Timothy J. Crawford

High resolution spectral analysis of oxygen. III. Laboratory investigation of the airglow bands

We report the first high spectral resolution laboratory measurements of simulated oxygen A-band night glow. Our static discharge system approximates the conditions of the mesospheric oxygen night glow--suggesting O((1)D) + O2 (X(3)Σg(-)) → O((3)P) + O2 (b(1)Σg(+)) → O2 (X(3)Σg(-)) + hν as the primary source of the emission. Additionally, use of the static cell has enabled us to collect spectra for all six molecular oxygen isotopologues using isotopically enriched samples. The (0,0), (0,1), and (1,1) b - X vibrational bands were observed for all six isotopologues. The (1,2) and (2,2) bands were also observed for (16)O2. The frequencies of the observed (0,1) transitions resolved discrepancies in Raman data for (16)O(17)O, (17)O2, and (17)O(18)O, enabling us to improve the vibrational parameterization of the ground electronic state global fit. Rotationally resolved intensities were determined for the (0,0), (0,1), and (1,1) bands. The experimental band intensity ratios I(0,0)/I(0,1) = 13.53(24); I(1,1)/I(1,0) = 11.9(65); I(0,0)/I(0,2) = 503(197); and I(1,1)/I(1,2) = 5.6(19) are in excellent agreement with the recent mesospheric remote sensing data and calculated Franck-Condon factors.

A High-Precision Near-Infrared Survey for Radial Velocity Variable Low-Mass Stars Using Cshell and a Methane Gas Cell

We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2-M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25-150 Myr) moving groups, the young field star ϵ Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8-15 m s-1with a long-term stability of 15-50 m s-1 over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25-50 m s-1 at ≈2.3125 μm, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3σ-5σ. Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s-1 in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.

Retrieval of precise radial velocities from near-infrared high-resolution spectra of low-mass stars

Given that low-mass stars have intrinsically low luminosities at optical wavelengths and a propensity for stellar activity, it is advantageous for radial velocity (RV) surveys of these objects to use near-infrared (NIR) wavelengths. In this work, we describe and test a novel RV extraction pipeline dedicated to retrieving RVs from low-mass stars using NIR spectra taken by the CSHELL spectrograph at the NASA Infrared Telescope Facility, where a methane isotopologue gas cell is used for wavelength calibration. The pipeline minimizes the residuals between the observations and a spectral model composed of templates for the target star, the gas cell, and atmospheric telluric absorption; models of the line-spread function, continuum curvature, and sinusoidal fringing; and a parameterization of the wavelength solution. The stellar template is derived iteratively from the science observations themselves without a need for separate observations dedicated to retrieving it. Despite limitations from CSHELLs narrow wavelength range and instrumental systematics, we are able to (1) obtain an RV precision of 35 m s^(−1) for the RV standard star GJ 15 A over a time baseline of 817 days, reaching the photon noise limit for our attained signal-to-noise ratio; (2) achieve ~3 m s^(−1) RV precision for the M giant SV Peg over a baseline of several days and confirm its long-term RV trend due to stellar pulsations, as well as obtain nightly noise floors of ~2–6 m s^(−1); and (3) show that our data are consistent with the known masses, periods, and orbital eccentricities of the two most massive planets orbiting GJ 876. Future applications of our pipeline to RV surveys using the next generation of NIR spectrographs, such as iSHELL, will enable the potential detection of super-Earths and mini-Neptunes in the habitable zones of M dwarfs.

Submillimeter wave spectrometry for in-situ planetary science

Absorption and emission of gases in the submillimeter wavelengths is currently exploited for laboratory spectroscopy as well as remote astronomy and limb sounding. We are developing a field-ready submillimeter spectrometer that will enable in-situ sensing with a goal for characterization of biogenic gases and life tracers. Progress toward a field-ready instrument includes: the development of a brass board THz transceiver module; the development of the brass board RF/IF subsystem; an embedded computer and runtime software. Science experiments, including the study of laboratory simulations of Titan, will be performed while the final field instrument components are developed.

A 90-102 GHz CMOS based pulsed Fourier transform spectrometer: New approaches for in situ chemical detection and millimeter-wave cavity-based molecular spectroscopy

We present a system level description of a cavity-enhanced millimeter-wave spectrometer that is the first in its class to combine source and detection electronics constructed from architectures commonly deployed in the mobile phone industry and traditional pulsed Fourier transform techniques to realize a compact device capable of sensitive and specific in situ gas detections. The instrument, which has an operational bandwidth of 90-102 GHz, employs several unique components, including a custom-designed pair of millimeter-wave transmitter and heterodyne receiver integrated circuit chips constructed with 65 nm complementary metal-oxide semiconductor (CMOS) techniques. These elements are directly mated to a hybrid coupling structure that enables free-space interaction of the electronics with a small gas volume while also acting as a cavity end mirror. Instrument performance for sensing of volatile compounds is highlighted with experimental trials taken in bulk gas flows and seeded molecular beam environments.

