Curtis DeWitt

We present the first Hubble Space Telescope - Space Telescope Imaging Spectrograph (HST-STIS) far-ultraviolet (FUV) and near-ultraviolet (NUV) high-resolution spectra of the red supergiant (RSG) Antares (M1.5 Iab), isolated from its long-period B-star binary companion, and compare them to spectra of Betelgeuse (M2 Iab) to assess the similarities and differences in chromospheric heating and atmospheric dynamics. While Betelgeuse has two well-known circumstellar CO outflows, previous radio and infrared observations of Antares did not detect the presence of circumstellar CO. The Antares FUV STIS spectra reveal CO electronic Fourth-Positive absorption bands formed exterior to the chromosphere. The derived column density is 4 orders of magnitude smaller than the CO MOLsphere located interior to 1.7 R _* . The numerous NUV Fe ii emission lines show classical wind-scattering profiles, with velocities close to the star of v _wind ≃ 19 km s ⁻¹ , consistent with that previously inferred from absorption spectra observed against the B star at a projected radius of ∼150 R _* . Surprisingly, the NUV semi-forbidden emission lines show evidence of wind scattering, indicative of the massive column densities present in the winds of low-surface-gravity RSGs. Differential comparison with Betelgeuse of chromospheric fluxes from emission lines excited by electron collisions, electron collisions combined with photospheric photoexcitation, and coincidental line pumping reveals similar levels of chromospheric heating. C ii ] indicates comparable chromospheric electron densities and column densities. With its well-constrained distance and stellar parameters, Antares provides a good source for understanding the processes driving RSG outflows. Chromospherically, Antares is effectively a twin of Betelgeuse.

Water and methanol are key components of interstellar ices and gas in star- and planet-forming regions, but direct observations of water in low-mass protostars are challenging due to atmospheric absorption. We present high-resolution ( R = 70,500) mid-infrared spectroscopy of the class I protostar SVS13-A with EXES on board SOFIA at 26 μ m, targeting both H ₂ O and CH ₃ OH absorption lines. Several lines of each species are detected, tracing warm gas with rotational temperatures of ∼140–170 K. Remarkably, the methanol column density is a factor of ∼4 higher than that of water, well above typical interstellar ice ratios (3 OH/H ₂ O ratio may reflect selective sublimation due to the distribution of binding energies or ice stratification in the inner envelope. These observations probe the inner regions of the protostar, where planets are expected to form and inherit the chemical composition of their natal environment, providing a direct link between ice sublimation and gas-phase chemistry. Our results represent the first high-spectral-resolution mid-infrared view of both water and methanol toward a low-mass protostar, offering a unique window into the chemical composition of the innermost envelope and planet-forming region and highlighting the diagnostic power of high-resolution mid-infrared spectroscopy to uncover hidden chemical layers and the ice-to-gas transition in embedded protostars.

Infrared spectra of hydrocarbon dust absorption bands toward the bright hypergiant Cygnus OB2-12 are compared to published spectra of the Quintuplet Cluster, a sightline to the Galactic center. The Cyg OB2-12 data include a new ground-based 2.86−3.70 μm spectrum and a previously published, but here further analyzed, spectrum of the 5.50–7.34 μm region. Higher-spectral-resolution data for the Cyg OB2-12 sightline in the 3 μm region allows a detailed comparison of the 3.4 μm aliphatic bands to those observed toward the Quintuplet. Despite differences in interstellar environments along each sightline, strong similarities are observed in the central wavelengths and relative strengths for bands at ∼3.3, 3.4, 5.85, 6.2, and 6.85 μm. Analysis of these bands, produced by aromatic, aliphatic, olefinic, hydrogenated, and oxygenated components, shows that carbonaceous dust is a significant component of the diffuse interstellar medium (ISM), second in abundance only to silicates, and is primarily aromatic in nature. The grains producing these bands likely consist of large aromatic carbon cores with thin aliphatic mantles composed of hydrogenated amorphous carbon. Laboratory analog spectra reproduce the observed aliphatic absorption bands well, supporting the presence of such mantles. We present evidence that the carriers of both the 3.4 μm aliphatic and the 3.3 μm aromatic bands reside exclusively in the diffuse ISM, and that the 3.3 μm bands observed in the diffuse ISM differ from the 3.25 μm band seen in dense clouds, implying chemically distinct carriers.

