3.3.6. barycentricCorrection

Calculate barycentric velocity corrections for science observations.

This primitive computes barycentric radial velocity corrections (BERV) for high-precision radial velocity measurements. It uses the barycorrpy library [1] to calculate Earth’s velocity projection toward the target at various exposure timestamps, accounting for exposure meter flux-weighted timing for maximum accuracy.

The primitive calculates BERV at the exposure midpoint and flux-weighted midpoint using exposure meter data from both PC and FRD channels. It queries SIMBAD for target coordinates or uses telescope pointing directly. Timing corrections account for instrument-specific offsets between UTC filename timestamps and actual exposure times.

3.3.6.1. Parameters

adinputslist of AstroData

Input AstroData objects containing 1D extracted science spectra with EXPOSUREMETER extension, timing information (UT_DATETIME, MJD), and telescope pointing data in headers.

target_namestr, optional

Target name substring for file filtering. Only files with OBJECT header matching this string are processed. If None, all files are processed. Default is None.

simbad_target_namestr, optional

SIMBAD-resolvable target name to override OBJECT header value. Use when the header target name differs from the SIMBAD catalog name. Only applies if target_name matches. Default is None.

use_coordsbool, optional

If True, use telescope pointing coordinates (TELRA, TELDEC) directly instead of querying SIMBAD for target coordinates. Recommended when target is not in SIMBAD or has unreliable proper motion data. Default is False.

zp_pcfloat, optional

Zeropoint for PC (Precision Coupler) exposure meter channel in counts. If 0.0, automatically determined from median of 20 lowest readings in a 10-minute window around exposure. Units: counts. Default is 0.0.

zp_frdfloat, optional

Zeropoint for FRD (Fiber Refractive Diffraction) exposure meter channel in counts. If 0.0, automatically determined from median of 20 lowest readings in a 10-minute window around exposure. Units: counts. Default is 0.0.

start_timestr, optional

Method for determining exposure start time. One of 'filename' (UTC from filename), 'mjd_start' (telescope MJD at exposure start), or 'mjd_end' (telescope MJD at readout end minus exposure time). Different methods account for varying instrument timing behaviors between red and blue arms. Default is 'filename'.

reportbool, optional

Generate diagnostic PDF of exposure meter time series. Default is True.

suffixstr, optional

Suffix to append to output filenames. Default is '_reduced'.

3.3.6.2. Returns

list of AstroData

Input frames with barycentric velocity corrections and exposure meter statistics added to the first extension header. Header keywords added:

BERV values (m/s):

• BERV_MIDPOINT : BERV at nominal exposure midpoint.

• BERV_FLUXWEIGHTED_PC : BERV at flux-weighted midpoint (PC channel).

• BERV_FLUXWEIGHTED_FRD : BERV at flux-weighted midpoint (FRD channel).

• BERV_DIFFERENCE_PC : Difference between flux-weighted and nominal.

• BERV_DIFFERENCE_FRD : Difference between flux-weighted and nominal.

Timing information:

• UTC_START : Corrected UTC start time (ISO format).

• UTC_MIDPOINT : UTC midpoint time.

• UTC_FLUXWEIGHTED_PC : Flux-weighted UTC (PC channel).

• UTC_FLUXWEIGHTED_FRD : Flux-weighted UTC (FRD channel).

• UTC_CORRECTION : Applied time correction in seconds.

• JD_UTC_START : Julian date at start.

• JD_UTC_MIDPOINT : Julian date at midpoint.

• JD_UTC_FLUXWEIGHTED_PC : Flux-weighted JD (PC channel).

• JD_UTC_FLUXWEIGHTED_FRD : Flux-weighted JD (FRD channel).

Exposure meter statistics (counts):

• COUNTS_PC_MIN/MAX/MEDIAN/STD : PC channel statistics.

• COUNTS_FRD_MIN/MAX/MEDIAN/STD : FRD channel statistics.

• COUNTS_PC_ZP : Applied PC zeropoint.

• COUNTS_FRD_ZP : Applied FRD zeropoint.

• SCALEFACTOR : Ratio of FRD to PC median counts.

Target information:

• BERV_SIMBAD_TARGET : Target name used for BERV calculation.

3.3.6.3. References

[1]

barycorrpy: https://github.com/shbhuk/barycorrpy

3.3.6.4. Parameter defaults and options

suffix               '_reduced'           Filename suffix
target_name          None                 Target name to downselect files
simbad_target_name   None                 SIMBAD resolvable target name
use_coords           False                Use telescope pointing coordinates instead of target name
zp_pc                0.0                  Zeropoint for counts_pc channel. Determined from data if not provided.
zp_frd               0.0                  Zeropoint for counts_frd channel. Determined from data if not provided.
start_time           'filename'           Time to consider to compute exposure start
   Allowed values:
     mjd_start       Telescope MJD written at start of exposure
     mjd_end Telescope MJD written at end of readout
     filename        UTC from filename

report               True                 Generate diagnostic PDF of exposure meter time series.

3.3.6.5. Algorithm

Todo

add description

3.3.6.6. Issues and Limitations

Todo

add description