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Sample records for carina dwarf spheroidal

  1. Flames High Resolution Spectroscopy of RGB Stars in the Carina Dwarf Spheroidal Galaxy

    NARCIS (Netherlands)

    Lemasle, B.; Hill, V.; Tolstoy, E.; Venn, K.

    2011-01-01

    Carina is a small and faint classical dwarf spheroidal galaxy in the halo of the Milky Way with a highly episodic star formation history (e.g., Hurley-Keller et al. 1998). Using VLT/FLAMES in high resolution mode, we significantly increase the sample of stars with abundance determinations in Carina,

  2. VLT/FLAMES spectroscopy of Red Giant Branch stars in the Carina dwarf spheroidal galaxy

    CERN Document Server

    Lemasle, B; Tolstoy, E; Venn, K A; Shetrone, M D; Irwin, M J; de Boer, T J L; Starkenburg, E; Salvadori, S

    2011-01-01

    The ages of individual Red Giant Branch stars (RGB) can range from 1 Gyr old to the age of the Universe, and it is believed that the abundances of most chemical elements in their photospheres remain unchanged with time (those that are not affected by the 1st dredge-up). This means that they trace the ISM in the galaxy at the time the star formed, and hence the chemical enrichment history of the galaxy. CMD analysis has shown the Carina dwarf spheroidal (dSph) to have had an unusually episodic star formation history (SFH) which is expected to be reflected in the abundances of different chemical elements. We use the VLT-FLAMES spectrograph in HR mode (R~20000) to measure the abundances of several chemical elements in a sample of 35 RGB stars in Carina. We also combine these abundances with photometry to derive age estimates for these stars. This allows us to determine which of two distinct star formation (SF) episodes the stars in our sample belong to, and thus to define the relationship between SF and chemical...

  3. A Comprehensive, Wide-Field Study of Pulsating Stars in the Carina Dwarf Spheroidal Galaxy

    OpenAIRE

    Vivas, A. Katherina; Mateo, Mario

    2013-01-01

    We report the detection of 388 pulsating variable stars (and some additional miscellaneous variables) in the Carina dSph galaxy over an area covering the full visible extent of the galaxy and extending a few times beyond its photometric (King) tidal radius along the direction of its major axis. Included in this total are 340 newly discovered dwarf Cepheids which are mostly located ~2.5 magnitudes below the horizontal branch and have very short periods (

  4. A Comprehensive, Wide-Field Study of Pulsating Stars in the Carina Dwarf Spheroidal Galaxy

    CERN Document Server

    Vivas, A Katherina

    2013-01-01

    We report the detection of 388 pulsating variable stars (and some additional miscellaneous variables) in the Carina dSph galaxy over an area covering the full visible extent of the galaxy and extending a few times beyond its photometric (King) tidal radius along the direction of its major axis. Included in this total are 340 newly discovered dwarf Cepheids which are mostly located ~2.5 magnitudes below the horizontal branch and have very short periods (<0.1 days) typical of their class and consistent with their location on the upper part of the extended main sequence of the younger populations of the galaxy. Several extra-tidal dwarf cepheids were found in our survey up to a distance of ~1 degree from the center of Carina. Our sample also includes RR Lyrae stars and anomalous Cepheids some of which were found outside the galaxy's tidal radius as well. This supports past works that suggests Carina is undergoing tidal disruption. We use the period-luminosity relationship for dwarf Cepheids to estimate a dist...

  5. A MegaCam Survey of Outer Halo Satellites. VI: The Spatially Resolved Star Formation History of the Carina Dwarf Spheroidal Galaxy

    CERN Document Server

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

    2016-01-01

    We present the spatially resolved star formation history (SFH) of the Carina dwarf spheroidal galaxy, obtained from deep, wide-field g,r imaging and a metallicity distribution from the literature. Our photometry covers $\\sim2$ deg$^2$, reaching up to $\\sim10$ times the half-light radius of Carina with a completeness higher than $50\\%$ at $g\\sim24.5$, 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 ($>10$ Gyr) and intermediate ($2$-$8$ Gyr) ages. Our measurements show that the old episode comprises the majority of the population, accounting for $54\\pm5\\%$ of the stellar mass within $1.3$ times the King tidal radius, while the total stellar mass derived for Carina is $1.60\\pm0.09\\tim...

  6. 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.

  7. Binary populations in Milky Way satellite galaxies: Constraints from multi-epoch data in the Carina, Fornax, Sculptor, and Sextans dwarf spheroidal galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Minor, Quinn E. [Department of Science, Borough of Manhattan Community College, City University of New York, New York, NY 10007 (United States); Department of Astrophysics, American Museum of Natural History, New York, NY 10024 (United States)

    2013-12-20

    We introduce a likelihood analysis of multi-epoch stellar line-of-sight velocities to constrain the binary fractions and binary period distributions of dwarf spheroidal galaxies. This method is applied to multi-epoch data from the Magellan/MMFS survey of the Carina, Fornax, Sculptor, and Sextans dSph galaxies, after applying a model for the measurement errors that accounts for binary orbital motion. We find that the Fornax, Sculptor, and Sextans dSphs are consistent with having binary populations similar to that of Milky Way field binaries to within 68% confidence limits, whereas the Carina dSph is remarkably deficient in binaries with periods less than ∼10 yr. If Carina is assumed to have a period distribution identical to that of the Milky Way field, its best-fit binary fraction is 0.14{sub −0.05}{sup +0.28}, and is constrained to be less than 0.5 at the 90% confidence level; thus it is unlikely to host a binary population identical to that of the Milky Way field. By contrast, the best-fit binary fraction of the combined sample of all four galaxies is 0.46{sub −0.09}{sup +0.13}, consistent with that of Milky Way field binaries. More generally, we infer probability distributions in binary fraction, mean orbital period, and dispersion of periods for each galaxy in the sample. Looking ahead to future surveys, we show that the allowed parameter space of binary fraction and period distribution parameters in dSphs will be narrowed significantly by a large multi-epoch survey. However, there is a degeneracy between the parameters that is unlikely to be broken unless the measurement error is of order ∼0.1 km s{sup –1} or smaller, presently attainable only by a high-resolution spectrograph.

  8. Manganese in dwarf spheroidal galaxies

    CERN Document Server

    North, P; Jablonka, P; Hill, V; Shetrone, M; Letarte, B; Lemasle, B; Venn, K A; Battaglia, G; Tolstoy, E; Irwin, M J; Primas, F; Francois, P

    2012-01-01

    We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other elements in these galaxies, including alpha and iron-peak ones, which allowed us to build [Mn/Fe] and [Mn/alpha] versus [Fe/H] diagrams. The Mn abundances imply sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]\\sim -1.8 and -1.4 and decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any significant way with [Fe/H]. The relation between [Mn/alpha] and [Fe/H] for the dSph galaxies is clearly systematically offset from that for the Milky Way, which reflects the different star formation histories of the respective galaxies. The [Mn/alpha] behavior can be interpreted as a result of the metal-dependent Mn yields of type II and ...

  9. Parametric Dwarf Spheroidal Tidal Interaction

    CERN Document Server

    Fleck, J J; Fleck, Jean-Julien; Kuhn, Jeff R.

    2003-01-01

    The time dependent tidal interaction of the Local Group Dwarf Spheroidal (dS) Galaxies with the Milky Way (MW) can fundamentally affect their dynamical properties. The model developed here extends earlier numerical descriptions of dS-MW tidal interactions. We explore the dynamical evolution of dS systems in circular or elliptical MW orbits in the framework of a parametric oscillator. An analytic model is developed and compared with more general numerical solutions and N-body simulation experiments.

  10. VLT/UVES abundances in four nearby dwarf spheroidal galaxies. I. Nucleosynthesis and abundance ratios

    NARCIS (Netherlands)

    Shetrone, M; Venn, KA; Tolstoy, E; Primas, F; Hill, [No Value; Kaufer, A

    2003-01-01

    We have used the Ultraviolet Echelle Spectrograph (UVES) on Kueyen (UT2) of the Very Large Telescope to take spectra of 15 individual red giants in the Sculptor, Fornax, Carina, and Leo I dwarf spheroidal galaxies (dSph's). We measure the abundances of alpha-, iron peak, first s-process, second s-pr

  11. VLT/UVES abundances in four nearby dwarf spheroidal galaxies. II. Implications for understanding galaxy evolution

    NARCIS (Netherlands)

    Tolstoy, E; Venn, KA; Shetrone, M; Primas, F; Hill, [No Value; Kaufer, A; Szeifert, T

    2003-01-01

    We have used the Ultraviolet Visual-Echelle Spectrograph (UVES) on Kueyen (UT2) of the Very Large Telescope to take spectra of 15 individual red giant stars in the centers of four nearby dwarf spheroidal galaxies (dSph's) : Sculptor, Fornax, Carina, and Leo I. We measure the abundance variations of

  12. VARIATIONS IN A UNIVERSAL DARK MATTER PROFILE FOR DWARF SPHEROIDALS

    Energy Technology Data Exchange (ETDEWEB)

    Jardel, John R.; Gebhardt, Karl, E-mail: jardel@astro.as.utexas.edu [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)

    2013-09-20

    Using a newly developed modeling technique, we present orbit-based dynamical models of the Carina, Draco, Fornax, Sculptor, and Sextans dwarf spheroidal (dSph) galaxies. These models calculate the dark matter profiles non-parametrically without requiring any assumptions to be made about their profile shapes. By lifting this restriction, we discover a host of dark matter profiles in the dSphs that are different from the typical profiles suggested by both theorists and observers. However, when we scale these profiles appropriately and plot them on a common axis, they appear to follow an approximate r {sup –1} power law with considerable scatter.

  13. Dwarf spheroidal galaxies keystones of galaxy evolution

    CERN Document Server

    Gallagher, S C; Gallagher, S; Wyse, F G

    1994-01-01

    Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

  14. NUCLEOSYNTHESIS AND THE INHOMOGENEOUS CHEMICAL EVOLUTION OF THE CARINA DWARF GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Venn, Kim A.; Divell, Mike [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1 (Canada); Shetrone, Matthew D. [McDonald Observatory, University of Texas at Austin, HC75 Box 1337-McD, Fort Davis, TX 79734 (United States); Irwin, Mike J. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB03 0HA (United Kingdom); Hill, Vanessa [Laboratoire Cassiopee UMR 6202, Universite de Nice Sophia-Antipolis, CNRS, Observatoire de la Cote d' Azur (France); Jablonka, Pascale [GEPI, Observatoire de Paris, CNRS UMR 8111, Universite Paris Diderot, F-92125, Meudon, Cedex (France); Tolstoy, Eline; Lemasle, Bertrand; Starkenburg, Else; Helmi, Amina [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen (Netherlands); Letarte, Bruno [South African Astronomical Observatory, Observatory Road, 7935 Observatory (South Africa); Baldner, Charles [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Battaglia, Giuseppina; Primas, Francesca [European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching (Germany); Kaufer, Andreas, E-mail: kvenn@uvic.ca [European Southern Observatory, Alonso de Cordova 3107, Santiago (Chile)

    2012-06-01

    The detailed abundances of 23 chemical elements in nine bright red giant branch stars in the Carina dwarf spheroidal galaxy are presented based on high-resolution spectra gathered at the Very Large Telescope (VLT) and Magellan telescopes. A spherical model atmospheres analysis is applied using standard methods (local thermodynamic equilibrium and plane-parallel radiative transfer) to spectra ranging from 380 to 680 nm. Stellar parameters are found to be consistent between photometric and spectroscopic analyses, both at moderate and high resolution. The stars in this analysis range in metallicity from -2.9 < [Fe/H] <-1.3, and adopting the ages determined by Lemasle et al., we are able to examine the chemical evolution of Carina's old and intermediate-aged populations. One of the main results from this work is the evidence for inhomogeneous mixing in Carina and therefore for a poor statistical sampling of the supernova contributions when forming stars; a large dispersion in [Mg/Fe] indicates poor mixing in the old population, an offset in the [{alpha}/Fe] ratios between the old and intermediate-aged populations (when examined with previously published results) suggests that the second star formation event occurred in {alpha}-enriched gas, and one star, Car-612, seems to have formed in a pocket enhanced in SN Ia/II products. This latter star provides the first direct link between the formation of stars with enhanced SN Ia/II ratios in dwarf galaxies to those found in the outer Galactic halo (Ivans et al.). Another important result is the potential evidence for SN II driven winds. We show that the very metal-poor stars in Carina have not been enhanced in asymptotic giant branch or SN Ia products, and therefore their very low ratios of [Sr/Ba] suggests the loss of contributions from the early SNe II. Low ratios of [Na/Fe], [Mn/Fe], and [Cr/Fe] in two of these stars support this scenario, with additional evidence from the low [Zn/Fe] upper limit for one star. It is

  15. Blue straggler stars in dwarf spheroidal galaxies

    NARCIS (Netherlands)

    Mapelli, M.; Ripamonti, E.; Tolstoy, E.; Sigurdsson, S.; Irwin, M. J.; Battaglia, G.

    2007-01-01

    Blue straggler star (BSS) candidates have been observed in all old dwarf spheroidal galaxies (dSphs), however whether or not they are authentic BSSs or young stars has been a point of debate. To both address this issue and obtain a better understanding of the formation of BSSs in different environme

  16. Pulsar searches in nearby dwarf spheroidal galaxies

    Science.gov (United States)

    Rubio-Herrera, Eduardo; Maccarone, Thomas

    2013-03-01

    We have been undertaking a comprehensive survey for pulsars and fast radio transients in the dwarf spheroidal satellite galaxies of the Milky Way using the Green Bank Radio Telescope operating at a central frequency of 350 MHz. Our search pipeline allows the detection of periodical signals and single dispersed pulses and it is optimized to search for millisecond radio pulsars. Here we present preliminary results of the searches we have conducted in the Ursa Minoris, Draco and Leo I dwarf spheroidal satellite galaxies. Our searches have revealed no periodic signals but a few unconfirmed millisecond single pulses at various dispersion measures, possibly related to neutron stars. Detecting neutron stars in these systems can potentially help to test the existence of haloes of dark matter surrounding these systems as predicted by Dehnen & King (2006).

  17. Tidal debris of dwarf spheroidals as a probe of structure formation models

    CERN Document Server

    Mayer, L; Quinn, T; Governato, F; Stadel, J; Mayer, Lucio; Moore, Ben; Quinn, Thomas; Governato, Fabio; Stadel, Joachim

    2002-01-01

    Recent observations suggest that Carina and other nearby dwarf spheroidal galaxies are surrounded by unbound stars tidally stripped by the Milky Way. We run high-resolution N-Body simulations of dwarf galaxies orbiting within the Milky Way halo to determine if such observations can be explained with dark matter potentials as those implied by current structure formation models. We show that tidal forces acting on dwarfs with constant density cores or with cuspy profiles having a low concentration parameter ($c < 5$) lead to flat outer stellar density profiles like that of Carina for a variety of orbital configurations. On the contrary, it is more difficult to remove stars from cuspy dark matter halos with concentrations as high as predicted by CDM models at the mass scale of dwarf galaxies ($c \\simgt 10$) and the data can only be reproduced assuming nearly radial orbits. Our simulations show that Carina is losing mass at a fractional rate $< 0.1$ Gyr$^{-1}$ and its mass-to-light ratio could be inflated b...

  18. UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Tolstoy, Eline; Venn, Kim; Shetrone, Matt; Primas, Francesca; Hill, Vanessa; Kaufer, Andreas; Szeifert, Thomas

    2002-07-01

    It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I & Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for

  19. Impact of axisymmetric mass models for dwarf spheroidal galaxies on indirect dark matter searches

    CERN Document Server

    Klop, Niki; Hayashi, Kohei; Ando, Shin'ichiro

    2016-01-01

    Dwarf spheroidals are low-luminosity satellite galaxies of the Milky Way highly dominated by dark matter. Therefore, they are prime targets to search for signals from dark matter annihilation using gamma-ray observations. We analyse about 7 years of PASS8 Fermi data for seven classical dwarf galaxies, including Draco, adopting both the widely used Navarro-Frenk-White (NFW) profile and observationally motivated axisymmetric density profiles. For four of the selected dwarfs (Sextans, Carina, Sculptor and Fornax) axisymmetric mass models suggest a cored density profile rather than the commonly adopted cusped profile. We found that upper limits on the annihilation cross section for some of these dwarfs are significantly higher than the ones achieved using an NFW profile. Therefore, upper limits in the literature obtained using cusped profiles like the NFW might have been overestimated. Our results eventually show that it is extremely important to use observationally motivated density profiles going beyond the usu...

  20. The effect of gravitational tides on dwarf spheroidal galaxies

    CERN Document Server

    Nichols, Matthew; Jablonka, Pascale

    2014-01-01

    The effect of the local environment on the evolution of dwarf spheroidal galaxies is poorly understood. We have undertaken a suite of simulations to investigate the tidal impact of the Milky Way on the chemodynamical evolution of dwarf spheroidals that resemble present day classical dwarfs using the SPH code GEAR. After simulating the models through a large parameter space of potential orbits the resulting properties are compared with observations from both a dynamical point of view, but also from the, often neglected, chemical point of view. In general, we find that tidal effects quench the star formation even inside gas-endowed dwarfs. Such quenching, may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations. We also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii. The model dwarfs also shift to higher $\\langle$[Fe/H]$\\rangle$/L ratios, but only when losing $>$$20...

  1. Wave Dark Matter and Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Parry, Alan R.

    We explore a model of dark matter called wave dark matter (also known as scalar field dark matter and boson stars) which has recently been motivated by a new geometric perspective by Bray. Wave dark matter describes dark matter as a scalar field which satisfies the Einstein-Klein-Gordon equations. These equations rely on a fundamental constant Upsilon (also known as the "mass term'' of the Klein-Gordon equation). Specifically, in this dissertation, we study spherically symmetric wave dark matter and compare these results with observations of dwarf spheroidal galaxies as a first attempt to compare the implications of the theory of wave dark matter with actual observations of dark matter. This includes finding a first estimate of the fundamental constant Upsilon. In the introductory Chapter 1, we present some preliminary background material to define and motivate the study of wave dark matter and describe some of the properties of dwarf spheroidal galaxies. In Chapter 2, we present several different ways of describing a spherically symmetric spacetime and the resulting metrics. We then focus our discussion on an especially useful form of the metric of a spherically symmetric spacetime in polar-areal coordinates and its properties. In particular, we show how the metric component functions chosen are extremely compatible with notions in Newtonian mechanics. We also show the monotonicity of the Hawking mass in these coordinates. Finally, we discuss how these coordinates and the metric can be used to solve the spherically symmetric Einstein-Klein-Gordon equations. In Chapter 3, we explore spherically symmetric solutions to the Einstein-Klein-Gordon equations, the defining equations of wave dark matter, where the scalar field is of the form f(t, r) = eiotF(r) for some constant o ∈ R and complex-valued function F(r). We show that the corresponding metric is static if and only if F( r) = h(r)eia for some constant alpha ∈ R and real-valued function h(r). We describe the

  2. The cold dark matter content of Galactic dwarf spheroidals: no cores, no failures, no problem

    CERN Document Server

    Fattahi, Azadeh; Sawala, Till; Frenk, Carlos S; Sales, Laura V; Oman, Kyle; Schaller, Matthieu; Wang, Jie

    2016-01-01

    We examine the dark matter content of satellite galaxies in Lambda-CDM cosmological hydrodynamical simulations of the Local Group from the APOSTLE project. We find excellent agreement between simulation results and estimates for the 9 brightest Galactic dwarf spheroidals (dSphs) derived from their stellar velocity dispersions and half-light radii. Tidal stripping plays an important role by gradually removing dark matter from the outside in, affecting in particular fainter satellites and systems of larger-than-average size for their luminosity. Our models suggest that tides have significantly reduced the dark matter content of Can Ven I, Sextans, Carina, and Fornax, a prediction that may be tested by comparing them with field galaxies of matching luminosity and size. Uncertainties in observational estimates of the dark matter content of individual dwarfs have been underestimated in the past, at times substantially. We use our improved estimates to revisit the `too-big-to-fail' problem highlighted in earlier N-...

  3. Testing Modified Gravity with Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Haghi, Hosein; Amiri, Vahid

    2016-08-01

    The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light (M★/L) ratios in the range of about 10 to more than 100 solar units, that are well outside the acceptable limit predicted by stellar population synthesis (SPS) models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion (σ _ph {los}) of stars in eight MW dSphs in the context of the Modified Gravity (MOG) theory of Moffat, assuming a constant M★/L ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters α and μ of the theory to be constant as has already been inferred from fitting to the observed rotational data of the THINGS catalog of galaxies. We find that the derived M★/L ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of the dSph with reasonable M★/L values we must vary α and μ on a case by case basis. A common pair of values cannot be found for all dSphs. Comparing with the values found from rotation curve fitting, it appears that μ correlates strongly with galaxy luminosity, shedding doubt on it as a universal constant.

  4. Testing modified gravity with dwarf spheroidal galaxies

    CERN Document Server

    Haghi, Hosein

    2016-01-01

    The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light ($M_*/L$) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion ($\\sigma_{\\emph{los}}$) of stars in eight MW dSphs in the context of the modified gravity (MOG) theory of Moffat, assuming a constant $M_*/L$ ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters $ \\alpha $ and $ \\mu $ of the theory to be constant as has already been inferred from fitting to the observed rotational data of The HI Nearby Galaxy Survey catalogue of galaxies. We find that the derived $M_*/L$ ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of ...

  5. Testing modified gravity with dwarf spheroidal galaxies

    Science.gov (United States)

    Haghi, Hosein; Amiri, Vahid

    2016-12-01

    The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light (M*/L) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion (σlos) of stars in eight MW dSphs in the context of the modified gravity (MOG) theory of Moffat, assuming a constant M*/L ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters α and μ of the theory to be constant as has already been inferred from fitting to the observed rotational data of The H I Nearby Galaxy Survey catalogue of galaxies. We find that the derived M*/L ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of the dSph with reasonable M*/L values, we must vary α and μ on a case by case basis. A common pair of values cannot be found for all dSphs. Comparing with the values found from rotation curve fitting, it appears that μ correlates strongly with galaxy luminosity, shedding doubt on it as a universal constant.

  6. Life and times of dwarf spheroidal galaxies

    CERN Document Server

    Salvadori, S; Schneider, R

    2008-01-01

    We propose a cosmological scenario for the formation and evolution of dwarf spheroidal galaxies (dSphs), satellites of the Milky Way (MW). An improved version of the semi-analytical code GAMETE (GAlaxy Merger Tree & Evolution) is used to follow the dSphs evolution simultaneously with the MW formation, matching the observed properties of both. In this scenario dSph galaxies represent fossil objects virializing at z = 7.2 +/- 0.7 (i.e. in the pre-reionization era z > z_rei = 6) in the MW environment, which at that epoch has already been pre-enriched up to [Fe/H] ~ -3; their dynamical masses are in the narrow range M = (1.6 +/- 0.7) x 10^8 M_sun, although a larger spread might be introduced by a more refined treatment of reionization. Mechanical feedback effects are dramatic in such low-mass objects, causing the complete blow-away of the gas ~100 Myr after the formation epoch: 99% of the present-day stellar mass, M_* = (3 +/- 0.7) x 10^6 M_sun, forms during this evolutionary phase, i.e. their age is >13 Gyr....

  7. Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Skúladóttir, Ása

    2016-01-01

    The Sculptor dwarf spheroidal galaxy is a Milky Way satellite with predominantly old stellar population, and therefore the ideal target to study early chemical evolution. The chemical abundances of photospheres of stars reveal the composition of their birth environment; studying stars of different a

  8. The mass content of the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Battaglia, G.; Helmi, A.; Tolstoy, E.; Irwin, M.; Andersen, J; BlandHawthorn, J; Nordstrom, B

    2009-01-01

    We present a new determination of the mass content of the Sculptor dwarf spheroidal galaxy, based on a novel approach which takes into account the two distinct stellar populations present in this galaxy. This method helps to partially break the well-known mass-anisotropy degeneracy present in the mo

  9. Search for dark matter annihilation signatures in H.E.S.S. observations of Dwarf Spheroidal Galaxies

    CERN Document Server

    :,; Aharonian, F; Benkhali, F Ait; Akhperjanian, A G; Angüner, E; Backes, M; Balenderan, S; Balzer, A; Barnacka, A; Becherini, Y; Tjus, J Becker; Berge, D; Bernhard, S; Bernlöhr, K; Birsin, E; Biteau, J; Böttcher, M; Boisson, C; Bolmont, J; Bordas, P; Bregeon, J; Brun, F; Brun, P; Bryan, M; Bulik, T; Carrigan, S; Casanova, S; Chadwick, P M; Chakraborty, N; Chalme-Calvet, R; Chaves, R C G; Chrétien, M; Colafrancesco, S; Cologna, G; Conrad, J; Couturier, C; Cui, Y; Dalton, M; Davids, I D; Degrange, B; Deil, C; deWilt, P; Djannati-Ata\\"ı, A; Domainko, W; Donath, A; Drury, L O'C; Dubus, G; Dutson, K; Dyks, J; Dyrda, M; Edwards, T; Egberts, K; Eger, P; Espigat, P; Farnier, C; Fegan, S; Feinstein, F; Fernandes, M V; Fernandez, D; Fiasson, A; Fontaine, G; Förster, A; Füßling, M; Gabici, S; Gajdus, M; Gallant, Y A; Garrigoux, T; Giavitto, G; Giebels, B; Glicenstein, J F; Gottschall, D; Goudelis, A; Grondin, M -H; Grudzińska, M; Hadsch, D; Häffner, S; Hahn, J; Harris, J; Heinzelmann, G; Henri, G; Hermann, G; Hervet, O; Hillert, A; Hinton, J A; Hofmann, W; Hofverberg, P; Holler, M; Horns, D; Ivascenko, A; Jacholkowska, A; Jahn, C; Jamrozy, M; Janiak, M; Jankowsky, F; Jung, I; Kastendieck, M A; Katarzyński, K; Katz, U; Kaufmann, S; Khélifi, B; Kieffer, M; Klepser, S; Klochkov, D; Kluźniak, W; Kolitzus, D; Komin, Nu; Kosack, K; Krakau, S; Krayzel, F; Krüger, P P; Laffon, H; Lamanna, G; Lefaucheur, J; Lefranc, V; Lemiére, A; Lemoine-Goumard, M; Lenain, J -P; Lohse, T; Lopatin, A; Lu, C -C; Marandon, V; Marcowith, A; Marx, R; Maurin, G; Maxted, N; Mayer, M; McComb, T J L; Méhault, J; Meintjes, P J; Menzler, U; Meyer, M; Mitchell, A M W; Moderski, R; Mohamed, M; Morå, K; Moulin, E; Murach, T; de Naurois, M; Niemiec, J; Nolan, S J; Oakes, L; Odaka, H; Ohm, S; Opitz, B; Ostrowski, M; Oya, I; Panter, M; Parsons, R D; Arribas, M Paz; Pekeur, N W; Pelletier, G; Perez, J; Petrucci, P -O; Peyaud, B; Pita, S; Poon, H; Pühlhofer, G; Punch, M; Quirrenbach, A; Raab, S; Reichardt, I; Reimer, A; Reimer, O; Renaud, M; Reyes, R de los; Rieger, F; Rob, L; Romoli, C; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Sahakian, V; Salek, D; Sanchez, D A; Santangelo, A; Schlickeiser, R; Schüssler, F; Schulz, A; Schwanke, U; Schwarzburg, S; Schwemmer, S; Serpico, P; Sol, H; Spanier, F; Spengler, G; Spieß, F; Stawarz, L; Steenkamp, R; Stegmann, C; Stinzing, F; Stycz, K; Sushch, I; Tavernet, J -P; Tavernier, T; Taylor, A M; Terrier, R; Tluczykont, M; Trichard, C; Valerius, K; van Eldik, C; van Soelen, B; Vasileiadis, G; Veh, J; Venter, C; Viana, A; Vincent, P; Vink, J; Völk, H J; Volpe, F; Vorster, M; Vuillaume, T; Wagner, S J; Wagner, P; Wagner, R M; Ward, M; Weidinger, M; Weitzel, Q; White, R; Wierzcholska, A; Willmann, P; Wörnlein, A; Wouters, D; Yang, R; Zabalza, V; Zaborov, D; Zacharias, M; Zdziarski, A A; Zech, A; Zechlin, H -S

    2014-01-01

    Dwarf spheroidal galaxies of the Local Group are close satellites of the Milky Way characterized by a large mass-to-light ratio and are not expected to be the site of non-thermal high-energy gamma-ray emission or intense star formation. Therefore they are amongst the most promising candidates for indirect dark matter searches. During the last years the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes observed five of these dwarf galaxies for more than 140 hours in total, searching for TeV gamma-ray emission from annihilation of dark matter particles. The new results of the deep exposure of the Sagittarius dwarf spheroidal galaxy, the first observations of the Coma Berenices and Fornax dwarves and the re-analysis of two more dwarf spheroidal galaxies already published by the H.E.S.S. Collaboration, Carina and Sculptor, are presented. In the absence of a significant signal new constraints on the annihilation cross-section applicable to Weakly Interacting Massive Particles (...

  10. H.E.S.S. constraints on Dark Matter annihilations towards the Sculptor and Carina Dwarf Galaxies

    CERN Document Server

    Abramowski, A; Aharonian, F; Akhperjanian, A G; Anton, G; Barnacka, A; de Almeida, U Barres; Bazer-Bachi, A R; Becherini, Y; Becker, J; Behera, B; Bernlöhr, K; Bochow, A; Boisson, C; Bolmont, J; Bordas, P; Borrel, V; Brucker, J; Brun, F; Brun, P; Bulik, T; Büsching, I; Carrigan, S; Casanova, S; Cerruti, M; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Chounet, L -M; Clapson, A C; Coignet, G; Conrad, J; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubois, F; Dubus, G; Dyks, J; Dyrda, M; Egberts, K; Eger, P; Espigat, P; Fallon, L; Farnier, C; Fegan, S; Feinstein, F; Fernandes, M V; Fiasson, A; Frster, A; Fontaine, G; Füßling, M; Gallant, Y A; Gast, H; Gérard, L; Gerbig, D; Giebels, B; Glicenstein, J F; Glück, B; Goret, P; Göring, D; Hague, J D; Hampf, D; Hauser, M; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Hofverberg, P; Horns, D; Jacholkowska, A; de Jager, O C; Jahn, C; Jamrozy, M; Jung, I; Kastendieck, M A; Katarzyński, K; Katz, U; Kaufmann, S; Keogh, D; Kerschhaggl, M; Khangulyan, D; Khélifi, B; Klochkov, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Kossakowski, R; Laffon, H; Lamanna, G; Lennarz, D; Lohse, T; Lopatin, A; Lu, C -C; Marandon, V; Marcowith, A; Masbou, J; Maurin, D; Maxted, N; McComb, T J L; Medina, M C; Méhault, J; Moderski, R; Moulin, E; Naumann, C L; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nguyen, N; Nicholas, B; Niemiec, J; Nolan, S J; Ohm, S; Olive, J-F; Wilhelmi, E de Oña; Opitz, B; Ostrowski, M; Panter, M; Arribas, M Paz; Pedaletti1, G; Pelletier, G; Petrucci, P -O; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raue, M; Rayner, S M; Reimer, A; Reimer, O; Renaud, M; Reyes, R de los; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Ruppel, J; Ryde, F; Sahakian, V; Santangelo, A; Schlickeiser, R; Schöck, F M; Schönwald, A; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sikora, M; Skilton, J L; Sol, H; Spengler, G; Stawarz, Ł; Steenkamp, R; Stegmann, C; Stinzing, F; Sushch, I; Szostek, A; Tavernet, J -P; Terrier, R; Tibolla, O; Tluczykont, M; Valerius, K; van Eldik, C; Vasileiadis, G; Venter, C; Vialle, J P; Viana, A; Vincent, P; Vivier, M; Völk, H J; Volpe, F; Vorobiov, S; Vorster, M; Wagner, S J; Ward, M; Wierzcholska, A; Zajczyk, A; Zdziarski, A A; Zech, A; Zechlin, H -S; 10.1016/j.astropartphys.2010.12.006

    2010-01-01

    The Sculptor and Carina Dwarf spheroidal galaxies were observed with the H.E.S.S. Cherenkov telescope array between January 2008 and December 2009. The data sets consist of a total of 11.8 and 14.8 hours of high quality data, respectively. No gamma-ray signal was detected at the nominal positions of these galaxies above 220 GeV and 320 GeV, respectively. Upper limits on the gamma-ray fluxes at 95% C.L. assuming two forms for the spectral energy distribution (a power law shape and one derived from dark matter annihilation) are obtained at the level of 10^-13 to 10^-12 cm^-2s^-1 in the TeV range. Constraints on the velocity weighted dark matter particle annihilation cross section for both Sculptor and Carina dwarf galaxies range from ~ 10^-21 cm^3s^-1 down to ~ 10^-22 cm^3s^-1 depending on the dark matter halo model used. Possible enhancements of the gamma-ray flux are studied: the Sommerfeld effect, which is found to exclude some dark matter particle masses, the internal Bremsstrahlung and clumps in the dark...

  11. H.E.S.S. constraints on dark matter annihilations towards the sculptor and carina dwarf galaxies

    Science.gov (United States)

    H.E.S.S. Collaboration; Abramowski, A.; Acero, F.; Aharonian, F.; Akhperjanian, A. G.; Anton, G.; Barnacka, A.; Barres de Almeida, U.; Bazer-Bachi, A. R.; Becherini, Y.; Becker, J.; Behera, B.; Bernlöhr, K.; Bochow, A.; Boisson, C.; Bolmont, J.; Bordas, P.; Borrel, V.; Brucker, J.; Brun, F.; Brun, P.; Bulik, T.; Büsching, I.; Carrigan, S.; Casanova, S.; Cerruti, M.; Chadwick, P. M.; Charbonnier, A.; Chaves, R. C. G.; Cheesebrough, A.; Chounet, L.-M.; Clapson, A. C.; Coignet, G.; Conrad, J.; Dalton, M.; Daniel, M. K.; Davids, I. D.; Degrange, B.; Deil, C.; Dickinson, H. J.; Djannati-Ataï, A.; Domainko, W.; Drury, L. O. C.; Dubois, F.; Dubus, G.; Dyks, J.; Dyrda, M.; Egberts, K.; Eger, P.; Espigat, P.; Fallon, L.; Farnier, C.; Fegan, S.; Feinstein, F.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Füßling, M.; Gallant, Y. A.; Gast, H.; Gérard, L.; Gerbig, D.; Giebels, B.; Glicenstein, J. F.; Glück, B.; Goret, P.; Göring, D.; Hague, J. D.; Hampf, D.; Hauser, M.; Heinz, S.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hoffmann, A.; Hofmann, W.; Hofverberg, P.; Horns, D.; Jacholkowska, A.; de Jager, O. C.; Jahn, C.; Jamrozy, M.; Jung, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kaufmann, S.; Keogh, D.; Kerschhaggl, M.; Khangulyan, D.; Khélifi, B.; Klochkov, D.; Kluźniak, W.; Kneiske, T.; Komin, Nu.; Kosack, K.; Kossakowski, R.; Laffon, H.; Lamanna, G.; Lennarz, D.; Lohse, T.; Lopatin, A.; Lu, C.-C.; Marandon, V.; Marcowith, A.; Masbou, J.; Maurin, D.; Maxted, N.; McComb, T. J. L.; Medina, M. C.; Méhault, J.; Moderski, R.; Moulin, E.; Naumann, C. L.; Naumann-Godo, M.; de Naurois, M.; Nedbal, D.; Nekrassov, D.; Nguyen, N.; Nicholas, B.; Niemiec, J.; Nolan, S. J.; Ohm, S.; Olive, J.-F.; de Oña Wilhelmi, E.; Opitz, B.; Ostrowski, M.; Panter, M.; Paz Arribas, M.; Pedaletti, G.; Pelletier, G.; Petrucci, P.-O.; Pita, S.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raue, M.; Rayner, S. M.; Reimer, A.; Reimer, O.; Renaud, M.; de Los Reyes, R.; Rieger, F.; Ripken, J.; Rob, L.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Ruppel, J.; Ryde, F.; Sahakian, V.; Santangelo, A.; Schlickeiser, R.; Schöck, F. M.; Schönwald, A.; Schwanke, U.; Schwarzburg, S.; Schwemmer, S.; Shalchi, A.; Sikora, M.; Skilton, J. L.; Sol, H.; Spengler, G.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Sushch, I.; Szostek, A.; Tavernet, J.-P.; Terrier, R.; Tibolla, O.; Tluczykont, M.; Valerius, K.; van Eldik, C.; Vasileiadis, G.; Venter, C.; Vialle, J. P.; Viana, A.; Vincent, P.; Vivier, M.; Völk, H. J.; Volpe, F.; Vorobiov, S.; Vorster, M.; Wagner, S. J.; Ward, M.; Wierzcholska, A.; Zajczyk, A.; Zdziarski, A. A.; Zech, A.; Zechlin, H.-S.; H.E.S.S. Collaboration

    2011-03-01

    The Sculptor and Carina dwarf spheroidal galaxies were observed with the H.E.S.S. Cherenkov telescope array between January 2008 and December 2009. The data sets consist of a total of 11.8 h and 14.8 h of high quality data, respectively. No gamma-ray signal was detected at the nominal positions of these galaxies above 220 GeV and 320 GeV, respectively. Upper limits on the gamma-ray fluxes at 95% CL assuming two forms for the spectral energy distribution (a power law shape and one derived from dark matter annihilation) are obtained at the level of 10-13-10-12 cm-2 s-1 in the TeV range. Constraints on the velocity weighted dark matter particle annihilation cross section for both Sculptor and Carina dwarf galaxies range from ˜ 10-21 cm3 s-1 down to ˜ 10-22 cm3 s-1 depending on the dark matter halo model used. Possible enhancements of the gamma-ray flux are studied: the Sommerfeld effect, which is found to exclude some dark matter particle masses, the internal Bremsstrahlung and clumps in the dark-matter halo distributions.

  12. Dwarf spheroidal galaxies and Bose-Einstein condensate dark matter

    CERN Document Server

    Diez-Tejedor, Alberto; Profumo, Stefano

    2014-01-01

    We constrain the parameters of a self-interacting massive dark matter scalar particle in a condensate using the kinematics of the eight brightest dwarf spheroidal satellites of the Milky Way. For the case of an attractive self-interaction the condensate develops a mass density profile with a characteristic scale radius that is closely related to the fundamental parameters of the theory. We find that the velocity dispersion of dwarf spheroidal galaxies suggests a scale radius of the order of 1 kpc, in tension with previous results found using the rotational curve of low-surface-brightness and dwarf galaxies. We discuss the implications of our findings for the particle dark matter model and argue that a single classical coherent state cannot play, in general, a relevant role for the description of dark matter in galaxies.

  13. A VIRIAL CORE IN THE SCULPTOR DWARF SPHEROIDAL GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Agnello, A.; Evans, N. W., E-mail: aagnello@ast.cam.ac.uk, E-mail: nwe@ast.cam.ac.uk [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)

    2012-08-01

    The projected virial theorem is applied to the case of multiple stellar populations in the nearby dwarf spheroidal galaxies. As each population must reside in the same gravitational potential, this provides strong constraints on the nature of the dark matter halo. We derive necessary conditions for two populations with Plummer or exponential surface brightnesses to reside in a cusped Navarro-Frenk-White (NFW) halo. We apply our methods to the Sculptor dwarf spheroidal, and show that there is no NFW halo compatible with the energetics of the two populations. The dark halo must possess a core radius of {approx}120 pc for the virial solutions for the two populations to be consistent. This conclusion remains true, even if the effects of flattening or self-gravity of the stellar populations are included.

  14. A low pre-infall mass for the Carina dwarf galaxy from disequilibrium modelling

    CERN Document Server

    Ural, Uğur; Read, Justin I; Walker, Matthew G

    2015-01-01

    Dark matter only simulations of galaxy formation predict many more subhalos around a Milky Way like galaxy than the number of observed satellites. Proposed solutions require the satellites to inhabit dark matter halos with masses between one to ten billion solar masses at the time they fell into the Milky Way. Here we use a modelling approach, independent of cosmological simulations, to obtain a preinfall mass of 360 (+380,-230) million solar masses for one of the Milky Way's satellites: Carina. This determination of a low halo mass for Carina can be accommodated within the standard model only if galaxy formation becomes stochastic in halos below ten billion solar masses. Otherwise Carina, the eighth most luminous Milky Way dwarf, would be expected to inhabit a significantly more massive halo. The implication of this is that a population of "dark dwarfs" should orbit the Milky Way: halos devoid of stars and yet more massive than many of their visible counterparts.

  15. VERITAS Deep Observations of the Dwarf Spheroidal Galaxy Segue 1

    CERN Document Server

    Aliu, E; Arlen, T; Aune, T; Beilicke, M; Benbow, W; Bouvier, A; Bradbury, S M; Buckley, J H; Bugaev, V; Byrum, K; Cannon, A; Cesarini, A; Christiansen, J L; Ciupik, L; Collins-Hughes, E; Connolly, M P; Cui, W; Decerprit, G; Dickherber, R; Dumm, J; Errando, M; Falcone, A; Feng, Q; Ferrer, F; Finley, J P; Finnegan, G; Fortson, L; Furniss, A; Galante, N; Gall, D; Godambe, S; Griffin, S; Grube, J; Gyuk, G; Hanna, D; Holder, J; Huan, H; Hughes, G; Humensky, T B; Kaaret, P; Karlsson, N; Kertzman, M; Khassen, Y; Kieda, D; Krawczynski, H; Krennrich, F; Lee, K; Madhavan, A S; Maier, G; Majumdar, P; McArthur, S; McCann, A; Moriarty, P; Mukherjee, R; Ong, R A; Orr, M; Otte, A N; Park, N; Perkins, J S; Pohl, M; Prokoph, H; Quinn, J; Ragan, K; Reyes, L C; Reynolds, P T; Roache, E; Rose, H J; Ruppel, J; Saxon, D B; Schroedter, M; Sembroski, G H; Senturk, G D; Skole, C; Smith, A W; Staszak, D; Telezhinsky, I; Tesic, G; Theiling, M; Thibadeau, S; Tsurusaki, K; Varlotta, A; Vassiliev, V V; Vincent, S; Vivier, M; Wagner, R G; Wakely, S P; Ward, J E; Weekes, T C; Weinstein, A; Weisgarber, T; Williams, D A; Zitzer, B

    2012-01-01

    The VERITAS array of Cherenkov telescopes has carried out a deep observational program on the nearby dwarf spheroidal galaxy Segue 1. We report on the results of nearly 48 hours of good quality selected data, taken between January 2010 and May 2011. No significant $\\gamma$-ray emission is detected at the nominal position of Segue 1, and upper limits on the integrated flux are derived. According to recent studies, Segue 1 is the most dark matter-dominated dwarf spheroidal galaxy currently known. We derive stringent bounds on various annihilating and decaying dark matter particle models. The upper limits on the velocity-weighted annihilation cross-section are $\\mathrm{^{95% CL} \\lesssim 10^{-23} cm^{3} s^{-1}}$, improving our limits from previous observations of dwarf spheroidal galaxies by at least a factor of two for dark matter particle masses $\\mathrm{m_{\\chi}\\gtrsim 300 GeV}$. The lower limits on the decay lifetime are at the level of $\\mathrm{\\tau^{95% CL} \\gtrsim 10^{24} s}$. Finally, we address the inte...

  16. Discs of Satellites: the new dwarf spheroidals

    CERN Document Server

    Metz, Manuel; Jerjen, Helmut

    2009-01-01

    The spatial distributions of the most recently discovered ultra faint dwarf satellites around the Milky Way and the Andromeda galaxy are compared to the previously reported discs-of-satellites (DoS) of their host galaxies. In our investigation we pay special attention to the selection bias introduced due to the limited sky coverage of SDSS. We find that the new Milky Way satellite galaxies follow closely the DoS defined by the more luminous dwarfs, thereby further emphasizing the statistical significance of this feature in the Galactic halo. We also notice a deficit of satellite galaxies with Galactocentric distances larger than 100 kpc that are away from the disc-of-satellites of the Milky Way. In the case of Andromeda, we obtain similar results, naturally complementing our previous finding and strengthening the notion that the discs-of-satellites are optical manifestations of a phase-space correlation of satellite galaxies.

  17. Inclusion of Horizontal Branch stars in the derivation of star formation histories of dwarf galaxies: the Carina dSph

    CERN Document Server

    Savino, Alessandro; Tolstoy, Eline

    2015-01-01

    We present a detailed analysis of the Horizontal Branch of the Carina Dwarf Spheroidal Galaxy by means of synthetic modelling techniques, taking consistently into account the star formation history and metallicity evolution as determined from main sequence and red giant branch spectroscopic observations. We found that a range of integrated red giant branch mass loss values of 0.1-0.14 M, increasing with metallicity, is able to reproduce the colour extension of the old Horizontal Branch. However, leaving the mass loss as the only free parameter is not enough to match the detailed morphology of Carina Horizontal Branch. We explored the role played by the star formation history on the discrepancies between synthetic and observed Horizontal Branches. We derived a toy bursty star formation history that reproduces the horizontal branch star counts, and also matches qualitatively the red giant and the turn off regions. This star formation history is made of a subset of age and [M/H] components of the star formation ...

  18. Mergers and the outside-in formation of dwarf spheroidals

    CERN Document Server

    Benítez-Llambay, Alejandro; Abadi, Mario G; Gottloeber, Stefan; Yepes, Gustavo; Hoffman, Yehuda; Steinmetz, Matthias

    2015-01-01

    We use a cosmological simulation of the formation of the Local Group to explore the origin of age and metallicity gradients in dwarf spheroidal galaxies. We find that a number of simulated dwarfs form "outside-in", with an old, metal-poor population that surrounds a younger, more concentrated metal-rich component, reminiscent of dwarf spheroidals like Sculptor or Sextans. We focus on a few examples where stars form in two populations distinct in age in order to elucidate the origin of these gradients. The spatial distributions of the two components reflect their diverse origin; the old stellar component is assembled through mergers, but the young population forms largely in situ. The older component results from a first episode of star formation that begins early but is quickly shut off by the combined effects of stellar feedback and reionization. The younger component forms when a late accretion event adds gas and reignites star formation. The effect of mergers is to disperse the old stellar population, incr...

  19. Chemical Evolution of Mn in Three Dwarf Spheroidal Galaxies

    Indian Academy of Sciences (India)

    Men-Quan Liu; Jie Zhang

    2014-09-01

    Based on an improved model, more reasonable nucleosyn-thesis and explosion rate of SNeIa and CCSNe, we studied Mn evolution for three local dwarf spheroidal galaxies (dSphs), considering the detailed SNe yield and explosion rates for different types of progenitors. The results can explain the main observation ofMn abundance for tens stars in those dSphs, and give some constraints to the nucleosynthesis and explosion ratio of different types of supernovae and Star Formation Rates (SFR) in those dSphs.

  20. Chemical Feature of Eu abundance in the Draco dwarf spheroidal galaxy

    CERN Document Server

    Tsujimoto, Takuji; Shigeyama, Toshikazu; Aoki, Wako

    2015-01-01

    Chemical abundance of r-process elements in nearby dwarf spheroidal (dSph) galaxies is a powerful tool to probe the site of r-process since their small-mass scale can sort out individual events producing r-process elements. A merger of binary neutron stars is a promising candidate of this site. In faint, or less massive dSph galaxies such as the Draco, a few binary neutron star mergers are expected to have occurred at most over the whole past. We have measured chemical abundances including Eu and Ba of three red giants in the Draco dSph by Subaru/HDS observation. The Eu detection for one star with [Fe/H]=-1.45 confirms a broadly constant [Eu/H] of ~-1.3 for stars with [Fe/H]>-2. This feature is shared by other dSphs with similar masses, i.e., the Sculptor and the Carina, and suggests that neutron star merger is the origin of r-process elements in terms of its rarity. In addition, two very metal-poor stars with [Fe/H]=-2.12 and -2.51 are found to exhibit very low Eu abundances such as [Eu/H]<-2 with an impl...

  1. VLT\\/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies I. Nucleosynthesis and Abundance Ratios

    CERN Document Server

    Shetrone, M; Tolstoy, E; Primas, F; Hill, V; Kaufer, A

    2003-01-01

    We have used UVES on VLT-UT2 to take spectra of 15 red giants in the Sculptor, Fornax, Carina and Leo I dwarf spheroidal galaxies. We measure the abundances of alpha, iron peak, s and r-process elements. No dSph giants in our sample show the deep mixing abundance pattern seen in nearly all globular clusters. At a given metallicity, the dSph giants exhibit lower [el/Fe] abundance ratios for the alpha elements than stars in the Galactic halo. This can be caused by a slow star formation rate and contribution from Type Ia SN, and/or a small star formation event (low total mass) and mass dependent Type II SN yields. Differences in the even-Z [el/Fe] ratios between these galaxies, as well as differences in the evolution of the s&r-process elements are interpreted in terms of their star formation histories. Comparison of the dSph abundances with those of the Galactic halo reveals some consistencies. In particular, we find stars that mimic the abundance pattern found by Nissen & Shuster (1997) for metal-rich,...

  2. VLT\\/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies II. Implications for Understanding Galaxy Evolution

    CERN Document Server

    Tolstoy, E; Shetrone, M; Primas, F; Hill, V; Szeifert, A K T; Tolstoy, Eline

    2003-01-01

    We have used UVES on VLT-UT2 to take spectra of 15 individual red giant stars in the centers of four nearby dwarf spheroidal galaxies: Sculptor, Fornax, Carina and Leo I. We measure the abundance variations of numerous elements in these low mass stars with a range of ages (1-15Gyr old). This means that we can effectively measure the chemical evolution of these galaxies WITH TIME. Our results show a significant spread in metallicity with age, but an overall trend consistent with what might be expected from a closed (or perhaps leaky) box chemical evolution scenario over the last 10-15Gyr. We notice that each of these galaxies show broadly similar abundance patterns for all elements measured. This suggests a fairly uniform progression of chemical evolution with time, despite quite a large range of star formation histories. It seems likely that these galaxies had similar initial conditions, and evolve in a similar manner with star formation occurring at a uniformly low rate, even if at different times. With our ...

  3. The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies

    CERN Document Server

    Spekkens, K; Mason, B S; Willman, B; Aguirre, J E

    2014-01-01

    We present new upper limits on the neutral hydrogen (HI) content within the stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with the Green Bank Telescope (GBT) as well as Arecibo L-band Fast ALFA (ALFALFA) survey and Galactic All-Sky Survey (GASS) data. All of the limits Mlim are more stringent than previously reported values, and those from the GBT improve upon contraints in the literature by a median factor of 23. Normalizing by V-band luminosity Lv and dynamical mass Mdyn, we find Mlim/Lv ~ 10^{-3} Mo/Lo and Mlim/Mdyn ~ 5 x 10^{-5}, irrespective of location in the Galactic halo. Comparing these relative HI contents to those of the Local Group and nearby neighbor dwarfs compiled by McConnachie, we find that the Galactic dSphs are extremely gas-poor. Our HI upper limits therefore provide the clearest picture yet of the environmental dependence of the HI content in Local Volume dwarfs. If ram pressure stripping explains the dearth of HI in these ...

  4. Detailed Studies of the Sculptor Dwarf Spheroidal Galaxy in the Milky Way halo

    NARCIS (Netherlands)

    Tolstoy, Eline

    2014-01-01

    In and around the Milky Way halo there are a number of low mass low luminosity dwarf galaxies. Several of these systems have been studied in great detail. I describe recent photometric and spectroscopic studies of the Sculptor dwarf spheroidal galaxy made as part of the DART survey of nearby dwarf s

  5. The influence of binary stars on dwarf spheroidal galaxy kinematics

    CERN Document Server

    Hargreaves, J C; Annan, J D

    1995-01-01

    We have completed a Monte-Carlo simulation to estimate the effect of binary star orbits on the measured velocity dispersion in dwarf spheroidal galaxies. This paper analyses previous attempts at this calculation, and explains the simulations which were performed with mass, period and ellipticity distributions similar to that measured for the solar neighbourhood. The conclusion is that with functions such as these, the contribution of binary stars to the velocity dispersion is small. The distributions are consistent with the percentage of binaries detected by observations, although this is quite dependent on the measuring errors and on the number of years over which measurements have been taken. For binaries to be making a significant contribution to the dispersion measured in dSph galaxies, the distributions of the orbital parameters would need to be very different from those of stars in the solar neighbourhood. In particular more smaller period orbits with higher mass secondaries would be required. The shape...

  6. The early days of the Sculptor dwarf spheroidal galaxy

    CERN Document Server

    Jablonka, P; Mashonkina, L; Hill, V; Revaz, Y; Shetrone, M; Starkenburg, E; Irwin, M; Tolstoy, E; Battaglia, G; Venn, K; Helmi, A; Primas, F; Francois, P

    2015-01-01

    We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed analysis of the chemical abundances of alpha, iron peak, light and heavy elements, and draw comparisons with the Milky Way halo and the ultra faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follows the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the TypeII supernovae. In addition to its value to help refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggesti...

  7. THE DEARTH OF NEUTRAL HYDROGEN IN GALACTIC DWARF SPHEROIDAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Spekkens, Kristine; Urbancic, Natasha [Department of Physics, Royal Military College of Canada, P.O. Box 17000, Station Forces, Kingston, Ontario K7K 7B4 (Canada); Mason, Brian S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Willman, Beth [Haverford College, 370 Lancaster Avenue, Haverford, PA 19041 (United States); Aguirre, James E., E-mail: kristine.spekkens@rmc.ca [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States)

    2014-11-01

    We present new upper limits on the neutral hydrogen (H I) content within the stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with the Green Bank Telescope (GBT) as well as Arecibo L-band Fast ALFA survey and Galactic All-Sky Survey data. All of the limits M{sub H} {sub I}{sup lim} are more stringent than previously reported values, and those from the GBT improve upon constraints in the literature by a median factor of 23. Normalizing by V-band luminosity L{sub V} and dynamical mass M {sub dyn}, we find M{sub H} {sub I}{sup lim}/L{sub V}∼10{sup −3} M{sub ⊙}/L{sub ⊙} and M{sub H} {sub I}{sup lim}/M{sub dyn}∼5×10{sup −5}, irrespective of location in the Galactic halo. Comparing these relative H I contents to those of the Local Group and nearby neighbor dwarfs compiled by McConnachie, we find that the Galactic dSphs are extremely gas-poor. Our H I upper limits therefore provide the clearest picture yet of the environmental dependence of the H I content in Local Volume dwarfs. If ram pressure stripping explains the dearth of H I in these systems, then orbits in a relatively massive Milky Way are favored for the outer halo dSph Leo I, while Leo II and Canes Venatici I have had a pericentric passage in the past. For Draco and Ursa Minor, the interstellar medium mass that should accumulate through stellar mass loss in between pericentric passages exceeds M{sub H} {sub I}{sup lim} by a factor of ∼30. In Ursa Minor, this implies that either this material is not in the atomic phase, or that another mechanism clears the recycled gas on shorter timescales.

  8. Model comparison of the dark matter profiles of Fornax, Sculptor, Carina and Sextans

    NARCIS (Netherlands)

    Breddels, Maarten A.; Helmi, Amina

    2013-01-01

    Aims: We compare dark matter profile models of four dwarf spheroidal galaxies satellites of the Milky Way using Bayesian evidence. Methods: We use orbit based dynamical models to fit the 2nd and 4th moments of the line of sight velocity distributions of the Fornax, Sculptor, Carina and Sextans dwarf

  9. The extremely low-metallicity tail of the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Starkenburg, E.; Hill, V.; Tolstoy, E.; François, P.; Irwin, M. J.; Boschman, L.; Venn, K. A.; de Boer, T. J. L.; Lemasle, B.; Jablonka, P.; Battaglia, G.; Groot, P.; Kaper, L.

    2013-01-01

    We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the dwarf abundances and radial velocities team (DART) using the lates

  10. Metals Removed by Outflows from Milky Way Dwarf Spheroidal Galaxies

    CERN Document Server

    Kirby, Evan N; Finlator, Kristian

    2011-01-01

    The stars in the dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are significantly more metal-poor than would be expected from a closed box model of chemical evolution. Gas outflows likely carried away most of the metals produced by the dSphs. Based on previous Keck/DEIMOS observations and models, we calculate the mass in Mg, Si, Ca, and Fe expelled from each of eight dSphs. Essentially, these masses are the differences between the observed amount of metals present in the dSphs' stars today and the inferred amount of metals produced by supernovae. We conclude that the dSphs lost 96% to >99% of the metals their stars manufactured. We apply the observed mass function of Milky Way dSphs to the ejected mass function to determine that a single large dSph, like Fornax, lost more metals over 10 Gyr than all smaller dSphs combined. Therefore, small galaxies like dSphs are not significant contributors to the metal content of the intergalactic medium. Finally, we compare our ejected mass function to previo...

  11. The effect of tides on the Fornax dwarf spheroidal galaxy

    CERN Document Server

    Battaglia, Giuseppina; Nipoti, Carlo

    2015-01-01

    Estimates of the mass distribution and dark-matter (DM) content of dwarf spheroidal galaxies (dSphs) are usually derived under the assumption that the effect of the tidal field of the host galaxy is negligible over the radial extent probed by kinematic data-sets. We assess the implications of this assumption in the specific case of the Fornax dSph by means of N-body simulations of a satellite orbiting around the Milky Way. We consider observationally-motivated orbits and we tailor the initial distributions of the satellite's stars and DM to match, at the end of the simulations, the observed structure and kinematics of Fornax. In all our simulations the present-day observable properties of Fornax are not significantly influenced by tidal effects. The DM component is altered by the interaction with the Galactic field (up to 20% of the DM mass within 1.6 kpc is lost), but the structure and kinematics of the stellar component are only mildly affected even in the more eccentric orbit (more than 99% of the stellar ...

  12. The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies

    CERN Document Server

    Revaz, Y; Sawala, T; Hill, V; Letarte, B; Irwin, M; Battaglia, G; Helmi, A; Shetrone, M D; Tolstoy, E; Venn, K A

    2009-01-01

    We present a large sample of fully self-consistent hydrodynamical Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It has enabled us to identify the key physical parameters and mechanisms at the origin of the observed variety in the Local Group dSph properties. The initial total mass (gas + dark matter) of these galaxies is the main driver of their evolution. Star formation (SF) occurs in series of short bursts. In massive systems, the very short intervals between the SF peaks mimic a continuous star formation rate, while less massive systems exhibit well separated SF bursts, as identified observationally. The delay between the SF events is controlled by the gas cooling time dependence on galaxy mass. The observed global scaling relations, luminosity-mass and luminosity-metallicity, are reproduced with low scatter. We take advantage of the unprecedentedly large sample size and data homogeneity of the ESO Large Programme DART, and add to it a few independent studies, to constrain the s...

  13. A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Yuan, Zhen; Jing, Y P

    2015-01-01

    Fornax is the brightest Milky Way (MW) dwarf spheroidal galaxy and its star formation history (SFH) has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH using a simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe) as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass M_x of the gas to mix with the ejecta from each SN. The choice of M_x depends on the evolution of SN remnants and on the global gas dynamics. It differs between the two types of SNe involved and between the periods before and after Fornax became an MW satellite at time t = t_sat . Our results indicate that due to the global gas outflow at t > t_sat , part of the ejecta from each SN may directly escape from Fornax. Sample results from our model are presented and compared with data.

  14. X-RAY SOURCES IN THE DWARF SPHEROIDAL GALAXY DRACO

    Energy Technology Data Exchange (ETDEWEB)

    Sonbas, E. [University of Adiyaman, Department of Physics, 02040 Adiyaman (Turkey); Rangelov, B.; Kargaltsev, O.; Dhuga, K. S.; Hare, J.; Volkov, I., E-mail: edasonbas@yahoo.com [Department of Physics, The George Washington University, Washington, DC 20052 (United States)

    2016-04-10

    We present the spectral analysis of an 87 ks XMM-Newton observation of Draco, a nearby dwarf spheroidal galaxy. Of the approximately 35 robust X-ray source detections, we focus our attention on the brightest of these sources, for which we report X-ray and multiwavelength parameters. While most of the sources exhibit properties consistent with active galactic nuclei, few of them possess the characteristics of low-mass X-ray binaries (LMXBs) and cataclysmic variable (CVs). Our analysis places constraints on the population of X-ray sources with L{sub X} > 3 × 10{sup 33} erg s{sup −1} in Draco, suggesting that there are no actively accreting black hole and neutron star binaries. However, we find four sources that could be quiescent state LMXBs/CVs associated with Draco. We also place constraints on the central black hole luminosity and on a dark matter decay signal around 3.5 keV.

  15. On the R-Process Enrichment of Dwarf Spheroidal Galaxies

    CERN Document Server

    Bramante, Joseph

    2016-01-01

    Recent observations of Reticulum II have uncovered an overabundance of r-process elements, compared to similar ultra-faint dwarf spheroidal galaxies (UFDs). Because the metallicity and star formation history of Reticulum II appear consistent with all known UFDs, the high r-process abundance of Reticulum II suggests enrichment through a single, rare event, such as a double neutron star (NS) merger. However, we note that this scenario is extremely unlikely, as binary stellar evolution models require significant supernova natal kicks to produce NS-NS or NS-black hole mergers, and these kicks would efficiently remove compact binary systems from the weak gravitational potentials of UFDs. We examine alternative mechanisms for the production of r-process elements in UFDs, including a novel mechanism wherein NSs in regions of high dark matter density implode after accumulating a black-hole-forming mass of dark matter. We find that r-process proto-material ejection by tidal forces, when a single neutron star implodes ...

  16. Unbiased constraints on ultralight axion mass from dwarf spheroidal galaxies

    CERN Document Server

    Gonzáles-Morales, Alma X; Peñarrubia, Jorge; Ureña-López, Luis

    2016-01-01

    It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_a\\sim 10^{-22}\\text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here we use realistic kinematic mock data catalogs of Milky Way dSph's to show that the "mass-anisotropy degeneracy" in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with ...

  17. Dwarf spheroidal galaxies as degenerate gas of free fermions

    CERN Document Server

    Domcke, Valerie

    2014-01-01

    In this paper we analyze a simple scenario in which Dark Matter (DM) consists of free fermions with mass $m_f$. We assume that on galactic scales these fermions are capable to form a degenerate Fermi gas, in which stability against gravitational collapse is ensured by the Pauli exclusion principle. The mass density of the resulting configuration is governed by a non-relativistic Lane-Emden equation, thus leading to a universal cored profile that depends only on one free parameter in addition to $m_f$. After reviewing the basic formalism, we test this scenario against experimental data describing the dispersion velocity of the eight classical dwarf spheroidal galaxies of the Milky Way. We find that, despite its extreme simplicity, the model exhibits a good fit of the data and realistic predictions for the size of DM halos providing that $m_f \\simeq 200$ eV. We propose a concrete realization of this model in which DM is produced non-thermally via inflaton decay. We show that imposing the correct relic abundance...

  18. Dwarf spheroidal galaxies as degenerate gas of free fermions

    Energy Technology Data Exchange (ETDEWEB)

    Domcke, Valerie; Urbano, Alfredo, E-mail: valerie.domcke@sissa.it, E-mail: alfredo.urbano@sissa.it [SISSA - International School for Advanced Studies, via Bonomea 256, Trieste, 34136 Italy (Italy)

    2015-01-01

    In this paper we analyze a simple scenario in which Dark Matter (DM) consists of free fermions with mass m{sub f}. We assume that on galactic scales these fermions are capable of forming a degenerate Fermi gas, in which stability against gravitational collapse is ensured by the Pauli exclusion principle. The mass density of the resulting con figuration is governed by a non-relativistic Lane-Emden equation, thus leading to a universal cored profile that depends only on one free parameter in addition to m{sub f}. After reviewing the basic formalism, we test this scenario against experimental data describing the velocity dispersion of the eight classical dwarf spheroidal galaxies of the Milky Way. We find that, despite its extreme simplicity, the model exhibits a good fit to the data and realistic predictions for the size of DM halos providing that m{sub f}≅ 200 eV. Furthermore, we show that in this setup larger galaxies correspond to the non-degenerate limit of the gas. We propose a concrete realization of this model in which DM is produced non-thermally via inflaton decay. We show that imposing the correct relic abundance and the bound on the free-streaming length constrains the inflation model in terms of inflaton mass, its branching ratio into DM and the reheating temperature.

  19. The structure of Andromeda II dwarf spheroidal galaxy

    CERN Document Server

    del Pino, Andrés; Hidalgo, Sebastian L; Fouquet, Sylvain

    2016-01-01

    We analyze in detail the spatial distribution and kinematic properties of two different stellar populations in Andromeda II (And II) dwarf spheroidal galaxy. We obtained their detailed surface density maps, together with their radial density profiles. The two populations differ not only in age and metallicity, but also in their spatial distribution and kinematics. Old stars ($\\gtrsim 11$ Gyr) follow a round distribution well fitted by truncated density profiles. These stars rotate around the projected optical major axis of the galaxy with line-of-sight velocities $v_{los}(r_h) = 16 \\pm 3$ km s$^{-1}$ and a velocity gradient of $2.06 \\pm 0.21$ km s$^{-1}$ arcmin$^{-1}$. Intermediate-age stars ($\\lesssim 9$ Gyr) concentrate in the centre of the galaxy and form an elongated structure extending along the projected optical major axis. This structure appears to rotate with a steeper velocity gradient, $2.24 \\pm 0.22$ km s$^{-1}$ arcmin$^{-1}$, and around the optical minor axis. The centres of rotation and kinetic p...

  20. Comptonization of cosmic microwave background photons in dwarf spheroidal galaxies

    Science.gov (United States)

    Culverhouse, Thomas L.; Evans, N. Wyn; Colafrancesco, S.

    2006-05-01

    We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich (SZ) effect. For an assumed neutralino mass of 10 GeV and beam size of 1 arcsec, the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as the Atacama Large Millimetre Array. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable now. None the less, we conclude that searching for the dark matter induced SZ effect is a promising way of constraining the dark distribution in dSphs, especially if the particles are light.

  1. Comptonisation of Cosmic Microwave Background Photons in Dwarf Spheroidal Galaxies

    CERN Document Server

    Culverhouse, T L; Colafrancesco, S; Culverhouse, Thomas L.

    2006-01-01

    We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco (2004) and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich effect. For an assumed neutralino mass of 10 GeV and beam size of 1'', the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as ALMA. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable soon. Nonetheless, we conclude that searching for the dark matter induced Sunyaev-Zeldovich effect is a promising way of constraining ...

  2. Multiple stellar population in the Sextans dwarf spheroidal galaxy?

    CERN Document Server

    Bellazzini, M; Pancino, E

    2001-01-01

    We present wide field (33 X 34 arcmin^2) multiband (BVI) CCD photometry (down to I <= 20.5) of the very low surface brightness dwarf Spheroidal (dSph) galaxy Sextans. In the derived Color Magnitude Diagrams we have found evidences suggesting the presence of multiple stellar populations in this dSph. In particular we discovered: {\\it (i)} a Blue Horizontal Branch (HB) tail that appears to lie on a brighter sequence with respect to the prominent Red HB and the RR Lyrae stars, very similar to what found by Majewski et al. (1999) for the Sculptor dSph; {\\it (ii)} hints of a bimodal distribution in color of the RGB stars; {\\it (iii)} a double RGB-bump. All these features suggest that (at least) two components are present in the old stellar population of this galaxy: a main one with [Fe/H]~ -1.8 and a minor component around [Fe/H]<~ -2.3. The similarity with the Sculptor case may indicate that multiple star formation episodes are common also in the most nearby dSphs that ceased their star formation activity a...

