Echelon Cross Echelle Spectrograph Research Articles

SOFIA-EXES Mid-IR Observations of Emission from the Extended Atmosphere of Betelgeuse

Abstract We present a NASA-DLR SOFIA-Echelon Cross Echelle Spectrograph (EXES) and NASA Infrared Telescope Facility-Texas Echelon Cross Echelle Spectrograph (TEXES) mid-IR spectral study of forbidden Fe ii transitions in the early-type M supergiants, Betelgeuse (α Ori: M2 Iab) and Antares (α Sco: M1 Iab + B3 V). With EXES, we spectrally resolve the ground term [Fe ii] 25.99 μm ( : K) emission from Betelgeuse. We find a small centroid blueshift of 1.9 ± 0.4 that is a significant fraction (20%) of the current epoch wind speed, with a FWHM of 14.3 ± 0.1 . The TEXES observations of [Fe ii] 17.94 μm ( : K) show a broader FWHM of 19.1 ± 0.2 , consistent with previous observations, and a small redshift of 1.6 ± 0.6 with respect to the adopted stellar center-of-mass velocity of . To produce [Fe ii] 25.99 μm blueshifts of 20% wind speed requires that the emission arises closer to the star than existing thermal models for α Ori’s circumstellar envelope predict. This implies a more rapid wind cooling to below 500 K within ( mas, dist = 200 pc) of the star, where the wind has also reached a significant fraction of the maximum wind speed. The line width is consistent with the turbulence in the outflow being close to the hydrogen sound speed. EXES observations of [Fe ii] 22.90 μm ( : K) reveal no emission from either star. These findings confirm the dominance of cool plasma in the mixed region where hot chromospheric plasma emits copiously in the UV, and they also constrain the wind heating produced by the poorly understood mechanisms that drive stellar outflows from these low variability and weak-dust signature stars.

The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216.

High spectral resolution mid-IR observations of ethylene (C2H4) towards the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Eighty ro-vibrational lines from the 10.5 µm vibrational mode ν7 with J ≲ 30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400 K (warm and hot lines). The warm lines peak at ≃ -14 km s-1 with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃ 20R⋆. The hot lines are centered at -10 km s-1 indicating that they come from a shell between 10 and 20R⋆. 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveal that the C2H4 abundance relative to H2 in the range 5 - 20R⋆ is 6.9 × 10-8 in average and it could be as high as 1.1 × 10-7. Beyond 20R⋆, it is 8.2 × 10-8. The total column density is (6.5 ± 3.0) × 1015 cm-2. C2H4 is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the C2H4 molecules at 20R⋆ could condense onto dust grains. This possible depletion would not influence significantly the gas acceleration although it could play a role in the surface chemistry on the dust grains.

Mid-infrared mapping of Jupiter’s temperatures, aerosol opacity and chemical distributions with IRTF/TEXES

