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Journal articles on the topic 'Action Stars'

Author: Grafiati

Published: 4 June 2021

Last updated: 9 February 2022

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1

Gray, David F. "Dynamo Action in Evolved Stars." International Astronomical Union Colloquium 130 (1991): 336–41. http://dx.doi.org/10.1017/s0252921100079872.

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AbstractEvolved stars tell us a great deal about dynamos. The granulation boundary shows us where solar-type convection begins. Since activity indicators also start at this boundary, it is a good bet that solar-type convection is an integral part of dynamo activity for all stars. The rotation boundary tells us where the magnetic fields of dynamos become effective in dissipating angular momentum, and rotation beyond the boundary tells us the limiting value needed for a dynamo to function. The observed uniqueness of rotation rates after the rotation boundary is crossed can be understood through the rotostat hypothesis. Quite apart from the reason for the unique rotation rate, its existence can be used to show that magnetic activity of giants is concentrated to the equatorial latitudes, as it is in the solar case. The coronal boundary in the H-R diagram is probably nothing more than a map of where rotation becomes too low to sustain dynamo activity.

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2

Aerts, Conny. "Massive Star Asteroseismology in Action." Proceedings of the International Astronomical Union 9, S307 (June 2014): 154–64. http://dx.doi.org/10.1017/s1743921314006644.

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AbstractAfter highlighting the principle and power of asteroseismology for stellar physics, we briefly emphasize some recent progress in this research for various types of stars. We give an overview of high-precision high duty-cycle space photometry of OB-type stars. Further, we update the overview of seismic estimates of stellar parameters of OB dwarfs, with specific emphasis on convective core overshoot. We discuss connections between pulsational, rotational, and magnetic variability of massive stars and end with future prospects for asteroseismology of evolved OB stars.

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3

Augustson, Kyle C., Allan S. Brun, and Juri Toomre. "Convection and dynamo action in B stars." Proceedings of the International Astronomical Union 6, S271 (June 2010): 361–62. http://dx.doi.org/10.1017/s1743921311017790.

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AbstractMain-sequence massive stars possess convective cores that likely harbor strong dynamo action. To assess the role of core convection in building magnetic fields within these stars, we employ the 3-D anelastic spherical harmonic (ASH) code to model turbulent dynamics within a 10 M⊙ main-sequence (MS) B-type star rotating at 4 Ω⊙. We find that strong (900 kG) magnetic fields arise within the turbulence of the core and penetrate into the stably stratified radiative zone. These fields exhibit complex, time-dependent behavior including reversals in magnetic polarity and shifts between which hemisphere dominates the total magnetic energy.

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Bonanno, A., L. Rezzolla, and V. Urpin. "Mean-field dynamo action in protoneutron stars." Astronomy & Astrophysics 410, no. 3 (November 2003): L33—L36. http://dx.doi.org/10.1051/0004-6361:20031459.

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5

Palouš, Jan, Jim Dale, Richard Wünsch, Sergiy Silich, Guillermo Tenorio-Tagle, and Anthony Whitworth. "Action of Winds Inside and Outside of Star Clusters." Proceedings of the International Astronomical Union 6, S270 (May 2010): 267–74. http://dx.doi.org/10.1017/s1743921311000494.

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AbstractThe feedback form pre-main sequence and young stars influences their vicinity. The stars are formed in clusters, which implies that the winds of individual stars collide with each other. Inside of a star cluster, winds thermalize a fraction of their kinetic energy, forming a very hot medium able to escape from the cluster in the form of a large-scale wind. Outside of the cluster, the cluster wind forms a shock front as it interacts with the ambient medium which is accreted onto the expanding shell. A variety of instabilities may develop in such shells, and in some cases they fragment, triggering second generation of star formation. However, if the cluster surpasses a certain mass (depending on the radius and other parameters) the hot medium starts to be thermally unstable even inside of the cluster, forming dense warm clumps. The formation of next generations of stars may start if the clumps are big enough to self-shield against stellar radiation creating cold dense cores.

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6

Browning, Matthew K. "Simulations of Dynamo Action in Fully Convective Stars." Astrophysical Journal 676, no. 2 (April 2008): 1262–80. http://dx.doi.org/10.1086/527432.

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7

F. Dorch, S. B. "A Magnetic Betelgeuse? Numerical Simulations of Non-Linear Dynamo Action." Symposium - International Astronomical Union 219 (2004): 656–60. http://dx.doi.org/10.1017/s0074180900182701.

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Betelgeuse is an example of a cool supergiant displaying brightness fluctuations and irregular surface structures. Simulations by Freytag, Steffen, & Dorch (2002) of the convective envelope of the star have shown that the fluctuations in the star's luminosity may be caused by giant cell convection. A related question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing detailed numerical simulations, I find that both linear kinematic and non-linear dynamo action are possible and that the non-linear magnetic field saturates at a value somewhat below equipartition: in the linear regime there are two modes of dynamo action.

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8

Augustson, Kyle C., Allan Sacha Brun, and Juri Toomre. "DYNAMO ACTION AND MAGNETIC CYCLES IN F-TYPE STARS." Astrophysical Journal 777, no. 2 (October 23, 2013): 153. http://dx.doi.org/10.1088/0004-637x/777/2/153.

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9

Turner, Brandon D. "Changing the Stars: Astrocytes Adapt to Coordinate Action Flexibility." Biological Psychiatry 89, no. 11 (June 2021): e59-e60. http://dx.doi.org/10.1016/j.biopsych.2021.03.028.

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10

Sanderson, Robyn E., Amina Helmi, and David W. Hogg. "Action-space clustering of tidal streams to map the Galactic potential." Proceedings of the International Astronomical Union 9, S298 (May 2013): 207–12. http://dx.doi.org/10.1017/s1743921313006388.