  3. Jeans Analysis for Dwarf Spheroidal Galaxies in Wave Dark Matter

    CERN Document Server

    Chen, Shu-Rong; Chiueh, Tzihong

    2016-01-01

    Observations suggest that dwarf spheroidal (dSph) galaxies exhibit large constant-density cores in the centers, which can hardly be explained by dissipationless cold dark matter simulations. Wave dark matter (${\\psi {\\rm DM}}$), characterized by a single parameter, the dark matter particle mass $m_{\\psi}$, predicts a central soliton core in every galaxy arising from quantum pressure against gravity. Here we apply Jeans analysis to the kinematic data of eight classical dSphs so as to constrain $m_{\\psi}$, and obtain $m_{\\psi}=1.18_{-0.24}^{+0.28}\\times10^{-22}{\\,\\rm eV}$ and $m_{\\psi}=1.79_{-0.33}^{+0.35}\\times10^{-22}{\\,\\rm eV}~(2\\sigma)$ using the observational data sets of Walker et al. (2007) and Walker et al. (2009b), respectively. We show that the estimate of $m_{\\psi}$ is sensitive to the dSphs kinematic data sets and is robust to various models of stellar density profile. We also consider multiple stellar subpopulations in dSphs and find consistent results. This mass range of $m_{\\psi}$ is in good agre...

  4. A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

    Directory of Open Access Journals (Sweden)

    Yuan Zhen

    2016-01-01

    Full Text Available Fornax is the brightest Milky Way (MW dwarf spheroidal galaxy and its star formation history (SFH has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH usinga simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass Mx of the gas to mix with the ejecta from each SN. The choice of Mx depends on the evolution of SN remnants and on the global gas dynamics. It differs between the two types of SNe involved and between the periods before and after Fornax became an MW satellite at time t = tsat. Our results indicate that due to the global gas outflow at t > tsat, part of the ejecta from each SN may directly escape from Fornax. Sample results from our model are presented and compared with data.

  5. Extended stellar substructure surrounding the Bo\\"otes I dwarf spheroidal galaxy

    CERN Document Server

    Roderick, T A; Jerjen, H; Da Costa, G S

    2016-01-01

    We present deep stellar photometry of the Bo\\"otes I dwarf spheroidal galaxy in g and i band filters, taken with the Dark Energy Camera at Cerro Tololo in Chile. Our analysis reveals a large, extended region of stellar substructure surrounding the dwarf, as well as a distinct over-density encroaching on its tidal radius. A radial profile of the Bo\\"otes I stellar distribution shows a break radius indicating the presence of extra-tidal stars. These observations strongly suggest that Bo\\"otes I is experiencing tidal disruption, although not as extreme as that exhibited by the Hercules dwarf spheroidal. Combined with revised velocity dispersion measurements from the literature, we see evidence suggesting the need to review previous theoretical models of the Bo\\"otes I dwarf spheroidal galaxy.

  6. The origin of prolate rotation in dwarf spheroidal galaxies formed by mergers of disky dwarfs

    CERN Document Server

    Ebrova, Ivana

    2015-01-01

    Motivated by the discovery of prolate rotation of stars in Andromeda II, a dwarf spheroidal companion of M31, we study the origin of this type of streaming motion via mergers of disky dwarf galaxies. We simulate merger events between two identical dwarfs changing the initial inclination of their disks with respect to the orbit and the amount of orbital angular momentum. On radial orbits the amount of prolate rotation in the merger remnants correlates strongly with the inclination of the disks and is well understood as due to the conservation of the angular momentum component of the disks along the merger axis. For non-radial orbits prolate rotation may still be produced if the orbital angular momentum is initially not much larger than the intrinsic angular momentum of the disks. The orbital structure of the remnants with significant rotation is dominated by box orbits in the center and long-axis tubes in the outer parts. We also detect significant figure rotation resulting from the tidal distortion of the dis...

  7. Local Group Dwarf Spheroidals: Correlated Deviations from the Baryonic Tully-Fisher Relation

    CERN Document Server

    McGaugh, Stacy S

    2010-01-01

    Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption. Fainter, more elliptical, and tidally more susceptible dwarfs deviate further from the BTFR. We consider a variety of mechanisms that might lead to this behavior. Reionization does not, by itself, suffice to explain all aspects of the data. Further mechanisms such as supernova feedback or ram pressure stripping may remove gas that would otherwise be present to satisfy the baryonic mass budget. The correlation with ellipticity and tidal susceptibility implies that the usual assumption of spherical systems in stable equilibria may not hol...

  8. Dark Matter Searches with the Fermi-LAT in the Direction of Dwarf Spheroidals

    Energy Technology Data Exchange (ETDEWEB)

    Wood, Matthew; Anderson, Brandon; Drlica-Wagner, Alex; Cohen-Tanugi, Johann; Conrad, Jan

    2015-07-13

    The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via gamma rays. Here we report on gamma-ray observations of Milky Way dwarf spheroidal satellite galaxies based on 6 years of Fermi Large Area Telescope data processed with the new Pass 8 reconstruction and event-level analysis. None of the dwarf galaxies are significantly detected in gamma rays, and we present upper limits on the dark matter annihilation cross section from a combined analysis of the 15 most promising dwarf galaxies. The constraints derived are among the strongest to date using gamma rays, and lie below the canonical thermal relic cross section for WIMPs of mass ≲ 100GeV annihilating via the bb-bar and τ⁺τ⁻ channels.

  9. Leo I - The youngest Milky Way dwarf spheroidal galaxy?

    Science.gov (United States)

    Lee, Myung G.; Freedman, Wendy; Mateo, Mario; Thompson, Ian; Roth, Miguel; Ruiz, Maria-Teresa

    1993-01-01

    Deep CCD photometry of about 16,000 stars in the Milky Way's Leo I spheroidal galaxy satellite is reported. An account is given of the features observed in the color-magnitude diagrams (CMDs) derived therefrom. A very blue and well-defined red giant branch (RGB) is noted. The CMDs of Leo I shows about 50 anomalous Cepheid candidates; there are another 50 or so asymptotic giant branch stars above the tip of the RGB, including 15 known carbon stars. The mean color of the RGB is estimated at M sub I = -3.5 mag.

  10. Weak Galactic halo--dwarf spheroidal connection from RR Lyrae stars

    CERN Document Server

    Fiorentino, Giuliana; Monelli, Matteo; Stetson, Peter B; Tolstoy, Eline; Gallart, Carme; Salaris, Maurizio; Martinez, Clara; Bernard, Edouard J

    2014-01-01

    We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in six dwarf spheroidals and eleven ultra faint dwarf galaxies (1,300) show a Gaussian period distribution well peaked around a mean period of =0.610+-0.001 days (sigma=0.03). The Halo RRL (15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dwarf spheroidals apart from Sagittarius are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P 0.75mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered eighteen globulars covering a broad range in metallicity (-2.3< [Fe/H]< -1.1) and hosting more than 35 R...

  11. Abundance ratios of red giants in low mass ultra faint dwarf spheroidal galaxies

    CERN Document Server

    François, P; Bonifacio, P; Bidin, C Moni; Geisler, D; Sbordone, L

    2015-01-01

    Low mass dwarf spheroidal galaxies are key objects for our understanding of the chemical evolution of the pristine Universe and the Local Group of galaxies. Abundance ratios in stars of these objects can be used to better understand their star formation and chemical evolution. We report on the analysis of a sample of 11 stars belonging to 5 different ultra faint dwarf spheroidal galaxies (UfDSph) based on X-Shooter spectra obtained at the VLT. Medium resolution spectra have been used to determine the detailed chemical composition of their atmosphere. We performed a standard 1D LTE analysis to compute the abundances. Considering all the stars as representative of the same population of low mass galaxies, we found that the [alpha/Fe] ratios vs [Fe/H] decreases as the metallicity of the star increases in a way similar to what is found for the population of stars belonging to dwarf spheroidal galaxies. The main difference is that the solar [alpha/Fe] is reached at a much lower metallicity for the UfDSph than the ...

  12. VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy

    CERN Document Server

    Lemasle, B; Hill, V; Tolstoy, E; Irwin, M; Jablonka, P; Venn, K; Battaglia, G; Starkenburg, E; Shetrone, M; Letarte, B; Francois, P; Helmi, A; Primas, F; Kaufer, A; Szeifert, T

    2014-01-01

    Fornax is one of the most massive dwarf spheroidal galaxies in the Local Group. The Fornax field star population is dominated by intermediate age stars but star formation was going on over almost its entire history. It has been proposed that Fornax experienced a minor merger event. Despite recent progress, only the high metallicity end of Fornax field stars ([Fe/H]>-1.2 dex) has been sampled in larger number via high resolution spectroscopy. We want to better understand the full chemical evolution of this galaxy by better sampling the whole metallicity range, including more metal poor stars. We use the VLT-FLAMES multi-fibre spectrograph in high-resolution mode to determine the abundances of several alpha, iron-peak and neutron-capture elements in a sample of 47 individual Red Giant Branch stars in the Fornax dwarf spheroidal galaxy. We combine these abundances with accurate age estimates derived from the age probability distribution from the colour-magnitude diagram of Fornax. Similar to other dwarf spheroid...

  13. The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda II

    CERN Document Server

    Pritzl, B J; Jacoby, G H; Costa, G S D; Pritzl, Barton J.; Armandroff, Taft E.; Jacoby, George H.

    2004-01-01

    (abridged) We present the results of a variable star search in Andromeda II, a dwarf spheroidal galaxy companion to M31, using HST/WFPC2 observations. Seventy-three variables were found, one of which is an anomalous Cepheid while the others are RR Lyrae stars. The anomalous Cepheid has properties consistent with those found in other dwarf spheroidal galaxies. For the RR Lyrae stars, the mean periods are 0.571 day and 0.363 day for the fundamental mode and first-overtone mode stars, respectively. With this fundamental mode mean period and the mean metallicity determined from the red giant branch (=-1.49), Andromeda II follows the period-metallicity relation defined by the Galactic globular clusters and other dwarf spheroidal galaxies. We also find that the properties of the RR Lyrae stars themselves indicate a mean abundance that is consistent with that determined from the red giants. There is, however, a significant spread among the RR Lyrae stars in the period-amplitude diagram, which is possibly related to ...

  14. ANDROMEDA XXIX: A NEW DWARF SPHEROIDAL GALAXY 200 kpc FROM ANDROMEDA

    Energy Technology Data Exchange (ETDEWEB)

    Bell, Eric F.; Slater, Colin T. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Martin, Nicolas F. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    2011-11-20

    We report the discovery of a new dwarf galaxy, Andromeda XXIX (And XXIX), using data from the recently released Sloan Digital Sky Survey Data Release 8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15 Degree-Sign from M31, with a distance inferred from the tip of the red giant branch of 730 {+-} 75 kpc, corresponding to a three-dimensional separation from M31 of 207{sup +20}{sub -2} kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, is M{sub V} = -8.3 {+-} 0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of [Fe/H] {approx}-1.8. The half-light radius of And XXIX is 360 {+-} 60 pc and its ellipticity is 0.35 {+-} 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.

  15. A New View of the Dwarf Spheroidal Satellites of the Milky Way From VLT/FLAMES: Where are the Very Metal Poor Stars?

    Energy Technology Data Exchange (ETDEWEB)

    Helmi, Amina; Irwin, M.J.; Tolstoy, E.; Battaglia, G.; Hill, V.; Jablonka, P.; Venn, K.; Shetrone, M.; Letarte, B.; Arimoto, N.; Abel, T.; Francois, P.; Kaufer, A.; Primas, F.; Sadakane, K.; Szeifert, T.; /Kapteyn Astron. Inst., Groningen /Cambridge U., Inst. of Astron. /Meudon Observ. /LASTRO Observ. /Victoria U. /Texas U., McDonald Observ.

    2006-11-20

    As part of the Dwarf galaxies Abundances and Radial-velocities Team (DART) Programme, we have measured the metallicities of a large sample of stars in four nearby dwarf spheroidal galaxies (dSph): Sculptor, Sextans, Fornax and Carina. The low mean metal abundances and the presence of very old stellar populations in these galaxies have supported the view that they are fossils from the early Universe. However, contrary to naive expectations, we find a significant lack of stars with metallicities below [Fe/H] {approx} -3 dex in all four systems. This suggests that the gas that made up the stars in these systems had been uniformly enriched prior to their formation. Furthermore, the metal-poor tail of the dSph metallicity distribution is significantly different from that of the Galactic halo. These findings show that the progenitors of nearby dSph appear to have been fundamentally different from the building blocks of the Milky Way, even at the earliest epochs.

  16. Improving the sensitivity of gamma-ray telescopes to dark matter annihilation in dwarf spheroidal galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Carlson, Eric [Univ. of California, Santa Cruz, CA (United States). Dept. of Physics; Hooper, Dan [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States). Center for Particle Astrophysics; Univ. of Chicago, IL (United States). Dept. of Astronomy and Astrophysics; Linden, Tim [Univ. of Chicago, IL (United States). Kavli Inst. for Cosmological Physics

    2015-03-01

    The Fermi-LAT Collaboration has studied the gamma-ray emission from a stacked population of dwarf spheroidal galaxies and used this information to set constraints on the dark matter annihilation cross section. Interestingly, their analysis uncovered an excess with a test statistic (TS) of 8.7. If interpreted naively, this constitutes a 2.95σ local excess (p-value=0.003), relative to the expectations of their background model. In order to further test this interpretation, the Fermi-LAT team studied a large number of blank sky locations and found TS>8.7 excesses to be more common than predicted by their background model, decreasing the significance of their dwarf excess to 2.2σ(p-value=0.027). We argue that these TS>8.7 blank sky locations are largely the result of unresolved blazars, radio galaxies, and star-forming galaxies, and show that multiwavelength information can be used to reduce the degree to which such sources contaminate the otherwise blank sky. In particular, we show that masking regions of the sky that lie within 1° of sources contained in the BZCAT or CRATES catalogs reduce the fraction of blank sky locations with TS>8.7 by more than a factor of 2. Taking such multiwavelength information into account can enable experiments such as Fermi to better characterize their backgrounds and increase their sensitivity to dark matter in dwarf galaxies, the most important of which remain largely uncontaminated by unresolved point sources. We also note that for the range of dark matter masses and annihilation cross sections currently being tested by studies of dwarf spheroidal galaxies, simulations predict that Fermi should be able to detect a significant number of dark matter subhalos. These subhalos constitute a population of subthreshold gamma-ray point sources and represent an irreducible background for searches for dark matter annihilation in dwarf galaxies.

  17. Radial Velocities of Dwarf Spheroidal Galaxies in the M81 Group

    OpenAIRE

    Sharina, M. E.; Karachentsev, I. D.; Burenkov, A. N.

    2001-01-01

    Long-slit observations of 4 dwarf spheroidal galaxies in the M81 group are presented. We have obtained a heliocentric velocity of globular cluster candidate located near the center of DDO78 to be +55 +- 10 km/s by cross-correlation with template stars. We estimated a heliocentric radial velocity of -116 +- 21 km/s for an HII region seen in the K 61. A red diffuse object near the K64 center is found to be a remote galaxy with a heliocentric velocity of +46530 km/s.

  18. Dynamical models for the Sculptor dwarf spheroidal in a Lambda CDM universe

    OpenAIRE

    2014-01-01

    The Sculptor dwarf spheroidal galaxy contains two distinct stellar populations: one metal-rich and the other metal-poor. Several authors have argued that in order for these two populations to reside in the same gravitational potential, the dark matter halo must have a core similar to that observed in the stellar count profile. This would rule out the cuspy Navarro-Frenk-White (NFW) density profiles predicted for halos and subhalos by dark matter only simulations of the Lambda Cold Dark Matter...

  19. The puzzling assembly of the Milky Way halo – contributions from dwarf Spheroidals and globular clusters

    Directory of Open Access Journals (Sweden)

    Lépine S.

    2012-02-01

    Full Text Available While recent sky surveys have uncovered large numbers of ever fainter Milky Way satellites, their classification as star clusters, low-luminosity galaxies, or tidal overdensities remains often unclear. Likewise, their contributions to the build-up of the halo is yet debated. In this contribution we will discuss the current knowledge of the stellar populations and chemo-dynamics in these puzzling satellites, with a particular focus on dwarf spheroidal galaxies and the globular clusters in the outer Galactic halo. Also the question of whether some of the outermost halo objects are dynamically associated with the (Milky Way halo at all is addressed in terms of proper measurements in the remote Leo I and II dwarf galaxies.

  20. Carbon and nitrogen abundances of individual stars in the Sculptor dwarf spheroidal galaxy

    CERN Document Server

    Lardo, C; Pancino, E; Romano, D; de Boer, T J L; Starkenburg, E; Tolstoy, E; Irwin, M J; Jablonka, P; Tosi, M

    2015-01-01

    We present [C/Fe] and [N/Fe] abundance ratios and CH({\\lambda}4300) and S({\\lambda}3883) index measurements for 94 red giant branch (RGB) stars in the Sculptor dwarf spheroidal galaxy from VLT/VIMOS MOS observations at a resolving power R= 1150 at 4020 {\\AA}. This is the first time that [N/Fe] abundances are derived for a large number of stars in a dwarf spheroidal. We found a trend for the [C/Fe] abundance to decrease with increasing luminosity on the RGB across the whole metallicity range, a phenomenon observed in both field and globular cluster giants, which can be interpreted in the framework of evolutionary mixing of partially processed CNO material. Both our measurements of [C/Fe] and [N/Fe] are in good agreement with the theoretical predictions for stars at similar luminosity and metallicity. We detected a dispersion in the carbon abundance at a given [Fe/H], which cannot be ascribed to measurement uncertainties alone. We interpret this observational evidence as the result of the contribution of differ...

  1. The first carbon-enhanced metal-poor star found in the Sculptor dwarf spheroidal

    CERN Document Server

    Skuladottir, Asa; Salvadori, Stefania; Hill, Vanessa; Pettini, Max; Shetrone, Matthew D; Starkenburg, Else

    2014-01-01

    The origin of carbon-enhanced metal-poor (CEMP) stars and their possible connection with the chemical elements produced by the first stellar generation is still highly debated. In contrast to the Galactic halo, not many CEMP stars have been found in the dwarf spheroidal galaxies around the Milky Way. Here we present detailed abundances from ESO VLT/UVES high-resolution spectroscopy for ET0097, the first CEMP star found in the Sculptor dwarf spheroidal. This star has $\\text{[Fe/H]}=-2.03\\pm0.10$, $\\text{[C/Fe]}=0.51\\pm0.10$ and $\\text{[N/Fe]}=1.18\\pm0.20$. The traditional definition of CEMP stars is $\\text{[C/Fe]}\\geq0.70$, but taking into account that this luminous red giant branch star has undergone mixing, it was intrinsically less nitrogen enhanced and more carbon-rich when it was formed, and so it falls under the definition of CEMP stars, as proposed by Aoki et al. (2007) to account for this effect. By making corrections for this mixing, we conclude that the star had $\\text{[C/Fe]}\\approx0.8$ during its e...

  2. WEAK GALACTIC HALO-DWARF SPHEROIDAL CONNECTION FROM RR LYRAE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Fiorentino, Giuliana [INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy); Bono, Giuseppe [Dipartimento di Fisica, Universitá di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy); Monelli, Matteo; Gallart, Carme; Martínez-Vásquez, Clara E. [Instituto de Astrofísica de Canarias, Calle Via Lactea s/n, E-38205 La Laguna, Tenerife (Spain); Stetson, Peter B. [National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Tolstoy, Eline [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Salaris, Maurizio [Astrophysics Research Institute, Liverpool John Moores University IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L35RF (United Kingdom); Bernard, Edouard J., E-mail: giuliana.fiorentino@oabo.inaf.it [SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)

    2015-01-01

    We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in 6 dwarf spheroidals (dSphs) and 11 ultra faint dwarf galaxies (∼1300) show a Gaussian period distribution well peaked around a mean period of (Pab) = 0.610 ± 0.001 days (σ = 0.03). The Halo RRL (∼15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dSphs apart from Sagittarius are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P ≲ 0.48 days and A{sub V} ≥ 0.75 mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered 18 globulars covering a broad range in metallicity (–2.3 ≲ [Fe/H] ≲ –1.1) and hosting more than 35 RRL each. The metallicity turns out to be the main parameter, since only globulars more metal-rich than [Fe/H] ∼ –1.5 host RRL in the HASP region. This finding suggests that dSphs similar to the surviving ones do not appear to be the major building-blocks of the Halo. Leading physical arguments suggest an extreme upper limit of ∼50% to their contribution. On the other hand, massive dwarfs hosting an old population with a broad metallicity distribution (Large Magellanic Cloud, Sagittarius) may have played a primary role in the formation of the Halo.

  3. Not too big, not too small: the dark haloes of the dwarf spheroidals in the Milky Way

    NARCIS (Netherlands)

    Vera-Ciro, Carlos A.; Helmi, Amina; Starkenburg, Else; Breddels, Maarten A.

    2013-01-01

    We present a new analysis of the Aquarius simulations done in combination with a semi-analytic galaxy formation model. Our goal is to establish whether the subhaloes present in Lambda cold dark matter simulations of Milky Way (MW) like systems could host the dwarf spheroidal (dSph) satellites of our

  4. Stellar Kinematics and Metallicities in the Draco and Ursa Minor Dwarf Spheroidal Galaxies from WHT/AF2-WYFFOS

    NARCIS (Netherlands)

    Jin, S.; Irwin, M.; Tolstoy, E.; Lewis, J.; Hartke, J.; Skillen, I.; Barcells, M.; Trager, S.

    2016-01-01

    We present preliminary results from our chemo-dynamical survey of two Milky Way dwarf spheroidal (dSph) galaxies, Draco and Ursa Minor. The two galaxies have similar radial velocities and reside in close proximity in the outskirts of the Milky Way halo, yet exhibit noteworthy differences in their mo

  5. Deep wide-field imaging down to the oldest main sequence turn-offs in the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    de Boer, T. J. L.; Tolstoy, E.; Saha, A.; Olsen, K.; Irwin, M. J.; Battaglia, G.; Hill, V.; Shetrone, M. D.; Fiorentino, G.; Cole, A.

    2011-01-01

    We present wide-field photometry of resolved stars in the nearby Sculptor dwarf spheroidal galaxy using CTIO/MOSAIC, going down to the oldest main sequence turn-off. The accurately flux calibrated wide field colour-magnitude diagrams can be used to constrain the ages of different stellar populations

  6. The ACS LCID project : RR Lyrae stars as tracers of old population gradients in the isolated dwarf spheroidal galaxy tucana

    NARCIS (Netherlands)

    Bernard, Edouard J.; Gallart, Carme; Monelli, Matteo; Aparicio, Antonio; Cassisi, Santi; Skillman, Evan D.; Stetson, Peter B.; Cole, Andrew A.; Drozdovsky, Igor; Hidalgo, Sebastian L.; Mateo, Mario; Tolstoy, Eline

    2008-01-01

    We present a study of the radial distribution of RR Lyrae variables, which present a range of photometric and pulsational properties, in the dwarf spheroidal galaxy Tucana. We find that the fainter RR Lyrae stars, having a shorter period, are more centrally concentrated than the more luminous, longe

  7. A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Letarte, B.; Hill, V.; Tolstoy, E.; Jablonka, P.; Shetrone, M.; Venn, K. A.; Spite, M.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Primas, F.; François, P.; Kaufer, A.; Szeifert, T.; Arimoto, N.; Sadakane, K.

    2010-01-01

    For the first time we show the detailed, late-stage, chemical evolution history of a small nearby dwarf spheroidal galaxy in the Local Group. We present the results of a high-resolution (R ~ 20 000, λ = 5340-5620; 6120-6701) FLAMES/GIRAFFE abundance study at ESO/VLT of 81 photometrically selected, r

  8. A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Letarte, B.; Hill, V.; Tolstoy, E.; Jablonka, P.; Shetrone, M.; Venn, K. A.; Spite, M.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Primas, F.; François, P.; Kaufer, A.; Szeifert, T.; Arimoto, N.; Sadakane, K.

    2010-01-01

    For the first time we show the detailed, late-stage, chemical evolution history of a small nearby dwarf spheroidal galaxy in the Local Group. We present the results of a high-resolution (R similar to 20 000, lambda = 5340-5620; 6120-6701) FLAMES/GIRAFFE abundance study at ESO/VLT of 81 photometrical

  9. The DART Imaging And CaT Survey of the Fornax Dwarf Spheroidal Galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Battaglia, Giuseppina; Tolstoy, E.; Helmi, A.; /Kapteyn Astron. Inst., Groningen; Irwin, M.J.; /Cambridge U., Inst. of Astron.; Letarte, B.; /Kapteyn Astron. Inst.,; Jablonka, P.; /LASTRO Observ.; Hill, V.; /Meudon Observ.; Venn, K.A.; /Victoria U.; Shetrone, M.D.; /Texas U., McDonald Observ.; Arimoto, N.; /Tokyo, Astron. Observ.; Primas,; /European Southern Observ.; Kaufer, A.; /European Southern Obs., Chile; Francois, P.; /Meudon Observ.; Szeifert, T.; /European Southern Obs., Chile; Abel, T.; /KIPAC, Menlo Park; Sadakane, K.; /Osaka Kyoiku U.

    2006-08-28

    As part of the DART project we have used the ESO/2.2m Wide Field Imager in conjunction with the VLT/FLAMES* GIRAFFE spectrograph to study the detailed properties of the resolved stellar population of the Fornax dwarf spheroidal galaxy out to and beyond its tidal radius. Fornax dSph has had a complicated evolution and contains significant numbers of young, intermediate age and old stars. We investigate the relation between these different components by studying their photometric, kinematic and abundance distributions. We re-derived the structural parameters of the Fornax dwarf spheroidal using our wide field imaging covering the galaxy out to its tidal radius, and analyzed the spatial distribution of the Fornax stars of different ages as selected from Colour-Magnitude Diagram analysis. We have obtained accurate velocities and metallicities from spectra in the Ca II triplet wavelength region for 562 Red Giant Branch stars which have velocities consistent with membership in Fornax dwarf spheroidal. We have found evidence for the presence of at least three distinct stellar components: a young population (few 100 Myr old) concentrated in the center of the galaxy, visible as a Main Sequence in the Colour-Magnitude Diagram; an intermediate age population (2-8 Gyr old); and an ancient population (> 10Gyr), which are distinguishable from each other kinematically, from the metallicity distribution and in the spatial distribution of stars found in the Colour-Magnitude Diagram. From our spectroscopic analysis we find that the ''metal rich'' stars ([Fe/H] > -1.3) show a less extended and more concentrated spatial distribution, and display a colder kinematics than the ''metal poor'' stars ([Fe/H] < -1.3). There is tentative evidence that the ancient stellar population in the center of Fornax does not exhibit equilibrium kinematics. This could be a sign of a relatively recent accretion of external material, such as the merger of another

  10. On the He burning phases of the Carina dSph

    CERN Document Server

    Fabrizio, M; Bono, G; Stetson, P B; Walker, A R; Buonanno, R; Cassisi, S; Ferraro, I; Iannicola, G; Monelli, M; Nonino, M; Pulone, L; Thevénin, F

    2013-01-01

    We performed a detailed comparison between predicted He burning phases and multiband photometry of the Carina dwarf spheroidal galaxy. We found a good agreement with the predictions computed assuming an {\\alpha}-enhanced chemical mixture, indicating a mean metallicity [Fe/H] ~ -1.8 with a raw observed peak-to-peak spread in iron abundance of 0.4\\pm0.2 dex.

  11. Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy

    CERN Document Server

    Bonnivard, V; Maurin, D; Geringer-Sameth, A; Koushiappas, S M; Walker, M G; Mateo, M; Olszewski, E; Bailey, J I

    2015-01-01

    The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most attractive targets for indirect searches of dark matter. In this work, we reconstruct the dark matter annihilation (J-factor) and decay profiles for the newly discovered dSph Reticulum~II. This is done using an optimized spherical Jeans analysis of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS). We find Reticulum~II to have one of the highest J-factor when compared to the other Milky Way dSphs. We have also checked the robustness of this result against several ingredients of the analysis. Unless it suffers from tidal disruption or significant inflation of its velocity dispersion from binary stars, Reticulum~II may provide a unique window on dark matter particle properties.

  12. Dark Matter Annihilation and Decay Profiles for the Reticulum II Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Bonnivard, Vincent; Combet, Céline; Maurin, David; Geringer-Sameth, Alex; Koushiappas, Savvas M.; Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.; Bailey, John I., III

    2015-08-01

    The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most attractive targets for indirect searches of dark matter (DM). In this work, we reconstruct the DM annihilation (J-factor) and decay profiles for the newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis of kinematic data obtained from the Michigan/Magellan Fiber System, we find Reticulum II’s J-factor to be among the largest of any Milky Way dSph. We have checked the robustness of this result against several ingredients of the analysis. Unless it suffers from tidal disruption or significant inflation of its velocity dispersion from binary stars, Reticulum II may provide a unique window on DM particle properties.

  13. Observations of MilkyWay Dwarf Spheroidal galaxies with the Fermi-LAT detector and

    Energy Technology Data Exchange (ETDEWEB)

    Abdo, A.A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bloom, E.D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, T.H.; Buson, S.; Caliandro, G.A.; /Naval Research Lab, Wash., D.C. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /SLAC /UC, Santa Cruz /INFN, Pisa /DAPNIA, Saclay /INFN, Trieste /Trieste U. /INFN, Padua /Padua U. /INFN, Perugia /Perugia U. /Bari Polytechnic /INFN, Bari /Ecole Polytechnique /Washington U., Seattle /IASF, Milan /George Mason U. /NASA, Goddard

    2010-05-26

    We report on the observations of 14 dwarf spheroidal galaxies with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky {gamma}-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected {gamma}-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dwarf spheroidal galaxies, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant {gamma}-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the {gamma}-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10{sup -9} photons cm{sup -2}s{sup -1}. Using recent stellar kinematic data, the {gamma}-ray flux limits are combined with improved determinations of the dark matter density profile in 8 of the 14 candidate dwarfs to place limits on the pair annihilation cross-section ofWIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g. in models where supersymmetry breaking occurs via anomaly mediation. The {gamma}-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e{sup +}e{sup -} data, including low-mass wino-like neutralinos and models with TeV masses pair

  14. The interstellar medium in Andromeda's dwarf spheroidal galaxies - I. Content and origin of the interstellar dust

    Science.gov (United States)

    De Looze, Ilse; Baes, Maarten; Bendo, George J.; Fritz, Jacopo; Boquien, Médéric; Cormier, Diane; Gentile, Gianfranco; Kennicutt, Robert C.; Madden, Suzanne C.; Smith, Matthew W. L.; Young, Lisa

    2016-07-01

    Dwarf spheroidal galaxies are among the most numerous galaxy population in the Universe, but their main formation and evolution channels are still not well understood. The three dwarf spheroidal satellites (NGC 147, NGC 185, and NGC 205) of the Andromeda galaxy are characterized by very different interstellar medium properties, which might suggest them being at different galaxy evolutionary stages. While the dust content of NGC 205 has been studied in detail in an earlier work, we present new Herschel dust continuum observations of NGC 147 and NGC 185. The non-detection of NGC 147 in Herschel SPIRE maps puts a strong constraint on its dust mass (≤128^{+124}_{-68} M⊙). For NGC 185, we derive a total dust mass Md = 5.1±1.0 × 103 M⊙, which is a factor of ˜2-3 higher than that derived from ISO and Spitzer observations and confirms the need for longer wavelength observations to trace more massive cold dust reservoirs. We, furthermore, estimate the dust production by asymptotic giant branch (AGB) stars and supernovae (SNe). For NGC 147, the upper limit on the dust mass is consistent with expectations of the material injected by the evolved stellar population. In NGC 185 and NGC 205, the observed dust content is one order of magnitude higher compared to the estimated dust production by AGBs and SNe. Efficient grain growth, and potentially longer dust survival times (3-6 Gyr) are required to account for their current dust content. Our study confirms the importance of grain growth in the gas phase to account for the current dust reservoir in galaxies.

  15. The Carina Project IX: on Hydrogen and helium burning variables

    CERN Document Server

    Coppola, G; Stetson, P B; Bono, G; Braga, V F; Ripepi, V; Dall'Ora, M; Musella, I; Buonanno, R; Fabrizio, M; Ferraro, I; Fiorentino, G; Iannicola, G; Monelli, M; Nonino, M; Thévenin, F; Walker, R

    2015-01-01

    We present new multi-band (UBVI) time-series data of helium burning variables in the Carina dwarf spheroidal galaxy. The current sample includes 92 RR Lyrae-six of them are new identifications-and 20 Anomalous Cepheids, one of which is new identification. The analysis of the Bailey diagram shows that the luminosity amplitude of the first overtone component in double-mode variables is located along the long-period tail of regular first overtone variables, while the fundamental component is located along the short-period tale of regular fundamental variables. This evidence further supports the transitional nature of these objects. Moreover, the distribution of Carina double-mode variables in the Petersen diagram (P_1/P_0 vs P_0) is similar to metal-poor globulars (M15, M68), to the dwarf spheroidal Draco and to the Galactic Halo. This suggests that the Carina old stellar population is metal-poor and affected by a small spread in metallicity. We use trigonometric parallaxes for five field RR Lyrae stars to provi...

  16. Mass modelling of dwarf spheroidal galaxies: the effect of unbound stars from tidal tails and the Milky Way

    CERN Document Server

    Klimentowski, J; Kazantzidis, S; Prada, F; Mayer, L; Mamon, G A; Klimentowski, Jaroslaw; Lokas, Ewa L.; Kazantzidis, Stelios; Prada, Francisco; Mayer, Lucio; Mamon, Gary A.

    2006-01-01

    We study the origin and properties of the population of unbound stars in the kinematic samples of dwarf spheroidal galaxies. For this purpose we have run a high resolution N-body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. In agreement with the tidal stirring scenario of Mayer et al., the dwarf is placed on a highly eccentric orbit, its initial stellar component is in the form of an exponential disk and it has a NFW-like dark matter halo. After 10 Gyrs of evolution the dwarf produces a spheroidal stellar component and is strongly tidally stripped so that mass follows light and the stars are on almost isotropic orbits. From this final state, we create mock kinematic data sets for 200 stars by observing the dwarf in different directions. We find that when the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. We also study another source of possible contamination by adding stars from the Milky Way. We demonst...

  17. The Composition of the Sagittarius Dwarf Spheroidal Galaxy and Implications for Nucleosynthesis and Chemical Evolution

    CERN Document Server

    McWilliam, A; William, Andrew Mc; Smecker-Hane, Tammy A.

    2004-01-01

    We outline the results of a study of the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). For the Sgr dSph stars with [Fe/H]>-1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the alpha- elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old, metal-poor population, including products of AGB stars and type Ia supernovae (SN). We suggest two scenarios to explain the observations: Prolonged chemical evolution in a galaxy experiencing significant mass-loss, and chemical enrichment with episodic bursts of star formation. The Galactic globular cluster Omega Cen, and the Fornax dwarf galaxy show similar abundance patterns, which suggests that those systems evolved similar to the Sgr dSph.

  18. The extremely low-metallicity tail of the Sculptor dwarf spheroidal galaxy

    CERN Document Server

    Starkenburg, Else; Tolstoy, Eline; Francois, Patrick; Irwin, Mike J; Boschman, Leon; Venn, Kim A; de Boer, Thomas J L; Lemasle, Bertrand; Jablonka, Pascale; Battaglia, Giuseppina; Groot, Paul; Kaper, Lex

    2012-01-01

    We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the Dwarf Abundances and Radial Velocities Team (DART) using the latest calibration. Of the seven extremely metal-poor candidates, five stars are confirmed to be extremely metal-poor (i.e., [Fe/H]<-3 dex), with [Fe/H]=-3.47 +/- 0.07 for our most metal-poor star. All are around or below [Fe/H]=-2.5 dex from the measurement of individual Fe lines. These values are in agreement with the CaT predictions to within error bars. None of the seven stars is found to be carbon-rich. We estimate a 2-13% possibility of this being a pure chance effect, which could indicate a lower fraction of carbon-rich extremely metal-poor stars in Sculptor compared to the Milky Way halo. The [alpha/Fe] ratios show a range from +0.5 to -0.5, a larger variation than seen in Galactic samples although typically ...

  19. OGLE Study of the Sagittarius Dwarf Spheroidal Galaxy and its M54 Globular Cluster

    CERN Document Server

    Hamanowicz, A; Udalski, A; Mroz, P; Soszynski, I; Szymanski, M K; Skowron, J; Poleski, R; Wyrzykowski, L; Kozlowski, S; Pawlak, M; Ulaczyk, K

    2016-01-01

    We use the fundamental-mode RR Lyr-type variable stars (RRab) from OGLE-IV to draw a 3D picture of the central part of the tidally disrupted Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. We estimate the line-of-sight thickness of the Sgr dSph stream to be 6sigma~6.2 kpc. Based on OGLE-IV observations collected in seasons 2011-2014 we conduct a comprehensive study of stellar variability in the field of the globular cluster M54 (NGC 6715) residing in the core of this dwarf galaxy. Among the total number of 270 detected variables we report the identification of 173 RR Lyr stars, 4 Type II Cepheids, 51 semi-regular variable red giants, 3 SX Phe-type stars, 18 eclipsing binary systems. Seventy-three variables are new discoveries. The distance to the cluster determined from RRab stars is d_M54=26.2+/-0.2_stat+/-1.3_sys kpc. From the location of RRab stars in the period-amplitude (Bailey) diagram we confirm the presence of two old populations, both in the cluster and the Sgr dSph stream.

  20. Investigation of the Puzzling Abundance Pattern in the Stars of the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Li, Hongjie; Zhang, Bo

    2013-01-01

    Many works have found unusual characteristics of elemental abundances in nearby dwarf galaxies. This implies that there is a key factor of galactic evolution that is different from that of the Milky Way (MW). The chemical abundances of the stars in the Fornax dwarf spheroidal galaxy (Fornax dSph) provide excellent information for setting constraints on the models of the galactic chemical evolution. In this work, adopting the five-component approach, we fit the abundances of the Fornax dSph stars, including $\\alpha$ elements, iron group elements and neutron-capture elements. For most sample stars, the relative contributions from the various processes to the elemental abundances are not usually in the MW proportions. We find that the contributions from massive stars to the primary $\\alpha$ elements and iron group elements increase monotonously with increasing [Fe/H]. This means that the effect of the galactic wind is not strong enough to halt star formation and the contributions from massive stars to $\\alpha$ e...

  1. Star formation history of And XVIII: a dwarf spheroidal galaxy in isolation

    CERN Document Server

    Makarova, L N; Karachentsev, I D; Tully, R B; Rizzi, L

    2016-01-01

    We present a photometric study of the Andromeda XVIII dwarf spheroidal galaxy associated with M31, and situated well outside of the virial radius of the M31 halo. The galaxy was resolved into stars with Hubble Space Telescope/Advanced Camera for Surveys revealing the old red giant branch and red clump. With the new observational data we determined the Andromeda XVIII distance to be D = 1.33+-0.08 Mpc using the tip of red giant branch method. Thus, the dwarf is situated at the distance of 579 kpc from M31. We model the star formation history of Andromeda XVIII from the stellar photometry and Padova theoretical stellar isochrones. An ancient burst of star formation occurred 12-14 Gyr ago. There is no sign of recent/ongoing star formation in the last 1.5 Gyr. The mass fractions of the ancient and intermediate age stars are 34 and 66 per cent, respectively, and the total stellar mass is 4.2x10^6 Msun. It is probable that the galaxy has not experienced an interaction with M31 in the past. We also discuss star form...

  2. Study of the Sextans dwarf spheroidal galaxy from the DART CaII triplet survey

    CERN Document Server

    Battaglia, G; Helmi, A; Irwin, M; Parisi, P; Hill, V; Jablonka, P

    2010-01-01

    We use VLT/FLAMES intermediate resolution (R~6500) spectra of individual red giant branch stars in the near-infrared CaII triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (+- 2 km/s) and CaT [Fe/H] measurements (+- 0.2 dex). We use the MgI line at 8806.8 \\AA\\, as an empirical discriminator for distinguishing between probable members of the dSph (giant stars) and probable Galactic contaminants (dwarf stars). Sextans shows a similar chemo-dynamical behaviour to other Milky Way dSphs, with its central regions being more metal rich than the outer parts and with the more metal-rich stars displaying colder kinematics than the more metal-poor stars. Hints of a velocity gradient are found along the projected major axis and along an axis at P.A.=191 deg, however a larger and more spatially extended sample may be necessary to p...

  3. VERITAS Search for VHE Gamma-ray Emission from Dwarf Spheroidal Galaxies

    CERN Document Server

    Acciari, V A; Aune, T; Beilicke, M; Benbow, W; Boltuch, D; Bradbury, S M; Buckley, J H; Bugaev, V; Byrum, K; Cannon, A; Cesarini, A; Christiansen, J L; Ciupik, L; Cui, W; Dickherber, R; Duke, C; Finley, J P; Finnegan, G; Furniss, A; Galante, N; Godambe, S; Grube, J; Guenette, R; Gyuk, G; Hanna, D; Holder, J; Hui, C M; Humensky, T B; Imran, A; Kaaret, P; Karlsson, N; Kertzman, M; Kieda, D; Konopelko, A; Krawczynski, H; Krennrich, F; Maier, G; McArthur, S; McCann, A; McCutcheon, M; Moriarty, P; Ong, R A; Otte, A N; Pandel, D; Perkins, J S; Pohl, M; Quinn, J; Ragan, K; Reyes, L C; Reynolds, P T; Roache, E; Rose, H J; Schroedter, M; Sembroski, G H; Senturk, G Demet; Smith, A W; Steele, D; Swordy, S P; Tešić, G; Theiling, M; Thibadeau, S; Varlotta, A; Vassiliev, V V; Vincent, S; Wagner, R G; Wakely, S P; Ward, J E; Weekes, T C; Weinstein, A; Weisgarber, T; Williams, D A; Wissel, S; Zitzer, B

    2010-01-01

    Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Bootes 1, and Willman 1 conducted by VERITAS. These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical background of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of ~20 hours. The 95% confidence upper limits on the integral gamma...

  4. The absence of diffuse gas around the dwarf spheroidal galaxy Leo I

    CERN Document Server

    Bowen, D V; Ferrara, A; Blades, J C; Brinks, E; Bowen, David V.; Tolstoy, Eline; Ferrara, Andrea; Brinks, Elias

    1996-01-01

    We have obtained spectra of three QSO/AGNs with the GHRS aboard the {\\it Hubble Space Telescope} to search for absorption from low column density gas in the halo of the dwarf spheroidal (dSph) galaxy Leo I. The probe sightlines pass 2.1, 3.7, and 8.1 kpc from the center of the galaxy, but no C IV, Si II, or Si IV absorption is found at the velocity of Leo I. We suggest that the column density of hydrogen which exists within 2 - 4 kpc of the galaxy is $N_H $< 10^{3}$ and $< 10^{4} M_{ødot}$ around Leo I, for simple models in which gas is distributed as a spherical halo, or as a shell, respectively. Although we cannot rule out the possibility that a significant fraction of hot gas exists along the lines of sight, in an ionization state higher than C IV or Si IV absorption lines would reveal, the results leave us with the impression that Leo I is a dSph galaxy which is isolated and inactive at the present epoch, a conclusion at odds with many theories of dwarf galaxy formation and evolution.

  5. VERITAS search for vhe gamma-ray emission from dwarf spheroidal galaxies.

    Energy Technology Data Exchange (ETDEWEB)

    Acciari, V. A.; Arlen, T.; Aune, T.; Beilicke, M.; Benbow, W.; Byrum, K.; Smith, A. W.; Wagner, R. G. (High Energy Physics); (Fred Lawrence Whipple Observatory); (Univ. of California at Los Angeles); (Univ. of California at Santa Cruz); (Washington Univ.)

    2010-09-10

    Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Bootes 1, and Willman 1 conducted by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical background of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of {approx}20 hr. The 95% confidence upper limits on the integral gamma-ray flux are in the range (0.4-2.2) x 10{sup -12} photons cm{sup -2} s{sup -1}. We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles (WIMPs) and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs (<{sigma}{nu}> {approx}< 10{sup -23} cm{sup 3} s{sup -1} for m{sub x} {approx}> 300 GeV c{sup -2}). This limit is obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and is approximately 3 orders of magnitude above the generic theoretical prediction for WIMPs in the minimal supersymmetric standard model framework. However, significant uncertainty exists in the dark matter distribution as well as the neutralino cross sections which under favorable assumptions could further lower this limit.

  6. VERITAS Search for VHE Gamma-ray Emission from Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Acciari, V. A.; Arlen, T.; Aune, T.; Beilicke, M.; Benbow, W.; Boltuch, D.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Byrum, K.; Cannon, A.; Cesarini, A.; Christiansen, J. L.; Ciupik, L.; Cui, W.; Dickherber, R.; Duke, C.; Finley, J. P.; Finnegan, G.; Furniss, A.; Galante, N.; Godambe, S.; Grube, J.; Guenette, R.; Gyuk, G.; Hanna, D.; Holder, J.; Hui, C. M.; Humensky, T. B.; Imran, A.; Kaaret, P.; Karlsson, N.; Kertzman, M.; Kieda, D.; Konopelko, A.; Krawczynski, H.; Krennrich, F.; Maier, G.; McArthur, S.; McCann, A.; McCutcheon, M.; Moriarty, P.; Ong, R. A.; Otte, A. N.; Pandel, D.; Perkins, J. S.; Pohl, M.; Quinn, J.; Ragan, K.; Reyes, L. C.; Reynolds, P. T.; Roache, E.; Rose, H. J.; Schroedter, M.; Sembroski, G. H.; Senturk, G. Demet; Smith, A. W.; Steele, D.; Swordy, S. P.; Tešić, G.; Theiling, M.; Thibadeau, S.; Varlotta, A.; Vassiliev, V. V.; Vincent, S.; Wagner, R. G.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A.; Weisgarber, T.; Williams, D. A.; Wissel, S.; Zitzer, B.; VERITAS Collaboration

    2010-09-01

    Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Boötes 1, and Willman 1 conducted by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical background of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of ~20 hr. The 95% confidence upper limits on the integral gamma-ray flux are in the range (0.4-2.2) × 10-12photonscm-2 s-1. We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles (WIMPs) and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs (langσvrang ~ 300 GeV c -2). This limit is obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and is approximately 3 orders of magnitude above the generic theoretical prediction for WIMPs in the minimal supersymmetric standard model framework. However, significant uncertainty exists in the dark matter distribution as well as the neutralino cross sections which under favorable assumptions could further lower this limit.

  7. Star formation history of And XVIII: a dwarf spheroidal galaxy in isolation

    Science.gov (United States)

    Makarova, L. N.; Makarov, D. I.; Karachentsev, I. D.; Tully, R. B.; Rizzi, L.

    2016-10-01

    We present a photometric study of the Andromeda XVIII dwarf spheroidal galaxy associated with M31, and situated well outside of the virial radius of the M31 halo. The galaxy was resolved into stars with Hubble Space Telescope/Advanced Camera for Surveys revealing the old red giant branch and red clump. With the new observational data we determined the Andromeda XVIII distance to be D = 1.33_{-0.09}^{+0.06} Mpc using the tip of red giant branch method. Thus, the dwarf is situated at the distance of 579 kpc from M31. We model the star formation history of Andromeda XVIII from the stellar photometry and Padova theoretical stellar isochrones. An ancient burst of star formation occurred 12-14 Gyr ago. There is no sign of recent/ongoing star formation in the last 1.5 Gyr. The mass fractions of the ancient and intermediate age stars are 34 and 66 per cent, respectively, and the total stellar mass is 4.2 × 106 M⊙. It is probable that the galaxy has not experienced an interaction with M31 in the past. We also discuss star formation processes of dSphs KKR 25, KKs 03, as well as dTr KK 258. Their star formation histories were uniformly measured by us from HST/ACS observations. All the galaxies are situated well beyond the Local Group and the two dSphs KKR 25 and KKs 03 are extremely isolated. Evidently, the evolution of these objects has proceeded without influence of neighbours.

  8. SCALING LAWS FOR DARK MATTER HALOS IN LATE-TYPE AND DWARF SPHEROIDAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Kormendy, John [Department of Astronomy, University of Texas at Austin, 2515 Speedway, Mail Stop C1400, Austin, TX 78712-1205 (United States); Freeman, K. C., E-mail: kormendy@astro.as.utexas.edu, E-mail: kenneth.freeman@anu.edu.au [Research School of Astronomy and Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611 (Australia)

    2016-02-01

    Dark matter (DM) halos of Sc–Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes M{sub V} > −18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention versus supernova-driven losses or decreasing baryon capture after cosmological reionization. (2) The structural differences between S+Im and Sph galaxies are small. Both are affected mostly by the physics that controls baryon depletion. (3) There is a linear correlation between the maximum rotation velocities of baryonic disks and the outer circular velocities V{sub circ} of test particles in their DM halos. Baryons become unimportant at V{sub circ} = 42 ± 4 km s{sup −1}. Smaller galaxies are dim or dark. (4) We find that, absent baryon “depletion” and with all baryons converted into stars, dSph galaxies would be brighter by ∼4.6 mag and dIm galaxies would be brighter by ∼3.5 mag. Both have DM halos that are massive enough to help to solve the “too big to fail” problem with DM galaxy formation. (5) We suggest that there exist many galaxies that are too dark to be discovered by current techniques, as required by cold DM theory. (6) Central surface densities of DM halos are constant from M{sub B} ∼ −5 to −22. This implies a Faber–Jackson law with halo mass M ∝ (halo dispersion){sup 4}.

  9. Star formation history of And XVIII: a dwarf spheroidal galaxy in isolation

    Science.gov (United States)

    Makarova, L. N.; Makarov, D. I.; Karachentsev, I. D.; Tully, R. B.; Rizzi, L.

    2017-01-01

    We present a photometric study of the Andromeda XVIII dwarf spheroidal galaxy associated with M31, and situated well outside of the virial radius of the M31 halo. The galaxy was resolved into stars with Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) revealing the old red giant branch and red clump. With the new observational data, we determined the Andromeda XVIII distance to be D = 1.33_{-0.09}^{+0.06} Mpc using the tip of red giant branch method. Thus, the dwarf is situated at the distance of 579 kpc from M31. We model the star formation history of Andromeda XVIII from the stellar photometry and Padova theoretical stellar isochrones. An ancient burst of star formation occurred 12-14 Gyr ago. There is no sign of recent/ongoing star formation in the last 1.5 Gyr. The mass fractions of the ancient and intermediate age stars are 34 and 66 per cent, respectively, and the total stellar mass is 4.2 × 106 M⊙. It is probable that the galaxy has not experienced an interaction with M31 in the past. We also discuss star formation processes of dSphs KKR 25, KKs 03, as well as dTr KK 258. Their star formation histories were uniformly measured by us from HST/ACS observations. All the galaxies are situated well beyond the Local Group, and the two dSphs KKR 25 and KKs 03 are extremely isolated. Evidently, the evolution of these objects has proceeded without influence of neighbours.

  10. Foreground effect on the $J$-factor estimation of classical dwarf spheroidal galaxies

    CERN Document Server

    Ichikawa, Koji; Matsumoto, Shigeki; Ibe, Masahiro; Sugai, Hajime; Hayashi, Kohei

    2016-01-01

    The gamma-ray observation of the dwarf spheroidal galaxies (dSphs) is a promising approach to search for the dark matter annihilation (or decay) signal. The dSphs are the nearby satellite galaxies with a clean environment and dense dark matter halo so that they give stringent constraints on the ${\\cal O}(1)$ TeV dark matter. However, recent studies have revealed that current estimation of astrophysical factors relevant for the dark matter searches are not conservative, where the various non-negligible systematic uncertainties are not taken into account. Among them, the effect of foreground stars on the astrophysical factors has not been paid much attention, which becomes more important for deeper and wider stellar surveys in the future. In this article, we assess the effects of the foreground contamination by generating the mock samples of stars and using a model of future spectrographs. We investigate various data cuts to optimize the quality of the data and find that the cuts on the velocity and surface gra...

  11. Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Cotta, R.C.; /SLAC; Drlica-Wagner, A.; Murgia, S.; /SLAC /KIPAC, Menlo Park; Bloom, E.D.; Hewett, J.L.; Rizzo, T.G.; /SLAC

    2012-03-15

    We examine the ability for the Large Area Telescope (LAT) to constrain Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest Supersymmetric Particles (LSPs) for a set of {approx}71k experimentally valid supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find that none of these models can be excluded at 95% confidence by the current analysis; nevertheless, many lie within the predicted reach of future LAT analyses. With two years of data, we find that the LAT is currently most sensitive to light LSPs (mLSP < 50 GeV) annihilating into {tau}-pairs and heavier LSPs annihilating into b{bar b}. Additionally, we find that future LAT analyses will be able to probe some LSPs that form a sub-dominant component of dark matter. We directly compare the LAT results to direct detection experiments and show the complementarity of these search methods.

  12. An Empirical Model for Halo Evolution and Global Gas Dynamics of the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Yuan, Zhen; Jing, Y P

    2015-01-01

    We present an empirical model for the halo evolution and global gas dynamics of Fornax, the brightest Milky Way (MW) dwarf spheroidal galaxy (dSph). Assuming a global star formation rate psi(t)=lambda_*[M_g(t)/M_sun]^alpha consistent with observations of star formation in nearby galaxies and using the data on Fornax's psi(t), we derive the evolution of the total mass M_g(t) for cold gas in Fornax's star-forming disk and the rate Delta F(t) of net gas flow to or from the disk. We identify the onset of the transition in Delta F(t) from a net inflow to a net outflow as the time t_sat at which the Fornax halo became an MW satellite and estimate the evolution of its total mass M_h(t) at t

  13. Estimating the GeV Emission of Millisecond Pulsars in Dwarf Spheroidal Galaxies

    CERN Document Server

    Winter, Miles; Bechtol, Keith; Vandenbroucke, Justin

    2016-01-01

    We estimate the conventional astrophysical emission intrinsic to dwarf spheroidal satellite galaxies (dSphs) of the Milky Way, focusing on millisecond pulsars (MSPs), and evaluate the potential for confusion with dark matter (DM) annihilation signatures at GeV energies. In low-density stellar environments, such as dSphs, the abundance of MSPs is expected to be proportional to stellar mass. Accordingly, we construct the $\\gamma$-ray luminosity function of MSPs in the Milky Way disk, where $>90$ individual MSPs have been detected with the $\\textit{Fermi}$ Large Area Telescope (LAT), and scale this luminosity function to the stellar masses of 30 dSphs to estimate the cumulative emission from their MSP populations. We predict that MSPs in the highest stellar mass dSphs, Fornax and Sculptor, produce a $\\gamma$-ray flux $>500$ MeV of $\\sim10^{-11}$~ph~cm$^{-2}$~s$^{-1}$, which is a factor $\\sim10$ below the current LAT sensitivity at high Galactic latitudes. The MSP emission in ultra-faint dSphs, including targets ...

  14. Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies.

    Science.gov (United States)

    Qian, Yong-Zhong; Wasserburg, G J

    2012-03-27

    We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relationship between the total stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos. The model further predicts as a natural consequence that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease for stellar populations at the higher end of the [Fe/H] range in a dSph. We show that, for infall rates far below the net rate of gas loss to star formation and outflows, the MD in our model is very sharply peaked at one [Fe/H] value, similar to what is observed in most globular clusters. This result suggests that globular clusters may be end members of the same family as dSphs.

  15. MEASURING DARK MATTER PROFILES NON-PARAMETRICALLY IN DWARF SPHEROIDALS: AN APPLICATION TO DRACO

    Energy Technology Data Exchange (ETDEWEB)

    Jardel, John R.; Gebhardt, Karl [Department of Astronomy, The University of Texas, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States); Fabricius, Maximilian H.; Williams, Michael J. [Max-Planck Institut fuer extraterrestrische Physik, Giessenbachstrasse, D-85741 Garching bei Muenchen (Germany); Drory, Niv, E-mail: jardel@astro.as.utexas.edu [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Avenida Universidad 3000, Ciudad Universitaria, C.P. 04510 Mexico D.F. (Mexico)

    2013-02-15

    We introduce a novel implementation of orbit-based (or Schwarzschild) modeling that allows dark matter density profiles to be calculated non-parametrically in nearby galaxies. Our models require no assumptions to be made about velocity anisotropy or the dark matter profile. The technique can be applied to any dispersion-supported stellar system, and we demonstrate its use by studying the Local Group dwarf spheroidal galaxy (dSph) Draco. We use existing kinematic data at larger radii and also present 12 new radial velocities within the central 13 pc obtained with the VIRUS-W integral field spectrograph on the 2.7 m telescope at McDonald Observatory. Our non-parametric Schwarzschild models find strong evidence that the dark matter profile in Draco is cuspy for 20 {<=} r {<=} 700 pc. The profile for r {>=} 20 pc is well fit by a power law with slope {alpha} = -1.0 {+-} 0.2, consistent with predictions from cold dark matter simulations. Our models confirm that, despite its low baryon content relative to other dSphs, Draco lives in a massive halo.

  16. Discovery of true, likely and possible symbiotic stars in the dwarf spheroidal NGC 205

    CERN Document Server

    Gonçalves, Denise R; de la Rosa, Ignacio G; Akras, Stavros

    2014-01-01

    In this paper we discuss the photometric and spectroscopic observations of newly discovered (symbiotic) systems in the dwarf spheroidal galaxy NGC 205. The Gemini Multi-Object Spectrograph on-off band [O III] 5007 A emission imaging highlighted several [O III] line emitters, for which optical spectra were then obtained (Gon\\c{c}alves et al. 2014). The detailed study of the spectra of three objects allow us to identify them as true, likely and possible symbiotic systems (SySts), the first ones discovered in this galaxy. SySt-1 is unambiguously classified as a symbiotic star, because of the presence of unique emission lines which belong only to symbiotic spectra, the well known O VI Raman scattered lines. SySt-2 is only possibly a SySt because the Ne VII Raman scattered line at 4881 A, recently identified in a well studied Galactic symbiotic as another very conspicuous property of symbiotic, could as well be identified as N III or [Fe III]. Finally, SySt-3 is likely a symbiotic binary because in the red part of...

  17. Neutron-capture element deficiency of the Hercules dwarf spheroidal galaxy

    CERN Document Server

    Koch, Andreas; Aden, Daniel; Matteucci, Francesca

    2013-01-01

    We present an assessment of the barium abundance ratios for red giant member stars in the faint Hercules dwarf spheroidal (dSph) galaxy. Our results are drawn from intermediate-resolution FLAMES/GIRAFFE spectra around the Ba II 6141.71 AA absorption line at low signal-to-noise ratios. For three brighter stars we were able to gain estimates from direct equivalent-width measurements, while for the remaining eight stars only upper limits could be obtained. These results are investigated in a statistical manner and indicate very low Ba abundances of log epsilon (Ba) < 0.7 dex (3 sigma). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 AA-line, but most of those would only lead to even lower abundances. A better match with metal-poor halo and dSph stars can only be reached by including a large uncertainty in the continuum placement. This contrasts with the high dispersions in iron and calcium (in excess of 1 dex) in this galaxy. While the latter spreads are typic...

  18. A unique isolated dwarf spheroidal galaxy at D=1.9 Mpc

    CERN Document Server

    Makarov, Dmitry; Sharina, Margarita; Uklein, Roman; Tikhonov, Anton; Guhathakurta, Puragra; Kirby, Evan; Terekhova, Natalya

    2012-01-01

    We present a photometric and spectroscopic study of the unique isolated nearby dSph galaxy KKR25. The galaxy was resolved into stars with HST/WFPC2 including old red giant branch and red clump. We have constructed a model of the resolved stellar populations and measured the star formation rate and metallicity as function of time. The main star formation activity period occurred about 12.6 to 13.7 Gyr ago. These stars are mostly metal-poor, with a mean metallicity [Fe/H]\\sim -1 to -1.6 dex. About 60 per cent of the total stellar mass was formed during this event. There are indications of intermediate age star formation in KKR25 between 1 and 4 Gyr with no significant signs of metal enrichment for these stars. Long-slit spectroscopy was carried out using the Russian 6-m telescope of the integrated starlight and bright individual objects in the galaxy. We have discovered a planetary nebula (PN) in KKR25. This is the first known PN in a dwarf spheroidal galaxy outside the Local Group. We have measured its oxygen ...

  19. Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies

    CERN Document Server

    Qian, Yong-Zhong

    2012-01-01

    We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relationship between the total stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos. The model further predicts as a natural consequence that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease for stellar populations at the higher end of the [Fe/H] range in a dSph. We show that for infall rates far below the net rate of gas loss to star formation and outflows...

  20. Structural properties of non-spherical dark halos in Milky Way and Andromeda dwarf spheroidal galaxies

    CERN Document Server

    Hayashi, Kohei

    2015-01-01

    We investigate the non-spherical density structure of dark halos of the dwarf spheroidal (dSph) galaxies in the Milky Way and Andromeda galaxies, based on revised axisymmetric mass models from our previous work. The models we adopt here fully take into account velocity anisotropy of tracer stars confined within a flattened dark halo. Applying our models to the available kinematic data of the twelve bright dSphs, we find that these galaxies associate, in general, elongated dark halos even considering the effect of this velocity anisotropy of stars. We also find that the best-fit parameters, especially for the shapes of dark halos and velocity anisotropy, are susceptible to both the availability of velocity data in the outer regions and the effect of the lack of sample stars in each spatial bin. Thus, to obtain more realistic limits on dark halo structures, we require photometric and kinematic data over much larger areas in the dSphs than previously explored. The results obtained from the currently available da...

  1. Enrichment of r-process elements in dwarf spheroidal galaxies in chemo-dynamical evolution model

    CERN Document Server

    Hirai, Yutaka; Saitoh, Takayuki R; Fujii, Michiko S; Hidaka, Jun; Kajino, Toshitaka

    2015-01-01

    The rapid neutron-capture process (r-process) is a major process to synthesize elements heavier than iron, but the astrophysical site(s) of r-process is not identified yet. Neutron star mergers (NSMs) are suggested to be a major r-process site from nucleosynthesis studies. Previous chemical evolution studies however require unlikely short merger time of NSMs to reproduce the observed large star-to-star scatters in the abundance ratios of r-process elements relative to iron, [Eu/Fe], of extremely metal-poor stars in the Milky Way (MW) halo. This problem can be solved by considering chemical evolution in dwarf spheroidal galaxies (dSphs) which would be building blocks of the MW and have lower star formation efficiencies than the MW halo. We demonstrate that enrichment of r-process elements in dSphs by NSMs using an N-body/smoothed particle hydrodynamics code. Our high-resolution model reproduces the observed [Eu/Fe] by NSMs with a merger time of 100 Myr when the effect of metal mixing is taken into account. Thi...

  2. DISCOVERY OF MIRA VARIABLE STARS IN THE METAL-POOR SEXTANS DWARF SPHEROIDAL GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Sakamoto, Tsuyoshi [Japan Spaceguard Association, 1716-3 Ookura, Bisei, Ibara, Okayama 714-1411 (Japan); Matsunaga, Noriyuki; Nakada, Yoshikazu [Kiso Observatory, Institute of Astronomy, School of Science, University of Tokyo, 10762-30 Mitake, Kiso-machi, Kiso-gun, Nagano 397-0101 (Japan); Hasegawa, Takashi, E-mail: sakamoto@spaceguard.or.jp [Gunma Astronomical Observatory, 6860-86 Nakayama, Takayama, Agatsuma, Gunma 377-0702 (Japan)

    2012-12-10

    We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal galaxy (dSph). We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the I{sub c} band show large-amplitude (3.7 and 0.9 mag) and long-period (326 {+-} 15 and 122 {+-} 5 days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras (75.3{sup +12.8}{sub -10.9} and 79.8{sup +11.5}{sub -9.9} kpc, respectively), together with the radial velocities available, support memberships of the Sextans dSph (90.0 {+-} 10.0 kpc). These are the first Miras found in a stellar system with a metallicity as low as [Fe/H] {approx} -1.9 than any other known system with Miras.

  3. Dynamical models for the Sculptor dwarf spheroidal in a Lambda CDM universe

    CERN Document Server

    Strigari, Louis E; White, Simon D M

    2014-01-01

    The Sculptor dwarf spheroidal galaxy contains two distinct stellar populations: one metal-rich and the other metal-poor. Several authors have argued that in order for these two populations to reside in the same gravitational potential, the dark matter halo must have a core similar to that observed in the stellar count profile. This would rule out the cuspy Navarro-Frenk-White (NFW) density profiles predicted for halos and subhalos by dark matter only simulations of the Lambda Cold Dark Matter (Lambda-CDM) cosmological model. We present a new theoretical framework to analyse stellar count and velocity observations in a self-consistent manner based on separable models, f(E,J)=g(J)h(E), for the distribution function of an equilibrium spherical system. We use this machinery to analyse available photometric and kinematic data for the two stellar populations in Sculptor. We find, contrary to some previous claims, that the data are consistent with populations in equilibrium within an NFW dark matter potential with s...

  4. Mass assembly history and infall time of the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Wang, Mei-Yu; Lovell, Mark R; Frenk, Carlos S; Zentner, Andrew R

    2015-01-01

    We use cosmological simulations to identify dark matter subhalo host candidates of the Fornax dwarf spheroidal galaxy using the stellar kinematic properties of Fornax. We consider cold dark matter (CDM), warm dark matter (WDM), and decaying dark matter (DDM) simulations for our models of structure formation. The subhalo candidates in CDM typically have smaller mass and higher concentrations at z = 0 than the corresponding candidates in WDM and DDM. We examine the formation histories of the ~ 100 Fornax candidate subhalos identified in CDM simulations and, using approximate luminosity-mass relationships for subhalos, we find two of these subhalos that are consistent with both the Fornax luminosity and kinematics. These two subhalos have a peak mass over ten times larger than their z = 0 mass. We suggest that in CDM the dark matter halo hosting Fornax must have been severely stripped of mass and that it had an infall time into the Milky Way of ~ 9 Gyr ago. In WDM, we find that candidate subhalos consistent with...

  5. The metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Hendricks, Benjamin; Lanfranchi, Gustavo A; Boeche, Corrado; Walker, Matthew; Johnson, Christian I; Penarrubia, Jorge; Gilmore, Gerard

    2014-01-01

    We present alpha-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal galaxy (dSph), obtained with VLT/GIRAFFE (R~16,000). Due to the large fraction of metal-poor stars in our sample, we are able to follow the alpha-element evolution from [Fe/H]=-2.5 continuously to [Fe/H]=-0.7 dex. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, alpha-enhanced plateau down to subsolar [alpha/Fe] values due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an alpha-enhanced plateau at early epochs, followed by a well-defined "knee", caused by the onset of SNe Ia, and finally a second plateau with sub-solar [alpha/Fe] values. We find the position of this knee to be at [Fe/H]=-1.9 and therefore significantly more metal-poor than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value ...