Global maps of Jupiter’s atmospheric temperatures, gaseous composition and aerosol opacity are derived from a programme of 5–20 µm mid-infrared spectroscopic observations using the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA’s Infrared Telescope Facility (IRTF). Image cubes from December 2014 in eight spectral channels, with spectral resolutions of R ∼2000−12,000 and spatial resolutions of 2–4° latitude, are inverted to generate 3D maps of tropospheric and stratospheric temperatures, 2D maps of upper tropospheric aerosols, phosphine and ammonia, and 2D maps of stratospheric ethane and acetylene. The results are compared to a re-analysis of Cassini Composite Infrared Spectrometer (CIRS) observations acquired during Cassini’s closest approach to Jupiter in December 2000, demonstrating that this new archive of ground-based mapping spectroscopy can match and surpass the quality of previous investigations, and will permit future studies of Jupiter’s evolving atmosphere. The visibility of cool zones and warm belts varies from channel to channel, suggesting complex vertical variations from the radiatively-controlled upper troposphere to the convective mid-troposphere. We identify mid-infrared signatures of Jupiter’s 5-µm hotspots via simultaneous M, N and Q-band observations, which are interpreted as temperature and ammonia variations in the northern Equatorial Zone and on the edge of the North Equatorial Belt (NEB). Equatorial plumes enriched in NH3 gas are located south-east of NH3-desiccated ‘hotspots’ on the edge of the NEB. Comparison of the hotspot locations in several channels across the 5–20 µm range indicate that these anomalous regions tilt westward with altitude. Aerosols and PH3 are both enriched at the equator but are not co-located with the NH3 plumes. The equatorial temperature minimum and PH3/aerosol maxima have varied in amplitude over time, possibly as a result of periodic equatorial brightenings and the fresh updrafts of disequilibrium material. Temperate mid-latitudes display a correlation between mid-IR aerosol opacity and the white albedo features in visible light (i.e., zones). We find hemispheric asymmetries in the distribution of tropospheric PH3, stratospheric hydrocarbons and the 2D wind field (estimated via the thermal-wind equation) that suggest a differing efficiency of mechanical forcing (e.g., vertical mixing and wave propagation) between the two hemispheres that we argue is driven by dynamics rather than Jupiter’s small seasonal cycle. Jupiter’s stratosphere is notably warmer at northern mid-latitudes than in the south in both 2000 and 2014, although the latter can be largely attributed to strong thermal wave activity near 30°N that dominates the 2014 stratospheric maps and may be responsible for elevated C2H2 in the northern hemisphere. A vertically-variable pattern of temperature and windshear minima and maxima associated with Jupiter’s Quasi Quadrennial Oscillation (QQO) is observed at the equator in both datasets, although the contrasts were more subdued in 2014. Large-scale equator-to-pole gradients in ethane and acetylene are superimposed on top of the mid-latitude mechanically-driven maxima, with C2H2 decreasing from equator to pole and C2H6 showing a polar enhancement, consistent with a radiatively-controlled circulation from low to high latitudes. Cold polar vortices beyond ∼60° latitude can be identified in the upper tropospheric and lower stratospheric temperature maps, suggesting enhanced radiative cooling from polar aerosols. Finally, compositional mapping of the Great Red Spot confirms the local enhancements in PH3 and aerosols, the north–south asymmetry in NH3 gas and the presence of a warm southern periphery that have been noted by previous authors.

Stratospheric aftermath of the 2010 Storm on Saturn as observed by the TEXES instrument. I. Temperature structure

We report on spectroscopic observations of Saturn’s stratosphere in July 2011 with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted on the NASA InfraRed Telescope Facility (IRTF). The observations, targeting several lines of the CH4ν4 band and the H2 S(1) quadrupolar line, were designed to determine how Saturn’s stratospheric thermal structure was disturbed by the 2010 Great White Spot. A study of Cassini Composite Infrared Spectrometer (CIRS) spectra had already shown the presence of a large stratospheric disturbance centered at a pressure of 2 hPa, nicknamed the beacon B0, and a tail of warm air at lower pressures (Fletcher et al. [2012] Icarus 221, 560–586). Our observations confirm that the beacon B0 vertical structure determined by CIRS, with a maximum temperature of 180 ± 1 K at 2 hPa, is overlain by a temperature decrease up to the 0.2-hPa pressure level. Our retrieved maximum temperature of 180 ± 1 K is colder than that derived by CIRS (200 ± 1 K), a difference that may be quantitatively explained by terrestrial atmospheric smearing. We propose a scenario for the formation of the beacon based on the saturation of gravity waves emitted by the GWS. Our observations also reveal that the tail is a planet-encircling disturbance in Saturn’s upper stratosphere, oscillating between 0.2 and 0.02 hPa, showing a distinct wavenumber-2 pattern. We propose that this pattern in the upper stratosphere is either the signature of thermal tides generated by the presence of the warm beacon in the mid-stratosphere, or the signature of Rossby wave activity.

