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1

The Origin of the Virgo Stellar Substructure  

NASA Astrophysics Data System (ADS)

We present three-dimensional space velocities of stars selected to be consistent with membership in the Virgo stellar substructure. Candidates were selected from SA 103, a single 40' × 40' field from our proper-motion (PM) survey in Kapteyn's Selected Areas (SAs), based on the PMs, Sloan Digital Sky Survey (SDSS) photometry, and follow-up spectroscopy of 215 stars. The signature of the Virgo substructure is clear in the SDSS color-magnitude diagram (CMD) centered on SA 103, and 16 stars are identified that have high Galactocentric-frame radial velocities (V GSR > 50 km s-1) and lie near the CMD locus of Virgo. The implied distance to the Virgo substructure from the candidates is 14 ± 3 kpc. We derive mean kinematics from these 16 stars, finding a radial velocity V GSR = 153 ± 22 km s-1 and proper motions (??cos ?, ??) = (- 5.24, -0.91) ± (0.43, 0.46) mas yr-1. From the mean kinematics of these members, we determine that the Virgo progenitor was on an eccentric (e ~ 0.8) orbit that recently passed near the Galactic center (pericentric distance Rp ~ 6 kpc). This destructive orbit is consistent with the idea that the substructure(s) in Virgo originated in the tidal disruption of a Milky Way satellite. N-body simulations suggest that the entire cloud-like Virgo substructure (encompassing the "Virgo Overdensity" and the "Virgo Stellar Stream") is likely the tidal debris remnant from a recently disrupted massive (~109 M ?) dwarf galaxy. The model also suggests that some other known stellar overdensities in the Milky Way halo (e.g., the Pisces Overdensity and debris near NGC 2419 and SEGUE 1) are explained by the disruption of the Virgo progenitor.

Carlin, Jeffrey L.; Yam, William; Casetti-Dinescu, Dana I.; Willett, Benjamin A.; Newberg, Heidi J.; Majewski, Steven R.; Girard, Terrence M.

2012-07-01

2

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

3

Probing Kinematic Substructures in the Virgo Overdensity using RR Lyrae from Recent Surveys  

NASA Astrophysics Data System (ADS)

The Virgo Overdensity is one of the most intriguing features of the galactic halo, as it covers a large portion of the sky and seems to contain several kinematic substructures. It has been suggested that the remnants of several merger events coexist in this region. RR Lyrae stars are an excellent tracer for disentangling the different components of this overdensity, since they are excellent standard candles; by using both positions and pulsation-corrected radial velocities, we can identify distinct groups in phase space. In the last year, several surveys for RR Lyraes covering the Virgo region have become publicly available. We present analysis of ~300 spectra for ~200 stars in the Virgo overdensity region. This is a significant increase in the known sample of these stars in the region, spanning a significantly larger area of the sky than previous studies. Photometry for these data are taken primarily from the La Silla and Venezuela QUEST variability surveys with spectra provided by SDSS Data Release 10. Radial velocities for type ab RR Lyrae stars are corrected using the new set of template radial velocity curves for Balmer and metallic lines given by Sesar (2012). We combine data from QUEST, the Catalina Sky Survey, LINEAR, and spectroscopic observations from Duffau (2014) to give our full sample. A preliminary analysis reveals confirmation for several known stellar streams.

Farmer, John; Vivas, A. Katherina

2015-01-01

4

The Stellar Populations of the M31 Halo Substructure  

Microsoft Academic Search

We present the first results from our survey of stellar substructure in the outskirts of M31 using the Advanced Camera for Surveys on board the Hubble Space Telescope. We discuss the stellar populations associated with five prominent stellar overdensities discovered during the course of our panoramic ground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera; a sixth pointing targets

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

2005-01-01

5

The Stellar Populations of M31 Halo Substructure  

Microsoft Academic Search

We present the first results from our survey of stellar substructure in the\\u000aoutskirts of M31 using the Advanced Camera for Surveys (ACS) on board the\\u000aHubble Space Telescope. We discuss the stellar populations associated with five\\u000aprominent stellar overdensities discovered during the course of our panoramic\\u000aground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera\\u000a(INT WFC); a

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

2005-01-01

6

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

7

The Stellar Populations of M31 Halo Substructure  

E-print Network

We present the first results from our survey of stellar substructure in the outskirts of M31 using the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We discuss the stellar populations associated with five prominent stellar overdensities discovered during the course of our panoramic ground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera (INT WFC); a sixth pointing targets a region of `clean' halo. The colour-magnitude diagrams (CMDs), which contain between ~10,000--90,000 stars and reach four magnitudes below the horizontal branch, reveal clear variations in morphology between most fields, indicating that the age and/or metallicity mix of stars is not constant at large radius. This directly confirms the existence of large-scale population inhomogeneities within the halo of M31 and lends further support to the notion that M31 has formed, at least in part, through satellite accretions. We find a striking similarity between the populations of the giant stellar stream and those of another overdensity, the NE shelf, which lies north-east of the galaxy center. If these overdensities are associated with the same population, then the difference in their red clump magnitudes implies the NE shelf lies in front of the stream by several tens of kpc, in good agreement with recent orbit calculations for the stream progenitor.

Annette Ferguson; Rachel Johnson; Daniel Faria; Mike Irwin; Rodrigo Ibata; Kathryn Johnston; Geraint Lewis; Nial Tanvir

2005-01-24

8

Search for Stellar Sub-Structure in the Galactic Bulge  

NASA Astrophysics Data System (ADS)

We propose to acquire spectra of ~350 M giants in two Galactic bulge fields that show evidence for candidate cold stream features. Our fields are selected from the Bulge Radial Velocity Assay (BRAVA) and show clear departures from normality in their stellar velocity distribution. The number of stars observed by BRAVA in each field (~100) is insufficient to allow a concrete detection of substructure, and we require subsequent observations to increase our sample size. Of the 87 BRAVA fields that cover the southern Galactic bulge, only these two fields show signs of deviations from a normal distribution in velocity space. Therefore both confirming or refuting the presence of a stream in these fields will place limits on the detection of cold streams from fossil infall events in the BRAVA database.

Kunder, Andrea; Rich, R. Michael; De Propris, Roberto; Koch, Andreas; Johnson, Christian I.

2012-08-01

9

The Stellar Populations of the M31 Halo Substructure  

NASA Astrophysics Data System (ADS)

We present the first results from our survey of stellar substructure in the outskirts of M31 using the Advanced Camera for Surveys on board the Hubble Space Telescope. We discuss the stellar populations associated with five prominent stellar overdensities discovered during the course of our panoramic ground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera; a sixth pointing targets a region of ``clean'' halo. The color-magnitude diagrams, which contain between ~10,000 and 90,000 stars and reach 4 mag below the horizontal branch, reveal clear variations in morphology between most fields, indicating that the age and/or metallicity mix of stars is not constant at large radius. This directly confirms the existence of large-scale population inhomogeneities within the halo of M31 and lends further support to the notion that M31 has formed, at least in part, through satellite accretions. We find a striking similarity between the populations of the giant stellar stream and those of another overdensity, the NE shelf, which lies northeast of the galaxy center. If these overdensities are associated with the same population, then the difference in their red clump magnitudes implies that the NE shelf lies in front of the stream by several tens of kiloparsecs, in good agreement with recent orbit calculations for the stream progenitor. 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 NAS 5-26555. These observations are associated with program GO9458.

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

2005-04-01

10

Evidence for Stellar Substructure in the Halo and Outer Disk of M31  

Microsoft Academic Search

We report the discovery of significant stellar substructure in the halo and\\u000aouter disk of our nearest large galactic neighbour, M31. Our deep panoramic\\u000asurvey with the Isaac Newton Telescope Wide Field Camera currently maps out an\\u000aarea of ~25 square degrees around M31, extending along the semi-major axis to\\u000a55 kpc, and is the first to allow an uninterrupted

Annette M. N. Ferguson; Michael J. Irwin; Rodrigo A. Ibata; Geraint F. Lewis; Nial R. Tanvir

2002-01-01

11

Integral-field Stellar and Ionized Gas Kinematics of Peculiar Virgo Cluster Spiral Galaxies  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

12

PROPER MOTIONS IN KAPTEYN SELECTED AREA 103: A PRELIMINARY ORBIT FOR THE VIRGO STELLAR STREAM  

SciTech Connect

We present absolute proper motions in Kapteyn Selected Area (SA) 103. This field is located 7 deg. west of the center of the Virgo Stellar Stream (VSS), and has a well-defined main sequence representing the stream. In SA 103, we identify one RR Lyrae star as a member of the VSS, according to its metallicity, radial velocity, and distance. VSS candidate turnoff and subgiant stars have proper motions consistent with that of the RR Lyrae star. The three-dimensional velocity data imply an orbit with a pericenter of {approx}11 kpc and an apocenter of {approx}90 kpc. Thus, the VSS comprises tidal debris found near the pericenter of a highly destructive orbit. Examining the six globular clusters at distances larger than 50 kpc from the Galactic center, and the proposed orbit of the VSS, we find one tentative association, NGC 2419. We speculate that NGC 2419 is possibly the nucleus of a disrupted system of which the VSS is a part.

Casetti-Dinescu, Dana I.; Girard, Terrence M.; Van Altena, William F. [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Majewski, Steven R.; Carlin, Jeffrey L. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Vivas, A. Katherina [Centro de Investigaciones de Astronomia (CIDA), Apartado Postal 264, Merida 5101-A (Venezuela, Bolivarian Republic of); Wilhelm, Ronald [Department of Physics, Texas Tech University, Lubbock, TX 79409 (United States); Beers, Timothy C. [Department of Physics and Astronomy, Center for the Study of Cosmic Evolution (CSCE), and Joint Institution for Nuclear Astrophysics (JINA), Michigan State University, East Lansing, MI 48824 (United States)

2009-08-10

13

Tidal Stripping Stellar Substructures Around Four Metal-Poor Globular Clusters in the Galactic Bulge  

NASA Astrophysics Data System (ADS)

We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color-magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok; Sohn, Young-Jong

2015-01-01

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

Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project  

NASA Astrophysics Data System (ADS)

We analyze the stellar kinematics of 39 dwarf early-type galaxies (dEs) in the Virgo cluster. This is the largest survey conducted so far on spatially resolved kinematics of dEs. This sample is representative of the early-type population in the absolute magnitude range -19.0 < M_r < -16.0. For each dE, we measure the rotation curve and velocity dispersion profile and fit an analytic function to the rotation curve. We study the significance of the departure of the rotation curve from the best fit analytic function (poorly fit) and of the difference between the approaching and receding sides of the rotation curve (asymmetry). We find that 62+/-8% (23 out of the 39) of the dEs have a significant anomaly in their rotation curve. Analysis of the images reveals photometric anomalies for most galaxies. However, there is no clear correlation between the significance of the photometric and kinematic anomalies. Based on the specific stellar angular momentum and the ellipticity, we find 11 slow rotators and 28 fast rotators. The fast rotators in the outer parts of the Virgo cluster rotate significantly faster than fast rotators in the inner parts of the cluster. Moreover, 10 out of the 11 slow rotators are located in the inner Mpc of the cluster. The fast rotators contain subtle disky structures that are visible in high-pass filtered optical images, while the slow rotators do not exhibit these structures. In addition, two of the dEs have kinematically decoupled cores and four more have emission partially filling in the Balmer absorption lines. These properties suggest that Virgo cluster dEs may have originated from late-type star-forming galaxies that were transformed by the environment after their infall into the cluster. The correlation between the specific angular momentum and the clustercentric distance can be explained by a scenario where low luminosity star-forming galaxies fall into the cluster, their gas is rapidly removed by ram pressure stripping, although some of it can be retained in their core, their star-formation is quenched but their stellar kinematics are preserved. After a long time in the cluster and several passes through its center, the galaxies are heated up and transformed into slow rotating dEs.

Toloba, Elisa; Guhathakurta, Puragra; Peletier, Reynier; Boselli, Alessandro; Lisker, Thorsten; Emsellem, Eric; Simon, Joshua D.; van de Ven, Glenn; Smakced Collaboration

2015-01-01

16

Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. III. Angular Momentum and Constraints on Formation Scenarios  

NASA Astrophysics Data System (ADS)

We analyze the stellar kinematics of 39 dwarf early-type galaxies (dEs) in the Virgo Cluster. Based on the specific stellar angular momentum ?Re and the ellipticity, we find 11 slow rotators and 28 fast rotators. The fast rotators in the outer parts of the Virgo Cluster rotate significantly faster than fast rotators in the inner parts of the cluster. Moreover, 10 out of the 11 slow rotators are located in the inner 3° (D < 1 Mpc) of the cluster. The fast rotators contain subtle disk-like structures that are visible in high-pass filtered optical images, while the slow rotators do not exhibit these structures. In addition, two of the dEs have kinematically decoupled cores and four more have emission partially filling in the Balmer absorption lines. These properties suggest that Virgo Cluster dEs may have originated from late-type star-forming galaxies that were transformed by the environment after their infall into the cluster. The correlation between ?Re and the clustercentric distance can be explained by a scenario where low luminosity star-forming galaxies fall into the cluster, their gas is rapidly removed by ram-pressure stripping, although some of it can be retained in their core, their star formation is quenched but their stellar kinematics are preserved. After a long time in the cluster and several passes through its center, the galaxies are heated up and transformed into slow rotating dEs.

Toloba, E.; Guhathakurta, P.; Boselli, A.; Peletier, R. F.; Emsellem, E.; Lisker, T.; van de Ven, G.; Simon, J. D.; Falcón-Barroso, J.; Adams, J. J.; Benson, A. J.; Boissier, S.; den Brok, M.; Gorgas, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Paudel, S.; Ry?, A.; Salo, H.

2015-02-01

17

The outer regions of the giant Virgo galaxy M87 II. Kinematic separation of stellar halo and intracluster light  

E-print Network

We present a spectroscopic study of 287 Planetary Nebulas (PNs) in a total area of ~0.4 deg^2 around the BCG M87 in Virgo A. With these data we can distinguish the stellar halo from the co-spatial intracluster light (ICL). PNs were identified from their narrow and symmetric redshifted lambda 5007\\4959 Angstrom [OIII] emission lines, and the absence of significant continuum. We implement a robust technique to measure the halo velocity dispersion from the projected phase-space to identify PNs associated with the M87 halo and ICL. The velocity distribution of the spectroscopically confirmed PNs is bimodal, containing a narrow component centred on the systemic velocity of the BCG and an off-centred broader component, that we identify as halo and ICL, respectively. Halo and ICPN have different spatial distributions: the halo PNs follow the galaxy's light, whereas the ICPNs are characterised by a shallower power-law profile. The composite PN number density profile shows the superposition of different PN populations...

Longobardi, Alessia; Gerhard, Ortwin; Hanuschik, Reinhard

2015-01-01

18

CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS  

SciTech Connect

Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

Craig, Jonathan; Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2013-06-01

19

The Nature and Origin of Substructure in the Outskirts of M31. I. Surveying the Stellar Content with the Hubble Space Telescope Advanced Camera for Surveys  

Microsoft Academic Search

We present the largest and most detailed survey to date of the stellar populations in the outskirts of M31 based on the homogeneous analysis of 14 deep Hubble Space Telescope Advanced Camera for Surveys (HST\\/ACS) pointings spanning the range 11.5 kpc lsim R proj lsim 45 kpc. Many of these pointings sample coherent substructure discovered in the course of the

J. C. Richardson; A. M. N. Ferguson; R. A. Johnson; M. J. Irwin; N. R. Tanvir; D. C. Faria; R. A. Ibata; K. V. Johnston; G. F. Lewis; A. W. McConnachie; S. C. Chapman

2008-01-01

20

Stellar substructures in the solar neighbourhood. III. Kinematic group 2 in the Geneva-Copenhagen survey  

NASA Astrophysics Data System (ADS)

Context. From correlations between orbital parameters, several new coherent groups of stars were recently identified in the Galactic disc and suggested to correspond to remnants of disrupted satellites. To reconstruct their origin at least three main observational parameters - kinematics, chemical composition and age - must be known. Aims: We determine detailed elemental abundances in stars belonging to the so-called Group 2 of the Geneva-Copenhagen Survey and compare the chemical composition with Galactic thin- and thick-disc stars, as well as with the Arcturus and AF06 streams (Arifyanto & Fuchs 2006, A&A, 449, 533). The aim is to search for chemical signatures that might give information about the formation 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 were 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 32 stars of Group 2 is - 0.42 ± 0.10 dex. The investigated group consists mainly of two 8- and 12-Gyr-old stellar populations. Abundances of oxygen, ?-elements, and r-process-dominated elements are higher than in Galactic thin-disc dwarfs. This elemental abundance pattern has similar characteristics as that of the Galactic thick-disc. Conclusions: The similarity in chemical composition of stars in Group 2 with that in stars of the thick-disc might suggest that their formation histories are linked. The chemical composition together with the kinematic properties and ages of stars in the stars investigated provides evidence of their common origin and possible relation to an ancient merging event. A gas-rich satellite merger scenario is proposed as the most likely origin. Groups 2 and 3 of the Geneva-Copenhagen Survey might have originated in the same merging event. Tables 4 and 5 are available in electronic form at http://www.aanda.org

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

2014-03-01

21

Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters  

NASA Astrophysics Data System (ADS)

We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

Toloba, E.; Guhathakurta, P.; van de Ven, G.; Boissier, S.; Boselli, A.; den Brok, M.; Falcón-Barroso, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Lisker, T.; Paudel, S.; Peletier, R. F.; Ry?, A.; Salo, H.

2014-03-01

22

Keck spectroscopy and NGVS photometry in the direction of the Virgo cluster: Globular cluster satellites of dwarf ellipticals, Milky Way halo substructure, and large-scale structure in the background  

NASA Astrophysics Data System (ADS)

The Virgo cluster, the nearest large galaxy cluster, is a rich repository of dwarf elliptical (dE) galaxies. The formation mechanism of dE galaxies remains the subject of much debate. Dwarf galaxies in general are believed to be building blocks in the hierarchical growth of galaxies as per the “cold dark matter” model of structure formation. Globular cluster (GC) satellites serve as important tracers of dark matter in the outer regions of dEs (beyond 1 half-light radius). This project presents new spectroscopic data from Keck's DEIMOS, which specifically targeted low-luminosity (-17 < Mv < -15) dEs and GC satellites, in the Virgo cluster. These data are among the deepest spectroscopic data ever taken in this region. Secondary science targets - Milky Way foreground stars and galaxies in the background - are also discussed. All targets were chosen based on photometric data from the Next Generation Virgo Survey (NGVS) and the Advanced Camera for Surveys Virgo Cluster Survey (ACSVCS). Further, these two surveys were critical to the tomographic analysis of spectroscopic targets. From this analysis we were able to: identify 117 GCs associated with any one of the 21 dE targets in the Virgo cluster, identify Milky Way foreground stars as part of the Virgo Overdensity or Sagittarius streams, quantify the velocity structure of these ongoing cannibalism events, and identify two new superclusters of galaxies in the background using redshift distribution. This research was carried out under the auspices of UCSC's Science Internship Program. We thank the National Science Foundation for funding support. ET was supported by a Fulbright fellowship.

Muller, Meredith; Toloba, E.; Guhathakurta, P.; Yagati, S.; Chen, J.; Cote, P.; Dorman, C.; Ferrarese, L.; Peng, E. W.; Next Generation Virgo Cluster Survey Collaboration

2014-01-01

23

The Nature and Origin of Substructure in the Outskirts of M31. I. Surveying the Stellar Content with the Hubble Space Telescope Advanced Camera for Surveys  

NASA Astrophysics Data System (ADS)

We present the largest and most detailed survey to date of the stellar populations in the outskirts of M31 based on the homogeneous analysis of 14 deep Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) pointings spanning the range 11.5 kpc lsim R proj lsim 45 kpc. Many of these pointings sample coherent substructure discovered in the course of the Isaac Newton Telescope Wide Field Camera (INT/WFC) imaging survey of M31 while others sample more diffuse structure in the extended disk. We conduct a quantitative comparison of the resolved stellar populations in these fields and identify several striking trends. The color-magnitude diagrams (CMDs), which reach gsim3 mag below the red clump with high completeness, can be classified into two main categories based on their morphologies. "Stream-like" fields, so named for their similarity to the CMD of the giant stellar stream, are characterized by a red clump that slants blueward at fainter magnitudes and an extended horizontal branch. They show no evidence for young populations. On the other hand, "disk-like" fields exhibit rounder red clumps with significant luminosity width, lack an obvious horizontal branch, and show evidence for recent star formation (~0.25-2 Gyr ago). We compare the spatial and line-of-sight distribution of stream-like fields with a recent simulation of the giant stream progenitor orbit and find an excellent agreement. These fields are found across much of the inner halo of M31, and attest to the high degree of pollution caused by this event. Disk-like material resides in the extended disk structure of M31 and is detected here up to R proj ~ 44 kpc; the uniform populations in these fields, including the ubiquitous presence of young populations, and the strong rotation reported elsewhere are most consistent with a scenario in which this structure has formed through heating and disruption of the existing thin disk, perhaps due to the impact of the giant stream progenitor. Our comparative analysis sheds new light on the likely composition of two of the ultra-deep pointings formerly presented as pure outer disk and pure halo in the literature. 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 NAS 5-26555.

Richardson, J. C.; Ferguson, A. M. N.; Johnson, R. A.; Irwin, M. J.; Tanvir, N. R.; Faria, D. C.; Ibata, R. A.; Johnston, K. V.; Lewis, G. F.; McConnachie, A. W.; Chapman, S. C.

2008-06-01

24

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

25

UPDATE ON THE NATURE OF VIRGO OVERDENSITY  

SciTech Connect

We use the Eighth Data Release of Sloan Digital Sky Survey catalog with its additional sky coverage of the southern Galactic hemisphere to measure the extent and to study the nature of the Virgo Overdensity (VOD). The data show that the VOD extends over no less than 2000 deg{sup 2}, with its true extent likely closer to 3000 deg{sup 2}. We test whether the VOD can be attributed to a tilt in the stellar halo ellipsoid with respect to the plane of the Galactic disk and find that the observed symmetry of the north-south Galactic hemisphere star counts excludes this possibility. We argue that the Virgo Overdensity, in spite of its wide area and cloud-like appearance, is still best explained by a minor merger. Its appearance and position are qualitatively similar to a near perigalacticon merger event and, assuming that the VOD and the Virgo Stellar Stream (VSS) share the same progenitor, consistent with the VSS orbit determined by Casetti-Dinescu et al.

Bonaca, Ana [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Juric, Mario [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Ivezic, Zeljko [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Bizyaev, Dmitry; Brewington, Howard; Malanushenko, Elena; Malanushenko, Viktor; Oravetz, Daniel; Pan, Kaike; Shelden, Alaina; Simmons, Audrey; Snedden, Stephanie, E-mail: ana.bonaca@yale.edu, E-mail: mjuric@cfa.harvard.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349 (United States)

2012-05-15

26

Signatures of LCDM substructure in tidal debris  

E-print Network

In the past decade, surveys of the stellar component of the Galaxy have revealed a number of streams from tidally disrupted dwarf galaxies and globular clusters. Simulations of hierarchical structure formation in LCDM cosmologies predict that the dark matter halo of a galaxy like the Milky Way contains hundreds of subhalos with masses of ~10^8 solar masses and greater, and it has been suggested that the existence of coherent tidal streams is incompatible with the expected abundance of substructure. We investigate the effects of dark matter substructure on tidal streams by simulating the disruption of a self-gravitating satellite on a wide range of orbits in different host models both with and without substructure. We find that the halo shape and the specific orbital path more strongly determine the overall degree of disruption of the satellite than does the presence or absence of substructure, i.e., the changes in the large-scale properties of the tidal debris due to substructure are small compared to variations in the debris from different orbits in a smooth potential. Substructure typically leads to an increase in the degree of clumpiness of the tidal debris in sky projection, and in some cases a more compact distribution in line-of-sight velocity. Substructure also leads to differences in the location of sections of debris compared to the results of the smooth halo model, which may have important implications for the interpretation of observed tidal streams. A unique signature of the presence of substructure in the halo which may be detectable by upcoming surveys is identified. We conclude, however, that predicted levels of substructure are consistent with a detection of a coherent tidal stream from a dwarf galaxy.

Jennifer M. Siegal-Gaskins; Monica Valluri

2007-10-01

27

Jet substructure in ATLAS  

E-print Network

Measurements are presented of the jet invariant mass and substructure in proton-proton collisions at sqrt{s} = 7 TeV with the ATLAS detector using an integrated luminosity of 37 pb-1. These results exercise the tools for distinguishing the signatures of new boosted massive particles in the hadronic final state. Two "fat" jet algorithms are used, along with the filtering jet grooming technique that was pioneered in ATLAS. New jet substructure observables are compared for the first time to data at the LHC. Finally, a sample of candidate boosted top quark events collected in the 2010 data is analyzed in detail for the jet substructure properties of hadronic "top-jets" in the final state. These measurements demonstrate not only our excellent understanding of QCD in a new energy regime but open the path to using complex jet substructure observables in the search for new physics.

David W. Miller; for the ATLAS Collaboration

2011-10-05

28

Jet Substructure Without Trees  

SciTech Connect

We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods. In preparation for the LHC, the past several years have seen extensive work on various aspects of collider searches. With the excellent resolution of the ATLAS and CMS detectors as a catalyst, one area that has undergone significant development is jet substructure physics. The use of jet substructure techniques, which probe the fine-grained details of how energy is distributed in jets, has two broad goals. First, measuring more than just the bulk properties of jets allows for additional probes of QCD. For example, jet substructure measurements can be compared against precision perturbative QCD calculations or used to tune Monte Carlo event generators. Second, jet substructure allows for additional handles in event discrimination. These handles could play an important role at the LHC in discriminating between signal and background events in a wide variety of particle searches. For example, Monte Carlo studies indicate that jet substructure techniques allow for efficient reconstruction of boosted heavy objects such as the W{sup {+-}} and Z{sup 0} gauge bosons, the top quark, and the Higgs boson.

Jankowiak, Martin; Larkoski, Andrew J.; /SLAC /Stanford U., ITP

2011-08-19

29

Defining Spatial Extent of Sagittarius Dwarf Tidal Stream and the Virgo Overdensity with MilkyWay@home  

NASA Astrophysics Data System (ADS)

We refine and present tests of the statistical photometric parallax methods used to measure substructure of the halo stars with MilkyWay@home. This newer algorithm is showing promise for separating three substructure components, including the two parts of the bifurcated Sagittarius tidal stream and the Virgo Overdensity, while also fitting a smooth background component simultaneously. We show that the Sagittarius tidal streams and the Virgo Overdensity are much wider than previously imagined. We present the new results in the context of previous measurements of the properties of these halo substructures. This research was funded by NSF grant AST 10-09670, the Rensselaer Center for Open Source Software (RCOS), and crowd funding from the MilkyWay@home volunteers.

Weiss, Jake; Newby, Matthew; Arsenault, Matthew; Bechtel, Torrin; Desell, Travis; Newberg, Heidi Jo; Thompson, Jeffery

2015-01-01

30

Substructures in WINGS clusters  

E-print Network

We search for and characterize substructures in the projected distribution of galaxies observed in the wide field CCD images of the 77 nearby clusters of the WIde-field Nearby Galaxy-cluster Survey (WINGS). This sample is complete in X-ray flux in the redshift range 0.04substructures in WINGS clusters with DEDICA, an adaptive-kernel procedure. We test the procedure on Monte-Carlo simulations of the observed frames and determine the reliability for the detected structures. DEDICA identifies at least one reliable structure in the field of 55 clusters. 40 of these clusters have a total of 69 substructures at the same redshift of the cluster (redshift estimates of substructures are from color-magnitude diagrams). The fraction of clusters with subclusters (73%) is higher than in most studies. The presence of subclusters affects the relative luminosities of the brightest cluster galaxies (BCGs). Down to L ~ 10^11.2 L_Sun, our observed differential distribution of subcluster luminosities is consistent with the theoretical prediction of the differential mass function of substructures in cosmological simulations.

M. Ramella; A. Biviano; A. Pisani; J. Varela; D. Bettoni; W. J. Couch; M. D'Onofrio; A. Dressler; G. Fasano; P. Kjaergaard; M. Moles; E. Pignatelli; B. M. Poggianti

2007-04-04

31

Jet Substructure by Accident  

E-print Network

We propose a new search strategy for high-multiplicity hadronic final states. When new particles are produced at threshold, the distribution of their decay products is approximately isotropic. If there are many partons in the final state, it is likely that several will be clustered into the same large-radius jet. The resulting jet exhibits substructure, even though the parent states are not boosted. This "accidental" substructure is a powerful discriminant against background because it is more pronounced for high-multiplicity signals than for QCD multijets. We demonstrate how to take advantage of accidental substructure to reduce backgrounds without relying on the presence of missing energy. As an example, we present the expected limits for several R-parity violating gluino decay topologies. This approach allows for the determination of QCD backgrounds using data-driven methods, which is crucial for the feasibility of any search that targets signatures with many jets and suppressed missing energy.

Cohen, Timothy; Lisanti, Mariangela; Lou, Hou Keong

2012-01-01

32

The Purple Rose of Virgo  

NASA Astrophysics Data System (ADS)

Until now NGC 5584 was just one galaxy among many others, located to the West of the Virgo Cluster. Known only as a number in galaxy surveys, its sheer beauty is now revealed in all its glory in a new VLT image. Since 1 March, this purple cosmic rose also holds the brightest stellar explosion of the year, known as SN 2007af. Located about 75 million light years away towards the constellation Virgo ('the Virgin'), NGC 5584 is a galaxy slightly smaller than the Milky Way. It belongs, however, to the same category: both are barred spirals. ESO PR Photo 16/07 ESO PR Photo 16/07 The Purple Rose of Virgo Spiral galaxies are composed of a 'bulge' and a flat disc. The bulge hosts old stars and usually a central supermassive black hole. Younger stars reside in the disc, forming the characteristic spiral structures from which the galaxies get their name. Barred spirals are crossed by a bright band of stars. In 2000, using ESO's Very Large Telescope, astronomers discovered the smallest, faintest, and most massive spirals (see ESO PR 12/00 and 25/00). In this amazing new image of NGC 5584 two dominant spiral arms are clearly visible, while the others are deformed, probably due to interactions with other galaxies. Luminous patches are spread all over the disc, indicating that stars are being formed in this gigantic rose at a frantic pace. Something even brighter, however, catches the eye in this picture. Any image taken before the end of February would not have shown the luminous spot located at the lower right of the galaxy's centre. As can be seen, the newly found object is much brighter than the centre of the galaxy itself. Its name? SN 2007af, the 32nd supernova discovered this year. Its presence signals the dramatic death of a star with a mass comparable to that of the Sun. SN 2007af, the brightest supernova of the year (so far), was discovered on 1 March by the Japanese supernova hunter Koichi Itagaki. He pointed his 60-centimetre telescope towards the Virgo constellation and discovered something that was not there before: SN 2007af. When it was discovered, its brightness (apparent visible magnitude of 15.4) was about seven times fainter than that of its host galaxy, NGC 5584. It has since brightened by the same factor of 7, reaching an apparent magnitude of 13.3 and making it observable by many amateur astronomers with smaller telescopes. Observations on 4 March with ESO's New Technology Telescope at La Silla revealed that this energetic explosion is a Type Ia supernova that was observed a few days before it reached its maximal luminosity. Matter from the doomed star is ejected with velocities above 15,000 km/s. Astronomers are observing SN2007af with ESO's VLT, with the aim of studying the geometry of the material ejected by the supernova, and thereby better understanding the explosion mechanism (see also ESO 44/06). A Type Ia supernova is thought to be the result of the explosion of a small and dense star - a white dwarf - inside a binary system. As its companion continuously spills matter onto the white dwarf, the white dwarf reaches a critical mass, leading to a fatal instability and the supernova. Type Ia supernovae are apparently quite similar to one another. This gives them a very useful role as 'standard candles' that can be used to measure cosmic distances. Their peak brightness rivals that of their parent galaxy, hence qualifying them as prime cosmic yardsticks. Astronomers have exploited this fortunate circumstance to study the expansion history of our Universe. However Type Ia supernovae are rare events: a galaxy like the Milky Way may host a Type Ia supernova on average only every 400 years. Even so, SN 2007af is not the only brilliant detonation recently recorded in NGC 5584. Furthermore, it seems that Japanese amateur astronomers have a special talent for catching supernova explosions in this purple spiral. Indeed, in 1996 Aoki Masakatsu identified SN 1996aq in NGC 5584, a difficult to classify supernova subject to a hot discussion due to its ambiguous nature.

2007-03-01

33

Jet Substructure Without Trees  

E-print Network

We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods.

Martin Jankowiak; Andrew J. Larkoski

2011-06-30

34

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

35

The Extended Virgo Cluster Catalog  

NASA Astrophysics Data System (ADS)

We present a new catalog of galaxies in the wider region of the Virgo cluster, based on the Sloan Digital Sky Survey (SDSS) Data Release 7. The Extended Virgo Cluster Catalog (EVCC) covers an area of 725 deg2 or 60.1 Mpc2. It is 5.2 times larger than the footprint of the classical Virgo Cluster Catalog (VCC) and reaches out to 3.5 times the virial radius of the Virgo cluster. We selected 1324 spectroscopically targeted galaxies with radial velocities less than 3000 km s-1. In addition, 265 galaxies that have been overlooked in the SDSS spectroscopic survey but have available redshifts in the NASA Extragalactic Database are also included. Our selection process secured a total of 1589 galaxies, 676 of which are not included in the VCC. The certain and possible cluster members are defined by means of redshift comparison with a cluster infall model. We employed two independent and complementary galaxy classification schemes: the traditional morphological classification based on the visual inspection of optical images and a characterization of galaxies from their spectroscopic features. SDSS u, g, r, i, and z passband photometry of all EVCC galaxies was performed using Source Extractor. We compare the EVCC galaxies with the VCC in terms of morphology, spatial distribution, and luminosity function. The EVCC defines a comprehensive galaxy sample covering a wider range in galaxy density that is significantly different from the inner region of the Virgo cluster. It will be the foundation for forthcoming galaxy evolution studies in the extended Virgo cluster region, complementing ongoing and planned Virgo cluster surveys at various wavelengths.

Kim, Suk; Rey, Soo-Chang; Jerjen, Helmut; Lisker, Thorsten; Sung, Eon-Chang; Lee, Youngdae; Chung, Jiwon; Pak, Mina; Yi, Wonhyeong; Lee, Woong

2014-12-01

36

EXPLORING THE VARIABLE SKY WITH LINEAR. II. HALO STRUCTURE AND SUBSTRUCTURE TRACED BY RR LYRAE STARS TO 30 kpc  

SciTech Connect

We present a sample of {approx}5000 RR Lyrae stars selected from the recalibrated LINEAR data set and detected at heliocentric distances between 5 kpc and 30 kpc over {approx}8000 deg{sup 2} of sky. The coordinates and light curve properties, such as period and Oosterhoff type, are made publicly available. We analyze in detail the light curve properties and Galactic distribution of the subset of {approx}4000 type ab RR Lyrae (RRab) stars, including a search for new halo substructures and the number density distribution as a function of Oosterhoff type. We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type II and I subsamples of about 1:4, but with a weaker separation than for globular cluster stars. The wide sky coverage and depth of this sample allow unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance: it can be described as an oblate ellipsoid with an axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range -2 to -3. Consistent with previous studies, we find that the Oosterhoff type II subsample has a steeper number density profile than the Oosterhoff type I subsample. Using the group-finding algorithm EnLink, we detected seven candidate halo groups, only one of which is statistically spurious. Three of these groups are near globular clusters (M53/NGC 5053, M3, M13), and one is near a known halo substructure (Virgo Stellar Stream); the remaining three groups do not seem to be near any known halo substructures or globular clusters and seem to have a higher ratio of Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the halo. The extended morphology and the position (outside the tidal radius) of some of the groups near globular clusters are suggestive of tidal streams possibly originating from globular clusters. Spectroscopic follow-up of detected halo groups is encouraged.

Sesar, Branimir [Division of Physics, Mathematics and Astronomy, Caltech, Pasadena, CA 91125 (United States); Ivezic, Zeljko; Morgan, Dylan M.; Becker, Andrew C. [University of Washington, Department of Astronomy, P.O. Box 351580, Seattle, WA 98195-1580 (United States); Stuart, J. Scott [Lincoln Laboratory, Massachusetts Institute of Technology, 244 Wood Street, Lexington, MA 02420-9108 (United States); Sharma, Sanjib [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Palaversa, Lovro [Observatoire astronomique de l'Universite de Geneve, 51 chemin des Maillettes, CH-1290 Sauverny (Switzerland); Juric, Mario [Steward Observatory, University of Arizona, Tucson, AZ 85121 (United States); Wozniak, Przemyslaw [Los Alamos National Laboratory, 30 Bikini Atoll Rd., Los Alamos, NM 87545-0001 (United States); Oluseyi, Hakeem [Florida Institute of Technology, Melbourne, FL 32901 (United States)

2013-08-01

37

Exploring the Variable Sky with LINEAR. II. Halo Structure and Substructure Traced by RR Lyrae Stars to 30 kpc  

NASA Astrophysics Data System (ADS)

We present a sample of ~5000 RR Lyrae stars selected from the recalibrated LINEAR data set and detected at heliocentric distances between 5 kpc and 30 kpc over ~8000 deg2 of sky. The coordinates and light curve properties, such as period and Oosterhoff type, are made publicly available. We analyze in detail the light curve properties and Galactic distribution of the subset of ~4000 type ab RR Lyrae (RRab) stars, including a search for new halo substructures and the number density distribution as a function of Oosterhoff type. We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type II and I subsamples of about 1:4, but with a weaker separation than for globular cluster stars. The wide sky coverage and depth of this sample allow unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance: it can be described as an oblate ellipsoid with an axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range -2 to -3. Consistent with previous studies, we find that the Oosterhoff type II subsample has a steeper number density profile than the Oosterhoff type I subsample. Using the group-finding algorithm EnLink, we detected seven candidate halo groups, only one of which is statistically spurious. Three of these groups are near globular clusters (M53/NGC 5053, M3, M13), and one is near a known halo substructure (Virgo Stellar Stream); the remaining three groups do not seem to be near any known halo substructures or globular clusters and seem to have a higher ratio of Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the halo. The extended morphology and the position (outside the tidal radius) of some of the groups near globular clusters are suggestive of tidal streams possibly originating from globular clusters. Spectroscopic follow-up of detected halo groups is encouraged.

Sesar, Branimir; Ivezi?, Željko; Stuart, J. Scott; Morgan, Dylan M.; Becker, Andrew C.; Sharma, Sanjib; Palaversa, Lovro; Juri?, Mario; Wozniak, Przemyslaw; Oluseyi, Hakeem

2013-08-01

38

Searching the All-WISE Data Release for Galactic Substructures  

NASA Astrophysics Data System (ADS)

We examine the distribution of point sources in the All-WISE data release to search for evidence of undiscovered Galactic stellar debris streams. The All-WISE data release is significantly deeper than the previous WISE All-Sky release and in principle allows us to explore a considerably larger volume. We discuss some of the limitations of the data for studies of Galactic substructure.

Grillmair, Carl J.

2015-01-01

39

Populating the Virgo Velocity Function with Early-Type Galaxies at Gemini  

NASA Astrophysics Data System (ADS)

We propose to sample the circular velocity function (CVF) and stellar-to-halo mass relation (SHMR) of Virgo early-type galaxies (ETGs) in the stellar mass range M* = 10^(7-10) Msol. This proposal is part of a large effort to characterize the dynamical and stellar population properties of a representative sample of Virgo ETGs for which deep near-UV/optical/near-IR imaging exists. The proposed sample will significantly augment the crucial low-mass range below M* < 10^9 Msol, where the sharp LCDM predictions for the CVF and SHMR (abundance matching) are fully unconstrained due to significant incompleteness (0-20%) of current data bases. Numerous tantalizing trends, such as bifurcations and possible bimodalities of mass relations for ETGs and LTGs, may prove transformational for galaxy structure studies and must be confirmed with a study like ours. We seek GMOS absorption spectra of 35 faint ETGs for a total of 100 hours of Canadian, US, and Chilean Gemini time. Our program exploits synergies of the Gemini and VLT observatories and will deliver a benchmark dataset of lasting legacy value, building upon our large Virgo cluster team expertise.

Ouellette, Nathalie; Courteau, Stephane; Holtzman, Jon; Puzia, Thomas; Bovill, Mia; Cappellari, Michele; Cote, Patrick; Dalcanton, Julianne; Dutton, Aaron; Eigenthaler, Paul; Emsellem, Eric; Ferrarese, Laura; McDonald, Michael; Munoz, Roberto; Roediger, Joel; Tully, Brent

2014-02-01

40

Dark Matter Substructure within Galactic Halos  

Microsoft Academic Search

We use numerical simulations to examine the substructure within galactic and cluster mass halos that form within a hierarchical universe. Clusters are easily reproduced with a steep mass spectrum of thousands of substructure clumps that closely matches the observations. However, the survival of dark matter substructure also occurs on galactic scales, leading to the remarkable result that galaxy halos appear

Ben Moore; Sebastiano Ghigna; Fabio Governato; George Lake; Thomas Quinn; Joachim Stadel; Paolo Tozzi

1999-01-01

41

Characterization of the Virgo Seismic Environment  

E-print Network

The Virgo gravitational wave detector is an interferometer (ITF) with 3km arms located in Pisa, Italy. From July to October 2010, Virgo performed its third science run (VSR3) in coincidence with the LIGO detectors. Despite several techniques adopted to isolate the interferometer from the environment, seismic noise remains an important issue for Virgo. Vibrations produced by the detector infrastructure (such as air conditioning units, water chillers/heaters, pumps) are found to affect Virgo's sensitivity, with the main coupling mechanisms being through beam jitter and scattered light processes. The Advanced Virgo (AdV) design seeks to reduce ITF couplings to environmental noise by having most vibration-sensitive components suspended and in-vacuum, as well as muffle and relocate loud machines. During the months of June and July 2010, a Guralp-3TD seismometer was stationed at various locations around the Virgo site hosting major infrastructure machines. Seismic data were examined using spectral and coherence analysis with seismic probes close to the detector. The primary aim of this study was to identify noisy machines which seismically affect the ITF environment and thus require mitigation attention. Analyzed machines are located at various distances from the experimental halls, ranging from 10m to 100m. An attempt is made to measure the attenuation of emitted noise at the ITF and correlate it to the distance from the source and to seismic attenuation models in soil.

The Virgo Collaboration; 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. 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; 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; M. Coughlin; J. -P. Coulon; E. Cuoco; S. DAntonio; 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. Gaspar; 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. Krolak; 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; 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. Racz; 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; J. F. J. van den Brand; C. Van Den Broeck; S. van der Putten; M. Vasuth; M. Vavoulidis; G. Vedovato; D. Verkindt; F. Vetrano; A. Vicere; J. -Y. Vinet; S. Vitale; H. Vocca; R. L. Ward; M. Was; M. Yvert; A. Zadrozny; J. -P. Zendri

2011-08-08

42

More evidence of substructure in the motions of nearby halo stars  

Microsoft Academic Search

We explore the stellar halo of the Milky Way to search for fossil signatures of past mergers. We use the Beers et al. (2000) catalog of non-kinematically selected metal poor stars in the solar neighborhood to select subsets of halo stars within 1-2 kpc of the Sun. Motivated by the results of high resolution CDM simulations, we look for substructure

P. Re Fiorentin; A. Helmi; M. G. Lattanzi; A. Spagna

2004-01-01

43

The Effect of the Transformation of Spiral Galaxies in the Virgo Cluster on Broadband Color Evolution  

NASA Astrophysics Data System (ADS)

Galaxy evolution and the effect of environment on that evolution is one of the central questions of modern extragalactic astronomy. The nearby Virgo Cluster provides us with an ideal laboratory to study galaxy-galaxy and galaxy-cluster interactions at a level of detail impossible at higher redshift. In detailed, pan-chromatic surveys of Virgo, we have seen galaxies transformed by their interaction with the intra-cluster medium, with star-forming gas stripped from spiral galaxies. Using data from the Sloan Digital Sky Survey, we present the results of a study of the global broadband optical properties of 44 Virgo Cluster spiral galaxies from the VIVA galaxy survey. These results show that spiral galaxies actively being stripped maintain blue colors while stripping is ongoing. However, a comparison between the colors of stripped spirals and their HI content suggests that more completely stripped galaxies are, indeed, redder than those that are only modestly HI deficient. This suggests that, as galaxies become more completely stripped, their global colors become redder and that in a cluster more massive than Virgo, such stripping could effectively transform galaxies from blue to red. By comparing broadband colors to the stripping timescales derived from optical spectroscopy and stellar population synthesis, we determine that the broadband color evolution is complex, with dust and the age of the stellar population both playing a role. By comparing detailed studies of a nearby cluster with statistical results from the much larger SDSS sample, we are able to gain insights into the details of how environmentally-driven galaxy evolution affects global broadband colors.

Crowl, Hugh H.; Chung, A.; Blanton, M. R.; Kenney, J. D. P.; van Gorkom, J. H.; Schiminovich, D.

2009-01-01

44

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

45

Universal Substructure Distributions in LCDM halos: Can we find a Fossil Group?  

E-print Network

We use large cosmological N-body simulations to study the subhalo population in galaxy group sized halos. In particular, we look for fossil group candidates with typical masses ~10-25% of Virgo cluster but with an order of magnitude less substructure. We examine recent claims that the earliest systems to form are deficient enough in substructure to explain the luminosity function found in fossil groups. Although our simulations show a correlation between the halo formation time and the number of subhalos, the maximum suppression of subhalos is a factor of 2-2.5, whereas a factor of 6 is required to match fossil groups and galaxies. While the number of subhalos depends weakly on the formation time, the slope of the halo substructure velocity function does not. The satellite population within Cold Dark Matter (CDM) halos is self-similar at scales between galaxies and galaxy clusters regardless of mass, whereas current observations show a break in self-similarity at a mass scale corresponding to group of galaxies.

E. D'Onghia; A. V. Maccio'; G. Lake; J. Stadel; B. Moore

2007-04-19

46

Virgo Galaxies with Long One-sided H I Tails  

NASA Astrophysics Data System (ADS)

In a new H I imaging survey of Virgo galaxies (VIVA: VLA Imaging of Virgo galaxies in Atomic gas), we find seven spiral galaxies with long H I tails. The morphology varies, but all the tails are extended well beyond the optical radii on one side. These galaxies are found in intermediate- to low-density regions (0.6-1 Mpc in projection from M87). The tails are all pointing roughly away from M87, suggesting that these tails may have been created by a global cluster mechanism. While the tidal effects of the cluster potential are too small, a rough estimate suggests that simple ram pressure stripping could have indeed formed the tails in all but two cases. At least three systems show H I truncation to within the stellar disk, providing evidence of a gas-gas interaction. Although most of these galaxies do not appear disturbed optically, some have close neighbors, suggesting that tidal interactions may have moved gas outward, making it more susceptible to the intracluster medium ram pressure or viscosity. Indeed, a simulation study of one of the tail galaxies, NGC 4654, suggests that the galaxy is most likely affected by the combined effect of a gravitational interaction and ram pressure stripping. We conclude that these one-sided H I tail galaxies have recently arrived in the cluster, falling in on highly radial orbits. It appears that galaxies begin to lose their gas already at intermediate distances from the cluster center through ram pressure or turbulent viscous stripping and tidal interactions with their neighbors, or a combination of both.

Chung, Aeree; van Gorkom, J. H.; Kenney, Jeffrey D. P.; Vollmer, Bernd

2007-04-01

47

Studying the metallicity gradient in Virgo Ellipticals with E-ELT photometry of resolved stars  

E-print Network

The next generation of large aperture ground based telescopes will offer the opportunity to perform accurate stellar photometry in very crowded fields. This future capability will allow one to study in detail the stellar population in distant galaxies. In this paper we explore the effect of photometric errors on the stellar metallicity distribution derived from the color distribution of the Red Giant Branch stars in the central regions of galaxies at the distance of the Virgo cluster. We focus on the analysis of the Color-Magnitude Diagrams at different radii in a typical giant Elliptical galaxy obtained from synthetic data constructed to exemplify observations of the European Extremely Large Telescope. The simulations adopt the specifications of the first light high resolution imager MICADO and the expected performance of the Multi-Conjugate Adaptive Optics Module MAORY. We find that the foreseen photometric accuracy allows us to recover the shape of the metallicity distribution with a resolution $\\lesssim 0...

Schreiber, Laura; Falomo, Renato; Fantinel, Daniela; Uslenghi, Michela

2013-01-01

48

Study of modeling of substructure damping matrices.  

