We discuss the properties of Hα emission stars across the sample of 22035 spectra from the Gaia-ESO Survey internal data release, observed with the GIRAFFE instrument and largely belonging to stars in young open clusters. Automated fits using two independent Gaussian profiles and a third component that accounts for the nebular emission allow us to discern distinct morphological types of Hα line profiles with the introduction of a simplified classification scheme. All in all, we find 3765 stars with intrinsic emission and sort their spectra into eight distinct morphological categories: single-component emission, emission blend, sharp emission peaks, double emission, P-Cygni, inverted P-Cygni, self-absorption, and emission in absorption. We have more than one observation for 1430 stars in our sample, thus allowing a quantitative discussion of the degree of variability of Hα emission profiles, which is expected for young, active objects. We present a catalogue of stars with properties of their Hα emission line profiles, morphological classification, analysis of variability with time and the supplementary information from the SIMBAD, VizieR, and ADS databases. The records in SIMBAD indicate the presence of Hα emission for roughly 25% of all stars in our catalogue, while at least 305 of them have already been more thoroughly investigated according to the references in ADS. The most frequently identified morphological categories in our sample of spectra are emission blend (23%), emission in absorption (22%), and self-absorption (16%). Objects with repeated observations demonstrate that our classification into discrete categories is generally stable through time, but categories P-Cygni and self-absorption seem less stable, which is the consequence of discrete classification rules, as well as of the fundamental change in profile shape. Such records of emission stars can be valuable for automatic pipelines in large surveys, where it may prove very useful for pinpointing outliers when calculating general stellar properties and elemental abundances. They can be used in studies of star formation processes, interacting binaries, and other fields of stellar physics.
COBISS.SI-ID: 566913
In this paper we study the soft X-ray (SXR) signatures of one particular prominence. The X-ray observations used here were made by the Hinode/X-Ray Telescope instrument using two different filters. Both of them have a pronounced peak of the response function around 10 Å. One of them has a secondary smaller peak around 170 Å, which leads to a contamination of SXR images. The observed darkening in both of these filters has a very large vertical extension. The position and shape of the darkening correspond nicely with the prominence structure seen in SDO/AIA images. First, we have investigated the possibility that the darkening is caused by X-ray absorption. However, detailed calculations of the optical thickness in this spectral range show clearly that this effect is completely negligible. Therefore, the alternative is the presence of an extended region with a large emissivity deficit, which can be caused by the presence of cool prominence plasmas within an otherwise hot corona. To reproduce the observed darkening, one needs a very large extension along the line of sight of the region amounting to around 10^5 km. We interpret this region as the prominence spine, which is also consistent with SDO/AIA observations in EUV.
COBISS.SI-ID: 548225
The Galactic Archaeology with HERMES (GALAH) survey is a large high-resolution spectroscopic survey using the newly commissioned High Efficiency and Resolution Multi-Element Spectrograph (HERMES) on the Anglo-Australian Telescope. The HERMES spectrograph provides high-resolution (R ~ 28 000) spectra in four passbands for 392 stars simultaneously over a 2 deg field of view. The goal of the survey is to unravel the formation and evolutionary history of the Milky Way, using fossil remnants of ancient star formation events which have been disrupted and are now dispersed throughout the Galaxy. Chemical tagging seeks to identify such dispersed remnants solely from their common and unique chemical signatures; these groups are unidentifiable from their spatial, photometric or kinematic properties. To carry out chemical tagging, the GALAH survey will acquire spectra for a million stars down to V ~ 14. The HERMES spectra of FGK stars contain absorption lines from 29 elements including light proton-capture elements, α-elements, odd-Z elements, iron-peak elements and n-capture elements from the light and heavy s-process and the r-process. This paper describes the motivation and planned execution of the GALAH survey, and presents some results on the first-light performance of HERMES.
COBISS.SI-ID: 520065