DETECTION OF WATER VAPOR IN THE TERRESTRIAL PLANET FORMING REGION OF A TRANSITION DISK

We report a detection of water vapor in the protoplanetary disk around DoAr 44 with the Texas Echelon Cross Echelle Spectrograph --- a visitor instrument on the Gemini north telescope. The DoAr 44 disk consists of an optically thick inner ring and outer disk, separated by a dust-cleared 36 AU gap, and has therefore been termed "pre-transitional". To date, this is the only disk with a large inner gap known to harbor detectable quantities of warm (T=450 K) water vapor. In this work, we detect and spectrally resolve three mid-infrared pure rotational emission lines of water vapor from this source, and use the shapes of the emission lines to constrain the location of the water vapor. We find that the emission originates near 0.3 AU --- the inner disk region. This characteristic region coincides with that inferred for both optically thick and thin thermal infrared dust emission, as well as rovibrational CO emission. The presence of water in the dust-depleted region implies substantial columns of hydrogen (>10^{22} cm-2) as the water vapor would otherwise be destroyed by photodissociation. Combined with the dust modeling, this column implies a gas/small-dust ratio in the optically thin dusty region of >1000. These results demonstrate that DoAr 44 has maintained similar physical and chemical conditions to classical protoplanetary disks in its terrestrial-planet forming regions, in spite of having formed a large gap.

Seasonal variations of hydrogen peroxide and water vapor on Mars: Further indications of heterogeneous chemistry

We have completed our seasonal monitoring of hydrogen peroxide and water vapor on Mars using ground-based thermal imaging spectroscopy, by observing the planet in March 2014, when water vapor is maximum, and July 2014, when, according to photochemical models, hydrogen peroxide is expected to be maximum. Data have been obtained with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted at the 3 m–Infrared Telescope Facility (IRTF) at Maunakea Observatory. Maps of HDO and H2 O2 have been obtained using line depth ratios of weak transitions of HDO and H2 O2 divided by CO2 . The retrieved maps of H2 O2 are in good agreement with predictions including a chemical transport model, for both the March data (maximum water vapor) and the July data (maximum hydrogen peroxide). The retrieved maps of HDO are compared with simulations by Montmessin et al. (2005, J. Geophys. Res., 110, 03006) and H2 O maps are inferred assuming a mean martian D/H ratio of 5 times the terrestrial value. For regions of maximum values of H2 O and H2 O2 , we derive, for March 1 2014 (Ls = 96°), H2 O2 = 20+/−7 ppbv, HDO = 450 +/−75 ppbv (45 +/−8 pr-nm), and for July 3, 2014 (Ls = 156°), H2 O2 = 30+/−7 ppbv, HDO = 375+/−70 ppbv (22+/−3 pr-nm). In addition, the new observations are compared with LMD global climate model results and we favor simulations of H2 O2 including heterogeneous reactions on water-ice clouds.

The origin of nitrogen on Jupiter and Saturn from the [formula omitted]N/[formula omitted]N ratio

The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA’s Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia absorption features on both Jupiter and Saturn in February 2013. Ammonia is the principle reservoir of nitrogen on the giant planets, and the ratio of isotopologues (15N/14N) can reveal insights into the molecular carrier (e.g., as N2 or NH3) of nitrogen to the forming protoplanets, and hence the source reservoirs from which these worlds accreted. We targeted two spectral intervals (900 and 960cm−1) that were relatively clear of terrestrial atmospheric contamination and contained close features of 14NH3 and 15NH3, allowing us to derive the ratio from a single spectrum without ambiguity due to radiometric calibration (the primary source of uncertainty in this study). We present the first ground-based determination of Jupiter’s 15N/14N ratio (in the range from 1.4×10-3 to 2.5×10-3), which is consistent with both previous space-based studies and with the primordial value of the protosolar nebula. On Saturn, we present the first upper limit on the 15N/14N ratio of no larger than 2.0×10-3 for the 900-cm−1 channel and a less stringent requirement that the ratio be no larger than 2.8×10-3 for the 960-cm−1 channel (1σ confidence). Specifically, the data rule out strong 15N-enrichments such as those observed in Titan’s atmosphere and in cometary nitrogen compounds. To the extent possible with ground-based radiometric uncertainties, the saturnian and jovian 15N/14N ratios appear indistinguishable, implying that 15N-enriched ammonia ices could not have been a substantial contributor to the bulk nitrogen inventory of either planet. This result favours accretion of primordial N2 on both planets, either in the gas phase from the solar nebula, or as ices formed at very low temperatures. Finally, spatially-resolved TEXES observations are used to derive zonal contrasts in tropospheric temperatures, phosphine and 14NH3 on both planets, allowing us to relate thermal conditions and chemical compositions to phenomena observed at visible wavelengths in 2013 (e.g., Jupiter’s faint equatorial red colouration event and wave activity in the equatorial belts, plus the remnant warm band on Saturn following the 2010–11 springtime storm).

