R. H. Parker - Liverpool John Moores University UK

R. H. Parker
Are you R. H. Parker?

Claim your profile, edit publications, add additional information:

Contact Details

Name
R. H. Parker
Affiliation
Liverpool John Moores University UK
City
Liverpool
Country
United Kingdom

Pubs By Year

External Links

Pub Categories

 
Astrophysics of Galaxies (37)
 
Solar and Stellar Astrophysics (22)
 
Earth and Planetary Astrophysics (8)
 
Physics - Atomic Physics (5)
 
Physics - Geophysics (4)
 
Nuclear Experiment (2)
 
Quantitative Biology - Neurons and Cognition (1)
 
Nonlinear Sciences - Adaptation and Self-Organizing Systems (1)
 
Instrumentation and Methods for Astrophysics (1)
 
High Energy Physics - Phenomenology (1)
 
High Energy Physics - Experiment (1)
 
Mathematics - Group Theory (1)
 
Physics - Plasma Physics (1)
 
Physics - Optics (1)

Publications Authored By R. H. Parker

2017May

We analyse N-body and Smoothed Particle Hydrodynamic (SPH) simulations of young star-forming regions to search for differences in the spatial distributions of massive stars compared to lower-mass stars. The competitive accretion theory of massive star formation posits that the most massive stars should sit in deeper potential wells than lower-mass stars. This may be observable in the relative surface density or spatial concentration of the most massive stars compared to other, lower-mass stars. Read More

We present analyses of the spatial distributions of stars in the young (1 - 3 Myr) star-forming regions IC348 and NGC1333 in the Perseus Giant Molecular Cloud. We quantify the spatial structure using the $\mathcal{Q}$-parameter and find that both IC348 and NGC1333 are smooth and centrally concentrated with $\mathcal{Q}$-parameters of 0.98 and 0. Read More

The young (~2 Myr) cluster Chamaeleon I is one of the closest laboratories to study the early stages of star cluster dynamics in a low-density environment. We studied its structural and kinematical properties combining parameters from the high-resolution spectroscopic survey Gaia-ESO with data from the literature. Our main result is the evidence of a large discrepancy between the velocity dispersion (sigma = 1. Read More

We present a hybrid laser frequency stabilization method combining modulation transfer spectroscopy (MTS) and frequency modulation spectroscopy (FMS) for the cesium D2 transition. In a typical pump-probe setup, the error signal is a combination of the DC-coupled MTS error signal and the AC-coupled FMS error signal. This combines the long-term stability of the former with the high signal-to-noise ratio of the latter. Read More

The presence and abundance of short lived radioisotopes (SLRs) $^{26}$Al and $^{60}$Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe). Massive stars are more likely to form in massive star clusters ($>$1000 M$_{\odot}$) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of $\sim$1 pc. Read More

Bragg diffraction has been used in atom interferometers because it allows signal enhancement through multiphoton momentum transfer and suppression of systematics by not changing the internal state of atoms. Its multi-port nature, however, can lead to parasitic interferometers, allows for intensity-dependent phase shifts in the primary interferometers, and distorts the ellipses used for phase extraction. We study and suppress these unwanted effects. Read More

In this chapter I review the effects of supernovae explosions on the dynamical evolution of (1) binary stars and (2) star clusters. (1) Supernovae in binaries can drastically alter the orbit of the system, sometimes disrupting it entirely, and are thought to be partially responsible for `runaway' massive stars - stars in the Galaxy with large peculiar velocities. The ejection of the lower-mass secondary component of a binary occurs often in the event of the more massive primary star exploding as a supernova. Read More

Heating by short-lived radioisotopes (SLRs) such as aluminum-26 and iron-60 fundamentally shaped the thermal history and interior structure of Solar System planetesimals during the early stages of planetary formation. The subsequent thermo-mechanical evolution, such as internal differentiation or rapid volatile degassing, yields important implications for the final structure, composition and evolution of terrestrial planets. SLR-driven heating in the Solar System is sensitive to the absolute abundance and homogeneity of SLRs within the protoplanetary disk present during the condensation of the first solids. Read More