NASA Technical Reports Server (NTRS)

Several methods are presented for developing proportional substructure damping matrices from modal test data. Examples demonstrate the significance of the nonuniqueness of the resulting proportional damping matrices. Several alternate modal synthesis procedures are presented for the systematic calculation of system modal damping from substructure damping information. The relative merits of these procedures are discussed, and one procedure is recommended.

Hart, G. C.; Collins, J. D.

1972-01-01

49

Substructure Topology Preserving Simplification of Tetrahedral Meshes  

E-print Network

the power of our system with real world scientific datasets from electromagnetism simulations. 1 the topology of the mesh and of its substructures. Our system combines this topological validity testSubstructure Topology Preserving Simplification of Tetrahedral Meshes Fabien Vivodtzev1, Georges

Hahmann, Stefanie

50

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

51

The Herschel Virgo Cluster Survey. XVIII. Star-forming dwarf galaxies in a cluster environment  

NASA Astrophysics Data System (ADS)

To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the far-infrared (FIR) and submillimetre (submm) properties of a sample of star-forming dwarf galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of a total 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than mB = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by ? = 1.5, with a median dust temperature Td = 22.4 K. Assuming ? = 1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 ?m in excess of the modified black-body model. The fraction of galaxies with a submillimetre excess decreases for lower values of ?, while a similarly high fraction (54%) is found if a ?-free SED modelling is applied. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample that come from environmental effects, we compare the Virgo dwarfs to other Herschel surveys,such as the Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH), the Dwarf Galaxy Survey (DGS), and the HeViCS Bright Galaxy Catalogue (BGC). We explore the relations between stellar mass and Hi fraction, specific star formation rate, dust fraction, gas-to-dust ratio over a wide range of stellar masses (from 107 to 1011 M?) for both dwarfs and spirals. Highly Hi-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, to explain the large dust-to-gas mass ratios observed in these systems, we find that the fraction of dust removed has to be less than that of the Hi component. The cluster environment seems to mostly affect the gas component and star formation activity of the dwarfs. Since the Virgo star-forming dwarfs are likely to be crossing the cluster for the first time, a longer timescale might be necessary to strip the more centrally concentrated dust distribution. Appendices are available in electronic form at http://www.aanda.org

Grossi, M.; Hunt, L. K.; Madden, S. C.; Hughes, T. M.; Auld, R.; Baes, M.; Bendo, G. J.; Bianchi, S.; Bizzocchi, L.; Boquien, M.; Boselli, A.; Clemens, M.; Corbelli, E.; Cortese, L.; Davies, J.; De Looze, I.; di Serego Alighieri, S.; Fritz, J.; Pappalardo, C.; Pierini, D.; Rémy-Ruyer, A.; Smith, M. W. L.; Verstappen, J.; Viaene, S.; Vlahakis, C.

2015-02-01

52

A SAURON study of dwarf elliptical galaxies in the Virgo Cluster  

E-print Network

Dwarf elliptical galaxies are the most common galaxy type in nearby galaxy clusters, yet they remain relatively poorly studied objects and many of their basic properties have yet to be quantified. In this contribution we present the preliminary results of a study of 4 Virgo and 1 field galaxy obtained with the SAURON integral field unit on the William Herschel Telescope (La Palma). While traditional long-slit observations are likely to miss more complicated kinematic features, with SAURON we are able to study both kinematics and stellar populations in two dimensions, obtaining a much more detailed view of the mass distribution and star formation histories.

Ry?, Agnieszka; Koleva, Mina

2010-01-01

53

The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

We investigate the connection between globular clusters and ultracompact dwarf galaxies (UCDs) by examining the properties of 10 compact, high-luminosity (-11.8 MV -10.8) objects associated with M87 (NGC 4486, VCC 1316), the cD galaxy in the Virgo Cluster. These objects, most of which were previously classified as M87 globular clusters, were selected from a combination of ground- and space-based imaging surveys. Our observational database for these objects - which we term DGTOs, or "dwarf-globular transition objects" - includes Advanced Camera for Surveys (ACS) F475W and F850LP imaging from the ACS Virgo Cluster Survey, integrated-light spectroscopy from Keck/ESI, and archival F606W WFPC2 imaging. We also present a search for DGTOs associated with other galaxies based on ACS imaging for 100 early-type galaxies in Virgo. Our main findings can be summarized as follows: 1. Of the six DGTOs in M87 with both ground-based spectroscopy and HST imaging, we find two objects to have half-light radii, velocity dispersions, and mass-to-light ratios that are consistent with the predictions of population synthesis models for old, metal-rich, high-luminosity globular clusters. 2. Three other DGTOs are much larger, with half-light radii rh ~ 20 pc, and have V-band mass-to-light ratios in the range 6 M/LV 9. These objects, which we consider to be UCDs, resemble the nuclei of nucleated dwarf elliptical galaxies in the Virgo Cluster, having similar mass-to-light ratios, luminosities, and colors. 3. The classification of the sixth object is more uncertain, but it bears a strong resemblance to simulated "stellar superclusters," which are presumed to form through the amalgamation of multiple young massive clusters. 4. In general, the UCDs in M87 are found to follow the extrapolated scaling relations of galaxies more closely than those of globular clusters. There appears to be a transition between the two types of stellar systems at a mass of 2 × 10^6 M. We suggest that the presence of dark matter is the fundamental property distinguishing globular clusters from UCDs. 5. We identify a sample of 13 DGTO candidates from the complete ACS Virgo Cluster Survey, selecting on the basis of half-light radius, magnitude, and color. For a number of these objects, membership in Virgo can be established through radial velocities or surface brightness fluctuation measurements with our ACS images. Three of these DGTO candidates are embedded in low-surface brightness envelopes. 6. Five of the 13 DGTOs in Virgo are associated with a single galaxy: M87. This finding suggests that proximity to the Virgo center may be of critical importance for the formation of these objects, although we find M87 to be more abundant in DGTOs than would be expected on the basis of its luminosity, the size of its globular cluster system, or the local galaxy density. These results show that distinguishing bona fide UCDs from high-luminosity globular clusters requires a careful analysis of their detailed structural and dynamical properties, particularly their mass-to-light ratios. In general, the properties of the UCDs in our sample are consistent with models in which these objects form through tidal stripping of nucleated dwarf galaxies. 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.

Ha?egan, Monica; Jordán, Andrés; Côté, Patrick; Djorgovski, S. G.; McLaughlin, Dean E.; Blakeslee, John P.; Mei, Simona; West, Michael J.; Peng, Eric W.; Ferrarese, Laura; Milosavljevi?, Miloš; Tonry, John L.; Merritt, David

2005-07-01

54

Precision Jet Substructure from Boosted Event Shapes  

E-print Network

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 ...

Feige, Ilya

55

Substructure Topology Preserving Simplification of Tetrahedral Meshes  

E-print Network

the power of our system with real world scientific datasets from electromagnetism simulations. 1. Our system combines this topological validity test with simple geometric and numeric error measuresSubstructure Topology Preserving Simplification of Tetrahedral Meshes Fabien Vivodtzev1, Georges

Boyer, Edmond

56

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

57

A structural design decomposition method utilizing substructuring  

NASA Technical Reports Server (NTRS)

A new method of design decomposition for structural analysis and optimization is described. For this method, the structure is divided into substructures where each substructure has its structural response described by a structural-response subproblem, and its structural sizing determined from a structural-sizing subproblem. The structural responses of substructures that have rigid body modes when separated from the remainder of the structure are further decomposed into displacements that have no rigid body components, and a set of rigid body modes. The structural-response subproblems are linked together through forces determined within a structural-sizing coordination subproblem which also determines the magnitude of any rigid body displacements. Structural-sizing subproblems having constraints local to the substructures are linked together through penalty terms that are determined by a structural-sizing coordination subproblem. All the substructure structural-response subproblems are totally decoupled from each other, as are all the substructure structural-sizing subproblems, thus there is significant potential for use of parallel solution methods for these subproblems.

Scotti, Stephen J.

1994-01-01

58

The Accretion Origin of the Milky Way's Stellar Halo  

NASA Astrophysics Data System (ADS)

We have used data from the Sloan Digital Sky Survey (SDSS) Data Release 5 to explore the overall structure and substructure of the stellar halo of the Milky Way using ~4 million color-selected main-sequence turnoff stars with 0.2stellar halo 0.5stellar masses between galactocentric radii of 1 and 40 kpc of 3.7+/-1.2×108 Msolar. The density profile of the stellar halo is approximately ?~r-?, where -2>?>-4. Yet, we found that all smooth and symmetric models were very poor fits to the distribution of stellar halo stars because the data exhibit a great deal of spatial substructure. We quantified deviations from a smooth oblate/triaxial model using the rms of the data around the model profile on scales >~100 pc, after accounting for the (known) contribution of Poisson uncertainties. Within the DR5 area of the SDSS, the fractional rms deviation ?/total of the actual stellar distribution from any smooth, parameterized halo model is >~40%: hence, the stellar halo is highly structured. We compared the observations with simulations of galactic stellar halos formed entirely from the accretion of satellites in a cosmological context by analyzing the simulations in the same way as the SDSS data. While the masses, overall profiles, and degree of substructure in the simulated stellar halos show considerable scatter, the properties and degree of substructure in the Milky Way's halo match well the properties of a ``typical'' stellar halo built exclusively out of the debris from disrupted satellite galaxies. Our results therefore point toward a picture in which an important fraction of the stellar halo of the Milky Way has been accreted from satellite galaxies.

Bell, Eric F.; Zucker, Daniel B.; Belokurov, Vasily; Sharma, Sanjib; Johnston, Kathryn V.; Bullock, James S.; Hogg, David W.; Jahnke, Knud; de Jong, Jelte T. A.; Beers, Timothy C.; Evans, N. W.; Grebel, Eva K.; Ivezi?, Željko; Koposov, Sergey E.; Rix, Hans-Walter; Schneider, Donald P.; Steinmetz, Matthias; Zolotov, Adi

2008-06-01

59

Studying the metallicity gradient in Virgo ellipticals with European-Extremely Large Telescope photometry of resolved stars  

NASA Astrophysics Data System (ADS)

The next generation of large aperture ground-based telescopes will offer the opportunity to perform accurate stellar photometry in very crowded fields. This future capability will allow one to study in detail the stellar population in distant galaxies. In this paper we explore the effect of photometric errors on the stellar metallicity distribution derived from the colour distribution of the red giant branch stars in the central regions of galaxies at the distance of the Virgo cluster. We focus on the analysis of the colour-magnitude diagrams at different radii in a typical giant elliptical galaxy obtained from synthetic data constructed to exemplify observations of the European-Extremely Large Telescope. The simulations adopt the specifications of the first light high-resolution imager Multi-AO Imaging Camera for Deep Observations and the expected performance of the Multi-Conjugate Adaptive Optics Relay. We find that the foreseen photometric accuracy allows us to recover the shape of the metallicity distribution with a resolution ?0.4 dex in the inner regions (?B = 20.5 mag arcsec-2) and ?0.2 dex in regions with ?B = 21.6 mag arcsec-2, that corresponds to approximately half of the effective radius for a typical giant elliptical in Virgo. At the effective radius (?B ? 23 mag arcsec-2), the metallicity distribution is recovered with a resolution of ?0.1 dex. It will thus be possible to study in detail the metallicity gradient of the stellar population over (almost) the whole extension of galaxies in Virgo. We also evaluate the impact of moderate degradations of the point spread function from the assumed optimal conditions and find similar results, showing that this science case is robust.

Schreiber, L.; Greggio, L.; Falomo, R.; Fantinel, D.; Uslenghi, M.

2014-01-01

60

Continuum radio emission from Virgo galaxies  

NASA Technical Reports Server (NTRS)

The paper presents single-antenna measurements of radio emission from 120 galaxies in the Virgo cluster at 2380 MHz using a 2.6 arc min beam (half-power beam width). It also presents interferometric measurements at the same frequency for 48 galaxies with less than or equal to 1 arc sec resolution. The relative concentration of the radio emission for these galaxies, particularly the emission from the galactic disk compared with that from the nucleus is discussed. It is found that the disk emission dominates in most cases. Some indications that the flux concentration is greater in elliptical and lenticular galaxies than it is in spirals are also found.

Turner, Kenneth C.; Helou, George; Terzian, Yervant

1988-01-01

61

SEXTANS' COLD SUBSTRUCTURES AS A DYNAMICAL JUDGE: CORE, CUSP, OR MOND?  

SciTech Connect

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 r{sub c} = 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 r{sub c} = 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 r{sub c} = 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.; Just, A. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Sánchez-Salcedo, F. J., E-mail: vlora@ari.uni-heidelberg.de [Instituto de Astronomía, Universidad Nacional Autónoma de México, AP 70-264, 04510 D.F. (Mexico)

2013-11-01

62

Finite element substructuring methods for composite mechanics  

NASA Technical Reports Server (NTRS)

Finite element substructuring strategies are presented to obtain numerical solutions for three typical problems of interest to the composites community: (1) impact and toughness characterization of composites using Charpy's impact test specimen; (2) free-edge stress analysis of composite laminates; and (3) fracture toughness predictions of composites for individual and combined fracture of modes I, II, and III. The key issue common to these problems is the presence of singular or near singular stress fields. The regions prone to see steep stress gradients are substructured with progressively refined meshes to study the local response simultaneously with the global response. The results from the select examples indicate that finite element substructuring methods are computationally effective for composite singularity mechanics.

Murthy, Pappu L. N.; Chamis, Christos C.

1988-01-01

63

Globular Clusters as Tracers of Dark Matter in Virgo Cluster Dwarf Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

Dwarf elliptical (dE) galaxies outnumber any other galaxy class in galaxy clusters, but their formation is still debated. Their angular momentum and mass distribution contains valuable information about the physical processes they have experienced since their formation. Combining the Next Generation Virgo Cluster Survey (NGVS) and the ACS Virgo Cluster Survey (ACSVCS), we have carried out a Keck/DEIMOS survey to estimate the dark matter mass and its distribution in dEs. We target globular cluster (GC) candidates as tracers of the potential well of a total of 21 dEs in the Virgo Cluster in the luminosity range -17 < Mv < -15. The sample comprises 117 GCs that are satellites of the 21 dEs and span out to ~7 half-light radii (Re). For each galaxy, we first compare the velocity distribution of the GCs against an escape velocity function for a pure stellar mass model, finding a moderate dark matter halo extending to ~7 Re. We then calculate the total mass within 1 Re with a dispersion-based estimator and the total mass to 7 Re with a projected mass estimator. We average our estimates to create a dE representative of our sample, finding mass-to-light ratios in solar units of ~4.5 for the inner regions and ~8-20 for the entire galaxy. This indicates that dEs are not dark matter dominated, neither in their inner nor in their outer regions. Our results represent the first estimate of dark matter content beyond ~2 Re for low-luminosity dEs. These mass estimates are consistent with the prevalent tidal stripping theory of dE formation, which explains the lack of a massive, extended dark matter halo. This research was carried out under UCSC’s Science Internship Program. We thank the National Science Foundation for funding support. ET was supported by a Fulbright fellowship.

Chen, Stephanie; Toloba, E.; Guhathakurta, P.; Chen, J.; Cote, P.; Ferrarese, L.; Peng, E. W.; NGVS Collaboration

2014-01-01

64

MAIN-SEQUENCE STAR POPULATIONS IN THE VIRGO OVERDENSITY REGION  

SciTech Connect

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 Almost-Equal-To 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1{sup +1.0}{sub -1.1} Gyr, a median abundance of [Fe/H] = -0.70{sup +0.15}{sub -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 ({Lambda}{sub Sun} Almost-Equal-To 265 Degree-Sign , B{sub Sun} Almost-Equal-To 13 Degree-Sign ) are located at a mean distance of 23.3 {+-} 1.6 kpc and have an age of {approx}8.2 Gyr, and an abundance of [Fe/H] = -0.67{sup +0.16}{sub -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] Almost-Equal-To -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 and 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 {approx}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.

Jerjen, H.; Da Costa, G. S.; Tisserand, P. [Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Observatory, via Cotter Road, Weston, ACT 2611 (Australia); Willman, B. [Haverford College, Department of Astronomy, 370 Lancaster Avenue, Haverford, PA 19041 (United States); Arimoto, N. [National Astronomical Observatory of Japan, Subaru Telescope, 650 North A'ohoku Place, Hilo, HI 96720 (United States); Okamoto, S. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Mateo, M. [Department of Astronomy, University of Michigan, Ann Arbor, MI (United States); Saviane, I. [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Walsh, S. [Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670 (Australia); Geha, M. [Astronomy Department, Yale University, New Haven, CT 06520 (United States); Jordan, A.; Zoccali, M. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, 7820436 Macul, Santiago (Chile); Olszewski, E. [Steward Observatory, University of Arizona, Tucson, AZ (United States); Walker, M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kroupa, P. [Argelander Institute for Astronomy, University of Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

2013-05-20

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

Distances, Metallicities, and Ages of Dwarf Elliptical Galaxies in the Virgo Cluster from Surface Brightness Fluctuations  

NASA Astrophysics Data System (ADS)

We have employed FORS1 and 2 at the Very Large Telescope at the European Southern Observatory (ESO) to acquire deep B and R-band CCD images of 16 dwarf elliptical (dE) galaxies in the direction of the Virgo cluster. For each dwarf, we measure the apparent R-band surface brightness fluctuation (SBF) magnitude mR and the (B-R)0 color in a number of fields at different galactocentric distances. From the field-to-field variation of the two quantities, we determine the SBF distance by means of the (B-R)0-MR relation. The derived distances of the dwarfs range from 14.9 to 21.3 Mpc, with a mean 1 ? uncertainty of 1.4 Mpc or 8% of the distance, which confirms that there is considerable depth in the distance distribution of early-type cluster members. For VCC 1104 (IC 3388), our SBF distance modulus of (m-M)SBF=31.15+/-0.19 (17.0+/-1.5 Mpc) is in good agreement with the Harris et al result of (m-M)TRGB=30.98+/-0.19 mag (15.7+/-1.5 Mpc) based on Hubble Space Telescope (HST) observations and the tip magnitude of the red giant branch. Combining our results with existing distances for giant Virgo ellipticals, we identify two major galaxy concentrations in the distance distribution: a broad primary clump around (M-m)=31.0 mag (15.8 Mpc) and a narrow secondary clump around 31.33 mag (18.5 Mpc). An adaptive kernel analysis finds the two concentrations to be significant at the 99% (2.5 ?) and 89% (1.6 ?) levels, respectively. While the near-side clump of Virgo early-type galaxies can be associated with the subcluster centered on M87, the second clump is believed to be mainly due to the far side infalling group of galaxies around M86. The ages and metallicities of the dE stellar populations are estimated by combining the observed (B-R)0 colors with Worthey's stellar population synthesis models. It appears that the Virgo dE galaxies cover a wider range in metallicity, from [Fe/H]~-1.4 (VCC 0815) to -0.5 (NGC 4415), than Fornax cluster dEs. The derived metallicities place the Virgo dEs on the extension of the metallicity-luminosity relation defined by the low-luminosity Local Group dEs. The data further suggest an age range from genuinely old (~17 Gyr) stellar systems such as IC 3019 and IC 0783 to intermediate-age (8-12 Gyr) dwarfs such as NGC 4431 and IC 3468.

Jerjen, H.; Binggeli, B.; Barazza, F. D.

2004-02-01

67

Exploiting Tractable Substructures in Intractable Networks  

Microsoft Academic Search

We develop a refined mean field approximation for inference andlearning in probabilistic neural networks. Our mean field theory,unlike most, does not assume that the units behave as independentdegrees of freedom; instead, it exploits in a principled way theexistence of large substructures that are computationally tractable.To illustrate the advantages of this framework, we show how toincorporate weak higher order interactions into

Lawrence K. Saul; Michael I. Jordan

1995-01-01

68

Advanced Virgo: a second-generation interferometric gravitational wave detector  

NASA Astrophysics Data System (ADS)

Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network, alongside the two Advanced LIGO detectors in the US and GEO HF in Germany, with the goal of contributing to the early detection of gravitational waves and to opening a new window of observation on the universe. In this paper we describe the main features of the Advanced Virgo detector and outline the status of the construction.

Acernese, F.; Agathos, M.; Agatsuma, K.; Aisa, D.; Allemandou, N.; Allocca, A.; Amarni, J.; Astone, P.; Balestri, G.; Ballardin, G.; Barone, F.; Baronick, J.-P.; Barsuglia, M.; Basti, A.; Basti, F.; Bauer, Th S.; Bavigadda, V.; Bejger, M.; Beker, M. G.; Belczynski, C.; Bersanetti, D.; Bertolini, A.; Bitossi, M.; Bizouard, M. A.; Bloemen, S.; Blom, M.; Boer, M.; Bogaert, G.; Bondi, D.; Bondu, F.; Bonelli, L.; Bonnand, R.; Boschi, V.; Bosi, L.; Bouedo, T.; Bradaschia, C.; Branchesi, M.; Briant, T.; Brillet, A.; Brisson, V.; Bulik, T.; Bulten, H. J.; Buskulic, D.; Buy, C.; Cagnoli, G.; Calloni, E.; Campeggi, C.; Canuel, B.; Carbognani, F.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cesarini, E.; Chassande-Mottin, E.; Chincarini, A.; Chiummo, A.; Chua, S.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Colombini, M.; Conte, A.; Coulon, J.-P.; Cuoco, E.; Dalmaz, A.; D’Antonio, S.; Dattilo, V.; Davier, M.; Day, R.; Debreczeni, G.; Degallaix, J.; Deléglise, S.; Del Pozzo, W.; Dereli, H.; De Rosa, R.; Di Fiore, L.; Di Lieto, A.; Di Virgilio, A.; Doets, M.; Dolique, V.; Drago, M.; Ducrot, M.; Endr?czi, G.; Fafone, V.; Farinon, S.; Ferrante, I.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Fournier, J.-D.; Franco, S.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Garufi, F.; Gaspard, M.; Gatto, A.; Gemme, G.; Gendre, B.; Genin, E.; Gennai, A.; Ghosh, S.; Giacobone, L.; Giazotto, A.; Gouaty, R.; Granata, M.; Greco, G.; Groot, P.; Guidi, G. M.; Harms, J.; Heidmann, A.; Heitmann, H.; Hello, P.; Hemming, G.; Hennes, E.; Hofman, D.; Jaranowski, P.; Jonker, R. J. G.; Kasprzack, M.; Kéfélian, F.; Kowalska, I.; Kraan, M.; Królak, A.; Kutynia, A.; Lazzaro, C.; Leonardi, M.; Leroy, N.; Letendre, N.; Li, T. G. F.; Lieunard, B.; Lorenzini, M.; Loriette, V.; Losurdo, G.; Magazzù, C.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mangano, V.; Mantovani, M.; Marchesoni, F.; Marion, F.; Marque, J.; Martelli, F.; Martellini, L.; Masserot, A.; Meacher, D.; Meidam, J.; Mezzani, F.; Michel, C.; Milano, L.; Minenkov, Y.; Moggi, A.; Mohan, M.; Montani, M.; Morgado, N.; Mours, B.; Mul, F.; Nagy, M. F.; Nardecchia, I.; Naticchioni, L.; Nelemans, G.; Neri, I.; Neri, M.; Nocera, F.; Pacaud, E.; Palomba, C.; Paoletti, F.; Paoli, A.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Petit, S.; Pichot, M.; Piergiovanni, F.; Pillant, G.; Piluso, A.; Pinard, L.; Poggiani, R.; Prijatelj, M.; Prodi, G. A.; Punturo, M.; Puppo, P.; Rabeling, D. S.; Rácz, I.; Rapagnani, P.; Razzano, M.; Re, V.; Regimbau, T.; Ricci, F.; Robinet, F.; Rocchi, A.; Rolland, L.; Romano, R.; Rosi?ska, D.; Ruggi, P.; Saracco, E.; Sassolas, B.; Schimmel, F.; Sentenac, D.; Sequino, V.; Shah, S.; Siellez, K.; Straniero, N.; Swinkels, B.; Tacca, M.; Tonelli, M.; Travasso, F.; Turconi, M.; Vajente, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; van der Sluys, M. V.; van Heijningen, J.; Vasúth, M.; Vedovato, G.; Veitch, J.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinet, J.-Y.; Visser, G.; Vocca, H.; Ward, R.; Was, M.; Wei, L.-W.; Yvert, M.; Zadro ?ny, A.; Zendri, J.-P.

2015-01-01

69

Advanced Virgo: a 2nd generation interferometric gravitational wave detector  

E-print Network

Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network with the two Advanced LIGO detectors in the US and GEO HF in Germany, with the goal of contributing to the early detections of gravitational waves and to opening a new observation window on the universe. In this paper we describe the main features of the Advanced Virgo detector and outline the status of the construction.

F. Acernese; M. Agathos; K. Agatsuma; D. Aisa; N. Allemandou; A. Allocca; J. Amarni; P. Astone; G. Balestri; G. Ballardin; F. Barone; J. -P. Baronick; M. Barsuglia; A. Basti; F. Basti; Th. S. Bauer; V. Bavigadda; M. Bejger; M. G. Beker; C. Belczynski; D. Bersanetti; A. Bertolini; M. Bitossi; M. A. Bizouard; S. Bloemen; M. Blom; M. Boer; G. Bogaert; D. Bondi; F. Bondu; L. Bonelli; R. Bonnand; V. Boschi; L. Bosi; T. Bouedo; C. Bradaschia; M. Branchesi; T. Briant; A. Brillet; V. Brisson; T. Bulik; H. J. Bulten; D. Buskulic; C. Buy; G. Cagnoli; E. Calloni; C. Campeggi; B. Canuel; F. Carbognani; F. Cavalier; R. Cavalieri; G. Cella; E. Cesarini; E. Chassande-Mottin; A. Chincarini; A. Chiummo; S. Chua; F. Cleva; E. Coccia; P. -F. Cohadon; A. Colla; M. Colombini; A. Conte; J. -P. Coulon; E. Cuoco; A. Dalmaz; S. D'Antonio; V. Dattilo; M. Davier; R. Day; G. Debreczeni; J. Degallaix; S. Deléglise; W. Del Pozzo; H. Dereli; R. De Rosa; L. Di Fiore; A. Di Lieto; A. Di Virgilio; M. Doets; V. Dolique; M. Drago; M. Ducrot; G. Endr?czi; V. Fafone; S. Farinon; I. Ferrante; F. Ferrini; F. Fidecaro; I. Fiori; R. Flaminio; J. -D. Fournier; S. Franco; S. Frasca; F. Frasconi; L. Gammaitoni; F. Garufi; M. Gaspard; A. Gatto; G. Gemme; B. Gendre; E. Genin; A. Gennai; S. Ghosh; L. Giacobone; A. Giazotto; R. Gouaty; M. Granata; G. Greco; P. Groot; G. M. Guidi; J. Harms; A. Heidmann; H. Heitmann; P. Hello; G. Hemming; E. Hennes; D. Hofman; P. Jaranowski; R. J. G. Jonker; M. Kasprzack; F. Kéfélian; I. Kowalska; M. Kraan; A. Królak; A. Kutynia; C. Lazzaro; M. Leonardi; N. Leroy; N. Letendre; T. G. F. Li; B. Lieunard; M. Lorenzini; V. Loriette; G. Losurdo; C. Magazzù; E. Majorana; I. Maksimovic; V. Malvezzi; N. Man; V. Mangano; M. Mantovani; F. Marchesoni; F. Marion; J. Marque; F. Martelli; L. Martellini; A. Masserot; D. Meacher; J. Meidam; F. Mezzani; C. Michel; L. Milano; Y. Minenkov; A. Moggi; M. Mohan; M. Montani; N. Morgado; B. Mours; F. Mul; M. F. Nagy; I. Nardecchia; L. Naticchioni; G. Nelemans; I. Neri; M. Neri; F. Nocera; E. Pacaud; C. Palomba; F. Paoletti; A. Paoli; A. Pasqualetti; R. Passaquieti; D. Passuello; M. Perciballi; S. Petit; M. Pichot; F. Piergiovanni; G. Pillant; A Piluso; L. Pinard; R. Poggiani; M. Prijatelj; G. A. Prodi; M. Punturo; P. Puppo; D. S. Rabeling; I. Rácz; P. Rapagnani; M. Razzano; V. Re; T. Regimbau; F. Ricci; F. Robinet; A. Rocchi; L. Rolland; R. Romano; D. Rosi?ska; P. Ruggi; E. Saracco; B. Sassolas; F. Schimmel; D. Sentenac; V. Sequino; S. Shah; K. Siellez; N. Straniero; B. Swinkels; M. Tacca; M. Tonelli; F. Travasso; M. Turconi; G. Vajente; N. van Bakel; M. van Beuzekom; J. F. J. van den Brand; C. Van Den Broeck; M. V. van der Sluys; J. van Heijningen; M. Vasúth; G. Vedovato; J. Veitch; D. Verkindt; F. Vetrano; A. Viceré; J. -Y. Vinet; G. Visser; H. Vocca; R. Ward; M. Was; L. -W. Wei; M. Yvert; A. Zadro?ny; J. -P. Zendri

2014-10-16

70

Boosted objects and jet substructure at the LHC  

E-print Network

This report of the BOOST2012 workshop presents the results of four working groups that studied key aspects of jet substructure. We discuss the potential of the description of jet substructure in first-principle QCD calculations and study the accuracy of state-of-the-art Monte Carlo tools. Experimental limitations of the ability to resolve substructure are evaluated, with a focus on the impact of additional proton proton collisions on jet substructure performance in future LHC operating scenarios. A final section summarizes the lessons learnt during the deployment of substructure analyses in searches for new physics in the production of boosted top quarks.

BOOST2012 participants- A. Altheimer; A. Arce; L. Asquith; J. Backus Mayes; E. Bergeaas Kuutmann; J. Berger; D. Bjergaard; L. Bryngemark; A. Buckley; J. Butterworth; M. Cacciari; M. Campanelli; T. Carli; M. Chala; B. Chapleau; C. Chen; J. P. Chou; Th. Cornelissen; D. Curtin; M. Dasgupta; A. Davison; F. de Almeida Dias; A. de Cosa; A. de Roeck; C. Debenedetti; C. Doglioni; S. D. Ellis; F. Fassi; J. Ferrando; S. Fleischmann; M. Freytsis; M. L. Gonzalez Silva; S. Gonzalez de la Hoz; F. Guescini; Z. Han; A. Hook; A. Hornig; E. Izaguirre; M. Jankowiak; J. Juknevich; M. Kaci; D. Kar; G. Kasieczka; R. Kogler; A. Larkoski; P. Loch; D. Lopez Mateos; S. Marzani; L. Masetti; V. Mateu; D. W. Miller; K. Mishra; P. Nef; K. Nordstrom; E. Oliver Garcia; J. Penwell; J. Pilot; T. Plehn; S. Rappoccio; A. Rizzi; G. Rodrigo; A. Safonov; G. P. Salam; J. Salt; S. Schaetzel; M. Schioppa; A. Schmidt; J. Scholtz; A. Schwartzman; M. D. Schwartz; M. Segala; M. Son; G. Soyez; M. Spannowsky; I. Stewart; D. Strom; M. Swiatlowski; V. Sanchez Martinez; M. Takeuchi; J. Thaler; E. Thompson; N. V. Tran; C. Vermilion; M. Villaplana; M. Vos; J. Wacker; J. Walsh

2013-12-04

71

Stellar Illumination  

NSDL National Science Digital Library

This is a lesson about discovering distant planets using an Earth-based observing technique called stellar occultation. Learners will explore how a stellar occultation occurs, how planetary atmospheres can be discovered, and how planetary diameters can be determined using actual light curves from stellar occultation events. Includes adaptations for younger students and those with visual impairments.

72

Substructure coupling in the frequency domain  

NASA Technical Reports Server (NTRS)

Frequency domain analysis was found to be a suitable method for determining the transient response of systems subjected to a wide variety of loads. However, since a large number of calculations are performed within the discrete frequency loop, the method loses it computational efficiency if the loads must be represented by a large number of discrete frequencies. It was also discovered that substructure coupling in the frequency domain work particularly well for analyzing structural system with a small number of interface and loaded degrees of freedom. It was discovered that substructure coupling in the frequency domain can lead to an efficient method of obtaining natural frequencies of undamped structures. It was also found that the damped natural frequencies of a system may be determined using frequency domain techniques.

1985-01-01

73

Direct Detection of Cold Dark Matter Substructure  

Microsoft Academic Search

We devise a method to measure the abundance of satellite halos in gravitational lens galaxies and apply our method to a sample of seven lens systems. After using Monte Carlo simulations to verify the method, we find that substructure comprises fsat=0.02 (median, 0.006

N. Dalal; C. S. Kochanek

2002-01-01

74

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

75

Design sensitivity analysis of boundary element substructures  

NASA Technical Reports Server (NTRS)

The ability to reduce or condense a three-dimensional model exactly, and then iterate on this reduced size model representing the parts of the design that are allowed to change in an optimization loop is discussed. The discussion presents the results obtained from an ongoing research effort to exploit the concept of substructuring within the structural shape optimization context using a Boundary Element Analysis (BEA) formulation. The first part contains a formulation for the exact condensation of portions of the overall boundary element model designated as substructures. The use of reduced boundary element models in shape optimization requires that structural sensitivity analysis can be performed. A reduced sensitivity analysis formulation is then presented that allows for the calculation of structural response sensitivities of both the substructured (reduced) and unsubstructured parts of the model. It is shown that this approach produces significant computational economy in the design sensitivity analysis and reanalysis process by facilitating the block triangular factorization and forward reduction and backward substitution of smaller matrices. The implementatior of this formulation is discussed and timings and accuracies of representative test cases presented.

Kane, James H.; Saigal, Sunil; Gallagher, Richard H.

1989-01-01

76

Cold Dark Matter Substructure and Galactic Disks. I. Morphological Signatures of Hierarchical Satellite Accretion  

NASA Astrophysics Data System (ADS)

We conduct dissipationless N-body simulations to investigate the cumulative effect of substructure impacts onto thin disk galaxies in the context of the ?CDM paradigm. Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. Substructure properties are culled from cosmological simulations of galaxy-sized CDM halos. We demonstrate that accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z~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. One host halo merger history is subsequently used to seed controlled N-body experiments of repeated satellite encounters with an initially thin Milky-Way (MW) type disk galaxy. These simulations track the effects of six dark matter substructures, with initial masses in the range ~(0.7-2)×1010 Msolar (~20%-60% of the disk mass), crossing the disk in the past ~8 Gyr. We demonstrate that these accretion events produce several distinctive morphological signatures in the disk, including long-lived, low surface brightness, ringlike features in the outskirts; significant flares; bars; and faint filamentary structures above the disk plane. The final distribution of disk stars exhibits a complex vertical structure that is well described by a standard ``thin-thick'' disk decomposition. We compare one of the resulting ringlike features in our simulations to the Monoceros Ring stellar structure in the MW. The comparison shows quantitative agreement in spatial distribution and kinematics, suggesting that such observed complex stellar components may arise naturally as disk stars are excited by encounters with CDM substructure. We conclude that satellite-disk interactions of the kind expected in ?CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way, M31, and other 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.

2008-11-01

77

5. DOWNSTREAM ELEVATION OF BRIDGE AND SUBSTRUCTURE (with graduated meter ...  

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

5. DOWNSTREAM ELEVATION OF BRIDGE AND SUBSTRUCTURE (with graduated meter pole); VIEW TO NORTH-NORTHEAST. - Auwaiakeakua Bridge, Spanning Auwaiakekua Gulch at Mamalahoa Highway, Waikoloa, Hawaii County, HI

78

Loopy Substructural Local Search for the Bayesian Optimization Algorithm  

NASA Astrophysics Data System (ADS)

This paper presents a local search method for the Bayesian optimization algorithm (BOA) based on the concepts of substructural neighborhoods and loopy belief propagation. The probabilistic model of BOA, which automatically identifies important problem substructures, is used to define the topology of the neighborhoods explored in local search. On the other hand, belief propagation in graphical models is employed to find the most suitable configuration of conflicting substructures. The results show that performing loopy substructural local search (SLS) in BOA can dramatically reduce the number of generations necessary to converge to optimal solutions and thus provides substantial speedups.

Lima, Claudio F.; Pelikan, Martin; Lobo, Fernando G.; Goldberg, David E.

79

CHEMTRAN and the Interconversion of Chemical Substructure Systems  

ERIC Educational Resources Information Center

The need for the interconversion of chemical substructure systems is discussed and CHEMTRAN, a new service, designed especially for creating interconversion programs, is introduced. (7 references) (Author)

Granito, Charles E.

1973-01-01

80

Measuring the Virgo area tilt noise with a laser gyroscope  

E-print Network

We report on the measurements of tilt noise performed at the Virgo site with a ring laser gyroscope. The apparatus is a He-Ne laser operating in a square cavity mounted on a vertical plane perpendicular to the north-south arm of the inteferometer. We discuss the possibility of using the ring laser signal to improve the performances of the control system of the Virgo seismic suspensions. The comparison between the ring laser signal and the control signals for the longitudinal translations of the inverted pendulum (IP) shows remarkable coherence in the frequency range 20-200 mHz.

Belfi, Jacopo; Bosi, Filippo; Carelli, Giorgio; Di Virgilio, Angela; Maccioni, Enrico; Stefani, Fabio

2011-01-01

81

Stellar Evolution  

NSDL National Science Digital Library

This Chandra X-Ray Observatory page links to several activities and articles on stellar evolution. It includes an interactive Flash activity featuring simulations of different-mass stars evolving and a detailed "story" of stellar evolution for the interested reader, available in PDF and HTML formats.

2010-05-28

82

Late-Type Dwarf Galaxies in the Virgo Cluster: II. Star Formation Properties  

E-print Network

We study star-formation-inducing mechanisms in galaxies through multi- wavelength measurements of a sample of dwarf galaxies in the Virgo cluster described in paper I. Our main goal is to test how star formation inducing mechanisms depend on several parameters of the galaxies, such as morphological type and hydrogen content. We derive the star formation rate and star formation histories of the galaxies, and check their dependence on other parameters. Comparison of the sample galaxies with population synthesis models shows that these objects have significantly lower metallicity than the Solar value. The colors can generally be explained as a combination of two different stellar populations: a young (3--20 Myr) population which represents the stars currently forming, and an older (0.1--1 Gyr) population of previous stellar generations. This is consistent with the explanation that star formation in this type of objects takes place in short bursts followed by long quiescent periods. No significant relation is found between the star formation properties of the sample galaxies and their hydrogen content. Apparently, when star formation occurs in bursts, other parameters influence the star formation properties more significantly than the amount of hydrogen. No correlation is found between the projected Virgocentric distance and the rate of star formation in the galaxies.

Elchanan Almoznino; Noah Brosch

1998-04-22

83

Virgo Cluster and field dwarf ellipticals in 3D - II. Internal dynamics points to tidal harassment?  

NASA Astrophysics Data System (ADS)

We present the dynamical analysis of a sample of 12 dwarf elliptical (dE) galaxies for which we have obtained SAURON large-scale two-dimensional spectroscopic data. We construct Jeans axisymmetric models and obtain total dynamical masses enclosed within one effective radius. We use the obtained values to show that the validity of the dynamical scaling relations of massive early-type galaxies can be extended to these low-mass systems, except that dEs seem to contain relatively larger fraction of dark matter in their inner parts. We then demonstrate that dE galaxies have lower angular momenta than the present-day analogues of their presumed late-type progenitors, and we show that dE circular velocity curves are steeper than the rotation curves of galaxies with equal and up to an order of magnitude higher luminosity. This requires a transformation mechanism that is not only able to lower the angular momentum but also one that needs to account for increased stellar concentration. Additionally, we match the dark matter fraction of our galaxies to their location in the Virgo Cluster and see that galaxies in the cluster outskirts tend to have a higher dark-to-stellar matter ratio. Transformation due to tidal harassment is able to explain all of the above, unless the dE progenitors were already compact and had lower angular momenta at higher redshifts.

Ry?, A.; van de Ven, G.; Falcón-Barroso, J.

2014-03-01

84

COLOR-MAGNITUDE RELATIONS OF EARLY-TYPE DWARF GALAXIES IN THE VIRGO CLUSTER: AN ULTRAVIOLET PERSPECTIVE  

SciTech Connect

We present ultraviolet (UV) color-magnitude relations (CMRs) of early-type dwarf galaxies in the Virgo cluster, based on Galaxy Evolution Explorer (GALEX) UV and Sloan Digital Sky Survey (SDSS) optical imaging data. We find that dwarf lenticular galaxies (dS0s), including peculiar dwarf elliptical galaxies (dEs) with disk substructures and blue centers, show a surprisingly distinct and tight locus separated from that of ordinary dEs, which is not clearly seen in previous CMRs. The dS0s in UV CMRs follow a steeper sequence than dEs and show bluer UV-optical color at a given magnitude. We also find that the UV CMRs of dEs in the outer cluster region are slightly steeper than that of their counterparts in the inner region, due to the existence of faint, blue dEs in the outer region. We explore the observed CMRs with population models of a luminosity-dependent delayed exponential star formation history. We confirm that the feature of delayed star formation of early-type dwarf galaxies in the Virgo cluster is strongly correlated with their morphology and environment. The observed CMR of dS0s is well matched by models with relatively long delayed star formation. Our results suggest that dS0s are most likely transitional objects at the stage of subsequent transformation of late-type progenitors to ordinary red dEs in the cluster environment. In any case, UV photometry provides a powerful tool to disentangle the diverse subpopulations of early-type dwarf galaxies and uncover their evolutionary histories.

Kim, Suk; Rey, Soo-Chang [Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Lisker, Thorsten [Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg (ZAH), Moenchhofstrasse 12-14, D-69120 Heidelberg (Germany); Sohn, Sangmo Tony, E-mail: s_kim@cnu.ac.k, E-mail: screy@cnu.ac.k [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2010-09-20

85

Color-Magnitude Relations of Early-type Dwarf Galaxies in the Virgo Cluster: An Ultraviolet Perspective  

NASA Astrophysics Data System (ADS)

We present ultraviolet (UV) color-magnitude relations (CMRs) of early-type dwarf galaxies in the Virgo cluster, based on Galaxy Evolution Explorer (GALEX) UV and Sloan Digital Sky Survey (SDSS) optical imaging data. We find that dwarf lenticular galaxies (dS0s), including peculiar dwarf elliptical galaxies (dEs) with disk substructures and blue centers, show a surprisingly distinct and tight locus separated from that of ordinary dEs, which is not clearly seen in previous CMRs. The dS0s in UV CMRs follow a steeper sequence than dEs and show bluer UV-optical color at a given magnitude. We also find that the UV CMRs of dEs in the outer cluster region are slightly steeper than that of their counterparts in the inner region, due to the existence of faint, blue dEs in the outer region. We explore the observed CMRs with population models of a luminosity-dependent delayed exponential star formation history. We confirm that the feature of delayed star formation of early-type dwarf galaxies in the Virgo cluster is strongly correlated with their morphology and environment. The observed CMR of dS0s is well matched by models with relatively long delayed star formation. Our results suggest that dS0s are most likely transitional objects at the stage of subsequent transformation of late-type progenitors to ordinary red dEs in the cluster environment. In any case, UV photometry provides a powerful tool to disentangle the diverse subpopulations of early-type dwarf galaxies and uncover their evolutionary histories.

Kim, Suk; Rey, Soo-Chang; Lisker, Thorsten; Sohn, Sangmo Tony

2010-09-01

86

Jet Substructure at the Large Hadron Collider  

E-print Network

I explore many aspects of jet substructure at the Large Hadron Collider, ranging from theoretical techniques for jet calculations, to phenomenological tools for better searches with jets, to software for implementing and comparing such tools. I begin with an application of soft-collinear effective theory, an effective theory of QCD applied to high-energy quarks and gluons. This material is taken from Ref. 1, in which we demonstrate factorization and logarithmic resummation for a certain class of observables in electron-positron collisions. I then explore various phenomenological aspects of jet substructure in simulated events. After observing numerous features of jets at hadron colliders, I describe a method -- jet pruning -- for improving searches for heavy particles that decay to one or more jets. This material is a greatly expanded version of Ref. 2. Finally, I give an overview of the software tools available for these kinds of studies, with a focus on SpartyJet, a package for implementing and comparing jet-based analyses I have collaborated on. Several detailed calculations and software examples are given in the appendices. Sections with no new content are italic in the Table of Contents.

Christopher K. Vermilion

2011-01-07

87

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

2012-12-21

88

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

89

Seeking Counterparts to Advanced LIGO/Virgo Transients with Swift  

NASA Technical Reports Server (NTRS)

Binary neutron star (NS) mergers are among the most promising astrophysical sources of gravitational wave 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 1-2 hours, and so is uniquely poised to find the X-ray counterparts to LIGO / Virgo triggers. Assuming 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(exp -12) ergs/s/sq cm 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 very short 100 s exposures to cover an area of approx 35 square degrees in about a day, and still be sensitive enough to image GW discovered GRB afterglows. These strategies demonstrate that the high X-ray luminosity of short GRBs and the relatively low X-ray transient background combine to make high confidence discoveries of X-ray band counterparts to GW triggers possible, though challenging, with current satellite facilities.

Kanner, Jonah; Camp, Jordan; Racusin, Judith; Gehrels, Neil; White, Darren

2012-01-01

90

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

2009-08-21

91

A case of poor substructure diagnostics  

NASA Technical Reports Server (NTRS)

The NASTRAN Manuals in the substructuring area are all geared toward instant success, but the solution paths are fraught with many traps for human error. Thus, the probability of suffering a fatal abort is high. In such circumstances, the necessity for diagnostics that are user friendly is paramount. This paper is written in the spirit of improving the diagnostics as well as the documentation in one area where the author felt he was backed into a blind corner as a result of his having committed a data oversight. This topic is aired by referring to an analysis of a particular structure. The structure, under discussion, used a number of local coordinate systems that simplified the preparation of input data. The principle features of this problem are introduced by reference to a series of figures.

Butler, Thomas G.

1992-01-01

92

Probabilistic Component Mode Synthesis of Nondeterministic Substructures  

NASA Technical Reports Server (NTRS)

Standard methods of structural dynamic analysis assume that the structural characteristics are deterministic. Recognizing that these characteristics are actually statistical in nature researchers have recently developed a variety of methods that use this information to determine probabilities of a desired response characteristic, such as natural frequency, without using expensive Monte Carlo simulations. One of the problems in these methods is correctly identifying the statistical properties of primitive variables such as geometry, stiffness, and mass. We present a method where the measured dynamic properties of substructures are used instead as the random variables. The residual flexibility method of component mode synthesis is combined with the probabilistic methods to determine the cumulative distribution function of the system eigenvalues. A simple cantilever beam test problem is presented that illustrates the theory.

Brown, Andrew M.; Ferri, Aldo A.

1996-01-01

93

First Results from the Survey of the MAgellanic Stellar History (SMASH)  

NASA Astrophysics Data System (ADS)

Clear observational signatures of hierarchical galaxy formation have been found around the Milky Way and other nearby massive galaxies. However, the build-up of smaller dwarf galaxies and the extent to which they harbor relics of past interactions such as stellar halos and substructure is not well-known. In an effort to observationally constrain structure formation on small scales, SMASH (Survey of the MAgellanic Stellar History), an approved NOAO community DECam survey, is imaging ~2400 square degrees (at 20% filling factor) to 24th mag in gri (uz~23) allowing us to map the expected stellar debris and extended stellar populations of the Clouds with unprecedented fidelity. SMASH will (a) search for the stellar components of the Magellanic Stream and Leading Arm, (b) detect and map the extended smooth components and substructure of the Magellanic Clouds, and (c) derive spatially resolved, precise star formation histories out to large radii. Our first year of data reveal (1) Large Magellanic Cloud (LMC) stellar populations extending out to a radius of at least 19 deg (~17 kpc) in several directions, (2) clear signatures of two dominant LMC star formation episodes at intermediate radii as revealed by multiple subgiant branches, and (3) evidence for an expansive stellar substructure in the Milky Way halo at a distance of ~30 kpc.

Nidever, David L.; Olsen, Knut A.; Gruendl, Robert A.; Besla, Gurtina; Saha, Abi; Olszewski, Edward; Munoz, Ricardo; Gallart, Carme; Monelli, Matteo; Walker, Alistair R.; Blum, Robert D.; Kaleida, Catherine C.; Vivas, Kathy; Majewski, Steven R.; Zaritsky, Dennis F.; van der Marel, Roeland P.; Bell, Eric F.; Conn, Blair; Stringfellow, Guy S.; Jin, Shoko; Monteagudo Nervion, Lara; Cioni, Maria-Rosa; Noel, Noelia; Martin, Nicolas; Monachesi, Antonela; de Boer, Thomas; Chu, You-Hua; Kim, Hwihyun; Martinez-Delgado, David; Johnson, Lent C.; Kunder, Andrea; Smash

2015-01-01

94

Stellar Winds  

NASA Astrophysics Data System (ADS)

A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ? evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ˜ ?? 1. 4M ?. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various dynamical driving processes and what they imply for key wind parameters like the wind flow speed and mass loss rate.

