* Astronomy

Title: The orbital poles of Milky Way satellite galaxies: a rotationally supported disc-of-satellites
Authors: Manuel Metz, Pavel Kroupa, Noam I. Libeskind

Available proper motion measurements of Milky Way (MW) satellite galaxies are used to calculate their orbital poles and projected uncertainties. These are compared to a set of recent cold dark-matter (CDM) simulations, tailored specifically to solve the MW satellite problem. We show that the CDM satellite orbital poles are fully consistent with being drawn from a random distribution, while the MW satellite orbital poles indicate that the disc-of-satellites of the Milky Way is rotationally supported. Furthermore, the bootstrapping analysis of the spatial distribution of theoretical CDM satellites also shows that they are consistent with being randomly drawn. The theoretical CDM satellite population thus shows a significantly different orbital and spatial distribution than the MW satellites, most probably indicating that the majority of the latter are of tidal origin rather than being DM dominated sub-structures. A statistic is presented that can be used to test a possible correlation of satellite galaxy orbits with their spatial distribution.
 
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Title: On the newly discovered Canes Venatici II dSph galaxy
Authors: C. Greco (1,2), M. Dall'Ora (3), G. Clementini (1), V. Ripepi (3), L. Di Fabrizio (4), K. Kinemuchi (5), M. Marconi (3), I. Musella (3), H. A. Smith (6), C. T. Rodgers (7), C. Kuehn (6), T. C. Beers (6,8), M. Catelan (9), B. J. Pritzl (10) ((1) INAF, Osservatorio Astronomico di Bologna, Bologna, Italy; (2) Current address: Observatoire de Geneve, Sauverny, Switzerland; (3) INAF, Osservatorio Astronomico di Capodimonte, Napoli, Italy; (4) INAF, Centro Galileo Galilei & Telescopio Nazionale Galileo, S.Cruz de La Palma, Spain; (5) Universidad de Concepcion, Departamento de Fisica, Concepcion, Chile, and University of Florida, Department of Astronomy, Gainesville, FL, USA; (6) Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA; (7) University of Wyoming, Department of Physics & Astronomy, Laramie, WY, US; (8) Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI, USA; (9) Pontificia Universidad Catolica de Chile, Departamento de Astronomia y Astrofisica, Santiago, Chile; (10) Department of Physics and Astronomy, University of Wisconsin Oshkosh, Oshkosh, WI, USA)

We report on the detection of variable stars in the Canes Venatici II (CVn II) dwarf spheroidal galaxy, a new satellite of the Milky Way recently discovered by the Sloan Digital Sky Survey. We also present a V, B-V colour-magnitude diagram that reaches V = 25.5 mag, showing the galaxy's main sequence turn off at V = 24.5 mag and revealing several candidate blue straggler stars. Two RR Lyrae stars have been identified within the half-light radius of CVn II,a fundamental-mode variable (RRab) with period P_ab = 0.743 days, and a first-overtone (RRc) RR Lyrae star with P_c = 0.358 days. The rather long periods of these variables along with their position on the period-amplitude diagram support an Oosterhoff type II classification for CVn II. The average apparent magnitude of the RR Lyrae stars, <V> = 21.48 ± 0.02 mag, is used to obtain a precision distance modulus of mu_0 = 21.02 ± 0.06 mag and a corresponding distance of 160(+4,-5} kpc, for an adopted reddening E(B-V) = 0.015 mag.

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Title: Observations of the Sagittarius Dwarf galaxy by the H.E.S.S. experiment and search for a Dark Matter signal
Authors: HESS Collaboration: F. Aharonian, et al

Observations of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy were carried out with the H.E.S.S. array of four imaging air Cherenkov telescopes in June 2006. A total of 11 hours of high quality data are available after data selection. There is no evidence for a very high energy gamma-ray signal above the energy threshold at the target position. A 95% C.L. flux limit of 3.6 x 10-12 cm-2s-1 above 250 GeV has been derived. Constraints on the velocity-weighted cross section <sigma v> are calculated in the framework of Dark Matter particle annihilation using realistic models for the Dark Matter halo profile of Sagittarius dwarf galaxy. Two different models have been investigated encompassing a large class of halo types. A 95% C.L. exclusion limit on <sigma v> of the order of 2 x 10-25 cm3s-1 is obtained for a core profile in the 100 GeV - 1 TeV neutralino mass range.

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Title: Dust mass-loss rates from AGB stars in the Fornax and Sagittarius dwarf Spheroidal galaxies
Authors: Eric Lagadec (University of Manchester), Albert A. Zijlstra (University of Manchester), Mikako Matsuura (NAOJ), J.W. Menzies (SAAO), Jacco Th. van Loon (Keele), Patricia A. Whitelock (SAAO)
(Version v2)

To study the effect of metallicity on the mass-loss rate of asymptotic giant branch (AGB) stars, we have conducted mid-infrared photometric measurements of such stars in the Sagittarius (Sgr dSph) and Fornax dwarf spheroidal galaxies with the 10-\mu m camera VISIR at the VLT. We derive mass-loss rates for 29 AGB stars in Sgr dSph and 2 in Fornax. The dust mass-loss rates are estimated from the K-[9] and K-[11] colours. Radiative transfer models are used to check the consistency of the method. Published IRAS and Spitzer data confirm that the same tight correlation between K-[12] colour and dust mass-loss rates is observed for AGB stars from galaxies with different metallicities, i.e. the Galaxy, the LMC and the SMC.
The derived dust mass-loss rates are in the range 5 x 10^{-10} to 3 x 10^{-8} M_{\odot}yr^{-1} for the observed AGB stars in Sgr dSph and around 5 x 10^{-9} M_{\odot}yr^{-1} for those in Fornax; while values obtained with the two different methods are of the same order of magnitude. The mass-loss rates for these stars are higher than the nuclear burning rates, so they will terminate their AGB phase by the depletion of their stellar mantles before their core can grow significantly. Some observed stars have lower mass-loss rates than the minimum value predicted by theoretical models.

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