Background: Octupole-deformed nuclei, such as that of $^{225}$Ra, are expected to amplify observable atomic electric dipole moments (EDMs) that arise from time-reversal and parity-violating interactions in the nuclear medium. In 2015, we reported the first "proof-of-principle" measurement of the $^{225}$Ra atomic EDM. Purpose: This work reports on the first of several experimental upgrades to improve the statistical sensitivity of our $^{225}$Ra EDM measurements by orders of magnitude and evaluates systematic effects that contribute to current and future levels of experimental sensitivity. Read More

We design an algorithm to find certain partial permutation representations of a finitely presented group $G$ (the bricks) that may be combined to a transitive permutation representation of $G$ (the mosaic) on the disjoint union. Read More

Mass segregation in star clusters is often thought to indicate the onset of energy equipartition, where the most massive stars impart kinetic energy to the lower-mass stars and brown dwarfs/free floating planets. The predicted net result of this is that the centrally concentrated massive stars should have significantly lower velocities than fast-moving low-mass objects on the periphery of the cluster. We search for energy equipartition in initially spatially and kinematically substructured N-body simulations of star clusters with N = 1500 stars, evolved for 100 Myr. Read More

We follow the dynamical evolution of young star-forming regions with a wide range of initial conditions and examine how the radial velocity dispersion, $\sigma$, evolves over time. We compare this velocity dispersion to the theoretically expected value for the velocity dispersion if a region were in virial equilibrium, $\sigma_{\rm vir}$ and thus assess the virial state ($\sigma / \sigma_{\rm vir}$) of these systems. We find that in regions that are initially subvirial, or in global virial equilibrium but subvirial on local scales, the system relaxes to virial equilibrium within several million years, or roughly 25 - 50 crossing times, according to the measured virial ratio. Read More

The presence and abundance of the short-lived radioisotopes (SLRs) $^{26}$Al and $^{60}$Fe during the formation of the Solar System is difficult to explain unless the Sun formed in the vicinity of one or more massive star(s) that exploded as supernovae. Two different scenarios have been proposed to explain the delivery of SLRs to the protosolar nebula: (i) direct pollution of the protosolar disc by supernova ejecta and (ii) the formation of the Sun in a sequential star formation event in which supernovae shockwaves trigger further star formation which is enriched in SLRs. The sequentially triggered model has been suggested as being more astrophysically likely than the direct pollution scenario. Read More

We compare the spatial distribution of stars which form in hydrodynamical simulations to the spatial distribution of the gas, using the $\mathcal{Q}$-parameter. The $\mathcal{Q}$-parameter enables a self-consistent comparison between the stars and gas because it uses a pixelated image of the gas as a distribution of points, in the same way that the stars (sink particles in the simulations) are a distribution of points. We find that, whereas the stars have a substructured, or hierarchical spatial distribution ($\mathcal{Q} \sim 0. Read More

The radioactive radium-225 ($^{225}$Ra) atom is a favorable case to search for a permanent electric dipole moment (EDM). Due to its strong nuclear octupole deformation and large atomic mass, $^{225}$Ra is particularly sensitive to interactions in the nuclear medium that violate both time-reversal symmetry and parity. We have developed a cold-atom technique to study the spin precession of $^{225}$Ra atoms held in an optical dipole trap, and demonstrated the principle of this method by completing the first measurement of its atomic EDM, reaching an upper limit of $|$$d$($^{225}$Ra)$|$ $<$ $5. Read More

2015Mar
Affiliations: 1Liverpool John Moores University UK, 2University of Sheffield, UK

We examine the performance of four different methods which are used to measure mass segregation in star-forming regions: the radial variation of the mass function $\mathcal{M}_{\rm MF}$; the minimum spanning tree-based $\Lambda_{\rm MSR}$ method; the local surface density $\Sigma_{\rm LDR}$ method; and the $\Omega_{\rm GSR}$ technique, which isolates groups of stars and determines whether the most massive star in each group is more centrally concentrated than the average star. All four methods have been proposed in the literature as techniques for quantifying mass segregation, yet they routinely produce contradictory results as they do not all measure the same thing. We apply each method to synthetic star-forming regions to determine when and why they have shortcomings. Read More

