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--- tests:astropars:challenge3 [2014/10/30 13:14] – created randrae
+++ tests:astropars:challenge3 [2022/10/24 12:26] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== Challenge 3: Fit BP/RP and RVS simultaneously ======
+===== Objectives =====
+  * Compare performance of GSP-Phot to Andy's SICK code when fitting only BP/RP.
+  * Investigate fitting BP/RP alone, RVS alone, and BP/RP+RVS simultaneously with Andy's SICK code.
+  * Is this a route to beat APSIS?
+  * Where can BP/RP help to estimate abundances from RVS?
+  * Where can RVS help to improve on BP/RP?
+  * This project employs synthetic MARCS spectra.
+===== GSP-Phot vs. SICK =====
+== Conclusions ==
+  * GSP-Phot and SICK overall agree very nicely. No algorithm clearly outperforms the other.
+  * logg: GSP-Phot is slightly better than SICK. SICK may suffer from some convergence problems (red dots below dwarfs).
+  * [Fe/H]: SICK is slightly better than GSP-Phot. GSP-Phot appears to systematically underestimate [Fe/H] by ~1dex for some stars. These problematic stars are fainter than G~15, i.e., SICK estimates [Fe/H] more robustly at lower S/N than GSP-Phot.
+== Test data ==
+  * 2000 synthetic MARCS spectra in Gaia BP/RP.
+  * Mostly Main-Sequence dwarfs but also some giants.
+  * Teff from 4000K to 8000K.
+  * Test spectra created by GOG. (Not by our own forward models!)
+== Examples of posterior samples ==
+  * Posterior distributions mostly well behaved for BP/RP, i.e., fast convergence, unimodal.
+  * Even in simple case the posteriors cannot be well approximated by a Gaussian.
+  * Rare examples with multimodal posterior.
+{{:tests:example-MCMC-unimodal.png|}}
+{{:tests:example-MCMC-multimodal.png|}}
+== Results for fitting BP/RP alone ==
+^  ^ GSP-Phot bias ^ SICK bias ^ GSP-Phot sigma ^ SICK sigma ^
+| Teff [K] | 14 | 18 | 100 | 100 |
+| AV [mag] | 0.02 | 0.03 | 0.07 | 0.08|
+| logg [dex] | 0.02 | 0.07 | 0.19 | 0.29 |
+| [Fe/H] [dex] | 0.12 | 0.00 | 0.37 | 0.28 |
+{{:tests:sick-gspphot-teff.png|}}
+{{:tests:sick-gspphot-A.png|}}
+{{:tests:sick-gspphot-logg.png|}}
+{{:tests:sick-gspphot-feh.png|}}
+== Future tests ==
+  * Compare initial guesses of GSP-Phot and SICK. (Possibly SVM fails for noisy data, which may explain why SICK estimates [Fe/H] better at faint magnitudes.)
+===== SICK: BP/RP alone vs. RVS alone =====
+===== SICK: Fitting BP/RP and RVS simultaneously =====