Protoplanetary nebulae (PPNe) play a significant role in the evolution of low and intermediate mass stars, serving as the link between the asymptotic giant branch (AGB) and planetary nebulae phases. Previous observations have revealed that planetary nebulae are rich in molecular content that varies considerably from the AGB phase, suggesting that significant chemical transformations take place during the brief intermediate PPN stage. To further investigate this problem, we have conducted new molecular observations towards M1-92, an oxygen-rich, bipolar PPN. These measurements have been conducted using the using the Kitt Peak 12 m antenna and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory, as well as the IRAM 30 m telescope. These observations have extended the molecular identifications to include CN, HCO⁺, H¹³CO⁺, HCN, HNC, H₂CO, H₂S, SO₂, SiO, Si¹⁷O, and other isotopologues of these species. Further, some spectra, for example, CS, contain at least five velocity components, tracing the equatorial disk of the nebula, the bipolar lobes and the bipolar tips. The “tips” may track a high velocity wind that has punctured through the slower-moving material in the lobes, sweeping up the lobe gas. These observations will be discussed, with implications for the chemical evolution in this O-rich PPN and its relationship to the kinematic structure.

Observations from the past decade show that a variety of polyatomic species such as HCN and HCO⁺ are present in over 30 planetary nebulae. Contrary to chemical models, which predict rapid photodissociation, molecular abundances appear to remain relatively constant with evolutionary age. To further explore molecular content of PNe, four planetary nebula containing HCO⁺ and/or HCN have been further investigated: Hu 1-1, M4-17, M1-59, and Na2. These nebulae were chosen on the basis of their varied morphologies (e.g., Hu 1-1 is elliptical, M1-59 is multipolar) or age (Na2 is   28,000 years old). Observations of these PNe were conducted using the ARO Submillimeter Telescope (1mm) and the IRAM 30m telescope (2mm). Current results include the detection of CS, c-C₃H₂, H₂CO, CCH, HNC and CN towards at least one of Hu1-1, M1-59, and M4-17, as well as various isotopologues of these species. These new identifications expand the known molecular species contained in these PNe. Molecular abundances and isotope ratios will be presented and compared with other PNe that foster similar chemistries.

A 2 mm survey has been conducted of IRC+10216 (135-175 GHz) using the new 2 mm receiver of the Arizona Radio Observatory (ARO) 12 m, coupled with the ARO Wideband Spectrometer (AROWS) 4 GHz backend. The mixers were developed at ARO and have exceptional noise temperatures. Due to the unparalleled sensitivity of this new receiver, a peak-to-peak noise of 3 mK was achieved over the whole frequency range. Over 900 lines were measured in this survey, many of which were previously undetected in prior surveys. Many of these lines display intensities of 1 or 2 mK and have yet to be identified. Combined with an ongoing survey of the 1mm (215-285 GHz) with the ARO SMT and previous data from a 3 mm (67-115 GHz) survey conducted by the Ziurys group, several molecules, including CCH, C₄H, CN, and their ¹³C isotopologues are being analyzed across a large frequency range, using the ESCAPADE code. From these data, a comprehensive study of the ¹²C/¹³C ratio for IRC+10216 is being carried out. Preliminary results indicate a ¹²C/¹³C ratio of  ∼ 38, but this value will be further refined. Other isotope ratios will also be examined.

The hypergiant star VY Canis Majoris, or VY CMa provides an excellent opportunity to study the evolution of massive stars, which undergo significant mass-loss and are characterized by asymmetric outflows. The arcs, knots, and clumps formed in these processes contain dust and molecules. Using the ALMA, images of PO, PN, NaCl, and Na³⁷Cl have been obtained in Band 6 at 0.25 and 1 arcsec resolution and combined with single-dish data from the ARO Submillimeter Telescope (SMT). While PO emission is confined to the spherical outflow directly on the star, that of PN is more extended, forming a bridge between the star and the SW Clump seen in HST data. NaCl and Na³⁷Cl, on the other hand, trace two distinct sources: the spherical outflow and the SW Clump. NaCl is known to condense out of the gas-phase rapidly in circumstellar material. The survival of NaCl in the SW Clump supports the idea that this material was ejected directly from the photosphere. PN and PO are not observed in the more extended structures seen in SO₂ and HCN, indicating likely grain condensation as well.

