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Sample records for blue straggler stars

  1. Ecology of blue straggler stars

    CERN Document Server

    Carraro, Giovanni; Beccari, Giacomo

    2015-01-01

    The existence of blue straggler stars, which appear younger, hotter, and more massive than their siblings, is at odds with a simple picture of stellar evolution. Such stars should have exhausted their nuclear fuel and evolved long ago to become cooling white dwarfs. They are found to exist in globular clusters, open clusters, dwarf spheroidal galaxies of the Local Group, OB associations and as field stars. This book summarises the many advances in observational and theoretical work dedicated to blue straggler stars. Carefully edited extended contributions by well-known experts in the field cover all the relevant aspects of blue straggler stars research: Observations of blue straggler stars in their various environments; Binary stars and formation channels; Dynamics of globular clusters; Interpretation of observational data and comparison with models. The book also offers an introductory chapter on stellar evolution written by the editors of the book.

  2. Variable blue straggler stars in NGC 5466

    International Nuclear Information System (INIS)

    Nine variable blue stragglers have been found in the globular cluster NGC 5466. The six dwarf Cepheids in this cluster coexist in the instability strip with other nonvariable stars. The three eclipsing binaries are among the hottest of the blue stragglers. The hypothesis is discussed that all blue stragglers in this cluster have undergone mass transfer in close binaries. Under this hypothesis, rotation and spin-down play important roles in controlling the evolution of blue stragglers in old clusters and in affecting some of their observational properties. 14 refs

  3. First Evidence of Circumstellar Disks around Blue Straggler Stars

    CERN Document Server

    De Marco, O; Ouellette, J A; Zurek, D R; Shara, M M; Marco, Orsola De; Lanz, Thierry; Ouellette, John A.; Zurek, David; Shara, Michael M.

    2004-01-01

    We present an analysis of optical HST/STIS and HST/FOS spectroscopy of 6 blue stragglers found in the globular clusters M3, NGC6752 and NGC6397. These stars are a subsample of a set of ~50 blue stragglers and stars above the main sequence turn-off in four globular clusters which will be presented in an forthcoming paper. All but the 6 stars presented here can be well fitted with non-LTE model atmospheres. The 6 misfits, on the other hand, possess Balmer jumps which are too large for the effective temperatures implied by their Paschen continua. We find that our data for these stars are consistent with models only if we account for extra absorption of stellar Balmer photons by an ionized circumstellar disk. Column densities of HI and CaII are derived as are the the disks' thicknesses. This is the first time that a circumstellar disk is detected around blue stragglers. The presence of magnetically-locked disks attached to the stars has been suggested as a mechanism to lose the large angular momentum imparted by ...

  4. Spinning like a blue straggler: the population of fast rotating blue straggler stars in ω Centauri

    Energy Technology Data Exchange (ETDEWEB)

    Mucciarelli, A.; Lovisi, L.; Ferraro, F. R.; Dalessandro, E.; Lanzoni, B. [Dipartimento di Fisica and Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Monaco, L. [European Southern Observatory, Casilla 19001, Santiago (Chile)

    2014-12-10

    By using high-resolution spectra acquired with FLAMES-GIRAFFE at the ESO/VLT, we measured the radial and rotational velocities for 110 blue straggler stars (BSSs) in ω Centauri, the globular cluster-like stellar system harboring the largest known BSS population. According to their radial velocities, 109 BSSs are members of the system. The rotational velocity distribution is very broad, with the bulk of BSSs spinning at less than ∼40 km s{sup –1} (in agreement with the majority of such stars observed in other globular clusters) and a long tail reaching ∼200 km s{sup –1}. About 40% of the sample has v{sub e} sin i > 40 km s{sup –1} and about 20% has v{sub e} sin i > 70 km s{sup –1}. Such a large fraction is very similar to the percentage of fast rotating BSSs observed in M4. Thus, ω Centauri is the second stellar cluster, beyond M4, with a surprisingly high population of fast spinning BSSs. We found a hint of radial behavior for a fraction of fast rotating BSSs, with a mild peak within one core radius, and a possible rise in the external regions (beyond four core radii). This may suggest that recent formation episodes of mass transfer BSSs occurred preferentially in the outskirts of ω Centauri, or that braking mechanisms able to slow down these stars are least efficient in the lowest density environments.

  5. Spectroscopy of Blue Stragglers and Turnoff Stars in M67 (NGC 2682)

    CERN Document Server

    Shetrone, M; Shetrone, Matthew; Sandquist, Eric

    2000-01-01

    We have analyzed high-resolution spectra of relatively cool blue stragglers and main sequence turnoff stars in the old open cluster M67 (NGC 2682). We attempt to identify blue stragglers whose spectra are least contaminated by binary effects (contamination by a binary companion or absorption by circumstellar material). These ``best'' stragglers have metallicities ([Fe/H] = -0.05) and abundance ratios of the blue stragglers are not significantly different from those of the turnoff stars. Based on arguments from hydrodynamical models of stellar collisions, we assert that the current upper limits for the lithium abundances of all blue stragglers observed in M67 (by us and others) are consistent with no mixing during the formation process, assuming pre-main sequence and main sequence depletion patterns observed for M67 main sequence stars. We discuss composition signatures that could more definitively distinguish between blue straggler formation mechanisms in open cluster stars. We confirm the spectroscopic detec...

  6. Spinning like a Blue Straggler: the population of fast rotating Blue Straggler stars in Omega Centauri

    CERN Document Server

    Mucciarelli, A; Ferraro, F R; Dalessandro, E; Lanzoni, B; Monaco, L

    2014-01-01

    By using high-resolution spectra acquired with FLAMES-GIRAFFE at the ESO/VLT, we measured radial and rotational velocities for 110 Blue Straggler stars (BSSs) in Omega Centauri, the globular cluster-like stellar system harboring the largest known BSS population. According to their radial velocities, 109 BSSs are members of the system. The rotational velocity distribution is very broad, with the bulk of BSSs spinning at less than ~40 km/s (in agreement with the majority of such stars observed in other globular clusters) and a long tail reaching ~200 km/s. About 40% of the sample has vsini >40 km/s and about 20% has vsini >70 km/s. Such a large fraction is very similar to the percentage of of fast rotating BSSs observed in M4. Thus, Omega Centauri is the second stellar cluster, beyond M4, with a surprisingly high population of fast spinning BSSs. We found a hint of a radial behaviour of the fraction of fast rotating BSSs, with a mild peak within one core radius, and a possibile rise in the external regions (bey...

  7. Chemical abundances of blue straggler stars in Galactic Globular Clusters

    CERN Document Server

    Lovisi, L

    2014-01-01

    By using the high resolution spectrograph FLAMES@VLT we performed the first systematic campaign devoted to measure chemical abundances of blue straggler stars (BSSs). These stars, whose existence is not predicted by the canonical stellar evolutionary theory, are likely the product of the interactions between stars in the dense environment of Globular Clusters. Two main scenarios for BSS formation (mass transfer in binary systems and stellar collisions) have been proposed and hydrodynamical simulations predict different chemical patterns in the two cases, in particular C and O depletion for mass transfer BSSs. In this contribution, the main results for BSS samples in 6 Globular Clusters and their interpretation in terms of BSS formation processes are discussed. For the first time, evidence of radiative levitation in the shallow envelopes of BSSs hotter than $\\sim$8000 K has been found. C and O depletion for some BSSs has been detected in 47 Tucanae, M30 and $\\omega$ Centauri thus suggesting a mass transfer ori...

  8. Ultra-Lithium-Deficient Halo Stars and Blue Stragglers A Common Origin?

    CERN Document Server

    Ryan, S G; Kajino, T; Rosolankova, K; Ryan, Sean G.; Beers, Timothy C.; Kajino, Toshitaka; Rosolankova, Katarina

    2000-01-01

    We present data for four ultra-Li-deficient, warm, halo stars. The Li deficiency of two of these is a new discovery. Three of the four stars have effective temperatures Teff ~ 6300 K, in contrast to previously known Li-deficient halo stars which spanned the temperature range of the Spite Plateau. In this paper we propose that these, and previously known ultra-Li-deficient halo stars, may have had their surface lithium abundances reduced by the same mechanism as produces halo field blue stragglers. Even though these stars have yet to reveal themselves as blue stragglers, they might be regarded as "blue-stragglers-to-be." In our proposed scenario, the surface abundance of Li in these stars could be destroyed (a) during the normal pre-main-sequence single star evolution of their low mass precursors, (b) during the post-main-sequence evolution of a evolved mass donor, and/or (c) via mixing during a mass-transfer event or stellar merger. The warmest Li-deficient stars at the turnoff would be regarded as emerging "...

  9. Two distinct sequences of blue straggler stars in the globular cluster M30

    CERN Document Server

    Ferraro, F R; Dalessandro, E; Lanzoni, B; Sills, A; Rood, R T; Pecci, F Fusi; Karakas, A I; Miocchi, P; Bovinelli, S; 10.1038/nature08607

    2010-01-01

    Stars in globular clusters are generally believed to have all formed at the same time, early in the Galaxy's history. 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago. Two possible mechanisms have been proposed for their formation: mass transfer between binary companions and stellar mergers resulting from direct collisions between two stars. Recently, the binary explanation was claimed to be dominant. Here we report that there are two distinct parallel sequences of blue stragglers in M30. This globular cluster is thought to have undergone 'core collapse', during which both the collision rate and the mass transfer activity in binary systems would have been enhanced. We suggest that the two observed sequences arise from the cluster core collapse, with the bluer population arising from direct stellar collisions and the redder one arising from the evolution of close binaries that are probably still experiencing an active phase of mass transfer.

  10. Weighing stars: the identification of an Evolved Blue Straggler Star in the globular cluster 47 Tucanae

    CERN Document Server

    Ferraro, F R; Mucciarelli, A; Lanzoni, B; Dalessandro, E; Pallanca, C; Massari, D

    2015-01-01

    Globular clusters are known to host peculiar objects, named Blue Straggler Stars (BSSs), significantly heavier than the normal stellar population. While these stars can be easily identified during their core hydrogen-burning phase, they are photometrically indistinguishable from their low-mass sisters in advanced stages of the subsequent evolution. A clear-cut identification of these objects would require the direct measurement of the stellar mass. We used the detailed comparison between chemical abundances derived from neutral and from ionized spectral lines as a powerful stellar "weighing device" to measure stellar mass and to identify an evolved BSS in 47 Tucanae. In particular, high-resolution spectra of three bright stars located slightly above the level of the "canonical" horizontal branch sequence in the color-magnitude diagram of 47 Tucanae, have been obtained with UVES spectrograph. The measurements of iron and titanium abundances performed separately from neutral and ionized lines reveal that two ta...

  11. Stellar Encounters with Multiple Star Systems and the Blue Straggler Problem

    CERN Document Server

    Leigh, Nathan

    2010-01-01

    We present a technique to identify the most probable dynamical formation scenario for an observed binary or triple system containing one or more merger products or, alternatively, to rule out the possibility of a dynamical origin. Our method relies on an analytic prescription for energy conservation during stellar encounters. With this, observations of the multiple star system containing the merger product(s) can be used to work backwards in order to constrain the initial orbital energies of any single, binary or triple systems that went into the encounter. The initial semi-major axes of the orbits provide an estimate for the collisional cross section and therefore the time-scale for the encounter to occur in its host cluster. We have applied our analytic prescription to observed binary and triple systems containing blue stragglers, in particular the triple system S1082 in M67 and the period distribution of the blue straggler binaries in NGC 188. We have shown that both S1082 and most of the blue straggler bi...

  12. Investigating mass segregation process in globular clusters with Blue Straggler Stars: the impact of dark remnants

    CERN Document Server

    Alessandrini, Emiliano; Ferraro, Francesco Rosario; Miocchi, Paolo; Vesperini, Enrico

    2016-01-01

    We present the results of a set of N-body simulations aimed at exploring how the process of mass segregation (as traced by the spatial distribution of blue straggler stars, BSSs) is affected by the presence of a population of heavy dark remnants (as neutron stars and black holes). To this end, clusters characterized by different initial concentrations and different fractions of dark remnants have been modeled. We find that an increasing fraction of stellar-mass black holes significantly delays the mass segregation of BSSs and the visible stellar component. In order to trace the evolution of BSS segregation, we introduce a new parameter ($A^+$) that can be easily measured when the cumulative radial distribution of these stars and a reference population are available. Our simulations show that $A^+$ might also be used as an approximate indicator of the time remaining to the core collapse of the visible component.

  13. Weighing Stars: The Identification of an Evolved Blue Straggler Star in the Globular Cluster 47 Tucanae

    Science.gov (United States)

    Ferraro, F. R.; Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Dalessandro, E.; Pallanca, C.; Massari, D.

    2016-01-01

    Globular clusters are known to host peculiar objects named blue straggler stars (BSSs), significantly heavier than the normal stellar population. While these stars can be easily identified during their core hydrogen-burning phase, they are photometrically indistinguishable from their low-mass sisters in advanced stages of the subsequent evolution. A clear-cut identification of these objects would require the direct measurement of the stellar mass. We used the detailed comparison between chemical abundances derived from neutral and from ionized spectral lines as a powerful stellar “weighing device” to measure stellar mass and to identify an evolved BSS in 47 Tucanae. In particular, high-resolution spectra of three bright stars, located slightly above the level of the “canonical” horizontal branch (HB) sequence in the color-magnitude diagram of 47 Tucanae, have been obtained with the UVES spectrograph. The measurements of iron and titanium abundances performed separately from neutral and ionized lines reveal that two targets have stellar parameters fully consistent with those expected for low-mass post-HB objects, while for the other target the elemental ionization balance is obtained only by assuming a mass of ˜ 1.4{M}⊙ , which is significantly larger than the main sequence turn-off mass of the cluster (˜ 0.85{M}⊙ ). The comparison with theoretical stellar tracks suggests that this is a BSS descendant possibly experiencing its core helium-burning phase. The large applicability of the proposed method to most of the globular clusters in our Galaxy opens the possibility to initiate systematic searches for evolved BSSs, thus giving access to still unexplored phases of their evolution. Based on UVES-FLAMES observations collected under Program 193.D-0232.

  14. Cannibals in the thick disk: the young $\\alpha-$rich stars as evolved blue stragglers

    CERN Document Server

    Jofre, P; Izzard, R G; Van Eck, S; Hawkins, K; Jorissen, A; Gilmore, G; Paladini, C

    2016-01-01

    Spectro-seismic measurements of red giant stars enabled the recent discovery of giant stars in the thick disk that are more massive than 1.4 M_sun (Martig et al 2015, Chiappini et al 2015). While it has been claimed that most of these stars are younger than the rest of the typical thick disk stars, we show evidence that they might be products of mass transfer in binary evolution, notably evolved blue stragglers. We took new measurements of the radial velocities in a sample of 26 stars from APOKASC, including 13 of the "young" stars of Martig et al (2015) and 13 "old" stars with similar stellar parameters but with masses below 1 M_sun and found that some stars are in binary systems, contrary to what has been claimed before. Furthermore, with a population synthesis of only low-mass stars but including binary evolution and mass transfer, we can reproduce the masses and the [C/N] ratios of the 26 stars. Our study shows how asteroseismology of solar-type red giants provides us with a unique opportunity to study th...

  15. Model computations of blue stragglers and W UMa-type stars in globular clusters

    CERN Document Server

    Stepien, Kazimierz

    2015-01-01

    It was recently demonstrated that contact binaries occur in globular clusters (GCs) only immediately below turn-off point and in the region of blue straggler stars (BSs). In addition, observations indicate that at least a significant fraction of BSs in these clusters was formed by the binary mass-transfer mechanism. The aim of our present investigation is to obtain and analyze a set of evolutionary models of cool, close detached binaries with a low metal abundance, which are characteristic of GC. We computed the evolution of 975 models of initially detached, cool close binaries with different initial parameters. The models include mass exchange between components as well as mass and angular momentum loss due to the magnetized winds for very low-metallicity binaries with Z = 0.001. The models are interpreted in the context of existing data on contact binary and blue straggler members of GCs. The model parameters agree well with the observed positions of the GC contact binaries in the Hertzsprung-Russell diagra...

  16. Blue Straggler Star Populations in Globular Clusters: I. Dynamical Properties of Blue Straggler Stars in NGC 3201, NGC 6218 and $\\omega$ Centauri

    CERN Document Server

    Simunovic, Mirko

    2013-01-01

    We present the first dynamical study of Blue Straggler Stars (BSSs) in three Galactic globular clusters, NGC\\,3201, NGC\\,5139 ($\\omega$Cen), and NGC\\,6218, based on medium-resolution spectroscopy (R 10000) obtained with IMACS. Our BSS candidate selection technique uses HST/ACS and ESO/WFI photometric data out to $>\\!4.5\\,r_c$. We use radial velocity measurements to discard non-members and achieve a success rate of $\\sim93\\%$, which yields a sample of 116 confirmed BSSs. Using the penalized pixel fitting method (pPXF) we measure the $v\\sin(i)$ values of the sample BSSs and find their distribution functions peaked at slow velocities with a long tail towards fast velocities in each globular cluster. We find that the BSSs in NGC\\,3201 and NGC\\,6218 which show $v\\sin(i)\\!>\\!50$ km s$^{-1}$ are all found in the central cluster regions, inside a projected $2\\,r_c$, of their parent clusters. We find a similar result in $\\omega$Cen for BSSs with $v\\sin(i)\\!>\\!70$ km s$^{-1}$ which are all, except for two, concentrated...

  17. MOCCA code for star cluster simulations - V. Initial globular cluster conditions influence on blue stragglers

    CERN Document Server

    Hypki, Arkadiusz

    2016-01-01

    The paper presents an analysis of properties of populations of blue stragglers (BSs) in evolving globular clusters, based on numerical simulations done with the MOCCA code for various initial globular clusters conditions. We find that various populations of BSs strongly depend on the initial semi-major axes distributions. With a significant number of compact binaries, the number of evolutionary BSs can be also significant. In turn, for semi-major axes distributions preferring binaries with wider orbits, dynamical BSs are the dominant ones. Their formation scenario is very distinct: for wide binaries the number of dynamical interactions is significantly larger. Most interactions are weak and increase only slightly the eccentricities. However, due to a large number of such interactions, the eccentricities of a number of binaries finally get so large that the stars collide. We study how larger initial clusters' concentrations influence the BSs. Besides the expected increase of the number of dynamically created B...

  18. Blue straggler star populations in globular clusters. I. Dynamical properties of blue straggler stars in NGC 3201, NGC 6218, and ω Centauri

    Energy Technology Data Exchange (ETDEWEB)

    Simunovic, Mirko; Puzia, Thomas H., E-mail: msimunov@astro.puc.cl, E-mail: tpuzia@astro.puc.cl [Institute of Astrophysics, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago (Chile)

    2014-02-10

    We present the first dynamical study of blue straggler stars (BSSs) in three Galactic globular clusters, NGC 3201, NGC 5139 (ω Cen), and NGC 6218, based on medium-resolution spectroscopy (R ≈ 10, 000) obtained with the Inamori-Magellan Areal Camera and Spectrograph mounted at the 6.5 m Baade Magellan telescope. Our BSS candidate selection technique uses HST/ACS and ESO/WFI photometric data out to >4.5 r{sub c} . We use radial velocity measurements to discard non-members and achieve a success rate of ∼93%, which yields a sample of 116 confirmed BSSs. Using the penalized pixel-fitting method (pPXF), we measure the vsin (i) values of the sample BSSs and find their distribution functions peaked at slow velocities with a long tail toward fast velocities in each globular cluster. About 90% of the BSS population in NGC 3201 and NGC 6218 exhibits values in the range 10-50 km s{sup –1}, while about 80% of the BSSs in ω Cen show vsin (i) values between 20 and 70 km s{sup –1}. We find that the BSSs in NGC 3201 and NGC 6218 that show vsin (i) > 50 km s{sup –1} are all found in the central cluster regions, inside a projected 2r{sub c} , of their parent clusters. We find a similar result in ω Cen for BSSs with vsin (i) > 70 km s{sup –1}, which are all, except for two, concentrated inside 2r{sub c} . In all globular clusters, we find rapidly rotating BSSs that have relatively high differential radial velocities that likely put them on hyperbolic orbits, suggestive of strong dynamical interactions in the past. Based on stellar spin-down and dynamical crossing timescales, we estimate that all the observed rapidly rotating BSSs are likely to form in their central cluster regions no longer than ∼300 Myr ago and may be subsequently ejected from their host globular clusters. Using dereddened V – I colors of our photometric selection, we show that blue BSSs in ω Cen with (V – I){sub 0} ≲ 0.25 mag show a significantly increased vsin (i) dispersion compared with

  19. Cosmic-Lab: Chemical and kinematical properties of Blue Straggler stars in Galactic Globular Clusters

    CERN Document Server

    Lovisi, L

    2014-01-01

    Blue straggler stars (BSSs) are brighter and bluer than the main-sequence (MS) turnoff and more massive than MS stars.Two scenarios for their formation have been proposed: collision-induced stellar mergers (COL-BSSs),or mass-transfer in binary systems (MT-BSSs).Depleted surface abundances of C and O are expected for MT-BSSs,whereas no chemical anomalies are predicted for COL-BSSs. Both MT and COL-BSSs should rotate fast,but braking mechanisms may intervene with efficiencies and time-scales unknown,thus preventing a clear prediction of the expected rotational velocities. In this context,an extensive survey is ongoing by using FLAMES@VLT, with the aim to obtain abundance patterns and rotational velocities for representative samples of BSSs in Galactic GCs.A sub-population of CO-depleted BSSs has been identified in 47 Tuc,with only one fast rotating star detected (Ferraro et al.2006). For this PhD Thesis work I analyzed FLAMES spectra of more than 130 BSSs in 4 GCs:M4,NGC 6397,M30 and {\\omega}Centauri.This is th...

  20. Blue Straggler Stars in Globular Clusters: a powerful tool to probe the internal dynamical evolution of stellar systems

    CERN Document Server

    Ferraro, Francesco R; Dalessandro, Emanuele; Mucciarelli, Alessio; Lovisi, Loredana

    2014-01-01

    This chapter presents an overview of the main observational results obtained to date about Blue Straggler Stars (BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency, radial distribution, chemical composition and rotational properties are presented and discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical age of stellar systems, thus allowing the definition of the first empirical "dynamical clock".

  1. MOCCA code for star cluster simulations - VI. Bimodal spatial distribution of blue stragglers

    CERN Document Server

    Hypki, Arkadiusz

    2016-01-01

    The paper presents an analysis of formation mechanism and properties of spatial distributions of blue stragglers in evolving globular clusters, based on numerical simulations done with the MOCCA code. First, there are presented N-body and MOCCA simulations which try to reproduce the simulations presented by Ferraro (2012). Then, the agreement between N-body and the MOCCA code is shown. Finally, we discuss the formation process of the bimodal distribution. We report that so-called bimodal spatial distribution of blue stragglers is a very transient feature. It is formed for one snapshot in time and it can easily vanish in the next one. Moreover, we show that the radius of avoidance proposed by Ferraro (2012) goes out of sync with the apparent minimum of the bimodal distribution after about two half-mass relaxation times. This finding creates a real challenge for the dynamical clock, which uses this radius to determine the dynamical age of globular clusters. Additionally, the paper discusses a few important prob...

  2. Blue straggler star populations in globular clusters - II. Proper-motion cleaned HST catalogues of BSSs in 38 Galactic GCs

    Science.gov (United States)

    Simunovic, Mirko; Puzia, Thomas H.

    2016-11-01

    We present new blue straggler star (BSS) catalogues in 38 Milky Way globular clusters (GCs) based on multipassband and multi-epoch treasury survey data from the Hubble Space Telescope. We measure precise astrometry and relative proper motions of stars in all target clusters and performed a subsequent cluster membership selection. We study the accuracy of our proper-motion measurements using estimates of central velocity dispersions and find very good agreement with previous studies in the literature. Finally, we present a homogeneous BSS selection method, that expands the classic BSS selection parameter space to more evolved BSS evolutionary stages. We apply this method to the proper-motion cleaned GC star catalogues in order to define proper-motion cleaned BSS catalogues in all 38 GCs, which we make publicly available to enable further study and follow-up observations.

  3. Blue Straggler Star Populations in Globular Clusters: II. Proper-Motion Cleaned HST Catalogs of BSSs in 38 Galactic GCs

    CERN Document Server

    Simunovic, Mirko

    2016-01-01

    We present new Blue Straggler Star (BSS) catalogs in 38 Milky Way globular clusters (GCs) based on multi-passband and multi-epoch treasury survey data from the Hubble Space Telescope. We measure precise astrometry and relative proper motions of stars in all target clusters and performed a subsequent cluster membership selection. We study the accuracy of our proper motion measurements using estimates of central velocity dispersions and find very good agreement with previous studies in the literature. Finally, we present a homogeneous BSS selection method, that expands the classic BSS selection parameter space to more evolved BSS evolutionary stages. We apply this method to the proper-motion cleaned GC star catalogs in order to define proper-motion cleaned BSS catalogs in all 38 GCs, which we make publicly available to enable further study and follow-up observations.

  4. Blue Straggler Stars a direct comparison of Star counts and population ratios in six Galactic Globular Clusters

    CERN Document Server

    Ferraro, F R; Rood, R T; Paltrinieri, B; Buonanno, R; Ferraro, Francesco R.; Sills, Alison; Rood, Robert T.; Paltrinieri, Barbara; Buonanno, Roberto

    2003-01-01

    The central regions of six Galactic Globular Clusters (GGCs) (M3, M80, M10, M13, M92 and NGC 288) have been imaged using HST-WFPC2 and the ultraviolet (UV) filters (F255W, F336W). The selected sample covers a large range in both central density and metallicity ([Fe/H]). In this paper, we present a direct cluster-to-cluster comparison of the Blue Stragglers Stars (BSS) population as selected from (m_{255},m_{255}-m_{336}) Color Magnitude Diagrams (CMDs). We have found:(a) BSS in three of the clusters (M3, M80, M92) are much more concentrated toward the center of the cluster than the red giants; because of the smaller BSS samples for the other clusters we can only note that the BSS radial distributions are consistent with central concentration; (b) the specific frequency of BSS varies greatly from cluster to cluster. The most interesting result is that the two clusters with largest BSS specific frequency are at the central density extremes of our sample: NGC 288 (lowest central density) and M80 (highest). This ...

  5. Where the Blue Stragglers Roam: Searching for a Link Between Formation and Environment

    CERN Document Server

    Leigh, N; Knigge, C; Leigh, Nathan; Sills, Alison; Knigge, Christian

    2007-01-01

    The formation of blue stragglers is still not completely understood, particularly the relationship between formation environment and mechanism. We use a large, homogeneous sample of blue stragglers in the cores of 57 globular clusters to investigate the relationships between blue straggler populations and their environments. We use a consistent definition of ``blue straggler'' based on position in the color-magnitude diagram, and normalize the population relative to the number of red giant branch stars in the core. We find that the previously determined anti-correlation between blue straggler frequency and total cluster mass is present in the purely core population. We find some weak correlations with central velocity dispersion and with half-mass relaxation time. The blue straggler frequency does not show any trend with any other cluster parameter. Even though collisions may be expected to be a dominant blue straggler formation process in globular cluster cores, we find no correlation between the frequency o...

  6. The Frequency of Field Blue-Straggler Stars in the Thick Disk and Halo System of the Galaxy

    CERN Document Server

    Santucci, Rafael M; Rossi, Silvia; Beers, Timothy C; Reggiani, Henrique M; Lee, Young Sun; Xue, Xiang-Xiang; Carollo, Daniela

    2015-01-01

    We present an analysis of a new, large sample of field blue-straggler stars (BSSs) in the thick disk and halo system of the Galaxy, based on stellar spectra obtained during the Sloan Digital Sky Survey (SDSS) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Using estimates of stellar atmospheric parameters obtained from application of the SEGUE Stellar Parameter Pipeline, we obtain a sample of some 8000 BSSs, which are considered along with a previously selected sample of some 4800 blue horizontal-branch (BHB) stars. We derive the ratio of BSSs to BHB stars, F$_{\\rm BSS/BHB}$, as a function of Galactocentric distance and distance from the Galactic plane. The maximum value found for F$_{\\rm BSS/BHB}$ is $\\sim~$4.0 in the thick disk (at 3 kpc $<$ $|$Z$|$ $<$ 4 kpc), declining to on the order of $\\sim~1.5-2.0$ in the inner-halo region; this ratio continues to decline to $\\sim~$1.0 in the outer-halo region. We associate a minority of field BSSs with a likely extragalactic origin; ...

  7. MOST satellite photometry of stars in the M67 field: Eclipsing binaries, blue stragglers and delta-Scuti variables

    CERN Document Server

    Pribulla, Theodor; Matthews, Jaymie M; Kuschnig, Rainer; Rowe, Jason F; Guenther, David B; Moffat, Anthony F J; Sasselov, Dimitar; Walker, Gordon A H; Weiss, Werner W

    2008-01-01

    We present two series of MOST (Microvariability & Oscillations of STars) space-based photometry, covering nearly continuously 10 days in 2004 and 30 days in 2007, of selected variable stars in the upper Main Sequence of the old open cluster M67. New high-precision light curves were obtained for the blue-straggler binary/triple systems AH Cnc, ES Cnc and EV Cnc. The precision and phase coverage of ES Cnc and EV Cnc is by far superior to any previous observations. The light curve of ES Cnc is modelled in detail, assuming two dark photospheric spots and Roche geometry. An analysis of the light curve of AH Cnc indicates a low mass ratio (q about 0.13) and a high inclination angle for this system. Two new long-period eclipsing binaries, GSC 814-323 and HD75638 (non-members of M67) were discovered. We also present ground-based DDO spectroscopy of ES Cnc and of the newly found eclipsing binaries. Especially interesting is HD75638, a member of a visual binary, which must itself be a triple or a higher-multiplicit...

  8. The ages of young star clusters, massive blue stragglers and the upper mass limit of stars: analysing age dependent stellar mass functions

    CERN Document Server

    Schneider, Fabian R N; de Mink, Selma E; Langer, Norbert; Stolte, Andrea; de Koter, Alex; Gvaramadze, Vasilii V; Hußmann, Benjamin; Liermann, Adriane; Sana, Hugues

    2013-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters which can be used to infer their ages and to identify products of binary evolution. We model the observed present day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages to 3.5$\\pm$0.7 Myr and 4.8$\\pm$1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e. the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte ...

  9. Blue straggler formation at core collapse

    CERN Document Server

    Banerjee, Sambaran

    2016-01-01

    Among the most striking feature of blue straggler stars (BSS) is the presence of multiple sequences of BSSs in the colour-magnitude diagrams (CMDs) of several globular clusters. It is often envisaged that such a multiple BSS sequence would arise due a recent core collapse of the host cluster, triggering a number of stellar collisions and binary mass transfers simultaneously over a brief episode of time. Here we examine this scenario using direct N-body computations of moderately massive star clusters (of order 10^4 Msun ). As a preliminary attempt, these models are initiated with approx. 8-10 Gyr old stellar population and King profiles of high concentrations, being "tuned" to undergo core collapse quickly. BSSs are indeed found to form in a "burst" at the onset of the core collapse and several of such BS-bursts occur during the post-core-collapse phase. In those models that include a few percent primordial binaries, both collisional and binary BSSs form after the onset of the (near) core-collapse. However, t...

  10. A MEGACAM SURVEY OF OUTER HALO SATELLITES. II. BLUE STRAGGLERS IN THE LOWEST STELLAR DENSITY SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Santana, Felipe A.; Munoz, Ricardo R. [Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago (Chile); Geha, Marla [Astronomy Department, Yale University, New Haven, CT 06520 (United States); Cote, Patrick; Stetson, Peter [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC, V9E 2E7 (Canada); Simon, Joshua D. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Djorgovski, S. G., E-mail: fsantana@das.uchile.cl, E-mail: rmunoz@das.uchile.cl [Astronomy Department, California Institute of Technology, Pasadena, CA, 91125 (United States)

    2013-09-10

    We present a homogeneous study of blue straggler stars across 10 outer halo globular clusters, 3 classical dwarf spheroidal galaxies, and 9 ultra-faint galaxies based on deep and wide-field photometric data taken with MegaCam on the Canada-France-Hawaii Telescope. We find blue straggler stars to be ubiquitous among these Milky Way satellites. Based on these data, we can test the importance of primordial binaries or multiple systems on blue straggler star formation in low-density environments. For the outer halo globular clusters, we find an anti-correlation between the specific frequency of blue stragglers and absolute magnitude, similar to that previously observed for inner halo clusters. When plotted against density and encounter rate, the frequency of blue stragglers is well fit by a single trend with a smooth transition between dwarf galaxies and globular clusters; this result points to a common origin for these satellites' blue stragglers. The fraction of blue stragglers stays constant and high in the low encounter rate regime spanned by our dwarf galaxies, and decreases with density and encounter rate in the range spanned by our globular clusters. We find that young stars can mimic blue stragglers in dwarf galaxies only if their ages are 2.5 {+-} 0.5 Gyr and they represent {approx}1%-7% of the total number of stars, which we deem highly unlikely. These results point to mass-transfer or mergers of primordial binaries or multiple systems as the dominant blue straggler formation mechanism in low-density systems.

  11. A Megacam Survey of Outer Halo Satellites. II. Blue Stragglers in the Lowest Stellar Density Systems

    CERN Document Server

    Santana, Felipe A; Geha, Marla; Cote, Patrick; Stetson, Peter; Simon, Joshua D; Djorgovski, S G

    2013-01-01

    We present a homogeneous study of blue straggler stars across ten outer halo globular clusters, three classical dwarf spheroidal and nine ultra-faint galaxies based on deep and wide-field photometric data taken with MegaCam on the Canada-France-Hawaii Telescope. We find blue straggler stars to be ubiquitous among these Milky Way satellites. Based on these data, we can test the importance of primordial binaries or multiple systems on blue straggler star formation in low density environments. For the outer halo globular clusters we find an anti-correlation between the specific frequency of blue straggler and absolute magnitude, similar to that previously observed for inner halo clusters. When plotted against density and encounter rate, the frequency of blue stragglers are well fitted by single trends with smooth transitions between dwarf galaxies and globular clusters, which points to a common origin for their blue stragglers. The fraction of blue stragglers stays constant and high in the low encounter rate reg...

  12. Modeling blue stragglers in young clusters

    Institute of Scientific and Technical Information of China (English)

    Pin Lu; Li-Cai Deng; Xiao-Bin Zhang

    2011-01-01

    A grid of binary evolution models are calculated for the study of a blue straggler (BS) population in intermediate age (log Age =7.85 - 8.95) star clusters.The BS formation via mass transfer and merging is studied systematically using our models.Both Case A and B close binary evolutionary tracks are calculated for a large range of parameters.The results show that BSs formed via Case B are generally bluer and even more luminous than those produced by Case A.Furthermore,the larger range in orbital separations of Case B models provides a probability of producing more BSs than in Case A.Based on the grid of models,several Monte-Carlo simulations of BS populations in the clusters in the age range are carried out.The results show that BSs formed via different channels populate different areas in the color magnitude diagram (CMD).The locations of BSs in CMD for a number of clusters are compared to our simulations as well.In order to investigate the influence of mass transfer efficiency in the models and simulations,a set of models is also calculated by implementing a constant mass transfer efficiency,β =0.5,during Roche lobe overflow (Case A binary evolution excluded).The result shows BSs can be formed via mass transfer at any given age in both cases.However,the distributions of the BS populations on CMD are different.

  13. DETECTION OF WHITE DWARF COMPANIONS TO BLUE STRAGGLERS IN THE OPEN CLUSTER NGC 188: DIRECT EVIDENCE FOR RECENT MASS TRANSFER

    Energy Technology Data Exchange (ETDEWEB)

    Gosnell, Natalie M.; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin - Madison, 475 N. Charter St., Madison, WI 53706 (United States); Geller, Aaron M. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208 (United States); Sills, Alison [Department of Physics and Astronomy, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4M1 (Canada); Leigh, Nathan [Department of Physics, University of Alberta, CCIS 4-183, Edmonton, AB T6G 2E1 (Canada); Knigge, Christian, E-mail: gosnell@astro.wisc.edu [School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 IBJ (United Kingdom)

    2014-03-01

    Several possible formation pathways for blue straggler stars have been developed recently, but no one pathway has yet been observationally confirmed for a specific blue straggler. Here we report the first findings from a Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel far-UV photometric program to search for white dwarf companions to blue straggler stars. We find three hot and young white dwarf companions to blue straggler stars in the 7 Gyr open cluster NGC 188, indicating that mass transfer in these systems ended less than 300 Myr ago. These companions are direct and secure observational evidence that these blue straggler stars were formed through mass transfer in binary stars. Their existence in a well-studied cluster environment allows for observational constraints of both the current binary system and the progenitor binary system, mapping the entire mass transfer history.

  14. Blue Stragglers in Globular Clusters: Observations, Statistics and Physics

    CERN Document Server

    Knigge, Christian

    2014-01-01

    This chapter explores how we might use the observed {\\em statistics} of blue stragglers in globular clusters to shed light on their formation. This means we will touch on topics also discussed elsewhere in this book, such as the discovery and implications of bimodal radial distributions and the "double sequences" of blue stragglers that have recently been found in some clusters. However, we will focus particularly on the search for a "smoking gun" correlation between the number of blue stragglers in a given globular cluster and a physical cluster parameter that would point towards a particular formation channel. As we shall see, there is little evidence for an intrinsic correlation between blue straggler numbers and stellar collision rates, even in dense cluster cores. On the other hand, there is a clear correlation between blue straggler numbers and the total (core) mass of the cluster. This would seem to point towards a formation channel involving binaries, rather than dynamical encounters. However, the cor...

  15. Hubble Space Telescope proper motion (HSTPROMO) catalogs of Galactic globular clusters. IV. Kinematic profiles and average masses of blue straggler stars

    CERN Document Server

    Baldwin, A T; van der Marel, R P; Bianchini, P; Bellini, A; Anderson, J

    2016-01-01

    We make use of the Hubble Space Telescope proper-motion catalogs derived by Bellini et al. (2014) to produce the first radial velocity-dispersion profiles sigma(R) for blue straggler stars (BSSs) in Galactic globular clusters (GCs), as well as the first dynamical estimates for the average mass of the entire BSS population. We show that BSSs typically have lower velocity dispersions than stars with mass equal to the main-sequence turnoff mass, as one would expect for a more massive population of stars. Since GCs are expected to experience some degree of energy equipartition, we use the relation sigma~M^-eta, where eta is related to the degree of energy equipartition, along with our velocity-dispersion profiles to estimate BSS masses. We estimate eta as a function of cluster relaxation from recent Monte Carlo cluster simulations by Bianchini et al. (2016b) and then derive an average mass ratio M_BSS /M_MSTO=1.50+/-0.14 and an average mass M_BSS=1.22+/-0.12 M_Sun from 598 BSSs across 19 GCs. The final error bars...

  16. Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. IV. Kinematic Profiles and Average Masses of Blue Straggler Stars

    Science.gov (United States)

    Baldwin, A. T.; Watkins, L. L.; van der Marel, R. P.; Bianchini, P.; Bellini, A.; Anderson, J.

    2016-08-01

    We make use of the Hubble Space Telescope proper-motion catalogs derived by Bellini et al. to produce the first radial velocity dispersion profiles σ (R) for blue straggler stars (BSSs) in Galactic globular clusters (GCs), as well as the first dynamical estimates for the average mass of the entire BSS population. We show that BSSs typically have lower velocity dispersions than stars with mass equal to the main-sequence turnoff mass, as one would expect for a more massive population of stars. Since GCs are expected to experience some degree of energy equipartition, we use the relation σ \\propto {M}-η , where η is related to the degree of energy equipartition, along with our velocity dispersion profiles to estimate BSS masses. We estimate η as a function of cluster relaxation from recent Monte Carlo cluster simulations by Bianchini et al. and then derive an average mass ratio {M}{BSS}/{M}{MSTO}=1.50+/- 0.14 and an average mass {M}{BSS}=1.22+/- 0.12 M ⊙ from 598 BSSs across 19 GCs. The final error bars include any systematic errors that are random between different clusters, but not any potential biases inherent to our methodology. Our results are in good agreement with the average mass of {M}{BSS}=1.22+/- 0.06 M ⊙ for the 35 BSSs in Galactic GCs in the literature with properties that have allowed individual mass determination. Based on proprietary and archival observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  17. Hydrodynamics of stellar mergers and the formation of blue stragglers

    CERN Document Server

    Rasio, F A

    1995-01-01

    The hydrodynamics of stellar collisions and mergers is discussed in the context of blue straggler formation. Emphasis is placed on the very important question of hydrodynamic mixing during the merger process. Recent results of three-dimensional hydrodynamic calculations suggest that the merger remnants produced by stellar collisions are typically {\\em not\\/} well-mixed. However, comparisons between the observed colors and numbers of blue stragglers in dense clusters and the predictions of theoretical calculations for their stellar evolution appear to require that the initial blue-straggler models be close to chemically homogeneous. The resolution of this apparent conflict is likely to involve the development of convection or other thermal instabilitites that can provide efficient mixing during the contraction of the merger remnant to a thermal equilibrium state on the main sequence.

  18. Formation and Evolution of Blue Stragglers in 47 Tucanae

    CERN Document Server

    Parada, Javiera; Heyl, Jeremy; Kalirai, Jason; Goldsbury, Ryan

    2016-01-01

    Blue stragglers (BSS) are stars whose position in the Color-Magnitude Diagram (CMD) places them above the main sequence turn-off (TO) point of a star cluster. Using data from the core of 47 Tuc in the ultraviolet (UV), we have identified various stellar populations in the CMD, and used their radial distributions to study the evolution and origin of BSS, and obtain a dynamical estimate of the mass of BSS systems. When we separate the BSS into two samples by their magnitude, we find that the bright BSS show a much more centrally concentrated radial distribution and thus higher mass estimate (over twice the TO mass for these BSS systems), suggesting an origin involving triple or multiple stellar systems. In contrast, the faint BSS are less concentrated, with a radial distribution similar to the main sequence (MS) binaries, pointing to the MS binaries as the likely progenitors of these BSS. Putting our data together with available photometric data in the visible and using MESA evolutionary models, we calculate th...

  19. Binary Evolution: Roche Lobe Overflow and Blue Stragglers

    CERN Document Server

    Ivanova, Natalia

    2014-01-01

    One of the principal mechanisms that is responsible for the origin of blue stragglers is mass transfer that takes place while one of the binary companions overfills its Roche lobe. In this Chapter, we overview the theoretical understanding of mass transfer via Roche lobe overflow: classification, how both the donor and of the accretor respond to the mass transfer on different timescales (adiabatic response, equilibrium response, superadiabatic response, time-dependent response) for different types of their envelopes (convective and radiative). These responses, as well as the assumption on how liberal the process is, are discussed in terms of the stability of the ensuing mass transfer. The predictions of the theory of mass transfer via Roche lobe overflow are then briefly compared with the observed mass-transferring systems with both degenerate and non-degenerate donors. We conclude with the discussion which cases of mass transfer and which primordial binaries could be responsible for blue stragglers formation...

  20. The K2 M67 Study: An Evolved Blue Straggler in M67 from K2 Mission Asteroseismology

    CERN Document Server

    Leiner, Emily; Stello, Dennis; Vanderburg, Andrew

    2016-01-01

    Yellow straggler stars (YSSs) fall above the subgiant branch in optical color-magnitude diagrams, between the blue stragglers and the red giants. YSSs may represent a population of evolved blue stragglers, but none have the direct and precise mass and radius measurements needed to determine their evolutionary states and formation histories. Here we report the first asteroseismic mass and radius measurements of such a star, the yellow straggler S1237 in the open cluster M67. We apply asteroseismic scaling relations to a frequency analysis of the Kepler K2 light curve and find a mass of 2.9 $\\pm$ 0.2 M$_{\\odot}$ and a radius of 9.2 $\\pm$ 0.2 R$_{\\odot}$. This is more than twice the mass of the main- sequence turnoff in M67, suggesting S1237 is indeed an evolved blue straggler. S1237 is the primary in a spectroscopic binary. We update the binary orbital solution and use spectral energy distribution (SED) fitting to constrain the color-magnitude diagram (CMD) location of the secondary star. We find that the secon...

  1. Blue Stragglers in Clusters and Integrated Spectral Properties of Stellar Populations

    CERN Document Server

    Xin, Yu

    2014-01-01

    Blue straggler stars are the most prominent bright objects in the colour-magnitude diagram of a star cluster that challenges the theory of stellar evolution. Star clusters are the closest counterparts of the theoretical concept of simple stellar populations (SSPs) in the Universe. SSPs are widely used as the basic building blocks to interpret stellar contents in galaxies. The concept of an SSP is a group of coeval stars which follows a given distribution in mass, and has the same chemical property and age. In practice, SSPs are more conveniently made by the latest stellar evolutionary models of single stars. In reality, however, stars can be more complicated than just single either at birth time or during the course of evolution in a typical environment. Observations of star clusters show that there are always exotic objects which do not follow the predictions of standard theory of stellar evolution. Blue straggler stars (BSSs), as discussed intensively in this book both observationally and theoretically, are...

  2. HIP 10725: The first solar twin/analogue field blue straggler

    Science.gov (United States)

    Schirbel, Lucas; Meléndez, Jorge; Karakas, Amanda I.; Ramírez, Iván; Castro, Matthieu; Faria, Marcos A.; Lugaro, Maria; Asplund, Martin; Tucci Maia, Marcelo; Yong, David; Howes, Louise; do Nascimento, José D.

    2015-12-01

    Context. Blue stragglers are easy to identify in globular clusters, but are much harder to identify in the field. Here we present the serendipitous discovery of one field blue straggler, HIP 10725, that closely matches the Sun in mass and age, but with a metallicity slightly lower than solar. Aims: We characterise the solar twin/analogue HIP 10725 to assess whether this star is a blue straggler. Methods: We employed spectra with high resolution (R ~ 105) and high signal-to-noise ratio (330) obtained with UVES at the VLT to perform a differential abundance analysis of the solar analogue HIP 10725. Radial velocities obtained by other instruments were also used to check for binarity. We also studied its chromospheric activity, age, and rotational velocity. Results: HIP 10725 is severely depleted in beryllium ([ Be/H ] ≤ -1.2 dex) for its stellar parameters and age. The abundances relative to solar of the elements with Z ≤ 30 show a correlation with condensation temperature, and the neutron capture elements produced by the s-process are greatly enhanced, while the r-process elements seem normal. We found its projected rotational velocity (vsini = 3.3 ± 0.1 km s-1) to be significantly higher than solar and incompatible with its isochrone-derived age. Radial velocity monitoring shows that the star has a binary companion. Conclusions: Based on the high s-process element enhancements and low beryllium abundance, we suggest that HIP 10725 has been polluted by mass transfer from an AGB star that probably had an initial mass of about 2 M⊙. The radial velocity variations suggest the presence of an unseen binary companion, probably the remnant of a former AGB star. Isochrones predict a solar-age star, but this disagrees with the high projected rotational velocity and high chromospheric activity. We conclude that HIP 10725 is a field blue straggler, rejuvenated by the mass-transfer process of its former AGB companion. Based on observations obtained at the European

  3. The WFPC2 ultraviolet survey: The blue straggler population in NGC 5824

    International Nuclear Information System (INIS)

    We have used a combination of high-resolution Hubble Space Telescope Wide Field Planetary Camera 2 and wide-field ground-based observations, in ultraviolet and optical bands, to study the blue straggler star population of the massive outer halo globular cluster NGC 5824 over its entire radial extent. We have computed the center of the cluster and constructed the radial density profile from detailed star counts. The profile is well reproduced by a Wilson model with a small core (rc ≅ 4.''4) and a concentration parameter c ≅ 2.74. We also present the first age determination for this cluster. From a comparison with isochrones, we find t = 13 ± 0.5 Gyr. We discuss this result in the context of the observed age-metallicity relation of Galactic globular clusters. A total of 60 bright blue stragglers has been identified. Their radial distribution is found to be bimodal, with a central peak, a well-defined minimum at r ∼ 20'', and an upturn at large radii. In the framework of the dynamical clock recently defined by Ferraro et al., this feature suggests that NGC 5824 is a cluster of intermediate dynamical age.

  4. Blue Straggler Masses from Pulsation Properties. II. Topology of the Instability Strip

    Science.gov (United States)

    Fiorentino, G.; Marconi, M.; Bono, G.; Dalessandro, E.; Ferraro, F. R.; Lanzoni, B.; Lovisi, L.; Mucciarelli, A.

    2015-09-01

    We present a new set of nonlinear, convective radial pulsation models for main-sequence stars computed assuming three metallicities: Z = 0.0001, 0.001, and 0.008. These chemical compositions bracket the metallicity of stellar systems hosting SX Phoenicis stars (SXPs, or pulsating Blue Stragglers), namely, Galactic globular clusters and nearby dwarf spheroidals. Stellar masses and luminosities of the pulsation models are based on alpha-enhanced evolutionary tracks from the BASTI website. We are able to define the topology of the instability strip (IS) and in turn the pulsation relations for the first four pulsation modes. We found that third overtones approach a stable nonlinear limit cycle. Predicted and empirical ISs agree quite well in the case of 49 SXPs belonging to ω Cen. We used theoretical period-luminosity (PL) relations in B and V bands to identify their pulsation mode. We assumed Z = 0.001 and Z = 0.008 as mean metallicities of SXPs in ω Cen. We found respectively 13-15 fundamental, 22-6 first-overtone, and 9-4 second-overtone modes. Five are unstable in the third-overtone mode only for Z = 0.001. Using the above mode identification and applying the proper mass-dependent PL relations, we found masses ranging from ˜1.0 to 1.2 {M}⊙ ( = 1.12, σ =0.04 {M}⊙ ) and from ˜1.2 to 1.5 {M}⊙ ( = 1.33, σ =0.03 {M}⊙ ) for Z = 0.001 and 0.008, respectively. Our investigation supports the use of evolutionary tracks to estimate SXP masses. We will extend our analysis to higher helium content, which may have an impact on our understanding of the blue straggler stars formation scenario.

  5. VizieR Online Data Catalog: Catalogue of Blue Stragglers (Moretti+, 2008)

    Science.gov (United States)

    Moretti, A.; de Angeli, F.; Piotto, G.

    2008-03-01

    We present the Blue Stragglers (BSS) Catalogues extracted from the photometric data base of 74 Galactic GCs published by Piotto et al., 2002, Cat. . All the clusters were observed in the F439W and F555W photometric bands pointing the HST/WFPC2 camera to the central core. Candidates were selected according to their position in the colour magnitude diagrams. A detailed description of the selection process is given in the paper. We give for each cluster a list of blue straggler candidates together with their photometric data. (2 data files).

  6. Double Blue Straggler sequences in GCs: the case of NGC 362

    CERN Document Server

    Dalessandro, E; Massari, D; Lanzoni, B; Miocchi, P; Beccari, G; Bellini, A; Sills, A; Sigurdsson, S; Mucciarelli, A; Lovisi, L

    2013-01-01

    We used high-quality images acquired with the WFC3 on board the HST to probe the blue straggler star (BSS) population of the Galactic globular cluster NGC 362. We have found two distinct sequences of BSS: this is the second case, after M 30, where such a feature has been observed. Indeed the BSS location, their extension in magnitude and color and their radial distribution within the cluster nicely resemble those observed in M 30, thus suggesting that the same interpretative scenario can be applied: the red BSS sub-population is generated by mass transfer binaries, the blue one by collisions. The discovery of four new W UMa stars, three of which lying along the red-BSS sequence, further supports this scenario. We also found that the inner portion of the density profile deviates from a King model and is well reproduced by either a mild power-law (\\alpha -0.2) or a double King profile. This feature supports the hypothesis that the cluster is currently undergoing the core collapse phase. Moreover, the BSS radial...

  7. Blue straggler masses from pulsation properties. II. Topology of the Instability Strip

    CERN Document Server

    Fiorentino, G; Bono, G; Dalessandro, E; Ferraro, F R; Lanzoni, B; Lovisi, L; Mucciarelli, A

    2015-01-01

    We present a new set of nonlinear, convective radial pulsation models for main sequence stars computed assuming three metallicities: Z=0.0001, 0.001 and 0.008. These chemical compositions bracket the metallicity of stellar systems hosting SX Phoenicis stars (SXPs or pulsating Blue Stragglers), namely Galactic globular clusters and nearby dwarf spheroidals. Stellar masses and luminosities of the pulsation models are based on alpha--enhanced evolutionary tracks from the BASTI website. We are able to define the topology of the instability strip (IS), and in turn the pulsation relations for the first four pulsation modes. We found that third overtones approach a stable nonlinear limit cycle. Predicted and empirical IS agree quite well in the case of 49 SXPs belonging to omega Cen. We used theoretical Period-Luminosity relations in B,V bands to identify their pulsation mode. We assumed Z=0.001 and Z=0.008 as mean metallicities of SXPs in omega Cen. We found respectively 13-15 fundamental, 22-6 first and 9-4 second...

