EXES - Science

EXES

Some Science Goals

Our primary driver for building EXES is the study of molecular gas in quiescent clouds and in protostellar disks. For maximum sensitivity and to resolve line profiles, we want to achieve 2-3 km/s resolution.

We have prepared some simple simulations to illustrate the possibilities of high resolution spectroscopy.

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The first simulation considers a population of H₂O between us and a background continuum source. Noise is added to give a continuum signal-to-noise of 100:1. The atmospheric transmission appropriate for 7 µm of precipitable water and a 45 degree zenith angle is shown at the top of the top panel. Subsequent curves represent absorption by a column with N(H_2O)=10¹⁸ cm^-2 and temperatures of T=1000, 300, and 25 K. We take a Doppler shift of -30 km/s to avoid telluric lines. The spectral resolving power is R=10⁵. The water lines are clearly resolved. In the lower panel, we have divided out the atmosphere, as is typical in the MIR. In the simulation, our atmospheric reference source is assumed to be noiseless.

The second simulation considers the H_2 rotational emission from a protostellar disk with a gap. The three lowest energy H_2 transitions from a Keplerian disk are considered. The disk has no continuum and a temperature distribution that scales as T proportional to r^(-.5) with T at 1 AU=300 K. The solid line profiles come from a disk with emission for 0.1 AU <= r <= 10 AU. The dotted line profiles come from an identical disk except for a 1 AU gap at 3 AU. All spectra have been normalized to a peak amplitude of 1 and displaced vertically by addition of an arbitrary constant for display purposes.