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Register a new userHigh resolution spectroscopy of Plutos atmosphere: detection of the 2.3 $mu$m CH$_4$ bands and evidence for carbon monoxide
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The goal is to determine the composition of Plutos atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high--resolution spectroscopic observations in the 2.33--2.36 $mu$m range, using CRIRES at the VLT. We obtain (i) the first detection of gaseous methane in this spectral range, through lines of the $ u_3$ + $ u_4$ and $ u_1$ + $ u_4$ bands (ii) strong evidence (6-$sigma$ confidence) for gaseous CO in Pluto. For an isothermal atmosphere at 90 K, the CH$_4$ and CO column densities are 0.75 and 0.07 cm-am, within factors of 2 and 3, respectively. Using a physically--based thermal structure model of Plutos atmosphere also satisfying constraints from stellar occultations, we infer CH$_4$ and CO mixing ratios q$_{CH_4}$= 0.6$^{+0.6}_{-0.3}$% (consistent with results from the 1.66 $mu$m range) and q$_{CO}$ = 0.5$^{+1}_{-0.25}$$times10^{-3}$. The CO atmospheric abundance is consistent with its surface abundance. As for Triton, it is probably controlled by a thin, CO-rich, detailed balancing layer resulting from seasonal transport and/or atmospheric escape.
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We report on high-resolution and spatially-resolved spectra of Io in the 4.0 {mu}m region, recorded with the VLT/CRIRES instrument in 2008 and 2010, which provide the first detection of the { u}1 + { u}3 band of SO2 in Ios atmosphere. Data are analyzed to constrain the latitudinal, longitudinal, and diurnal distribution of Ios SO2 atmosphere as well as its characteristic temperature. equatorial SO2 column densities clearly show longitudinal asymmetry, but with a maximum of around 1.5e17 cm-2 at central meridian longitude L = 200-220 and a minimum of around 3e16 cm-2 at L = 285-300, the longitudinal pattern somewhat differs from earlier inferences from Ly {alpha} and thermal IR measurements. Within the accuracy of the measurements, no evolution of the atmospheric density from mid-2008 to mid-2010 can be distinguished. The decrease of the SO2 column density towards high latitude is apparent, and the typical latitudinal extent of the atmosphere found to be (+-) 40{deg} at half-maximum. The data show moderate diurnal variations of the equatorial atmosphere, which is evidence for a partially sublimation-supported atmospheric component. Compared to local noon, factor of 2 lower densities are observed around 40{deg} before and 80{deg} after noon. Best-fit gas temperatures range from 150 to 220 K, with a weighted mean value of 170 (+-) 20 K, which should represent the column-weighted mean kinetic temperature of Ios atmosphere. Finally, although the data include clear thermal emission due to Pillan (in outburst in July 2008) and Loki, no detectable enhancements in the SO2 atmosphere above these volcanic regions are found, with an upper limit of 4e16 cm-2 at Pillan and 1e17 cm-2 at Loki.
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Yakiv V. Pavlenko Main Astronomicaln Observatory of Academy of Sciences of Ukraine
, Golosiiv woods
2002
We compare the observational and theoretical spectra of the $Delta v$ = 2 CO bands in a range of M dwarfs. We investigate the dependence of theoretical spectra on effective temperatures as well as carbon abundance. In general we find that the synthetic CO bands fit the observed data extremely well and are excellent diagnostics. In particular the synthetic spectra reasonably match observations and the best fit temperatures are similar to those found by empirical methods. We also examine the CDC isotopic ratio. We find that fundamental $^{13}$CO bands around 2.345 and 2.375 $mu$m are good discriminators for the CDC ratio in M dwarfs. The 2.375 $mu$m is more useful because it doesnt suffer such serious contamination by water vapour transitions. Our current dataset does not quite have the wavelength coverage to perform a reliable determination of the CDC ratio in M dwarfs. For this we recommend observing the region 2.31--2.40 $mu$m at a resolution of better than 1000. Alternatively the observational problems of contamination by water vapour at 2.345 $mu$m maybe solved by observing at resolutions of around 50000. We also investigated the possibility of using the $Delta v$ = 1 CO bands around 4.5 $mu$m. We find that the contamination due to water vapour is even more of a problem at these wavelengths.
In an echelle spectrum of X Per acquired with the Space Telescope Imaging Spectrograph we have identified individual rotational lines of 11 triplet-singlet (intersystem) absorption bands of ^12CO. Four bands provide first detections for interstellar clouds. From a comparison with the zeta Oph sight line we find that X Per is obscured by a higher 12CO column density of 1.4 x 10^16 cm-2. Together with the high spectral resolution of 1.3 km s-1, this allows (i) an improved measurement of previously published f-values for seven bands, and (ii) an extraction of the first astrophysical oscillator strengths for d-X (8-0), (9-0), and (10-0), as well as for e-X (12-0). The ^13CO d-X (12-0) band, previously suspected to exist toward zeta Oph, is now readily resolved and modeled. Our derived intersystem f-values for ^12CO include a few mild (leq 34%) disagreements with recent predictions from a perturbation analysis calculated for the interstellar excitation temperature. Overall, the comparison confirms the superiority of employing multiple singlet levels in the calculations of mixing coefficients over previous single-level predictions.
Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen, in which the detection of methane has been reported. Aims: The goal is to constrain essential but so far unknown parameters of Plutos atmosphere such as the surface pressure, lower atmosphere thermal stucture, and methane mixing ratio. Methods: We use high-resolution spectroscopic observations of gaseous methane, and a novel analysis of occultation light-curves. Results: We show that (i) Plutos surface pressure is currently in the 6.5-24 microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to explain Plutos inverted thermal structure and ~100 K upper atmosphere temperature (iii) a troposphere is not required by our data, but if present, it has a depth of at most 17 km, i.e. less than one pressure scale height; in this case methane is supersaturated in most of it. The atmospheric and bulk surface abundance of methane are strikingly similar, a possible consequence of the presence of a CH4-rich top surface layer.
The hydrogen cyanide (HCN) molecule in the planetary atmosphere is key to the formation of building blocks of life. We present the spectroscopic detection of the rotational molecular line of nitrile species hydrogen cyanide (HCN) in the atmosphere of Saturn using the archival data of the Atacama Large Millimeter/Submillimeter Array (ALMA) in band 7 observation. The strong rotational emission line of HCN is detected at frequency $ u$ = 354.505 GHz (>4$sigma$ statistical significance). We also detect the rotational emission line of carbon monoxide (CO) at frequency $ u$ = 345.795 GHz. The statistical column density of hydrogen cyanide and carbon monoxide emission line is N(HCN)$sim$2.42$times$10$^{16}$ cm$^{-2}$ and N(CO)$sim$5.82$times$10$^{17}$ cm$^{-2}$. The abundance of HCN and CO in the atmosphere of Saturn relative to the H$_{2}$ is estimated to be f(HCN)$sim$1.02$times$10$^{-9}$ and f(CO)$sim$2.42$times$10$^{-8}$. We discussed possible chemical pathways to the formation of the detected nitrile gas HCN in the atmosphere of Saturn.
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