  8. The ACS LCID project VII: the blue stragglers population in the isolated dSph galaxies Cetus and Tucana

    CERN Document Server

    Monelli, M; Mapelli, M; Bernard, E J; Aparicio, A; Skillman, E D; Stetson, P B; Gallart, C; Hidalgo, S L; Mayer, L; Tolstoy, E

    2011-01-01

    We present the first investigation of the Blue Straggler star (BSS) population in two isolated dwarf spheroidal galaxies of the Local Group, Cetus and Tucana. Deep HST/ACS photometry allowed us to identify samples of 940 and 1214 candidates, respectively. The analysis of the star formation histories of the two galaxies suggests that both host a population of BSSs. Specifically, if the BSS candidates are interpreted as young main sequence stars, they do not conform to their galaxy's age-metallicity relationship. The analysis of the luminosity function and the radial distributions support this conclusion, and suggest a non-collisional mechanism for the BSS formation, from the evolution of primordial binaries. This scenario is also supported by the results of new dynamical simulations presented here. Both galaxies coincide with the relationship between the BSS frequency and the absolute visual magnitude Mv found by Momany et al (2007). If this relationship is confirmed by larger sample, then it could be a valuab...

  9. Evolutionary history of four binary blue stragglers from the globular clusters \\omega Cen, M55, 47 Tuc and NGC 6752

    CERN Document Server

    Stepien, K; Rozyczka, M

    2016-01-01

    Context. Origin and evolution of blue stragglers in globular clusters is still a matter of debate. Aims. The aim of the present investigation is to reproduce the evolutionary history of four binary blue stragglers in four different clusters, for which precise values of global parameters are known. Methods. Using the model for cool close binary evolution, developed by one of us (KS), progenitors of all investigated binaries were found and their parameters evolved into the presently observed values. Results. The results show that the progenitors of the binary blue stragglers are cool close binaries with period of a few days, which transform into stragglers by rejuvenation of the initially less massive component by mass transfer from its more massive companion overflowing the inner critical Roche surface. The parameters of V209 from \\omega Cen indicate that the binary is substantially enriched in helium. This is an independent and strong evidence for the existence of the helium rich subpopulation in this cluster...

  10. HIP 10725: The First Solar Twin/Analogue Field Blue Straggler

    CERN Document Server

    Schirbel, Lucas; Karakas, Amanda I; Ramirez, Ivan; Castro, Matthieu; Faria, Marcos A; Lugaro, Maria; Asplund, Martin; Maia, Marcelo Tucci; Yong, David; Howes, Louise; Nascimento, J D do

    2015-01-01

    [Context]. Blue stragglers are easy to identify in globular clusters, but are much harder to identify in the field. Here we present the serendipitous discovery of one field blue straggler, HIP 10725, that closely matches the Sun in mass and age, but with a metallicity slightly lower than the Sun's. [Methods]. We employ high resolution (R $\\sim 10^5$) high S/N (330) VLT/UVES spectra to perform a differential abundance analysis of the solar analogue HIP 10725. Radial velocities obtained by other instruments were also used to check for binarity. We also study its chromospheric activity, age and rotational velocity. [Results]. We find that HIP 10725 is severely depleted in beryllium ([Be/H] <= -1.2 dex) for its stellar parameters and age. The abundances relative to solar of the elements with Z <= 30 show a correlation with condensation temperature and the neutron capture elements produced by the s-process are greatly enhanced, while the r-process elements seem normal. We found its projected rotational veloc...

  11. The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study

    CERN Document Server

    Beccari, G; Ferraro, F R; Pulone, L; Bellazzini, M; Pecci, F Fusi; Rood, R T; Giallongo, E; Ragazzoni, R; Grazian, A; Baruffolo, A; Bouche, N; Buschkamp, P; De Santis, C; Diolaiti, E; Di Paola, A; Farinato, J; Fontana, A; Gallozzi, S; Gasparo, F; Gentile, G; Pasian, F; Pedichini, F; Smareglia, R; Speziali, R; Testa, V; Vernet, E

    2008-01-01

    We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ~60'' (~2 r_c) from the cluster center. This value turns out to be a factor of two smaller than the radius of avoidance (r_avoid, the radius within which all the stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r_avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less e...

  12. THE ACS LCID PROJECT. VII. THE BLUE STRAGGLERS POPULATION IN THE ISOLATED dSph GALAXIES CETUS AND TUCANA

    International Nuclear Information System (INIS)

    We present the first investigation of the Blue Straggler star (BSS) population in two isolated dwarf spheroidal galaxies of the Local Group, Cetus and Tucana. Deep Hubble Space Telescope/Advanced Camera for Surveys photometry allowed us to identify samples of 940 and 1214 candidates, respectively. The analysis of the star formation histories of the two galaxies suggests that both host a population of BSSs. Specifically, if the BSS candidates are interpreted as young main sequence stars, they do not conform to their galaxy's age-metallicity relationship. The analysis of the luminosity function and the radial distributions supports this conclusion, and suggests a non-collisional mechanism for the BSS formation, from the evolution of primordial binaries. This scenario is also supported by the results of new dynamical simulations presented here. Both galaxies coincide with the relationship between the BSS frequency and the absolute visual magnitude MV found by Momany et al. If this relationship is confirmed by larger sample, then it could be a valuable tool to discriminate between the presence of BSSs and galaxies hosting truly young populations.

  13. CENSUS OF BLUE STARS IN SDSS DR8

    Energy Technology Data Exchange (ETDEWEB)

    Scibelli, Samantha [Burnt Hills-Ballston Lake High School, 88 Lake Hill Road, Ballston, NY 12027 (United States); Newberg, Heidi Jo; Carlin, Jeffrey L. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States); Yanny, Brian, E-mail: heidi@rpi.edu [Experimental Astrophysics Group, Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States)

    2015-01-01

    We present a census of the 12,060 spectra of blue objects ((g – r){sub 0} < –0.25) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies, and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10,856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise ratio, and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf-M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179, quasi-stellar objects (QSOs), and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by eye, and diagnostic plots that show the positions, colors, apparent magnitudes, proper motions, etc., for each classification. Future surveys will be able to use templates similar to stars in each of the classes we identify to automatically classify blue stars, including rare types.

  14. Census of blue stars in SDSS DR8

    CERN Document Server

    Scibelli, Samantha; Carlin, Jeffrey L; Yanny, Brian

    2014-01-01

    We present a census of the 12,060 spectra of blue objects ($(g-r)_0<-0.25$) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10,856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise (S/N), and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf - M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179 QSOs, and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by ...

  15. Today a Duo, But Once a Trio? The Double White Dwarf HS 2220$+$2146 May Be A Post-Blue Straggler Binary

    CERN Document Server

    Andrews, Jeff J; Brown, Warren R; Gosnell, Natalie M; Gianninas, A; Kilic, Mukremin; Koester, Detlev

    2016-01-01

    For sufficiently wide orbital separations {\\it a}, the two members of a stellar binary evolve independently. This implies that in a wide double white dwarf (DWD), the more massive WD should always be produced first, when its more massive progenitor ends its main-sequence life, and should therefore be older and cooler than its companion. The bound, wide DWD HS 2220$+$2146 ($a\\approx500$ AU) does not conform to this picture: the more massive WD is the younger, hotter of the pair. We show that this discrepancy is unlikely to be due to past mass-transfer phases or to the presence of an unresolved companion. Instead, we propose that HS 2220$+$2146 formed through a new wide DWD evolutionary channel involving the merger of the inner binary in a hierarchical triple system. The resulting blue straggler and its wide companion then evolved independently, forming the WD pair seen today. Although we cannot rule out other scenarios, the most likely formation channel has the inner binary merging while both stars are still o...

  16. When stars collide

    NARCIS (Netherlands)

    Glebbeek, E.; Pols, O.R.

    2007-01-01

    When two stars collide and merge they form a new star that can stand out against the background population in a star cluster as a blue straggler. In so called collision runaways many stars can merge and may form a very massive star that eventually forms an intermediate mass blackhole. We have perfor

  17. High-resolution spectroscopic observations of binary stars and yellow stragglers in three open clusters: NGC 2360, NGC 3680, and NGC 5822

    Energy Technology Data Exchange (ETDEWEB)

    Sales Silva, J. V.; Peña Suárez, V. J.; Katime Santrich, O. J.; Pereira, C. B.; Drake, N. A.; Roig, F., E-mail: joaovictor@on.br, E-mail: jearim@on.br, E-mail: osantrich@on.br, E-mail: claudio@on.br, E-mail: drake@on.br, E-mail: froig@on.br [Observatório Nacional/MCT, Rua Gen. José Cristino, 77, 20921-400 Rio de Janeiro (Brazil)

    2014-11-01

    Binary stars in open clusters are very useful targets in constraining the nucleosynthesis process. The luminosities of the stars are known because the distances of the clusters are also known, so chemical peculiarities can be linked directly to the evolutionary status of a star. In addition, binary stars offer the opportunity to verify a relationship between them and the straggler population in both globular and open clusters. We carried out a detailed spectroscopic analysis to derive the atmospheric parameters for 16 red giants in binary systems and the chemical composition of 11 of them in the open clusters NGC 2360, NGC 3680, and NGC 5822. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employ the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that the stars NGC 2360-92 and 96, NGC 3680-34, and NGC 5822-4 and 312 are yellow straggler stars. We show that the spectra of NGC 5822-4 and 312 present evidence of contamination by an A-type star as a secondary star. For the other yellow stragglers, evidence of contamination is given by the broad wings of the Hα. Detection of yellow straggler stars is important because the observed number can be compared with the number predicted by simulations of binary stellar evolution in open clusters. We also found that the other binary stars are not s-process enriched, which may suggest that in these binaries the secondary star is probably a faint main-sequence object. The lack of any s-process enrichment is very useful in setting constraints for the number of white dwarfs in the open cluster, a subject that is related to the birthrate of these kinds of stars in open clusters and also to the age of a

  18. Blue Horizontal Branch Stars in M92

    CERN Document Server

    Cohen, J G

    1997-01-01

    We have analyzed high dispersion and high precision spectra of 5 blue horizontal branch stars in the globular cluster M92 to establish that the projected rotational velocity for these stars ranges from 15 to 40 \\kms. This is larger than that expected based on the rotation of their main sequence progenitors, the spin down of rotation with age, and the conservation of angular momentum. Possible explanations include a rapidly rotating stellar core. An abundance analysis of these spectra of these blue HB stars in M92 yields the same results as have been obtained from the giants in this cluster. There is a hint of a trend of higher abundance as the projected surface rotational velocity increases, which could be chance and requires confirmation.

  19. Characterizing Pale Blue Dots Around FGKM Stars

    Science.gov (United States)

    Rugheimer, Sarah; Kaltenegger, Lisa; Sasselov, Dimitar; Segura, Antigona

    2015-12-01

    Exoplanet characterization of small rocky worlds will be a main focus in the coming decades. For future telescopes like JWST and UVOIR/HDST, an exoplanet’s host star will influence our ability to detect and interpret spectral features, including biosignatures. We present a complete suit of stellar models and a grid of model atmospheres for Earth-like planets at equivalent stages of geological evolution in their HZ for stellar effective temperature from Teff = 2300K to 7000K, sampling the entire FGKM stellar type range. Since M dwarfs are simultaneously the most numerous in the universe, the most active, and the most likely stars to host terrestrial exoplanets, we focus in particular on the range of UV emission possible in each sub M spectral class. The UV emission from a planet's host star dominates the photochemistry and thus the resultant observable spectral features of the planet. Using the latest UV spectra obtained by HST and IUE we model the effect of stellar activity on Earth-like planets. We also model the amount of UV flux reaching the surface for Earth-like planets at various geological epochs ranging from a pre-biotic world through the rise of oxygen and for Earth-like planets orbiting FGKM stars at equivalent stages of evolution. When modeling the remotely detectable spectra of these planets we focus on the primary detectable atmospheric features that indicate habitability on Earth, namely: H2O, CO2, O3, CH4, N2O and CH3Cl. We model spectra of Earth-like planets orbiting our grid of FGKM stars in the VIS/NIR (0.4 - 4 μm) and the IR (5 - 20 μm) range as input for future missions and concepts like UVOIR/HDST and JWST.

  20. Super Star Clusters in the Blue Dwarf Galaxy UM 462

    OpenAIRE

    Vanzi, Leonardo

    2003-01-01

    I present optical observations of the Blue Compact Dwarf Galaxy UM 462. The images of this galaxy show several bright compact sources. A careful study of these sources has revealed their nature of young Super Star Clusters. The ages determined from the analysis of the stellar continuum and $H\\alpha$ are between few and few tens Myr. The total star formation taking place into the clusters is about 0.05 $\\mathrm{M_{\\odot}/yr}$. The clusters seem to be located at the edges of two large round-lik...

  1. Blue supergiants as descendants of magnetic main sequence stars

    Science.gov (United States)

    Petermann, I.; Langer, N.; Castro, N.; Fossati, L.

    2015-12-01

    About 10% of the massive main sequence stars have recently been found to host a strong, large scale magnetic field. Both, the origin and the evolutionary consequences of these fields are largely unknown. We argue that these fields may be sufficiently strong in the deep interior of the stars to suppress convection near the outer edge of their convective core. We performed parametrised stellar evolution calculations and assumed a reduced size of the convective core for stars in the mass range 16M⊙ to 28M⊙ from the zero age main sequence until core carbon depletion. We find that such models avoid the coolest part of the main sequence band, which is usually filled by evolutionary models that include convective core overshooting. Furthermore, our "magnetic" models populate the blue supergiant region during core helium burning, i.e., the post-main sequence gap left by ordinary single star models, and some of them end their life in a position near that of the progenitor of Supernova 1987A in the Hertzsprung-Russell diagram. Further effects include a strongly reduced luminosity during the red supergiant stage, and downward shift of the limiting initial mass for white dwarf and neutron star formation.

  2. On the Blue Loops of Intermediate-Mass Stars

    CERN Document Server

    Walmswell, J J; Eldridge, J J

    2015-01-01

    We consider the blue loops in the Hertzsprung-Russell diagram that occur when intermediate-mass stars begin core helium burning. It has long been known that the excess of helium above the burning shell, the result of the contraction of the convective core during core hydrogen burning, has the effect of making such stars redder and larger than they would be otherwise. The outward motion of the burning shell in mass removes this excess and triggers the loop. Hitherto nobody has attempted to demonstrate why the excess helium has this effect. We consider the effect of the local opacity, which is reduced by excess helium, the shell fuel supply, which is also reduced, and the local mean molecular weight, which is increased. We demonstrate that the mean molecular weight is the decisive reddening factor. The opacity has a much smaller effect and a reduced fuel supply actually favours blueward motion.

  3. Blue supergiants as descendants of magnetic main sequence stars

    CERN Document Server

    Petermann, I; Castro, N; Fossati, L

    2015-01-01

    About 10$\\%$ of the massive main sequence stars have recently been found to host a strong, large scale magnetic field. Both, the origin and the evolutionary consequences of these fields are largely unknown. We argue that these fields may be sufficiently strong in the deep interior of the stars to suppress convection near the outer edge of their convective core. We performed parametrised stellar evolution calculations and assumed a reduced size of the convective core for stars in the mass range 16 M$_{\\odot}$ to 28 M$_{\\odot}$ from the zero age main sequence until core carbon depletion. We find that such models avoid the coolest part of the main sequence band, which is usually filled by evolutionary models that include convective core overshooting. Furthermore, our `magnetic' models populate the blue supergiant region during core helium burning, i.e., the post-main sequence gap left by ordinary single star models, and some of them end their life in a position near that of the progenitor of Supernova 1987A in t...

  4. Revealing the nature of star forming blue early-type galaxies at low redshift

    CERN Document Server

    George, Koshy

    2015-01-01

    Context: Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on star forming blue early-type galaxies with tidal trails and in close proximity to neighbouring galaxies that are evidence of ongoing or recent interactions between galaxies. There are 12 galaxies with close companions with similar redshifts, among which two galaxies are having ongoing interactions that potentially trigger the star formation. Two galaxies show a jet feature that could be due to the complete tidal disrupti...

  5. Revealing the nature of star forming blue early-type galaxies at low redshift

    Science.gov (United States)

    George, Koshy; Zingade, Kshama

    2015-11-01

    Context. Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on star forming blue early-type galaxies with tidal trails and in close proximity to neighbouring galaxies that are evidence of ongoing or recent interactions between galaxies. There are 12 galaxies with close companions with similar redshifts, among which two galaxies are having ongoing interactions that potentially trigger the star formation. Two galaxies show a jet feature that could be due to the complete tidal disruption of the companion galaxy. The interacting galaxies have high star formation rates and very blue optical colours. Galaxies with no companion could have undergone a minor merger in the recent past. Conclusions: The recent or ongoing interaction with a gas-rich neighbouring galaxy could be responsible for bringing cold gas to an otherwise passively evolving early-type galaxy. The sudden gas supply could trigger the star formation, eventually creating a blue early-type galaxy. The galaxies with ongoing tidal interaction are blue and star forming, thereby implying that blue early-type galaxies can exist even when the companion is on flyby so does not end up in a merger. Based on data compiled from Galaxy Zoo project, and the volunteers contribution are acknowledged at http://www.galaxyzoo.org/Volunteers.aspx

  6. Tracing the star formation history of three Blue Compact galaxies through the analysis of their star clusters

    CERN Document Server

    Adamo, Angela; Zackrisson, Erik; Hayes, Matthew

    2009-01-01

    We present preliminary results from a study of the compact star cluster populations in three local luminous blue compact galaxies: ESO 185-IG 013, ESO 350-IG 038 (a.k.a. Haro 11), and MRK 930. These systems show peculiar morphologies and the presence of hundreds of SCs that have been produced by the past, recent, and/or current starburst phases. We use a complete set of HST images ranging from the UV to IR for each galaxy. Deep images in V (WFPC2/f606w) and I (WFPC2/f814w) are used to capture most of the star cluster candidates up to the old ones (fainter) which have had, in the past, less possibility to be detected. The other bands are used in the SED fitting technique for constraining ages and masses. Our goals are to investigate the evolution of these three blue compact galaxies and the star cluster formation impact on their star formation history.

  7. BLUE LUMINOUS STARS IN NEARBY GALAXIES-UIT 005: A POSSIBLE LINK TO THE LUMINOUS BLUE VARIABLE STAGE

    International Nuclear Information System (INIS)

    A detailed study of the blue supergiant UIT 005 (B2-2.5Ia+) in M 33 is presented. The results of our quantitative spectral analysis indicate that the star is a very luminous (log L/Lsun ∼ 5.9 dex) and massive (M ∼ 50 Msun) object, showing a very high nitrogen-to-oxygen ratio in its surface (N/O∼8, by mass). Based on the derived Mg and Si abundances, we argue that this high N/O ratio cannot be the result of an initial low O content due to its location on the disk of M 33, a galaxy known to present a steep metallicity gradient. In combination with the He abundance, the most plausible interpretation is that UIT 005 is in an advanced stage of evolution, showing in its surface N enrichment and O depletion resulting from mixing with CNO processed material from the stellar interior. A comparison with the predictions of current stellar evolutionary models indicates that there are significant discrepancies, in particular with regard to the degree of chemical processing, with the models predicting a much lower degree of O depletion than observed. At the same time, the mass-loss rate derived in our analysis is an order of magnitude lower than the values considered in the evolutionary calculations. Based on a study of the surrounding stellar population and the nearby cluster, NGC 588, using Hubble Space Telescope/WFPC2 photometry, we suggest that UIT 005 could be in fact a runaway star from this cluster. Regardless of its origin, the derived parameters place the star in a region of the Hertzsprung-Russell diagram where luminous blue variables (LBVs) are usually found, but we find no evidence supporting photometric or spectroscopic variability, except for small Hα changes, otherwise observed in Galactic B-type supergiants. Whether UIT 005 is an LBV in a dormant state or a regular blue supergiant could not be discerned in this study. Subsequent monitoring would help us to improve our knowledge of the more massive stars, bridging the gap between regular and more exotic

  8. The different star-formation histories of blue and red spiral and elliptical galaxies

    CERN Document Server

    Tojeiro, Rita; Richards, Joshua; Percival, Will J; Bamford, Steven P; Maraston, Claudia; Nichol, Robert C; Skibba, Ramin; Thomas, Daniel

    2013-01-01

    [Abridged] We study the spectral properties of intermediate mass galaxies as a function of colour and morphology. We use Galaxy Zoo to define three morphological classes of galaxies, namely early-types (ellipticals), late-type (disk-dominated) face-on spirals and early-type (bulge-dominated) face-on spirals. We classify these galaxies as blue or red according to their SDSS g-r colour and use the spectral fitting code VESPA to calculate time-resolved star-formation histories, metallicity and total starlight dust extinction from their SDSS fibre spectra. We find that red late-type spirals show less star-formation in the last 500 Myr than blue late-type spirals by up to a factor of three, but share similar star-formation histories at earlier times. This decline in recent star-formation explains their redder colour: their chemical and dust content are the same. We postulate that red late-type spirals are recent descendants of blue late-type spirals, with their star-formation curtailed in the last 500 Myrs. The re...

  9. Spectroscopy of blue horizontal branch stars in NGC 6656 (M22)

    CERN Document Server

    Salgado, C; Villanova, S; Geisler, D; Catelan, M

    2013-01-01

    Recent investigations revealed very peculiar properties of blue horizontal branch (HB) stars in \\omega Centauri, which show anomalously low surface gravity and mass compared to other clusters and to theoretical models. \\omega Centauri, however, is a very unusual object, hosting a complex mix of multiple stellar populations with different metallicity and chemical abundances. We measured the fundamental parameters (temperature, gravity, and surface helium abundance) of a sample of 71 blue HB stars in M22, with the aim of clarifying if the peculiar results found in \\omega Cen are unique to this cluster. M22 also hosts multiple sub-populations of stars with a spread in metallicity, analogous to \\omega Cen. The stellar parameters were measured on low-resolution spectra fitting the Balmer and helium lines with a grid of synthetic spectra. From these parameters, the mass and reddening were estimated. Our results on the gravities and masses agree well with theoretical expectations, matching the previous measurements ...

  10. Hypervelocity stars from young stellar clusters in the Galactic Centre

    CERN Document Server

    Fragione, Giacomo; Kroupa, Pavel

    2016-01-01

    The enormous velocities of the so called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of hypervelocity stars as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

  11. GAS MASS FRACTIONS AND STAR FORMATION IN BLUE-SEQUENCE E/S0 GALAXIES

    International Nuclear Information System (INIS)

    Recent work has identified a population of low-redshift E/S0 galaxies that lie on the blue sequence in color versus stellar mass parameter space, where spiral galaxies typically reside. While high-mass blue-sequence E/S0s often resemble young merger or interaction remnants likely to fade to the red sequence, we focus on blue-sequence E/S0s with lower stellar masses (M*10 Msun), which are characterized by fairly regular morphologies and low-density field environments where fresh gas infall is possible. This population may provide an evolutionary link between early-type galaxies and spirals through disk regrowth. Focusing on atomic gas reservoirs, we present new GBT H I data for 27 E/S0s on both sequences as well as a complete tabulation of archival H I data for other galaxies in the Nearby Field Galaxy Survey. Normalized to stellar mass, the atomic gas masses for 12 of the 14 blue-sequence E/S0s range from 0.1 to >1.0, demonstrating that morphological transformation is possible if the detected gas can be converted into stars. These gas-to-stellar mass ratios are comparable to those of spiral and irregular galaxies and have a similar dependence on stellar mass. Assuming that the H I is accessible for star formation, we find that many of our blue-sequence E/S0s can increase in stellar mass by 10%-60% in 3 Gyr in both of two limiting scenarios, exponentially declining star formation (i.e., closed box) and constant star formation (i.e., allowing gas infall). In a constant star formation scenario, about half of the blue-sequence E/S0s require fresh gas infall on a timescale of ∼<3 Gyr to avoid exhausting their atomic gas reservoirs and evolving to the red sequence. We present evidence that star formation in these galaxies is bursty and likely involves externally triggered gas inflows. Our analysis suggests that most blue-sequence E/S0s are indeed capable of substantial stellar disk growth on relatively short timescales.

  12. Spectroscopic observations of blue stars with infrared excesses in NGC 6611

    CERN Document Server

    Bonito, R; Guarcello, M G; Micela, G

    2013-01-01

    The young open cluster NGC 6611 includes among its candidate members a class of peculiar objects with interesting properties: blue stars with infrared IR excesses. These stars show excesses in IR bands, signature of the presence of a circumstellar disk, but optical colors typical of older field stars. In order to confirm their membership to the cluster, it is therefore important to use new spectroscopic observations, together with previous photometric data. We aim at confirming the membership of these objects and at investigating their physical properties to verify whether the observed colors are intrinsic or altered by the presence of the disk or by the accretion processes. We analyze the intermediate resolution spectroscopic data obtained for a subsample of blue stars in NGC 6611 with FLAMES. In particular, we focus on the study of: 1) the profile of the Ha emission line, to select stars with accretion and outflow activity; 2) the Li absorption line, used as a youth indicator; 3) the radial velocity. Using ...

  13. Hyperbranched polymer-cored star polyfluorenes as blue light-emitting materials

    Institute of Scientific and Technical Information of China (English)

    HAN Yang; SUN MingHao; FEI ZhuPing; BO ZhiShan

    2008-01-01

    Hyperbranched polymer-cored star polyfluorenes with high molecular weights and narrow molecular weight distribution were prepared by palladium-catalyzed one-pot Suzuki polycondensation of multi-functional cores and an AB-type monomer. The optical, electrochemical and thermal properties of the hyperbranched polymer-cored star polymers were investigated. These polymers exhibited good ther-mal and color stability in solid state, and there was no significant blue-green emission after the poly-mers had been annealed in air for 2.5 h. Their three-dimensional hyperbranched structures could ef-fectively reduce the aggregation of the peripheral rigid linear conjugated polyfluorene chains.

  14. The Chemical Compositions of Non-Variable Red and Blue Field Horizontal Branch Stars

    CERN Document Server

    For, Bi-Qing

    2010-01-01

    We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high S/N echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7 m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints, and computed relative abundance ratios for 24 species of 19 elements. The species include Si II and Ca II, which have not been previously studied in RHB and BHB (Teff ~ [Fe/H] >~ -2.5. This yielded effective temperatures estimates of 5900K and 7400 K for the red and blue edges of the RR Lyrae instability strip.

  15. Late stages of the evolution of A-type stars on the main sequence: comparison between observed chemical abundances and diffusion models for 8 Am stars of the Praesepe cluster

    CERN Document Server

    Fossati, L; Monier, R; Khan, S A; Kochukhov, O; Landstreet, J; Wade, G; Weiss, W

    2007-01-01

    Aims. We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak magnetic field. Methods. We have obtained high resolution, high signal-to-noise ratio spectra of eight previously-classified Am stars, two normal A-type stars and one Blue Straggler, considered to be members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements, with a higher precision than was ever obtained before for this cluster. For seven of these stars we also obtained spectra in circular polarization and applied the LSD technique to constrain the longitudinal magnetic field. Results. No magnetic field was detected in any of the analysed stars. HD 73666, a Blue Straggler previously considered as an Ap (Si) star, turns out to have the abundances of a no...

  16. Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13

    CERN Document Server

    Behr, B B; McCarthy, J K; Djorgovski, S G; Behr, Bradford B.; Cohen, Judith G.; Carthy, James K. Mc

    1999-01-01

    High-resolution optical spectra of thirteen blue horizontal-branch (BHB) stars in the globular cluster M13 show enormous deviations in element abundances from the expected cluster metallicity. In the hotter stars (T_eff > 12000 K), helium is depleted by factors of 10 to 100 below solar, while iron is enhanced to three times the solar abundance, two orders of magnitude above the canonical metallicity [Fe/H] ~= -1.5 dex for this globular cluster. Nitrogen, phosphorus, and chromium exhibit even more pronounced enhancements, and other metals are also mildly overabundant, with the exception of magnesium, which stays very near the expected cluster metallicity. These photospheric anomalies are most likely due to diffusion --- gravitational settling of helium, and radiative levitation of the other elements --- in the stable radiative atmospheres of these hot stars. The effects of these mechanisms may have some impact on the photometric morphology of the cluster's horizontal branch and on estimates of its age and dist...

  17. Chemical Abundances and Rotation Velocities of Blue Horizontal-Branch Stars in Six Globular Clusters

    CERN Document Server

    Behr, B B

    2003-01-01

    High-resolution spectroscopic measurements of blue horizontal-branch stars in six metal-poor globular clusters -- M3, M13, M15, M68, M92, and NGC 288 -- reveal remarkable variations in photospheric composition and rotation velocity as a function of a star's position along the horizontal branch. For the cooler stars (Teff < 11200 K), the derived abundances are in good agreement with the canonical cluster metallicities, and we find a wide range of v sin i rotation velocities, some as high as 40 km/s. In the hotter stars, however, most metal species are strongly enhanced, by as much as 3 dex, relative to the expected cluster metallicity, while helium is depleted by 2 dex or more. In addition, the hot stars all rotate slowly, with v sin i < 8 km/s. The anomalous abundances appear to be due to atomic diffusion mechanisms -- gravitational settling of helium, and radiative levitation of metals -- in the non-convective atmospheres of these hot stars. We discuss the influence of these photospheric metal enhancem...

  18. Chronography of the Milky Way's Halo System with Field Blue Horizontal-Branch Stars

    CERN Document Server

    Santucci, R M; Placco, V M; Carollo, D; Rossi, S; Lee, Y S; Denissenkov, P; Tumlinson, J; Tissera, P B

    2015-01-01

    In a pioneering effort, Preston et al. reported that the colors of blue horizontal-branch (BHB) stars in the halo of the Galaxy shift with distance, from regions near the Galactic center to about 12 kpc away, and interpreted this as a correlated variation in the ages of halo stars, from older to younger, spanning a range of a few Gyrs. We have applied this approach to a sample of some 4700 spectroscopically confirmed BHB stars selected from the Sloan Digital Sky Survey to produce the first "chronographic map" of the halo of the Galaxy. We demonstrate that the mean de-reddened g$-$r color, , increases outward in the Galaxy from $-$0.22 to $-$0.08 (over a color window spanning [$-$0.3:0.0]) from regions close to the Galactic center to ~40 kpc, independent of the metallicity of the stars. Models of the expected shift in the color of the field BHB stars based on modern stellar evolutionary codes confirm that this color gradient can be associated with an age difference of roughly 2-2.5 Gyrs, with the oldest stars ...

  19. Vertical stratification of iron in atmospheres of blue horizontal-branch stars

    CERN Document Server

    Khalack, V; Behr, B B

    2010-01-01

    The aim of this study is to search for observational evidence of vertical iron stratification in the atmosphere of fourteen blue horizontal-branch (BHB) stars. We have found from our numerical simulations that five BHB stars: B22, B186 in the globular cluster NGC 288, WF2-820, WF2-2692 in M13 and B203 in M15 show clear signatures of the vertical stratification of iron whose abundance increases toward the lower atmosphere. Two other BHB stars (B334 in M15 and B176 in M92) also show possible iron stratification in their atmosphere. A dependence of the slope of iron stratification on the effective temperature was also discovered. It is found that the vertical stratification of iron is strongest in BHB stars with Teff around 11,500K. The slope of iron abundance decreases as Teff increases and becomes negligible for the BHB stars with Teff= 14,000K. These results support the hypothesis regarding the efficiency of atomic diffusion in the stellar atmospheres of BHB stars with Teff > 11,500K.

  20. FROM BLUE STAR-FORMING TO RED PASSIVE: GALAXIES IN TRANSITION IN DIFFERENT ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Vulcani, Benedetta [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa 277-8582 (Japan); Poggianti, Bianca M.; Fasano, Giovanni; Moretti, Alessia [INAF-Astronomical Observatory of Padova, I-35122 Padova (Italy); Fritz, Jacopo [Sterrenkundig Observatorium Vakgroep Fysica en Sterrenkunde Universiteit Gent, Krijgslaan 281, S9 B-9000 Gent (Belgium); Calvi, Rosa; Paccagnella, Angela [Dipartimento di Fisica e Astronomia, Universitá degli Studi di Padova, vicolo Osservatorio 2, I-35122 Padova (Italy)

    2015-01-01

    Exploiting a mass-complete (M {sub *} > 10{sup 10.25} M {sub ☉}) sample at 0.03 star-formation activity and/or morphology: green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M {sub *} < 10{sup 10.7} M {sub ☉} on environment. The incidence of red galaxies increases with increasing mass, and, for M {sub *} < 10{sup 10.7} M {sub ☉}, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment and increases monotonically with galaxy mass. We also inspect galaxy structural parameters, star-formation properties, histories, and ages and propose an evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of the star-formation rate in both bulges and disks that does not noticeably affect galaxy structure. Morphological transitions are linked to an enhanced bulge-to-disk ratio that is due to the removal of the disk, not to an increase of the bulge. Our modeling suggests that green colors might be due to star-formation histories declining with long timescales, as an alternative scenario to the classical ''quenching'' processes. Our results suggest that galaxy transformations in star-formation activity and morphology depend neither on the environment nor on being a satellite or the most massive galaxy of a halo. The only environmental dependence we find is the higher fast quenching efficiency in groups giving origin to poststarburst signatures.

  1. A possible formation channel for blue hook stars in globular clusters

    Science.gov (United States)

    Lei, Zhenxin; Chen, Xuemei; Zhang, Fenghui; Han, Zhanwen

    2015-05-01

    The formation mechanism for blue hook (BHk) stars in globular clusters (GCs) is still unclear. Following one of the possible scenarios, called the late hot flash scenario, we propose that a tidally enhanced stellar wind in binary evolution might provide the huge mass loss on the red giant branch (RGB) and produce BHk stars. Employing the detailed stellar evolution code MESA (Modules for Experiments in Stellar Astrophysics), we have investigated the contributions of tidally enhanced stellar wind as a possible formation channel for BHk stars in GCs. We evolved the primary stars with different initial orbital periods using the binary module in MESA (version 6208) from the zero-age main-sequence (ZAMS) to the post-horizontal branch (HB) stage, and obtained their evolution parameters, which are compared with the observation. The results are consistent with observations in the colour-magnitude diagram and the log g-Teff plane for NGC 2808, which is an example GC hosting BHk stars. However, the helium abundance in the surface for our models is higher than the one obtained in BHk stars. This discrepancy between our models and observations is possibly due to the fact that gravitational settling and radiative levitation, which are common processes in hot HB stars, are not considered in the models as well as the fact that the flash mixing efficiency might be overestimated in the calculations. Our results suggest that tidally enhanced stellar wind in binary evolution is able to naturally provide the huge mass loss on the RGB needed for the late hot flash scenario, and it is a possible and reasonable formation channel for BHk stars in GCs.

  2. Evolution of binary stars and its implications for evolutionary population synthesis

    CERN Document Server

    Han, Z; Zhang, F; Podsiadlowski, Ph

    2009-01-01

    Most stars are members of binaries, and the evolution of a star in a close binary system differs from that of an ioslated star due to the proximity of its companion star. The components in a binary system interact in many ways and binary evolution leads to the formation of many peculiar stars, including blue stragglers and hot subdwarfs. We will discuss binary evolution and the formation of blue stragglers and hot subdwarfs, and show that those hot objects are important in the study of evolutionary population synthesis (EPS), and conclude that binary interactions should be included in the study of EPS. Indeed, binary interactions make a stellar population younger (hotter), and the far-ultraviolet (UV) excess in elliptical galaxies is shown to be most likely resulted from binary interactions. This has major implications for understanding the evolution of the far-UV excess and elliptical galaxies in general. In particular, it implies that the far-UV excess is not a sign of age, as had been postulated prviously ...

  3. The Sample Properties of Metallic-line, A-stars in SDSS, Data Release 8

    Science.gov (United States)

    Keeling, Chloe; Wilhelm, Ronald J.

    2015-01-01

    It has been known for many years that some stars in the spectral range of mid-A to early-F show chemically peculiar spectral lines characterized by very weak absorption in the calcium and scandium lines and overly strong absorption in metallic lines (such as iron) compared to the spectral strength of hydrogen lines in the star. This Am effect is caused by photospheric differentiation and is manifest through a combination of gravitational settling and radiative levitation of the various elements in the quiescent atmosphere of non-convective, slowly rotating A-stars. We identify this effect in a large sample of field blue straggler stars from SDSS DR8, by comparing the strength of the CaII K line to that of metallic regions. We will present results for spatial and kinematic distribution of the Am sample and compare these distributions and specific frequency to the chemically normal sample of blue stragglers. These results will be used to help constrain the nature of stellar features such as the Monoceros stream of stars.

  4. GRACES observations of young [α/Fe]-rich stars

    Science.gov (United States)

    Yong, David; Casagrande, Luca; Venn, Kim A.; Chené, André-Nicolas; Keown, Jared; Malo, Lison; Martioli, Eder; Alves-Brito, Alan; Asplund, Martin; Dotter, Aaron; Martell, Sarah L.; Meléndez, Jorge; Schlesinger, Katharine J.

    2016-06-01

    We measure chemical abundance ratios and radial velocities in four massive (i.e. young) [α/Fe]-rich red giant stars using high-resolution high-S/N spectra from ESPaDOnS fed by Gemini-GRACES. Our differential analysis ensures that our chemical abundances are on the same scale as the Alves-Brito et al. (2010) study of bulge, thin, and thick disc red giants. We confirm that the program stars have enhanced [α/Fe] ratios and are slightly metal poor. Aside from lithium enrichment in one object, the program stars exhibit no chemical abundance anomalies when compared to giant stars of similar metallicity throughout the Galaxy. This includes the elements Li, O, Si, Ca, Ti, Cr, Ni, Cu, Ba, La, and Eu. Therefore, there are no obvious chemical signatures that can help to reveal the origin of these unusual stars. While our new observations show that only one star (not the Li-rich object) exhibits a radial velocity variation, simulations indicate that we cannot exclude the possibility that all four could be binaries. In addition, we find that two (possibly three) stars show evidence for an infrared excess, indicative of a debris disc. This is consistent with these young [α/Fe]-rich stars being evolved blue stragglers, suggesting their apparent young age is a consequence of a merger or mass transfer. We would expect a binary fraction of ˜50 per cent or greater for the entire sample of these stars, but the signs of the circumbinary disc may have been lost since these features can have short time-scales. Radial velocity monitoring is needed to confirm the blue straggler origin.

  5. A possible formation channel for blue hook stars in globular cluster

    CERN Document Server

    Lei, Zhenxin; Zhang, Fenghui; Han, Zhanwen

    2015-01-01

    The formation mechanism for blue hook (BHk) stars in globular clusters (GCs) is still unclear. Following one of the possible scenario, named late hot flash scenario, we proposed that tidally enhanced stellar wind in binary evolution may provide the huge mass loss on the red giant branch (RGB) and produce BHk stars. Employing the detailed stellar evolution code, Modules for Experiments in Stellar Astrophysics (MESA), we investigated the contributions of tidally enhanced stellar wind as a possible formation channel for BHk stars in GCs. We evolved the primary stars with different initial orbital periods using the binary module in MESA (version 6208) from zero age main-sequence (ZAMS) to post horizontal branch (HB) stage, and obtained their evolution parameters which are compared with the observation. The results are consistent with observation in the color-magnitude diagram (CMD) and the logg-Teff plane for NGC 2808, which is an example GC hosting BHk stars. However, the helium abundance in the surface for our ...

  6. The Stellar Population and Star Formation Properties of Blue Compact Dwarf Galaxies

    CERN Document Server

    Zhao, Yinghe; Gao, Yu

    2010-01-01

    We study the stellar populations, star formation histories and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. (2003) sample with the Sloan Digital Sky Survey Data Release 6 (SDSS DR6). The sample includes 31 BCDs, which span a large range in galactic parameters. Using a stellar population synthesis method, we derive the stellar populations and reconstruct the star formation histories for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation but old systems undergoing a starburst activity. The stellar mass-weighted ages can be as old as 10 Gyr while the luminosity-weighted ages might be up to $\\sim 3$ orders of magnitude younger ($\\sim 10$ Myr) for most galaxies. Based on multi-wavelength data, we also study the integrated star formation properties. The SFR for our sample galaxies spans nearly 3 orders of magnitude, from a few $10^{-3}$ to $\\sim1\\,M_\\odot$ yr$^{-1}$, with the medi...

  7. THE STELLAR POPULATION AND STAR FORMATION PROPERTIES OF BLUE COMPACT DWARF GALAXIES

    International Nuclear Information System (INIS)

    We study stellar populations, star formation histories (SFHs), and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. sample with the Sloan Digital Sky Survey Data Release 6. The sample includes 31 BCDs, which span a large range of galactic parameters. Using a stellar population synthesis method, we derive stellar populations and reconstruct SFHs for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation, but old systems undergoing a starburst activity. The stellar mass-weighted ages can be up to 10 Gyr, while the luminosity-weighted ages might be up to approximately three orders of magnitude younger (∼10 Myr) for most galaxies. Based on multiwavelength data, we also study the integrated star formation properties. The star formation rate (SFR) for our sample galaxies spans nearly three orders of magnitude, from a few 10-3 to ∼1 Msun yr-1, with a median value of ∼0.1 Msun yr-1. We find that about 90% of BCDs in our sample have their birthrate parameter (the ratio of the current SFR to the averaged past SFR) b>2-3. We further discuss correlations of the current SFR with the integrated galactic stellar mass and explore the connection between SFR and metallicity.

  8. Spectroscopic analyses of the blue hook stars in NGC 2808:A more stringent test of the late hot flasher scenario

    OpenAIRE

    Moehler, S.; Sweigart, A. V.; Landsman, W. B.; Hammer, N. J.; Dreizler, S.

    2004-01-01

    Recent UV observations of the globular cluster NGC 2808 (Brown et al. 2001) show a significant population of hot stars fainter than the zero-age horizontal branch ("blue hook" stars), which cannot be explained by canonical stellar evolution. Their results suggest that stars which experience unusually large mass loss on the red giant branch and which subsequently undergo the helium core flash while descending the white dwarf cooling curve could populate this region. Theory predicts that these ...

  9. From blue star-forming to red passive: galaxies in transition in different environments

    CERN Document Server

    Vulcani, Benedetta; Fritz, Jacopo; Fasano, Giovanni; Moretti, Alessia; Calvi, Rosa; Paccagnella, Angela

    2014-01-01

    Exploiting a mass complete (M_*>10^(10.25)M_sun) sample at 0.03star formation activity and/or morphology - green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M_*<10^(10.7)M_sun on environment. The incidence of red galaxies increases with increasing mass, and, for M_*<10^(10.7)M_sun, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment, and increases monotonically with galaxy mass. We also inspect galaxy structural parameters, star-formation properties, histories and ages and propose an evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of SFR in bot...

  10. Study of the luminous blue variable star candidate G26.47+0.02 and its environment

    OpenAIRE

    Paron, S.; Combi, J. A.; Petriella, A.; Giacani, E.

    2012-01-01

    The luminous blue variable (LBV) stars are peculiar very massive stars. The study of these stellar objects and their surroundings is important for understanding the evolution of massive stars and its effects on the interstellar medium. We study the LBV star candidate G26.47+0.02. Using several large-scale surveys in different frequencies we performed a multiwavelength study of G26.47+0.02 and its surroundings. We found a molecular shell (seen in the 13CO J=1-0 line) that partially surrounds t...

  11. Vertical abundance stratification in the blue horizontal branch star HD135485

    CERN Document Server

    Khalack, V R; Bohlender, D A; Wade, G A; Behr, B B

    2007-01-01

    It is commonly believed that the observed overabundances of many chemical species relative to the expected cluster metallicity in blue horizontal branch (BHB) stars appear as a result of atomic diffusion in the photosphere. The slow rotation of BHB stars (with T_eff > 11,500K), typically v sin{i} < 10 km/s, is consistent with this idea. In this work we search for observational evidence of vertical chemical stratification in the atmosphere of HD135485. If this evidence exists, it will demonstrate the importance of atomic diffusion processes in the atmospheres of BHB stars. We undertake an extensive abundance stratification analysis of the atmosphere of HD135485, based on recently acquired high resolution and S/N CFHT ESPaDOnS spectra and a McDonald-CE spectrum. Our numerical simulations show that nitrogen and sulfur reveal signatures of vertical abundance stratification in the stellar atmosphere. It appears that the abundances of these elements increase toward the upper atmosphere. This fact cannot be expla...

  12. Characterizing stellar halo populations II: The age gradient in blue horizontal-branch stars

    CERN Document Server

    Das, Payel; Binney, James

    2016-01-01

    The distribution of Milky Way halo blue horizontal-branch (BHB) stars is examined using action-based extended distribution functions (EDFs) that describe the locations of stars in phase space, metallicity, and age. The parameters of the EDFs are fitted using stars observed in the Sloan Extension for Galactic Understanding and Exploration-II (SEGUE-II) survey that trace the phase-space kinematics and chemistry out to ~70 kpc. A maximum a posteriori probability (MAP) estimate method and a Markov Chain Monte Carlo method are applied, taking into account the selection function in positions, distance, and metallicity for the survey. The best-fit EDF declines with actions less steeply at actions characteristic of the inner halo than at the larger actions characteristic of the outer halo, and older ages are found at smaller actions than at larger actions. In real space, the radial density profile steepens smoothly from -2 at ~2 kpc to -4 in the outer halo, with an axis ratio ~0.7 throughout. There is no indication f...

  13. The supergiant B[e] star LHA 115-S 18 - binary and/or luminous blue variable?

    CERN Document Server

    Clark, J S; Coe, M J; Dorda, R; Haberl, F; Lamb, J B; Negueruela, I; Udalski, A

    2013-01-01

    The mechanism by which supergiant (sg)B[e] stars support cool, dense dusty discs/tori and their physical relationship with other evolved, massive stars such as luminous blue variables is uncertain. In order to investigate both issues we have analysed the long term behaviour of the canonical sgB[e] star LHA 115-S 18. We employed the OGLE II-IV lightcurve to search for (a-)periodic variability and supplemented these data with new and historic spectroscopy. In contrast to historical expectations for sgB[e] stars, S18 is both photometrically and spectroscopically highly variable. The lightcurve is characterised by rapid aperiodic `flaring' throughout the 16 years of observations. Changes in the high excitation emission line component of the spectrum imply evolution in the stellar temperature - as expected for luminous blue variables - although somewhat surprisingly, spectroscopic and photometric variability appears not to be correlated. Characterised by emission in low excitation metallic species, the cool circum...

  14. First results from the Edinburgh-Cape faint blue object survey - Normal stars at high galactic latitudes

    Science.gov (United States)

    Kilkenny, D.; O'Donoghue, D.; Stobie, R. S.

    1991-02-01

    A simple analysis using low-dispersion Reticon spectroscopy and Stromgren photometry is presented for a sample of 20 apparently normal early-type stars detected in the Edinburgh-Cape faint blue object survey of high galactic latitudes. Four stars are not normal, showing high gravity or helium abundance anomalies; 12 stars appear to be at moderate distances from the galactic plane and four stars have derived z-distances greater than about 5 kpc. The sample was selected from 33 survey fields completed to B = 16.5 mag and indicates that the total galactic population of 'very high-z' B stars is only of the order 100-1000. The Dyson and Hartquist (1983) model for the formation of such objects by cloudlet-cloudlet collisions within high-velocity clouds cannot therefore be ruled out on the basis of star formation rates.

  15. Atmospheric NLTE-models for the spectroscopic analysis of luminous blue stars with winds.

    Science.gov (United States)

    Santolaya-Rey, A. E.; Puls, J.; Herrero, A.

    1997-07-01

    We present a new, fast and easy to use NLTE line formation code for ``unified atmospheres'' with spherical extension and stellar winds, developed for the (routine) spectroscopic analysis of luminous blue stars, covering the spectral range from ``A'' to ``O'' and including central stars of planetary nebulae. The major features of our code are: Data driven input of atomic models; consistent photospheric stratification including continuum radiative acceleration and photospheric extension; ``β-velocity law'' for the wind; comoving frame or Sobolev plus continuum line transfer; fast solution algorithm for calculating line profiles, allowing for a consistent treatment of incoherent electron scattering. We describe the code and perform thorough tests for models with H/He opacity, especially with respect to a comparison with plane-parallel, hydrostatic models in cases of thin winds. Our conclusions are: Due in particular to our numerical treatment of the radiative transfer in the ionization and recombination integrals, the convergence rate of the solution algorithm is fast. The flux conservation is good, (maximum flux errors of order 2 to 3%), unless the atmospheric conditions are extreme, either with respect to mass-loss or to a large extension of the photosphere. (In these cases, our treatment of the temperature structure has to be improved). A comparison with plane-parallel results shows perfect agreement with the thin wind case. However, this comparison also reveals two interesting effects: First, the strength of the Hei lines in hot O-stars is very sensitive to the treatment of electron scattering in the EUV. This might affect the effective temperature scale of early O spectral types. Second, the effects of photospheric extension become decisive for the gravity determination of stars close to the Eddington limit. Finally, we demonstrate the differences in using the Sobolev vs. the comoving line transfer in the rate equations. We conclude that, in cases of moderate

  16. Characterizing stellar halo populations II: The age gradient in blue horizontal-branch stars

    Science.gov (United States)

    Das, Payel; Williams, Angus; Binney, James

    2016-08-01

    The distribution of Milky Way halo blue horizontal-branch (BHB) stars is examined using action-based extended distribution functions (EDFs) that describe the locations of stars in phase space, metallicity, and age. The parameters of the EDFs are fitted using stars observed in the Sloan Extension for Galactic Understanding and Exploration-II (SEGUE-II) survey that trace the phase-space kinematics and chemistry out to ˜70 kpc. A maximum a posteriori probability (MAP) estimate method and a Markov Chain Monte Carlo method are applied, taking into account the selection function in positions, distance, and metallicity for the survey. The best-fit EDF declines with actions less steeply at actions characteristic of the inner halo than at the larger actions characteristic of the outer halo, and older ages are found at smaller actions than at larger actions. In real space, the radial density profile steepens smoothly from -2 at ˜2 kpc to -4 in the outer halo, with an axis ratio ˜0.7 throughout. There is no indication for rotation in the BHBs, although this is highly uncertain. A moderate level of radial anisotropy is detected, with βs varying from isotropic to between ˜0.1 and ˜0.3 in the outer halo depending on latitude. The BHB data are consistent with an age gradient of -0.03 Gyr kpc-1, with some uncertainty in the distribution of the larger ages. These results are consistent with a scenario in which older, larger systems contribute to the inner halo, whilst the outer halo is primarily comprised of younger, smaller systems.

  17. Luminous and variable stars in M31 and M33. II. Luminous blue variables, candidate LBVs, Fe II emission line stars, and other supergiants

    Energy Technology Data Exchange (ETDEWEB)

    Humphreys, Roberta M.; Davidson, Kris [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Weis, Kerstin; Bomans, D. J.; Burggraf, Birgitta, E-mail: roberta@umn.edu, E-mail: kweis@astro.rub.de [Astronomical Institute, Ruhr-Universitaet Bochum (Germany)

    2014-07-20

    An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33.

  18. Luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution

    Science.gov (United States)

    Smith, Nathan; Tombleson, Ryan

    2015-02-01

    Based on their relatively isolated environments, we argue that luminous blue variables (LBVs) must be primarily the product of binary evolution, challenging the traditional single-star view wherein LBVs mark a brief transition between massive O-type stars and Wolf-Rayet (WR) stars. If the latter were true, then LBVs should be concentrated in young massive clusters like early O-type stars. This is decidedly not the case. Examining locations of LBVs in our Galaxy and the Magellanic Clouds reveals that, with only a few exceptions, LBVs systematically avoid clusters of O-type stars. In the Large Magellanic Cloud, LBVs are statistically much more isolated than O-type stars, and (perhaps most surprisingly) even more isolated than WR stars. This makes it impossible for LBVs to be single `massive stars in transition' to WR stars. Instead, we propose that massive stars and supernova (SN) subtypes are dominated by bifurcated evolutionary paths in interacting binaries, wherein most WR stars and Type Ibc supernovae (SNe Ibc) correspond to the mass donors, while LBVs (and their lower mass analogues like B[e] supergiants, which are even more isolated) are the mass gainers. In this view, LBVs are evolved massive blue stragglers. Through binary mass transfer, rejuvinated mass gainers get enriched, spun up, and sometimes kicked far from their clustered birth sites by their companion's SN. This scenario agrees better with LBVs exploding as SNe IIn in isolation, and it predicts that many massive runaway stars may be rapid rotators. Mergers or blue Thorne-Zytkow-like objects might also give rise to LBVs, but these scenarios may have a harder time explaining why LBVs avoid clusters.

