fluid model consisting of cosmic rays and thermal stellar wind gas is used in which the cosmic rays are coupled to the background flow via scattering with magnetohydrodynamic waves or irregularities. A polytropic model is used to describe the thermal stellar wind gas, and the cosmic-rays are modeled as a hot, low-density gas with negligible mass flux. The positive galactic cosmic-ray pressure gradient serves to brake the outflowing stellar wind gas, and the cosmic rays modify the location of the critical point of the wind, the location of the shock, the wind fluid velocity profile, and the thermal gas entropy constants on both sides of the shock. The transfer of energy to the cosmic rays results in an outward radial flux of cosmic-ray energy. 21 references

AN EXPLORATION OF THE STATISTICAL SIGNATURES OF STELLAR FEEDBACK

Energy Technology Data Exchange (ETDEWEB)

Boyden, Ryan D.; Offner, Stella S. R. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Koch, Eric W.; Rosolowsky, Erik W., E-mail: soffner@astro.umass.edu [Department of Physics, University of Alberta, Edmonton, T6G 2E1 (Canada)

2016-12-20

All molecular clouds are observed to be turbulent, but the origin, means of sustenance, and evolution of the turbulence remain debated. One possibility is that stellar feedback injects enough energy into the cloud to drive observed motions on parsec scales. Recent numerical studies of molecular clouds have found that feedback from stars, such as protostellar outflows and winds, injects energy and impacts turbulence. We expand upon these studies by analyzing magnetohydrodynamic simulations of molecular clouds, including stellar winds, with a range of stellar mass-loss rates and magnetic field strengths. We generate synthetic {sup 12}CO(1–0) maps assuming that the simulations are at the distance of the nearby Perseus molecular cloud. By comparing the outputs from different initial conditions and evolutionary times, we identify differences in the synthetic observations and characterize these using common astrostatistics. We quantify the different statistical responses using a variety of metrics proposed in the literature. We find that multiple astrostatistics, including the principal component analysis, the spectral correlation function, and the velocity coordinate spectrum (VCS), are sensitive to changes in stellar mass-loss rates and/or time evolution. A few statistics, including the Cramer statistic and VCS, are sensitive to the magnetic field strength. These findings demonstrate that stellar feedback influences molecular cloud turbulence and can be identified and quantified observationally using such statistics.

A comparison of shock-cloud and wind-cloud interactions: effect of increased cloud density contrast on cloud evolution

Science.gov (United States)

Goldsmith, K. J. A.; Pittard, J. M.

2018-05-01

The similarities, or otherwise, of a shock or wind interacting with a cloud of density contrast χ = 10 were explored in a previous paper. Here, we investigate such interactions with clouds of higher density contrast. We compare the adiabatic hydrodynamic interaction of a Mach 10 shock with a spherical cloud of χ = 103 with that of a cloud embedded in a wind with identical parameters to the post-shock flow. We find that initially there are only minor morphological differences between the shock-cloud and wind-cloud interactions, compared to when χ = 10. However, once the transmitted shock exits the cloud, the development of a turbulent wake and fragmentation of the cloud differs between the two simulations. On increasing the wind Mach number, we note the development of a thin, smooth tail of cloud material, which is then disrupted by the fragmentation of the cloud core and subsequent `mass-loading' of the flow. We find that the normalized cloud mixing time (tmix) is shorter at higher χ. However, a strong Mach number dependence on tmix and the normalized cloud drag time, t_{drag}^' }, is not observed. Mach-number-dependent values of tmix and t_{drag}^' } from comparable shock-cloud interactions converge towards the Mach-number-independent time-scales of the wind-cloud simulations. We find that high χ clouds can be accelerated up to 80-90 per cent of the wind velocity and travel large distances before being significantly mixed. However, complete mixing is not achieved in our simulations and at late times the flow remains perturbed.

Habitable zones exposed: astrosphere collapse frequency as a function of stellar mass.

Science.gov (United States)

Smith, David S; Scalo, John M

2009-09-01

Stellar astrospheres--the plasma cocoons carved out of the interstellar medium by stellar winds--are one of several buffers that partially screen planetary atmospheres and surfaces from high-energy radiation. Screening by astrospheres is continually influenced by the passage of stars through the fluctuating density field of the interstellar medium (ISM). The most extreme events occur inside dense interstellar clouds, where the increased pressure may compress an astrosphere to a size smaller than the liquid-water habitable-zone distance. Habitable planets then enjoy no astrospheric buffering from exposure to the full flux of galactic cosmic rays and interstellar dust and gas, a situation we call "descreening" or "astrospheric collapse." Under such conditions the ionization fraction in the atmosphere and contribution to radiation damage of putative coding organisms at the surface would increase significantly, and a series of papers have suggested a variety of global responses to descreening. These possibilities motivate a more careful calculation of the frequency of descreening events. Using a ram-pressure balance model, we compute the size of the astrosphere in the apex direction as a function of parent-star mass and velocity and ambient interstellar density, emphasizing the importance of gravitational focusing of the interstellar flow. The interstellar densities required to descreen planets in the habitable zone of solar- and subsolar-mass stars are found to be about 600(M/M[middle dot in circle])(-2) cm(-3) for the Sun's velocity relative to the local ISM. Such clouds are rare and small, indicating that descreening encounters are rare. We use statistics from two independent catalogues of dense interstellar clouds to derive a dependence of descreening frequency on the parent-star mass that decreases strongly with decreasing stellar mass, due to the weaker gravitational focusing and smaller habitable-zone distances for lower-mass stars. We estimate an uncertain

Cosmic-ray acceleration at stellar wind terminal shocks

International Nuclear Information System (INIS)

Webb, G.M.; Forman, M.A.; Axford, W.I.

1985-01-01

Steady-state, spherically symmetric, analytic solutions of the cosmic-ray transport equations, applicable to the problem of acceleration of cosmic rays at the terminal shock to a stellar wind, are studied. The spectra, gradients, and flow patterns of particle modulated and accelerated by the stellar wind and shock are investigated by means of monoenergetic-source solutions at finite radius, as well as solutions with monoenergetic and power-law Galactic spectra. The solutions obtained apply in the test particle limit in which the cosmic rays do not modify the background flow. The solutions show a characteristic power-law momentum spectrum for accelerated particles and a more complex spectrum of particles that are decelerated in the stellar wind. The power-law spectral index depends on the compression ratio of the shock and on the modulation parameters characterizing propagation conditions in the upstream and downstream regions of the shock. Solutions of the transport equations for the total density N (integrated over all energies), pressure P/sub c/, and energy flux F/sub c/ of Galactic cosmic rays interacting with a stellar wind and shock are also studied. The density N(r) increases with radius r, and for strong shocks with large enough modulation parameters, there may be a significant enhancement of the pressure of weakly relativistic particles near the shock compared to the cosmic-ray background pressure P/sub infinity/. The emergent energy flux at infinity is of the order of 4π R 2 V 1 P/sub infinity/ (V 1 is wind velocity upstream of the shock, R is shock radius)

The dependence of stellar properties on initial cloud density

Science.gov (United States)

Jones, Michael O.; Bate, Matthew R.

2018-05-01

We investigate the dependence of stellar properties on the initial mean density of the molecular cloud in which stellar clusters form using radiation hydrodynamical simulations that resolve the opacity limit for fragmentation. We have simulated the formation of three star clusters from the gravitational collapse of molecular clouds whose densities vary by a factor of a hundred. As with previous calculations including radiative feedback, we find that the dependence of the characteristic stellar mass, Mc, on the initial mean density of the cloud, ρ, is weaker than the dependence of the thermal Jeans mass. However, unlike previous calculations, which found no statistically significant variation in the median mass with density, we find a weak dependence approximately of the form Mc∝ρ-1/5. The distributions of properties of multiple systems do not vary significantly between the calculations. We compare our results to the result of observational surveys of star-forming regions, and suggest that the similarities between the properties of our lowest density calculation and the nearby Taurus-Auriga region indicate that the apparent excess of solar-type stars observed may be due to the region's low density.

Stellar Winds and Dust Avalanches in the AU Mic Debris Disk

Energy Technology Data Exchange (ETDEWEB)

Chiang, Eugene; Fung, Jeffrey, E-mail: echiang@astro.berkeley.edu, E-mail: jeffrey.fung@berkeley.edu [Department of Astronomy, University of California at Berkeley, Campbell Hall, Berkeley, CA 94720-3411 (United States)

2017-10-10

We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.

Polarized bow shocks reveal features of the winds and environments of massive stars

Science.gov (United States)

Shrestha, Manisha

2018-01-01

Massive stars strongly affect their surroundings through their energetic stellar winds and deaths as supernovae. The bow shock structures created by fast-moving massive stars contain important information about the winds and ultimate fates of these stars as well as their local interstellar medium (ISM). Since bow shocks are aspherical, the light scattered in the dense shock material becomes polarized. Analyzing this polarization reveals details of the bow shock geometry as well as the composition, velocity, density, and albedo of the scattering material. With these quantities, we can constrain the properties of the stellar wind and thus the evolutionary state of the star, as well as the dust composition of the local ISM.In my dissertation research, I use a Monte Carlo radiative transfer code that I optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (SWBS) illuminated by a central star and by shock emission. I derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (SPH) models. In the case of the analytical SWBS and electron scattering, I find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. This is due to the geometrical properties of the bow shock combined with multiple scattering effects. For dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, and viewing angle. The behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models for the local ISM. In the case of SPH density structures, I investigate how the polarization changes as a function of the evolutionary phase of the SWBS. My dissertation compares these simulations with polarization data from Betelgeuse and other massive stars with bow shocks. I discuss the

Stellar and wind parameters of massive stars from spectral analysis

Science.gov (United States)

Araya, Ignacio; Curé, Michel

2017-11-01

The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

Gas expulsion vs gas retention in young stellar clusters II: effects of cooling and mass segregation

Science.gov (United States)

Silich, Sergiy; Tenorio-Tagle, Guillermo

2018-05-01

Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds and supernova explosions, or that the enrichment of the residual gas and the formation of the second stellar generation occur so rapidly, that the negative stellar feedback is not significant. Here we continue our study of the early development of star clusters in the extreme environments and discuss the restrictions that strong radiative cooling and stellar mass segregation provide on the gas expulsion from dense star-forming clouds. A large range of physical initial conditions in star-forming clouds which include the star-forming cloud mass, compactness, gas metallicity, star formation efficiency and effects of massive stars segregation are discussed. It is shown that in sufficiently massive and compact clusters hot shocked winds around individual massive stars may cool before merging with their neighbors. This dramatically reduces the negative stellar feedback, prevents the development of the global star cluster wind and expulsion of the residual and the processed matter into the ambient interstellar medium. The critical lines which separate the gas expulsion and the gas retention regimes are obtained.

Disintegration of Dust Aggregates in Interstellar Shocks and the Lifetime of Dust Grains in the ISM

Science.gov (United States)

Dominik, C.; Jones, A. P.; Tielens, A. G. G. M.; Cuzzi, Jeff (Technical Monitor)

1994-01-01

Interstellar grains are destroyed by shock waves moving through the ISM. In fact, the destruction of grains may be so effective that it is difficult to explain the observed abundance of dust in the ISM as a steady state between input of grains from stellar sources and destruction of grains in shocks. This is especially a problem for the larger grains. Therefore, the dust grains must be protected in some way. Jones et al. have already considered coatings and the increased post-shock drag effects for low density grains. In molecular clouds and dense clouds, coagulation of grains is an important process, and the largest interstellar grains may indeed be aggregates of smaller grains rather than homogeneous particles. This may provide a means to protect the larger grains, in that, in moderate velocity grain-grain collisions in a shock the aggregates may disintegrate rather than be vaporized. The released small particles are more resilient to shock destruction (except in fast shocks) and may reform larger grains later, recovering the observed size distribution. We have developed a model for the binding forces in grain aggregates and apply this model to the collisions between an aggregate and fast small grains. We discuss the results in the light of statistical collision probabilities and grain life times.

On unravelling mechanism of interplay between cloud and large scale circulation: a grey area in climate science

Science.gov (United States)

De, S.; Agarwal, N. K.; Hazra, Anupam; Chaudhari, Hemantkumar S.; Sahai, A. K.

2018-04-01

The interaction between cloud and large scale circulation is much less explored area in climate science. Unfolding the mechanism of coupling between these two parameters is imperative for improved simulation of Indian summer monsoon (ISM) and to reduce imprecision in climate sensitivity of global climate model. This work has made an effort to explore this mechanism with CFSv2 climate model experiments whose cloud has been modified by changing the critical relative humidity (CRH) profile of model during ISM. Study reveals that the variable CRH in CFSv2 has improved the nonlinear interactions between high and low frequency oscillations in wind field (revealed as internal dynamics of monsoon) and modulates realistically the spatial distribution of interactions over Indian landmass during the contrasting monsoon season compared to the existing CRH profile of CFSv2. The lower tropospheric wind error energy in the variable CRH simulation of CFSv2 appears to be minimum due to the reduced nonlinear convergence of error to the planetary scale range from long and synoptic scales (another facet of internal dynamics) compared to as observed from other CRH experiments in normal and deficient monsoons. Hence, the interplay between cloud and large scale circulation through CRH may be manifested as a change in internal dynamics of ISM revealed from scale interactive quasi-linear and nonlinear kinetic energy exchanges in frequency as well as in wavenumber domain during the monsoon period that eventually modify the internal variance of CFSv2 model. Conversely, the reduced wind bias and proper modulation of spatial distribution of scale interaction between the synoptic and low frequency oscillations improve the eastward and northward extent of water vapour flux over Indian landmass that in turn give feedback to the realistic simulation of cloud condensates attributing improved ISM rainfall in CFSv2.

Variable accretion of stellar winds onto Sgr A*

Science.gov (United States)

Cuadra, Jorge; Nayakshin, Sergei

2006-12-01

We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

Variable accretion of stellar winds onto Sgr A*

Energy Technology Data Exchange (ETDEWEB)

Cuadra, Jorge [Max-Planck-Institut fuer Astrophysik, D-85741 Garching (Germany); Nayakshin, Sergei [Department of Physics and Astronomy, University of Leicester, LEI 7RH (United Kingdom)

2006-12-15

We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

Variable accretion of stellar winds onto Sgr A*

International Nuclear Information System (INIS)

Cuadra, Jorge; Nayakshin, Sergei

2006-01-01

We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre

THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

Energy Technology Data Exchange (ETDEWEB)

Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

2017-01-20

We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

2D hydrodynamic simulations of super star cluster winds in a bimodal regime

Czech Academy of Sciences Publication Activity Database

Wünsch, Richard; Palouš, Jan; Tenorio-Tagle, G.; Silich, S.

2009-01-01

Roč. 324, 2-4 (2009), s. 219-223 ISSN 0004-640X R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : stellar winds * star clusters * dynamics of ISM Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.404, year: 2009

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

Energy Technology Data Exchange (ETDEWEB)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

2015-03-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

International Nuclear Information System (INIS)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

2015-01-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear

Cosmic ray-modified stellar winds. I. Solution topologies and singularities

International Nuclear Information System (INIS)

Ko, C.M.; Webb, G.M.

1987-01-01

In the present two-fluid hydrodynamical model for stellar wind flow modification due to its interaction with Galactic cosmic rays, these rays are coupled to the stellar wind by either hydromagnetic wave scattering or background flow irregularity propagation. The background flow is modified by the cosmic rays via their pressure gradient. The system of equations used possesses a line of singularities in (r, u, P/sub c/)-space, or a two-dimensional hypersurface of singularities in (r, u, P/sub c/, dP/sub c/dr)-space, where r, u, and P/sub c/ are respectively the radial distance from the star, the radial wind flow speed, and the cosmic ray pressure. The singular points may be nodes, foci, or saddle points. 64 references

Colliding Stellar Winds Structure and X-ray Emission

Science.gov (United States)

Pittard, J. M.; Dawson, B.

2018-04-01

We investigate the structure and X-ray emission from the colliding stellar winds in massive star binaries. We find that the opening angle of the contact discontinuity (CD) is overestimated by several formulae in the literature at very small values of the wind momentum ratio, η. We find also that the shocks in the primary (dominant) and secondary winds flare by ≈20° compared to the CD, and that the entire secondary wind is shocked when η ≲ 0.02. Analytical expressions for the opening angles of the shocks, and the fraction of each wind that is shocked, are provided. We find that the X-ray luminosity Lx∝η, and that the spectrum softens slightly as η decreases.

Dynamical instabilities in magnetohydrodynamic wind-cloud interactions

Science.gov (United States)

Banda-Barragan, Wladimir Eduardo; Parkin, Elliot Ross; Crocker, Roland M.; Federrath, Christoph; Bicknell, Geoffrey Vincent

2015-08-01

We report the results from a comprehensive numerical study that investigates the role of dynamical instabilities in magnetohydrodynamic interactions between winds and spherical clouds in the interstellar medium. The growth of Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) instabilities at interfaces between wind and cloud material is responsible for the disruption of clouds and the formation of filamentary tails. We show how different strengths and orientations of the initial magnetic field affect the development of unstable modes and the ultimate morphology of these filaments. In the weak field limit, for example, KH instabilities developing at the flanks of clouds are dominant, whilst they are suppressed when stronger fields are considered. On the other hand, perturbations that originate RT instabilities at the leading edge of clouds are enhanced when fields are locally stronger. The orientation of the field lines also plays an important role in the structure of filaments. Magnetic ropes are key features of systems in which fields are aligned with the wind velocity, whilst current sheets are favoured when the initial field is preferentially transverse to the wind velocity. We compare our findings with analytical predictions obtained from the linear theory of hydromagnetic stability and provide a classification of filamentary tails based on their morphology.

Local ISM 3D Distribution and Soft X-ray Background Inferences for Nearby Hot Gas

Science.gov (United States)

Puspitarini, L.; Lallement, R.; Snowden, Steven L.; Vergely, J.-L.; Snowden, S.

2014-01-01

Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and are filled by hot gas. To demonstrate this, and to derive a clearer picture of the local ISM, we compare our recent 3D IS dust distribution maps to the ROSAT diffuse Xray background maps after removal of heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred mean pressure in the local cavities is found to be approx.9,400/cu cm K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in those regions, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas and as a consequence a reduction of the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy

CloudSat observations of cloud-type distribution over the Indian summer monsoon region

Directory of Open Access Journals (Sweden)

K. V. Subrahmanyam

2013-07-01

Full Text Available The three-dimensional distribution of various cloud types over the Indian summer monsoon (ISM region using five years (2006–2010 of CloudSat observations during June-July-August-September months is discussed for the first time. As the radiative properties, latent heat released and microphysical properties of clouds differ largely depending on the cloud type, it becomes important to know what types of clouds occur over which region. In this regard, the present analysis establishes the three-dimensional distribution of frequency of occurrence of stratus (St, stratocumulus (Sc, nimbostratus (Ns, cumulus (Cu, altocumulus (Ac, altostratus (As, cirrus (Ci and deep convective (DC clouds over the ISM region. The results show that the various cloud types preferentially occur over some regions of the ISM, which are consistent during all the years of observations. It is found that the DC clouds frequently occur over northeast of Bay of Bengal (BoB, Ci clouds over a wide region of south BoB–Indian peninsula–equatorial Indian Ocean, and Sc clouds over the north Arabian Sea. Ac clouds preferentially occur over land, and a large amount of As clouds are found over BoB. The occurrence of both St and Ns clouds over the study region is much lower than all other cloud types.The interannual variability of all these clouds including their vertical distribution is discussed. It is envisaged that the present study opens up possibilities to quantify the feedback of individual cloud type in the maintenance of the ISM through radiative forcing and latent heat release.

Weaving the history of the solar wind with magnetic field lines

Science.gov (United States)

Alvarado Gomez, Julian

2017-08-01

Despite its fundamental role for the evolution of the solar system, our observational knowledge of the wind properties of the young Sun comes from a single stellar observation. This unexpected fact for a field such as astrophysics arises from the difficulty of detecting Sun-like stellar winds. Their detection relies on the appearance of an astrospheric signature (from the stellar wind-ISM interaction region), visible only with the aid of high-resolution HST Lyman-alpha spectra. However, observations and modelling of the present day Sun have revealed that magnetic fields constitute the main driver of the solar wind, providing guidance on how such winds would look like back in time. In this context we propose observations of four young Sun-like stars in order to detect their astrospheres and characterise their stellar winds. For all these objects we have recovered surface magnetic field maps using the technique of Zeeman Doppler Imaging, and developed detailed wind models based on these observed field distributions. Even a single detection would represent a major step forward for our understanding of the history of the solar wind, and the outflows in more active stars. Mass loss rate estimates from HST will be confronted with predictions from realistic models of the corona/stellar wind. In one of our objects the comparison would allow us to quantify the wind variability induced by the magnetic cycle of a star, other than the Sun, for the first time. Three of our targets are planet hosts, thus the HST spectra would also provide key information on the high-energy environment of these systems, guaranteeing their legacy value for the growing field of exoplanet characterisation.

THE MAGELLANIC INTER-CLOUD PROJECT (MAGIC). I. EVIDENCE FOR INTERMEDIATE-AGE STELLAR POPULATIONS IN BETWEEN THE MAGELLANIC CLOUDS

Energy Technology Data Exchange (ETDEWEB)

Noeel, N. E. D.; Read, J. I. [ETH Zuerich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, CH-8093 Zuerich (Switzerland); Conn, B. C.; Rix, H.-W. [Max Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Carrera, R. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, E-38200, La Laguna, Tenerife (Spain); Dolphin, A., E-mail: noelia@phys.ethz.ch [Raytheon Company, P.O. Box 11337, Tucson, AZ 85734-1337 (United States)

2013-05-10

The origin of the gas in between the Magellanic Clouds (MCs)-known as the ''Magellanic Bridge'' (MB)-is puzzling. Numerical simulations suggest that the MB formed from tidally stripped gas and stars in a recent interaction between the MCs. However, the apparent lack of stripped intermediate- or old-age stars associated with the MB is at odds with this picture. In this paper, we present the first results from the MAGellanic Inter-Cloud program (MAGIC) aimed at probing the stellar populations in the inter-Cloud region. We present observations of the stellar populations in two large fields located in between the Large and Small Magellanic Clouds (LMC/SMC), secured using the WFI camera on the 2.2 m telescope in La Silla. Using a synthetic color-magnitude diagram technique, we present the first quantitative evidence for the presence of intermediate-age and old stars in the inter-Cloud region. The intermediate-age stars-which make up {approx}28% of all stars in the region-are not present in fields at a similar distance from the SMC in a direction pointing away from the LMC. This provides potential evidence that these intermediate-age stars could have been tidally stripped from the SMC. However, spectroscopic studies will be needed to confirm or rule out the tidal origin for the inter-Cloud gas and stars.

The X CO Conversion Factor from Galactic Multiphase ISM Simulations

Science.gov (United States)

Gong, Munan; Ostriker, Eve C.; Kim, Chang-Goo

2018-05-01

{CO}(J=1{--}0) line emission is a widely used observational tracer of molecular gas, rendering essential the X CO factor, which is applied to convert CO luminosity to {{{H}}}2 mass. We use numerical simulations to study how X CO depends on numerical resolution, non-steady-state chemistry, physical environment, and observational beam size. Our study employs 3D magnetohydrodynamics (MHD) simulations of galactic disks with solar neighborhood conditions, where star formation and the three-phase interstellar medium (ISM) are self-consistently regulated by gravity and stellar feedback. Synthetic CO maps are obtained by postprocessing the MHD simulations with chemistry and radiation transfer. We find that CO is only an approximate tracer of {{{H}}}2. On parsec scales, W CO is more fundamentally a measure of mass-weighted volume density, rather than {{{H}}}2 column density. Nevertheless, =(0.7{\\textstyle {--}}1.0)× {10}20 {{{cm}}}-2 {{{K}}}-1 {{{km}}}-1 {{s}}, which is consistent with observations and insensitive to the evolutionary ISM state or radiation field strength if steady-state chemistry is assumed. Due to non-steady-state chemistry, younger molecular clouds have slightly lower and flatter profiles of X CO versus extinction than older ones. The {CO}-dark {{{H}}}2 fraction is 26%–79%, anticorrelated with the average extinction. As the observational beam size increases from 1 to 100 pc, increases by a factor of ∼2. Under solar neighborhood conditions, in molecular clouds is converged at a numerical resolution of 2 pc. However, the total CO abundance and luminosity are not converged even at the numerical resolution of 1 pc. Our simulations successfully reproduce the observed variations of X CO on parsec scales, as well as the dependence of X CO on extinction and the CO excitation temperature.

A COMPREHENSIVE SEARCH FOR STELLAR BOWSHOCK NEBULAE IN THE MILKY WAY: A CATALOG OF 709 MID-INFRARED SELECTED CANDIDATES

Energy Technology Data Exchange (ETDEWEB)

Kobulnicky, Henry A.; Chick, William T.; Schurhammer, Danielle P.; Andrews, Julian E.; Munari, Stephan A.; Olivier, Grace M.; Sorber, Rebecca L.; Wernke, Heather N.; Dale, Daniel A. [Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY 82070 (United States); Povich, Matthew S.; Dixon, Don M. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States)

2016-12-01

We identify 709 arc-shaped mid-infrared nebula in 24 μ m Spitzer Space Telescope or 22 μ m Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks powered by early-type stars. About 20% are visible at 8 μ m or at shorter mid-infrared wavelengths. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near the Galactic mid-plane, with an angular scale height of ∼0.°6. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate “runaway” stars potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology—kinematic evidence that many of these are “runaway” stars with large peculiar motions responsible for the bowshock signature. We discuss a population of “in situ” bowshocks (∼103 objects) that face giant H ii regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify ∼58 objects that face 8 μ m bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (PEF) from an eroding molecular cloud interface (i.e., “PEF bowshocks”). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as H ii regions are responsible for producing some bowshock nebulae. However, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences.

Cosmic ray acceleration by stellar wind. Simulation for heliosphere

International Nuclear Information System (INIS)

Petukhov, S.I.; Turpanov, A.A.; Nikolaev, V.S.

1985-01-01

The solar wind deceleration by the interstellar medium may result in the existence of the solar wind terminal shock. In this case a certain fraction of thermal particles after being heated at the shock would obtain enough energy to be injected to the regular acceleration process. An analytical solution for the spectrum in the frame of a simplified model that includes particle acceleration at the shock front and adiabatic cooling inside the stellar wind cavity has been derived. It is shown that the acceleration of the solar wind particles at the solar wind terminal shock is capable of providing the total flux, spectrum and radial gradients of the low-energy protons close to one observed in the interplanetary space

Clouds blown by the solar wind

International Nuclear Information System (INIS)

Voiculescu, M; Condurache-Bota, S; Usoskin, I

2013-01-01

In this letter we investigate possible relationships between the cloud cover (CC) and the interplanetary electric field (IEF), which is modulated by the solar wind speed and the interplanetary magnetic field. We show that CC at mid–high latitudes systematically correlates with positive IEF, which has a clear energetic input into the atmosphere, but not with negative IEF, in general agreement with predictions of the global electric circuit (GEC)-related mechanism. Thus, our results suggest that mid–high latitude clouds might be affected by the solar wind via the GEC. Since IEF responds differently to solar activity than, for instance, cosmic ray flux or solar irradiance, we also show that such a study allows distinguishing one solar-driven mechanism of cloud evolution, via the GEC, from others. (letter)

Scientists Find X Rays from Stellar Winds That May Play Significant Role in Galactic Evolution

Science.gov (United States)

2001-09-01

Colorful star-forming regions that have captivated stargazers since the advent of the telescope 400 years ago contain gas thousands of times more energetic than previously recognized, powered by colliding stellar winds. This multimillion-degree gas radiated as X rays is one of the long-sought sources of energy and elements in the Milky Way galaxy's interstellar medium. A team led by Leisa Townsley, a senior research associate in astronomy and astrophysics at Penn State University, uncovered this wind phenomenon in the Rosette Nebula, a stellar nursery. With the Chandra X-ray Observatory, the team found that the most massive stars in the nebula produce winds that slam into each other, create violent shocks, and infuse the region with 6-million-degree gas. The findings are presented in Washington, D.C., today at a conference entitled "Two Years of Science with Chandra." "A ghostly glow of diffuse X-ray emission pervades the Rosette Nebula and perhaps many other similar star-forming regions throughout the Galaxy," said Townsley. "We now have a new view of the engine lighting the beautiful Rosette Nebula and new evidence for how the interstellar medium may be energized." Townsley and her colleagues created a striking X-ray panorama of the Rosette Molecular Cloud from four images with Chandra's Advanced CCD Imaging Spectrometer. This is a swath of the sky nearly 100 light years across sprayed with hundreds of X-ray-emitting young stars. In one corner of the Rosette Molecular Cloud lies the Rosette Nebula, called an "H II region" because the hydrogen gas there has been stripped of its electrons due to the strong ultraviolet radiation from its young stars. This region, about 5,000 light years away in the constellation Monoceros, the Unicorn, has long been a favorite among amateur astronomers. The wispy, colorful display is visible with small telescopes. The Chandra survey reveals, for the first time, 6-million-degree gas at the center of the Rosette Nebula, occupying a

THE PROPAGATION OF UNCERTAINTIES IN STELLAR POPULATION SYNTHESIS MODELING. II. THE CHALLENGE OF COMPARING GALAXY EVOLUTION MODELS TO OBSERVATIONS

International Nuclear Information System (INIS)

Conroy, Charlie; Gunn, James E.; White, Martin

2010-01-01

Models for the formation and evolution of galaxies readily predict physical properties such as star formation rates, metal-enrichment histories, and, increasingly, gas and dust content of synthetic galaxies. Such predictions are frequently compared to the spectral energy distributions of observed galaxies via the stellar population synthesis (SPS) technique. Substantial uncertainties in SPS exist, and yet their relevance to the task of comparing galaxy evolution models to observations has received little attention. In the present work, we begin to address this issue by investigating the importance of uncertainties in stellar evolution, the initial stellar mass function (IMF), and dust and interstellar medium (ISM) properties on the translation from models to observations. We demonstrate that these uncertainties translate into substantial uncertainties in the ultraviolet, optical, and near-infrared colors of synthetic galaxies. Aspects that carry significant uncertainties include the logarithmic slope of the IMF above 1 M sun , dust attenuation law, molecular cloud disruption timescale, clumpiness of the ISM, fraction of unobscured starlight, and treatment of advanced stages of stellar evolution including blue stragglers, the horizontal branch, and the thermally pulsating asymptotic giant branch. The interpretation of the resulting uncertainties in the derived colors is highly non-trivial because many of the uncertainties are likely systematic, and possibly correlated with the physical properties of galaxies. We therefore urge caution when comparing models to observations.

The origin of stellar winds: Subatmospheric nonthermal storage modes versus radiation pressure

International Nuclear Information System (INIS)

Cannon, C.J.; Thomas, R.N.

1977-01-01

Most current models of matter-flux in hot stars place its origin in radiation pressure, and then model the flow explicitly to produce no chromosphere-corona. Our model of the stellar atmosphere as a transition zone between stellar interior and interstellar medium places the origin of matter-flux, chromosphere-corona, and spectral ''emission classes'' in subatmospheric nonthermal kinetic energy storage, equally for all stars, hot or cold. Current observations of both hot and cold stars suggest chromospheres to be a universal phenomenon, correlated with matter-fluxes, and enhanced in ''emission-class'' stars. To clarify the difference between the two kinds of models above, we reformulate the wind-tunnel analogy to stellar winds, suggesting that stars satisfy and ''imperfect,'' such model;i.e., transsonic shocks occur before the throat, corresponding to an imposed outward velocity in the storage section, or subatmosphere. We then investigate the stability of an arbitrary stellar atmosphere, hot or cold, to suggest a cause for such an outward subatmospheric velocity

Dynamics of H II regions around exiled O stars

Science.gov (United States)

Mackey, Jonathan; Langer, Norbert; Gvaramadze, Vasilii V.

2013-11-01

At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurized H II regions impart kinetic energy and momentum to the ISM, compress and/or evaporate dense clouds, and can constrain properties of both the star and the ISM. Here, we present one-, two- and (the first) three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetized ISM, with properties appropriate for the nearby O star ζ Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the shell is strongly influenced by the ISM magnetic field strength and orientation. Hα emission maps show that H II region remains roughly circular, although the star is displaced somewhat from the centre of emission. For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is >100 times larger than that from the wind and ≈10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main-sequence lifetime is >100 times less, but the momentum feedback is up to 4 times larger. H II region dynamics are found to have only a small effect on the ISM conditions that a bow shock close to the star would encounter.

TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

Energy Technology Data Exchange (ETDEWEB)

Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

2013-05-21

We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent SN explosions. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of the global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over timescales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback. However, different feedback schemes are found to produce significant differences in the density and thermodynamic structure of the ISM, and are hence expected to have a qualitatively different impact on galaxy evolution.

TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

International Nuclear Information System (INIS)

Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

2013-01-01

We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent SN explosions. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of the global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over timescales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback. However, different feedback schemes are found to produce significant differences in the density and thermodynamic structure of the ISM, and are hence expected to have a qualitatively different impact on galaxy evolution.

TRIGGERING COLLAPSE OF THE PRESOLAR DENSE CLOUD CORE AND INJECTING SHORT-LIVED RADIOISOTOPES WITH A SHOCK WAVE. II. VARIED SHOCK WAVE AND CLOUD CORE PARAMETERS

Energy Technology Data Exchange (ETDEWEB)

Boss, Alan P.; Keiser, Sandra A., E-mail: boss@dtm.ciw.edu, E-mail: keiser@dtm.ciw.edu [Department of Terrestrial Magnetism, Carnegie Institution, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States)

2013-06-10

A variety of stellar sources have been proposed for the origin of the short-lived radioisotopes that existed at the time of the formation of the earliest solar system solids, including Type II supernovae (SNe), asymptotic giant branch (AGB) and super-AGB stars, and Wolf-Rayet star winds. Our previous adaptive mesh hydrodynamics models with the FLASH2.5 code have shown which combinations of shock wave parameters are able to simultaneously trigger the gravitational collapse of a target dense cloud core and inject significant amounts of shock wave gas and dust, showing that thin SN shocks may be uniquely suited for the task. However, recent meteoritical studies have weakened the case for a direct SN injection to the presolar cloud, motivating us to re-examine a wider range of shock wave and cloud core parameters, including rotation, in order to better estimate the injection efficiencies for a variety of stellar sources. We find that SN shocks remain as the most promising stellar source, though planetary nebulae resulting from AGB star evolution cannot be conclusively ruled out. Wolf-Rayet (WR) star winds, however, are likely to lead to cloud core shredding, rather than to collapse. Injection efficiencies can be increased when the cloud is rotating about an axis aligned with the direction of the shock wave, by as much as a factor of {approx}10. The amount of gas and dust accreted from the post-shock wind can exceed that injected from the shock wave, with implications for the isotopic abundances expected for a SN source.

Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies

Science.gov (United States)

Vidal-García, A.; Charlot, S.; Bruzual, G.; Hubeny, I.

2017-09-01

We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (∼10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.

Stellar winds in binary X-ray systems

Science.gov (United States)

Macgregor, K. B.; Vitello, P. A. J.

1982-01-01

It is thought that accretion from a strong stellar wind by a compact object may be responsible for the X-ray emission from binary systems containing a massive early-type primary. To investigate the effect of X-ray heating and ionization on the mass transfer process in systems of this type, an idealized model is constructed for the flow of a radiation-driven wind in the presence of an X-ray source of specified luminosity, L sub x. It is noted that for low values of L sub x, X-ray photoionization gives rise to additional ions having spectral lines with wavelengths situated near the peak of the primary continuum flux distribution. As a consequence, the radiation force acting on the gas increases in relation to its value in the absence of X-rays, and the wind is accelerated to higher velocities. As L sub x is increased, the degree of ionization of the wind increases, and the magnitude of the radiation force is diminished in comparison with the case in which L sub x = 0. This reduction leads at first to a decrease in the wind velocity and ultimately (for L sub x sufficiently large) to the termination of radiatively driven mass loss.

TWO REGIMES OF INTERACTION OF A HOT JUPITER’S ESCAPING ATMOSPHERE WITH THE STELLAR WIND AND GENERATION OF ENERGIZED ATOMIC HYDROGEN CORONA

Energy Technology Data Exchange (ETDEWEB)

Shaikhislamov, I. F.; Prokopov, P. A.; Berezutsky, A. G.; Zakharov, Yu. P.; Posukh, V. G. [Institute of Laser Physics SB RAS, Novosibirsk (Russian Federation); Khodachenko, M. L.; Lammer, H.; Kislyakova, K. G.; Fossati, L. [Space Research Institute, Austrian Acad. Sci., Graz (Austria); Johnstone, C. P., E-mail: maxim.khodachenko@oeaw.ac.at [Department of Astrophysics, University of Vienna, Vienna (Austria)

2016-12-01

The interaction of escaping the upper atmosphere of a hydrogen-rich non-magnetized analog of HD 209458b with a stellar wind (SW) of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic (HD) model. A realistic Sun-like spectrum of X-ray and ultraviolet radiation, which ionizes and heats the planetary atmosphere, together with hydrogen photochemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric HD outflow. Two different regimes of the planetary and SW interaction have been modeled. These are: (1) the “ captured by the star ” regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe toward the star, and (2) the “ blown by the wind ” regime, when sufficiently strong SW confines the escaping planetary atmosphere and channels it into the tail. The model simulates in detail the HD interaction between the planetary atoms, protons and the SW, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud, either as a paraboloid shell between the ionopause and bowshock (for the “ blown by the wind ” regime), or a turbulent layer at the contact boundary between the planetary stream and SW (for the “ captured by the star ” regime) are of importance for the interpretation of Ly α absorption features in exoplanetary transit spectra and characterization of the plasma environments.

TWO REGIMES OF INTERACTION OF A HOT JUPITER’S ESCAPING ATMOSPHERE WITH THE STELLAR WIND AND GENERATION OF ENERGIZED ATOMIC HYDROGEN CORONA

International Nuclear Information System (INIS)

Shaikhislamov, I. F.; Prokopov, P. A.; Berezutsky, A. G.; Zakharov, Yu. P.; Posukh, V. G.; Khodachenko, M. L.; Lammer, H.; Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.

2016-01-01

The interaction of escaping the upper atmosphere of a hydrogen-rich non-magnetized analog of HD 209458b with a stellar wind (SW) of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic (HD) model. A realistic Sun-like spectrum of X-ray and ultraviolet radiation, which ionizes and heats the planetary atmosphere, together with hydrogen photochemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric HD outflow. Two different regimes of the planetary and SW interaction have been modeled. These are: (1) the “ captured by the star ” regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe toward the star, and (2) the “ blown by the wind ” regime, when sufficiently strong SW confines the escaping planetary atmosphere and channels it into the tail. The model simulates in detail the HD interaction between the planetary atoms, protons and the SW, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud, either as a paraboloid shell between the ionopause and bowshock (for the “ blown by the wind ” regime), or a turbulent layer at the contact boundary between the planetary stream and SW (for the “ captured by the star ” regime) are of importance for the interpretation of Ly α absorption features in exoplanetary transit spectra and characterization of the plasma environments.

SDP_wlanger_3: State of the Diffuse ISM: Galactic Observations of the Terahertz CII Line (GOT CPlus)

Science.gov (United States)

Langer, W.

2011-09-01

Star formation activity throughout the Galactic disk depends on the thermal and dynamical state of the interstellar gas, which in turn depends on heating and cooling rates, modulated by the gravitational potential and shock and turbulent pressures. Molecular cloud formation, and thus the star formation, may be regulated by pressures in the interstellar medium (ISM). To understand these processes we need information about the properties of the diffuse atomic and diffuse molecular gas clouds, and Photon Dominated Regions (PDR). An important tracer of these regions is the CII line at 158 microns (1900.5 GHz). We propose a "pencil-beam" survey of CII with HIFI band 7b, based on deep integrations and systematic sparse sampling of the Galactic disk plus selected targets, totaling over 900 lines of sight. We will detect both emission and, against the bright inner Galaxy and selected continuum sources, absorption lines. These spectra will provide the astronomical community with a large rich statistical database of the diffuse cloud properties throughout the Galaxy for understanding the Milky Way ISM and, by extension, other galaxies. It will be extremely valuable for determining the properties of the atomic gas, the role of barometric pressure and turbulence in cloud evolution, and the properties of the interface between the atomic and molecular clouds. The CII line is one of the major ISM cooling lines and is present throughout the Galactic plane. It is the strongest far-IR emission line in the Galaxy, with a total luminosity about a 1000 times that of the CO J=1-0 line. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds, and PDRs, and their dynamics via velocity fields. HSO is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

KPOT_wlanger_1: State of the Diffuse ISM: Galactic Observations of the Terahertz CII Line (GOT CPlus)

Science.gov (United States)

Langer, W.

2007-10-01

Star formation activity throughout the Galactic disk depends on the thermal and dynamical state of the interstellar gas, which in turn depends on heating and cooling rates, modulated by the gravitational potential and shock and turbulent pressures. Molecular cloud formation, and thus the star formation, may be regulated by pressures in the interstellar medium (ISM). To understand these processes we need information about the properties of the diffuse atomic and diffuse molecular gas clouds, and Photon Dominated Regions (PDR). An important tracer of these regions is the CII line at 158 microns (1900.5 GHz). We propose a "pencil-beam" survey of CII with HIFI band 7b, based on deep integrations and systematic sparse sampling of the Galactic disk plus selected targets, totaling over 900 lines of sight. We will detect both emission and, against the bright inner Galaxy and selected continuum sources, absorption lines. These spectra will provide the astronomical community with a large rich statistical database of the diffuse cloud properties throughout the Galaxy for understanding the Milky Way ISM and, by extension, other galaxies. It will be extremely valuable for determining the properties of the atomic gas, the role of barometric pressure and turbulence in cloud evolution, and the properties of the interface between the atomic and molecular clouds. The CII line is one of the major ISM cooling lines and is present throughout the Galactic plane. It is the strongest far-IR emission line in the Galaxy, with a total luminosity about a 1000 times that of the CO J=1-0 line. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds, and PDRs, and their dynamics via velocity fields. HSO is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

New method to design stellarator coils without the winding surface

Science.gov (United States)

Zhu, Caoxiang; Hudson, Stuart R.; Song, Yuntao; Wan, Yuanxi

2018-01-01

Finding an easy-to-build coils set has been a critical issue for stellarator design for decades. Conventional approaches assume a toroidal ‘winding’ surface, but a poorly chosen winding surface can unnecessarily constrain the coil optimization algorithm, This article presents a new method to design coils for stellarators. Each discrete coil is represented as an arbitrary, closed, one-dimensional curve embedded in three-dimensional space. A target function to be minimized that includes both physical requirements and engineering constraints is constructed. The derivatives of the target function with respect to the parameters describing the coil geometries and currents are calculated analytically. A numerical code, named flexible optimized coils using space curves (FOCUS), has been developed. Applications to a simple stellarator configuration, W7-X and LHD vacuum fields are presented.

Stellar winds and coronae of low-mass Population II/III stars

Science.gov (United States)

Suzuki, Takeru K.

2018-06-01

We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

Stellar winds and coronae of low-mass Population II/III stars

Science.gov (United States)

Suzuki, Takeru K.

2018-04-01

We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

Dust cloud evolution in sub-stellar atmospheres via plasma deposition and plasma sputtering

Science.gov (United States)

Stark, C. R.; Diver, D. A.

2018-04-01

Context. In contemporary sub-stellar model atmospheres, dust growth occurs through neutral gas-phase surface chemistry. Recently, there has been a growing body of theoretical and observational evidence suggesting that ionisation processes can also occur. As a result, atmospheres are populated by regions composed of plasma, gas and dust, and the consequent influence of plasma processes on dust evolution is enhanced. Aim. This paper aims to introduce a new model of dust growth and destruction in sub-stellar atmospheres via plasma deposition and plasma sputtering. Methods: Using example sub-stellar atmospheres from DRIFT-PHOENIX, we have compared plasma deposition and sputtering timescales to those from neutral gas-phase surface chemistry to ascertain their regimes of influence. We calculated the plasma sputtering yield and discuss the circumstances where plasma sputtering dominates over deposition. Results: Within the highest dust density cloud regions, plasma deposition and sputtering dominates over neutral gas-phase surface chemistry if the degree of ionisation is ≳10-4. Loosely bound grains with surface binding energies of the order of 0.1-1 eV are susceptible to destruction through plasma sputtering for feasible degrees of ionisation and electron temperatures; whereas, strong crystalline grains with binding energies of the order 10 eV are resistant to sputtering. Conclusions: The mathematical framework outlined sets the foundation for the inclusion of plasma deposition and plasma sputtering in global dust cloud formation models of sub-stellar atmospheres.

Simulating the formation and evolution of galaxies: multi-phase description of the interstellar medium, star formation, and energy feedback

Science.gov (United States)

Merlin, E.; Chiosi, C.

2007-10-01

Context: Modelling the gaseous component of the interstellar medium (ISM) by Smoothed Particles Hydrodynamics in N-Body simulations (NB-TSPH) is still very crude when compared to the complex real situation. In the real ISM, many different and almost physically decoupled components (phases) coexist for long periods of time, and since they spread over wide ranges of density and temperature, they cannot be correctly represented by a unique continuous fluid. This would influence star formation which is thought to take place in clumps of cold, dense, molecular clouds, embedded in a warmer, neutral medium, that are almost freely moving throughout the tenuous hot ISM. Therefore, assuming that star formation is simply related to the gas content without specifying the component in which this is both observed and expected to occur may not be physically sound. Aims: We consider a multi-phase representation of the ISM in NB-TSPH simulations of galaxy formation and evolution with particular attention to the case of early-type galaxies. Methods: Cold gas clouds are described by the so-called sticky particles algorithm. They can freely move throughout the hot ISM medium; stars form within these clouds and the mass exchange among the three baryonic phases (hot gas, cold clouds, stars) is governed by radiative and Compton cooling and energy feedback by supernova (SN) explosions, stellar winds, and UV radiation. We also consider thermal conduction, cloud-cloud collisions, and chemical enrichment. Results: Our model agrees with and improves upon previous studies on the same subject. The results for the star formation rate agree with recent observational data on early-type galaxies. Conclusions: These models lend further support to the revised monolithic scheme of galaxy formation, which has recently been strengthened by high redshift data leading to the so-called downsizing and top-down scenarios.

Star Formation in High Pressure, High Energy Density Environments: Laboratory Experiments of ISM Dust Analogs

International Nuclear Information System (INIS)

Breugel, W. van; Bajt, S.; Bradley, J.; Bringa, E.; Dai, Z.; Felter, T.; Graham, G.; Kucheyev, S.; Torres, D.; Tielens, A.; Baragiola, R.; Dukes, C.; Loeffler, M.

2005-01-01

Dust grains control the chemistry and cooling, and thus the gravitational collapse of interstellar clouds. Energetic particles, shocks and ionizing radiation can have a profound influence on the structure, lifetime and chemical reactivity of the dust, and therefore on the star formation efficiency. This would be especially important in forming galaxies, which exhibit powerful starburst (supernovae) and AGN (active galactic nucleus) activity. How dust properties are affected in such environments may be crucial for a proper understanding of galaxy formation and evolution. The authors present the results of experiments at LLNL which show that irradiation of the interstellar medium (ISM) dust analog forsterite (Mg 2 SiO 4 ) with swift heavy ions (10 MeV Xe) and a large electronic energy deposition amorphizes its crystalline structure, without changing its chemical composition. From the data they predict that silicate grains in the ISM, even in dense and cold giant molecular clouds, can be amorphized by heavy cosmic rays (CR's). This might provide an explanation for the observed absence of crystalline dust in the ISM clouds of the Milky Way galaxy. This processing of dust by CR's would be even more important in forming galaxies and galaxies with active black holes

HUBBLE SPACE TELESCOPE AND HI IMAGING OF STRONG RAM PRESSURE STRIPPING IN THE COMA SPIRAL NGC 4921: DENSE CLOUD DECOUPLING AND EVIDENCE FOR MAGNETIC BINDING IN THE ISM

Energy Technology Data Exchange (ETDEWEB)

Kenney, Jeffrey D. P.; Abramson, Anne [Yale University Astronomy Department, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Bravo-Alfaro, Hector, E-mail: jeff.kenney@yale.edu [Institut d’Astrophysique de Paris, CNRS/UPMC, 98bis, Boulevard Arago F-75014, Paris (France)

2015-08-15

Remarkable dust extinction features in the deep Hubble Space Telescope (HST) V and I images of the face-on Coma cluster spiral galaxy NGC 4921 show in unprecedented ways how ram pressure strips the ISM from the disk of a spiral galaxy. New VLA HI maps show a truncated and highly asymmetric HI disk with a compressed HI distribution in the NW, providing evidence for ram pressure acting from the NW. Where the HI distribution is truncated in the NW region, HST images show a well-defined, continuous front of dust that extends over 90° and 20 kpc. This dust front separates the dusty from dust-free regions of the galaxy, and we interpret it as galaxy ISM swept up near the leading side of the ICM–ISM interaction. We identify and characterize 100 pc–1 kpc scale substructure within this dust front caused by ram pressure, including head–tail filaments, C-shaped filaments, and long smooth dust fronts. The morphology of these features strongly suggests that dense gas clouds partially decouple from surrounding lower density gas during stripping, but decoupling is inhibited, possibly by magnetic fields that link and bind distant parts of the ISM.

The tropical Atlantic surface wind divergence belt and its effect on clouds

OpenAIRE

Y. Tubul; I. Koren; O. Altaratz

2015-01-01

A well-defined surface wind divergence (SWD) belt with distinct cloud properties forms over the equatorial Atlantic during the boreal summer months. This belt separates the deep convective clouds of the intertropical convergence zone (ITCZ) from the shallow marine stratocumulus cloud decks forming over the cold-water subtropical region of the southern Hadley cell. Using the QuikSCAT-SeaWinds and Aqua-MODIS instruments, we examined the large-scale spatiotemporal ...

THERMAL X-RAY EMISSION FROM THE SHOCKED STELLAR WIND OF PULSAR GAMMA-RAY BINARIES

Energy Technology Data Exchange (ETDEWEB)

Zabalza, V.; Paredes, J. M. [Departament d' Astronomia i Meteorologia, Institut de Ciencies del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Marti i Franques 1, E08028 Barcelona (Spain); Bosch-Ramon, V., E-mail: vzabalza@am.ub.es [Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland)

2011-12-10

Gamma-ray-loud X-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their winds will collide producing broadband non-thermal emission, most likely originated in the shocked pulsar wind. Thermal X-ray emission is expected from the shocked stellar wind, but until now it has neither been detected nor studied in the context of gamma-ray binaries. We present a semi-analytic model of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, and find that the thermal X-ray emission increases monotonically with the pulsar spin-down luminosity, reaching luminosities of the order of 10{sup 33} erg s{sup -1}. The lack of thermal features in the X-ray spectrum of gamma-ray binaries can then be used to constrain the properties of the pulsar and stellar winds. By fitting the observed X-ray spectra of gamma-ray binaries with a source model composed of an absorbed non-thermal power law and the computed thermal X-ray emission, we are able to derive upper limits on the spin-down luminosity of the putative pulsar. We applied this method to LS 5039, the only gamma-ray binary with a radial, powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of {approx}6 Multiplication-Sign 10{sup 36} erg s{sup -1}. Given the energetic constraints from its high-energy gamma-ray emission, a non-thermal to spin-down luminosity ratio very close to unity may be required.

Far-infrared line images of dwarf galaxies

Science.gov (United States)

Poglitsch, A.; Geis, N.; Herrmann, F.; Madden, S. C.; Stacey, G. J.; Townes, C. H.; Genzel, R.

