26 research outputs found

    Chemical composition of Galactic OB stars II. The fast rotator Z Oph

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    Z Oph, HD149757, is an O9.5 Vnn star with a very high projected rotational velocity (vsini >= 340 km\s). It is also a classical runaway star due to its high proper motion. We perform a quantitative analysis of its optical spectrum in order to measure important observables of the star such as its mass, effective temperature, luminosity and He, C, N, and O abundances. Comparing these observed values to those predicted by the rotating evolutionary models of the Geneva group we find that none of the two sets of models is capable of reproducing the characteristics of the star. Nevertheless, due to its runaway nature, the reason for this discrepancy may be that the star is not the result of the evolution of a single object, but the product of the evolution of a close binary system.Comment: Accepted for publication in A&

    Chemical composition of Galactic OB stars I. CNO abundances in O9 stars

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    We present NLTE abundances of CNO for a sample of four O9 stars in the Galaxy, together with new determinations of their stellar parameters, TeffT_{\rm eff}, logg\log g, ϵ\epsilon(He) and microturbulence. These new analyses take into account the effect of {\it line--blocking} in the spectral synthesis with our classical NLTE, plane--parallel and hydrostatic model atmospheres. The sample includes three O9 He normal stars: two dwarfs, HD 214680 and HD 34078, and one supergiant, HD 209975, and one fast rotating giant with a preliminary high He overabundance, HD 191423 with ϵ\epsilon(He)=0.20. We find first that the consideration of microturbulence in the spectral synthesis for the fast rotator leads to a considerably lower He abundance, ϵ\epsilon(He)=0.12. The CNO abundances of the three He normal stars are in good agreement with the values in the literature for Galactic B dwarfs with no evidence of mixing, and show that they all have the same chemical composition. We also discuss however the possible CNO contamination of the supergiant HD 209975. For the fast rotator we find that the abundances show the trend of the CNO contamination: a N overabundance together with C and O depletion. The N/C and N/O ratios of our stars as a function of their projected rotational velocities are consistent with the predictions of the recent evolutionary models of Meynet & Maeder [Mey&Mae00].Comment: 19 pages, 12 figures, 13 tables, accepted by A&

    The VLT-FLAMES survey of massive stars: Mass loss and rotation of early-type stars in the SMC

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    We have studied the optical spectra of a sample of 31 O- and early B-type stars in the Small Magellanic Cloud, 21 of which are associated with the young massive cluster NGC 346. Stellar parameters are determined using an automated fitting method. Comparison with predictions of stellar evolution that account for stellar rotation does not result in a unique age, though most stars are best represented by an age of 1-3 Myr. The present day v_sini distribution of the 21 dwarf stars in our sample is consistent with an underlying rotational velocity (v_r) distribution that can be characterised by a mean velocity of about 160-190 km/s and an effective half width of 100-150 km/s. The v_r distribution must include a small percentage of slowly rotating stars. If predictions of the time evolution of the equatorial velocity for massive stars within the environment of the SMC are correct, the young age of the cluster implies that this underlying distribution is representative for the initial rotational velocity distribution. The location in the Hertzsprung-Russell diagram of the stars showing helium enrichment is in qualitative agreement with evolutionary tracks accounting for rotation, but not for those ignoring v_r. The mass loss rates of the SMC objects having luminosities of log L/L_sun > 5.4 are in excellent agreement with predictions. However, for lower luminosity stars the winds are too weak to determine M_dot accurately from the optical spectrum. Two of three spectroscopically classified Vz stars from our sample are located close to the theoretical zero age main sequence, as expected.Comment: 35 pages, accepted for publication in A&

    O stars with weak winds: the Galactic case

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    We study the stellar and wind properties of a sample of Galactic O dwarfs to track the conditions under which weak winds (i.e mass loss rates lower than ~ 1e-8 Msol/yr) appear. The sample is composed of low and high luminosity dwarfs including Vz stars and stars known to display qualitatively weak winds. Atmosphere models including non-LTE treatment, spherical expansion and line blanketing are computed with the code CMFGEN. Both UV and Ha lines are used to derive wind properties while optical H and He lines give the stellar parameters. Mass loss rates of all stars are found to be lower than expected from the hydrodynamical predictions of Vink et al. (2001). For stars with log L/Lsol > 5.2, the reduction is by less than a factor 5 and is mainly due to the inclusion of clumping in the models. For stars with log L/Lsol < 5.2 the reduction can be as high as a factor 100. The inclusion of X-ray emission in models with low density is crucial to derive accurate mass loss rates from UV lines. The modified wind momentum - luminosity relation shows a significant change of slope around this transition luminosity. Terminal velocities of low luminosity stars are also found to be low. The physical reason for such weak winds is still not clear although the finding of weak winds in Galactic stars excludes the role of a reduced metallicity. X-rays, through the change in the ionisation structure they imply, may be at the origin of a reduction of the radiative acceleration, leading to lower mass loss rates. A better understanding of the origin of X-rays is of crucial importance for the study of the physics of weak winds.Comment: 31 pages, 42 figures. A&A accepted. A version of the paper with full resolution figures is available at http://www.mpe.mpg.de/~martins/publications.htm

