tokens: shift for all sources in each track, the task uti _ doppler _ fix is then called. Applying this calibration technique is straightforward and is described in the MIR cookbook. We applied this new correction to every calibrated data set for the MASSES program, including the previously published data described in Paper I . The effect of the correction is significant for Perseus protostars given the relatively narrow lines (on order of 1 km s −1 ). We found that over the course of a track for Perseus, the Doppler velocity correction for each integration could amount to differences of up to ∼1 km s −1 . In comparison of pre- and post-correction data at locations where the spectral lines are bright, flux differences in each channel of up to 50% were not uncommon. The correction, by removing the effects of the smearing, significantly improved the sharpness of all narrow spectral line features, allowing for easier identification of weak narrow lines and higher signal-to-noise ratio for stronger ones. In Figure 1 , the products before and after applying the Doppler correction fix are shown for C 18 O(2–1) spectra at a single pixel for Per-emb-2 and Per-emb-40. It is apparent that without the fix, the velocity has a significant shift, and the spectral features are smoothed. Because the real-time error was not identified until after the publication of Paper I , the results presented there were adversely affected; we stress that the data presented in this paper improves on and supersedes that presented in Paper I . After the Doppler shift correction was applied, all data were converted to MIRIAD format (Sault et al. 1995 ). Figure 1. Primary-beam-corrected C 18 O(2–1) spectra, taken at the 1.3 mm continuum peak pixel for Per-emb-2 (top panel) and Per-emb-40 (bottom panel). The blue spectra show what the spectra looked before the fix, while the red spectra show after the fix. 3.2. Data Imaging All imaging was done using MIRIAD and is also described in detail in Paper I . We repeat most of the details here, as there are a couple of minor differences which will be specified below. For spectral lines, the continuum is first subtracted using task uvlin , where a range of line-free channels (visually identified) is specified by the user. The task fits a DC offset to these channels and subtracts the offset from the window. For both continuum and spectral lines, an inverse Fourier transform was used on all visibilities (i.e., specifying all tracks for each target as specified in Table 1 ) to create a dirty image using the MIRIAD task invert and specifying options “systemp” and “double.” During the invert task, we create two data products of different resolutions by specifying Brigg’s robust parameters of both −1 and 1. This differs from the subcompact release (Paper I ), where we only delivered products that use robust = 1. A robust parameter of 2 is similar to natural weighting, which minimizes the noise in the image, while a robust parameter of −2 is
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