always mask strong lines; lower-order smooth-continuum fitting

py/fastspecfit/continuum.py

@@ -218,9 +218,10 @@ def _smooth_percamera(camwave, camflux, camivar, camlinemask):
 
                 # We supply estimates local inverse stddev in each window
                 # (i.e., how noisy the data is there) so that variation is
-                # down-weighted in noisier regions.
+                # down-weighted in noisier regions. Note: ext=3 means constant
+                # extrapolation.
                 if len(swave) > 3:
-                    spl_flux = UnivariateSpline(swave, sflux, w=sisig, ext=3, k=3)
+                    spl_flux = UnivariateSpline(swave, sflux, w=sisig, ext=3, k=2)
                     smoothflux = spl_flux(camwave)
                 else:
                     smoothflux = np.zeros_like(camflux)

py/fastspecfit/linemasker.py

@@ -838,10 +838,12 @@ def fit_patches(continuum_patches, patchMap, linemodel,
             snrpix = pix['snr']
 
 
-        # remove low signal-to-noise ratio lines from the mask
+        # remove low signal-to-noise ratio lines from the mask, but always keep
+        # the "expected" strong lines (see, e.g., CIV 1549 in
+        # sv3-dark-25960-39627770216580342).
         linenames = snrpix.keys()
-        for linename in linenames:
-            if snrpix[linename] < minsnr_linemask:
+        for linename, isstrong in zip(linenames, EMFit.line_table[EMFit.line_in_range]['isstrong'].value):
+            if not isstrong and snrpix[linename] < minsnr_linemask:
                 log.debug(f'Removing {linename} from linepix: S/N={snrpix[linename]:.1f}<{minsnr_linemask:.1f}.')
                 linepix.pop(linename)