A COMPARATIVE ASTROCHEMICAL STUDY OF THE HIGH-MASS PROTOSTELLAR OBJECTS NGC 7538 IRS 9 AND IRS 1

We report the results of a spectroscopic study of the high-mass protostellar object NGC 7538 IRS 9 and compare our observations to published data on the nearby object NGC 7538 IRS 1. Both objects originated in the same molecular cloud and appear to be at different points in their evolutionary histo- ries, offering an unusual opportunity to study the temporal evolution of envelope chemistry in objects sharing a presumably identical starting composition. Observations were made with the Texas Echelon Cross Echelle Spectrograph (TEXES), a sensitive, high spectral resolution (R = {\lambda}/{\Delta}{\lambda} \simeq 100,000) mid-infrared grating spectrometer. Forty-six individual lines in vibrational modes of the molecules C2H2, CH4, HCN, NH3 and CO were detected, including two isotopologues (13CO, 12C18O) and one combination mode ({\nu}4 + {\nu}5 C2H2). Fitting synthetic spectra to the data yielded the Doppler shift, excitation temperature, Doppler b parameter, column density and covering factor for each molecule observed; we also computed column density upper limits for lines and species not detected, such as HNCO and OCS. We find differences among spectra of the two objects likely attributable to their differing radiation and thermal environments. Temperatures and column densities for the two objects are generally consistent, while the larger line widths toward IRS 9 result in less saturated lines than those toward IRS 1. Finally, we compute an upper limit on the size of the continuum-emitting region (\sim2000 AU) and use this constraint and our spectroscopy results to construct a schematic model of IRS 9.

A spatially resolved high spectral resolution study of Neptune’s stratosphere

Using TEXES, the Texas Echelon cross Echelle Spectrograph, mounted on the Gemini North 8-m telescope we have mapped the spatial variation of H 2, CH 4, C 2H 2 and C 2H 6 thermal-infrared emission of Neptune. These high-spectral-resolution, spatially resolved, thermal-infrared observations of Neptune offer a unique glimpse into the state of Neptune’s stratosphere in October 2007, L S = 275.4° just past Neptune’s southern summer solstice ( L S = 270°). We use observations of the S(1) pure rotational line of molecular hydrogen and a portion of the ν 4 band of methane to retrieve detailed information on Neptune’s stratospheric vertical and meridional thermal structure. We find global-average temperatures of 163.8 ± 0.8, 155.0 ± 0.9, and 123.8 ± 0.8 K at the 7.0 × 10 −3-, 0.12-, and 2.1-mbar levels with no meridional variations within the errors. We then use the inferred temperatures to model the emission of C 2H 2 and C 2H 6 in order to derive stratospheric volume mixing ratios (hence forth, VMR) as a function of pressure and latitude. There is a subtle meridional variation of the C 2H 2 VMR at the 0.5-mbar level with the peak abundance found at −28° latitude, falling off to the north and south. However, the observations are consistent within error to a meridionally constant C 2H 2 VMR of 3.3 - 0.9 + 1.2 × 10 - 8 at 0.5 mbar. We find that the VMR of C 2H 6 at 1-mbar peaks at the equator and falls by a factor of 1.6 at −70° latitude. However, a meridionally constant VMR of 9.3 - 2.6 + 3.5 × 10 - 7 at the 1-mbar level for C 2H 6 is also statistically consistent with the retrievals. Temperature predictions from a radiative-seasonal climate model of Neptune that assumes the hydrocarbon abundances inferred in this paper are lower than the measured temperatures by 40 K at 7 × 10 −3 mbar, 30 K at 0.12 mbar and 25 K at 2.1 mbar. The radiative-seasonal model also predicts meridional temperature variations on the order of 10 K from equator to pole, which are not observed. Assuming higher stratospheric CH 4 abundance at the equator relative to the south pole would bring the meridional trends of the inferred temperatures and radiative-seasonal model into closer agreement. We have also retrieved observations of C 2H 4 emission from Neptune’s stratosphere using TEXES on the NASA Infrared Telescope Facility (IRTF) in June 2003, L S = 266°. Using the observations from the middle of the planet and an average of the middle three latitude temperature profiles from the 2007 observations (9.5° of L S later, the seasonal equivalent of 9.5 Earth days within Earth’s seasonal cycle), we infer a C 2H 4 VMR of 5.9 - 0.8 + 1.0 × 10 - 7 at 1.5 × 10 −3 mbar, a value that is 3.25 times that predicted by global-average photochemical models.