We present a large-scale, volume-limited companion survey of 245 late-K to mid-M (K7-M6) dwarfs within 15 pc. Infrared adaptive optics (AO) data were analysed from the Very Large Telescope, Subaru Telescope, Canada-France-Hawaii Telescope, and MMT Observatory to detect close companions to the sample from $\sim$1 au to 100 au, while digitised wide-field archival plates were searched for wide companions from $\sim$100 au to 10,000 au. With sensitivity to the bottom of the main sequence over a separation range of 3 au to 10,000 au, multiple AO and wide-field epochs allow us to confirm candidates with common proper motions, minimize background contamination, and enable a measurement of comprehensive binary statistics. Read More

The gravitational instability model of planet/brown dwarf formation proposes that protostellar discs can fragment into objects with masses above a few Jupiter masses at large semimajor axis. Tidal downsizing may reduce both the object mass and semimajor axis. However, most studies of tidal downsizing end when the protostellar disc disperses, while the system is embedded in its parent star-forming region. Read More

We take the end result of smoothed particle hydrodynamics (SPH) simulations of star formation which include feedback from photoionisation and stellar winds and evolve them for a further 10Myr using $N$-body simulations. We compare the evolution of each simulation to a control run without feedback, and to a run with photoionisation feedback only. In common with previous work, we find that the presence of feedback prevents the runaway growth of massive stars, and the resulting star-forming regions are less dense, and preserve their initial substructure for longer. Read More

The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the "density degeneracy problem": an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the $\mathcal{Q}$-parameter and comparing the structure and present-day density to the results of $N$-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. Read More

Recent observations of binary stars in the Galactic field show that the binary fraction and the mean orbital separation both decrease as a function of decreasing primary mass. We present $N$-body simulations of the effects of dynamical evolution in star-forming regions on primordial binary stars to determine whether these observed trends can be explained by the dynamical processing of a common binary population. We find that dynamical processing of a binary population with an initial binary fraction of unity and an initial excess of intermediate/wide separation (100 - 10$^4$ au) binaries does not reproduce the observed properties in the field, even in initially dense ($\sim 10^3$M$_\odot$ pc$^{-3}$) star-forming regions. Read More

2014May
Affiliations: 1Liverpool John Moores University, UK

One of the fundamental questions in star formation is whether or not brown dwarfs form in the same way as stars, or more like giant planets. If their formation scenarios are different, we might expect brown dwarfs to have a different spatial distribution to stars in nearby star-forming regions. In this contribution, we discuss methods to look for differences in their spatial distributions and show that in the only nearby star-forming region with a significantly different spatial distribution (the Orion Nebula Cluster), this is likely due to dynamical evolution. Read More

We use $N$-body simulations to compare the evolution of spatial distributions of stars and brown dwarfs in young star-forming regions. We use three different diagnostics; the ratio of stars to brown dwarfs as a function of distance from the region's centre, $\mathcal{R}_{\rm SSR}$, the local surface density of stars compared to brown dwarfs, $\Sigma_{\rm LDR}$, and we compare the global spatial distributions using the $\Lambda_{\rm MSR}$ method. From a suite of twenty initially statistically identical simulations, 6/20 attain $\mathcal{R}_{\rm SSR} << 1$ $and$ $\Sigma_{\rm LDR} << 1$ $and$ $\Lambda_{\rm MSR} << 1$, indicating that dynamical interactions could be responsible for observed differences in the spatial distributions of stars and brown dwarfs in star-forming regions. Read More