1993-01-01

Irregular dwarf galaxies are about ten times more widespread in the universe than regular spiral galaxies. They are characterized by a relatively low metallicity, i.e., lower abundance of the heavier elements (metals) with respect to hydrogen than in the solar neighborhood. These heavier elements in the form of molecules, atoms, or ions, which have radiative transitions in the infrared play a decisive role in the energy balance of the ISM and thereby for the formation of stars. Dwarf galaxies are thus model cases for the physical conditions in the early phase of the universe. Large Magellanic Cloud: 30 Doradus. The two nearest dwarf galaxies are the Magellanic clouds at a distance approximately 50 kpc. The LMC contains 30 Dor, a region with young, extremely massive stars which strongly interact with the surrounding ISM on account of their stellar winds and intense UV radiation. 30 Dor is the brightest object in the LMC at almost all wavelengths.

The tropical Atlantic surface wind divergence belt and its effect on clouds

OpenAIRE

Y. Tubul; I. Koren; O. Altaratz

2015-01-01

A well-defined surface wind divergence (SWD) belt with distinct cloud properties forms over the equatorial Atlantic during the boreal summer months. This belt separates the deep convective clouds of the Intertropical Convergence Zone (ITCZ) from the shallow marine stratocumulus cloud decks forming over the cold-water subtropical region of the southern branch of the Hadley cell in the Atlantic. Using the QuikSCAT-SeaWinds and Aqua-MODIS instruments, we examined the large-scal...

Green Bank Telescope Detection of HI Clouds in the Fermi Bubble Wind

Science.gov (United States)

Lockman, Felix; Di Teodoro, Enrico M.; McClure-Griffiths, Naomi M.

2018-01-01

We used the Robert C. Byrd Green Bank Telescope to map HI 21cm emission in two large regions around the Galactic Center in a search for HI clouds that might be entrained in the nuclear wind that created the Fermi bubbles. In a ~160 square degree region at |b|>4 deg. and |long|<10 deg we detect 106 HI clouds that have large non-circular velocities consistent with their acceleration by the nuclear wind. Rapidly moving clouds are found as far as 1.5 kpc from the center; there are no detectable asymmetries in the cloud populations above and below the Galactic Center. The cloud kinematics is modeled as a population with an outflow velocity of 330 km/s that fills a cone with an opening angle ~140 degrees. The total mass in the clouds is ~10^6 solar masses and we estimate cloud lifetimes to be between 2 and 8 Myr, implying a cold gas mass-loss rate of about 0.1 solar masses per year into the nuclear wind.The Green Bank Telescope is a facility of the National Science Foundation, operated under a cooperative agreement by Associated Universities, Inc.

DISCOVERY OF A HALO AROUND THE HELIX NEBULA NGC 7293 IN THE WISE ALL-SKY SURVEY

International Nuclear Information System (INIS)

Zhang Yong; Hsia, Chih-Hao; Kwok, Sun

2012-01-01

We report the discovery of an extended halo (∼40' in diameter) around the planetary nebula NGC 7293 (the Helix Nebula) observed in the 12 μm band from the Wide-field Infrared Survey Explorer all-sky survey. The mid-infrared halo has an axisymmetric structure with a sharp boundary to the northeast and a more diffuse boundary to the southwest, suggesting an interaction between the stellar wind and the interstellar medium (ISM). The symmetry axis of the halo is well aligned with that of a northeast arc, suggesting that the two structures are physically associated. We have attempted to fit the observed geometry with a model of a moving steady-state stellar wind interacting with the ISM. Possible combinations of the ISM density and the stellar velocity are derived from these fittings. The discrepancies between the model and the observations suggest that the stellar mass loss has a more complicated history, including possible time and angle dependences.

SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

International Nuclear Information System (INIS)

Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

2012-01-01

We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

Laboratory Experiments on the Low-temperature Formation of Carbonaceous Grains in the ISM

Science.gov (United States)

Fulvio, Daniele; Góbi, Sándor; Jäger, Cornelia; Kereszturi, Ákos; Henning, Thomas

2017-11-01

The life cycle of cosmic dust grains is far from being understood and the origin and evolution of interstellar medium (ISM) grains is still under debate. In the ISM, the cosmic dust destruction rate is faster than the production rate by stellar sources. However, observations of ISM refractory matter suggest that to maintain a steady amount of cosmic grains, some supplementary production mechanism takes place. In this context, we aimed to study possible reformation mechanisms of cosmic grains taking place at low temperature directly in the ISM. The low-temperature condensation of carbonaceous materials has been investigated in experiments mimicking the ISM conditions. Gas-phase carbonaceous precursors created by laser ablation of graphite were forced to accrete on cold substrates (T ≈ 10 K) representing surviving dust grains. The growing and evolution of the condensing carbonaceous precursors have been monitored by MIR and UV spectroscopy under a number of experimental scenarios. For the first time, the possibility to form ISM carbonaceous grains in situ is demonstrated. The condensation process is governed by carbon chains that first condense into small carbon clusters and finally into more stable carbonaceous materials, of which structural characteristics are comparable to the material formed in gas-phase condensation experiments at very high temperature. We also show that the so-formed fullerene-like carbonaceous material is transformed into a more ordered material under VUV processing. The cold condensation mechanisms discussed here can give fundamental clues to fully understand the balance between the timescale for dust injection, destruction, and reformation in the ISM.

Detecting stellar-wind bubbles through infrared arcs in H II regions

Science.gov (United States)

Mackey, Jonathan; Haworth, Thomas J.; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert; Harries, Tim J.

2016-02-01

Mid-infrared arcs of dust emission are often seen near ionizing stars within H II regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional, radiation-hydrodynamics simulations of wind bubbles within H II regions around individual stars to predict the infrared emission properties of the dust within the H II region. We assume that dust and gas are dynamically well-coupled and that dust properties (composition, size distribution) are the same in the H II region as outside it, and that the wind bubble contains no dust. We post-process the simulations to make synthetic intensity maps at infrared wavebands using the torus code. We find that the outer edge of a wind bubble emits brightly at 24 μm through starlight absorbed by dust grains and re-radiated thermally in the infrared. This produces a bright arc of emission for slowly moving stars that have asymmetric wind bubbles, even for cases where there is no bow shock or any corresponding feature in tracers of gas emission. The 24 μm intensity decreases exponentially from the arc with increasing distance from the star because the dust temperature decreases with distance. The size distribution and composition of the dust grains has quantitative but not qualitative effects on our results. Despite the simplifications of our model, we find good qualitative agreement with observations of the H II region RCW 120, and can provide physical explanations for any quantitative differences. Our model produces an infrared arc with the same shape and size as the arc around CD -38°11636 in RCW 120, and with comparable brightness. This suggests that infrared arcs around O stars in H II regions may be revealing the extent of stellar wind bubbles, although we have not excluded other explanations.

Multiple stellar generations in the Large Magellanic Cloud Star Cluster NGC 1846

Science.gov (United States)

Milone, Antonino

2010-09-01

The recent discovery of multiple stellar populations in massive Galactic globular clusters poses a serious challenge for models of star cluster formation and evolution. The finding of multiple main sequences in the massive clusters NGC 2808 and omega Centauri, and multiple sub-giant-branch in NGC 1851 and many other globulars have demonstrated that star clusters are not as simple as we have imagined for decades. Surprisingly the only way to explain the main sequence splitting appears to be Helium enrichment, up to an astonishingly high Y 0.40.An unique angle on this problem can be provided by intermediate-age clusters in the Magellanic Clouds with peculiar main-sequence turn-off morphologies. Recent discoveries, based on ACS data of unparalleled photometric accuracy, have demonstrated that the CMDs of a large fraction of these clusters { 70 %} are not consistent with the simple, single stellar population hypothesis. Explanations for what conditions could give rise to multiple populations in Galactic Globular Clusters remain controversial; this is even more the case for LMC clustersTo properly constraint the multipopulation phenomenon in Magellanic Cloud star clusters, we propose deep UV/IR imaging of NGC 1846, a star cluster where multiple populations have already been identified. The proposed observation will allow us to accurately measure the age difference between the stellar populations providing fundamental clues on the formation mechanism. Our simulations of WFC3 performance suggest that we will be able to detect even the main sequence splitting caused by small He differences {Delta Y 0.02}.

Gemini/GNIRS infrared spectroscopy of the Wolf-Rayet stellar wind in Cygnus X-3

Science.gov (United States)

Koljonen, K. I. I.; Maccarone, T. J.

2017-12-01

The microquasar Cygnus X-3 was observed several times with the Gemini North Infrared Spectrograph while the source was in the hard X-ray state. We describe the observed 1.0-2.4 μm spectra as arising from the stellar wind of the companion star and suggest its classification as a WN 4-6 Wolf-Rayet star. We attribute the orbital variations of the emission line profiles to the variations in the ionization structure of the stellar wind caused by the intense X-ray emission from the compact object. The strong variability observed in the line profiles will affect the mass function determination. We are unable to reproduce earlier results, from which the mass function for the Wolf-Rayet star was derived. Instead, we suggest that the system parameters are difficult to obtain from the infrared spectra. We find that the near-infrared continuum and the line spectra can be represented with non-LTE Wolf-Rayet atmosphere models if taking into account the effects arising from the peculiar ionization structure of the stellar wind in an approximative manner. From the representative models we infer the properties of the Wolf-Rayet star and discuss possible mass ranges for the binary components.

Assessing the Habitability of TRAPPIST-1e: MHD Simulations of Atmospheric Loss Due to CMEs and Stellar Wind

Science.gov (United States)

Harbach, Laura Marshall; Drake, Jeremy J.; Garraffo, Cecilia; Alvarado-Gomez, Julian D.; Moschou, Sofia P.; Cohen, Ofer

2018-01-01

Recently, three rocky planets were discovered in the habitable zone of the nearby planetary system TRAPPIST-1. The increasing number of exoplanet detections has led to further research into the planetary requirements for sustaining life. Habitable zone occupants have, in principle, the capacity to retain liquid water, whereas actual habitability might depend on atmospheric retention. However, stellar winds and photon radiation interactions with the planet can lead to severe atmospheric depletion and have a catastrophic impact on a planet’s habitability. While the implications of photoevaporation on atmospheric erosion have been researched to some degree, the influence of stellar winds and Coronal Mass Ejections (CMEs) has yet to be analyzed in detail. Here, we model the effect of the stellar wind and CMEs on the atmospheric envelope of a planet situated in the orbit of TRAPPIST-1e using 3D magnetohydrodynamic (MHD) simulations. In particular, we discuss the atmospheric loss due to the effect of a CME, and the relevance of the stellar and planetary magnetic fields on the sustainability of M-dwarf exoplanetary atmospheres.

HI Clouds Near the Galactic Center: Possible Tracers of the Nuclear Wind

Science.gov (United States)

Lockman, Felix J.; McClure-Griffiths, Naomi; DiTeodoro, Enrico

2017-01-01

We have used the Green Bank Telescope to discover more than one hundred neutral hydrogen clouds that appear to be embedded in the Fermi Bubble -- the Milky Way’s nuclear wind. With the other members of this population that were previously found with the Australia Telescope Compact Array, we now have a sample of about 200 such clouds. They are identified by their peculiar velocities. The cloud kinematics show no trace of Galactic rotation or association with the Galactic bar. Near longitude zero the clouds can have values of VLSR = +-200 km/s. No clouds have been detected with |VLSR| > 350 km/s. The clouds are concentrated toward the Galactic plane, but some are still found to |b|=10 degrees, or z > 1 kpc at the Galactic Center, where the current surveys end. These clouds are important tracers of conditions in the nuclear wind of the Milky Way.

Gamma radiation associated to stellar formation in the galaxy (cosmic ray astronomy)

International Nuclear Information System (INIS)

Casse, Michel.

1980-05-01

The gamma ray sky revealed by the COS-B satellite is very peculiar: a few 'gamma ray stars' lying along the galactic plane emerge from a bright milky way. A possible interpretation of this sky is to invoke the existence of regions in which stars, cosmic rays and interstellar matter are very concentrated. A genetic link is established between clouds, stars and cosmic rays: the partial fragmentation of a cloud give birth to stars, the most massive stars accelerate cosmic rays through their supersonic stellar winds, cosmic ray interact in turn with the cloud material to copiously produce high energy gamma rays: a gamma ray source is born

The Evolution of the Large-Scale ISM: Bubbles, Superbubbles and Non-Equilibrium Ionization

Science.gov (United States)

de Avillez, M. A.; Breitschwerdt, D.

2010-12-01

The ISM, powered by SNe, is turbulent and permeated by a magnetic field (with a mean and a turbulent component). It constitutes a frothy medium that is mostly out of equilibrium and is ram pressure dominated on most of the temperature ranges, except for T 106K, where magnetic and thermal pressures dominate, respectively. Such lack of equilibrium is also imposed by the feedback of the radiative processes into the ISM flow. Many models of the ISM or isolated phenomena, such as bubbles, superbubbles, clouds evolution, etc., take for granted that the flow is in the so-called collisional ionization equilibrium (CIE). However, recombination time scales of most of the ions below 106 K are longer than the cooling time scale. This implies that the recombination lags behind and the plasma is overionized while it cools. As a consequence cooling deviates from CIE. This has severe implications on the evolution of the ISM flow and its ionization structure. Here, besides reviewing several models of the ISM, including bubbles and superbubbles, the validity of the CIE approximation is discussed, and a presentation of recent developments in modeling the ISM by taking into account the time-dependent ionization structure of the flow in a full-blown numerical 3D high resolution simulation is presented.

The Relationship Between Infrared Dark Cloud and Stellar Properties

Science.gov (United States)

Calahan, Jenny; Hora, Joseph L.

2018-01-01

Massive stars are known to form within infrared dark clouds (IRDCs), but many details about how molecular clouds collapse and form stars remain poorly understood.We determine the relationship between the dark cloud mass and the population of young stellar objects (YSOs) associated with the cloud to shed light on the physical processes occurring within these star forming regions. We chose to use a sample of IRDCs and YSOs within the Cygnus-X region, a close-by giant star formation complex that has every stage of star formation represented. Using observations from IRAC, MIPS, PACS, and SPIRE on Spitzer and Herschel we identified a sample of 30,903 YSOs and 167 IRDCs. We derived the class of each YSO as well as the mass of YSO and IRDCs from the flux information. Using these parameters, as well as their locations in the cloud, we were sorted IRDC fragments into larger filaments and associate a set of YSOs with each IRDC. By measuring and comparing parameters such as YSO total mass, number of YSOs, Class 0, Class I, and Class II populations, distance from host filament, and filament mass we tested for correlations between the YSO and IRDC parameters. Using this treasure trove of information, we find that Class 0 and I objects are located more closely to their host IRDC than their Class II counterparts. We also find that high-density IRDCs are better environments for star formation than low-density IRDCs. However, we find no correlation between the total mass of the IRDC and the largest YSO mass in the IRDC, suggesting that IRDCs of any mass can have massive YSOs associated with them.The SAO REU program is funded by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant AST-1659473, and by the Smithsonian Institution.

Evidence for a Multiphase ISM in Early Type Galaxies and Elliptical Galaxies with Strong Radio Continuum

Science.gov (United States)

Kim, Dong Woo

1997-01-01

We have observed NGC 1316 (Fornax A) with the ROSAT HRI. In this paper, we present the results of these observations and we complement them with the spectral analysis of the archival PSPC data. The spectral properties suggest the presence of a significant component of thermal X-ray emission (greater than 60%), amounting to approx. 10(exp 9) solar mass of hot ISM. Within 3 feet from the nucleus of NGC 1316, the HRI X-ray surface brightness falls as r(exp -2) following the stellar light. In the inner approx. 30 inch., however, the X-ray surface brightness is significantly elongated, contrary to the distribution of stellar light, which is significantly rounder within 10 inch. This again argues for a non-stellar origin of the X-ray emission. This flattened X-ray feature is suggestive of either the disk-like geometry of a rotating cooling flow and/or the presence of extended, elongated dark matter. By comparing the morphology of the X-ray emission with the distribution of optical dust patches, we find that the X-ray emission is significantly reduced at the locations where the dust patches are more pronounced, indicating that at least some of the X-ray photons are absorbed by the cold ISM. We also compare the distribution of the hot and cold ISM with that of the ionized gas, using recently obtained H(sub alpha) CCD data. We find that the ionized gas is distributed roughly along the dust patches and follows the large scale X-ray distribution at r greater than 1 foot from the nucleus. However, there is no one-to-one correspondence between ionized gas and hot gas. Both morphological relations and kinematics suggest different origins for hot and cold ISM. The radio jets in projection appear to pass perpendicularly through the central X-ray ellipsoid. Comparison of thermal and radio pressures suggests that the radio jets are confined by the surrounding hot gaseous medium.

PRESSURE EQUILIBRIUM BETWEEN THE LOCAL INTERSTELLAR CLOUDS AND THE LOCAL HOT BUBBLE

Energy Technology Data Exchange (ETDEWEB)

Snowden, S. L.; Chiao, M.; Collier, M. R.; Porter, F. S.; Thomas, N. E. [NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Cravens, T.; Robertson, I. P. [Department of Physics and Astronomy, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045 (United States); Galeazzi, M.; Uprety, Y.; Ursino, E. [Department of Physics, University of Miami, 1320 Campo Sano Drive, Coral Gables, FL 33146 (United States); Koutroumpa, D. [Université Versailles St-Quentin, Sorbonne Universités, UPMC Univ. Paris 06, CNRS/INSU, LATMOS-IPSL, 11 Boulevard d' Alembert, F-78280 Guyancourt (France); Kuntz, K. D. [The Henry A. Rowland Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218 (United States); Lallement, R.; Puspitarini, L. [GEPI, Observatoire de Paris, CNRS UMR8111, Université Paris Diderot, 5 Place Jules Janssen, F-92190 Meudon (France); Lepri, S. T. [University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States); McCammon, D.; Morgan, K. [Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, WI 53706 (United States); Walsh, B. M., E-mail: steven.l.snowden@nasa.gov [Space Sciences Laboratory, 7 Gauss Way, Berkeley, CA 94720 (United States)

2014-08-10

Three recent results related to the heliosphere and the local interstellar medium (ISM) have provided an improved insight into the distribution and conditions of material in the solar neighborhood. These are the measurement of the magnetic field outside of the heliosphere by Voyager 1, the improved mapping of the three-dimensional structure of neutral material surrounding the Local Cavity using extensive ISM absorption line and reddening data, and a sounding rocket flight which observed the heliospheric helium focusing cone in X-rays and provided a robust estimate of the contribution of solar wind charge exchange emission to the ROSAT All-Sky Survey 1/4 keV band data. Combining these disparate results, we show that the thermal pressure of the plasma in the Local Hot Bubble (LHB) is P/k = 10, 700 cm{sup –3} K. If the LHB is relatively free of a global magnetic field, it can easily be in pressure (thermal plus magnetic field) equilibrium with the local interstellar clouds, eliminating a long-standing discrepancy in models of the local ISM.

C+/CO Transitions in the Diffuse ISM: Transitional Cloud Sample from the GOT C+ Survey of [CII] in the inner Galaxy at l = -30deg to 30deg

Science.gov (United States)

Velusamy, T.; Pineda, J. L.; Langer, W. D.; Willacy, K.; Goldsmith, P. F.

2011-05-01

Our knowledge of interstellar gas has been limited primarily to the diffuse atomic phase traced by HI and the well-shielded molecular phase traced by CO. Recently, using the first results of the Herschel Key Project GOT C+, a HIFI C+ survey of the Galactic plane, Velusamy, Langer, Pineda et al. (A&A 521, L18, 2010) have shown that in the diffuse interstellar transition clouds a significant fraction of the carbon exists primarily as C^+ with little C^0 and CO in a warm 'dark gas' layer in which hydrogen is mostly H_2 with little atomic H, surrounding a modest 12CO-emitting core. The [CII] fine structure transition, at 1.9 THz (158 μm) is the best tracer of this component of the interstellar medium, which is critical to our understanding of the atomic to molecular cloud transitions. The Herschel Key Project GOT C+ is designed to study such clouds by observing with HIFI the [CII] line emission along 500 lines of sight (LOSs) throughout the Galactic disk. Here we present the identification and chemical status of a few hundred diffuse and transition clouds traced by [CII], along with auxiliary HI and CO data covering ~100 LOSs in the inner Galaxy between l= -30° and 30°. We identify transition clouds as [CII] components that are characterized by the presence of both HI and 12CO, but no 13CO emission. The intensities, I(CII) and I(HI), are used as measures of the visual extinction, AV, in the cloud up to the C^+/C^0/CO transition layer and a comparison with I(12CO) yields a more complete H_2 molecular inventory. Our results show that [CII] emission is an excellent tool to study transition clouds and their carbon chemistry in the ISM, in particular as a unique tracer of molecular H_2, which is not easily observed by other means. The large sample presented here will serve as a resource to study the chemical and physical status of diffuse transition clouds in a wide range of Galactic environments and constrain the physical parameters such as the FUV intensity and cosmic

Assessment of the Effects of Entrainment and Wind Shear on Nuclear Cloud Rise Modeling

Science.gov (United States)

Zalewski, Daniel; Jodoin, Vincent

2001-04-01

Accurate modeling of nuclear cloud rise is critical in hazard prediction following a nuclear detonation. This thesis recommends improvements to the model currently used by DOD. It considers a single-term versus a three-term entrainment equation, the value of the entrainment and eddy viscous drag parameters, as well as the effect of wind shear in the cloud rise following a nuclear detonation. It examines departures from the 1979 version of the Department of Defense Land Fallout Interpretive Code (DELFIC) with the current code used in the Hazard Prediction and Assessment Capability (HPAC) code version 3.2. The recommendation for a single-term entrainment equation, with constant value parameters, without wind shear corrections, and without cloud oscillations is based on both a statistical analysis using 67 U.S. nuclear atmospheric test shots and the physical representation of the modeling. The statistical analysis optimized the parameter values of interest for four cases: the three-term entrainment equation with wind shear and without wind shear as well as the single-term entrainment equation with and without wind shear. The thesis then examines the effect of cloud oscillations as a significant departure in the code. Modifications to user input atmospheric tables are identified as a potential problem in the calculation of stabilized cloud dimensions in HPAC.

Altitude dependent neutral wind effects on the nonlinear motion of a small barium cloud

International Nuclear Information System (INIS)

Book, D.L.; Ossakow, S.L.; Goldman, S.R.

1975-01-01

The nonlinear motion of a small F region barium release electrostatically coupled to the E region is studied in the presence of a neutral wind with differing values for the E and F regions. In a reference frame moving with the E region neutral wind and F region neutral wind transverse to the background E 0 field is shown to retard or accelerate the evolution of the cloud without otherwise altering the development of the system. When the relative neutral wind has a component parallel to the background E 0 field, there is also a change in the direction of the axis of elongation of the cloud as a function of time, although the final direction is independent of the relative neutral wind. Barium cloud and image behavior are shown to be substantially identical for periodic and Dirichlet boundary conditions

Search for C2- in Diffuse Clouds

Czech Academy of Sciences Publication Activity Database

Civiš, Svatopluk; Hosaki, Y.; Kagi, E.; Izumiura, H.; Yanagisawa, K.; Šedivcová, Tereza; Kawaguchi, K.

2005-01-01

Roč. 57, - (2005), 605-609 ISSN 0004-6264 R&D Projects: GA AV ČR(CZ) IAA4040104; GA MŠk(CZ) LC512 Grant - others:JSPS(JP) C13640247; JSPS(JP) A14204018 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506 Keywords : ISM : clouds * ISM : lines and bands * ISM : molecules * molecular processes Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.376, year: 2005

Role of Turbulent Damping in Cosmic Ray Galactic Winds

Science.gov (United States)

Holguin, Francisco; Ruszkowski, Mateusz; Lazarian, Alex; Yang, H. Y. Karen

2018-06-01

Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, pushing and redistributing material throughout the interstellar medium (ISM) and galactic halo. A detailed understanding of the exact physical mechanisms responsible for these winds is lacking. Non-thermal feedback from galactic cosmic rays (CR), high-energy charged particles accelerated in supernovae and young stars, can impact the efficiency in accelerating the wind. In the self-confinement model, CR stream along magnetic field lines at the Alfven speed due to scattering off self-excited Aflv{é}n waves. However, magneto-hydrodynamic (MHD) turbulence stirred up by stellar feedback dissipates these confining waves, allowing CR to be super Aflvenic. Previous simulations relying on a simplified model of transport have shown that super-Alfv{é}nic streaming of CRs can launch a stronger wind. We perform three-dimensional MHD simulations of a section of a galactic disk, including CR streaming dependent on the local environment, using a realistic model of turbulent dissipation of Alfven waves presented in Lazarian (2016). In this implementation, the CR streaming speed can be super Alfv{é}nic depending on local conditions. We compare results for Alfv{é}nic and locally determined streaming, and find that gas/CR distributions and instantaneous mass loading factor of the wind are different depending on the level of turbulence.Lazarian, A. “Damping of Alfven waves by turbulence and its consequences: from cosmic-ray streaming to launching winds.” ApJ. Vol. 833, Num. 2. (2016).

The design construction and installation of the helical winding for the CLEO stellarator

International Nuclear Information System (INIS)

Hunt, R.R.; Bayes, D.V.

1979-03-01

The CLEO stellarator has a torus 900mm major radius and 166mm minor radius, fitted externally with a 7 field period, l = 3, 120kAT helical winding of 179mm mean radius. The winding and torus have to withstand the large forces produced by the interaction of the current flowing in the winding with the toroidal magnetic field of 2 tesla produced by 24 coils spaced around the torus. To allow the torus to be divided the winding has to be split requiring a total of 240 demountable current-carrying joints at the torus vacuum joint positions. The design, development, manufacture, installation and operation of the helical winding is discussed. From the early development stages to installation took four years. When completed this was the largest installation of its type in Europe. (author)

Eyes in the sky. Interactions between asymptotic giant branch star winds and the interstellar magnetic field

Science.gov (United States)

van Marle, A. J.; Cox, N. L. J.; Decin, L.

2014-10-01

Context. The extended circumstellar envelopes (CSEs) of evolved low-mass stars display a large variety of morphologies. Understanding the various mechanisms that give rise to these extended structures is important to trace their mass-loss history. Aims: Here, we aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow dusty winds of asymptotic giant branch (AGB) stars in an effort to pin-point the origin of so-called eye shaped CSEs of three carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary nebula (PN) shaping can be responsible for asymmetries observed in PNe. Methods: Hydrodynamical simulations are used to study the effect of typical interstellar magnetic fields on the free-expanding spherical stellar winds as they sweep up the local interstellar medium (ISM). Results: The simulations show that typical Galactic interstellar magnetic fields of 5 to 10 μG are sufficient to alter the spherical expanding shells of AGB stars to appear as the characteristic eye shape revealed by far-infrared observations. The typical sizes of the simulated eyes are in accordance with the observed physical sizes. However, the eye shapes are transient in nature. Depending on the stellar and interstellar conditions, they develop after 20 000 to 200 000 yrs and last for about 50 000 to 500 000 yrs, assuming that the star is at rest relative to the local interstellar medium. Once formed, the eye shape develops lateral outflows parallel to the magnetic field. The explosion of a PN in the centre of the eye-shaped dust shell gives rise to an asymmetrical nebula with prominent inward pointing Rayleigh-Taylor instabilities. Conclusions: Interstellar magnetic fields can clearly affect the shaping of wind-ISM interaction shells. The occurrence of the eyes is most strongly influenced by stellar space motion and ISM density. Observability of this transient phase is favoured for lines-of-sight perpendicular to the

THE DUST BUDGET OF THE SMALL MAGELLANIC CLOUD: ARE ASYMPTOTIC GIANT BRANCH STARS THE PRIMARY DUST SOURCE AT LOW METALLICITY?

International Nuclear Information System (INIS)

Boyer, M. L.; Gordon, K. D.; Meixner, M.; Sargent, B. A.; Srinivasan, S.; Riebel, D.; McDonald, I.; Van Loon, J. Th.; Clayton, G. C.; Sloan, G. C.

2012-01-01

We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud, using the 8 μm excess emission as a proxy for the dust-production rate (DPR). We find that asymptotic giant branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) × 10 –7 M ☉ yr –1 of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual DPRs). RSGs contribute the least ( –3 M ☉ of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SN dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.

Solar control on the cloud liquid water content and integrated water vapor associated with monsoon rainfall over India

Science.gov (United States)

Maitra, Animesh; Saha, Upal; Adhikari, Arpita

2014-12-01

A long-term observation over three solar cycles indicates a perceptible influence of solar activity on rainfall and associated parameters in the Indian region. This paper attempts to reveal the solar control on the cloud liquid water content (LWC) and integrated water vapor (IWV) along with Indian Summer Monsoon (ISM) rainfall during the period of 1977-2012 over nine different Indian stations. Cloud LWC and IWV are positively correlated with each other. An anti-correlation is observed between the Sunspot Number (SSN) and ISM rainfall for a majority of the stations and a poor positive correlation obtained for other locations. Cloud LWC and IWV possess positive correlations with Galactic Cosmic Rays (GCR) and SSN respectively for most of the stations. The wavelet analyses of SSN, ISM rainfall, cloud LWC and IWV have been performed to investigate the periodic characteristics of climatic parameters and also to indicate the varying relationship of solar activity with ISM rainfall, cloud LWC and IWV. SSN, ISM rainfall and IWV are found to have a peak at around 10.3 years whereas a dip is observed at that particular period for cloud LWC.

DEVIATION OF STELLAR ORBITS FROM TEST PARTICLE TRAJECTORIES AROUND SGr A* DUE TO TIDES AND WINDS

International Nuclear Information System (INIS)

Psaltis, Dimitrios; Li, Gongjie; Loeb, Abraham

2013-01-01

Monitoring the orbits of stars around Sgr A* offers the possibility of detecting the precession of their orbital planes due to frame dragging, of measuring the spin and quadrupole moment of the black hole, and of testing the no-hair theorem. Here we investigate whether the deviations of stellar orbits from test-particle trajectories due to wind mass loss and tidal dissipation of the orbital energy compromise such measurements. We find that the effects of stellar winds are, in general, negligible. On the other hand, for the most eccentric orbits (e > 0.96) for which an optical interferometer, such as GRAVITY, will detect orbital plane precession due to frame dragging, the tidal dissipation of orbital energy occurs at timescales comparable to the timescale of precession due to the quadrupole moment of the black hole. As a result, this non-conservative effect is a potential source of systematic uncertainty in testing the no-hair theorem with stellar orbits

DEVIATION OF STELLAR ORBITS FROM TEST PARTICLE TRAJECTORIES AROUND SGr A* DUE TO TIDES AND WINDS

Energy Technology Data Exchange (ETDEWEB)

Psaltis, Dimitrios [Astronomy Department, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Li, Gongjie; Loeb, Abraham, E-mail: dpsaltis@email.arizona.edu, E-mail: gli@cfa.harvard.edu, E-mail: aloeb@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian CfA, 60 Garden Street, Cambridge, MA (United States)

2013-11-01

Monitoring the orbits of stars around Sgr A* offers the possibility of detecting the precession of their orbital planes due to frame dragging, of measuring the spin and quadrupole moment of the black hole, and of testing the no-hair theorem. Here we investigate whether the deviations of stellar orbits from test-particle trajectories due to wind mass loss and tidal dissipation of the orbital energy compromise such measurements. We find that the effects of stellar winds are, in general, negligible. On the other hand, for the most eccentric orbits (e > 0.96) for which an optical interferometer, such as GRAVITY, will detect orbital plane precession due to frame dragging, the tidal dissipation of orbital energy occurs at timescales comparable to the timescale of precession due to the quadrupole moment of the black hole. As a result, this non-conservative effect is a potential source of systematic uncertainty in testing the no-hair theorem with stellar orbits.

X-ray emission due to interaction of SN1987A ejecta with its progenitor's stellar-wind matter

International Nuclear Information System (INIS)

Masai, Kuniaki.

1990-06-01

The progenitor of the supernova 1987A, Sk-69 202 probably had lost a considerable amount of mass in its stellar wind in the past evolutionary track through a red supergiant to a blue supergiant. In about 10 years, the expanding ejecta of SN1987A will catch up to collide with the wind matter ejected in the red supergiant phase. Shocks due to the collision will heat up the ejecta and the wind matter to cause an enhancement of thermal X-ray emission lasting for several decades. We predict the X-ray light curve and the spectrum as well as the epoch of the enhancement intending to encourage future X-ray observations, which will give a clue for the study of such peculiar stellar evolution with a blueward transition as Sk-69 202. (author)

Optimization of a stellarator design including modulation of the helical winding geometry

International Nuclear Information System (INIS)

Sharp, L.E.; Petersen, L.F.; Blamey, J.W.

1979-06-01

The optimization of the helical winding geometry of the next generation of high performance stellarators is of critical importance as the current in the helical conductors must be kept to a minimum to reduce the very large electromechanical forces on the conductors. Using a modified version of the Culham computer code MAGBAT, steps towards optimization are described

Vertical wind velocity measurements using a five-hole probe with remotely piloted aircraft to study aerosol–cloud interactions

Directory of Open Access Journals (Sweden)

R. Calmer

2018-05-01

Full Text Available The importance of vertical wind velocities (in particular positive vertical wind velocities or updrafts in atmospheric science has motivated the need to deploy multi-hole probes developed for manned aircraft in small remotely piloted aircraft (RPA. In atmospheric research, lightweight RPAs ( <  2.5 kg are now able to accurately measure atmospheric wind vectors, even in a cloud, which provides essential observing tools for understanding aerosol–cloud interactions. The European project BACCHUS (impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding focuses on these specific interactions. In particular, vertical wind velocity at cloud base is a key parameter for studying aerosol–cloud interactions. To measure the three components of wind, a RPA is equipped with a five-hole probe, pressure sensors, and an inertial navigation system (INS. The five-hole probe is calibrated on a multi-axis platform, and the probe–INS system is validated in a wind tunnel. Once mounted on a RPA, power spectral density (PSD functions and turbulent kinetic energy (TKE derived from the five-hole probe are compared with sonic anemometers on a meteorological mast. During a BACCHUS field campaign at Mace Head Atmospheric Research Station (Ireland, a fleet of RPAs was deployed to profile the atmosphere and complement ground-based and satellite observations of physical and chemical properties of aerosols, clouds, and meteorological state parameters. The five-hole probe was flown on straight-and-level legs to measure vertical wind velocities within clouds. The vertical velocity measurements from the RPA are validated with vertical velocities derived from a ground-based cloud radar by showing that both measurements yield model-simulated cloud droplet number concentrations within 10 %. The updraft velocity distributions illustrate distinct relationships between vertical cloud fields in different meteorological

Formation of giant molecular clouds in global spiral structures: the role of orbital dynamics and cloud-cloud collisions

International Nuclear Information System (INIS)

Roberts, W.W. Jr.; Stewart, G.R.

1987-01-01

The different roles played by orbital dynamics and dissipative cloud-cloud collisions in the formation of giant molecular clouds (GMCs) in a global spiral structure are investigated. The interstellar medium (ISM) is simulated by a system of particles, representing clouds, which orbit in a spiral-perturbed, galactic gravitational field. The overall magnitude and width of the global cloud density distribution in spiral arms is very similar in the collisional and collisionless simulations. The results suggest that the assumed number density and size distribution of clouds and the details of individual cloud-cloud collisions have relatively little effect on these features. Dissipative cloud-cloud collisions play an important steadying role for the cloud system's global spiral structure. Dissipative cloud-cloud collisions also damp the relative velocity dispersion of clouds in massive associations and thereby aid in the effective assembling of GMC-like complexes

The destruction of an Oort Cloud in a rich stellar cluster

Science.gov (United States)

Nordlander, T.; Rickman, H.; Gustafsson, B.

2017-07-01

Context. It is possible that the formation of the Oort Cloud dates back to the earliest epochs of solar system history. At that time, the Sun was almost certainly a member of the stellar cluster where it was born. Since the solar birth cluster is likely to have been massive (103-104ℳ⊙), and therefore long-lived, an issue concerns the survival of such a primordial Oort Cloud. Aims: We have investigated this issue by simulating the orbital evolution of Oort Cloud comets for several hundred Myr, assuming the Sun to start its life as a typical member of such a massive cluster. Methods: We have devised a synthetic representation of the relevant dynamics, where the cluster potential is represented by a King model, and about 20 close encounters with individual cluster stars are selected and integrated based on the solar orbit and the cluster structure. Thousands of individual simulations are made, each including 3000 comets with orbits with three different initial semi-major axes. Results: Practically the entire initial Oort Cloud is found to be lost for our choice of semi-major axes (5000-20 000 au), independent of the cluster mass, although the chance of survival is better for the smaller cluster, since in a certain fraction of the simulations the Sun orbits at relatively safe distances from the dense cluster centre. Conclusions: For the range of birth cluster sizes that we investigate, a primordial Oort Cloud will likely survive only as a small inner core with semi-major axes ≲3000 au. Such a population of comets would be inert to orbital diffusion into an outer halo and subsequent injection into observable orbits. Some mechanism is therefore needed to accomplish this transfer, in case the Oort Cloud is primordial and the birth cluster did not have a low mass. From this point of view, our results lend some support to a delayed formation of the Oort Cloud, that occurred after the Sun had left its birth cluster.

ASSESSMENT OF STELLAR STRATIFICATION IN THREE YOUNG STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Gouliermis, Dimitrios A.; Rochau, Boyke; Mackey, Dougal; Xin Yu

2010-01-01

We present a comprehensive study of stellar stratification in young star clusters in the Large Magellanic Cloud (LMC). We apply our recently developed effective radius method for the assessment of stellar stratification on imaging data obtained with the Advanced Camera for Surveys of three young LMC clusters to characterize the phenomenon and develop a comparative scheme for its assessment in such clusters. The clusters of our sample, NGC 1983, NGC 2002, and NGC 2010, are selected on the basis of their youthfulness, and their variety in appearance, structure, stellar content, and surrounding stellar ambient. Our photometry is complete for magnitudes down to m 814 ≅ 23 mag, allowing the calculation of the structural parameters of the clusters, the estimation of their ages, and the determination of their stellar content. Our study shows that each cluster in our sample demonstrates stellar stratification in a quite different manner and at different degree from the others. Specifically, NGC 1983 shows partial segregation, with the effective radius increasing with fainter magnitudes only for the faintest stars of the cluster. Our method on NGC 2002 provides evidence of strong stellar stratification for both bright and faint stars; the cluster demonstrates the phenomenon with the highest degree in the sample. Finally, NGC 2010 is not segregated, as its bright stellar content is not centrally concentrated, the relation of effective radius to magnitude for stars of intermediate brightness is rather flat, and we find no evidence of stratification for its faintest stars. For the parameterization of the phenomenon of stellar stratification and its quantitative comparison among these clusters, we propose the slope derived from the change in the effective radius over the corresponding magnitude range as indicative parameter of the degree of stratification in the clusters. A positive value of this slope indicates mass segregation in the cluster, while a negative or zero value

Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

Science.gov (United States)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

2013-01-01

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

Energy Technology Data Exchange (ETDEWEB)

Wagner, A. Y.; Umemura, M. [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577 (Japan); Bicknell, G. V., E-mail: ayw@ccs.tsukuba.ac.jp [Research School of Astronomy and Astrophysics, Australian National University, ACT 2611 (Australia)

2013-01-20

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

International Nuclear Information System (INIS)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

2013-01-01

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

Clouds, Wind and the Biogeography of Central American Cloud Forests: Remote Sensing, Atmospheric Modeling, and Walking in the Jungle

Science.gov (United States)

Lawton, R.; Nair, U. S.

2011-12-01

Cloud forests stand at the core of the complex of montane ecosystems that provide the backbone to the multinational Mesoamerican Biological Corridor, which seeks to protect a biodiversity conservation "hotspot" of global significance in an area of rapidly changing land use. Although cloud forests are generally defined by frequent and prolonged immersion in cloud, workers differ in their feelings about "frequent" and "prolonged", and quantitative assessments are rare. Here we focus on the dry season, in which the cloud and mist from orographic cloud plays a critical role in forest water relations, and discuss remote sensing of orographic clouds, and regional and atmospheric modeling at several scales to quantitatively examine the distribution of the atmospheric conditions that characterize cloud forests. Remote sensing using data from GOES reveals diurnal and longer scale patterns in the distribution of dry season orographic clouds in Central America at both regional and local scales. Data from MODIS, used to calculate the base height of orographic cloud banks, reveals not only the geographic distributon of cloud forest sites, but also striking regional variation in the frequency of montane immersion in orographic cloud. At a more local scale, wind is known to have striking effects on forest structure and species distribution in tropical montane ecosystems, both as a general mechanical stress and as the major agent of ecological disturbance. High resolution regional atmospheric modeling using CSU RAMS in the Monteverde cloud forests of Costa Rica provides quantitative information on the spatial distribution of canopy level winds, insight into the spatial structure and local dynamics of cloud forest communities. This information will be useful in not only in local conservation planning and the design of the Mesoamerican Biological Corridor, but also in assessments of the sensitivity of cloud forests to global and regional climate changes.

Formation of new stellar populations from gas accreted by massive young star clusters.

Science.gov (United States)

Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

2016-01-28

Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

On origin of stellar clusters

International Nuclear Information System (INIS)

Tovmasyan, G.M.

1977-01-01

The ratios of the gas component of the mass of young stellar clusters to their stellar mass are considered. They change by more than four orders from one cluster to another. The results are in direct contradiction with the hypothesis of formation of cluster stars from a preliminarily existing gas cloud by its condensation, and they favour the Ambartsumian hypothesis of the joint origin of stars and gas clouds from superdense protostellar matter

Infrared Extinction and Stellar Populations in the Milky Way Midplane

Science.gov (United States)

Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

2012-01-01

The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

A Green Bank Telescope 21cm survey of HI clouds in the Milky Way's nuclear wind

Science.gov (United States)

Denbo, Sara; Endsley, Ryan; Lockman, Felix J.; Ford, Alyson

2015-01-01

Feedback processes such as large-scale galactic winds are thought to be responsible for distributing enriched gas throughout a galaxy and even into the IGM. Such winds have been found in many galaxies with active star formation near their center, and the Fermi bubbles provide evidence for such a nuclear wind in our own Milky Way. A recent 21 cm HI survey by the Australia Telescope Compact Array discovered a population of compact, isolated clouds surrounding the Galactic Center that may be entrained in the Fermi bubble wind. We present data from a survey of 21cm HI over an extended region around the Galactic Center using the Green Bank Telescope. These observations provide more strict constraints on neutral clouds in the Fermi bubble wind, and a more robust description of the parameters of HI clouds (i.e., mass, column density, and lifetime) near the Galactic Center.

Venus winds at cloud level from VIRTIS during the Venus Express mission

Science.gov (United States)

Hueso, Ricardo; Peralta, Javier; Sánchez-Lavega, Agustín.; Pérez-Hoyos, Santiago; Piccioni, Giuseppe; Drossart, Pierre

2010-05-01

The Venus Express (VEX) mission has been in orbit to Venus for almost four years now. The VIRTIS instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet. Images in the ultraviolet range are used to study the upper cloud at 66 km while images in the infrared (1.74 μm) map the opacity of the lower cloud deck at 48 km. Here we present our latest results on the analysis of the global atmospheric dynamics at these cloud levels using a large selection over the full VIRTIS dataset. We will show the atmospheric zonal superrotation at these levels and the mean meridional motions. The zonal winds are very stable in the lower cloud at mid-latitudes to the tropics while it shows different signatures of variability in the upper cloud where solar tide effects are manifest in the data. While the upper clouds present a net meridional motion consistent with the upper branch of a Hadley cell the lower cloud present almost null global meridional motions at all latitudes but with particular features traveling both northwards and southwards in a turbulent manner depending on the cloud morphology on the observations. A particular important atmospheric feature is the South Polar vortex which might be influencing the structure of the zonal winds in the lower cloud at latitudes from the vortex location up to 55°S. Acknowledgements This work has been funded by the Spanish MICIIN AYA2009-10701 with FEDER support and Grupos Gobierno Vasco IT-464-07.

Classifying Structures in the ISM with Machine Learning Techniques

Science.gov (United States)

Beaumont, Christopher; Goodman, A. A.; Williams, J. P.

2011-01-01

The processes which govern molecular cloud evolution and star formation often sculpt structures in the ISM: filaments, pillars, shells, outflows, etc. Because of their morphological complexity, these objects are often identified manually. Manual classification has several disadvantages; the process is subjective, not easily reproducible, and does not scale well to handle increasingly large datasets. We have explored to what extent machine learning algorithms can be trained to autonomously identify specific morphological features in molecular cloud datasets. We show that the Support Vector Machine algorithm can successfully locate filaments and outflows blended with other emission structures. When the objects of interest are morphologically distinct from the surrounding emission, this autonomous classification achieves >90% accuracy. We have developed a set of IDL-based tools to apply this technique to other datasets.

Instabilities of line-driven stellar winds. V. Effect of an optically thick continuum

International Nuclear Information System (INIS)

Owocki, S.P.; Rybicki, G.B.

1991-01-01

Earlier analyses of the linear instability of line-driven stellar winds are extended to the case, relevant to Wolf-Rayet stars, in which the continuum remains optically thick well above the sonic point. It is found that an optically thick flow driven by pure scattering lines is stabilized by the drag effect of the diffuse, scattered radiation. However, even a relatively small photon destruction probability can cause a flow with continuum optical thickness much greater than 1 to remain unstable, with a given growth rate. The implications of these results for the variability characteristics of winds from Wolf-Rayet stars are briefly discussed. 16 refs

Long-term Behaviour Of Venus Winds At Cloud Level From Virtis/vex Observations

Science.gov (United States)

Hueso, Ricardo; Peralta, J.; Sánchez-Lavega, A.; Pérez-Hoyos, S.; Piccioni, G.; Drossart, P.

2009-09-01

The Venus Express (VEX) mission has been in orbit to Venus for more than three years now. The VIRTIS instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet. Images in the ultraviolet range are used to study the upper cloud at 66 km while images in the infrared (1.74 μm) map the opacity of the lower cloud deck at 48 km. Here we present an analysis of the overall dynamics of Venus’ atmosphere at both levels using observations that cover a large fraction of the VIRTIS dataset. We will present our latest results concerning the zonal winds, the overall stability in the lower cloud deck motions and the variability in the upper cloud. Meridional winds are also observed in the upper and lower cloud in the UV and IR images obtained with VIRTIS. While the upper clouds present a net meridional motion consistent with the upper branch of a Hadley cell the lower cloud present more irregular, variable and less intense motions in the meridional direction. Acknowledgements This work has been funded by Spanish MEC AYA2006-07735 with FEDER support and Grupos Gobierno Vasco IT-464-07. RH acknowledges a "Ramón y Cajal” contract from MEC.

Recent advances in non-LTE stellar atmosphere models

Science.gov (United States)

Sander, Andreas A. C.

2017-11-01

In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters. After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.

Submillimeter Spectroscopy of the R Coronae Australis Molecular Cloud Region

Science.gov (United States)

Dunn, Marina Madeline; Walker, Christopher K.; Pat, Terrance; Sirsi, Siddhartha; Swift, Brandon J.; Peters, William L.

2018-01-01

The Interstellar Medium is comprised of large amounts of gas and dust which coalesce to form stars. Observing in the Terahertz regime of the electromagnetic spectrum, approximately 0.3 -300 microns, allows astronomers to study the ISM in unprecedented detail. Using the high spectral resolution imaging system of the SuperCam receiver, a 64-pixel array previously installed on the Submillimeter Telescope on Mt. Graham, AZ, we have begun a 500 square degree survey of the galactic plane. This instrument was designed to do a complete survey of the Milky Way from the ground, with the main focus being to observe two specific transitions of the carbon monoxide molecule, 12CO(3-2) and 13CO(3-2), at 345 GHz. In this work, we present results from these observations for the R Coronae Australis (R Cr A) complex, a region in the southern hemisphere of the sky, using spectroscopic data from a portion of the survey to gain better insight into the life cycle of the ISM. The majority of stars being formed here are similar to the stellar class of the Sun, making it an excellent area of observing interest. Using these results, we attempt to better ascertain the large-scale structure and kinematics inside of the molecular cloud.

Star formation in the Monoceros OB1 dark cloud

International Nuclear Information System (INIS)

Margulis, M.S.

1987-01-01

A survey of the Monoceros OB1 dark cloud was made for molecular outflows and young stellar objects. In all, nine molecular outflows and thirty far-infrared sources were identified in a portion of the cloud composed of about 3 x 10 4 M of material. Statistical arguments suggest that 90% of the far-infrared sources actually are young stellar objects embedded in the cloud. If the star formation rate in the Mon OB1 cloud is roughly constant with time, then molecular outflows in the cloud should be able to support it against collapse due to gravity. This suggests that the birthrate of outflows in the solar neighborhood is very high. In fact, regardless of considerations of cloud support, the large number of outflows identified in the Mon OB1 cloud and the propensity of the youngest stellar objects in the cloud to be associated with outflows suggest that outflows have a high birthrate in the solar neighborhood and are part of a common stage in early stellar evolution. The young stellar objects identified in the cloud can be fit into a spectral classification system. Also, the outflow phase in early stellar evolution tends to occur at about the time that young stellar objects lose a large fraction of their circumstellar envelopes

The impact of magnetic fields on the chemical evolution of the supernova-driven ISM

Czech Academy of Sciences Publication Activity Database

Pardi, A.; Girichidis, P.; Naab, T.; Walch, S.; Peters, T.; Heitsch, F.; Glover, S.C.O.; Klessen, R.S.; Wünsch, Richard; Gatto, A.

2017-01-01

Roč. 465, č. 4 (2017), s. 4611-4633 ISSN 0035-8711 R&D Projects: GA ČR GA15-06012S Institutional support: RVO:67985815 Keywords : turbulent interstellar-medium * molecular cloud formation * ISM: supernova remnants Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 4.961, year: 2016

THE INTERACTION OF ASYMPTOTIC GIANT BRANCH STARS WITH THE INTERSTELLAR MEDIUM

Energy Technology Data Exchange (ETDEWEB)

Villaver, Eva [Departamento de Fisica Teorica, Universidad Autonoma de Madrid, Cantoblanco 28049 Madrid (Spain); Manchado, Arturo [Instituto de Astrofisica de Canarias, Via Lactea S/N, E-38200 La Laguna, Tenerife (Spain); Garcia-Segura, Guillermo, E-mail: eva.villaver@uam.es, E-mail: amt@ll.iac.es, E-mail: ggs@astrosen.unam.mx [Instituto de Astronomia-UNAM, Apartado postal 877, Ensenada, 22800 Baja California (Mexico)

2012-04-01

We study the hydrodynamical behavior of the gas expelled by moving asymptotic giant branch stars interacting with the interstellar medium (ISM). Our models follow the wind modulations prescribed by stellar evolution calculations, and we cover a range of expected relative velocities (10-100 km s{sup -1}), ISM densities (between 0.01 and 1 cm{sup -3}), and stellar progenitor masses (1 and 3.5 M{sub Sun }). We show how and when bow shocks and cometary-like structures form, and in which regime the shells are subject to instabilities. Finally, we analyze the results of the simulations in terms of the different kinematical stellar populations expected in the Galaxy.

Stellarator-Spheromak

International Nuclear Information System (INIS)

Moroz, P.E.