A stringent upper limit to SO2in the Martian atmosphere

Surfur-bearing molecules have been found at the surface of Mars by the Viking lander, the Spirit and Opportunity rovers, and the OMEGA infrared spectrometer aboard Mars Express. However, no gaseous sulfur-bearing species have ever been detected in the Martian atmosphere. We search for SO2 signatures in the thermal spectrum of Mars at 7.4 μm using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Data were obtained on Oct. 12, 2009 (Ls = 353 ◦ ), in the 1350–1360 cm −1 range, with a spatial resolution of 1 arcsec (after convolution over three pixels along the N-S axis and two steps along the E-W axis) and a resolving power of 80 000. To improve the signal-to-noise ratio (S/N), we co-added the Martian spectrum around the positions of nine selected SO2 transitions with a high S/N and no telluric contamination. From a mean spectrum, averaged over 35 pixels in the region of maximum continuum, we infer a 2σ upper limit of 0.3 ppb to the SO2 mixing ratio, assuming that our instrumental errors are combined according to Gaussian statistics. Our upper limit is three times lower than the upper limit derived by Krasnopolsky (2005, Icarus, 178, 487), who used the same technique on previous TEXES data. In addition, we derive an upper limit of 2 ppb at each spatial pixel of the region observed by TEXES, which covers the longitude ranges 50 E–170 E for latitudes above 30 N, 100 E–170 E for latitudes between 0 and 30 N, and 110 E–170 E for latitudes between 15 S and 0. The non-detection of localized SO2 sources in the observed area is consistent with a homogeneous distribution being expected around equinox for noncondensible species with a lifetime longer than the global mixing time. In view of the typically large SO2/CH4 ratio observed in terrestrial volcanoes, and assuming a comparable volcanic composition for Mars and the Earth, our result reaffirms that a volcanic origin is unlikely for any methane in the Martian atmosphere.

Water vapor map of Mars near summer solstice using ground-based infrared spectroscopy

Ground-based spatial mapping of Mars provides a unique way to retrieve the global distribution of minor atmospheric species and to study transient phenomena or possible variations with the local hour. We have obtained an instantaneous map of water vapor on Mars near summer solstice (Ls = 80°) using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF) at Mauna Kea Observatory. Data have been obtained in the 1230-1245 cm-1 range (λ = 8.1 μm), with a spatial resolution of 1.1 arcsec (after convolution) and a spectral resolution of 0.012 cm-1 (R = 105). The map has been retrieved from the line depth of a weak HDO transition, compared with the line depth of a weak CO2 nearby transition. The TEXES map exhibits a strong maximum around the northern pole, as expected from previous observations and from climate model predictions. More interestingly, it shows longitudinal variations, both at high northern latitudes and at mid-latitudes, in close agreement with the predictions of the Global Climate Model developed at the Laboratoire de Meteorologie Dynamique (LMD GCM). The inferred water vapor mixing ratio is also in good agreement with the model predictions. The longitudinal variations at mid latitudes show a general enhancement toward the east. They do not seem to be due to the effect of local hour, but can be explained by dynamical effects generated by the topography. The map of surface temperatures, inferred from the continuum flux, is surprisingly different from the map expected from the climate models; the source of this discrepancy is still unclear.

