Orbits and abundance patterns, based on many-abundance LAMOST DR4 (Maosheng Xiang)

Starting point:

The GALAH-label-transferred LAMOST DR4 data set is the (by far?) largest set of stars in the Milky Way with multi-element abundance information. [Of course, only to the extent that the labels can be trusted; see previous post]

Johanna Coronado has augmented this sample of >5M objects with action estimates she did that primarily to look at the correlation of abundances and detailed orbit structure in the Solar neighbourhood. But the sample should also be very good to look at the non-disk components of the MW. In particular, the population of 'inner halo' stars in very radial orbits (sausage, Enceladus, PEM=presumed-early-merger) bear a closer look. This is something that Yua-Sen Ting and Maosheng Xiang may want to pursue as an 'application of the data set'.

All subsequent points were done using a) a sample of 'giants' and b) 'MS stars', just to get at least one test on abundance-robustnes..

First glance intriguing results

Here are some issues to follow-up:

I isolated the set of "stars on slightly-counter-rotating, radial orbits", by picking all stars with
-0.4 < "Lz" < 0.1, where Lz is the normalized angular momentum "Lz" == Lz / (8kpc * 220 km/s);

and asking that these stars are at the same time on highly radial orbits,  sqrt("JR")>0.6, where
"JR" == J_R / (8kpc * 220 km/s).

If we look at the abundance abundance distributions of (only) these radial-orbit 'halo' stars (about 8500 giants, and 6500 MS stars), we find (always "radial orbits" first, then "all orbits").

For Magnesium:

For Manganese

 

For Aluminum:






For Europium (can we believe LAMOST from-GALAH-label-transferred Eu?)

in every case, the stars on highly radial orbits are just one striking feature of the overall abundance distribution.





The 'halo' below FeH<-2 looks different; but (see last post) we need to see whether this is an artifact of the abundance analysis.

Next steps 

These plots bring up many questions:

1. Is the "tight" abundance feature -2<FeH<-0.7 a consequence of the label-transfer? E.g. if there are only 20 GALA stars in that regime that show no [X/Fe]-spred, then this is what we expect.  
2. Do we now have a large-sample, many-abundance handle of Sausage/Gaia-Enceladus? How much larger is this sample than others? 
3. Do the abundance trends that we see make astrophysical sense (esp. in the context of the trends expected for a mid-sized satellite galaxy)?
4. The plots for dwarfs look analogous, but do not extend below FeH<-1.4. HWR suspects that this is because there are no very metal poor MS stars in the label-transfer training sample.