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AbstractGiven a parametrized model of the Galactic potential, the best-fit parameters can be obtained by maximizing the Kullback-Leibler divergence of the action distribution of a set of stars initially clustered in action space (e.g. stars in tidal streams). This method will allow us to map the Milky Way's gravitational potential by simultaneously fitting multiple tidal streams without requiring stream membership information. With 20 streams of at least 20 stars each, including observational errors consistent with predictions for Gaia, this technique recovers the input potential parameters to a precision of 10-60% and an accuracy of 10%. With all the observed streams in our mock stellar halo (about 40) that fit the error criteria, the precision improves to 10%.

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11

Bisnovatyi-Kogan, Gennady, and Alexei Pozanenko. "Annihilation line from the galactic bulge due to action of low-mass flare stars." International Journal of Modern Physics D 27, no. 10 (July 2018): 1844003. http://dx.doi.org/10.1142/s0218271818440030.

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We consider the low-mass flare stars which form the bulk of the population in the galactic bulge as a source of the positrons needed to form the observed narrow annihilation line from the galactic bulge. Estimates based on the observed flares in low-mass stars, together with observations of the annihilation line in solar flares, show that the rate of production of positrons in flares in the stars in the bulge may be sufficient to explain the formation of the narrow stationary annihilation line observed from the region of the galactic bulge.

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12

Deinzer, W. "Dynamo–Action in Accretion Disks." Symposium - International Astronomical Union 157 (1993): 185–92. http://dx.doi.org/10.1017/s0074180900174091.

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Accretion disks are approximated by thin tori and the generation of magnetic fields by torus–dynamos is investigated. Solutions for the general α2ω–dynamo embedded into vacuum and into an ideally conducting medium are presented. Whereas the former solutions are qualitatively similar to those obtained for thin disks, there is a mode for the latter peculiar to torus–geometry. Excitation conditions for torus–dynamos are compared to those realized in accretion disks in cataclysmic variables, around T Tauri stars and in AGN's.

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13

Hunt, Jason A. S., Kathryn V. Johnston, Alex R. Pettitt, Emily C. Cunningham, Daisuke Kawata, and David W. Hogg. "The power of coordinate transformations in dynamical interpretations of Galactic structure." Monthly Notices of the Royal Astronomical Society 497, no. 1 (July 9, 2020): 818–28. http://dx.doi.org/10.1093/mnras/staa1987.

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ABSTRACT Gaia DR2 has provided an unprecedented wealth of information about the positions and motions of stars in our Galaxy and has highlighted the degree of disequilibria in the disc. As we collect data over a wider area of the disc, it becomes increasingly appealing to start analysing stellar actions and angles, which specifically label orbit space, instead of their current phase space location. Conceptually, while $\bar {x}$ and $\bar {v}$ tell us about the potential and local interactions, grouping in action puts together stars that have similar frequencies and hence similar responses to dynamical effects occurring over several orbits. Grouping in actions and angles refines this further to isolate stars that are travelling together through space and hence have shared histories. Mixing these coordinate systems can confuse the interpretation. For example, it has been suggested that by moving stars to their guiding radius, the Milky Way spiral structure is visible as ridge-like overdensities in the Gaia data (Khoperskov et al. 2020). However, in this work, we show that these features are in fact the known kinematic moving groups, both in the Lz − ϕ and the vR − vϕ planes. Using simulations, we show how this distinction will become even more important as we move to a global view of the Milky Way. As an example, we show that the radial velocity wave seen in the Galactic disc in Gaia and APOGEE should become stronger in the action-angle frame, and that it can be reproduced by transient spiral structure.

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14

Zubizarreta, Javi Aitor. "Action Stars Who Don't Get Any Action: Hong Kong Actors in U.S. Roles." Film Matters 1, no. 2 (April 1, 2010): 15–20. http://dx.doi.org/10.1386/fm.1.2.15.

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15

Fuller, Jim. "Inverse tides in pulsating binary stars." Monthly Notices of the Royal Astronomical Society 501, no. 1 (November 21, 2020): 483–90. http://dx.doi.org/10.1093/mnras/staa3636.

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ABSTRACT In close binary stars, the tidal excitation of pulsations typically dissipates energy, causing the system to evolve towards a circular orbit with aligned and synchronized stellar spins. However, for stars with self-excited pulsations, we demonstrate that tidal interaction with unstable pulsation modes can transfer energy in the opposite direction, forcing the spins of the stars away from synchronicity, and potentially pumping the eccentricity and spin–orbit misalignment angle. This ‘inverse’ tidal process only occurs when the tidally forced mode amplitude is comparable to the mode’s saturation amplitude, and it is thus most likely to occur in main-sequence gravity mode pulsators with orbital periods of a few days. We examine the long-term evolution of inverse tidal action, finding the stellar rotation rate can potentially be driven to a very large or very small value, while maintaining a large spin–orbit misalignment angle. Several recent asteroseismic analyses of pulsating stars in close binaries have revealed extremely slow core rotation periods, which we attribute to the action of inverse tides.

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16

Trigilio, C., S. Catalano, E. Marilli, V. Reglero, and G. Umana. "The Age Evolution of Ca II Emission in Late Type Stars." International Astronomical Union Colloquium 130 (1991): 480–82. http://dx.doi.org/10.1017/s0252921100080192.

