# Stellar Parameters from multi-band Photometry

Yuan, Huang et al.

* Zhen Yuan (Y)
* Yang Huang (H)

## :link: Useful Links

- Gaia DR3 content
https://www.cosmos.esa.int/web/gaia/dr3
- SN of BP/RP spectra
https://cosmos.esa.int/web/gaia/iow_20220519
- Tool to download ana analyze BP/RP spectra
https://gaia-dpci.github.io/GaiaXPy-website/tutorials.html
- RVS spectra
https://www.cosmos.esa.int/web/gaia/iow_20210709
- Gaiahub (better pm for stars G > 18 mag in Hubble)
https://arxiv.org/abs/2205.08009

## :book: Shared files:
### Spectra
- [name=Y] Ferre synthetic spectra (only Giants for now)
- Name: [Fe/H]_[C/Fe]_Teff_logg
https://www.dropbox.com/sh/g7gr9uj597b5c6l/AAAg9qOOFuawc-K3fO8hU8HQa?dl=0
- [name=H] from BOSZ, very large about 1TB
- Name: [Fe/H]_[C/Fe]_Teff_logg_[alpha/Fe]
https://archive.stsci.edu/prepds/bosz/
- [name=H] PHOENIX spectra, no carbon
- Name: [Fe/H]_Teff_logg_[alpha/Fe]
https://phoenix.astro.physik.uni-goettingen.de/

### Documents
- [name=H] Some previous PPT documents
https://www.dropbox.com/scl/fi/r4bwa7h11k0486u9ajj62/JPLUS-parameters-20220516.pptx?dl=0&rlkey=9ytipfokz35opbuikc7uh3g31
https://www.dropbox.com/scl/fi/8dzp8u3joxmnfrt3iaqny/Mephisto-SP.pptx?dl=0&rlkey=t84jw9brpai4k8mxhjq9xx2ys
- [name=H] Filters response curves

## Notes

- [name=Y] Notes on NN model for stellar parameters https://hackmd.io/@ZYuan/r1-R77HT5
- [name=H]

## Workflow

- [name=Y] Create a graph-neural-network (node regression)
- Each node represents one pixel in de-reddened photometry space
- Node features: X-band (Gaia BP/RP spectra+medium/narrow-Ax)
- Node Label: [Fe/H], [Z/Fe] (Z=C, N, alpha … )
- Edge features: f(X1 - X2) – Metals absorb photons and re-emit them. It is equivalent to move photons from band X1 to band X2. Imagine f(X1-X2) as the message passage between band X1 and X2. The training process to obtain the regression model for each pair in X.

- Questions: Do we need Teff, logg in node labels? How to involve Ax in the training process?

- Exploration Steps:
- Create synthetic spectra grid (Ferre’s grid of non-CEMPs)
- Add extinction to synthetic spectra
- Generate J-plus band (d=13) from synthetic spectra
- Node regression to get metallicities

- Training Sample
- HR samples
- LR samples