Owocki, Stan

95

Clustering and similarity of chemical structures represented by binary substructure descriptors  

Microsoft Academic Search

A set of 1365 substructures has been created for the representation of organic chemical structures by binary substructure descriptors. Software SubMat calculates a matrix of binary fingerprint vectors for given sets of molecular structures and substructures (both in Molfile format). The distribution of the substructures in two spectral databases (IR, MS) has been investigated. Examples of structure similarity searches based

H Scsibrany; M Karlovits; W Demuth; F Müller; K Varmuza

2003-01-01

96

Advanced VIRGO: detector optimization for gravitational waves by inspiralling binaries  

E-print Network

For future configurations, we study the relation between the abatement of the noise sources and the Signal to Noise Ratio (SNR) for coalescing binaries. Our aim is not the proposition of a new design, but an indication of where in the bandwidth or for which noise source, a noise reduction would be most efficient. We take VIRGO as the reference for our considerations, solely applicable to the inspiralling phase of a coalescing binary. Thus, only neutron stars and small black holes of few solar masses are encompassed by our analysis. The contributions to the SNR given by final merge and quasi-normal ringing are neglected. It is identified that i) the reduction in the mirror thermal noise band provides the highest gain for the SNR, when the VIRGO bandwidth is divided according to the dominant noises; ii) it exists a specific frequency at which lies the potential largest increment in the SNR, and that the enlargement of the bandwidth, where the noise is reduced, produces a shift of such optimal frequency to higher values; iii) the abatement of the pendulum thermal noise provides the largest, but modest, gain, when noise sources are considered separately. Our recent astrophysical analysis on event rates for neutron stars leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO, respectively, while a recently proposed and improved, but still conservative, VIRGO configuration would provide an increase to 1.5 events per year. Instead, a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such gain could be achieved.

Alessandro D. A. M. Spallicci; Sofiane Aoudia; Jose De Freitas Pacheco; Giorgio Frossati; Tania Regimbau

2004-06-20

97

NASA EM Followup of LIGO-Virgo Candidate Events  

NASA Technical Reports Server (NTRS)

We present a strategy for a follow-up of LIGO-Virgo candidate events using offline survey data from several NASA high-energy photon instruments aboard RXTE, Swift, and Fermi. Time and sky-location information provided by the GW trigger allows for a targeted search for prompt and afterglow EM signals. In doing so, we expect to be sensitive to signals which are too weak to be publicly reported as astrophysical EM events.

Blackburn, Lindy L.

2011-01-01

98

The maraging-steel blades of the Virgo super attenuator  

Microsoft Academic Search

The blades are crucial components of the Virgo super attenuators. The material used for their construction is maraging steel, a low-carbon-content alloy with high ultimate tensile strength and low creep under stress. Young's modulus, the shear modulus, the Poisson ratio and the corresponding elastic energy-loss coefficients have been measured. The measurements have been performed on specimens subjected to the same

S. Braccini; C. Casciano; F. Cordero; F. Corvace; M. DeSanctis; R. Franco; F. Frasconi; E. Majorana; G. Paparo; R. Passaquieti; P. Rapagnani; F. Ricci; D. Righetti; A. Solina; R. Valentini

2000-01-01

99

10. DETAIL OF BRIDGE SUBSTRUCTURE, SHOWING ORIGINAL CONNECTION WITH IRON ...  

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

10. DETAIL OF BRIDGE SUBSTRUCTURE, SHOWING ORIGINAL CONNECTION WITH IRON PINS. VIEW LOOKING WEST FROM FACE OF EAST ABUTMENT. - Annisquam Bridge, Spanning Lobster Cove between Washington & River Streets, Gloucester, Essex County, MA

100

Weak lensing flexion as a probe of galaxy cluster substructure  

E-print Network

Measuring galaxy cluster total masses and the amount of dark matter substructure within galaxy cluster haloes is a fundamental probe of the ACDM model of structure formation, as well as the interactions between baryonic ...

Cain, Benjamin Martin

2011-01-01

101

OPTICAL COLORS OF INTRACLUSTER LIGHT IN THE VIRGO CLUSTER CORE  

SciTech Connect

We continue our deep optical imaging survey of the Virgo cluster using the CWRU Burrell Schmidt telescope by presenting B-band surface photometry of the core of the Virgo cluster in order to study the cluster's intracluster light (ICL). We find ICL features down to {mu}{sub B} {approx}29 mag arcsec{sup -2}, confirming the results of Mihos et al., who saw a vast web of low surface brightness streams, arcs, plumes, and diffuse light in the Virgo cluster core using V-band imaging. By combining these two data sets, we are able to measure the optical colors of many of the cluster's low surface brightness features. While much of our imaging area is contaminated by galactic cirrus, the cluster core near the cD galaxy, M87, is unobscured. We trace the color profile of M87 out to over 2000'', and find a blueing trend with radius, continuing out to the largest radii. Moreover, we have measured the colors of several ICL features which extend beyond M87's outermost reaches and find that they have similar colors to the M87's halo itself, B - V {approx}0.8. The common colors of these features suggest that the extended outer envelopes of cD galaxies, such as M87, may be formed from similar streams, created by tidal interactions within the cluster, that have since dissolved into a smooth background in the cluster potential.

Rudick, Craig S.; Mihos, J. Christopher; Harding, Paul; Morrison, Heather L. [Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 (United States); Feldmeier, John J. [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH 44555 (United States); Janowiecki, Steven, E-mail: csr10@case.ed [Department of Astronomy, Indiana University, 727 East 3rd Street, Bloomington, IN 47405 (United States)

2010-09-01

102

gSpan: Graph-Based Substructure Pattern Mining  

Microsoft Academic Search

We investigate new approaches for frequent graph-based pattern mining in graph datasets and propose a novel algo- rithm called gSpan (graph-based Substructure pattern min- ing), which discovers frequent substructures without can- didate generation. gSpan builds a new lexicographic or- der among graphs, and maps each graph to a unique mini- mum DFS code as its canonical label. Based on this

Xifeng Yan; Jiawei Han

2002-01-01

103

A 3D view of the Hydra I galaxy cluster core - I. Kinematic substructures  

NASA Astrophysics Data System (ADS)

We used FORS2 in MXU mode to mimic a coarse `IFU' in order to measure the 3D large-scale kinematics around the central Hydra I cluster galaxy NGC 3311. Our data show that the velocity dispersion field varies as a function of radius and azimuthal angle and violates point symmetry. Also, the velocity field shows similar dependence, hence the stellar halo of NGC 3311 is a dynamically young structure. The kinematic irregularities coincide in position with a displaced diffuse halo North-East of NGC 3311 and with tidal features of a group of disrupting dwarf galaxies. This suggests that the superposition of different velocity components is responsible for the kinematic substructure in the Hydra I cluster core.

Hilker, Michael; Barbosa, Carlos Eduardo; Richtler, Tom; Coccato, Lodovico; Arnaboldi, Magda; Mendes de Oliveira, Claudia

2015-02-01

104

Population Gradients in Stellar Halos from GHOSTS  

NASA Astrophysics Data System (ADS)

We report on recent results from the Galaxy Halos, Outer disks, Substructure, Thick disks, and Star clusters (GHOSTS) survey, an HST ACS+WFC3 imaging survey to study stellar populations in and around 16 nearby spiral galaxies. By using HST resolution to resolve the stellar halos into individual red giant branch (RGB) stars, we are able to detect distinct stellar populations at several points throughout the halo of the half dozen massive highly-inclined galaxies in the sample. In approximately half of these galaxies, we detect a gradient in the color of the RGB; which we interpret as a metallicity gradient. Stellar halo formation models predict a wide variety of metallicity gradients: those in which the halos are dominated by stars formed in situ predict stronger gradients than we observe, while accretion-dominated halo models predict weaker or nonexistent gradients. Our measurements therefore provide a useful discriminator between stellar halo models, and at first look appear most consistent with the accretion-based model of Cooper et al. (2010).

Bailin, Jeremy; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Ghosts Survey

2015-01-01

105

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

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

Pre-peak ram pressure stripping in the Virgo cluster spiral galaxy NGC 4501  

NASA Astrophysics Data System (ADS)

VIVA Hi observations of the Virgo spiral galaxy NGC 4501 are presented. The Hi disk is sharply truncated to the southwest, well within the stellar disk. A region of low surface-density gas, which is more extended than the main Hi disk, is discovered northeast of the galaxy center. These data are compared to existing 6 cm polarized radio continuum emission, H?, and optical broad band images. We observe a coincidence between the western Hi and polarized emission edges, on the one hand, and a faint H? emission ridge, on the other. The polarized emission maxima are located within the gaps between the spiral arms and the faint H? ridge. Based on the comparison of these observations with a sample of dynamical simulations with different values for maximum ram pressure and different inclination angles between the disk and the orbital plane, we conclude that ram pressure stripping can account for the main observed characteristics. NGC 4501 is stripped nearly edge-on, is heading southwest, and is 200{-}300 Myr before peak ram pressure, i.e. its closest approach to M 87. The southwestern ridge of enhanced gas surface density and enhanced polarized radio-continuum emission is due to ram pressure compression. It is argued that the faint western H? emission ridge is induced by nearly edge-on ram pressure stripping. NGC 4501 represents an especially clear example of early stage ram pressure stripping of a large cluster-spiral galaxy.

Vollmer, B.; Soida, M.; Chung, A.; van Gorkom, J. H.; Otmianowska-Mazur, K.; Beck, R.; Urbanik, M.; Kenney, J. D. P.

2008-05-01

108

Transformation of the Virgo Dwarf Irregular Galaxy IC3418 by Ram Pressure Stripping  

NASA Astrophysics Data System (ADS)

We present optical imaging and spectroscopy of the Virgo Cluster dwarf irregular galaxy IC3418, which appears to be a "smoking gun" example of the transformation of a dwarf irregular (dI) into a dwarf elliptical (dE) by ram pressure stripping. GALEX UV and WIYN optical images show a spectacular 1-sided, 17 kpc length tail of UV-bright knots, head-tail, and linear stellar features. The only H$\\alpha$ emission arises from a few HII regions in the outer half of the tail, the brightest of which are at the heads of head-tail UV sources, whose tails point back toward the galaxy. In several of the elongated tail sources the H$\\alpha$ peaks are outwardly offset from the UV peaks. The head-tail (``fireballs'') and linear stellar features in the stripped tail are likely formed from dense gas clumps which continue to accelerate through ram pressure, leaving behind streams of newly formed stars which are not affected by ram pressure. Kinematics of HII regions in the tail show that the tail gas has experienced only modest acceleration, as the knots have velocities much closer to the galaxy than the cluster. Neither H-alpha nor HI emission are detected in the main body of the galaxy, despite structure in optical images resembling star forming regions and spiral arms, and several bright supergiants. Deep optical images show a relatively undisturbed stellar body and no smooth stellar component to the tail, but only clusters and streams of young stars, properties inconsistent with a tidal interaction. Keck optical spectra indicate star formation in the main body stopped ~200 Myr ago, with a radial gradient in quenching time of less than 100 Myr, indicating rapid stripping from the outside in. A starburst occurred prior to quenching, perhaps due to ram-pressure induced star formation. In IC3418, we propose that we are witnessing a critical stage in the transformation of a dI into a dE, the removal of nearly all of the ISM by ICM ram pressure stripping.

Kenney, Jeffrey D.

2013-06-01

109

Substructure Depletion in the Milky Way Halo by the Disk  

NASA Astrophysics Data System (ADS)

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 ~30 kpc of the Milky Way center, where disk shocking is expected to reduce the substructure abundance by a factor of 2 at 109 M sun and a factor of 3 at 107 M sun. The most massive subhalos with 1010 M 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; Springel, Volker; Hernquist, Lars; Keres, Dusan

2010-02-01

110

LAPP-EXP-2007-09 Data Acquisition System of the Virgo Gravitational Waves  

E-print Network

LAPP-EXP-2007-09 June 2007 Data Acquisition System of the Virgo Gravitational Waves Interferometric 2007 #12;Data Acquisition System of the Virgo Gravitational Waves Interferometric Detector F. Acernese of gravitational waves emitted by astrophysical sources. Its detector, based on a 3km arms interferometer

Boyer, Edmond

111

Search for gravitational waves from low mass compact binary coalescence in LIGO’s sixth science run and Virgo’s science runs 2 and 3  

E-print Network

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 ...

Barsotti, Lisa

112

Gamma-ray probes of dark matter substructure  

SciTech Connect

The substructure content of dark matter halos is interesting because it can be affected by complex galaxy physics and dark matter particle physics. However, observing the small scale structure of dark matter is a challenge. The subhalo abundance (mass function, minimum mass) and morphology (density profile, subhalo shape, subsubstructure) contain information about complex astrophysics (halo formation processes) and new exotic fundamental physics (dark matter interactions). Indirect detection of dark matter annihilation radiation (DMAR) in gamma rays may be the most direct method for observing small scale structure. I outline the ways in which gamma rays may probe halo substructure. If substructure is bountiful, it may be responsible for the eventual discovery of DMAR, for instance in galaxy clusters or the diffuse gamma-ray background. Otherwise, the observation of DMAR in places without much substructure, such as the Galactic center, would lead to strict limits on the properties of small scale structure. Properties of the gamma-ray angular power spectrum will also provide information or constraints on Milky Way halo substructure.

Campbell, Sheldon [Department of Physics and Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State University, 191 W. Woodruff Ave., Columbus, OH 43210 (United States)

2014-06-24

113

Investigation of dwarf galaxies in the Virgo cluster  

SciTech Connect

We have obtained 21-cm H I observations of a sample of 32 dwarf irregular (dI) and 12 dwarf elliptical (dE) galaxies that are located in the Virgo cluster. Altogether, 18 of 32 DIs were detected in H I, but none of the dEs were detected at a sensitivity level of M/sub Htsi/ = 2--3 x 10/sup 6/ M/sub sun/. The detected dIs have M/sub Htsi/>3 x 10/sup 7/ M/sub sun/. This disparity in H I content between dIs and dEs effectively dispels the possibility that the dEs are presently in a stage of quiescence (hibernation), between bursts of star formation. In order to supplement the 21-cm data, we have acquired optical spectroscopy, CCD images, and infrared photometry for a limited subsample of these dwarfs. The most significant result provided by this additional data is that the dEs, although very H I poor, nevertheless have observed (J-K) colors which indicate somewhat high metallicity, implying some degree of enrichment due to multiple generations of star formation. In contrast, most of the dIs are quite H I rich (with some having fractional H I contents that exceed 30% by mass), yet they are apparently in a quiescent phase, judging by their low central surface brightnesses (<10% of sky) and lack of resolution into obvious regions of star formation. A small gas-poor contingent of dIs have been found but there is no apparent correlation between dI gas content and either their velocity with respect to the Virgo ICM or their position in the cluster. In general, the velocity distribution of the dIs is flat with only a weak peak that corresponds to the mean velocity of the brighter galaxies in Virgo.

Bothun, G.D.; Mould, J.R.; Wirth, A.; Caldwell, N.

1985-05-01

114

The Effect of Thermal Conduction on the Virgo Cluster  

E-print Network

Thermal conduction has been suggested as a possible mechanism by which sufficient energy is supplied to the central regions of galaxy clusters to balance the effect of radiative cooling. Here we present the results of a simulated, high-resolution, 3-d Virgo cluster for different values of thermal conductivity (1, 1/10, 1/100, 0 times the full Spitzer value). Starting from an initially isothermal cluster atmosphere we allow the cluster to evolve freely over timescales of roughly $ 1.3-4.7 \\times 10^{9} $ yrs. Our results show that thermal conductivity at the Spitzer value can increase the central ICM radiative cooling time by a factor of roughly 3.6. In addition, for larger values of thermal conductvity the simulated temperature and density profiles match the observations significantly better than for the lower values. However, no physically meaningful value of thermal conductivity was able to postpone the cooling catastrophe (characterised by a rapid increase in the central density) for longer than a fraction of the Hubble time nor explain the absence of a strong cooling flow in the Virgo cluster today. We also calculate the effective adiabatic index of the cluster gas for both simulation and observational data and compare the values with theoretical expectations. Using this method it appears that the Virgo cluster is being heated in the cluster centre by a mechanism other than thermal conductivity. Based on this and our simulations it is also likely that the thermal conductvity is suppressed by a factor of at least 10 and probably more. Thus, we suggest that thermal conductvity, if present at all, has the effect of slowing down the evolution of the ICM, by radiative cooling, but only by a factor of a few.

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

2005-07-19

115

Detecting Gravitational Waves with the LIGO and Virgo Detectors  

NASA Astrophysics Data System (ADS)

The upcoming start of Advanced LIGO and Advanced Virgo will mark the beginning of a new era in gravitational wave astronomy. In this talk I will outline the path towards first direct detection with the second generation of gravitational wave interferometers, with focus on gravitational wave transients: coalescences of neutron star and/or black hole binary systems, core-collapse supernovae, isolated neutron star instabilities. I will describe the status of detector readiness, the analysis plan, prospects for detection rates and astrophysical inference and the potential for multi-messenger astronomy.

Cadonati, Laura; LIGO Scientific Collaboration, Virgo Collaboration

2015-01-01

116

Present star formation in sprials of the Virgo cluster  

NASA Technical Reports Server (NTRS)

From a study of spiral galaxies in the Virgo Cluster (VC), it is shown that the RDDO anemics with smooth arms and no sign of present formation of (massive) stars have HI surface densities below a threshold value of 2 to 5 x 10 to the 20th power atoms/sq cm. This value is very consistent with predictions of theoretical models. It is likely that the HI disks of VC HI-deficient RDDO anemics were deeply affected by ram pressure stripping in the gaseous intracluster medium, while VC HI deficient RDDO spirals were only peripherally stripped.

Guiderdoni, B.

1987-01-01

117

[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

118

Detecting dark matter substructures around the Milky Way with Gaia  

NASA Astrophysics Data System (ADS)

Cold dark matter (CDM) theory, a pillar of modern cosmology and astrophysics, predicts the existence of a large number of starless dark matter haloes surrounding the Milky Way (MW). However, clear observational evidence of these `dark' substructures remains elusive. Here, we present a detection method based on the small, but detectable, velocity changes that an orbiting substructure imposes on the stars in the MW disc. Using high-resolution numerical simulations we estimate that the new space telescope Gaia should detect the kinematic signatures of a few starless substructures provided the CDM paradigm holds. Such a measurement will provide unprecedented constraints on the primordial matter power spectrum at low-mass scales and potentially presents a new avenue to explore the particle physics properties of dark matter.

Feldmann, Robert; Spolyar, Douglas

2015-01-01

119

An E-ELT Case Study: Colour-Magnitude Diagrams of an Old Galaxy in the Virgo Cluster  

E-print Network

One of the key science goals for a diffraction limited imager on an Extremely Large Telescope (ELT) is the resolution of individual stars down to faint limits in distant galaxies. The aim of this study is to test the proposed capabilities of a multi-conjugate adaptive optics (MCAO) assisted imager working at the diffraction limit, in IJHK$_s$ filters, on a 42m diameter ELT to carry out accurate stellar photometry in crowded images in an Elliptical-like galaxy at the distance of the Virgo cluster. As the basis for realistic simulations we have used the phase A studies of the European-ELT project, including the MICADO imager (Davies & Genzel 2010) and the MAORY MCAO module (Diolaiti 2010). We convolved a complex resolved stellar population with the telescope and instrument performance expectations to create realistic images. We then tested the ability of the currently available photometric packages STARFINDER and DAOPHOT to handle the simulated images. Our results show that deep Colour-Magnitude Diagrams (p...

Deep, A; Tolstoy, E; Diolaiti, E; Bellazzini, M; Ciliegi, P; Davies, R I; Conan, J -M

2011-01-01

120

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

121

The Distribution of Barred Galaxies in the Virgo Cluster  

E-print Network

A study of the distribution of barred and nonbarred disk galaxies in the Virgo cluster is presented in an attempt to use the frequency and spatial distribution of galaxies with specific morphological features to study the efficiency of various environmental effects on the evolution of disk galaxies in clusters. The velocity distribution of the barred spirals in the Virgo region is clearly different than that of the nonbarred spirals, suggesting that barred spirals are more common in the main condensation of the cluster. A sample cleansed of galaxies not belonging to the main cluster condensation using the subcluster assignments of Binggeli et al. [A&AS, 98, 275 (1993)] bears this out, showing that the radial distribution of barred spirals is more centrally condensed than that of nonbarred spirals. In contrast to the spiral galaxies, the distribution of barred S0 galaxies is statistically indistinguishable from that of nonbarred S0's. Consideration of the level of tidal perturbation due to the cluster mass distribution as compared to that due to individual galaxies suggests that tidal triggering by the cluster mass distribution is the most likely source of the enhanced fraction of barred spirals in the cluster center.

Victor Andersen

1996-03-22

122

Seismic Attenuation Technology for the Advanced Virgo Gravitational Wave Detector  

NASA Astrophysics Data System (ADS)

The current interferometric gravitational wave detectors are being upgraded to what are termed 'second generation' devices. Sensitivities will be increased by an order of magnitude and these new instruments are expected to uncover the ?eld of gravitational astronomy. A main challenge in this endeavor is the mitigation of noise induced by seismic motion. Detailed studies with Virgo show that seismic noise can be reinjected into the dark fringe signal. For example, laser beam jitter and backscattered light limit the sensitivity of the interferometer. Here, we focus on seismic attenuators based on compact inverted pendulums in combination with geometric anti-prings to obtain 40 dB of attenuation above 4 Hz in six degrees of freedom. Low frequency resonances (< 0.5 Hz) are damped by using a control system based on input from LVDTs and geophones. Such systems are under development for the seismic attenuation of optical benches operated both in air and vacuum. The design and realization of the seismic attenuation system for the Virgo external injection bench, including its control scheme, will be discussed and stand-alone performance presented.

Beker, M. G.; Blom, M.; van den Brand, J. F. J.; Bulten, H. J.; Hennes, E.; Rabeling, D. S.

123

The Evolution of H I Disks in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We present the result of a new VLA H I imaging survey of Virgo galaxies, VIVA (VLA Imaging of Virgo in Atomic gas). The goal is to investigate the influence of the cluster on H I gas disks in different density regions. In order to sample various processes at work, we have carefully selected 48 spirals and 5 dwarfs/irregulars showing a range of star formation properties throughout the cluster. Overall, we confirm that galaxies near the cluster core (d_{M 87}<0.5 Mpc) are severely H I stripped while gas rich galaxies with extended H I disks are always found in the cluster outskirts (d_{M87}>1.0 Mpc). At intermediate distances from the cluster center however, our high resolution, high sensitivity H I data have revealed a range of H I features that are likely to represent different stripping stages through various effects. In particular, we find evidence for H I stripping due to the surrounding cluster gas even at the distances where the approximated intra-cluster medium (ICM) density is not high enough to affect galaxies. It appears that in some cases a dynamic ICM or a combination of tidal forces and ram-pressure are responsible for gas stripping at those locations. The survey result clearly shows that the impact of the cluster reaches quite far out from the cluster center.

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

2008-10-01

124

Stellar Populations Classification  

E-print Network

Outline Stellar Populations Classification Surface photometry STRUCTURE OF GALAXIES 2. Stellar Populations, classification, surface photometry Piet van der Kruit Kapteyn Astronomical Institute University Populations, classification, surface photometry #12;Outline Stellar Populations Classification Surface

Kruit, Piet van der

125

PubChem Substructure Fingerprint V1.3 http://pubchem.ncbi.nlm.nih.gov  

E-print Network

PubChem Substructure Fingerprint V1.3 http://pubchem.ncbi.nlm.nih.gov Page 1 of 21 5/1/2009 7:21:06 AM The PubChem System generates a binary substructure fingerprint for chemical structures. These fingerprints are used by PubChem for similarity neighboring and similarity searching. A substructure

Levin, Judith G.

126

A Galactic-Scale Origin for Stellar Clustering  

NASA Astrophysics Data System (ADS)

We recently presented a model for the cluster formation efficiency (CFE), i.e. the fraction of star formation occurring in bound stellar clusters. It utilizes the idea that the formation of stars and stellar clusters occurs across a continuous spectrum of ISM densities. Bound stellar clusters naturally arise from the high-density end of this density spectrum. Due to short free-fall times, these high-density regions can achieve high star formation efficiencies (SFEs) and can be unaffected by gas expulsion. Lower-density regions remain gas-rich and substructured, and are unbound upon gas expulsion. The model enables the CFE to be calculated using galactic-scale observables. I present a brief summary of the model physics, assumptions and caveats, and show that it agrees well with observations. Fortran and IDL routines for calculating the CFE are publicly available at http://www.mpa-garching.mpg.de/cfe.

Kruijssen, J. M. Diederik

127

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

128

Substructure depletion in the Milky Way halo by the disk  

E-print Network

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 the high-resolution Aquarius simulations and analytically estimate the cumulative 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 ~30 kpc of the Milky Way center, where disk shocking is expected to reduce the substructure abundance by a factor of several. This sugges...

D'Onghia, Elena; Hernquist, Lars; Keres, Dusan

2009-01-01

129

Dark matter substructure: cosmology the initial power spectrum  

Microsoft Academic Search

We explore the substructure content of Cold Dark Matter (CDM) halos expected for various assumptions about cosmology and the input inflationary power spectrum. Our model follows the mass accretion history of galaxy-sized halos using the Extended Press-Schechter formalism and tracks the orbital evolution of accreted subhalos under the influence of dynamical friction and tidal forces from the host potential. We

J. S. Bullock; A. R. Zentner

2002-01-01

130

FAMCS: finding all maximal common substructures in proteins.  

PubMed

Finding the common substructures shared by two proteins is considered as one of the central issues in computational biology because of its usefulness in understanding the structure-function relationship and application in drug and vaccine design. In this paper, we propose a novel algorithm called FAMCS (Finding All Maximal Common Substructures) for the common substructure identification problem. Our method works initially at the protein secondary structural element (SSE) level and starts with the identification of all structurally similar SSE pairs. These SSE pairs are then merged into sets using a modified Apriori algorithm, which will test the similarity of various sets of SSE pairs incrementally until all the maximal sets of SSE pairs that deemed to be similar are found. The maximal common substructures of the two proteins will be formed from these maximal sets. A refinement algorithm is also proposed to fine tune the alignment from the SSE level to the residue level. Comparison of FAMCS with other methods on various proteins shows that FAMCS can address all four requirements and infer interesting biological discoveries. PMID:16393147

Yao, Zhen; Xiao, Juan; Tung, Anthony K H; Sung, Wing Kin

2005-05-01

131

Fast Detection of Common Geometric Substructure in L. Paul Chew  

E-print Network

Fast Detection of Common Geometric Substructure in Proteins L. Paul Chew Dan Huttenlocher Klara Kedem § Jon Kleinberg ¶ Abstract We consider the problem of identifying common three orientation vectors of the two proteins. Our measure has several advantages over measures that are commonly

Field, David

132

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

133

Predicting High-Speed Machining Dynamics by Substructure Analysis  

Microsoft Academic Search

The practical implementation of high-speed machining (HSM) requires accurate knowledge of the machine dynamics. We apply receptance coupling substructure analysis to the prediction of the tool point dynamic response, combining frequency response measurements of individual components through appropriate connections to determine assembly dynamics using simple vector manipulations. This paper shows that the dynamic response before and after system changes may

T. L. Schmitz; R. R. Donalson

2000-01-01

134

Relational Proof System for Linear and Other Substructural Logics  

Microsoft Academic Search

In this paperwe give relationalsemanticsand an accompanyingrelationalproofsystem for a variety of intuitionistic substructural logics, including (intuitionistic) linear logic with exponentials. Starting with the (Kripke-style) semantics for F L as discussed in (13), we developed, in (11), a relational semantics and a relational proof system for full Lambek calculus. Here, we take this as a base and extend the results to

Wendy Maccaull

1997-01-01

135

Stellar substructures in the solar neighbourhood IV. Kinematic Group 1 in the Geneva-Copenhagen survey  

E-print Network

We determine detailed elemental abundances in stars belonging to the so-called Group 1 of the Geneva-Copenhagen survey (GCS) and compare the chemical composition with the Galactic thin- and thick-disc stars, with the GCS Group 2 and Group 3 stars, as well as with several kinematic streams of similar metallicities. The aim is to search for chemical signatures that might give information about the formation history of this kinematic group of stars. High-resolution spectra were obtained with the Fibre-fed Echelle Spectrograph (FIES) spectrograph at the Nordic Optical Telescope, La Palma, and were analysed with a differential model atmosphere method. Comparison stars were observed and analysed with the same method. The average value of [Fe/H] for the 37 stars of Group 1 is -0.20 +- 0.14 dex. Investigated Group 1 stars can be separated into three age subgroups. Along with the main 8- and 12-Gyr-old populations, a subgroup of stars younger than 5 Gyr can be separated as well. Abundances of oxygen, alpha-elements, a...

Ženovien?, R; Nordström, B; Stonkut?, E; Barisevi?ius, G

2015-01-01

136

Hubble Space Telescope Imaging of Decoupled Dust Clouds in the Ram Pressure Stripped Virgo Spirals NGC 4402 and NGC 4522  

NASA Astrophysics Data System (ADS)

We present the highest-resolution study to date of the interstellar medium (ISM) in galaxies undergoing ram pressure stripping, using Hubble Space Telescope BVI imaging of NGC 4522 and NGC 4402, Virgo Cluster spirals that are well known to be experiencing intracluster medium (ICM) ram pressure. We find that throughout most of both galaxies, the main dust lane has a fairly well-defined edge, with a population of giant molecular cloud (GMC) sized (tens- to hundreds-of-pc scale), isolated, highly extincting dust clouds located up to ~1.5 kpc radially beyond it. Outside of these dense clouds, the area has little or no diffuse dust extinction, indicating that the clouds have decoupled from the lower-density ISM material that has already been stripped. Several of the dust clouds have elongated morphologies that indicate active ram pressure, including two large (kpc scale) filaments in NGC 4402 that are elongated in the projected ICM wind direction. We calculate a lower limit on the H I + H2 masses of these clouds based on their dust extinctions and find that a correction factor of ~10 gives cloud masses consistent with those measured in CO for clouds of similar diameters, probably due to the complicating factors of foreground light, cloud substructure, and resolution limitations. Assuming that the clouds' actual masses are consistent with those of GMCs of similar diameters (~104-105 M ?), we estimate that only a small fraction (~1%-10%) of the original H I + H2 remains in the parts of the disks with decoupled clouds. Based on H? images, a similar fraction of star formation persists in these regions, 2%-3% of the estimated pre-stripping star formation rate. We find that the decoupled cloud lifetimes may be up to 150-200 Myr.

Abramson, Anne; Kenney, Jeffrey D. P.

2014-03-01

137

The WSRT Virgo H i filament survey. I. Total power data  

NASA Astrophysics Data System (ADS)

Context. Observations of neutral hydrogen can provide a wealth of information about the kinematics of galaxies. To learn more about the large-scale structures and accretion processes, the extended environment of galaxies have to be observed. Numerical simulations predict a cosmic web of extended structures and gaseous filaments. Aims: To observe the direct vicinity of galaxies, column densities have to be achieved that probe the regime of Lyman limit systems. Typically, H i observations are limited to a brightness sensitivity of NHI ~ 1019 cm-2, but this has to be improved by ~2 orders of magnitude. Methods: With the Westerbork Synthesis Radio Telescope (WSRT), we mapped the galaxy filament connecting the Virgo Cluster with the Local Group. About 1500 square degrees on the sky was surveyed with Nyquist sampled pointings. By using the WSRT antennas as single-dish telescopes instead of the more conventional interferometer, we were very sensitive to extended emission. The survey consists of a total of 22 000 pointings, and each pointing was observed for two minutes with 14 antennas. Results: We reached a flux sensitivity of 16 mJy beam-1 over 16 km s-1, corresponding to a brightness sensitivity of NHI ~ 3.5 × 1016 cm-2 for sources that fill the beam. At a typical distance of ten Mpc probed by this survey, the beam extent corresponds to about 145 kpc on linear scale. Although the processed data cubes are affected by confusion owing to the very large beam size, we can identify most of the galaxies that have been observed in HIPASS. Furthermore we made 20 new candidate detections of neutral hydrogen. Several of the candidate detections can be linked to an optical counterpart. The majority of the features, however, do not show any signs of stellar emission. Their origin is investigated further with accompanying H i surveys, which will be published in follow-up papers. Appendix is only available in electronic form at http://www.aanda.org

Popping, A.; Braun, R.

2011-03-01

138

Environmental Effects in Clusters: Modified Far-Infrared--Radio Relations within Virgo Cluster Galaxies  

E-print Network

(abridged) We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo cluster spiral galaxies using {\\it Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the FIR-radio correlation within normal galaxies, we use our infrared data to create model radio maps which we compare to the observed radio images. For 6 of our sample galaxies we find regions along their outer edges that are highly deficient in the radio compared with our models. We believe these observations are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit region to lie just exterior to a region of high radio polarization and flat radio spectral index, although the total 20 cm radio continuum in this region does not appear strongly enhanced. These characteristics seem consistent for other galaxies with radio polarization data in the literature. The strength of the radio deficit is inversely correlated with the time since peak pressure as inferred from stellar population studies and gas stripping simulations, suggesting the strength of the radio deficit is good indicator of the strength of the current ram pressure. We also find that galaxies having {\\it local} radio {\\it deficits} appear to have {\\it enhanced global} radio fluxes. Our preferred physical picture is that the observed radio deficit regions arise from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated magnetic field, thereby creating synchrotron tails as observed for some of our galaxies. We propose that CR particles are also re-accelerated by ICM-driven shocklets behind the observed radio deficit regions which in turn enhances the remaining radio disk brightness.

E. J. Murphy; J. D. P. Kenney; G. Helou; A. Chung; J. H. Howell

2008-12-15

139

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

140

TIDAL STRIPPING OF GLOBULAR CLUSTERS IN THE VIRGO CLUSTER  

SciTech Connect

With the aim of finding evidence of tidal stripping of globular clusters (GCs) we analyzed a sample of 13 elliptical galaxies taken from the ACS Virgo Cluster Survey (VCS). These galaxies belong to the main concentration of the Virgo Cluster (VC) and present absolute magnitudes -18.5 < M{sub z} < -22.5. We used the public GC catalog of Jordan et al. and separated the GC population into metal poor (blue) and metal rich (red) according to their integrated colors. The galaxy properties were taken from Peng et al. We found the following. (1) The specific frequencies (S{sub N} ) of total and blue GC populations increase as a function of the projected galaxy distances r{sub p} to M87. A similar result is observed when three-dimensional distances r {sub 3D} are used. The same behaviors are found if the analysis is made using the number of GCs per 10{sup 9} M{sub odot} (T). No correlations between S{sub N} or T and r{sub p} or r {sub 3D} is observed for the red GC population. The correlations for the blue GCs (typically more extended) and the lack of correlations for the red GCs (more concentrated) with the clustocentric distance of the host galaxy are interpreted as evidence of GCs stripping due to tidal forces. (2) No correlation is found between the slope of GC density profiles of host galaxies and the galaxy distance to M87 (Virgo central galaxy). The lack of such a correlation is interpreted in terms of a shrinkage of the GC distribution after the stripping of GCs in the outermost region of galaxies. (3) We also computed the local density of GCs ({rho}{sub out}) located further than 6.2 kpc from the galaxy center for nine galaxies of our sample. We find that the GC population around most of these galaxies is mainly composed of blue GCs. The two highest values of {rho}{sub out} are found in the core of the VC (up to 100 kpc) and correspond to the two lowest values of S{sub N} . Our results suggest that the number and the fraction of blue and red GCs observed in elliptical galaxies located near the centers of massive clusters could be significantly different from the underlying GC population. These differences could be explained by tidal stripping effects that occur as galaxies approach the centers of clusters.

Coenda, Valeria; Muriel, Hernan; Donzelli, Carlos [Instituto de Investigaciones en Astronomia Teorica y Experimental (IATE), Observatorio Astronomico OAC, Laprida 854, X5000BGR, Cordoba (Argentina)], E-mail: vcoenda@oac.uncor.edu, E-mail: hernan@oac.uncor.edu, E-mail: donzelli@stsci.edu

2009-08-01

141

Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO's Sixth Science Run and Virgo's Science Runs 2 and 3  

NASA Technical Reports Server (NTRS)

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20. 2010. We searched for signals from binaries with total mass between 2 and 25 Stellar Mass; this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass. including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron star-black hole, and binary black hole systems are 1.3 x 10(exp -4), 3.1 x 10(exp -5), and 6.4 x 10(exp -6)/cu Mpc/yr, respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.

Abadie, J.; Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M.; Accadia, T.; Acernese, F.; Adams, C.; Adhikari, R.; Affeldt, C.; Agathos, M.; Ajith, P.; Allen, B.; Allen, G. S.; Ceron, E. Amador; Amariutei, D.; Amin, R. S.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Arain, M. A.; Araya, M. C.; Blackburn, L.; Camp, J. B.; Cannizzo, J.

2012-01-01

142

{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

143

Far-Infrared Emission from Dust in the ISOPHOT Virgo Cluster Deep Sample  

E-print Network

We review the characteristics of the dust continuum emission from normal galaxies, as revealed by the ISOPHOT Virgo Cluster Deep Survey (Tuffs et al. 2002; Popescu et al. 2002, Popescu & Tuffs 2002b).

Richard J. Tuffs

2002-08-05

144

Neutral hydrogen detection survey of dwarf galaxies. II. Faint Virgo dwarfs and a field sample  

SciTech Connect

Neutral hydrogen spectra are presented for 53 faint dwarf galaxies in Virgo, completing the Arecibo survey of all late-type dwarfs in the Virgo Cluster Catalog, and for 42 dwarf galaxies from the field sample of Binggeli et al. (1989). For detected galaxies, heliocentric velocities, profile widths, and single-beam fluxes are tabulated. The field sample has been used to investigate the field luminosity function and the clustering of dwarf galaxies vis-a-vis bright galaxies. 31 refs.

Hoffman, G.L.; Williams, H.L.; Salpeter, E.E.; Sandage, A.; Binggeli, B. (Lafayette College, Easton, PA (USA) Delaware Univ., Newark (USA) Cornell Univ., Ithaca, NY (USA) Mount Wilson and Las Campanas Observatories, Pasadena, CA (USA) Arcetri, Osservatorio Astrofisico, Florence (Italy))

1989-12-01

145

Distance to the Virgo cluster galaxy M100 from Hubble Space Telescope observations of Cepheids  

Microsoft Academic Search

Accurate distances to galaxies are critical for determining the present expansion rate of the Universe or Hubble constant (H0). An important step in resolving the current uncertainty in H0 is the measurement of the distance to the Virgo cluster of galaxies. New observations using the Hubble Space Telescope yield a distance of 17.1 +\\/- 1.8 Mpc to the Virgo cluster

Wendy L. Freedman; Barry F. Madore; Jeremy R. Mould; Robert Hill; Laura Ferrarese; Robert C. Kennicutt; Abhijit Saha; Peter B. Stetson; John A. Graham; Holland Ford; John G. Hoessel; John Huchra; Shaun M. Hughes; Garth D. Illingworth

1994-01-01

146

VizieR Online Data Catalog: Virgo Photometry Catalogue (VPC) (Young+ 1998)  

NASA Astrophysics Data System (ADS)

The Virgo Photometry Catalogue (VPC) contains independently calibrated surface photometry in the U, BJ and RC bands for over 1000 galaxies (including background objects) brighter than BJ25=19.0 in a 23°2 area of the sky centred on R.A., Dec.(1950)= 12h26m, +13°08'. The angular resolution of the photometry varies from band to band and was in each case determined from the FWHM of stellar profiles: 4.75+/-0.1arcsec in the U band, 5.0+/-0.1arcsec in the BJ band and 6.0+/-0.1arcsec in the RC band. The photometry was intended for the derivation of accurate magnitudes and colours and is therefore not of high resolution. Stellar contamination of the galaxy sample is minimal, and cannot exceed about 3 faint-end objects in total (i.e. it is less than about 0.25%). Parameters listed for catalogued galaxies include: equatorial coordinates; morphological types; surface-brightness profile parameters (which preserve the majority of the surface photometry information); U, BJ and RC isophotal magnitudes; U, BJ, RC and [transformed] B total magnitudes; (U-BJ) and (BJ-RC) equal-area colours, apparent angular radii, ellipticities, position angles, heliocentric radial velocities and alternative designations. All total magnitudes and total colours are extrapolated according to the "t" system of Young et al. (1998A&AS..130..173Y). The VPC is based primarily on four UK-Schmidt plates, all of which were scanned using the COSMOS measuring machine at the Royal Observatory Edinburgh. All magnitudes, colours and surface-brightness parameters are derived from numerical integrations of segmented plate-scan data; except for (in 109 cases) saturated and (in 51 cases) inextricably merged images. The latter 51 images are listed in Table 14 (Appendix D) of the original paper, whilst data for the remaining 1129 objects [i.e. including ones for which the VPC photometry is saturated in one or more bands] are listed in the main catalogue. (6 data files).

Young, C. K.; Currie, M. J.

1998-05-01

147

Creating mock catalogues of stellar haloes from cosmological simulations  

NASA Astrophysics Data System (ADS)

We present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmological simulations and show how the catalogues can be used to test and interpret observational data. The catalogues are constructed from a combination of methods. A semi-analytic galaxy formation model is used to calculate the star formation history in haloes in an N-body simulation and dark matter particles are tagged with this stellar mass. The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained. A set of catalogues based on the ? cold dark matter Aquarius simulations of Milky Way mass haloes have been created and made publicly available on a website. Two example applications are discussed that demonstrate the power and flexibility of the mock catalogues. We show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. We also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stellar populations, allow streams to be easily identified.

Lowing, Ben; Wang, Wenting; Cooper, Andrew; Kennedy, Rachel; Helly, John; Cole, Shaun; Frenk, Carlos

2015-01-01

148

The nature and origin of substructure in the outskirts of M31 - II. Detailed star formation histories  

NASA Astrophysics Data System (ADS)

While wide-field surveys of M31 have revealed much substructure at large radii, understanding the nature and origin of this material is not straightforward from morphology alone. Using deep Hubble Space Telescope/Advanced Camera for Surveys data, we have derived further constraints in the form of quantitative star formation histories (SFHs) for 14 inner halo fields which sample diverse substructures. In agreement with our previous analysis of colour-magnitude diagram morphologies, we find the resultant behaviours can be broadly separated into two categories. The SFHs of `disc-like' fields indicate that most of their mass has formed since z ˜ 1, with one quarter of the mass formed in the last 5 Gyr. We find `stream-like' fields to be on average 1.5 Gyr older, with ? 10 per cent of their stellar mass formed within the last 5 Gyr. These fields are also characterized by an age-metallicity relation showing rapid chemical enrichment to solar metallicity by z = 1, suggestive of an early-type progenitor. We confirm a significant burst of star formation 2 Gyr ago, discovered in our previous work, in all the fields studied here. The presence of these young stars in our most remote fields suggests that they have not formed in situ but have been kicked-out from the thin disc through disc heating in the recent past.

Bernard, Edouard J.; Ferguson, Annette M. N.; Richardson, Jenny C.; Irwin, Mike J.; Barker, Michael K.; Hidalgo, Sebastian L.; Aparicio, Antonio; Chapman, Scott C.; Ibata, Rodrigo A.; Lewis, Geraint F.; McConnachie, Alan W.; Tanvir, Nial R.

2015-01-01

149

Stick-slip substructure in rapid tape peeling  

NASA Astrophysics Data System (ADS)

The peeling of adhesive tape is known to proceed with a stick-slip mechanism and produces a characteristic ripping sound. The peeling also produces light and when peeled in a vacuum, even X-rays have been observed, whose emissions are correlated with the slip events. Here we present direct imaging of the detachment zone when Scotch tape is peeled off at high speed from a solid surface, revealing a highly regular substructure, during the slip phase. The typical 4-mm-long slip region has a regular substructure of transverse 220?m wide slip bands, which fracture sideways at speeds over 300 m/s. The fracture tip emits waves into the detached section of the tape at ˜100m/s , which promotes the sound, so characteristic of this phenomenon.

Thoroddsen, S. T.; Nguyen, H. D.; Takehara, K.; Etoh, T. G.

2010-10-01

150

Substructure: Clues to the Formation of Clusters of Galaxies  

E-print Network

We have examined the spatial distribution of substructure in clusters of galaxies using Einstein X-ray observations. Subclusters are found to have a markedly anisotropic distribution that reflects the surrounding matter distribution on supercluster scales. Our results suggest a picture in which cluster formation proceeds by mergers of subclusters along large-scale filaments. The implications of such an anisotropic formation process for the shapes, orientations and kinematics of clusters are discussed briefly.

Michael J. West; Christine Jones; William Forman

1995-07-26

151

Substructure depletion in the Milky Way halo by the disk  

Microsoft Academic Search

We employ numerical simulations and simple analytical estimates to argue that\\u000adark matter substructures orbiting in the inner regions of the Galaxy can be\\u000aefficiently destroyed by disk shocking, a dynamical process known to affect\\u000aglobular star clusters. We carry out a set of fiducial high-resolution\\u000acollisionless simulations in which we adiabatically grow a disk, allowing us to\\u000aexamine the

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

2009-01-01

152

ON POSSIBLE NON-HOMEOMORPHIC SUBSTRUCTURES OF THE REAL LINE  

E-print Network

cardinal ; (ii) ZFC+9M a suÃ?ciently elementary submodel of the universe of sets with RM not homeomorphic space X = hX; T i when X 2 M , where M is a submodel, not necessar- ily transitive, of the universe, as a \\substructure" of hX; T i. (In fact, as they observe, it suÃ?ces to take M a submodel of the class of sets

Welch, Philip

153

The evolution of substructure - I. A new identification method  

NASA Astrophysics Data System (ADS)

We describe our new `MLAPM halo finder' (MHF), which is based on the adaptive grid structure of the N-body code MLAPM. We then extend the MHF code in order to track the orbital evolution of gravitationally bound objects through any given cosmological N-body simulation - our so-called `MLAPM halo tracker' (MHT). The mode of operation of MHT is demonstrated using a series of eight high-resolution N-body simulations of galaxy clusters. Each of these haloes hosts more than one million particles within their virial radii rvir. We use MHT as well as MHF to follow the temporal evolution of hundreds of individual satellites, and show that the radial distribution of these substructure satellites follows a `universal' radial distribution irrespective of the environment and formation history of the host halo. This in fact might pose another problem for simulations of cold dark matter structure formation, as there are recent findings by Taylor, Silk & Babul that the Milky Way satellites are found preferentially closer to the Galactic Centre and simulations underestimate the amount of central substructure. Further, this universal substructure profile is anti-biased with respect to the underlying dark matter profile. The halo finder MHF will become part of the open source MLAPM distribution.

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

2004-06-01

154

The evolution substructure I: a new identification method  

E-print Network

We describe our new "MLAPM-halo-finder" (MHF) which is based on the adaptive grid structure of the N-body code MLAPM. We then extend the MHF code in order to track the orbital evolution of gravitationally bound objects through any given cosmological N-body simulation - our so-called "MLAPM-halo-tracker" (MHT). The mode of operation of MHT is demonstrated using a series of eight high-resolution N-body simulations of galaxy clusters. Each of these halos hosts more than one million particles within their virial radii Rvir. We use MHT as well as MHF to follow the temporal evolution of hundreds of individual satellites, and show that the radial distribution of these substructure satellites follows a "universal" radial distribution irrespective of the host halo's environment and formation history. This in fact might pose another problem for simulations of CDM structure formation as there are recent findings by Taylor et al. (2003) that the Milky Way satellites are found preferentially closer to the galactic centre and simulations underestimate the amount of central substructure, respectively. Further, this universal substructure profile is anti-biased with respect to the underlying dark matter profile. Both the halo finder MHF and the halo tracker MHT will become part of the open source MLAPM distribution.

