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

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 the 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 colormagnitude relations. A small fraction of stars are too faint compared to main-sequence fitting relations bymag, but the differences are marginal at a 2s level, partly due to relatively large parallax errors. On the other hand, we find that the photometric distances of stars showing signatures of youth as determined from lithium absorption line strengths and R 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 longdistance scale of the Pleiades.

Stellar twins determine the distance of the Pleiades

“…This comparison between the Hipparcos field stars implies that the reference parallax of the field twins are accurate. It further confirms the analysis of Kim et al (2016) who found that Hipparcos parallax to FGK field stars similar to Pleiades member stars are in good agreement with stellar models. Figure 3 shows the parallax of individual Pleiades stars, in which our results are compared with the literature (Makarov 2002;Soderblom et al 2005;van Leeuwen 2007).…”

Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri

“…SSPP has successfully passed a series of tests for validating the accuracy of spectroscopic parameters using high-resolution spectra and Galactic cluster data (Allende Prieto et al 2008;Lee et al 2008a,b). Recently, Kim et al (2016) applied the modified spectral matching technique, like the one used in this work, to high-S/N (> 100) spectra of bright G-and K-type dwarfs in the solar neighborhood, after downgrading spectra to R ∼ 10, 000, to validate stellar parameters against those based on equivalent-width analysis using MOOG (Sneden 1973).…”

“…To briefly summarize the spectral matching technique adopted in this study (see also Kim et al 2016), we employed the χ 2 minimization routine MPFIT (Markwardt 2009) to search the grid of synthetic spectra for the best-fitting set of T eff , log g, and [Fe/H] for an observed spectrum. Radial velocity (v r ) measurements were followed through cross-correlation with a synthetic spectrum.…”

The Galactic Bulge Survey: Completion of the X-Ray Survey Observations

“…To mitigate the effects that small differences in exposure time across our survey can have, we use count rates as a measure of intensity. We define the hardness ratio as the ratio between the count rate in the 2.5-8 keV minus that in the 0.3-2.5 keV band to the count rate in the full 0.3-8 keV energy band (after Kim et al 2004). We derived the hardness using XSPEC version 12.7 (Arnaud 1996) by determining the count rates in the soft and hard band taking the response and ancillary response file for each of the sources.…”