7 research outputs found
Empirical line lists and absorption cross sections for methane at high temperature
Hot methane is found in many "cool" sub-stellar astronomical sources
including brown dwarfs and exoplanets, as well as in combustion environments on
Earth. We report on the first high-resolution laboratory absorption spectra of
hot methane at temperatures up to 1200 K. Our observations are compared to the
latest theoretical spectral predictions and recent brown dwarf spectra. The
expectation that millions of weak absorption lines combine to form a continuum,
not seen at room temperature, is confirmed. Our high-resolution transmittance
spectra account for both the emission and absorption of methane at elevated
temperatures. From these spectra, we obtain an empirical line list and
continuum that is able to account for the absorption of methane in high
temperature environments at both high and low resolution. Great advances have
recently been made in the theoretical prediction of hot methane, and our
experimental measurements highlight the progress made and the problems that
still remain.Comment: 9 pages, 5 figures and 3 tables. For associated online data see
http://dx.doi.org/10.1088/0004-637X/813/1/1
Studying the Physical Diversity of Late-M Dwarfs with Dynamical Masses
We present a systematic study of the physical properties of late-M dwarfs
based on high-quality dynamical mass measurements and near-infrared (NIR)
spectra. We use astrometry from Keck NGS and LGS AO imaging to determine orbits
for late-M binaries. We find that LP 349-25 (M7.5+M8) is a pair of young brown
dwarfs (Mtot = 0.120 Msun) for which Lyon and Tucson evolutionary models
jointly predict an age of 140+/-30 Myr. This is consistent with the age of the
Pleiades, but at least LP 349-25A defies the empirical Pleiades lithium
depletion boundary, implying that the system is in fact older and that
evolutionary models underpredict the component luminosities. We find that LHS
1901AB (M6.5+M6.5) is a pair of very low-mass stars (Mtot = 0.194 Msun) with
model-derived ages consistent with limits from its lack of activity (> 6 Gyr).
Our improved orbit for Gl 569Bab (M8.5+M9) results in a higher mass for this
binary (Mtot = 0.140 Msun) compared to previous work (0.125 Msun). We use these
masses along with our published results for 2MASS J2206-2047AB (M8+M8) to test
four sets of ultracool model atmospheres currently in use. Fitting these models
to our NIR integrated-light spectra provides temperature estimates warmer by
~250 K than those derived independently from Dusty evolutionary models given
the measured masses and luminosities. We propose that model atmospheres are
more likely to be the source of this discrepancy, as it would be difficult to
explain a uniform temperature offset over such a wide range of masses, ages,
and activity levels in the context of evolutionary models. Our results contrast
those of Konopacky et al. as we find an opposite and smaller mass discrepancy
from what they report when we adopt their model-testing approach since our Teff
estimates from fitting spectra are ~650 K higher than from their fitting of
broadband photometry alone.Comment: 53 pages, 12 figures, accepted to Ap
Spectroscopic studies of the diatomic rare-earth oxides
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1983.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCEIncludes bibliographical references.by Michael Dulick.Ph.D
High resolution far infrared spectroscopy of IBr using a synchrotron source
The high resolution far infrared absorption spectrum of IBr was recorded with a Fourier transform spectrometer. The fundamental 1-0 vibration-rotation band and the 2-1 and 3-2 hot bands were recorded at a resolution of 0.001 25 cm-1. The infrared continuum was provided by synchrotron radiation emission from the Max-I storage ring. For high resolution spectroscopy at 250cm-1 synchrotron radiation is about 5 times brighter than a conventional infrared glower. This increase in flux at the detector resulted in a corresponding increase in the signal-to-noise ratio and a much improved infrared spectrum.SCOPUS: ar.jinfo:eu-repo/semantics/publishe