We examine substructure and mass segregation in the massive OB association Cygnus OB2 to better understand its initial conditions. Using a well understood Chandra X-ray selected sample of young stars we find that Cyg OB2 exhibits considerable physical substructure and has no evidence for mass segregation, both indications that the association is not dynamically evolved. Combined with previous kinematical studies we conclude that Cyg OB2 is dynamically very young, and what we observe now is very close to its initial conditions: Cyg OB2 formed as a highly substructured, unbound association with a low volume density (< 100 stars/pc^3). Read More

We model the dynamical evolution of star forming regions with a wide range of initial properties. We follow the evolution of the regions' substructure using the Q-parameter, we search for dynamical mass segregation using the Lambda_MSR technique, and we also quantify the evolution of local density around stars as a function of mass using the Sigma_LDR method. The amount of dynamical mass segregation measured by Lambda_MSR is generally only significant for subvirial and virialised, substructured regions - which usually evolve to form bound clusters. Read More

We use N-body simulations of star cluster evolution to explore the hypothesis that short-lived radioactive isotopes found in meteorites, such as 26-Al, were delivered to the Sun's protoplanetary disc from a supernova at the epoch of Solar System formation. We cover a range of star cluster formation parameter space and model both clusters with primordial substructure, and those with smooth profiles. We also adopt different initial virial ratios - from cool, collapsing clusters to warm, expanding associations. Read More

2013Aug

We determine the fraction of G-dwarf stars that could host stable planetary systems based on the observed properties of binaries in the Galactic field, and in various postulated primordial binary populations, which assume that the primordial binary fraction is higher than that in the field. We first consider the frequency of Solar System analogues - planetary systems that form either around a single G-dwarf star, or a binary containing a G-dwarf where the binary separation exceeds 100-300au. If the primordial binary fraction and period distribution is similar to that in the field, then up to 63 per cent of G-dwarf systems could potentially host a Solar System analogue. Read More

We demonstrate a technique for transferring $^{226}$Ra atoms from a 3-dimensional magneto-optical-trap (MOT) into a standing wave optical dipole trap (ODT) in an adjacent chamber. The resulting small trapping volume (120 $\mu$m in diameter) allows for high control of the electric and magnetic fields applied to the atoms. The atoms are first transferred to a traveling-wave optical dipole trap, which is then translated 46 cm to a science chamber. Read More

We explore the effects of dynamical evolution in dense clusters on the companion mass ratio distribution (CMRD) of binary stars. Binary systems are destroyed by interactions with other stars in the cluster, lowering the total binary fraction and significantly altering the initial semi-major axis distribution. However, the shape of the CMRD is unaffected by dynamics; an equal number of systems with high mass ratios are destroyed compared to systems with low mass ratios. Read More

2013Mar
Affiliations: 1ETH Zurich, Switzerland, 2Excellence Cluster, Garching, Germany

We present the results of N-body simulations in which we take the masses, positions and velocities of sink particles from five pairs of hydrodynamical simulations of star formation by Dale et al. (2012, 2013) and evolve them for a further 10Myr. We compare the dynamical evolution of star clusters that formed under the influence of mass-loss driven by photoionization feedback, to the evolution of clusters that formed without feedback. Read More

Radial velocity measurements can be used to constrain the dynamical state of a stellar cluster. However, for clusters with velocity dispersions smaller than a few km/s the observed radial velocity distribution tends to be dominated by the orbital motions of binaries rather than the stellar motions through the potential well of the cluster. Our goal is to characterize the intrinsic velocity distribution of a cluster from a single epoch of radial velocity data, even for a cluster with a velocity dispersion of a fraction of a km/s, using a maximum likelihood procedure. Read More

We have measured the multiplicity fractions and separation distributions of seven young star-forming regions using a uniform sample of young binaries. Both the multiplicity fractions and separation distributions are similar in the different regions. A tentative decline in the multiplicity fraction with increasing stellar density is apparent, even for binary systems with separations too close (19-100au) to have been dynamically processed. Read More

2012Jul
Affiliations: 1ETH Zurich, Switzerland, 2IPAG, Grenoble, France, 3ESA, Madrid, Spain