  19. Luminous Blue Variables are Antisocial: Their Isolation Implies they are Kicked Mass Gainers in Binary Evolution

    Science.gov (United States)

    Tombleson, Ryan; Smith, Nathan

    2015-01-01

    Based on their relatively isolated environments, we argue that luminous blue variables (LBVs) must be primarily the product of binary evolution, challenging the traditional single-star view wherein LBVs mark a brief transition between massive O-type stars and Wolf-Rayet (WR) stars. If the latter were true, then LBVs should be concentrated in young massive clusters like early O-type stars. This is decidedly not the case. Examining locations of LBVs in our Galaxy and the Magellanic Clouds reveals that, with few exceptions, LBVs systematically avoid clusters of O-type stars. In the Large Magellanic Cloud, LBVs are statistically much more isolated than O-type stars, and (perhaps most surprisingly) even more isolated than WR stars. This makes it impossible for LBVs to be single 'massive stars in transition' to WR stars. Instead, we propose that massive stars and supernova (SN) subtypes are dominated by bifurcated evolutionary paths in interacting binaries, wherein most WR stars and SNe Ibc correspond to the mass donors, while LBVs (and their lower-mass analogs like B[e] supergiants, which are even more isolated) are the mass gainers. In this view, LBVs are evolved massive blue stragglers. Through binary mass transfer, rejuvinated mass gainers get enriched, spun up, and sometimes kicked far from their clustered birthsites by their companion's SN. This scenario agrees better with LBVs exploding as Type IIn SNe in isolation, and it predicts that many massive runaway stars may be rapid rotators. Mergers or Thorne-Zykow objects might also give rise to LBVs, but these scenarios may have a harder time explaining why LBVs avoid clusters.

  20. The Century Survey Galactic Halo Project II: Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars

    CERN Document Server

    Brown, W R; Kenyon, S J; Kurtz, M J; Allende-Prieto, C; Beers, T C; Wilhelm, R; Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Prieto, Carlos Allende; Beers, Timothy C.; Wilhelm, Ronald

    2005-01-01

    We discuss a 175 deg^2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and find that the 2MASS and SDSS color-selection is 38% and 50% efficient, respectively, for BHB stars. Our samples include one likely run-away B7 star 6 kpc below the Galactic plane. The global properties of the BHB samples are consistent with membership in the halo population: the median metallicity is [Fe/H]=-1.7, the velocity dispersion is 108 km/s, and the mean Galactic rotation of the BHB stars 3<|z|<15 kpc is -4 +- 30 km/s. We discuss the theoretical basis of the Preston, Shectman & Beers M_V-color relation for BHB stars, and conclude that intrinsic shape of the BHB M_V-color relation results from the physics of stars on the horizontal branch. We calculate the luminosity function for the field BHB star samples using the Efstathiou, Ellis, & Peterson maximum-likelihood method w...

  1. Bending of Light Near a Star and Gravitational Red/Blue Shift Alternative Explanation Based on Refraction of Light

    CERN Document Server

    Gupta, D R C

    2004-01-01

    Many of the general-relativity-tests such as bending of light near a star and gravitational red/blue shift are explained without general-relativity and without Newtonian-approach. The author first casts doubts on both, the Newtonian and the relativistic approach; and proposes a novel alternative-explanation. The new alternative-explanation is based on refraction-phenomenon of optics. It predicts that as the ray passes through/near the stars atmospheric-medium, it bends due to refraction-phenomenon towards star-core, like a ray bends while passing through a prism or water-drop. A semi-empirical estimation of the atmospheric-height and its refractive-index are made to find the refraction-results. The refraction-based theory also suggests new explanation for gravitational red/blue shift; it tells that frequency remains constant (as it is so in refraction-phenomenon) and the red/blue shift is due to change in wavelength due to change in velocity of light in the medium . Estimated results for bending of light and ...

  2. The Type IIn Supernova 2002kg: The Outburst of a Luminous Blue Variable Star in NGC 2403

    CERN Document Server

    Van Dyk, S D; Chornock, R; Filippenko, A V; Foley, R; Humphreys, R M; Li, W; Challis, Peter M.; Chornock, Ryan; Dyk, Schuyler D. Van; Filippenko, Alexei V.; Foley, Ryan; Humphreys, Roberta M.; Li, Weidong

    2006-01-01

    We show that Supernova (SN) 2002kg in NGC 2403, initially classified as Type II-narrow (IIn), has photometric and spectroscopic properties unlike those of normal SNe. Its behavior, instead, is more typical of highly massive stars which experience the short-lived luminous blue variable (LBV) phase toward the end of their lives. The star, in fact, most resembles the LBV S Doradus in outburst. The precursor of SN 2002kg is the irregular, bright blue variable star 37 (V37), catalogued by Tammann & Sandage in 1968. Using high-quality ground-based, multi-band images we can constrain the initial mass of V37 to be M_ini >~ 40 M_sun. We find that, although the spectra indicate a nitrogen enhancement, possibly revealing the products of CNO processing by V37 in the ejecta, the star lacks a substantial LBV nebula. The outburst from SN 2002kg/V37 is not nearly as energetic as the giant eruptions of the eta Carinae-like variables, such as SN 1954J/V12, also in NGC 2403. SN 2002kg/V37, however, is among a growing number...

  3. Stellar Populations and the Star Formation Histories of LSB Galaxies: III. Stellar Population Models

    Science.gov (United States)

    Schombert, James; McGaugh, Stacy

    2014-09-01

    A series of population models are designed to explore the star formation history of gas-rich, low surface brightness (LSB) galaxies. LSB galaxies are unique in having properties of very blue colors, low Hα emission and high gas fractions that indicated a history of constant star formation (versus the declining star formation models used for most spirals and irregulars). The model simulations use an evolving multi-metallicity composite population that follows a chemical enrichment scheme based on Milky Way observations. Color and time sensitive stellar evolution components (i.e., BHB, TP-AGB and blue straggler stars) are included, and model colors are extended into the Spitzer wavelength regions for comparison to new observations. In general, LSB galaxies are well matched to the constant star formation scenario with the variation in color explained by a fourfold increase/decrease in star formation over the last 0.5 Gyrs (i.e., weak bursts). Early-type spirals, from the S4G sample, are better fit by a declining star formation model where star formation has decreased by 40% in the last 12 Gyrs.

  4. The Rise and Fall of Star Formation Histories of Blue Galaxies at Redshifts 0.2 < z < 1.4

    Science.gov (United States)

    Pacifici, Camilla; Kassin, Susan A.; Weiner, Benjamin; Charlot, Stephane; Gardner, Jonathan P.

    2012-01-01

    Popular cosmological scenarios predict that galaxies form hierarchically from the merger of many progenitor, each with their own unique star formation history (SFH). We use the approach recently developed by Pacifici et al. to constrain the SFHs of 4517 blue (presumably star-forming) galaxies with spectroscopic redshifts in the range O.2 star formation and chemical enrichment histories, stellar population synthesis, nebular emission and attenuation by dust. We constrain the SFH of each galaxy in our sample by comparing the observed fluxes in the B, R,l and K(sub s) bands and rest-frame optical emission-line luminosities with those of one million model spectral energy distributions. We explore the dependence of the resulting SFH on galaxy stellar mass and redshift. We find that the average SFHs of high-mass galaxies rise and fall in a roughly symmetric bell-shaped manner, while those of low-mass galaxies rise progressively in time, consistent with the typically stronger activity of star formation in low-mass compared to high-mass galaxies. For galaxies of all masses, the star formation activity rises more rapidly at high than at low redshift. These findings imply that the standard approximation of exponentially declining SFHs wIdely used to interpret observed galaxy spectral energy distributions is not appropriate to constrain the physical parameters of star-forming galaxies at intermediate redshifts.

  5. Liquid-Crystalline Star-Shaped Supergelator Exhibiting Aggregation-Induced Blue Light Emission.

    Science.gov (United States)

    Pathak, Suraj Kumar; Pradhan, Balaram; Gupta, Monika; Pal, Santanu Kumar; Sudhakar, Achalkumar Ammathnadu

    2016-09-13

    A family of closely related star-shaped stilbene-based molecules containing an amide linkage are synthesized, and their self-assembly in liquid-crystalline and gel states was investigated. The number and position of the peripheral alkyl tails were systematically varied to understand the structure-property relation. Interestingly, one of the molecules with seven peripheral chains was bimesomorphic, exhibiting columnar hexagonal and columnar rectangular phases, whereas the rest of them stabilized the room-temperature columnar hexagonal phase. The self-assembly of these molecules in liquid-crystalline and organogel states is extremely sensitive to the position and number of alkoxy tails in the periphery. Two of the compounds with six and seven peripheral tails exhibited supergelation behavior in long-chain hydrocarbon solvents. One of these compounds with seven alkyl chains was investigated further, and it has shown higher stability and moldability in the gel state. The xerogel of the same compound was characterized with the help of extensive microscopic and X-ray diffraction studies. The nanofibers in the xerogel are found to consist of molecules arranged in a lamellar fashion. Furthermore, this compound shows very weak emission in solution but an aggregation-induced emission property in the gel state. Considering the dearth of solid-state blue-light-emitting organic materials, this molecular design is promising where the self-assembly and emission in the aggregated state can be preserved. The nonsymmetric design lowers the phase-transition temperatures.The presence of an amide bond helps to stabilize columnar packing over a long range because of its polarity and intermolecular hydrogen bonding in addition to promoting organogelation.

  6. Metallicity estimates for A-, F-, and G-type stars from the Edinburgh-Cape blue object survey

    CERN Document Server

    Beers, T C; O'Donoghue, D; Kilkenny, D; Stobie, R S; Koen, C; Wilhelm, R

    2000-01-01

    The Edinburgh-Cape Blue Object Survey is an ongoing project to identify and analyse a large sample of hot stars selected initially on the basis of photographic colours (down to a magnitude limit B~18.0) over the entire high-Galactic-latitude southern sky, then studied with broadband UBV photometry and medium-resolution spectroscopy. Due to unavoidable errors in the initial candidate selection, stars that are likely metal-deficient dwarfs and giants of the halo and thick-disk populations are inadvertently included, yet are of interest in their own right. In this paper we discuss a total of 206 candidate metal-deficient dwarfs, subgiants, giants, and horizontal-branch stars with photoelectric colours redder than (B-V)o = 0.3, and with available spectroscopy. Radial velocities, accurate to ~10-15 km/s, are presented for all of these stars. Spectroscopic metallicity estimates for these stars are obtained using a recently re-calibrated relation between Ca II K-line strength and (B-V)o colour. The identification of...

  7. The Progenitor Stars of Gamma-Ray Bursts

    CERN Document Server

    Woosley, S; Woosley, Stan; Heger, Alexander

    2006-01-01

    Those massive stars that, during their deaths, give rise to gamma-ray bursts (GRBs) must be endowed with an unusually large amount of angular momentum in their inner regions, one to two orders of magnitude greater than the ones that make common pulsars. Yet the inclusion of mass loss and angular momentum transport by magnetic torques during the precollapse evolution is known to sap the core of the necessary rotation. Here we explore the evolution of very rapidly rotating, massive stars, including stripped down helium cores that might result from mergers or mass transfer in a binary, and single stars that rotate unusually rapidly on the main sequence. For the highest possible rotation rates (about 400 km/s), a novel sort of evolution is encountered in which single stars mix completely on the main sequence, never becoming red giants. Such stars, essentially massive "blue stragglers", produce helium-oxygen cores that rotate unusually rapidly. Such stars might comprise roughly 1% of all stars above 10 solar masse...

  8. Mapping the Galactic Halo with blue horizontal branch stars from the 2dF quasar redshift survey

    CERN Document Server

    De Propris, Roberto; Mares, Peter J; CTIO,; University, Cornell

    2010-01-01

    We use 666 blue horizontal branch (BHB) stars from the 2Qz redshift survey to map the Galactic halo in four dimensions (position, distance and velocity). We find that the halo extends to at least 100 kpc in Galactocentric distance, and obeys a single power-law density profile of index ~-2.5 in two different directions separated by 150 degrees on the sky. This suggests that the halo is spherical. Our map shows no large kinematically coherent structures (streams, clouds or plumes) and appears homogeneous. However, we find that at least 20% of the stars in the halo reside in substructures and that these substructures are dynamically young. The velocity dispersion profile of the halo appears to increase towards large radii while the stellar velocity distribution is non Gaussian beyond 60 kpc. We argue that the outer halo consists of a multitude of low luminosity overlapping tidal streams from recently accreted objects.

  9. Chemical evolution of A- and B-type stars in open clusters: observed abundances vs. diffusion models. Am stars in the Praesepe cluster

    Science.gov (United States)

    Fossati, L.; Bagnulo, S.; Monier, R.; Khan, S. A.; Kochukhov, O.; Landstreet, J. D.; Wade, G. A.; Weiss, W. W.

    2008-04-01

    We have decided to address the problem of how abundances and peculiarities change during main sequence evolution. We have setup a program to measure the atmospheric abundance patterns from tens of A-type star members of clusters of different ages, and compare the results with theory predictions. In this paper we present the overall project and we focus on the results obtained for a sample of Am stars of the Praesepe cluster (log t= 8.85 ± 0.15; González-García et al., 2006). We have obtained spectra for eight Am stars, two normal A-type stars and one blue straggler, that are probable members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements. For seven stars we also obtained spectra in circular polarisation and applied the LSD technique to measure the mean longitudinal magnetic field. We have found good agreement between abundance predictions of diffusion models and measured abundances, except for Na and S. Li appears to be overabundant in three stars of our sample. No magnetic field was detected in any of the analysed stars.

  10. Stellar Populations and the Star Formation Histories of LSB Galaxies: III. Stellar Population Models

    CERN Document Server

    Schombert, James

    2014-01-01

    A series of population models are designed to explore the star formation history of gas-rich, low surface brightness (LSB) galaxies. LSB galaxies are unique in having properties of very blue colors, low H$\\alpha$ emission and high gas fractions that indicated a history of constant star formation (versus the declining star formation models used for most spirals and irregulars). The model simulations use an evolving multi-metallicity composite population that follows a chemical enrichment scheme based on Milky Way observations. Color and time sensitive stellar evolution components (i.e., BHB, TP-AGB and blue straggler stars) are included, and model colors are extended into the Spitzer wavelength regions for comparison to new observations. In general, LSB galaxies are well matched to the constant star formation scenario with the variation in color explained by a fourfold increase/decrease in star formation over the last 0.5 Gyrs (i.e., weak bursts). Early-type spirals, from the S$^4$G sample, are better fit by a...

  11. The Nature of Faint Blue Stars in the PHL and Ton Catalogues based on Digital Sky Surveys

    CERN Document Server

    Andernach, H; W., W Copo Cordova; Santiago-Bautista, I del C

    2015-01-01

    We determined accurate positions for 3000 of the "faint blue stars" in the PHL (Palomar-Haro-Luyten) and Ton/TonS catalogues. These were published from 1957 to 1962, and, aimed at finding new white dwarfs, provide approximate positions for about 10750 blue stellar objects. Some of these "stars" had become known as quasars, a type of objects unheard-of before 1963. We derived subarcsec positions from a comparison of published finding charts with images from the first-epoch Digitized Sky Survey. Numerous objects are now well known, but unfortunately neither their PHL or Ton numbers, nor their discoverers, are recognized in current databases. A comparison with modern radio, IR, UV and X-ray surveys leads us to suggest that the fraction of extragalactic objects in the PHL and Ton catalogues is at least 15 per cent. However, because we failed to locate the original PHL plates or finding charts, it may be impossible to correctly identify the remaining 7726 PHL objects.

  12. Two bi-stability jumps in theoretical wind models for massive stars and the implications for Luminous Blue Variable supernovae

    CERN Document Server

    Petrov, Blagovest; Gräfener, Götz

    2016-01-01

    Luminous Blue Variables have been suggested to be the direct progenitors of supernova types IIb and IIn, with enhanced mass loss prior to explosion. However, the mechanism of this mass loss is not yet known. Here, we investigate the qualitative behaviour of theoretical stellar wind mass-loss as a function of Teff across two bi-stability jumps in blue supergiant regime and also in proximity to the Eddington limit, relevant for LBVs. To investigate the physical ingredients that play a role in the radiative acceleration we calculate blue supergiant wind models with the CMFGEN non-LTE model atmosphere code over an effective temperature range between 30000 and 8800 K. Although our aim is not to provide new mass-loss rates for BA supergiants, we study and confirm the existence of two bi-stability jumps in mass-loss rates predicted by Vink, de Koter, & Lamers (1999). However, they are found to occur at somewhat lower Teff (20000 and 9000 K, respectively) than found previously, which would imply that stars may ev...

  13. A Spectroscopic Study of Blue Supergiant Stars in the Sculptor Galaxy NGC 55: Chemical Evolution and Distance

    Science.gov (United States)

    Kudritzki, R. P.; Castro, N.; Urbaneja, M. A.; Ho, I.-T.; Bresolin, F.; Gieren, W.; Pietrzyński, G.; Przybilla, N.

    2016-10-01

    Low-resolution (4.5-5 Å) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities, and metallicities (from iron peak and α-elements). A metallicity gradient of -0.22 ± 0.06 dex/R 25 is detected. The central metallicity on a logarithmic scale relative to the Sun is [Z] = -0.37 ± 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H ii regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity-luminosity relationship is used to determine a distance modulus of 26.85 ± 0.10 mag.

  14. Herschel imaging and spectroscopy of the nebula around the luminous blue variable star WRAY 15-751

    CERN Document Server

    Vamvatira-Nakou, C; Royer, P; Naze, Y; Magain, P; Exter, K; Waelkens, C; Groenewegen, M A T

    2013-01-01

    We have obtained far-infrared Herschel PACS imaging and spectroscopic observations of the nebular environment of the luminous blue variable WRAY 15-751. These images clearly show that the main, dusty nebula is a shell of radius 0.5 pc and width 0.35 pc extending outside the H-alpha nebula. They also reveal a second, bigger and fainter dust nebula, observed for the first time. Both nebulae lie in an empty cavity, likely the remnant of the O-star wind bubble formed when the star was on the main sequence. The kinematic ages of the nebulae are about 20000 and 80000 years and each nebula contains about 0.05 Msun of dust. Modeling of the inner nebula indicates a Fe-rich dust. The far-infrared spectrum of the main nebula revealed forbidden emission lines coming from ionized and neutral gas. Our study shows that the main nebula consists of a shell of ionized gas surrounded by a thin photodissociation region illuminated by an "average" early-B star. The derived abundance ratios N/O=1.0+/-0.4 and C/O=0.4+/-0.2 indicate...

  15. Herschel imaging and spectroscopy of the nebula around the luminous blue variable star WRAY 15-751

    Science.gov (United States)

    Vamvatira-Nakou, C.; Hutsemékers, D.; Royer, P.; Nazé, Y.; Magain, P.; Exter, K.; Waelkens, C.; Groenewegen, M. A. T.

    2013-09-01

    We have obtained far-infrared Herschel-PACS imaging and spectroscopic observations of the nebular environment of the luminous blue variable (LBV) WRAY 15-751. The far-infrared images clearly show that the main, dusty nebula is a shell of radius 0.5 pc and width 0.35 pc extending outside the Hα nebula. Furthermore, these images reveal a second, bigger and fainter dust nebula that is observed for the first time. Both nebulae lie in an empty cavity, very likely the remnant of the O-star wind bubble formed when the star was on the main sequence. The kinematic ages of the nebulae are calculated to be about 2 × 104 and 8 × 104 years, and we estimated that each nebula contains ~0.05 M⊙ of dust. Modeling of the inner nebula indicates a Fe-rich dust. The far-infrared spectrum of the main nebula revealed forbidden emission lines coming from ionized and neutral gas. Our study shows that the main nebula consists of a shell of ionized gas surrounded by a thin photodissociation region illuminated by an "average" early-B star. We derive the abundance ratios N/O = 1.0 ± 0.4 and C/O = 0.4 ± 0.2, which indicate a mild N/O enrichment. From both the ionized and neutral gas components we estimate that the inner shell contains 1.7 ± 0.6 M⊙ of gas. Assuming a similar dust-to-gas ratio for the outer nebula, the total mass ejected by WRAY 15-751 amounts to 4 ± 2 M⊙. The measured abundances, masses and kinematic ages of the nebulae were used to constrain the evolution of the star and the epoch at which the nebulae were ejected. Our results point to an ejection of the nebulae during the red super-giant (RSG) evolutionary phase of an ~40 M⊙ star. The multiple shells around the star suggest that the mass-loss was not a continuous ejection but rather a series of episodes of extreme mass-loss. Our measurements are compatible with the recent evolutionary tracks computed for an ~40 M⊙ star with little rotation. They support the O-BSG-RSG-YSG-LBV filiation and the idea that high

  16. The swift UVOT stars survey. I. Methods and test clusters

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, Michael H.; Porterfield, Blair L.; Linevsky, Jacquelyn S.; Bond, Howard E.; Hoversten, Erik A.; Berrier, Joshua L.; Gronwall, Caryl A. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Holland, Stephen T. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Breeveld, Alice A. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom); Brown, Peter J., E-mail: siegel@astro.psu.edu, E-mail: blp14@psu.edu, E-mail: heb11@psu.edu, E-mail: caryl@astro.psu.edu, E-mail: sholland@stsci.edu, E-mail: aab@mssl.ucl.ac.uk, E-mail: grbpeter@yahoo.com [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A. and M. University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843 (United States)

    2014-12-01

    We describe the motivations and background of a large survey of nearby stellar populations using the Ultraviolet Optical Telescope (UVOT) on board the Swift Gamma-Ray Burst Mission. UVOT, with its wide field, near-UV sensitivity, and 2.″3 spatial resolution, is uniquely suited to studying nearby stellar populations and providing insight into the near-UV properties of hot stars and the contribution of those stars to the integrated light of more distant stellar populations. We review the state of UV stellar photometry, outline the survey, and address problems specific to wide- and crowded-field UVOT photometry. We present color–magnitude diagrams of the nearby open clusters M67, NGC 188, and NGC 2539, and the globular cluster M79. We demonstrate that UVOT can easily discern the young- and intermediate-age main sequences, blue stragglers, and hot white dwarfs, producing results consistent with previous studies. We also find that it characterizes the blue horizontal branch of M79 and easily identifies a known post-asymptotic giant branch star.

  17. Blue Horizontal-Branch Stars The "Jump" in Strömgren u, Low Gravities, and Radiative Levitation of Metals

    CERN Document Server

    Grundahl, F; Landsman, W B; Stetson, P B; Andersen, M I

    1999-01-01

    We study the ``jump'' in the blue horizontal--branch (BHB) distribution first detected by Grundahl et al. (1998) in the Galactic globular cluster (GC) M13. On the basis of Stromgren photometry for a sample of fourteen GC's we show that: 1) The jump is best characterized as a systematic shift, on a (u, u-y) color-magnitude diagram, from canonical zero-age HB (ZAHB) models, in the sense that the stars appear brighter and/or hotter than the models; 2) the jump is a ubiquitous phenomenon, ocurring over the temperature range 11,500 < Teff < 20,000K; 3) An analogous feature is present in (log g, log Teff) diagrams -- indicating a common physical origin for the two phenomena; 4) The physical mechanism responsible for the jump phenomenon is most likely radiative levitation of iron and other

  18. Two bi-stability jumps in theoretical wind models for massive stars and the implications for luminous blue variable supernovae

    Science.gov (United States)

    Petrov, Blagovest; Vink, Jorick S.; Gräfener, Götz

    2016-05-01

    Luminous blue variables (LBVs) have been suggested to be the direct progenitors of supernova Types IIb and IIn, with enhanced mass loss prior to explosion. However, the mechanism of this mass loss is not yet known. Here, we investigate the qualitative behaviour of theoretical stellar wind mass loss as a function of Teff across two bi-stability jumps in blue supergiant regime and also in proximity to the Eddington limit, relevant for LBVs. To investigate the physical ingredients that play a role in the radiative acceleration we calculate blue supergiant wind models with the CMFGEN non-local thermodynamic equilibrium model atmosphere code over an effective temperature range between 30 000 and 8800 K. Although our aim is not to provide new mass-loss rates for BA supergiants, we study and confirm the existence of two bi-stability jumps in mass-loss rates predicted by Vink et al. However, they are found to occur at somewhat lower Teff (20 000 and 9000 K, respectively) than found previously, which would imply that stars may evolve towards lower Teff before strong mass loss is induced by the bi-stability jumps. When the combined effects of the second bi-stability jump and the proximity to Eddington limit are accounted for, we find a dramatic increase in the mass-loss rate by up to a factor of 30. Further investigation of both bi-stability jumps is expected to lead to a better understanding of discrepancies between empirical modelling and theoretical mass-loss rates reported in the literature, and to provide key inputs for the evolution of both normal AB supergiants and LBVs, as well as their subsequent supernova Type II explosions.

  19. Evolution of Mass Functions of Coeval Stars through Wind Mass Loss and Binary Interactions

    CERN Document Server

    Schneider, F R N; Langer, N; de Mink, S E

    2015-01-01

    Accurate determinations of stellar mass functions and ages of stellar populations are crucial to much of astrophysics. We analyse the evolution of stellar mass functions of coeval main sequence stars including all relevant aspects of single- and binary-star evolution. We show that the slope of the upper part of the mass function in a stellar cluster can be quite different to the slope of the initial mass function. Wind mass loss from massive stars leads to an accumulation of stars which is visible as a peak at the high mass end of mass functions, thereby flattening the mass function slope. Mass accretion and mergers in close binary systems create a tail of rejuvenated binary products. These blue straggler stars extend the single star mass function by up to a factor of two in mass and can appear up to ten times younger than their parent stellar cluster. Cluster ages derived from their most massive stars that are close to the turn-off may thus be significantly biased. To overcome such difficulties, we propose t...

  20. Auto-consistent metallicity and star formation history of the nearest blue compact dwarf galaxy NGC 6789

    CERN Document Server

    García-Benito, Rubén

    2012-01-01

    We present a detailed auto-consistent study of the nearest blue compact dwarf galaxy NGC 6789 by means of optical and UV archive photometry data and optical long-slit ISIS-WHT spectroscopy observations of the five brightest star-forming knots. The analysis of the spectra in all knots allowed the derivation of ionic chemical abundances of oxygen, nitrogen, sulphur, argon and neon using measures of both the high- and low-excitation electron temperatures, leading to the conclusion that NGC 6789 is chemically homogeneous with low values of the abundance of oxygen in the range 12+log(O/H) = 7.80-7.93, but presenting at the same time higher values of the nitrogen-to-oxygen ratio than expected for its metal regime. We used archival HST/WFPC2 F555W and F814W observations of NGC 6789 to perform a photometric study of the colour-magnitude diagram (CMD) of the resolved stellar populations and derive its star formation history (SFH), which is compatible with the presence of different young and old stellar populations who...

  1. A spectroscopic study of blue supergiant stars in the Sculptor galaxy NGC 55: chemical evolution and distance

    CERN Document Server

    Kudritzki, Rolf; Castro, Norberto; Ho, I-Ting; Bresolin, Fabio; Gieren, Wolfgang; Pietrzynski, Grzegorz; Przybilla, Norbert

    2016-01-01

    Low resolution (4.5 to 5 Angstroem) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities and metallicities (from iron peak and alpha-elements). A metallicity gradient of -0.22 +/- 0.06$ dex/R_25 is detected. The central metallicity on a logarithmic scale relative to the Sun is [Z] = -0.37 +\\- 0.03. A chemical evolution model using the observed distribution of stellar and interstellar medium gas mass column densities reproduces the observed metallicity distribution well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extra-planar metal poor HII regions detected in previous work 1.13 to 2.22 kpc above th...

  2. The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

    CERN Document Server

    Meynet, Georges; Georgy, Cyril

    2015-01-01

    (abridged) The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g = Teff^4. BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool to determine extragalactic distances. Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal to be used as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation of the FGLR as an extragalactic distance indicator. We use different grids of stellar models for initial masses between 9 and 40 Msun, for metallicities between Z = 0.002 and 0.014, with and without rotation, computed with various mass loss rates during the red supergiant phase. For each of these models we discuss the details of post-main sequence evolution and constru...

  3. Continuum and line emission of flares on red dwarf stars: origin of the blue continuum radiation

    CERN Document Server

    Morchenko, E S

    2016-01-01

    There are two types of models that explain the appearance of the blue continuum radiation during the impulsive phase of stellar flares. Grinin and Sobolev (Astrophysics, vol. 13, 348, 1977) argue that this component of the optical continuum is formed in "the transition layer between the chromosphere and the photosphere". Katsova et al. (Astrophysics, vol. 17, 156, 1981) have "raised" the source of the white-light continuum up to the dense region in the perturbed chromosphere. In the present contribution (the main paper was submitted to journal "Astrophysics"), we show that the statement by Katsova et al. is erroneous.

  4. Radio detection of nebulae around four luminous blue variable stars in the Large Magellanic Cloud

    OpenAIRE

    Agliozzo, C.; Umana, G.; Trigilio, C.; Buemi, C; Leto, P.; Ingallinera, A.; T. Franzen; Noriega-Crespo, A.

    2012-01-01

    The nebulae associated with four luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC) have been observed at 5.5 and 9 GHz using the Australia Telescope Compact Array, and radio emission has been detected for first time in sources R127, R143, S61 and S119. The radio maps of the nebulae have an angular resolution of ∼1.5 arcsec and a sensitivity of 1.5–3.0 × 10^(−2)  mJy  beam^(−1) and show a very similar morphology to that observed in Hα. This similarity permits us to assume that...

  5. Deep multiband surface photometry on star forming galaxies: I. A sample of 24 blue compact galaxies

    CERN Document Server

    Micheva, Genoveva; Bergvall, Nils; Zackrisson, Erik; Masegosa, Josefa; Marquez, Isabel; Marquart, Thomas; Durret, Florence

    2012-01-01

    [Abridged] We present deep optical and near-infrared UBVRIHKs imaging data for 24 blue compact galaxies (BCGs). The sample contains luminous dwarf and intermediate-mass BCGs which are predominantly metal-poor, although a few have near-solar metallicities. We have analyzed isophotal and elliptical integration surface brightness and color profiles, extremely deep (mu_B<29 mag arcsec^{-2}) contour maps and RGB images for each galaxy in the sample. The colors are compared to different spectral evolutionary models. We detect extremely extended low surface brightness (LSB) components dominant beyond the Holmberg radius as well as optical bridges between companion galaxies at the mu_V~28th mag arcsec^{-2} isophotal level. The central surface brightness mu_0 and scale length h_r are derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. We find that mu_0 and h_r of the BCGs host deviate from those of dwarf ellipticals (dE) and dwarf irregulars (dI) solely due to a strong bu...

  6. The Swift UVOT Stars Survey: I. Methods and Test Clusters

    CERN Document Server

    Siegel, Michael H; Linevsky, Jacquelyn S; Bond, Howard E; Holland, Stephen T; Hoversten, Erik A; Berrier, Joshua L; Breeveld, Alice A; Brown, Peter J; Gronwall, Caryl A

    2014-01-01

    We describe the motivations and background of a large survey of nearby stel- lar populations using the Ultraviolet Optical Telescope (UVOT) aboard the Swift Gamma-Ray Burst Mission. UVOT, with its wide field, NUV sensitivity, and 2.3 spatial resolution, is uniquely suited to studying nearby stellar populations and providing insight into the NUV properties of hot stars and the contribution of those stars to the integrated light of more distant stellar populations. We review the state of UV stellar photometry, outline the survey, and address problems spe- cific to wide- and crowded-field UVOT photometry. We present color-magnitude diagrams of the nearby open clusters M 67, NGC 188, and NGC 2539, and the globular cluster M 79. We demonstrate that UVOT can easily discern the young- and intermediate-age main sequences, blue stragglers, and hot white dwarfs, pro- ducing results consistent with previous studies. We also find that it characterizes the blue horizontal branch of M 79 and easily identifies a known post-...

  7. Deep Imaging of Eridanus II and Its Lone Star Cluster

    Science.gov (United States)

    Crnojević, D.; Sand, D. J.; Zaritsky, D.; Spekkens, K.; Willman, B.; Hargis, J. R.

    2016-06-01

    We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey, Eridanus II (Eri II). Our Magellan/Megacam stellar photometry reaches ˜3 mag deeper than previous work and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II’s center. This makes Eri II, at {M}V=-7.1, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at {M}V=-3.5 it accounts for ˜4% of Eri II’s luminosity. We derive updated structural parameters for Eri II, which has a half-light radius of ˜280 pc and is elongated (ɛ ˜ 0.48) at a measured distance of D ˜ 370 kpc. The color-magnitude diagram displays a blue, extended horizontal branch, as well as a less populated red horizontal branch. A central concentration of stars brighter than the old main-sequence turnoff hints at a possible intermediate-age (˜3 Gyr) population; alternatively, these sources could be blue straggler stars. A deep Green Bank Telescope observation of Eri II reveals no associated atomic gas. This paper includes data gathered with the 6.5 m Magellan Telescopes at Las Campanas Observatory, Chile.

  8. KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS

    International Nuclear Information System (INIS)

    Here, we present a kinematic study of the Galactic halo out to a radius of ∼60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates (σr, σθ, σφ) and the anisotropy profile (β). The radial velocity dispersion profile (σr) is measured out to a galactocentric radius of r ∼ 60 kpc, but due to the lack of proper-motion information, σθ, σφ, and β could only be derived directly out to r ∼ 25 kpc. From a starting value of β ≈ 0.5 in the inner parts (9 circ) of the Galaxy out to r ∼ 25 kpc. The mass of the Galaxy within r ∼11 M☉, and with a three-component fit to vcirc(r), we determine the virial mass of the Milky Way dark matter halo to be Mvir = 0.9+0.4–0.3 × 1012 M☉ (Rvir = 249+34–31 kpc).

  9. The Century Survey Galactic Halo Project III: A Complete 4300 deg^2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo

    CERN Document Server

    Brown, Warren R; Wilhelm, Ronald; Prieto, Carlos Allende; Geller, Margaret J; Kenyon, Scott J; Kurtz, Michael J

    2007-01-01

    We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch (BHB) candidates selected over 4300 deg^2 of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane |Z|<4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H]= -1.7, a rotation velocity gradient of dv_{rot}/d|Z|= -28+-3.4 km/s in the region |Z|<6 kpc, and a density scale height of h_Z= 1.26+-0.1 kpc. The BHB stars located at 5<|Z|<9 kpc are a predominantly inner-halo population, with a mean metallicity of [Fe/H]= -2.0 and a mean Galactic rotation of -4+-31 km/s. We infer the density of halo and thick disk BHB stars is 104+-37 kpc^-3 near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4+-1% near the Sun.

  10. The Clusters AgeS Experiment (CASE). Variable stars in the field of the globular cluster NGC 362

    CERN Document Server

    Rozyczka, M; Narloch, W; Pych, W; Czerny, A Schwarzenberg -

    2016-01-01

    The field of the globular cluster NGC 362 was monitored between 1997 and 2015 in a search for variable stars. BV light curves were obtained for 151 periodic or likely periodic variables, over a hundred of which are new detections. Twelve newly detected variables are proper motion members of the cluster: two SX Phe and two RR Lyr pulsators, one contact binary, three detached or semi-detached eclipsing binaries, and four spotted variables. The most interesting objects among these are the binary blue straggler V20 with an asymmetric light curve, and the 8.1 d semidetached binary V24 located on the red giant branch of NGC 362, which is a Chandra X-ray source. We also provide substantial new data for 24 previously known variables.

  11. Testing asteroseismic scaling relations using eclipsing binaries in star clusters and the field

    Science.gov (United States)

    Brogaard, K.; Jessen-Hansen, J.; Handberg, R.; Arentoft, T.; Frandsen, S.; Grundahl, F.; Bruntt, H.; Sandquist, E. L.; Miglio, A.; Beck, P. G.; Thygesen, A. O.; Kjærgaard, K. L.; Haugaard, N. A.

    2016-09-01

    The accuracy of stellar masses and radii determined from asteroseismology is not known! We examine this issue for giant stars by comparing classical measurements of detached eclipsing binary systems (dEBs) with asteroseismic measurements from the Kepler mission. For star clusters, we extrapolate measurements of dEBs in the turn-off region to the red giant branch and the red clump where we investigate the giants as an ensemble. For the field stars, we measure dEBs with an oscillating giant component. These measurements allow a comparison of masses and radii calculated from a classical eclipsing binary analysis to those calculated from asteroseismic scaling relations and/or other asteroseismic methods. Our first results indicate small but significant systematic differences between the classical and asteroseismic measurements. In this contribution we show our latest results and summarize the current status and future plans. We also stress the importance of realizing that for giant stars mass cannot always be translated to age, since an unknown fraction of these evolved through a blue straggler phase with mass transfer in a binary system. Rough estimates of how many such stars to expect are given based on our findings in the open clusters NGC 6819 and NGC 6791.

  12. A study of the old galactic star cluster Berkeley 32

    CERN Document Server

    Richtler, T; Richtler, Tom; Sagar, Ram

    2001-01-01

    We present new CCD photometry of the distant old open star cluster Berkeley 32 in Johnson V and Cousins I passbands. A total of about 3200 stars have been observed in a field of 13X13 arcmin**2. The colour-magnitude diagram in V, (V-I) has been generated down to V = 22 mag. A broad but well defined main sequence is clearly visible. Some blue stragglers, a well developed subgiant branch and a Red Clump are also seen. By fitting isochrones to this CMD as well as to other CMDs available in the literature, and using the Red Clump location, the reddening, distance and age of the star cluster have been determined. The cluster has a distance of 3.3 kpc, its radius is about 2.4 pc; the reddening E(B-V) is 0.08 mag and the age is 6.3 Gyr. By comparison with theoretical isochrones, a metallicity of [Fe/H]= -0.2 dex has been estimated. We find a much flatter mass function than what has been found for young clusters. If the mass function is a power law dN/dm = const.*m**alpha, then we get alpha = -0.5+-0.3 in the mass ra...

  13. A possible formation channel for blue hook stars in globular cluster - II. Effects of metallicity, mass ratio, tidal enhancement efficiency and helium abundance

    CERN Document Server

    Lei, Zhenxin; Zeng, Aihua; Shen, Lihua; Lan, Zhongjian; Jiang, Dengkai; Han, Zhanwen

    2016-01-01

    Employing tidally enhanced stellar wind, we studied in binaries the effects of metallicity, mass ratio of primary to secondary, tidal enhancement efficiency and helium abundance on the formation of blue hook (BHk) stars in globular clusters (GCs). A total of 28 sets of binary models combined with different input parameters are studied. For each set of binary model, we presented a range of initial orbital periods that is needed to produce BHk stars in binaries. All the binary models could produce BHk stars within different range of initial orbital periods. We also compared our results with the observation in the Teff-logg diagram of GC NGC 2808 and {\\omega} Cen. Most of the BHk stars in these two GCs locate well in the region predicted by our theoretical models, especially when C/N-enhanced model atmospheres are considered. We found that mass ratio of primary to secondary and tidal enhancement efficiency have little effects on the formation of BHk stars in binaries, while metallicity and helium abundance would...

  14. Blue and IR Light Curves of the Mysterious Pre-Main Sequence Star V582 Mon (KH 15D) from 1955 to 1970

    CERN Document Server

    Maffei, P; Tosti, G; Maffei, Paolo; Ciprini, Stefano; Tosti, Gino

    2004-01-01

    In recent years, an increasing number of publications have been addressed to the peculiar and mysterious pre-main sequence star V582 Mon, also known as KH 15D. This extraordinary T Tauri star, located in the young star cluster NGC 2264, appears as to be an eclipsing variable. In the present paper, we report a unique and self-consistent set of light curves in the blue and near-infrared bands, spanning a 15-year interval (epoch 1955-1970). Our photometric data show clearly the beginning of the eclipse stage occurred in early 1958 in the blue, and perhaps around four years later in the infrared. The light curve period turns out to be the same reported by recent observations (about 48.3 days), so that no evidence for a period change results. On the other hand, in our data the light curve shape appears as sinusoidal and is therefore different from the one displayed today. The photometric behaviour, determined with time-series and colour-index analysis, suggests that V582 Mon (KH 15D) could be initially surrounded ...

  15. Discovery of a stripped red giant core in a bright eclipsing binary star

    CERN Document Server

    Maxted, P F L; Burleigh, M R; Collier-Cameron, A; Heber, U; Gänsicke, B T; Geier, S; Kupfer, T; Marsh, T R; Nelemans, G; O'Toole, S J; Østensen, R H; Smalley, B; West, R G; Bloemen, S

    2012-01-01

    We report the serendipitous discovery from WASP archive photometry of a binary star in which an apparently normal A-type star (J0247-25A) eclipses a smaller, hotter subdwarf star (J0247-25B). The kinematics of J0247-25A show that it is a blue-straggler member of the Galactic thick-disk. We present follow-up photometry and spectroscopy from which we derive approximate values for the mass, radius and luminosity for J0247-25B assuming that J0247-25A has the mass appropriate for a normal thick-disk star. We find that the properties of J0247-25B are well matched by models for a red giant stripped of its outer layers and currently in a shell hydrogen-burning stage. In this scenario, J0247-25B will go on to become a low mass white dwarf (M~0.25 solar masses) composed mostly of helium. J0247-25B can be studied in much greater detail than the handful of pre helium white dwarfs (pre-He-WD) identified to-date. These results have been published by Maxted et al., 2011. We also present a preliminary analysis of more recent...

  16. NON-LOCAL THERMODYNAMICAL EQUILIBRIUM EFFECTS ON THE IRON ABUNDANCE OF ASYMPTOTIC GIANT BRANCH STARS IN 47 TUCANAE

    Energy Technology Data Exchange (ETDEWEB)

    Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Massari, D. [Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Origlia, L. [INAF- Osservatorio Astronomico di Bologna, Via Ranzani, 1, 40127 Bologna (Italy)

    2014-12-20

    We present the iron abundance of 24 asymptotic giant branch (AGB) stars, members of the globular cluster 47 Tucanae, obtained with high-resolution spectra collected with the FEROS spectrograph at the MPG/ESO 2.2 m Telescope. We find that the iron abundances derived from neutral lines (with a mean value [Fe I/H] =–0.94 ± 0.01, σ = 0.08 dex) are systematically lower than those derived from single ionized lines ([Fe II/H] =–0.83 ± 0.01, σ = 0.05 dex). Only the latter are in agreement with those obtained for a sample of red giant branch (RGB) cluster stars, for which the Fe I and Fe II lines provide the same iron abundance. This finding suggests that non-local thermodynamical equilibrium (NLTE) effects driven by overionization mechanisms are present in the atmosphere of AGB stars and significantly affect the Fe I lines while leaving Fe II features unaltered. On the other hand, the very good ionization equilibrium found for RGB stars indicates that these NLTE effects may depend on the evolutionary stage. We discuss the impact of this finding on both the chemical analysis of AGB stars and on the search for evolved blue stragglers.

  17. KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; Bland-Hawthorn, Joss, E-mail: p.kafle@physics.usyd.edu.au [Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006 (Australia)

    2012-12-20

    Here, we present a kinematic study of the Galactic halo out to a radius of {approx}60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates ({sigma}{sub r}, {sigma}{sub {theta}}, {sigma}{sub {phi}}) and the anisotropy profile ({beta}). The radial velocity dispersion profile ({sigma}{sub r}) is measured out to a galactocentric radius of r {approx} 60 kpc, but due to the lack of proper-motion information, {sigma}{sub {theta}}, {sigma}{sub {phi}}, and {beta} could only be derived directly out to r {approx} 25 kpc. From a starting value of {beta} Almost-Equal-To 0.5 in the inner parts (9 < r/kpc < 12), the profile falls sharply in the range r Almost-Equal-To 13-18 kpc, with a minimum value of {beta} = -1.2 at r = 17 kpc, rising sharply at larger radius. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of {beta} Almost-Equal-To 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (v{sub circ}) of the Galaxy out to r {approx} 25 kpc. The mass of the Galaxy within r {approx}< 25 kpc is determined to be 2.1 Multiplication-Sign 10{sup 11} M{sub Sun }, and with a three-component fit to v{sub circ}(r), we determine the virial mass of the Milky Way dark matter halo to be M{sub vir} = 0.9{sup +0.4}{sub -0.3} Multiplication-Sign 10{sup 12} M{sub Sun} (R{sub vir} = 249{sup +34}{sub -31} kpc).

  18. 2,4-Dicyano-3-diethylamino-9,9-diethylfluorene Based Blue Light-emitting Star-shaped Compounds: Synthesis and Properties

    Institute of Scientific and Technical Information of China (English)

    CHEN,Xiaohang; CHEN,Xiaopeng; ZHAO,Zujin; L(U),Ping; WANG,Yanguang

    2009-01-01

    Two new star-shaped molecules 1 and 2 containing a triphenylamine/benzene moiety as the central core and three 2,4-dicyano-3-diethylamino-9,9-diethylfluorene moieties as the peripheral functional groups were synthesized and characterized. Charge transfer properties for these compounds were observed in photophysical experiments due to their D-A molecular structure. Compound 1 presented dual fluorescence in high polar solvents. Moreover, these compounds exhibited moderate fluorescence and high thermal stabilities, indicating their potential application to blue light emitting materials.

  19. Statistical Properties of Blue Horizontal Branch Stars in the Spheroid: Detection of a Moving Group approximately 50 kpc from the Sun

    CERN Document Server

    Harrigan, Matthew J; Newberg, Lee A; Yanny, Brian; Beers, Timothy C; Lee, Young Sun; Fiorentin, Paola Re

    2010-01-01

    A new moving group comprising at least four Blue Horizontal Branch (BHB) stars is identified at (l,b) = (65 deg, 48 deg). The horizontal branch at g0=18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric radial velocity is RV = -157 +/- 4 km/s, corresponding to V(gsr) = -10 km/s; the dispersion in line-of-sight velocity is consistent with the instrumental errors for these stars. The mean metallicity of the moving group is [Fe/H] approximately -2.4, which is significantly more metal poor than the stellar spheroid. We estimate that the BHB stars in the outer halo have a mean metallicity of [Fe/H] = -2.0, with a wide scatter and a distribution that does not change much as a function of distance from the Sun. We explore the systematics of SDSS DR7 surface gravity metallicity determinations for faint BHB stars, and present a technique for estimating the significance of clumps discovered in multidimensional data. This moving group cannot be distinguished in density, and highlights the need to c...

  20. Massive Stars in Interactive Binaries

    Science.gov (United States)

    St.-Louis, Nicole; Moffat, Anthony F. J.

    Massive stars start their lives above a mass of ~8 time solar, finally exploding after a few million years as core-collapse or pair-production supernovae. Above ~15 solar masses, they also spend most of their lives driving especially strong, hot winds due to their extreme luminosities. All of these aspects dominate the ecology of the Universe, from element enrichment to stirring up and ionizing the interstellar medium. But when they occur in close pairs or groups separated by less than a parsec, the interaction of massive stars can lead to various exotic phenomena which would not be seen if there were no binaries. These depend on the actual separation, and going from wie to close including colliding winds (with non-thermal radio emission and Wolf-Rayet dust spirals), cluster dynamics, X-ray binaries, Roche-lobe overflow (with inverse mass-ratios and rapid spin up), collisions, merging, rejuventation and massive blue stragglers, black-hole formation, runaways and gamma-ray bursts. Also, one wonders whether the fact that a massive star is in a binary affects its parameters compared to its isolated equivalent. These proceedings deal with all of these phenomena, plus binary statistics and determination of general physical properties of massive stars, that would not be possible with their single cousins. The 77 articles published in these proceedings, all based on oral talks, vary from broad revies to the lates developments in the field. About a third of the time was spent in open discussion of all participants, both for ~5 minutes after each talk and 8 half-hour long general dialogues, all audio-recorded, transcribed and only moderately edited to yield a real flavour of the meeting. The candid information in these discussions is sometimes more revealing than the article(s) that preceded them and also provide entertaining reading. The book is suitable for researchers and graduate students interested in stellar astrophysics and in various physical processes involved when

  1. SN 2015bh: NGC 2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?

    CERN Document Server

    Thöne, C C; Leloudas, G; Gall, C; Cano, Z; Maeda, K; Schulze, S; Campana, S; Wiersema, K; Groh, J; de la Rosa, J; Bauer, F E; Malesani, D; Maund, J; Morrell, N; Beletsky, Y

    2016-01-01

    Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, "SN impostors", but the distinction is not always straigthforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 years that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN or "main event" was preceded by a precursor peaking $\\sim$ 40 days before maximum. The total energy release of the main event is $\\sim$1.8$\\times$10$^{49}$ erg, which can be modeled by a $<$ 0.5 M$_\\odot$ shell plunging into a dense CSM. All emission lines show a single narrow P-Cygni profile during the LBV phase and a double P-Cygni profile post maximum suggesting an association of this second component with the possible SN. Since 1994 the star has been redder than during a typical S-Dor like outburst. SN 2015bh lies within a spiral arm of NGC 2770 next to a number of small star-forming regions with a m...

  2. Stellar envelope inflation near the Eddington limit. Implications for the radii of Wolf-Rayet stars and luminous blue variables

    CERN Document Server

    Gräfener, G; Vink, J S

    2011-01-01

    (shortened) It has been proposed that the envelopes of luminous stars may be subject to substantial radius inflation. The inflation effect has been discussed in relation to the radius problem of WR stars, but has yet failed to explain the large observed radii of Galactic WR stars. We wish to obtain a physical perspective of the inflation effect, and study the consequences for the radii of WR stars, and LBVs. For WR stars the observed radii are up to an order of magnitude larger than predicted by theory, whilst S Doradus-type LBVs are subject to humongous radius variations, which remain as yet ill-explained. We use a dual approach to investigate the envelope inflation, based on numerical models for stars near the Eddington limit, and a new analytic formalism to describe the effect. An additional new aspect is that we take the effect of density inhomogeneities (clumping) within the outer stellar envelopes into account. Due to the effect of clumping we are able to bring the observed WR radii in agreement with th...

  3. The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-Violet at R~2500

    CERN Document Server

    Sota, A; Walborn, N R; Alfaro, E J; Barbá, R H; Morrell, N I; Gamen, R C; Arias, J I

    2011-01-01

    We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R~2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of Ma\\'iz Apell\\'aniz et al. (2004) and Sota et al. (2008). The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B=8 and north of delta = -20 and includes all of the northern objects in Ma\\'iz Apell\\'aniz et al. (2004) that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent invest...

  4. Engineering the Interconnecting Position of Star-Shaped Donor-π-Acceptor Molecules Based on Triazine, Spirofluorene, and Triphenylamine Moieties for Color Tuning from Deep Blue to Green.

    Science.gov (United States)

    Wang, Yafei; Liu, Wanhui; Deng, Jiyong; Xie, Guohua; Liao, Yuanwei; Qu, Zuoming; Tan, Hua; Liu, Yu; Zhu, Weiguo

    2016-09-20

    Pi-conjugated organic molecules featuring the donor-bridge-acceptor (D-π-A) structure have been widely used in semiconducting materials owing to their rigid structure, good thermal stability, excellent charge transfer, and high emission efficiency. To investigate the effect of the D-π-A molecular structure on the photophysical properties, in this contribution, three star-shaped D-π-A isomers based on the 2,4,6-triphenyl-1,3,5-triazine, spirofluorene, and triphenylamine moieties, that is, p-TFTPA, mp-TFTPA, and m-TFTPA, were synthesized by elaborately engineering the interconnecting position in the building-block units. The optophysical properties of these compounds were systematically explored by experiments and theory calculations. Definitively, changing the interconnecting position in these molecules played a significant role in the degree of π conjugation, which resulted in tunable emission colors from deep blue to green. Moreover, these isomers were employed as emissive dopants in organic light-emitting diodes. The highest external quantum efficiency of 2.3 % and current efficiency of 6.2 cd A(-1) were achieved by using the p-TFTPA based device. This research demonstrates a feasible way to realize blue emitters by engineering D-π-A conjugation.

  5. Observational Investigations on Contact Binaries in Multiple-star Systems and Star Clusters

    Science.gov (United States)

    Liu, L.

    2013-01-01

    ER Cep is three times larger than that of the star at the turn-off point of the cluster's main-sequence, suggesting that ER Cep is at least a triple system. There is weak evidence showing that the system has another small cyclic oscillation with a period of 17.6 years. If this is true, ER Cep is likely to be a quadruple system. It is not surprise that such system can be found in an old open cluster like NGC 188. The periodic long-term increase of EQ Cep may be caused by mass transfer from the less massive component to the more massive one. As the mass ratio decreases, the system will evolve into a blue straggler. This conclusion is supported by the fact that 76% of the blue stragglers in NGC 188 are currently in binary systems. The values of the acceleration of gravity on the surface of V371 Cep reveal that this system is composed of two post main-sequence stars. It is the first example whose components are post main-sequence stars. Because of the short evolutionary time scale for the subgiants, V371 Cep is a rare object which will demonstrate a picture of a contact binary at the end of its evolution stage. (4) The contact binary QX And in the moderate-age open cluster NGC 752 has a very strong magnetic activity, with a period of about 2 years. (5) The contact binary V47 in the globular cluster M4 has an extreme mass ratio and a moderate contact factor. The mass ratio is the smallest one in this thesis. However, V53, which is also in the M4, is a system with a large mass ratio and a deep contact factor. It is meanwhile a blue straggler, which is a good target for the study of the merging binaries. (6) The contact binary V95 in the globular cluster 47 Tuc has an extreme mass ratio and a deep contact factor. The most interesting thing is that V95 shows strong magnetic activity in a metal poor cluster. (7) Through analyzing the data of the ASAS survey, we find that the distribution of the detached and semi-detached binaries tend to be located in the galactic plane

  6. Accurate age determinations of several nearby open clusters containing magnetic Ap stars

    CERN Document Server

    Silaj, J

    2014-01-01

    Aims: Our aim is to obtain ages that are as accurate as possible for the seven nearby open clusters alpha Per, Coma Ber, IC 2602, NGC 2232, NGC 2451A, NGC 2516, and NGC 6475, each of which contains at least one magnetic Ap or Bp star. Simultaneously, we test the current calibrations of Te and luminosity for the Ap/Bp star members, and identify clearly blue stragglers in the clusters studied. Methods: We explore the possibility that isochrone fitting in the theoretical Hertzsprung-Russell diagram (i.e. log (L/L&sun;) vs. log Te), rather than in the conventional colour-magnitude diagram, can provide more precise and accurate cluster ages, with well-defined uncertainties. Results: Well-defined ages are found for all the clusters studied. For the nearby clusters studied, the derived ages are not very sensitive to the small uncertainties in distance, reddening, membership, metallicity, or choice of isochrones. Our age determinations are all within the range of previously determined values, but the associated u...

