Note: This page contains sample records for the topic virgo stellar substructure from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

The Virgo Stellar Stream: Extended sample  

NASA Astrophysics Data System (ADS)

We have completed a spectroscopic study of the “12.4 hr clump”, the second largest substructure in the Quasar Equatorial Survey Team (QUEST) catalog. First discovered as an over-density of RR Lyrae stars (Vivas et al. 2001, ApJL 554 33), the region containing the “12.4 hr clump” has generated much interest (Newberg et al. (2002), Martinez-Delgado et al. (2007), Juric et al. (2008), amongst many others). Our first spectroscopic study of this clump revealed the presence of a sharp peak in the radial velocity histogram for the candidate stars (Duffau et al. 2006). The combination of this result and metal abundance estimates for the sample was then interpreted as a signature of the presence of a stellar stream within the clump. This sub-structure was named the “Virgo Stellar Stream” (VSS), given its location in the direction of the Virgo Constellation, at approximately 20 kpc from the Sun. Several other groups have studied this region and have suggested that the over-density containing the VSS could extend to larger areas of the sky (outside QUEST's observing range). We present the complete spectroscopic follow up of the clump candidates present in QUEST and the composite of the studies we performed along the same l.o.s., including data at brighter magnitudes (Vivas et al. 2008). Our study confirmed the nature of the VSS, revealed its likely extent within the QUEST survey and defined a number of its relevant properties.

Duffau, S.; Vivas, A. K.; Zinn, R.; Méndez, R. A.; Ruiz, M. T.

2010-04-01

2

Stellar Populations of Stripped Spiral Galaxies in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

Clusters play an important role in the evolution of their member galaxies. In the nearby Virgo cluster, we can observe galaxy-galaxy and galaxy-cluster interactions at a level of detail not easily accessible at higher redshift. We present results of an observational study of spiral galaxies in the Virgo Cluster, utilizing optical and UV imaging, HI observations, and optical spectroscopy. These galaxies, many of which have normal stellar distributions and truncated gas disks, are likely the result of ram-pressure stripping by hot cluster gas. Our results indicate that there is a correlation between HI morphology and the age-sensitive Balmer absorption line strength. Specifically, those galaxies with asymmetric HI distributions or extraplanar HI, indicating a recent disturbance by the intra-cluster medium, have the youngest stellar populations in the gas-free outer disk. Observations of both gas and stellar populations allow us to understand when and where galaxies are transformed by gas stripping effects in clusters. One of the most striking galaxies in our sample is NGC 4522. This galaxy, with a large fraction of its neutral gas displaced to one side of the stellar disk, is one of the best examples of ongoing ram pressure stripping in Virgo. Optical spectroscopy of the outer disk of NGC 4522 (i.e. beyond the sites of active star formation), shows strong H? absorption, indicative of a young stellar population and consistent with a recent truncation of star formation in the outer disk. Additionally, we observe strong H? and H? absorption, similar to post-starburst k+a galaxies at higher redshift. This suggests that some k+a galaxies observed at higher redshift may be recently stripped cluster spirals.

Crowl, H. H.

2005-12-01

3

Mapping the Stellar Mass within Virgo Cluster Galaxies  

NASA Astrophysics Data System (ADS)

Measuring the total stellar masses and the distributions thereof in all types of galaxies represents a cornerstone toward our understanding of many problems pertaining to the baryonic physics involved in galaxy formation. Two advantages of carrying out this exercise for cluster galaxies include: the capability (i) to assess how environment affects the relationship between baryonic physics and galaxies' stellar masses, and (ii) to study many galaxy types contained within a relatively small patch of sky. Using the latest (and deepest) images available in the ultraviolet, optical and near-infrared domains, we have begun a campaign to measure (2D) stellar surface mass density maps out to large galactocentric radii for all manner of galaxies belonging to the Virgo cluster. Although the signal-to-noise per resolution element is inherently weaker in the absence of azimuthal averaging (i.e. 1D analyses), this deficiency is outweighed by our ability to spatially correlate interesting, non-axisymmetric features from the images (e.g. bars) with specific pixels in the mass maps. Therefore, a 2D approach to mapping the stellar mass distributions within galaxies ultimately leads to a more accurate account of the rich structure which they possess. In this talk, I will describe the machinery by which we transform multi-band images of a given galaxy into a stellar mass map, including the systematics associated therewith, as well as the many possible applications of the maps themselves. An example which will be elaborated on in more detail is our efforts to use these data to constrain galaxy structure in terms of stellar mass, instead of light.

Roediger, Joel; Courteau, S.

2013-01-01

4

Stellar Populations and Radial Migrations in Virgo Disk Galaxies  

NASA Astrophysics Data System (ADS)

We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ("U-shapes") in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (<=36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (~11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (>=50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field galaxies, fail to reproduce these results, thus calling for adequate hydrodynamical simulations of dense galaxy environments if we are to understand cluster disks. The current paper highlights numerous constraints for such simulations. In the Appendix, we confirm the claim by Erwin et al. that Type II breaks are absent in Virgo cluster S0s and discuss the detection of Type III breaks in such galaxies.

Roediger, Joel C.; Courteau, Stéphane; Sánchez-Blázquez, Patricia; McDonald, Michael

2012-10-01

5

STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES  

SciTech Connect

We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field galaxies, fail to reproduce these results, thus calling for adequate hydrodynamical simulations of dense galaxy environments if we are to understand cluster disks. The current paper highlights numerous constraints for such simulations. In the Appendix, we confirm the claim by Erwin et al. that Type II breaks are absent in Virgo cluster S0s and discuss the detection of Type III breaks in such galaxies.

Roediger, Joel C.; Courteau, Stephane [Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario (Canada); Sanchez-Blazquez, Patricia [Deptartamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); McDonald, Michael, E-mail: jroediger@astro.queensu.ca, E-mail: courteau@astro.queensu.ca, E-mail: p.sanchezblazquez@uam.es, E-mail: mcdonald@space.mit.edu [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology Cambridge, MA (United States)

2012-10-10

6

KINEMATICS AND CHEMISTRY OF HALO SUBSTRUCTURES: THE VICINITY OF THE VIRGO OVERDENSITY  

SciTech Connect

We present observations obtained with the Anglo-Australian Telescope's 2dF wide field spectrograph AAOmega of K-type stars located within a region of the sky which contains the Virgo Overdensity and the leading arm of the Sagittarius Stream. On the basis of the resulting velocity histogram, we isolate halo substructures in these overlapping regions including Sagittarius and previously discovered Virgo groups. Through comparisons with N-body models of the Galaxy-Sagittarius interaction, we find a tri-axial dark matter halo is favored and we exclude a prolate shape. This result is contradictory with other observations along the Sagittarius leading arm, which typically favor prolate models. We have also uncovered K-giant members of Sagittarius that are notably more metal-poor (([Fe/H]) = -1.7 {+-} 0.3 dex) than previous studies. This suggests a significantly wider metallicity distribution exists in the Sagittarius Stream than formerly considered. We also present data on five carbon stars which were discovered in our sample.

Casey, Andrew R.; Keller, Stefan C.; Da Costa, Gary [Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, via Cotter Rd, Weston, ACT 2611 (Australia)

2012-04-15

7

SUBSTRUCTURE IN THE STELLAR HALOS OF THE AQUARIUS SIMULATIONS  

SciTech Connect

We characterize the substructure in the simulated stellar halos of Cooper et al. which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius project. These stellar halos exhibit a wealth of tidal features: broad overdensities and very narrow faint streams akin to those observed around the Milky Way. The substructures are distributed anisotropically on the sky, a characteristic that should become apparent in the next generation of photometric surveys. The normalized RMS of the density of stars on the sky appears to be systematically larger for our halos compared with the value estimated for the Milky Way from main-sequence turnoff stars in the Sloan Digital Sky Survey. We show that this is likely to be due in part to contamination by faint QSOs and redder main-sequence stars, and might suggest that {approx}10% of the Milky Way halo stars have formed in situ.

Helmi, Amina [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen (Netherlands); Cooper, A. P.; Cole, S.; Frenk, C. S. [Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom); White, S. D. M. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); Navarro, J. F., E-mail: ahelmi@astro.rug.nl [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2 (Canada)

2011-05-20

8

Stellar Populations of Dwarf Elliptical Galaxies: UBVRI Photometry of Dwarf Elliptical Galaxies in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We present UBVRI surface photometry for 16 dwarf elliptical galaxies in the Virgo Cluster with previously measured kinematic properties. The global optical colors are red, with median values for the sample of 0.24+/-0.03 in U-B, 0.77+/-0.02 in B-V, and 1.02+/-0.03 in V-I. We recover the well-known color-magnitude relation for cluster galaxies but find no significant difference in dominant stellar population between rotating and nonrotating dwarf elliptical galaxies; the average age of the dominant stellar population is 5-7 Gyr in all 16 galaxies in this sample. Analysis of optical spectra confirm these age estimates and indicate Fe and Mg abundances in the range of 1/20 to one-third of solar, as expected for low-luminosity galaxies. Based on Lick indices and simple stellar population models, the derived [?/Fe] ratios are subsolar to solar, indicating a more gradual chemical enrichment history for dE's as compared with giant elliptical galaxies in the Virgo Cluster. These observations confirm the marked difference in stellar population and stellar distribution between dwarf and giant elliptical galaxies and further substantiate the need for alternative evolutionary scenarios for the lowest mass cluster galaxies. We argue that it is likely that several different physical mechanisms played a significant role in the production of the Virgo Cluster dE galaxies including in situ formation, infall of dE's that were once part of Local Group analogs, and transformation of dwarf irregular galaxies by the cluster environment. The observations support the hypothesis that a large fraction of the Virgo Cluster dE's are formed by ram pressure stripping of gas from infalling dI's. Based on observations with the VATT: the Alice P. Lennon Telescope and the Thomas J. Bannan Astrophysics Facility.

van Zee, Liese; Barton, Elizabeth J.; Skillman, Evan D.

2004-12-01

9

Galaxy transformation in the Virgo Cluster: Gas stripping and stellar population evolution  

NASA Astrophysics Data System (ADS)

This study utilizes optical imaging, optical spectroscopy, HI radio maps and UV imaging to study the effects of environment on the evolution of spiral galaxies in the nearby Virgo Cluster. Optical, HI and radio continuum observations of NGC 4402, a highly inclined HI- deficient Virgo 0.5 L * spiral galaxy, show evidence for ram pressure stripping and dense cloud ablation. Optical images show dust curving up and out of the stellar disk at the HI truncation radius. South of the main dust disk, we have discovered two linear dust filaments aligned with each other and with the skewed radio continuum halo. We interpret these dust filaments as large, dense clouds which were initially left behind as the low-density ISM was stripped, but are now being ablated by the ICM wind. We present results from 10 spiral galaxies in Virgo that have truncated star- forming disks, with normal star formation in the inner disk and little or no star formation beyond a truncation radius. Models of observed spectra from just beyond the Ha truncation radius demonstrate that stripping was recent, within the last 500 Myr. This implies that ram pressure stripping is effective in halting star formation in the outer disks of spiral galaxies and plays a role in the morphological transformation of spiral galaxies. The outer disk of one of our sample, NGC 4522, shows a post-star formation K+A type spectrum, consistent with star formation being truncated ~ 100 Myr ago. >From its location in the cluster, we conclude that such stripping could not have taken place in the cluster core and must have taken place near its current location, ~ 1 Mpc from the cluster center. The outer disk stellar populations roughly correlate with the neutral gas distributions, as measured from HI maps. Galaxies with extraplanar HI have more recently had star formation in their outer disks truncated. In the three cases where our data overlap with ram pressure simulations of Virgo galaxies, the star formation truncation times from our data agree with the time since peak pressure in the simulations. This suggests that star formation is quickly disrupted during ISM-ICM interactions.

Crowl, Hugh Horgan

10

Quantifying Kinematic Substructure in the Milky Way's Stellar Halo  

Microsoft Academic Search

We present and analyze the positions, distances, and radial velocities for\\u000aover 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn\\u000afrom SDSS DR8. We search for position-velocity substructure in these data,\\u000awhich is expected from hierarchical galaxy formation models, where most of the\\u000ahalo stars are still-detectable tidal debris from disrupted satellite galaxies.\\u000aUsing a cumulative \\

Xiang-Xiang Xue; Hans-Walter Rix; Brian Yanny; Timothy C. Beers; Eric F. Bell; Gang Zhao; James S. Bullock; Kathryn V. Johnston; Heather Morrison; Constance Rockosi; Sergey E. Koposov; Xi Kang; Chao Liu; Ali Luo; Young Sun Lee; Benjamin. A. Weaver

2010-01-01

11

A continuum of structure and stellar content from Virgo cluster early-type dwarfs to giants?  

NASA Astrophysics Data System (ADS)

Based on the wealth of multiwavelength imaging data from the SDSS, we investigate whether dwarf and giant early-type galaxies in the Virgo cluster follow a continuum in their structural parameters and their stellar population characteristics. More specifically we study the relation between size and brightness for the galaxies and their color magnitude relation. In both cases, we find noticeable deviations from a simple joint behavior of dwarfs and giants. We discuss these findings in the light of the different formation mechanisms commonly assumed for dwarf and giant early types, thereby taking into account the existence of several distinct early-type dwarf subclasses. By comparing our results to a semianalytic model of galaxy formation, we argue that the analyzed relations might be reproduced by processes that form dwarfs and giants altogether. The work presented here is based on Janz & Lisker (2008, 2009).

Janz, J.; Lisker, T.

2009-12-01

12

The Virgo stellar over-density: Mapping the infall of the Sagittarius tidal stream onto the Milky Way disk  

Microsoft Academic Search

The recently discovered Virgo stellar over-density, which expands over\\u000a\\\\~1000deg^2 perpendicularly to the Galactic disk plane (7< Z <15 kpc, R~7 kpc),\\u000ais the largest clump of tidal debris ever detected in the outer halo and is\\u000alikely related with the accretion of a nearby dwarf galaxy by the Milky Way. We\\u000acarry out N-body simulations of the Sagittarius stream

David Mart ´ õnez-Delgado; Jorge Penarrubia; Mario Juric; Emilio J. Alfaro; Zeljko Ivezic

2006-01-01

13

The Virgo Stellar Overdensity: Mapping the Infall of the Sagittarius Tidal Stream onto the Milky Way Disk  

Microsoft Academic Search

The recently discovered Virgo stellar overdensity, which extends over ~1000 deg2 perpendicular to the Galactic disk plane (7 kpc

David Martínez-Delgado; Jorge Peñarrubia; Mario Juric; Emilio J. Alfaro; Zeljko Ivezic

2007-01-01

14

Extending the Virgo Stellar Stream with SEKBO Survey RR Lyrae Stars  

NASA Astrophysics Data System (ADS)

A subset of the RR Lyrae (RRL) candidates identified from the Southern Edgeworth-Kuiper Belt Object (SEKBO) survey data have been followed up photometrically (n = 106) and spectroscopically (n = 51). Period and light curve fitting reveals a 24% ± 7% contamination of SEKBO survey data by non-RRLs. This paper focuses on the region of the Virgo Stellar Stream (VSS), particularly on its extension to the south of the declination limits of the Sloan Digital Sky Survey and of the Quasar Equatorial Survey Team RRL survey. The distribution of radial velocities in the Galactic standard of rest frame (V GSR) for the 11 RRLs observed in the VSS region has two apparent peaks. The larger peak coincides with the four RRLs having langV GSRrang = 127 ± 10 km s-1 and dispersion ? = 27 km s-1, marginally larger than that expected from the errors alone. The two type ab RRLs in this group have lang[Fe/H]rang = -1.95 ± 0.1. Both the radial velocities and metal abundances are consistent with membership in the VSS. The second velocity peak, which occurs at langV GSRrang = -175 ± 10 km s-1 may indicate the presence of stars from the Sgr leading tidal tail, which is expected to have large negative velocities in this region. We explore the spatial extent of the VSS by constructing luminosity functions from the SEKBO data and comparing them to data synthesized with the Besançon Galactic model. Analysis of the excess over the model predictions reveals the VSS as a large (~760 deg2) overdensity centered at roughly (R.A., decl.) ~ (186°, -4°), spanning a length of ~15 kpc in projection, assuming a heliocentric distance of 19 kpc. The data reveal for the first time the more southern regions of the stream and trace it to decl. ?-15° and Galactic latitudes as low as b ? 45°.

Prior, Sayuri L.; Da Costa, G. S.; Keller, Stefan C.; Murphy, Simon J.

2009-01-01

15

The Photometric Properties of a Vast Stellar Substructure in the Outskirts of M33  

NASA Astrophysics Data System (ADS)

We have surveyed approximately 40 deg2 surrounding M33 with Canada-France-Hawaii Telescope MegaCam/MegaPrime in the g and i filters out to a maximum projected radius from this galaxy of 50 kpc, as part of the Pan-Andromeda Archaeological Survey (PAndAS). Our observations are deep enough to resolve the top ~4 mag of the red giant branch population in this galaxy. We have previously shown that the disk of M33 is surrounded by a large, irregular, low surface brightness substructure. Here, we quantify the stellar populations and structure of this feature using the PAndAS data. We show that the stellar populations of this feature are consistent with an old population with lang[Fe/H]rang ~ -1.6 dex and an interquartile range in metallicity of ~0.5 dex. We construct a surface brightness map of M33 that traces this feature to ? V ~= 33 mag arcsec-2. At these low surface brightness levels, the structure extends to projected radii of ~40 kpc from the center of M33 in both the northwest and southeast quadrants of the galaxy. Overall, the structure has an "S-shaped" appearance that broadly aligns with the orientation of the H I disk warp. We calculate a lower limit to the integrated luminosity of the structure of -12.7 ± 0.5 mag, comparable to a bright dwarf galaxy such as Fornax or Andromeda II and slightly less than 1% of the total luminosity of M33. Further, we show that there is tentative evidence for a distortion in the distribution of young stars near the edge of the H I disk that occurs at similar azimuth to the warp in H I. The data also hint at a low-level, extended stellar component at larger radius that may be an M33 halo component. We revisit studies of M33 and its stellar populations in light of these new results and discuss possible formation scenarios for the vast stellar structure. Our favored model is that of the tidal disruption of M33 in its orbit around M31.

McConnachie, Alan W.; Ferguson, Annette M. N.; Irwin, Michael J.; Dubinski, John; Widrow, Lawrence M.; Dotter, Aaron; Ibata, Rodrigo; Lewis, Geraint F.

2010-11-01

16

The Resolved Stellar Populations of a Dwarf Spheroidal Galaxy in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We report on the discovery of a faint (MV~-10.6+/-0.2) dwarf spheroidal galaxy on deep F606W and F814W Hubble Space Telescope images of a Virgo intracluster field. The galaxy is easily resolved in our images, as our color magnitude diagram (CMD) extends >~1 magnitude beyond the tip of the red giant branch (RGB). Thus, it is the deepest CMD for a small dwarf galaxy inside a cluster environment. Using the colors of the RGB stars, we derive a metal abundance for the dwarf of [M/H]=-2.3+/-0.3 and show that the metallicity dispersion is less than 0.6 dex at 95% confidence. We also use the galaxy's lack of AGB stars and the absence of objects brighter than Mbol~-4.1+/-0.2 to show that the system is old (t>~10 Gyr). Finally, we derive the object's structural parameters and show that the galaxy displays no obvious evidence of tidal threshing. Since the tip of the red giant branch distance [(m-M)0=31.23+/-0.17 or D=17.6+/-1.4 Mpc] puts the galaxy near the core of the Virgo cluster, one might expect the object to have undergone some tidal processing. Yet the chemical and morphological similarity between the dwarf and the dSph galaxies of the Local and M81 Group demonstrates that the object is indeed pristine and not the shredded remains of a much larger galaxy. We discuss the possible origins of this galaxy and suggest that it is just now falling into Virgo for the first time.

Durrell, Patrick R.; Williams, Benjamin F.; Ciardullo, Robin; Feldmeier, John J.; von Hippel, Ted; Sigurdsson, Steinn; Jacoby, George H.; Ferguson, Henry C.; Tanvir, Nial R.; Arnaboldi, Magda; Gerhard, Ortwin; Aguerri, J. Alfonso L.; Freeman, Ken; Vinciguerra, Matt

2007-02-01

17

Virgo cluster and field dwarf ellipticals in 3D - I. On the variety of stellar kinematic and line-strength properties  

NASA Astrophysics Data System (ADS)

We present the first large-scale stellar kinematic and line-strength maps for dwarf elliptical galaxies (nine in the Virgo cluster and three in the field environment) obtained with the SAURON (Spectrographic Areal Unit for Research on Optical Nebulae) integral-field unit. No two galaxies in our sample are alike: we see that the level of rotation is not tied to flattening (we have, e.g., round rotators and flattened non-rotators); we observe kinematic twists in one Virgo and one field object; we discover large-scale kinematically decoupled components in two field galaxies; we see varying gradients in line-strength maps, from nearly flat to strongly peaked in the centre. The great variety of morphological, kinematic and stellar population parameters seen in our data points to a formation scenario in which properties are shaped stochastically. A combined effect of ram-pressure stripping and galaxy harassment is the most probable explanation. We show the need for a comprehensive analysis of kinematic, dynamical and stellar population properties which will enable us to place dwarf ellipticals and processes that govern their evolution in the wider context of galaxy formation.

Ry?, Agnieszka; Falcón-Barroso, Jesús; van de Ven, Glenn

2013-02-01

18

Imaging Virgo's Diffuse Intracluster Light  

NASA Astrophysics Data System (ADS)

We use deep broad-band imaging of the Virgo Cluster using Case's Burrell Schmidt telescope to study the properties of its diffuse intracluster light (ICL). Our image -- 1.5 degrees on a side with a limiting depth of mu(V)=28.5 magnitudes per square arcsecond -- reveals an intricate web of diffuse intracluster light, including long (>100 kpc) tidal streams and a myriad of tidal tails and bridges between galaxies. The diffuse halo of M87 is traced out to nearly 200 kpc, and significant diffuse light is also detected around the M84/M86 pair. The complex substructure seen in Virgo's diffuse ICL reflects the hierarchical nature of cluster assembly, rather than being the product of smooth accretion around a central galaxy. We also present quantitative comparisons between our measurements of Virgo's ICL and those obtained from discrete tracers of starlight such as planetary nebulae and red giants. This work has been sponsored by the National Science Foundation and Research Corporation.

Mihos, C.; Harding, P.; Feldmeier, J.; Morrison, H.

2005-12-01

19

Status of the Virgo project  

Microsoft Academic Search

We describe the present state and future evolution of the Virgo gravitational wave detector, realized by the Virgo Collaboration at the European Gravitational Observatory, in Cascina near Pisa in Italy. We summarize basic principles of the operation and the design features of the Virgo detector. We present the sensitivity evolution due to a series of intermediate upgrades called Virgo+ which

T. Accadia; F. Acernese; F. Antonucci; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; A. Basti; Th S. Bauer; M. Bebronne; M. G. Beker; A. Belletoile; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; M. Branchesi; T. Briant; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; O. Chaibi; E. Chassande Mottin; A. Chincarini; F. Cleva; E. Coccia; P.-F. Cohadon; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S D’Antonio; V. Dattilo; M. Davier; R. Day; R. De Rosa; G. Debreczeni; W. Del Pozzo; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; L. A. Forte; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; A. Heidmann; H. Heitmann; P. Hello; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; N. Liguori; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. Swinkels; M. Tacca; L. Taffarello; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; C. Van Den Broeck; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; S. Vitale; H. Vocca; R. L. Ward; M. Yvert; J.-P. Zendri

2011-01-01

20

Multifrequency surveys of the Virgo cluster: ALFALFA, HeViCS, SMAKCED, NGVS, GUViCS  

NASA Astrophysics Data System (ADS)

The Virgo cluster, the largest nearby concentration of galaxies, is the target of several multifrequency surveys aimed at studying the effects of the environment on galaxy evolution. These blind or pointed surveys are: the Arecibo Legacy Fast ALFA Survey (ALFALFA; PI. R. Giovanelli), the Herschel Virgo Cluster Survey (HeViCS; PI J. Davies), the Stellar content, MAss and Kinematics of Cluster Early-type Dwarfs (SMAKCED, PI T. Lisker), the Next Generation Virgo Cluster Survey (NGVS; PI L. Ferrarese) and the GALEX UV Virgo Cluster Survey (GUViCS; PI A. Boselli). I briefly describe the surveys mentioning some of the most interesting results obtained so far.

Boselli, A.

2012-12-01

21

THE ONGOING ASSEMBLY OF A CENTRAL CLUSTER GALAXY: PHASE-SPACE SUBSTRUCTURES IN THE HALO OF M87  

SciTech Connect

The halos of galaxies preserve unique records of their formation histories. We carry out the first combined observational and theoretical study of phase-space halo substructure in an early-type galaxy: M87, the central galaxy in the Virgo cluster. We analyze an unprecedented wide-field, high-precision photometric and spectroscopic data set for 488 globular clusters (GCs), which includes new, large-radius Subaru/Suprime-Cam and Keck/DEIMOS observations. We find signatures of two substructures in position-velocity phase space. One is a small, cold stream associated with a known stellar filament in the outer halo; the other is a large shell-like pattern in the inner halo that implies a massive, hitherto unrecognized accretion event. We perform extensive statistical tests and independent metallicity analyses to verify the presence and characterize the properties of these features, and to provide more general methodologies for future extragalactic studies of phase-space substructure. The cold outer stream is consistent with a dwarf galaxy accretion event, while for the inner shell there is tension between a low progenitor mass implied by the cold velocity dispersion, and a high mass from the large number of GCs, which might be resolved by a {approx}0.5 L* E/S0 progenitor. We also carry out proof-of-principle numerical simulations of the accretion of smaller galaxies in an M87-like gravitational potential. These produce analogous features to the observed substructures, which should have observable lifetimes of {approx}1 Gyr. The shell and stream GCs together support a scenario where the extended stellar envelope of M87 has been built up by a steady rain of material that continues until the present day. This phase-space method demonstrates unique potential for detailed tests of galaxy formation beyond the Local Group.

Romanowsky, Aaron J.; Brodie, Jean P.; Arnold, Jacob A. [University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Strader, Jay [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Mihos, J. Christopher [Department of Astronomy, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106 (United States); Spitler, Lee R.; Forbes, Duncan A.; Foster, Caroline [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia)

2012-03-20

22

Milky Way Substructure Catalogue and Detection of Potential New Dwarf Galaxy  

Microsoft Academic Search

In order to facilitate the identification of new Milky Way halo substructures, We have created an online catalog of Milky Way substructures, including dwarf galaxies, globular clusters, stellar over-densities, tidal tails and stellar streams. The catalogue is located at: http:\\/\\/www.rpi.edu\\/ newbeh\\/mwstructure\\/MilkyWaySpheroidSubstructure.html. The vast majority of the substructures were discovered after 1995. In addition, We show evidence for the detection of

John Dellomo

2010-01-01

23

The Kinematics of Virgo's Intracluster Stars  

NASA Astrophysics Data System (ADS)

Radial velocity measurements of intracluster planetary nebulae (IPNe) have the potential to revolutionize our understanding of galaxy clusters. Ultra-low surface brightness images, such as that taken by Mihos ?l (2005) demonstrate the complexity of the intracluster stellar distribution, but by examining the distribution of IPNe in phase space, we can probe the physics of tidal stripping, the dark matter around galaxies, and the initial conditions of cluster formation. A recent example of the value of IPN measurements is presented by Doherty ?l (2009), who have used a very small sample of IPN velocities to argue that M87's stellar halo abruptly truncates at a galactocentric distance of ~ 150 kpc, and beyond this region, the potential of the cluster dominates. The recent improvements to the bench spectrograph of the WIYN+Hydra system now place large numbers of Virgo IPNe within reach. We propose to use this instrument to obtain the radial velocities of between 100 and 150 IPNe spanning the region from M87 to the Virgo Cluster ``core''. These measurements will triple the number of stellar radial velocities known in the cluster, and allow us to probe the origins of the intracluster stars and the process of hierarchical assembly.

Ciardullo, Robin; Feldmeier, John; Jacoby, George; Mihos, Chris; Herrmann, Kim

2010-02-01

24

Sub-structures in the inner halo of the Milky Way  

NASA Astrophysics Data System (ADS)

We present a spectroscopic study of a sample of 238 RR Lyrae stars, from the QUEST survey, located in the Galactic halo at distances between 4 and 20 kpc from the Sun. Combining their spatial position and kinematics we were able to identify sub-structures in this part of the halo. Some of those sub-structures may be associated with known halo features like the Virgo Overdensity, the Hercules-Aquila Cloud, and the Anticenter Stream.

Vivas, A. K.; Zinn, R.; Duffau, S.; Jaffé, Y.

2012-02-01

25

The Herschel Virgo Cluster Survey - XIV. Transition-type dwarf galaxies in the Virgo cluster  

NASA Astrophysics Data System (ADS)

We use dust scaling relations to investigate the hypothesis that Virgo cluster transition-type dwarfs are infalling star-forming field galaxies, which is argued based on their optical features (e.g. discs, spiral arms and bars) and kinematic properties similar to late-type galaxies. After their infall, environmental effects gradually transform them into early-type galaxies through the removal of their interstellar medium and quenching of all star formation activity. In this paper, we aim to verify whether this hypothesis holds using far-infrared diagnostics based on Herschel observations of the Virgo cluster taken as part of the Herschel Virgo Cluster Survey. We select transition-type objects in the nearest cluster, Virgo, based on spectral diagnostics indicative for their residual or ongoing star formation. We detect dust (Md ˜ 105-6 M?) in 36 per cent of the transition-type dwarfs located on the high end of the stellar mass distribution. This suggests that the dust reservoirs present in non-detections fall just below the Herschel detection limit (?1.1 × 105 M?). Dust scaling relations support the hypothesis of a transformation between infalling late-type galaxies to quiescent low-mass spheroids governed by environmental effects, with dust-to-stellar mass fractions for transition-type dwarfs in between values characteristic for late-type objects and the lower dust fractions observed in early-type galaxies. Several transition-type dwarfs demonstrate blue central cores, hinting at the radially outside-in removal of gas and quenching of star formation activity. The fact that dust is also confined to the inner regions suggests that metals are stripped in the outer regions along with the gas. In the scenario of most dust being stripped from the galaxy along with the gas, we argue that the ejected metals by transition-type dwarfs significantly contribute to the enrichment of the intracluster medium over the lifetime of the Virgo cluster. The accretion of gas through tidal interactions and re-ignition of star formation in the centres of transition-type dwarfs could provide an alternative explanation for the observed dust scaling relations and blue central cores.

De Looze, Ilse; Baes, Maarten; Boselli, Alessandro; Cortese, Luca; Fritz, Jacopo; Auld, Robbie; Bendo, George J.; Bianchi, Simone; Boquien, Médéric; Clemens, Marcel; Ciesla, Laure; Davies, Jonathan; di Serego Alighieri, Sperello; Grossi, Marco; Jones, Anthony; Madden, Suzanne C.; Pappalardo, Ciro; Pierini, Daniele; Smith, Matthew W. L.; Verstappen, Joris; Vlahakis, Catherine; Zibetti, Stefano

2013-09-01

26

From Virgo Cluster Early-Type Dwarfs to Giants  

NASA Astrophysics Data System (ADS)

We analyze the structural parameters and stellar population characteristics of early types in the Virgo cluster. In both cases, we find noticeable deviations from a simple joint behavior of dwarfs and giants; nevertheless, by comparison to a semianalytic model of galaxy formation, we conclude the relations might be reproduced by processes that form dwarfs and giants altogether. The work presented here is based on Janz & Lisker (2008, 2009).

Janz, J.; Lisker, T.

2011-07-01

27

H? Morphologies and Environmental Effects in Virgo Cluster Spiral Galaxies  

NASA Astrophysics Data System (ADS)

We describe the various H? morphologies of Virgo Cluster and isolated spiral galaxies and associate the H? morphologies with the types of environmental interactions that have altered the cluster galaxies. The spatial distributions of H? and R-band emission are used to divide the star formation morphologies of the 52 Virgo Cluster spiral galaxies into several categories: normal (37%), anemic (6%), enhanced (6%), and (spatially) truncated (52%). Truncated galaxies are further subdivided on the basis of their inner star formation rates into truncated/normal (37%), truncated/compact (6%), truncated/anemic (8%), and truncated/enhanced (2%). The fraction of anemic galaxies is relatively small (6%-13%) in both environments, suggesting that starvation is not a major factor in the reduced star formation rates of Virgo spiral galaxies. The majority of Virgo spiral galaxies have their H? disks truncated (52%), whereas truncated H? disks are rarer in isolated galaxies (12%). Most of the H?-truncated galaxies have relatively undisturbed stellar disks and normal to slightly enhanced inner disk star formation rates, suggesting that intracluster medium-interstellar medium (ICM-ISM) stripping is the main mechanism causing the reduced star formation rates of Virgo spiral galaxies. Several of the truncated galaxies are peculiar, with enhanced central star formation rates, disturbed stellar disks, and barlike distributions of luminous H II complexes inside the central 1 kpc but no star formation beyond, suggesting that recent tidal interactions or minor mergers have also influenced their morphology. Two highly inclined H?-truncated spiral galaxies have numerous extraplanar H II regions and are likely in an active phase of ICM-ISM stripping. Several spiral galaxies have one-sided H? enhancements at the outer edge of their truncated H? disks, suggesting modest local enhancements in their star formation rates due to ICM-ISM interactions. Low-velocity tidal interactions and perhaps outer cluster H I accretion seem to be the triggers for enhanced global star formation in four Virgo galaxies. These results indicate that most Virgo spiral galaxies experience ICM-ISM stripping, many experience significant tidal effects, and many experience both.

Koopmann, Rebecca A.; Kenney, Jeffrey D. P.

2004-10-01

28

Mapping the Galactic Halo. VIII. Quantifying Substructure  

NASA Astrophysics Data System (ADS)

We have measured the amount of kinematic substructure in the Galactic halo using the final data set from the Spaghetti project, a pencil-beam high-latitude sky survey. Our sample contains 101 photometrically selected and spectroscopically confirmed giants with accurate distance, radial velocity, and metallicity information. We have developed a new clustering estimator: the "4distance" measure, which when applied to our data set leads to the identification of one group and seven pairs of clumped stars. The group, with six members, can confidently be matched to tidal debris of the Sagittarius dwarf galaxy. Two pairs match the properties of known Virgo structures. Using models of the disruption of Sagittarius in Galactic potentials with different degrees of dark halo flattening, we show that this favors a spherical or prolate halo shape, as demonstrated by Newberg et al. using the Sloan Digital Sky Survey data. One additional pair can be linked to older Sagittarius debris. We find that 20% of the stars in the Spaghetti data set are in substructures. From comparison with random data sets, we derive a very conservative lower limit of 10% to the amount of substructure in the halo. However, comparison to numerical simulations shows that our results are also consistent with a halo entirely built up from disrupted satellites, provided that the dominating features are relatively broad due to early merging or relatively heavy progenitor satellites.

Starkenburg, Else; Helmi, Amina; Morrison, Heather L.; Harding, Paul; van Woerden, Hugo; Mateo, Mario; Olszewski, Edward W.; Sivarani, Thirupathi; Norris, John E.; Freeman, Kenneth C.; Shectman, Stephen A.; Dohm-Palmer, R. C.; Frey, Lucy; Oravetz, Dan

2009-06-01

29

The Next Generation Virgo Cluster Survey. IV. NGC 4216: A Bombarded Spiral in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

The final stages of mass assembly of present-day massive galaxies are expected to occur through the accretion of multiple satellites. Cosmological simulations thus predict a high frequency of stellar streams resulting from this mass accretion around the massive galaxies in the Local Volume. Such tidal streams are difficult to observe, especially in dense cluster environments, where they are readily destroyed. We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird telescope. Using the deeper, higher-resolution, and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low surface brightness features and investigate their origin. The likely progenitors of the structures were identified as either already cataloged Virgo Cluster Catalog dwarfs or newly discovered satellites caught in the act of being destroyed. They have the same g - i color index and likely contain similar stellar populations. The alignment of three dwarfs along an apparently single stream is intriguing, and we cannot totally exclude that these are second-generation dwarf galaxies being born inside the filament from the debris of an original dwarf. The observed complex structures, including in particular a stream apparently emanating from a satellite of a satellite, point to a high rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster where NGC 4216 is located. We discuss the age of the interactions and whether they occurred in a group that is just falling into the cluster and shows signs of the so-called pre-processing before it gets affected by the cluster environment, or in a group which already ventured toward the central regions of Virgo Cluster. In any case, compared to the other spiral galaxies in the Virgo Cluster, but also to those located in lower density environments, NGC 4216 seems to suffer an unusually heavy bombardment. Further studies will be needed to determine whether, given the surface brightness limit of our survey, about 29 mag arcsec-2, the number of observed streams around that galaxy is as predicted by cosmological simulations or conversely, whether the possible lack of similar structures in other galaxies poses a challenge to the merger-based model of galaxy mass assembly. Based on observations obtained with MegaPrime/MegaCam, a joint project of Canada-France-Hawaii Telescope (CFHT) and CEA/DAPNIA, at the CFHT which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Paudel, Sanjaya; Duc, Pierre-Alain; Côté, Patrick; Cuillandre, Jean-Charles; Ferrarese, Laura; Ferriere, Etienne; Gwyn, Stephen D. J.; Mihos, J. Christopher; Vollmer, Bernd; Balogh, Michael L.; Carlberg, Ray G.; Boissier, Samuel; Boselli, Alessandro; Durrell, Patrick R.; Emsellem, Eric; MacArthur, Lauren A.; Mei, Simona; Michel-Dansac, Leo; van Driel, Wim

2013-04-01

30

Dynamic Structural Analysis with Substructures.  

National Technical Information Service (NTIS)

A method for dynamic structural analysis with substructures and the subspace iteration is developed. The method does not use component mode synthesis concepts. Therefore eigenproblem for each substructure is not solved. The method uses only substructural ...

J. S. Arora D. T. Nguyen

1978-01-01

31

WARM GAS IN THE VIRGO CLUSTER. I. DISTRIBUTION OF Ly{alpha} ABSORBERS  

SciTech Connect

The first systematic study of the warm gas (T = 10{sup 4-5} K) distribution across a galaxy cluster is presented using multiple background QSOs in and around the Virgo Cluster. We detect 25 Ly{alpha} absorbers (N{sub HI} = 10{sup 13.1-15.4} cm{sup -2}) in the Virgo velocity range toward 9 of 12 QSO sightlines observed with the Cosmic Origin Spectrograph, with a cluster impact parameter range of 0.36-1.65 Mpc (0.23-1.05 R{sub vir}). Including 18 Ly{alpha} absorbers previously detected by STIS or GHRS toward 7 of 11 background QSOs in and around the Virgo Cluster, we establish a sample of 43 absorbers toward a total of 23 background probes for studying the incidence of Ly{alpha} absorbers in and around the Virgo Cluster. With these absorbers, we find (1) warm gas is predominantly in the outskirts of the cluster and avoids the X-ray-detected hot intracluster medium (ICM). Also, Ly{alpha} absorption strength increases with cluster impact parameter. (2) Ly{alpha}-absorbing warm gas traces cold H I-emitting gas in the substructures of the Virgo Cluster. (3) Including the absorbers associated with the surrounding substructures, the warm gas covering fraction (100% for N{sub HI} > 10{sup 13.1} cm{sup -2}) is in agreement with cosmological simulations. We speculate that the observed warm gas is part of large-scale gas flows feeding the cluster both in the ICM and galaxies.

Yoon, Joo Heon; Putman, Mary E.; Bryan, Greg L. [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Thom, Christopher [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21211 (United States); Chen, Hsiao-Wen, E-mail: jhyoon@astro.columbia.edu [Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States)

2012-08-01

32

Halo Substructure and Milky Way Formation  

NASA Astrophysics Data System (ADS)

The accretion history of the Milky Way is partially encoded in its halo substructure. I describe the results of a systematic statistical search for elements of cold halo substructure (ECHOS) in the radial velocity distribution of stars in the inner halo of the Milky Way observed during the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. Radial velocity substructure is systematically older than surface brightness substructure (e.g., tidal streams), and therefore provides a direct measure of the accretion history of the Milky Way in a region and time interval that has yet to be fully explored. In addition, I measure average chemical abundance properties in both ECHOS and in the kinematically smooth inner halo stellar population. I find that ECHOS are unlikely to be disrupted globular clusters or ultrafaint dwarf spheroidal (dSph) galaxies, and there is evidence to suggest they are the debris of Mtot 109 solar mass dSph galaxy or galaxies. Spatial correlations in line of sight averaged abundance measurements in the smooth halo population indicate that the contribution of disrupted dSph galaxies to the smooth halo population increases with Galactocentric radius. This material is based upon work supported under a National Science Foundation Graduate Research Fellowship.

Schlaufman, Kevin

2011-01-01

33

Halo substructure and Milky Way formation  

NASA Astrophysics Data System (ADS)

The accretion history of the Milky Way is partially encoded in its halo substructure. I describe the results of a systematic statistical search for elements of cold halo substructure (ECHOS) in the radial velocity distribution of stars in the inner halo of the Milky Way observed during the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. Radial velocity substructure is systematically older than surface brightness substructure (e.g., tidal streams), and therefore provides a direct measure of the accretion history of the Milky Way in a region and time interval that has yet to be fully explored. I measure average chemical abundance properties in both ECHOS and in the kinematically smooth inner halo stellar population, and I find that ECHOS are unlikely to be disrupted globular clusters or ultrafaint dwarf spheroidal (dSph) galaxies. The chemical abundances of stars in ECHOS indicate that ECHOS are likely the debris of a Mtot ˜ 109 solar mass dSph galaxy or galaxies. Spatial autocorrelation in line of sight averaged abundance measurements in the smooth halo population indicates that the contribution of disrupted dSph galaxies to the smooth halo population increases with Galactocentric radius, becoming comparable to the classical smooth halo population at about 15 Galactocentric kpc.

Schlaufman, Kevin C.

34

Globular Cluster Systems in Dwarf Elliptical Galaxies. II. The Virgo Cluster  

Microsoft Academic Search

Deep R-band CFHT images for 8 dE,N and 3 dE galaxies in the Virgo Cluster have been used to search for globular cluster systems (GCSs) around these galaxies. Almost every galaxy studied shows an excess of stellar-like objects that indicate the presence of a GCS. The specific frequencies of the GCSs cover a wide range in values, but most appear

Patrick R. Durrell; William E. Harris; Doug Geisler; Ralph E. Pudritz

1996-01-01

35

Milky Way Substructure Catalogue and Detection of Potential New Dwarf Galaxy  

NASA Astrophysics Data System (ADS)

In order to facilitate the identification of new Milky Way halo substructures, We have created an online catalog of Milky Way substructures, including dwarf galaxies, globular clusters, stellar over-densities, tidal tails and stellar streams. The catalogue is located at: http://www.rpi.edu/ newbeh/mwstructure/MilkyWaySpheroidSubstructure.html. The vast majority of the substructures were discovered after 1995. In addition, We show evidence for the detection of a new, low-luminosity Milky Way dwarf galaxy in Sloan Digital Sky Survey (SDSS) data. The candidate dwarf galaxy is about 3.6 kpc from the Sun in the Hercules constellation. This work was supported by an NSF REU supplement, AST-08-32409 and AST 09-34538 and the NASA/NY Space Grant.

Dellomo, John

2010-01-01

36

GMOS Spectroscopy of Globular Clusters in Virgo and Fornax dEs  

NASA Astrophysics Data System (ADS)

We present preliminary results of a program to obtain ages, metallicities, and radial velocities of globular clusters (GCs) in dwarf elliptical galaxies and the Virgo and Fornax clusters using the GMOS instruments on the Gemini telescopes. Photometry of GCs in a large sample of dEs (Lotz et al. 2004) suggest that the globulars are old and metal-poor, like Milky Way globulars. However, the age-metallicity degeneracy in broad-band colors makes it difficult to distinguish old and intermediate-age stellar populations. We have now obtained spectra of GCs in four galaxies in the Virgo and Fornax clusters using GMOS-N and GMOS-S in order to derive ages and metallicities via line indices. Radial velocities will verify that the objects are GCs and may provide some kinematic information.

Miller, B.; Lotz, J.; Hilker, M.; Kissler-Patig, M.; Puzia, T.; Stiavelli, M.

2004-05-01

37

VIRGO: computational prediction of gene functions.  

PubMed

Dramatic advances in sequencing technology and sophisticated experimental assays that interrogate the cell, combined with the public availability of the resulting data, herald the era of systems biology. However, the biological functions of more than 40% of the genes in sequenced genomes are unknown, posing a fundamental barrier to progress in systems biology. The large scale and diversity of available data requires the development of techniques that can automatically utilize these datasets to make quantified and robust predictions of gene function that can be experimentally verified. We present a service called the VIRtual Gene Ontology (VIRGO) that (i) constructs a functional linkage network (FLN) from gene expression and molecular interaction data, (ii) labels genes in the FLN with their functional annotations in the Gene Ontology and (iii) systematically propagates these labels across the FLN in order to precisely predict the functions of unlabelled genes. VIRGO assigns confidence estimates to predicted functions so that a biologist can prioritize predictions for further experimental study. For each prediction, VIRGO also provides an informative 'propagation diagram' that traces the flow of information in the FLN that led to the prediction. VIRGO is available at http://whipple.cs.vt.edu:8080/virgo. PMID:16845022

Massjouni, Naveed; Rivera, Corban G; Murali, T M

2006-07-01

38

The WSRT virgo filament survey  

NASA Astrophysics Data System (ADS)

In the last few years, the realization has emerged that the universal baryons are almost equally distributed by mass in three components: (1) galactic concentrations, (2) a warm-hot intergalactic medium (WHIM) and (3) a diffuse intergalactic medium. These three components are predicted by hydrodynamical simulations and are probed by QSO absorption lines. To observe the WHIM in neutral hydrogen, observations are needed which are deeper than log(NHI) = 18. The WHIM should appear as a Cosmic Web, underlying the galaxies with higher column densities. We have used the WSRT to simulate a filled aperture by observing at very high hour angles, to reach very high column density sensitivity. To achieve even higher image fidelity, an accurate model of the WSRT primary beam was developed. This will be used in the joint deconvolution of the observations. To get a good overview of the distribution and kinematics of the Cosmic Web, a deep survey of 1500 square degrees of sky was undertaken, containing the galaxy filament extending between the Local Group and the Virgo Cluster. The auto-correlation data have been reduced and has an RMS of ?NHI = 4.2 × 1016 cm-2 over 20 km s-1. Several sources have been tentatively detected, which were previously unknown, as well as an indication for diffuse intergalactic filaments.

Popping, A.; Braun, R.

2007-02-01

39

Detecting dark matter substructure spectroscopically in strong gravitational lenses  

NASA Astrophysics Data System (ADS)

The cold dark matter (CDM) model for galaxy formation predicts that a significant fraction of mass in the dark matter haloes that surround L~L* galaxies is bound in substructures of mass 104-107 Msolar. The number of observable baryonic substructures (such as dwarf galaxies and globular clusters) falls short of these predictions by at least an order of magnitude. We present a method for searching for substructure in the haloes of gravitational lenses that produce multiple images of quasi-stellar objects (QSOs), such as four-image Einstein Cross lenses. Current methods based on broad-band flux ratios cannot cleanly distinguish between substructure, differential extinction, scattering in the radio by ionized regions in the lens galaxy, microlensing by stars and, most importantly, ambiguities in the host lens model. These difficulties may be overcome by utilizing the prediction that, when substructure is present, the magnification will be a function of source size. QSO broad-line and narrow-line emission regions are ~1 pc and >100 pc in size, respectively. The radio emission region is typically intermediate to these and the continuum emission region is much smaller. When narrow-line region (NLR) features are used as a normalization, the relative intensity and equivalent width of broad-line region (BLR) features will respectively reflect substructure-lensing and microlensing effects. Spectroscopic observations of just a few image pairs would probably be able to extract the desired substructure signature cleanly and distinguish it from microlensing - depending on the actual level of projected mass in substructure. In the rest-optical, the H?/[OIII] region is ideal, since the narrow wavelength range also largely eliminates differential reddening problems. In the rest-ultraviolet, the region longward of and including Ly? may also work. Simulations of Q2237+0305 are done as an example, to determine the level of substructure that is detectable in this way. Possible systematic difficulties are also discussed. This is an ideal experiment to be carried out with near-infrared integral field unit spectrographs on 8-m class telescopes, and will provide a fundamentally new probe of the internal structure of dark matter haloes.

Moustakas, Leonidas A.; Metcalf, R. Benton

2003-03-01

40

The Virgo Cluster Through The AGES  

NASA Astrophysics Data System (ADS)

I describe the final results of the Arecibo Galaxy Environment Survey in two regions of the Virgo Cluster. This blind HI survey reaches a sensitivity of 2E7 Msolar at 17Mpc. 364 sources are detected, of which 114 are cluster members. I describe the early-type galaxies detected in HI within the cluster as well as those detections without any obvious optical counterparts. I comment on the likelihood that these are features are tidal debris or so-called "dark galaxies". I compare the HI mass function from AGES and ALFALFA within the Virgo Cluster, and show that AGES detects significantly more low-mass objects.

Taylor, Rhys

2012-05-01

41

The First Generation of Virgo Cluster Dwarf Elliptical Galaxies?  

NASA Astrophysics Data System (ADS)

In the light of the question whether most early-type dwarf (dE) galaxies in clusters formed through infall and transformation of late-type progenitors, we search for an imprint of such an infall history in the oldest, most centrally concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no signatures of disks or central residual star formation. We select dEs in a (projected) region around the central elliptical galaxies, and subdivide them by their line-of-sight velocity into fast-moving and slow-moving ones. These subsamples turn out to have significantly different shapes: while the fast dEs are relatively flat objects, the slow dEs are nearly round. Likewise, when subdividing the central dEs by their projected axial ratio into flat and round ones, their distributions of line-of-sight velocities differ significantly: the flat dEs have a broad, possibly two-peaked distribution, whereas the round dEs show a narrow single peak. We conclude that the round dEs probably are on circularized orbits, while the flat dEs are still on more eccentric or radial orbits typical for an infalling population. In this picture, the round dEs would have resided in the cluster already for a long time, or would even be a cluster-born species, explaining their nearly circular orbits. They would thus be the first generation of Virgo cluster dEs. Their shape could be caused by dynamical heating through repeated tidal interactions. Further investigations through stellar population measurements and studies of simulated galaxy clusters would be desirable to obtain definite conclusions on their origin.

Lisker, Thorsten; Janz, Joachim; Hensler, Gerhard; Kim, Suk; Rey, Soo-Chang; Weinmann, Simone; Mastropietro, Chiara; Hielscher, Oliver; Paudel, Sanjaya; Kotulla, Ralf

2009-11-01

42

Atlas of Virgo galaxies (McDonald+ 2011)  

NASA Astrophysics Data System (ADS)

This database contains surface brightness profiles in the optical g, r, i, z bands and near-IR H-band for 286 Virgo cluster galaxies. This morphologically-complete sample spans a huge range in galaxy size, luminosity, surface brightness and stellar populations. These data have been used to study the luminosity and surface brightness distribution of Virgo cluster galaxies, in McDonald et al. (2009MNRAS.394.2022M). We find compelling evidence for bimodal populations in surface brightness, with both early- and late-type galaxies having a dearth of intermediate surface brightness galaxies. Most convincing is our confirmation of the result by Tully and Verheijen that the surface brightness of galaxy disks are strongly bimodal (1997ApJ...484..145T) The near-IR H-band data have been obtained from a variety of telescopes. We downloaded archival images for 31/286 and 84/286 bright galaxies from the 2MASS and GOLDMine online databases, respectively. The remaining 171 galaxies have new observations from the UH 2.2-m (130/286), CFHT (20/286) and UKIRT (21/286) telescopes. These data were all reduced in a homogeneous way, as outlined in our data paper. The optical g, r, i, z data were all obtained from the SDSS archives. Surface brightness profiles were extracted homogeneously from the optical and near-IR data following similar procedures, as outlined in our paper (2011MNRAS.414.2055M) The parametric and non-parametric parameters from bulge-disk decompositions of 285 optical griz and near-IR H-band surface brightness (SB) profiles are given in the bdd_* files in this directory. The profiles are stored in the "profg", "profr", "profi", "profz" and "prof_h" subdirectories, one for each color. (12 data files).

McDonald, M.; Courteau, S.; Tully, R. B.; Roediger, J.

2011-04-01

43

The Virgo Interferometer for Gravitational Wave Detection  

Microsoft Academic Search

The Virgo interferometer for gravitational wave detection is described. During the commissioning phase that followed the first scientific data taking run an unprecedented sensitivity was obtained in the range 10-60 Hz. Since then an upgrade program has begun, with the aim of increasing the sensitivity, mainly through the introduction of fused silica wires to suspend mirrors and by increasing the

T. Accadia; F. Acernese; F. Antonucci; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; Th. S. Bauer; M. G. Beker; A. Belletoile; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; C. Boccara; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D'Antonio; V. Dattilo; M. Davier; R. Day; R. De Rosa; G. Debreczeni; M. Del Prete; L. di Fiore; A. di Lieto; M. di Paolo Emilio; A. di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; J. Moreau; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2011-01-01

44

Mass and Substructure in Dwarf Spheroidal Galaxies  

NASA Astrophysics Data System (ADS)

I present results from a large spectroscopic survey of individual stars in dwarf spheroidal (dSph) galaxies, conducted using the Michigan/MIKE Fiber System (MMFS) at the Magellan Telescopes. dSph galaxies have come under intense scrutiny because they represent the lower extreme of the galaxy mass function, and thereby provide important constraints on models of structure formation. The proximity of the Milky Way's (MW's) dSph satellites allows us to study the resolved stellar populations of these systems in detail. Toward this end I have acquired MMFS spectra (5140-5180 Angstroms at resolution 20000) for more than 5000 stars in the MW dSphs Carina, Fornax, Sculptor, and Sextans. The spectra yield measurements of both radial velocity (median precision ± 1.8 km/s) and [Fe/H] metallicity (± 0.2 dex). I present radial velocity dispersion profiles for each dSph, as well as halo mass profiles derived using a variety of models and nonparametric estimation techniques. In some cases, the bulk stellar component is separable into populations following distinct distributions in position, kinematics, and chemistry, indicating a surprising level of complexity in these diminutive galaxies. Taking advantage of the fine spatial sampling of the MMFS data, I identify regions showing tentative evidence of localized chemo-dynamical substructure. This work is supported by grants from the National Science Foundation and the University of Michigan.

Walker, Matthew G.

2006-12-01

45

VIVA (VLA Imaging of Virgo in Atomic gas): H I Stripping in Virgo Galaxies  

NASA Astrophysics Data System (ADS)

We present results of a new Very Large Array survey of 53 Virgo galaxies (48 spirals and 5 dwarf/irregular systems). The goal is to study how the H I gas properties are affected by the cluster environment. The survey covers galaxies in a wide range of densities from the center of the cluster to more than 3 Mpc from M 87. The gas is imaged down to a column-density sensitivity of a few times 1019cm-2. We find examples of gas stripping at all stages. Within ˜0.5 Mpc from M 87, most galaxies are severely H I stripped. The H I disks are truncated to well within the optical disks. While the H I looks asymmetric, the outer stellar disks look undisturbed. The fact that only the gas and not the stars has been stripped suggests that those galaxies have been affected by the hot and dense cluster gas. Interestingly we also find a few truncated disks at large projected distances from the center. Although some of these may have been stripped while crossing the cluster core, a detailed population-synthesis study of the outer disk of one of these shows that star formation was terminated recently. The time since stripping is too short for the galaxy to have traveled from the core to its current location. So at least one galaxy has lost its gas from the outer disk by another mechanism than ram-pressure stripping in the dense cluster core. At intermediate- to low-density regions (>0.6 Mpc) we find H I tails with various lengths. We find seven galaxies with long one-sided H I tails pointing away from M 87. The galaxies are at 0.6-1 Mpc from M 87. Since these galaxies are only mildly H I deficient and the tails point away from M 87, these galaxies are probably falling into the cluster for the first time on highly radial orbits. For all but two of the galaxies the estimated ram pressure at their location in the cluster would be sufficient to pull out the H I in the very outer disks. One galaxy also looks optically disturbed and a simulation suggests that a combination of ram pressure plus a tidal interaction has pulled out the tail. In the outskirts of the cluster we find several examples of tidally interacting galaxies. We possibly see evidence for some accretion of gas as well. Lastly, the merging of subclusters with Virgo can cause bulk motions of the ICM. We see one example of a galaxy far out that appears to be ram-pressure stripped by a dynamic ICM. In summary, our results show that galaxies are already affected in the low-density outer regions of the cluster through ram-pressure stripping and tidal interactions, or a combination of both.