1997-03-01

A novel concept for magnetic plasma confinement, Stellarator-Spheromak (SSP), is proposed. Numerical analysis with the classical-stellarator-type outboard stellarator windings demonstrates a number of potential advantages of SSP for controlled nuclear fusion. Among the main ones are: simple and compact magnet coil configuration, absence of material structures (e.g. magnet coils or conducting walls) in the center of the torus, high rotational transform, and a possibility of MHD equilibria with very high β (pressure/magnetic pressure) of the confined plasma

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

Energy Technology Data Exchange (ETDEWEB)

Asahina, Yuta; Ohsuga, Ken [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan); Nomura, Mariko, E-mail: asahina@cfca.jp [Keio University, Hiyoshi, Kohoku, Yokohama, Kanagawa 223-8522 (Japan)

2017-05-01

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tension force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

International Nuclear Information System (INIS)

Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko

2017-01-01

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tension force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.

Hydrodynamic Simulations of the Inner Accretion Flow of Sagittarius A* Fueled By Stellar Winds

Science.gov (United States)

Ressler, S. M.; Quataert, E.; Stone, J. M.

2018-05-01

We present Athena++ grid-based, hydrodynamic simulations of accretion onto Sagittarius A* via the stellar winds of the ˜30 Wolf-Rayet stars within the central parsec of the galactic center. These simulations span ˜ 4 orders of magnitude in radius, reaching all the way down to 300 gravitational radii of the black hole, ˜32 times further in than in previous work. We reproduce reasonably well the diffuse thermal X-ray emission observed by Chandra in the central parsec. The resulting accretion flow at small radii is a superposition of two components: 1) a moderately unbound, sub-Keplerian, thick, pressure-supported disc that is at most (but not all) times aligned with the clockwise stellar disc, and 2) a bound, low-angular momentum inflow that proceeds primarily along the southern pole of the disc. We interpret this structure as a natural consequence of a few of the innermost stellar winds dominating accretion, which produces a flow with a broad distribution of angular momentum. Including the star S2 in the simulation has a negligible effect on the flow structure. Extrapolating our results from simulations with different inner radii, we find an accretion rate of ˜ a few × 10-8M⊙/yr at the horizon scale, consistent with constraints based on modeling the observed emission of Sgr A*. The flow structure found here can be used as more realistic initial conditions for horizon scale simulations of Sgr A*.

GOT C+: A Herschel Space Observatory Key Program to Study the Diffuse ISM

Science.gov (United States)

Langer, William; Velusamy, T.; Goldsmith, P. F.; Li, D.; Pineda, J.; Yorke, H.

2010-01-01

Star formation activity is regulated by pressures in the interstellar medium, which in turn depend on heating and cooling rates, modulated by the gravitational potential, and shock and turbulent pressures. To understand these processes we need information about the diffuse atomic and diffuse molecular gas cloud properties. The ionized carbon CII fine structure line at 1.9 THz is an important tracer of the atomic gas in the diffuse regions and the atomic to molecular cloud transformation. Furthermore, C+ is a major ISM coolant, the Galaxy's strongest emission line, with a total luminosity about a 1000 times that of CO J=1-0. Galactic Observations of the Terahertz C+ Line (GOT C+) is a Herschel Space Observatory Open Time Key Program to study the diffuse interstellar medium by sampling CII line emission throughout the Galactic disk. GOT C+ will obtain high spectral resolution CII using the Heterodyne Instrument for the Far Infrared (HIFI) instrument. It employees deep integrations, wide velocity coverage (350 km s-1) with 0.22 km s-1 resolution, and systematic sparse sampling of the Galactic disk together with observations of selected targets, of over 900 lines of sight. It will be a resource of the atomic gas properties, in the (a) Galactic disk, (b) Galaxy's central 300pc, (c) Galactic warp, (d) high latitude HI clouds, and (e) Photon Dominated Regions (PDRs). Along with HI, CO isotopes, and CI spectra, our C+ data will provide the astronomical community with a rich statistical database of diffuse cloud properties, for understanding the role of barometric pressure and turbulence in cloud evolution in the Galactic ISM and, by extension, other galaxies. The GOT C+ project will provide a template for future even larger-scale CII surveys. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology and is supported by a NASA grant.

Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

Science.gov (United States)

Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

2018-04-01

We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Science.gov (United States)

Martínez-Núñez, Silvia; Kretschmar, Peter; Bozzo, Enrico; Oskinova, Lidia M.; Puls, Joachim; Sidoli, Lara; Sundqvist, Jon Olof; Blay, Pere; Falanga, Maurizio; Fürst, Felix; Gímenez-García, Angel; Kreykenbohm, Ingo; Kühnel, Matthias; Sander, Andreas; Torrejón, José Miguel; Wilms, Jörn

2017-10-01

Massive stars, at least ˜10 times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy. In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense "clumps". The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution. Supergiant high mass X-ray binaries (SgXBs) are among the brightest X

FIRST INVESTIGATION OF THE COMBINED IMPACT OF IONIZING RADIATION AND MOMENTUM WINDS FROM A MASSIVE STAR ON A SELF-GRAVITATING CORE

International Nuclear Information System (INIS)

Ngoumou, Judith; Hubber, David; Dale, James E.; Burkert, Andreas

2015-01-01

Massive stars shape the surrounding interstellar matter (ISM) by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum-conserving wind scheme in the smoothed particle hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self-gravitating sphere shows that on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing ultraviolet (UV) radiation, we find the momentum-driven wind to have little direct effect on the gas. We conclude that during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas

Dust and gas distribution in molecular clouds: an observational approach

International Nuclear Information System (INIS)

Campeggio, Loretta; Elia, Davide; Maiolo, Berlinda M T; Strafella, Francesco; Cecchi-Pestellini, Cesare

2005-01-01

The interstellar medium (ISM), gas and dust, appears to be arranged in clouds, whose dimensions, masses and densities span a large range of scales: from giant molecular clouds to small isolated globules. The structure of these objects show a high degree of complexity appearing, in the range of the observed scales, as a non-homogeneous ('clumpy') distribution of matter. The arrangement of the ISM is clearly relevant for the study of the fragmentation of the clouds and then of the star formation processes. To quantify observationally the ISM structure, many methods have been developed and our study is focused on some of them, exploiting multiwavelength observations of IS objects. The investigations presented here have been carried out by considering both the dust absorption (in optical and near IR wavelengths) and the gas emission (in the submm-radio spectral range). We present the maps obtained from the reduction of raw data and a first tentative analysis by means of methods as the structure function, the autocorrelation, and the Δ-variance. These are appropriate tools to highlight the complex structure of the ISM with reference to the paradigm given by the supersonic turbulence. Three observational cases are briefly discussed. In order to analyse the structure of objects characterized by different sizes, we applied the above-mentioned algorithms to the extinction map of the dark globule CB 107 and to the CO(J = 1-0) integrated intensity map of Vela Molecular Ridge, D Cloud. Finally we compare the results obtained with synthetic fractal maps known as 'fractional Brownian motion' fBm images

Closed and open magnetic fields in stellar winds

Science.gov (United States)

Mullan, D. J.; Steinolfson, R. S.

1983-01-01

A numerical study of the interaction between a thermal wind and a global dipole field in the sun and in a giant star is reported. In order for closed field lines to persist near the equator (where a helmet-streamer-like configuration appears), the coronal temperature must be less than a critical value Tc, which scales as M/R. This condition is found to be equivalent to the following: for a static helmet streamer to persist, the sonic point above the helmet must not approach closer to the star than 2.2-2.6 stellar radii. Implications for rapid mass loss and X-ray emission from cool giants are pointed out. The results strengthen the case for identifying empirical dividing lines in the H-R diagram with a magnetic topology transition locus (MTTL). Support for the MTTL concept is also provided by considerations of the breakdown of magnetostatic equilibrium.

3D distribution of interstellar medium in the Galaxy: Preparation for analysis of Gaia observations

Energy Technology Data Exchange (ETDEWEB)

Puspitarini, Lucky, E-mail: rosine.lallement@obspm.fr [GEPI Observatoire de Paris, CNRS, Paris Diderot University, 5 Place Jules Janssen, 92190, Meudon (France); Bosscha Observatory and Department of Astronomy, FMIPA, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132 (Indonesia); Lallement, Rosine, E-mail: rosine.lallement@obspm.fr [GEPI Observatoire de Paris, CNRS, Paris Diderot University, 5 Place Jules Janssen, 92190, Meudon (France)

2015-09-30

Accurate and detailed three-dimensional (3D) maps of Galactic interstellar medium (ISM) are still lacking. One way to obtain such 3D descriptions is to record a large set of individual absorption or reddening measurements toward target stars located at various known distances and directions. The inversion of these measurements using a tomographic method can produce spatial distribution of the ISM. Until recently absorption data were very limited and distances to the target stars are still uncertain, but the situation will greatly improve thanks to current and future massive stellar surveys from ground, and to Gaia mission. To prepare absorption data for inversion from a huge number of stellar spectra, automated tools are needed. We have developed various spectral analysis tools adapted to different type of spectra, early- or late- type star. We also have used diffuse interstellar bands (DIBs) to trace IS structures and kinematics. Although we do not know yet their carriers, they can be a promising tool to trace distant interstellar clouds or Galactic arms. We present some examples of the interstellar fitting and show the potentiality of DIBs in tracing the ISM. We will also briefly show and comment the latest 3D map of the local ISM which reveal nearby cloud complexes and cavities.

3D distribution of interstellar medium in the Galaxy: Preparation for analysis of Gaia observations

International Nuclear Information System (INIS)

Puspitarini, Lucky; Lallement, Rosine

2015-01-01

Accurate and detailed three-dimensional (3D) maps of Galactic interstellar medium (ISM) are still lacking. One way to obtain such 3D descriptions is to record a large set of individual absorption or reddening measurements toward target stars located at various known distances and directions. The inversion of these measurements using a tomographic method can produce spatial distribution of the ISM. Until recently absorption data were very limited and distances to the target stars are still uncertain, but the situation will greatly improve thanks to current and future massive stellar surveys from ground, and to Gaia mission. To prepare absorption data for inversion from a huge number of stellar spectra, automated tools are needed. We have developed various spectral analysis tools adapted to different type of spectra, early- or late- type star. We also have used diffuse interstellar bands (DIBs) to trace IS structures and kinematics. Although we do not know yet their carriers, they can be a promising tool to trace distant interstellar clouds or Galactic arms. We present some examples of the interstellar fitting and show the potentiality of DIBs in tracing the ISM. We will also briefly show and comment the latest 3D map of the local ISM which reveal nearby cloud complexes and cavities

A 'special effort' to provide improved sounding and cloud-motion wind data for FGGE. [First GARP Global Experiment

Science.gov (United States)

Greaves, J. R.; Dimego, G.; Smith, W. L.; Suomi, V. E.

1979-01-01

Enhancement and editing of high-density cloud motion wind assessments and research satellite soundings have been necessary to improve the quality of data used in The Global Weather Experiment. Editing operations are conducted by a man-computer interactive data access system. Editing will focus on such inputs as non-US satellite data, NOAA operational sounding and wind data sets, wind data from the Indian Ocean satellite, dropwindsonde data, and tropical mesoscale wind data. Improved techniques for deriving cloud heights and higher resolution sounding in meteorologically active areas are principal parts of the data enhancement program.

Modelling interstellar structures around Vela X-1

Science.gov (United States)

Gvaramadze, V. V.; Alexashov, D. B.; Katushkina, O. A.; Kniazev, A. Y.

2018-03-01

We report the discovery of filamentary structures stretched behind the bow-shock-producing high-mass X-ray binary Vela X-1 using the SuperCOSMOS H-alpha Survey and present the results of optical spectroscopy of the bow shock carried out with the Southern African Large Telescope. The geometry of the detected structures suggests that Vela X-1 has encountered a wedge-like layer of enhanced density on its way and that the shocked material of the layer partially outlines a wake downstream of Vela X-1. To substantiate this suggestion, we carried out 3D magnetohydrodynamic simulations of interaction between Vela X-1 and the layer for three limiting cases. Namely, we run simulations in which (i) the stellar wind and the interstellar medium (ISM) were treated as pure hydrodynamic flows, (ii) a homogeneous magnetic field was added to the ISM, while the stellar wind was assumed to be unmagnetized, and (iii) the stellar wind was assumed to possess a helical magnetic field, while there was no magnetic field in the ISM. We found that although the first two simulations can provide a rough agreement with the observations, only the third one allowed us to reproduce not only the wake behind Vela X-1, but also the general geometry of the bow shock ahead of it.

Role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures

International Nuclear Information System (INIS)

Roberts, W.W. Jr.; Stewart, G.R.

1987-01-01

The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors. 68 references

Dense solar wind cloud geometries deduced from comparisons of radio signal delay and in situ plasma measurements

Science.gov (United States)

Landt, J. A.

1974-01-01

The geometries of dense solar wind clouds are estimated by comparing single-location measurements of the solar wind plasma with the average of the electron density obtained by radio signal delay measurements along a radio path between earth and interplanetary spacecraft. Several of these geometries agree with the current theoretical spatial models of flare-induced shock waves. A new class of spatially limited structures that contain regions with densities greater than any observed in the broad clouds is identified. The extent of a cloud was found to be approximately inversely proportional to its density.

Mechanisms and Model Diversity of Trade-Wind Shallow Cumulus Cloud Feedbacks: A Review

Science.gov (United States)

Vial, Jessica; Bony, Sandrine; Stevens, Bjorn; Vogel, Raphaela

2017-11-01

Shallow cumulus clouds in the trade-wind regions are at the heart of the long standing uncertainty in climate sensitivity estimates. In current climate models, cloud feedbacks are strongly influenced by cloud-base cloud amount in the trades. Therefore, understanding the key factors controlling cloudiness near cloud-base in shallow convective regimes has emerged as an important topic of investigation. We review physical understanding of these key controlling factors and discuss the value of the different approaches that have been developed so far, based on global and high-resolution model experimentations and process-oriented analyses across a range of models and for observations. The trade-wind cloud feedbacks appear to depend on two important aspects: (1) how cloudiness near cloud-base is controlled by the local interplay between turbulent, convective and radiative processes; (2) how these processes interact with their surrounding environment and are influenced by mesoscale organization. Our synthesis of studies that have explored these aspects suggests that the large diversity of model responses is related to fundamental differences in how the processes controlling trade cumulus operate in models, notably, whether they are parameterized or resolved. In models with parameterized convection, cloudiness near cloud-base is very sensitive to the vigor of convective mixing in response to changes in environmental conditions. This is in contrast with results from high-resolution models, which suggest that cloudiness near cloud-base is nearly invariant with warming and independent of large-scale environmental changes. Uncertainties are difficult to narrow using current observations, as the trade cumulus variability and its relation to large-scale environmental factors strongly depend on the time and/or spatial scales at which the mechanisms are evaluated. New opportunities for testing physical understanding of the factors controlling shallow cumulus cloud responses using

Mechanisms and Model Diversity of Trade-Wind Shallow Cumulus Cloud Feedbacks: A Review

Science.gov (United States)

Vial, Jessica; Bony, Sandrine; Stevens, Bjorn; Vogel, Raphaela

Shallow cumulus clouds in the trade-wind regions are at the heart of the long standing uncertainty in climate sensitivity estimates. In current climate models, cloud feedbacks are strongly influenced by cloud-base cloud amount in the trades. Therefore, understanding the key factors controlling cloudiness near cloud-base in shallow convective regimes has emerged as an important topic of investigation. We review physical understanding of these key controlling factors and discuss the value of the different approaches that have been developed so far, based on global and high-resolution model experimentations and process-oriented analyses across a range of models and for observations. The trade-wind cloud feedbacks appear to depend on two important aspects: (1) how cloudiness near cloud-base is controlled by the local interplay between turbulent, convective and radiative processes; (2) how these processes interact with their surrounding environment and are influenced by mesoscale organization. Our synthesis of studies that have explored these aspects suggests that the large diversity of model responses is related to fundamental differences in how the processes controlling trade cumulus operate in models, notably, whether they are parameterized or resolved. In models with parameterized convection, cloudiness near cloud-base is very sensitive to the vigor of convective mixing in response to changes in environmental conditions. This is in contrast with results from high-resolution models, which suggest that cloudiness near cloud-base is nearly invariant with warming and independent of large-scale environmental changes. Uncertainties are difficult to narrow using current observations, as the trade cumulus variability and its relation to large-scale environmental factors strongly depend on the time and/or spatial scales at which the mechanisms are evaluated. New opportunities for testing physical understanding of the factors controlling shallow cumulus cloud responses using

Meteorological explanation of wake clouds at Horns Rev wind farm

Energy Technology Data Exchange (ETDEWEB)

Emeis, S. [Karlsruhe Institute of Technology (Germany). Inst. for Meteorology and Climate Research

2010-08-15

The occurrence of wake clouds at Horns Rev wind farm is explained as mixing fog. Mixing fog forms when two nearly saturated air masses with different temperature are mixed. Due to the non-linearity of the dependence of the saturation water vapour pressure on temperature, the mixed air mass is over-saturated and condensation sets in. On the day in February 2008, when the wake clouds were observed at Horns Rev, cold and very humid air was advected from the nearby land over the warmer North Sea and led to the formation of a shallow layer with sea smoke or fog close above the sea surface. The turbines mixed a much deeper layer and thus provoked the formation of cloud trails in the wakes of the turbines. (orig.)

Mapping diffuse interstellar bands in the local ISM on small scales via MUSE 3D spectroscopy. A pilot study based on globular cluster NGC 6397

Science.gov (United States)

Wendt, Martin; Husser, Tim-Oliver; Kamann, Sebastian; Monreal-Ibero, Ana; Richter, Philipp; Brinchmann, Jarle; Dreizler, Stefan; Weilbacher, Peter M.; Wisotzki, Lutz

2017-11-01

Context. We map the interstellar medium (ISM) including the diffuse interstellar bands (DIBs) in absorption toward the globular cluster NGC 6397 using VLT/MUSE. Assuming the absorbers are located at the rim of the Local Bubble we trace structures on the order of mpc (milliparsec, a few thousand AU). Aims: We aimed to demonstrate the feasibility to map variations of DIBs on small scales with MUSE. The sightlines defined by binned stellar spectra are separated by only a few arcseconds and we probe the absorption within a physically connected region. Methods: This analysis utilized the fitting residuals of individual stellar spectra of NGC 6397 member stars and analyzed lines from neutral species and several DIBs in Voronoi-binned composite spectra with high signal-to-noise ratio (S/N). Results: This pilot study demonstrates the power of MUSE for mapping the local ISM on very small scales which provides a new window for ISM observations. We detect small scale variations in Na I and K I as well as in several DIBs within few arcseconds, or mpc with regard to the Local Bubble. We verify the suitability of the MUSE 3D spectrograph for such measurements and gain new insights by probing a single physical absorber with multiple sight lines.

Assisted stellar suicide: the wind-driven evolution of the recurrent nova T Pyxidis

Science.gov (United States)

Knigge, Ch.; King, A. R.; Patterson, J.

2000-12-01

We show that the extremely high luminosity of the short-period recurrent nova T Pyx in quiescence can be understood if this system is a wind-driven supersoft x-ray source (SSS). In this scenario, a strong, radiation-induced wind is excited from the secondary star and accelerates the binary evolution. The accretion rate is therefore much higher than in an ordinary cataclysmic binary at the same orbital period, as is the luminosity of the white dwarf primary. In the steady state, the enhanced luminosity is just sufficient to maintain the wind from the secondary. The accretion rate and luminosity predicted by the wind-driven model for T Pyx are in good agreement with the observational evidence. X-ray observations with Chandra or XMM may be able to confirm T Pyx's status as a SSS. T Pyx's lifetime in the wind-driven state is on the order of a million years. Its ultimate fate is not certain, but the system may very well end up destroying itself, either via the complete evaporation of the secondary star, or in a Type Ia supernova if the white dwarf reaches the Chandrasekhar limit. Thus either the primary, the secondary, or both may currently be committing assisted stellar suicide.

Height profile of particle concentration in an aeolian saltating cloud: A wind tunnel investigation by PIV MSD

Science.gov (United States)

Dong, Zhibao; Wang, Hongtao; Zhang, Xiaohang; Ayrault, Michael

2003-10-01

Attempt is made to define the particle concentration in an aeolian saltating cloud and its variation with height using artificial spherical quartz sand in a wind tunnel. The height profiles of the relative particle concentration in aeolian saltating cloud at three wind velocities were detected by the state of the art PIV (Particle Image Velocimetry) MSD (Mie Scattering Diffusion) technique, and converted to actual concentration based on sand transport rate and the variation with height of velocity of the saltating cloud. The particle concentration was found to decay exponentially with height and to increase with wind velocity. It decayed more rapidly when the wind velocity decreased. The volume/volume concentration in the near-surface layer was at the order of 10-4. The results obtained by PIV MSD technique were in good agreement with those derived from the sand flux and velocity profiles, the former being about 15% greater than the later.

Interaction of Supernova Blast Waves with Interstellar Clouds: Experiments on the Omega Laser

International Nuclear Information System (INIS)

Klein, R.I.; Robey, H.F.; Perry, T.S.; Kane, J.O.; Greenough, J.A.; Marinak, M.M.

2001-01-01

The interaction of strong shock waves, such as those generated by the explosion of supernovae with interstellar clouds, is a problem of fundamental importance in understanding the evolution and the dynamics of the interstellar medium (ISM) as it is disrupted by shock waves. The physics of this essential interaction is critical to understanding the evolution of the ISM, the mixing of interstellar clouds with the ISM and the viability of this mechanism for triggered star formation. Here we present the results of a series of new OMEGA laser experiments investigating the evolution of a high density sphere embedded in a low density medium after the interaction of a strong shock wave, thereby emulating the supernova shock-cloud interaction. The interaction is viewed from two orthogonal directions enabling visualization of the both the initial distortion of the sphere into a vortex ring as well as the onset of an azimuthal instability that ultimately results in the three-dimensional breakup of the ring. These studies augment previous studies [1,2] on the NOVA laser by enabling the full three-dimensional topology of the interaction to be understood. We show that the experimental results for the vortex ring are in remarkable agreement with the incompressible theory of Widnall [3]. Implications for mixing in the ISM are discussed

Primordial Molecular Cloud Material in Metal-Rich Carbonaceous Chondrites

Science.gov (United States)

Taylor, G. J.

2016-03-01

The menagerie of objects that make up our Solar System reflects the composition of the huge molecular cloud in which the Sun formed, a late addition of short-lived isotopes from an exploding supernova or stellar winds from a neighboring massive star, heating and/or alteration by water in growing planetesimals that modified and segregated the primordial components, and mixing throughout the Solar System. Outer Solar System objects, such as comets, have always been cold, hence minimizing the changes experienced by more processed objects. They are thought to preserve information about the molecular cloud. Elishevah Van Kooten (Natural History Museum of Denmark and the University of Copenhagen) and co-authors in Denmark and at the University of Hawai'i, measured the isotopic compositions of magnesium and chromium in metal-rich carbonaceous chondrites. They found that the meteorites preserve an isotopic signature of primordial molecular cloud materials, providing a potentially detailed record of the molecular cloud's composition and of materials that formed in the outer Solar System.

Vertical wind velocity measurements using a five-hole probe with remotely piloted aircraft to study aerosol-cloud interactions

Science.gov (United States)

Calmer, Radiance; Roberts, Gregory C.; Preissler, Jana; Sanchez, Kevin J.; Derrien, Solène; O'Dowd, Colin

2018-05-01

The importance of vertical wind velocities (in particular positive vertical wind velocities or updrafts) in atmospheric science has motivated the need to deploy multi-hole probes developed for manned aircraft in small remotely piloted aircraft (RPA). In atmospheric research, lightweight RPAs ( power spectral density (PSD) functions and turbulent kinetic energy (TKE) derived from the five-hole probe are compared with sonic anemometers on a meteorological mast. During a BACCHUS field campaign at Mace Head Atmospheric Research Station (Ireland), a fleet of RPAs was deployed to profile the atmosphere and complement ground-based and satellite observations of physical and chemical properties of aerosols, clouds, and meteorological state parameters. The five-hole probe was flown on straight-and-level legs to measure vertical wind velocities within clouds. The vertical velocity measurements from the RPA are validated with vertical velocities derived from a ground-based cloud radar by showing that both measurements yield model-simulated cloud droplet number concentrations within 10 %. The updraft velocity distributions illustrate distinct relationships between vertical cloud fields in different meteorological conditions.

Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.

Science.gov (United States)

Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

2013-05-01

Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

ISM simulations: an overview of models

Science.gov (United States)

de Avillez, M. A.; Breitschwerdt, D.; Asgekar, A.; Spitoni, E.

2015-03-01

Until recently the dynamical evolution of the interstellar medium (ISM) was simulated using collisional ionization equilibrium (CIE) conditions. However, the ISM is a dynamical system, in which the plasma is naturally driven out of equilibrium due to atomic and dynamic processes operating on different timescales. A step forward in the field comprises a multi-fluid approach taking into account the joint thermal and dynamical evolutions of the ISM gas.

The impact of atmospheric stability and wind shear on vertical cloud overlap over the Tibetan Plateau

Directory of Open Access Journals (Sweden)

J. Li

2018-05-01

Full Text Available Studies have shown that changes in cloud cover are responsible for the rapid climate warming over the Tibetan Plateau (TP in the past 3 decades. To simulate the total cloud cover, atmospheric models have to reasonably represent the characteristics of vertical overlap between cloud layers. Until now, however, this subject has received little attention due to the limited availability of observations, especially over the TP. Based on the above information, the main aim of this study is to examine the properties of cloud overlaps over the TP region and to build an empirical relationship between cloud overlap properties and large-scale atmospheric dynamics using 4 years (2007–2010 of data from the CloudSat cloud product and collocated ERA-Interim reanalysis data. To do this, the cloud overlap parameter α, which is an inverse exponential function of the cloud layer separation D and decorrelation length scale L, is calculated using CloudSat and is discussed. The parameters α and L are both widely used to characterize the transition from the maximum to random overlap assumption with increasing layer separations. For those non-adjacent layers without clear sky between them (that is, contiguous cloud layers, it is found that the overlap parameter α is sensitive to the unique thermodynamic and dynamic environment over the TP, i.e., the unstable atmospheric stratification and corresponding weak wind shear, which leads to maximum overlap (that is, greater α values. This finding agrees well with the previous studies. Finally, we parameterize the decorrelation length scale L as a function of the wind shear and atmospheric stability based on a multiple linear regression. Compared with previous parameterizations, this new scheme can improve the simulation of total cloud cover over the TP when the separations between cloud layers are greater than 1 km. This study thus suggests that the effects of both wind shear and atmospheric stability on cloud overlap

The impact of atmospheric stability and wind shear on vertical cloud overlap over the Tibetan Plateau

Science.gov (United States)

Li, Jiming; Lv, Qiaoyi; Jian, Bida; Zhang, Min; Zhao, Chuanfeng; Fu, Qiang; Kawamoto, Kazuaki; Zhang, Hua

2018-05-01

Studies have shown that changes in cloud cover are responsible for the rapid climate warming over the Tibetan Plateau (TP) in the past 3 decades. To simulate the total cloud cover, atmospheric models have to reasonably represent the characteristics of vertical overlap between cloud layers. Until now, however, this subject has received little attention due to the limited availability of observations, especially over the TP. Based on the above information, the main aim of this study is to examine the properties of cloud overlaps over the TP region and to build an empirical relationship between cloud overlap properties and large-scale atmospheric dynamics using 4 years (2007-2010) of data from the CloudSat cloud product and collocated ERA-Interim reanalysis data. To do this, the cloud overlap parameter α, which is an inverse exponential function of the cloud layer separation D and decorrelation length scale L, is calculated using CloudSat and is discussed. The parameters α and L are both widely used to characterize the transition from the maximum to random overlap assumption with increasing layer separations. For those non-adjacent layers without clear sky between them (that is, contiguous cloud layers), it is found that the overlap parameter α is sensitive to the unique thermodynamic and dynamic environment over the TP, i.e., the unstable atmospheric stratification and corresponding weak wind shear, which leads to maximum overlap (that is, greater α values). This finding agrees well with the previous studies. Finally, we parameterize the decorrelation length scale L as a function of the wind shear and atmospheric stability based on a multiple linear regression. Compared with previous parameterizations, this new scheme can improve the simulation of total cloud cover over the TP when the separations between cloud layers are greater than 1 km. This study thus suggests that the effects of both wind shear and atmospheric stability on cloud overlap should be taken into

The Cool ISM in Galaxies

NARCIS (Netherlands)

van der Hulst, J. M.; Blok, W. J. G. de; Oswalt, Terry D.; Keel, William C.

2013-01-01

This chapter describes the different constituents of the observable interstellar medium (ISM) in galaxies and reviews the relationships between the ISM and the star formation in galaxies. The emphasis is on the component which is most widespread and most easily observable, the neutral atomic

ON THE ORIGIN OF STELLAR MASSES

International Nuclear Information System (INIS)

Krumholz, Mark R.

2011-01-01

It has been a longstanding problem to determine, as far as possible, the characteristic masses of stars in terms of fundamental constants; the almost complete invariance of this mass as a function of the star-forming environment suggests that this should be possible. Here I provide such a calculation. The typical stellar mass is set by the characteristic fragment mass in a star-forming cloud, which depends on the cloud's density and temperature structure. Except in the very early universe, the latter is determined mainly by the radiation released as matter falls onto seed protostars. The energy yield from this process is ultimately set by the properties of deuterium burning in protostellar cores, which determines the stars' radii. I show that it is possible to combine these considerations to compute a characteristic stellar mass almost entirely in terms of fundamental constants, with an extremely weak residual dependence on the interstellar pressure and metallicity. This result not only explains the invariance of stellar masses, it resolves a second mystery: why fragmentation of a cold, low-density interstellar cloud, a process with no obvious dependence on the properties of nuclear reactions, happens to select a stellar mass scale such that stellar cores can ignite hydrogen. Finally, the weak residual dependence on the interstellar pressure and metallicity may explain recent observational hints of a smaller characteristic mass in the high-pressure, high-metallicity cores of giant elliptical galaxies.

STAR FORMATION LAWS AND THRESHOLDS FROM INTERSTELLAR MEDIUM STRUCTURE AND TURBULENCE

International Nuclear Information System (INIS)

Renaud, Florent; Kraljic, Katarina; Bournaud, Frédéric

2012-01-01

We present an analytical model of the relation between the surface density of gas and star formation rate in galaxies and clouds, as a function of the presence of supersonic turbulence and the associated structure of the interstellar medium (ISM). The model predicts a power-law relation of index 3/2, flattened under the effects of stellar feedback at high densities or in very turbulent media, and a break at low surface densities when ISM turbulence becomes too weak to induce strong compression. This model explains the diversity of star formation laws and thresholds observed in nearby spirals and their resolved regions, the Small Magellanic Cloud, high-redshift disks and starbursting mergers, as well as Galactic molecular clouds. While other models have proposed interstellar dust content and molecule formation to be key ingredients to the observed variations of the star formation efficiency, we demonstrate instead that these variations can be explained by ISM turbulence and structure in various types of galaxies.

Evolved stars as complex chemical laboratories - the quest for gaseous chemistry

Science.gov (United States)

Katrien Els Decin, Leen

2015-08-01

At the end of their life, most stars lose a large fraction of their mass through a stellar wind. The stellar winds of evolved (super)giant stars are the dominant suppliers for the pristine building blocks of the interstellar medium (ISM). Crucial to the understanding of the chemical life cycle of the ISM is hence a profound insight in the chemical and physical structure governing these stellar winds.These winds are really unique chemical laboratories in which currently more than 70 different molecules and 15 different dust species are detected. Several chemical processes such as neutral-neutral and ion-molecule gas-phase reactions, dust nucleation and growth, and photo-processes determine the chemical content of these winds. However, gas-phase and dust-nucleation chemistry for astronomical environments still faces many challenges. One should realize that only ˜15% of the rate coefficients for gas-phase reactions considered to occur in (inter/circum)stellar regions at temperatures (T) below 300K have been subject to direct laboratory determinations and that the temperature dependence of the rate constants is often not known; only ˜2% have rate constants at Tgrant, we are now in the position to solve some riddles involved in understanding the gas-phase chemistry in evolved stars. In this presentation, I will demonstrate the need for accurate temperature-dependent gas-phase reaction rate constants and will present our new laboratory equipment built to measure the rate constants for species key in stellar wind chemistry. Specifically, we aim to obtain the rate constants of reactions involving silicon- and sulphur bearing species and HCCO for 30

First Observation of the Submillimeter Polarization Spectrum in a Translucent Molecular Cloud

Science.gov (United States)

Ashton, Peter C.; Ade, Peter A. R.; Angilè, Francesco E.; Benton, Steven J.; Devlin, Mark J.; Dober, Bradley; Fissel, Laura M.; Fukui, Yasuo; Galitzki, Nicholas; Gandilo, Natalie N.; Klein, Jeffrey; Korotkov, Andrei L.; Li, Zhi-Yun; Martin, Peter G.; Matthews, Tristan G.; Moncelsi, Lorenzo; Nakamura, Fumitaka; Netterfield, Calvin B.; Novak, Giles; Pascale, Enzo; Poidevin, Frédérick; Santos, Fabio P.; Savini, Giorgio; Scott, Douglas; Shariff, Jamil A.; Soler, Juan D.; Thomas, Nicholas E.; Tucker, Carole E.; Tucker, Gregory S.; Ward-Thompson, Derek

2018-04-01

Polarized emission from aligned dust is a crucial tool for studies of magnetism in the ISM, but a troublesome contaminant for studies of cosmic microwave background polarization. In each case, an understanding of the significance of the polarization signal requires well-calibrated physical models of dust grains. Despite decades of progress in theory and observation, polarized dust models remain largely underconstrained. During its 2012 flight, the balloon-borne telescope BLASTPol obtained simultaneous broadband polarimetric maps of a translucent molecular cloud at 250, 350, and 500 μm. Combining these data with polarimetry from the Planck 850 μm band, we have produced a submillimeter polarization spectrum, the first for a cloud of this type. We find the polarization degree to be largely constant across the four bands. This result introduces a new observable with the potential to place strong empirical constraints on ISM dust polarization models in a previously inaccessible density regime. Compared to models by Draine & Fraisse, our result disfavors two of their models for which all polarization arises due only to aligned silicate grains. By creating simple models for polarized emission in a translucent cloud, we verify that extinction within the cloud should have only a small effect on the polarization spectrum shape, compared to the diffuse ISM. Thus, we expect the measured polarization spectrum to be a valid check on diffuse ISM dust models. The general flatness of the observed polarization spectrum suggests a challenge to models where temperature and alignment degree are strongly correlated across major dust components.

Chinese isms dimensions in mainland China and Taiwan: Convergence and extension of American isms dimensions.

Science.gov (United States)

Chen, Zhuo Job; Hsu, Kung-Yu; Zhou, Xinyue; Saucier, Gerard

2017-07-21

Previous studies of American English isms terms have uncovered as many as five broad factors: tradition-oriented religiousness (TR), subjective spirituality (SS), communal rationalism (CR), unmitigated self-interest (USI), and inequality aversion (IA). The present studies took a similar lexical approach to investigate the Chinese-language isms structures in both mainland China and Taiwan. In Study 1, exploratory factor analyses with 915 mainland Chinese subjects uncovered four interpretable factors dimensionalizing 165 mainland Chinese dictionary isms terms. These factors represented contents of a combination of TR and SS, USI, CR, and a culturally unique Communist Party of China (CPC) ideology factor. In Study 2, exploratory factor analyses with 467 Taiwan Chinese subjects revealed four interpretable factors categorizing 291 Taiwan Chinese dictionary isms terms. These factors represented contents of a combination of TR and SS, USI, CR, and a culturally unique dimension expressing aspirations for happiness. The results gave evidence for the existence of the isms factors TR and SS, USI, and CR in Chinese culture. Cultural uniqueness was reflected in the merging of TR and SS into the factor Syncretic Religiousness and the culture-specific factors of CPC ideology in China and Happiness/Peace Promotion in Taiwan. © 2017 Wiley Periodicals, Inc.

Numerical modeling of the pulsar wind interaction with ISM

NARCIS (Netherlands)

Bogovalov, S. V.; Chechetkin, V. M.; Koldoba, A. V.; Ustyugova, G. V.; Battiston, R; Shea, MA; Rakowski, C; Chatterjee, S

2006-01-01

Time dependent numerical simulation of relativistic wind interaction with interstellar medium was performed. The winds are ejected from magnetosphere of rotation powered pulsars. The particle flux in the winds is assumed to be isotropic. The energy flux is taken as strongly anisotropic in accordance

A Comparison between Physics-based and Polytropic MHD Models for Stellar Coronae and Stellar Winds of Solar Analogs

Energy Technology Data Exchange (ETDEWEB)

Cohen, O. [Lowell Center for Space Science and Technology, University of Massachusetts, Lowell, MA 01854 (United States)

2017-02-01

The development of the Zeeman–Doppler Imaging (ZDI) technique has provided synoptic observations of surface magnetic fields of low-mass stars. This led the stellar astrophysics community to adopt modeling techniques that have been used in solar physics using solar magnetograms. However, many of these techniques have been neglected by the solar community due to their failure to reproduce solar observations. Nevertheless, some of these techniques are still used to simulate the coronae and winds of solar analogs. Here we present a comparative study between two MHD models for the solar corona and solar wind. The first type of model is a polytropic wind model, and the second is the physics-based AWSOM model. We show that while the AWSOM model consistently reproduces many solar observations, the polytropic model fails to reproduce many of them, and in the cases where it does, its solutions are unphysical. Our recommendation is that polytropic models, which are used to estimate mass-loss rates and other parameters of solar analogs, must first be calibrated with solar observations. Alternatively, these models can be calibrated with models that capture more detailed physics of the solar corona (such as the AWSOM model) and that can reproduce solar observations in a consistent manner. Without such a calibration, the results of the polytropic models cannot be validated, but they can be wrongly used by others.

Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with a Clumpy Interstellar Medium

International Nuclear Information System (INIS)

Asahina, Yuta; Kawashima, Tomohisa; Furukawa, Naoko; Enokiya, Rei; Yamamoto, Hiroaki; Fukui, Yasuo; Matsumoto, Ryoji

2017-01-01

The formation mechanism of CO clouds observed with the NANTEN2 and Mopra telescopes toward the stellar cluster Westerlund 2 is studied by 3D magnetohydrodynamic simulations, taking into account the interstellar cooling. These molecular clouds show a peculiar shape composed of an arc-shaped cloud on one side of the TeV γ -ray source HESS J1023-575 and a linear distribution of clouds (jet clouds) on the other side. We propose that these clouds are formed by the interaction of a jet with clumps of interstellar neutral hydrogen (H i). By studying the dependence of the shape of dense cold clouds formed by shock compression and cooling on the filling factor of H i clumps, we found that the density distribution of H i clumps determines the shape of molecular clouds formed by the jet–cloud interaction: arc clouds are formed when the filling factor is large. On the other hand, when the filling factor is small, molecular clouds align with the jet. The jet propagates faster in models with small filling factors.

Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with a Clumpy Interstellar Medium

Energy Technology Data Exchange (ETDEWEB)

Asahina, Yuta; Kawashima, Tomohisa [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan); Furukawa, Naoko; Enokiya, Rei; Yamamoto, Hiroaki; Fukui, Yasuo [Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Matsumoto, Ryoji, E-mail: asahina@cfca.jp [Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)

2017-02-20

The formation mechanism of CO clouds observed with the NANTEN2 and Mopra telescopes toward the stellar cluster Westerlund 2 is studied by 3D magnetohydrodynamic simulations, taking into account the interstellar cooling. These molecular clouds show a peculiar shape composed of an arc-shaped cloud on one side of the TeV γ -ray source HESS J1023-575 and a linear distribution of clouds (jet clouds) on the other side. We propose that these clouds are formed by the interaction of a jet with clumps of interstellar neutral hydrogen (H i). By studying the dependence of the shape of dense cold clouds formed by shock compression and cooling on the filling factor of H i clumps, we found that the density distribution of H i clumps determines the shape of molecular clouds formed by the jet–cloud interaction: arc clouds are formed when the filling factor is large. On the other hand, when the filling factor is small, molecular clouds align with the jet. The jet propagates faster in models with small filling factors.

Characterizing the turbulent porosity of stellar wind structure generated by the line-deshadowing instability

Science.gov (United States)

Owocki, Stanley P.; Sundqvist, Jon O.

2018-03-01

We analyse recent 2D simulations of the non-linear evolution of the line-deshadowing instability (LDI) in hot-star winds, to quantify how the associated highly clumped density structure can lead to a `turbulent porosity' reduction in continuum absorption and/or scattering. The basic method is to examine the statistical variations of mass column as a function of path length, and fit these to analytic forms that lead to simple statistical scalings for the associated mean extinction. A key result is that one can characterize porosity effects on continuum transport in terms of a single `turbulent porosity length', found here to scale as H ≈ (fcl - 1)a, where fcl ≡ 〈ρ2〉/〈ρ〉2 is the clumping factor in density ρ, and a is the density autocorrelation length. For continuum absorption or scattering in an optically thick layer, we find the associated effective reduction in opacity scales as ˜ 1/√{1+τ_H}, where τH ≡ κρH is the local optical thickness of this porosity length. For these LDI simulations, the inferred porosity lengths are small, only about a couple per cent of the stellar radius, H ≈ 0.02R*. For continuum processes like bound-free absorption of X-rays that are only marginally optically thick throughout the full stellar wind, this implies τH ≪ 1, and thus that LDI-generated porosity should have little effect on X-ray transport in such winds. The formalism developed here could however be important for understanding the porous regulation of continuum-driven, super-Eddington outflows from luminous blue variables.

THE OPTICAL STRUCTURE OF THE STARBURST GALAXY M82. II. NEBULAR PROPERTIES OF THE DISK AND INNER WIND

International Nuclear Information System (INIS)

Westmoquette, M. S.; Smith, L. J.; Konstantopoulos, I. S.; Gallagher, J. S.; Trancho, G.; Bastian, N.

2009-01-01

In this second paper of the series, we present the results from optical Gemini-North GMOS-IFU and WIYN DensePak IFU spectroscopic observations of the starburst and inner wind zones of M82, with a focus on the state of the T ∼ 10 4 K ionized interstellar medium. Our electron density maps show peaks of a few 1000 cm -3 (implying very high thermal pressures), local small spatial-scale variations, and a falloff in the minor axis direction. We discuss the implications of these results with regards to the conditions/locations that may favor the escape of individual cluster winds that ultimately power the large-scale superwind. Our findings, when combined with the body of literature built up over the last decade on the state of the interstellar medium (ISM) in M82, imply that the starburst environment is highly fragmented into a range of clouds from small/dense clumps with low-filling factors ( e ∼> 10 4 cm -3 ) to larger filling factor, less dense gas. The most compact clouds seem to be found in the cores of the star cluster complexes, whereas the cloud sizes in the inter-complex region are larger. These dense clouds are bathed with an intense radiation field and embedded in an extensive high temperature (T ∼> 10 6 K), X-ray-emitting ISM that is a product of the high star formation rates in the starburst zones of M82. The near-constant state of the ionization state of the ∼10 4 K gas throughout the M82 starburst zone can be explained as a consequence of the small cloud sizes, which allow the gas conditions to respond quickly to any changes. In Paper I, we found that the observed emission lines are composed of multiple components, including a broad (FWHM ∼ 150-350 km s -1 ) feature that we associate with emission from turbulent mixing layers on the surfaces of the gas clouds, resulting from the interaction of the fast wind outflows from the synchrotron self-Comptons. The large number of compact clouds and wind sources provides an ideal environment for broad line

The VMC survey. XXX. Stellar proper motions in the central parts of the Small Magellanic Cloud

Science.gov (United States)

Niederhofer, F.; Cioni, M.-R. L.; Rubele, S.; Schmidt, T.; Bekki, K.; Grijs, R. de; Emerson, J.; Ivanov, V. D.; Marconi, M.; Oliveira, J. M.; Petr-Gotzens, M. G.; Ripepi, V.; van Loon, J. Th.; Zaggia, S.

2018-05-01

We present the first spatially resolved map of stellar proper motions within the central ( 3.1 × 2.4 kpc) regions of the Small Magellanic Cloud (SMC). The data used for this study encompasses four tiles from the ongoing near-infrared VISTA survey of the Magellanic Clouds system and covers a total contiguous area on the sky of 6.81 deg2. Proper motions have been calculated independently in two dimensions from the spatial offsets in the Ks filter over time baselines between 22 and 27 months. The reflex motions of approximately 33 000 background galaxies are used to calibrate the stellar motions to an absolute scale. The resulting catalog is composed of more than 690 000 stars which have been selected based on their position in the (J - Ks, Ks) color-magnitude diagram. For the median absolute proper motion of the SMC, we find (μαcos(δ), μδ) = (1.087 ± 0.192 (sys.) ± 0.003 (stat.), -1.187 ± 0.008 (sys.) ± 0.003 (stat.)) mas yr-1, consistent with previous studies. Mapping the proper motions as a function of position within the SMC reveals a nonuniform velocity pattern indicative of a tidal feature behind the main body of the SMC and a flow of stars in the south-east moving predominantly along the line-of-sight. Based on observations made with VISTA at the Paranal Observatory under program ID 179.B-2003.

Galactic Winds Driven by Supernovae and Radiation Pressure: Theory and Simulations

Science.gov (United States)

Zhang, Dong; Davis, Shane

2018-01-01

Galactic winds are ubiquitous in most rapidly star-forming galaxies. They are crucial to the process of galaxy formation and evolution, regulating star formation, shaping the stellar mass function and the mass-metallicity relation, and enriching the intergalactic medium with metals. Although important, the physics of galactic winds is still unclear. Winds may be driven by many mechanisms including overlapping supernovae explosions, radiation pressure of starlight on dust grains, and cosmic rays. However, the growing observations of multiphase structure in galactic winds in a large number of galaxies have not been well explained by any models. In this talk I will focus on the models of supernova- and radiation-pressure-driven winds. Using the state-of-the-art numerical simulations, I will assess the relative merits of these driving mechanisms for accelerating cold and warm clouds to observed velocities, and momentum flux boost during wind propagation.

High rate of destruction of molecular clouds by hot stars

International Nuclear Information System (INIS)

Heydari-Malayeri, M.; Lortet, M.C.; Deharveng, L.

1980-01-01

Tenorio-Tagle (1979) first proposed the idea of a third dynamical phase, the champagne phase, following the formation and expansion phases of an HII region. The champagne phase begins when the high pressure gas of an HII region formed inside a molecular cloud reaches the edge of the cloud and bursts into the lower pressure, low density, intercloud medium. One important implication of the model is the prediction of an enormous enhancement of the rate of erosion of the molecular cloud by the ionising radiation of hot stars, which begins as soon as the process of the decrease of the gas density between the star and the cloud is started. The proportion of hydrogen molecules eroded by ionising photons may reach about 10 -2 . The mass eroded may exceed the mass of the ionised gas in the case where the ionisation front reaching the edge of the cloud is of D-type. Additional mechanisms (for instance stellar winds), if at work, may even increase the efficiency of the mechanism. (Auth.)

SUPERGIANT SHELLS AND MOLECULAR CLOUD FORMATION IN THE LARGE MAGELLANIC CLOUD

Energy Technology Data Exchange (ETDEWEB)

Dawson, J. R.; Dickey, John M. [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); Wong, T. [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States); Hughes, A. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Fukui, Y. [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

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.

Star clouds of Magellan

International Nuclear Information System (INIS)

Tucker, W.

1981-01-01

The Magellanic Clouds are two irregular galaxies belonging to the local group which the Milky Way belongs to. By studying the Clouds, astronomers hope to gain insight into the origin and composition of the Milky Way. The overall structure and dynamics of the Clouds are clearest when studied in radio region of the spectrum. One benefit of directly observing stellar luminosities in the Clouds has been the discovery of the period-luminosity relation. Also, the Clouds are a splendid laboratory for studying stellar evolution. It is believed that both Clouds may be in the very early stage in the development of a regular, symmetric galaxy. This raises a paradox because some of the stars in the star clusters of the Clouds are as old as the oldest stars in our galaxy. An explanation for this is given. The low velocity of the Clouds with respect to the center of the Milky Way shows they must be bound to it by gravity. Theories are given on how the Magellanic Clouds became associated with the galaxy. According to current ideas the Clouds orbits will decay and they will spiral into the Galaxy

Clumpy molecular clouds: A dynamic model self-consistently regulated by T Tauri star formation

International Nuclear Information System (INIS)

Norman, C.; Silk, J.

1980-01-01

A new model is proposed which can account for the longevity, energetics, and dynamical structure of dark molecular clouds. It seems clear that the kinetic and gravitational energy in macroscopic cloud motions cannot account for the energetic of many molecular clouds. A stellar energy source must evidently be tapped, and infrared observations indicate that one cannot utilize massive stars in dark clouds. Recent observations of a high space density of T Tauri stars in some dark clouds provide the basis for our assertion that high-velocity winds from these low-mass pre--main-sequence stars provide a continuous dynamic input into molecular clouds. The T Tauri winds sweep up shells of gas, the intersections or collisions of which form dense clumps embedded in a more rarefied interclump medium. Observations constrain the clumps to be ram-pressure confined, but at the relatively low Mach numbers, continuous leakage occurs. This mass input into the interclump medium leads to the existence of two phases; a dense, cold phase (clumps of density approx.10 4 --10 5 cm -3 and temperature approx.10 K) and a warm, more diffuse, interclump medium (ICM, of density approx.10 3 --10 4 cm -3 and temperature approx.30 K). Clump collisions lead to coalescence, and the evolution of the mass spectrum of clumps is studied

Large Interstellar Polarisation Survey. II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM

Science.gov (United States)

Siebenmorgen, R.; Voshchinnikov, N. V.; Bagnulo, S.; Cox, N. L. J.; Cami, J.; Peest, C.

2018-03-01

It is well known that the dust properties of the diffuse interstellar medium exhibit variations towards different sight-lines on a large scale. We have investigated the variability of the dust characteristics on a small scale, and from cloud-to-cloud. We use low-resolution spectro-polarimetric data obtained in the context of the Large Interstellar Polarisation Survey (LIPS) towards 59 sight-lines in the Southern Hemisphere, and we fit these data using a dust model composed of silicate and carbon particles with sizes from the molecular to the sub-micrometre domain. Large (≥6 nm) silicates of prolate shape account for the observed polarisation. For 32 sight-lines we complement our data set with UVES archive high-resolution spectra, which enable us to establish the presence of single-cloud or multiple-clouds towards individual sight-lines. We find that the majority of these 35 sight-lines intersect two or more clouds, while eight of them are dominated by a single absorbing cloud. We confirm several correlations between extinction and parameters of the Serkowski law with dust parameters, but we also find previously undetected correlations between these parameters that are valid only in single-cloud sight-lines. We find that interstellar polarisation from multiple-clouds is smaller than from single-cloud sight-lines, showing that the presence of a second or more clouds depolarises the incoming radiation. We find large variations of the dust characteristics from cloud-to-cloud. However, when we average a sufficiently large number of clouds in single-cloud or multiple-cloud sight-lines, we always retrieve similar mean dust parameters. The typical dust abundances of the single-cloud cases are [C]/[H] = 92 ppm and [Si]/[H] = 20 ppm.

Contribution of stellar winds to the composition of cosmic rays - exotic Ne and Fe from Wolf-Rayet stars

International Nuclear Information System (INIS)

Blake, J.B.; Dearborn, D.S.P.

