Is missing Fe I opacity in stellar atmospheres a significant problem?

Abstract

Abstract.We present an empirical model-atmosphere investigation of missing Fe I opacity. Houdashelt et al. (2000) estimated that if Dragon & Mutschlecner (1980) Fe I cross sections used in the MARCS model atmospheres (Gustafsson et al. 1975) were replaced by the Bautista (1997) cross sections the solar continuous flux would be reduced by 15% in the near ultraviolet. That would imply systematic errors in models for F, G, and K stars. As a consequence, since ATLAS9 (Kurucz 1993a) uses an approximation to the same Dragon & Mutschlecner (1980) opacities, there should also be similar systematic errors in ATLAS9 models that required this investigation. Bound-free Fe I cross sections computed by Bautista (1997) in the framework of the IRON Project were used to generate the continuous Fe I absorption coefficient. It was incorporated in the Kurucz (1993a) ATLAS9 code, in place of that currently used, which is based on approximate cross sections by Kurucz. By combining Opacity Distribution Functions (ODFs) computed without the contribution of Fe I autoionization lines with the new Fe I absorption coefficient which is crowded with autoionization resonances, we obtained solar metallicity model atmospheres and energy distributions for several combinations of T eff and log g. The comparison of these models with the standard ATLAS9 models has shown that there are no differences in the T -τ Ross relations, while there are some changes in the energy distributions for T eff ≤ 7000 K, but limited to small wavelength regions around 2150 Å, where Kurucz has less opacity, and 3350 Å, where Bautista has less opacity. The differences are of the order of 25% and less than 10%, respectively. That around 2150 Å disappears for T eff ≤ 5500 K owing to the fall of the emergent flux at these wavelengths in cool stars. This behaviour is independent of the gravity. The explanation is that our line list actually has more autoionizing opacity than Bautista's but it is treated as bound-bound line opacity rather than as bound-free opacity.

RAPID CIRCUMSTELLAR DISK EVOLUTION AND AN ACCELERATING STAR FORMATION RATE IN THE INFRARED DARK CLOUD M17 SWex

“…Using the SED fitting tool of Robitaille et al (2007), we fit stellar atmosphere models from Castelli & Kurucz (2004), incorporating interstellar reddening as a free parameter (   A 0 45 V SED mag; the upper limit set by inspection of the near-IR colors of all point sources detected in the field, see P13) using the extinction law of Indebetouw et al (2005), to all sources with  N 4 data detections in the seven combined NIR-MIR bands. Following P13, we set the minimum photometric error bars used in SED fitting to 5% in the JHK S , [3.6], and is the goodness-of-fit parameter for the best-fitting model) to 26,625 sources; this is more than an order of magnitude more than the 1498 sources found by PW10 at the same step.…”

The Kepler-454 System: A Small, Not-Rocky Inner Planet, a Jovian World, and a Distant Companion

“…We also determined the atmospheric parameters using the line analysis code MOOG (Sneden 1973(Sneden , version 2014) and a Kurucz model atmosphere with the new opacity distribution function (ODFNEW; Castelli & Kurucz 2004;Kurucz 1992), as done in Dumusque et al (2014). We measured the equivalent widths of iron spectral lines on a coadded spectrum of S/N  400 using ARES v2 with automatic continuum determination (Sousa et al 2015).…”

K s-band secondary eclipses of WASP-19b and WASP-43b with the Anglo-Australian Telescope★

“…We listed all molecular and atomic absorbers used in our models with references to the line databases in Table 2 of Zhou et al (2013). The spectra of host stars WASP-19 and WASP-43 were obtained from the STScI stellar atmosphere models (Castelli & Kurucz 2004) for stars with effective temperature, T eff of 5500K and 4500K respectively. Finally, we explore the effect of clouds and hazes models to the model spectra.…”