TEXES OBSERVATIONS OF M SUPERGIANTS: DYNAMICS AND THERMODYNAMICS OF WIND ACCELERATION

We have detected [Fe ii] 17.94 μm and 24.52 μm emission from a sample of M supergiants (μ Cep, α Sco, α Ori, CE Tau, AD Per, and α Her) using the Texas Echelon Cross Echelle Spectrograph on NASA's Infrared Telescope Facility. These low opacity emission lines are resolved at R ≃ 50, 000 and provide new diagnostics of the dynamics and thermodynamics of the stellar wind acceleration zone. The [Fe ii] lines, from the first excited term (a4F), are sensitive to the warm plasma where energy is deposited into the extended atmosphere to form the chromosphere and wind outflow. These diagnostics complement previous Kuiper Airborne Observatory and Infrared Space Observatory observations which were sensitive to the cooler and more extended circumstellar envelopes. The turbulent velocities of Vturb ≃ 12–13 km s−1 observed in the [Fe ii] a4F forbidden lines are found to be a common property of our sample, and are less than that derived from the hotter chromospheric C ii] 2325 Å lines observed in α Ori, where Vturb ≃ 17–19 km s−1. For the first time, we have dynamically resolved the motions of the dominant cool atmospheric component discovered in α Ori from multiwavelength radio interferometry by Lim et al. Surprisingly, the emission centroids are quite Gaussian and at rest with respect to the M supergiants. These constraints combined with model calculations of the infrared emission line fluxes for α Ori imply that the warm material has a low outflow velocity and is located close to the star. We have also detected narrow [Fe i] 24.04 μm emission that confirms Fe ii is the dominant ionization state in α Ori's extended atmosphere.

The TEXES Survey for H2Emission from Protoplanetary Disks

We report the results of a search for pure rotational molecular hydrogen emission from the circumstellar environments of young stellar objects with disks using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for mid-infrared H2 emission in the S(1), S(2), and S(4) transitions. Keck/NIRSPEC observations of the H2 S(9) transition were included for some sources as an additional constraint on the gas temperature. We detected H2 emission from 6 of 29 sources observed: AB Aur, DoAr 21, Elias 29, GSS 30 IRS 1, GV Tau N, and HL Tau. Four of the six targets with detected emission are class I sources that show evidence for surrounding material in an envelope in addition to a circumstellar disk. In these cases, we show that accretion shock heating is a plausible excitation mechanism. The detected emission lines are narrow (~10 km/s), centered at the stellar velocity, and spatially unresolved at scales of 0.4 arcsec, which is consistent with origin from a disk at radii 10-50 AU from the star. In cases where we detect multiple emission lines, we derive temperatures > 500 K from ~1 M_earth of gas. Our upper limits for the non-detections place upper limits on the amount of H2 gas with T > 500 K of less than a few Earth masses. Such warm gas temperatures are significantly higher than the equilibrium dust temperatures at these radii, suggesting that the gas is decoupled from the dust in the regions we are studying and that processes such as UV, X-ray, and accretion heating may be important.

Simultaneous mapping of H 2O and H 2O 2 on Mars from infrared high-resolution imaging spectroscopy