Chung, A.; van Gorkom, J. H.; Crowl, H.; Kenney, J. D. P.; Vollmer, B.

2008-08-01

46

Main-Sequence Star Populations in the Virgo Overdensity Region  

NASA Astrophysics Data System (ADS)

We present deep color-magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Overdensity (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g ? 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1^{+1.0}_{-1.1} Gyr, a median abundance of [Fe/H] = -0.70^{+0.15}_{-0.20} dex, and a heliocentric distance of 30.9 ± 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields (?? ? 265°, B ? ? 13°) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ~8.2 Gyr, and an abundance of [Fe/H] = -0.67^{+0.16}_{-0.12} dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0 ± 1.5 Gyr). They also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] ?-0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law & Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at ~9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42-53 kpc. At best there is only marginal evidence for the presence of these populations in our data. Our findings then suggest that while there are probably some Sgr debris stars present, the dominant stellar population in the VOD originates from a different halo structure that has an almost identical age and metallicity as some sections of the Sgr tidal stream. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Jerjen, H.; Da Costa, G. S.; Willman, B.; Tisserand, P.; Arimoto, N.; Okamoto, S.; Mateo, M.; Saviane, I.; Walsh, S.; Geha, M.; Jordán, A.; Olszewski, E.; Walker, M.; Zoccali, M.; Kroupa, P.

2013-05-01

47

Substructure Search by Set Reduction  

ERIC Educational Resources Information Center

|The set reduction algorithm is based on set theory and Boolean algebra rather than the graph-theoretic approach. Time trials with a small file of organic chemical structures indicate that the algorithm can be economically used for substructure (or complete structure) sequential searches on a file containing 30,000-50,000 computer-coded…

Figueras, John

1972-01-01

48

FSP: Frequent Substructure Pattern mining  

Microsoft Academic Search

Graphs have become increasingly important in modeling the complicated structures. Mining frequent subgraph patterns is an important research topic in graph mining that helps to analyze the structured database. It has been applied in many applications, such as chemistry, biology, computer networks, and world-wide web. In this paper, we propose a new algorithm called FSP (frequent substructure pattern mining), which

Shuguo Han; Wee Keong Ng; Yang Yu

2007-01-01

49

The Impact of Ram Pressure Stripping on Virgo Cluster Spirals  

NASA Astrophysics Data System (ADS)

In recent years, both observations and simulations have shown that ICM-ISM stripping is likely an important driver of galaxy evolution. In order to understand the impact of stripping on galaxy evolution, it is vital to determine how the multi-phase ISM behaves during stripping, how long it takes to strip a galaxy, and how stripping influences star formation. We present multi-wavelength studies of three Virgo Cluster spirals undergoing active ram pressure stripping, including two with HST imaging. We estimate timescales for various stripping-related processes in the galaxies and identify signatures of stripping in the galaxies’ ISM and star formation distributions. All three have undisturbed old stellar disks and show one-sided extraplanar ISM distributions. This extraplanar ISM hosts regions of ongoing and recent star formation that has taken place within the past few hundred Myr, with some regions significantly younger. The galaxy NGC 4330 has distinct leading and trailing sides, including a striking ISM “upturn” feature at the leading edge. There are significant differences between the galaxy’s optical, UV, H ?, and HI morphologies, and we use stellar population models to estimate that it has taken 200-400 Myr to strip the ISM from a radius of >8 to 5 kpc on the galaxy’s leading side. HST imaging reveals that NGC 4522 and NGC 4402 have GMC-mass dust clouds located outside of their main ISM truncation radii, showing that the most massive clouds can decouple from the rest of the ISM during stripping. Dust features with linear morphologies in both galaxies reveal the projected ICM wind direction. By identifying morphological characteristics related to the ram pressure stripping process, we constrain the physics of interactions between the ICM and the complex multi-phase ISM, and we provide a foundation for future observational and theoretical studies investigating the extent to which ICM-ISM interactions drive galaxy evolution.

Abramson, Anne; Kenney, J. D. P.

2011-01-01

50

Spitzer IR Colors and ISM Distributions of Virgo Cluster Spirals  

NASA Astrophysics Data System (ADS)

IRAC infrared images of 44 spiral and peculiar galaxies from the Spitzer Survey of the Virgo Cluster help reveal the interactions which transform galaxies in clusters. We explore how the location of galaxies in the IR 3.6-8?m color-magnitude diagram is related to the spatial distributions of ISM/star formation, as traced by PAH emission in the 8?m band. Based on their 8?m/PAH radial distributions, we divide the galaxies into 4 groups: normal, truncated, truncated/compact, and anemic. Normal galaxies have relatively normal PAH distributions. They are the "bluest" galaxies, with the largest 8/3.6?m ratios. They are relatively unaffected by the cluster environment, and have probably never passed through the cluster core. Truncated galaxies have a relatively normal 8?m/PAH surface brightness in the inner disk, but are abruptly truncated with little or no emission in the outer disk. They have intermediate ("green") colors, while those which are more severely truncated are "redder". Most truncated galaxies have undisturbed stellar disks and many show direct evidence of active ram pressure stripping. Truncated/compact galaxies have high 8?m/PAH surface brightness in the very inner disk (central 1 kpc) but are abruptly truncated close to center with little or no emission in the outer disk. They have intermediate global colors, similar to the other truncated galaxies. While they have the most extreme ISM truncation, they have vigorous circumnuclear star formation. Most of these have disturbed stellar disks, and they are probably produced by a combination of gravitational interaction plus ram pressure stripping. Anemic galaxies have a low 8?m/PAH surface brightness even in the inner disk. These are the "reddest" galaxies, with the smallest 8/3.6?m ratios. The origin of the anemics seems to a combination of starvation, gravitational interactions, and long-ago ram pressure stripping.

Kenney, Jeffrey D.; Wong, I.; Kenney, Z.; Murphy, E.; Helou, G.; Howell, J.

2012-01-01

51

The environmental impact of the Virgo Cluster on the evolution of dwarf irregular galaxies  

NASA Astrophysics Data System (ADS)

Dwarf galaxies are the greatest contributor to the total number of galaxies and most are believed to be systems consisting of matter in a near-primordial state. Containing H I gas and H II regions, dwarf irregular galaxies (dIs) can be used as test bodies to evaluate the impact of the environment on their evolution. Oxygen abundances relative to hydrogen within H II regions are a measure of how far the conversion of gas in the interstellar medium into stars has proceeded as a whole, as abundances do not vary significantly with galactocentric radius in dIs. Measurements of the [O III]?4363 emission line from H II region spectroscopy provide accurate probes of the electron temperature from which oxygen abundances are directly computed. The impact of the Virgo Cluster environment is investigated by comparing the properties of a set of Virgo dIs with those of a set of dIs in the field. To ensure accurate measures of luminosity and abundance, dIs in the field are chosen to have distance determinations from well-calibrated techniques and oxygen abundances derived from [O III]?4363 measurements. Spectroscopic data are obtained for H II regions in 11 dIs distributed in the central and outer regions of the Virgo Cluster. There is no systematic difference in oxygen abundance between field dIs and Virgo dIs at a given luminosity, showing that there is no detectable difference in their stellar populations. Oxygen abundances for field dIs are well correlated with the gas fraction in a way which shows definitively that evolution has been isolated, i.e., consistent with the “closed-box” model of chemical evolution. For the gas-poor dI UGC 7636 (VCC 1249), the oxygen abundance of a newly discovered intergalactic H II region is combined with the optical luminosity of the dI and the gas mass of the adjacent H I cloud (STET) to show that STET must have once been the interstellar medium of the dI. Tidal interactions of the dI with the elliptical NGC 4472 combined with ram-pressure stripping by the intracluster medium (ICM) best explain the observed properties of the detached cloud and the dI. A “staged” model is described to examine the chemical evolution of a gas-poor dI in the Virgo Cluster. Motivated by the observations, the model is characterized by three phases: isolated evolution, then sudden stripping which removes most of the gas, followed by a second stage of isolated evolution for the residual gas. The time since a typical stripping event is found to be approximately 1 Gyr or less. The GDIs for Virgo dIs correlate roughly with values of the projected X-ray surface brightness of the intracluster gas at the positions of the dIs. Thus, ram-pressure stripping best explains the observed gas-poor dIs in the Virgo sample. Together with the lack of significant fading, these observations suggest that dIs have recently encountered the ICM for the first time. A faded remnant of a gas-poor dI in Virgo will resemble a bright dE/dSph-like object like those presently seen in the cluster core. (Abstract shortened by UMI.)

Lee, Henry

52

Status and perspectives of the Virgo gravitational wave detector  

Microsoft Academic Search

Virgo is designed to detect gravitational waves of both astrophysical and cosmological origin in the frequency range from a few Hz to a few kHz. After the end of the first science run, partially overlapped with the LIGO fifth science run, the detector underwent several upgrades to improve its sensitivity. The second Virgo science run started at the beginning of

T. Accadia; F. Acernese; F. Antonucci; S. Aoudia; K. G. Arun; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; Th S. Bauer; M. G. Beker; A. Belletoile; S. Bigotta; S. Birindelli; M. A. Bizouard; M. Blom; C. Boccara; F. Bondu; L. Bonelli; R. Bonnand; L. Bosi; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D'Antonio; A. Dari; V. Dattilo; M. Davier; R. Day; R. De Rosa; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. Guidi; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; P. La Penna; N. Leroy; N. Letendre; T. G. F. Li; M. Lorenzini; V. Loriette; G. Losurdo; J.-M. Mackowski; E. Majorana; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; F. Menzinger; C. Michel; L. Milano; Y. Minenkov; M. Mohan; J. Moreau; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; O. Rabaste; D. S. Rabeling; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; E. Tournefier; F. Travasso; J. Trummer; G. Vajente; S. van der Putten; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2010-01-01

53

A state observer for the Virgo inverted pendulum  

Microsoft Academic Search

We report an application of Kalman filtering to the inverted pendulum (IP) of the Virgo gravitational wave interferometer. Using subspace method system identification techniques, we calculated a linear mechanical model of Virgo IP from experimental transfer functions. We then developed a Kalman filter, based on the obtained state space representation, that estimates from open loop time domain data, the state

T. Accadia; F. Acernese; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; A. Basti; Th. S. Bauer; M. Bebronne; M. G. Beker; A. Belletoile; M. A. Bizouard; M. Blom; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; M. Branchesi; T. Briant; A. Brillet; V. Brisson; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; O. Chaibi; E. Chassande-Mottin; A. Chincarini; A. Chiummo; F. Cleva; E. Coccia; P.-F. Cohadon; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Conte; A. Corsi; J.-P. Coulon; E. Cuoco; S. D'Antonio; V. Dattilo; M. Davier; R. Day; R. de Rosa; G. Debreczeni; W. Del Pozzo; M. Del Prete; L. di Fiore; A. di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; G. EndroCzi; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; L. A. Forte; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; A. Heidmann; H. Heitmann; P. Hello; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; N. Liguori; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; N. Morgado; A. Morgia; B. Mours; L. Naticchioni; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. Swinkels; M. Tacca; L. Taffarello; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; C. van den Broeck; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; S. Vitale; H. Vocca; R. L. Ward; M. Yvert; A. Zadrozny; J.-P. Zendri

2011-01-01

54

Noise from scattered light in Virgo's second science run data  

Microsoft Academic Search

Virgo is one of the large, ground-based interferometers aimed at detecting gravitational waves. One of the technical problems limiting its sensitivity is caused by light in the output beams which is backscattered by seismically excited surfaces and couples back into the main beam of the interferometer. The resulting noise was thoroughly studied, measured and mitigated before Virgo's second science run

T. Accadia; F. Acernese; F. Antonucci; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; Th S. Bauer; M. G. Beker; A. Belletoile; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D'Antonio; V. Dattilo; M. Davier; R. Day; R. De Rosa; G. Debreczeni; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. L. Swinkels; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2010-01-01

55

Performances of the Virgo interferometer longitudinal control system  

Microsoft Academic Search

The performances of the longitudinal sensing and control system of the Virgo gravitational wave detector are described. This system is able to stably maintain the RMS residual fluctuation of the interferometer longitudinal degrees of freedom around or below 10-11m, compatible with the original Virgo requirements. Moreover the detector sensitivity is not limited by longitudinal control noise at any frequency. Indeed

F. Acernese; F. Antonucci; S. Aoudia; K. G. Arun; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; Th. S. Bauer; M. G. Beker; S. Bigotta; S. Birindelli; M. A. Bizouard; M. Blom; C. Boccara; F. Bondu; L. Bonelli; L. Bosi; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; C. Corda; A. Corsi; J.-P. Coulon; E. Cuoco; S. D’Antonio; A. Dari; V. Dattilo; M. Davier; R. Day; R. De Rosa; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; L. Gammaitoni; F. Garufi; G. Gemme; E. Genin; A. Gennai; A. Giazotto; M. Granata; C. Greverie; G. Guidi; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; P. La Penna; N. Leroy; N. Letendre; T. G. F. Li; M. Lorenzini; V. Loriette; G. Losurdo; J.-M. Mackowski; E. Majorana; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; F. Menzinger; C. Michel; L. Milano; Y. Minenkov; M. Mohan; J. Moreau; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; O. Rabaste; D. S. Rabeling; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; F. Salemi; B. Sassolas; D. Sentenac; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; E. Tournefier; F. Travasso; J. Trummer; G. Vajente; S. van der Putten; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2010-01-01

56

Hot gas in Mach cones around Virgo cluster spiral galaxies  

Microsoft Academic Search

Context. The detailed comparison between observations and simulations of ram-pressure stripped spiral galaxies in the Virgo cluster has led to a 3D view of the galaxy orbits within the hot intracluster medium. The 3D velocities and Mach numbers derived from simulations can be used to derive simple Mach cone geometries for Virgo spiral galaxies. Aims: We search for indications of

M. Wezgowiec; B. Vollmer; M. Ehle; R.-J. Dettmar; D. J. Bomans; K. T. Chyzy; M. Urbanik; M. Soida

2011-01-01

57

FSP: Frequent Substructure Pattern Mining  

Microsoft Academic Search

Abstract—Graphs have become,increasingly important in modeling the complicated structures. Mining frequent subgraph patterns is an important research topic in graph mining that helps to analyze the structured database. It has been applied in many applications, such as chemistry, biology, computer networks, and World-Wide Web. In this paper, we propose a new algorithm called FSP (Frequent Substructure Pattern mining), which im-

Shuguo Han; Wee Keong; Ng Yang Yu

2007-01-01

58

Chemical Abundances in Virgo Spiral Galaxies. II. Effects of Cluster Environment  

Microsoft Academic Search

We present new measurements of chemical abundances in H II regions in spiral galaxies of the Virgo cluster and a comparison of Virgo galaxies and field spirals. With these new data there now exist nine Virgo spirals with abundance measurements for at least four H II regions. Our sample of Virgo galaxies ranges from H I deficient objects near the

Evan D. Skillman; Robert C. Kennicutt Jr.; Gregory A. Shields; Dennis Zaritsky

1996-01-01

59

Inertial control of the VIRGO superattenuator  

NASA Astrophysics Data System (ADS)

The VIRGO superattenuator (SA) is effective in depressing the seismic noise below the thermal noise level above 4 Hz. On the other hand, the residual mirror motion associated to the SA normal modes can saturate the dynamics of the interferometer locking system. This motion is reduced implementing a wideband (DC-5 Hz) multidimensional control (the so called inertial damping) which makes use of both accelerometers and position sensors and of a DSP system. Feedback forces are exerted by coil-magnet actuators on the top of the inverted pendulum. The inertial damping is successful in reducing the mirror motion within the requirements. The results are presented. .

Pisa; Florence VIRGO Groups,

2000-06-01

60

Star formation history of Virgo Cluster galaxies  

NASA Astrophysics Data System (ADS)

We propose to image in UV 25 carefully selected Virgo cluster galaxies. The goal is to study the impact of different environmental effects on the star formation history of the galaxies. Our sample is selected from Virgo spiral and peculiar galaxies brighter than 0.2L*, with a range of masses and morphologies in H alpha and HI. The galaxies are located in a wide range of local galaxy densities and show evidence for tidal interactions (harassment), merging and ICM-ISM interactions. By studying in detail individual galaxies which apparently are undergoing trauma of different kinds we hope to elucidate the physical mechanisms that cause the density-morphology, density-luminosity and mass-luminosity relation. Our sample consists of 41 galaxies. Excluding the 16 galaxies that are already done as part of the NGS, we propose to observe the remaining 25 galaxies with GALEX. We already have deep H alpha imaging for the entire sample and are currently carrying out a 15'' resolution deep HI imaging survey with the VLA. By combining H alpha, NUV and FUV images we can trace when, where and by how much the star formation rate has been enhanced or diminished during the last 1-100 Myrs. Since these are the very timescales on which dynamical and gas-gas interactions work, the data will greatly constrain the environmentally-driven evolution of these galaxies.

van Gorkom, Jacqueline

61

Fast Construction of Plant Architectural Models Based on Substructure Decomposition  

Microsoft Academic Search

Plant structure, representing the physical link among different organs, includes many similar substructures. In this paper, a new method is presented to construct plant architectural models of most plant species. The plant structure is decomposed into a stem, a set of lateral substructures and a terminal substructure, which is called substructure decomposition; then based on substructure decomposition, the plant structures

Hongping Yan; Philippe De Reffye; Chunhong Pan; Bao-gang Hu

2003-01-01

62

THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY  

SciTech Connect

The Next Generation Virgo Cluster Survey (NGVS) is a program that uses the 1 deg{sup 2} MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical imaging survey of the Virgo cluster, from its core to its virial radius-covering a total area of 104 deg{sup 2}-in the u*griz bandpasses. Thanks to a dedicated data acquisition strategy and processing pipeline, the NGVS reaches a point-source depth of g Almost-Equal-To 25.9 mag (10{sigma}) and a surface brightness limit of {mu}{sub g} {approx} 29 mag arcsec{sup -2} (2{sigma} above the mean sky level), thus superseding all previous optical studies of this benchmark galaxy cluster. In this paper, we give an overview of the technical aspects of the survey, such as areal coverage, field placement, choice of filters, limiting magnitudes, observing strategies, data processing and calibration pipelines, survey timeline, and data products. We also describe the primary scientific topics of the NGVS, which include: the galaxy luminosity and mass functions; the color-magnitude relation; galaxy scaling relations; compact stellar systems; galactic nuclei; the extragalactic distance scale; the large-scale environment of the cluster and its relationship to the Local Supercluster; diffuse light and the intracluster medium; galaxy interactions and evolutionary processes; and extragalactic star clusters. In addition, we describe a number of ancillary programs dealing with 'foreground' and 'background' science topics, including the study of high-inclination trans-Neptunian objects; the structure of the Galactic halo in the direction of the Virgo Overdensity and Sagittarius Stream; the measurement of cosmic shear, galaxy-galaxy, and cluster lensing; and the identification of distant galaxy clusters, and strong-lensing events.

Ferrarese, Laura; Cote, Patrick; Gwyn, S. D. J.; MacArthur, Lauren A.; McConnachie, Alan W.; Blakeslee, John P. [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC, V9E 2E7 (Canada); Cuillandre, Jean-Charles [Canada-France-Hawaii Telescope Corporation, Kamuela, HI 96743 (United States); Peng, Eric W. [Department of Astronomy, Peking University, Beijing 100871 (China); Duc, Pierre-Alain [AIM Paris Saclay, CNRS/INSU, CEA/Irfu, Universite Paris Diderot, Orme des Merisiers, F-91191 Gif sur Yvette cedex (France); Boselli, A. [Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS, 38 rue F. Joliot-Curie, F-13388 Marseille (France); Mei, Simona [GEPI, Observatoire de Paris, CNRS, 5 Place Jules Jannssen, F-92195 Meudon (France); Erben, Thomas [Argelander-Institut fuer Astronomie, University of Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany); Durrell, Patrick R. [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH (United States); Christopher Mihos, J. [Department of Astronomy, Case Western Reserve University, Cleveland, OH (United States); Jordan, Andres; Puzia, Thomas H. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, 7820436 Macul, Santiago (Chile); Lancon, Ariane [Observatoire Astronomique, Universite de Strasbourg and CNRS UMR 7550, 11 rue de l'Universite, F-67000 Strasbourg (France); Emsellem, Eric [Universite de Lyon 1, CRAL, Observatoire de Lyon, 9 av. Charles Andre, F-69230 Saint-Genis Laval (France); CNRS, UMR 5574, ENS de Lyon (France); Balogh, Michael L. [Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Van Waerbeke, Ludovic [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C., V6T 1Z1 (Canada); and others

2012-05-01

63

Mid-IR emission of galaxies in the Virgo cluster III. The data  

NASA Astrophysics Data System (ADS)

We present ISOCAM imaging data at 6.75 and 15 mu m for 145 galaxies in the Virgo cluster and in the Coma/A1367 supercluster. Of these, 99 form a complete, optically-selected, volume-limited sample including galaxies in the core and in the periphery of the Virgo cluster, suitable for statistical analysis. 34 of the Virgo galaxies were resolved by ISOCAM: for these objects we present mid-IR images, radial light and colour profiles, as well as effective and isophotal radii, surface brightness and light concentration indices. The mid-IR colours of the target galaxies show a weak trend with the H band luminosity, with values of F(6.75 mu m)/F(15 mu m) ge 1 found generally in massive objects (LH>=1010 LHsun), and F(6.75 mu m)/F(15 mu m) le 1 in low-mass (LH <= 1010 LHsun) dwarf galaxies. All early-type galaxies (type le S0a) have F(6.75 mu m)/F(15 mu m) ge 1, as expected when the mid-IR emission is dominated by the photosphere of the cold stellar population. The mid-IR, near-IR and visible light concentration indices of bright galaxies are tightly correlated with one another, indicating that the spatial distribution of the mid-IR emitting sources is, to the first order, similar to that of the stars. Figures 1 and 2, and Tables 1, 2, 4, 5 are only available in electronic form at http://www.edpsciences.org

Boselli, A.; Sauvage, M.; Lequeux, J.; Donati, A.; Gavazzi, G.

2003-08-01

64

The dispersion in the near-infrared surface brightness fluctuations in the Virgo cluster  

NASA Astrophysics Data System (ADS)

We observed NGC 3379 and nine Virgo elliptical galaxies at 2.16 micrometers using a NICMOS3 256 x 256 detector array. We have measured the surface brightness fluctuations in the K-band for all but one Virgo galaxy (an E/S0), thus extending the previous measurements in K by a factor of 3. We find for NGC 3379 that the apparent fluctuations magnitude (bar-m)K = 24.48 +/- 0.11, and we find no evidence at the 0.20 mag level for radial gradients in the apparent fluctuations magnitude. In the Virgo Cluster, we find that NGC 4365 has a similar fluctuation magnitude to the other galaxies in the sample, which is in contrast to previous I-band fluctuation observations which put it in the background W cloud. We also find an anomalous bright apparent fluctuation magnitude for the dwarf, low-surface brightness elliptical NGC 4489, which might be attributable to its lower signal-to-noise ratio (but is significant at the 3 sigma level) or to an unusual stellar population. The average fluctuation magnitude for the Virgo galaxies (excluding NGC 4489) is (bar-m)K = 25.16 +/- 0.18 with a 1 sigmarms dispersion of 0.25 mag. When we assume the distance moduli to these galaxies from I-band surface brightness fluctuation measurements, we find that for the sample of Virgo galaxies (excluding NGC 4365 and 4489), plus NGC 3379, M31, and M32 (the latter two from Luppino & Tonry 1993), the absolute fluctuation magnitude (bar-M)K = -5.74 +/- 0.18. We find an observed 1 sigmarms dispersion in the measurements of (bar-M)K of 0.20 magnitude, which is nearly that of our typical uncertainty of 0.18 mag in each measurement of (bar-M)K. The theoretical predictions of Worthey (1993) for (bar-M)K as a function of both (V-I) color and Mg2 index are shown to be consistent with the observations, differing only by +0.31 and -0.09 mag, respectively, from our mean measurement of (bar-M)K = -5.74 +/- 0.18. The simple stellar population models of Buzzoni (1993) are shown to be too faint in (bar-M)K by approximately 0.5 mag, which we suggest to be due to their exclusion of an empirically based M-giant population. We suggest that the origin of the dispersion in the measurement of (bar-M)K may be due to variations in metallicity; larger samples of early-type galaxies should be able to determine if there is such a relationship between metallicity and (bar-M)K. We present models of (bar-M)K based upon the addition to the stellar population of an anomalous asymptotic giant branch population contributing 10% of the light at 2 micrometers and show that this produces an absolute fluctuation magnitude 0.7 to 1.5 mag brighter. Such a population may be consistent with the observations of (bar-M)K in M32 by Luppino & Tonry (1993), but could only be present in NGC 4365 and 4489 of our sample, the two galaxies which are measured to have brighter (bar-m)K relative to (bar-m)I. Finally, we suggest that with the typically better seeing at the K band (compared with the optical), and with the brightness of the fluctuations at this wavelength, measurements of distances to greater redshifts are possible than with optical measurements of surface brightness fluctuations, although the problem of calibrating the relationship between (bar-M)K and (V-I) color or Mg2 index needs to be solved in order to reduce the uncertainties of such distance measurements.

Pahre, Michael A.; Mould, Jeremy R.

1994-10-01

65

Spitzer Observations of Environomental Effects on Virgo Cluster Galaxies  

NASA Astrophysics Data System (ADS)

We propose Spitzer MIPS and IRAC observations for a carefully selected sample of 36 Virgo cluster spiral and peculiar galaxies. The detailed information that Spitzer provides on the interstellar medium, star formation, and stellar populations, when combined with our considerable data base and simulations, will greatly improve our understanding of interactions in clusters and the consequences for galaxy evolution. For this sample, we already have VLA HI and radio continuum images from the VIVA survey, optical BVRH-alpha imaging, GALEX UV images, and optical spectroscopy. Mapping the unobscured distributions of star formation at 24um will reveal the effects of interactions, such as tidally triggered central starbursts, and ram-pressure induced star formation at the outer edges of stripped gas disks. We will compare the observed distributions of star formation with predictions from simulations which are already tightly constrained by the optical and HI data. The Spitzer 8um PAH images show outer galaxy ISM with a combination of sensitivity and resolution better than optical and HI images. This outer galaxy dust is a powerful tracer of the types of interactions and their timescales. Comparisons with B-I ``dust extinction'' maps will constrain interaction models by clarifying the ISM geometry. The near-IR data from IRAC, together with GALEX UV, H-alpha, and optical spectroscopy, will provide spatially-resolved star formation histories. Analyzing the expected variations in the radio-to-FIR ratio in extraplanar regions will also provide strong constraints on the physical processes which generally link these two emissions so tightly in star-forming galaxies. These galaxies are different from galaxies outside of clusters, since most of them have been significantly modified by their environment. The science goals are distinct from SINGS, although complementary, and would use the SINGS data as a benchmark for comparison with non-cluster galaxies.

Kenney, Jeffrey; Beck, Ranier; Helou, George; Makovoz, David; Murphy, Eric; Noriega-Crespo, Alberto; Schiminovich, David; Struck, Curtis; Vollmer, Bernd; van Gorkom, Jacqueline

2006-05-01

66

Insight into the Formation of the Milky Way through Cold Halo Substructure. II. The Elemental Abundances of ECHOS  

Microsoft Academic Search

We determine the average metallicities of the elements of cold halo substructure (ECHOS) that we previously identified in the inner halo of the Milky Way within 17.5 kpc of the Sun. As a population, we find that stars kinematically associated with ECHOS are chemically distinct from the background kinematically smooth inner halo stellar population along the same Sloan Extension for

Kevin C. Schlaufman; Constance M. Rockosi; Young Sun Lee; Timothy C. Beers; Carlos Allende Prieto

2011-01-01

67

Kinematic Properties as Probes of the Evolution of Dwarf Galaxies in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo Cluster and in the field, which show that 52% of the dEs (1) are rotationally supported, (2) exhibit structural signs of typical rotating systems such as disks, bars, or spiral arms, (3) are younger (~3 Gyr) than non-rotating dEs, and (4) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late-type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting disks are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment, and ram pressure stripping).

Toloba, E.; Boselli, A.; Gorgas, J.; Peletier, R. F.; Cenarro, A. J.; Gadotti, D. A.; Gil de Paz, A.; Pedraz, S.; Yildiz, U.

2009-12-01

68

Galactic Stellar Populations in the Era of the Sloan Digital Sky Survey and Other Large Surveys  

NASA Astrophysics Data System (ADS)

Studies of stellar populations, understood to mean collections of stars with common spatial, kinematic, chemical, and/or age distributions, have been reinvigorated during the past decade by the advent of large-area sky surveys such as the Sloan Digital Sky Survey, the Two-Micron All Sky Survey, the Radial Velocity Experiment, and others. We review recent analyses of these data that, together with theoretical and modeling advances, are revolutionizing our understanding of the nature of the Milky Way and galaxy formation and evolution in general. The formation of galaxies like the Milky Way was long thought to be a steady process leading to a smooth distribution of stars. However, the abundance of substructure in the multidimensional space of various observables, such as position, kinematics, and metallicity, is now proven beyond doubt and demonstrates the importance of mergers in the growth of galaxies. Unlike smooth models that involve simple components, the new data reviewed here clearly exhibit many irregular structures, such as the Sagittarius dwarf tidal stream and the Virgo and Pisces overdensities in the halo and the Monoceros stream closer to the Galactic plane. These recent developments have made it clear that the Milky Way is a complex and dynamic structure, one that is still being shaped by the merging of neighboring smaller galaxies. We also briefly discuss the next generation of wide-field sky surveys, such as SkyMapper, Panoramic Survey Telescope & Rapid Response System, Global Astrometric Interferometer for Astrophysics, and the Large Synoptic Survey Telescope, which will improve measurement precision manyfold and include billions of individual stars. The ultimate goal, development of a coherent and detailed story of the assembly and evolutionary history of the Milky Way and other large spirals like it, now appears well within reach.

Ivezi?, Željko; Beers, Timothy C.; Juri?, Mario

2012-09-01

69

RADIAL VELOCITIES OF GALACTIC HALO STARS IN VIRGO  

SciTech Connect

We present multi-slit radial velocity measurements for 111 stars in the direction of the Virgo Stellar Stream (VSS). The stars were photometrically selected to be probable main-sequence stars in the Galactic halo. When compared with the radial velocity distribution expected for the halo of the Milky Way, as well as the distribution seen in a control field, we observe a significant excess of negative velocity stars in the field, which can likely be attributed to the presence of a stellar stream. This kinematic excess peaks at a Galactic standard of rest radial velocity of -75 km s{sup -1}. A rough distance estimate suggests that this feature extends from {approx}15 kpc out to, and possibly beyond, the {approx}30 kpc limit of the study. The mean velocity of these stars is incompatible with those of the VSS itself (V{sub gsr} {approx} 130 km s{sup -1}), which we weakly detect, but it is consistent with radial velocity measurements of nearby 2MASS M-giants and SDSS+SEGUE K/M-giants and blue horizontal branch stars that constitute the leading tidal tail of the Sagittarius dwarf spheroidal galaxy. Some oblate models for the shape of the Milky Way's dark matter halo predict that the leading arm of the Sagittarius Stream should pass through this volume, and have highly negative (V{sub gsr} {approx}< -200 km s{sup -1}) radial velocities, as it descends down from the northern Galactic hemisphere toward the Galactic plane. The kinematic feature observed in this study, if it is in fact Sagittarius debris, is not consistent with these predictions, and instead, like other leading stream radial velocity measurements, is consistent with a recently published triaxial halo model, or, if axisymmetry is imposed, favors a prolate shape for the Galactic halo potential. However, a rough distance estimate to the observed kinematic feature places it somewhat closer (D {approx} 15-30 kpc) than the Sagittarius models predict (D {approx} 35-45 kpc).

Brink, Thomas G.; Mateo, Mario [Department of Astronomy, University of Michigan, 830 Dennison Building, Ann Arbor, MI 48109-1042 (United States); Martinez-Delgado, David, E-mail: tbrink@umich.ed, E-mail: mmateo@umich.ed [Max Planck Institut fuer Astronomie, Koenigstuhl 17, 69117, Heidelberg (Germany)

2010-11-15

70

Evolution of the spiral galaxies in the Virgo cluster  

SciTech Connect

Integrated Balmer emission line fluxes have been measured for 26 spiral galaxies in the core of the Virgo cluster. They are combined with published 21-cm and UBV color data in order to compare the disk properties of the cluster galaxies with galaxies in the field. Virgo spirals of a given Hubble type possess less star formation, less neutral hydrogen, and are redder than their field counterparts. Various possible selection effects are examined, but they cannot explain the differences. The relationships between color, M/sub H/ /L and H..cap alpha.. strengths, however, are indistinguishable in Virgo and the field. Some of the Virgo spirals may simply be normal spirals of slightly earlier type, but at least a few appear to be genuinely anemic galaxies, as suggested by van den Bergh.

Kennicutt, R.C. Jr.

1983-04-01

71

GALEX Ultraviolet Virgo Cluster Survey (GUViCS) (Boselli+, 2011)  

Microsoft Academic Search

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering ~40 sq. deg in the far UV (FUV, lambdaeff=1539Å, Deltalambda=442Å) and ~120 sq. deg in the near UV (NUV, lambdaeff=2316Å, Deltalambda=1060Å). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide

A. Boselli; S. Boissier; S. Heinis; L. Cortese; O. Ilbert; T. Hughes; O. Cucciati; J. Davies; L. Ferrarese; R. Giovanelli; M. P. Haynes; M. Baes; C. Balkowski; N. Brosch; S. C. Chapman; V. Charmandaris; M. S. Clemens; A. Dariush; I. de Looze; S. di Serego Alighieri; P.-A. Duc; P. R. Durrell; E. Emsellem; T. Erben; J. Fritz; D. A. Garcia-Appadoo; G. Gavazzi; M. Grossi; A. Jordan; K. M. Hess; L. K. Hunt; B. R. Kent; D. G. Lambas; A. Lancon; L. A. MacArthur; S. C. Madden; L. Magrini; S. Mei; E. Momjian; R. P. Olowin; E. Papastergis; M. W. L. Smith; J. M. Solanes; O. Spector; K. Spekkens; J. E. Taylor; C. Valotto; W. van Driel; J. Verstappen; C. Vlahakis; B. Vollmer; E. M. Xilouris

2011-01-01

72

Hubble Space Telescope IR Surface Brightness Fluctuation Color Measurements in the Virgo and Fornax Clusters  

NASA Astrophysics Data System (ADS)

We have measured infrared surface brightness fluctuations (SBF) in a sample of 16 elliptical, S0, and dwarf galaxies in the Virgo and Fornax clusters using the WFC3 IR channel on the Hubble Space Telescope. SBF measurements in the F110W and F160W filters were used to compute the fluctuation color, a distance-independent quantity that, when combined with stellar population models and optical SBF data from ACS, breaks the age-metallicity degeneracy and illuminates the star formation histories of these galaxies. We also present the F110W SBF absolute magnitude calibration as a function of optical (g-z) color, and compare the color dependence of that calibration to the F160W calibration that is commonly used for extragalactic distance measurements.

Jensen, Joseph B.; Boyer, N. E.; Blakeslee, J. P.; Lee, H.

2013-06-01

73

Morphological segregation of early-type galaxies in the Virgo cluster  

NASA Astrophysics Data System (ADS)

We present evidence for a morphological segregation of early-type galaxies with different isophote shapes in the Virgo cluster. Comparing local projected densities around galaxies, we find that, independently of their classification as elliptical or lenticular, galaxies with boxy isophotes are located in local density enhancements, while galaxies with discy isophotes lie in regions of lower local densities. This segregation is therefore not just the reflection of ordinary morphological segregation between elliptical and lenticular galaxies, and it shows that the property of galaxies that is more sensitive to the environment is the presence or not of a stellar disc, rather than the bulge-to-disco ratio (and therefore the classification as an E or an S0 galaxy).

Caon, N.; Einasto, M.

1995-04-01

74

Sextans' Cold Substructures as a Dynamical Judge: Core, Cusp, or MOND?  

NASA Astrophysics Data System (ADS)

The cold dark matter model predicts cuspy dark matter (DM) halos. However, it has been found that in some low-mass galaxies, cored dark halos provide a better description of their internal dynamics. Here we give constraints on the dark halo profile in the Sextans dwarf spheroidal galaxy by studying the longevity of two cold kinematic substructures detected in this galaxy. We perform N-body simulations of a stellar clump in the Sextans dwarf galaxy, including a live DM halo and the main stellar component. We find that if the dark halo is cuspy, stellar clumps orbiting with semi-major axis ?400 pc are disrupted in ~5 Gyr, even if the clump is initially as compact stellar cluster with a radius of rc = 5 pc. Stellar clusters in an initial orbit with semi-major axis <=250 pc may survive to dissolution, but their orbits decay toward the center by dynamical friction. In contrast, the stellar clumps can persist for a Hubble time within a cored DM halo, even if the initial clump's radius is as extended as rc = 80 pc. We also study the evolution of the clump in the MONDian context. In this scenario, we find that even an extended stellar clump with radius rc = 80 pc survives for a Hubble time, but an unrealistic value for the stellar mass-to-light ratio of 9.2 is needed.

Lora, V.; Grebel, E. K.; Sánchez-Salcedo, F. J.; Just, A.

2013-11-01

75

STELLAR POPULATION VARIATIONS IN THE MILKY WAY's STELLAR HALO  

SciTech Connect

If the stellar halos of disk galaxies are built up from the disruption of dwarf galaxies, models predict highly structured variations in the stellar populations within these halos. We test this prediction by studying the ratio of blue horizontal branch stars (BHB stars; more abundant in old, metal-poor populations) to main-sequence turn-off stars (MSTO stars; a feature of all populations) in the stellar halo of the Milky Way using data from the Sloan Digital Sky Survey. We develop and apply an improved technique to select BHB stars using ugr color information alone, yielding a sample of {approx}9000 g < 18 candidates where {approx}70% of them are BHB stars. We map the BHB/MSTO ratio across {approx}1/4 of the sky at the distance resolution permitted by the absolute magnitude distribution of MSTO stars. We find large variations of the BHB/MSTO star ratio in the stellar halo. Previously identified, stream-like halo structures have distinctive BHB/MSTO ratios, indicating different ages/metallicities. Some halo features, e.g., the low-latitude structure, appear to be almost completely devoid of BHB stars, whereas other structures appear to be rich in BHB stars. The Sagittarius tidal stream shows an apparent variation in the BHB/MSTO ratio along its extent, which we interpret in terms of population gradients within the progenitor dwarf galaxy. Our detection of coherent stellar population variations between different stellar halo substructures provides yet more support to cosmologically motivated models for stellar halo growth.

Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109 (United States); Xue Xiangxiang; Rix, Hans-Walter; Ruhland, Christine; Hogg, David W., E-mail: ericbell@umich.ed [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

2010-12-15

76

Substructure Discovery Using Minimum Description Length and Background Knowledge  

Microsoft Academic Search

The ability to identify interesting and repetitive substructures is an essential componentto discovering knowledge in structural data. We describe a new version of our Subdue substructure discovery system based on the minimum description length principle.The Subdue system discovers substructures that compress the original data and representstructural concepts in the data. By replacing previously-discovered substructures in thedata, multiple passes of Subdue

Diane J. Cook; Lawrence B. Holder

1994-01-01

77

Algebraic Sub-Structuring for Electromagnetic Applications  

SciTech Connect

Algebraic sub-structuring refers to the process of applying matrix reordering and partitioning algorithms to divide a large sparse matrix into smaller submatrices from which a subset of spectral components are extracted and combined to form approximate solutions to the original problem. In this paper, they show that algebraic sub-structuring can be effectively used to solve generalized eigenvalue problems arising from the finite element analysis of an accelerator structure.

Yang, C.; Gao, W.G.; Bai, Z.J.; Li, X.Y.S.; Lee, L.Q.; Husbands, P.; Ng, E.G.; /LBL, Berkeley /UC, Davis /SLAC

2006-06-30

78

Modeling Substructure in the Milky Way Galaxy  

NASA Astrophysics Data System (ADS)

We model substructure in the Milky Way halo using data taken from the five fields of the Deep Lens Survey (DLS). We select DLS objects that are consistent with the PSF to create color-magnitude Hess diagrams for each field. We observe significant substructure in at least two out of the five fields. To enhance the visibility of the substructure, we model and subtract the population of unresolved background galaxies, and subtract a smooth model of the Milky Way halo. This halo model is constructed by remapping the observed Hess diagram of stars in DLS Field 5 (F5), which has a smooth appearance. We use colors and absolute magnitudes from the Yonsei-Yale isochrones to create a map of distance modulus for main sequence stars in color-magnitude space for each DLS field. An Einasto model of the galaxy is used to predict the model density ratio of stars in each field as a function of distance modulus. The F5 Hess diagram is then multiplied by the model density ratio maps for F1 - F4 to yield semi-empirical model Hess diagrams. Subtracting these models from the observed Hess diagrams emphasizes the substructure of a given field. We fit simple models to the residual substructure in each DLS field using a Gaussian with three free parameters: distance of enhancement, depth along the LOS, and amplitude (i.e. strength). We discuss the use of this galaxy substructure model in calculating the overall density profile of the Milky Way.

Grishaw-Jones, Claire; Thorman, P.; Iyer, T.; Guhathakurta, P.; Deep Lens Survey Collaboration

2013-01-01

79

Solar-stellar connection: the frequency of maximum oscillation power from solar data  

NASA Astrophysics Data System (ADS)

Stellar oscillations provide powerful tools to derive stellar fundamental parameters such as the mass and radius. These global quantities are derived from scaling relations linking seismic quantities [?max and ?? to global stellar parameters. These relations use the Sun as a reference. In this work, we used VIRGO and GOLF data to study how the solar frequency at the maximum oscillation power (?max) varies with time along the solar cycle. We show that these variations imply differences of about 4% in radius and 12% in mass. We showed also that the observational method based on intensity or velocity data has also an impact, implying differences in mass of about 22% and 7% in radius.

Barban, C.; Beuret, M.; Baudin, F.; Belkacem, K.; Goupil, M. J.; Samadi, R.

2013-06-01

80

Lensing degeneracies and mass substructure  

NASA Astrophysics Data System (ADS)

The inversion of gravitational lens systems is hindered by the fact that multiple mass distributions are often equally compatible with the observed properties of the images. Besides using clear examples to illustrate the effect of the so-called monopole and mass-sheet degeneracies, this paper introduces the most general form of said mass-sheet degeneracy. While the well-known version of this degeneracy rescales a single source plane, this generalization allows any number of sources to be rescaled. Furthermore, it shows how it is possible to rescale each of those sources with a different scalefactor. Apart from illustrating that the mass-sheet degeneracy is not broken by the presence of multiple sources at different redshifts, it will become apparent that the newly constructed mass distribution necessarily alters the existing mass density precisely at the locations of the images in the lens system, and that this change in mass density is linked to the factors with which the sources were rescaled. Combined with the fact that the monopole degeneracy introduces a large amount of uncertainty about the density in between the images, this means that both degeneracies are in fact closely related to substructure in the mass distribution. An example of a simulated lensing situation based on an elliptical version of a Navarro-Frenk-White profile explicitly shows that such degeneracies are not easily broken by observational constraints, even when multiple sources are present. Instead, the fact that each lens inversion method makes certain assumptions, implicit or explicit, about the smoothness of the mass distribution means that in practice the degeneracies are broken in an artificial manner rather than by observed properties of the lens system.

Liesenborgs, J.; De Rijcke, S.

2012-09-01

81

Thermal effects and their compensation in Advanced Virgo  

NASA Astrophysics Data System (ADS)

Thermal effects in the test masses of the gravitational waves interferometric detectors may result in a strong limitation to their operation and sensitivity. Already in initial LIGO and Virgo, these effects have been observed and required the installation of dedicated compensation systems. Based on CO2 laser projectors, the thermal compensators heat the peripheral of the input test masses to reduce the lensing effect. In advanced detectors, the power circulating in the interferometer will increase, thus making thermal effects more relevant. In this paper, the concept of the compensation system for Advanced Virgo is described.

Rocchi, A.; Coccia, E.; Fafone, V.; Malvezzi, V.; Minenkov, Y.; Sperandio, L.

2012-06-01

82

Optical metrology tools for the Virgo projet  

NASA Astrophysics Data System (ADS)

For more than thirty years the search for gravitationnal waves, predicted by Einstein's relativistic theory of gravitation, has been an intense research field in experimental as well as theoretical physics. Today, with the constant advance of technology in optics, lasers, data analysis and processing, ... a promising way of directly detecting gravitationnal waves with earth-based instruments is optical interferometry. Before the end of this century many experiments will be carried on in Australia, Europe, Japan and the United States to detect the passage of a gravitationnal wave through giant Michelson-type interferometers. The effects predicted are so small, (a gravitationnal wave changes the length of three kilometer long arms by one thousandth of a fermi) that the need for “perfect” optical components is a key to the success of these experiments. Still a few years ago it would have been impossible to make optical components that would satisfy the required specifications for such interferometric detectors. For nearly ten years constant R&D efforts in optical coating manufacturing, optical material fabrication and optical metrology, allow us today to make such components. This text is intended to describe the field of optical metrology as it is needed for the testing of optical parts having performances far beyond than everything previously made. The first chapter is an introduction to gravitationnal waves, their sources and their effects on detectors. Starting by newtonian mechanics we jump rapidly to the general theory of relativity and describe particular solutions of Einstein's equations in the case of weak gravitationnal fields, which are periodic perturbations of the space-time metric in the form of plane waves, the so-called gravitationnal waves. We present various candidate sources, terrestrial and extra-terrestrial and give a short description of the two families of detectors: resonnant bars and optical interferometers. The second part of this chapter is a description of the various optical components that have to be manufactured and tested for Virgo. The next sections are dedicated to the description of various metrology instruments. In chapter 2 we focus on absorption of light in multilayer coatings. The sensitivity of interferometric detectors is degraded by this loss process, not only because it decreases the laser beam power, but also and chiefly because thermo-elastic deformations and changes of the indexes of refraction modify the beam profile. Optical coatings have now reached an absorption level lower than at m. We present a method based on the mirage effect, i.e. the deflexion of light by an index of refraction gradient induced by non homogeneous heating. This “mirage bench” has a sensitivity better than 10^{-8}. We start by a discussion of the approximations that are useful to simplify the problem, we then derive the equation that give the signal amplitude versus the absorption factor. Afterwards we describe the instrument and give a few results with home made Virgo mirrors as well as commercial samples. In the following chapter we discuss the problem of measuring reflexion factors. We focus on two particular problems, the first one is common, it is to measure high (higher than 0.9999) reflexion factors by the use of Fabry-Perot cavities. We present various possible schemes and we detail a particular one which seems to be the easiest to implement. We use a pulsed laser source and measure the average reflexion factor of the two Fabry-Perot mirrors by studying the pulse shape modification after transmission by the cavity. We estimate the sensitivity of this intrument to 10^{-6}. The second problem is a less common one and is to evaluate the relative homogeneity of reflexion factors on large components. Because inhomogeneities of this parameter will degrade the sensitivity of Virgo by coupling various modes of the laser beam with the fundamental one, homogeneity higher than 1{-}10^{-4} is required. We propose a simple scheme and describe a bench built following this scheme. This bench, being

Loriette, V.

83

The Next Generation Virgo Cluster Survey (NGVS). I. Introduction to the Survey  

NASA Astrophysics Data System (ADS)

The Next Generation Virgo Cluster Survey (NGVS) is a program that uses the 1 deg2 MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical imaging survey of the Virgo cluster, from its core to its virial radius—covering a total area of 104 deg2—in the u*griz bandpasses. Thanks to a dedicated data acquisition strategy and processing pipeline, the NGVS reaches a point-source depth of g ? 25.9 mag (10?) and a surface brightness limit of ? g ~ 29 mag arcsec-2 (2? above the mean sky level), thus superseding all previous optical studies of this benchmark galaxy cluster. In this paper, we give an overview of the technical aspects of the survey, such as areal coverage, field placement, choice of filters, limiting magnitudes, observing strategies, data processing and calibration pipelines, survey timeline, and data products. We also describe the primary scientific topics of the NGVS, which include: the galaxy luminosity and mass functions; the color-magnitude relation; galaxy scaling relations; compact stellar systems; galactic nuclei; the extragalactic distance scale; the large-scale environment of the cluster and its relationship to the Local Supercluster; diffuse light and the intracluster medium; galaxy interactions and evolutionary processes; and extragalactic star clusters. In addition, we describe a number of ancillary programs dealing with "foreground" and "background" science topics, including the study of high-inclination trans-Neptunian objects; the structure of the Galactic halo in the direction of the Virgo Overdensity and Sagittarius Stream; the measurement of cosmic shear, galaxy-galaxy, and cluster lensing; and the identification of distant galaxy clusters, and strong-lensing events. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France and the University of Hawaii.

Ferrarese, Laura; Côté, Patrick; Cuillandre, Jean-Charles; Gwyn, S. D. J.; Peng, Eric W.; MacArthur, Lauren A.; Duc, Pierre-Alain; Boselli, A.; Mei, Simona; Erben, Thomas; McConnachie, Alan W.; Durrell, Patrick R.; Mihos, J. Christopher; Jordán, Andrés; Lançon, Ariane; Puzia, Thomas H.; Emsellem, Eric; Balogh, Michael L.; Blakeslee, John P.; van Waerbeke, Ludovic; Gavazzi, Raphaël; Vollmer, Bernd; Kavelaars, J. J.; Woods, David; Ball, Nicholas M.; Boissier, S.; Courteau, Stéphane; Ferriere, E.; Gavazzi, G.; Hildebrandt, Hendrik; Hudelot, P.; Huertas-Company, M.; Liu, Chengze; McLaughlin, Dean; Mellier, Y.; Milkeraitis, Martha; Schade, David; Balkowski, Chantal; Bournaud, Frédéric; Carlberg, R. G.; Chapman, S. C.; Hoekstra, Henk; Peng, Chien; Sawicki, Marcin; Simard, Luc; Taylor, James E.; Tully, R. Brent; van Driel, Wim; Wilson, Christine D.; Burdullis, Todd; Mahoney, Billy; Manset, Nadine

2012-05-01

84

The Herschel Virgo Cluster Survey. XIII. Dust in early-type galaxies  

NASA Astrophysics Data System (ADS)

Aims: We study the dust content of a large optical input sample of 910 early-type galaxies (ETG) in the Virgo cluster, also extending to the dwarf ETG, and examine the results in relation to those on the other cold ISM components. Methods: We have searched for far-infrared emission in all galaxies in the input sample using the 250 ?m image of the Herschel Virgo Cluster Survey (HeViCS). This image covers a large fraction of the cluster with an area of ~55 square degrees. For the detected ETG we measured fluxes in five bands from 100 to 500 ?m, and estimated the dust mass and temperature with modified black-body fits. Results: Dust is detected above the completeness limit of 25.4 mJy at 250 ?m in 46 ETG, 43 of which are in the optically complete part of the input sample. In addition, dust is present at fainter levels in another six ETG. We detect dust in the four ETG with synchrotron emission, including M 87. Dust appears to be much more concentrated than stars and more luminous ETG have higher dust temperatures. Considering only the optically complete input sample and correcting for the contamination by background galaxies, dust detection rates down to the 25.4 mJy limit are 17% for ellipticals, about 40% for lenticulars (S0 + S0a), and around 3% for dwarf ETG. Dust mass does not correlate clearly with stellar mass and is often much greater than expected for a passive galaxy in a closed-box model. The dust-to-stars mass ratio anticorrelates with galaxy luminosity, and for some dwarf ETG reaches values as high as for dusty late-type galaxies. In the Virgo cluster slow rotators appear more likely to contain dust than fast ones. Comparing the dust results with those on Hi there are only eight ETG detected both in dust and in Hi in the HeViCS area; 39 have dust but only an upper limit on Hi, and eight have Hi but only an upper limit on dust. The locations of these galaxies in the cluster are different, with the dusty ETG concentrated in the densest regions, while the Hi rich ETG are at the periphery. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Table A.1 is available in electronic form at http://www.aanda.org

di Serego Alighieri, S.; Bianchi, S.; Pappalardo, C.; Zibetti, S.; Auld, R.; Baes, M.; Bendo, G.; Corbelli, E.; Davies, J. I.; Davis, T.; De Looze, I.; Fritz, J.; Gavazzi, G.; Giovanardi, C.; Grossi, M.; Hunt, L. K.; Magrini, L.; Pierini, D.; Xilouris, E. M.

2013-04-01

85

VLA IMAGING OF VIRGO SPIRALS IN ATOMIC GAS (VIVA). I. THE ATLAS AND THE H I PROPERTIES  

SciTech Connect

We present the results of a new VLA H I Imaging survey of Virgo galaxies, the VLA Imaging survey of Virgo galaxies in Atomic gas (VIVA). The survey includes high-resolution H I data of 53 carefully selected late type galaxies (48 spirals and five irregular systems). The goal is to study environmental effects on H I gas properties of cluster galaxies to understand which physical mechanisms affect galaxy evolution in different density regions, and to establish how far out the impact of the cluster reaches. As a dynamically young cluster, Virgo contains examples of galaxies experiencing a variety of environmental effects. Its nearness allows us to study each galaxy in great detail. We have selected Virgo galaxies with a range of star formation properties in low to high density regions (at projected distances from M87, d {sub 87} = 0.3-3.3 Mpc). Contrary to previous studies, more than half of the galaxies in the sample ({approx}60%) are fainter than 12 mag in B{sub T} . Overall, the selected galaxies represent the late type Virgo galaxies (S0/a to Sd/Irr) down to m{sub p} {approx}< 14.6 fairly well in morphological type, systemic velocity, subcluster membership, H I mass, and deficiency. The H I observations were done in C short (CS) configuration of the VLA radio telescope, with a typical spatial resolution of 15'' and a column density sensitivity of {approx}3-5 x 10{sup 19} cm{sup -2} in 3{sigma} per 10 km s{sup -1} channel. The survey was supplemented with data of comparable quality from the NRAO archive, taken in CS or C configuration. In this paper, we present H I channel maps, total intensity maps, velocity fields, velocity dispersions, global/radial profiles, position-velocity diagrams and overlays of H I/1.4 GHz continuum maps on the optical images. We also present H I properties such as total flux (S {sub HI}), H I mass (M {sub HI}), linewidths (W{sub 20} and W{sub 50}), velocity (V{sub HI}), deficiency (def{sub HI}), and size (D {sup eff}{sub HI} and D {sup iso}{sub HI}), and describe the H I morphology and kinematics of individual galaxies in detail. The survey has revealed details of H I features that were never seen before. In this paper, we briefly discuss differences in typical H I morphology for galaxies in regions of different galaxy densities. We confirm that galaxies near the cluster core (d {sub 87} {approx}< 0.5 Mpc) have H I disks that are smaller compared to their stellar disks (D{sub HI}/D{sub 25} < 0.5). Most of these galaxies in the core also show gas displaced from the disk, which is either currently being stripped or falling back after a stripping event. At intermediate distances (d{sub 87} {approx} 1 Mpc) from the center, we find a remarkable number of galaxies with long one-sided H I tails pointing away from M87. In a previous letter, we argue that these galaxies are recent arrivals, falling into the Virgo core for the first time. In the outskirts, we find many gas-rich galaxies, with gas disks extending far beyond their optical disks. Interestingly, we also find some galaxies with H I disks that are smaller compared to their stellar disks at large clustercentric distances.