Stuart P. D. Gill; Alexander Knebe; Brad K. Gibson

2004-04-13

155

Halo Substructure in the Hercules-Aquila Cloud  

NASA Astrophysics Data System (ADS)

We present the velocity substructure in the direction of the northern portion of the Hercules-Aquila Cloud using observations taken at Apache Point Observatory (APO), in conjunction with Data Release 10 of the Sloan Digital Sky Survey (SDSS). The Hercules Aquila Cloud is an overdensity of halo stars found at low Galactic latitudes in the direction of the Galactic center. Using Blue Horizontal Branch stars (BHBs), we identify several structures as overdensities in distance and velocity. The most prominent of these structures covers ~ 250 deg2 of the sky centered around (l,b)~(55°,45°) and ranges in distance from 16~27 kpc. This structure is found to be metal poor, [Fe/H] ~ -2.0, with a tight velocity distribution of -60 km/s < vgsr < -20 km/s. Although this halo substructure has about the same location and distance as the Hercules Aquila Cloud, the line-of-sight velocity differs by 220 km/s from the published velocity for this cloud. The other low metallicity substructures that appear to clump in distance and velocity have similarly large spatial distributions on the sky, which may point to additional ancient accretion events. This research is supported by the NSF through grants AST 09-37523 and AST 10-09670, as well as the NASA-NY Space Grant.

Martin, Charles; Newberg, Heidi Jo; Carlin, Jeffrey L.; Willett, Benjamin A.; Yanny, Brian; Kent, Stephen M.

2015-01-01

156

Substructure in the lens HE 0435-1223  

NASA Astrophysics Data System (ADS)

We investigate the properties of dark matter substructure in the gravitational lens HE 0435-1223 (zl=0.455) via its effects on the positions and flux ratios of the quadruply imaged background quasar (zs= 1.689). We start with a smooth mass model, add individual, truncated isothermal clumps near the lensed images and use the Bayesian evidence to compare the quality of different models. Compared with smooth models, models with at least one clump near image A are strongly favoured. The mass of this clump within its Einstein radius is log10(MAEin) = 7.65+0.87- 0.84 (in units of h-170 M?). The Bayesian evidence provides weaker support for a second clump near image B, with log10(MBEin) = 6.55+1.01- 1.51. We also examine models with a full population of substructure, and find the mass fraction in substructure at the Einstein radius to be fsub>rsim 0.000 77, assuming the total clump masses follow a mass function dN/dM?M-1.9 over the range M= 107-1010 M?. Few-clump and population models produce similar Bayesian evidence values, so neither type of model is objectively favoured.

Fadely, Ross; Keeton, Charles R.

2012-01-01

157

The Effect of Substructure on Mass Estimates of Galaxies  

E-print Network

Large galaxies are thought to form hierarchically, from the accretion and disruption of many smaller galaxies. Such a scenario should naturally lead to galactic phase-space distributions containing some degree of substructure. We examine the errors in mass estimates of galaxies and their dark halos made using the projected phase-space distribution of a tracer population (such as a globular cluster system or planetary nebulae) due to falsely assuming that the tracers are distributed randomly. The level of this uncertainty is assessed by applying a standard mass estimator to samples drawn from 11 random realizations of galaxy halos containing levels of substructure consistent with current models of structure formation. We find that substructure will distort our mass estimates by up to ~20% - a negligible error compared to statistical and measurement errors in current derivations of masses for our own and other galaxies. However, this represents a fundamental limit to the accuracy of any future mass estimates made under the assumption that the tracer population is distributed randomly, regardless of the size of the sample or the accuracy of the measurements.

Brian M. Yencho; Kathryn V. Johnston; James S. Bullock; Katherine L. Rhode

2006-04-04

158

Major substructure in the M31 outer halo: the South-West Cloud  

NASA Astrophysics Data System (ADS)

We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo of M31. The South-West Cloud lies at a projected distance of ˜100 kpc from the centre of M31 and extends for at least ˜50 kpc in projection. We use Pan-Andromeda Archaeological Survey photometry of red giant branch stars to determine a distance to the South-West Cloud of 793^{+45}_{-45} kpc. The metallicity of the cloud is found to be [Fe/H] = -1.3 ± 0.1. This is consistent with the coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities determined using an independent technique of [Fe/H] = -1.35 ± 0.15. We measure a brightness for the Cloud of MV = -12.1 mag; this is ˜75 per cent of the luminosity implied by the luminosity-metallicity relation. Under the assumption that the South-West Cloud is the visible remnant of an accreted dwarf satellite, this suggests that the progenitor object was amongst M31's brightest dwarf galaxies prior to disruption.

Bate, N. F.; Conn, A. R.; McMonigal, B.; Lewis, G. F.; Martin, N. F.; McConnachie, A. W.; Veljanoski, J.; Mackey, A. D.; Ferguson, A. M. N.; Ibata, R. A.; Irwin, M. J.; Fardal, M.; Huxor, A. P.; Babul, A.

2014-02-01

159

Multicolor photometry of the galaxy cluster A98: substructures and star formation properties  

NASA Astrophysics Data System (ADS)

An optical photometric observation with the Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor system is carried out for A98 (z = 0.104), a galaxy cluster with two large enhancements in X-ray surface brightness. Spectral energy distributions (SEDs) covering 15 intermediate bands are obtained for all sources detected down to V ~ 20 mag in a field of 58' × 58'. After star-galaxy separation with color-color diagrams, a photometric redshift technique is applied to the galaxy sample for further membership determination. The color-magnitude relation is taken as a further restriction of the early-type cluster galaxies. As a result, a list of 198 faint member galaxies is achieved. Based on the newly generated sample of member galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated in detail. A separate galaxy group, A98X, is also found to the south of the main concentration of A98, which is gravitationally unbound to A98. For 74 spectroscopically confirmed member galaxies, the environmental effect on the star formation history is investigated. The bright galaxies in the core region are found to have shorter time scales of star formation, longer mean stellar ages, and higher interstellar medium metallicities, which can be interpreted in the context of the hierarchical cosmological scenario.

Zhang, Li; Yuan, Qi-Rong; Zhou, Xu; Jiang, Zhao-Ji; Yang, Yan-Bin; Ma, Jun; Wu, Jiang-Hua; Wu, Zhen-Yu

2010-01-01

160

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

161

Transformation of a Virgo Cluster Dwarf Irregular Galaxy by Ram Pressure Stripping: IC3418 and its Fireballs  

E-print Network

We present optical imaging and spectroscopy and HI imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only H-alpha emission arises from a few HII regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have H-alpha peaks outwardly offset by 80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300+/-100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither H-alpha nor H...

Kenney, Jeffrey D P; Jachym, Pavel; Crowl, Hugh H; Dague, William; Chung, Aeree; van Gorkom, Jacqueline; Vollmer, Bernd

2013-01-01

162

THE ACS VIRGO CLUSTER SURVEY. XVII. THE SPATIAL ALIGNMENT OF GLOBULAR CLUSTER SYSTEMS WITH EARLY-TYPE HOST GALAXIES  

SciTech Connect

We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation ({epsilon} > 0.2) and intermediate to high luminosities (M{sub z} < -19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, we also find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and that the present-day major axis is an indicator of the preferred merging axis.

Wang Qiushi; Peng, Eric W. [Department of Astronomy, Peking University, Beijing 100871 (China); Blakeslee, John P.; Cote, Patrick; Ferrarese, Laura [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Jordan, Andres [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Mei, Simona [University of Paris 7 Denis Diderot, F-75205 Paris Cedex 13 (France); West, Michael J., E-mail: peng@pku.edu.cn [Maria Mitchell Observatory, 4 Vestal Street, Nantucket, MA 02554 (United States)

2013-06-01

163

History of Stellar Interferometry  

NASA Technical Reports Server (NTRS)

This viewgraph presentation reviews the history of stellar interferometry from the suggestion of Fizeau that stellar interferometry was possible,to the use of the Mark I, II and III for astrometry. Photographs, and parts of original articles are presented.

Lawson, Peter R.

2004-01-01

164

Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy  

NASA Astrophysics Data System (ADS)

We study the dynamics of faint stellar substructures around the Umbrella Galaxy, NGC 4651, which hosts a dramatic system of streams and shells formed through the tidal disruption of a nucleated dwarf elliptical galaxy. We elucidate the basic characteristics of the system (colours, luminosities, stellar masses) using multiband Subaru/Suprime-Cam images. The implied stellar mass ratio of the ongoing merger event is ˜1:50. We identify candidate kinematic tracers (globular clusters, planetary nebulae, H II regions) and follow up a subset with Keck/DEIMOS (DEep Imaging Multi-object Spectrograph) spectroscopy to obtain velocities. We find that 15 of the tracers are likely associated with halo substructures, including the probable stream progenitor nucleus. These objects delineate a kinematically cold feature in position-velocity phase space. We model the stream using single test particle orbits, plus a rescaled pre-existing N-body simulation. We infer a very eccentric orbit with a period of ˜0.35 Gyr and turning points at ˜2-4 and ˜40 kpc, implying a recent passage of the satellite through the disc, which may have provoked the visible disturbances in the host galaxy. This work confirms that the kinematics of low surface brightness substructures can be recovered and modelled using discrete tracers - a breakthrough that opens up a fresh avenue for unravelling the detailed physics of minor merging.

Foster, C.; Lux, H.; Romanowsky, A. J.; Martínez-Delgado, D.; Zibetti, S.; Arnold, J. A.; Brodie, J. P.; Ciardullo, R.; GaBany, R. J.; Merrifield, M. R.; Singh, N.; Strader, J.

2014-08-01

165

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

166

A 3D view of the Hydra I cluster core- II. Stellar populations  

NASA Astrophysics Data System (ADS)

Several observations of the central region of the Hydra I galaxy cluster point to a multi-epoch assembly history. Using our novel FORS2/VLT spectroscopic data set, we were able to map the luminosity-weighted age, [Fe/H] and [?/Fe] distributions for the stellar populations around the cD galaxy NGC 3311. Our results indicate that the stellar populations follow the trends of the photometric substructures, with distinct properties that may aid to constrain the evolutionary scenarios for the formation of the cluster core.

Barbosa, Carlos Eduardo; Arnaboldi, Magda; Hilker, Michael; Coccato, Lodovico; Richtler, Tom; Mendes de Oliveira, Cláudia

2015-02-01

167

Comparative properties of Virgo Cluster dwarf irregulars and spirals  

SciTech Connect

The optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog are analyzed. In particular, the continuity of optical properties, hydrogen masses, and dynamical properties are examined as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals. 88 references.

Hoffman, G.L.; Helou, G.; Salpeter, E.E.

1988-01-01

168

Comparative properties of Virgo Cluster dwarf irregulars and spirals  

NASA Technical Reports Server (NTRS)

The optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog are analyzed. In particular, the continuity of optical properties, hydrogen masses, and dynamical properties are examined as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals.

Hoffman, G. Lyle; Helou, George; Salpeter, E. E.

1988-01-01

169

Interstellar Gas in Low Mass Virgo Cluster Spiral Galaxies  

E-print Network

We have measured the strengths of the [C II] 158 micron, [N II] 122 micron, and CO (1 - 0) lines from five low blue luminosity spiral galaxies in the Virgo Cluster, using the Infrared Space Observatory and the NRAO 12m millimeter telescope. Two of the five galaxies have high L([C II)]/L(CO) and L(FIR)/L(CO) ratios compared to higher mass spirals. These two galaxies, NGC 4294 and NGC 4299, have L([C II])/L(CO) ratios of >14,300 and 15,600, respectively, which are similar to values found in dwarf irregular galaxies. This is the first time that such enhanced L([C II])/L(CO) ratios have been found in spiral galaxies. This result may be due to low abundances of dust and heavy elements, which can cause the CO (1 - 0) measurements to underestimate the molecular gas content. Another possibility is that radiation from diffuse HI clouds may dominate the [C II] emission from these galaxies. Less than a third of the observed [C II] emission arises from HII regions.

Beverly J. Smith; Suzanne C. Madden

1997-04-14

170

H I Observations of the Virgo Cluster: Catalog Statistics, Optically Inert Detections, and H I Streams  

NASA Astrophysics Data System (ADS)

The Arecibo Legacy Fast ALFA survey (Giovanelli, R., et al. 2005, AJ, 130, 2598) has yielded a complete H I dataset of the Virgo Cluster and its environs (Kent et al. in preparation, and Giovanelli, R., et al. 2007, AJ, 133, 2569). Several H I candidates have been detected in the vicinity of the Virgo Cluster, all at cz? < 3,000 km s-1. Assuming a distance to Virgo of 16.7 Mpc, the minimum detectable H I mass is of order 2× 107 M?. 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 H I detections do not coincide with any nearby counterparts visible in optical surveys (Kent, B.R., et al. 2007, ApJ, 665, L15). The detections lie outside the influence of effects from ram-pressure stripping in the Virgo Cluster. The parameters of these detections and their follow-up observations will be described, as well as the contents of the first Virgo region catalogs released from the survey. The effects of the cluster environment on the formation and evolution of such objects will be corroborated with observed properties.

Kent, B. R.

2008-08-01

171

Prospects and challenges in the electromagnetic follow-up of LIGO-Virgo gravitational wave transients  

NASA Astrophysics Data System (ADS)

The kilometer-scale ground based gravitational wave (GW) detectors, LIGO and Virgo, are being upgraded to their advanced configurations. We expect the two LIGO observatories to undertake a 3 month science run in 2015 with a limited sensitivity. Virgo should come online in 2016, and join LIGO for a 6 month science run. Through a sequence of science runs and commissioning periods, the final sensitivity should be reached by ~2019. LIGO and Virgo are expected to deliver the first direct detection of gravitational wave transients in the next few years. Most of the known sources of GWs targeted by LIGO and Virgo will likely be luminous in the electromagnetic (EM) spectrum as well. Compact binary coalescences are thought to be progenitors of short gamma-ray bursts, while long gamma-ray bursts are likely to be associated with core collapse supernova. A joint detection of gravitational and EM radiation may help confirm these associations, and expand our understanding of those astrophysical systems. Due to the transient nature, a search for the EM counterparts to GW events should be done with the shortest latency. In this paper we describe the EM follow-up program of Advanced LIGO and Virgo, from the search for GWs to the production of sky maps. Furthermore, we quantify the expected sky localization errors in the first two years of operation of the advanced detectors network.

Vitale, Salvatore

2014-07-01

172

Structure, mass and distance of the Virgo cluster from a Tolman-Bondi model  

E-print Network

We have applied a relativistic Tolman-Bondi model of the Virgo cluster to a sample of 183 galaxies with measured distances within a radius of 8 degrees from M87. We find that the sample is significantly contaminated by background galaxies which lead to too large a cluster mean distance if not excluded. The Tolman-Bondi model predictions, together with the HI deficiency of spiral galaxies, allows one to identify these background galaxies. One such galaxy is clearly identified among the 6 calibrating galaxies with Cepheid distances. As the Tolman-Bondi model predicts the expected distance ratio to the Virgo distance, this galaxy can still be used to estimate the Virgo distance, and the average value over the 6 galaxies is 15.4 +- 0.5 Mpc. Well-known background groups of galaxies are clearly recovered, together with filaments of galaxies which link these groups to the main cluster, and are falling into it. No foreground galaxy is clearly detected in our sample. Applying the B-band Tully-Fisher method to a sample of 51 true members of the Virgo cluster according to our classification gives a cluster distance of 18.0 +- 1.2 Mpc, larger than the mean Cepheid distance. Finally, the same model is used to estimate the Virgo cluster mass, which is M = 1.2 10^{15} Msun within 8 degrees from the cluster center (2.2 Mpc radius), and amounts to 1.7 virial mass.

Pascal Fouque; Jose M. Solanes; Teresa Sanchis; Chantal Balkowski

2001-06-14

173

The First Two Years of Electromagnetic Follow-Up with Advanced LIGO and Virgo  

E-print Network

We anticipate the first direct detections of gravitational waves (GWs) with Advanced LIGO and Virgo later this decade. Though this groundbreaking technical achievement will be its own reward, a still greater prize could be observations of compact binary mergers in both gravitational and electromagnetic channels simultaneously. During Advanced LIGO and Virgo's first two years of operation, 2015 through 2016, we expect the global GW detector array to improve in sensitivity and livetime and expand from two to three detectors. We model the detection rate and the sky localization accuracy for binary neutron star (BNS) mergers across this transition. We have analyzed a large, astrophysically motivated source population using real-time detection and sky localization codes and higher-latency parameter estimation codes that have been expressly built for operation in the Advanced LIGO/Virgo era. We show that for most BNS events the rapid sky localization, available about a minute after a detection, is as accurate as the full parameter estimation. We demonstrate that Advanced Virgo will play an important role in sky localization, even though it is anticipated to come online with only one-third as much sensitivity as the Advanced LIGO detectors. We find that the median 90% confidence region shrinks from ~500 square degrees in 2015 to ~200 square degrees in 2016. A few distinct scenarios for the first LIGO/Virgo detections emerge from our simulations.

Leo P. Singer; Larry R. Price; Ben Farr; Alex L. Urban; Chris Pankow; Salvatore Vitale; John Veitch; Will M. Farr; Chad Hanna; Kipp Cannon; Tom Downes; Philip Graff; Carl-Johan Haster; Ilya Mandel; Trevor Sidery; Alberto Vecchio

2014-10-22

174

The Characterization of Virgo Data and Its Impact on Gravitational-Wave Searches  

NASA Technical Reports Server (NTRS)

Between 2007 and 2010 Virgo collected data in coincidence with the LIGO and GEO gravitational-wave (GW) detectors. These data have been searched for GWs emitted by cataclysmic phenomena in the universe, by non-axisymmetric rotating neutron stars or from a stochastic background in the frequency band of the detectors. The sensitivity of GW searches is limited by noise produced by the detector or its environment. It is therefore crucial to characterize the various noise sources in a GW detector. This paper reviews the Virgo detector noise sources, noise propagation, and conversion mechanisms which were identified in the three first Virgo observing runs. In many cases, these investigations allowed us to mitigate noise sources in the detector, or to selectively flag noise events and discard them from the data. We present examples from the joint LIGO-GEO-Virgo GW searches to show how well noise transients and narrow spectral lines have been identified and excluded from the Virgo data. We also discuss how detector characterization can improve the astrophysical reach of gravitational wave searches.

Aasi, J.; Abadie, J.; Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M.; Accadia, T.; Acernese, F.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Ajith, P.; Allen, B.; Allocca, A.; Ceron, E. Amador; Amariutei, D.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Blackburn, L.; Buonanno, A.; Camp, J. B.; Capano, C.D.; Kanner, J. B.; Pan, Y.; Shawhan, P.; Yancey, C. C.

2012-01-01

175

Detection of Nucleosomal Substructures using Solid-State Gautam V. Soni and Cees Dekker*  

E-print Network

apoptosis. Nucleosomal (sub)structures are however hard to detect and characterize. Here, we show that solid. Structural reorganization (assembly, partial disintegration into subcomplexes or complete removal

Dekker, Cees

176

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

177

All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run  

E-print Network

We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo ...

Barsotti, Lisa

178

Sensitivity to Gravitational Waves from Compact Binary Coalescences Achieved during LIGO's Fifth and Virgo's First Science Run  

Microsoft Academic Search

We summarize the sensitivity achieved by the LIGO and Virgo gravitational wave detectors for compact binary coalescence (CBC) searches during LIGO's fifth science run and Virgo's first science run. We present noise spectral density curves for each of the four detectors that operated during these science runs which are representative of the typical performance achieved by the detectors for CBC

B. P. Abbott; R. Abbott; M Abernathy; T. Accadia; F. Acernese; C. Adams; R. Adhikari; P. Ajith; B. Allen; G. Allen; E. Amador Ceron; R. S. Amin; S. B. Anderson; W. G. Anderson; F. Antonucci; S. Aoudia; M. A. Arain; M. Araya; M. Aronsson; K. G. Arun; Y. Aso; S. Aston; P. Astone; D. E. Atkinson; P. Aufmuth; C. Aulbert; S. Babak; P. Baker; G. Ballardin; S. Ballmer; D. Barker; S. Barnum; F. Barone; B. Barr; P. Barriga; L. Barsotti; M. Barsuglia; M. A. Barton; I. Bartos; R. Bassiri; M. Bastarrika; J. Bauchrowitz; Th. S. Bauer; B. Behnke; M. G. Beker; M. Benacquista; A. Bertolini; J. Betzwieser; N. Beveridge; P. T. Beyersdorf; S. Bigotta; I. A. Bilenko; G. Billingsley; J. Birch; S. Birindelli; R. Biswas; M. Bitossi; M. A. Bizouard; E. Black; J. K. Blackburn; L. Blackburn; D. Blair; B. Bland; M. Blom; C. Boccara; O. Bock; T. P. Bodiya; R. Bondarescu; F. Bondu; L. Bonelli; R. Bork; M. Born; S. Bose; L. Bosi; M. Boyle; S. Braccini; C. Bradaschia; P. R. Brady; V. B. Braginsky; J. E. Brau; J. Breyer; D. O. Bridges; A. Brillet; M. Brinkmann; V. Brisson; M. Britzger; A. F. Brooks; D. A. Brown; R. Budzynski; T. Bulik; H. J. Bulten; A. Buonanno; J. Burguet--Castell; O. Burmeister; D. Buskulic; R. L. Byer; L. Cadonati; G. Cagnoli; E. Calloni; J. B. Camp; E. Campagna; P. Campsie; J. Cannizzo; K. C. Cannon; B. Canuel; J. Cao; C. Capano; F. Carbognani; S. Caride; S. Caudill; M. Cavaglià; F. Cavalier; R. Cavalieri; G. Cella; C. Cepeda; E. Cesarini; T. Chalermsongsak; E. Chalkley; P. Charlton; E. Chassande-Mottin; S. Chelkowski; Y. Chen; A. Chincarini; N. Christensen; S. S. Y. Chua; C. T. Y. Chung; D. Clark; J. Clark; J. H. Clayton; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; R. Conte; D. Cook; T. R. Corbitt; C. Corda; N. Cornish; A. Corsi; C. A. Costa; J.-P. Coulon; D. Coward; D. C. Coyne; J. D. E. Creighton; T. D. Creighton; A. M. Cruise; R. M. Culter; A. Cumming; L. Cunningham; E. Cuoco; K. Dahl; S. L. Danilishin; R. Dannenberg; S. D'Antonio; K. Danzmann; A. Dari; K. Das; V. Dattilo; B. Daudert; M. Davier; G. Davies; A. Davis; E. J. Daw; R. Day; T. Dayanga; R. De Rosa; D. DeBra; J. Degallaix; M. del Prete; V. Dergachev; R. DeRosa; R. DeSalvo; P. Devanka; S. Dhurandhar; L. Di Fiore; A. Di Lieto; I. Di Palma; M. Di Paolo Emilio; A. Di Virgilio; M. Díaz; A. Dietz; F. Donovan; K. L. Dooley; E. E. Doomes; S. Dorsher; E. S. D. Douglas; M. Drago; R. W. P. Drever; J. C. Driggers; J. Dueck; J.-C. Dumas; T. Eberle; M. Edgar; M. Edwards; A. Effler; P. Ehrens; R. Engel; T. Etzel; M. Evans; T. Evans; V. Fafone; S. Fairhurst; Y. Fan; B. F. Farr; D. Fazi; H. Fehrmann; D. Feldbaum; I. Ferrante; F. Fidecaro; L. S. Finn; I. Fiori; R. Flaminio; M. Flanigan; K. Flasch; S. Foley; C. Forrest; E. Forsi; N. Fotopoulos; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; M. Frede; M. Frei; Z. Frei; A. Freise; R. Frey; T. T. Fricke; D. Friedrich; P. Fritschel; V. V. Frolov; P. Fulda; M. Fyffe; L. Gammaitoni; J. A. Garofoli; F. Garufi; G. Gemme; E. Genin; A. Gennai; I. Gholami; S. Ghosh; J. A. Giaime; S. Giampanis; K. D. Giardina; A. Giazotto; C. Gill; E. Goetz; L. M. Goggin; G. González; M. L. Gorodetsky; S. Goßler; R. Gouaty; C. Graef; M. Granata; A. Grant; S. Gras; C. Gray; R. J. S. Greenhalgh; A. M. Gretarsson; C. Greverie; R. Grosso; H. Grote; S. Grunewald; G. M. Guidi; E. K. Gustafson; R. Gustafson; B. Hage; P. Hall; J. M. Hallam; D. Hammer; G. Hammond; J. Hanks; C. Hanna; J. Hanson; J. Harms; G. M. Harry; I. W. Harry; E. D. Harstad; K. Haughian; K. Hayama; J. Heefner; H. Heitmann; P. Hello; I. S. Heng; A. Heptonstall; M. Hewitson; S. Hild; E. Hirose; D. Hoak; K. A. Hodge; K. Holt; D. J. Hosken; J. Hough; E. Howell; D. Hoyland; D. Huet; B. Hughey; S. Husa; S. H. Huttner; T. Huynh--Dinh; D. R. Ingram; R. Inta; T. Isogai; A. Ivanov; P. Jaranowski; W. W. Johnson; D. I. Jones; G. Jones; R. Jones; L. Ju; P. Kalmus; V. Kalogera; S. Kandhasamy; J. Kanner; E. Katsavounidis; K. Kawabe; S. Kawamura; F. Kawazoe; W. Kells; D. G. Keppel; A. Khalaidovski; F. Y. Khalili; E. A. Khazanov; C. Kim; H. Kim; P. J. King; D. L. Kinzel; J. S. Kissel; S. Klimenko; V. Kondrashov; R. Kopparapu; S. Koranda; I. Kowalska; D. Kozak; T. Krause; V. Kringel; S. Krishnamurthy; B. Krishnan; A. Królak; G. Kuehn; J. Kullman; R. Kumar; P. Kwee; M. Landry; M. Lang; B. Lantz; N. Lastzka; A. Lazzarini; P. Leaci; J. Leong; I. Leonor; N. Leroy; N. Letendre; J. Li; T. G. F. Li; H. Lin; P. E. Lindquist; N. A. Lockerbie; D. Lodhia; M. Lorenzini; V. Loriette; M. Lormand; G. Losurdo; P. Lu; J. Luan; M. Lubinski; A. Lucianetti; H. Lück; A. Lundgren; B. Machenschalk; M. MacInnis; J. M. Mackowski; M. Mageswaran; K. Mailand; E. Majorana; C. Mak; N. Man; I. Mandel; V. Mandic; M. Mantovani; F. Marchesoni; F. Marion; S. Márka; Z. Márka; E. Maros; J. Marque; F. Martelli; I. W. Martin; R. M. Martin; J. N. Marx; K. Mason; A. Masserot; F. Matichard; L. Matone

2010-01-01

179

Galactic densities, substructure and the initial power spectrum  

NASA Astrophysics Data System (ADS)

Although the currently favored cold dark matter plus cosmological constant model for structure formation assumes an n = 1 scale-invariant initial power spectrum, most inflation models produce at least mild deviations from n = 1. Because the lever arm from the CMB normalization to galaxy scales is long, even a small ``tilt'' can have important implications for galactic observations. Here we calculate the COBS-normalized power spectra for several well-motivated models of inflation and compute implications for the substructure content and central densities of galaxy halos. Using an analytic model, normalized against N-body simulations, we show that while halos in the standard (n = 1) model are overdense by a factor of ~ 6 compared to observations, several of our example inflation+LCDM models predict halo densities well within the range of observations, which prefer models with n ~ 0.85. We go on to use a semi-analytic model (also normalized against N-body simulations) to follow the merger histories of galaxy-sized halos and track the orbital decay, disruption, and evolution of the merging substructure. Models with n ~ 0.85 predict a factor of ~ 3 fewer subhalos at a fixed circular velocity than the standard n = 1 case. Although this level of reduction does not resolve the ``dwarf satellite problem', it does imply that the level of feedback required to match the observed number of dwarfs is sensitive to the initial power spectrum. Finally, the fraction of galaxy-halo mass that is bound up in substructure is consistent with limits imposed by multiply imaged quasars for all models considered: fsat > 0.01 even for an effective tilt of n ~ 0.8. We conclude that, at their current level, lensing constraints of this kind do not provide an interesting probe of the primordial power spectrum.

Bullock, J. S.; Zentner, A. R.

2003-07-01

180

Dark halo densities, substructure, and the initial power spectrum  

E-print Network

Although the currently favored cold dark matter plus cosmological constant model for structure formation assumes an n=1 scale-invariant initial power spectrum, most inflation models produce at least mild deviations from n=1. Because the lever arm from the CMB normalization to galaxy scales is long, even a small ``tilt'' can have important implications for galactic observations. Here we calculate the COBE-normalized power spectra for several well-motivated models of inflation and compute implications for the substructure content and central densities of galaxy halos. Using an analytic model, normalized against N-body simulations, we show that while halos in the standard (n=1) model are overdense by a factor of ~6 compared to observations, several of our example inflation+LCDM models predict halo densities well within the range of observations, which prefer models with n ~ 0.85. We go on to use a semi-analytic model (also normalized against N-body simulations) to follow the merger histories of galaxy-sized halos and track the orbital decay, disruption, and evolution of the merging substructure. Models with n ~0.85 predict a factor of ~3 fewer subhalos at a fixed circular velocity than the standard $n = 1$ case. Although this level of reduction does not resolve the ``dwarf satellite problem'', it does imply that the level of feedback required to match the observed number of dwarfs is sensitive to the initial power spectrum. Finally, the fraction of galaxy-halo mass that is bound up in substructure is consistent with limits imposed by multiply imaged quasars for all models considered: f_sub > 0.01 even for an effective tilt of n ~0.8.We conclude that, at their current level, lensing constraints of this kind do not provide strong limits on the primordial power spectrum.

James S. Bullock; Andrew R. Zentner

2002-07-24

181

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

182

GLAST And Dark Matter Substructure in the Milky Way  

SciTech Connect

We discuss the possibility of GLAST detecting gamma-rays from the annihilation of neutralino dark matter in the Galactic halo. We have used 'Via Lactea', currently the highest resolution simulation of cold dark matter substructure, to quantify the contribution of subhalos to the annihilation signal. We present a simulated allsky map of the expected gamma-ray counts from dark matter annihilation, assuming standard values of particle mass and cross section. In this case GLAST should be able to detect the Galactic center and several individual subhalos. One of the most exciting discoveries that the Gamma-ray Large Area Space Telescope (GLAST) could make, is the detection of gamma-rays from the annihilation of dark matter (DM). Such a measurement would directly address one of the major physics problems of our time: the nature of the DM particle. Whether or not GLAST will actually detect a DM annihilation signal depends on both unknown particle physics and unknown astrophysics theory. Particle physics uncertainties include the type of particle (axion, neutralino, Kaluza-Klein particle, etc.), its mass, and its interaction cross section. From the astrophysical side it appears that DM is not smoothly distributed throughout the Galaxy halo, but instead exhibits abundant clumpy substructure, in the form of thousands of so-called subhalos. The observability of DM annihilation radiation originating in Galactic DM subhalos depends on their abundance, distribution, and internal properties. Numerical simulations have been used in the past to estimate the annihilation flux from DM substructure, but since the subhalo properties, especially their central density profile, which determines their annihilation luminosity, are very sensitive to numerical resolution, it makes sense to re-examine their contribution with higher resolution simulations.

Kuhlen, Michael; /Princeton, Inst. Advanced Study; Diemand, Jurg; /UC, Santa Cruz, Astron. Astrophys.; Madau, Piero; /UC, Santa Cruz, Astron. Astrophys. /Garching, Max Planck Inst.

2011-11-29

183

PAndAS IN THE MIST: THE STELLAR AND GASEOUS MASS WITHIN THE HALOS OF M31 AND M33  

SciTech Connect

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. [Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006 (Australia)] [Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006 (Australia); Braun, Robert [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia)] [CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia); McConnachie, Alan W. [Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)] [Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Irwin, Michael J.; Chapman, Scott C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)] [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Ibata, Rodrigo A.; Martin, Nicolas F. [Observatoire de Strasbourg, 11, rue de l'Universite, F-67000 Strasbourg (France)] [Observatoire de Strasbourg, 11, rue de l'Universite, F-67000 Strasbourg (France); Ferguson, Annette M. N. [Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)] [Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Fardal, Mark [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States)] [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States); Dubinski, John [Department of Astronomy and Astrophysics, 50 St. George Street, University of Toronto, ON M5S 3H4 (Canada)] [Department of Astronomy and Astrophysics, 50 St. George Street, University of Toronto, ON M5S 3H4 (Canada); Widrow, Larry [Department of Physics, Queen's University, 99 University Avenue, Kingston, ON K7L 3N6 (Canada)] [Department of Physics, Queen's University, 99 University Avenue, Kingston, ON K7L 3N6 (Canada); Mackey, A. Dougal [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611 (Australia)] [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611 (Australia); Babul, Arif [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6 (Canada)] [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6 (Canada); Tanvir, Nial R. [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)] [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Rich, Michael, E-mail: geraint.lewis@sydney.edu.au [Division of Astronomy, University of California, 8979 Math Sciences, Los Angeles, CA 90095-1562 (United States)] [Division of Astronomy, University of California, 8979 Math Sciences, Los Angeles, CA 90095-1562 (United States)

2013-01-20

184

Unexpected relationships of substructured populations in Chinese Locusta migratoria  

PubMed Central

Background Highly migratory species are usually expected to have minimal population substructure because strong gene flow has the effect of homogenizing genetic variation over geographical populations, counteracting random drift, selection and mutation. The migratory locust Locusta migratoria belongs to a monotypic genus, and is an infamous pest insect with exceptional migratory ability – with dispersal documented over a thousand kilometers. Its distributional area is greater than that of any other locust or grasshopper, occurring in practically all the temperate and tropical regions of the eastern hemisphere. Consequently, minimal population substructuring is expected. However, in marked contrast to its high dispersal ability, three geographical subspecies have been distinguished in China, with more than nine being biologically and morphologically identified in the world. Such subspecies status has been under considerable debate. Results By multilocus microsatellite genotyping analysis, we provide ample genetic evidence for strong population substructure in this highly migratory insect that conforms to geography. More importantly, our genetic data identified an unexpected cryptic subdivision and demonstrated a strong affiliation of the East China locusts to those in Northwest/Northern China. The migratory locusts in China formed three distinct groups, viz. (1) the Tibetan group, comprising locusts from Tibet and nearby West China high mountain regions; this is congruent with the previously recognized Tibetan subspecies, L. m. tibetensis; (2) the South China group, containing locusts from the Hainan islands; this corresponds to the Southeast Asia oriental tropical subspecies L. m. manilensis; (3) the North China group, including locusts from the Northwest and Northern China (the Asiatic subspecies L. m. migratoria), Central China and Eastern China regions. Therefore, the traditional concept on Locusta subspecies status established from Uvarov in 1930s needs to be revised. The three groups of locusts probably have separate evolutionary histories that were most likely linked to Quaternary glaciations events, and derived from different ancestral refugial populations following postglacial expansions. Conclusion The migratory locust populations in China have differentiated into three genetically distinct groups despite high dispersal capability. While this clarified long-standing suspicions on the subspecific diversification of this species in China, it also revealed that the locusts in the vast area of East China are not the oriental subspecies but the Asiatic subspecies, an unexpected substructuring pattern. The distribution pattern of the three locust groups in China may be primarily defined by adaptive differentiation coupled to Quaternary glaciations events. Our results are of general significance both for locust research and for phylogeographical study of flora and fauna in China, illustrating the potential importance of phylogeographical history in shaping the divergence and distribution patterns of widespread species with strong dispersal ability. PMID:19558707

Zhang, De-Xing; Yan, Lu-Na; Ji, Ya-Jie; Hewitt, Godfrey M; Huang, Zu-Shi

2009-01-01

185

Simulating and Synthesizing Substructures Using Neural Network and Genetic Algorithms  

NASA Technical Reports Server (NTRS)

The feasibility of simulating and synthesizing substructures by computational neural network models is illustrated by investigating a statically indeterminate beam, using both a 1-D and a 2-D plane stress modelling. The beam can be decomposed into two cantilevers with free-end loads. By training neural networks to simulate the cantilever responses to different loads, the original beam problem can be solved as a match-up between two subsystems under compatible interface conditions. The genetic algorithms are successfully used to solve the match-up problem. Simulated results are found in good agreement with the analytical or FEM solutions.

Liu, Youhua; Kapania, Rakesh K.; VanLandingham, Hugh F.

1997-01-01

186

Hierarchically Parallelized Constrained Nonlinear Solvers with Automated Substructuring  

NASA Technical Reports Server (NTRS)

This paper develops a parallelizable multilevel multiple constrained nonlinear equation solver. The substructuring process is automated to yield appropriately balanced partitioning of each succeeding level. Due to the generality of the procedure,_sequential, as well as partially and fully parallel environments can be handled. This includes both single and multiprocessor assignment per individual partition. Several benchmark examples are presented. These illustrate the robustness of the procedure as well as its capability to yield significant reductions in memory utilization and calculational effort due both to updating and inversion.

Padovan, Joe; Kwang, Abel

1994-01-01

187

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

188

ROSAT PSPC observations of NGC 4636: Interaction with Virgo gas ?  

NASA Technical Reports Server (NTRS)

ROSAT Position Sensitive Proportional Counter (PSPC) observations of NGC 4636 have provided a deep image of the galaxy and its surroundings, which reveal the presence of emission well outside the optical galaxy. The source emission is measured out to r approximately 18 min, where the instrument support structure prevents us at this time from following it farther out. The nature of this emission is not fully understood, but could be evidence that the Virgo cluster gas extends as far out as this galaxy (greater than 3 Mpc from M87). Spectral analysis of the X-ray emission suggests a relatively cool (kT approximately 0.5 to 0.9 keV) interstellar medium, with temperatures increasing with radius. However, the detailed properties of the interstellar gas cannot be unambiguously determined with the present data, since the results we obtain depend strongly on the choice of the spectral model. Comparison of the spectral distributions in concentric annuli clearly indicates significant differences with radius, which can be parameterized as a general increase of the temperature. For low cosmic abundance models, kT varies from approximately 0.55 keV in the inner 1 min to approximately 0.8 keV at r approximately 6 to 8 min. Outside 8 min the average temperature is higher than in the inner region (kT approximately 0.8 to 1.2 keV) and the low-energy absorption is significantly lower. For 100% cosmic abundance and galactic line-of-sight absorption, multi-temperature fits are required, suggesting the possibility that the interstellar medi um is inhomogeneous.

Trinchieri, G.; Kim, D. -W.; Fabbiano, G.; Canizares, C. R. C.

1994-01-01

189

EFFECT OF GRAIN ORIENTATION ON THE DEVELOPMENT OF DISLOCATION SUBSTRUCTURES DURING COLD  

E-print Network

annealed. Some grains developed a cell substructure whereas others exhibited a uniform dislocation density] in an IF steel. Cellular substructures develop in the unstable-orientation grains. The aim of this study was compressed in the Z direction up to a true strain of 0.5 at an average strain rate of 0.01 s-1

Paris-Sud XI, Université de

190

Fast Detection of Common Geometric Substructure in Proteins L. Paul Chew  

E-print Network

and discovering common evolutionary origins. There is now widespread agreement that similarities among distantlyFast Detection of Common Geometric Substructure in Proteins L. Paul Chew Computer Science­vector RMS, efficient algorithms. 1 #12; Fast Detection of Common Geometric Substructure in Proteins Abstract

Kedem, Klara

191

Predicting Stellar Angular Sizes  

E-print Network

Our survey of long-baseline infrared and optical interferometry measurements is producing considerable numbers of directly determined stellar angular sizes. We use our sample of 124 high-precision (5\\%) angular stellar diameter values and correlate them with stellar magnitude values from the literature to produce empirical relations for main-sequence stars between observed apparent magnitudes, stellar colors, and angular sizes (surface brightness relations). We find a significant dependence on stellar metallicity for ($B-V$) colors. The scatter in the calculated relations is small ($\\sim$5\\%), which makes them a robust tool for the prediction of main-sequence stellar angular sizes based on photometry. We apply these relations via the calculation of the radius of the multiplanet host star GJ 667C.

von Braun, Kaspar; van Belle, Gerard T

2013-01-01

192

The First Two Years of Electromagnetic Follow-Up with Advanced LIGO and Virgo  

NASA Astrophysics Data System (ADS)

We anticipate the first direct detections of gravitational waves with Advanced LIGO and Virgo later this decade. Though this groundbreaking technical achievement will be its own reward, a still greater prize could be observations of compact binary mergers in both gravitational and electromagnetic channels simultaneously. During Advanced LIGO and Virgo's first two years of operation, 2015 through 2016, we expect the global gravitational-wave detector array to improve in sensitivity and livetime and expand from two to three detectors. We model the detection rate and the sky localization accuracy for binary neutron star mergers across this transition. We have analyzed a large, astrophysically motivated source population using real-time detection and sky localization codes and higher-latency parameter estimation codes that have been expressly built for operation in the Advanced LIGO/Virgo era. We show that for most binary neutron star events the rapid sky localization, available about a minute after a detection, is as accurate as the full parameter estimation. We demonstrate that Advanced Virgo will play an important role in sky localization, even though it is anticipated to come online with only 1/3 as much sensitivity as the Advanced LIGO detectors. We find that the median 90% confidence region shrinks from ~500 square degrees in 2015 to ~200 square degrees in 2016. From hundreds of simulated events unfold some likely detection scenarios.

Farr, Benjamin F.; Singer, Leo; Price, Larry; Urban, Alex; Pankow, Chris; Vitale, Salvatore; Veitch, John; Farr, Will; Hanna, Chad; Cannon, Kipp; Downes, Tom; Graff, Philip; Haster, Carl-Johan; Mandel, Ilya; Sidery, Trevor; Vecchio, Alberto

2014-08-01

193

Immunocompetence and resource holding potential in the damselfly, Calopteryx virgo L  

Microsoft Academic Search

It is generally believed that resource holding potential reliably reflects male quality, but empirical evidence showing this is scarce. Here we show that the outcome of male-male competition may predict male immunocompetence in the territorial damselfly, Calopteryx virgo (Odonata: Calopterygidae). We staged contests between 27 pairs of males and found that winners of the contests showed higher immunocompetence, measured as

Jani Koskimäki; Markus J. Rantala; Jouni Taskinen; Katja Tynkkynen; Jukka Suhonen

2004-01-01

194

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

195

Planetary nebulae as standard candles. V. The distance to the Virgo Cluster  

Microsoft Academic Search

The O III forbiden 5007-A line fluxes of 486 planetary nebula candidates in six early-type galaxies (NGC 4374, 4382, 4406, 4472, 4486, and 4649) in the core of the Virgo Cluster are identified and measured. Following the procedures and calibrations outlined in previous papers in this series, the observed planetary nebula luminosity functions are compared to an empirical model based

George H. Jacoby; Robin Ciardullo; Holland C. Ford

1990-01-01

196

The characterization of Virgo data and its impact on gravitational-wave searches  

Microsoft Academic Search

Between 2007 and 2010 Virgo collected data in coincidence with the LIGO and GEO gravitational-wave (GW) detectors. These data have been searched for GWs emitted by cataclysmic phenomena in the universe, by non-axisymmetric rotating neutron stars or from a stochastic background in the frequency band of the detectors. The sensitivity of GW searches is limited by noise produced by the

J Aasi; J Abadie; B P Abbott; R Abbott; T D Abbott; M Abernathy; T Accadia; F Acernese; C Adams; T Adams; P Addesso; R Adhikari; C Affeldt; M Agathos; K Agatsuma; P Ajith; B Allen; A Allocca; E Amador Ceron; D Amariutei; S B Anderson; W G Anderson; K Arai; M C Araya; S Ast; S M Aston; P Astone; D Atkinson; P Aufmuth; C Aulbert; B E Aylott; S Babak; P Baker; G Ballardin; T Ballinger; S Ballmer; Y Bao; J C B Barayoga; D Barker; F Barone; B Barr; L Barsotti; M Barsuglia; M A Barton; I Bartos; R Bassiri; M Bastarrika; A Basti; J Batch; J Bauchrowitz; Th S Bauer; M Bebronne; D Beck; B Behnke; M Bejger; M G Beker; A S Bell; C Bell; I Belopolski; M Benacquista; J M Berliner; A Bertolini; J Betzwieser; N Beveridge; P T Beyersdorf; T Bhadbade; I A Bilenko; G Billingsley; J Birch; R Biswas; M Bitossi; M A Bizouard; E Black; J K Blackburn; L Blackburn; D Blair; B Bland; M Blom; O Bock; T P Bodiya; C Bogan; C Bond; R Bondarescu; F Bondu; L Bonelli; R Bonnand; R Bork; M Born; V Boschi; S Bose; L Bosi; B Bouhou; S Braccini; C Bradaschia; P R Brady; V B Braginsky; M Branchesi; J E Brau; J Breyer; T Briant; D O Bridges; A Brillet; M Brinkmann; V Brisson; M Britzger; A F Brooks; D A Brown; T Bulik; H J Bulten; A Buonanno; D Buskulic; C Buy; R L Byer; L Cadonati; G Cagnoli; E Calloni; J B Camp; P Campsie; K Cannon; B Canuel; J Cao; C D Capano; F Carbognani; L Carbone; S Caride; S Caudill; M Cavaglià; F Cavalier; R Cavalieri; G Cella; C Cepeda; E Cesarini; T Chalermsongsak; P Charlton; E Chassande-Mottin; W Chen; X Chen; Y Chen; A Chincarini; A Chiummo; H S Cho; J Chow; N Christensen; S S Y Chua; C T Y Chung; S Chung; G Ciani; F Clara; D E Clark; J A Clark; J H Clayton; F Cleva; E Coccia; P-F Cohadon; C N Colacino; A Colla; M Colombini; A Conte; R Conte; D Cook; T R Corbitt; M Cordier; N Cornish; A Corsi; C A Costa; M Coughlin; J-P Coulon; P Couvares; D M Coward; M Cowart; D C Coyne; J D E Creighton; T D Creighton; A M Cruise; A Cumming; L Cunningham; E Cuoco; R M Cutler; K Dahl; M Damjanic; S L Danilishin; S D’Antonio; K Danzmann; V Dattilo; B Daudert; H Daveloza; M Davier; E J Daw; R Day; T Dayanga; R De Rosa; D DeBra; G Debreczeni; J Degallaix; W Del Pozzo; T Dent; V Dergachev; R DeRosa; S Dhurandhar; L Di Fiore; A Di Lieto; I Di Palma; M Di Paolo Emilio; A Di Virgilio; M Díaz; A Dietz; F Donovan; K L Dooley; S Doravari; S Dorsher; M Drago; R W P Drever; J C Driggers; Z Du; J-C Dumas; S Dwyer; T Eberle; M Edgar; M Edwards; A Effler; P Ehrens; G Endr?czi; R Engel; T Etzel; K Evans; M Evans; T Evans; M Factourovich; V Fafone; S Fairhurst; B F Farr; M Favata; D Fazi; H Fehrmann; D Feldbaum; I Ferrante; F Ferrini; F Fidecaro; L S Finn; I Fiori; R P Fisher; R Flaminio; S Foley; E Forsi; L A Forte; N Fotopoulos; J-D Fournier; J Franc; S Franco; S Frasca; F Frasconi; M Frede; M A Frei; Z Frei; A Freise; R Frey; T T Fricke; D Friedrich; P Fritschel; V V Frolov; M-K Fujimoto; P J Fulda; M Fyffe; J Gair; M Galimberti; L Gammaitoni; J Garcia; F Garufi; M E Gáspár; G Gelencser; G Gemme; E Genin; A Gennai; L Á Gergely; S Ghosh; J A Giaime; S Giampanis; K D Giardina; A Giazotto; S Gil-Casanova; C Gill; J Gleason; E Goetz; G González; M L Gorodetsky; S Goßler; R Gouaty; C Graef; P B Graff; M Granata; A Grant; C Gray; R J S Greenhalgh; A M Gretarsson; C Griffo; H Grote; K Grover; S Grunewald; G M Guidi; C Guido; R Gupta; E K Gustafson; R Gustafson; J M Hallam; D Hammer; G Hammond; J Hanks; C Hanna; J Hanson; A Hardt; J Harms; G M Harry; I W Harry; E D Harstad; M T Hartman; K Haughian; K Hayama; J-F Hayau; J Heefner; A Heidmann; M C Heintze; H Heitmann; P Hello; G Hemming; M A Hendry; I S Heng; A W Heptonstall; V Herrera; M Heurs; M Hewitson; S Hild; D Hoak; K A Hodge; K Holt; M Holtrop; T Hong; S Hooper; J Hough; E J Howell; B Hughey; S Husa; S H Huttner; T Huynh-Dinh; D R Ingram; R Inta; T Isogai; A Ivanov; K Izumi; M Jacobson; E James; Y J Jang; P Jaranowski; E Jesse; W W Johnson; D I Jones; R Jones; R J G Jonker; L Ju; P Kalmus; V Kalogera; S Kandhasamy; G Kang; J B Kanner; M Kasprzack; R Kasturi; E Katsavounidis; W Katzman; H Kaufer; K Kaufman; K Kawabe; S Kawamura; F Kawazoe; D Keitel; D Kelley; W Kells; D G Keppel; Z Keresztes; A Khalaidovski; F Y Khalili; E A Khazanov; B K Kim; C Kim; H Kim; K Kim; N Kim; Y M Kim; P J King; D L Kinzel; J S Kissel; S Klimenko; J Kline; K Kokeyama; V Kondrashov; S Koranda; W Z Korth; I Kowalska; D Kozak; V Kringel; B Krishnan; A Królak; G Kuehn; P Kumar; R Kumar; R Kurdyumov; P Kwee; P K Lam; M Landry; A Langley; B Lantz; N Lastzka; C Lawrie; A Lazzarini; A Le Roux; P Leaci; C H Lee; H K Lee; H M Lee; J R Leong; I Leonor; N Leroy; N Letendre; V Lhuillier; J Li; T G F Li; P E Lindquist; V Litvine; Y Liu; Z Liu; N A Lockerbie; D Lodhia; J Logue; M Lorenzini; V Loriette; M Lormand; G Losurdo; J Lough; M Lubinski; H Lück; A P Lundgren; J Macarthur; E Macdonald; B Machenschalk; M MacInnis; D M Macleod; M Mageswaran; K Mailand; E Majorana; I Maksimovic; V Malvezzi; N Man; I Mandel; V Mandic

2012-01-01

197

The LabelHash algorithm for substructure matching  

PubMed Central

Background There is an increasing number of proteins with known structure but unknown function. Determining their function would have a significant impact on understanding diseases and designing new therapeutics. However, experimental protein function determination is expensive and very time-consuming. Computational methods can facilitate function determination by identifying proteins that have high structural and chemical similarity. Results We present LabelHash, a novel algorithm for matching substructural motifs to large collections of protein structures. The algorithm consists of two phases. In the first phase the proteins are preprocessed in a fashion that allows for instant lookup of partial matches to any motif. In the second phase, partial matches for a given motif are expanded to complete matches. The general applicability of the algorithm is demonstrated with three different case studies. First, we show that we can accurately identify members of the enolase superfamily with a single motif. Next, we demonstrate how LabelHash can complement SOIPPA, an algorithm for motif identification and pairwise substructure alignment. Finally, a large collection of Catalytic Site Atlas motifs is used to benchmark the performance of the algorithm. LabelHash runs very efficiently in parallel; matching a motif against all proteins in the 95% sequence identity filtered non-redundant Protein Data Bank typically takes no more than a few minutes. The LabelHash algorithm is available through a web server and as a suite of standalone programs at http://labelhash.kavrakilab.org. The output of the LabelHash algorithm can be further analyzed with Chimera through a plugin that we developed for this purpose. Conclusions LabelHash is an efficient, versatile algorithm for large-scale substructure matching. When LabelHash is running in parallel, motifs can typically be matched against the entire PDB on the order of minutes. The algorithm is able to identify functional homologs beyond the twilight zone of sequence identity and even beyond fold similarity. The three case studies presented in this paper illustrate the versatility of the algorithm. PMID:21070651

2010-01-01

198

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

199

Next Generation Virgo Survey Photometry and Keck/DEIMOS Spectroscopy of Globular Cluster Satellites of Dwarf Elliptical Galaxies in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We present results from an ongoing study of globular cluster (GC) satellites of low-luminosity dwarf elliptical (dE) galaxies in the Virgo cluster. Our 21 dE targets and candidate GC satellites around them in the apparent magnitude range g ~ 20–24 were selected from the Next Generation Virgo Survey (NGVS) and followed up with medium-resolution Keck/DEIMOS spectroscopy (resolving power: R ~ 2000; wavelength coverage: 4800–9500 Angstrom). In addition, the remaining space available on the nine DEIMOS multi-slit masks were populated with "filler" targets in the form of distant Milky Way halo star candidates in a comparable apparent magnitude range. A combination of radial velocity information (measured from the Keck/DEIMOS spectra), color-color information (from four-band NGVS photometry), and sky position information was used to sort the sample into the following categories: (1) GC satellites of dEs, (2) other non-satellite GCs in the Virgo cluster (we dub them "orphan" GCs), (3) foreground Milky Way stars that are members of the Sagittarius stream, the Virgo overdensity, or the field halo population, and (4) distant background galaxies. We stack the GC satellite population across all 21 host dEs and carry out dynamical modeling of the stacked sample in order to constrain the average mass of dark matter halos that these dEs are embedded in. We study rotation in the system of GC satellites of dEs in the handful of more populated systems in our sample – i.e., those that contain 10 or more GC satellites per dE. A companion AAS poster presented at this meeting (Chu, J. et al. 2015) presents chemical composition and age constraints for these GC satellites relative to the nuclei of the host dEs based on absorption line strengths in co-added spectra. The orphan GCs are likely to be intergalactic GCs within the Virgo cluster (or, equivalently, GCs in the remote outer envelope of the cluster's central galaxy, the giant elliptical M87).This project is funded in part by the National Science Foundation. Some of this research was conducted by high-school students working under the auspices of the Science Internship Program at the University of California Santa Cruz.