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It has been widely demonstrated that chromospheric emission is dependent on rotation rate (Hartmann and Noyes, 1987, Catalano, 1990, for recent reviews). Since the rotation decays with time, the chromospheric activity of single main sequence stars is also dependent on age. Catalano and Marilli (1983) suggested that the chromospheric emission of solar mass stars decays exponentially with the square root of the time, as recently confirmed by Barry (1988). Magnetic activity depends also on the convection parameters, i.e. on the mass. Since the evolution of surface rotation is faster for lower mass stars (Catalano et al., 1988), the internal rotation distribution, and therefore the dynamo action, should change with time in a different way for different masses.In order to get insight into the evolution of dynamo action we have studied the CaII chromospheric emission as a function of mass and age. Here we present some preliminary results of observations of late type stars in young clusters and old moving groups.

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17

Todt, Helga, Miriam Peña, Julia Zühlke, Lida Oskinova, Wolf-Rainer Hamann, and Götz Gräfener. "Weak emission line central stars of planetary nebulae." Proceedings of the International Astronomical Union 7, S283 (July 2011): 510–11. http://dx.doi.org/10.1017/s1743921312012173.

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AbstractTo understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.

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18

Kley, Wilhelm. "Planet formation in binary stars." Proceedings of the International Astronomical Union 3, S249 (October 2007): 251–60. http://dx.doi.org/10.1017/s1743921308016657.

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AbstractAs of today more than 30 planetary systems have been discovered in binary stars. In all cases the configuration is circumstellar, where the planets orbit around one of the stars. The formation process of planets in binary stars is more difficult than around single stars due to the gravitational action of the companion. An overview of the research done in this field will be given. The dynamical influence that a secondary companion has on a circumstellar disk, and how this affects the planet formation process in this challenging environment will be summarized. Finally, new fully hydrodynamical simulations of protoplanets embedded in disks residing in a binary star will be presented. Applications with respect to the planet orbiting the primary in the system γ Cephei will be presented.

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Lander, S. K. "Generating neutron-star magnetic fields: three dynamo phases." Monthly Notices of the Royal Astronomical Society: Letters 507, no. 1 (July 26, 2021): L36—L40. http://dx.doi.org/10.1093/mnrasl/slab086.

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ABSTRACT Young neutron stars (NSs) have magnetic fields in the range 1012–1015 G, believed to be generated by dynamo action at birth. We argue that such a dynamo is actually too inefficient to explain the strongest of these fields. Dynamo action in the mature star is also unlikely. Instead we propose a promising new precession-driven dynamo and examine its basic properties, as well as arguing for a revised mean-field approach to NS dynamos. The precession-driven dynamo could also play a role in field generation in main-sequence stars.

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Nikolaiev, V. A. "Lower drive of continuous action unit to form underlying layer of road." Russian Automobile and Highway Industry Journal 18, no. 1 (March 30, 2021): 30–41. http://dx.doi.org/10.26518/2071-7296-2021-18-1-30-41.

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Introduction. A continuous action unit for the formation of an underlying layer is designed to increase productivity in the construction of roads and other facilities, for which it is necessary to remove the top layer of soil. In the bucket of the continuous action unit to form an underlying layer of roads provides the use of working bodies, cutting the ground with blades of knives. The cut-off soil enters the buckets. The forces attached to the bucket are considered. Theoretically reasonable total energy costs for ground cutting of one cubic meter by buckets of continuous action unit to form an underlying layer of roads requires 109 kilojoules. Based on the calculations carried out, it is possible to determine the torque, the power required for the lower drive, the transmission ratio from the hydraulic motor to the stars, to develop the design of many elements of the continuous action unit to form the underlying layer of the road.The method of research. To determine the torque, the power required for the lower drive, the transmission ratio from the hydraulic motor to the asterisks, to the projection of the bucket on the horizontal plane attached all forces are applied directed along the bucket. As a result of their addition, the total maximum traction force of moving all the boilers during their filling with soil was revealed. On the basis of this, the method of calculating the parameters of the required is given. There is a danger of the ground being poured out of the bucket when it is rotated on the leading stars of the lower drive. To check the parameters received, the bucket is rotated by 90 degrees on the leading stars of the lower drive. The forces acting on the ground, located in the bucket, at the moment of the beginning of the turn of the bucket were revealed. A system of equations has been created, on the basis of which the condition of inadmissibility of the dumping of soil from the bucket at its turn on the leading stars has been established.Results. As a result of the addition of forces directed in the course of the bucket, the total maximum traction force of moving all the boilers during their filling with the ground, traction force on the right chain and left chain is defined. Traction chains are chosen by destructive load. The torque of the lower drive, the angular speed of the drive stars, the power required for the lower drive, the transmission ratio from the hydraulic motor to the asterisk are calculated. Based on the transferable power, a gerotor motor is chosen for the lower drive of the unit. On the basis of the calculations the design of chains, support rink, chain suspension have been developed.Conclusion. Based on the calculations made, the maximum traction force of all the buckets during the period when they are filled with soil is 11,870 newtons, the torque of the lower drive is 2,362 newtonometers, the speed of the chains is 1,686 meters per second, the angular velocity of the drive stars is 8,47 radians per second, power required for lower drive is 20 kilowatts. Based on the transferable power, it is advisable to use MT-160 gerotor motor and a single-stage planetary gearbox with a transmission ratio from the hydraulic motor to the stars 7,674. The calculations made it possible to develop the design of many elements of the continuous action unit to form an underlying layer of roads.

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Trick, Wilma H., Francesca Fragkoudi, Jason A. S. Hunt, J. Ted Mackereth, and Simon D. M. White. "Identifying resonances of the Galactic bar in Gaia DR2: I. Clues from action space." Monthly Notices of the Royal Astronomical Society 500, no. 2 (October 27, 2020): 2645–65. http://dx.doi.org/10.1093/mnras/staa3317.