We apply two different algorithms to search for mass segregation to a recent observational census of the rho Ophiuchi star forming region. Firstly, we apply the Lambda_MSR method, which compares the minimum spanning tree (MST) of a chosen subset of stars to MSTs of random subsets of stars in the cluster, and determine the mass segregation ratio, Lambda_MSR. Secondly, we apply the m-Sigma method, which calculates the local stellar surface density around each star and determines the statistical significance of the average surface density for a chosen mass bin, compared to the average surface density in the whole cluster. Read More

We determine the distribution of stellar surface densities, \Sigma, from models of static and dynamically evolving star clusters with different morphologies, including both radially smooth and substructured clusters. We find that the \Sigma distribution is degenerate, in the sense that many different cluster morphologies (smooth or substructured) produce similar cumulative distributions. However, when used in tandem with a measure of structure, such as the Q-parameter, the current spatial and dynamical state of a star cluster can be inferred. Read More

2012Jul
Affiliations: 1ETH Zurich, Switzerland

In this contribution I present a review of star formation in clusters. I begin by discussing the various definitions of what constitutes a star cluster, and then compare the outcome of star formation (IMF, multiplicity, mass segregation and structure and morphology) in different star-forming regions. I also review recent numerical models of star formation in clusters, before ending with a summary of the potential effects of dynamical evolution in star clusters. Read More

The injection of lower hybrid waves for current drive into a tokamak affects the profile of intrinsic rotation. In this article, the momentum deposition by the lower hybrid wave on the electrons is studied. Due to the increase in the poloidal momentum of the wave as it propagates into the tokamak, the parallel momentum of the wave increases considerably. Read More

