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be_halpha_ew

H-alpha equivalent width and V/R ratio of a Be star on a reduced, wavelength- calibrated spectrum: the wavelengths are brought to the barycentric frame from the header and the observer's site, the continuum is set on a line-free band on the blue side of the line, the equivalent width is integrated over a fixed window with the Vollmann & Eversberg (2006) error, and the V/R ratio of a double-peaked profile is measured. Every observer who runs this recipe measures the same quantity the same way, whatever the instrument; only the site coordinates come from the observer's profile.
Kind campaign
Status draft - draft: conventions still open for discussion
Version 1.0.0
Source package:spectro-kernel-recipes
Requires spectro-kernel >=0.7

Conventions

Barycentric correction applied before any measurement (BeSS stores spectra in the heliocentric frame, BSS_VHEL). Continuum fixed on 6500-6520 Angstrom (blue side, free of strong lines at the resolutions of amateur spectrographs). Equivalent width integrated over 60 Angstrom centred on 6562.79 Angstrom (rest, air), wide enough to enclose the wings of broad Be emission; negative EW = emission. V/R measured within +/- 15 Angstrom of the line centre. These bands are this recipe's choice, not prescribed by the literature: discuss them before promoting the recipe.

References

  • Vollmann & Eversberg 2006, Astronomische Nachrichten 327, 862 - equivalent width and its error
  • Neiner et al. 2011, AJ 142, 149 - the BeSS database of Be star spectra
  • Hanuschik et al. 1996, A&AS 116, 309 - atlas of H-alpha emission and shell profiles in Be stars

Variables

The instrument- or observer-dependent values. Provide them with a profile file, --set name=value, or variables={...} in Python.

Variable Type Required / default Description
latitude_deg float required observatory latitude (deg, north positive)
longitude_deg float required observatory longitude (deg, east positive)
elevation_m float default 0.0 observatory elevation (m)

Steps

# Algorithm Parameters
1 barycentric_correction Barycentric correction from the header and the site latitude_deg='${latitude_deg}', longitude_deg='${longitude_deg}', elevation_m='${elevation_m}'
2 normalize_to_region Continuum to unity on the blue band wave_lo=6500.0, wave_hi=6520.0
3 snr_der Signal-to-noise (DER_SNR) -
4 equivalent_width H-alpha equivalent width line_center_angstrom=6562.79, window_angstrom=60.0, label='H-alpha'
5 vr_ratio V/R ratio of the H-alpha profile line_center_aa=6562.79, window_half_width_aa=15.0

Run it

# profile.yaml holds your instrument values:
#   latitude_deg: 0.0
#   longitude_deg: 0.0
#   elevation_m: 0.0
spectro pipeline be_halpha_ew --input spectrum.fits --profile profile.yaml
spectro preset show be_halpha_ew      # variables and steps

from spectro_kernel import WorkContext
from spectro_kernel.pipeline import PipelineBuilder

variables = {"latitude_deg": 0.0, "longitude_deg": 0.0, "elevation_m": 0.0}
pipeline = PipelineBuilder().from_preset("be_halpha_ew", variables).build()
result = pipeline.execute(ctx)        # ctx holds the spectrum / frames
print(result.history[-1])             # pipeline:<name> vX.Y.Z + variables

{
  "tool": "run_preset",
  "arguments": {
    "session_id": "<session_id>",
    "preset_name": "be_halpha_ew",
    "variables": {
      "latitude_deg": 0.0,
      "longitude_deg": 0.0,
      "elevation_m": 0.0
    }
  }
}