We present the first astrophysical detection of methanol (CH₃OH) in the torsional band near 25 μm. Using high-resolution mid-infrared (MIR) spectroscopy, we identified over 70 gas-phase CH₃OH absorption lines between 20 and 28 μm toward the massive protostar NGC 7538 IRS 1 with the Stratospheric Observatory for Infrared Astronomy/Echelon-Cross-Echelle Spectrograph. We derive a temperature of 180 K and a total column density of 2 × 10¹⁷ cm⁻², comparable to submillimeter measurements. Complementary analysis of acetylene (C₂H₂) absorption lines is also included. Both CH₃OH and C₂H₂ reveal an unresolved second velocity component. These MIR absorption lines likely probe the molecular material in two edge-on disks, supporting the scenario that NGC 7538 IRS 1 consists of multiple protostars. We provide an updated line list for the torsional band of CH₃OH, which was generated from lab work and model calculations. This discovery and the updated line list will enable the search for CH₃OH in JWST/MIRI spectra.

The near-infrared (NIR) emission of the youngest protostars still needs to be characterized to better understand the evolution of their accretion and ejection activity. We analyze James Webb Space Telescope NIRSpec 1.7–5.3 μm observations of two deeply embedded sources in the S68N protostellar core in Serpens. The North Central source exhibits a highly obscured spectrum (A _K ∼ 4.8 mag) that is modeled with a pre-main-sequence photosphere and a hot disk component. The photospheric parameters are consistent with a young, low-mass photosphere, as suggested by the low surface gravity, log g of 1.95 ±0.15 cm s⁻². The hot disk suggests that accretion onto the central protostellar embryo is ongoing, although prototypical accretion-tracing emission lines H i are not detected. The South Central source, which is even more embedded (A _K ∼ 8 mag; no continuum is detected shortward of 3.6 μm) appears to be driving the large-scale S68N protostellar outflow, and launches a collimated hot molecular jet detected in H₂ and CO rovibrational lines. Shock modeling of the H₂ (ro)vibrational lines establishes that fast C-type shocks (≥30 km s⁻¹), with high pre-shock density (≥10⁷ cm⁻³), and strong magnetic field (b ∼ 3–10, where B = b × n H ( cm − 3 ) μ G ) best match the data. The bright CO fundamental line forest suggests energetic excitation, with the contribution of non-LTE effects, i.e., irradiation pumping. Detected OH and CH⁺ rovibrational lines support this hypothesis. These two Class 0 protostars seem to be in very young evolutionary stages and still have to acquire the bulk of their final stellar masses. These results demonstrate that JWST enables unprecedented diagnostics of these first stages of the protostellar evolutionary phase.

We present radiative transfer analyses of IRTF-TEXES and SOFIA-EXES mid-infrared spectra of Jupiter's mid- to high latitudes recorded between 2019 April 16 and 2023 July 20. The spectra were inverted across a photochemical model grid of varying eddy diffusion coefficient profiles, and the quality of fit of the synthetic spectra to the observed was used to constrain the CH₄ homopause level. For a subset of latitudes/dates, we find that the CH₄ homopause level is elevated in the region enclosed inside of, or magnetospherically poleward of, the northern ultraviolet main auroral emissions (MAEs) in comparison to the region outside or equatorward of the MAE. For example, using SOFIA-EXES results on 2021 June 10, we derived a CH₄ homopause level of log(p _H(nbar)) = 1.54 − 0.69 + 0.51 or z _H = 453 − 76 + 128 km above 1 bar poleward of the northern MAE at 68^∘N compared to a lower limit of log(p _H) > 2.43 and upper limit of z _H < 322 km derived equatorward of the northern MAE. We therefore conclude that the region poleward of the northern MAE is, at times, subject to enhanced vertical transport resulting from auroral energy deposition. The exact mechanisms responsible for the enhanced vertical transport in Jupiter's auroral regions are uncertain: time-dependent circulation modeling of Jupiter's polar atmosphere is required to better understand this phenomenon. Poleward of the southern MAE, derived homopause levels agreed within uncertainty with those at equatorward locations. However, we consider this result a spatial sampling artifact rather than concluding that the southern auroral region is not subject to enhanced vertical transport.