2012May
Authors: J. L. Hewett, H. Weerts, R. Brock, J. N. Butler, B. C. K. Casey, J. Collar, A. de Gouvea, R. Essig, Y. Grossman, W. Haxton, J. A. Jaros, C. K. Jung, Z. T. Lu, K. Pitts, Z. Ligeti, J. R. Patterson, M. Ramsey-Musolf, J. L. Ritchie, A. Roodman, K. Scholberg, C. E. M. Wagner, G. P. Zeller, S. Aefsky, A. Afanasev, K. Agashe, C. Albright, J. Alonso, C. Ankenbrandt, M. Aoki, C. A. Arguelles, N. Arkani-Hamed, J. R. Armendariz, C. Armendariz-Picon, E. Arrieta Diaz, J. Asaadi, D. M. Asner, K. S. Babu, K. Bailey, O. Baker, B. Balantekin, B. Baller, M. Bass, B. Batell, J. Beacham, J. Behr, N. Berger, M. Bergevin, E. Berman, R. Bernstein, A. J. Bevan, M. Bishai, M. Blanke, S. Blessing, A. Blondel, T. Blum, G. Bock, A. Bodek, G. Bonvicini, F. Bossi, J. Boyce, R. Breedon, M. Breidenbach, S. J. Brice, R. A. Briere, S. Brodsky, C. Bromberg, A. Bross, T. E. Browder, D. A. Bryman, M. Buckley, R. Burnstein, E. Caden, P. Campana, R. Carlini, G. Carosi, C. Castromonte, R. Cenci, I. Chakaberia, M. C. Chen, C. H. Cheng, B. Choudhary, N. H. Christ, E. Christensen, M. E. Christy, T. E. Chupp, E. Church, D. B. Cline, T. E. Coan, P. Coloma, J. Comfort, L. Coney, J. Cooper, R. J. Cooper, R. Cowan, D. F. Cowen, D. Cronin-Hennessy, A. Datta, G. S. Davies, M. Demarteau, D. P. DeMille, A. Denig, R. Dermisek, A. Deshpande, M. S. Dewey, R. Dharmapalan, J. Dhooghe, M. R. Dietrich, M. Diwan, Z. Djurcic, S. Dobbs, M. Duraisamy, B. Dutta, H. Duyang, D. A. Dwyer, M. Eads, B. Echenard, S. R. Elliott, C. Escobar, J. Fajans, S. Farooq, C. Faroughy, J. E. Fast, B. Feinberg, J. Felde, G. Feldman, P. Fierlinger, P. Fileviez Perez, B. Filippone, P. Fisher, B. T. Flemming, K. T. Flood, R. Forty, M. J. Frank, A. Freyberger, A. Friedland, R. Gandhi, K. S. Ganezer, A. Garcia, F. G. Garcia, S. Gardner, L. Garrison, A. Gasparian, S. Geer, V. M. Gehman, T. Gershon, M. Gilchriese, C. Ginsberg, I. Gogoladze, M. Gonderinger, M. Goodman, H. Gould, M. Graham, P. W. Graham, R. Gran, J. Grange, G. Gratta, J. P. Green, H. Greenlee, R. C. Group, E. Guardincerri, V. Gudkov, R. Guenette, A. Haas, A. Hahn, T. Han, T. Handler, J. C. Hardy, R. Harnik, D. A. Harris, F. A. Harris, P. G. Harris, J. Hartnett, B. He, B. R. Heckel, K. M. Heeger, S. Henderson, D. Hertzog, R. Hill, E. A Hinds, D. G. Hitlin, R. J. Holt, N. Holtkamp, G. Horton-Smith, P. Huber, W. Huelsnitz, J. Imber, I. Irastorza, J. Jaeckel, I. Jaegle, C. James, A. Jawahery, D. Jensen, C. P. Jessop, B. Jones, H. Jostlein, T. Junk, A. L. Kagan, M. Kalita, Y. Kamyshkov, D. M. Kaplan, G. Karagiorgi, A. Karle, T. Katori, B. Kayser, R. Kephart, S. Kettell, Y. K. Kim, M. Kirby, K. Kirch, J. Klein, J. Kneller, A. Kobach, M. Kohl, J. Kopp, M. Kordosky, W. Korsch, I. Kourbanis, A. D. Krisch, P. Krizan, A. S. Kronfeld, S. Kulkarni, K. S. Kumar, Y. Kuno, T. Kutter, T. Lachenmaier, M. Lamm, J. Lancaster, M. Lancaster, C. Lane, K. Lang, P. Langacker, S. Lazarevic, T. Le, K. Lee, K. T. Lesko, Y. Li, M. Lindgren, A. Lindner, J. Link, D. Lissauer, L. S. Littenberg, B. Littlejohn, C. Y. Liu, W. Loinaz, W. Lorenzon, W. C. Louis, J. Lozier, L. Ludovici, L. Lueking, C. Lunardini, D. B. MacFarlane, P. A. N. Machado, P. B. Mackenzie, J. Maloney, W. J. Marciano, W. Marsh, M. Marshak, J. W. Martin, C. Mauger, K. S. McFarland, C. McGrew, G. McLaughlin, D. McKeen, R. McKeown, B. T. Meadows, R. Mehdiyev, D. Melconian, H. Merkel, M. Messier, J. P. Miller, G. Mills, U. K. Minamisono, S. R. Mishra, I. Mocioiu, S. Moed Sher, R. N. Mohapatra, B. Monreal, C. D. Moore, J. G. Morfin, J. Mousseau, L. A. Moustakas, G. Mueller, P. Mueller, M. Muether, H. P. Mumm, C. Munger, H. Murayama, P. Nath, O. Naviliat-Cuncin, J. K. Nelson, D. Neuffer, J. S. Nico, A. Norman, D. Nygren, Y. Obayashi, T. P. O'Connor, Y. Okada, J. Olsen, L. Orozco, J. L. Orrell, J. Osta, B. Pahlka, J. Paley, V. Papadimitriou, M. Papucci, S. Parke, R. H. Parker, Z. Parsa, K. Partyka, A. Patch, J. C. Pati, R. B. Patterson, Z. Pavlovic, G. Paz, G. N. Perdue, D. Perevalov, G. Perez, R. Petti, W. Pettus, A. Piepke, M. Pivovaroff, R. Plunkett, C. C. Polly, M. Pospelov, R. Povey, A. Prakesh, M. V. Purohit, S. Raby, J. L. Raaf, R. Rajendran, S. Rajendran, G. Rameika, R. Ramsey, A. Rashed, B. N. Ratcliff, B. Rebel, J. Redondo, P. Reimer, D. Reitzner, F. Ringer, A. Ringwald, S. Riordan, B. L. Roberts, D. A. Roberts, R. Robertson, F. Robicheaux, M. Rominsky, R. Roser, J. L. Rosner, C. Rott, P. Rubin, N. Saito, M. Sanchez, S. Sarkar, H. Schellman, B. Schmidt, M. Schmitt, D. W. Schmitz, J. Schneps, A. Schopper, P. Schuster, A. J. Schwartz, M. Schwarz, J. Seeman, Y. K. Semertzidis, K. K. Seth, Q. Shafi, P. Shanahan, R. Sharma, S. R. Sharpe, M. Shiozawa, V. Shiltsev, K. Sigurdson, P. Sikivie, J. Singh, D. Sivers, T. Skwarnicki, N. Smith, J. Sobczyk, H. Sobel, M. Soderberg, Y. H. Song, A. Soni, P. Souder, A. Sousa, J. Spitz, M. Stancari, G. C. Stavenga, J. H. Steffen, S. Stepanyan, D. Stoeckinger, S. Stone, J. Strait, M. Strassler, I. A. Sulai, R. Sundrum, R. Svoboda, B. Szczerbinska, A. Szelc, T. Takeuchi, P. Tanedo, S. Taneja, J. Tang, D. B. Tanner, R. Tayloe, I. Taylor, J. Thomas, C. Thorn, X. Tian, B. G. Tice, M. Tobar, N. Tolich, N. Toro, I. S. Towner, Y. Tsai, R. Tschirhart, C. D. Tunnell, M. Tzanov, A. Upadhye, J. Urheim, S. Vahsen, A. Vainshtein, E. Valencia, R. G. Van de Water, R. S. Van de Water, M. Velasco, J. Vogel, P. Vogel, W. Vogelsang, Y. W. Wah, D. Walker, N. Weiner, A. Weltman, R. Wendell, W. Wester, M. Wetstein, C. White, L. Whitehead, J. Whitmore, E. Widmann, G. Wiedemann, J. Wilkerson, G. Wilkinson, P. Wilson, R. J. Wilson, W. Winter, M. B. Wise, J. Wodin, S. Wojcicki, B. Wojtsekhowski, T. Wongjirad, E. Worcester, J. Wurtele, T. Xin, J. Xu, T. Yamanaka, Y. Yamazaki, I. Yavin, J. Yeck, M. Yeh, M. Yokoyama, J. Yoo, A. Young, E. Zimmerman, K. Zioutas, M. Zisman, J. Zupan, R. Zwaska