PHOTOACOUSTIC SPECTROSCOPY OF PRESSURE- AND TEMPERATURE- DEPENDENCE IN THE O2 A-BAND

MATTHEW J. CICH, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; ELIZABETH M LUNNY, GAUTAM STROSCIO, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA; THINH QUOC BUI, JILA, National Institute of Standards and Technology and Univ. of Colorado Department of Physics, University of Colorado, Boulder, Boulder, CO, USA; PRIYANKA RUPASINGHE, Physical Sciences, Cameron University, Lawton, OK, USA; DANIEL HOGAN, Department of Applied Physics, Stanford University, Stanford, CA, USA; CAITLIN BRAY, Department of Chemistry, Wesleyan University, Middletown, CT, USA; DAVID A. LONG, JOSEPH T. HODGES, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA; TIMOTHY J. CRAWFORD, CHARLES MILLER, BRIAN DROUIN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; MITCHIO OKUMURA, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA.

PROGRESS IN THE MEASUREMENT ON TEMPERATURE-DEPENDENCE OF H2-BROADENING OF COLD AND HOT CH4

KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; V. MALATHY DEVI, D. CHRIS BENNER, Department of Physics, College of William and Mary, Williamsburg, VA, USA; TIMOTHY J. CRAWFORD, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; ARLAN MANTZ, Department of Physics, Astronomy and Geophysics, Connecticut College, New London, CT, USA; MARY ANN H. SMITH, Science Directorate, NASA Langley Research Center, Hampton, VA, USA.

FT-IR measurements of mid-IR propene (C3H6) cross sections for titan stratosphere

We present temperature dependent cross sections of propene (C3H6; CH2-CH-CH3, propylene), which was detected in the stratosphere of Titan.a For this study, a series of high-resolution (0.0022 cm−1) spectra of pure and N2-mixture samples were recorded at 150 – 296 K in the 650 – 1530 cm−1(6.5 – 15.3 μm) at the Jet Propulsion Laboratory using a Fourier-transform spectrometer and a custom-designed cold cellbc. The observed spectral features cover the strongest band (ν19) with its outstanding Q-branch peak at 912 cm−1and three other strong bands: ν18, ν16 and ν7 at 990, 1442, and 1459 cm−1, respectively. In addition, we have generated a HITRAN-format empirical ‘pseudoline list’ consisting of line positions, intensities, and effective lower state energies, which were determined by fitting all the observed propene spectra simultaneously. A newly derived partition function was used in the analysis. The results are compared with early work from relatively warm temperatures (278 – 323 K).d

Precise Near-Infrared Radial Velocities

We present the results of two 2.3 μm near-infrared (NIR) radial velocity (RV) surveys to detect exoplanets around 36 nearby and young M dwarfs. We use the CSHELL spectrograph ( R ~ 46,000) at the NASA InfraRed Telescope Facility (IRTF), combined with an isotopic methane absorption gas cell for common optical path relative wavelength calibration. We have developed a sophisticated RV forward modeling code that accounts for fringing and other instrumental artifacts present in the spectra. With a spectral grasp of only 5 nm, we are able to reach long-term radial velocity dispersions of ~20–30 m s −1 on our survey targets.

PERFORMANCE OF A CRYOGENIC MULTIPATH HERRIOTT CELL VACUUM-COUPLED TO A BRUKER IFS-125HR SYSTEM

Accurate modeling of atmospheric trace gases requires detailed knowledge of spectroscopic line parameters at temperatures and pressures relevant to the atmospheric layers where the spectroscopic signatures form. Pressure-broadened line shapes, frequency shifts, and their temperature dependences, are critical spectroscopic parameters that limit the accuracy of state-of-the-art atmospheric remote sensing. In order to provide temperature dependent parameters from controlled laboratory experiments, a 20.946 ± 0.001 m long path Herriott cell and associated transfer optics were designed and fabricated at Connecticut College to operate in the near infrared using a Bruker 125 HR Fourier transform spectrometer. The cell body and gold coated mirrors are fabricated with Oxygen-Free High Conductivity (OFHC) copper. Transfer optics are throughput matched for entrance apertures smaller than 2 mm. A closed-cycle Helium refrigerator cools the cell and cryopumps the surrounding vacuum box. This new system and its transfer optics are fully evacuated to ̃ 10 mTorr (similar to the pressure inside the interferometer). Over a period of several months, this system has maintained extremely good stability in recording spectra at gas sample temperatures between 75 and 250 K. The absorption path length and cell temperatures are validated using CO spectra. The characterization of the Herriott cell is described along with its performance and future applications.a b