Chung, Aeree; Van Gorkom, J. H. [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Kenney, Jeffrey D. P.; Crowl, Hugh [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Vollmer, Bernd [Observatoire astronomique de Strasbourg, 11 rue de l'universite, 67000 Strasbourg (France)], E-mail: achung@aoc.nrao.edu, E-mail: jvangork@astro.columbia.edu, E-mail: kenney@astro.yale.edu, E-mail: hugh@astro.yale.edu, E-mail: hugh@astro.umass.edu, E-mail: bvollmer@astro.u-strasbg.fr

2009-12-15

86

THE NORTHERN WRAPS OF THE SAGITTARIUS STREAM AS TRACED BY RED CLUMP STARS: DISTANCES, INTRINSIC WIDTHS, AND STELLAR DENSITIES  

SciTech Connect

We trace the tidal Stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Red Clump (RC) stars from the catalog of the Sloan Digital Sky Survey-Data Release 6, in the range 150{sup 0} {approx}< R.A. {approx}< 220{sup 0}, corresponding to the range of orbital azimuth 220{sup 0} {approx}< {Lambda} {approx}< 290{sup 0}. Substructures along the line of sight (los) are identified as significant peaks in the differential star count profiles (SCPs) of candidate RC stars. A proper modeling of the SCPs allows us to obtain (1) {<=}10% accurate, purely differential distances with respect to the main body of Sgr, (2) estimates of the FWHM along the los, and (3) estimates of the local density, for each detected substructure. In the range 255{sup 0} {approx}< {Lambda} {approx}< 290{sup 0} we cleanly and continuously trace various coherent structures that can be ascribed to the Stream, in particular: the well-known northern portion of the leading arm, running from d {approx_equal} 43 kpc at {Lambda} {approx_equal} 290{sup 0} to d {approx_equal} 30 kpc at {Lambda} {approx_equal} 255{sup 0}, and a more nearby coherent series of detections lying at a constant distance d {approx_equal} 25 kpc, that can be identified with a wrap of the trailing arm. The latter structure, predicted by several models of the disruption of Sgr dSph, was never traced before; comparison with existing models indicates that the difference in distance between these portions of the leading and trailing arms may provide a powerful tool to discriminate between theoretical models assuming different shapes of the Galactic potential. A further, more distant wrap in the same portion of the sky is detected only along a couple of los. For {Lambda} {approx}< 255{sup 0} the detected structures are more complex and less easily interpreted. We are confident of being able to trace the continuation of the leading arm down to {Lambda} {approx_equal} 220{sup 0} and d {approx_equal} 20 kpc; the trailing arm is seen up to {Lambda} {approx_equal} 240{sup 0} where it is replaced by more distant structures. Possible detections of more nearby wraps and of the Virgo Stellar Stream are also discussed. These measured properties provide a coherent set of observational constraints for the next generation of theoretical models of the disruption of Sgr.

Correnti, M.; Ferraro, F. R. [Dipartimento di Astronomia, Universita di Bologna, via Ranzani 1, 40127 Bologna (Italy); Bellazzini, M. [INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna (Italy); Ibata, R. A.; Varghese, A., E-mail: matteo.correnti@studio.unibo.i [Observatoire Astronomique, Universite de Strasbourg, CNRS, 11, rue de l'Universite, F-67000 Strasbourg (France)

2010-09-20

87

Noise monitor tools and their application to Virgo data  

Microsoft Academic Search

The understanding of noise in interferometric gravitational wave detectors is fundamental in terms of both enabling prompt reactions in the mitigation of noise disturbances and in the establishment of appropriate data-cleaning strategies. Monitoring tools to perform online and offline noise analysis in areas such as transient signal detection, line identification algorithms and coherence are used to characterise the Virgo detector

T Accadia; F Acernese; M Agathos; P Astone; G Ballardin; F Barone; M Barsuglia; A Basti; Th S Bauer; M Bebronne; M Bejger; M G Beker; M Bitossi; M A Bizouard; M Blom; F Bondu; L Bonelli; R Bonnand; V Boschi; L Bosi; B Bouhou; S Braccini; C Bradaschia; M Branchesi; Gabriel chardin T Briant; A Brillet; V Brisson; T Bulik; H J Bulten; D Buskulic; C Buy; E Calloni; B Canuel; F Carbognani; F Cavalier; R Cavalieri; G Cella; E Cesarini; O Chaibi; E Chassande-Mottin; A Chincarini; A Chiummo; F Cleva; E Coccia; P-F Cohadon; C N Colacino; J Colas; A Colla; M Colombini; A Conte; J-P Coulon; E Cuoco; S D'Antonio; V Dattilo; M Davier; R Day; R De Rosa; G Debreczeni; W Del Pozzo; L Di Fiore; A Di Lieto; M Di Paolo Emilio; A Di Virgilio; A Dietz; M Drago; G Endröczi; V Fafone; I Ferrante; F Fidecaro; I Fiori; R Flaminio; L A Forte; J-D Fournier; J Franc; S Franco; S Frasca; F Frasconi; M Galimberti; L Gammaitoni; F Garufi; M E Gáspár; G Gemme; E Genin; A Gennai; A Giazotto; R Gouaty; M Granata; C Greverie; G M Guidi; J-F Hayau; A Heidmann; H Heitmann; P Hello; G Hemming; P Jaranowski; R J G Jonker; M Kasprzack; I Kowalska; A Królak; N Leroy; N Letendre; T G F Li; N Liguori; M Lorenzini; V Loriette; G Losurdo; E Majorana; I Maksimovic; V Malvezzi; N Man; M Mantovani; F Marchesoni; F Marion; J Marque; F Martelli; A Masserot; C Michel; L Milano; Y Minenkov; M Mohan; N Morgado; A Morgia; S Mosca; B Mours; L Naticchioni; F Nocera; L Palladino; C Palomba; F Paoletti; R Paoletti; M Parisi; A Pasqualetti; R Passaquieti; D Passuello; G Persichetti; F Piergiovanni; M Pietka; L Pinard; R Poggiani; M Prato; G A Prodi; M Punturo; P Puppo; D S Rabeling; I Racz; P Rapagnani; V Re; T Regimbau; F Ricci; F Robinet; A Rocchi; L Rolland; R Romano; D Rosi?ska; P Ruggi; B Sassolas; D Sentenac; L Sperandio; R Sturani; B Swinkels; M Tacca; L Taffarello; A P M ter Braack; A Toncelli; M Tonelli; O Torre; E Tournefier; F Travasso; G Vajente; C Van Den Broeck; S van der Putten; M Vasuth; M Vavoulidis; G Vedovato; D Verkindt; F Vetrano; A Viceré; J-Y Vinet; S Vitale; H Vocca; R L Ward; K Yamamoto; M Yvert; A Zadro?ny; J-P Zendri

2012-01-01

88

Measurements of Superattenuator seismic isolation by Virgo interferometer  

Microsoft Academic Search

Each mirror of the interferometric gravitational wave antenna Virgo is attached to a Superattenuator, a chain of mechanical filters designed to suppress seismic vibrations, starting from a few Hz. The filter chain attenuation has been measured by exciting its suspension point with sinuisodal forces and using the interferometer as sensor. The attenuation, measured at different frequencies, is compliant with the

F. Acernese; F. Antonucci; S. Aoudia; K. G. Arun; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; Th. S. Bauer; M. G. Beker; S. Bigotta; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; C. Boccara; F. Bondu; L. Bonelli; L. Bosi; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; C. Corda; A. Corsi; J.-P. Coulon; E. Cuoco; S. D’Antonio; A. Dari; V. Dattilo; M. Davier; R. Day; R. De Rosa; M. Del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; L. Gammaitoni; F. Garufi; G. Gemme; E. Genin; A. Gennai; A. Giazotto; M. Granata; C. Greverie; G. Guidi; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; P. La Penna; N. Leroy; N. Letendre; T. G. F. Li; M. Lorenzini; V. Loriette; G. Losurdo; J.-M. Mackowski; E. Majorana; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; F. Menzinger; C. Michel; L. Milano; Y. Minenkov; M. Mohan; J. Moreau; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; O. Rabaste; D. S. Rabeling; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; F. Salemi; B. Sassolas; D. Sentenac; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; E. Tournefier; F. Travasso; J. Trummer; G. Vajente; S. van der Putten; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2010-01-01

89

Virgo: a laser interferometer to detect gravitational waves  

Microsoft Academic Search

This paper presents a complete description of Virgo, the French-Italian gravitational wave detector. The detector, built at Cascina, near Pisa (Italy), is a very large Michelson interferometer, with 3 km-long arms. In this paper, following a presentation of the physics requirements, leading to the specifications for the construction of the detector, a detailed description of all its different elements is

T Accadia; F Acernese; M Alshourbagy; P Amico; F Antonucci; S Aoudia; N Arnaud; C Arnault; K G Arun; P Astone; S Avino; D Babusci; G Ballardin; F Barone; G Barrand; L Barsotti; M Barsuglia; A Basti; Th S Bauer; F Beauville; M Bebronne; M Bejger; M G Beker; F Bellachia; A Belletoile; J L Beney; M Bernardini; S Bigotta; R Bilhaut; S Birindelli; M Bitossi; M A Bizouard; M Blom; C Boccara; D Boget; F Bondu; L Bonelli; R Bonnand; V Boschi; L Bosi; T Bouedo; B Bouhou; A Bozzi; L Bracci; S Braccini; C Bradaschia; M Branchesi; T Briant; A Brillet; V Brisson; L Brocco; T Bulik; H J Bulten; D Buskulic; C Buy; G Cagnoli; G Calamai; E Calloni; E Campagna; B Canuel; F Carbognani; L Carbone; F Cavalier; R Cavalieri; R Cecchi; G Cella; E Cesarini; E Chassande-Mottin; S Chatterji; R Chiche; A Chincarini; A Chiummo; N Christensen; A C Clapson; F Cleva; E Coccia; P-F Cohadon; C N Colacino; J Colas; A Colla; M Colombini; G Conforto; A Corsi; S Cortese; F Cottone; J-P Coulon; E Cuoco; S DAntonio; G Daguin; A Dari; V Dattilo; P Y David; M Davier; R Day; G Debreczeni; G De Carolis; M Dehamme; R Del Fabbro; W Del Pozzo; M del Prete; L Derome; R De Rosa; R DeSalvo; M Dialinas; L Di Fiore; A Di Lieto; M Di Paolo Emilio; A Di Virgilio; A Dietz; M Doets; P Dominici; A Dominjon; M Drago; C Drezen; B Dujardin; B Dulach; C Eder; A Eleuteri; D Enard; M Evans; L Fabbroni; V Fafone; H Fang; I Ferrante; F Fidecaro; I Fiori; R Flaminio; D Forest; L A Forte; J-D Fournier; L Fournier; J Franc; O Francois; S Frasca; F Frasconi; A Freise; A Gaddi; M Galimberti; L Gammaitoni; P Ganau; C Garnier; F Garufi; M E Gáspár; G Gemme; E Genin; A Gennai; G Gennaro; L Giacobone; A Giazotto; G Giordano; L Giordano; C Girard; R Gouaty; A Grado; M Granata; V Granata; X Grave; C Greverie; H Groenstege; G M Guidi; S Hamdani; J-F Hayau; S Hebri; A Heidmann; H Heitmann; P Hello; G Hemming; E Hennes; R Hermel; P Heusse; L Holloway; D Huet; M Iannarelli; P Jaranowski; D Jehanno; L Journet; S Karkar; T Ketel; H Voet; J Kovalik; I Kowalska; S Kreckelbergh; A Krolak; J C Lacotte; B Lagrange; P La Penna; M Laval; J C Le Marec; N Leroy; N Letendre; T G F Li; B Lieunard; N Liguori; O Lodygensky; B Lopez; M Lorenzini; V Loriette; G Losurdo; M Loupias; J M Mackowski; T Maiani; E Majorana; C Magazzù; I Maksimovic; V Malvezzi; N Man; S Mancini; B Mansoux; M Mantovani; F Marchesoni; F Marion; P Marin; J Marque; F Martelli; A Masserot; L Massonnet; G Matone; L Matone; M Mazzoni; F Menzinger; C Michel; L Milano; Y Minenkov; S Mitra; M Mohan; J-L Montorio; R Morand; F Moreau; J Moreau; N Morgado; A Morgia; S Mosca; V Moscatelli; B Mours; P Mugnier; F-A Mul; L Naticchioni; I Neri; F Nocera; E Pacaud; G Pagliaroli; A Pai; L Palladino; C Palomba; F Paoletti; R Paoletti; A Paoli; S Pardi; G Parguez; M Parisi; A Pasqualetti; R Passaquieti; D Passuello; M Perciballi; B Perniola; G Persichetti; S Petit; M Pichot; F Piergiovanni; M Pietka; R Pignard; L Pinard; R Poggiani; P Popolizio; T Pradier; M Prato; G A Prodi; M Punturo; P Puppo; K Qipiani; O Rabaste; D S Rabeling; I Rácz; F Raffaelli; P Rapagnani; S Rapisarda; V Re; A Reboux; T Regimbau; V Reita; A Remilleux; F Ricci; I Ricciardi; F Richard; M Ripepe; F Robinet; A Rocchi; L Rolland; R Romano; D Rosi?ska; P Roudier; P Ruggi; G Russo; L Salconi; V Sannibale; B Sassolas; D Sentenac; S Solimeno; R Sottile; L Sperandio; R Stanga; R Sturani; B Swinkels; M Tacca; R Taddei; L Taffarello; M Tarallo; S Tissot; A Toncelli; M Tonelli; O Torre; E Tournefier; F Travasso; C Tremola; E Turri; G Vajente; C Van Den Broeck; S van der Putten; M Vasuth; M Vavoulidis; G Vedovato; D Verkindt; F Vetrano; O Véziant; A Viceré; J-Y Vinet; S Vilalte; S Vitale; H Vocca; R L Ward; K Yamamoto; M Yvert; J-P Zendri; Z Zhang

2012-01-01

90

Software engineering for the Virgo project at EGO  

Microsoft Academic Search

The VIRGO Gravitational Waves Detector is continuing its commissioning phase. An important element in this phase is the application of Software Engineering (SE) practices to the Control and Data Analysis Software. This article focuses on the most recent achievements in applying and evolving those SE practices as a simple but effective set of standards and tools. The main areas covered

F. Acernese; P. Amico; M. Alshourbagy; S. Aoudia; S. Avino; D. Babusci; G. Ballardin; F. Barone; L. Barsotti; M. Barsuglia; F. Beauville; M. A. Bizouard; C. Boccara; F. Bondu; L. Bosi; C. Bradaschia; S. Birindelli; S. Braccini; A. Brillet; V. Brisson; L. Brocco; D. Buskulic; E. Calloni; E. Campagna; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Chassande-Mottin; C. Corda; J. P. Coulon; E. Cuoco; V. Dattilo; M. Davier; R. de Rosa; L. di Fiore; A. di Virgilio; B. Dujardin; A. Eleuteri; D. Enard; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; O. Francois; S. Frasca; F. Frasconi; A. Freise; L. Gammaitoni; A. Gennai; A. Giazotto; G. Giordano; L. Giordano; R. Gouaty; D. Grosjean; G. Guidi; S.. Hebri; H. Heitmann; P. Hello; L. Holloway; S. Karkar; S. Kreckelbergh; P. La Penna; N. Letendre; V. Loriette; M. Loupias; G. Losurdo; C. N. Man; M. Mantovani; F. Marchesoni; J. Marque; F. Martelli; A. Masserot; M. Mazzoni; L. Milano; C. Moins; J. Moreau; N. Morgado; B. Mours; A. Pai; C. Palomba; F. Paoletti; S. Pardi; A. Pasqualetti; R. Passaquieti; D. Passuello; B. Perniola; F. Piergiovanni; L. Pinard; R. Poggiani; M. Punturo; P. Puppo; V. Reita; A. Remillieux; F. Ricci; I. Ricciardi; P. Ruggi; G. Russo; S. Solimeno; A. Spallicci; R. Stanga; R. Taddei; M. Tonelli; A. Toncelli; E. Tournefier; F. Travasso; G. Vajente; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert; Z. Zhang; J. D. Wet

2005-01-01

91

Software engineering practices for the EGO Virgo project  

Microsoft Academic Search

The Virgo Gravitational Waves Detector has recently entered its commissioning phase. An important element in this phase is the application of Software Engineering (SE) practices to the Control and Data Analysis Software. This article focus on the experience in applying those SE practices as a simple but effective set of standards and tools. The main areas covered are software configuration

Franco Carbognani; Jacques de Wet

2004-01-01

92

Do allopatric male Calopteryx virgo damselflies learn species recognition?  

PubMed

There is a growing amount of empirical evidence that premating reproductive isolation of two closely related species can be reinforced by natural selection arising from avoidance of maladaptive hybridization. However, as an alternative for this popular reinforcement theory, it has been suggested that learning to prefer conspecifics or to discriminate heterospecifics could cause a similar pattern of reinforced premating isolation, but this possibility is much less studied. Here, we report results of a field experiment in which we examined (i) whether allopatric Calopteryx virgo damselfly males that have not encountered heterospecific females of the congener C. splendens initially show discrimination, and (ii) whether C. virgo males learn to discriminate heterospecifics or learn to associate with conspecifics during repeated experimental presentation of females. Our experiment revealed that there was a statistically nonsignificant tendency for C. virgo males to show initial discrimination against heterospecific females but because we did not use sexually naïve individuals in our experiment, we were not able to separate the effect of innate or associative learning. More importantly, however, our study revealed that species discrimination might be further strengthened by learning, especially so that C. virgo males increase their association with conspecific females during repeated presentation trials. The role of learning to discriminate C. splendens females was less clear. We conclude that learning might play a role in species recognition also when individuals are not naïve but have already encountered potential conspecific mates. PMID:22822438

Kuitunen, Katja; Haukilehto, Elina; Raatikainen, Kaisa J; Hakkarainen, Hanne; Miettinen, Minna; Högmander, Harri; Kotiaho, Janne S

2012-03-01

93

Galaxy Properties and Substructure in the Cluster Abell 160  

NASA Astrophysics Data System (ADS)

We continue development of a procedure for building a large catalog of cluster galaxies and their photometric properties, as measured with CCDs. Our first case, Abell 160, is relatively nearby and we have already obtained spectroscopic redshifts for its brightest galaxies. We have mosaiced this cluster in R and V filters using a CCD imager on the 1.3-meter McGraw-Hill telescope. For each CCD frame we fit a WCS (world coordinate system), remove bright cosmic rays, and extract sources using ``SExtractor.'' We create software for merging source catalogs in such a way as to reject residual cosmic rays and other invalid sources, and to combine redundant measurements without double counting. The measured properties include magnitude, ellipticity, position angle, size, and color (V-R). We compare our data to those of the HST (Hubble Space Telescope) and SDSS (Sloan Digital Sky Survey) archives to examine the accuracy of our star/galaxy separation and our color measurements. For our substructure investigation, we draw several subsamples of galaxies based on stellarity index, color (the color-magnitude relation), magnitude and velocity. The smallest subsample of spectroscopically confirmed members produces significant substructure signals from 1D (velocity) and 3D (x,y,velocity) diagnostics - a small, offset group may be the culprit. The 2D (x,y) diagnostics applied to the larger samples produce some significant statistics, the cause does not seem to be a large-scale merger, but perhaps several small groups. This is consistent with previous X-ray data showing X-ray emitting gas clumped around small groupings of galaxies.

Koontz, Craig; Pinkney, Jason

2008-10-01

94

Substructure and properties of thick palladium films  

NASA Astrophysics Data System (ADS)

Thick (up to 9 ?m) condensates are deposited by electron-beam evaporation (EBE) and magnetron sputtering of palladium. The surface substructure and morphology of these condensates are studied by electron microscopy. The strength and hydrogen permeability of these vacuum condensates are measured. It is found that condensation-stimulated processes give rise to a gradient substructure across the film thickness and that the gradient films are substantially stronger than epitaxial films. The epitaxial films grown by EBE proved to be most permeable to hydrogen.

Ievlev, V. M.; Belonogov, E. K.; Maksimenko, A. A.; Burkhanov, G. S.; Roshan, N. R.

2008-02-01

95

SEEKING COUNTERPARTS TO ADVANCED LIGO/Virgo TRANSIENTS WITH SWIFT  

SciTech Connect

Binary neutron star (NS) mergers are among the most promising astrophysical sources of gravitational wave (GW) emission for Advanced LIGO and Advanced Virgo, expected to be operational in 2015. Finding electromagnetic counterparts to these signals will be essential to placing them in an astronomical context. The Swift satellite carries a sensitive X-Ray Telescope (XRT), and can respond to target-of-opportunity requests within one to two hours, and so is uniquely poised to find the X-ray counterparts to LIGO/Virgo triggers. Assuming that NS mergers are the progenitors of short gamma-ray bursts (GRBs), some percentage of LIGO/Virgo triggers will be accompanied by X-ray band afterglows that are brighter than 10{sup -12} erg s{sup -1} cm{sup -2} in the XRT band one day after the trigger time. We find that a soft X-ray transient of this flux is bright enough to be extremely rare, and so could be confidently associated with even a moderately localized GW signal. We examine two possible search strategies with the Swift XRT to find bright transients in LIGO/Virgo error boxes. In the first strategy, XRT could search a volume of space with a {approx}100 Mpc radius by observing {approx}30 galaxies over the course of a day, with sufficient depth to observe the expected X-ray afterglow. For an extended LIGO/Virgo horizon distance, the XRT could employ 100 s exposures to cover an area of {approx}35 deg{sup 2} in about a day and remain sensitive enough to image GW-discovered GRB afterglows. These strategies demonstrate that discovery of X-ray band counterparts to GW triggers will be possible, though challenging, with current facilities.

Kanner, Jonah; Camp, Jordan [NASA Goddard Space Flight Center, Mail Code 663, Greenbelt, MD 20771 (United States); Racusin, Judith; Gehrels, Neil [NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771 (United States); White, Darren, E-mail: jonah.b.kanner@nasa.gov [Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

2012-11-01

96

Stellar Imager  

NASA Astrophysics Data System (ADS)

The Stellar Imager (SI) is one of NASA's "Vision Missions" - concepts for future, space-based, strategic missions that could enormously increase our capabilities for observing the Cosmos. SI is designed as a UV/Optical Interferometer which will enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI, with a characteristic angular resolution of 0.1 milli-arcseconds at 2000 Angstroms, represents an advance in image detail of several hundred times over that provided by the Hubble Space Telescope. The Stellar Imager will zoom in on what today-with few exceptions - we only know as point sources, revealing processes never before seen, thus providing a tool as fundamental to astrophysics as the microscope is to the study of life on Earth. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. It's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. Stellar Imager is included as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005) and as such is a candidate mission for the 2025-2030 timeframe. An artist's drawing of the current "baseline" concept for SI is presented.

Carpenter, Kenneth

2007-02-01

97

Uncertainty quantification in experimental frequency based substructuring  

Microsoft Academic Search

Numerical conditioning of the subsystems’ interface flexibility matrix is an important issue in experimental frequency based substructuring (FBS) methods. As this matrix needs to be inverted, it is believed that ill numerical conditioning could severely magnify even small random errors in experimentally obtained subsystems, yielding erroneous FRFs of the coupled system. In this paper a method is introduced with which

S. N. Voormeeren; D. de Klerk; D. J. Rixen

2010-01-01

98

Stellar neutrinos  

SciTech Connect

Neutrino provide an important diagnostic of behavior deep inside the solar core. They also play a major role in the evolution of red giants. Horizontal branch stars, and core-collapse supernovae. I discuss some of the interesting neutrino physics issues that have arisen in studies of stellar evolution.

Haxton, W.C.

1992-09-01

99

Streams in the Aquarius stellar haloes  

NASA Astrophysics Data System (ADS)

We use the very high resolution, fully cosmological simulations from the Aquarius Project, coupled to a semi-analytical model of galaxy formation, to study the phase-space distribution of halo stars in `solar neighbourhood' like volumes. We find that this distribution is very rich in substructure in the form of stellar streams for all five stellar haloes we have analysed. These streams can be easily identified in velocity space, as well as in spaces of pseudo-conserved quantities such as E versus Lz. In our best resolved local volumes, the number of identified streams ranges from ?300 to 600, in very good agreement with previous analytical predictions, even in the presence of chaotic mixing. The fraction of particles linked to (massive) stellar streams in these volumes can be as large as 84 per cent. The number of identified streams is found to decrease as a power law with galactocentric radius. We show that the strongest limitation to the quantification of substructure in our poorest resolved local volumes is particle resolution rather than strong diffusion due to chaotic mixing.

Gómez, Facundo A.; Helmi, Amina; Cooper, Andrew P.; Frenk, Carlos S.; Navarro, Julio F.; White, Simon D. M.

2013-10-01

100

Studies of the Virgo Cluster - Part Five - Luminosity Functions of Virgo Cluster Galaxies  

NASA Astrophysics Data System (ADS)

The luminosity functions of galaxies of various Hubble types in the central 6° radius core of the Virgo cluster show fundamentally different forms for the high- and low-surface-brightness systems. The classical E, S0, and all of the spiral types have luminosity functions that are closely Gaussian, bounded at both the bright and faint limits, similar to what was originally proposed by Hubble. Dwarf ellipticals have an ever-increasing differential luminosity function to the completeness limit of our data at BT = 18 (MBT = - 13.7) which, when corrected for the known incompleteness to BT = 20(MBT = - 11.7), is similar to the exponential LF proposed by Zwicky. There are no dwarf spirals. Nucleated dE's exist at all magnitudes, but their percentage relative to the total dE population decreases with decreasing absolute luminosity of the parent. Gauss and Schechter LF's are fitted to the data, variously binned by Hubble types. The E and dE functions do not fit together, suggesting separate families with no continuity between them, contrary to the continuity displayed by certain integrated physical parameters (Paper I). The total luminosity of all supposed member galaxies in the central 6° core is 2.4 X 1012 blue solar luminosities. The luminosity density averaged over the 6° core is 5.6 x 1010 LBsun Mpc-3, which is 615 times larger than the mean luminosity density of the base4evel "homogeneous" universe.

Sandage, A.; Binggeli, B.; Tammann, G. A.

1985-09-01

101

Post-Newtonian Dynamics in Dense Stellar Systems  

NASA Astrophysics Data System (ADS)

Dense stellar systems (star clusters and galactic nuclei) are some of the most promising sources of gravitational waves since black holes may form and grow in them. In the talk I will describe how relativistic dynamics is included in N-body simulations of such systems, and discuss examples how we model sources in different wavelength regimes, showing results from triple and binary black holes in galactic nuclei, and giving an outlook to projected work for star clusters. Also I'll explain how these theoretical activities are embedded into collaborative programs with gravitational wave observatories, such as the VESF (Virgo-EGO science collaboration) and the German LISA cooperation.

Spurzem, Rainer; Merritt, D.; Berczik, Peter; Berentzen, Ingo; Preto, Miguel; Downing, Jonathan

2007-08-01

102

Spectroscopy of H II Dwarf Galaxies in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

A spectrophotometric study of a sample of dwarf H II galaxies located in the Virgo Cluster has been performed. Long-slit optical spectroscopy has been obtained for 25 blue dwarf galaxies selected across the Virgo central field with the aim of understanding the role played by the environment in the evolution of dwarf galaxies. This sample is a subset of a larger list of dwarf galaxies for which deep H alpha imaging has been collected. Chemical abundances have been derived for the sample using either a direct estimation of the electron temperature or empirical calibrations. Abundances obtained using different empirical calibrations have been compared. Preliminary results show abundances to be correlated with blue and near-infrared luminosity, total H I mass and color, with lower abundances associated with the fainter, gas-rich, bluer galaxies.

Vílchez, J. M.; Iglesias-Páramo, J.

2002-02-01

103

An online substructure identification method for local structural health monitoring  

NASA Astrophysics Data System (ADS)

This paper proposes a substructure isolation method, which uses time series of measured local response for online monitoring of substructures. The proposed monitoring process consists of two key steps: construction of the isolated substructure, and its identification. The isolated substructure is an independent virtual structure, which is numerically isolated from the global structure by placing virtual supports on the interface. First, the isolated substructure is constructed by a specific linear combination of time series of its measured local responses. Then, the isolated substructure is identified using its local natural frequencies extracted from the combined responses. The substructure is assumed to be linear; the outside part of the global structure can have any characteristics. The method has no requirements on the initial state of the structure, and so the process can be carried out repetitively for online monitoring. Online isolation and monitoring is illustrated in a numerical example with a frame model, and then verified in a cantilever beam experiment.

Hou, Jilin; Jankowski, ?ukasz; Ou, Jinping

2013-09-01

104

A NEW CHANNEL FOR DETECTING DARK MATTER SUBSTRUCTURE IN GALAXIES: GRAVITATIONAL LENS TIME DELAYS  

SciTech Connect

We show that dark matter substructure in galaxy-scale halos perturbs the time delays between images in strong gravitational lens systems. The variance of the effect depends on the subhalo mass function, scaling as the product of the substructure mass fraction, and a characteristic mass of subhalos (namely (m {sup 2})/(m)). Time delay perturbations therefore complement gravitational lens flux ratio anomalies and astrometric perturbations by measuring a different moment of the subhalo mass function. Unlike flux ratio anomalies, 'time delay millilensing' is unaffected by dust extinction or stellar microlensing in the lens galaxy. Furthermore, we show that time delay ratios are immune to the radial profile degeneracy that usually plagues lens modeling. We lay out a mathematical theory of time delay perturbations and find it to be tractable and attractive. We predict that in 'cusp' lenses with close triplets of images, substructure may change the arrival-time order of the images (compared with smooth models). We discuss the possibility that this effect has already been observed in RX J1131-1231.

Keeton, Charles R. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Moustakas, Leonidas A. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 169-327, Pasadena, CA 91109 (United States)

2009-07-10

105

The Next Generation Virgo Cluster Survey: status and first results  

NASA Astrophysics Data System (ADS)

We present recent results from the Next Generation Virgo Cluster Survey (NGVS). NGVS is a CFHT MegaCam large program to observe the Virgo Cluster from its core to virial radius, for a total coverage of 104 square degrees. The survey is performing deep imaging (10 sigma detection for point sources of 25.9 mag in the g-band) in five band-passes (u*,g',r',i',z') and will reach a depth never attained before in optical studies of the Virgo cluster. The program's main scientific objectives are: the characterization of the faint-end of the galaxy luminosity function, the characterization of galaxy scaling relations from low to high masses, the cluster/intracluster medium/galaxy connection, the role of environmental effects in galaxy evolution,and the fossil record of star formation and chemical enrichment in dense environments. Numerous ancillary projects --- from a survey of the Galactic halo to a cosmic shear measurement of the matter power spectrum on large scales --- are also under way. We present the status of the survey and multi--wavelength projects, and results on recently detected high--redshift galaxy clusters.

Mei, S.; Ferrarese, L.; Boselli, A.; Boissier, S.; Bournaud, F.; Cuillandre, J. C.; Duc, P.-A.; Ferrière, E.; Gavazzi, R.; Gwyn, S. D. J.; Hudelot, P.; Ilbert, O.; Lançon, A.; Huertas-Company, M.; Mellier, Y.; Milkeraitis, M.; Muñoz, R.; Puzia, T. H.; van Waerbeke, L.; Vollmer, B.; Woods, D.; Balkowski, C.; Balogh, M. L.; Ball, N.; Blakeslee, J. P.; Carignan, C.; Carlberg, R. G.; Chapman, S. G.; Côté, P.; Courteau, S.; Davidge, T. J.; Demers, S.; Durrell, P. R.; Erben, T.; Emsellem, E.; Gavazzi, G.; Hoekstra, H.; Jordán, A.; Kavelaars, J. J.; MacArthur, L.; McConnachie, A. W.; McLaughlin, D.; Mihos, J. C.; Peng, C.; Peng, E. W.; Sawicki, M.; Schade, D.; Simard, L.; Taylor, J. E.; Tonry, J. L.; Tully, R. B.; van Driel, W.; Wilson, C. D.

2011-12-01

106

SUBARU SPECTROSCOPY OF THE GLOBULAR CLUSTERS IN THE VIRGO GIANT ELLIPTICAL GALAXY M86  

SciTech Connect

We present the first spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy (gE) M86 in the Virgo Cluster. Using spectra obtained in the Multi-Object Spectroscopy mode of the Faint Object Camera and Spectrograph on the Subaru telescope, we measure the radial velocities for 25 GCs in M86. The mean velocity of the GCs is derived to be v-bar{sub p} = -354{sub -79}{sup +81} km s{sup -1}, which is different from the velocity of the M86 nucleus (v{sub gal} = -234 {+-} 41 km s{sup -1}). We estimate the velocity dispersion of the GCs, {sigma}{sub p} = 292{sup +32}{sub -32} km s{sup -1}, and find a hint of rotation in the M86 GC system. A comparison of the observed velocity dispersion profiles of the GCs and stars with a prediction based on the stellar mass profile strongly suggests the existence of an extended dark matter halo in M86. We also estimate the metallicities and ages for 16 and 8 GCs, respectively. The metallicities of M86 GCs are in the range of -2.0 < [Fe/H] <-0.2 with a mean value of -1.13 {+-} 0.47. These GCs show a wide age distribution from 4 to 15 Gyr.

Park, Hong Soo; Lee, Myung Gyoon [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Hwang, Ho Seong, E-mail: hspark@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr, E-mail: hhwang@cfa.harvard.edu [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

2012-10-01

107

Towards an understanding of jet substructure  

NASA Astrophysics Data System (ADS)

We present first analytic, resummed calculations of the rates at which wide-spread jet substructure tools tag QCD jets. As well as considering trimming, pruning and the mass-drop tagger, we introduce modified tools with improved analytical and phenomenological behaviours. Most taggers have double logarithmic resummed structures. The modified mass-drop tagger is special in that it involves only single logarithms, and is free from a complex class of terms known as non-global logarithms. The modification of pruning brings an improved ability to discriminate between the different colour structures that characterise signal and background. As we outline in an extensive phenomenological discussion, these results provide valuable insight into the performance of existing tools and help lay robust foundations for future substructure studies.

Dasgupta, Mrinal; Fregoso, Alessandro; Marzani, Simone; Salam, Gavin P.

2013-09-01

108

Investigating halo substructures with annual modulation signature  

Microsoft Academic Search

Galaxy hierarchical formation theories, numerical simulations, the discovery of the Sagittarius Dwarf Elliptical Galaxy (SagDEG)\\u000a in 1994 and more recent investigations suggest that the dark halo of the Milky Way can have a rich phenomenology containing\\u000a non-thermalized substructures. In the present preliminary study, we investigate the case of the SagDEG (the best known satellite\\u000a galaxy in the Milky Way crossing

R. Bernabei; P. Belli; F. Montecchia; F. Nozzoli; F. Cappella; A. Incicchitti; D. Prosperi; R. Cerulli; C. J. Dai; H. L. He; H. H. Kuang; J. M. Ma; X. D. Sheng; Z. P. Ye; M. Martinez; G. Giuffrida

2006-01-01

109

Composite Octet Searches with Jet Substructure  

SciTech Connect

Many new physics models with strongly interacting sectors predict a mass hierarchy between the lightest vector meson and the lightest pseudoscalar mesons. We examine the power of jet substructure tools to extend the 7 TeV LHC sensitivity to these new states for the case of QCD octet mesons, considering both two gluon and two b-jet decay modes for the pseudoscalar mesons. We develop both a simple dijet search using only the jet mass and a more sophisticated jet substructure analysis, both of which can discover the composite octets in a dijet-like signature. The reach depends on the mass hierarchy between the vector and pseudoscalar mesons. We find that for the pseudoscalar-to-vector meson mass ratio below approximately 0.2 the simple jet mass analysis provides the best discovery limit; for a ratio between 0.2 and the QCD-like value of 0.3, the sophisticated jet substructure analysis has the best discovery potential; for a ratio above approximately 0.3, the standard four-jet analysis is more suitable.

Bai, Yang; /SLAC; Shelton, Jessie; /Yale U.

2012-02-14

110

Recognizing Protein Substructure Similarity Using Segmental Threading  

PubMed Central

Summary Protein template identification is essential to protein structure and function predictions. However, conventional whole-chain threading approaches often fail to recognize conserved substructure motifs when the target and templates do not share the same fold. We develop a new approach, SEGMER, for identifying protein substructure similarities by segmental threading. The target sequence is split into segments of 2–4 consecutive or non-consecutive secondary structural elements, which are then threaded through PDB to identify appropriate substructure motifs. SEGMER is tested on 144 non-redundant hard proteins. When combined with whole-chain threading, the TM-score of alignments and accuracy of spatial restraints of SEGMER increase by 16% and 25%, respectively, compared to that by the whole-chain threading methods only. When tested on 12 Free Modeling targets from CASP8, SEGMER increases the TM-score and contact accuracy by 28% and 48%, respectively. This significant improvement should have important impact on protein structure modeling and functional inference.

Wu, Sitao; Zhang, Yang

2010-01-01

111

Precision jet substructure from boosted event shapes.  

PubMed

Jet substructure has emerged as a critical tool for LHC searches, but studies so far have relied heavily on shower Monte Carlo simulations, which formally approximate QCD at the leading-log level. We demonstrate that systematic higher-order QCD computations of jet substructure can be carried out by boosting global event shapes by a large momentum Q and accounting for effects due to finite jet size, initial-state radiation (ISR), and the underlying event (UE) as 1/Q corrections. In particular, we compute the 2-subjettiness substructure distribution for boosted Z?qq[over ¯] events at the LHC at next-to-next-to-next-to-leading-log order. The calculation is greatly simplified by recycling known results for the thrust distribution in e(+)e(-) collisions. The 2-subjettiness distribution quickly saturates, becoming Q independent for Q > or approximately equal to 400 GeV. Crucially, the effects of jet contamination from ISR/UE can be subtracted out analytically at large Q without knowing their detailed form. Amusingly, the Q=? and Q=0 distributions are related by a scaling by e up to next-to-leading-log order. PMID:23002825

Feige, Ilya; Schwartz, Matthew D; Stewart, Iain W; Thaler, Jesse

2012-08-30

112

Searching for a stochastic gravitational-wave background from a population of neutron stars in the Virgo cluster with data from the LIGO and Virgo detectors  

NASA Astrophysics Data System (ADS)

We describe an in-progress search with LIGO and Virgo data for a stochastic gravitational-wave background (SGWB) from the population of rotating non-axisymmetric neutron stars in the Virgo cluster. Employing multi-baseline radiometry, bounds on the GW strain power from the Virgo cluster can be obtained, which, in turn, can constrain neutron star equations of state. The current status of the search will be presented. We also assess (a) the expected performance of this search using forthcoming second-generation detectors, including the improvement from locating one of the advanced LIGO detectors in India and (b) the reach of third generation detectors to astrophysical SGWBs.

Talukder, Dipongkar

2013-04-01

113

VLT optical BVR observations of two bright supernova Ia hosts in the Virgo cluster. Surface brightness fluctuation analysis  

NASA Astrophysics Data System (ADS)

Aims: We study the characteristics of field stars in the two bright ellipticals NGC 4621 and NGC 4374 in the Virgo cluster to derive accurate distances and stellar population properties. Moreover, since the target galaxies have hosted three type Ia supernova events, we investigate the possible correlations between the SNe Ia properties and their host stellar systems. Methods: Using deep imaging BVR data, obtained with the FORS2 camera mounted at the VLT, we analysed the surface brightness fluctuations (SBF) properties of the targets. We adopted our measurements and existing empirical or theoretical calibrations to estimate the distance of the NGC 4621 and NGC 4374. For stellar population analysis, we measured SBF amplitudes in different galaxy regions, allowing us to study the changes in field star properties. The three-band coverage of present data, coupled with existing SBF measures available from the literature, provides us with the broadest wavelength coverage of SBF magnitudes for single objects. We present a detailed comparison between SBF data and models to constrain the physical characteristics of the dominant stellar components at i) various galactic radii; and ii) in the regions where SNe Ia events were recorded. Results: Our V and R SBF measures, coupled with either empirical or theoretical calibrations, provide distance moduli in agreement with literature estimates. The median of our and literature SBF-based distances agrees with the median obtained from non-SBF methods, indicating the absence of any systematic effect in the SBF technique. The same result holds for SBF and SN Ia distances. Comparing either the SBF versus integrated colour diagrams, or the SBF versus SBF colour diagrams, with SPoT models, we find that stellar population properties do not change significantly along the galactic radius, with a dominant population having old age and nearly solar chemical composition. The galaxies appear similar in all properties analysed, except for B-band SBF. Since the SBF magnitudes in this band are sensitive to the properties of the hot stellar component, we speculate that such behaviour can be a consequence of different diffuse hot stellar components in the two objects. By using specific models, we find that the presence of a percentage of hot HB stars in old and metal-rich stellar population could be at the origin of the observed differences. Finally, we find a good uniformity in the V and R SBF and integrated colours in the regions where the three SNe Ia, presenting different absolute luminosities, exploded. On the other hand, the SBF signal measured in the B-band shows intriguing differences.

Cantiello, M.; Biscardi, I.; Brocato, E.; Raimondo, G.

2011-08-01

114

H?3: an H? imaging survey of HI selected galaxies from ALFALFA. II. Star formation properties of galaxies in the Virgo cluster and surroundings  

NASA Astrophysics Data System (ADS)

Context. We present the analysis of H?3, an H? narrow-band imaging follow-up survey of 409 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster, in the region 11h < RA < 16h ; 4o < Dec < 16°; 350 < cz < 2000 km s-1. Aims: Taking advantage of H?3, which provides the complete census of the recent massive star formation rate (SFR) in HI-rich galaxies in the local Universe and of ancillary optical data from SDSS we explore the relations between the stellar mass, the HI mass, and the current, massive SFR of nearby galaxies in the Virgo cluster. We compare these with those of isolated galaxies in the Local Supercluster, and we investigate the role of the environment in shaping the star formation properties of galaxies at the present cosmological epoch. Methods: By using the H? hydrogen recombination line as a tracer of recent star formation, we investigated the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), for many morphological types (spirals and dwarfs), and over a wide range of stellar masses (107.5 to 1011.5 M?). To quantify the degree of environmental perturbation, we adopted an updated calibration of the HI deficiency parameter which we used to divide the sample into three classes: unperturbed galaxies (DefHI ? 0.3), perturbed galaxies (0.3 < DefHI < 0.9), and highly perturbed galaxies (DefHI ? 0.9). Results: Studying the mean properties of late-type galaxies in the Local Supercluster, we find that galaxies in increasing dense local galaxy conditions (or decreasing projected angular separation from M 87) show a significant decrease in the HI content and in the mean specific SFR, along with a progressive reddening of their stellar populations. The gradual quenching of the star formation occurs outside-in, consistently with the predictions of the ram pressure model. Once considered as a whole, the Virgo cluster is effective in removing neutral hydrogen from galaxies, and this perturbation is strong enough to appreciably reduce the SFR of its entire galaxy population. Conclusions: An estimate of the present infall rate of 300-400 galaxies per Gyr in the Virgo cluster is obtained from the number of existing HI-rich late-type systems, assuming 200-300 Myr as the time scale for HI ablation. If the infall process has been acting at a constant rate, this would imply that the Virgo cluster has formed approximately 2 Gyr ago, consistently with the idea that Virgo is in a young state of dynamical evolution. Based on observations taken at the observatory of San Pedro Martir (Baja California, Mexico), belonging to the Mexican Observatorio Astronómico Nacional.

Gavazzi, G.; Fumagalli, M.; Fossati, M.; Galardo, V.; Grossetti, F.; Boselli, A.; Giovanelli, R.; Haynes, M. P.

2013-05-01

115

Automatic Alignment system during the second science run of the Virgo interferometer  

Microsoft Academic Search

In this paper the performances of the Automatic Alignment sensing and control system in the Virgo gravitational wave detector, during the second scientific run from July 7th 2009 to January 8th 2010, are described. The accuracy of the angular control loops fulfills the original Virgo requirements, reaching the accuracy of a few nano-radians for the most critical angular degrees of

T. Accadia; F. Acernese; F. Antonucci; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; A. Basti; Th. S. Bauer; M. G. Beker; A. Belletoile; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; O. Chaibi; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D’Antonio; V. Dattilo; M. Davier; R. Day; R. De Rosa; G. Debreczeni; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; L. A. Forte; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; N. Liguori; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; R. L. Ward; M. Yvert

2011-01-01

116

Extraction of Substructural Flexibility from Global Frequencies and Mode Shapes  

SciTech Connect

A computational procedure for extracting substructure-by-substructure flexibility properties from global modal parameters is presented. The present procedure consists of two key features: an element-based direct flexibility method which uniquely determines the global flexibility without resorting to case-dependent redundancy selections; and, the projection of cinematically inadmissible modes that are contained in the iterated substructural matrices. The direct flexibility method is used as the basis of an inverse problem, whose goal is to determine substructural flexibilities given the global flexibility, geometrically-determined substructural rigid-body modes, and the local-to-global assembly operators. The resulting procedure, given accurate global flexibility, extracts the exact element-by-element substructural flexibilities for determinate structures. For indeterminate structures, the accuracy depends on the iteration tolerance limits. The procedure is illustrated using both simple and complex numerical examples, and appears to be effective for structural applications such as damage localization and finite element model reconciliation.

Alvin, K.F.; Park, K.C.

1999-07-16

117

Prospecting for Elements: Galactic Halo Planetary Nebulae Abundances and Virgo Spiral Galaxy Color Profiles  

NASA Astrophysics Data System (ADS)

Halo planetary nebulae. Using published spectral line data for nine halo planetary nebulae (HPNe), I have calculated photoionization models in an attempt to gain insight into the physical conditions and chemical abundances of these nebulae. The nine HPNE reported upon are K648, DdDm-1, NGC2242, NGC4361, PN243.8-37.1, PN006-41.9, M2-29, BB-1, and H4-1. The derived abundance ranges for the HPNe are: C 6.60-8.95, N 7.18-8.00, O 7.56-8.56, Ne 6.24-7.71, Ar 4.12-7.70, and S 4.90-7.00 (log(x) + 12). The temperature range for the central stars of these nebulae is 40,000 to 140,000K. Specifically, with a few exceptions, I find that all nine objects exhibit subsolar O/H; most show enhanced C/O and N/O, and a constant Ne/O ration. I also note the existence of comparatively larger abundance scatter in the HPNe as opposed to disk PNe, and suggest that this is consistent with the accretion model of halo formation formulated by Searle & Zinn. In addition, I test the effects on derived abundances and central star temperatures of a variety of model atmospheres as well as blackbodies for input ionizing spectra. I find that nebular line strengths are relatively insensitive to atmospheric details; thus blackbody spectra are suitable for central star continua. Near-infrared Virgo cluster spiral colors. Near-infrared (NIR) surface photometry in J (1.2?m), H (1.6?m) and K (2.2?m) have been obtained for a sample of Virgo cluster spirals; NGC4321, NGC4303, NGC4571, NGC4689, and NGC4254 which span a large range in HI deficiency. The spirals range from a normal gas content to a deficiency of a factor of 10 compared to normal galaxies. Using previous HII region abundance studies along with the NIR colors an attempt has been made to calibrate any correlation between the J-K index to the overall gas phase abundance gradients as a first step to probing the underlying stellar metallicity. Decomposition techniques have been used to produce estimates of spiral bulge/disk masses and luminosities in all three J, H, & K bands, as well as to explore the variation of mass-to-light ratios within the separate galaxy components. An analysis of the NIR colors is performed in an attempt to unravel the similar effects that stellar ages, dust content, metallicity, and some non-stellar emission processes has upon colors. The derived color gradients for the J-K index are very shallow and show a range of behaviors across the galaxy sample.

Howard, Joseph William

118

4. VIEW NORTH, DETAIL OF SUBSTRUCTURE CONNECTIONS ON EAST END ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

4. VIEW NORTH, DETAIL OF SUBSTRUCTURE CONNECTIONS ON EAST END OF BRIDGE - Cincinnati, Jackson & Mackinaw Railroad Bridge, Abandonned Penn Central Route, spanning Tom's Run, Farmersville, Montgomery County, OH

119

Damage detection using the eigenparameter decomposition of substructural flexibility matrix  

NASA Astrophysics Data System (ADS)

The crack or local damage on a structure reduces the stiffness of the structure, and thus leads to the modification of the dynamic properties. Damage detection is widely performed by comparing the initial modal data of the intact structure with those of the damaged structure. For a large-scale structure, the local damage usually introduces slight change to the global modal data, which makes the local damage difficult to be detected. This paper proposes a new substructuring method for the damage detection of a structure. The global structure is divided into manageable substructures. The modal data measured on the global structure are disassembled for obtaining the independent substructural dynamic flexibility matrices, under the force and displacement compatibility constraints. Thereafter, the substructural flexibility matrix is decomposed into its eigenvalues and eigenvectors to be used as the indicators for damage detection. Since the substructuring method concerns the local area by treating it as an independent structure, the substructural eigenparameters are more sensitive to the local damage than the global eigenparameters. The proposed substructuring method is firstly verified by a laboratory-tested portal frame structure. The location of the artificial cuts can be detected successfully by comparing the change of substructural eigenparameters. The proposed method is then applied to the 600 m tall Guangzhou New TV Tower. As compared with the global eigenparameters, the substructural eigenparameters bear larger changes caused by the local damage and thus are more sensitive to the local damage.

Weng, Shun; Zhu, Hong-Ping; Xia, Yong; Mao, Ling

2013-01-01

120

Fragmented substructure and crack formation in low-alloy steel  

NASA Astrophysics Data System (ADS)

In the work we studied the substructure of 30KhGSA steel after rolling. A relation has been established between the macrofracture of the specimen and its dislocation substructure. The formation and completion of a fragmented substructure with precipitation of carbides at the junctions of fragments during rolling indicate that the lifetime is close to exhaustion. Annealing that partially or completely destroys the fragmented substructure causes microcracks to collapse and heal, eliminates the microcrack nucleation sites, eliminates trajectories of facilitated microcrack growth, which follow subboundaries, and restores the plasticity of the steel.

Kozlov, É. V.; Veter, V. V.; Popova, N. A.; Ignatenko, L. N.

1994-08-01

121

Convergence of a substructuring methodwith Lagrange multipliers  

Microsoft Academic Search

Summary.  \\u000a We analyze the convergence of a substructuring iterative method\\u000a with Lagrange multipliers, proposed recently by Farhat and Roux.\\u000a The method decomposes finite element\\u000a discretization of an elliptic boundary value problem into\\u000a Neumann problems on the subdomains plus a coarse problem for the\\u000a subdomain nullspace components. For linear conforming elements and\\u000a preconditioning by the Dirichlet problems on the subdomains,\\u000a we

Jan Mandel; Radek Tezaur

1996-01-01

122

The Local Group velocity and the Virgo cluster  

NASA Astrophysics Data System (ADS)

The presented measurement of the Local Group velocity, which has been determined relative to the backdrop of galaxies extending out to 5000 km/s, is compared with the discrepant results of Rubin et al (1976) and with the measurement of the dipole component of the cosmic microwave background, which yields the Local Group velocity relative to the microwave reference frame at z of about 1000. Attention is also given to the estimation of the infall velocity of the Local Group towards the Virgo cluster. The results obtained for the Local Group velocity are noted to be in agreement with the dipole component-based derivation.

Davies, R. D.; Staveley-Smith, L.

123

[Studies on molluscicidal effect of bromoacetamide against Ganesella virgo].  

PubMed

Molluscicidal effect of bromoacetamide against the snails in laboratory and field trials were observed. Grassland of Guiliu River in Keerqinyouyiquanqi District, Neimengol Autonomous Region was selected for field trials. The results showed that bromoacetamide was fairly effective against Ganesella virgo, the intermediate host of Dicrocoelium chinensis and Eurytrema pancreaticum. In field trials, 7 days after spraying at a dosage of 0.5g/m2, 74.7-84.7% of snails were killed. When a dosage of 1g/m2 was used, the mortality of snails reached 84.8-95.7%. PMID:2364507

Zhu, D; Yin, J; Da, L; Zhang, Q; Li, Q

1990-01-01

124

Noise monitor tools and their application to Virgo data  

NASA Astrophysics Data System (ADS)

The understanding of noise in interferometric gravitational wave detectors is fundamental in terms of both enabling prompt reactions in the mitigation of noise disturbances and in the establishment of appropriate data-cleaning strategies. Monitoring tools to perform online and offline noise analysis in areas such as transient signal detection, line identification algorithms and coherence are used to characterise the Virgo detector noise. In this paper, we describe the framework into which these tools are integrated - the Noise Monitor Application Programming Interface (NMAPI) - and provide examples of its application.

Accadia, T.; Acernese, F.; Agathos, M.; Astone, P.; Ballardin, G.; Barone, F.; Barsuglia, M.; Basti, A.; Bauer, Th S.; Bebronne, M.; Bejger, M.; Beker, M. G.; Bitossi, M.; Bizouard, M. A.; Blom, M.; Bondu, F.; Bonelli, L.; Bonnand, R.; Boschi, V.; Bosi, L.; Bouhou, B.; Braccini, S.; Bradaschia, C.; Branchesi, M.; Briant, Gabriel chardin T.; Brillet, A.; Brisson, V.; Bulik, T.; Bulten, H. J.; Buskulic, D.; Buy, C.; Calloni, E.; Canuel, B.; Carbognani, F.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cesarini, E.; Chaibi, O.; Chassande-Mottin, E.; Chincarini, A.; Chiummo, A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colacino, C. N.; Colas, J.; Colla, A.; Colombini, M.; Conte, A.; Coulon, J.-P.; Cuoco, E.; D'Antonio, S.; Dattilo, V.; Davier, M.; Day, R.; De Rosa, R.; Debreczeni, G.; Del Pozzo, W.; Di Fiore, L.; Di Lieto, A.; Emilio, M. Di Paolo; Di Virgilio, A.; Dietz, A.; Drago, M.; Endröczi, G.; Fafone, V.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Forte, L. A.; Fournier, J.-D.; Franc, J.; Franco, S.; Frasca, S.; Frasconi, F.; Galimberti, M.; Gammaitoni, L.; Garufi, F.; Gáspár, M. E.; Gemme, G.; Genin, E.; Gennai, A.; Giazotto, A.; Gouaty, R.; Granata, M.; Greverie, C.; Guidi, G. M.; Hayau, J.-F.; Heidmann, A.; Heitmann, H.; Hello, P.; Hemming, G.; Jaranowski, P.; Jonker, R. J. G.; Kasprzack, M.; Kowalska, I.; Królak, A.; Leroy, N.; Letendre, N.; Li, T. G. F.; Liguori, N.; Lorenzini, M.; Loriette, V.; Losurdo, G.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marque, J.; Martelli, F.; Masserot, A.; Michel, C.; Milano, L.; Minenkov, Y.; Mohan, M.; Morgado, N.; Morgia, A.; Mosca, S.; Mours, B.; Naticchioni, L.; Nocera, F.; Palladino, L.; Palomba, C.; Paoletti, F.; Paoletti, R.; Parisi, M.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Persichetti, G.; Piergiovanni, F.; Pietka, M.; Pinard, L.; Poggiani, R.; Prato, M.; Prodi, G. A.; Punturo, M.; Puppo, P.; Rabeling, D. S.; Racz, I.; Rapagnani, P.; Re, V.; Regimbau, T.; Ricci, F.; Robinet, F.; Rocchi, A.; Rolland, L.; Romano, R.; Rosi?ska, D.; Ruggi, P.; Sassolas, B.; Sentenac, D.; Sperandio, L.; Sturani, R.; Swinkels, B.; Tacca, M.; Taffarello, L.; ter Braack, A. P. M.; Toncelli, A.; Tonelli, M.; Torre, O.; Tournefier, E.; Travasso, F.; Vajente, G.; van den Brand, J. F. J.; Van Den Broeck, C.; van der Putten, S.; Vasuth, M.; Vavoulidis, M.; Vedovato, G.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinet, J.-Y.; Vitale, S.; Vocca, H.; Ward, R. L.; Was, M.; Yamamoto, K.; Yvert, M.; Zadro?ny, A.; Zendri, J.-P.

2012-06-01

125

Applications of a nuclear spectroscopic survey of Virgo spiral galaxies  

NASA Astrophysics Data System (ADS)

A data base on the nuclear spectrophotometric survey of Virgo and field spirals is used as the basis of a critical discussion of the results presented by Kennicutt (1983) and Scoville et al. (1983). The optical spectra of the data base furnish no evidence of continuing nuclear star formation in any of the Scoville et al. galaxies, which had been detected at 10 microns; the 10-micron emission and optical emission lines are more simply attributed to some kind of nonthermal activity. A comment on the distance to NGC 4569 is furnished.

Stauffer, J. R.

