Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era

Abstract

We present fits to the broadband photometric spectral energy distributions (SEDs) of 158 eclipsing binaries (EBs) in the Tycho-2 catalog. These EBs were selected because they have highly precise stellar radii, effective temperatures, and in many cases metallicities previously determined in the literature, and thus have bolometric luminosities that are typically good to 10%. In most cases the available broadband photometry spans a wavelength range 0.4-10 µm, and in many cases spans 0.15-22 µm. The resulting SED fits, which have only extinction as a free parameter, provide a virtually model-independent measure of the bolometric flux at Earth. The SED fits are satisfactory for 156 of the EBs, for which we achieve typical precisions in the bolometric flux of ≈3%. Combined with the accurately known bolometric luminosity, the result for each EB is a predicted parallax that is typically precise to 5%. These predicted parallaxeswith typical uncertainties of 200 µas-are 4-5 times more precise than those determined by Hipparcos for 99 of the EBs in our sample, with which we find excellent agreement. There is no evidence among this sample for significant systematics in the Hipparcos parallaxes of the sort that notoriously afflicted the Pleiades measurement. The EBs are distributed over the entire sky, span more than 10 mag in brightness, reach distances of more than 5 kpc, and in many cases our predicted parallaxes should also be more precise than those expected from the Gaia first data release. The EBs studied here can thus serve as empirical, independent benchmarks for these upcoming fundamental parallax measurements.

The Araucaria project: High-precision orbital parallax and masses of eclipsing binaries from infrared interferometry

“…From spectroscopic and photometric observations, Andersen et al (1988) derived the parallax to be 6.17 ± 0.23 mas, consistent with the 5.94 ± 0.24 mas from Graczyk et al (2017) using the same method and the 5.98 ± 0.31 mas from Stassun & Torres (2016) from absolute stellar luminosity and bolometric flux fitting. The value from Hipparcos (van Leeuwen 2007, assuming a single star) is ∼ 2σ away from the more recent estimate (Graczyk et al 2017), but the Gaia measurement is within 1σ with 5.8336 ± 0.0262 mas (Gaia Collaboration et al 2018).…”

The Canonical Luminous Blue Variable AG Car and Its Neighbor Hen 3-519 Are Much Closer than Previously Assumed

“…Lindegren et al (2016) and Sesar et al (2016) similarly use samples such as RR Lyrae stars at intermediate distances to argue that no correction is needed beyond ∼1 kpc. Finally, Davies et al (2017) uses red clump stars over a large range of galactic distances to broadly confirm the above findings, with an offset similar to that of Stassun & Torres (2016a) for nearby stars that vanishes at d1.2 kpc. Therefore, since the distances of the LBVs in our study sample are all greater than ∼1 kpc (Table 1), we do not apply any offset to the parallaxes and moreover do not add any further systematic error to the reported measurement uncertainties.…”

“…Jao et al (2016) found a similar offset among a sample of nearby, high-proper-motion stars in the solar neighborhood. However, at larger distances, Stassun & Torres (2016a) found that the systematic offset vanishes for π1 mas (d1 kpc). This is corroborated by Casertano et al (2016), who found excellent agreement between the Gaia distances and a large sample of Galactic Cepheids at d∼2 kpc.…”

“…Consequently, ABJ provide a version of their catalog that includes this additional 0.3 mas error. However, Stassun & Torres (2016b) used a set of nearby, benchmark eclipsing binary stars (Stassun & Torres 2016a) to quantify the systematic error, finding it to be −0.25 ± 0.05 mas in the sense that the Gaia parallaxes are systematically too small (distances too long). Jao et al (2016) found a similar offset among a sample of nearby, high-proper-motion stars in the solar neighborhood.…”

Empirical Relations for the Accurate Estimation of Stellar Masses and Radii

“…The first Gaia data release (Gaia Collaboration et al 2016) has offered a new framework, providing accurate stellar luminosities for a significantly increased sample of stars. This has allowed a revision of the characteristics of some EB (Stassun & Torres 2016). Recently, the new Gaia DR2 (Gaia Collaboration et al 2018) has provided parallaxes with unprecedented precision.…”