  7. Red or blue? A potential kilonova imprint of the delay until black hole formation following a neutron star merger

    CERN Document Server

    Metzger, Brian D

    2014-01-01

    Mergers of binary neutron stars (NSs) usually result in the formation of a hypermassive neutron star (HMNS). Whether- and when this remnant collapses to a black hole (BH) depends primarily on the equation of state and on angular momentum transport processes, both of which are uncertain. Here we show that the lifetime of the merger remnant may be directly imprinted in the radioactively powered kilonova emission following the merger. We employ axisymmetric, time-dependent hydrodynamic simulations of remnant accretion disks orbiting a HMNS of variable lifetime, and characterize the effect of this delay to BH formation on the disk wind ejecta. Our models follow the system evolution over several seconds, and include the effect of nuclear recombination, viscous heating, and neutrino irradiation by both the HMNS and the disk. When BH formation is relatively prompt ( 140, resulting in ~week-long emission with a spectral peak in the near-infrared (NIR), similar to that produced by the dynamical ejecta. In contrast, de...

  8. Bona-fide, strong-variable galactic Luminous Blue Variable stars are fast rotators: detection of a high rotational velocity in HR Carinae

    CERN Document Server

    Groh, Jose H; Hillier, D John; Barba, Rodolfo; Fernandez-Lajus, Eduardo; Gamen, Roberto C; Moises, Alessandro; Solivella, Gladys; Teodoro, Mairan

    2009-01-01

    We report optical observations of the Luminous Blue Variable (LBV) HR Carinae which show that the star has reached a visual minimum phase in 2009. More importantly, we detected absorptions due to Si IV 4088-4116 Angstroms. To match their observed line profiles from 2009 May, a high rotational velocity of vrot=150 +- 20 km/s is needed (assuming an inclination angle of 30 degrees), implying that HR Car rotates at ~0.88 +- 0.2 of its critical velocity for break-up (vcrit). Our results suggest that fast rotation is typical in all strong-variable, bona-fide galactic LBVs, which present S Dor-type variability. Strong-variable LBVs are located in a well-defined region of the HR diagram during visual minimum (the "LBV minimum instability strip"). We suggest this region corresponds to where vcrit is reached. To the left of this strip, a forbidden zone with vrot/vcrit>1 is present, explaining why no LBVs are detected in this zone. Since dormant/ex LBVs like P Cygni and HD 168625 have low vrot, we propose that LBVs can ...

  9. Postpartum Blues

    Medline Plus

    Full Text Available ... blues The postpartum blues E-mail to a friend Please fill in all fields. Please enter a ... blues: Talk to your partner or a good friend about how you feel Get plenty of rest ...

  10. A Deep Catalog of Variable Stars in a 0.66deg^2 Lupus Field

    CERN Document Server

    Weldrake, David T F

    2007-01-01

    We have conducted a wide-field photometric survey in a single 52'x52' field towards the Lupus Galactic Plane in an effort to detect transiting Hot Jupiter planets. The planet Lupus-TR-3b was identified from this work. The dataset also led to the detection of 494 field variables, all of which are new discoveries. This paper presents an overview of the project, along with the total catalog of variables, which comprises 190 eclipsing binaries (of contact, semi-contact and detached configurations), 51 miscellaneous pulsators of various types, 237 long period variables (P>=2d), 11 delta Scuti stars, 4 field RR Lyrae (3 disk and 1 halo) and 1 irregular variable. Our survey provides a complete catalog of W UMa eclipsing binaries in the field to V=18.8, which display a Gaussian period distribution of 0.277+/-0.036d. Several binary systems are likely composed of equal mass M-dwarf components and others display evidence of mass transfer. We find 17 candidate blue stragglers and one binary that has the shortest period k...

  11. Close binary stars in the solar-age Galactic open cluster M67

    CERN Document Server

    Yakut, K; Kalomeni, B; Van Winckel, H; Waelkens, C; De Cat, P; Bauwens, E; Vuckovic, M; Saesen, S; Guillou, L Le; Parmaksizoglu, M; Uluc, K; Khamitov, I; Raskin, G; Aerts, C

    2009-01-01

    We present multi-colour time-series CCD photometry of the solar-age galactic open cluster M67 (NGC 2682). About 3600 frames spread over 28 nights were obtained with the 1.5 m Russian-Turkish and 1.2 m Mercator telescopes. High-precision observations of the close binary stars AH Cnc, EV Cnc, ES Cnc, the $\\delta$ Scuti type systems EX Cnc and EW Cnc, and some long-period variables belonging to M67 are presented. Three full multi-colour light curves of the overcontact binary AH Cnc were obtained during three observing seasons. Likewise we gathered three light curves of EV Cnc, an EB-type binary, and two light curves of ES Cnc, a blue straggler binary. Parts of the light change of long-term variables S1024, S1040, S1045, S1063, S1242, and S1264 are obtained. Period variation analysis of AH Cnc, EV Cnc, and ES Cnc were done using all times of mid-eclipse available in the literature and those obtained in this study. In addition, we analyzed multi-colour light curves of the close binaries and also determined new fre...

  12. A close hidden stellar companion to the SX Phe-type variable star DW Psc

    Energy Technology Data Exchange (ETDEWEB)

    Qian, S.-B.; Li, L.-J.; Wang, S.-M.; He, J.-J.; Zhou, X.; Jiang, L.-Q., E-mail: qsb@ynao.ac.cn [Yunnan Observatories, Chinese Academy of Sciences (CAS), P.O. Box 110, 650011 Kunming (China)

    2015-01-01

    DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the observed-calculated (O-C) diagram are analyzed. It is discovered that the O-C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion (M{sub 2}sini∼0.45(±0.03) M{sub ⊙}). The two-component stars in the binary system are orbiting each other in an eccentric orbit (e ∼ 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Roche-lobe overflow, and the system may be a progenitor of a cataclysmic variable. The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future.

  13. A close hidden stellar companion to the SX Phe-type variable star DW Psc

    International Nuclear Information System (INIS)

    DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the observed-calculated (O-C) diagram are analyzed. It is discovered that the O-C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion (M2sini∼0.45(±0.03) M⊙). The two-component stars in the binary system are orbiting each other in an eccentric orbit (e ∼ 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Roche-lobe overflow, and the system may be a progenitor of a cataclysmic variable. The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future.

  14. A Close Hidden Stellar Companion to the SX Phe-Type Variable Star DW Psc

    Science.gov (United States)

    Qian, S.-B.; Li, L.-J.; Wang, S.-M.; He, J.-J.; Zhou, X.; Jiang, L.-Q.

    2015-01-01

    DW Psc is a high-amplitude SX Phe-type variable with a period of pulsation of 0.05875 days. Using a few newly determined times of maximum light together with those collected from the literature, the changes in the observed-calculated (O-C) diagram are analyzed. It is discovered that the O-C curve of DW Psc shows a cyclic variation with a period of 6.08 years and a semi-amplitude of 0.0066 days. The periodic variation is analyzed for the light travel time effect, which is due to the presence of a stellar companion ({{M}2}sin i˜ 0.45(+/- 0.03) {{M}⊙ }). The two-component stars in the binary system are orbiting each other in an eccentric orbit (e ˜ 0.4) at an orbital separation of about 2.7(±0.3) AU. The detection of a close stellar companion to an SX Phe-type star supports the idea that SX Phe-type pulsating stars are blue stragglers that were formed from the merging of close binaries. The stellar companion has played an important role in the merging of the original binary by removing angular momentum from the central binary during early dynamical interaction or/and late dynamical evolution. After the more massive component in DW Psc evolves into a red giant, the cool close companion should help to remove the giant envelope via possible critical Roche-lobe overflow, and the system may be a progenitor of a cataclysmic variable. The detection of a close stellar companion to DW Psc makes it a very interesting system to study in the future.

  15. Postpartum Blues

    Medline Plus

    Full Text Available ... Quality Collaboratives Launch Prematurity research centers What is team science? More than 75 years of solving problems ... delivery cause the postpartum blues. How can you manage the baby blues? The American College of Obstetricians ...

  16. Postpartum Blues

    Medline Plus

    Full Text Available ... with this condition are happy most of the time. But compared to how she usually feels, the ... the "blues" usually lessens and goes away over time. What causes the baby blues? Medical experts believe ...

  17. Postpartum Blues

    Medline Plus

    Full Text Available ... Postpartum care > The postpartum blues The postpartum blues E-mail to a friend Please fill in all fields. Please enter a valid e-mail address. Your information: Your recipient's information: Your ...

  18. Postpartum Blues

    Medline Plus

    Full Text Available ... can you manage the baby blues? The American College of Obstetricians and Gynecologists recommends that women do ... can you manage the baby blues? The American College of Obstetricians and Gynecologists recommends that women do ...

  19. Postpartum Blues

    Medline Plus

    Full Text Available ... Feels sad Feels confused The postpartum blues peak three to five days after delivery. They usually end ... Feels sad Feels confused The postpartum blues peak three to five days after delivery. They usually end ...

  20. Postpartum Blues

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    Full Text Available ... postpartum blues The postpartum blues E-mail to a friend Please fill in all fields. Please enter ... hear about breakthroughs for babies and families. Ask a question Our health experts can answer questions about ...

  1. Postpartum Blues

    Medline Plus

    Full Text Available ... Medical experts believe that changes in the woman's hormones after delivery cause the postpartum blues. How can ... Medical experts believe that changes in the woman's hormones after delivery cause the postpartum blues. How can ...

  2. CARMA Survey Toward Infrared-bright Nearby Galaxies (STING) II: Molecular Gas Star Formation Law and Depletion Time Across the Blue Sequence

    CERN Document Server

    Rahman, Nurur; Xue, Rui; Wong, Tony; Leroy, Adam K; Walter, Fabian; Bigiel, Frank; Rosolowsky, Erik; Fisher, David B; Vogel, Stuart N; Blitz, Leo; West, Andrew A; Ott, Juergen

    2011-01-01

    We present an analysis of the relationship between molecular gas and current star formation rate surface density at sub-kpc and kpc scales in a sample of 14 nearby star-forming galaxies. Measuring the relationship in the bright, high molecular gas surface density ($\\Shtwo\\gtrsim$20 \\msunpc) regions of the disks to minimize the contribution from diffuse extended emission, we find an approximately linear relation between molecular gas and star formation rate surface density, $\

  3. 基于ITIL标准的移动变更与配置管理系统研究与实现%ITIL-Compliant Mobility Change and Configuration Management in BlueStar

    Institute of Scientific and Technical Information of China (English)

    刘培妮; 刘亮; 陈杨; 王浩

    2009-01-01

    With the rapid growth of powerful mobile devices.to improve the speed and quality of customer service,mobilizing their workforce became more and more important tO many companies.Consequently,all kinds of enterprise applications,policies and data access ale enabled through mobile platforms.However,how to manage such various mobile types and mobile applications and to integrate them with existing enterprise IT infrastructure becomes a great challenge.In this paper,we propose a novel approach to manage the enterprise mobiles through IT service management by using standard ITIL processes.Motivated by real cases of insurance industry mobile solution,firstly,a system architecture named BlueStar iS designed which integrated ITIL-compliant mobile management and enterprise IT service management into a uniform platform.Secondly,typical ITIL processes and best practices:Change and configuration workflow ale introduced for mobility management.Thirdly,the BlueStar system included device management component is implemented and evaluated by the motivating cases.

  4. Kind of Blue - Europa Blues

    DEFF Research Database (Denmark)

    Mortensen, Tore; Kirkegaard, Peter

    2009-01-01

    Bidraget reflekterer over sammenhænge mellem to værker fra det musikalske og litterære område. Det drejer sig om Miles Davis' Kind of Blue fra 1959 og Arne Dahls krimi, Europa Blues fra 2001. Den grundlæggende indfaldsvinkel er det performative, den frie, men samtidigt disciplinerede musikalske...

  5. Fundamental properties of nearby single early B-type stars

    Science.gov (United States)

    Nieva, María-Fernanda; Przybilla, Norbert

    2014-06-01

    Aims: Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in OB associations and in the field within a distance of ≲400 pc from the Sun are presented and compared to high-precision data from detached eclipsing binaries (DEBs). Together with surface abundances for light elements the data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models for core hydrogen-burning stars in the mass-range ~6 to 18 M⊙ at metallicity Z = 0.014. Methods: The fundamental parameters are derived on the basis of accurate and precise atmospheric parameters determined earlier by us from non-LTE analyses of high-quality spectra of the sample stars, utilising the new Geneva stellar evolution models. Results: Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass-radius and mass-luminosity relationships to be recovered for single core hydrogen-burning objects with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically ~0.15-0.20 mag uncertainty. Metallicities are constrained to better than 15-20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Overall, the spectroscopic distances and ages of individual sample stars agree with independently derived values for the host OB associations. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. The presence of magnetic fields appears to augment the mixing efficiency. In addition, a few objects are possibly the product of binary evolution. In particular, the unusual characteristics of τ Sco point to a blue straggler nature, due to a binary merger. Conclusions: The accuracy

  6. Postpartum Blues

    Medline Plus

    Full Text Available ... leader Partner Spotlight Become a partner World Prematurity Day Your support helps babies We are determined to ... confused The postpartum blues peak three to five days after delivery. They usually end by the tenth ...

  7. Postpartum Blues

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    Full Text Available ... Saving Just a moment, please. You've saved this page It's been added to your dashboard . After ... blues" is not really correct since women with this condition are happy most of the time. But ...

  8. Postpartum Blues

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    Full Text Available ... dashboard . After the baby is born, many new mothers have the postpartum blues (also called the baby ... compared to how she usually feels, the new mother: Is more irritable Cries more easily Feels sad ...

  9. Postpartum Blues

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    Full Text Available ... for your baby Feeding your baby Common illnesses New parents Family health & safety Complications & Loss Pregnancy complications ... your dashboard . After the baby is born, many new mothers have the postpartum blues (also called the ...

  10. Star formation and the interstellar medium in low surface brightness galaxies III. Why they are blue, thin and poor in molecular gas

    NARCIS (Netherlands)

    Gerritsen, JPE; de Blok, WJG

    1999-01-01

    We present N-body simulations of Low Surface Brightness (LSB) galaxies and their Interstellar Medium to investigate the cause for their low star formation rates (SFR). Due to their massive halos, stellar disks of LSB galaxies are very stable and thin. Lack of dust makes the projected edge-on surface

  11. Globular clusters in the blue compact galaxy ESO 338-IG04 (Tol 1924-416), as tracers of the star formation history. Results from HST/WFPC2 observations

    CERN Document Server

    Östlin, G A; Rönnback, J; Bergvall, Nils; Rönnback, Jari

    1998-01-01

    Multicolour images of the starbursting metal poor blue compact galaxy ESO338-IG04 have been obtained with WFPC2/HST. In the images we find numerous point-like sources concentrated towards the main body of the galaxy, which we identify as globular cluster candidates. We show that these objects are physically associated with the galaxy and that they are spatially extended. Given their high intrinsic luminosities, these objects cannot be individual stars. Using photometric evolution models we show that the objects constitute a rich population of massive star clusters with ages ranging from a few Myr to 10 Gyr, and masses ranging from 10^4 to more than 10^7 solar masses. We show that these objects are most likely globular clusters of varying age. There are peaks in the age distribution of the clusters: at <30 Myr, ~100 Myr, ~600 Myr, 2.5-5 Gyr and ~10 Gyr. The youngest objects are found in the crowded starburst region. The galaxy presently appears to be involved in a merger, which is the probable cause of the ...

  12. Evolution of the remnants of stellar collisions

    OpenAIRE

    Glebbeek, E.

    2008-01-01

    Collisions between stars occur naturally in star clusters. The outcome of such collisions is a new single star that may have peculiar properties that affect its subsequent evolution. For low mass stars, such merger events are a possible formation channel for blue straggler stars, stars more massive than expected for a starcluster of a given age. For high mass stars, such a merger can result in the production of blue supergiants. If circumstances are right, repeated collisions between stars ma...

  13. CARMA SURVEY TOWARD INFRARED-BRIGHT NEARBY GALAXIES (STING). II. MOLECULAR GAS STAR FORMATION LAW AND DEPLETION TIME ACROSS THE BLUE SEQUENCE

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, Nurur; Bolatto, Alberto D.; Fisher, David B.; Vogel, Stuart N. [Department of Astronomy, University of Maryland, College Park, MD (United States); Xue Rui; Wong, Tony [Department of Astronomy, University of Illinois, Urbana-Champaign, IL (United States); Leroy, Adam K. [National Radio Astronomy Observatory, Charlottesville, VA (United States); Walter, Fabian [Max-Planck-Institute fur Astronomie, Heidelberg (Germany); Bigiel, Frank [Institut fuer Theoretische Astrophysik, Universitaet Heidelberg, D-69120 Heidelberg (Germany); Rosolowsky, Erik [I. K. Barber School of the Arts and Science, University of British-Columbia, Kelowna, BC (Canada); Blitz, Leo [Department of Astronomy, University of California, Berkeley, CA (United States); West, Andrew A. [Department of Astronomy, Boston University, Boston, MA (United States); Ott, Juergen, E-mail: nurur@astro.umd.edu [National Radio Astronomy Observatory, Socorro, NM (United States)

    2012-02-01

    We present an analysis of the relationship between molecular gas and current star formation rate surface density at sub-kiloparsec and kiloparsec scales in a sample of 14 nearby star-forming galaxies. Measuring the relationship in the bright, high molecular gas surface density ({Sigma}{sub H{sub 2}}{approx}>20 M{sub Sun} pc{sup -2}) regions of the disks to minimize the contribution from diffuse extended emission, we find an approximately linear relation between molecular gas and star formation rate surface density, N{sub mol} {approx} 0.96 {+-} 0.16, with a molecular gas depletion time, {tau}{sup mol}{sub dep} {approx} 2.30 {+-} 1.32 Gyr. We show that in the molecular regions of our galaxies there are no clear correlations between {tau}{sup mol}{sub dep} and the free-fall and effective Jeans dynamical times throughout the sample. We do not find strong trends in the power-law index of the spatially resolved molecular gas star formation law or the molecular gas depletion time across the range of galactic stellar masses sampled (M{sub *} {approx} 10{sup 9.7}-10{sup 11.5} M{sub Sun }). There is a trend, however, in global measurements that is particularly marked for low-mass galaxies. We suggest that this trend is probably due to the low surface brightness CO J = 1-0, and it is likely associated with changes in CO-to-H{sub 2} conversion factor.

  14. Ionized Gas Kinematics at High Resolution V: [NeII], Multiple Clusters, High Efficiency Star Formation and Blue Flows in He 2-10

    CERN Document Server

    Beck, Sara C; Lacy, John; Greathouse, Thomas

    2015-01-01

    We measured the $12.8\\mu$m [NeII] line in the dwarf starburst galaxy He 2-10 with the high-resolution spectrometer TeXeS on the NASA IRTF. The data cube has diffraction-limited spatial resolution $\\sim1^{\\prime\\prime}$ and total velocity resolution including thermal broadening of $\\sim5$km/s. This makes it possible to compare the kinematics of individual star-forming clumps and molecular clouds in the three dimensions of space and velocity, and allows us to determine star formation efficiencies. The kinematics of the ionized gas confirm that the starburst contains multiple dense clusters. From the $M/R$ of the clusters and the $\\simeq30-40$% star formation efficiencies the clusters are likely to be bound and long lived, like globulars. Non-gravitational features in the line profiles show how the ionized gas flows through the ambient molecular material, as well as a narrow velocity feature which we identify with the interface of the HII region and a cold dense clump. These data offer an unprecedented view of t...

  15. IONIZED GAS KINEMATICS AT HIGH RESOLUTION. V. [Ne ii], MULTIPLE CLUSTERS, HIGH EFFICIENCY STAR FORMATION, AND BLUE FLOWS IN HE 2–10

    Energy Technology Data Exchange (ETDEWEB)

    Beck, Sara [School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978 (Israel); Turner, Jean [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States); Lacy, John [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Greathouse, Thomas [Southwest Research Institute, San Antonio, TX 78228-0510 (United States)

    2015-11-20

    We measured the 12.8 μm [Ne ii] line in the dwarf starburst galaxy He 2–10 with the high-resolution spectrometer TEXES on the NASA IRTF. The data cube has a diffraction-limited spatial resolution of ∼1″ and a total velocity resolution, including thermal broadening, of ∼5 km s{sup −1}. This makes it possible to compare the kinematics of individual star-forming clumps and molecular clouds in the three dimensions of space and velocity, and allows us to determine star formation efficiencies. The kinematics of the ionized gas confirm that the starburst contains multiple dense clusters. From the M/R of the clusters and the ≃30%–40% star formation efficiencies, the clusters are likely to be bound and long lived, like globulars. Non-gravitational features in the line profiles show how the ionized gas flows through the ambient molecular material, as well as a narrow velocity feature, which we identify with the interface of the H ii region and a cold dense clump. These data offer an unprecedented view of the interaction of embedded H ii regions with their environment.

  16. High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?

    CERN Document Server

    Terlevich, R; Bosch, G; Diaz, A I; Hagele, G; Cardaci, M; Firpo, V

    2014-01-01

    X-shooter and ISIS WHT spectra of the starforming galaxy PHL 293B also known as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000km/s) and very broad (FWZI = 4000km/s) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800km/s, previously undetected FeII multiplet (42) absorptions also blueshifted by 800km/s, IR CaII triplet stellar absorptions consistent with [Fe/H] < -2.0 and no broad components or blushifted absorptions in the HeI lines. Based on historical records, we found no optical variability at the 5 sigma level of 0.02 mag between 2005 and 2013 and no optical variability at the level of 0.1mag for the past 24 years. The lack of variability rules out transient phenomena like luminous blue variables or SN IIn as the origin of the blue shifted absorptions of HI and FeII. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster w...

  17. Blue gods, blue oil, and blue people.

    Science.gov (United States)

    Fairbanks, V F

    1994-09-01

    Studies of the composition of coal tar, which began in Prussia in 1834, profoundly affected the economies of Germany, Great Britain, India, and the rest of the world, as well as medicine and surgery. Such effects include the collapse of the profits of the British indigo monopoly, the growth in economic power of Germany based on coal tar chemistry, and an economic crisis in India that led to more humane tax laws and, ultimately, the independence of India and the end of the British Empire. Additional consequences were the development of antiseptic surgery and the synthesis of a wide variety of useful drugs that have eradicated infections and alleviated pain. Many of these drugs, particularly the commonly used analgesics, sulfonamides, sulfones, and local anesthetics, are derivatives of aniline, originally called "blue oil" or "kyanol." Some of these aniline derivatives, however, have also caused aplastic anemia, agranulocytosis, and methemoglobinemia (that is, "blue people"). Exposure to aniline drugs, particularly when two or three aniline drugs are taken concurrently, seems to be the commonest cause of methemoglobinemia today. PMID:8065194

  18. Double White Dwarfs as Probes of Single and Binary Star Evolution

    Science.gov (United States)

    Andrews, Jeffrey John

    2016-01-01

    the more massive WD in this system evolved second. We construct an evolutionary formation scenario in which the system began as a hierarchical triple in which the inner binary merged (possibly due to Kozai-Lidov oscillations) forming a post-blue straggler binary. The system then evolved into the DWD we observe today. We further discuss the potential for identifying more wide DWDs, including peculiar systems like HS 2220+2146, in future surveys such as Gaia.

  19. Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks

    CERN Document Server

    Carneiro, Luiz P; Sundqvist, J O; Hoffmann, T L

    2016-01-01

    X-rays/EUV radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres, and can be the mechanism responsible for the production of highly ionized species. To allow for these processes in the context of spectral analysis, we have implemented such emission into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. The shock structure and corresponding emission is calculated as a function of user-supplied parameters. We account for a temperature and density stratification inside the post-shock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included into the NLTE network. We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from s...

  20. A MegaCam Survey of Outer Halo Satellites. VI. The Spatially Resolved Star-formation History of the Carina Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Santana, Felipe A.; Muñoz, Ricardo R.; de Boer, T. J. L.; Simon, Joshua D.; Geha, Marla; Côté, Patrick; Guzmán, Andrés E.; Stetson, Peter; Djorgovski, S. G.

    2016-10-01

    We present the spatially resolved star-formation history (SFH) of the Carina dwarf spheroidal galaxy, obtained from deep, wide-field g and r imaging and a metallicity distribution from the literature. Our photometry covers ˜2 deg2, reaching up to ˜10 times the half-light radius of Carina with a completeness higher than 50% at g ˜ 24.5, more than one magnitude fainter than the oldest turnoff. This is the first time a combination of depth and coverage of this quality has been used to derive the SFH of Carina, enabling us to trace its different populations with unprecedented accuracy. We find that Carina’s SFH consists of two episodes well separated by a star-formation temporal gap. These episodes occurred at old (\\gt 10 Gyr) and intermediate (2-8 Gyr) ages. Our measurements show that the old episode comprises the majority of the population, accounting for 54 ± 5% of the stellar mass within 1.3 times the King tidal radius, while the total stellar mass derived for Carina is 1.60+/- 0.09× {10}6 {M}⊙ , and the stellar mass-to-light ratio is 1.8 ± 0.2. The SFH derived is consistent with no recent star formation, which hints that the observed blue plume is due to blue stragglers. We conclude that the SFH of Carina evolved independently of the tidal field of the Milky Way, since the frequency and duration of its star-formation events do not correlate with its orbital parameters. This result is supported by the age-metallicity relation observed in Carina and the gradients calculated indicating that outer regions are older and more metal-poor. Based on observations obtained with the MegaCam imager on the Magellan II-Clay telescope at Las Campanas Observatory in the Atacama Region, Chile. This telescope is operated by a consortium consisting of the Carnegie Institution of Washington, Harvard University, MIT, the University of Michigan, and the University of Arizona.

  1. Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds. III. X-ray emission from wind-embedded shocks

    Science.gov (United States)

    Carneiro, L. P.; Puls, J.; Sundqvist, J. O.; Hoffmann, T. L.

    2016-05-01

    Context. Extreme ultraviolet (EUV) and X-ray radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres and can be the mechanism responsible for producing highly ionized atomic species detected in stellar wind UV spectra. Aims: To allow for these processes in the context of spectral analysis, we have implemented the emission from wind-embedded shocks and related physics into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. Methods: The shock structure and corresponding emission is calculated as a function of user-supplied parameters (volume filling factor, radial stratification of shock strength, and radial onset of emission). We account for a temperature and density stratification inside the postshock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included in the NLTE network. To test our implementation and to check the resulting effects, we calculated a comprehensive model grid with a variety of X-ray emission parameters. Results: We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of O iv/O v (particularly in dwarfs with Teff~ 45 000 K). Finally, we investigated the frequency dependence and radial behavior of the mass absorption coefficient, κν(r), which is important in the context of X-ray line formation in massive star winds. Conclusions: In almost all of the cases considered, direct ionization is of major influence because of the enhanced EUV radiation field, and Auger ionization only affects N vi

  2. Posthuman blues

    CERN Document Server

    Tonnies, Mac

    2013-01-01

    Posthuman Blues, Vol. I is first volume of the edited version of the popular weblog maintained by author Mac Tonnies from 2003 until his tragic death in 2009. Tonnies' blog was a pastiche of his original fiction, reflections on his day-to-day life, trenchant observations of current events, and thoughts on an eclectic range of material he culled from the Internet. What resulted was a remarkably broad portrait of a thoughtful man and the complex times in which he lived, rendered with intellige...

  3. Color vision: retinal blues.

    Science.gov (United States)

    Johnston, Jamie; Esposti, Federico; Lagnado, Leon

    2012-08-21

    Two complementary studies have resolved the circuitry underlying green-blue color discrimination in the retina. A blue-sensitive interneuron provides the inhibitory signal required for computing green-blue color opponency.

  4. P Cygni: An Extraordinary Luminous Blue Variable

    OpenAIRE

    Israelian, G.; de Groot, M

    1999-01-01

    P Cygni is a prototype for understanding mass loss from massive stars. This textbook star is known first of all because of two great eruptions in the 17th century. In the first half of this century it has given its name to a class of stars which are characterized by spectral lines consisting of nearly undisplaced emissions accompanied by a blue-displaced absorption component. This characteristic P Cygni-type profile betrays the presence of a stellar wind, but P Cygni's wind is quite unlike th...

  5. Blue cures blue but be cautious

    Directory of Open Access Journals (Sweden)

    Pranav Sikka

    2011-01-01

    Full Text Available Methemoglobinemia is a disorder characterized by the presence of >1% methemoglobin (metHb in the blood. Spontaneous formation of methemoglobin is normally counteracted by protective enzyme systems, for example, nicotinamide adenine dinucleotide phosphate (NADPH methemoglobin reductase. Methemoglobinemia is treated with supplemental oxygen and methylene blue (1-2 mg/kg administered slow intravenously, which acts by providing an artificial electron acceptor for NADPH methemoglobin reductase. But known or suspected glucose-6-phosphate dehydrogenase (G6PD deficiency is a relative contraindication to the use of methylene blue because G6PD is the key enzyme in the formation of NADPH through pentose phosphate pathway and G6PD-deficient individuals generate insufficient NADPH to efficiently reduce methylene blue to leukomethylene blue, which is necessary for the activation of the NADPH-dependent methemoglobin reductase system. So, we should be careful using methylene blue in methemoglobinemia patient before G6PD levels.

  6. The evolution of circumstellar medium around rotating massive stars

    NARCIS (Netherlands)

    Chita, S.M.; Marle, A.J.; Langer, N.; García-Segura, G.

    2007-01-01

    A rotating 12Mȯ star, after its main-sequence evolution, becomes a redsupergiant when it starts core He burning. During core helium burning, as consequence of a variation of the hydrogen shell burning efficiency, the star undergoes a so called ``blue loop'', i.e. it evolves into a blue supergiant st

  7. Star Formation Regions in LDN 1667

    Science.gov (United States)

    Gyulbudaghian, A. L.

    2015-09-01

    A group of three star formation regions in the dark cloud LDN 1667 is examined. All three of these regions contain Trapezium type systems. 12C(1-0) observations are made of the part of the molecular cloud LDN 1667 associated with one of the star formation regions. Three molecular clouds were detected, one of which (the main cloud) has a red and a blue outflow. Three stars from the star formation regions are found to have annular nebulae and one star has a conical nebula. The dark cloud LDN 1667 is associated with a radial system of dark globules which is formed by the star HD 57061.

  8. The Star Formation Camera

    OpenAIRE

    Scowen, Paul A.; Jansen, Rolf; Beasley, Matthew; Calzetti, Daniela; Desch, Steven; Fullerton, Alex; Gallagher, John; Lisman, Doug; Macenka, Steve; Malhotra, Sangeeta; McCaughrean, Mark; Nikzad, Shouleh; O'Connell, Robert; Oey, Sally; Padgett, Deborah

    2009-01-01

    The Star Formation Camera (SFC) is a wide-field (~15'x19, >280 arcmin^2), high-resolution (18x18 mas pixels) UV/optical dichroic camera designed for the Theia 4-m space-borne space telescope concept. SFC will deliver diffraction-limited images at lambda > 300 nm in both a blue (190-517nm) and a red (517-1075nm) channel simultaneously. Our aim is to conduct a comprehensive and systematic study of the astrophysical processes and environments relevant for the births and life cycles of stars and ...

  9. Blue and White Pot

    Institute of Scientific and Technical Information of China (English)

    1996-01-01

    Many recent archaeological studies have proven that the earliest blue and white porcelain was produced from the kiln in Gongxian County, Henan Province in the Tang Dynasty (618-907). It was an important variety of porcelain available for export then. The early blue and white porcelain in the Yuan Dynasty appeared dark and gray. During the reign of Zhizheng, clear blue and white porcelain was produced, indicating

  10. Feeling blue? Blue phosphors for OLEDs

    Directory of Open Access Journals (Sweden)

    Hungshin Fu

    2011-10-01

    Full Text Available Research on organic light emitting diodes (OLEDs has been revitalized, partly due to the debut of the OLED TV by SONY in 2008. While there is still plenty of room for improvement in efficiency, cost-effectiveness and longevity, it is timely to report on the advances of light emitting materials, the core of OLEDs, and their future perspectives. The focus of this account is primarily to chronicle the blue phosphors developed in our laboratory. Special attention is paid to the design strategy, synthetic novelty, and their OLED performance. The report also underscores the importance of the interplay between chemistry and photophysics en route to true-blue phosphors.

  11. Blue Willow Story Plates

    Science.gov (United States)

    Fontes, Kris

    2009-01-01

    In the December 1997 issue of "SchoolArts" is a lesson titled "Blue Willow Story Plates" by Susan Striker. In this article, the author shares how she used this lesson with her middle-school students many times over the years. Here, she describes a Blue Willow plate painting project that her students made.

  12. From blue jeans to blue genes.

    Science.gov (United States)

    Boon, Laurence M; Vikkula, Miikka

    2009-03-01

    Cutaneous venous anomalies are common. They are blue and vary in size, number, and location and account for most consultations at specialized interdisciplinary clinics for vascular anomalies. Venous lesions are clinically important because they cause pain, dysfunction, destruction of adjacent tissues, and esthetic concern. Only resection and sclerotherapy are helpful, although not always curative. Understanding etiopathogenesis could help design animal models and develop novel therapeutic approaches. John B. Mulliken, MD, envisioned a project to uncover the genetic basis of an inherited form of venous malformation in a large New England family. Recruitment of 2 young fellows resulted in a collaborative project that unraveled the searched-for gene and its mutation. This was an opening for a new era in vascular anomalies. Two blue genes' mutations were discovered, which account for most, if not all, of the inherited forms of venous anomalies, but other genes as well, for rheologically diverse lesions. Differential diagnosis and management has improved, and animal models are being made. This was achieved through the help of Dr Mulliken, who inspired 2 young investigators in blue jeans to find 2 blue genes.

  13. Blue ocean strategy.

    Science.gov (United States)

    Kim, W Chan; Mauborgne, Renée

    2004-10-01

    Despite a long-term decline in the circus industry, Cirque du Soleil profitably increased revenue 22-fold over the last ten years by reinventing the circus. Rather than competing within the confines of the existing industry or trying to steal customers from rivals, Cirque developed uncontested market space that made the competition irrelevant. Cirque created what the authors call a blue ocean, a previously unknown market space. In blue oceans, demand is created rather than fought over. There is ample opportunity for growth that is both profitable and rapid. In red oceans--that is, in all the industries already existing--companies compete by grabbing for a greater share of limited demand. As the market space gets more crowded, prospects for profits and growth decline. Products turn into commodities, and increasing competition turns the water bloody. There are two ways to create blue oceans. One is to launch completely new industries, as eBay did with online auctions. But it's much more common for a blue ocean to be created from within a red ocean when a company expands the boundaries of an existing industry. In studying more than 150 blue ocean creations in over 30 industries, the authors observed that the traditional units of strategic analysis--company and industry--are of limited use in explaining how and why blue oceans are created. The most appropriate unit of analysis is the strategic move, the set of managerial actions and decisions involved in making a major market-creating business offering. Creating blue oceans builds brands. So powerful is blue ocean strategy, in fact, that a blue ocean strategic move can create brand equity that lasts for decades. PMID:15559577

  14. Blue ocean strategy.

    Science.gov (United States)

    Kim, W Chan; Mauborgne, Renée

    2004-10-01

    Despite a long-term decline in the circus industry, Cirque du Soleil profitably increased revenue 22-fold over the last ten years by reinventing the circus. Rather than competing within the confines of the existing industry or trying to steal customers from rivals, Cirque developed uncontested market space that made the competition irrelevant. Cirque created what the authors call a blue ocean, a previously unknown market space. In blue oceans, demand is created rather than fought over. There is ample opportunity for growth that is both profitable and rapid. In red oceans--that is, in all the industries already existing--companies compete by grabbing for a greater share of limited demand. As the market space gets more crowded, prospects for profits and growth decline. Products turn into commodities, and increasing competition turns the water bloody. There are two ways to create blue oceans. One is to launch completely new industries, as eBay did with online auctions. But it's much more common for a blue ocean to be created from within a red ocean when a company expands the boundaries of an existing industry. In studying more than 150 blue ocean creations in over 30 industries, the authors observed that the traditional units of strategic analysis--company and industry--are of limited use in explaining how and why blue oceans are created. The most appropriate unit of analysis is the strategic move, the set of managerial actions and decisions involved in making a major market-creating business offering. Creating blue oceans builds brands. So powerful is blue ocean strategy, in fact, that a blue ocean strategic move can create brand equity that lasts for decades.

  15. Hot subluminous stars

    CERN Document Server

    Heber, Ulrich

    2016-01-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich vs. He-poor hot subdwarf stars of the globular clusters omega Cen and NGC~2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope phase of evolution.They provide a clean-cut laboratory to study this important but yet purely understood phase of stellar evolution. Substellar companions to sdB stars have also been found. For HW~Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the pulsator V391 ...

  16. Blue Ribbon Panel Report

    Science.gov (United States)

    An NCI Cancer Currents blog by the NCI acting director thanking the cancer community for contributing to the Cancer Moonshot Blue Ribbon Panel report, which was presented to the National Cancer Advisory Board on September 7.

  17. New York Blue

    Data.gov (United States)

    Federal Laboratory Consortium — New York Blue is used cooperatively by the Laboratory and Stony Brook University as part of the New York Center for Computation Sciences. Ranked as the 28th fastest...

  18. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  19. Star Product and Star Exponential

    OpenAIRE

    Tomihisa, Toshio; Yoshioka, Akira

    2010-01-01

    Here we extend the star products by means of complex symmetric matrices. In this way we obtain a family of star products. Next we consider the star exponentials with respect to these star products, and finally we obtain several interesting identities.

  20. Life Cycle of Stars

    Science.gov (United States)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  1. VizieR Online Data Catalog: Young star groups in NGC 300 (Rodriguez+, 2016)

    Science.gov (United States)

    Rodriguez, M. J.; Baume, G.; Feinstein, C.

    2016-08-01

    Fundamental characteristics of 1147 young star groups identified in 6 ACS/WFC fields of the galaxy NGC 300. For each group: field of the ACS/WFC, equatorial coordinates, radius, number of stars (the suffix bri indicates bright stars with F555W<25, the suffix dct indicate stars belonging to the decontaminated region, the suffixes blue and red refer to blue and red stars respectively), the magnitude of the brightest star in the group, PDMF slope with its error, and galactocentric distance. (1 data file).

  2. The Blues of David Lynch

    OpenAIRE

    Roche, David

    2009-01-01

    This article is an attempt to elaborate a typology of the color blue in the color films of David Lynch up to and including Mulholland Drive (2001). The color blue is considered alternately as light, matter or verbal language. The author studies the use, function, value and meaning of blue lighting, divided into static and flashing light, and of the blue objects in Blue Velvet (1986) and Mulholland Drive. The author shows how Lynch appropriates connotations Western culture, under the influence...

  3. Stellar science from a blue wavelength range - A possible design for the blue arm of 4MOST

    CERN Document Server

    Hansen, C J; Seifert, W; Koch, A; Xu, W; Caffau, E; Christlieb, N; Korn, A J; Lind, K; Sbordone, L; Ruchti, G; Feltzing, S; de Jong, R S; Barden, S; Schnurr, O

    2015-01-01

    From stellar spectra, a variety of physical properties of stars can be derived. In particular, the chemical composition of stellar atmospheres can be inferred from absorption line analyses. These provide key information on large scales, such as the formation of our Galaxy, down to the small-scale nucleosynthesis processes that take place in stars and supernovae. By extending the observed wavelength range toward bluer wavelengths, we optimize such studies to also include critical absorption lines in metal-poor stars, and allow for studies of heavy elements (Z>38) whose formation processes remain poorly constrained. In this context, spectrographs optimized for observing blue wavelength ranges are essential, since many absorption lines at redder wavelengths are too weak to be detected in metal-poor stars. This means that some elements cannot be studied in the visual-redder regions, and important scientific tracers and science cases are lost. The present era of large public surveys will target millions of stars. ...

  4. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

  5. Beyond Deep Blue

    CERN Document Server

    Newborn, Monty

    2011-01-01

    More than a decade has passed since IBM's Deep Blue computer stunned the world by defeating Garry Kasparov, the world chess champion at that time. Beyond Deep Blue tells the continuing story of the chess engine and its steady improvement. The book provides analysis of the games alongside a detailed examination of the remarkable technological progress made by the engines - asking which one is best, how good is it, and how much better can it get. Features: presents a total of 118 games, played by 17 different chess engines, collected together for the first time in a single reference; details the

  6. A Blue Lagoon Function

    DEFF Research Database (Denmark)

    Markvorsen, Steen

    2007-01-01

    We consider a specific function of two variables whose graph surface resembles a blue lagoon. The function has a saddle point $p$, but when the function is restricted to any given straight line through $p$ it has a {\\em{strict local minimum}} along that line at $p$.......We consider a specific function of two variables whose graph surface resembles a blue lagoon. The function has a saddle point $p$, but when the function is restricted to any given straight line through $p$ it has a {\\em{strict local minimum}} along that line at $p$....

  7. The Blue Collar Brain

    Directory of Open Access Journals (Sweden)

    Guy eVan Orden

    2012-06-01

    Full Text Available Much effort has gone into elucidating control of the body by the brain, less so the role of the body in controlling the brain. This essay develops the idea that the brain does a great deal of work in the service of behavior that is controlled by the body, a blue collar role compared to the white collar control exercised by the body. The argument that supports a blue collar role for the brain is also consistent with recent discoveries clarifying the white collar role of synergies across the body's tensegrity structure, and the evidence of critical phenomena in brain and behavior.

  8. The Star Formation Camera

    CERN Document Server

    Scowen, Paul A; Beasley, Matthew; Calzetti, Daniela; Desch, Steven; Fullerton, Alex; Gallagher, John; Lisman, Doug; Macenka, Steve; Malhotra, Sangeeta; McCaughrean, Mark; Nikzad, Shouleh; O'Connell, Robert; Oey, Sally; Padgett, Deborah; Rhoads, James; Roberge, Aki; Siegmund, Oswald; Shaklan, Stuart; Smith, Nathan; Stern, Daniel; Tumlinson, Jason; Windhorst, Rogier; Woodruff, Robert

    2009-01-01

    The Star Formation Camera (SFC) is a wide-field (~15'x19, >280 arcmin^2), high-resolution (18x18 mas pixels) UV/optical dichroic camera designed for the Theia 4-m space-borne space telescope concept. SFC will deliver diffraction-limited images at lambda > 300 nm in both a blue (190-517nm) and a red (517-1075nm) channel simultaneously. Our aim is to conduct a comprehensive and systematic study of the astrophysical processes and environments relevant for the births and life cycles of stars and their planetary systems, and to investigate and understand the range of environments, feedback mechanisms, and other factors that most affect the outcome of the star and planet formation process. This program addresses the origins and evolution of stars, galaxies, and cosmic structure and has direct relevance for the formation and survival of planetary systems like our Solar System and planets like Earth. We present the design and performance specifications resulting from the implementation study of the camera, conducted ...

  9. Massive Stars

    Science.gov (United States)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  10. Star Card:Blue Ocean of Fans Interest Export and Sports Collection%球星卡:球迷的“兴趣出口”与体育藏品的另类蓝海

    Institute of Scientific and Technical Information of China (English)

    杜恺

    2014-01-01

    体育藏品一直是宣传与弘扬体育文化的一个重要载体。从我国古代体育的蹴鞠到现代奥林匹克运动的器械,这些承载着历史价值的收藏品正不断地将体育的核心价值传递给世人。本文通过研究分析篮球球星卡的收藏价值和文化内涵,得出该类收藏的前景可观,意义深远,在我国篮球迷中具有可观的推广价值,并对推动篮球运动,加深篮球文化能够起到举足轻重的作用。%sports collections isan important carrier of publicity and promotion of sports culture .From Cuju ball sports in ancient China to the modern Olympic movement device , which carry the historical value of the collections are the core value of sports to the world .Through analysis and research of basketball star card collection value and cultural connotation, the author of this collectionis promising , far-reaching, and has considerable application value in theChinesebasketball fans , and to promote basketball sport , deepen thebasketball culture can play a deci-sive role.

  11. Infrared properties of Active OB stars in the Magellanic Clouds from the Spitzer SAGE Survey

    OpenAIRE

    Bonanos, A. Z.; Lennon, D.J.; Massa, D. L.; Sewilo, M.; Köhlinger, F.; Panagia, N.; van Loon, J. Th.; Evans, C. J.; Smith, L J; Meixner, M.; Gordon, K; teams, the SAGE

    2010-01-01

    We present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared t...

  12. Blue-green algae

    Science.gov (United States)

    ... for 6 months relieves allergy symptoms in adults. Arsenic poisoning. Early research shows that taking a combination of blue-green algae and zinc by mouth twice daily for 12 weeks reduces arsenic levels and its effects on the skin in ...

  13. The Blue Denmark

    DEFF Research Database (Denmark)

    Hansen, Carsten Ørts; Sornn-Friese, Henrik

    This paper makes an important contribution to the discussion about knowledge based localised externalities in the context of shipping and the maritime sector in Denmark. In the paper we ask if there is a national, knowledge‐based maritime cluster configured around the shipowners in Denmark. This ...... talk about The Blue Denmark....

  14. The "Blue Banana" Revisited

    NARCIS (Netherlands)

    Faludi, A.K.F.

    2015-01-01

    This essay is about the “Blue Banana”. Banana is the name given subsequently by others to a Dorsale européenne (European backbone) identified empirically by Roger Brunet. In a background study to the Communication of the European Commission ‘Europe 2000’, Klaus Kunzmann and Michael Wegener put forwa

  15. The BlueTides Simulation: First Galaxies and Reionization

    CERN Document Server

    Feng, Yu; Croft, Rupert A; Bird, Simeon; Battaglia, Nicholas; Wilkins, Stephen

    2015-01-01

    We introduce the BlueTides simulation and report initial results for the luminosity functions of the first galaxies and AGN, and their contribution to reionization. BlueTides was run on the BlueWaters cluster at NCSA from $z=99$ to $z=8.0$ and includes 2$\\times$7040$^3$ particles in a $400$Mpc/h per side box, making it the largest hydrodynamic simulation ever performed at high redshift. BlueTides includes a pressure-entropy formulation of smoothed particle hydrodynamics, gas cooling, star formation (including molecular hydrogen), black hole growth and models for stellar and AGN feedback processes. The star formation rate density in the simulation is a good match to current observational data at $z\\sim 8-10$. We find good agreement between observations and the predicted galaxy luminosity function in the currently observable range $-18\\le M_{\\mathrm UV} \\le -22.5$ with some dust extinction required to match the abundance of brighter objects. BlueTides implements a patchy reionization model that produces a fluct...

  16. Hadron star models. [neutron stars

    Science.gov (United States)

    Cohen, J. M.; Boerner, G.

    1974-01-01

    The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

  17. Classification of O Stars in the Yellow-Green: The Exciting Star VES 735

    OpenAIRE

    Kerton, C. R.; Ballantyne, D. R.; Martin, P. G.

    1999-01-01

    Acquiring data for spectral classification of heavily reddened stars using traditional criteria in the blue-violet region of the spectrum can be prohibitively time consuming using small to medium sized telescopes. One such star is the Vatican Observatory emission-line star VES 735, which we have found excites the HII region KR140. In order to classify VES 735, we have constructed an atlas of stellar spectra of O stars in the yellow-green (4800 - 5420 A). We calibrate spectral type versus the ...

  18. High-angular resolution observations of the Pistol Star

    CERN Document Server

    Martayan, Christophe; Bouquin, Jean-Baptiste Le; Merand, Antoine; Montagnier, Guillaume; Selman, Fernando; Girard, Julien; Fox, Andrew; Baade, Dietrich; Fremat, Yves; Lobel, Alex; Martins, Fabrice; Patru, Fabien; Rivinius, Thomas; Sana, Hugues; Stefl, Stan; Zorec, Jean; Semaan, Thierry

    2010-01-01

    First results of near-IR adaptive optics (AO)-assisted imaging, interferometry, and spectroscopy of this Luminous Blue Variable (LBV) are presented. They suggest that the Pistol Star is at least double. If the association is physical, it would reinforce questions concerning the importance of multiplicity for the formation and evolution of extremely massive stars.

  19. Hot Subluminous Stars

    Science.gov (United States)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung–Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  20. Hot Subluminous Stars

    Science.gov (United States)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  1. The Blue Emu

    Science.gov (United States)

    Descalzi, Doug; Gillett, John; Gordon, Carlton; Keener, ED; Novak, Ken; Puente, Laura

    1993-01-01

    The primary goal in designing the Blue Emu was to provide an airline with a cost efficient and profitable means of transporting passengers between the major cities in Aeroworld. The design attacks the market where a demand for inexpensive transportation exists and for this reason the Blue Emu is an attractive investment for any airline. In order to provide a profitable aircraft, special attention was paid to cost and economics. For example, in manufacturing, simplicity was stressed in structural design to reduce construction time and cost. Aerodynamic design employed a tapered wing which reduced the induced drag coefficient while also reducing the weight of the wing. Even the propulsion system was selected with cost effectiveness in mind, yet also to maintain the marketability of the aircraft. Thus, in every aspect of the design, consideration was given to economics and marketability of the final product.

  2. Synthesizing a Blue Ocean

    OpenAIRE

    Vester, Daniel

    2012-01-01

    The purpose of this Master thesis was to determine how electronic musical instrument companies could utilize innovation strategies to add value to their products and create new business markets beyond their core. The theoretical framework was established by outlining competitive strategies suitable for adoption by electronic musical instrument companies. The Blue Ocean Strategy was compared to traditional competitive strategies such as Porter’s Five Forces, and subsequently chosen because of ...

  3. Star Formation and the Growth of Stellar Mass

    CERN Document Server

    Bell, Eric F; Papovich, Casey; Borch, Andrea; Wolf, Christian; Meisenheimer, Klaus

    2007-01-01

    Recent observations have demonstrated a significant growth in the integrated stellar mass of the red sequence since z=1, dominated by a steadily increasing number of galaxies with stellar masses M* 3x10^10 M_sun blue galaxies would also be overproduced; i.e., most of the new stars formed in blue cloud galaxies are in the massive galaxies. We explore a simple truncation scenario in which these `extra' blue galaxies have their star formation suppressed by an unspecified mechanism or mechanisms; simple cessation of star formation in these extra blue galaxies is approximately sufficient to build up the red seq uence at M*<10^11 M_sun.

  4. Shooting stars

    Energy Technology Data Exchange (ETDEWEB)

    Maurette, M.; Hammer, C.

    A shooting star passage -even a star shower- can be sometimes easily seen during moonless black night. They represent the partial volatilization in earth atmosphere of meteorites or micrometeorites reduced in cosmic dusts. Everywhere on earth, these star dusts are searched to be gathered. This research made one year ago on the Greenland ice-cap is the object of this article; orbit gathering projects are also presented.

  5. Constraining the Axion-Photon Coupling with Massive Stars

    CERN Document Server

    Friedland, Alexander; Wise, Michael

    2012-01-01

    We point out that stars in the mass window ~ 8-12 Msun can serve as sensitive probes of the axion-photon interaction, g_{A\\gamma\\gamma}. Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually eliminate the blue loop phase of the evolution. This would contradict observational data, since the blue loops are required, e.g., to account for the existence of Cepheid stars. Using the MESA stellar evolution code, modified to include the extra cooling, we conservatively find g_{A\\gamma\\gamma} <~ 0.8 * 10^{-10} GeV^{-1}, which compares favorably with the existing bounds.

  6. Visual Distortions Near a Neutron Star and Black Hole

    OpenAIRE

    Nemiroff, Robert J.

    1993-01-01

    The visual distortion effects visible to an observer traveling around and descending to the surface of an extremely compact star are described. Specifically, trips to a ``normal" neutron star, a black hole, and an ultracompact neutron star with extremely high surface gravity, are described. Concepts such as multiple imaging, red- and blue-shifting, conservation of surface brightness, the photon sphere, and the existence of multiple Einstein rings are discussed in terms of what the viewer woul...

