Forty-eight candidate massive protostar regions were surveyed for methyl cyanide (CH₃CN) emission using the Heinrich Hertz Telescope (HHT) on Mount Graham, AZ. CH₃CN J = 12-11 emission at 220 GHz was detected toward 25 regions. Thirteen of these are new detections, yielding a substantial number of new candidates for massive protostars. The CH₃¹³CN (J = 12-11) isotopomer was included in the bandpass of all observed sources and was detected toward eight sources in our sample. These sources are probably optically thick in some of the CH₃CN lines. CH₃CN J = 25-24 emission at 460 GHz was detected in at least one K-component toward five of 11 sources observed in this transition. Using a rotational equilibrium temperature analysis we estimate the CH₃CN rotation temperatures and beam-averaged column densities for 20 of the sources.

New spectropolarimetric observations of the unique white dwarf GD356 are presented. These observations show resolved Zeeman triplets of Hα and Hβ in emission with distinctive circular polarization properties. A detailed modelling of the spectropolarimetric observations points to the existence of a latitudinally extended spherical sector/strip covering approximately 0.1 of the stellar surface over which the stellar atmosphere has an inverted temperature distribution at low optical depths. Magneto-optical effects from regions producing photospheric absorption appear to be responsible for narrow circular polarization features which are observed near the π component of the emission lines. Radio observations of GD 356 were obtained at the Very Large Array at 8439.9 and 4860.1 MHz, to gain clues on the origin of the emission lines, but the failure to detect the star in either frequency band does not provide a useful test for the presence of a corona. Also, new infrared (IR) observations to search for a low-mass stellar companion as a possible source of matter for accretion yielded null results. We have investigated the possibility that the temperature inversion is caused by Bondi-Hoyle accretion from the interstellar medium. The absence of additional components of radiation in the X-ray, ultraviolet, optical and near-IR wavelengths implies that the accretion luminosity must be significantly less than the white dwarf luminosity. The implied low value for the specific accretion rate (ṁ<10⁻⁶ g cm⁻² s⁻¹) indicates that a shock would not form, but that the atmosphere will be particle heated by direct bombardment by the infalling protons. A detailed model of the bombardment solution in the very low- accretion regime is required before the viability of such a model can be fully evaluated.

The molecular cloud associated with the Sh 254-258 group of five small H II regions appears to be forming a (late)-OB association. We have mapped the associated molecular cloud in the J = 2-1 line of the CO and ¹³CO molecules over 075 × 1°, and the CO J = 3-2 line toward the two main peaks, with the University of Arizona Heinrich Hertz Submillimeter Telescope. The data are analyzed with a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with images at optical, IR, and radio wavelengths. From this analysis, we propose a scenario for sequential formation of the stars exciting the H II regions, triggered by the compression of the molecular gas as a consequence of the expansion of the adjacent H II regions.

The aim of this work is to study structure and gas kinematics in the photodissociation regions (PDRs) around the compact H ii regions S235 A and S235 C. We observe the [C ii], [¹³C ii], and [O i] line emission, using SOFIA/upGREAT, and complement them by data of HCO⁺ and CO. We use the [¹³C ii] line to measure the optical depth of the [C ii] emission, and find that the [C ii] line profiles are influenced by self-absorption, while the [¹³C ii] line remains unaffected by these effects. Hence, for dense PDRs, [¹³C ii] emission is a better tracer of gas kinematics. The optical depth of the [C ii] line is up to 10 in S235 A. We find an expanding motion of the [C ii]-emitting layer of the PDRs into the front molecular layer in both regions. Comparison of the gas and dust columns shows that gas components visible neither in the [C ii] nor in low-J CO lines may contribute to the total column across S235 A. We test whether the observed properties of the PDRs match the predictions of spherical models of expanding H ii region + PDR + molecular cloud. Integrated intensities of the [¹³C ii], [C ii], and [O i] lines are well represented by the model, but the models do not reproduce the double-peaked [C ii] line profiles due to an insufficient column density of C⁺. The model predicts that the [O i] line could be a more reliable tracer of gas kinematics, but the foreground self-absorbing material does not allow using it in the considered regions.