[en] Radio continuum and H₂O maser emission have been detected from the semiregular variable W Hya. The continuum emission at radio frequencies probably comes from the outer photosphere of the red giant star. A partial resolution of the stellar disk shows it to be approximately 0.09 arcsec in diameter. The H₂O maser emission arises from a ring of diameter 0.3 arcsec that is well centered on the star. These results for the first time yield a clear detection of a stellar photosphere at radio frequencies (except for the sun) and a radio measurement of the size of a stellar disk. Also, these are the first observations that precisely locate circumstellar maser emission with respect to the exciting star, allowing a detailed modeling of the maser amplification. The H₂O masers are unsaturated, amplify spontaneous emission, and are highly beamed. 13 refs

[en] The first astronomical detection of two millimeter-wave emission lines from vibrationally excited water is reported. The 96 GHz 4(40)-5(33) and the 232 GHz 5(50)-6(43) rotational transitions within the nu2 vibrationally excited state of H2O have been discovered toward the supergiant star VY CMa. The latter transition was also detected toward the semiregular variable W Hya. The 4(40)-5(33) transition shows definite signs of maser action while the 5(50)-6(43) emission may be of (quasi-)thermal nature. Based on a comparison of the line profiles of the 22 GHz H2O masers, various SiO maser lines, and the nu2 H2O emission, it is concluded that the vibrationally excited H2O and the SiO masers probably arise from a region in which the expansion of the circumstellar envelope has not yet begun and some infalling motions are present. This region is closer to the star than the part of the envelope that gives rise to the 22 GHz H2O masers. 18 refs

[en] The detection of a strong new maser emission line from the 5(-1)-4(0)E transition of methanol toward DR 21(OH) is reported. Interferometric observations with a resolution of 8.3 arcsec x 6.2 arcsec show that the line does not coincide in position with any of the known maser or infrared emission features toward this source. This strongly indicates an excitation mechanism for this methanol maser which is different from the physical conditions leading to the excitation of the water and OH masers. In addition, maser emission is found toward a condensation which has been detected in emission in the 2(11)-2(12) transition of formaldehyde. Besides maser emission, thermal emission lines from several compact sources are detected. Two of these sources are found very close to the OH maser position. 16 references

[en] Measurements at 2'' resolution of the 9₂--10₁ A⁺ emission line of methanol toward W3(OH) are presented. The frequency resolution was 12.2 kHz, or 0.16 km s^-1 at the line rest frequency 23121.01 MHz. The two velocity components seen in single-dish spectra are separated by approx.1'', but each is unresolved. This implies intrinsic source sizes of < or =1''. For the masing spike feature at -43.3 km s^-1, the line brightness temperature is > or =2 x 10⁴ K. For the broader emission at -43.9 km s^-1, it is > or =5000 K, showing that this emission is also caused by masing. The spike is 0''.5 southwest and the broader feature is 1''.5 northwest of the continuum peak. An absorption-line spectrum of the 10₁--9₂ A^- line taken with the 100 m telescope is also presented, and it is concluded that this absorption and the 9₂--10₁ A⁺ maser emission are both formed in the same cloud where OH masers and ammonia absorption are present

[en] The BIMA array is used to map the 95-GHz 8(0) to 7 1A(+) transition of methanol and the 98-GHz J = 2-1 transition of CS toward the DR 21(OH) and DR 21 star-forming regions. Several strong methanol masers were found. The positions of the two brightest masers were measured with an accuracy of about + or - 0.3 arcsec. Toward DR 21(OH), the positions, velocities, and line shapes of the 95 GHz masers are in excellent agreement with those of the 84-GHz 5(-1) to 4 () methanol masers previously mapped by Batrla and Menten (1988), demonstrating that maser emission in both transitions originates from the same clumps of gas. The methanol masers are offset from CS emission peaks and from other known infrared and maser sources; they may possibly be clustered along the interface between outflows, traced by shock-excited H2 emission, and dense ambient gas, traced by CS emission. 25 refs

[en] The Haystack Observatory 37-m antenna was used to search for emission from the 44 GHz 7(0)-6(1)A(+) transition of interstellar methanol toward 50 galactic star-forming regions. The line was detected toward half the observed sources. Several of these regions were also observed in the 36 GHz 4(-1)-3(0)E line. In most sources, the detected emission shows one or more narrow components indicating maser action. The spectral appearance and spatial distribution of these methanol masers closely resembles the properties of the well-studied 25 GHz methanol masers: in some cases, distances between individual methanol maser components are of order 1 pc. Unlike the now well-studied 12 GHz methanol masers, these masers appear well separated from OH/H2O maser centers and compact H II regions. 52 refs

[en] The first successful VLBI observations of 10 extragalactic H2O masers in the M33 galaxy are reported. A spectral-line VLBI synthesis map is constructed, the first of any extragalactic H2O maser sources. The map has the lowest noise of any K-band spectral line VLBI map yet produced. The maser emission extends over about 300 milliarcseconds and is divided into 14 distinct spatial components, the strongest of which has a correlated flux density of about 0.7 Jy. The relative positions of some of these components are determined accurately enough to provide first-epoch measurements for proper motion studies. The characteristics of the maser are similar to those of the most powerful maser in the Galaxy, W49N. A compact H II region is found close to the maser which is 1 pc in diameter and whose emission measure is about 6 x 10 to the 7th pc/cm exp 6. This region is the compact component of a more extended H II complex that extends over about 100 pc. 89 refs

[en] A number of CH3OH lines toward the H-II region F in the NGC 6334 star-forming region have been observed in April 1987 with the 140-foot Green Bank telescope. Strong maser emission is found in the 2(1) to 3(0)E transition at 19.9 GHz and in the 9(2) to 10(1)A(+) transition at 23.1 GHz. The results suggest that the 12.1, 19.9, and 23.1 GHz methanol masers may be closely associated with compact H-II regions and OH masers, and that the 25 GHz masers may be associated with dense condensations in an earlier evolutionary state. 26 refs

[en] By using the Haystack 37 m antenna, a discovery was made of maser emission in the 7(-2)-8(-1)E, 6(2)-5(3)A(-), and 6(2)-5(3)A(+) transitions of interstellar methanol. All three lines were detected toward the compact H II regions W3(OH) and NGC 6334-F. Toward the latter source intensities in excess of 100 Jy are observed in all three transitions. Masers in the 7(-2)-8(-1)E line were detected in three additional sources. All sources toward which maser action was found are associated with compact H II regions and are known to show strong maser emission in the 12.2 GHz 2(0)-3(-1)E line of methanol at similar velocities. For this reason the newly detected masers are classified as class B methanol masers. Toward Orion-KL, thermal emission is observed. 29 refs

[en] The first astronomical detection of the 10(29) - 9(36) transition of water vapor (H2O) at a frequency near 321 GHz is reported. The line was detected toward the star-forming regions W3(OH), W49N, W51 IRS 2, and W51 Main, and the supergiant star VY CMa. In all cases, probably, maser action is observed. Since the 10(29) level of H2O is at an energy of 1861 K above the ground state, the 10(29) - 9(36) line probes very hot molecular material. The 10(29) - 9(36) emission is found at velocities that are near the systemic velocities of the regions studied. The strongest features in spectra of the well-studied 22 GHz 6(16) - 5(23) transition are generally found at similar velocities. The 10(29) - 9(36) spectra do not show counterparts to the high-velocity features observed in the 22 GHz line, but this may be due to the limited sensitivity of the observations. 21 refs