Context. Molecular maser lines are signposts of high-mass star formation, probing the excitation and kinematics of very compact regions in the close environment of young stellar objects and providing useful targets for trigonometric parallax measurements. Aims. Only a few NH3 (9,6) masers are known so far, and their origin is still poorly understood. Here we aim to find new NH3 (9,6) masers to provide a better observational basis for studying their role in high-mass star-forming regions. Methods. We carried out NH3 (9,6) observations toward Cepheus A and G34.26+0.15 with the Effelsberg 100-meter telescope (beam size 49′′) and the Karl G. Jansky Very Large Array (JVLA; beam size about 1′′.2). Results. We discovered new NH3 (9,6) masers in Cep A and G34.26+0.25, which increases the number of known high-mass star-forming regions hosting NH3 (9,6) masers from five to seven. Long-term monitoring (20 months) at Effelsberg shows that the intensity of the (9,6) maser in G34.26+0.25 is decreasing, while the Cep A maser remains stable. Compared to the Effelsberg data and assuming linear variations between the epochs of observation, the JVLA data indicate no missing flux. This suggests that the NH3 (9,6) emission arises from single compact emission regions that are not resolved by the interferometric measurements. As JVLA imaging shows, the NH3 (9,6) emission in Cep A originates from a sub-arcsecond-sized region, slightly to the west (0′′.28 ± 0′′.10) of the peak position of the 1.36 cm continuum object, HW2. In G34.26+0.25, three NH3 (9,6) maser spots are observed: one is close to the head of the cometary ultracompact H II region C, and the other two are emitted from a compact region to the west of the hypercompact H II region A. Conclusions. The newly found (9,6) masers appear to be related to outflows. The higher angular resolution of JVLA and very long baseline interferometry observations are needed to provide more accurate positions and constraints for pumping scenarios.

Our aim is to measure the interstellar 14N/15N ratio across the Galaxy, to establish a standard data set on interstellar ammonia isotope ratios, and to provide new constraints on the Galactic chemical evolution. The (J, K) = (1, 1), (2, 2), and (3, 3) lines of 14NH3 and 15NH3 were observed with the Shanghai Tianma 65 m radio telescope (TMRT) and the Effelsberg 100 m telescope toward a large sample of 210 sources. One hundred fourty-one of these sources were detected by the TMRT in 14NH3. Eight of them were also detected in 15NH3. For 10 of the 36 sources with strong NH3 emission, the Effelsberg 100 m telescope successfully detected their 15NH3(1, 1) lines, including 3 sources (G081.7522, W51D, and Orion-KL) with detections by the TMRT telescope. Thus, a total of 15 sources are detected in both the 14NH3 and 15NH3 lines. Line and physical parameters for these 15 sources are derived, including optical depths, rotation and kinetic temperatures, and total column densities. 14N/15N isotope ratios were determined from the 14NH3/15NH3 abundance ratios. The isotope ratios obtained from both telescopes agree for a given source within the uncertainties, and no dependence on heliocentric distance and kinetic temperature is seen. 14N/15N ratios tend to increase with galactocentric distance, confirming a radial nitrogen isotope gradient. This is consistent with results from recent Galactic chemical model calculations, including the impact of superasymptotic giant branch stars and novae.

To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace the chemical evolution of the Galaxy, we have performed with the IRAM 30 m and the SMT 10 m telescopes a systematic study of Galactic interstellar 18 O/ 17 O ratios toward a sample of 421 molecular clouds, covering a galactocentric distance range of ∼1 -22 kpc. The results presented in this paper are based on the J=2-1 transition and encompass 364 sources showing both C 18 O and C 17 O detections. The previously suggested 18 O/ 17 O gradient is confirmed. For the 41 sources detected with both facilities, good agreement is obtained. A correlation of 18 O/ 17 O ratios with heliocentric distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18 O/ 17 O = (0.12 ± 0.02)R GC + (2.38 ± 0.13) with a correlation coefficient of R = 0.67. While the slope is consistent with our J=1-0 measurement, ratios are systematically lower. This should be caused by larger optical depths of C 18 O 2-1 lines, w.r.t the corresponding 1-0 transitions, which is supported by RADEX calculations and the fact that C 18 O/C 17 O is positively correlated with 13 CO/C 18 O. After considering optical depth effects with C 18 O J=2-1 reaching typically an optical depth of ∼0.5, corrected 18 O/ 17 O ratios from the J=1-0 and J=2-1 lines become consistent. A good numerical fit to the data is provided by the MWG-12 model, including both rotating stars and novae.

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Context. Cyanopolyynes (HC2n+1 N, n = 1,2,3), which are the linear carbon chain molecules, are precursors for the prebiotic synthesis of simple amino acids. They are important for understanding prebiotic chemistry and may be good tracers of the star formation sequence. Aims. We aim to search for cyanopolyynes in high-mass star-forming regions (HMSFRs) at possibly different evolutionary stages, investigate the evolution of HC3N and its relation with shock tracers, and detect the existence of HC5N and HC7N in HMSFRs with a formed protostar. Methods. We carried out a cyanopolyyne line survey towards a large sample of HMSFRs using the Shanghai Tian Ma 65 m Radio Telescope (TMRT). Our sample consisted of 123 targets taken from the TMRT C band line survey. It included three kinds of sources, namely those with detection of the 6.7 GHz CH3OH maser alone, with detection of the radio recombination line (RRL) alone, and with detection of both (hereafter referred to as Maser-only, RRL-only, and Maser-RRL sources, respectively). For our sample with detection of cyanopolyynes, their column densities were derived using the rotational temperature measured from the NH3 lines. We constructed and fitted the far-infrared (FIR) spectral energy distributions (SED; obtained from the Herschel FIR data and the Atacama Pathfinder Experiment data at 870 µm) of our HC3N sources. Moreover, by analysing the relation between HC3N and other shock tracers, we also investigate whether HC3N is a good tracer of shocks. Results. We detected HC3N in 38 sources, HC5N in 11 sources, and HC7N in G24.790+0.084, with the highest detection rate being found for Maser-RRL sources and a very low detection rate found for RRL-only sources. The mean column density of HC3N was found to be (1.75 ± 0.42) × 1013, (2.84 ± 0.47) × 1013, and (0.82 ± 0.15) × 1013 cm−2 for Maser-only, Maser-RRL, and RRL-only sources, respectively. Based on a fit of the FIR SED, we derive their dust temperatures, H2 column densities, and abundances of cyanopolyynes relative to H2. The mean relative abundance of HC3N was found to be (1.22 ± 0.52) × 10−10 for Maser-only, (5.40 ± 1.45) × 10−10 for Maser-RRL, and (1.65 ± 1.50) × 10−10 for RRL-only sources, respectively. Conclusions. The detection rate, the column density, and the relative abundance of HC3N increase from Maser-only to Maser-RRL sources and decrease from Maser-RRL to RRL-only sources. This trend is consistent with the proposed evolutionary trend of HC3N under the assumption that our Maser-only, Maser-RRL, and RRL-only sources correspond to massive young stellar objects, ultracompact H ii regions, and normal classical H ii regions, respectively. Our detections enlarge the sample of HC3N in HMSFRs and support the idea that unsaturated complex organic molecules can exist in HMSFRs with a formed protostar. Furthermore, a statistical analysis of the integrated line intensity and column density of HC3N and shock-tracing molecules (SiO, H2CO) enabled us to find positive correlations between them. This suggests that HC3N may be another tracer of shocks, and should therefore be the subject of further observations and corresponding chemical simulations. Our results indirectly support the idea that the neutral-neutral reaction between C2H2 and CN is the dominant formation pathway of HC3N.