New maps of martian water vapor and hydrogen peroxide have been obtained in November–December 2005, using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infra Red Telescope facility (IRTF) at Mauna Kea Observatory. The solar longitude L s was 332° (end of southern summer). Data have been obtained at 1235–1243 cm −1, with a spectral resolution of 0.016 cm −1 ( R = 8 × 10 4 ). The mean water vapor mixing ratio in the region [0°–55° S; 345°–45° W], at the evening limb, is 150 ± 50 ppm (corresponding to a column density of 8.3 ± 2.8 pr-μm ). The mean water vapor abundance derived from our measurements is in global overall agreement with the TES and Mars Express results, as well as the GCM models, however its spatial distribution looks different from the GCM predictions, with evidence for an enhancement at low latitudes toward the evening side. The inferred mean H 2O 2 abundance is 15 ± 10 ppb , which is significantly lower than the June 2003 result [Encrenaz, T., Bézard, B., Greathouse, T.K., Richter, M.J., Lacy, J.H., Atreya, S.K., Wong, A.S., Lebonnois, S., Lefèvre, F., Forget, F., 2004. Icarus 170, 424–429] and lower than expected from the photochemical models, taking in account the change in season. Its spatial distribution shows some similarities with the map predicted by the GCM but the discrepancy in the H 2O 2 abundance remains to be understood and modeled.

TEXES Observations of Pure Rotational H 2 Emission from AB Aurigae

We present observations of pure rotational molecular hydrogen emission from the Herbig Ae star, AB Aurigae. Our observations were made using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for H2 emission in the S(1), S(2), and S(4) lines at high spectral resolution and detected all three. By fitting a simple model for the emission in the three transitions, we derive T = 670 +/- 40 K and M = 0.52 +/- 0.15 earth masses for the emitting gas. Based on the 8.5 km/s FWHM of the S(2) line, assuming the emission comes from the circumstellar disk, and with an inclination estimate of the AB Aur system taken from the literature, we place the location for the emission near 18 AU. Comparison of our derived temperature to a disk structure model suggests that UV and X-ray heating are important in heating the disk atmosphere.

Infrared imaging spectroscopy of Mars: H 2O mapping and determination of CO 2 isotopic ratios

High-resolution infrared imaging spectroscopy of Mars has been achieved at the NASA Infrared Telescope Facility (IRTF) on June 19–21, 2003, using the Texas Echelon Cross Echelle Spectrograph (TEXES). The areocentric longitude was 206°. Following the detection and mapping of hydrogen peroxide H 2O 2 [Encrenaz et al., 2004. Icarus 170, 424–429], we have derived, using the same data set, a map of the water vapor abundance. The results appear in good overall agreement with the TES results and with the predictions of the Global Circulation Model (GCM) developed at the Laboratory of Dynamical Meteorology (LMD), with a maximum abundance of water vapor of 3 ± 1.5 × 10 −4 ( 17 ± 9 pr - μm ). We have searched for CH 4 over the martian disk, but were unable to detect it. Our upper limits are consistent with earlier reports on the methane abundance on Mars. Finally, we have obtained new measurements of CO 2 isotopic ratios in Mars. As compared to the terrestrial values, these values are: ( 18O/ 17O)[M/E] = 1.03 ± 0.09; ( 13C/ 12C)[M/E] = 1.00 ± 0.11. In conclusion, in contrast with the analysis of Krasnopolsky et al. [1996. Icarus 124, 553–568], we conclude that the derived martian isotopic ratios do not show evidence for a departure from their terrestrial values.

H2Pure Rotational Lines in the Orion Bar

Photodissociation regions (PDRs), where UV radiation dominates the energetics and chemistry of the neutral gas, contain most of the mass in the dense interstellar medium of our Galaxy. Observations of H2 rotational and rovibrational lines reveal that PDRs contain unexpectedly large amounts of very warm (400-700 K) molecular gas. Theoretical models have difficulty explaining the existence of so much warm gas. Possible problems include errors in the heating and cooling functions or in the formation rate for H2. To date, observations of H2 rotational lines smear out the structure of the PDR. Only by resolving the hottest layers of H2 can one test the predictions and assumptions of current models. Using the Texas Echelon Cross Echelle Spectrograph (TEXES) we mapped emission in the H2 v = 0-0 S(1) and S(2) lines toward the Orion Bar PDR at 2'' resolution. We also observed H2 v = 0-0 S(4) at selected points toward the front of the PDR. Our maps cover a 12'' by 40'' region of the bar where H2 rovibrational lines are bright. The distributions of H2 0-0 S(1), 0-0 S(2), and 1-0 S(1) line emission agree in remarkable detail. The high spatial resolution (0.002 pc) of our observations allows us to probe the distribution of warm gas in the Orion Bar to a distance approaching the scale length for FUV photon absorption. We use these new observational results to set parameters for the PDR models described in a companion paper in preparation by Draine et al. The best-fit model can account for the separation of the H2 emission from the ionization front and the intensities of the ground-state rotational lines, as well as the 1-0 S(1) and 2-1 S(1) lines. This model requires significant adjustments to the commonly used values for the dust UV attenuation cross section and the photoelectric heating rate.

