We report VLBI monitoring observations of the 22 GHz H2O masers toward the Mira variable BX Cam. Data from 37 epochs spanning ∼3 stellar pulsation periods were obtained between May 2018 and June 2021 with a time interval of 3–4 weeks. In particular, the VERA dual-beam system was used to measure the kinematics and parallaxes of the H2O maser features. The obtained parallax, 1.79±0.08 mas, is consistent with Gaia EDR3 and previous VLBI measurements. The position of the central star was estimated relied on Gaia EDR3 data and the center position of the 43 GHz SiO maser ring imaged with KVN. Analysis of the 3D maser kinematics revealed an expanding circumstellar envelope with a velocity of 13±4 km s−1 and significant spatial and velocity asymmetries. The H2O maser animation achieved by our dense monitoring program manifests the propagation of shock waves in the circumstellar envelope of BX Cam.

It is well established that circumstellar envelopes (CSEs) around evolved stars are active sites of molecular synthesis, and CSEs are one of the major sources of chemical enrichment in the interstellar space. The investigation of molecular compositions in CSEs is essential to understand the chemical evolution of the Galaxy. In order to study circumstellar chemistry in different environments, we have been systematically performing molecular line surveys of a sample of evolved stars from asymptotic giant branch (AGB) stars, proto-planetary nebulae (PPNs), to planetary nebulae (PNs). The dynamical time scales in different evolutionary stages can impose a time limit on the reaction time scales. Here we report our results for CRL 2688.

A “water fountain” is a transitional object between an AGB star and a PN. The VLBA observations of 22.2 GHz water maser emission reveal a “double-helix” outflow pattern from one of the water fountains, IRAS 18286–0959. The pattern is reasonably fit by a model consisting of two precessing jets. We propose that the two jets observed are a result of a single driving source with a significant proper motion. Using data from the AKARI catalogs, we also found that water fountains might have their own IR colors which are affected by the 9.7 μm silicate feature and the optical thickness of stellar envelopes. The colors could serve as new criteria for searching this type of rare objects.

Due to interstellar extinction, optical census of Galactic planetary nebulae (PNs) is highly incomplete, and some compact H ii regions might have been mis-classified as PNs. The problem is particularly severe in the Galactic plane where the extinction in the optical is significant and hampers the detections of PNs. Unlike optical observations, infrared (IR) observations are hardly affected by interstellar extinction, and provide a good opportunity to study highly obscured PNs. In this study, we use the data from the Spitzer Legacy Infrared Mid-Plane Survey Extraordinaire 3D (GLIMPSE 3D) to investigate the mid-infrared (MIR) properties of PNs and PN candidates.

We obtained a high-resolution CO map of IRAS 22272+5435 in the CO J = 2–1 line using CARMA. The target exhibits a second biggest angular size of the circumstellar molecular envelope among known 21 μm sources. In the preliminary results, we found that the CO properties of IRAS 22272+5435 is clearly different from those of IRAS 07134+1005, which is another well-investigated 21 μm source. For example, elongations seen in the mid-infrared and CO images are extended in mutually perpendicular directions, although in case of IRAS 07134+1005 the CO feature coincides well with the mid-infrared structure.

We present the results of SiO line observations of a sample of known SiO maser sources covering a wide dust-temperature range. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. We observed in total 75 SiO maser sources with the Nobeyama 45m telescope quasi-simultaneously in the SiO J = 1-0 v = 0, 1, 2, 3, 4 and J = 2-1 v = 1, 2 lines. We also observed the sample in the 29SiO J = 1-0 v = 0 and J = 2-1 v = 0, and 30SiO J = 1-0 v = 0 lines, and the H2O 61,6-52,3 line. As reported in previous papers, we confirmed that the intensity ratios of the SiO J = 1-0 v = 2 to v = 1 lines clearly correlate with infrared colors. In addition, we found possible correlation between infrared colors and the intensity ratios of the SiO J = 1-0 v = 3 to v = 1&2 lines.

The author presents the results of Berkeley-Illinois-Maryland (BIMA) array interferometric observations in the CO $J=1$–0 line toward X Her and EP Aqr, semiregular pulsating stars with a composite CO line profile, and also reports finding a disklike structure in X Her. In the CO spectrum both of X Her and EP Aqr, a composite profile including narrow and broad components is seen as reported by the previous single-dish observations. The spatial structure of the broad component region of X Her shows a bipolar shape, and that of the narrow component shows an elliptical/spherical shape. The blue- and red-shifted parts of the X Her narrow component show a systematic difference in the velocity integrated intensity map. The spatio-kinematic properties of the X Her narrow component are reminiscent of a Keplerian rotating disk with a central mass of 0.9 M$_{\odot}$. The spatial distributions of both the narrow and the broad components of EP Aqr appear to be roughly round with the same peak positions; no significant velocity gradient is seen. The spatio-kinematic properties of EP Aqr are reminiscent of a multiple-shell structure model rather than of a bipolar flow and disk model.

We give a summary of radio molecular-line and infrared imaging observations of the newly found O-rich protoplanetary nebula, IRAS 19312+1950. This object exhibits a bipolar nebulosity of size ~ 30″ on the near-IR (JHK) images. A ring-like structure with a diameter of about 10″ is seen surrounding the central star. Toward this object, we detected thermal lines of CO, HCO+, SO, and SiO (O-bearing) molecules and CN, CS, HNC, NH3, N2H+, and HC3N (C- and N-bearing) molecules, as well as H2O and SiO masers lines. The line profiles of 12CO, HCN, SO, and HCO+ are composed of broad (Δv ~ 30–40 km s-1) and narrow (Δv < 5 km s-1) components. The SiO profile (J = 2—1 v = 0 thermal line) has only broad component, and the line profiles of non-O-bearing molecules (except HCN) have only a narrow component. Both components are spatially strongly peaked in intensity at the center of this object within a ~ 15″ telescope beam. We infer that both components originate from cool material surrounding the central star. This object is most likely an O-rich protoplanetary nebula with high mass loss rate and envelope chemistry similar to that of OH 231.8+0.4.