Previous computations of low-temperature Rosseland and Planck mean opacities from Alexander & Ferguson areupdatedandexpanded.Thenewcomputationsincludeamorecompleteequationofstate(EOS)withmoregrain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the EOS calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high-temperature condensates such as Al2O3 and CaTiO3 significantly affects the total opacityoveranarrowrangeoftemperaturesbeforetheappearanceofthefirstsilicategrains.Thenewopacitytables are tabulated for temperatures ranging from 30,000 to 500 K with gas densities from 10 � 4 to 10 � 19 gc m � 3 .C omparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method is shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided. Subject heading gs: atomic data — equation of state — methods: numerical — molecular data

http://iopscience.iop.org/article/10.1086/428642/pdf

Low-temperature opacities

We present our NextGen Model Atmosphere grid for low-mass stars for effective temperatures larger than 3000 K. These LTE models are calculated with the same basic model assumptions and input physics as the VLMS part of the NextGen grid so that the complete grid can be used, e.g., for consistent stellar evolution calculations and for internally consistent analysis of cool star spectra. This grid is also the starting point for a large grid of detailed NLTE model atmospheres for dwarfs and giants. The models were calculated from 3000 to 10,000 K (in steps of 200 K) for 3.5{le}logthinspg{le}5.5 (in steps of 0.5) and metallicities of {minus}4.0{le}[M/H]{le}0.0. We discuss the results of the model calculations and compare our results to the Kurucz grid. Some comparisons to standard stars like Vega and the Sun are presented and compared with detailed NLTE calculations. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}

The NextGen Model Atmosphere Grid for 3000 ≤ Teff ≤ 10,000 K

We present opacity sampling model atmospheres, synthetic spectra, and colors for brown dwarfs and very low mass stars in the following two limiting cases of dust grain formation: (1) Inefficient gravitational settling (i.e., the dust is distributed according to the chemical equilibrium predictions) and (2) efficient gravitational settling (i.e., the dust forms and depletes refractory elements from the gas, but their opacity does not affect the thermal structure). The models include the formation of over 600 gas-phase species and 1000 liquids and crystals and the opacities of 30 different types of grains including corundum (Al2O3), the magnesium aluminum spinel MgAl2O4, iron, enstatite (MgSiO3), forsterite (Mg2SiO4), amorphous carbon, SiC, and a number of calcium silicates. The models extend from the beginning of the grain formation regime well into the condensation regime of water ice (Teff = 3000-100 K) and encompass the range of log g = 2.5-6.0 at solar metallicity. We find that silicate dust grains can form abundantly in the outer atmospheric layers of red and brown dwarfs with a spectral type later than M8. The greenhouse effects of dust opacities provide a natural explanation for the peculiarly red spectroscopic distribution of the latest M dwarfs and young brown dwarfs. The grainless (cond) models, on the other hand, correspond closely to methane brown dwarfs such as Gliese 229B. We also discover that the λλ5891, 5897 Na I D and λλ7687, 7701 K I resonance doublets play a critical role in T dwarfs, in which their red wings define the pseudocontinuum from the I to the Z bandpass.

https://iopscience.iop.org/article/10.1086/321547/pdf

The limiting effects of dust in brown dwarf model atmospheres

MIPAS, the Michelson Interferometer for Pas- sive Atmospheric Sounding, is a mid-infrared emission spectrometer which is part of the core payload of ENVISAT. It is a limb sounder, i.e. it scans across the horizon detecting atmospheric spectral radiances which are inverted to verti- cal temperature, trace species and cloud distributions. These data can be used for scientific investigations in various re- search fields including dynamics and chemistry in the alti- tude region between upper troposphere and lower thermo- sphere. The instrument is a well calibrated and characterized Fourier transform spectrometer which is able to detect many trace constituents simultaneously. The different concepts of retrieval methods are described including multi-target and two-dimensional retrievals. Operationally generated data sets consist of temperature, H2O, O3, CH4, N2O, HNO3, and NO2 profiles. Measurement errors are investigated in de- tail and random and systematic errors are specified. The re- sults are validated by independent instrumentation which has been operated at ground stations or aboard balloon gondolas and aircraft. Intercomparisons of MIPAS measurements with other satellite data have been carried out, too. As a result, it