VY CMa is one of the best examples to study the stellar evolution of massive stars. Such stars are characterized by complex envelope dynamics resulting from highly directional ejecta of molecular gas and dust. Previous studies of VY CMa using HST show two SE arcs (Arc I, Arc II), an NW arc, SW clumps, and multiple knots. Using ALMA at Band 6 with 1 and 0.25-arcsecond resolution, combined with previous single-dish observations, VY CMa has been imaged in various molecules at 1 mm. From the combined data sets, all the flux from the molecular envelope has been recovered, resulting in the first complete image of the ejecta on a 15-arcsecond scale. In addition to the well-known features such as Arcs 1 and 2, new, more extended structures have been found in CO and HCN, reaching as far as  8 arcseconds from the star, including a NE plume and an E arc. Additionally, images of ¹³CO and H¹³CN have been created to compare isotopic ratio variations of known features. These data will complement previous studies conducted on smaller spatial scales star and provide a more complete picture of the mass loss history of VY CMa.

Our 15 years’ observations of the infrared spectra of H₃⁺ and CO toward 30 young and bright stars with smooth continuum and their analyses have led to the following conclusions. ,05in I. Predominance of Warm and Diffuse Gas and High H₂ Ionization RateOka, T., Geballe, T.R., Goto, M., Usuda, T., McCall, B.J., Indriolo, N. 2019, ApJ. 883, 54 (31pp) The CMZ is filled with warm (T  ∼  200 K) and diffuse (n  ∼  50 cm⁻³) hydrogen gas with a volume-filling factor f  ∼  2/3 and atomic and molecular hydrogen number densities are comparable. The cosmic ray H₂ ionization rate, ζ  ∼  2 × 10⁻¹⁴ s⁻¹, is 1000 times higher than in the solar vicinity suggesting stray magnetic field of  ∼  100 μG in the CMZ if equipartition between cosmic rays and magnetic field is assumed. The X-ray-emitting ultra-hot (10⁸ K) plasma, which some thought to dominate the CMZ, does not exist. ,05in II. Expansion and Morphology of the Warm Diffuse GasOka, T., Geballe, T.R. 2020, ApJ. 902, 9 (17pp) The wide velocity profiles of H₃⁺ lines have allowed us to draw longitude-velocity diagrams toward 18 stars. They indicated that the diffuse molecular gas is expanding with a front speed of  ∼  150 km s⁻¹. This revives the Expanding Molecular Ring proposed by Kaifu et al. and Scoville in 1972 but there are three differences: (1) the expanding gas is diffuse, (2) the expansion is radial, and (3) the gas fills the CMZ. This revives the circular geometry of the CMZ, as viewed face-on. The elliptic structure with high eccentricity is negated. ,05in III. Locations of Sgr B2 and Star IotaOka, T., Geballe, T.R. 2022, ApJ. 927, 97 (8pp) The radial motion of the diffuse gas allows us to determine radial location of a star from velocity profiles of H₃⁺ or other molecules. Star ι, which has a strong H₃⁺ absorption spectrum and is at galactic longitude 0^°.5476 , is close to Sgr B2 (at 0^°.6667). Using velocity profiles of H₃⁺ lines toward Star ι and of H₂O⁺, OH⁺, and ¹³CH⁺ spectra toward Sgr B2 observed by HIFI on the Herschel Space Observatory, we find that both Star ι and Sgr B2 are  ∼  90 pc behind the GC’s central black hole, Sgr A*. This contradicts the previous conclusion based on trigonometric parallax, which placed Sgr B2 130 ± 60 pc in front of Sgr A*, as well as most models of the CMZ.

---

Footnotes:

Oka, T., Geballe, T.R., Goto, M., Usuda, T., McCall, B.J., Indriolo, N. 2019, ApJ. 883, 54 (31pp): Oka, T., Geballe, T.R. 2020, ApJ. 902, 9 (17pp): Oka, T., Geballe, T.R. 2022, ApJ. 927, 97 (8pp):