Next Generation Virgo Survey collaboration

2015-01-01

200

Next Generation Virgo Survey Photometry and Keck/DEIMOS Spectroscopy of Globular Cluster Satellites of Dwarf Elliptical Galaxies in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We present results from an ongoing study of globular cluster (GC) satellites of low-luminosity dwarf elliptical (dE) galaxies in the Virgo cluster. Our 21 dE targets and candidate GC satellites around them in the apparent magnitude range g ~ 20-24 were selected from the Next Generation Virgo Survey (NGVS) and followed up with medium-resolution Keck/DEIMOS spectroscopy (resolving power: R ~ 2000; wavelength coverage: 4800-9500 Angstrom). In addition, the remaining space available on the nine DEIMOS multi-slit masks were populated with "filler" targets in the form of distant Milky Way halo star candidates in a comparable apparent magnitude range. A combination of radial velocity information (measured from the Keck/DEIMOS spectra), color-color information (from four-band NGVS photometry), and sky position information was used to sort the sample into the following categories: (1) GC satellites of dEs, (2) other non-satellite GCs in the Virgo cluster (we dub them "orphan" GCs), (3) foreground Milky Way stars that are members of the Sagittarius stream, the Virgo overdensity, or the field halo population, and (4) distant background galaxies. We stack the GC satellite population across all 21 host dEs and carry out dynamical modeling of the stacked sample in order to constrain the average mass of dark matter halos that these dEs are embedded in. We study rotation in the system of GC satellites of dEs in the handful of more populated systems in our sample - i.e., those that contain 10 or more GC satellites per dE. A companion AAS poster presented at this meeting (Chu, J. et al. 2015) presents chemical composition and age constraints for these GC satellites relative to the nuclei of the host dEs based on absorption line strengths in co-added spectra. The orphan GCs are likely to be intergalactic GCs within the Virgo cluster (or, equivalently, GCs in the remote outer envelope of the cluster's central galaxy, the giant elliptical M87).This project is funded in part by the National Science Foundation. Some of this research was conducted by high-school students working under the auspices of the Science Internship Program at the University of California Santa Cruz.

Guhathakurta, Puragra; Toloba, Elisa; Peng, Eric W.; Li, Biao; Gwyn, Stephen; Ferrarese, Laura; Cote, Patrick; Chu, Jason; Sparkman, Lea; Chen, Stephanie; Yagati, Samyukta; Muller, Meredith; Next Generation Virgo Survey Collaboration

2015-01-01

201

Potent Oxazolidinone Antibacterials with Heteroaromatic C-Ring Substructure  

PubMed Central

Novel oxazolidinone analogues bearing a condensed heteroaromatic ring as the C-ring substructure were synthesized as candidate antibacterial agents. Analogues 16 and 21 bearing imidazo[1,2-a]pyridine and 18 and 23 bearing [1,2,4]triazolo[1,5-a]pyridine as the C-ring had excellent in vitro antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE), and penicillin-resistant Streptococcus pneumoniae (PRSP). They also showed promising therapeutic effects in a mouse model of lethal infection. Preliminary safety data (inhibitory effects on cytochrome P450 isoforms and monoamine oxidases) were satisfactory. Further evaluation of 18 and 23 is ongoing. PMID:24900607

2013-01-01

202

Population substructure in Cache County, Utah: the Cache County study  

PubMed Central

Background Population stratification is a key concern for genetic association analyses. In addition, extreme homogeneity of ethnic origins of a population can make it difficult to interpret how genetic associations in that population may translate into other populations. Here we have evaluated the genetic substructure of samples from the Cache County study relative to the HapMap Reference populations and data from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Results Our findings show that the Cache County study is similar in ethnic diversity to the self-reported "Whites" in the ADNI sample and less homogenous than the HapMap CEU population. Conclusions We conclude that the Cache County study is genetically representative of the general European American population in the USA and is an appropriate population for conducting broadly applicable genetic studies. PMID:25078123

2014-01-01

203

STELLAR STRUCTURE AND EVOLUTION  

E-print Network

STELLAR STRUCTURE AND EVOLUTION O.R. Pols September 2009 #12;#12;Preface These lecture notes application to the theory of stellar structure and evolution, at a level appro- priate for a third and Evolution, 1990, Springer-Verlag, ISBN 3-540-50211-4 (KIPPENHAHN; K&W) Some sections of this book are still

Mojzsis, Stephen J.

204

Transformation of a Virgo Cluster Dwarf Irregular Galaxy by Ram Pressure Stripping: IC3418 and Its Fireballs  

NASA Astrophysics Data System (ADS)

We present optical imaging and spectroscopy and H I imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only H? emission arises from a few H II regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have H? peaks outwardly offset by ~80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300 ± 100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither H? nor H I emission are detected in the main body of the galaxy, we have detected 4 × 107 M ? of H I from the tail with the Very Large Array. The velocities of tail H II regions, measured from Keck LRIS spectra, extend only a small fraction of the way to the cluster velocity, suggesting that star formation does not happen in more distant parts of the tail. Stars in the outer tail have velocities exceeding the escape speed, but some in the inner tail should fall back into the galaxy, forming halo streams.

Kenney, Jeffrey D. P.; Geha, Marla; Jáchym, Pavel; Crowl, Hugh H.; Dague, William; Chung, Aeree; van Gorkom, Jacqueline; Vollmer, Bernd

2014-01-01

205

KCF-S: KEGG Chemical Function and Substructure for improved interpretability and prediction in chemical bioinformatics  

PubMed Central

Background In order to develop hypothesis on unknown metabolic pathways, biochemists frequently rely on literature that uses a free-text format to describe functional groups or substructures. In computational chemistry or cheminformatics, molecules are typically represented by chemical descriptors, i.e., vectors that summarize information on its various properties. However, it is difficult to interpret these chemical descriptors since they are not directly linked to the terminology of functional groups or substructures that the biochemists use. Methods In this study, we used KEGG Chemical Function (KCF) format to computationally describe biochemical substructures in seven attributes that resemble biochemists' way of dealing with substructures. Results We established KCF-S (KCF-and-Substructures) format as an additional structural information of KCF. Applying KCF-S revealed the specific appearance of substructures from various datasets of molecules that describes the characteristics of the respective datasets. Structure-based clustering of molecules using KCF-S resulted the clusters in which molecular weights and structures were less diverse than those obtained by conventional chemical fingerprints. We further applied KCF-S to find the pairs of molecules that are possibly converted to each other in enzymatic reactions, and KCF-S clearly improved predictive performance than that presented previously. Conclusions KCF-S defines biochemical substructures with keeping interpretability, suggesting the potential to apply more studies on chemical bioinformatics. KCF and KCF-S can be automatically converted from Molfile format, enabling to deal with molecules from any data sources. PMID:24564846

2013-01-01

206

Effect of load eccentricity and substructure deformation on ultimate strength of shuttle orbiter thermal protection system  

NASA Technical Reports Server (NTRS)

The effect of load eccentricity and substructure deformation on the ultimate strength and stress displacement properties of the shuttle orbiter thermal protection system (TPS) was determined. The LI-900 Reusable Surface Insulation (RSI) tiles mounted on the .41 cm thick Strain Isolator Pad (SIP) were investigated. Substructure deformations reduce the ultimate strength of the SIP/tile TPS and increase the scatter in the ultimate strength data. Substructure deformations that occur unsymmetric to the tile can cause the tile to rotate when subjected to a uniform applied load. Load eccentricity reduces SIP/tile TPS ultimate strength and causes tile rotation.

Sawyer, J. W.

1981-01-01

207

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

E-print Network

In this report 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, harmonise, and publish software implementations of these techniques.

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

2012-05-25

208

Galaxy Populations and Evolution in Clusters IV Deep H 1 Observations of Dwarf Elliptical Galaxies in the Virgo Cluster  

NASA Technical Reports Server (NTRS)

In this paper we present deep Arecibo H I and WIYN optical observations of Virgo Cluster dwarf elliptical galaxies. Based on this data we argue that a significant fraction of low-mass galaxies in the Virgo Cluster recently underwent evolution. Our new observations consist of H I 21 cm line observations for 22 classified dE galaxies with optical radial velocities consistent with membership in the Virgo Cluster. Cluster members VCC 390 and VCC 1713 are detected with H 1 masses M H1= 6 x 10 sup 7 and 8 x 10 sup 7 M , respectively, while MH I values in the remaining 20 dE galaxies have upper limits as low as about 5 x 1O sup 5 M. We combine our results with those for 26 other Virgo Cluster dE galaxies with H 1 observations in the literature, seven of which have H I detection claims.

Conselice, Christopher J.; ONeil, Karen; Gallagher, John S.; Wyse, Rosemary F. G.

2003-01-01

209

Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1  

E-print Network

We report the results of the first search for gravitational waves from compact binary coalescence using data from the Laser Interferometer Gravitational-Wave Observatory and Virgo detectors. Five months of data were collected ...

Barsotti, Lisa

210

All-sky search for gravitational-wave bursts in the first joint LIGO-GEO-Virgo run  

E-print Network

We present results from an all-sky search for unmodeled gravitational-wave bursts in the data collected by the LIGO, GEO 600 and Virgo detectors between November 2006 and October 2007. The search is performed by three ...

Weiss, Rainer

211

Search for gravitational wave ringdowns from perturbed intermediate mass black holes in LIGO-Virgo data from 2005–2010  

E-print Network

We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources ...

Aggarwal, Nancy

212

Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1  

Microsoft Academic Search

We report the results of the first search for gravitational waves from compact binary coalescence using data from the Laser Interferometer Gravitational-Wave Observatory and Virgo detectors. Five months of data were collected during the Laser Interferometer Gravitational-Wave Observatory's S5 and Virgo's VSR1 science runs. The search focused on signals from binary mergers with a total mass between 2 and 35M&sun;.

J. Abadie; B. P. Abbott; R. Abbott; M. Abernathy; T. Accadia; F. Acernese; C. Adams; R. Adhikari; P. Ajith; B. Allen; G. Allen; E. Amador Ceron; R. S. Amin; S. B. Anderson; W. G. Anderson; F. Antonucci; M. A. Arain; M. Araya; M. Aronsson; K. G. Arun; Y. Aso; S. Aston; P. Astone; D. E. Atkinson; P. Aufmuth; C. Aulbert; S. Babak; P. Baker; G. Ballardin; T. Ballinger; S. Ballmer; D. Barker; S. Barnum; F. Barone; B. Barr; P. Barriga; L. Barsotti; M. Barsuglia; M. A. Barton; I. Bartos; R. Bassiri; M. Bastarrika; J. Bauchrowitz; Th. S. Bauer; B. Behnke; M. G. Beker; A. Belletoile; M. Benacquista; A. Bertolini; J. Betzwieser; N. Beveridge; P. T. Beyersdorf; S. Bigotta; I. A. Bilenko; G. Billingsley; J. Birch; S. Birindelli; R. Biswas; M. Bitossi; M. A. Bizouard; E. Black; J. K. Blackburn; L. Blackburn; D. Blair; B. Bland; M. Blom; C. Boccara; O. Bock; T. P. Bodiya; R. Bondarescu; F. Bondu; L. Bonelli; R. Bonnand; R. Bork; M. Born; S. Bose; L. Bosi; B. Bouhou; M. Boyle; S. Braccini; C. Bradaschia; P. R. Brady; V. B. Braginsky; J. E. Brau; J. Breyer; D. O. Bridges; A. Brillet; M. Brinkmann; V. Brisson; M. Britzger; A. F. Brooks; D. A. Brown; R. Budzynski; T. Bulik; H. J. Bulten; A. Buonanno; J. Burguet--Castell; O. Burmeister; D. Buskulic; C. Buy; R. L. Byer; L. Cadonati; G. Cagnoli; J. Cain; E. Calloni; J. B. Camp; E. Campagna; P. Campsie; J. Cannizzo; K. C. Cannon; B. Canuel; J. Cao; C. Capano; F. Carbognani; S. Caudill; M. Cavaglià; F. Cavalier; R. Cavalieri; G. Cella; C. Cepeda; E. Cesarini; T. Chalermsongsak; E. Chalkley; P. Charlton; E. Chassande-Mottin; S. Chelkowski; Y. Chen; A. Chincarini; N. Christensen; S. S. Y. Chua; C. T. Y. Chung; D. Clark; J. Clark; J. H. Clayton; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; R. Conte; D. Cook; T. R. Corbitt; N. Cornish; A. Corsi; C. A. Costa; J.-P. Coulon; D. Coward; D. C. Coyne; J. D. E. Creighton; T. D. Creighton; A. M. Cruise; R. M. Culter; A. Cumming; L. Cunningham; E. Cuoco; K. Dahl; S. L. Danilishin; R. Dannenberg; S. D'Antonio; K. Danzmann; K. Das; V. Dattilo; B. Daudert; M. Davier; G. Davies; A. Davis; E. J. Daw; R. Day; T. Dayanga; R. de Rosa; D. Debra; J. Degallaix; M. Del Prete; V. Dergachev; R. Derosa; R. Desalvo; P. Devanka; S. Dhurandhar; L. di Fiore; A. di Lieto; I. di Palma; M. di Paolo Emilio; A. di Virgilio; M. Díaz; A. Dietz; F. Donovan; K. L. Dooley; E. E. Doomes; S. Dorsher; E. S. D. Douglas; M. Drago; R. W. P. Drever; J. C. Driggers; J. Dueck; J.-C. Dumas; T. Eberle; M. Edgar; M. Edwards; A. Effler; P. Ehrens; G. Ely; R. Engel; T. Etzel; M. Evans; T. Evans; V. Fafone; S. Fairhurst; Y. Fan; B. F. Farr; D. Fazi; H. Fehrmann; D. Feldbaum; I. Ferrante; F. Fidecaro; L. S. Finn; I. Fiori; R. Flaminio; M. Flanigan; K. Flasch; S. Foley; C. Forrest; E. Forsi; N. Fotopoulos; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; M. Frede; M. Frei; Z. Frei; A. Freise; R. Frey; T. T. Fricke; D. Friedrich; P. Fritschel; V. V. Frolov; P. Fulda; M. Fyffe; M. Galimberti; L. Gammaitoni; J. A. Garofoli; F. Garufi; G. Gemme; E. Genin; A. Gennai; S. Ghosh; J. A. Giaime; S. Giampanis; K. D. Giardina; A. Giazotto; C. Gill; E. Goetz; L. M. Goggin; G. González; S. Goßler; R. Gouaty; C. Graef; M. Granata; A. Grant; S. Gras; C. Gray; R. J. S. Greenhalgh; A. M. Gretarsson; C. Greverie; R. Grosso; H. Grote; S. Grunewald; G. M. Guidi; E. K. Gustafson; R. Gustafson; B. Hage; P. Hall; J. M. Hallam; D. Hammer; G. Hammond; J. Hanks; C. Hanna; J. Hanson; J. Harms; G. M. Harry; I. W. Harry; E. D. Harstad; K. Haughian; K. Hayama; J.-F. Hayau; T. Hayler; J. Heefner; H. Heitmann; P. Hello; I. S. Heng; A. Heptonstall; M. Hewitson; S. Hild; E. Hirose; D. Hoak; K. A. Hodge; K. Holt; D. J. Hosken; J. Hough; E. Howell; D. Hoyland; D. Huet; B. Hughey; S. Husa; S. H. Huttner; T. Huynh--Dinh; D. R. Ingram; R. Inta; T. Isogai; A. Ivanov; P. Jaranowski; W. W. Johnson; D. I. Jones; G. Jones; R. Jones; L. Ju; P. Kalmus; V. Kalogera; S. Kandhasamy; J. Kanner; E. Katsavounidis; K. Kawabe; S. Kawamura; F. Kawazoe; W. Kells; D. G. Keppel; A. Khalaidovski; F. Y. Khalili; E. A. Khazanov; H. Kim; P. J. King; D. L. Kinzel; J. S. Kissel; S. Klimenko; V. Kondrashov; R. Kopparapu; S. Koranda; I. Kowalska; D. Kozak; T. Krause; V. Kringel; S. Krishnamurthy; B. Krishnan; A. Królak; G. Kuehn; J. Kullman; R. Kumar; P. Kwee; M. Landry; M. Lang; B. Lantz; N. Lastzka; A. Lazzarini; P. Leaci; J. Leong; I. Leonor; N. Leroy; N. Letendre; J. Li; T. G. F. Li; H. Lin; P. E. Lindquist; N. A. Lockerbie; D. Lodhia; M. Lorenzini; V. Loriette; M. Lormand; G. Losurdo; P. Lu; J. Luan; M. Lubinski; A. Lucianetti; H. Lück; A. Lundgren; B. Machenschalk; M. Macinnis; M. Mageswaran; K. Mailand; E. Majorana; C. Mak; I. Maksimovic; N. Man; I. Mandel; V. Mandic; M. Mantovani; F. Marchesoni; F. Marion; S. Márka; Z. Márka; E. Maros; J. Marque; F. Martelli; I. W. Martin; R. M. Martin; J. N. Marx

2010-01-01

213

The Next Generation Virgo Cluster Survey. V. Modeling the Dynamics of M87 with the Made-to-measure Method  

NASA Astrophysics Data System (ADS)

We study the dynamics of the giant elliptical galaxy M87 from the central to the outermost regions with the made-to-measure (M2M) method. We use a new catalog of 922 globular cluster line-of-sight velocities extending to a projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON integral field unit data within the central 2.4 kpc. There are 263 globular clusters, mainly located beyond 40 kpc, newly observed by the Next Generation Virgo Survey. For the M2M modeling, the gravitational potential is taken as a combination of a luminous matter potential with a constant stellar mass-to-light ratio and a dark matter potential modeled as a logarithmic potential. Our best-fit dynamical model returns a stellar mass-to-light ratio in the I band of M/LI = 6.0 ± 0.3 M_{\\odot } \\,L_{\\odot }^{-1} with a dark matter potential scale velocity of 591 ± 50 km s-1 and scale radius of 42 ± 10 kpc. We determine the total mass of M87 within 180 kpc to be (1.5 ± 0.2) × 1013 M ?. The mass within 40 kpc is smaller than previous estimates determined using globular cluster kinematics that did not extend beyond ~45 kpc. With our new globular cluster velocities at much larger radii, we see that globular clusters around 40 kpc show an anomalously large velocity dispersion which affected previous results. The mass we derive is in good agreement with that inferred from ROSAT X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent with that inferred from Chandra and XMM-Newton X-ray observations, while within 120 kpc it is about 20% smaller. The model velocity dispersion anisotropy ? parameter for the globular clusters in M87 is small, varying from -0.2 at the center to 0.2 at ~40 kpc, and gradually decreasing to zero at ~120 kpc.

Zhu, Ling; Long, R. J.; Mao, Shude; Peng, Eric W.; Liu, Chengze; Caldwell, Nelson; Li, Biao; Blakeslee, John P.; Côté, Patrick; Cuillandre, Jean-Charles; Durrell, Patrick; Emsellem, Eric; Ferrarese, Laura; Gwyn, Stephen; Jordán, Andrés; Lançon, Ariane; Mei, Simona; Muñoz, Roberto; Puzia, Thomas

2014-09-01

214

Nucleosynthesis in stellar flares  

E-print Network

Nuclear interactions of ions accelerated at the surface of flaring stars can produce fresh isotopes in stellar atmospheres. Although this nucleosynthesis is not significant for the chemical evolution of the Galaxy, it can be important for a number of measurements of "anomalously" high 6-Li and 7-Li abundances. We discuss the possible role of stellar flares to explain the recent report of high 6-Li abundances in metal-poor halo stars and the well-established correlation between Li abundance and stellar activity in young open clusters. We then study the possibility of observing directly Li production during flares of nearby and active dwarfs of spectral type M.

V. Tatischeff; J. -P. Thibaud; I. Ribas

2008-01-11

215

Multicolor stellar photometry  

NASA Astrophysics Data System (ADS)

The monograph describes all multicolor photometric systems which were in use for stellar photometry before 1990, particularly the UBV, Strömgren and Vilnius systems. The reviews of common properties of photometric systems, energy distribution in stellar spectra, interstellar and atmospheric extinction, photometric classification methods of stars are also given. The book includes calibrations of spectral MK types in absolute magnitudes, bolometric corrections, effective temperatures, surface gravities, masses and radii. Intrinsic color indices of the UBV, Strömgren, Vilnius and infrared systems are tabulated. The volume of the book is 570 pages. A pdf file of the book is available at: http://www.itpa.lt/MulticolorStellarPhotometry/

Straižys, Vytautas

216

Stellar atmospheric structural patterns  

NASA Technical Reports Server (NTRS)

The thermodynamics of stellar atmospheres is discussed. Particular attention is given to the relation between theoretical modeling and empirical evidence. The characteristics of distinctive atmospheric regions and their radical structures are discussed.

Thomas, R. N.

1983-01-01

217

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.

218

Stellar Populations Surface photometry  

E-print Network

Outline Stellar Populations Surface photometry Luminosity distributions Component separation Surface photometry Luminosity distributions Component separation Photometric parameters Elliptical photometry Luminosity distributions Bulge luminosity laws Luminosity distributions in disks Component

Kruit, Piet van der

219

Population Substructure and Patterns of Quantitative Variation among the Gollas of Southern Andhra Pradesh, India  

E-print Network

Population substructure and biological differentiation was studied among the Golla, a pastoral caste living in the southern areas of Andhra Pradesh (AP) in India, using 11 anthropometric measurements and 20 quantitative dermatoglyphic variables...

Reddy, B. Mohan; Pfeffer, Alexa; Crawford, Michael H.; Langstieh, Banrida T.

2001-04-01

220

Galaxy and Stellar Spectra  

NSDL National Science Digital Library

In this activity students learn that galaxies shine on the basis of their intergrated stellar population, therefore, adding together different stellar spectra should reproduce the spectra of a galaxy. This activity contains an applet which allows one to add spectra of up to four different stars to produce a resultant spectra. To reproduce qualitatively a spectra of a galaxy one can add together and F main sequence star and a K Giant. The spectra are normalized by V-band luminosity.

Department, University O.

2005-06-17

221

Stellar Evolution A Statistical Model  

E-print Network

Stellar Evolution A Statistical Model Statistical Computation Analysis of the Hyades Cluster Embedding Computer Models for Stellar Evolution into a Coherent Statistical Analysis David A. van Dyk1 Analysis of Stellar Evolution #12;Stellar Evolution A Statistical Model Statistical Computation Analysis

van Dyk, David

222

Stellar Evolution A Statistical Model  

E-print Network

Stellar Evolution A Statistical Model Statistical Computation Analysis of the Hyades Cluster Statistical Analysis of Stellar Evolution David A. van Dyk1 Steven DeGennaro2 Nathan Stein2 William H Statistical Analysis of Stellar Evolution #12;Stellar Evolution A Statistical Model Statistical Computation

van Dyk, David

223

Structural optimization of the fibre-reinforced composite substructure in a three-unit dental bridge  

Microsoft Academic Search

IntroductionFailures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC substructure and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will

Li Shi; Alex S. L. Fok

2009-01-01

224

Gap comparison between single crown and three-unit bridge zirconia substructures  

PubMed Central

PURPOSE To compare marginal and internal gaps of zirconia substructure of single crowns with those of three-unit fixed dental prostheses. MATERIALS AND METHODS Standardized Co-Cr alloy simulated second premolar and second molar abutments were fabricated and subsequently duplicated into type-III dental stone for working casts. After that, all zirconia substructures were made using Lava™ system. Marginal and internal gaps were measured in 2 planes (mesial-distal plane and buccal-palatal plane) at 5 locations: marginal opening (MO), chamfer area (CA), axial wall (AW), cusp tip (CT) and mid-occlusal (OA) using Replica technique. RESULTS There were significant differences between gaps at all locations. The mean ± SD of marginal gap in premolar was 43.6 ± 0.4 µm and 46.5 ± 0.5 µm for single crown and 3-unit bridge substructure respectively. For molar substructure the mean ± SD of marginal gap was 48.5 ± 0.4 µm and 52.6 ± 0.4 µm for single crown and 3-unit bridge respectively. The largest gaps were found at the occlusal area, which was 150.5 ± 0.5 µm and 154.5 ± 0.4 µm for single and 3-unit bridge premolar substructures respectively and 146.5 ± 0.4 µm and 211.5 ± 0.4 µm for single and 3-unit bridge molar substructure respectively. CONCLUSION Independent-samples t-test showed significant differences of gap in zirconia substructure between single crowns and three-unit bridge (P<.001). Therefore, the span length has the effect on the fit of zirconia substructure that is fabricated using CAD/CAM technique especially at the occlusal area. PMID:25177467

Charoenchitt, Masnisa; Asvanund, Chanavut

2014-01-01

225

Cold Dark Matter Substructure and Galactic Disks. I. Morphological Signatures of Hierarchical Satellite Accretion  

Microsoft Academic Search

We conduct dissipationless N-body simulations to investigate the cumulative effect of substructure impacts onto thin disk galaxies in the context of the LambdaCDM paradigm. Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. Substructure properties are culled from cosmological simulations of galaxy-sized CDM halos. We demonstrate that accretions of massive subhalos onto the

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

2008-01-01

226

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

227

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. PMID:19472325

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

2009-01-01

228

Candidate galaxies for study of the local velocity field and distance scale using Space Telescope. I - The most easily resolved. II - The more difficult cases. III - Galaxies in the Virgo cluster core  

NASA Technical Reports Server (NTRS)

A subset of 1246 Shapley-Ames galaxies is presented which holds promise for some degree of useful resolution by the Space Telescope. The 95 candidate galaxies easiest to resolve are described and illustrated first. Many of these can be readily resolved into brightest stars from the ground with presently available telescopes at a few sites, while others might be resolved from the ground into at least the brightest blue supergiants. Then, 152 additional candidates are presented which can only be adequately studied with the Space Telescope. Finally, the most promising galaxies for studies of the resolved stellar content that occur in the central six degree core of the Virgo cluster are given. These are expected to be useful for any direct attack on the distance to the cluster itself.

Sandage, A.; Bedke, J.

1985-01-01

229

Low Mass X-Ray Binaries and Globular Clusters in Virgo Early-Type Galaxies  

NASA Astrophysics Data System (ADS)

We propose observations of NGC 4526, NGC 4473, and NGC 4762, three optically bright but X-ray faint early-type galaxies in the Virgo cluster. We will detect the Low Mass X-ray Binary (LMXB) population in these galaxies, and determine the luminosities, luminosity function, spectral properties, X-ray colors, and variability of these sources. These galaxies will be observed as part of the Hubble Space Telescope ACS Virgo Survey, which will determine the globular cluster (GC) populations of these galaxies. Previous observations have shown that a high fraction of LMXBs in E/S0 galaxies are located in GCs. We will compare the properties of the GC and non-GC LMXBs, with the aim to understand the origin of LMXBs, and to constrain the evolution of GCs and E/S0 galaxies.

Sarazin, Craig

2002-09-01

230

H I properties of dwarf irregular galaxies in the Virgo Cluster  

NASA Technical Reports Server (NTRS)

A neutral hydrogen survey was carried out at Arecibo on 91 dwarf irregular galaxies, with morphological types Sdm through Im, in and around the direction of the Virgo Cluster. Only nine of these were found to be background galaxies, and 19 remain undetected, i.e., most of the candidate galaxies are indeed members of the Virgo Cluster or Supercluster. The distribution of positions and systemic velocities (compared with large spirals) shows no evidence for mass segregation. The H I depletion for dwarfs in the cluster core is only moderate, no more than for spirals. The magnitude-velocity width correlation is continous from spirls to dwarfs. Satistics on H I masses agree only partially with a simple stochastic star formation model.

Hoffman, G. L.; Helou, G.; Salpeter, E. E.; Sandage, A.

1985-01-01

231

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

232

Molecular gas and star formation in HI-deficient Virgo cluster galaxies  

NASA Technical Reports Server (NTRS)

Mapping of the CO emission line in 42 Virgo cluster galaxies reveals that the molecular gas contents and distributions are roughly normal in severaly HI-deficient Virgo spirals. The survival of the molecular component mitigates the impact of the HI-stripping on star formation and subsequent galactic evolution. For spirals which are deficient in HI by a factor of 10, far-infrared, H alpha line, and nonthermal radio continuum luminosities are lower by no more than a factor of 2. The fact that the inner galactic disks are stripped of HI, while CO is normal, suggests that the lifetime of the molecular phase is approximately one billion years in the inner regions of luminous spirals.

Kenney, Jeffrey D.; Young, Judith S.

1987-01-01

233

Distribution of Spiral Galaxies in the Virgo and Fornax Clusters and Their Dynamic Features  

NASA Astrophysics Data System (ADS)

The dynamic characteristics of spiral galaxies with absolute magnitudes M ? -20m.6 in the Virgo and Fornax clusters are studied using data from the Merged Catalog of Galaxies MERCG. The galactic diameters from MERCG are used to determine the radius RD that defines the region of possible concentration of dark matter, and the dynamic parameters Mdyn and Mdyn/LB of the spiral galaxies are calculated based on the centrifugal equilibrium condition. Results from the theory of angular momentum transfer are used to estimate the central surface density m0 and angular momentum K of stars in these galaxies. A comparison of the dynamic parameters of the spiral galaxies with M ? -20.6 and M ? -20.6 reveals a statistically significant higher fraction of dark matter in the spiral galaxies with M ? -20.6, at 26.3% in Virgo and 27% in Fornax.

Kogoshvili, N. G.; Borchkhadze, T. M.; Kalloghlian, A. T.

2014-12-01

234

Simulation of large-scale numerical substructure in real-time dynamic hybrid testing  

NASA Astrophysics Data System (ADS)

A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element (FE) numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom (DOFs). Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.

Zhu, Fei; Wang, Jinting; Jin, Feng; Zhou, Mengxia; Gui, Yao

2014-12-01

235

The evolution substructure I: a new identification method  

E-print Network

We describe our new "MLAPM-halo-finder" (MHF) which is based on the adaptive grid structure of the N-body code MLAPM. We then extend the MHF code in order to track the orbital evolution of gravitationally bound objects through any given cosmological N-body simulation - our so-called "MLAPM-halo-tracker" (MHT). The mode of operation of MHT is demonstrated using a series of eight high-resolution N-body simulations of galaxy clusters. Each of these halos hosts more than one million particles within their virial radii Rvir. We use MHT as well as MHF to follow the temporal evolution of hundreds of individual satellites, and show that the radial distribution of these substructure satellites follows a "universal" radial distribution irrespective of the host halo's environment and formation history. This in fact might pose another problem for simulations of CDM structure formation as there are recent findings by Taylor et al. (2003) that the Milky Way satellites are found preferentially closer to the galactic centre ...

Gill, S P D; Gibson, B

2004-01-01

236

Dark halo densities, substructure, and the initial power spectrum  

E-print Network

Although the currently favored cold dark matter plus cosmological constant model for structure formation assumes an n=1 scale-invariant initial power spectrum, most inflation models produce at least mild deviations from n=1. Because the lever arm from the CMB normalization to galaxy scales is long, even a small ``tilt'' can have important implications for galactic observations. Here we calculate the COBE-normalized power spectra for several well-motivated models of inflation and compute implications for the substructure content and central densities of galaxy halos. Using an analytic model, normalized against N-body simulations, we show that while halos in the standard (n=1) model are overdense by a factor of ~6 compared to observations, several of our example inflation+LCDM models predict halo densities well within the range of observations, which prefer models with n ~ 0.85. We go on to use a semi-analytic model (also normalized against N-body simulations) to follow the merger histories of galaxy-sized halo...

Bullock, J S; Bullock, James S.; Zentner, Andrew R.

2002-01-01

237

Detecting dark matter substructure with narrow line lensing  

NASA Astrophysics Data System (ADS)

The abundance of low mass halos is one of the key predictions of LCDM and remains at apparent odds with observations of luminous structure. Strong gravitational lensing provides a straightforward means of testing this theory as it enables the detection of dark matter subhalos at cosmological distances, without requiring the structure to contain any baryons at all. The fluxes of strongly lensed, parsec scale sources in particular, are excellent probes as they are extremely sensitive to the presence of low mass subhalos, while still being extended enough to remain unaffected by microlensing by stars which is a dominant contaminant for smaller sources. Traditionally this field has been limited to the analysis of the small number of strongly lensed, radio-loud quasars. Quasar narrow-line emission offers an alternative to radio. It is also parsec scale and microlensing free, but has the benefit of detectable in a much larger sample of systems. This proposal will combine milliarcsecond astrometry, and percent level photometry attainable with WFC3 IR grism, in order to measure spatially resolved narrow line lensing in six new systems, which cannot be studied from the ground. We have demonstrated that data of this quality can be used to detect subhalos as small as a million solar masses. This proposal will double the sample of systems which can be used to detect dark, low mass substructure using flux ratio anomalies.

Nierenberg, Anna

2014-10-01

238

Resonance-related Spiral Substructure in a Galactic Gaseous Disk  

NASA Astrophysics Data System (ADS)

We use high-resolution (20482 zones) 2D hydrodynamic simulations to study the formation of spiral substructure in the gaseous disk of a galaxy. The obtained gaseous response is driven by a self-consistent nonaxisymmetric potential obtained from an imposed spiral mass distribution. We highlight the importance of ultraharmonic resonances in generating these features. The temporal evolution of the system is followed with the parallel ZEUS-MP code, and we follow the steepening of perturbations induced by the spiral potential until large-scale shocks emerge. These shocks exhibit bifurcations that protrude from the gaseous arms and continue to steepen until new shocks are formed. When the contribution from the spiral potential relative to the axisymmetric background is increased from our default value, spurs protrude from the main arms after several revolutions of the gaseous disk. Such spurs overlap on top of the aforementioned shocks. These results support the hypothesis that a complicated gaseous response can coexist with an orderly spiral potential term, in the sense that the underlying background potential can be smooth yet drive a gaseous response that is far more spatially complex.

Yáñez, Miguel A.; Norman, Michael L.; Martos, Marco A.; Hayes, John C.

2008-01-01

239

Evidence of Substructure in the Cluster of Galaxies A3558  

E-print Network

We investigate the dynamical properties of the cluster of galaxies A3558 (Shapley 8). Studying a region of one square degree ($\\sim$ 3 Mpc$^2$) 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 $B \\sim 21$). This catalog has been matched to the recent velocity data obtained by Mazure et al. (1997) and from the literature, yielding a radial velocity catalog containing 322 galaxies. Our analysis shows that the position/velocity space distribution of galaxies shows significant substructure. A central bimodal core detected previously in preliminary studies is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We show that this central bimodal subtructure 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 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 an anisotropic merger scenario.

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

1997-04-09

240

The VIRGO Project: A wide band antenna for gravitational wave detection  

Microsoft Academic Search

The status of advancement of the VIRGO Project is presented: the first-generation results from the Pisa seismic noise super attenuator give an upper limit to the noise transfer function of 2 × 10-8 at 10 Hz. The upper limit to the absolute noise of the 400 kg test mass at 10 Hz has been measured to be 1.5 × 10-13

C. Bradaschia; R. del Fabbro; A. di Virgilio; A. Giazotto; H. Kautzky; V. Montelatici; D. Passuello; A. Brillet; O. Cregut; P. Hello; C. N. Man; P. T. Manh; A. Marraud; D. Shoemaker; J. Y. Vinet; F. Barone; L. di Fiore; L. Milano; G. Russo; J. M. Aguirregabiria; H. Bel; J. P. Duruisseau; G. Le Denmat; Ph. Tourrenc; M. Capozzi; M. Longo; M. Lops; I. Pinto; G. Rotoli; T. Damour; S. Bonazzola; J. A. Marck; Y. Gourghoulon; L. E. Holloway; F. Fuligni; V. Iafolla; G. Natale

1990-01-01

241

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

E-print Network

HI observations of the Virgo Cluster pair NGC 4532/DDO 137, conducted as part of the Arecibo Legacy Fast ALFA Survey (ALFALFA), reveal an HI feature extending ~500 kpc to the southwest. The structure has a total mass of up to 7 x 10^8 solar masses, equivalent to 10% of the pair HI mass. Optical R imaging reveals no counterparts to a level of 26.5 magnitudes per square arcsec. The structure is likely the result of galaxy harassment.

Rebecca A. Koopmann

2007-07-22

242

Helioseismic inferences of the solar cycles 23 and 24: GOLF and VIRGO observations  

NASA Astrophysics Data System (ADS)

The Sun-as-a star helioseismic spectrophotometer GOLF and photometer VIRGO instruments onboard the SoHO spacecraft are collecting high-quality, continuous data since April 1996. We analyze here these unique datasets in order to investigate the peculiar and weak on-going solar cycle 24. As this cycle 24 is reaching its maximum, we compare its rising phase with the rising phase of the previous solar cycle 23.

Salabert, D.; García, R. A.; Jiménez, A.

2014-12-01

243

Abell 154 and Virgo - Pilot study for H I observations of distant clusters of galaxies  

SciTech Connect

As a test of procedures required to study the H I contents of spiral galaxies in distant clusters of galaxies, the cluster Abell 154 has been observed from Arecibo. Fourteen candidate detections were found in two regions of the cluster comprising about 10 percent of the cluster area. These results are compared in detail with those expected for the exhaustively studied Virgo cluster displaced to the distance of A 154. Most of the candidate detections are likely to be the combined profiles of two or more spiral galaxies, many of them too faint to appear on the list of morphological types classified by Dressler (1980). Any attempt to identify these H I signals with known bright spirals is problematic at best. The A 154 profiles are systematically broader than expected for Virgo, but a crude application of the Tully-Fisher correlation indicates that they are still consistent with available photometric data. While the H I deficiency in Virgo would still be apparent at the A 154 distance, no significant evidence is found for H I deficiency in A 154. 46 refs.

Hoffman, G.L.; Williams, H.L. (Lafayette College, Easton, PA (USA))

1991-02-01

244

INSIGHT INTO THE FORMATION OF THE MILKY WAY THROUGH COLD HALO SUBSTRUCTURE. III. STATISTICAL CHEMICAL TAGGING IN THE SMOOTH HALO  

SciTech Connect

We find that the relative contribution of satellite galaxies accreted at high redshift to the stellar population of the Milky Way's smooth halo increases with distance, becoming observable relative to the classical smooth halo about 15 kpc from the Galactic center. In particular, we determine line-of-sight-averaged [Fe/H] and [{alpha}/Fe] in the metal-poor main-sequence turnoff (MPMSTO) population along every Sloan Extension for Galactic Understanding and Exploration (SEGUE) spectroscopic line of sight. Restricting our sample to those lines of sight along which we do not detect elements of cold halo substructure (ECHOS), we compile the largest spectroscopic sample of stars in the smooth component of the halo ever observed in situ beyond 10 kpc. We find significant spatial autocorrelation in [Fe/H] in the MPMSTO population in the distant half of our sample beyond about 15 kpc from the Galactic center. Inside of 15 kpc however, we find no significant spatial autocorrelation in [Fe/H]. At the same time, we perform SEGUE-like observations of N-body simulations of Milky Way analog formation. While we find that halos formed entirely by accreted satellite galaxies provide a poor match to our observations of the halo within 15 kpc of the Galactic center, we do observe spatial autocorrelation in [Fe/H] in the simulations at larger distances. This observation is an example of statistical chemical tagging and indicates that spatial autocorrelation in metallicity is a generic feature of stellar halos formed from accreted satellite galaxies.

Schlaufman, Kevin C.; Rockosi, Constance M.; Rashkov, Valery; Madau, Piero [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); Prieto, Carlos Allende [Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife (Spain); Bizyaev, Dmitry, E-mail: kcs@ucolick.org, E-mail: crockosi@ucolick.org, E-mail: valery@ucolick.org, E-mail: pmadau@ucolick.org, E-mail: lee@pa.msu.edu, E-mail: beers@pa.msu.edu, E-mail: callende@iac.es, E-mail: dmbiz@apo.nmsu.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349 (United States)

2012-04-10

245

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. PMID:20459833

2010-01-01

246

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

SciTech Connect

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 distributions of nuclear subcompartment proteins and assayed for caspase-induced cleavage of subcompartmental target proteins in mouse erythroblasts. We found that patterns of lamin B in the filamentous network interacting with both the nuclear envelope and DNA, nuclear matrix protein NuMA, and splicing factors Sm and SC35 persisted during nuclear condensation, consistent with effective transcription of genes expressed late in differentiation. Thus nuclear reorganization prior to enucleation is selective, allowing maintenance of critical transcriptional processes independent of extensive chromosomal reorganization. Consistent with these data, we found no evidence for caspase-induced cleavage of major nuclear subcompartment proteins during late erythropoiesis, in contrast to what has been observed in early erythropoiesis and in lens epithelial and keratinocyte differentiation. These findings imply that nuclear condensation and extrusion during terminal erythroid differentiation involve novel mechanisms that do not entail major activation of apoptotic machinery.

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

2005-04-06

247

STELLAR POPULATIONS IN THE OUTER HALO OF THE MASSIVE ELLIPTICAL M49  

SciTech Connect

We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our data trace M49's stellar halo out to {approx}100 kpc (7r{sub e}), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B - V {approx} 0.7); if this is purely a metallicity effect, it argues for extremely metal-poor stellar populations with [Fe/H] < -1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxy's surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49's outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49's halo. Thus the extremely metal-poor nature of M49's extended halo provides some tension against current models for elliptical galaxy formation.

Mihos, J. Christopher; Harding, Paul [Department of Astronomy, Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106 (United States); Rudick, Craig S. [Institute for Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland); Feldmeier, John J., E-mail: mihos@case.edu, E-mail: paul.harding@case.edu, E-mail: craig.rudick@phys.ethz.ch, E-mail: jjfeldmeier@ysu.edu [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH 44555 (United States)

2013-02-20

248

Discovering Higgs Bosons of the MSSM using Jet Substructure  

SciTech Connect

We present a qualitatively new approach to discover Higgs bosons of the 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 b{bar b} throughout the entire parameter space, while the heavier neutral Higgs bosons, if light enough to be produced in a cascade, also predominantly decay to b{bar b}. 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 {tilde q}},m{sub {tilde g}} > m{sub {tilde W}},{sub {tilde B}} > m{sub h} + {mu}; m{tilde q};m{sub {tilde q}},m{sub {tilde g}} > m{sub {tilde W}},{sub {tilde B}} > m {sub h,H,A} + {mu}; and m{sub {tilde q}},m{sub {tilde g}} > m{sub {tilde W}} > m{sub h} + {mu} with m{sub {tilde B}} {approx} {mu}. In these cascades, the Higgs bosons are boosted, with pT > 200 GeV a large fraction of the time. Since Higgs bosons appear in cascades originating from squarks and/or gluinos, the cross section for events with at least one Higgs boson can be the same order as squark/gluino production. Given 10 fb{sup -1} of 14 TeV LHC data, with m{sub {tilde q}} {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 b{bar b} mode can become the discovery mode of the lightest Higgs boson of the MSSM.

Kribs, Graham D.; Martin, Adam; Roy, Tuhin S.; Spannowsky, Michael

2010-06-01

249

Stellar population and the origin of intra-cluster stars around brightest cluster galaxies: the case of NGC 3311  

NASA Astrophysics Data System (ADS)

Context. We investigate the stellar population and the origin of diffuse light around brightest cluster galaxies. Aims: We study the stellar population of the dynamically hot stellar halo of NGC 3311, the brightest galaxy in the Hydra I cluster, and that of photometric substructures in the diffuse light to constrain the origin of these components. Methods: We analyze absorption lines in medium-resolution, long-slit spectra in the wavelength range 4800-5800 Å obtained with FORS2 at the Very Large Telescope. We measure the equivalent width of Lick indices out to 20 kpc from the center of NGC 3311 and fit them with stellar population models that account for the [?/Fe] overabundance. Results: Stars in the dynamically hot halo of NGC 3311 are old (age >13 Gyr), metal-poor ([Z/H] ~ -0.35), and alpha-enhanced ([?/Fe] ~ 0.48). Together with the high velocity dispersion, these measurements indicate that the stars in the halo were accreted from the outskirts of other early-type galaxies, with a possible contribution from dwarf galaxies. We identify a region in the halo of NGC 3311 associated with a photometric substructure where the stellar population is even more metal-poor ([Z/H] ~ -0.73). In this region, our measurements are consistent with a composite stellar population superposed along the line of sight, consisting of stars from the dynamically hot halo of NGC 3311 and stars stripped from dwarf galaxies. The latter component contributes ?28% to the local surface brightness. Conclusions: The build-up of diffuse light around NGC 3311 is on-going. Based on the observed stellar population properties, the dominant part of these stars may have come from the outskirts of bright early-type galaxies, while stars from stripped dwarf galaxies are presently being added. Based on observations collected at the European Southern Observatory for the program 082.A-0255(A).