    Identifying birth places of young isolated neutron stars

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    Young isolated radio-quiet neutron stars are still hot enough to be detectable at X-ray and optical wavelengths due to their thermal emission and can hence probe cooling curves. An identification of their birth sites can constrain their age. For that reason we try to identify the parent associations for four of the so-called Magnificent Seven neutron stars for which proper motion and distance estimates are available. We are tracing back in time each neutron star and possible birth association centre to find close encounters. The associated time of the encounter expresses the kinematic age of the neutron star which can be compared to its characteristic spin-down age. Owing to observational uncertainties in the input data, we use Monte-Carlo simulations and evaluate the outcome of our calculations statistically. RX J1856.5-3754 most probably originated from the Upper Scorpius association about 0.3 Myr ago. RX 0720.4-3125 was either born in the young local association TWA about 0.4 Myr ago or in Tr 10 0.5 Myr in the past. Also RX J1605.3+3249 and RBS 1223 seem to come from a nearby young association such as the Sco-Cen complex or the extended Corona-Australis association. For RBS 1223 also a birth in Sct OB2 is possible. We also give constraints on the observables as well as on the radial velocity of the neutron star. Given the birth association, its age and the flight time of the neutron star, we estimate the mass of the progenitor star. Some of the potential supernovae were located very nearby (<100pc) and thus should have contributed to the 10Be and 60Fe material found in the Earth's crust. In addition we reinvestigate the previously suggested neutron star/ runaway pair PSR B1929+10/ zeta Ophiuchi and conclude that it is very likely that both objects were ejected during the same supernova event.Comment: 14 figures, 13 table

    The evolution of rotating stars

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    First, we review the main physical effects to be considered in the building of evolutionary models of rotating stars on the Upper Main-Sequence (MS). The internal rotation law evolves as a result of contraction and expansion, meridional circulation, diffusion processes and mass loss. In turn, differential rotation and mixing exert a feedback on circulation and diffusion, so that a consistent treatment is necessary. We review recent results on the evolution of internal rotation and the surface rotational velocities for stars on the Upper MS, for red giants, supergiants and W-R stars. A fast rotation is enhancing the mass loss by stellar winds and reciprocally high mass loss is removing a lot of angular momentum. The problem of the ``break-up'' or Ω\Omega-limit is critically examined in connection with the origin of Be and LBV stars. The effects of rotation on the tracks in the HR diagram, the lifetimes, the isochrones, the blue to red supergiant ratios, the formation of W-R stars, the chemical abundances in massive stars as well as in red giants and AGB stars, are reviewed in relation to recent observations for stars in the Galaxy and Magellanic Clouds. The effects of rotation on the final stages and on the chemical yields are examined, as well as the constraints placed by the periods of pulsars. On the whole, this review points out that stellar evolution is not only a function of mass M and metallicity Z, but of angular velocity Ω\Omega as well.Comment: 78 pages, 7 figures, review for Annual Review of Astronomy and Astrophysics, vol. 38 (2000

    PREDIKSI KUANTITAS AIR BERSIH DARI PDAM KABUPATEN KARANGFANYAR DI KECAMATAN MATESIH PADA TAHUN 2025

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    IsniGhofarSholeh, 2015, “PREDIKSI KUANTITAS AIR BERSIH DARI PDAM KABUPATENKARANGANYAR DI KECAMATAN MATESIH PADA TAHUN 2025”,TugasAkhir, Program D-III TeknikSipilFakultasTeknik, UniversitasSebelasMaretSurakarta. Air merupakan kebutuhan yang sangat penting bagi kelangsungan hidup manusia.Tingkat pertumbuhan penduduk yang tinggi serta besarnya arus urbanisasi menyebabkanbertambahnyakebutuhan air yang dipenuhioleh Perusahaan Daerah Air Minum (PDAM). Dalampemenuhankebutuhan air padaKecamtanMatesihKabupatenKaranganyar, PDAM KabupatenKaranganyarmemanfaatkansumbermata air yang ada. JenisPenelitianiniadalahdeskripsikuantitatif.Studiuntukmengetahuiproduksi air minumdari PDAM KabupatenKaranganyardanmengetahuikebutuhan air bersih di KecamatanMatesihKabupatenKaranganyar. Data yang diperlukandalampenelitianiniadalahjumlahpendudukKecamatanMatesihKabupatenKaranganyar, data debit air yang adamenurut Unit Wilayah di KabupatenKaranganyar. Bertujuanmengetahuihasilprediksijumlahpendudukdanmenurutmetodegeometrik yang digunakanuntukmengetahuihasilprediksikebutuhan air padatahun 2025. Berdasarkananalisis data jumlahpenduduktahun 2025 terdapathasilprediksikebutuhan air bersihpadatahun 2025 di KecamatanMatesihKaranganyarsebesar57.497lt/dt, kebutuhanharianmaksimum12,598 lt/dt, dan debit pada jam puncak16,33lt/dt.HasilperhitunganpadaRancanganAnggaranBiaya (RAB) pemasangansambunganrumahbaru (SR) di KecamatanMatesihKabupatenKaranganyaradalahsebesar Rp.2.280.767,- Kata Kunci :Prediksi,JumlahPenduduk, Kebutuhan Air PDAM
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