1,052 research outputs found

    Four new HgMn stars: HD 18104, HD 30085, HD 32867, HD 53588

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    We have detected four new HgMn stars, while monitoring a sample of apparently slowly rotating superficially normal bright late B and early A stars in the northern hemisphere. Important classification lines of Hg II and Mn II are found as conspicuous features in the high resolution SOPHIE spectra of these stars (R = 75000). Several lines of Hg II, Mn II and Fe II have been synthesized using model atmospheres and the spectrum synthesis code SYNSPEC48 including hyperfine structure of various isotopes when relevant. These synthetic spectra have been compared to high resolution high signal-to-noise observations of these stars in order to derive abundances of these key elements. The four stars are found to have distinct enhancements of Hg and Mn which show that these stars are not superficially normal B and A stars, but actually are new HgMn stars and should reclassified as such.Comment: 4 pages, 3 figures, accepted in A&

    A new method for the inversion of atmospheric parameters of A/Am stars

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    We present an automated procedure that derives simultaneously the effective temperature TeffT_{eff}, the surface gravity logg, the metallicity [Fe/H], and the equatorial projected rotational velocity vsini for "normal" A and Am stars. The procedure is based on the principal component analysis inversion method of Paletou et al. (2015a). A sample of 322 high resolution spectra of F0-B9 stars, retrieved from the Polarbase, SOPHIE, and ELODIE databases, were used to test this technique with real data. We have selected the spectral region from 4400-5000\AA\ as it contains many metallic lines and the Balmer HÎČ\beta line. Using 3 datasets at resolving powers of R=42000, 65000 and 76000, about 6.6x10610^6 synthetic spectra were calculated to build a large learning database. The Online Power Iteration algorithm was applied to these learning datasets to estimate the principal components (PC). The projection of spectra onto the few PCs offered an efficient comparison metric in a low dimensional space. The spectra of the well known A0- and A1-type stars, Vega and Sirius A, were used as control spectra in the three databases. Spectra of other well known A-type stars were also employed in order to characterize the accuracy of the inversion technique. All observational spectra were inverted and atmospheric parameters derived. After removal of a few outliers, the PCA-inversion method appears to be very efficient in determining TeffT_{eff}, [Fe/H], and vsini for A/Am stars. The derived parameters agree very well with previous determinations. Using a statistical approach, deviations of around 150 K, 0.35 dex, 0.15 dex, and 2 km/s were found for TeffT_{eff}, logg, [Fe/H], and vsini with respect to literature values for A-type stars. The PCA-inversion proves to be a very fast, practical, and reliable tool for estimating stellar parameters of FGK and A stars, and deriving effective temperatures of M stars.Comment: 16 pages, 9 figures. Accepted in A&

    The Quasar-frame Velocity Distribution of Narrow CIV Absorbers

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    We report on a survey for narrow (FWHM < 600 km/s) CIV absorption lines in a sample of bright quasars at redshifts 1.8≀z<2.251.8 \le z < 2.25 in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow CIV absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad MgII emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find a substantial number (≄43±6\ge 43\pm6 per cent) of absorbers with REW >0.3> 0.3 \AA in the velocity range +750 km/s \la v \la +12000 km/s are intrinsic to the AGN outflow. This `outflow fraction' peaks near v=+2000v=+2000 km/s with a value of foutflow≃0.81±0.13f_{outflow} \simeq 0.81 \pm 0.13. At velocities below v≈+2000v \approx +2000 km/s the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disk. Furthermore, we find that outflow-absorbers are on average broader and stronger than cosmologically-intervening systems. Finally, we find that ∌14\sim 14 per cent of the quasars in our sample exhibit narrow, outflowing CIV absorption with REW >0.3> 0.3\AA, slightly larger than that for broad absorption line systems.Comment: 11 pages, 9 figures, accepted for publication in MNRA
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