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ABSTRACT Action space synthesizes the orbital information of stars and is well suited to analyse the rich kinematic substructure of the disc in the second Gaia data release's radial velocity sample. We revisit the strong perturbation induced in the Milky Way disc by an m = 2 bar, using test particle simulations and the actions (JR, Lz, Jz) estimated in an axisymmetric potential. These make three useful diagnostics cleanly visible. (1) We use the well-known characteristic flip from outward to inward motion at the outer Lindblad resonance (OLR; l = +1, m = 2), which occurs along the axisymmetric resonance line (ARL) in (Lz, JR), to identify in the Gaia action data three candidates for the bar’s OLR and pattern speed Ωbar: 1.85Ω0, 1.20Ω0, and 1.63Ω0 (with ∼0.1Ω0 systematic uncertainty). The Gaia data is therefore consistent with both slow and fast bar models in the literature, but disagrees with recent measurements of ∼1.45Ω0. (2) For the first time, we demonstrate that bar resonances – especially the OLR – cause a gradient in vertical action 〈Jz〉 with Lz around the ARL via ‘Jz-sorting’ of stars. This could contribute to the observed coupling of 〈vR〉 and 〈|vz|〉 in the Galactic disc. (3) We confirm prior results that the behaviour of resonant orbits is well approximated by scattering and oscillation in (Lz, JR) along a slope ΔJR/ΔLz = l/m centred on the l:m ARL. Overall, we demonstrate that axisymmetrically estimated actions are a powerful diagnostic tool even in non-axisymmetric systems.

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Mikkola, Daniel, Paul J. McMillan, and David Hobbs. "Radial migration and vertical action in N-body simulations." Monthly Notices of the Royal Astronomical Society 495, no. 3 (January 2020): 3295–306. http://dx.doi.org/10.1093/mnras/staa1223.

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ABSTRACT We study the radial migration of stars as a function of orbital action as well as the structural properties of a large suite of N-body simulations of isolated disc galaxies. Our goal is to establish a relationship between the radial migration efficiency of stars and their vertical action. We aim to describe how that relationship depends on the relative gravitational dominance between the disc and the dark matter halo. By changing the mass ratio of our disc and dark matter halo, we find a relationship between disc dominance, number, and strength of spiral arms, and the ensuing radial migration as a function of the vertical action. We conclude that the importance of migration at large vertical action depends on the strength of the spiral arms and therefore the dominance of the disc. Populations with more radial action undergo less radial migration, independently of disc dominance. Our results are important for the future of analytical modelling of radial migration in galaxies and further the understanding of radial migration that is a key component of the restructuring of galaxies, including the Milky Way.

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Field, G. B., and E. G. Blackman. "Magnetic Helicity, Dynamo Action, Reconnection, and Particle Acceleration." Symposium - International Astronomical Union 195 (2000): 389–90. http://dx.doi.org/10.1017/s0074180900163223.

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Blackman & Field have shown that a working α-Ω dynamo requires finite but opposite flows of small- and large-scale magnetic helicity through a body's surface. The helicity is accompanied by magnetic energy available for dissipation. The observed solar coronal nonthermal power is consistent with the derived lower limit required. This link between dynamo field generation and nonthermal emission should generally apply to stars, spiral galaxies, and accretion disks.

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Garmany, Catharine D. "Luminous Blue Stars: Distribution and Numbers." Symposium - International Astronomical Union 116 (1986): 19–30. http://dx.doi.org/10.1017/s0074180900148600.

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Because the term “luminous blue stars” is relative, let me begin by delineating what region of the H-R diagram I am considering. For the purpose of this talk, I will discuss primarily 0-type stars, with Teff > 30,000 K and Mbol > − 7, but I will also mention their evolved descendants the B supergiants with 30,000 K > Teff > 10,000 K and Mbol > −8, and their even later evolutionary form, the Wolf-Rayet (W-R) stars with Teff > 30,000 K and uncertain Mbol. Although these stars are not among the visually brightest stars, they are the bolo-metrically most luminous as well as the hottest stars. They are also the most massive. They are an important channel in the metal enrichment in a galaxy through the action of mass loss via stellar winds and their ultimate disruption as supernovae (Maeder 1981). They also contribute in a major way to the energy balance of the interstellar medium (Abbott 1982).

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Briggs, K., M. Güdel, M. Audard, K. Smith, R. Mewe, and T. den Boggende. "X-ray Emission from Young Stars in Suburban Orion." Symposium - International Astronomical Union 219 (2004): 228–32. http://dx.doi.org/10.1017/s0074180900182154.

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X-ray emission from > 100 pre-main sequence (PMS) stars in the Orion star-forming complex is studied in a 20-ks observation by XMM-Newton. No relation between the ratio of X-ray and bolometric luminosities, LX/Lbol, and rotation period or Rossby number is exhibited, though the action of a solar-like dynamo is not excluded because all stars would appear to be in the “saturated regime” of such a dynamo. Low-mass stars showing a strong U — V excess have lower median X-ray luminosity, suggesting that accretion suppresses magnetic activity.

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Brighenti, F., and A. D'Ercole. "Ring nebulae around moving Wolf-Rayet stars." Symposium - International Astronomical Union 163 (1995): 70–71. http://dx.doi.org/10.1017/s0074180900201666.

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We present 2D numerical simulations of evolving ring nebulae around moving Wolf-Rayet stars. We have considered the interaction of the fast WR wind with the circumstellar matter modified by the previous action of the slow RSG wind. The resulting shell morphology is far from spherical and shows scallops due to several kinds of instabilities. The exact appearance of the ring nebula depends on the value of several parameters such as the unperturbed medium density and the velocity of the star.

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Browning, Matthew K. "Differential Rotation and Magnetism in Simulations of Fully Convective Stars." Proceedings of the International Astronomical Union 6, S271 (June 2010): 69–77. http://dx.doi.org/10.1017/s1743921311017467.

