Search NASA⌕ Search

SEARCH · Search NASA

Results for “ALMA”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Mapping Vinyl Cyanide and Other Nitriles in Titan's Atmosphere Using ALMA

Vinyl cyanide (C2H3CN) is theorized to form in Titan's atmosphere via high-altitude photochemistry and is of interest regarding the astrobiology of cold planetary surfaces due to its predicted ability to form cell membrane-like structures (azotosomes) in liquid methane. In this work, we follow up on the initial spectroscopic detection of C2H3CN on Titan by Palmer et al. with the detection of three new C2H3CN rotational emission lines at submillimeter frequencies. These new, high-resolution detections have allowed for the first spatial distribution mapping of C2H3CN on Titan. We present simultaneous observations of C2H5CN, HC3N, and CH3CN emission, and obtain the first (tentative) detection of C3H8 (propane) at radio wavelengths. We present disk-averaged vertical abundance profiles, two-dimensional spatial maps, and latitudinal flux profiles for the observed nitriles. Similarly to HC3N and C2H5CN, which are theorized to be short-lived in Titan's atmosphere, C2H3CN is most abundant over the southern (winter) pole, whereas the longer-lived CH3CN is more concentrated in the north. This abundance pattern is consistent with the combined effects of high-altitude photochemical production, poleward advection, and the subsequent reversal of Titan's atmospheric circulation system following the recent transition from northern to southern winter. We confirm that C2H3CN and C2H5CN are most abundant at altitudes above 200 km. Using a 300 km step model, the average abundance of C2H3CN is found to be 3.03 +/- 0.29ppb, with a C2H5CN/C2H3CN abundance ratio of 2.43 +/- 0.26. Our HC3N and CH3CN spectra can be accurately modeled using abundance gradients above the tropopause, with fractional scale-heights of 2.05 +/- 0.16 and 1.63 +/- 0.02, respectively.

Lai, J. C.-Y.↗
NASA NTRS2020

Grain Formation around the AGB Star L2 Puppis Based On ALMA Observations

While models of grain formation in the outflows of carbon-rich stars have been relatively successful, models of outflows from oxygen-rich, asymptotic giant branch stars have been less fortunate. Under current modeling, it is difficult to produce sufficient amounts of silicate grains with high enough opacity to form a dust-driven wind from these stars. To investigate the cause of this difference, this work is a comparison between typical outflow model results and a model using input from Atacama Large Millimeter/submillimeter Array observations of L2Puppis. The temperatures from these observations are much lower than would typically be used in the standard outflow model. In addition, the observed gas densities are much higher than predicted from typical outflow models. Both of these differences make the formation of silicate grains much more favorable than predicted in current outflow models. We then explore the effects of other possible nonideal conditions including the efficiency of cluster growth prior to nucleation, the efficiency of grain growth following nucleation and the variation of grain coupling to stellar radiation during grain growth. Finally, we calculate the potential enhancement in grain production based on possible increased refractory abundances resulting from the vaporization of millimeter-scale and larger particles left over from the presence of a former planetary system.

Joseph A Nuth↗
NASA NTRS2022

Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA

NGC 602 is a young, low-metallicity star cluster in the "Wing" of the Small Magellanic Cloud. We reveal the recent evolutionary past of the cluster through analysis of high-resolution (∼0.4 pc) Atacama Large Millimeter/submillimeter Array observations of molecular gas in the associated H ii region N90. We identify 110 molecular clumps (R < 0.8 pc) traced by CO emission, and study the relationship between the clumps and associated young stellar objects (YSOs) and pre-main-sequence (PMS) stars. The clumps have high virial parameters (typical αvir = 4–11) and may retain signatures of a collision in the last ≲8 Myr between H i components of the adjacent supergiant shell SMC-SGS 1. We obtain a CO-bright-to-H2 gas conversion factor of XCO,B = (3.4 ± 0.2) × 10 20 cm−2 (K km s −1 ) −1 , and correct observed clump properties for CO-dark H 2 gas to derive a total molecular gas mass in N90 of 16,600 ± 2400 M ⊙ . We derive a recent (≲1 Myr) star formation rate of 130 ± 30 M ⊙ Myr −1 with an efficiency of 8% ± 3% assessed through comparing total YSO mass to total molecular gas mass. Very few significant radial trends exist between clump properties or PMS star ages and distance from NGC 602. We do not find evidence for a triggered star formation scenario among the youngest (≲2 Myr) stellar generations, and instead conclude that a sequential star formation process in which NGC 602 did not directly cause recent star formation in the region is likely.

