feat(hfbcat): Move get_doppler_shifted_freq from ephemeris

ch_util/ephemeris.py

@@ -820,90 +820,18 @@ def peak_RA(body, date=None, deg=False):
     return ra
 
 
-def get_doppler_shifted_freq(
-    source: Union[skyfield.starlib.Star, str],
-    date: Union[float, list],
-    freq_rest: Union[float, list] = None,
-    obs: Observer = chime,
-) -> np.array:
-    """Calculate Doppler shifted frequency of spectral feature with rest
-    frequency `freq_rest`, seen towards source `source` at time `date`, due to
-    Earth's motion and rotation, following the relativistic Doppler effect.
-
-    Parameters
-    ----------
-    source
-        Position(s) on the sky. If the input is a `str`, attempt to resolve this
-        from `ch_util.hfbcat.HFBCatalog`.
-    date
-        Unix time(s) for which to calculate Doppler shift.
-    freq_rest
-        Rest frequency(ies) in MHz. If None, attempt to obtain rest frequency
-        of absorption feature from `ch_util.hfbcat.HFBCatalog.freq_abs`.
-    obs
-        An Observer instance to use. If not supplied use `chime`. For many
-        calculations changing from this default will make little difference.
-
-    Returns
-    -------
-    freq_obs
-        Doppler shifted frequencies in MHz. Array where rows correspond to the
-        different input rest frequencies and columns correspond either to input
-        times or to input sky positions (whichever contains multiple entries).
-
-    Notes
-    -----
-    Only one of `source` and `date` can contain multiple entries.
-
-    Example
-    -------
-    To get the Doppler shifted frequencies of a feature with a rest frequency
-    of 600 MHz for two positions on the sky at a single point in time (Unix
-    time 1717809534 = 2024-06-07T21:18:54+00:00), run:
-
-    >>> from skyfield.starlib import Star
-    >>> from skyfield.positionlib import Angle
-    >>> from ch_util.tools import get_doppler_shifted_freq
-    >>> coord = Star(ra=Angle(degrees=[100, 110]), dec=Angle(degrees=[45, 50]))
-    >>> get_doppler_shifted_freq(coord, 1717809534, 600)
-    """
-
-    from scipy.constants import c as speed_of_light
-
-    from ch_util.fluxcat import _ensure_list
-    from ch_util.hfbcat import HFBCatalog
-
-    # For source string inputs, get skyfield Star object from HFB catalog
-    if isinstance(source, str):
-        try:
-            source = HFBCatalog[source].skyfield
-        except KeyError:
-            raise ValueError(f"Could not find source {source} in HFB catalog.")
-
-    # Get rest frequency from HFB catalog
-    if freq_rest is None:
-        if not source.names or source.names not in HFBCatalog:
-            raise ValueError(
-                "Rest frequencies must be supplied unless source can be found "
-                "in ch_util.hfbcat.HFBCatalog. "
-                f"Got source {source} with names {source.names}"
-            )
-        else:
-            freq_rest = HFBCatalog[source.names].freq_abs
-
-    # Prepare rest frequencies for broadcasting
-    freq_rest = np.asarray(_ensure_list(freq_rest))[:, np.newaxis]
+# For backwards compatibility
+def get_doppler_shifted_freq(*args, **kwargs):
+    """Deprecated.  Use `ch_util.hfbcat.get_doppler_shifted_freq`."""
+    from . import hfbcat
 
-    # Get rate at which the distance between the observer and source changes
-    # (positive for observer and source moving appart)
-    range_rate = get_range_rate(source, date, obs)
+    import warnings
 
-    # Compute observed frequencies from rest frequencies
-    # using relativistic Doppler effect
-    beta = range_rate / speed_of_light
-    freq_obs = freq_rest * np.sqrt((1.0 - beta) / (1.0 + beta))
+    warnings.warn(
+        "Use `ch_util.hfbcat.get_doppler_shifted_freq` instead.", DeprecationWarning
+    )
 
