Moreover, there is no guarantee that the derived stellar parameters will coincide with any isochrone. It is difficult to accurately propagate the uncertainties in the stellar parameters to the isochrone-based parameters (unless the full covariance matrices are preserved). Furthermore, even with precise parallaxes, model isochrones are still necessary for estimating masses and ages.Ī limitation of existing isochrone-based methods is the reliance on stellar parameters that have been derived elsewhere (e.g., from a separate spectroscopic pipeline). Therefore, even in the Gaia era, there is a need for complementary distance constraints provided by stellar isochrones (e.g., Mints & Hekker 2018 Sanders & Das 2018) or empirically calibrated data-driven models (e.g., Leistedt & Hogg 2017 Anderson et al. For fainter and more distant sources the Gaia parallax becomes quite uncertain, and hence distances are also uncertain and depend on various subtleties such as the method of parallax inversion and assumed priors (e.g., Bailer-Jones et al. Comparison to the observed flux enables a measurement of distance (an estimate of the extinction must also be available).įor relatively bright and nearby sources, Gaia DR2 now provides very precise parallaxes. In essence, this approach translates stellar properties that can be measured independent of distance and age, such as T eff,, and, into a predicted age and absolute luminosity. In order to estimate masses, ages, and distances, one often combines these derived stellar parameters with model stellar isochrones (e.g., Pont & Eyer 2004 Jørgensen & Lindegren 2005 Takeda et al. For example, different methods for analysis of stellar spectra can deliver, with varying degrees of reliability, estimates of T eff,, radial velocities, and abundances (e.g., Smiljanic et al. In previous work the measurement of these quantities has been performed in separate steps. These include stellar properties such as T eff,, ,, mass, and age, as well as 3D positions and velocities. In order to make progress, the raw observations must be converted into physical quantities. ![]() In turn, these maps should deliver new insight into the formation and assembly history of the Galaxy, its dynamical state, and possibly the nature of dark matter. Together, these observational efforts promise to provide new, much sharper maps of the stellar components of the Galaxy. The field of Galactic astronomy is undergoing a dramatic change driven by multiple large-scale ground-based photometric and spectroscopic surveys and the space-based Gaia mission (Gaia Collaboration et al. Comparison between the two reveals good agreement within their formal uncertainties after accounting for the Gaia zero-point uncertainties. These stars are fit without the Gaia parallaxes so that the geometric parallaxes can serve as an independent test of the spectrophotometric distances. Finally, we fit a large sample of stars from the H3 Spectroscopic Survey in which high-quality Gaia parallaxes are also available. ![]() Derived distances,, , and − T eff relations are in overall good agreement with literature values, although there are trends between metallicity and within clusters that point to systematic uncertainties at the ≈0.1 dex level. We then fit combined spectra and photometry of stars in the open and globular clusters M92, M13, M3, M107, M71, and M67. ![]() ![]() Fits to a variety of benchmark stars including Procyon, Arcturus, and the Sun result in derived stellar parameters that are in good agreement with the literature. We then fit a selection of data in order to validate the model outputs. Mock data are fit in order to demonstrate how the precision of derived parameters depends on evolutionary phase and signal-to-noise ratio. MINESweeper employs a Bayesian framework and can easily incorporate a variety of priors, including Gaia parallaxes. This approach enables the measurement of spectrophotometric distances, in addition to stellar parameters such as T eff,, ,, and radial velocity. We present MINESweeper, a tool to measure stellar parameters by jointly fitting observed spectra and broadband photometry to model isochrones and spectral libraries.
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