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The characterization of the starsThe set of stars in common between empirical spectral stellar libraries (SSL) and key reference stars within empirical SSLs provide a useful insight into how consistent the SSLs are in their reported stellar parameters. This Task is focused on comparing the stellar parameters of empirical and theoretical SSLs, using the tools and resources of Tasks 1 and 2, to investigate the origins of the reported parameters and discrepencies between them. Key to this Task is to identify the set of stars with which to make the comparisons. There are two types of stars that can be identified:
1. Independent Reference Stars There are two types of stars that come under this heading:
These stars are useful as their parameters can be determine by means (somewhat) independent to spectropscopy and photometry and so provide a check on the reported parameters in the SSLs.
2. Stars in Common between Multiple SSLs The stars in common between SSLs present a useful set for exploring the range of parameters that can be attributed to a single star. They also represent stars that are used commonly by different groups for sometimes obvious and sometimes not obvious reasons. Generating a SiCn set involves an exploration of the parameter space of each library ingested into the SVO, and the extent of the cross-match between the libraries. Restricting the sample to be stars that are present in all available libraries would limit the available parameter space as the intersect between different libraries may be small. Hence obtaining a good coverage of the parameter space (Teff, log g, [Fe/H]) will be more easily accomplished by a constraint of at least three libraries in common.
Proposed Sub-Tasks and Contributed Effort Several sub-tasks were identified that could help define the issues of parameter consistency between stellar libraries and explore how to improve such issues for the community. They are:
The resources of the Libraries of Stellar Spectra webpage (Task 1) and Stellar Libraries in the Spanish Virtual Observatory (Task 2) and have been used to define the key set of stars to be considered. This work has been carried out cumulatively by members of the IAU WG independently, in collaborative meetings (Warsaw: Smiljanic, Worley, Gonneau), and at the ISSI-BJ Stellar Libraries of 2020 Team Meeting in April 2018 (http://svo2.cab.inta-csic.es/projects/issibj/main/index.php). The current status is that a SiCn set has been defined and a review of the sources of the parameters for each SSL being used is being undertaken. This will investigate the current precision of the parameters of stars in SSLs indicated by the dispersion of the reported parameters, and an update to most recent literature values. Key compilations of catalogues (VIZIER, PASTEL) have been exploited to provide the full extent of available parameters for the SSL stars, and to obtain ancillary information that can be used to provide other parameter reference scales. In particular, the SiCn set has been cross-matched with the recent Gaia Data Release 2. The astrometric log g, derived from the Gaia parallax, provides a key scale against which to compare the SSL parameters and the up-to-date literature sources. Assuming Gaia to be the 'true' reference scale, this comparison gives us an estimate of the accuracy of the parameters of the SSLs. This work will be summaried in a paper, Gonneau et al. 2018, as an outcome of the work of the ISSI-BJ Stellar Libraries of 2020 Team Meeting 1. The exploration of the parameters of SSLs will continue in upcoming meetings such as ISSI-BJ Stellar Libraries of 2020 Team Meeting 2 in 2019, and the next IWSSL meeting in China in 2020.
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