The Proceedings of the 2011 workshop on Fundamental Physics at the Intensity Frontier. Science opportunities at the intensity frontier are identified and described in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms. Read More

2012Apr
Affiliations: 1ETH Zurich, Switzerland, 2University of Sheffield, UK

Observations of binaries in clusters tend to be of visual binaries with separations of 10s - 100s au. Such binaries are 'intermediates' and their destruction or survival depends on the exact details of their individual dynamical history. We investigate the stochasticity of the destruction of such binaries and the differences between the initial and processed populations using N-body simulations. Read More

Whether massive stars can occasionally form in relative isolation or if they require a large cluster of lower-mass stars around them is a key test in the differentiation of star formation theories as well as how the initial mass function of stars is sampled. Previous attempts to find O-type stars that formed in isolation were hindered by the possibility that such stars are merely runaways from clusters, i.e. Read More

Self-organized critical states are found in many natural systems, from earthquakes to forest fires, they have also been observed in neural systems, particularly, in neuronal cultures. However, the presence of critical states in the awake brain remains controversial. Here, we compared avalanche analyses performed on different in vivo preparations during wakefulness, slow-wave sleep and REM sleep, using high-density electrode arrays in cat motor cortex (96 electrodes), monkey motor cortex and premotor cortex and human temporal cortex (96 electrodes) in epileptic patients. Read More