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AbstractStars of sufficiently low mass are convective throughout their interiors, and so do not possess an internal boundary layer akin to the solar tachocline. Because that interface figures so prominently in many theories of the solar magnetic dynamo, a widespread expectation had been that fully convective stars would exhibit surface magnetic behavior very different from that realized in more massive stars. Here I describe how recent observations and theoretical models of dynamo action in low-mass stars are partly confirming, and partly confounding, this basic expectation. In particular, I present the results of 3–D MHD simulations of dynamo action by convection in rotating spherical shells that approximate the interiors of 0.3 solar-mass stars at a range of rotation rates. The simulated stars can establish latitudinal differential rotation at their surfaces which is solar-like at “rapid” rotation rates (defined within) and anti-solar at slower rotation rates; the differential rotation is greatly reduced by feedback from strong dynamo-generated magnetic fields in some parameter regimes. I argue that this “flip” in the sense of differential rotation may be observable in the near future. I also briefly describe how the strength and morphology of the magnetic fields varies with the rotation rate of the simulated star, and show that the maximum magnetic energies attained are compatible with simple scaling arguments.

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Sato, S., M. Cuntz, C. M. Guerra Olvera, D. Jack, and K. P. Schröder. "Habitability around F-type stars." International Journal of Astrobiology 13, no. 3 (March 25, 2014): 244–58. http://dx.doi.org/10.1017/s1473550414000020.

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AbstractWe explore the general astrobiological significance of F-type main-sequence stars with masses between 1.2 and 1.5 M⊙. Special consideration is given to stellar evolutionary aspects due to nuclear main-sequence evolution. DNA is taken as a proxy for carbon-based macromolecules following the paradigm that extraterrestrial biology may be most likely based on hydrocarbons. Consequently, the DNA action spectrum is utilized to represent the impact of the stellar ultraviolet (UV) radiation. Planetary atmospheric attenuation is taken into account based on parameterized attenuation functions. We found that the damage inflicted on DNA for planets at Earth-equivalent positions is between a factor of 2.5 and 7.1 higher than for solar-like stars, and there are intricate relations for the time-dependence of damage during stellar main-sequence evolution. If attenuation is considered, smaller factors of damage are obtained in alignment to the attenuation parameters. This work is motivated by earlier studies indicating that the UV environment of solar-type stars is one of the most decisive factors in determining the suitability of exosolar planets and exomoons for biological evolution and sustainability.

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Feuillet, Diane K., Sofia Feltzing, Christian L. Sahlholdt, and Luca Casagrande. "The SkyMapper-Gaia RVS view of the Gaia–Enceladus–Sausage – an investigation of the metallicity and mass of the Milky Way’s last major merger." Monthly Notices of the Royal Astronomical Society 497, no. 1 (July 2, 2020): 109–24. http://dx.doi.org/10.1093/mnras/staa1888.

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ABSTRACT We characterize the Gaia–Enceladus–Sausage kinematic structure recently discovered in the Galactic halo using photometric metallicities from the SkyMapper survey, and kinematics from Gaia radial velocities measurements. By examining the metallicity distribution functions (MDFs) of stars binned in kinematic/action spaces, we find that the $\sqrt{J_R}$ versus Lz space allows for the cleanest selection of Gaia–Enceladus–Sausage stars with minimal contamination from disc or halo stars formed in situ or in other past mergers. Stars with $30 \le \sqrt{J_R} \le 50$ (kpc km s−1)1/2 and −500 ≤ Lz ≤ 500 kpc km s−1 have a narrow MDF centred at [Fe/H] = −1.17 dex with a dispersion of 0.34 dex. This [Fe/H] estimate is more metal-rich than literature estimates by 0.1−0.3 dex. Based on the MDFs, we find that selection of Gaia–Enceladus–Sausage stars in other kinematic/action spaces without additional population information leads to contaminated samples. The clean Gaia–Enceladus–Sausage sample selected according to our criteria is slightly retrograde and lies along the blue sequence of the high VT halo colour magnitude diagram dual sequence. Using a galaxy mass–metallicity relation derived from cosmological simulations and assuming a mean stellar age of 10 Gyr, we estimate the mass of the Gaia–Enceladus–Sausage progenitor satellite to be 108.85–9.85 M⊙, which is consistent with literature estimates based on disc dynamic and simulations. Additional information on detailed abundances and ages would be needed for a more sophisticated selection of purely Gaia–Enceladus–Sausage stars.

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Goldin,, Marlienne. "Rising Stars: From High School To Healthcare, Caritas, And Communitas In Action." International Journal of Human Caring 9, no. 2 (March 2005): 46. http://dx.doi.org/10.20467/1091-5710.9.2.46.

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Brun, Allan Sacha, Matthew K. Browning, and Juri Toomre. "Simulations of Core Convection in Rotating A‐Type Stars: Magnetic Dynamo Action." Astrophysical Journal 629, no. 1 (August 10, 2005): 461–81. http://dx.doi.org/10.1086/430430.

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32

Bailey, J. D., J. D. Landstreet, and S. Bagnulo. "Discovery of Secular Evolution of the Atmospheric Abundances of Ap Stars." Proceedings of the International Astronomical Union 9, S307 (June 2014): 365–66. http://dx.doi.org/10.1017/s1743921314007091.

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AbstractThe stars of the middle main-sequence have relatively quiescent outer layers, and unusual chemical abundance patterns may develop in their atmospheres, revealing the action of such subsurface phenomena as gravitational settling and radiatively driven levitation of trace elements, and their competition with mixing processes such as turbulent diffusion. We report the discovery of the time evolution of such chemical tracers through the main-sequence lifetime of magnetic chemically peculiar stars.