  6. Searching for decaying dark matter in deep XMM-Newton observation of the Draco dwarf spheroidal

    CERN Document Server

    Ruchayskiy, Oleg; Iakubovskyi, Dmytro; Bulbul, Esra; Eckert, Dominique; Franse, Jeroen; Malyshev, Denys; Markevitch, Maxim; Neronov, Andrii

    2015-01-01

    We present results of a search for the 3.5 keV emission line in our recent very long (~1.4 Ms) XMM-Newton observation of the Draco dwarf spheroidal galaxy. The astrophysical X-ray emission from such dark matter-dominated galaxies is faint, thus they provide a test for the dark matter origin of the 3.5 keV line previously detected in other massive, but X-ray bright objects, such as galaxies and galaxy clusters. We do not detect a statistically significant emission line from Draco; this constrains the lifetime of a decaying dark matter particle to tau > (7-9) x 10^27 s at 95% CL (combining all three XMM-Newton cameras; the interval corresponds to the uncertainty of the dark matter column density in the direction of Draco). The PN camera, which has the highest sensitivity of the three, does show a positive spectral residual (above the carefully modeled continuum) at E = 3.54 +/- 0.06 keV with a 2.3 sigma significance. The two MOS cameras show less-significant or no positive deviations, consistently within 1 sigm...

  7. The Chemical Enrichment History of the Fornax Dwarf Spheroidal Galaxy from the Infrared Calcium Triplet

    CERN Document Server

    Pont, F; Gallart, C; Hardy, E; Winnick, R A; Pont, Frederic; Zinn, Robert; Gallart, Carme; Hardy, Eduardo; Winnick, Rebeccah

    2004-01-01

    Near infrared spectra were obtained for 117 red giants in the Fornax dwarf spheroidal galaxy with the FORS1 spectrograph on the VLT, in order to study the metallicity distribution of the stars and to lift the age-metallicity degeneracy of the red giant branch (RGB) in the color-magnitude diagram (CMD). Metallicities are derived from the equivalent widths of the infrared Calcium triplet lines at 8498, 8542, and 8662 A, calibrated with data from globular clusters, the open cluster M67 and the LMC. For a substantial portion of the sample, the strength of the Calcium triplet is unexpectedly high, clearly indicating that the main stellar population of Fornax is significantly more metal-rich than could be inferred from the position of its RGB in the CMD. We show that the relative narrowness of the RGB in Fornax is caused by the superposition of stars of very different ages and metallicities. The metallicity distribution in Fornax is centered at [Fe/H]= -0.9, with a metal-poor tail extending to [Fe/H] ~= -2. While t...

  8. Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies

    CERN Document Server

    Kirby, Evan N; Zhang, Andrew J; Deng, Michelle; Cohen, Judith G; Guhathakurta, Puragra; Shetrone, Matthew D; Lee, Young Sun; Rizzi, Luca

    2015-01-01

    We present carbon abundances of red giants in Milky Way globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above log(L/L_sun) ~= 1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of Type Ia supernovae at higher metallicities. We also identified 11 very carbon-rich giants (8 previously known) in...

  9. Dwarf spheroidal satellites of M31: I. Variable stars and stellar populations in Andromeda XIX

    CERN Document Server

    Cusano, Felice; Garofalo, Alessia; Cignoni, Michele; Federici, Luciana; Marconi, Marcella; Musella, Ilaria; Ripepi, Vincenzo; Boutsia, Konstantina; Fumana, Marco; Gallozzi, Stefano; Testa, Vincenzo

    2013-01-01

    We present B,V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.2') of Andromeda's dwarf spheroidal companions, that we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23'x 23' area centered on And XIX and present the deepest color magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V~26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which, however, extends to the blue to significantly populate the classical instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and 3 of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ( = 0.62 d, \\sigma= 0.03 d) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermedia...

  10. Metal-rich carbon stars in the Sagittarius Dwarf Spheroidal galaxy

    CERN Document Server

    Lagadec, Eric; Sloan, G C; Wood, Peter R; Matsuura, Mikako; Bernard-Salas, Jeronimo; Blommaert, J A D L; Cioni, M -R L; Feast, M W; Groenewegen, M A T; Hony, Sacha; Menzies, J W; van Loon, J Th; Whitelock, P A

    2009-01-01

    We present spectroscopic observations from the {\\it Spitzer Space Telescope} of six carbon-rich AGB stars in the Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph) and two foreground Galactic carbon stars. The band strengths of the observed C$_2$H$_2$ and SiC features are very similar to those observed in Galactic AGB stars. The metallicities are estimated from an empirical relation between the acetylene optical depth and the strength of the SiC feature. The metallicities are higher than those of the LMC, and close to Galactic values. While the high metallicity could imply an age of around 1 Gyr, for the dusty AGB stars, the pulsation periods suggest ages in excess of 2 or 3 Gyr. We fit the spectra of the observed stars using the DUSTY radiative transfer model and determine their dust mass-loss rates to be in the range 1.0--3.3$\\times 10^{-8} $M$_{\\odot}$yr$^{-1}$. The two Galactic foreground carbon-rich AGB stars are located at the far side of the solar circle, beyond the Galactic Centre. One of these two stars ...

  11. r-Process enrichment by magnetorotational core-collapse supernovae in the early dwarf spheroidal galaxies

    CERN Document Server

    Tsujimoto, Takuji

    2015-01-01

    One of the hottest open issues in chemical evolution of $r$-process elements is fast enrichment in the early Universe. Clear evidence for it is seen in stellar abundances of extremely metal-poor stars in the Galactic halo. On the other hand, small-mass galaxies are the ideal testbed to follow the evolutionary features of r-process enrichment, given the potential rarity of production events yielding heavy r-process elements. Their occurrences become countable and thus an enrichment path due to each event can be found in the stellar abundances. We examine the chemical feature of Eu abundance at an early stage of [Fe/H] $\\lesssim -2$ in the Draco and Sculptor dwarf spheroidal (dSph) galaxies. Accordingly we constrain the properties of the Eu production in the early dSphs. We find that the Draco dSph experienced a few Eu production events while Eu enrichment took place more continuously in the Sculptor dSph due to its larger stellar mass. The event rate of Eu production is estimated to be about one per $100-200$ ...

  12. The metal abundance distribution of the oldest stellar component in the Sculptor dwarf spheroidal galaxy

    CERN Document Server

    Clementini, G; Bragaglia, A; Fiorenzano, A F M; Held, E V; Gratton, R G

    2005-01-01

    (abridged) Low resolution spectroscopy obtained with FORS2 at the Very Large Telescope (VLT) has been used to measure individual metal abundances ([Fe/H]) for 107 RR Lyrae stars, and trace the metal distribution of the oldest stellar component in the Sculptor dwarf spheroidal galaxy. Their metallicities have an average value of [Fe/H]=-1.83 +/- 0.03 (r.m.s. 0.26 dex) and cover the metallicity range -2.40-1, only 5 stars with -1.4 -1.7). The star-to-star scatter is small (0.19-0.23 dex) but larger than typical errors on individual metallicities (+/- 0.15-0.16 dex), indicating a real spread in metal abundances. The radial velocities have a dispersion of 12.9 km/s, consistent with the dispersion derived for blue horizontal branch stars in Sculptor by Tolstoy et al. (2004), suggesting, along with the metallicity distribution, that most of the RR Lyr's arise from the same burst of stellar formation that produced the metal-poor component giving origin to the galaxy blue horizontal branch, and only a few (if any) co...

  13. How to make an ultra-faint dwarf spheroidal galaxy: tidal stirring of disky dwarfs with shallow dark matter density profiles

    CERN Document Server

    Lokas, Ewa L; Mayer, Lucio

    2012-01-01

    In recent years the Sloan Digital Sky Survey has unraveled a new population of ultra-faint dwarf galaxies (UFDs) in the vicinity of the Milky Way (MW) whose origin is still a puzzle. Using a suite of collisionless N-body simulations, we investigate the formation of UFDs in the context of the tidal stirring model for the formation of dwarf spheroidal galaxies in the Local Group (LG). Our simulations are designed to reproduce the tidal interactions between MW-sized host galaxies and rotationally supported dwarfs embedded in 10^9 M_sun dark matter (DM) halos. We explore a wide variety of inner density slopes \\rho \\propto r^{-\\alpha} for the dwarf DM halos, ranging from core-like (\\alpha = 0.2) to cuspy (\\alpha = 1), and different dwarf orbital configurations. Our experiments demonstrate that UFDs can be produced via the tidal stirring of disky dwarfs on relatively tight orbits, consistent with a redshift of accretion by the host galaxy of z~1, and with intermediate values for the halo inner density slopes (\\rho ...

  14. The Effect of Black Holes in Local Dwarf Spheroidal Galaxies on Gamma-Ray Constraints on Dark Matter Annihilation

    CERN Document Server

    Gonzalez-Morales, Alma X; Queiroz, Farinaldo S

    2014-01-01

    The recent evidence for black holes of intermediate mass in dwarf galaxies motivates the assessment of the resulting effect on the host dark matter density profile, and the consequences for the constraints on the plane of the dark matter annihilation cross section versus mass, stemming from the non-observation of gamma rays from local dwarf spheroidals with the Fermi Large Area Telescope. We compute the density profile using three different prescriptions for the black hole mass associated with a given dwarf galaxy, and taking into account the cutoff to the density from dark matter pair-annihilation. We find that the limits on the dark matter annihilation rate from observations of individual dwarfs are enhanced by factors of a few up to $10^6$, depending on the specific galaxy, on the black hole mass prescription, and on the dark matter particle mass. We estimate limits from combined observations of a sample of 15 dwarfs, for a variety of assumptions on the dwarf black hole mass and on the dark matter density ...

  15. The interstellar medium in Andromeda's dwarf spheroidal galaxies - II. Multiphase gas content and ISM conditions

    Science.gov (United States)

    De Looze, Ilse; Baes, Maarten; Cormier, Diane; Kaneko, Hiroyuki; Kuno, Nario; Young, Lisa; Bendo, George J.; Boquien, Médéric; Fritz, Jacopo; Gentile, Gianfranco; Kennicutt, Robert C.; Madden, Suzanne C.; Smith, Matthew W. L.; Wilson, Christine D.

    2017-03-01

    We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC 147, NGC 185 and NGC 205). Ancillary H I, CO, Spitzer Infrared Spectrograph spectra, Hα and X-ray observations are combined to trace the atomic, cold and warm molecular, ionized and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [C I] observations of NGC 205 to revise its molecular gas content. We derive total gas masses of Mg = 1.9-5.5 × 105 M⊙ for NGC 185 and Mg = 8.6-25.0 × 105 M⊙ for NGC 205. Non-detections combine to an upper limit on the gas mass of Mg ≤ 0.3-2.2 × 105 M⊙ for NGC 147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR ∼ 37-107 and 48-139 are also considerably lower compared to the expected GDR ∼ 370 and 520 for the low metal abundances in NGC 185 (0.36 Z⊙) and NGC 205 (0.25 Z⊙), respectively. To simultaneously account for the gas deficiency and low gas-to-dust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (∼1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC 147, NGC 185 and NGC 205.

  16. ENRICHMENT OF r-PROCESS ELEMENTS IN DWARF SPHEROIDAL GALAXIES IN CHEMO-DYNAMICAL EVOLUTION MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Hirai, Yutaka; Kajino, Toshitaka [Department of Astronomy, Graduate School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Ishimaru, Yuhri [Department of Material Science,International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585 (Japan); Saitoh, Takayuki R. [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); Fujii, Michiko S.; Hidaka, Jun, E-mail: yutaka.hirai@nao.ac.jp [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa Mitaka, Tokyo 181-8588 (Japan)

    2015-11-20

    The rapid neutron-capture process (r-process) is a major process for the synthesis of elements heavier than iron-peak elements, but the astrophysical site(s) of the r-process has not yet been identified. Neutron star mergers (NSMs) are suggested to be a major r-process site according to nucleosynthesis studies. Previous chemical evolution studies, however, required unlikely short merger times of NSMs to reproduce the observed large star-to-star scatters in the abundance ratios of r-process elements to iron: the [Eu/Fe] of extremely metal-poor stars in the Milky Way (MW) halo. This problem can be solved by considering chemical evolution in dwarf spheroidal galaxies (dSphs), which would be building blocks of the MW and have lower star formation efficiencies than the MW halo. We demonstrate the enrichment of r-process elements in dSphs by NSMs using an N-body/smoothed particle hydrodynamics code. Our high-resolution model reproduces the observed [Eu/Fe] due to NSMs with a merger time of 100 Myr when the effect of metal mixing is taken into account. This is because metallicity is not correlated with time ∼300 Myr from the start of the simulation due to the low star formation efficiency in dSphs. We also confirm that this model is consistent with observed properties of dSphs such as radial profiles and metallicity distribution. The merger time and the Galactic rate of NSMs are suggested to be ≲300 Myr and ∼10{sup −4} year{sup −1}, respectively, which are consistent with the values suggested by population synthesis and nucleosynthesis studies. This study supports the argument that NSMs are the major astrophysical site of the r-process.

  17. Dwarf spheroidal satellites of M31. I. Variable stars and stellar populations in Andromeda XIX

    Energy Technology Data Exchange (ETDEWEB)

    Cusano, Felice; Clementini, Gisella; Garofalo, Alessia; Federici, Luciana, E-mail: felice.cusano@oabo.inaf.it, E-mail: gisella.clementini@oabo.inaf.it, E-mail: luciana.federici@oabo.inaf.it, E-mail: alessia.garofalo@studio.unibo.it [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); and others

    2013-12-10

    We present B, V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.'2) of Andromeda's dwarf spheroidal companions, which we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23' × 23' area centered on And XIX and present the deepest color-magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V ∼ 26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which extends to the blue to significantly populate the classical instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and three of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars ((P {sub ab}) = 0.62 days, σ = 0.03 days) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average luminosity of the RR Lyrae stars ((V(RR)) = 25.34 mag, σ = 0.10 mag), we determine a distance modulus of (m – M){sub 0} = 24.52 ± 0.23 mag in a scale where the distance to the Large Magellanic Cloud (LMC) is 18.5 ± 0.1 mag. The ACs follow a well-defined Period-Wesenheit (PW) relation that appears to be in very good agreement with the PW relationship defined by the ACs in the LMC.

  18. Mass modelling of dwarf spheroidal galaxies: the effect of unbound stars from tidal tails and the Milky Way

    Science.gov (United States)

    Klimentowski, Jarosław; Łokas, Ewa L.; Kazantzidis, Stelios; Prada, Francisco; Mayer, Lucio; Mamon, Gary A.

    2007-06-01

    We study the origin and properties of the population of unbound stars in the kinematic samples of dwarf spheroidal (dSph) galaxies. For this purpose we have run a high-resolution N-body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. In agreement with the tidal stirring scenario of Mayer et al., the dwarf is placed on a highly eccentric orbit, its initial stellar component is in the form of an exponential disc and it has a NFW-like dark matter (DM) halo. After 10 Gyr of evolution the dwarf produces a spheroidal stellar component and is strongly tidally stripped so that mass follows light and the stars are on almost isotropic orbits. From this final state, we create mock kinematic data sets for 200 stars by observing the dwarf in different directions. We find that when the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. We also study another source of possible contamination by adding stars from the Milky Way. We demonstrate that most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert and recently tested on simulated DM haloes. We model the cleaned-up kinematic samples using solutions of the Jeans equation with constant mass-to-light ratio (M/L) and velocity anisotropy parameter. We show that even for such a strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and M/L of the dwarf with accuracy typically better than 25 per cent and almost exactly in the case when the line of sight is perpendicular to the tidal tails. The analysis was applied to the new data for the Fornax dSph galaxy. We show that after careful removal of interlopers the velocity dispersion profile of Fornax can be reproduced by a model in which mass traces light with a M/L of 11 solar units and isotropic orbits. We demonstrate that most of the contamination in the kinematic sample of

  19. A new method of estimating the mass-to-light ratio of the Ursa Minor dwarf spheroidal galaxy

    CERN Document Server

    Gómez-Flechoso, M A

    2003-01-01

    Dwarf satellite galaxies undergo strong tidal forces produced by the main galaxy potential. These forces disturb the satellite, producing asymmetries in its stellar distribution, tidal tail formation, and modifications of the velocity dispersions profiles. Most of these features are observed in the Ursa Minor (UMi) dwarf spheroidal galaxy, which is one of the closest satellites of the Milky Way. These features show that UMi is been tidally disrupted and probably not in virial equilibrium. The high velocity dispersion of UMi could also be a reflection of this tidal disruption and not the signature of the large dark matter content that would be deduced if virial equilibrium is assumed. In order to avoid the uncertainty produced when virial equilibrium is assumed in systems in strong tidal fields, we present a new method of calculating the mass-to-luminosity ratio of disrupted dwarf galaxies. This method is based on numerical simulations and only takes into account the shape of the dwarf density profile and the ...

  20. CARBON ABUNDANCES FOR RED GIANTS IN THE DRACO DWARF SPHEROIDAL GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Shetrone, Matthew D.; Stanford, Laura M. [McDonald Observatory, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Smith, Graeme H. [University of California ObservatoriesLick Observatory, Department of Astronomy and Astrophysics, UC Santa Cruz, 1156 High St., Santa Cruz, CA 95064 (United States); Siegel, Michael H. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, State College, PA 16801 (United States); Bond, Howard E., E-mail: shetrone@astro.as.utexas.edu, E-mail: graeme@ucolick.org, E-mail: siegel@astro.psu.edu, E-mail: bond@stsci.edu [9615 Labrador Ln., Cockeysville, MD 21030 (United States)

    2013-05-15

    Measurements of [C/Fe], [Ca/H], and [Fe/H] have been derived from Keck I LRISb spectra of 35 giants in the Draco dwarf spheroidal galaxy. The iron abundances are derived by a spectrum synthesis modeling of the wavelength region from 4850 to 5375 A, while calcium and carbon abundances are obtained by fitting the Ca II H and K lines and the CH G band, respectively. A range in metallicity of -2.9 {<=} [Fe/H] {<=} -1.6 is found within the giants sampled, with a good correlation between [Fe/H] and [Ca/H]. The great majority of stars in the sample would be classified as having weak absorption in the {lambda}3883 CN band, with only a small scatter in band strengths at a given luminosity on the red giant branch. In this sense the behavior of CN among the Draco giants is consistent with the predominantly weak CN bands found among red giants in globular clusters of metallicity [Fe/H] < -1.8. Over half of the giants in the Draco sample have [Fe/H] > -2.25, and among these there is a trend for the [C/Fe] abundance to decrease with increasing luminosity on the red giant branch. This is a phenomenon that is also seen among both field and globular cluster giants of the Galactic halo, where it has been interpreted as a consequence of deep mixing of material between the base of the convective envelope and the outer limits of the hydrogen-burning shell. However, among the six Draco giants observed that turn out to have metallicities -2.65 < [Fe/H] < -2.25 there is no such trend seen in the carbon abundance. This may be due to small sample statistics or primordial inhomogeneities in carbon abundance among the most metal-poor Draco stars. We identify a potential carbon-rich extremely metal-poor star in our sample. This candidate will require follow-up observations for confirmation.

  1. 'Sculptor'-ing the Galaxy? The Chemical Compositions of Red Giants in the Sculptor Dwarf Spheroidal Galaxy

    CERN Document Server

    Geisler, D; Wallerstein, G; González, G; Charbonnel, C; Geisler, Doug; Smith, Verne V.; Wallerstein, George; Gonzalez, Guillermo; Charbonnel, Corinne

    2004-01-01

    We have used high-resolution, high signal-to-noise spectra obtained with the VLT and UVES to determine abundances of 17 elements in 4 red giants in the Sculptor dwarf spheroidal galaxy. Our [Fe/H] values range from --2.10 to --0.97, confirming previous findings of a large metallicity spread. We have combined our data with similar data for five Sculptor giants studied recently to form one of the largest samples of high resolution abundances yet obtained for a dwarf spheroidal galaxy, covering essentially the full known metallicity range. These properties allow us to establish trends of [X/Fe] with [Fe/H] for many elements, X. The trends are significantly different from the trends seen in galactic halo and globular cluster stars. We compare our Sculptor sample to their most similar Galactic counterparts and find substantial differences remain even with these stars. The many discrepancies in the relationships between [X/Fe] as seen in Sculptor compared with Galactic field stars indicates that our halo cannot be ...

  2. The evolutionary history of low-luminosity local group dwarf galaxies

    Science.gov (United States)

    van den Bergh, Sidney

    1994-06-01

    The stellar content of Local Group dwarfs fainter than MV = -14.0 is found to correlate with distance from the Galaxy (or M31). Dwarf spheroidals located close to the Galaxy, such as Ursa Minor and Draco, only experienced star formation early in their lifetimes. Dwarf spheroidals at intermediate distances, like Leo I, Fornax, and Carina, underwent significant star formation more recently. Finally, star formation is presently still going on in distant dwarfs such as DDO 210 and Phoenix. Leo II and Tucana are, however, dwarfs that do not conform to this pattern. It is tentatively suggested that ram pressure stripping, strong supernova-driven winds, or a high UV flux form the protoGalaxy (or proto-M31) might have removed gas from dwarf galaxies at small galactocentric distances.

  3. The PAndAS View of the Andromeda Satellite System. II. Detailed Properties of 23 M31 Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Martin, Nicolas F.; Ibata, Rodrigo A.; Lewis, Geraint F.; McConnachie, Alan; Babul, Arif; Bate, Nicholas F.; Bernard, Edouard; Chapman, Scott C.; Collins, Michelle M. L.; Conn, Anthony R.; Crnojević, Denija; Fardal, Mark A.; Ferguson, Annette M. N.; Irwin, Michael; Mackey, A. Dougal; McMonigal, Brendan; Navarro, Julio F.; Rich, R. Michael

    2016-12-01

    We present a comprehensive analysis of the structural properties and luminosities of the 23 dwarf spheroidal galaxies that fall within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS). These dwarf galaxies represent the large majority of Andromeda’s known satellite dwarf galaxies and cover a wide range in luminosity (-11.6≲ {M}V≲ -5.8 or {10}4.2≲ L≲ {10}6.5 {L}⊙ ) and surface brightness (25.1≲ {μ }0≲ 29.3 mag arcsec-2). We confirm most previous measurements, but we find And XIX to be significantly larger than before ({r}h={3065}-935+1065 {pc}, {M}V=-{10.1}-0.4+0.8) and cannot derive parameters for And XXVII as it is likely not a bound stellar system. We also significantly revise downward the luminosities of And XV and And XVI, which are now {M}V˜ -7.5 or L˜ {10}5 {L}⊙ . Finally, we provide the first detailed analysis of Cas II/And XXX, a fairly faint system ({M}V=-{8.0}-0.3+0.4) of typical size ({r}h=270+/- 50 {pc}), located in close proximity to the two bright elliptical dwarf galaxies NGC 147 and NGC 185. Combined with the set of homogeneous distances published in an earlier contribution, our analysis dutifully tracks all relevant sources of uncertainty in the determination of the properties of the dwarf galaxies from the PAndAS photometric catalog. We further publish the posterior probability distribution functions of all the parameters we fit for in the form of MCMC chains available online; these inputs should be used in any analysis that aims to remain truthful to the data and properly account for covariance between parameters.

  4. THE CHEMICAL SIGNATURE OF A RELIC STAR CLUSTER IN THE SEXTANS DWARF SPHEROIDAL GALAXY-IMPLICATIONS FOR NEAR-FIELD COSMOLOGY

    Energy Technology Data Exchange (ETDEWEB)

    Karlsson, Torgny [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Bland-Hawthorn, Joss [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Freeman, Ken C. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611 (Australia); Silk, Joe, E-mail: torgny.karlsson@physics.uu.se [Physics Department, University of Oxford, Oxford OX1 3RH (United Kingdom)

    2012-11-10

    We present tentative evidence for the existence of a dissolved star cluster at [Fe/H] = -2.7 in the Sextans dwarf spheroidal galaxy. We use the technique of chemical tagging to identify stars that are highly clustered in a multi-dimensional chemical abundance space (C-space). In a sample of six stars, three, possibly four, stars are identified as potential cluster stars. The initial stellar mass of the parent cluster is estimated from two independent observations to be M{sub *,init}=1.9{sup +1.5}{sub -0.9}(1.6{sup +1.2}{sub -0.8}) Multiplication-Sign 10{sup 5} M{sub sun}, assuming a Salpeter (Kroupa) initial mass function. If corroborated by follow-up spectroscopy, this star cluster is the most metal-poor system identified to date. Chemical signatures of remnant clusters in dwarf galaxies like Sextans provide us with a very powerful probe to the high-redshift universe. From available observational data, we argue that the average star cluster mass in the majority of the newly discovered ultra-faint dwarf galaxies was notably lower than it is in the Galaxy today and possibly lower than in the more luminous, classical dwarf spheroidal galaxies. Furthermore, the mean cumulative metallicity function of the dwarf spheroidals falls below that of the ultra-faints, which increases with increasing metallicity as predicted from our stochastic chemical evolution model. These two findings, together with a possible difference in the ([Mg/Fe]) ratio suggest that the ultra-faint dwarf galaxy population, or a significant fraction thereof, and the dwarf spheroidal population were formed in different environments and would thus be distinct in origin.

  5. The PAndAS view of the Andromeda satellite system - II. Detailed properties of 23 M31 dwarf spheroidal galaxies

    CERN Document Server

    Martin, Nicolas F; Lewis, Geraint F; McConnachie, Alan; Babul, Arif; Bate, Nicholas F; Bernard, Edouard; Chapman, Scott C; Collins, Michelle M L; Conn, Anthony R; Crnojević, Denija; Fardal, Mark A; Ferguson, Annette M N; Irwin, Michael; Mackey, A Dougal; McMonigal, Brendan; Navarro, Julio F; Rich, R Michael

    2016-01-01

    We present a comprehensive analysis of the structural properties and luminosities of the 23 dwarf spheroidal galaxies that fall within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS). These dwarf galaxies represent the large majority of Andromeda's known satellite dwarf galaxies and cover a wide range in luminosity ($-11.6

  6. The Carina Project. X. On the Kinematics of Old and Intermediate-age Stellar Populations1,2

    Science.gov (United States)

    Fabrizio, M.; Bono, G.; Nonino, M.; Łokas, E. L.; Ferraro, I.; Iannicola, G.; Buonanno, R.; Cassisi, S.; Coppola, G.; Dall’Ora, M.; Gilmozzi, R.; Marconi, M.; Monelli, M.; Romaniello, M.; Stetson, P. B.; Thévenin, F.; Walker, A. R.

    2016-10-01

    We present new radial velocity (RV) measurements of old (horizontal branch) and intermediate-age (red clump) stellar tracers in the Carina dwarf spheroidal. They are based on more than 2200 low-resolution spectra collected with VIMOS at Very Large Telescope (VLT). The targets are faint (20 ≲ V ≲ 21.5 mag), but the accuracy at the faintest limit is ≤9 km s‑1. These data were complemented with RV measurements either based on spectra collected with FORS2 and FLAMES/GIRAFFE at VLT or available in the literature. We ended up with a sample of 2748 stars and among them, 1389 are candidate Carina stars. We found that the intermediate-age stellar component shows a well-defined rotational pattern around the minor axis. The western and the eastern side of the galaxy differ by +5 and ‑4 km s‑1 when compared with the main RV peak. The old stellar component is characterized by a larger RV dispersion and does not show evidence of the RV pattern. We compared the observed RV distribution with N-body simulations for a former disky dwarf galaxy orbiting a giant Milky Way–like galaxy. We rotated the simulated galaxy by 60° with respect to the major axis, we kept the observer on the orbital plane of the dwarf and extracted a sample of stars similar to the observed one. Observed and predicted {V}{rot}/σ ratios across the central regions are in remarkable agreement. This evidence indicates that Carina was a disky dwarf galaxy that experienced several strong tidal interactions with the Milky Way. Owing to these interactions, Carina transformed from a disky to a prolate spheroid and the rotational velocity transformed into random motions.

  7. Clean Kinematic Samples in Dwarf Spheroidals: An Algorithm for Evaluating Membership and Estimating Distribution Parameters When Contamination is Present

    CERN Document Server

    Walker, Matthew G; Olszewski, Edward W; Sen, Bodhisattva; Woodroofe, Michael

    2008-01-01

    (abridged) We develop an algorithm for estimating parameters of a distribution sampled with contamination, employing a statistical technique known as ``expectation maximization'' (EM). Given models for both member and contaminant populations, the EM algorithm iteratively evaluates the membership probability of each discrete data point, then uses those probabilities to update parameter estimates for member and contaminant distributions. The EM approach has wide applicability to the analysis of astronomical data. Here we tailor an EM algorithm to operate on spectroscopic samples obtained with the Michigan-MIKE Fiber System (MMFS) as part of our Magellan survey of stellar radial velocities in nearby dwarf spheroidal (dSph) galaxies. These samples are presented in a companion paper and contain discrete measurements of line-of-sight velocity, projected position, and Mg index for ~1000 - 2500 stars per dSph, including some fraction of contamination by foreground Milky Way stars. The EM algorithm quantifies both dSp...

  8. Searching for Dark Matter Annihilation from Milky Way Dwarf Spheroidal Galaxies with Six Years of Fermi Large Area Telescope Data.

    Science.gov (United States)

    Ackermann, M; Albert, A; Anderson, B; Atwood, W B; Baldini, L; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Bissaldi, E; Blandford, R D; Bloom, E D; Bonino, R; Bottacini, E; Brandt, T J; Bregeon, J; Bruel, P; Buehler, R; Caliandro, G A; Cameron, R A; Caputo, R; Caragiulo, M; Caraveo, P A; Cecchi, C; Charles, E; Chekhtman, A; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cuoco, A; Cutini, S; D'Ammando, F; de Angelis, A; de Palma, F; Desiante, R; Digel, S W; Di Venere, L; Drell, P S; Drlica-Wagner, A; Essig, R; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Gomez-Vargas, G A; Grenier, I A; Guiriec, S; Gustafsson, M; Hays, E; Hewitt, J W; Horan, D; Jogler, T; Jóhannesson, G; Kuss, M; Larsson, S; Latronico, L; Li, J; Li, L; Llena Garde, M; Longo, F; Loparco, F; Lubrano, P; Malyshev, D; Mayer, M; Mazziotta, M N; McEnery, J E; Meyer, M; Michelson, P F; Mizuno, T; Moiseev, A A; Monzani, M E; Morselli, A; Murgia, S; Nuss, E; Ohsugi, T; Orienti, M; Orlando, E; Ormes, J F; Paneque, D; Perkins, J S; Pesce-Rollins, M; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Ritz, S; Sánchez-Conde, M; Schulz, A; Sehgal, N; Sgrò, C; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Strigari, L; Tajima, H; Takahashi, H; Thayer, J B; Tibaldo, L; Torres, D F; Troja, E; Vianello, G; Werner, M; Winer, B L; Wood, K S; Wood, M; Zaharijas, G; Zimmer, S

    2015-12-04

    The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are some of the most dark matter (DM) dominated objects known. We report on γ-ray observations of Milky Way dSphs based on six years of Fermi Large Area Telescope data processed with the new Pass8 event-level analysis. None of the dSphs are significantly detected in γ rays, and we present upper limits on the DM annihilation cross section from a combined analysis of 15 dSphs. These constraints are among the strongest and most robust to date and lie below the canonical thermal relic cross section for DM of mass ≲100  GeV annihilating via quark and τ-lepton channels.

  9. MOND Calculations of Bulk Dispersions and Radial Dispersion Profiles of Milky Way and Andromeda Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Alexander, S. G.; Walentosky, M. J.; Messinger, Justin; Staron, Alexander; Blankartz, Benjamin; Clark, Tristan

    2017-02-01

    We present a new computational method for calculating the motion of stars in a dwarf spheroidal galaxy (dSph) that can use either Newtonian gravity or Modified Newtonian Dynamics (MOND). In our model, we explicitly calculate the motion of several thousand stars in a spherically symmetric gravitational potential, and we statistically obtain both the line-of-sight bulk velocity dispersion and dispersion profile. Our results for MOND calculated bulk dispersions for Local Group dSph’s agree well with previous calculations and observations. Our MOND calculated dispersion profiles are compared with the observations of Walker et al. for Milky Way dSph’s, and we present calculated dispersion profiles for a selection of Andromeda dSph’s.

  10. Lack of nuclear clusters in dwarf spheroidal galaxies: implications for massive black holes formation and the cusp/core problem

    Science.gov (United States)

    Arca-Sedda, Manuel; Capuzzo-Dolcetta, Roberto

    2017-01-01

    One of the leading scenarios for the formation of nuclear star clusters in galaxies is related to the orbital decay of globular clusters (GCs) and their subsequent merging, though alternative theories are currently debated. The availability of high-quality data for structural and orbital parameters of GCs allows us to test different nuclear star cluster formation scenarios. The Fornax dwarf spheroidal (dSph) galaxy is the heaviest satellite of the Milky Way and it is the only known dSph hosting five GCs, whereas there are no clear signatures for the presence of a central massive black hole. For this reason, it represents a suited place to study the orbital decay process in dwarf galaxies. In this paper, we model the future evolution of the Fornax GCs simulating them and the host galaxy by means of direct N-body simulations. Our simulations also take into account the gravitational field generated by the Milky Way. We found that if the Fornax galaxy is embedded in a standard cold dark matter halo, the nuclear cluster formation would be significantly hampered by the high central galactic mass density. In this context, we discuss the possibility that infalling GCs drive the flattening of the galactic density profile, giving a possible alternative explanation to the so-called cusp/core problem. Moreover, we briefly discuss the link between GC infall process and the absence of massive black holes in the centre of dSphs.

  11. Non-parametric star formation histories for 5 dwarf spheroidal galaxies of the local group

    CERN Document Server

    Hernández, X; Valls-Gabaud, D; Gilmore, Gerard; Valls-Gabaud, David

    2000-01-01

    We use recent HST colour-magnitude diagrams of the resolved stellar populations of a sample of local dSph galaxies (Carina, LeoI, LeoII, Ursa Minor and Draco) to infer the star formation histories of these systems, $SFR(t)$. Applying a new variational calculus maximum likelihood method which includes a full Bayesian analysis and allows a non-parametric estimate of the function one is solving for, we infer the star formation histories of the systems studied. This method has the advantage of yielding an objective answer, as one need not assume {\\it a priori} the form of the function one is trying to recover. The results are checked independently using Saha's $W$ statistic. The total luminosities of the systems are used to normalize the results into physical units and derive SN type II rates. We derive the luminosity weighted mean star formation history of this sample of galaxies.

  12. Inside the whale: the structure and dynamics of the isolated Cetus dwarf spheroidal

    CERN Document Server

    Lewis, G F; Chapman, S C; McConnachie, A; Irwin, M J; Tolstoy, E; Tanvir, N R

    2006-01-01

    This paper presents a study of the Cetus dwarf, an isolated dwarf galaxy within the Local Group. A matched-filter analysis of the INT/WFC imaging of this system reveals no evidence for significant tidal debris that could have been torn from the galaxy, bolstering the hypothesis that Cetus has never significantly interacted with either the Milky Way or M31. Additionally, Keck/Deimos spectroscopic observations identify this galaxy as a distinct kinematic population possessing a systematic velocity of $-87\\pm2{\\rm km\\ s^{-1}}$ and with a velocity dispersion of $17\\pm2{\\rm km s^{-1}}$; while tentative, these data also suggest that Cetus possesses a moderate rotational velocity of $\\sim8{\\rm km s^{-1}}$. The population is confirmed to be relatively metal-poor, consistent with ${\\rm [Fe/H]\\sim-1.9}$, and, assuming virial equilibrium, implies that the Cetus dwarf galaxy possesses a $M/L\\sim70$. It appears, therefore, that Cetus may represent a primordial dwarf galaxy, retaining the kinematic and structural propertie...

  13. Environmental Mechanisms Shaping the Nature of Dwarf Spheroidal Galaxies: The View of Computer Simulations

    Directory of Open Access Journals (Sweden)

    Lucio Mayer

    2010-01-01

    cosmic ultraviolet ionizing flux was much higher than today, and was thus able to keep the gas in the dwarfs warm and diffuse, were rapidly stripped of their baryons via ram pressure and tidal forces, producing very dark-matter-dominated objects with truncated star-formation histories, such as the Draco dSph. The low star-formation efficiency expected in such low-metallicity objects prior to their infall was crucial for keeping their disks gas dominated until stripping took over. Therefore gas stripping along with inefficient star-formation provides a new feedback mechanism, alternative to photoevaporation or supernovae feedback, playing a crucial role in dwarf galaxy formation and evolution. We also discuss how the ultra-faint dSphs belong to a different population of lower-mass dwarf satellites that were mostly shaped by reionization rather than by environmental mechanisms (“reionization fossils”. Finally, we scrutinize the various caveats in the current understanding of environmental effects as well as other recent ideas on the origin of Local Group dSphs.

  14. Dwarf spheroidal satellites of the Milky Way from dark matter free tidal dwarf galaxy progenitors: maps of orbits

    CERN Document Server

    Casas, R A; Ramírez, K Pena; Kroupa, P

    2012-01-01

    The long term time evolution of tidal dwarf satellite galaxies with two different initial densities orbiting a host galaxy that resembles the Milky Way has been studied using a large set of Newtonian N-Body simulations. From the simulations two maps of the orbital conditions that lead to quasi-equilibrium objects were constructed. It has been found that several orbits of the satellites allow for the existence, for about 1 Gyr or more, of out-of-equilibrium bodies with high apparent mass-to-light ratios. Within this framework the satellites in the quasi-stable phase reproduce the observed satellite properties for about 16% of the orbit for high density progenitors, and for about 66% for progenitors with lower densities An additional simulation for a single satellite with initial mass of 10^7 Msun and Plummer radius of 0.15 kpc leads to remnants in the quasi- equilibrium phase that simultaneously reproduce remarkably well the observational quantities of the UFDGs of the Milky Way. This satellite in the quasi-st...

  15. Insights from the Outskirts: Chemical and Dynamical Properties in the outer Parts of the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Hendricks, Benjamin; Walker, Matthew; Johnson, Christian I; Penarrubia, Jorge; Gilmore, Gerard

    2014-01-01

    We present radial velocities and [Fe/H] abundances for 340 stars in the Fornax dwarf spheroidal from R~16,000 spectra. The targets have been obtained in the outer parts of the galaxy, a region which has been poorly studied before. Our sample shows a wide range in [Fe/H], between -0.5 and -3.0 dex, in which we detect three subgroups. Removal of stars belonging to the most metal-rich population produces a truncated metallicity distribution function that is identical to Sculptor, indicating that these systems have shared a similar early evolution, only that Fornax experienced a late, intense period of star formation (SF). The derived age-metallicity relation shows a fast increase in [Fe/H] at early ages, after which the enrichment flattens significantly for stars younger than ~8 Gyr. Additionally, the data indicate a strong population of stars around 4 Gyr, followed by a second rapid enrichment in [Fe/H]. A leaky-box chemical enrichment model generally matches the observed relation but does not predict a signifi...

  16. Bayesian analysis of resolved stellar spectra: application to MMT/Hectochelle Observations of the Draco dwarf spheroidal

    CERN Document Server

    Walker, Matthew G; Mateo, Mario

    2015-01-01

    We introduce a Bayesian method for fitting faint, resolved stellar spectra in order to obtain simultaneous estimates of redshift and stellar-atmospheric parameters. We apply the method to thousands of spectra---covering 5160-5280 Angs. at resolution R~20,000---that we have acquired with the MMT/Hectochelle fibre spectrograph for red-giant and horizontal branch candidates along the line of sight to the Milky Way's dwarf spheroidal satellite in Draco. The observed stars subtend an area of ~4 deg^2, extending ~3 times beyond Draco's nominal `tidal' radius. For each spectrum we tabulate the first four moments---central value, variance, skewness and kurtosis---of posterior probability distribution functions representing estimates of the following physical parameters: line-of-sight velocity v_los, effective temperature (T_eff), surface gravity (logg) and metallicity ([Fe/H]). After rejecting low-quality measurements, we retain a new sample consisting of 2813 independent observations of 1565 unique stars, including ...

  17. The Low-Mass Stellar IMF at High Redshift Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy

    CERN Document Server

    Wyse, R F G; Feltzing, S; Houdashelt, M L; Wyse, Rosemary F.G.; Gilmore, Gerard; Feltzing, Sofia; Houdashelt, Mark

    1999-01-01

    Low-mass stars, those with main-sequence lifetimes that are of order the age of the Universe, provide unique constraints on the Initial Mass Function (IMF) when they formed. Star counts in systems with simple star-formation histories are particularly straightforward to interpret, and those in old systems allow one to determine the low-mass stellar IMF at large look-back times and thus at high redshift. We present the faint stellar luminosity function (based on optical HST data) in an external galaxy, the Ursa Minor dwarf Spheroidal (dSph). This relatively-nearby (distance 70kpc) companion galaxy to the Milky Way has a stellar population with narrow distributions of age and of metallicity, remarkably similar to that of a classical halo globular cluster such as M92 or M15, i.e. old and metal-poor. Contrasting with globular clusters, the internal velocity dispersion of the Ursa Minor dSph indicates the presence of significant amounts of dark matter. We find that the main sequence stellar luminosity function of t...

  18. Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data

    CERN Document Server

    :,; Albert, A; Bechtol, K; Wood, M; Strigari, L; Sanchez-Conde, M; Baldini, L; Essig, R; Cohen-Tanugi, J; Anderson, B; Bellazzini, R; Bloom, E D; Caputo, R; Cecchi, C; Charles, E; Chiang, J; Conrad, J; de Angelis, A; Funk, S; Fusco, P; Gargano, F; Giglietto, N; Giordano, F; Guiriec, S; Gustafsson, M; Kuss, M; Loparco, F; Lubrano, P; Mirabal, N; Mizuno, T; Morselli, A; Ohsugi, T; Orlando, E; Persic, M; Raino, S; Spada, F; Suson, D J; Zaharijas, G; Zimmer, S; Abbott, T; Allam, S; Balbinot, E; Bauer, A H; Benoit-Levy, A; Bernstein, R A; Bernstein, G M; Bertin, E; Brooks, D; Buckley-Geer, E; Burke, D L; Rosell, A Carnero; Castander, F J; Covarrubias, R; D'Andrea, C B; da Costa, L N; DePoy, D L; Desai, S; Diehl, H T; Cunha, C E; Eifler, T F; Estrada, J; Evrard, A E; Neto, A Fausti; Fernandez, E; Finley, D A; Flaugher, B; Frieman, J; Gaztanaga, E; Gerdes, D; Gruen, D; Gruendl, R A; Gutierrez, G; Honscheid, K; Jain, B; James, D; Jeltema, T; Kent, S; Kron, R; Kuropatkin, N; Lahav, O; Li, T S; Luque, E; Maia, M A G; Makler, M; March, M; Marshall, J; Martini, P; Merritt, K W; Miller, C; Miquel, R; Mohr, J; Neilsen, E; Nord, B; Ogando, R; Peoples, J; Petravick, D; Pieres, A; Plazas, A A; Queiroz, A; Romer, A K; Roodman, A; Rykoff, E S; Sako, M; Sanchez, E; Santiago, B; Scarpine, V; Schubnell, M; Sevilla, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Swanson, M E C; Tarle, G; Thaler, J; Thomas, D; Tucker, D; Walker, A; Wechsler, R H; Wester, W; Williams, P; Yanny, B; Zuntz, J

    2015-01-01

    Due to their proximity, high dark matter content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of dark matter. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with dark matter halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged dark matter annihilation cross section for these new targets. If confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for dark matter particles with masses < 20 GeV annihilating via the b-bbar or tau+tau- channels.

  19. Chemical analysis of carbon stars in the Local Group: I. The Small Magellanic Cloud and the Sagittarius dwarf spheroidal galaxy

    CERN Document Server

    De Laverny, P; Dominguez, I; Plez, B; Straniero, O; Wahlin, R; Eriksson, K; Jørgensen, U G

    2005-01-01

    We present the first results of our ongoing chemical study of carbon stars in the Local Group of galaxies. We used spectra obtained with UVES at the 8.2 m Kueyen-VLT telescope and a new grid of spherical model atmospheres for cool carbon-rich stars which include polyatomic opacities, to perform a full chemical analysis of one carbon star, BMB-B~30, in the Small Magellanic Cloud (SMC) and two, IGI95-C1 and IGI95-C3, in the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. Our main goal is to test the dependence on the stellar metallicity of the s-process nucleosynthesis and mixing mechanism occurring in AGB stars. For these three stars, we find important s-element enhancements with respect to the mean metallicity ([M/H]), namely [s/M]$\\approx$+1.0, similar to the figure found in galactic AGB stars of similar metallicity. The abundance ratios derived between elements belonging to the first and second s-process abundance peaks, corresponding to nuclei with a magic number of neutrons N=50 (88Sr, 89Y, 90Zr) and N=82...

  20. The interstellar medium in Andromeda's dwarf spheroidal galaxies: II. Multi-phase gas content and ISM conditions

    CERN Document Server

    De Looze, Ilse; Cormier, Diane; Kaneko, Hiroyuki; Kuno, Nario; Young, Lisa; Bendo, George J; Boquien, Mederic; Fritz, Jacopo; Gentile, Gianfranco; Kennicutt, Robert C; Madden, Suzanne C; Smith, Matthew W L; Wilson, Christine D

    2016-01-01

    We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC147, NGC185 and NGC205). Ancillary HI, CO, Spitzer IRS spectra, H{\\alpha} and X-ray observations are combined to trace the atomic, cold and warm molecular, ionised and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [CI] observations of NGC205 to revise its molecular gas content. We derive total gas masses of M_gas = 1.9-5.5x10^5 Msun for NGC185 and M_gas = 8.6-25.0x10^5 Msun for NGC205. Non-detections combine to an upper limit on the gas mass of M_gas =< 0.3-2.2x10^5 Msun for NGC147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR~37-107 and GDR~48-139 are also considerably lower compared to the expected GDR~370 and GDR~520 for the low metal abundances in NGC 1...

  1. Dwarf spheroidal J-factors without priors: A likelihood-based analysis for indirect dark matter searches

    Science.gov (United States)

    Chiappo, A.; Cohen-Tanugi, J.; Conrad, J.; Strigari, L. E.; Anderson, B.; Sánchez-Conde, M. A.

    2017-04-01

    Line-of-sight integrals of the squared density, commonly called the J-factor, are essential for inferring dark matter (DM) annihilation signals. The J-factors of DM-dominated dwarf spheroidal satellite galaxies (dSphs) have typically been derived using Bayesian techniques, which for small data samples implies that a choice of priors constitutes a non-negligible systematic uncertainty. Here we report the development of a new fully frequentist approach to construct the profile likelihood of the J-factor. Using stellar kinematic data from several classical and ultra-faint dSphs, we derive the maximum likelihood value for the J-factor and its confidence intervals. We validate this method, in particular its bias and coverage, using simulated data from the Gaia Challenge. We find that the method possesses good statistical properties. The J-factors and their uncertainties are generally in good agreement with the Bayesian-derived values, with the largest deviations restricted to the systems with the smallest kinematic data sets. We discuss improvements, extensions, and future applications of this technique.

  2. Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data

    Energy Technology Data Exchange (ETDEWEB)

    Drlica-Wagner, A.; et al.

    2015-08-04

    Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses $\\lesssim 20\\,\\mathrm{GeV}$ annihilating via the $b\\bar{b}$ or τ(+)τ(-) channels.

  3. A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation

    CERN Document Server

    Zhu, Ling; Watkins, Laura L; Posti, Lorenzo

    2016-01-01

    We present a new discrete chemo-dynamical axisymmetric modeling technique, which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement over previous Jeans models is that realistic chemical distributions are included directly in the dynamical modelling of the discrete data. This avoids loss of information due to spatial binning and eliminates the need for hard cuts to remove contaminants and to separate stars based on their chemical properties. Using a combined likelihood in position, metallicity and kinematics, we find that our models naturally separate Sculptor stars into a metal-rich and a metal-poor population. Allowing for non-spherical symmetry, our approach provides a central slope of the dark matter density of $\\gamma = 0.5 \\pm 0.3$. The metal-rich population is nearly isotropic (with $\\beta_r^{red} = 0.0\\pm0.1$) while the metal-poor population is tangentially anisotropic (with $\\beta_r^{blue} = -0.2\\pm0.1$) around the half light radius of $0.26$ kpc. A weak internal rotation of the m...

  4. Chemical Abundances in the PN Wray16-423 in the Sagittarius Dwarf Spheroidal Galaxy: Constraining the Dust Composition

    CERN Document Server

    Otsuka, Masaaki

    2015-01-01

    We performed a detailed analysis of elemental abundances, dust features, and polycyclic aromatic hydrocarbons (PAHs) in the C-rich planetary nebula (PN) Wray16-423 in the Sagittarius dwarf spheroidal galaxy, based on a unique dataset taken from the Subaru/HDS, MPG/ESO FEROS, HST/WFPC2, and Spitzer/IRS. We performed the first measurements of Kr, Fe, and recombination O abundance in this PN. The extremely small [Fe/H] implies that most Fe atoms are in the solid phase, considering into account the abundance of [Ar/H]. The Spitzer/IRS spectrum displays broad 16-24 um and 30 um features, as well as PAH bands at 6-9 um and 10-14 um. The unidentified broad 16-24 um feature may not be related to iron sulfide (FeS), amorphous silicate, or PAHs. Using the spectral energy distribution model, we derived the luminosity and effective temperature of the central star, and the gas and dust masses. The observed elemental abundances and derived gas mass are in good agreement with asymptotic giant branch nucleosynthesis models f...

  5. Dwarf spheroidal J-factors without priors: A likelihood-based analysis for indirect dark matter searches

    CERN Document Server

    Chiappo, A; Conrad, J; Strigari, L E; Anderson, B; Sanchez-Conde, M A

    2016-01-01

    Line-of-sight integrals of the squared density, commonly called the J-factor, are essential for inferring dark matter annihilation signals. The J-factors of dark matter-dominated dwarf spheroidal satellite galaxies (dSphs) have typically been derived using Bayesian techniques, which for small data samples implies that a choice of priors constitutes a non-negligible systematic uncertainty. Here we report the development of a new fully frequentist approach to construct the profile likelihood of the J-factor. Using stellar kinematic data from several classical and ultra-faint dSphs, we derive the maximum likelihood value for the J-factor and its confidence intervals. We validate this method, in particular its bias and coverage, using simulated data from the Gaia Challenge. We find that the method possesses good statistical properties. The J-factors and their uncertainties are generally in good agreement with the Bayesian-derived values, with the largest deviations restricted to the systems with the smallest kine...

  6. Identifying Type Ia Supernova Mechanisms in Dwarf Spheroidal Galaxies through Analysis of Iron-peak Elemental Abundances

    Science.gov (United States)

    Guo, Rachel; Xie, Justin Long; Kirby, Evan N.

    2017-01-01

    Through the fusion of nucleons to produce elements heavier than hydrogen and helium, stellar nucleosynthesis produces most of the elements in the universe. Such is the case in a supernova explosion, which creates most of the elements on the periodic table—including iron-peak elements, atomic numbers 21 through 30—through nucleosynthesis and ejects them into the interstellar medium. In this study, we determine the best theoretical supernova model appropriate for the stars in the dwarf spheroidal galaxies Sculptor, Fornax, Ursa Minor, and Leo II by calculating the abundances of iron-peak elements in these stars. To determine iron-peak elemental abundances, we compare synthesized spectra with observed spectra from medium-resolution spectroscopy and determine the best-fitting spectrum by way of a chi-squared minimization. Through inspecting the relationship between the iron-peak element abundances and the abundance of iron itself and by comparing them to previously hypothesized supernova model theories, we discover that the near-Chandrasekhar mass “n1” model, as predicted by Seitenzahl et al., most accurately represents the trends and patterns within our data, presenting new insight into Type Ia supernovae mechanisms within the Milky Way and beyond.

  7. Scl-1013644: a CEMP-s star in the Sculptor dwarf spheroidal galaxy

    Science.gov (United States)

    Salgado, C.; Da Costa, G. S.; Yong, D.; Norris, J. E.

    2016-11-01

    Recent studies of the Milky Way and its satellites have paid special attention to the importance of carbon-enhanced metal-poor (CEMP) stars due to their involvement in Galactic formation history and their possible connection with the chemical elements originating in the first stellar generation. In an ongoing study of red giants in the Sculptor dwarf galaxy, we have discovered a star with extremely strong CN and CH molecular bands. This star, Scl-1013644, has previously been identified by Geisler et al. as a star with an enrichment in the heavy elements. Spectrum synthesis has been used to derive the carbon, nitrogen and barium abundances for Scl-1013644. Our findings are [C/Fe] = +0.8, [N/Fe] = -0.3 and [Ba/Fe] = +2.1 with the latter result consistent with the value found by Geisler et al. These results reveal Scl-1013644 as a CEMP-s star, the third such star discovered in this dwarf galaxy.

  8. The intrinsic ellipticity of dwarf spheroidal galaxies: constraints from the Andromeda system

    CERN Document Server

    Salomon, Jean-Baptiste; Martin, Nicolas; Famaey, Benoit

    2015-01-01

    We present a study of the intrinsic deprojected ellipticity distribution of the satellite dwarf galaxies of the Andromeda galaxy, assuming that their visible components have a prolate shape, which is a natural outcome of simulations. Different possibilities for the orientation of the major axis of the prolate dwarf galaxies are tested, pointing either as close as possible to the radial direction towards the centre of Andromeda, or tangential to the radial direction, or with a random angle in the plane that contains the major axis and the observer. We find that the mean intrinsic axis ratio is ~ 1/2, with small differences depending on the assumed orientation of the population. Our deprojections also suggest that a significant fraction of the satellites, ~ 10%, are tidally disrupted remnants. We find that there is no evidence of any obvious difference in the morphology and major axis orientation between satellites that belong to the vast thin plane of co-rotating galaxies around Andromeda and those that do not...

  9. An Internal Second Parameter Problem in the Sculptor Dwarf Spheroidal Galaxy

    CERN Document Server

    Majewski, S R; Patterson, R J; Rood, R T; Patterson, Richard J.

    1999-01-01

    We present BV photometry of the Sculptor dwarf galaxy to V=22. These data give evidence for a bimodality in Sculptor's metallicity distribution based on a discontinuity in the luminosities of horizontal branch (HB) stars and by the presence of two distinct red giant branch (RGB) bumps. A consistent picture of the evolved stars in Sculptor is given by the presence of (1) a metal-poor population of [Fe/H] ~ -2.3 with an exclusively blue HB and that corresponds to the blueward side of the Sculptor RGB and the more luminous RGB bump, and (2) a less metal-poor population of [Fe/H] ~ -1.5 required to explain the less luminous red HB, the red side of the RGB, and a second, less luminous RGB bump. Best fits to the HB populations are obtained with enhanced oxygen abundances, [O/Fe] ~ +0.5. Variations in the global HB and RGB morphology of Sculptor can be explained by differences in the radial distribution of these two populations. The presence of these two populations shows that the Sculptor dwarf galaxy has an intern...

  10. Scl-1013644: a CEMP-s star in the Sculptor Dwarf Spheroidal Galaxy

    CERN Document Server

    Salgado, C; Yong, D; Norris, J E

    2016-01-01

    Recent studies of the Milky Way and its satellites have paid special attention to the importance of carbon-enhanced metal-poor (CEMP) stars due to their involvement in Galactic formation history and their possible connection with the chemical elements originating in the first stellar generation. In an ongoing study of red giants in the Sculptor dwarf galaxy we have discovered a star with extremely strong CN and CH molecular bands. This star, Scl-1013644, has previously been identified by Geisler et al. (2005) as a star with an enrichment in the heavy elements. Spectrum synthesis has been used to derive the carbon, nitrogen and barium abundances for Scl-1013644. Our findings are [C/Fe] = +0.8, [N/Fe] = -0.3 and [Ba/Fe] = +2.1 with the latter result consistent with the value found by Geisler et al. (2005). These results reveal Scl-1013644 as a CEMP-s star, the third such star discovered in this dwarf galaxy.

  11. Discovery of Super-Li Rich Red Giants in Dwarf Spheroidal Galaxies

    CERN Document Server

    Kirby, Evan; Guhathakurta, Puragra; Deng, Licai

    2012-01-01

    Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of K, hot enough for the 7Li(p,alpha)4He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants--14 of which are new discoveries--among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] <~ -0.7) Li-rich red giants, and it includes the most-metal poor Li-enhanced star known ([Fe/H] = -2.82, A(Li)_NLTE = 3.15). Because most of these stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider ...

  12. Clearing the Gas from Globular Clusters & Dwarf Spheroidals with Classical Novae

    CERN Document Server

    Moore, Kevin

    2010-01-01

    Observations of the intra-cluster medium (ICM) in galactic globular clusters (GCs) show a systematic deficiency in ICM mass as compared to that expected from accumulation of stellar winds in the time available between galactic plane crossings. In this paper, we reexamine the original hypothesis of Scott and Durisen that hydrogen-rich explosions on accreting white dwarfs, classical novae (CNe), will sweep out the ICM from the cluster more frequently than galactic plane crossings. From the CNe rate and stellar mass-loss rate, this clearing mechanism predicts that ~ 0.03 M_sun should be present in 5x10^5 M_sun) GCs. We find that nova shells are effective at clearing the ICM in low-mass GCs (<= 10^5 M_sun), whereas higher-mass clusters may experience a quiescent time between novae long enough to prevent the next nova shell from escaping. The nova clearing mechanism will also operate in ultra-faint Milky Way satellites, where many upper limits on gas masses are available.

  13. Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy

    CERN Document Server

    Sadakane, K; Ikuta, C; Aoki, W; Jablonka, P; Tajitsu, A

    2004-01-01

    With the HDS (High Dispersion Spectrograph) on the Subaru telescope, we obtained high resolution optical region spectra of three red giant stars (cos 4, cos 82, and cos 347) in the Ursa Minor dwarf spheriodal galaxy. Chemical abundances in these stars have been analysed for 26 elements including alpha-, iron-peak, and neutron capture elements. All three stars show low abundances of alpha-elements (Mg, Si, and Ca) and two stars (cos 82 and cos 347) show high abundance of Mn compared to Galactic halo stars of similar metallicity. One star (cos 4) has been confirmed to be very metal deficient ([Fe/H]=-2.7) and found to show anomalously low abundances of Mn, Cu, and Ba. In another star cos 82 ([Fe/H]=-1.5), we have found large excess of heavy neutron-capture elements with the general abundance pattern similar to the scaled solar system r-process abundance curve. These observational results are rather puzzling: low abundances of alpha-elements and high abundance of Mn seem to sugggest a significant contribution of...

  14. Extremely metal-poor stars in classical dwarf spheroidal galaxies: Fornax, Sculptor and Sextans

    CERN Document Server

    Tafelmeyer, M; Hill, V; Shetrone, M; Tolstoy, E; Irwin, M J; Battaglia, G; Helmi, A; Starkenburg, E; Venn, K A; Abel, T; Francois, P; Kaufer, A; North, P; Primas, F; Szeifert, T

    2010-01-01

    We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to have [Fe/H] <= -3 and three stars are below [Fe/H]~-3.5. This constitutes the first evidence that the classical dSphs Fornax and Sextans join Sculptor in containing extremely metal-poor stars and suggests that all of the classical dSphs contain extremely metal-poor stars. One giant in Sculptor at [Fe/H]=-3.96 +- 0.10 is the most metal-poor star ever observed in an external galaxy. We carried out a detailed analysis of the chemical abundances of the alpha, iron peak, and the heavy elements, and we performed a comparison with the Milky Way halo and the ultra faint dwarf stellar populations. Carbon, barium and strontium show distinct features characterized by the early stages of galaxy formation and can constrain the o...

  15. Variable stars in the ultra-faint dwarf spheroidal galaxy Ursa Major I

    CERN Document Server

    Garofalo, Alessia; Clementini, Gisella; Ripepi, Vincenzo; Dall'Ora, Massimo; Moretti, Maria Ida; Coppola, Giuseppina; Musella, Ilaria; Marconi, Marcella

    2013-01-01

    We have performed the first study of the variable star population of Ursa Major I (UMa I), an ultra-faint dwarf satellite recently discovered around the Milky Way by the Sloan Digital Sky Survey. Combining time series observations in the B and V bands from four different telescopes, we have identified seven RR Lyrae stars in UMa I, of which five are fundamental-mode (RRab) and two are first-overtone pulsators (RRc). Our V, B-V color-magnitude diagram of UMa I reaches V~23 mag (at a signal-to-noise ratio of ~ 6) and shows features typical of a single old stellar population. The mean pulsation period of the RRab stars = 0.628, {\\sigma} = 0.071 days (or = 0.599, {\\sigma} = 0.032 days, if V4, the longest period and brightest variable, is discarded) and the position on the period-amplitude diagram suggest an Oosterhoff-intermediate classification for the galaxy. The RR Lyrae stars trace the galaxy horizontal branch at an average apparent magnitude of = 20.43 +/- 0.02 mag (average on 6 stars and discarding V4), ...

  16. A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation

    Science.gov (United States)

    Zhu, Ling; van de Ven, Glenn; Watkins, Laura L.; Posti, Lorenzo

    2016-11-01

    We present a new discrete chemo-dynamical axisymmetric modelling technique, which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement over previous Jeans models is that realistic chemical distributions are included directly in the dynamical modelling of the discrete data. This avoids loss of information due to spatial binning and eliminates the need for hard cuts to remove contaminants and to separate stars based on their chemical properties. Using a combined likelihood in position, metallicity and kinematics, we find that our models naturally separate Sculptor stars into a metal-rich and a metal-poor population. Allowing for non-spherical symmetry, our approach provides a central slope of the dark matter density of γ = 0.5 ± 0.3. The metal-rich population is nearly isotropic (with β _r^{red} = 0.0± 0.1), while the metal-poor population is tangentially anisotropic (with β _r^{blue} = -0.2± 0.1) around the half-light radius of 0.26 kpc. A weak internal rotation of the metal-rich population is revealed with vmax/σ0 = 0.15 ± 0.15. We run tests using mock data to show that a discrete data set with ˜6000 stars is required to distinguish between a core (γ = 0) and cusp (γ = 1), and to constrain the possible internal rotation to better than 1σ confidence with our model. We conclude that our discrete chemo-dynamical modelling technique provides a flexible and powerful tool to robustly constrain the internal dynamics of multiple populations, and the total mass distribution in a stellar system.

  17. Searching for dwarf spheroidal galaxies and other galactic dark matter substructures with the Fermi large area telescope

    Energy Technology Data Exchange (ETDEWEB)

    Drlica-Wagner, Alex [Stanford Univ., CA (United States). Dept. of Physics

    2013-08-01

    Over the past century, it has become clear that about a quarter of the known universe is composed of an invisible, massive component termed ''dark matter''. Some of the most popular theories of physics beyond the Standard Model suggest that dark matter may be a new fundamental particle that could self-annihilate to produce γ rays. Nearby over-densities in the dark matter halo of our Milky Way present some of the most promising targets for detecting the annihilation of dark matter. We used the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope to search for γ rays produced by dark matter annihilation in Galactic dark matter substructures. We searched for γ-ray emission coincident with Milky Way dwarf spheroidal satellite galaxies, which trace the most massive Galactic dark matter substructures. We also sought to identify nearby dark matter substructures that lack all astrophysical tracers and would be detectable only through γ-ray emission from dark matter annihilation. We found no conclusive evidence for γ-ray emission from dark matter annihilation, and we set stringent and robust constraints on the dark matter annihilation cross section. While γ-ray searches for dark matter substructure are currently the most sensitive and robust probes of dark matter annihilation, they are just beginning to intersect the theoretically preferred region of dark matter parameter space. Thus, we consider future prospects for increasing the sensitivity of γ-ray searches through improvements to the LAT instrument performance and through upcoming wide- field optical surveys.

  18. A DEEP SEARCH FOR EXTENDED RADIO CONTINUUM EMISSION FROM DWARF SPHEROIDAL GALAXIES: IMPLICATIONS FOR PARTICLE DARK MATTER

    Energy Technology Data Exchange (ETDEWEB)

    Spekkens, Kristine [Department of Physics, Royal Military College of Canada, P.O. Box 17000, Station Forces, Kingston, Ontario K7K 7B4 (Canada); Mason, Brian S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Aguirre, James E. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Nhan, Bang, E-mail: kristine.spekkens@rmc.ca [Department of Astrophysical and Planetary Sciences, University of Colorado, 391 UCB, Boulder, CO 80309 (United States)

    2013-08-10

    We present deep radio observations of four nearby dwarf spheroidal (dSph) galaxies, designed to detect extended synchrotron emission resulting from weakly interacting massive particle (WIMP) dark matter annihilations in their halos. Models by Colafrancesco et al. (CPU07) predict the existence of angularly large, smoothly distributed radio halos in such systems, which stem from electron and positron annihilation products spiraling in a turbulent magnetic field. We map a total of 40.5 deg{sup 2} around the Draco, Ursa Major II, Coma Berenices, and Willman 1 dSphs with the Green Bank Telescope (GBT) at 1.4 GHz to detect this annihilation signature, greatly reducing discrete-source confusion using the NVSS catalog. We achieve a sensitivity of {sigma}{sub sub} {approx}< 7 mJy beam{sup -1} in our discrete source-subtracted maps, implying that the NVSS is highly effective at removing background sources from GBT maps. For Draco we obtained approximately concurrent Very Large Array observations to quantify the variability of the discrete source background, and find it to have a negligible effect on our results. We construct radial surface brightness profiles from each of the subtracted maps, and jackknife the data to quantify the significance of the features therein. At the {approx}10' resolution of our observations, foregrounds contribute a standard deviation of 1.8 mJy beam{sup -1} {<=} {sigma}{sub ast} {<=} 5.7 mJy beam{sup -1} to our high-latitude maps, with the emission in Draco and Coma dominated by foregrounds. On the other hand, we find no significant emission in the Ursa Major II and Willman 1 fields, and explore the implications of non-detections in these fields for particle dark matter using the fiducial models of CPU07. For a WIMP mass M{sub {chi}} = 100 GeV annihilating into b b-bar final states and B = 1 {mu}G, upper limits on the annihilation cross-section for Ursa Major II and Willman I are log (({sigma}v){sub {chi}}, cm{sup 3} s{sup -1}) {approx}< -25

  19. The Carina Project. X. On the kinematics of old and intermediate-age stellar populations

    CERN Document Server

    Fabrizio, M; Nonino, M; Lokas, E L; Ferraro, I; Iannicola, G; Buonanno, R; Cassisi, S; Coppola, G; Dall'Ora, M; Gilmozzi, R; Marconi, M; Monelli, M; Romaniello, M; Stetson, P B; Thévenin, F; Walker, A R

    2016-01-01

    We present new radial velocity (RV) measurements of old (horizontal branch) and intermediate-age (red clump) stellar tracers in the Carina dwarf spheroidal. They are based on more than 2,200 low-resolution spectra collected with VIMOS at VLT. The targets are faint (20Carina stars. We found that the intermediate-age stellar component shows a well defined rotational pattern around the minor axis. The western and the eastern side of the galaxy differ by +5 and -4 km s-1 when compared with the main RV peak. The old stellar component is characterized by a larger RV dispersion and does not show evidence of RV pattern. We compared the observed RV distribution with N-body simulations for a former disky dwarf galaxy orbit...