Measurements of CH 3 D and CH 4 in Titan from Infrared Spectroscopy

We measured the CH4 column abundance in Titan's atmosphere through an analysis of Titan's monodeuterated methane (CH3D) spectral features. CH3D is several orders of magnitude less abundant in Titan's atmosphere than CH4. Thus, unlike CH4, the strong and well-studied CH3D 3ν2 lines are not saturated and provide a sensitive measure of its column abundance. We recorded the CH3D 3ν2 lines at 1.55 μm at NASA's Infrared Telescope Facility (IRTF) equipped with the Cryogenic Echelle Spectrograph. We derive a total integrated column abundance of 2.1 ± 0.1 m amagat for CH3D. We also measured stratospheric emission lines of both CH3D and CH4 at 8.6 μm at higher resolution than previously possible to better constrain the CH3D/CH4 ratio. These observations, recorded at the IRTF using the Texas Echelon Cross Echelle Spectrograph, were analyzed with radiative transfer calculations. We determine a CH3D/CH4 ratio of (50 ± 10) × 10-5. Taken together, our measurements of the CH3D column abundance and the CH3D/CH4 ratio indicate a total CH4 column abundance of 4.2 km amagat, close to the column abundance of an atmosphere with 100% saturation in the entire troposphere.

A sensitive search for SO 2 in the martian atmosphere: Implications for seepage and origin of methane

Mars was observed near the peak of the strongest SO 2 band at 1364–1373 cm −1 with resolving power of 77,000 using the Texas Echelon Cross Echelle Spectrograph on the NASA Infrared Telescope Facility. The observation covered the Tharsis volcano region which may be preferable to search for SO 2. The spectrum shows absorption lines of three CO 2 isotopomers and three H 2O isotopomers. The water vapor abundance derived from the HDO lines assuming D/H = 5.5 times the terrestrial value is 12 ± 1.0 pr. μm , in agreement with the simultaneous MGS/TES observations of 14 pr. μm at the latitudes (50° S to 10° N) of our observation. Summing of spectral intervals at the expected positions of sixteen SO 2 lines puts a 2 σ upper limit on SO 2 of 1 ppb. SO 2 may be emitted into the martian atmosphere by seepage and is removed by three-body reactions with OH and O. The SO 2 lifetime, 2 years, is longer than the global mixing time 0.5 year, so SO 2 should be rather uniformly distributed across Mars. Seepage of SO 2 is less than 15,000 tons per year on Mars which is smaller than the volcanic production of SO 2 on the Earth by a factor of 700. Because CH 4/SO 2 is typically 10 −4–10 −3 in volcanic gases on the Earth, our results show seepage is unlikely to be the source of the recently discovered methane on Mars and therefore strengthen its biogenic origin.

Looking for Pure Rotational H[TINF]2[/TINF] Emission from Protoplanetary Disks

We report on a limited search for pure rotational molecular hydrogen emission associated with young, pre-main-sequence stars. We looked for H_2 v = 0, J = 3 → 1 and 4 → 2 emission in the mid-infrared using the Texas Echelon Cross Echelle Spectrograph at NASA's 3 m Infrared Telescope Facility. The high spectral and spatial resolutions of our observations lead to more stringent limits on narrow-line emission close to the source than previously achieved. One star, AB Aur, shows a possible (2 σ) H_2 detection, but further observations are required to make a confident statement. Our nondetections suggest that a significant fraction, perhaps all, of previously reported H_2 emission toward these objects could be extended on scales of 5 or more.