Theo J O’Neill↗
NASA NTRS2023

Gas Sources from the Coma and Nucleus of Comet 46P/Wirtanen Observed Using ALMA

Gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical processes. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production/release mechanisms remain uncertain. Here we present observations of six molecular species toward comet 46P/Wirtanen, obtained using the Atacama Large Millimeter/submillimeter Array during the comet's unusually close (∼0.1 au) approach to Earth in 2018 December. Interferometric maps of HCN, CH 3 OH, CH 3 CN, H 2 CO, CS, and HNC were obtained at an unprecedented sky-projected spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be accurately quantified. The HCN, CH 3 OH, and CH 3 CN spatial distributions are consistent with production by direct outgassing from (or very close to) the nucleus, with a significant proportion of the observed CH 3 OH originating from sublimation of icy grains in the near-nucleus coma (at a scale length L p = 36 ± 7 km). On the other hand, H 2 CO, CS, and HNC originate primarily from distributed coma sources (with L p values in the range 550–16,000 km), the identities of which remain to be established. The HCN, CH 3 OH, and HNC abundances in 46P are consistent with the average values previously observed in comets, whereas the H 2 CO, CH 3 CN, and CS abundances are relatively low.

Short period comets↗
NASA NTRS2010

Mineralogy of Pyroxene and Olivine in the Almahata Sitta Ureilite

The Almahata Sitta meteorite (hereafter "Alma") is the first example of a recovered asteroidal sample that fell to earth after detection still in the orbit (2008TC3 asteroid), and thus is critical to understand the relationship between meteorites and their asteroidal parent bodies [1]. Alma is a polymict ureilite showing a fine-grained brecciated texture with variable lithologies from black, porous to denser, white stones [1]. It is an anomalous ureilite because of wide compositional ranges of silicates with abundant pores often coated by vapor-deposit crystals [1]. Nevertheless, Alma has general similarities to all ureilites because of reduction textures of silicates suggestive of rapid cooling from high temperature as well as heterogeneous oxygen isotope compositions [e.g., 1-5]. Alma is especially unique because it spans the compositional range of known ureilites [1]. In this abstract we report detailed mineralogical and crystallographic investigations of two different fragments to further constrain its thermal history with regards to the nature of the ureilite parent body.

Mikouchi, T.↗
NASA NTRS2017

Radial Surface Density Profiles of Gas and Dust in the Debris Disk Around 49 Ceti

We present approximately 0".4 resolution images of CO(3-2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We analyze the ALMA visibilities in tandem with the broadband spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The dust surface density decreases with radius between approximately 100 and 310 au, with a marginally significant enhancement of surface density at a radius of approximately 110 au. The SED requires an inner disk of small grains in addition to the outer disk of larger grains resolved by ALMA. The gas disk exhibits a surface density profile that increases with radius, contrary to most previous spatially resolved observations of circumstellar gas disks. While approximately 80% of the CO flux is well described by an axisymmetric power-law disk in Keplerian rotation about the central star, residuals at approximately 20% of the peak flux exhibit a departure from axisymmetry suggestive of spiral arms or a warp in the gas disk. The radial extent of the gas disk (approx. 220 au) is smaller than that of the dust disk (approx. 300 au), consistent with recent observations of other gasbearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti's disk shows a markedly different structure from two radially resolved gas-poor debris disks, implying that the physical processes generating and sculpting the gas and dust are fundamentally different.

Atacama Large Millimeter Submillimeter Array(ALMA)↗
NASA NTRS2010

Olivine in Almahata Sitta - Curiouser and Curiouser

Almahata Sitta (hereafter Alma) is an anomalous, polymict ureilite. Anomalous features include low abundance of olivine, large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and overall finegrained texture. Tomography suggests the presence of foliation, which is known from other ureilites. Alma pyroxenes and their interpretation are discussed in two companion abstracts. In this abstract we discuss the composition of olivine in Alma, which is indicative of the complexity of this meteorite.

Zolensky, M. E.↗