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--- tests:astropars:challenge2 [2014/10/30 13:14] – created randrae
+++ tests:astropars:challenge2 [2022/10/24 12:26] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== Challenge 2: Reference stars ======
+===== Objectives =====
+  * Employ high-resolution spectra from X-shooter archive to investigate how the Gaia spectra will look like.
+  * Investigate GSP-Phot performance on X-shooter spectra.
+===== Comparison to RVS and BP/RP spectra =====
+  * Gaia RVS spectra and corresponding segments of x-shooter spectra look very similar. Ca-Triplet lines are easily identified and other prominent lines are also in obvious correspondence.
+  * x-shooter spectra contain telluric bands around 760nm and 950nm. In fact, BP/RP shows prominent dips there, which are NOT reflected by space-based instrument models. That must be a problem when modelling those spectra with GSP-Phot.
+{{:tests:compare-spectra.png|}}
+===== GSP-Phot performance on x-shooter spectra =====
+  * Paula compiled mean parameters for all stars from Pastel. (These are no "true" values but mean literature values.)
+  * Paula's data contains a lot of giants. GSP-Phot lacks giants in its training data, i.e., it is unlikely to perform well on giants (c.f. [[:tests:astropars:challenge4|Challenge 4]]).
+  * GSP-Phot performs very poorly on x-shooter spectra: Teff is loosely related for some stars, but logg looks rather random and GSP-Phot tends to assign too low [Fe/H].
+{{:compare-pastel-masked-tellurics.png|}}
+== Possible explanations for poor GSP-Phot performance ==
+  * x-shooter spectra are ground-based spectra, including telluric features, that are not part of the Gaia spectra.
+  * Lack of giants in GSP-Phot training data.
+  * x-shooter spectra were processed with GOG version 14, whereas GSP-Phot training data was processed with GOG version 8.
+===== Andy's SICK performance on x-shooter spectra =====