  7. Pre-supernova mass loss predictions for massive stars

    OpenAIRE

    Vink, Jorick S.; de Koter, Alex; Kotak, Rubina

    2006-01-01

    Massive stars and supernovae (SNe) have a huge impact on their environment. Despite their importance, a comprehensive knowledge of which massive stars produce which SNe is hitherto lacking. We use a Monte Carlo method to predict the mass-loss rates of massive stars in the Hertzsprung-Russell Diagram (HRD) covering all phases from the OB main sequence, the unstable Luminous Blue Variable (LBV) stage, to the final Wolf-Rayet (WR) phase. Although WR produce their own metals, a strong dependence ...

  8. The Gaia Attitude Star Catalog

    Science.gov (United States)

    Smart, R. L.

    2016-04-01

    We describe the Attitude Star Catalog produced for the Gaia mission. This catalog is being used by Gaia for the first on-ground attitude reconstruction. Originally it was simply a subset of the Initial Gaia Source List but this subset did not meet the isolation requirements and it contained a significant number of double entries. As a result during the commissioning phase of Gaia a new generation of this catalog, that better fulfills the attitude reconstruction requirements, was requested. Here we describe the production and properties of this new Attitude Star Catalog. The Attitude Star Catalog was made by combining 7 all sky catalogs and selecting entries based on magnitude, isolation and astrometric precision criteria. The catalog has 8173331 entries with estimates of the positions at 2000, proper motions and magnitudes (Gaia G, Gaia Grvs, red RF & blue BJ) in the magnitude range 7.0 publically available from the CDS Strasbourg and the IGSL web-site.

  9. Massive Stars in the Quintuplet Cluster

    CERN Document Server

    Figer, D F; Morris, M; Figer, Donald F.; Lean, Ian S. Mc

    1999-01-01

    We present near-infrared photometry and K-band spectra of newly-identified massive stars in the Quintuplet Cluster, one of the three massive clusters projected within 50 pc of the Galactic Center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any cluster in the Galaxy, and over a dozen stars in earlier stages of evolution, i.e., LBV, Ofpe/WN9, and OB supergiants. One newly identified star is the second ``Luminous Blue Variable'' in the cluster, after the ``Pistol Star.'' Given the evolutionary stages of the identified stars, the cluster appears to be about 4 \\pm 1 Myr old, assuming coeval formation. The total mass in observed stars is $\\sim 10^3 \\Msun$, and the implied mass is initial mass function. The implied mass density in stars is at least a few thousand $\\Msun pc^{-3}$. The newly-identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 10^{50.9...

  10. Radio continuum detection in blue early-type weak-emission-line galaxies

    Science.gov (United States)

    Paswan, A.; Omar, A.

    2016-06-01

    The star formation rates (SFRs) in weak-emission-line (WEL) galaxies in a volume-limited (0.02 Hz-1, respectively. The radio far-infrared correlation in four WEL galaxies suggests that the radio continuum emission from WEL galaxies is most likely a result of star formation activities. The median SFR for WEL galaxies is estimated as 0.23 ± 0.06 M⊙ yr-1, which is much less than SFRs (0.5-50 M⊙ yr-1) in purely star-forming blue ETGs. The SFRs in blue ETGs are found to be correlated with their stellar velocity dispersions (σ) and decreasing gradually beyond σ of ˜100 km s-1. This effect is most likely linked to the growth of a black hole and the suppression of star formation via active galactic nucleus (AGN) feedback. The colour differences between star-forming and WEL subtypes of blue ETGs appear to be driven to a large extent by the level of current star formation activities. In a likely scenario of an evolutionary sequence between subtypes, the observed colour distribution in blue ETGs can be explained best in terms of fast evolution through AGN feedback.

  11. Nonradial pulsations of hot evolved stars

    International Nuclear Information System (INIS)

    There are three classes of faint blue variable stars: the ZZ Ceti variables (DAV degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (DOV degenerate dwarfs). None of these classes of variable stars were known at the time of the last blue star meeting. Observational and theoretical studies of the ZZ Ceti variables, the DBV variables, and the GW Vir variables have shown them to be pulsating in nonradial g-modes. The cause of the pulsation has been determined for each class of variable star and, in all cases, also involves predictions of the stars envelope composition. The predictions are that the ZZ Ceti variables must have pure hydrogen surface layers, the DBV stars must have pure helium surface layers, and the GW Vir stars must have carbon and oxygen rich surface layers with less than 30% (by mass) of helium. Given these compositions, it is found that pulsation driving occurs as a result of the kappa and gamma effects operating in the partial ionization zones of either hydrogen or helium. In addition, a new driving mechanism, called convection blocking, also occurs in these variables. For the GW Vir variables, it is the kappa and gamma effects in the partial ionization regions of carbon and oxygen. 45 refs

  12. IN-SPIRALING CLUMPS IN BLUE COMPACT DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Elmegreen, Bruce G. [IBM Research Division, T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Zhang Hongxin; Hunter, Deidre A., E-mail: bge@watson.ibm.com [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)

    2012-03-10

    Giant star formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the blue compact dwarf (BCD) phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. An additional indication that the dense central regions of BCDs are like bulges is the high ratio of the inner disk scale height to the scale length, which is comparable to 1 for four of the galaxies.

  13. Radio stars.

    Science.gov (United States)

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars. PMID:17836594

  14. Star Imager

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Jørgensen, John Leif; Thuesen, Gøsta;

    1997-01-01

    The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol.......The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol....

  15. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star.......Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star....

  16. The growth of the central region by acquisition of counter-rotating gas in star-forming galaxies

    CERN Document Server

    Chen, Yan-Mei; Tremonti, Christy A; Bershady, Matt; Merrifield, Michael; Emsellem, Eric; Jin, Yi-Fei; Huang, Song; Fu, Hai; Wake, David A; Bundy, Kevin; Stark, David; Lin, Lihwai; Argudo-Fernandez, Maria; Bergmann, Thaisa Storchi; Bizyaev, Dmitry; Brownstein, Joel; Bureau, Martin; Chisholm, John; Drory, Niv; Guo, Qi; Hao, Lei; Hu, Jian; Li, Cheng; Li, Ran; Lopes, Alexandre Roman; Pan, Kai-Ke; Riffel, Rogemar A; Thomas, Daniel; Wang, Lan; Westfall, Kyle; Yan, Ren-Bin

    2016-01-01

    Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (< 1 kpc) to form new stars.

  17. Estruturas fundamentais no blues

    OpenAIRE

    Silva, Rafael Palmeira da

    2012-01-01

    Resumo: Esta pesquisa tem como objeto de estudo a aplicação e adaptação da teoria de Schenker como ferramenta analítica aplicada ao jazz, tendo em vista a possibilidade de encontrar estruturas fundamentais distintas na música popular. Tendo como base as análises feitas por Larson (1998; 2009), Forte (2011) e Stock (1993) a pesquisa abordará, em um primeiro momento, as origens do jazz (blues e ragtime) como parte essencial para sua abordagem analítica, através da ótica etno-schenkeriana propos...

  18. Blue ocean leadership.

    Science.gov (United States)

    Kim, W Chan; Mauborgne, Renée

    2014-05-01

    Ten years ago, two INSEAD professors broke ground by introducing "blue ocean strategy," a new model for discovering uncontested markets that are ripe for growth. In this article, they apply their concepts and tools to what is perhaps the greatest challenge of leadership: closing the gulf between the potential and the realized talent and energy of employees. Research indicates that this gulf is vast: According to Gallup, 70% of workers are disengaged from their jobs. If companies could find a way to convert them into engaged employees, the results could be transformative. The trouble is, managers lack a clear understanding of what changes they could make to bring out the best in everyone. Here, Kim and Mauborgne offer a solution to that problem: a systematic approach to uncovering, at each level of the organization, which leadership acts and activities will inspire employees to give their all, and a process for getting managers throughout the company to start doing them. Blue ocean leadership works because the managers' "customers"-that is, the people managers oversee and report to-are involved in identifying what's effective and what isn't. Moreover, the approach doesn't require leaders to alter who they are, just to undertake a different set of tasks. And that kind of change is much easier to implement and track than changes to values and mind-sets. PMID:24956870

  19. Blue ocean leadership.

    Science.gov (United States)

    Kim, W Chan; Mauborgne, Renée

    2014-05-01

    Ten years ago, two INSEAD professors broke ground by introducing "blue ocean strategy," a new model for discovering uncontested markets that are ripe for growth. In this article, they apply their concepts and tools to what is perhaps the greatest challenge of leadership: closing the gulf between the potential and the realized talent and energy of employees. Research indicates that this gulf is vast: According to Gallup, 70% of workers are disengaged from their jobs. If companies could find a way to convert them into engaged employees, the results could be transformative. The trouble is, managers lack a clear understanding of what changes they could make to bring out the best in everyone. Here, Kim and Mauborgne offer a solution to that problem: a systematic approach to uncovering, at each level of the organization, which leadership acts and activities will inspire employees to give their all, and a process for getting managers throughout the company to start doing them. Blue ocean leadership works because the managers' "customers"-that is, the people managers oversee and report to-are involved in identifying what's effective and what isn't. Moreover, the approach doesn't require leaders to alter who they are, just to undertake a different set of tasks. And that kind of change is much easier to implement and track than changes to values and mind-sets.

  20. Blue emitting undecaplatinum clusters

    Science.gov (United States)

    Chakraborty, Indranath; Bhuin, Radha Gobinda; Bhat, Shridevi; Pradeep, T.

    2014-07-01

    A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents.A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents. Electronic supplementary information (ESI) available: Details of experimental procedures, instrumentation, chromatogram of the crude cluster; SEM/EDAX, DLS, PXRD, TEM, FT-IR, and XPS of the isolated Pt11 cluster; UV/Vis, MALDI MS and SEM/EDAX of isolated 2 and 3; and 195Pt NMR of the K2PtCl6 standard. See DOI: 10.1039/c4nr02778g

  1. Postpartum Blues and Postpartum Depression

    Directory of Open Access Journals (Sweden)

    Erdem Ö et al.

    2009-09-01

    Full Text Available Postpartum blues which is seen during the postpartum period is a transient psychological state. Most of the mothers experience maternity blues in postpartum period. It remains usually unrecognized by the others. Some sensitive families can misattribute these feelings as depression. In this article, we tried to review the characteristics of maternity blues and its differences from depression. We defined depression and presented the incidence and diagnostic criteria, of major depression as well as the risk factors and clinic findings of postpartum depression. Thus, especially at primary care we aimed to prevent misdiagnosis of both maternity blues and depression

  2. Horndeski's Stars

    CERN Document Server

    Cisterna, Adolfo; Rinaldi, Massimiliano

    2015-01-01

    We consider the sector of Horndeski's gravity characterized by a coupling between the kinetic scalar field term and the Einstein tensor. Our goal is to find realistic neutron star configurations in this framework. We show that, in a certain limit, there exist solutions that are identical to the Schwarzschild metric outside the star but change considerably inside, where the scalar field is not trivial. We study numerically the equations and find the region of the parameter space where neutron stars exist. We determine their internal pressure and mass-radius relation, and we compare them with standard general relativity models.

  3. An interferometric view of binary stars

    CERN Document Server

    Boffin, Henri M J

    2016-01-01

    The study of binary stars is critical to apprehend many of the most interesting classes of stars. Moreover, quite often, the study of stars in binary systems is our only mean to constrain stellar properties, such as masses and radii. Unfortunately, a great fraction of the most interesting binaries are so compact that they can only be apprehended by high-resolution techniques, mostly by interferometry. I present some results highlighting the use of interferometry in the study of binary stars, from finding companions and deriving orbits, determining the mass and radius of stars, to studying mass transfer in symbiotic stars, and tackling luminous blue variables. In particular, I show how interferometric studies using the PIONIER instrument have allowed us to confirm a dichotomy within symbiotic stars, obtain masses of stars with a precision better than 1%, and help us find a new Eta Carinae-like system. I will also illustrate the benefits for the study of binary stars one would get from upgrading the VLT Interfe...

  4. What are the Luminous Compact Blue Galaxies?

    CERN Document Server

    Pisano, D J; Guzmán, R; Gallego, J Perez; Castander, F J; Gruel, N

    2007-01-01

    Luminous Compact Blue Galaxies (LCBGs) are common at z~1, contributing significantly to the total star formation rate density. By z~0, they are a factor of ten rarer. While we know that LCBGs evolve rapidly, we do not know what drives their evolution nor into what types of galaxies they evolve. We present the results of a single-dish HI survey of local LCBGs undertaken to address these questions. Our results indicate that LCBGs have M(HI) and M(DYN) consistent with low-mass spirals, but typically exhaust their gas reservoirs in less than 2 Gyr. Overall, the properties of LCBGs are consistent with them evolving into high-mass dwarf elliptical or dwarf irregular galaxies or low-mass, late-type spiral galaxies.

  5. A Sparkling Spray of Stars

    Science.gov (United States)

    2008-12-01

    The festive season has arrived for astronomers at the European Southern Observatory (ESO) in the form of this dramatic new image. It shows the swirling gas around the region known as NGC 2264 -- an area of sky that includes the sparkling blue baubles of the Christmas Tree star cluster. Omega Centauri ESO PR Photo 48/08 NGC 2264 and the Christmas Tree cluster NGC 2264 lies about 2600 light-years from Earth in the obscure constellation of Monoceros, the Unicorn, not far from the more familiar figure of Orion, the Hunter. The image shows a region of space about 30 light-years across. William Herschel discovered this fascinating object during his great sky surveys in the late 18th century. He first noticed the bright cluster in January 1784 and the brightest part of the visually more elusive smudge of the glowing gas clouds at Christmas nearly two years later. The cluster is very bright and can easily be seen with binoculars. With a small telescope (whose lenses will turn the view upside down) the stars resemble the glittering lights on a Christmas tree. The dazzling star at the top is even bright enough to be seen with the unaided eye. It is a massive multiple star system that only emerged from the dust and gas a few million years ago. As well as the cluster there are many interesting and curious structures in the gas and dust. At the bottom of the frame, the dark triangular feature is the evocative Cone Nebula, a region of molecular gas flooded by the harsh light of the brightest cluster members. The region to the right of the brightest star has a curious, fur-like texture that has led to the name Fox Fur Nebula. Much of the image appears red because the huge gas clouds are glowing under the intense ultra-violet light coming from the energetic hot young stars. The stars themselves appear blue as they are hotter, younger and more massive than our own Sun. Some of this blue light is scattered by dust, as can be seen occurring in the upper part of the image. This

  6. Bursts of star formation in computer simulations of dwarf galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Comins, N.F.

    1984-09-01

    A three-dimensional Stochastic Self-Propagating Star Formation (SSPSF) model of compact galacies is presented. Two phases of gas, active and inactive, are present, and permanent depletion of gas in the form of long lived, low mass stars and remnants occurs. Similarly, global infall of gas from a galactic halo or through galactic cannibalism is permitted. We base our parameters on the observed properties of the compact blue galaxy I Zw 36. Our results are that bursts of star formation occur much more frequently in these runs than continuous nonbursting star formation, suggesting that the blue compact galaxies are probably undergoing bursts rather than continuous, nonbursting low-level star formation activity.

  7. Star formation

    Energy Technology Data Exchange (ETDEWEB)

    Woodward, P.R.

    1978-09-27

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references.

  8. Star formation

    International Nuclear Information System (INIS)

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references

  9. Carbon Stars

    Indian Academy of Sciences (India)

    T. Lloyd Evans

    2010-12-01

    In this paper, the present state of knowledge of the carbon stars is discussed. Particular attention is given to issues of classification, evolution, variability, populations in our own and other galaxies, and circumstellar material.

  10. Rock Stars

    Institute of Scientific and Technical Information of China (English)

    张国平

    2000-01-01

    Around the world young people are spending unbelievable sums of money to listen to rock music. Forbes Magazine reports that at least fifty rock stars have incomes between two million and six million dollars per year.

  11. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star....

  12. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Andersen, Thomas Lykke

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star....

  13. Instant BlueStacks

    CERN Document Server

    Judge, Gary

    2013-01-01

    Get to grips with a new technology, understand what it is and what it can do for you, and then get to work with the most important features and tasks. A fast-paced, example-based approach guide for learning BlueStacks.This book is for anyone with a Mac or PC who wants to run Android apps on their computer. Whether you want to play games that are freely available for Android but not your computer, or you want to try apps before you install them on a physical device or use it as a development tool, this book will show you how. No previous experience is needed as this is written in plain English

  14. SPECTROSCOPIC ANALYSES OF MASSIVE BLUE STARS (GALACTIC OR EXTRAGALACTIC

    Directory of Open Access Journals (Sweden)

    A. Herrero

    2008-01-01

    Full Text Available Repasamos los recientes avances en nuestro conocimiento de las estrellas masivas a través del análisis de sus espectros. Discutimos brevemente las mejoras en los modelos de atmósfera y en los métodos de análisis. Se comparan los resultados obtenidos en estrellas del Grupo Local y se describe el estado actual de diferentes cuestiones que permanecen abiertas, como la escala de temperaturas de las estrellas OB, la Relación entre el Momento del Viento y la Luminosidad o la rotación estelar.

  15. The evolutionary status of the UX Orionis star RZ Piscium

    CERN Document Server

    Grinin, V P; Musaev, F A; 10.1051/0004-6361/201014889

    2011-01-01

    The star RZ Psc is one of the most enigmatic members of the UX Ori star family. It shows all properties that are typical for these stars (the light variability, high linear polarization in deep minima, the blueing effect) except for one: it lacks any signatures of youth. With the Li I line, as a rough estimate for the stellar age, we show that the "lithium" age of RZ Psc lies between the age of stars in the Pleiades (approximately 70 Myr) and the Orion (approximately 10 Myr) clusters. We also roughly estimated the age of RZ Psc based on the proper motion of the star using the Tycho-2 catalog. We found that the star has escaped from its assumed birthplace near to the Galactic plane about 30-40 Myr ago. We conclude that RZ Psc is a post-UXOr star, and its sporadic eclipses are caused by material from the debris disk.

  16. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    Science.gov (United States)

    2010-07-01

    raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them," explains Crowther. Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers' findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years. Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," concludes Crowther. Notes [1] The star A1 in NGC 3603 is a double star, with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they have formed as stars weighing, respectively, 148 and 106 solar masses. [2] The team used the SINFONI, ISAAC and MAD instruments, all attached to ESO's Very Large Telescope at Paranal, Chile. [3] (note added on 26 July 2010) The "bigger" in the title does not imply that these stars are the biggest observed. Such stars, called red supergiants, can have radii up to about a thousand solar radii, while R136a1, which is blue, is about 35 times as large as the Sun. However, R136a1 is the star with the greatest mass known to date. More information This work is presented in an article published in the Monthly Notices of the Royal Astronomical Society ("The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit", by

  17. Indications of Inflow Motions in Regions Forming Massive Stars

    CERN Document Server

    Wu, J

    2003-01-01

    Observational evidence for inflowing motions in massive star forming regions has been extremely rare. We have made a spectroscopic survey of a sample of 28 massive star forming cores associated with water masers. An optically thick line of HCN (3-2) was used in combination with optically thin lines [H^{13}CN (3-2) or C^{34}S (5-4), (3-2), and (2-1)], to identify ``blue'' line profiles that can indicate inflow. Comparing intensities for 18 double-peaked line profiles yields 11 blue and 3 red profiles that are statistically significant. In the full sample of 28 sources, 12 show blue profiles and 6 show red profiles that are statistically significant based on the velocity offsets of lines that are optically thick from those that are optically thin. These results indicate that HCN (3-2) emission may trace inflow in regions forming high-mass stars.

  18. NoSOCS in SDSS - V. Red disc and blue bulge galaxies across different environments

    Science.gov (United States)

    Lopes, P. A. A.; Rembold, S. B.; Ribeiro, A. L. B.; Nascimento, R. S.; Vajgel, B.

    2016-09-01

    We investigated the typical environment and physical properties of `red discs' and `blue bulges', comparing those to the `normal' objects in the blue cloud and red sequence. Our sample is composed of cluster members and field galaxies at z ≤ 0.1, so that we can assess the impact of the local and global environment. We find that disc galaxies display a strong dependence on environment, becoming redder for higher densities. This effect is more pronounced for objects within the virial radius, being also strong related to the stellar mass. We find that local and global environment affect galaxy properties, but the most effective parameter is stellar mass. We find evidence for a scenario where `blue discs' are transformed into `red discs' as they grow in mass and move to the inner parts of clusters. From the metallicity differences of red and blue discs, and the analysis of their star formation histories, we suggest the quenching process is slow. We estimate a quenching time-scale of ˜2-3 Gyr. We also find from the sSFR-M* plane that `red discs' gradually change as they move into clusters. The `blue bulges' have many similar properties than `blue discs', but some of the former show strong signs of asymmetry. The high asymmetry `blue bulges' display enhanced recent star formation compared to their regular counterparts. That indicates some of these systems may have increased their star formation due to mergers. None the less, there may not be a single evolutionary path for these blue early-type objects.

  19. Blue-sky thinking

    International Nuclear Information System (INIS)

    Global environmental problems - such as the greenhouse effect, the depletion of natural resources and the accumulation of wastes - have been recognized as common international issues affecting humanity since the 1990s. Sustainable development on a global scale is now sought, for instance, with the establishment of the targets for greenhouse gas reduction in the 1997 Kyoto Protocol, and with the adoption of the Declaration on Sustainable Development at the 2002 Johannesburg Summit. Honda launched the slogan 'Blue Sky for Children' in the 1960s when environmental pollution became a highly visible issue. During that decade we started an aggressive approach aimed at substantial environmental improvement, and unveiled the Compound Vortex Controlled Combustion (CVCC) engine - which used unique low-emission technology - in the United States and Japan. Since then, we have developed the Variable Valve Timing and Lift Electric Control System (VTEC) and the i-VTEC series with innovative engine technology, permitting global production of vehicles that combine high performance with state-of-the-art low-emission technologies. And we continued to work to preserve the global environment by releasing a hybrid vehicle, the Insight, which achieved the most efficient fuel consumption in the world at the time of its introduction in 1998

  20. Blue Man袭东京

    Institute of Scientific and Technical Information of China (English)

    Naomi Saeki; 李宝怡

    2008-01-01

    <正>20年前在美国曼克顿风靡一时的Blue Man Group,最近在东京出现,马上成为城中话题。在东京,每年有不少舞台剧演出,但是像Blue Man Group这样备受注目的,近年罕见。Blue Man Group in Tokyo于上年12月开始公演·1个月的门票早在9月中旬

  1. Blue Angel for green electronics

    Energy Technology Data Exchange (ETDEWEB)

    Boettcher-Tiedemann, C.; Jacobs, B. [Federal Environmental Agency, Berlin (Germany)

    2004-07-01

    The Blue Angel was the first eco-label worldwide. It has been in existence for 26 years. For the last 12 years, modern electronic office and communications equipment has been among the products that are eligible for award of the Blue Angel. The Blue Angel eco-label is an important element of integrated product policy and is aimed towards environmentally sound product design. In addition, health aspects are increasingly being taken into account in criteria development. The use of the label gives innovative companies better market opportunities for products so labelled. For consumers and for purchasers in businesses and public administrations, it gives valuable guidance for product purchase. (orig.)

  2. The hot Gamma-Doradus and Maia stars

    CERN Document Server

    Balona, L A; Joshi, Yogesh C; Joshi, S; Sharma, K; Semenko, E; Pandey, G; Chakradhari, N K; Mkrtichian, David; Hema, B P; Nemec, J M

    2016-01-01

    The hot $\\gamma$~Doradus stars have multiple low frequencies characteristic of $\\gamma$~Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the $\\gamma$~Dor instability strips where all low-frequency modes are stable in current models of these stars. Though $\\delta$~Sct stars also have low frequencies, there is no sign of high frequencies in hot $\\gamma$~Dor stars. We obtained spectra to refine the locations of some of these stars in the H-R diagram and conclude that these are, indeed, anomalous pulsating stars. The Maia variables have multiple high frequencies characteristic of $\\beta$~Cep and $\\delta$~Sct stars, but lie between the red edge of the $\\beta$~Cep and the blue edge of the $\\delta$~Sct instability strips. We compile a list of all Maia candidates and obtain spectra of two of these stars. Again, it seems likely that these are anomalous pulsating stars which are currently not understood.

  3. The advanced stages of stellar evolution: impact of mass loss, rotation, and link with B[e] stars

    CERN Document Server

    Georgy, Cyril; Ekström, Sylvia; Meynet, Georges

    2016-01-01

    In this paper, we discuss some consequences of rotation and mass loss on the evolved stages of massive star evolution. The physical reasons of the time evolution of the surface velocity are explained, and then we show how the late-time evolution of massive stars are impacted in combination with the effects of mass loss. The most interesting result is that in some cases, a massive star can have a blue-red-blue evolution, opening the possibility that Blue Supergiants are composed by two distinct populations of stars: one just leaving the main sequence and crossing the HRD for the first time, and the other one evolving back to the blue side of the HRD after a Red Supergiant phase. We discuss a few possible observational tests that can allow to distinguish these two populations, and how supergiant B[e] stars fit in this context.

  4. Rainbow's Stars

    CERN Document Server

    Garattini, Remo

    2016-01-01

    In recent years, a growing interest on the equilibrium of compact astrophysical objects like white dwarf and neutron stars has been manifested. In particular, various modifications due to Planck scale energy effects have been considered. In this paper we analyze the modification induced by Gravity's Rainbow on the equilibrium configurations described by the Tolman-Oppenheimer-Volkoff (TOV) equation. Our purpose is to explore the possibility that the Rainbow Planck-scale deformation of space-time could support the existence of different compact stars.

  5. MN112: a new Galactic candidate Luminous Blue Variable

    CERN Document Server

    Gvaramadze, V V; Fabrika, S; Sholukhova, O; Berdnikov, L N; Cherepashchuk, A M; Zharova, A V

    2009-01-01

    We report the discovery of a new Galactic candidate Luminous Blue Variable (cLBV) via detection of an infrared circular nebula and follow-up spectroscopy of its central star. The nebula, MN112, is one of many dozens of circular nebulae detected at 24 $\\mu$m the Spitzer Space Telescope archival data, whose morphology is similar to that of nebulae associated with known (c)LBVs and related evolved massive stars. Specifically, the core-halo morphology of MN112 bears a striking resemblance to the circumstellar nebula associated with the Galactic cLBV GAL 079.29+00.46, which suggests that both nebulae might have a similar origin and that the central star of MN112 is a LBV. The spectroscopy of the central star showed that its spectrum is almost identical to that of the bona fide LBV P Cygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude ($\\ga 1$ mag) photometric variability of the central star using archival a...

  6. Karner Blue Butterfly Recovery Plan

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This recovery plan has been prepared by the Karner Blue Butterfly Recovery Team under the leadership of Dr. David Andow, University of Minnesota-St. Paul. Dr. John...

  7. China Mobile: Expanding "Blue Ocean"

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Driving force is crucial for realizing high-speed growth. The strong driving force from "Blue Ocean Strategy" is an important advantage for China Mobile to realize harmonious and leap-forward development.

  8. Star Product and Applications

    OpenAIRE

    Iida, Mari; Yoshioka, Akira

    2011-01-01

    A family of star products parametrized by complex matrices is defined. Especially commutative associative star products are treated, and star exponentials with respect to these star products are considered. Jacobi's theta functions are given as infinite sums of star exponentials. As application, several concrete identities are obtained by properties of the star exponentials.

  9. Stars Underground

    CERN Multimedia

    Jean Leyder

    1996-01-01

    An imaginary voyage in time where we were witness of the birth of the universe itself, the time of the Big-Bang 15 billion years ago. Particules from the very first moments of time : protons, neutrons and electrons, and also much more energetic one. These particules are preparing to interact collider and generating others which will be the birth to the stars ........

  10. Pulsating stars

    CERN Document Server

    Catelan, M?rcio

    2014-01-01

    The most recent and comprehensive book on pulsating stars which ties the observations to our present understanding of stellar pulsation and evolution theory.  Written by experienced researchers and authors in the field, this book includes the latest observational results and is valuable reading for astronomers, graduate students, nuclear physicists and high energy physicists.

  11. Blue Ocean vs. Five Forces

    OpenAIRE

    Burke, Andrew; Stel, André; Thurik, Roy

    2010-01-01

    textabstractThe article reports on the authors' research in the Netherlands which focused on a profit model in Dutch retail stores and a so-called blue-ocean approach which requires a new market that attracts consumers and increases profits. Topics include the competitive strategy approach to increasing profits. The authors conclude that the blue-ocean strategy or innovation approach is sustainable.

  12. The Stars behind the Curtain

    Science.gov (United States)

    2010-02-01

    ESO is releasing a magnificent VLT image of the giant stellar nursery surrounding NGC 3603, in which stars are continuously being born. Embedded in this scenic nebula is one of the most luminous and most compact clusters of young, massive stars in our Milky Way, which therefore serves as an excellent "local" analogue of very active star-forming regions in other galaxies. The cluster also hosts the most massive star to be "weighed" so far. NGC 3603 is a starburst region: a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust. Located 22 000 light-years away from the Sun, it is the closest region of this kind known in our galaxy, providing astronomers with a local test bed for studying intense star formation processes, very common in other galaxies, but hard to observe in detail because of their great distance from us. The nebula owes its shape to the intense light and winds coming from the young, massive stars which lift the curtains of gas and clouds revealing a multitude of glowing suns. The central cluster of stars inside NGC 3603 harbours thousands of stars of all sorts (eso9946): the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars - extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae. Using another recent set of observations performed with the SINFONI instrument on ESO's Very Large Telescope (VLT), astronomers have confirmed that one of these stars is about 120 times more massive than our Sun, standing out as the most massive star known so far in the Milky Way [1]. The clouds of NGC 3603 provide us with a family picture of stars in different stages of their life, with gaseous structures that are

  13. Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way

    International Nuclear Information System (INIS)

    In this paper the fundamental properties of the brightest known stars in our Galaxy are determined for future comparison with results for the most luminous stars in other galaxies. The H-R diagrams (M/sub v/ versus spectral type and M/sub bol/ versus log T/sub e/), the luminosities of the brightest stars, and the ratios of blue to red supergiants are all discussed, and a catalog of over 1000 supergiants and O stars in associations and clusters is included at the end of the paper.The ''theoretical'' H-R diagram (M/sub bol/ versus log T/sub e/) reveals a group of superluminous O stars with M/sub bol/ between -12 mag, a lack of evolved supergiants at these very high luminosities, and an apparent upper limit to the luminosities of the later-type supergiants (>B5) near M/sub bol/=-9.5 mag.The most luminous red supergiants have a maximum visual luminosity near M/sub v/approx. =-8 mag, supporting the suggestion by Sandage and Tammann that they are good distance indicators. Excluding the superluminous star Cyg OB 2 No. 12 (M/sub v/approx. =-9.9 mag), the brightest blue stars are found at M/sub v/approx. =-8.5 mag.The variation of the ratio of blue to red supergiants with luminosity is discussed. There is also evidence for a gradient in this ratio with distance from the galactic center, although the results are limited by the incompleteness of the data

  14. Observational Constraints on Red and Blue Helium Burning Sequences

    CERN Document Server

    McQuinn, Kristen B W; Dalcanton, Julianne J; Dolphin, Andrew E; Holtzman, Jon; Weisz, Daniel R; Williams, Benjamin F

    2011-01-01

    We derive the optical luminosity, colors, and ratios of the blue and red helium burning (HeB) stellar populations from archival Hubble Space Telescope observations of nineteen starburst dwarf galaxies and compare them with theoretical isochrones from Padova stellar evolution models across metallicities from Z=0.001 to 0.009. We find that the observational data and the theoretical isochrones for both blue and red HeB populations overlap in optical luminosities and colors and the observed and predicted blue to red HeB ratios agree for stars older than 50 Myr over the time bins studied. These findings confirm the usefulness of applying isochrones to interpret observations of HeB populations. However, there are significant differences, especially for the red HeB population. Specifically we find: (1) offsets in color between the observations and theoretical isochrones of order 0.15 mag (0.5 mag) for the blue (red) HeB populations brighter than M_V ~ -4 mag, which cannot be solely due to differential extinction; (2...

  15. The Nebula around the Luminous Blue Variable WRAY 15-751 as seen by Herschel

    Science.gov (United States)

    Vamvatira-Nakou, C.; Hutsemekers, D.; Royer, P.; Naze, Y.; Magain, P.; Exter, K.; Waelkens, C.; Groenewegen, M.

    2013-06-01

    To understand the evolution of massive stars it is crucial to study the nebulae associated to Luminous Blue Variables which can reveal the star mass-loss history. We obtained far-infrared Herschel PACS imaging and spectroscopic observations of the nebula associated with the Luminous Blue Variable star WRAY 15-751. These images revealed a second nebula, bigger and cooler, lying in an empty cavity that probably delineates the remnant of the O-star bubble formed when the star was on the Main Sequence. The dust mass and temperature were derived from the modeling of the far-infrared SED. The analysis of the emission line spectrum revealed that the main nebula consists of a region of photoionised gas surrounded by a thin photodissociation region. Both regions are mixed with dust. The calculated C, N, O abundances, together with the estimated mass-loss rate, show that the nebula was ejected from the star during a Red Supergiant phase. This is compatible with the latest evolutionary tracks for a ~40 Mo star with little rotation.

  16. Cold Gas in Blue-Sequence E/S0s: Galaxies in Transition

    CERN Document Server

    Wei, Lisa H; Vogel, Stuart N; Baker, Andrew J

    2009-01-01

    We examine the HI+H_2 content of blue-sequence E/S0s -- a recently identified population of galaxies that are morphologically early type, but reside alongside spiral galaxies in color vs. stellar mass space. We test the idea that the majority of low-to-intermediate mass blue-sequence E/S0s may be settled products of past mergers evolving toward later-type morphology via disk regrowth. We find that blue-sequence E/S0s with stellar masses 1.0, comparable to those of spiral galaxies. Preliminary CO(1-0) maps reveal disk-like rotation of molecular gas in the inner regions of several of our blue-sequence E/S0s, which suggests that they may have gas disks suitable for stellar disk regrowth. At the current rate of star formation, many of our blue-sequence E/S0s will exhaust their atomic gas reservoirs in <~ 3 Gyr. Over the same time period, most of these galaxies are capable of substantial growth in the stellar component. Star formation in blue-sequence E/S0s appears to be bursty, and likely involves inflow trig...

  17. Bipolar Outflows and the Evolution of Stars

    OpenAIRE

    Frank, Adam

    1998-01-01

    Hypersonic bipolar outflows are a ubiquitous phenomena associated with both young and highly evolved stars. Observations of Planetary Nebulae, the nebulae surrounding Luminous Blue Variables such as $\\eta$ Carinae, Wolf Rayet bubbles, the circumstellar environment of SN 1987A and Young Stellar Objects all revealed high velocity outflows with a wide range of shapes. In this paper I review the current state of our theoretical understanding of these outflows. Beginning with Planetary Nebulae con...

  18. An Atlas of Spectrophotometric Landolt Standard Stars

    OpenAIRE

    Stritzinger, Maximilian; Suntzeff, Nicholas B.; Hamuy, Mario; Challis, Peter; Demarco, Ricardo; Germany, Lisa; Soderberg, A. M.

    2005-01-01

    We present CCD observations of 102 Landolt standard stars obtained with the R-C spectrograph on the CTIO 1.5 m telescope. Using stellar atmosphere models we have extended the flux points to our six spectrophotometric secondary standards, in both the blue and the red, allowing us to produce flux-calibrated spectra that span a wavelength range from 3050 \\AA to 1.1 \\micron. Mean differences between UBVRI spectrophotometry computed using Bessell's standard passbands and Landolt's published photom...

  19. 21 CFR 73.50 - Ultramarine blue.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Ultramarine blue. 73.50 Section 73.50 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL LISTING OF COLOR ADDITIVES EXEMPT FROM CERTIFICATION Foods § 73.50 Ultramarine blue. (a) Identity. The color additive ultramarine blue is a blue pigment obtained...

  20. Cold Dust in Three Massive Evolved Stars in the LMC

    CERN Document Server

    Boyer, M L; van Loon, J Th; Srinivasan, S; Clayton, G C; Kemper, F; Smith, L J; Matsuura, M; Woods, Paul M; Marengo, M; Meixner, M; Engelbracht, C; Gordon, K D; Hony, S; Indebetouw, R; Misselt, K; Okumura, K; Panuzzo, P; Riebel, D; Roman-Duval, J; Sauvage, M; Sloan, G C

    2010-01-01

    Massive evolved stars can produce large amounts of dust, and far-infrared (IR) data are essential for determining the contribution of cold dust to the total dust mass. Using Herschel, we search for cold dust in three very dusty massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red supergiant. We model the spectral energy distributions using radiative transfer codes and find that these three stars have mass-loss rates up to 10^-3 solar masses/year, suggesting that high-mass stars are important contributors to the life-cycle of dust. We found far-IR excesses in two objects, but these excesses appear to be associated with ISM and star-forming regions. Cold dust (T < 100 K) may thus not be an important contributor to the dust masses of evolved stars.

  1. The half-century history of studies of Romano's star

    CERN Document Server

    Olga, Maryeva

    2014-01-01

    Luminous blue variables (LBVs) are rare objects of very high luminosity and mass loss rates, low wind velocities, exhibiting strong irregular photometric and spectral variability. They are generally believed to be a relatively short evolutionary stage in the life of a massive star, marking the transition from the Main Sequence toward Wolf-Rayet (WR) stars. However, recent studies indicate that progenitors of several supernovae underwent LBV-like eruptions. These studies support the view that at least some LBV stars are the end point of the evolution but not a transition phase. LBVs are rare objects, observations of whose in the Galaxy are inevitably connected with difficulties in determination of the distance and interstellar extinction. Hence, studying these rare objects in nearby galaxies is potentially more prospective. Therefore, investigation of the extragalactic star Romano's star (V532 or GR290) which is now classified as LBV/post-LBV star and shows late-WN spectrum, is very important for our understan...

  2. The Circumstellar Medium of Massive Stars in Motion

    CERN Document Server

    Mackey, Jonathan; Meyer, Dominique M -A; Gvaramadze, Vasilii V; Mohamed, Shazrene; Neilson, Hilding R; Mignone, Andrea

    2014-01-01

    The circumstellar medium around massive stars is strongly impacted by stellar winds, radiation, and explosions. We use numerical simulations of these interactions to constrain the current properties and evolutionary history of various stars by comparison with observed circumstellar structures. Two- and three-dimensional simulations of bow shocks around red supergiant stars have shown that Betelgeuse has probably only recently evolved from a blue supergiant to a red supergiant, and hence its bow shock is very young and has not yet reached a steady state. We have also for the first time investigated the magnetohydrodynamics of the photoionised H II region around the nearby runaway O star Zeta Oph. Finally, we have calculated a grid of models of bow shocks around main sequence and evolved massive stars that has general application to many observed bow shocks, and which forms the basis of future work to model the explosions of these stars into their pre-shaped circumstellar medium.

  3. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter; Brorsen, Michael

    Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004.......Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004....

  4. The nature of hypervelocity stars as inferred from their galactic trajectories

    CERN Document Server

    Svensson, Karl M; Davies, Melvyn B

    2007-01-01

    We have computed the galactic trajectories of twelve hypervelocity stars (HVSs) under the assumption that they originated in the Galactic Centre. We show that eight of these twelve stars are bound to the Galaxy. We consider the subsequent trajectories of the bound stars to compute their characteristic orbital period, which is 2 Gyr. All eight bound stars are moving away from the centre of the Galaxy, which implies that the stars' lifetimes are less than 2 Gyr. We thus infer that the observed HVSs are massive main sequence stars, rather than blue horizontal branch stars. The observations suggest that blue HVSs are ejected from the Galactic Centre roughly every 15 Myr. This is consistent with the observed population of blue stars in extremely tight orbits round the central super-massive black hole (SMBH), the so-called S-stars, if we assume that the HVSs are produced by the breakup of binaries. One of the stars in such a binary is ejected at high velocities to form a HVS; the other remains bound to the SMBH as ...

  5. "Clothed in triple blues": sorting out the Italian blues.

    Science.gov (United States)

    Bimler, David; Uusküla, Mari

    2014-04-01

    Cross-cultural comparisons of color perception and cognition often feature versions of the "similarity sorting" procedure. By interpreting the assignment of two color samples to different groups as an indication that the dissimilarity between them exceeds some threshold, sorting data can be regarded as low-resolution similarity judgments. Here we analyze sorting data from speakers of Italian, Russian, and English, applying multidimensional scaling to delineate the boundaries between perceptual categories while highlighting differences between the three populations. Stimuli were 55 color swatches, predominantly from the blue region. Results suggest that at least two Italian words for "blue" are basic, a similar situation to Russian, in contrast to English where a single "blue" term is basic.

  6. Extreme Star Formation

    OpenAIRE

    Turner, JL

    2010-01-01

    Extreme star formation includes star formation in starbursts and regions forming super star clusters. We survey the current problems in our understanding of the star formation process in starbursts and super star clusters - initial mass functions, cluster mass functions, star formation efficiencies, and radiative feedback into molecular clouds - that are critical to our understanding of the formation and survival of large star clusters, topics that will be the drivers of the observations of t...

  7. Planck stars

    CERN Document Server

    Rovelli, Carlo

    2014-01-01

    A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density --not by size-- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

  8. The Fate of Luminous Compact Blue Galaxies: An Environmental Approach

    CERN Document Server

    Crawford, S M; Glenn, A; Hössel, J G

    2004-01-01

    Luminous Compact Blue Galaxies (LCBGs) are a heterogeneous class which dominate an intermediate phase of galaxy evolution. These sources account for the majority of the star formation between 0.3star formation rates (SFR) and metallicities from low dispersion Mulit-Object Spectroscopy (MOS); (2) dynamical masses from line-widths measured via high dispersion MOS; and (3) cluster velocity dispersions of LCBGs relative to other cluster em...

  9. Why Do Proteins Glow Blue?

    CERN Document Server

    Sarkar, Sohini; Hazra, Partha; Mandal, Pankaj

    2014-01-01

    Recent literatures reported blue-green emission from amyloid fibril as exclusive signature of fibril formation. This unusual visible luminescence is regularly used to monitor fibril growth. Blue-green emission has also been observed in crystalline protein and in solution. However, the origin of this emission is not known exactly. Our spectroscopic study of serum proteins reveals that the blue-green emission is a property of protein monomer. Evidences suggest that semiconductor-like band structure of proteins with the optical band-gap in the visible region is possibly the origin of this phenomenon. We show here that the band structure of proteins is primarily the result of electron delocalization through the peptide chain, rather than through the hydrogen bond network in secondary structure.

  10. Measure of the stars

    Energy Technology Data Exchange (ETDEWEB)

    Henbest, N.

    1984-12-13

    The paper concerns the Hertzsprung-Russel (H-R) diagram, which is graph relating the brightness to the surface temperature of the stars. The diagram provides a deep insight into the fundamental properties of the stars. Evolution of the stars; the death of a star; distances; and dating star clusters, are all briefly discussed with reference to the H-R diagram.

  11. The blue-collar brain.

    Science.gov (United States)

    Van Orden, Guy; Hollis, Geoff; Wallot, Sebastian

    2012-01-01

    Much effort has gone into elucidating control of the body by the brain, less so the role of the body in controlling the brain. This essay develops the idea that the brain does a great deal of work in the service of behavior that is controlled by the body, a blue-collar role compared to the white-collar control exercised by the body. The argument that supports a blue-collar role for the brain is also consistent with recent discoveries clarifying the white-collar role of synergies across the body's tensegrity structure, and the evidence of critical phenomena in brain and behavior. PMID:22719730

  12. The blue supergiant MN18 and its bipolar circumstellar nebula

    CERN Document Server

    Gvaramadze, V V; Bestenlehner, J M; Bodensteiner, J; Langer, N; Greiner, J; Grebel, E K; Berdnikov, L N; Beletsky, Y

    2015-01-01

    We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope. Using the optical spectrum obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code CMFGEN, obtaining a stellar effective temperature of \\approx 21 kK. The star is highly reddened, E(B-V)\\approx 2 mag. Adopting an absolute visual magnitude of M_V=-6.8\\pm0.5 (typical of B1 supergiants), MN18 has a luminosity of log L/Lsun \\approx 5.42\\pm0.30, a mass-loss rate of \\approx (2.8-4.5)\\times10^{-7} Msun/yr, and resides at a distance of \\approx 5.6^{+1.5} _{-1.2} kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy (She...

  13. Star Formation Rates in Low Surface Brightness Galaxies

    NARCIS (Netherlands)

    Pickering, T. E.; Impey, C. D.; van Gorkom, J.; Bothun, G. D.

    1994-01-01

    The low surface brightness (LSB) disk galaxies found in recent surveys (e.g.,\\ Schombert et al. 1992, AJ, 103, 1107) tend to be blue and gas rich. These properties along with their low mean surface luminosity and H i densities imply an inefficient mode of star formation. The Hα images that we presen

  14. Chemical Evolution of Blue Compact Galaxies

    Institute of Scientific and Technical Information of China (English)

    Fei Shi; Xu Kong; Fu-Zhen Cheng

    2006-01-01

    Based on a sample of 72 Blue Compact Galaxies (BCGs) observed with the 2.16 m telescope of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC) and about 4000 strong emission line galaxies from the Sloan Digital Sky Survey,we analyzed their chemical evolution history using the revised chemical evolution model of Larsen et al. Our sample covers a much larger metallicity range (7.2<12+log(O/H) <9.0). We found that, in order to reproduce the observed abundance pattern and gas fraction over the whole metallicity range, a relatively continuous star formation history is needed for high metallicity galaxies, while assuming a series of instantaneous bursts with long quiescent periods (some Gyrs) for low metallicity galaxies. Model calculations also show that only the closed-box model is capable of reproducing the observational data over the whole metallicity range. Models that consider the ordinary winds and/or inflow can only fit the observations in the low metallicity range, and a model with enriched wind cannot fit the data in the whole metallicity range. This implies that the current adopted simple wind and inflow models are not applicable to massive galaxies, where the underlying physics of galactic winds or inflow could be more complicated.

  15. The Star Formation History of LGS 3

    CERN Document Server

    Miller, B W; Lee, M G; Kim, S C; Hodge, P

    2001-01-01

    We have determined the distance and star formation history of the Local Group dwarf galaxy LGS 3 from deep Hubble Space Telescope WFPC2 observations. LGS 3 is intriguing because ground-based observations showed that, while its stellar population is dominated by old, metal-poor stars, there is a handful of young, blue stars. Also, the presence of HI gas makes this a possible ``transition object'' between dwarf spheroidal and dwarf irregular galaxies. The HST data are deep enough to detect the horizontal branch and young main sequence for the first time. A new distance of D=620+/-20 kpc has been measured from the positions of the TRGB, the red clump, and the horizontal branch. The mean metallicity of the stars older than 8 Gyr is Fe/H = -1.5 +/- 0.3. The most recent generation of stars has Fe/H ~ -1. For the first few Gyr the global star formation rate was several times higher than the historical average and has been fairly constant since then. However, we do see significant changes in stellar populations and s...

  16. SPITZER SAGE-SMC INFRARED PHOTOMETRY OF MASSIVE STARS IN THE SMALL MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 μm in the UBVIJHKs +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 μm in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A and F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.

  17. Tight LMC massive star clusters R 127 and R 128

    CERN Document Server

    Heydari-Malayeri, M; Walborn, N R; Walborn, Nolan R.

    2003-01-01

    We study the Large Magellanic Cloud (LMC) star clusters R 127 and R 128 using imaging and spectroscopy obtained at the ESO NTT telescope. An advanced image restoration technique allows us to resolve these two clusters into at least 14 and 33 stars respectively and obtain their photometry. In particular, we show that the core of R 127 is composed of at least four stars and identify the Luminous Blue Variable (LBV) component. The closest neighbor of the LBV (star #8) is 1".5 away. Moreover, from medium dispersion spectroscopy we determine the spectral types for 19 stars in and near both clusters, and in particular present the first spatially resolved observation of the second brightest component of the R 127 cluster (star #3) situated 3".3 from the LBV. By comparing with evolutionary models we also look into the stellar ages. The oldest stars of the cluster are ~ 6-8 Myr old, whereas the most massive star of the region (#7), formed ~ 3 Myr ago as an 80 solar mass star, has turned into an LBV, the ``R 127'' star...

  18. The Blue Revolution in Asia

    DEFF Research Database (Denmark)

    Ponte, Stefano; Kelling, Ingrid; Jespersen, Karen Sau;

    2014-01-01

    In this article, we examine the upgrading trajectories of selected aquaculture value chains in four Asian countries and the links between upgrading and three factors of value chain governance: coordination mechanisms; types of drivers; and domestic regulation. We find instances of improving produ...... of upgrading the "blue revolution" in Asia...

  19. Liquid biofuels from blue biomass

    DEFF Research Database (Denmark)

    Kádár, Zsófia; Jensen, Annette Eva; Bangsø Nielsen, Henrik;

    2011-01-01

    Marine (blue) biomasses, such as macroalgaes, represent a huge unexploited amount of biomass. With their various chemical compositions, macroalgaes can be a potential substrate for food, feed, biomaterials, pharmaceuticals, health care products and also for bioenergy. Algae use seawater as a growth...

  20. Nobel Prize for blue LEDs

    Science.gov (United States)

    Kraftmakher, Yaakov

    2015-05-01

    A brief review of lighting technologies is presented. Unavoidable restrictions for incandescent light bulbs caused by the Planck distribution and properties of the human eye are illustrated. The efficiency and luminous efficacy of thermal radiation are calculated for various temperatures; the results clearly show the limitations for thermal radiators. The only way to overcome these limitations is using non-thermal radiators, such as fluorescent lamps and light-emitting diodes (LEDs). Unique advantages of LEDs undoubtedly made a revolution in this field. A crucial element of this progress is the blue LEDs (Nobel Prize 2014). Some experiments with a blue and a green LED are described: (i) the luminescence triggered in a green-yellow phosphor inside a white LED by the blue LED; (ii) radiant spectra and ‘efficiency droop’ in the LEDs; (iii) modulation of the blue LED up to 4 MHz; and (iv) the h/e ratio from the turn-on voltage of the green LED. The experiments are suitable for undergraduate laboratories and usable as classroom demonstrations.

  1. Blue Ocean vs. Five Forces

    NARCIS (Netherlands)

    A.E. Burke (Andrew); A.J. van Stel (André); A.R. Thurik (Roy)

    2010-01-01

    textabstractThe article reports on the authors' research in the Netherlands which focused on a profit model in Dutch retail stores and a so-called blue-ocean approach which requires a new market that attracts consumers and increases profits. Topics include the competitive strategy approach to increa

  2. Discovery of an opportunistic starfish pathogen, Orchitophrya stellarum, in captive blue crabs, Callinectes sapidus.

    Science.gov (United States)

    Small, H J; Miller, T L; Coffey, A H; Delaney, K L; Schott, E; Shields, J D

    2013-10-01

    Histophagous scuticociliate infections were discovered in blue crabs, Callinectes sapidus, held in research facilities at the Virginia Institute of Marine Science. Ciliates were observed infecting every tissue examined including the gills, heart, muscle, hepatopancreas, and epidermis. Hemolymph smears and histological tissue sections indicated a morphological similarity to Mesanophrys chesapeakensis, the only recorded histophagous ciliate infecting blue crabs. However, subsequent analysis of the ribosomal ITS region (ITS1-5.8S-ITS2) of the ciliate indicated the parasite was Orchitophrya stellarum, a parasitic ciliate previously reported infecting sea stars from Europe, Australia, and North America. A simple Polymerase Chain Reaction (PCR-RFLP) assay was developed to detect and differentiate between O. stellarum and M. chesapeakensis. Its application confirmed the presence of O. stellarum infecting blue crabs held in an additional research facility in Maryland. For growth studies, cultures of O. stellarum grew optimally on 10% blue crab serum in crustacean saline held at 10-20°C. A field survey of blue crabs collected during the winters of 2011-2012 and sea stars (Asterias forbesi) during the winter of 2010 from the Chesapeake Bay and eastern shore of Virginia did not identify additional infected individuals.

  3. Supernovae from yellow, blue supergiants: origin and consequences for stellar evolution

    Science.gov (United States)

    Meynet, Georges; Georgy, Cyril; Saio, Hideyuki; Kudritzki, Rolf-Peter; Groh, Jose

    2015-08-01

    A few core collapse supernovae progenitors have been found to be yellow or blue supergiants. We shall discuss possible scenarios involving single and close binary evolution allowing to explain this kind of core collapse supernova progenitors. According to stellar models for both single and close binaries, blue supergiants, at the end of their nuclear lifetimes and thus progenitors of core collapse supernovae, present very different characteristics for what concerns their surface compositions, rotational surface velocities and pulsational properties with respect to blue supergiants in their core helium burning phase. We discuss how the small observed scatter of the flux-weighted gravity-luminosity (FWGL) relation of blue supergiants constrains the evolution of massive stars after the Main-Sequence phase and the nature of the progenitors of supernovae in the mass range between 12 and 40 solar masses. The present day observed surface abundances of blue supergiants, of their pulsational properties, as well as the small scatter of the FWGL relation provide strong constraints on both internal mixing and mass loss in massive stars and therefore on the end point of their evolution.

