respectively. We obtained 35 images of and 34 frames of with a sampling period of $\approx$14 days. One example image of the time series for each of our science targets is shown in Fig. \[GalLPV\]. The time series exhibits two larger gaps of approximately six months during which the targets were not observable. Calibration frames to correct for sky and bias were recorded for each night of observation. In the rare cases of missing sky flats, these were replaced by average flats from the previous and the following observation.

$K_s$-band photometry
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As can be seen from spectral energy distributions of cool AGB stars (Nowotny et al. [@nowo2]), they emit most of their flux in near-infrared wavelengths. Hence, the $K_{s}$-band is a good measure of the bolometric flux. The most evolved, dust-enshrouded AGB stars can be detected only at infrared wavelengths. Therefore, the $K_{s}$-band has been widely used (e.g. Wood [@woodc]) to construct PLRs of LPVs. To allow a comparison of our results with previous studies, we carried out single-epoch $K_{s}$-band photometry for our target systems using NOTCam during two consecutive nights in September 2004. This camera is equipped with a $1024 \times 1024$ HgCdTe Rockwell Hawaii array with a 