1984-01-01

The results of previous calculations of the production of Al-26 and the enhancement of heavy isotopes of Fe by Wolf-Rayet (WR) stars are discussed. Mass fractions of Al-26 in WR ejects and in WR H-rich envelopes are given as a function of stellar mass. It is concluded that the predicted mass of Al-26 in the ISM and its galactic distribution are such that WR stars are expected to be a significant if not the major source of the Al-26. The results suggest that He-22 enhancement must be accompanied by 4-8X enhancement of Fe-57, 20-45X enhancement of Fe-58, and 5-10X enhancement of Co-59. The isotopes of Fe are found to be affected before an appreciable enhancement of Ne-22 occurs. The size of the Ne-22 enhancement depends on the details of the mass-loss history whereas the Fe enhancement does not. 11 references

SAGE-SMC: Surveying the Agents of Galaxy Evolution in the Tidally-Disrupted, Low-Metallicity Small Magellanic Cloud

Science.gov (United States)

Gordon, Karl; Babler, Brian; Bernard, Jean-Philippe; Block, Miwa; Blum, Robert; Bolatto, Alberto; Bot, Caroline; Bracker, Steve; Carlson, Lynn; Churchwell, Ed; Clayton, Geoffrey; Cohen, Martin; Engelbracht, Charles; Fukui, Yasuo; Gorjian, Varoujan; Harris, Jason; Hony, Sacha; Hora, Joseph; Indebetouw, Remy; Israel, Frank; Kawamura, Akiko; Leroy, Adam; Li, Aigen; Madden, Suzanne; Markwick-Kemper, Ciska; Meade, Marilyn; Meixner, Margaret; Misselt, Karl; Mizuno, Norikazu; Mizuno, Akira; Muller, Erik; Oliveira, Joana; Olsen, Knut; Onishi, Toshikazu; Paladini, Roberta; Points, Sean; Reach, William; Robitaille, Thomas; Rubin, Douglas; Sandstrom, Karin; Sato, Shuji; Sewilo, Marta; Shibai, Hiroshi; Simon, Josh; Smith, Linda; Srinivasan, Sundar; Tielens, Xander; van Dyk, Schuyler; van Loon, Jacco; Vijh, Uma; Volk, Kevin; Whitney, Barbara; Zaritsky, Dennis

2007-05-01

The observable properties of galaxy evolution are largely driven by the life-cycle of baryonic matter: stars precipitate out of a complex, multi-phase interstellar medium; and eventually, evolved stellar populations return enriched material back to the ISM via stellar winds or supernova explosions. As demonstrated by the SAGE-LMC survey, comprehensive Spitzer imaging of a nearby galaxy provides an incredibly rich view of this baryonic lifecycle, allowing for an unprecedented understanding of the physical processes which drive galaxy evolution. This proposal will extend the SAGE analysis to the whole SMC (Bar, Wing, and high-density portion of the Magellanic Bridge), a galaxy whose properties are uniquely similar to those of star-forming galaxies at high redshift. Specifically, the SMC's metallicity is below the critical threshold (1/3-1/4 Z_sun) where interstellar medium properties are observed to change dramatically (sharp reduction in the PAH dust mass fraction, reduced dust-to-gas ratio, and extreme ultraviolet extinction curve variations). In addition, the SMC has been profoundly influenced by past interactions with the LMC and Milky Way, allowing us to study the impact of periodic interactions on the structure of the ISM and the physical processes of star formation. We will gain crucial insight into the ISM and star formation in a known tidal debris structure (Bridge portion of SMC), which has a metallicity 4 times lower than the rest of the SMC. When combined with observations of the Milky Way (GLIMPSE, MIPSGAL) and the LMC (SAGE-LMC), our survey of the SMC (SAGE-SMC) will provide a complete and detailed picture of the life-cycle of baryons in galactic environments spanning orders of magnitude in metallicity, and wide ranges in star formation history. This understanding will equip us to properly interpret the infrared properties of more distant galaxies, both in the local (e.g., SINGS) and high-redshift (e.g., GOODS and SWIRE) universe.

Multiple Lightning Discharges in Wind Turbines Associated with Nearby Cloud-to-Ground Lightning

DEFF Research Database (Denmark)

Candela Garolera, Anna; Cummins, Kenneth L.; Madsen, Søren Find

2015-01-01

This paper presents the analysis of five events where simultaneous lightning currents were registered in different wind turbines of a wind farm with lightning monitoring equipment installed. Measurements from current monitoring devices installed at the wind turbines and observations from auto......-triggering video cameras were correlated with data from the U.S. National Lighting Detection Network. In all five events, the correlation showed that a cloud-to-ground (CG) lightning stroke with high peak current struck the ground within 10 km of the affected turbines at the time of the currents in the wind...... by the nearby CG strokes, involving mechanisms that vary depending on the polarity of the associated CG stroke. The analysis also suggests that the event of upward lightning from wind turbines triggered by nearby lightning activity occurs very often and therefore it should be considered carefully...

Effects of turbulence on mixed-phase deep convective clouds under different basic-state winds and aerosol concentrations

Science.gov (United States)

Lee, Hyunho; Baik, Jong-Jin; Han, Ji-Young

2014-12-01

The effects of turbulence-induced collision enhancement (TICE) on mixed-phase deep convective clouds are numerically investigated using a 2-D cloud model with bin microphysics for uniform and sheared basic-state wind profiles and different aerosol concentrations. Graupel particles account for the most of the cloud mass in all simulation cases. In the uniform basic-state wind cases, graupel particles with moderate sizes account for some of the total graupel mass in the cases with TICE, whereas graupel particles with large sizes account for almost all the total graupel mass in the cases without TICE. This is because the growth of ice crystals into small graupel particles is enhanced due to TICE. The changes in the size distributions of graupel particles due to TICE result in a decrease in the mass-averaged mean terminal velocity of graupel particles. Therefore, the downward flux of graupel mass, and thus the melting of graupel particles, is reduced due to TICE, leading to a decrease in the amount of surface precipitation. Moreover, under the low aerosol concentration, TICE increases the sublimation of ice particles, consequently playing a partial role in reducing the amount of surface precipitation. The effects of TICE are less pronounced in the sheared basic-state wind cases than in the uniform basic-state wind cases because the number of ice crystals is much smaller in the sheared basic-state wind cases than in the uniform basic-state wind cases. Thus, the size distributions of graupel particles in the cases with and without TICE show little difference.

A flux-limited treatment for the conductive evaporation of spherical interstellar gas clouds

Science.gov (United States)

Dalton, William W.; Balbus, Steven A.

1993-01-01

In this work, we present and analyze a new analytic solution for the saturated (flux-limited) thermal evaporation of a spherical cloud. This work is distinguished from earlier analytic studies by allowing the thermal conductivity to change continuously from a diffusive to a saturated form, in a manner usually employed only in numerical calculations. This closed form solution will be of interest as a computational benchmark. Using our calculated temperature profiles and mass-loss rates, we model the thermal evaporation of such a cloud under typical interstellar medium (ISM) conditions, with some restrictions. We examine the ionization structure of the cloud-ISM interface and evaluate column densities of carbon, nitrogen, oxygen, neon, and silicon ions toward the cloud. In accord with other investigations, we find that ionization equilibrium is far from satisfied under the assumed conditions. Since the inclusion of saturation effects in the heat flux narrows the thermal interface relative to its classical structure, we also find that saturation effects tend to lower predicted column densities.

Compact Starburst Galaxies with Fast Outflows: Spatially Resolved Stellar Mass Profiles

Science.gov (United States)

Gottlieb, Sophia; Diamond-Stanic, Aleksandar; Lipscomb, Charles; Ohene, Senyo; Rines, Josh; Moustakas, John; Sell, Paul; Tremonti, Christy; Coil, Alison; Rudnick, Gregory; Hickox, Ryan C.; Geach, James; Kepley, Amanda

2018-01-01

Powerful galactic winds driven by stellar feedback and black hole accretion are thought to play an important role in regulating star formation in galaxies. In particular, strong stellar feedback from supernovae, stellar winds, radiation pressure, and cosmic rays is required by simulations of star-forming galaxies to prevent the vast majority of baryons from cooling and collapsing to form stars. However, it remains unclear whether these stellar processes play a significant role in expelling gas and shutting down star formation in massive progenitors of quiescent galaxies. What are the limits of stellar feedback? We present multi-band photometry with HST/WFC3 (F475W, F814W, F160W) for a dozen compact starburst galaxies at z~0.6 with half-light radii that suggest incredibly large central escape velocities. These massive galaxies are driving fast (>1000 km/s) outflows that have been previously attributed to stellar feedback associated with the compact (r~100 pc) starburst. But how compact is the stellar mass? In the context of the stellar feedback hypothesis, it is unclear whether these fast outflows are being driven at velocities comparable to the escape velocity of an incredibly dense stellar system (as predicted by some models of radiation-pressure winds) or at velocities that exceed the central escape velocity by large factor. Our spatially resolved measurements with HST show that the stellar mass is more extended than the light, and this requires that the physical mechanism responsible for driving the winds must be able to launch gas at velocities that are factors of 5-10 beyond the central escape velocity.

Feedback first: the surprisingly weak effects of magnetic fields, viscosity, conduction and metal diffusion on sub-L* galaxy formation

Science.gov (United States)

Su, Kung-Yi; Hopkins, Philip F.; Hayward, Christopher C.; Faucher-Giguère, Claude-André; Kereš, Dušan; Ma, Xiangcheng; Robles, Victor H.

2017-10-01

Using high-resolution simulations with explicit treatment of stellar feedback physics based on the FIRE (Feedback In Realistic Environments) project, we study how galaxy formation and the interstellar medium (ISM) are affected by magnetic fields, anisotropic Spitzer-Braginskii conduction and viscosity, and sub-grid metal diffusion from unresolved turbulence. We consider controlled simulations of isolated (non-cosmological) galaxies but also a limited set of cosmological 'zoom-in' simulations. Although simulations have shown significant effects from these physics with weak or absent stellar feedback, the effects are much weaker than those of stellar feedback when the latter is modelled explicitly. The additional physics have no systematic effect on galactic star formation rates (SFRs). In contrast, removing stellar feedback leads to SFRs being overpredicted by factors of ˜10-100. Without feedback, neither galactic winds nor volume-filling hot-phase gas exist, and discs tend to runaway collapse to ultra-thin scaleheights with unphysically dense clumps congregating at the galactic centre. With stellar feedback, a multi-phase, turbulent medium with galactic fountains and winds is established. At currently achievable resolutions and for the investigated halo mass range 1010-1013 M⊙, the additional physics investigated here (magnetohydrodynamic, conduction, viscosity, metal diffusion) have only weak (˜10 per cent-level) effects on regulating SFR and altering the balance of phases, outflows or the energy in ISM turbulence, consistent with simple equipartition arguments. We conclude that galactic star formation and the ISM are primarily governed by a combination of turbulence, gravitational instabilities and feedback. We add the caveat that active galactic nucleus feedback is not included in the present work.

Large dust grains in the wind of VY Canis Majoris

Science.gov (United States)

Scicluna, P.; Siebenmorgen, R.; Wesson, R.; Blommaert, J. A. D. L.; Kasper, M.; Voshchinnikov, N. V.; Wolf, S.

2015-12-01

Massive stars live short lives, losing large amounts of mass through their stellar wind. Their mass is a key factor determining how and when they explode as supernovae, enriching the interstellar medium with heavy elements and dust. During the red supergiant phase, mass-loss rates increase prodigiously, but the driving mechanism has proven elusive. Here we present high-contrast optical polarimetric-imaging observations of the extreme red supergiant VY Canis Majoris and its clumpy, dusty, mass-loss envelope, using the new extreme-adaptive-optics instrument SPHERE at the VLT. These observations allow us to make the first direct and unambiguous detection of submicron dust grains in the ejecta; we derive an average grain radius ~0.5 μm, 50 times larger than in the diffuse ISM, large enough to receive significant radiation pressure by photon scattering. We find evidence for varying grain sizes throughout the ejecta, highlighting the dynamical nature of the envelope. Grains with 0.5 μm sizes are likely to reach a safe distance from the eventual explosion of VY Canis Majoris; hence it may inject upwards of 10-2 M⊙ of dust into the ISM. Based on observations made with European Southern Observatory (ESO) telescopes at the La Silla Paranal Observatory under program 60.A-9368(A).Appendix A is available in electronic form at http://www.aanda.org

CO and IRAS detection of an intermediate-velocity cloud

International Nuclear Information System (INIS)

Desert, F.X.; Bazell, D.; Blitz, L.

1990-01-01

In the course of a radio survey of high-Galactic-latitude clouds, CO emission was detected at the position l = 210.8 deg and b = 63.1 deg with an LSR velocity of -39 km/sec. This molecular cloud constitutes the third one with an unusually large absolute velocity at these latitudes, as compared with the 5.4-km/sec cloud-to-cloud velocity dispersion of the high-latitude molecular clouds. The position is coincident with an H I intermediate-velocity cloud (GHL 11, Verschuur H, OLM 268) and the IR-excess cloud 306 in the list by Desert et al. (1988). This cloud is clearly detected at all four IRAS wavelengths and has warmer colors than the local ISM. 27 refs

Spectrophotometry of emission-line stars in the magellanic clouds

Science.gov (United States)

Bohannan, Bruce

1990-01-01

The strong emission lines in the most luminous stars in the Magellanic Clouds indicate that these stars have such strong stellar winds that their photospheres are so masked that optical absorption lines do not provide an accurate measure of photospheric conditions. In the research funded by this grant, temperatures and gravities of emission-line stars both in the Large (LMC) and Small Magellanic Clouds (SMC) have been measured by fitting of continuum ultraviolet-optical fluxes observed with IUE with theoretical model atmospheres. Preliminary results from this work formed a major part of an invited review 'The Distribution of Types of Luminous Blue Variables'. Interpretation of the IUE observations obtained in this grant and archive data were also included in a talk at the First Boulder-Munich Hot Stars Workshop. Final results of these studies are now being completed for publication in refereed journals.

Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

Energy Technology Data Exchange (ETDEWEB)

Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

2014-06-01

A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

Active Galactic Nuclei Feedback and the Origin and Fate of the Hot Gas in Early-type Galaxies

Science.gov (United States)

Pellegrini, Silvia; Ciotti, Luca; Negri, Andrea; Ostriker, Jeremiah P.

2018-04-01

A recent determination of the relationships between the X-ray luminosity of the ISM (L X) and the stellar and total mass for a sample of nearby early-type galaxies (ETGs) is used to investigate the origin of the hot gas, via a comparison with the results of hydrodynamical simulations of the ISM evolution for a large set of isolated ETGs. After the epoch of major galaxy formation (after z ≃ 2), the ISM is replenished by stellar mass losses and SN ejecta, at the rate predicted by stellar evolution, and is depleted by star formation; it is heated by the thermalization of stellar motions, SNe explosions, and the mechanical (from winds) and radiative AGN feedback. The models agree well with the observed relations, even for the largely different L X values at the same mass, thanks to the sensitivity of the gas flow to many galaxy properties; this holds for models including AGN feedback, and those without. Therefore, the mass input from the stellar population is able to account for a major part of the observed L X; and AGN feedback, while very important to maintain massive ETGs in a time-averaged quasi-steady state, keeping low star formation and the black hole mass, does not dramatically alter the gas content originating in stellar recycled material. These conclusions are based on theoretical predictions for the stellar population contributions in mass and energy, and on a self-consistent modeling of AGN feedback.

Optical light curve of GRB 121011A: a textbook for the onset of GRB afterglow in a mixture of ISM and wind-type medium

International Nuclear Information System (INIS)

Xin, Li-Ping; Wei, Jian-Yan; Qiu, Yu-Lei; Deng, Jin-Song; Wang, Jing; Han, Xu-Hui

2016-01-01

We report the optical observations of GRB 121011A by the 0.8m TNT facility at Xinglong observatory, China. The light curve of the optical afterglow shows a smooth and featureless bump during the epoch of ∼130 s and ∼5000 s with a rising index of 1.57 ± 0.28 before the break time of 539 ± 44 s, and a decaying index of about 1.29 ± 0.07 up to the end of our observations. Moreover, the X-ray light curve decays in a single power-law with a slope of about 1.51 ± 0.03 observed by XRT onboard Swift from 100 s to about 10 000 s after the burst trigger. The featureless optical light curve could be understood as an onset process under the external-shock model. The typical frequency has been below or near the optical one before the deceleration time, and the cooling frequency is located between the optical and X-ray wavelengths. The external medium density has a transition from a mixed stage of ISM and wind-type medium before the peak time to the ISM at the later phase. The joint-analysis of X-ray and optical light curves shows that the emissions from both frequencies are consistent with the prediction of the standard afterglow model without any energy injections, indicating that the central engine has stopped its activity and does not restart anymore after the prompt phase. (paper)

Distinct spatiotemporal expression of ISM1 during mouse and chick development.

Science.gov (United States)

Osório, Liliana; Wu, Xuewei; Zhou, Zhongjun

2014-01-01

Isthmin 1 (ISM1) constitutes the founder of a new family of secreted proteins characterized by the presence of 2 functional domains: thrombospondin type 1 repeat (TSR1) and adhesion-associated domain in MUC4 and other proteins (AMOP). ISM1 was identified in the frog embryo as a member of the FGF8 synexpression group due to its expression in the brain midbrain-hindbrain boundary (MHB) or isthmus. In zebrafish, ISM1 was described as a WNT- and NODAL-regulated gene. The function of ISM1 remains largely elusive. So far, ISM1 has been described as an angiogenesis inhibitor that has a dual function in endothelial cell survival and cell death. For a better understanding of ISM1 function, we examined its spatiotemporal distribution in mouse and chick using RT-PCR, ISH, and IHC analyses. In the mouse, ISM1 transcripts are found in tissues such as the anterior mesendoderm, paraxial and lateral plate mesoderm, MHB and trunk neural tube, as well as in the somites and dermomyotome. In the newborn and adult, ISM1 is prominently expressed in the lung and brain. In addition to its putative role during embryonic and postnatal development, ISM1 may also be important for organ homeostasis in the adult. In the chick embryo, ISM1 transcripts are strongly detected in the ear, eye, and spinal cord primordia. Remarkable differences in ISM1 spatiotemporal expression were found during mouse and chick development, despite the high homology of ISM1 orthologs in these species.

AN IN-DEPTH VIEW OF THE MID-INFRARED PROPERTIES OF POINT SOURCES AND THE DIFFUSE ISM IN THE SMC GIANT H II REGION, N66

International Nuclear Information System (INIS)

Whelan, David G.; Johnson, Kelsey E.; Indebetouw, Rémy; Lebouteiller, Vianney; Galliano, Frédéric; Peeters, Els; Bernard-Salas, Jeronimo; Brandl, Bernhard R.

2013-01-01

The focus of this work is to study mid-infrared point sources and the diffuse interstellar medium (ISM) in the low-metallicity (∼0.2 Z ☉ ) giant H II region N66 in order to determine properties that may shed light on star formation in these conditions. Using the Spitzer Space Telescope's Infrared Spectrograph, we study polycyclic aromatic hydrocarbon (PAH), dust continuum, silicate, and ionic line emission from 14 targeted infrared point sources as well as spectra of the diffuse ISM that is representative of both the photodissociation regions (PDRs) and the H II regions. Among the point source spectra, we spectroscopically confirm that the brightest mid-infrared point source is a massive embedded young stellar object, we detect silicates in emission associated with two young stellar clusters, and we see spectral features of a known B[e] star that are commonly associated with Herbig Be stars. In the diffuse ISM, we provide additional evidence that the very small grain population is being photodestroyed in the hard radiation field. The 11.3 μm PAH complex emission exhibits an unexplained centroid shift in both the point source and ISM spectra that should be investigated at higher signal-to-noise and resolution. Unlike studies of other regions, the 6.2 μm and 7.7 μm band fluxes are decoupled; the data points cover a large range of I 7.7 /I 11.3 PAH ratio values within a narrow band of I 6.2 /I 11.3 ratio values. Furthermore, there is a spread in PAH ionization, being more neutral in the dense PDR where the radiation field is relatively soft, but ionized in the diffuse ISM/PDR. By contrast, the PAH size distribution appears to be independent of local ionization state. Important to unresolved studies of extragalactic low-metallicity star-forming regions, we find that emission from the infrared-bright point sources accounts for only 20%-35% of the PAH emission from the entire region. These results make a comparative data set to other star-forming regions with

Warm gas towards young stellar objects in Corona Australis

DEFF Research Database (Denmark)

Lindberg, Johan; Jørgensen, Jes Kristian; D. Green, Joel

2014-01-01

The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an interm......The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated...... by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented...... Be star R CrA. Our results show that a nearby luminous star does not increase the molecular excitation temperatures in the warm gas around a young stellar object (YSO). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated...

MOLECULAR CLOUD EVOLUTION. III. ACCRETION VERSUS STELLAR FEEDBACK

International Nuclear Information System (INIS)

Vazquez-Semadeni, Enrique; ColIn, Pedro; Gomez, Gilberto C.; Ballesteros-Paredes, Javier; Watson, Alan W.

2010-01-01

We numerically investigate the effect of feedback from the ionization heating from massive stars on the evolution of giant molecular clouds (GMCs) and their star formation efficiency (SFE), which we treat as an instantaneous, time-dependent quantity. We follow the GMCs' evolution from their formation to advanced star-forming stages. After an initial period of contraction, the collapsing clouds begin forming stars, whose feedback evaporates part of the clouds' mass, opposing the continuing accretion from the infalling gas. Our results are as follows: (1) in the presence of feedback, the clouds attain levels of the SFE that are consistent at all times with observational determinations for regions of comparable star formation rates. (2) However, the dense gas mass is larger in general in the presence of feedback, while the total mass (dense gas + stars) is nearly insensitive to the presence of feedback, suggesting that it is determined mainly by the accretion, while the feedback inhibits mainly the conversion of dense gas to stars, because it acts directly to reheat and disperse the gas that is directly on its way to forming stars. (3) The factor by which the SFE is reduced upon the inclusion of feedback is a decreasing function of the cloud's mass, for clouds of size ∼10 pc. This naturally explains the larger observed SFEs of massive-star-forming regions. (4) The clouds may attain a pseudo-virialized state, with a value of the virial mass very similar to the actual cloud mass. However, this state differs from true virialization in that the clouds, rather than being equilibrium entities, are the centers of a larger-scale collapse, in which accretion replenishes the mass consumed by star formation. (5) The higher-density regions within the clouds are in a similar situation, accreting gas infalling from the less-dense, more extended regions of the clouds. (6) The density probability density functions of the regions containing the clouds in general exhibit a shape

Teaching Teachers: The Problem with Emphasizing "Isms."

Science.gov (United States)

Ormrod, Jeanne Ellis

This paper argues that in teaching educational psychology, different experts often compartmentalize theories in substantially different ways, and there is considerable disagreement within the field regarding the dividing lines that separate various "isms." The four main "isms" (behaviorism, information processing theory, constructivism, and social…

Engineering aspects of compact stellarators

International Nuclear Information System (INIS)

Nelson, B.E.; Benson, R.D.; Brooks, A.

2003-01-01

Compact stellarators could combine the good confinement and high beta of a tokamak with the inherently steady state, disruption-free characteristics of a stellarator. Two U.S. compact stellarator facilities are now in the conceptual design phase: the National Compact Stellarator Experiment (NCSX) and the Quasi- Poloidal Stellarator (QPS). NCSX has a major radius of 1.4 m and a toroidal field up to 2 T. The primary feature of both NCSX and QPS is the set of modular coils that provide the basic magnetic configuration. These coils represent a major engineering challenge due to the complex shape, precise geometric accuracy, and high current density of the windings. The winding geometry is too complex for conventional hollow copper conductor construction. Instead, the modular coils will be wound with flexible, multi strand cable conductor that has been compacted to a 75% copper packing fraction. Inside the NCSX coil set and surrounding the plasma is a highly contoured vacuum vessel. The vessel consists of three identical, 120 deg. segments that are bolted together at double sealed joints. The QPS device has a major radius of 0.9 m, a toroidal field of 1 T, and an aspect ratio of only 2.7. Instead of an internal vacuum vessel, the QPS modular coils will operate in an external vacuum tank. (author)

YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD STAR-FORMING REGION N206

International Nuclear Information System (INIS)

Romita, Krista Alexandra; Meixner, M.; Sewilo, M.; Shiao, B.; Carlson, Lynn Redding; Whitney, B.; Babler, B.; Meade, M.; Indebetouw, R.; Hora, J. L.

2010-01-01

We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 μm and MIPS 24 μm), Infrared Survey Facility near-infrared survey (J, H, K s ), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24 μm. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of ∼14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is ∼520 M sun . We calculate a current star formation rate of 0.27 x 10 -1 M sun yr -1 kpc -2 . The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.

A spectroscopic search for colliding stellar winds in O-type close binary systems. IV - Iota Orionis

Science.gov (United States)

Gies, Douglas R.; Wiggs, Michael S.; Bagnuolo, William G., Jr.

1993-01-01

We present H-alpha and He I 6678 A line profiles for the eccentric orbit binary Iota Ori. We have applied a tomography algorithm which uses the established orbital velocity curves and intensity ratio to reconstruct the spectral line profiles for each star. The He I profiles appear as pure photospheric lines, and H-alpha shows variable emission in the line core throughout the orbit (which is typical of O giants) and in the blue wing near periastron passage. We show that the blue wing emission is consistent with an origin between the stars which probably results from a dramatic focusing of the primary's stellar wind at periastron. We also present IUE archival spectra of the UV wind lines N V 1240 A and C IV 1550 A.

Astrophysical contributions of the International Ultraviolet Explorer

International Nuclear Information System (INIS)

Kondo, Y.; Boggess, A.; Maran, S.P.

1989-01-01

Findings that have been made by the IUE in a variety of astrophysical areas are reviewed. Results on stellar chromospheres and transition regions, evolutionary processes in interacting binaries, winds from early-type stars, the ISM, SN 1987A, active galactic nuclei, and solar system objects are addressed. 158 refs

Plant Reliability - an Integrated System for Management (PR-ISM)

International Nuclear Information System (INIS)

Aukeman, M.C.; Leininger, E.G.; Carr, P.

1984-01-01

The Toledo Edison Company, located in Toledo, Ohio, United States of America, recently implemented a comprehensive maintenance management information system for the Davis-Besse Nuclear Power Station. The system is called PR-ISM, meaning Plant Reliability - An Integrated System for Management. PR-ISM provides the tools needed by station management to effectively plan and control maintenance and other plant activities. The PR-ISM system as it exists today consists of four integrated computer applications: equipment data base maintenance, maintenance work order control, administrative activity tracking, and technical specification compliance. PR-ISM is designed as an integrated on-line system and incorporates strong human factors features. PR-ISM provides each responsible person information to do his job on a daily basis and to look ahead towards future events. It goes beyond 'after the fact' reporting. In this respect, PR-ISM is an 'interactive' control system which: captures work requirements and commitments as they are identified, provides accurate and up-to-date status immediately to those who need it, simplifies paperwork and reduces the associated time delays, provides the information base for work management and reliability analysis, and improves productivity by replacing clerical tasks and consolidating maintenance activities. The functional and technical features of PR-ISM, the experience of Toledo Edison during the first year of operation, and the factors which led to the success of the development project are highlighted. (author)

Wide-field infrared survey explorer observations of young stellar objects in the Lynds 1509 dark cloud in Auriga

Energy Technology Data Exchange (ETDEWEB)

Liu, Wilson M.; McCollum, Bruce; Fajardo-Acosta, Sergio [Infrared Processing and Analysis Center, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Padgett, Deborah L. [National Aeronautics and Space Administration, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Terebey, Susan; Angione, John [Department of Physics and Astronomy, California State University, Los Angeles, CA 90032 (United States); Rebull, Luisa M. [Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125 (United States); Leisawitz, David, E-mail: wliu@ipac.caltech.edu [National Aeronautics and Space Administration, Goddard Space Flight Center, Code 605, Greenbelt, MD 20771 (United States)

2014-06-01

The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4 μm, 4.6 μm, 12 μm, and 22 μm, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

Halo Emission of the Cat's Eye Nebula, NGC 6543 Shock Excitation by Fast Stellar Winds

Directory of Open Access Journals (Sweden)

Siek Hyung

2002-09-01

Full Text Available Images taken with the Chandra X-ray telescope have for the the first time revealed the central, wind-driven, hot bubble (Chu et al. 2001, while Hubble Space Telescope (HST WFPC2 images of the Cat's Eye nebula, NGC 6543, show that the temperature of the halo region of angular radius ~ 20'', is much higher than that of the inner bright H II region. With the coupling of a photoionization calculation to a hydrodynamic simulation, we predict the observed [O III] line intensities of the halo region with the same O abundance as in the core H II region: oxygen abundance gradient does not appear to exist in the NGC 6543 inner halo. An interaction between a (leaky fast stellar wind and halo gas may cause the higher excitation temperatures in the halo region and the inner hot bubble region observed with the Chandra X-ray telescope.

Formation of massive, dense cores by cloud-cloud collisions

Science.gov (United States)

Takahira, Ken; Shima, Kazuhiro; Habe, Asao; Tasker, Elizabeth J.

2018-05-01

We performed sub-parsec (˜ 0.014 pc) scale simulations of cloud-cloud collisions of two idealized turbulent molecular clouds (MCs) with different masses in the range of (0.76-2.67) × 104 M_{⊙} and with collision speeds of 5-30 km s-1. Those parameters are larger than in Takahira, Tasker, and Habe (2014, ApJ, 792, 63), in which study the colliding system showed a partial gaseous arc morphology that supports the NANTEN observations of objects indicated to be colliding MCs using numerical simulations. Gas clumps with density greater than 10-20 g cm-3 were identified as pre-stellar cores and tracked through the simulation to investigate the effects of the mass of colliding clouds and the collision speeds on the resulting core population. Our results demonstrate that the smaller cloud property is more important for the results of cloud-cloud collisions. The mass function of formed cores can be approximated by a power-law relation with an index γ = -1.6 in slower cloud-cloud collisions (v ˜ 5 km s-1), and is in good agreement with observation of MCs. A faster relative speed increases the number of cores formed in the early stage of collisions and shortens the gas accretion phase of cores in the shocked region, leading to the suppression of core growth. The bending point appears in the high-mass part of the core mass function and the bending point mass decreases with increase in collision speed for the same combination of colliding clouds. The higher-mass part of the core mass function than the bending point mass can be approximated by a power law with γ = -2-3 that is similar to the power index of the massive part of the observed stellar initial mass function. We discuss implications of our results for the massive-star formation in our Galaxy.

GOT C+ Survey of Transition Clouds in the Inner Galaxy

Science.gov (United States)

Velusamy, Thangasamy; Langer, W. D.; Pineda, J. L.; Goldsmith, P. F.; Li, D.; Yorke, H. W.

2010-05-01

To understand star formation and the lifecycle of the interstellar gas we need detailed information about the transition of diffuse atomic to molecular clouds. The C+ line at 1.9 THz traces a so-far poorly studied stage in cloud evolution - the transitional clouds going from atomic HI to molecular H2 The transition cloud phase, which is difficult to observe in HI and CO alone, may be best characterized via CII emission or absorption. Here we present the first results on transition clouds along a few representative lines of sight in the inner Galaxy from longitude 325 degrees to 10 degrees, observed under the GOT C+ program, a HIFI Herschel Key Project to study the diffuse ISM. We can separate out the different ISM components along each line of sight by comparisons of the high spectral resolution ( 1 km/s) and high sensitivity (rms 0.1 K to 0.2 K) HIFI data on C+ with HI, 12CO, and 13CO spectra. These observations are being carried out with the Herschel Space Observatory. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. JLP is supported under the NASA Postdoctoral Program at JPL, Caltech, administered by Oak Ridge Associated Universities through a contract with NASA.

The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

Science.gov (United States)

Belkus, H.; van Bever, J.; Vanbeveren, D.

In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

The formation of secondary stellar generations in massive young star clusters from rapidly cooling shocked stellar winds

Czech Academy of Sciences Publication Activity Database

Wünsch, Richard; Palouš, Jan; Tenorio-Tagle, G.; Ehlerová, Soňa

2017-01-01

Roč. 835, č. 1 (2017), 60/1-60/15 ISSN 0004-637X R&D Projects: GA ČR GA15-06012S Grant - others:Ga MŠk(CZ) LM2015070 Institutional support: RVO:67985815 Keywords : galaxies * ISM * star clusters Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.533, year: 2016

STAR FORMATION IN TURBULENT MOLECULAR CLOUDS WITH COLLIDING FLOW

International Nuclear Information System (INIS)

Matsumoto, Tomoaki; Dobashi, Kazuhito; Shimoikura, Tomomi

2015-01-01

Using self-gravitational hydrodynamical numerical simulations, we investigated the evolution of high-density turbulent molecular clouds swept by a colliding flow. The interaction of shock waves due to turbulence produces networks of thin filamentary clouds with a sub-parsec width. The colliding flow accumulates the filamentary clouds into a sheet cloud and promotes active star formation for initially high-density clouds. Clouds with a colliding flow exhibit a finer filamentary network than clouds without a colliding flow. The probability distribution functions (PDFs) for the density and column density can be fitted by lognormal functions for clouds without colliding flow. When the initial turbulence is weak, the column density PDF has a power-law wing at high column densities. The colliding flow considerably deforms the PDF, such that the PDF exhibits a double peak. The stellar mass distributions reproduced here are consistent with the classical initial mass function with a power-law index of –1.35 when the initial clouds have a high density. The distribution of stellar velocities agrees with the gas velocity distribution, which can be fitted by Gaussian functions for clouds without colliding flow. For clouds with colliding flow, the velocity dispersion of gas tends to be larger than the stellar velocity dispersion. The signatures of colliding flows and turbulence appear in channel maps reconstructed from the simulation data. Clouds without colliding flow exhibit a cloud-scale velocity shear due to the turbulence. In contrast, clouds with colliding flow show a prominent anti-correlated distribution of thin filaments between the different velocity channels, suggesting collisions between the filamentary clouds

STAR FORMATION IN TURBULENT MOLECULAR CLOUDS WITH COLLIDING FLOW

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, Tomoaki [Faculty of Humanity and Environment, Hosei University, Fujimi, Chiyoda-ku, Tokyo 102-8160 (Japan); Dobashi, Kazuhito; Shimoikura, Tomomi, E-mail: matsu@hosei.ac.jp [Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501 (Japan)

2015-03-10

Using self-gravitational hydrodynamical numerical simulations, we investigated the evolution of high-density turbulent molecular clouds swept by a colliding flow. The interaction of shock waves due to turbulence produces networks of thin filamentary clouds with a sub-parsec width. The colliding flow accumulates the filamentary clouds into a sheet cloud and promotes active star formation for initially high-density clouds. Clouds with a colliding flow exhibit a finer filamentary network than clouds without a colliding flow. The probability distribution functions (PDFs) for the density and column density can be fitted by lognormal functions for clouds without colliding flow. When the initial turbulence is weak, the column density PDF has a power-law wing at high column densities. The colliding flow considerably deforms the PDF, such that the PDF exhibits a double peak. The stellar mass distributions reproduced here are consistent with the classical initial mass function with a power-law index of –1.35 when the initial clouds have a high density. The distribution of stellar velocities agrees with the gas velocity distribution, which can be fitted by Gaussian functions for clouds without colliding flow. For clouds with colliding flow, the velocity dispersion of gas tends to be larger than the stellar velocity dispersion. The signatures of colliding flows and turbulence appear in channel maps reconstructed from the simulation data. Clouds without colliding flow exhibit a cloud-scale velocity shear due to the turbulence. In contrast, clouds with colliding flow show a prominent anti-correlated distribution of thin filaments between the different velocity channels, suggesting collisions between the filamentary clouds.

ISMS Implementation in Nuclear Malaysia

International Nuclear Information System (INIS)

Radhiah Jamalludin; Siti Nurbahyah Hamdan; Mohd Dzul Aiman Aslan

2015-01-01

Nuclear Malaysia provides important services and functions that depend on the resources including information. Use of the information assets must be consistent with good professional practices and procedures and legal requirements, regulations and contracts and the need to ensure the confidentiality, integrity and availability of all information assets of the Agency. ISO / IEC 27001, the international safety standard for information security management system provides the mandatory requirement to implement, review and continuously improve the Information Security Management System (ISMS). Information security policies and the implementation of ISMS is important to protect information assets from all threats; internal or external; intentionally or unintentionally. (author)

Happiness in Economics as Understood Across Ism and Religion

Directory of Open Access Journals (Sweden)

Abdul Ghafar Ismail

2014-12-01

Full Text Available The concept of happiness has been discussed long time ago by economists. Recently, it became the most related and important thing to be studied because of its impact in societies. Discussion about happiness basically interprets within two separate views. First, happiness related with economic variable, for instance, how money can create happiness. Second happiness is discussed within the context of religion. However, the discussion did not combine both contexts, economic variable and religion, to interpret happiness. Therefore, it is important to highlight the concept of happiness in a different way such as in this article. Different cultures will have their own perspective on the determination of happiness. From just “individual perspective” of happiness, they then formed an ism through involvement of a big society from the same culture. Some isms such as hedonism and materialism are synonyms in characterizing the concept of happiness in this modern world. At the same time, the isms are actually working with the economic and non-economic indicators as elements to strengthen the ism itself. On the other hand, the concept of happiness from the perspective of religion will also be a part of discussion in this article. Therefore, this article will reveal that the meaning of happiness is different in terms of religion and ism. So, to carry out both ism and religion simultaneously in shaping a more intrinsic value of happiness is not an easy task. Furthermore, religion is always associated with spiritual value that makes it hard for some people to practice religion and their isms at the same time. Thus, this article will propose that the right interpretation of isms based on their faith in religion can contribute to the concept of genuine happiness.

Hydrodynamic model of a self-gravitating optically thick gas and dust cloud

Science.gov (United States)

Zhukova, E. V.; Zankovich, A. M.; Kovalenko, I. G.; Firsov, K. M.

2015-10-01

We propose an original mechanism of sustained turbulence generation in gas and dust clouds, the essence of which is the consistent provision of conditions for the emergence and maintenance of convective instability in the cloud. We considered a quasi-stationary one-dimensional model of a selfgravitating flat cloud with stellar radiation sources in its center. The material of the cloud is considered a two-component two-speed continuous medium, the first component of which, gas, is transparent for stellar radiation and is supposed to rest being in hydrostatic equilibrium, and the second one, dust, is optically dense and is swept out by the pressure of stellar radiation to the periphery of the cloud. The dust is specified as a set of spherical grains of a similar size (we made calculations for dust particles with radii of 0.05, 0.1, and 0.15 μm). The processes of scattering and absorption of UV radiation by dust particles followed by IR reradiation, with respect to which the medium is considered to be transparent, are taken into account. Dust-driven stellar wind sweeps gas outwards from the center of the cloud, forming a cocoon-like structure in the gas and dust. For the radiation flux corresponding to a concentration of one star with a luminosity of about 5 ×104 L ⊙ per square parsec on the plane of sources, sizes of the gas cocoon are equal to 0.2-0.4 pc, and for the dust one they vary from tenths of a parsec to six parsecs. Gas and dust in the center of the cavity are heated to temperatures of about 50-60 K in the model with graphite particles and up to 40 K in the model with silicate dust, while the background equilibrium temperature outside the cavity is set equal to 10 K. The characteristic dust expansion velocity is about 1-7 kms-1. Three structural elements define the hierarchy of scales in the dust cocoon. The sizes of the central rarefied cavity, the dense shell surrounding the cavity, and the thin layer inside the shell in which dust is settling provide

H I Clouds in the Lower Halo. I. The Galactic All-Sky Survey Pilot Region

International Nuclear Information System (INIS)

Ford, H. Alyson; McClure-Griffiths, N. M.; Calabretta, M. R.; Lockman, Felix J.; Pisano, D. J.; Bailin, J.; Kalberla, P. M. W.; Murphy, T.

2008-01-01

We have detected over 400 H I clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans 18 deg. in longitude, 40 deg. in latitude, and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6 K, a median velocity width of 12.8 km s -1 , and angular sizes ∼ -1 . A sample of clouds likely to be near tangent points was analyzed in detail. These clouds have radii on the order of 30 pc and a median H I mass of 630 M sun . The population has a vertical scale height of 400 pc and is concentrated in Galactocentric radius, peaking at R = 3.8 kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.

Cloud fraction and cloud base measurements from scanning Doppler lidar during WFIP-2

Science.gov (United States)

Bonin, T.; Long, C.; Lantz, K. O.; Choukulkar, A.; Pichugina, Y. L.; McCarty, B.; Banta, R. M.; Brewer, A.; Marquis, M.

2017-12-01

The second Wind Forecast Improvement Project (WFIP-2) consisted of an 18-month field deployment of a variety of instrumentation with the principle objective of validating and improving NWP forecasts for wind energy applications in complex terrain. As a part of the set of instrumentation, several scanning Doppler lidars were installed across the study domain to primarily measure profiles of the mean wind and turbulence at high-resolution within the planetary boundary layer. In addition to these measurements, Doppler lidar observations can be used to directly quantify the cloud fraction and cloud base, since clouds appear as a high backscatter return. These supplementary measurements of clouds can then be used to validate cloud cover and other properties in NWP output. Herein, statistics of the cloud fraction and cloud base height from the duration of WFIP-2 are presented. Additionally, these cloud fraction estimates from Doppler lidar are compared with similar measurements from a Total Sky Imager and Radiative Flux Analysis (RadFlux) retrievals at the Wasco site. During mostly cloudy to overcast conditions, estimates of the cloud radiating temperature from the RadFlux methodology are also compared with Doppler lidar measured cloud base height.

Satellite retrieved cloud optical thickness sensitive to surface wind speed in the subarctic marine boundary layer

International Nuclear Information System (INIS)

Glantz, Paul

2010-01-01

The optical and microphysical properties of low level marine clouds, presented over the Norwegian Sea and Barents Sea, have been investigated for the period 2000-2006. The air masses were transported for more or less seven days over the warmer North Atlantic before they arrived at the area investigated. The main focus in this study is on investigating the relationship between cloud optical thickness (COT) and surface wind speed (U 10m ) using satellite retrievals in combination with operational meteorological data. A relatively strong correlation (R 2 = 0.97) is obtained for wind speeds up to 12 m s -1 , in air masses that were probably to a major degree influenced by wind shears and to a minor degree by buoyancy. The relationship (U 2.5 ) is also in between those most commonly found in the literature for water vapor (∼U 1 ) and sea salt (∼U 3.4 ). The present results highlight the magnitude of marine sea-spray influence on COT and their global climatic importance.

The Magellanic clouds

International Nuclear Information System (INIS)

1989-01-01

As the two galaxies nearest to our own, the Magellanic Clouds hold a special place in studies of the extragalactic distance scale, of stellar evolution and the structure of galaxies. In recent years, results from the South African Astronomical Observatory (SAAO) and elsewhere have shown that it is possible to begin understanding the three dimensional structure of the Clouds. Studies of Magellanic Cloud Cepheids have continued, both to investigate the three-dimensional structure of the Clouds and to learn more about Cepheids and their use as extragalactic distance indicators. Other research undertaken at SAAO includes studies on Nova LMC 1988 no 2 and red variables in the Magellanic Clouds

A new long instrumental serie for the Etesian winds since 1877

Science.gov (United States)

Gómez-Delgado, F. de Paula; Vega, Inmaculada; Gallego, David; Peña-Ortiz, Cristina; Ribera, Pedro; García-Herrera, Ricardo

2016-04-01

The meteorological observations found in old ships' logbooks have been recognized as a useful source of climatic information in periods and areas not covered by other sources. In the last five years several studies have employed the wind direction observations contained in logbooks to generate climatic indices of instrumental character related to large scale patterns such as the atmospheric westerly circulation in North Atlantic, the strength of the West African Monsoon or the start date of the Indian Summer Monsoon (ISM). This study is focused on the winds in the eastern Mediterranean (EM) and its relation to the subtropical climate at decadal scale. Previous studies have shown a significant link between the frequency and strength of the prevalent summer northerly winds (Etesian winds) of the EM and the strength of the ISM. This relationship had only been studied in detail for the second half of the 20th century due to the absence of long and continuous series of wind observations in the EM for previous periods. In this work, we use historical wind data contained in ship's logbooks to generate a new climatic index, the "Etesian Wind Index", which can be defined as the percentage of days with prevalent northerly wind (between 315° and 45°) in a fixed region [10°W-20°W, 32°N-36°N]. We have been able to produce an index of the Etesian winds starting in 1877 suitable to analyze its long term variability and its relation with the ISM in unprecedented detail. Our first results show that the frequency of the northerly winds in the EM was significantly larger in the first half of the studied period, mainly due to an intensification of the zonal component in the second half of the studied period. Interestingly, the comparison with analogous Etesian wind indices computed from reanalysis products (NCEP/NCAR 20th Century (V2c) and ERA20C), shows strong discrepancies among them and with our instrumental reconstruction, which could indicate a misrepresentation of the

Detection of water masers toward young stellar objects in the Large Magellanic Cloud

International Nuclear Information System (INIS)

Johanson, A. K.; Migenes, V.; Breen, S. L.

2014-01-01

We present results from a search for water maser emission toward N4A, N190, and N206, three regions of massive star formation in the Large Magellanic Cloud (LMC). Four water masers were detected; two toward N4A, and two toward N190. In the latter region, no previously known maser emission has been reported. Future studies of maser proper motion to determine the galactic dynamics of the LMC will benefit from the independent data points the new masers in N190 provide. Two of these masers are associated with previously identified massive young stellar objects (YSOs), which strongly supports the authenticity of the classification. We argue that the other two masers identify previously unknown YSOs. No masers were detected toward N206, but it does host a newly discovered 22 GHz continuum source, also associated with a massive YSO. We suggest that future surveys for water maser emission in the LMC be targeted toward the more luminous, massive YSOs.

Evaluating the impact of ERP systems on SC performance with ISM

Directory of Open Access Journals (Sweden)

Cristina López Vargas

2017-06-01

Full Text Available Most companies nowadays have already implemented on-premise or cloud -based ERP systems into their IT infraestrutures. These packages allow firms to integrate, standardize and execute the whole business processes in real time, improving their productivity and operational efficiency. Previous studies highlight their beneficial effects go beyond the single firm. Indeed, ERP system can assist supply‐chain partners to work in close coordination. In order to reach a better understanding in this matter, the present study aims to develop a comprehensive framework. This will represent the benefits derived from ERP adoption in Supply Chain performance. In doing so, we applied an interpretive structural modelling (ISM. Finally, we provide a case study that explores the viability of this framework.

Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

NARCIS (Netherlands)

Meyer, D.M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V.V.; Mignone, A.; Izzard, R.G.; Kaper, L.

2014-01-01

At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional

Impacts of Wind Farms on Cumulus Cloud Development in the Central Great Plains

Science.gov (United States)

Mahoney, L. C.; Wagner, T. J.; L'Ecuyer, T. S.; Kulie, M.

2014-12-01

Cumulus clouds have a net cooling effect on the surface radiative balance by reflecting more downwelling solar radiation than absorbing upwelling terrestrial radiation. As boundary layer cumuli form from buoyant, moist plumes ascending from the surface, their growth may be hindered by the turbulent deformation of the plume by wind farms. A natural laboratory to study the impact of wind farms on cumulus formation are the states of Iowa and Nebraska. Despite their prime location for wind resources and similar synoptic forcings, regulatory issues cause these two states to vary vastly in their wind power offerings. In 2013, Iowa ranked 3rd in the nation for total megawatts installed and generates over a quarter of its electricity from wind energy, more than any other state. In contrast, Nebraska has an order of magnitude fewer turbines installed, and less than five percent of the state's electrical load is wind-generated. This variance in wind power in close proximity makes Iowa and Nebraska a prime area for initial research. This study uses Geostationary Operational Environmental Satellite (GOES) visible satellite imagery from the summer of 2009 to 2013 to investigate cumulus development in these adjacent states, as the majority of large-scale wind farms in Iowa were completed by 2009. Image reflectances in Nebraska and Iowa are compared to determine the magnitude of cumulus growth. Preliminary analysis indicates a reduction in cumulus development near the existing wind farms; a synoptic investigation of these cases will be completed to determine causality.

Stochastic evolution of refractory interstellar dust during the chemical evolution of a two-phase interstellar medium

International Nuclear Information System (INIS)

Liffman, K.; Clayton, D.D.

1989-01-01

The evolution course of refractory interstellar dust during the chemical evolution of a two-phase interstellar medium (ISM) is studied using a simple model of the chemical evolution of ISM. It is assumed that, in this medium, the stars are born in molecular clouds, but new nucleosynthesis products and stellar return are entered into a complementary diffuse medium; the well-mixed matter of each interstellar phase is repeatedly cycled stochastically through the complementary phase and back. The dust is studied on a particle-by-particle bases as it is sputtered by shock waves in the diffuse medium, accretes an amorphous mantle of gaseous refractory atoms while its local medium joins the molecular cloud medium, and encounters the possibility of astration within molecular clouds. Results are presented relevant to the size spectrum of accreted mantles, its age spectrum and the distinction among its several lifetimes, depletion factors of refractory atoms in the diffuse gas, and isotopic anomalies. 26 refs

THE SECOND SURVEY OF THE MOLECULAR CLOUDS IN THE LARGE MAGELLANIC CLOUD BY NANTEN. II. STAR FORMATION

International Nuclear Information System (INIS)

Kawamura, Akiko; Mizuno, Yoji; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Fukui, Yasuo; Fillipovic, Miroslav D.; Staveley-Smith, Lister; Kim, Sungeun; Mizuno, Akira

2009-01-01

We studied star formation activities in the molecular clouds in the Large Magellanic Cloud. We have utilized the second catalog of 272 molecular clouds obtained by NANTEN to compare the cloud distribution with signatures of massive star formation including stellar clusters, and optical and radio H II regions. We find that the molecular clouds are classified into three types according to the activities of massive star formation: Type I shows no signature of massive star formation; Type II is associated with relatively small H II region(s); and Type III with both H II region(s) and young stellar cluster(s). The radio continuum sources were used to confirm that Type I giant molecular clouds (GMCs) do not host optically hidden H II regions. These signatures of massive star formation show a good spatial correlation with the molecular clouds in the sense that they are located within ∼100 pc of the molecular clouds. Among possible ideas to explain the GMC types, we favor that the types indicate an evolutionary sequence; i.e., the youngest phase is Type I, followed by Type II, and the last phase is Type III, where the most active star formation takes place leading to cloud dispersal. The number of the three types of GMCs should be proportional to the timescale of each evolutionary stage if a steady state of massive star and cluster formation is a good approximation. By adopting the timescale of the youngest stellar clusters, 10 Myr, we roughly estimate the timescales of Types I, II, and III to be 6 Myr, 13 Myr, and 7 Myr, respectively, corresponding to a lifetime of 20-30 Myr for the GMCs with a mass above the completeness limit, 5 x 10 4 M sun .

The steady state solutions of radiatively driven stellar winds for a non-Sobolev, pure absorption model

International Nuclear Information System (INIS)

Poe, C.H.; Owocki, S.P.; Castor, J.I.

1990-01-01

The steady state solution topology for absorption line-driven flows is investigated for the condition that the Sobolev approximation is not used to compute the line force. The solution topology near the sonic point is of the nodal type with two positive slope solutions. The shallower of these slopes applies to reasonable lower boundary conditions and realistic ion thermal speed v(th) and to the Sobolev limit of zero of the usual Castor, Abbott, and Klein model. At finite v(th), this solution consists of a family of very similar solutions converging on the sonic point. It is concluded that a non-Sobolev, absorption line-driven flow with a realistic values of v(th) has no uniquely defined steady state. To the extent that a pure absorption model of the outflow of stellar winds is applicable, radiatively driven winds should be intrinsically variable. 34 refs

The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics

Science.gov (United States)

Wurster, James; Bate, Matthew R.; Price, Daniel J.