126

Morphology of flows and buoyant bubbles in the Virgo cluster  

NASA Astrophysics Data System (ADS)

There is growing evidence that the active galactic nuclei (AGN) associated with the central elliptical galaxy in clusters of galaxies are playing an important role in the evolution of the intracluster medium (ICM) and clusters themselves. We use high-resolution three-dimensional simulations to study the interaction of the cavities created by AGN outflows (bubbles) with the ambient ICM. The gravitational potential of the cluster is modelled using the observed temperature and density profiles of the Virgo cluster. We demonstrate the importance of the hydrodynamical Kutta-Zhukovsky forces associated with the vortex ring structure of the bubbles, and discuss possible effects of diffusive processes on their evolution.

Pavlovski, Georgi; Kaiser, Christian R.; Pope, Edward C. D.; Fangohr, Hans

2008-03-01

127

The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax-Virgo Relative Distance  

NASA Astrophysics Data System (ADS)

We present (g 475 - z 850) color and z 850-band surface brightness fluctuations (SBFs) measurements for 43 early-type galaxies in the Fornax cluster imaged with the Hubble Space Telescope Advanced Camera for Surveys. These are combined with our earlier measurements for Virgo cluster galaxies to derive a revised, nonlinear calibration of the z 850-band SBF absolute magnitude \\overline{M}_z as a function of (g 475 - z 850) color, valid for the AB color range 0.8 < (g 475 - z 850) < 1.6. In all, we tabulate recalibrated SBF distances for 134 galaxies in Virgo, Fornax, the Virgo W' group, and NGC 4697 in the Virgo Southern Extension. The calibration procedure yields a highly precise relative distance modulus for Fornax with respect to Virgo of ?(m - M) FV = 0.42 ± 0.03 mag, or a distance ratio dF /dV = 1.214 ± 0.017. The resulting Fornax distance modulus is (m - M)For = 31.51 ± 0.03 ± 0.15 mag, corresponding to dF = 20.0 ± 0.3 ± 1.4 Mpc, where the second set of error bars reflects the total systematic uncertainty from our assumed Virgo distance of 16.5 Mpc. The rms distance scatter for the early-type Fornax cluster galaxies is ? d = 0.49+0.11 -0.15 Mpc, or a total line-of-sight depth of 2.0+0.4 -0.6 Mpc, consistent with its compact appearance on the sky. This translates to a depth scatter smaller than the intrinsic, or "cosmic," scatter ?cos in the SBF calibration, unlike the case for the larger Virgo cluster. As a result, we are able to place the first tight constraints on the value of ?cos. We find ?cos = 0.06 ± 0.01 mag, with a firm upper limit of ?cos < 0.08 mag, for the subsample of galaxies with (g 475 - z 850)>1.02, but it is about twice as large for bluer galaxies. We also present an alternative SBF calibration based on the "fluctuation count" parameter \\overline{N}= \\overline{m}- m_tot, a proxy for galaxy mass. This gives a consistent relative distance but with larger intrinsic scatter, and we adopt the result from the calibration on (g 475 - z 850) because of its basis in stellar population properties alone. Finally, we find no evidence for systematic trends of the galaxy distances with position or velocity (e.g., no current infall); the Fornax cluster appears both compact and well virialized. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Blakeslee, John P.; Jordán, Andrés; Mei, Simona; Côté, Patrick; Ferrarese, Laura; Infante, Leopoldo; Peng, Eric W.; Tonry, John L.; West, Michael J.

2009-03-01

128

Searching for substructures in fragment spaces.  

PubMed

A common task in drug development is the selection of compounds fulfilling specific structural features from a large data pool. While several methods that iteratively search through such data sets exist, their application is limited compared to the infinite character of molecular space. The introduction of the concept of fragment spaces (FSs), which are composed of molecular fragments and their connection rules, made the representation of large combinatorial data sets feasible. At the same time, search algorithms face the problem of structural features spanning over multiple fragments. Due to the combinatorial nature of FSs, an enumeration of all products is impossible. In order to overcome these time and storage issues, we present a method that is able to find substructures in FSs without explicit product enumeration. This is accomplished by splitting substructures into subsubstructures and mapping them onto fragments with respect to fragment connectivity rules. The method has been evaluated on three different drug discovery scenarios considering the exploration of a molecule class, the elaboration of decoration patterns for a molecular core, and the exhaustive query for peptides in FSs. FSs can be searched in seconds, and found products contain novel compounds not present in the PubChem database which may serve as hints for new lead structures. PMID:23205736

Ehrlich, Hans-Christian; Volkamer, Andrea; Rarey, Matthias

2012-12-12

129

Cosmic Ray Diffusion Fronts in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

The pair of large radio lobes in the Virgo cluster, each about 23 kpc in radius, have curiously sharp outer edges where the radio-synchrotron continuum flux declines abruptly. However, just adjacent to this sharp transition, the radio flux increases. This radio limb-brightening is observed over at least half of the perimeter of both lobes. We describe slowly propagating steady-state diffusion fronts that explain these counterintuitive features. Because of the natural buoyancy of radio lobes, the magnetic field is largely tangent to the lobe boundary, an alignment that polarizes the radio emission and dramatically reduces the diffusion coefficient of relativistic electrons. As cosmic ray electrons diffuse slowly into the cluster gas, the local magnetic field and gas density are reduced as gas flows back toward the radio lobe. Radio emission peaks can occur because the synchrotron emissivity increases with magnetic field and then decreases with the density of non-thermal electrons. A detailed comparison of steady diffusion fronts with quantitative radio observations may reveal information about the spatial variation of magnetic fields and the diffusion coefficient of relativistic electrons. On larger scales, some reduction of the gas density inside the Virgo lobes due to cosmic ray pressure must occur and may be measurable. Such X-ray observations could reveal important information about the presence of otherwise unobservable non-thermal components such as relativistic electrons of low energy or proton cosmic rays.

Mathews, William G.; Guo, Fulai

2011-07-01

130

Compact massive objects in Virgo galaxies: the black hole population  

NASA Astrophysics Data System (ADS)

We investigate the distribution of massive black holes (MBHs) in the Virgo cluster. Observations suggest that active galactic nuclei activity is widespread in massive galaxies (M* >~ 1010Msolar), while at lower galaxy masses star clusters are more abundant, which might imply a limited presence of central black holes in these galaxy-mass regimes. We explore if this possible threshold in MBH hosting is linked to nature, nurture or a mixture of both. The nature scenario arises naturally in hierarchical cosmologies, as MBH formation mechanisms typically are efficient in biased systems, which would later evolve into massive galaxies. Nurture, in the guise of MBH ejections following MBH mergers, provides an additional mechanism that is more effective for low mass, satellite galaxies. The combination of inefficient formation, and lower retention of MBHs, leads to the natural explanation of the distribution of compact massive objects in Virgo galaxies. If MBHs arrive to the correlation with the host mass and velocity dispersion during merger-triggered accretion episodes, sustained tidal stripping of the host galaxies creates a population of MBHs which lie above the expected scaling between the holes and their host mass, suggesting a possible environmental dependence.

Volonteri, Marta; Haardt, Francesco; Gültekin, Kayhan

2008-03-01

131

Young Clusters in Virgo and Fornax Dwarf Irregulars  

NASA Astrophysics Data System (ADS)

We present the results of a search for massive star clusters in dwarf irregular galaxies in the Virgo and Fornax Cluster using HST WFPC2 snapshot data. We detect 237 cluster candidates in 11 confirmed Virgo and Fornax cluster galaxies. We separated the young cluster (< 1 Gyr) candidates from the sample using their V-I color. After statistical subtraction of background and foreground sources we detect a total of 114 young cluster candidates. In addition to V and I magnitudes, we used a sequence of model cluster profiles to derive radii for the cluster candidates. Based on this information we find that most of the young cluster candidates appear to have masses between 104 and 105 solar masses and 40% are reliably resolved with rcore ˜ 2 pc. Using ground based H? data we find that about a quarter of the young cluster candidates are most likely HII regions. Additionally we find that a large number of the young candidate clusters detected lie around the periphery of the galaxies.

Seth, A.; Olsen, K.; Miller, B.

2004-12-01

132

Matter Substructure in High Redshift Clusters of Galaxies  

NASA Astrophysics Data System (ADS)

We investigate substructure via weak gravitational lensing shear measurements of high redshift clusters with existing ACS imaging. We use a principal component analysis technique to characterize the PSF ellipticity pattern and a variable aperture filter to characterize the level of substructure. This work supported by the NASA Rhode Island Space Grant program.

Huwe, Paul M.

2012-05-01

133

Correcting indefinite mass matrices due to substructure uncoupling  

NASA Astrophysics Data System (ADS)

The transmission simulator method of experimental dynamic substructuring captures the interface forces and motions through a fixture called a transmission simulator. The transmission simulator method avoids the need to measure connection point rotations, facilitates substructuring for systems with continuous connections and enriches the modal basis of the substructure model. To use this approach, one first attaches the transmission simulator to the experimental substructure and then measures the free modes of the assembly. A finite element model of the transmission simulator is then used to subtract the transmission simulator and to couple the experimental substructure to the assembly of interest. Unfortunately, in several cases the process of subtracting the transmission simulator has caused the mass matrix for the experimental substructure to become indefinite, making the substructure model difficult or impossible to use and potentially leading to erroneous results. The authors previously developed metrics that could be used to identify which modes of the experimental model led to the indefinite mass matrix. This work presents a method that utilizes those metrics with a sensitivity analysis to adjust the transmission simulator mass matrix so that the subtraction does not produce an indefinite mass matrix. A second method is presented in which the mass matrix is made positive definite by coupling additional mass to the substructure. The methods are evaluated using both numerical and experimental test cases, showing promising results.

Mayes, Randy L.; Allen, Mathew S.; Kammer, Daniel C.

2013-10-01

134

A survey of 286 Virgo cluster galaxies at optical griz and near-IR H band: surface brightness profiles and bulge-disc decompositions  

NASA Astrophysics Data System (ADS)

We present and g-, r-, i-, z- and H-band surface brightness profiles and bulge-disc decompositions for a morphologically broad sample of 286 Virgo Cluster Catalogue (VCC) galaxies. The H-band data come from a variety of sources including our survey of 171 VCC galaxies at the University of Hawaii (UH) 2.2-m telescope, Canada-France-Hawaii Telescope (CFHT) and United Kingdom Infrared Telescope (UKIRT), and another 115 galaxies from the Two Micron All Sky Survey (2MASS) and GOLDMine archives. The optical data for all 286 VCC galaxies were extracted from the Sloan Digital Sky Survey (SDSS) images. The H-band and the SDSS griz data were analysed in a homogeneous manner using our own software, yielding a consistent set of deep, multiband surface brightness profiles for each galaxy. Average surface brightness profiles per morphological bin were created in order to characterize the variety of galaxy light profiles across the Hubble sequence. The 1D bulge-disc decomposition parameters, as well as non-parametric galaxy measures, such as effective radius, effective surface brightness and light concentration, are presented for all 286 VCC galaxies in each of the five optical/near-infrared wavebands. The profile decompositions account for bulge and disc components, spiral arms, nucleus and atmospheric blurring. The Virgo spiral galaxy bulges typically have a Sérsic index n˜ 1, while elliptical galaxies prefer n˜ 2. No galaxy spheroid requires n > 3. The light profiles for 70 per cent of the Virgo elliptical galaxies reveal the presence of both a spheroid and disc component. A more in-depth discussion of the structural parameter trends can be found in McDonald, Courteau & Tully. The data provided here should serve as a base for studies of galaxy structure and stellar populations in the cluster environment. The galaxy light profiles and bulge-disc decomposition results are available at the Centre de Données astronomiques de Strasbourg (CDS; ) and the author's own website ().

McDonald, Michael; Courteau, Stéphane; Tully, R. Brent; Roediger, Joel

2011-07-01

135

The spatial evolution of stellar structures in the LMC/SMC  

NASA Astrophysics Data System (ADS)

We present an analysis of the spatial distribution of various stellar populations within the Large and Small Magellanic Clouds. We use optically selected stellar samples with mean ages between ~9 and ~1000 Myr, and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC/SMC. We use two statistical techniques to study the evolution of structure within these galaxies, the Q-parameter and the two-point correlation function (TPCF). In both galaxies we find the stars are born with a high degree of substructure (i.e. are highly fractal) and that the stellar distribution approaches that of the “background” population on timescales similar to the crossing times of the galaxy (~ 80 Myr & ~ 150 Myr for the SMC/LMC respectively). By comparing our observations to simple models of structural evolution we find that “popping star clusters” do not significantly influence structural evolution in these galaxies. Instead we argue that general galactic dynamics are the main drivers, and that substructure will be erased in approximately the crossing time, regardless of spatial scale, from small clusters to whole galaxies. This can explain why many young Galactic clusters have high degrees of substructure, while others are smooth and centrally concentrated. We conclude with a general discussion on cluster “infant mortality”, in an attempt to clarify the time/spatial scales involved.

Bastian, Nate; Gieles, Mark; Ercolano, Barbara; Gutermuth, Robert

2009-03-01

136

Stellar Dynamos  

NASA Astrophysics Data System (ADS)

This chapter steps finally away from the sun and towards the stars, the idea being to apply the physical insight gained so far to see how much of stellar magnetism can be understood in terms of dynamo action. Dynamo action in the convective core of massive main-sequence stars is first considered and shown viable. For intermediate-mass main-sequence stars the fossil field hypothesis will carry the day, although possible dynamo alternatives are also briefly discussed. The extension of the solar dynamo models investigated in Chap. 3 (10.1007/978-3-642-32093-4_3) to other solar-type stars will first take us through an important detour in first having to understand rotational evolution in response to angular momentum loss in a magnetized wind. Dynamo action in fully convective stars comes next, and the chapter closes with an overview of the situation for pre- and post-main-sequence stars and compact objects, leading finally to the magnetic fields of galaxies and beyond.

Charbonneau, Paul

137

Acerca de la linealidad de la relación color-magnitud del cúmulo de Virgo  

NASA Astrophysics Data System (ADS)

In this work we revisite the color-magnitude relation (CMR) of the Virgo cluster by means of the realization of our own photometry and the analysis of images of 100 early-type galaxies, observed as part of the ACS Virgo Cluster Survey of the Hubble Space Telescope (HST). Our objective, within the framework of the discussion about the nonlinearity of the CMR in the Virgo cluster, is to draw a comparison between the results of the photometry performed in this work and the results obtained in previous ones. FULL TEXT IN SPANISH

González, N.; Smith Castelli, A.; Faifer, F.; Forte, J. C.

138

Caught in the Act: Strong, Active Ram Pressure Stripping in Virgo Cluster Spiral NGC 4330  

NASA Astrophysics Data System (ADS)

We present multi-wavelength data of NGC 4330, a highly-inclined spiral galaxy in the Virgo Cluster which is a very clear example of strong, ongoing ICM-ISM stripping. Although the older stellar disk appears undisturbed, multi-wavelength data (WIYN BVR-H?, VLA 21-cm HI and radio continuum, and GALEX NUV and FUV) reveal one-sided extraplanar structures in dust, H?, HI, and NUV. At the leading edge of the interaction, the ISM, as traced by H? and dust extinction, curves sharply out of the disk. This upturn feature suggests that many different phases of the ISM are affected by ram pressure at around the same time in the stripping process. On the trailing side, the ISM forms a tail which contains 10% of the galaxy's total HI emission, as well as 8% of its NUV and FUV, and several HII regions. A strong gradient in the UV-optical colors on the leading side of the gas-stripped disk suggests that it has taken 200 - 500 Myr to strip the gas from a radius of >8 to 5 kpc. However, there are clear indications that the gas distribution on the downstream (tail) side of the galaxy is changing rapidly. The disk from 5 - 10 kpc on the tail side is FUV-bright but lacks H? and HI emission, suggesting either a recent change in the direction of ram pressure or highly turbulent motions in the gas. The HI and HII peaks in the tail are offset, suggesting that the tail is currently moving away from the disk at 100 km/s. These observations are consistent with a scenario in which ram pressure increased rapidly 200 - 400 years ago, stripping the disk from >8 to 5 kpc. Within the past 50 Myr, the gas disk has gone from highly asymmetric to relatively symmetric.

Abramson, Anne; Kenney, J. D. P.; Crowl, H. H.; Chung, A.; van Gorkom, J. H.; Vollmer, B.; Schiminovich, D.

2010-01-01

139

Preliminary results on the determination of the theoretical non-adiabatic observable phase lag (?T) using VIRGO color photometry  

NASA Astrophysics Data System (ADS)

The helioseismic instruments aboard the SOHO satellite make it possible to measure solar oscillations as variations of the irradiance (VIRGO) or as variations of the photospheric velocity (GOLF). Theoretically, phase differences between different photometric bands are expected to be around 0 degrees over the p-mode frequency range. By using VIRGO (red) and VIRGO (blue) data, we find a mean phase shift of 8.05±1.81°, whereas by using VIRGO (green) and VIRGO (blue) data, we got a mean value of -1.04±0.19°. Hence, when the analysis includes the VIRGO infrared range, the Sun's atmosphere does not follow an exact adiabatic behavior. In this study, we use the phase shifts obtained by VIRGO (green) and VIRGO (blue) to determine the non-adiabatic parameter phase lag (?T) as a function of frequency. To this aim, we applied the non radial linearized formula put in the complex form by Garrido: we found a mean value of ?T = 179.95°. The lowest value being ?T = 179.90°, the departure from theoretical predictions is less then a tenth of a degree over the entire p mode frequency range. We can state that the solar atmosphere has a behavior close to the adiabatic case, when the phase shifts and amplitude ratios are computed using VIRGO (green) and VIRGO (blue) data. Nevertheless this small deviation is significant.

Simoniello, R.; Garrido, R.; Jiménez, A.

2008-06-01

140

{sup 12}CO(J = 1 - 0) ON-THE-FLY MAPPING SURVEY OF THE VIRGO CLUSTER SPIRALS. I. DATA AND ATLAS  

SciTech Connect

We have performed an On-The-Fly (OTF) mapping survey of {sup 12}CO(J = 1-0) emission in 28 Virgo cluster spiral galaxies using the Five College Radio Astronomy Observatory (FCRAO) 14 m telescope. This survey aims to characterize the CO distribution, kinematics, and luminosity of a large sample of galaxies covering the full extents of stellar disks, rather than sampling only the inner disks or the major axis as was done by many previous single dish and interferometric CO surveys. CO emission is detected in 20 galaxies among the 28 Virgo spirals observed. An atlas consisting of global measures, radial measures, and maps is presented for each detected galaxy. A note summarizing the CO data is also presented along with relevant information from the literature. The CO properties derived from our OTF observations are presented and compared with the results from the FCRAO Extragalactic CO Survey by Young et al. which utilized position-switching observations along the major axis and a model fitting method. We find that our OTF-derived CO properties agree well with the Young et al. results in many cases, but the Young et al. measurements are larger by a factor of 1.4-2.4 for seven (out of 18) cases. We will explore further the possible causes for the discrepancy in the analysis paper currently under preparation.

Chung, E. J. [Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of); Rhee, M.-H. [Yonsei University Observatory, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, H. [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Yun, Min S.; Heyer, M.; Young, J. S. [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)], E-mail: rigelej@yonsei.ac.kr

2009-10-01

141

Exploring dark matter with Milky Way substructure.  

PubMed

The unambiguous detection of dark matter annihilation in our Galaxy would unravel one of the most outstanding puzzles in particle physics and cosmology. Recent observations have motivated models in which the annihilation rate is boosted by the Sommerfeld effect, a nonperturbative enhancement arising from a long-range attractive force. We applied the Sommerfeld correction to Via Lactea II, a high-resolution N-body simulation of a Milky Way-sized galaxy, to investigate the phase-space structure of the galactic halo. We found that the annihilation luminosity from kinematically cold substructure could be enhanced by orders of magnitude relative to previous calculations, leading to the prediction of gamma-ray fluxes from as many as several hundred dark clumps that should be detectable by the Fermi satellite. PMID:19608862

Kuhlen, Michael; Madau, Piero; Silk, Joseph

2009-07-16

142

Star-forming Substructure within Molecular Clouds  

NASA Astrophysics Data System (ADS)

Wide-field far-infrared/submillimeter continuum maps of molecular clouds by the Herschel Space Observatory GBS and HOBYS surveys are revealing the star-forming substructures that lead to star formation in dense gas. In particular, these maps have revealed the central role in clouds of filaments, likely formed through turbulent motions. These filaments appear to be non-isothermal and fragment into cores only when their column densities exceed a stability threshold. Organizations of filament networks suggest the relative role of turbulence and gravity can be traced in different parts of a cloud, and filament intersections may lead to larger amounts of mass flow that form the precursors of high-mass stars or clusters.

Di Francesco, James

2013-03-01

143

Microscopic substructure effects in nucleon capture reactions  

NASA Astrophysics Data System (ADS)

Nucleon capture reactions at low energies, such as ^7Be(p,?)^8B, ^16O(p,?)^17F, or ^7Li (n,?)^8Li, play an important role in our understanding of astrophysical phenomena. For example, exact knowledge of the first two reaction rates is necessary for modeling the energy generation and evolution of hydrogen-burning stars. In addition, the ^7Be(p,?)^8B reaction at solar energies (E_cm<= 20 keV) plays a key role in the `solar neutrino puzzle' since the neutrino event rate in the existing chlorine and water Cerenkov detectors is dominated by the high-energy neutrinos produced in the subsequent ? decay of ^8B. The ^7Li (n,?)^8Li reaction is a key element of primordial nucleosynthesis in inhomogeneous Big Bang scenarios. Direct measurements of capture reactions at energies corresponding to astrophysically relevant temperatures are often very difficult, since the cross sections diminish exponentially at low energies. Thus, theoretical studies of these processes become very valuable. Cross sections of external capture reactions depend primarily on the asymptotic normalization of the final bound-state wave function. The asymptotic normalization, however, is in turn connected to the short-distance behavior of the wave function through the bound-state Lippmann-Schwinger equation. We discuss the implications of this connection for theoretical determinations of the low-energy S factor. In particular, we study the role that microscopic substructure effects play in the low-energy cross sections of capture reactions. We discuss various approximation schemes for the full many-body problem and clarify the role of one-body models in the description of direct capture reactions. We illustrate how microscopic substructure effects arise naturally in the relevant transition matrix element and can be (in part) accounted for via a spectroscopic factor.

Escher, Jutta; Jennings, Byron K.; Sherif, Helmy S.

2001-10-01

144

The magnetic fields of large Virgo cluster spirals. II  

NASA Astrophysics Data System (ADS)

Context. The Virgo cluster of galaxies provides excellent conditions for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated in detail. Aims: We extend our systematic search for possible anomalies in the magnetic field structures of Virgo cluster spirals in order to characterize a variety of effects and attribute them to different disturbing agents. Methods: Six angularly large Virgo cluster spiral galaxies (NGC 4192, NGC 4302, NGC 4303, NGC 4321, NGC 4388, and NGC 4535) were targets of a sensitive total power and polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz and 8.35 GHz (except for NGC 4388 observed only at 4.85 GHz, and NGC 4535 observed only at 8.35 GHz). The presented two-frequency studies allow Faraday rotation analysis. Results: Magnetic field structures distorted to various extent are found in all galaxies. Three galaxies (NGC 4302, NGC 4303, and NGC 4321) show some signs of possible tidal interactions, while NGC 4388 and NGC 4535 have very likely experienced strong ram-pressure and shearing effects, respectively, visible as distortions and asymmetries of polarized intensity distributions. As in our previous study, even strongly perturbed galaxies closely follow the radio-far-infrared correlation. In NGC 4303 and NGC 4321, we observe symmetric spiral patterns of the magnetic field and in NGC 4535 an asymmetric pattern. Conclusions: The cluster environment clearly affects the evolution of its member galaxies via various effects. Magnetic fields allow us to trace even weak interactions that are difficult to detect with other observations. Our results show that the degree of distortions of a galaxy is not a simple function of the distance to the cluster center but reflects also the history of its interactions. The angle ? between the velocity vector v and the rotation vector ? of a galaxy may be a general parameter that describes the level of distortions of galactic magnetic fields. Information about the motions of galaxies in the sky plane and their three-dimensional distribution, as well as information about the intracluster medium can also be obtained from the Faraday rotation analysis. Based on the observations with the 100-m telescope at Effelsberg operated by the Max-Planck-Institut für Radioastronomie (MPIfR) on behalf of the Max-Planck-Gesellschaft.

We?gowiec, M.; Urbanik, M.; Beck, R.; Chy?y, K. T.; Soida, M.

2012-09-01

145

The magnetic fields of large Virgo Cluster spirals  

NASA Astrophysics Data System (ADS)

Context: Because of its proximity the Virgo Cluster is an excellent target for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated. Aims: Optical and/or H I observations do not always show the effects of weak interactions between galaxies and their encounters with the cluster medium. For this reason we searched for possible anomalies in the magnetic field structure in Virgo Cluster spirals that could be attributed to perturbations in their gas distribution and kinematics. Methods: Five angularly large Virgo Cluster spiral galaxies (NGC 4501, NGC 4438, NGC 4535, NGC 4548, and NGC 4654) were the targets of a sensitive total power and polarization study using the 100-m radio telescope in Effelsberg at 4.85 GHz. For two objects, polarization data at higher frequencies were obtained allowing Faraday rotation analysis. Results: Distorted magnetic field structures were identified in all galaxies. Interaction-induced magnetized outflows were found in NGC 4438 (due to nuclear activity) and NGC 4654 (a combination of tidal tails and ram pressure effects). Almost all objects (except the anaemic NGC 4548), exhibit distortions in polarized radio continuum attributable to the influence of the ambient gas. For some galaxies they agree with observations of other species, but the magnetic field is sometimes (NGC 4535) the only tracer of the interaction with the cluster environment. Conclusions: The cluster environment clearly affects the evolution of the galaxies due to ram pressure and tidal effects. Magnetic fields provide a very long lasting memory of past interactions. Therefore, they are a good tracer of weak interactions that are difficult to detect by other observations. Information about motions of galaxies in the sky plane and their three-dimensional distribution can also be obtained. Based on the observations with the 100-m telescope at Effelsberg operated by the Max-Planck-Institut für Radioastronomie (MPIfR) on behalf of the Max-Planck-Gesellschaft.

We?gowiec, M.; Urbanik, M.; Vollmer, B.; Beck, R.; Chy?y, K. T.; Soida, M.; Balkowski, Ch.

2007-08-01

146

CAUGHT IN THE ACT: STRONG, ACTIVE RAM PRESSURE STRIPPING IN VIRGO CLUSTER SPIRAL NGC 4330  

SciTech Connect

We present a multi-wavelength study of NGC 4330, a highly inclined spiral galaxy in the Virgo Cluster which is a clear example of strong, ongoing intracluster medium-interstellar medium (ICM-ISM) ram pressure stripping. The H I has been removed from well within the undisturbed old stellar disk, to 50%-65% of R{sub 25}. Multi-wavelength data (WIYN BVR-H{alpha}, Very Large Array 21 cm H I and radio continuum, and Galaxy Evolution Explorer NUV and FUV) reveal several one-sided extraplanar features likely caused by ram pressure at an intermediate disk-wind angle. At the leading edge of the interaction, the H{alpha} and dust extinction curve sharply out of the disk in a remarkable and distinctive 'upturn' feature that may be generally useful as a diagnostic indicator of active ram pressure. On the trailing side, the ISM is stretched out in a long tail which contains 10% of the galaxy's total H I emission, 6%-9% of its NUV-FUV emission, but only 2% of the H{alpha}. The centroid of the H I tail is downwind of the UV/H{alpha} tail, suggesting that the ICM wind has shifted most of the ISM downwind over the course of the past 10-300 Myr. Along the major axis, the disk is highly asymmetric in the UV, but more symmetric in H{alpha} and H I, also implying recent changes in the distributions of gas and star formation. The UV-optical colors indicate very different star formation histories for the leading and trailing sides of the galaxy. On the leading side, a strong gradient in the UV-optical colors of the gas-stripped disk suggests that it has taken 200-400 Myr to strip the gas from a radius of >8 to 5 kpc, but on the trailing side there is no age gradient. All our data suggest a scenario in which NGC 4330 is falling into the cluster center for the first time and has experienced a significant increase in ram pressure over the last 200-400 Myr. Many of the UV-bright stars that form outside the thin disk due to ram pressure will ultimately produce stellar thick disk and halo components with characteristic morphologies and age distributions distinct from those produced by gravitational interactions.

Abramson, Anne; Kenney, Jeffrey D. P. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Crowl, Hugh H.; Van Gorkom, J. H.; Schiminovich, David [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Chung, Aeree [Department of Astronomy, Yonsei University, 134 Shinchonding, Seodaemungu, Seoul 120-749 (Korea, Republic of); Vollmer, Bernd, E-mail: anne.abramson@yale.edu, E-mail: jeff.kenney@yale.edu, E-mail: hugh@astro.columbia.edu, E-mail: jvangork@astro.columbia.edu, E-mail: ds@astro.columbia.edu, E-mail: achung@yonsei.ac.kr, E-mail: bvollmer@astro.u-strasbg.fr [Observatoire astronomique de Strasbourg, 11 rue de l'universite, 67000 Strasbourg (France)

2011-05-15

147

Caught in the Act: Strong, Active Ram Pressure Stripping in Virgo Cluster Spiral NGC 4330  

NASA Astrophysics Data System (ADS)

We present a multi-wavelength study of NGC 4330, a highly inclined spiral galaxy in the Virgo Cluster which is a clear example of strong, ongoing intracluster medium-interstellar medium (ICM-ISM) ram pressure stripping. The H I has been removed from well within the undisturbed old stellar disk, to 50%-65% of R 25. Multi-wavelength data (WIYN BVR-H?, Very Large Array 21 cm H I and radio continuum, and Galaxy Evolution Explorer NUV and FUV) reveal several one-sided extraplanar features likely caused by ram pressure at an intermediate disk-wind angle. At the leading edge of the interaction, the H? and dust extinction curve sharply out of the disk in a remarkable and distinctive "upturn" feature that may be generally useful as a diagnostic indicator of active ram pressure. On the trailing side, the ISM is stretched out in a long tail which contains 10% of the galaxy's total H I emission, 6%-9% of its NUV-FUV emission, but only 2% of the H?. The centroid of the H I tail is downwind of the UV/H? tail, suggesting that the ICM wind has shifted most of the ISM downwind over the course of the past 10-300 Myr. Along the major axis, the disk is highly asymmetric in the UV, but more symmetric in H? and H I, also implying recent changes in the distributions of gas and star formation. The UV-optical colors indicate very different star formation histories for the leading and trailing sides of the galaxy. On the leading side, a strong gradient in the UV-optical colors of the gas-stripped disk suggests that it has taken 200-400 Myr to strip the gas from a radius of >8 to 5 kpc, but on the trailing side there is no age gradient. All our data suggest a scenario in which NGC 4330 is falling into the cluster center for the first time and has experienced a significant increase in ram pressure over the last 200-400 Myr. Many of the UV-bright stars that form outside the thin disk due to ram pressure will ultimately produce stellar thick disk and halo components with characteristic morphologies and age distributions distinct from those produced by gravitational interactions.

Abramson, Anne; Kenney, Jeffrey D. P.; Crowl, Hugh H.; Chung, Aeree; van Gorkom, J. H.; Vollmer, Bernd; Schiminovich, David

2011-05-01

148

Flexible substructure online hybrid test system using conventional testing devices  

NASA Astrophysics Data System (ADS)

This paper presents a substructure online hybrid test system that is extensible for geographically distributed tests. This system consists of a set of devices conventionally used for cyclic tests to load the tested substructures onto the target displacement or the target force. Due to their robustness and portability, individual sets of conventional loading devices can be transported and reconfigured to realize physical loading in geographically remote laboratories. Another appealing feature is the flexible displacement-force mixed control that is particularly suitable for specimens having large disparities in stiffness during various performance stages. To conduct a substructure online hybrid test, an extensible framework is developed, which is equipped with a generalized interface to encapsulate each substructure. Multiple tested substructures and analyzed substructures using various structural program codes can be accommodated within the single framework, simply interfaced with the boundary displacements and forces. A coordinator program is developed to keep the boundaries among all substructures compatible and equilibrated. An Internet-based data exchange scheme is also devised to transfer data among computers equipped with different software environments. A series of online hybrid tests are introduced, and the portability, flexibility, and extensibility of the online hybrid test system are demonstrated.

Wang, Tao; Nakashima, Masayoshi

2013-09-01

149

Automatic Alignment for the first science run of the Virgo interferometer  

NASA Astrophysics Data System (ADS)

During the past few years a network of large-scale laser interferometers, including the Virgo detector, has been developed with the aim of detecting gravitational waves. To properly operate the detectors, the longitudinal and angular positions of the suspended detector test masses, the interferometer mirrors, must be kept within a small range from the operating point. The design of the Virgo angular control system, called Automatic Alignment is based on a modified version of the Anderson-Giordano technique, a wave-front sensing scheme which uses the modulation-demodulation technique. This paper will present the theoretical background of the Virgo Automatic Alignment system, the implementation issues and the performances observed during the first Virgo science run (VSR1). A total RMS of 4 × 10 -2 to 3 × 10 -3 ?rad for all angular degrees of freedom has been achieved.

Acernese, F.; Alshourbagy, M.; Antonucci, F.; Aoudia, S.; Arun, K. G.; Astone, P.; Ballardin, G.; Barone, F.; Barsuglia, M.; Bauer, Th. S.; Bigotta, S.; Birindelli, S.; Bizouard, M. A.; Boccara, C.; Bondu, F.; Bonelli, L.; Bosi, L.; Braccini, S.; Bradaschia, C.; Brillet, A.; Brisson, V.; Bulten, H. J.; Buskulic, D.; Cagnoli, G.; Calloni, E.; Campagna, E.; Canuel, B.; Carbognani, F.; Carbone, L.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cesarini, E.; Chassande-Mottin, E.; Chatterji, S.; Cleva, F.; Coccia, E.; Colas, J.; Colombini, M.; Corda, C.; Corsi, A.; Coulon, J.-P.; Cuoco, E.; D'Antonio, S.; Dari, A.; Dattilo, V.; Davier, M.; De Rosa, R.; Del Prete, M.; Di Fiore, L.; Di Lieto, A.; Di Paolo Emilio, M.; Di Virgilio, A.; Fafone, V.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Garufi, F.; Genin, E.; Gennai, A.; Giazotto, A.; Granata, M.; Granata, V.; Greverie, C.; Guidi, G.; Heitmann, H.; Hello, P.; Hild, S.; Huet, D.; La Penna, P.; Laval, M.; Leroy, N.; Letendre, N.; Lorenzini, M.; Loriette, V.; Losurdo, G.; Mackowski, J.-M.; Majorana, E.; Man, C. N.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marque, J.; Martelli, F.; Masserot, A.; Menzinger, F.; Michel, C.; Milano, L.; Minenkov, Y.; Mohan, M.; Moreau, J.; Morgado, N.; Mosca, S.; Mours, B.; Neri, I.; Nocera, F.; Pagliaroli, G.; Palomba, C.; Paoletti, F.; Pardi, S.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Persichetti, G.; Piergiovanni, F.; Pinard, L.; Poggiani, R.; Punturo, M.; Puppo, P.; Rabaste, O.; Rapagnani, P.; Regimbau, T.; Ricci, F.; Rocchi, A.; Rolland, L.; Romano, R.; Ruggi, P.; Sassolas, B.; Sentenac, D.; Swinkels, B. L.; Terenzi, R.; Toncelli, A.; Tonelli, M.; Tournefier, E.; Travasso, F.; Trummer, J.; Vajente, G.; van den Brand, J. F. J.; van der Putten, S.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinet, J.-Y.; Vocca, H.; Was, M.; Yvert, M.

2010-04-01

150

Multiband photometric decomposition of nuclear stellar disks  

NASA Astrophysics Data System (ADS)

Context. Small, bright stellar disks with scale lengths of a few tens of parsec are known to reside in the center of galaxies. They are believed to have formed in a dissipational process as the end result of star formation in gas either accreted during a merging (or acquisition) event or piled up by the secular evolution of a nuclear bar. Only a few of them have been studied in detail to date. Aims: Using archival Hubble Space Telescope (HST) imaging, we investigate the photometric parameters of the nuclear stellar disks hosted by three early-type galaxies in the Virgo cluster, NGC 4458, NGC 4478, and NGC 4570, to constrain the process that forms their stars. Methods: The central surface brightness, scale length, inclination, and position angle of the nuclear disks were derived by adopting the photometric decomposition method introduced by Scorza & Bender and assuming the disks to be infinitesimally thin and exponential. Results: The location, orientation, and size of the nuclear disks is the same in all the images obtained with the Wide Field Planetary Camera 2 and Advanced Camera for Surveys and available in the HST Science Archive. The scale length, inclination, and position angle of each disk are constant within the errors in the observed U, B, V, and I passbands, independently of their values and the properties of the host spheroid. Conclusions: We interpret the absence of color gradients in the stellar population of the nuclear disks as the signature that star formation homogeneously occurred along their length. An inside-out formation scenario is, instead, expected to produce color gradients and is therefore ruled out.

Morelli, L.; Cesetti, M.; Corsini, E. M.; Pizzella, A.; Dalla Bontà, E.; Sarzi, M.; Bertola, F.

2010-07-01

151

Parameter Estimation in Practice for Advanced LIGO/Virgo  

NASA Astrophysics Data System (ADS)

In the next few years the LIGO and Virgo gravitational waves observatories will enter their advanced phase, when detections are highly anticipated. Among them, detections of signals from compact binary coalescences are particularly promising for astrophysical studies. Parameter estimation of those signals to recover the source properties is a necessary but complex problem which can be simplified under several assumptions, which have various effect on the level of biases in parameter recovery. We focus on simplifying assumptions on the spins of the compact objects, such as neglecting them or setting them aligned with the orbital angular momentum. And we use our Bayesian inference code to evaluate the resulting accuracy in intrinsic and extrinsic parameter recovery. Sky location recovery is particularly relevant as a balance needs to be reached between a fast analysis which may not be accurate enough and a complete analysis which may take too long to be of use for electromagnetic follow-up.

Raymond, Vivien; LVC

2013-01-01

152

The Impact of the Virgo Cluster Environment on the Chemical Evolution of Dwarf Irregular Galaxies  

Microsoft Academic Search

Chemical and structural properties of Virgo Cluster dwarf irregular galaxies are compared with those of Local Group dwarf irregulars to determine the extent of the effect of cluster environment on dwarf galaxies. A sample of seven Virgo dwarf irregular galaxies with luminosities -15 ga M_B ga -16 was selected. Results obtained from recent optical long-slit spectrophotometry and broad-band photometry of

H. Lee; M. L. McCall; M. G. Richer

1998-01-01

153

The Origin of Dwarf Ellipticals in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We study the evolution of dwarf (LH<109.6 LHsolar) star-forming and quiescent galaxies in the Virgo Cluster by comparing their UV to radio centimetric properties to the predictions of multizone chemospectrophotometric models of galaxy evolution especially tuned to take into account the perturbations induced by the interaction with the cluster intergalactic medium. Our models simulate one or multiple ram pressure stripping events and galaxy starvation. Models predict that all star-forming dwarf galaxies entering the cluster for the first time loose most, if not all, of their atomic gas content, quenching on short timescales (<=150 Myr) their activity of star formation. These dwarf galaxies soon become red and quiescent, gas metal-rich objects with spectrophotometric and structural properties similar to those of dwarf ellipticals. Young, low-luminosity, high surface brightness star-forming galaxies such as late-type spirals and BCDs are probably the progenitors of relatively massive dwarf ellipticals, while it is likely that low surface brightness Magellanic irregulars evolve into very low surface brightness quiescent objects hardly detectable in ground-based imaging surveys. The small number of dwarf galaxies with physical properties intermediate between those of star-forming and quiescent systems is consistent with a rapid (<1 Gyr) transitional phase between the two dwarf galaxy populations. These results, combined with statistical considerations, are consistent with the idea that most of the dwarf ellipticals dominating the faint end of the Virgo luminosity function were initially star-forming systems, accreted by the cluster and stripped of their gas by one or subsequent ram pressure stripping events.

Boselli, A.; Boissier, S.; Cortese, L.; Gavazzi, G.

2008-02-01

154

Software engineering practices for the EGO Virgo project  

NASA Astrophysics Data System (ADS)

The Virgo Gravitational Waves Detector has recently entered its commissioning phase. An important element in this phase is the application of Software Engineering (SE) practices to the Control and Data Analysis Software. This article focus on the experience in applying those SE practices as a simple but effective set of standards and tools. The main areas covered are software configuration management, problem reporting, integration planning, software testing and systems performance monitoring. Key elements of Software Configuration Management (SCM) are source code control allowing checkin/checkout of sources from a software archive combined with a backup plan. The tool SCVS developed on top of CVS in order to provide an easier and more structured use mode is supporting this. Tracking bugs and modifications is a necessary complement of SCM. A central database with email and web interface to submit, query and modify Software Problem Reports (SPR) has been implemented on top of the WREQ tool. Integrating software components that were not designed with integration in mind is one of the major problems in software development. An explicit Integration Plan is therefore absolutely essential. We are currently implementing a slow upgrade cycle Common Software Releases management as structured integration plan. Software Testing must be closely integrated with development and to the most feasible extent automatic. With the use of the automated test tool tat, the developer can incrementally build a unit/regression test suite that will help measure progress, spot unintended side effects, and focus the development efforts. One of the characteristics of large and complex projects, like Virgo, is the difficulty in understanding how well the different subsystems are performing and then plan for changes. In order to support System Performance Monitoring the tool Big Brother has been adopted to make it possible to trace the reliability of the different subsystems and thus providing essential information for software improvements.

Carbognani, Franco; de Wet, Jacques

2004-09-01

155

Prediction of CNS activity of compound libraries using substructure analysis.  

PubMed

An in silico ADME/Tox prediction tool based on substructural analysis has been developed. The tool called SUBSTRUCT has been used to predict CNS activity. Data sets with CNS active and nonactive drugs were extracted from the World Drug Index (WDI). The SUBSTRUCT program predicts CNS activity as good as a much more complicated artificial neural network model. SUBSTRUCT separates the data sets with approximately 80% accuracy. Substructural analysis also shows surprisingly large differences in substructure profiles between CNS active and nonactive drugs. PMID:12546548

Engkvist, Ola; Wrede, Paul; Rester, Ulrich

156

Candidates for Intracluster Planetary Nebulae in the Virgo Cluster Based on the Suprime-Cam Narrow-Band Imaging in [O III] and H?  

NASA Astrophysics Data System (ADS)

We have identified 38 candidates of intracluster planetary nebulae (ICPNe) in a 34' × 27' field in the core of the Virgo cluster based on Suprime-Cam imaging through two narrow-band filters centered at redshifted wavelengths of the [O III] ?=5007Å and the H? ?=6563Å lines. Broad-band images in the V and R bands are used to check for any emissions in the adjacent continuum. We describe the method briefly and present a list of the intracluster planetary nebula candidates, together with their finding charts. The ICPN candidates show a highly inhomogeneous distribution, which may suggest an association with the M 86-M 84 subcluster. The fraction of diffuse intracluster light with respect to the total light in galaxies is estimated to be about 10%, leading to an estimate of about 20% for the baryon fraction. A spectroscopic follow up and a wider survey are critical to reveal the nature of the intracluster stellar population.

Okamura, Sadanori; Yasuda, Naoki; Arnaboldi, Magda; Freeman, Kenneth C.; Ando, Hiroyasu; Doi, Mamoru; Furusawa, Hisanori; Gerhard, Ortwin; Hamabe, Masaru; Kimura, Masahiko; Kajino, Toshitaka; Komiyama, Yutaka; Miyazaki, Satoshi; Nakata, Fumiaki; Napolitano, Nicola R.; Ouchi, Masami; Pannella, Maurilio; Sekiguchi, Maki; Shimasaku, Kazuhiro; Yagi, Masafumi

2002-12-01

157

A ``DIVA'' for observational stellar dynamics  

NASA Astrophysics Data System (ADS)

The planned astrometry and photometry satellite DIVA will provide a wealth of observational data on the Galaxy and its stellar content. It can be expected that these data will allow critical tests of stellar-dynamical models for the galactic disk, inner halo and star clusters, as well as give additional impetus to their further development. At present, the Hipparcos data are the best source for empirical investigations of the kinematic and dynamic structure of the solar neighbourhood within the Galaxy. Recent findings include very clear indications for an outer warp, for a central bar and for local kinematic substructures. For the research on star clusters, Hipparcos e.g. provided the first six-dimensional (i.e. distance-resolved) observational model case: the Hyades. Its structure generally agrees with stellar-dynamical models for mass segregation and cluster dissolution in the galactic tidal field. Not unexpectedly, the small number of stars in the Hipparcos Catalogue turns out to be the major limitation for further progress, both for clusters and for the galactic structure at larger scales. Compared to Hipparcos, DIVA will provide significantly more precise proper motions and parallaxes, for a very much larger number of stars. Possible developments using this improved empirical basis will be sketched during the talk.

Bastian, U.; Dehnen, W.; Schilbach, E.

158

Creep induced substructures in titanium aluminide  

NASA Astrophysics Data System (ADS)

Many investigations have examined the creep properties of titanium aluminides. Attempts to classify observed behaviors with existing models for high temperature deformation have been met with limited success. Several researchers have shown that an understanding of substructural evolution in the early stages of the creep curve may offer insight into the mechanisms, which control the rate of deformation. Creep deformation has been shown to include twinning, recrystallization, grain boundary sliding, ordinary and super dislocation activity, and faulting depending on the microstructure of the alloy and testing conditions. However, the environments that these alloys are likely to be exposed to are not similar to the test conditions in the literature. Furthermore the emphasis of much of the research into this group of alloys has been on the effects of microstructure particularly, the volume fraction of lamellar phase and ternary elemental additions. With all of these studies little information is available on the deformation behavior of the gamma phase. The alloys in these studies are mostly composed of the gamma phase and yet its creep behavior is not well understood. For this reason single phase binary gamma titanium aluminides were investigated in this study. To understand the effects of aluminum, interstitial oxygen content, and stress on creep, five alloys of varying Al concentrations and interstitial oxygen contents were deformed at temperatures ranging from 700--800°C and at stresses of 150, 200, and 250MPa. Full creep curves were developed under these conditions and phenomenological parameters for creep were calculated from these data. Additional tests were interrupted during primary and secondary creep at 760°C. Specimens from the interrupted tests as well as from the as-processed materials were examined optically and by TEM. Creep data and the microscopy were analyzed in concert to determine rate-controlling mechanisms for creep. Evolution of the substructure with strain and as a function of interstitial oxygen content and stress will be discussed. Finally, mechanisms for the formation of deformation twins and accommodation reactions for the stresses associated with twins terminating within the TiAl matrix will be presented.

Cerreta, Ellen Kathleen

159

Advanced stellarator power plants  

SciTech Connect

The stellarator is a class of helical/toroidal magnetic fusion devices. Recent international progress in stellarator power plant conceptual design is reviewed and comparisons in the areas of physics, engineering, and economics are made with recent tokamak design studies.

Miller, R.L.

1994-07-01

160

11. General view of substructure, with concentrate pier in the ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. General view of substructure, with concentrate pier in the immediate foreground right side of frame - Robertson Bridge, Spanning Rogue River on Rogue River Highway Loop No. 260, Merlin, Josephine County, OR

161

98. DETAIL VIEW OF STORM DAMAGE AND EXPOSED SUBSTRUCTURE, NORTHWEST ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

98. DETAIL VIEW OF STORM DAMAGE AND EXPOSED SUBSTRUCTURE, NORTHWEST SIDE OF 4TH TEE, LOOKING WEST - Huntington Beach Municipal Pier, Pacific Coast Highway at Main Street, Huntington Beach, Orange County, CA

162

65. VIEW LOOKING UPSTREAM FROM FLUME SUBSTRUCTURE, SHOWING COLUMBIA IMPROVEMENT ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

65. VIEW LOOKING UPSTREAM FROM FLUME SUBSTRUCTURE, SHOWING COLUMBIA IMPROVEMENT COMPANY'S NEISSON CREEK SAWMILL. Print No. 177, November 1903 - Electron Hydroelectric Project, Along Puyallup River, Electron, Pierce County, WA

163

Rapid Bridge Construction Technology: Precast Elements for Substructures.  

National Technical Information Service (NTIS)

The goal of this research was to propose an alternate system of precast bridge substructures which can substitute for conventional cast in place systems in Wisconsin to achieve accelerated construction. Three types of abutment modules (hollow wall with ca...

D. Unlu M. G. Oliva P. Okumus

2011-01-01

164

2. SUBSTRUCTURE DETAIL OF SOUTH FACE FACING WEST ACROSS EL ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

2. SUBSTRUCTURE DETAIL OF SOUTH FACE FACING WEST ACROSS EL CAPITAN MEADOW WITH CATHEDRAL ROCK IN DISTANCE. - El Capitan Bridge, Spanning Merced River on El Capitan crossover road, Yosemite Village, Mariposa County, CA

165

5. DETAIL OF THE SOUTHWEST SIDE OF THE SUBSTRUCTURE OF ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

5. DETAIL OF THE SOUTHWEST SIDE OF THE SUBSTRUCTURE OF GOVERNMENT BRIDGE, FACING NORTHEAST. - Georgia DOT Bridge No. 047-00820F-00347E, County Road 382 Spanning Chickamauga Creek, Ringgold, Catoosa County, GA

166

23. DETAIL VIEW OF FIXED SPAN SUBSTRUCTURE, EAST SPAN, SHOWING ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

23. DETAIL VIEW OF FIXED SPAN SUBSTRUCTURE, EAST SPAN, SHOWING CONDITION OF GRANITE PIERS AND PILES OF ADJACENT PIER, LOOKING SOUTHEAST - Congress Street Bascule Bridge, Spanning Fort Point Channel at Congress Street, Boston, Suffolk County, MA

167

10. Substructure of bridge, showing timber bents, piles, crossbracing, caps ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

10. Substructure of bridge, showing timber bents, piles, cross-bracing, caps and stringers under deck. View to northeast. - Outlet Creek Bridge, Sullivan Lake Ranger Administrative Site, Metaline Falls, Pend Oreille County, WA

168

Observations of Cluster Substructure Using Weakly Lensed Sextupole Moments.  

National Technical Information Service (NTIS)

Since dark matter clusters and groups may have substructure, we have examined the sextupole content of Hubble images looking for a curvature signature in background galaxies that would arise from galaxy-galaxy lensing. We describe techniques for extractin...

J. Irwin M. Shmakova

2003-01-01

169

Substructural Development During Strain Cycling of Alpha Iron.  

National Technical Information Service (NTIS)

Substructural developments during reversed axial strain cycling of alpha iron have been studies at room temperature. The nature of the structure varied considerably at different stages of fatigue life. A distinct cell structure developed gradually with co...

O. K. Chopra C. V. B. Gowda

1974-01-01

170

Cold Dark Matter Substructure and Galactic Disks I: Morphological Signatures of Hierarchical SatelliteAccretion  

SciTech Connect

We conduct a series of high-resolution, fully self-consistent dissipation less N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the {Lambda}CDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. Substructure mass functions, orbital distributions, internal structures, and accretion times are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. We demonstrate that accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z {approx} 1 should be common occurrences. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. This is due to the fact that massive subhalos with small orbital pericenters that are most capable of strongly perturbing the disk become either tidally disrupted or suffer substantial mass loss prior to z = 0. One host halo merger history is subsequently used to seed controlled N-body experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. These simulations track the effects of six dark matter substructures, with initial masses in the range {approx} (0.7-2) x 10{sup 10} M{sub {circle_dot}} ({approx} 20-60% of the disk mass), crossing the disk in the past {approx} 8 Gyr. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a long-lived, low-surface brightness, ring-like feature in the outskirts; a significant flare; a central bar; and faint filamentary structures that (spuriously) resemble tidal streams in configuration space. The final distribution of disk stars exhibits a complex vertical structure that is well-described by a standard 'thin-thick' disk decomposition, where the 'thick' disk component has emerged primarily as a result of the interaction with the most massive subhalo. We conclude that satellite-disk encounters of the kind expected in {Lambda}CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way, M31, and in other nearby and distant disk galaxies. These results highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution. Upcoming galactic structure surveys and astrometric satellites may be able to distinguish between competing cosmological models by testing whether the detailed structure of galactic disks is as excited as predicted by the CDM paradigm.

Kazantzidis, Stelios; Bullock, James S.; Zentner, Andrew R.; Kravtsov, Andrey V.; Moustakas, Leonidas A.

2007-12-03

171

Finding Nonoverlapping Substructures of a Sparse Matrix  

SciTech Connect

Many applications of scientific computing rely on computations on sparse matrices. The design of efficient implementations of sparse matrix kernels is crucial for the overall efficiency of these applications. Due to the high compute-to-memory ratio and irregular memory access patterns, the performance of sparse matrix kernels is often far away from the peak performance on a modern processor. Alternative data structures have been proposed, which split the original matrix A into A{sub d} and A{sub s}, so that A{sub d} contains all dense blocks of a specified size in the matrix, and A{sub s} contains the remaining entries. This enables the use of dense matrix kernels on the entries of A{sub d} producing better memory performance. In this work, we study the problem of finding a maximum number of nonoverlapping dense blocks in a sparse matrix, which is previously not studied in the sparse matrix community. We show that the maximum nonoverlapping dense blocks problem is NP-complete by using a reduction from the maximum independent set problem on cubic planar graphs. We also propose a 2/3-approximation algorithm that runs in linear time in the number of nonzeros in the matrix. This extended abstract focuses on our results for 2x2 dense blocks. However we show that our results can be generalized to arbitrary sized dense blocks, and many other oriented substructures, which can be exploited to improve the memory performance of sparse matrix operations.

Pinar, Ali; Vassilevska, Virginia

2005-08-11

172

Substructure Formation Induced by Gravitational Tides?  

NASA Astrophysics Data System (ADS)

Physics lectures always refer to the tides as a disruptive effect. However, tides can also be compressive. When the potential of two galaxies overlap, as happens during a merger, fully compressive tides can develop and have a strong impact on the dynamics of substructures such as star clusters or tidal dwarf galaxies. Using N-body simulations of a large set of mergers, we noticed the importance of these tidal modes at cluster scale. With a model of the Antennae galaxies, we conclude that the positions and timescales of these tidal modes match the actual distribution of young clusters. A detailed study of the statistics of the compressive tides shows a stunning correlation between this purely gravitational effect and the observed properties of the star clusters. In this contribution, we introduce the concept of compressive tide and show its relevance in the special case of the Antennae galaxies. We extend our conclusions to a broad range of parameters and discuss their implications on several critical points such as infant mortality, multiple star formation epochs in clusters or the age distribution.

Renaud, F.; Theis, C.; Naab, T.; Boily, C. M.

2010-06-01

173

UPDATED ANALYSIS OF A 'DARK' GALAXY AND ITS BLUE COMPANION IN THE VIRGO CLOUD H I 1225 + 01  

SciTech Connect

H I 1225+01 is an intergalactic gas cloud located on the outskirts of Virgo cluster. Its main components are two large clumps of comparable H I masses (M{sub Hi}{approx}10{sup 9} M{sub Sun }) separated by about 100 kpc. One of the clumps hosts a blue low-surface-brightness galaxy J1227+0136, while the other has no identified stellar emission and is sometimes referred to as a promising candidate of a 'dark galaxy', an optically invisible massive intergalactic system. We present a deep optical image covering the whole H I 1225+01 structure for the first time, as well as a collection of archival data from ultraviolet to far-infrared (IR) spectral region of the brightest knot 'R1' in J1227+0136. We find that R1 has a young stellar population 10-100 Myr in age and mass {approx}10{sup 6} M{sub Sun }, near-IR excess brightness which may point to the presence of hot dust with color temperature {approx}600 K, and relatively faint mid- to far-IR fluxes corresponding to the dust mass of up to {approx}100 M{sub Sun }. Overall, it seems to share the general properties with low-metallicity blue compact dwarf galaxies. On the other hand, no optical counterpart to the other clump is found in our deepest-ever image. Now the limiting surface brightness reaches down to R{sub AB} > 28 mag arcsec{sup -2} for any emission extended over 10'' (comparable to R1), which is more than one hundred times fainter than the brightest part of the companion galaxy J1227+0136.