/pdf/mipas-an-instrument-for-atmospheric-and-climate-research-4mo2zpjq4z.pdf

MIPAS: an instrument for atmospheric and climate research

https://www.lpl.arizona.edu/~yelle/eprints/Yelle04b.pdf

Aeronomy of extra-solar giant planets at small orbital distances

A new list of H{sup +}{sub 3} infrared transition frequencies and intensities is presented. This list greatly extends the range of transitions considered to both higher energy and higher rotational states. The 3{times}10{sup 6} transitions are found to significantly affect both the absorption coefficient of H{sup +}{sub 3} and its cooling properties at temperatures above 1000 K. It is hoped these new data will be used for models of cool stars of low metallicity, the giant planets, and other warm bodies composed largely of H{sub 2}. {copyright} {ital 1996 The American Astronomical Society.}

Spectroscopic Properties of the H 3 + Molecule: A New Calculated Line List

Infrared spectra of the Jovian atmosphere around 2.1 and 4.0 microns, measured using the NASA Infrared Telescope Facility at Mauna Kea, Hawaii, are presented. The observations were made between February 6 and 8, 1990. In both spectral regions, features attributable to H3(+) were visible. The intensity ratio of lines in the 2 and 4 microns regions measured from the northern auroral hot spot during the same night leads to a rovibrational temperature of 1100 + or - 100 K for this molecular ion, close to a previous measurement of the rotational temperature of 1099 + or - 100 K. This indicates that the upper energy levels are being populated by purely thermal processes, rather than by resonant energy exchange. The para-H3(+) fractional abundance of 0.58 determined by previous workers is found to be consistent with this study. The time dependency of the H3(+) emission phenomena is confirmed. 9 refs.

Infrared emissions of H3(+) in the atmosphere of Jupiter in the 2. 1 and 4. 0 micron region

A table of transition frequencies and Einstein A(ij) coefficients for the astronomically important molecular ion H3+ is presented. The table consists of calculated frequencies and A(ij)-values, and frequencies measured in the laboratory, augmented by recent observations of the H3+ spectrum taken from the upper atmosphere of Jupiter. The frequencies given cover the L and K atmospheric windows.

A table of astronomically important ro-vibrational transitions for the h-3(+) molecular ion

The two‐dimensional interaction potential of the N+2(X 2Σ+g) –He(X 1S) system has been calculated using highly correlated ab initio MCSCF‐CI wave functions for a fixed value of the N+2 bond length (2.110 a0). It is found to have a minimum about 140 cm−1 below the N+2 +He dissociation limit, significantly deeper than the minimum in the neutral system N2–He. This well depth is enough to give rise to a cluster‐like, bound structure with a considerable number of vibration–rotation levels in the electronic ground state. The well depth is almost independent of the N2–He angle, which leads to large amplitude bending motions. Rovibrational calculations have been performed on the surface for J=0, 1, and 2. Values for the rotational constant B, the fundamental stretching frequency νs, and its first and second overtones, and the rotational constant Cn in each nνs manifold, have been obtained from the energy levels computed. It is found that B=1.879 cm−1, 1νs =55.231 cm−1, 2νs =83.404 cm−1, 3νs =92.491 cm−1, C0=0.477...

Ab initio investigation of the bound rovibrational states in the electronic ground state of HeN+2

The dynamics of the reactions of N({sup 2}D,{sup 2}P) with O{sub 2} have been investigated by observing the initial vibrational-state population distributions of NO(X{sup 2}II) formed in the interaction of oxygen and discharge-excited nitrogen in a cryogenically pumped, low-pressure reaction volume. Infrared chemiluminescence from vibrationally and rotationally excited NO(v = 1-14) was observed in the 5-7-{mu}m spectral region, and spectral data were analyzed to obtain NO(v,J) number densities. The results show multimodal vibrational and rotational distributions, indicative of several concurrent processes. In particular, extensive rotational excitation is evident in several vibrational levels of NO, resulting in sharply peaked R-branch band heads characteristic of J {ge} 80. Surprisal analysis was applied to the data to infer the contributions of the various reaction pathways. This analysis indicates that all the possible reaction pathways for producing NO(X{sup 2}II), some of which leads to formation of metastable atomic oxygen, occur with significant probability. The results are discussed in terms of their implications for the detailed collisional dynamics of the reactions and their relevance to the study of upper atmospheric auroral chemistry.

Steven Miller

Papers

Spectroscopic Properties of the H 3 + Molecule: A New Calculated Line List

Infrared emissions of H3(+) in the atmosphere of Jupiter in the 2. 1 and 4. 0 micron region

A table of astronomically important ro-vibrational transitions for the h-3(+) molecular ion

Ab initio investigation of the bound rovibrational states in the electronic ground state of HeN+2

Rovibrational excitation of nitric oxide in the reaction of oxygen with metastable atomic nitrogen