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Hawkins K.,Institute of Astronomy | Kordopatis G.,Institute of Astronomy | Kordopatis G.,Leibniz Institute for Astrophysics Potsdam | Gilmore G.,Institute of Astronomy | And 22 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We aim to characterize high-velocity (HiVel) stars in the solar vicinity both chemically and kinematically using the fourth data release of the RAdial Velocity Experiment (RAVE). We used a sample of 57HiVel starswith Galactic rest-frame velocities larger than 275 km s-1.With 6D position and velocity information, we integrated the orbits of the HiVel stars and found that, on average, they reach out to 13 kpc from the Galactic plane and have relatively eccentric orbits consistent with the Galactic halo. Using the stellar parameters and [α/Fe] estimates from RAVE, we found the metallicity distribution of the HiVel stars peak at [M/H] = -1.2 dex and is chemically consistent with the inner halo. There are a few notable exceptions that include a hypervelocity star candidate, an extremely HiVel bound halo star, and one star that is kinematically consistent with the halo but chemically consistent with the disc. High-resolution spectra were obtained for the metal-rich HiVel star candidate and the second highest velocity star in the sample. Using these high-resolution data, we report the discovery of a metal-rich halo star that has likely been dynamically ejected into the halo from the Galactic thick disc. This discovery could aid in explaining the assembly of the most metal-rich component of the Galactic halo. © 2015 The Authors.

Zerjal M.,University of Ljubljana | Zwitter T.,University of Ljubljana | Matijevic G.,Villanova University | Strassmeier K.G.,Leibniz Institute for Astrophysics Potsdam | And 16 more authors.
Astrophysical Journal | Year: 2013

RAVE, the unbiased magnitude limited survey of southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the Ca II infrared triplet (IRT) range, which is a known indicator of chromospheric activity. Our previous work classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here, we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-local thermal equilibrium profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5 Å wide interval and their sum EWIRT for ∼44,000 candidate active dwarf stars with signal-to-noise ratio >20, with no cuts on the basis of the source of their emission flux. From these, ∼14,000 show a detectable chromospheric flux with at least a 2σ confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and, in some cases, radial velocities of active stars derived from automatic pipelines suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity, and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre-main-sequence cases. The catalog will be made publicly available with the next RAVE public data releases. © 2013. The American Astronomical Society. All rights reserved.

Conn B.,Max Planck Institute for Astronomy | Ederoclite A.,Institute of Astrophysics of Canarias | Rix H.-W.,Max Planck Institute for Astronomy | Martin N.,Max Planck Institute for Astronomy | And 8 more authors.
EPJ Web of Conferences | Year: 2012

EMPhaSSiS is a photometric and spectroscopic survey of the disk of the Milky Way. The survey covers 33 fields in the 3rd quadrant of the Milky Way and probes every ten degrees in Galactic Longitude between l = 180 â̂̃ - 280â̂̃ and at Galactic Latitudes of b = -20â̂̃, - 30 â̂̃ and - 40â̂̃. Each field is observed in four filters, U, B, V and R, reaching depths of 21.5, 24.0, 23.5 and 23.5 respectively. Spectroscopic observations have been carried out in 11 of these fields and in so doing, main sequence turn-off stars are being traced into the outer disk. This survey will provide metallicities and distances to the stellar populations that reside in the very outer disk of the Milky Way and help trace its evolution with increasing Galactic radius. © Owned by the authors, published by EDP Sciences, 2012.

Lykou F.,University of Vienna | Hron J.,University of Vienna | Zijlstra A.A.,Jodrell Bank Center for Astrophysics | Tuthill P.G.,Sydney Institute for Astronomy | And 7 more authors.
EAS Publications Series | Year: 2015

It is commonly accepted that asymmetries found in the post-AGB stars and planetary nebulae should originate as early as during the AGB phase. We present results from our high-angular resolution observing programs, with an aperture masking technique on the VLT, of a sample of evolved stars that were known to present asymmetries at larger spatial scales (e.g. jets, torii and/or bipolar nebulae). Disk-like structures have been found in the vicinity of at least two of these stars. © 2015 EAS, EDP Sciences.

Bland-Hawthorn J.,Sydney Institute for Astronomy | Leon-Saval S.,Sydney Institute for Astronomy
2011 Int. Quantum Electron. Conf., IQEC 2011 and Conf. Lasers and Electro-Optics, CLEO Pacific Rim 2011 Incorporating the Australasian Conf. Optics, Lasers and Spectroscopy and the Australian Conf. | Year: 2011

Recent developments in astrophotonics herald a new era for ground-based astronomy. These technologies are now being extended and adapted to space-borne instrumentation over the coming decade. One of the revolutionary developments is the photonic integrated multimode microspectrograph (PIMMS) that greatly reduces the size of any spectrograph, independent of the telescope aperture, the slit aperture or the spectroscopic resolution of the instrument. We now extend these ideas to space instrumentation where a much broader spectral range can be explored. We are focusing our efforts on the extremes of the UV to mid-infrared (0.15-15μm) window that is increasingly becoming more accessible to photonic technologies. © 2011 IEEE.

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