Matsuoka, Y.; Oyabu, S. [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Ienaka, N. [Institute of Astronomy, University of Tokyo, Osawa 2-21-1, Mitaka, Tokyo 181-0015 (Japan); Wada, K. [Department of Earth and Space Science, Osaka University, Osaka 560-0043 (Japan); Takino, S., E-mail: matsuoka@a.phys.nagoya-u.ac.jp [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan)

2012-12-01

174

VIVA: VLA imaging of Virgo galaxies in atomic gas  

NASA Astrophysics Data System (ADS)

In this thesis I present high resolution HI maps and kinematics of 53 carefully selected galaxies in the Virgo cluster. The goal is to study details of the cluster environmental effect on galaxy evolution, i.e. in which density regions and by which processes do galaxies feel the impact of the cluster. Studying HI content is essential to achieve this goal as it is often a useful probe of both gas-gas and tidal interactions and also a reservoir of star formation. Virgo as a dynamically young and nearby cluster, it contains many candidates for various mechanisms at work (e.g. ram-pressure or turbulent/viscous stripping, thermal evaporation, and tidal interactions) and allows us to see the details. We have sampled 48 spirals and 5 irregular/dwarf systems which show a wide range of star formation properties from anemic to starburst. The galaxies in the sample are spread throughout the cluster from near the dense cluster core to the outskirts (0.3--3.3 Mpc in projection). The result has revealed a whole spectrum of gas stripping stages from severely HI stripped galaxies to the HI as it is leaving the disk. Most HI stripped but optically undisturbed galaxies are found within 0.5 Mpc radius in projection from the cluster center. These galaxies show signatures of ongoing interactions with the hot cluster gas. Galaxies with truncated HI disks are also found at lower density regions. Some of those might have gone through the cluster core a while ago and currently be in their way out. Some however show gas stripping epochs that is inconsistent with their locations within the cluster which requires more than a simple interaction with static cluster gas; such as tidal interactions with other galaxies or locally enhanced ram-pressure due to subclusters' falling in. Beyond this region, most galaxies show normal (.08 < or = [Special characters omitted.] < 1.2) to extended ([Special characters omitted.] > or = 1.2) HI disks. Especially, 7 galaxies were found with one-sided long Hi tails in intermediate to low density regions (0.6--1.0 Mpc in projection from the cluster center). Their HI distribution and kinematics are suggestive of current/recent stripping (within < 2 × 10 8 yrs before/after the peak pressure clue to the cluster gas). We argue that these galaxies are recent arrivals, falling into the cluster for the first time. It seems that galaxies already feel the cluster impact far out from the cluster center, by losing some gas in the outer disk through interactions with the cluster gas or tidal interactions with neighbors, or combinations of both.

Chung, Aeree

175

The SLUGGS survey: globular cluster system kinematics and substructure in NGC 4365  

NASA Astrophysics Data System (ADS)

We present a kinematic analysis of the globular cluster (GC) system of the giant elliptical galaxy NGC 4365 and find several distinct kinematic substructures. This analysis is carried out using radial velocities for 269 GCs, obtained with the DEIMOS (DEep Imaging Multi-Object Spectrograph) instrument on the Keck II telescope as part of the SAGES Legacy Unifying Globulars and Galaxies Survey (SLUGGS). We find that each of the three (formerly identified) GC colour subpopulations reveal distinct rotation properties. The rotation of the green GC subpopulation is consistent with the bulk of NGC 4365's stellar light, which 'rolls' about the photometric major axis. The blue and red GC subpopulations show 'normal' rotation about the minor axis. We also find that the red GC subpopulation is rotationally dominated beyond 2.5 arcmin (˜17 kpc) and that the root mean squared velocity of the green subpopulation declines sharply with radius suggesting a possible bias towards radial orbits relative to the other GC subpopulations. Additionally, we find a population of low-velocity GCs that form a linear structure running from the SW to the NE across NGC 4365 which aligns with the recently reported stellar stream towards NGC 4342. These low-velocity GCs have g' - i' colours consistent with the overall NGC 4365 GC system but have velocities consistent with the systemic velocity of NGC 4342. We discuss the possible formation scenarios for the three GC subpopulations as well as the possible origin of the low-velocity GC population.

Blom, Christina; Forbes, Duncan A.; Brodie, Jean P.; Foster, Caroline; Romanowsky, Aaron J.; Spitler, Lee R.; Strader, Jay

2012-11-01

176

Investigating Chemical Substructure in the Galactic Disk  

NASA Astrophysics Data System (ADS)

We will present high resolution spectra measurements for Lanthanum, Europium and Iron in 760 disk stars. The bulk of our data are planet search spectra taken with HIRES on the Keck I telescope at R 50,000. A small subset of kinematicly selected stars were observed on the Harlan J. Smith Telescope at McDonald Observatory at R 60,000 and S/N 100 at the 3988 Å Lanthanum line and S/N 250 around 5240 Å near our Iron lines. We use the technique of chemical tagging to investigate the possibility that these kinematicly selected stars are remnants of accreted objects of extragalactic origin or, alternatively, dynamical in origin. Lanthanum and Europium are of special interest because they are produced primarily by the s and r processes, respectively. Because these elements are synthesized in different mass stars and are returned to the interstellar medium on different timescales, the ratio [Eu/La] is a tracer of the star formation rate. To apply spectroscopy to such a large set of data, we have developed an automated process that fits the observations to synthetic spectra using an unnormalized ?2 metric to determine [Fe/H], [Eu/H],[La/H], and vbroad. We estimate log(g) from parallax data, and then verify the results spectroscopically. We are using ATLAS 9 model atmospheres and synthetic spectra calculated using MOOG. Our kinematicly selected subset was originally noticed by Helmi et al (2006) where they statistically argued for kinematic substructure in the disk. The stars are interesting at first glance because they are in overdense portions of phase space, a hallmark of accreted objects according to computer models. Further, these stars have different photometric metallicities than the disk at large, and in color-magnitude plots one or more turn offs can be seen.

Stringer, Christopher; Carney, B. W.

2010-01-01

177

SUBSTRUCTURE DEPLETION IN THE MILKY WAY HALO BY THE DISK  

SciTech Connect

We employ numerical simulations and simple analytical estimates to argue that dark matter substructures orbiting in the inner regions of the Galaxy can be efficiently destroyed by disk shocking, a dynamical process known to affect globular star clusters. We carry out a set of fiducial high-resolution collisionless simulations in which we adiabatically grow a disk, allowing us to examine the impact of the disk on the substructure abundance. We also track the orbits of dark matter satellites in high-resolution Aquarius simulations and analytically estimate the cumulative halo and disk-shocking effect. Our calculations indicate that the presence of a disk with only 10% of the total Milky Way mass can significantly alter the mass function of substructures in the inner parts of halos. This has important implications especially for the relatively small number of satellites seen within approx30 kpc of the Milky Way center, where disk shocking is expected to reduce the substructure abundance by a factor of 2 at 10{sup 9} M{sub sun} and a factor of 3 at 10{sup 7} M{sub sun}. The most massive subhalos with 10{sup 10} M{sub sun} survive even in the presence of the disk. This suggests that there is no inner missing satellite problem and calls into question whether these substructures can produce transient features in disks, like multi-armed spiral patterns. Also, the depletion of dark matter substructures through shocking on the baryonic structures of the disk and central bulge may aggravate the problem to fully account for the observed flux anomalies in gravitational lens systems, and significantly reduces the dark matter annihilation signal expected from nearby substructures in the inner halo.

D'Onghia, Elena; Hernquist, Lars; Keres, Dusan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Springel, Volker, E-mail: edonghia@cfa.harvard.ed [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85740 Garching (Germany)

2010-02-01

178

Stellar substructures in the solar neighbourhood. I. Kinematic group 3 in the Geneva-Copenhagen survey  

NASA Astrophysics Data System (ADS)

Context. Galactic archeology is a powerful tool for investigating the formation and evolution of the Milky Way. We use this technique to study kinematic groups of F- and G-stars in the solar neighbourhood. From correlations between orbital parameters, three new coherent groups of stars were recently identified and suggested to correspond to remnants of disrupted satellites. Aims: We determine detailed elemental abundances in stars belonging to one of these groups and compare their chemical composition with Galactic disc stars. The aim is to look for possible chemical signatures that might give information about the history of this kinematic group of stars. Methods: High-resolution spectra were obtained with the FIES spectrograph at the Nordic Optical Telescope, La Palma, and analysed with a differential model atmosphere method. Comparison stars were observed and analysed with the same method. Results: The average value of [Fe/H] for the 20 stars investigated in this study is -0.69 ± 0.05 dex. Elemental abundances of oxygen and ?-elements are overabundant in comparison with Galactic thin-disc dwarfs and thin-disc chemical evolution models. This abundance pattern has similar characteristics as the Galactic thick-disc. Conclusions: The homogeneous chemical composition together with the kinematic properties and ages of stars in the investigated Group 3 of the Geneva-Copenhagen survey provides evidence of their common origin and possible relation to an ancient merging event. The similar chemical composition of stars in the investigated group and the thick-disc stars might suggest that their formation histories are linked. Table 3 is available in electronic form at http://www.aanda.org

Stonkut?, E.; Tautvaišien?, G.; Nordström, B.; Ženovien?, R.

2012-05-01

179

Mapping Dark Matter Halos with Stellar Kinematics  

NASA Astrophysics Data System (ADS)

Galaxies of all sizes form and evolve in the centers of dark matter halos. As these halos constitute the large majority of the total mass of a galaxy, dark matter certainly plays a central role in the galaxy's formation and evolution. Yet despite our understanding of the importance of dark matter, observations of the extent and shape of dark matter halos have been slow in coming. The paucity of data is particularly acute in elliptical galaxies. Happily, concerted effort over the past several years by a number of groups has been shedding light on the dark matter halos around galaxies over a wide range in mass. The development of new instrumentation and large surveys, coupled with the tantalizing evidence for a direct detection of dark matter from the AMS experiment, has brought on a golden age in the study of galactic scale dark matter halos. I report on results using extended stellar kinematics from integrated light to dynamically model massive elliptical galaxies in the local universe. I use the integral field power of the Mitchell Spectrograph to explore the kinematics of stars to large radii (R > 2.5 r_e). Once the line-of-sight stellar kinematics are measured, I employ orbit-based, axisymmetric dynamical modeling to explore a range of dark matter halo parameterizations. Globular cluster kinematics at even larger radii are used to further constrain the dynamical models. The dynamical models also return information on the anisotropy of the stars which help to further illuminate the primary formation mechanisms of the galaxy. Specifically, I will show dynamical modeling results for the first and second rank galaxies in the Virgo Cluster, M49 and M87. Although similar in total luminosity and ellipticity, these two galaxies show evidence for different dark matter halo shapes, baryon to dark matter fractions, and stellar anisotropy profiles. Moreover, the stellar velocity dispersion at large radii in M87 is significantly higher than the globular clusters at the same radial extent, reinforcing the need for broad comparisons between the different methods and assumptions underlying the dynamical analysis of massive ellipticals.

Murphy, Jeremy; Gebhardt, K.; Greene, J. E.; Graves, G.

2013-07-01

180

A Full Census of Intracluster Light in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We have begun a new multi-wavelength project to explore the interaction history and evolution of galaxies in clusters. As a cluster hierarchically grows, gravitational and gas dynamical effects (e.g. galaxy-galaxy interactions, harassment, ram pressure stripping, starvation) are capable of removing stars, gas, and dust from galaxies. The intracluster light (ICL) therefore holds a record of the growth history of the cluster. We intend to explore a full mass census of the intracluster light in the central degree of the Virgo cluster by looking at the stars, dust, and gas components. We have recently been awarded Spitzer Warm IRAC 3.6 and 4.5micron data to compare with the published V-band imaging of Mihos et al. 2005. In addition we have discovered the first ever detected ICL feature in the UV with GALEX. This feature is ˜50 kpc long, ˜40 kpc from the interacting galaxy pair NGC4438/4435, and is spatially coincident with a tidal plume detected in deep V -band imaging. The presence of this feature in the UV is extremely surpising because previous optical analyses indicate that IC stars are old, and should therefore be undetected in the FUV. Spectral energy distribution(SED) fitting of the GALEX and optical data of this plume reveal not only a population of young IC stars but also significant amounts of IC dust.

Krick, Jessica; Desai, V.; Murphy, E.; Bridge, C.; Mihos, C.; Rudick, C.; Neill, J.; Surace, J.; Kenney, J.; van Gorkom, J.; Carlberg, R.

2010-01-01

181

The infall velocity toward Virgo, the Hubble constant, and a search for motion toward the microwave background  

Microsoft Academic Search

From data on distance ratios of eight clusters and groups of galaxies in the velocity interval 800 - 2000 km s-1, the infall of the Local Group toward the Virgo Cluster center due to the overdensity of the Virgo complex is determined to be vvc = 200±50 km s-1. This gives a low value of M\\/LB ≈ 70 averaged over

G. A. Tammann; A. Sandage

1985-01-01

182

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). I. The UV luminosity function of the central 12 sq. deg  

Microsoft Academic Search

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering ~40 sq. deg in the far UV (FUV, lambdaeff = 1539 Å, Deltalambda = 442 Å) and ~120 sq. deg in the near UV (NUV, lambdaeff = 2316 Å, Deltalambda = 1060 Å). The goal of the survey is to study the ultraviolet

A. Boselli; S. Boissier; S. Heinis; L. Cortese; O. Ilbert; T. Hughes; O. Cucciati; J. Davies; L. Ferrarese; R. Giovanelli; M. P. Haynes; M. Baes; C. Balkowski; N. Brosch; S. C. Chapman; V. Charmandaris; M. S. Clemens; A. Dariush; I. de Looze; S. di Serego Alighieri; P.-A. Duc; P. R. Durrell; E. Emsellem; T. Erben; J. Fritz; D. A. Garcia-Appadoo; G. Gavazzi; M. Grossi; A. Jordán; K. M. Hess; L. K. Hunt; B. R. Kent; D. G. Lambas; A. Lançon; L. A. MacArthur; S. C. Madden; L. Magrini; S. Mei; S. Mei; R. P. Olowin; E. Papastergis; M. W. L. Smith; J. M. Solanes; O. Spector; K. Spekkens; J. E. Taylor; C. Valotto; W. van Driel; J. Verstappen; C. Vlahakis; B. Vollmer; E. M. Xilouris

2011-01-01

183

Investigating the observational signatures of magnetic cloud substructure  

NASA Astrophysics Data System (ADS)

Magnetic clouds (MCs) represent a subset of interplanetary coronal mass ejections (ICMEs) that exhibit a magnetic flux rope structure. They are primarily identified by smooth, large-scale rotations of the magnetic field. However, both small- and large-scale fluctuations of the magnetic field are observed within some magnetic clouds. We analyzed the magnetic field in the frames of the flux ropes, approximated using a minimum variance analysis (MVA), and have identified a small number of MCs within which multiple reversals of the gradient of the azimuthal magnetic field are observed. We herein use the term “substructure” to refer to regions that exhibit this signature. We examine, in detail, one such MC observed on 13 April 2006 by the ACE and WIND spacecraft and show that substructure has distinct signatures in both the magnetic field and plasma observations. We identify two thin current sheets within the substructure and find that they bound the region in which the observations deviate most significantly from those typically expected in MCs. The majority of these clouds are followed by fast solar wind streams, and a comparison of the properties of this magnetic cloud with five similar events reveals that they have lower nondimensional expansion rates than nonovertaken magnetic clouds. We discuss and evaluate several possible explanations for this type of substructure, including the presence of multiple flux ropes and warping of the MC structure, but we conclude that none of these scenarios is able to fully explain all of the aspects of the substructure observations.

Steed, K.; Owen, C. J.; Démoulin, P.; Dasso, S.

2011-01-01

184

Probing Warm-Hot Intergalactic Medium Associated with the Virgo Cluster Using an Oxygen Absorption Line  

NASA Astrophysics Data System (ADS)

To detect a warm-hot intergalactic medium (WHIM) associated with the large-scale structure of the universe, we observed a quasar behind the Virgo cluster with XMM-Newton. With 54ks exposure, we marginally detected an O VIII K? absorption line at 650.9+0.8-1.9eV in the RGS spectra, with a statistical confidence of 96.4%. The observed line center energy is consistent with the redshift of M 87, and hence the absorber is associated with the Virgo cluster. From the curve of growth, the O VIII column density was estimated to be ? 7 × 1016 cm-2. In the EPIC spectra, excess emission was found after evaluating the hot ICM in the Virgo cluster and various background components. We inspected the RASS map of the diffuse soft X-ray background, and confirmed that the level of the north and west regions just outside of the Virgo cluster is consistent with the background model that we used, while that of the east side is significantly higher and the enhancement is comparable with the excess emission found in the EPIC data. We consider a significant portion of the excess emission to be associated with the Virgo cluster, although a possible contribution from the North Polar Spur cannot be excluded. Using the column density and the emission measure and assuming an oxygen abundance of 0.1 and an ionization fraction of 0.4, we estimate that the mean electron density and the line-of-sight distance of the warm-hot gas are ? 6 × 10-5 cm-3 and ? 9 Mpc. These strongly suggest detection of a WHIM in a filament associated with the Virgo cluster.

Fujimoto, Ryuichi; Takei, Yoh; Tamura, Takayuki; Mitsuda, Kazuhisa; Yamasaki, Noriko Y.; Shibata, Ryo; Ohashi, Takaya; Ota, Naomi; Audley, Michael D.; Kelley, Richard L.; Kilbourne, Caroline A.

2004-10-01

185

Functional Group and Substructure Searching as a Tool in Metabolomics  

PubMed Central

Background A direct link between the names and structures of compounds and the functional groups contained within them is important, not only because biochemists frequently rely on literature that uses a free-text format to describe functional groups, but also because metabolic models depend upon the connections between enzymes and substrates being known and appropriately stored in databases. Methodology We have developed a database named “Biochemical Substructure Search Catalogue” (BiSSCat), which contains 489 functional groups, >200,000 compounds and >1,000,000 different computationally constructed substructures, to allow identification of chemical compounds of biological interest. Conclusions This database and its associated web-based search program (http://bisscat.org/) can be used to find compounds containing selected combinations of substructures and functional groups. It can be used to determine possible additional substrates for known enzymes and for putative enzymes found in genome projects. Its applications to enzyme inhibitor design are also discussed.

Kotera, Masaaki; McDonald, Andrew G.; Boyce, Sinead; Tipton, Keith F.

2008-01-01

186

Shock induced deformation substructures in a copper bicrystal  

SciTech Connect

Controlled shock recovery experiments have been conducted to assess the role of shock pressure and orientation dependence on the substructure evolution of a [100]/[01{ovr 1}] copper bicrystal. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were utilized to characterize orientation variation and substructure evolution of the post-shock specimens. Well defined dislocation cell structures were displayed in both grains and the average cell size was observed to decrease with increasing shock pressure. Twinning was occasionally observed in the 5 GPa shocked [100] grain and became the dominant substructure at higher shock pressure. The stress and directional dependence of twinning in the bicrystal was analyzed with consideration of the energetically favorable dissociation of dislocations into Shockley partials and the stress-orientation effect on the partial width. Moreover, a critical 'tear apart' stress is proposed and a good agreement is obtained between the calculated value and the experimental observations.

Cao, Fang [Los Alamos National Laboratory; Beyerlein, Irene J [Los Alamos National Laboratory; Cerreta, Ellen K [Los Alamos National Laboratory; Trujillo, Carl P [Los Alamos National Laboratory; Gray Ill, George T [Los Alamos National Laboratory; Sencer, Bulent H [NON LANL

2008-01-01

187

EFFECT OF DARK MATTER HALO SUBSTRUCTURES ON GALAXY ROTATION CURVES  

SciTech Connect

In this paper, the effect of halo substructures on galaxy rotation curves is investigated using a simple model of dark matter clustering. A dark matter halo density profile is developed based only on the scale-free nature of clustering that leads to a statistically self-similar distribution of the substructures at the galactic scale. A semi-analytical method is used to derive rotation curves for such a clumpy dark matter density profile. It is found that the halo substructures significantly affect the galaxy velocity field. Based on the fractal geometry of the halo, this self-consistent model predicts a Navarro-Frenk-White-like rotation curve and a scale-free power spectrum of the rotation velocity fluctuations.

Roy, Nirupam, E-mail: nroy@aoc.nrao.ed [NRAO, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States)

2010-11-01

188

A first study of environmental noise coupling to the Virgo interferometer  

NASA Astrophysics Data System (ADS)

During the commissioning of the Virgo interferometer, a search for environmental noise contributions to the dark fringe signal was undertaken. Dedicated tests have been performed to identify major sources of disturbances and to understand the coupling mechanism with the interferometer. The major effect is due to seismic/acoustic noise coupling to the laser beam before the input mode cleaner, then propagating as beam power noise to the ITF dark fringe output signal. In this paper we illustrate the tests performed and preliminary results of our investigation. Presented by I Fiori for the Virgo Collaboration.

Acernese, F.; Amico, P.; Al-Shourbagy, M.; Aoudia, S.; Avino, S.; Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsotti, L.; Barsuglia, M.; Beauville, F.; Bizouard, M. A.; Boccara, C.; Bondu, F.; Bosi, L.; Bradaschia, C.; Braccini, S.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.; Calloni, E.; Campagna, E.; Cavalier, F.; Cavalieri, R.; Cella, G.; Chassande-Mottin, E.; Corda, C.; Clapson, A. C.; Cleva, F.; Coulon, J. P.; Cuoco, E.; Dattilo, V.; Davier, M.; De Rosa, R.; Di Fiore, L.; Di Virgilio, A.; Dujardin, B.; Eleuteri, A.; Enard, D.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Fournier, J. D.; Frasca, S.; Frasconi, F.; Freise, A.; Gammaitoni, L.; Gennai, A.; Giazotto, A.; Giordano, G.; Giordano, L.; Gouaty, R.; Grosjean, D.; Guidi, G.; Hebri, S.; Heitmann, H.; Hello, P.; Holloway, L.; Kreckelbergh, S.; La Penna, P.; Loriette, V.; Loupias, M.; Losurdo, G.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marque, J.; Martelli, F.; Masserot, A.; Mazzoni, M.; Milano, L.; Moins, C.; Moreau, J.; Morgado, N.; Mours, B.; Pai, A.; Palomba, C.; Paoletti, F.; Pardi, S.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perniola, B.; Piergiovanni, F.; Pinard, L.; Poggiani, R.; Punturo, M.; Puppo, P.; Qipiani, K.; Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Ricciardi, I.; Ruggi, P.; Russo, G.; Solimeno, S.; Spallicci, A.; Stanga, R.; Taddei, R.; Tombolato, D.; Tonelli, M.; Toncelli, A.; Tournefier, E.; Travasso, F.; Vajente, G.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z.

2005-09-01

189

A search for low surface brightness galaxies in Virgo using Tech Pan films.  

NASA Astrophysics Data System (ADS)

We report on a pilot study for a new survey of low surface brightness galaxies in the Virgo Cluster using Kodak Technical Pan 4415 films from the UK Schmidt Telescope. The film offers significant gains in depth, resolution and S/N when compared with conventional photographic plate data. This translates to direct scientific benefits as we clearly demonstrate with the effectiveness of Tech Pan in searching for faint extended objects. From only a small pilot region we present photometry on two newly discovered low surface brightness galaxies not found in previous studies of Virgo. The new surface brightness and size limits expected for the overall automated survey are discussed.

Schwartzenberg, J. M.; Phillipps, S.; Parker, Q. A.

1995-01-01

190

Hubble constant from Pritchet and von den Bergh's nova distance to the Virgo cluster  

SciTech Connect

Two reasons are offered why the value for H(0) of 69 + or - 14 km/s/Mpc of Pritchet and van den Bergh (1987) is likely to be too high by about 20 percent even when their value of 6.8 + or - 0.4 for the M31-Virgo modulus difference is adopted. One reason concerns the free expansion velocity of the Virgo cluster core and the other concerns the apparent distance modulus of M31. Reasons for adopting a global H(0) value of 56 + or - 12 km/s/Mpc are discussed. 25 references.

Sandage, A.; Tammann, G.A.

1988-05-01

191

An Integral View on Virgo and Field Dwarf Elliptical Galaxies: Late-Type Origin and Environmental Transformations  

NASA Astrophysics Data System (ADS)

Dwarf elliptical galaxies (dEs) are the most common galaxy class in dense environments. They are also a surprisingly inhomogenous class, which has made it challenging both to relate different dE subtypes to each other, as well as place the whole class in the larger context of galaxy assembly and (trans)formation processes. Here we will show the effects of environmental evolution on Virgo Cluster and field dEs, presenting the first large-scale integral-field spectroscopic (SAURON) data for this galaxy class. Our sample consists of 12 galaxies and no two of them are alike. We find that the level of rotation is not tied to flattening; we observe kinematic twists; we discover large-scale kinematically-decoupled components; we see varying gradients in line-strength maps. This great variety of morphological, kinematic, and stellar population parameters supports the claim that dEs are defunct dwarf spiral/irregular galaxies and points to a formation scenario that allows for a stochastic shaping of galaxy properties. The combined influence of ram-pressure stripping and harassment fulfils this requirement, still, their exact impact is not yet understood. We thus further investigate the properties of our sample by performing a detailed comprehensive analysis of its kinematic, dynamical, and stellar population properties. We infer the total (dark and baryonic) matter distribution by fitting the observed stellar velocity and velocity dispersion with the solutions of the Jeans equations. We obtain 2D age, metallicity, and enrichment information from line-strength analysis. We then tie these results to the galaxies' intrinsic (i.e. deprojected) locations in the cluster with the use of surface-brightness fluctuation distances. This step is essential to providing unbiased correlations with the local environment density. We show that the dark matter fraction, unlike the level of rotational support, appears to correlate with the clustrocentric distance, and that our dwarfs have kinematic properties similar to those of fast-rotating giant early-type galaxies.

Rys, Agnieszka; Falcon-Barroso, J.; van de Ven, G.

2013-01-01

192

A simple method of identifying symmetric substructures of proteins.  

PubMed

Accurate identifications of internal symmetric substructures of proteins are needed in protein evolution study and protein design. To overcome the difficulties met by previous methods, here we propose a simple quantitative one by using a similarity matrix plus Pearson's correlation analysis. The distance root-mean-square deviation (dRMSD) is used to measure the similarity of two substructures in a protein. We applied this method to the proteins of the beta-propeller, jelly roll, and beta-trefoil families and the results show that this method cannot only detect the internal repetitive structures in proteins effectively, but also can identify their locations easily. PMID:18782681

Chen, Hanlin; Huang, Yanzhao; Xiao, Yi

2008-08-03

193

Unveiling the Secret of a Virgo Dwarf Galaxy  

NASA Astrophysics Data System (ADS)

Dwarf galaxies may not be as impressive in appearance as their larger brethren, but they are at least as interesting from a scientific point of view. And sometimes they may have hidden properties that will only be found by means of careful observations, probing the signals of their stars at the faintest level. Such as the entirely unexpected, well developed spiral structure within an otherwise seemingly normal dwarf elliptical galaxy! This is the surprise result of a new study by a team of astronomers [1], headed by Helmut Jerjen from the Australian National University (Canberra) who obtained detailed observations with the ESO Very Large Telescope (VLT) of the dwarf galaxy IC 3328 in the Virgo Cluster of Galaxies, some 50 million light-years away. Dwarf galaxies Dwarf galaxies are present in all major clusters of galaxies and dominate by numbers in the universe. They may contain a few (tens of) millions of stars, as compared to galaxies of normal size with hundreds of billions of stars. About two dozen dwarf galaxies are known in the "Local Group" of galaxies of which the Milky Way galaxy in which we live is also a member. The Large and Small Magellanic Clouds are some of the best known dwarf galaxies - they are of the irregular type - while NGC 147 and NGC 205, two companions to the great Andromeda Galaxy, are of the elliptical type. Dwarf elliptical galaxies are characterized by their smooth appearance. From various studies, it is known that they are tri-axial ellipsoids of different degrees of elongation. Some are almost spherical while others are more pancake- or cigar-shaped. Like the elliptical galaxies of normal size, dwarf ellipticals are almost pure aggregates of stars. In contrast, spiral galaxies also contain clouds of gas and dust. The visible mass of spiral galaxies is in a rotating disk. Dwarf ellipticals generally keep their form because of the random motions of their stars. VLT observations of dwarf elliptical galaxies Using the FORS1 multi-mode instrument mounted at the first 8.2-m VLT Unit telescope, ANTU , the astronomers observed a series of dwarf elliptical galaxies in the Virgo Cluster of Galaxies, in the constellation of that name (The Virgin). The primary goal of the observations was to obtain carefully calibrated images of the galaxies in different colours. They can be used to study the distribution of light over the galaxy and thus its content of stars. The galaxies that are found to have smooth light distributions are of special interest, because it is then possible to measure their approximate distance by means of the so-called Surface Brightness Fluctuation method [2]. The distance to the Virgo Cluster is still not known with high accuracy, although it constitutes a most important step towards the universal distance ladder. Any additional determination of this distance would therefore be most valuable. A matter of a small difference ESO PR Photo 11/00 ESO PR Photo 11/00 [Preview - JPEG: 400 x 252 pix - 67k] [Normal - JPEG: 800 x 504 pix - 224k] Caption : The deep R-band CCD image of IC3328 (left; rendered in "negative" with dark objects and a bright background), obtained with FORS1 at VLT ANTU, illustrates the overall morphology of this galaxy that was classified as a dwarf elliptical galaxy: a quite smooth radially waning light distribution with a central nucleus. The total integration time of this composite image is 20 min with a seeing of 0.6 arcsec. After removal of the axis-symmetrical part of the light from the galaxy by a special image processing algorithm, the "residual" image reveals a remarkable 2-armed spiral structure (right). The field is 4 x 4 arcmin 2 ; North is up and east is left. The central task of the Surface Brightness Fluctuation method is to determine the pixel-to-pixel fluctuations in the light distribution of the galaxy that is due to the finite number of unresolved stars. These fluctuations are obtained by subtracting a suitably smoothed galaxy model from the CCD image. In the case of the seemingly inconspicuous dwarf galaxy IC 3382 , th

2000-05-01

194

PAndAS in the Mist: The Stellar and Gaseous Mass within the Halos of M31 and M33  

NASA Astrophysics Data System (ADS)

Large-scale surveys of the prominent members of the Local Group have provided compelling evidence for the hierarchical formation of massive galaxies, revealing a wealth of substructure that is thought to be the debris from ancient and ongoing accretion events. In this paper, we compare two extant surveys of the M31-M33 subgroup of galaxies: the Pan-Andromeda Archaeological Survey of the stellar structure, and a combination of observations of the H I gaseous content, detected at 21 cm. Our key finding is a marked lack of spatial correlation between these two components on all scales, with only a few potential overlaps between stars and gas. The paucity of spatial correlation significantly restricts the analysis of kinematic correlations, although there does appear to be H I kinematically associated with the Giant Stellar Stream where it passes the disk of M31. These results demonstrate that different processes must significantly influence the dynamical evolution of the stellar and H I components of substructures, such as ram pressure driving gas away from a purely gravitational path. Detailed modeling of the offset between the stellar and gaseous substructures will provide a determination of the properties of the gaseous halos of M31 and M33.

Lewis, Geraint F.; Braun, Robert; McConnachie, Alan W.; Irwin, Michael J.; Ibata, Rodrigo A.; Chapman, Scott C.; Ferguson, Annette M. N.; Martin, Nicolas F.; Fardal, Mark; Dubinski, John; Widrow, Larry; Mackey, A. Dougal; Babul, Arif; Tanvir, Nial R.; Rich, Michael

2013-01-01

195

Investigation of the substructure of sintered iron powder by transmission electron microscopy  

Microsoft Academic Search

mechanical action by pressing, stamping, rolling, and other processes a deformation substructure normally called fragmented or cellular may occur in the material. The substructure influences the formation of the strength and plastic properties of wrought materials. The ruies of formation and transformation of the cellular substructure of compact bodycentered cubic metals have been studied in detail in [1-4]. Literature information

S. A. Firstov; N. I. Danilenko; Yu. N. Podrezov; A. E. Kushchevskii; L. G. Shtyka

1990-01-01

196

Direct Observations of the Substructure Network in Iron  

Microsoft Academic Search

The existence of substructure within high-energy grain boundaries has been proven for different materials.' -4 These subgrains are actually low-angle boundaries in which the orientation differences across the boundary are very small. Since this orientation difference is so slight, the procedures to show the presence of sub- structure are involved and often difficult. This Letter describes a new technique and

W. L. Mitchell; C. Hays; R. E. Swift

197

A dual Craig–Bampton method for dynamic substructuring  

Microsoft Academic Search

A novel component mode synthesis method for dynamic analysis of structures is presented. It is based on free interface vibration modes and residual flexibility components. Although the ingredients are the same as in previously published procedures (e.g. MacNeal or Rubin), our method is fundamentally different in that it assembles the substructures using interface forces (dual assembly) and enforces only weak

Daniel J. Rixen

2004-01-01

198

Reducing Huge Gyroscopic Eigenproblems by Automated Multilevel Substructuring  

Microsoft Academic Search

Simulating numerically the sound radiation of a rolling tire requires the solution of a very large and sparse gyroscopic eigenvalue problem. Taking advantage of the automated multi-level substructuring (AMLS) method it can be projected to a much smaller gyroscopic problem, the solution of which however is still quite costly since the eigenmodes are non-real and complex arithmetic is necessary. This

Kolja Elssel; Heinrich Voss

2006-01-01

199

Experimentally implementable criteria revealing substructures of genuine multipartite entanglement  

SciTech Connect

We present a general framework that reveals substructures of genuine multipartite entanglement. Via simple inequalities it is possible to discriminate different sets of multipartite qubit states. These inequalities are beneficial regarding experimental examinations as only local measurements are required. Furthermore, the number of observables scales favorably with system size. In exemplary cases we demonstrate the noise resistance and discuss implementations.

Huber, Marcus; Schimpf, Hans; Gabriel, Andreas; Spengler, Christoph [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria); Bruss, Dagmar [Heinrich-Heine-Universitaet Duesseldorf, Universitaetsstrasse 1, D-40225 Duesseldorf (Germany); Hiesmayr, Beatrix C. [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria); Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, SK-84511 Bratislava (Slovakia)

2011-02-15

200

Weak Lensing Studies of Mass Substructure in Clusters of Galaxies  

NASA Astrophysics Data System (ADS)

Cluster mass substructure is an important test of the hierarchical model of CDM. We use weak gravitational lensing shear measurements, combined with variable aperture filter methods and PSF correction, to extract information about mass subclumping in HST observations of clusters of galaxies. This work is funded by NASA Rhode Island Space Grant.

Huwe, Paul M.

2012-01-01

201

Substructure Control by Solidification Control in Cu Crystals.  

National Technical Information Service (NTIS)

In an attempt to systematically control dislocation substructure, seeded (111) Cu single crystals have been grown from the melt at rates from 1.1 to 730 cm/h. Soft and hard graphite molds are used, with the hard molds surrounded by graphite or firebrick s...

D. S. Sampar H. Akita N. F. Flore

1972-01-01

202

Fast Algorithms of Plant Computation Based on Substructure Instances  

Microsoft Academic Search

ABSTRACT Fast rendering and botanically faithful description of plants are a real challenge in computer graphics Usually, plant production is computed using the method internode by internode, while there exist a lot of buds in an individual tree, therefore, this approach is quite time In this paper, we present a new algorithm based on substructure instances to quickly compute plants\\

Hong-Ping YAN; Jean Francois Barczi; Philippe De Reffye; Bao-gang Hu; Marc Jaeger; J. Le Roux

2002-01-01

203

Substructure Depletion in the Milky Way Halo by the Disk  

Microsoft Academic Search

We employ numerical simulations and simple analytical estimates to argue that dark matter substructures orbiting in the inner regions of the Galaxy can be efficiently destroyed by disk shocking, a dynamical process known to affect globular star clusters. We carry out a set of fiducial high-resolution collisionless simulations in which we adiabatically grow a disk, allowing us to examine the

Elena D'Onghia; Volker Springel; Lars Hernquist; Dusan Keres

2010-01-01

204

HYPERCOMPACT STELLAR SYSTEMS AROUND RECOILING SUPERMASSIVE BLACK HOLES  

SciTech Connect

A supermassive black hole ejected from the center of a galaxy by gravitational-wave recoil carries a retinue of bound stars - a 'hypercompact stellar system' (HCSS). The numbers and properties of HCSSs contain information about the merger histories of galaxies, the late evolution of binary black holes, and the distribution of gravitational-wave kicks. We relate the structural properties (size, mass, density profile) of HCSSs to the properties of their host galaxies and to the size of the kick in two regimes: collisional (M {sub BH} {approx}< 10{sup 7} M {sub sun}), i.e., short nuclear relaxation times, and collisionless (M {sub BH} {approx}> 10{sup 7} M {sub sun}), i.e., long nuclear relaxation times. HCSSs are expected to be similar in size and luminosity to globular clusters, but in extreme cases (large galaxies, kicks just above escape velocity) their stellar mass can approach that of ultracompact dwarf galaxies. However, they differ from all other classes of compact stellar system in having very high internal velocities. We show that the kick velocity is encoded in the velocity dispersion of the bound stars. Given a large enough sample of HCSSs, the distribution of gravitational-wave kicks can therefore be empirically determined. We combine a hierarchical merger algorithm with stellar population models to compute the rate of production of HCSSs over time and the probability of observing HCSSs in the local universe as a function of their apparent magnitude, color, size, and velocity dispersion, under two different assumptions about the star formation history prior to the kick. We predict that {approx}10{sup 2} HCSSs should be detectable within 2 Mpc of the center of the Virgo cluster, and that many of these should be bright enough that their kick velocities (i.e., velocity dispersions) could be measured with reasonable exposure times. We discuss other strategies for detecting HCSSs and speculate on some exotic manifestations.

Merritt, David [Center for Computational Relativity and Gravitation and Department of Physics, Rochester Institute of Technology, Rochester, NY 14623 (United States); Schnittman, Jeremy D. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Komossa, S. [Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, D-85741 Garching (Germany)

2009-07-10

205

The creep problem in the VIRGO suspensions: a possible solution using Maraging steel  

Microsoft Academic Search

Each optical component of the interferometric gravitational wave detector VIRGO is suspended from a cascade of mechanical filters designed to suppress the transmission of seismic vibrations. Each mechanical filter supports the weight of the filters below it by means of a set of steel cantilever blade springs. The stress from the load acting on the blades was found to induce

M. Beccaria; M. Bernardini; S. Braccini; C. Bradaschia; G. Cagnoli; C. Casciano; G. Cella; E. Cuoco; V. Dattilo; G. De Carolis; R. De Salvo; A. Di Virgilio; G. T. Feng; I. Ferrante; F. Fidecaro; F. Frasconi; A. Gaddi; L. Gammaitoni; A. Gennai; A. Giazotto; L. Holloway; J. Kovalik; P. La Penna; G. Losurdo; S. Malik; S. Mancini; F. Marchesoni; J. Nicolas; F. Palla; H. B. Pan; F. Paoletti; A. Pasqualetti; D. Passuello; R. Poggiani; P. Popolizio; M. Punturo; F. Raffaelli; V. Rubino; R. Valentini; A. Vicere; F. Waharte; Z. Zhang

1998-01-01

206

A STRONG DICHOTOMY IN S0 DISK PROFILES BETWEEN THE VIRGO CLUSTER AND THE FIELD  

SciTech Connect

We report evidence for a striking difference between S0 galaxies in the local field and the Virgo Cluster. While field S0 galaxies have disks whose surface-brightness profiles are roughly equally divided between the three main types (Types I, II, and III: single-exponential, truncated, and antitruncated), Virgo S0s appear to be entirely lacking in disk truncations. More specifically, the fraction of truncations in S0 galaxies with M{sub B} < -17 is 28{sup +7}{sub -6}% for the field versus 0{sup +4}{sub -0}% for the Virgo Cluster galaxies; the difference is significant at the 99.7% level. The discrepancy is made up almost entirely by Type I profiles, which are almost twice as frequent in the Virgo Cluster as they are in the field. This suggests that S0 formation may be driven by different processes in cluster and field environments, and that outer-disk effects can be useful tests of S0 formation models.

Erwin, Peter [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Gutierrez, Leonel; Beckman, John E., E-mail: erwin@mpe.mpg.de [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, 38200 La Laguna, Tenerife (Spain)

2012-01-15

207

The Real-time Distributed Control of the Virgo Interferometric Detector of Gravitational Waves  

Microsoft Academic Search

The VIRGO experiment for the detection of gravitational waves is a big challenge both for physics and for technology, in particular, to satisfy the stringent requirements on the alignment and position of its suspended optical components to keep the detector at its working point, a very complex distributed and supervised control system has been implemented. The current constraints are about

F. Acernese; P. Amico; M. Alshourbagy; F. Antonucci; S. Aoudia; P. Astone; S. Avino; D. Babusci; G. Ballardin; F. Barone; L. Barsotti; M. Barsuglia; T. S. Bauer; F. Beauville; S. Bigotta; M. A. Bizouard; C. Boccara; F. Bondu; L. Bosi; C. Bradaschia; S. Birindelli; S. Braccini; A. Brillet; V. Brisson; D. Buskulic; E. Calloni; E. Campagna; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; C. Mottin; N. Christensen; A.-C. Clapson; F. Cleva; C. Corda; A. Corsi; F. Cottone; J.-P. Coulon; E. Cuoco; A. Dari; V. Dattilo; M. Davier; M. del Prete; R. De Rosa; L. Di Fiori; A. Di Virgilio; B. Dujardin; A. Eleuteri; M. Evans; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; S. Frasca; F. Frasconi; L. Gamaitoni; F. Garuli; E. Genin; A. Gennai; A. Giazotto; G. Giordano; L. Giordano; R. Gouaty; D. Grosjean; G. Guidi; S. Hamdani; S. Hebri; H. Heitmann; P. Hello; D. Huet; S. Karkar; S. Kreckelbergh; P. La Penna; M. Laval; N. Leroy; N. Letendre; B. Lopez; M. Lorenzini; V. Loriette; G. Losurdo; J.-M. Mackowski; E. Majorana; C. N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; M. Mazzoni; F. Menzinger; L. Milano; C. Moins; J. Moreau; N. Morgado; B. Mours; F. Nocera; C. Palomba; F. Paoletti; S. Pardi; A. Pasqualetti; R. Passaquieti; F. P. D. Passuello; D. Passuello; F. Piergiovanni; L. Pinard; R. Poggiani; M. Punturo; P. Puppo; S. van der Putten; K. Qipiani; P. Rapagnani; V. Reita; A. Remillieux; F. Ricci; I. Ricciardi; P. Ruggi; G. Russo; S. Solimeno; A. Spallicci; M. Tarallo; M. Tonelli; A. Toncelli; E. Tournefier; F. Travasso; C. Tremola; G. Vajente; D. Verkindt; F. Vetrano; A. Vicere; J.-Y. Vinet; H. Vocca; M. Yvert

2007-01-01

208

Calibration and sensitivity of the Virgo detector during its second science run  

Microsoft Academic Search

The Virgo detector is a kilometer-length interferometer for gravitational wave detection located near Pisa (Italy). During its second science run (VSR2) in 2009, 6 months of data were accumulated with a sensitivity close to its design. In this paper, the methods used to determine the parameters for sensitivity estimation and gravitational wave reconstruction are described. The main quantities to be

T. Accadia; F. Acernese; F. Antonucci; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; A. Basti; Th S. Bauer; M. G. Beker; A. Belletoile; S. Birindelli; M. Bitossi; M. A. Bizouard; F. Bondu; L. Bonelli; R. Bonnand; B. Bouhou; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; R. Cavalieri; G. Cella; E. Cesarini; O. Chaibi; E. Chassande Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D'Antonio; V. Dattilo; M. Davier; R. Day; R. De Rosa; G. Debreczeni; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; L. A. Forte; J.-D. Fournier; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; N. Liguori; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. Swinkels; M. Tacca; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; R. L. Ward; M. Yvert

2011-01-01

209

First joint gravitational wave search by the AURIGA EXPLORER NAUTILUS Virgo Collaboration  

Microsoft Academic Search

We present a methodology of network data analysis applied to the search for coincident burst excitations over a 24 h long data set collected by AURIGA, EXPLORER, NAUTILUS and Virgo detectors during September 2005. The search of candidate triggers was performed independently on each of the data sets from single detectors. We looked for two-fold time coincidences between these candidates

F. Acernese; M. Alshourbagy; P. Amico; F. Antonucci; S. Aoudia; P. Astone; S. Avino; D. Babusci; L. Baggio; G. Ballardin; F. Barone; L. Barsotti; M. Barsuglia; M. Bassan; Th S. Bauer; M. Bignotto; S. Birindelli; M. A. Bizouard; C. Boccara; M. Bonaldi; F. Bondu; L. Bosi; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; D. Buskulic; G. Cagnoli; E. Calloni; M. Camarda; E. Campagna; F. Carbognani; P. Carelli; F. Cavalier; R. Cavalieri; G. Cavallari; G. Cella; M. Cerdonio; E. Cesarini; E. Chassande-Mottin; A. Chincarini; A.-C. Clapson; F. Cleva; E. Coccia; L. Conti; C. Corda; A. Corsi; F. Cottone; J.-P. Coulon; E. Cuoco; S. D'Antonio; A. Dari; V. Dattilo; M. Davier; R. De Rosa; M. DelPrete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; M. Drago; F. Dubath; M. Evans; V. Fafone; P. Falferi; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; S. Foffa; P. Fortini; J.-D. Fournier; S. Frasca; F. Frasconi; L. Gammaitoni; F. Garufi; G. Gemme; E. Genin; A. Gennai; A. Giazotto; G. Giordano; L. Giordano; V. Granata; C. Greverie; D. Grosjean; G. Guidi; S. Hamdani; S. Hebri; H. Heitmann; P. Hello; D. Huet; S. Kreckelbergh; P. La Penna; M. Laval; N. Leroy; N. Letendre; N. Liguori; S. Longo; B. Lopez; M. Lorenzini; V. Loriette; G. Losurdo; J.-M. Mackowski; M. Maggiore; E. Majorana; C. N. Man; M. Mantovani; F. Marchesoni; A. Marini; F. Marion; J. Marque; F. Martelli; A. Masserot; F. Menzinger; R. Mezzena; L. Milano; Y. Minenkov; A. Mion; I. Modena; G. Modestino; C. Moins; A. Moleti; J. Moreau; N. Morgado; S. Mosca; B. Mours; I. Neri; F. Nocera; A. Ortolan; G. Pagliaroli; G. V. Pallottino; C. Palomba; F. Paoletti; S. Pardi; R. Parodi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Piano Mortari; F. Piergiovanni; L. Pinard; G. Pizzella; S. Poggi; R. Poggiani; G. A. Prodi; M. Punturo; P. Puppo; L. Quintieri; P. Rapagnani; V. Re; T. Regimbau; A. Remillieux; F. Ricci; I. Ricciardi; A. Rocchi; L. Rolland; R. Romano; F. Ronga; P. Ruggi; G. Russo; F. Salemi; S. Solimeno; A. Spallicci; R. Sturani; L. Taffarello; M. Tarallo; R. Terenzi; A. Toncelli; M. Tonelli; G. Torrioli; E. Tournefier; F. Travasso; C. Tremola; R. Vaccarone; G. Vajente; G. Vandoni; G. Vedovato; J. F. J. van der Brand; S. van der Putten; D. Verkindt; F. Vetrano; A. Viceré; A. Vinante; J.-Y. Vinet; M. Visco; S. Vitale; H. Vocca; M. Yvert; J. P. Zendri

2008-01-01

210

Performance of the Virgo interferometer longitudinal control system during the second science run  

Microsoft Academic Search

The second science run of the Virgo gravitational wave interferometer took place between July 2009 and January 2010. This paper describes the performance of the interferometer longitudinal control system in terms of duty cycle, stability and control noise. A science data taking duty cycle of about 80% was obtained over the six month run. Control noise was not limiting the

T. Accadia; F. Acernese; F. Antonucci; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; A. Basti; Th. S. Bauer; M. G. Beker; A. Belletoile; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; O. Chaibi; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D’Antonio; V. Dattilo; M. Davier; R. Day; R. De Rosa; G. Debreczeni; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; L. A. Forte; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; M. E. Gáspár; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; J.-F. Hayau; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; N. Liguori; M. Lorenzini; V. Loriette; G. Losurdo; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; L. Sperandio; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; G. Vajente; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; R. L. Ward; M. Yvert; M. Tacca; A. Chiummo

2011-01-01

211

Einstein Observatory Solid State Spectrometer Observations of M87 and the Virgo Cluster.  

National Technical Information Service (NTIS)

X-ray observations of the galaxy M87 and of a region in the Virgo cluster displaced 7 minutes from the center of M87 are presented. X-ray spectra are obtained at these two locations with the slid state spectrometer onboard the Einstein Observatory. Emissi...

S. M. Lea R. F. Mushotzky S. S. Holt

1982-01-01

212

21 cm Synthesis Observations of VIRGOHI 21-A Possible Dark Galaxy in the Virgo Cluster  

Microsoft Academic Search

Many observations indicate that dark matter dominates the extragalactic universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Previously, we have suggested that VIRGOHI 21, a 21 cm source we found in the Virgo Cluster using Jodrell Bank, was a possible dark galaxy because of its broad line width (~200 km s-1) unaccompanied by any

Robert Minchin; Jonathan Davies; Michael Disney; Marco Grossi; Sabina Sabatini; Peter Boyce; Diego Garcia; Chris Impey; Christine Jordan; Robert Lang; Andrew Marble; Sarah Roberts; Wim van Driel

2007-01-01

213

Velocity Imager for Resolving Galaxy Origins (VIRGO): A Proposed Midex Mission  

Microsoft Academic Search

The proposed Velocity Imager for Resolving Galaxy Origins (VIRGO) is a highly capable instrument for collecting 3-D data cubes, one spectral and two spatial dimensions. The telescope will be a Hubble-class instrument having a 2.5 m aperture primary. The instrument will include an Integral Field Spectrograph (IFS) covering approx. 2\\

C. L. Joseph

2001-01-01

214

The Mayfly, Ephoron Virgo (Olivier), back in the Dutch parts of the rivers Rhine and Meuse  

Microsoft Academic Search

Due to severe water pollution, the mayflyEphoron virgo (Olivier) disappeared from the Dutch parts of the rivers Rhine and Meuse in the first half of this century. In August 1991, however, larvae were found in the littoral zone of the Rhine near the Dutch-German border. Later, other stages were found along the Rhine branches and a small section of the

Abraham Bij De Vaate; Alexander Klink; Frank Oosterbroek

1992-01-01

215

Nuclear substructure reorganization during late stageerythropoiesis is selective and does not involve caspase cleavage ofmajor nuclear substructural proteins  

Microsoft Academic Search

Enucleation, a rare feature of mammalian differentiation, occurs in three cell types: erythroblasts, lens epithelium and keratinocytes. Previous investigations suggest that caspase activation functions in lens epithelial and keratinocyte enucleation, as well as in early erythropoiesis encompassing BFU-E differentiation to proerythroblast. To determine whether caspase activation contributes to later erythropoiesis and whether nuclear substructures other than chromatin reorganize, we analyzed

Sharon Wald Krauss; Annie J. Lo; Sarah A. Short; Mark J. Koury; Narla Mohandas; Joel Anne Chasis

2005-01-01

216

Double-helix stellarator  

SciTech Connect

A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A {approx} 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-{beta} MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications.

Moroz, P.E.

1997-09-01

217

The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies  

NASA Astrophysics Data System (ADS)

Context. Using Herschel data from the open time key project the Herschel Virgo Cluster Survey (HeViCS), we investigated the relationship between the metallicity gradients expressed by metal abundances in the gas phase as traced by the chemical composition of HII regions, and in the solid phase, as traced by the dust-to-gas mass ratio. Aims: We derived the radial gradient of the dust-to-gas mass ratio for all galaxies observed by HeViCS whose metallicity gradients are available in the literature. They are all late type Sbc galaxies, namely NGC 4254, NGC 4303, NGC 4321, and NGC 4501. Methods: We fitted PACS and SPIRE observations with a single-temperature modified blackbody, inferred the dust mass, and calculated two dimensional maps of the dust-to-gas mass ratio, with the total mass of gas from available HI and CO maps. HI moment-1 maps were used to derive the geometric parameters of the galaxies and extract the radial profiles. We examined different dependencies on metallicity of the CO-to-H2 conversion factor (XCO), used to transform the 12CO observations into the amount of molecular hydrogen. Results: We found that in these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive to choice of the XCO value, since the molecular gas is the dominant component in the inner parts. We found that for three galaxies of our sample, namely NGC 4254, NGC 4321, and NGC 4501, the slopes of the oxygen and of the dust-to-gas radial gradients agree up to ~0.6-0.7 R25 using XCO values in the range 1/3-1/2 Galactic XCO. For NGC 4303 a lower value of XCO ~ 0.1 × 1020 is necessary. Conclusions: We suggest that such low XCO values might be due to a metallicity dependence of XCO (from close to linear for NGC 4254, NGC 4321, and NGC 4501 to superlinear for NGC 4303), especially in the radial regions RG < 0.6-0.7 R25 where the molecular gas dominates. On the other hand, the outer regions, where the atomic gas component is dominant, are less affected by the choice of XCO, and thus we cannot put constraints on its value there.

Magrini, L.; Bianchi, S.; Corbelli, E.; Cortese, L.; Hunt, L.; Smith, M.; Vlahakis, C.; Davies, J.; Bendo, G. J.; Baes, M.; Boselli, A.; Clemens, M.; Casasola, V.; de Looze, I.; Fritz, J.; Giovanardi, C.; Grossi, M.; Hughes, T.; Madden, S.; Pappalardo, C.; Pohlen, M.; di Serego Alighieri, S.; Verstappen, J.

2011-11-01

218

Stellar Sea Lion Research  

NSDL National Science Digital Library

The phenomenon is the decline in population of western Stellar Sea Lions from 1969 to 1986, shown in a series of three images. The accompanying text describes the possible factors that may be contributing to the change in population.

219

GHOSTS | Bulges, Halos, and the Resolved Stellar Outskirts of Massive Disk Galaxies  

NASA Astrophysics Data System (ADS)

In hierarchical galaxy formation the stellar halos of galaxies are formed by the accretion of minor satellites and therefore contain valuable information about the (early) assembly process of galaxies. Our GHOSTS survey measures the stellar envelope properties of 14 nearby disk galaxies by imaging their resolved stellar populations with HST/ACS and WFPC2. Most of the massive galaxies in the sample (V_{rot}>200 km s^{-1}) have very extended stellar envelopes with ?(r) ˜ r^{-2.5} power law profiles in the outer regions. For these massive galaxies there is some evidence that the stellar surface density of the profiles correlates with Hubble type and bulge-to-disk ratio, begging the question whether these envelopes are more related to bulges than to a Milky Way-type stellar halo. Smaller galaxies (V_{rot}˜100 km s^{-1}) have much smaller stellar envelopes, but depending on geometry, they could still be more luminous than expected from satellite remnants in hierarchical galaxy formation models. Alternatively, they could be created by disk heating through the bombardment of small dark matter sub-halos. We find that galaxies show varying amounts of halo substructure.

de Jong, R. S.; Radburn-Smith, D. J.; Sick, J. N.

2008-10-01

220

INSIGHT INTO THE FORMATION OF THE MILKY WAY THROUGH COLD HALO SUBSTRUCTURE. I. THE ECHOS OF MILKY WAY FORMATION  

SciTech Connect

We identify 10-seven for the first time-elements of cold halo substructure (ECHOS) in the volume within 17.5 kpc of the Sun in the inner halo of the Milky Way. Our result is based on the observed spatial and radial velocity distribution of metal-poor main-sequence turnoff (MPMSTO) stars in 137 Sloan Extension for Galactic Understanding and Exploration lines of sight. We point out that the observed radial velocity distribution is consistent with a smooth stellar component of the Milky Way's inner halo overall, but disagrees significantly at the radial velocities that correspond to our detections. We show that all of our detections are statistically significant and that we expect no false positives. These ECHOS represent the observable stellar debris of ancient merger events in the stellar accretion history of the Milky Way, and we use our detections and completeness estimates to infer a formal upper limit of 0.34{sup +0.02} {sub -0.02} on the fraction of the MPMSTO population in the inner halo that belong to ECHOS. Our detections and completeness calculations also suggest that there is a significant population of low fractional overdensity ECHOS in the inner halo, and we predict that 1/3 of the inner halo (by volume) harbors ECHOS with MPMSTO star number densities n approx 15 kpc{sup -3}. In addition, we estimate that there are of order 10{sup 3} ECHOS in the entire inner halo. ECHOS are likely older than known surface brightness substructure, so our detections provide us with a direct measure of the accretion history of the Milky Way in a region and time interval that has yet to be fully explored. In concert with previous studies, our result suggests that the level of merger activity has been roughly constant over the past few Gyr and that there has been no accretion of single stellar systems more massive than a few percent of a Milky Way mass in that interval.