  20. Searching for Dark Matter signatures in dwarf spheroidal galaxies with the ASTRI mini-array in the framework of Cherenkov Telescope Array

    Science.gov (United States)

    Giammaria, P.; Lombardi, S.; Antonelli, L. A.; Brocato, E.; Bigongiari, C.; Di Pierro, F.; Stamerra, A.; ASTRI Collaboration; CTA Consortium, the

    2016-07-01

    The nature of Dark Matter (DM) is an open issue of modern physics. Cosmological considerations and observational evidences indicate a behaviour beyond the Standard Model for feasible DM particle candidates. Non-baryonic DM is compatible with cold and weakly interacting massive particles (WIMPs) expected to have a mass in the range between ∼10 GeV and ∼100 TeV. Indirect DM searches with imaging atmospheric Cherenkov telescopes may play a crucial role in constraining the nature of the DM particle(s) through the study of their annihilation in very high energy (VHE) gamma rays from promising targets, such as the dwarf spheroidal satellite galaxies (dSphs) of the Milky Way. Here, we focus on indirect DM searches in dSphs, presenting the preliminary prospects of this research beyond the TeV mass region achievable with the ASTRI mini-array, proposed to be installed at the Cherenkov Telescope Array southern site.

  1. Spectroscopic confirmation of the dwarf spheroidal galaxy d0944+71 as a member of the M81 group of galaxies

    CERN Document Server

    Toloba, Elisa; Guhathakurta, Puragra; Chiboucas, Kristin; Crnojevic, Denija; Simon, Joshua

    2016-01-01

    We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual stars and measure a heliocentric radial velocity of $-38\\pm10$~km/s. This velocity is consistent with d0944+71 being gravitationally bound to M81. We coadd the spectra of the 23 stars that are consistent with being red giant branch stars and measure an overall metallicity of ${\\rm [Fe/H]}=-1.3 \\pm 0.3$ based on the calcium triplet lines. This metallicity is consistent with d0944+71 following the metallicity$-$luminosity relation for Local Group dSphs. We investigate several potential sources of observational bias but find that our sample of targeted stars is representative of the metallicity distribution function of d0944+71 and any stellar contamination due to seeing effects is negligible. The low ellipticit...

  2. Search for Gamma-ray emission from the eight newly-released DES dwarf spheroidal galaxy candidates with Fermi-LAT data

    CERN Document Server

    Li, Shang; Duan, Kai-Kai; Shen, Zhao-Qiang; Huang, Xiaoyuan; Li, Xiang; Fan, Yi-Zhong; Liao, Neng-Hui; Feng, Lei; Chang, Jin

    2015-01-01

    Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for $\\gamma-$ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $\\gamma-$ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of $\\chi\\chi \\rightarrow \\tau^{+}\\tau^{-}$ is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass $m_\\chi>250$ GeV. In the direction of Tuc III, one of the nearest dSph galaxy candidates that is $\\sim 25$ kpc away, there is a weak $\\gamma-$ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $\\chi\\chi\\rightarrow \\tau^{+}\\tau^{-1}$ is $\\approx 6.7$. The significance of the pos...

  3. Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf Spheroidal galaxy?

    CERN Document Server

    Sbordone, L; Bidin, C Moni; Bonifacio, P; Villanova, S; Bellazzini, M; Ibata, R; Chiba, M; Geisler, D; Caffau, E; Duffau, S

    2015-01-01

    The tidal disruption of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, the Sgr dSph is suspected to have lost a number of globular clusters (GC). Many Galactic GC are suspected to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed due to chemical similarities, others exist whose chemical composition has never been investigated. NGC 5053 and NGC 5634 are two among these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. We analize high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of "unassociated" MW halo globulars, and of the metal poor Sgr dSph main body population...

  4. The Sagittarius Dwarf spheroidal Galaxy Survey (SDGS); 2, The stellar content and constraints on the star formation history

    CERN Document Server

    Bellazzini, M; Buonanno, R; Bellazzini, Michele; Ferraro, Francesco R.; Buonanno, Roberto

    1999-01-01

    A detailed study of the Star Formation History of the Sgr dSph galaxy is performed through the analysis of the data from the Sagittarius Dwarf Galaxy Survey (SDGS; Bellazzini, Ferraro & Buonanno 1999). Accurate statistical decontamination of the SDGS Color - Magnitude diagrams allow us to obtain many useful constraints on the age and metal content of the Sgr stellar populations in three different region of the galaxy. A coarse metallicity distribution of Sgr stars is derived, ranging from [Fe/H]~ -2.0 to [Fe/H]~ -0.7, the upper limit being somewhat higher in the central region of the galaxy. A qualitative global fit to all the observed CMD features is attempted, and a general scheme for the Star Formation History of the Sgr is derived. According to this scheme, star formation began at very early time from a low metal content Inter Stellar Medium and lasted for several Gyr, coupled with progressive chemical enrichment. The Star Formation Rate (SFR) had a peak from 8 to 10 gyr ago when the mean metallicity ...

  5. The [Fe/H], [C/Fe], and [α/Fe] Distributions of the Boötes I Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Lai, David K.; Lee, Young Sun; Bolte, Michael; Lucatello, Sara; Beers, Timothy C.; Johnson, Jennifer A.; Sivarani, Thirupathi; Rockosi, Constance M.

    2011-09-01

    We present the results of a low-resolution spectral abundance study of 25 stars in the Boötes I dwarf spheroidal (dSph) galaxy. The data were obtained with the low resolution imaging spectrometer instrument at Keck Observatory and allow us to measure [Fe/H], [C/Fe], and [α/Fe] for each star. We find both a large spread in metallicity (2.1 dex in [Fe/H]) as well as a low average metallicity in this system, lang[Fe/H]rang = -2.59, matching previous estimates. This sample includes a newly discovered extremely metal-poor star, with [Fe/H] = -3.8, that is one of the most metal-poor stars yet found in a dSph. We compare the metallicity distribution function of Boötes I to analytic chemical evolution models. While the metallicity distribution function of Boötes I is best fit by an Extra Gas chemical evolution model, leaky-box models also provide reasonable fits. We also find that the [α/Fe] distribution and the carbon-enhanced metal-poor fraction of our sample (12%) are reasonable matches to Galactic halo star samples in the same metallicity range, indicating that at these low metallicities, systems like the Boötes I ultra-faint dSph could have been contributors to the Galactic halo. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  6. MOLECULES IN {eta} CARINAE

    Energy Technology Data Exchange (ETDEWEB)

    Loinard, Laurent; Menten, Karl M.; Guesten, Rolf [Max-Planck Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany); Zapata, Luis A.; Rodriguez, Luis F. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 3-72, 58090 Morelia, Michoacan (Mexico)

    2012-04-10

    We report the detection toward {eta} Carinae of six new molecules, CO, CN, HCO{sup +}, HCN, HNC, and N{sub 2}H{sup +}, and of two of their less abundant isotopic counterparts, {sup 13}CO and H{sup 13}CN. The line profiles are moderately broad ({approx}100 km s{sup -1}), indicating that the emission originates in the dense, possibly clumpy, central arcsecond of the Homunculus Nebula. Contrary to previous claims, CO and HCO{sup +} do not appear to be underabundant in {eta} Carinae. On the other hand, molecules containing nitrogen or the {sup 13}C isotope of carbon are overabundant by about one order of magnitude. This demonstrates that, together with the dust responsible for the dimming of {eta} Carinae following the Great Eruption, the molecules detected here must have formed in situ out of CNO-processed stellar material.

  7. Molecules in \\eta\\ Carinae

    CERN Document Server

    Loinard, Laurent; Guesten, Rolf; Zapata, Luis A; Rodriguez, Luis F

    2012-01-01

    We report the detection toward \\eta\\ Carinae of six new molecules, CO, CN, HCO+, HCN, HNC, and N2H+, and of two of their less abundant isotopic counterparts, 13CO and H13CN. The line profiles are moderately broad (about 100 km /s) indicating that the emission originates in the dense, possibly clumpy, central arcsecond of the Homunculus Nebula. Contrary to previous claims, CO and HCO+ do not appear to be under-abundant in \\eta\\ Carinae. On the other hand, molecules containing nitrogen or the 13C isotope of carbon are overabundant by about one order of magnitude. This demonstrates that, together with the dust responsible for the dimming of eta Carinae following the Great Eruption, the molecules detected here must have formed in situ out of CNO-processed stellar material.

  8. Investigating Dwarf Spiral Galaxies

    Science.gov (United States)

    Weerasooriya, Sachithra; Dunn, Jacqueline M.

    2017-01-01

    Several studies have proposed that dwarf elliptical / spheroidal galaxies form through the transformation of dwarf irregular galaxies. Early and late type dwarfs resemble each other in terms of their observed colors and light distributions (each can often be represented by exponential disks), providing reason to propose an evolutionary link between the two types. The existence of dwarf spirals has been largely debated. However, more and more recent studies are using the designation of dwarf spiral to describe their targets of interest. This project seeks to explore where dwarf spirals fit into the above mentioned evolutionary sequence, if at all. Optical colors will be compared between a sample of dwarf irregular, dwarf elliptical, and dwarf spiral galaxies. The dwarf irregular and dwarf elliptical samples have previously been found to overlap in both optical color and surface brightness profile shape when limiting the samples to their fainter members. A preliminary comparison including the dwarf spiral sample will be presented here, along with a comparison of available ultraviolet and near-infrared data. Initial results indicate a potential evolutionary link that merits further investigation.

  9. FUSE Observations of eta Carinae

    CERN Document Server

    Iping, R C; Gull, T R

    2004-01-01

    Eta Carinae was observed by FUSE through the LWRS (30 arcsec x30 arcsec) and HIRS (1.25 arcsec x 20 arcsec) apertures in March and April 2004. There are significant differences between the two spectra. About half of the LWRS flux appears to be due to two B-type stars near the edge of the LWRS aperture, 14 arcsec from eta Carinae. The HIRS spectrum (LiF1 channel) therefore reveals the intrinsic FUV spectrum of eta Carinae without this stellar contamination. The HIRS spectrum contains strong interstellar H2 having high rotational excitation (up to J=8). Most of the atomic species with prominent ISM features (C II, Fe II, Ar I, P II, etc) also have strong blue-shifted absorption to v= ~ -580 km/s that is associated with expanding debris from the 1840 eruption.

  10. Spheroidal wave functions

    CERN Document Server

    Flammer, Carson

    2005-01-01

    Intended to facilitate the use and calculation of spheroidal wave functions, this applications-oriented text features a detailed and unified account of the properties of these functions. Addressed to applied mathematicians, mathematical physicists, and mathematical engineers, it presents tables that provide a convenient means for handling wave problems in spheroidal coordinates.Topics include separation of the scalar wave equation in spheroidal coordinates, angle and radial functions, integral representations and relations, and expansions in spherical Bessel function products. Additional subje

  11. Atlantic CFC data in CARINA

    Directory of Open Access Journals (Sweden)

    R. Steinfeldt

    2010-01-01

    Full Text Available Water column data of carbon and carbon-relevant parameters have been collected and merged into a new database called CARINA (CARbon IN the Atlantic. In order to provide a consistent data set, all data have been examined for systematic biases and adjusted if necessary (secondary quality control (QC. The CARINA data set is divided into three regions: the Arctic/Nordic Seas, the Atlantic region and the Southern Ocean. Here we present the CFC data for the Atlantic region, including the chlorofluorocarbons CFC-11, CFC-12 and CFC-113 as well as carbon tetrachloride (CCl4. The methods applied for the secondary quality control, a crossover analyses, the investigation of CFC ratios in the ocean and the CFC surface saturation are presented. Based on the results, the CFC data of some cruises are adjusted by a certain factor or given a "poor'' quality flag.

  12. Arctic Ocean data in CARINA

    Directory of Open Access Journals (Sweden)

    S. Jutterström

    2010-02-01

    Full Text Available The paper describes the steps taken for quality controlling chosen parameters within the Arctic Ocean data included in the CARINA data set and checking for offsets between the individual cruises. The evaluated parameters are the inorganic carbon parameters (total dissolved inorganic carbon, total alkalinity and pH, oxygen and nutrients: nitrate, phosphate and silicate. More parameters can be found in the CARINA data product, but were not subject to a secondary quality control. The main method in determining offsets between cruises was regional multi-linear regression, after a first rough basin-wide deep-water estimate of each parameter. Lastly, the results of the secondary quality control are discussed as well as applied adjustments.

  13. Arctic Ocean data in CARINA

    Directory of Open Access Journals (Sweden)

    S. Jutterström

    2009-08-01

    Full Text Available The paper describes the steps taken for quality controlling chosen parameters within the Arctic Ocean data included in the CARINA data set and checking for offsets between the individual cruises. The evaluated parameters are the inorganic carbon parameters (total dissolved inorganic carbon, total alkalinity and pH, oxygen and nutrients: nitrate, phosphate and silicate. More parameters can be found in the CARINA data product, but were not subject to a secondary quality control. The main method in determining offsets between cruises was regional multi-linear regression, after a first rough basin-wide deep-water estimate of each parameter. Lastly, the results of the secondary quality control are discussed as well as suggested adjustments.

  14. A Smoking Gun in the Carina Nebula

    Science.gov (United States)

    Hamaguchi, Kenji; Corcoran, Michael F.; Ezoe, Yuichiro; Townsley, Leisa; Broos, Patrick; Gruendl, Robert; Vaidya, Kaushar; White, Stephen M.; Petre, Rob; Chu, You-Hua

    2009-01-01

    The Carina Nebula is one of thc youngest, most active sites of massive star formation in our Galaxy. In this nebula, we have discovered a bright X-ray source that has persisted for approx.30 years. The soft X-ray spectrum. consistent with kT approx.130 eV blackbody radiation with mild extinction, and no counterpart in the near- and mid-infrared wavelengths indicate that it is a, approx. 10(exp 6)-year-old neutron star housed in the Carina Nebula. Current star formation theory does not suggest that the progenitor of the neutron star and massive stars in the Carina Nebula, in particular (eta)Car, are coeval. This result demonstrates that the Carina Nebula experienced at least two major episodes of massive star formation. The neutron star would be responsible for remnants of high energy activity seen in multiple wavelengths.

  15. CARINA: nutrient data in the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    T. Tanhua

    2009-07-01

    Full Text Available Data on carbon and carbon-relevant hydrographic and hydrochemical parameters from previously non-publicly available cruise data sets in the Arctic, Atlantic and Southern Ocean have been retrieved and merged to a new database: CARINA (CARbon IN the Atlantic. These data have gone through rigorous quality control (QC procedures to assure the highest possible quality and consistency. The data for most of the measured parameters in the CARINA data base were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the data products, i.e. three merged data files with measured, calculated and interpolated data for each of the three CARINA regions; Arctic, Atlantic and Southern Ocean. Out of a total of 188 cruise entries in the CARINA database, 98 were conducted in the Atlantic Ocean and of these 84 cruises report nitrate values, 79 silicate, and 78 phosphate. Here we present details of the secondary QC for nutrients for the Atlantic Ocean part of CARINA. Procedures of quality control, including crossover analysis between cruises and inversion analysis of all crossover data are briefly described. Adjustments were applied to the nutrient values for 43 of the cruises in the Atlantic Ocean region. With these adjustments the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s (Key et al., 2004. Based on our analysis we estimate the internal accuracy of the CARINA-ATL nutrient data to be: nitrate 1.5%; phosphate 2.6%; silicate 3.1%. The CARINA data are now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation.

  16. Morphological transformations of Dwarf Galaxies in the Local Group

    CERN Document Server

    Carraro, Giovanni

    2014-01-01

    In the Local Group there are three main types of dwarf galaxies: Dwarf Irregulars, Dwarf Spheroidals, and Dwarf Ellipticals. Intermediate/transitional types are present as well. This contribution reviews the idea that the present day variety of dwarf galaxy morphologies in the Local Group might reveal the existence of a transformation chain of events, of which any particular dwarf galaxy represents a manifestation of a particular stage. In other words, all dwarf galaxies that now are part of the Local Group would have formed identically in the early universe, but then evolved differently because of morphological transformations induced by dynamical processes like galaxy harassment, ram pressure stripping, photo-evaporation, and so forth. We start describing the population of dwarf galaxies and their spatial distribution in the LG. Then, we describe those phenomena that can alter the morphology of a dwarf galaxies, essentially by removing, partially or completely, their gas content. Lastly, we discuss morpholo...

  17. Galaxy And Mass Assembly (GAMA): the Stellar Mass Budget of Galaxy Spheroids and Disks

    CERN Document Server

    Moffett, Amanda J; Driver, Simon P; Robotham, Aaron S G; Kelvin, Lee S; Alpaslan, Mehmet; Andrews, Stephen K; Bland-Hawthorn, Joss; Brough, Sarah; Cluver, Michelle E; Colless, Matthew; Davies, Luke J M; Holwerda, Benne W; Hopkins, Andrew M; Kafle, Prajwal R; Liske, Jochen; Meyer, Martin

    2016-01-01

    We build on a recent photometric decomposition analysis of 7506 Galaxy and Mass Assembly (GAMA) survey galaxies to derive stellar mass function fits to individual spheroid and disk component populations down to a lower mass limit of log(M_*/M_sun)= 8. We find that the spheroid/disk mass distributions for individual galaxy morphological types are well described by single Schechter function forms. We derive estimates of the total stellar mass densities in spheroids (rho_spheroid = 1.24+/-0.49 * 10^8 M_sun Mpc^-3 h_0.7) and disks (rho_disk = 1.20+/-0.45 * 10^8 M_sun Mpc^-3 h_0.7), which translates to approximately 50% of the local stellar mass density in spheroids and 48% in disks. The remaining stellar mass is found in the dwarf "little blue spheroid" class, which is not obviously similar in structure to either classical spheroid or disk populations. We also examine the variation of component mass ratios across galaxy mass and group halo mass regimes, finding the transition from spheroid to disk mass dominance ...

  18. He II λ4686 in η Carinae

    DEFF Research Database (Denmark)

    Teodoro, M.; Damineli, A.; Arias, J.I.;

    2012-01-01

    The periodic spectroscopic events in eta Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind colli...

  19. Superluminous Supernovae: No Threat from Eta Carinae

    Science.gov (United States)

    Thomas, Brian; Melott, A. L.; Fields, B. D.; Anthony-Twarog, B. J.

    2008-05-01

    Recently Supernova 2006gy was noted as the most luminous ever recorded, with a total radiated energy of 1044 Joules. It was proposed that the progenitor may have been a massive evolved star similar to η Carinae, which resides in our own galaxy at a distance of about 2.3 kpc. η Carinae appears ready to detonate. Although it is too distant to pose a serious threat as a normal supernova, and given its rotation axis is unlikely to produce a Gamma-Ray Burst oriented toward the Earth, η Carinae is about 30,000 times nearer than 2006gy, and we re-evaluate it as a potential superluminous supernova. We find that given the large ratio of emission in the optical to the X-ray, atmospheric effects are negligible. Ionization of the atmosphere and concomitant ozone depletion are unlikely to be important. Any cosmic ray effects should be spread out over 104 y, and similarly unlikely to produce any serious perturbation to the biosphere. We also discuss a new possible effect of supernovae, endocrine disruption induced by blue light near the peak of the optical spectrum. This is a possibility for nearby supernovae at distances too large to be considered "dangerous” for other reasons. However, due to reddening and extinction by the interstellar medium, η Carinae is unlikely to trigger such effects to any significant degree.

  20. Forming Planets in the Hostile Carina Nebula

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    Can protoplanetary disks form and be maintained around low-mass stars in the harsh environment of a highly active, star-forming nebula? A recent study examines the Carina nebula to answer this question.Crowded ClustersStars are often born in clusters that contain both massive and low-mass stars. The most massive stars in these clusters emit far-ultraviolet and extreme-ultraviolet light that irradiates the region around them, turning the surrounding area into a hostile environment for potential planet formation.Planet formation from protoplanetary disks typically requires timescales of at least 12 million years. Could the harsh radiation from massive stars destroy the protoplanetary disks around low-mass stars by photoevaporation before planets even have a chance to form?Artists impression of a protoplanetary disk. Such disks can be photoevaporated by harsh ultraviolet light from nearby massive stars, causing the disk to be destroyed before planets have a chance to form within them. [ESO/L. Calada]Turning ALMA Toward CarinaA perfect case study for exploring hostile environments is the Carina nebula, located about 7500 lightyears away and home to nearly 100 O-type stars as well as tens of thousands of lower-mass young stars. The Carina population is ~14 Myr old: old enough to form planets within protoplanetary disks, but also old enough that photoevaporation could already have wreaked havoc on those disks.Due to the dense stellar populations in Carinas clusters, this is a difficult region to explore, but the Atacama Large Millimeter-submillimeter Array (ALMA) is up to the task. In a recent study, a team of scientists led by Adal Mesa-Delgado (Pontifical Catholic University of Chile) made use of ALMAs high spatial resolution to image four regions spaced throughout Carina, searching for protoplanetary disks.Detections and Non-DetectionsTwo evaporating gas globules in the Carina nebula, 104-593 and 105-600, that each contain a protoplanetary disk. The top panels are

  1. Spheroidal Wave Functions in Electromagnetic Theory

    Science.gov (United States)

    Li, Le-Wei; Kang, Xiao-Kang; Leong, Mook-Seng

    2001-11-01

    The flagship monograph addressing the spheroidal wave function and its pertinence to computational electromagnetics Spheroidal Wave Functions in Electromagnetic Theory presents in detail the theory of spheroidal wave functions, its applications to the analysis of electromagnetic fields in various spheroidal structures, and provides comprehensive programming codes for those computations. The topics covered in this monograph include: Spheroidal coordinates and wave functions Dyadic Green's functions in spheroidal systems EM scattering by a conducting spheroid EM scattering by a coated dielectric spheroid Spheroid antennas SAR distributions in a spheroidal head model The programming codes and their applications are provided online and are written in Mathematica 3.0 or 4.0. Readers can also develop their own codes according to the theory or routine described in the book to find subsequent solutions of complicated structures. Spheroidal Wave Functions in Electromagnetic Theory is a fundamental reference for scientists, engineers, and graduate students practicing modern computational electromagnetics or applied physics.

  2. Morphological Mutations of Dwarf Galaxies

    CERN Document Server

    Hensler, Gerhard

    2012-01-01

    Dwarf galaxies (DGs) are extremely challenging objects in extragalactic astrophysics. They are expected to originate as the first units in Cold Dark-Matter cosmology. They are the galaxy type most sensitive to environmental influences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has affected the evolution. Here we review peculiarities of general morphological DG types and refer to processes which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while gas replenishment implies an evolutionary cycling. Finally, as the less understood DG types the Milky Way satellite dwarf spheroidal galaxies are discussed in the context of transformation.

  3. Gravitational fragmentation of the Carina Flare supershell

    Science.gov (United States)

    Wünsch, Richard

    2015-03-01

    We study the gravitational fragmentation of a thick shell comparing the analytical theory to 3D hydrodynamic simulations and to observations of the Carina Flare supershell. We use both grid-based (AMR) and particle-based (SPH) codes to follow the idealised model of the fragmenting shell and found an excellent agreement between the two codes. Growth rates of fragments at different wavelength are well described by the pressure assisted gravitational instability (PAGI) - a new theory of the thick shell fragmentation. Using the APEX telescope we observe a part of the surface of the Carina Flare supershell (GSH287+04-17) in the 13CO(2-1) line. We apply a new clump-finding algorithm DENDROFIND to identify 50 clumps. We determine the clump mass function and we construct the minimum spanning tree connecting clumps positions to estimate the typical distance among clumps. We conclude that the observed masses and distances correspond well to the prediction of PAGI.

  4. The Mass Dependence of Dwarf Satellite Galaxy Quenching

    Science.gov (United States)

    Slater, Colin T.; Bell, Eric F.

    2014-09-01

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low-mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic Clouds. While almost all of the low-mass (M sstarf 5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

  5. Superluminous supernovae: No threat from Eta Carinae

    CERN Document Server

    Thomas, Brian C; Fields, Brian D; Anthony-Twarog, Barbara J

    2007-01-01

    Recently Supernova 2006gy was noted as the most luminous ever recorded, with a total radiated energy of ~10^44 Joules. It was proposed that the progenitor may have been a massive evolved star similar to Eta Carinae, which resides in our own galaxy at a (poorly determined) distance of ~2.5 kpc. Eta Carinae appears ready to detonate, and in fact had an outburst in 1843. Although it is too distant to pose a serious threat as a normal supernova, and given its rotation axis is unlikely to produce a Gamma Ray Burst oriented toward the Earth, Eta Carinae is about 30,000 times nearer than 2006gy, and we re-evaluate it as a potential superluminous supernova. We find that given the large ratio of emission in the optical to the X-ray, atmospheric effects are negligible. Ionization of the atmosphere and concomitant ozone depletion are unlikely to be important. Any cosmic ray effects should be spread out over ~10^4 y, and similarly unlikely to produce any serious perturbation to the biosphere. We also discuss a new possib...

  6. HESS observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae

    Science.gov (United States)

    HESS Collaboration; Abramowski, A.; Acero, F.; Aharonian, F.; Akhperjanian, A. G.; Anton, G.; Balzer, A.; Barnacka, A.; Becherini, Y.; Becker, J.; Bernlöhr, K.; Birsin, E.; Biteau, J.; Bochow, A.; Boisson, C.; Bolmont, J.; Bordas, P.; Brucker, J.; Brun, F.; Brun, P.; Bulik, T.; Büsching, I.; Carrigan, S.; Casanova, S.; Cerruti, M.; Chadwick, P. M.; Charbonnier, A.; Chaves, R. C. G.; Cheesebrough, A.; Cologna, G.; Conrad, J.; Dalton, M.; Daniel, M. K.; Davids, I. D.; Degrange, B.; Deil, C.; Dickinson, H. J.; Djannati-Ataï, A.; Domainko, W.; Drury, L. O'C.; Dubus, G.; Dutson, K.; Dyks, J.; Dyrda, M.; Egberts, K.; Eger, P.; Espigat, P.; Fallon, L.; Fegan, S.; Feinstein, F.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Füßling, M.; Gallant, Y. A.; Garrigoux, T.; Gast, H.; Gérard, L.; Giebels, B.; Glicenstein, J. F.; Glück, B.; Göring, D.; Grondin, M.-H.; Häffner, S.; Hague, J. D.; Hahn, J.; Hampf, D.; Harris, J.; Hauser, M.; Heinz, S.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hillert, A.; Hinton, J. A.; Hofmann, W.; Hofverberg, P.; Holler, M.; Horns, D.; Jacholkowska, A.; Jahn, C.; Jamrozy, M.; Jung, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kaufmann, S.; Khélifi, B.; Klochkov, D.; Kluźniak, W.; Kneiske, T.; Komin, Nu.; Kosack, K.; Kossakowski, R.; Krayzel, F.; Laffon, H.; Lamanna, G.; Lenain, J.-P.; Lennarz, D.; Lohse, T.; Lopatin, A.; Lu, C.-C.; Marandon, V.; Marcowith, A.; Masbou, J.; Maurin, G.; Maxted, N.; Mayer, M.; McComb, T. J. L.; Medina, M. C.; Méhault, J.; Moderski, R.; Mohamed, M.; Moulin, E.; Naumann, C. L.; Naumann-Godo, M.; de Naurois, M.; Nedbal, D.; Nekrassov, D.; Nguyen, N.; Nicholas, B.; Niemiec, J.; Nolan, S. J.; Ohm, S.; de Oña Wilhelmi, E.; Opitz, B.; Ostrowski, M.; Oya, I.; Panter, M.; Paz Arribas, M.; Pekeur, N. W.; Pelletier, G.; Perez, J.; Petrucci, P.-O.; Peyaud, B.; Pita, S.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raue, M.; Reimer, A.; Reimer, O.; Renaud, M.; de los Reyes, R.; Rieger, F.; Ripken, J.; Rob, L.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Sanchez, D. A.; Santangelo, A.; Schlickeiser, R.; Schulz, A.; Schwanke, U.; Schwarzburg, S.; Schwemmer, S.; Sheidaei, F.; Skilton, J. L.; Sol, H.; Spengler, G.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Szostek, A.; Tavernet, J.-P.; Terrier, R.; Tluczykont, M.; Valerius, K.; van Eldik, C.; Vasileiadis, G.; Venter, C.; Viana, A.; Vincent, P.; Völk, H. J.; Volpe, F.; Vorobiov, S.; Vorster, M.; Wagner, S. J.; Ward, M.; White, R.; Wierzcholska, A.; Zacharias, M.; Zajczyk, A.; Zdziarski, A. A.; Zech, A.; Zechlin, H.-S.; Montmerle, T.

    2012-07-01

    The massive binary system Eta Carinae and the surrounding H II complex, the Carina nebula, are potential particle acceleration sites from which very high energy (VHE; E≥ 100 GeV) γ-ray emission could be expected. This paper presents data collected during VHE γ-ray observations with the HESS telescope array from 2004 to 2010, which cover a full orbit of Eta Carinae. In the 33.1-h data set no hint of significant γ-ray emission from Eta Carinae has been found and an upper limit on the γ-ray flux of ? (99 per cent confidence level) is derived above the energy threshold of 470 GeV. Together with the detection of high energy (HE; 0.1 ≤E≤ 100 GeV) γ-ray emission by the Fermi Large Area Telescope up to 100 GeV, and assuming a continuation of the average HE spectral index into the VHE domain, these results imply a cut-off in the γ-ray spectrum between the HE and VHE γ-ray range. This could be caused either by a cut-off in the accelerated particle distribution or by severe γ-γ absorption losses in the wind collision region. Furthermore, the search for extended γ-ray emission from the Carina nebula resulted in an upper limit on the γ-ray flux of ? (99 per cent confidence level). The derived upper limit of ˜23 on the cosmic ray enhancement factor is compared with results found for the old-age mixed-morphology supernova remnant W28.

  7. η Carinae Baby Homunculus uncovered by ALMA

    Energy Technology Data Exchange (ETDEWEB)

    Abraham, Zulema; Beaklini, Pedro P. B. [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, R. do Matão 1226, Cidade Universitária, CEP 05508-900 São Paulo, SP (Brazil); Falceta-Gonçalves, Diego, E-mail: zulema.abraham@iag.usp.br [Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, R. Arlindo Bettio 1000, 03828-000 São Paulo, SP (Brazil)

    2014-08-20

    We report observations of η Carinae obtained with ALMA in the continuum of 100, 230, 280, and 660 GHz in 2012 November, with a resolution that varied from 2.''88 to 0.''45 for the lower and higher frequencies, respectively. The source is not resolved, even at the highest frequency; its spectrum is characteristic of thermal bremsstrahlung of a compact source, but different from the spectrum of optically thin wind. The recombination lines H42α, He42α, H40α, He40α, H50β, H28α, He28α, H21α, and He21α were also detected, and their intensities reveal non-local thermodynamic equilibrium effects. We found that the line profiles could only be fit by an expanding shell of dense and ionized gas, which produces a slow shock in the surroundings of η Carinae. Combined with fittings to the continuum, we were able to constrain the shell size, radius, density, temperature, and velocity. The detection of the He recombination lines is compatible with the high-temperature gas and requires a high-energy ionizing photon flux, which must be provided by the companion star. The mass-loss rate and wind velocity, necessary to explain the formation of the shell, are compatible with an luminous blue variable eruption. The position, velocity, and physical parameters of the shell coincide with those of the Weigelt blobs. The dynamics found for the expanding shell correspond to matter ejected by η Carinae in 1941 in an event similar to that which formed the Little Homunculus; for that reason, we called the new ejecta the 'Baby Homunculus'.

  8. $\\eta$ Carinae Baby Homunculus Uncovered by ALMA

    CERN Document Server

    Abraham, Zulema; Beaklini, Pedro P B

    2014-01-01

    We report observations of $\\eta$ Carinae obtained with ALMA in the continuum of 100, 230, 280 and 660 GHz in 2012 November, with a resolution that varied from 2.88" to 0.45" for the lower and higher frequencies respectively. The source is not resolved, even at the highest frequency; its spectrum is characteristic of thermal bremsstrahlung of a compact source, but different from the spectrum of optically thin wind. The recombination lines H42$\\alpha$, He42$\\alpha$, H40$\\alpha$, He40$\\alpha$, H50$\\beta$, H28$\\alpha$, He28$\\alpha$, H21$\\alpha$ and He21$\\alpha$ were also detected and their intensities reveal non local thermodynamic equilibrium (NLTE) effects. We found that the line profiles could only be fit by an expanding shell of dense and ionized gas, which produces a slow shock in the surroundings of $\\eta$ Carinae. Combined with fittings to the continuum, we were able to constrain the shell size, radius, density, temperature and velocity. The detection of the He recombination lines is compatible with the hi...

  9. The Horizontal Branch of the Sculptor Dwarf galaxy

    NARCIS (Netherlands)

    Salaris, Maurizio; Boer, Thomas de; Tolstoy, Eline; Fiorentino, Giuliana; Cassisi, Santi

    2013-01-01

    We have performed the first detailed simulation of the horizontal branch of the Sculptor dwarf spheroidal galaxy by means of synthetic modelling techniques, taking consistently into account the star formation history and metallicity evolution as determined from the main sequence and red giant branch

  10. Indirect dark matter detection for flattened dwarf galaxies

    Science.gov (United States)

    Sanders, Jason L.; Evans, N. Wyn; Geringer-Sameth, Alex; Dehnen, Walter

    2016-09-01

    Gamma-ray experiments seeking to detect evidence of dark matter annihilation in dwarf spheroidal galaxies require knowledge of the distribution of dark matter within these systems. We analyze the effects of flattening on the annihilation (J) and decay (D) factors of dwarf spheroidal galaxies with both analytic and numerical methods. Flattening has two consequences: first, there is a geometric effect as the squeezing (or stretching) of the dark matter distribution enhances (or diminishes) the J-factor; second, the line of sight velocity dispersion of stars must hold up the flattened baryonic component in the flattened dark matter halo. We provide analytic formulas and a simple numerical approach to estimate the correction to the J- and D-factors required over simple spherical modeling. The formulas are validated with a series of equilibrium models of flattened stellar distributions embedded in flattened dark-matter distributions. We compute corrections to the J- and D-factors for the Milky Way dwarf spheroidal galaxies under the assumption that they are all prolate or all oblate and find that the hierarchy of J-factors for the dwarf spheroidals is slightly altered (typical correction factors for an ellipticity of 0.4 are 0.75 for the oblate case and 1.6 for the prolate case). We demonstrate that spherical estimates of the D-factors are very insensitive to the flattening and introduce uncertainties significantly less than the uncertainties in the D-factors from the other observables for all the dwarf spheroidals (for example, +10 per cent/-3 per cent for a typical ellipticity of 0.4). We conclude by investigating the spread in correction factors produced by triaxial figures and provide uncertainties in the J-factors for the dwarf spheroidals using different physically motivated assumptions for their intrinsic shape and axis alignments. We find that the uncertainty in the J-factors due to triaxiality increases with the observed ellipticity and, in general, introduces

  11. The Variable Stars of the DRACO DWARF Spheroidal Glaxay: Revisited

    Science.gov (United States)

    2008-11-01

    The exceptions are V19 in NGC 5466 (Zinn & Dahn 1976) and two candidates in ω Cen ( Wallerstein & Cox 1984). XZ Ceti is a well-known field AC. The...2006, ApJ, 652, 643 Walker, A. R. 1994, AJ, 108, 555 Walker, A. R., & Nemec, J. M. 1996, AJ, 112, 2026 Wallerstein , G., & Cox, A. N. 1984, PASP, 96

  12. No WIMP mini-spikes in dwarf spheroidal galaxies

    NARCIS (Netherlands)

    Wanders, M.; Bertone, G.; Volonteri, M.; Weniger, C.

    2015-01-01

    The formation of black holes inevitably affects the distribution of dark and baryonic matter in their vicinity, leading to an enhancement of the dark matter density, called spike, and if dark matter is made of WIMPs, to a strong enhancement of the dark matter annihilation rate. Spikes at the center

  13. Metallicities and kinematics for dwarf spheroidals in the local group

    NARCIS (Netherlands)

    Battaglia, G.; Tolstoy, E.; Helmi, A.; Irwin, M.; Randich, S; Pasquini, L

    2006-01-01

    We present the first results of Call triplet observations from VLT/FLAMES for Sculptor, Fornax and Sextans dSphs. For each galaxy, we obtained accurate velocity and metallicity measurements for hundreds of stars out to and beyond the tidal radius. In each case, we find clear evidence for the presenc

  14. UVES abundances of stars in nearby dwarf spheroidal galaxies

    NARCIS (Netherlands)

    Tolstoy, E; Venn, K; Shetrone, M; Primas, F; Hill, [No Value; Kaufer, A; Szeifert, T

    2002-01-01

    It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of contr

  15. The Fundamental Manifold of Spheroids

    CERN Document Server

    Zaritsky, D; Zabludoff, A I; Zaritsky, Dennis; Gonzalez, Anthony H.; Zabludoff, Ann I.

    2006-01-01

    We present a unifying empirical description of the structural and kinematic properties of all spheroids embedded in dark matter halos. We find that the stellar spheroidal components of galaxy clusters, which we call cluster spheroids (CSphs) and which are typically one hundred times the size of normal elliptical galaxies, lie on a "fundamental plane" as tight as that defined by ellipticals (rms in effective radius of ~0.07), but that has a different slope. The slope, as measured by the coefficient of the log(sigma) term, declines significantly and systematically between the fundamental planes of ellipticals, brightest cluster galaxies (BCGs), and CSphs.We attribute this decline primarily to a continuous change in M_e/L_e, the mass-to-light ratio within the effective radius r_e, with spheroid scale. The magnitude of the slope change requires that it arises principally from differences in the relative distributions of luminous and dark matter, rather than from stellar population differences such as in age and m...

  16. CARINA oxygen data in the Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    I. Stendardo

    2009-12-01

    Full Text Available In the CARINA (Carbon dioxide in the Atlantic Ocean project, a new dataset with many previously unpublished hydrographic data from the Atlantic, Arctic and Southern Ocean was assembled and subjected to careful quality control (QC procedures. Here, we present the dissolved oxygen measurements in the Atlantic region of the dataset and describe in detail the secondary QC procedures that aim to ensure that the data are internally consistent. This is achieved by a cross-over analysis, i.e. the comparison of deep ocean data at places that were sampled by different cruises at different times. Initial adjustments to the individual cruises were then determined by an inverse procedure that computes a set of adjustments that requires the minimum amount of adjustment and at the same time reduces the offsets in an optimal manner. The initial adjustments were then reviewed by the CARINA members, and only those that passed the following two criteria were adopted: (i the region is not subject to substantial temporal variability, and (ii the adjustment must be based on at least three stations from each cruise. No adjustment was recommended for cruises that did not fit these criteria. The final CARINA-Oxygen dataset has 103414 oxygen samples from 9491 stations obtained during 98 cruises covering three decades. The sampling density of the oxygen data is particularly good in the North Atlantic north of about 40° N especially after 1987. In contrast, the sample density in the South Atlantic is much lower. Some cruises appear to have poor data quality, and were subsequently omitted from the adjusted dataset. Of the data included in the adjusted dataset, 20% were adjusted with a mean adjustment of 2%. Due to the achieved internal consistency, the resulting product is well suited to produce an improved climatology or to study long-term changes in the oxygen content of the ocean. However, the adjusted dataset is not necessarily better suited than the unadjusted data to

  17. Dwarf galaxies in multistate Scalar Field Dark Matter haloes

    CERN Document Server

    Martinez-Medina, L A; Matos, T

    2014-01-01

    We analyse the velocity dispersion for eight of the Milky Way dwarf spheroidal satellites in the context of finite temperature scalar field dark mater. In this model the finite temperature allows the scalar field to be in configurations that possess excited states, a feature that has proved to be necessary in order to explain the asymptotic rotational velocities found in low surface brightness (LSB) galaxies. In this work we show that excited states are not only important in large galaxies but also have visible effects in dwarf spheroidals. Additionally, we stress that contrary to previous works where the scalar field dark matter haloes are consider to be purely Bose-Einstein condensates, the inclusion of excited states in these halo configurations provides a consistent framework capable of describing LSBs and dwarf galaxies of different sizes without arriving to contradictions within the scalar field dark matter model. Using this new framework we find that the addition of excited states accounts very well fo...

  18. Spectrophotometry of the shell around AG Carinae

    Science.gov (United States)

    Mitra, P. Mila; Dufour, Reginald J.

    1990-01-01

    Spatially-resolved long-slit spectrophotometry are presented for two regions of the shell nebula around the P-Cygni variable star AG Carinae. The spectra cover the 3700-6800 A wavelength range. Emission-line diagnostics are used to derive extinction, electron temperatures, and densities for various positions in the nebula. The chemical abundances and ionization structure are calculated and compared with other types of planetary nebulae and shells around other luminous stars. It is found that the N/O and N/S ratios of Ag Car are high compared to solar neighborhood ISM values. The O/H depletion found for the AG Car shell approaches that found in the condensations of the Eta Car system.

  19. Spheroidal Degeneration of the Cornea

    Directory of Open Access Journals (Sweden)

    Erdem Dinç

    2011-08-01

    Full Text Available A thirty-one-year-old male patient presented with bilateral epiphora and stinging sensation in the cornea. Detailed history revealed that a bilateral corneal scraping had been made regarding the initial diagnosis of fungal keratitis. His bestcorrected visual acuities were 20/20 and 20/30 in right and left eyes, respectively. Biomicroscopy showed bilateral amber colored spherules in the anterior stroma of the central cornea. The diagnosis of spheroidal corneal degeneration was established and symptomatic therapy with artificial tear drops was prescribed. Ultraviolet light is widely accepted to be the main etiological factor in the pathogenesis of spheroidal degeneration. Because of difficulties in the early stages of the diagnostic process of the disease, incorrect diagnoses can be made with inappropriate interventions. (Turk J Ophthalmol 2011; 41: 264-6

  20. Atlantic Ocean CARINA data: overview and salinity adjustments

    Energy Technology Data Exchange (ETDEWEB)

    Tanhua, T. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany; Steinfeldt, R. [University of Bremen, Bremen, Germany; Key, Robert [Princeton University; Brown, P. [University of East Anglia, Norwich, United Kingdom; Gruber, N. [ETH Zurich, Switzerland; Wanninkhof, R. [Atlantic Oceanographic & Meteorological Laboratory, NOAA; Perez, F.F. [Instituto de Investigaciones Marinas de Vigo, CSIC, Vigo, Spain; Kortzinger, A. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany; Velo, A. [Instituto de Investigaciones Marinas de Vigo, CSIC, Vigo, Spain; Schuster, U. [University of East Anglia, Norwich, United Kingdom; Van Heuven, S. [University of Groningen, The Netherlands; Bullister, J.L. [NOAA Pacific Marine Environmental Laboratory; Stendardo, I. [ETH Zurich, Switzerland; Hoppema, M. [Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; Olsen, Are [Bjerknes Centre for Climate Research, UNIFOB AS, Bergen, Norway; Kozyr, Alexander [ORNL; Pierrot, D. [Cooperative Institute of Marine and Atmospheric Sciences, U. Miami; Schirnick, C. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany; Wallace, D.W.R. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany

    2010-01-01

    Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon dioxide IN the Atlantic Ocean). The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the three data products: merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. the Arctic Mediterranean Seas, the Atlantic and the Southern Ocean. These products have been corrected to be internally consistent. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30 S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report the details of the secondary QC (Quality Control) for salinity for this data set. Procedures of quality control including crossover analysis between stations and inversion analysis of all crossover data are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal consistency of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA data products are consistent both internally was well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, oceanic carbon inventories

  1. Scalable robotic biofabrication of tissue spheroids

    Energy Technology Data Exchange (ETDEWEB)

    Mehesz, A Nagy; Hajdu, Z; Visconti, R P; Markwald, R R; Mironov, V [Advanced Tissue Biofabrication Center, Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC (United States); Brown, J [Department of Mechanical Engineering, Clemson University, Clemson, SC (United States); Beaver, W [York Technical College, Rock Hill, SC (United States); Da Silva, J V L, E-mail: mironovv@musc.edu [Renato Archer Information Technology Center-CTI, Campinas (Brazil)

    2011-06-15

    Development of methods for scalable biofabrication of uniformly sized tissue spheroids is essential for tissue spheroid-based bioprinting of large size tissue and organ constructs. The most recent scalable technique for tissue spheroid fabrication employs a micromolded recessed template prepared in a non-adhesive hydrogel, wherein the cells loaded into the template self-assemble into tissue spheroids due to gravitational force. In this study, we present an improved version of this technique. A new mold was designed to enable generation of 61 microrecessions in each well of a 96-well plate. The microrecessions were seeded with cells using an EpMotion 5070 automated pipetting machine. After 48 h of incubation, tissue spheroids formed at the bottom of each microrecession. To assess the quality of constructs generated using this technology, 600 tissue spheroids made by this method were compared with 600 spheroids generated by the conventional hanging drop method. These analyses showed that tissue spheroids fabricated by the micromolded method are more uniform in diameter. Thus, use of micromolded recessions in a non-adhesive hydrogel, combined with automated cell seeding, is a reliable method for scalable robotic fabrication of uniform-sized tissue spheroids.

  2. A New M Dwarf Debris Disk Candidate in a Young Moving Group Discovered with Disk Detective

    CERN Document Server

    Silverberg, Steven M; Wisniewski, John P; Gagne, Jonathan; Bans, Alissa S; Bhattacharjee, Shambo; Currie, Thayne R; Debes, John R; Biggs, Joseph R; Bosch, Milton; Doll, Katharina; Durantini-Luca, Hugo A; Enachioaie, Alexandru; Griffith,, Philip; Hyogo, Michiharu; Piniero, Fernanda

    2016-01-01

    We used the Disk Detective citizen science project and the BANYAN II Bayesian analysis tool to identify a new candidate member of a nearby young association with infrared excess. WISE J080822.18-644357.3, an M5.5-type debris disk system with significant excess at both 12 and 22 $\\mu$m, is a likely member ($\\sim 90\\%$ BANYAN II probability) of the $\\sim 45$ Myr-old Carina association. Since this would be the oldest M dwarf debris disk detected in a moving group, this discovery could be an important constraint on our understanding of M dwarf debris disk evolution.

  3. Dwarf galaxies in multistate scalar field dark matter halos

    Science.gov (United States)

    Martinez-Medina, L. A.; Robles, V. H.; Matos, T.

    2015-01-01

    We analyze the velocity dispersion for eight of the Milky Way dwarf spheroidal satellites in the context of finite temperature scalar field dark matter. In this model the finite temperature allows the scalar field to be in configurations that possess excited states, a feature that has proved to be necessary in order to explain the asymptotic rotational velocities found in low surface brightness (LSB) galaxies. In this work we show that excited states are not only important in large galaxies but also have visible effects in dwarf spheroidals. Additionally, we stress that contrary to previous works where the scalar field dark matter halos are consider to be purely Bose-Einstein condensates, the inclusion of excited states in these halo configurations provides a consistent framework capable of describing LSB and dwarf galaxies of different sizes without arriving to contradictions within the scalar field dark matter model. Using this new framework we find that the addition of excited states accounts very well for the raise in the velocity dispersion in Milky Way dwarf spheroidal galaxies improving the fit compared to the one obtained assuming all the dark matter to be in the form of a Bose-Einstein condensate.

  4. High Spatial/Spectral Resolution Studies of Eta Carinae

    Science.gov (United States)

    Gull, Theodore R.; Eta Carinae HST Treasury Team

    2005-01-01

    The ejecta of Eta Carinae revealed by HST/STIS are in a large range of physical conditions. As Eta Carinae undergoes a 5.52 period changes occur in nebular emission and nebular absorption. ""Warm"" neutral regions partially ionized regions and fully ionized regions undergo significant changes. Over 2000 emission lines most of Fe-like elements have been indentified in the Weigelt blobs B and D. Over 500 emission lines have been identifed in the Strontium Filament. An ionized Little Homunculus is nestled within the neutral-shelled Homunculus. In line of sight over 500 nebular absorption lines have been identified with up to twenty velocity components. STIS is following changes in many nebular emission and absorption lines as Eta Carinae approaches the minimum predicted to be in June/July 2003 during the General Assembly. Coordinated observations with HST CHANDRA RXTE FUSE UVES/VLT Gemini and other observatories are following this minimum.

  5. Is the Ejecta of ETA Carinae Overabundant or Overexcited

    Science.gov (United States)

    Gull, Theodore; Davidson, Kris; Johansson, Sveneric; Damineli, Augusto; Ishibashi, Kaxunori; Corcoran, Michael; Hartman, Henrick; Viera, Gladys; Nielsen, Krister

    2003-01-01

    The ejecta of Eta Carinae, revealed by HST/STIS, are in a large range of physical conditions. As Eta Carinae undergoes a 5.52 period, changes occur in nebular emission and nebular absorption. "Warm" neutral regions, partially ionized regions, and fully ionized regions undergo significant changes. Over 2000 emission lines, most of Fe-like elements, have been indentified in the Weigelt blobs B and D. Over 500 emission lines have been indentified in the Strontium Filament. An ionized Little Homunculus is nestled within the neutral-shelled Homunculus. In line of sight, over 500 nebular absorption lines have been identified with up to twenty velocity components. STIS is following changes in many nebular emission and absorption lines as Eta Carinae approaches the minimum, predicted to be in June/July 2003, during the General Assembly. Coordinated observations with HST, CHANDRA, RXTE, FUSE, UVES/VLT, Gemini and other observatories are following this minimum.

  6. Is the Ejecta of Eta Carinae Overabundant or Overexcited?

    Science.gov (United States)

    Gull, Theodore; Davidson, Kris; Johansson, Sveneric; Damineli, Augusto; Ishibashi, Kazunori; Corcoran, Michael; Hartman, Henrick; Viera, Gladys; Nielsen, Krister; Eta Carinae Teams

    The ejecta of Eta Carinae revealed by HST/STIS are in a large range of physical conditions. As Eta Carinae undergoes a 5.52 period changes occur in nebular emission and nebular absorption. ""Warm"" neutral regions partially ionized regions and fully ionized regions undergo significant changes. Over 2000 emission lines most of Fe-like elements have been indentified in the Weigelt blobs B and D. Over 500 emission lines have been identifed in the Strontium Filament. An ionized Little Homunculus is nestled within the neutral-shelled Homunculus. In line of sight over 500 nebular absorption lines have been identified with up to twenty velocity components. STIS is following changes in many nebular emission and absorption lines as Eta Carinae approaches the minimum predicted to be in June/July 2003 during the General Assembly. Coordinated observations with HST CHANDRA RXTE FUSE UVES/VLT Gemini and other observatories are following this minimum.

  7. The periodicity of the eta Carinae events

    CERN Document Server

    Damineli, A; Hillier, D J; Stahl, O; Levenhagen, R S; Leister, N V; Groh, J H; Teodoro, M; Colombo, J F Albacete; Gonzalez, F; Arias, J; Levato, H; Grosso, M; Morrell, N; Gamen, R; Wallerstein, G; Niemela, V

    2007-01-01

    Extensive spectral observations of eta Carinae over the last cycle, and particularly around the 2003.5 low excitation event, have been obtained. The variability of both narrow and broad lines, when combined with data taken from two earlier cycles, reveal a common and well defined period. We have combined the cycle lengths derived from the many lines in the optical spectrum with those from broad-band X-rays, optical and near-infrared observations, and obtained a period length of 2022.7+-1.3 d. Spectroscopic data collected during the last 60 years yield an average period of 2020+-4 d, consistent with the present day period. The period cannot have changed by more than $\\Delta$P/P=0.0007 since 1948. This confirms the previous claims of a true, stable periodicity, and gives strong support to the binary scenario. We have used the disappearance of the narrow component of HeI 6678 to define the epoch of the Cycle 11 minimum, T_0=JD 2,452,819.8. The next event is predicted to occur on 2009 January 11 (+-2 days). The d...

  8. Eta Carinae -- Physics of the Inner Ejecta

    CERN Document Server

    Hamann, Fred

    2012-01-01

    Eta Carinae's inner ejecta are dominated observationally by the bright Weigelt blobs and their famously rich spectra of nebular emission and absorption lines. They are dense (n_e ~ 10^7 to 10^8 cm^-3), warm (T_e ~ 6000 to 7000 K) and slow moving (~40 km/s) condensations of mostly neutral (H^0) gas. Located within 1000 AU of the central star, they contain heavily CNO-processed material that was ejected from the star about a century ago. Outside the blobs, the inner ejecta include absorption-line clouds with similar conditions, plus emission-line gas that has generally lower densities and a wider range of speeds (reaching a few hundred km/s) compared to the blobs. The blobs appear to contain a negligible amount of dust and have a nearly dust-free view of the central source, but our view across the inner ejecta is severely affected by uncertain amounts of dust having a patchy distribution in the foreground. Emission lines from the inner ejecta are powered by photoionization and fluorescent processes. The variabl...

  9. Tidal Dwarf Galaxies and Missing Baryons

    Directory of Open Access Journals (Sweden)

    Frederic Bournaud

    2010-01-01

    Full Text Available Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons,” known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”.

  10. Seeking footprints of the primeval Universe in dwarf galaxies

    Science.gov (United States)

    Hidalgo, Sebastian L.

    2015-03-01

    We present the star formation histories (SFHs) of four isolated dwarf galaxies, Cetus, Tucana, LGS-3, and Phoenix, as a function of galactocentric radius. Our results suggest that beyond some distance from the center, there are no significative differences in fundamental properties of these galaxies, such as the star formation rate (SFR) or age-metallicity relation (AMR). The stellar content of this region would be composed of old (>~ 10.5 Gyr) metal-poor stars only. In the innermost regions, dwarf galaxies appear to have formed stars during time intervals which duration varies from galaxy to galaxy. This extended star formation produces the dichotomy between dwarf spheroidal (dSph) and dwarf Transition (dTr) galaxy types.

  11. Star formation in proto dwarf galaxies

    Science.gov (United States)

    Noriega-Crespo, A.; Bodenheimer, P.; Lin, D. N. C.; Tenorio-Tagle, G.

    1990-01-01

    The effects of the onset of star formation on the residual gas in primordial low-mass Local-Group dwarf spheroidal galaxies is studied by a series of hydrodynamical simulations. The models have concentrated on the effect of photoionization. The results indicate that photoionization in the presence of a moderate gas density gradient can eject most of the residual gas on a time scale of a few 10 to the 7th power years. High central gas density combined with inefficient star formation, however, may prevent mass ejection. The effect of supernova explosions is discussed briefly.

  12. White dwarf-red dwarf binaries in the Galaxy

    NARCIS (Netherlands)

    Besselaar, E.J.M. van den

    2007-01-01

    This PhD thesis shows several studies on white dwarf - red dwarf binaries. White dwarfs are the end products of most stars and red dwarfs are normal hydrogen burning low-mass stars. White dwarf - red dwarf binaries are both blue (white dwarf) and red (red dwarf). Together with the fact that they are

  13. Detection of the compressed primary stellar wind in eta Carinae

    CERN Document Server

    Teodoro, M; Gull, T R; Corcoran, M F; Hamaguchi, K

    2013-01-01

    A series of three HST/STIS spectroscopic mappings, spaced approximately one year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving outward from eta Carinae. We identify these arcs with the shell-like structures, seen in the 3D hydrodynamical simulations, formed by compression of the primary wind by the secondary wind during periastron passages.

  14. An Introduction to the Chandra Carina Complex Project

    CERN Document Server

    Townsley, Leisa K; Corcoran, Michael F; Feigelson, Eric D; Gagné, Marc; Montmerle, Thierry; Oey, M S; Smith, Nathan; Garmire, Gordon P; Getman, Konstantin V; Povich, Matthew S; Evans, Nancy Remage; Nazé, Yaël; Parkin, E R; Preibisch, Thomas; Wang, Junfeng; Wolk, Scott J; Chu, You-Hua; Cohen, David H; Gruendl, Robert A; Hamaguchi, Kenji; King, Robert R; Mac Low, Mordecai-Mark; McCaughrean, Mark J; Moffat, Anthony F J; Oskinova, L M; Pittard, Julian M; Stassun, Keivan G; ud-Doula, Asif; Walborn, Nolan R; Waldron, Wayne L; Churchwell, Ed; Nichols, J S; Owocki, Stanley P; Schulz, N S

    2011-01-01

    The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant HII regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of >14,000 X-ray point sources; >9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, pr...

  15. Atlantic Ocean CARINA data: overview and salinity adjustments

    Directory of Open Access Journals (Sweden)

    T. Tanhua

    2010-02-01

    Full Text Available Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon dioxide IN the Atlantic Ocean. The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the three data products: merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. the Arctic Mediterranean Seas, the Atlantic and the Southern Ocean. These products have been corrected to be internally consistent. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report the details of the secondary QC (Quality Control for salinity for this data set. Procedures of quality control – including crossover analysis between stations and inversion analysis of all crossover data – are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal consistency of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA data products are consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example

  16. Constrained spheroids for prolonged hepatocyte culture.

    Science.gov (United States)

    Tong, Wen Hao; Fang, Yu; Yan, Jie; Hong, Xin; Hari Singh, Nisha; Wang, Shu Rui; Nugraha, Bramasta; Xia, Lei; Fong, Eliza Li Shan; Iliescu, Ciprian; Yu, Hanry

    2016-02-01

    Liver-specific functions in primary hepatocytes can be maintained over extended duration in vitro using spheroid culture. However, the undesired loss of cells over time is still a major unaddressed problem, which consequently generates large variations in downstream assays such as drug screening. In static culture, the turbulence generated by medium change can cause spheroids to detach from the culture substrate. Under perfusion, the momentum generated by Stokes force similarly results in spheroid detachment. To overcome this problem, we developed a Constrained Spheroids (CS) culture system that immobilizes spheroids between a glass coverslip and an ultra-thin porous Parylene C membrane, both surface-modified with poly(ethylene glycol) and galactose ligands for optimum spheroid formation and maintenance. In this configuration, cell loss was minimized even when perfusion was introduced. When compared to the standard collagen sandwich model, hepatocytes cultured as CS under perfusion exhibited significantly enhanced hepatocyte functions such as urea secretion, and CYP1A1 and CYP3A2 metabolic activity. We propose the use of the CS culture as an improved culture platform to current hepatocyte spheroid-based culture systems.

  17. The CARINA data synthesis project: introduction and overview

    Energy Technology Data Exchange (ETDEWEB)

    Key, Robert [Princeton University; Tanhua, T. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany; Olsen, Are [Bjerknes Centre for Climate Research, UNIFOB AS, Bergen, Norway; Hoppema, M. [Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; Jutterström, S. [University of Gothenburg, Sweden; Schirnick, C. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany; Van Heuven, S. [University of Groningen, The Netherlands; Kozyr, Alexander [ORNL; Lin, X. [Princeton University; Velo, A. [Instituto de Investigaciones Marinas de Vigo, CSIC, Vigo, Spain; Wallace, D.W.R. [IFM-GEOMAR, Leibniz Institute for Marine Sciences, Chemical Oceanography, Kiel, Germany; Mintrop, L. [MARIANDA marine analytics and data, Kiel, Germany

    2010-01-01

    The original goal of the CARINA (Carbon in Atlantic Ocean) data synthesis project was to create a merged calibrated data set from open ocean subsurface measurements by European scientists that would be generally useful for biogeochemical investigations in the North Atlantic and in particular, studies involving the carbon system. Over time the geographic extent expanded to include the entire Atlantic, the Arctic and the Southern Ocean and the international collaboration broadened significantly. In this paper we give a brief history of the project, a general overview of data included and an outline of the procedures used during the synthesis. The end result of this project was a set of 3 data products, one for each of the listed ocean regions. It is critical that anyone who uses any of the CARINA data products recognize that the data products are not simply concatenations of the originally measured values. Rather, the data have been through an extensive calibration procedure designed to remove measurement bias and bad data. Also a significant fraction of the individual values in the data products were derived either by direct calculation or some means of approximation. These data products were constructed for basin scale biogeochemical investigations and may be inappropriate for investigations involving small areal extent or similar detailed analysis. More information on specific parts of this project can be found in companion articles in this issue. In particular, Tanhua et al. (2010) and Tanhua (2009) describe the procedures and software used to remove measurement bias from the original data. The three data products and a significant volume of supporting information are available from the CARINA web site hosted by the Carbon Dioxide Information Analysis Center (CDIAC: http://cdiac.esd.ornl.gov/oceans/CARINA/Carina inv.html). Anyone wanting to use the data is advised to get the highest version number of each data product. Incremental versions represent either

  18. Bistable flows in precessing spheroids

    CERN Document Server

    Cébron, D

    2015-01-01

    Precession driven flows are found in any rotating container filled with liquid, when the rotation axis itself rotates about a secondary axis that is fixed in an inertial frame of reference. Because of its relevance for planetary fluid layers, many works consider spheroidal containers, where the uniform vorticity component of the bulk flow is reliably given by the well-known equations obtained by Busse in 1968. So far however, no analytical result on the solutions is available. Moreover, the cases where multiple flows can coexist have not been investigated in details since their discovery by Noir et al. (2003). In this work, we aim at deriving analytical results on the solutions, aiming in particular at, first estimating the ranges of parameters where multiple solutions exist, and second studying quantitatively their stability. Using the models recently proposed by Noir \\& C{\\'e}bron (2013), which are more generic in the inviscid limit than the equations of Busse, we analytically describe these solutions, ...

  19. Magnetic-directed patterning of cell spheroids.

    Science.gov (United States)

    Whatley, Benjamin R; Li, Xiaowei; Zhang, Ning; Wen, Xuejun

    2014-05-01

    We have described an approach to fabricate three-dimensional (3D) cell-based structures using functionalized super paramagnetic iron oxide nanoparticles (SPIONs) as patterning agents to guide the assembly of endothelial cell spheroids into 3D patterns using the magnetic forces generated by a prefabricated magnetic template. SPIONs were first uptaken by endothelial cells before they were assembled into uniform-sized spheroids through a home-made robotic spheroid maker. To guide the magnetic spheroids, a unique magnetic template was fabricated using computer-aided design and cut from a magnetic sheet. The spheroids were then guided to the prefabricated magnetic template through the attractive magnetic forces between the SPIONs inside the endothelial cells and the magnetic template. Fusion of endothelial cell spheroids over time while adhered to the magnetic template allowed for the formation of 3D cell-based structures. Subsequent removal of the prefabricated magnetic template left 3-D endothelial cell sheets, which may be stacked to fabricate complicated 3D multicellular tissue structures. To enhance the cytocompatibility, SPIONs were silica-coated before use. At low concentrations, the SPIONs did not adversely affect cell viability, proliferation, and phenotype stability. Light and confocal microscopy showed that endothelial cell spheroids could be reproducibly created with high uniformity. The endothelial cells were able to remain viable and maintain the 3D structure in vitro. We have proved the concept to use SPIONs as a patterning agent to direct the attachment and self assembly of SPION-loaded endothelial cell spheroids on a prefabricated magnetic template for the formation of 3D cell based structures. A magnetic-directed technique allows quick patterning of cell spheroids in accordance with desirable magnetic patterns, therefore, holding promise for scalable fabrication of complicated 3D multicellular tissue structures. By varying the cell types and the

  20. H.E.S.S. observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae

    CERN Document Server

    Abramowski, A; Aharonian, F; Akhperjanian, A G; Anton, G; Balzer, A; Barnacka, A; Becherini, Y; Becker, J; Bernlöhr, K; Birsin, E; Biteau, J; Bochow, A; Boisson, C; Bolmont, J; Bordas, P; Brucker, J; Brun, F; Brun, P; Bulik, T; Büsching, I; Carrigan, S; Casanova, S; Cerruti, M; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Cologna, G; Conrad, J; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubus, G; Dutson, K; Dyks, J; Dyrda, M; Egberts, K; Eger, P; Espigat, P; Fallon, L; Fegan, S; Feinstein, F; Fernandes, M V; Fiasson, A; Fontaine, G; Förster, A; Füßling, M; Gallant, Y A; Garrigoux, T; Gast, H; Gèrard, L; Giebels, B; Glicenstein, J F; Glück, B; Göring, D; Grondin, M -H; Häffner, S; Hague, J D; Hahn, J; Hampf, D; Harris, J; Hauser, M; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hillert, A; Hinton, J A; Hofmann, W; Hofverberg, P; Holler, M; Horns, D; Jacholkowska, A; Jahn, C; Jamrozy, M; Jung, I; Kastendieck, M A; Katarzyński, K; Katz, U; Kaufmann, S; Khélifi, B; Klochkov, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Kossakowski, R; Krayzel, F; Laffon, H; Lamanna, G; Lenain, J -P; Lennarz, D; Lohse, T; Lopatin, A; Lu, C -C; Marandon, V; Marcowith, A; Masbou, J; Maurin, G; Maxted, N; Mayer, M; McComb, T J L; Medina, M C; Méhault, J; Moderski, R; Mohamed, M; Moulin, E; Naumann, C L; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nguyen, N; Nicholas, B; Niemiec, J; Nolan, S J; Ohm, S; Wilhelmi, E de Oña; Opitz, B; Ostrowski, M; Oya, I; Panter, M; Arribas, M Paz; Pekeur, N W; Pelletier, G; Perez, J; Petrucci, P -O; Peyaud, B; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raue, M; Reimer, A; Reimer, O; Renaud, M; Reyes, R de los; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Sahakian, V; Sanchez, D A; Santangelo, A; Schlickeiser, R; Schulz, A; Schwanke, U; Schwarzburg, S; Schwemmer, S; Sheidaei, F; Skilton, J L; Sol, H; Spengler, G; Stawarz, Ł; Steenkamp, R; Stegmann, C; Stinzing, F; Stycz, K; Sushch, I; Szostek, A; Tavernet, J -P; Terrier, R; Tluczykont, M; Valerius, K; van Eldik, C; Vasileiadis, G; Venter, C; Viana, A; Vincent, P; Völk, H J; Volpe, F; Vorobiov, S; Vorster, M; Wagner, S J; Ward, M; White, R; Wierzcholska, A; Zacharias, M; Zajczyk, A; Zdziarski, A A; Zech, A; Zechlin, H -S; Montmerle, T

    2012-01-01

    The massive binary system Eta Carinae and the surrounding HII complex, the Carina Nebula, are potential particle acceleration sites from which very-high-energy (VHE; E > 100 GeV) \\gamma-ray emission could be expected. This paper presents data collected during VHE \\gamma-ray observations with the H.E.S.S. telescope array from 2004 to 2010, which cover a full orbit of Eta Carinae. In the 33.1-hour data set no hint of significant \\gamma-ray emission from Eta Carinae has been found and an upper limit on the \\gamma-ray flux of 7.7 x 10-13 ph cm-2 s-1 (99% confidence level) is derived above the energy threshold of 470 GeV. Together with the detection of high-energy (HE; 0.1 GeV > E > 100 GeV) \\gamma-ray emission by the Fermi-LAT up to 100 GeV, and assuming a continuation of the average HE spectral index into the VHE domain, these results imply a cut-off in the \\gamma-ray spectrum between the HE and VHE \\gamma-ray range. This could be caused either by a cut-off in the accelerated particle distribution or by severe \\...

  1. Dark Matter Cores in the Fornax and Sculptor Dwarf Galaxies

    DEFF Research Database (Denmark)

    C. Amorisco, Nicola; Zavala Franco, Jesus; J. L. de Boer, Thomas

    2014-01-01

    We combine the detailed Star Formation Histories of the Fornax and Sculptor dwarf Spheroidals with the mass assembly history of their dark matter halo progenitors to estimate if the energy deposited by Supernova type II (SNeII) is sufficient to create a substantial dark matter core. Assuming...... the efficiency of energy injection of the SNeII into dark matter particles is \\epsilon=0.05, we find that a single early episode, z...

