Minor updates to NB 305_1

Author: jeffcarlin

DP1/300_Science_Demos/305_Galactic_variables_and_transients/305_1_Variable_star_light_curves.ipynb

@@ -22,7 +22,7 @@
     "Data Release: <a href=\"https://dp1.lsst.io/\">Data Preview 1</a> <br>\n",
     "Container Size: large <br>\n",
     "LSST Science Pipelines version: r29.2.0 <br>\n",
-    "Last verified to run: 2025-09-02 <br>\n",
+    "Last verified to run: 2025-09-30 <br>\n",
     "Repository: <a href=\"https://github.com/lsst/tutorial-notebooks\">github.com/lsst/tutorial-notebooks</a> <br>"
    ]
   },
@@ -426,7 +426,7 @@
     "\n",
     "Use the known period of the variable star to \"phase-fold\" the light curve.\n",
     "\n",
-    "Define the period in days for the SX Phe star from Carlin+2025."
+    "Define the period in days for the SX Phe star from [Carlin et al. 2025](https://ui.adsabs.harvard.edu/abs/2025RNAAS...9..161C/abstract)."
    ]
   },
   {
@@ -513,9 +513,7 @@
    "source": [
     "### 3.3. Plot magnitude vs. phase\n",
     "\n",
-    "Convert the direct image forced fluxes to magnitudes, then plot a light curve.\n",
-    "\n",
-    "> **Warning:** the following code cell produces a pink RuntimeWarning about invalid values encountered in log10, which represents the danger of converting fluxes to magnitudes: direct-image forced fluxes can be negative."
+    "Filter out catalog entries with spurious negative flux measurements. Then convert the direct image forced fluxes to magnitudes, and plot a light curve."
    ]
   },
   {
@@ -525,6 +523,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "forced_source = forced_source[forced_source['psfFlux'] > 0]\n",
+    "\n",
     "mag = forced_source['psfFlux'].to(u.ABmag).value"
    ]
   },