Schlaufman, Kevin C.; Rockosi, Constance M., E-mail: kcs@ucolick.or, E-mail: crockosi@ucolick.or [Astronomy and Astrophysics Department, University of California, Santa Cruz, CA 95064 (United States)

2009-10-01

221

Stellar Astrophysical Fluid Dynamics  

NASA Astrophysics Data System (ADS)

Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A. Spiegel and Jean-Luc Thiffeault; 27. Formation of planetary systems Douglas N. C. Lin; 28. The solar-cycle global warming as inferred from sky brightness variation Wasaburo Unno and Hiromoto Shibahashi.

Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

2003-05-01

222

Stellar Astrophysical Fluid Dynamics  

NASA Astrophysics Data System (ADS)

Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A. Spiegel and Jean-Luc Thiffeault; 27. Formation of planetary systems Douglas N. C. Lin; 28. The solar-cycle global warming as inferred from sky brightness variation Wasaburo Unno and Hiromoto Shibahashi.

Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

2008-02-01

223

PREFACE: A Stellar Journey A Stellar Journey  

Microsoft Academic Search

The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor

M. Asplund

2008-01-01

224

Mapping the substructure in the Galactic halo with the next generation of astrometric satellites  

NASA Astrophysics Data System (ADS)

We run numerical simulations of the disruption of satellite galaxies in a Galactic potential to build up the entire stellar halo, in order to investigate what the next generation of astrometric satellites will reveal by observing the halo of the Milky Way. We generate artificial DIVA, FAME and GAIA halo catalogues, in which we look for the signatures left by the accreted satellites. We develop a method based on the standard Friends-of-Friends algorithm applied to the space of integrals of motion. We find this simple method can recover about 50per cent of the different accretion events, when the observational uncertainties expected for GAIA are taken into account, even when the exact form of the Galactic potential is unknown. The recovery rate for DIVA and FAME is much smaller, but these missions, like GAIA, should be able to test the hierarchical formation paradigm on our Galaxy by measuring the amount of halo substructure in the form of nearby kinematically cold streams with, for example, a two-point correlation function in velocity space.

Helmi, Amina; de Zeeuw, P. Tim

2000-12-01

225

The Impact of Cluster Substructure on Galaxies: a Case Study in Abell 2125  

NASA Astrophysics Data System (ADS)

We propose to image three regions of the Butcher-Oemler {BO} cluster, A2125 {z=0.247}, to better understand the BO effect. VLA data show that, as well as a large blue-galaxy fraction {0.19} for its redshift, it has an unprecedented number of radio galaxies {30 with confirmed redshifts}, evenly split between old stellar populations and starbursting galaxies. There is also optical and X-ray evidence that a cluster- cluster merger is underway. A prominent radial ``filament'' is rich in both blue galaxies and radio sources. This combination, of unusually low redshift and radio activity suggesting that we are seeing a BO ``event'' soon after the fact, makes this cluster especially attractive in trying to distinguish various physical mechanisms at work in producing blue galaxies in rich clusters, and in tracing the links between events on cluster scales with the response within individual galaxies. We propose to image the core and filament regions of the cluster in WFPC2 filters F450W and F675W {1} to look for color and morphological evidence of the dominant mechanism among the competing theories for the BO effect and {2} to understand the origin of the enhanced radio activity. Enhancement of AGN in the substructure region would suggest that the environment is affecting the galaxy on very small nuclear scales. For star-forming galaxies, the color distribution can discriminate among several proposed mechanisms for producing a blue excess during cluster mergers.

Owen, Frazer

1997-12-01

226

High-frequency response analysis via algebraic substructuring  

Microsoft Academic Search

SUMMARY High-frequency response analysis (Hi-FRA) of large-scale dynamical systems is critical to predict the resonant behavior of modern micro-devices and systems operated over MHz or GHz frequency range. Algebraic substructuring (AS) is a powerful technique to extract a large number of natural frequencies. In this work, we extend the AS technique for FRA between two specified cutoff frequencies min and

Jin Hwan Ko; Zhaojun Bai

2008-01-01

227

Galaxy Properties and Substructure in the Cluster Abell 160  

NASA Astrophysics Data System (ADS)

We have developed a procedure for building a large catalog of cluster galaxies and their photometric properties as measured with CCDs. Our first case, Abell 160, is relatively nearby and redshifts exist for its brightest galaxies. We have mosaiced this cluster in R and V filters using a CCD imager on the 1.3-meter McGraw-Hill telescope. We fitted a world coordinate system to the images using the software ``WCStools,'' then used ``Source Extractor'' to extract sources from the images. We have created software for merging catalogs in such a way as to avoid double counting, to reject cosmic rays, and to combine redundant measurements. The software also corrects magnitude differences by comparing the mean difference and adding this to each individual catalog before merging it to a master catalog. The measured properties included in this study were magnitude, ellipticity, position angle, size, and color (V-R). We investigate the efficacy of our separation of galaxies and stars and find that it begins breaking down around R=19.0. We divide our master catalog into several subsamples for substructure analysis. For one subsample, we attempt to separate cluster members from foreground and background galaxies using the color-magnitude relation. We compare the results of substructure diagnostics for the subsamples. In future work, we will examine correlation of substructure with galaxy properties (especially color, size and morphology).

Koontz, Craig; Pinkney, Jason

2009-04-01

228

Quasar Mesolensing as a Probe of CDM Substructures  

NASA Astrophysics Data System (ADS)

We investigate methods to detect numerous CDM substructures around galaxies predicted by cosmological N-body simulations via medium-scale gravitational-lens effect. Magnification anomaly due to such substructures have already been noted by some researchers and applied to gravitationally lensed quasars. In this presentation we focus on other phenomena produced by gravitational lens effects multiple images and the time delays between images at the same situation i.e. the lens is a galaxy and the source is a distant quasar. Here we have included the effect of the galaxy itself so-called ""Chang-Refsdal lens"" situation and estimated image separations and the time delays. The expected values are from 1 to 100 mas for the image separation and from 10 to 1000 sec for the time delay with slight lens model dependence. Event rate for such phenomena is the order of percent but such signals in one image of a gravitationally lensed quasar must be a direct evidence for the numerous CDM substructures. Image separations and time delays are reflect mass of the lens and our methods will provide better constraints on the substructres compared with magnification anomaly.

Yonehara, A.; Umemura, M.; Susa, H.

2004-07-01

229

Advancements in hybrid dynamic models combining experimental and finite element substructures  

NASA Astrophysics Data System (ADS)

This paper presents very practical enhancements to the transmission simulator method (TSM); also known as the Modal Constraints for Fixtures and Subsystems (MCFS). The enhancements allow this method to be implemented directly in finite element software, instead of having to extract the reduced finite element model from its software and implement the substructure coupling in another code. The transmission simulator method is useful for coupling substructures where one substructure is derived experimentally and the other is generated from a finite element model. This approach uses a flexible fixture in the experimental substructure to improve the modal basis of the substructure; thus, providing a higher quality substructure. The flexible fixture substructure needs to be removed (decoupled) from the experimental substructure to obtain the true system characteristics. A modified method for this removal and coupling of the experimental and analytical substructures is provided. An additional improvement guarantees that the experimental substructure matrices are positive definite, a requirement for many finite element codes. Guidelines for designing robust transmission simulator hardware are provided. The concepts are applied to two sample cases. The first case consists of a cylinder connected by eight bolts to a plate with a beam. The second example is an outer shell structure that is connected through a bolted flange to a complex internal payload structure.

Mayes, R. L.; Ross, M. R.

2012-08-01

230

VIRGO: a large interferometer for gravitational wave detection started its first scientific run  

NASA Astrophysics Data System (ADS)

The VIRGO interferometer is the largest ground based European gravitational wave detector operating at the EGO Laboratory in the Pisa, Italy; countryside. During the last commissioning period relevant progress have been done in approaching its design sensitivity all over the detection bandwidth. Thanks to the effort of the whole Collaboration a long scientific run has been done collecting data for more than 4 months in conjunction with the LIGO detectors. The results obtained from the detector point of view are: a very good stability and a duty-cycle as high as 81% in science mode. In this paper we present the status of the VIRGO interferometer giving an overview of the experimental apparatus together with its most relevant features.

Acernese, F.; Alshourbagy, M.; Amico, P.; Antonucci, F.; Aoudia, S.; Astone, P.; Avino, S.; Baggio, L.; Barone, F.; Barsotti, L.; Barsuglia, M.; Bauer, T. S.; Bigotta, S.; Birindelli, S.; Bizouard, M.; Boccara, C.; Bondu, F.; Bosi, L.; Braccini, S.; Bradaschia, C.; Brillet, A.; Brisson, V.; Buskulic, D.; Cagnoli, G.; Calloni, E.; Campagna, E.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cesarini, E.; C-Mottin, E.; Clapson, A.-C.; Cleva, F.; Coccia, E.; Corda, C.; Corsi, A.; Cottone, F.; Coulon, J.-P.; Cuoco, E.; D'Antonio, S.; Dari, A.; Dattilo, V.; Davier, M.; DeRosa, R.; DelPrete, M.; Di Fiore, L.; Di Lieto, A.; Di Virgilio, A.; Dujardin, B.; Evans, M.; Fafone, V.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Garufi, F.; Genin, E.; Gennai, A.; Giazotto, A.; Giordano, L.; Granata, V.; Greverie, C.; Grosjean, D.; Guidi, G.; Hamdani, S.; Hebri, S.; Heitmann, H.; Hello, P.; Huet, D.; Kreckelbergh, S.; La Penna, P.; Laval, M.; Leroy, N.; Letendre, N.; Lopez, B.; Lorenzini, M.; Loriette, V.; Losurdo, G.; Mackowski, J.-M.; Majorana, E.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marque, J.; Martelli, F.; Masserot, A.; Menzinger, F.; Milano, L.; Minenkov, Y.; Moins, C.; Moreau, J.; Morgado, N.; Mosca, S.; Mours, B.; Man, C. N.; Neri, I.; Nocera, F.; Pagliaroli, G.; Palomba, C.; Paoletti, F.; Pardi, S.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Piergiovanni, F.; Pinard, L.; Poggiani, R.; Punturo, M.; Puppo, P.; Rapagnani, P.; Regimbau, T.; Remillieux, A.; Ricci, F.; Ricciardi, I.; Rocchi, A.; Rolland, L.; Romano, R.; Ruggi, P.; Russo, G.; Solimeno, S.; Spallicci, A.; Tarallo, M.; Terenzi, R.; Toncelli, A.; Tonelli, M.; Tournefier, E.; Travasso, F.; Tremola, C.; Vajente, G.; van der Brand, J. F. J.; van der Putten, S.; Verkindt, D.; Vetrano, F.; Vicerè, A.; Vinet, J.-Y.; Vocca, H.; Yvert, M.

2008-07-01

231

The planetary nebulae luminosity function and distances to the Virgo, Hydra i, and Coma Clusters  

NASA Astrophysics Data System (ADS)

The luminosity function of planetary nebula populations in galaxies at distances within 10-15 Mpc exhibits a cut-off at bright magnitudes and a functional form that is observed to be invariant among different galactic morphological types. Therefore, it is used as a secondary distance indicator applicable to both early- and late-type galaxies. Recent deep surveys of planetary nebula populations in brightest cluster galaxies (BCGs) seem to indicate that their luminosity functions deviate from those observed in the nearby galaxies. We discuss the evidence for such deviations in the Virgo Cluster, and indicate which physical mechanisms may alter the evolution of a planetary nebula envelope and its central star in the halo of BCGs. We then discuss preliminary results for distances to the Virgo, Hydra i, and Coma Clusters based on the observed planetary nebulae luminosity functions.

Arnaboldi, Magda; Longobardi, Alessia; Gerhard, Ortwin; Okamura, S.

2013-02-01

232

Evaluating the gamma-ray evidence for self-annihilating dark matter from the Virgo cluster  

NASA Astrophysics Data System (ADS)

Based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the bb¯ channel has been reported by Han et al. [arXiv:1201.1003]. After an in-depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalog (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data are included.

Macías-Ramírez, Oscar; Gordon, Chris; Brown, Anthony M.; Adams, Jenni

2012-10-01

233

Large-Scale Structure in the Direction of the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We explore the distribution of galaxies behind the Virgo cluster out to z < 0.1, using the CfA redshift catalog, ZCAT, in conjunction with Abell clusters and pencil beam surveys as other tracers of large-scale structure. The field galaxies of ZCAT are found to trace the same overdensity as indicated by a supercluster defined by Abell clusters in the catalog of Einasto et al. [MNRAS, 269,351(1994)]. On even larger scales, galaxy peaks in three different pencil beam lines of sight toward the Virgo cluster are all found to fall at z ~ 0.08. We show this similarity in redshift to have a small probability of being caused by a random alignment, suggesting a sheet-like structure at that redshift, spanning >~ 150h_75_^-1^ Mpc.

Flint, K. P.; Impey, C. D.

1996-09-01

234

A search for extended halos of hot gas in the Perseus, Virgo, and Coma Clusters  

NASA Astrophysics Data System (ADS)

Observations of the Perseus cluster by the HEAO 1 satellite have revealed a faint X-ray halo extending at least 2.5 deg from the center and contributing between 5% and 20% to the total luminosity. This may be of nonthermal origin, but it also may be explained in terms of hot gas bound by the gravitational field of the cluster. Statistical uncertainties made it impossible to detect any such halo in the Coma cluster. Observations of the Virgo cluster confirmed the detection by the Ariel 5 satellite of a broad region of faint X-ray emission (core radius 60 arcmin). If the very extended X-ray emission from Virgo is due to hot intracluster gas, the density of this gas is lower than expected from a consideration of gas and galaxy densities in the Perseus cluster.

Ulmer, M. P.; Cruddace, R. G.; Wood, K.; Meekins, J.; Yentis, D.; Evans, W. D.; Smathers, H. W.; Byram, E. T.; Chubb, T. A.; Friedman, H.

1980-02-01

235

A 500 kpc HI Tail of the Virgo Pair NGC4532/DDO137 Detected by ALFALFA  

NASA Astrophysics Data System (ADS)

HI observations of the Virgo Cluster pair NGC 4532/DDO 137, conducted as part of the Arecibo Legacy Fast ALFA Survey, reveal an HI feature extending ~500kpc to the southwest. The structure has a total mass of up to 7 x 108 M, equivalent to 10% of the pair HI mass. Optical R imaging reveals no counterparts to a level of 26.5 mag arcsec-2. The structure is likely the result of galaxy harassment.

Koopmann, Rebecca A.

2008-05-01

236

Virgo calibration and reconstruction of the gravitationnal wave strain during VSR1  

Microsoft Academic Search

Virgo is a kilometer-length interferometer for gravitationnal waves detection located near Pisa. Its first science run, VSR1, occured from May to October 2007. The aims of the calibration are to measure the detector sensitivity and to reconstruct the time series of the gravitationnal wave strain h(t). The absolute length calibration is based on an original non-linear reconstruction of the differential

T. Accadia; F. Acernese; F. Antonucci; S. Aoudia; K. G. Arun; P. Astone; G. Ballardin; F. Barone; M. Barsuglia; Th S. Bauer; M. G. Beker; A. Belletoile; S. Bigotta; S. Birindelli; M. Bitossi; M. A. Bizouard; M. Blom; C. Boccara; F. Bondu; L. Bonelli; R. Bonnand; L. Bosi; S. Braccini; C. Bradaschia; A. Brillet; V. Brisson; R. Budzynski; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; E. Campagna; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande-Mottin; A. Chincarini; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; A. Corsi; J.-P. Coulon; E. Cuoco; S. D'Antonio; A. Dari; V. Dattilo; M. Davier; R. Day; R. De Rosa; M. del Prete; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; A. Dietz; M. Drago; V. Fafone; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; A. Freise; M. Galimberti; L. Gammaitoni; F. Garufi; G. Gemme; E. Genin; A. Gennai; A. Giazotto; R. Gouaty; M. Granata; C. Greverie; G. M. Guidi; H. Heitmann; P. Hello; S. Hild; D. Huet; P. Jaranowski; I. Kowalska; A. Królak; N. Leroy; N. Letendre; T. G. F. Li; M. Lorenzini; V. Loriette; G. Losurdo; J. M. Mackowski; E. Majorana; I. Maksimovic; N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; C. Michel; L. Milano; Y. Minenkov; M. Mohan; J. Moreau; N. Morgado; A. Morgia; S. Mosca; V. Moscatelli; B. Mours; I. Neri; F. Nocera; G. Pagliaroli; L. Palladino; C. Palomba; F. Paoletti; S. Pardi; M. Parisi; A. Pasqualetti; R. Passaquieti; D. Passuello; G. Persichetti; M. Pichot; F. Piergiovanni; M. Pietka; L. Pinard; R. Poggiani; M. Prato; G. A. Prodi; M. Punturo; P. Puppo; O. Rabaste; D. S. Rabeling; P. Rapagnani; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosinska; P. Ruggi; B. Sassolas; D. Sentenac; R. Sturani; B. Swinkels; A. Toncelli; M. Tonelli; O. Torre; E. Tournefier; F. Travasso; J. Trummer; G. Vajente; S. van der Putten; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2010-01-01

237

Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster  

Microsoft Academic Search

X-ray observations of the galaxy M87 and of a region in the Virgo cluster displaced 7 arcmin from the center of M87 are reported. X-ray spectra were obtained at these two locations with the Solid State Spectrometer onboard the Einstein Observatory. Emission lines were observed in both locations, indicating the presence of heavy elements at abundances near solar. There is

S. M. Lea; R. Mushotzky; S. S. Holt

1982-01-01

238

Discovery of 0.5 MK Gas in the Center of the Virgo Cluster  

Microsoft Academic Search

An observation of M87, the central galaxy of the Virgo Cluster, was performed by the deep survey telescope aboard the Extreme-Ultraviolet Explorer, in the 0.065--0.245 keV energy band. A point source and an extended emission halo of radius ~20' are clearly visible in the data, and represent the first detection of cluster gas emission in the EUV. The emission cannot

Richard Lieu; Jonathan P. D. Mittaz; Stuart Bowyer; Felix J. Lockman; Chorng-Yuan Hwang; Jurgen H. M. M. Schmitt

1996-01-01

239

Evidence for a radio flare in the nucleus of Virgo A  

SciTech Connect

An increase in radio emission has been observed in the nucleus of the galaxy Virgo A by use of VLBI measurements. These 2.29 GHz observations show that the correlated flux density of the milliarcsec structure increased by 30 percent during a four month period in 1977, and eventually returned to the preflare level of about 0.6 Jy. Previous evidence had indicated that the nuclear radio emission was stable, a surprising result for an active galactic nucleus. 14 references.

Morabito, D.D.; Preston, R.A.; Jauncey, D.L.

1988-04-01

240

Optical studies of galaxies in clusters. Observations of spirals in Virgo. III.  

NASA Astrophysics Data System (ADS)

We present the analysis of the rotation curves of a sample of 32 spiral galaxies derived from the spectroscopic observations of a sample of 47 galaxies. For 15 galaxies we were either unable to detect emission lines or measure a reasonably good rotation curve. Of the 32 rotation curves 23 are of galaxies member of the Virgo Cluster and 9 selected from the "field". Analysis of mass and density distribution have been obtained. The mass distribution of cluster galaxies belongs to the Type III proposed by Burstein & Rubin (1985) with few exceptions (NGC 4519 Type I, NGC 2280, NGC 4189, NGC 5861, NGC 6070 Type II) and, is unrelated to the morphological type. Density distribution curves from equidensity surface spheroids model, computed for the Virgo sample, result to be primarily composed of three classes. Rotation curves, none of which shows a peculiar trend, have been parametrized using the criteria introduced by Whitmore et al. (1984). The clustercentric distance of Virgo spirals does not correlate neither with OG nor with OGML in agreement with the findings of Distefano et al. (1990) and Amram et al. (1993, 1994) for other clusters.

Sperandio, M.; Chincarini, G.; Rampazzo, R.; de Souza, R.

1995-04-01

241

CLOUDS TOWARD THE VIRGO CLUSTER PERIPHERY: GAS-RICH OPTICALLY INERT GALAXIES  

SciTech Connect

Aperture synthesis observations of two H I cloud complexes located in the periphery of the Virgo galaxy cluster are presented. These low H I-mass clouds (M{sub H{sub I}}< 10{sup 9} M{sub sun}) are seen projected on the M region of the western Virgo cluster, where the galaxy population is thought to lie behind the main A cluster surrounding M87. The kinematic measurements of both unresolved Arecibo and resolved Very Large Array (VLA)-C observations are in good agreement. The H I detections cannot be identified with any optical, IR, or UV emission from available archival imaging. They are inert at these wavelengths. The H I masses of the individual VLA detections range from 7.28 {<=} log(M{sub H{sub I}}/M{sub sun}){<=} 7.85. The total dynamical mass estimates are several times their H I content, ranging from 7.00 {<=} log(M{sub dyn}/M{sub sun}){<=} 9.07, with the assumption that the clouds are self-gravitating and in dynamical equilibrium. We report the observed parameters derived from the VLA observations. One of these H I clouds appears to be the most isolated optically inert detection observed in the outer reaches of Virgo.

Kent, Brian R., E-mail: bkent@nrao.ed [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)

2010-12-20

242

Mapping the Stellar Structure of the Milky Way Thick Disk and Halo Using SEGUE Photometry  

NASA Astrophysics Data System (ADS)

We map the stellar structure of the Galactic thick disk and halo by applying color-magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1 kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75 ± 0.07 kpc and 4.1 ± 0.4 kpc, respectively. We find a stellar halo flattening within ~25 kpc of c/a = 0.88 ± 0.03 and a power-law index of 2.75 ± 0.07 (for 7 kpc lsimRGC <~ 30 kpc). The model fits yield thick-disk and stellar halo densities at the solar location of ?thick,sun = 10-2.3±0.1 M sun pc-3 and ?halo,sun = 10-4.20±0.05 M sun pc-3, averaging over any substructures. Our analysis provides the first clear in situ evidence for a radial metallicity gradient in the Milky Way's stellar halo: within R <~ 15 kpc the stellar halo has a mean metallicity of [Fe/H] ~= -1.6, which shifts to [Fe/H] ~= -2.2 at larger radii, in line with the two-component halo deduced by Carollo et al. from a local kinematic analysis. Subtraction of the best-fit smooth and symmetric model from the overall density maps reveals a wealth of substructures at all latitudes, some attributable to known streams and overdensities, and some new. A simple warp cannot account for the low latitude substructure, as overdensities occur simultaneously above and below the Galactic plane.

de Jong, Jelte T. A.; Yanny, Brian; Rix, Hans-Walter; Dolphin, Andrew E.; Martin, Nicolas F.; Beers, Timothy C.

2010-05-01

243

MAPPING THE STELLAR STRUCTURE OF THE MILKY WAY THICK DISK AND HALO USING SEGUE PHOTOMETRY  

SciTech Connect

We map the stellar structure of the Galactic thick disk and halo by applying color-magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1 kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75 {+-} 0.07 kpc and 4.1 {+-} 0.4 kpc, respectively. We find a stellar halo flattening within {approx}25 kpc of c/a = 0.88 {+-} 0.03 and a power-law index of 2.75 {+-} 0.07 (for 7 kpc {approx_lt}R{sub GC} {approx_lt} 30 kpc). The model fits yield thick-disk and stellar halo densities at the solar location of {rho}{sub thick,sun} = 10{sup -2.3{+-}0.1} M{sub sun} pc{sup -3} and {rho}{sub halo,sun} = 10{sup -4.20{+-}0.05} M{sub sun} pc{sup -3}, averaging over any substructures. Our analysis provides the first clear in situ evidence for a radial metallicity gradient in the Milky Way's stellar halo: within R {approx_lt} 15 kpc the stellar halo has a mean metallicity of [Fe/H] {approx_equal} -1.6, which shifts to [Fe/H] {approx_equal} -2.2 at larger radii, in line with the two-component halo deduced by Carollo et al. from a local kinematic analysis. Subtraction of the best-fit smooth and symmetric model from the overall density maps reveals a wealth of substructures at all latitudes, some attributable to known streams and overdensities, and some new. A simple warp cannot account for the low latitude substructure, as overdensities occur simultaneously above and below the Galactic plane.

De Jong, Jelte T. A.; Rix, Hans-Walter; Martin, Nicolas F. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Beers, Timothy C., E-mail: dejong@mpia.d [Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)

2010-05-01

244

Substructures in the temporal distribution of atmospheric Cerenkov light in EAS  

NASA Astrophysics Data System (ADS)

Particle density and arrival time distribution of atmospheric Cerenkov light (ACL) was measured simultaneously in individual air showers at Pic du Midi. Substructures were observed in the arrival time distribution of the ACL. The arrival time is related to a position in the shower plane which indicates the existence of density variations, i.e., substructures in the lateral distribution of particles. The frequency of substructures is a few percent, and core distances of up to tens of meters were observed.

Bosia, G.; Navarra, G.; Saavedra, O.; Boehm, E.

1980-06-01

245

PREFACE: A Stellar Journey A Stellar Journey  

NASA Astrophysics Data System (ADS)

The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an astronomical talk, student lecture, musical concert or theatre play. Another attribute of Bengt is his boundless optimism, which not the least has helped many of his students overcome the unavoidable moments of despair (this is only true as long as one is aware of the well-known BG factor: multiply any of Bengt's estimates for the time required to complete a task by at least a factor of three). His personal traits make working with Bengt always very enjoyable as well as highly educating. Bengt's work also extends well beyond the domain of astronomy, including music, literature, theatre, religion, research ethics, science policy and science popularization. Bengt is an excellent role model for a successful scientist with a rich and rewarding life outside of academia. The symposium A Stellar Journey was divided into five sessions covering basically the main research areas Bengt has worked on: Stellar atmospheres, Solar/stellar spectroscopy, Stellar parameters, Stellar evolution and nucleosynthesis and Stellar populations. In addition, one afternoon was devoted to a session entitled Anything but astronomy (see the symposium program), which tried to showcase Bengt's diverse interests outside of astronomy with talks ranging from religion and history of science over science popularization and future studies to literature and music. My task, as chair of the Scientific Organizing Committee, to put together an exciting scientific program of invited reviews and talks was made considerably easier thanks to the excellent suggestions by the other SOC members: Ann Boesgaard, Sofia Feltzing, John Lattanzio, Andre Maeder, Bertrand Plez and Monique Spite. I believe in the end we were successful in achieving our charge, an impression corroborated by the many encouraging comments from various participants during and after the conference. I am particularly grateful to Nils Bergvall, Bengt Edvardsson and Bertrand Plez for their time-consuming efforts in arranging the extraordinary and greatly appreciated non-astronomical session on Tuesday afternoon; Sigbritt Ernald provided a rich sourc

Asplund, M.

2008-10-01

246

An Impulse Based Substructuring approach for impact analysis and load case simulations  

NASA Astrophysics Data System (ADS)

In the present paper we outline the basic theory of assembling substructures for which the dynamics are described as Impulse Response Functions. The assembly procedure computes the time response of a system by evaluating per substructure the convolution product between the Impulse Response Functions and the applied forces, including the interface forces that are computed to satisfy the interface compatibility. We call this approach the Impulse Based Substructuring method since it transposes to the time domain the Frequency Based Substructuring approach. In the Impulse Based Substructuring technique the Impulse Response Functions of the substructures can be gathered either from experimental tests using a hammer impact or from time-integration of numerical submodels. In this paper the implementation of the method is outlined for the case when the impulse responses of the substructures are computed numerically. A simple bar example is shown in order to illustrate the concept. The Impulse Based Substructuring allows fast evaluation of impact response of a structure when the impulse response of its components is known. It can thus be used to efficiently optimize designs of consumer products by including impact behavior at the early stage of the design, but also for performing substructured simulations of complex structures such as offshore wind turbines.

Rixen, Daniel J.; van der Valk, Paul L. C.

2013-12-01

247

Observing stellar bow shocks  

Microsoft Academic Search

For stars, the bow shock is typically the boundary between their stellar wind and the interstellar medium. Named for the wave made by a ship as it moves through water, the bow shock wave can be created in the space when two streams of gas collide. The space is actually filled with the interstellar medium consisting of tenuous gas and

A. C. Sparavigna; R. Marazzato

2010-01-01

248

Stellar Structure and Evolution  

Microsoft Academic Search

This text gives a complete and comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star's life. The authors have written a unique text based on

Rudolf Kippenhahn; Alfred Weigert

1990-01-01

249

Commission 35: Stellar Constitution  

Microsoft Academic Search

The Commission home page is maintained by Claus Leitherer and contains general information on the Commission structure and activities, including links to stellar structure resources that were made available by the owners. The resources contain evolutionary tracks and isochrones from various groups, nuclear reaction, EOS, and opacity data as well as links to main astronomical journals. As a routine activity,

Francesca D'Antona; Corinne Charbonnel; Wojciech Dziembowski; Gilles Fontaine; Richard B. Larson; John Lattanzio; Jim W. Liebert; Ewald Müller; Achim Weiss; Lev R. Yungelson

2009-01-01

250

Stellar Ontogeny: From Dust...  

ERIC Educational Resources Information Center

|Discusses the process of star formation. Infrared and radio astronomy, particularly microwave astronomy is used to provide information on different stages of stellar formation. The role of dust and gas which swirl through the interstellar regions of a galaxy and the collapse of a cloud in star formation are also presented. (HM)|

MOSAIC, 1978

1978-01-01

251

Libraries of Stellar Spectra  

NSDL National Science Digital Library

This is a guide to online and abstract libraries of stellar spectra. This reference list also includes information about the spectra of Late-M, L, and T Dwarf stars, Morgan-Keenan spectral classification, the solar spectrum, spectrophotometric atlases, and automated and neural network classification.

2005-04-25

252

Stellar physics with Gaia  

NASA Astrophysics Data System (ADS)

Gaia will provide a three-dimensional map of our Galaxy, with unprecedented positional and radial velocity measurements for about one per cent of the Galactic stellar population. Combined with astrophysical information derived from spectroscopy and photometry for each star, this will lead to a detailed understanding of Êthe formation, and dynamical and chemical evolution of our Galaxy. Other scientific products include extra-solar planets, minor bodies in the solar system, or distant quasars. The contribution of Gaia to stellar physics is less publicized, although very significant.Ê I show here a number of illustrative examples. For example, we will have access to very precise HR diagrams with very large sample of stars allowing extensive tests of fine effects in stellar evolution. Accurate parameters (esp. luminosities, and masses) will allow the independent determination of surface gravities, the characterization of non-LTE effects, and the derivation of more accurate chemical abundances. We will be able to quantify transport processes in various populations of stars, and shed new light on abundance anomalies. In addition, the preparation of Gaia induces a very large effort devoted to homogenize the stellar parameters of a great number of reference stars, and the development of performant tools designed to automatically extract parameters from tremendous amounts of spectra.

Plez, B.

2011-12-01

253

Advanced Stellar Astrophysics  

Microsoft Academic Search

In the past two decades, scientists have made remarkable progress in understanding stars. This graduate-level textbook provides a systematic, self-contained and lucid introduction to the physical processes and fundamental equations underlying all aspects of stellar astrophysics. The timely volume provides authoritative astronomical discussions as well as rigorous mathematical derivations and illuminating explanations of the physical concepts involved. In addition to

William K. Rose

1998-01-01

254

Stellarator and Heliotron Devices  

Microsoft Academic Search

Stellarators and tokamaks are the most advanced devices that have been developed for magnetic fusion applications. The two approaches have much in common; tokamaks have received the most attention because their axisymmetry justifies the use of simpler models and provides a more forgiving geometry. However, recent advances in treating more complicated three dimensional systems have made it possible to design

John L. Johnson

1999-01-01

255

Progress Toward Attractive Stellarators  

SciTech Connect

The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

Neilson, G H; Brown, T G; Gates, D A; Lu, K P; Zarnstorff, M C; Boozer, A H; Harris, J H; Meneghini, O; Mynick, H E; Pomphrey, N; Reiman, A H

2011-01-05

256

Deformation substructures induced by high-rate deformation  

SciTech Connect

The influence of increasing strain on the deformation substructures in metals and alloys which deform predominately by slip is very similar to that seen following quasi-static deformation at increasingly lower temperatures or due to a decrease in stacking fault energy ({gamma}{sub sf}). For constant strain, deformation at higher rates: (1) produces more uniform dislocation distributions for the same amount of strain, (2) hinders dislocation cell formation, (3) decreases the cell size, and (4) increases misorientaion with more dislocations trapped within the cell interiors. The suppression of thermally-activated dislocation processes in this regime, added to high temperature and strain-rate sensitivity of the yield stress exhibited by many materials, can lead to stresses high enough to nucleate and grow deformation twins even in high stacking fault energy FCC metals such as copper and Al-4.8 wt % Mg. In addition, substructures formed under high-rate conditions differ from those formed under low-rate conditions due to the suppression of dynamic recovery process. Finally, in high-rate deformation such as shock loading, the subsonic restriction on dislocation motion leads to higher dislocation and point defect generation rates, resulting in enhanced hardening when compared to materials deformed to equivalent strains at quasi-static rates. In this paper examples of the deformation substructure evolution observed in aluminum, copper, Ni{sub 3}Al, iron, Ti-6Al-4V, and TiAl at high and shock-loading strain rates will be presented and compared to that seen following low-rate deformation paths. 41 refs., 15 figs.

Gray, G.T. III.

1991-01-01

257

Evidence of Substructure in the Cluster of Galaxies A3558  

NASA Astrophysics Data System (ADS)

We investigate the dynamical properties of the cluster of galaxies A3558 (Shapley 8). Studying a region of 1 deg2 (~3 Mpc2) centered on the cluster cD galaxy, we have obtained a statistically complete photometric catalog with positions and magnitudes of 1421 galaxies (down to a limiting magnitude of B ~ 21). This catalog has been matched to the recent velocity data obtained by Mazure et al. and from the literature, yielding a radial velocity catalog containing 322 galaxies. We analyze the resulting catalog in search of substructure, using different statistical techniques. This analysis shows that the position/velocity space distribution of galaxies shows significant substructure. A central bimodal core, detected previously in a preliminary study by Dantas, de Carvalho, & Capelato and by an analysis of the X-ray emission map by Slezak, Durret, & Gerbal, is confirmed using the adaptive kernel technique and wavelet analysis. We show that this central bimodal substructure is nevertheless composed of a projected feature, kinematically unrelated to the cluster, plus a group of galaxies probably in its initial merging phase into a relaxed core. The cD galaxy's velocity offset with respect to the average cluster redshift, reported earlier by several authors, is completely eliminated as a result of our dynamical analysis. The untangling of the relaxed core component also allows a better, more reliable determination of the central velocity dispersion, which in turn eliminates the " beta problem" for A3558. The cluster also shows a "preferential" distribution of subclumps coinciding with the direction of the major-axis position angle of the cD galaxy and of the central X-ray emission ellipsoidal distribution, in agreement with the anisotropic merger scenario described by West.

Dantas, Christine C.; de Carvalho, Reinaldo R.; Capelato, Hugo V.; Mazure, Alain

1997-08-01

258

An iterative substructuring algorithm for problems in three dimensions  

SciTech Connect

In domain decomposition algorithms with more than a few subdomains, there is a crucial need for a mechanism to provide for global communication of information at each step of the iterative process. The convergence rate will decay rapidly with an increasing number of subdomains if communication is only between neighboring subdomains. For iterative substructuring algorithms (those domain decomposition algorithms that use nonoverlapping subdomains), the method that provides for good global communication in two dimensions does not work well for problems in three dimensions. In this paper we present an alternative approach for providing global communication that works well in three dimensions. Sample theoretical and numerical results are presented. 13 refs., 3 tabs.

Smith, B.F.

1991-01-01

259

Dark Matter Halos:. Shapes, the Substructure Crisis, and Indirect Detection  

NASA Astrophysics Data System (ADS)

In this proceeding, we review three recent results. First, we show that halos formed in simulations with gas cooling are significantly rounder than halos formed in dissipationless N-body simulations. The increase in principle axis ratios is ~ 0.2 - 0.4 in the inner halo and remains significant at large radii. Second, we discuss the CDM substructure crisis and demonstrate the sensitivity of the crisis to the spectrum of primordial density fluctuations on small scales. Third, we assess the ability of experiments like VERITAS and GLAST to detect ?-rays from neutralino dark matter annihilation in dark subhalos about the MW.

Zentner, A. R.; Koushiappas, S. M.; Kazantzidis, S.

2005-04-01

260

Velocity-space substructure from nearby RAVE and SDSS stars  

NASA Astrophysics Data System (ADS)

We extract a sample of disc stars within 200 pc of the Sun from the RAVE and SDSS surveys. Distances are estimated photometrically and proper motions are from ground-based data. We show that the velocity-space substructure first revealed in the Geneva-Copenhagen sample is also present in this completely independent sample. We also evaluate action-angle variables for these stars and show that the Hyades stream stars in these data are again characteristic of having been scattered at a Lindblad resonance. Unfortunately, the analysis of such local samples can determine neither whether it is an inner or an outer Lindblad resonance, nor the multiplicity of the pattern.

Hahn, Chang Hoon; Sellwood, J. A.; Pryor, Carlton

2011-12-01

261

The infall velocity toward Virgo, the Hubble constant, and a search for motion toward the microwave background  

NASA Astrophysics Data System (ADS)

From data on distance ratios of eight clusters and groups of galaxies in the velocity interval 800 - 2000 km s-1, the infall of the Local Group toward the Virgo Cluster center due to the overdensity of the Virgo complex is determined to be vvc = 200±50 km s-1. This gives a low value of M/LB ? 70 averaged over the 20 Mpc volume of the Virgo Cluster complex inside the Local Group circle and requires the local cosmic density parameter to be ?0 = 0.09. The global value of the Hubble constant is H0 = 50±7 km s-1Mpc-1, if the distance to the Virgo Cluster is 21.6 Mpc. It scales directly with any other assumed Virgo distance. The mean random motion of galaxies about an ideal Hubble flow may increase with scale of the structure, ranging from ?(v) = 90 km s-1 for scales of ?1 Mpc to ?(v) ? 500 km s-1 for scales of ?50 Mpc.

Tammann, G. A.; Sandage, A.

1985-07-01

262

The evolution of substructure - II. Linking dynamics to environment  

NASA Astrophysics Data System (ADS)

We present results from a series of high-resolution N-body simulations that focus on the formation and evolution of eight dark matter haloes, each of the order of a million particles within the virial radius. We follow the time evolution of hundreds of satellite galaxies with unprecedented time resolution, relating their physical properties to the differing halo environmental conditions. The self-consistent cosmological framework in which our analysis was undertaken allows us to explore satellite disruption within live host potentials, a natural complement to earlier work conducted within static potentials. Our host haloes were chosen to sample a variety of formation histories, ages and triaxialities; despite their obvious differences, we find striking similarities within the associated substructure populations. Namely, all satellite orbits follow nearly the same eccentricity distribution with a correlation between eccentricity and pericentre. We also find that the destruction rate of the substructure population is nearly independent of the mass, age and triaxiality of the host halo. There are, however, subtle differences in the velocity anisotropy of the satellite distribution. We find that the local velocity bias at all radii is greater than unity for all haloes and this increases as we move closer to the halo centre, where it varies from 1.1 to 1.4. For the global velocity bias, we find a small but slightly positive bias, although when we restrict the global velocity bias calculation to satellites that have had at least one orbit, the bias is essentially removed.

Gill, Stuart P. D.; Knebe, Alexander; Gibson, Brad K.; Dopita, Michael A.

2004-06-01

263

Substructure lensing: effects of galaxies, globular clusters and satellite streams  

NASA Astrophysics Data System (ADS)

Lensing flux-ratio anomalies have been frequently observed and taken as evidence for the presence of abundant dark matter substructures in lensing galaxies, as predicted by the cold dark matter (CDM) model of cosmogony. In previous work, we examined the cusp-caustic relations of the multiple images of background quasars lensed by galaxy-scale dark matter haloes, using a suite of high-resolution N-body simulations (the Aquarius simulations). In this work, we extend our previous calculations to incorporate both the baryonic and diffuse dark components in lensing haloes. We include in each lensing simulation: (1) a satellite galaxy population derived from a semi-analytic model applied to the Aquarius haloes; (2) an empirical Milky Way globular cluster population and (3) satellite streams (diffuse dark component) identified in the simulations. Accounting for these extra components, we confirm our earlier conclusion that the abundance of intrinsic substructures (dark or bright, bound or diffuse) is not sufficient to explain the observed frequency of cusp-caustic violations in the Cosmic Lens All-Sky Survey (CLASS). We conclude that the observed effect could be the result of the small number statistics of CLASS, or intergalactic haloes along the line of sight acting as additional sources of lensing flux anomalies. Another possibility is that this discrepancy signals a failure of the CDM model.

Xu, D. D.; Mao, Shude; Cooper, Andrew P.; Wang, Jie; Gao, Liang; Frenk, Carlos S.; Springel, V.

2010-11-01

264

Population genetic analysis and sub-structuring in Babesia bovis.  

PubMed

The tick-borne protozoan parasite, Babesia bovis is one of the causes of bovine babesiosis, an economically important disease of cattle in tropical and sub-tropical countries. Using the recently published genome sequence of the parasite, we developed a panel of eight mini- and micro-satellite markers and used these to investigate the role of genetic exchange in the population structure and diversity of the parasite using isolates from Zambia and Turkey. This population genetic analysis showed that genetic exchange occurs and that there are high levels of genetic diversity, with geographical sub-structuring quantified using Wright's F Index. Linkage disequilibrium was observed when isolates from both countries were treated as one population, but when isolates from Zambia were analysed separately linkage equilibrium was observed. The Turkish isolates were sub-structured, containing two genetically distinct sub-groups, both of which appeared to be in linkage equilibrium. The results of the Zambian study suggest that a sub-set of the parasite population is responsible for the westward spread of babesiosis into the previously disease-free central region of the country. The Zambian isolates had a significantly higher number of genotypes per sample than those from Turkey and age was found to be a significant predictor of the multiplicity of infection. The high levels of diversity seen in the Zambian and Turkish B. bovis populations have implications in the development of subunit vaccines against the disease and the spread of drug resistance. PMID:21316400

Simuunza, Martin; Bilgic, Huseyin; Karagenc, Tulin; Syakalima, Michelo; Shiels, Brian; Tait, Andy; Weir, William

2011-02-21

265

INSIGHT INTO THE FORMATION OF THE MILKY WAY THROUGH COLD HALO SUBSTRUCTURE. II. THE ELEMENTAL ABUNDANCES OF ECHOS  

SciTech Connect

We determine the average metallicities of the elements of cold halo substructure (ECHOS) that we previously identified in the inner halo of the Milky Way within 17.5 kpc of the Sun. As a population, we find that stars kinematically associated with ECHOS are chemically distinct from the background kinematically smooth inner halo stellar population along the same Sloan Extension for Galactic Understanding and Exploration (SEGUE) line of sight. ECHOS are systematically more iron-rich, but less {alpha}-enhanced than the kinematically smooth component of the inner halo. ECHOS are also chemically distinct from other Milky Way components: more iron-poor than typical thick-disk stars and both more iron-poor and {alpha}-enhanced than typical thin-disk stars. In addition, the radial velocity dispersion distribution of ECHOS extends beyond {sigma} {approx} 20 km s{sup -1}. Globular clusters are unlikely ECHOS progenitors, as ECHOS have large velocity dispersions and are found in a region of the Galaxy in which iron-rich globular clusters are very rare. Likewise, the chemical composition of stars in ECHOS does not match predictions for stars formed in the Milky Way and subsequently scattered into the inner halo. Dwarf spheroidal (dSph) galaxies are possible ECHOS progenitors, and if ECHOS are formed through the tidal disruption of one or more dSph galaxies, the typical ECHOS [Fe/H] {approx} - 1.0 and radial velocity dispersion {sigma} {approx} 20 km s{sup -1} implies a dSph with M{sub tot} {approx}> 10{sup 9} M{sub sun}. Our observations confirm the predictions of theoretical models of Milky Way halo formation that suggest that prominent substructures are likely to be metal-rich, and our result implies that the most likely metallicity for a recently accreted star currently in the inner halo is [Fe/H] {approx} - 1.0.

Schlaufman, Kevin C.; Rockosi, Constance M. [Astronomy and Astrophysics Department, University of California, Santa Cruz, CA 95064 (United States); Lee, Young Sun; Beers, Timothy C. [Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI 48824 (United States); Allende Prieto, Carlos, E-mail: kcs@ucolick.org, E-mail: crockosi@ucolick.org, E-mail: lee@pa.msu.edu, E-mail: beers@pa.msu.edu, E-mail: callende@iac.es [Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife (Spain)

2011-06-10

266

Stellar Blackbody Radiation Curves  

NSDL National Science Digital Library

Stellar Blackbody Radiation Curves model simulates the blackbody radiation curve of stars and how this leads to the observed color and luminosity of the star. If a star can be treated as a blackbody, the blackbody radiation curve of the star, the power density per area (or intensity) per wavelength (energy/time/volume) vs wavelength, is dependent on the star's temperature (spectral class). In the simulation, the star is shown along with its luminosity and spectral class. In separate graph, the blackbody radiation curve, the visible part of the spectrum, and the integrated stellar surface intensity (integrating the blackbody curve over all wavelengths) are shown. In another window the HR diagram can be shown indicating the current star's parameters. The radius of the star (in Rsun) and the temperature of the star in Kelvin (5780 K is Tsun) can be changed.

Belloni, Mario

2010-11-11

267

Gravitational waves from binaries and dense stellar clusters  

NASA Astrophysics Data System (ADS)

It is an exciting time for gravitational wave astrophysics! The LIGO and Virgo gravitational wave detectors are currently undergoing an upgrade that will improve their sensitivity by a factor of about 10. At this ``advanced'' sensitivity, it is likely that they will detect at least one gravitational wave signal from a coalescing compact binary per year; it is possible that detection rates may be several hundred times that. Many of these sources are possibly formed in dense stellar environments---though the exact rates of field and cluster formation are uncertain. I will discuss the state-of-the-art in extracting information about the binary system's properties from these signals and what this information can tell us about the formation environment of the coalescing objects. I will review our current knowledge---and uncertainty---about the formation mechanisms of these objects, highlighting the ways that gravitational wave observations can inform our understanding. Finally, I will discuss some recent modeling results that run contrary to decades old assumptions about the formation of binary black hole gravitational wave sources in globular clusters and the implications for gravitational wave astronomy.

Farr, Will

2013-04-01

268

HI Clouds, Debris, and Galactic HI Toward the Virgo Region with the Arecibo Legacy Fast ALFA Survey  

NASA Astrophysics Data System (ADS)

A sample of HI data from the Arecibo Legacy Fast ALFA survey is described. Several unusual HI candidates have been detected in the vicinity of the Virgo Cluster, all at czsolar<3000 km s-1. Assuming a distance to Virgo of 16.7 Mpc, the minimum detectable HI mass is of order 2×107Msolar. Some objects appear to be located near low surface brightness optical counterparts, or are the result of tidal interactions with nearby large galaxies. Such detections are clearly the result of a larger group or system. However, other isolated HI detections do not coincide with any nearby counterparts visible in optical surveys. The detections lie outside the influence of effects from ram-pressure stripping in the Virgo Cluster. In addition, a preliminary wide-field view of galactic HI observed by the ALFALFA survey will be shown.

Kent, Brian R.

2008-08-01

269

Compressing the free energy range of substructure stabilities in iso-1-cytochrome c  

PubMed Central

Evolutionary conservation of substructure architecture between yeast iso-1-cytochrome c and the well-characterized horse cytochrome c is studied with limited proteolysis, the alkaline conformational transition and global unfolding with guanidine-HCl. Mass spectral analysis of limited proteolysis cleavage products for iso-1-cytochrome c show that its least stable substructure is the same as horse cytochrome c. The limited proteolysis data yield a free energy of 3.8 ± 0.4 kcal mol?1 to unfold the least stable substructure compared with 5.05 ± 0.30 kcal mol?1 for global unfolding of iso-1-cytochrome c. Thus, substructure stabilities of iso-1-cytochrome c span only ?1.2 kcal mol?1 compared with ?8 kcal mol?1 for horse cytochrome c. Consistent with the less cooperative folding thus expected for the horse protein, the guanidine-HCl m-values are ?3 kcal mol?1M?1 versus ?4.5 kcal mol?1M?1 for horse versus yeast cytochrome c. The tight free energy spacing of the yeast cytochrome c substructures suggests that its folding has more branch points than for horse cytochrome c. Studies on a variant of iso-1-cytochrome c with an H26N mutation indicate that the least and most stable substructures unfold sequentially and the two least stable substructures unfold independently as for horse cytochrome c. Thus, important aspects of the substructure architecture of horse cytochrome c, albeit compressed energetically, are preserved evolutionally in yeast iso-1-cytochrome c.

Duncan, Michael G; Williams, Michael D; Bowler, Bruce E

2009-01-01

270

Identification of population substructure among Jews using STR markers and dependence on reference populations included  

Microsoft Academic Search

BACKGROUND: Detecting population substructure is a critical issue for association studies of health behaviors and other traits. Whether inherent in the population or an artifact of marker choice, determining aspects of a population's genetic history as potential sources of substructure can aid in design of future genetic studies. Jewish populations, among which association studies are often conducted, have a known

Jennifer B Listman; Deborah Hasin; Henry R Kranzler; Robert T Malison; Apiwat Mutirangura; Atapol Sughondhabirom; Efrat Aharonovich; Baruch Spivak; Joel Gelernter

2010-01-01

271

Characteristic Substructures in Sets of Organic Compounds with Similar Infrared Spectra  

Microsoft Academic Search

A method based on the determination of maximum common substructures is applied for the generation of substructures which are characteristic for a given set of molecular structures. The molecular structures are from hitlists obtained by spectral library searches; the hitlists contain those reference compounds, which have infrared spectra most similar to that from the query compound. The influences of various

Plamen N. Penchev; Kurt Varmuza

2001-01-01

272

Ballast and Subgrade Requirements Study: Railroad Track Substructure - Materials Evaluation and Stabilization Practices.  

National Technical Information Service (NTIS)

Earth materials--i.e., soil and rock--form the substructure of all railroad track. In this report, the functions and performance characteristics of each of the substructure elements (i.e., ballast, subballast, and subgrade), and the material properties th...

J. V. Errico L. Edgers R. M. Simon

1983-01-01

273

Effect of substructures upon failure behavior of steel reticulated domes subjected to the severe earthquake  

Microsoft Academic Search

This paper presents the study on the influence of substructures on the failure behavior of steel reticulated domes subjected to the severe earthquake. The full-range dynamic response analysis method is applied to investigate the failure characteristics of single-layer steel reticulated domes with substructures subjected to the severe earthquake. The natural vibration properties are studied. Two typical failure modes of steel

Zhi-Wei Yu; Xu-Dong Zhi; Feng Fan; Chen Lu

2011-01-01

274

TYCHO: Stellar evolution code  

NASA Astrophysics Data System (ADS)

TYCHO is a general, one dimensional (spherically symmetric) stellar evolution code written in structured Fortran 77; it is designed for hydrostatic and hydrodynamic stages including mass loss, accretion, pulsations and explosions. Mixing and convection algorithms are based on 3D time-dependent simulations. It offers extensive on-line graphics using Tim Pearson's PGPLOT with X-windows and runs effectively on Linux and Mac OS X laptop and desktop computers.

Arnett, D.

2013-03-01

275

Helium in stellar atmospheres  

Microsoft Academic Search

Helium, which was first discovered on the sun with the help of spectral analysis, plays, together with hydrogen, a principal\\u000a role in astrophysics. We consider here two fundamental quantities: primordial helium abundance formed during Big Bang nucleosynthesis\\u000a and the current initial helium abundances in nearby stars. It is shown that stellar atmospheres are enriched in helium during\\u000a the main-sequence stage.

L. S. Lyubimkov

2010-01-01

276

Panchromatic averaged stellar populations  

NASA Astrophysics Data System (ADS)

We study how the spectral fitting of galaxies, in terms of light fractions, derived in one spectral region translates into another region, by using results from evolutionary synthesis models. In particular, we examine propagation dependencies on evolutionary population synthesis (EPS) models (GRASIL, GALEV, Maraston and GALAXEV), age, metallicity and stellar evolution tracks over the near-ultraviolet-near-infrared (NUV-NIR, 3500 Å to 2.5 ?m) spectral region. Our main results are as follows: as expected, young (t? 400 Myr) stellar population fractions derived in the optical cannot be directly compared to those derived in the NIR, and vice versa. In contrast, intermediate to old age (t? 500 Myr) fractions are similar over the whole spectral region studied. The metallicity has a negligible effect on the propagation of the stellar population fractions derived from NUV to NIR. The same applies to the different EPS models, but restricted to the range between 3800 and 9000 Å. However, a discrepancy between GALEV/Maraston and GRASIL/GALAXEV models occurs in the NIR. Furthermore, the initial mass function is not important for the synthesis propagation. Compared to STARLIGHT synthesis results, our propagation predictions agree at ˜95 per cent confidence level in the optical, and ˜85 per cent in the NIR. In summary, spectral fitting performed in a restricted spectral range should not be directly propagated from the NIR to the UV/optical, or vice versa. We provide equations and an on-line form [panchromatic averaged stellar population (PaASP)] to be used for this purpose.

Riffel, R.; Bonatto, C.; Cid Fernandes, R.; Pastoriza, M. G.; Balbinot, E.

2011-03-01

277

Magellanic Clouds: Stellar Populations  

NASA Astrophysics Data System (ADS)

The Magellanic Clouds (figure 1) have long been seen as the prototypical young STELLAR POPULATION. The presence of young GLOBULAR CLUSTERS in the Clouds spoke to southern hemisphere observers of the opportunity to study close up processes which have not occurred in the Milky Way for a long time. Young globulars are also seen in other gas-rich, highly disturbed environments, such as merging galaxi...

Mould, J.; Murdin, P.

2000-11-01

278

Stellar population synthesis diagnostics  

NASA Astrophysics Data System (ADS)

A quantitative method is presented to compare observed and synthetic colour-magnitude diagrams (CMDs). The method is based on a chi (2) merit function for a point (c_i,m_i) in the observed CMD, which has a corresponding point in the simulated CMD within nsigma (c_i,m_i) of the error ellipse. The chi (2) merit function is then combined with the Poisson merit function of the points for which no corresponding point was found within the nsigma (c_i,m_i) error ellipse boundary. Monte-Carlo simulations are presented to demonstrate the diagnostics obtained from the combined (chi (2) , Poisson) merit function through variation of different parameters in the stellar population synthesis tool. The simulations indicate that the merit function can potentially be used to reveal information about the initial mass function. Information about the star formation history of single stellar aggregates, such as open or globular clusters and possibly dwarf galaxies with a dominating stellar population, might not be reliable if one is dealing with a relatively small age range.

Ng, Y. K.

1998-10-01

279

Characterising stellar micro-variability for planetary transit searches  

NASA Astrophysics Data System (ADS)

A method for simulating light curves containing stellar micro-variability for a range of spectral types and ages is presented. It is based on parameter-by-parameter scaling of a multi-component fit to the solar irradiance power spectrum (based on VIRGO/PMO6 data), and scaling laws derived from ground based observations of various stellar samples. A correlation is observed in the Sun between the amplitude of the power spectrum on long (weeks) timescales and the BBSO Ca II K-line index of chromospheric activity. On the basis of this evidence, the chromospheric activity level, predicted from rotation period and B-V colour estimates according to the relationship first introduced by \\citet{noy83} and \\citet{nhb+84}, is used to predict the variability power on weeks time scales. The rotation period is estimated on the basis of a fit to the distribution of rotation period versus B-V observed in the Hyades and the \\citet{sku72} spin-down law. The characteristic timescale of the variability is also scaled according to the rotation period. This model is used to estimate the impact of the target star spectral type and age on the detection capability of space based transit searches such as Eddington and Kepler. K stars are found to be the most promising targets, while the performance drops significantly for stars earlier than G and younger than 2.0 Gyr. Simulations also show that Eddington should detect terrestrial planets orbiting solar-age stars in most of the habitable zone for G2 types and all of it for K0 and K5 types.