  2. How chameleons core dwarfs with cusps

    CERN Document Server

    Lombriser, Lucas

    2014-01-01

    The presence of a scalar field that couples nonminimally and universally to matter can enhance gravitational forces on cosmological scales while restoring general relativity in the Solar neighborhood. In the intermediate regime, kinematically inferred masses experience an additional radial dependence with respect to the underlying distribution of matter, which is caused by the increment of gravitational forces with increasing distance from the Milky Way center. The same effect can influence the internal kinematics of subhalos and cause cuspy matter distributions to appear core-like. Specializing to the chameleon model as a worked example, we demonstrate this effect by tracing the scalar field from the outskirts of the Milky Way halo to its interior, simultaneously fitting observed velocity dispersions of chemo-dynamically discriminated red giant populations in the Fornax and Sculptor dwarf spheroidals. Whereas in standard gravity these observations suggest that the matter distribution of the dwarfs is cored, ...

  3. Multi-Wavelength Implications of the Companion Star in eta Carinae

    Science.gov (United States)

    Madura, Thomas I.; Gull, Theodore R.; Groh, Jose H.; Owocki, Stanley P.; Okazaki, Atsuo; Hillier, D. John; Russell, Christopher

    2012-01-01

    Eta-Carinae is considered to be a massive colliding wind binary system with a highly eccentric (e approximately 0.9), 5.54-yr orbit. However, the companion star continues to evade direct detection as the primary dwarfs its emission at most wavelengths. Using three-dimensional (3-D) SPH simulations of eta-Car's colliding winds and radiative transfer codes, we are able to compute synthetic observables across multiple wavebands for comparison to the observations. The models show that the presence of a companion star has a profound influence on the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the ground-based photometric monitoring. Here, we focus on the Bore Hole effect, wherein the fast wind from the hot secondary star carves a cavity in the dense primary wind, allowing increased escape of radiation from the hotter/deeper layers of the primary's extended wind photosphere. The results have important implications for interpretations of eta-Car's observables at multiple wavelengths.

  4. Multi-Wavelength Implications of the Companion Star in Eta Carinae

    CERN Document Server

    Madura, Thomas I; Groh, Jose H; Owocki, Stanley P; Okazaki, Atsuo; Hillier, D John; Russell, Christopher

    2011-01-01

    Eta Carinae is considered to be a massive colliding wind binary system with a highly eccentric (e \\sim 0.9), 5.54-yr orbit. However, the companion star continues to evade direct detection as the primary dwarfs its emission at most wavelengths. Using three-dimensional (3-D) SPH simulations of Eta Car's colliding winds and radiative transfer codes, we are able to compute synthetic observables across multiple wavebands for comparison to the observations. The models show that the presence of a companion star has a profound influence on the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the ground-based photometric monitoring. Here, we focus on the Bore Hole effect, wherein the fast wind from the hot secondary star carves a cavity in the dense primary wind, allowing increased escape of radiation from the hotter/deeper layers of the primary's extended wind photosphere. The results have important implications for interpretations of Eta Car's observables at multiple wavelengths.

  5. Indirect Dark Matter Detection for Flattened Dwarf Galaxies

    CERN Document Server

    Sanders, Jason L; Geringer-Sameth, Alex; Dehnen, Walter

    2016-01-01

    We analyze the effects of flattening on the annihilation (J) and decay (D) factors of dwarf spheroidal galaxies with both analytic and numerical methods. Flattening has two consequences: first, there is a geometric effect as the squeezing (or stretching) of the dark matter distribution enhances (or diminishes) the J-factor; second, the line of sight velocity dispersion of stars must hold up the flattened baryonic component in the flattened dark matter halo. We provide analytic formulae and a simple numerical approach to estimate the correction to the J- and D-factors required over simple spherical modeling. The formulae are validated with a series of equilibrium models of flattened stellar distributions embedded in flattened dark-matter distributions. We compute corrections to the J- and D-factors for the Milky Way dwarf spheroidal galaxies under the assumption that they are prolate or oblate and find that the hierarchy of J-factors for the dwarf spheroidals is slightly altered. We demonstrate that spherical ...

  6. Conjunctival spheroid degeneration. Recurrence after excision.

    Science.gov (United States)

    Norn, M S

    1982-06-01

    After excision of part of the conjunctiva in 15 eyes (14 subjects) due to spheroid degeneration, the author noticed only fairly small, varying numbers of autofluorescent and colourless spheroids-after an observation period of 18 months, only 6% of autofluorescent and 13% of colourless bodies were observed compared to the number before biopsy. Around the biopsy site only a few spheroids were seen, with a non-significant tendency to increase in number of the colourless bodies. In the cornea the band-shaped keratopathy had aggravated, with the formation of a small number of large, autofluorescent spheroids. A pinguecula recurred in a mild degree only in 3 out of 13 cases within 18 months.

  7. On the formation of dwarf galaxies and stellar haloes

    Science.gov (United States)

    Read, J. I.; Pontzen, A. P.; Viel, M.

    2006-09-01

    Using analytic arguments and a suite of very high resolution (~103Msolar per particle) cosmological hydrodynamical simulations, we argue that high-redshift, z ~ 10, M ~ 108Msolar haloes, form the smallest `baryonic building block' (BBB) for galaxy formation. These haloes are just massive enough to efficiently form stars through atomic line cooling and to hold on to their gas in the presence of supernova (SN) winds and reionization. These combined effects, in particular that of the SN feedback, create a sharp transition: over the mass range 3-10 × 107Msolar, the BBBs drop two orders of magnitude in stellar mass. Below ~2 × 107Msolar, galaxies will be dark with almost no stars and no gas. Above this scale is the smallest unit of galaxy formation: the BBB. We show that the BBBs have stellar distributions which are spheroidal, of low rotational velocity, old and metal poor: they resemble the dwarf spheroidal galaxies (dSphs) of the Local Group (LG). Unlike the LG dSphs, however, they contain significant gas fractions. We connect these high-redshift BBBs to the smallest dwarf galaxies observed at z = 0 using linear theory. A small fraction (~100) of these gas-rich BBBs at high redshift fall in to a galaxy the size of the Milky Way (MW). We suggest that 10 per cent of these survive to become the observed LG dwarf galaxies at the present epoch. This is consistent with recent numerical estimates. Those infalling haloes on benign orbits which keep them far away from the MW or Andromeda manage to retain their gas and slowly form stars - these become the smallest dwarf irregular galaxies; those on more severe orbits lose their gas faster than they can form stars and become the dwarf spheroidals. The remaining 90 per cent of the BBBs will be accreted. We show that this gives a metallicity and total stellar mass consistent with the MW old stellar halo.

  8. Equilibrium figures of dwarf planets

    Science.gov (United States)

    Rambaux, Nicolas; Chambat, Frederic; Castillo-Rogez, Julie; Baguet, Daniel

    2016-10-01

    Dwarf planets including transneptunian objects (TNO) and Ceres are >500 km large and display a spheroidal shape. These protoplanets are left over from the formation of the solar System about 4.6 billion years ago and their study could improve our knowledge of the early solar system. They could be formed in-situ or migrated to their current positions as a consequence of large-scale solar system dynamical evolution. Quantifying their internal composition would bring constraints on their accretion environment and migration history. That information may be inferred from studying their global shapes from stellar occultations or thermal infrared imaging. Here we model the equilibrium shapes of isolated dwarf planets under the assumption of hydrostatic equilibrium that forms the basis for interpreting shape data in terms of interior structure. Deviations from hydrostaticity can shed light on the thermal and geophysical history of the bodies. The dwarf planets are generally fast rotators spinning in few hours, so their shape modeling requires numerically integration with Clairaut's equations of rotational equilibrium expanded up to third order in a small parameter m, the geodetic parameter, to reach an accuracy better than a few kilometers depending on the spin velocity and mean density. We also show that the difference between a 500-km radius homogeneous model described by a MacLaurin ellipsoid and a stratified model assuming silicate and ice layers can reach several kilometers in the long and short axes, which could be measurable. This type of modeling will be instrumental in assessing hydrostaticity and thus detecting large non-hydrostatic contributions in the observed shapes.

  9. Abundances as Tracers of the Formation and Evolution of (Dwarf) Galaxies

    CERN Document Server

    Tolstoy, E

    2004-01-01

    This aims to be an overview of what detailed observations of individual stars in nearby dwarf galaxies may teach us about galaxy evolution. This includes some early results from the DART (Dwarf Abundances and Radial velocity Team) Large Programme at ESO. This project has used 2.2m/WFI and VLT/FLAMES to obtain spectra of large samples of individual stars in nearby dwarf spheroidal galaxies and determine accurate abundances and kinematics. These results can be used to trace the formation and evolution of nearby galaxies from the earliest times to the present.

  10. Formation of Isolated Dwarf Galaxies with Feedback

    CERN Document Server

    Sawala, Till; White, Simon D M

    2009-01-01

    We present results of high resolution hydrodynamical simulations of the formation and evolution of dwarf spheroidal galaxies. Our simulations start from cosmological initial conditions at high redshift. They include metal-dependent cooling, star formation, feedback from type II and type Ia supernovae and UV background radiation, with sub-grid recipes identical to those applied in a previous study of Milky Way type galaxies. We find that a combination of feedback and the cosmic UV background is necessary to explain the properties of dwarf spheroidal galaxies in isolation, and that their effect is strongly moderated by the depth of the gravitational potential. Taking this into account, our models naturally reproduce the observed luminosities and metallicities. The final objects have halo masses between 2.3*10^8 and 1.1*10^9 solar masses, mean velocity dispersions between 6.5 and 9.7 kms^-1, stellar masses ranging from 5*10^5 to 1.2*10^7 solar masses, median metallicities between [Fe/H] = -1.8 and -1.1, and half...

  11. Naming Disney's Dwarfs.

    Science.gov (United States)

    Sidwell, Robert T.

    1980-01-01

    Discusses Disney's version of the folkloric dwarfs in his production of "Snow White" and weighs the Disney rendition of the dwarf figure against the corpus of traits and behaviors pertaining to dwarfs in traditional folklore. Concludes that Disney's dwarfs are "anthropologically true." (HOD)

  12. Volumetric Image Guidance Using Carina vs Spine as Registration Landmarks for Conventionally Fractionated Lung Radiotherapy

    Energy Technology Data Exchange (ETDEWEB)

    Lavoie, Caroline; Higgins, Jane; Bissonnette, Jean-Pierre [Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, M5G 2M9 (Canada); Le, Lisa W. [Department of Biostatistics, Princess Margaret Hospital, Toronto, Ontario, M5G 2M9 (Canada); Sun, Alexander; Brade, Anthony; Hope, Andrew; Cho, John [Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, M5G 2M9 (Canada); Bezjak, Andrea, E-mail: andrea.bezjak@rmp.uhn.on.ca [Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, Ontario, M5G 2M9 (Canada)

    2012-12-01

    Purpose: To compare the relative accuracy of 2 image guided radiation therapy methods using carina vs spine as landmarks and then to identify which landmark is superior relative to tumor coverage. Methods and Materials: For 98 lung patients, 2596 daily image-guidance cone-beam computed tomography scans were analyzed. Tattoos were used for initial patient alignment; then, spine and carina registrations were performed independently. A separate analysis assessed the adequacy of gross tumor volume, internal target volume, and planning target volume coverage on cone-beam computed tomography using the initial, middle, and final fractions of radiation therapy. Coverage was recorded for primary tumor (T), nodes (N), and combined target (T+N). Three scenarios were compared: tattoos alignment, spine registration, and carina registration. Results: Spine and carina registrations identified setup errors {>=}5 mm in 35% and 46% of fractions, respectively. The mean vector difference between spine and carina matching had a magnitude of 3.3 mm. Spine and carina improved combined target coverage, compared with tattoos, in 50% and 34% (spine) to 54% and 46% (carina) of the first and final fractions, respectively. Carina matching showed greater combined target coverage in 17% and 23% of fractions for the first and final fractions, respectively; with spine matching, this was only observed in 4% (first) and 6% (final) of fractions. Carina matching provided superior nodes coverage at the end of radiation compared with spine matching (P=.0006), without compromising primary tumor coverage. Conclusion: Frequent patient setup errors occur in locally advanced lung cancer patients. Spine and carina registrations improved combined target coverage throughout the treatment course, but carina matching provided superior combined target coverage.

  13. Submillimeter and Far-Infrared Observations of the Carina Nebula

    Science.gov (United States)

    Oberst, Thomas E.; Parshley, S. C.; Nikola, T.; Stacey, G. J.; Loehr, A.; Lane, A. P.; Stark, A. A.; Kamenetzky, J.

    2011-05-01

    We present the results of a 250 arcmin2 mapping of the 205 μm [NII] fine-structure emission over the northern Carina Nebula, including the Car I and Car II HII regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at South Pole. We supplement the 205 μm data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) in 63 μm [OI], 122 μm [NII], 146 μm [OI], and 158 μm [CII]. Morphological comparisons are made with optical, radio continuum and CO maps. The 122 [NII] / 205 [NII] line ratio is used to probe the density of the low-ionization gas, and the 158 [C II] / 205 [NII] line ratio is used to probe the fraction of C+ arising from photodissociation regions (PDRs). From the [OI] and [CII] data, we construct a PDR model of Carina following Kaufman et al. (1999). When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than Galactic star-forming regions such as the Orion Bar, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ever ground-based detection of the 205 μm [NII] line, and only the third detection overall since those of the COBE FIRAS and the KAO in the early 1990s.

  14. Overview of the Nordic Seas CARINA data and salinity measurements

    Directory of Open Access Journals (Sweden)

    R. M. Key

    2009-07-01

    Full Text Available Water column data of carbon and carbon relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruises in the Arctic, Atlantic, and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic. The data have been subject to rigorous quality control (QC in order to ensure highest possible quality and consistency. The data for most of the parameters included were examined in order to quantify systematic biases in the reported values, i.e. secondary quality control. Significant biases have been corrected for in the data products, i.e. the three merged files with measured, calculated and interpolated values for each of the three CARINA regions; the Arctic Mediterranean Seas (AMS, the Atlantic (ATL and the Southern Ocean (SO. With the adjustments the CARINA database is consistent both internally as well as with GLODAP (Key et al., 2004 and is suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation. The Arctic Mediterranean Seas includes the Arctic Ocean and the Nordic Seas, and the quality control was carried out separately in these two areas. This contribution provides an overview of the CARINA data from the Nordic Seas and summarises the findings of the QC of the salinity data. One cruise had salinity data that were of questionable quality, and these have been removed from the data product. An evaluation of the consistency of the quality controlled salinity data suggests that they are consistent to at least 0.05.

  15. Overview of the Nordic Seas CARINA data and salinity measurements

    Directory of Open Access Journals (Sweden)

    A. Olsen

    2009-11-01

    Full Text Available Water column data of carbon and carbon relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruises in the Arctic, Atlantic, and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic. The data have been subject to rigorous quality control (QC in order to ensure highest possible quality and consistency. The data for most of the parameters included were examined in order to quantify systematic biases in the reported values, i.e. secondary quality control. Significant biases have been corrected for in the data products, i.e. the three merged files with measured, calculated and interpolated values for each of the three CARINA regions; the Arctic Mediterranean Seas (AMS, the Atlantic (ATL and the Southern Ocean (SO. With the adjustments the CARINA database is consistent both internally as well as with GLODAP (Key et al., 2004 and is suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation. The Arctic Mediterranean Seas include the Arctic Ocean and the Nordic Seas, and the quality control was carried out separately in these two areas. This contribution provides an overview of the CARINA data from the Nordic Seas and summarises the findings of the QC of the salinity data. One cruise had salinity data that were of questionable quality, and these have been removed from the data product. An evaluation of the consistency of the quality controlled salinity data suggests that they are consistent to at least ±0.005.

  16. The 1981 mass-loss phase of Eta Carinae

    Science.gov (United States)

    Bidelman, William P.; Galen, Tamara A.; Wallerstein, George

    1993-07-01

    A visual-region coude spectrogram of Eta Carinae taken in 1981 May is described, and the portion of the spectrum containing H-alpha is reproduced. This was taken during one of Eta Car's 'abnormal' stages, which have been suggested by Zanella et al. (1984) to be times of large mass loss from this unique object. The 1981 spectrum is compared with the 'normal' spectrum as observed in 1985.

  17. A multicellular spheroid array to realize spheroid formation, culture, and viability assay on a chip.

    Science.gov (United States)

    Torisawa, Yu-suke; Takagi, Airi; Nashimoto, Yuji; Yasukawa, Tomoyuki; Shiku, Hitoshi; Matsue, Tomokazu

    2007-01-01

    We describe a novel multicellular spheroid culture system that facilitates the easy preparation and culture of a spheroid microarray for the long-term monitoring of cellular activity. A spheroid culture device with an array of pyramid-like microholes was constructed in a silicon chip that was equipped with elastomeric microchannels. A cell suspension was introduced via the microfluidic channel into the microstructure that comprised silicon microholes and elastomeric microwells. A single spheroid can be formed and localized precisely within each microstructure. Since the culture medium could be replaced via the microchannels, a long-term culture (of approximately 2 weeks) is available on the chip. Measurement of albumin production in the hepatoma cell line (HepG2) showed that the liver-specific functions were maintained for 2 weeks. Based on the cellular respiratory activity, the cellular viability of the spheroid array on the chip was evaluated using scanning electrochemical microscopy. Responses to four different chemical stimulations were simultaneously detected on the same chip, thus demonstrating that each channel could be evaluated independently under various stimulation conditions. Our spheroid culture system facilitated the understanding of spheroid formation, culture, and viability assay on a single chip, thus functioning as a useful drug-screening device for cancer and liver cells.

  18. Atmospheres of Brown Dwarfs

    CERN Document Server

    Helling, Christiane

    2014-01-01

    Brown Dwarfs are the coolest class of stellar objects known to date. Our present perception is that Brown Dwarfs follow the principles of star formation, and that Brown Dwarfs share many characteristics with planets. Being the darkest and lowest mass stars known makes Brown Dwarfs also the coolest stars known. This has profound implication for their spectral fingerprints. Brown Dwarfs cover a range of effective temperatures which cause brown dwarfs atmospheres to be a sequence that gradually changes from a M-dwarf-like spectrum into a planet-like spectrum. This further implies that below an effective temperature of < 2800K, clouds form already in atmospheres of objects marking the boundary between M-Dwarfs and brown dwarfs. Recent developments have sparked the interest in plasma processes in such very cool atmospheres: sporadic and quiescent radio emission has been observed in combination with decaying Xray-activity indicators across the fully convective boundary.

  19. Bars and spheroids in gravimetry problem

    CERN Document Server

    Sizikov, Valery

    2016-01-01

    The direct gravimetry problem is solved by dividing each deposit body into a set of vertical adjoining bars, whereas in the inverse problem, each deposit body is modelled by a homogeneous ellipsoid of revolution (spheroid). Well-known formulae for the z-component of gravitational intensity for a spheroid are transformed to a convenient form. Parameters of a spheroid are determined by minimizing the Tikhonov smoothing functional with constraints on the parameters, which makes the ill-posed inverse problem by unique and stable. The Bulakh algorithm for initial estimating the depth and mass of a deposit is modified. The proposed technique is illustrated by numerical model examples of deposits in the form of two and five bodies. The inverse gravimetry problem is interpreted as a gravitational tomography problem or, in other words, as "introscopy" of Earth's crust and mantle.

  20. Use of spheroidal models in gravitational tomography

    CERN Document Server

    Sizikov, Valery

    2015-01-01

    The direct gravimetry problem is solved using the subdivision of each body of a deposit into a set of vertical adjoining bars, and in the inverse problem each body of a deposit is modeled by a uniform ellipsoid of revolution (spheroid). Well-known formulas for z-component of gravitational intensity of a spheroid are transformed to a convenient form. Parameters of a spheroid are determined by minimizing the Tikhonov smoothing functional using constraints on the parameters. This makes the ill-posed inverse problem by unique and stable. The Bulakh algorithm for initial estimating the depth and mass of a deposit is modified. The technique is illustrated by numerical model examples of deposits in the form of two and five bodies. The inverse gravimetry problem is interpreted as a gravitational tomography problem or the intravision of the Earth's crust and mantle.

  1. Charged fluid distribution in higher dimensional spheroidal space-time

    Indian Academy of Sciences (India)

    G P Singh; S Kotambkar

    2005-07-01

    A general solution of Einstein field equations corresponding to a charged fluid distribution on the background of higher dimensional spheroidal space-time is obtained. The solution generates several known solutions for superdense star having spheroidal space-time geometry.

  2. The Mass Dependence of Dwarf Satellite Galaxy Quenching

    CERN Document Server

    Slater, Colin T

    2014-01-01

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic clouds. While almost all of the low mass ($M_\\star \\lesssim 10^7$ $M_\\odot$) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40-50%. This change in the quenched fraction is large, and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell in to their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to acco...

  3. Stress Clamp Experiments on Multicellular Tumor Spheroids

    CERN Document Server

    Montel, Fabien; Elgeti, Jens; Malaquin, Laurent; Basan, Markus; Risler, Thomas; Cabane, Bernard; Vignjevic, Danijela; Prost, Jacques; Cappello, Giovanni; Joanny, Jean-François; 10.1103/PhysRevLett.107.188102

    2011-01-01

    The precise role of the microenvironment on tumor growth is poorly understood. Whereas the tumor is in constant competition with the surrounding tissue, little is known about the mechanics of this interaction. Using a novel experimental procedure, we study quantitatively the effect of an applied mechanical stress on the long-term growth of a spheroid cell aggregate. We observe that a stress of 10 kPa is sufficient to drastically reduce growth by inhibition of cell proliferation mainly in the core of the spheroid. We compare the results to a simple numerical model developed to describe the role of mechanics in cancer progression.

  4. Photometric properties of Local Volume dwarf galaxies

    CERN Document Server

    Sharina, M E; Dolphin, A E; Karachentseva, V E; Tully, R Brent; Karataeva, G M; Makarov, D I; Makarova, L N; Sakai, S; Shaya, E J; Nikolaev, E Yu; Kuznetsov, A N

    2007-01-01

    We present surface photometry and metallicity measurements for 104 nearby dwarf galaxies imaged with the Advanced Camera for Surveys and Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. In addition, we carried out photometry for 26 galaxies of the sample and for Sextans~B on images of the Sloan Digital Sky Survey. Our sample comprises dwarf spheroidal, irregular and transition type galaxies located within ~10 Mpc in the field and in nearby groups: M81, Centaurus A, Sculptor, and Canes Venatici I cloud. It is found that the early-type galaxies have on average higher metallicity at a given luminosity in comparison to the late-type objects. Dwarf galaxies with M_B > -12 -- -13 mag deviate toward larger scale lengths from the scale length -- luminosity relation common for spiral galaxies, h \\propto L^{0.5}_B. The following correlations between fundamental parameters of the galaxies are consistent with expectations if there is pronounced gas-loss through galactic winds: 1) between the luminosit...

  5. THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?

    Energy Technology Data Exchange (ETDEWEB)

    Gallart, Carme; Monelli, Matteo; Aparicio, Antonio; Battaglia, Giuseppina; Drozdovsky, Igor; Hidalgo, Sebastian L. [Instituto de Astrofísica de Canarias, La Laguna, Tenerife (Spain); Mayer, Lucio [Institut für Theoretische Physik, University of Zurich, Zürich (Switzerland); Bernard, Edouard J. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Cassisi, Santi [INAF-Osservatorio Astronomico di Collurania, Teramo (Italy); Cole, Andrew A. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, TAS 7005 (Australia); Dolphin, Andrew E. [Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States); Navarro, Julio F. [Department of Physics and Astronomy, University of Victoria, PO Box 1700, STN CSC, Victoria, BC V8W 3P6 (Canada); Salvadori, Stefania [Kapteyn Astronomical Institute, Landleven 12, NL-9747 AD Groningen (Netherlands); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN (United States); Stetson, Peter B. [Herzberg Astronomy and Astrophysics, National Research Council Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Weisz, Daniel R., E-mail: monelli@iac.es [Astronomy Department, University of Washington, Box 351580, Seattle, WA (United States)

    2015-10-01

    We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.

  6. Fractal Model of the Spheroidal Graphite

    Institute of Scientific and Technical Information of China (English)

    Z.Y.HE; K.Z.HWANG

    1996-01-01

    In this paper,a fractal model about the microstructure of spheroidal-graphite is presented through the research on the surface form and the analysis to microregion.The fractal dimension is calculated and the forming mechanism is also discussed.

  7. Convection in Slab and Spheroidal Geometries

    Science.gov (United States)

    Porter, David H.; Woodward, Paul R.; Jacobs, Michael L.

    2000-01-01

    Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.

  8. Zero-point energy in spheroidal geometries

    OpenAIRE

    Kitson, A. R.; Signal, A. I.

    2005-01-01

    We study the zero-point energy of a massless scalar field subject to spheroidal boundary conditions. Using the zeta-function method, the zero-point energy is evaluated for small ellipticity. Axially symmetric vector fields are also considered. The results are interpreted within the context of QCD flux tubes and the MIT bag model.

  9. Theoretical lower limits on sizes of ultrafaint dwarf galaxies from dynamical friction

    Science.gov (United States)

    Hernandez, X.

    2016-11-01

    Dwarf spheroidal galaxies (dSphs) are the smallest known stellar systems where under Newtonian interpretations, a significant amount of dark matter is required to explain observed kinematics. In fact, they are, in this sense, the most heavily dark matter-dominated objects known. That, plus the increasingly small sizes of the newly discovered ultrafaint dwarfs, puts these systems in the regime where dynamical friction on individual stars starts to become relevant. We calculate the dynamical friction time-scales for pressure-supported isotropic spherical dark matter-dominated stellar systems, yielding τDF = 0.93(rh/10 pc)2(σ/km s-1) Gyr, where rh is the half-light radius. For a stellar velocity dispersion value of 3 km s-1, as typical for the smallest of the recently detected ultrafaint dwarf spheroidals, dynamical friction time-scales become smaller than the 10 Gyr typical of the stellar ages for these systems, for rh present a comparison with structural parameters of the smallest ultrafaint dwarf spheroidals known, showing that these are already close to the stability limit derived, any future detection of yet smaller such systems would be inconsistent with a particle dark matter hypothesis.

  10. Modelling the Radio Light Curve of Eta Carinae

    OpenAIRE

    Kashi, Amit; Soker, Noam

    2007-01-01

    We study the propagation of the ionizing radiation emitted by the secondary star in Eta Carinae. We find that a large fraction of this radiation is absorbed by the primary stellar wind, mainly after it encounters the secondary wind and passes through a shock wave. The amount of absorption depends on the compression factor of the primary wind in the shock wave. We build a model where the compression factor is limited by the magnetic pressure in the primary wind. We find that the variation of t...

  11. METALLICITY DISTRIBUTION FUNCTIONS OF FOUR LOCAL GROUP DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Ross, Teresa L.; Holtzman, Jon [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Saha, Abhijit [NOAO, 950 Cherry Avenue, Tucson, AZ 85726-6732 (United States); Anthony-Twarog, Barbara J., E-mail: rosst@nmsu.edu, E-mail: holtz@nmsu.edu, E-mail: bjat@ku.edu [Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045-7582 (United States)

    2015-06-15

    We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color–color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color–color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%–50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.

  12. Nordic Seas and Arctic Ocean CFC data in CARINA

    Directory of Open Access Journals (Sweden)

    E. Jeansson

    2009-10-01

    Full Text Available Water column data of carbon and carbon relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruises in the Arctic, Atlantic, and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic. The data have been subject to rigorous quality control (QC in order to ensure highest possible quality and consistency. The data for most of the parameters included were examined in order to quantify systematic biases in the reported values, i.e. secondary quality control. Significant biases have been corrected for in the data products, i.e. the three merged files with measured, calculated and interpolated values for each of the three CARINA regions; the Arctic Mediterranean Seas (AMS, the Atlantic (ATL and the Southern Ocean (SO. The Arctic Mediterranean Seas is comprised of the Arctic Ocean and the Nordic Seas, and the quality control was carried out separately in these two areas.

    Here we present an overview of the QC of the CFC data for the Arctic Mediterranean Seas, including the chlorofluorocarbons CFC-11, CFC-12 and CFC-113, as well as carbon tetrachloride (CCl4. For the secondary QC of the CFCs we used a combination of tools, including the evaluation of depth profiles and CFC ratios, surface saturations and a crossover analysis. This resulted in a multiplicative adjustment of some cruise data, while some other cruises were flagged with questionable quality, which excluded them from the final data product.

  13. Protoplanetary disks in the hostile environment of Carina

    CERN Document Server

    Mesa-Delgado, A; Henney, W J; Puzia, T H; Tsamis, Y G

    2016-01-01

    We report the first direct imaging of protoplanetary disks in the star-forming region of Carina, the most distant, massive cluster in which disks have been imaged. Using the Atacama Large Millimeter/sub-millimeter Array (ALMA), disks are observed around two young stellar objects (YSOs) that are embedded inside evaporating gaseous globules and exhibit jet activity. The disks have an average size of 120 AU and total masses of 30 and 50 M_Jup. Given the measured masses, the minimum timescale required for planet formation (~1-2 Myr) and the average age of the Carina population (~1-4 Myr), it is plausible that young planets are present or their formation is currently ongoing in these disks. The non-detection of millimeter emission above the 4sigma threshold (~7 M_Jup) in the core of the massive cluster Trumpler~14, an area containing previously identified proplyd candidates, suggest evidence for rapid photo-evaporative disk destruction in the cluster's harsh radiation field. This would prevent the formation of gia...

  14. Spectroscopic and photometric observations of M supergiants in Carina.

    Science.gov (United States)

    Humphreys, R. M.; Strecker, D. W.; Ney, E. P.

    1972-01-01

    Spectroscopic study of 30 Southern-Hemisphere M supergiants mostly in Carina in the blue and near-infrared, and photometrical study of these stars from 0.4 to 18 microns. The uncertainties in the determinations of interstellar extinction are discussed, and the spatial distribution of the M supergiants in the Carina arm is shown. The presence of the 11-micron excess attributed to silicate dust is a common feature. Stars of the same spectral type and luminosity class are remarkably homogeneous in their long-wave behavior. The silicate feature becomes more prominent in the more luminous stars and in stars of later spectral type. Four composite systems show little long-wave excess. The two VV Cephei objects have excesses probably produced by gas emission, and the other two have little or no excess - supporting the suggestion that the presence of the early star prohibits the formation of a dust envelope. Three stars - VY CMa, VX Sgr, and HD 9767 - appear to be extreme examples of stars with large excesses over the entire long-wave region. It is suggested that these objects are surrounded by large amounts of particulate material over a great range of distances from the stars.

  15. Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo

    CERN Document Server

    Geisler, Doug; Smith, Verne V; Casetti-Dinescu, Dana I

    2007-01-01

    We review Galactic halo formation theories and supporting evidence, in particular kinematics and detailed chemical abundances of stars in some relevant globular clusters as well as Local Group dwarf galaxies. Outer halo red HB clusters tend to have large eccentricities and inhabit the area populated by dwarf spheroidal stars, favoring an extraGalactic origin. Old globulars show the full range of eccentricities, while younger ones seem to have preferentially high eccentricities, again hinting at their extraGalactic origin. We compare detailed abundances of a variety of elements between the halo and all dwarf galaxies studied to date, including both dwarf spheroidals and irregulars. The salient feature is that halo abundances are essentially unique. In particular, the general alpha vs. [Fe/H] pattern of 12 of the 13 galaxies studied are similar to each other and very different from the Milky Way. Sagittarius appears to be the only possible exception. It appears very unlikely that a significant fraction of the m...

  16. Construction and compression of Dwarf

    Institute of Scientific and Technical Information of China (English)

    XIANG Long-gang; FENG Yu-cai; GUI Hao

    2005-01-01

    There exists an inherent difficulty in the original algorithm for the construction of Dwarf, which prevents it from constructing true Dwarfs. We explained when and why it introduces suffix redundancies into the Dwarf structure. To solve this problem, we proposed a completely new algorithm called PID. It bottom-up computes partitions of a fact table, and inserts them into the Dwarf structure. Ifa partition is an MSV partition, coalesce its sub-Dwarf; otherwise create necessary nodes and cells. Our performance study showed that PID is efficient. For further condensing of Dwarf, we proposed Condensed Dwarf, a more compressed structure, combining the strength of Dwarf and Condensed Cube. By eliminating unnecessary stores of "ALL" cells from the Dwarf structure, Condensed Dwarf could effectively reduce the size of Dwarf, especially for Dwarfs of the real world, which was illustrated by our experiments. Its query processing is still simple and, only two minor modifications to PID are required for the construction of Condensed Dwarf.

  17. Predicting the Velocity Dispersions of the Dwarf Satellite Galaxies of Andromeda

    Science.gov (United States)

    McGaugh, Stacy S.

    2016-05-01

    Dwarf Spheroidal galaxies in the Local Group are the faintest and most diffuse stellar systems known. They exhibit large mass discrepancies, making them popular laboratories for studying the missing mass problem. The PANDAS survey of M31 revealed dozens of new examples of such dwarfs. As these systems were discovered, it was possible to use the observed photometric properties to predict their stellar velocity dispersions with the modified gravity theory MOND. These predictions, made in advance of the observations, have since been largely confirmed. A unique feature of MOND is that a structurally identical dwarf will behave differently when it is or is not subject to the external field of a massive host like Andromeda. The role of this "external field effect" is critical in correctly predicting the velocity dispersions of dwarfs that deviate from empirical scaling relations. With continued improvement in the observational data, these systems could provide a test of the strong equivalence principle.

  18. Andromeda XXVIII: A Dwarf Galaxy More Than 350 kpc from Andromeda

    CERN Document Server

    Slater, Colin T; Martin, Nicolas F

    2011-01-01

    We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently-released SDSS DR8. The galaxy is a likely satellite of Andromeda, and, at a separation of $365^{+17}_{-1}$ kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is $650^{+150}_{-80}$ kpc, and analysis of its structure and luminosity show that it has an absolute magnitude of $M_V = -8.5^{+0.4}_{-1.0}$ and half-light radius of $r_h = 210^{+60}_{-50}$ pc, similar to many other faint Local Group dwarfs. With presently-available imaging we are unable to determine if there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or dwarf irregular.

  19. ANDROMEDA XXVIII: A DWARF GALAXY MORE THAN 350 kpc FROM ANDROMEDA

    Energy Technology Data Exchange (ETDEWEB)

    Slater, Colin T.; Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Martin, Nicolas F. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    2011-11-20

    We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently released Sloan Digital Sky Survey Data Release 8. The galaxy is a likely satellite of Andromeda, and, at a separation of 365{sup +17}{sub -1} kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is 650{sup +150}{sub -80} kpc, and analysis of its structure and luminosity shows that it has an absolute magnitude of M{sub V} = -8.5{sup +0.4}{sub -1.0} and half-light radius of r{sub h} = 210{sup +60}{sub -50} pc, similar to many other faint Local Group dwarfs. With presently available imaging we are unable to determine whether there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or a dwarf irregular.

  20. At the heart of the matter: the origin of bulgeless dwarf galaxies and Dark Matter cores

    CERN Document Server

    Governato, Fabio; Mayer, Lucio; Brooks, Alyson; Rhee, George; Wadsley, James; Jonsson, Patrik; Willman, Beth; Stinson, Greg; Quinn, Thomas; Madau, Piero

    2009-01-01

    For almost two decades the properties of "dwarf" galaxies have challenged the Cold Dark Matter (CDM) paradigm of galaxy formation. Most observed dwarf galaxies consists of a rotating stellar disc embedded in a massive DM halo with a near constant-density core. Yet, models based on the CDM scenario invariably form galaxies with dense spheroidal stellar "bulges" and steep central DM profiles, as low angular momentum baryons and DM sink to the center of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different DM particle candidate. This Letter presents new hydrodynamical simulations in a Lambda$CDM framework where analogues of dwarf galaxies, bulgeless and with a shallow central DM profile, are formed. This is achieved by resolving the inhomogeneous interstellar medium, resultin...

  1. Footprints of the early Universe in the SFHs of dwarf galaxies

    Science.gov (United States)

    Hidalgo, S. L.; LCID Group

    We present the star formation histories (SFHs) as a function of galactocentric radius of four isolated dwarf galaxies, Cetus, Tucana, LGS-3, and Phoenix. Our results suggest that beyond some distance from the center, there are no significative differences in fundamental properties of these galaxies. In the innermost regions, dwarf galaxies appear to have formed stars during time intervals which duration varies from galaxy to galaxy. This extended star formation produces the dichotomy between dwarf spheroidal (dSph) and dwarf Transition (dTr) galaxy types. This behavior is compatible with a scenario in which global reionization stops the star formation in the outer galaxy regions and self-shielding allows extended star formation in the inner regions.

  2. Interstellar Extinction by Spheroidal Dust Grains

    OpenAIRE

    Gupta, Ranjan; Mukai, Tadashi; Vaidya, D. B.; Sen, Asoke K.; Okada, Yasuhiko

    2005-01-01

    Observations of interstellar extinction and polarization indicate that the interstellar medium consists of aligned non-spherical dust grains which show variation in the interstellar extinction curve for wavelengths ranging from NIR to UV. To model the extinction and polarization, one cannot use the Mie theory which assumes the grains as solid spheres. We have used a T-matrix based method for computing the extinction efficiencies of spheroidal silicate and graphite grains of different shapes (...

  3. New Classes of Charged Spheroidal Models

    Directory of Open Access Journals (Sweden)

    S. Thirukkanesh

    2013-01-01

    Full Text Available New classes of exact solutions to the Einstein-Maxwell system is found in closed form by assuming that the hypersurface is spheroidal. This is achieved by choosing a particular form for the electric field intensity. A class of solution is found for all positive spheroidal parameter for a specific form of electric field intensity. In general, the condition of pressure isotropy reduces to a difference equation with variable, rational coefficients that can be solved. Consequently, an explicit solution in series form is found. By placing restrictions on the parameters, it is shown that the series terminates and there exist two classes of solutions in terms of elementary functions. These solutions contain the models found previously in the limit of vanishing charge. Solutions found are directly relating the spheroidal parameter and electric field intensity. Masses obtained are consistent with the previously reported experimental and theoretical studies describing strange stars. A physical analysis indicates that these models may be used to describe a charged sphere.

  4. Directly spheroidizing during hot deformation in GCr15 steels

    Institute of Scientific and Technical Information of China (English)

    Guo-hui ZHU; Gang ZHENG

    2008-01-01

    The spheroidizing heat treatment is normally required prior to the cold forming in GCr15 steel in order to improve its machinability. In the conventional spher-oidizing process, very long annealing time, generally more than 10 h, is needed to assure proper spheroidizing. It results in low productivity, high cost, and especially high energy consumption. Therefore, the possibility of directly spheroidizing during hot deformation in GCr15 steel is preliminarily explored. The effect of hot deformation parameters on the final microstructure and hardness is investigated systematically in order to develop a directly spheroidizing technology. Experimental results illustrate that low deformation temperature and slow cooling rate is the favorite in directly softening and/or spheroidizing dur-ing hot deformation, which allows the properties of as-rolled GCr15 to be applicable for post-machining without requirement of prior annealing.

  5. Orbits in Homogeneous Oblate Spheroidal Gravitational Space-Time

    Directory of Open Access Journals (Sweden)

    Chifu E. N.

    2009-07-01

    Full Text Available The generalized Lagrangian in general relativistic homogeneous oblate spheroidal gravitational fields is constructed and used to study orbits exterior to homogenous oblate spheroids. Expressions for the conservation of energy and angular momentum for this gravitational field are obtained. The planetary equation of motion and the equation of motion of a photon in the vicinity of an oblate spheroid are derived. These equations have additional terms not found in Schwarzschild's space time.

  6. Constraints on mass loss of globular clusters in dwarf galaxies

    CERN Document Server

    Larsen, S S; Brodie, J P

    2013-01-01

    The Fornax dwarf spheroidal galaxy is well known for its very high globular cluster specific frequency, SN=26. Furthermore, while the field star metallicity distribution peaks at [Fe/H]=-1, four of the five GCs have [Fe/H]<-2. Only about 5 percent of the field stars have such low metallicities. Hence, a very large fraction of about 1/5-1/4 of the most metal-poor stars belong to the four most metal-poor GCs. This implies that these clusters could, at most, have been a factor of 4-5 more massive initially. A second, even more extreme case may be the IKN dwarf galaxy where SN=124. Although metallicities are not accurately known, the GCs account for about 13 percent of the total V-band luminosity of IKN.

  7. Feedback and the scaling relations of dwarf/LSB galaxies

    CERN Document Server

    Dekel, A; Dekel, Avishai; Woo, Joanna

    2002-01-01

    We study the role of feedback in establishing the scaling relations of low surface brightness (LSB) or dwarf galaxies, as measured from the SDSS and in the Local Group. The galaxies with stellar masses in the broad range 6x10^5 10km/s, possibly due to the cooling barrier at T~10^4 K. We propose that the distinction between dwarf spheroidals (dE) and irregulars (dI) is due to radiative feedback associated with the cosmological reionization at z_ion~6. The dEs, typically of $V30km/s, the incomplete gas removal leads to gas-rich discs in which star formation is regulated by feedback.

  8. The Ejecta of Eta Carinae as Studied by STIS

    Science.gov (United States)

    Gull, Theodore R.; Oegerle, William R. (Technical Monitor)

    2002-01-01

    The Space Telescope Imaging Spectrograph has been used to study the emission and absorption spectra of ejecta surrounding Eta Carinae. Discussion will be presented on the overall structure of the Homunculus, the Weigelt blobs and the Strontium filament. Three visits have been accomplished with the Position Angle precisely the same and covering the Central Source and Weigelt Blobs B and D. Deep spectra have been done at several positions to obtain the overall velocity structure of the Homunculus and the disk region. Mapping has been done with the STIS medium dispersion gratings set near H beta and H alpha. We have obtained full coverage of the strontium filament from 1640 Angstroms to 10300 Angstroms. The structure and physical properties will be described.

  9. Detection of a Hot Binary Companion of $\\eta$ Carinae

    CERN Document Server

    Iping, R C; Gull, T R; Massa, D L; Hillier, D J; Iping, Rosina C.; Sonneborn, George; Gull, Theodore R.; Massa, Derck L.

    2005-01-01

    We report the detection of a hot companion of $\\eta$ Carinae using high resolution spectra (905 - 1180 \\AA) obtained with the Far Ultraviolet Spectroscopic Explorer (\\fuse) satellite. Observations were obtained at two epochs of the 2024-day orbit: 2003 June during ingress to the 2003.5 X-ray eclipse and 2004 April several months after egress. These data show that essentially all the far-UV flux from \\etacar shortward of \\lya disappeared at least two days before the start of the X-ray eclipse (2003 June 29), implying that the hot companion, \\etaB, was also eclipsed by the dense wind or extended atmosphere of \\etaA. Analysis of the far-UV spectrum shows that \\etaB is a luminous hot star. The \

  10. The Purple Haze of Eta Carinae: Binary-Induced Variability?

    CERN Document Server

    Smith, N; Collins, N R; Gull, T R; Smith, Nathan; Morse, Jon A.; Collins, Nicholas R.; Gull, Theodore R.

    2004-01-01

    Asymmetric variability in ultraviolet images of the Homunculus obtained with the Advanced Camera for Surveys/High Resolution Camera on the Hubble Space Telescope suggests that Eta Carinae is indeed a binary system. Images obtained before, during, and after the recent ``spectroscopic event'' in 2003.5 show alternating patterns of bright spots and shadows on opposite sides of the star before and after the event, providing a strong geometric argument for an azimuthally-evolving, asymmetric UV radiation field as one might predict in some binary models. The simplest interpretation of these UV images, where excess UV escapes from the secondary star in the direction away from the primary, places the major axis of the eccentric orbit roughly perpendicular to our line of sight, sharing the same equatorial plane as the Homunculus, and with apastron for the hot secondary star oriented toward the southwest of the primary. However, other orbital orientations may be allowed with more complicated geometries. Selective UV il...

  11. The -145 km/S Absorption System of Eta Carinae

    Science.gov (United States)

    Vieira, G.; Gull, T. R.; Danks, A.; Johansson, S.

    2002-01-01

    With the STIS E230H mode (R-118,000) , we have identified about twenty absorption components in line of sight from Eta Carinae. Two components, one at -513 km/s and another at -145 W s , are quite different in character from the others, mostly at intermediate velocities. The -145 km/s component is significantly wider in fwhm, is seen in many more species, and the lower level can be above 20,000/cm, well above the 2000/cm noted in the -513 km/s component. In the spectral region from 2400 to 3160A, approximately 500 absorption lines have been identified. In this poster, we will present line identifications and atomic parameters of the measured lines, hopefully providing insight as to what levels are being excited and by what processes.

  12. Valence electron theory of graphite spheroidizing in primary crystallization

    Institute of Scientific and Technical Information of China (English)

    刘志林; 孙振国; 李志林

    1995-01-01

    Bond-length-difference (BLD) analysis results show that austenrte and cementite containing Mg, Zr. S have very different valence electron structures from Fe -C austenite and cementite. We find that this difference is the tie of absorption hypothesis, surface tension hypothesis, undercooling hypothesis in graphite spheroidizing theory. By using "the model of valence electron theory of drag-like effect" in our previous paper in crystallization theory, the spheroidizing effect of Mg and Zr and the anti-spheroidizing effect of S can be explained with the valence electron structure data of phases. Therefore, electron theory of graphite spheroidizing can be advanced.

  13. An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10.

    Science.gov (United States)

    Reines, Amy E; Sivakoff, Gregory R; Johnson, Kelsey E; Brogan, Crystal L

    2011-02-03

    Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

  14. Juvenile Ultracool Dwarfs

    CERN Document Server

    Rice, Emily L; Cruz, Kelle; Barman, Travis; Looper, Dagny; Malo, Lison; Mamajek, Eric E; Metchev, Stanimir; Shkolnik, Evgenya L

    2011-01-01

    Juvenile ultracool dwarfs are late spectral type objects (later than ~M6) with ages between 10 Myr and several 100 Myr. Their age-related properties lie intermediate between very low mass objects in nearby star-forming regions (ages 1-5 Myr) and field stars and brown dwarfs that are members of the disk population (ages 1-5 Gyr). Kinematic associations of nearby young stars with ages from ~10-100 Myr provide sources for juvenile ultracool dwarfs. The lowest mass confirmed members of these groups are late-M dwarfs. Several apparently young L dwarfs and a few T dwarfs are known, but they have not been kinematically associated with any groups. Normalizing the field IMF to the high mass population of these groups suggests that more low mass (mainly late-M and possibly L dwarf) members have yet to be found. The lowest mass members of these groups, along with low mass companions to known young stars, provide benchmark objects with which spectroscopic age indicators for juvenile ultracool dwarfs can be calibrated and...

  15. Dwarf-Galaxy Cosmology

    CERN Document Server

    Schulte-Ladbeck, Regina; Brinks, Elias; Kravtsov, Andrey

    2010-01-01

    Dwarf galaxies provide opportunities for drawing inferences about the processes in the early universe by observing our "cosmological backyard"-the Local Group and its vicinity. This special issue of the open-access journal Advances in Astronomy is a snapshot of the current state of the art of dwarf-galaxy cosmology.

  16. Digital microfluidics for automated hanging drop cell spheroid culture.

    Science.gov (United States)

    Aijian, Andrew P; Garrell, Robin L

    2015-06-01

    Cell spheroids are multicellular aggregates, grown in vitro, that mimic the three-dimensional morphology of physiological tissues. Although there are numerous benefits to using spheroids in cell-based assays, the adoption of spheroids in routine biomedical research has been limited, in part, by the tedious workflow associated with spheroid formation and analysis. Here we describe a digital microfluidic platform that has been developed to automate liquid-handling protocols for the formation, maintenance, and analysis of multicellular spheroids in hanging drop culture. We show that droplets of liquid can be added to and extracted from through-holes, or "wells," and fabricated in the bottom plate of a digital microfluidic device, enabling the formation and assaying of hanging drops. Using this digital microfluidic platform, spheroids of mouse mesenchymal stem cells were formed and maintained in situ for 72 h, exhibiting good viability (>90%) and size uniformity (% coefficient of variation screen was performed on human colorectal adenocarcinoma spheroids to demonstrate the ability to recapitulate physiologically relevant phenomena such as insulin-induced drug resistance. With automatable and flexible liquid handling, and a wide range of in situ sample preparation and analysis capabilities, the digital microfluidic platform provides a viable tool for automating cell spheroid culture and analysis.

  17. Attenuation of microwaves by poly-disperse small spheroid particles

    Science.gov (United States)

    Zhang, Peichang; Wang, Zhenhui

    1998-08-01

    Expressions for calculating the attenuation cross sections of poly-disperse, small spheroids, whose rotatory axes are in specific status, have been derived from a universal formula for calculating the attenuation cross section of a particle of arbitrary shape. Attenuation cross sections of liquid, ice, and spongy spheroidal droplets in different size and eccentricity at different wave lengths have been computed and analyzed.

  18. Design of a Uranium Dioxide Spheroidization System

    Science.gov (United States)

    Cavender, Daniel P.; Mireles, Omar R.; Frendi, Abdelkader

    2013-01-01

    The plasma spheroidization system (PSS) is the first process in the development of tungsten-uranium dioxide (W-UO2) fuel cermets. The PSS process improves particle spherocity and surface morphology for coating by chemical vapor deposition (CVD) process. Angular fully dense particles melt in an argon-hydrogen plasma jet at between 32-36 kW, and become spherical due to surface tension. Surrogate CeO2 powder was used in place of UO2 for system and process parameter development. Particles range in size from 100 - 50 microns in diameter. Student s t-test and hypothesis testing of two proportions statistical methods were applied to characterize and compare the spherocity of pre and post process powders. Particle spherocity was determined by irregularity parameter. Processed powders show great than 800% increase in the number of spherical particles over the stock powder with the mean spherocity only mildly improved. It is recommended that powders be processed two-three times in order to reach the desired spherocity, and that process parameters be optimized for a more narrow particles size range. Keywords: spherocity, spheroidization, plasma, uranium-dioxide, cermet, nuclear, propulsion

  19. Spatial Distribution and Kinematics of the Molecular Material Associated with eta Carinae

    Science.gov (United States)

    Loinard, Laurent; Kamiński, Tomasz; Serra, Paolo; Menten, Karl M.; Zapata, Luis A.; Rodríguez, Luis F.

    2016-12-01

    Single-dish submillimeter observations have recently revealed the existence of a substantial, chemically peculiar molecular gas component located in the innermost circumstellar environment of the very massive luminous blue variable star, η Carinae. Here, we present 5″-resolution interferometric observations of the 1\\to 0 rotational transition of hydrogen cyanide (HCN) toward this star obtained with the Australia Telescope Compact Array. The emission is concentrated in the central few arcseconds around η Carinae and shows a clear 150 km s-1 velocity gradient running from west-north-west (blue) to east-south-east (red). Given the extent, location, and kinematics of this molecular material, we associate it with the complex of dusty arcs and knots seen in mid-infrared emission near the center of the Homunculus nebula. Indeed, the shielding provided by this dust could help explain how molecules survive in the presence of the intense UV radiation field produced by η Carinae. The dust located in the central few arcseconds around η Carinae and the molecular component described here most likely formed in situ and out of material expelled by the massive interacting binary system. Thus, η Carinae offers us a rare glimpse of the processes that lead to the formation of dust and molecules around massive stars, which are relevant to the interpretation of dust and molecule detections at high redshifts.

  20. Modelagem do vento e da fotosfera de AG Carinae

    Science.gov (United States)

    Groh, J. H.; Damineli, A.

    2003-08-01

    A trajetória evolutiva das estrelas de alta massa depende fortemente de suas taxas de perda de massa. Apesar do rápido progresso no estudo destas estrelas, a taxa de perda de massa e outros parâmetros físicos básicos, como a temperatura superficial e a velocidade terminal do vento ainda não estão bem determinados. Isto ocorre devido à presença de ventos irregulares, rápidos e fortes ao redor destas estrelas, tornando a interpretação dos seus espectros uma tarefa difícil. Assim, a modelagem do vento e da fotosfera dessas estrelas está sendo cada vez mais usada para obter tais parâmetros a partir dos espectros. O aumento da taxa de perda de massa durante a fase LBV (Variáveis Luminosas Azuis), comparado com outros tipos de estrelas, tem sido atribuído a instabilidades do tipo S Doradus. Dispomos de uma base de dados espectroscópicos cobrindo 22 anos de observações de AG Carinae, incluindo um ciclo S Doradus completo, com espectros CCD em alta resolução na faixa óptica e infravermelha. Utilizamos o programa desenvolvido por Schmutz (1997) para uma análise preliminar desse ciclo, obtendo a taxa de perda de massa a partir da linha do Ha. Não existe uma correlação clara da taxa de perda de massa com mudanças da temperatura efetiva, do raio da estrela e do fluxo na banda V. A estrela atingiu seu mínimo fotométrico (raio mínimo) em 1990 e o máximo fotométrico (raio máximo) em 1995, enquanto que o fluxo máximo da linha do Ha ocorreu em 1996. Além disso a taxa de perda de massa não segue esse ciclo, contrariamente às idéias correntes. Para fazer um modelo mais realista estamos usando o programa CMFGEN (Hillier & Miller), que trata a fotosfera e o vento estelar de forma consistente, considerando a radiação fora do equilíbrio termodinâmico (NLTE) e com blanketting total de linhas. Simulamos o espectro de AG Carinae em duas épocas extremas do ciclo S Dor para testar os resultados obtidos com o modelo mais simplificado.

  1. On The gamma-ray emission from Reticulum II and other dwarf galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Hooper, Dan; Linden, Tim

    2015-09-01

    The recent discovery of ten new dwarf galaxy candidates by the Dark Energy Survey (DES) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) could increase the Fermi Gamma-Ray Space Telescope's sensitivity to annihilating dark matter particles, potentially enabling a definitive test of the dark matter interpretation of the long-standing Galactic Center gamma-ray excess. In this paper, we compare the previous analyses of Fermi data from the directions of the new dwarf candidates (including the relatively nearby Reticulum II) and perform our own analysis, with the goal of establishing the statistical significance of any gamma-ray signal from these sources. We confirm the presence of an excess from Reticulum II, with a spectral shape that is compatible with the Galactic Center signal. The significance of this emission is greater than that observed from 99.84% of randomly chosen high-latitude blank-sky locations, corresponding to a local detection significance of 3.2σ. We caution that any dark matter interpretation of this excess must be validated through observations of additional dwarf spheroidal galaxies, and improved calculations of the relative J-factor of dwarf spheroidal galaxies. We improve upon the standard blank-sky calibration approach through the use of multi-wavelength catalogs, which allow us to avoid regions that are likely to contain unresolved gamma-ray sources.

  2. THE THREE-DIMENSIONAL FUNDAMENTAL SOLUTION TO STOKES FLOW IN THE OBLATE SPHEROIDAL COORDINATES WITH APPLICATIONS TO MULTIPLES SPHEROID PROBLEMS

    Institute of Scientific and Technical Information of China (English)

    庄宏; 严宗毅; 吴望一

    2002-01-01

    A new three-dimensional fundamental solution to the Stokes flow was proposedby transforming the solid harmonic functions in Lamb' s solution into expressions in terms ofthe oblate spheroidal coordinates. These fundamental solutions are advantageous in treatingflows past an arbitrary number of arbitrarily positioned and oriented oblate spheroids. Theleast squares technique was adopted herein so that the convergence difficulties oftenencountered in solving three-dimensional problems were completely avoided. The examplesdemonstrate that present approach is highly accurate, consistently stable andcomputationally efficient.The oblate spheroid may be used to model a variety of particle shapes between acircular disk and a sphere. For the first time, the effect of various geometric factors on theforces and torques exerted on two oblate spheroids were systematically studied by using theproposed fundamental solutions. The generality of this approach was illustrated by twoproblems of three spheroids.

  3. Spatial distribution and kinematics of the molecular material associated with $\\eta$ Carinae

    CERN Document Server

    Loinard, L; Serra, P; Menten, K; Zapata, L; Rodriguez, L

    2016-01-01

    Single-dish sub-millimeter observations have recently revealed the existence of a substantial, chemically peculiar, molecular gas component located in the innermost circumstellar environment of the very massive luminous blue variable star $\\eta$ Carinae. Here, we present 5$"$-resolution interferometric observations of the 1$\\rightarrow$0 rotational transition of hydrogen cyanide (HCN) obtained with the Australia Telescope Compact Array (ATCA) toward this star. The emission is concentrated in the central few arcseconds around $\\eta$ Carinae and shows a clear 150 km s$^{-1}$ velocity gradient running from west-north-west (blue) to east-south-east (red). Given the extent and location of this molecular material, we associate it with the complex of dusty arcs and knots seen in mid-infrared emission along the equatorial plane of the Homunculus nebula. The dust located in the central few arcseconds around $\\eta$ Carinae and the molecular component described here have most likely formed in situ, out of material expel...

  4. Stellar Populations in Dwarf Galaxies A Review of the Contribution of HST to our Understanding of the Nearby Universe

    CERN Document Server

    Tolstoy, E

    2000-01-01

    This review aims to give an overview of the contribution of the Hubble Space Telescope to our understanding of the detailed properties of Local Group dwarf galaxies and their older stellar populations. The exquisite stable high spatial resolution combined with photometric accuracy of images from the Hubble Space Telescope have allowed us to probe further back into the history of star formation of a large variety of different galaxy types with widely differing star formation properties. We have learnt several important things about dwarf galaxy evolution from these studies. Firstly we have found that no two galaxies have identical star formation histories; some galaxies may superficially look the same today, but they have invariably followed different paths to this point. Now that we have managed to probe deep into the star formation history of dwarf irregular galaxies in the Local Group it is obvious that there are a number of similarities with the global properties of dwarf elliptical/spheroidal type galaxie...

  5. The ACS LCID Project: On the origin of dwarf galaxy types: a manifestation of the halo assembly bias?

    CERN Document Server

    Gallart, C; Mayer, L; Aparicio, A; Battaglia, G; Bernard, E J; Cassisi, S; Cole, A A; Dolphin, A E; Drozdovsky, I; HIdalgo, S L; Navarro, J F; Salvadori, S; Skillman, E D; Stetson, P B; Weisz, D R

    2015-01-01

    We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than being only the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from colour-magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event, and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal vs dwarf irregular). Slow and fast dwarfs also differ in their ...

  6. Eta Carinae: At the Crossroads of becoming a Supernova

    Science.gov (United States)

    Gull, Theodore

    2007-01-01

    Since the 1840's, when Eta Carinae's visual magnitude rivaled Sirius, the brightest star in the night sky, astronomers have wondered what major event took place. Today with the Hubble Space Telescope Imaging Spectrograph, with CHANDRA X-ray spectroscopy and the Very Large Telescope spectrographs and interferometers, we have learned that over 12 solar masses of material was ejected at 500 to 700 km/s into interstellar space. This ejecta is quite different from the normal interstellar medium. It is rich in nitrogen, poor in oxygen and carbon. The dust properties are quite peculiar and many metals such as vanadium, strontium, cadmium are seen in both absorption against the central source, plus a number of molecules. The chemical and dust formation is likely dominated by nitrogen as we see H_2, CH, CH+, OH, NH, HCl and NH-3, but no CO. Other metals and molecules are being searched out in the FUSE, HST/STIS, VLT/UVES and VLT/CRIRES spectra. I will describe what we know about the massive binary stellar system, how it changes every 5.54 year in UV and X-ray output and how the massive ejecta responds in this astrophysical laboratory.

  7. The Trumpler 14 photodissociation region in the Carina Nebula

    Science.gov (United States)

    Brooks, K. J.; Cox, P.; Schneider, N.; Storey, J. W. V.; Poglitsch, A.; Geis, N.; Bronfman, L.

    2003-12-01

    We report the results of observations of the fine-structure emission lines [C II] 158 μm and [O I] 63 μm using FIFI on the Kuiper Airborne Observatory (KAO) and the Long Wavelength Spectrometer (LWS) on board ISO, towards the molecular cloud associated with the stellar cluster Trumpler 14 (Tr 14) in the Carina Nebula. These data are compared with selected CO and CS transitions obtained with the SEST as well as IRAS and MSX images to produce a detailed view of the morphology and the physical conditions prevailing in the photodissociation region (PDR) at the interface between the ionized gas and the molecular dust lane. The relative intensity distribution observed for the various tracers is consistent with the stratification expected for a molecular cloud seen edge-on and exposed to a radiation field of ~ 104 G_0, which is dominated by the most massive stars of Tr 14. The grain photoelectric heating efficiency, \\epsilon, is estimated to be ~5 x 10-3 and is comparable to other galactic PDRs. The molecular gas has a complicated velocity structure with a high velocity dispersion resulting from the impact of the stellar winds arising from Tr 14. There is evidence of small-scale clumping with a very low volume filling factor. Despite the rich concentration of massive O stars in Tr 14 we find that the parameters of the PDR are much less-extreme than those of the Orion and M 17 massive star-forming regions.

  8. A multispectral view of the periodic events in eta Carinae

    CERN Document Server

    Damineli, A; Corcoran, M F; Stahl, O; Groh, J H; Arias, J; Teodoro, M; Morrell, N; Gamen, R; Gonzalez, F; Leister, N V; Levato, H; Levenhagen, R S; Grosso, M; Colombo, J F Albacete; Wallerstein, G

    2007-01-01

    A full description of the 5.5-yr low excitation events in eta Carinae is presented. We show that they are not simple and brief, as thought before, but a combination of two components. The first, the `slow variation' component, is revealed by slow changes in the ionization level of circumstellar matter across the whole cycle and is caused by the gradual immersion of the secondary star in the wind of the primary. The second, the `collapse' component, is restricted to some months around the minimum, and is due to the immersion of the secondary deep in the primary wind. During this stage there is a general collapse of the wind-wind collision shock, and the Weigelt blobs are strongly shielded from high energy photons (E > 16 eV). High energy phenomena are sensitive only to the `collapse', low energy only to the `slow variation' and that of intermediate energy to both components. Simple eclipses and mechanisms effective only near periastron (e.g., shell ejection or accretion onto the secondary star) cannot account ...

  9. The bipolar structure of the LBV nebula around HR Carinae

    CERN Document Server

    Weis, K; Bomans, D J; Chu, Y H; Joner, M D

    1997-01-01

    HR Carinae is one of the few Luminous Blue Variables (LBVs) in the Galaxy. It has a nebula that appears bipolar. We have obtained imaging and high-dispersion, long-slit echelle data of the HR Car nebula, and confirmed that it is a bipolar nebula. Its polar axis lies along the position angle of 125 +- 5 degree; each lobe has, at a distance of 5 kpc a diameter of about 0.65 pc and a line-of-sight expansion velocity of 75-150 km/sec. Beside the expanding bipolar lobes, a number of [NII]-bright knots are detected. These knots have lower expansion velocities than the lobes and are detected only within the projected boundary of the lobes. These knots are most likely nitrogen-enriched material ejected by HR Car. On a larger scale, a funnel-shaped nebula is detected at 2.5" northwest of HR Car. The axis of the funnel is roughly aligned with the polar axis of the HR Car nebula, suggesting that HR Car may be responsible for the ionization and shaping of this nebula. Future observations of kinematics and abundances are ...

  10. The sub-arcsecond dusty environment of Eta Carinae

    CERN Document Server

    Chesneau, O; Herbst, T; Waters, L B F M; Hillier, D J; Leinert, C; De Koter, A; Pascucci, I; Jaffe, W; Köhler, R; Alvarez, C; Van Boekel, R; Brandner, W; Graser, U; Lagrange, A M; Lenzen, R; Morel, S; Schöller, M; Leinert, Ch

    2005-01-01

    The core of the nebula surrounding Eta Carinae has been observed with the VLT Adaptive Optics system NACO and with the interferometer VLTI/MIDI to constrain spatially and spectrally the warm dusty environment and the central object. In particular, narrow-band images at 3.74 and 4.05 micron reveal the butterfly shaped dusty environment close to the central star with unprecedented spatial resolution. A void whose radius corresponds to the expected sublimation radius has been discovered around the central source. Fringes have been obtained in the Mid-IR which reveal a correlated flux of about 100Jy situated 0.3" south-east of the photocenter of the nebula at 8.7 micron, which corresponds with the location of the star as seen in other wavelengths. This correlated flux is partly attributed to the central object, and these observations provide an upper limit for the SED of the central source from 2.2 to 13.5 micron. Moreover, we have been able to spectrally disperse the signal from the nebula itself at PA=318 degre...

  11. Accretion at the periastron passage of Eta Carinae

    CERN Document Server

    Kashi, Amit

    2016-01-01

    We present high resolution numerical simulations of the colliding wind system $\\eta$ Carinae, showing accretion onto the secondary star close to periastron passage. Our hydrodynamical simulations include self gravity and radiative cooling. The smooth stellar winds collide and develop instabilities, mainly the non-linear thin shell instability, and form filaments and clumps. We find that a few days before periastron passage the dense filaments and clumps flow towards the secondary as a result of its gravitational attraction, and reach the zone where we inject the secondary wind. We run our simulations for the conventional stellar masses, $M_1=120 ~\\rm{M_\\odot}$ and $M_2=30 ~\\rm{M_\\odot}$, and for a high mass model, $M_1=170 ~\\rm{M_\\odot}$ and $M_2=80 ~\\rm{M_\\odot}$, that was proposed to better fit the history of giant eruptions. As expected, the simulations results show that the accretion processes is more pronounced for a more massive secondary star.

  12. [Fe II] jets from intermediate-mass protostars in Carina

    CERN Document Server

    Reiter, Megan; Bally, John

    2016-01-01

    We present new HST/WFC3-IR narrowband [Fe II] images of protostellar jets in the Carina Nebula. Combined with 5 previously published sources, we have a sample of 18 jets and 2 HH objects. All of the jets we targeted with WFC3 show bright infrared [Fe II] emission, and a few H$\\alpha$ candidate jets are confirmed as collimated outflows based on the morphology of their [Fe II] emission. Continuum-subtracted images clearly separate jet emission from the adjacent ionization front, providing a better tracer of the collimated jet than H$\\alpha$ and allowing us to connect these jets with their embedded driving sources. The [Fe II] 1.64 $\\mu$m/H$\\alpha$ flux ratio measured in the jets is $\\gtrsim 5$ times larger than in the adjacent ionization fronts. The low-ionization jet core requires high densities to shield Fe$^+$ against further ionization by the FUV radiation from O-type stars in the H II region. High jet densities imply high mass-loss rates, consistent with the intermediate-mass driving sources we identify fo...

  13. The three-dimensional structure of the Eta Carinae Homunculus

    CERN Document Server

    Steffen, W; Madura, T I; Groh, J H; Gull, T R; Mehner, A; Corcoran, M F; Damineli, A; Hamaguchi, K

    2014-01-01

    We investigate, using the modeling code SHAPE, the three-dimensional structure of the bipolar Homunculus nebula surrounding Eta Carinae, as mapped by new ESO VLT/X-Shooter observations of the H2 $\\lambda=2.12125$ micron emission line. Our results reveal for the first time important deviations from the axisymmetric bipolar morphology: 1) circumpolar trenches in each lobe positioned point-symmetrically from the center and 2) off-planar protrusions in the equatorial region from each lobe at longitudinal (~55 degrees) and latitudinal (10-20 degrees) distances from the projected apastron direction of the binary orbit. The angular distance between the protrusions (~110 degrees) is similar to the angular extent of each polar trench (~130 degrees) and nearly equal to the opening angle of the wind-wind collision cavity (~110 degrees). As in previous studies, we confirm a hole near the centre of each polar lobe and no detectable near-IR H2 emission from the thin optical skirt seen prominently in visible imagery. We con...