Coccato, L.; Gerhard, O.; Arnaboldi, M.; Ventimiglia, G.

2011-09-01

250

Simulations of Spheroidal Systems with Substructure: Trees in Fields  

E-print Network

We present a hybrid technique of N-body simulation to deal with collisionless stellar systems having an inhomogeneous global structure. We combine a treecode and a self-consistent field code such that each of the codes model a different component of the system being investigated. The treecode is suited to treatment of dynamically cold or clumpy systems which may undergo significant evolution within a dynamically hot system. The hot system is appropriately evolved by the self-consistent field code. This combined code is particularly suited to a number of problems in galactic dynamics. Applications of the code to these problems are briefly discussed.

S. Vine; S. Sigurdsson

1997-02-09

251

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

252

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

253

Efficient substructure searching of large chemical libraries: the ABCD chemical cartridge.  

PubMed

Efficient substructure searching is a key requirement for any chemical information management system. In this paper, we describe the substructure search capabilities of ABCD, an integrated drug discovery informatics platform developed at Johnson & Johnson Pharmaceutical Research & Development, L.L.C. The solution consists of several algorithmic components: 1) a pattern mapping algorithm for solving the subgraph isomorphism problem, 2) an indexing scheme that enables very fast substructure searches on large structure files, 3) the incorporation of that indexing scheme into an Oracle cartridge to enable querying large relational databases through SQL, and 4) a cost estimation scheme that allows the Oracle cost-based optimizer to generate a good execution plan when a substructure search is combined with additional constraints in a single SQL query. The algorithm was tested on a public database comprising nearly 1 million molecules using 4,629 substructure queries, the vast majority of which were submitted by discovery scientists over the last 2.5 years of user acceptance testing of ABCD. 80.7% of these queries were completed in less than a second and 96.8% in less than ten seconds on a single CPU, while on eight processing cores these numbers increased to 93.2% and 99.7%, respectively. The slower queries involved extremely generic patterns that returned the entire database as screening hits and required extensive atom-by-atom verification. PMID:22035187

Agrafiotis, Dimitris K; Lobanov, Victor S; Shemanarev, Maxim; Rassokhin, Dmitrii N; Izrailev, Sergei; Jaeger, Edward P; Alex, Simson; Farnum, Michael

2011-12-27

254

DARK MATTER SUBSTRUCTURE DETECTION USING SPATIALLY RESOLVED SPECTROSCOPY OF LENSED DUSTY GALAXIES  

SciTech Connect

We investigate how strong lensing of dusty, star-forming galaxies (DSFGs) by foreground galaxies can be used as a probe of dark matter halo substructure. We find that spatially resolved spectroscopy of lensed sources allows dramatic improvements to measurements of lens parameters. In particular, we find that modeling of the full, three-dimensional (angular position and radial velocity) data can significantly facilitate substructure detection, increasing the sensitivity of observables to lower mass subhalos. We carry out simulations of lensed dusty sources observed by early ALMA (Cycle 1) and use a Fisher matrix analysis to study the parameter degeneracies and mass detection limits of this method. We find that even with conservative assumptions, it is possible to detect galactic dark matter subhalos of {approx}10{sup 8} M{sub Sun} with high significance in most lensed DSFGs. Specifically, we find that in typical DSFG lenses, there is a {approx}55% probability of detecting a substructure with M > 10{sup 8} M{sub Sun} with more than 5{sigma} detection significance in each lens, if the abundance of substructure is consistent with previous lensing results. The full ALMA array, with its significantly enhanced sensitivity and resolution, should improve these estimates considerably. Given the sample of {approx}100 lenses provided by surveys such as the South Pole Telescope, our understanding of dark matter substructure in typical galaxy halos is poised to improve dramatically over the next few years.

Hezaveh, Yashar; Holder, Gilbert [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada)] [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada); Dalal, Neal [Astronomy Department, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)] [Astronomy Department, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States); Kuhlen, Michael [Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States)] [Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States); Marrone, Daniel [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)] [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Murray, Norman [CITA, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)] [CITA, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Vieira, Joaquin [California Institute of Technology, 1200 East California Blvd, MC 249-17, Pasadena, CA 91125 (United States)] [California Institute of Technology, 1200 East California Blvd, MC 249-17, Pasadena, CA 91125 (United States)

2013-04-10

255

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

256

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

257

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

258

Stellar Coronal Astronomy  

NASA Astrophysics Data System (ADS)

Coronal astronomy is by now a fairly mature discipline, with a quarter century having gone by since the detection of the first stellar X-ray coronal source (Capella), and having benefitted from a series of major orbiting observing facilities. Serveral observational characteristics of coronal X-ray and EUV emission have been solidly established through extensive observations, and are by now common, almost text-book, knowledge. At the same time the implications of coronal astronomy for broader astrophysical questions (e.g.Galactic structure, stellar formation, stellar structure, etc.) have become appreciated. The interpretation of stellar coronal properties is however still often open to debate, and will need qualitatively new observational data to book further progress. In the present review we try to recapitulate our view on the status of the field at the beginning of a new era, in which the high sensitivity and the high spectral resolution provided by Chandra and SMM-Newton will address new questions which were not accessible before.

Favata, Fabio; Micela, Giuseppina

2003-10-01

259

A Stellar Demonstrator  

ERIC Educational Resources Information Center

The main purpose of the stellar demonstrator is to help explain the movement of stars. In particular, students have difficulties understanding why, if they are living in the Northern Hemisphere, they may observe starts in the Southern Hemisphere, or why circumpolar stars are not the same in different parts of Europe. Using the demonstrator, these…

Ros, Rosa M.

2009-01-01

260

Stellar Cycles Post Assessment Activity  

NSDL National Science Digital Library

Stellar Cycles is a performance task - an assessment tool to determine student understanding of stellar evolution. Teacher guides and materials are available in powerpoint, PDF and HTML formats. An answer key is included.

261

Kinematically-Decoupled Cores in Dwarf Ellipticals in the Virgo Cluster: Implications for Infallen Groups in Clusters  

NASA Astrophysics Data System (ADS)

A small fraction 8%) of elliptical galaxies contain kinematically-decoupled cores (KDCs), where the kinematical properties of the central region of the galaxy are distinct from those of the main body of the galaxy. KDCs are difficult to detect in dwarf elliptical (dE) galaxies because of their low central surface brightnesses. There was only one statistically robust detection of a KDC in a dE prior to our study. We present spectroscopic evidence for KDCs in two Virgo cluster dEs, VCC 1183 and VCC 1453, that were studied as part of the SMAKCED project. These KDCs have radii of 1.8$''$ (0.14 kpc) and 4.2$''$ (0.33 kpc), respectively. They are distinct from the main body of the galaxy is three ways: (1) inverted sense of rotation; (2) younger and more metal-rich stellar population; and (3) rounder isophotal shape. The frequency of occurence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs and for dEs in general. The fact that dEs represent the most common galaxy class in clusters and have never been seen in isolation suggests that they are products of environmental processes that transformed their progenitors. However, it is unclear which types of galaxies are dE progenitors and which environmental processes are the most important. These KDCs provide new clues. Dwarf-dwarf wet mergers and gas accretion are argued to be the only mechanisms that can simultaneously explain all of the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a small relative velocity. Thus, we conclude that KDCs in cluster dEs were formed in galaxy pairs residing in poor groups or in isolation whose subsequent infall into the cluster quenched their star formation. This research was supported by a Fulbright fellowship and by a grant from the National Science Foundation.

Toloba, Elisa; Guhathakurta, P.; van de Ven, G.; Boselli, A.; Lisker, T.; Peletier, R.; SMAKCED Collaboration

2014-01-01

262

Impact of Dark Matter Substructure on the Matter and Weak Lensing Power Spectra  

E-print Network

We explore the effect of substructure in dark matter halos on the power spectrum and bispectrum of matter fluctuations and weak lensing shear. By experimenting with substructure in a cosmological N = 512^3 simulation, we find that when a larger fraction of the host halo mass is in subhalos, the resulting power spectrum has less power at 1 power at k > 100 h Mpc^{-1}. We explain this effect using an analytic halo model including subhalos, which shows that the 1 100 h Mpc^{-1}. The corresponding effect due to substructures on the weak lensing power spectrum is up to about 11% at angular scale l power spectrum to a few percent accuracy for future surveys would therefore require large cosmological simulations that also have exquisite numerical resolution to model accurately the survivals of dark matter subhalos in the tidal fields of their hosts.

Bradley Hagan; Chung-Pei Ma; Andrey V. Kravtsov

2005-07-25

263

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

Microsoft Academic Search

Background Structural variations caused by a wide range of\\u000a\\u0009\\u0009 physicochemical and biological sources directly influence\\u000a\\u0009\\u0009 the function of a protein. For enzymatic proteins, the\\u000a\\u0009\\u0009 structure and chemistry of the catalytic binding site\\u000a\\u0009\\u0009 residues can be loosely defined as a substructure of the\\u000a\\u0009\\u0009 protein. Comparative analysis of drug-receptor\\u000a\\u0009\\u0009 substructures across and within species has been used for\\u000a\\u0009\\u0009 lead evaluation. Substructure-level similarity

Drew H. Bryant; Mark Moll; Brian Y. Chen; Viacheslav Y Fofanov; Lydia E. Kavraki

2010-01-01

264

Structure and kinematics of galaxy clusters II. Substructures and luminosity segregation  

E-print Network

A homogeneous sample of galaxy redshifts in the core regions (R < 0.5 h$^{-1}$ Mpc) of 12 clusters is used to measure the frequency of substructure with different tests. In 50 % of the cases substructure is detected, a frequency which agrees well with previous studies of cluster cores. Magnitude information and rough morphological classes are also available for 80 % of the sample, allowing us to confirm that bright galaxies (M < -22 mag) have a significantly lower velocity dispersion than the rest. Elliptical galaxies are the main responsibles for this luminosity segregation in velocity space, whereas no segregation can be seen for spiral galaxies. Given the coincidence of substructure and luminosity segregation, a cluster model with an old population of ellipticals which are under the effect of dynamical friction in each subcluster is thus favoured by these observations. Spiral galaxies seem to be late arrivals, or are passing in front or behind the core of the cluster.

P. Stein

1996-06-25

265

A multi-beam HI survey of the Virgo Cluster - two isolated HI clouds ?  

E-print Network

We have carried out a fully sampled large area ($4^{\\circ} \\times 8^{\\circ}$) 21cm \\HI line survey of part of the Virgo cluster using the Jodrell Bank multi-beam instrument. The survey has a sensitivity some 3 times better than the standard HIJASS and HIPASS 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 3 have no obvious optical counter parts upon inspection of the digital sky survey fields. These 3 objects were mapped at Arecibo with a smaller \\am{3}{6} HPBW and a 4 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 $5 \\times 10^{7}$ $\\frac{\\Delta v}{50 km s^{-1}}$ $M_{\\odot}$ and column density limit of $3 \\times 10^{18}$ $\\frac{\\Delta v}{50 km s^{-1}}$ atoms cm$^{-2}$ these new detections represent only about 2% 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 to \\HI selected samples of field galaxies, confirming the 'anaemic spirals' view of Virgo cluster late type galaxies.

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

2003-12-19

266

Gas Dynamics in the Virgo Cluster: The Ram-Pressure Stripped Tail of NGC 4472  

NASA Astrophysics Data System (ADS)

We propose a 3 imes50 ks XMM-Newton mosaic observation of the ram pressure stripped tail of NGC 4472. Our goal is to measure the width, length, and mass profile of the tail of stripped gas to constrain the infall history. Simultaneously, the morphology, density, and temperature of the gas in the tail will provide unique constraints on the transport processes of the Virgo ICM at the virial radius. We compare the observation with ram pressure stripping simulations tailored for NGC 4472. The simulations explore the observable effects of the ICM properties like effective viscosity or magnetic field structure in the dynamical context of NGC 4472.

Kraft, Ralph

2012-10-01

267

Luminosity-velocity diagrams for Virgo Cluster spirals. I - Inner rotation curves  

NASA Technical Reports Server (NTRS)

Optical rotation curves are presented for the innermost portions of nine spiral galaxies in the Virgo Cluster. The emission-line (H-alpha and forbidden N II) velocity data are to be used in combination with new CCD photometry to construct luminosity-velocity diagrams, in a continuing investigation of an apparent initial linear branch and its potential as a distance indicator. Compared to recent H I data, the present optical rotation curves generally show systematically steeper inner gradients. This effect is ascribed to the poorer resolution of the H I data and/or to holes in the gas distribution.

Woods, David; Fahlman, Gregory G.; Madore, Barry F.

1990-01-01

268

Late-Type Dwarf Galaxies in the Virgo Cluster: I. The Samples  

E-print Network

We selected samples of late-type dwarf galaxies in the Virgo cluster with HI information. The galaxies were observed at the Wise-Observatory using several broad-band and H$\\alpha$ bandpasses. UV measurements were carried out with the IUE Observatory from VILSPA, and with the FAUST shuttle-borne UV telescope. We describe our observations in detail, paying particular attention to the determination of measurement errors, and present the observational results together with published data and far-infrared information from IRAS. The sample will be analyzed in subsequent papers, in order to study star formation mechanisms.

Elchanan Almoznino; Noah Brosch

1998-04-22

269

The simultaneous formation of massive stars and stellar clusters  

NASA Astrophysics Data System (ADS)

We show that massive stars and stellar clusters are formed simultaneously, the global evolution of the forming cluster is what allows the central stars to become massive. We predict that massive star-forming clumps, such as those observed in Motte et al., contract and grow in mass leading to the formation of massive stars. This occurs as mass is continually channelled from large radii on to the central protostars, which can become massive through accretion. Using smoothed particle hydrodynamic simulations of massive star-forming clumps in a giant molecular cloud, we show that clumps are initially diffuse and filamentary, and become more concentrated as they collapse. Simulated interferometry observations of our data provide an explanation as to why young massive star-forming regions show more substructure than older ones. The most massive stars in our model are found within the most bound cluster. Most of the mass accreted by the massive stars was originally distributed throughout the clump at low densities and was later funnelled to the star due to global infall. Even with radiative feedback no massive pre-stellar cores are formed. The original cores are of intermediate mass and gain their additional mass in the protostellar stage. We also find that cores which form low-mass stars exist within the volume from which the high-mass stars accrete, but are largely unaffected by this process.

Smith, Rowan J.; Longmore, Steven; Bonnell, Ian

2009-12-01

270

A COSMOLOGICAL KINETIC THEORY FOR THE EVOLUTION OF COLD DARK MATTER HALOS WITH SUBSTRUCTURE: QUASI-LINEAR THEORY  

E-print Network

A COSMOLOGICAL KINETIC THEORY FOR THE EVOLUTION OF COLD DARK MATTER HALOS WITH SUBSTRUCTURE: QUASI-space distribution of dark matter particles in galaxy halos in the presence of a cosmological spectrum from stochastic fluctuations in the gravitational potential due to substructures in the dark matter

Ma, Chung-Pei

271

Galactic substructure and dark-matter annihilation in the Milky Way halo Marc Kamionkowski,1,* Savvas M. Koushiappas,2,  

E-print Network

Galactic substructure and dark-matter annihilation in the Milky Way halo Marc Kamionkowski,1 of substructure on the rate of dark-matter annihilation in the Galactic halo. We use an analytic model massive particles (WIMPs) provide perhaps the most promising class of dark-matter candi- dates

Militzer, Burkhard

272

GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. I. SURFACE BRIGHTNESS PROFILE  

SciTech Connect

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 {approx}175 kpc ({approx}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.

Gilbert, Karoline M. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Guhathakurta, Puragra [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Beaton, Rachael L.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Bullock, James; Tollerud, Erik J. [Center for Cosmology, Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697 (United States); Geha, Marla C. [Astronomy Department, Yale University, New Haven, CT 06520 (United States); Kalirai, Jason S. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Kirby, Evan N. [California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Tanaka, Mikito; Chiba, Masashi, E-mail: kgilbert@astro.washington.edu [Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578 (Japan)

2012-11-20

273

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

274

Automated stellar abundance analysis  

NASA Astrophysics Data System (ADS)

The advent of Milky Way high-resolution spectroscopic surveys has brought our attention to the importance of precise chemical abundance measurements to disentangle the stellar population puzzle of the Galaxy. Moreover, automated stellar parameters are the bedrock of Galactic spectroscopic surveys science. They allow a rapid and homogeneous processing of extensive data sets, necessary for an efficient scientific return. In this review, I discuss the different parametrization techniques, focusing on the automated determination of individual element abundances. Each of them has its optimal application conditions that mainly depend on the computation time constraints, the spectral resolution, the wavelength domain, the data signal-to-noise ratio and parameter degeneracy problems. The main algorithms in the literature are also reviewed.

Recio-Blanco, Alejandra

2014-01-01

275

Local Stellarator Equilibrium Model  

NASA Astrophysics Data System (ADS)

Extensive calculations of ballooning and drift waves spectrums in asymmetric toroidal configurations (e.g. stellarators) to appreciate the role of magnetic geometry and profile variations are usually are usually prohibitive as the evaluation of the magneto-hydrodynamic (MHD) equilibrium is in itself a non-trivial problem. Although simple analytical MHD model equilibria do exist for tokamak configurations, their stellarator counterparts are usually crude or very approximate. In order to make more extensive stability calculations (of both ideal ballooning and drift-type modes), a technique for generating three-dimensional magneto-static equilibria, localized to a magnetic surface, has been developed. The technique allows one to easily manipulate various 3-D shaping and profile effects on a magnetic surface avoiding the need to recompute an entire three dimensional solution of the equilibrium. The model equilibrium has been implemented into existing ideal MHD ballooning and drift wave numerical codes. Marginal ballooning stability diagrams and drift wave calculations will be reported.

Hudson, Stuart R.; Hegna, Chris C.; Lewandowski, Jerome W.

2000-10-01

276

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

277

Ion transport in stellarators  

SciTech Connect

Stellarator ion transport in the low-collisionality regime with a radial electric field is calculated by a systematic expansion of the drift-Boltzmann equation. The shape of the helical well is taken into account in this calculation. It is found that the barely trapped ions with three to four times the thermal energy give the dominant contribution to the diffusion. Expressions for the ion particle and energy fluxes are derived.

Ho, D.D.M.; Kulsrud, R.M.

1985-09-01

278

Stellar Inertial Navigation Workstation  

NASA Technical Reports Server (NTRS)

Software and hardware assembled to support specific engineering activities. Stellar Inertial Navigation Workstation (SINW) is integrated computer workstation providing systems and engineering support functions for Space Shuttle guidance and navigation-system logistics, repair, and procurement activities. Consists of personal-computer hardware, packaged software, and custom software integrated together into user-friendly, menu-driven system. Designed to operate on IBM PC XT. Applied in business and industry to develop similar workstations.

Johnson, W.; Johnson, B.; Swaminathan, N.

1989-01-01

279

Stellar population synthesis diagnostics  

E-print Network

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 n*sigma(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 n*sigma(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.

Y. K. Ng

1998-03-30

280

Parametric studies of stitching effectiveness for preventing substructure disbond  

NASA Technical Reports Server (NTRS)

A methodology is desired that will allow a designer to select appropriate amounts of through-thickness reinforcement needed to meet design requirements. The goal is to use a relatively simple analysis to minimize the amount of testing that needs to be performed, and to make test results from simple configurations applicable to more general structures. Using this methodology one should be able to optimize the selection of stitching materials, the weight of the yarn, and the stitching density. The analysis approach is to treat substructure disbond as a crack propagation problem. In this approach, the stitches have little influence until a delamination begins to grow. Once the delamination reaches, or extends beyond a stitch, the stitch serves to reduce the strain-energy-release-rate (G) at the crack tip for a given applied load. The reduced G can then be compared to the unstitched materials toughness to predict the load required to further extend the crack. The current model treats the stitch as a simple spring which responds to displacements in the vertical (through-thickness) direction. In concept, this approach is similar to that proposed by other authors. Test results indicate that the model should be refined to include the shearing stiffness of the stitch. The strain-energy-release-rate calculations are performed using a code which uses interconnected higher-order plates to model built-up composite cross-sections. When plates are stacked vertically, the interfacial tractions between the plates can be computed. The plate differential equations are solved in closed-form. The code, called SUBLAM, was developed as part of this section in one dimension. Because of this limitation, rows of stitches are treated as a two-dimensional sheet. The spring stiffness of a row of stitches can be estimated from the stitch material, weight, and density. As a practical and conservative approach, we can assume that the stitch is bonded until a crack passes the stitch location. After the crack passes, it is fully bonded. A series of tests were performed to exercise this methodology and incorporated an attached flange such that the sudden change in thickness initiated a delamination. The analysis was used to estimate the materials' critical G from that of the unstitched specimens. With this data, a prediction was made for the load required to delaminate the stitched specimens. Using the methodology, design charts have been created for simplified geometries. These charts give stitch force, along with G(sub 1) and G(sub 2) as as function of the stitch spring stiffness. Using the charts, it should be possible to determine the stitch spring stiffness and strength required to reduce the G to a desired level. From these parameters, the actual stitching material, weight, and density can be computed.

Flanagan, Gerry; Furrow, Keith

1995-01-01

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

Characterization of a subset of large amplitude noise events in VIRGO science run 1 (VSR1)  

NASA Astrophysics Data System (ADS)

We report about a characterization study of a subset of large amplitude noise events present in the main data channel of the VIRGO detector. The main motivation of this study is the identification of auxiliary channels which can be used to define veto procedures. We characterized large amplitude events both in the time and in the frequency domain. We found evidence of coincidences among these and disturbances detected by magnetometer's sensors or inside the main power supply. In some cases the disturbances were produced by events in the VIRGO environment such as lightnings, main power supply glitches and airplane traffic. We have found two auxiliary channels that can be used to veto events generated by main power supply glitches or lightnings. A procedure to clean the main channel based on them has been successfully tested. We have also identified two auxiliary channels which are useful for the identification of events generated by airplane traffic. These can be used to implement a vetoing procedure both in the time and in the frequency domain.

Del Prete, M.; Virgo Collaboration; LSC Collaboration

2009-10-01

283

The Arecibo Legacy Fast ALFA Survey: III. HI Source Catalog of the Northern Virgo Cluster Region  

E-print Network

We present the first installment of HI sources extracted from the Arecibo Legacy Fast ALFA (ALFALFA) extragalactic survey, initiated in 2005. Sources have been extracted from 3-D spectral data cubes and then examined interactively to yield global HI parameters. A total of 730 HI detections are catalogued within the solid angle 11h44m HI Parkes All-Sky Survey (HIPASS) detected 40 HI signals in the same region. Optical counterparts are assigned via examination of digital optical imaging databases. ALFALFA HI detections are reported for three distinct classes of signals: (a) detections, typically with S/N > 6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c) signals of lower S/N (to ~ 4.5) which coincide spatially with an optical object of known similar redshift. Although this region of the sky has been heavily surveyed by previous targeted observations based on optical flux-- or size-- limited samples, 69% of the extracted sources are newly reported HI detections. The resultant positional accuracy of HI sources is 20" (median). The median redshift of the sample is ~7000 \\kms and its distribution reflects the known local large scale structure including the Virgo cluster. Several extended HI features are found in the vicinity of the Virgo cluster. A small percentage (6%) of HI detections have no identifiable optical counterpart, more than half of which are high velocity clouds in the Milky Way vicinity; the remaining 17 objects do not appear connected to or associated with any known galaxy.

R. Giovanelli; M. P. Haynes; B. R. Kent; A. Saintonge; S. Stierwalt; A. Altaf; T. Balonek; N. Brosch; S. Brown; B. Catinella; A. Furniss; J. Goldstein; G. L. Hoffman; R. A. Koopmann; D. A. Kornreich; B. Mahmood; A. M. Martin; K. L. Masters; A. Mitschang; E. Momjian; P. H. Nair; J. L. Rosenberg; B. Walsh

2007-02-12

284

Automatic Learning of Chemical Concepts: Research Octane Number and Molecular Substructures  

Microsoft Academic Search

A set of 230 hydrocarbons is analyzed with respect to the research octane number (RON) using an extended version of the ID3 machine learning method of Quinlan. The basic ID3 method produces a decision tree. The questions within the decision tree ask whether given substructures are present or absent within a molecule (for example, is the hexane carbon skeleton present

Edward S. Blurock

1995-01-01

285

Structure, Phase Composition, and Defective Substructure of Rails of the Highest Quality Grade  

NASA Astrophysics Data System (ADS)

Methods of transmission electron microscopy are used for layer-by-layer analysis of rails of the highest quality grade. Quantitative parameters of structure gradients, phase composition, and dislocation substructures formed by various mechanisms of ?-? transformation are determined. Sources of long-range stress fields are revealed. It is determined that possible places of microcrack origin in the steel are interfaces cementite particles - matrix.

Gromov, V. E.; Volkov, K. V.; Ivanov, Yu. F.; Morozov, K. V.; Konovalov, S. V.; Alsaraeva, K. V.

2014-06-01

286

Modelling and control issues of dynamically substructured systems: adaptive forward prediction taken as an example.  

PubMed

Testing techniques of dynamically substructured systems dissects an entire engineering system into parts. Components can be tested via numerical simulation or physical experiments and run synchronously. Additional actuator systems, which interface numerical and physical parts, are required within the physical substructure. A high-quality controller, which is designed to cancel unwanted dynamics introduced by the actuators, is important in order to synchronize the numerical and physical outputs and ensure successful tests. An adaptive forward prediction (AFP) algorithm based on delay compensation concepts has been proposed to deal with substructuring control issues. Although the settling performance and numerical conditions of the AFP controller are improved using new direct-compensation and singular value decomposition methods, the experimental results show that a linear dynamics-based controller still outperforms the AFP controller. Based on experimental observations, the least-squares fitting technique, effectiveness of the AFP compensation and differences between delay and ordinary differential equations are discussed herein, in order to reflect the fundamental issues of actuator modelling in relevant literature and, more specifically, to show that the actuator and numerical substructure are heterogeneous dynamic components and should not be collectively modelled as a homogeneous delay differential equation. PMID:25104902

Tu, Jia-Ying; Hsiao, Wei-De; Chen, Chih-Ying

2014-08-01

287

Genomic Dissection of Population Substructure of Han Chinese and Its Implication in Association Studies  

E-print Network

of detailed characteriza- tion of genetic diversity in non-European populations, such as Africans,18 Pacific) and studies of fine-scale population structure have been conducted primarily on Europeans. Han Chinese spurious associations in GWAS. In this study, we examined population substructures in a diverse set of over

Xu, Shuhua

288

Hydrodynamic Simulations of A Moving Substructure in A Cluster of Galaxies: Cold Fronts and Turbulence Generation  

E-print Network

We perform three dimensional hydrodynamical simulations of a moving substructure in a cluster of galaxies. We investigate dynamical evolution of the intracluster medium (ICM) in and around the substructure moving radially in the larger cluster's gravitational potential, and its observational consequences. After the substructure passes the larger cluster's center, a bow shock and clear contact discontinuity form in front of it. The contact discontinuity looks like a sharp cold front in the X-ray image synthesized from the simulation results. This agrees with a structure found in 1E 0657-56. The flow structure remains laminar before the first turnaround because the ram-pressure stripping is dominant over the development of Kelvin-Helmholtz instabilities on the boundary between the substructure and the ambient ICM. When a subcluster oscillates radially around the larger cluster's center, both Kelvin-Helmholtz and Rayleigh-Taylor instabilities develop well and the flow structure becomes highly turbulent. Around the turnaround, the subcluster's cold gas is pushed out of its potential well. Therefore, the cold gas component appears to be in front of the subcluster. A relatively blunt cold front appears in the simulated X-ray image because the contact discontinuity is perturbed by Rayleigh-Taylor instabilities. This can explain the ICM structure found in A168.

Motokazu Takizawa

2005-05-13

289

Can galactic dark matter substructure contribute to the cosmic gamma-ray anisotropy?  

NASA Astrophysics Data System (ADS)

The annihilation of dark matter (DM) particles in the Milky Way can contribute to the diffuse gamma-ray background (DGRB). Due to the presence of substructures, this emission will appear anisotropic in a predictable way. We generate full-sky maps of the gamma-ray emission in galactic substructures from results of the high-resolution Via Lactea II N-body simulation of the Milky Way DM halo. We calculate the anisotropy pattern, taking into account different radial profiles of the DM distribution in substructures, cosmic variance, and the detection threshold, and compare it to the anisotropy in the DGRB observed by the Fermi Large Area Telescope (LAT). By comparing the upper limits on the DM self-annihilation cross-section, , implied by the anisotropy to the intensity of the DGRB and detected sources in the LAT 2-yr Point Source Catalog, we find that galactic substructure cannot contribute to the anisotropies in the DGRB without strongly violating these observations. Our results challenge the perception that small-scale anisotropies in the DGRB can be used as a probe of DM annihilation in galactic subhaloes.

Lange, J. U.; Chu, M.-C.

2015-02-01

290

The great disk of Milky-Way satellites and cosmological sub-structures  

E-print Network

We show that the shape of the observed distribution of Milky Way (MW) satellites is inconsistent with being drawn from a cosmological sub-structure population with a confidence of 99.5 per cent. Most of the MW satellites therefore cannot be related to dark-matter dominated satellites.

Pavel Kroupa; Christian Theis; Christian M. Boily

2004-10-18

291

Can galactic dark matter substructure contribute to the cosmic gamma-ray anisotropy?  

E-print Network

The annihilation of dark matter (DM) particles in the Milky Way can contribute to the diffuse gamma-ray background (DGRB). Due to the presence of substructures, this emission will appear anisotropic in a predictable way. We generate full-sky maps of the gamma-ray emission in galactic substructures from results of the high-resolution Via Lactea II N-body simulation of the Milky Way DM halo. We calculate the anisotropy pattern, taking into account different radial profiles of the DM distribution in substructures, cosmic variance, and the detection threshold, and compare it to the anisotropy in the DGRB observed by the Fermi Large Area Telescope (LAT). By comparing the upper limits on the DM self-annihilation cross-section, , implied by the anisotropy to the intensity of the DGRB and detected sources in the LAT 2-yr Point Source Catalog, we find that galactic substructure cannot contribute to the anisotropies in the DGRB without strongly violating these observations. Our results challenge the perception that sma...

Lange, J U

2014-01-01

292

Loading and substructure-induced irreversibility in texture during route C equal channel angular extrusion  

Microsoft Academic Search

The experimental texture after two equal channel angular extrusion (ECAE) passes by route C differs qualitatively from that calculated using standard polycrystal models assuming forward and reverse simple shear. Agreement between orientation imaging microscopy measured textures of ECAE copper and polycrystal model calculations is obtained by accounting for strain hardening, substructure formation, and non-uniform distribution of the bulk deformation.

S. Mahesh; I. J. Beyerlein; C. N. Tomé

2005-01-01

293

Implementation of automated multilevel substructuring for frequency response analysis of structures  

Microsoft Academic Search

In the design of vehicles, such as automobiles, aircraft, spacecraft, or submarines, it is important to be able to accurately predict dynamic behavior of the structure. With the extremely high cost of building physical prototypes of these vehicles, there is a growing emphasis on analysis of computer models. In this dissertation, a method known as Automated Multilevel Substructuring (AMLS) is

Matthew Frederick Kaplan

2001-01-01

294

Association of Systemic Lupus Erythematosus Clinical Features with European Population Genetic Substructure  

Microsoft Academic Search

Systemic Lupus Erythematosus (SLE) is an autoimmune disease with a very varied spectrum of clinical manifestations that could be partly determined by genetic factors. We aimed to determine the relationship between prevalence of 11 clinical features and age of disease onset with European population genetic substructure. Data from 1413 patients of European ancestry recruited in nine countries was tested for

Elisa Alonso-Perez; Marian Suarez-Gestal; Manuel Calaza; Torsten Witte; Chryssa Papasteriades; Maurizio Marchini; Sergio Migliaresi; Attila Kovacs; Josep Ordi-Ros; Marc Bijl; Maria Jose Santos; Sarka Ruzickova; Rudolf Pullmann; Patricia Carreira; Fotini N. Skopouli; Sandra DAlfonso; Gian Domenico Sebastiani; Ana Suarez; Francisco J. Blanco; Juan J. Gomez-Reino; Antonio Gonzalez

2011-01-01

295

Kinematic and Spatial Substructure in NGC 2264\\footnotemark  

E-print Network

We present an expanded kinematic study of the young cluster NGC 2264 based upon optical radial velocities measured using multi-fiber echelle spectroscopy at the 6.5 meter MMT and Magellan telescopes. We report radial velocities for 695 stars, of which approximately 407 stars are confirmed or very likely members. Our results more than double the number of members with radial velocities from F{\\H u}r{\\'e}sz et al., resulting in a much better defined kinematic relationship between the stellar population and the associated molecular gas. In particular, we find that there is a significant subset of stars that are systematically blueshifted with respect to the molecular ($^{13}$CO) gas. The detection of Lithium absorption and/or infrared excesses in this blue-shifted population suggests that at least some of these stars are cluster members; we suggest some speculative scenarios to explain their kinematics. Our results also more clearly define the redshifted population of stars in the northern end of the cluster; we...

Tobin, John J; Furesz, Gabor; Hsu, Wen-Hsin; Mateo, Mario

2015-01-01

296

The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey. I. Star-Forming Molecular Gas in Virgo Cluster Spiral Galaxies  

Microsoft Academic Search

We present large-area maps of the CO J = 3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J = 1-0, 24 mum, and Halpha images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our

C. D. Wilson; B. E. Warren; F. P. Israel; S. Serjeant; G. Bendo; E. Brinks; D. Clements; S. Courteau; J. Irwin; J. H. Knapen; J. Leech; H. E. Matthews; S. Mühle; A. M. J. Mortier; G. Petitpas; E. Sinukoff; K. Spekkens; B. K. Tan; R. P. J. Tilanus; A. Usero; P. van der Werf; T. Wiegert; M. Zhu

2009-01-01

297

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. PMID:20546593

2010-01-01

298

Stellar figure sensor  

NASA Technical Reports Server (NTRS)

A compilation of analytical and experimental data is presented concerning the stellar figure sensor. The sensor is an interferometric device which is located in the focal plane of an orbiting large space telescope (LST). The device was designed to perform interferometry on the optical wavefront of a single star after it has propagated through the LST. An analytical model of the device was developed and its accuracy was verified by an operating laboratory breadboard. A series of linear independent control equations were derived which define the operations required for utilizing a focal plane figure sensor in the control loop for the secondary mirror position and for active control of the primary mirror.

Peters, W. N.

1973-01-01

299

Stellar evolution@EURO-VObs  

NASA Astrophysics Data System (ADS)

Stellar evolutionary models are a fundamental tool for addressing many astrophysical issues. For such a reason, it is of fundamental relevance to make them available to the whole scientific community in an easy and direct way. We briefly review the main ingredients requested for computing stellar models and show some illustrative scientific cases concerning the comparison between model predictions and suitable empirical evidence. We discuss also some problems related to the implementation of stellar models library inside the Virtual Observatory, and report about our experience with the our BaSTI stellar model repository.

Cassisi, S.; Pasian, F.; Salaris, M.; Manzato, P.; Pietrinferni, A.; Taffoni, G.; Molinaro, M.; Gasparo, F.

300

Investigation of the internal substructure of microbands in a deformed copper single crystal: experiments and dislocation dynamics simulation  

NASA Astrophysics Data System (ADS)

We investigate the internal structure of microbands in a shear-deformed copper single crystal. The microstructure is characterized using high-resolution electron backscatter diffraction. The occurrence of microbands is due to the alternation of local orientation, which is characteristic of a deformation laminate. These microbands contain a substructure consisting of further local 1°-orientation alternations. A two-dimensional discrete dislocation dynamics model is used to describe the orientation substructure within the microbands. The boundary conditions for the simulation were estimated from the distribution of the geometrically necessary dislocation density obtained from the orientation map. The dislocation arrangement in the dynamic simulation explains the formation of the experimentally observed substructure.

Dmitrieva, O.; Svirina, J. V.; Demir, E.; Raabe, D.

2010-12-01

301

CLASH-VLT: Insights on the Mass Substructures in the Frontier Fields Cluster MACS J0416.1–2403 through Accurate Strong Lens Modeling  

NASA Astrophysics Data System (ADS)

We present a detailed mass reconstruction and a novel study on the substructure properties in the core of the Cluster Lensing And Supernova survey with Hubble (CLASH) and Frontier Fields galaxy cluster MACS J0416.1–2403. We show and employ our extensive spectroscopic data set taken with the VIsible Multi-Object Spectrograph instrument as part of our CLASH-VLT program, to confirm spectroscopically 10 strong lensing systems and to select a sample of 175 plausible cluster members to a limiting stellar mass of log (M */M ?) ~= 8.6. We reproduce the measured positions of a set of 30 multiple images with a remarkable median offset of only 0.''3 by means of a comprehensive strong lensing model comprised of two cluster dark-matter halos, represented by cored elliptical pseudo-isothermal mass distributions, and the cluster member components, parameterized with dual pseudo-isothermal total mass profiles. The latter have total mass-to-light ratios increasing with the galaxy HST/WFC3 near-IR (F160W) luminosities. The measurement of the total enclosed mass within the Einstein radius is accurate to ~5%, including the systematic uncertainties estimated from six distinct mass models. We emphasize that the use of multiple-image systems with spectroscopic redshifts and knowledge of cluster membership based on extensive spectroscopic information is key to constructing robust high-resolution mass maps. We also produce magnification maps over the central area that is covered with HST observations. We investigate the galaxy contribution, both in terms of total and stellar mass, to the total mass budget of the cluster. When compared with the outcomes of cosmological N-body simulations, our results point to a lack of massive subhalos in the inner regions of simulated clusters with total masses similar to that of MACS J0416.1–2403. Our findings of the location and shape of the cluster dark-matter halo density profiles and on the cluster substructures provide intriguing tests of the assumed collisionless, cold nature of dark matter and of the role played by baryons in the process of structure formation. This work is based in large part on data collected at ESO VLT (prog. ID 186.A-0798) and NASA HST.

Grillo, C.; Suyu, S. H.; Rosati, P.; Mercurio, A.; Balestra, I.; Munari, E.; Nonino, M.; Caminha, G. B.; Lombardi, M.; De Lucia, G.; Borgani, S.; Gobat, R.; Biviano, A.; Girardi, M.; Umetsu, K.; Coe, D.; Koekemoer, A. M.; Postman, M.; Zitrin, A.; Halkola, A.; Broadhurst, T.; Sartoris, B.; Presotto, V.; Annunziatella, M.; Maier, C.; Fritz, A.; Vanzella, E.; Frye, B.

2015-02-01

302

Improving corrosion resistance of post-tensioned substructures emphasizing high performance grouts  

NASA Astrophysics Data System (ADS)

The use of post-tensioning in bridges can provide durability and structural benefits to the system while expediting the construction process. When post-tensioning is combined with precast elements, traffic interference can be greatly reduced through rapid construction. Post-tensioned concrete substructure elements such as bridge piers, hammerhead bents, and straddle bents have become more prevalent in recent years. Chloride induced corrosion of steel in concrete is one of the most costly forms of corrosion each year. Coastal substructure elements are exposed to seawater by immersion or spray, and inland bridges may also be at risk due to the application of deicing salts. Corrosion protection of the post-tensioning system is vital to the integrity of the structure because loss of post-tensioning can result in catastrophic failure. Documentation for durability design of the grout, ducts, and anchorage systems is very limited. The objective of this research is to evaluate the effectiveness of corrosion protection measures for post-tensioned concrete substructures by designing and testing specimens representative of typical substructure elements using state-of-the-art practices in aggressive chloride exposure environments. This was accomplished through exposure testing of twenty-seven large-scale beam specimens and ten large-scale column specimens. High performance grout for post-tensioning tendon injection was also developed through a series of fresh property tests, accelerated exposure tests, and a large-scale pumping test to simulate field conditions. A high performance fly ash grout was developed for applications with small vertical rises, and a high performance anti-bleed grout was developed for applications involving large vertical rises such as tall bridge piers. Long-term exposure testing of the beam and column specimens is ongoing, but preliminary findings indicate increased corrosion protection with increasing levels of post-tensioning, although traditional fully prestressed sections may not give as high a benefit to cost ratio as partially prestressed sections with high percentages of prestressing steel. Specimens with low permeable concrete are showing better corrosion protection than specimens with the standard concrete for bridge substructures used by the Texas Department of Transportation. Recommendations and guidelines for durable design of post-tensioned bridge substructures were developed from the findings to date, and supplementary information will be provided after final autopsy of all specimens.

Schokker, Andrea Jeanne

303

Multimessenger search for sources of gravitational waves and high-energy neutrinos: Initial results for LIGO-Virgo and IceCube  

E-print Network

We report the results of a multimessenger search for coincident signals from the LIGO and Virgo gravitational-wave observatories and the partially completed IceCube high-energy neutrino detector, including periods of joint ...

Aartsen, M.?G.

304

Search for gravitational radiation from intermediate mass black hole binaries in data from the second LIGO-Virgo joint science run  

E-print Network

This paper reports on an unmodeled, all-sky search for gravitational waves from merging intermediate mass black hole binaries (IMBHB). The search was performed on data from the second joint science run of the LIGO and Virgo ...

Aggarwal, Nancy

305

The Dartmouth Stellar Evolution Database  

E-print Network

The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from -2.5 to +0.5, [alpha/Fe] from -0.2 to +0.8 (for [Fe/H] 0), and initial He mass fractions from Y=0.245 to 0.40. Stellar evolution tracks were computed for masses between 0.1 and 4 Msun, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)c, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS-WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a website at http://stellar.dartmouth.edu/~models/ where all tracks, isochrones, and additional files can be downloaded.

Aaron Dotter; Brian Chaboyer; Darko Jevremovic; Veselin Kostov; E. Baron; J. W. Ferguson

2008-04-28

306

A catalog of stellar spectrophotometry  

NASA Technical Reports Server (NTRS)

A machine-readable catalog of stellar spectrophotometric measurements made with rotating grating scanner is introduced. Consideration is given to the processes by which the stellar data were collected and calibrated with the fluxes of Vega (Hayes and Latham, 1975). A sample page from the spectrophotometric catalog is presented.

Adelman, S. J.; Pyper, D. M.; Shore, S. N.; White, R. E.; Warren, W. H., Jr.

1989-01-01

307

Solar and Stellar Magnetic Activity  

Microsoft Academic Search

Magnetic activity in the sun and similar stars results in a wealth of phenomena--including starspots, nonradiatively heated outer atmospheres, activity cycles, deceleration of rotation rates, and even, in close binaries, stellar cannibalism. This volume uniquely combines studies of the sun with those of other stars to provide a comprehensive picture of stellar magnetic activity. Coverage brings together recent results in

Carolus J. Schrijver; Cornelius Zwaan

2000-01-01

308

X-rays from the radio halo of Virgo A = M87  

NASA Technical Reports Server (NTRS)

The purpose of this study is to investigate in more detail the associated X-ray and radio emission in the Virgo A halo discovered by SGF. Improved Einstein HRI data and new radio maps obtained with the Very Large Array are described and the relation between the X-ray and radio structures is carefully examined. Several possible explanations are presented for the X-ray emission. The inverse compton model is found to be viable only if the magnetic field is variable and substantially weaker than the equipartition value. The principal alternative is excess thermal X-rays due to compression of the intracluster medium by the radio lobe. In either case, the association of such prominent radio and X-ray structures is unique among known radio galaxies.

1985-01-01

309

The Next Generation Virgo Cluster Survey. XV. The Photometric Redshift Estimation for Background Sources  

NASA Astrophysics Data System (ADS)

The Next Generation Virgo Cluster Survey (NGVS) is an optical imaging survey covering 104 deg2 centered on the Virgo cluster. Currently, the complete survey area has been observed in the u*giz bands and one third in the r band. We present the photometric redshift estimation for the NGVS background sources. After a dedicated data reduction, we perform accurate photometry, with special attention to precise color measurements through point-spread function homogenization. We then estimate the photometric redshifts with the Le Phare and BPZ codes. We add a new prior that extends to i AB = 12.5 mag. When using the u* griz bands, our photometric redshifts for 15.5 mag <= i <~ 23 mag or z phot <~ 1 galaxies have a bias |?z| < 0.02, less than 5% outliers, a scatter ?outl.rej., and an individual error on z phot that increases with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u*giz bands over the same magnitude and redshift range, the lack of the r band increases the uncertainties in the 0.3 <~ z phot <~ 0.8 range (–0.05 < ?z < –0.02, ?outl.rej ~ 0.06, 10%-15% outliers, and z phot.err. ~ 0.15). We also present a joint analysis of the photometric redshift accuracy as a function of redshift and magnitude. We assess the quality of our photometric redshifts by comparison to spectroscopic samples and by verifying that the angular auto- and cross-correlation function w(?) of the entire NGVS photometric redshift sample across redshift bins is in agreement with the expectations.

Raichoor, A.; Mei, S.; Erben, T.; Hildebrandt, H.; Huertas-Company, M.; Ilbert, O.; Licitra, R.; Ball, N. M.; Boissier, S.; Boselli, A.; Chen, Y.-T.; Côté, P.; Cuillandre, J.-C.; Duc, P. A.; Durrell, P. R.; Ferrarese, L.; Guhathakurta, P.; Gwyn, S. D. J.; Kavelaars, J. J.; Lançon, A.; Liu, C.; MacArthur, L. A.; Muller, M.; Muñoz, R. P.; Peng, E. W.; Puzia, T. H.; Sawicki, M.; Toloba, E.; Van Waerbeke, L.; Woods, D.; Zhang, H.

2014-12-01

310

All Sky Search for Gravitational-Wave Bursts in the Second Joint LIGO-Virgo Run  

NASA Technical Reports Server (NTRS)

We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration approx. < 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal wa.veform, polarization, direction or occurrence time. All identified events are c.onsistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGOVirgo search on the data collected "between November 2005 and October 2007. The upper limit on the rate of strong gravita.tional-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per yea.r and Mpc3 for sample popula.tions of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range approx 5 x 10(exp -22 Hz(exp-1/2) approx 1 X 10(exp -20) Hz(exp -1/2) . The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.

Abadie, J.; Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M.; Accadia, T.; Acernese, F.; Adams, C.; Adhikari, R.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Ajith, P.; Allen, B.; Ceron, E. Amador; Amariutei, D.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Arain, M. A.; Araya, M. C.; Aylott, B. E.; Blackburn, L.; Camp, J. B.; Cannizzo, J.

2012-01-01

311

Modeling the Formation of Globular Cluster Systems in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

The mass distribution and chemical composition of globular cluster (GC) systems preserve fossil record of the early stages of galaxy formation. The observed distribution of GC colors within massive early-type galaxies in the ACS Virgo Cluster Survey (ACSVCS) reveals a multi-modal shape, which likely corresponds to a multi-modal metallicity distribution. We present a simple model for the formation and disruption of GCs that aims to match the ACSVCS data. This model tests the hypothesis that GCs are formed during major mergers of gas-rich galaxies and inherit the metallicity of their hosts. To trace merger events, we use halo merger trees extracted from a large cosmological N-body simulation. We select 20 halos in the mass range of 2 × 1012 to 7 × 1013 M ? and match them to 19 Virgo galaxies with K-band luminosity between 3 × 1010 and 3 × 1011 L ?. To set the [Fe/H] abundances, we use an empirical galaxy mass-metallicity relation. We find that a minimal merger ratio of 1:3 best matches the observed cluster metallicity distribution. A characteristic bimodal shape appears because metal-rich GCs are produced by late mergers between massive halos, while metal-poor GCs are produced by collective merger activities of less massive hosts at early times. The model outcome is robust to alternative prescriptions for cluster formation rate throughout cosmic time, but a gradual evolution of the mass-metallicity relation with redshift appears to be necessary to match the observed cluster metallicities. We also affirm the age-metallicity relation, predicted by an earlier model, in which metal-rich clusters are systematically several billion younger than their metal-poor counterparts.

Li, Hui; Gnedin, Oleg Y.

