K‐Band Calibration of the Red Clump Luminosity

Abstract

The average near-infrared (K-band) luminosity of 238 Hipparcos red clump giants is derived and then used to measure the distance to the Galactic center. These Hipparcos red clump giants have been previously employed as I-band standard candles. The advantage of the K-band is a decreased sensitivity to reddening, and perhaps also a reduced systematic dependence on metallicity. In order to investigate the latter, and also to refer our calibration to a known metallicity zero-point, we restrict our sample of red clump calibrators to those with abundances derived from high-resolution spectroscopic data. The mean metallicity of the sample is [Fe/H] = −0.18 dex (σ = 0.17 dex). The data are consistent with no correlation between M K and [Fe/H], and only weakly constrain the slope of this relation. The luminosity function of the sample peaks at M K = −1.61 ± 0.03 mag. Next, we assemble published optical and near-infrared photometry for ∼ 20 red clump giants in a Baade's Window field with a mean metallicity of [Fe/H] = −0.17 ± 0.09 dex, which is nearly identical to that of the Hipparcos red clump. Assuming that the average (V − I) 0 and (V − K) 0 colors of these two red clumps are the same, the extinctions in the Baade's Window field are found to be A V /A I /A K = 1.56/0.87/0.15, in agreement with previous estimates. We derive the distance to the Galactic center: (m − M ) 0 = 14.58 ± 0.11 mag, or R = 8.24 ± 0.42 kpc. The uncertainty in this distance measurement is dominated by the small number of Baade's Window red clump giants examined here.

The chemical composition of carbon stars. The R-type stars

“…Arenou & Luri 1999), were then estimated with a Monte-Carlo simulation by adopting different distributions for the abscissa residuals of the IAD (see also Pourbaix & Jorissen 2000). Following this procedure, these authors derived a true average absolute K-magnitude for the early-R stars: M K 0 = −2 ±1, similar to the value −1.61 ±0.03 found by Alves (2000) for red clump giant stars near the Sun observed by Hipparcos. Another major study on the parallaxes of R stars was made by Bergeat et al (2002a).…”

A spectroscopic survey of faint, high-Galactic-latitude red clump stars

“…Udalski (2000), using the same selection conditions as Paczynsky & Stanek (1998), found instead a weak dependence on metallicity in the form M I = −0.26(±0.02) +(0.13 ±0.07)([Fe/H]+0.25). Alves (2000) found M K = −1.61 ± 0.03, with a negligible dependence on metallicity in the form M K = −1.64(±0.07) + (0.57 ± 0.36)([Fe/H] + 0.25). Groenewegen (2008), working this time with the revised Hipparcos parallaxes of van Leeuwen (2007), found slightly fainter absolute magnitudes for RC stars, M I = −0.22(±0.03), and M K = −1.54(±0.04), confirming a null or very weak dependence on metallicity.…”

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

“…We then measure the mean distances to both samples in (l, b)-space at a fixed latitude of 3.5 • b 4.5 • in 1 • -spaced longitude bins between −9 • l +9 • . As we did in comparing with the observed X-shape, in order to match the observational uncertainties, we first convert the line of sight distance of every star particle to an observed magnitude by adopting an absolute magnitude for the red clump of MK = -1.61 mag (Alves 2000). The magnitude distribution of stars towards each line of sight is then convolved with a Gaussian with σ = 0.17 mag.…”