2018-04-01

We present results from radiation non-ideal magnetohydrodynamics (MHD) calculations that follow the collapse of rotating, magnetized, molecular cloud cores to stellar densities. These are the first such calculations to include all three non-ideal effects: ambipolar diffusion, Ohmic resistivity, and the Hall effect. We employ an ionization model in which cosmic ray ionization dominates at low temperatures and thermal ionization takes over at high temperatures. We explore the effects of varying the cosmic ray ionization rate from ζcr = 10-10 to 10-16 s-1. Models with ionization rates ≳10-12 s-1 produce results that are indistinguishable from ideal MHD. Decreasing the cosmic ray ionization rate extends the lifetime of the first hydrostatic core up to a factor of 2, but the lifetimes are still substantially shorter than those obtained without magnetic fields. Outflows from the first hydrostatic core phase are launched in all models, but the outflows become broader and slower as the ionization rate is reduced. The outflow morphology following stellar core formation is complex and strongly dependent on the cosmic ray ionization rate. Calculations with high ionization rates quickly produce a fast (≈14 km s-1) bipolar outflow that is distinct from the first core outflow, but with the lowest ionization rate, a slower (≈3-4 km s-1) conical outflow develops gradually and seamlessly merges into the first core outflow.

Cloud County Community College Wind Energy Technology Project and Renewable Energy Center of Excellence

Energy Technology Data Exchange (ETDEWEB)

Graham, Bruce [Cloud County Community College, Concordia, KS (United States)

2016-02-26

Cloud County Community College's (CCCC) Wind Energy Technology (WET) program is a leader in the renewable energy movement across Kansas and the USA. The field of renewable energy is a growing industry which continues to experience high demand for career opportunities. This CCCC/DOE project entailed two phases: 1) the installation of two Northwind 100 wind turbines, and 2) the continued development of the WET program curriculum, including enhancement of the CCCC Blade Repair Certificate program. This report provides a technical account of the total work performed, and is a comprehensive description of the results achieved.

Fast Molecular Cloud Destruction Requires Fast Cloud Formation

Energy Technology Data Exchange (ETDEWEB)

Mac Low, Mordecai-Mark [American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024 (United States); Burkert, Andreas [Universitäts Sternwarte München, Ludwigs-Maximilian-Universität, D-81679 München (Germany); Ibáñez-Mejía, Juan C., E-mail: mordecai@amnh.org, E-mail: burkert@usm.lmu.de, E-mail: ibanez@ph1.uni-koeln.de [Max-Planck-Institut für Extraterrestrische Physik, D-85748 Garching bei München (Germany)

2017-09-20

A large fraction of the gas in the Galaxy is cold, dense, and molecular. If all this gas collapsed under the influence of gravity and formed stars in a local free-fall time, the star formation rate in the Galaxy would exceed that observed by more than an order of magnitude. Other star-forming galaxies behave similarly. Yet, observations and simulations both suggest that the molecular gas is indeed gravitationally collapsing, albeit hierarchically. Prompt stellar feedback offers a potential solution to the low observed star formation rate if it quickly disrupts star-forming clouds during gravitational collapse. However, this requires that molecular clouds must be short-lived objects, raising the question of how so much gas can be observed in the molecular phase. This can occur only if molecular clouds form as quickly as they are destroyed, maintaining a global equilibrium fraction of dense gas. We therefore examine cloud formation timescales. We first demonstrate that supernova and superbubble sweeping cannot produce dense gas at the rate required to match the cloud destruction rate. On the other hand, Toomre gravitational instability can reach the required production rate. We thus argue that, although dense, star-forming gas may last only around a single global free-fall time; the dense gas in star-forming galaxies can globally exist in a state of dynamic equilibrium between formation by gravitational instability and disruption by stellar feedback. At redshift z ≳ 2, the Toomre instability timescale decreases, resulting in a prediction of higher molecular gas fractions at early times, in agreement with the observations.

SMASH: Survey of the MAgellanic Stellar History

Energy Technology Data Exchange (ETDEWEB)

Nidever, David L.; Olsen, Knut; Blum, Robert D.; Saha, Abhijit [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Walker, Alistair R.; Vivas, A. Katherina [Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile); Kaleida, Catherine [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Choi, Yumi; Besla, Gurtina; Olszewski, Edward W. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson AZ, 85721 (United States); Conn, Blair C. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Gruendl, Robert A. [National Center for Supercomputing Applications, 1205 West Clark Street, Urbana, IL 61801 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109-1107 (United States); Muñoz, Ricardo R. [Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago (Chile); Gallart, Carme; Monelli, Matteo [Instituto de Astrofísica de Canarias, La Laguna, Tenerife (Spain); Martin, Nicolas F. [Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg (France); Monachesi, Antonela [Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); De Boer, Thomas J. L. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Johnson, L. Clifton, E-mail: dnidever@noao.edu [Center for Astrophysics and Space Sciences, UC San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0424 (United States); and others

2017-11-01

The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg{sup 2} (distributed over ∼2400 square degrees at ∼20% filling factor) to ∼24th mag in ugriz . The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ∼15 mas and the accuracy is ∼2 mas with respect to the Gaia reference frame. The photometric precision is ∼0.5%–0.7% in griz and ∼1% in u with a calibration accuracy of ∼1.3% in all bands. The median 5 σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R  ∼ 18.4 kpc. SMASH DR1 contains measurements of ∼100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

SMASH: Survey of the MAgellanic Stellar History

Science.gov (United States)

Nidever, David L.; Olsen, Knut; Walker, Alistair R.; Vivas, A. Katherina; Blum, Robert D.; Kaleida, Catherine; Choi, Yumi; Conn, Blair C.; Gruendl, Robert A.; Bell, Eric F.; Besla, Gurtina; Muñoz, Ricardo R.; Gallart, Carme; Martin, Nicolas F.; Olszewski, Edward W.; Saha, Abhijit; Monachesi, Antonela; Monelli, Matteo; de Boer, Thomas J. L.; Johnson, L. Clifton; Zaritsky, Dennis; Stringfellow, Guy S.; van der Marel, Roeland P.; Cioni, Maria-Rosa L.; Jin, Shoko; Majewski, Steven R.; Martinez-Delgado, David; Monteagudo, Lara; Noël, Noelia E. D.; Bernard, Edouard J.; Kunder, Andrea; Chu, You-Hua; Bell, Cameron P. M.; Santana, Felipe; Frechem, Joshua; Medina, Gustavo E.; Parkash, Vaishali; Serón Navarrete, J. C.; Hayes, Christian

2017-11-01

The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg2 (distributed over ˜2400 square degrees at ˜20% filling factor) to ˜24th mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ˜15 mas and the accuracy is ˜2 mas with respect to the Gaia reference frame. The photometric precision is ˜0.5%-0.7% in griz and ˜1% in u with a calibration accuracy of ˜1.3% in all bands. The median 5σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R ˜ 18.4 kpc. SMASH DR1 contains measurements of ˜100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

The unusual ISM in Blue and Dusty Gas Rich Galaxies (BADGRS).

Science.gov (United States)

Dunne, L.; Zhang, Z.; De Vis, P.; Clark, C. J. R.; Oteo, I.; Maddox, S. J.; Cigan, P.; de Zotti, G.; Gomez, H. L.; Ivison, R. J.; Rowlands, K.; Smith, M. W. L.; van der Werf, P.; Vlahakis, C.; Millard, J. S.

2018-06-01

The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (FUV - K 0.5). Dubbed `Blue and Dusty Gas Rich Sources' (BADGRS) they have cold diffuse dust temperatures, and the highest dust-to-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular ISM in a representative sample of BADGRS, using very deep {CO(J_{up}=1,2,3)} observations across the central and outer disk regions. We find very low CO brightnesses (Tp = 5 - 30 mK), despite the bright far-infrared emission and metallicities in the range 0.5 UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-β space as z ˜ 5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe.

LOCAL INTERSTELLAR HYDROGEN'S DISAPPEARANCE AT 1 AU: FOUR YEARS OF IBEX IN THE RISING SOLAR CYCLE

International Nuclear Information System (INIS)

Saul, Lukas; Rodríguez, Diego; Scheer, Juergen; Wurz, Peter; Bzowski, Maciej; Kubiak, Marzena; Sokół, Justina; Fuselier, Stephen; McComas, Dave; Möbius, Eberhard

2013-01-01

NASA's Interstellar Boundary Explorer (IBEX) mission has recently opened a new window on the interstellar medium (ISM) by imaging neutral atoms. One ''bright'' feature in the sky is the interstellar wind flowing into the solar system. Composed of remnants of stellar explosions as well as primordial gas and plasma, the ISM is by no means uniform. The interaction of the local ISM with the solar wind shapes our heliospheric environment with hydrogen being the dominant component of the very local ISM. In this paper, we report on direct sampling of the neutral hydrogen of the local ISM over four years of IBEX observations. The hydrogen wind observed at 1 AU has decreased and nearly disappeared as the solar activity has increased over the last four years; the signal at 1 AU has dropped off in 2012 by a factor of ∼8 to near background levels. The longitudinal offset has also increased with time presumably due to greater radiation pressure deflecting the interstellar wind. We present longitudinal and latitudinal arrival direction measurements of the bulk flow as measured over four years beginning at near solar minimum conditions. The H distribution we observe at 1 AU is expected to be different from that outside the heliopause due to ionization, photon pressure, gravity, and filtration by interactions with heliospheric plasma populations. These observations provide an important benchmark for modeling of the global heliospheric interaction. Based on these observations we suggest a further course of scientific action to observe neutral hydrogen over a full solar cycle with IBEX.

Distinct spatiotemporal expression of ISM1 during mouse and chick development

OpenAIRE

Os?rio, Liliana; Wu, Xuewei; Zhou, Zhongjun

2014-01-01

Isthmin 1 (ISM1) constitutes the founder of a new family of secreted proteins characterized by the presence of 2 functional domains: thrombospondin type 1 repeat (TSR1) and adhesion-associated domain in MUC4 and other proteins (AMOP). ISM1 was identified in the frog embryo as a member of the FGF8 synexpression group due to its expression in the brain midbrain-hindbrain boundary (MHB) or isthmus. In zebrafish, ISM1 was described as a WNT- and NODAL-regulated gene. The function of ISM1 remains ...

The galaxy population of Abell 1367: the stellar mass-metallicity relation

Science.gov (United States)

Mouhcine, M.; Kriwattanawong, W.; James, P. A.

2011-04-01

Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

DOE handbook: Integrated safety management systems (ISMS) verification. Team leader's handbook

International Nuclear Information System (INIS)

1999-06-01

The primary purpose of this handbook is to provide guidance to the ISMS verification Team Leader and the verification team in conducting ISMS verifications. The handbook describes methods and approaches for the review of the ISMS documentation (Phase I) and ISMS implementation (Phase II) and provides information useful to the Team Leader in preparing the review plan, selecting and training the team, coordinating the conduct of the verification, and documenting the results. The process and techniques described are based on the results of several pilot ISMS verifications that have been conducted across the DOE complex. A secondary purpose of this handbook is to provide information useful in developing DOE personnel to conduct these reviews. Specifically, this handbook describes methods and approaches to: (1) Develop the scope of the Phase 1 and Phase 2 review processes to be consistent with the history, hazards, and complexity of the site, facility, or activity; (2) Develop procedures for the conduct of the Phase 1 review, validating that the ISMS documentation satisfies the DEAR clause as amplified in DOE Policies 450.4, 450.5, 450.6 and associated guidance and that DOE can effectively execute responsibilities as described in the Functions, Responsibilities, and Authorities Manual (FRAM); (3) Develop procedures for the conduct of the Phase 2 review, validating that the description approved by the Approval Authority, following or concurrent with the Phase 1 review, has been implemented; and (4) Describe a methodology by which the DOE ISMS verification teams will be advised, trained, and/or mentored to conduct subsequent ISMS verifications. The handbook provides proven methods and approaches for verifying that commitments related to the DEAR, the FRAM, and associated amplifying guidance are in place and implemented in nuclear and high risk facilities. This handbook also contains useful guidance to line managers when preparing for a review of ISMS for radiological

A PORTRAIT OF COLD GAS IN GALAXIES AT 60 pc RESOLUTION AND A SIMPLE METHOD TO TEST HYPOTHESES THAT LINK SMALL-SCALE ISM STRUCTURE TO GALAXY-SCALE PROCESSES

International Nuclear Information System (INIS)

Leroy, Adam K.; Hughes, Annie; Schruba, Andreas; Rosolowsky, Erik; Blanc, Guillermo A.; Escala, Andres; Bolatto, Alberto D.; Colombo, Dario; Kramer, Carsten; Kruijssen, J. M. Diederik; Meidt, Sharon; Querejeta, Miguel; Schinnerer, Eva; Sliwa, Kazimierz; Pety, Jerome; Sandstrom, Karin

2016-01-01

The cloud-scale density, velocity dispersion, and gravitational boundedness of the interstellar medium (ISM) vary within and among galaxies. In turbulent models, these properties play key roles in the ability of gas to form stars. New high-fidelity, high-resolution surveys offer the prospect to measure these quantities across galaxies. We present a simple approach to make such measurements and to test hypotheses that link small-scale gas structure to star formation and galactic environment. Our calculations capture the key physics of the Larson scaling relations, and we show good correspondence between our approach and a traditional “cloud properties” treatment. However, we argue that our method is preferable in many cases because of its simple, reproducible characterization of all emission. Using, low- J 12 CO data from recent surveys, we characterize the molecular ISM at 60 pc resolution in the Antennae, the Large Magellanic Cloud (LMC), M31, M33, M51, and M74. We report the distributions of surface density, velocity dispersion, and gravitational boundedness at 60 pc scales and show galaxy-to-galaxy and intragalaxy variations in each. The distribution of flux as a function of surface density appears roughly lognormal with a 1 σ width of ∼0.3 dex, though the center of this distribution varies from galaxy to galaxy. The 60 pc resolution line width and molecular gas surface density correlate well, which is a fundamental behavior expected for virialized or free-falling gas. Varying the measurement scale for the LMC and M31, we show that the molecular ISM has higher surface densities, lower line widths, and more self-gravity at smaller scales.

A PORTRAIT OF COLD GAS IN GALAXIES AT 60 pc RESOLUTION AND A SIMPLE METHOD TO TEST HYPOTHESES THAT LINK SMALL-SCALE ISM STRUCTURE TO GALAXY-SCALE PROCESSES

Energy Technology Data Exchange (ETDEWEB)

Leroy, Adam K. [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Hughes, Annie [CNRS, IRAP, 9 av. du Colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France); Schruba, Andreas [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Rosolowsky, Erik [Department of Physics, University of Alberta, Edmonton, AB (Canada); Blanc, Guillermo A.; Escala, Andres [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Bolatto, Alberto D. [Department of Astronomy, Laboratory for Millimeter-wave Astronomy, and Joint Space Institute, University of Maryland, College Park, MD 20742 (United States); Colombo, Dario [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Kramer, Carsten [Instituto Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Nucleo Central, E-18012 Granada (Spain); Kruijssen, J. M. Diederik [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, D-69120 Heidelberg (Germany); Meidt, Sharon; Querejeta, Miguel; Schinnerer, Eva; Sliwa, Kazimierz [Max Planck Institute für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany); Pety, Jerome [Institut de Radioastronomie Millimtrique (IRAM), 300 Rue de la Piscine, F-38406 Saint-Martin-d’Hères (France); Sandstrom, Karin [Center for Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093 (United States); and others

2016-11-01

The cloud-scale density, velocity dispersion, and gravitational boundedness of the interstellar medium (ISM) vary within and among galaxies. In turbulent models, these properties play key roles in the ability of gas to form stars. New high-fidelity, high-resolution surveys offer the prospect to measure these quantities across galaxies. We present a simple approach to make such measurements and to test hypotheses that link small-scale gas structure to star formation and galactic environment. Our calculations capture the key physics of the Larson scaling relations, and we show good correspondence between our approach and a traditional “cloud properties” treatment. However, we argue that our method is preferable in many cases because of its simple, reproducible characterization of all emission. Using, low- J {sup 12}CO data from recent surveys, we characterize the molecular ISM at 60 pc resolution in the Antennae, the Large Magellanic Cloud (LMC), M31, M33, M51, and M74. We report the distributions of surface density, velocity dispersion, and gravitational boundedness at 60 pc scales and show galaxy-to-galaxy and intragalaxy variations in each. The distribution of flux as a function of surface density appears roughly lognormal with a 1 σ width of ∼0.3 dex, though the center of this distribution varies from galaxy to galaxy. The 60 pc resolution line width and molecular gas surface density correlate well, which is a fundamental behavior expected for virialized or free-falling gas. Varying the measurement scale for the LMC and M31, we show that the molecular ISM has higher surface densities, lower line widths, and more self-gravity at smaller scales.

Solar System Connections to the Organic Material In the ISM

Science.gov (United States)

Pendleton, Yvonne J.

2003-01-01

The organic component of the interstellar medium (ISM) has relevance to the formation of the early solar nebula, since our solar system formed out of ISM material. Comparisons of near infrared spectra of the diffuse ISM dust with those of primitive solar system bodies (such as comets and meteorites) show a remarkable similarity, suggesting that perhaps some of the interstellar organic material made its way, unaltered, into our solar system. Tracing the interstellar organic material is necessary to understand how these materials may be important links in the development of prebiotic phenomena. Studies of the ISM reveal that the organic refractory component of the diffuse ISM is largely hydrocarbon in nature, possessing little N or O, with carbon distributed between the aromatic and aliphatic forms. There is a strong similarity in the near IR spectra of the diffuse ISM (the 3.4 micron hydrocarbon bands) and those seen in the Murchison and Orgueil meteorites, however, detailed comparisons at longer wavelengths reveal critical dissimilarities. Here we will present comparisons and discussion of relevant spectra. As we continue to explore, we will gain insight into the connection between planetesimals in the solar system and chemistry in the dusty space between the stars.

Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868

Energy Technology Data Exchange (ETDEWEB)

Li, Chengyuan; De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai, E-mail: joshuali@pku.edu.cn, E-mail: grijs@pku.edu.cn [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

2014-04-01

Using a combination of high-resolution Hubble Space Telescope/Wide-Field and Planetary Camera-2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters, NGC 1831 and NGC 1868, in the Large Magellanic Cloud based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and the fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. We first establish the clusters' main-sequence binary fractions using the bulk of the clusters' main-sequence stellar populations ≳ 1 mag below their turn-offs. The extent of the turn-off regions in color-magnitude space, corrected for the effects of binarity, implies that age spreads of order 300 Myr may be inferred for both clusters if the stellar distributions in color-magnitude space were entirely due to the presence of multiple populations characterized by an age range. Invoking rapid rotation of the population of cluster members characterized by a single age also allows us to match the observed data in detail. However, when taking into account the extent of the red clump in color-magnitude space, we encounter an apparent conflict for NGC 1831 between the age dispersion derived from that based on the extent of the main-sequence turn off and that implied by the compact red clump. We therefore conclude that, for this cluster, variations in stellar rotation rate are preferred over an age dispersion. For NGC 1868, both models perform equally well.

Compact stellarator coils

International Nuclear Information System (INIS)

Pomphrey, N.; Berry, L.A.; Boozer, A.H.

2001-01-01

Experimental devices to study the physics of high-beta (β>∼4%), low aspect ratio (A<∼4.5) stellarator plasmas require coils that will produce plasmas satisfying a set of physics goals, provide experimental flexibility, and be practical to construct. In the course of designing a flexible coil set for the National Compact Stellarator Experiment, we have made several innovations that may be useful in future stellarator design efforts. These include: the use of Singular Value Decomposition methods for obtaining families of smooth current potentials on distant coil winding surfaces from which low current density solutions may be identified; the use of a Control Matrix Method for identifying which few of the many detailed elements of the stellarator boundary must be targeted if a coil set is to provide fields to control the essential physics of the plasma; the use of Genetic Algorithms for choosing an optimal set of discrete coils from a continuum of potential contours; the evaluation of alternate coil topologies for balancing the tradeoff between physics objective and engineering constraints; the development of a new coil optimization code for designing modular coils, and the identification of a 'natural' basis for describing current sheet distributions. (author)

Modeling CO, CO2, and H2O Ice Abundances in the Envelopes of Young Stellar Objects in the Magellanic Clouds

Science.gov (United States)

Pauly, Tyler; Garrod, Robin T.

2018-02-01

Massive young stellar objects (MYSOs) in the Magellanic Clouds show infrared absorption features corresponding to significant abundances of CO, CO2, and H2O ice along the line of sight, with the relative abundances of these ices differing between the Magellanic Clouds and the Milky Way. CO ice is not detected toward sources in the Small Magellanic Cloud, and upper limits put its relative abundance well below sources in the Large Magellanic Cloud and the Milky Way. We use our gas-grain chemical code MAGICKAL, with multiple grain sizes and grain temperatures, and further expand it with a treatment for increased interstellar radiation field intensity to model the elevated dust temperatures observed in the MCs. We also adjust the elemental abundances used in the chemical models, guided by observations of H II regions in these metal-poor satellite galaxies. With a grid of models, we are able to reproduce the relative ice fractions observed in MC MYSOs, indicating that metal depletion and elevated grain temperature are important drivers of the MYSO envelope ice composition. Magellanic Cloud elemental abundances have a subgalactic C/O ratio, increasing H2O ice abundances relative to the other ices; elevated grain temperatures favor CO2 production over H2O and CO. The observed shortfall in CO in the Small Magellanic Cloud can be explained by a combination of reduced carbon abundance and increased grain temperatures. The models indicate that a large variation in radiation field strength is required to match the range of observed LMC abundances. CH3OH abundance is found to be enhanced in low-metallicity models, providing seed material for complex organic molecule formation in the Magellanic Clouds.

Developing ISM Dust Grain Models with Precision Elemental Abundances from IXO

Science.gov (United States)

Valencic, L. A.; Smith, R. K.; Juet, A.

2009-01-01

The exact nature of interstellar dust grains in the Galaxy remains mysterious, despite their ubiquity. Many viable models exist, based on available IR-UV data and assumed elemental abundances. However, the abundances, which are perhaps the most stringent constraint, are not well known: modelers must use proxies in the absence of direct measurements for the diffuse interstellar medium (ISM). Recent revisions of these proxy values have only added to confusion over which is the best representative for the diffuse ISM, and highlighted the need for direct, high signal-to-noise measurements from the ISM itself. The International X-ray Observatory's superior facilities will enable high-precision elemental abundance measurements. We ill show how these results will measure both the overall ISM abundances and challenge dust models, allowing us to construct a more realistic picture of the ISM.

Interaction and conflict between Sufism and Shi`ism during Safavid era

Directory of Open Access Journals (Sweden)

E Naghibi

2017-10-01

Full Text Available 14th century was considered as the conciliation of Imami Shi`ism and Sufism. But, the relation at the beginning of Safavid dynasty developed to the extent that concepts such as guardianship in a mixture of Shi’ite and Sufi themes made the situation prone to political functions. Imami Shi`ism became official for the first time by Safavids however, their reliance on the support of Turkmen to acquire power urged them to make Sufism superior to Shi`ism. Thus, Ghezelbash people representing Sufism depicted a great kinglike image of the Absent Imam which did not comply with religion and was against the claim of jurists. The perspective did not remain stable after Safavid dynasty was completely established. The idea was in conflict with the interests of the ruling authority, so Safavid rulers turned to Shi`ism from Sufism. The issue not only made Shi`ism and jurists superior to Sufism but also caused Shi`ites confront Sufism for several centuries. The aim of the present article is to investigate the process of peace and conflict between Sufism and Shi`ism during Safavid dynasty.

Explaining the luminosity spread in young clusters: proto and pre-main sequence stellar evolution in a molecular cloud environment

Science.gov (United States)

Jensen, Sigurd S.; Haugbølle, Troels

2018-02-01

Hertzsprung-Russell diagrams of star-forming regions show a large luminosity spread. This is incompatible with well-defined isochrones based on classic non-accreting protostellar evolution models. Protostars do not evolve in isolation of their environment, but grow through accretion of gas. In addition, while an age can be defined for a star-forming region, the ages of individual stars in the region will vary. We show how the combined effect of a protostellar age spread, a consequence of sustained star formation in the molecular cloud, and time-varying protostellar accretion for individual protostars can explain the observed luminosity spread. We use a global magnetohydrodynamic simulation including a sub-scale sink particle model of a star-forming region to follow the accretion process of each star. The accretion profiles are used to compute stellar evolution models for each star, incorporating a model of how the accretion energy is distributed to the disc, radiated away at the accretion shock, or incorporated into the outer layers of the protostar. Using a modelled cluster age of 5 Myr, we naturally reproduce the luminosity spread and find good agreement with observations of the Collinder 69 cluster, and the Orion Nebular Cluster. It is shown how stars in binary and multiple systems can be externally forced creating recurrent episodic accretion events. We find that in a realistic global molecular cloud model massive stars build up mass over relatively long time-scales. This leads to an important conceptual change compared to the classic picture of non-accreting stellar evolution segmented into low-mass Hayashi tracks and high-mass Henyey tracks.

Dissecting Diffuse X-ray Emission in 30 Doradus with T-ReX

Science.gov (United States)

Townsley, Leisa K.; Broos, Patrick

2017-08-01

30 Doradus (the Tarantula Nebula) offers us a microscope on starburst astrophysics, having endured 25 Myrs of the birth and death of the most massive stars known. Across 30 Dor's 250-pc extent, stellar winds and supernovae have carved its ISM into an amazing display of arcs, pillars, and bubbles. For over 40 years, we have also known that 30 Dor is a bright X-ray emitter, so its familiar stars and cold ISM structures suffer irradiation by multi-million-degree plasmas. The 2-Ms Chandra X-ray Visionary Project ``The Tarantula -- Revealed by X-rays'' (T-ReX) exploits Chandra's fine spatial resolution and the ACIS-I field of view to study ISM interfaces on 1--10 pc scales across the entire 30 Dor complex. Here we give preliminary results from ongoing analyses of these data, focusing on the diffuse X-ray emission. Massive star winds and cavity supernovae over the millenia have contributed to a broad mix of X-ray-emitting plasmas and absorbing columns, showing that 30 Dor's hot ISM is just as complex and confusing as that seen at colder temperatures.

Cloud-particle galactic gas dynamics and star formation

International Nuclear Information System (INIS)

Roberts, W.W. Jr.

1983-01-01

Galactic gas dynamics, spiral structure, and star formation are discussed in the context of N-body computational studies based on a cloud-particle model of the interstellar medium. On the small scale, the interstellar medium appears to be cloud-dominated and supernova-perturbed. The cloud-particle model simulates cloud-cloud collisions, the formation of stellar associations, and supernova explosions as dominant local processes. On the large scale in response to a spiral galactic gravitational field, global density waves and galactic shocks develop with large-scale characteristics similar to those found in continuum gas dynamical studies. Both the system of gas clouds and the system of young stellar associations forming from the clouds share in the global spiral structure. However, with the attributes of neither assuming a continuum of gas (as in continuum gas dynamical studies) nor requiring a prescribed equation of state such as the isothermal condition so often employed, the cloud-particle picture retains much of the detail lost in earlier work: namely, the small-scale features and structures so important in understanding the local, turbulent state of the interstellar medium as well as the degree of raggedness often observed superposed on global spiral structure. (Auth.)

Irradiated ISM : Discriminating between cosmic rays and X-rays

NARCIS (Netherlands)

Meijerink, R.; Spaans, M.; Israel, F. P.

2006-01-01

The interstellar medium ( ISM) at the centers of active galaxies is exposed to a combination of cosmic-ray, far-ultraviolet (FUV), and X-ray radiation. We apply photodissociation region (PDR) models to this ISM with both "normal" and highly elevated (5 x 10(-15) s(-1)) cosmic- ray (CR) rates and

Comparison of the 3.36 micrometer feature to the ISM

International Nuclear Information System (INIS)

Tokunaga, A.T.; Brooke, T.Y.

1988-01-01

It has been noted that the 3.36 micrometer emission feature is not the same as that of any ISM band at 3.4 micrometer. This is documented herein. There is no convincing analog to the cometary 3.36 micrometer emission feature seen in the Interstellar Matter band. This fact suggests that if the carbonaceous material in comets came from the ISM, it was either further processed in the solar nebula or has a different appearance because of the different excitation environment of the sun and ISM

Comparison of the 3.36 micrometer feature to the ISM

Science.gov (United States)

Tokunaga, Alan T.; Brooke, Timothy Y.

1988-01-01

It has been noted that the 3.36 micrometer emission feature is not the same as that of any ISM band at 3.4 micrometer. This is documented herein. There is no convincing analog to the cometary 3.36 micrometer emission feature seen in the Interstellar Matter band. This fact suggests that if the carbonaceous material in comets came from the ISM, it was either further processed in the solar nebula or has a different appearance because of the different excitation environment of the sun and ISM.

THE YOUNG STELLAR POPULATION OF LYNDS 1340. AN INFRARED VIEW

International Nuclear Information System (INIS)

Kun, M.; Moór, A.; Wolf-Chase, G.; Apai, D.; Balog, Z.; O’Linger-Luscusk, J.; Moriarty-Schieven, G. H.

2016-01-01

We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low- and intermediate-mass stars. Our goals are to identify and characterize the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects (YSOs) from the Spitzer and WISE databases using various published color criteria and classified them based on the slope of the spectral energy distribution (SED). We identified 170 Class II, 27 flat SED, and 45 Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of YSOs shows three groups, associated with the three major molecular clumps of L1340, each consisting of ≲100 members, including both pre-main-sequence stars and embedded protostars. New Herbig–Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.

THE YOUNG STELLAR POPULATION OF LYNDS 1340. AN INFRARED VIEW

Energy Technology Data Exchange (ETDEWEB)

Kun, M.; Moór, A. [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege út 15-17 (Hungary); Wolf-Chase, G. [Astronomy Department, Adler Planetarium, 1300 South Lake Shore Drive, Chicago, IL 60605 (United States); Apai, D. [Steward Observatory, 933 N. Cherry Avenue, Tucson, AZ 85719 (United States); Balog, Z. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); O’Linger-Luscusk, J. [On leave from California Institute of Technology, 1200 E. California Avenue, Pasadena, CA 91125 (United States); Moriarty-Schieven, G. H., E-mail: kun@konkoly.hu [National Research Council—Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

2016-06-01

We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low- and intermediate-mass stars. Our goals are to identify and characterize the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects (YSOs) from the Spitzer and WISE databases using various published color criteria and classified them based on the slope of the spectral energy distribution (SED). We identified 170 Class II, 27 flat SED, and 45 Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of YSOs shows three groups, associated with the three major molecular clumps of L1340, each consisting of ≲100 members, including both pre-main-sequence stars and embedded protostars. New Herbig–Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.

Gamma titanium aluminide production using the Induction Skull Melting (ISM) process

International Nuclear Information System (INIS)

Reed, S.

1995-01-01

Since 1985, more than 2,000 titanium aluminide heats have been produced using the Induction Skull Melting (ISM) process. The history of ISM/Gamma production will be discussed in this paper. Gamma titanium aluminide processing with Induction Skull Melting offers many advantages over other types of reactive alloy melting methods. These advantages will be discussed as well as drawbacks. Also, potential markets and applications for ISM/Gamma will be presented

A tidally stripped stellar component of the Magellanic bridge

Energy Technology Data Exchange (ETDEWEB)

Nidever, David L.; Monachesi, Antonela; Bell, Eric F. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48104 (United States); Majewski, Steven R.; Beaton, Rachael L. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Muñoz, Ricardo R., E-mail: dnidever@umich.edu, E-mail: rmunoz@das.uchile.cl [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile)

2013-12-20

Deep photometry of the Small Magellanic Cloud (SMC) stellar periphery (R = 4°, 4.2 kpc) is used to study its line-of-sight depth with red clump (RC) stars. The RC luminosity function is affected little by young (≲1 Gyr) blue-loop stars in these regions because their main-sequence counterparts are not observed in the color-magnitude diagrams. The SMCs eastern side is found to have a large line-of-sight depth (∼23 kpc) while the western side has a much shallower depth (∼10 kpc), consistent with previous photographic plate photometry results. We use a model SMC RC luminosity function to deconvolve the observed RC magnitudes and construct the density function in distance for our fields. Three of the eastern fields show a distance bimodality with one component at the 'systemic' ∼67 kpc SMC distance and a second component at ∼55 kpc. Our data are not reproduced well by the various extant Magellanic Cloud and Stream simulations. However, the models predict that the known H I Magellanic Bridge (stretching from the SMC eastward toward the Large Magellanic Cloud, LMC) has a decreasing distance with angle from the SMC and should be seen in both the gaseous and stellar components. From comparison with these models, we conclude that the most likely explanation for our newly identified ∼55 kpc stellar structure in the eastern SMC is a stellar counterpart of the H I Magellanic Bridge that was tidally stripped from the SMC ∼200 Myr ago during a close encounter with the LMC. This discovery has important implications for microlensing surveys of the SMC.

SPH simulations of star/planet formation triggered by cloud-cloud collisions

OpenAIRE

Kitsionas, Spyridon; Whitworth, Anthony Peter; Klessen, Ralf S.

2007-01-01

We present results of hydrodynamic simulations of star formation triggered by cloud-cloud collisions. During the early stages of star formation, low-mass objects form by gravitational instabilities in protostellar discs. A number of these low-mass objects are in the sub-stellar mass range, including a few objects of planetary mass. The disc instabilities that lead to the formation of low-mass objects in our simulations are the product of disc-disc interactions and/or interactions between the ...

Massive runaway stars in the Small Magellanic Cloud

Science.gov (United States)

Gvaramadze, V. V.; Pflamm-Altenburg, J.; Kroupa, P.

2011-01-01

Using archival Spitzer Space Telescope data, we identified for the first time a dozen runaway OB stars in the Small Magellanic Cloud (SMC) through the detection of their bow shocks. The geometry of detected bow shocks allows us to infer the direction of motion of the associated stars and to determine their possible parent clusters and associations. One of the identified runaway stars, AzV 471, was already known as a high-velocity star on the basis of its high peculiar radial velocity, which is offset by ≃ 40 km s-1 from the local systemic velocity. We discuss implications of our findings for the problem of the origin of field OB stars. Several of the bow shock-producing stars are found in the confines of associations, suggesting that these may be “alien” stars contributing to the age spread observed for some young stellar systems. We also report the discovery of a kidney-shaped nebula attached to the early WN-type star SMC-WR3 (AzV 60a). We interpreted this nebula as an interstellar structure created owing to the interaction between the stellar wind and the ambient interstellar medium.

Survey of the MAgellanic Stellar History -- SMASH

NARCIS (Netherlands)

Nidever, David; Olsen, Knut; Besla, Gurtina; Gruendl, Robert; Saha, Abhijit; Gallart, Carme; Olszewski, Edward W.; Munoz, Ricardo; Monelli, Matteo; Kunder, Andrea; Kaleida, Catherine; Walker, Alistair; Stringfellow, Guy; Zaritsky, Dennis; van der Marel, Roeland; Blum, Robert; Vivas, Kathy; Chu, You-Hua; Martin, Nicolas; Conn, Blair; Noel, Noelia; Majewski, Steven; Jin, Shoko; Kim, Hwihyun; Cioni, Maria-Rosa; Bell, Eric; Monachesi, Antonela; de Boer, Thomas

Over the last several years, various discoveries have drastically altered our view of the iconic Magellanic Clouds (MCs), the nearest interacting galaxy system. The best evidence is now that they are on first infall into the Milky Way, that their stellar populations extend much further than

Interactions between exoplanets and the winds of young stars

Directory of Open Access Journals (Sweden)

Vidotto A. A.

2014-01-01

Full Text Available The topology of the magnetic field of young stars is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. Here, we investigate the interaction between winds of young stars and hypothetical planets. For that, we model the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt simplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star, we show that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.

Plasma cloud expansion in the ionosphere: Three-dimensional simulation

International Nuclear Information System (INIS)

Ma, T.Z.; Schunk, R.W.

1991-01-01

A three-dimensional time-dependent model was developed to study the characteristics of a plasma cloud expansion in the ionosphere. The electrostatic potential is solved in three dimensions taking into account the large parallel-to-perpendicular conductivity ratio. Three sample simulations are presented: a plasma expansion of a nearly spherical 1 km Ba + cloud, both with and without a background neutral wind, and a long thin Ba + cloudlet. With or without the neutral wind the effective potential, which is different from the electrostatic potential if the electron temperature is included, is constant along the magnetic field for typical cloud sizes. The expanding plasma clouds become elongated in the magnetic field direction. The released Ba + ions push the background O + ions away along the magnetic field as they expand. Consequently, a hole develops in the background O + distribution at the cloud location and on the two sides of the cloud O + bumps form. The entire three-dimensional structure, composed of the plasma cloud and the background plasma embedded in the cloud, slowly rotates about the magnetic field, with the ions and electrons rotating in opposite directions. The cloud configuration takes the shape of a rotating ellipsoid with a major axis that expands with time. Perpendicular to the magnetic field, in the absence of the neutral wind the motion is insignificant compared to the parallel motion. With a neutral wind the motion along the magnetic field and the rotational motion are qualitatively unchanged, but the cloud and the perturbed background structure move in the direction of the wind, with a speed less than the wind speed. Perpendicular to the magnetic field the deformation of the cloud indiced by the wind is characterized by steepening of the backside

Small Galactic H II regions. II. The molecular clouds and star formation

International Nuclear Information System (INIS)

Hunter, D.A.; Thronson, H.A. Jr.; Wilton, C.

1990-01-01

CO maps of molecular clouds associated with 11 small Galactic H II regions are presented and compared with IR images obtained by IRAS. The molecular masses of the clouds are computed and compared with the masses of the stellar content. The mapped clouds have masses of 1000-60,000 solar and are typical of the more numerous, smaller Galactic molecular clouds. All of the clouds have recently made massive OB stars, and many have complex spatial and kinematic structures. The coincidence of IRAS sources and CO peaks suggests that many of the clouds have sites of star formation other than the optically visible H II region. Star-formation efficiencies are uncertain, with values for the clouds ranging from 0.02 to 0.6 with an average value of 0.2. There is no trend of the upper stellar mass limit with Galactic radius and with molecular cloud mass. 53 refs

A comparison of the reduced and approximate systems for the time dependent computation of the polar wind and multiconstituent stellar winds

International Nuclear Information System (INIS)

Browning, G.L.; Holzer, T.E.

1992-01-01

The reduced system of equations commonly used to describe the time evolution of the polar wind and multiconstituent stellar winds is derived from the equations for a multispecies plasma with known temperature profiles by assuming that the electron thermal speed approaches infinity. The reduced system is proved to have unbounded growth near the sonic point of the protons for many of the standard parameter cases. For the same parameter cases, however, the unmodified system (from which the reduced system is derived) exhibits growth in some of the Fourier modes, but this growth is bounded. An alternate system (the approximate system) in which the electron thermal speed is slowed down is introduced. The approximate system retains the mathematical behavior of the unmodified system and can be shown to accurately describe the smooth solutions of the unmodified system. The approximate system has a number of other advantages over the reduced system becomes inaccurate. Also, for three-dimensional flows the correct reduced system requires the solution of an elliptic equation, while the approximate system is hyperbolic and only requires a time step approximately 1 order of magnitude less than the reduced system. Numerical solutions from models based on the two systems are compared with each other to illustrate these points

Characterizing star formation activity in infrared dark cloud MSXDC G048.65-00.29

NARCIS (Netherlands)

van der Wiel, M. H. D.; Shipman, R. F.

2008-01-01

Context. Infrared dark clouds (IRDCs), condensed regions of the ISM with high column densities, low temperatures and high masses, are suspected sites of star formation. Thousands of IRDCs have already been identified. To date, it has not been resolved whether IRDCs always show star formation

Data-ism

CERN Document Server

Lohr, Steve

2015-01-01

Coal, iron ore and oil were the fuel of the Industrial Revolution. Today's economies and governments are powered by something far less tangible: the explosive abundance of digital data.Steve Lohr, the New York Times' chief technology reporter, charts the ascent of Data-ism, the dominating philosophy of the day in which data is at the forefront of everything and decisions of all kinds are based on data analysis rather than experience and intuition. Taking us behind the scenes and introducing the DOPs (Data Oriented-People), the key personalities behind this revolution, he reveals how consuming

Quantifying chemical uncertainties in simulations of the ISM

Science.gov (United States)

Glover, Simon

2018-06-01

The ever-increasing power of large parallel computers now makes it possible to include increasingly sophisticated chemical models in three-dimensional simulations of the interstellar medium (ISM). This allows us to study the role that chemistry plays in the thermal balance of a realistically-structured, turbulent ISM, as well as enabling us to generated detailed synthetic observations of important atomic or molecular tracers. However, one major constraint on the accuracy of these models is the accuracy with which the input chemical rate coefficients are known. Uncertainties in these chemical rate coefficients inevitably introduce uncertainties into the model predictions. In this talk, I will review some of the methods we can use to quantify these uncertainties and to identify the key reactions where improved chemical data is most urgently required. I will also discuss a few examples, ranging from the local ISM to the high-redshift universe.

ON THE HEATING EFFICIENCY DERIVED FROM OBSERVATIONS OF YOUNG SUPER STAR CLUSTERS IN M82

International Nuclear Information System (INIS)

Silich, Sergiy; Tenorio-Tagle, Guillermo; Torres-Campos, Ana; Munoz-Tunon, Casiana; Monreal-Ibero, Ana; Melo, Veronica

2009-01-01

Here, we discuss the mechanical feedback that massive stellar clusters provide to the interstellar medium of their host galaxy. We apply an analytic theory developed in a previous study for M82-A1 to a sample of 10 clusters located in the central zone of the starburst galaxy M82, all surrounded by compact and dense H II regions. We claim that the only way that such H II regions can survive around the selected clusters, is if they are embedded into a high-pressure ISM and if the majority of their mechanical energy is lost within the star cluster volume via strong radiative cooling. The latter implies that these clusters have a low heating efficiency, η, and evolve in the bimodal hydrodynamic regime. In this regime, the shock-heated plasma in the central zones of a cluster becomes thermally unstable, loses its pressure and is accumulated there, whereas the matter injected by supernovae and stellar winds outside this volume forms a high-velocity outflow-the star cluster wind. We calculated the heating efficiency for each of the selected clusters and found that in all cases it does not exceed 10%. Such low heating efficiency values imply a low mechanical energy output and the impact that the selected clusters provide to the ISM of M82 is thus much smaller than what one would expect using stellar cluster synthetic models.

Can the chirality of the ISM be measured

Science.gov (United States)

Pendleton, Y.; Sandford, S. A.; Werner, Michael W.; Lauer, J.; Chang, Sherwood

1990-01-01

Many moderately complex carbon-based molecules of the type associated with biological systems can exist in one of two mirror-image forms (left-handed and right-handed), which can be distinguished on the basis of their influence on the state of polarization of a light beam. Both forms are possible in nature; yet in living organisms it is invariably the rule that one of these two species predominates. This gives rise to a net chirality. One possible explanation for the net chirality is that the early earth was somehow seeded from the ISM with an excess of chiral organic compounds which led to the development of life forms which are based on left-handed amino acids and right-handed sugars. Molecular spectroscopy of the interstellar medium (ISM) has revealed a complex variety of molecular species similar to those thought to have been available in the oceans and atmospheres of the earth at the time life formed. The detection of such molecules demonstrates the generality of the chemical processes occurring in both environments. If this generality extends to the processes which produce chirality, it may be possible to detect a net chirality in the ISM. This is of particular interest because determining whether or not net chirality exists elsewhere in the universe is an essential aspect of understanding how life developed on earth and how widely distributed it might be. Researchers report preliminary results of a feasibility study to determine whether or not a net chirality in the ISM can be measured. If laboratory results identify candidate chiral molecules that might exist in the ISM, the next step in this feasibility study will be to estimate the detectability of the chiral signature in astrophysical environments.

Can the chirality of the ISM be measured

International Nuclear Information System (INIS)

Pendleton, Y.; Sandford, S.A.; Werner, M.W.; Lauer, J.; Chang, S.

1990-01-01

Many moderately complex carbon-based molecules of the type associated with biological systems can exist in one of two mirror-image forms (left-handed and right-handed), which can be distinguished on the basis of their influence on the state of polarization of a light beam. Both forms are possible in nature; yet in living organisms it is invariably the rule that one of these two species predominates. This gives rise to a net chirality. One possible explanation for the net chirality is that the early earth was somehow seeded from the ISM with an excess of chiral organic compounds which led to the development of life forms which are based on left-handed amino acids and right-handed sugars. Molecular spectroscopy of the interstellar medium (ISM) has revealed a complex variety of molecular species similar to those thought to have been available in the oceans and atmospheres of the earth at the time life formed. The detection of such molecules demonstrates the generality of the chemical processes occurring in both environments. If this generality extends to the processes which produce chirality, it may be possible to detect a net chirality in the ISM. This is of particular interest because determining whether or not net chirality exists elsewhere in the universe is an essential aspect of understanding how life developed on earth and how widely distributed it might be. Researchers report preliminary results of a feasibility study to determine whether or not a net chirality in the ISM can be measured. If laboratory results identify candidate chiral molecules that might exist in the ISM, the next step in this feasibility study will be to estimate the detectability of the chiral signature in astrophysical environments

UNDERSTANDING TRENDS ASSOCIATED WITH CLOUDS IN IRRADIATED EXOPLANETS

International Nuclear Information System (INIS)

Heng, Kevin; Demory, Brice-Olivier

2013-01-01

Unlike previously explored relationships between the properties of hot Jovian atmospheres, the geometric albedo and the incident stellar flux do not exhibit a clear correlation, as revealed by our re-analysis of Q0-Q14 Kepler data. If the albedo is primarily associated with the presence of clouds in these irradiated atmospheres, a holistic modeling approach needs to relate the following properties: the strength of stellar irradiation (and hence the strength and depth of atmospheric circulation), the geometric albedo (which controls both the fraction of starlight absorbed and the pressure level at which it is predominantly absorbed), and the properties of the embedded cloud particles (which determine the albedo). The anticipated diversity in cloud properties renders any correlation between the geometric albedo and the stellar flux weak and characterized by considerable scatter. In the limit of vertically uniform populations of scatterers and absorbers, we use an analytical model and scaling relations to relate the temperature-pressure profile of an irradiated atmosphere and the photon deposition layer and to estimate whether a cloud particle will be lofted by atmospheric circulation. We derive an analytical formula for computing the albedo spectrum in terms of the cloud properties, which we compare to the measured albedo spectrum of HD 189733b by Evans et al. Furthermore, we show that whether an optical phase curve is flat or sinusoidal depends on whether the particles are small or large as defined by the Knudsen number. This may be an explanation for why Kepler-7b exhibits evidence for the longitudinal variation in abundance of condensates, while Kepler-12b shows no evidence for the presence of condensates despite the incident stellar flux being similar for both exoplanets. We include an 'observer's cookbook' for deciphering various scenarios associated with the optical phase curve, the peak offset of the infrared phase curve, and the geometric albedo

Proposal for a security management in cloud computing for health care.

Science.gov (United States)

Haufe, Knut; Dzombeta, Srdan; Brandis, Knud

2014-01-01

Cloud computing is actually one of the most popular themes of information systems research. Considering the nature of the processed information especially health care organizations need to assess and treat specific risks according to cloud computing in their information security management system. Therefore, in this paper we propose a framework that includes the most important security processes regarding cloud computing in the health care sector. Starting with a framework of general information security management processes derived from standards of the ISO 27000 family the most important information security processes for health care organizations using cloud computing will be identified considering the main risks regarding cloud computing and the type of information processed. The identified processes will help a health care organization using cloud computing to focus on the most important ISMS processes and establish and operate them at an appropriate level of maturity considering limited resources.

Proposal for a Security Management in Cloud Computing for Health Care

Directory of Open Access Journals (Sweden)

Knut Haufe

2014-01-01

Full Text Available Cloud computing is actually one of the most popular themes of information systems research. Considering the nature of the processed information especially health care organizations need to assess and treat specific risks according to cloud computing in their information security management system. Therefore, in this paper we propose a framework that includes the most important security processes regarding cloud computing in the health care sector. Starting with a framework of general information security management processes derived from standards of the ISO 27000 family the most important information security processes for health care organizations using cloud computing will be identified considering the main risks regarding cloud computing and the type of information processed. The identified processes will help a health care organization using cloud computing to focus on the most important ISMS processes and establish and operate them at an appropriate level of maturity considering limited resources.

The re-flight of the Colorado high-resolution Echelle stellar spectrograph (CHESS): improvements, calibrations, and post-flight results

Science.gov (United States)

Hoadley, Keri; France, Kevin; Kruczek, Nicholas; Fleming, Brian; Nell, Nicholas; Kane, Robert; Swanson, Jack; Green, James; Erickson, Nicholas; Wilson, Jacob

2016-07-01

In this proceeding, we describe the scientific motivation and technical development of the Colorado High- resolution Echelle Stellar Spectrograph (CHESS), focusing on the hardware advancements and testing supporting the second flight of the payload (CHESS-2). CHESS is a far ultraviolet (FUV) rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium (ISM). CHESS is an objective f/12.4 echelle spectrograph with resolving power > 100,000 over the band pass 1000 - 1600 Å. The spectrograph was designed to employ an R2 echelle grating with "low" line density. We compare the FUV performance of experimental echelle etching processes (lithographically by LightSmyth, Inc. and etching via electron-beam technology by JPL Microdevices Laboratory) with traditional, mechanically-ruled gratings (Bach Research, Inc. and Richardson Gratings). The cross-dispersing grating, developed and ruled by Horiba Jobin-Yvon, is a holographically-ruled, "low" line density, powered optic with a toroidal surface curvature. Both gratings were coated with aluminum and lithium fluoride (Al+LiF) at Goddard Space Flight Center (GSFC). Results from final efficiency and reflectivity measurements for the optical components of CHESS-2 are presented. CHESS-2 utilizes a 40mm-diameter cross-strip anode readout microchannel plate (MCP) detector fabricated by Sensor Sciences, Inc., to achieve high spatial resolution with high count rate capabilities (global rates 1 MHz). We present pre-flight laboratory spectra and calibration results. CHESS-2 launched on 21 February 2016 aboard NASA/CU sounding rocket mission 36.297 UG. We observed the intervening ISM material along the sightline to epsilon Per and present initial characterization of the column densities, temperature, and kinematics of atomic and molecular species in the observation.

High excitation ISM and gas

NARCIS (Netherlands)

Peeters, E; Martinez-Hernandez, NL; Rodriguez-Fernandez, NJ; Tielens, [No Value

An overview is given of ISO results on regions of high excitation ISM and gas, i.e. H II regions, the Galactic Centre and Supernova Remnants. IR emission due to fine-structure lines, molecular hydrogen, silicates, polycyclic aromatic hydrocarbons and dust are summarised, their diagnostic

Cinc qüestions entorn el plurilingüisme estatal

OpenAIRE

Marí, Isidor

2006-01-01

Aquest article presenta cinc reflexions sobre el plurilingüisme de l'estat espanyol, la més important de les quals gira al voltant de la igualtat lingüística sense sobirania política. Aquesta qüestió, que clou l'article, es veu precedida i complementada per altres aspectes com un marc satisfactori de debat polític, una igualtat formal de les llengües de l'estat, un model satisfactori de plurilingüisme estatal igualitari i la introducció del plurilingüisme en àmbits d'ús d'eficàcia simbòlica i...

Computer simulation of dust grain evolution

Science.gov (United States)

Liffman, K.

