Rebecca A. H. Butler

Biosignatures from Earth-like planets around M dwarfs.

Coupled one-dimensional photochemical-climate calculations have been performed for hypothetical Earth-like planets around M dwarfs. Visible/near-infrared and thermal-infrared synthetic spectra of these planets were generated to determine which biosignature gases might be observed by a future, space-based telescope. Our star sample included two observed active M dwarfs-AD Leo and GJ 643-and three quiescent model stars. The spectral distribution of these stars in the ultraviolet generates a different photochemistry on these planets. As a result, the biogenic gases CH4, N2O, and CH3Cl have substantially longer lifetimes and higher mixing ratios than on Earth, making them potentially observable by space-based telescopes. On the active M-star planets, an ozone layer similar to Earths was developed that resulted in a spectroscopic signature comparable to the terrestrial one. The simultaneous detection of O2 (or O3) and a reduced gas in a planets atmosphere has been suggested as strong evidence for life. Planets circling M stars may be good locations to search for such evidence.

THE MILLIMETER- AND SUBMILLIMETER-WAVE SPECTRUM OF GLYCOLALDEHYDE (CH 2 OHCHO)

The simplest monosaccharide, glycolaldehyde (CH2OHCHO), has recently been detected toward the Galactic center in the source Sgr B2(N) at five frequencies from 71-104 GHz. None of the individual lines used in the detection had been measured previously in the laboratory; rather, their frequencies were predicted based on lower frequency measurements. We have now recorded and analyzed many new rotational transitions of glycolaldehyde through 354 GHz using two spectrometers. Lines through 48 GHz in frequency were measured with a spectrometer that uses Stark modulation, while the higher frequency transitions were measured with a FASSST (Fast Scan Submillimeter Spectroscopic Technique) apparatus. Analysis of the data has allowed us to confirm the interstellar identifications and to predict the frequencies of many additional lines not measured in the laboratory.

Millimeter-Wave and Vibrational State Assignments for the Rotational Spectrum of Glycolaldehyde

Glycolaldehyde (CHOCH2OH), the simplest two-carbon α-hydroxy aldehyde, has become of great interest in the field of astrochemistry due to its recent detection toward the Sagittarius B2 (N-LMH) molecular cloud. The original interstellar identification was based on an extrapolation of prior microwave rotational spectroscopy of glycolaldehyde. The millimeter and submillimeter spectra of this molecule from 128 to 354 GHz were subsequently measured after the interstellar detection. We present here the millimeter spectrum of this molecule from 72 to 122.5 GHz along with a combined millimeter and submillimeter pure rotational analysis of the ground and the first three vibrationally excited states of glycolaldehyde that enables a more complete molecular partition function to be determined. These results show that excited vibrational state contributions to the partition function are an important consideration when determining the column density of a molecule with low-lying torsional states.

Observation and analysis of high-J o1−e1 inter-state transitions in CH2DOH

We report the observation and assignments of several series of transitions in CH2DOH, including a new and intense series of Q-branch c-type transitions between the e1 and o1 torsional substates through high values of the rotational quantum number J. Other transitions assigned are c-type R-branch and P-branch transitions between these two substates and a-type lines within the e1 and o1 substates. The assignments were facilitated by initial analysis of the strong Q-branch series, as recorded by the fast scan submillimeter spectroscopy technique (FASSST). The assigned lines of CH2DOH include the first inter-state transitions in the sub-millimeter-wave region and the first to possess high J-values. The completeness of the data generated by FASSST and the success of a simple power series analysis suggest that many parts of the spectrum of CH2DOH may be far more tractable than previously believed. The data should be useful in the development of a full Hamiltonian and in the assignment of astronomical emission f...

The Millimeter- and Submillimeter-Wave Spectrum of Cyanoformamide

The organic species cyanoformamide (NCCONH2) is the cyano (CN) derivative of formamide (NH2CHO), a known interstellar molecule with a role in the synthesis of nucleic acid precursors under prebiotic conditions. Until quite recently, the rotational spectrum of cyanoformamide had not been studied. Based partially on the results of a newly published microwave study and on the results of our ab initio calculations, we have measured and assigned 2691 transitions of the millimeter- and submillimeter-wave spectrum of this molecule through 360 GHz with the fast-scan submillimeter spectroscopic technique (FASSST). These transitions have been added to the previously measured 135 microwave transitions to produce a global data set of 2826 transitions that was analyzed to within experimental accuracy with a standard asymmetric-top fitting procedure. With the determined spectroscopic constants and dipole moment components, we are able to predict the frequencies and intensities of many additional lines through 400 GHz. Cyanoformamide can now be searched for over a wide frequency range in likely interstellar sources such as hot molecular cores.