ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject B-Citation I-Citation I-Citation I-Citation O O O O O O O B-CelestialObject O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: HEMT receiver followed by an autocorrelation spectrometer configured to record 4096 channels over 4 MHz for each polarization, yielding a spectral resolution of 0.09 km s −1 after Hanning smoothing. The system temperature varied between approximately 30 and 50 K during the observations. The telescope has a half power beam-width of 5.8 arcmin and rms pointing errors of 25arcsec. The spectra were obtained in a frequency-switching mode as a series of 30 s integrations. Most sources had an on-source integration of approximately 30 min. The system was regularly calibrated by observing the continuum source 3C123 (Ott et al. 1994 ) and daily checked using the source G32.744−0.076. This methanol maser source was reported as non-variable within ∼5 per cent (Caswell et al. 1995b ). Indeed, high-cadence observations reveal that some spectral features of the source have not shown variability higher than 8 per cent on time-scales from weeks to a few years. Detailed analysis of the light curves of five main spectral features of the source was reported in Szymczak et al. ( 2014 ). The features at 30.3, 38.5 and 39.1 km s −1 were non-variable during the monitoring period and the standard deviation of the flux density of these features indicates that the resulting accuracy of the absolute flux density is better than 10 per cent (Szymczak et al. 2014 ). The system temperature for the observations was measured by a continuously switched noise diode. Standard procedures were used to reduce the spectra. The typical rms noise level in the final spectra was 0.20-0.35 Jy at 0.09 km s −1 velocity resolution after averaging over polarization and time. There was no detectable interference on the spectra of our targets with the exception of G27.286+0.151. 2.3 Effect of offset observation and confusion For several sites in the sample (Table 1 ), accurate positions have recently been published (e.g. Bartkiewicz et al. 2014 , 2016 ; Breen et al. 2015 ), which show that for a majority of the targets the observed positions deviate from the interferometric positions by less than 0.4 arcmin. These differences (the fourth column of Table 1 ) are much less or comparable to the telescope pointing errors and have no significant effect on the flux density measurements. The measured profile of the telescope beam (Fig. 2 ) implies that our observations at an offset higher than 1.3 arcmin systematically underestimate the flux density by 9 per cent and its uncertainty increases by more than 10 per cent due to the pointing errors. There are 10 sites (11 distinct sources) in the sample for which the flux density measurements are significantly influenced by these effects and all of them are discarded in the following statistical analysis. Furthermore, the spectra of 18 sources (12 star-forming sites) are contaminated by confusion introduced by other sources in the telescope beam or side-lobe response from nearby bright sources and these sources are also excluded from the statistical