  14. A Deep Study of the Dwarf Satellites Andromeda XXVIII & Andromeda XXIX

    CERN Document Server

    Slater, Colin T; Martin, Nicolas F; Tollerud, Erik J; Ho, Nhung

    2015-01-01

    We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomposing the horizontal branch into blue (metal poor, assumed to be older) and red (relatively more metal rich, assumed to be younger) populations shows that the metal rich are also more spatially concentrated in the center of the galaxy. We use spectroscopic measurements of the Calcium triplet, combined with the improved precision of the Gemini photometry, to measure the metallicity of the galaxies, confirming the metallicity spread and showing that they both lie on the luminosity-metallicity relation for dwarf satellites. ...

  15. Differentiation of human mesenchymal stem cell spheroids under microgravity conditions

    Directory of Open Access Journals (Sweden)

    Cerwinka Wolfgang H

    2012-06-01

    Full Text Available Abstract To develop and characterize a novel cell culture method for the generation of undifferentiated and differentiated human mesenchymal stem cell 3D structures, we utilized the RWV system with a gelatin-based scaffold. 3 × 106 cells generated homogeneous spheroids and maximum spheroid loading was accomplished after 3 days of culture. Spheroids cultured in undifferentiated spheroids of 3 and 10 days retained expression of CD44, without expression of differentiation markers. Spheroids cultured in adipogenic and osteogenic differentiation media exhibited oil red O staining and von Kossa staining, respectively. Further characterization of osteogenic lineage, showed that 10 day spheroids exhibited stronger calcification than any other experimental group corresponding with significant expression of vitamin D receptor, alkaline phosphatase, and ERp60 . In conclusion this study describes a novel RWV culture method that allowed efficacious engineering of undifferentiated human mesenchymal stem cell spheroids and rapid osteogenic differentiation. The use of gelatin scaffolds holds promise to design implantable stem cell tissue of various sizes and shapes for future regenerative treatment.

  16. The ``Ghost Shell'': Discovery of the Forward Shock from Colliding Winds about Eta Carinae

    Science.gov (United States)

    Dorland, B. N.; Currie, D. G.; Kaufer, A.; Bacciotti, F.

    2003-01-01

    We report on the newly discovered ``Ghost Shell'' around eta Carinae. We have detected a high-velocity ( ~ - 850 km /s), spatially extended, narrow emission feature lying in front of the southeast lobe of eta Carinae's homunculus. This feature has the speed of a high-velocity shock but the spectrum of a low-velocity shock. We propose that the Ghost Shell is the forward shock between the fast stellar wind of the great eruption of 1842 and the older, slow, massive wind. This discovery is described in more detail in Currie, Dorland, & Kaufer (2002).

  17. A Study of the Warm Ionized Medium Throughout the Sagittarius-Carina Arm

    CERN Document Server

    Krishnarao, Dhanesh; Benjamin, Robert A

    2016-01-01

    We present velocity-channel maps and analysis of the warm ionized medium (WIM) throughout the Sagittarius- Carina arm at Galactic longitudes 20 1000 pc along the far Carina arm. Physical conditions of the ionized gas are analyzed using the [S II]/H-alpha line ratio, which more closely traces H-alpha intensity than height above the plane, z, suggesting a stronger relationship with the in-situ electron density. We interpret this result as further evidence for the majority of the observed diffuse emission originating from in-situ ionized gas as opposed to scattered light from classical H II regions in the plane.

  18. An Aboriginal Australian Record of the Great Eruption of Eta Carinae

    CERN Document Server

    Hamacher, Duane W

    2010-01-01

    We present evidence that the Boorong Aboriginal people of northwestern Victoria observed the Great Eruption of Eta ({\\eta}) Carinae in the nineteenth century and incorporated the event into their oral traditions. We identify this star, as well as others not specifically identified by name, using descriptive material presented in the 1858 paper by William Edward Stanbridge in conjunction with early southern star catalogues. This identification of a transient astronomical event supports the assertion that Aboriginal oral traditions are dynamic and evolving, and not static. This is the only definitive indigenous record of {\\eta} Carinae's outburst identified in the literature to date.

  19. Irradiated brown dwarfs

    CERN Document Server

    Casewell, S L; Lawrie, K A; Maxted, P F L; Dobbie, P D; Napiwotzki, R

    2014-01-01

    We have observed the post common envelope binary WD0137-349 in the near infrared $J$, $H$ and $K$ bands and have determined that the photometry varies on the system period (116 min). The amplitude of the variability increases with increasing wavelength, indicating that the brown dwarf in the system is likely being irradiated by its 16500 K white dwarf companion. The effect of the (primarily) UV irradiation on the brown dwarf atmosphere is unknown, but it is possible that stratospheric hazes are formed. It is also possible that the brown dwarf (an L-T transition object) itself is variable due to patchy cloud cover. Both these scenarios are discussed, and suggestions for further study are made.

  20. Are z>2 Herschel galaxies proto-spheroids?

    CERN Document Server

    Pozzi, F; Gruppioni, C; Granato, G L; Cresci, G; Silva, L; Pozzetti, L; Matteucci, F; Zamorani, G

    2015-01-01

    We present a backward approach for the interpretation of the evolution of the near-infrared and the far-infrared luminosity functions across the redshift range 02 can be explained as progenitors of local spheroids caught during their formation. We also test the effects of mass downsizing by dividing the spheroids into three populations of different present-day stellar masses. The results obtained in this case confirm the validity of our approach, i.e. that the bulk of proto-spheroids can be modelled by means of a single model which describes the evolution of galaxies at the break of the present-day early type K-band LF.

  1. Modeling a spheroidal microswimmer and cooperative swimming in thin films

    CERN Document Server

    Theers, Mario; Gompper, Gerhard; Winkler, Roland G

    2016-01-01

    We propose a hydrodynamic model for a spheroidal microswimmer with two tangential surface velocity modes. This model is analytically solvable and reduces to Lighthill's and Blake's spherical squirmer model in the limit of equal major and minor semi-axes. Furthermore, we present an implementation of such a spheroidal squirmer by means of multiparticle collision dynamics simulations. We investigate its properties as well as the scattering of two spheroidal squirmers in a slit geometry. Thereby we find a stable fixed point, where two pullers swim cooperatively forming a wedge-like conformation with a small constant angle.

  2. Dwarfs in ancient Egypt.

    Science.gov (United States)

    Kozma, Chahira

    2006-02-15

    Ancient Egypt was one of the most advanced and productive civilizations in antiquity, spanning 3000 years before the "Christian" era. Ancient Egyptians built colossal temples and magnificent tombs to honor their gods and religious leaders. Their hieroglyphic language, system of organization, and recording of events give contemporary researchers insights into their daily activities. Based on the record left by their art, the ancient Egyptians documented the presence of dwarfs in almost every facet of life. Due to the hot dry climate and natural and artificial mummification, Egypt is a major source of information on achondroplasia in the old world. The remains of dwarfs are abundant and include complete and partial skeletons. Dwarfs were employed as personal attendants, animal tenders, jewelers, and entertainers. Several high-ranking dwarfs especially from the Old Kingdom (2700-2190 BCE) achieved important status and had lavish burial places close to the pyramids. Their costly tombs in the royal cemeteries and the inscriptions on their statutes indicate their high-ranking position in Egyptian society and their close relation to the king. Some of them were Seneb, Pereniankh, Khnumhotpe, and Djeder. There were at least two dwarf gods, Ptah and Bes. The god Ptah was associated with regeneration and rejuvenation. The god Bes was a protector of sexuality, childbirth, women, and children. He was a favored deity particularly during the Greco-Roman period. His temple was recently excavated in the Baharia oasis in the middle of Egypt. The burial sites and artistic sources provide glimpses of the positions of dwarfs in daily life in ancient Egypt. Dwarfs were accepted in ancient Egypt; their recorded daily activities suggest assimilation into daily life, and their disorder was not shown as a physical handicap. Wisdom writings and moral teachings in ancient Egypt commanded respect for dwarfs and other individuals with disabilities.

  3. The no-spin zone: rotation versus dispersion support in observed and simulated dwarf galaxies

    Science.gov (United States)

    Wheeler, Coral; Pace, Andrew B.; Bullock, James S.; Boylan-Kolchin, Michael; Oñorbe, Jose; Elbert, Oliver D.; Fitts, Alex; Hopkins, Philip F.; Kereš, Dušan

    2017-02-01

    We perform a systematic Bayesian analysis of rotation versus dispersion support (vrot/σ) in 40 dwarf galaxies throughout the local volume (LV) over a stellar mass range of 10^{3.5} M_{⊙}sample have vrot/σ ≲ 1.0, while all have vrot/σ ≲ 2.0. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally supported stellar discs, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion-supported stars. We see no clear trend between vrot/σ and distance to the closest L⋆ galaxy, nor between vrot/σ and M⋆ within our mass range. We apply the same Bayesian analysis to four FIRE hydrodynamic zoom-in simulations of isolated dwarf galaxies (10^9 M_{⊙}population of dIrrs and dSphs without the need to subject these dwarfs to any external perturbations or tidal forces. We posit that most dwarf galaxies form as puffy, dispersion-dominated systems, rather than cold, angular-momentum-supported discs. If this is the case, then transforming a dIrr into a dSph may require little more than removing its gas.

  4. Eta Carinae and the Homunculus: an Astrophysical Laboratory

    Science.gov (United States)

    Gull, T. R.

    2007-08-01

    High spatial resolution spectroscopy with HST/STIS between 1998.0 and 2004.2 has provided much exciting information about the central binary system and the physics of its N-rich, C,O-poor ejecta. Stellar He I profiles, noticeably blue-shifted relative to P Cygni H and Fe II line profiles, originate from the ionized wind region between two massive companions. Changes in profiles of He I singlet and triplet lines provide clues to the excitation mechanisms involved as the hot, UV companion moves in its highly eccentric orbit. For 90% of the 5.54-year period, the spectra of nearby Weigelt blobs and the Little Homunculus include highly excited emission lines of Ar, Ne, and Fe. During the few month-long spectroscopic minimum, these systems are deprived of Lyman continuum. Recombination, plus cooling, occurs. In the skirt region between the bipolar Homunculus, a neutral emission region, devoid of hydrogen emission, glows in Ti II, Fe I, Sr II, Sc II, etc. We find the ejecta to have Ti/Ni abundances nearly 100 times solar, not due to nuclear processing, but due to lack of oxygen. Many metals normally tied up in interstellar dust remain in gaseous phase. Much information is being obtained on the physical processes in these warm N-rich gases, whose excitation varies with time in a predictable pattern. Indeed recent GRB high dispersion spectra include signatures of circumGRB warm gases. This indicates that the early, primordial massive stars have warm massive ejecta reminiscent to that around Eta Carinae.

  5. New static spheroidal solution in Jordan-Brands-Dicke theory

    CERN Document Server

    Kozyrev, S M

    2010-01-01

    The static spheroidal solutions of Jordan-Brands-Dicke theory (JBD) are studied. We consider the effect of the anisotropic stresses of scalar field on the shape of JBD self-graviting objects. It is shown that scalar fields can have significant effect on the structure and properties of self-graviting objects. In contrast with general relativity in JBD theory there are nonflat static spheroidal solutions.

  6. Diversity of cell-mediated adhesions in breast cancer spheroids.

    Science.gov (United States)

    Ivascu, Andrea; Kubbies, Manfred

    2007-12-01

    Due to their three dimensional (3D) architecture, multicellular tumor spheroids mimic avascular tumor areas comprising the establishment of diffusion gradients, reduced proliferation rates and increased drug resistance. We have shown recently that the spontaneous formation of spheroids is restricted to a limited number of cell lines whereas the majority grow only as aggregates of cells with loose cell-cell contacts when cultured in 3D. However, by the addition of reconstituted basement membrane (rBM, Matrigel), aggregates can be transformed into spheroids with diffusion barriers and development of quiescent therapy-resistant cells. In this report, we investigated adhesion molecules responsible for rBM-driven versus spontaneous spheroid formation in a diverse population of eight breast tumor cell lines relevant for in vitro and in vivo antitumor drug testing. Inhibition of spheroid formation was monitored in the presence of adhesion molecule functional blocking antibodies and after siRNA-mediated down-regulation of E- and N-cadherin and integrin beta1 adhesion receptors. We identified that E-cadherin mediates the spontaneous formation of spheroids in MCF7, BT-474, T-47D and MDA-MB-361 cells, whereas N-cadherin is responsible for tight packing of MDA-MB-435S cells. In contrast, the matrix protein-induced transformation of 3D aggregates into spheroids in MDA-MB-231 and SK-BR-3 cells is mediated primarily by the collagen I/integrin beta1 interaction with no cadherin involvement. A combination of both, homophilic E-cadherin and integrin beta1/collagen I interaction establishes spheroids in MDA-MB-468 cells. These findings indicate that an evolutionary diverse and complex pattern of interacting cell surface proteins exists in breast cancer cells that determines the 3D growth characteristic in vitro, thereby influencing small molecule or antibody permeation in preclinical in vitro and in vivo tumor models.

  7. Delivery of Human Adipose Stem Cells Spheroids into Lockyballs

    Science.gov (United States)

    Pereira, Frederico D. A. S.; Gruber, Peter; Stuart, Mellannie P.; Ovsianikov, Aleksandr; Brakke, Ken; Kasyanov, Vladimir; da Silva, Jorge V. L.; Granjeiro, José M.; Mironov, Vladimir

    2016-01-01

    Adipose stem cells (ASCs) spheroids show enhanced regenerative effects compared to single cells. Also, spheroids have been recently introduced as building blocks in directed self-assembly strategy. Recent efforts aim to improve long-term cell retention and integration by the use of microencapsulation delivery systems that can rapidly integrate in the implantation site. Interlockable solid synthetic microscaffolds, so called lockyballs, were recently designed with hooks and loops to enhance cell retention and integration at the implantation site as well as to support spheroids aggregation after transplantation. Here we present an efficient methodology for human ASCs spheroids biofabrication and lockyballs cellularization using micro-molded non-adhesive agarose hydrogel. Lockyballs were produced using two-photon polymerization with an estimated mechanical strength. The Young’s modulus was calculated at level 0.1362 +/-0.009 MPa. Interlocking in vitro test demonstrates high level of loading induced interlockability of fabricated lockyballs. Diameter measurements and elongation coefficient calculation revealed that human ASCs spheroids biofabricated in resections of micro-molded non-adhesive hydrogel had a more regular size distribution and shape than spheroids biofabricated in hanging drops. Cellularization of lockyballs using human ASCs spheroids did not alter the level of cells viability (p › 0,999) and gene fold expression for SOX-9 and RUNX2 (p › 0,195). The biofabrication of ASCs spheroids into lockyballs represents an innovative strategy in regenerative medicine, which combines solid scaffold-based and directed self-assembly approaches, fostering opportunities for rapid in situ biofabrication of 3D building-blocks. PMID:27829016

  8. Faint Dwarf Galaxies in Hickson Compact Group 90

    CERN Document Server

    Ordenes-Briceño, Yasna; Puzia, Thomas H; Muñoz, Roberto P; Eigenthaler, Paul; Georgiev, Iskren Y; Goudfrooij, Paul; Hilker, Michael; Lançon, Ariane; Mamon, Gary; Mieske, Steffen; Miller, Bryan W; Peng, Eric W; Sánchez-Janssen, Rubén

    2016-01-01

    We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with VLT/VIMOS. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range $0.7\\!\\lesssim\\! r_{\\rm eff}/{\\rm kpc}\\! \\lesssim\\! 1.5$ with luminosities of $-11.65\\!\\lesssim\\! M_U\\! \\lesssim\\! -9.42$ and $-12.79\\!\\lesssim\\! M_I\\! \\lesssim\\! -10.58$ mag, corresponding to a color range of $(U\\!-\\!I)_0\\!\\simeq\\!1.1\\!-\\!2.2$ mag and surface brightness levels of $\\mu_U\\!\\simeq\\!28.1\\,{\\rm mag/arcsec^2}$ and $\\mu_I\\!\\simeq\\!27.4\\,{\\rm mag/arcsec^2}$. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z$_\\odot$ metallicities we obtain stellar masses in the range $M_*|_{Z_\\odot} \\simeq 10^{5.7-6.3} M_{\\odot}$ and $M_*|_{0.02\\,Z_\\odot}\\!\\simeq\\!10^{6.3-8}\\,M_{\\odot}$. Three dwarfs are ol...

  9. A Catalog of New Spectroscopically Confirmed Massive OB Stars in Carina

    CERN Document Server

    Alexander, Michael J; Povich, Matthew S; McSwain, M Virginia

    2016-01-01

    The Carina star-forming region is one of the largest in the Galaxy, and its massive star population is still being unveiled. The large number of stars combined with high, and highly variable, interstellar extinction makes it inherently difficult to find OB stars in this type of young region. We present the results of a spectroscopic campaign to study the massive star population of the Carina Nebula, with the primary goal to confirm or reject previously identified Carina OB star candidates. A total of 141 known O- and B-type stars and 94 candidates were observed, of which 73 candidates had a high enough signal-to-noise ratio to classify. We find 23 new OB stars within the Carina Nebula, a 32% confirmation rate. One of the new OB stars has blended spectra and is suspected to be a double-lined spectroscopic binary (SB2). We also reclassify the spectral types of the known OB stars and discover nine new SB2s among this population. Finally, we discuss the spatial distribution of these new OB stars relative to known...

  10. X-ray Gyrations of Eta Carinae, or, Is Presence of Evidence Evidence of Presence?

    CERN Document Server

    Corcoran, M F; Gull, T R; Damineli, A; Davidson, K

    2004-01-01

    We review the properties of the variable X-ray emission from the extremely massive star Eta Carinae concentrating on the last X-ray minimum, and briefly consider the possible role of a binary companion star on the observational properties of the system.

  11. Deep wide-field near-infrared survey of the Carina Nebula

    CERN Document Server

    Preibisch, Thomas; Kuderna, Benjamin; Ohlendorf, Henrike; King, Robert R; Hodgkin, Simon; Irwin, Mike; Lewis, James R; McCaughrean, Mark J; Zinnecker, Hans

    2011-01-01

    (abbreviated) We used HAWK-I at the ESO VLT to produce a near-infrared survey of the Carina Nebula that is deep enough to detect the full low-mass stellar population. The results of a recent deep X-ray survey are used to distinguish between young stars in Carina and background contaminants. We find that the ages of the low-mass stars (derived from color-magnitude diagrams of the invidual cluster in the Carina Nebula) agree with previous age estimates for the massive stars. About 3200 of the X-ray selected stars have masses >= 1 Msun; this number is in good agreement with extrapolations of the field IMF based on the number of high-mass stars and shows that there is no deficit of low-mass stars. The near-infrared excess fractions for the stellar populations in Carina are lower than typical for other, less massive clusters of similar age, suggesting a faster timescale of circumstellar disk dispersal than in the more quiescent regions, most likely due to the very high level of massive star feedback. Narrow-band i...

  12. The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies with GEAR

    CERN Document Server

    Revaz, Yves

    2011-01-01

    We present a fully parallel chemo-dynamical Tree/SPH code, GEAR, which allows to perform high resolution simulations with detailed chemical diagnostics. Starting from the public version of Gadget-2, we included the complex treatment of the baryon physics: gas cooling, star formation law, chemical evolution and supernovae feedback. We qualified the performances of GEAR with the case of dSph galaxies. GEAR conserves the total energy budget of the systems to better than 5% over 14Gyr and proved excellent convergence of the results with numerical resolution. We showed that models of dSphs in a static Euclidean space, where the expansion of the universe is neglected are valid. In addition, we tackled some of the existing open questions in the field, like the stellar mass fraction of dSphs and its link with the predicted dark matter halo mass function, the effect of the supernova feedback, the spatial distribution of the stellar populations, and the origin of the diversity in star formation histories and chemical a...

  13. The Star Formation & Chemical Evolution timescales of two nearby dwarf spheroidal galaxies

    Science.gov (United States)

    den Brok, Mark

    2012-05-01

    Dit proefschrift beschrijft onderzoek naar elliptische dwergmelkwegstelsels. Vanwege de voor veel mensen enigzins esoterische aard van dit soort objecten, is het goedomuit te leggenwat precies een melkwegstelsel is. Melkwegstelsels zijn wolken van miljoenen tot duizenden miljarden sterren. In zo’n wolk bewegen de sterren, grotendeels gedreven door hun onderlinge aantrekkingskracht, langs elkaar heen. Twee soorten melkwegstelsels zijn algemeen bekend. Het eerste type melkwegstelsel staat bekend als spiraalstelsel. Spiraalstelsels bevatten, naast sterren, een grote hoeveelheid interstellair gas en stof. Uit dit gas en stof kunnen nieuwe sterren worden gevormd en de aanwezigheid van veel jonge sterren geeft deze melkwegstelsels een enigzins blauwe kleur. Omdat wij spiraalstelsels onder verschillende inclinatiehoeken zien en soms zelfs van de zijkant, weten wij dat de sterren en het gas zich ophouden in een platte, schijfachtige vorm. Onze zon bevindt zich ook in een spiraalstelsel, dat door de schijfvorm als een band aan de hemel verschijnt: de melkweg. Metingen aan de snelheden van sterren en gas in spiraalstelsels tonen aan dat sterren en gas in spiraalstelsels op hoge snelheid om het centrum van het melkwegstelsel roteren. In het midden van de schijf van spiraalstelsels ziet men vaak een verdikking. De sterren in deze verdikking, in het Engels aangeduid met de naam bulge, hebben minder impulsmoment dan de sterren in de schijf, en bewegen zich daardoor in chaotischer banen. De sterren in de bulge zijn gemiddeld wat ouder dan de sterren in de schijf, waardoor de bulge vaak een wat gelige kleur heeft.

  14. Extremely metal-poor stars in classical dwarf spheroidal galaxies : Fornax, Sculptor, and Sextans

    NARCIS (Netherlands)

    Tafelmeyer, M.; Jablonka, P.; Hill, V.; Shetrone, M.; Tolstoy, E.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Starkenburg, E.; Venn, K. A.; Abel, T.; Francois, P.; Kaufer, A.; North, P.; Primas, F.; Szeifert, T.

    2010-01-01

    We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor, and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to hav

  15. Study of the Sextans dwarf spheroidal galaxy from the DART CaII triplet survey

    NARCIS (Netherlands)

    Battaglia, G.; Tolstoy, E.; Helmi, A.; Irwin, M.; Parisi, P.; Hill, V.; Jablonka, P.

    2011-01-01

    We use Very Large Telescope (VLT)/Fibre Large Array Multi Element Spectrograph (FLAMES) intermediate-resolution (R similar to 6500) spectra of individual red giant branch stars in the near-infrared Ca ii triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics

  16. Spheroidal galactic halos and mirror dark matter

    CERN Document Server

    Foot, R

    2004-01-01

    Mirror matter has been proposed as a dark matter candidate. It has several very attractive features, including automatic stability and darkness, the ability to mimic the broad features of cold dark matter while in the linear density perturbation regime, and consistency with all direct dark matter search experiments, both negative (e.g. CDMS II) and positive (DAMA). In this paper we consider an important unsolved problem: Are there plausible reasons to explain why most of the mirror matter in spiral galaxies exists in the form of gaseous {\\it spheroidal} galactic halos around ordinary matter {\\it disks}? We compute an order-of-magnitude estimate that the mirror photon luminosity of a typical spiral galaxy today is around $10^{44}$ erg/s. Interestingly, this rate of energy loss is similar to the power supplied by ordinary supernova explosions. We discuss circumstances under which supernova power can be used to heat the gaseous part of the mirror matter halo and hence prevent its collapse to a disk. The {\\it mac...

  17. Chemistry and Kinematics of the Late-forming Dwarf Irregular Galaxies Leo A, Aquarius, and Sagittarius DIG

    Science.gov (United States)

    Kirby, Evan N.; Rizzi, Luca; Held, Enrico V.; Cohen, Judith G.; Cole, Andrew A.; Manning, Ellen M.; Skillman, Evan D.; Weisz, Daniel R.

    2017-01-01

    We present Keck/DEIMOS spectroscopy of individual stars in the relatively isolated Local Group dwarf galaxies Leo A, Aquarius, and the Sagittarius dwarf irregular galaxy. The three galaxies—but especially Leo A and Aquarius—share in common delayed star formation histories (SFHs) relative to many other isolated dwarf galaxies. The stars in all three galaxies are supported by dispersion. We found no evidence of stellar velocity structure, even for Aquarius, which has rotating H i gas. The velocity dispersions indicate that all three galaxies are dark-matter-dominated, with dark-to-baryonic mass ratios ranging from {4.4}-0.8+1.0 (SagDIG) to {9.6}-1.8+2.5 (Aquarius). Leo A and SagDIG have lower stellar metallicities than Aquarius, and they also have higher gas fractions, both of which would be expected if Aquarius were further along in its chemical evolution. The metallicity distribution of Leo A is inconsistent with a closed or leaky box model of chemical evolution, suggesting that the galaxy was pre-enriched or acquired external gas during star formation. The metallicities of stars increased steadily for all three galaxies, but possibly at different rates. The [α/Fe] ratios at a given [Fe/H] are lower than that of the Sculptor dwarf spheroidal galaxy, which indicates more extended SFHs than Sculptor, consistent with photometrically derived SFHs. Overall, the bulk kinematic and chemical properties for the late-forming dwarf galaxies do not diverge significantly from those of less delayed dwarf galaxies, including dwarf spheroidal galaxies. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  18. White Dwarf Mass Distribution

    CERN Document Server

    Kepler, S O; Romero, Alejandra Daniela; Ourique, Gustavo; Pelisoli, Ingrid

    2016-01-01

    We present the mass distribution for all S/N > 15 pure DA white dwarfs detected in the Sloan Digital Sky Survey up to Data Release 12, fitted with Koester models for ML2/alpha=0.8, and with Teff > 10 000 K, and for DBs with S/N >10, fitted with ML2/alpha=1.25, for Teff > 16 000 K. These mass distributions are for log g > 6.5 stars, i.e., excluding the Extremely Low Mass white dwarfs. We also present the mass distributions corrected by volume with the 1/Vmax approach, for stars brighter than g=19. Both distributions have a maximum at M=0.624 Msun but very distinct shapes. From the estimated z-distances, we deduce a disk scale height of 300 pc. We also present 10 probable halo white dwarfs, from their galactic U, V, W velocities.

  19. Temperature, salinity, nutrients, carbon, and other profile data collected worldwide as part of the CARINA project (NODC Accession 0057766)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The CARINA (CARbon dioxide IN the Atlantic Ocean) data synthesis project is an international collaborative effort of the EU IP CARBOOCEAN, and US partners. It has...

  20. Theoretical lower limits on sizes of ultra faint dwarf galaxies from dynamical friction

    CERN Document Server

    Hernandez, X

    2016-01-01

    Dwarf spheroidal galaxies are the smallest known stellar systems where under Newtonian interpretations, a significant amount of dark matter is required to explain observed kinematics. In fact, they are in this sense the most heavily dark matter dominated objects known. That, plus the increasingly small sizes of the newly discovered ultra faint dwarfs, puts these systems in the regime where dynamical friction on individual stars starts to become relevant. We calculate the dynamical friction timescales for pressure supported isotropic spherical dark matter dominated stellar systems, yielding $\\tau_{DF} =0.93 (r_{h}/10 pc)^{2} (\\sigma/ kms^{-1}) Gyr$. For a stellar velocity dispersion value of $3 km/s$, as typical for the smallest of the recently detected ultra faint dwarf spheroidals, dynamical friction timescales becomes smaller than the $10 Gyr$ typical of the stellar ages for these systems, for half-light radii $r_{h}<19 pc$. Thus, this becomes a theoretical lower limit below which dark matter dominated s...

  1. Dwarf Elliptical Galaxies Structure, Star Formation, and Color-Magnitude Diagrams

    CERN Document Server

    Carraro, G; Girardi, L; Lia, C

    2001-01-01

    The aim of this paper is to cast light on the formation and evolution of elliptical galaxies by means of N-body/hydro-dynamical simulations that include star formation, feed-back and chemical evolution. Particular attention is paid to the case of dwarf spheroidals of the Local Group which, thanks to their proximity and modern ground-based and space instrumentation, can be resolved into single stars so that independent determinations of their age and star formation history can be derived. Dwarf galaxies are known to exhibit complicated histories of star formation ranging from a single very old episode to a series of bursts over most of the Hubble time. We start from virialized haloes of dark matter, and follow the infall of gas into the potential wells and the formation of stars. We find that in objects of the same total mass, different star formation histories are possible, if the collapse phase started at different initial densities. We predict the final structure of dwarf spheroidal galaxies, their kinemati...

  2. Axions and White Dwarfs

    CERN Document Server

    Isern, J; Garcia-Berro, E; Salaris, M; Torres, S

    2010-01-01

    White dwarfs are almost completely degenerate objects that cannot obtain energy from the thermonuclear sources and their evolution is just a gravothermal process of cooling. The simplicity of these objects, the fact that the physical inputs necessary to understand them are well identified, although not always well understood, and the impressive observational background about white dwarfs make them the most well studied Galactic population. These characteristics allow to use them as laboratories to test new ideas of physics. In this contribution we discuss the robustness of the method and its application to the axion case.

  3. Dwarf Galaxy Sized Monopoles as Dark Matter?

    CERN Document Server

    Evslin, Jarah

    2012-01-01

    We propose a model of dark matter: galaxy-sized 't Hooft-Polyakov magnetic monopoles in a new, extraordinarily weakly coupled SU(2) gauge sector with an adjoint Higgs field and two flavors of fundamental fermions. We fit the parameters by asserting that the dark matter halos of the lightest dwarf spheroidal (dSph) galaxies consist of a single charge Q=1 monopole. Lensing and wide binary bounds are then easily satisfied and the monopoles form in time to help with CMB fluctuations. In this model dSph and low surface brightness (LSB) halos automatically have (1) A minimum mass - Dirac quantization solves the missing satellite problem, (2) A constant density core (r

  4. R-process enrichment from a single event in an ancient dwarf galaxy.

    Science.gov (United States)

    Ji, Alexander P; Frebel, Anna; Chiti, Anirudh; Simon, Joshua D

    2016-03-31

    Elements heavier than zinc are synthesized through the rapid (r) and slow (s) neutron-capture processes. The main site of production of the r-process elements (such as europium) has been debated for nearly 60 years. Initial studies of trends in chemical abundances in old Milky Way halo stars suggested that these elements are produced continually, in sites such as core-collapse supernovae. But evidence from the local Universe favours the idea that r-process production occurs mainly during rare events, such as neutron star mergers. The appearance of a plateau of europium abundance in some dwarf spheroidal galaxies has been suggested as evidence for rare r-process enrichment in the early Universe, but only under the assumption that no gas accretes into those dwarf galaxies; gas accretion favours continual r-process enrichment in these systems. Furthermore, the universal r-process pattern has not been cleanly identified in dwarf spheroidals. The smaller, chemically simpler, and more ancient ultrafaint dwarf galaxies assembled shortly after the first stars formed, and are ideal systems with which to study nucleosynthesis events such as the r-process. Reticulum II is one such galaxy. The abundances of non-neutron-capture elements in this galaxy (and others like it) are similar to those in other old stars. Here, we report that seven of the nine brightest stars in Reticulum II, observed with high-resolution spectroscopy, show strong enhancements in heavy neutron-capture elements, with abundances that follow the universal r-process pattern beyond barium. The enhancement seen in this 'r-process galaxy' is two to three orders of magnitude higher than that detected in any other ultrafaint dwarf galaxy. This implies that a single, rare event produced the r-process material in Reticulum II. The r-process yield and event rate are incompatible with the source being ordinary core-collapse supernovae, but consistent with other possible sources, such as neutron star mergers.

  5. New insights into the nature of the peculiar star θ Carinae

    Science.gov (United States)

    Hubrig, S.; Briquet, M.; Morel, T.; Schöller, M.; González, J. F.; De Cat, P.

    2008-09-01

    Context: θ Carinae belongs to a group of peculiar early-type stars (OBN) with enhanced nitrogen and carbon deficiency. It is also known as a binary system, but it is not clear yet whether the chemical anomalies can be explained by mass transfer between the two components. On the basis of the previously reported spectral variability of a few metal lines it may be expected that θ Car possesses a weak magnetic field. Aims: A study of the physical nature of this hot massive binary which is furthermore a well-known blue straggler lying ~2 mag above the turnoff of the young open cluster IC 2602 is important to understand the origin of its strong chemical anomalies. Methods: We acquired high resolution spectroscopic and low resolution spectropolarimetric observations to achieve the following goals: a) to improve the orbital parameters to allow a more in-depth discussion on the possibility of mass transfer in the binary system; b) to carry out a non-local thermodynamic equilibrium (NLTE) abundance analysis; and c) to search for the presence of a magnetic field. Results: The study of the radial velocities using CORALIE spectra allowed us to significantly improve the orbital parameters. A comparative NLTE abundance analysis was undertaken for θ Car and two other early B-type stars with recently detected magnetic fields, τ Sco and ξ1 CMa. The analysis revealed significantly different abundance patterns: a one-order-of-magnitude nitrogen overabundance and carbon depletion was found in θ Car, while the oxygen abundance is roughly solar. For the stars ξ1 CMa and τ Sco the carbon abundance is solar and, while an N excess is also detected, it is of much smaller amplitude (0.4-0.6 dex). Such an N overabundance is typical of the values already found for other slowly-rotating (magnetic) B-type dwarfs. For θ Car, we attribute instead the chemical peculiarities to a past episode of mass transfer between the two binary components. The results of the search for a magnetic field

  6. Human Cardiac Progenitor Spheroids Exhibit Enhanced Engraftment Potential.

    Directory of Open Access Journals (Sweden)

    Francesca Oltolina

    Full Text Available A major obstacle to an effective myocardium stem cell therapy has always been the delivery and survival of implanted stem cells in the heart. Better engraftment can be achieved if cells are administered as cell aggregates, which maintain their extra-cellular matrix (ECM. We have generated spheroid aggregates in less than 24 h by seeding human cardiac progenitor cells (hCPCs onto methylcellulose hydrogel-coated microwells. Cells within spheroids maintained the expression of stemness/mesenchymal and ECM markers, growth factors and their cognate receptors, cardiac commitment factors, and metalloproteases, as detected by immunofluorescence, q-RT-PCR and immunoarray, and expressed a higher, but regulated, telomerase activity. Compared to cells in monolayers, 3D spheroids secreted also bFGF and showed MMP2 activity. When spheroids were seeded on culture plates, the cells quickly migrated, displaying an increased wound healing ability with or without pharmacological modulation, and reached confluence at a higher rate than cells from conventional monolayers. When spheroids were injected in the heart wall of healthy mice, some cells migrated from the spheroids, engrafted, and remained detectable for at least 1 week after transplantation, while, when the same amount of cells was injected as suspension, no cells were detectable three days after injection. Cells from spheroids displayed the same engraftment capability when they were injected in cardiotoxin-injured myocardium. Our study shows that spherical in vivo ready-to-implant scaffold-less aggregates of hCPCs able to engraft also in the hostile environment of an injured myocardium can be produced with an economic, easy and fast protocol.

  7. The sub-arcsecond dusty environment of Eta Carinae

    Science.gov (United States)

    Chesneau, O.; Min, M.; Herbst, T.; Waters, L. B. F. M.; Leinert, Ch.; Hillier, D. J.

    2005-09-01

    The core of the nebula surrounding Eta Carinae was observed with the VLT Adaptive Optics system NACO and with the interferometer VLTI/MIDI to spatially and spectrally isolate the warm dusty environment and the central object. Narrow-band images at 3.74 μm and 4.05 μm reveal a butterfly shaped dusty environment close to the central star with unprecedented spatial resolution. Fringes have been obtained in the Mid-IR and a correlated flux of about 100 Jy situated 0.3 arcsec south-east from the photocenter of the nebula at 8.7 μm is detected. This flux is partly attributed to the central object and provides an upper limit for the SED of the central source from 3.8 μm to 13.5 μm. We have been able to spectrally disperse the signal from the nebula itself at PA=318 degree, i.e. in the direction of the bipolar nebula (˜310°) within the MIDI field of view of 3 arcsec. A large amount of corundum (Al2O3) is discovered, peaking at 0.6-1.2 arcsec south-east from the star, whereas the dust content of the Weigelt blobs, in the equatorial plane, is dominated by silicates. We propose a geometry for the Butterfly nebulae assuming a similar axis for the large and little Homunculus. We suggest that the Butterfly nebulae is a consequence of the 1890 outburst and is embedded in the Little Homonculus its geometry is, mostly shaped by the local dust formation conditions which are directly affected by the latitudinal dependance of the ejection and the present wind. The dust is mostly formed in the bright rims of the Butterfly nebula. The dust condenses closer to the poles of the star owing to the larger mass-loss rate and the relative velocity between the stellar wind and the ejecta at these latitudes. In this geometry, the bright southern clump directly sees the southern pole of the central object. At intermediate latitudes, the mass-loss rate and the relative velocity of the wind are decreased and dust forms further out. We suggest that the survival and the large mass of the

  8. The no-spin zone: rotation vs dispersion support in observed and simulated dwarf galaxies

    CERN Document Server

    Wheeler, Coral; Bullock, James S; Boylan-Kolchin, Michael; Onorbe, Jose; Fitts, Alex; Hopkins, Philip F; Keres, Dusan

    2015-01-01

    We perform a systematic Bayesian analysis of rotation vs. dispersion support ($v_{\\rm rot} / \\sigma$) in $40$ dwarf galaxies throughout the Local Volume (LV) over a stellar mass range $10^{3.5} M_{\\rm \\odot} < M_{\\star} < 10^8 M_{\\rm \\odot}$. We find that the stars in $\\sim 90\\%$ of the LV dwarf galaxies studied -- both satellites and isolated systems -- are dispersion-supported. In particular, we show that $7/10$ *isolated* dwarfs in our sample have stellar populations with $v_{\\rm rot} / \\sigma < 0.6$. All have $v_{\\rm rot} / \\sigma \\lesssim 2$. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally-supported stellar disks, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion-supported stars. We see no clear trend between $v_{\\rm rot} / \\sigma$ and distance to the closest $\\rm L_{\\star}$ galaxy, nor between $v_{\\rm rot} / \\sigma$ and $M_{\\star}$ within our mass range. We apply the sam...

  9. A VLT/FORS2 spectroscopic survey of individual stars in a transforming dwarf galaxy

    CERN Document Server

    Battaglia, G; Rejkuba, M

    2016-01-01

    Understanding the properties of dwarf galaxies is important not only to put them in their proper cosmological context, but also to understand the formation and evolution of the most common type of galaxies. Dwarf galaxies are divided into two main classes, dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs), which differ from each other mainly because the former are gas-rich objects currently forming stars, while the latter are gas-deficient with no on-going star formation. Transition types (dT) are thought to represent dIs in the process of losing their gas, and can therefore shed light into the possible process of dwarf irregulars (dIrrs) becoming gas-deficient, passively evolving galaxies. Here we present preliminary results from our wide-area VLT/FORS2 MXU spectroscopic survey of the Phoenix dT, from which we obtained line-of-sight velocities and metallicities from the nIR Ca II triplet lines for a large sample of individual Red Giant Branch stars.

  10. Practical Rhumb Line Calculations on the Spheroid

    Science.gov (United States)

    Bennett, G. G.

    About ten years ago this author wrote the software for a suite of navigation programmes which was resident in a small hand-held computer. In the course of this work it became apparent that the standard text books of navigation were perpetuating a flawed method of calculating rhumb lines on the Earth considered as an oblate spheroid. On further investigation it became apparent that these incorrect methods were being used in programming a number of calculator/computers and satellite navigation receivers. Although the discrepancies were not large, it was disquieting to compare the results of the same rhumb line calculations from a number of such devices and find variations of some miles when the output was given, and therefore purported to be accurate, to a tenth of a mile in distance and/or a tenth of a minute of arc in position. The problem has been highlighted in the past and the references at the end of this show that a number of methods have been proposed for the amelioration of this problem. This paper summarizes formulae that the author recommends should be used for accurate solutions. Most of these may be found in standard geodetic text books, such as, but also provided are new formulae and schemes of solution which are suitable for use with computers or tables. The latter also take into account situations when a near-indeterminate solution may arise. Some examples are provided in an appendix which demonstrate the methods. The data for these problems do not refer to actual terrestrial situations but have been selected for illustrative purposes only. Practising ships' navigators will find the methods described in detail in this paper to be directly applicable to their work and also they should find ready acceptance because they are similar to current practice. In none of the references cited at the end of this paper has the practical task of calculating, using either a computer or tabular techniques, been addressed.

  11. The dynamics of Andromeda's dwarf galaxies and stellar streams

    CERN Document Server

    Collins, Michelle L M; Ibata, Rodrigo A; Martin, Nicolas F; Preston, Janet

    2016-01-01

    As part of the Z-PAndAS Keck II DEIMOS survey of resolved stars in our neighboring galaxy, Andromeda (M31), we have built up a unique data set of measured velocities and chemistries for thousands of stars in the Andromeda stellar halo, particularly probing its rich and complex substructure. In this contribution, we will discuss the structural, dynamical and chemical properties of Andromeda's dwarf spheroidal galaxies, and how there is no observational evidence for a difference in the evolutionary histories of those found on and off M31's vast plane of satellites. We will also discuss a possible extension to the most significant merger event in M31 - the Giant Southern Stream - and how we can use this feature to refine our understanding of M31's mass profile, and its complex evolution.

  12. The Horizontal Branch of the Sculptor Dwarf galaxy

    CERN Document Server

    Salaris, Maurizio; Tolstoy, Eline; Fiorentino, Giuliana; Cassisi, Santi

    2013-01-01

    We have performed the first detailed simulation of the horizontal branch of the Sculptor dwarf spheroidal galaxy by means of synthetic modelling techniques,taking consistently into account the star formation history and metallicity evolution as determined from the main sequence and red giant branch spectroscopic observations. The only free parameter in the whole analysis is the integrated mass loss of red giant branch stars. This is the first time that synthetic horizontal branch models, consistent with the complex star formation history of a galaxy, are calculated and matched to the observations. We find that the metallicity range covered by the star formation history, as constrained by observations, plus a simple mass loss law, enable us to cover both the full magnitude and colour range of HB stars. In addition the number count distribution along the observed horizontal branch, can be also reproduced, provided that the red giant branch mass loss is mildly metallicity dependent, with a very small dispersion ...

  13. Dark Matter in $\\gamma$ lines: Galactic Center vs dwarf galaxies

    CERN Document Server

    Lefranc, Valentin; Panci, Paolo; Sala, Filippo; Silk, Joseph

    2016-01-01

    We provide CTA sensitivities to Dark Matter (DM) annihilation in $\\gamma$-ray lines, from the observation of the Galactic Center (GC) as well as, for the first time, of dwarf Spheroidal galaxies (dSphs). We compare the GC reach with that of dSphs as a function of a putative core radius of the DM distribution, which is itself poorly known. We find that the currently best dSph candidates constitute a more promising target than the GC, for core radii of one to a few kpc. We use the most recent instrument response functions and background estimations by CTA, on top of which we add the diffuse photon component. Our analysis is of particular interest for TeV-scale electroweak multiplets as DM candidates, such as the supersymmetric Wino and the Minimal Dark Matter fiveplet, whose predictions we compare with our projected sensitivities.

  14. The distribution of alpha elements in Andromeda dwarf galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Vargas, Luis C.; Geha, Marla C.; Tollerud, Erik J., E-mail: luis.vargas@yale.edu [Department of Astronomy, Yale University, 260 Whitney Avenue, New Haven, CT 06511 (United States)

    2014-07-20

    We present alpha to iron abundance ratios for 226 individual red giant branch stars in nine dwarf galaxies of the Andromeda (M31) satellite system. The abundances are measured from the combined signal of Mg, Si, Ca, and Ti lines in Keck/DEIMOS medium-resolution spectra. This constitutes the first large sample of alpha abundance ratios measured in the M31 satellite system. The dwarf galaxies in our sample exhibit a variety of alpha abundance ratios, with the average values in each galaxy ranging from approximately solar ([α/Fe] ∼ + 0.0) to alpha-enhanced ([α/Fe] ∼ + 0.5). These variations do not show a correlation with internal kinematics, environment, or stellar density. We confirm radial gradients in the iron abundance of two galaxies out of the five with sufficient data (NGC 185 and And II). There is only tentative evidence for an alpha abundance radial gradient in NGC 185. We homogeneously compare our results to the Milky Way classical dwarf spheroidals, finding evidence for wider variation in average alpha abundance. In the absence of chemical abundances for the M31 stellar halo, we compare to the Milky Way stellar halo. A stellar halo comprised of disrupted M31 satellites is too metal-rich and inconsistent with the Milky Way halo alpha abundance distribution even if considering only satellites with predominantly old stellar populations. The M31 satellite population provides a second system in which to study chemical abundances of dwarf galaxies and reveals a wider variety of abundance patterns than the Milky Way.

  15. Outliers from the Mass--Metallicity Relation I: A Sample of Metal-Rich Dwarf Galaxies from SDSS

    CERN Document Server

    Peeples, Molly S; Stanek, K Z

    2008-01-01

    We have identified a sample of 41 low-mass high--oxygen abundance outliers from the mass--metallicity relation of star-forming galaxies measured by Tremonti et al (2004). These galaxies, which have 8.6 M_B > -19.1 and 7.4 < log M_*/M_solar < 10, are surprisingly non-pathological. They have typical specific star formation rates, they are fairly isolated and, with few exceptions, have no obvious companions. Morphologically, they are similar to dwarf spheroidal or dwarf elliptical galaxies. We predict that their observed high oxygen abundances are due to relatively low gas masses, concluding that these are transitional dwarf galaxies nearing the end of their star formation activity.

  16. Numerical Study of the Sedimentation of Spheroidal Particles

    CERN Document Server

    Ardekani, Mehdi Niazi; Breugem, Wim-Paul; Brandt, Luca

    2016-01-01

    The gravity-driven motion of rigid particles in a viscous fluid is relevant in many natural and industrial processes, yet this has mainly been investigated for spherical particles. We therefore consider the sedimentation of non-spherical (spheroidal) isolated and particle pairs in a viscous fluid via numerical simulations using the Immersed Boundary Method. The simulations performed here show that the critical Galileo number for the onset of secondary motions decreases as the spheroid aspect ratio departs from 1. Above this critical threshold, oblate particles perform a zigzagging motion whereas prolate particles rotate around the vertical axis while having their broad side facing the falling direction. Instabilities of the vortices in the wake follow when farther increasing the Galileo number. We also study the drafting-kissing-tumbling associated with the settling of particle pairs. We find that the interaction time increases significantly for non-spherical particles and, more interestingly, spheroidal part...

  17. Induction plasma spheroidization of tungsten and molybdenum powders

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The melting, evaporation and oxidation behaviors as well as the solidification phenomena of tungsten and molybdenum in induction plasma were studied. Scanning electron microscopy was used to examine the morphology and the cross section of plasma-processed powders. X-ray diffraction was used to analyze the oxides formed on the particle surface of these two metals. The influence of spray chamber pressure on the spheroidization and oxidation phenomena was discussed. The results show that fewer Mo particles than W particles are spheroidized at the same powder feed rate under the same plasma spray condition although molybdenum has a lower melting point. A small fraction of tungsten is evaporized and condensed either on the surface of tungsten particles nearby or on the wall of spray chamber. Tungsten oxides were found in tungsten powder processed under soft vacuum condition. Extremely large grains form inside some spheroidized particles of tungsten powder.

  18. Stokesian swimming of a prolate spheroid at low Reynolds number

    CERN Document Server

    Felderhof, B U

    2016-01-01

    The swimming of a spheroid immersed in a viscous fluid and performing surface deformations periodically in time is studied on the basis of Stokes equations of low Reynolds number hydrodynamics. The average over a period of time of the swimming velocity and the rate of dissipation are given by integral expressions of second order in the amplitude of surface deformations. The first order flow velocity and pressure, as functions of spheroidal coordinates, are expressed as sums of basic solutions of Stokes equations. Sets of superposition coefficients of these solutions which optimize the mean swimming speed for given power are derived from an eigenvalue problem. The maximum eigenvalue is a measure of the efficiency of the optimal stroke within the chosen class of motions. The maximum eigenvalue for sets of low order is found to be a strongly increasing function of the aspect ratio of the spheroid.

  19. Monoenergetic electron parameters in a spheroid bubble model

    Institute of Scientific and Technical Information of China (English)

    H.Sattarian; Sh.Rahmatallahpur; T.Tohidi

    2013-01-01

    A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived.The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal models and it explains the mono-energetic electron trajectory more accurately,especially at the relativistic region.The maximum energy of electrons is calculated and it is shown that the maximum energy of the spheroid model is less than that of the spherical model.The electron energy spectrum is also calculated and it is found that the energy distribution ratio of electrons △E/E for the spheroid model under the conditions reported here is half that of the spherical model and it is in good agreement with the experimental value in the same conditions.As a result,the quasi-mono-energetic electron output beam interacting with the laser plasma can be more appropriately described with this model.

  20. Cell proliferation kinetics and radiation response in 9L tumor spheroids

    Energy Technology Data Exchange (ETDEWEB)

    Sweigert, S.E.

    1984-05-01

    Cell kinetic parameters, including population doubling-time, cell cycle time, and growth fraction, were measured in 9L gliosarcoma spheroids. These parameters were studied as the spheroids grew from 50 ..mu..m to over 900 ..mu..m in diameter. Experiments relating the cell kinetic parameters to the radiation response of 9L spheroids were also carried out. The major findings were that the average cell cycle time (T/sub c/), is considerably longer in large spheroids than in exponentially-growing monolayers, the radiosensitivity of noncycling (but still viable) cells in spheroids is not significantly different from that of cycling spheroid cells, and the radiation-induced division delay is approximately twice as long in spheroid cells as in monolayer cells given equal radiation doses. The cell loss factor for spheroids of various sizes was calculated, by using the measured kinetic parameters in the basic equations for growth of a cell population. 157 references, 6 figures, 3 tables.

  1. Study of the Chemotactic Response of Multicellular Spheroids in a Microfluidic Device

    Science.gov (United States)

    Ayuso, Jose M.; Basheer, Haneen A.; Monge, Rosa; Sánchez-Álvarez, Pablo; Doblaré, Manuel; Shnyder, Steven D.; Vinader, Victoria; Afarinkia, Kamyar

    2015-01-01

    We report the first application of a microfluidic device to observe chemotactic migration in multicellular spheroids. A microfluidic device was designed comprising a central microchamber and two lateral channels through which reagents can be introduced. Multicellular spheroids were embedded in collagen and introduced to the microchamber. A gradient of fetal bovine serum (FBS) was established across the central chamber by addition of growth media containing serum into one of the lateral channels. We observe that spheroids of oral squamous carcinoma cells OSC–19 invade collectively in the direction of the gradient of FBS. This invasion is more directional and aggressive than that observed for individual cells in the same experimental setup. In contrast to spheroids of OSC–19, U87-MG multicellular spheroids migrate as individual cells. A study of the exposure of spheroids to the chemoattractant shows that the rate of diffusion into the spheroid is slow and thus, the chemoattractant wave engulfs the spheroid before diffusing through it. PMID:26444904

  2. The white dwarf luminosity function

    Science.gov (United States)

    García-Berro, Enrique; Oswalt, Terry D.

    2016-06-01

    White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for ∼ 10 Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling theory, although other relevant ingredients are needed to compare theory and observations. In this review we summarize the recent attempts to empirically determine the white dwarf luminosity function for the different Galactic populations. We also discuss the biases that may affect its interpretation. Finally, we elaborate on the theoretical ingredients needed to model the white dwarf luminosity function, paying special attention to the remaining uncertainties, and we comment on some applications of the white dwarf cooling theory. Astrophysical problems for which white dwarf stars may provide useful leverage in the near future are also discussed.

  3. M Dwarf Mysteries

    Science.gov (United States)

    Henry, Todd J.; Jao, Wei-Chun; Irwin, Jonathan; Dieterich, Sergio; Finch, Charlie T.; Riedel, Adric R.; Subasavage, John P.; Winters, Jennifer; RECONS Team

    2017-01-01

    During RECONS' 17-year (so far) astrometry/photometry program at the CTIO/SMARTS 0.9m, we have observed thousands of the ubiquitous red dwarfs in the solar neighborhood. During this reconnaissance, a few mysterious characters have emerged ...The Case of the Mercurial Stars: One M dwarf has been fading steadily for more than a decade, at last measure 6% fainter than when it was first observed. Another has grown brighter by 7% over 15 years. Are these brightness changes part of extremely long stellar cycles, or something else entirely?The Case of Identical Stellar Twins that Aren't: Two M dwarfs seem at first to be identical siblings traveling together through the Galaxy. They have virtually identical spectra at optical wavelengths and identical colors throughout the VRIJHK bands. Long-term astrometry indicates that they are, indeed, at the same distance via parallax measurements, and their proper motions match precisely. Yet, one of the twins is FOUR times brighter than the other. Followup work has revealed that the brighter component is a very close spectroscopic double, but no other stars are seen. So, the mystery may be half solved, but why do the close stars remain twice as bright as their widely-separated twin?The Case of the Great Kaboom!: After more than 1000 nights of observing on the reliable 0.9m telescope, with generally routine frames reading out upon the screen, one stellar system comprised of five red dwarfs flared in stunning fashion. Of the two distinct sources, the fainter one (an unresolved double) surpassed the brightness of the brighter one (an unresolved triple), increasing by more than three full magnitudes in the V filter. Which component actually flared? Is this magnificent outburst an unusual event, or in fact typical for this system and other M dwarfs?At the AAS meeting, we hope to probe the cognoscenti who study the Sun's smaller cousins to solve these intriguing M Dwarf Mysteries.This effort has been supported by the NSF through grants

  4. Investigating Cepheid $\\ell$ Carinae's Cycle-to-cycle Variations via Contemporaneous Velocimetry and Interferometry

    CERN Document Server

    Anderson, R I; Kervella, P; Breitfelder, J; LeBouquin, J -B; Eyer, L; Gallenne, A; Palaversa, L; Semaan, T; Saesen, S; Mowlavi, N

    2015-01-01

    Baade-Wesselink-type (BW) techniques enable geometric distance measurements of Cepheid variable stars in the Galaxy and the Magellanic clouds. The leading uncertainties involved concern projection factors required to translate observed radial velocities (RVs) to pulsational velocities and recently discovered modulated variability. We carried out an unprecedented observational campaign involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy (Euler/Coralie) to search for modulated variability in the long-period (P $\\sim$ 35.5 d) Cepheid Carinae. We determine highly precise angular diameters from squared visibilities and investigate possible differences between two consecutive maximal diameters, $\\Delta_{\\rm{max}} \\Theta$. We characterize the modulated variability along the line-of-sight using 360 high-precision RVs. Here we report tentative evidence for modulated angular variability and confirm cycle-to-cycle differences of $\\ell$ Carinae's RV variability. Two successive maxima yield $\\Delta_{\\rm...

  5. The Abundance of Iron-Peak Elements and the Dust Composition in eta Carinae: Manganese

    Science.gov (United States)

    Bautista, M. A.; Melendez, M.; Hartman, H.; Gull, T. R.; Lodders, K.

    2010-01-01

    We study the chemical abundances of the Strontium Filament found in the ejecta of (eta) Carinae. In particular, we derive the abundances of iron-peak elements front spectra of their singly ionized ions present in the optical/IR spectra. In this paper we analyze the spectrum of Mn II using a new non-LTE model for this system. In constructing this models we carried out theoretical calculations of radiative transition rates and electron impact excitation rate coefficients. We find that relative to Ni the gas phase abundance ratio of Mn is roughly solar, similar to the Cr abundance but in contrast to the large enhancements in the abundances of Sc and Ti. NVe interpret this result as an indication of non-equilibrium condensation in the ejecta of (eta) Carinae.

  6. The Dark and Luminous Matter coupling in the formation of spheroids a SPH investigation

    CERN Document Server

    Lia, C; Salucci, P; Lia, Cesario; Carraro, Giovanni; Salucci, Paolo

    2000-01-01

    Using N-body/hydrodynamical simulations which include prescriptions for Star Formation, Feed-Back and Chemical Evolution, we explore the interaction between baryons and Dark Matter at galactic scale. The N-body simulations are performed using a Tree-SPH code that follows the evolution of individual DM halos inside which stars form from cooling gas, and evolve delivering in the interstellar medium mass, metals, and energy. We examine the formation and evolution of a giant and a dwarf elliptical galaxy of total mass 10^12 and 10^9 solar masses, respectively. Starting from an initial density profile like the universal Navarro profile in the inner region, baryons sink towards the center due to cooling energy losses. At the end of the collapse, the innermost part (1/20 of the halo size) of the galaxy is baryon-dominated, whereas the outer regions are DM dominated. The Star Formation proceeds at much faster speed in the giant galaxy where a spheroid of 8 \\times 10^10 solar masses is formed in 2 Gyr, with respect to...

  7. A 205 μm [N II] Map of the Carina Nebula

    Science.gov (United States)

    Oberst, T. E.; Parshley, S. C.; Nikola, T.; Stacey, G. J.; Löhr, A.; Lane, A. P.; Stark, A. A.; Kamenetzky, J.

    2011-10-01

    We present the results of a ~250 arcmin2 mapping of the 205 μm [N II] fine-structure emission over the northern Carina Nebula, including the Car I and Car II H II regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. We supplement the 205 μm data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) in 63 μm [O I], 122 μm [N II], 146 μm [O I], and 158 μm [C II]; the 146 μm [O I] data include 90 raster positions which have not been previously published. Morphological comparisons are made with optical, radio continuum, and CO maps. The 122/205 line ratio is used to probe the density of the low-ionization gas, and the 158/205 line ratio is used to probe the fraction of C+ arising from photodissociation regions (PDRs). The [O I] and [C II] lines are used to construct a PDR model of Carina. When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than galactic star-forming regions such as Orion, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ground-based detection of the 205 μm [N II] line, and the third detection overall since those of COBE FIRAS and the Kuiper Airborne Observatory in the early 1990s.

  8. The white dwarf luminosity function

    CERN Document Server

    García-Berro, Enrique

    2016-01-01

    White dwarfs are the final remnants of low- and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for $\\sim 10$ Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling theory, although other...

  9. Was the nineteenth century giant eruption of Eta Carinae a merger event in a triple system?

    CERN Document Server

    Zwart, Simon Portegies

    2015-01-01

    We discuss the events that led to the giant eruption of Eta Carinae, and find that the mid-nineteenth century (in 1838-1843) giant mass-loss outburst has the characteristics of being produced by the merger event of a massive close binary, triggered by the gravitational interaction with a massive third companion star, which is the current binary companion in the Eta Carinae system. We come to this conclusion by a combination of theoretical arguments supported by computer simulations using the Astrophysical Multipurpose Software Environment. According to this model the $\\sim 90$\\,\\MSun\\, present primary star of the highly eccentric Eta Carinae binary system is the product of this merger, and its $\\sim 30$\\,\\MSun\\, companion originally was the third star in the system. In our model the Homunculus nebula was produced by an extremely enhanced stellar wind, energized by tidal energy dissipation prior to the merger, which enormously boosted the radiation-driven wind mass-loss. The current orbital plane is then align...

  10. Carina® and Esteem®: a systematic review of fully implantable hearing devices.

    Directory of Open Access Journals (Sweden)

    Janaina Oliveira Bentivi Pulcherio

    Full Text Available To review the outcomes of the fully implantable middle ear devices Carina and Esteem regarding the treatment of hearing loss.PubMed, Embase, Scielo, and Cochrane Library databases were searched.Abstracts of 77 citations were screened, and 43 articles were selected for full review. From those, 22 studies and two literature reviews in English directly demonstrating the results of Carina and Esteem were included.There were a total of 244 patients ranging from 18 to 88 years. One hundred and 10 patients were implanted with Carina and with 134 Esteem. There were registered 92 males and 67 females. Five studies provided no information about patients' age or gender. From the data available, the follow-up ranged from 2 to 29.4 months.The comparison of the results about word recognition is difficult as there was no standardization of measurement. The results were obtained from various sound intensities and different frequencies. The outcomes comparing to conventional HAs were conflicting. Nevertheless, all results comparing to unaided condition showed improvement and showed a subjective improvement of quality of life.There are still some problems to be solved, mainly related to device functioning and price. Due to the relatively few publications available and small sample sizes, we must be careful in extrapolating these results to a broader population. Additionally, none of all these studies represented level high levels of evidence (i.e. randomized controlled trials.

  11. XMM-Newton Observations of the 2003 X-ray Minimum of Eta Carinae

    CERN Document Server

    Hamaguchi, K; Gull, T R; White, N E; Damineli, A; Davidson, K

    2004-01-01

    The XMM-Newton X-ray observatory took part in the multi-wavelength observing campaign of the massive, evolved star Eta Carinae in 2003 during its recent X-ray minimum. This paper reports on the results of these observations, mainly from the aspect of spectral change. Hard X-ray emission from the point source of Eta Carinae was detected even during the minimum. During the minimum the observed flux above 3 keV was ~3e-12 ergs cm-2 s-1, which is about one percent of the flux before the minimum. Changes in the spectral shape revealed two X-ray emission components in the central point source. One component is non-variable and has relatively cool plasma of kT~1 keV and moderate absorption, NH~5e22 cm-2. The plasma is probably located far from the star, possibly produced by the high speed polar wind from Eta Carinae. The other high temperature component has kT~5 keV and is strongly variable. This component shows an increase in the apparent column density from 5e22 cm-2 to 2e23 cm-2, probably originating near the hea...

  12. Stellar populations in the Carina region: The Galactic plane at l = 291

    CERN Document Server

    Molina-Lera, J A; Gamen, R; Costa, E; Carraro, G

    2016-01-01

    Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. In many cases, these studies only concentrated on the central region or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. The aim of this work is to study in detail an area of the Galactic plane in Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of YSOs and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. We obtained photometric data for six young open clusters located in Carina at l = 291, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional infor...

  13. A critical reassessment of particle Dark Matter limits from dwarf satellites

    CERN Document Server

    Ullio, Piero

    2016-01-01

    Dwarf satellite galaxies are ideal laboratories for identifying particle Dark Matter signals. When advocating limits on particle Dark Matter properties from null searches, it becomes however crucial the level at which the Dark Matter density profile within these systems is constrained by observations. In the limit in which the spherical Jeans equation is assumed to be valid for a given tracer stellar population, we study the solution of this equation having the Dark Matter mass profile as an output rather than as a trial parametric input. Within our new formulation, we address to what level dwarf spheroidal galaxies feature a reliable mass estimator. We assess then possible extrapolation of the density profiles in the inner regions and -- keeping explicit the dependence on the orbital anisotropy profile of the tracer population -- we derive general trends on the line-of-sight integral of the density profile squared, a quantity commonly dubbed $J$-factor and crucial to estimate fluxes from prompt Dark Matter p...

  14. Searching for Brown Dwarf Outflows

    CERN Document Server

    Whelan, E T; Bacciotti, F; Randich, S; Natta, A

    2009-01-01

    As outflow activity in low mass protostars is strongly connected to ac- cretion it is reasonable to expect accreting brown dwarfs to also be driving out- flows. In the last three years we have searched for brown dwarf outflows using high quality optical spectra obtained with UVES on the VLT and the technique of spectro-astrometry. To date five brown dwarf outflows have been discovered. Here the method is discussed and the results to date outlined.

  15. Dwarf Dark Matter Halos

    CERN Document Server

    Colin, Pierre; Valenzuela, O; Gottlöber, S

    2003-01-01

    We use N-body simulations to study properties of dwarf halos with virial masses in the range 10^7-10^9 Msun/h. Unlike recent reported results, we find that the density profiles of relaxed dwarf halos are well fitted by the NFW profile and do not have cores. We estimate the distribution of concentrations for halos in mass range that covers six orders of magnitude from 10^7 Msun/h to 10^13 Msun/h, and find that the data are well reproduced by the model of Bullock et al. (2001). We predict that present-day isolated dwarf halos should have a very large median concentration of ~ 35. For halos with masses that range from 4.6 x 10^9 Msun/h to 10^13 Msun/h we measure the subhalo circular velocity function and find that they are similar when normalized to the circular velocity of the parent halo. We compute the halo mass function and the halo spin parameter distribution and find that the former is very well reproduced by the Sheth and Tormen model while the latter is well fitted by a lognormal distribution with lambda...

  16. Analytical Equation for Estimating Terminal Velocities of Spheroidal Particles

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, Douglas W.

    2007-06-01

    An analytical method for estimating the terminal velocities of spheroidal particles in a fluid medium has been derived form a graphical approach proposed by Haider and Levenspiel. Using an analytical equation enables the researcher to calculate the terminal velocities without resorting to graphical interpolations, thereby reducing errors and enabling terminal velocities to be estimated in automated calculations.

  17. The Birth of Open Separation on a Prolate Spheroid

    Science.gov (United States)

    1988-09-01

    Vollmers (1983), and Costis, Polen , Hoang and Telionis (1988), will agree in detail with the solu- tions of the model problem but the latter allows the...7, pp. 435-454. Costis, C.E., Polen , D.M. Hoang, N.T. and Telionis, D.P. 1988 Laminar Separating Flow Over a Prolate Spheroid. To be published in J

  18. Axisymmetric acoustic scattering from submerged prolate spheroidal shells

    Science.gov (United States)

    Boisvert, Jeffrey E.; Hayek, Sabih I.

    2005-09-01

    The equations of motion for nonaxisymmetric vibration of prolate spheroidal shells of constant thickness were derived using Hamilton's principle [S. I. Hayek and J. E. Boisvert, J. Acoust. Soc. Am. 114, 2799-2811 (2003)]. The shell theory used in this derivation includes shear deformations and rotatory inertias. The shell displacements and rotations were expanded in infinite series of comparison functions. These include associated Legendre functions in terms of the prolate spheroidal angular coordinate and circular functions in the azimuthal angle coordinate. The shell is insonified by a plane wave incident along the major axis. The external (heavy) fluid loading impedance was computed using an eigenfunction expansion of prolate spheroidal wavefunctions. Far-field scattered acoustic pressure spectra are presented for several shell thickness-to-half-length ratios ranging from 0.005 to 0.1, and for various shape parameters, a, ranging from an elongated spheroidal shell (a=1.01) to a spherical shell (a~100). The far-field directivity of acoustic scattering is presented at selected frequencies. [Work supported by the ONR/ASEE Summer Faculty Research Program.