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33

Featherstone, Nicholas A., Matthew K. Browning, Allan Sacha Brun, and Juri Toomre. "Exploring the deep convection and magnetism of A-type stars." Proceedings of the International Astronomical Union 6, S273 (August 2010): 111–15. http://dx.doi.org/10.1017/s1743921311015092.

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AbstractA-type stars have both a near-surface layer of fast convection that can excite acoustic modes and a deep zone of core convection whose properties may be probed with asteroseismology. Many A-type stars also exhibit large magnetic spots that are often attributed to surviving primordial fields of global scale in the intervening radiative zone. We have explored the potential for core convection in rotating A-type stars to build strong magnetic fields through dynamo action. These 3-D simulations using the ASH code provide guidance on the nature of differential rotation and magnetic fields that may be present in the deep interiors of these stars, thus informing the asteroseismic deductions now becoming feasible. Our models encompass the inner 30% by radius of a two solar mass A-type star, rotating at four times the solar rate and capturing the convective core and a portion of the overlying radiative envelope. Convection in these stars drives a strong retrograde differential rotation and yields a core that is prolate in shape. When dynamo action is admitted, the convection generates strong magnetic fields largely in equipartition with the dynamics. Remarkably, introducing a modest but large-scale external field threading the radiative envelope (which may be of primordial origin) can substantially alter the turbulent dynamics of the convective interior. The resulting convection involves a complex assembly of helical rolls that link distant portions of the core and stretch and advect magnetic field, ultimately yielding magnetic fields of super-equipartition strength.

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34

Breen, John. "Inside Tokugawa Religion: Stars, Planets and the Calendar-as-method." Culture and Cosmos 10, no. 1 and 2 (October 2006): 63–78. http://dx.doi.org/10.46472/cc.01210.0209.

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The study of religion in early modern (Tokugawa) Japan has failed to keep pace with the study of religion in the periods that preceded and followed it. What has been lacking particularly are explorations of religious praxis. The present study proposes a novel approach to this subject with its critical focus on the Tokugawa calendar and its almanac commentaries. Calendars, and their multiple prescriptions for particular types of action and non-action, informed as they are by the cosmic wisdom of yin yang (onmyō) and five-phases-of-matter thinking (gogyō shisō), offer unique insights into precisely the neglected field of religious practice. This study sets out to decode the calendar and explore the ways in which it determined religious practice in early modern Japan. It discloses the centrality of the worship of stellar kami.

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35

Stout–Batalha, N. M., and S. S. Vogt. "Doppler images of the Pleiades ZAMS stars HII 686 and HII 3163." Symposium - International Astronomical Union 176 (1996): 337–44. http://dx.doi.org/10.1017/s0074180900083352.

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Of the steadily increasing number of Doppler Images appearing in the literature, the majority are of the RS CVn subclass of binary stars. The large rotational velocities and dynamo action of these stars is probably attributable to tidal spin-up of the active subgiant star by its binary companion. Their dynamos and resultant surface features (starspots) are thus almost certainly influenced by the companion. As such, these objects are not the ideal testing ground for comparison with single-star solar-like activity. Recently, a handful of Doppler images of single late-type main sequence and pre-main sequence stars have appeared in the literature. Pre-main sequence stars include V410 Tau (Joncour, Bertout, & Menard 1994), (Strassmeier, Welty, & Rice 1994), (Hatzes 1995) and HD 283572 (Joncour, Bertout, & Bouvier 1994). The main sequence stars include AB Dor (Collier Cameron & Unruh 1994), (Kürster, Schmitt, & Cutispoto 1994) and LQ Hya (Strassmeier, et al. 1993), (Saar & Piskunov 1994). These studies suggest that high-latitude dark spots are common to all rapidly-rotating stars, although, the spots found in the above work do not symmetrically straddle the pole as do polar spots of rapidly-rotating RS CVn binary stars.

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36

Kuhi, Leonard V. "Wolf-Rayet Stars in the Old Days." Symposium - International Astronomical Union 143 (1991): 11–16. http://dx.doi.org/10.1017/s0074180900044831.

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This morning, as part of the welcoming ceremonies opening this conference, we were reminded that Indonesia consists of over 13,000 islands and that the coat of arms carries the phrase: “Unity in Diversity.” We might take the same theme for the study of Wolf-Rayet Stars. There has certainly been no shortage of diversity over the 120 years since their discovery and we all keep hoping for unity; perhaps IAU Symposium No. 143 will provide it! The conference was opened this morning with three strokes of the ceremonial gong to chase away all the bad spirits. So far that symbolic action has been most successful but perhaps more likely due to the kind hospitality of our hosts and the special warmth of Bali. We owe them all a vote of thanks!

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Talon, Suzanne. "Rotational Transport Processes." Symposium - International Astronomical Union 215 (2004): 336–45. http://dx.doi.org/10.1017/s0074180900195841.

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In this review, I discuss physical mechanisms leading to momentum and chemical transport in stars. Various instabilities leading to turbulence are discussed. I then present a self-consistent description of rotational mixing under the action of turbulence and meridional circulation in 1D models. Limitations of the model are discussed, both in terms of an extra mechanism for momentum transport in the Sun and solar-type stars (magnetic field and/or gravity waves) and in terms of our understanding of turbulent properties.

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38

Işık, Emre. "Theoretical Models of Stellar Activity Cycles." Proceedings of the International Astronomical Union 10, H16 (August 2012): 113–14. http://dx.doi.org/10.1017/s1743921314004785.