1989-01-01

The latest results are reported from a Monte Carlo code that is being developed at NASA Ames. The goal of this program, is to derive from the observed and presumed properties of the interstellar medium (ISM) the following information: (1) the size spectrum of interstellar dust; (2) the chemical structure of interstellar dust; (3) interstellar abundances; and (4) the lifetime of a dust grain in the ISM. Presently this study is restricted to refractory interstellar material, i.e., the formation and destruction of ices are not included in the program. The program is embedded in an analytic solution for the bulk chemical evolution of a two-phase interstellar medium in which stars are born in molecular clouds, but new nucleosynthesis products and stellar return are entered into a complementary intercloud medium. The well-mixed matter of each interstellar phase is repeatedly cycled stochastically through the complementary phase and back. Refractory dust is created by thermal condensation as stellar matter flows away from sites of nucleosynthesis such as novae and supernovae and/or from the matter returned from evolved intermediate stars. The history of each particle is traced by standard Monte Carlo techniques as it is sputtered and fragmented by supernova shock waves in the intercloud medium. It also accretes an amorphous mantle of gaseous refractory atoms when its local medium joins with the molecular cloud medium. Finally it encounters the possibility of astration (destruction by star formation) within the molecular clouds.

Star formation in evolving molecular clouds

Science.gov (United States)

Völschow, M.; Banerjee, R.; Körtgen, B.

2017-09-01

Molecular clouds are the principle stellar nurseries of our universe; they thus remain a focus of both observational and theoretical studies. From observations, some of the key properties of molecular clouds are well known but many questions regarding their evolution and star formation activity remain open. While numerical simulations feature a large number and complexity of involved physical processes, this plethora of effects may hide the fundamentals that determine the evolution of molecular clouds and enable the formation of stars. Purely analytical models, on the other hand, tend to suffer from rough approximations or a lack of completeness, limiting their predictive power. In this paper, we present a model that incorporates central concepts of astrophysics as well as reliable results from recent simulations of molecular clouds and their evolutionary paths. Based on that, we construct a self-consistent semi-analytical framework that describes the formation, evolution, and star formation activity of molecular clouds, including a number of feedback effects to account for the complex processes inside those objects. The final equation system is solved numerically but at much lower computational expense than, for example, hydrodynamical descriptions of comparable systems. The model presented in this paper agrees well with a broad range of observational results, showing that molecular cloud evolution can be understood as an interplay between accretion, global collapse, star formation, and stellar feedback.

On the Clouds of Bubbles Formed by Breaking Wind-Waves in Deep Water, and their Role in Air -- Sea Gas Transfer

Science.gov (United States)

Thorpe, S. A.

1982-02-01

Clouds of small bubbles generated by wind waves breaking and producing whitecaps in deep water have been observed below the surface by using an inverted echo sounder. The bubbles are diffused down to several metres below the surface by turbulence against their natural tendency to rise. Measurements have been made at two sites, one in fresh water at Loch Ness and the other in the sea near Oban, northwest Scotland. Sonagraph records show bubble clouds of two distinct types, `columnar clouds' which appear in unstable or convective conditions when the air temperature is less than the surface water temperature, and `billow clouds' which appear in stable conditions when the air temperature exceeds that of the water. Clouds penetrate deeper as the wind speed increases, and deeper in convective conditions than in stable conditions at the same wind speed. The response to a change in wind speed occurs in a period of only a few minutes. Measurements of the acoustic scattering cross section per unit volume, Mv, of the bubbles have been made at several depths. The distributions of Mv at constant depth are close to logarithmic normal. The time-averaged value of Mv, {M}v, decreases exponentially with depth over scales of 40-85 cm (winds up to 12 m s-1),, the scale increasing as the wind increases. Values of {M}v at the same depth and at the same wind speed are greater in the sea than in the fresh-water loch, even at smaller fetches. Estimates have been made of the least mean vertical speed at which bubbles must be advected for them to reach the observed depths. Several centimetres per second are needed, the speeds increasing with wind. Results depend on the conditions at the surfaces of the bubbles, that is whether they are covered by a surface active-film. The presence of oxygen (or gases other than nitrogen) in the gas composing the bubbles appears not to be important in determining their general behaviour. The presence of turbulence in the water also appears unlikely to affect

MHD Interaction of Pulsar Wind Nebulae with SNRs and the ISM

OpenAIRE

van der Swaluw, Eric

2005-01-01

In the late 1960s the discovery of the Crab pulsar in its associated supernova remnant, launched a new field in supernova remnant research: the study of pulsar-driven or plerionic supernova remnants. In these type of remnants, the relativistic wind emitted by the pulsar, blows a pulsar wind nebula into the interior of its supernova remnant. Now, more then forty years after the discovery of the Crab pulsar, there are more then fifty plerionic supernova remnants known, due to the ever-increasin...

All-Sky Cataloging and Analysis of Interstellar Clouds

Science.gov (United States)

Hojaev, Alisher S.

2015-08-01

Recent quick instrumental progress provides possibilities to careful study the interstellar medium (ISM) in the Galaxy and in the nearest galaxies (M31, LMC, SMC, etc.). Significant enough baryon mass of the galactic and extragalactic ISM is concentrated in the clouds with molecular content in the densest parts. The molecular clouds (MoC) are closely related to cold dust-gas clouds, particularly HI ones and should play a key-role in the star forming processes as well as in the dynamics of the Galaxy. These arguments show the importance of counting and surveying of the MoC populations. In order to attempt to solve at least some problems of the physics and evolution of the MoC system in the Galaxy (as well as in other galaxies), its impact on the dynamics and evolution of the Galaxy itself, and to extend the results to the MoC systems in other galaxies we drafted a consolidated composite catalog of molecular and dust-gas clouds based on the recent data. Online data banks and services such as VizieR, SIMBAD at CDS as well as original publications were used. In our Galaxy there are about 200 large molecular clouds, more than 2500 smaller cold dark clouds (including clumps and cores this value exceeds approximately 5000 objects) observed in 11 kpc Solar neighborhood. The general catalog has been divided into 3 sub-catalogs: 1)large and giant MoC; 2) MoC with moderate masses and sizes; 3) small MoC including the clumps and cores. All main catalogs and subcatalogs contain the coordinates, sizes, distances, masses and other physical parameters (density, temperature, radial velocity, etc.) that are available for the different clouds. Statistical and correlation analyses of the data has been performed, the spatial distribution is drawn and the total number is estimated, the dynamic model of formation and evolution of MoC system is proposed. Our results are compared and discussed with data of other investigations as well as the ways to complete and improve the catalog data

Wolf-Rayet stars in the Magellanic Clouds: Spectroscopic binaries and masses

International Nuclear Information System (INIS)

Moffat, A.F.J.

1982-01-01

Repeated spectra to V-mag 13.0 (13.5) have been obtained since 1978 for the 25 (5) brightest WR stars in the LMC (SMC). More than half of these are orbiting spectroscopic binaries, mainly SB1 for the luminous subclasses WN6-9, and SB2 for the rest. Together with galactic data, the Cloud SB2's lead to a correlation between mass ratio WR/OB and WR spectral subclass for each of the WN and WC sequences. This correlation is interpreted as an evolutionary sequence in which the peeling-off process of the strong stellar wind exposes successively hotter regions and eventually converts WN to WC at a point in time which appears to depend on the ambient metal abundance. (Auth.)

Design, construction and validation of the UST-1 modular stellarator

Energy Technology Data Exchange (ETDEWEB)

Queral, V., E-mail: vicentemanuel.queral@ciemat.es

2016-11-15

Highlights: • A small and simple low cost two period modular stellarator is reviewed. • It is defined as a monolithic circular surface torus with carved grooves. • The grooves are accurately mechanised by a new toroidal milling machine. • A very simple e-beam field mapping system has been built and utilized. - Abstract: Stellarator advancement is hindered, among others, by the requirement of geometric complexity at high accuracy and the still scarce universities and research centres following the stellarator line. In this framework, the objectives of the small UST-1 stellarator development were to: (i) explore and test the performance of one possible accurate construction method for stellarators (ii) encourage universities and small fusion research centres to build simple and economical stellarators (iii) educative purpose. Therefore, UST-1 was properly designed to be easily built by a milling machine working on toroidal coordinates, being the winding surface circular poloidally and toroidally. The coil frame is a sole monolithic toroidal thick surface equipped with grooves mechanised by the toroidal milling machine. Only one double pancake is wound in each groove so as to compress the conductor on the laterals of the groove in order to speed up and simplify the winding process. The physics design, the conceptual engineering design and the construction process of UST-1 is presented. The toroidal milling machine is described. The e-beam field line mapping experiments carried out to validate the resulting magnetic configuration are reported. The developed construction method has been proved for the small UST-1 stellarator. Small stellarators are valuable for quick tests of diagnostics, educative purposes, assessment of new confinement concepts, turbulence studies and other applications.

Design, construction and validation of the UST-1 modular stellarator

International Nuclear Information System (INIS)

Queral, V.

2016-01-01

Highlights: • A small and simple low cost two period modular stellarator is reviewed. • It is defined as a monolithic circular surface torus with carved grooves. • The grooves are accurately mechanised by a new toroidal milling machine. • A very simple e-beam field mapping system has been built and utilized. - Abstract: Stellarator advancement is hindered, among others, by the requirement of geometric complexity at high accuracy and the still scarce universities and research centres following the stellarator line. In this framework, the objectives of the small UST-1 stellarator development were to: (i) explore and test the performance of one possible accurate construction method for stellarators (ii) encourage universities and small fusion research centres to build simple and economical stellarators (iii) educative purpose. Therefore, UST-1 was properly designed to be easily built by a milling machine working on toroidal coordinates, being the winding surface circular poloidally and toroidally. The coil frame is a sole monolithic toroidal thick surface equipped with grooves mechanised by the toroidal milling machine. Only one double pancake is wound in each groove so as to compress the conductor on the laterals of the groove in order to speed up and simplify the winding process. The physics design, the conceptual engineering design and the construction process of UST-1 is presented. The toroidal milling machine is described. The e-beam field line mapping experiments carried out to validate the resulting magnetic configuration are reported. The developed construction method has been proved for the small UST-1 stellarator. Small stellarators are valuable for quick tests of diagnostics, educative purposes, assessment of new confinement concepts, turbulence studies and other applications.

ON THE MAXIMUM MASS OF STELLAR BLACK HOLES

International Nuclear Information System (INIS)

Belczynski, Krzysztof; Fryer, Chris L.; Bulik, Tomasz; Ruiter, Ashley; Valsecchi, Francesca; Vink, Jorick S.; Hurley, Jarrod R.

2010-01-01

We present the spectrum of compact object masses: neutron stars and black holes (BHs) that originate from single stars in different environments. In particular, we calculate the dependence of maximum BH mass on metallicity and on some specific wind mass loss rates (e.g., Hurley et al. and Vink et al.). Our calculations show that the highest mass BHs observed in the Galaxy M bh ∼ 15 M sun in the high metallicity environment (Z = Z sun = 0.02) can be explained with stellar models and the wind mass loss rates adopted here. To reach this result we had to set luminous blue variable mass loss rates at the level of ∼10 -4 M sun yr -1 and to employ metallicity-dependent Wolf-Rayet winds. With such winds, calibrated on Galactic BH mass measurements, the maximum BH mass obtained for moderate metallicity (Z = 0.3 Z sun = 0.006) is M bh,max = 30 M sun . This is a rather striking finding as the mass of the most massive known stellar BH is M bh = 23-34 M sun and, in fact, it is located in a small star-forming galaxy with moderate metallicity. We find that in the very low (globular cluster-like) metallicity environment the maximum BH mass can be as high as M bh,max = 80 M sun (Z = 0.01 Z sun = 0.0002). It is interesting to note that X-ray luminosity from Eddington-limited accretion onto an 80 M sun BH is of the order of ∼10 40 erg s -1 and is comparable to luminosities of some known ultra-luminous X-ray sources. We emphasize that our results were obtained for single stars only and that binary interactions may alter these maximum BH masses (e.g., accretion from a close companion). This is strictly a proof-of-principle study which demonstrates that stellar models can naturally explain even the most massive known stellar BHs.

Superluminous Transients at AGN Centers from Interaction between Black Hole Disk Winds and Broad-line Region Clouds

Energy Technology Data Exchange (ETDEWEB)

Moriya, Takashi J.; Tanaka, Masaomi; Ohsuga, Ken [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Morokuma, Tomoki, E-mail: takashi.moriya@nao.ac.jp [Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)

2017-07-10

We propose that superluminous transients that appear at central regions of active galactic nuclei (AGNs) such as CSS100217:102913+404220 (CSS100217) and PS16dtm, which reach near- or super-Eddington luminosities of the central black holes, are powered by the interaction between accretion-disk winds and clouds in broad-line regions (BLRs) surrounding them. If the disk luminosity temporarily increases by, e.g., limit–cycle oscillations, leading to a powerful radiatively driven wind, strong shock waves propagate in the BLR. Because the dense clouds in the AGN BLRs typically have similar densities to those found in SNe IIn, strong radiative shocks emerge and efficiently convert the ejecta kinetic energy to radiation. As a result, transients similar to SNe IIn can be observed at AGN central regions. Since a typical black hole disk-wind velocity is ≃0.1 c , where c is the speed of light, the ejecta kinetic energy is expected to be ≃10{sup 52} erg when ≃1 M {sub ⊙} is ejected. This kinetic energy is transformed to radiation energy in a timescale for the wind to sweep up a similar mass to itself in the BLR, which is a few hundred days. Therefore, both luminosities (∼10{sup 44} erg s{sup −1}) and timescales (∼100 days) of the superluminous transients from AGN central regions match those expected in our interaction model. If CSS100217 and PS16dtm are related to the AGN activities triggered by limit–cycle oscillations, they become bright again in coming years or decades.

Stellarmak a hybrid stellarator: Spheromak

International Nuclear Information System (INIS)

Hartman, C.W.

1980-01-01

This paper discusses hybridization of modified Stellarator-like transform windings (T-windings) with a Spheromak or Field-Reversed-Mirror configuration. This configuration, Stellarmak, retains the important topological advantage of the Spheromak or FRM of having no plasma linking conductors or blankets. The T-windings provide rotational transformation in toroidal angle of the outer poloidal field lines, in effect creating a reversed B/sub Toroidal/ Spheromak or adding average B/sub T/ to the FRM producing higher shear, increased limiting β, and possibly greater stability to kinks and tilt. The presence of field ripple in the toroidal direction may be sufficient to inhibit cancellation of directed ion current by electron drag to allow steady state operation with the toroidal as well as poloidal current maintained by neutral beams

Overview of ISM bands and Software-defined Radio Experimentation

OpenAIRE

Kumbhar, Abhaykumar

2016-01-01

Wireless systems using low-power wireless communication protocol are rapidly gain popularity in the license-free industrial scientific, and medical (ISM) frequency bands. One such emerging trend in ISM frequency bands is home automation. Historically, all the home devices were once unconnected, today are now being connected either by a wired or wireless connection. The low-power wireless communication protocols enable integration of all the digital home devices into a single system and enhanc...

Nuclear abundances and evolution of the interstellar medium

International Nuclear Information System (INIS)

Wannier, P.G.

1980-01-01

Observations of molecular and elemental abundances in the interstellar medium (ISM) are reviewed, with special attention given to isotope ratios. The derivation of molecular isotope abundances for the ISM is discussed, along with H and C fractionation. Millimeter- and centimeter-wave spectra of giant clouds are examined with respect to isotope abundances of C, O, N, Si, S, and D. Evidence for the current enrichment of the ISM by mass loss from evolved stars is considered, together with chemical abundance gradients in H II regions and planetary nebulae. Cosmic-ray observations pertaining to abundances in the ISM are summarized, with emphasis on available results for Ne, Mg, Si, Fe, and Ni. The observations reviewed are shown to support arguments in favor of: (1) the cosmological production of D and He-3 (2) the production of the CNO elements by hydrostatic hydrogen burning (3) the nucleosynthesis of Ne, Mg, Si, S, Fe, and Ni as a result of He burning (4) solar abundances of interstellar S, Fe, and Ni and (5) a direct association between observed inhomogeneities in the ISM and mass loss from evolved stellar objects

A Wolf-Rayet-Like Progenitor of SN 2013cu from Spectral Observations of a Stellar Wind

Science.gov (United States)

Gal-Yam, Avishay; Arcavi, I.; Ofek, E. O.; Ben-Ami, S.; Cenko, S. B.; Kasliwal, M. M.; Cao, Y.; Yaron, O.; Tal, D.; Silverman, J. M.;

The structure and origin of magnetic clouds in the solar wind

Directory of Open Access Journals (Sweden)

V. Bothmer

Full Text Available Plasma and magnetic field data from the Helios 1/2 spacecraft have been used to investigate the structure of magnetic clouds (MCs in the inner heliosphere. 46 MCs were identified in the Helios data for the period 1974–1981 between 0.3 and 1 AU. 85% of the MCs were associated with fast-forward interplanetary shock waves, supporting the close association between MCs and SMEs (solar mass ejections. Seven MCs were identified as direct consequences of Helios-directed SMEs, and the passage of MCs agreed with that of interplanetary plasma clouds (IPCs identified as white-light brightness enhancements in the Helios photometer data. The total (plasma and magnetic field pressure in MCs was higher and the plasma-β lower than in the surrounding solar wind. Minimum variance analysis (MVA showed that MCs can best be described as large-scale quasi-cylindrical magnetic flux tubes. The axes of the flux tubes usually had a small inclination to the ecliptic plane, with their azimuthal direction close to the east-west direction. The large-scale flux tube model for MCs was validated by the analysis of multi-spacecraft observations. MCs were observed over a range of up to ~60° in solar longitude in the ecliptic having the same magnetic configuration. The Helios observations further showed that over-expansion is a common feature of MCs. From a combined study of Helios, Voyager and IMP data we found that the radial diameter of MCs increases between 0.3 and 4.2 AU proportional to the distance, R, from the Sun as R^0.8 (R in AU. The density decrease inside MCs was found to be proportional to R^–2.4, thus being stronger compared to the average solar wind. Four different magnetic configurations, as expected from the flux-tube concept, for MCs have been observed in situ by the Helios probes. MCs with left- and right-handed magnetic helicity occurred with about equal frequencies during 1974–1981, but surprisingly, the majority (74% of the MCs had

High Excitation Gas and ISM

Science.gov (United States)

Peeters, E.; Martin-Hernandez, N. L.; Rodriguez-Fernandez, N. J.; Tielens, A. G. G. M.

2004-01-01

An overview is given of ISO results on regions of high excitation ISM and gas, i.e. HII regions, the Galactic Centre and Supernovae Remnants. IR emission due to fine-structure lines, molecular hydrogen, silicates, polycyclic aromatic hydrocarbons and dust are summarized, their diagnostic capabilities illustrated and their implications highlighted.

Component Manufacturing Development for the National Compact Stellarator Experiment (NCSX)

International Nuclear Information System (INIS)

Heitzenroeder, P.J.; Brown, T.G.; Chrzanowski, J.H.; Cole, M.J.; Goranson, P.L.; Neilson, G.H.; Nelson, B.E.; Reiersen, W.T.; Sutton, L.L.; Williamson, D.E.; Viola, M.E.

2004-11-01

NCSX [National Compact Stellarator Experiment] is the first of a new class of stellarators called compact stellarators which hold the promise of retaining the steady state feature of the stellarator but at a much lower aspect ratio and using a quasi-axisymmetric magnetic field to obtain tokamak-like performance. Although much of NCSX is conventional in design and construction, the vacuum vessel and modular coils provide significant engineering challenges due to their complex shapes, need for high dimensional accuracy, and the high current density required in the modular coils due space constraints. Consequently, a three-phase development program has been undertaken. In the first phase, laboratory/industrial studies were performed during the development of the conceptual design to permit advances in manufacturing technology to be incorporated into NCSX's plans. In the second phase, full-scale prototype modular coil winding forms, compacted cable conductors, and 20 degree sectors of the vacuum vessel were fabricated in industry. In parallel, the NCSX project team undertook RandD studies that focused on the windings. The third (production) phase began in September 2004. First plasma is scheduled for January 2008

Analysis of factors that inhibiting implementation of Information Security Management System (ISMS) based on ISO 27001

Science.gov (United States)

Tatiara, R.; Fajar, A. N.; Siregar, B.; Gunawan, W.

2018-03-01

The purpose of this research is to determine multi factors that inhibiting the implementation of the ISMS based on ISO 2700. It is also to propose a follow-up recommendation on the factors that inhibit the implementation of the ISMS. Data collection is derived from questionnaires to 182 respondents from users in data center operation (DCO) at bca, Indonesian telecommunication international (telin), and data centre division at Indonesian Ministry of Health. We analysing data collection with multiple linear regression analysis and paired t-test. The results are multiple factors which inhibiting the implementation of the ISMS from the three organizations which has implement and operate the ISMS, ISMS documentation management, and continual improvement. From this research, we concluded that the processes of implementation in ISMS is the necessity of the role of all parties in succeeding the implementation of the ISMS continuously.

Stellar astrophysics

International Nuclear Information System (INIS)

1988-01-01

Enhanced mass loss occurs at critical stages in the evolution of stars over a wide range of stellar mass. Observationally, these stages are difficult to identify because of their short duration and because the star is often obscured by dust which condenses in the ejecta. A study of a G-type star, of which only the outer envelope was directly visible, was undertaken by the South African Astronomical Observatory (SAAO). The star itself was obscured by dust clouds and its light was only feebly seen by reflection from some of these clouds. Other studies of the galaxy undertaken by the SAAO include observations of the following: the extreme carbon star IRAS 15194-5115; RV Tauri and T Tauri stars; pre-main sequence stars; the properties of circumstellar dust; rotational modulation and flares on RS CVn and BY Dra stars; heavy-element stars; hydrogen-deficient stars; the open cluster NGC6192; stars in Omega Centauri, and lunar occulations of stars. Simultaneous x-ray, radio and optical data of the flare star YZ CMi were also obtained. 1 fig

THE STELLAR AND GAS KINEMATICS OF THE LITTLE THINGS DWARF IRREGULAR GALAXY NGC 1569

International Nuclear Information System (INIS)

Johnson, Megan; Hunter, Deidre A.; Zhang, Hong-Xin; Herrmann, Kimberly; Oh, Se-Heon; Elmegreen, Bruce; Brinks, Elias; Tollerud, Erik

2012-01-01

In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, σ z , coupled with the maximum rotational velocity derived from H I observations, V max , gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V max /σ z = 2.4 ± 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, ∼1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V max , shows that the disk may be dark matter deficient in the inner region, although, when compared to the

EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS

International Nuclear Information System (INIS)

Cleeves, L. Ilsedore; Adams, Fred C.; Bergin, Edwin A.

2013-01-01

Cosmic rays (CRs) are thought to provide an important source of ionization in the outermost and densest regions of protoplanetary disks; however, it is unknown to what degree they are physically present. As is observed in the solar system, stellar winds can inhibit the propagation of CRs within the circumstellar environment and subsequently into the disk. In this work, we explore the hitherto neglected effects of CR modulation by both stellar winds and magnetic field structures and study how these processes act to reduce disk ionization rates. We construct a two-dimensional protoplanetary disk model of a T-Tauri star system, focusing on ionization from stellar and interstellar FUV, stellar X-ray photons, and CRs. We show that stellar winds can power a heliosphere-like analog, i.e., a ''T-Tauriosphere,'' diminishing CR ionization rates by several orders of magnitude at low to moderate CR energies (E CR ≤ 1 GeV). We explore models of both the observed solar wind CR modulation and a highly simplified estimate for ''elevated'' CR modulation as would be expected from a young T-Tauri star. In the former (solar analog) case, we estimate the ionization rate from galactic CRs to be ζ CR ∼ (0.23-1.4) × 10 –18 s –1 . This range of values, which we consider to be the maximum CR ionization rate for the disk, is more than an order of magnitude lower than what is generally assumed in current models for disk chemistry and physics. In the latter elevated case, i.e., for a ''T-Tauriosphere,'' the ionization rate by CRs is ζ CR ∼ –20 s –1 , which is 1000 times smaller than the interstellar value. We discuss the implications of a diminished CR ionization rate on the gas physics by estimating the size of the resulting magnetorotational instability dead zones. Indeed, if winds are as efficient at CR modulation as predicted here, short-lived radionuclides (now extinct) would have provided the major source of ionization (ζ RN ∼ 7.3 × 10 –19 s –1 ) in the planet

SNe Ia AND THEIR ENVIRONMENT: THEORY AND APPLICATIONS TO SN 2014J

International Nuclear Information System (INIS)

Dragulin, Paul; Hoeflich, Peter

2016-01-01

We present theoretical semi-analytic models for the interaction of stellar winds with the interstellar medium (ISM) or prior mass loss implemented in our code SPICE, assuming spherical symmetry and power-law ambient density profiles and using the Π-theorem. This allows us to test a wide variety of configurations, their functional dependencies, and to find classes of solutions for given observations. Here, we study Type Ia Supernova (SN Ia) surroundings of single and double degenerate systems, and their observational signatures. Winds may originate from the progenitor prior to the white dwarf (WD) stage, the WD, a donor star, or an accretion disk (AD). For M Ch explosions, the AD wind dominates and produces a low-density void several light years across, surrounded by a dense shell. The bubble explains the lack of observed interaction in late time SN light curves for, at least, several years. The shell produces narrow ISM lines Doppler shifted by 10–100 km s −1 , and equivalent widths of ≈100 mÅ and ≈1 mÅ in cases of ambient environments with constant density and produced by prior mass loss, respectively. For SN2014J, both mergers and M Ch mass explosions have been suggested based on radio and narrow lines. As a consistent and most likely solution, we find an AD wind running into an environment produced by the red giant wind of the progenitor during the pre-WD stage, and a short delay, 0.013–1.4 Myr, between the WD formation and the explosion. Our framework may be applied more generally to stellar winds and star formation feedback in large scale galactic evolution simulations

SNe Ia AND THEIR ENVIRONMENT: THEORY AND APPLICATIONS TO SN 2014J

Energy Technology Data Exchange (ETDEWEB)

Dragulin, Paul; Hoeflich, Peter, E-mail: pd09@my.fsu.edu, E-mail: phoeflich77@gmail.com [Department of Physics, Florida State University, Tallahassee, FL 32306 (United States)

2016-02-10

We present theoretical semi-analytic models for the interaction of stellar winds with the interstellar medium (ISM) or prior mass loss implemented in our code SPICE, assuming spherical symmetry and power-law ambient density profiles and using the Π-theorem. This allows us to test a wide variety of configurations, their functional dependencies, and to find classes of solutions for given observations. Here, we study Type Ia Supernova (SN Ia) surroundings of single and double degenerate systems, and their observational signatures. Winds may originate from the progenitor prior to the white dwarf (WD) stage, the WD, a donor star, or an accretion disk (AD). For M{sub Ch} explosions, the AD wind dominates and produces a low-density void several light years across, surrounded by a dense shell. The bubble explains the lack of observed interaction in late time SN light curves for, at least, several years. The shell produces narrow ISM lines Doppler shifted by 10–100 km s{sup −1}, and equivalent widths of ≈100 mÅ and ≈1 mÅ in cases of ambient environments with constant density and produced by prior mass loss, respectively. For SN2014J, both mergers and M{sub Ch} mass explosions have been suggested based on radio and narrow lines. As a consistent and most likely solution, we find an AD wind running into an environment produced by the red giant wind of the progenitor during the pre-WD stage, and a short delay, 0.013–1.4 Myr, between the WD formation and the explosion. Our framework may be applied more generally to stellar winds and star formation feedback in large scale galactic evolution simulations.

The Origin of Fast Molecular Outflows in Quasars: Molecule Formation in AGN-Driven Galactic Winds

Science.gov (United States)

Richings, Alexander James; Faucher-Giguere, Claude-Andre

2017-07-01

Observations of AGN host galaxies have detected fast molecular outflows, with velocities up to 1000 km s-1. However, the origin of these molecular outflows is currently unclear. One possibility is that they are formed from molecular gas that is swept up from the host galaxy by the AGN wind. However, previous studies have suggested that molecular clouds that are swept up by an AGN wind are unlikely to survive being accelerated to such high velocities. An alternative scenario is that molecules may form within the AGN wind material itself. We present a suite of 3D hydrodynamic simulations of an idealised AGN wind that we have run to explore this scenario. These simulations are coupled to a time-dependent chemical model to follow the creation and destruction of molecules, including H2, CO, OH and HCO+. We find that molecules do form within the wind, with molecular outflow rates up to 140 M⊙ yr-1 after 1 Myr. This is sensitive to the ambient ISM density, metallicity, and AGN luminosity. We also compute observable CO emission lines from these simulations using a radiative transfer code in post-processing. The CO-derived outflow rates are comparable to those seen in observations, although the maximum line of sight velocities are a factor ≍2 lower than observed. We find a CO (1-0) to H2 conversion factor of αCO = 0.15 M⊙ (K km s-1 pc2)-1 at solar metallicity, 5 times lower than is typically assumed in observations of such systems.

UNDERSTANDING TRENDS ASSOCIATED WITH CLOUDS IN IRRADIATED EXOPLANETS

Energy Technology Data Exchange (ETDEWEB)

Heng, Kevin [University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012 Bern (Switzerland); Demory, Brice-Olivier, E-mail: kevin.heng@csh.unibe.ch, E-mail: demory@mit.edu [Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)

2013-11-10

Unlike previously explored relationships between the properties of hot Jovian atmospheres, the geometric albedo and the incident stellar flux do not exhibit a clear correlation, as revealed by our re-analysis of Q0-Q14 Kepler data. If the albedo is primarily associated with the presence of clouds in these irradiated atmospheres, a holistic modeling approach needs to relate the following properties: the strength of stellar irradiation (and hence the strength and depth of atmospheric circulation), the geometric albedo (which controls both the fraction of starlight absorbed and the pressure level at which it is predominantly absorbed), and the properties of the embedded cloud particles (which determine the albedo). The anticipated diversity in cloud properties renders any correlation between the geometric albedo and the stellar flux weak and characterized by considerable scatter. In the limit of vertically uniform populations of scatterers and absorbers, we use an analytical model and scaling relations to relate the temperature-pressure profile of an irradiated atmosphere and the photon deposition layer and to estimate whether a cloud particle will be lofted by atmospheric circulation. We derive an analytical formula for computing the albedo spectrum in terms of the cloud properties, which we compare to the measured albedo spectrum of HD 189733b by Evans et al. Furthermore, we show that whether an optical phase curve is flat or sinusoidal depends on whether the particles are small or large as defined by the Knudsen number. This may be an explanation for why Kepler-7b exhibits evidence for the longitudinal variation in abundance of condensates, while Kepler-12b shows no evidence for the presence of condensates despite the incident stellar flux being similar for both exoplanets. We include an 'observer's cookbook' for deciphering various scenarios associated with the optical phase curve, the peak offset of the infrared phase curve, and the geometric

Self-consistent atmosphere modeling with cloud formation for low-mass stars and exoplanets

Science.gov (United States)

Juncher, Diana; Jørgensen, Uffe G.; Helling, Christiane

2017-12-01

Context. Low-mass stars and extrasolar planets have ultra-cool atmospheres where a rich chemistry occurs and clouds form. The increasing amount of spectroscopic observations for extrasolar planets requires self-consistent model atmosphere simulations to consistently include the formation processes that determine cloud formation and their feedback onto the atmosphere. Aims: Our aim is to complement the MARCS model atmosphere suit with simulations applicable to low-mass stars and exoplanets in preparation of E-ELT, JWST, PLATO and other upcoming facilities. Methods: The MARCS code calculates stellar atmosphere models, providing self-consistent solutions of the radiative transfer and the atmospheric structure and chemistry. We combine MARCS with a kinetic model that describes cloud formation in ultra-cool atmospheres (seed formation, growth/evaporation, gravitational settling, convective mixing, element depletion). Results: We present a small grid of self-consistently calculated atmosphere models for Teff = 2000-3000 K with solar initial abundances and log (g) = 4.5. Cloud formation in stellar and sub-stellar atmospheres appears for Teff day-night energy transport and no temperature inversion.

Hyper-massive cloud, shock and stellar formation efficiency

International Nuclear Information System (INIS)

Louvet, Fabien

2014-01-01

O and B types stars are of paramount importance in the energy budget of galaxies and play a crucial role enriching the interstellar medium. However, their formation, unlike that of solar-type stars, is still subject to debate, if not an enigma. The earliest stages of massive star formation and the formation of their parent cloud are still crucial astrophysical questions that drew a lot of attention in the community, both from the theoretical and observational perspective, during the last decade. It has been proposed that massive stars are born in massive dense cores that form through very dynamic processes, such as converging flows of gas. During my PhD, I conducted a thorough study of the formation of dense cores and massive stars in the W43-MM1 supermassive structure, located at 6 kpc from the sun. At first, I showed a direct correlation between the star formation efficiency and the volume gas density of molecular clouds, in contrast with scenarios suggested by previous studies. Indeed, the spatial distribution and mass function of the massive dense cores currently forming in W43-MM1 suggests that this supermassive filament is undergoing a star formation burst, increasing as one approaches its center. I compared these observational results with the most recent numerical and analytical models of star formation. This comparison not only provides new constraints on the formation of supermassive filaments, but also suggests that understanding star formation in high density, extreme ridges requires a detailed portrait of the structure of these exceptional objects. Second, having shown that the formation of massive stars depends strongly on the properties of the ridges where they form, I studied the formation processes of these filaments, thanks of the characterization of their global dynamics. Specifically, I used a tracer of shocks (SiO molecule) to disentangle the feedback of local star formation processes (bipolar jets and outflows) from shocks tracing the pristine

Comet Grains: Their IR Emission and Their Relation to ISM Grains

Science.gov (United States)

Wooden, Diane H.; DeVincenzi, Donald (Technical Monitor)

2002-01-01

Comets and the chodritic, porous interplanetary dust particles (CP IDPs) that they shed in their comae are reservoirs of primitive solar nebula materials. The high porosity and fragility of cometary grains and CP IDPs, and anomalously high deuterium contents of highly fragile, pyroxene-rich Cluster IDPs imply these aggregate particles contain significant abundances of grains from the interstellar medium (ISM). IR spectra of comets (3 - 40 micron) reveal the presence of a warm (nearIR) featureless emission modeled by amorphous carbon grains. Broad and narrow resonances near 10 and 20 microns are modeled by warm chondritic (50% Fe and 50% Mg) amorphous silicates and cooler Mg-rich crystalline silicate minerals, respectively. Cometary amorphous silicates resonances are well matched by IR spectra of CP IDPs dominated by GEMS (0.1 micron silicate spherules) that are thought to be the interstellar Fe-bearing amorphous silicates produced in AGB stars. Acid-etched ultramicrotomed CP IDP samples, however, show that both the carbon phase (amorphous and aliphatic) and the Mg-rich amorphous silicate phase in GEMS are not optically absorbing. Rather, it is Fe and FeS nanoparticles embedded in the GEMS that makes the CP IDPs dark. Therefore, CP IDPs suggest significant processing has occurred in the ISM. ISM processing probably includes in He' ion bombardment in supernovae shocks. Laboratory experiments show He+ ion bombardment amorphizes crystalline silicates, increases porosity, and reduces Fe into nanoparticles. Cometary crystalline silicate resonances are well matched by IR spectra of laboratory submicron Mg-rich olivine crystals and pyroxene crystals. Discovery of a Mg-pure olivine crystal in a Cluster IDP with isotopically anomalous oxygen indicates that a small fraction of crystalline silicates may have survived their journey from AGB stars through the ISM to the early solar nebula. The ISM does not have enough crystalline silicates (ISM Mg-rich crystals leads to the

Young star clusters in nearby molecular clouds

Science.gov (United States)

Getman, K. V.; Kuhn, M. A.; Feigelson, E. D.; Broos, P. S.; Bate, M. R.; Garmire, G. P.

2018-06-01

The SFiNCs (Star Formation in Nearby Clouds) project is an X-ray/infrared study of the young stellar populations in 22 star-forming regions with distances ≲ 1 kpc designed to extend our earlier MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey of more distant clusters. Our central goal is to give empirical constraints on cluster formation mechanisms. Using parametric mixture models applied homogeneously to the catalogue of SFiNCs young stars, we identify 52 SFiNCs clusters and 19 unclustered stellar structures. The procedure gives cluster properties including location, population, morphology, association with molecular clouds, absorption, age (AgeJX), and infrared spectral energy distribution (SED) slope. Absorption, SED slope, and AgeJX are age indicators. SFiNCs clusters are examined individually, and collectively with MYStIX clusters, to give the following results. (1) SFiNCs is dominated by smaller, younger, and more heavily obscured clusters than MYStIX. (2) SFiNCs cloud-associated clusters have the high ellipticities aligned with their host molecular filaments indicating morphology inherited from their parental clouds. (3) The effect of cluster expansion is evident from the radius-age, radius-absorption, and radius-SED correlations. Core radii increase dramatically from ˜0.08 to ˜0.9 pc over the age range 1-3.5 Myr. Inferred gas removal time-scales are longer than 1 Myr. (4) Rich, spatially distributed stellar populations are present in SFiNCs clouds representing early generations of star formation. An appendix compares the performance of the mixture models and non-parametric minimum spanning tree to identify clusters. This work is a foundation for future SFiNCs/MYStIX studies including disc longevity, age gradients, and dynamical modelling.

Blowing in the Milky Way Wind: Neutral Hydrogen Clouds Tracing the Galactic Nuclear Outflow

Science.gov (United States)

Di Teodoro, Enrico M.; McClure-Griffiths, N. M.; Lockman, Felix J.; Denbo, Sara R.; Endsley, Ryan; Ford, H. Alyson; Harrington, Kevin

2018-03-01

We present the results of a new sensitive survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. The observations extend up to Galactic latitude | b| resolution of 9.‧5 and an average rms brightness temperature noise of 40 mK in a 1 {km} {{{s}}}-1 channel. The survey reveals the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5 kpc from the Galactic plane and showing no signature of Galactic rotation. These clouds have local standard of rest velocities | {V}LSR}| ≲ 360 {km} {{{s}}}-1, and assuming a Galactic Center origin, they have sizes of a few tens of parsec and neutral hydrogen masses spanning 10{--}{10}5 {M}ȯ . Accounting for selection effects, the cloud population is symmetric in longitude, latitude, and V LSR. We model the cloud kinematics in terms of an outflow expanding from the Galactic Center and find the population consistent with being material moving with radial velocity {V}{{w}}≃ 330 {km} {{{s}}}-1 distributed throughout a bicone with opening angle α > 140^\\circ . This simple model implies an outflow luminosity {L}{{w}}> 3× {10}40 erg s‑1 over the past 10 Myr, consistent with star formation feedback in the inner region of the Milky Way, with a cold gas mass-loss rate ≲ 0.1 {{M}ȯ {yr}}-1. These clouds may represent the cold gas component accelerated in the nuclear wind driven by our Galaxy, although some of the derived properties challenge current theoretical models of the entrainment process.

ISM chemical abundances in two intermediate-velocity clouds in the line of sight to SN 1987A

Science.gov (United States)

Morgan, Siobahn; Bohm-Vitense, Erika

1988-01-01

The earliest IUE high-resolution spectra of SN 1987A have been studied and reveal the presence of several clouds in the line of sight to the LMC. In particular, there are two clouds with radial velocities of about 130 km/s and about 180 km/s. These clouds' velocities are between those of Galactic clouds at 0-80 km/s and those of LMC gas at about 270 km/s. Chemical-abundance determinations may help to determine the origin and location of these clouds. Curve-of-growth analysis and 21-cm observations show that they may be underabundant in heavy elements by about a factor of 2 as compared to solar abundances. No depletion indicative of grain formation can be seen.

Magnetohydrodynamic theory of plasma equilibrium and stability in stellarators: Survey of results

International Nuclear Information System (INIS)

Shafranov, V.D.

1983-01-01

The main advantage of a stellarator is its capability of steady-state operation. It can be exploited as a reactor if stable plasma confinement can be achieved with #betta#approx.10%. Therefore, this limiting pressure value is a key factor in stellarator development. This paper contains a survey of current ideas on the magnetohydrodynamic equilibrium and stability properties of stellarators with sufficiently high pressure. Here, any system of nested toroidal magnetic surfaces generated by external currents is considered a stellarator. Systems produced by helical or equivalent windings, including torsatrons and heliotrons, will be called ordinary stellarators, in contrast to those with spatial axes. It is shown that adequate confinement can be achieved

THE Onfp CLASS IN THE MAGELLANIC CLOUDS

International Nuclear Information System (INIS)

Walborn, Nolan R.; Howarth, Ian D.; Evans, Christopher J.

2010-01-01

The Onfp class of rotationally broadened, hot spectra was defined some time ago in the Galaxy, where its membership to date numbers only eight. The principal defining characteristic is a broad, centrally reversed He II λ 4686 emission profile; other emission and absorption lines are also rotationally broadened. Recent surveys in the Magellanic Clouds (MCs) have brought the class membership there, including some related spectra, to 28. We present a survey of the spectral morphology and rotational velocities, as a first step toward elucidating the nature of this class. Evolved, rapidly rotating hot stars are not expected theoretically, because the stellar winds should brake the rotation. Luminosity classification of these spectra is not possible, because the principal criterion (He II λ4686) is peculiar; however, the MCs provide reliable absolute magnitudes, which show that they span the entire range from dwarfs to supergiants. The Onfp line-broadening distribution is distinct and shifted toward larger values from those of normal O dwarfs and supergiants with >99.99% confidence. All cases with multiple observations show line-profile variations, which even remove some objects from the class temporarily. Some of them are spectroscopic binaries; it is possible that the peculiar profiles may have multiple causes among different objects. The origin and future of these stars are intriguing; for instance, they could be stellar mergers and/or gamma-ray-burst progenitors.

ISO 9001 laatujärjestelmän liittäminen osaksi ISM manuaalia

OpenAIRE

Koskinen, Ville

2016-01-01

Lopputyön aiheena on Turkulaisen varustamon VG-Shipping Oy toimeksiantona selvittää ISO 9001 standardin vaatimusten mukaisten ohjeistuksien liittäminen yrityksen voimassa olevaan turvallisuusjohtamisjärjestelmään (ISM) ja yhdistetyn manuaalin rakentaminen vastaamaan molempien standardien (ISM koodi ja ISO 9001 standardi) vaatimuksia, siten että varustamon alukset eivät ole ISO 9001 luokiteltuja vaan ainoastaan ISM koodin mukaan auditoituja. Lopullisena toimenpiteenä on hyväksyttää ja audit...

Thermal radio emission from the winds of single stars

International Nuclear Information System (INIS)

Abbott, D.C.

1985-01-01

Observations of thermal emission at radio wavelengths provides a powerful diagnostic of the rate of mass loss and temperature of the winds of early-type stars. Some winds are also strong sources of nonthermal emission. Case studies of known thermal and nonthermal sources provide empirical criteria for classifying the observed radio radiation. Mass loss rates are derived for 37 OB and Wolf-Rayet stars considered definite or probable thermal wind sources by these criteria. The rate of mass loss is strongly linked to stellar luminosity in OB stars and probably linked to stellar mass in Wolf-Rayet stars, with no measurable correlation with any other stellar property. A few late-type giants and supergiants also have detectable thermal emission, which arises from extended, accelerating, partially-ionized chromospheres. (orig.)

Isthmin 1 (ism1) is required for normal hematopoiesis in developing zebrafish.

Science.gov (United States)

Berrun, Arturo; Harris, Elena; Stachura, David L

2018-01-01

Hematopoiesis is an essential and highly regulated biological process that begins with hematopoietic stem cells (HSCs). In healthy organisms, HSCs are responsible for generating a multitude of mature blood cells every day, yet the molecular pathways that instruct HSCs to self-renew and differentiate into post-mitotic blood cells are not fully known. To understand these molecular pathways, we investigated novel genes expressed in hematopoietic-supportive cell lines from the zebrafish (Danio rerio), a model system increasingly utilized to uncover molecular pathways important in the development of other vertebrate species. We performed RNA sequencing of the transcriptome of three stromal cell lines derived from different stages of embryonic and adult zebrafish and identified hundreds of highly expressed transcripts. For our studies, we focused on isthmin 1 (ism1) due to its shared synteny with its human gene ortholog and because it is a secreted protein. To characterize ism1, we performed loss-of-function experiments to identify if mature blood cell production was disrupted. Myeloid and erythroid lineages were visualized and scored with transgenic zebrafish expressing lineage-specific markers. ism1 knockdown led to reduced numbers of neutrophils, macrophages, and erythrocytes. Analysis of clonal methylcellulose assays from ism1 morphants also showed a reduction in total hematopoietic stem and progenitor cells (HSPCs). Overall, we demonstrate that ism1 is required for normal generation of HSPCs and their downstream progeny during zebrafish hematopoiesis. Further investigation into ism1 and its importance in hematopoiesis may elucidate evolutionarily conserved processes in blood formation that can be further investigated for potential clinical utility.

Isthmin 1 (ism1) is required for normal hematopoiesis in developing zebrafish

Science.gov (United States)

Berrun, Arturo; Harris, Elena

2018-01-01

Hematopoiesis is an essential and highly regulated biological process that begins with hematopoietic stem cells (HSCs). In healthy organisms, HSCs are responsible for generating a multitude of mature blood cells every day, yet the molecular pathways that instruct HSCs to self-renew and differentiate into post-mitotic blood cells are not fully known. To understand these molecular pathways, we investigated novel genes expressed in hematopoietic-supportive cell lines from the zebrafish (Danio rerio), a model system increasingly utilized to uncover molecular pathways important in the development of other vertebrate species. We performed RNA sequencing of the transcriptome of three stromal cell lines derived from different stages of embryonic and adult zebrafish and identified hundreds of highly expressed transcripts. For our studies, we focused on isthmin 1 (ism1) due to its shared synteny with its human gene ortholog and because it is a secreted protein. To characterize ism1, we performed loss-of-function experiments to identify if mature blood cell production was disrupted. Myeloid and erythroid lineages were visualized and scored with transgenic zebrafish expressing lineage-specific markers. ism1 knockdown led to reduced numbers of neutrophils, macrophages, and erythrocytes. Analysis of clonal methylcellulose assays from ism1 morphants also showed a reduction in total hematopoietic stem and progenitor cells (HSPCs). Overall, we demonstrate that ism1 is required for normal generation of HSPCs and their downstream progeny during zebrafish hematopoiesis. Further investigation into ism1 and its importance in hematopoiesis may elucidate evolutionarily conserved processes in blood formation that can be further investigated for potential clinical utility. PMID:29758043

A study of the stellar population in the Lynds 1641 dark cloud. I. The IRAS catalog sources

International Nuclear Information System (INIS)

Strom, K.M.; Newton, G.; Strom, S.E.; Seaman, R.L.; Carrasco, L.

1989-01-01

The character of the sources identified in the IRAS Point Source Catalog and located within the boundaries of the nearest giant molecular cloud, Lynds 1641 is discussed. New optical and near-infrared photometry are combined to provide spectral energy distributions (SEDs) for these objects divided into three classes: class I objects with flat or rising spectra, class II objects with spectra intermediate in slope between a flat and blackbody spectrum, and class III objects with spectra similar to those of blackbodies. It is found that L1641 contains a much larger percentage of class I sources than does the nearby Taurus-Auriga star-forming complex. Spectral energy distributions for the IRAS-selected sample are examined and compared with SEDs for young stellar objects (YSOs) located in Taurus-Auriga. The IRAS-selected sources having optical counterparts in the H-R diagram are identified and discussed along with the distribution of masses and ages for these YSOs. 86 refs

Looking for Galaxies in All the Right Places: A Search for Stellar Populations in ALFALFA’s Ultra-compact High Velocity Clouds

Science.gov (United States)

Janesh, William; Rhode, Katherine L.; Salzer, John J.; Janowiecki, Steven; Adams, Elizabeth; Haynes, Martha P.; Giovanelli, Riccardo; Cannon, John M.

2018-01-01

Nearby gas-rich dwarf galaxies are excellent laboratories for investigating the baryonic feedback processes that govern star formation and galaxy evolution in galaxies at the extreme end of the mass function. Detecting and studying such objects may help resolve the well-known tension between cosmological model predictions for low-mass dark matter halos and observations. The ALFALFA neutral hydrogen (Hi) survey has detected a sample of isolated ultra-compact high-velocity Hi clouds (UCHVCs) with kinematic properties that make them likely members of the Local Volume, but that have no optical counterparts in existing optical surveys. This UCHVC sample possesses Hi properties (at 1 Mpc, Hi masses of ~105-106 M⊙, Hi diameters of ~2-3 kpc, and dynamical masses of ~107-108 M⊙) similar to other known ultra-faint dwarf galaxies like Leo T. Following the discovery of Leo P, an extremely metal-poor, gas-rich star-forming dwarf galaxy associated with an ALFALFA UCHVC, we have initiated a campaign to obtain deep optical imaging of 56 UCHVCs using the wide field-of-view, high-resolution ODI camera on the WIYN 3.5-m telescope. Here we present a brief overview of our campaign to search for resolved stellar populations associated with the UCHVCs in our optical images, and initial results from our survey.After creating a stellar catalog from the pipeline-reduced and stacked ODI g- and i-band images, we apply a color-magnitude filter tuned for old, metal-poor stellar populations to select red giant branch stars at distances between 250 kpc and 2 Mpc. The spatial distribution of the stars selected by the filter is then smoothed, and overdensities in the fields are identified. Of the 22 targets analyzed to date, seven have associated stellar populations detected at a high confidence (92% to 99.9% significance). The detected objects have a range of distances (from 350 kpc to 1.6 Mpc) and have optical properties similar to those of ultra-faint dwarf galaxies. These objects have

The AstroBiology Explorer (ABE) Mission Concept

Science.gov (United States)

Sandford, Scott A.

2004-01-01

Infrared spectroscopy in the 2.5-16 micron range is a principle means by which organic compounds can be detected and identified in space via their vibrational transitions. Ground-based, airborne, and spaceborne IR spectral studies have already demonstrated that a significant fraction of the carbon in the interstellar medium (ISM) resides in the form of complex organic molecular species. Unfortunately, neither the distribution of these materials nor their genetic and evolutionary relationships with each other or their environments are well understood. The Astrobiology Explorer (ABE) is a MIDEX mission concept currently under study by a team of partners: NASA's Ames Research Center, Ball Aerospace and Technologies Corporation, and the Jet Propulsion Laboratory. ABE will conduct IR spectroscopic observations to address outstanding important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding (1) The evolution of ices and organic matter in dense molecular clouds and young forming stellar systems, (2) The chemical evolution of organic molecules in the ISM as they transition from AGB outflows to planetary nebulae to the general diffuse ISM to HII regions and dense clouds, (3) The distribution of organics in the diffuse ISM, (4) The nature of organics in the Solar System (in comets, asteroids, satellites), and (5) The nature and distribution of organics in local galaxies. The technical considerations of achieving these science objectives in a MIDEX-sized mission will be presented.

Interaction of Supernova Remnants with Interstellar Clouds: From the Nova Laser to the Galaxy

International Nuclear Information System (INIS)

Klein, Richard I.; Budil, Kimberly S.; Perry, Theodore S.; Bach, David R.