  19. Building blocks of the Milky Way's accreted spheroid

    NARCIS (Netherlands)

    van Oirschot, Pim; Starkenburg, Else; Helmi, Amina; Nelemans, Gijs

    2017-01-01

    In the $\\Lambda$CDM model of structure formation, a stellar spheroid grows by the assembly of smaller galaxies, the so-called building blocks. Combining the Munich-Groningen semi-analytical model of galaxy formation with the high resolution Aquarius simulations of dark matter haloes, we study the as

  20. Stellar populations in the Carina region. The Galactic plane at l = 291°

    Science.gov (United States)

    Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

    2016-08-01

    Context. Previous studies of the Carina region have revealed its complexity and richness as well as a significant number of early-type stars. However, in many cases, these studies only concentrated on the central region (Trumpler 14/16) or were not homogeneous. This latter aspect, in particular, is crucial because very different ages and distances for key clusters have been claimed in recent years. Aims: The aim of this work is to study in detail an area of the Galactic plane in Carina, eastward η Carina. We analyze the properties of different stellar populations and focus on a sample of open clusters and their population of young stellar objects and highly reddened early stars. We also studied the stellar mass distribution in these clusters and the possible scenario of their formation. Finally, we outline the Galactic spiral structure in this direction. Methods: We obtained deep and homogeneous photometric data (UBVIKC) for six young open clusters: NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11, and 12, located in Carina at l ~ 291°, and their adjacent stellar fields, which we complemented with spectroscopic observations of a few selected targets. We also culled additional information from the literature, which includes stellar spectral classifications and near-infrared photometry from 2MASS. We finally developed a numerical code that allowed us to perform a homogeneous and systematic analysis of the data. Our results provide more reliable estimates of distances, color excesses, masses, and ages of the stellar populations in this direction. Results: We estimate the basic parameters of the studied clusters and find that they identify two overdensities of young stellar populations located at about 1.8 kpc and 2.8 kpc, with EB - V ~ 0.1 - 0.6. We find evidence of pre-main-sequence populations inside them, with an apparent coeval stellar formation in the most conspicuous clusters. We also discuss apparent age and distance gradients in the direction NW-SE. We study the

  1. Estimation of scattering from a moist rough surface with spheroidal dust particles

    Indian Academy of Sciences (India)

    Mukesh Kumar

    2009-08-01

    The scattering from moisture rough surface with spheroidal dust particles having surface with spheroidal dust particles has recently received much attention. In part due to the recent prediction and observation of the spheroidal dust particles in rough surfaces under elastic wave by the Kirchhoff scattering model and scalar approximation with slope. Our analysis shows that the scattering depends on the moisture (2–4.5%) with spheroidal dust particles. At slightly moisture rough surface the dielectric properties increase with change in field amplitude in a rough surface with spheroidal dust particles.

  2. Reproducibility of Uniform Spheroid Formation in 384-Well Plates: The Effect of Medium Evaporation.

    Science.gov (United States)

    Das, Viswanath; Fürst, Tomáš; Gurská, Soňa; Džubák, Petr; Hajdúch, Marián

    2016-10-01

    Spheroid cultures of cancer cells reproduce the spatial dimension-induced in vivo tumor traits more effectively than the conventional two-dimensional cell cultures. With growing interest in spheroids for high-throughput screening (HTS) assays, there is an increasing demand for cost-effective miniaturization of reproducible spheroids in microtiter plates (MPs). However, well-to-well variability in spheroid size, shape, and growth is a frequently encountered problem with almost every culture method that has prevented the transfer of spheroids to the HTS platform. This variability partly arises due to increased susceptibility of MPs to edge effects and evaporation-induced changes in the growth of spheroids. In this study, we examined the effect of evaporation on the reproducibility of spheroids of tumor and nontumor cell lines in 384-well plates, and show that culture conditions that prevent evaporation-induced medium loss result in the formation of uniform spheroids across the plate. Additionally, we also present a few technical improvements to increase the scalability of the liquid-overlay spheroid culturing technique in MPs, together with a simple software routine for the quantification of spheroid size. We believe that these cost-effective improvements will aid in further improvement of spheroid cultures for HTS drug discovery.

  3. Automated, Multiplexed Electrical Impedance Spectroscopy Platform for Continuous Monitoring of Microtissue Spheroids.

    Science.gov (United States)

    Bürgel, Sebastian C; Diener, Laurin; Frey, Olivier; Kim, Jin-Young; Hierlemann, Andreas

    2016-11-15

    Microtissue spheroids in microfluidic devices are increasingly used to establish novel in vitro organ models of the human body. As the spheroids are comparably sizable, it is difficult to monitor larger numbers of them by optical means. Therefore, electrical impedance spectroscopy (EIS) emerges as a viable alternative to probing spheroid properties. Current spheroid EIS systems are, however, not suitable for investigating multiple spheroids in parallel over extended time in an automated fashion. Here we address this issue by presenting an automated, multiplexed EIS (AMEIS) platform for impedance analysis in a microfluidic setting. The system was used to continuously monitor the effect of the anticancer drug fluorouracil (5-FU) on HCT116 cancer spheroids. Simultaneous EIS monitoring of up to 15 spheroids was performed in parallel over 4 days at a temporal resolution of 2 min without any need for pumps. The measurements were continuous in nature, and the setup was kept in a standard incubator under controlled conditions during the measurements. A baseline normalization method to improve robustness and to reduce the influence of slow changes in the medium conductivity on the spheroid EIS readings has been developed and validated by experiments and means of a finite-element model. The same method and platform was then used for online monitoring of cardiac spheroids. The beating frequency of each cardiac spheroid could be read out in a completely automated fashion. The developed system constitutes a promising method for simultaneously evaluating drug impact and/or toxic effects on multiple microtissue spheroids.

  4. Star formation history and evolution of gas-rich dwarf galaxies in the Centaurus A group

    CERN Document Server

    Grossi, M; Pritzl, B J; Knezek, P M; Gallagher, J S; Minchin, R F; Freeman, K C

    2006-01-01

    We analyse the properties of three unusual dwarf galaxies in the Centaurus A group discovered with the HIPASS survey. From their optical morphology they appear to be low surface brightness dwarf spheroidals, yet they are gas-rich (M_{HI}/L_{B} > 1) with gas-mass-to-stellar light ratios larger than typical dwarf irregular galaxies. Therefore these systems appear different from any dwarfs of the Local Group. They should be favoured hosts for starburst, whereas we find a faint star formation region in only one object. We have obtained 21-cm data and Hubble Space Telescope photometry in V and I bands, and have constructed Colour Magnitude Diagrams (CMDs) to investigate their stellar populations and to set a constraint on their age. From the comparison of the observed and model CMDs we infer that all three galaxies are at least older than 2 Gyr (possibly even as old as 10 Gyr) and remain gas-rich because their star formation rates (SFRs) have been very low (< 10^{-3} M_{sun}/yr) throughout. In such systems, sta...

  5. Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows.

    Science.gov (United States)

    Governato, F; Brook, C; Mayer, L; Brooks, A; Rhee, G; Wadsley, J; Jonsson, P; Willman, B; Stinson, G; Quinn, T; Madau, P

    2010-01-14

    For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.

  6. COMPARING THE OBSERVABLE PROPERTIES OF DWARF GALAXIES ON AND OFF THE ANDROMEDA PLANE

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Michelle L. M.; Martin, Nicolas F. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Rich, R. M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); Ibata, Rodrigo A. [Observatoire de Strasbourg, 11, Rue de l' Université, F-67000 Strasbourg (France); Chapman, Scott C. [Department of Physics and Atmospheric Science, Dalhousie University, Coburg Road, Halifax B3H1A6 (Canada); McConnachie, Alan W. [NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, British Columbia, Victoria V9E 2E7 (Canada); Ferguson, Annette M. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Irwin, Michael J. [Institute of Astronomy, Madingley Rise, Cambridge CB3 0HA (United Kingdom); Lewis, Geraint F., E-mail: michelle.collins@yale.edu [Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006 (Australia)

    2015-01-20

    The thin, extended planes of satellite galaxies detected around both the Milky Way and Andromeda are not a natural prediction of the Λ-cold dark matter paradigm. Galaxies in these distinct planes may have formed and evolved in a different way (e.g., tidally) from their off-plane neighbors. If this were the case, one would expect the on- and off-plane dwarf galaxies in Andromeda to have experienced different evolutionary histories, which should be reflected by the chemistries, dynamics, and star formation histories of the two populations. In this work, we present new, robust kinematic observations for two on-plane M31 dwarf spheroidal galaxies (And XVI and XVII) and compile and compare all available observational metrics for the on- and off-plane dwarfs to search for a signal that would corroborate such a hypothesis. We find that, barring their spatial alignment, the on- and off-plane Andromeda dwarf galaxies are indistinguishable from one another, arguing against vastly different formative and evolutionary histories for these two populations.

  7. Axion cooling of white dwarfs

    CERN Document Server

    Isern, J; Garcia--Berro, E; Salaris, M; Torres, S

    2013-01-01

    The evolution of white dwarfs is a simple gravothermal process. This process can be tested in two ways, through the luminosity function of these stars and through the secular variation of the period of pulsation of those stars that are variable. Here we show how the mass of the axion can be constrained using the white dwarf luminosity function.

  8. Dynamical mass modeling of dispersion-supported dwarf galaxies

    Science.gov (United States)

    Wolf, Joseph

    The currently favored cold dark matter cosmology (LCDM) has had much success in reproducing the large scale structure of the universe. However, on smaller scales there are some possible discrepancies when attempting to match galactic observations with properties of halos in dissipationless LCDM simulations. One advantageous method to test small scale simulations with observations is through dynamical mass modeling of nearby dwarf spheroidal galaxies (dSphs). The stellar tracers of dSphs are dispersion-supported, which poses a significant challenge in accurately deriving mass profiles. Unlike rotationally-supported galaxies, the dynamics of which can be well-approximated by one-dimensional physics, modeling dispersion-supported systems given only line-of-sight data results in a well-known degeneracy between the mass profile and the velocity dispersion anisotropy. The core of this dissertation is rooted in a new advancement which we have discovered: the range of solutions allowed by the mass-anisotropy degeneracy varies as a function of radius, with a considerable minimal near the deprojected half-light radius of almost all observed dispersion-supported galaxies. This finding allows for a wide range of applications in galaxy formation scenarios to be explored in an attempt to address, amongst other hypotheses, whether the LCDM framework needs to be modified in order to reproduce observations on the small scale. This thesis is comprised of both the derivation of this finding, and its applicability to all dispersion-supported systems, ranging from dwarfs galaxies consisting of a few hundred stars to systems of 'intracluster light', containing over a trillion stars. Rarely does one have the privilege of working with systems that span such a large range in luminosity (or any intrinsic property) in a short graduate career. Although the large applicability of this scale-free finding allows for discussion in many subfields, this thesis will mainly focus on one topic: dwarf

  9. Cool carbon stars in the halo and in dwarf galaxies: Halpha, colours, and variabiity

    CERN Document Server

    Mauron, Nicolas; Berlioz-Arthaud, Paul; Klotz, Alain

    2013-01-01

    The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Halpha in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution ...

  10. Lack of nuclear clusters in dwarf sferoidal galaxies: implications for massive black holes formation and the cusp/core problem

    CERN Document Server

    Arca-Sedda, Manuel

    2016-01-01

    One of the leading scenarios for the formation of nuclear star clusters in galaxies is related to the orbital decay of globular clusters (GCs) and their subsequent merging, though alternative theories are currently debated. The availability of high-quality data for GCs structural and orbital parameters allow to test different nuclear star cluster formation scenarios. The Fornax dwarf spheroidal (dSph) galaxy is the heaviest satellite of the Milky Way and it is the only known dwarf spheroidal hosting 5 GCs, whereas there are no clear signatures for the presence of a central massive black hole. For this reason, it represents a suited place to study the orbital decay process in dwarf galaxies. In this paper we model the future evolution of the Fornax GCs simulating them and the host galaxy by means of direct $N$-body simulations. Our simulations take in account also the gravitational field generated by the Milky Way. We found that if the Fornax galaxy is embedded in a standard Cold Dark Matter Halo, the nuclear ...

  11. Stellar populations in dwarf galaxies: A review of the contribution of HST to our understanding of the nearby universe

    Science.gov (United States)

    Tolstoy, Eline

    This review aims to give an overview of the contribution of the Hubble Space Telescope to our understanding of the detailed properties of Local Group dwarf galaxies and their older stellar populations. The exquisite stable high spatial resolution combined with photometric accuracy of images from the Hubble Space Telescope have allowed us to probe further back into the history of star formation of a large variety of different galaxy types with widely differing star formation properties. It has allowed us to extend our studies out to the edges of the Local Group and beyond with greater accuracy than ever before. We have learned several important things about dwarf galaxy evolution from these studies. Firstly we have found that no two galaxies have identical star formation histories; some galaxies may superficially look the same today, but they have invariably followed different paths to this point. Now that we have managed to probe deep into the star formation history of dwarf irregular galaxies in the Local Group it is obvious that there are a number of similarities with the global properties of dwarf elliptical/spheroidal type galaxies, which were previously thought to be quite distinct. The elliptical/spheroidals tend to have one or more discrete episodes of star formation through-out their history and dwarf irregulars are characterized by quasi-continuous star-formation. The previous strong dichotomy between these two classes has been weakened by these new results and may stem from the differences in the environment in which these similar mass galaxies were born into or have inhabited for most of their lives. The more detailed is our understanding of star formation processes and their effect on galaxy evolution in the nearby Universe the better we will understand the results from studies of the integrated light of galaxies in the high-redshift Universe.

  12. Alfalfa discovery of the nearby gas-rich dwarf galaxy Leo P. IV. Distance measurement from LBT optical imaging

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Berg, Danielle [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street, S.E., University of Minnesota, Minneapolis, MN 55455 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Salzer, John J.; Rhode, Katherine L. [Department of Astronomy, Indiana University, 727 East 3rd Street, Bloomington, IN 47405 (United States); Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P. [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Dolphin, Andrew, E-mail: kmcquinn@astro.umn.edu, E-mail: skillman@astro.umn.edu, E-mail: berg@astro.umn.edu, E-mail: jcannon@macalester.edu, E-mail: rhode@astro.indiana.edu, E-mail: slaz@astro.indiana.edu, E-mail: betsey@astro.cornell.edu, E-mail: riccardo@astro.cornell.edu, E-mail: haynes@astro.cornell.edu [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States)

    2013-12-01

    Leo P is a low-luminosity dwarf galaxy discovered through the blind H I Arecibo Legacy Fast ALFA survey. The H I and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with both active star formation and an underlying older population, as well as an extremely low oxygen abundance. Here, we measure the distance to Leo P by applying the tip of the red giant branch (TRGB) distance method to photometry of the resolved stellar population from new Large Binocular Telescope V and I band imaging. We measure a distance modulus of 26.19{sub −0.50}{sup +0.17} mag corresponding to a distance of 1.72{sub −0.40}{sup +0.14} Mpc. Although our photometry reaches 3 mag below the TRGB, the sparseness of the red giant branch yields higher uncertainties on the lower limit of the distance. Leo P is outside the Local Group with a distance and velocity consistent with the local Hubble flow. While located in a very low-density environment, Leo P lies within ∼0.5 Mpc of a loose association of dwarf galaxies which include NGC 3109, Antlia, Sextans A, and Sextans B, and 1.1 Mpc away from its next nearest neighbor, Leo A. Leo P is one of the lowest metallicity star-forming galaxies known in the nearby universe, comparable in metallicity to I Zw 18 and DDO 68, but with stellar characteristics similar to dwarf spheriodals (dSphs) in the Local Volume such as Carina, Sextans, and Leo II. Given its physical properties and isolation, Leo P may provide an evolutionary link between gas-rich dwarf irregular galaxies and dSphs that have fallen into a Local Group environment and been stripped of their gas.

  13. Binding and interstitial penetration of liposomes within avascular tumor spheroids.

    Science.gov (United States)

    Kostarelos, Kostas; Emfietzoglou, Dimitris; Papakostas, Alexandros; Yang, Wei-Hong; Ballangrud, Ase; Sgouros, George

    2004-11-20

    The liposomal delivery of cancer therapeutics, including gene therapy vectors, is an area of intense study. Poor penetration of liposomes into interstitial tumor spaces remains a problem, however. In this work, the penetration of different liposomal formulations into prostate carcinoma spheroids was examined. Spheroid penetration was assessed by confocal microscopy of fluorescently labeled liposomes. The impact of liposomal surface charge, mean diameter, lipid bilayer fluidity and fusogenicity on spheroid penetration was examined. A variety of different liposome systems relevant to clinical or preclinical protocols have been studied, including classical zwitterionic (DMPC:chol) and sterically stabilized liposomes (DMPC:chol:DOPE-PEG2000), both used clinically, and cationic liposomes (DMPC:DOPE:DC-chol and DOTAP), forming the basis of the vast majority of nonviral gene transfer vectors tested in various cancer trials. Surface interactions between strongly cationic vesicles and the tumor cells led to an electrostatically derived binding-site barrier effect, inhibiting further association of the delivery systems with the tumor spheroids (DMPC:DC-chol). However, inclusion of the fusogenic lipid DOPE and use of a cationic lipid of lower surface charge density (DOTAP instead of DC-chol) led to improvements in the observed intratumoral distribution characteristics. Sterically stabilized liposomes did not interact with the tumor spheroids, whereas small unilamellar classical liposomes exhibit extensive distribution deeper into the tumor volume. Engineering liposomal delivery systems with a relatively low charge molar ratio and enhanced fusogenicity, or electrostatically neutral liposomes with fluid bilayers, offered enhanced intratumoral penetration. This study shows that a delicate balance exists between the strong affinity of delivery systems for the tumor cells and the efficient penetration and distribution within the tumor mass, similar to previous work studying

  14. Habitability of planets around red dwarf stars.

    Science.gov (United States)

    Heath, M J; Doyle, L R; Joshi, M M; Haberle, R M

    1999-08-01

    Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible.

  15. Magnetized White Dwarfs

    CERN Document Server

    Terrero, D Alvear; Martínez, A Pérez

    2016-01-01

    The purpose of this thesis is to obtain more realistic equations of state to describe the matter forming magnetized white dwarfs, and use them to solve its structure equations. The equations of state are determined by considering the weak magnetic field approximation $Bdwarfs. Also, we consider the energy and pressure correction due to the Coulomb interaction of the electron gas with the ions located in a crystal lattice. Moreover, spherically symmetric Tolman-Oppenheimer-Volkoff structure equations are solved independently for the perpendicular and parallel pressures, confirming the necessity of using axisymmetric structure equations, more adequate to describe the anisotropic system. Therefore, we study the solutions in cylindrical coordinates. In this case, the mass per longitude unit is obtained instead of the total mass of the whit...

  16. Tethered spheroids as an in vitro hepatocyte model for drug safety screening.

    Science.gov (United States)

    Xia, Lei; Sakban, Rashidah Binte; Qu, Yinghua; Hong, Xin; Zhang, Wenxia; Nugraha, Bramasta; Tong, Wen Hao; Ananthanarayanan, Abhishek; Zheng, Baixue; Chau, Ian Yin-Yan; Jia, Ruirui; McMillian, Michael; Silva, Jose; Dallas, Shannon; Yu, Hanry

    2012-03-01

    Hepatocyte spheroids mimic many in vivo liver-tissue phenotypes but increase in size during extended culture which limits their application in drug testing applications. We have developed an improved hepatocyte 3D spheroid model, namely tethered spheroids, on RGD and galactose-conjugated membranes using an optimized hybrid ratio of the two bioactive ligands. Cells in the spheroid configuration maintained 3D morphology and uncompromised differentiated hepatocyte functions (urea and albumin production), while the spheroid bottom was firmly tethered to the substratum maintaining the spheroid size in multi-well plates. The oblate shape of the tethered spheroids, with an average height of 32 μm, ensured efficient nutrient, oxygen and drug access to all the cells within the spheroid structure. Cytochrome P450 induction by prototypical inducers was demonstrated in the tethered spheroids and was comparable or better than that observed with hepatocyte sandwich cultures. These data suggested that tethered 3D hepatocyte spheroids may be an excellent alternative to 2D hepatocyte culture models for drug safety applications.

  17. The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations

    CERN Document Server

    Weisz, Daniel R; Skillman, Evan D; Holtzman, Jon; Gilbert, Karoline M; Dalcanton, Julianne J; Williams, Benjamin F

    2014-01-01

    We present uniformly measured star formation histories (SFHs) of 40 Local Group dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with $\\tau$ $\\sim$ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs (dTrans), and dwarf ellipticals (dEs) can be approximated by the combination of an exponentially declining SFH ($\\tau$ $\\sim$ 3-4 Gyr) for lookback ages $>$ 10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z=2 ranges considerably (80\\%...

  18. PROPERTIES OF THE COOLEST DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    SAUMON, DIDIER [Los Alamos National Laboratory; LEGGETT, SANDY K. [NON LANL; FREEDMAN, RICHARD S. [NON LANL; GEBALLE, THOMAS R. [NON LANL; GOLIMOWSKI, DAVID A. [NON LANL; LODIEU, NICOLAS [NON LANL; MARLEY, MARK S. [NON LANL; STEPHENS, DENISE [NON LANL; PINFIELD, DAVID J. [NON LANL; WARREN, STEPHEN J. [NON LANL

    2007-01-18

    Eleven years after the discovery of the first T dwarf, we have a population of ultracool L and T dwarfs that is large enough to show a range of atmospheric properties, as well as model atmospheres advanced enough to study these properties in detail. Since the last Cool Stars meeting, there have been observational developments which aid in these studies. they present recent mid-infrared photometry and spectroscopy from the Spitzer Space Telescope which confirms the prevalence of vertical mixing in the atmospheres of L and T dwarfs. Hence, the 700 K to 2200 K L and t dwarf photspheres require a large number of parameters for successful modeling: effective temperature, gravity, metallicity, grain sedimentation and vertical mixing efficiency. They also describe initial results of a search for ultracool dwarfs in the UKIRT Infrared Deep Sky Survey, and present the latest T dwarf found to date. They conclude with a discussion of the definition of the later-than-T spectral type, the Y dwarf.

  19. Eutectic solidification mode of spheroidal graphite cast iron and graphitization

    Institute of Scientific and Technical Information of China (English)

    Hideo Nakae; Sanghoon Jung; Takayuki Kitazawa

    2007-01-01

    The shrinkage and chilling tendency of spheroidal graphite (abbreviated SG) east iron is much greater than that of the flake graphite cast iron in spite of its higher amount of C and Si contents. Why? The main reason should be the difference in their graphitization during the eutectic solidification. In this paper, we discuss the difference in the solidification mechanism of both cast irons for solving these problems using unidirectional solidification and the cooling curves of the spheroidal graphite cast iron. The eutectic solidification rate of the SG cast iron is controlled by the diffusion of carbon through the austenite shell, and the final thickness is 1.4 times the radius of the SG, therefore, the reduction of the SG size, namely, the increase in the number, is the main solution of these problems.

  20. A method of smoothed particle hydrodynamics using spheroidal kernels

    Science.gov (United States)

    Fulbright, Michael S.; Benz, Willy; Davies, Melvyn B.

    1995-01-01

    We present a new method of three-dimensional smoothed particle hydrodynamics (SPH) designed to model systems dominated by deformation along a preferential axis. These systems cause severe problems for SPH codes using spherical kernels, which are best suited for modeling systems which retain rough spherical symmetry. Our method allows the smoothing length in the direction of the deformation to evolve independently of the smoothing length in the perpendicular plane, resulting in a kernel with a spheroidal shape. As a result the spatial resolution in the direction of deformation is significantly improved. As a test case we present the one-dimensional homologous collapse of a zero-temperature, uniform-density cloud, which serves to demonstrate the advantages of spheroidal kernels. We also present new results on the problem of the tidal disruption of a star by a massive black hole.

  1. Plasma spheroidization of nickel powders in a plasma reactor

    Indian Academy of Sciences (India)

    G Shanmugavelayutham; V Selvarajan

    2004-10-01

    Thermal spray coatings of surfaces with metal, alloy and ceramic materials for protection against corrosion, erosion and wear is an intense field of research. The technique involves injection of the powder into a plasma flame, melting, acceleration of the powder particles, impact and bonding with the substrate. Feedstock powders of metals, alloys and ceramics for thermal spray applications have to meet several requirements. Particle shape, size and its distribution, powder flow characteristics and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. For smooth and uniform feeding of powders into plasma jet, the powder particles have to be spherical in shape. High temperatures and steep temperatures present in thermal plasma is exploited to spheroidize particles in the present investigation. Nickel powder particles in the size range from 40–100 m were spheroidized using plasma processing. SEM and optical micrographs showed spherical shape of processed particles.

  2. Mass transfer inside oblate spheroidal solids: modelling and simulation

    Directory of Open Access Journals (Sweden)

    J. E. F. Carmo

    2008-03-01

    Full Text Available A numerical solution of the unsteady diffusion equation describing mass transfer inside oblate spheroids, considering a constant diffusion coefficient and the convective boundary condition, is presented. The diffusion equation written in the oblate spheroidal coordinate system was used for a two-dimensional case. The finite-volume method was employed to discretize the basic equation. The linear equation set was solved iteratively using the Gauss-Seidel method. As applications, the effects of the Fourier number, the Biot number and the aspect ratio of the body on the drying rate and moisture content during the process are presented. To validate the methodology, results obtained in this work are compared with analytical results of the moisture content encountered in the literature and good agreement was obtained. The results show that the model is consistent and it may be used to solve cases such as those that include disks and spheres and/or those with variable properties with small modifications.

  3. PAndAS' Progeny: Extending the M31 Dwarf Galaxy Cabal

    Science.gov (United States)

    Richardson, Jenny C.; Irwin, Mike J.; McConnachie, Alan W.; Martin, Nicolas F.; Dotter, Aaron L.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Chapman, Scott C.; Lewis, Geraint F.; Tanvir, Nial R.; Rich, R. Michael

    2011-05-01

    We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were discovered during the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 subgroup conducted with the MegaPrime/MegaCam wide-field camera on the Canada-France-Hawaii Telescope. The current PAndAS survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ~150 kpc. Here we present for the first time the metal-poor stellar density map for this whole region, not only as an illustration of the discovery space for satellite galaxies, but also as a birds-eye view of the ongoing assembly process of an L * disk galaxy. Four of the newly discovered satellites appear as well-defined spatial overdensities of stars lying on the expected locus of metal-poor (-2.5 < [Fe/H] < -1.3) red giant branch stars at the distance of M31. The fifth overdensity, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. Based on distance estimates from horizontal branch magnitudes, all five have metallicities typical of dwarf spheroidal galaxies ranging from [Fe/H] =-1.7 ± 0.2 to [Fe/H] =-1.9 ± 0.2 and absolute magnitudes ranging from MV = -7.1 ± 0.5 to MV = -10.2 ± 0.5. These five additional satellites bring the number of dwarf spheroidal galaxies in this region to 25 and continue the trend whereby the brighter dwarf spheroidal satellites of M31 generally have much larger half-light radii than their Milky Way counterparts. With an extended sample of M31 satellite galaxies, we also revisit the spatial distribution of this population and in particular we find that, within the current projected limits of the PAndAS survey, the surface density of satellites is essentially constant out to 150 kpc. This corresponds to a radial density distribution of satellites varying as r -1, a result

  4. Assessing the internal consistency of the CARINA database in the Indian sector of the Southern Ocean

    Directory of Open Access Journals (Sweden)

    C. Lo Monaco

    2010-02-01

    Full Text Available Carbon and carbon-relevant hydrographic and hydrochemical ancillary data from previously not publicly available cruises were retrieved and recently merged to a new data base, CARINA (CARbon IN the Atlantic. The initial North Atlantic project, an international effort for ocean carbon synthesis, was extended to include the Arctic Mediterranean Seas (Arctic Ocean and Nordic Seas and all three sectors of the Southern Ocean. Of a total of 188 cruises, 37 cruises are part of the Southern Ocean. The present work focuses on data collected in the Indian sector (20° S–70° S; 30° E–150° E. The Southern Indian Ocean dataset covers the period 1992–2004 and includes seasonal repeated observations. Parameters including salinity, dissolved inorganic carbon (TCO2, total alkalinity (TA, oxygen, nitrate, phosphate and silicate were examined for cruise-to-cruise and overall consistency. In addition, data from an existing, quality controlled data base (GLODAP were introduced in the CARINA analysis to improve data coverage in the Southern Ocean. A global inversion was performed to synthesize the information deduced from objective comparisons of deep measurements (>1500 m at nearby stations (generally <220 km. The corrections suggested by the inversion were allowed to vary within a fixed envelope, thus accounting for ocean interior variability. The adjustments applied to CARINA data and those recommended for GLODAP data, in order to obtain a consistent merged dataset, are presented and discussed. The final outcome of this effort is a new quality controlled data base for TCO2 and other properties of the carbon system that can now be used to investigate the natural variability or stability of ocean chemistry and the accumulation of anthropogenic carbon. This data product also offers an important new synthesis of seasonal to decadal observations to validate ocean biogeochemical models in a region where available historical data were very

  5. Assessing the internal consistency of the CARINA database in the Indian sector of the Southern Ocean

    Science.gov (United States)

    Lo Monaco, C.; Álvarez, M.; Key, R. M.; Lin, X.; Tanhua, T.; Tilbrook, B.; Bakker, D. C. E.; van Heuven, S.; Hoppema, M.; Metzl, N.; Ríos, A. F.; Sabine, C. L.; Velo, A.

    2010-02-01

    Carbon and carbon-relevant hydrographic and hydrochemical ancillary data from previously not publicly available cruises were retrieved and recently merged to a new data base, CARINA (CARbon IN the Atlantic). The initial North Atlantic project, an international effort for ocean carbon synthesis, was extended to include the Arctic Mediterranean Seas (Arctic Ocean and Nordic Seas) and all three sectors of the Southern Ocean. Of a total of 188 cruises, 37 cruises are part of the Southern Ocean. The present work focuses on data collected in the Indian sector (20° S-70° S; 30° E-150° E). The Southern Indian Ocean dataset covers the period 1992-2004 and includes seasonal repeated observations. Parameters including salinity, dissolved inorganic carbon (TCO2), total alkalinity (TA), oxygen, nitrate, phosphate and silicate were examined for cruise-to-cruise and overall consistency. In addition, data from an existing, quality controlled data base (GLODAP) were introduced in the CARINA analysis to improve data coverage in the Southern Ocean. A global inversion was performed to synthesize the information deduced from objective comparisons of deep measurements (>1500 m) at nearby stations (generally accounting for ocean interior variability. The adjustments applied to CARINA data and those recommended for GLODAP data, in order to obtain a consistent merged dataset, are presented and discussed. The final outcome of this effort is a new quality controlled data base for TCO2 and other properties of the carbon system that can now be used to investigate the natural variability or stability of ocean chemistry and the accumulation of anthropogenic carbon. This data product also offers an important new synthesis of seasonal to decadal observations to validate ocean biogeochemical models in a region where available historical data were very sparse.

  6. Changes in the distance between carina and orotracheal tube during open or videolaparoscopic bariatric surgery

    Directory of Open Access Journals (Sweden)

    Giovani de Figueiredo Locks

    2015-10-01

    Full Text Available ABSTRACTOBJECTIVE: To examine whether there are changes in the distance between the orotracheal tube and carina induced by orthostatic retractor placement or by pneumoperitoneum insufflation in obese patients undergoing gastroplasty.METHODS: 60 patients undergoing bariatric surgery by two techniques: open (G1 or videolaparoscopic (G2 gastroplasty were studied. After tracheal intubation, adequate ventilation of both hemitoraxes was confirmed by lung auscultation. The distance orotracheal tube-carina was estimated with the use of a fiber bronchoscope before and after installation of orthostatic retractors in G1 or before and after insufflation of pneumoperitoneum in patients in G2.RESULTS: G1 was composed of 22 and G2 of 38 patients. No cases of endobronchial intubation were detected in either group. The mean orotracheal tube-carina distance variation was estimated in -0.03 cm (95% CI 0.06 to -0.13 in the group of patients undergoing open gastroplasty and in -0.42 cm (95% CI -0.56 to -1.4 in the group of patients undergoing videolaparoscopic gastroplasty. The extremes of variation in each group were: 0.5 cm to -1.6 cm in patients undergoing open surgery and 0.1 cm to -2.2 cm in patients undergoing videolaparoscopic surgery.CONCLUSIONS: There was no significant change in orotracheal tube-CA distance after placement of orthostatic retractors in patients undergoing open gastroplasty. There was a reduction in orotracheal tube-CA distance after insufflation of pneumoperitoneum in patients undergoing videolaparoscopic gastroplasty. We recommend attention to lung auscultation and to signals of ventilation monitoring and reevaluation of orotracheal tube placement after peritoneal insufflation.

  7. A New Benchmark Brown Dwarf

    CERN Document Server

    Tinney, C G; Forveille, T; Delfosse, Xavier

    1997-01-01

    We present optical spectroscopy of three brown dwarf candidates identified in the first 1% of the DENIS sky survey. Low resolution spectra from 6430--9000A show these objects to have similar spectra to the uncertain brown dwarf candidate GD 165B. High resolution spectroscopy shows that one of the objects -- DBD 1228-1547 -- has a strong EW=2.3+-0.05A absorption line of Li I 6708A, and is therefore a brown dwarf with mass below 0.065 Msol. DBD 1228-1547 can now be the considered proto-type for objects JUST below the hydrogen burning limit.

  8. Pluto and other dwarf planets

    CERN Document Server

    Saxena, Shalini

    2017-01-01

    The reclassification of Pluto in 2006 not only decreased the number of planets in our solar system by one but also introduced the new category of dwarf planet. Readers will come to understand what separates a dwarf planet from a planet-or for that matter from any of the other bodies found within the solar system. They'll learn about Pluto itself, as well as its fellow dwarf planets, Ceres, Makemake, Haumea, and Eris. Full of recent information, this title is sure to inspire an interest in space science among young readers.

  9. Reparative Spheroids in HPV-Associated Chronic Cervicitis

    Directory of Open Access Journals (Sweden)

    Gennadiy T. Sukhikh

    2013-09-01

    Full Text Available Background: Spheroid cell structures (SCS described in cell culture are used to study cell-cell and cell-matrix interactions. However, the role of the SCS in the repair process in vivo remains unexplored. The aim of the study was to examine the cellular composition of the spherical structures and their functional significance in the repair of the squamous epithelium in human papilloma virus-associated chronic cervicitis (HPV-CC. Methods and Results: The cytology and biopsy materials from 223 patients with HPV-CC were subjected to molecular testing for HPV DNA by Real-Time Polymerase Chain Reaction (Real-Time PCR with genotyping and chromogenic in situ hybridization (CISH, as well as immunocytological and immunohistochemical analyses of p16INK4A, Ki67, SMA, Vimentin, CD34, E-cadherin, Oct4, CD44, CKW markers. In the stem cell niche zone, these spheroid structures were discovered having proliferative activity and showing signs of producing stem cells involved in the repair of the cervical mucosa in HPV-CC. Conclusion: The persistence of the HPV in the stem cell niche zone cells in the cervix determines the chronization of inflammation in this area, with the ability to perform pathological repair. The immunophenotype of the spheroid cell structures in the HPV-CC includes cells with signs of stem cells (‘stemness’ and the mesenchymal-epithelial transition.

  10. Vibration of fluid-loaded hemi-prolate spheroidal shells

    Science.gov (United States)

    Boisvert, Jeffrey E.; Hayek, Sabih I.

    2003-04-01

    The equations of motion for nonaxisymmetric vibration of hemi-prolate spheroidal shells of constant thickness were derived using Hamilton's principle. The shell is clamped at the equator and is excited by mechanical surface force fields. The shell theory used in this derivation includes shear deformations and rotatory inertias. The displacements and rotations were expanded in an infinite series of comparison functions. The shell is fluid-filled and is submerged in an infinite fluid medium. The external and internal fluid loading impedances were computed using expansions of prolate spheroidal wavefunctions in each domain. The dynamic response of the fluid-loaded shell was determined using an axisymmetric normal surface force as the excitation input. Numerical results were obtained for the driving and transfer mobilities for several shell thickness-to-length ratios ranging from 0.005 to 0.1, and for various shape parameters, ``a,'' ranging from an elongated hemi-spheroidal shell (a=1.01) to a hemispherical shell (a=100). Results are presented for various combinations of external and internal fluid loading, and comparisons are made to the in-vacuo shell vibration. [Work supported by ONR and the Navy/ASEE Summer Faculty Program.

  11. Silicon spheroidization treatment of thixoformed Al-Si-Mg alloys

    Energy Technology Data Exchange (ETDEWEB)

    Ogris, E.; Uggowitzer, P.J. [Eidgenoessische Technische Hochschule, Zurich (Switzerland). Inst. of Metallurgy; Luechinger, H. [SAG-Aluminium Lend GmbH und Co KG and THIXALLOY trademark Components GmbH und Co KG, Lend (Austria)

    2002-07-01

    Al-Si-Mg alloys are commonly used in the automobile industry because of their outstanding mechanical properties and corrosion resistance. The need of lighter and safer cars is the driving force behind research in the area of high strength light metal safety part applications. The strength level can be tuned by varying the amount of alloyed magnesium. Usually if strength is increased, ductility will decrease. Following the demands of the automotive industry, safety parts should have a minimum fracture elongation of 15% and a minimum yield strength of 150 MPa. The huge hurdle is the 15% fracture elongation which can not be reached by sand or die casting, but some relatively new alternative casting technologies, like Thioxocasting or New Rheocasting, yield encouraging ductility values. Recent research activity has focused on increasing strength and ductility, but so far the results have not yet been satisfying. This paper presents investigations on the spheroidization process of eutectic silicon and its positive effect on mechanical properties. It is shown that the spheroidization process is already finished after minutes of exposure to heat treatment. Metallographical and quantitative microstructural analysis is used to describe the growth and spheroidization process of the silicon crystals. Specimens of THIXALLOY trademark 630 (A356) thixocast components were heat treated for varied periods of time, aged and tested. Results show amazing improvements of ductility and strength in comparison to the as cast state. Maximum values of 18% fracture elongation and 230 MPa yield strength are reached. (orig.)

  12. Exclusion of canonical weakly interacting massive particles by joint analysis of Milky Way dwarf galaxies with data from the Fermi Gamma-Ray Space Telescope.

    Science.gov (United States)

    Geringer-Sameth, Alex; Koushiappas, Savvas M

    2011-12-01

    Dwarf spheroidal galaxies are known to be excellent targets for the detection of annihilating dark matter. We present new limits on the annihilation cross section of weakly interacting massive particles based on the joint analysis of seven Milky Way dwarfs using a frequentist Neyman construction and Pass 7 data from the Fermi Gamma-Ray Space Telescope. We exclude generic weakly interacting massive particle candidates annihilating into bb with a mass less than 40 GeV that reproduce the observed relic abundance. To within 95% systematic errors on the dark matter distribution within the dwarfs, the mass lower limit can be as low as 19 GeV or as high as 240 GeV. For annihilation into τ+ τ-, these limits become 19, 13, and 80 GeV, respectively.

  13. Formation mechanism of spheroidal carbide in ultra-low carbon ductile cast iron

    Directory of Open Access Journals (Sweden)

    Bin-guo Fu

    2016-09-01

    Full Text Available The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal carbide belonged to eutectic carbide and crystallized in the isolated eutectic liquid phase area. The formation process of the spheroidal carbide was related to the contact and the intersection between the primary dendrite and the secondary dendrite of austenite. The oxides of magnesium, rare earths and other elements can act as heterogeneous nucleation sites for the spheroidal carbide. It was also found that the amount of the spheroidal carbide would increase with an increase in carbon content. The cooling rate has an important influence on the spheroidal carbide under the same chemical composition condition.

  14. Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

    Science.gov (United States)

    Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

    2014-02-01

    The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

  15. Is Sextans dwarf galaxy in a scalar field dark matter halo?

    Energy Technology Data Exchange (ETDEWEB)

    Lora, V. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg (Germany); Magaña, Juan, E-mail: vlora@ari.uni-heidelberg.de, E-mail: juan.magana@uv.cl [Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso (Chile)

    2014-09-01

    The Bose-Einstein condensate/scalar field dark matter model, considers that the dark matter is composed by spinless-ultra-light particles which can be described by a scalar field. This model is an alternative model to the Λ-cold dark matter paradigm, and therefore should be studied at galactic and cosmological scales. Dwarf spheroidal galaxies have been very useful when studying any dark matter theory, because the dark matter dominates their dynamics. In this paper we study the Sextans dwarf spheroidal galaxy, embedded in a scalar field dark matter halo. We explore how the dissolution time-scale of the stellar substructures in Sextans, constrain the mass, and the self-interacting parameter of the scalar field dark matter boson. We find that for masses in the range (0.12< m{sub φ}<8) ×10{sup -22} eV, scalar field dark halos without self-interaction would have cores large enough to explain the longevity of the stellar substructures in Sextans, and small enough mass to be compatible with dynamical limits. If the self-interacting parameter is distinct to zero, then the mass of the boson could be as high as m{sub φ}≈2×10{sup -21} eV, but it would correspond to an unrealistic low mass for the Sextans dark matter halo . Therefore, the Sextans dwarf galaxy could be embedded in a scalar field/BEC dark matter halo with a preferred self-interacting parameter equal to zero.

  16. Multiparametric Analysis of Oncology Drug Screening with Aqueous Two-Phase Tumor Spheroids.

    Science.gov (United States)

    Shahi Thakuri, Pradip; Ham, Stephanie L; Luker, Gary D; Tavana, Hossein

    2016-11-07

    Spheroids present a biologically relevant three-dimensional model of avascular tumors and a unique tool for discovery of anticancer drugs. Despite being used in research laboratories for several decades, spheroids are not routinely used in the mainstream drug discovery pipeline primarily due to the difficulty of mass-producing uniformly sized spheroids and intense labor involved in handling, drug treatment, and analyzing spheroids. We overcome this barrier using a polymeric aqueous two-phase microtechnology to robotically microprint spheroids of well-defined size in standard 384-microwell plates. We use different cancer cells and show that resulting spheroids grow over time and display characteristic features of solid tumors. We demonstrate the feasibility of robotic, high-throughput screening of 25 standard chemotherapeutics and molecular inhibitors against tumor spheroids of three different cancer cell lines. This screening uses over 7000 spheroids to elicit high quality dose-dependent drug responses from spheroids. To quantitatively compare performance of different drugs, we employ a multiparametric scoring system using half-maximum inhibitory concentration (IC50), maximum inhibition (Emax), and area under the dose-response curve (AUC) to take into account both potency and efficacy parameters. This approach allows us to identify several compounds that effectively inhibit growth of spheroids and compromise cellular viability, and distinguish them from moderately effective and ineffective drugs. Using protein expression analysis, we demonstrate that spheroids generated with the aqueous two-phase microtechnology reliably resolve molecular targets of drug compounds. Incorporating this low-cost and convenient-to-use tumor spheroid technology in preclinical drug discovery will make compound screening with realistic tumor models a routine laboratory technique prior to expensive and tedious animal tests to dramatically improve testing throughput and efficiency and

  17. A gigantic X-ray flare from the star Trumpler 14 Y442 in the Carina star forming complex

    Science.gov (United States)

    Hamaguchi, Kenji; Drake, Stephen A.; Corcoran, Michael F.; Richardson, Noel; Teodoro, Mairan

    2015-09-01

    XMM-Newton, NuSTAR and Swift observations of the Carina star forming complex on 2015 July 16 (ObsID - XMM:0762910401, NuSTAR:30101005002, Swift:00081578001) detected an X-ray flare at the coordinates (R.A., Dec)[J2000] = (10 44 02.80, -59 39 46.7).

  18. VizieR Online Data Catalog: UBVI CCD photometry of Carina region stars (Molina-Lera+, 2016)

    Science.gov (United States)

    Molina-Lera, J. A.; Baume, G.; Gamen, R.; Costa, E.; Carraro, G.

    2016-08-01

    Photometric parameters for 62730 stars in the carina region covering 6 stellar clusters (NGC 3752, Trumpler 18, NGC 3590, Hogg 10, 11 and 12) and the surrounding field. The photometry was secured in March 2006 and March 2009 with the Y4KCAM camera attached to the Cerro Tololo Inter American Observatory (CTIO, Chile) 1.0-m telescope. (1 data file).

  19. Galaxy and Mass Assembly (GAMA): the stellar mass budget of galaxy spheroids and discs

    OpenAIRE

    Moffett, Amanda J.; Lange, Rebecca; Driver, Simon P.; Robotham, Aaron S G; Kelvin, Lee S; Alpaslan, Mehmet; Andrews, Stephen K.; Bland-Hawthorn, Joss; Brough, Sarah; Cluver, Michelle E.; Colless, Matthew; Davies, Luke J. M.; Holwerda, Benne W.; Hopkins, Andrew M; Kafle, Prajwal R.

    2016-01-01

    We build on a recent photometric decomposition analysis of 7506 Galaxy and Mass Assembly (GAMA) survey galaxies to derive stellar mass function fits to individual spheroid and disc component populations down to a lower mass limit of log(M*/M⊙) = 8. We find that the spheroid/disc mass distributions for individual galaxy morphological types are well described by single Schechter function forms. We derive estimates of the total stellar mass densities in spheroidsspheroid = 1.24 ± 0.49 × 108 M...

  20. Increased Survival and Function of Mesenchymal Stem Cell Spheroids Entrapped in Instructive Alginate Hydrogels

    Science.gov (United States)

    Ho, Steve S.; Murphy, Kaitlin C.; Binder, Bernard Y.K.; Vissers, Caroline B.

    2016-01-01

    Mesenchymal stem cell (MSC)-based therapies are under broad investigation for applications in tissue repair but suffer from poor cell persistence and engraftment upon transplantation. MSC spheroids exhibit improved survival, anti-inflammatory, and angiogenic potential in vitro, while also promoting vascularization when implanted in vivo. However, these benefits are lost once cells engage the tissue extracellular matrix and migrate from the aggregate. The efficacy of cell therapy is consistently improved when using engineered materials, motivating the need to investigate the role of biomaterials to instruct spheroid function. In order to assess the contribution of adhesivity on spheroid activity in engineered materials and promote the bone-forming potential of MSCs, we compared the function of MSC spheroids when entrapped in Arg-Gly-Asp (RGD)-modified alginate hydrogels to nonfouling unmodified alginate. Regardless of material, MSC spheroids exhibited reduced caspase activity and greater vascular endothelial growth factor (VEGF) secretion compared with equal numbers of dissociated cells. MSC spheroids in RGD-modified hydrogels demonstrated significantly greater cell survival than spheroids in unmodified alginate. After 5 days in culture, spheroids in RGD-modified gels had similar levels of apoptosis, but more than a twofold increase in VEGF secretion compared with spheroids in unmodified gels. All gels contained mineralized tissue 8 weeks after subcutaneous implantation, and cells entrapped in RGD-modified alginate exhibited greater mineralization versus cells in unmodified gels. Immunohistochemistry confirmed more diffuse osteocalcin staining in gels containing spheroids compared with dissociated controls. This study demonstrates the promise of cell-instructive biomaterials to direct survival and function of MSC spheroids for bone tissue engineering applications. Significance Mesenchymal stem cell (MSC) spheroids exhibit improved therapeutic potential in vitro

  1. Eclipse and Collapse of the Colliding Wind X-ray Emission from Eta Carinae

    Science.gov (United States)

    Hamaguchi, Kenji; Corcoran, Michael F.

    2012-01-01

    X-ray emission from the massive stellar binary system, Eta Carinae, drops strongly around periastron passage; the event is called the X-ray minimum. We launched a focused observing campaign in early 2009 to understand the mechanism of causing the X-ray minimum. During the campaign, hard X-ray emission (<10 keV) from Eta Carinae declined as in the previous minimum, though it recovered a month earlier. Extremely hard X-ray emission between 15-25 keV, closely monitored for the first time with the Suzaku HXD/PIN, decreased similarly to the hard X-rays, but it reached minimum only after hard X-ray emission from the star had already began to recover. This indicates that the X-ray minimum is produced by two composite mechanisms: the thick primary wind first obscured the hard, 2-10 keV thermal X-ray emission from the wind-wind collision (WWC) plasma; the WWC activity then decays as the two stars reach periastron.

  2. Gaia-ESO Survey: Gas dynamics in the Carina Nebula through optical emission lines

    CERN Document Server

    Damiani, F; Magrini, L; Prisinzano, L; Mapelli, M; Micela, G; Kalari, V; Apellaniz, J Maiz; Gilmore, G; Randich, S; Alfaro, E; Flaccomio, E; Koposov, S; Klutsch, A; Lanzafame, A C; Pancino, E; Sacco, G G; Bayo, A; Carraro, G; Casey, A R; Costado, M T; Franciosini, E; Hourihane, A; Lardo, C; Lewis, J; Monaco, L; Morbidelli, L; Worley, C; Zaggia, S; Zwitter, T; Dorda, R

    2016-01-01

    We present observations from the Gaia-ESO Survey in the lines of H$\\alpha$, [N II], [S II] and He I of nebular emission in the central part of the Carina Nebula. We investigate the properties of the two already known kinematic components (approaching and receding, respectively), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV $>$50 km/s) gas emission. We show that gas giving rise to H$\\alpha$ and He I emission is dynamically well correlated, but not identical, to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arises from several distinct shell-like expanding regions, the most evident found around $\\eta$ Car, the Trumpler 14...

  3. Jet-driving protostars identified from infrared observations of the Carina Nebula complex

    CERN Document Server

    Ohlendorf, Henrike; Gaczkowski, Benjamin; Ratzka, Thorsten; Grellmann, Rebekka; McLeod, Anna F

    2012-01-01

    Aims: Jets are excellent signposts for very young embedded protostars, so we want to identify jet-driving protostars as a tracer of the currently forming generation of stars in the Carina Nebula, which is one of the most massive galactic star-forming regions and which is characterised by particularly high levels of massive-star feedback on the surrounding clouds. Methods: We used archive data to construct large (> 2 deg x 2 deg) Spitzer IRAC mosaics of the Carina Nebula and performed a spatially complete search for objects with excesses in the 4.5 micron band, typical of shock-excited molecular hydrogen emission. We also identified the mid-infrared point sources that are the likely drivers of previously discovered Herbig-Haro jets and molecular hydrogen emission line objects. We combined the Spitzer photometry with our recent Herschel far-infrared data to construct the spectral energy distributions, and used the Robitaille radiative-transfer modelling tool to infer the properties of the objects. Results: The ...

  4. A deep wide-field sub-mm survey of the Carina Nebula complex

    CERN Document Server

    Preibisch, Thomas; Ohlendorf, Henrike; Pekruhl, Stephanie; Menten, Karl M; Zinnecker, Hans

    2010-01-01

    The Great Nebula in Carina is a superb location in which to study the physics of violent massive star-formation and the resulting feedback effects, including cloud dispersal and triggered star-formation. In order to reveal the cold dusty clouds in the Carina Nebula complex, we used the Large APEX Bolometer Camera LABOCA at the APEX telescope to map a 1.25 deg x 1.25 deg (= 50 x 50 pc^2) region at 870 micrometer. From a comparison to Halpha images we infer that about 6% of the 870 micrometer flux in the observed area is likely free-free emission from the HII region, while about 94% of the flux is very likely thermal dust emission. The total (dust + gas) mass of all clouds for which our map is sensitive is ~ 60 000 Msun, in good agreement with the mass of the compact clouds in this region derived from 13CO line observations. We generally find good agreement in the cloud morphology seen at 870 micrometer and the Spitzer 8 micrometer emission maps, but also identify a prominent infrared dark cloud. Finally, we co...

  5. 3D printing meets computational astrophysics: deciphering the structure of η Carinae's inner colliding winds

    Science.gov (United States)

    Madura, T. I.; Clementel, N.; Gull, T. R.; Kruip, C. J. H.; Paardekooper, J.-P.

    2015-06-01

    We present the first 3D prints of output from a supercomputer simulation of a complex astrophysical system, the colliding stellar winds in the massive (≳120 M⊙), highly eccentric (e ˜ 0.9) binary star system η Carinae. We demonstrate the methodology used to incorporate 3D interactive figures into a PDF (Portable Document Format) journal publication and the benefits of using 3D visualization and 3D printing as tools to analyse data from multidimensional numerical simulations. Using a consumer-grade 3D printer (MakerBot Replicator 2X), we successfully printed 3D smoothed particle hydrodynamics simulations of η Carinae's inner (r ˜ 110 au) wind-wind collision interface at multiple orbital phases. The 3D prints and visualizations reveal important, previously unknown `finger-like' structures at orbital phases shortly after periastron (φ ˜ 1.045) that protrude radially outwards from the spiral wind-wind collision region. We speculate that these fingers are related to instabilities (e.g. thin-shell, Rayleigh-Taylor) that arise at the interface between the radiatively cooled layer of dense post-shock primary-star wind and the fast (3000 km s-1), adiabatic post-shock companion-star wind. The success of our work and easy identification of previously unrecognized physical features highlight the important role 3D printing and interactive graphics can play in the visualization and understanding of complex 3D time-dependent numerical simulations of astrophysical phenomena.

  6. A Survey of Irradiated Pillars, Globules, and Jets in the Carina Nebul

    CERN Document Server

    Hartigan, P; Smith, N; Bally, J

    2015-01-01

    We present wide-field, deep narrowband H$_2$, Br$\\gamma$, H$\\alpha$, [S II], [O III], and broadband I and K-band images of the Carina star formation region. The new images provide a large-scale overview of all the H$_2$ and Br$\\gamma$ emission present in over a square degree centered on this signature star forming complex. By comparing these images with archival HST and Spitzer images we observe how intense UV radiation from O and B stars affects star formation in molecular clouds. We use the images to locate new candidate outflows and identify the principal shock waves and irradiated interfaces within dozens of distinct areas of star-forming activity. Shocked molecular gas in jets traces the parts of the flow that are most shielded from the intense UV radiation. Combining the H$_2$ and optical images gives a more complete view of the jets, which are sometimes only visible in H$_2$. The Carina region hosts several compact young clusters, and the gas within these clusters is affected by radiation from both the...

  7. He II 4686 in eta Carinae and the nature of the 5.538-yr cycle

    CERN Document Server

    Teodoro, M; Arias, J I; de Araújo, F X; Barbá, R H; Corcoran, M F; Fernandes, M Borges; Fernández-Lajús, E; Fraga, L; Gamen, R C; González, J F; Groh, J H; Marshall, J L; McGregor, P J; Morrell, N; Nicholls, D C; Parkin, E R; Pereira, C B; Phillips, M M; Solivella, G R; Steiner, J E; Stritzinger, M; Thompson, I; Torres, C A O; Torres, M A P; Zevallos-Herencia, M I

    2011-01-01

    The periodic minima in eta Carinae are now well defined and interpreted as due to periastron passage of two massive stars in a very eccentric orbit. Different mechanisms have been proposed to explain the light curve of different spectral features, such as eclipse, shell ejection, accretion and/or collapse of the primary wind onto the secondary star. All of them face difficulties to explain the observations in the full range of wavelengths. To better understand the nature of cyclic events, we performed a dense monitoring of eta Carinae along the 2009 spectroscopic event, focusing on the high-energy He II 4686 emission line. Our results indicate that the intensity curve of He II 4686 peaks at L~310 L_sun, has a phase-locked behaviour and shows a temporal correlation with the X-ray emission, ruling out many proposed sources of energy. The most suitable location for the He II 4686 emission region is the shocked primary wind, about 4-5 AU downstream from the apex. The 'collapse' component seen in light curves of X...

  8. Suzaku Observation of Diffuse X-ray Emission from the Carina Nebula

    CERN Document Server

    Hamaguchi, K; Matsumoto, H; Tsujimoto, M; Holt, S S; Ezoe, Y; Ozawa, H; Tsuboi, Y; Soong, Y; Kitamoto, S; Sekiguchi, A; Kokubun, M; Hamaguchi, Kenji; Petre, Robert; Matsumoto, Hironori; Tsujimoto, Masahiro; Holt, Stephan S.; Ezoe, Yuichiro; Ozawa, Hideki; Tsuboi, Yohko; Soong, Yang; Kitamoto, Shunji; Sekiguchi, Akiko; Kokubun, Motohide

    2006-01-01

    We studied extended X-ray emission from the Carina Nebula taken with the Suzaku CCD camera XIS on 2005 Aug. 29. The X-ray morphology, plasma temperature and absorption to the plasma are consistent with the earlier Einstein results. The Suzaku spectra newly revealed emission lines from various species including oxygen, but not from nitrogen. This result restricts the N/O ratio significantly low, compared with evolved massive stellar winds, suggesting that the diffuse emission is originated in an old supernova remnant or a super shell produced by multiple supernova remnants. The X-ray spectra from the north and south of Eta Carinae showed distinct differences between 0.3-2 keV. The south spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon ions, while the north spectrum shows them weak in intensity. This means that silicon and iron abundances are a factor of 2-4 higher in the south region than in the north region. The abundance variation may be produced by an SNR ejecta, or relate to th...

  9. The UV Scattering Halo of the Central Source Associated with Eta Carinae

    CERN Document Server

    Hillier, D J; Damineli, A; Gull, T R; Hamann, F W; Iping, R; Martin, J C; Nielsen, K; Smith, N; Sonneborn, G; Weis, K; Smith, Nathan

    2006-01-01

    We have made an extensive study of the UV spectrum of Eta Carinae, and find that we do not directly observe the star and its wind in the UV. Because of dust along our line of sight, the UV light that we observe arises from bound-bound scattering at large impact parameters. We obtain a reasonable fit to the UV spectrum by using only the flux that originates outside 0.033". This explains why we can still observe the primary star in the UV despite the large optical extinction -- it is due to the presence of an intrinsic coronagraph in the Eta Carinae system, and to the extension of the UV emitting region. It is not due to peculiar dust properties alone. We have computed the spectrum of the purported companion star, and show that it could only be directly detected in the UV spectrum preferentially in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectral region (912-1175 Ang.). However, we find no direct evidence for a companion star, with the properties indicated by X-ray studies and studies of the Weigelt b...

  10. X-ray Spectral Variation of Eta Carinae through the 2003 X-ray Minimum

    CERN Document Server

    Hamaguchi, K; Gull, T; Ishibashi, K; Pittard, J M; Hillier, D J; Damineli, A; Davidson, K; Nielsen, K E; Kober, G V; Hamaguchi, Kenji; Corcoran, Michael F.; Gull, Theodore; Ishibashi, Kazunori; Pittard, Julian M.; Damineli, Augusto; Davidson, Kris; Nielsen, Krister E.; Kober, Gladys Vieira

    2007-01-01

    We report the results of an X-ray observing campaign on the massive, evolved star Eta Carinae, concentrating on the 2003 X-ray minimum as seen by the XMM-Newton observatory. These are the first spatially-resolved X-ray monitoring observations of the stellar X-ray spectrum during the minimum. The hard X-ray emission, believed to be associated with the collision of Eta Carinae's wind with the wind from a massive companion star, varied strongly in flux on timescales of days, but not significantly on timescales of hours. The lowest X-ray flux in the 2-10 keV band seen by XMM-Newton was only 0.7% of the maximum seen by RXTE just before the X-ray minimum. The slope of the X-ray continuum above 5 keV did not vary in any observation, which suggests that the electron temperature of the hottest plasma associated with the stellar source did not vary significantly at any phase. Through the minimum, the absorption to the stellar source increased by a factor of 5-10 to NH ~3-4E23 cm-2. The thermal Fe XXV emission line show...

  11. 3D Printing Meets Computational Astrophysics: Deciphering the Structure of Eta Carinae's Inner Colliding Winds

    CERN Document Server

    Madura, Thomas I; Gull, Theodore R; Kruip, Chael J H; Paardekooper, Jan-Pieter

    2015-01-01

    We present the first 3D prints of output from a supercomputer simulation of a complex astrophysical system, the colliding stellar winds in the massive (>120 M_Sun), highly eccentric (e ~ 0.9) binary star system Eta Carinae. We demonstrate the methodology used to incorporate 3D interactive figures into a PDF journal publication and the benefits of using 3D visualization and 3D printing as tools to analyze data from multidimensional numerical simulations. Using a consumer-grade 3D printer (MakerBot Replicator 2X), we successfully printed 3D smoothed particle hydrodynamics (SPH) simulations of Eta Carinae's inner (r ~ 110 au) wind-wind collision interface at multiple orbital phases. The 3D prints and visualizations reveal important, previously unknown 'finger-like' structures at orbital phases shortly after periastron (phi ~ 1.045) that protrude radially outward from the spiral wind-wind collision region. We speculate that these fingers are related to instabilities (e.g. thin-shell, Rayleigh-Taylor) that arise a...

  12. Extended Red Objects and Stellar Wind Bow Shocks in the Carina Nebula

    CERN Document Server

    Sexton, Remington O; Smith, Nathan; Babler, Brian L; Meade, Marilyn R; Rudolph, Alexander L

    2014-01-01

    We report the results of infrared photometry on 39 extended red objects (EROs) in the Carina Nebula, observed with the Spitzer Space Telescope. Most EROs are identified by bright, extended 8.0 um emission, which ranges from 10'' to 40'' in size, but our sample also includes 4 EROs identified by extended 24 um emission. Of particular interest are nine EROs associated with late O or early B-type stars and characterized by arc-shaped morphology, suggesting dusty, stellar-wind bow shocks. These objects are preferentially oriented towards the central regions of the Carina Nebula, suggesting that these bow shocks are generally produced by the interactions of OB winds with the bulk expansion of the H II region rather than high proper motion. We identify preferred regions of mid-infrared color space occupied by our bow shock candidates, which also contain bow shock candidates in M17 and RCW 49 but are well-separated from polycyclic aromatic hydrocarbon emission or circumstellar discs. Color cuts identify an additiona...

  13. SECULAR CHANGES IN ETA CARINAE'S WIND 1998-2011

    Energy Technology Data Exchange (ETDEWEB)

    Mehner, Andrea [ESO, Alonso de Cordova 3107, Vitacura, Santiago de Chile (Chile); Davidson, Kris; Humphreys, Roberta M. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Ishibashi, Kazunori [Global COE, Division of Particle Physics and Astrophysics, Nagoya University, Nagoya 464-8602 (Japan); Martin, John C. [Department of Physics and Astronomy, University of Illinois Springfield, Springfield, IL 62703 (United States); Ruiz, Maria Teresa [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago de Chile (Chile); Walter, Frederick M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)

    2012-05-20

    Stellar wind-emission features in the spectrum of eta Carinae have decreased by factors of 1.5-3 relative to the continuum within the last 10 years. We investigate a large data set from several instruments (STIS, GMOS, UVES) obtained between 1998 and 2011 and analyze the progression of spectral changes in direct view of the star, in the reflected polar-on spectra at FOS4, and at the Weigelt knots. We find that the spectral changes occurred gradually on a timescale of about 10 years and that they are dependent on the viewing angle. The line strengths declined most in our direct view of the star. About a decade ago, broad stellar wind-emission features were much stronger in our line-of-sight view of the star than at FOS4. After the 2009 event, the wind-emission line strengths are now very similar at both locations. High-excitation He I and N II absorption lines in direct view of the star strengthened gradually. The terminal velocity of Balmer P Cyg absorption lines now appears to be less latitude dependent, and the absorption strength may have weakened at FOS4. Latitude-dependent alterations in the mass-loss rate and the ionization structure of eta Carinae's wind are likely explanations for the observed spectral changes.

  14. Interaction of planetary nebulae, Eta-Carinae and supernova remnants with the Interstellar Medium

    CERN Document Server

    Zaninetti, L

    2012-01-01

    The image of planetary nebulae (PN), supernova remnant (SNR) and Eta-Carinae is made by three different physical processes. The first process is the expansion of the shell that can be modeled by the canonical laws of motion in the spherical case and by the momentum conservation when gradients of density are present in the interstellar medium. The quality of the simulations is introduced along one direction as well along many directions. The second process is the diffusion of particles that radiate from the advancing layer. The 3D diffusion from a sphere, the 1D diffusion with drift and 1D random walk are analyzed. The third process is the composition of the image through an integral operation along the line of sight. The developed framework is applied to three PN which are A39, the Ring nebula and the etched hourglass nebula MyCn 18, the hybrid object Eta-Carinae, and to two SNR which are SN 1993J and SN 1006. In all the considered cases a careful comparison between the observed and theoretical profiles in in...

  15. Diffuse X-ray Emission from the Carina Nebula Observed with Suzaku

    CERN Document Server

    Hamaguchi, Kenji

    2007-01-01

    A number of giant HII regions are associated with soft diffuse X-ray emission. Among these, the Carina nebula possesses the brightest soft diffuse emission. The required plasma temperature and thermal energy can be produced by collisions or termination of fast winds from main-sequence or embedded young O stars, but the extended emission is often observed from regions apart from massive stellar clusters. The origin of the X-ray emission is unknown. The XIS CCD camera onboard Suzaku has the best spectral resolution for extended soft sources so far, and is therefore capable of measuring key emission lines in the soft band. Suzaku observed the core and the eastern side of the Carina nebula (Car-D1) in 2005 Aug and 2006 June, respectively. Spectra of the south part of the core and Car-D1 similarly showed strong L-shell lines of iron ions and K-shell lines of silicon ions, while in the north of the core these lines were much weaker. Fitting the spectra with an absorbed thin-thermal plasma model showed kT~0.2, 0.6 k...

  16. Enhanced angiogenic effect of adipose-derived stromal cell spheroid with low-level light therapy in hindlimb ischemia mice

    Science.gov (United States)

    Park, In-Su; Ahn, Jin-Chul; Chung, Phil-Sang

    2014-02-01

    Adipose-derived stromal cells (ASCs) are attractive cell source for tissue engineering. However, one obstacle to this approach is that the transplanted ASC population can decline rapidly in the recipient tissue. The aim of this study was to investigate the effects of low-level laser therapy (LLLT) on transplanted human ASCs (hASCs) spheroid in a hindlimb ischemia animal model. LLLT, hASCs spheroid and hASCs spheroid transplantation with LLLT (spheroid + LLLT) were applied to the ischemic hindlimbs in athymic mice. The survival, differentiation and secretion of vascular endothelial growth (VEGF) of spheroid ASCs were evaluated by immunohistochemistry. The spheroid + LLLT group enhanced the tissue regeneration, including angiogenesis, compared with other groups. The spheroid contributed tissue regeneration via differentiation and secretion of growth factors. In the spheroid + LLLT group, the survival of spheroid hASCs was increased by the decreased apoptosis of spheroid hASCs in the ischemic hindlimb. The secretion of growth factors was stimulated in the spheroid + LLLT group compared with the ASCs group and spheroid group. These data suggest that LLLT is an effective biostimulator of spheroid hASCs in tissue regeneration that enhances the survival of ASCs and stimulates the secretion of growth factors in the ischemic hindlimb.

  17. White dwarfs, red dwarfs and halo dark matter

    Energy Technology Data Exchange (ETDEWEB)

    GarcIa-Berro, E; Torres, S; Camacho, J [Departament de Fisica Aplicada, Escola Politecnica Superior de Castelldefels, Universitat Politecnica de Catalunya, Av. del Canal Olimpic, s/n, 08860 Castelldefels (Spain); Isern, J, E-mail: garcia@fa.upc.ed [Institut de Ciencies de l' Espai, CSIC, Campus UAB, Facultat de Ciencies, Torre C-5, 08193 Bellaterra (Spain)

    2009-06-01

    The nature of the microlensing events observed by the MACHO team towards the LMC still remains controversial. Low-mass substellar objects and stars with masses larger than approx 1M{sub o-dot} have been ruled out, while stars of approx 0.5 M{sub o-dot} are the most probable candidates. This means that the microlenses should be either red or white dwarfs. Consequently, we assess jointly the relative contributions of both types of stars to the mass budget of the Galactic halo. We use a Monte Carlo code that incorporates up-to-date evolutionary sequences of both red dwarfs and white dwarfs as well as detailed descriptions of both our Galaxy and the LMC and we compare the synthetic populations obtained with our simulator with the results obtained by the MACHO and EROS experiments. We find that the contribution of the red dwarf population is not enough to explain the number of events measured by the MACHO team. Even though, the optical depth obtained in our simulations almost doubles that obtained when taking into account the white dwarf population alone. Finally, we also find that the contribution to the halo dark matter of the entire population under study is smaller than 10%, at the 95% confidence level.