  4. Blue lobes in the Hydra A cluster central galaxy

    Science.gov (United States)

    Mcnamara, Brian R.

    1995-01-01

    We present new U- and I-band images of the centrally dominant galaxy in the Hydra A cluster, obtained with the 2.5 m Isaac Newton Telescope at La Palma. The galaxy is centered in a poor, X-ray-luminous cluster whose gaseous intracluster medium is apparently cooling at a rate of m-dot(sub CF) approximately 3000 solar masses/yr. The galaxy's structure is that of a normal giant elliptical galaxy, apart from the central approximately 8 x 6 arcsec (approximately 12 x 9 kpc) region which contains an unusually blue, lobelike structure that is spatially coincident with a luminous emission-line nebula in rotation about the nucleus. Based on near spatial coincidence of the central continuum structure and the emission-line nebula, we suggest that the blue continuum is due to a warm stellar population in a central disk. In order to isolate and study the structure of the disk, we have subtracted a smooth galactic background model from the U-band image. The disk's surface brightness profiles along its major and minor axes decline roughly exponentially with radius. The disk's axial ratio is consistent with a nearly edge-on thick disk or a thin disk that is inclined with respect to the line of sight. The bluest regions, located a few arcsec on either side of the nucleus (giving the lobelike appearance), may be due to locally enhanced star formation or a seeing-blurred ring of young stars embedded in the disk observed nearly edge-on. If star-formation is occurring with the local initial mass function, the central color, surface brightness, and dynamical mass would be consistent with models for star formation at a rate of less than and approximately 1 solar masses/yr which has persisted for the past approximately 10(exp 9) yr, a short burst (10(exp 7) yr) of star formation at a rate of approximately 30 solar masses/yr which occurred less than and approximately 10(exp 8) yr ago, or an instantaneous burst of star formation which occurred approximately 5 x 10(exp 7) yr ago. While the

  5. The Neutral ISM in Nearby Luminous Compact Blue Galaxies

    CERN Document Server

    Garland, C A; Williams, J P; Guzmán, R; Castander, F J

    2003-01-01

    We observed 20 nearby Luminous Compact Blue Galaxies (LCBGs) in HI and CO(J=2-1) with the GBT and JCMT. These ~L^star galaxies are blue, high surface brightness, starbursting, high metallicity galaxies with an underlying older stellar population. They are common at z~1, but rare in the local Universe. It has been proposed that intermediate redshift LCBGs may be the progenitors of local dwarf ellipticals or low luminosity spirals, or that they may be more massive disks forming from the center outward to become L^star galaxies. To discriminate among various possible evolutionary scenarios, we have measured the dynamical masses and gas depletion time scales of this sample of nearby LCBGs. We find that local LCBGs span a wide range of dynamical masses, from 4 x 10^9 to 1 x 10^11 M_solar (measured within R_25). Molecular gas in local LCBGs is depleted quite quickly, in 30 to 200 million years. The molecular plus atomic gas is depleted in 30 million to 10 billion years; however, ~80% of the local LCBGs deplete thei...

  6. Peculiar early-type galaxies with central star formation

    Institute of Scientific and Technical Information of China (English)

    Chong Ge; Qiu-Sheng Gu

    2012-01-01

    Early-type galaxies (ETGs) are very important for understanding the formation and evolution of galaxies.Recent observations suggest that ETGs are not simply old stellar spheroids as we previously thought.Widespread recent star formation,cool gas and dust have been detected in a substantial fraction of ETGs.We make use of the radial profiles of g - r color and the concentration index from the Sloan Digital Sky Survey database to pick out 31 peculiar ETGs with central blue cores.By analyzing the photometric and spectroscopic data,we suggest that the blue cores are caused by star formation activities rather than the central weak active galactic nucleus.From the results of stellar population synthesis,we find that the stellar population of the blue cores is relatively young,spreading from several Myr to less than one Gyr.In 14 galaxies with H I observations,we find that the average gas fraction of these galaxies is about 0.55.The bluer galaxies show a higher gas fraction,and the total star formation rate (SFR) correlates very well with the H l gas mass.The star formation history of these ETGs is affected by the environment,e.g.in the denser environment the H 1 gas is less and the total SFR is lower.We also discuss the origin of the central star formation of these early-type galaxies.

  7. An Unwelcome Place for New Stars (artist concept)

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] Poster Version Suppression of Star Formation from Supermassive Black Holes This artist's concept depicts a supermassive black hole at the center of a galaxy. NASA's Galaxy Evolution Explorer found evidence that black holes -- once they grow to a critical size -- stifle the formation of new stars in elliptical galaxies. Black holes are thought to do this by heating up and blasting away the gas that fuels star formation. The blue color here represents radiation pouring out from material very close to the black hole. The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. Beyond the torus, only the old red-colored stars that make up the galaxy can be seen. There are no new stars in the galaxy.

  8. Variable stars in the open cluster NGC 2141

    CERN Document Server

    Luo, Yanping

    2014-01-01

    We report the results of a search for variable stars in the open cluster NGC 2141. Ten variable stars are detected, among which nine are new variable stars and they are classified as three short period W UMa type eclipsing binaries, two EA type eclipsing binaries, one EB type eclipsing binary, one very short period RS CVn type eclipsing binary, one d type RR Lyrae variable star, and one unknown type variable star. The membership and physical properties are discussed, based on their light curves, positions in the CMDs, spatial locations and periods. A known EB type eclipsing binary is also identified as a blue struggler candidate of the cluster. Furthermore, we find that all eclipsing contact binaries have prominently asymmetric eclipses and O Connell effect (O Connell 1951) which increases with the decrease of the orbital periods. This suggests that the O Connell effect is probably related to the evolution of the orbital period in short period eclipsing binary systems.

  9. The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?

    CERN Document Server

    Pisano, D J; Garland, C A; Guzman, R; Castander, F J; Perez-Gallego, J

    2011-01-01

    Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies characterized by high luminosity, blue color, and high surface brightness that sit at the critical juncture of galaxies evolving from the blue to the red sequence. As part of our multi-wavelength survey of local LCBGs, we have been studying the HI content of these galaxies using both single-dish telescopes and interferometers. Our goals are to determine if single-dish HI observations represent a true measure of the dynamical mass of LCBGs and to look for signatures of recent interactions that may be triggering star formation in LCBGs. Our data show that while some LCBGs are undergoing interactions, many appear isolated. While all LCBGs contain HI and show signatures of rotation, the population does not lie on the Tully-Fisher relation nor can it evolve onto it. Furthermore, the HI maps of many LCBGs show signatures of dynamically hot components, suggesting that we are seeing the formation of a thick disk or spheroid in at least some LCBGs....

  10. Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift

    CERN Document Server

    Barton, E J; Barton, Elizabeth J.; Zee, Liese van

    2001-01-01

    We identify nearby disk galaxies with optical structural parameters similar to those of intermediate-redshift compact blue galaxies. By comparing HI and optical emission-line widths, we show that the optical widths substantially underestimate the true kinematic widths of the local galaxies. By analogy, optical emission-line widths may underrepresent the masses of intermediate-z compact objects. For the nearby galaxies, the compact blue morphology is the result of tidally-triggered central star formation: we argue that interactions and minor mergers may cause apparently compact morphology at higher redshift.

  11. Flavour production of Stilton blue cheese microflora

    OpenAIRE

    Gkatzionis, Konstantinos

    2010-01-01

    In the blue cheese Stilton the starter mould Penicillium roqueforti grows and sporulates during the ripening period and is considered to be responsible for the unique blue cheese aroma. However, the sporulation of the mould, which results in the formation of blue veins, takes place in a fraction of the Stilton matrix which overall is very heterogeneous. Most blue cheeses develop a secondary microflora of yeasts which may affect their aroma. The aim of this study was to investigate the yeast f...

  12. Triggered Star Formation by Massive Stars

    OpenAIRE

    Lee, Hsu-Tai; Chen, W. P.

    2005-01-01

    We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the Lambda Ori region, Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars and Herbig Ae/Be stars tend to line up between luminous O stars and bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively younger they are. Our positional and chronological study lends support to the validity of the radiation-driven implos...

  13. Food habits of blue grouse

    Science.gov (United States)

    Stewart, R.E.

    1944-01-01

    The food habits of Blue Grouse vary from a simple winter diet that is made up predominantly of coniferous needles to a complex diet during the summer months, characterized by great variety of foods including green leaves, fruits and seeds, flowers, animal matter and coniferous needles. The spring and fall, which represent the transition periods between these two, are characterized by feeding habits that are generally intermediate. The diets of the two species of Blue Grouse, Dendrugapus obscurus and Dendragapus juliginosus, are quite similar as far as major types of food are concerned, but they differ considerably in the species that are taken. Such differences reflect differences in the vegetation within the ecologic and geographic ranges occupied by the two species.

  14. Thermoluminescence (TL) of Egyptian Blue

    Energy Technology Data Exchange (ETDEWEB)

    Schvoerer, M.; Delavergne, M.-C.; Chapoulie, R.

    1988-01-01

    Egyptian Blue is a synthesized crystalline pictorial pigment with formula CaCuSi/sub 4/O/sub 10/. It has been used in Egypt and Mesopotamia from the 3rd millenium B.C. A preliminary experiment on a recently synthesized sample showed that this pigment is thermoluminescent after ..beta.. irradiation (/sup 90/Sr). As the signal intensity grows linearly with the administered dose within the temperature range commonly used in TL dating, we have been looking for this phenomenon from archaeological pigments. It was encountered with two samples found in excavation. From its intensity and stability we concluded that Egyptian Blue can be dated using TL. This first and positive result encouraged us to extend the method to other types of mineral pigments synthesized by early man, and to suggest that it may be used for direct dating of ancient murals.

  15. The Physics of the Blues

    Science.gov (United States)

    Gibson, J. Murray

    2009-03-01

    In looking at the commonalities between music and science, one sees that the musician's palette is based on the principles of physics. The pitch of a musical note is determined by the frequency of the sound wave. The scales that musicians use to create and play music can be viewed as a set of rules. What makes music interesting is how musicians develop those rules and create ambiguity with them. I will discuss the evolution of western musical scales in this context. As a particular example, ``Blue'' notes are very harmonic notes that are missing from the equal temperament scale. The techniques of piano blues and jazz represent the melding of African and Western music into something totally new and exciting. Live keyboard demonstrations will be used. Beyond any redeeming entertainment value the talk will emphasize the serious connections between science and art in music. Nevertheless tips will be accepted.

  16. WIYN open cluster study. LIX. Radial velocity membership of the evolved population of the old open cluster NGC 6791

    International Nuclear Information System (INIS)

    The open cluster NGC 6791 has been the focus of much recent study due to its intriguing combination of old age and high metallicity (∼8 Gyr, [Fe/H] = +0.30), as well as its location within the Kepler field. As part of the WIYN Open Cluster Study, we present precise (σ = 0.38 km s–1) radial velocities for proper motion candidate members of NGC 6791 from Platais et al. Our survey, extending down to g' ∼ 16.8, is comprised of the evolved cluster population, including blue stragglers, giants, and horizontal branch stars. Of the 280 proper-motion-selected stars above our magnitude limit, 93% have at least one radial velocity measurement and 79% have three measurements over the course of at least 200 days, sufficient for secure radial-velocity-determined membership of non-velocity-variable stars. The Platais et al. proper motion catalog includes 12 anomalous horizontal branch candidates blueward of the red clump, of which we find only 4 to be cluster members. Three fall slightly blueward of the red clump and the fourth is consistent with being a blue straggler. The cleaned color-magnitude diagram shows a richly populated red giant branch and a blue straggler population. Half of the blue stragglers are in binaries. From our radial velocity measurement distribution, we find the cluster's radial velocity dispersion to be σ c = 0.62 ± 0.10 km s–1. This corresponds to a dynamical mass of ∼4600 M ☉.

  17. WIYN open cluster study. LIX. Radial velocity membership of the evolved population of the old open cluster NGC 6791

    Energy Technology Data Exchange (ETDEWEB)

    Tofflemire, Benjamin M.; Gosnell, Natalie M.; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States); Platais, Imants, E-mail: tofflemi@astro.wisc.edu, E-mail: imants@pha.jhu.edu [Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218 (United States)

    2014-10-01

    The open cluster NGC 6791 has been the focus of much recent study due to its intriguing combination of old age and high metallicity (∼8 Gyr, [Fe/H] = +0.30), as well as its location within the Kepler field. As part of the WIYN Open Cluster Study, we present precise (σ = 0.38 km s{sup –1}) radial velocities for proper motion candidate members of NGC 6791 from Platais et al. Our survey, extending down to g' ∼ 16.8, is comprised of the evolved cluster population, including blue stragglers, giants, and horizontal branch stars. Of the 280 proper-motion-selected stars above our magnitude limit, 93% have at least one radial velocity measurement and 79% have three measurements over the course of at least 200 days, sufficient for secure radial-velocity-determined membership of non-velocity-variable stars. The Platais et al. proper motion catalog includes 12 anomalous horizontal branch candidates blueward of the red clump, of which we find only 4 to be cluster members. Three fall slightly blueward of the red clump and the fourth is consistent with being a blue straggler. The cleaned color-magnitude diagram shows a richly populated red giant branch and a blue straggler population. Half of the blue stragglers are in binaries. From our radial velocity measurement distribution, we find the cluster's radial velocity dispersion to be σ {sub c} = 0.62 ± 0.10 km s{sup –1}. This corresponds to a dynamical mass of ∼4600 M {sub ☉}.

  18. First supernova companion star found

    Science.gov (United States)

    2004-01-01

    Supernova 1993J exploding hi-res Size hi-res: 222 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Supernova 1993J exploding (artist’s impression) New observations with the Hubble Space Telescope allow a look into a supernova explosion under development. In this artist’s view the red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). This interaction process happened over about 250 years and affected the supernova explosion to such an extent that SN 1993J was later known as one of the most peculiar supernovae ever seen. Supernova 1993J exploding hi-res Size hi-res: 4200 kb Credits: ESA and Justyn R. Maund (University of Cambridge) The site of the Supernova 1993J explosion A virtual journey into one of the spiral arms of the grand spiral Messier 81 (imaged with the Isaac Newton Telescope on La Palma, left) reveals the superb razor-sharp imaging power of the NASA/ESA Hubble Space Telescope (Hubble’s WFPC2 instrument, below). The close-up (with Hubble’s ACS, to the right) is centred on the newly discovered companion star to Supernova 1993J that itself is no longer visible. The quarter-circle around the supernova companion is a so-called light echo originating from sheets of dust in the galaxy reflecting light from the original supernova explosion. Supernova 1993J explosing site hi-res Size hi-res: 1502 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Close-up of the Supernova 1993J explosion site (ACS/HRC image) This NASA/ESA Hubble Space Telescope image shows the area in Messier 81 where Supernova 1993J exploded. The companion to the supernova ‘mother star’ that remains after the explosion is seen in the centre of the image. The image is taken with Hubble’s Advanced Camera for Surveys and is a combination of four exposures taken with ACS’ High Resolution Camera. The exposures were taken through two near-UV filters (250W

  19. UIT Detection of Hot Stars in the Globular Cluster NGC362

    CERN Document Server

    Dorman, B; O'Connell, R W; Landsman, W B; Rood, R T; Bohlin, R C; Neff, S G; Roberts, M S; Smith, A M; Stecher, T P; Dorman, Ben; Shah, Ronak Y.; Connell, Robert W. O'; Landsman, Wayne B.; Rood, Robert T.; Bohlin, Ralph C.; Neff, Susan G.; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

    1997-01-01

    We used the Ultraviolet Imaging Telescope during the March 1995 Astro-2 mission to obtain a deep far-UV image of the globular cluster NGC 362, which was formerly thought to have an almost entirely red horizontal branch (HB). 84 hot (T_eff > 8500 K) stars were detected within a radius of 8'.25 of the cluster center. Of these, 43 have FUV magnitudes consistent with HB stars in NGC 362, and at least 34 are cluster members. The number of cluster members is made uncertain by background contamination from blue stars in the Small Magellanic Cloud (SMC). There are six candidate supra-HB stars which have probably evolved from the HB. We discuss the implications of these results for the production of hot blue stars in stellar populations.

  20. Star Formation in Henize 206

    Science.gov (United States)

    2004-01-01

    [figure removed for brevity, see original site] IRA-MIPS Composite [figure removed for brevity, see original site] Visible [figure removed for brevity, see original site] IRAC [figure removed for brevity, see original site] MIPS The LMC is a small satellite galaxy gravitationally bound to our own Milky Way. Yet the gravitational effects are tearing the companion to shreds in a long-playing drama of 'intergalactic cannibalism.' These disruptions lead to a recurring cycle of star birth and star death. Astronomers are particularly interested in the LMC because its fractional content of heavy metals is two to five times lower than is seen in our solar neighborhood. [In this context, 'heavy elements' refer to those elements not present in the primordial universe. Such elements as carbon, oxygen and others are produced by nucleosynthesis and are ejected into the interstellar medium via mass loss by stars, including supernova explosions.] As such, the LMC provides a nearby cosmic laboratory that may resemble the distant universe in its chemical composition. The primary Spitzer image, showing the wispy filamentary structure of Henize 206, is a four-color composite mosaic created by combining data from an infrared array camera (IRAC) at near-infrared wavelengths and the mid-infrared data from a multiband imaging photometer (MIPS). Blue represents invisible infrared light at wavelengths of 3.6 and 4.5 microns. Note that most of the stars in the field of view radiate primarily at these short infrared wavelengths. Cyan denotes emission at 5.8 microns, green depicts the 8.0 micron light, and red is used to trace the thermal emission from dust at 24 microns. The separate instrument images are included as insets to the main composite. An inclined ring of emission dominates the central and upper regions of the image. This delineates a bubble of hot, x-ray emitting gas that was blown into space when a massive star died in a supernova explosion millions of years ago. The shock waves

  1. Helium enhanced stars and multiple populations along the horizontal branch of NGC2808: direct spectroscopic measurements

    CERN Document Server

    Marino, A F; Przybilla, N; Bergemann, M; Lind, K; Asplund, M; Cassisi, S; Catelan, M; Casagrande, L; Valcarce, A A R; Bedin, L R; Cortes, C; D'Antona, F; Jerjen, H; Piotto, G; Schlesinger, K; Zoccali, M; Angeloni, R

    2013-01-01

    We present an abundance analysis of 96 horizontal branch (HB) stars in NGC2808, a globular cluster exhibiting a complex multiple stellar population pattern. These stars are distributed in different portions of the HB and cover a wide range of temperature. By studying the chemical abundances of this sample, we explore the connection between HB morphology and the chemical enrichment history of multiple stellar populations. For stars lying on the red HB, we use GIRAFFE and UVES spectra to determine Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y, Ba, and Nd abundances. For colder, blue HB stars, we derive abundances for Na, primarily from GIRAFFE spectra. We were also able to measure direct NLTE He abundances for a subset of these blue HB stars with temperature higher than ~9000 K. Our results show that: (i) HB stars in NGC2808 show different content in Na depending on their position in the color-magnitude diagram, with blue HB stars having higher Na than red HB stars; (ii) the red HB is not consistent with an uni...

  2. MASSIVE INFANT STARS ROCK THEIR CRADLE

    Science.gov (United States)

    2002-01-01

    Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B, also known as NGC 1748. A new NASA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation of a star-forming region in a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our Milky Way in regions like the Orion Nebula. The Hubble telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighboring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our Milky Way and can easily be seen with the naked eye from the Southern Hemisphere. Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then only with very high-resolution telescopes. Astronomers from France, the U.S., and Germany have used Hubble to study the fascinating interplay between gas, dust, and radiation from the newly born stars in this nebula. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars

  3. Two Ring Nebulae around Blue Supergiants in the Large Magellanic Cloud

    CERN Document Server

    Weis, K; Duschl, W J; Bomans, D J

    1997-01-01

    Ring nebulae are often found around massive stars such as Wolf-Rayet stars, OB and Of stars and Luminous Blue Variables (LBVs). In this paper we report on two ring nebulae around blue supergiants in the Large Magellanic Cloud. The star Sk-69 279 is classified as O9f and is surrounded by a closed shell with a diameter of 4.5 pc. Our echelle observations show an expansion velocity of 14 km/s and a high [N II]6583A/H alpha ratio. This line ratio suggests nitrogen abundance enhancement consistent with those seen in ejectas from LBVs. Thus the ring nebula around Sk-69 279 is a circumstellar bubble. The star Sk-69 271, a B2 supergiant, is surrounded by an H alpha arc resembling an half shell. Echelle observations show a large expanding shell with the arc being part of the approaching surface. The expansion velocity is about 24 km/s and the [N II]6583A/H alpha is not much higher than that of the background emission. The lack of nitrogen abundance anomaly suggests that the expanding shell is an interstellar bubble wi...

  4. Localized Eruptive Blue Nevi after Herpes Zoster

    Science.gov (United States)

    Colson, Fany; Arrese, Jorge E.; Nikkels, Arjen F.

    2016-01-01

    A 52-year-old White man presented with a dozen small, well-restricted, punctiform, asymptomatic, blue-gray macules on the left shoulder. A few months earlier, he had been treated with oral acyclovir for herpes zoster (HZ) affecting the left C7–C8 dermatomes. All the blue macules appeared over a short period of time and then remained stable. The patient had not experienced any previous trauma or had tattooing in this anatomical region. The clinical diagnosis suggested blue nevi. Dermatoscopy revealed small, well-limited, dark-blue, compact, homogeneous areas evoking dermal blue nevi. An excisional biopsy was performed and the histological examination confirmed a blue nevus. As far as we are aware of, this is the first report of eruptive blue nevi following HZ, and it should be included in the differential diagnosis of zosteriform dermatoses responding to an isotopic pathway. In addition, a brief review concerning eruptive nevi is presented. PMID:27462219

  5. Inflation and alternatives with blue tensor spectra

    International Nuclear Information System (INIS)

    We study the tilt of the primordial gravitational waves spectrum. A hint of blue tilt is shown from analyzing the BICEP2 and POLARBEAR data. Motivated by this, we explore the possibilities of blue tensor spectra from the very early universe cosmology models, including null energy condition violating inflation, inflation with general initial conditions, and string gas cosmology, etc. For the simplest G-inflation, blue tensor spectrum also implies blue scalar spectrum. In general, the inflation models with blue tensor spectra indicate large non-Gaussianities. On the other hand, string gas cosmology predicts blue tensor spectrum with highly Gaussian fluctuations. If further experiments do confirm the blue tensor spectrum, non-Gaussianity becomes a distinguishing test between inflation and alternatives

  6. Radio Continuum and HI study of Blue Compact Dwarf Galaxies

    CERN Document Server

    Ramya, S; Prabhu, T P

    2010-01-01

    The multifrequency radio continuum and 21cm HI observations of five blue compact dwarf (BCD) galaxies, Mrk 104, Mrk 108, Mrk 1039, Mrk 1069 and I Zw 97 using the Giant Meterwave Radio Telescope (GMRT) are presented here. Radio continuum emission at 610 MHz and 325 MHz is detected from all the observed galaxies whereas only a few are detected at 240 MHz. In our sample, three galaxies are members of groups and two galaxies (Mrk 1069 and I Zw 97) are isolated galaxies. The radio emission from Mrk 104 and Mrk 108 is seen to encompass the entire optical galaxy whereas the radio emission from Mrk 1039, Mrk 1069, I Zw 97 is confined to massive HII regions. This, we suggest, indicates that the star formation in the latter group of galaxies has recently been triggered and that the environment in which the galaxy is evolving plays a role. Star formation rates (SFR) calculated from 610 MHz emission is in the range 0.01-0.1 M_sun/yr; this is similar to the SFR obtained for individual star forming regions in BCDs. The int...

  7. The Birth of Massive Stars and Star Clusters

    OpenAIRE

    Tan, Jonathan C.

    2005-01-01

    In the present-day universe, it appears that most, and perhaps all, massive stars are born in star clusters. It also appears that all star clusters contain stars drawn from an approximately universal initial mass function, so that almost all rich young star clusters contain massive stars. In this review I discuss the physical processes associated with both massive star formation and with star cluster formation. First I summarize the observed properties of star-forming gas clumps, then address...

  8. Polish Terms for "Blue" in the Perspective of Vantage Theory

    Science.gov (United States)

    Stanulewicz, Danuta

    2010-01-01

    The Polish set of terms for blue includes, inter alia, the following adjectives: "niebieski" "blue", "blekitny" "(sky) blue", "granatowy" "navy blue", "lazurowy" "azure", "modry" "(intense) blue" and "siny" "(grey) violet-blue". The adjective "niebieski" is the basic term; however, it shares some of its functions with "blekitny", which is…

  9. The WHIQII Survey: Metallicities and Spectroscopic Properties of Luminous Compact Blue Galaxies

    CERN Document Server

    Tollerud, Erik J; van Zee, Liese; Cooke, Jeff

    2009-01-01

    As part of the WIYN High Image Quality Indiana Irvine (WHIQII) survey, we present 123 spectra of emission-line galaxies, selected on intermediate redshift (.4blue colors that appear physically compact. The sample includes 15 true Luminous Compact Blue Galaxies (LCBGs) and an additional 27 slightly less extreme emission-line systems. These galaxies represent a highly evolving class that may play an important role in the decline of star formation since z~1, but their exact nature and evolutionary pathways remain a mystery. Here, we use emission lines to determine metallicities and ionization parameters, constraining their intrinsic properties and state of star formation. Some LCBG metallicities are consistent with a "bursting dwarf" scenario, while a substantial fraction of others are not, further confirming that LCBGs are a highly heterogeneous population but are broadly consistent with the intermediate redshift field. In agreement with previous studies, we observe overall evolution ...

  10. The Colorful Demise of a Sun-like Star

    Science.gov (United States)

    2007-01-01

    This image, taken by NASA's Hubble Space Telescope, shows the colorful 'last hurrah' of a star like our Sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the center. Our Sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years. Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers named them planetary nebulae because through small telescopes they resembled the disks of the distant planets Uranus and Neptune. The planetary nebula in this image is called NGC 2440. The white dwarf at the center of NGC 2440 is one of the hottest known, with a surface temperature of nearly 400,000 degrees Fahrenheit (200,000 degrees Celsius). The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bow tie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis. The image was taken Feb. 6, 2007 with Hubble's Wide Field Planetary Camera 2. The colors correspond to material expelled by the star. Blue corresponds to helium; blue-green to oxygen; and red to nitrogen and hydrogen.

  11. The Cambridge Double Star Atlas

    Science.gov (United States)

    MacEvoy, Bruce; Tirion, Wil

    2015-12-01

    Preface; What are double stars?; The binary orbit; Double star dynamics; Stellar mass and the binary life cycle; The double star population; Detecting double stars; Double star catalogs; Telescope optics; Preparing to observe; Helpful accessories; Viewing challenges; Next steps; Appendices: target list; Useful formulas; Double star orbits; Double star catalogs; The Greek alphabet.

  12. On the origins of enigmatic stellar populations in Local Group galactic nuclei

    CERN Document Server

    Leigh, Nathan W C; Stone, Nicholas C; Shara, Michael M; Merritt, David

    2016-01-01

    We consider the origins of enigmatic stellar populations in four Local Group galactic nuclei, specifically the Milky Way, M31, M32 and M33. These are centrally concentrated blue stars, found in three out of the four nuclear star clusters (NSCs) considered here. Their origins are unknown, but could include blue straggler (BS) stars, extended horizontal branch stars and young recently formed stars. Here, we calculate order-of-magnitude estimates for various collision rates, as a function of the host NSC environment and distance from the cluster centre. These rates are sufficiently high that BSs, formed via collisions between main sequence (MS) stars, could contribute non-negligibly ($\\sim$ 1-10% in mass) to every surface brightness profile, with the exception of the Milky Way. Stellar evolution models show that the envelopes of red giant branch (RGB) stars must be nearly completely stripped to significantly affect their photometric appearance, which requires multiple collisions. Hence, the collision rates for i...

  13. THE NATURE OF STARBURSTS. III. THE SPATIAL DISTRIBUTION OF STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street, S.E., University of Minnesota, Minneapolis, MN 55455 (United States); Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Benjamin F. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Holtzman, Jon, E-mail: kmcquinn@astro.umn.edu [Department of Astronomy, New Mexico State University, Box 30001-Department 4500, 1320 Frenger Street, Las Cruces, NM 88003 (United States)

    2012-11-01

    We map the spatial distribution of recent star formation over a few Multiplication-Sign 100 Myr timescales in 15 starburst dwarf galaxies using the location of young blue helium burning stars identified from optically resolved stellar populations in archival Hubble Space Telescope observations. By comparing the star formation histories from both the high surface brightness central regions and the diffuse outer regions, we measure the degree to which the star formation has been centrally concentrated during the galaxies' starbursts, using three different metrics for the spatial concentration. We find that the galaxies span a full range in spatial concentration, from highly centralized to broadly distributed star formation. Since most starbursts have historically been identified by relatively short timescale star formation tracers (e.g., H{alpha} emission), there could be a strong bias toward classifying only those galaxies with recent, centralized star formation as starbursts, while missing starbursts that are spatially distributed.

  14. The Nature of Starbursts: III. The Spatial Distribution of Star Formation

    CERN Document Server

    McQuinn, Kristen B W; Dalcanton, Julianne J; Cannon, John M; Dolphin, Andrew E; Holtzman, Jon; Weisz, Daniel R; Williams, Benjamin F

    2012-01-01

    We map the spatial distribution of recent star formation over a few x 100 Myr timescales in fifteen starburst dwarf galaxies using the location of young blue helium burning stars identified from optically resolved stellar populations in archival Hubble Space Telescope observations. By comparing the star formation histories from both the high surface brightness central regions and the diffuse outer regions, we measure the degree to which the star formation has been centrally concentrated during the galaxies' starbursts, using three different metrics for the spatial concentration. We find that the galaxies span a full range in spatial concentration, from highly centralized to broadly distributed star formation. Since most starbursts have historically been identified by relatively short timescale star formation tracers (e.g., Halpha emission), there could be a strong bias towards classifying only those galaxies with recent, centralized star formation as starbursts, while missing starbursts that are spatially dis...

  15. Discovery of Five New R. Coronae Borealis Stars in the MACHO Galactic Bulge Database

    Energy Technology Data Exchange (ETDEWEB)

    Zaniewshi, A; Clayton, G C; Welch, D; Gordon, K D; Minniti, D; Cook, K

    2005-06-16

    We have identified five new R Coronae Borealis (RCB) stars in the Galactic bulge using the MACHO Project photometry database, raising the total number of known Galactic RCB stars to about 40. We have obtained spectra to confirm the identifications. The fact that four out of the five newly identified RCB stars are ''cool'' (T{sub eff} < 6000 K) rather than ''warm'' (T{sub eff} > 6000 K) suggests that the preponderance of warm RCB stars among the existing sample is a selection bias. These cool RCB stars are redder and fainter than their warm counterparts and may have been missed in surveys done with blue plates. Based on the number of new RCB stars discovered in the MACHO bulge fields, there may be {approx}250 RCB stars in the reddened ''exclusion'' zone toward the bulge.

  16. Pulsars and quark stars

    CERN Document Server

    Xu, R

    2005-01-01

    Members of the family of pulsar-like stars are distinguished by their different manifestations observed, i.e., radio pulsars, accretion-driven X-ray pulsars, X-ray bursts, anomalous X-ray pulsars/soft gamma-ray repeaters, compact center objects, and dim thermal neutron stars. Though one may conventionally think that these stars are normal neutron stars, it is still an open issue whether they are actually neutron stars or quark stars, as no convincing work, either theoretical from first principles or observational, has confirmed Baade-Zwicky's original idea that supernovae produce neutron stars. After introducing briefly the history of pulsars and quark stars, the author summarizes the recent achievements in his pulsar group, including quark matter phenomenology at low temperature, starquakes of solid pulsars, low-mass quark stars, and the pulsar magnetospheric activities.

  17. FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Bekki, Kenji [ICRAR, M468, The University of Western Australia 35 Stirling Highway, Crawley Western Australia, 6009 (Australia)

    2015-10-10

    We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z{sub ⊙}). We also find that the remnants of these mergers can have rather high mass densities (10{sup 4} M{sub ⊙} pc{sup −3}) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs.

  18. Radio continuum detection in blue early-type weak emission line galaxies

    CERN Document Server

    Paswan, A

    2016-01-01

    The star formation rates (SFRs) in weak emission line (WEL) galaxies in a volume-limited ($0.02 < z < 0.05$) sample of blue early-type galaxies (ETGs) identified from SDSS, are constrained here using 1.4 GHz radio continuum emission. The direct detection of 1.4 GHz radio continuum emission is made in 8 WEL galaxies and a median stacking is performed on 57 WEL galaxies using VLA FIRST images. The median stacked 1.4 GHz flux density and luminosity are estimated as 79 $\\pm$ 19 $\\mu$Jy and 0.20 $\\pm$ 0.05 $\\times$ 10$^{21}$ W Hz$^{-1}$ respectively. The radio far-infrared correlation in 4 WEL galaxies suggests that the radio continuum emission from WEL galaxies is most likely due to star formation activities. The median SFR for WEL galaxies is estimated as 0.23 $\\pm$ 0.06 M$_{\\odot}$yr$^{-1}$, which is much less compared to SFRs ($0.5 - 50$ M$_{\\odot}$yr$^{-1}$) in purely star forming blue ETGs. The SFRs in blue ETGs are found to be correlated with their stellar velocity dispersions ($\\sigma$) and decreasin...

  19. Various Shades of Blue's Functions

    CERN Document Server

    Janik, R A; Papp, G; Zahed, I; Janik, Romuald A.; Nowak, Maciej A.; Papp, Gabor; Zahed, Ismail

    1997-01-01

    We discuss random matrix models in terms of elementary operations on Blue's functions (functional inverse of Green's functions). We show that such operations embody the essence of a number of physical phenomena whether at/or away from the critical points. We illustrate these assertions by borrowing on a number of recent results in effective QCD in vacuum and matter. We provide simple physical arguments in favor of the universality of the continuum QCD spectral oscillations, whether at zero virtuality, in the bulk of the spectrum or at the chiral critical points. We also discuss effective quantum systems of disorder with strong or weak dissipation (Hatano-Nelson localization).

  20. Bimodal star formation - Constraints from galaxy colors at high redshift

    Science.gov (United States)

    Wyse, Rosemary F. G.; Silk, Joseph

    1987-01-01

    The possibility that at early epochs the light from elliptical galaxies is dominated by stars with an initial mass function (IMF) which is deficient in low-mass stars, relative to the solar neighborhood is investigated. V-R colors for the optical counterparts of 3CR radio sources offer the most severe constraints on the models. Reasonable fits are obtained to both the blue, high-redshift colors and the redder, low-redshift colors with a model galaxy which forms with initially equal star formation rates in each of two IMF modes: one lacking low-mass stars, and one with stars of all masses. The net effect is that the time-integrated IMF has twice as many high-mass stars as the solar neighborhood IMF, relative to low mass stars. A conventional solar neighborhood IMF does not simultaneously account for both the range in colors at high redshift and the redness of nearby ellipticals, with any single star formation epoch. Models with a standard IMF require half the stellar population to be formed in a burst at low redshift z of about 1.

  1. Blue-sheet instability of Schwarzschild wormholes

    International Nuclear Information System (INIS)

    The Schwarzschild wormhole geometry is found to be unstable against the gravitational effects of accumulated, blue-shifted matter and radiation, or ''blue sheets'', accreting along the past horizons. This is shown by constructing a simple model of a wormhole geometry featuring such blue sheets and manifesting their effects. In this model the blue sheets are treated as null delta-function surface layers, and we derive here general conditions for matching spacetime geometries across such null hypersurfaces of discontinuity. These junction conditions are then applied to the construction of the wormhole model. The wormhole evolution depicted in this model shows that the gravitational focussing produced by the blue-sheet mass-energy eventually encloses the blue sheets and past horizons within future horizons, leaving a black-hole geometry. These effects limit emission processes from the region of a wormhole's past singularity into the external universe, and severely restrict the possible role of wormholes in cosmological contexts. (author)

  2. Nucleosynthesis and Evolution of Massive Metal-Free Stars

    CERN Document Server

    Heger, Alexander

    2008-01-01

    The evolution and explosion of metal-free stars with masses 10--100 solar masses are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. When the supernova yields are integrated over a Salpeter initial mass function, the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 <= Z <= 13. Neglecting the contribution of the neutrino wind from the neutron stars that they make, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] ~< -3. Most of the stars end their lives as blue supergiants and make supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen by dredge up and become red supergiants. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and initial mass function in the large model ...

  3. Pair Instability Supernovae of Very Massive Population III Stars

    CERN Document Server

    Chen, Ke-Jung; Woosley, Stan; Almgren, Ann; Whalen, Daniel

    2014-01-01

    Numerical studies of primordial star formation suggest that the first stars in the universe may have been very massive. Stellar models indicate that non-rotating Population III stars with initial masses of 140-260 Msun die as highly energetic pair-instability supernovae. We present new two-dimensional simulations of primordial pair-instability supernovae done with the CASTRO code. Our simulations begin at earlier times than previous multidimensional models, at the onset of core collapse, to capture any dynamical instabilities that may be seeded by collapse and explosive burning. Such instabilities could enhance explosive yields by mixing hot ash with fuel, thereby accelerating nuclear burning, and affect the spectra of the supernova by dredging up heavy elements from greater depths in the star at early times. Our grid of models includes both blue supergiants and red supergiants over the range in progenitor mass expected for these events. We find that fluid instabilities driven by oxygen and helium burning ari...

  4. The Galactic O-Star Spectroscopic Survey (GOSSS)

    CERN Document Server

    Apellániz, J Maíz; Walborn, N R; Alfaro, E J; Barbá, R H; Morrell, N I; Gamen, R C; Arias, J I; Ordaz, M Penadés

    2010-01-01

    We present a massive spectroscopic survey of Galactic O stars, GOSSS, based on new, high signal-to-noise ratio, R~2500 blue-violet digital observations from both hemispheres. The sample size and selection criteria; the relationship between GOSSS, the Galactic O-Star Catalog (GOSC), and three sister surveys (OWN, IACOB, and Lucky Imaging); the current status; and our plans for the future are discussed. We also show some of our first results, which include the new Ofc category, two new examples of Of?p stars, a new atlas for O stars, and the introduction of the O9.7 type for luminosity classes III to V. Finally, our scientific objectives are discussed.

  5. THE MASSIVE STAR POPULATION IN M101. III. SPECTRA AND PHOTOMETRY OF THE LUMINOUS AND VARIABLE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Grammer, Skyler H.; Humphreys, Roberta M. [Minnesota Institute for Astrophysics, 116 Church Street SE, University of Minnesota , Minneapolis, MN 55455 (United States); Gerke, Jill, E-mail: grammer@astro.umn.edu, E-mail: roberta@umn.edu [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

    2015-05-15

    We discuss moderate-resolution spectra, multicolor photometry, and light curves of 31 of the most luminous stars and variables in the giant spiral M101. The majority are intermediate A- to F-type supergiants. We present new photometry and light curves for three known “irregular blue variables,” V2, V4, and V9, and identify a new candidate. Their spectra and variability confirm that they are luminous blue variable (LBV) candidates and V9 may be in an LBV-like maximum light state or eruption.

  6. Observing Faint Companions Close to Bright Stars

    Science.gov (United States)

    Serabyn, Eugene

    2012-04-01

    Progress in a number of technical areas is enabling imaging and interferometric observations at both smaller angular separations from bright stars and at deeper relative contrast levels. Here we discuss recent progress in several ongoing projects at the Jet Propulsion Laboratory. First, extreme adaptive optics wavefront correction has recently enabled the use of very short (i.e., blue) wavelengths to resolve close binaries. Second, phase-based coronagraphy has recently allowed observations of faint companions to within nearly one diffraction beam width of bright stars. Finally, rotating interferometers that can observe inside the diffraction beam of single aperture telescopes are being developed to detect close-in companions and bright exozodiacal dust. This paper presents a very brief summary of the techniques involved, along with some illustrative results.

  7. The Star-Formation Region SNO 87

    Science.gov (United States)

    Gyulbudaghian, A. L.

    2014-06-01

    The star-formation region SNO 87 is associated with the dark cloud LDN 212. 12CO(1-0) observations of a part of the molecular cloud associated with SNO 87 show that it lies somewhat to the north of the densest part of the molecular cloud. There is a bipolar molecular outflow from SNO 87, both branches of which are blue, i.e., the velocity is directed toward us with a velocity of ~3.5 km/s relative to the cloud. 12CO(1-0) observations of a part of the cloud lying to the E of SNO 87 show that this part of the cloud rotates with an angular velocity Ω = 2.44·10-14 s-1. SNO 87 contains several stars that are coupled with nebular filaments, bursts, and Herbig-Haro objects. It is also associated with the point source IRAS 18064-2413.

  8. An Atlas of Spectrophotometric Landolt Standard Stars

    CERN Document Server

    Stritzinger, M; Hamuy, M; Challis, P M; Demarco, R; Germany, L; Soderberg, A M; Stritzinger, Maximilian; Suntzeff, Nicholas B.; Hamuy, Mario; Challis, Peter; Demarco, Ricardo; Germany, Lisa

    2005-01-01

    We present CCD observations of 102 Landolt standard stars obtained with the R-C spectrograph on the CTIO 1.5 m telescope. Using stellar atmosphere models we have extended the flux points to our six spectrophotometric secondary standards, in both the blue and the red, allowing us to produce flux-calibrated spectra that span a wavelength range from 3050 \\AA to 1.1 \\micron. We find mean differences between $UBVRI$ spectrophotometry computed using Bessell's standard passbands and Landolt's published photometry to be 1% or less. Observers in both hemispheres will find these spectra useful for flux-calibrating spectra and through the use of accurately constructed instrumental passbands be able to compute accurate corrections to bring instrumental magnitudes to any desired standard photometric system (S-corrections). In addition, by combining empirical and modeled spectra of the Sun, Sirius and Vega, we calculate and compare synthetic photometry to observed photometry taken from the literature for these three stars.

  9. The MACHO Project LMC Variable Star Inventory; 4, Multimode RR Lyrae Stars, Distance to the LMC and Age of the Oldest Stars

    CERN Document Server

    Alcock, C B; Alves, D R; Axelrod, T S; Becker, A C; Bennett, D P; Cook, K H; Freeman, K C; Griest, K; Guern, J A; Lehner, M J; Marshall, S L; Minniti, D; Peterson, B A; Pratt, M R; Quinn, P J; Rodgers, A W; Sutherland, W; Welch, D L

    1996-01-01

    We report the discovery of 73 double-mode RR Lyrae (RRd) stars in fields near the bar of the LMC. The stars are detected among the MACHO database of short-period variables that currently contains about 7900 RR Lyrae stars. Fundamental periods (P_0) for these stars are found in the range 0.46-0.55 days and first overtone-to-fundamental period ratios are found to be in the range 0.742 < P_1/P_0 < 0.748. A significant fraction of our current sample have period ratios smaller than any previously discovered RRd variables. We present mean magnitudes, colors, and lightcurve properties for all LMC RRd stars detected to date. The range in period ratios is unexpectedly large. We present a determination of absolute magnitudes for these stars based primarily on pulsation theory and the assumption that all observed stars are at the fundamental blue edge (FBE) of the instability strip. Comparison of the calibrated MACHO V and R_KC photometry with these derived absolute magnitudes yields an absorption-corrected distan...

  10. Geothermal Technologies Program Blue Ribbon Panel Recommendations

    Energy Technology Data Exchange (ETDEWEB)

    none,

    2011-06-17

    The Geothermal Technologies Program assembled a geothermal Blue Ribbon Panel on March 22-23, 2011 in Albuquerque, New Mexico for a guided discussion on the future of geothermal energy in the United States and the role of the DOE Program. The Geothermal Blue Ribbon Panel Report captures the discussions and recommendations of the experts. An addendum is available here: http://www.eere.energy.gov/geothermal/pdfs/gtp_blue_ribbon_panel_report_addendum10-2011.pdf

  11. African Music: Source of the Blues

    OpenAIRE

    Bayer, Konrad Sidney

    2010-01-01

    [Abstract] African music is the primary source for the blues. Scholars have supplied ample evidence to support this assertion. However, the African retentions still present in the blues are not immediately apparent. African music and the blues share many similarities, including the predominance of rhythm, the uses of music as social commentary and critique, types of instruments, and musical structure. Slaves brought their culture with them to the New World when they were forcibly taken from t...

  12. OB stars at the lowest Local Group metallicity: GTC-OSIRIS observations of Sextans A

    CERN Document Server

    Camacho, I; Herrero, A; Simón-Díaz, S

    2016-01-01

    Our aim is to find and classify OB stars in Sextans A, to later determine accurate stellar parameters of these blue massive stars in this low metallicity region $(Z \\sim 0.1 \\rm Z_{\\odot})$. Using UBV photometry, the reddening-free index Q and GALEX imaging, we built a list of blue massive star candidates in Sextans A. We obtained low resolution (R $\\sim$ 1000) GTC-OSIRIS spectra for a fraction of them and carried out spectral classification. For the confirmed O-stars we derive preliminary stellar parameters. The target selection criteria and observations were successful and have produced the first spectroscopic atlas of OB-type stars in Sextans A. From the whole sample of 18 observed stars, 12 were classified as early OB-types, including 5 O-stars. The radial velocities of all target stars are in agreement with their Sextans A membership, although three of them show significant deviations. We determined the stellar parameters of the O-type stars using the stellar atmosphere code FASTWIND, and revisited the s...

  13. The environment of nearby Blue Compact Dwarf Galaxies

    CERN Document Server

    Lopez-Sanchez, Angel R; van Eymeren, Janine; Esteban, Cesar; Popping, Attila; Hibbard, John

    2009-01-01

    We are obtaining deep multiwavelength data of a sample of nearby blue compact dwarf galaxies (BCDGs) combining broad-band optical/NIR and H$\\alpha$ photometry, optical spectroscopy and 21-cm radio observations. Here we present HI results obtained with the Australia Telescope Compact Array for some BCDGs, all showing evident interaction features in their neutral gas component despite the environment in which they reside. Our analysis strongly suggests that interactions with or between low-luminosity dwarf galaxies or HI clouds are the main trigger mechanism of the star-forming bursts in BCDGs; however these dwarf objects are only detected when deep optical images and complementary HI observations are performed. Are therefore BCDGs real isolated systems?

  14. A New Luminous Blue Variable in M31

    CERN Document Server

    Humphreys, Roberta M; Gordon, Michael S

    2015-01-01

    We report the fifth confirmed Luminous Blue Variable/S Doradus variable in M31. In 2006, J004526.62+415006.3 had the spectrum of hot Fe II emission line star with strong P Cygni profiles in the Balmer lines. In 2010, its absorption line spectrum resembled an early A-type supergiant with H and Fe II emission lines with strong P Cygni profiles, and in 2013 the spectrum had fully transitioned to an F-type supergiant due to the formation of the optically thick, cool wind which characterizes LBVs at maximum light. The photometric record supports the LBV/S Dor nature of the variability. Its bolometric luminosity ~ -9.65 mag places it on the HR Diagram near the known LBVs, AE And, Var C in M33 and S Dor.

  15. Star Formation in Galaxies

    Science.gov (United States)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  16. ENERGY STAR Certified Boilers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Boilers that are effective as of October 1,...

  17. ENERGY STAR Certified Furnaces

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Furnaces that are effective as of February 1,...

  18. ENERGY STAR Certified Computers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 6.1 ENERGY STAR Program Requirements for Computers that are effective as of June 2,...

  19. 'Polaris, Mark Kummerfeldt's Star, and My Star.'

    Science.gov (United States)

    McLure, John W.

    1984-01-01

    In most astronomy courses, descriptions of stars and constellations reveal the western European origins of the astronomers who named them. However, it is suggested that a study of non-western views be incorporated into astronomy curricula. Descriptions of various stars and constellations from different cultures and instructional strategies are…

  20. The Na-O anticorrelation in horizontal branch stars. II. NGC1851

    CERN Document Server

    Gratton, R G; Carretta, E; Bragaglia, A; D'Orazi, V; Momany, Y Al; Sollima, A; Salaris, M; Cassisi, S

    2012-01-01

    We studied the Na-O anti-correlation from moderately high resolution spectra for 35 stars on the blue HB (BHB), one RR Lyrae, and 55 stars are on the red HB (RHB) of NGC1851. We also derived abundances for He and N in BHB stars, and Ba and upper limits for N in RHB stars. The RHB stars clearly separate into two groups: the vast majority are O-rich and Na-poor, while about 10-15% are Na-rich and moderately O-poor. Most Na-rich RHB stars are also Ba-rich and there is an overall correlation between Na and Ba abundances within the RHB. The group of Ba-rich RHB stars resides on the warmer edge and includes ~10% of the RHB stars. We propose that they are the descendant of the stars on the RGB sequence with very red v-y colour. This sequence is known also to consist of Ba and perhaps CNO-rich stars. However, the upper limit we obtain for N ([N/Fe]<1.55) for one of the Ba-rich stars coupled with the low C-abundances for RGB Ba-rich stars from the literature suggests that the total CNO might not be particularly hig...

  1. Cool Stars in Hot Places

    OpenAIRE

    Megeath, S. T.; Gaidos, E.; Hester, J. J.; Adams, F. C.; Bally, J.; Lee, J. -E.; Wolk, S.

    2007-01-01

    During the last three decades, evidence has mounted that star and planet formation is not an isolated process, but is influenced by current and previous generations of stars. Although cool stars form in a range of environments, from isolated globules to rich embedded clusters, the influences of other stars on cool star and planet formation may be most significant in embedded clusters, where hundreds to thousands of cool stars form in close proximity to OB stars. At the cool stars 14 meeting, ...

  2. Metal-Poor Stars

    OpenAIRE

    Frebel, Anna

    2008-01-01

    The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements and the involved nucleosynthesis processes. This knowledge is invaluable for our understanding of the cosmic chemical evolution and the onset of star- and galaxy formation. Metal-poor stars are the local equivalent of the high-redshift Universe, and offer cru...

  3. Autonomous Star Tracker Algorithms

    DEFF Research Database (Denmark)

    Betto, Maurizio; Jørgensen, John Leif; Kilsgaard, Søren;

    1998-01-01

    Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances.......Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances....

  4. Cooling compact stars and phase transitions in dense QCD

    Energy Technology Data Exchange (ETDEWEB)

    Sedrakian, Armen [J.W. Goethe University, Institute for Theoretical Physics, Frankfurt am Main (Germany)

    2016-03-15

    We report new simulations of cooling of compact stars containing quark cores and updated fits to the Cas A fast cooling data. Our model is built on the assumption that the transient behaviour of the star in Cas A is due to a phase transition within the dense QCD matter in the core of the star. Specifically, the fast cooling is attributed to an enhancement in the neutrino emission triggered by a transition from a fully gapped, two-flavor, red-green color-superconducting quark condensate to a superconducting crystalline or an alternative gapless, color-superconducting phase. The blue-colored condensate is modeled as a Bardeen-Cooper-Schrieffer (BCS)-type color superconductor with spin-one pairing order parameter. We study the sensitivity of the fits to the phase transition temperature, the pairing gap of blue quarks and the timescale characterizing the phase transition (the latter modelled in terms of a width parameter). Relative variations in these parameter around their best-fit values larger than 10{sup -3} spoil the fit to the data. We confirm the previous finding that the cooling curves show significant variations as a function of compact star mass, which allows one to account for dispersion in the data on the surface temperatures of thermally emitting neutron stars. (orig.)

  5. Massive stars in their death-throes

    CERN Document Server

    Eldridge, J J

    2008-01-01

    The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently there are 8 detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants as theory has long predicted. However no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae which, given the expected progenitors, is an unlikely result. Also observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict current stellar evolution theory. This suggests that we may need to update our understanding.

  6. Massive stars in their death throes.

    Science.gov (United States)

    Eldridge, John J

    2008-12-13

    The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently, there are eight detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants, as theory has long predicted. However, no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae, which, given the expected progenitors, is an unlikely result. Also, observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict the current stellar evolution theory. This suggests that we may need to update our understanding.

  7. The unusual interacting S star binary HR 1105

    Science.gov (United States)

    Ake, Thomas B., III; Johnson, Hollis R.; Bopp, Bernard W.

    1994-01-01

    IUE observations of HR 1105 over its 596-day orbit show strong orbital modulation of both continuum and emission lines. These are most intense just before both conjunctions and nearly disappear near quadratures, the most intense phase being just before the hot component passes in front of the S star. High dispersion observations exhibit a blue-shifted absorption feature in Mg II, representing an outflow of material of about 55 km/s. These observations are consistent with the UV source being an optically thin gas stream between the components of the system, which is partially eclipsed when the S star is in front.

  8. The MONS Star Trackers

    CERN Document Server

    Bedding, T R; Bedding, Timothy R.; Kjeldsen, Hans

    2000-01-01

    The MONS satellite will have two Star Trackers to sense the spacecraft attitude, and we plan to use them as scientific instruments to perform high-precision photometry of thousands of stars. We briefly describe the current plans for the Star Trackers and their expected capabilities.

