Best¶

The Best pipeline (internally MWMBest) selects the single best set of stellar parameters and auxiliary measurements for each source observed by the Milky Way Mapper (MWM), drawing from across all available analysis pipelines.

What it does¶

Best produces one row per source that consolidates:

Stellar parameters (Teff, log g, metallicity, abundances)
Radial velocities from multiple methods
Chemical abundances (up to 20+ elements)
White dwarf classifications (from Snow White)
M dwarf spectral types (from MDwarfType)
Spectrum metadata (SNR, MJD range, number of visits)

How it works¶

The Best pipeline queries results from multiple analysis pipelines in a priority-ordered sequence. For each source, it takes the result from the first pipeline in the sequence that has a valid measurement. Once a source has been assigned results, it is excluded from subsequent queries.

Pipeline priority order¶

Snow White (white dwarf classifications) – for sources in the mwm_wd program
BOSSNet (hot stars) – for sources in the mwm_ob program, with no result flags
ASPCAP (hot stars) – for sources in the mwm_ob program
APOGEENet (YSOs) – for sources in the mwm_yso program, with no result flags
BOSSNet (YSOs) – for sources in the mwm_yso program, with no result flags
SLAM (M dwarfs) – for sources with no result flags
ASPCAP (general) – for sources not flagged as bad
AstroNN (general) – for sources with no result flags
APOGEENet (general) – for sources with no result flags
BOSSNet (general) – for sources with no result flags
APOGEENet (any remaining) – no quality cuts
BOSSNet (any remaining) – no quality cuts

This priority order reflects the science strategy: specialized pipelines are preferred for their target populations (e.g., Snow White for white dwarfs, SLAM for M dwarfs), and higher-quality results are preferred over lower-quality ones.

Spectrum metadata¶

Each Best result also carries metadata from the underlying spectrum:

APOGEE spectra: release, apred, apstar, telescope, field, fiber information, Doppler RV parameters, cross-correlation RV, visit statistics
BOSS spectra: release, run2d, telescope, XCSAO parameters, zwarning flags, visit statistics

Output fields¶

Radial velocity¶

Field	Description
`v_rad`	Best radial velocity (km/s)
`e_v_rad`	Uncertainty on radial velocity
`std_v_rad`	Standard deviation of visit radial velocities
`median_e_v_rad`	Median per-visit RV uncertainty

Radial velocity (method-specific)¶

Field	Description
`xcsao_teff`, `xcsao_logg`, `xcsao_fe_h`	XCSAO template parameters
`xcsao_meanrxc`	XCSAO cross-correlation R-value
`doppler_teff`, `doppler_logg`, `doppler_fe_h`	Doppler template parameters
`doppler_rchi2`	Doppler fit reduced chi-squared
`xcorr_v_rad`, `xcorr_v_rel`, `ccfwhm`	Cross-correlation RV results
`boss_net_v_rad`, `boss_net_e_v_rad`	BOSSNet radial velocity

Stellar parameters¶

Field	Description
`teff`, `e_teff`	Effective temperature (K)
`logg`, `e_logg`	Surface gravity (log cm/s^2)
`v_micro`, `e_v_micro`	Microturbulent velocity (km/s)
`v_sini`, `e_v_sini`	Projected rotational velocity (km/s)
`m_h_atm`, `e_m_h_atm`	Overall metallicity [M/H] (dex)
`alpha_m_atm`, `e_alpha_m_atm`	Alpha-element abundance [alpha/M] (dex)
`c_m_atm`, `e_c_m_atm`	Atmospheric carbon abundance [C/M] (dex)
`n_m_atm`, `e_n_m_atm`	Atmospheric nitrogen abundance [N/M] (dex)

Chemical abundances¶

Individual element abundances are provided for: Al, C, C_1, Ca, Ce, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, Nd, Ni, O, P, S, Si, Ti, Ti_2, V, and C_12_13 (carbon isotope ratio).

Each element X has four fields:

X_h: Abundance [X/H] (dex)
e_X_h: Uncertainty
X_h_flags: Quality flags
X_h_rchi2: Reduced chi-squared for the abundance window fit

White dwarf classifications¶

Field	Description
`classification`	White dwarf classification string
`p_da`, `p_db`, `p_dc`, …	Probabilities for each white dwarf subtype

M dwarf classifications¶

Field	Description
`spectral_type`	M dwarf spectral type
`sub_type`	Numerical sub-type

Observing metadata¶

Field	Description
`snr`	Signal-to-noise ratio
`min_mjd`, `max_mjd`	MJD range of visits
`n_visits`	Number of visits
`n_good_visits`	Number of good visits
`n_good_rvs`	Number of good radial velocities
`telescope`	Telescope used
`release`, `filetype`	Data release and file type

Key caveats¶

The Best result for a given source depends on which pipelines ran successfully and the priority order. The “best” designation reflects the operational strategy, not necessarily the most accurate measurement for a particular science case.
A single source has at most one Best entry (unique on source_pk and v_astra). If a source was observed by both APOGEE and BOSS, the Best result comes from whichever pipeline ranks higher in the priority list.
Fields that are not provided by the selected pipeline will be null. For example, chemical abundances are only populated when ASPCAP or AstroNN is the selected pipeline.
The pipeline_flags field is an amalgamated bitfield that may combine flags from the selected source pipeline.
Users interested in results from a specific pipeline should query that pipeline’s table directly rather than relying on Best.