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We have performed a high-resolution 4–13 μm spectral survey of the hot molecular gas associated with the massive protostars AFGL 2591 and AFGL 2136. Here we present the results of the analysis of the ν 2 band of H2O, detected with the Echelon Cross Echelle Spectrograph on board the Stratospheric Observatory for Infrared Astronomy between wavelengths of 5 and 8 μm. All lines are seen in absorption. Rotation diagrams indicate that the gas is optically thick and lines are observed to saturate at 40% and 15% relative to the continuum for AFGL 2136 and AFGL 2591, respectively. We applied two curve of growth analyses to derive the physical conditions, one assuming a foreground origin and one a circumstellar disk origin. We find temperatures of 400–600 K. A foreground origin would require the presence of externally heated clumps that are smaller than the continuum source. The disk analysis is based on stellar atmosphere theory, which takes into consideration the temperature gradient in the disk. We discuss the challenges with each model, taking into consideration the properties of other species detected in the spectral survey, and conclude that further modeling efforts are required to establish whether the absorption has a disk or foreground origin. The main challenge to the foreground model is that molecules are expected to be observed in emission. The main challenges to the disk model are the midplane heating mechanism and the presence of narrow absorption lines shifted from the systemic velocity.

We present results from a high spectral resolution (6 km s-1) survey of five massive protostars in the wavelength range of 2.95 and 3.25 µm, conducted with iSHELL at the InfraRed Telescope Facility (IRTF). Our targets are Mon R2 IRS 2, Mon R2 IRS 3, AFGL 2136, Orion BN and S140 IRS 1. Two of our five targets (Mon R2 IRS 3 and AFGL 2136) show transitions from organic species, with MonR2 IRS 3 showing HCN lines in emission, and AFGL 2136 showing HCN and C2H2 lines in absorption. The velocity of the emission lines of HCN of MonR2 IRS 3A are consistent with CO emission features in lines up to J = 26, as both are red-shifted with respect to the systemic velocity. Carbon monoxide lines also show blue-shifted absorption. This P-Cygni line profile, commonly observed towards massive young stellar objects, is likely due to an expanding shell, which is supported by sub-millimetre velocity maps of HCN. Alternatively HCN emission may arise from the upper layers of a disk photosphere, as has been suggested for the massive protostar AFGL 2591. Absorption lines in AFGL 2136 may either originate in foreground cloud or in the disk photosphere. For a foreground cloud, the data require that the foreground gas only covers the source partially (0.3) at 13 µm. In contrast, absorption lines at 3 and 7 µm require a covering factor of >0.9. Analysing the 13 µm HCN absorption lines in terms of absorption by gas in the photosphere of a disk, results in physical conditions that are consistent over all three vibrational modes. C2H2 absorption lines reveal an increasing temperature and abundance with decreasing wavelength, indicative of a radial abundance gradient. We conclude that the disk model is the best interpretation of the absorption lines of AFGL 2136.

The chemical composition of high-mass protostars reflects the physical evolution associated with different stages of star formation. In this study, the molecular inventory of the forming high-mass star AFGL 4176 is studied in detail at high angular resolution (~0.35 arcsec) using ALMA. This high resolution makes it possible to separate the emission associated with the inner hot envelope and disk around the forming star from that of its cool outer envelope. In addition, the high sensitivity of ALMA makes it possible to identify weak and optically thin lines and allows for many isotopologues to be detected, providing a more complete and accurate inventory of the source. A total of 23 different molecular species and their isotopologues are detected in the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH), remaining species are present at levels between 0.003 % and 15 % with respect to CH3OH. Hints that N-bearing species peak slightly closer to the location of the peak continuum emission than the O-bearing species are seen. AFGL 4176 comprises a rich chemical inventory including many complex species present on disk-scales. On average, the derived column density ratios with respect to methanol of O-bearing species are higher than those derived for N-bearing species by a factor of three. This may indicate that AFGL 4176 is a relatively young source since nitrogen chemistry generally takes longer to evolve in the gas-phase. Taking methanol as a reference, the composition of AFGL 4176 more closely resembles that of the low-mass protostar IRAS 16293-2422B than that of high-mass star-forming regions located near the Galactic centre. This similarity hints that the chemical composition of complex species is already set in the cold cloud stage and implies that AFGL 4176 is a young source whose chemical composition has not yet been strongly processed by the central protostar., Accepted for publication in Astronomy & Astrophysics

