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sofiacovarrubias committed Feb 29, 2024
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Expand Up @@ -24,21 +24,21 @@ In the ``orbitize!`` coordinate system, relative R.A. and declination can be exp
of orbital parameters

.. math::
\Delta R.A. = \pi a(1-ecosE)[cos^2{i\over 2}sin(f+\omega_p+\Omega)-sin^2{i\over 2}sin(f+\omega_p-\Omega)]
\
\Delta R.A. = \pi a(1-ecosE)[cos^2{i\over 2}sin(f+\omega_p+\Omega)-sin^2{i\over 2}sin(f+\omega_p-\Omega)] \\
\Delta decl. = \pi a(1-ecosE)[cos^2{i\over 2}cos(f+\omega_p+\Omega)+sin^2{i\over 2}cos(f+\omega_p-\Omega)]
where 𝑎, 𝑒, :math:`\omega_p`, Ω, and 𝑖 are orbital parameters, and 𝜋 is the system parallax. f is
the true anomaly, and E is the eccentric anomaly, which are related to elapsed time
through Kepler’s equation and Kepler’s third law

.. math::
M = 2\pi ({t\over P}-(\tau -\tau_{ref}))
\
({P\over yr})^2 =({a\over au})^3({M_\odot \over M_{tot}})
\
M =E-esinE
\
M = 2\pi ({t\over P}-(\tau -\tau_{ref})) \\
({P\over yr})^2 =({a\over au})^3({M_\odot \over M_{tot}}) \\
M =E-esinE \\
f = 2tan^{-1}[\sqrt{{1+e\over 1-e}}tan{E\over 2}]
``orbitize!`` employs two Kepler solvers to convert between mean
Expand All @@ -49,23 +49,25 @@ orbit. See `Blunt et al. (2020) <https://iopscience.iop.org/article/10.3847/1538
From scrutinizing the above sets of equations, one may observe
a few important degeneracies:

1. Individual component masses do not show up anywhere in this equation set.
#. Individual component masses do not show up anywhere in this equation set.

2. The degeneracy between semimajor axis 𝑎, total mass :math:`𝑀_{tot}`, and
parallax 𝜋. If we just had relative astrometric measurements and no external knowledge of the system parallax,
we would not be able to distinguish between a system
that has larger distance and larger semimajor axis (and therefore larger total mass,
assuming a fixed period) from a system that has smaller distance, smaller semimajor
axis, and smaller total mass.
#. The degeneracy between semimajor axis 𝑎, total mass :math:`𝑀_{tot}`, and
parallax 𝜋. If we just had relative astrometric measurements and no external knowledge of the system parallax,
we would not be able to distinguish between a system
that has larger distance and larger semimajor axis (and therefore larger total mass,
assuming a fixed period) from a system that has smaller distance, smaller semimajor
axis, and smaller total mass.

#. The argument of periastron :math:`\omega_p` and the position angle of nodes Ω.
The above defined R.A. and decl. functions are invariant to the transformation:
.. math::
\omega_p' = \omega_p + \pi \\
\Omega' = \Omega - \pi
3. The argument of periastron :math:`\omega_p` and the position angle of nodes Ω.
The above defined R.A. and decl. functions are invariant to the transformation:
which creates a 180◦ degeneracy between particular values of :math:`\omega_p` and Ω, and
a characteristic “double-peaked” structure in marginalized 1D posteriors of these
parameters.

.. math::
\omega_p' = \omega_p + \pi
\
\Omega' = \Omega - \pi

which creates a 180◦ degeneracy between particular values of :math:`\omega_p` and Ω, and
a characteristic “double-peaked” structure in marginalized 1D posteriors of these
parameters.
More coming soon!

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