  9. Superfluid neutron stars

    OpenAIRE

    Langlois, David

    2001-01-01

    Neutron stars are believed to contain (neutron and proton) superfluids. I will give a summary of a macroscopic description of the interior of neutron stars, in a formulation which is general relativistic. I will also present recent results on the oscillations of neutron stars, with superfluidity explicitly taken into account, which leads in particular to the existence of a new class of modes.

  10. America's Star Libraries

    Science.gov (United States)

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  11. Feedback of the HBe star IL Cep on nearby molecular cloud and star formation

    Science.gov (United States)

    Zhang, Si-Ju; Wu, Yuefang; Li, Jin Zeng; Yuan, Jing-Hua; Liu, Hong-Li; Dong, Xiaoyi; Huang, Ya-Fang

    2016-06-01

    We present investigations of the feedback of a luminous Herbig Be star, IL Cep. We mapped the vicinity of IL Cep in the J = 1-0 transitions of 12CO, 13CO and C18O molecular lines with the Purple Mountain Observatory 13.7 m telescope. Archival data from Wide-field Infrared Survey Explorer were also employed. A parsec-scale cavity that has probably been excavated by the dominant HBe star, IL Cep, is revealed. An expanding shell-like structure featured by 12CO(J = 1-0) emission was found surrounding the cavity, which embeds several 13CO(J = 1-0) molecular clumps. The density and velocity gradients imply strong stellar winds from exciting stars, this is consistent with the morphology of molecular cloud. The 12CO(J = 1-0) spectra show broad blue wings with a width of about 3.5 km s-1. We suggest that the broad blue wings could be emission from the molecular gas shocked by stellar winds, while the main narrow component may originate from pre-shocked gas. Several bright bow-shaped rims have been detected at 12 μm, which serve as the interface of the molecular cloud facing UV dissipation from the exciting stars. The rims all have an orientation facing IL Cep, this may indicate the pre-dominant effects of IL Cep on its surroundings. A very young star candidate (about 104.8 yr) was found in the head of one bright rim, but its triggered origin is uncertain. All results achieved in this paper suggest that IL Cep has violent effects on its surroundings.

  12. WS1: one more new Galactic bona fide luminous blue variable

    CERN Document Server

    Kniazev, A Y; Berdnikov, L N

    2015-01-01

    In this Letter, we report the results of spectroscopic and photometric monitoring of the candidate luminous blue variable (LBV) WS1, which was discovered in 2011 through the detection of a mid-infrared circular shell and follow-up optical spectroscopy of its central star. Our monitoring showed that WS1 brightened in the B, V and I bands by more than 1 mag during the last three years, while its spectrum revealed dramatic changes during the same time period, indicating that the star became much cooler. The light curve of WS1 demonstrates that the brightness of this star has reached maximum in 2013 December and then starts to decline. These findings unambiguously proved the LBV nature of WS1 and added one more member to the class of Galactic bona fide LBVs, bringing their number to sixteen (an updated census of these objects is provided).

  13. Long-persistence blue phosphors

    Science.gov (United States)

    Yen, William M. (Inventor); Jia, Weiyi (Inventor); Lu, Lizhu (Inventor); Yuan, Huabiao (Inventor)

    2000-01-01

    This invention relates to phosphors including long-persistence blue phosphors. Phosphors of the invention are represented by the general formula: MO . mAl.sub.2 O.sub.3 :Eu.sup.2+,R.sup.3+ wherein m is a number ranging from about 1.6 to about 2.2, M is Sr or a combination of Sr with Ca and Ba or both, R.sup.3+ is a trivalent metal ion or trivalent Bi or a mixture of these trivalent ions, Eu.sup.2+ is present at a level up to about 5 mol % of M, and R.sup.3+ is present at a level up to about 5 mol % of M. Phosphors of this invention include powders, ceramics, single crystals and single crystal fibers. A method of manufacturing improved phosphors and a method of manufacturing single crystal phosphors are also provided.

  14. Physical Parameters of Hot Horizontal-Branch Stars in NGC 6752: Deep Mixing and Radiative Levitation

    Science.gov (United States)

    Moehler, S.; Sweigart, A. V.; Landsman, W. B.; Heber, U.; Catelan, M.

    1999-01-01

    Atmospheric parameters (T(sub eff), log g and log n(sub He)/n(sub H-dot)) are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC 6752. For 19 stars Mg II and Fe II lines are detected indicating an iron enrichment by a factor 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster metallicity. This finding adds to the growing evidence that radiative levitation plays a significant role in determining the physical parameters of blue HB stars. Indeed, we find that iron enrichment can explain part, but not all, of the problem of anomalously low gravities along the blue HB. Thus the physical parameters of horizontal branch stars hotter than about 11,500 K in NGC 6752, as derived in this paper, are best explained by a combination of helium mixing and radiative levitation effects.

  15. Stellar Populations and the Star Formation Histories of LSB Galaxies. V. WFC3 Color-Magnitude Diagrams

    Science.gov (United States)

    Schombert, James; McGaugh, Stacy

    2015-09-01

    We present WFC3 observations of three low surface brightness (LSB) galaxies from the Schombert et al. LSB catalog that are within 11 Mpc of the Milky Way. Deep imaging at F336W, F555W, and F814W allow the construction of the V - I color-magnitude diagrams (CMD) to MI = -2. Overall 1869, 465, and 501 stellar sources are identified in the three LSB galaxies F415-3, F608-1, and F750-V1, respectively. The spatial distribution of young blue stars matches the Hα maps from ground-based imaging, indicating that star formation in LSB galaxies follows the same style as in other irregular galaxies. Several star complexes are identified, matching regions of higher surface brightness as seen from ground-based imaging. The CMD for each LSB galaxy has a similar morphology to Local Volume (LV) dwarf galaxies (i.e., a blue main sequence, blue and red He burning branches, and asymptotic giant branch (AGB) stars). The LSB CMD’s distinguish themselves from nearby dwarf CMD’s by having a higher proportion of blue main sequence stars and fewer AGB stars than expected from their mean metallicities. Current [Fe/H] values below -0.6 are deduced from the position of the red helium-burning branch (rHeB) stars in the V - I diagram. The distribution of stars on the blue helium-burning branch (bHeB) and rHeB from the U - V and V - I CMD indicate a history of constant star formation for the last 100 Myr.

  16. STELLAR POPULATIONS AND THE STAR FORMATION HISTORIES OF LSB GALAXIES. V. WFC3 COLOR–MAGNITUDE DIAGRAMS

    Energy Technology Data Exchange (ETDEWEB)

    Schombert, James [Department of Physics, University of Oregon, Eugene, OR 97403 (United States); McGaugh, Stacy, E-mail: jschombe@uoregon.edu, E-mail: stacy.mcgaugh@case.edu [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States)

    2015-09-15

    We present WFC3 observations of three low surface brightness (LSB) galaxies from the Schombert et al. LSB catalog that are within 11 Mpc of the Milky Way. Deep imaging at F336W, F555W, and F814W allow the construction of the V − I color–magnitude diagrams (CMD) to M{sub I} = −2. Overall 1869, 465, and 501 stellar sources are identified in the three LSB galaxies F415-3, F608-1, and F750-V1, respectively. The spatial distribution of young blue stars matches the Hα maps from ground-based imaging, indicating that star formation in LSB galaxies follows the same style as in other irregular galaxies. Several star complexes are identified, matching regions of higher surface brightness as seen from ground-based imaging. The CMD for each LSB galaxy has a similar morphology to Local Volume (LV) dwarf galaxies (i.e., a blue main sequence, blue and red He burning branches, and asymptotic giant branch (AGB) stars). The LSB CMD’s distinguish themselves from nearby dwarf CMD’s by having a higher proportion of blue main sequence stars and fewer AGB stars than expected from their mean metallicities. Current [Fe/H] values below −0.6 are deduced from the position of the red helium-burning branch (rHeB) stars in the V − I diagram. The distribution of stars on the blue helium-burning branch (bHeB) and rHeB from the U − V and V − I CMD indicate a history of constant star formation for the last 100 Myr.

  17. Blue Skies, Coffee Creamer, and Rayleigh Scattering

    Science.gov (United States)

    Liebl, Michael

    2010-01-01

    The first physical explanation of Earths blue sky was fashioned in 1871 by Lord Rayleigh. Many discussions of Rayleigh scattering and approaches to studying it both in and out of the classroom are available. Rayleigh scattering accounts for the blue color of the sky and the orange/red color of the Sun near sunset and sunrise, and a number of…

  18. Rotating Stars in Relativity

    Directory of Open Access Journals (Sweden)

    Stergioulas Nikolaos

    2003-01-01

    Full Text Available Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densities and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is reviewed in this updated article. The sections on the equilibrium properties and on the nonaxisymmetric instabilities in f-modes and r-modes have been updated and several new sections have been added on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativity.

  19. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2015-01-01

    Most elements are synthesized, or ""cooked"", by thermonuclear reactions in stars. The newly formed elements are released into the interstellar medium during a star's lifetime, and are subsequently incorporated into a new generation of stars, into the planets that form around the stars, and into the life forms that originate on the planets. Moreover, the energy we depend on for life originates from nuclear reactions that occur at the center of the Sun. Synthesis of the elements and nuclear energy production in stars are the topics of nuclear astrophysics, which is the subject of this book

  20. Revealing evolved massive stars with Spitzer, WISE and SALT

    CERN Document Server

    Kniazev, A

    2016-01-01

    We present the results of optical spectroscopic observations of 54 candidate evolved massive stars revealed through the detection of mid-infrared nebulae of various shapes surrounding them with the {\\it Spitzer Space Telescope} and {\\it Wide-field Infrared Survey Explorer}. These observations, carried out with the Southern African Large Telescope (SALT) in 2010-2015, led to the discovery of about two dozens emission-line stars, of which 15 stars we classify as candidate luminous blue variables (cLBVs). Spectroscopic and photometric monitoring revealed significant changes in the spectra and brightness of four newly identified cLBVs, meaning that they are new members of the class of bona fide LBVs. We present an updated list of the Galactic bona fide LBVs. Currently, this list contains eighteen stars, of which more than 70 per cent are associated with circumstellar nebulae. We also discovered a very rare [WN] star - the central star of the planetary nebula Abell 48, and a WN3 star in a close, eccentric binary s...

  1. A Be-type star with a black hole companion

    CERN Document Server

    Casares, J; Ribo, M; Ribas, I; Paredes, J M; Herrero, A; Simon-Diaz, S

    2014-01-01

    Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the ~80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions. A black hole was formally allowed as a solution for the companion to the Be star MWC 656 (also known as HD 215227), although that was based on a single radial velocity curve of the Be star, a mistaken spectral classification and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of the Be star. This, together with an improved radial velocity curve of ...

  2. Starbursts versus Truncated Star Formation in Nearby Clusters of Galaxies

    CERN Document Server

    Rose, J A; Caldwell, N; Chaboyer, B; Rose, James A.; Gaba, Alejandro E.; Caldwell, Nelson; Chaboyer, Brian

    2001-01-01

    We present long-slit spectroscopy, B and R bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters which are known to be either in a star-forming phase or to have had star formation which recently terminated. From the long-slit spectra, obtained with the Blanco 4-m telescope, we find that emission lines in the star-forming cluster galaxies are significantly more centrally concentrated than in a sample of field galaxies. The broadband imaging reveals that two currently star-forming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has been concentrated. In contrast, the two galaxies for which star formation has already ended show no central color gradient. The Pegasus I galaxy with the most evident signs of ongoing star formation (NGC7648), exhibits signatures of a tidal encounter. Neutral hydrogen observations of that galaxy with the Arecibo radiotelescope reveal the presence of ~4 x 10^8 solar masses of HI. Arecib...

  3. Triboelectric Nanogenerators for Blue Energy Harvesting.

    Science.gov (United States)

    Khan, Usman; Kim, Sang-Woo

    2016-07-26

    Blue energy in the form of ocean waves offers an enormous energy resource. However, it has yet to be fully exploited in order to make it available for the use of mankind. Blue energy harvesting is a challenging task as the kinetic energy from ocean waves is irregular in amplitude and is at low frequencies. Though electromagnetic generators (EMGs) are well-known for harvesting mechanical kinetic energies, they have a crucial limitation for blue energy conversion. Indeed, the output voltage of EMGs can be impractically low at the low frequencies of ocean waves. In contrast, triboelectric nanogenerators (TENGs) are highly suitable for blue energy harvesting as they can effectively harvest mechanical energies from low frequencies (blue energy harvesting. In this Perspective, we describe some of the recent progress and also address concerns related to durable packaging of TENGs in consideration of harsh marine environments and power management for an efficient power transfer and distribution for commercial applications.

  4. THE FIRST STARS

    Directory of Open Access Journals (Sweden)

    Daniel J. Whalen

    2013-12-01

    Full Text Available Pop III stars are the key to the character of primeval galaxies, the first heavy elements, the onset of cosmological reionization, and the seeds of supermassive black holes. Unfortunately, in spite of their increasing sophistication, numerical models of Pop III star formation cannot yet predict the masses of the first stars. Because they also lie at the edge of the observable universe, individual Pop III stars will remain beyond the reach of observatories for decades to come, and so their properties are unknown. However, it will soon be possible to constrain their masses by direct detection of their supernovae, and by reconciling their nucleosynthetic yields to the chemical abundances measured in ancient metal-poor stars in the Galactic halo, some of which may bear the ashes of the first stars. Here, I review the state of the art in numerical simulations of primordial stars and attempts to directly and indirectly constrain their properties.

  5. The First Stars

    CERN Document Server

    Whalen, Daniel J

    2012-01-01

    Pop III stars are the key to the character of primeval galaxies, the first heavy elements, the onset of cosmological reionization, and the seeds of supermassive black holes. Unfortunately, in spite of their increasing sophistication, numerical models of Pop III star formation cannot yet predict the masses of the first stars. Because they lie at the edge of the observable universe, individual Pop III stars will also remain beyond the reach of telescopes for the foreseeable future, and so their properties remain unknown. However, it will soon be possible to constrain their masses by the direct detection of their supernovae and by reconciling their nucleosynthetic yields to the chemical abundances measured in ancient metal-poor stars in the Galactic halo, some of which may be bear the ashes of the first stars. Here, I review current problems on the simulation frontier in Pop III star formation and discuss the best prospects for constraining their properties observationally in the near term.

  6. Confirmation of the Luminous Blue Variable status of MWC 930

    CERN Document Server

    Miroshnichenko, A S; Zharikov, S V; Zsargo, J; Jimenez, J A Juarez; Groh, J H; Levato, H; Grosso, M; Rudy, R J; Laag, E A; Crawford, K B; Puetter, R C; Reichart, D E; Ivarsen, K M; Haislip, J B; Nysewander, M C; LaCluyze, A P

    2014-01-01

    We present spectroscopic and photometric observations of the emission-line star MWC 930 (V446 Sct) during its long-term optical brightening in 2006--2013. Based on our earlier data we suggested that the object has features found in Luminous Blue Variables (LBV), such as a high luminosity (~3 10^5 Lsun, a low wind terminal velocity (~ 140 km/s), and a tendency to show strong brightness variations (~1 mag over 20 years). For the last ~7 years it has been exhibiting a continuous optical and near-IR brightening along with a change of the emission-line spectrum appearance and cooling of the star's photosphere. We present the object's $V$--band light curve, analyze the spectral variations, and compare the observed properties with those of other recognized Galactic LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide Galactic LBV that is currently in the middle of an S Dor cycle.

  7. Asphericity and clumpiness in the winds of Luminous Blue Variables

    CERN Document Server

    Davies, B; Vink, J S; Davies, Ben; Oudmaijer, Rene D.; Vink, Jorick S.

    2005-01-01

    We present the first systematic spectropolarimetric study of Luminous Blue Variables (LBVs) in the Galaxy and the Magellanic Clouds, in order to investigate the geometries of their winds. We find that at least half of our sample show changes in polarization across the strong H$\\alpha$ emission line, indicating that the light from the stars is intrinsically polarized and therefore that asphericity already exists at the base of the wind. Multi-epoch spectropolarimetry on four targets reveals variability in their intrinsic polarization. Three of these, AG Car, HR Car and P Cyg, show a position angle (PA) of polarization which appears random with time. Such behaviour can be explained by the presence of strong wind-inhomogeneities, or `clumps' within the wind. Only one star, R 127, shows variability at a constant PA, and hence evidence for axi-symmetry as well as clumpiness. However, if viewed at low inclination, and at limited temporal sampling, such a wind would produce a seemingly random polarization of the typ...

  8. Do the nearby BHB stars belong to the Thick Disk or the Halo?

    CERN Document Server

    Kinman, T D; Brown, Warren R

    2008-01-01

    We study the Milky Way region Z<3.0 kpc, where the thick disk and inner halo overlap, by using the kinematics of local blue horizontal branch (BHB) stars (within 1 kpc) and new samples of BHB stars and A-type stars from the Century Survey. We derive Galactic U,V,W velocities for these BHB and A-type star samples using proper motions from the NOMAD catalog. The mean velocities and the velocity dispersions of the BHB samples (Z<3 kpc) are characteristic of the halo, while those of the Century Survey A-type stars are characteristic of the thick disk. There is no evidence from our samples that the BHB stars rotate with the thick disk in the region Z<3 kpc. Nearly a third of the nearby local RR Lyrae stars have disk kinematics and are more metal-rich than [Fe/H]~-1. Only a few percent of the Century Survey BHB stars have these properties. Only one nearby BHB star (HD 130201) is likely to be such a disk star but selection based on high proper motions will have tended to exclude such stars from the local sa...

  9. The Hottest Horizontal-Branch Stars in Omega Centauri: Late Hot Flasher vs. Helium Enrichment

    Science.gov (United States)

    Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A V.; Calamida, A.; Monelli, M.; Nonino, M.

    2007-01-01

    UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario here stars experience the helium flash while on the white dwarf cooling curve or by the helium-rich sub-population recently postulated to exist in some clusters. Spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified from existing data. We want to determine effective temperatures, surface gravities and abundances of He, C, N in blue hook and canonical extreme horizontal branch (EHB) star candidates. Moderately high resolution spectra of stars at the hot end of the blue horizontal branch in the globular cluster omega Cen were analysed for atmospheric parameters (T(sub eff), log g) and abundances using LTE and Non-LTE model atmospheres. In the temperature range 30,000 K to 50,000 K we find that 37% of our stars are helium-poor (log nHe/nH less than -2), 49% have solar helium abundance within a factor of 3 (-1.5 less than or equal to log nHe/nH less than or equal to -0.5) and 14% are helium rich (log nHe/nH greater than -0.4). We also find carbon enrichment in step with helium enrichment, with a maximum carbon enrichment of 3% by mass. At least 30% of the hottest HB stars in omega Centauri show helium abundances well above the predictions from the helium enrichment scenario (Y = 0.42 corresponding to log nHe/nH approximately equal to -0.74). In addition the most helium-rich stars show strong carbon enrichment as predicted by the late hot flasher scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

  10. Tapered photonic crystal fibers for blue-enhanced supercontinuum generation

    DEFF Research Database (Denmark)

    Møller, Uffe; Sørensen, Simon Toft; Larsen, Casper;

    2012-01-01

    Tapering of photonic crystal fibers is an effective way of shifting the blue edge of a supercontinuum spectrum down in the deep-blue. We discuss the optimum taper profile for enhancing the power in the blue edge.......Tapering of photonic crystal fibers is an effective way of shifting the blue edge of a supercontinuum spectrum down in the deep-blue. We discuss the optimum taper profile for enhancing the power in the blue edge....

  11. Metal-Poor Stars

    CERN Document Server

    Frebel, Anna

    2008-01-01

    The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements and the involved nucleosynthesis processes. This knowledge is invaluable for our understanding of the cosmic chemical evolution and the onset of star- and galaxy formation. Metal-poor stars are the local equivalent of the high-redshift Universe, and offer crucial observational constraints on the nature of the first stars. This review presents the history of the first discoveries of metal-poor stars that laid the foundation to this field. Observed abundance trends at the lowest metallicities are described, as well as particular classes of metal-poor stars such as r-process and C-rich stars. Scenarios on the origins of the abundances of metal-poor stars and the application of large samples of metal-poor stars to cosmological questions are discussed.

  12. The Second Stars

    CERN Document Server

    Herwig, Falk

    2005-01-01

    The ejecta of the first probably very massive stars polluted the Big Bang primordial element mix with the first heavier elements. The resulting ultra metal-poor abundance distribution provided the initial conditions for the second stars of a wide range of initial masses reaching down to intermediate and low masses. The importance of these second stars for understanding the origin of the elements in the early universe are manifold. While the massive first stars have long vanished the second stars are still around and currently observed. They are the carriers of the information about the first stars, but they are also capable of nuclear production themselves. For example, in order to use ultra or extremely metal-poor stars as a probe for the r-process in the early universe a reliable model of the s-process in the second stars is needed. Eventually, the second stars may provide us with important clues on questions ranging from structure formation to how the stars actually make the elements, not only in the early...

  13. Dark stars: a review.

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars. PMID:27214049

  14. Dark stars: a review.

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  15. Dark stars: a review

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  16. Blue jays nest in an unusual structure

    Science.gov (United States)

    Muths, Erin L.; Lyons, Curtis P.; Sedgwick, James A.

    2007-01-01

    We describe a successful Blue Jay (Cyanocitta cristata) nest in an unusual structure on the side of a building.  The nest was located near the edge of the species' range along the Front Range of the Rocky Mountains in Colorado.  The nest was completely obvious, suggesting that the structure itself provided adequate cover and sercurity for the jays.  Blue Jays appear to be declining in some areas of the United States such as the Southeast.  Structures such as the one we describe may be more useful in attracting Blue Jays than the nesting platforms available commercially.

  17. Discovery of blue companions to two southern Cepheids: WW Car and FN Vel

    CERN Document Server

    Kovtyukh, V; Chekhonadskikh, F; Lemasle, B; Belik, S

    2015-01-01

    A large number of high-dispersion spectra of classical Cepheids were obtained in the region of the CaII H+K spectral lines. The analysis of these spectra allowed us to detect the presence of a strong Balmer line, H$\\epsilon$, for several Cepheids, interpreted as the signature of a blue companion: the presence of a sufficiently bright blue companion to the Cepheid results in a discernible strengthening of the CaII H + Hepsilon line relative to the CaII K line. We investigated 103 Cepheids, including those with known hot companions (B5-B6 main-sequence stars) in order to test the method. We could confirm the presence of a companion to WW Car and FN Vel (the existence of the former was only suspected before) and we found that these companions are blue hot stars. The method remains efficient when the orbital velocity changes in a binary system cannot be revealed and other methods of binarity detection are not efficient.

  18. STAR in CTO PCI: When is STAR not a star?

    Science.gov (United States)

    Hira, Ravi S; Dean, Larry S

    2016-04-01

    Subintimal tracking and reentry (STAR) has been used as a bailout strategy and involves an uncontrolled dissection and recanalization into the distal lumen to reestablish vessel patency. In the current study, thrombolysis in myocardial infarction (TIMI) flow < 3 was the only variable which they found to be significantly associated with restenosis and reocclusion after stent placement. It may be reasonable to consider second generation drug eluting stent placement in patients receiving STAR that have TIMI 3 flow, however, this should only be done if there is no compromise of major side branches. If unsure, we recommend to perform balloon angioplasty without stenting.

  19. The First Stars

    Science.gov (United States)

    Yoshida, Naoki

    2010-10-01

    The standard cosmological model predicts that the first cosmological objects are formed when the age of the universe is a few hundred million years. Recent theoretical studies and numerical simulations consistently suggest that the first objects are very massive primordial stars. We introduce the key physics and explain why the first stars are thought to be massive, rather than to be low-mass stars. The state-of-the-art simulations include all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to very high ``stellar'' densities. Evolutionary calculations of the primordial stars suggest the formation of massive blackholes in the early universe. Finally, we show the results from high-resolution simulations of star formation in a low-metallicity gas. Vigorous fragmentation is triggered in a star-forming gas cloud at a metallicity of as low as Z = 10-5Zsolar.

  20. Intelligent Star Tracker

    OpenAIRE

    Clark, Natalie; Furth, Paul; Horan, Steven

    2000-01-01

    We describe our Intelligent Star Tracker System. Our Intelligent Star Tracker System incorporates an adaptive optic catadioptric telescope in a silicon carbide housing. Leveraging off of our active optic technologies, the novel active pixel position sensors (APPS) enable wide dynamic range and allows simultaneous imagery of faint and bright stars in a single image. Moreover, the APPS, in conjunction with the adaptive optics technologies, offer unprecedented accuracy in altitude and navigation...

  1. Evolution of massive stars

    International Nuclear Information System (INIS)

    The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

  2. Dynamical Processes in Globular Clusters

    CERN Document Server

    McMillan, Stephen L W

    2014-01-01

    Globular clusters are among the most congested stellar systems in the Universe. Internal dynamical evolution drives them toward states of high central density, while simultaneously concentrating the most massive stars and binary systems in their cores. As a result, these clusters are expected to be sites of frequent close encounters and physical collisions between stars and binaries, making them efficient factories for the production of interesting and observable astrophysical exotica. I describe some elements of the competition among stellar dynamics, stellar evolution, and other processes that control globular cluster dynamics, with particular emphasis on pathways that may lead to the formation of blue stragglers.

  3. Resolved photometry of extragalactic young massive star clusters

    CERN Document Server

    Larsen, S S; Eldridge, J J; Langer, N; Bastian, N; Seth, A; Smith, L J; Brodie, J; Efremov, Y N

    2011-01-01

    We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793. The clusters have ages in the range 5-50 million years and masses of 10^5 -10^6 Msun. Although crowding prevents us from obtaining photometry in the central regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergi...

  4. Kerr black hole parameters in terms of red/blue shifts of photons emitted by geodesic particles

    CERN Document Server

    Herrera-Aguilar, Alfredo

    2015-01-01

    We are motivated by the recently reported dynamical evidence of stars with short orbital periods moving around the center of the Milky Way and the corresponding hypothesis about the existence of a supermassive black hole hosted at its center. In this paper we show how the mass and rotation parameters of a Kerr black hole (assuming that the putative supermassive black hole is of this type), as well as the distance that separates the black hole from the Earth, can be estimated in a relativistic way in terms of i) the red and blue shifts of photons that are emitted by geodesic massive particles (stars and galactic gas) and travel along null geodesics towards a distant observer, and ii) the radius of these star/gas orbits. As a concrete example and as a first step towards a full relativistic analysis of the above mentioned star orbits around the center of our galaxy, we consider stable equatorial circular orbits of stars and express their corresponding red/blue shifts in terms of the metric parameters (mass and a...

  5. BRITE-Constellation: Nanosatellites for precision photometry of bright stars

    Science.gov (United States)

    Weiss, W. W.; Moffat, A. F. J.; Schwarzenberg-Czerny, A.; Koudelka, O. F.; Grant, C. C.; Zee, R. E.; Kuschnig, R.; Mochnacki, St.; Rucinski, S. M.; Matthews, J. M.; Orleański, P.; Pamyatnykh, A. A.; Pigulski, A.; Alves, J.; Guedel, M.; Handler, G.; Wade, G. A.; Scholtz, A. L.; Scholtz

    2014-02-01

    BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, brightness and temperature variations of stars brighter than V ~ 4, with precision and time coverage not possible from the ground. The current mission design consists of three pairs of 7 kg nanosats (hence ``Constellation'') from Austria, Canada and Poland carrying optical telescopes (3 cm aperture) and CCDs. One instrument in each pair is equipped with a blue filter; the other, a red filter. The first two nanosats (funded by Austria) are UniBRITE, designed and built by UTIAS-SFL (University of Toronto Institute for Aerospace Studies-Space Flight Laboratory) and its twin, BRITE-Austria, built by the Technical University Graz (TUG) with support of UTIAS-SFL. They were launched on 25 February 2013 by the Indian Space Agency, under contract to the Canadian Space Agency. Each BRITE instrument has a wide field of view (~ 24 degrees), so up to 15 bright stars can be observed simultaneously in 32 × 32 sub-rasters. Photometry (with reduced precision but thorough time sampling) of additional fainter targets will be possible through on-board data processing. A critical technical element of the BRITE mission is the three-axis attitude control system to stabilize a nanosat with very low inertia. The pointing stability is better than 1.5 arcminutes rms, a significant advance by UTIAS-SFL over any previous nanosatellite. BRITE-Constellation will primarily measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology. The BRITE sample of many of the brightest stars in the night sky is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases (cool giants and AGB stars). The Hertzsprung-Russell diagram for stars brighter than mag V=4 from which the BRITE-Constellation sample

  6. Interacting binary stars

    CERN Document Server

    Sahade, Jorge; Ter Haar, D

    1978-01-01

    Interacting Binary Stars deals with the development, ideas, and problems in the study of interacting binary stars. The book consolidates the information that is scattered over many publications and papers and gives an account of important discoveries with relevant historical background. Chapters are devoted to the presentation and discussion of the different facets of the field, such as historical account of the development in the field of study of binary stars; the Roche equipotential surfaces; methods and techniques in space astronomy; and enumeration of binary star systems that are studied

  7. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jiong; Ibragimov, Rashid

    2015-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting...... tree is isomorphic to T? We prove that in the general setting, CST is NP-complete, which implies that the tree edit distance considered here is also NP-hard, even when both input trees having diameters bounded by 10. We also show that, when the number of distinct stars is bounded by a constant k, CTS...

  8. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jian-Ying; Ibragimov, Rashid

    2013-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting...... tree is isomorphic to T? We prove that in the general setting, CST is NP-complete, which implies that the tree edit distance considered here is also NP-hard, even when both input trees having diameters bounded by 10. We also show that, when the number of distinct stars is bounded by a constant k, CTS...

  9. ENERGY STAR Unit Reports

    Data.gov (United States)

    Department of Housing and Urban Development — These quarterly Federal Fiscal Year performance reports track the ENERGY STAR qualified HOME units that Participating Jurisdictions record in HUD's Integrated...

  10. Combinations of 148 navigation stars and the star tracker

    Science.gov (United States)

    Duncan, R.

    1980-01-01

    The angular separation of all star combinations for 148 nav star on the onboard software for space transportation system-3 flight and following missions is presented as well as the separation of each pair that satisfies the viewing constraints of using both star trackers simultaneously. Tables show (1) shuttle star catalog 1980 star position in M 1950 coordinates; (2) two star combination of 148 nav stars; and (3) summary of two star-combinations of the star tracker 5 deg filter. These 148 stars present 10,875 combinations. For the star tracker filters of plus or minus 5 deg, there are 875 combinations. Formalhaut (nav star 26) has the best number of combinations, which is 33.

  11. Horizontal Branch stars as AmFm/HgMn stars

    CERN Document Server

    Michaud, G

    2008-01-01

    Recent observations and models for horizontal branch stars are briefly described and compared to models for AmFm stars. The limitations of those models are emphasized by a comparison to observations and models for HgMn stars.

  12. Properties of blue-stained wood

    Directory of Open Access Journals (Sweden)

    Miha Humar

    2008-07-01

    Full Text Available Discoloration of wood is frequently caused by blue-stain fungi. Among them Aureobasidium pullulans and Sclerophoma pithyophila are reported as the most important staining organism. In previous researches, it was generally considered that blue-stain fungi do not influence mechanical properties. However, there were some opposite results published as well. In order to elucidate this issue, specimens made of Scots pine (Pinus sylvestris sapwood were exposed to two blue stain fungi A. pullulans and S. pithyophila for periods between two and eight weeks. FTIR, weight, colour and non-destructive modulus of elasticity measurements were performed before and after exposure. The results showed that blue stain fungi, besides considerable discoloration, do not cause any significant damage to wood. Surprisingly the non-destructive MoE analysis showed that modulus of elasticity even slightly increase after fungal exposure.

  13. Blue Ribbon Panel Report - BRP - Cancer Moonshot

    Science.gov (United States)

    The Blue Ribbon Panel Report outlines 10 recommendations to accelerate progress against cancer. The panel was established to ensure that the Cancer Moonshot's approaches are grounded in the best science.

  14. Blue Ribbon Panel 2016 Video Playlist

    Science.gov (United States)

    Blue Ribbon Panel members discuss recommendations from the panel report that was presented to the National Cancer Advisory Board on September 7, 2016. The playlist includes an overview video and 10 videos on the specific recommendations.

  15. Pulsations as a mass-loss trigger in evolved hot stars

    CERN Document Server

    Kraus, Michaela; Haucke, Maximiliano; Cidale, Lydia; Venero, Roberto; Fernandes, Marcelo Borges; Tomic, Sanja; Cure, Michel

    2013-01-01

    During the post-main sequence evolution massive stars pass through several short-lived phases, in which they experience enhanced mass loss in the form of clumped winds and mass ejection events of unclear origin. The discovery that stars populating the blue, luminous part of the Hertzsprung-Russell diagram can pulsate hence suggests that stellar pulsations might influence or trigger enhanced mass loss and eruptions. We present recent results for two objects in different phases: a B[e] star at the end of the main sequence and a B-type supergiant.

  16. Central stars of mid-infrared nebulae discovered with Spitzer and WISE

    CERN Document Server

    Gvaramadze, V V

    2016-01-01

    Searches for compact mid-IR nebulae with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE), accompanied by spectroscopic observations of central stars of these nebulae led to the discovery of many dozens of massive stars at different evolutionary stages, of which the most numerous are candidate luminous blue variables (LBVs). In this paper, we give a census of candidate and confirmed Galactic LBVs revealed with Spitzer and WISE, and present some new results of spectroscopic observations of central stars of mid-IR nebulae.

  17. VizieR Online Data Catalog: Candidate BHB stars in Ophiuchus stream (Sesar+, 2016)

    Science.gov (United States)

    Sesar, B.; Price-Whelan, A. M.; Cohen, J. G.; Rix, H.-W.; Pearson, S.; Johnston, K. V.; Bernard, E. J.; Ferguson, A. M. N.; Martin, N. F.; Slater, C. T.; Chambers, K. C.; Flewelling, H.; Wainscoat, R. J.; Waters, C.

    2016-03-01

    In Figure 1, we show the spatial distribution of candidate blue horizontal branch (BHB) stars selected for spectroscopic follow-up, and in Table 1 we list their positions. A total of 16 stars were observed using the DEIMOS spectrograph on the WMKO Keck II 10-m telescope (project ID 2015A-C252D, PI: J. Cohen). The remaining 27 stars were observed using the TWIN spectrograph on the Calar Alto 3.5-m telescope (project ID H15-3.5-011, PI: B. Sesar). (1 data file).

  18. Star formation at high redshift and the importance of dust obscuration

    DEFF Research Database (Denmark)

    Michalowski, Michal

    One of the aspects of the understanding of the Universe evolution is its star formation history. In order to gain a complete picture of the Universe evolution it is important to know when the stars we see today were formed. One of the method to study this problem is to use far-infrared and radio...... and/or radio, namely their enhanced submillimeter / radio emission combined with optical faintness and blue colors. I find that these four galaxies are young, highly star-forming, low-mass and dusty....

  19. The Galactic O-Star Spectral Survey (GOSSS) Project status and first results

    CERN Document Server

    Sota, Alfredo; Barbá, Rodolfo H; Walborn, Nolan R; Alfaro, Emilio J; Gamen, Roberto C; Morrell, Nidia I; Arias, Julia I; Ordaz, Miguel Penadés

    2011-01-01

    The Galactic O-Star Spectroscopic Survey (GOSSS) is a project that is observing all known Galactic O stars with B < 13 (~2000 objects) in the blue-violet part of the spectrum with R~2500. It also includes two companion surveys (a spectroscopic one at R~1500 and a high resolution imaging one). It is based on v2.0 of the Galactic O star catalog (v1, Ma\\'iz-Apell\\'aniz et al. 2004; v2, Sota et al. 2008). We have completed the first part of the main project. Here we present results on the first 400 objects of the sample.

  20. Signatures of inflow motion in cores of massive star formation: Potential collapse candidates

    CERN Document Server

    Wu, Yuefang; Xue, Rui; Guan, Xin; Miller, Martin

    2007-01-01

    Using the IRAM 30 m telescope, a mapping survey in optically thick and thin lines was performed towards 46 high mass star-forming regions. The sample includes UC H{\\sc ii} precursors and UC H{\\sc ii} regions. Seventeen sources are found to show "blue profiles", the expected signature of collapsing cores. The excess of sources with blue over red profiles ([$N_{\\rm blue}$ -- $N_{\\rm red}$]/$N_{\\rm total}$) is 29% in the HCO$^+$ $J$=1--0 line, with a probability of 0.6% that this is caused by random fluctuations. UC H{\\sc ii} regions show a higher excess (58%) than UC H{\\sc ii} precursors (17%), indicating that material is still accreted after the onset of the UC H{\\sc ii} phase. Similar differences in the excess of blue profiles as a function of evolutionary state are not observed in low mass star-forming regions. Thus, if confirmed for high mass star-forming sites, this would point at a fundamental difference between low- and high-mass star formation. Possible explanations are inadequate thermalization, strong...

  1. Blue Ocean Strategy and marketing Icelandic fish

    OpenAIRE

    Sigrún Guðbjartsdóttir 1976

    2012-01-01

    The aim of the thesis is to explore if practice of Blue Ocean Strategy, through value innovation, or certain tools and framework of the strategy can be useful for Icelandic fish marketing companies. Blue Ocean Strategy is an innovative strategy that pushes companies to look beyond conventional boundaries of an industry and discover new market space through value innovation and consequently make competition irrelevant. Data was gathered through qualitative research methods, interviews as we...

  2. Blue Flag: a Symbol of Environmental Protection

    Directory of Open Access Journals (Sweden)

    Ioan Petroman

    2010-10-01

    Full Text Available Blue Flag is a high standard symbol of environmental protection and it is awarded to the beaches and agreement ports by the Foundation of Education for the Environment. The beaches having been awarded this distinction warrant particular protection for their visitors, which is a particular point of tourism attractiveness: the result, they are preferred by tourists and, therefore, by tour operators selling tourism packages for the littoral. In 2009, Romanian beaches were not awarded any Blue Flags.

  3. Blue emitting organic semiconductors under high pressure

    DEFF Research Database (Denmark)

    Knaapila, Matti; Guha, Suchismita

    2016-01-01

    This review describes essential optical and emerging structural experiments that use high GPa range hydrostatic pressure to probe physical phenomena in blue-emitting organic semiconductors including π-conjugated polyfluorene and related compounds. The work emphasizes molecular structure and inter......This review describes essential optical and emerging structural experiments that use high GPa range hydrostatic pressure to probe physical phenomena in blue-emitting organic semiconductors including π-conjugated polyfluorene and related compounds. The work emphasizes molecular structure...

  4. Blue Whales Respond to Anthropogenic Noise

    OpenAIRE

    Mariana L Melcón; Amanda J Cummins; Kerosky, Sara M; Lauren K Roche; Wiggins, Sean M.; John A. Hildebrand

    2012-01-01

    Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to...

  5. Star Position Estimation Improvements for Accurate Star Tracker Attitude Estimation

    OpenAIRE

    Delabie, Tjorven

    2015-01-01

    This paper presents several methods to improve the estimation of the star positions in a star tracker, using a Kalman Filter. The accuracy with which the star positions can be estimated greatly influences the accuracy of the star tracker attitude estimate. In this paper, a Kalman Filter with low computational complexity, that can be used to estimate the star positions based on star tracker centroiding data and gyroscope data is discussed. The performance of this Kalman Filter can be increased...

  6. A Quest for PMS candidate stars at low metallicity: Variable HAe/Be and Be stars in the Small Magellanic Cloud

    CERN Document Server

    De Wit, W J; Lamers, Henny J G L M; Lesquoy, E; Marquette, J B

    2003-01-01

    We report the discovery of 5 new Herbig Ae/Be candidate stars in the Small Magellanic Cloud in addition to the 2 reported in Beaulieu et al. (2001). We discuss these 7 HAeBe candidate stars in terms of (1) their irregular photometric variability, (2) their near infrared emission, (3) their Halpha emission and (4) their spectral type. One star has the typical photometric behaviour that is observed only among Pre-Main Sequence UX Orionis type stars. The objects are more luminous than Galactic HAeBe stars and Large Magellanic Cloud HAeBe candidates of the same spectral type. The stars were discovered in a systematic search for variable stars in a subset of the EROS2 database consisting of 115,612 stars in a field of 24x24 arcmin in the Small Magellanic Cloud. In total we discovered 504 variable stars. After classifying the different objects according to their type of variability, we concentrate on 7 blue objects with irregular photometric behaviour. We cross-identified these objects with emission line catalogues...

  7. Binary interactions with high accretion rates onto main sequence stars

    Science.gov (United States)

    Shiber, Sagiv; Schreier, Ron; Soker, Noam

    2016-07-01

    Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; red novae; red transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to ≈ 10-2 M ⊙ yr-1 for solar type stars, and up to ≈ 1 M ⊙ yr-1 for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.

  8. Cold gas and star formation in a merging galaxy sequence

    Science.gov (United States)

    Georgakakis, Antonis; Forbes, Duncan A.; Norris, Ray P.

    2000-10-01

    We explore the evolution of the cold gas (molecular and neutral hydrogen) and star formation activity during galaxy interactions, using a merging galaxy sequence comprising both pre- and post-merger candidates. Data for this study come from the literature, but are supplemented by some new radio observations presented here. First, we confirm that the ratio of far-infrared luminosity to molecular hydrogen mass (LFIRM(H2); star formation efficiency) increases close to nuclear coalescence. After the merging of the two nuclei there is evidence that the star formation efficiency declines again to values typical of ellipticals. This trend can be attributed to M(H2) depletion arising from interaction induced star formation. However, there is significant scatter, likely to arise from differences in the interaction details (e.g., disc-to-bulge ratio, geometry) of individual systems. Secondly, we find that the central molecular hydrogen surface density, ΣH2, increases close to the final stages of the merging of the two nuclei. Such a trend, indicating gas inflows caused by gravitational instabilities during the interaction, is also predicted by numerical simulations. Furthermore, there is evidence for a decreasing fraction of cold gas mass from early interacting systems to merger remnants, attributed to neutral hydrogen conversion into other forms (e.g., stars, hot gas) and molecular hydrogen depletion resulting from ongoing star formation. The evolution of the total-radio to blue-band luminosity ratio, reflecting the total (disc and nucleus) star formation activity, is also investigated. Although this ratio is on average higher than that for isolated spirals, we find a marginal increase along the merging sequence, attributed to the relative insensitivity of disc star formation to interactions. However, a similar result is also obtained for the nuclear radio emission, although galaxy interactions are believed to significantly affect the activity (star formation, AGN) in the

  9. Brilliant Star in a Colourful Neighbourhood

    Science.gov (United States)

    2010-07-01

    A spectacular new image from ESO's Wide Field Imager at the La Silla Observatory in Chile shows the brilliant and unusual star WR 22 and its colourful surroundings. WR 22 is a very hot and bright star that is shedding its atmosphere into space at a rate many millions of times faster than the Sun. It lies in the outer part of the dramatic Carina Nebula from which it formed. Very massive stars live fast and die young. Some of these stellar beacons have such intense radiation passing through their thick atmospheres late in their lives that they shed material into space many millions of times more quickly than relatively sedate stars such as the Sun. These rare, very hot and massive objects are known as Wolf-Rayet stars [1], after the two French astronomers who first identified them in the mid-nineteenth century, and one of the most massive ones yet measured is known as WR 22. It appears at the centre of this picture, which was created from images taken through red, green and blue filters with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile. WR 22 is a member of a double star system and has been measured to have a mass at least 70 times that of the Sun. WR 22 lies in the southern constellation of Carina, the keel of Jason's ship Argo in Greek mythology. Although the star lies over 5000 light-years from the Earth it is so bright that it can just be faintly seen with the unaided eye under good conditions. WR 22 is one of many exceptionally brilliant stars associated with the beautiful Carina Nebula (also known as NGC 3372) and the outer part of this huge region of star formation in the southern Milky Way forms the colourful backdrop to this image. The subtle colours of the rich background tapestry are a result of the interactions between the intense ultraviolet radiation coming from hot massive stars, including WR 22, and the vast gas clouds, mostly hydrogen, from which they formed. The central part of this enormous complex

  10. Making Stars … With a Little Help

    Science.gov (United States)

    Kohler, Susanna

    2015-11-01

    Extremely high star formation rates have been observed in galaxies at high redshifts, posing somewhat of a mystery: how are these enormous rates achieved? A team of scientists has proposed that these high rates of star formation could be explained by feedback from active nuclei at the centers of the galaxies.Pressurized BubbleWe believe that star formation occurs in galaxies as a result of gas clumps that collapse under their own gravity, eventually becoming dense enough to launch nuclear fusion. Recently, theres been mounting evidence that the star formation rate is significantly higher in high-redshift galaxies, particularly those with active galactic nuclei (AGN). Could this simply be caused by a higher gas fraction at higher redshifts? Or is it possible that a different mechanism is at work in these galaxies, producing more efficient star formation?A team of authors led by Rebekka Bieri (Paris Institute of Astrophysics) has proposed that this enhanced star formation may be caused by positive feedback from the active nucleus of the galaxy. The team suggests that an outflow from the AGN could create an over-pressurized bubble around the galactic disk that pushes back on the disk, leading to a higher rate of star formation.Simulating a BoostThe authors test this toy model by simulating the scenario. They model a disk galaxy with roughly a tenth of the mass of the Milky Way, which starts in a relaxed state. The galaxy is then evolved either with or without an applied external pressure, representing the isotropic pressure from the bubble created by the AGN outflow. These models are tested in two different scenarios: one where the initial gas fraction is 10%, and one where the initial gas fraction is 50%.Star formation rates for the low-gas-fraction (left) and high-gas-fraction (right) simulated galaxies. The blue lines show the rates without external pressure; the red lines show the rates with external pressure applied. [Bieri et al. 2015]The simulations show that

  11. TIME-SERIES BVI PHOTOMETRY FOR THE GLOBULAR CLUSTER NGC 6981 {sup ,} {sup ,}

    Energy Technology Data Exchange (ETDEWEB)

    Amigo, P.; Catelan, M.; Zoccali, M. [Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile); Stetson, P. B. [Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Smith, H. A., E-mail: mcatelan@astro.puc.cl, E-mail: mzoccali@astro.puc.cl, E-mail: pia.amigo@dfa.uv.cl, E-mail: Peter.Stetson@nrc-cnrc.gc.ca, E-mail: smith@pa.msu.edu [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

    2013-11-01

    We present new BVI photometry of the globular cluster NGC 6981, based mostly on ground-based CCD archival images. We present a new color-magnitude diagram (CMD) that reaches almost four magnitudes below the turn-off level. We performed new derivations of metallicity and morphological parameters of the evolved sequences, in good agreement with the results of previous authors, and obtain a value of [Fe/H] ≅ –1.50 in the new UVES scale. We also identify the cluster's blue straggler population. Comparing the radial distribution of these stars with the red giant branch population, we find that the blue stragglers are more centrally concentrated, as found in previous studies of blue stragglers in globular clusters. Taking advantage of the large field of view covered by our study, we analyzed the surface density profile of the cluster, and find extratidal main sequence stars out to r ≈ 14.'1, or about twice the tidal radius. We speculate that the presence of these stars may be due to tidal disruption in the course of NGC 6981's orbit, in which case tidal tails associated with the cluster may exist. We also take a fresh look at the variable stars in the cluster, recovering all previously known variables, including three SX Phoenicis stars. We also add three previously unknown RR Lyrae (one c-type and two ab-type) to the total census. Finally, comparing our CMD with unpublished data for M3 (NGC 5272), a cluster with a similar metallicity and horizontal branch morphology, we found that both objects are essentially coeval.

  12. Time-series BVI Photometry for the Globular Cluster NGC 6981

    Science.gov (United States)

    Amigo, P.; Stetson, P. B.; Catelan, M.; Zoccali, M.; Smith, H. A.

    2013-11-01

    We present new BVI photometry of the globular cluster NGC 6981, based mostly on ground-based CCD archival images. We present a new color-magnitude diagram (CMD) that reaches almost four magnitudes below the turn-off level. We performed new derivations of metallicity and morphological parameters of the evolved sequences, in good agreement with the results of previous authors, and obtain a value of [Fe/H] ~= -1.50 in the new UVES scale. We also identify the cluster's blue straggler population. Comparing the radial distribution of these stars with the red giant branch population, we find that the blue stragglers are more centrally concentrated, as found in previous studies of blue stragglers in globular clusters. Taking advantage of the large field of view covered by our study, we analyzed the surface density profile of the cluster, and find extratidal main sequence stars out to r ≈ 14.'1, or about twice the tidal radius. We speculate that the presence of these stars may be due to tidal disruption in the course of NGC 6981's orbit, in which case tidal tails associated with the cluster may exist. We also take a fresh look at the variable stars in the cluster, recovering all previously known variables, including three SX Phoenicis stars. We also add three previously unknown RR Lyrae (one c-type and two ab-type) to the total census. Finally, comparing our CMD with unpublished data for M3 (NGC 5272), a cluster with a similar metallicity and horizontal branch morphology, we found that both objects are essentially coeval. This paper makes use of data obtained from the Isaac Newton Group Archive, which is maintained as part of the CASU Astronomical Data Centre at the Institute of Astronomy, Cambridge.

  13. Forecasts for the WFIRST High Latitude Survey using the BlueTides Simulation

    CERN Document Server

    Waters, Dacen; Feng, Yu; Wilkins, Stephen M; Croft, Rupert A C

    2016-01-01

    We use the BlueTides simulation to predict the properties of the high-$z$ galaxy and active galactic nuclei (AGN) populations for the planned 2200deg$^2$ Wide-Field Infrared Survey Telescope's (WFIRST)-AFTA High Latitude Survey (HLS). BlueTides is a cosmological hydrodynamic simulation, which incorporates a variety of baryon physics in a $(400h^{-1} \\mathrm{Mpc})^3$ volume evolved to $z=8$ with 0.7 trillion particles. The galaxy luminosity functions in the simulation show good agreement with all the current observational constraints (up to $z=11$) and predicts an enhanced number of UV bright galaxies. At the proposed depth of the HLS ($m < 26.75$), BlueTides predicts $10^6$ galaxies at $z=8$ with a few up to $z\\sim 15$ due to the enhanced bright end of the galaxy luminosity function. At $z=8$, galaxies in the mock HLS have specific star formation rates of $\\sim 10 {\\rm Gyr}^{-1}$ and ages of $\\sim 80 {\\rm Myr}$ (both evolving linearly with redshift) and a non-evolving mass-metallicity relation. BlueTides a...

  14. NoSOCS in SDSS. V. Red Disc and Blue Bulge Galaxies Across Different Environments

    CERN Document Server

    Lopes, P A A; Ribeiro, A L B; Nascimento, R S; Vajgel, B

    2016-01-01

    We investigated the typical environment and physical properties of "red discs" and "blue bulges", comparing those to the "normal" objects in the blue cloud and red sequence. Our sample is composed of cluster members and field galaxies at $z \\le 0.1$, so that we can assess the impact of the local and global environment. We find that disc galaxies display a strong dependence on environment, becoming redder for higher densities. This effect is more pronounced for objects within the virial radius, being also strong related to the stellar mass. We find that local and global environment affect galaxy properties, but the most effective parameter is stellar mass. We find evidence for a scenario where "blue discs" are transformed into "red discs" as they grow in mass and move to the inner parts of clusters. From the metallicity differences of red and blue discs, and the analysis of their star formation histories, we suggest the quenching process is slow. We estimate a quenching time scale of $\\sim $ 2$-$3 Gyr. We also...

  15. Stars and Flowers, Flowers and Stars

    Science.gov (United States)

    Minti, Hari

    2012-12-01

    The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

  16. Neutron Stars: Formation and Structure

    OpenAIRE

    Kutschera, Marek

    1998-01-01

    A short introduction is given to astrophysics of neutron stars and to physics of dense matter in neutron stars. Observed properties of astrophysical objects containing neutron stars are discussed. Current scenarios regarding formation and evolution of neutron stars in those objects are presented. Physical principles governing the internal structure of neutron stars are considered with special emphasis on the possible spin ordering in the neutron star matter.

  17. The (Un)Lonely Planet Guide: Formation and Evolution of Planetary Systems from a `Blue Dots' Perspective

    OpenAIRE

    Meyer, Michael R.

    2010-01-01

    In this contribution I summarize some recent successes, and focus on remaining challenges, in understanding the formation and evolution of planetary systems in the context of the Blue Dots initiative. Because our understanding is incomplete, we cannot yet articulate a "design reference mission" engineering matrix suitable for an exploration mission where success is defined as obtaining a spectrum of a potentially habitable world around a nearby star. However, as progress accelerates, we can i...

  18. 2D radiaition-hydrodynamic simulations of supernova shock breakout in bipolar explosions of a blue supergiant progenitor

    OpenAIRE

    Suzuki, Akihiro; Maeda, Keiichi; Shigeyama, Toshikazu

    2016-01-01

    A two-dimensional special relativistic radiation-hydrodynamics code is developed and applied to numerical simulations of supernova shock breakout in bipolar explosions of a blue supergiant. Our calculations successfully simulate the dynamical evolution of a blast wave in the star and its emergence from the surface. Results of the model with spherical energy deposition show a good agreement with previous simulations. Furthermore, we calculate several models with bipolar energy deposition and c...