2014-11-01

312

Localization of Short Duration Gravitational-wave Transients with the Early Advanced LIGO and Virgo Detectors  

NASA Astrophysics Data System (ADS)

The Laser Interferometer Gravitational wave Observatory (LIGO) and Virgo advanced ground-based gravitational-wave detectors will begin collecting science data in 2015. With first detections expected to follow, it is important to quantify how well generic gravitational-wave transients can be localized on the sky. This is crucial for correctly identifying electromagnetic counterparts as well as understanding gravitational-wave physics and source populations. We present a study of sky localization capabilities for two search and parameter estimation algorithms: coherent WaveBurst, a constrained likelihood algorithm operating in close to real-time, and LALInferenceBurst, a Markov chain Monte Carlo parameter estimation algorithm developed to recover generic transient signals with latency of a few hours. Furthermore, we focus on the first few years of the advanced detector era, when we expect to only have two (2015) and later three (2016) operational detectors, all below design sensitivity. These detector configurations can produce significantly different sky localizations, which we quantify in detail. We observe a clear improvement in localization of the average detected signal when progressing from two-detector to three-detector networks, as expected. Although localization depends on the waveform morphology, approximately 50% of detected signals would be imaged after observing 100-200 deg2 in 2015 and 60-110 deg2 in 2016, although knowledge of the waveform can reduce this to as little as 22 deg2. This is the first comprehensive study on sky localization capabilities for generic transients of the early network of advanced LIGO and Virgo detectors, including the early LIGO-only two-detector configuration.

Essick, Reed; Vitale, Salvatore; Katsavounidis, Erik; Vedovato, Gabriele; Klimenko, Sergey

2015-02-01

313

Population sub-structure and patterns of quantitative variation among the Gollas of Southern Andhra Pradesh, India  

E-print Network

Population substructure and biological differentiation was studied among the Golla, a pastoral caste living in the southern areas of Andhra Pradesh (AP) in India, using 11 anthropometric measurements and 20 quantitative dermatoglyphic variables...

Reddy, B. Mohan; Pfeffer, Alexa; Crawford, Michael H.; Langstieh, Banrida T.

2001-08-01

314

A Note on Substructuring Preconditioning for Nonconforming Finite Element Approximations of Second Order Elliptic Problems  

NASA Technical Reports Server (NTRS)

In this paper an algebraic substructuring preconditioner is considered for nonconforming finite element approximations of second order elliptic problems in 3D domains with a piecewise constant diffusion coefficient. Using a substructuring idea and a block Gauss elimination, part of the unknowns is eliminated and the Schur complement obtained is preconditioned by a spectrally equivalent very sparse matrix. In the case of quasiuniform tetrahedral mesh an appropriate algebraic multigrid solver can be used to solve the problem with this matrix. Explicit estimates of condition numbers and implementation algorithms are established for the constructed preconditioner. It is shown that the condition number of the preconditioned matrix does not depend on either the mesh step size or the jump of the coefficient. Finally, numerical experiments are presented to illustrate the theory being developed.

Maliassov, Serguei

1996-01-01

315

Interference substructure of above-threshold ionization peaks in the stabilization regime  

NASA Astrophysics Data System (ADS)

The photoelectron spectra produced in the photodetachment of H- (treated in the single-active-electron approximation) by strong high-frequency laser pulses with adequately chosen laser parameters in the stabilization regime are theoretically studied for elliptic polarization over an extended parameter range. An oscillating substructure in the above-threshold ionization peaks is observed, which confirms similar findings in the one-dimensional (1D) [K. Toyota , Phys. Rev. A 76, 043418 (2007)] and 3D calculations for linear polarization [O. I. Tolstikhin, Phys. Rev. A 77, 032712 (2008)]. The mechanism is an interference between the photoelectron wave packets created in the rising and falling parts of the pulse which is specific to the stabilization regime. We thus conclude that this interference substructure is robust for any polarization and over a wide range of the laser parameters, and hence should be observable experimentally.

Toyota, Koudai; Tolstikhin, Oleg I.; Morishita, Toru; Watanabe, Shinichi

2008-09-01

316

Programming substructure computations for elliptic problems on the CHiP system  

NASA Technical Reports Server (NTRS)

A number of studies have been conducted with the aim to apply parallel computation to problems associated with solving finite element equations arising in structural mechanics and fluid dynamics. These studies have provided many important results. The present investigation is concerned with a set of experiments designed to test two ideas, including configurability and substructuring. The considered algorithms and tests are intended for implementation on the Configurable, Highly Parallel (CHiP) family of architecture described by Snyder (1982). The ChiP computer is composed of homogeneous processing elements (PEs) placed at regular intervals in a lattice of programmable switches. Two examples of the role of configurability and substructuring for simple iterative algorithms are considered, giving attention to conjugate gradient iterations, and tridiagonal systems of equations.

Gannon, D.; Snyder, L.; Van Rosendale, J.

1983-01-01

317

How well can cold dark matter substructures account for the observed radio flux-ratio anomalies  

NASA Astrophysics Data System (ADS)

Discrepancies between the observed and model-predicted radio flux ratios are seen in a number of quadruply-lensed quasars. The most favoured interpretation of these anomalies is that cold dark matter (CDM) substructures present in lensing galaxies perturb the lens potentials and alter image magnifications and thus flux ratios. So far no consensus has emerged regarding whether or not the predicted CDM substructure abundance fully accounts for the lensing flux anomaly observations. Accurate modelling relies on a realistic lens sample in terms of both the lens environment and internal structures and substructures. In this paper, we construct samples of generalized and specific lens potentials, to which we add (rescaled) subhalo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites. We further investigate the lensing effects from subhaloes of masses several orders of magnitude below the simulation resolution limit. The resulting flux-ratio distributions are compared to the currently best available sample of radio lenses. The observed anomalies in B0128+437, B0712+472 and B1555+375 are more likely to be caused by propagation effects or oversimplified/improper lens modelling, signs of which are already seen in the data. Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM subhaloes to its macroscopic lens potential, with a probability of 5-20 per cent; for B0712+472, B1422+231, B1555+375 and B2045+265, these probabilities are only of a few per cent. We hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies. We discuss other possible effects that might also be at work.

Xu, Dandan; Sluse, Dominique; Gao, Liang; Wang, Jie; Frenk, Carlos; Mao, Shude; Schneider, Peter; Springel, Volker

2015-03-01

318

Substructure of bovine casein micelles by small-angle X-ray and neutron scattering  

Microsoft Academic Search

The casein micelles of cow's milk are polydisperse, more-or-less spherical, protein particles of up to several hundred nanometer in size, containing about 7% by dry weight of calcium phosphate. Small-angle neutron scattering with contrast variation and small-angle X-ray scattering were used in critical tests of models of casein micelle substructure. An inflexion in the neutron scattering curve near Q=0.35 nm?1

C. Holt; C. G. de Kruif; R. Tuinier; P. A. Timmins

2003-01-01

319

Discovering the Higgs boson in new physics events using jet substructure  

Microsoft Academic Search

We present a novel method to discover the Higgs boson in new physics event\\u000asamples at the LHC. Our technique applies to broad classes of models where the\\u000aHiggs has a significant branching fraction to b-bbar. We exploit the recently\\u000adeveloped techniques for discovering a boosted Higgs using jet substructure.\\u000aOur requirements of new physics are quite general: there must

Graham D. Kribs; Adam Martin; Tuhin S. Roy; Michael Spannowsky

2010-01-01

320

Creep deformation behavior and dislocation substructures of Mg–Y binary alloys  

Microsoft Academic Search

Compressive creep behavior and deformation substructures of binary Mg–Y alloys containing 0.2–2.4 mol% Y were investigated at 550–650 K under 4–200 MPa. The addition of yttrium improves creep strength of magnesium more efficiently than aluminum and manganese. This efficiency decreases with increasing temperature. The apparent activation energy for creep is substantially greater than that for self-diffusion in magnesium. Transmission electron

Mayumi Suzuki; Hiroyuki Sato; Kouich Maruyama; Hiroshi Oikawa

2001-01-01

321

Delayed fracture and the nature of substructural defects formed in aluminum alloys due to sustained loading  

Microsoft Academic Search

We analyze and generalize experimental and theoretical data on substructural defects associated with dislocation pileups, hydrogenation, and excess vacancies formed in Al-Mg, Al-Mg-Li, and Al-Zn-Mg-(Cu) alloys subjected to long-term loading under normal conditions. It is shown that the key role in the formation of defects of the last two kinds is played by selective oxidation of magnesium and\\/or lithium. We

V. M. Polyanskii; L. A. Kurtasova

1995-01-01

322

Vibration mode localization in two-dimensional systems with multiple substructural modes  

Microsoft Academic Search

Free vibration mode localization in randomly disordered weakly coupled two-dimensional cantilever-mesh-spring arrays, in which S substructural modes are considered for each cantilever, is studied in this paper. A method of regular perturbation is applied to determine the localization factors, which are defined in terms of the angles of orientation and characterize the average exponential rates of growth or decay of

Wei-Chau Xie

2001-01-01

323

Dislocation substructure in Ta-Re-N alloys deformed at 77 K  

Microsoft Academic Search

High purity Ta, Ta-Re, and Ta-Re-N alloy single crystals were deformed in tension at 77 K, and the resulting dislocation arrangements were studied by transmission electron microscopy. Re and N have similar effects on the dislocation substructure. Alloying increases the fraction of primary screw dislocations at the expense of debris, tangling, and secondary dislocations. For a given increment in yield

J. A. Shields; R. Gibala; T. E. Mitchell

1976-01-01

324

Dislocation substructure in Ta-Re-N alloys deformed at 77 K  

Microsoft Academic Search

High purity Ta, Ta-Re, and Ta-Re-N alloy single crystals were deformed in tension at 77 K, and the resulting dislocation arrangements\\u000a were studied by transmission electron microscopy. Re and N have similar effects on the dislocation substructure. Alloying\\u000a increases the fraction of primary screw dislocations at the expense of debris, tangling, and secondary dislocations. For a\\u000a given increment in yield

J. A. Shields; R. Gibala; T. E. Mitchell

1976-01-01

325

DWARFS GOBBLING DWARFS: A STELLAR TIDAL STREAM AROUND NGC 4449 AND HIERARCHICAL GALAXY FORMATION ON SMALL SCALES  

SciTech Connect

A candidate diffuse stellar substructure was previously reported in the halo of the nearby dwarf starburst galaxy NGC 4449 by Karachentsev et al. We map and analyze this feature using a unique combination of deep integrated-light images from the BlackBird 0.5 m telescope, and high-resolution wide-field images from the 8 m Subaru Telescope, which resolve the nebulosity into a stream of red giant branch stars, and confirm its physical association with NGC 4449. The properties of the stream imply a massive dwarf spheroidal progenitor, which after complete disruption will deposit an amount of stellar mass that is comparable to the existing stellar halo of the main galaxy. The stellar mass ratio between the two galaxies is {approx}1:50, while the indirectly measured dynamical mass ratio, when including dark matter, may be {approx}1:10-1:5. This system may thus represent a 'stealth' merger, where an infalling satellite galaxy is nearly undetectable by conventional means, yet has a substantial dynamical influence on its host galaxy. This singular discovery also suggests that satellite accretion can play a significant role in building up the stellar halos of low-mass galaxies, and possibly in triggering their starbursts.

Martinez-Delgado, David; Rix, Hans-Walter; Maccio, Andrea V. [Max-Planck-Institut fuer Astronomy, Heidelberg (Germany); Romanowsky, Aaron J.; Arnold, Jacob A.; Brodie, Jean P. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Jay Gabany, R. [Black Bird Observatory, Mayhill, New Mexico (United States); Annibali, Francesca [Osservatorio Astronomico di Bologna, INAF, Via Ranzani 1, I-40127 Bologna (Italy); Fliri, Juergen [LERMA, CNRS UMR 8112, Observatoire de Paris, 61 Avenue de l'Observatoire, F-75014 Paris (France); Zibetti, Stefano [Dark Cosmology Centre, Niels Bohr Institute-University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Van der Marel, Roeland P.; Aloisi, Alessandra [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Chonis, Taylor S. [Department of Astronomy, University of Texas at Austin, Texas (United States); Carballo-Bello, Julio A. [Instituto de Astrofisica de Canarias, Tenerife (Spain); Gallego-Laborda, J. [Fosca Nit Observatory, Montsec Astronomical Park, Ager (Spain); Merrifield, Michael R. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)

2012-04-01

326

Modeling the Role of Dislocation Substructure During Class M and Exponential Creep. Revised  

NASA Technical Reports Server (NTRS)

The different substructures that form in the power-law and exponential creep regimes for single phase crystalline materials under various conditions of stress, temperature and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential creep as well as with steady state and non-steady state deformation behavior. These observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the creep substructure is examined in both of these creep regimes during stress and temperature change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary creep is interpreted as a series of constant structure exponential creep rate-stress relationships. The implications of this viewpoint on the magnitude of the stress exponent and steady state behavior are discussed. A theory is developed to predict the macroscopic creep behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated deformation mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure creep model. This procedure leads to several coupled differential equations interrelating macroscopic creep plasticity with microstructural evolution.

Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.

1995-01-01

327

Constraining dark matter sub-structure with the dynamics of astrophysical systems  

SciTech Connect

The accuracy of the measurements of some astrophysical dynamical systems allows to constrain the existence of incredibly small gravitational perturbations. In particular, the internal Solar System dynamics (planets, Earth-Moon) opens up the possibility, for the first time, to prove the abundance, mass and size, of dark sub-structures at the Earth vicinity. We find that adopting the standard dark matter density, its local distribution can be composed by sub-solar mass halos with no currently measurable dynamical consequences, regardless of the mini-halo fraction. On the other hand, it is possible to exclude the presence of dark streams with linear mass densities higher than ?{sub st} > 10{sup ?10}M{sub ?}/AU (about the Earth mass spread along the diameter of the SS up to the Kuiper belt). In addition, we review the dynamics of wide binaries inside the dwarf spheroidal galaxies in the Milky Way. The dynamics of such kind of binaries seem to be compatible with the presence of a huge fraction of dark sub-structure, thus their existence is not a sharp discriminant of the dark matter hypothesis as been claimed before. However, there are regimes where the constraints from different astrophysical systems may reveal the sub-structure mass function cut-off scale.

González-Morales, Alma X. [Instituto de Ciencias Nucleares, UNAM, A.P. 70-543, 04510, Ciudad Universitaria, D.F. (Mexico); Valenzuela, Octavio [Instituto de Astronomia, UNAM, A.P. 70-264, 04510, Ciudad Universitaria, D.F. (Mexico); Aguilar, Luis A., E-mail: alma.gonzalez@nucleares.unam.mx, E-mail: octavio@astro.unam.mx, E-mail: aguilar@astrosen.unam.mx [Instituto de Astronomia, UNAM, A.P. 877, 22860, Ensenada, B.C. (Mexico)

2013-03-01

328

Stellar Snowflake Cluster  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Figure 1 Stellar Snowflake Cluster Combined Image [figure removed for brevity, see original site] Figure 2 Infrared Array CameraFigure 3 Multiband Imaging Photometer

Newborn stars, hidden behind thick dust, are revealed in this image of a section of the Christmas Tree cluster from NASA's Spitzer Space Telescope, created in joint effort between Spitzer's infrared array camera and multiband imaging photometer instruments.

The newly revealed infant stars appear as pink and red specks toward the center of the combined image (fig. 1). The stars appear to have formed in regularly spaced intervals along linear structures in a configuration that resembles the spokes of a wheel or the pattern of a snowflake. Hence, astronomers have nicknamed this the 'Snowflake' cluster.

Star-forming clouds like this one are dynamic and evolving structures. Since the stars trace the straight line pattern of spokes of a wheel, scientists believe that these are newborn stars, or 'protostars.' At a mere 100,000 years old, these infant structures have yet to 'crawl' away from their location of birth. Over time, the natural drifting motions of each star will break this order, and the snowflake design will be no more.

While most of the visible-light stars that give the Christmas Tree cluster its name and triangular shape do not shine brightly in Spitzer's infrared eyes, all of the stars forming from this dusty cloud are considered part of the cluster.

Like a dusty cosmic finger pointing up to the newborn clusters, Spitzer also illuminates the optically dark and dense Cone nebula, the tip of which can be seen towards the bottom left corner of each image.

This combined image shows the presence of organic molecules mixed with dust as wisps of green, which have been illuminated by nearby star formation. The larger yellowish dots neighboring the baby red stars in the Snowflake Cluster are massive stellar infants forming from the same cloud. The blue dots sprinkled across the image represent older Milky Way stars at various distances along this line of sight. This image is a five-channel, false-color composite, showing emission from wavelengths of 3.6 and 4.5 microns (blue), 5.8 microns (cyan), 8 microns (green), and 24 microns (red).

The top right (fig. 2) image from the infrared array camera show that the nebula is still actively forming stars. The wisps of red (represented as green in the combined image) are organic molecules mixed with dust, which has been illuminated by nearby star formation. The infrared array camera picture is a four-channel, false-color composite, showing emission from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red).

The bottom right image (fig. 3) from the multiband imaging photometer shows the colder dust of the nebula and unwraps the youngest stellar babies from their dusty covering. This is a false-color image showing emission at 24 microns (red).

2005-01-01

329

Molecular gas mass and star formation of 12 Virgo spiral galaxies along the ram pressure time sequence  

NASA Astrophysics Data System (ADS)

The ram pressure stripping is known as one of the most efficient mechanisms to deplete the ISM of a galaxy in the clusters of galaxies. As being affected continuously by ICM pressure, a galaxy may lose their gas that is the fuel of star formation, and consequently star formation rate would be changed. We select twelve Virgo spiral galaxies according to their stage of the ram pressure stripping event to probe possible consequences of star formation of spiral galaxies in the ram pressure and thus the evolution of galaxies in the Virgo cluster. We investigate the molecular gas properties, star formation activity, and gas depletion time along the time from the ram pressure peak. We also discussed the evolution of galaxies in the cluster.

Chung, Eun Jung; Kim, S.

2014-01-01

330

H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area  

NASA Technical Reports Server (NTRS)

New single-beam Arecibo H I observations of 298 late-type galaxies in the Virgo Cluster drawn mostly from the new catalog of Binggeli, Sandage, and Tammann (1985) are presented. Two hundred seventeen of these constitute a magnitude-limited 'complete sample' of such galaxies, types Sdm through Im and BCD. Sixty-one percent of this 'complete sample' was detected, greatly enhancing the store of redshifts and H I masses for such galaxies in the Virgo Cluster. For detected galaxies, heliocentric velocities, 50 percent profile widths, and single-beam fluxes are presented. For those that escaped detection, upper limits are computed to the flux appropriate to the redshift range (-600 to +3000 km/s).

Hoffman, G. Lyle; Glosson, John; Helou, George; Salpeter, E. E.; Sandage, A.

1987-01-01

331

H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area  

SciTech Connect

New single-beam Arecibo H I observations of 298 late-type galaxies in the Virgo Cluster drawn mostly from the new catalog of Binggeli, Sandage, and Tammann (1985) are presented. Two hundred seventeen of these constitute a magnitude-limited complete sample of such galaxies, types Sdm through Im and BCD. Sixty-one percent of this complete sample was detected, greatly enhancing the store of redshifts and H I masses for such galaxies in the Virgo Cluster. For detected galaxies, heliocentric velocities, 50 percent profile widths, and single-beam fluxes are presented. For those that escaped detection, upper limits are computed to the flux appropriate to the redshift range (-600 to +3000 km/s). 27 references.

Hoffman, G.L.; Glosson, J.; Helou, G.; Salpeter, E.E.; Sandage, A.

1987-02-01

332

A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007  

E-print Network

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.

Adrián-Martínez, S; Samarai, I Al; Albert, A; André, M; Anghinolfi, M; Anton, G; Anvar, S; Ardid, M; Jesus, A C Assis; Astraatmadja, T; Aubert, J-J; Baret, B; Basa, S; Bertin, V; Biagi, S; Bigi, A; Bigongiari, C; Bogazzi, C; Bou-Cabo, M; Bouhou, B; Bouwhuis, M C; Brunner, J; Busto, J; Camarena, F; Capone, A; Cârloganu, C; Carr, J; Cecchini, S; Charif, Z; Charvis, Ph; Chiarusi, T; Circella, M; Coniglione, R; Costantini, H; Coyle, P; Curtil, C; Decowski, M P; Dekeyser, I; Deschamps, A; Distefano, C; Donzaud, C; Dornic, D; Dorosti, Q; Drouhin, D; Eberl, T; Emanuele, U; Enzenhöfer, A; Ernenwein, J-P; Escoffier, S; Fermani, P; Ferri, M; Flaminio, V; Folger, F; Fritsch, U; Fuda, J-L; Galatà, S; Gay, P; Giacomelli, G; Giordano, V; Gómez-González, J P; Graf, K; Guillard, G; Halladjian, G; Hallewell, G; van Haren, H; Hartman, J; Heijboer, A J; Hello, Y; Hernández-Rey, J J; Herold, B; Hößl, J; Hsu, C C; de Jong, M; Kadler, M; Kalekin, O; Kappes, A; Katz, U; Kavatsyuk, O; Kooijman, P; Kopper, C; Kouchner, A; Kreykenbohm, I; Kulikovskiy, V; Lahmann, R; Lamare, P; Larosa, G; Lattuada, D; Lefèvre, D; Lim, G; Presti, D Lo; Loehner, H; Loucatos, S; Mangano, S; Marcelin, M; Margiotta, A; Martínez-Mora, J A; Meli, A; Montaruli, T; Morganti, M; Moscoso, L; Motz, H; Neff, M; Nezri, E; Palioselitis, D; P?v?la?, G E; Payet, K; Payre, P; Petrovic, J; Piattelli, P; Picot-Clemente, N; Popa, V; Pradier, T; Presani, E; Racca, C; Reed, C; Richardt, C; Richter, R; Rivière, C; Robert, A; Roensch, K; Rostovtsev, A; Ruiz-Rivas, J; Rujoiu, M; Russo, G V; Salesa, F; Samtleben, D F E; Sapienza, P; Schöck, F; Schuller, J-P; Schüssler, F; Seitz, T; Shanidze, R; Simeone, F; Spies, A; Spurio, M; Steijger, J J M; Stolarczyk, Th; Sánchez-Losa, A; Taiuti, M; Tamburini, C; Toscano, S; Vallage, B; Van Elewyck, V; Vannoni, G; Vecchi, M; Vernin, P; Wagner, S; Wijnker, G; Wilms, J; de Wolf, E; Yepes, H; Zaborov, D; Zornoza, J D; Zúñiga, J; Aasi, J; Abadie, J; Abbott, B P; Abbott, R; Abbott, T D; Abernathy, M; Accadia, T; Acernese, F; Adams, C; Adams, T; Addesso, P; Adhikari, R; Affeldt, C; Agathos, M; Agatsuma, K; Ajith, P; Allen, B; Allocca, A; Ceron, E Amador; Amariutei, D; Anderson, S B; Anderson, W G; Arai, K; Araya, M C; Ast, S; Aston, S M; Astone, P; Atkinson, D; Aufmuth, P; Aulbert, C; Aylott, B E; Babak, S; Baker, P; Ballardin, G; Ballmer, S; Bao, Y; Barayoga, J C B; Barker, D; Barone, F; Barr, B; Barsotti, L; Barsuglia, M; Barton, M A; Bartos, I; Bassiri, R; Bastarrika, M; Basti, A; Batch, J; Bauchrowitz, J; Bauer, Th S; Bebronne, M; Beck, D; Behnke, B; Bejger, M; Beker, M G; Bell, A S; Bell, C; Belopolski, I; Benacquista, M; Berliner, J M; Bertolini, A; Betzwieser, J; Beveridge, N; Beyersdorf, P T; Bhadbade, T; Bilenko, I A; Billingsley, G; Birch, J; Biswas, R; Bitossi, M; Bizouard, M A; Black, E; Blackburn, J K; Blackburn, L; Blair, D; Bland, B; Blom, M; Bock, O; Bodiya, T P; Bogan, C; Bond, C; Bondarescu, R; Bondu, F; Bonelli, L; Bonnand, R; Bork, R; Born, M; Boschi, V; Bose, S; Bosi, L; Braccini, S; Bradaschia, C; Brady, P R; Braginsky, V B; Branchesi, M; Brau, J E; Breyer, J; Briant, T; Bridges, D O; Brillet, A; Brinkmann, M; Brisson, V; Britzger, M; Brooks, A F; Brown, D A; Bulik, T; Bulten, H J; Buonanno, A; Burguet--Castell, J; Buskulic, D; Buy, C; Byer, R L; Cadonati, L; Cagnoli, G; Calloni, E; Camp, J B; Campsie, P; Cannon, K; Canuel, B; Cao, J; Capano, C D; Carbognani, F; Carbone, L; Caride, S; Caudill, S; Cavaglià, M; Cavalier, F; Cavalieri, R; Cella, G; Cepeda, C; Cesarini, E; Chalermsongsak, T; Charlton, P; Chassande-Mottin, E; Chen, W; Chen, X; Chen, Y; Chincarini, A; Chiummo, A; Cho, H S; Chow, J; Christensen, N; Chua, S S Y; Chung, C T Y; Chung, S; Ciani, G; Clara, F; Clark, D E; Clark, J A; Clayton, J H; Cleva, F; Coccia, E; Cohadon, P -F; Colacino, C N; Colla, A; Colombini, M; Conte, A; Conte, R; Cook, D; Corbitt, T R; Cordier, M; Cornish, N; Corsi, A; Costa, C A; Coughlin, M; Coulon, J -P; Couvares, P; Coward, D M; Cowart, M; Coyne, D C; Creighton, J D E; Creighton, T D; Cruise, A M; Cumming, A; Cunningham, L; Cuoco, E; Cutler, R M; Dahl, K; Damjanic, M; Danilishin, S L; D'Antonio, S; Danzmann, K; Dattilo, V; Daudert, B; Daveloza, H; Davier, M; Daw, E J; Day, R; Dayanga, T; De Rosa, R; DeBra, D; Debreczeni, G; Degallaix, J; Del Pozzo, W; Dent, T; Dergachev, V; DeRosa, R; Dhurandhar, S; Di Fiore, L; Di Lieto, A; Di Palma, I; Emilio, M Di Paolo; Di Virgilio, A; Díaz, M; Dietz, A; Donovan, F; Dooley, K L; Doravari, S; Dorsher, S; Drago, M; Drever, R W P; Driggers, J C; Du, Z; Dumas, J -C; Dwyer, S; Eberle, T; Edgar, M; Edwards, M; Effler, A; Ehrens, P; Endr?czi, G; Engel, R; Etzel, T; Evans, K; Evans, M; Evans, T; Factourovich, M; Fafone, V; Fairhurst, S; Farr, B F; Favata, M; Fazi, D; Fehrmann, H; Feldbaum, D; Ferrante, I; Ferrini, F; Fidecaro, F; Finn, L S; Fiori, I; Fisher, R P

2012-01-01

333

A first search for coincident gravitational waves and high energy neutrinos using LIGO, Virgo and ANTARES data from 2007  

SciTech Connect

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.

Adrián-Martínez, S.; Ardid, M.; Bou-Cabo, M. [Institut d'Investigació per a la Gestió Integrada de les Zones Costaneres (IGIC) - Universitat Politècnica de València. C/ Paranimf 1 , 46730 Gandia, Spain. (Spain); Samarai, I. Al; Aubert, J-J.; Bertin, V.; Brunner, J. [CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille (France); Albert, A. [GRPHE - Institut universitaire de technologie de Colmar, 34 rue du Grillenbreit BP 50568 - 68008 Colmar (France); André, M. [Technical University of Catalonia, Laboratory of Applied Bioacoustics, Rambla Exposició, 08800 Vilanova i la Geltrú, Barcelona (Spain); Anghinolfi, M. [INFN - Sezione di Genova, Via Dodecaneso 33, 16146 Genova (Italy); Anton, G. [Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Str. 1, 91058 Erlangen (Germany); Anvar, S. [Direction des Sciences de la Matière - Institut de recherche sur les lois fondamentales de l'Univers - Service d'Electronique des Détecteurs et d'Informatique, CEA Saclay, 91191 Gif-sur-Yvette Cedex (France); Astraatmadja, T.; Bogazzi, C.; Bouwhuis, M.C. [Nikhef, Science Park, Amsterdam (Netherlands); Baret, B.; Bouhou, B. [APC, Université Paris Diderot, CNRS/IN2P3, CEA/IRFU, Observatoire de Paris, Sorbonne Paris Cité, 75205 Paris (France); Basa, S. [LAM - Laboratoire d'Astrophysique de Marseille, Pôle de l'Étoile Site de Château-Gombert, rue Frédéric Joliot-Curie 38, 13388 Marseille Cedex 13 (France); Biagi, S. [INFN - Sezione di Bologna, Viale C. Berti-Pichat 6/2, 40127 Bologna (Italy); Bigongiari, C., E-mail: antares.spokesperson@in2p3.fr, E-mail: lsc-spokesperson@ligo.org, E-mail: virgo-spokesperson@ego-gw.it, E-mail: Irene.DiPalma@aei.mpg.de, E-mail: thierry.pradier@iphc.cnrs.fr [IFIC - Instituto de Física Corpuscular, Edificios Investigación de Paterna, CSIC - Universitat de València, Apdo. de Correos 22085, 46071 Valencia (Spain); and others

2013-06-01

334

All-sky search for gravitational-wave bursts in the first joint LIGO-GEO-Virgo run  

Microsoft Academic Search

We present results from an all-sky search for unmodeled\\u000a\\u0009\\u0009 gravitational-wave bursts in the data collected by the\\u000a\\u0009\\u0009 {LIGO}, GEO 600 and Virgo detectors between November 2006\\u000a\\u0009\\u0009 and October 2007. The search is performed by three\\u000a\\u0009\\u0009 different analysis algorithms over the frequency band\\u000a\\u0009\\u0009 50-6000 Hz. Data are analyzed for times with at least two\\u000a\\u0009\\u0009 of the four {LIGO}-Virgo detectors in coincident

J. Abadie; B. P. Abbott; R. Abbott; T. Accadia; F. Acernese; R. Adhikari; P. Ajith; B. Allen; G. Allen; E. Amador Ceron; R. S. Amin; S. B. Anderson; W. G. Anderson; F. Antonucci; M. A. Arain; M. Araya; K. G. Arun; Y. Aso; S. Aston; P. Astone; P. Aufmuth; C. Aulbert; S. Babak; P. Baker; G. Ballardin; S. Ballmer; D. Barker; F. Barone; B. Barr; P. Barriga; L. Barsotti; M. Barsuglia; M. A. Barton; I. Bartos; R. Bassiri; M. Bastarrika; Th. S. Bauer; B. Behnke; M. G. Beker; A. Belletoile; M. Benacquista; J. Betzwieser; P. T. Beyersdorf; S. Bigotta; I. A. Bilenko; G. Billingsley; S. Birindelli; R. Biswas; M. A. Bizouard; E. Black; J. K. Blackburn; L. Blackburn; D. Blair; B. Bland; M. Blom; C. Boccara; O. Bock; T. P. Bodiya; R. Bondarescu; F. Bondu; L. Bonelli; R. Bonnand; R. Bork; M. Born; S. Bose; L. Bosi; B. Bouhou; S. Braccini; C. Bradaschia; P. R. Brady; V. B. Braginsky; J. E. Brau; J. Breyer; D. O. Bridges; A. Brillet; M. Brinkmann; V. Brisson; M. Britzger; A. F. Brooks; D. A. Brown; R. Budzynski; T. Bulik; A. Bullington; H. J. Bulten; A. Buonanno; O. Burmeister; D. Buskulic; C. Buy; R. L. Byer; L. Cadonati; G. Cagnoli; J. Cannizzo; E. Calloni; J. B. Camp; E. Campagna; K. C. Cannon; B. Canuel; J. Cao; C. D. Capano; F. Carbognani; L. Cardenas; S. Caudill; M. Cavaglià; F. Cavalier; R. Cavalieri; G. Cella; C. Cepeda; E. Cesarini; T. Chalermsongsak; E. Chalkley; P. Charlton; E. Chassande-Mottin; S. Chatterji; S. Chelkowski; Y. Chen; A. Chincarini; N. Christensen; S. S. Y. Chua; C. T. Y. Chung; D. Clark; J. Clark; J. H. Clayton; F. Cleva; E. Coccia; C. N. Colacino; J. Colas; A. Colla; M. Colombini; R. Conte; D. Cook; T. R. C. Corbitt; N. Cornish; A. Corsi; J.-P. Coulon; D. Coward; D. C. Coyne; J. D. E. Creighton; T. D. Creighton; A. M. Cruise; R. M. Culter; A. Cumming; L. Cunningham; E. Cuoco; K. Dahl; S. L. Danilishin; S. D’Antonio; K. Danzmann; V. Dattilo; B. Daudert; M. Davier; G. Davies; E. J. Daw; R. Day; T. Dayanga; R. De Rosa; D. Debra; J. Degallaix; M. del Prete; V. Dergachev; R. Desalvo; S. Dhurandhar; L. Di Fiore; A. Di Lieto; M. Di Paolo Emilio; A. Di Virgilio; M. Díaz; A. Dietz; F. Donovan; K. L. Dooley; E. E. Doomes; M. Drago; R. W. P. Drever; J. Driggers; J. Dueck; I. Duke; J.-C. Dumas; M. Edgar; M. Edwards; A. Effler; P. Ehrens; T. Etzel; M. Evans; T. Evans; V. Fafone; S. Fairhurst; Y. Faltas; Y. Fan; D. Fazi; H. Fehrmann; I. Ferrante; F. Fidecaro; Lee Samuel Finn; I. Fiori; R. Flaminio; K. Flasch; S. Foley; C. Forrest; N. Fotopoulos; J.-D. Fournier; J. Franc; S. Frasca; F. Frasconi; M. Frede; M. Frei; Z. Frei; A. Freise; R. Frey; T. T. Fricke; D. Friedrich; P. Fritschel; V. V. Frolov; P. Fulda; M. Fyffe; M. Galimberti; L. Gammaitoni; J. A. Garofoli; F. Garufi; G. Gemme; E. Genin; A. Gennai; S. Ghosh; J. A. Giaime; S. Giampanis; K. D. Giardina; A. Giazotto; E. Goetz; L. M. Goggin; G. González; S. Goßler; R. Gouaty; M. Granata; A. Grant; S. Gras; C. Gray; R. J. S. Greenhalgh; A. M. Gretarsson; C. Greverie; R. Grosso; H. Grote; S. Grunewald; G. M. Guidi; E. K. Gustafson; R. Gustafson; B. Hage; J. M. Hallam; D. Hammer; G. D. Hammond; C. Hanna; J. Hanson; J. Harms; G. M. Harry; I. W. Harry; E. D. Harstad; K. Haughian; K. Hayama; J.-F. Hayau; T. Hayler; J. Heefner; H. Heitmann; P. Hello; I. S. Heng; A. Heptonstall; M. Hewitson; S. Hild; E. Hirose; D. Hoak; K. A. Hodge; K. Holt; D. J. Hosken; J. Hough; E. Howell; D. Hoyland; D. Huet; B. Hughey; S. Husa; S. H. Huttner; D. R. Ingram; T. Isogai; A. Ivanov; P. Jaranowski; W. W. Johnson; D. I. Jones; G. Jones; R. Jones; L. Ju; P. Kalmus; V. Kalogera; S. Kandhasamy; J. Kanner; E. Katsavounidis; K. Kawabe; S. Kawamura; F. Kawazoe; W. Kells; D. G. Keppel; A. Khalaidovski; F. Y. Khalili; R. Khan; E. Khazanov; H. Kim; P. J. King; J. S. Kissel; S. Klimenko; K. Kokeyama; V. Kondrashov; R. Kopparapu; S. Koranda; I. Kowalska; D. Kozak; V. Kringel; B. Krishnan; A. Królak; G. Kuehn; J. Kullman; R. Kumar; P. Kwee; P. K. Lam; M. Landry; M. Lang; B. Lantz; N. Lastzka; A. Lazzarini; P. Leaci; M. Lei; N. Leindecker; I. Leonor; N. Leroy; N. Letendre; T. G. F. Li; H. Lin; P. E. Lindquist; T. B. Littenberg; N. A. Lockerbie; D. Lodhia; M. Lorenzini; V. Loriette; M. Lormand; G. Losurdo; P. Lu; M. Lubinski; A. Lucianetti; H. Lück; A. Lundgren; B. Machenschalk; M. Macinnis; M. Mageswaran; K. Mailand; E. Majorana; C. Mak; I. Maksimovic; N. Man; I. Mandel; V. Mandic; M. Mantovani; F. Marchesoni; F. Marion; S. Márka; Z. Márka; A. Markosyan; J. Markowitz; E. Maros; J. Marque; F. Martelli; I. W. Martin; R. M. Martin; J. N. Marx; K. Mason; A. Masserot; F. Matichard; L. Matone; R. A. Matzner; N. Mavalvala; R. McCarthy; D. E. McClelland; S. C. McGuire; G. McIntyre; D. J. A. McKechan; M. Mehmet; A. Melatos; A. C. Melissinos; G. Mendell; D. F. Menendez; R. A. Mercer; L. Merill; S. Meshkov; C. Messenger; M. S. Meyer; H. Miao; C. Michel; L. Milano; J. Miller

2010-01-01

335

A First Search for Coincident Gravitational Waves and High Energy Neutrinos Using LIGO, Virgo and ANTARES Data from 2007  

NASA Technical Reports Server (NTRS)

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.

Adrian-Martinez, S.; Samarai, Al; Albert, A.; Andre, M.; Anghinolfi, M.; Anton, G.; Anvar, S.; Ardid, M; Astraatmadja, T.; Aubert, J.-J.; Baret, B.; Basa, S.; Bertin, V.; Biagi, S.; Bigongiari, C.; Bogazzi, C; Bou-Cabo, M.; Bouhou, B.; Bowhuis, M. C.; Bertin, V.; Brunner, J.; Busto, J.; Blackburn, L.; Camp, J. B.; Kanner, J. B.

2013-01-01

336

Atomic diffusion and stellar evolution  

NASA Astrophysics Data System (ADS)

Stellar models including atomic diffusion processes (gravitational settling, radiative accelerations, thermal diffusion, in addition to the purely diffusive term) have now been evolved throughout most of stellar evolution. We review some of the major roles of diffusion processes in stellar evolution. The emphasis is on interior properties. Examples include Populations I and II stars. It is emphasized that competing advective processes such as mass loss or meridional circulation modify internal concentrations differently from turbulent diffusion even when they lead to the same surface abundances. Radiative accelerations play a major role in horizontal branch and sdB stars.

Michaud, G.; Richer, J.

2013-12-01

337

Decoding Debris System Substructures: Imprints of Planets/Planetesimals and Signatures of Extrinsic Influences on Material in Ring-Like Disks  

NASA Astrophysics Data System (ADS)

How do circumstellar (CS) disks evolve and form planetary systems? Is our solar system's two-component debris disk (DD) typical? Are planets implicated by evidence of dynamical stirring in disks? Are DD architectures correlated with stellar mass? To address these highly-compelling questions of fundamental astrophysical import, we propose follow-up STIS coronagraphy of five intermediate-inclination ring-like DDs. These images will provide unprecedented clarity, sensitivity, and photometric efficacy to: 1) Study the spatial distribution of dust as close as 0.2" from the host stars enabling us to infer the existence and properties of unseen co-orbiting planets, and to probe disk-planet interactions across stellar ages and spectral types; 2) Provide spatially resolved imaging within DD regions previously unsampled to significantly improve constraints on disk grain properties and radial segregation of grain populations as a function of stellocentric distance (and thus temperature); 3) Produce high-fidelity images of DD substructures for dynamical interpretation, constraining the possibilities for planetary system architectures; 4) Obtain deep images of regions beyond the primary, bright debris features to study small-grain populations that might be unbound from the system and affected by both extrinsic and intrinsic forces and may inform about the level of dynamical activity in the planetesimal belt; 5) Provide, through the HLA, the highest quality and most complete, value-added data products for a seminal legacy data set of spatially resolvable light-scattering DDs, thus enabling multi-wavelength investigations with new and future ground- and space-based facilities.

Schneider, Glenn

2014-10-01

338

Stellar mergers are common  

NASA Astrophysics Data System (ADS)

The observed Galactic rate of stellar mergers or the initiation of common envelope phases brighter than MV = -3 (MI = -4) is of the order of ˜0.5 (0.3) yr-1 with 90 per cent confidence statistical uncertainties of 0.24-1.1 (0.14-0.65) and factor of ˜2 systematic uncertainties. The (peak) luminosity function is roughly {d}N/{d} L ? L^{-1.4± 0.3}, so the rates for events more luminous than V1309 Sco (MV ? -7 mag) or V838 Mon (MV ? -10 mag) are lower at r ˜ 0.1 and ˜0.03/year, respectively. The peak luminosity is a steep function of progenitor mass, L ? M2 - 3. This very roughly parallels the scaling of luminosity with mass on the main sequence, but the transients are ˜2000-4000 times more luminous at peak. Combining these, the mass function of the progenitors, dN/dM ? M-2.0 ± 0.8, is consistent with the initial mass function, albeit with broad uncertainties. These observational results are also broadly consistent with the estimates of binary population synthesis models. While extragalactic variability surveys can better define the rates and properties of the high-luminosity events, systematic, moderate depth (I ? 16 mag) surveys of the Galactic plane are needed to characterize the low-luminosity events. The existing Galactic samples are only ˜20 per cent complete, and Galactic surveys are (at best!) reaching a typical magnitude limit of ? 13 mag.

Kochanek, C. S.; Adams, Scott M.; Belczynski, Krzysztof

2014-09-01

339

Ultraviolet stellar astronomy  

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. During all three Skylab missions, prism-on observations were obtained in 188 starfields and prism-off observations in 31 starfields. In general, the fields are concentrated in the Milky Way where the frequency of hot stars is highest. These fields cover an area approximately 3660 degrees and include roughly 24 percent of a band 30 deg wide centered on the plane of the Milky Way. A census of stars in the prism-on fields shows that nearly 6,000 stars have measurable flux data at a wavelength of 2600A, that 1,600 have measurable data at 2000A, and that 400 show useful data at 1500A. Obvious absorption or emission features shortward of 2000A are visible in approximately 120 stars. This represents a bonanza of data useful for statistical studies of stellar classification and of interstellar reddening as well as for studies of various types of peculiar stars.

Henize, K. G.; Wray, J. D.; Kondo, Y.; Ocallaghan, F. (principal investigators)

1975-01-01

340

SI: The Stellar Imager  

NASA Technical Reports Server (NTRS)

The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI 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 by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe.

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2006-01-01

341

Stellar Abundance Observations  

E-print Network

Ground- and space-based observations of stellar heavy element abundances are providing a clearer picture of the chemical evolution of the Galaxy. A large number of (r)apid and (s)low neutron capture process elements, including the first Hubble Space Telescope observations of Pt, Os, Pb and Ge, have been identified in metal-poor, galactic halo stars. In the very low metallicity (i.e. [Fe/H] $<$ --2.0) stars, the abundance pattern of the elements from Ba through the third neutron-capture peak (Os-Pt) is consistent with a scaled solar {\\it r}-process distribution. These results support previous observations that demonstrate the operation of the {\\it r}-process, including the synthesis of the heaviest such elements, early in the history of the Galaxy. New ground-based observations further confirm that the {\\it s}-process element Ba and the {\\it r}-process element Eu were both synthesized solely by the r-process at low metallicities, and indicate the onset of the {\\it s}-process occurred near [Fe/H] = --2. Over a range of metallicity (--2.90 $<$ [Fe/H] $<$ --0.86) the data indicate that there exist real star-to-star differences in the ratios of the [n-capture/Fe] abundances as well as in the actual spectra of the stars.

John J Cowan; Christopher Sneden; James W Truran; Debra L Burris

1998-03-16

342

All-Sky Search for Gravitational-Wave Bursts in the First Joint LIGO-GEO-Virgo Run  

NASA Technical Reports Server (NTRS)

We present results from an aU-sky search for unmodeled gravitational-wave bursts in the data collected by the LIGO, GEO 600 and Virgo detectors between November 2006 and October 2007. The search is performed. by three different analysis algorithms over the frequency band 50 - 6000 Hz. Data are analyzed for times with at least two of the four LIGO-Virgo detectors in coincident operation, with a total live time of 266 days, No events produced by the search algorithms survive the selection cuts. We set a frequentist upper limit on the rate of gravitational-wave bursts impinging on our network of detectors. When combined with the previous LIGO search of the data collected between November 2005 and November 2006, the upper limit on the rate of detectable gra.vitational. wave bursts in the 64-2048 Hz band is 2,0 events per year at 90% confidence. We also present event rate versus strength exclusion plots for several types of plausible burst waveforms. The sensitivity of the combined search is expressed in terms of the root-sum-squared strain amplitude for a variety of simulated waveforms and lies in the range 6 X 10(exp -22) Hz(exp - 1/2) to 2 X 10(exp -20) Hz(exp -l/2). This is the first untriggered burst search to use data from the LIGO and Virgo detectors together, and the most sensitive untriggered burst search performed so far.

Camp, J. B.; Camizzo, J.

2012-01-01

343

ABOUT THE LINEARITY OF THE COLOR-MAGNITUDE RELATION OF EARLY-TYPE GALAXIES IN THE VIRGO CLUSTER  

SciTech Connect

We revisit the color-magnitude relation of Virgo Cluster early-type galaxies in order to explore its alleged nonlinearity. To this aim, we reanalyze the relation already published from data obtained within the ACS Virgo Cluster Survey of the Hubble Space Telescope and perform our own photometry and analysis of the images of 100 early-type galaxies observed as part of this survey. In addition, we compare our results with those reported in the literature from data of the Sloan Digital Sky Survey. We have found that when the brightest galaxies and untypical systems are excluded from the sample, a linear relation arises in agreement with what is observed in other groups and clusters. The central regions of the brightest galaxies also follow this relation. In addition, we notice that Virgo contains at least four compact elliptical galaxies besides the well-known object VCC 1297 (NGC 4486B). Their locations in the ({mu}{sub eff})-luminosity diagram define a trend different from that followed by normal early-type dwarf galaxies, setting an upper limit in effective surface brightness and a lower limit in the effective radius for their luminosities. Based on the distribution of different galaxy sub-samples in the color-magnitude and ({mu}{sub eff})-luminosity diagrams, we draw some conclusions on their formation and the history of their evolution.

Smith Castelli, Analia V.; Faifer, Favio R. [Instituto de Astrofisica de La Plata (CCT-La Plata, CONICET-UNLP), Paseo del Bosque s/n, B1900FWA, La Plata (Argentina); Gonzalez, Nelida M. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, B1900FWA (Argentina); Forte, Juan Carlos, E-mail: asmith@fcaglp.unlp.edu.ar, E-mail: ngonzalez@fcaglp.unlp.edu.ar, E-mail: favio@fcaglp.unlp.edu.ar, E-mail: forte@fcaglp.unlp.edu.ar [CONICET-Planetario de la Ciudad de Buenos Aires ''Galileo Galilei'', Av. Sarmiento y B. Roldan, Ciudad Autonoma de Buenos Aires (Argentina)

2013-07-20

344

The radial velocity profile of the filament galaxies in the vicinity of the Virgo cluster as a test of gravity  

E-print Network

The radial velocities of the galaxies in the vicinity of a massive cluster shows deviation from the pure Hubble flow due to their gravitational interaction with the cluster. According to a recent study of Falco et al. with a high-resolution N-body simulation based on General Relativity (GR), the radial velocity profile of the galaxies located at distances larger than three times the virial radius of a neighbour cluster has a universal shape and could be reconstructed from direct observables provided that the galaxies are distributed along one dimensional filament. Analyzing the narrow filamentary structure identified by Kim et al. in the vicinity of the Virgo cluster from the NASA-Sloan-Atlas catalog, we reconstruct the radial velocity profile of the Virgo filament galaxies and compare it with the universal formula derived by Falco et al. It is found that unless the virial mass of the Virgo cluster exceeds $10^{15}\\,h^{-1}M_{\\odot}$ the universal formula fails to describe the reconstructed radial velocity pro...

Lee, Jounghun; Rey, Soo-Chang

2015-01-01

345

15 Stellar Winds Stan Owocki  

E-print Network

15 Stellar Winds Stan Owocki Bartol Research Institute, Department of Physics and Astronomy . . . . . . . . . . . . . . . . . . . . . . . 740 2.1 Solar Corona and Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740 2.2 Spectral Signatures of Dense Winds from Hot and Cool Stars

Owocki, Stanley P.