2000-01-01

The interaction of strong shock waves, such as those generated by the explosion of supernovae with interstellar clouds, is a problem of fundamental importance in understanding the evolution and the dynamics of the interstellar medium (ISM) as it is disrupted by shock waves. The physics of this essential interaction sheds light on several key questions: (1) What is the rate and total amount of gas stripped from the cloud, and what are the mechanisms responsible? (2) What is the rate of momentum transfer to the cloud? (3) What is the appearance of the shocked cloud, its morphology and velocity dispersion? (4) What is the role of vortex dynamics on the evolution of the cloud? (5) Can the interaction result in the formation of a new generation of stars? To address these questions, one of us has embarked on a comprehensive multidimensional numerical study of the shock cloud problem using high-resolution adaptive mesh refinement (AMR) hydrodynamics. Here we present the results of a series of Nova laser experiments investigating the evolution of a high-density sphere embedded in a low-density medium after the passage of a strong shock wave, thereby emulating the supernova shock-cloud interaction. The Nova laser was utilized to generate a strong (∼Mach 10) shock wave which traveled along a miniature beryllium shock tube, 750 μm in diameter, filled with a low-density plastic emulating the ISM. Embedded in the plastic was a copper microsphere (100 μm in diameter) emulating the interstellar cloud. Its morphology and evolution as well as the shock wave trajectory were diagnosed via side-on radiography. We describe here experimental results of this interaction for the first time out to several cloud crushing times and compare them to detailed two- and three-dimensional radiation hydrodynamic simulations using both arbitrary Lagrangian and Eulerian hydrodynamics (ALE) as well as high-resolution AMR hydrodynamics. We briefly discuss the key hydrodynamic instabilities

THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES

International Nuclear Information System (INIS)

Riebel, D.; Meixner, M.; Srinivasan, S.; Sargent, B.

2012-01-01

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ∼30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 × 10 –5 M ☉ yr –1 , equivalent to a total mass injection rate (including the gas) into the ISM of ∼6 × 10 –3 M ☉ yr –1 . Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K s band as a function of J – K s color, BC K s = -0.40(J-K s ) 2 + 1.83(J-K s ) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot d ) from C-rich AGB stars, such as log M-dot d = (-18.90/((K s -[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

Integrated Services Management System (ISMS): A management and decision making tool

Energy Technology Data Exchange (ETDEWEB)

Barber, D.S.; Brockman, D.L.; Buxton, L.D. [and others

1995-10-01

This document provides information concerning the Integrated Services Management System (ISMS) that was developed for the Laboratories Services Division during the period February 1994 through May 1995. ISMS was developed as a formal method for centralized management of programs within the Division. With minor modifications, this system can be adapted for management of all overhead functions at SNL or for sector level program management. Included in this document are the reasons for the creation of this system as well as the resulting benefits. The ISMS consists of six interlinked processes; Issues Management, Task/Activity Planning, Work Decision, Commitment Management, Process/Project Management, and Performance Assessment. Those processes are described in detail within this document. Additionally, lessons learned and suggestions for future improvements are indicated.

Infrared analysis of LMC superbubbles

International Nuclear Information System (INIS)

Verter, F.; Dwek, E.

1990-01-01

Researchers are analyzing three superbubbles in the Large Magellanic Cloud (LMC), cataloged by Meaburn (1980) as LMC-1, LMC-4 (a.k.a. Shapley Constellation III), and LMC-5. Superbubbles are the largest infrared sources in the disks of external galaxies. Their expansion requires multiple supernovae from successive generations of star formation. In LMC superbubbles, the grains swept up by shocks and winds represent an interstellar medium (ISM) whose abundances are quite different from the Galaxy. By applying the Dwek (1986) grain model, we can derive the composition and size spectrum of the grains. The inputs to this model are the dust emission in the four Infrared Astronomy Satellite (IRAS) bands and the interstellar radiation field (ISRF) that provides the heating. The first step in the project is to derive the ISRF for star-forming regions on the periphery of superbubbles. Researchers are doing this by combining observations at several wavelengths to determine the energy budget of the region. They will use a UV image to trace the ionizing stellar radiation that escapes, an H alpha image to trace the ionizing stellar radiation that is absorbed by gas, and the four IRAS images to trace the stellar radiation, both ionizing and non-ionizing, that is absorbed by dust. This multi-wavelength approach has the advantages that we do not have to assume the shape of the IMF or the extinction of the source

Ross Ice Shelf, Antarctic Ice and Clouds

Science.gov (United States)

1991-01-01

In this view of Antarctic ice and clouds, (56.5S, 152.0W), the Ross Ice Shelf of Antarctica is almost totally clear, showing stress cracks in the ice surface caused by wind and tidal drift. Clouds on the eastern edge of the picture are associated with an Antarctic cyclone. Winds stirred up these storms have been known to reach hurricane force.

THE STELLAR AND GAS KINEMATICS OF THE LITTLE THINGS DWARF IRREGULAR GALAXY NGC 1569

Energy Technology Data Exchange (ETDEWEB)

Johnson, Megan [National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States); Hunter, Deidre A.; Zhang, Hong-Xin; Herrmann, Kimberly [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Oh, Se-Heon [International Centre for Radio Astronomy Research (ICRAR), University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Elmegreen, Bruce [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Hts., NY 10598 (United States); Brinks, Elias [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB (United Kingdom); Tollerud, Erik, E-mail: mjohnson@nrao.edu, E-mail: dah@lowell.edu, E-mail: hxzhang@lowell.edu, E-mail: herrmann@lowell.edu, E-mail: se-heon.oh@uwa.edu.au, E-mail: bge@us.ibm.com, E-mail: E.Brinks@herts.ac.uk, E-mail: etolleru@uci.edu [Center For Cosmology, Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States)

2012-11-01

In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, {sigma}{sub z}, coupled with the maximum rotational velocity derived from H I observations, V{sub max}, gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V{sub max}/{sigma}{sub z} = 2.4 {+-} 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, {approx}1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V{sub max}, shows that the disk may be dark matter deficient in the inner

THE STELLAR ANCESTRY OF SUPERNOVAE IN THE MAGELLANIC CLOUDS. I. THE MOST RECENT SUPERNOVAE IN THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Badenes, Carles; Harris, Jason; Zaritsky, Dennis; Prieto, Jose L.

2009-01-01

We use the star formation history (SFH) map of the Large Magellanic Cloud recently published by Harris and Zaritsky to study the sites of the eight smallest (and presumably youngest) supernova remnants (SNRs) in the Cloud: SN 1987A, N158A, N49, and N63A (core collapse remnants), 0509 - 67.5, 0519 - 69.0, N103B, and DEM L71 (Type Ia remnants). The local SFHs provide unique insights into the nature of the supernova (SN) progenitors, which we compare with the properties of the SN explosions derived from the remnants themselves and from SN light echoes. We find that all the core collapse SNe that we have studied are associated with vigorous star formation (SF) in the recent past. In the case of SN 1987A, the time of the last peak of SF (12 Myr) matches the lifetime of a star with the known mass of its blue supergiant progenitor (∼20 M sun ). More recent peaks of SF can lead to SNe with more massive progenitors, which opens the possibility of a Type Ib/c origin for SNRs N158A and N63A. Stars more massive than 21.5 M sun are very scarce around SNR N49, implying that the magnetar SGR 0526 - 66 in this SNR was either formed elsewhere or came from a progenitor with a mass well below the 30M sun threshold suggested in the literature. Three of our four Ia SNRs are associated with old, metal-poor stellar populations. This includes SNR 0509 - 67.5, which is known to have been originated by an extremely bright Type Ia event, and yet is located very far away from any sites of recent SF, in a population with a mean age of 7.9 Gyr. The Type Ia SNR N103B, on the other hand, is associated with recent SF, and might have had a relatively younger and more massive progenitor with substantial mass loss before the explosion. We discuss these results in the context of our present understanding of core collapse and Type Ia SN progenitors.

A plausible energy source and structure for quasi-stellar objects

Science.gov (United States)

Daltabuit, E.; Cox, D.

1972-01-01

If a collision of two large, massive, fast gas clouds occurs, their kinetic energy is converted to radiation in a pair of shock fronts at their interface. The resulting structure is described, and the relevance of this as a radiation source for quasi-stellar objects is considered.

Herschel HIFI GOT C+ Survey: CII, HI, and CO Emissions in a Sample of Transition Clouds and Star-Forming regions in the Inner Galaxy

Science.gov (United States)

Pineda, Jorge; Velusamy, Thangasamy; Langer, William D.; Goldsmith, Paul; Li, Di; Yorke, Harold

The GOT C+ a HIFI Herschel Key Project, studies the diffuse ISM throughout the Galactic Plane, using C+ as cloud tracer. The C+ line at 1.9 THz traces a so-far poorly studied stage in ISM cloud evolution -the transitional clouds going from atomic HI to molecular H2. This transition cloud phase, which is difficult to observe in HI and CO alone, may be best characterized via CII emission or absorption. The C+ line is also an excellent tracer of the warm diffuse gas and the warm, dense gas in the Photon Dominated Regions (PDRs). We can, therefore, use the CII emission as a probe to understand the effects of star formation on their interstellar environment. We present our first results on the transition between dense and hot gas (traced by CII) and dense and cold gas (traced by 12CO and 13CO) along a few representative lines of sight in the inner Galaxy from longitude 325 degrees to 25 degrees, taken during the HIFI Priority Science Phase. Comparisons of the high spectral resolution ( 1 km/s) HIFI data on C+ with HI, 12CO, and 13CO spectra allow us to separate out the different ISM components along each line of sight. Our results provide detailed information about the transition of diffuse atomic to molecular gas clouds needed to understand star formation and the lifecycle of the interstellar gas. These observations are being carried out with the Herschel Space Observatory, which is an ESA cornerstone mission, with contributions from NASA. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. JLP was supported under the NASA Postdoctoral Program at JPL, Caltech, administered by Oak Ridge Associated Universities through a contract with NASA, and is currently supported as a Caltech-JPL Postdoctoral associate.

INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

International Nuclear Information System (INIS)

Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P.

2015-01-01

We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between the optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ R . An evaluation of the galaxies in the λ R ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects

Improved automatic estimation of winds at the cloud top of Venus using superposition of cross-correlation surfaces

Science.gov (United States)

Ikegawa, Shinichi; Horinouchi, Takeshi

2016-06-01

Accurate wind observation is a key to study atmospheric dynamics. A new automated cloud tracking method for the dayside of Venus is proposed and evaluated by using the ultraviolet images obtained by the Venus Monitoring Camera onboard the Venus Express orbiter. It uses multiple images obtained successively over a few hours. Cross-correlations are computed from the pair combinations of the images and are superposed to identify cloud advection. It is shown that the superposition improves the accuracy of velocity estimation and significantly reduces false pattern matches that cause large errors. Two methods to evaluate the accuracy of each of the obtained cloud motion vectors are proposed. One relies on the confidence bounds of cross-correlation with consideration of anisotropic cloud morphology. The other relies on the comparison of two independent estimations obtained by separating the successive images into two groups. The two evaluations can be combined to screen the results. It is shown that the accuracy of the screened vectors are very high to the equatorward of 30 degree, while it is relatively low at higher latitudes. Analysis of them supports the previously reported existence of day-to-day large-scale variability at the cloud deck of Venus, and it further suggests smaller-scale features. The product of this study is expected to advance the dynamics of venusian atmosphere.

A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

Energy Technology Data Exchange (ETDEWEB)

Harvey, Paul M. [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Fallscheer, Cassandra [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2 (Canada); Ginsburg, Adam [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309-0389 (United States); Terebey, Susan [Department of Physics and Astronomy PS315, 5151 State University Drive, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Andre, Philippe; Koenyves, Vera [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d' Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Di Francesco, James; Matthews, Brenda C. [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Peterson, Dawn E., E-mail: pmh@astro.as.utexas.edu, E-mail: Cassandra.Fallscheer@nrc-cnrc.gc.ca, E-mail: adam.ginsburg@colorado.edu, E-mail: sterebe@calstatela.edu, E-mail: pandre@cea.fr, E-mail: vera.konyves@cea.fr, E-mail: tbourke@cfa.harvard.edu, E-mail: James.DiFrancesco@nrc-cnrc.gc.ca, E-mail: Brenda.Matthews@nrc-cnrc.gc.ca, E-mail: dpeterson@spacescience.org [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80303 (United States)

2013-02-20

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few Multiplication-Sign 10{sup 22} cm{sup -2} (N {sub H2}) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to {approx}10 K from values {approx}14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

International Nuclear Information System (INIS)

Harvey, Paul M.; Fallscheer, Cassandra; Ginsburg, Adam; Terebey, Susan; André, Philippe; Könyves, Vera; Bourke, Tyler L.; Di Francesco, James; Matthews, Brenda C.; Peterson, Dawn E.

2013-01-01

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 μm sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few × 10 22 cm –2 (N H2 ) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to ∼10 K from values ∼14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

The star-forming content of the W3 giant molecular cloud

Science.gov (United States)

Moore, T. J. T.; Bretherton, D. E.; Fujiyoshi, T.; Ridge, N. A.; Allsopp, J.; Hoare, M. G.; Lumsden, S. L.; Richer, J. S.

2007-08-01

We have surveyed a ˜0.9 square degree area of the W3 giant molecular cloud (GMC) and star-forming region in the 850-μm continuum, using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. A complete sample of 316 dense clumps were detected with a mass range from around 13 to 2500 M⊙. Part of the W3 GMC is subject to an interaction with the H ii region and fast stellar winds generated by the nearby W4 OB association. We find that the fraction of total gas mass in dense, 850-μm traced structures is significantly altered by this interaction, being around 5-13 per cent in the undisturbed cloud but ˜25-37 per cent in the feedback-affected region. The mass distribution in the detected clump sample depends somewhat on assumptions of dust temperature and is not a simple, single power law but contains significant structure at intermediate masses. This structure is likely to be due to crowding of sources near or below the spatial resolution of the observations. There is little evidence of any difference between the index of the high-mass end of the clump mass function in the compressed region and in the unaffected cloud. The consequences of these results are discussed in terms of current models of triggered star formation.

PHYSICS OF THE GALACTIC CENTER CLOUD G2, ON ITS WAY TOWARD THE SUPERMASSIVE BLACK HOLE

Energy Technology Data Exchange (ETDEWEB)

Burkert, A.; Schartmann, M.; Alig, C. [University Observatory Munich, Scheinerstrasse 1, D-81679 Munich (Germany); Gillessen, S.; Genzel, R.; Fritz, T. K.; Eisenhauer, F., E-mail: burkert@usm.lmu.de [Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85758 Garching (Germany)

2012-05-01

We investigate the origin, structure, and evolution of the small gas cloud G2, which is on an orbit almost straight into the Galactic central supermassive black hole (SMBH). G2 is a sensitive probe of the hot accretion zone of Sgr A*, requiring gas temperatures and densities that agree well with models of captured shock-heated stellar winds. Its mass is equal to the critical mass below which cold clumps would be destroyed quickly by evaporation. Its mass is also constrained by the fact that at apocenter its sound crossing timescale was equal to its infall timescale. Our numerical simulations show that the observed structure and evolution of G2 can be well reproduced if it forms in pressure equilibrium with its surroundings in 1995 at a distance from the SMBH of 7.6 Multiplication-Sign 10{sup 16} cm. If the cloud had formed at apocenter in the 'clockwise' stellar disk as expected from its orbit, it would be torn into a very elongated spaghetti-like filament by 2011, which is not observed. This problem can be solved if G2 is the head of a larger, shell-like structure that formed at apocenter. Our numerical simulations show that this scenario explains not only G2's observed kinematical and geometrical properties but also the Br{gamma} observations of a low surface brightness gas tail that trails the cloud. In 2013, while passing the SMBH, G2 will break up into a string of droplets that within the next 30 years will mix with the surrounding hot gas and trigger cycles of active galactic nucleus activity.

Wind bubbles within H ii regions around slowly moving stars

Science.gov (United States)

Mackey, Jonathan; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert

2015-01-01

Interstellar bubbles around O stars are driven by a combination of the star's wind and ionizing radiation output. The wind contribution is uncertain because the boundary between the wind and interstellar medium is difficult to observe. Mid-infrared observations (e.g., of the H ii region RCW 120) show arcs of dust emission around O stars, contained well within the H ii region bubble. These arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by density gradients and/or stellar motion. We present two-dimensional, radiation-hydrodynamics simulations investigating the evolution of wind bubbles and H ii regions around massive stars moving through a dense (nH = 3000 cm-3), uniform medium with velocities ranging from 4 to 16 km s-1. The H ii region morphology is strongly affected by stellar motion, as expected, but the wind bubble is also very aspherical from birth, even for the lowest space velocity considered. Wind bubbles do not fill their H ii regions (we find filling factors of 10-20 per cent), at least for a main sequence star with mass M⋆ ~ 30 M⊙. Furthermore, even for supersonic velocities the wind bow shock does not significantly trap the ionization front. X-ray emission from the wind bubble is soft, faint, and comes mainly from the turbulent mixing layer between the wind bubble and the H ii region. The wind bubble radiates <1 per cent of its energy in X-rays; it loses most of its energy by turbulent mixing with cooler photoionized gas. Comparison of the simulations with the H ii region RCW 120 shows that its dynamical age is ≲0.4 Myr and that stellar motion ≲4 km s-1 is allowed, implying that the ionizing source is unlikely to be a runaway star but more likely formed in situ. The region's youth, and apparent isolation from other O or B stars, makes it very interesting for studies of massive star formation and of initial mass functions. Movies are available in electronic form at http://www.aanda.org

The simulation of molecular clouds formation in the Milky Way

Science.gov (United States)

Khoperskov, S. A.; Vasiliev, E. O.; Sobolev, A. M.; Khoperskov, A. V.

2013-01-01

Using 3D hydrodynamic calculations we simulate formation of molecular clouds in the Galaxy. The simulations take into account molecular hydrogen chemical kinetics, cooling and heating processes. Comprehensive gravitational potential accounts for contributions from the stellar bulge, two- and four-armed spiral structure, stellar disc, dark halo and takes into account self-gravitation of the gaseous component. Gas clouds in our model form in the spiral arms due to shear and wiggle instabilities and turn into molecular clouds after t ≳ 100 Myr. At the times t ˜ 100-300 Myr the clouds form hierarchical structures and agglomerations with the sizes of 100 pc and greater. We analyse physical properties of the simulated clouds and find that synthetic statistical distributions like mass spectrum, `mass-size' relation and velocity dispersion are close to those observed in the Galaxy. The synthetic l-v (galactic longitude-radial velocity) diagram of the simulated molecular gas distribution resembles observed one and displays a structure with appearance similar to molecular ring of the Galaxy. Existence of this structure in our modelling can be explained by superposition of emission from the galactic bar and the spiral arms at ˜3-4 kpc.

The Stellar IMF from Isothermal MHD Turbulence

Science.gov (United States)

Haugbølle, Troels; Padoan, Paolo; Nordlund, Åke

2018-02-01

We address the turbulent fragmentation scenario for the origin of the stellar initial mass function (IMF), using a large set of numerical simulations of randomly driven supersonic MHD turbulence. The turbulent fragmentation model successfully predicts the main features of the observed stellar IMF assuming an isothermal equation of state without any stellar feedback. As a test of the model, we focus on the case of a magnetized isothermal gas, neglecting stellar feedback, while pursuing a large dynamic range in both space and timescales covering the full spectrum of stellar masses from brown dwarfs to massive stars. Our simulations represent a generic 4 pc region within a typical Galactic molecular cloud, with a mass of 3000 M ⊙ and an rms velocity 10 times the isothermal sound speed and 5 times the average Alfvén velocity, in agreement with observations. We achieve a maximum resolution of 50 au and a maximum duration of star formation of 4.0 Myr, forming up to a thousand sink particles whose mass distribution closely matches the observed stellar IMF. A large set of medium-size simulations is used to test the sink particle algorithm, while larger simulations are used to test the numerical convergence of the IMF and the dependence of the IMF turnover on physical parameters predicted by the turbulent fragmentation model. We find a clear trend toward numerical convergence and strong support for the model predictions, including the initial time evolution of the IMF. We conclude that the physics of isothermal MHD turbulence is sufficient to explain the origin of the IMF.

MAGNETIC NESTED-WIND SCENARIOS FOR BIPOLAR OUTFLOWS: PREPLANETARY AND YSO NEBULAR SHAPING

International Nuclear Information System (INIS)

Dennis, Timothy J.; Frank, Adam; Blackman, Eric G.; DeMarco, Orsola; Balick, Bruce; Mitran, Sorin

2009-01-01

We present results of a series of magnetohydrodynamic (MHD) and hydrodynamic (HD) 2.5 dimensional simulations of the morphology of outflows driven by nested wide-angle winds, i.e., winds that emanate from a central star as well as from an orbiting accretion disk. While our results are broadly relevant to nested-wind systems, we have tuned the parameters of the simulations to touch on issues in both young stellar objects and planetary nebula (PN) studies. In particular, our studies connect to open issues in the early evolution of PNs. We find that nested MHD winds exhibit marked morphological differences from the single MHD wind case along both dimensions of the flow. Nested HD winds, on the other hand, give rise mainly to geometric distortions of an outflow that is topologically similar to the flow arising from a single stellar HD wind. Our MHD results are insensitive to changes in ambient temperature between ionized and un-ionized circumstellar environments. The results are sensitive to the relative mass-loss rates and the relative speeds of the stellar and disk winds. We also present synthetic emission maps of both nested MHD and HD simulations. We find that nested MHD winds show knots of emission appearing on-axis that do not appear in the HD case.

Clouds and the Near-Earth Environment: Possible Links

Directory of Open Access Journals (Sweden)

Condurache-Bota Simona

2015-12-01

Full Text Available Climate variability is a hot topic not only for scientists and policy-makers, but also for each and every one of us. The anthropogenic activities are considered to be responsible for most climate change, however there are large uncertainties about the magnitude of effects of solar variability and other extraterrestrial influences, such as galactic cosmic rays on terrestrial climate. Clouds play an important role due to feedbacks of the radiation budget: variation of cloud cover/composition affects climate, which, in turn, affects cloud cover via atmospheric dynamics and sea temperature variations. Cloud formation and evolution are still under scientific scrutiny, since their microphysics is still not understood. Besides atmospheric dynamics and other internal climatic parameters, extraterrestrial sources of cloud cover variation are considered. One of these is the solar wind, whose effect on cloud cover might be modulated by the global atmospheric electrical circuit. Clouds height and composition, their seasonal variation and latitudinal distribution should be considered when trying to identify possible mechanisms by which solar energy is transferred to clouds. The influence of the solar wind on cloud formation can be assessed also through the ap index - the geomagnetic storm index, which can be readily connected with interplanetary magnetic field, IMF structure. This paper proposes to assess the possible relationship between both cloud cover and solar wind proxies, as the ap index, function of cloud height and composition and also through seasonal studies. The data covers almost three solar cycles (1984-2009. Mechanisms are looked for by investigating observed trends or correlation at local/seasonal scale

Influence of Solar Wind on the Global Electric Circuit, and Inferred Effects on Cloud Microphysics, Temperature, and Dynamics in the Troposphere

Science.gov (United States)

Tinsley, Brian A.

2000-11-01

There are at least three independent ways in which the solar wind modulates the flow of current density (Jz) in the global electric circuit. These are (A) changes in the galactic cosmic ray energy spectrum, (B) changes in the precipitation of relativistic electrons from the magnetosphere, and (C) changes in the ionospheric potential distribution in the polar caps due to magnetosphere-ionosphere coupling. The current density J_z flows between the ionosphere and the surface, and as it passes through conductivity gradients it generates space charge concentrations dependent on J_z and the conductivity gradient. The gradients are large at the surfaces of clouds and space charge concentrations of order 1000 to 10,000 elementary charges per cm^3 can be generated at cloud tops. The charge transfers to droplets, many of which are evaporating at the cloud-clear air interface. The charge remains on the residual evaporation nuclei with a lifetime against leakage of order 1000 sec, and for a longer period the nuclei also retain coatings of sulfate and organic compounds adsorbed by the droplet while in the cloud. The charged evaporation nuclei become well mixed with more droplets in many types of clouds with penetrative mixing. The processes of entrainment and evaporation are also efficient for these clouds. The collection of such nuclei by nearby droplets is greatly increased by the electrical attraction between the charge on the particle and the image charge that it creates on the droplet. This process is called electroscavenging. Because the charge on the evaporation nuclei is derived from the original space charge, it depends on J_z, giving a rate of electroscavenging responsive to the solar wind inputs. There may be a number of ways in which the electroscavenging has consequences for weather and climate. One possibility is enhanced production of ice. The charged evaporation nuclei have been found to be good ice forming nuclei because of their coatings, and so in supercooled

Photometric Metallicities of the Small and Large Magellanic Clouds

Science.gov (United States)

Miller, Amy Elizabeth

2018-06-01

In the field of astronomy, the study of galaxies is vitally important to understanding the structure and evolution of the universe. Within the study of galaxies, of particular interest are the Small and Large Magellanic Clouds (SMC and LMC, respectively), two of the Milky Way’s closest and most massive satellite galaxies. Their close proximity make them ideal candidates for understanding astrophysical processes such as galaxy interactions. In order to fully understand the Magellanic Clouds, it is imperative that the metallicity of the clouds be mapped in detail. In order to accomplish this task, I will use data from the Survey of Magellanic Stellar History (SMASH) which is a deep, multi-band (ugriz) photometric survey of the Magellanic Clouds that contains approximately 400 million objects in 197 fully-calibrated fields. SMASH is an extensive and deep photometric data set that enables the full-scale study of the galactic structure in the Clouds. The SMASH u-band is sensitive to metallicity for main-sequence turn-off stars which we calibrate using SDSS spectroscopy in overlapping regions (mainly standard star fields). The final steps will be to make metallicity maps of the main bodies and peripheries of the LMC and SMC. Ultimately, these metallicity maps will help us trace out population gradients in the Clouds and uncover the origin of their very extended stellar peripheries.

The Abundances of the Fe Group Elements in AV 304, an Abundance Standard in the Small Magellanic Cloud

Science.gov (United States)

Peters, Geraldine J.; Lanz, Thierry; Bouret, Jean-Claude; Proffitt, Charles R.; Adelman, Saul J.; Hubeny, Ivan

2018-06-01

AV 304 is a B0.5 IV field star in the Small Magellanic Cloud with ultra-sharp spectral lines that has emerged as an abundance standard. We have combined recent spectroscopic observations from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope with archival data from the Far Ultraviolet Spectroscopic Explorer (FUSE) and ESO’s VLT/UVES to determine the abundances of the Fe group elements (Ti, V, Cr, Mn, Fe, Co, & Ni). The analysis was carried through using the Hubeny/Lanz NLTE programs TLUSTY/SYNSPEC. The COS observations were secured with the G130M, G160M, G185M, and G225M gratings. Combined with the FUSE data, we have achieved spectral coverage in the UV from 950 to 2400 A. Measurable lines from the Fe group, except for a very few multiplets of Fe II, III are not observed in optical spectra. The following stellar parameters were found: Teff = 27500±500 K, log g = 3.7±0.1 cm/s2, Vturb= 1±1 km/s, and v sin i = 8 ±2 km/s. The Fe abundance appears to be only slightly lower than the mean depletion in the SMC, but the other Fe group elements are underabundant by 0.3 dex or more. This study confirmed the low abundance of nitrogen (-1.25 dex relative to the solar value) that was reported by Peters & Adelman (ASP Conf. Series, 348, p. 136, 2006). Whereas the light elements are delivered to the ISM by core-collapse supernovae (CCSNe), the Fe group elements are believed to come mostly from low/intermediate mass binaries containing white dwarfs that undergo SNe Ia explosions. A single SNe Ia can deliver 0.5 solar masses of pure Fe (and maybe Mn) to the ISM compared with about 0.07 solar masses from a CCSNe. It appears that there is very little processed material from its interior in the atmosphere of AV 304 and that the star did not form from an interstellar cloud that was enriched by material from earlier supernova activity. Support from STScI grants HST-GO-14081.002 and HST-GO-13346.022, and USC’s Women in Science and Engineering (WiSE) program is

Banner clouds observed at Mount Zugspitze

Directory of Open Access Journals (Sweden)

V. Wirth

2012-04-01

Full Text Available Systematic observations of banner clouds at Mount Zugspitze in the Bavarian Alps are presented and discussed. One set of observations draws on daily time lapse movies, which were taken over several years at this mountain. Identifying banner clouds with the help of these movies and using simultaneous observations of standard variables at the summit of the mountain provides climatological information regarding the banner clouds. In addition, a week-long measurement campaign with an entire suite of instruments was carried through yielding a comprehensive set of data for two specific banner cloud events.

The duration of banner cloud events has a long-tailed distribution with a mean of about 40 min. The probability of occurrence has both a distinct diurnal and a distinct seasonal cycle, with a maximum in the afternoon and in the warm season, respectively. These cycles appear to correspond closely to analogous cycles of relative humidity, which maximize in the late afternoon and during the warm season. In addition, the dependence of banner cloud occurrence on wind speed is weak. Both results suggest that moisture conditions are a key factor for banner cloud occurrence. The distribution of wind direction during banner cloud events slightly deviates from climatology, suggesting an influence from the specific Zugspitz orography.

The two banner cloud events during the campaign have a number of common features: the windward and the leeward side are characterized by different wind regimes, however, with mean upward flow on both sides; the leeward air is both moister and warmer than the windward air; the background atmosphere has an inversion just above the summit of Mt. Zugspitze; the lifting condensation level increases with altitude. The results are discussed, and it is argued that they are consistent with previous Large Eddy Simulations using idealized orography.

Molecular clouds toward the super star cluster NGC 3603; possible evidence for a cloud-cloud collision in triggering the cluster formation

Energy Technology Data Exchange (ETDEWEB)

Fukui, Y.; Ohama, A.; Hanaoka, N.; Furukawa, N.; Torii, K.; Hasegawa, K.; Fukuda, T.; Soga, S.; Moribe, N.; Kuroda, Y.; Hayakawa, T.; Kuwahara, T.; Yamamoto, H.; Okuda, T. [Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Dawson, J. R. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); Mizuno, N.; Kawamura, A. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Onishi, T.; Maezawa, H. [Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531 (Japan); Mizuno, A., E-mail: fukui@a.phys.nagoya-u.ac.jp [Solar-terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601 (Japan)

2014-01-01

We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions {sup 12}CO(J = 2-1, J = 1-0) and {sup 13}CO(J = 2-1, J = 1-0). We suggest that two molecular clouds at 13 km s{sup –1} and 28 km s{sup –1} are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s{sup –1}. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.

Meteorological observations in support of a hill cap cloud experiment

Energy Technology Data Exchange (ETDEWEB)

Nielsen, Morten

1998-06-01

Humid air flows form a hill cap cloud over the Agana mountain ridge in the north-east of Tenerife. The HILLCLOUD project utilised this cloud formation to investigate the chemical and physical properties of cloud aerosols by land based observations. The project was part of the second Aerosol characterisation Experiment (ACE-2) of the International Global Atmospheric chemistry project (IGAC). The present report describes meteorological observations in support of the hill cap cloud experiment. Time-series of wind speed, wind direction, temperature and humidity were collected at ground-based meteorological stations during a period starting one year in advance of the main campaign. A series of radiosonde detecting the upstream stability and wind profile were launched during the main campaign. (au) 5 tabs., 32 ills., 6 refs.

Face-ism and Objectification in Mainstream and LGBT Magazines.

Science.gov (United States)

Cheek, Nathan N

2016-01-01

In visual media, men are often shown with more facial prominence than women, a manifestation of sexism that has been labeled face-ism. The present research extended the study of facial prominence and gender representation in media to include magazines aimed at lesbian, gay, bisexual, and transgender (LGBT) audiences for the first time, and also examined whether overall gender differences in facial prominence can still be found in mainstream magazines. Face-ism emerged in Newsweek, but not in Time, The Advocate, or Out. Although there were no overall differences in facial prominence between mainstream and LGBT magazines, there were differences in the facial prominence of men and women among the four magazines included in the present study. These results suggest that face-ism is still a problem, but that it may be restricted to certain magazines. Furthermore, future research may benefit from considering individual magazine titles rather than broader categories of magazines, given that the present study found few similarities between different magazines in the same media category--indeed, Out and Time were more similar to each other than they were to the other magazine in their respective categories.

Face-ism and Objectification in Mainstream and LGBT Magazines

Science.gov (United States)

Cheek, Nathan N.

2016-01-01

In visual media, men are often shown with more facial prominence than women, a manifestation of sexism that has been labeled face-ism. The present research extended the study of facial prominence and gender representation in media to include magazines aimed at lesbian, gay, bisexual, and transgender (LGBT) audiences for the first time, and also examined whether overall gender differences in facial prominence can still be found in mainstream magazines. Face-ism emerged in Newsweek, but not in Time, The Advocate, or Out. Although there were no overall differences in facial prominence between mainstream and LGBT magazines, there were differences in the facial prominence of men and women among the four magazines included in the present study. These results suggest that face-ism is still a problem, but that it may be restricted to certain magazines. Furthermore, future research may benefit from considering individual magazine titles rather than broader categories of magazines, given that the present study found few similarities between different magazines in the same media category—indeed, Out and Time were more similar to each other than they were to the other magazine in their respective categories. PMID:27074012

Face-ism and Objectification in Mainstream and LGBT Magazines.

Directory of Open Access Journals (Sweden)

Nathan N Cheek

Full Text Available In visual media, men are often shown with more facial prominence than women, a manifestation of sexism that has been labeled face-ism. The present research extended the study of facial prominence and gender representation in media to include magazines aimed at lesbian, gay, bisexual, and transgender (LGBT audiences for the first time, and also examined whether overall gender differences in facial prominence can still be found in mainstream magazines. Face-ism emerged in Newsweek, but not in Time, The Advocate, or Out. Although there were no overall differences in facial prominence between mainstream and LGBT magazines, there were differences in the facial prominence of men and women among the four magazines included in the present study. These results suggest that face-ism is still a problem, but that it may be restricted to certain magazines. Furthermore, future research may benefit from considering individual magazine titles rather than broader categories of magazines, given that the present study found few similarities between different magazines in the same media category--indeed, Out and Time were more similar to each other than they were to the other magazine in their respective categories.

Radio continuum emission from young stellar objects in L1641

International Nuclear Information System (INIS)

Morgan, J.A.; Snell, R.L.; Strom, K.M.

1990-01-01

The results of a 6 and 20 cm radio continuum survey of young stellar objects in the L1641 region located south of the Orion Nebula are presented. Four are identified as low-luminosity young stellar objects in L1641 and three more as Herbig-Haro or Herbig-Haro-like objects. These objects have bolometric luminosities between 80 and 300 solar, and their 6-20 cm spectral index suggests optically thick, free-free emission. They are characterized by a rising spectrum between 2.2 and 25 microns, have no optical counterparts, and are associated with stellar wind activity. Thus, detectable radio continuum emission may be produced only by the youngest and most luminous objects in L1641. 34 refs

A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

Energy Technology Data Exchange (ETDEWEB)

Ohno, Kazumasa; Okuzumi, Satoshi [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan)

2017-02-01

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our model by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation–coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.

A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

International Nuclear Information System (INIS)

Ohno, Kazumasa; Okuzumi, Satoshi

2017-01-01

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our model by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation–coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.

Component manufacturing development for the National Compact Stellarator Experiment (NCSX)

International Nuclear Information System (INIS)

Heitzenroeder, P.J.; Brown, T.G.; Chrzanowski, J.H.; Neilson, G.H.; Reiersen, W.T.; Sutton, L.L.; Viola, M.E.; Cole, M.J.; Goranson, P.L.; Nelson, B.E.; Williamson, D.E.

2005-01-01

NCSX is the first of a new class of stellarators called compact stellarators which hold the promise of retaining the steady state feature of the stellarator but at a much lower aspect ratio and using a quasi-axisymmetric magnetic field to obtain tokamak-like performance. Although much of NCSX is conventional in design and construction, the vacuum vessel and modular coils provide significant engineering challenges due to their complex shapes, need for high dimensional accuracy, and the need for high current density in the modular coils due space constraints. Consequently, a three-phase development program has been undertaken. In the first phase, laboratory / industrial studies were performed during the development of the conceptual design to permit advances in manufacturing technology to be incorporated into NCSX's plans. In the second phase, full-scale prototype modular coil winding forms, compacted cable conductors, and 20-degree sectors of the vacuum vessel were fabricated in industry. In parallel, the NCSX project team undertook R and D studies that focused on the windings. The third (production) phase began in September 2004. First plasma is scheduled for January 2008. (author)

Not-so-simple stellar populations in nearby, resolved massive star clusters

Science.gov (United States)

de Grijs, Richard; Li, Chengyuan

2018-02-01

Around the turn of the last century, star clusters of all kinds were considered ‘simple’ stellar populations. Over the past decade, this situation has changed dramatically. At the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. In this review of where the field has moved to in recent years, we place particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Magellanic Cloud star clusters across the full age range. Our most recent results imply a reverse paradigm shift, back to the old simple stellar population picture for at least some intermediate-age (˜1-3 Gyr old) star clusters, opening up exciting avenues for future research efforts.

QUASI-STELLAR OBJECT SELECTION ALGORITHM USING TIME VARIABILITY AND MACHINE LEARNING: SELECTION OF 1620 QUASI-STELLAR OBJECT CANDIDATES FROM MACHO LARGE MAGELLANIC CLOUD DATABASE

International Nuclear Information System (INIS)

Kim, Dae-Won; Protopapas, Pavlos; Alcock, Charles; Trichas, Markos; Byun, Yong-Ik; Khardon, Roni

2011-01-01

We present a new quasi-stellar object (QSO) selection algorithm using a Support Vector Machine, a supervised classification method, on a set of extracted time series features including period, amplitude, color, and autocorrelation value. We train a model that separates QSOs from variable stars, non-variable stars, and microlensing events using 58 known QSOs, 1629 variable stars, and 4288 non-variables in the MAssive Compact Halo Object (MACHO) database as a training set. To estimate the efficiency and the accuracy of the model, we perform a cross-validation test using the training set. The test shows that the model correctly identifies ∼80% of known QSOs with a 25% false-positive rate. The majority of the false positives are Be stars. We applied the trained model to the MACHO Large Magellanic Cloud (LMC) data set, which consists of 40 million light curves, and found 1620 QSO candidates. During the selection none of the 33,242 known MACHO variables were misclassified as QSO candidates. In order to estimate the true false-positive rate, we crossmatched the candidates with astronomical catalogs including the Spitzer Surveying the Agents of a Galaxy's Evolution LMC catalog and a few X-ray catalogs. The results further suggest that the majority of the candidates, more than 70%, are QSOs.

Large Scale Variability of Phytoplankton Blooms in the Arctic and Peripheral Seas: Relationships with Sea Ice, Temperature, Clouds, and Wind

Science.gov (United States)

Comiso, Josefino C.; Cota, Glenn F.

2004-01-01

Spatially detailed satellite data of mean color, sea ice concentration, surface temperature, clouds, and wind have been analyzed to quantify and study the large scale regional and temporal variability of phytoplankton blooms in the Arctic and peripheral seas from 1998 to 2002. In the Arctic basin, phytoplankton chlorophyll displays a large symmetry with the Eastern Arctic having about fivefold higher concentrations than those of the Western Arctic. Large monthly and yearly variability is also observed in the peripheral seas with the largest blooms occurring in the Bering Sea, Sea of Okhotsk, and the Barents Sea during spring. There is large interannual and seasonal variability in biomass with average chlorophyll concentrations in 2002 and 2001 being higher than earlier years in spring and summer. The seasonality in the latitudinal distribution of blooms is also very different such that the North Atlantic is usually most expansive in spring while the North Pacific is more extensive in autumn. Environmental factors that influence phytoplankton growth were examined, and results show relatively high negative correlation with sea ice retreat and strong positive correlation with temperature in early spring. Plankton growth, as indicated by biomass accumulation, in the Arctic and subarctic increases up to a threshold surface temperature of about 276-277 degree K (3-4 degree C) beyond which the concentrations start to decrease suggesting an optimal temperature or nutrient depletion. The correlation with clouds is significant in some areas but negligible in other areas, while the correlations with wind speed and its components are generally weak. The effects of clouds and winds are less predictable with weekly climatologies because of unknown effects of averaging variable and intermittent physical forcing (e.g. over storm event scales with mixing and upwelling of nutrients) and the time scales of acclimation by the phytoplankton.

AGN feedback through UFO and galaxy-wide winds in the early Universe

Science.gov (United States)

Feruglio, C.; Piconcelli, E.; Bischetti, M.; Zappacosta, L.; Fiore, F.

2017-10-01

AGN feedback through massive molecular winds is today routinely observed in local AGN host galaxies, but not as such in the early universe. I will present the first evidence for a massive, AGN-driven molecular wind in the z 4 QSO APM08279, which also hosts the most well studied and persistent nuclear semi-raltivistic wind (UFO). This observation directly probes the expansion mechanism of a nuclear wind into the ISM on galaxy wide scales, that so far was constrained by a couple of other objects only (Feruglio et al. 2015, Tombesi et al. 2015). This result also opens the path toward the exploration of molecular AGN-driven winds at early epochs, close after the end of the Epoch of Reionisation (EoR).

An induction/synchronous motor with high temperature superconductor/normal conductor hybrid double-cage rotor windings

International Nuclear Information System (INIS)

Nakamura, T; Nagao, K; Nishimura, T; Matsumura, K

2009-01-01

We propose hybrid double-cage rotor windings that consist of a high temperature superconductor (HTS) and a normal conductor, which are introduced into an HTS induction/synchronous motor (HTS-ISM). The motor rotates as a conventional induction motor when the operating temperature of the hybrid rotor is above the critical temperature of the HTS bars, i.e., in the normal conducting state. On the other hand, the HTS-ISM rotates as a synchronous motor when the temperature is below the critical temperature, i.e., in the superconducting (zero resistance) state. In other words, we do not always need to take care of the cooling conditions, if the HTS-ISM is automatically, as well as appropriately, controlled, depending upon the rotation mode. Namely, the above-mentioned hybrid double-cage HTS-ISM is possibly a breakthrough in solving the cooling problems of HTS rotating machines, especially for industrial applications. The experimental results of the aforementioned motor are reported. An example of an operation flowchart of the motor is also presented and discussed.

Preparing Educational Leaders To Eradicate the 'Isms'.

Science.gov (United States)

Terry, Paul M.

Educational administration programs have an obligation to link theory with practical applications. However, the content of programs must also emphasize that aspiring administrators have a moral responsibility to eradicate the "isms"--classism, racism, sexism, homophobia, ageism, and ableism. This paper asserts that administrators must develop a…

TIDALLY ENHANCED STELLAR WIND: A WAY TO MAKE THE SYMBIOTIC CHANNEL TO TYPE Ia SUPERNOVA VIABLE

International Nuclear Information System (INIS)

Chen, X.; Han, Z.; Tout, C. A.

2011-01-01

In the symbiotic (or WD+RG) channel of the single-degenerate scenario for type Ia supernovae (SNe Ia), the explosions occur a relatively long time after star formation. The birthrate from this channel would be too low to account for all observed SNe Ia were it not for some mechanism to enhance the rate of accretion on to the white dwarf. A tidally enhanced stellar wind, of the type which has been postulated to explain many phenomena related to giant star evolution in binary systems, can do this. Compared to mass stripping, this model extends the space of SNe Ia progenitors to longer orbital periods and hence increases the birthrate to about 0.0069 yr -1 for the symbiotic channel. Two symbiotic stars, T CrB and RS Oph, considered to be the most likely progenitors of SNe Ia through the symbiotic channel, are well inside the period-companion mass space predicted by our models.

Turbulence and star formation in molecular clouds

International Nuclear Information System (INIS)

Larson, R.B.

1981-01-01

Data for many molecular clouds and condensations show that the internal velocity dispersion of each region is well correlated with its size and mass, and these correlations are approximately of power-law form. The dependence of velocity dispersion on region size is similar to the Kolmogoroff law for subsonic turbulence, suggesting that the observed motions are all part of a common hierarchy of interstellar turbulent motions. The regions studied are mostly gravitationally bound and in approximate virial equilibrium. However, they cannot have formed by simple gravitational collapse, and it appears likely that molecular clouds and their substructures have been created at least partly by processes of supersonic hydrodynamics. The hierarchy of subcondensations may terminate with objects so small that their internal motions are no longer supersonic; this predicts a minimum protostellar mass of the order of a few tenths of a solar mass. Massive 'protostellar' clumps always have supersonic internal motions and will therefore develop complex internal structures, probably leading to the formation of many pre-stellar condensation nuclei that grow by accretion to produce the final stellar mass spectrum. Molecular clouds must be transient structures, and are probably dispersed after not much more than 10 7 yr. (author)

DISCOVERY OF X-RAY EMISSION FROM YOUNG SUNS IN THE SMALL MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Oskinova, L. M.; Hainich, R.; Sun, W.; Chen, Y.; Evans, C. J.; Hénault-Brunet, V.; Chu, Y.-H.; Gruendl, R. A.; Gallagher, J. S. III; Guerrero, M. A.; Güdel, M.; Silich, S.; Nazé, Y.; Reyes-Iturbide, J.

2013-01-01

We report the discovery of extended X-ray emission within the young star cluster NGC 602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-Ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the H II region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low- and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the newborn stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low- and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy.

Solar variability and clouds

CERN Document Server

Kirkby, Jasper

2000-01-01

Satellite observations have revealed a surprising imprint of the 11- year solar cycle on global low cloud cover. The cloud data suggest a correlation with the intensity of Galactic cosmic rays. If this apparent connection between cosmic rays and clouds is real, variations of the cosmic ray flux caused by long-term changes in the solar wind could have a significant influence on the global energy radiation budget and the climate. However a direct link between cosmic rays and clouds has not been unambiguously established and, moreover, the microphysical mechanism is poorly understood. New experiments are being planned to find out whether cosmic rays can affect cloud formation, and if so how. (37 refs).

A new ejecta shell surrounding a Wolf-Rayet star in the LMC

Science.gov (United States)

Garnett, Donald R.; Chu, You-Hua

1994-01-01

We have obtained CCD spectra of newly discovered shell-like nebulae around the WN4 star Breysacher 13 and the WN1 star Breysacher 2 in the Large Magellanic Cloud (LMC). The shell around Br 13 shows definite signs of enrichment in both nitrogen and helium, having much stronger (N II) and He I emission lines than are seen in typical LMC H II regions. From the measured electron temperature of about 17,000 K in the shell, we derive He/H and N/O abundance ratios which are factors of 2 and more than 10 higher, respectively, than the average LMC interstellar values. The derived oxygen abundance in the Br 13 shell is down by a factor of 8 compared to the local LMC interstellar medium (ISM); however, the derived electron temperature is affected by the presence of an incomplete shock arising from the interaction of the stellar wind with photoionized material. This uncertainty does not affect the basic conclusion that the Br 13 shell is enriched by processed material from the Wolf-Rayet star. In contrast, the shell around Br 2 shows no clear evidence of enrichment. The nebular spectrum is characterized by extremely strong (O III) and He II emission and very weak (N II). We derive normal He, O, and N abundances from our spectrum. This object therefore appears to be simply a wind-blown structure associated with a relatively dense cloud near the Wolf-Rayet star, although the very high-ionization state of the gas is unusual for a nebula associated with a Wolf-Rayet star.

DUST AND GAS IN THE MAGELLANIC CLOUDS FROM THE HERITAGE HERSCHEL KEY PROJECT. II. GAS-TO-DUST RATIO VARIATIONS ACROSS INTERSTELLAR MEDIUM PHASES

International Nuclear Information System (INIS)

Roman-Duval, Julia; Gordon, Karl D.; Meixner, Margaret; Bot, Caroline; Bolatto, Alberto; Jameson, Katherine; Hughes, Annie; Hony, Sacha; Wong, Tony; Babler, Brian; Bernard, Jean-Philippe; Clayton, Geoffrey C.; Fukui, Yasuo; Galametz, Maud; Galliano, Frederic; Lebouteiller, Vianney; Lee, Min-Young; Glover, Simon; Israel, Frank; Li, Aigen

2014-01-01

The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21 cm, CO, and Hα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380 −130 +250 ± 3 in the LMC, and 1200 −420 +1600 ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M ☉  pc –2 in the LMC and 0.03 M ☉  pc –2 in the SMC, corresponding to A V ∼ 0.4 and 0.2, respectively. We investigate the range of CO-to-H 2 conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on X CO to be 6 × 10 20  cm –2  K –1  km –1 s in the LMC (Z = 0.5 Z ☉ ) at 15 pc resolution, and 4 × 10 21  cm –2  K –1  km –1 s in the SMC (Z = 0.2 Z ☉ ) at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor ∼2, even after accounting for the effects of CO-dark H 2 in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H 2 . Within the expected 5-20 times Galactic X CO range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further modeling and observations are required to break the degeneracy between dust grain coagulation, accretion, and CO-dark H 2

Protostellar formation in rotating interstellar clouds. I. Numerical methods and tests

International Nuclear Information System (INIS)

Boss, A.P.

1980-01-01

The details of how dense interstellar clouds collapse to form protostars are obscured from observation by the very clouds in which the condensation takes place, leaving an observational gap between the clouds and pre--main-sequence (PMS) stars. There is also a gap of roughly four orders of magnitude between the specific spin angular momentum of such clouds and that of PMS stars. Thus in order to fully understand the sequence of events in stellar formation, we must construct theoretical models of the collapse and fragmentation of rotating interstellar clouds into single or multiple protostellar systems

OGLE-ing the Magellanic system: stellar populations in the Magellanic Bridge

International Nuclear Information System (INIS)

Skowron, D. M.; Jacyszyn, A. M.; Udalski, A.; Szymański, M. K.; Skowron, J.; Poleski, R.; Kozłowski, S.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Mróz, P.; Pietrukowicz, P.; Ulaczyk, K.; Wyrzykowski, Ł.

2014-01-01

We report the discovery of a young stellar bridge that forms a continuous connection between the Magellanic Clouds. This finding is based on number density maps for stellar populations found in data gathered by OGLE-IV that fully cover over 270 deg 2 of the sky in the Magellanic Bridge area. This is the most extensive optical survey of this region to date. We find that the young population is present mainly in the western half of the MBR, which, together with the newly discovered young population in the eastern Bridge, form a continuous stream of stars connecting both galaxies along δ ∼ –73.5 deg. The young population distribution is clumped, with one of the major densities close to the SMC and the other fairly isolated and located approximately mid-way between the Clouds, which we call the OGLE island. These overdensities are well matched by H I surface density contours, although the newly found young population in the eastern Bridge is offset by ∼2 deg north from the highest H I density contour. We observe a continuity of red clump stars between the Magellanic Clouds which represent an intermediate-age population. Red clump stars are present mainly in the southern and central parts of the Magellanic Bridge, below its gaseous part, and their presence is reflected by a strong deviation from the radial density profiles of the two galaxies. This may indicate either a tidal stream of stars, or that the stellar halos of the two galaxies overlap. On the other hand, we do not observe such an overlap within an intermediate-age population represented by the top of the red giant branch and the asymptotic giant branch stars. We also see only minor mixing of the old populations of the Clouds in the southern part of the Bridge, represented by the lowest part of the red giant branch.

OGLE-ing the Magellanic system: stellar populations in the Magellanic Bridge

Energy Technology Data Exchange (ETDEWEB)

Skowron, D. M.; Jacyszyn, A. M.; Udalski, A.; Szymański, M. K.; Skowron, J.; Poleski, R.; Kozłowski, S.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Mróz, P.; Pietrukowicz, P.; Ulaczyk, K.; Wyrzykowski, Ł., E-mail: dszczyg@astrouw.edu.pl [Warsaw University Astronomical Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa (Poland)

2014-11-10

We report the discovery of a young stellar bridge that forms a continuous connection between the Magellanic Clouds. This finding is based on number density maps for stellar populations found in data gathered by OGLE-IV that fully cover over 270 deg{sup 2} of the sky in the Magellanic Bridge area. This is the most extensive optical survey of this region to date. We find that the young population is present mainly in the western half of the MBR, which, together with the newly discovered young population in the eastern Bridge, form a continuous stream of stars connecting both galaxies along δ ∼ –73.5 deg. The young population distribution is clumped, with one of the major densities close to the SMC and the other fairly isolated and located approximately mid-way between the Clouds, which we call the OGLE island. These overdensities are well matched by H I surface density contours, although the newly found young population in the eastern Bridge is offset by ∼2 deg north from the highest H I density contour. We observe a continuity of red clump stars between the Magellanic Clouds which represent an intermediate-age population. Red clump stars are present mainly in the southern and central parts of the Magellanic Bridge, below its gaseous part, and their presence is reflected by a strong deviation from the radial density profiles of the two galaxies. This may indicate either a tidal stream of stars, or that the stellar halos of the two galaxies overlap. On the other hand, we do not observe such an overlap within an intermediate-age population represented by the top of the red giant branch and the asymptotic giant branch stars. We also see only minor mixing of the old populations of the Clouds in the southern part of the Bridge, represented by the lowest part of the red giant branch.