  18. OVCAR-3 spheroid-derived cells display distinct metabolic profiles.

    Directory of Open Access Journals (Sweden)

    Kathleen A Vermeersch

    Full Text Available Recently, multicellular spheroids were isolated from a well-established epithelial ovarian cancer cell line, OVCAR-3, and were propagated in vitro. These spheroid-derived cells displayed numerous hallmarks of cancer stem cells, which are chemo- and radioresistant cells thought to be a significant cause of cancer recurrence and resultant mortality. Gene set enrichment analysis of expression data from the OVCAR-3 cells and the spheroid-derived putative cancer stem cells identified several metabolic pathways enriched in differentially expressed genes. Before this, there had been little previous knowledge or investigation of systems-scale metabolic differences between cancer cells and cancer stem cells, and no knowledge of such differences in ovarian cancer stem cells.To determine if there were substantial metabolic changes corresponding with these transcriptional differences, we used two-dimensional gas chromatography coupled to mass spectrometry to measure the metabolite profiles of the two cell lines.These two cell lines exhibited significant metabolic differences in both intracellular and extracellular metabolite measurements. Principal components analysis, an unsupervised dimensional reduction technique, showed complete separation between the two cell types based on their metabolite profiles. Pathway analysis of intracellular metabolomics data revealed close overlap with metabolic pathways identified from gene expression data, with four out of six pathways found enriched in gene-level analysis also enriched in metabolite-level analysis. Some of those pathways contained multiple metabolites that were individually statistically significantly different between the two cell lines, with one of the most broadly and consistently different pathways, arginine and proline metabolism, suggesting an interesting hypothesis about cancerous and stem-like metabolic phenotypes in this pair of cell lines.Overall, we demonstrate for the first time that metabolism

  19. SUPERMASSIVE BLACK HOLES AND THEIR HOST SPHEROIDS. I. DISASSEMBLING GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Savorgnan, G. A. D.; Graham, A. W., E-mail: gsavorgn@astro.swin.edu.au [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122 (Australia)

    2016-01-15

    Several recent studies have performed galaxy decompositions to investigate correlations between the black hole mass and various properties of the host spheroid, but they have not converged on the same conclusions. This is because their models for the same galaxy were often significantly different and not consistent with each other in terms of fitted components. Using 3.6 μm Spitzer imagery, which is a superb tracer of the stellar mass (superior to the K band), we have performed state-of-the-art multicomponent decompositions for 66 galaxies with directly measured black hole masses. Our sample is the largest to date and, unlike previous studies, contains a large number (17) of spiral galaxies with low black hole masses. We paid careful attention to the image mosaicking, sky subtraction, and masking of contaminating sources. After a scrupulous inspection of the galaxy photometry (through isophotal analysis and unsharp masking) and—for the first time—2D kinematics, we were able to account for spheroids; large-scale, intermediate-scale, and nuclear disks; bars; rings; spiral arms; halos; extended or unresolved nuclear sources; and partially depleted cores. For each individual galaxy, we compared our best-fit model with previous studies, explained the discrepancies, and identified the optimal decomposition. Moreover, we have independently performed one-dimensional (1D) and two-dimensional (2D) decompositions and concluded that, at least when modeling large, nearby galaxies, 1D techniques have more advantages than 2D techniques. Finally, we developed a prescription to estimate the uncertainties on the 1D best-fit parameters for the 66 spheroids that takes into account systematic errors, unlike popular 2D codes that only consider statistical errors.

  20. PAndAS' progeny: extending the M31 dwarf galaxy cabal

    CERN Document Server

    Richardson, Jenny C; McConnachie, Alan W; Martin, Nicolas F; Dotter, Aaron; Ferguson, Annette M N; Ibata, Rodrigo A; Chapman, Scott; Lewis, Geraint F; Tanvir, Nial R; Rich, R Michael

    2011-01-01

    We present the discovery of five new dwarf galaxies, Andromeda XXIII-XXVII, located in the outer halo of M31. These galaxies were found in the second year of data from the Pan-Andromeda Archaeological Survey (PAndAS) of the M31/M33 subgroup. This survey now provides an almost complete panoramic view of the M31 halo out to an average projected radius of ~150 kpc. The metal-poor stellar density map for this whole region serves, not only as an illustration of the discovery space for satellite galaxies, but also gives a birds-eye view of the ongoing assembly process of an L* disk galaxy. Four of the new dwarfs appear as well-defined spatial over-densities of stars lying on the expected locus of metal-poor red giant branch stars at the distance of M31. The fifth over-density, And XXVII, is embedded in an extensive stream of such stars and is possibly the remnant of a strong tidal disruption event. All five satellites have metallicities and luminosities typical of dwarf spheroidal galaxies and continue the trend wh...

  1. Chemical Abundances of Seven Irregular and Three Tidal Dwarf Galaxies in the M81 Group

    CERN Document Server

    Croxall, Kevin V; Lee, Henry; Skillman, Evan D; Lee, Janice C; Côté, Stéphanie; Kennicutt, Robert C; Miller, Bryan W; 10.1088/0004-637X/705/1/723

    2009-01-01

    We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H \\ii regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H \\ii region had a detection of the temperature sensitive [OIII] $\\lambda$4363 line, allowing a "direct" determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies and the observed oxygen abundances are typically in agreement with the well known metallicity-luminosity relation. However, three candidate "tidal dwarf" galaxies lie well off this relation, UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sigh...

  2. A tidally disrupting dwarf galaxy in the halo of NGC 253

    CERN Document Server

    Toloba, Elisa; Spekkens, Kristine; Crnojevic, Denija; Simon, Joshua; Guhathakurta, Puragra; Strader, Jay; Caldwell, Nelson; McLeod, Brian; Seth, Anil

    2015-01-01

    We report the discovery of Scl-MM-Dw2, a new dwarf galaxy at a projected separation of $\\sim$50 kpc from NGC 253, as part of the PISCeS (Panoramic Imaging Survey of Centaurus and Sculptor) project. We measure a tip of the red giant branch distance of $3.12\\pm0.30$ Mpc, suggesting that Scl-MM-Dw2 is likely a satellite of NGC 253. We qualitatively compare the distribution of red giant branch (RGB) stars in the color-magnitude diagram with theoretical isochrones and find that it is consistent with an old, $\\sim$12 Gyr, and metal poor, $-2.3<$[Fe/H]$<-1.1$, stellar population. We also detect a small number of asymptotic giant branch stars consistent with a metal poor $2-3$ Gyr population in the center of the dwarf. Our non-detection of HI in a deep Green Bank Telescope spectrum implies a gas fraction $M_{HI}/L_V<0.02$ Msun/Lsun. The stellar and gaseous properties of Scl-MM-Dw2 suggest that it is a dwarf spheroidal galaxy. Scl-MM-Dw2 has a luminosity of $M_V=-12.1\\pm0.5$ mag and a half-light radius of $r_...

  3. The effect of feedback and reionization on star formation in low-mass dwarf galaxy haloes

    CERN Document Server

    Simpson, Christine M; Johnston, Kathryn V; Smith, Britton D; Mac Low, Mordecai-Mark; Sharma, Sanjib; Tumlinson, Jason

    2012-01-01

    We simulate the evolution of a 10^9 Msun dark matter halo in a cosmological setting with an adaptive-mesh refinement code as an analogue to local low luminosity dwarf irregular and dwarf spheroidal galaxies. The primary goal of our study is to investigate the roles of reionization and supernova feedback in determining the star formation histories of low mass dwarf galaxies. We include a wide range of physical effects, including metal cooling, molecular hydrogen formation and cooling, photoionization and photodissociation from a metagalactic background, a simple prescription for self-shielding, star formation, and a simple model for supernova driven energetic feedback. We carry out simulations excluding each major effect in turn. We find that reionization is primarily responsible for expelling most of the gas in our simulations, but that supernova feedback is required to disperse the dense, cold gas in the core of the halo. Moreover, we show that the timing of reionization can produce an order of magnitude dif...

  4. The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies

    CERN Document Server

    Kirby, Evan N; Guhathakurta, Puragra; Cheng, Lucy; Bullock, James S; Gallazzi, Anna

    2013-01-01

    We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* ~ M_*^(0.30 +/- 0.02). The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M_* = 10^12 M_sun. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the s...

  5. Short-term effects of radiation in glioblastoma spheroids

    DEFF Research Database (Denmark)

    Asferg Petterson, Stine; Pind Jakobsen, Ida; Jensen, Stine Skov;

    2016-01-01

    and five days. We found a small reduction in primary spheroid size after radiation and an associated small increase in uptake of the cell death marker propidium iodide. Using immunohistochemistry, P53 expression was found to be significantly increased, whereas the Ki-67 proliferation index...... capacity. Gene expression analysis of nine stem cell- and two hypoxia-related genes did not reveal any upregulation after radiation. In conclusion, this study suggests that a major short-term effect of radiation is pronounced reduction of tumor cell proliferation. We found no upregulation of stem cell...

  6. Characterisation of austempered spheroidal graphite aluminium cast iron

    Energy Technology Data Exchange (ETDEWEB)

    Boutorabi, S.M.A. [Iran Univ. of Science and Technology, Tehran (Iran, Islamic Republic of). Dept. of Metallurgy and Materials

    1997-06-01

    The micro constituents of austempered spheroidal graphite aluminium cast iron were investigated. The heat tinting, special etching and microhardness measurement techniques were used. The results showed that the colour of each micro constituents and the hardness values in austempered ductile iron depend on the carbon content of each phase. The above techniques were supported by using an special etching which showed similar differences in each phase. It was shown that the heat tinting and special etching are reliable tools to characterise the complex matrix of ADI. The microhardness data supported interestingly the colour changes in above technique. (orig.)

  7. Note: 3D printed spheroid for uniform magnetic field generation

    Science.gov (United States)

    Öztürk, Y.; Aktaş, B.

    2016-10-01

    This article is focused on a novel and practical production method for a uniform magnetic field generator. The method involves building of a surface coil template using a desktop 3D printer and winding of a conducting wire onto the structure using surface grooves as a guide. Groove pattern was based on the parametric spheroidal helical coil formula. The coil was driven by a current source and the magnetic field inside was measured using a Hall probe placed into the holes on the printed structure. The measurements are found to be in good agreement with our finite element analysis results and indicate a fairly uniform field inside.

  8. Ejection of Supernova-Enriched Gas From Dwarf Disk Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Fragile, P C; Murray, S D; Lin, D C

    2004-06-15

    We examine the efficiency with which supernova-enriched gas may be ejected from dwarf disk galaxies, using a methodology previously employed to study the self-enrichment efficiency of dwarf spheroidal systems. Unlike previous studies that focused on highly concentrated starbursts, in the current work we consider discrete supernova events spread throughout various fractions of the disk. We model disk systems having gas masses of 10{sup 8} and 10{sup 9} M{sub {circle_dot}} with supernova rates of 30, 300, and 3000 Myr{sup -1}. The supernova events are confined to the midplane of the disk, but distributed over radii of 0, 30, and 80% of the disk radius, consistent with expectations for Type II supernovae. In agreement with earlier studies, we find that the enriched material from supernovae is largely lost when the supernovae are concentrated near the nucleus, as expected for a starburst event. In contrast, we find the loss of enriched material to be much less efficient (as low as 21%) when the supernovae occur over even a relatively small fraction of the disk. The difference is due to the ability of the system to relax following supernova events that occur over more extended regions. Larger physical separations also reduce the likelihood of supernovae going off within low-density ''chimneys'' swept out by previous supernovae. We also find that, for the most distributed systems, significant metal loss is more likely to be accompanied by significant mass loss. A comparison with theoretical predications indicates that, when undergoing self-regulated star formation, galaxies in the mass range considered shall efficiently retain the products of Type II supernovae.

  9. Brown dwarfs as close companions to white dwarfs

    Science.gov (United States)

    Stringfellow, Guy S.; Bodenheimer, Peter; Black, David C.

    1990-01-01

    The influence of the radiation flux emitted by a white dwarf primary on the evolution of a closely orbiting brown dwarf (BD) companion is investigated. Full stellar evolutionary calculations are presented for both isolated and thermal bath cases, including effects of large variations in the atmospheric grain opacities. High grain opacities significantly increase the radii of the BDs, but the thermal bath does not. The major influence of the thermal bath is to increase substantially the surface temperature and luminosity of the BD at a given age. These results are compared with the observational properties of the possible BD companion of the white dwarf G29-38. Inclusion of both physical effects, high grain opacities and thermal bath, increases the mass range (0.034-0.063 solar masses) of viable models significantly, yet the final determination of whether the object is indeed a BD requires improvements in the observations of the system's properties.

  10. Generation of Multicellular Breast Cancer Tumor Spheroids: Comparison of Different Protocols.

    Science.gov (United States)

    Froehlich, Karolin; Haeger, Jan-Dirk; Heger, Julia; Pastuschek, Jana; Photini, Stella Mary; Yan, Yan; Lupp, Amelie; Pfarrer, Christiane; Mrowka, Ralf; Schleußner, Ekkehard; Markert, Udo R; Schmidt, André

    2016-12-01

    Multicellular tumor spheroids are widely used models in tumor research. Because of their three dimensional organization they can simulate avascular tumor areas comprising proliferative and necrotic cells. Nonetheless, protocols for spheroid generation are still inconsistent. Therefore, in this study the breast cancer cell lines MCF-7, MDA-MB-231 and SK-BR-3 have been used to compare different spheroid generation models including hanging drop, liquid overlay and suspension culture techniques, each under several conditions. Experimental approaches differed in cell numbers (400-10,000), media and additives (25 % methocel, 25 % methocel plus 1 % Matrigel, 3.5 % Matrigel). In total, 42 different experimental setups have been tested. Generation of spheroids was evaluated by light microscopy and the structural composition was assessed immunohistochemically by means of Ki-67, cleaved poly (ADP-ribose) polymerase (cPARP) and mucin-1 (MUC-1) expression. Although the tested cell lines diverged widely in their capacity of forming spheroids we recommend hanging drops supplemented with 25 % methocel as the most reliable and efficient method with regard to success of generation of uniform spheroids, costs, experimental complexity and time expenditure in the different cell lines. MCF-7 cells formed spheroids under almost all analyzed conditions, and MDA-MB-231 cells under only one protocol (liquid overlay technique, 3.5 % Matrigel), while SK-BR-3 did not under neither condition. Therefore, we outline specific methods and recommend the use of adapted and standardized spheroid generation protocols for each cell line.

  11. Rapid generation of single-tumor spheroids for high-throughput cell function and toxicity analysis.

    Science.gov (United States)

    Ivascu, Andrea; Kubbies, Manfred

    2006-12-01

    Spheroids are widely used in biology because they provide an in vitro 3-dimensional (3D) model to study proliferation, cell death, differentiation, and metabolism of cells in tumors and the response of tumors to radiotherapy and chemotherapy. The methods of generating spheroids are limited by size heterogeneity, long cultivation time, or mechanical accessibility for higher throughput fashion. The authors present a rapid method to generate single spheroids in suspension culture in individual wells. A defined number of cells ranging from 1000 to 20,000 were seeded into wells of poly-HEMA-coated, 96-well, round-or conical-bottom plates in standard medium and centrifuged for 10 min at 1000 g. This procedure generates single spheroids in each well within a 24-h culture time with homogeneous sizes, morphologies, and stratification of proliferating cells in the rim and dying cells in the core region. Because a large number of tumor cell lines form only loose aggregates when cultured in 3D, the authors also performed a screen for medium additives to achieve a switch from aggregate to spheroid morphology. Small quantities of the basement membrane extract Matrigel, added to the culture medium prior to centrifugation, most effectively induced compact spheroid formation. The compact spheroid morphology is evident as early as 24 h after centrifugation in a true suspension culture. Twenty tumor cell lines of different lineages have been used to successfully generate compact, single spheroids with homogenous size in 96-well plates and are easily accessible for subsequent functional analysis.

  12. Surface electric current distributions on spheres and spheroids as sources of pure quadrupole magnetic fields

    OpenAIRE

    L. Medina; E. Ley-Koo

    2011-01-01

    Neutral atom magnetic traps and nuclear magnetic resonance imaging require internal regions with constant gradient magnetic induction fields, which are identified as pure quadrupole fields. This contribution starts from such fields in the interior of spheres and spheroids in cartesian coordinates, identifying immediately their respective scalar magnetic potentials. Next, the corresponding potentials inside and outside are constructed using spherical and spheroidal harmonic functions, respecti...

  13. Trigonometric potentials arising from the spheroidal equation: Supersymmetric partners and integral formulas

    Science.gov (United States)

    Schulze-Halberg, Axel

    2016-06-01

    We construct supersymmetric partners of a quantum system featuring a class of trigonometric potentials that emerge from the spheroidal equation. Examples of both standard and confluent supersymmetric transformations are presented. Furthermore, we use integral formulas arising from the confluent supersymmetric formalism to derive new representations for single and multiple integrals of spheroidal functions.

  14. Abnormal hepatic copper accumulation of spheroid composed of liver cells from LEC rats in vitro.

    Science.gov (United States)

    Ueno, K; Yoshizawa, M; Satoh, T; Yoneda, S; Ohmichi, M; Yamazaki, M; Mori, Y; Suzuki, K T

    1995-11-01

    The LEC rat is a mutant strain displaying hereditary hepatitis, and shows abnormal accumulation of copper (Cu) similar to that occurring in Wilson's disease. We prepared a multicellular spheroid composed of LEC rat liver cells to investigate the mechanism for abnormal accumulation of Cu. These multicellular spheroids were prepared by detaching the monolayer on the collagen-conjugated thermo-responsive polymer coated culture dish at a temperature below the critical solution temperature and culturing on the non-adhesive substratum. Long-term cultured spheroids of LEC rat liver cells as well as SD rat liver cells were attempted. Non-parenchymal cells obtained by collagenase perfusion from the LEC liver were fewer than those from the SD liver. Cells from the LEC rat, over 11 weeks of age, did not form a cell sheet; however, a mixture of parenchymal cells from LEC rats over aged 11 weeks and non-parenchymal cells from SD rats of any age yielded intact spheroids. We examined the toxicity, the accumulation and distribution of Cu in spheroids. The accumulation of Cu in LEC spheroids was higher than that in SD spheroids. Results suggest that spheroids consisting of LEC liver cells are useful as an alternative model to in vivo tests to investigate the mechanism for abnormal accumulation of Cu in liver.

  15. Multiplexing spheroid volume, resazurin and acid phosphatase viability assays for high-throughput screening of tumour spheroids and stem cell neurospheres.

    Science.gov (United States)

    Ivanov, Delyan P; Parker, Terry L; Walker, David A; Alexander, Cameron; Ashford, Marianne B; Gellert, Paul R; Garnett, Martin C

    2014-01-01

    Three-dimensional cell culture has many advantages over monolayer cultures, and spheroids have been hailed as the best current representation of small avascular tumours in vitro. However their adoption in regular screening programs has been hindered by uneven culture growth, poor reproducibility and lack of high-throughput analysis methods for 3D. The objective of this study was to develop a method for a quick and reliable anticancer drug screen in 3D for tumour and human foetal brain tissue in order to investigate drug effectiveness and selective cytotoxic effects. Commercially available ultra-low attachment 96-well round-bottom plates were employed to culture spheroids in a rapid, reproducible manner amenable to automation. A set of three mechanistically different methods for spheroid health assessment (Spheroid volume, metabolic activity and acid phosphatase enzyme activity) were validated against cell numbers in healthy and drug-treated spheroids. An automated open-source ImageJ macro was developed to enable high-throughput volume measurements. Although spheroid volume determination was superior to the other assays, multiplexing it with resazurin reduction and phosphatase activity produced a richer picture of spheroid condition. The ability to distinguish between effects on malignant and the proliferating component of normal brain was tested using etoposide on UW228-3 medulloblastoma cell line and human neural stem cells. At levels below 10 µM etoposide exhibited higher toxicity towards proliferating stem cells, whereas at concentrations above 10 µM the tumour spheroids were affected to a greater extent. The high-throughput assay procedures use ready-made plates, open-source software and are compatible with standard plate readers, therefore offering high predictive power with substantial savings in time and money.

  16. Multiplexing spheroid volume, resazurin and acid phosphatase viability assays for high-throughput screening of tumour spheroids and stem cell neurospheres.

    Directory of Open Access Journals (Sweden)

    Delyan P Ivanov

    Full Text Available Three-dimensional cell culture has many advantages over monolayer cultures, and spheroids have been hailed as the best current representation of small avascular tumours in vitro. However their adoption in regular screening programs has been hindered by uneven culture growth, poor reproducibility and lack of high-throughput analysis methods for 3D. The objective of this study was to develop a method for a quick and reliable anticancer drug screen in 3D for tumour and human foetal brain tissue in order to investigate drug effectiveness and selective cytotoxic effects. Commercially available ultra-low attachment 96-well round-bottom plates were employed to culture spheroids in a rapid, reproducible manner amenable to automation. A set of three mechanistically different methods for spheroid health assessment (Spheroid volume, metabolic activity and acid phosphatase enzyme activity were validated against cell numbers in healthy and drug-treated spheroids. An automated open-source ImageJ macro was developed to enable high-throughput volume measurements. Although spheroid volume determination was superior to the other assays, multiplexing it with resazurin reduction and phosphatase activity produced a richer picture of spheroid condition. The ability to distinguish between effects on malignant and the proliferating component of normal brain was tested using etoposide on UW228-3 medulloblastoma cell line and human neural stem cells. At levels below 10 µM etoposide exhibited higher toxicity towards proliferating stem cells, whereas at concentrations above 10 µM the tumour spheroids were affected to a greater extent. The high-throughput assay procedures use ready-made plates, open-source software and are compatible with standard plate readers, therefore offering high predictive power with substantial savings in time and money.

  17. The most metal-poor damped Lyman alpha systems: An insight into dwarf galaxies at high redshift

    CERN Document Server

    Cooke, Ryan; Jorgenson, Regina A

    2014-01-01

    In this paper, we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyman alpha systems (DLAs), to uncover their links to modern-day galaxies. We present evidence that the DLA population as a whole exhibits a `knee' in the relative abundances of the alpha-capture and Fe-peak elements when the metallicity is [Fe/H] ~ -2.0. In this respect, the chemical evolution of DLAs is clearly different from that experienced by Milky Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. We also find a close correspondence between the kinematics of Local Group dwarf galaxies and of high redshift metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, we propose that the most metal-poor DLAs provide us with a unique opportunity to directly study the dwarf galaxy population more than ten billion years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, we have m...

  18. Planetary nebulae: the universal mass-metallicity relation for Local Group dwarf galaxies and the chemistry of NGC 205

    CERN Document Server

    Gonçalves, D R; Teodorescu, Ana M; Carneiro, Carolina M

    2014-01-01

    Here we study 16 planetary nebulae (PNe) in the dwarf irregular galaxy NGC 205 by using GMOS@Gemini spectra to derive their physical and chemical parameters. The chemical patterns and evolutionary tracks for 14 of our PNe suggest that there are no type I PNe among them. These PNe have an average oxygen abundance of 12+log(O/H)=8.08$\\pm$0.28, progenitor masses of 2-2.5M$_{\\odot}$ and thus were born ~1.0-1.7Gyr ago. Our results are in good agreement with previous PN studies in NGC 205. The present 12+log(O/H) is combined with our previous works and with the literature to study the PN metallicity trends of the Local Group (LG) dwarf galaxies, in an effort to establish the PN luminosity- and mass-metallicity relations (LZR and MZR) for the LG dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs). Previous attempts to obtain such relations failed to provide correct conclusions because were based on limited samples (Richer & McCall 1995; Gon\\c{c}calves et al. 2007). As far as we are able to compare stellar wit...

  19. The evolution of iron white dwarf stars

    Directory of Open Access Journals (Sweden)

    J. A. Panei

    2001-01-01

    Full Text Available Recent measurements by Hipparcos provide strong observational evidence supporting the existence of white dwarf stars with iron-rich core composition. Here we examine the evolution of iron-rich white dwarfs, for which the cooling is substancially accelerated as compared with the standard carbon-oxigen white dwarfs.

  20. A theoretical study of the spheroidal droplet evaporation in forced convection

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jie, E-mail: leejay1986@163.com; Zhang, Jian

    2014-11-07

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet.

  1. The low-frequency dielectric response of charged oblate spheroidal particles immersed in an electrolyte

    CERN Document Server

    Hou, Chang-Yu; Sen, Pabitra N

    2016-01-01

    We study the low-frequency polarization response of a surface-charged oblate spheroidal particle immersed in an electrolyte solution. Because the charged spheroid attracts counter-ions which form the electric double layer around the particle, using usual boundary conditions at the interface between the particle and electrolyte can be quite complicated and challenging. Hence, we generalize Fixman's boundary conditions, originally derived for spherical particles, to the case of the charged oblate spheroid. Given two different counter-ion distributions in the thin electric double layer limit, we obtain analytic expressions for the polarization coefficients to the first non-trivial order in frequency. We find that the polarization response normal to the symmetry axis depends on the total amount of charge carried by the oblate spheroid while that parallel to the symmetry axis is suppressed when there is less charge on the edge of the spheroid. We further study the overall dielectric response for a dilute suspensio...

  2. Dynamics of prolate spheroidal mass distributions with varying eccentricity

    CERN Document Server

    Rathulnath, R

    2013-01-01

    In this paper we calculate the potential for a prolate spheroidal distribution as in a dark matter halo with a radially varying eccentricity. This is obtained by summing up the shell-by-shell contributions of isodensity surfaces, which are taken to be concentric and with a common polar axis and with an axis ratio that varies with radius. Interestingly, the constancy of potential inside a shell is shown to be a good approximation even when the isodensity contours are dissimilar spheroids, as long as the radial variation in eccentricity is small as seen in realistic systems. We consider three cases where the isodensity contours are more prolate at large radii, or are less prolate, or have a constant eccentricity. Other relevant physical quantities like the rotation velocity, the net orbital and vertical frequency due to the halo and an exponential disc of finite thickness embedded in it are obtained. We apply this to the kinematical origin of Galactic warp, and show that a prolate shaped halo is not conducive t...

  3. Building Blocks of the Milky Way's Accreted Spheroid

    CERN Document Server

    van Oirschot, Pim; Helmi, Amina; Nelemans, Gijs

    2016-01-01

    In the $\\Lambda$CDM model of structure formation, a stellar spheroid grows by the assembly of smaller galaxies, the so-called building blocks. Combining the Munich-Groningen semi-analytical model of galaxy formation with the high resolution Aquarius simulations of dark matter haloes, we study the assembly history of the stellar spheroids of six Milky Way-mass galaxies, focussing on building block properties such as mass, age and metallicity. These properties are compared to those of the surviving satellites in the same models. We find that the building blocks have higher star formation rates on average, and this is especially the case for the more massive objects. At high redshift these dominate in star formation over the satellites, whose star formation timescales are longer on average. These differences ought to result in a larger $\\alpha$-element enhancement from Type II supernovae in the building blocks (compared to the satellites) by the time Type Ia supernovae would start to enrich them in iron, explain...

  4. Discriminating Between the Physical Processes that Drive Spheroid Size Evolution

    CERN Document Server

    Hopkins, Philip F; Hernquist, Lars; Wuyts, Stijn; Cox, Thomas J

    2009-01-01

    Massive galaxies at high-z have smaller effective radii than those today, but similar central densities. Their size growth therefore relates primarily to the evolving abundance of low-density material. Various models have been proposed to explain this evolution, which have different implications for galaxy, star, and BH formation. We compile observations of spheroid properties as a function of redshift and use them to test proposed models. Evolution in progenitor gas-richness with redshift gives rise to initial formation of smaller spheroids at high-z. These systems can then evolve in apparent or physical size via several channels: (1) equal-density 'dry' mergers, (2) later major or minor 'dry' mergers with less-dense galaxies, (3) adiabatic expansion, (4) evolution in stellar populations & mass-to-light-ratio gradients, (5) age-dependent bias in stellar mass estimators, (6) observational fitting/selection effects. If any one of these is tuned to explain observed size evolution, they make distinct predict...

  5. Faint Dwarfs in Nearby Groups

    CERN Document Server

    Speller, Ryan

    2013-01-01

    The number and distribution of dwarf satellite galaxies remain a critical test of cold dark matter-dominated structure formation on small scales. Until recently, observational information about galaxy formation on these scales has been limited mainly to the Local Group. We have searched for faint analogues of Local Group dwarfs around nearby bright galaxies, using a spatial clustering analysis of the photometric catalog of the Sloan Digital Sky Survey (SDSS) Data Release 8. Several other recent searches of SDSS have detected clustered satellite populations down to $\\Delta m_r \\equiv ({m}_{r,\\, {\\rm sat}} -\\, {m}_{r,\\, {\\rm main}}) \\sim 6$-$8$, using photometric redshifts to reduce background contamination. SDSS photometric redshifts are relatively imprecise, however, for faint and nearby galaxies. Instead we use angular size to select potential nearby dwarfs, and consider only the nearest isolated bright galaxies as primaries. As a result, we are able to detect an excess clustering signal from companions down...

  6. The rotation of brown dwarfs

    CERN Document Server

    Scholz, Aleks

    2016-01-01

    One of the characteristic features of low-mass stars is their propensity to shed large amounts of angular momentum throughout their evolution. This distinguishs them from brown dwarfs which remain fast rotators over timescales of gigayears. Brown dwarfs with rotation periods longer than a couple of days have only been found in star forming regions and young clusters. This is a useful constraint on the mass dependency of mechanisms for angular momentum regular in stars. Rotational braking by disks and winds become highly inefficient in the substellar regime. In this short review I discuss the observational evidence for the fast rotation in brown dwarfs, the implications, and the link to the spin-mass relation in planets.

  7. Branes constrictions with White Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    García-Aspeitia, Miguel A., E-mail: aspeitia@fisica.uaz.edu.mx [Consejo Nacional de Ciencia y Tecnología, Av, Insurgentes Sur 1582, Colonia Crédito Constructor, Del. Benito Juárez, C.P. 03940, Mexico, D.F. (Mexico); Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo a la Bufa S/N, C.P. 98060, Zacatecas (Mexico)

    2015-11-06

    We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane–Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of <λ>≳84.818 MeV{sup 4}, with a standard deviation σ≃82.021 MeV{sup 4}, which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others.

  8. Branes constrictions with White Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Aspeitia, Miguel A. [Consejo Nacional de Ciencia y Tecnologia, Mexico (Mexico); Unidad Academica de Fisica, Universidad Autonoma de Zacatecas (Mexico)

    2015-11-15

    We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane-Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of left angle λ right angle >or similar 84.818 MeV{sup 4}, with a standard deviation σ ≅ 82.021 MeV{sup 4}, which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others. (orig.)

  9. Study on the effects of nylon-chitosan-blended membranes on the spheroid-forming activity of human melanocytes.

    Science.gov (United States)

    Lin, Sung-Jan; Hsiao, Wen-Chu; Jee, Shiou-Hwa; Yu, Hsin-Su; Tsai, Tsen-Fang; Lai, Juin-Yih; Young, Tai-Horng

    2006-10-01

    Though reported limitedly in tissue engineering, modification of cellular functions can be achieved by culturing them into multicellular spheroids. We have shown melanocytes form spheroids on chitosan surface. However, how biomaterials promote spheroid formation has never been systemically investigated. In this work, nylon, which inhibits melanocyte spheroid formation, and chitosan, which promotes melanocyte spheroid formation, are used to prepare nylon/chitosan-blended membranes. Membranes composed of pure nylon, pure chitosan and various ratios of nylon and chitosan are employed to examine their effects on spheroid formation. Melanocytes show better adhesion to nylon membranes than that to chitosan membranes. In blended membranes, as more nylon is incorporated, cell adhesion increases and the trend for spheroid formation decreases. Melanocytes can only form spheroids on membranes with poorer cell adhesion. Examining the surface of the blended membranes shows phase separation of nylon and chitosan. As nylon content increases, the nylon phase on the membrane surface increases and thereby enhances cell adhesion. The opposite trend for cell adhesion and spheroid formation substantiates our hypothesis of spheroid formation on biomaterials: a balance between cell-substrate interaction and cell-cell interaction. The decrease in cell-substrate interaction tilts the balance to a state more favorable for spheroid formation. Our work can serve as a model to investigate the relative strengths of cell-cell and cell-substrate interactions and also pave way to design blended membranes with desired physical properties while preserving the spheroid-forming activity.

  10. Satellite Dwarf Galaxies in a Hierarchical Universe: The Prevalence of Dwarf-Dwarf Major Mergers

    CERN Document Server

    Deason, Alis; Garrison-Kimmel, Shea

    2014-01-01

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ~10% of satellite dwarf galaxies with M_star > 10^6 M_sun that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased towards larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger ...

  11. Explosions Triggered by Violent Binary-Star Collisions: Application to Eta Carinae and other Eruptive Transients

    CERN Document Server

    Smith, Nathan

    2010-01-01

    This paper discusses a model where a violent periastron collision of stars in an eccentric binary system induces an eruption or explosion seen as a brief transient source, attributed to LBVs, SN impostors, or other transients. The key ingredient is that an evolved primary increases its photospheric radius on relatively short timescales, to a point where the radius is comparable to or larger than the periastron separation in an eccentric binary. In such a configuration, a violent and sudden collision would ensue, possibly leading to substantial mass ejection instead of a binary merger. Repeated periastral grazings in an eccentric system could quickly escalate to a catastrophic encounter, wherein the companion star actually plunges deep inside the photosphere of a bloated primary during periastron, as a result of the primary star increasing its own radius. This is motivated by the case of $\\eta$~Carinae, where such a collision must have occured if conventional estimates of the present-day orbit are correct, and...

  12. LBVs AND THE NATURE OF THE S DOR CYCLES: THE CASE OF AG CARINAE

    Directory of Open Access Journals (Sweden)

    J. H. Groh

    2008-01-01

    Full Text Available Presentamos los resultados de un análisis espectroscópico detallado sobre 20 a~nos de observaciones de AG Carinae, usando el código de transferencia radiativa llamado CMFGEN. Entre las conclusiones de este trabajo, resaltamos la importancia de incluir efectos dependientes del tiempo en el análisis del ciclo completo de S Dor. Hemos obtenido que la tasa de pérdida de masa es aproximadamente constante durante las fases fras, implicando que las erupciones en los objetos de tipo S Dor comienzan bastante más temprano que durante el máximo observado en la curva de luz visual. Hemos determinado ademías que los ciclos S Dor son, en ultima instancia, consecuencia de un aumento/disminución del radio hidrostático en combinación con una pseudo-fotosfera.

  13. Early-type massive stars in Carina Nebula within the Gaia-ESO Survey.

    Science.gov (United States)

    Berlanas, S. R.; Herrero, A.; Martins, F.; Simón-Díaz, S.; Mahy, L.; Blomme, R.; GES WG-13

    2017-03-01

    The Gaia-ESO Survey (GES) is obtaining high quality spectra of ˜ 10^5 stars in our Galaxy, providing an homogeneous and unique overview of all the main components of the Milky Way, its formation history and the evolution of young, mature and ancient Galactic populations. Our group is in charge of the early-type massive stars that define the youngest population in the survey. In this contribution, we present the results of the quantitative spectroscopic analysis of O-type stars in the Carina Nebula within the Gaia-ESO Survey. For this aim, we have used FASTWIND and CMFGEN stellar atmosphere codes, providing stellar parameters for the current sample (GES data release iDR4).

  14. Deep census of variable stars in a VLT/VIMOS field in Carina

    CERN Document Server

    Pietrukowicz, P; Fernández, J M; Pietrzynski, G; Ruiz, M T; Gieren, W; Diaz, R F; Zoccali, M; Hempel, M

    2009-01-01

    We have searched for variable stars in deep V-band images of a field towards the Galactic plane in Carina. The images were taken with VIMOS instrument at ESO VLT during 4 contiguous nights in April 2005. We detected 348 variables among 50897 stars in the magnitude range between V=15.4 and V=24.5 mag. Upon detection, we classified the variables by direct eye inspection of their light curves. All variable objects but 9 OGLE transits in the field are new discoveries. We provide a complete catalog of all variables which includes eclipsing/ellipsoidal binaries, miscellaneous pulsators (mostly delta Scuti-type variables), stars with flares and other (irregular and likely long-period) variables. Only two of the stars in our sample are known to host planets. Our result give some implications for future large variability surveys.

  15. Modelling the Central Constant Emission X-ray component of η Carinae

    Science.gov (United States)

    Russell, Christopher M. P.; Corcoran, Michael F.; Hamaguchi, Kenji; Madura, Thomas I.; Owocki, Stanley P.; Hillier, D. John

    2016-05-01

    The X-ray emission of η Carinae shows multiple features at various spatial and temporal scales. The central constant emission (CCE) component is centred on the binary and arises from spatial scales much smaller than the bipolar Homunculus nebula, but likely larger than the central wind-wind collision region between the stars as it does not vary over the ˜2-3 month X-ray minimum when it can be observed. Using large-scale 3D smoothed particle hydrodynamics (SPH) simulations, we model both the colliding-wind region between the stars, and the region where the secondary wind collides with primary wind ejected from the previous periastron passage. The simulations extend out to one hundred semimajor axes and make two limiting assumptions (strong coupling and no coupling) about the influence of the primary radiation field on the secondary wind. We perform 3D radiative transfer calculations on the SPH output to synthesize the X-ray emission, with the aim of reproducing the CCE spectrum. For the preferred primary mass-loss rate dot{M}_A≈ 8.5× 10^{-4} M_{⊙} yr-1, the model spectra well reproduce the observation as the strong- and no-coupling spectra bound the CCE observation for longitude of periastron ω ≈ 252°, and bound/converge on the observation for ω ≈ 90°. This suggests that η Carinae has moderate coupling between the primary radiation and secondary wind, that both the region between the stars and the comoving collision on the backside of the secondary generate the CCE, and that the CCE cannot place constraints on the binary's line of sight. We also discuss comparisons with common X-ray fitting parameters.

  16. XMM-Newton Observations of the 2003 X-Ray Minimum of Eta Carinae

    Science.gov (United States)

    Hamaguchi, K.; Corcoran, M. F.; White, N. E.; Damineli, A.; Davidson, K.; Gull, T. R.

    2004-01-01

    The XMM-Newton X-ray observatory took part in the multi-wavelength observing campaign of the massive, evolved star Eta Carinae in 2003 during its recent X-ray minimum in June 2003. This paper reports on the first results of these observations, which were performed (1) before the minimum (five times in January, 2003), (2) near the X-ray maximum just before the minimum (two times in June) and (3) during the minimum (four times in July-August). Hard X-ray emission from the point source of Eta Carinae was detected even during the minimum. The observed flux above 3 keV was approx. 3x10(exp -12) ergs cm(exp -2)/s, which is about one percent of the flux before the minimum. Light curves from the individual observations show no time variability on the scale of a few kilo-seconds. Changes in the spectral shape occurred, but these changes were smaller than expected if the minimum is produced solely by an increase of hydrogen column density. Fits of the hard X-Ray source by an absorbed 1T model show a constant plasma temperature at around 5 keV and an increase of column density from 5x10(exp 22) cm(exp -2) to 2x10(exp 23) cm(exp -2). The spectra below 6 keV significantly deviate from the models that fit the higher energy emission. The X-ray minimum seems to be dominated by an apparent decrease of the emission measure, suggesting that the brightest part of the X-ray emitting region is completely obscured during the minimum in the form of an eclipse. Partial covering plasma emission models might be considered for the spectral variation. The spectra also showed strong iron K line emission from both hot and cold gases, and weak line emission from Ni, Ca, Ar, S and Si.

  17. Unveiling the Secret of a Virgo Dwarf Galaxy

    Science.gov (United States)

    2000-05-01

    case of the seemingly inconspicuous dwarf galaxy IC 3382 , the astronomers made an amazing discovery. When the best fitting model was removed from the observed image, a neat and regular spiral structure appeared in the residual image, cf. PR Photo 11/00 ! Nothing like this has ever been seen before in a dwarf elliptical galaxy. The light associated with the spiral constitutes a 3% modulation of the surface brightness. To see this effect at all, requires the excellent image quality of FORS1 and ANTU. The origin of the spiral structure What is the cause for this faintest and smallest spiral ever discovered in a galaxy? Two possible explanations have been proposed by the astronomers. It has been known for several decades that the spiral patterns seen in disk galaxies, like for instance in the Milky Way galaxy, are "density waves". The patterns are due to collective oscillations in the gravitational field that moves the stars and gas back and forth. The presence of a spiral pattern in IC3328 implies that it harbours a thin disk. The available data do not allow to distinguish between a pure disk galaxy, or a disk embedded in a spheroidal mass distribution. Both configurations are known to exist. Transient spiral patterns, as that seen in the well-known, nearby galaxy Messier 51, can be generated by tidal interactions . In the present case, there are two close and faint dwarf galaxies which may have disturbed IC3328 in the past and thereby produced the spiral pattern we now see. If what we see is a pure disk galaxy, the exceptionally small amplitude of the spiral pattern suggests another possibility: it could be swing-amplified noise . A modest amount of cold lumpy gas in the disk may have provided some initial "graininess" which was then gradually amplified by a shearing effect of the stellar orbits in the disk to produce the striking spiral pattern we now see. More information about this project A research article about this discovery is being published in the European

  18. Microlensing Binaries with Candidate Brown Dwarf Companions

    DEFF Research Database (Denmark)

    Shin, I.-G; Han, C.; Gould, A.

    2012-01-01

    Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing...... masses of the brown dwarf companions are 0.02 ± 0.01 M⊙ and 0.019 ± 0.002 M⊙ for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events...

  19. ANAESTHESIA FOR EVALUATION AND EXCISION OF TRACHEAL TUMOUR AT CARINA EXTENDING INTO RIGHT MAIN BRONCHUS: CASE REPORT

    Directory of Open Access Journals (Sweden)

    Deepraj Singh

    2014-04-01

    Full Text Available A tracheal tumor at carinal angle is uncommon. Presented here is an interesting case of a 22 year old, HBsAg positive female with a tracheal tumor at carina extending into the right main bronchus. The patient reported shortness of breath along with fatigue and cough. Routine and other appropriate investigations were done during which X-ray chest and CT scan revealed right lung collapse with ipsilateral shift of mediastinum. Telescopic evaluation and biopsy performed under general anesthesia using supraglottic Jet Ventilation further revealed proliferative growth arising from the anterior wall of the carina extending into the right main bronchus. Subsequently, excision of the tumor through tracheotomy under general anesthesia was carried out. The patient recovered completely with no postoperative complications.

  20. Results of two multi-chord stellar occultations by dwarf planet (1) Ceres

    CERN Document Server

    Gomes-Júnior, A R; Braga-Ribas, F; Assafin, M; Vieira-Martins, R; Camargo, J I B; Sicardy, B; Timerson, B; George, T; Broughton, J; Blank, T; Benedetti-Rossi, G; Brooks, J; Dantowitz, R F; Dunham, D W; Dunham, J B; Ellington, C K; Emilio, M; Herpich, F R; Jacques, C; Maley, P D; Mehret, L; Mello, A J T; Milone, A C; Pimentel, E; Schoenell, W; Weber, N S

    2015-01-01

    We report the results of two multi-chord stellar occultations by the dwarf planet (1) Ceres that were observed from Brazil on 2010 August 17, and from the USA on 2013 October 25. Four positive detections were obtained for the 2010 occultation, and nine for the 2013 occultation. Elliptical models were adjusted to the observed chords to obtain Ceres' size and shape. Two limb fitting solutions were studied for each event. The first one is a nominal solution with an indeterminate polar aspect angle. The second one was constrained by the pole coordinates as given by Drummond et al. Assuming a Maclaurin spheroid, we determine an equatorial diameter of 972 $\\pm$ 6 km and an apparent oblateness of 0.08 $\\pm$ 0.03 as our best solution. These results are compared to all available size and shape determinations for Ceres made so far, and shall be confirmed by the NASA's Dawn space mission.

  1. White dwarfs in cataclysmic variables

    Science.gov (United States)

    Gaensicke, Boris

    2016-07-01

    Cataclysmic variables (CVs) provide excellent laboratories to study the effect that the accretion of matter, energy and angular momentum has on the structure of white dwarfs, with important implications on the evolution of these compact binaries, the ignition of thermonuclear surface burning, and potentially their explosion as SNIa. I will provide an overview of our current understanding of CV white dwarfs, with a particular emphasis on the results of a recent large HST program. I will review our knowledge regarding the mass distribution of CV white dwarfs, as well as the secular mean accretion rates that can be inferred from their effective temperatures, and compare those statistics with predictions from CV population models. I will also discuss a sub-set of CVs which underwent thermal-time scale mass transfer, one of the channels that is often discussed as a pathway to SN Ia, and I will illustrate how the study of these "failed SNIa" can contribute to the discussion of SNIa progenitors. Finally, I will discuss the occurrence of non-radial pulsations in white dwarfs, both in CVs and their detached progenitors.

  2. Fully Automated One-Step Production of Functional 3D Tumor Spheroids for High-Content Screening.

    Science.gov (United States)

    Monjaret, François; Fernandes, Mathieu; Duchemin-Pelletier, Eve; Argento, Amelie; Degot, Sébastien; Young, Joanne

    2016-04-01

    Adoption of spheroids within high-content screening (HCS) has lagged behind high-throughput screening (HTS) due to issues with running complex assays on large three-dimensional (3D) structures.To enable multiplexed imaging and analysis of spheroids, different cancer cell lines were grown in 3D on micropatterned 96-well plates with automated production of nine uniform spheroids per well. Spheroids achieve diameters of up to 600 µm, and reproducibility was experimentally validated (interwell and interplate CV(diameter) integration of micropatterned spheroid models within fundamental research and drug discovery applications.

  3. A Deep Study of the Dwarf Satellites Andromeda XXVIII and Andromeda XXIX

    Science.gov (United States)

    Slater, Colin T.; Bell, Eric F.; Martin, Nicolas F.; Tollerud, Erik J.; Ho, Nhung

    2015-06-01

    We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomposing the horizontal branch into blue (metal-poor, assumed to be older) and red (relatively more metal-rich, assumed to be younger) populations shows that the metal-rich are also more spatially concentrated in the center of the galaxy. We use spectroscopic measurements of the calcium triplet, combined with the improved precision of the Gemini photometry, to measure the metallicity of the galaxies, confirming the metallicity spread and showing that they both lie on the luminosity-metallicity relation for dwarf satellites. Taken together, the galaxies exhibit largely typical properties for dSphs despite their significant distances from M31. These dwarfs thus place particularly significant constraints on models of dSph formation involving environmental processes such as tidal or ram pressure stripping. Such models must be able to completely transform the two galaxies into dSphs in no more than two pericentric passages around M31, while maintaining a significant stellar population gradient. Reproducing these features is a prime requirement for models of dSph formation to demonstrate not just the plausibility of environmental transformation but the capability of accurately recreating real dSphs.

  4. A DEEP STUDY OF THE DWARF SATELLITES ANDROMEDA XXVIII AND ANDROMEDA XXIX

    Energy Technology Data Exchange (ETDEWEB)

    Slater, Colin T.; Bell, Eric F. [Department of Astronomy, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109 (United States); Martin, Nicolas F. [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, F-67000 Strasbourg (France); Tollerud, Erik J.; Ho, Nhung [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06510 (United States)

    2015-06-20

    We present the results of a deep study of the isolated dwarf galaxies Andromeda XXVIII and Andromeda XXIX with Gemini/GMOS and Keck/DEIMOS. Both galaxies are shown to host old, metal-poor stellar populations with no detectable recent star formation, conclusively identifying both of them as dwarf spheroidal galaxies (dSphs). And XXVIII exhibits a complex horizontal branch morphology, which is suggestive of metallicity enrichment and thus an extended period of star formation in the past. Decomposing the horizontal branch into blue (metal-poor, assumed to be older) and red (relatively more metal-rich, assumed to be younger) populations shows that the metal-rich are also more spatially concentrated in the center of the galaxy. We use spectroscopic measurements of the calcium triplet, combined with the improved precision of the Gemini photometry, to measure the metallicity of the galaxies, confirming the metallicity spread and showing that they both lie on the luminosity–metallicity relation for dwarf satellites. Taken together, the galaxies exhibit largely typical properties for dSphs despite their significant distances from M31. These dwarfs thus place particularly significant constraints on models of dSph formation involving environmental processes such as tidal or ram pressure stripping. Such models must be able to completely transform the two galaxies into dSphs in no more than two pericentric passages around M31, while maintaining a significant stellar population gradient. Reproducing these features is a prime requirement for models of dSph formation to demonstrate not just the plausibility of environmental transformation but the capability of accurately recreating real dSphs.

  5. Improved photometry of SDSS crowded field images: Structure and dark matter content in the dwarf spheroidal galaxy Leo I

    CERN Document Server

    Smolcic, V; Bell, E F; Coleman, M G; Rix, H W; Schinnerer, E; Ivezic, Z; Kniazev, A

    2007-01-01

    We explore how well crowded field point-source photometry can be accomplished with SDSS data: We present a photometric pipeline based on DoPhot, and tuned for analyzing crowded-field images from the SDSS. Using Monte Carlo simulations we show that the completeness of source extraction is above 80% to i >6 ( Ic_sol), and possibly >75 if the DM halo dominates the mass and extends further out than 12'. In summary, our results show that Leo I is a symmetric, relaxed and bound system; this supports the idea that Leo I is a dark-matter dominated system.

  6. THREE NEW ECLIPSING WHITE-DWARF-M-DWARF BINARIES DISCOVERED IN A SEARCH FOR TRANSITING PLANETS AROUND M-DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Law, Nicholas M. [Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, ON M5S 3H4 (Canada); Kraus, Adam L. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Street, Rachel; Fulton, Benjamin J.; Shporer, Avi; Lister, Tim [Las Cumbres Observatory Global Telescope Network, Inc., 6740 Cortona Dr. Suite 102, Santa Barbara, CA 93117 (United States); Hillenbrand, Lynne A.; Baranec, Christoph; Bui, Khanh; Davis, Jack T. C.; Dekany, Richard G.; Kulkarni, S. R.; Ofek, Eran O. [Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Bloom, Joshua S.; Cenko, S. Bradley; Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Burse, Mahesh P.; Das, H. K. [Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Pune-411007 (India); Kasliwal, Mansi M. [Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101 (United States); Nugent, Peter [Computational Cosmology Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); and others

    2012-10-01

    We present three new eclipsing white-dwarf/M-dwarf binary systems discovered during a search for transiting planets around M-dwarfs. Unlike most known eclipsing systems of this type, the optical and infrared emission is dominated by the M-dwarf components, and the systems have optical colors and discovery light curves consistent with being Jupiter-radius transiting planets around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part of the Palomar Transient Factory (PTF). We present a graphics processing unit (GPU)-based box-least-squares search for transits that runs approximately 8 Multiplication-Sign faster than similar algorithms implemented on general purpose systems. For the discovered systems, we decompose low-resolution spectra of the systems into white-dwarf and M-dwarf components, and use radial velocity measurements and cooling models to estimate masses and radii for the white dwarfs. The systems are compact, with periods between 0.35 and 0.45 days and semimajor axes of approximately 2 R{sub Sun} (0.01 AU). The M-dwarfs have masses of approximately 0.35 M{sub Sun }, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000 K and have masses of approximately 0.5 M{sub Sun }. We use the Robo-AO laser guide star adaptive optics system to tentatively identify one of the objects as a triple system. We also use high-cadence photometry to put an upper limit on the white-dwarf radius of 0.025 R{sub Sun} (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that 0.08%{sub -0.05%}{sup +0.10%} (90% confidence) of M-dwarfs are in these short-period, post-common-envelope white-dwarf/M-dwarf binaries where the optical light is dominated by the M-dwarf. The lack of detections at shorter periods, despite near-100% detection efficiency for such systems, suggests that binaries including these relatively low-temperature white dwarfs are preferentially found at

  7. Isolation, identification, and spheroids formation of breast cancer stem cells, therapeutics implications

    Directory of Open Access Journals (Sweden)

    Maytham Abbas Abboodi

    2014-01-01

    Full Text Available Aims: Cancer stem cells (CSCs are population of cells present in tumors, which can undergo self-renewal and differentiation. Three-dimensional (3D in vitro models mimic features of the in vivo environment and provide unique perspectives on the behavior of stem cells. Materials and Methods: In this study, MDA-MB 231 cells were grown in two-dimensional (2D monolayers and 3D spheroid formats and CSCs were isolated and grown as spheroids. The isolated CSCs were subjected to molecular studies for detection of CD44, CD24, MMP1, ABCG2, ALDH1, and GAPDH markers. Results: The monolayer of CSCs grown as spheroids showed better growth rate than the MDA-MB 231 cells, which shows the efficacy of 3D spheroid format of growing CSCs. CD44 show increased expression in spheroids compared to 2D culture of MDA-MB 231. ALDH1 a key marker of breast stem cells was highly expressed in BCSCs and MDA-MB 231 grown in 3D, while being absent in CSCs and MDA-MB 231 cells grown in 2D. Conclusions: The CSCs grown as spheroids showed better growth rate, which showed the efficacy of 3D spheroid format for CSCs culture. Since the association between BCSCs prevalence and clinical outcome and the evidence presented in this study support key roles of CSCs in breast cancer metastasis and drug resistance, it has been proposed that new therapies must target these cells.

  8. Evaluation of bioactivity of octacalcium phosphate using osteoblastic cell aggregates on a spheroid culture device

    Directory of Open Access Journals (Sweden)

    Takahisa Anada

    2016-03-01

    Full Text Available Much attention has been paid to three-dimensional cell culture systems in the field of regenerative medicine, since three-dimensional cellular aggregates, or spheroids, are thought to better mimic the in vivo microenvironments compared to conventional monolayer cultured cells. Synthetic calcium phosphate (CaP materials are widely used as bone substitute materials in orthopedic and dental surgeries. Here we have developed a technique for constructing a hybrid spheroid consisting of mesenchymal stem cells (MSCs and synthetic CaP materials using a spheroid culture device. We found that the device is able to generate uniform-sized CaP/cell hybrid spheroids rapidly and easily. The results showed that the extent of osteoblastic differentiation from MSCs was different when cells were grown on octacalcium phosphate (OCP, hydroxyapatite (HA, or β-tricalcium phosphate (β-TCP. OCP showed the greatest ability to increase the alkaline phosphatase activity of the spheroid cells. The results suggest that the spheroids with incorporated OCP may be an effective implantable hybrid consisting of scaffold material and cells for bone regeneration. It is also possible that this CaP–cell spheroid system may be used as an in vitro method for assessing the osteogenic induction ability of CaP materials.

  9. A comparison between semi-spheroid- and dome-shaped quantum dots coupled to wetting layer

    Directory of Open Access Journals (Sweden)

    Mohammadreza Shahzadeh

    2014-06-01

    Full Text Available During the epitaxial growth method, self-assembled semi-spheroid-shaped quantum dots (QDs are formed on the wetting layer (WL. However for sake of simplicity, researchers sometimes assume semi-spheroid-shaped QDs to be dome-shaped (hemisphere. In this work, a detailed and comprehensive study on the difference between electronic and transition properties of dome- and semi-spheroid-shaped quantum dots is presented. We will explain why the P-to-S intersubband transition behaves the way it does. The calculated results for intersubband P-to-S transition properties of quantum dots show two different trends for dome-shaped and semi-spheroid-shaped quantum dots. The results are interpreted using the probability of finding electron inside the dome/spheroid region, with emphasis on the effects of wetting layer. It is shown that dome-shaped and semi-spheroid-shaped quantum dots feature different electronic and transition properties, arising from the difference in lateral dimensions between dome- and semi-spheroid-shaped QDs. Moreover, an analogy is presented between the bound S-states in the quantum dots and a simple 3D quantum mechanical particle in a box, and effective sizes are calculated. The results of this work will benefit researchers to present more realistic models of coupled QD/WL systems and explain their properties more precisely.

  10. Identification of Lgr5-Independent Spheroid-Generating Progenitors of the Mouse Fetal Intestinal Epithelium

    Directory of Open Access Journals (Sweden)

    Roxana C. Mustata

    2013-10-01

    Full Text Available Immortal spheroids were generated from fetal mouse intestine using the culture system initially developed to culture organoids from adult intestinal epithelium. Spheroid proportion progressively decreases from fetal to postnatal period, with a corresponding increase in production of organoids. Like organoids, spheroids show Wnt-dependent indefinite self-renewing properties but display a poorly differentiated phenotype reminiscent of incompletely caudalized progenitors. The spheroid transcriptome is strikingly different from that of adult intestinal stem cells, with minimal overlap of Wnt target gene expression. The receptor LGR4, but not LGR5, is essential for their growth. Trop2/Tacstd2 and Cnx43/Gja1, two markers highly enriched in spheroids, are expressed throughout the embryonic-day-14 intestinal epithelium. Comparison of in utero and neonatal lineage tracing using Cnx43-CreER and Lgr5-CreERT2 mice identified spheroid-generating cells as developmental progenitors involved in generation of the prenatal intestinal epithelium. Ex vivo, spheroid cells have the potential to differentiate into organoids, qualifying as a fetal type of intestinal stem cell.

  11. Early formation of massive, compact, spheroidal galaxies with classical profiles by violent disc instability or mergers

    CERN Document Server

    Ceverino, Daniel; Tweed, Dylan; Primack, Joel

    2014-01-01

    We address the formation of massive stellar spheroids between redshifts $z=4$ and 1 using a suite of AMR hydro-cosmological simulations. The spheroids form as bulges, and the spheroid mass growth is partly driven by violent disc instability (VDI) and partly by mergers. A kinematic decomposition to disc and spheroid yields that the mass fraction in the spheroid is between 50% and 90% and is roughly constant in time, consistent with a cosmological steady state of VDI discs that are continuously fed from the cosmic web. The density profile of the spheroid is typically classical, with a Sersic index $n = 4.5\\pm 1$, independent of whether it grew by mergers or VDI. The disc is characterized by $n=1.5\\pm 0.5$, and the whole galaxy by $n=3\\pm 1$. The high-redshift spheroids are compact due to the dissipative inflow of gas and the high universal density. The stellar surface density within the effective radius of each galaxy as it evolves remains roughly constant in time after its first growth. For galaxies of a fixed...

  12. Encapsulated multicellular tumor spheroids as a novel in vitro model to study small size tumors

    Directory of Open Access Journals (Sweden)

    Markvicheva Elena

    2003-01-01

    Full Text Available Presently multicellular tumor spheroids (MTS are being widely used in various aspects of tumor biology, including studies in biology and photodynamic therapy. The cellular organization of spheroids allows the recreation of in vivo small tumors much better than all common two-dimensional in vitro models. The cell encapsulation method could be proposed as a novel technique to quickly and easily prepare a large number of spheroids with narrow size distribution within a desirable diameter range. Moreover, the proposed technique for spheroid generation using encapsulated growing tumor cells could provide entirely new avenues to develop a novel spheroid co-culture model (for instance, the in vitro co-cultvation of tumor cells and monocytes, or epithelial cells, or fibroblasts etc. The current research was aimed at developing a simple and reliable method to encapsulate tumor cells and to cultivate them in vitro. In order to generate spheroids, MCF-7 cells were encapsulated and cultivated in 200 ml T-flasks in a 5% CO2 atmosphere at 37°C for 4-5 weeks. The cell proliferation was easily observed using a light microscope. The cells grew in aggregates increasing in size with time. The cell growth resulted in the formation of large cell clusters (spheroids which filled the whole microcapsule volume in 4-5 weeks.

  13. Assessing the internal consistency of the CARINA data base in the Pacific sector of the Southern Ocean

    Directory of Open Access Journals (Sweden)

    C. L. Sabine

    2010-07-01

    Full Text Available The CARINA project is aimed at gathering and providing secondary quality control checks on carbon and carbon-relevant hydrographic and geochemical data from cruises all across the Atlantic, Arctic and Southern Ocean. In total the project gathered 188 cruises that were not previously available to the public. Of these 188 cruises, 37 are part of the Southern Ocean. Parameters from the Southern Ocean cruises, including total carbon dioxide (TCO2, total alkalinity, oxygen, nitrate, phosphate and silicate, were examined for cruise-to-cruise consistency. pH and chlorofluorocarbons (CFCs are also part of the data base, but are not discussed here. This paper focuses on the quality control of the Southern Ocean data from the Pacific sector which consisted of 29 cruises of which 17 were included in a previous synthesis called GLODAP, 11 were new cruises from the CARINA dataset, and one cruise was included in GLODAP but was updated with new data and therefore also included in CARINA. The Pacific sector quality control procedures included crossover analysis between stations and inversion analysis of all crossover data. The GLODAP data were included into the analysis as reference cruises but without applying the GLODAP recommended adjustments so the corrections could be independently verified. The outcome of this effort is an internally consistent, high-quality carbon data set for all cruises, including the reference cruises.

  14. Eta Carinae across the 2003.5 Minimum: Analysis in the visible and near infrared spectral region

    CERN Document Server

    Nielsen, K E; Weis, K; Gull, T R; Stahl, O; Bomans, D J

    2009-01-01

    We present an analysis of the visible through near infrared spectrum of Eta Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES at the ESO VLT". This is a part of larger effort to present a complete Eta Carinae spectrum, and extends the previously presented analyses with the HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near UV is characterized by the ejecta absorption. At longer wavelengths, stellar wind features from the central source and narrow emission lines from the Weigelt condensations dominate the spectrum. However, narrow absorption lines from the circumstellar shells are present. This paper provides a description of the spectrum between 3060 and 10,430 A, including line identifications of the ejecta absorption spectrum, the emission spectrum from the Weigelt condensations and the P-Cygni stellar wind features. The high spectral resolving power of VLT/UVES enables equivalent width measurements of atomic and molecular absorption lines for element...

  15. Near-Infrared properties of the X-ray emitting young stellar objects in the Carina Nebula

    CERN Document Server

    Preibisch, Thomas; Irwin, Mike; Lewis, James R; King, Robert R; McCaughrean, Mark J; Zinnecker, Hans; Townsley, Leisa; Broos, Patrick

    2011-01-01

    Abbreviated Abstract: The near-infrared study of the Carina Nebula in this paper builds on the results of the Chandra Carina Complex Project (CCCP), that detected 14368 X-ray sources in the 1.4 square-degree survey region, an automatic source classification study that classified 10714 of these as very likely young stars in Carina, and an analysis of their clustering properties. We used HAWK-I at the ESO VLT to conduct a very deep near-IR survey with sub-arcsecond angular resolution, covering about 1280 square-arcminutes. The HAWK-I images reveal more than 600000 individual infrared sources, whereby objects as faint as J ~ 23, H ~ 22, and Ks ~ 21 are detected at S/N >= 3. While less than half of the Chandra X-ray sources have counterparts in the 2MASS catalog, the ~5 mag deeper HAWK-I data reveal infrared counterparts to 6636 (= 88.8%) of the 7472 Chandra X-ray sources in the HAWK-I field. We analyze near-infrared color-color and color-magnitude diagrams to derive information about the extinctions, infrared ex...

  16. Eigenvalue spectrum of the spheroidal harmonics: A uniform asymptotic analysis

    CERN Document Server

    Hod, Shahar

    2015-01-01

    The spheroidal harmonics $S_{lm}(\\theta;c)$ have attracted the attention of both physicists and mathematicians over the years. These special functions play a central role in the mathematical description of diverse physical phenomena, including black-hole perturbation theory and wave scattering by nonspherical objects. The asymptotic eigenvalues $\\{A_{lm}(c)\\}$ of these functions have been determined by many authors. However, it should be emphasized that all previous asymptotic analyzes were restricted either to the regime $m\\to\\infty$ with a fixed value of $c$, or to the complementary regime $|c|\\to\\infty$ with a fixed value of $m$. A fuller understanding of the asymptotic behavior of the eigenvalue spectrum requires an analysis which is asymptotically uniform in both $m$ and $c$. In this paper we analyze the asymptotic eigenvalue spectrum of these important functions in the double limit $m\\to\\infty$ and $|c|\\to\\infty$ with a fixed $m/c$ ratio.

  17. Landslides and Mass Shedding on Spinning Spheroidal Asteroids

    CERN Document Server

    Scheeres, D J

    2014-01-01

    Conditions for regolith landslides to occur on spinning, gravitating spheroidal asteroids and their aftermath are studied. These conditions are developed by application of classical granular mechanics stability analysis to the asteroid environment. As part of our study we determine how slopes evolve across the surface of these bodies as a function of spin rate, the dynamical fate of material that exceeds the angle of repose, and an analysis of how the shape of the body may be modified based on these results. We find specific characteristics for body surfaces and shapes when spun near the surface disruption limit and develop what their observable implications are. The small, oblate and rapidly spinning asteroids such as 1999 KW4 Alpha and 2008 EV5 exhibit some of these observable traits. The detailed mechanisms outlined here can also provide insight and constraints on the recently observed active asteroids such as P/2013 P5, and the creation of asteroidal meteor streams.

  18. Formation of microstructures in the spheroidal graphite cast iron

    Science.gov (United States)

    Wang, S.; Daloz, D.; Bruneseaux, F.; Lesoult, G.

    2012-01-01

    Pipeline systems for hydraulic networks are obtained via centrifugal casting of spheroidal graphite cast iron. The very high cooling rate that is achieved in the skin of the product can sometimes lead to carbide instead of graphite in cast iron. An experimental device has been built in the laboratory that allows reproducing the extreme thermal conditions encountered during formation of skin of centrifugally cast pipes. Liquid metal droplets fall on a cold substrate. Rapid directional solidification occurs. The temperature evolution of the lower surface of the droplet is recorded during the very first moment of the solidification (t cast state and the heat-treated state. They are compared to the centrifugally cast ones. A model of directional solidification of cast iron under a very large temperature gradient has been built. It allows explaining the transition from stable to metastable micro structure that was observed in the products and reproduced in the laboratory samples.

  19. Eigenvalue spectrum of the spheroidal harmonics: A uniform asymptotic analysis

    Science.gov (United States)

    Hod, Shahar

    2015-06-01

    The spheroidal harmonics Slm (θ ; c) have attracted the attention of both physicists and mathematicians over the years. These special functions play a central role in the mathematical description of diverse physical phenomena, including black-hole perturbation theory and wave scattering by nonspherical objects. The asymptotic eigenvalues {Alm (c) } of these functions have been determined by many authors. However, it should be emphasized that all the previous asymptotic analyzes were restricted either to the regime m → ∞ with a fixed value of c, or to the complementary regime | c | → ∞ with a fixed value of m. A fuller understanding of the asymptotic behavior of the eigenvalue spectrum requires an analysis which is asymptotically uniform in both m and c. In this paper we analyze the asymptotic eigenvalue spectrum of these important functions in the double limit m → ∞ and | c | → ∞ with a fixed m / c ratio.

  20. Spheroid degeneration of conjunctiva and cornea. Two years' follow up.

    Science.gov (United States)

    Norn, M

    1980-10-01

    Twenty-six subjects with spheroid degeneration were followed up after two years. The number of colourless conjunctival droplets was seen to have increased by on an average 46% (2 alpha = 0.05) and that of autofluorescent conjunctival droplets by 223% (2 alpha less than 0.01). Counting within the individual sites sites disclosed that some droplets will disappear (not less than 30 and 21% respectivelY), while recently formed will constitute at least 76 and 243%. The number of areas with band-shaped keratopathy was found to rise from 3 to 26 (P less than 0.001) out of 104 possibilities, (nasally and temporally of right and left eye). Vital staining (fluorescein, rose bengal, tetrazolium, alcian blue) showed the epithelium above the droplets to be intact, and the droplet-containing eyes were found not to be abnormally dry (break up time, tear production).