346

The Milky Way's Stellar Disk  

E-print Network

A suite of vast stellar surveys mapping the Milky Way, culminating in the Gaia mission, is revolutionizing the empirical information about the distribution and properties of stars in the Galactic stellar disk. We review and lay out what analysis and modeling machinery needs to be in place to test mechanisms of disk galaxy evolution and to stringently constrain the Galactic gravitational potential, using such Galactic star-by-star measurements. We stress the crucial role of stellar survey selection functions in any such modeling; and we advocate the utility of viewing the Galactic stellar disk as made up from `mono-abundance populations' (MAPs), both for dynamical modeling and for constraining the Milky Way's evolutionary processes. We review recent work on the spatial and kinematical distribution of MAPs, and lay out how further study of MAPs in the Gaia era should lead to a decisively clearer picture of the Milky Way's dark matter distribution and formation history.

Rix, Hans-Walter

2013-01-01

347

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

348

Stellar Cycles Post Assessment Activity  

NSDL National Science Digital Library

This activity from the Chandra X-Ray Observatory tests knowledge of stellar evolution through a task to correctly order an image set of stars in all stages of evolution. The image set includes optical, x-ray, and radio pictures, as well as light curves, H-R diagrams, and artist representations. More stellar evolution information is available on the activity page. An answer key with explanations and possible correct answers is provided.

2009-06-08

349

Solar and stellar coronal plasmas  

NASA Technical Reports Server (NTRS)

Progress made in describing and interpreting coronal plasma processes and the relationship between the solar corona and its stellar counterparts is reported. Topics covered include: stellar X-ray emission, HEAO 2 X-ray survey of the Pleiades, closed coronal structures, X-ray survey of main-sequence stars with shallow convection zones, implications of the 1400 MHz flare emission, and magnetic field stochasticity.

Golub, L.

1985-01-01

350

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

351

Stellar masers, circumstellar envelopes, and supernova remnants  

E-print Network

This paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.

Athol J. Kemball

2007-05-15

352

Apex determination and detection of stellar clumps in the open cluster M 67  

NASA Astrophysics Data System (ADS)

We determined the cluster’s apex coordinates, studied the substructures and performed membership analysis in the central part (34?×33?) of the open cluster M 67. We used the individual stellar apexes method developed earlier and classical technique of proper motion diagrams in coordinate system connected with apex. The neighbour-to-neighbour distance technique was applied to detect space details. The membership list was corrected and some stars were excluded from the most probable members list. The apex coordinates have been determined as: A0=132.97° ± 0.81° and D0=11.85° ± 0.90°. The 2D-space star density field was analysed and high degree of inhomogeneity was found.

Vereshchagin, S. V.; Chupina, N. V.; Sariya, Devesh P.; Yadav, R. K. S.; Kumar, Brijesh

2014-08-01

353

Kinematics and Stellar Populations of Low-Luminosity Early-Type Galaxies in the Abell 496 Cluster  

E-print Network

The morphology and stellar populations of low-luminosity early-type galaxies in clusters have until now been limited to a few relatively nearby clusters such as Virgo or Fornax. Scenarii for the formation and evolution of dwarf galaxies in clusters are therefore not well constrained. We investigate here the morphology and stellar populations of low-luminosity galaxies in the relaxed cluster Abell 496 (z=0.0330). Deep multiband imaging obtained with the CFHT Megacam allowed us to select a sample of faint galaxies (-18.8stellar population properties have been obtained for a large sample of faint galaxies in a cluster, allowing for the extension of relations between stellar populations and internal kinematics to the low-velocity dispersion regime. We have revealed a peculiar population of elliptical galaxies in the core of the cluster, resembling massive early-type galaxies by their stellar population properties and velocity dispersions, but having luminosities of about 2 mag fainter. External mechanisms of gas removal (ram pressure stripping and gravitational harassment) are more likely to have occurred than internal mechanisms such as supernova-driven winds. The violent tidal stripping of intermediate-luminosity, early-type galaxies in the cluster core can explain the properties of the peculiar elliptical galaxies surrounding the cD galaxy.

Igor Chilingarian; Veronique Cayatte; Florence Durret; Christophe Adami; Chantal Balkowski; Laurent Chemin; Tatiana Lagana; Philippe Prugniel

2008-05-02

354

The Importance of Spin for Observing Gravitational Waves from Coalescing Compact Binaries with LIGO and Virgo  

NASA Astrophysics Data System (ADS)

General Relativity predicts the existence of gravitational waves, which carry information about the physical and dynamical properties of their source. One of the many promising sources of gravitational waves observable by ground-based instruments, such as in LIGO and Virgo, is the coalescence of two compact objects (neutron star or black hole). Black holes and neutron stars sometimes form binaries with short orbital periods, radiating so strongly in gravitational waves that they coalesce on astrophysically short timescales. General Relativity gives precise predictions for the form of the signal emitted by these systems. The most recent searches for theses events used waveform models that neglected the effects of black hole and neutron star spin. However, real astrophysical compact objects, especially black holes, are expected to have large spins. We demonstrate here a data analysis infrastructure which achieves an improved sensitivity to spinning compact binaries by the inclusion of spin effects in the template waveforms. This infrastructure is designed for scalable, low-latency data analysis, ideal for rapid electromagnetic followup of gravitational wave events.

Privitera, Stephen

355

The Search for Shock-excited H2 in Virgo Spirals Experiencing Ram Pressure Stripping  

NASA Astrophysics Data System (ADS)

We investigate the presence of shock-excited H2 in four Virgo cluster galaxies that show clear evidence of ongoing ram pressure stripping. Mid-infrared spectral mapping of the rotational H2 emission lines were performed using the Infrared Spectrograph on board the Spitzer Space Telescope. We target four regions along the leading side of galaxies where the intracluster medium appears to be pushing back the individual galaxy's interstellar medium. For comparison purposes, we also study two regions on the trailing side of these galaxies: a region within an edge-on disk and an extraplanar star-forming region. We find a factor of 2.6 excess of warm H2/PAH in our sample relative to the observed fractions in other nearby galaxies. We attribute the H2/PAH excess to contributions of shock-excited H2 which is likely to have been triggered by ongoing ram pressure interaction in our sample galaxies. Ram pressure driven shocks may also be responsible for the elevated ratios of [Fe II]/[Ne II] found in our sample.

Wong, O. Ivy; Kenney, Jeffrey D. P.; Murphy, Eric J.; Helou, George

2014-03-01

356

A WIYN Study of the Globular Cluster Population of the Virgo Elliptical Galaxy NGC 4473  

NASA Astrophysics Data System (ADS)

We present results from an analysis of the globular cluster system of NGC 4473, a moderate-luminosity elliptical galaxy in the Virgo Cluster. The properties of globular clusters - in particular, their ages, luminosities, and spatial distributions - make them especially useful probes of the star formation and assembly histories of their host galaxies. We used the 10' x 10' Minimosaic camera on the WIYN 3.5-meter telescope to image the globular cluster system of NGC 4473 over its full radial extent. Globular cluster candidates were identified as point sources and selected by their magnitudes and colors in three filters (B, V, R) in order to minimize contamination from foreground and background sources. Our deep images, which have 0.5' - 0.7' seeing and 50% completeness levels for point-source detection at B = 25.7, V = 25.5, and R = 25.2, allow us to cover 75 percent of the intrinsic globular cluster luminosity function (GCLF) for NGC 4473. The surface density of globular clusters in our final corrected radial profile drops to zero within the errors at ~7', or ~33 kpc from the galaxy center. These results will be presented along with our findings regarding the total number (NGC = 480 ± 50), specific frequency (SN = 2.2 ± 0.4), and color (metallicity) distribution of the globular clusters in this galaxy.

Panetta, Margaret; Rhode, Katherine L.; West, Michael, , Dr.

2015-01-01

357

Hubble Space Telescope photometry of the central regions of Virgo cluster elliptical galaxies. 3: Brightness profiles  

NASA Technical Reports Server (NTRS)

We have used the Planetary Camera on the Hubble Space Telescope (HST) to study the morphology and surface brightness parameters of a luminosity-limited sample of fourteen elliptical galaxies in the Virgo cluster. The total apparent blue magnitudes of the galaxies range between 9.4 and 13.4. In this paper, the core brightness profiles are presented, while the overall morphology and the isophotal shapes are discussed in two companion papers (Jaffe et al. (1994); van den Bosch et al. (1994)). We show that, in spite of the spherical aberration affecting the HST primary mirror, deconvolution techniques allow recovery of the brightness profile up to 0.2 arcsec from the center of the galaxies. We find that none of the galaxies has an isothermal core. On the basis of their morphological and photometrical properties, the galaxies can be divided in two physically distinct groups, referred to as Type I and Type II. All of the Type I galaxies are classified as E1 to E3 in the Revised Shapley Ames Catalog (Sandage & Tammann 1981), while Type II galaxies are classified as E5 to E7. The characteristics of Type II galaxies are explained by the presence of disks component on both the 1 arcsec and the 10 arcsec scales, while Type I galaxies correspond to the classical disk-free ellipticals.

Ferrarese, Laura; Bosch, Frank C. Van Den; Ford, Holland C.; Jaffe, Walter; O'Connell, Robert W.

1994-01-01

358

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. PMID:23425154

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

2012-01-01

359

Chandra Observations of Nuclear Outflows in the Elliptical Galaxy NGC 4552 in the Virgo Cluster  

NASA Astrophysics Data System (ADS)

We use a 54.4 ks Chandra observation to study nuclear outflow activity in NGC 4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandra images in the 0.5-2 keV band show two ringlike features ~1.7 kpc in diameter in the core of NGC 4552, as reported previously by Filho et al. We use spherically symmetric point explosion shock models to argue that the shape of the surface brightness profile across the rims of the rings and the temperature of hot gas in the rings are consistent with a Mach 1.7 shock carrying mean mechanical power Lshock~3×1041 ergs s-1 produced by a ~1.4×1055 ergs nuclear outburst ~1-2 Myr ago. We find the gas temperature in the central ~100 pc of the galaxy to be 1.0+/-0.2 keV, hotter than elsewhere in the galaxy, suggesting that we may be directly observing the reheating of the galaxy ISM by the outburst.

Machacek, M.; Nulsen, P. E. J.; Jones, C.; Forman, W. R.

2006-09-01

360

Prediction of the Virgo axis anisotropy: CMB radiation illuminates the nature of things  

E-print Network

Recent findings of the anisotropy in the Cosmic Microwave Background (CMB) radiation are confusing for standard cosmology. Remarkably, this fact has been predicted several years ago in the framework of our model of the physical world. Moreover, in exact agreement with our prediction the CMB has a preferred direction towards the Virgo Cluster. The transpired structure of the CMB shows workings of the suggested model of the physical world. Comprising the information processes of Nature, this model presents a high-tech version of the previous low-tech developments for mechanical ether and quantum vacuum. In the current model, the phenomenon of Life turns up as a collective effect on the "Internet of the Physical Universe" using DNA structures for access codes. Most convincingly, this construction points to a harmful analogy with so-called "identity theft" - improper manipulations with DNA of individual organisms can destroy these organisms from a remote location without any physical contact. Appearing incredible, such a possibility creates a superlative Experimentum Crucis. In a broad sense, this surmised biological effect is intimately related to the cosmological prediction of the structurization of the CMB, but it is more compelling.

Simon Berkovich

2005-09-25

361

Stellar Diameters and Temperatures IV. Predicting Stellar Angular Diameters  

E-print Network

The number of stellar angular diameter measurements has greatly increased over the past few years due to innovations and developments in the field of long baseline optical interferometry (LBOI). We use a collection of high-precision angular diameter measurements for nearby, main-sequence stars to develop empirical relations that allow the prediction of stellar angular sizes as a function of observed photometric color. These relations are presented for a combination of 48 broad-band color indices. We empirically show for the first time a dependence on metallicity to these relations using Johnson $(B-V)$ and Sloan $(g-r)$ colors. Our relations are capable of predicting diameters with a random error of less than 5% and represent the most robust and empirical determinations to stellar angular sizes to date.

Boyajian, Tabetha; von Braun, Kaspar

2013-01-01

362

Stellar features in integrated starburst spectra as stellar population diagnostics  

E-print Network

We review the main stellar features observed in starburst spectra from the UV to the near-IR and their use as fundamental tools to determine the properties of stellar populations from integrated spectra. The origin and dependence of the features on stellar properties are discussed, and we summarise existing modeling techniques used for quantitative analysis. Recent results from studies based on UV, optical and near-IR observations of starbursts and active galaxies are summarised. Finally, we briefly discuss combined starburst + photoionisation models including also observations from nebular emission lines. The present review is complementary to the recent summary by Schaerer (2000) (http://xxx.lpthe.jussieu.fr/abs/astro-ph/0007307) discussing more extensively nebular analysis of starbursts and related objects.

Daniel Schaerer

2000-12-19

363

On substructuring algorithms and solution techniques for the numerical approximation of partial differential equations  

NASA Technical Reports Server (NTRS)

Substructuring methods are in common use in mechanics problems where typically the associated linear systems of algebraic equations are positive definite. Here these methods are extended to problems which lead to nonpositive definite, nonsymmetric matrices. The extension is based on an algorithm which carries out the block Gauss elimination procedure without the need for interchanges even when a pivot matrix is singular. Examples are provided wherein the method is used in connection with finite element solutions of the stationary Stokes equations and the Helmholtz equation, and dual methods for second-order elliptic equations.

Gunzburger, M. D.; Nicolaides, R. A.

1986-01-01

364

Dark Matter Substructure and Gamma-Ray Annihilation in the Milky Way Halo  

Microsoft Academic Search

We present initial results from ``Via Lactea,'' the highest resolution simulation to date of Galactic CDM substructure. It follows the formation of a Milky Way-sized halo with Mhalo=1.8×1012 Msolar in a WMAP three-year cosmology, using 234 million particles. Over 10,000 subhalos can be identified at z=0: their cumulative mass function is well-fit by N(>Msub)=0.0064(Msub\\/Mhalo)-1 down to Msub=4×106 Msolar. The total

Jürg Diemand; Michael Kuhlen; Piero Madau

2007-01-01

365

Small-angle neutron scattering investigation of the substructure of nickel irradiated with fast neutrons  

NASA Astrophysics Data System (ADS)

The method of small-angle neutron scattering has been used to investigate the samples of pure nickel before and after irradiation with fast neutron fluences of ? = 1018, 1019, and 1020 cm-2 ( E n ? 0.1 MeV). It has been found that the substructure of the samples consists of vacancy clusters with two characteristic sizes of 2.5-4 and ˜7 nm. The sizes of precipitates weakly depend on fast neutron fluence. The magnitude of their density is on the order of 1022 and 1019 m-3, respectively, and increases by three to ten times as the fluence grows.

Bogdanov, S. G.; Goshchitskii, B. N.; Parkhomenko, V. D.

2014-06-01

366

Coupling Semi-Analytic Models and N-Body Simulations: A New Way of Making Galaxies and Stellar Halos  

NASA Astrophysics Data System (ADS)

Stellar halos give insight to the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites by looking at the different stellar populations. An algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. Currently being developed is CoSANG (Coupled Semi-Analytic/N-body Galaxies), a new computational method that will couple pure dark matter N-body simulations with a semi-analytic model. At each timestep, results from the N-body simulation will feed into the semi-analytic code, whose results will feed back into the N-body code making the evolution of the dark matter and baryonic matter dependent on one another. CoSANG will require much less computing power than hydrodynamical simulations, and will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection.

McCord, Krista M.; Bailin, Jeremy; Croton, Darren; Valluri, Monica

2015-01-01

367

Stellar Parallax and Aberration Package  

NSDL National Science Digital Library

The Stellar Parallax and Aberration Launcher package is a self-contained file for teaching the concepts of parallax and aberration of light as they apply to astronomy. The file contains ready-to-run Easy Java Simulations (EJS) programs and curricular materials. The curricular materials consist of two activities for students. The first activity guides the student through an investigation of two forms of astronomical parallax (diurnal and annual) and Robert Hooke's early attempt to measure the annual parallax of stars. The second activity allows the student to examine James Bradley's failure to replicate Hooke's measurement, and how this failure led Bradley to the idea of the aberration of light. The activity helps students understand the effects of stellar aberration and how it masked stellar parallax.

Timberlake, Todd

2012-06-02

368

Stellar Alignments - Identification and Analysis  

NASA Astrophysics Data System (ADS)

Fortuitous stellar alignments can be fitted to structural orientations with relative ease by the unwary. Nonetheless, cautious approaches taking into account a broader range of cultural evidence, as well as paying due attention to potential methodological pitfalls, have been successful in identifying credible stellar alignments—and constructing plausible assessments of their cultural significance—in a variety of circumstances. These range from single instances of alignments upon particular asterisms where the corroborating historical or ethnographic evidence is strong to repeated instances of oriented structures with only limited independent cultural information but where systematic, data-driven approaches can be productive. In the majority of cases, the identification and interpretation of putative stellar alignments relates to groups of similar monuments or complex single sites and involves a balance between systematic studies of the alignments themselves, backed up by statistical analysis where appropriate, and the consideration of a range of contextual evidence, either derived from the archaeological record alone or from other relevant sources.

Ruggles, Clive L. N.

369

Stellar Populations in the SMC  

NASA Astrophysics Data System (ADS)

The Magellanic Clouds {MC} are the nearest major galaxies and therefore afford unique opportunities for studies of stellar populations and star formation histories through observations of color-magnitude diagrams {CMDs; e.g. Bertelli et al. 1992, ApJ, 388, 400}. In this program we extend HST WFPC2 studies of low mass stars in the LMC through observations of a field in the SMC which is near the bar. The resulting CMDs will be modelled using isochrones such as those by Bergbusch & Vandenberg {1992, ApJS, 81, 163} to recover the lower stellar IMF and to search for the signatures of episodic star formation in these galaxies.

Trauger, John

1996-07-01

370

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

371

Stellar Imager (SI) Space Mission: Stellar Magnetic Activity  

NASA Technical Reports Server (NTRS)

The Stellar Imager (SI) is a UV-Optical, Space-Based interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and stellar interiors (via asteroseismology) and of the Universe in general. SI is identified 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). The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes: The 0.1 mas resolution of this deep-space telescope will transform point sources into extended sources, and snapshots into evolving views. SI'S science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI'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. In this paper we will discuss the science goals of the SI Mission and a mission architecture that could meet those goals.

Carpenter, K. G.

2006-01-01

372

Deriving stellar inclination of slow rotators using stellar activity  

E-print Network

Stellar inclination is an important parameter for many astrophysical studies. Although different techniques allow us to estimate stellar inclinationt for fast rotators, it becomes much more difficult when stars are rotating slower than $\\sim2$-2.5 \\kms. By using the new activity simulation SOAP 2.0 that can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit observations of solar-type stars and derive their inclination. For HD189733, we estimate the stellar inclination to be $i=84^{+6}_{-20}$ degrees, which implies a star-planet obliquity of $\\psi=4^{+18}_{-4}$ considering previous measurements of the spin-orbit angle. For $\\alpha$ Cen B, we derive an inclination of $i=45^{+9}_{-19}$, which implies that the rotational spin of the star is not aligned with the orbital spin of the $\\alpha$ Cen binary system. In addition, assuming that $\\alpha$ Cen Bb is aligned with its host star, no transit would occur. The inclination of $\\alpha$ Cen B can be measured using 40...

Dumusque, X

2014-01-01

373

Deriving Stellar Inclination of Slow Rotators Using Stellar Activity  

NASA Astrophysics Data System (ADS)

Stellar inclination is an important parameter for many astrophysical studies. Although different techniques allow us to estimate stellar inclination for fast rotators, it becomes much more difficult when stars are rotating slower than ~2-2.5 km s–1. By using the new activity simulation SOAP 2.0 which can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit observations of solar-type stars and derive their inclination. For HD 189733, we estimate the stellar inclination to be i=84+6-20 deg, which implies a star-planet obliquity of \\psi =4+18-4 considering previous measurements of the spin-orbit angle. For ? Cen B, we derive an inclination of i=45+9-19, which implies that the rotational spin of the star is not aligned with the orbital spin of the ? Cen binary system. In addition, assuming that ? Cen Bb is aligned with its host star, no transit would occur. The inclination of ? Cen B can be measured using 40 radial-velocity measurements, which is remarkable given that the projected rotational velocity of the star is smaller than 1.15 km s–1. Based on observations made with the MOST satellite, the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory (Chile), and the SOPHIE instrument at the Observatoire de Haute Provence (France).

Dumusque, X.

2014-12-01

374

Formation and evolution of galaxy dark matter halos and their substructure  

E-print Network

We use the ``Via Lactea'' simulation to study the co-evolution of a Milky Way-size LambdaCDM halo and its subhalo population. While most of the host halo mass is accreted over the first 6 Gyr in a series of major mergers, the physical mass distribution [not M_vir(z)] remains practically constant since z=1. The same is true in a large sample of LambdaCDM galaxy halos. Subhalo mass loss peaks between the turnaround and virialization epochs of a given mass shell, and the abundance of substructure within the shell freezes afterwards. 97% of the z=1 subhalos have a surviving bound remnant at the present epoch. The retained mass fraction is larger for initially lighter subhalos: satellites with maximum circular velocities Vmax=10 km/s at z=1 have today about 40% of their mass back then. At the first pericenter passage a larger average mass fraction is lost than during each following orbit. Tides remove mass in substructure from the outside in, leading to higher concentrations compared to field halos of the same mas...

Diemand, J; Madau, P; Diemand, Juerg; Kuhlen, Michael; Madau, Piero

2007-01-01

375

Reheating effects in the matter power spectrum and implications for substructure  

NASA Astrophysics Data System (ADS)

The thermal and expansion history of the Universe before big bang nucleosynthesis is unknown. We investigate the evolution of cosmological perturbations through the transition from an early matter era to radiation domination. We treat reheating as the perturbative decay of an oscillating scalar field into relativistic plasma and cold dark matter. After reheating, we find that subhorizon perturbations in the decay-produced dark matter density are significantly enhanced, while subhorizon radiation perturbations are instead suppressed. If dark matter originates in the radiation bath after reheating, this suppression may be the primary cutoff in the matter power spectrum. Conversely, for dark matter produced nonthermally from scalar decay, enhanced perturbations can drive structure formation during the cosmic dark ages and dramatically increase the abundance of compact substructures. For low reheat temperatures, we find that as much as 50% of all dark matter is in microhalos with M?0.1M? at z?100, compared to a fraction of ˜10-10 in the standard case. In this scenario, ultradense substructures may constitute a large fraction of dark matter in galaxies today.

Erickcek, Adrienne L.; Sigurdson, Kris

2011-10-01

376

Application of finite element substructuring to composite micromechanics. M.S. Thesis - Akron Univ., May 1984  

NASA Technical Reports Server (NTRS)

Finite element substructuring is used to predict unidirectional fiber composite hygral (moisture), thermal, and mechanical properties. COSMIC NASTRAN and MSC/NASTRAN are used to perform the finite element analysis. The results obtained from the finite element model are compared with those obtained from the simplified composite micromechanics equations. A unidirectional composite structure made of boron/HM-epoxy, S-glass/IMHS-epoxy and AS/IMHS-epoxy are studied. The finite element analysis is performed using three dimensional isoparametric brick elements and two distinct models. The first model consists of a single cell (one fiber surrounded by matrix) to form a square. The second model uses the single cell and substructuring to form a nine cell square array. To compare computer time and results with the nine cell superelement model, another nine cell model is constructed using conventional mesh generation techniques. An independent computer program consisting of the simplified micromechanics equation is developed to predict the hygral, thermal, and mechanical properties for this comparison. The results indicate that advanced techniques can be used advantageously for fiber composite micromechanics.

Caruso, J. J.

1984-01-01

377

Reheating effects in the matter power spectrum and implications for substructure  

SciTech Connect

The thermal and expansion history of the Universe before big bang nucleosynthesis is unknown. We investigate the evolution of cosmological perturbations through the transition from an early matter era to radiation domination. We treat reheating as the perturbative decay of an oscillating scalar field into relativistic plasma and cold dark matter. After reheating, we find that subhorizon perturbations in the decay-produced dark matter density are significantly enhanced, while subhorizon radiation perturbations are instead suppressed. If dark matter originates in the radiation bath after reheating, this suppression may be the primary cutoff in the matter power spectrum. Conversely, for dark matter produced nonthermally from scalar decay, enhanced perturbations can drive structure formation during the cosmic dark ages and dramatically increase the abundance of compact substructures. For low reheat temperatures, we find that as much as 50% of all dark matter is in microhalos with M > or approx. 0.1M{sub +} at z{approx_equal}100, compared to a fraction of {approx}10{sup -10} in the standard case. In this scenario, ultradense substructures may constitute a large fraction of dark matter in galaxies today.

Erickcek, Adrienne L. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada); Perimeter Institute for Theoretical Physics, 31 Caroline St. N, Waterloo, Ontario N2L 2Y5 (Canada); Sigurdson, Kris [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada)

2011-10-15

378

On the density profile of dark matter substructure in gravitational lens galaxies  

NASA Astrophysics Data System (ADS)

We consider three extensions of the Navarro, Frenk and White (NFW) profile and investigate the intrinsic degeneracies among the density profile parameters on the gravitational lensing effect of satellite galaxies on highly magnified Einstein rings. In particular, we find that the gravitational imaging technique can be used to exclude specific regions of the considered parameter space, and therefore, models that predict a large number of satellites in those regions. By comparing the lensing degeneracy with the intrinsic density profile degeneracies, we show that theoretical predictions based on fits that are dominated by the density profile at larger radii may significantly over- or under-estimate the number of satellites that are detectable with gravitational lensing. Finally, using the previously reported detection of a satellite in the gravitational lens system JVAS B1938+666 as an example, we derive for this detected satellite values of rmax and vmax that are, for each considered profile, consistent within 1? with the parameters found for the luminous dwarf satellites of the Milky Way and with a mass density slope ? < 1.6. We also find that the mass of the satellite within the Einstein radius as measured using gravitational lensing is stable against assumptions on the substructure profile. In the future thanks to the increased angular resolution of very long baseline interferometry at radio wavelengths and of the E-ELT in the optical we will be able to set tighter constraints on the number of allowed substructure profiles.

Vegetti, Simona; Vogelsberger, Mark

2014-08-01

379

CLCA: Maximum Common Molecular Substructure Queries within the MetRxn Database.  

PubMed

The challenge of automatically identifying the preserved molecular moieties in a chemical reaction is referred to as the atom mapping problem. Reaction atom maps provide the ability to locate the fate of individual atoms across an entire metabolic network. Atom maps are used to track atoms in isotope labeling experiments for metabolic flux elucidation, trace novel biosynthetic routes to a target compound, and contrast entire pathways for structural homology. However, rapid computation of the reaction atom mappings remains elusive despite significant research. We present a novel substructure search algorithm, canonical labeling for clique approximation (CLCA), with polynomial run-time complexity to quickly generate atom maps for all the reactions present in MetRxn. CLCA uses number theory (i.e., prime factorization) to generate canonical labels or unique IDs and identify a bijection between the vertices (atoms) of two distinct molecular graphs. CLCA utilizes molecular graphs generated by combining atomistic information on reactions and metabolites from 112 metabolic models and 8 metabolic databases. CLCA offers improvements in run time, accuracy, and memory utilization over existing heuristic and combinatorial maximum common substructure (MCS) search algorithms. We provide detailed examples on the various advantages as well as failure modes of CLCA over existing algorithms. PMID:25412255

Kumar, Akhil; Maranas, Costas D

2014-12-22

380

The Substructure of the Solar Corona Observed in the Hi-C Telescope  

NASA Astrophysics Data System (ADS)

In the summer of 2012, the High-resolution Coronal Imager (Hi-C) flew aboard a NASA sounding rocket and collected the highest spatial resolution images ever obtained of the solar corona. One of the goals of the Hi-C flight was to characterize the substructure of the solar corona. We therefore calculate how the intensity scales from a low-resolution (AIA) pixels to high-resolution (Hi-C) pixels for both the dynamic events and “background” emission (meaning, the steady emission over the 5 minutes of data acquisition time). We find there is no evidence of substructure in the background corona; the intensity scales smoothly from low-resolution to high-resolution Hi-C pixels. In transient events, however, the intensity observed with Hi-C is, on average, 2.6 times larger than observed with AIA. This increase in intensity suggests that AIA is not resolving these events. This result suggests a finely structured dynamic corona embedded in a smoothly varying background.

Winebarger, Amy R.; Cirtain, Jonathan W.; Golub, Leon; DeLuca, Ed; Savage, Sabrina; Alexander, Caroline; Schuler, Timothy

2014-06-01

381

X-ray Substructure Studies of Four Galaxy Clusters using XMM-Newton Data  

E-print Network

Mahdavi et al. find that the degree of agreement between weak lensing and X-ray mass measurements is a function of cluster radius. Numerical simulations also point out that X-ray mass proxies do not work equally well at all radii. The origin of the effect is thought to be associated with cluster mergers. Recent work presenting the cluster maps showed an ability of X-ray maps to reveal and study cluster mergers in detail. Here we present a first attempt to use the study of substructure in assessing the systematics of the hydrostatic mass measurements using two-dimensional (2-D) X-ray diagnostics. The temperature map is uniquely able to identify the substructure in an almost relaxed cluster which would be unnoticed in the ICM electron number density and pressure maps. We describe the radial fluctuations in the 2-D maps by a cumulative/differential scatter profile relative to the mean profile within/at a given radius. The amplitude indicates ~10 fluctuations in the temperature, electron number density and entrop...

Zhang, Yu-Ying; Finoguenov, Alexis; Hudson, Daniel S; Sarazin, Craig L

2009-01-01

382

What does the Observed, Universal Dark Matter Surface Density of Galaxies tell us about Halo Substructure?  

NASA Astrophysics Data System (ADS)

Recent observations suggest a universal, core dark matter (DM) surface density (?0 = ?0r0) for galaxies at all observed mass and luminosity scales. We show that this result emerges naturally if the gravitational field at the core radius of a DM halo is spherically symmetric. This result is independent of the scale of the DM halo core being considered as well as the assumed DM density profile. If a spherically symmetric gravitational field is the correct interpretation of the universal value of ?0, it implies that no dark matter substructure can exist, even within the largest core radius for which the universal ?0 relation holds, lest it spoil the symmetry -- except in the highly contrived scenario that substructure is symmetrically distributed in the cores of DM halos at all scales for which the universal ?0 relation is observed. Ignoring this extremely unlikely special case, the symmetry condition translates into an upper bound on the mass of the dark matter particle. Our result, which favors lower mass candidates, is consistent with the findings of several other recent studies.

Pelikan, Chris; Watson, Casey

2013-03-01

383

Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes  

NASA Astrophysics Data System (ADS)

At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF-driven galaxy evolution using both existing NASA databases and operating instruments, in addition to upcoming space telescopes. While a legacy of our project will be the hierarchical photometric database (disseminated via MAST and NED) which supports extragalactic community science, our own goals from the proposed comprehensive measurements address some vital issues: (i) Currently there is controversy regarding the power-law slope of the empirical star formation law (SFL). Is there constant star formation efficiency above the HI-to-H_2 transition gas surface density (implying ~unity slope, see papers by Bigiel et al. and Leroy et al.), or is the SFL relation a stronger function of gas density with a super-linear form (as observed by Kennicutt et al. 2007)? Liu et al. (2011) have shown that the answer may depend critically on whether or not diffuse emission underlying star-forming substructures is removed. Our analysis will allow firm resolution of this issue, as we will also apply our photometry algorithm to Spitzer imaging for a subset of our sample galaxies, thus providing background-subtracted L(UV) and L(IR) measurements for substructures which can then be compared to existing and forthcoming (ALMA) CO imaging. (ii) We will also verify/calibrate our SED-fit based determination of age, extinction, and mass for UV-bright structures via direct comparison to the ground-truth stemming from resolved stellar populations (e.g. in ANGST galaxies) and also high-resolution HST UV-optical star cluster surveys (further out in the Local Volume). (iii) Finally, we will measure the diffuse UV fraction in a few hundred of the nearest galaxies (accounting for variation tied only to spatial resolution), trying to ascertain the characteristic fraction in galaxies of different Hubble type and dust-to-gas ratio. Systematic local variations in diffuse fraction and color will also be quantified as a function of environment.

Thilker, David

384

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

385

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

386

The Herschel Virgo Cluster Survey. XVII. SPIRE point-source catalogs and number counts  

NASA Astrophysics Data System (ADS)

Aims: We present three independent catalogs of point-sources extracted from SPIRE images at 250, 350, and 500 ?m, acquired with the Herschel Space Observatory as a part of the Herschel Virgo Cluster Survey (HeViCS). The catalogs have been cross-correlated to consistently extract the photometry at SPIRE wavelengths for each object. Methods: Sources have been detected using an iterative loop. The source positions are determined by estimating the likelihood to be a real source for each peak on the maps, according to the criterion defined in the sourceExtractorSussextractor task. The flux densities are estimated using the sourceExtractorTimeline, a timeline-based point source fitter that also determines the fitting procedure with the width of the Gaussian that best reproduces the source considered. Afterwards, each source is subtracted from the maps, removing a Gaussian function in every position with the full width half maximum equal to that estimated in sourceExtractorTimeline. This procedure improves the robustness of our algorithm in terms of source identification. We calculate the completeness and the flux accuracy by injecting artificial sources in the timeline and estimate the reliability of the catalog using a permutation method. Results: The HeViCS catalogs contain about 52 000, 42 200, and 18 700 sources selected at 250, 350, and 500 ?m above 3? and are ~75%, 62%, and 50% complete at flux densities of 20 mJy at 250, 350, 500 ?m, respectively. We then measured source number counts at 250, 350, and 500 ?m and compare them with previous data and semi-analytical models. We also cross-correlated the catalogs with the Sloan Digital Sky Survey to investigate the redshift distribution of the nearby sources. From this cross-correlation, we select ~2000 sources with reliable fluxes and a high signal-to-noise ratio, finding an average redshift z ~ 0.3 ± 0.22 and 0.25 (16-84 percentile). Conclusions: The number counts at 250, 350, and 500 ?m show an increase in the slope below 200 mJy, indicating a strong evolution in number of density for galaxies at these fluxes. In general, models tend to overpredict the counts at brighter flux densities, underlying the importance of studying the Rayleigh-Jeans part of the spectral energy distribution to refine the theoretical recipes of the models. Our iterative method for source identification allowed the detection of a family of 500 ?m sources that are not foreground objects belonging to Virgo and not found in other catalogs. Herschel is an ESA space observatory with science instruments provided by a European-led principal investigator consortia and with an important participation from NASA.The 250, 350, 500 ?m, and the total catalogs are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A129

Pappalardo, Ciro; Bendo, George J.; Bianchi, Simone; Hunt, Leslie; Zibetti, Stefano; Corbelli, Edvige; di Serego Alighieri, Sperello; Grossi, Marco; Davies, Jonathan; Baes, Maarten; De Looze, Ilse; Fritz, Jacopo; Pohlen, Michael; Smith, Matthew W. L.; Verstappen, Joris; Boquien, Médéric; Boselli, Alessandro; Cortese, Luca; Hughes, Thomas; Viaene, Sebastien; Bizzocchi, Luca; Clemens, Marcel

2015-01-01

387

VCC 2062: an old Tidal Dwarf Galaxy in the Virgo Cluster?  

E-print Network

Numerical simulations predict the existence of old Tidal Dwarf Galaxies (TDGs) that would have survived several Gyr after the collision lying at their origin. Such survivors, which would by now have become independent relaxed galaxies, would be ideal laboratories, if nearby enough, to tackle a number of topical issues, including the distribution of Dark Matter in and around galaxies. However finding old dwarf galaxies with a confirmed tidal origin is an observational challenge. A dwarf galaxy in the Virgo Cluster, VCC 2062, exhibits several unusual properties that are typical of a galaxy made out of recycled material. We discuss whether it may indeed be a TDG. We analysed multi-wavelength observations of VCC 2062, including an IRAM CO map, an optical spectrum of its HII regions, GALEX ultraviolet and archival broad-band and narrow-band optical images as well as a VLA HI datacube, originally obtained as part of the VIVA project. VCC 2062 appears to be the optical, low surface brightness counterpart of a kinematically detached, rotating condensation that formed within an HI tail apparently physically linked to the disturbed galaxy NGC 4694. In contrast to its faint optical luminosity, VCC 2062 is characterised by strong CO emission and a high oxygen abundance more typical of spiral disks. Its dynamical mass however, is that of a dwarf galaxy. VCC 2062 was most likely formed within a pre-enriched gaseous structure expelled from a larger galaxy as a result of a tidal interaction. The natural provider for the gaseous tail is NGC 4694 or rather a former companion which subsequently has been accreted by the massive galaxy. According to that scenario, VCC 2062 has been formed by a past tidal encounter. Since its parent galaxies have most probably already totally merged, it qualifies as an old TDG.

Pierre-Alain Duc; Jonathan Braine; Ute Lisenfeld; Elias Brinks; Mederic Boquien

2007-09-17

388

Hubble Space Telescope Imaging of Bipolar Nuclear Shells in the Disturbed Virgo Cluster Galaxy NGC 4438  

E-print Network

We present broadband and narrowband Hubble Space Telescope images of the central region of the heavily disturbed Virgo cluster galaxy NGC 4438 (Arp120), whose nucleus has been described as a type 1 LINER or dwarf Seyfert. Narrowband H-alpha and [NII] HST images reveal striking bipolar shell features, 1 kpc in projected length from end-to-end, which are likely the result of an outflow from the nuclear region experiencing a strong interaction with the ISM. While these outflow shells share similarities with those in some other starburst or AGN galaxies, these in NGC 4438 are notable because NGC 4438 harbors neither a luminous circumnuclear starburst nor a luminous AGN. The shells appear to be closed at their outer ends, suggesting that the outflow in NGC 4438 is dynamically younger than those in some other galaxies. The radio continuum emission is strongly enhanced near the outer ends of the shells, suggesting working surfaces arising from collimated nuclear outflows which have impacted and shocked the surrounding ISM. The 2 shells are quite different, as the northwestern (NW) shell is luminous and compact, while the southeastern (SE) shell is 2.5 times longer and much fainter, in both optical emission lines and the non-thermal radio continuum. The differences between the 2 shells may be attributed to a difference in ISM density on the 2 sides of the nuclear disk. Such an ISM asymmetry exists on larger scales in this heavily disturbed galaxy. At the base of the outflow is a nuclear source, which is the highest surface brightness source in the galaxy at optical wavelengths, We discuss whether the outflow is powered by a low luminosity AGN or a compact nuclear starburst.

Jeffrey D. P. Kenney; Elizabeth E. Yale

2001-12-04

389

How the Intracluster Medium Affects the Far-Infrared--Radio Correlation within Virgo Cluster Galaxies  

E-print Network

We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo cluster galaxies using {\\it Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the FIR-radio correlation {\\it within} normal galaxies, we use our infrared data to create model radio maps which we compare to the observed radio images. For 6 of our sample galaxies we find regions along their outer edges that are highly deficient in the radio compared with our models. We believe these observations are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit region to lie just exterior to a region of high radio polarization and flat radio spectral index, however the total radio continuum in this region does not appear significantly enhanced. This scenario seems consistent for other galaxies with radio polarization data in the literature. We also find that galaxies having local radio deficits appear to have enhanced global radio fluxes. Our preferred physical picture is that the observed radio deficit regions arise from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated magnetic field, thereby creating synchrotron tails observed for some of our galaxies. CR particles are also re-accelerated by ICM-driven shocklets behind the observed radio deficit regions which in turn enhances the remaining radio disk brightness. The high radio polarization and lack of coincidental signatures in the total synchrotron power in these regions arises from shear, and possibly mild compression, as the ICM wind drags and stretches the magnetic field.

E. J. Murphy; J. D. P. Kenney; G. Helou; A. Chung; J. H. Howell

2008-02-15

390

VCC 2062: an old tidal dwarf galaxy in the Virgo cluster?  

NASA Astrophysics Data System (ADS)

Context: Numerical simulations predict the existence of old Tidal Dwarf Galaxies (TDGs) that would have survived several Gyr after the collision lying at their origin. Such survivors, which would by now have become independent relaxed galaxies, would be ideal laboratories, if nearby enough, to tackle a number of topical issues, including the distribution of Dark Matter in and around galaxies. However finding old dwarf galaxies with a confirmed tidal origin is an observational challenge. Aims: A dwarf galaxy in the nearby Virgo Cluster, VCC 2062, exhibits several unusual properties that are typical of a galaxy made out of recycled material. We discuss whether it may indeed be a TDG. Methods: We analysed multi-wavelength observations of VCC 2062, including a CO map acquired with the IRAM 30 m dish, an optical spectrum of its HII regions, GALEX ultraviolet and archival broad-band and narrow-band optical images as well as a VLA HI datacube, originally obtained as part of the VIVA project. Results: VCC 2062 appears to be the optical, low surface brightness counterpart of a kinematically detached, rotating condensation that formed within an HI tail apparently physically linked to the disturbed galaxy NGC 4694. In contrast to its faint optical luminosity, VCC 2062 is characterised by strong CO emission and a high oxygen abundance more typical of spiral disks. Its dynamical mass however, is that of a dwarf galaxy. Conclusions: VCC 2062 was most likely formed within a pre-enriched gaseous structure expelled from a larger galaxy as a result of a tidal interaction. The natural provider for the gaseous tail is NGC 4694 or rather a former companion which subsequently has been accreted by the massive galaxy. According to that scenario, VCC 2062 has been formed by a past tidal encounter. Since its parent galaxies have most probably already totally merged, it qualifies as an old Tidal Dwarf Galaxy.

Duc, P.-A.; Braine, J.; Lisenfeld, U.; Brinks, E.; Boquien, M.

2007-11-01

391

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.

392

Stellar Ontogeny:...to Ashes  

ERIC Educational Resources Information Center

Discusses the process of stellar death and the correlation between the size of a star in solar masses and its way of death. The amount of mass loss that occurs during the life and death of a star is also discussed. (HM)

MOSAIC, 1978

1978-01-01

393

Flicker: Mean stellar densities from flicker  

NASA Astrophysics Data System (ADS)

Flicker calculates the mean stellar density of a star by inputting the flicker observed in a photometric time series. Written in Fortran90, its output may be used as an informative prior on stellar density when fitting transit light curves.

Kipping, David

2014-11-01

394

Electric fields and transport in optimized stellarators  

E-print Network

Recent stellarator experiments have been designed with one of two types of neoclassical optimization: quasisymmetry or quasi-isodynamism. Both types of stellarator have perfectly confined collisionless particle orbits as ...

Landreman, Matthew Joseph

2011-01-01

395

Physica D 112 (1998) 275280 Stellarator symmetry  

E-print Network

Physica D 112 (1998) 275­280 Stellarator symmetry R.L. Dewar , S.R. Hudson 1 Department of stellarator symmetry is presented and its relation to previous definitions discussed. It is shown that the field-line flow in systems possessing stellarator symmetry is time-reversal invariant

Hudson, Stuart

396

Sagittarius A*: Stellar Observations and Analysis  

E-print Network

Sagittarius A*: Stellar Observations and Analysis Brett Chizinski Boston University Department ­ Andrea Ghez ­ Data Reduction ­ Stellar Orbits: Ghez et al. ­ Orbit of S2 with NAOS-CONICA · Analysis Inferometry #12;27 April 2006 SgrA*: Stellar Observations and Analysis- Brett Chizinski 1 1. Average all short

397

VictoriaReginaModels: Stellar evolutionary tracks  

NASA Astrophysics Data System (ADS)

The Victoria-Regina stellar models are comprised of seventy-two grids of stellar evolutionary tracks accompanied by complementary zero-age horizontal branches and are presented in “equivalent evolutionary phase” (.eep) files. This Fortran 77 software interpolates isochrones, isochrone population functions, luminosity functions, and color functions of stellar evolutionary tracks.

VandenBerg, Don A.; Bergbusch, Peter A.; Dowler, Patrick D.

2014-04-01

398

Stellar Populations with the LSST  

NASA Astrophysics Data System (ADS)

The LSST will produce a multi-color map and photometric object catalog of half the sky to g 27.5(5?). Strategically cadenced time-space sampling of each field spanning ten years will allow variability, proper motion and parallax measurements for objects brighter than g 25. As part of providing an unprecedented map of the Galaxy, the accurate multi-band photometry will permit photometric parallaxes, chemical abundances and a handle on ages via colors at turn-off for main-sequence stars at all distances within the Galaxy, permitting a comprehensive study of star formation histories (SFH) and chemical evolution for field stars. With a geometric parallax accuracy of 1mas, LSST will produce a robust complete sample of the solar neighborhood stars. While delivering parallax accuracy comparable to HIPPARCOS, LSST will extend the catalog to more than a 10 magnitudes fainter limit, and will be complete to MV 15. In the Magellanic Clouds too, the photometry will reach MV +8, allowing the SFH and chemical signatures in the expansive outer extremities to be gleaned from their main sequence stars. This in turn will trace the detailed interaction of the Clouds with the Galaxy halo. The LSST time sampling will identify and characterize variable stars of all types, from time scales of 1hr to several years, a feast for variable star astrophysics. Cepheids and LPVs in all galaxies in the Sculptor, M83 and Cen-A groups are obvious data products: comparative studies will reveal systematic differences with galaxy properties, and help to fine tune the rungs of the distance ladder. Dwarf galaxies within 10Mpc that are too faint to find from surface brightness enhancements will be revealed via over-densities of their red giants: this systematic census will extend the luminosity function of galaxies to the faint limit. Novae discovered by LSST time sampling will trace intergalactic stars out to the Virgo and Fornax clusters.

Saha, Abhijit; Olsen, K.; LSST Stellar Populations Collaboration

2006-12-01

399

Implementation of automated multilevel substructuring for frequency response analysis of structures  

NASA Astrophysics Data System (ADS)

In the design of vehicles, such as automobiles, aircraft, spacecraft, or submarines, it is important to be able to accurately predict dynamic behavior of the structure. With the extremely high cost of building physical prototypes of these vehicles, there is a growing emphasis on analysis of computer models. In this dissertation, a method known as Automated Multilevel Substructuring (AMLS) is presented for accurately solving frequency response problems involving large, complex models with millions of degrees of freedom. Conventional methods for addressing these problems, such as mode superposition using a Lanczos eigensolver or model reduction using component mode synthesis, are reviewed. The Automated Multilevel Substructuring (AMLS) method partitions finite element models into substructures, similar to component mode synthesis methods, but uses an automated partitioning procedure that reduces the burden on the analyst. The finite element matrices are projected onto a reduced subspace, on which the frequency response is computed. Two frequency response algorithms are presented. Both methods require the solution of a global eigenvalue problem on the reduced subspace. The first method uses straightforward mode superposition. The second method employs a new iterative approach in which the modal frequency response leads to a residual problem that is solved using an iterative splitting method. The global eigensolution and frequency response algorithms are specifically designed to take advantage of the properties of the reduced subspace. Numerical examples are presented for models with millions of degrees of freedom. The performance and accuracy of the AMLS method are compared to the standard commercial software package for large-scale linear dynamic analysis. These examples establish that AMLS can be used to accurately obtain the response of very large models with significantly less computational resources than competing methods. In comparison to the modal frequency response obtained with the standard commercial software package using a shifted block Lanczos algorithm, AMLS ran up to 6.4 times faster, used less memory, and required an order of magnitude less data transfer. Thus, the AMLS method makes it possible to do frequency response analysis of large, complex structures at higher frequencies than was previously practical.

Kaplan, Matthew Frederick

400

Substructure analysis using NICE/SPAR and applications of force to linear and nonlinear structures. [spacecraft masts  

NASA Technical Reports Server (NTRS)

Parallel computing studies are presented for a variety of structural analysis problems. Included are the substructure planar analysis of rectangular panels with and without a hole, the static analysis of space mast, using NICE/SPAR and FORCE, and substructure analysis of plane rigid-jointed frames using FORCE. The computations are carried out on the Flex/32 MultiComputer using one to eighteen processors. The NICE/SPAR runstream samples are documented for the panel problem. For the substructure analysis of plane frames, a computer program is developed to demonstrate the effectiveness of a substructuring technique when FORCE is enforced. Ongoing research activities for an elasto-plastic stability analysis problem using FORCE, and stability analysis of the focus problem using NICE/SPAR are briefly summarized. Speedup curves for the panel, the mast, and the frame problems provide a basic understanding of the effectiveness of parallel computing procedures utilized or developed, within the domain of the parameters considered. Although the speedup curves obtained exhibit various levels of computational efficiency, they clearly demonstrate the excellent promise which parallel computing holds for the structural analysis problem. Source code is given for the elasto-plastic stability problem and the FORCE program.

Razzaq, Zia; Prasad, Venkatesh; Darbhamulla, Siva Prasad; Bhati, Ravinder; Lin, Cai

1987-01-01