We have collated multiplicity data for five clusters (Taurus, Chamaeleon I, Ophiuchus, IC348, and the Orion Nebula Cluster). We have applied the same mass ratio (flux ratios of delta K <= 2.5) and primary mass cuts (~0. Read More

We present N-body simulations of young substructured star clusters undergoing various dynamical evolutionary scenarios and examine the direct effects of interactions in the cluster on planetary systems. We model clusters initially in cool collapse, in virial equilibrium and expanding, and place a 1 Jupiter-mass planet at either 5au or 30au from their host stars, with zero eccentricity. We find that after 10Myr 10% of planets initially orbiting at 30au have been liberated from their parent star and form a population of free-floating planets. Read More

2011Aug
Affiliations: 1Kavli Institute for Astronomy and Astrophysics, Peking University, 2University of Sheffield, 3Lund Observatory, 4ETH Zurich, 5AIfA Bonn, 6Lund Observatory

A large population of fragile, wide (> 1000 AU) binary systems exists in the Galactic field and halo. These wide binary stars cannot be primordial because of the high stellar density in star forming regions, while formation by capture in the Galactic field is highly improbable. We propose that these binary systems were formed during the dissolution phase of star clusters (see Kouwenhoven et al. Read More

2011Aug
Affiliations: 1ETH Zurich, Switzerland, 2University of Sheffield, UK, 3ITA, Heidelberg, Germany

Observations and theory suggest that star clusters can form in a subvirial (cool) state and are highly substructured. Such initial conditions have been proposed to explain the level of mass segregation in clusters through dynamics, and have also been successful in explaining the origin of trapezium-like systems. In this paper we investigate, using N-body simulations, whether such a dynamical scenario is consistent with the observed binary properties in the Orion Nebula Cluster (ONC). Read More

We use the new minimum spanning tree (MST) method to look for mass segregation in the Taurus association. The method computes the ratio of MST lengths of any chosen subset of objects, including the most massive stars and brown dwarfs, to the MST lengths of random sets of stars and brown dwarfs in the cluster. This mass segregation ratio (Lambda_MSR) enables a quantitative measure of the spatial distribution of high-mass and low-mass stars, and brown dwarfs to be made in Taurus. Read More

2010Sep
Affiliations: 1ETH Zurich, Switzerland, 2University of Sheffield, UK

Very low-mass binaries (VLMBs), with system masses <0.2 Msun appear to have very different properties to stellar binaries. This has led to the suggestion that VLMBs form a distinct and different population. Read More

Spectroscopic analyses of H-rich WN5-6 stars within the young star clusters NGC 3603 and R136 are presented, using archival HST & VLT spectroscopy, & high spatial resolution near-IR photometry. We derive high T* for the WN stars in NGC 3603 (T*~42+/-2 kK) & R136 (T*~53+/-3 kK) plus clumping-corrected dM/dt ~ 2-5x10^-5 Msun/yr which closely agree with theoretical predictions. These stars make a disproportionate contribution to the global budget of their host clusters. Read More

Observations and theory both suggest that star clusters form sub-virial (cool) with highly sub-structured distributions. We perform a large ensemble of N-body simulations of moderate-sized (N=1000) cool, fractal clusters to investigate their early dynamical evolution. We find that cool, clumpy clusters dynamically mass segregate on a short timescale, that Trapezium-like massive higher-order multiples are commonly formed, and that massive stars are often ejected from clusters with velocities > 10 km/s (c. Read More

2010Jan

Over the past few decades, numerous wide (>1000 au) binaries in the Galactic field and halo have been discovered. Their existence cannot be explained by the process of star formation or by dynamical interactions in the field, and their origin has long been a mystery. We explain the origin of these wide binaries by formation during the dissolution phase of young star clusters: an initially unbound pair of stars may form a binary when their distance in phase-space is small. Read More