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- Eyer, L., et al.
(författare)
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Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623
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Tidskriftsartikel (refereegranskat)abstract
- Context. The ESA Gaia mission provides a unique time-domain survey for more than 1.6 billion sources with G less than or similar to 21 mag. Aims. We showcase stellar variability in the Galactic colour-absolute magnitude diagram (CaMD). We focus on pulsating, eruptive, and cataclysmic variables, as well as on stars that exhibit variability that is due to rotation and eclipses. Methods. We describe the locations of variable star classes, variable object fractions, and typical variability amplitudes throughout the CaMD and show how variability-related changes in colour and brightness induce "motions". To do this, we use 22 months of calibrated photometric, spectro-photometric, and astrometric Gaia data of stars with a significant parallax. To ensure that a large variety of variable star classes populate the CaMD, we crossmatched Gaia sources with known variable stars. We also used the statistics and variability detection modules of the Gaia variability pipeline. Corrections for interstellar extinction are not implemented in this article. Results. Gaia enables the first investigation of Galactic variable star populations in the CaMD on a similar, if not larger, scale as was previously done in the Magellanic Clouds. Although the observed colours are not corrected for reddening, distinct regions are visible in which variable stars occur. We determine variable star fractions to within the current detection thresholds of Gaia. Finally, we report the most complete description of variability-induced motion within the CaMD to date. Conclusions. Gaia enables novel insights into variability phenomena for an unprecedented number of stars, which will benefit the understanding of stellar astrophysics. The CaMD of Galactic variable stars provides crucial information on physical origins of variability in a way that has previously only been accessible for Galactic star clusters or external galaxies. Future Gaia data releases will enable significant improvements over this preview by providing longer time series, more accurate astrometry, and additional data types (time series BP and RP spectra, RVS spectra, and radial velocities), all for much larger samples of stars.
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2. |
- Hatzidimitriou, D., et al.
(författare)
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The Gaia-ESO Survey : The inner disc, intermediate-Age open cluster Pismis 18
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 626
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Tidskriftsartikel (refereegranskat)abstract
- Context. Pismis 18 is a moderately populated, intermediate-Age open cluster located within the solar circle at a Galactocentric distance of about seven kpc. Few open clusters have been studied in detail in the inner disc region before the Gaia-ESO Survey. Aims. New data from the Gaia-ESO Survey allowed us to conduct an extended radial velocity membership study as well as spectroscopic metallicity and detailed chemical abundance measurements for this cluster. Methods. Gaia-ESO Survey data for 142 potential members, lying on the upper main sequence and on the red clump, yielded radial velocity measurements, which, together with proper motion measurements from the Gaia Second Data Release (Gaia DR2), were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry from Gaia DR2 was used to re-determine cluster parameters based on high confidence member stars only. Cluster abundance measurements of six radial-velocity member stars with UVES high-resolution spectroscopy are presented for 23 elements. Results. The average radial velocity of 26 high confidence members is-27.5 ± 2.5 (std) km s-1 with an average proper motion of pmra =-5.65 ± 0.08 (std) mas yr-1 and pmdec =-2.29 ± 0.11 (std) mas yr-1. According to the new estimates, based on high confidence members, Pismis 18 has an age of τ = 700+40-50 Myr, interstellar reddening of E(B-V) = 0.562+0.012-0.026 mag and a de-reddened distance modulus of DM0 = 11.96+0.10-0.24 mag. The median metallicity of the cluster (using the six UVES stars) is [Fe/H] = +0.23 ± 0.05 dex, with [α/Fe] = 0.07 ± 0.13 and a slight enhancement of s-and r-neutron-capture elements. Conclusions. With the present work, we fully characterized the open cluster Pismis 18. We confirmed its present location in the inner disc. We estimated a younger age than the previous literature values and we gave, for the first time, its metallicity and its detailed abundances. Its [α/Fe] and [s-process/Fe], both slightly super-solar, are in agreement with other inner-disc open clusters observed by the Gaia-ESO survey.
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