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AbstractWe discuss possible mechanisms underlying the observed features of stellar activity cycles, such as multiple periodicities in very active stars, non-cyclic activity observed in moderately active stars, and spatial distribution of stellar magnetic regions. We review selected attempts to model the dependence of stellar activity cycles on stellar properties, and their comparison with observations. We suggest that combined effects of dynamo action, flux emergence and surface flux transport have substantial effects on the long-term manifestations of stellar magnetism.

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Russeil, Delphine. "OB stars towards NGC 6357 and NGC 6334." Proceedings of the International Astronomical Union 12, S330 (April 2017): 341–42. http://dx.doi.org/10.1017/s1743921317005385.

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AbstractThe star forming regions NGC6334 and NGC6357 are amid the most active star-forming complexes of our Galaxy where massive star formation is occuring. Both complexes gather several HII regions but they exhibit different aspects: NGC6334 is characterised by a dense molecular ridge where recent massive star formation is obvious while NGC6357 is dominated by the action of the stellar cluster Pismis 24 which have shaped a large cavity. To understand and compare the formation of massive stars in these two regions requires to precise the distance and characterise the proper motions of the O to B3 stellar population in these regions.

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40

Jin, W., Z. Tang, J. Li, and S. Wang. "A Preliminary Study on The Improvement of Proper Motions For HipparcosStars by Using Photographic Plates." Highlights of Astronomy 11, no. 1 (1998): 552. http://dx.doi.org/10.1017/s1539299600022085.

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The 3435 photographic plates, which were obtained by using the 40cm astrograph at Zô-Sè station of Shanghai Observatory during 1901-1993, have been accumulated for observing open clusters, extragalatic nebulas, radio stars and variable stars etc. These plates cover 764 unoverlapping regions (2°.3 * 1°.7) on the sky. Most of the plates distribute along the ecliptic, about 10 000 Hipparcos stars, 27 000 PPM stars and 500 FK5 stars are included in these regions. Among these plates, there are 2718 plates having two observing epochs, and they cover 359 different regions; there are 142 and 92 regions where the intervals of two epochs are about 50 and 70 years, and the numbers of plates in these regions are about1494 and 1023 respectively. About 372 plates were photographed before 1949,which play an important action for improvement of proper motions of Hipparcos stars. Four methods used to improve the proper motions for Hipparcos stars were designed. If the 2718 plates mentioned above having two epochs were used for improvement of the proper motions of Hipparcos stars, the stellar number of 299, 1378, 377 and 1664 corresponding to the four methods will be obtained with final precision 0.7 mas/yr. If supplementary observations are made in 1997, the stellar number of 494, 2431, 1534 and 2899 will be obtained with the same precision.

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Browning, Matthew K., Allan S. Brun, and Juri Toomre. "Simulations of core convection and resulting dynamo action in rotating A-type stars." Proceedings of the International Astronomical Union 2004, IAUS224 (July 2004): 149–54. http://dx.doi.org/10.1017/s1743921304004491.

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42

Hayne, K. J. R., and A. R. Palmer. "Intertidal sea stars (Pisaster ochraceus) alter body shape in response to wave action." Journal of Experimental Biology 216, no. 9 (April 17, 2013): 1717–25. http://dx.doi.org/10.1242/jeb.078964.

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43

Schleicher, D. R. G., R. Banerjee, S. Sur, T. G. Arshakian, R. S. Klessen, R. Beck, and M. Spaans. "Small-scale dynamo action during the formation of the first stars and galaxies." Astronomy & Astrophysics 522 (November 2010): A115. http://dx.doi.org/10.1051/0004-6361/201015184.

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44

Reino, Stella, Elena M. Rossi, Robyn E. Sanderson, Elena Sellentin, Amina Helmi, Helmer H. Koppelman, and Sanjib Sharma. "Galactic potential constraints from clustering in action space of combined stellar stream data." Monthly Notices of the Royal Astronomical Society 502, no. 3 (February 4, 2021): 4170–93. http://dx.doi.org/10.1093/mnras/stab304.

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ABSTRACT Stream stars removed by tides from their progenitor satellite galaxy or globular cluster act as a group of test particles on neighbouring orbits, probing the gravitational field of the Milky Way. While constraints from individual streams have been shown to be susceptible to biases, combining several streams from orbits with various distances reduces these biases. We fit a common gravitational potential to multiple stellar streams simultaneously by maximizing the clustering of the stream stars in action space. We apply this technique to members of the GD-1, Palomar 5 (Pal 5), Orphan, and Helmi streams, exploiting both the individual and combined data sets. We describe the Galactic potential with a Stäckel model, and vary up to five parameters simultaneously. We find that we can only constrain the enclosed mass, and that the strongest constraints come from the GD-1, Pal 5, and Orphan streams whose combined data set yields $M(\lt 20\, \mathrm{kpc}) = 2.96^{+0.25}_{-0.26} \times 10^{11} \, \mathrm{ M}_{\odot}$. When including the Helmi stream in the data set, the mass uncertainty increases to $M(\lt 20\, \mathrm{kpc}) = 3.12^{+3.21}_{-0.46} \times 10^{11} \, \mathrm{M}_{\odot}$.

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45

Monty, Stephanie, Kim A. Venn, James M. M. Lane, Deborah Lokhorst, and David Yong. "Chemo-dynamics of outer halo dwarf stars, including Gaia-Sausage and Gaia-Sequoia candidates." Monthly Notices of the Royal Astronomical Society 497, no. 1 (July 10, 2020): 1236–55. http://dx.doi.org/10.1093/mnras/staa1995.