-    return freq_obs
+    return hfbcat.get_doppler_shifted_freq(*args, **kwargs)
 
 
 def get_range_rate(

ch_util/hfbcat.py

@@ -2,9 +2,16 @@
 Catalog of HFB test targets
 """
 
+from __future__ import annotations
 import os
+import numpy as np
+from typing import TYPE_CHECKING, Union
 
-from .fluxcat import FluxCatalog
+from . import ephemeris
+from .fluxcat import FluxCatalog, _ensure_list
+
+if TYPE_CHECKING:
+    import skyfield.starlib.Star
 
 # Define the source collection that should be loaded when this module is imported.
 HFB_COLLECTION = os.path.join(
@@ -79,5 +86,88 @@ def __init__(
         self.freq_abs = freq_abs
 
 
+def get_doppler_shifted_freq(
+    source: Union[skyfield.starlib.Star, str],
+    date: Union[float, list],
+    freq_rest: Union[float, list] = None,
+    obs: ephemeris.Observer = ephemeris.chime,
+) -> np.array:
+    """Calculate Doppler shifted frequency of spectral feature with rest
+    frequency `freq_rest`, seen towards source `source` at time `date`, due to
+    Earth's motion and rotation, following the relativistic Doppler effect.
+
+    Parameters
+    ----------
+    source
+        Position(s) on the sky. If the input is a `str`, attempt to resolve this
+        from `ch_util.hfbcat.HFBCatalog`.
+    date
+        Unix time(s) for which to calculate Doppler shift.
+    freq_rest
+        Rest frequency(ies) in MHz. If None, attempt to obtain rest frequency
+        of absorption feature from `ch_util.hfbcat.HFBCatalog.freq_abs`.
+    obs
+        An Observer instance to use. If not supplied use `chime`. For many
+        calculations changing from this default will make little difference.
+
+    Returns
+    -------
+    freq_obs
+        Doppler shifted frequencies in MHz. Array where rows correspond to the
+        different input rest frequencies and columns correspond either to input
+        times or to input sky positions (whichever contains multiple entries).
+
+    Notes
+    -----
+    Only one of `source` and `date` can contain multiple entries.
+
+    Example
+    -------
+    To get the Doppler shifted frequencies of a feature with a rest frequency
+    of 600 MHz for two positions on the sky at a single point in time (Unix
+    time 1717809534 = 2024-06-07T21:18:54+00:00), run:
+
+    >>> from skyfield.starlib import Star
+    >>> from skyfield.units import Angle
+    >>> from ch_util.hfbcat import get_doppler_shifted_freq
+    >>> coord = Star(ra=Angle(degrees=[100, 110]), dec=Angle(degrees=[45, 50]))
+    >>> get_doppler_shifted_freq(coord, 1717809534, 600)
+    """
+
+    from scipy.constants import c as speed_of_light
+
+    # For source string inputs, get skyfield Star object from HFB catalog
+    if isinstance(source, str):
+        try:
+            source = HFBCatalog[source].skyfield
+        except KeyError:
+            raise ValueError(f"Could not find source {source} in HFB catalog.")
+
+    # Get rest frequency from HFB catalog
+    if freq_rest is None:
+        if not source.names or source.names not in HFBCatalog:
+            raise ValueError(
+                "Rest frequencies must be supplied unless source can be found "
+                "in ch_util.hfbcat.HFBCatalog. "
+                f"Got source {source} with names {source.names}"
+            )
+        else:
+            freq_rest = HFBCatalog[source.names].freq_abs
+
+    # Prepare rest frequencies for broadcasting
+    freq_rest = np.asarray(_ensure_list(freq_rest))[:, np.newaxis]
+
+    # Get rate at which the distance between the observer and source changes
+    # (positive for observer and source moving appart)
+    range_rate = ephemeris.get_range_rate(source, date, obs)
+
+    # Compute observed frequencies from rest frequencies
+    # using relativistic Doppler effect
+    beta = range_rate / speed_of_light
+    freq_obs = freq_rest * np.sqrt((1.0 - beta) / (1.0 + beta))
+
+    return freq_obs
+
+
 # Load the HFB target list
 HFBCatalog.load(HFB_COLLECTION)