Aigrain, S.; Favata, F.; Gilmore, G.

2004-02-01

280

HEAO 1 high energy X-ray observations of the Virgo cluster and A2142  

SciTech Connect

We report observations of the Virgo cluster and Abell 2142 taken with the UCSD/MIT hard X-ray and low energy ..gamma..-ray instrument (A-4) on board the HEAO 1 spacecraft, during 1977 and 1978. We observe a mean flux from the Virgo cluster of (1.3 +- 0.3) x 10/sup -3/ photons cm/sup -2/ s/sup -1/ between 20 and 100 keV. We also present the complete spectrum of this cluster from 0.2 to 100 keV, using data from both the A-2 and A-4 detectors on HEAO 1. Our data are best fitted by a two component model, a thermal with kT = 2 keV and a power law. We derive a limit of EM< or =1.2 x 10/sup 65/ cm/sup -3/ for the emission measure of any moderate temperature (kTapprox.6 keV) gas. For A2142 we obtain a marginally significant (15--40) keV flux of (2 +- 0.8) x 10/sup -3/ photons cm/sup -2/ s/sup -1/ and a 2 sigma upper limit to the 40--150 keV flux of <2 x 10/sup -4/ photons cm/sup -2/ s/sup -1/. We use our results to derive limits to the intracluster magnetic field of B> or approx. =5 x 10/sup -7/ gauss and B> or approx. = x 10/sup -8/ gauss in the Virgo cluster and A2142, respectively. We also discuss our results in terms of possible variability of the hard X-ray emission in these two clusters.

Lea, S.M.; Reichert, G.; Mushotzky, R.; Baity, W.A.; Gruber, D.E.; Rothschild, R.; Primini, F.A.

1981-06-01

281

Stellar Vampires Unmasked  

NASA Astrophysics Data System (ADS)

Astronomers have found possible proofs of stellar vampirism in the globular cluster 47 Tucanae. Using ESO's Very Large Telescope, they found that some hot, bright, and apparently young stars in the cluster present less carbon and oxygen than the majority of their sisters. This indicates that these few stars likely formed by taking their material from another star. "This is the first detection of a chemical signature clearly pointing to a specific scenario to form so-called 'Blue straggler stars' in a globular cluster", said Francesco Ferraro, from the Astronomy Department of Bologna University (Italy) and lead-author of the paper presenting the results. Blue stragglers are unexpectedly young-looking stars found in stellar aggregates, such as globular clusters, which are known to be made up of old stars. These enigmatic objects are thought to be created in either direct stellar collisions or through the evolution and coalescence of a binary star system in which one star 'sucks' material off the other, rejuvenating itself. As such, they provide interesting constraints on both binary stellar evolution and star cluster dynamics. To date, the unambiguous signatures of either stellar traffic accidents or stellar vampirism have not been observed, and the formation mechanisms of Blue stragglers are still a mystery. The astronomers used ESO's Very Large Telescope to measure the abundance of chemical elements at the surface of 43 Blue straggler stars in the globular cluster 47 Tucanae [1]. They discovered that six of these Blue straggler stars contain less carbon and oxygen than the majority of these peculiar objects. Such an anomaly indicates that the material at the surface of the blue stragglers comes from the deep interiors of a parent star [2]. Such deep material can reach the surface of the blue straggler only during the mass transfer process occurring between two stars in a binary system. Numerical simulations indeed show that the coalescence of stars should not result in anomalous abundances. ESO PR Photo 37/06 ESO PR Photo 37/06 Abundances in Blue Straggler Stars In the core of a globular cluster, stars are packed extremely close to each other: more than 4000 stars are found in the innermost light-year-sized cube of 47 Tucanae. Thus, stellar collisions are thought to be very frequent and the collision channel for the formation of blue stragglers should be extremely efficient. The chemical signature detected by these observations demonstrates that also the binary mass-transfer scenario is fully active even in a high-density cluster like 47 Tuc. "Our discovery is therefore a fundamental step toward the solution of the long-standing mystery of blue straggler formation in globular clusters," said Ferraro. Measurements of so many faint stars are only possible since the advent of 8-m class telescopes equipped with multiplexing capability spectrographs. In this case, the astronomers used the FLAMES/Giraffe instrument that allows the simultaneous observation of up to 130 targets at a time, making it ideally suited for surveying individual stars in closely populated fields.

2006-10-01

282

Dynamical versus stellar masses of ultracompact dwarf galaxies in the Fornax cluster  

NASA Astrophysics Data System (ADS)

The origin of ultracompact dwarf (UCD) galaxies, compact extragalactic stellar systems, is still a puzzle for present galaxy formation models. We present the comprehensive analysis of high-resolution multi-object spectroscopic data for a sample of 24 Fornax cluster UCDs obtained with VLT with Fibre Large Array Multi Element Spectrograph (FLAMES). It comprises previously published data for 19 objects which we re-analysed, including 13 with available Hubble Space Telescope (HST) photometric data. Using Virtual Observatory technologies we found archival HST images for two more UCDs and then determined their structural properties. For all objects we derived internal velocity dispersions, stellar population parameters and stellar mass-to-light ratios (M/L)* by fitting individual simple stellar population (SSP) synthetic spectra convolved with a Gaussian against the observed spectra using the NBURSTS full spectral fitting technique. For 14 objects we estimated dynamical masses suggesting no dark matter (DM) in 12 of them and no more than 40 per cent DM mass fraction in the remaining two, in contrast to findings for several UCDs in the Virgo cluster. Some Fornax UCDs even have too high values of (M/L)* estimated using the Kroupa stellar initial mass function (IMF) resulting in negative formally computed DM mass fractions. The objects with too high (M/L)* ratios compared to the dynamical ones have relatively short dynamical relaxation time-scales, close to the Hubble time or below. We therefore suggest that their lower dynamical ratios (M/L)dyn are caused by low-mass star depletion due to dynamical evolution. Overall, the observed UCD characteristics suggest at least two formation channels: tidal threshing of nucleated dwarf galaxies for massive UCDs (?108 M?), and a classical scenario of red globular cluster formation for lower-mass UCDs (?107 M?). Based on the archival ESO VLT with Fibre Large Array Multi Element Spectrograph (FLAMES) (programme 078.B-0496) available through and Hubble Space Telescope archival data (programmes 8090 and 10129) available through

Chilingarian, Igor V.; Mieske, Steffen; Hilker, Michael; Infante, Leopoldo

2011-04-01

283

Towards solar activity maximum 24 as seen by GOLF and VIRGO/SPM instruments  

NASA Astrophysics Data System (ADS)

All p-mode parameters vary with time as a response to the changes induced by the cyclic behavior of solar magnetic activity. After the unusual long solar-activity minimum between cycles 23 and 24 -where the p-mode parameters have shown a different behavior than the surface magnetic proxies- we analyze the temporal variation of low-degree p-mode parameters measured by GOLF (in velocity) and VIRGO (in intensity) Sun-as-a-star instruments on board SoHO. We compare our results with other activity proxies.

García, R. A.; Salabert, D.; Mathur, S.; Régulo, C.; Ballot, J.; Davies, G. R.; Jiménez, A.; Simoniello, R.

2013-06-01

284

The inertial damping of the VIRGO superattenuator and the residual motion of the mirror  

NASA Astrophysics Data System (ADS)

The VIRGO superattenuator (SA) is effective in suppressing seismic noise below the expected thermal noise level above 4 Hz. However, the residual mirror motion associated with the SA normal modes can saturate the interferometer control system. This motion is reduced by implementing a wideband (DC-5 Hz) multidimensional active control (the so-called inertial damping) which makes use of both accelerometers and position sensors and of a digital signal processing (DSP) system. Feedback forces are exerted by coil-magnet actuators on the top of an inverted pendulum pre-isolator stage. The residual root mean square motion of the mirror in 10 s is less than 0.1 ?m.

Losurdo, Giovanni; Virgo Collaboration

2002-04-01

285

Uncombed Penumbrae: Formation, Ongoing Reconnections and Fine Substructures  

NASA Astrophysics Data System (ADS)

Sunspot penumbrae consist of an ``uncombed'' system of thin, interlaced magnetic flux tubes with varying physical parameters and inclinations. Recent high-resolution observations from space and ground based instruments reveal previously unobservable details in structure and dynamics of penumbra. Based on these observation we propose a mechanism that explains the fine structures of penumbra filaments, their dynamics and their formation process. The mechanism is based on the fact that the umbra itself is a dense conglomerate of twisted, interlaced flux tubes with peripheral filaments branching out from the ``trunk'' at different heights due to ongoing reconnection processes. The twist of individual filaments, and resulting distribution of magnetic fields and temperature forming sub-structure of filaments, is due to the onset of the post-reconnection screw pinch instability, the parameters and details of which are well observed and can be measured from our data.

Ryutova, Margarita

2012-10-01

286

A Multivariate Approach to Jet Substructure and Jet Superstructure  

NASA Astrophysics Data System (ADS)

This thesis explores the powerful computer visualization and analysis techniques, developed and applied both to the search for the Higgs Boson and the problem of discriminating between quark and gluon jets. Both situations require not only understanding the high-level structure of relevant events (the energies and locations of the muons, electrons, photons, and jets) but also examining the distribution of particles within and between the jets. In complicated situations, multivariate techniques are necessary to examine correlations between these many observables. I've developed procedures that optimally handle the large number of inputs involved. On some occasions, physical insight is gained by looking at the automated rankings and correlations. The two applications required the multivariate techniques to optimize different measures. In the Higgs search, the observable rankings and visualizations are used to maximize statistical significance of a potential Higgs discovery. In the quark/gluon tagger, a more general approach was taken since different uses require different levels of quark or gluon purity at the expense of throwing away different numbers of events. This thesis contains chapters which are sightly edited versions of five papers. The first proposes a method to measure the underlying QCD structure of an event (the color superstructure) by its effect on the showering of jets. This is applied to the difficult case of a light Higgs decaying to two b-quarks, the full kinematics of which are exhaustively explored in the following chapter. Next, the accumulated knowledge of jet substructure is used to distinguish light quark jets from and gluon jets. This requires novel observables to quantify various aspects of substructure. Finally, in addition to studying the tagging of individual jets, it was crucial to find relatively pure samples of quark and gluon events so that their properties could be measured at the LHC.

Gallicchio, Jason Richard

287

VirGO: A Visual Browser for the ESO Science Archive Facility  

NASA Astrophysics Data System (ADS)

VirGO is the next generation Visual Browser for the ESO Science Archive Facility developed by the Virtual Observatory (VO) Systems Department. It is a plug-in for the popular open source software Stellarium adding capabilities for browsing professional astronomical data. VirGO gives astronomers the possibility to easily discover and select data from millions of observations in a new visual and intuitive way. Its main feature is to perform real-time access and graphical display of a large number of observations by showing instrumental footprints and image previews, and to allow their selection and filtering for subsequent download from the ESO SAF web interface. It also allows the loading of external FITS files or VOTables, the superimposition of Digitized Sky Survey (DSS) background images, and the visualization of the sky in a `real life' mode as seen from the main ESO sites. All data interfaces are based on Virtual Observatory standards which allow access to images and spectra from external data centers, and interaction with the ESO SAF web interface or any other VO applications supporting the PLASTIC messaging system.

Chéreau, Fabien

2012-04-01

288

The Herschel Virgo Cluster Survey . VII. Dust in cluster dwarf elliptical galaxies  

NASA Astrophysics Data System (ADS)

We use the science demonstration phase data of the Herschel Virgo Cluster Survey to search for dust emission of early-type dwarf galaxies in the central regions of the Virgo cluster as an alternative way of identifying the interstellar medium. We present the first possible far-infrared detection of cluster early-type dwarf galaxies: VCC 781 and VCC 951 are detected at the 10? level in the SPIRE 250 ?m image. Both detected galaxies have dust masses of the order of 105 M_? and average dust temperatures ?20 K. The detection rate (less than 1%) is quite high compared to the 1.7% detection rate for Hi emission, considering that dwarfs in the central regions are more Hi deficient. We conclude that the removal of interstellar dust from dwarf galaxies resulting from ram pressure stripping, harassment, or tidal effects must be as efficient as the removal of interstellar gas. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

de Looze, I.; Baes, M.; Zibetti, S.; Fritz, J.; Cortese, L.; Davies, J. I.; Verstappen, J.; Bendo, G. J.; Bianchi, S.; Clemens, M.; Bomans, D. J.; Boselli, A.; Corbelli, E.; Dariush, A.; di Serego Alighieri, S.; Fadda, D.; Garcia-Appadoo, D. A.; Gavazzi, G.; Giovanardi, C.; Grossi, M.; Hughes, T. M.; Hunt, L. K.; Jones, A. P.; Madden, S.; Pierini, D.; Pohlen, M.; Sabatini, S.; Smith, M. W. L.; Vlahakis, C.; Xilouris, E. M.

2010-07-01

289

Are Stellar Over-Densities in Dwarf Galaxies the ``Smoking Gun'' of Triaxial Dark Matter Haloes?  

NASA Astrophysics Data System (ADS)

We use N-body simulations to study the tidal evolution of globular clusters (GCs) in dwarf spheroidal (dSph) galaxies. Our models adopt a cosmologically motivated scenario in which the dSph is approximated by a static NFW halo with a triaxial shape. For a large set of orbits and projection angles we examine the spatial and velocity distribution of stellar debris deposited during the complete disruption of stellar clusters. Our simulations show that such debris appears as shells, isolated clumps and elongated over-densities at low surface brightness (>=26 mag/arcsec2), reminiscent of substructure observed in several MW dSphs. Such features arise from the triaxiality of the galaxy potential and do not dissolve in time. Stellar over-densities reported in several MW dSphs may thus be the telltale evidence of dark matter haloes being triaxial in shape. We explore a number of kinematical signatures that would help to validate (or falsify) this scenario. The mean angular momentum of the cluster debris associated with box and resonant orbits, which are absent in spherical potentials, is null. As a result, we show that the line-of-sight velocity distribution may exhibit a characteristic ``double-peak'' depending on the oriention of the viewing angle with respect to the progenitor's orbital plane. Kinematic surveys of dSphs may help to detect and identify substructures associated with the disruption of stellar clusters, as well as to address the shape of the dark matter haloes in which dSphs are embedded.

Peñarrubia, Jorge; Walker, Matthew G.; Gilmore, Gerard

2010-06-01

290

Starspots and Stellar Rotation: Stellar Activity with Kepler  

NASA Astrophysics Data System (ADS)

While the telescopic study of starspots dates back to Galileos observations of our own Sun, recent space-borne photometric missions (such as MOST, CoRoT, and Kepler) are opening a new window into understanding these ubiquitous manifestations of stellar activity. Because of the intimate link between stellar rotation and the generation of the magnetic field, starspots cause a modulation in the lightcurve at the rate of stellar rotation. To complicate matters, stars rotate differentially, so the stellar rotation rate is not really best characterized by a single value but rather by a range of rotation rates. Through high-precision, long-term photometric monitoring of stars of different spectral types and activity strengths, it is possible to determine stellar rotation rates and differential rotation measures. In addition, modeling these lightcurves can tell us about the properties of stellar spots, such as location, areal coverage, and lifetime. New observations provide precision photometry for a large cohort of stars, ranging from Sun-like to rather different stellar properties, at a spread of ages, making these lightcurves a powerful tool for understanding magnetic activity for stars of all activity levels. Here, I will discuss how Kepler can provide new insight into the continuum of stellar activity and our own Suns place amongst the stars.

Walkowicz, L. M.; Basri, G. S.

2011-12-01

291

Stellarator Saddle Coils  

NASA Astrophysics Data System (ADS)

Modern stellarators are designed using J. Nuehrenberg’s method of varying Fourier coefficients in the shape of the plasma boundary to maximize a target function. The matrix of second derivatives of the target function at the optimum determines a quality matrix. This matrix gives the degradation in the quality of the configuration as the normal magnetic field is varied on a control surface, which lies on or outside the plasma surface. The task is finding saddle coils that produce the desired configuration in the presence of a given toroidal field. An eigenvector of the quality matrix can be important for two reasons: (1) the normal field that must be produced by the saddles is large or (2) the eigenvalue is large (an island-causing resonant perturbation). The rank of the important part of the quality matrix is the number of important eigenvectors. The current in each saddle coil produces a normal field on the control surface, which can be described by an inductance matrix. The relevant part of the inductance matrix has large eigenvalues. The coils can produce the configuration if the rank of the important part of the quality matrix and its product with the relevant part of the inductance matrix are the same. Existing coil design codes, pioneered by P. Merkel, approximate the quality matrix by the unit matrix. Stellarator flexibility could be enhanced by using a more realistic quality matrix and by using trim coils to balance large eigenvalues.

Boozer, Allen H.

1999-11-01

292

Gravitational waves by gamma-ray bursts and the Virgo detector: the case of GRB 050915a  

Microsoft Academic Search

In the framework of the expected association between gamma-ray bursts and gravitational wave signals, we present the preliminary results of an analysis aimed to search for bursts of gravitational waves associated with the long GRB 050915a. GRB 050915a was detected by the Swift satellite in 2005, when the Virgo detector was engaged in one of its science runs, namely the

F. Acernese; M. Alshourbagy; F. Antonucci; S. Aoudia; P. Astone; S. Avino; D. Babusci; G. Ballardin; F. Barone; L. Barsotti; M. Barsuglia; S Birindelli; F. Beauville; S. Bigotta; M. A. Bizouard; C. Boccara; F. Bondu; L. Bosi; C. Bradaschia; S. Braccini; F. J. van den Brand; A. Brillet; V. Brisson; D. Buskulic; E. Calloni; E Chassande-Mottin; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; N. Christensen; C. Corda; A. Corsi; F. Cottone; A.-C. Clapson; F. Cleva; J.-P. Coulon; E. Cuoco; A. Dari; V. Dattilo; M. Davier; M. del Prete; R. De Rosa; L. Di Fiore; A. Di Virgilio; B. Dujardin; A. Eleuteri; M. Evans; I. Ferrante; F. Fidecaro; I. Fiori; R. Flaminio; J.-D. Fournier; S. Frasca; F. Frasconi; L. Gammaitoni; F. Garufi; E. Genin; A. Gennai; A. Giazotto; G. Giordano; L. Giordano; R. Gouaty; D. Grosjean; G. Guidi; S. Hamdani; S. Hebri; H. Heitmann; P. Hello; D. Huet; S. Karkar; S. Kreckelbergh; P. La Penna; M. Laval; N. Leroy; N. Letendre; B. Lopez; M. Lorenzini; V. Loriette; G. Losurdo; J.-M. Mackowski; E. Majorana; C. N. Man; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; A. Masserot; M. Mazzoni; L. Milano; F. Menzinger; C. Moins; J. Moreau; N. Morgado; B. Mours; F. Nocera; C. Palomba; F. Paoletti; S. Pardi; A. Pasqualetti; R. Passaquieti; D. Passuello; F. Piergiovanni; L. Pinard; R. Poggiani; M. Punturo; P. Puppo; S. van der Putten; K. Qipiani; P. Rapagnani; V. Reita; A. Remillieux; F. Ricci; I. Ricciardi; P. Ruggi; G. Russo; S. Solimeno; A. Spallicci; M. Tarallo; M. Tonelli; A. Toncelli; E. Tournefier; F. Travasso; C. Tremola; G. Vajente; D. Verkindt; F. Vetrano; A. Viceré; J.-Y. Vinet; H. Vocca; M. Yvert

2007-01-01

293

Analysis of LIGO and VIRGO Data for Burst Gravitational Wave Signals: Plans for Online Analysis with Electromagnetic Follow-up  

Microsoft Academic Search

The laser interferometric gravitational wave detectors LIGO and VIRGO recently completed observations of unprecedented sensitivity and will recommence their coordinated search for gravitational waves with increased astrophysical range in 2009. We are now implementing a procedure for online analysis of data from this network for transient signals from astrophysical bursts. In the Advanced LIGO era (starting in 2014), when detections

Joshua Smith

2009-01-01

294

HIERARCHICAL STELLAR STRUCTURES IN THE LOCAL GROUP DWARF GALAXY NGC 6822  

SciTech Connect

We present a comprehensive study of the star cluster population and the hierarchical structure in the clustering of blue stars with ages {approx}<500 Myr in the Local Group dwarf irregular galaxy NGC 6822. Our observational material comprises the most complete optical stellar catalog of the galaxy from imaging with the Suprime-Cam at the 8.2 m Subaru Telescope. We identify 47 distinct star clusters with the application of the nearest-neighbor density method to this catalog for a detection threshold of 3{sigma} above the average stellar density. The size distribution of the detected clusters can be very well approximated by a Gaussian with a peak at {approx}68 pc. The total stellar masses of the clusters are estimated by extrapolating the cumulative observed stellar mass function of all clusters to be in the range 10{sup 3}-10{sup 4} M{sub sun}. Their number distribution is fitted very well by a power law with index {alpha} {approx} 1.5 {+-} 0.7, which is consistent with the cluster mass functions of other Local Group galaxies and the cluster initial mass function. In addition to the detected star clusters of the galaxy, the application of the nearest-neighbor density method for various density thresholds, other than 3{sigma}, enabled the identification of stellar concentrations in various lengthscales. The stellar density maps constructed with this technique provide a direct proof of hierarchically structured stellar concentrations in NGC 6822, in the sense that smaller dense stellar concentrations are located inside larger and looser ones. We illustrate this hierarchy by the so-called dendrogram, or structure tree of the detected stellar structures, which demonstrates that most of the detected structures split up into several substructures over at least three levels. We quantify the hierarchy of these structures with the use of the minimum spanning tree method. We find that structures detected at 1, 2, and 3{sigma} density thresholds are hierarchically constructed with a fractal dimension of D {approx} 1.8. Some of the larger stellar concentrations, particularly in the northern part of the central star-forming portion of the galaxy, coincide with IR-bright complexes previously identified with Spitzer and associated with high column density neutral gas, indicating structures that currently form stars. The morphological hierarchy in stellar clustering, which we observe in NGC 6822, resembles that of the turbulent interstellar matter, suggesting that turbulence on pc and kpc scales has been probably the major agent that regulated clustered star formation in NGC 6822.

Gouliermis, Dimitrios A.; Walter, Fabian [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Schmeja, Stefan; Klessen, Ralf S. [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); De Blok, W. J. G., E-mail: dgoulier@mpia-hd.mpg.d, E-mail: walter@mpia-hd.mpg.d, E-mail: sschmeja@ita.uni-heidelberg.d, E-mail: rklessen@ita.uni-heidelberg.d, E-mail: edeblok@ast.uct.ac.z [University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)

2010-12-20

295

STRUCTURE AND POPULATION OF THE NGC 55 STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY  

SciTech Connect

As part of our survey of galactic stellar halos, we investigate the structure and stellar populations of the northern outer part of the stellar halo in NGC 55, a member galaxy of the Sculptor Group, using deep and wide-field V- and I-band images taken with Subaru/Suprime-Cam. Based on the analysis of the color-magnitude diagrams for red giant branch (RGB) stars, we derive a tip of RGB based distance modulus to the galaxy of (m - M){sub 0} = 26.58 {+-} 0.11(d = 2.1 {+-} 0.1 Mpc). From the stellar density maps, we detect the asymmetrically disturbed, thick disk structure and two metal-poor overdense substructures in the north region of NGC 55, which may correspond to merger remnants associated with hierarchical formation of NGC 55's halo. In addition, we identify a diffuse metal-poor halo extended out to at least z {approx} 16 kpc from the galactic plane. The surface brightness profiles toward the z-direction perpendicular to the galactic plane suggest that the stellar density distribution in the northern outer part of NGC 55 is described by a locally isothermal disk at z {approx}< 6 kpc and a likely diffuse metal-poor halo with V-band surface brightness of {mu}{sub V} {approx}> 32 mag arcsec{sup -2}, where old RGB stars dominate. We derive the metallicity distributions (MDs) of these structures on the basis of the photometric comparison of RGB stars with the theoretical stellar evolutionary models. The MDs of the thick disk structures show the peak and mean metallicity of [Fe/H]{sub peak} {approx} -1.4 and [Fe/H]{sub mean} {approx} -1.7, respectively, while the outer substructures show more metal-poor features than the thick disk structure. Combined with the current results with our previous study for M31's halo, we discuss the possible difference in the formation process of stellar halos among different Hubble types.

Tanaka, Mikito; Chiba, Masashi [Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578 (Japan); Komiyama, Yutaka [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Guhathakurta, Puragra [University of California Observatories/Lick Observatory, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Kalirai, Jason S., E-mail: mikito@astr.tohoku.ac.jp [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

2011-09-10

296

Statistical Hypotheses in Stellar Dynamics  

Microsoft Academic Search

This paper starts with a short review of the usual methods of stellar dynamics and analyzes the underlying hypotheses. The most successful approach to stellar dynamics has been the one which neglects interactions between nearby stars (because they are weak) and takes into consideration the motion of stars in a smooth field of force only, produced by the smeared-out mass

Herbert Jehle

1946-01-01

297

Do gravitational lens galaxies have an excess of luminous substructure?  

NASA Astrophysics Data System (ADS)

Strong gravitational lensing can be used to directly measure the mass function of their satellites, thus testing one of the fundamental predictions of cold dark matter cosmological models. Given the importance of this test, it is essential to ensure that galaxies acting as strong lenses have dark and luminous satellites which are representative of the overall galaxy population. We address this issue by measuring the number and spatial distribution of luminous satellites in ACS imaging around lens galaxies from the Sloan Lens Advanced Camera for Surveys (SLACS) lenses, and comparing them with the satellite population in ACS imaging of non-lens galaxies selected from Cosmological Evolution Survey (COSMOS), which has similar depth and resolution to the ACS images of SLACS lenses. In order to compare the samples of lens and non-lens galaxies, which have intrinsically different stellar mass distributions, we measure, for the first time, the number of satellites per host as a continuous function of host stellar mass for both populations. We find that the number of satellites as a function of host stellar mass as well as the spatial distribution are consistent between the samples. Using these results, we predict the number of satellites we would expect to find around a subset of the Cosmic Lens All Sky Survey lenses, and find a result consistent with the number observed by Jackson et al. Thus, we conclude that within our measurement uncertainties there is no significant difference in the satellite populations of lens and non-lens galaxies.

Nierenberg, A. M.; Oldenburg, D.; Treu, T.

2013-10-01

298

Nucleosynthesis in stellar explosions  

SciTech Connect

The final evolution and explosion of stars from 10 M/sub solar/ to 10/sup 6/ M/sub solar/ are reviewed with emphasis on factors affecting the expected nucleosynthesis. We order our paper in a sequence of decreasing mass. If, as many suspect, the stellar birth function was peaked towards larger masses at earlier times (see e.g., Silk 1977; but also see Palla, Salpeter, and Stahler 1983), this sequence of masses might also be regarded as a temporal sequence. At each stage of Galactic chemical evolution stars form from the ashes of preceding generations which typically had greater mass. A wide variety of Type I supernova models, most based upon accreting white dwarf stars, are also explored using the expected light curves, spectra, and nucleosynthesis as diagnostics. No clearly favored Type I model emerges that is capable of simultaneously satisfying all three constraints.

Woosley, S.E.; Axelrod, T.S.; Weaver, T.A.

1983-01-01

299

Lectures on stellar dynamics  

NASA Astrophysics Data System (ADS)

The aim of these lectures is to give some understanding of how orbits react to the gravity of other orbits and how these reactions can lead to cooperative instabilities. We show that Angle-Action variables are peculiarly well adapted to this problem. Although these variables may at first seem unfamiliar or even esoteric, I and many others have come to appreciate them as a vital tool in galactic dynamics - so much so that those who do .not use them are working at a severe disadvantage. I strongly advocate that you make the effort to learn them now. Although much of this material has been developed over the years since 1971, some parts have been developed more recently with my students J.L. Collett and C. Pichon for whose collaboration I am most grateful. In Part II we discuss the evolution of globular clusters under the influence of the gravitational stellar encounters. In part III, the dynamics of relativistic disks is discussed.

Lynden-Bell, D.

300

Unbiased Stellar Parameters  

NASA Astrophysics Data System (ADS)

I report about ongoing efforts of the USM cool-star group to refine our ability to derive fundamental stellar parameters Teff, log g and [Xi / H] (chemical composition) for solar-type stars. In this contribution the focus lies on a universal gravity indicator, namely the iron ionization equilibrium. It is shown that a kinetic equilibrium or non-LTE approach for Fe i succeeds in fulfilling the trigonometric constraints coming from the Hipparcos satellite mission if and only if inelastic collisions with hydrogen are properly accounted for. Our model makes testable predictions for the gravities of metal-poor globular cluster giants in which non-LTE corrections are expected to reach up to +0.5 dex.

Korn, A. J.

301

Design of chemical libraries with potentially bioactive molecules applying a maximum common substructure concept.  

PubMed

Success in small molecule screening relies heavily on the preselection of compounds. Here, we present a strategy for the enrichment of chemical libraries with potentially bioactive compounds integrating the collected knowledge of medicinal chemistry. Employing a genetic algorithm, substructures typically occurring in bioactive compounds were identified using the World Drug Index. Availability of compounds containing the selected substructures was analysed in vendor libraries, and the substructure-specific sublibraries were assembled. Compounds containing reactive, undesired functional groups were omitted. Using a diversity filter for both physico-chemical properties and the substructure composition, the compounds of all the sublibraries were ranked. Accordingly, a screening collection of 16,671 compounds was selected. Diversity and chemical space coverage of the collection indicate that it is highly diverse and well-placed in the chemical space spanned by bioactive compounds. Furthermore, secondary assay-validated hits presented in this study show the practical relevance of our library design strategy. PMID:19685275

Lisurek, Michael; Rupp, Bernd; Wichard, Jörg; Neuenschwander, Martin; von Kries, Jens Peter; Frank, Ronald; Rademann, Jörg; Kühne, Ronald

2009-08-15

302

A finite element based substructuring procedure for design analysis of large smart structural systems  

NASA Astrophysics Data System (ADS)

A substructuring based design analysis procedure is presented for large smart structural system using the Craig-Bampton method. The smart structural system is distinctively characterized as an active substructure, modelled as a design problem, and a passive substructure, idealized as an analysis problem. Furthermore, a novel thought has been applied by introducing the electro-elastic coupling into the reduction scheme to solve the global structural control problem in a local domain. As an illustration, a smart composite box beam with surface bonded actuators/sensors is considered, and results of the local to global control analysis are presented to show the potential use of the developed procedure. The present numerical scheme is useful for optimally designing the active substructures to study their locations, coupled structure-actuator interaction and provide a solution to the global design of large smart structural systems.

Ashwin, U.; Raja, S.; Dwarakanathan, D.

2009-04-01

303

A multibeam HI survey of the Virgo cluster - two isolated HI clouds?  

NASA Astrophysics Data System (ADS)

We have carried out a fully sampled large area (4°× 8°) 21-cm HI line survey of part of the Virgo cluster using the Jodrell Bank multibeam instrument. The survey has a sensitivity some three times better than the standard HIJASS (HI Jodrell All Sky Survey) and HIPASS (HI Parkes All Sky Survey) surveys. We detect 31 galaxies, 27 of which are well-known cluster members. The four new detections have been confirmed in the HIPASS data and by follow-up Jodrell Bank pointed observations. One object lies behind M86, but the other three have no obvious optical counterparts upon inspection of the digital sky survey fields. These three objects were mapped at Arecibo with a smaller 3.6-arcmin half power beam width (HPBW) and a four times better sensitivity than the Jodrell Bank data, which allow an improved determination of the dimensions and location of two of the objects, but surprisingly failed to detect the third. The two objects are resolved by the Arecibo beam, giving them a size far larger than any optical images in the nearby field. To our mass limit of 5 × 107(?v/50 km s-1) Msolar and column density limit of 3 × 1018(?v/50 km s-1) atom cm-2, these new detections represent only about 2 per cent of the cluster atomic hydrogen mass. Our observations indicate that the HI mass function of the cluster turns down at the low-mass end, making it very different to the field galaxy HI mass function. This is quite different to the Virgo cluster optical luminosity function, which is much steeper than that in the general field. Many of the sample galaxies are relatively gas-poor compared with HI selected samples of field galaxies, confirming the `anaemic spirals' view of Virgo cluster late-type galaxies. The velocity distribution of the HI detected galaxies is also very different to that of the cluster as a whole. There are relatively more high-velocity galaxies in the HI sample, suggesting that they form part of a currently infalling population. The HI sample with optical identifications has a minimum HI column density cut-off more than an order of magnitude above that expected from the sensitivity of the survey. This observed column density is above the normally expected level for star formation to occur. The two detections with no optical counterparts have very much lower column densities than that of the rest of the sample, below the star formation threshold.

Davies, J.; Minchin, R.; Sabatini, S.; van Driel, W.; Baes, M.; Boyce, P.; de Blok, W. J. G.; Disney, M.; Evans, Rh.; Kilborn, V.; Lang, R.; Linder, S.; Roberts, S.; Smith, R.

2004-04-01

304

Application of Resin Transfer Molding to the Manufacture of Wind Turbine Blade Substructures. Final Report  

SciTech Connect

The U.S. has generally lacked the capability for an iterative process of detailed structural design, manufacturing, and testing at the full blade level to achieve specific structural performance, cost, and weight targets. This project examined the effects that different composites processing methods had on the performance of representative blade substructures. In addition, the results of the testing of these substructures was used to validate NuMAD, the design tool developed at Sandia National Laboratories.

Hedley, C. W.; Ritter, W. J.; Ashwill, T.

2001-07-26

305

A NEW METHOD TO QUANTIFY X-RAY SUBSTRUCTURES IN CLUSTERS OF GALAXIES  

SciTech Connect

We present a new method to quantify substructures in clusters of galaxies, based on the analysis of the intensity of structures. This analysis is done in a residual image that is the result of the subtraction of a surface brightness model, obtained by fitting a two-dimensional analytical model ({beta}-model or Sersic profile) with elliptical symmetry, from the X-ray image. Our method is applied to 34 clusters observed by the Chandra Space Telescope that are in the redshift range z in [0.02, 0.2] and have a signal-to-noise ratio (S/N) greater than 100. We present the calibration of the method and the relations between the substructure level with physical quantities, such as the mass, X-ray luminosity, temperature, and cluster redshift. We use our method to separate the clusters in two sub-samples of high- and low-substructure levels. We conclude, using Monte Carlo simulations, that the method recuperates very well the true amount of substructure for small angular core radii clusters (with respect to the whole image size) and good S/N observations. We find no evidence of correlation between the substructure level and physical properties of the clusters such as gas temperature, X-ray luminosity, and redshift; however, analysis suggest a trend between the substructure level and cluster mass. The scaling relations for the two sub-samples (high- and low-substructure level clusters) are different (they present an offset, i.e., given a fixed mass or temperature, low-substructure clusters tend to be more X-ray luminous), which is an important result for cosmological tests using the mass-luminosity relation to obtain the cluster mass function, since they rely on the assumption that clusters do not present different scaling relations according to their dynamical state.

Andrade-Santos, Felipe; Lima Neto, Gastao B.; Lagana, Tatiana F. [Departamento de Astronomia, Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Geofisica e Ciencias Atmosfericas, Rua do Matao 1226, Cidade Universitaria, 05508-090 Sao Paulo, SP (Brazil)

2012-02-20

306

Substructure-finite element method for soil-foundation-structure interaction of CFST arch bridges  

Microsoft Academic Search

In order to study the soil-foundation-structure interaction of concrete filled steel tube(CFST) arch bridges, the theory of substructure is introduced and the substructure-finite element method is adopted. Taking the Nanning Yonghe Bridge for example, three models are developed, which the soil-foundation interaction is introduced in model 1, the interaction is analyzed using Finite Element Method (FEM) in model 2 and

Kai-zhong Xie; Wen-gao Lv; Ru-yi Zhou; Fang-cheng Meng

2011-01-01

307

Stability analysis of real-time dynamic substructuring using delay differential equation models  

Microsoft Academic Search

Real-time dynamic substructuring is an experimental technique for testing the dynamic behaviour of complex structures. It involves creating a hybrid model of the entire structure by combining an experimental test piece-the substructure-with a numerical model describing the remainder of the system. The technique is useful when it is impractical to experimentally test the entire structure or complete numerical modelling is

M. I. Wallace; J. Sieber; S. A. Neild; D. J. Wagg; B. Krauskopf

2005-01-01

308

Nondeterministic Approach to Tree-Based Jet Substructure  

NASA Astrophysics Data System (ADS)

Jet substructure is typically studied using clustering algorithms, such as kT, which arrange the jets’ constituents into trees. Instead of considering a single tree per jet, we propose that multiple trees should be considered, weighted by an appropriate metric. Then each jet in each event produces a distribution for an observable, rather than a single value. Advantages of this approach include (1) observables have significantly increased statistical stability, and (2) new observables, such as the variance of the distribution, provide new handles for signal and background discrimination. For example, we find that employing a set of trees substantially reduces the observed fluctuations in the pruned mass distribution, enhancing the likelihood of new particle discovery for a given integrated luminosity. Furthermore, the resulting pruned mass distributions for (background) QCD jets are found to be substantially wider than that for (signal) jets with intrinsic mass scales, e.g., boosted W jets. A cut on this width yields a substantial enhancement in significance relative to a cut on the standard pruned jet mass alone. In particular the luminosity needed for a given significance requirement decreases by a factor of 2 relative to standard pruning.

Ellis, Stephen D.; Hornig, Andrew; Roy, Tuhin S.; Krohn, David; Schwartz, Matthew D.

2012-05-01

309

Systematic benchmark of substructure search in molecular graphs - From Ullmann to VF2  

PubMed Central

Background Searching for substructures in molecules belongs to the most elementary tasks in cheminformatics and is nowadays part of virtually every cheminformatics software. The underlying algorithms, used over several decades, are designed for the application to general graphs. Applied on molecular graphs, little effort has been spend on characterizing their performance. Therefore, it is not clear how current substructure search algorithms behave on such special graphs. One of the main reasons why such an evaluation was not performed in the past was the absence of appropriate data sets. Results In this paper, we present a systematic evaluation of Ullmann’s and the VF2 subgraph isomorphism algorithms on molecular data. The benchmark set consists of a collection of 1235 SMARTS substructure expressions and selected molecules from the ZINC database. The benchmark evaluates substructures search times for complete database scans as well as individual substructure-molecule pairs. In detail, we focus on the influence of substructure formulation and size, the impact of molecule size, and the ability of both algorithms to be used on multiple cores. Conclusions The results show a clear superiority of the VF2 algorithm in all test scenarios. In general, both algorithms solve most instances in less than one millisecond, which we consider to be acceptable. Still, in direct comparison, the VF2 is most often several folds faster than Ullmann’s algorithm. Additionally, Ullmann’s algorithm shows a surprising number of run time outliers.

2012-01-01

310

NIR observations of dEs in the Virgo cluster: a structural continuity with giant ellipticals  

NASA Astrophysics Data System (ADS)

The structural properties of a sample of 50 dEs in the Virgo cluster are here derived from Near InfraRed (NIR, H-band 1.65 ?m) surface photometry and analysed. One-dimensional surface brightness (SB) profiles are extracted using elliptical isophote fitting. They are characterised by means of structural parameters, namely the half light radius Re, the average surface brightness within Re (?e), and a concentration index (c31). We show that typical dEs have close-to-exponential NIR SB distributions.The relations between dEs and giant ellipticals (Es) are investigated by comparing the NIR structural parameters of 273 Es in nearby clusters. Further analysis is conducted using the optical-NIR colour B-H and by studying the relationships between structural and dynamical parameters (fundamental plane) for the two classes of galaxies. The transition between the two regimes is smooth and no dichotomy is seen.

Zibetti, Stefano; Goldmine Research Team

311

The spatial evolution of stellar structures in the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

We present an analysis of the spatial distribution of various stellar populations within the Large Magellanic Cloud (LMC). We combine mid-infrared selected young stellar objects, optically selected samples with mean ages between ~9 and ~1000 Myr and existing stellar cluster catalogues to investigate how stellar structures form and evolve within the LMC. For the analysis we use Fractured Minimum Spanning Trees, the statistical Q parameter and the two-point correlation function. Restricting our analysis to young massive (OB) stars, we confirm our results obtained for M33, namely that the luminosity function of the groups is well described by a power law with index -2, and that there is no characteristic length-scale of star-forming regions. We find that stars in the LMC are born with a large amount of substructure, consistent with a two-dimensional fractal distribution with dimension and evolve towards a uniform distribution on a time-scale of ~175 Myr. This is comparable to the crossing time of the galaxy, and we suggest that stellar structure, regardless of spatial scale, will be eliminated in a crossing time. This may explain the smooth distribution of stars in massive/dense young clusters in the Galaxy, while other, less massive, clusters still display large amounts of structure at similar ages. By comparing the stellar and star cluster distributions and evolving time-scales, we show that infant mortality of clusters (or `popping clusters') has a negligible influence on the galactic structure. Finally, we quantify the influence of the elongation, differential extinction and contamination of a population on the measured Q value.

Bastian, Nate; Gieles, Mark; Ercolano, Barbara; Gutermuth, Rob

2009-01-01

312

Effects of environment on neutral hydrogen distribution for disk galaxies in the Virgo cluster area  

SciTech Connect

A statistical analysis is carried out on H I observations of galaxies, which include mapping with the Arecibo beam (reported in previous papers), both inside and outside the direction of the Virgo cluster core (radius 5/sup 0/ or 6/sup 0/). The galaxies were classified both according to the revised Hubble (RH) scheme and the RDDO scheme suggested by van den Bergh. SO galaxies on the RH scheme have a larger detection probability outside than inside; ''true SO'' galaxies on the RDDO scheme have a small detection probability everywhere; ''anemics'' have a larger detection probability and are more common outside the cluster core. Anemic and spiral galaxies of all types have an average H I mass content M/sub H/ which is smaller inside the Virgo cluster core by a factor of about 2 to 2.5 than galaxies of the same type outside the core. This result agrees with that obtained by Chamaraux et al., using different methods, and seems now firmly established. H I diameters D/sub H/, defined in terms of a scale length, are also smaller inside the core than outside so that the surface density sigma/sub H/proportionalM/sub H//D/sub H//sup 2/ is almost the same inside and outside (always comparing galaxies of the same morphological type). Ram pressure stripping of an outer galactic disk by intracluster gas predicts just such results. By contrast, ''anemics'' have almost the same D/sub H/ as a ''true spirals'' (or even larger) but smaller sigma/sub H/, suggesting they lost hydrogen gas by some means other than stripping.

Giovanardi, C.; Helou, G.; Salpeter, E.E.; Krumm, N.

1983-04-01

313

Analysis of substructural variation in families of enzymatic proteins with applications to protein function prediction  

PubMed Central

Background Structural variations caused by a wide range of physico-chemical and biological sources directly influence the function of a protein. For enzymatic proteins, the structure and chemistry of the catalytic binding site residues can be loosely defined as a substructure of the protein. Comparative analysis of drug-receptor substructures across and within species has been used for lead evaluation. Substructure-level similarity between the binding sites of functionally similar proteins has also been used to identify instances of convergent evolution among proteins. In functionally homologous protein families, shared chemistry and geometry at catalytic sites provide a common, local point of comparison among proteins that may differ significantly at the sequence, fold, or domain topology levels. Results This paper describes two key results that can be used separately or in combination for protein function analysis. The Family-wise Analysis of SubStructural Templates (FASST) method uses all-against-all substructure comparison to determine Substructural Clusters (SCs). SCs characterize the binding site substructural variation within a protein family. In this paper we focus on examples of automatically determined SCs that can be linked to phylogenetic distance between family members, segregation by conformation, and organization by homology among convergent protein lineages. The Motif Ensemble Statistical Hypothesis (MESH) framework constructs a representative motif for each protein cluster among the SCs determined by FASST to build motif ensembles that are shown through a series of function prediction experiments to improve the function prediction power of existing motifs. Conclusions FASST contributes a critical feedback and assessment step to existing binding site substructure identification methods and can be used for the thorough investigation of structure-function relationships. The application of MESH allows for an automated, statistically rigorous procedure for incorporating structural variation data into protein function prediction pipelines. Our work provides an unbiased, automated assessment of the structural variability of identified binding site substructures among protein structure families and a technique for exploring the relation of substructural variation to protein function. As available proteomic data continues to expand, the techniques proposed will be indispensable for the large-scale analysis and interpretation of structural data.

2010-01-01

314

Stellar population models at high spectral resolution  

Microsoft Academic Search

We present new, high-to-intermediate spectral resolution stellar population models, based on four popular libraries of empirical stellar spectra, namely Pickles, ELODIE, STELIB and MILES. These new models are the same as our previous models, but with higher resolution and based on empirical stellar spectra, while keeping other ingredients the same including the stellar energetics, the atmospheric parameters and the treatment

C. Maraston; G. Strömbäck

2011-01-01

315

Elimination of Stochasticity in Stellarators.  

National Technical Information Service (NTIS)

A method for optimizing stellarator vacuum magnetic fields is introduced. Application of this method shows that the stochasticity of vacuum magnetic fields can be made negligible by proper choice of the coil configuration. This optimization is shown to in...

J. D. Hanson J. R. Cary

1983-01-01

316

Instability of prolate stellar systems  

SciTech Connect

A general method is proposed for testing the stability of highly elongated stellar systems. If a nonrotating system is sufficiently prolate, it will inevitably be unstable. The stabilizing influence of various factors is assessed.

Polyachenko, V.L.

1979-11-01

317

Optimization of transport in stellarators  

SciTech Connect

Here we relate two stellarator transport optimization schemes to single particle orbits. We also show that reducing transport in the 1/..nu.. regime reduces transport over a much broader range of collisionality. 6 refs., 2 figs.

Hedrick, C.L.; Beasley, C.O.; Van Rij, W.I.

1989-01-01

318

Solar and Stellar Flares  

NASA Astrophysics Data System (ADS)

Flares in the atmosphere of the Sun and of many other stars appear to result from the sudden conversion of electromagnetic field energy into a wide array of observable forms. Of these products the definitive modern observations are the X-rays and ?-rays, signifying the common occurrence of particle acceleration to mildly relativistic or higher energies. Abundant direct (the radiation) and indirect information confirms that this particle acceleration is energetically significant, as well as common. We are thus led to the physics of particle distribution functions that may deviate radically from Maxwellian distributions. Stellar observations allow us to study these phenomena across a wide variety of environments, whereas solar and planetary observations allow us to do imaging spectroscopy and thereby get a better understanding of the global structures of the processes. In particular we have spectacular new data from satellite solar observatories such as RHESSI (hard X-rays and ?-rays) and others, most recently the Solar Dynamics Observatory. Of particular interest from the point of view of plasma physics is the flare environment: a low-beta corona linked to a massive body through an intermediate weakly-ionized layer (the chromosphere). The chromosphere is extraordinarily complicated; its behavior is coming again to be recognized as fundamental to the overall flare process, and in this presentation I will attempt to clarify its role.

Hudson, Hugh

2011-04-01

319

Stellar Aberration 2D  

NSDL National Science Digital Library

The Stellar Aberration 2D Model illustrates the phenomenon known as the aberration of starlight, first reported by James Bradley in 1729. Aberration occurs because light has a finite speed, and thus light from a star takes a finite amount of time to travel through the tube of a telescope. During this time, the telescope moves as a result of Earth's rotational and orbital motions (in this case, the orbital motion is more important because it is faster). Therefore, if the telescope is pointed directly at the star the starlight will hit the sides of the tube before reaching the eyepiece. To see the star the telescope must be pointed forward (i.e. in the direction of Earth's motion) very slightly. The simulation shows a telescope (depicted as a red rectangle) and a star (white point) directly overhead. When the simulation is run a pulse of light is emitted from the star and travels straight downward to Earth. The telescope moves to the right due to Earth's motion. As a result, if the telescope is pointed straight up (ie toward the actual location of the star) the pulse of light will not reach the bottom of the telescope. Controls allow the user to set the speed of Earth and the tilt of the telescope. The user can modify the tilt until the starlight reaches the bottom of the telescope. Alternately, the user can use the Options menu to set the telescope to the correct tilt for the current speed setting.

Timberlake, Todd

2011-05-18

320

Drift waves in stellarator geometry  

SciTech Connect

Drift waves are investigated in a real three-dimensional stellarator geometry. A linear system, based on the cold ion fluid model and a ballooning mode formalism, is solved numerically in the geometry of the stellarator H1-NF. The spectra of stable and unstable modes, as well as localization, are discussed. The dependence of the spectrum of the unstable modes on the wavevector, plasma density variation, and the location in the plasma is presented.

Persson, M.; Nadeem, M.; Lewandowski, J.L.V.; Gardner, H.J.

2000-02-07

321

Multiprocessing Optimization for Compact Stellarators  

Microsoft Academic Search

Compact quasi-omnigeneous stellarator (QOS) and quasi-axisymmetric stellarator (QAS) configurations have been developed. These are designed to align flux surfaces with surfaces of constant J (QOS), or to obtain a symmetric |B| spectrum (QAS), using a Levenberg-Marquardt (LM) optimizer.(D. A. Spong, et al., Phys. Plasmas, 5), 1752 (1998). The VMEC code is used to evaluate 3D MHD equilibria needed for stability

S. P. Hirshman; A. S. Ware; M. C. Zarnstorff; S. Ethier

1999-01-01

322

The Formation of Stellar Clusters  

Microsoft Academic Search

We review recent work that investigates the formation of stellar clusters,\\u000aranging in scale from globular clusters through open clusters to the small\\u000ascale aggregates of stars observed in T associations. In all cases, recent\\u000aadvances in understanding have been achieved through the use of state of the\\u000aart stellar dynamical and gas dynamical calculations, combined with the\\u000apossibility of

Cathie J. Clarke; Ian A. Bonnell; Lynne A. Hillenbrand

1999-01-01

323

Gamma-ray background anisotropy from Galactic dark matter substructure  

NASA Astrophysics Data System (ADS)

Dark matter annihilation in Galactic substructure will imprint characteristic angular signatures on the all-sky map of the diffuse gamma-ray background. We study the gamma-ray background anisotropy due to the subhalos and discuss detectability at the Fermi Gamma-ray Space Telescope. In contrast to earlier work that relies on simulated all-sky maps, we derive analytic formulae that enable to directly compute the angular power spectrum, given parameters of subhalos such as mass function, and radial profile of gamma-ray luminosity. As our fiducial subhalo models, we adopt M-1.9 mass spectrum, subhalos radial distribution suppressed toward the Galactic center, and luminosity profile of each subhalo dominated by its smooth component. We find that, for multipole regime corresponding to ??5°, the angular power spectrum is dominated by a noiselike term, with suppression due to internal structure of relevant subhalos. If the mass spectrum extends down to Earth-mass scale, then the subhalos would be detected in the anisotropy with Fermi at angular scales of ˜10°, if their contribution to the gamma-ray background is larger than ˜20%. If the minimum mass is around 104M?, on the other hand, the relevant angular scale for detection is ˜1°, and the anisotropy detection requires that the subhalo contribution to the gamma-ray background intensity is only ˜4%. These can be achieved with a modest boost for particle-physics parameters. We also find that the anisotropy analysis could be a more sensitive probe for the subhalos than individual detection. We also study dependence on model parameters, where we reach the similar conclusions for all the models investigated. The analytic approach should be very useful when Fermi data are analyzed, and the obtained angular power spectrum is interpreted in terms of subhalo models.

Ando, Shin'Ichiro

2009-07-01

324

Discovering Higgs bosons of the MSSM using jet substructure  

SciTech Connect

We present a qualitatively new approach to discover Higgs bosons of the minimal supersymmetric standard model (MSSM) at the LHC using jet substructure techniques applied to boosted Higgs decays. These techniques are ideally suited to the MSSM, since the lightest Higgs boson overwhelmingly decays to bb throughout the entire parameter space, while the heavier neutral Higgs bosons, if light enough to be produced in a cascade, also predominantly decay to bb. The Higgs production we consider arises from superpartner production where superpartners cascade decay into Higgs bosons. We study this mode of Higgs production for several superpartner hierarchies: m{sub q}-tilde, m{sub g}-tilde>m{sub W}-tilde{sub ,B}-tilde>m{sub h}+{mu}; m{sub q}-tilde, m{sub g}-tilde>m{sub W}-tilde{sub ,B}-tilde>m{sub h,H,A}+{mu}; and m{sub q}-tilde, m{sub g}-tilde>m{sub W}-tilde>m{sub h}+{mu} with m{sub B}-tilde{approx_equal}{mu}. In these cascades, the Higgs bosons are boosted, with p{sub T}>200 GeV a large fraction of the time. Since Higgses appear in cascades originating from squarks and/or gluinos, the cross section for events with at least one Higgs can be the same order as squark/gluino production. Given 10 fb{sup -1} of 14 TeV LHC data, with m{sub q}-tilde < or approx. 1 TeV, and one of the above superpartner mass hierarchies, our estimate of S/{radical}(B) of the Higgs signal is sufficiently high that the bb mode can become the discovery mode of the lightest Higgs boson of the MSSM.

Kribs, Graham D.; Roy, Tuhin S.; Spannowsky, Michael [Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States); Martin, Adam [Theoretical Physics Department, Fermilab, Batavia, Illinois 60510 (United States)

2010-11-01

325

Effect of substructure on intergranular cavitation at high temperature  

SciTech Connect

When loaded at high temperatures under either low strain rate or constant load conditions, metals and alloys often fail by the nucleation and growth of cavities at grain boundaries with limited ductility. It has now been accepted that vacancies can cluster at sites of high stress concentration at grain boundaries to form cavities, which would then grow under practical creep conditions to effect fracture. The ways that stress concentrations are generated at grain boundaries, however, have been the subject of much debate. This work investigates the effect of various microstructural variables, especially the substructure, on high temperature fracture behavior of single-phase metals. The materials used were copper of two different purities (99.9% and 99.99%) and an Al-5% Mg alloy. Both the annealed and subgrain-containing copper specimens were pulled to fracture at 773 K in purified argon, either at a strain rate of 8.3 [times] 10[sup [minus]5] s[sup [minus]1] or under a constant load corresponding to a nominal stress of 20 MPa. The Al-5% Mg specimens were crept in tension to fracture under constant stress conditions at 523 K (0.56 T[sub M]) in air. The creep stresses applied ranged from 100 to 230 MPa. After the tests, the fracture surfaces were examined by means of SEM. Longitudinal sections of the fractured specimens were also prepared, polished and etched with 0.5 ml HF/99.5 ml H[sub 2]O solution for 80 s, and then examined under an optical microscope.

Lim, L.C.; Lu, H.H. (National Univ. of Singapore, Kent Ridge (Singapore). Dept. of Mechanical and Production Engineering)

1994-09-15

326

A possible excess rotation measure and large-scale magnetic field in the Virgo Supercluster of galaxies  

SciTech Connect

A search of the Broten et al. (1988) all-sky rotation-measure (RM) catalog for galaxies and quasars resulted in a possible discovery of a cluster-wide magnetic field in the Virgo Supercluster, with a magnetic field intensity near 1.5 microG consistent with an RM excess of -10 rad/sq m. The magnetic energy density of a 1.5 microG field is about 10 to the -13 ergs/cu cm, comparable to the energy density in the 2.7 K cosmic blackbody radiation of 5 x 10 to the -13th ergs/cu cm. The energetic implications for a 1.5 microG cluster-wide field in Virgo are also reasonable in view of the current theoretical models predicting such large-scale magnetic fields in cluster of galaxies. 16 refs.

Vallee, J.P. (Grenoble, Observatoire (France) National Research Council of Canada, Herzberg Institute of Astrophysics, Ottawa (Canada))

1990-02-01

327

Multifrequency observations of the Virgo blazars 3C 273 and 3C 279 in CGRO cycle 8  

NASA Astrophysics Data System (ADS)

We report first observational results of multifrequency campaigns on the prominent Virgo blazars 3C 273 and 3C 279 which were carried out in January and February 1999. Both blazars are detected from radio to ?-ray energies. We present the measured X- to ?-ray spectra of both sources, and for 3C 279 we compare the 1999 broad-band (radio to ?-ray) spectrum to measured previous ones. .