Methyl mercaptan, CH₃SH, has been detected in the interstellar medium (ISM) with abundances that make detection of minor isotopic species, like the deuterated isotopologues, plausible (e.g.Drozdovskaya, M. N., et al., MNRAS, 476, 4 (2018). Isotopologue abundance ratios are pivotal for tracing the origin and evolution of the molecular material in the process of star and planet formation. The search for deuterated isotopologues of CH₃SH, however, is limited by the lack of spectroscopy on these molecules. The microwave spectra of CH₂DSH and CHD₂SH have been reported, but provides insufficient rotational information for extension up to higher frequencies needed for astronomical observationSu, C. F., and Quade, C. R., JCP, 79, 5828, (1983)^,Su, C. F., Liu, M. J., and Quade, C. R., JMS, 158, 21 (1993) Therefore, additional spectral information is required for their interstellar identification. We have recently collected the millimetre spectrum of CH_2DSH from 70 and 500 GHz to provide the necessary spectral information for its detection in the ISM. The analysis of this spectrum, however, is complicated by the hindered torsional rotation of the CH_2D group. The torsional potential resulting from this internal motion has three minima corresponding to three different substates, two gauche (e₀ and o₁) and one anti (e₁). We have, so far, identified and assigned about 800 transitions including the dominant a−type R branch band structure of all three substates, the weaker b−type Q branch transitions as well as transitions between the torsional substates. We will present on the spectral analysis of CH_2 Su, C. F., Liu, M. J., and Quade, C. R., JMS, 158, 21 (1993).

Carbon-Sulfur species represent a good fraction of the chemical content of interstellar gas and dust. The electronic properties of these compounds generate peculiar molecular structure and chemical reactivity. Detected C-S molecules in space span from the simplest diatomic carbon monosulfide to long carbon chain (e.g. C₅SCernicharo, J. et al. A&A 648, L3 (2021) and complex organic (e.g. CH₃CH₂SHKolesniková L. et al. ApJ 784, L7,(2014). Sulfur chemistry is also particularly interesting due to the still puzzling "missing sulfur" behaviour away from diffuse interstellar regionsLaas J.C. and Caselli P. A&A 624, A108 (2019)
In this talk we review some of the current projects undergoing in our laboratories, involving the characterisation of rotational spectra of carbon-sulfur species. Techniques adopted for our study, and here briefly reviewed, comprise absorption spectroscopy in cells and in microwave/millimeter supersonic jet, chirped-pulse broadband and frequency modulation spectroscopy.

---

Footnotes:

Cernicharo, J. et al. A&A 648, L3 (2021)) Kolesniková L. et al. ApJ 784, L7,(2014)) Laas J.C. and Caselli P. A&A 624, A108 (2019).

To investigate the effects of stellar feedback on the gravitational state of giant molecular clouds, we study ALMA maps of nine molecular clouds distributed throughout the Large Magellanic Cloud (LMC), the nearest star-forming galaxy to our own. Each cloud has been observed in both CO and ¹³CO, enabling analysis based on assuming LTE conditions. We trace molecular hydrogen mass using the J=1-0 transitions for five of the clouds and J=2-1 for the other four. We perform noise and resolution matching on the sample, with a common resolution of 3.5 arcseconds (0.9 pc at the LMC distance of 50 kpc), and use the SCIMES clustering algorithm to identify discrete substructure, or "clumps." We supplement these data with tracers of recent star formation, such as resolution-matched Spitzer IRAC 8μm maps. The CO (¹³CO) clumps identified cover a range of 4.4 (2.6) dex in luminosity-based mass and 2.3 dex in average 8μm surface brightness. The excess linewidth relative to the best-fit size-linewidth relation is well-correlated to the average 8μm flux in a clump, suggesting that the combined effects of radiative feedback and turbulence driven on large scales can explain the local energy injection observed at the clump scales. The magnitude of the excess linewidths we measure does not appear to result from opacity broadening. Further multi-line analysis may better constrain the assumptions made in these calculations.

The Galactic Habitable Zone (GHZ) is characterized by orbital kinematics, star formation rates, lack of SN explosions, time, metallicity, and, specifically, the NCHOPS elements – those required for life. Recently, molecules containing all the NCHOPS elements have been identified in dense clouds located in the Outer Galaxy ( > 16 kpc from the Galactic Center), with the exception of phosphorus. Because this element is integral for biological chemistry, a search was conducted for P-bearing molecules in dense clouds in the Outer Galaxy using the 12 m telescope of the Arizona Radio Observatory (ARO) at 2 mm in wavelength and the 30 m telescope of the Institut de radioastronomie millimétrique (IRAM) at 3mm. The J=2→1 and J=3→2 rotational transitions of PN were detected in WB89-621, located 22.6 kpc from the Galactic Center, as well as four hyperfine components of the J=2.5→1.5 of PO. The fractional abundance, relative to H₂, of PN was determined to be 3.0(±1.6) ×10⁻¹², and that of PO to be 2.0(±1.1)×10⁻¹¹. The identification of PN and PO at the edge of the Galaxy represents the furthest detection of phosphorus from the Galactic Center. All the NCHOPS elements have now been confirmed in out to  ∼  20 kpc, possibly extending the GHZ to the outer regions of the Galaxy.