Supernova shocks into dense molecular cores in IC 443 (clumps B, C, and G) and 3C 391 were observed using the Stratospheric Observatory for Infrared Astronomy and complemented by archival data from the Herschel Space Observatory. The pure rotational transitions 0–0 S(1) and S(5) of H₂, and the ground-state 1₁₀–1₀₁ transition of H₂O, are all broadened, arising from molecules that survive the passage of the shock front. Theoretical models from the Paris–Durham shock code were analyzed to generate velocity profiles that approximately match the observations. The observations can be fit with two shock conditions, which approximate the range of densities in the preshock molecular cloud. The width and brightness of the S(5) lines require shocks into gas with a density of order 2000 cm⁻³, into which the IC 443 blast wave drives shocks with speed 60 km s⁻¹. The brightness and narrower width of the S(1) lines requires different shocks, into gas with density of order 10⁵ cm⁻³, with shock speeds of 10 km s⁻¹. The H₂O velocity distribution is also consistent with these shocks. The existence of shocks into dense gas shows that the bright shocked clumps in IC 443 were prestellar cores. It is unlikely that they will form stars soon after the passage of the shock front, given the input of kinetic and thermal energy from the shocks.

We present in this paper mid-infrared (5–8 μm) spectroscopy toward the massive young binary W3 IRS 5, using the Echelon Cross Echelle Spectrograph (EXES) spectrometer in high-resolution mode (R ∼ 50,000) from the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA). Many (∼180) ν ₂ = 1–0 and (∼90) ν ₂ = 2–1 absorption rovibrational transitions are identified. Two hot components over 500 K and one warm component of 190 K are identified through Gaussian fittings and rotation diagram analysis. Each component is linked to a CO component identified in the IRTF/iSHELL observations (R = 88,100) through their kinematic and temperature characteristics. Revealed by the large scatter in the rotation diagram, opacity effects are important, and we adopt two curve-of-growth analyses, resulting in column densities of ∼10¹⁹ cm⁻². In one analysis, the model assumes a foreground slab. The other assumes a circumstellar disk with an outward-decreasing temperature in the vertical direction. The disk model is favored because fewer geometry constraints are needed, although this model faces challenges as the internal heating source is unknown. We discuss the chemical abundances along the line of sight based on the CO-to-H₂O connection. In the hot gas, all oxygen not locked in CO resides in water. In the cold gas, we observe a substantial shortfall of oxygen and suggest that the potential carrier could be organics in solid ice.

We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2–28.3 μm. With SOFIA/EXES, we target the enigmatic source Orion IRc2. While this is in the most prolifically studied massive star-forming region, longer wavelengths and molecular emission lines dominated previous spectral surveys. The mid-infrared observations in this work access different components and molecular species in unprecedented detail. We unambiguously identify two new kinematic components, both chemically rich with multiple molecular absorption lines. The “blue clump” has v _LSR = −7.1 ± 0.7 km s⁻¹, and the “red clump” has 1.4 ± 0.5 km s⁻¹. While the blue and red clumps have similar temperatures and line widths, molecular species in the blue clump have higher column densities. They are both likely linked to pure rotational H₂ emission also covered by this survey. This work provides evidence for the scenario that the blue and red clumps are distinct components unrelated to the classic components in the Orion BN/KL region. Comparison to spectroscopic surveys toward other infrared targets in the region show that the blue clump is clearly extended. We analyze, compare, and present in-depth findings on the physical conditions of C₂H₂, ¹³CCH₂, CH₄, CS, H₂O, HCN, H 13 CN , HNC, NH₃, and SO₂ absorption lines and an H₂ emission line associated with the blue and red clumps. We also provide limited analysis of H₂O and SiO molecular emission lines toward Orion IRc2 and the atomic forbidden transitions [Fe ii], [S i], [S iii], and [Ne ii].