Activity Module (sbpy.activity)

sbpy.activity models cometary dust and gas activity. It is separated into two main sub-modules: Dust comae and tails (sbpy.activity.dust) and Gas Comae (sbpy.activity.gas). The base module itself defines photometric apertures that may be useful for observations of comets.

Table of Contents

• Dust comae and tails (sbpy.activity.dust)
  • Afρ and εfρ models
  • Reference/API
• Gas Comae (sbpy.activity.gas)
  • Photolysis
  • Fluorescence
  • Gas coma models
  • Production Rate calculations
  • Reference/API

Apertures

Four photometric aperture classes are defined, primarily for use with cometary comae:

• CircularAperture: a circle,

• AnnularAperture: an annulus,

• RectangularAperture: a rectangle,

• GaussianAperture: a Gaussian-weighted beam.

All apertures assume they are centered on the source, i.e., offsets are not supported, but may be added in the future.

Each object is initialized with the dimensions of the aperture, which may be in linear or angular units:

>>> import astropy.units as u
>>> import sbpy.activity as sba
>>>
>>> sba.CircularAperture(10 * u.arcsec)
<CircularAperture: radius 10.0 arcsec>
>>>
>>> sba.RectangularAperture((2000, 5000) * u.km)
<RectangularAperture: dimensions 2000.0×5000.0 km>

Apertures may be converted between linear and angular units using as_angle() and as_length(). The conversion requires the observer-target distance ('delta') as a Quantity or Ephem.

>>> ap = sba.CircularAperture(1 * u.arcsec)
>>> ap.as_length(1 * u.au)  
<CircularAperture: radius [725.27094381] km>

Ideal comae (constant production rate, free-expansion, infinite lifetime) have 1/ρ surface brightness distributions. With coma_equivalent_radius(), we may convert the aperture into a circular aperture that would contain the same total flux at the telescope:

>>> ap = sba.RectangularAperture((2000, 5000) * u.km)
>>> sba.CircularAperture(ap.coma_equivalent_radius())  
<CircularAperture: radius 1669.4204086589311 km>

Through the coma_equivalent_radius() method, all apertures may be used to initialize a CircularAperture instance using the from_coma_equivalent() method:

>>> sba.CircularAperture.from_coma_equivalent(ap)
<CircularAperture: radius 1669.4204086589311 km>

Reference/API

Cometary activity and observations.

Classes

AnnularAperture(shape)	Annular aperture projected at the distance of the target.
Aperture(dim)	Abstract base class for photometric apertures.
CircularAperture(radius)	Circular aperture projected at the distance of the target.
GaussianAperture([sigma, fwhm])	Gaussian-shaped aperture, e.g., for radio observations.
RectangularAperture(shape)	Rectangular aperture projected at the distance of the target.

Class Inheritance Diagram