Interstellar Magnetic Fields and Polarimetry of Dust Emission

Science.gov (United States)

Dowell, Darren

2010-01-01

Magnetic fields are an important ingredient in the stormy cosmos. Magnetic fields: (1) are intimately involved with winds from Active Galactic Nuclei (AGN) and stars (2) create at least some of the structures observed in the ISM (3) modulate the formation of clouds, cores, and stars within a turbulent medium (4) may be dynamically important in protostellar accretion disks (5) smooth weak shocks (C-shocks).

The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR

Science.gov (United States)

King, Ashley L.; Walton, Dominic J.; Miller, Jon M.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Fabian, Andy C.; Furst, Felix; Hailey, Charles J.;

Light, Wind and Fire - Beautiful Image of a Cosmic Sculpture

Science.gov (United States)

2010-02-01

Today ESO has released a dramatic new image of NGC 346, the brightest star-forming region in our neighbouring galaxy, the Small Magellanic Cloud, 210 000 light-years away towards the constellation of Tucana (the Toucan). The light, wind and heat given off by massive stars have dispersed the glowing gas within and around this star cluster, forming a surrounding wispy nebular structure that looks like a cobweb. NGC 346, like other beautiful astronomical scenes, is a work in progress, and changes as the aeons pass. As yet more stars form from loose matter in the area, they will ignite, scattering leftover dust and gas, carving out great ripples and altering the face of this lustrous object. NGC 346 spans approximately 200 light-years, a region of space about fifty times the distance between the Sun and its nearest stellar neighbours. Astronomers classify NGC 346 as an open cluster of stars, indicating that this stellar brood all originated from the same collapsed cloud of matter. The associated nebula containing this clutch of bright stars is known as an emission nebula, meaning that gas within it has been heated up by stars until the gas emits its own light, just like the neon gas used in electric store signs. Many stars in NGC 346 are relatively young in cosmic terms with their births dating back only a few million years or so (eso0834). Powerful winds thrown off by a massive star set off this recent round of star birth by compressing large amounts of matter, the first critical step towards igniting new stars. This cloud of material then collapses under its own gravity, until some regions become dense and hot enough to roar forth as a brilliantly shining, nuclear fusion-powered furnace - a star, illuminating the residual debris of gas and dust. In sufficiently congested regions like NGC 346, with high levels of recent star birth, the result is a glorious, glowing vista for our telescopes to capture. NGC 346 is in the Small Magellanic Cloud, a dwarf galaxy some 210

THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. II. THE SPATIAL DISTRIBUTION AND DEMOGRAPHICS OF DUSTY YOUNG STELLAR OBJECTS

International Nuclear Information System (INIS)

Megeath, S. T.; Kryukova, E.; Gutermuth, R.; Muzerolle, J.; Hora, J. L.; Myers, P. C.; Fazio, G. G.; Allen, L. E.; Flaherty, K.; Hartmann, L.; Pipher, J. L.; Stauffer, J.; Young, E. T.

2016-01-01

We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc −2 to over 10,000 pc −2 , with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc −2 , we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions

Multifrequency survey of the intergalactic cloud in the M96 group

International Nuclear Information System (INIS)

Schneider, S.E.; Skrutskie, M.F.; Hacking, P.B.; Young, J.S.; Dickman, R.L.

1989-01-01

The intergalactic cloud of neutral hydrogen in the M96 group are examined for signs of emission over a wide range of frequencies, from radio waves to X rays. Past or present stellar activity in the gas might have been expected to produce detectable visual infrared, CO, OH, or radio recombination-line emission. None was detected. The limits are used to study physical conditions in the intergalactic gas. In particular, B and V band limits on starlight and IRAS limits on the presence of dust strongly constrain the presence of stars or stellar by-products. However, given the uncertainties about physical conditions in the intergalactic environment, it is difficult to rule out entirely the presence of stellar-processed materials. Results of neutral hydrogen mapping from a large-scale survey of the intergalactic cloud and surrounding region are also presented. These observations confirm that the gas is confined to a large ringlike structure. The simplest interpretation remains that the intergalactic gas in Leo is primordial. 36 references

Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces. II. Radiation-Gas Interactions and Outflows

Science.gov (United States)

Raskutti, Sudhir; Ostriker, Eve C.; Skinner, M. Aaron

2017-12-01

Momentum deposition by radiation pressure from young, massive stars may help to destroy molecular clouds and unbind stellar clusters by driving large-scale outflows. We extend our previous numerical radiation hydrodynamic study of turbulent star-forming clouds to analyze the detailed interaction between non-ionizing UV radiation and the cloud material. Our simulations trace the evolution of gas and star particles through self-gravitating collapse, star formation, and cloud destruction via radiation-driven outflows. These models are idealized in that we include only radiation feedback and adopt an isothermal equation of state. Turbulence creates a structure of dense filaments and large holes through which radiation escapes, such that only ˜50% of the radiation is (cumulatively) absorbed by the end of star formation. The surface density distribution of gas by mass as seen by the central cluster is roughly lognormal with {σ }{ln{{Σ }}}=1.3{--}1.7, similar to the externally projected surface density distribution. This allows low surface density regions to be driven outwards to nearly 10 times their initial escape speed {v}{esc}. Although the velocity distribution of outflows is broadened by the lognormal surface density distribution, the overall efficiency of momentum injection to the gas cloud is reduced because much of the radiation escapes. The mean outflow velocity is approximately twice the escape speed from the initial cloud radius. Our results are also informative for understanding galactic-scale wind driving by radiation, in particular, the relationship between velocity and surface density for individual outflow structures and the resulting velocity and mass distributions arising from turbulent sources.

STABILIZING CLOUD FEEDBACK DRAMATICALLY EXPANDS THE HABITABLE ZONE OF TIDALLY LOCKED PLANETS

International Nuclear Information System (INIS)

Yang Jun; Abbot, Dorian S.; Cowan, Nicolas B.

2013-01-01

The habitable zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one-dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope.

In-Space Manufacturing (ISM): Pioneering Space Exploration

Science.gov (United States)

Werkheiser, Niki

2015-01-01

ISM Objective: Develop and enable the manufacturing technologies and processes required to provide on-demand, sustainable operations for Exploration Missions. This includes development of the desired capabilities, as well as the required processes for the certification, characterization & verification that will enable these capabilities to become institutionalized via ground-based and ISS demonstrations.

A general theory for the lifetimes of giant molecular clouds under the influence of galactic dynamics

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Jeffreson, Sarah M. R.; Kruijssen, J. M. Diederik

2018-05-01

We propose a simple analytic theory for environmentally dependent molecular cloud lifetimes, based on the large-scale (galactic) dynamics of the interstellar medium. Within this theory, the cloud lifetime is set by the time-scales for gravitational collapse, galactic shear, spiral arm interactions, epicyclic perturbations, and cloud-cloud collisions. It is dependent on five observable quantities, accessible through measurements of the galactic rotation curve, the gas and stellar surface densities, and the gas and stellar velocity dispersions of the host galaxy. We determine how the relative importance of each dynamical mechanism varies throughout the space of observable galactic properties, and conclude that gravitational collapse and galactic shear play the greatest role in setting the cloud lifetime for the considered range of galaxy properties, while cloud-cloud collisions exert a much lesser influence. All five environmental mechanisms are nevertheless required to obtain a complete picture of cloud evolution. We apply our theory to the galaxies M31, M51, M83, and the Milky Way, and find a strong dependence of the cloud lifetime upon galactocentric radius in each case, with a typical cloud lifetime between 10 and 50 Myr. Our theory is ideally suited for systematic observational tests with the Atacama Large Millimetre/submillimetre array.

Curtain-Lifting Winds Allow Rare Glimpse into Massive Star Factory

Science.gov (United States)

2003-06-01

Formation of Exceedingly Luminous and Hot Stars in Young Stellar Cluster Observed Directly Summary Based on a vast observational effort with different telescopes and instruments, ESO-astronomer Dieter Nürnberger has obtained a first glimpse of the very first stages in the formation of heavy stars. These critical phases of stellar evolution are normally hidden from the view, because massive protostars are deeply embedded in their native clouds of dust and gas, impenetrable barriers to observations at all but the longest wavelengths. In particular, no visual or infrared observations have yet "caught" nascent heavy stars in the act and little is therefore known so far about the related processes. Profiting from the cloud-ripping effect of strong stellar winds from adjacent, hot stars in a young stellar cluster at the center of the NGC 3603 complex, several objects located near a giant molecular cloud were found to be bona-fide massive protostars, only about 100,000 years old and still growing. Three of these objects, designated IRS 9A-C, could be studied in more detail. They are very luminous (IRS 9A is about 100,000 times intrinsically brighter than the Sun), massive (more than 10 times the mass of the Sun) and hot (about 20,000 degrees). They are surrounded by relative cold dust (about 0°C), probably partly arranged in disks around these very young objects. Two possible scenarios for the formation of massive stars are currently proposed, by accretion of large amounts of circumstellar material or by collision (coalescence) of protostars of intermediate masses. The new observations favour accretion, i.e. the same process that is active during the formation of stars of smaller masses. PR Photo 16a/03: Stellar cluster and star-forming region NGC 3603. PR Photo 16b/03: Region near very young, massive stars IRS 9A-C in NGC 3603 (8 bands from J to Q). How do massive stars form? This question is easy to pose, but so far very difficult to answer. In fact, the processes

Cloud Spirals and Outflow in Tropical Storm Katrina

Science.gov (United States)

2005-01-01

On Tuesday, August 30, 2005, NASA's Multi-angle Imaging SpectroRadiometer retrieved cloud-top heights and cloud-tracked wind velocities for Tropical Storm Katrina, as the center of the storm was situated over the Tennessee valley. At this time Katrina was weakening and no longer classified as a hurricane, and would soon become an extratropical depression. Measurements such as these can help atmospheric scientists compare results of computer-generated hurricane simulations with observed conditions, ultimately allowing them to better represent and understand physical processes occurring in hurricanes. Because air currents are influenced by the Coriolis force (caused by the rotation of the Earth), Northern Hemisphere hurricanes are characterized by an inward counterclockwise (cyclonic) rotation towards the center. It is less widely known that, at high altitudes, outward-spreading bands of cloud rotate in a clockwise (anticyclonic) direction. The image on the left shows the retrieved cloud-tracked winds as red arrows superimposed across the natural color view from MISR's nadir (vertical-viewing) camera. Both the counter-clockwise motion for the lower-level storm clouds and the clockwise motion for the upper clouds are apparent in these images. The speeds for the clockwise upper level winds have typical values between 40 and 45 m/s (144-162 km/hr). The low level counterclockwise winds have typical values between 7 and 24 m/s (25-86 km/hr), weakening with distance from the storm center. The image on the right displays the cloud-top height retrievals. Areas where cloud heights could not be retrieved are shown in dark gray. Both the wind velocity vectors and the cloud-top height field were produced by automated computer recognition of displacements in spatial features within successive MISR images acquired at different view angles and at slightly different times. The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously, viewing the entire globe

Calibrating the HISA temperature: Measuring the temperature of the Riegel-Crutcher cloud

Science.gov (United States)

Dénes, H.; McClure-Griffiths, N. M.; Dickey, J. M.; Dawson, J. R.; Murray, C. E.

2018-06-01

H I self absorption (HISA) clouds are clumps of cold neutral hydrogen (H I) visible in front of warm background gas, which makes them ideal places to study the properties of the cold atomic component of the interstellar medium (ISM). The Riegel-Crutcher (R-C) cloud is the most striking HISA feature in the Galaxy. It is one of the closest HISA clouds to us and is located in the direction of the Galactic Centre, which provides a bright background. High-resolution interferometric measurements have revealed the filamentary structure of this cloud, however it is difficult to accurately determine the temperature and the density of the gas without optical depth measurements. In this paper we present new H I absorption observations with the Australia Telescope Compact Array (ATCA) against 46 continuum sources behind the Riegel-Crutcher cloud to directly measure the optical depth of the cloud. We decompose the complex H I absorption spectra into Gaussian components using an automated machine learning algorithm. We find 300 Gaussian components, from which 67 are associated with the R-C cloud (0 temperature and find it to be between 20 and 80 K. Our measurements uncover a temperature gradient across the cloud with spin temperatures decreasing towards positive Galactic latitudes. We also find three new OH absorption lines associated with the cloud, which support the presence of molecular gas.

Difficulties on study of ISM 26Al and a possible new way to nucleosynthesize 26Al-SNIa

International Nuclear Information System (INIS)

Peng Qiuhe

1995-01-01

Some observational results of the 1.809 MeV gamma-ray emitted by decay of the interstellar medium (ISM) 26 Al, which are obtained by spacecraft during (1979-1992) are firstly introduced. Secondly, both Mg-Al chain and Ne-Na cycle of nuclear reactions are discussed. Thirdly, some new experiments of nuclear physics, which are related with the question of the ISM 26 Al(e.g. measurements of the cross section of the nuclear reactions in the MgAl chain and in the NeNa cycle) are introduced. Then, comparing some experiments of nuclear physics, some difficulties confronted on various models responsible for the ISM 26 Al are discussed. The conclusions are: 1) all of hydrostatic H-burning models and all current nova models are hard to provide enough ISM 26 Al to be detected; 2) SN II + SN I b models are promising on responsibility for the half of ISM 26 Al, although current SN II + SN I b models should be improved, besides. Proposal of a new way to nucleosynthesizse 26 Al, 14 N + 16 O→ 26 Al + α, is suggested. SNI a as a possible source of the ISM 26 Al is discussed (63 refs.)

On the Feasibility of Tracking the Monsoon History by Using Ancient Wind Direction Records

Science.gov (United States)

Gallego, D.; Ribera, P.; Peña-Ortiz, C.; Vega, I.; Gómez, F. D. P.; Ordoñez-Perez, P.; Garcia-Hererra, R.

2015-12-01

In this work, we use old wind direction records to reconstruct indices for the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). Since centuries ago, ships departing from the naval European powers circumnavigated Africa in their route to the Far East. Most of these ships took high-quality observations preserved in logbooks. We show that wind direction observations taken aboard ships can be used to track the seasonal wind reversal typical of monsoonal circulations. The persistence of the SW winds in the 20W-17W and 7N-13N region is highly correlated with the WAM strength and Sahel's precipitation. It has been possible to build a WAM index back to the 19th Century. Our results show that in the Sahel, the second half of the 19thCentury was significantly wetter than present day. The relation of the WAM with the ENSO cycle, and the Atlantic Multidecadal Oscillation was low and instable from the 1840s to the 1970s, when they abruptly suffered an unprecedented reinforcement which last up to the present day. The persistence of the SSW wind in the 60E-80E and 8N-12N area has been used to track the ISM onset since the 1880s. We found evidences of later than average onset dates during the 1900-1925 and 1970-1990 periods and earlier than average onset between 1940 and 1965. A significant relation between the ISM onset and the PDO restricted to shifts from negative to positive PDO phases has been found. The most significant contribution of our study is the fact that we have shown that it is possible to build consistent monsoon indices of instrumental character using solely direct observations of wind direction. Our indices have been generated by using data currently available in the ICOADS 2.5 database, but a large amount of wind observations for periods previous to the 20thcentury still remain not explored in thousands of logbooks preserved in British archives. The interest of unveil these data to track the monsoons for more than 200 -or even 300 years- it is

Is the dissociation of coronene in stellar winds a source of molecular hydrogen? application to the HD 44179 nebula

Science.gov (United States)

Champeaux, J.-P.; Moretto-Capelle, P.; Cafarelli, P.; Deville, C.; Sence, M.; Casta, R.

2014-06-01

The physical interactions of polycyclic aromatic hydrocarbons (PAHs) with stellar particular radiation are key to understanding the life cycle of PAHs, their abundance and their role in the complex astrochemistry of the interstellar medium. In this context, we present experimental results on the ionization/fragmentation of isolated coronene by a 100-keV proton, reproducing interactions between stellar winds and PAH molecules in the star's environment. In particular, we show, without ambiguity, that such ionization/fragmentation induces intense dehydrogenation processes for which the loss of even numbers of hydrogen atoms and the detection of CH_2+ cations as a possible H2 precursor strongly suggest the formation of H2 neutral molecules along a scenario revealed by a quantum chemical calculation. We have evaluated the H2 emission cross-section from the coronene/proton interaction at 100 and 1.6 keV to be 2.97 × 10-16 and 3.3 × 10-16 cm2, respectively. A qualitative discussion on the formation rate of H2 in the HD 44179 Red Rectangle (RR) nebula leads to the conclusion that such processes could be very efficient, especially inside planetary nebulae rich in PAH molecules interacting with high proton mass-loss rate stars (such as post-asymptotic giant branch stars) or high velocity jets produced by an accretion disc.

Clustered star formation and the origin of stellar masses.

Science.gov (United States)

Pudritz, Ralph E

2002-01-04

Star clusters are ubiquitous in galaxies of all types and at all stages of their evolution. We also observe them to be forming in a wide variety of environments, ranging from nearby giant molecular clouds to the supergiant molecular clouds found in starburst and merging galaxies. The typical star in our galaxy and probably in others formed as a member of a star cluster, so star formation is an intrinsically clustered and not an isolated phenomenon. The greatest challenge regarding clustered star formation is to understand why stars have a mass spectrum that appears to be universal. This review examines the observations and models that have been proposed to explain these fundamental issues in stellar formation.

An LTE effective temperature scale for red supergiants in the Magellanic clouds

Science.gov (United States)

Tabernero, H. M.; Dorda, R.; Negueruela, I.; González-Fernández, C.

2018-05-01

We present a self-consistent study of cool supergiants (CSGs) belonging to the Magellanic clouds. We calculated stellar atmospheric parameters using LTE KURUCZ and MARCS atmospheric models for more than 400 individual targets by fitting a careful selection of weak metallic lines. We explore the existence of a Teff scale and its implications in two different metallicity environments (each Magellanic cloud). Critical and in-depth tests have been performed to assess the reliability of our stellar parameters (i.e. internal error budget, NLTE systematics). In addition, several Monte Carlo tests have been carried out to infer the significance of the Teff scale found. Our findings point towards a unique Teff scale that seems to be independent of the environment.

Cosmic-Ray Propagation in Turbulent Spiral Magnetic Fields Associated with Young Stellar Objects

Science.gov (United States)

Fatuzzo, Marco; Adams, Fred C.

2018-04-01

External cosmic rays impinging upon circumstellar disks associated with young stellar objects provide an important source of ionization, and, as such, play an important role in disk evolution and planet formation. However, these incoming cosmic rays are affected by a variety of physical processes internal to stellar/disk systems, including modulation by turbulent magnetic fields. Globally, these fields naturally provide both a funneling effect, where cosmic rays from larger volumes are focused into the disk region, and a magnetic mirroring effect, where cosmic rays are repelled due to the increasing field strength. This paper considers cosmic-ray propagation in the presence of a turbulent spiral magnetic field, analogous to that produced by the solar wind. The interaction of this wind with the interstellar medium defines a transition radius, analogous to the heliopause, which provides the outer boundary to this problem. We construct a new coordinate system where one coordinate follows the spiral magnetic field lines and consider magnetic perturbations to the field in the perpendicular directions. The presence of magnetic turbulence replaces the mirroring points with a distribution of values and moves the mean location outward. Our results thus help quantify the degree to which cosmic-ray fluxes are reduced in circumstellar disks by the presence of magnetic field structures that are shaped by stellar winds. The new coordinate system constructed herein should also be useful in other astronomical applications.

THE CALIFORNIA MOLECULAR CLOUD

International Nuclear Information System (INIS)

Lada, Charles J.; Lombardi, Marco; Alves, Joao F.

2009-01-01

We present an analysis of wide-field infrared extinction maps of a region in Perseus just north of the Taurus-Auriga dark cloud complex. From this analysis we have identified a massive, nearby, but previously unrecognized, giant molecular cloud (GMC). Both a uniform foreground star density and measurements of the cloud's velocity field from CO observations indicate that this cloud is likely a coherent structure at a single distance. From comparison of foreground star counts with Galactic models, we derive a distance of 450 ± 23 pc to the cloud. At this distance the cloud extends over roughly 80 pc and has a mass of ∼ 10 5 M sun , rivaling the Orion (A) molecular cloud as the largest and most massive GMC in the solar neighborhood. Although surprisingly similar in mass and size to the more famous Orion molecular cloud (OMC) the newly recognized cloud displays significantly less star formation activity with more than an order of magnitude fewer young stellar objects than found in the OMC, suggesting that both the level of star formation and perhaps the star formation rate in this cloud are an order of magnitude or more lower than in the OMC. Analysis of extinction maps of both clouds shows that the new cloud contains only 10% the amount of high extinction (A K > 1.0 mag) material as is found in the OMC. This, in turn, suggests that the level of star formation activity and perhaps the star formation rate in these two clouds may be directly proportional to the total amount of high extinction material and presumably high density gas within them and that there might be a density threshold for star formation on the order of n(H 2 ) ∼ a few x 10 4 cm -3 .

The Effects of ISM1 Medium on Embryo Quality and Outcomes of IVF/ICSI Cycles.

Science.gov (United States)

Hassani, Fatemeh; Eftekhari-Yazdi, Poopak; Karimian, Leila; Rezazadeh Valojerdi, Mojtaba; Movaghar, Bahar; Fazel, Mohammad; Fouladi, Hamid Reza; Shabani, Fatemeh; Johansson, Lars

2013-07-01

The aim of this study is to investigate the effect of ISM1 culture medium on embryo development, quality and outcomes of in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles. This study compares culture medium commonly used in the laboratory setting for oocyte recovery and embryo development with a medium from MediCult. We have assessed the effects of these media on embryo development and newborn characteristics. In this prospective randomized study, fertilized oocytes from patients were randomly assigned to culture in ISM1 (MediCult, cycles: n=293) or routine lab culture medium (G-1TM v5; Vitrolife, cycles: n=290) according to the daily media schedule for oocyte retrieval. IVF or ICSI and embryo transfer were performed with either MediCult media or routine lab media. Embryo quality on days 2/3, cleavage, pregnancy and implantation rates, baby take home rate (BTHR), in addition to the weight and length of newborns were compared between groups. There were similar cleavage rates for ISM1 (86%) vs. G-1TM v5 (88%). We observed a significantly higher percentage of excellent embryos in ISM1 (42.7%) compared to G-1TM v5 (39%, pISM1 had both higher birth weight (3.03 kg) and length (48.8 cm) compared to G-1TM v5 babies that had a birth weight of 2.66 kg and a length of 46.0 cm (pISM1 is a more effective culture medium in generating higher quality embryos, which may be reflected in the characteristics of babies at birth.

Aerosol-Cloud Interactions During Puijo Cloud Experiments - The effects of weather and local sources

Science.gov (United States)

Komppula, Mika; Portin, Harri; Leskinen, Ari; Romakkaniemi, Sami; Brus, David; Neitola, Kimmo; Hyvärinen, Antti-Pekka; Kortelainen, Aki; Hao, Liqing; Miettinen, Pasi; Jaatinen, Antti; Ahmad, Irshad; Lihavainen, Heikki; Laaksonen, Ari; Lehtinen, Kari E. J.

2013-04-01

The Puijo measurement station has provided continuous data on aerosol-cloud interactions since 2006. The station is located on top of the Puijo observation tower (306 m a.s.l, 224 m above the surrounding lake level) in Kuopio, Finland. The top of the tower is covered by cloud about 15 % of the time, offering perfect conditions for studying aerosol-cloud interactions. With a twin-inlet setup (total and interstitial inlets) we are able to separate the activated particles from the interstitial (non-activated) particles. The continuous twin-inlet measurements include aerosol size distribution, scattering and absorption. In addition cloud droplet number and size distribution are measured continuously with weather parameters. During the campaigns the twin-inlet system was additionally equipped with aerosol mass spectrometer (AMS) and Single Particle Soot Photometer (SP-2). This way we were able to define the differences in chemical composition of the activated and non-activated particles. Potential cloud condensation nuclei (CCN) in different supersaturations were measured with two CCN counters (CCNC). The other CCNC was operated with a Differential Mobility Analyzer (DMA) to obtain size selected CCN spectra. Other additional measurements included Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) for particle hygroscopicity. Additionally the valuable vertical wind profiles (updraft velocities) are available from Halo Doppler lidar during the 2011 campaign. Cloud properties (droplet number and effective radius) from MODIS instrument onboard Terra and Aqua satellites were retrieved and compared with the measured values. This work summarizes the two latest intensive campaigns, Puijo Cloud Experiments (PuCE) 2010 & 2011. We study especially the effect of the local sources on the cloud activation behaviour of the aerosol particles. The main local sources include a paper mill, a heating plant, traffic and residential areas. The sources can be categorized and identified

Revealing the Physics of Galactic Winds Through Massively-Parallel Hydrodynamics Simulations

Science.gov (United States)

Schneider, Evan Elizabeth

This thesis documents the hydrodynamics code Cholla and a numerical study of multiphase galactic winds. Cholla is a massively-parallel, GPU-based code designed for astrophysical simulations that is freely available to the astrophysics community. A static-mesh Eulerian code, Cholla is ideally suited to carrying out massive simulations (> 20483 cells) that require very high resolution. The code incorporates state-of-the-art hydrodynamics algorithms including third-order spatial reconstruction, exact and linearized Riemann solvers, and unsplit integration algorithms that account for transverse fluxes on multidimensional grids. Operator-split radiative cooling and a dual-energy formalism for high mach number flows are also included. An extensive test suite demonstrates Cholla's superior ability to model shocks and discontinuities, while the GPU-native design makes the code extremely computationally efficient - speeds of 5-10 million cell updates per GPU-second are typical on current hardware for 3D simulations with all of the aforementioned physics. The latter half of this work comprises a comprehensive study of the mixing between a hot, supernova-driven wind and cooler clouds representative of those observed in multiphase galactic winds. Both adiabatic and radiatively-cooling clouds are investigated. The analytic theory of cloud-crushing is applied to the problem, and adiabatic turbulent clouds are found to be mixed with the hot wind on similar timescales as the classic spherical case (4-5 t cc) with an appropriate rescaling of the cloud-crushing time. Radiatively cooling clouds survive considerably longer, and the differences in evolution between turbulent and spherical clouds cannot be reconciled with a simple rescaling. The rapid incorporation of low-density material into the hot wind implies efficient mass-loading of hot phases of galactic winds. At the same time, the extreme compression of high-density cloud material leads to long-lived but slow-moving clumps

Bright soil units on Mars determined from ISM imaging spectrometer data

Science.gov (United States)

Murchie, Scott; Mustard, John

1993-01-01

The lithology of bright Martian soil provides evidence for chemical and physical processes that have modified the planet's surface. Data from the ISM imaging spectrometer, which observed much of the equatorial region at a spatial resolution of approximately 22 km, cover the NIR wavelength range critical to ascertaining the presence and abundance of Fe-containing phases, hydroxylated silicates, and H2O in the bright soil. ISM data previously have revealed spatial variations in depth of the 3.0-microns H2O absorption suggesting differences in water content, a weak absorption at 2.2 microns indicative of metal-OH in phyllosilicate, and variations in the 1-micron Fe absorption indicative of differences in Fe mineralogy. This paper summarizes first results of a systematic investigation of spectral heterogeneity in bright soils observed by ISM. At least seven 'units' with distinctive properties were discriminated. Comparison of their spatial distributions with Viking data shows that they generally correspond with previously recognized morphologic, color, and thermal features. These correspondences and the units' spectral attributes provide evidence for lithologic differences between the soils in different geologic settings.

Roadmap for Lean implementation in Indian automotive component manufacturing industry: comparative study of UNIDO Model and ISM Model

Science.gov (United States)

Jadhav, J. R.; Mantha, S. S.; Rane, S. B.

2015-06-01

The demands for automobiles increased drastically in last two and half decades in India. Many global automobile manufacturers and Tier-1 suppliers have already set up research, development and manufacturing facilities in India. The Indian automotive component industry started implementing Lean practices to fulfill the demand of these customers. United Nations Industrial Development Organization (UNIDO) has taken proactive approach in association with Automotive Component Manufacturers Association of India (ACMA) and the Government of India to assist Indian SMEs in various clusters since 1999 to make them globally competitive. The primary objectives of this research are to study the UNIDO-ACMA Model as well as ISM Model of Lean implementation and validate the ISM Model by comparing with UNIDO-ACMA Model. It also aims at presenting a roadmap for Lean implementation in Indian automotive component industry. This paper is based on secondary data which include the research articles, web articles, doctoral thesis, survey reports and books on automotive industry in the field of Lean, JIT and ISM. ISM Model for Lean practice bundles was developed by authors in consultation with Lean practitioners. The UNIDO-ACMA Model has six stages whereas ISM Model has eight phases for Lean implementation. The ISM-based Lean implementation model is validated through high degree of similarity with UNIDO-ACMA Model. The major contribution of this paper is the proposed ISM Model for sustainable Lean implementation. The ISM-based Lean implementation framework presents greater insight of implementation process at more microlevel as compared to UNIDO-ACMA Model.

ISMS: A New Model for Improving Student Motivation and Self-Esteem in Primary Education

Science.gov (United States)

Ghilay, Yaron; Ghilay, Ruth

2015-01-01

In this study we introduce a new model for primary education called ISMS: Improving Student Motivation and Self-esteem. Following a two-year study undertaken in a primary school (n = 67), the new model was found to be successful. Students who participated in the research, reported that a course based on ISMS principles was very helpful for…

Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

Science.gov (United States)

Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

2018-01-01

We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

DETAILED INTERSTELLAR POLARIMETRIC PROPERTIES OF THE PIPE NEBULA AT CORE SCALES

International Nuclear Information System (INIS)

Franco, G. A. P.; Alves, F. O.; Girart, J. M.

2010-01-01

We use R-band CCD linear polarimetry collected for about 12,000 background field stars in 46 fields of view toward the Pipe nebula to investigate the properties of the polarization across this dark cloud. Based on archival Two Micron All Sky Survey data, we estimate that the surveyed areas present total visual extinctions in the range 0.6 mag ≤ A V ≤ 4.6 mag. While the observed polarizations show a well-ordered large-scale pattern, with polarization vectors almost perpendicularly aligned to the cloud's long axis, at core scales one sees details that are characteristics of each core. Although many observed stars present degrees of polarization that are unusual for the common interstellar medium (ISM), our analysis suggests that the dust grains constituting the diffuse parts of the Pipe nebula seem to have the same properties as the normal Galactic ISM. Estimates of the second-order structure function of the polarization angles suggest that most of the Pipe nebula is magnetically dominated and that turbulence is sub-Alvenic. The Pipe nebula is certainly an interesting region to investigate the processes that prevailed during the initial phases of low-mass stellar formation.

Radiative thermal conduction fronts

International Nuclear Information System (INIS)

Borkowski, K.J.; Balbus, S.A.; Fristrom, C.C.

1990-01-01

The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence

Simulating the UV escape fractions from molecular cloud populations in star-forming dwarf and spiral galaxies

Science.gov (United States)

Howard, Corey S.; Pudritz, Ralph E.; Harris, William E.; Klessen, Ralf S.

2018-04-01

The escape of ultraviolet photons from the densest regions of the interstellar medium (ISM) - giant molecular clouds (GMCs) - is a poorly constrained parameter which is vital to understanding the ionization of the ISM and the intergalactic medium. We characterize the escape fraction, fesc,GMC, from a suite of individual GMC simulations with masses in the range 104-6 M⊙ using the adaptive-mesh refinement code FLASH. We find significantly different fesc,GMC depending on the GMC mass that can reach >90 per cent in the evolution of 5 × 104 and 105 M⊙ clouds or remain low at ˜5 per cent for most of the lifetime of more massive GMCs. All clouds show fluctuations over short, sub-Myr time-scales produced by flickering H II regions. We combine our results to calculate the total escape fraction (fesc,tot) from GMC populations in dwarf starburst and spiral galaxies by randomly drawing clouds from a GMC mass distribution (dN/dM ∝ Mα, where α is either -1.5 or -2.5) over fixed time intervals. We find typical fesc,tot values of 8 per cent for both the dwarf and spiral models. The fluctuations of fesc,tot, however, are much larger for the dwarf models with values as high as 90 per cent. The photons escaping from the 5 × 104 and 105 M⊙ GMCs are the dominant contributors to fesc,tot in all cases. We also show that the accompanying star formation rates (SFRs) of our model (˜2 × 10-2 and 0.73 M⊙yr-1) are consistent with observations of SFRs in dwarf starburst and spiral galaxies, respectively.

Modelling the supernova-driven ISM in different environments

Czech Academy of Sciences Publication Activity Database

Gatto, A.; Walch, S.; Mac Low, M.-M.; Naab, T.; Girichidis, P.; Glover, S.C.O.; Wünsch, Richard; Klessen, R.S.; Clark, P.C.; Baczynski, C.; Peters, T.; Ostriker, J.P.; Ibanez-Mejia, J.C.; Haid, S.

2015-01-01

Roč. 449, č. 1 (2015), s. 1057-1075 ISSN 0035-8711 R&D Projects: GA ČR GAP209/12/1795 Institutional support: RVO:67985815 Keywords : numerical methods * ISM evolution * kinematics and dynamics Subject RIV: BN - Astronomy , Celestial Mechanics, Astrophysics Impact factor: 4.952, year: 2015

Investigating stellar surface rotation using observations of starspots

DEFF Research Database (Denmark)

Korhonen, Heidi Helena

2011-01-01

Rapid rotation enhances the dynamo operating in stars, and thus also introduces significantly stronger magnetic activity than is seen in slower rotators. Many young cool stars still have the rapid, primordial rotation rates induced by the interstellar molecular cloud from which they were formed....... Also older stars in close binary systems are often rapid rotators. These types of stars can show strong magnetic activity and large starspots. In the case of large starspots which cause observable changes in the brightness of the star, and even in the shapes of the spectral line profiles, one can get...... information on the rotation of the star. At times even information on the spot rotation at different stellar latitudes can be obtained, similarly to the solar surface differential rotation measurements using magnetic features as tracers. Here, I will review investigations of stellar rotation based...

DUST AND GAS IN THE MAGELLANIC CLOUDS FROM THE HERITAGE HERSCHEL KEY PROJECT. II. GAS-TO-DUST RATIO VARIATIONS ACROSS INTERSTELLAR MEDIUM PHASES

Energy Technology Data Exchange (ETDEWEB)

Roman-Duval, Julia; Gordon, Karl D.; Meixner, Margaret [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bot, Caroline [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l' université, F-67000 Strasbourg (France); Bolatto, Alberto; Jameson, Katherine [Department of Astronomy, Lab for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Hughes, Annie; Hony, Sacha [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Wong, Tony [University of Illinois at Urbana-Champaign, 1002 W. Green St., Urbana, IL 61801 (United States); Babler, Brian [Department of Astronomy, University of Wisconsin, 475 North Charter St., Madison, WI 53706 (United States); Bernard, Jean-Philippe [CNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse Cedex 4 (France); Clayton, Geoffrey C. [Louisiana State University, Department of Physics and Astronomy, 233-A Nicholson Hall, Tower Dr., Baton Rouge, LA 70803-4001 (United States); Fukui, Yasuo [Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Galametz, Maud [European Southern Observatory, Karl-Schwarzschild-Str 2, D-85748 Garching (Germany); Galliano, Frederic; Lebouteiller, Vianney; Lee, Min-Young [CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Glover, Simon [Zentrum für Astronomie, Institut für Theoretische Astrophysik, Universität Heidelberg, Albert-Ueberle Strasse 2, D-69120 Heidelberg (Germany); Israel, Frank [Sterrewacht Leiden, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Li, Aigen, E-mail: duval@stsci.edu [314 Physics Building, Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); and others

2014-12-20

The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21 cm, CO, and Hα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380{sub −130}{sup +250} ± 3 in the LMC, and 1200{sub −420}{sup +1600} ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M {sub ☉} pc{sup –2} in the LMC and 0.03 M {sub ☉} pc{sup –2} in the SMC, corresponding to A {sub V} ∼ 0.4 and 0.2, respectively. We investigate the range of CO-to-H{sub 2} conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on X {sub CO} to be 6 × 10{sup 20} cm{sup –2} K{sup –1} km{sup –1} s in the LMC (Z = 0.5 Z {sub ☉}) at 15 pc resolution, and 4 × 10{sup 21} cm{sup –2} K{sup –1} km{sup –1} s in the SMC (Z = 0.2 Z {sub ☉}) at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor ∼2, even after accounting for the effects of CO-dark H{sub 2} in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H{sub 2}. Within the expected 5-20 times Galactic X {sub CO} range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further modeling

The Effects of ISM1 Medium on Embryo Quality and Outcomes of IVF/ICSI Cycles

Directory of Open Access Journals (Sweden)

Fatemeh Shabani

2013-01-01

Full Text Available Background: The aim of this study is to investigate the effect of ISM1 culture mediumon embryo development, quality and outcomes of in vitro fertilization/intracytoplasmicsperm injection (IVF/ICSI cycles. This study compares culture medium commonly usedin the laboratory setting for oocyte recovery and embryo development with a mediumfrom MediCult. We have assessed the effects of these media on embryo development andnewborn characteristics.Materials and Methods: In this prospective randomized study, fertilized oocytesfrom patients were randomly assigned to culture in ISM1 (MediCult, cycles:n=293 or routine lab culture medium (G-1TM v5; Vitrolife, cycles: n=290 accordingto the daily media schedule for oocyte retrieval. IVF or ICSI and embryotransfer were performed with either MediCult media or routine lab media. Embryoquality on days 2/3, cleavage, pregnancy and implantation rates, baby take homerate (BTHR, in addition to the weight and length of newborns were comparedbetween groups.Results: There were similar cleavage rates for ISM1 (86% vs. G-1TM v5 (88%. Weobserved a significantly higher percentage of excellent embryos in ISM1 (42.7% comparedto G-1TM v5 (39%, p<0.05. Babies born after culture in ISM1 had both higherbirth weight (3.03 kg and length (48.8 cm compared to G-1TM v5 babies that had a birthweight of 2.66 kg and a length of 46.0 cm (p<0.001 for both.Conclusion: This study suggests that ISM1 is a more effective culture medium ingenerating higher quality embryos, which may be reflected in the characteristics ofbabies at birth.

Supernova-regulated ISM. V. Space and Time Correlations

Science.gov (United States)

Hollins, J. F.; Sarson, G. R.; Shukurov, A.; Fletcher, A.; Gent, F. A.

2017-11-01

We apply correlation analysis to random fields in numerical simulations of the supernova-driven interstellar medium (ISM) with the magnetic field produced by dynamo action. We solve the magnetohydrodynamic (MHD) equations in a shearing Cartesian box representing a local region of the ISM, subject to thermal and kinetic energy injection by supernova explosions, and parameterized, optically thin radiative cooling. We consider the cold, warm, and hot phases of the ISM separately; the analysis mostly considers the warm gas, which occupies the bulk of the domain. Various physical variables have different correlation lengths in the warm phase: 40,50, and 60 {pc} for the random magnetic field, density, and velocity, respectively, in the midplane. The correlation time of the random velocity is comparable to the eddy turnover time, about {10}7 {year}, although it may be shorter in regions with a higher star formation rate. The random magnetic field is anisotropic, with the standard deviations of its components {b}x/{b}y/{b}z having approximate ratios 0.5/0.6/0.6 in the midplane. The anisotropy is attributed to the global velocity shear from galactic differential rotation and locally inhomogeneous outflow to the galactic halo. The correlation length of Faraday depth along the z axis, 120 {pc}, is greater than for electron density, 60{--}90 {pc}, and the vertical magnetic field, 60 {pc}. Such comparisons may be sensitive to the orientation of the line of sight. Uncertainties of the structure functions of synchrotron intensity rapidly increase with the scale. This feature is hidden in a power spectrum analysis, which can undermine the usefulness of power spectra for detailed studies of interstellar turbulence.

TRACING THE EVOLUTION OF HIGH-REDSHIFT GALAXIES USING STELLAR ABUNDANCES

Energy Technology Data Exchange (ETDEWEB)

Crosby, Brian D.; O’Shea, Brian W. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Beers, Timothy C. [Department of Physics and JINA—Center for the Evolution of the Elements, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Tumlinson, Jason, E-mail: crosby.bd@gmail.com [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2016-03-20

This paper presents the first results from a model for chemical evolution that can be applied to N-body cosmological simulations and quantitatively compared to measured stellar abundances from large astronomical surveys. This model convolves the chemical yield sets from a range of stellar nucleosynthesis calculations (including asymptotic giant branch stars, Type Ia and II supernovae, and stellar wind models) with a user-specified stellar initial mass function (IMF) and metallicity to calculate the time-dependent chemical evolution model for a “simple stellar population” (SSP) of uniform metallicity and formation time. These SSP models are combined with a semianalytic model for galaxy formation and evolution that uses merger trees from N-body cosmological simulations to track several α- and iron-peak elements for the stellar and multiphase interstellar medium components of several thousand galaxies in the early (z ≥ 6) universe. The simulated galaxy population is then quantitatively compared to two complementary data sets of abundances in the Milky Way stellar halo and is capable of reproducing many of the observed abundance trends. The observed abundance ratio distributions are best reproduced with a Chabrier IMF, a chemically enriched star formation efficiency of 0.2, and a redshift of reionization of 7. Many abundances are qualitatively well matched by our model, but our model consistently overpredicts the carbon-enhanced fraction of stars at low metallicities, likely owing to incomplete coverage of Population III stellar yields and supernova models and the lack of dust as a component of our model.

Multiple Stellar Populations in Star Clusters

Science.gov (United States)

Piotto, G.

2013-09-01

For half a century it had been astronomical dogma that a globular cluster (GC) consists of stars born at the same time out of the same material, and this doctrine has borne rich fruits. In recent years, high resolution spectroscopy and high precision photometry (from space and ground-based observations) have shattered this paradigm, and the study of GC populations has acquired a new life that is now moving it in new directions. Evidence of multiple stellar populations have been identified in the color-magnitude diagrams of several Galactic and Magellanic Cloud GCs where they had never been imagined before.

The slow ionized wind and rotating disklike system that are associated with the high-mass young stellar object G345.4938+01.4677

Energy Technology Data Exchange (ETDEWEB)

Guzmán, Andrés E.; Garay, Guido; Bronfman, Leonardo; Mardones, Diego [Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago (Chile); Rodríguez, Luis F. [Centro de Radioastronomía y Astrofísica (UNAM), Morelia 58089 (Mexico); Moran, James [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA (United States); Brooks, Kate J. [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, 1710 NSW (Australia); Nyman, Lars-Åke [Joint ALMA Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago (Chile); Sanhueza, Patricio [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States)

2014-12-01

We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562–3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings imply electron densities of 5 × 10{sup 7} cm{sup –3} on average. In addition, we detect SO and SO{sub 2} emission arising from a compact (∼3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.

The National Programme of Stellar Physics. Assessment 2011-2014. Prospective 2015-2018

International Nuclear Information System (INIS)

Bontemps, Sylvain; Bouchy, Francois; Charbonnel, Corinne; Chieze, Jean-Pierre; Dessart, Luc; Dintrans, Boris; Dougados, Catherine; Josselin, Eric; Kervella, Pierre; Martins, Fabrice; Michel, Eric; Moraux, Estelle; Recio-Blanco, Alejandra; Ristorcelli, Isabelle; Reyle, Celine; Alecian, Evelyne; Bouchy, Francois; Ciardi, Andrea; Dintrans, Boris; Herpin, Fabrice; Jouve, Laurene; Lebreton, Yveline; Motte, Frederique; Nardetto, Nicolas; Robin, Annie; Royer, Frederic; Samadi, Reza

2015-04-01

After an introduction which outlines the role of stellar physics as a keystone of research in astrophysics, this report proposes a presentation of the operation of the French national programme of stellar physics (PNPS): status and general operation, annual operation, statistics of budget and calls for bids, scientific animation, education, communication, community census, assessment of projects and thesis. It presents an overview of priority research theses between 2011 and 2014, according to their theme: stellar formation and protoplanetary disks, stellar structure and evolutions, origin and impact of magnetism, and atmospheres, winds and mass loss. Transverse theses are also presented the same way for the same period, with the following themes: basic physics, numeric simulations. The last part presents prospectives in terms of events (colloquium), bodies (new scientific council), themes to be studied, operation (interdisciplinarity and interfaces), means, general recommendations, and strengths and weaknesses of the national community

The Research of Dr. Joanne Simpson: Fifty Years Investigating Hurricanes, Tropical Clouds and Cloud Systems

Science.gov (United States)

Tao, W. -K.; Halverson, J.; Adler, R.; Garstang, M.; Houze, R., Jr.; LeMone, M.; Pielke, R., Sr.; Woodley, W.; O'C.Starr, David (Technical Monitor)

2001-01-01

This AMS Meteorological Monographs is dedicated to Dr. Joanne Simpson for her many pioneering research efforts in tropical meteorology during her fifty-year career. Dr. Simpson's major areas of scientific research involved the "hot tower" hypothesis and its role in hurricanes, structure and maintenance of trade winds, air-sea interaction, and observations and the mechanism for hurricanes and waterspouts. She was also a pioneer in cloud modeling with the first one-dimensional model and had the first cumulus model on a computer. She also played a major role in planning and leading observational experiments on convective cloud systems. The launch of the Tropical Rainfall Measuring Mission (TRMM) satellite, a joint U.S.-Japan project, in November of 1997 made it possible for quantitative measurements of tropical rainfall to be obtained on a continuous basis over the entire global tropics. Dr. Simpson was the TRAM Project Scientist from 1986 until its launch in 1997. Her efforts during this crucial period ensured that the mission was both well planned scientifically and well engineered as well as within budget. In this paper, Dr. J. Simpson's nine specific accomplishments during her fifty-year career: (1) hot tower hypothesis, (2) hurricanes, (3) airflow and clouds over heated islands, (4) cloud models, (5) trade winds and their role in cumulus development, (6) air-sea interaction, (7) cloud-cloud interactions and mergers, (8) waterspouts, and (9) TRMM science, will be described and discussed.

EARLY AFTERGLOWS OF GAMMA-RAY BURSTS IN A STRATIFIED MEDIUM WITH A POWER-LAW DENSITY DISTRIBUTION

International Nuclear Information System (INIS)

Yi, Shuang-Xi; Dai, Zi-Gao; Wu, Xue-Feng

2013-01-01

A long-duration gamma-ray burst (GRB) has been widely thought to arise from the collapse of a massive star, and it has been suggested that its ambient medium is a homogenous interstellar medium (ISM) or a stellar wind. There are two shocks when an ultra-relativistic fireball that has been ejected during the prompt gamma-ray emission phase sweeps up the circumburst medium: a reverse shock that propagates into the fireball, and a forward shock that propagates into the ambient medium. In this paper, we investigate the temporal evolution of the dynamics and emission of these two shocks in an environment with a general density distribution of n∝R –k (where R is the radius) by considering thick-shell and thin-shell cases. A GRB afterglow with one smooth onset peak at early times is understood to result from such external shocks. Thus, we can determine the medium density distribution by fitting the onset peak appearing in the light curve of an early optical afterglow. We apply our model to 19 GRBs and find that their k values are in the range of 0.4-1.4, with a typical value of k ∼ 1, implying that this environment is neither a homogenous ISM with k = 0 nor a typical stellar wind with k = 2. This shows that the progenitors of these GRBs might have undergone a new mass-loss evolution

Star formation rates and stellar masses in z ~ 1 gamma-ray burst hosts

DEFF Research Database (Denmark)

Castro Cerón, José María; Michalowski, Michal; Hjorth, J.

2006-01-01

Cosmology: Observations, ISM: Dust, Extinction, Galaxies: High-Redshift, Galaxies: ISM, Gamma Rays: Bursts, Infrared: Galaxies Udgivelsesdato: Dec. 4......Cosmology: Observations, ISM: Dust, Extinction, Galaxies: High-Redshift, Galaxies: ISM, Gamma Rays: Bursts, Infrared: Galaxies Udgivelsesdato: Dec. 4...

The Evolution of Dust in the Multiphase ISM: Grain Destruction Processes

Science.gov (United States)

Wolfire, Mark

1999-01-01

This proposal covered year one of a long term project in which we acquired the necessary hardware and softwaxe needed to calculate grain destruction processes in the interstellar medium (ISM). The long term goal of this research is to develop a model for the dust evolution in the ISM capable of explaining observations of elemental depletions, the grain size distribution, and the emission characteristics of the ISM from the X-ray through the FIR. We purchased a SUN Ultra 10 workstation and peripheral devices including an Exabyte Tape drive, HP Laser Printer, and Seagate External Hard Disk. The PI installed the hardware and Solaris operating system on the workstation and integrated the hardware into the network. Software was also purchased to enable connections to the workstation from a PC (Hummingbird Exceed). Additional freeware required to carry out the proposed program was installed on the system including compilers (g77, gcc, g++), editors (emacs), a markup language (LaTeX), and display programs (WIP, XV, SAOtng). We have also successfully modified the required plot files to work with our system which display the results of grain processing.

Dust Destruction in the ISM: A Re-Evaluation of Dust Lifetimes

Science.gov (United States)

Jones, A. P.; Nuth, J. A., III

2011-01-01

There is a long-standing conundrum in interstellar dust studies relating to the discrepancy between the time-scales for dust formation from evolved stars and the apparently more rapid destruction in supernova-generated shock waves. Aims. We re-examine some of the key issues relating to dust evolution and processing in the interstellar medium. Methods. We use recent and new constraints from observations, experiments, modelling and theory to re-evaluate dust formation in the interstellar medium (ISM). Results. We find that the discrepancy between the dust formation and destruction time-scales may not be as significant as has previously been assumed because of the very large uncertainties involved. Conclusions. The derived silicate dust lifetime could be compatible with its injection time-scale, given the inherent uncertainties in the dust lifetime calculation. The apparent need to re-form significant quantities of silicate dust in the tenuous interstellar medium may therefore not be a strong requirement. Carbonaceous matter, on the other hand, appears to be rapidly recycled in the ISM and, in contrast to silicates, there are viable mechanisms for its re-formation in the ISM.

Computer Simulation Tests of Feedback Error Learning Controller with IDM and ISM for Functional Electrical Stimulation in Wrist Joint Control

Directory of Open Access Journals (Sweden)

Takashi Watanabe

2010-01-01

Full Text Available Feedforward controller would be useful for hybrid Functional Electrical Stimulation (FES system using powered orthotic devices. In this paper, Feedback Error Learning (FEL controller for FES (FEL-FES controller was examined using an inverse statics model (ISM with an inverse dynamics model (IDM to realize a feedforward FES controller. For FES application, the ISM was tested in learning off line using training data obtained by PID control of very slow movements. Computer simulation tests in controlling wrist joint movements showed that the ISM performed properly in positioning task and that IDM learning was improved by using the ISM showing increase of output power ratio of the feedforward controller. The simple ISM learning method and the FEL-FES controller using the ISM would be useful in controlling the musculoskeletal system that has nonlinear characteristics to electrical stimulation and therefore is expected to be useful in applying to hybrid FES system using powered orthotic device.