Spectroscopic Survey of G and K Dwarfs in the Hipparcos Catalog. I. Comparison between the Hipparcos and Photometric Parallaxes

TL;DR

This study compares Hipparcos parallaxes with photometric distances for G and K dwarfs, finding consistency with Hipparcos and supporting the longer Pleiades distance scale despite previous discrepancies.

Contribution

It provides spectroscopic validation of Hipparcos parallaxes for nearby stars, challenging claims that stellar activity affects distance estimates to the Pleiades.

Findings

Most stars follow empirical color-magnitude relations with Hipparcos data.

A small fraction of stars are marginally sub-luminous, but within error margins.

Youth indicators align with Hipparcos distances, supporting the long Pleiades distance.

Abstract

The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data and the development of a new geometric distance measurement for the cluster. A short Pleiades distance from the Hipparcos parallax predicts a number of stars in the solar neighborhood that are sub-luminous at a given photospheric abundance. We test this hypothesis using spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram. We derive stellar parameters for 170 nearby G and K type field dwarfs in the Hipparcos catalog based on high-resolution spectra obtained using KPNO 4-m echelle spectrograph. Our analysis shows that, when the Hipparcos parallaxes are adopted, most of our sample stars follow empirical color-magnitude relations. A small fraction of stars are too faint compared to main-sequence fitting relations by $\Delta M_V \geq 0.3$ mag, but the differences are marginal at a $2\sigma$ level partly due to relatively large parallax errors. On the other hand, we find that photometric distances of stars showing signatures of youth as determined from lithium absorption line strengths and $R'_{\rm HK}$ chromospheric activity indices are consistent with the Hipparcos parallaxes. Our result is contradictory to a suggestion that the Pleiades distance from main-sequence fitting is significantly altered by stellar activity and/or the young age of its stars, and provides an additional supporting evidence for the long distance scale of the Pleiades.