  19. Celestial Fireworks from Dying Stars

    Science.gov (United States)

    2011-04-01

    This image of the nebula NGC 3582, which was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile, shows giant loops of gas bearing a striking resemblance to solar prominences. These loops are thought to have been ejected by dying stars, but new stars are also being born within this stellar nursery. These energetic youngsters emit intense ultraviolet radiation that makes the gas in the nebula glow, producing the fiery display shown here. NGC 3582 is part of a large star-forming region in the Milky Way, called RCW 57. It lies close to the central plane of the Milky Way in the southern constellation of Carina (The Keel of Jason's ship, the Argo). John Herschel first saw this complex region of glowing gas and dark dust clouds in 1834, during his stay in South Africa. Some of the stars forming in regions like NGC 3582 are much heavier than the Sun. These monster stars emit energy at prodigious rates and have very short lives that end in explosions as supernovae. The material ejected from these dramatic events creates bubbles in the surrounding gas and dust. This is the probable cause of the loops visible in this picture. This image was taken through multiple filters. From the Wide Field Imager, data taken through a red filter are shown in green and red, and data taken through a filter that isolates the red glow characteristic of hydrogen are also shown in red. Additional infrared data from the Digitized Sky Survey are shown in blue. The image was processed by ESO using the observational data identified by Joe DePasquale, from the United States [1], who participated in ESO's Hidden Treasures 2010 astrophotography competition [2]. The competition was organised by ESO in October-November 2010, for everyone who enjoys making beautiful images of the night sky using astronomical data obtained using professional telescopes. Notes [1] Joe searched through ESO's archive and identified datasets that he used to compose his

  20. Quark Neutron Layer Stars

    CERN Document Server

    Carinhas, P A

    1993-01-01

    Typical nuclear equations of state and a quark bag model, surprisingly, allow compact stars with alternate layers of neutrons and quarks. One can determine on the basis of the Gibbs free energy which phase, nuclear or quark, is energetically favorable. Using the nuclear equation of state of Wiringa, and a quark equation of state given by Freedman and McLerran, the allowed quark parameter space for such layer stars is searched. This paper differs from past work in that configurations are found in which quark matter is located exterior and interior to shells of nuclear matter, i.e., dependent on quark parameters, a star may contain several alternating layers of quark and nuclear matter. Given the uncertainty in the quark parameter space, one can estimate the probability for finding pure neutron stars, pure quark stars (strange stars), stars with a quark core and a nucleon exterior, or layer stars. Several layer models are presented. The physical characteristics, stability, and results of a thorough search of th...

  1. Neutrostriction in Neutron stars

    OpenAIRE

    Ignatovich, V. K.

    2003-01-01

    It is demonstrated that not only gravity, but also neutrostriction forces due to optical potential created by coherent elastic neutron-neutron scattering can hold a neutron star together. The latter forces can be stronger than gravitational ones. The effect of these forces on mass, radius and structure of the neutron star is estimated.

  2. The violent neutron star

    OpenAIRE

    Watts, Anna L.

    2012-01-01

    Neutron stars enable us to study both the highest densities and the highest magnetic fields in the known Universe. In this article I review what can be learned about such fundamental physics using magnetar bursts. Both the instability mechanisms that trigger the bursts, and the subsequent dynamical and radiative response of the star, can be used to explore stellar and magnetospheric structure and composition.

  3. Observing Double Stars

    Science.gov (United States)

    Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

    2012-05-01

    Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

  4. Star spot location estimation using Kalman filter for star tracker.

    Science.gov (United States)

    Liu, Hai-bo; Yang, Jian-kun; Wang, Jiong-qi; Tan, Ji-chun; Li, Xiu-jian

    2011-04-20

    Star pattern recognition and attitude determination accuracy is highly dependent on star spot location accuracy for the star tracker. A star spot location estimation approach with the Kalman filter for a star tracker has been proposed, which consists of three steps. In the proposed approach, the approximate locations of the star spots in successive frames are predicted first; then the measurement star spot locations are achieved by defining a series of small windows around each predictive star spot location. Finally, the star spot locations are updated by the designed Kalman filter. To confirm the proposed star spot location estimation approach, the simulations based on the orbit data of the CHAMP satellite and the real guide star catalog are performed. The simulation results indicate that the proposed approach can filter out noises from the measurements remarkably if the sampling frequency is sufficient. PMID:21509065

  5. Producing Runaway Stars

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    How are the hypervelocity stars weve observed in our galaxy produced? A recent study suggests that these escapees could be accelerated by a massive black hole in the center of the Large Magellanic Cloud.A Black Hole SlingshotSince their discovery in 2005, weve observed dozens of candidate hypervelocity stars stars whose velocity in the rest frame of our galaxy exceeds the local escape velocity of the Milky Way. These stars present a huge puzzle: how did they attain these enormous velocities?One potential explanation is known as the Hills mechanism. In this process, a stellar binary is disrupted by a close encounter with a massive black hole (like those thought to reside at the center of every galaxy). One member of the binary is flung out of the system as a result of the close encounter, potentially reaching very large velocities.A star-forming region known as LHA 120-N 11, located within the LMC. Some binary star systems within the LMC might experience close encounters with a possible massive black hole at the LMCs center. [ESA/NASA/Hubble]Blame the LMC?Usually, discussions of the Hills mechanism assume that Sagittarius A*, the supermassive black hole at the center of the Milky Way, is the object guilty of accelerating the hypervelocity stars weve observed. But what if the culprit isnt Sgr A*, but a massive black hole at the center of the Large Magellanic Cloud (LMC), one of the Milky Ways satellite galaxies?Though we dont yet have evidence of a massive black hole at the center of the LMC, the dwarf galaxy is large enough to potentially host one as large as 100,000 solar masses. Assuming that it does, two scientists at the University of Cambridge, Douglas Boubert and Wyn Evans, have now modeled how this black hole might tear apart binary star systems and fling hypervelocity stars around the Milky Way.Models for AccelerationBoubert and Evans determined that the LMCs hypothetical black hole could easily eject stars at ~100 km/s, which is the escape velocity of the

  6. Revised Anatomy of Stars

    CERN Document Server

    Dubin, M; Dubin, Maurice; Soberman, Robert K.

    1997-01-01

    Stars accrete near invisible hydrogen dominated agglomerates. This population, the `dark matter,' effects the nature of stars. Measurements show plasma streams impacting Earth, planets, Sun and stars. This mass-energy source contradicts nebula collapse model for stars. The visual derived model, to which later discoveries (e.g., fusion) were appended, is confounded and contradicted by new observations. Discovery of a quantity of beryllium 7 (53 day half-life) in the Earth's upper atmosphere, fusion produced, hence from the solar outer zone, proves core fusion wrong. Magnetically pinched plasmas from aggregates impact stars at hundreds of km/s, create impulsive conditions for nuclear explosions below the surface. Disks with planets aid cluster capture. Planets modulate the influx varying fusion, hence luminosity (e.g., solar cycle). This population, with no assumptions or ad hoc physics, explains mysterious phenomena, e.g., luminosity/wind variation, sunspots, high temperature corona, CMEs, etc. Standard explan...

  7. Neutron Stars and Pulsars

    CERN Document Server

    Becker, Werner

    2009-01-01

    Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

  8. Ages of young stars

    CERN Document Server

    Soderblom, David R; Jeffries, Rob D; Mamajek, Eric E; Naylor, Tim

    2013-01-01

    Determining the sequence of events in the formation of stars and planetary systems and their time-scales is essential for understanding those processes, yet establishing ages is fundamentally difficult because we lack direct indicators. In this review we discuss the age challenge for young stars, specifically those less than ~100 Myr old. Most age determination methods that we discuss are primarily applicable to groups of stars but can be used to estimate the age of individual objects. A reliable age scale is established above 20 Myr from measurement of the Lithium Depletion Boundary (LDB) in young clusters, and consistency is shown between these ages and those from the upper main sequence and the main sequence turn-off -- if modest core convection and rotation is included in the models of higher-mass stars. Other available methods for age estimation include the kinematics of young groups, placing stars in Hertzsprung-Russell diagrams, pulsations and seismology, surface gravity measurement, rotation and activ...

  9. Comparison of Alcian Blue, Trypan Blue, and Toluidine Blue for Visualization of the Primo Vascular System Floating in Lymph Ducts

    Directory of Open Access Journals (Sweden)

    Da-Un Kim

    2015-01-01

    Full Text Available The primo vascular system (PVS, floating in lymph ducts, was too transparent to be observed by using a stereomicroscope. It was only detectable with the aid of staining dyes, for instance, Alcian blue, which was injected into the lymph nodes. Some dyes were absorbed preferentially by the PVS than the lymph wall. It remains a standing problem to know what dyes are absorbed better by the PVS than the lymph walls. Such information would be useful to unravel the biochemical properties of the PVS that are badly in need for obtaining large amount of PVS specimens. In the current work we tried two other familiar dyes which were used in PVS research before. We found that Trypan blue and toluidine blue did not visualize the PVS. Trypan blue was cleared by the natural washing. Toluidine blue did not stain the PVS, but it did leave stained spots in the lymph wall and its surrounding tissues, and it leaked out of the lymph wall to stain surrounding connective tissues. These completely different behaviors of the three dyes were found for the first time in the current work and provide valuable information to elucidate the mechanism through which some special dyes stained the PVS preferentially compared to the lymphatic wall.

  10. Comparison of Alcian Blue, Trypan Blue, and Toluidine Blue for Visualization of the Primo Vascular System Floating in Lymph Ducts

    Science.gov (United States)

    Kim, Da-Un; Han, Jae Won; Jung, Sharon Jiyoon; Lee, Seung Hwan; Cha, Richard; Chang, Byung-Soo; Soh, Kwang-Sup

    2015-01-01

    The primo vascular system (PVS), floating in lymph ducts, was too transparent to be observed by using a stereomicroscope. It was only detectable with the aid of staining dyes, for instance, Alcian blue, which was injected into the lymph nodes. Some dyes were absorbed preferentially by the PVS than the lymph wall. It remains a standing problem to know what dyes are absorbed better by the PVS than the lymph walls. Such information would be useful to unravel the biochemical properties of the PVS that are badly in need for obtaining large amount of PVS specimens. In the current work we tried two other familiar dyes which were used in PVS research before. We found that Trypan blue and toluidine blue did not visualize the PVS. Trypan blue was cleared by the natural washing. Toluidine blue did not stain the PVS, but it did leave stained spots in the lymph wall and its surrounding tissues, and it leaked out of the lymph wall to stain surrounding connective tissues. These completely different behaviors of the three dyes were found for the first time in the current work and provide valuable information to elucidate the mechanism through which some special dyes stained the PVS preferentially compared to the lymphatic wall. PMID:26379749

  11. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Energy Technology Data Exchange (ETDEWEB)

    Theodorakis, P E [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Avgeropoulos, A [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Universidad Nacional de Educacion a Distancia, Facultad de Ciencias, Senda del Rey 9, 28040 Madrid (Spain); Kosmas, M [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece); Vlahos, C [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece)

    2007-11-21

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  12. Detailed photometric analysis of young star groups in the galaxy NGC 300

    CERN Document Server

    Jimena, Rodríguez María; Carlos, Feinstein

    2016-01-01

    The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study their hierarchical organization. The research was conducted using archival point spread function fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope. Using the path linkage criterion, we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color. A stati...

  13. How to Become a Star

    Science.gov (United States)

    2001-01-01

    because of the obscuring effect of dust particles in its interior. PR Photo 02b/01 is a false-colour composite based on a visible (here rendered as blue), a near-infrared (green) and an infrared (red) image. Since the light from stars behind the cloud is only visible at the longest (infrared) wavelengths, they appear red. In PR Photo 02c/01 , the central area of these two photos may be directly compared. Technical information about these photos is available below. At a distance of only 410 light-years, Barnard 68 is one of the nearest dark clouds. Its size is about 12,500 AU (= 2 million million km; 1 Astronomical Unit [AU] = 150 million km), or just about the same as the so-called "Oort Cloud" of long-period comets that surrounds the solar system. The temperature of Barnard 68 is 16 Kelvin (-257 °C) and the pressure at its boundary is 0.0025 nPa, or about 10 times higher than in the interstellar medium (but still 40,000 million million times less than the atmospheric pressure at the Earth's surface!). The total mass of the cloud is about twice that of the Sun. A new investigation of Barnard 68 was carried out by means of instruments at the 3.58-m New Technology Telescope (NTT) at La Silla and the Very Large Telescope (VLT) at Paranal. Long exposures revealed a total of about 3700 background stars (of which over 1000 can only be seen at infrared wavelengths), cf. PR Photos 02a-c/01 . Careful measurements of the colours of these stars and hence, the degree of obscuration, allowed the most finely sampled (in more than 1000 individual areas) and most accurate mapping of the dust distribution inside a dark cloud ever performed. In order to further increase the accuracy, the mean dust density was measured in concentric circles around the centre - this resulted in a very accurate determination of the change in dust density with the distance from the centre. It was found that this dependance is almost exactly as that predicted for a sphere in which the opposite forces of

  14. The Edinburgh-Cape Blue Object Survey - V. The end: Partial Zones 4-6; Galactic latitudes -50° > b > -90°

    Science.gov (United States)

    Kilkenny, D.; Worters, H. L.; O'Donoghue, D.; Koen, C.; Koen, T.; Hambly, N.; MacGillivray, H.; Stobie, R. S.

    2016-07-01

    Results for the remaining zones of the Edinburgh-Cape (EC) Blue Object survey are presented. These are incomplete, but lie in that part of the South Galactic Cap between 50° and 90° from the Galactic plane and south of about -12.3° of declination. This part of the survey comprises 79 UK Schmidt Telescope fields covering about 2150 deg2, in which we find 536 blue objects - including hot subdwarfs (˜33 per cent), white dwarfs (˜30 per cent), binaries (˜12 per cent), cataclysmic variables (˜1.5 per cent) and some `star-like' galaxies (˜12 per cent). A further 254 stars observed in the survey, mainly low-metallicity F- and G-type stars, are also listed. Low-dispersion spectroscopic classification is given for all the hot objects and UBV photometry for most of them. Either spectroscopy or photometry is listed for the cooler types.

  15. Rotating Stars Can Help Planets Become Habitable

    Science.gov (United States)

    Kohler, Susanna

    2015-12-01

    ), average (green), or fast (blue). [Johnstone et al. 2015]Case A(Initial atmospheric mass of 10-4 Earth masses)Entire atmosphere evaporates quickly, regardless of the rotation speed of the host star.Case B(Initial atmospheric mass of 10-3 Earth masses)Entire atmosphere evaporates, but the timescale is much shorter if the stellar host is fast-rotating as opposed to slow-rotating.Case C(Initial atmospheric mass of 10-2 Earth masses)If the stellar host is fast-rotating, entire atmosphere evaporates on a short timescale. If the host is slow-rotating, very little of the atmosphere evaporates.Case D(Initial atmospheric mass of 10-1 Earth masses)Very little of the atmosphere evaporates, regardless of the rotation speed of the host star.These results demonstrate that the initial rotation rate of a host star not only determines whether a planet will lose its protoatmosphere, but also how long this process will take. Thus, the evolution of host stars rotation rates is an important component in our understanding of how planets might evolve to become habitable.CitationC. P. Johnstone et al 2015 ApJ 815 L12. doi:10.1088/2041-8205/815/1/L12

  16. Radio continuum detection in blue early-type weak emission line galaxies

    OpenAIRE

    Paswan, A.; Omar, A.

    2016-01-01

    The star formation rates (SFRs) in weak emission line (WEL) galaxies in a volume-limited ($0.02 < z < 0.05$) sample of blue early-type galaxies (ETGs) identified from SDSS, are constrained here using 1.4 GHz radio continuum emission. The direct detection of 1.4 GHz radio continuum emission is made in 8 WEL galaxies and a median stacking is performed on 57 WEL galaxies using VLA FIRST images. The median stacked 1.4 GHz flux density and luminosity are estimated as 79 $\\pm$ 19 $\\mu$Jy and 0.20 $...

  17. Catch a Star!

    Science.gov (United States)

    2006-11-01

    ESO and the European Association for Astronomy Education are launching today the 2007 edition of 'Catch a Star!', their international astronomy competition for school students. Now in its fifth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. Students are invited to 'become astronomers' and embark on a journey to explore the Universe. ESO PR Photo 42/06 The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. For the artistically minded, 'Catch a Star!' also includes an artwork competition, 'Catch a Star Artists'. "'Catch a Star!' offers a unique opportunity for students to learn more about astronomy and about the methods scientists use to discover new things about the Universe", said Douglas Pierce-Price, Education Officer at ESO. In teams, students choose an astronomical topic to study and produce an in-depth report. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes or a telescope of the future can contribute to their investigations of the subject. As well as the top prize - a trip to one of ESO's observatory sites in Chile - visits to observatories in Germany, Austria and Spain, and many other prizes are also available to be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners chosen with the help of a public online vote. The first editions of 'Catch a Star!' have attracted several hundred entries from more than 25 countries worldwide. Previous winning entries have included "Star clusters and the structure of the Milky Way" (Budapest, Hungary), "Vega" (Acqui Terme, Italy) and "Venus

  18. "Blue-Collar Blues" uurib töösuhteid uutes oludes / Janar Ala

    Index Scriptorium Estoniae

    Ala, Janar, 1979-

    2009-01-01

    Tööproblemaatikat käsitlev näitus "Blue-Collar Blues" Tallinna Kunstihoones ja Tallinna Kunstihoone galeriis 31. jaanuarini 2010, kuraator Anders Härm. Lähemalt belgia-mehhiko kunstniku Francis Alys'e videost, austria kunstniku Oliver Ressleri ning venetsueela-saksa politoloogi Dario Azzelini videost "Viis tehast. Tööliste kontroll Venezuelas"

  19. 75 FR 65525 - Anthem Blue Cross Blue Shield, Claim Management Services, Inc. Operations, a Division of...

    Science.gov (United States)

    2010-10-25

    ... Management Services, Inc. Operations, a Division of Wellpoint, Inc., Green Bay, Wisconsin (the subject firm... Employment and Training Administration Anthem Blue Cross Blue Shield, Claim Management Services, Inc. Operations, a Division of Wellpoint, Inc., Green Bay, WI; Notice of Negative Determination...

  20. Dyes adsorption blue vegetable and blue watercolor by natural zeolites modified with surfactants

    International Nuclear Information System (INIS)

    In this work was carried out the dyes removal blue vegetable and blue watercolor of aqueous solutions, to 20 C, at different times and using a zeolite mineral of Parral (Chihuahua, Mexico) modified with hexadecyl trimethyl ammonium bromide or dodecyl trimethyl ammonium bromide. The zeolite was characterized before and after of its adaptation with NaCl and later with HDTMABr and DTMABr. For the materials characterization were used the scanning electron microscopy of high vacuum; elementary microanalysis by X-ray spectroscopy of dispersed energy and X-ray diffraction techniques. It was found that the surfactant type absorbed in the zeolite material influences on the adsorption process of the blue dye. Likewise, the chemical structure between the vegetable blue dye and the blue watercolor, determines the efficiency of the color removal of the water, by the zeolites modified with the surfactants. (Author)

  1. Triboelectric Nanogenerators for Blue Energy Harvesting.

    Science.gov (United States)

    Khan, Usman; Kim, Sang-Woo

    2016-07-26

    Blue energy in the form of ocean waves offers an enormous energy resource. However, it has yet to be fully exploited in order to make it available for the use of mankind. Blue energy harvesting is a challenging task as the kinetic energy from ocean waves is irregular in amplitude and is at low frequencies. Though electromagnetic generators (EMGs) are well-known for harvesting mechanical kinetic energies, they have a crucial limitation for blue energy conversion. Indeed, the output voltage of EMGs can be impractically low at the low frequencies of ocean waves. In contrast, triboelectric nanogenerators (TENGs) are highly suitable for blue energy harvesting as they can effectively harvest mechanical energies from low frequencies (easy to fabricate. Several important steps have been taken by Wang's group to develop TENG technology for blue energy harvesting. In this Perspective, we describe some of the recent progress and also address concerns related to durable packaging of TENGs in consideration of harsh marine environments and power management for an efficient power transfer and distribution for commercial applications. PMID:27408982

  2. Making star teams out of star players.

    Science.gov (United States)

    Mankins, Michael; Bird, Alan; Root, James

    2013-01-01

    Top talent is an invaluable asset: In highly specialized or creative work, for instance, "A" players are likely to be six times as productive as "B" players. So when your company has a crucial strategic project, why not multiply all that firepower and have a team of your best performers tackle it? Yet many companies hesitate to do this, believing that all-star teams don't work: Big egos will get in the way. The stars won't be able to work with one another. They'll drive the team Leader crazy. Mankins, Bird, and Root of Bain & Company believe it's time to set aside that thinking. They have seen all-star teams do extraordinary work. But there is a right way and a wrong way to organize them. Before you can even begin to assemble such a team, you need to have the right talent management practices, so you hire and develop the best people and know what they're capable of. You have to give the team appropriate incentives and leaders and support staffers who are stars in their own right. And projects that are ill-defined or small scale are not for all-star teams. Use them only for critical missions, and make sure their objectives are clear. Even with the right setup, things can still go wrong. The wise executive will take steps to manage egos, prune non-team-players, and prevent average coworkers from feeling completely undervalued. She will also invest a lot of time in choosing the right team Leader and will ask members for lots of feedback to monitor how that leader is doing. PMID:23390743

  3. Discovery of a new Galactic bona fide luminous blue variable with Spitzer

    CERN Document Server

    Gvaramadze, V V; Berdnikov, L N; Langer, N; Grebel, E K; Bestenlehner, J M

    2014-01-01

    We report the discovery of a circular mid-infrared shell around the emission-line star Wray 16-137 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of Wray 16-137 with the Southern African Large Telescope revealed a rich emission spectrum typical of the classical luminous blue variables (LBVs) like P Cygni. Subsequent spectroscopic and photometric observations showed drastic changes in the spectrum and brightness during the last three years, meaning that Wray 16-137 currently undergoes an S Dor-like outburst. Namely, we found that the star has brightened by \\approx 1 mag in the V and I_c bands, while its spectrum became dominated by Fe ii lines. Taken together, our observations unambiguously show that Wray 16-137 is a new member of the family of Galactic bona fide LBVs.

  4. Dense Axion Stars

    Science.gov (United States)

    Mohapatra, Abhishek; Braaten, Eric; Zhang, Hong

    2016-03-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. If the axion mass energy is mc2 =10-4 eV, these dilute axion stars have a maximum mass of about 10-14M⊙ . We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If mc2 =10-4 4 eV, the first branch of these dense axion stars has mass ranging from about 10-11M⊙ toabout M⊙.

  5. Dense Axion Stars

    CERN Document Server

    Braaten, Eric; Zhang, Hong

    2015-01-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure.If the axion mass energy is $mc^2= 10^{-4}$ eV, these dilute axion stars have a maximum mass of about $10^{-14} M_\\odot$. We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If $mc^2 = 10^{-4}$ eV, the first branch of these dense axion stars has mas...

  6. HUBBLE'S PANORAMIC PORTRAIT OF A VAST STAR-FORMING REGION

    Science.gov (United States)

    2002-01-01

    NASA's Hubble Space Telescope has snapped a panoramic portrait of a vast, sculpted landscape of gas and dust where thousands of stars are being born. This fertile star-forming region, called the 30 Doradus Nebula, has a sparkling stellar centerpiece: the most spectacular cluster of massive stars in our cosmic neighborhood of about 25 galaxies. The mosaic picture shows that ultraviolet radiation and high-speed material unleashed by the stars in the cluster, called R136 [the large blue blob left of center], are weaving a tapestry of creation and destruction, triggering the collapse of looming gas and dust clouds and forming pillar-like structures that are incubators for nascent stars. The photo offers an unprecedented, detailed view of the entire inner region of 30 Doradus, measuring 200 light-years wide by 150 light-years high. The nebula resides in the Large Magellanic Cloud (a satellite galaxy of the Milky Way), 170,000 light-years from Earth. Nebulas like 30 Doradus are the 'signposts' of recent star birth. High-energy ultraviolet radiation from the young, hot, massive stars in R136 causes the surrounding gaseous material to glow. Previous Hubble telescope observations showed that R136 contains several dozen of the most massive stars known, each about 100 times the mass of the Sun and about 10 times as hot. These stellar behemoths all formed at the same time about 2 million years ago. The stars in R136 are producing intense 'stellar winds' (streams of material traveling at several million miles an hour), which are wreaking havoc on the gas and dust in the surrounding neighborhood. The winds are pushing the gas away from the cluster and compressing the inner regions of the surrounding gas and dust clouds [the pinkish material]. The intense pressure is triggering the collapse of parts of the clouds, producing a new generation of star formation around the central cluster. The new stellar nursery is about 30 to 50 light-years from R136. Most of the stars in the

  7. Anomalous Blue Colors in Extremely Isolated Early-Type Galaxies

    Science.gov (United States)

    Fuse, Christopher R.

    2009-01-01

    Highly isolated systems provide a baseline for assessing the role of interactions within galaxy evolution. We use the Sloan Digital Sky Survey (SDSS) data release 1 - 5 to identify extremely isolated early-type galaxies (IEGs) in the nearby universe. Redshifts derived from the SDSS spectra permit a robust three-dimensional assessment of the local environment surrounding candidate IEGs. Isolated galaxies are chosen utilizing a projected physical separation of 2.5 Mpc from any neighboring non-dwarf galaxy brighter than M$_{V}$ = $-$16.5. A minimum redshift separation of 350 km s$^{-1}$ between a candidate galaxy and a neighboring was imposed to further insure the candidate's isolation. The IEG sample contains 33 galaxies that exhibit a number of unexpected features. Through the use of a bulge/disk decomposition technique using standard surface photometry, brightness profiles and model-subtracted images were created. Radial profiles of eccentricity, position angle, and surface brightness were employed with the model images to constrain the merger and interaction histories of the IEGs. The presence of shell and fan structures, signatures of recent mergers, were detected in approximately 12% of the sample. Dominant features of the IEG sample are blue colors and active star formation, atypical of normal early-type galaxies. The IEGs would require a substantial reservoir of neutral gas to fuel the levels of on-going star formation observed. We speculate that some of the IEGs may be the remains of a coalesced group of gas-rich dwarf galaxies. Three sample galaxies have red colors and undisturbed morphologies expected of a pristine isolated early-type galaxy formed early in cosmic time. We acknowledge support from NASA's Astrophysical Data Program; grant #NNG05C53G, the GALEX Guest Investigator program, and a Texas Space Grant Consortium Fellowship.

  8. A Novel Approach for Star Extraction from Star Image

    Institute of Scientific and Technical Information of China (English)

    ZHENGSheng; LIUJian; TIANJinwen; YANGRuijuan

    2005-01-01

    Star acquisition is one of the most timeconsuming routines in star tracker operation. One star Point spread function (PSF) forms a near Gaussian distribution in the star image, the star image can be regarded as 2-D intensity surface, and every pixel is the sampled point. The star cluster grouping is to find the highes tintensity pixel among the PSFs and collect the adjacent pixels and group them. The possible highest intensity pixels are the maximum extremum points of the 2-D intensity surface. To efficiently extract star from the star image, a novel star acquisition approach, which uses the simplified least squares support vector machines regression algorithm to find the optimal intensity surface function and predictthe maximum extremum points, is proposed. Comput erexperiments are carried out for the simulated star images.The experimental results demonstrate that the proposed method has a lot of advantages, including the high efficiency and good robustness over a wide range of sensor noise.

  9. The Very Massive Star Content of the Nuclear Star Clusters in NGC 5253

    Science.gov (United States)

    Smith, L. J.; Crowther, P. A.; Calzetti, D.; Sidoli, F.

    2016-05-01

    The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the Hα emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3-5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M ⊙, at an age of 1-2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope. We emphasize that population synthesis models with upper mass cutoffs greater than 100 M ⊙ are crucial for future studies of young massive star clusters at all redshifts.

  10. Vidicon star tracker.

    Science.gov (United States)

    Schuck, W H

    1966-04-01

    In many applications of star trackers, extremely short acquisition times, as well as accuracy and sensitivity, are required. Tracking systems employing the vidicon as a radiation sensor have been shown to provide the necessary speed of acquisition for such applications. This paper discusses the various theoretical and practical considerations involved in using the vidicon as a sensor in a star tracking system. A typical system configuration including telescope, sensor, and processing electronics is presented. The various optical and sensor parametric relationships required in the design of a vidicon star tracker are fully discussed and analyzed. PMID:20048884

  11. STARs in the CNS.

    Science.gov (United States)

    Ehrmann, Ingrid; Fort, Philippe; Elliott, David J

    2016-08-15

    STAR (signal transduction and activation of RNA) proteins regulate splicing of target genes that have roles in neural connectivity, survival and myelination in the vertebrate nervous system. These regulated splicing targets include mRNAs such as the Neurexins (Nrxn), SMN2 (survival of motor neuron) and MAG (myelin-associated glycoprotein). Recent work has made it possible to identify and validate STAR protein splicing targets in vivo by using genetically modified mouse models. In this review, we will discuss the importance of STAR protein splicing targets in the CNS (central nervous system). PMID:27528753

  12. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  13. Chemical Abundances in the Secondary Star of the Black Hole Binary V4641 Sagittarii (SAX J1819.3-2525)

    CERN Document Server

    Sadakane, K; Aoki, W; Arimoto, N; Takada-Hidai, M; Ohnishi, T; Tajitsu, A; Beers, T C; Iwamoto, N; Tominaga, N; Umeda, H; Maeda, K; Nomoto, K; Sadakane, Kozo; Arai, Akira; Aoki, Wako; Arimoto, Nobuo; Takada-Hidai, Masahide; Ohnishi, Takashi; Tajitsu, Akito; Beers, Timothy C.; Iwamoto, Nobuyuki; Tominaga, Nozomu; Umeda, Hideyuki; Maeda, Keiichi; Nomoto, Ken'ichi

    2006-01-01

    We report on detailed spectroscopic studies performed for the secondary star in the black hole binary (micro-quasar) V4641 Sgr in order to examine its surface chemical composition and to see if its surface shows any signature of pollution by ejecta from a supernova explosion. High-resolution spectra of V4641 Sgr observed in the quiescent state in the blue-visual region are compared with those of the two bright well-studied B9 stars (14 Cyg and $\

  14. The multiplicity of massive stars: A high angular resolution survey with the HST fine guidance sensor

    Energy Technology Data Exchange (ETDEWEB)

    Aldoretta, E. J.; Gies, D. R.; Henry, T. J.; Jao, W.-C.; Norris, R. P., E-mail: emily@astro.umontreal.ca, E-mail: gies@chara.gsu.edu, E-mail: thenry@chara.gsu.edu, E-mail: jao@chara.gsu.edu, E-mail: norris@chara.gsu.edu [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P. O. Box 5060, Atlanta, GA 30302-5060 (United States); and others

    2015-01-01

    We present the results of an all-sky survey made with the Fine Guidance Sensor on the Hubble Space Telescope to search for angularly resolved binary systems among massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and luminous blue variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to the detection of companions with an angular separation between 0.″01 and 1.″0 and brighter than △m=5. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of logP. We identify a number of systems of potential interest for long-term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions.

  15. The multiplicity of massive stars: A high angular resolution survey with the HST fine guidance sensor

    International Nuclear Information System (INIS)

    We present the results of an all-sky survey made with the Fine Guidance Sensor on the Hubble Space Telescope to search for angularly resolved binary systems among massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and luminous blue variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to the detection of companions with an angular separation between 0.″01 and 1.″0 and brighter than △m=5. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of logP. We identify a number of systems of potential interest for long-term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions.

  16. A Stable Blue Organic Electroluminescent Material

    Institute of Scientific and Technical Information of China (English)

    郑新友; 吴有智; 等

    2002-01-01

    In order to compare two kinds of blue electroluminescent materials,we have investigated two kinds of blue OLEDs with the similar structure ITO/CuPc/NPB/JBEM:perylene/Alq/Mg:Ag[device(J)] and ITO/CuPc/NPB/DPVBi:perylene/Alq/Mg:Ag[device(D)].The difference of luminance and efficiency was not obvious for the two devices,However,there was remarkable difference for their lifetime.The device(J) achieved longer half lifetime of 1035h at initial luminance of 100 cd/m2,and that of device(D) was only255h,According to their energy level diagrams,the differentce of their stability may originate from different host materials in the two devices.It may be attributed to the better thermal stability of JBEM molecues than that of DPVBi.It is shown that JBEM may be a promising blue organic electroluminescent material with great stability.

  17. Chinese Jingdezhen blue and white imperial porcelain

    Institute of Scientific and Technical Information of China (English)

    WU; Juan; LI; Jiazhi; DENG; Zequn; WANG; Changsui

    2004-01-01

    Jingdezhen blue and white imperial porcelain specimens from the Yuan, Ming and Qing dynasties have been systematically analyzed using a nondestructive test method--?energy dispersive X-ray fluorescence analysis (EDXRF). The derived data of major and trace element compositions have been treated by correspondence analysis. The variation laws of the composition patterns for Jingdezhen blue and white imperial porcelain in different historical periods owing to the change in raw materials, recipe and technology have been discussed, and a time model related to variation of element composition has been preliminarily established, It would be helpful for scientific dating of Jingdezhen blue and white imperial porcelain, and even for the studies on the whole field of identification of ancient ceramics.

  18. On the conversion of neutron stars into quark stars

    CERN Document Server

    Pagliara, Giuseppe

    2013-01-01

    The possible existence of two families of compact stars, neutron stars and quark stars, naturally leads to a scenario in which a conversion process between the two stellar objects occurs with a consequent release of energy of the order of $10^{53}$ erg. We discuss recent hydrodynamical simulations of the burning process and neutrino diffusion simulations of cooling of a newly formed strange star. We also briefly discuss this scenario in connection with recent measurements of masses and radii of compact stars.

  19. Blurred Star Image Processing for Star Sensors under Dynamic Conditions

    OpenAIRE

    Lei Guo; Weina Zhang; Wei Quan

    2012-01-01

    The precision of star point location is significant to identify the star map and to acquire the aircraft attitude for star sensors. Under dynamic conditions, star images are not only corrupted by various noises, but also blurred due to the angular rate of the star sensor. According to different angular rates under dynamic conditions, a novel method is proposed in this article, which includes a denoising method based on adaptive wavelet threshold and a restoration method based on the large ang...

  20. Dance of the double stars

    Energy Technology Data Exchange (ETDEWEB)

    Theokas, A.

    1985-09-19

    The paper concerns pairs of stars orbiting one another. The evolutionary path model for close binary stars, involving a mass transfer of gases between the stars, is described. The life history of a single star; cataclysmic variables; the algol paradox, matter and lagranges' point; x-ray binaries and bursters; and pulsars; are all briefly discussed.

  1. Blue light inhibits proliferation of melanoma cells

    Science.gov (United States)

    Becker, Anja; Distler, Elisabeth; Klapczynski, Anna; Arpino, Fabiola; Kuch, Natalia; Simon-Keller, Katja; Sticht, Carsten; van Abeelen, Frank A.; Gretz, Norbert; Oversluizen, Gerrit

    2016-03-01

    Photobiomodulation with blue light is used for several treatment paradigms such as neonatal jaundice, psoriasis and back pain. However, little is known about possible side effects concerning melanoma cells in the skin. The aim of this study was to assess the safety of blue LED irradiation with respect to proliferation of melanoma cells. For that purpose we used the human malignant melanoma cell line SK-MEL28. Cell proliferation was decreased in blue light irradiated cells where the effect size depended on light irradiation dosage. Furthermore, with a repeated irradiation of the melanoma cells on two consecutive days the effect could be intensified. Fluorescence-activated cell sorting with Annexin V and Propidium iodide labeling did not show a higher number of dead cells after blue light irradiation compared to non-irradiated cells. Gene expression analysis revealed down-regulated genes in pathways connected to anti-inflammatory response, like B cell signaling and phagosome. Most prominent pathways with up-regulation of genes were cytochrome P450, steroid hormone biosynthesis. Furthermore, even though cells showed a decrease in proliferation, genes connected to the cell cycle were up-regulated after 24h. This result is concordant with XTT test 48h after irradiation, where irradiated cells showed the same proliferation as the no light negative control. In summary, proliferation of melanoma cells can be decreased using blue light irradiation. Nevertheless, the gene expression analysis has to be further evaluated and more studies, such as in-vivo experiments, are warranted to further assess the safety of blue light treatment.

  2. Binary Popldation Synthcsis Study

    Institute of Scientific and Technical Information of China (English)

    HAN Zhanwen

    2011-01-01

    Binary population synthesis (BPS), an approach to evolving millions of stars (including binaries) simultaneously, plays a crucial role in our understanding of stellar physics, the structure and evolution of galaxies, and cosmology. We proposed and developed a BPS approach, and used it to investigate the formation of many peculiar stars such as hot subdwarf stars, progenitors of type la supernovae, barium stars, CH stars, planetary nebulae, double white dwarfs, blue stragglers, contact binaries, etc. We also established an evolution population synthesis (EPS) model, the Yunnan Model, which takes into account binary interactions for the first time. We applied our model for the origin of hot subdwarf stars in the study of elliptical galaxies and explained their far-UV radiation.

  3. On Luminous Blue Variables as the Progenitors of Core-Collapse Supernovae, especially Type IIn Supernovae

    CERN Document Server

    Dwarkadas, Vikram V

    2010-01-01

    Luminous blue variable (LBV) stars are very massive, luminous, unstable stars that suffer frequent eruptions. In the last few years, these stars have been proposed as the direct progenitors of some core-collapse supernovae (SNe), particularly Type IIn SNe, in conflict with stellar evolution theory. In this paper we investigate various scenarios wherein LBV stars have been suggested as the immediate progenitors of SNe. Many of these suggestions stem from the fact that the SNe appear to be expanding in a high density medium, which has been interpreted as resulting from a wind with a high mass-loss rate. Others arise due to perceived similarities between the SN characteristics and those of LBVs. Only in the case of SN 2005gl do we find a valid possibility for an LBV-like progenitor. Other scenarios encounter various levels of difficulty. The evidence that points to LBVs as direct core-collapse SNe progenitors is far from convincing. High mass-loss rates are often deduced by making assumptions regarding the wind ...

  4. MN48: a new Galactic bona fide luminous blue variable revealed by Spitzer and SALT

    CERN Document Server

    Kniazev, A Y; Berdnikov, L N

    2016-01-01

    In this paper, we report the results of spectroscopic and photometric observations of the candidate evolved massive star MN48 disclosed via detection of a mid-infrared circular shell around it with the Spitzer Space Telescope. Follow-up optical spectroscopy of MN48 with the Southern African Large Telescope (SALT) carried out in 2011--2015 revealed significant changes in the spectrum of this star, which are typical of luminous blue variables (LBVs). The LBV status of MN48 was further supported by photometric monitoring which shows that in 2009--2011 this star has brightened by approx 0.9 and 1 mag in the V and I_c bands, respectively, then faded by approx 1.1 and 1.6 mag during the next four years, and apparently started to brighten again recently. The detected changes in the spectrum and brightness of MN48 make this star the 18th known Galactic bona fide LBV and increase the percentage of LBVs associated with circumstellar nebulae to more than 70 per cent. We discuss the possible birth place of MN48 and sugge...

  5. Luminous blue variables: An imaging perspective on their binarity and near environment

    CERN Document Server

    Martayan, Christophe; Baade, Dietrich; Mehner, Andrea; Rivinius, Thomas; Boffin, H M J; Girard, Julien; Mawet, Dimitri; Montagnier, Guillaume; Blomme, Ronny; Kervella, Pierre; Sana, Hugues; Štefl, Stanislav; Zorec, Juan; Lacour, Sylvestre; Bouquin, Jean-Baptiste Le; Martins, Fabrice; Mérand, Antoine; Patru, Fabien; Selman, Fernando; Frémat, Yves

    2016-01-01

    Context. Luminous blue variables (LBVs) are rare massive stars with very high luminosity. They are characterized by strong photo-metric and spectroscopic variability related to transient eruptions. The mechanisms at the origin of these eruptions is not well known. In addition, their formation is still problematic and the presence of a companion could help to explain how they form. Aims. This article presents a study of seven LBVs (about 20% of the known Galactic population), some Wolf-Rayet stars, and massive binaries. We probe the environments that surround these massive stars with near-, mid-, and far-infrared images, investigating potential nebula/shells and the companion stars. Methods. To investigate large spatial scales, we used seeing-limited and near diffraction-limited adaptive optics images to obtain a differential diagnostic on the presence of circumstellar matter and to determine their extent. From those images, we also looked for the presence of binary companions on a wide orbit. Once a companion...

  6. Photometric Monitoring of a New Sample of Candidate Luminous Blue Variables

    Science.gov (United States)

    Mauerhan, Jon; Van Dyk, Schuyler; Wachter, Stefanie

    2012-02-01

    Luminous Blue Variables (LBV) are evolved massive stars in transition from the main-sequence to the Wolf-Rayet phase. They are characterized by extreme luminosities, large photometric variations, and circumstellar nebulae. LBV variability is believed to be linked with the enigmatic processes driving recurrent outbursts of mass which liberate these stars of their hydrogen envelopes. Because of the small sample of 10 Galactic LBVs, progress toward understanding the physics of these processes has been very limited. Fortunately, the Spitzer/MIPSGAL survey revealed a population of ~100 circular nebulae surrounding bright central stars that are heavily obscured in the optical; we have determined that ~50 of them have spectral types similar to active LBVs, such as P Cyg and the Pistol Star. We suspect many of these are LBVs, and that their circumstellar shells are the result of recent mass eruptions. If they are active LBVs, we expect them to exhibit large-amplitude oscillations (~0.5-1 mag) on month-to-year timescales, and/or small eruptions (~1-2 mag) on year-to-decade timescales, like P Cyg and AG Car. Therefore we propose a SMARTS program to identify active LBVs within our sample of 43 candidates by monitoring their IR brightness with CT1.3+ANDICAM. Using an cadence of one month, we will probe for evidence of oscillations. Comparison with 2MASS will probe decade-long changes and potentially reveal evidence for eruptions.

  7. DISCOVERY OF A LUMINOUS BLUE VARIABLE WITH AN EJECTION NEBULA NEAR THE QUINTUPLET CLUSTER

    International Nuclear Information System (INIS)

    We report on the discovery of a luminous blue variable (LBV) lying ∼7 pc in projection from the Quintuplet cluster. This source, which we call LBV G0.120 - 0.048, was selected for spectroscopy owing to its detection as a strong source of Paschen-α (Pα) excess in a recent narrowband imaging survey of the Galactic center region with the Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectrometer. The K-band spectrum is similar to that of the Pistol Star and other known LBVs. The new LBV was previously cataloged as a photometric variable star, exhibiting brightness fluctuations of up to ∼1 mag between 1994 and 1997, with significant variability also occurring on month-to-month timescales. The luminosity of LBV G0.120 - 0.048, as derived from Two-Micron All Sky Survey photometry, is approximately equivalent to that of the Pistol Star. However, the time-averaged brightness of LBV G0.120 - 0.048 between 1994 and 1997 exceeded that of the Pistol Star; LBV G0.120 - 0.048 also suffers more extinction, which suggests that it was intrinsically more luminous in the infrared than the Pistol Star between 1994 and 1997. Pα images reveal a thin circular nebula centered on LBV G0.120 - 0.048 with a physical radius of ∼0.8 pc. We suggest that this nebula is a shell of ejected material launched from a discrete eruption that occurred between 5000 and 10,000 years ago. Because of the very short amount of time that evolved massive stars spend in the LBV phase, and the close proximity of LBV G0.120 - 0.048 to the Quintuplet cluster, we suggest that this object might be coeval with the cluster, and may have once resided within it.

  8. The chemical compositions of RR Lyrae type c variable stars

    Energy Technology Data Exchange (ETDEWEB)

    Govea, Jose; Gomez, Thomas; Sneden, Christopher [Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712 (United States); Preston, George W., E-mail: jgovea@utexas.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: iii@ociw.edu [The Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States)

    2014-02-20

    We present a detailed chemical abundance study of eight RR Lyrae variable stars of subclass c (RRc). The target RRc stars chosen for study exhibit 'Blazhko-effect' period and amplitude modulations to their pulsational cycles. Data for this study were gathered with the echelle spectrograph of the 100 inch du Pont telescope at Las Campanas Observatory. Spectra were obtained throughout each star's pulsation cycle. Atmospheric parameters—effective temperature, surface gravity, microturbulent velocity, and metallicity—were derived at multiple phase points. We found metallicities and element abundance ratios to be constant within observational uncertainties over the pulsational cycles of all stars. Moreover, the α-element and Fe-group abundance ratios with respect to iron are consistent with other horizontal-branch members (RRab, blue and red non-variables). Finally, we have used the [Fe/H] values of these eight RRc stars to anchor the metallicity estimates of a large-sample RRc snapshot spectroscopic study being conducted with the same telescope and instrument combination employed here.

  9. Superbursts from Strange Stars

    CERN Document Server

    Page, D; Page, Dany; Cumming, Andrew

    2005-01-01

    Recent models of carbon ignition on accreting neutron stars predict superburst ignition depths that are an order of magnitude larger than observed. We explore a possible solution to this problem, that the compact stars in low mass X-ray binaries that have shown superbursts are in fact strange stars with a crust of normal matter. We calculate the properties of superbursts on strange stars, and the resulting constraints on the properties of strange quark matter. We show that the observed ignition conditions exclude fast neutrino emission in the quark core, for example by the direct Urca process, which implies that strange quark matter at stellar densities should be in a color superconducting state. For slow neutrino emission in the quark matter core, we find that reproducing superburst properties requires a definite relation between three poorly constrained properties of strange quark matter: its thermal conductivity, its slow neutrino emissivity and the energy released by converting a nucleon into strange quar...

  10. Star-Planet Interactions

    CERN Document Server

    Shkolnik, Evgenya; Cranmer, Steven; Fares, Rim; Fridlund, Malcolm; Pont, Frederic; Schmitt, Juergen; Smith, Alexis; Suzuki, Takeru

    2008-01-01

    Much effort has been invested in recent years, both observationally and theoretically, to understand the interacting processes taking place in planetary systems consisting of a hot Jupiter orbiting its star within 10 stellar radii. Several independent studies have converged on the same scenario: that a short-period planet can induce activity on the photosphere and upper atmosphere of its host star. The growing body of evidence for such magnetic star-planet interactions includes a diverse array of photometric, spectroscopic and spectropolarimetric studies. The nature of which is modeled to be strongly affected by both the stellar and planetary magnetic fields, possibly influencing the magnetic activity of both bodies, as well as affecting irradiation and non-thermal and dynamical processes. Tidal interactions are responsible for the circularization of the planet orbit, for the synchronization of the planet rotation with the orbital period, and may also synchronize the outer convective envelope of the star with...

  11. Temperature of neutron stars

    Science.gov (United States)

    Tsuruta, Sachiko

    2016-07-01

    We start with a brief introduction to the historical background in the early pioneering days when the first neutron star thermal evolution calculations predicted the presence of neutron stars hot enough to be observable. We then report on the first detection of neutron star temperatures by ROSAT X-ray satellite, which vindicated the earlier prediction of hot neutron stars. We proceed to present subsequent developments, both in theory and observation, up to today. We then discuss the current status and the future prospect, which will offer useful insight to the understanding of basic properties of ultra-high density matter beyond the nuclear density, such as the possible presence of such exotic particles as pion condensates.

  12. Interferometric star tracker Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Optical Physics Company (OPC) proposes to develop a high accuracy version of its interferometric star tracker capable of meeting the milli-arcsecond-level pointing...

  13. Variable star data online

    Science.gov (United States)

    Pickard, Roger; Wilson, Andy; Poyner, Gary

    2012-06-01

    Roger Pickard, Andy Wilson and Gary Poyner describe the online database of the British Astronomical Association Variable Star Section, a treasure trove of observations stretching back nearly 125 years.

  14. White Dwarf Stars

    Science.gov (United States)

    Kawaler, Steven; Dahlstrom, Michael

    2000-12-01

    A white dwarf is a very dense star: The earth-sized remains of a Sun-like star that has burned all of its nuclear fuel. Although it's unable to carry out the workaday activities of a living star, a white dwarf is still an interesting object to astronomers. For one thing, white dwarfs experience "starquakes"—gentle pulsations that allow astronomers to deduce certain physical qualities of the star, such as its mass, rate of rotation, its structure and the strength of its magnetic field. The authors have been studying the starquakes with a global network of instruments, collectively called the Whole Earth Telescope, which provide around-the-clock observations of a white dwarf's seismic activity. Kawaler and Dahlstrom discuss what we know about white dwarfs and their significance for questions concerning the age of our Galaxy and the composition of dark matter.

  15. Sports Stars Shine

    Institute of Scientific and Technical Information of China (English)

    Yu Yan

    2012-01-01

    Alive and exciting award ceremony drew the attention of numerous Chinese households on the night of January 15.The most popular Chinese sports stars attended the 2011 CCTV Sports Personality Award Ceremony at the National Indoor Stadium in Beijing.

  16. Notes on Star Formation

    CERN Document Server

    Krumholz, Mark R

    2015-01-01

    This book provides an introduction to the field of star formation at a level suitable for graduate students or advanced undergraduates in astronomy or physics. The structure of the book is as follows. The first two chapters begin with a discussion of observational techniques, and the basic phenomenology they reveal. The goal is to familiarize students with the basic techniques that will be used throughout, and to provide a common vocabulary for the rest of the book. The next five chapters provide a similar review of the basic physical processes that are important for star formation. Again, the goal is to provide a basis for what follows. The remaining chapters discuss star formation over a variety of scales, starting with the galactic scale and working down to the scales of individual stars and their disks. The book concludes with a brief discussion of the clearing of disks and the transition to planet formation. The book includes five problem sets, complete with solutions.

  17. Worlds around other stars

    Science.gov (United States)

    Black, David C.

    1991-01-01

    The possible, though tentative, detection of planetary companions to other stars which may be capable of supporting life as we know it through the use of a new generation of detectors and telescopes, combined with some innovative detection techniques, is discussed. The current view of the origin of the solar system, based on the nebular hypothesis, is discussed as it pertains to the formation of how and where planets form and, hence, how and where to search for them. Both direct methods of search for other planetary systems, which involve detecting reflected light or infrared radiation form the planets themselves, and indirect methods, which involve the scrutinization of a star for signs that it is responding to the gravitational tug of an orbiting planet, are discussed at length. In particular, various methods for detecting minute velocity perturbations of stars are discussed. It is noted that the study of brown dwarfs may also provide clues on the formation of stars and planets.

  18. Change in NO2 reveals Parade Blue is cleaner than APEC Blue

    Science.gov (United States)

    Liu, Haoran; Liu, Cheng; Xie, Zhouqing; Xie, Pinhua; Xing, Chengzhi; Xu, Jin; Liu, Jianguo

    2016-04-01

    The spectacular Parade Blue (blue sky), and APEC Blue (blue sky) were renowned worldwide caused by the limiting discharge policy of the Chinese government. For evaluating the reduction of these two events, we analyzed the variation of NO2 columns Beijing by looking at a long-term monitoring using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) and the Ozone Monitoring Instrument (OMI) satellite observations from August 2014 to November 2015, covering Grand Military Parade (GMP, September 2015) and APEC (November 2014) period. We found that the NO2 columns abruptly decreased both GMP and APEC. However, change in the MAX-DOAS and the OMI NO2 during GMP was larger than during APEC via comparison with the same period in 2014, indicating Parade Blue is cleaner than APEC Blue. The spatial distribution of NO2 and backward trajectories together with meterological parameters suggested that GMP Blue may be due to the regional significant decreasing discharge in peripheral cities. No weekend effect during GMP further confirmed the role of controlling discharge. This study provides direct evidence that it is possible to clean air in China.

  19. Cooling compact stars and phase transitions in dense QCD

    CERN Document Server

    Sedrakian, Armen

    2015-01-01

    We report new simulations of cooling of compact stars containing quark cores and updated fits to the Cas A fast cooling data. Our model is built on the assumption that the transient behaviour of the star in Cas A is due to a phase transition within the dense QCD matter in the core of the star. Specifically, the fast cooling is attributed to an enhancement in the neutrino emission triggered by a transition from a fully gapped, two-flavor, red-green color-superconducting quark condensate to a superconducting crystalline or an alternative gapless, color-superconducting phase. The blue colored condensate is modeled as a Bardeen-Cooper-Schrieffer (BCS)-type color superconductor with spin-one pairing order parameter. We study the sensitivity of the fits to the phase transition temperature, the pairing gap of blue quarks and the time-scale characterizing the phase transition (the latter modelled in terms of a width parameter). Relative variations in these parameter around their best fit values larger than $10^{-3}$ ...

  20. Chaotic Star Birth

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives. The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region. The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333. In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.