Collmar, W.; Benlloch, S.; Grove, J. E.; Hartman, R. C.; Heindl, W. A.; Kraus, A.; Teräsranta, H.; Villata, M.; Bennett, K.; Bloemen, H.; Johnson, W. N.; Krichbaum, T. P.; Raiteri, C. M.; Ryan, J.; Sobrito, G.; Schönfelder, V.; Williams, O. R.; Wilms, J.

2000-04-01

328

Near-infrared imaging and spectroscopy of the nuclear region of the disturbed Virgo cluster spiral NGC4438  

Microsoft Academic Search

We present near-infrared (NIR) Very Large Telescope (VLT) Infrared Spectrometer and Array Camera (ISAAC) imaging and spectroscopy of the peculiar Virgo galaxy NGC4438, whose nucleus has been classified as a low-ionization nuclear emission-line region (LINER). The data are supplemented by mid-infrared imaging, and compared to previous HST broad-band images. Images and position-velocity maps of the [FeII] and H2 line emissions

Sebastian Perez; Simon Casassus; Juan R. Cortés; Jeffrey D. P. Kenney

2009-01-01

329

The acoustic low-degree modes of the Sun measured with 14 years of continuous GOLF & VIRGO measurements  

NASA Astrophysics Data System (ADS)

The helioseismic Global Oscillation at Low Frequency (GOLF) and the Variability of solar Irradiance and Gravity Oscillations (VIRGO) instruments onboard SoHO, have been observing the Sun continuously for the last 14 years. In this preliminary work, we characterize the acoustic modes over the entire p-mode range in both, Doppler velocity and luminosity, with a special care for the low-frequency modes taking advantage of the stability and the high duty cycle of space observations.

García, R. A.; Salabert, D.; Ballot, J.; Sato, K.; Mathur, S.; Jiménez, A.

2011-01-01

330

Solar and Stellar Dynamos  

NASA Astrophysics Data System (ADS)

The Sun, solar and later spectral type stars show cyclical magnetic activity that manifests itself through the presence of spots on their surfaces. The characteristics of this activity show broad variations both in spot periods, which range from a few to more than 20 years, and spot surface coverages, which range from 0.002 for the Sun to more than 0.5 for the most active stars. In the case of the Sun, owing to its proximity, the spots and their cyclic behaviour are directly observable in detail since Galileo's times. In the case of the point-like stars, indirect methods, as the Doppler imaging or brightness rotational modulation, allow the determination of the spot coverage and its behaviour with time. It is commonly believed that the occurrence of such phenomena in the Sun and similar stars with surface convection zones is governed by a dynamo mechanism which acts in the deepest convective layers at the interface with the underlying radiative envelope. This mechanism is based on the mutual interaction between rotation, convection and magnetic fields, which produces non uniform rotation (?-effect), able to intensify magnetic field, and cyclonic turbulence (?-effect), able to regenerate magnetic field against diffusion. These are the basic working principles of the ?-? dynamo, that is essentially governed by the motion and induction equations. The competitive role of the convective and diffusive terms in the induction equation determines the time evolution of magnetic field. This is a formidable, highly non-linear problem of magneto-hydrodynamics of stellar plasmas, and various approaches have been experienced for its solution, from the linearized dynamos, to the asymptotic dynamos, useful for stars in that simple relationships between the relevant parameters are derived, to the non linear and eventually fully hydromagnetic dynamos in which the whole set of equations are solved at once, by means of very sophisticated two- or three-dimensional numerical codes.

Paternò, Lucio

2004-04-01

331

Stellar Aberration 3D  

NSDL National Science Digital Library

The EJS Stellar Aberration 3D Model illustrates the phenomenon known as the aberration of starlight, first reported by James Bradley in 1729. Aberration occurs because light has a finite speed, and thus light from a star takes a finite amount of time to travel through the tube of a telescope. During this time, the telescope moves as a result of Earth's rotational and orbital motions (in this case, the orbital motion is more important because it is faster). Therefore, if the telescope is pointed directly at the star the starlight will hit the sides of the tube before reaching the eyepiece. To see the star the telescope must be pointed forward (ie in the direction of Earth's motion) very slightly. As a result the apparent location of the star on the sky is different from its true location. The simulation illustrates the effects of aberration for a star at any location in the sky, during any time of year. A 3D view shows the Earth orbiting the sun, the star, and the apparent position of the star on the Celestial Sphere. This view can also display vectors detailing how the velocity of Earth combines with the velocity of light from the star to produce a new relative velocity vector that indicates the apparent location of the star. A separate 2D view shows the "true" location of the star as well as the apparent location for an observer looking up from Earth. Note that some features have been simplified or exaggerated. The Earth's orbit is treated as a circle. The size of Earth, Sun, and Earth's orbit are greatly exaggerated compared to the distance to the star. The speed controls allow the user to set Earth's orbital speed to an appreciable fraction of light speed, which is not realistic. Finally, the simulation illustrates the "classical" aberration effect, not the (more correct) relativistic aberration.

Timberlake, Todd

2011-05-18

332

Identification of population substructure among Jews using STR markers and dependence on reference populations included  

PubMed Central

Background Detecting population substructure is a critical issue for association studies of health behaviors and other traits. Whether inherent in the population or an artifact of marker choice, determining aspects of a population's genetic history as potential sources of substructure can aid in design of future genetic studies. Jewish populations, among which association studies are often conducted, have a known history of migrations. As a necessary step in understanding population structure to conduct valid association studies of health behaviors among Israeli Jews, we investigated genetic signatures of this history and quantified substructure to facilitate future investigations of these phenotypes in this population. Results Using 32 autosomal STR markers and the program STRUCTURE, we differentiated between Ashkenazi (AJ, N = 135) and non-Ashkenazi (NAJ, N = 226) Jewish populations in the form of Northern and Southern geographic genetic components (AJ north 73%, south 23%, NAJ north 33%, south 60%). The ability to detect substructure within these closely related populations using a small STR panel was contingent on including additional samples representing major continental populations in the analyses. Conclusions Although clustering programs such as STRUCTURE are designed to assign proportions of ancestry to individuals without reference population information, when Jewish samples were analyzed in the absence of proxy parental populations, substructure within Jews was not detected. Generally, for samples with a given grandparental country of birth, STRUCTURE assignment values to Northern, Southern, African and Asian clusters agreed with mitochondrial DNA and Y-chromosomal data from previous studies as well as historical records of migration and intermarriage.

2010-01-01

333

An algebraic sub-structuring method for large-scale eigenvaluecalculation  

SciTech Connect

We examine sub-structuring methods for solving large-scalegeneralized eigenvalue problems from a purely algebraic point of view. Weuse the term "algebraic sub-structuring" to refer to the process ofapplying matrix reordering and partitioning algorithms to divide a largesparse matrix into smaller submatrices from which a subset of spectralcomponents are extracted and combined to provide approximate solutions tothe original problem. We are interested in the question of which spectralcomponentsone should extract from each sub-structure in order to producean approximate solution to the original problem with a desired level ofaccuracy. Error estimate for the approximation to the small esteigen pairis developed. The estimate leads to a simple heuristic for choosingspectral components (modes) from each sub-structure. The effectiveness ofsuch a heuristic is demonstrated with numerical examples. We show thatalgebraic sub-structuring can be effectively used to solve a generalizedeigenvalue problem arising from the simulation of an acceleratorstructure. One interesting characteristic of this application is that thestiffness matrix produced by a hierarchical vector finite elements schemecontains a null space of large dimension. We present an efficient schemeto deflate this null space in the algebraic sub-structuringprocess.

Yang, C.; Gao, W.; Bai, Z.; Li, X.; Lee, L.; Husbands, P.; Ng, E.

2004-05-26

334

Substructure identification for shear structures: cross-power spectral density method  

NASA Astrophysics Data System (ADS)

In this paper, a substructure identification method for shear structures is proposed. A shear structure is divided into many small substructures; utilizing the dynamic equilibrium of a one-floor substructure, an inductive identification problem is formulated, using the cross-power spectral densities between structural floor accelerations and a reference response, to estimate the parameters of that one story. Repeating this procedure, all story parameters of the shear structure are identified from top to bottom recursively. An identification error analysis is performed for the proposed substructure method, revealing how uncertain factors (e.g. measurement noise) in the identification process affect the identification accuracy. According to the error analysis, a smart reference selection rule is designed to choose the optimal reference response that further enhances the identification accuracy. Moreover, based on the identification error analysis, explicit formulae are developed to calculate the variances of the parameter identification errors. A ten-story shear structure is used to illustrate the effectiveness of the proposed substructure method. The simulation results show that the method, combined with the reference selection rule, can very accurately identify structural parameters despite large measurement noise. Furthermore, the proposed formulae provide good predictions for the variances of the parameter identification errors, which are vital for providing accurate warnings of structural damage.

Zhang, Dongyu; Johnson, Erik A.

2012-05-01

335

Metrics for diagnosing negative mass and stiffness when uncoupling experimental and analytical substructures.  

SciTech Connect

Recently, a new substructure coupling/uncoupling approach has been introduced, called Modal Constraints for Fixture and Subsystem (MCFS) [Allen, Mayes, & Bergman, Journal of Sound and Vibration, vol. 329, 2010]. This method reduces ill-conditioning by imposing constraints on substructure modal coordinates instead of the physical interface coordinates. The experimental substructure is tested in a free-free configuration, and the interface is exercised by attaching a flexible fixture. An analytical representation of the fixture is then used to subtract its effects in order to create an experimental model for the subcomponent of interest. However, it has been observed that indefinite mass and stiffness matrices can be obtained for the experimental substructure in some situations. This paper presents two simple metrics that can be used by the analyst to determine the cause of indefinite mass or stiffness matrices after substructure uncoupling. The metrics rank the experimental and fixture modes based upon their contribution to offending negative eigenvalues. Once the troublesome modes have been identified, they can be inspected and often reveal why the mass has become negative. Two examples are presented to demonstrate the metrics and to illustrate the physical phenomena that they reveal.

Allen, Matthew S. (University of Wisconsin, Madison, WI); Kammer, Daniel C. (University of Wisconsin, Madison, WI); Mayes, Randall Lee

2010-10-01

336

Compact Stellarator Path to DEMO  

NASA Astrophysics Data System (ADS)

Issues for a DEMO reactor are sustaining an ignited/high-Q plasma in steady state, avoiding disruptions and large variations in power flux to the wall, adequate confinement of thermal plasma and alpha-particles, control of a burning plasma, particle and power handling, etc. Compact stellarators have key advantages -- steady-state high-plasma-density operation without external current drive or disruptions, stability without a close conducting wall or active feedback systems, and low recirculating power -- in addition to moderate plasma aspect ratio, good confinement, and high-beta potential. The ARIES-CS study established that compact stellarators can be competitive with tokamaks as reactors. Many of the issues for a compact stellarator DEMO can be answered using results from large tokamaks, ITER D-T experiments and fusion materials, technology and component development programs, in addition to stellarators in operation, under construction or in development. However, a large next-generation stellarator will be needed to address some physics issues: size scaling and confinement at higher parameters, burning plasma issues, and operation with a strongly radiative divertor. Technology issues include simpler coils, structure, and divertor fabrication, and better cost information.

Lyon, J. F.

2007-11-01

337

The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies  

NASA Astrophysics Data System (ADS)

The influence of the environment on gas surface density and star formation efficiency of cluster spiral galaxies is investigated. We extend previous work on radial profiles by a pixel-to pixel analysis looking for asymmetries due to environmental interactions. The star formation rate is derived from GALEX UV and Spitzer total infrared data based on the 8, 24, 70, and 160 ?m data. As in field galaxies, the star formation rate for most Virgo galaxies is approximately proportional to the molecular gas mass. Except for NGC 4438, the cluster environment does not affect the star formation efficiency with respect to the molecular gas. Gas truncation is not associated with major changes in the total gas surface density distribution of the inner disk of Virgo spiral galaxies. In three galaxies (NGC 4430, NGC 4501, and NGC 4522), possible increases in the molecular fraction and the star formation efficiency with respect to the total gas, of factors of 1.5 to 2, are observed on the windward side of the galactic disk. A significant increase of the star formation efficiency with respect to the molecular gas content on the windward side of ram pressure-stripped galaxies is not observed. The ram-pressure stripped extraplanar gas of 3 highly inclined spiral galaxies (NGC 4330, NGC 4438, and NGC 4522) shows a depressed star formation efficiency with respect to the total gas, and one of them (NGC 4438) shows a depressed rate even with respect to the molecular gas. The interpretation is that stripped gas loses the gravitational confinement and associated pressure of the galactic disk, and the gas flow is diverging, so the gas density decreases and the star formation rate drops. We found two such regions of low star formation efficiency in the more face-on galaxies NGC 4501 and NGC 4654 which are both undergoing ram pressure stripping. These regions show low radio continuum emission or unusually steep radio spectral index. However, the stripped extraplanar gas in one highly inclined galaxy (NGC 4569) shows a normal star formation efficiency with respect to the total gas. We propose this galaxy is different because it is observed long after peak pressure, and its extraplanar gas is now in a converging flow as it resettles back into the disk. Appendices are available in electronic form http://www.aanda.org

Vollmer, B.; Wong, O. I.; Braine, J.; Chung, A.; Kenney, J. D. P.

2012-07-01

338

Quantified H I morphology - V. H I discs in the Virgo cluster  

NASA Astrophysics Data System (ADS)

We explore the quantified morphology of atomic hydrogen (H I) discs in the Virgo cluster. These galaxies display a wealth of phenomena in their H I morphology, e.g., tails, truncation and warps. These morphological disturbances are related to the ram pressure stripping and tidal interaction that galaxies undergo in this dense cluster environment. To quantify the morphological transformation of the H I discs, we compute the morphological parameters of Concentration, Asymmetry, Smoothness, Gini and M20 and our own GM for 51 galaxies in 48 H I column density maps from the VLA Imaging of Virgo spirals in Atomic gas (VIVA) project. Some morphological phenomena can be identified in this space of relatively low-resolution H I data. Truncation of the H I disc can be cleanly identified via the Concentration parameter (C < 1), and Concentration can also be used to identify H I deficient discs (1 < C < 5). Tidal interaction is typically identified using combinations of these morphological parameters, applied to (optical) images of galaxies. We find that some selection criteria (Gini-M20, Asymmetry and a modified Concentration-M20) are still applicable for the coarse (˜15 arcsec full width at half - maximum) VIVA H I data. We note that Asymmetry is strongly affected by the choice for the centre of these galaxies. The phenomena of tidal tails can be reasonably well identified using the Gini-M20 criterion (60 per cent of galaxies with tails identified but with as many contaminants). Ram pressure does move H I discs into and out of most of our interaction criteria: the ram pressure sequence identified by previous authors tracks into and out of some of these criteria (Asymmetry-based and the Gini-M20 selections, but not the Concentration-M20 or the GM-based ones). Therefore, future searches for interaction using H I morphologies should take ram pressure into account as a mechanism to disturb H I discs enough to make them appear as gravitationally interacting. One mechanism would be to remove all the H I deficient (C < 5) discs from the sample, as these have undergone more than one H I removal mechanism.

Holwerda, B. W.; Pirzkal, N.; de Blok, W. J. G.; van Driel, W.

2011-10-01

339

Jet substructure at the Tevatron and LHC: new results, new tools, new benchmarks  

NASA Astrophysics Data System (ADS)

In this paper, we review recent theoretical progress and the latest experimental results in jet substructure from the Tevatron and the LHC. We review the status of and outlook for calculation and simulation tools for studying jet substructure. Following up on the report of the Boost 2010 workshop, we present a new set of benchmark comparisons of substructure techniques, focusing on the set of variables and grooming methods that are collectively known as ‘top taggers’. To facilitate further exploration, we have attempted to collect, harmonize and publish software implementations of these techniques. Report prepared by the participants of the BOOST 2011 Workshop at Princeton University, 22-26 May 2011. L Asquith (lasquith@hep.anl.gov), S Rappoccio (rappocc@fnal.gov) and C K Vermilion (verm@uw.edu), editors.

Altheimer, A.; Arora, S.; Asquith, L.; Brooijmans, G.; Butterworth, J.; Campanelli, M.; Chapleau, B.; Cholakian, A. E.; Chou, J. P.; Dasgupta, M.; Davison, A.; Dolen, J.; Ellis, S. D.; Essig, R.; Fan, J. J.; Field, R.; Fregoso, A.; Gallicchio, J.; Gershtein, Y.; Gomes, A.; Haas, A.; Halkiadakis, E.; Halyo, V.; Hoeche, S.; Hook, A.; Hornig, A.; Huang, P.; Izaguirre, E.; Jankowiak, M.; Kribs, G.; Krohn, D.; Larkoski, A. J.; Lath, A.; Lee, C.; Lee, S. J.; Loch, P.; Maksimovic, P.; Martinez, M.; Miller, D. W.; Plehn, T.; Prokofiev, K.; Rahmat, R.; Rappoccio, S.; Safonov, A.; Salam, G. P.; Schumann, S.; Schwartz, M. D.; Schwartzman, A.; Seymour, M.; Shao, J.; Sinervo, P.; Son, M.; Soper, D. E.; Spannowsky, M.; Stewart, I. W.; Strassler, M.; Strauss, E.; Takeuchi, M.; Thaler, J.; Thomas, S.; Tweedie, B.; Vasquez Sierra, R.; Vermilion, C. K.; Villaplana, M.; Vos, M.; Wacker, J.; Walker, D.; Walsh, J. R.; Wang, L.-T.; Wilbur, S.; Zhu, W.

2012-06-01

340

Recombination algorithms and jet substructure: Pruning as a tool for heavy particle searches  

SciTech Connect

We discuss jet substructure in recombination algorithms for QCD jets and single jets from heavy particle decays. We demonstrate that the jet algorithm can introduce significant systematic effects into the substructure. By characterizing these systematic effects and the substructure from QCD, splash-in, and heavy particle decays, we identify a technique, pruning, to better identify heavy particle decays into single jets and distinguish them from QCD jets. Pruning removes protojets typical of soft, wide-angle radiation, improves the mass resolution of jets reconstructing heavy particle decays, and decreases the QCD background to these decays. We show that pruning provides significant improvements over unpruned jets in identifying top quarks and W bosons and separating them from a QCD background, and may be useful in a search for heavy particles.

Ellis, Stephen D.; Vermilion, Christopher K.; Walsh, Jonathan R. [University of Washington, Seattle, Washington 98195-1560 (United States)

2010-05-01

341

Can substructure in the Galactic halo explain the ATIC and PAMELA results?  

SciTech Connect

Recently, ATIC and PAMELA measured an anomalously large flux of leptonic cosmic rays which may arise from dark matter self-annihilation. While the annihilation signal predicted for a smooth halo is 10{sup 2}-10{sup 3} times smaller than the measured excess, the signal can be boosted by the presence of subhalos. We investigate the feasibility of large boost factors using a new Monte Carlo calculation technique that is constrained by previous simulation work on halo substructure. The model accounts for the observed decrease in the amount of substructure with decreasing halo mass and the scatter in halo structural parameters such as the density concentration parameter. Our results suggest that boost factors of {approx}10{sup 2} are highly unlikely and are ruled out at > or approx. 14{sigma} within the context of our model. We conclude that substructure alone, at least with commonly assumed annihilation cross sections, cannot explain the anomalous flux measured by ATIC and PAMELA.

Elahi, Pascal J.; Widrow, Lawrence M. [Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario (Canada); Thacker, Robert J. [Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia (Canada)

2009-12-15

342

A new method to quantify X-ray substructure in clusters of galaxies  

NASA Astrophysics Data System (ADS)

We present a new method to quantify substructures in clusters of galaxies, based on the analysis of the number and intensity of structures detected by an algorithm of the type ``friends-of-friends''. This analysis is done in a residual image that is the result of the subtraction of a surface brightness model, obtained by fitting a two-dimensional analytical model (?-model or Sérsic profile) with elliptical symmetry, from the X-ray image. Our method was applied to 47 clusters observed by the Chandra Space Telescope for more than 10 ks that are in the redshift range z?[0.02, 0.2]. We obtained relations between the substructure level and physical quantities, such as the intra-cluster metallicity, total mass, X-ray luminosity, temperature, and cluster redshift. However, because of the 2 pages limit of this proceeding, we just present here how the substructure level changes with cluster morphology.

Andrade-Santos, Felipe; Lima Neto, Gasta~O. B.; Laganá, Tatiana F.

2010-07-01

343

Design studies for the transmission simulator method of experimental dynamic substructuring.  

SciTech Connect

In recent years, a successful method for generating experimental dynamic substructures has been developed using an instrumented fixture, the transmission simulator. The transmission simulator method solves many of the problems associated with experimental substructuring. These solutions effectively address: (1) rotation and moment estimation at connection points; (2) providing substructure Ritz vectors that adequately span the connection motion space; and (3) adequately addressing multiple and continuous attachment locations. However, the transmission simulator method may fail if the transmission simulator is poorly designed. Four areas of the design addressed here are: (1) designating response sensor locations; (2) designating force input locations; (3) physical design of the transmission simulator; and (4) modal test design. In addition to the transmission simulator design investigations, a review of the theory with an example problem is presented.

Mayes, Randall Lee; Arviso, Michael

2010-05-01

344

Transport Processes in Stellar Interiors  

NASA Astrophysics Data System (ADS)

Stars are rotating and magnetic bodies. Moreover, more and more constraints are obtained on such dynamical processes using, for example, seismology and spectropolarimetry. Therefore, it is now necessary to get a complete and coherent picture of dynamical processes in stellar interiors. However, to simulate such processes in a star in full details would require treating length scales and time scales spanning many orders of magnitude. This is clearly not feasible, even with the most powerful computers available today. This is the reason why it is nowadays necessary to use and couple 1-D, 2-D, and 3-D modelings to get a global picture of macroscopic MHD transport processes in stellar interiors. In this review, we report the state of the art of the modeling of transport processes in stellar interiors (both in radiation and in convection zones) aimed to study the stars angular momentum history, the related profile of differential rotation, and their magnetism.

Mathis, Stéphane

345

Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes  

NASA Astrophysics Data System (ADS)

In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user subroutine DISP and URDFIL of ABAQUS, respectively, while constitutive formulations of the FEM model are coded and implemented in UMAT. The results of the simulations are compared to experiments. This model verified the validity of Winter's two-phase model and Taylor's uniform stress assumption, explored substructure evolution and "intrinsic" behavior in substructures and successfully simulated the process of PSB band formation and propagation.

Zhou, Dong

346

The Via Lactea INCITE simulation: galactic dark matter substructure at high resolution  

NASA Astrophysics Data System (ADS)

It is a clear and unique prediction of the cold dark matter paradigm of cosmological structure formation that galaxies form hierarchically and are embedded in massive, extended dark halos teeming with self-bound substructure, or 'subhalos.' The amount and spatial distribution of subhalos around their host provide unique information and clues on the galaxy assembly process and the nature of the dark matter. Here we present results from the Via Lactea INCITE simulation, a one billion particle, one million CPU-hour simulation of the formation and evolution of a galactic dark matter halo and its substructure population.

Kuhlen, M.; Diemand, J.; Madau, P.; Zemp, M.

2008-07-01

347

Multimodality in galaxy clusters from SDSS DR8: substructure and velocity distribution  

NASA Astrophysics Data System (ADS)

Context. The study of the signatures of multimodality in groups and clusters of galaxies, an environment for most of the galaxies in the Universe, gives us information about the dynamical state of clusters and about merging processes, which affect the formation and evolution of galaxies, groups and clusters, and larger structures - superclusters of galaxies and the whole cosmic web. Aims: We search for the presence of substructure, a non-Gaussian, asymmetrical velocity distribution of galaxies, and large peculiar velocities of the main galaxies in clusters with at least 50 member galaxies, drawn from the SDSS DR8. Methods: We employ a number of 3D, 2D, and 1D tests to analyse the distribution of galaxies in clusters: 3D normal mixture modelling, the Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests, as well as the Anscombe-Glynn and the D'Agostino tests. We find the peculiar velocities of the main galaxies, and use principal component analysis to characterise our results. Results: More than 80% of the clusters in our sample have substructure according to 3D normal mixture modelling, and the Dressler-Shectman (DS) test shows substructure in about 70% of the clusters. The median value of the peculiar velocities of the main galaxies in clusters is 206 km s-1 (41% of the rms velocity). The velocities of galaxies in more than 20% of the clusters show significant non-Gaussianity. While multidimensional normal mixture modelling is more sensitive than the DS test in resolving substructure in the sky distribution of cluster galaxies, the DS test determines better substructure expressed as tails in the velocity distribution of galaxies (possible line-of-sight mergers). Richer, larger, and more luminous clusters have larger amount of substructure and larger (compared to the rms velocity) peculiar velocities of the main galaxies. Principal component analysis of both the substructure indicators and the physical parametres of clusters shows that galaxy clusters are complicated objects, the properties of which cannot be explained with a small number of parametres or delimited by one single test. Conclusions: The presence of substructure, the non-Gaussian velocity distributions, as well as the large peculiar velocities of the main galaxies, shows that most of the clusters in our sample are dynamically young. Tables 3 and 4 are available in electronic form at http://www.aanda.org

Einasto, M.; Vennik, J.; Nurmi, P.; Tempel, E.; Ahvensalmi, A.; Tago, E.; Liivamägi, L. J.; Saar, E.; Heinämäki, P.; Einasto, J.; Martínez, V. J.

2012-04-01

348

GRAVITATIONAL WAVES FROM STELLAR COLLAPSE  

SciTech Connect

Stellar core-collapse plays an important role in nearly all facets of astronomy: cosmology (as standard candles), formation of compact objects, nucleosynthesis and energy deposition in galaxies. In addition, they release energy in powerful explosions of light over a range of energies, neutrinos, and the subject of this meeting, gravitational waves. Because of this broad range of importance, astronomers have discovered a number of constraints which can be used to help them understand the importance of stellar core-collapse as gravitational wave sources.

C. L. FRYER

2001-01-01

349

MHD Stability in Compact Stellarators  

NASA Astrophysics Data System (ADS)

A key issue for current carrying compact stellarators(S.P. Hirshman et al., "Physics of compact stellarators", Phys. Plasmas 6, 1858 (1999).) is the stability of ideal MHD modes. We present recent stability results of external kink modes, ballooning mode, and vertical modes in Quasi-axisymmetric Stellarators (QAS)( A. Reiman et al, "Physics issue in the design of a high beta Quasi-Axisymmetric Stellarator" the 17th IAEA Fusion Energy conference, (Yokohama, Japan, October 1998), Paper ICP/06.) as well as Quasi-Omnigeneous Stellarators (QOS)^2. The 3D stability code Terpsichore(W. A. Cooper et al., Phys. Plasmas 3, 275 (1996)) is used in this study. The vertical stability in a current carrying stellarator is studied for the first time. The vertical mode is found to be stabilized by externally generated poloidal flux(G.Y. Fu et al., "Stability of vertical mode in a current carrying stellarator"., to be submitted). Physically, this is because the external poloidal flux enhances the field line bending energy relative to the current drive term in the MHD energy principle, ? W. A simple stability criteria is derived in the limit of large aspect ratio and constant current density. For wall at infinite distance from the plasma, the amount of external flux needed for stabilization is given by f=(?^2-?)/(?^2+1) where ? is the axisymmetric elongation and f is the fraction of the external rotational transform at the plasma edge. A systematic parameter study shows that the external kink in QAS can be stabilized at high beta ( ~ 5%) without a conducting wall by combination of edge magnetic shear and 3D shaping(G. Y. Fu et al., "MHD stability calculations of high-beta Quasi-Axisymmetric Stellarators", the 17th IAEA Fusion Energy conference, (Yokohama, Japan, October 1998), paper THP1/07.). The optimal shaping is obtained by using an optimizer with kink stability included in its objective function. The physics mechanism for the kink modes is studied by examining relative contributions of individual terms in ? W. It is found the external kinks are mainly driven by the parallel current. The pressure contributes significantly to the overall drive through the curvature term and the Pfirsch-Schluter current. These results demonstrate potential of QAS and QOS for disruption-free operations at high-beta without a close-fitting conducting wall and feedback stabilization.

Fu, Guoyong

1999-11-01

350

VIBRATIONAL ENERGY FLOW ANALYSIS USING A SUBSTRUCTURE APPROACH: THE APPLICATION OF RECEPTANCE THEORY TO FEA AND SEA  

Microsoft Academic Search

A method for studying the vibrational energy flows through structures based on receptance theory is presented. The structures are considered to be made up of subsystems, which may, in turn, be substructures modelled by using finite element analysis (FEA), each having been separately analyzed for its eigenvalues and eigenvectors. The method may be classified as a form of substructuring using

K. Shankar; A. J. Keane

1997-01-01

351

Changes in the Radio Properties of Virgo Cluster Spirals Due to ICM Ram Pressure  

NASA Astrophysics Data System (ADS)

We present evidence for changes in the radio morphologies and luminosities of Virgo cluster spiral galaxies caused by ICM ram pressure. Spitzer 70um maps and the FIR-radio correlation are used to predict what the radio continuum distribution would be in the absence of ICM ram pressure. Differences between the predicted and observed VLA 20cm radio maps show "radio deficit" regions near the leading edges of several galaxies, and "radio excesses" on the trailing side, clearly indicating ongoing ICM-ISM interactions. These FIR-radio comparisons demonstrate the selective disturbance by ram pressure to different components of the ISM: the radio-emitting plasma is more strongly disturbed than the denser FIR-emitting molecular medium. The radio deficit regions are located outside the ridges of enhanced linear radio polarization recently discovered by Vollmer etal. Thus at the leading edges of galaxies experiencing ICM-ISM interactions, there is an outer zone where cosmic rays and/or magnetic fields are pushed away, and an inner zone where magnetic fields are compressed and/or sheared. The galaxies with local radio deficits seem to have global radio enhancements, perhaps due to the acceleration of cosmic rays by shocks driven into the ISM by ICM ram pressure. Radio deficit regions may be an excellent diagnostic of active ram pressure.

Kenney, Jeffrey

352

Morphological and physical characteristics of the Virgo Cluster - First results from the Las Campanas photographic survey  

NASA Astrophysics Data System (ADS)

Preliminary results are presented of a photographic survey of the Virgo cluster to the faintest convenient limit of the Las Campanas du Pont 2.5 m reflector, performed in order to study the complexity of both the surface and velocity distributions within the central 6 degree radius region. The survey is described and the resulting Catalog is discussed, and the frequency of galaxy types found and listed in the Catalog is described. The physical properties of the dwarfs are summarized, and luminosity functions are given separately for each morphological type. The progressive change of (MBT) faintward along the morphological sequence from Sc I through Sm and Im types is shown, leading to a calibration of the de Vaucouleurs Lambda luminosity index and a determination of its intrinsic dispersion. The preliminary results on the distribution of galaxies of all types in the two principal subclustering regions found are summarized, and the velocity distributions over the face of the 6 degree core are discussed for the various galaxy types.

Sandage, A.; Binggeli, B.; Tammann, G. A.

353

Wing Shape and Its Influence on the Outcome of Territorial Contests in the Damselfly Calopteryx virgo  

PubMed Central

Male mating success is often determined by territory ownership and traits associated with successful territory defense. Empirical studies have shown that the territory owner wins the majority of fights with challenging males. Several physical and physiological traits have been found to correlate with resource holding potential. In addition, in aerial insects, wing design may also have a strong influence on resource holding potential, since it determines efficiency and precision during flight. However, this possibility has not yet been thoroughly evaluated using the modern technique of geometric morphometrics to analyze shape. Therefore, this study examined whether wing shape affects the outcome of male-male contests in the territorial damselfly, Calopteryx virgo (L.) (Odonata: Calopterygidae). Wing shape and also traditional flight-related morphological measures were compared between 27 pairs of winners and losers from experimental territorial contests. Contrary to expectations, there were no differences between winners and losers in all studied wing traits (shape, length, width, total surface, aspect ratio, and wing loading). However, highly significant differences in wing shape and size were detected between the fore- and hindwing. It is currently not known how these differences relate to flight performance, since previous biomechanical studies in damselflies assumed fore- and hindwings to have an identical planform.

Bots, Jessica; Breuker, Casper J.; Kaunisto, Kari M.; Koskimaki, Jani; Gossum, Hans Van; Suhonen, Jukka

2012-01-01

354

The colours of Virgo dEs as seen by SDSS  

NASA Astrophysics Data System (ADS)

A colour analysis of a carefully selected sample of over 200 Virgo cluster dEs and 8 giant ellipticals (Es) in the SDSS yields the following results: a) the nucleated dEs (dENs) follow a tight colour-magnitude relation (CMR) which does not broaden significantly at fainter (Mr ? -15) magnitudes, b) the CMR of dENs smoothly transitions to the CMR of Es, but the latter changes its slope at about Mr ? -20, c) the brighter dENs are consistent with ages of t ? 5 Gyr and a decrease of metallicity towards fainter magnitudes, but a possible additional luminosity-age relation is not ruled out, d) it is crucial to treat dS0s separately from dEs since their different colour properties would otherwise bias the comparison of nucleated and non-nucleated dEs (dEnoNs), e) the dEnoNs show a weak trend towards bluer colours than dENs.

Lisker, Thorsten; Grebel, Eva K.; Binggeli, Bruno

355

A Virgo high-resolution H? kinematical survey - II. The Atlas  

NASA Astrophysics Data System (ADS)

A catalogue of ionized gas velocity fields for a sample of 30 spiral and irregular galaxies of the Virgo cluster has been obtained by using 3D optical data. The aim of this survey is to study the influence of high-density environments on the gaseous kinematics of local cluster galaxies. Observations of the H? line by means of Fabry-Perot interferometry have been performed at the Canada-France-Hawaii Telescope, European Southern Observatory 3.6-m telescope, Observatoire de Haute-Provence 1.93-m telescope and Observatoire du mont Mégantic telescope at angular and spectral samplings from 0.4 to 1.6arcsec and 7 to 16kms-1. A recently developed, automatic and adaptive spatial binning technique is used to reach a nearly constant signal-to-noise ratio (S/N) over the whole field of view, allowing us to keep a high spatial resolution in high-S/N regions and extend the detection of signal in low-S/N regions. This paper is part of a series and presents the integrated emission-line and velocity maps of the galaxies. Both H? morphologies and kinematics exhibit signs of perturbations in the form of, for example, external filaments, inner and nuclear spiral- and ring-like structures, inner kinematical twists, kinematical decoupling of a nuclear spiral, streaming motions along spiral arms and misalignment between kinematical and photometric orientation axes.

Chemin, L.; Balkowski, C.; Cayatte, V.; Carignan, C.; Amram, P.; Garrido, O.; Hernandez, O.; Marcelin, M.; Adami, C.; Boselli, A.; Boulesteix, J.

2006-03-01

356

Three dimensional ray tracing in toroidal stellarators  

Microsoft Academic Search

We have applied a fully 3-dimensional ray-tracing code to stellarators to examine the propagation of electromagnetic radiation near the electron-cyclotron frequency in straight stellarators, toroidal stellarators, and tokamaks. The stellarators are simulated by using numerically computed vacuum magnetic fields and are assumed to have temperatures and densities which are constant on the flux surfaces. A comparison of the topology shows

W. D. DHaeseleer; J. L. Shohet; K. R. Audenaerde

1985-01-01

357

The Supernova - A Stellar Spectacle.  

ERIC Educational Resources Information Center

|This booklet is part of an American Astronomical Society curriculum project designed to provide teaching materials to teachers of secondary school chemistry, physics, and earth science. The following topics concerning supernovae are included: the outburst as observed and according to theory, the stellar remnant, the nebular remnant, and a summary…

Straka, W. C.

358

A Stellar Tracking Reference System.  

National Technical Information Service (NTIS)

A stellar attitude reference system concept for satellites was studied which promises to permit continuous precision pointing of payloads with accuracies of 0.001 degree without the use of gyroscopes. It is accomplished with the use of a single, clustered...

B. Klestadt

1971-01-01

359

Integrated Circuit Stellar Magnitude Simulator  

ERIC Educational Resources Information Center

|Describes an electronic circuit which can be used to demonstrate the stellar magnitude scale. Six rectangular light-emitting diodes with independently adjustable duty cycles represent stars of magnitudes 1 through 6. Experimentally verifies the logarithmic response of the eye. (Author/GA)|

Blackburn, James A.

1978-01-01

360

Stellar Variability and Global Warning.  

National Technical Information Service (NTIS)

The sun appears to be less variable in its total light output than other stars of comparable magnetic activity. A recent model for solar variability appears unable to account completely and correctly for these stellar observations. Until we have a consist...

R. R. Radick

1994-01-01

361

Stellar variability and global warning  

SciTech Connect

The sun appears to be less variable in its total light output than other stars of comparable magnetic activity. A recent model for solar variability appears unable to account completely and correctly for these stellar observations. Until we have a consistent explanation for the observed behavior of solar analog stars, we must remain in doubt about the range of possible solar variability.

Radick, R.R.

1994-11-11

362

Observational studies of stellar rotation  

NASA Astrophysics Data System (ADS)

This course reviews the rotational properties of non- degenerate stars as observed from the protostellar stage to the end of the main sequence. It includes an introduction to the various observational techniques used to measure stellar rotation. Angular momentum evolution models developed over the mass range from the substellar domain to high-mass stars are briefly discussed.

Bouvier, J.

2013-09-01

363

Stellar Variability and Global Warming.  

National Technical Information Service (NTIS)

Stellar observations suggest that the sun is less variable in its total light output than other stars of comparable magnetic activity. In his report Peter Foukal offers an interpretation of this result in terms of a model for solar variability. It appears...

R. R. Radick

1994-01-01

364

Stellar evolution: Theory and observations  

Microsoft Academic Search

The evolution of single and binary starts of different mass from their birth to their transformation into white dwarfs, neutron stars, and black holes is considered. The main trends in stellar evolution theory are presented, and attention is given to possible applications of this theory to the evolution of star clusters and galaxies. Particular emphasis is placed on a comparison

Alla G. Masevich; Aleksandr V. Tutukov

1988-01-01

365

Stellar Maser Observations (Benson+ 1990)  

Microsoft Academic Search

This catalog contains about 2958 stellar sources. For the searching of the maser emission of the sources listed, 368 were detected in H2O, 209 in SiO, and 713 in OH. In the catalog, one can find information about the stars including alternate names, the 1950 epoch position, velocity (LSR), spectral type, variability type, and period, as well as the references

P. J. Benson; I. R. Little-Marenin; J. Attridge; K. Blais; D. Randolph; T. Woods; M. Rubiera; H. Keefe

1997-01-01

366

Bending instabilities in stellar systems  

Microsoft Academic Search

We discuss the physics of bending instabilities in inhomogeneous stellar systems and propose a simple criterion for stability. We derive the bending modes of a family of thin disk models and show that long-wavelength modes in thin systems with realistic density profiles are not always stabilized by gravity, in contrast to an infinite sheet. We also present the results of

David Merritt; J. A. Sellwood

1994-01-01

367

The Stellar Imager (SI) ``Vision Mission  

Microsoft Academic Search

The Stellar Imager (SI) is a `Vision' mission in the Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar\\/stellar magnetic activity and its

K. Carpenter; W. Danchi; J. Leitner; A. Liu; R. Lyon; L. Mazzuca; R. Moe; D. Chenette; C. Schrijver; S. Kilston; M. Karovska; R. Allen; A. Brown; J. Marzouk; N. Murphy; F. Walter

2004-01-01

368

Dynamics of flexible multibody systems using loaded-interface substructure synthesis approach  

Microsoft Academic Search

A simple numerical method for dynamic simulation of multibody systems consisting of rigid and flexible bodies is presented. This paper investigates the multibody systems with inertia properties of flexible components that undergo large angular rotations. The equation of motion is derived using the finite element\\/Lagrange formulation. A substructure synthesis method is employed to reduce the number of elastic coordinates of

S. P. Lim; A. Q. Liu; K. M. Liew

1994-01-01

369

A maximum common substructure-based algorithm for searching and predicting drug-like compounds  

Microsoft Academic Search

Motivation: The prediction of biologically active compounds is of great importance for high-throughput screening (HTS) approaches in drug discovery and chemical genomics. Many computational methods in this area focus on measuring the structural similarities between chemical structures. However, traditional similarity measures are often too rigid or consider only global similarities between structures. The maximum common substructure (MCS) approach provides a

Yiqun Cao; Tao Jiang; Thomas Girke

2008-01-01

370

The influence of temperature and grain size on substructure evolution in stainless steel 316L  

Microsoft Academic Search

The flow stress of polycrystals is controlled by the processes occurring in the grain interior as well as in the mantle, i.e. at the grain boundary and its immediate vicinity. The early stages of evolution of dislocation substructure in these two regions with strain in 316L stainless steel polycrystals have been studied at 293 K, 673 K and 1123 K

M. Janecek; K. Tangri

1995-01-01

371

Gravitational collapse in an expanding background and the role of substructure - I. Planar collapse  

Microsoft Academic Search

We study the interplay of clumping at small scales with the collapse and relaxation of perturbations at much larger scales. We present results of our analysis when the large-scale perturbation is modelled as a plane wave. We find that in the absence of substructure, collapse leads to formation of a pancake with multistream regions. Dynamical relaxation of the plane wave

J. S. Bagla; Jayanti Prasad; Suryadeep Ray

2005-01-01

372

Data Mining in Chemometrics Sub-structures Learning Via Peak Combinations Searching in Mass Spectra  

Microsoft Academic Search

In this paper, a new approach of finding sub-structures in chemical compounds by searching peak combinations in mass spectra is given. Based on these peak combinations, further identification and classification methods are also proposed. As an application of these methods, saturated Alcohol and Ether are classified eciently by using a variable selection method.

Yu Tang; Yizeng Liang; Kai-Tai Fang

373

Large and frequently occurring substructures in organic compounds obtained by library search of infrared spectra  

Microsoft Academic Search

Comparing the infrared spectrum of a compound whose chemical structure is unknown with the spectra of a library is a routinely used method to obtain information about the unknown structure. The resulting hitlist contains compounds exhibiting the most similar spectra. If the unknown is not contained in the library, a method based on the maximum common substructure concept can be

K. Varmuza; P. N. Penchev; H. Scsibrany

1999-01-01

374

The compressed feature matrix—a fast method for feature based substructure search  

Microsoft Academic Search

The compressed feature matrix (CFM) is a feature based molecular descriptor for the fast processing of pharmacochemical applications such as adaptive similarity search, pharmacophore development and substructure search. Depending on the particular purpose, the descriptor may be generated upon either topological or Euclidean molecular data. To assure a variable utilizability, the assignment of the structural patterns to feature types is

S. F. Badreddin Abolmaali; Jörg K. Wegner; Andreas Zell

2003-01-01

375

Load-transfer system for mating an integrated deck with an offshore platform substructure  

Microsoft Academic Search

This patent describes a load transfer system for use in mating an integrated deck with an offshore platform substructure. The load transfer system comprising: a probe extending downwardly from the integrated deck and having a lower end with a first load bearing surface formed thereon; shock-load absorbing means mounted between the integrated deck and the probe, the shock-load absorbing means

Weyler

1989-01-01

376

A Computer Process for Substructure Searches on Compound Structures Ciphered in the IUPAC Notation  

ERIC Educational Resources Information Center

|Computer programs have been written which enable substructure searches to be carried out on a file of compounds ciphered using a modified version of the IUPAC (Dyson) notation. The search system outlined is to be linked with one which uses input from the chemical structure typewriter. (3 references) (Author)|

Polton, D. J.

1972-01-01

377

Toward Optimization of the Linker Substructure Common to Transthyretin Amyloidogenesis Inhibitors Using Biochemical And Structural Studies  

SciTech Connect

To develop potent and highly selective transthyretin (TTR) amyloidogenesis inhibitors, it is useful to systematically optimize the three substructural elements that compose a typical TTR kinetic stabilizer: the two aryl rings and the linker joining them. Herein, we evaluated 40 bisaryl molecules based on 10 unique linker substructures to determine how these linkages influence inhibitor potency and selectivity. These linkers connect one unsubstituted aromatic ring to either a 3,5-X{sub 2} or a 3,5-X{sub 2}-4-OH phenyl substructure (X = Br or CH{sub 3}). Coconsideration of amyloid inhibition and ex vivo plasma TTR binding selectivity data reveal that direct connection of the two aryls or linkage through nonpolar E-olefin or -CH{sub 2}CH{sub 2}- substructures generates the most potent and selective TTR amyloidogenesis inhibitors exhibiting minimal undesirable binding to the thyroid hormone nuclear receptor or the COX-1 enzyme. Five high-resolution TTR.inhibitor crystal structures (1.4-1.8 {angstrom}) provide insight into why such linkers afford inhibitors with greater potency and selectivity.

Johnson, S.M.; Connelly, S.; Wilson, I.A.; Kelly, J.W.

2009-05-18

378

An Algorithm for Finding the Largest Approximately Common Substructures of Two Trees  

Microsoft Academic Search

Ordered, labeled trees are trees in which each node has a label and the left-to-rightorder of its children (if it has any) is fixed. Such trees have many applications in vision, patternrecognition, molecular biology and natural language processing. We consider a substructure of anordered labeled tree T to be a connected subgraph of T . Given two ordered labeled trees

Jason Tsong-li Wang; Bruce A. Shapiro; Dennis Shasha; Kaizhong Zhang; Kathleen M. Currey

1998-01-01

379

Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile  

NASA Astrophysics Data System (ADS)

We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 ± 0.2 and extends to a projected distance of at least ~175 kpc (~2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Gilbert, Karoline M.; Guhathakurta, Puragra; Beaton, Rachael L.; Bullock, James; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J.; Tollerud, Erik J.; Tanaka, Mikito; Chiba, Masashi

2012-11-01

380

Probing the Nature of the G1 Clump Stellar Overdensity in the Outskirts of M31  

NASA Astrophysics Data System (ADS)

We present deep Hubble Space Telescope ACS observations of the G1 clump, a distinct stellar overdensity lying at ~30 kpc along the southwestern major axis of M31, close to the G1 globular cluster (from the work of Ferguson and coworkers). Our well-populated color-magnitude diagram reaches ~7 mag below the red giant branch tip with 90% completeness, and allows the detection of various morphological features that can be used to derive detailed constraints on the age and metallicity of the constituent stellar population. We find that the color-magnitude diagram is best described by a population with a large age range (gtrsim10 Gyr) and a relatively high mean metallicity [M/H] = -0.4. The spread in metallicity is constrained to be lesssim0.5 dex. The star formation rate in this region has declined over time, with the bulk of the stellar mass having formed >6 Gyr ago. Nonetheless, a nonnegligible mass fraction (approx10%) of the population has formed in the last 2 Gyr. We discuss the nature of the G1 clump in light of these new stellar population constraints and argue that the combination of stellar content and physical size make it unlikely that the structure is the remnant of an accreted dwarf galaxy. Instead, the strong similarity between the stellar content of the G1 clump and that of the M31 outer disk suggests that the substructure is a fragment of the outer disk, perhaps torn off from the main body during a past accretion/merger event; this interpretation is consistent with extant kinematical data. If this interpretation is correct, our analysis of the stellar content provides further evidence that the outskirts of large disk galaxies have been in place for a significant time. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program GO9458.

Faria, Daniel; Johnson, Rachel A.; Ferguson, Annette M. N.; Irwin, Mike J.; Ibata, Rodrigo A.; Johnston, Kathryn V.; Lewis, Geraint F.; Tanvir, Nial R.

2007-04-01

381

HOMOGENEOUS UGRIZ PHOTOMETRY FOR ACS VIRGO CLUSTER SURVEY GALAXIES: A NON-PARAMETRIC ANALYSIS FROM SDSS IMAGING  

SciTech Connect

We present photometric and structural parameters for 100 ACS Virgo Cluster Survey (ACSVCS) galaxies based on homogeneous, multi-wavelength (ugriz), wide-field SDSS (DR5) imaging. These early-type galaxies, which trace out the red sequence in the Virgo Cluster, span a factor of nearly {approx}10{sup 3} in g-band luminosity. We describe an automated pipeline that generates background-subtracted mosaic images, masks field sources and measures mean shapes, total magnitudes, effective radii, and effective surface brightnesses using a model-independent approach. A parametric analysis of the surface brightness profiles is also carried out to obtain Sersic-based structural parameters and mean galaxy colors. We compare the galaxy parameters to those in the literature, including those from the ACSVCS, finding good agreement in most cases, although the sizes of the brightest, and most extended, galaxies are found to be most uncertain and model dependent. Our photometry provides an external measurement of the random errors on total magnitudes from the widely used Virgo Cluster Catalog, which we estimate to be {sigma}(B{sub T}){approx} 0.13 mag for the brightest galaxies, rising to {approx} 0.3 mag for galaxies at the faint end of our sample (B{sub T} {approx} 16). The distribution of axial ratios of low-mass ('dwarf') galaxies bears a strong resemblance to the one observed for the higher-mass ('giant') galaxies. The global structural parameters for the full galaxy sample-profile shape, effective radius, and mean surface brightness-are found to vary smoothly and systematically as a function of luminosity, with unmistakable evidence for changes in structural homology along the red sequence. As noted in previous studies, the ugriz galaxy colors show a nonlinear but smooth variation over a {approx}7 mag range in absolute magnitude, with an enhanced scatter for the faintest systems that is likely the signature of their more diverse star formation histories.

Chen, Chin-Wei [Graduate Institute of Astronomy, National Central University, No. 300 Jungda Road, Taoyuan 32054, Taiwan (China); Cote, Patrick; Ferrarese, Laura [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Ave., Boston, MA 02215 (United States); Peng, Eric W., E-mail: cwchen2014@gmail.co [Department of Astronomy, Peking University, Beijing 100871 (China)

2010-11-15

382

Joint searches for gravitational waves and high-energy neutrinos with the ANTARES, LIGO and VIRGO detectors  

NASA Astrophysics Data System (ADS)

Cataclysmic cosmic events can be plausible sources of both gravitational waves (GW) and high-energy neutrinos (HEN). Both GW and HEN are alternative cosmic messengers that may escape very dense media and travel unaffected over cosmological distances. For this reason, they could also reveal new or hidden sources that were not observed by conventional photon astronomy, such as the putative failed GRBs. After a brief discussion on the plausible common sources of GW and HEN, this constribution presents the strategies for coincident searches of GW and HEN that are currently developed by the ANTARES and VIRGO/LIGO collaborations within the GWHEN working group.

van Elewyck, V.

2010-12-01

383

STELLAR WIND INFLUENCE ON PLANETARY DYNAMOS  

SciTech Connect

We examine the possible influence of early stellar wind conditions on the evolution of planetary dynamo action. In our model, the dynamo operates within a significant ambient magnetospheric magnetic field generated by the interaction between the stellar wind and the planetary magnetic field. This provides a negative feedback mechanism which quenches the dynamo growth. The external magnetic field magnitude which the dynamo experiences, and thus the strength of the quenching, depends on the stellar wind dynamic pressure. As this pressure significantly changes during stellar evolution, we argue that under early stellar system conditions the coupling between the stellar wind and the interior dynamics of a planet is much more important than has been thought up to now. We demonstrate the effects of the feedback coupling in the course of stellar evolution with a planet at a similar distance to the central star as Mercury is to the Sun.

Heyner, Daniel; Glassmeier, Karl-Heinz [Institut fuer Geophysik und extraterrestrische Physik, Technische Universitaet Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig (Germany); Schmitt, Dieter [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau (Germany)

2012-05-10

384

Search for gravitational waves from LIGO-Virgo science run and data interpretation  

NASA Astrophysics Data System (ADS)

Search for gravitational wave events was performed on data jointly taken during LIGO's fifth science run (S5) and Virgo's first science mn (VSR1). The data taken during this period was broken down into five separate months. I shall report the analysis performed on one of these months. Apart from the search, I shall describe the work related to estimation of rate based on the loudest event in the search. I shall demonstrate methods used in construction of rate intervals at 90% confidence level and combination of rates from multiple experiments of similar duration. To have confidence in our detection, accurate estimation of false alarm probability (F.A.P.) associated with the event candidate is required. Current false alarm estimation techniques limit our ability to measure the F.A.P. to about 1 in 100. I shall describe a method that significantly improves this estimate using information from multiple detectors. Besides accurate knowledge of F.A.P., detection is also dependent on our ability to distinguish real signals to those from noise. Several tests exist which use the quality of the signal to differentiate between real and noise signal. The chi-square test is one such computationally expensive test applied in our search; we shall understand the dependence of the chi-square parameter on the signal to noise ratio (SNR) for a given signal, which will help us to model the chi-square parameter based on SNR. The two detectors at Hanford, WA, H1(4km) and H2(2km), share the same vacuum system and hence their noise is correlated. Our present method of background estimation cannot capture this correlation and often underestimates the background when only H1 and H2 are operating. I shall describe a novel method of time reversed filtering to correctly estimate the background.

Biswas, Rahul

385

Spectral Solar Irradiance over Solar Cycle 23 from Sunphotometers of VIRGO on SOHO (Invited)  

NASA Astrophysics Data System (ADS)

Within the VIRGO experiment on SOHO two 3-channel sunphotometers (SPM) measure solar spectral irradiance at 402, 500 and 862 nm with a bandwidth (FWHM) of 5 nm. The time series cover the period from April 1996 until present, more than 14 years and a full solar cycle from the minimum in 1996 to the one in late 2008. SPMA measures the irradiance continuously with a 1-minute sampling and after being exposed to the sun during more than 14 years the sensitivities of the red, green and blue channels are at 74.1, 24.3 and 7.1 percent of their first light values, respectively. SPMB, is exposed rarely and is used to monitor degradation; the result of a detailed analysis of these data can then be used to correct SPMA for long-term changes and degradation effects. These are determined by a degradation model and the result shows that the changes due to exposure to the sun depend not only on the exposure time and the cumulated dose of radiation received, but also on the temperature of the instrument (Boltzmann factor). This indicates that simple degradation corrections by e.g. fitting multi-degree polynomials may not be adequate. The result of this detailed analysis are reliable time series of solar spectral irradiance at the three wavelengths. The results confirm the positive correlation of all three channels with solar activity and TSI, which is in contrast to the results from SIM on SORCE - at least for the green channel. A possible long-term trend of the spectral irradiance is also discussed in comparison with the behaviour of total solar irradiance (TSI).

Frohlich, C.

2010-12-01

386

Gemini/GMOS imaging of globular clusters in the Virgo galaxy NGC 4649 (M60)  

NASA Astrophysics Data System (ADS)

We present Sloan g and i imaging from the Gemini Multi-object Spectrograph (GMOS) instrument on the Gemini North telescope for the globular cluster (GC) system around the Virgo galaxy NGC 4649 (M60). Our three pointings, taken in good seeing conditions, cover an area of about 90 square arcmin. We detect 2151 unresolved sources. Applying colour and magnitude selection criteria to this source list gives 995 candidate GCs. Our source list is greater than 90 per cent complete to a magnitude of i= 23.6, and has little contamination from background galaxies. We find fewer than half a dozen potential ultracompact dwarf galaxies around NGC 4649. Foreground extinction from the nearby spiral NGC 4647 is limited to be AV < 0.1. We confirm the bimodality in the GC colour distribution found by earlier work using Hubble Space Telescope/WFPC2 imaging. As is commonly seen in other galaxies, the red GCs are concentrated towards the centre of the galaxy, having a steeper number density profile than the blue GC subpopulation. The varying ratio of red-to-blue GCs with radius can largely explain the overall GC system colour gradient. The underlying galaxy starlight has a similar density profile slope and colour to the red GCs. This suggests a direct connection between the galaxy field stars and the red GC subpopulation. We estimate a total GC population of 3700 +/- 900, with the uncertainty dominated by the extrapolation to larger radii than observed. This total number corresponds to a specific frequency SN= 4.1 +/- 1.0. Future work will present properties derived from GMOS spectra of the NGC 4649 GCs.

Forbes, Duncan A.; Faifer, Favio Raúl; Forte, Juan Carlos; Bridges, Terry; Beasley, Michael A.; Gebhardt, Karl; Hanes, David A.; Sharples, Ray; Zepf, Stephen E.