Sulfur has been observed to be severely depleted in dense clouds leading to uncertainty in the molecules that contain it and the chemistry behind their evolution. Here, we aim to shed light on the sulfur chemistry in young stellar objects (YSOs) by using high-resolution infrared spectroscopy of absorption by the ν(3) rovibrational band of SO(2) obtained with the Echelon-Cross-Echelle Spectrograph on the Stratospheric Observatory for Infrared Astronomy. Using local thermodynamic equilibrium models we derive physical parameters for the SO(2) gas in the massive YSO MonR2 IRS3. This yields a SO(2)/H abundance lower limit of 5.6 ± 0.5 × 10(−7), or >4% of the cosmic sulfur budget, and an intrinsic line width (Doppler parameter) of b < 3.20 km s(−1). The small line widths and high temperature (T(ex) = 234 ± 15 K) locate the gas in a relatively quiescent region near the YSO, presumably in the hot core where ices have evaporated. This sublimation unlocks a volatile sulfur reservoir (e.g., sulfur allotropes as detected abundantly in comet 67P/Churyumov–Gerasimenko), which is followed by SO(2) formation by warm, dense gas-phase chemistry. The narrowness of the lines makes formation of SO(2) from sulfur sputtered off grains in shocks less likely toward MonR2 IRS3.

We have performed a high resolution 4-13 ${\mu}m$ spectral survey of the hot molecular gas associated with the massive protostars AFGL 2591 and AFGL 2136, utilising the Echelon-Cross-Echelle-Spectrograph (EXES) on-board the Stratospheric Observatory for Infrared Astronomy (SOFIA), and the iSHELL instrument and Texas Echelon Cross Echelle Spectrograph (TEXES) on the NASA Infrared Telescope Facility (IRTF). Here we present results of this survey with analysis of CO, HCN, C$_2$H$_2$, NH$_3$ and CS, deriving the physical conditions for each species. Also from the IRTF, iSHELL data at 3 ${\mu}m$ for AFGL 2591 are presented that show HCN and C$_2$H$_2$ in emission. In the EXES and TEXES data, all species are detected in absorption, and temperatures and abundances are found to be high (600 K and 10$^{-6}$, respectively). Differences of up to an order of magnitude in the abundances of transitions that trace the same ground state level are measured for HCN and C$_2$H$_2$. The mid-infrared continuum is known to originate in a disk, hence we attribute the infrared absorption to arise in the photosphere of the disk. As absorption lines require an outwardly decreasing temperature gradient, we conclude that the disk is heated in the mid-plane by viscous heating due to accretion. We attribute the near-IR emission lines to scattering by molecules in the upper layers of the disk photosphere. The absorption lines trace the disk properties at 50 AU where a high temperature gas-phase chemistry is taking place. Abundances are consistent with chemical models of the inner disk of Herbig disks.

We have observed the massive protostar AFGL 2136 IRS 1 in multiple wavelength windows in the near-to-mid-infrared at high ($\sim3$ km s$^{-1}$) spectral resolution using VLT+CRIRES, SOFIA+EXES, and Gemini North+TEXES. There is an abundance of H$_2$O absorption lines from the $\nu_1$ and $\nu_3$ vibrational bands at 2.7 $\mu$m, from the $\nu_2$ vibrational band at 6.1 $\mu$m, and from pure rotational transitions near 10-13 $\mu$m. Analysis of state-specific column densities derived from the resolved absorption features reveals that an isothermal absorbing slab model is incapable of explaining the relative depths of different absorption features. In particular, the strongest absorption features are much weaker than expected, indicating optical depth effects resulting from the absorbing gas being well-mixed with the warm dust that serves as the "background" continuum source at all observed wavelengths. The velocity at which the strongest H$_2$O absorption occurs coincides with the velocity centroid along the minor axis of the compact disk in Keplerian rotation recently observed in H$_2$O emission with ALMA. We postulate that the warm regions of this dust disk dominate the continuum emission at near-to-mid infrared wavelengths, and that H$_2$O and several other molecules observed in absorption are probing this disk. Absorption line profiles are not symmetric, possibly indicating that the warm dust in the disk that produces the infrared continuum has a non-uniform distribution similar to the substructure observed in 1.3 mm continuum emission., Comment: 30 pages, 12 figures, 3 tables, ApJ accepted

