We use thermochemical equilibrium calculations to model iron, magnesium, and silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar giant planets (EGPs), and low-mass stars. The behavior of individual Fe-, Mg-, and Si-bearing gases and condensates is determined as a function of temperature, pressure, and metallicity. Our equilibrium results are thus independent of any particular model atmosphere. The condensation of Fe metal strongly affects iron chemistry by efficiently removing Fe-bearing species from the gas phase. Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of EGPs and L dwarfs, and in the deep atmospheres of giant planets and T dwarfs. Mg- and Si-bearing gases are effectively removed from the atmosphere by forsterite (Mg2SiO4) and enstatite (MgSiO3) cloud formation. Monatomic Mg is the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO) is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and EGPs, whereas SiH4 is dominant in the deep atmosphere of Jupiter and other gas giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly important with decreasing effective temperature. In principle, a number of Fe, Mg, and Si gases are potential tracers of weather or diagnostic of temperature in substellar atmospheres.

https://iopscience.iop.org/article/10.1088/0004-637X/716/2/1060/pdf

Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon

A discussion and an evaluation of the degradation in sensitivity is given for a heterodyne spectrometer employing a HgCdTe photodiode mixer and tunable diode lasers. The minimum detectable source brightness is considered as a function of the mixer parameters, transmission coefficient of the beam splitter, and local oscillator emission powers. The degradation in the minimum detectable line source brightness which results from the bandwidth being a function of the line width is evaluated and plotted as a function of the wavelength and bandwidth for various temperature to mass ratios. It is shown that the minimum achievable degradation in the sensitivity of a practical astronomical heterodyne spectrometer is approximately 30. Estimates of signal-to-noise ratios with which infrared line emission from astronomical sources of interest may be detected are given.

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Sensitivity limits of an infrared heterodyne spectrometer for astrophysical applications.

The infrared spectrum of SiO near 1240 cm−1 and its relation to the circumstellar SiO maser

Vibration-rotation intensities of SiO

We studied the circumnuclear MIR emission in a sample of 19 local active galactic nuclei (AGN) with high spatial resolution spectra using T-ReCS (Gemini) and CanariCam (GTC), together with IRS/Spitzer observations. We measured the flux and the equivalent width for the 11.3 micron PAH feature and the [SIV] line emission as a function of galactocentric distance. This allowed to study the star formation (SF) at sub-kpc scales from the nucleus for a large sample of nearby AGN. The [SIV] line emission could be tracing the AGN radiation field within a few thousand times the sublimation radius (R_sub), but it often peaks at distances greater than 1000 R_sub. One possibility is that the SF is contributing to the [SIV] total flux. We found an 11.3 micron PAH emission deficit within the inner few tens of parsecs from the AGN. This deficit might be due to the destruction of the molecules responsible for this feature or the lack of SF at these distances. We found a sensible agreement in the expected shift of the relation of the AGN bolometric luminosity and the SF rate. This indicates that numerical models attributing the link between AGN activity and host galaxy growth to mergers are in agreement with our data, for most inner galaxy parts.

Circumnuclear star-formation and AGN activity: Clues from surface brightness radial profile of PAHs and [SIV]

Observations of silicon monoxide in cool stars at 4.05 microns

Planetary nebula NGC 7027 IR line spectra emission, examining S IV and AR III line intensities

Detection of 10.5-micron line emission from the planetary nebula ngc 7027.

Planetary nebulae NGC 6572, NGC 7009, NGC 7027 IR line emission, examining fine structure for Ne II, Cl IV, S IV and Ar III

J. Z. Holtz

Papers

Observations of silicon monoxide in cool stars at 4.05 microns

Detection of 10.5-micron line emission from the planetary nebula ngc 7027.

Infrared line emission from planetary nebulae