APOGEE Spectrum Models

Module: astra.models.apogee

APOGEE spectra are infrared spectra (H-band, ~1.5–1.7 micron) with 8575 pixels on a log-lambda wavelength grid. There are three APOGEE spectrum models in Astra, each corresponding to a different stage of processing.

ApogeeVisitSpectrum

An individual visit spectrum from the APOGEE data reduction pipeline, stored in an apVisit file. A “visit” is a single observation of a source (possibly combining multiple dithered exposures within the same night).

Key Fields

Field	Type	Description
spectrum_pk	ForeignKeyField	Unique spectrum identifier, links to the Spectrum table
source	ForeignKeyField	Foreign key to the Source this spectrum belongs to
release	TextField	Data release (e.g., "sdss5" or "dr17")
apred	TextField	APOGEE reduction pipeline version
telescope	TextField	Telescope used (e.g., "apo25m", "lco25m", "apo1m")
plate	TextField	Plate identifier
field	TextField	Field identifier
fiber	IntegerField	Fiber number
mjd	IntegerField	Modified Julian Date of observation
obj	TextField	Object name (computed per-spectrum from input RA/Dec)
snr	FloatField	Signal-to-noise ratio
wavelength	PixelArray	Wavelength array (vacuum, observed frame)
flux	PixelArray	Flux array
ivar	PixelArray	Inverse variance array
pixel_flags	PixelArray	Per-pixel quality flags

Radial velocity fields:

Field	Type	Description
v_rad	FloatField	Absolute radial velocity (km/s)
v_rel	FloatField	Relative radial velocity (km/s)
e_v_rel	FloatField	Uncertainty on relative radial velocity (km/s)
bc	FloatField	Barycentric correction (km/s)
doppler_teff	FloatField	Effective temperature from Doppler RV code
doppler_logg	FloatField	Surface gravity from Doppler RV code
doppler_fe_h	FloatField	Metallicity from Doppler RV code

Quality flags:

Field	Type	Description
spectrum_flags	BitField	Bit field encoding quality warnings
flag_bad_pixels	bit 0	Spectrum has many bad pixels
flag_bright_neighbor	bit 2	Star has a neighbor more than 10x brighter
flag_very_bright_neighbor	bit 3	Star has a neighbor more than 100x brighter
flag_low_snr	bit 4	Low S/N spectrum
flag_rv_failure	bit 22	RV failure

Methods and Properties

path (property)

Returns the file path to the apVisit FITS file for this spectrum. The path template depends on release and telescope.

visit = ApogeeVisitSpectrum.get_by_id(1)
print(visit.path)
# e.g., "$SAS_BASE_DIR/ipl-4/spectro/apogee/redux/1.3/visit/apo25m/..."

get_path_template(release, telescope) (classmethod)

Returns the file path template string for a given release and telescope combination.

flag_bad (hybrid property)

Returns True if any of the critical quality flags are set (flag_bad_pixels, flag_very_bright_neighbor, flag_bad_rv_combination, flag_rv_failure). Can be used in database queries.

flag_warn (hybrid property)

Returns True if any spectrum flag is set. Can be used in database queries.

ApogeeVisitSpectrumInApStar

A visit spectrum as stored within an apStar file. Unlike the raw apVisit, these spectra have been resampled onto a common log-lambda wavelength grid and shifted to the source rest frame.

Key Fields

Fields are similar to ApogeeVisitSpectrum, with these additions:

Field	Type	Description
drp_spectrum_pk	ForeignKeyField	Links back to the original ApogeeVisitSpectrum
apstar	TextField	apStar version (default: "stars")
healpix	IntegerField	HEALPix index (may differ from Source due to APOGEE DRP computation)

Spectral data arrays:

Field	Type	Description
wavelength	PixelArray	Log-lambda wavelength grid (8575 pixels, crval=4.179, cdelt=6e-6)
flux	PixelArray	Flux on the common grid
ivar	PixelArray	Inverse variance on the common grid
pixel_flags	PixelArray	Per-pixel quality flags

Methods and Properties

path (property)

Returns the file path to the apStar FITS file. Path templates differ between "sdss5" and "dr17" releases.

ApogeeCoaddedSpectrumInApStar

A co-added (stacked) APOGEE spectrum from an apStar file, created by combining all good visit spectra for a source. This represents the highest signal-to-noise APOGEE spectrum available for a given source.

Key Fields

Field	Type	Description
spectrum_pk	ForeignKeyField	Unique spectrum identifier
source	ForeignKeyField	Foreign key to the Source
star_pk	BigIntegerField	APOGEE DRP star primary key
release	TextField	Data release
apred	TextField	APOGEE reduction pipeline version
obj	TextField	Object name
telescope	TextField	Telescope used

Observation summary:

Field	Type	Description
n_entries	IntegerField	Number of entries in apStar file
n_visits	IntegerField	Number of visits
n_good_visits	IntegerField	Number of good visits
n_good_rvs	IntegerField	Number of good RV measurements
min_mjd	IntegerField	Minimum MJD of contributing visits
max_mjd	IntegerField	Maximum MJD of contributing visits

Summary statistics and radial velocity:

Field	Type	Description
snr	FloatField	Signal-to-noise ratio of co-added spectrum
mean_fiber	FloatField	S/N-weighted mean fiber number
std_fiber	FloatField	Standard deviation of fiber numbers
v_rad	FloatField	Mean radial velocity (km/s)
e_v_rad	FloatField	Uncertainty on mean radial velocity (km/s)
std_v_rad	FloatField	Scatter in radial velocity across visits (km/s)
doppler_teff	FloatField	Effective temperature from Doppler
doppler_logg	FloatField	Surface gravity from Doppler
doppler_fe_h	FloatField	Metallicity from Doppler

Spectral data:

Field	Type	Description
wavelength	PixelArray	Log-lambda wavelength grid (8575 pixels, crval=4.179, cdelt=6e-6)
flux	PixelArray	Co-added flux
ivar	PixelArray	Co-added inverse variance
pixel_flags	PixelArray	Per-pixel quality flags

Methods and Properties

path (property)

Returns the file path to the apStar FITS file containing this co-added spectrum.

coadd = ApogeeCoaddedSpectrumInApStar.get_by_id(1)
print(coadd.path)