Sulfur has been observed to be severely depleted in dense clouds leading to uncertainty in the molecules that contain it and the chemistry behind their evolution. Here, we aim to shed light on the sulfur chemistry in young stellar objects (YSOs) by using high-resolution infrared spectroscopy of absorption by the $��_3$ rovibrational band of SO$_2$ obtained with the Echelon-Cross-Echelle Spectrograph on the Stratospheric Observatory for Infrared Astronomy. Using local thermodynamic equilibrium models we derive physical parameters for the SO$_2$ gas in the massive YSO MonR2 IRS3. This yields a SO$_2$/$\mathrm{H}$ abundance lower limit of $5.6\pm0.5\times10^{-7}$, or $>\!4\%$ of the cosmic sulfur budget, and an intrinsic line width (Doppler parameter) of $b, 9 pages, 2 figures, accepted for publication in ApJL

We have performed a 5-8 $\mu$m spectral line survey of the hot molecular core associated with the massive protostar AFGL 2591, using the Echelon-Cross-Echelle Spectrograph (EXES) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). We have supplemented these data with a ground based study in the atmospheric M band around 4.5 $\mu$m using the iSHELL instrument on the Infrared Telescope Facility (IRTF), and the full N band window from 8-13 $\mu$m using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the IRTF. Here we present the first detection of ro-vibrational transitions of CS in this source. The absorption lines are centred on average around -10 kms$^{-1}$ and the line widths of CS compare well with the hot component of $^{13}$CO (around 10 kms$^{-1}$). Temperatures for CS, hot $^{13}$CO and $^{12}$CO v=1-2 agree well and are around 700 K. We derive a CS abundance of 8$\times$10$^{-3}$ and 2$\times$10$^{-6}$ with respect to CO and H$_2$ respectively. This enhanced CS abundance with respect to the surrounding cloud (1$\times$10$^{-8}$) may reflect sublimation of H$_2$S ice followed by gas-phase reactions to form CS. Transitions are in LTE and we derive a density of $>$10$^7$ cm$^{-3}$, which corresponds to an absorbing region of $

snail is not firmly attached to the substrate by its foot, it can be blown away by the spray and lost. We have found this to be less of a problem in the field, where attachment to the substrate appears to be better, but it can be a problem in the laboratory. To counteract this we have developed a way of freezing small snails indirectly. The snail is allowed to crawl onto a piece of aluminium foil. It can then be lifted without being disturbed and the spray directed to the underside of the foil. Since the foil is thin and of high thermal conductivity, the snail is again frozen almost instantaneously. We have used this technique most frequently for studying the genital anatomy of snails of the genus Heterostoma. These are small helicids, usually below 7 mm in maximum shell width. Freezing and thawing is extremely rapid and effective. The foot always remains extended and the tentacles are usually only partly retracted. Initially, we found that attempting to withdraw the body of the snail created a vacuum in the shell often resulting in damage to the body. This could be avoided by making a small hole near the protoconch with a mounted needle. Most of the genitalia were almost always removed intact, but the hermaphrodite gland was usually left behind. Also, the digestive tract often remained within the shell and the method would need to be adapted if this part of the anatomy were required. Other than the problem of a small amount of damage to the shell near the protoconch, the main disadvantage with this method is its cost compared to more traditional methods. At the time of writing, a 400-ml can of spray from RS Components costs about £8 (around US $11 or €13). With care, we have found a can of this size can successfully be used on about 150 Heterostoma individuals. Obviously, more spray is needed for larger individuals and so cost would be increased. Costs incurred in the drowning method are negligible. However, where the drowning method is inappropriate or where it is essential to collect samples from the field without disturbance, we have found this method to be an effective alternative, especially in the field where the spray’s portability and ease of use are clear advantages.