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ABSTRACT The low-metallicity, kinematically interesting dwarf stars studied by Stephens & Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with [Fe/H] > −2; however, large disagreements are found for stars with [Fe/H] ≤ −2, with offsets as large as ΔTeff ∼ +500 K and Δlog g ∼ +1.0. A subset of six stars (test cases) are analysed ab initio using high-resolution spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to include two α-challenged dwarf stars, suggestive of origins in a low-mass, accreted dwarf galaxy. The orbital parameters for the entire SB02 sample are re-determined using Gaia DR2 data. We find 11 stars that are dynamically coincident with the Gaia-Sausage accretion event and another 17 with the Gaia-Sequoia event in action space. Both associations include low-mass, metal-poor stars with isochrone ages older than 10 Gyr. Two dynamical subsets are identified within Gaia-Sequoia. When these subsets are examined separately, a common knee in [α/Fe] is found for the Gaia-Sausage and low orbital energy Gaia-Sequoia stars. A lower metallicity knee is tentatively identified in the Gaia-Sequoia high orbital energy stars. If the metal-poor dwarf stars in these samples are true members of the Gaia-Sausage and Gaia-Sequoia events, then they present a unique opportunity to probe the earlier star formation histories of these systems.

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46

Schrijver, C. J. "Observational Constraints on Dynamos in Cool Stars." International Astronomical Union Colloquium 137 (1993): 591–604. http://dx.doi.org/10.1017/s0252921100018510.

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AbstractNon-radiatively heated outer atmospheres are common among stars on the cool side of the HR diagram. These atmospheres resemble that of the Sun in which the bulk of the heating is associated with magnetic fields. Consequently it is assumed that other cool stars also generate and maintain an internal magnetic field through a dynamo action. This field gives rise to a wide spectrum of phenomena in the stellar atmosphere. The dynamo process that sustains the field thrives on the interaction of rotation and turbulent convection. In this review I formulate a set of propositions outlining our present knowledge of this interaction as distilled from stellar observations. In doing so, I outline the effects of stellar evolution on rotation rate, discuss some of the proposed “dividing lines” in the HR-diagram, and comment on the possible role of the convective turnover time in dynamo efficiency and on dynamo activity for extremely slowly and rapidly rotating stars.

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47

Browning, Matthew, Allan Sacha Brun, and Juri Toomre. "Simulations of Core Convection Dynamos in Rotating A-type Stars." Symposium - International Astronomical Union 215 (2004): 376–77. http://dx.doi.org/10.1017/s0074180900195907.

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We have conducted preliminary numerical simulations of a core convection dynamo operating within an A-type star of two solar masses. Convection within the core clearly can admit magnetic dynamo action. Magnetic field strengths in our three-dimensional simulations grow by many orders of magnitude, from an initial seed field to kilo-Gauss levels. We discuss the differential rotation and magnetic field sustained in our simulations.

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48

Weber, Maria A. "Dynamo Processes Constrained by Solar and Stellar Observations." Proceedings of the International Astronomical Union 13, S340 (February 2018): 275–80. http://dx.doi.org/10.1017/s1743921318001424.

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AbstractOur understanding of stellar dynamos has largely been driven by the phenomena we have observed of our own Sun. Yet, as we amass longer-term datasets for an increasing number of stars, it is clear that there is a wide variety of stellar behavior. Here we briefly review observed trends that place key constraints on the fundamental dynamo operation of solar-type stars to fully convective M dwarfs, including: starspot and sunspot patterns, various magnetism-rotation correlations, and mean field flows such as differential rotation and meridional circulation. We also comment on the current insight that simulations of dynamo action and flux emergence lend to our working knowledge of stellar dynamo theory. While the growing landscape of both observations and simulations of stellar magnetic activity work in tandem to decipher dynamo action, there are still many puzzles that we have yet to fully understand.

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49

Navin, Anita, Don Vinson, Alison Croad, Jennifer Turnnidge, and Jean Côté. "The Birth of the Stars: A Participatory and Appreciative Action and Reflection Investigation into the Leadership and Development of a New Superleague Netball Club." Sport Psychologist 34, no. 3 (September 1, 2020): 220–31. http://dx.doi.org/10.1123/tsp.2019-0087.

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This Participatory and Appreciative Action and Reflection (PAAR) investigation illustrates a leader’s first steps in a “values-to-action” journey. Drawing on the interface between transformational leadership and organizational culture, this study focused on the birth of the Severn Stars—a professional netball club in the United Kingdom. In particular, this PAAR investigation explored how the leader’s values were operationalized through the club’s inaugural year. Fourteen operational managers, coaches, and players were individually interviewed in order to gain an appreciative gaze and subsequently reframe their lived experience. Results demonstrated how transformational leadership was manifested through the pragmatic deployment of club values and how the organizational culture was, in part, characterized by individualized consideration, intellectual stimulation, idealized influence, and inspirational motivation. These behaviors and the organizational culture were shown to enhance prosocial relationships and social connections across the club, the influence of the Super Stars, and stakeholders’ perceptions of autonomy.

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50

Mathis, S., and C. Neiner. "Stochastic excitation of gravity waves in rapidly rotating massive stars." Proceedings of the International Astronomical Union 9, S307 (June 2014): 220–21. http://dx.doi.org/10.1017/s1743921314006784.

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AbstractStochastic gravity waves have been recently detected and characterised in stars thanks to space asteroseismology and they may play an important role in the evolution of stellar angular momentum. In this context, the observational study of the CoRoT hot Be star HD 51452 suggests a potentially strong impact of rotation on stochastic excitation of gravito-inertial waves in rapidly rotating stars. In this work, we present our results on the action of the Coriolis acceleration on stochastic wave excitation by turbulent convection. We study the change of efficiency of this mechanism as a function of the waves' Rossby number and we demonstrate that the excitation presents two different regimes for super-inertial and sub-inertial frequencies. Consequences for rapidly rotating early-type stars and the transport of angular momentum in their interiors are discussed.

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