factor of five the sample of subdwarfs presented in @rajpurohit16a and extend that recent work to the full sequence of the three metallicity classes of M subdwarfs. We will make publicly available all spectra through the late-type subdwarf archive at http://svo2.cab.inta-csic.es/vocats/ltsa/ [@lodieu17a].

[@c @c c c c c c c@]{} R.A (J2000) & dec (J2000) & $i'$ & SpT & Date & Airm & ExpT & Cycles hh:mm:ss.ss & dd:mm:ss.s & mag & & & & sec/sec/sec & 23:46:59.87 & $-$00:59:43.9 & 15.166 & sdM0.0 & 13Aug2012 & 1.30 & 90/66/66 & 2AB 21:22:02.76 & $+$00:44:56.8 & 14.996 & sdM0.5 & 21May2012 & 1.13 & 90/66/66 & 2AB 00:48:00.05 & $+$00:28:49.4 & 15.260 & sdM1.0 & 13Aug2012 & 1.22 & 90/66/66 & 2AB 00:51:25.68 & $-$00:37:16.9 & 16.666 & sdM1.5 & 18Aug2012 & 1.10 & 216/216/240 & 2AB 23:57:32.54 & $-$01:10:36.3 & 15.692 & sdM2.0 & 17Aug2012 & 1.32 & 90/66/66 & 2AB 01:17:46.53 & $-$00:01:05.3 & 16.196 & sdM2.5 & 13Aug2012 & 1.36 & 90/66/66 & 2AB 03:24:49.81 & $-$00:15:05.0 & 14.942 & sdM3.0 & 15Aug2012 & 1.14 & 90/66/66 & 2AB 02:12:08.59 & $+$00:37:01.5 & 14.918 & sdM3.5 & 19Aug2012 & 1.11 & 90/66/66 & 2AB 03:46:01.58 & 